JP2012171616A - Torque distributor and method of distributing torque - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform torque distribution in which the slip state of a driving wheel is taken into account.SOLUTION: A torque distributor 100 includes a total torque command acquirer 101, which acquires input entire torque commands, an efficiency map acquirer 105, which acquires a motor efficiency map 104 for a mounted motor, a car body speed detector 102a, which detects the car body speed of a vehicle, a driving wheel rotating speed detector 102b, which detects the rotating speed of a driving wheel, a slip rate calculator 103, which calculates the slip rate of the driving wheel, based on the car body speed and the rotating speed of the driving wheel, a calculator 106, which makes an equation of efficiency change that shows the efficiency value on an operation line that shows the relation between the rotating speed of the driving wheel and the torque, based on the slip rate, and calculates an optimally efficient torque value of the equation of the efficiency change on the operation line, a distributing part 107, which calculates a torque distribution value to each motor, based on the total torque command and the optimally efficient torque value, and a controller 108, which controls the torque distribution to each motor, based on the calculated torque distribution value.

Description

  The present invention relates to a torque distribution device and a torque distribution method for distributing torque when driving a plurality of drive wheels of a moving body. However, utilization of this invention is not restricted to the torque distribution apparatus and torque distribution method which were mentioned above.

  Conventionally, the following technologies have been disclosed as torque distribution in which a plurality of motors are provided in an electric vehicle (EV), which is a moving body, and torque for driving a plurality of drive wheels (wheels) is distributed.

  The first technique is a configuration in which the electric power consumption is obtained by calculation for each combination of motor torques, a graph with the driving force distribution on the horizontal axis is obtained, and the torque is distributed. In this configuration, the output power Pout [kW] and the minimum value of power consumption (hereinafter referred to as the minimum power consumption) when the combination of the motor torque that realizes the transient required driving force within the range of the torque limit value is realized. Compare magnitude relationships. When it is determined that the outputtable power Pout [kW] is equal to or greater than the minimum power consumption, the motor torques of the front and rear wheels that cause the minimum power consumption are directly used as torque command values (see Patent Document 1 below).

  The second technique is a configuration in which the total torque is distributed to a plurality of motors, and the system efficiency is maximized as the torque distribution is equal between the two front drive wheels and the two rear drive wheels. In this configuration, a system efficiency map indicating a torque distribution ratio is created and used (see Patent Document 2 below).

  In the third technique, a map showing the relationship among the fuel consumption, the charge / discharge power of the power storage device, and the driving force distribution of the front and rear wheels is searched based on the required driving power and the vehicle speed. Thereafter, by extracting the driving force distribution that minimizes the fuel consumption with respect to the charge / discharge power of the power storage device from the extracted map, the driving power distribution map before and after improving the fuel efficiency is obtained (Patent Document 3 below). reference.).

  In the fourth technique, the driving force distribution determining unit determines whether the motor generator generates a motor based on the motor required driving torque and the vehicle speed corresponding to the motor required driving force, and the efficiency characteristics of the motor generator with respect to each torque and vehicle speed. The drive torque distribution at is determined. At this time, the drive torque distribution in the low output region and the drive torque distribution in the high output region are controlled using different patterns, so that the efficiency of the entire motor generator is maximized (see Patent Document 4 below). ).

  The fifth technique is based on the sum of the drive torques required for the left and right front wheels and the rotational speed of the motor generator so that the drive efficiency of the entire motor generator is maximized. Determine the drive torque distribution. And it is the structure which determines the drive torque distribution of a right front wheel and a left front wheel so that only either one of a motor generator may be driven according to a turning direction (refer the following patent document 5).

  The sixth technology is a choice between wheel torque distribution control based on energy efficiency (energy efficiency control) and wheel torque distribution control based on each wheel load distribution (load distribution control). This is a possible configuration (see Patent Document 6 below).

  Such a control that uses the required torque and energy efficiency as parameters to drive the front wheels and rear wheels of a four-wheel drive vehicle as parameters and makes the energy efficiency relatively high is, for example, Patent Document As disclosed in No. 2 etc., it is a known technique. The load distribution ratio between the front wheel and the rear wheel is, for example, the height of the center of gravity of a four-wheel drive vehicle, the distance from the center of gravity to the front wheel, the distance from the center of gravity to the rear wheel, the axle of the front wheel and the axle of the rear wheel. It is determined by the distance between the wheels (wheelbase), the width of the left and right wheels (tread), the turning acceleration of the vehicle (lateral acceleration), the acceleration in the longitudinal direction of the vehicle, etc., and matches the load distribution ratio between the front wheels and the rear wheels Thus, the torque distribution ratio in the front wheels and the rear wheels is determined. With respect to the control for obtaining the load distribution ratio of the front wheels and the rear wheels using this parameter and determining the torque distribution ratio according to the load distribution ratio, for example, a technique already known from Patent Document 7 below, for example It is.

JP 2006-180657 A JP 2006-345677 A JP 2007-37217 A JP 2007-313982 A International Publication No. 2007/064025 Pamphlet JP 2009-159682 A JP 2006-213130 A

  However, the techniques described in Patent Documents 1 to 7 are technical ideas that motor torque is distributed for the purpose of high efficiency of the motor, and the optimum efficiency torque on the motor efficiency map is utilized using the motor efficiency map. The torque is not distributed based on the value.

  In addition, all of the techniques described in Patent Documents 1 to 3 are configured to distribute the drive wheels to the front part and the rear part, and do not assume that each drive wheel is controlled independently. Further, the technique described in Patent Document 4 is applied to a hybrid vehicle, and is applied to an in-wheel motor in which only left and right rear wheels are independent, and does not assume that all driving wheels are controlled independently. In such a configuration, for example, four drive wheels cannot be controlled independently, and optimal torque distribution cannot be performed for a plurality of drive wheels.

  Further, in each of Patent Documents 1 to 7 described above, since the slip state of the drive wheels (wheels) is not taken into consideration, the torque distribution control is insufficient and cannot be highly efficient. The slip state of the driving wheel with respect to the road surface changes depending on factors such as the speed of the moving body, more specifically the rotational speed of the driving wheel. For this reason, unless the slip state of the drive wheels is taken into account, torque distribution to each drive wheel cannot be made efficient, and optimal torque distribution cannot be performed when the drive wheels are actually driven, and the efficiency of the entire drive system Cannot be optimized to the maximum.

  In order to solve the above-described problems and achieve the object, a torque distribution device according to the present invention distributes all input torque command values to each of a plurality of motors connected to drive wheels. An apparatus for obtaining a total torque command value for obtaining the inputted total torque command value; an efficiency map obtaining unit for obtaining a motor efficiency map corresponding to the motor; and a vehicle body speed of a vehicle on which the motor is mounted. A vehicle wheel speed detecting means for detecting the driving wheel, a driving wheel rotating speed detecting means for detecting a driving wheel rotating speed of the driving wheel, and a slip ratio in the driving wheel based on the vehicle body speed and the driving wheel rotating speed. Based on the slip ratio detection means and the slip ratio, an operation line expression indicating a relationship between the drive wheel rotation speed and the torque is created, and based on the operation line expression, the drive An efficiency change equation indicating the torque and an efficiency value of the motor efficiency map for each rotation speed is created, calculating means for calculating an optimum efficiency torque value of the efficiency change equation, the slip ratio, the total torque command value, and Based on the optimum efficiency torque value, the total efficiency ηtotal = Σ ((Tn / T) × ηdn × ηλn) (where T: total torque command value, Tn: torque distribution value of each motor, ηdn: Distribution means for calculating a torque distribution value for each of the motors so that the drive system efficiency, ηλn (traveling system efficiency of each drive wheel) is maximized, and each of the motors based on the calculated torque distribution value Control means for controlling torque distribution to the motor, wherein the distribution means distributes the optimum efficiency torque value only to the torque distribution value of any one of a plurality of motors, or all or All the torque command values are equally distributed to some motors so that the respective torque distribution values are closest to the optimum efficiency torque value.

  The torque distribution method according to the present invention is a torque distribution method for distributing the input total torque command value to each of the plurality of motors connected to the drive wheels, wherein the input total torque A total torque command value acquiring step for acquiring a command value; an efficiency map acquiring step for acquiring a motor efficiency map corresponding to the motor; a vehicle body speed detecting step for detecting a vehicle body speed of a vehicle equipped with the motor; and the driving A driving wheel rotational speed detecting step for detecting a driving wheel rotational speed in the wheel; a slip ratio detecting step for detecting a slip ratio in the driving wheel based on the vehicle body speed and the driving wheel rotational speed; and on the basis of the slip ratio. Then, an operation line expression indicating a relationship between the drive wheel rotation speed and the torque is created, and the torque and the motor are generated for each drive wheel rotation speed based on the operation line expression. An efficiency change equation indicating an efficiency value of the rate map is created, based on the calculation step of calculating the optimum efficiency torque value of the efficiency change equation, the slip ratio, the total torque command value, and the optimum efficiency torque value , Total efficiency ηtotal = Σ ((Tn / T) × ηdn × ηλn) (where T: total torque command value, Tn: torque distribution value of each motor, ηdn: drive system efficiency of each motor, ηλn: each drive wheel A distribution step of calculating a torque distribution value for each of the motors so as to maximize the traveling system efficiency), and a control step of controlling torque distribution to each of the motors based on the calculated torque distribution values; And the distribution step distributes the optimum efficiency torque value only to the torque distribution value of any one of the plurality of motors, or each torque for all or some of the motors. The torque distribution value is evenly distributed so that the torque distribution value is closest to the optimum efficiency torque value.

