JPS63151580A - Four-wheel steering apparatus for vehicle - Google Patents

Abstract

PURPOSE:To prevent the steering ratios from being delayed in shifting to the opposite phase side while a vehicle is turning by inhibiting the steering ratios from being controlled so as to shift to the opposite phase side only when it is considered that the steering angle is large, and the vehicle is running while it is turning. CONSTITUTION:A stepping motor 51 and a solenoid opening/closing valve 28 are designed so that their operation is controlled by virtue of the output from a control unit 100 including a microcomputer. In the control unit 100 are stored the detected signals from a vehicle speed sensor 102, a steering angle sensor 103, an acceleration sensor 104, and a steering ratio sensor 101. When it is decided, in the control unit, that the vehicle is in a decelerated state, and the steering angle is larger than a fixed value, by virtue of a controlling means 107, an antiphase control inhibiting means 106 is operated so that the steering ratios for the front and rear wheels are controlled so as to shift to the opposite phase side. Thereby, a scooping phenomenon in the vehicle at the time of its decelerating turning can be reduced.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a four-wheel steering device that steers the front and rear wheels of a vehicle, and particularly relates to steering control during turning after deceleration. .

(Prior art) In recent years, this type of four-wheel steering system for vehicles has attracted attention as a device that can greatly change the driving characteristics of the vehicle. The steering ratio is controlled to be in the opposite phase and the steering characteristics are changed to oversteer characteristics to improve the vehicle's retrospective ability.At the same time, at high vehicle speeds or at small steering angles, the steering ratio is kept in the same phase and the steering characteristics are changed to understeer characteristics. This is to ensure the running stability of the vehicle.

By the way, in such a four-wheel steering system, the steering ratios of the front and rear wheels are controlled to be in opposite phases at low vehicle speeds and in the same phase at high vehicle speeds, so for example, when the steering wheel is turned while releasing the accelerator pedal, In a deceleration state where the vehicle decelerates while turning, the phase that was previously the same changes to the opposite phase, resulting in a behavior called "squeezing" in which the steering wheel turns more than expected. However, in order to correct this scooping phenomenon, it is necessary to reverse the operation of the steering wheel, which requires skill, so it is necessary to eliminate this phenomenon as much as possible from the point of view of safety.

For this reason, conventionally, in the four-wheel steering device disclosed in Taiko Sho 60-135370, the steering ratio is controlled to the same phase side when the vehicle is decelerated, and the steering ratio is controlled to the opposite phase side. An idea has been proposed that would prohibit the use of

(Problems to be Solved by the Invention) However, if the steering ratio is always prohibited from being controlled to the opposite phase side during deceleration as in the above proposed example, the following problems arise. In other words, for example, when driving on a straight road that curves at the end, if you decelerate while driving straight and then turn the steering wheel, the steering ratio will always shift to the opposite phase side when decelerating. Since the control of the steering ratio to the opposite phase side is prohibited at the same time as deceleration in the straight-ahead state, the steering ratio is maintained at the same phase.

After this, when the vehicle transitions to a turning state, since it is held on the same phase side, it takes time for the steering ratio to shift from the same phase side to the opposite phase side, and due to the transition delay, the steering ratio during the turn The problem is that the rotational speed is not controlled to an appropriate opposite phase, and as a result, the turning performance of the vehicle deteriorates.

(Objective of the Invention) The present invention is intended to solve the above problem, and its purpose is not to always prohibit control of the steering ratio to the opposite phase side when the vehicle decelerates, but to prohibit it. By linking it to the steering condition of the steering wheel, even when turning after decelerating while driving straight, the delay in shifting to the opposite phase side during turning is eliminated, improving and maintaining the turning performance of the vehicle. The goal is to make it possible.

(Means for solving the problem) In order to achieve this object, the solution taken by the present invention detects the steering wheel angle (rotation angle of the steering wheel) while the vehicle is running, and Control of the steering ratio to the opposite phase side is prohibited only when the angle is large and the vehicle is considered to be turning.

