JP3347096B2 - Driving force control system for electric vehicles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driving force control system which can generate uniform braking forces for respective wheels, and further, brake the wheels safely so as to respond instantaneously to a change in μ of a road surface, when a brake device is operated. SOLUTION: This driving force control system has a wheel driving motor which supplies a driving force to the driving wheels of a vehicle, a creeping torque command generation unit which issues a command to the motor to generate a creeping torque under predetermined conditions even if an acceleration pedal is in an off-state and a motor control unit which generates a signal in accordance with the creeping torque command to control a power converter. A μ detection unit which detects μ of the road surface, on which the vehicle runs, is provided in the control system. The creeping torque command generation unit changes the creeping torque command in accordance with detected μ of the road surface, so as to reduce the creeping torque when μ is small and to increase the creeping torque when μ is large.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a driving force control system for an electric vehicle, and more particularly to a driving force control system for an electric vehicle having a creep torque control device for controlling a creep torque of a vehicle.

[0002]

2. Description of the Related Art In various vehicles such as an electric drive vehicle having an electric motor as a power source, or a hybrid vehicle having an engine and an electric motor as a power source, an accelerator is provided for the purpose of facilitating starting on a slope. The state where the pedal is not depressed (accelerator OFF state)
However, a device having a creep torque control device that issues a command to generate a creep torque under predetermined conditions and activates the drive source to generate a predetermined creep torque on a driving wheel is disclosed in, for example, Japanese Patent Application Laid-Open No. 7-184304. And JP-A-10-290502.

Japanese Unexamined Patent Publication No. 11-41708 discloses a hybrid vehicle having a means for estimating a friction coefficient of a road surface, and switching a control pattern of powering and regenerative braking of an electric motor according to the estimated value. It is shown. Furthermore, JP-A-10-94110 discloses that
A control device for a hybrid vehicle that runs on an electric motor when traveling on a low μ road and performs traction control using the electric motor is described.

On the other hand, a driving force control system having an antilock brake system (ABS) for controlling a brake pressure based on information from a wheel speed sensor provided for each wheel is also known.

[0005]

SUMMARY OF THE INVENTION
In an electric vehicle equipped with a creep torque command generation unit that issues a command to generate a constant creep torque to the electric motor under predetermined conditions even in the state of F, the accelerator pedal is turned off, the brake pedal is depressed, and the vehicle stops. After that, a creep torque is applied to the drive wheels as a braking force, and the vehicle continues to stop.

[0006] At this time, if the creep torque is too large with respect to the actual road surface condition, in a two-wheel drive four-wheeled vehicle, etc., the braking force may not be equally generated on the four wheels and the vehicle body may become unstable. There is.

[0007] If the creep torque is not appropriate, there is a possibility that when the brake pedal is turned off and the accelerator pedal is depressed from the state where the creep torque is applied, proper start assist cannot be performed.

The present invention has been made in view of such circumstances, and an object of the present invention is to control each wheel so as to generate a uniform braking force according to the road surface condition. An object of the present invention is to provide a driving force control system for an electric vehicle.

Another object of the present invention is to provide a driving force control system for an electric vehicle that can safely brake in response to a change in μ of a road surface when a braking device is actuated.

Another object of the present invention is to provide a driving force control system for an electric vehicle that can always perform appropriate starting assistance.

[0011]

SUMMARY OF THE INVENTION The present invention provides a vehicle driving motor for supplying driving force to driving wheels of a vehicle, a battery connected to the motor via a power converter, and an operation state of an accelerator pedal. A drive torque command calculation unit that calculates a drive torque command for the motor in accordance with the following conditions; and a creep torque command generation unit that issues a command to cause the motor to generate a predetermined creep torque under predetermined conditions even when the accelerator pedal is OFF. Unit, a motor control unit that generates a signal for controlling the power converter based on the driving torque command and the creep torque command, and controls a brake pressure based on information from a wheel speed sensor provided on each wheel of the vehicle. A driving force control system for an electric vehicle having an anti-lock brake system, comprising a μ detection mechanism for detecting μ on a road surface on which the vehicle travels. The driving force control system for an electric vehicle is characterized in that the creep torque command is reduced when μ detected by the μ detection mechanism is smaller than a predetermined value.