It is a block diagram which shows the functional structure of the torque distribution apparatus concerning embodiment. It is a flowchart which shows the procedure of the torque distribution process by a torque distribution apparatus. It is a schematic diagram which shows the structure of a moving body. It is a block diagram which shows the hardware constitutions of a torque distribution apparatus. It is a figure which shows an example of a motor efficiency map. It is a figure which shows the relationship between a slip ratio and a friction coefficient. It is a figure which shows the relationship between the rotational speed and torque which considered the slip ratio. It is a figure which shows the state which accumulated the change curve shown in FIG. 7 on the motor efficiency map. It is a figure which shows the relationship between the torque and efficiency which differ for every vehicle body speed (the 1). It is a figure which shows the relationship between the torque which changes for every vehicle body speed, and efficiency (the 2). It is a figure which shows the relationship between a torque and efficiency. It is a figure which shows the torque-efficiency characteristic intrinsic | native to a motor (the 1). It is a figure which shows the torque-efficiency characteristic intrinsic | native to a motor (the 2). It is a figure which shows the torque-efficiency characteristic intrinsic | native to a motor (the 3). It is a figure which shows the characteristic of each wheel in a reverse U type torque-efficiency characteristic (the 1). It is a figure which shows the characteristic of each wheel in a reverse U type torque-efficiency characteristic (the 2). It is a figure which shows the characteristic of each wheel in a reverse U type torque-efficiency characteristic (the 3). It is a figure which shows the characteristic of each wheel in a reverse U type torque-efficiency characteristic (the 4). It is a figure which shows the characteristic of each wheel in a reverse U type torque-efficiency characteristic (the 5). It is a figure which shows the characteristic of each wheel in a reverse U type torque-efficiency characteristic (the 6). It is a figure which shows the characteristic of each wheel in a delta type torque-efficiency characteristic (the 1). It is a figure which shows the characteristic of each wheel in (DELTA) type torque-efficiency characteristic (the 2). It is a figure which shows the characteristic of each wheel in (triangle | delta) type torque-efficiency characteristic (the 3). It is a figure which shows the characteristic of each wheel in (triangle | delta) type torque-efficiency characteristic (the 4). It is a figure which shows the characteristic of each wheel in (triangle | delta) type torque-efficiency characteristic (the 5). It is a figure which shows the characteristic of each wheel in (triangle | delta) type torque-efficiency characteristic (the 6). It is a figure which shows the characteristic of each wheel in a human-type torque-efficiency characteristic (the 1). It is a figure which shows the characteristic of each wheel in a human-type torque-efficiency characteristic (the 2). It is a figure which shows the characteristic of each wheel in a human-type torque-efficiency characteristic (the 3). It is a figure which shows the characteristic of each wheel in a human-type torque-efficiency characteristic (the 4). It is a figure which shows the characteristic of each wheel in a human-type torque-efficiency characteristic (the 5). It is a figure which shows the characteristic of each wheel in a human-type torque-efficiency characteristic (the 6). It is a figure for demonstrating torque distribution in the case of four drive wheels (the 1). It is a figure for demonstrating the torque distribution in the case of four drive wheels (the 2). It is a figure for demonstrating the torque distribution in the case of four drive wheels (the 3). It is a figure for demonstrating torque distribution in the case of four drive wheels (the 4). It is a figure for demonstrating torque distribution in the case of four drive wheels (the 5). It is a figure explaining the difference in the change rate in the characteristic of torque-efficiency. It is a figure explaining the distance from the optimal efficiency torque value in the characteristic of torque-efficiency. It is a figure explaining dynamic torque distribution according to a run pattern. It is a table | surface which shows the setting data of the optimal drive wheel number based on a rotational speed-total torque command value. It is a figure for demonstrating total efficiency. It is a figure which shows the relationship of torque-running efficiency when normal force is made constant. It is a figure explaining the state from which the normal force for every driving wheel differs. It is a graph which shows the torque-traveling efficiency according to perpendicular force. It is a figure for demonstrating the total efficiency of the whole moving body. It is a block diagram which shows the functional structure of the torque distribution apparatus concerning Example 2. FIG. It is a figure which shows the example of calculation of total efficiency (the 1). It is a figure which shows the example of calculation of total efficiency (the 2).

  Exemplary embodiments of a torque distribution device and a torque distribution method according to the present invention will be explained below in detail with reference to the accompanying drawings. In the following description, “rotational speed” will be described as “drive wheel rotational speed”.

(Embodiment)
(Configuration of torque distribution device)
FIG. 1 is a block diagram illustrating a functional configuration of the torque distribution device according to the embodiment. The torque distribution device 100 according to the embodiment uses a motor efficiency map and controls torque distribution for a plurality of drive wheels based on the optimum efficiency torque value on the motor efficiency map.

  The torque distribution device 100 includes an all torque command value acquisition unit 101, a vehicle body speed detection unit 102a, a drive wheel speed detection unit 102b, a slip ratio calculation unit 103, a motor efficiency map 104, and an efficiency map acquisition unit 105. , Calculation unit 106, distribution unit 107, and control unit 108.

  The total torque command value acquisition unit 101 acquires a total torque command value for driving the moving body. That is, all torque command values inputted to drive a plurality of n motors M (M1, M2,... Mn) respectively provided on the drive wheels are acquired. In this embodiment, the plurality of motors M will be described on the assumption that the same type of motor is used.

The vehicle body speed detection unit 102a detects the speed of the moving body. The drive wheel speed detection unit 102b detects the drive wheel speed provided in the moving body. The drive wheel speed v _w is calculated from the tire radius r × drive wheel rotation speed ω (v _w = r × ω).

  The slip ratio calculation unit 103 is described later based on the speed of the moving body detected by the vehicle body speed detection unit 102a and the drive wheel speed (drive wheel rotation speed and tire radius) detected by the drive wheel speed detection unit 102b. Thus, the slip ratio in each drive wheel is calculated. The motor efficiency map 104 is a map showing the relationship between the speed and torque in each motor M as shown in FIG. 5 described later. On this map, a substantially linear operation line is shown based on the torque and speed. Can be drawn. The efficiency map acquisition unit 105 acquires a motor efficiency map 104 corresponding to the motor M.

  To obtain a motor efficiency map: 1. A motor efficiency map prepared in advance by a motor manufacturer or car manufacturer is stored in a memory or the like. For example, a motor efficiency map may be created while the moving body is running.

  Based on the slip ratio calculated by the slip ratio calculation unit 103, the calculation unit 106 creates an efficiency change equation indicating an efficiency value on the operation line indicating the relationship between the rotational speed and the torque, and the efficiency change equation on the operation line. The optimum efficiency torque value at is calculated.

  The distribution unit 107 calculates a torque distribution value for each motor M based on the total torque command value acquired by the total torque command value acquisition unit 101 and the optimum efficiency torque value calculated by the calculation unit 106 as described later. . The control unit 108 controls the torque distribution to each motor M based on the torque distribution value calculated by the distribution unit 107.

(About torque distribution processing)
FIG. 2 is a flowchart showing a procedure of torque distribution processing by the torque distribution device. First, the total torque command value acquisition unit 101 acquires the total torque command value T input from the accelerator pedal in order to drive a plurality of motors M (M1, M2,... Mn) respectively provided on the drive wheels. (Step S201). Next, the vehicle body speed detection unit 102a detects the vehicle body speed of the moving body (step S202), and the drive wheel speed detection unit 102b detects the wheel speed of the drive wheels (step S203). Then, the slip ratio calculation unit 103 calculates the slip ratio in the drive wheels using the moving body speed and the drive wheel speed (drive wheel rotation speed and tire radius) (step S204).

  Next, the efficiency map acquisition unit 105 acquires the motor efficiency map 104 corresponding to the motor M (step S205). Next, based on the wheel speed detected by the driving wheel speed detection unit 102b by the calculation unit 106 and the slip rate calculated by the slip rate calculation unit 103, the efficiency value on the operation line indicating the relationship between the rotational speed and the torque. An optimum efficiency torque value To in the efficiency change equation on the operating line is calculated (step S206). Next, the distribution unit 107 calculates a torque distribution value for each motor M based on the total torque command value T acquired by the total torque command value acquisition unit 101 and the optimum efficiency torque value To calculated by the calculation unit 106. (Step S207). Then, the control unit 108 controls the torque distribution to each motor M based on the torque distribution value calculated by the distribution unit 107 (step S208).

  In general, the operation line on the motor efficiency map is a straight line. However, when the torque distribution is changed, the torque of the driving wheel changes, and the rotational speed of the driving wheel changes accordingly. Therefore, under a condition where the vehicle body speed is constant, the operation line on the motor efficiency map is not linear but has an inclination (strictly, a predetermined curve) as shown in FIG. The efficiency value with respect to the torque value on the operation line can be expressed as a torque-efficiency characteristic. Since this torque-efficiency characteristic is a curve as shown in FIG. 10 described later, the torque with the highest efficiency appears. The torque at which the efficiency is highest is referred to as the optimum efficiency torque value To. Then, using this optimum efficiency torque value To as a reference, all torque command values T are distributed to a plurality of n motors M with a predetermined torque distribution.