Specifically, in the present invention, as shown in FIG. The present invention is based on a four-wheel steering system for a vehicle that controls the steering ratio of the wheels to the target steering ratio.

In contrast to this premise, there is a deceleration detecting means 105 that detects the deceleration state of the vehicle, and the output of the deceleration detecting means 105 is received, and when the vehicle is decelerated, the target steering ratio to the actuator 51 is shifted to the opposite phase side. Antiphase control inhibiting means 106 for inhibiting I'l control is provided.

Roughly speaking, a steering angle detecting means 103 is provided for detecting the steering wheel steering angle θH of the vehicle, and when the steering wheel steering angle θH detected by the steering angle detecting means 103 is greater than or equal to a predetermined value, the reverse phase control inhibiting means 106 is activated. Control means 10 for actuation
7.

(Function) With this configuration, in the present invention, when the vehicle is running, the actuator 51 is operated so that the steering ratio of the front and rear wheels of the vehicle becomes the target steering ratio determined based on the steering ratio characteristics. be done.

During this period, the steering angle θH of the vehicle is detected by the steering angle detection means 103, and the deceleration detection means 10
5, the deceleration state of the vehicle is detected, and only when the vehicle is in the deceleration state and the steering wheel steering angle θH is greater than or equal to a predetermined value, it is determined that the vehicle is turning while decelerating, and the control means 107 This allows the operation of the anti-phase control inhibiting means 106, and the steering ratios of the front and rear wheels are controlled to the anti-phase side, and this control prevents the vehicle from squeezing into the vehicle.

However, even if the vehicle is in a deceleration state, as long as the steering wheel angle θH is smaller than a predetermined value, it is determined that the vehicle is traveling straight, and the reverse phase control inhibiting means 106 does not operate. Therefore, even when the vehicle decelerates while traveling straight and then turns, the steering ratio is quickly controlled to the opposite phase during the turn, thereby improving the turning performance of the vehicle. I can maintain it.

(Example) Hereinafter, an example of the present invention will be described based on the drawings from FIG. 2 onwards.

In FIG. 2, IL to 2R are four wheels of the vehicle, and the left and right front wheels 1L and 1R are linked by a front wheel steering mechanism 3, and the left and right rear wheels 2L and 2R are linked by a rear wheel steering mechanism 12. ing.

The front wheel steering mechanism 3 includes a pair of left and right knuckle arms 4L.
, 4R, tie rods 5L, 5R, and a relay rod 6 that connects the left and right tie rods 5L, 5R. A steering wheel 10 is connected to the front wheel steering mechanism 3 via a rack and pinion type steering mechanism 7.
are linked. That is, a rack 8 is formed on the relay rod 6, while a pinion 9 that meshes with the rack 8 is attached to the lower end of the steering shaft 11, to which the steering wheel 10 is connected to the upper end. The left and right front wheels 1L and 1R are steered according to the operation.

On the other hand, the rear wheel steering mechanism 12, like the front wheel steering gate structure 3, includes left and right knuckle arms 13L, '+3R and tie rods 14L, '+4R, and the tie rods 14L, 1
It has a relay rod 15 that connects the 4Rs, and is roughly equipped with a hydraulic power steering mechanism 16. The power steering mechanism 16 includes a power cylinder 17 that is fixed to the vehicle body and uses the relay rod 15 as a piston rod, and inside the power cylinder 17, two hydraulic pressures 117b are generated by a piston 17a that is integrally attached to the relay rod 15. , 17C, and the hydraulic chambers 17b and 17C in this cylinder 17 are connected to the control valve 20 via hydraulic piping 18 and 19, respectively. Furthermore, two pipes, an oil supply pipe 22 and an oil discharge pipe 23, leading to a reserve tank 21 are connected to the control valve 20, and a hydraulic pump 24 driven by an on-vehicle engine (not shown) is connected to the oil supply pipe 22. It is arranged. The control valve 20 is a known spool valve type, and includes a cylindrical valve casing 20a integrally attached to the relay rod 15 via a connecting member 25, and a cylindrical valve casing 20a inside the valve casing 2Oa. The relay rod 15 is driven by supplying pressure oil from the hydraulic pump 24 to one hydraulic chamber 17b (17c) of the power cylinder 17 according to the movement of the spool valve (not shown). It is something that assists in power.

