JP2006168650A - Power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power steering device capable of certainly obtaining operation stability in backward traveling. <P>SOLUTION: The power steering device has a motor 5 for outputting assist torque for reducing steering burden of a driver to a steering system from a steering wheelto front wheels. The power steering device is provided with a retreating detection means (vehicle speed sensor 14 and inhibitor switch 16) for detecting whether or not the vehicle retreats; and an assist torque operation part 13e for driving/controlling the motor 5 such that reverse assist torque is generated in a direction in which steering torque required from steering operation of the driver is increased in backward traveling of the vehicle. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention belongs to the technical field of a power steering device that reduces a driver's steering burden.

In conventional power steering systems, steering stability is ensured by subtracting the damping torque proportional to the steering angular velocity of the steering wheel from the assist torque corresponding to the steering torque when the vehicle is traveling backward, where the steering reaction force is smaller than when traveling forward. (For example, refer to Patent Document 1).
Japanese Patent Laid-Open No. 11-59468

  However, the conventional technique has a problem that the steering angular speed is low near the neutral position of the steering wheel, so that the damping amount is insufficient and the steering stability is deteriorated.

  The present invention has been made paying attention to the above problems, and an object of the present invention is to provide a power steering device that can reliably obtain steering stability during reverse travel.

In order to achieve the above object, the present invention provides:
In a power steering device having an assist actuator that outputs an assist torque that reduces a driver's steering burden on a steering system from a steering wheel to a steered wheel,
Reverse detection means for detecting whether the vehicle is moving backward,
A reverse assist control means for driving and controlling the assist actuator so as to generate a reverse assist torque in a direction in which a steering torque required for a driver's steering wheel operation increases when the vehicle moves backward;
It is characterized by providing.

  Therefore, in the power steering device of the present invention, the reverse assist torque is generated in the direction of increasing the steering torque with respect to the steering torque during the reverse travel, so that the steering operation becomes heavy during the reverse travel, and the steering stability can be reliably obtained. Can do.

  Hereinafter, the best mode for carrying out the power steering apparatus of the present invention will be described based on Examples 1 and 2.

First, the configuration will be described.
FIG. 1 is a block diagram illustrating a configuration of the electric power steering apparatus according to the first embodiment.

  A steering shaft 3 that connects a steering wheel 1 for steering operation of the driver and a steering mechanism 2 that performs a steering operation, a torque sensor (steering torque detection means) 4 that detects steering torque applied to the steering wheel 1, and a steering shaft 3 An electric motor (an assist actuator, hereinafter abbreviated as a motor) 5 that outputs an assist torque (assist force) is disposed.

  The handle 1 is provided so as to be rotatable around an axis at a position facing a driver in a vehicle interior (not shown). The steering mechanism 2 is constituted by a rack and pinion type steering device including a pinion 6 integrally formed at the lower end of the steering shaft 3 and a rack shaft 7 meshing with the pinion 6. The rack shaft 7 is fixed to the front portion of the vehicle (not shown) so as to be slidable in the left-right direction. Both ends of the rack shaft 7 are slid in the left-right direction to the front portion of the front-wheel vehicle for steering through the left and right tie rods 8 and 9. The both ends are connected to front steering wheels 10 and 11 via left and right tie rods 8 and 9.

  The motor 5 is coupled to the steering shaft 3 via a speed reducer 12 that converts torque generated by the motor 5 into rotational torque of the steering shaft 3. The motor current supplied to the motor 5 is controlled by the controller 13.

Next, a control system of the first embodiment will be described with reference to a control block diagram of the controller 13 of FIG.
When the steering wheel 1 is steered by the driver, the front wheels 10 and 11 mechanically connected to the steering wheel 1 are steered. At this time, the torsional load input to the torque sensor 4 is input to the controller 13 as a steering torque. Further, the controller 13 is provided with signals such as a vehicle speed sensor (vehicle speed detecting means) 14 for detecting the traveling speed of the vehicle and an inhibitor switch 16 for detecting the range position of the automatic transmission. The vehicle speed sensor 14 and the inhibitor switch 16 constitute reverse detection means for detecting whether or not the vehicle is moving backward.

  The controller 13 has a built-in motor terminal voltage sensor 13a for detecting the motor voltage, a motor current sensor 13b for detecting the motor current, and a motor speed estimating unit 13c for estimating the rotational speed of the motor 5 from the motor voltage and motor current. Yes.

The rotational speed N of the motor 5 is calculated from the following equation (1) using the back electromotive force coefficient ke of the motor 5.
N = (V − RI) / Ke (1)
Here, N is the rotation speed of the motor 5, V is the voltage between the motor terminals, R is the motor internal resistance, and I is the motor current. That is, since the motor 5 is mechanically coupled to the steering shaft 3 via the speed reducer 12, the steering angular speed is calculated by converting the rotational speed of the motor 5 by the reduction ratio.

