JPH04310468A - Rear wheel steering mechanism for vehicle - Google Patents

Abstract

PURPOSE:To maintain driving stability during frequent steering wheel operations as during driving on a meandering road by employing a toe angle control means to keep the toe-in angles of the right and left rear wheels constant by stopping the operation of an actuator. CONSTITUTION:During frequent steering wheel operations, a rear wheel toe-in control device 40 detects from the steering angle if the absolute value of the steering operation speed is greater than a specified value K and checks the signs of the steering angle QH and the steering operation speed dQH/dt. If it is detected that the steering operation speed dQH/dt is greater than the specified value K and that the signs of QH and dQH/dt are not in agreement with each other, namely if it is detected that the steering wheel is being reversed, it is judged that frequent steering operations are made and the toe-in angle at that time is maintained to secure driving stability.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear wheel steering system for a vehicle, and more particularly, the left and right rear wheels are configured to be steered at least in the toe-in direction by an actuator using at least the amount of steering wheel steering angle as a parameter. It relates to a steering device.

0002

[Prior Art] Some four-wheel steering (4WS) vehicles are constructed so that not only the front wheels but also the rear wheels are steered.
For example, as disclosed in Japanese Patent Application Laid-Open No. 62-18309, there is a vehicle in which the left and right rear wheels are simultaneously steered in the toe-in direction by actuators depending on the vehicle speed. In this way, when both the left and right rear wheels are steered in the toe-in direction, the running stability of the vehicle can be improved during high-speed driving, and conversely, when both the left and right rear wheels are steered in the toe-out direction, can improve steering performance when driving at low speeds.

On the other hand, a rear wheel steering device is also known in which the left and right rear wheels are configured to be steered in the toe-in direction by an actuator using at least the amount of steering wheel steering angle as a parameter. In this case, running stability when the vehicle turns can be improved.

0004

By the way, when a vehicle travels on a slalom road, the steering wheel is frequently turned and turned back in succession. Therefore, in the case of a vehicle configured such that the left and right rear wheels are steered in the toe-in direction using the amount of steering wheel steering angle as a parameter as described above, following frequent steering wheel operations,
The toe-in angles of the left and right rear wheels must be changed frequently, which not only gives the occupants a sense of discomfort, but also impairs driving stability, and furthermore, there are problems in that the actuator requires quick follow-up action. Ta.

Accordingly, the present invention provides a rear wheel steering system for a vehicle configured such that the left and right rear wheels are steered at least in the toe-in direction by an actuator using at least the amount of steering wheel steering angle as a parameter. The purpose is to maintain driving stability when frequent steering operations are performed.

[0006]

[Means for Solving the Problems] The invention as set forth in claim 1 includes means for detecting that frequent steering wheel operations have been performed, and when the above-mentioned detection is made by the detecting means,
The above problem is solved by providing a toe angle control means that responds to this by stopping the operation of the actuator and controlling the toe-in angles of the left and right rear wheels to be kept constant.

[0007] The above-mentioned frequent steering wheel operation can be detected using, for example, a sensor that detects the amount of steering wheel steering angle;
This is possible in combination with an arithmetic circuit that differentiates the steering angle amount detected by this sensor.

[0008] Furthermore, the invention described in claim 2 includes means for detecting that frequent steering wheel operations have been performed, and when the above detection is made by the detecting means, in response to the detection, the actuator follows up. The above-mentioned problem is solved by providing a toe angle control means that slows down the operating speed and controls the toe-in angle of the left and right rear wheels to alleviate changes.

Furthermore, the invention as set forth in claim 3 is characterized in that the toe angle control means set forth in claim 2 is provided with means for performing integral processing (low-pass filter processing) on the turning back of the steering wheel. , the follow-up operation of the actuator is slowed down, thereby alleviating changes in the toe-in angle of the left and right rear wheels.

0010

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

In FIG. 1, the left and right front wheels 1L, 1R are linked by a front wheel steering mechanism A, and the left and right rear wheels 2L,
2R is linked by rear wheel steering mechanism B.

The front wheel steering mechanism A is composed of a pair of left and right knuckle arms 3L, 3R and tie rods 4L, 4R, and a relay rod 5 that connects these pair of left and right tie rods 4L, 4R. A rack-and-pinion type steering mechanism C is linked to the front wheel steering mechanism A, and the left and right front wheels 1L and 1R are steered by operating the handle 6.

