JP2007020354A - Steering gear for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steering gear for a vehicle which reduces the steering load without accompanying idling or back-and-forth movement of a running the vehicle, at turning of a steering wheel. <P>SOLUTION: In the vehicle which independently drives the right and left front wheels, respectively, there are provided a means of determining the start of operation for turning the steering wheel, without running the vehicle (steps S1, S2, S4), and a steering effort auxiliary control means (a step S5), wherein the determination means detects the start of such an operation by the driver, and the control means provides back-and-forth rotational vibrations of a micro range in the right and the left front wheels, when it is determined that such an operation has started. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention belongs to the technical field of a vehicle steering device used in a vehicle capable of independently driving left and right steering wheels.

In the conventional vehicle steering system, the required steering assist force is obtained based on the steering torque, the drive torques of the left and right steered wheels from which the necessary steering assist force is obtained are obtained, and the wheel-in motor attached to the steered wheel is obtained. Driven (see Patent Document 1 and Patent Document 2).
Japanese Patent Laid-Open No. 7-7816 Japanese Patent Laid-Open No. 9-117016

  However, in the above prior art, when a torque is applied to a wheel to generate a steering assist force for steering in a so-called stationary state where a steering request is given at a vehicle speed of zero, a kingpin is caused by a road surface reaction force. Trying to generate a turning moment, but if the required value of steering assist force is large, the frictional force between the tire and the road surface must be exceeded, and there is a problem that it is necessary to apply torque to the wheel until the wheel idles. . Moreover, in order to steer without exceeding the static friction limit between the tire and the road surface, it is necessary to rotate the wheel, but in this case, there is a problem that the vehicle moves.

  The present invention has been made paying attention to the above problems, and an object of the present invention is to provide a vehicle steering apparatus that can reduce a steering burden at the time of stationary without causing idling or forward / backward movement of the vehicle. It is in.

In order to achieve the above object, the present invention provides:
In vehicles that can drive the left and right steering wheels independently,
A stationary operation start judging means for judging the start of the stationary operation of the driver;
Steering force assist control means for applying a minute range of longitudinal rotational vibration to the left and right steered wheels when it is determined that the stationary operation starts.
It is characterized by providing.

  In the present invention, when the driver starts stationary, the front-rear rotational vibration is applied to the left and right steered wheels, so that the frictional force in the steered wheel steering direction changes from static friction force to dynamic friction force, The power is reduced. At this time, since the left and right steered wheels are moved within a minute range, the vehicle does not move forward or backward as the left and right steered wheels rotate. Therefore, it is possible to reduce the driver's steering burden at the time of stationary without accompanying the idling of the wheel or the forward / backward movement of the vehicle.

  Hereinafter, the best mode for carrying out the present invention will be described based on Examples 1 to 4.

First, the configuration will be described.
FIG. 1 is a diagram illustrating a configuration of a vehicle steering apparatus according to a first embodiment. The vehicle steering apparatus according to the first embodiment includes a handle 1 that is operated by a driver, and a steering mechanism 3 that steers left and right front wheels (left and right steered wheels) 2a and 2b according to an operation amount of the handle 1. . The steering mechanism 3 includes a vehicle speed sensitive hydraulic power steering system.

  The column shaft 4 integrally coupled with the handle 1 has a steering angle sensor 5 and a steering torque sensor 6 on the shaft. A rack and pinion type steering gear 7 is provided at the tip of the column shaft 4. In the steering mechanism 3, knuckle arms (not shown) of the left and right front wheels 2, 2 are connected to both ends of a rack 8 that reciprocates in the vehicle width direction according to the rotation of the handle 1 via left and right tie rods 9a, 9b. Yes. The left and right front wheels 2a and 2b are provided with wheel-in motors (hereinafter referred to as motors) 10a and 10b as drive sources.

  The control unit 13 includes a steering angle detected by the steering angle sensor 5, a steering torque detected by the steering torque sensor 6, a vehicle speed detected by the vehicle speed sensor 11, and a throttle detected by the throttle opening sensor 12. The opening is input.

  The control unit 13 calculates the target driving force of the vehicle in accordance with the throttle opening detected by the throttle opening sensor 12, and the vehicle speed detected by the vehicle speed sensor 11 and the steering angle detected by the steering angle sensor 5. From this, the target yaw rate of the vehicle is calculated. Then, the motors 10a and 10b are driven according to the target driving force and the target yaw rate.