Another feature of the present invention is that, in the driving force control system for an electric vehicle, the detected μ of the road surface is passed through a digital filter to suppress the fluctuation of μ input to the creep torque command generation unit. It is in.

According to the present invention, when μ is small, the creep force is small, and when μ is large, the creep force is large according to μ of the road surface detected by the ABS.
Therefore, it is possible to provide a driving force control system for an electric vehicle that can generate a uniform braking force on each wheel.

Further, it is possible to provide a driving force control system for an electric vehicle that can safely brake in response to a change in μ of the road surface when the brake device is actuated. Does not cause any discomfort to the driver.

Further, it is possible to provide a driving force control system for an electric vehicle which can always perform appropriate starting assistance in accordance with a change in μ of a road surface.

In the driving force control system for an electric vehicle according to the present invention, the creep torque command generating section may detect the brake operation amount by a brake pipe pressure detecting section. Further, the brake operation amount may be detected by a brake depression force detection unit. Further, the brake operation amount may be detected by a brake pedal stroke detection unit. On a low μ road, the creep torque may be reduced.

[0017]

FIG. 1 is a diagram showing a configuration of a drive system for a hybrid electric vehicle according to an embodiment of the present invention. The hybrid electric vehicle includes a motor / generator (hereinafter simply referred to as a motor) 4 connected to an engine 1 and an output shaft 2 thereof via a clutch 3 as a driving source of the vehicle.
The output shaft is transmitted to the axle 6 of the rear wheel 7 via a speed change mechanism (not shown) and the final drive 5. Each axle of the rear wheel 7 and the front wheel 9 has a wheel speed sensor 8
A and 8B are provided.

The hybrid drive unit comprises a hybrid control controller 10, an engine controller 1
1, a motor controller 12 and an anti-lock brake system (hereinafter, ABS) controller 13 are provided. The hybrid control controller 10 generates an operation command N * _E for the engine 1 and an operation command N * _MG for the motor 4 according to the operation mode and the operation state such as the accelerator operation amount θA, and the engine controller 11 and the motor controller 12. Send to Engine controller 11
Determines the opening degree of the throttle valve 22 of the engine 1, the fuel injection amount, the ignition timing, etc., according to the operation command N * _E and the intake air amount detected by the air flow meter 21, and the like. It controls the ignition device and the like. Further, the motor controller 12 transmits the operation command N *
_The motor 4 is controlled based on μ and the like sent from the _MG or the ABS controller 13. The clutch 3 between the engine 1 and the motor 4 is switched between an engaged state and a released state by the hybrid control controller 10 by an electromagnetic valve or the like. Reference numeral 23 denotes a motor generator for starting the engine and charging the battery.

A hydraulic pressure corresponding to the operation amount of the brake pedal 15 is generated by the hydraulic brake booster 16,
A brake pressure is applied to each wheel 7, 9 of the vehicle via the actuator 17 and the pipe 18. The ABS controller 13 controls the brake pressure based on information from wheel speed sensors 8 (8A to 8D) provided on the wheels 7, 9 of the vehicle.

Each of the controllers 10 to 13 includes a CPU and R
It comprises a microcomputer having an AM, a ROM, etc., and operates a shift lever operating range, a foot brake ON, an OF from a shift position sensor of a transmission, a brake switch, a vehicle speed sensor, an accelerator SW, etc.
Signals representing F, vehicle speed V, and accelerator operation amount are supplied. Furthermore, the engine speed N _E , Motor speed N _MG ,
Information about the battery voltage VB and the like is supplied from various sensors and the like, and performs predetermined processing according to a program incorporated in advance.