Similar to the front wheel steering mechanism A, the rear wheel steering mechanism B also includes a pair of left and right knuckle arms 10L, 10R and tie rods 11L, 11R, as well as a coupling mechanism D that connects the tie rods 11L, 11R. have

As shown in more detail in FIG. 2, the coupling mechanism D connects a point 20 between the left and right rear wheels 2L and 2R.
A pair of rocking pieces 20L and 20 are attached to the vehicle body so as to be swingable in the left and right directions with L' and 20R' as rocking centers.
It has R. The inner end of the left relay rod 21L in the vehicle width direction is connected to the swinging piece 20L, and the relay rod 21L is connected to the swinging piece 20L.
The outer end of L is connected to tie rod 11L. Similarly, the inner end in the vehicle width direction of the right relay rod 21R is connected to the swinging piece 20R, and the outer end of the right relay rod 21R is connected to the tie rod 11R. In addition, the swing piece 20L
, 20R are connected to the outer ends of a pair of left and right connecting rods 22L, 22R, and the inner ends of the connecting rods 22L, 22R are connected to a ball nut 23.

The ball nut 23 is supported by the vehicle body so as to be movable in the axial direction with its axis directed in the longitudinal direction of the vehicle body. A threaded rod 24 is inserted into the ball nut 23, and a number of balls 25 are rotatably disposed between the outer peripheral surface of the threaded rod 24 and the inner peripheral surface of the ball nut 23. Note that the inner peripheral surface of the ball nut 23 and the threaded rod 24
A threaded groove in which the ball 25 rolls is formed on the outer circumferential surface of the ball 25, but since such a structure is well known, it is shown in a simplified manner in the drawings. According to the forward and reverse rotation of the threaded rod 24, the ball nut 23 is displaced in the longitudinal direction of the vehicle body, and the left and right relay rods 21L and 21R move in the vehicle width direction so as to approach or separate from each other. That is, when the ball nut 23 is displaced to the rear of the vehicle body, the left relay rod 21L is displaced to the left in FIG. 2, and the right relay rod 21R is displaced to the right in FIG. The vehicle will be steered in the toe-in direction.

By driving the rear wheel steering mechanism B, the left and right rear wheels 2L
, 2R comprises a step motor 30 fixed to the vehicle body, and the output shaft 30a of this step motor 30 is connected to the threaded rod 24. Therefore, the forward and reverse rotation of the step motor 30 displaces the ball nut 23 in the longitudinal direction of the vehicle body, and the displacement of the ball nut 23 causes the left and right rear wheels 2L, 2R to be simultaneously steered in the toe-in or toe-out direction.

Next, the control means and control method of the rear wheel steering mechanism B will be explained.

In FIGS. 1 and 2, 40 is a control unit constituted by a microcomputer, and includes control means for setting the rotation direction and amount of rotation of the step motor 30, and control means for changing the rotation speed of the step motor 30. Built-in. Signals from sensors 31 to 35 are input to this control unit 40. Sensor 31 is a sensor that detects vehicle speed, and sensor 32 is a sensor that detects throttle position. The sensor 33 is a brake switch that detects depression of the brake pedal. Further, the sensor 34 is a sensor that detects the steering angle of the steering wheel 6, and the sensor 35 is an encoder that detects the rotational displacement of the step motor 30.

The toe angles of the rear wheels 2L and 2R are controlled in the toe-in direction or the toe-out direction, based on a predetermined reference toe angle T0 (initial toe angle), depending on the driving condition. Here, this rear wheel steering control is performed according to the vehicle speed, the brake switch being turned on (depressing the brake pedal), and the steering wheel angle, and the control target value is uniform, except for the steering wheel angle. is set to a predetermined value. For example, when a control target value based on vehicle speed and a control target value based on braking are set, these control target values are added together and set as the final control target value.

As shown in FIG. 3, the control target value based on vehicle speed is 90 km/h when the vehicle is in an accelerating state.
H is taken as the reference vehicle speed for starting the control in the toe-in direction, and when the vehicle speed exceeds 90 km/H, a control target value of +6 mm is uniformly set as shown by the solid line in FIG. Here, +6 mm means that the initial toe angle in FIG. 7 is further steered by a-b=6 mm in the toe-in direction. During acceleration, the vehicle is controlled in the toe-in direction when the speed exceeds 90 km/H, and is controlled in the toe-out direction from 20 km/H to 70 km/H. on the other hand,
During deceleration, as shown by the broken line in Figure 3, toe-in control is stopped when the speed drops below 80 km/h, and the
From the time the speed drops below m/h to 10 km/h, the vehicle is controlled in the toe-out direction. In this way, by controlling the toe angle at different reference vehicle speeds during acceleration and deceleration, it is possible to
This prevents toe-in control from repeatedly starting or stopping due to small accelerations or decelerations when the vehicle is running at low speed. Furthermore, since a non-control area (2WS area) is provided between the control in the toe-out direction and the control in the toe-in direction, the control amount during acceleration or deceleration is reduced compared to the case where this area is not provided. Can be made smaller.