  An example of torque distribution to the n motors M by the distribution unit 107 will be described. The distribution unit 107 distributes all of the optimal efficiency torque values To only to the torque distribution values of any one of the plurality of n motors, or each of all or some of the motors M. All torque command values T are evenly distributed so that the torque distribution values are closest to the optimum efficiency torque value To.

Here, the efficiency change equation indicating the efficiency place on the operation line indicating the relationship between the wheel speed and the slip ratio, the rotation speed and the torque is obtained by the following procedure.
1. 1. Detection of current vehicle speed 2. Detection of current driving wheel speed 3. Calculation of slip ratio 4. Detect current torque from motor drive current Calculate the operating line formula (using formula (8) described later)
6). 6. Draw an action line on the efficiency map and obtain multiple points of combinations of torque value and efficiency value along the action line. Creating an efficiency change formula from torque values and efficiency values at multiple points At this time, the accuracy of the approximate formula of the efficiency change formula can be increased as the number of points increases.

  Since the torque Td is μ · N · r (μ: friction coefficient between road surface and tire, N: vertical drag, r: tire radius) (equation (5) described later), the friction coefficient μ changes when the torque Td changes. Change. As the friction coefficient μ changes, the slip ratio λ changes (described in FIG. 6). When the acceleration or deceleration is not large, the change in the rotational speed v is small, so that the rotational speed ω changes when the slip ratio λ changes. That is, the rotational speed of the drive wheel changes according to the torque value applied to the drive wheel. The relationship is expressed by equation (8) described later and FIG. In order to use this formula (8), the relationship between the slip ratio and the friction coefficient (formula (6) described later) is used. With respect to this relationship, either the equation (6) of the traveling road surface is acquired from a server or the like outside the moving body, or is created by the own vehicle.

The following procedure is used to create the relationship (6) between the slip ratio and the friction coefficient in the vehicle.
1. The current vehicle speed and drive wheel rotation speed are detected to determine the slip ratio λ.
2. A torque value is obtained from the current motor drive current, and a μ value is calculated from Td = μ · N · r.
3. While traveling, the λ and μ values at a plurality of points are obtained, and the μ-λ characteristic shown in FIG. 6 is created to generate the equation (6).
The torque value is obtained by multiplying a known torque constant by the drive current. In this case, since the tire normally travels without idling, it is possible to detect the λ value and μ value (λ is 0.2 or less in FIG. 6) in a range not exceeding the peak portion of μ. A point in the range exceeding the peak portion of μ (λ is 0.2 or more in FIG. 6) cannot be detected. However, since the region required in the present invention is a range not exceeding the peak portion of μ, μ− There is no problem if the formula (6) can be generated by creating the λ characteristic.

  The torque distribution device 100 according to the embodiment described above considers the calculated slip ratio when calculating the optimum efficiency torque value To on the motor efficiency map 104. The slip state of the drive wheel with respect to the road surface varies depending on factors such as the speed of the moving body, and more specifically, the rotational speed of the drive wheel. However, by considering the slip state of the drive wheel, the torque distribution to each drive wheel is efficiently performed. The optimal torque distribution when the drive wheels are actually driven can be performed and the motor can be driven in a region where the motor efficiency is high, so that the optimization of the drive system efficiency can be maximized. become. The drive system refers to a configuration related to driving of a moving body including a motor and an inverter.

Example 1
Example 1 of the present invention will be described below. In the first embodiment, an example will be described in which the torque distribution device is applied to a moving body such as a vehicle equipped with an in-wheel type motor that is incorporated in each of four drive wheels and driven independently. In this case, four motors M1 to M4 are used. As the motor M, a three-phase AC motor or a DC motor can be used. In the following embodiments, the same motor is used for the four drive wheels. As will be described later, the number of drive wheels is not limited to four, and the present invention can be applied to two, three, five, or more.

(Configuration of mobile body)
FIG. 3 is a schematic diagram showing the configuration of the moving body. The moving body 300 is a four-wheel drive vehicle having left and right front drive wheels FL and FR and left and right rear drive wheels RL and RR. These four drive wheels FL, FR, RL, RR are provided with in-wheel type motors M1 to M4, respectively, and are driven independently.

  Each of the motors M1 to M4 is provided with an inverter INV for driving the motor, and each inverter INV drives the motors M1 to M4 based on the control of the controller (ECU) 301. Various information is input to the controller 301, and the motors M1 to M4 are driven as a result of torque distribution.

  Input to the controller 301 includes the following. A steering angle is input from the handle 302. From the accelerator pedal 303, the total torque command value is input. A brake amount is input from the brake pedal 304. A side brake amount is input from the side brake 305. A shift position such as R, N, and D is input from the gear 306.

  Each of the driving wheels FL, FR, RL, RR is provided with sensors 307a to 307d for detecting the rotational speed V, and the rotational speeds Vfl, Vfr, Vrl, Vrr of the driving wheels FL, FR, RL, RR are provided. Is input to the controller 301. Each of the driving wheels FL, FR, RL, and RR is provided with sensors 308a to 308d that detect the vertical drag N that the tire receives from the ground, and the vertical drag Nfl of each of the driving wheels FL, FR, RL, and RR, Nfr, Nrl, and Nrr are input to the controller 301.

  Further, the moving body 300 is provided with an acceleration sensor 309, and the detected acceleration is input to the controller 301. Further, the moving body 300 is provided with a yaw rate sensor 310, and the detected yaw rate is input to the controller 301.

  The controller 301 drives each driving wheel FL, FR, RL, RR based on the above input. A control signal for driving is appropriately distributed for each driving wheel FL, FR, RL, RR and supplied to each of the motors M1 to M4 via the inverter INV.

  The battery 312 supplies power to the entire moving body 300. In particular, it becomes a drive source for driving the motors M1 to M4 of the drive wheels FL, FR, RL, RR via the inverter INV. As the battery 312, a secondary battery such as nickel hydride or lithium ion, a fuel cell, or the like is applied.

  The inverter INV can convert the AC voltage generated by the motors M <b> 1 to M <b> 4 into a DC voltage when the mobile body 300 is regenerated, and supply the converted DC voltage to the battery 312. The regeneration indicates power generation by operating the brake pedal 304 by a driver who operates the moving body 300 or power generation by relaxing the depression of the accelerator pedal 303 during traveling.

  Incidentally, drive efficiency η = motor M output / power supplied from battery 312 = (T × ω) / (V × I).

(Hardware configuration of torque distribution device)
Next, the hardware configuration of the torque distribution device 400 will be described. FIG. 4 is a block diagram illustrating a hardware configuration of the torque distribution device. 4, the torque distribution device 400 includes a CPU 401, a ROM 402, a RAM 403, a communication I / F 415, a GPS unit 416, and various sensors 417. Each component 401 to 417 is connected by a bus 420.

  The CPU 401 governs overall control of the torque distribution device 400. The ROM 402 stores programs such as a boot program and a torque distribution program, and can hold a motor efficiency map and the like. The RAM 403 is used as a work area for the CPU 401. That is, the CPU 401 controls the entire torque distribution device 400 by executing a program recorded in the ROM 402 while using the RAM 403 as a work area.

  The communication I / F 415 is connected to a network via wireless and functions as an interface between the torque distribution device 400 and the CPU 401. Communication networks that function as networks include public line networks, mobile phone networks, DSRC (Dedicated Short Range Communication), LANs, WANs, and the like. The communication I / F 415 is, for example, a public line connection module, an ETC unit, an FM tuner, a VICS (Vehicle Information and Communication System (registered trademark)) / beacon receiver, or the like.

  The GPS unit 416 receives radio waves from GPS satellites and outputs information indicating the current position of the mobile object. The output information of the GPS unit 416 is used when the CPU 401 calculates the current position of the moving body together with output values of various sensors 417 described later. The information indicating the current position is information for specifying one point on the map data, such as latitude / longitude and altitude.

Here, when acquiring the slip ratio and friction coefficient (μ-λ) characteristic of the traveling road surface from a server outside the moving body, the communication I / F 415 and the GPS unit 416 are used. The various sensors 417 are used for detecting the vehicle body speed and the normal force. The vehicle body speed is detected by the following method, for example.
1. 1. Integrate acceleration sensor output. 2. Calculated from the rotational speed of non-driving wheels Calculated from distance traveled per hour by GPS and other position sensors

Further, in order to detect the vertical drag, a load sensor provided for each tire is used, or is detected by the following method.
1. 1. Calculate the load balance between the front and rear wheels by calculating the displacement of the center of gravity from the acceleration sensor output. 2. Calculate the load balance between the right and left wheels by calculating the deviation of the center of gravity from the output of the yaw rate sensor. Calculate the load balance between the front and rear wheels and the right and left wheels by calculating the deviation of the center of gravity from the tilt sensor (gyro) output.

  The calculation unit 106, the distribution unit 107, and the control unit 108 of the torque distribution device 100 illustrated in FIG. 1 use the programs and data recorded in the ROM 402, the RAM 403, and the like in the torque distribution device 400 described above to perform predetermined processing by the CPU 401. The function is realized by executing the program and controlling each part in the torque distribution device 400.