FIG. 2 shows a configuration example of the ABS controller 13. The ABS controller 13 controls each wheel 7 of the vehicle,
A wheel speed calculator 1 for calculating a wheel speed VR based on information from four wheel speed sensors 8 (8A to 8D) provided in
31, an estimated vehicle speed calculator 132 for estimating and calculating the vehicle speed from the wheel speed, a slip ratio calculator 133 for calculating the slip ratio of the wheel from the wheel speed and the estimated vehicle speed, and calculating the wheel deceleration by differentiating the wheel speed. Wheel deceleration calculation unit 134 and μ calculation unit 13 that calculates μ from the slip ratio and wheel deceleration
5 is provided. The original function of the anti-lock brake system that controls the brake pressure based on the information of the wheel speed sensors provided on each wheel by the ABS controller 13 or the like is not a feature of the present invention, and thus the description thereof is omitted here.

FIG. 3 shows a configuration example of a drive circuit of the motor 4. The motor controller 12 controls the motor 4 based on an operation command N * _MG from the hybrid control controller 10 and μ transmitted from the ABS controller 13.
The battery 31 is an inverter (power converter) via a main contactor which is opened and closed by turning on and off a key switch.
32. The motor controller 12 includes a current command generator 33, a dq-axis current controller 34, a PWM controller 35, a phase calculator 38, and a speed calculator 39. The phase calculation unit 38 and the speed calculation unit 39 include the resolver 36
It is connected to the. The motor controller 12 further includes a driving torque calculation unit 40, a creep torque calculation unit 41
And a command value selection unit 42.

[0023] The drive torque driving finger decree to the calculation unit 40 N * _MG
However, μ is input to the creep torque calculation unit 41, and the creep torque corresponding to μ is calculated. When the motor operates as a generator, the operation command N * _MG becomes negative.

The current command generator 33 calculates a torque command value τMG * based on the operation command value τM * and the rotation speed calculated from the pulse signal from the resolver 36. Based on the torque command value τMG *, current command values Iq * and Id * necessary for motor high efficiency control are calculated. The dq-axis current control unit 34 converts the three-phase alternating current of the motor current detected by the current detector 30 into three-phase / two-phase coordinates and converts the d- and q-axis current I
d and Iq are processed and calculated. Then, based on these detected values and the command values Iq * and Id *, a proportional or proportional-integral current control process is performed to calculate voltage command values Vq * and Vd *.
Furthermore, two-phase / 3 the coordinate transformation phase three-phase AC voltage command values _{V U} *, V V *, and calculates a V _W *.

The PWM control unit 35, the voltage command value V _U
The PWM signal of the inverter 32 is generated by comparing the triangular wave signal with the carrier signal from *, V _V *, and V _W *, and the switching element of the inverter 32 is turned on and off.
By applying the PWM-controlled voltage to the motor 32 in this manner, the motor current is reduced to the current command values Iq * and Iq *.
Control to d *.

FIG. 4 shows an example of calculation of the slip ratio λ during deceleration. In (A) in FIG. 4, vehicle <br/> speed from the wheel speed V _R V _Rf and wheel deceleration -α and two slip ratio lambda (-
λ1, −λ2) are calculated. On the high μ road surface shown in FIG. 4B, only slip-λ1 is obtained, and the low μ road shown in FIG.
Large reduction in the wheel speed V _R in road -λ1, -λ2 is obtained.

As shown in FIG. 5, the creep torque calculating section 41 calculates a raw μ storage section 410 for holding the latest value of μ (hereinafter, raw μ) of the road surface detected by the ABS and a creep force τMs *. A creep force calculation unit 411 and a μ correction unit 412 that corrects the creep force τMs * based on the latest value of raw μ are provided.

As shown in FIG. 6A, the μ correction unit 412 reduces the creep force τMμ * on a low μ road where μ detected by the ABS is smaller than a predetermined value, and when μ is greater than μs, The creep force τMμ * is set to a constant position value τMs0 *.
In some cases, when μ is equal to or more than μs, the creep force τMμ * may be increased according to μ. Further, as shown in FIG. 6B, the creep force may be changed in two stages depending on whether μ is larger or smaller than μs.
In order to further suppress the fluctuation of creep, creep may be operated only when μ is low.