FIG. 4 shows the control target value in the toe-in direction during braking. This control is performed under the condition that the vehicle speed exceeds 50 km/h.

FIG. 5 shows the setting of the control target value in the toe-in direction based on the steering angle of the steering wheel. In this case, even if the steering angle is the same, the larger the vehicle speed is, the larger the value is set. Furthermore, the toe angle control based on the steering angle of the steering wheel increases the rotational speed of the step motor 30 as the operating speed of the steering wheel 6 increases.
This allows the 2R steering to be performed quickly. This improves driving stability during cornering.

Furthermore, when the steering wheel 6 is operated frequently, such as when the vehicle runs on a slalom road, the step motor 30 is stopped or its rotational speed is slowed down to control the steering of the rear wheels 2L and 2R. has stopped or slowed down. Figure 6 shows a state in which the toe-in angles of the rear wheels 2L and 2R are maintained at a constant value (Figure 6B) when the steering wheel steering angle θH changes frequently (Figure 6A), and changes in the toe-in angles of the rear wheels 2L and 2R. 6C shows a state where is relaxed (FIG. 6C). By performing such toe angle control, running stability can be maintained even when the steering wheel is frequently operated. In addition, in FIGS. 6B and 6C, the change in the toe-in angle when the step motor 30 faithfully follows the steering wheel angle θH is shown by a dashed-dotted line.

On the premise of the above, the toe angle control routine executed by the control unit 40 will be explained based on the flowcharts shown in FIG. 8 and subsequent figures. Note that the rotational displacement of the step motor 30 is fed back by the encoder 35.

FIG. 8 shows a routine for setting control set values based on vehicle speed (see FIG. 3).

First, in step S1, the vehicle speed V is input, and in the next step S2, the acceleration/deceleration state of the vehicle is determined. When it is determined that the vehicle is in an acceleration or steady running state, the vehicle speed region is determined in steps S3 to S5;
When the vehicle speed is lower than 20 km/h, an initial toe T0 is set in step S6, and the 2WS state is set. When the vehicle speed is in the range of 20km/H to 70km/H, the initial toe is changed from initial toe T0 to 4 in the toe-out direction in step S7.
A target value for steering by mm is set. Vehicle speed is 70km/h
In the range of ~90 km/H, an initial toe T0 is set in step S8, resulting in a 2WS state. 90km/
In the area above H, the initial toe T0 is set in step S9.
A target value for steering the vehicle 6 mm toward the toe-in direction is set to ensure high-speed running stability.

On the other hand, if it is determined in step S2 that the vehicle is in a decelerated running state, the process moves to step S10 and subsequent steps. The standard vehicle speed for this deceleration is 8.
The vehicle speed is changed to a slower speed than that at the time of acceleration, such as 0 km/H, 60 km/H, etc., and the steps S13 to S
At step 15, each vehicle speed region is determined. Note that T1 shown in FIG. 8 indicates a control target value based on vehicle speed,
In this toe angle control based on vehicle speed, the step motor 30
is rotated relatively slowly at a speed of 1 sec.

FIG. 9 shows toe-in control during braking. First, in step S20, it is determined whether the flag F=1. Flag F=1 indicates that toe-in control based on braking is being performed. now,
When F=0, the process advances to step S21 and the vehicle speed is 50kph.
If the brake switch 35 is turned on, that is, the brake pedal is depressed, the process proceeds to step S22 on the condition that the speed exceeds m/H.
23, a target value is set by adding 6 mm in the toe-in direction to the control target value T1 based on the vehicle speed. The toe-in control speed during this braking, that is, the rotational speed of the step motor 30 is rapidly rotated at a speed of 50 msec. This quickly ensures driving stability during braking. In this toe-in control, the flag F is set to 1 in step S24 until the braking is released, and the process moves from step S20 to step S22, where this toe-in state is continued.

Toe-in control based on this braking is not performed when the vehicle speed is less than 50 km/H and the brake pedal is not depressed, and the target value T1 based on the vehicle speed is set as is in step S25 or S26. Note that with the release of braking, step S2
The flag F is reset in step S7, but the change in toe angle accompanying the release of braking in step S26 is performed relatively slowly, with the rotational speed of the step motor 22 being 1 second, to ensure running stability. It is being In addition, in FIG. 9, T2 indicates a control target value that takes into account braking.