(Torque distribution control by torque distribution device)
The torque distribution device 400 of the present embodiment performs optimization that maximizes the drive system efficiency. Assuming that the torque applied to each drive wheel is T1, T2, T3, T4 and the efficiency is η1, η2, η3, η4, the overall efficiency η for the four wheels is expressed by the following equation (1).

η = (T1 · η1 + T2 · η2 + T3 · η3 + T4 · η4) / T (1)
(Total drive torque T = T1 + T2 + T3 + T4)

FIG. 5 is a diagram illustrating an example of a motor efficiency map. The horizontal axis is the rotation speed, and the vertical axis is the torque. The following drive wheel selection is considered using the efficiency obtained on the linear operation line C when the vehicle body is at a certain speed shown in FIG.
(1) Equal torque drive with 4 wheels (2) Equal torque drive with 2 wheels (3) Drive with only 1 wheel

(1) In the case of equal torque drive with 4 wheels (1/4 (0.25) torque distribution to 4 wheels)
η1 = 0.25 · 0.77 + 0.25 · 0.77 + 0.25 · 0.77 + 0.25 · 0.77 = 0.77
(2) In the case of equal torque drive with 2 wheels (1/2 (0.5) torque distribution to 2 wheels)
η2 = 0.5 · 0.83 + 0.5 · 0.83 + 0 + 0 = 0.83
(3) When driving with only one wheel (all (1) torque distribution for only one wheel)
η3 = 1 · 0.72 + 0 + 0 + 0 = 0.72
According to the above, it is understood that the total efficiency is improved by performing torque distribution that increases the torque in the high efficiency region.

Here, the relationship between torque and rotational speed will be described.
The equation of motion of each driving wheel and the driving force of the driving wheel are shown in the following formulas (2), (3), and (4).

(Tm: torque command value to motor, Td: driving torque of driving wheel, Fd: driving force, Jw: moment of inertia of driving wheel, μ: coefficient of friction between road surface and tire, N: vertical drag, r: tire radius)
Here, the driving torque of the driving wheel means the torque of the motor mounted on the driving wheel.
When rapid acceleration or rapid deceleration is not performed, the change in speed is gentle and the change in rotational speed is small, so the following equation (5) is obtained.
dω / dt≈0 (5)
Therefore, the torque command value Tm to the motor and the drive torque Td of the drive wheel are substantially equal,
∴Tm≈Td = Fd · r = μ · N · r
In the following description, it is assumed that the change in the speed of the vehicle is gentle and the torque command value Tm to the motor and the drive torque Td of the drive wheels are substantially equal.

  FIG. 6 is a diagram showing the relationship between the slip ratio and the friction coefficient. The horizontal axis represents the slip ratio λ, and the vertical axis represents the friction coefficient μ. The slip ratio λ and the friction coefficient μ have the relationship shown in FIG. In the characteristic diagram shown in FIG. 6, the friction coefficient μ is the highest when the slip ratio λ is 0.2. When the slip ratio λ is 1, this corresponds to a state where the driving wheel is idling. Then, by performing the control so that the slip ratio λ falls within the range of 0 to 0.2, the drive wheels can travel without idling. In the characteristics shown in FIG. 6, the maximum value of μ and the value of λ that maximizes μ vary depending on the tire and the road surface condition. Even in that case, it can be approximated by changing the values of parameters B, C, D, and E in the following equation (6). However, in general, the physical characteristics of tires and asphalt road surfaces are unlikely to change rapidly, so that the change in μ-λ characteristics during running is gradual.

Λ = (r · ω−v) / (r · ω) = 1−v / (r · ω) (7)
Therefore, Td is represented by the following formula (8).

  Td = Fd · r = μ · N · r (8)

  When rapid acceleration or rapid deceleration is not performed, the speed change is gentle, so that the vehicle body speed v can be regarded as substantially constant, and the relationship between Td and ω can be obtained by the above equation (8).

FIG. 7 is a diagram showing the relationship between the rotational speed and the torque in consideration of the slip ratio. The state which calculated the torque and the rotational speed based on the said formula is shown. Here, vertical drag N: 400 [kg] × 9.8 [m / s ² ], tire radius r: 0.3 [m], vehicle speed v = 25, 50, 75, 100 [km / h] did.

  Accordingly, when the torque of the drive wheels changes by changing the torque distribution, the rotational speed changes correspondingly. The characteristic lines for the respective vehicle speeds shown in FIG. 7 are not linear, and all of them become a change curve that becomes gradual as the torque increases and saturates at the maximum torque.

  FIG. 8 is a diagram showing a state where the change curve shown in FIG. 7 is superimposed on the motor efficiency map. The horizontal axis represents the rotational speed ω, and the vertical axis represents the torque Td. In this embodiment, the motor efficiency map shows not only the characteristics of the motor M but also the characteristics including the characteristics (efficiency) of the inverter INV included in the drive system.

  As shown in FIG. 8, when the torque of one driving wheel is at point a on the operation line C at a certain speed (for example, 75 [km / h]), the torque of the driving wheel is changed by changing the torque distribution. When it is changed greatly, it moves to other points b and c on the operation line C. At this time, since the operation line C is inclined, the value of the rotational speed ω is also increased. Therefore, if torque distribution is performed without considering the change in the rotational speed ω, an accurate operating point is not known, and an error occurs in the efficiency value. Therefore, as shown in FIG. 8, the efficiency is accurately calculated even when the torque distribution is changed by drawing an operation line for each vehicle speed on the motor efficiency map and obtaining the torque-efficiency relationship. become able to.

  FIGS. 9A and 9B are diagrams illustrating the relationship between torque and efficiency that differ for each vehicle body speed. 9A is a torque-efficiency characteristic on the operation line at 50 [km / h], and FIG. 9-2 is a torque-efficiency characteristic on the operation line at 75 [km / h]. .

Further, the efficiency η obtained by approximating the operation line corresponding to FIG.
^{η = -1.7088E-14Td 6 + 1.8521E} -11Td 5 - 7.9786E-09Td 4 + 1.7336E-06Td 3 - 2.0447E-04Td 2 + 1.1782E-02Td + 4.4673E-01 ... (9)
Further, the efficiency η obtained by approximating the operation line corresponding to FIG.
^{η = 1.1253E-14Td 6 - 1.0197E} -11Td 5 + 3.2448E-09Td 4 - 3.5952E-07Td 3 - 2.6286E-05Td 2 + 7.8911E-03Td + 4.9954E-01 ... (10)
It becomes.

  If a value is substituted for the torque Td in the above approximate expression, the efficiency η can be obtained. According to the above equation (1), in the case of four-wheel drive, the optimum efficiency is that T1 · η1 + T2 · η2 + T3 · η3 + T4 · η4 is maximized in the condition range of T1 + T2 + T3 + T4 = T (total torque command value).

  Next, a method for calculating the slip ratio described above will be described. The slip ratio λ is defined by the following formula (11).

Here, (v: moving body speed, v _w : driving wheel speed, ω: driving wheel rotation speed, r: tire radius) Since the larger of v and v _w is the denominator, the denominator is _Vw , and at the time of deceleration, the denominator becomes v. A supplementary explanation will be given of the difference between the moving body speed, the drive wheel speed, and the drive wheel rotation speed. Multiplying the tire rotational speed by the tire radius gives the tire moving speed. When driving with the motor driven, the tire speed is higher than the car speed. On the other hand, when the vehicle is running with the motor braked, the tire speed is slower than the automobile speed. The relationship between the speed of the tire and the speed of the automobile is the slip ratio, which is expressed by the following formula (12).

Slip rate = (wheel speed−vehicle speed) / body speed and wheel speed, whichever is greater λ = (v _w −v) / Max (v _w , v) (12)
The wheel of the motor that is neither driven nor braked has a slip ratio of almost zero, so the speed of this wheel is substantially equal to the vehicle body speed (v _w ≈v).

  The rotational speed of the drive wheel can be calculated using a pulse output signal from a resolver, encoder, Hall element, or the like of the motor M. The speed of the moving body is as follows: 1. Since the slip ratio of the non-driving wheels is almost zero, the speed of the non-driving wheels is detected as the vehicle body speed. 2. Obtain the vehicle speed by integrating the output of the acceleration sensor. For example, the position of the vehicle body is detected by a sensor to determine the moving distance speed per time.

(Example of torque distribution)
FIG. 10 is a diagram illustrating the relationship between torque and efficiency. As in FIGS. 9-1 and 9-2, the horizontal axis represents torque and the vertical axis represents efficiency. As shown in FIG. 10, the point with the highest efficiency η on the operating line is defined as the optimum efficiency torque value To. In addition, the efficiency corresponding to the torque twice the optimum efficiency torque value To on the operation line is expressed as 2To.

(Characteristics of operation line on motor efficiency map)
Here, torque distribution with respect to the torque-efficiency characteristic specific to each motor will be described. The torque-efficiency characteristics in FIGS. 9-1 and 9-2 described above have characteristic lines that are unique to each motor M. 11-1 to 11-3 are diagrams showing torque-efficiency characteristics specific to the motor. FIG. 11-1 is an inverted U type, FIG. 11-2 is a Δ type, and FIG. 11-3 is a human type. Abbreviated. For simplification, the torque distribution when there are two drive wheels is considered. The efficiency η when the total torque command value T is distributed by two wheels is based on the above equation (1).
η = (T1 · η1 + T2 · η2) / T (13)
(Torque of driving wheel 1: T1, efficiency at that time: η1, torque of driving wheel 2: T2, efficiency at that time: η2)
It becomes.