  The output of the controller 13 is given to the motor 5 via the drive circuit 13d. The controller 13 calculates the drive current of the motor 5 using the steering torque, the rotation speed of the motor, the vehicle speed, etc., and controls and drives the motor 5 while referring to the motor current by the motor current sensor 13b. To do. The power supplied from the drive circuit 13d to the motor 5 is provided by the battery 15.

  The controller 13 includes an assist torque calculation unit 13e, a viscosity compensation unit 13f, an inertia compensation unit 13g, a target current value setting unit 13h, and a current feedback (FB) unit 13i.

  The assist torque calculation unit 13e determines a target assist torque that reduces the driver's operation load in accordance with the steering torque when the vehicle moves forward including zero vehicle speed. In addition, the target assist torque is increased so that the steering wheel 1 can be lightly turned off during stationary driving, and the target assist torque is decreased at high speed so that the steering torque becomes heavier as the speed increases and a solid steering characteristic is realized. Yes.

  The assist torque calculation unit 13e detects when the vehicle is moving backward based on signals output from the vehicle speed sensor 14 and the inhibitor switch 16. When the vehicle moves backward, reverse assist torque is output in a direction to increase the driver's steering torque (corresponding to reverse assist control means). Specifically, it is determined that the vehicle is moving backward when the vehicle speed is greater than zero and a signal indicating the R range is output from the inhibitor switch.

  As shown in the assist current map for the steering torque in FIG. 3, the characteristics of the reverse assist torque are set so as to increase as the steering torque [Nm] increases and as the vehicle speed [km / h] increases. . Further, when the vehicle speed is an extremely low speed used for parking and stopping, the assist current is set to zero and the reverse assist torque is not generated.

  Furthermore, the reverse assist torque is set not to be generated in the torque dead zone where the steering torque is equal to or less than a predetermined minute torque. Since the assist current map at the time of forward movement is the same as the conventional one, the description is omitted.

  The viscosity compensation unit 13f adds a viscosity compensation amount proportional to the motor rotation speed estimated by the motor speed estimation unit 13c to the target assist torque, and performs viscosity compensation of the steering system. The inertia compensation unit 13g adds an inertia compensation amount proportional to the motor rotational acceleration to the target assist torque, and performs inertia compensation of the steering system. The motor rotational acceleration is obtained by differentiating the motor rotational speed with time by the differentiator 13j.

  The target current value setting unit 13h corresponds to the target assist torque calculated by the assist torque calculation unit 13e, the viscosity compensation amount calculated by the viscosity compensation unit 13f, and the inertia compensation amount calculated by the inertia compensation unit 13g. The target assist current value of the motor 5 is set. The current FB unit 13i subtracts the actual motor current value detected by the current sensor 13b from the target assist current value, and outputs it to the drive circuit 13d. The drive circuit 13d supplies the motor 5 with a drive current that matches the actual motor current value with the target assist current value.

Next, the operation will be described.
[Deterioration of steering stability due to decrease in steering reaction force during reverse travel]
The pneumatic trail of the tire is the distance from the tire ground contact center to the cornering force action point, and the cornering force or side force multiplied by the pneumatic trail is the self-aligning torque. Thus, the longer the pneumatic trail, the greater the self-aligning torque.

  As shown in Fig. 4 (a), the front wheel of the car has a caster angle so that the moment length of the lateral force input to the tire is reversed when the vehicle is moving forward. Becomes longer in proportion to the vehicle speed. For this reason, when the vehicle moves forward, the self-aligning torque increases as the vehicle speed increases.

  On the other hand, the pneumatic trail at the time of reverse travel becomes shorter in proportion to the vehicle speed, as shown in FIG. Accordingly, the steering reaction force for the reverse travel is reduced because the moment length is shortened even when the same lateral force as that for the forward travel is input. Therefore, when the vehicle is traveling backward, there is a problem that the gain of the vehicle behavior with respect to the steering input is increased compared to the vehicle traveling forward, the steering stability is deteriorated, and the neutral position of the steering wheel is difficult to understand.

  In order to solve the above problem, in the electric power steering apparatus described in Japanese Patent Application Laid-Open No. 11-59468, the steering stability is improved by increasing the damping amount proportional to the steering angular velocity with respect to the assist amount when the vehicle moves backward. We are trying to secure it. However, there is a problem that the steering stability is poor near the neutral position where the steering angular velocity of the steering wheel is low because the damping amount is insufficient.