In addition, the relay rod 15 is placed in the neutral position (rear wheel 2L) through the piston 17a in the power cylinder 17.
, 2R, a pair of return springs 17d bias the steering angle θR to zero.

17d has been reduced. In addition, the above hydraulic piping 1B, 1
9 are connected to a normally closed electromagnetic on-off valve 28 via hydraulic piping 26 and 27, respectively, and when this electromagnetic on-off valve 28 is opened, both internal pressure chambers 17b of the power cylinder 17,
The return spring 17d uses the same pressure as the oil pressure in 17c.
, 17d positions the piston 17a at the neutral position, and the steering angle of the rear wheels 2L, 2R is always set at 6R=o, so that the steering characteristic of the vehicle is in a two-wheel steering state.

In addition to the rack 8 constituting the steering mechanism 7, another rack 2 is attached to the steering rod 6 of the front wheel steering mechanism 3.
9 is formed, and a pinion 30 attached to the front end of a rotating shaft 31 extending in the longitudinal direction of the vehicle body is engaged with the rack 29, and the rear end of the rotating shaft 31 is connected to the rear wheel steering system via a steering ratio control mechanism 32. It is linked to mechanism 12.

As detailed in FIG. 3, the steering ratio control mechanism 32 includes:
The control rod 33 is slidably held on the movement axis f11 in the vehicle width direction with respect to the vehicle body, and one end of the control rod 33 is connected to the spool valve of the control valve 20. Further, the steering ratio control mechanism 32 includes a swing arm 36 whose base end is swingably supported by a U-shaped holder 34 via a support pin 35, and the holder 34 is connected to a casing ( (not shown) via a support shaft 37 having a rotation axis 2 perpendicular to the movement axis g1 of the control rod 33. The support pin 35 of the swing arm 36 is connected to the two wheel line M1. It is located at the intersection of L and extends in a direction perpendicular to the rotation axis g2, and by rotating the holder 34 around the support shaft 37 (rotation axis 12), the support pin 35 at the tip and the control rod 33 with the movement axis Ω1, that is, the inclination angle that the swing locus plane of the swing arm 36 centered on the support pin 35 makes with respect to a plane perpendicular to the movement axis p1 (hereinafter referred to as the reference plane). It is designed to change.

Further, one end of a connecting rod 39 is connected to the tip of the swing arm 36 via a ball joint 38, and the other end of the connecting rod 39 is connected to the control rod 33 via a ball joint 40. The third end of the swinging arm 36 is connected to the other end.
The control rod 33 is moved in the left-right direction in response to displacement in the left-right direction in the figure.

The connecting rod 39 is slidably supported by a rotation imparting arm 41 via a ball joint 42 at a portion thereof close to the ball joint 38 . The rotation imparting arm 41 is provided integrally with a large-diameter bevel gear 44 rotatably supported on the movement axis 91 via a support shaft 43, and the bevel gear 44 is attached to the rear end of the rotation shaft 31. A bevel gear 45 attached to the steering wheel 10 is meshed with the bevel gear 45 so that the rotation of the steering wheel 10 is transmitted to the rotation imparting arm 41. Therefore, the rotation arm 41 and the connecting rod 39 rotate about the movement axis f11 by an amount corresponding to the rotation angle of the steering wheel 10, and the swing arm 36 swings about the support pin 35 accordingly. In this case, when the axis of the pin 35 coincides with the movement axis 9 of the control rod 33, the ball joint 38 at the tip of the swing arm 36 only swings on the reference plane, and the control rod 33 However, if the axis of the pin 35 is inclined with respect to the movement axis g1 and the swing locus plane of the swing arm 36 deviates from the reference plane, the swing arm 36 will swing around the pin 35. As the ball joint 38 moves, the ball joint 38 is displaced in the left-right direction in FIG. , is configured to operate the spool valve of the control valve 20. That is, even if the swinging angle of the swinging arm 36 about the axis of the support pin 35 remains the same, the displacement of the control rod 33 in the left-right direction is due to the change in the tilt angle of the pin 35, that is, the rotation angle of the boulder 34. It changes accordingly.