  For example, when the total torque command value T is 160 [Nm], there are many combinations such as (T1, T2) = (100, 60) and (80, 80). By substituting into 13), the efficiency can be calculated. Therefore, it is only necessary to select a combination of torque values that maximizes efficiency. A specific example will be described below.

  12-1 to 12-6 are graphs showing the characteristics of the respective wheels in the inverted-U type torque-efficiency characteristics. In FIG. 12A, the total torque command value T is 100 [Nm], and the efficiency η is maximized when (T1, T2) = (0, 100), (100, 0). The total efficiency is a characteristic obtained by substituting into the above equation (13). 12-2, the total torque command value T is 120 [Nm], and the efficiency η is maximized when (T1, T2) = (0, 120), (120, 0). In FIG. 12-3, the total torque command value T is 140 [Nm], and the efficiency η is maximized when (T1, T2) = (0, 140), (140, 0). In FIG. 12-4, the total torque command value T is 160 [Nm], and the efficiency η is maximized when (T1, T2) = (80, 80). In FIG. 12-5, the total torque command value T is 180 [Nm], and the efficiency η is maximized when (T1, T2) = (90, 90). In FIG. 12-6, the total torque command value T is 200 [Nm], and the efficiency η is maximized when (T1, T2) = (100, 100).

  FIGS. 13-1 to 13-6 are graphs showing the characteristics of the respective wheels in the Δ-type torque-efficiency characteristics. In FIG. 13A, the total torque command value T is 100 [Nm], and the efficiency η is maximized when (T1, T2) = (0, 100), (100, 0). In FIG. 13B, the total torque command value T is 120 [Nm], and the efficiency η is maximized when (T1, T2) = (0, 120), (120, 0). In FIG. 13C, the total torque command value T is 140 [Nm], and the efficiency η is maximized when (T1, T2) = (40, 100), (100, 40). In FIG. 13-4, the total torque command value T is 160 [Nm], and the efficiency η is maximized when (T1, T2) = (60, 100), (100, 60). In FIG. 13-5, the total torque command value T is 180 [Nm], and the efficiency η is maximized when (T1, T2) = (80, 100), (100, 80). In FIG. 13-6, the total torque command value T is 200 [Nm], and the efficiency η is maximized when (T1, T2) = (100, 100).

  FIGS. 14-1 to 14-6 are diagrams illustrating the characteristics of the respective wheels in the human-type torque-efficiency characteristics. In FIG. 14A, the total torque command value T is 100 [Nm], and the efficiency η is maximized when (T1, T2) = (0, 100), (100, 0). 14-2, the total torque command value T is 120 [Nm], and the efficiency η is maximized when (T1, T2) = (20, 100), (100, 20). 14C, the total torque command value T is 140 [Nm], and the efficiency η is maximized when (T1, T2) = (40, 100), (100, 40). In FIG. 14-4, the total torque command value T is 160 [Nm], and the efficiency η is maximized when (T1, T2) = (60, 100), (100, 60). In FIG. 14-5, the total torque command value T is 180 [Nm], and the efficiency η is maximized when (T1, T2) = (80, 100), (100, 80). In FIG. 14-6, the total torque command value T is 200 [Nm], and the efficiency η is maximized when (T1, T2) = (100, 100).

From the above, the combination that maximizes the efficiency η is one of the following.
(T1, T2) = (0, T), (T, 0), (To, T-To), (T-To, To), (T / 2, T / 2) (14)
(To: optimal efficiency torque value)
Therefore, even if the curve shape of the torque-efficiency characteristic is any of the types shown in FIGS. 11-1 to 11-3, there is a combination that maximizes the efficiency η among the combinations of (14). Focused on.

  That is, even when the curve shape of the torque-efficiency characteristic is not clear, the combination that maximizes the result of calculating the combination shown in (14) is the torque distribution combination that maximizes the efficiency η. When the torque-efficiency characteristic is a complicated curve shape, it is conceivable that the efficiency other than the combination of (14) is the maximum efficiency. Some combinations have maximum efficiency. That is, there are an infinite number of combinations of torque distribution, but it is possible to obtain an optimal torque distribution value only by calculating the combination shown in (14) above. In the above example, torque distribution for two wheels has been described as an example, but the same applies to torque distribution for a plurality of drive wheels such as four wheels.

  Accordingly, there is a combination in which η is maximized in the distribution shown in FIGS. 15-1 to 15-5 described below. In addition, since there are many motor efficiency maps showing the torque-efficiency characteristics of the inverted U type, it is possible to simplify the torque distribution described in FIGS. 16-1 and 16-2 described later.

When the number of motors M is n (n is a natural number), the distribution unit 107
(1) When the total torque command value T is less than the optimum efficiency torque value To, the total torque command value T is distributed to the torque distribution value of one motor M.

(2) When the total torque command value T is equal to or greater than the optimum efficiency torque value To and less than n times the optimum efficiency torque value To, torque is distributed according to any of the following (a) to (c). At this time, one having the optimum drive system efficiency is selected from any one of (a) to (c).
(A) The optimal efficiency torque value To is distributed to the torque distribution values of some motors M, and the remainder obtained by dividing the total torque command value T by the optimal efficiency torque value To is one or n motors M Divide evenly into any of these and distribute.
(B) The optimal efficiency torque value To is allocated to the torque distribution values of some motors M, and the remainder allocated to some motors M is equally divided into the torque distribution values of other motors M. To distribute.
(C) All torque command values T are equally divided and distributed to all the motors M.

(3) When the total torque command value T is not less than n times the optimal efficiency torque value To, the optimal efficiency torque value To is distributed to the respective torque distribution values of the n motors M, and the total torque command value T Is divided by one or n motors M evenly and distributed, and the combination having the optimum drive system efficiency is selected.

  15-1 to 15-5 are diagrams for explaining torque distribution in the case where there are four drive wheels. A distribution example in which the distribution unit 107 distributes to each motor M of n = 4 will be described.

(When T <To)
As shown in FIG. 15A, when the total torque command value T is less than the optimum efficiency torque value To, the total torque command value T is distributed to the torque distribution value of one motor.

(When To ≦ T <2To)
As shown in FIG. 15-2, when the total torque command value T is equal to or greater than the optimum efficiency torque value To and less than twice the optimum efficiency torque value To, any one of (a) to (c) Of these, the combination having the optimum drive system efficiency is selected.
(A) All torque command values T are distributed to the torque distribution values of any one of the motors.
(B) The optimum efficiency torque value To is distributed to the torque distribution value of any one motor, and the remaining torque value is distributed to the torque distribution value of another motor.
(C) Distribute 1/2 of the total torque command value T to each of the torque distribution values of any two motors.

(When 2To ≦ T <3To)
Further, as shown in FIG. 15C, when the total torque command value T is not less than twice the optimum efficiency torque value To and less than three times the optimum efficiency torque value To, (a) to (e) Among these, the combination having the optimum drive system efficiency is selected.
(A) The optimum efficiency torque value To is distributed to the torque distribution value of any one motor, and the remaining torque value is distributed to the torque distribution value of another motor.
(B) Distribute 1/2 of the total torque command value T to each of the torque distribution values of any two motors.
(C) The optimal efficiency torque value To is distributed to the torque distribution values of any two motors, and the remaining torque value is distributed to the torque distribution value of another motor.
(D) The optimum efficiency torque value To is allocated to the torque distribution value of any one of the motors, and ½ of the remaining torque value is allocated to the torque distribution values of the remaining two motors.
(E) Distribute 1/3 of the total torque command value T to each of the torque distribution values of any three motors.

(When 3To ≦ T <4To)
As shown in FIG. 15-4, when the total torque command value T is not less than three times the optimum efficiency torque value To and less than four times the optimum efficiency torque value To, (a) to (g) Among these, the combination having the optimum drive system efficiency is selected.
(A) The optimal efficiency torque value To is distributed to the torque distribution values of any two motors, and the remaining torque value is distributed to the torque distribution value of one of the remaining motors.
(B) The optimum efficiency torque value To is allocated to the torque distribution value of any one of the motors, and ½ of the remaining torque value is allocated to the torque distribution values of the remaining two motors.
(C) Distribute 1/3 of the total torque command value T to each of the torque distribution values of any three motors.
(D) The optimum efficiency torque value To is distributed to the torque distribution values of any three motors, and the remaining torque values are distributed to the torque distribution values of the remaining motors.
(E) The optimum efficiency torque value To is distributed to the torque distribution values of any two motors, and ½ of the remaining torque values are allocated to the torque distribution values of the remaining two motors.
(F) The optimum efficiency torque value To is allocated to the torque distribution value of any one of the motors, and 1/3 of the remaining torque values are allocated to the torque distribution values of the remaining three motors.
(G) Distribute 1/4 of the total torque command value T to the torque distribution values of the four motors.