Further, in the power steering apparatus described in Japanese Patent No. 2741037, the steering neutral position is made easy to understand by increasing the return control amount proportional to the steering angle in the torque dead zone regardless of forward and backward travel. However, since the steering reaction force becomes light when the steering torque is large, there is a problem that stability is lost if the steering wheel is turned during reverse travel.
[Reverse assist action during reverse travel]
On the other hand, in the power steering device of the first embodiment, when the vehicle reverses, the motor 5 is driven and controlled so that the reverse assist torque is generated in the direction in which the steering torque required for the driver's steering wheel operation increases. Steering stability is ensured by making the steering wheel operation heavy.

  As shown in FIG. 3, in the first embodiment, the assist current for the steering torque during reverse travel is a function corresponding to the vehicle speed, and is generated in the opposite direction to the steering torque as the vehicle speed during reverse travel increases. The assist current is set so that the motor torque to be increased (arrow A in FIG. 3).

  As a result, as shown in FIG. 5, as the vehicle speed increases, the reaction force of the driver becomes heavier with respect to the steering angle (arrow A in FIG. 5), so that the self-aligning torque decreases in proportion to the vehicle speed. At times, a stable steering feeling can be realized regardless of the vehicle speed.

  Further, since the reverse assist torque is increased as the steering torque is increased, the force with which the handle 1 is returned to the neutral position is increased as the handle 1 is largely turned. That is, the self-alignment at the time of forward movement can be simulated, a stable steering feeling can be obtained, and a neutral feeling that is a solid feeling in the vicinity of the neutral position can be given to the driver.

  Further, in the first embodiment, since the reverse assist torque is set not to be generated in the torque dead zone where the steering torque is equal to or less than a predetermined minute torque, the driver operates the handle 1 in the vicinity of the steering neutral position. In this case, it is possible to prevent the reverse assist torque from being generated excessively.

  In the first embodiment, when the vehicle speed is 0 km / h, the assist current map in FIG. 3 is not used and the assist characteristic is set to be the same as that at the time of forward movement. Simply changing does not cause a reaction force change and does not give the driver a sense of incongruity.

  Furthermore, it is set so that the reverse assist torque is not generated regardless of the steering torque up to the vehicle speed range used when parking and stopping, for example, about 5 km / h, so the lightness of the steering reaction force when parking and stopping can be realized. . And when traveling backwards beyond the vehicle speed used for parking and stopping, for example, in a traveling scene where the vehicle travels backward over a long distance, by generating a reverse assist torque against the steering torque, the steering force is increased and the vehicle is firmly operated during backward steering. A feeling can be given.

Next, the effect will be described.
In the power steering apparatus according to the first embodiment, the following effects can be obtained.

  (1) In a power steering device having a motor 5 that outputs an assist torque that reduces the driver's steering burden on the steering system from the steering wheel 1 to the front wheels 10 and 11, it is detected whether or not the vehicle is moving backward. Backward detection means (vehicle speed sensor 14 and inhibitor switch 16), and assist torque calculation for driving and controlling the motor 5 so as to generate reverse assist torque in a direction in which the steering torque required for the driver's steering wheel operation increases when the vehicle moves backward Therefore, when the vehicle is moved backward, the steering operation is made heavy so that the steering reaction force can be secured, that is, the steering stability can be obtained.

  (2) The torque sensor 4 for detecting the steering torque applied to the steering wheel 1 is provided, and the assist torque calculator 13e increases the reverse assist torque as the steering torque increases, so that the self-aligning torque similar to that during forward movement can be simulated. At the same time, it can convey a neutral feeling to the driver.

  (3) The vehicle speed sensor 14 for detecting the vehicle speed is provided, and the assist torque calculation unit 13e increases the reverse assist torque as the vehicle speed increases. Therefore, the steering reaction force during reverse operation where the self-aligning torque decreases as the vehicle speed increases. It is possible to achieve both the firmness and neutrality of the vehicle, and the steering characteristics that are light and easy to handle when moving backwards when stationary or parked.

  (4) Since the assist torque calculation unit 13e does not generate reverse assist torque when the vehicle speed is extremely low, it is possible to realize a light steering reaction force during parking and stopping.

  (5) The assist torque calculation unit 13e does not generate the reverse assist torque when the steering torque is in the torque dead zone where the steering torque is equal to or less than a predetermined minute torque. Therefore, the reverse assist torque is excessively generated near the steering neutral position, and the driver This can prevent the user from feeling uncomfortable.

  The second embodiment is an example in which the region of the torque dead zone in which the reverse assist torque is not generated during reverse travel is narrowed as the vehicle speed increases. In addition, since the structure of Example 2 is the same as Example 1, description is abbreviate | omitted.