  Further, the control unit 13 determines whether the driver is stationary based on the throttle opening detected by the throttle opening sensor 12, the vehicle speed detected by the vehicle speed sensor 11, and the steering torque detected by the steering torque sensor 6. Determine the start of operation. When the driver starts the stationary operation, a control command is output to the motors 10a and 10b to cause the front wheels 2a and 2b to rotate back and forth within a minute range. At this time, as shown in FIG. 2, the left and right front wheels 2a, 2b are oscillated back and forth with amplitudes opposite to each other. Here, the amplitude that causes the left and right front wheels 2a and 2b to rotate back and forth is at least large enough to change the ground contact position of the tire.

Next, the operation will be described.
[Steering force assist control process at stationary]
FIG. 3 is a flowchart showing a flow of steering force assist control processing at the time of stationary according to the first embodiment, and each step will be described below.

  In step S1, the vehicle speed is read from the vehicle speed sensor 11, and it is determined whether or not the vehicle speed is zero. If YES, the process proceeds to step S2, and if NO, the process proceeds to step S9.

  In step S2, the throttle opening is read from the throttle opening sensor 12, and it is determined whether or not the throttle opening is zero. If YES, the process proceeds to step S3. If NO, the process proceeds to step S9.

  In step S3, it is determined whether or not the control start flag F is set (= 1). If YES, the process proceeds to step S7. If NO, the process proceeds to step S4.

  In step S4, the steering torque is read from the steering torque sensor 6, and it is determined whether or not the steering torque exceeds a preset stationary start determination value. If YES, the process proceeds to step S5. If NO, the process proceeds to step S9. Step S1, step S2, and step S4 constitute a stationary operation start determining means for determining the start of the stationary operation of the driver.

  In step S5, a control command for causing the left and right front wheels 2a and 2b to oscillate back and forth within a minute range within a range where the vehicle does not move in the front-rear direction is output to the motors 10a and 10b, and the process proceeds to step S6 (steering force assist control). Equivalent to means).

  In step S6, the control start flag F is set, and the process proceeds to return.

  In step S7, the steering torque is read from the steering torque sensor 6, and it is determined whether or not the steering torque is below a preset stationary end determination value. If YES, the process moves to step S8, and if NO, the process moves to step S5. In the first embodiment, the stationary end determination value is set to a value smaller than the stationary start determination value to prevent control hunting.

  In step S8, the control start flag F is reset (= 0), and the process proceeds to return.

  In step S9, the control start flag F is reset, and the process proceeds to return.

[Auxiliary steering force assist control operation]
When the driver starts stationary, the flow proceeds from step S1, step S2, step S3, step S4, step S5, and step S6 in the flowchart of FIG. That is, the vehicle speed is zero in step S1, the driver does not request acceleration in step S2, and the steering torque exceeds the stationary start determination value in step S4, so it is determined that the driver's stationary operation has started, and in step S4, the control start flag F is set. In step S5, a minute range of longitudinal vibration is applied to the left and right front wheels 2a, 2b.

  Thereby, since the left and right front wheels 2a, 2b are steered in the front-rear direction within a range that does not involve the movement of the vehicle with respect to the road surface, the frictional force in the steering direction between the tire and the road surface changes from static friction force to dynamic friction force, The frictional force in the turning direction is reduced. Therefore, the steering torque required to steer the front wheels 2a, 2b is reduced, and the driver's steering load is reduced.

  Further, since the left and right front wheels 2a and 2b are oscillated back and forth with amplitudes of opposite phases, the driving force generated by the front and rear rotation vibrations of the left and right front wheels 2a and 2b can be canceled in the left and right front wheels 2a and 2b. Can suppress forward or backward movement.

  While the driver is stationary, the control start flag F is set, and the flow from step S1, step S2, step S3, step S7, step S5, step S6 is repeated, and step S5 is repeated. Then, the control for adding a minute range of longitudinal vibration to the left and right front wheels 2a, 2b is continued.

  When the driver finishes stationary, the process proceeds from step S1, step S2, step S3, step S7, and step S8. In step S8, the control start flag F is reset, and the front wheels 2a and 2b are caused by the front and rear rotational vibration. Stop steering force assistance.