(When 4To ≦ T)
As shown in FIG. 15-5, when the total torque command value T is n (4) times or more of the optimum efficiency torque value To, the optimum drive system efficiency among (a) to (d) is obtained. Select the combination you have.
(A) The optimal efficiency torque value To is distributed to the torque distribution values of any three motors, and the remaining torque values are distributed to the torque distribution values of the remaining one motor.
(B) The optimum efficiency torque value To is allocated to the torque distribution values of any two motors, and 1/2 of the remaining torque values are allocated to the torque distribution values of the remaining two motors.
(C) The optimal efficiency torque value To is allocated to the torque distribution value of any one of the motors, and 1/3 of the remaining torque values are allocated to the torque distribution values of the remaining three motors.
(D) Distribute 1/4 of the total torque command value T to the torque distribution values of the four motors.

Each of the above distribution examples is represented by mathematical formulas as follows.
(When T <To)
T1 = T, T2 = T3 = T4 = 0

(When To ≦ T <2To)
Efficiency is calculated in the following three ways (a) to (c), and a combination that provides optimum efficiency is selected.
(A) T1 = To + (T−To), T2 = T3 = T4 = 0
(B) T1 = To, T2 = To− (2To−T), T3 = T4 = 0
(C) T1 = T2 = To- (2To-T) / 2, T3 = T4 = 0

(When 2To ≦ T <3To)
Efficiency is calculated in the following five ways (a) to (e), and a combination that provides the optimum efficiency is selected.
(A) T1 = To + (T-2To), T2 = To, T3 = T4 = 0
(B) T1 = T2 = To + (T-2To) / 2, T3 = T4 = 0
(C) T1 = T2 = To, T3 = To− (3To−T), T4 = 0
(D) T1 = To, T2 = T3 = To- (3To-T) / 2, T4 = 0
(E) T1 = T2 = T3 = To- (3To-T) / 3, T4 = 0

(When 3To ≦ T <4To)
Efficiency is calculated in the following seven ways (a) to (g), and a combination that provides the optimum efficiency is selected.
(A) T1 = To + (T-3To), T2 = T3 = To, T4 = 0
(B) T1 = T2 = To + (T-3To) / 2, T3 = To, T4 = 0
(C) T1 = T2 = T3 = To + (T-3To) / 3, T4 = 0
(D) T1 = T2 = T3 = To, T4 = To- (4To-T)
(E) T1 = T2 = To, T3 = T4 = To- (4To-T) / 2
(F) T1 = To, T2 = T3 = T4 = To− (4To−T) / 3
(G) T1 = T2 = T3 = T4 = To- (4To-T) / 4

(When 4To ≦ T)
Efficiency is calculated in the following four ways (a) to (d), and a combination that provides optimum efficiency is selected.
(A) T1 = To + (T-4To), T2 = T3 = T4 = To
(B) T1 = T2 = To + (T-4To) / 2, T3 = T4 = To
(C) T1 = T2 = T3 = To + (T-4To) / 3, T4 = To
(D) T1 = T2 = T3 = T4 = To + (T-4To) / 4

Next, a general expression for torque distribution during driving using n motors M will be shown.
(When T <k · To (k = 1))
T1 = T, T2 = T3 = ... = _Tn = 0

(When (k−1) · To ≦ T <k · To, the efficiency is calculated according to the following (2k−1), and the combination that provides the optimum efficiency is selected (k = 2 to n))
T1 = To + (T- (k-1) .To) / 1, T2 = T3 = ... = _Tk-1 = To, _Tk = _{Tk + 1} = ... = _Tn = 0
T1 = T2 = To + (T- (k-1) .To) / 2, T3 = T4 = ... = _Tk-1 = To, _Tk = _{Tk + 1} = ... = _Tn = 0
...
T1 = T2 = ... = _Tk-2 = To + (T- (k-1) .To) / (k-2), _Tk-1 = To, _Tk = _{Tk + 1} = ... = _Tn = 0
T1 = T2 = ... = _Tk-1 = To + (T- (k-1) .To) / (k-1), _Tk = _{Tk + 1} = ... = _Tn = 0
That's all for k-1.

_{T1 = T2 = ... = T k} -1 = To, T k = To- (k · To-T) / 1, T k + 1 = ... = T n = 0
_{T1 = T2 = ... = T k} -2 = To, T k-1 = T k = To- (k · To-T) / 2, T k + 1 = ... = T n = 0
...
T1 = To, T2 = ... = T k-1 = T k = To- (k · To-T) / (k-1), T k + 1 = ... = T n = 0
_{T1 = T2 = ... = T k} -1 = T k = To- (k · To-T) / k, T k + 1 = ... = T n = 0
That's all for k.
Together with the above k-1 ways, there are 2k-1 ways.

(When n · To ≦ T, calculate the efficiency in the following n ways and select the combination that gives the optimum efficiency)
T1 = To + (Tn · To) / 1, T2 = T3 =... = T _n-1 = T _n = To
T1 = T2 = To + (Tn · To) / 2, T3 = T4 =... = T _n-1 = T _n = To
...
T1 = T2 = ... = _Tn-1 = To + (Tn.To) / (n-1), _Tn = To
T1 = T2 = ... = _Tn-1 = _Tn = To + (Tn.To) / n
This is n ways.

  According to the above, the present invention can be applied not only to four-wheel drive but also to torque distribution in moving bodies such as six-wheel drive and eight-wheel drive.

(Simplified torque distribution in four-wheel drive)
In general, since there are many motor efficiency maps showing an inverted U-type torque-efficiency characteristic as shown in FIG. 11A, torque distribution can be simplified. As for the efficiency relationship with respect to the torque at a certain speed, the deterioration of the efficiency increases as the distance from the torque value To at which the optimum efficiency is obtained increases. Therefore, the torque of each drive wheel is equally distributed so as to be close to the optimum efficiency torque value To. Since the efficiency curve in the torque-efficiency characteristic diagram may be asymmetric with the optimum efficiency torque value To as the center, the efficiency change on the side where the torque is smaller than the optimum efficiency torque value To and the torque is greater than the optimum efficiency torque value To There is a difference in efficiency change on the side. Therefore, the ratio of the efficiency change rate between the lower torque side than the optimum efficiency torque value To and the higher torque side than the optimum efficiency torque value To is used to determine the relationship between the commanded total torque command value T and the optimum efficiency torque value To. Simple torque distribution can be performed.

  FIG. 16A is a diagram illustrating a difference in change rate in the torque-efficiency characteristic. The rate of change on the low torque side is twice the rate of change on the high torque side with the optimum efficiency torque value To shown in the figure as the center. In such a case, simple torque distribution in the case where the drive wheels are four wheels is performed as follows (1) to (4). In FIG. 16A, 150 [Nm] and 75 [Nm] have the same efficiency, 128.6 [Nm] and 85.7 [Nm] have the same efficiency, and 120 [Nm] and 90 [Nm] have the same efficiency. It is.

(1) When T <To + 2To / 4 (when T <150 [Nm] in the example shown in FIG. 16-1)
T1 = T, T2 = T3 = T4 = 0
(2) When 2 (To−To / 4) ≦ T <2 (To + 2To / 7) (in the example shown in FIG. 16A, when 75 [Nm] · 2 ≦ T <128.6 [Nm] · 2 )
T1 = T2 = T / 2, T3 = T4 = 0
(3) When 3 (To−To / 7) ≦ T <3 (To + 2To / 10) (in the example shown in FIG. 16A, when 85.7 [Nm] · 3 ≦ T <120 [Nm] · 3 )
T1 = T2 = T3 = T / 3, T4 = 0
(4) When 4 (To−To / 10) ≦ (in the example shown in FIG. 16A, when 90 [Nm] · 4 ≦ T)
T1 = T2 = T3 = T4 = T / 4
Note that the torque-efficiency characteristics in FIG. 16A are the same as those in FIG. 11A, which illustrates the torque distribution of the inverted U-type torque-efficiency characteristics. Substituting a value of 100 to 200 [Nm] for T in the above case division formula, when T <150 [Nm], (T1, T2) = (T, 0) is the optimum efficiency allocation. Yes, when 150 [Nm] ≦ T <257.2 [Nm], (T1, T2) = (T / 2, T / 2) is the optimal efficiency distribution, so that the reverse U-type torque-efficiency characteristics It can be confirmed that the results agree with the results of FIGS.
Therefore, if it is known that the torque-efficiency characteristic is an inverted U type, optimal torque distribution can be performed by such simple torque distribution.

(Simplified torque distribution as seen in general systems in the case of n-wheel drive)
FIG. 16B is a diagram for explaining the distance from the optimum efficiency torque value in the torque-efficiency characteristic. Here, k: the number of drive wheels, X: the distance from the optimum efficiency torque value To on the low torque side, Y: the distance from the optimum efficiency torque value To on the high torque side, a: (change rate on the high torque side) ) / (Change rate on the low torque side), torque distribution is divided into the following (1) to (3).
(1) When T <k · (To + (a · To) / (a · k + k + 1)), (k = 1)
T1 = T, T2 = ... = _Tn = 0
(2) When k · (To− (To) / (a · (k−1) + (k−1) +1)) ≦ T <k · (To + (a · To) / (a · k + k + 1)) , (K = 2 to n−1)
T1 = T2 = ... = _Tk = T / k, _{Tk + 1} = ... = _Tn = 0
(3) When n · (To− (To) / (a · (n−1) + (n−1) +1)) ≦ T, (k = n)
T1 = T2 = ... = _Tn-1 = _Tn = T / n
It becomes.