In a two-wheel drive four-wheeled vehicle or the like, if the creep is strong, the drivability deteriorates because the braking force at the time of braking is not generated equally on the four wheels. By using this control, creep is weakened on a low μ road, which is safe.

The command value selecting section 42 includes a driving torque calculating section 4
The output τMA * of 0 or the output τMμ * (absolute value) of the creep torque calculation unit 41 on the larger side is selected and output as the final drive torque to the current command generation unit 33, that is, the operation command value τM *.

In this way, as shown in FIG.
According to the latest value of μ of the road surface detected by the BS, a predetermined creep torque force is applied to the drive wheels even when the accelerator is not depressed, that is, the creep force is large when μ is large. Is small, and when μ is small, the final driving torque τ is set so as to generate a large creep force.
M * is set, and the motor is operated based on the torque τM *.

In this case, the creep force always outputs a torque equal to or greater than a predetermined value (creep torque) regardless of the brake depression amount. Accordingly, the creep torque is transmitted when the brake pedal is released, and the vehicle can start in the traveling direction without retreating.

From the state of execution of the creep torque control,
When the brake is turned off and the accelerator is depressed to shift to the normal control to increase the motor torque, the creep torque should be smoothed in consideration of the change in the gear ratio to prevent shock and uncomfortable feeling due to a sudden change in the creep torque. It is desirable to control the motor torque to increase.

FIG. 8 shows an example of the relationship between the vehicle operating mode and the creep torque based on the above embodiment. While running, A
The BS controller 13 calculates the vehicle speed VR from the wheel speed VR.
f and the wheel deceleration -α are obtained, and the slip ratio λ1 is calculated. When the accelerator pedal is released, the vehicle decelerates and the brake pedal is depressed to stop. A
Since the latest value of μ on the road surface detected by the BS is μ1,
While the vehicle is stopped, a creep torque force corresponding to μ1 is applied to the drive wheels. Then, μ of the road surface that starts and runs is μ
2 or μ3, a creep torque force corresponding to μ2 or μ3 is applied to the drive wheels while the vehicle is stopped thereafter.

If the creep is strong in a two-wheel drive four-wheeled vehicle or the like, the braking force during braking is not generated equally on the four wheels, and the vehicle body may become unstable. By using this control,
On low μ roads, creep is weakened, so it is safe.

In the above-described embodiment, the torque command value is output. However, the present invention is not limited to this. The motor speed command value for controlling the motor speed may be output. May be configured to output a speed control command value for controlling the speed.

Next, another embodiment of the creep torque calculating section 41 will be described with reference to FIGS. As shown in FIG. 9, the raw μ detected by the ABS in the creep torque calculation unit 41 is sent to the μ correction unit 412 via the digital filter 420. That is, the fluctuation of the road surface μ detected by the ABS is suppressed through a digital filter. The output of the brake switch is also applied to the μ correction unit 412. This makes it possible to perform control such that the digital filter processing of μ is performed only during braking, or the digital filter processing value of μ is maintained during non-braking (see FIG. 11).

FIG. 10 shows an example of the digital filter 420. In the oversampling method shown in FIG.
The average of four non-wrappings is used. In the moving average method of (b), the average is obtained by shifting each time.
In the weighted average method of (c), the old sampling value is calculated as 9 /
10. A weighted average is obtained by setting the new sampling value to 1/10.

The road surface condition is not constant, and there is a road surface in which μ immediately before has a large fluctuation of μ such as an ice snowy road. Even on a large road surface, the creep force is less likely to fluctuate every time, so that the driver is not discomforted.

As shown in FIG. 11, the digital filter 420 calculates an average value μAVE of raw μ at predetermined time intervals when the brake is on, and calculates the creep force based on the μAVE. In (A) of FIG. 12, a digital filter value mu, in non-braking are heavy digital filter. In (B), the digital filter processing value of μ is not updated during non-braking but is held. This is because μ can be detected only during braking.