Next, FIG. 10 shows toe-in control based on the steering angle of the steering wheel. First, in step S30, the vehicle speed V is input, and in step S31, the steering wheel steering angle θH is input. Using these vehicle speed and steering wheel angle as parameters, in step S32, the toe-in control target value f based on the steering wheel steering angle is input.
(V・θH) is set (see Figure 5), and step S3
3, a control target value T3 that takes into account the steering wheel angle is set. Note that the toe-in control based on the steering wheel angle is performed at a speed that corresponds to the steering speed of the steering wheel, as described above, and the rotational speed of the step motor 30 is set at a speed that matches the steering speed of the steering wheel. It is now held in

FIG. 11 is a subroutine showing rear wheel toe-in control based on the steering angle when the steering wheel is operated frequently. First, in step S41, it is checked whether the absolute value of the steering wheel steering speed dθH/dt is greater than or equal to a predetermined value k, and then in step S42, the signs of the steering wheel steering angle θH and the steering wheel steering speed dθH/dt are checked. If it is detected that the steering wheel steering speed dθH/dt is equal to or higher than the predetermined value k, and the signs of θH and dθH/dt do not match, that is, if it is detected that the steering wheel is being turned back, It is determined that frequent steering wheel operations are being performed, and the step motor 30 is stopped in step S43 to maintain the current toe-in angle and ensure running stability (see FIG. 6B). After maintaining such a toe-in angle, the steering wheel steering angle θH and the steering wheel steering speed dθH/dt are determined in steps S44 and S45.
It is checked whether or not the value has become almost zero, and steps S44 and S
When the determinations in step S45 are both "YES", the toe-in angle based on the steering angle θH is gradually returned to zero in step S46, and this subroutine is ended.

The following FIG. 12 also shows a subroutine showing rear wheel toe-in control based on the steering angle when the steering wheel is operated frequently; this subroutine is similar to that shown in FIG.
Rather than keeping the toe-in angle constant as shown in Figure 6C, the system performs an integral process (low-pass filter process) on the steering wheel steering angle θH to slow down the operating speed of the actuator that follows it (see Figure 6C). ). That is, FIG.
Similarly to steps S41 and S42, step S5
1 and S52, it is detected that the steering wheel is frequently operated, and integration processing is performed in step S53. If the steering wheel is not frequently operated, the integral processing is canceled in step S54. By performing such control, it is also possible to ensure running stability when running on a slalom road.

[0033]

As is clear from the above description, according to the present invention, when driving on a slalom road, the toe-in angle of the rear wheels is maintained constant or with little change, thereby improving the running stability of the vehicle. can be ensured. Further, according to the present invention, since quick follow-up of the actuator is not required, the device can be constructed at a lower cost, the durability of the actuator is improved, and the power consumption of the actuator can be reduced.

[Brief explanation of drawings]

FIG. 1 is a system diagram of a control system in an embodiment of the present invention.

FIG. 2 is a detailed view of the main part of FIG. 1;

FIG. 3 is a diagram showing rear wheel toe-in control target values based on vehicle speed.

FIG. 4 is a diagram showing rear wheel toe-in control target values based on braking.

FIG. 5 is a diagram showing a rear wheel toe-in control target value based on the steering wheel angle.

FIG. 6 is a diagram showing rear wheel toe-in control based on the steering wheel angle when frequent steering wheel operations are performed.

FIG. 7 is an explanatory diagram of rear wheel toe-in control target value setting.

FIG. 8 is a flowchart of a rear wheel toe-in control routine based on vehicle speed.

FIG. 9 is a flowchart of a rear wheel toe-in control routine based on braking.

FIG. 10 is a flowchart of a rear wheel toe-in control routine based on the steering wheel angle.

FIG. 11 is a flowchart of a rear wheel toe-in control subroutine based on the steering wheel angle.

FIG. 12 is a flowchart of a rear wheel toe-in control subroutine based on the steering wheel angle.

[Explanation of symbols]

2L, 2R Left and right rear wheels B Rear wheel steering mechanism D Connection mechanism E Rear wheel drive mechanism 23 Ball nut 30 Step motor 31 Vehicle speed sensor 32 Throttle position sensor 33
Brake switch 34 Steering wheel angle sensor 35 Encoder

Claims (3)

[Claims] [Claim 1] Frequent steering operations were performed in a rear wheel steering system of a vehicle in which the left and right rear wheels are configured to be steered at least in the toe-in direction by an actuator using at least the amount of steering wheel steering angle as a parameter. and toe angle control means for controlling the toe-in angle of the left and right rear wheels to be kept constant by stopping the operation of the actuator in response to the detection made by the detection means. A rear wheel steering device for a vehicle, comprising: [Claim 2] Frequent steering operations were performed in a rear wheel steering system of a vehicle in which the left and right rear wheels are configured to be steered at least in the toe-in direction by an actuator using at least the amount of steering wheel steering angle as a parameter. a toe control means for detecting a change in the toe-in angle of the left and right rear wheels; A rear wheel steering device for a vehicle, comprising angle control means. 3. A rear wheel steering system for a vehicle according to claim 2, wherein said toe angle control means includes means for performing integral processing on turning the steering wheel back.