Note that the torque value that gives the same efficiency when driving with k wheels and when driving with k + 1 wheels is the boundary value for the cases (1) to (3). This can be expressed as an expression:
(K + 1) · (To−X) = k · (To + Y) (15)
Y = a · X (16)
It becomes. When X and Y are obtained by solving the above equations (15) and (16), the following is obtained.
X = To / (a · k + k + 1) (17)
Y = (a · To) / (a · k + k + 1) (18)
Using these equations (17) and (18), it is possible to divide cases when driving n-wheels.

(About dynamic torque distribution)
Next, since the optimum efficiency torque value To varies depending on the speed of the moving body (drive wheel), an example in which dynamic torque distribution is performed according to a change in speed will be described. FIG. 17 is a diagram for explaining dynamic torque distribution according to a running pattern. The traveling pattern of the moving body is described on the motor efficiency map in which the horizontal axis is the rotation speed and the vertical axis is the torque.

  In the travel pattern of FIG. 17, the torque distribution is T1 = T and T2 = T3 = T4 = 0 until acceleration reaches point A. Further, T1 = T2 = T / 2 and T3 = T4 = 0 between the points A and B. Between point B and point C, T1 = T2 = T3 = T / 3 and T4 = 0. Between point C and point D, T1 = T2 = T / 2 and T3 = T4 = 0. After point D, T1 = T and T2 = T3 = T4 = 0. In this way, since the optimum torque distribution is always performed for the speed and load torque that change from moment to moment, dynamic torque distribution by broadband control can be performed.

  FIG. 18 is a table showing setting data for the optimum number of drive wheels based on the rotational speed-total torque command value. Depending on the speed of the moving body (drive wheels) and the total torque command value T, a table or calculation formula for obtaining the number of drive wheels that provides the best overall efficiency can be created in real time during travel. Optimal torque distribution can be performed.

  For example, dynamic torque distribution in the case of the travel pattern shown in FIG. 18 will be described. Until the point A is reached, torque distribution is T1 = T, T2 = T3 = T4 = 0, and one-wheel drive is performed. In addition, between the points A and B, T1 = T2 = T / 2 and T3 = T4 = 0, and two-wheel drive is performed. Between point B and point C, T1 = T2 = T3 = T / 3, T4 = 0, and three-wheel drive is performed. Between point C and point D, T1 = T2 = T3 = T4 = T / 4, and four-wheel drive is performed. Between point D and point E, T1 = T2 = T3 = T / 3, T4 = 0, and three-wheel drive is performed. After point E, T1 = T2 = T / 2, T3 = T4 = 0, and two-wheel drive is performed.

  FIG. 18 shows the results of the above-described torque distribution algorithm, that is, the number of drive wheels and the torque value of each drive wheel, which are outputs when the motor efficiency map is not held in the memory and the input is speed and torque. Alternatively, it may be stored in the memory as a calculation formula.

  According to the first embodiment described above, it is possible to accurately detect the operating point of the rotational speed and the torque by drawing an operating line having an inclination in consideration of the slip ratio on the motor efficiency map. Thereby, the efficiency calculation by torque distribution can be performed accurately. In addition, optimal torque distribution can be performed for each drive wheel. When the total torque of the left driving wheel and the total torque of the right driving wheel are traveling at different torque values, the angle of the handle 302 and the angle of the vehicle body by the yaw rate sensor 310 are detected, and it is determined that the difference is large. Therefore, it is only necessary to adjust the torque distribution amount so as to reduce the difference in torque between the left and right to ensure traveling stability.

(Example 2)
(Configuration for improving overall efficiency)
In the second embodiment, a configuration for improving the overall efficiency will be described. FIG. 19 is a diagram for explaining the overall efficiency. The moving body travels by driving the motor M with the power supplied from the battery 312. In the motor M, loss due to copper loss due to the resistance of the coil, iron loss due to eddy current or magnetic hysteresis, or the like occurs. The efficiency from the power source to the motor M output is the efficiency of the drive system. The moving body 1900 that travels by the driving force of the motor M actually has a traveling system 1901 that receives the output of the motor M and travels by rotating the tire. Also in this traveling system 1901, loss due to slip between the tire and the road surface occurs. The efficiency from the output of the motor M to the output as traveling power is the efficiency of the traveling system. The overall efficiency of the moving body is expressed by the efficiency of these drive systems × the efficiency of the traveling system.

  Drive efficiency ηd = motor M output / power supplied from battery 312 = (T × ω) / (V × I).

  The torque distribution described in the first embodiment is related to the driving efficiency. In the second embodiment, a configuration that maximizes the overall overall efficiency by improving the efficiency of the traveling system will be described.

The driving force Fd per driving wheel is expressed by the following equation.
Fd = μ · N (19)
(Μ: friction coefficient, N: vertical drag)
Therefore, Td = Fd · r = μ · N · r (20)
(R: tire radius)

The efficiency ηλ of the traveling system is
ηλ = running power / motor output = (Fd · v) / (Td · ω) = (Fd · v) / (Fd · r · ω) = v / (r · ω) = v / v _w (21)
(V: body speed [m / s], v _w : wheel speed [m / s])
The slip ratio λ is expressed by the above formula (11). Therefore, the efficiency ηλ of the traveling system can be expressed using the slip ratio λ.
∴ηλ = 1−λ (22)

When the slip ratio λ is regarded as a function of the friction coefficient μ based on the characteristics of the slip ratio and the friction coefficient in FIG. 6 described above, the efficiency ηλ of the traveling system can be expressed as follows.
ηλ = 1−λ = 1−f (μ) = 1−f (Td / (N · r)) (23)
∵μ = Td / (N · r) (24)

  From equation (20), when N is constant, μ increases as Td increases. From the relationship of FIG. 6, in the region where λ is 0.2 or less, λ increases as μ increases. Therefore, 1-λ becomes small.

  FIG. 20 is a diagram showing the relationship between torque and running efficiency when the normal force is constant. In this case, as shown in the figure, when the torque Td increases, the traveling efficiency ηλ decreases, and the degree of decrease increases as the torque Td increases. That is, when the driving wheel torque Td is increased, the traveling efficiency ηλ decreases, and when the driving wheel torque Td is decreased, the traveling efficiency ηλ increases. Thus, when performing the torque distribution described in the first embodiment, it is necessary to consider not only the driving efficiency but also the traveling efficiency in order to improve the overall efficiency. As described above, the traveling efficiency ηλ is not limited to a configuration in which a previously created characteristic map of slip ratio λ−friction coefficient μ is held in a memory or the like. As another configuration, for example, the vehicle speed at that time is detected by a sensor (or estimated calculation) while the moving body is running, and the slip ratio λ is approximately calculated by detecting the speed of the driving wheel by the sensor. It is also conceivable to use it as a parameter of the running efficiency ηλ.

(Changes in running efficiency due to load changes)
When the above equation (20) indicating the torque is modified, the following equation is obtained.
μ = Td / (N · r) (25)

  FIG. 21 is a diagram illustrating a state in which the vertical drag for each drive wheel is different. According to the above equation (25), when a certain torque command value is given to a certain drive wheel, the friction coefficient μ changes according to the change in the normal force N from the road surface to the tire. As shown in FIG. 21, when the moving body travels uphill, incline, accelerates, curves, etc., the load balance of the moving body changes, and when the vertical drag N of a certain drive wheel decreases, the friction coefficient μ increases. Also, the slip ratio λ increases. As a result, 1-λ shown in the above equation (22) becomes small, and the efficiency ηλ of the traveling system decreases.

  FIG. 22 is a chart showing torque-running efficiency for each vertical drag. According to the above equation (23), the greater the vertical drag N, the greater the efficiency ηλ of the traveling system, and the degree of decrease in the efficiency ηλ of the traveling system associated with the increase in the torque Td is also reduced. Therefore, when the vertical drag N of each drive wheel changes, the drive wheel having a large vertical drag N increases the efficiency ηλ of the traveling system, and the drive wheel having a small vertical drag N decreases the efficiency ηλ of the traveling system. Thereby, the driving efficiency can be improved by increasing the torque of the driving wheel having a large load and decreasing the torque of the driving wheel having a small load.

(About overall efficiency)
FIG. 23 is a diagram for explaining the overall efficiency of the entire moving object. All torque command values T are distributed to the drive wheels FL, FR, RL, RR of the moving body 300 by T1, T2, T3, T4. The overall efficiency of the moving body 300 can be obtained by the sum of the torque distribution ratio of each drive wheel FL, FR, RL, RR × drive efficiency η _d × running efficiency ηλ.

The drive wheel FL in FIG. 23 will be described as an example. Using the motor efficiency map 2301, the drive efficiency η _d 1 is obtained based on the torque T1 distributed to the drive wheel FL and the rotational speed ω1. Further, based on the torque-running efficiency characteristic 2302, the running efficiency ηλ1 is obtained from the torque T1 distributed to the drive wheels FL. Similarly, the driving efficiencies η _d 2, η _d 3 and η _d 4 and the traveling efficiencies ηλ 2, ηλ 3 and ηλ 4 are obtained for the other driving wheels FR, RL and RR, respectively.