In (C), when the raw value of μ is smaller than the filtered value, the filtered value is replaced with the raw value of μ. As a result, it is possible to quickly reduce creep on a low μ road.

In (D), the range of change in creep torque is limited. Thereby, it is possible to prevent the creep torque from suddenly changing during the damping during the ABS operation. (Decrease in creep force → wheel lock → μ low judgment →
FIG. 12 shows the driving state of the vehicle and μAVE
4 shows an example of the relationship between the pressure and the creep force. By passing the μ of the road surface detected by the ABS through a digital filter,
Fluctuation is suppressed, and control is stabilized. Further, the road surface condition is not constant, and the μ immediately before may vary greatly in the case of an ice snowy road or the like. The adoption of the digital filter makes it difficult for the creep force to fluctuate every time even on such a road surface, so that the driver does not feel uncomfortable.

FIG. 13 shows an example of the relationship between the driving mode of the vehicle and the creep torque based on the above embodiment. Running,
The μ value of the road surface detected by the ABS is reduced by the digital filter. For example, the value of μ3 at the previous stop is reduced to μ2 and μ1 sequentially during traveling. At the time of stop, a creep torque force corresponding to μ2 is applied.

The digital filter processing of μ may be performed at a constant processing cycle. Alternatively, the digital filter processing of μ may be performed only during braking. This is because μ can be detected only during braking. Further, the digital filter processing value of μ is retained during non-braking. (Not updated).

As another embodiment, the digital filter processing value of μ may be a heavy digital filter during non-braking.

Further, the variation of μ on the road surface detected by the ABS is suppressed by passing through a digital filter, and when the raw value of μ is smaller than the filtered value (value after filtering), the value after filtering is changed to μ. It may be replaced with raw value. As a result, it is possible to quickly reduce the creep on a low μ road, and it is possible to prevent a sudden change in the creep torque during the damping during the ABS operation. That is, it is possible to eliminate a vicious cycle of decreasing the creep force → locking the wheels → decreasing μ → decreasing the creep force, thereby preventing a sudden change in the creep torque.

FIGS. 14 and 1 show another embodiment of the present invention.
As shown in FIG. 5, in addition to the above configuration, the creep itself may be determined according to the brake pedaling force. In this case, a measuring unit for measuring the operation amount of the brake device is required. The creep torque may be reduced when the operation amount of the brake device is large, and may be increased when the operation amount of the brake device is small. This makes it possible to save extra power for generating creep force during stoppage.

For example, the brake operation amount is detected by a brake pipe pressure detector. Thereby, a value close to the brake operating force can be detected.

Alternatively, the brake operation amount may be detected by the brake pedal force detection unit, or may be detected when a brake pipe failure occurs. Further, the brake operation amount may be detected by a brake pedal stroke detection unit.
As a result, it is possible to detect even when the brake pipe fails.

FIG. 16 shows another embodiment of the present invention.
The creep force is calculated by the creep force calculation unit 606 through the filter 604 using the lower value of μ detected by the other traction control system 600. If the creep is strong in a two-wheel drive four-wheeled vehicle or the like, the braking force during braking is not generated equally on the four wheels, and the vehicle body may become unstable. By using this control method, low μ
It's safe on the road because creeping creep is low.

[0051]

According to the present invention, in accordance with μ of the road surface detected by the ABS, when μ is small, the creep force is small, and when μ is large, the creep force is large.
Therefore, it is possible to provide a driving force control system for an electric vehicle that can generate a uniform braking force on each wheel.

In addition, it is possible to provide a driving force control system for an electric vehicle that can safely brake in response to a change in μ of the road surface when the brake device is actuated. Does not cause any discomfort to the driver.

Further, it is possible to provide a driving force control system for an electric vehicle that can always perform appropriate starting assistance in accordance with a change in μ of the road surface.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a drive system for a hybrid electric vehicle according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration example of an ABS controller 13;

FIG. 3 is a diagram illustrating a configuration example of a drive circuit of the motor in FIG. 1;

FIG. 4 shows vehicle speed VRf and wheel deceleration -α from wheel speed VR.
FIG. 7 is a diagram illustrating an example of calculating two slip ratios λ (λ1, λ2).