  When the driver is stationary, if the vehicle speed exceeds zero, or if the accelerator pedal is depressed, the process proceeds from step S1 → step S9 or step S1 → step S2 → step S9. The control start flag F is reset, and the steering force assist by the front and rear rotational vibrations of the front wheels 2a and 2b is stopped.

  That is, when the vehicle starts to move, the necessary steering torque is reduced, and therefore, the steering wheel 1 is prevented from becoming too light due to excessive steering force assistance. Further, when the driver's acceleration request is detected, the responsiveness at the start can be improved by stopping the front-rear rotational vibration of the left and right front wheels 2a, 2b.

[Rearing friction reduction effect by front / rear front / rear vibration]
When the suspension system is configured so that the point at which the steering rotation center of the steering wheel touches the road surface does not coincide with the point at which the tire center line contacts the road surface, the moment about the steering rotation center due to the reaction force that the tire receives from the road surface Will occur. That is, a moment for turning the steered wheel is generated according to the driving force transmitted from the tire to the road surface.

  Therefore, in a vehicle that can drive the left and right steered wheels independently, the steered wheels can be steered by making the driving forces of the left and right wheels unbalanced. Based on vehicle information such as vehicle speed, throttle opening, steering angle, steering torque, etc. and driver request values, it is possible to combine the functions of steering assist force by calculating the drive torque for each of the left and right wheels and controlling the drive source. It becomes. In particular, in a vehicle equipped with a drive source with excellent control responsiveness such as an electric motor, steering assistance can be performed with good response by the driving force.

  However, even with a vehicle having such a function, when the vehicle is steered without moving the vehicle body, in order to steer with the steered wheels held in that position, the tire is placed on the road surface. Therefore, excessive torque exceeding the maximum static frictional force between the tire and the road surface is required.

  On the other hand, in the vehicle steering apparatus according to the first embodiment, when a stationary request is made, the front wheels 2a and 2b are rotated forward and backward by a small amount to reverse the frictional force in the steering direction between the tire and the road surface. By changing from force to dynamic friction force, the driver's steering is assisted. At this time, by applying rotations in opposite phases to the left and right front wheels 2a and 2b, the force can be canceled between the left and right wheels, and the vehicle can be prevented from moving forward or backward.

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

  (1) In a vehicle capable of independently driving the left and right front wheels 2a and 2b, a stationary operation start determining means (steps S1, S2 and S4) for detecting the start of the stationary operation of the driver and a stationary operation start are determined. Steering force auxiliary control means (step S5) for applying a minute range of longitudinal rotational vibration to the left and right front wheels 2a, 2b. Therefore, it is possible to reduce the driver's steering burden by reducing the frictional force in the front wheel turning direction without idling the wheels or moving the vehicle back and forth.

  (2) The stationary operation start determining means determines that the stationary operation start is started when the steering torque exceeds a preset stationary start determination value when the vehicle speed is zero and the driver does not request acceleration. Can be determined more accurately.

  (3) Steering force assist control means is set in advance when the front and rear rotational vibration is applied to the left and right front wheels 2a, 2b, when the vehicle speed exceeds zero, when the throttle opening exceeds zero, or when the steering torque is preset In any case when it falls below the set stationary end determination value, the application of the longitudinal rotational vibration to the left and right front wheels 2a, 2b is stopped. Therefore, unnecessary front / rear rotational vibrations of the left and right front wheels 2a, 2b when steering force assistance is not required can be prevented, and the start operation or parking operation after the stationary operation can be performed smoothly.

  (4) Since the steering force assist control means causes the left and right front wheels 2a and 2b to vibrate in the front-rear direction with the amplitudes opposite to each other, the movement of the vehicle accompanying the front-rear rotational vibration of the left and right front wheels 2a and 2b can be suppressed.

  The second embodiment is an example in which a braking force is applied to the non-steering wheel when the front-rear rotational vibration is applied to the left and right steering wheels.

First, the configuration will be described.
FIG. 4 is a diagram illustrating the configuration of the vehicle steering apparatus according to the second embodiment. The vehicle steering apparatus according to the second embodiment includes a brake actuator 16 capable of supplying brake fluid to the wheel cylinders 15a and 15b of the left and right rear wheels (non-steering wheels) 14a and 14b regardless of the driver's brake pedal operation. Yes.