FIG. 6 is an assist current map for each vehicle speed with respect to the steering torque of the second embodiment.
In the second embodiment, as in the first embodiment, the relationship of the assist current with respect to the steering torque at the time of reverse travel is a function corresponding to the vehicle speed, and the vehicle speed at the time of reverse travel increases as shown by the arrow B in FIG. Accordingly, a current command value for generating motor torque in the opposite direction of the steering torque is generated. Further, in the second embodiment, as indicated by an arrow C in FIG. 6, the steering torque value for starting the reverse assist is reduced by narrowing the torque dead zone as the vehicle speed during reverse travel increases.

  As a result, as shown in FIG. 7, the reaction force of the driver becomes heavier with respect to the steering angle (arrow B in FIG. 7), and the higher the vehicle speed in the steering pattern near the neutral position where the steering torque becomes minute. Since the gain of the steering torque with respect to the steering angle becomes high (arrow C in FIG. 7), a neutral feeling that is a firm feeling in the vicinity of the neutral position can be more noticeably transmitted to the driver.

Next, the effect will be described.
In the power steering apparatus according to the second embodiment, in addition to the effects (1) to (5) of the first embodiment, the following effects can be obtained.

  (6) The assist torque calculation unit 13e narrows the torque dead zone as the vehicle speed increases. Therefore, in the steering pattern near the neutral position where the steering torque is minute, the gain of the steering torque with respect to the steering angle increases as the vehicle speed increases. A neutral feeling, which is a solid feeling near the neutral position, can be transmitted to the driver.

(Other examples)
As described above, the present invention has been described based on the first and second embodiments. However, the present invention is not applied only to the electric power steering. For example, the present invention is applied to a so-called electrohydraulic power steering capable of arbitrarily changing the steering torque. It may be used.

  In the first and second embodiments, the steering angular velocity is calculated (estimated) from the motor back electromotive force. However, the sensor that directly measures the rotational speed of the motor or the steering shaft, or the sensor that measures the angle of the motor or the steering shaft. The steering angular velocity may be calculated by differentiating the signal measured by this sensor with respect to time.

  In the first and second embodiments, the example in which it is detected whether or not the vehicle is moving backward is shown based on the signal from the vehicle speed sensor and the signal from the inhibitor switch. However, the configuration of the backward movement detecting means is arbitrary. .

1 is a block diagram illustrating a configuration of an electric power steering device according to Embodiment 1. FIG. 3 is a control block diagram of a controller 13. FIG. 4 is an assist current map for each vehicle speed with respect to the steering torque according to the first embodiment. It is a figure which shows the pneumatic trail at the time of advance and reverse. It is a figure which shows the relationship between the steering angle which shows the reverse assist effect | action at the time of reverse travel of Example 1, and steering torque. 6 is an assist current map for each vehicle speed with respect to the steering torque according to the second embodiment. It is a figure which shows the relationship between the steering angle which shows the reverse assist effect | action at the time of reverse travel of Example 2, and a steering torque.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Handle 2 Steering mechanism 3 Steering shaft 4 Torque sensor 5 Motor 6 Pinion 7 Rack shaft 8, 9 Tie rod 10, 11 Front wheel 12 Reducer 13 Controller 13a Motor terminal voltage sensor 13b Motor current sensor 13c Motor speed estimation part 13d Drive circuit 13e Assist torque calculation unit 13f Viscosity compensation unit 13g Inertia compensation unit 13h Target current value setting unit 13i Current feedback unit 13j Differentiator 14 Vehicle speed sensor 15 Battery 16 Inhibitor switch

Claims (6)

In a power steering device having an assist actuator that outputs an assist force that reduces a driver's steering burden on a steering system from a steering wheel to a steered wheel,
Reverse detection means for detecting whether the vehicle is moving backward,
Reverse assist control means for driving and controlling the assist actuator so as to generate a reverse assist force in a direction in which a steering torque required for a driver's steering wheel operation increases when the vehicle is moving backward;
A power steering apparatus comprising: The power steering according to claim 1, wherein
A steering torque detecting means for detecting a steering force applied to the steering wheel;
The power assist device according to claim 1, wherein the reverse assist control means increases the reverse assist force as the steering force increases. In the power steering device according to claim 1 or 2,
Vehicle speed detection means for detecting the vehicle speed,
The reverse assist control means increases the reverse assist force as the vehicle speed increases. In the power steering device according to claim 3,
The reverse assist control unit does not generate reverse assist torque when the vehicle speed is extremely low. In the power steering device according to any one of claims 2 to 4,
The power assist device according to claim 1, wherein the reverse assist control means does not generate the reverse assist force when the steering force is in a steering force dead zone where the steering force is equal to or less than a predetermined minute torque. The power steering according to claim 5,
The power steering apparatus, wherein the reverse assist control means narrows the steering force dead zone as the vehicle speed increases.

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