FIG. 5 is a diagram illustrating a configuration of a creep torque calculation unit.

FIG. 6 is a diagram illustrating characteristics of a creep force calculation unit.

FIG. 7 is a diagram showing a relationship between an accelerator opening and a final drive torque τM *.

FIG. 8 is a diagram illustrating an example of a relationship between a driving mode of a vehicle and a creep torque according to the embodiment of the present invention.

FIG. 9 is a diagram illustrating a configuration of a creep torque calculation unit.

FIG. 10 is a diagram illustrating an example of a digital filter.

FIG. 11 is a diagram illustrating the operation of a digital filter.

FIG. 12 is a diagram illustrating an example of a relationship between a driving state of a vehicle, μAVE, and creep force according to another embodiment of the present invention.

FIG. 13 is a diagram illustrating an example of a relationship between a driving mode of a vehicle and a creep torque according to the embodiment of the present invention.

FIG. 14 is a diagram showing a main part configuration of another embodiment of the present invention.

15 is an explanatory diagram of characteristics of the embodiment of FIG.

FIG. 16 is a diagram showing a main part configuration of another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Engine, 3 ... Clutch, 4 ... Motor, 8 ... Wheel speed sensor, 10 ... Hybrid control controller, 11
... Engine controller, 12 ... Motor controller,
13: ABS controller, 40: drive torque calculator,
41 ... creep torque calculation unit, 42 ... command value selection unit,

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Naoyuki Ozaki 2520 Ojitakaba, Hitachinaka-shi, Ibaraki Hitachi, Ltd. Automotive Equipment Division (72) Inventor Nobuhiro Akasaka 2520 Ojitakaba, Hitachinaka-shi, Ibaraki Hitachi, Ltd. (56) References JP-A-9-327101 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B60L 1/00-15/42 B60K 6/02- 6/06 B60T 7/12-8/96 B60K 41/00-41/28

Claims (6)

(57) [Claims] 1. A vehicle driving motor for supplying driving force to driving wheels of a vehicle, a battery connected to the motor via a power converter, and a driving torque of the motor according to an operation state of an accelerator pedal. Drive torque command calculation means for calculating a command, creep torque command generation means for outputting a command to generate a predetermined creep torque to the motor under predetermined conditions even when the accelerator pedal is OFF, and the drive torque command A motor control means for generating a signal for controlling the power converter based on the creep torque command, and an anti-lock brake system for controlling a brake pressure based on information from a wheel speed sensor provided on each wheel of the vehicle. A driving force control system for an automobile, wherein μ detection means for detecting μ on a road surface on which the vehicle travels; a creep torque command generating means for reducing the creep torque command when μ is smaller than a predetermined value; and a digital filter for performing the filtering of the detected μ at a predetermined cycle during braking of the vehicle. A driving force control system for an electric vehicle, comprising: a filter unit. 2. The digital filter means according to claim 1, wherein said digital filter means holds and outputs the digital filter processing value of μ performed during braking of the vehicle and the processed value during non-braking of the vehicle. A driving force control system for an electric vehicle, wherein the driving force control system is a digital filter means. 3. The digital filter according to claim 1, wherein said digital filter means is configured to output said μ while said vehicle is not braking.
A driving force control system for an electric vehicle, characterized in that the digital filter processing is a heavy digital filter processing. 4. A description of the claim 1, suppressing the variation through a digital filter μ of the detected road surface, when the raw value of the μ is less than the filtering value (the value after filtering), the A driving force control system for an electric vehicle, wherein a value after filtering is replaced with the raw value. 5. The claim 4, the digital filtering values of the mu, electric vehicle drive force control system, characterized in that during non-braking of the vehicle is to be heavy digital filter. 6. A driving force control system according to claim 1, wherein the creep torque command generating section, the creep torque is reduced when the operation amount of the brake device is large, the operation amount of the brake device is small A driving force control system for an electric vehicle, wherein the creep torque is sometimes increased.