When it is determined that the driver has started the stationary operation, the control unit 13 outputs a control command to the motors 10a and 10b to cause the left and right front wheels 2a and 2b to oscillate back and forth (in the same phase, left and right in the same range). At the same time, a control command for supplying brake fluid to the left and right wheel cylinders 15 a and 15 b is output to the brake actuator 16.
The other configuration of the second embodiment is the same as that of the first embodiment shown in FIG.

Next, the operation will be described.
[Vehicle start prevention action by braking force of rear wheels]
In the second embodiment, as shown in FIG. 5, in order to brake the left and right rear wheels 14a and 14b at the start of the driver's stationary operation, the force that the vehicle tries to start by the front and rear rotation of the left and right front wheels 2a and 2b is It can be suppressed by the braking force of the rear wheels 14a, 14b.

Next, the effect will be described.
In the vehicle steering apparatus according to the second embodiment, the following effects can be obtained in addition to the effects (1) to (3) of the first embodiment.

  (5) Since the steering force assisting control means brakes the rear wheels 14a and 14b when applying the front and rear rotational vibration to the left and right front wheels 2a and 2b, it is possible to reliably prevent the vehicle from starting at the time of stationary.

  The third embodiment is an example in which, when applying a longitudinal rotational vibration to the left and right steered wheels, imparting a longitudinal rotational vibration having an amplitude opposite to that of the steered wheel to the left and right non-steered wheels.

  FIG. 6 is a diagram illustrating a configuration of the vehicle steering device of the third embodiment. In the vehicle steering apparatus according to the third embodiment, left and right rear wheels 14a and 14b are provided with wheel-in motors (hereinafter referred to as motors) 17a and 17b as drive sources. The control unit 13 drives the motors 10a, 10b, 17a, and 17b according to the target driving force and the target yaw rate.

Further, when it is determined that the driver has started the stationary operation, the control unit 13 causes the front wheels 2a and 2b and the rear wheels 14a and 14b to rotate and vibrate in a minute range with respect to the motors 10a and 10b and the motors 17a and 17b. Output control commands. At this time, the left and right front wheels 2a and 2b and the left and right rear wheels 14a and 14b are oscillated back and forth with amplitudes opposite to each other.
The other configuration of the third embodiment is the same as the configuration of the first embodiment shown in FIG.

Next, the operation will be described.
[Start prevention action by front and rear wheel reverse phase vibration]
In the third embodiment, as shown in FIG. 7, when it is determined that the driver has started the stationary operation, the left and right front wheels 2a and 2b are caused to rotate back and forth within a minute range with respect to the motors 10a and 10b, and the left and right rear The wheels 14a and 14b are oscillated back and forth with amplitudes opposite to those of the left and right front wheels 2a and 2b. As a result, the driving forces of the left and right front wheels 2a and 2b and the left and right rear wheels 14a and 14b cancel each other, so that the vehicle can be prevented from starting.

Next, the effect will be described.
In the vehicle steering apparatus of the third embodiment, the following effects are obtained in addition to the effects (1) to (3) of the first embodiment.

  (6) When the steering force assisting control means applies the front-rear rotational vibration to the left and right front wheels 2a, 2b, it applies the front-rear rotational vibration of the opposite phase to the left and right front wheels 2a, 2b to the left and right rear wheels 14a, 14b. The start of the vehicle at the time of stationary can be surely prevented.

  The fourth embodiment is an example in which damping means is interposed between the left and right steering wheels and the vehicle body.

FIG. 8 is a diagram illustrating a configuration of a main part on the left front wheel side of the vehicle steering system according to the fourth embodiment. As shown in FIG. 8, in the vehicle steering system of the fourth embodiment, an attenuation device (attenuating means) 19 is interposed between the left front wheel 2 a and the vehicle body 18. The damping device 19 has one end connected to a steering knuckle 21 connected to the wheel 20 of the left front wheel 2 a and the other end connected to the vehicle body 18. Similarly, a damping device 19 is interposed between the right front wheel 2 b and the vehicle body 18.
The other configuration of the fourth embodiment is the same as that of the first embodiment shown in FIG.

Next, the operation will be described.
[Steering torque fluctuation suppression effect by damping device]
Since the force exchange between the tire and the road surface generates a moment around the steering center of the wheel, if the left and right front wheels 2a, 2b are oscillated back and forth during a stationary operation, the steering force or the steering force will fluctuate. .