The overall efficiency ηtotal is obtained by the following formula.
ηtotal = (T1 / T) · η _d 1 · ηλ1 + (T2 / T) · η _d 2 · ηλ2 + (T3 / T) · η _d 3 · ηλ3 + (T4 / T) · η _d 4 · ηλ4 (26)

  The vertical drag of each drive wheel FL, FR, RL, RR is detected or estimated, and the torque distribution is performed so that the value of the above equation (26) becomes maximum according to the vertical drag, thereby improving the running efficiency. Can be improved.

  FIG. 24 is a block diagram of a functional configuration of the torque distribution device according to the second embodiment. Constituent parts similar to those in FIG. Then, the vertical drag Nfl, Nfr, Nrl, Nrr of each drive wheel FL, FR, RL, RR is input from the sensors 308a to 308d (see FIG. 3) to the distribution unit 107, and the distribution unit 107 receives each drive wheel. The torque distribution ratio for a drive wheel having a large vertical drag N (load) is increased, and the torque distribution ratio for a drive wheel having a small vertical drag N (load) is decreased.

(Example of total efficiency calculation)
FIGS. 25A and 25B are diagrams illustrating calculation examples of the total efficiency. In both cases, the vehicle body weight of the moving body 300 is 1600 [kg], the total torque command value T is 800 [Nm], the load balance moves backward by uphill or acceleration, the front wheel load is 300 [kg], and the rear It is assumed that the wheel load is 500 [kg].

In the example shown in FIG. 25A, four wheels are driven with a torque distribution of 200 [Nm] for each driving wheel. Using the motor efficiency map 2501, a driving efficiency η _d = 0.82 is obtained based on the torque Td = 200 [Nm] allocated to the front wheels FL and FR and the rotational speed ω = 80 [rad / s]. Further, based on the torque-running efficiency characteristic 2502, the running efficiency ηλ = 0.976 is obtained from the torque Td = 200 [Nm] distributed to the drive wheels FL. Similarly, for the rear wheels RL and RR, the driving efficiency η _d = 0.82 and the traveling efficiency ηλ = 0.986 are obtained. As a result, the overall efficiency ηtotal is based on the above equation (26).
ηtotal = ((200/800) · 0.82 · 0.976) · 2 + ((200/800) · 0.82 · 0.986) · 2 = 0.080442
It becomes.

In the example shown in FIG. 25-2, the rear wheel torque distribution is two wheels driven at 400 [Nm]. Using the motor efficiency map 2501, a driving efficiency η _d = 0.69 is obtained based on the torque Td = 0 [Nm] distributed to the front wheels FL and FR and the rotational speed ω = 80 [rad / s]. Further, based on the torque-running efficiency characteristic 2502, the running efficiency ηλ = 1 is obtained from the torque Td = 400 [Nm] distributed to the drive wheels FL. Similarly, for the rear wheels RL and RR, the driving efficiency η _d = 0.93 and the traveling efficiency ηλ = 0.971 are obtained. As a result, the overall efficiency ηtotal is based on the above equation (26).
ηtotal = ((0/800) · 0.691 · 1) · 2 + ((400/800) · 0.93 · 0.971) · 2 = 0.930303
It becomes.

  Not limited to the above calculation example, even if the vertical drag against the driving wheels is different, the driving efficiency and the traveling efficiency can be calculated for each driving wheel. Therefore, the overall efficiency based on the driving efficiency and the traveling efficiency is calculated. Can be calculated. Note that the torque distribution algorithm according to the first embodiment selects a combination having the optimum drive system efficiency, whereas the torque distribution algorithm according to the second embodiment selects the combination having the optimum overall efficiency.

  According to the second embodiment described above, similarly to the first embodiment described above, the operating point of the rotational speed and the torque is accurately detected by drawing an operation line having an inclination in consideration of the slip ratio on the motor efficiency map. be able to. Thereby, the efficiency calculation by torque distribution can be performed accurately. In addition, optimal torque distribution can be performed for each drive wheel. In addition, in the second embodiment, since the vertical drag (load) on each drive wheel is taken into account, the efficiency of the traveling system can be accurately detected and the overall efficiency can be improved. In addition, optimal torque distribution that improves the overall efficiency for each drive wheel can be performed. As in the first embodiment, when the total torque of the left driving wheel and the total torque of the right driving wheel are traveling at different torque values, the angle of the handle 302 and the angle of the vehicle body by the yaw rate sensor 310 are detected, If it is determined that the difference is large, the torque distribution amount is adjusted so as to reduce the torque difference between the left and right to ensure traveling stability.

  Note that the torque distribution method described in the present embodiment can be realized by executing a program prepared in advance on a computer such as a personal computer or a workstation. This program is recorded on a computer-readable recording medium such as a hard disk, a flexible disk, a CD-ROM, an MO, and a DVD, and is executed by being read from the recording medium by the computer. The program may be a transmission medium that can be distributed via a network such as the Internet.

DESCRIPTION OF SYMBOLS 100,400 Torque distribution apparatus 101 Total torque command value acquisition part 102a Vehicle body speed detection part 102b Driving wheel speed detection part 103 Slip ratio calculation part 104 Motor efficiency map 105 Efficiency map acquisition part 106 Calculation part 107 Distribution part 108 Control part 300 Mobile body 301 controller 307a to 307d (rotational speed) sensor 308a to 308d (vertical drag) sensor 309 acceleration sensor 310 yaw rate sensor 312 battery FL, FR, RL, RR drive wheel M (M1 to M4) motor INV inverter

Claims (3)

A torque distribution device that distributes all input torque command values to each of a plurality of motors connected to drive wheels,
A total torque command value acquiring means for acquiring the input total torque command value;
Efficiency map acquisition means for acquiring a motor efficiency map corresponding to the motor;
Vehicle body speed detecting means for detecting a vehicle body speed of a vehicle equipped with the motor;
Drive wheel rotation speed detection means for detecting the drive wheel rotation speed of the drive wheel;
A slip ratio detecting means for detecting a slip ratio in the drive wheel based on the vehicle body speed and the drive wheel rotation speed;
Based on the slip ratio, an operation line expression indicating the relationship between the driving wheel rotation speed and the torque is created, and the torque and the efficiency value of the motor efficiency map are calculated for each driving wheel rotation speed based on the operation line expression. And calculating means for calculating an optimum efficiency torque value of the efficiency change formula,
Based on the slip ratio, the total torque command value, and the optimum efficiency torque value,
Total efficiency ηtotal = Σ ((Tn / T) × ηdn × ηλn) (where T: total torque command value, Tn: torque distribution value of each motor, ηdn: drive system efficiency of each motor, ηλn: of each drive wheel Distribution means for calculating a torque distribution value for each of the motors so that the traveling system efficiency) is maximized;
Control means for controlling torque distribution to each of the motors based on the calculated torque distribution value;
With
The distribution means includes
The optimal efficiency torque value is allocated only to the torque distribution value of any one of the plurality of motors, or the torque distribution value is the most optimal efficiency torque value for all or some of the motors. A torque distribution device that distributes all the torque command values equally so as to approach When the total torque command value is T, the optimum efficiency torque value is To, the number of driving wheels is k, and (the rate of change on the high torque side) / (the rate of change on the low torque side) is a, the distribution means is:
(1) When T <k · (To + (a · To) / (a · k + k + 1)), (k = 1)
T1 = T, T2 = ... = Tn = 0
(2) When k · (To− (To) / (a · (k−1) + (k−1) +1)) ≦ T <k · (To + (a · To) / (a · k + k + 1)) , (K = 2 to n−1)
T1 = T2 = ... = Tk = T / k, Tk + 1 = ... = Tn = 0
(3) When n · (To− (To) / (a · (n−1) + (n−1) +1)) ≦ T, (k = n)
T1 = T2 = ... = Tn-1 = Tn = T / n
The torque distribution device according to claim 1, wherein the torque distribution value is calculated. A torque distribution method for distributing all input torque command values to each of a plurality of motors connected to drive wheels,
A total torque command value acquisition step of acquiring the input total torque command value;
An efficiency map acquisition step of acquiring a motor efficiency map corresponding to the motor;
A vehicle body speed detecting step for detecting a vehicle body speed of a vehicle equipped with the motor;
A drive wheel rotation speed detection step for detecting a drive wheel rotation speed in the drive wheel;
A slip ratio detection step of detecting a slip ratio in the drive wheel based on the vehicle body speed and the drive wheel rotation speed;
Based on the slip ratio, an operation line expression indicating the relationship between the driving wheel rotation speed and the torque is created, and the torque and the efficiency value of the motor efficiency map are calculated for each driving wheel rotation speed based on the operation line expression. A calculation step of creating an efficiency change equation indicating the optimal efficiency torque value of the efficiency change equation;
Based on the slip ratio, the total torque command value, and the optimum efficiency torque value,
Total efficiency ηtotal = Σ ((Tn / T) × ηdn × ηλn) (where T: total torque command value, Tn: torque distribution value of each motor, ηdn: drive system efficiency of each motor, ηλn: of each drive wheel A distribution step of calculating a torque distribution value for each of the motors so that the traveling system efficiency) is maximized;
A control step of controlling torque distribution to each of the motors based on the calculated torque distribution value;
Including
The distribution step includes
The optimal efficiency torque value is allocated only to the torque distribution value of any one of the plurality of motors, or the torque distribution value is the most optimal efficiency torque value for all or some of the motors. The torque distribution method is characterized by equally distributing all the torque command values so as to approach

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