  On the other hand, in the fourth embodiment, since the damping device 19 is provided between the left and right front wheels 2a, 2b and the vehicle body 18, a part of the moment around the steering center of the wheel can be attenuated, and unnecessary steering torque fluctuations are caused. Can be made difficult to communicate to the driver.

Next, the effect will be described.
In the vehicle steering apparatus of the fourth embodiment, the following effects can be obtained in addition to the effects (1) to (4) of the first embodiment.

  (7) Since the damping device 19 is interposed between the left and right front wheels 2a and 2b and the vehicle body 18, it is possible to suppress the road surface reaction force that changes every moment depending on the contact state between the tire and the road surface from being transmitted to the steering wheel 1, which is unnecessary. It is possible to prevent the change in the steering force from being transmitted to the driver.

(Other examples)
The best mode for carrying out the present invention has been described based on the first to fourth embodiments. However, the specific configuration of the present invention is not limited to the first to fourth embodiments. Design changes and the like within a range that does not depart from the gist are also included in the present invention.

  For example, in the first to fourth embodiments, an example in which the front wheels are steered wheels has been shown. However, the present invention also applies to the rear wheels of a four-wheel steering system that steers the rear wheels in reverse phase with the front wheels in a low vehicle speed range. Applicable.

It is a figure which shows the structure of the steering apparatus for vehicles of Example 1. FIG. It is a figure which shows the steering force assistance effect | action of Example 1. FIG. 3 is a flowchart illustrating a flow of steering force assist control processing at the time of stationary according to the first embodiment. It is a figure which shows the structure of the steering apparatus for vehicles of Example 2. FIG. It is a figure which shows the steering force assistance effect | action of Example 2. FIG. FIG. 6 is a diagram illustrating a configuration of a vehicle steering device according to a third embodiment. It is a figure which shows the steering force assistance effect | action of Example 3. FIG. It is a figure which shows the front left wheel side principal part structure of the steering apparatus for vehicles of Example 4. FIG.

Explanation of symbols

1 Steering wheel 2a, 2b Left and right front wheel 3 Steering mechanism 4 Column shaft 5 Steering angle sensor 6 Steering torque sensor 7 Steering gear 8 Rack 9a, 9b Left and right tie rods 10a, 10b Left and right wheel in motor 11 Vehicle speed sensor 12 Throttle opening sensor 13 Control unit

Claims (8)

In vehicles that can drive the left and right steering wheels independently,
A stationary operation start judging means for judging the start of the stationary operation of the driver;
Steering force assist control means for applying a minute range of longitudinal rotational vibration to the left and right steered wheels when it is determined that the stationary operation starts.
A vehicle steering apparatus comprising: The vehicle steering apparatus according to claim 1,
The stationary operation start determining means determines that the stationary operation starts when the steering torque exceeds a preset stationary start determination value when the vehicle speed is zero and the driver does not request acceleration. Vehicle steering system. The vehicle steering apparatus according to claim 1 or 2,
The steering force assist control means is configured to apply a forward / backward rotational vibration to the left and right steering wheels, when the vehicle speed exceeds zero, when there is a driver acceleration request, or when the steering torque is set in advance. In any of the cases when the end determination value is not reached, the application of the longitudinal rotational vibration to the left and right steering wheels is stopped. The vehicle steering apparatus according to any one of claims 1 to 3,
The steering force assisting control means causes the left and right steered wheels to vibrate in the front-rear direction with amplitudes opposite in phase to each other. The vehicle steering apparatus according to any one of claims 1 to 4, wherein:
The steering force assisting control means applies a braking force to the non-steering wheel when the front-rear rotational vibration is applied to the left and right steering wheels. The vehicle steering apparatus according to any one of claims 1 to 3,
The steering force auxiliary control means applies a longitudinal rotational vibration having an amplitude opposite to that of the steering wheel to a non-steering wheel when the longitudinal steering vibration is applied to the left and right steering wheels. Steering device. The vehicle steering apparatus according to any one of claims 1 to 6, wherein:
A vehicular steering apparatus, wherein a damping means is interposed between the left and right steering wheels and the vehicle body. In vehicles that can drive the left and right steering wheels independently,
A vehicular steering apparatus characterized in that, when a driver's stationary operation starts, the left and right steered wheels are oscillated back and forth within a very small range to reduce the frictional force in the steered wheel steered direction.

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