In order to change the movement axis of the support pin 35 and the inclination angle with respect to I21, that is, the inclination angle of the holder 34 with respect to the reference plane, a sector gear 46 as a worm wheel is attached to the support shaft 37 of the holder 34. This sector gear 46 has one T-mgya 48 on the rotating shaft 47.
are engaged.

Further, a bevel gear 49 is attached to the rotating shaft 47,
This bevel gear 49 has a bevel gear 50 attached to the output shaft 51a of a stepping motor 51 as an actuator.
are engaged with each other, and by operating the stepping motor 51 and rotating the sector gear 46, the holder 34
The steering angle θR of the rear wheels 2L, 2R, that is, the steering ratio (rear wheel steering angle θR/front wheel steering angle θF) of the front and rear wheels IL, 2L (IR, 2R) is controlled by changing the inclination angle with respect to the reference plane. For example, the center line of the sector gear 46 is the worm gear 48.
At this time, the ball joint 38 at the tip of the swing arm 36 rotates on the reference plane, and the steering angle θR of the rear wheels 2L and 2R is 0n.
= O) when rotating in one direction, the steering ratio of the front and rear wheels 1L and 2L is changed from the rear wheels 2L and 2R to the front wheels 1L and 1R.
On the other hand, when the wheels are rotated in the other direction, the steering ratio is changed so that the rear wheels 2L and 2R are turned in the opposite direction to the front wheels 1.
It is configured to control RA to the same phase facing in the same direction as L and 'IR.

In general, the support shaft 37 of the holder 34 is provided with a potentiometer as a steering ratio detection means for detecting the actual steering ratio R controlled by the stepping motor 51 based on the rotation angle of the sector gear 46. A steering ratio sensor 101 is provided. The casing that supports the holder 34 is provided with anti-phase and same-phase stopper members 52 and 53, which are made of pins that restrict the rotation range of the sector gear 46, on both left and right sides of the sector gear 46. The control position of the stepping motor 51 when the stepping motor 46 comes into contact with the stopper member 52 on the opposite phase side is set as its initial position. Moreover, in FIG. 3, 54 is a rod stopper that restricts the maximum movement range of the relay rod 15 in rear wheel steering II@12.

The stepping motor 51 and the electromagnetic on-off valve 28 are
The operation is controlled by an output from a control unit 100 containing a microcomputer. This control unit 100 includes a vehicle speed sensor 102 that detects the running speed of the vehicle (vehicle speed), and a vehicle steering angle θH (for example, the steering wheel angle θH).
a steering angle sensor 103 serving as a steering angle detection means for detecting a rotation angle of 0), an accelerator sensor 104 detecting depression fiQA of an accelerator pedal (not shown) of the vehicle, and the steering ratio sensor 101. Detection signal is input.

Here, a signal processing procedure performed in the microcomputer of the control unit 100 to control the operation of the stepping motor 51 when the vehicle is decelerated will be schematically explained based on FIG. 6.

First, in the first step S1 after the start, it is determined whether the accelerator pedal depression ωQA detected by the accelerator sensor 104 is less than or equal to a predetermined value,
If it is determined that QA>K is No, step S6
Then proceed to perform normal four-wheel steering control.

To explain this normal control, the vehicle speed sensor 102
inputs a signal of the vehicle speed V detected by the vehicle speed V, and sets target steering ratios for the front and rear wheels IL, 2L (1R, 2R) according to the vehicle speed V based on preset and stored steering ratio characteristics; The stepping motor 51 is driven so that the steering ratio of the front and rear wheels 1L, 2L becomes the target steering ratio set above. That is, as shown in FIGS. 4 and 5, the steering ratio characteristics described above change the steering ratios of the front and rear wheels 1L and 2L depending on the vehicle speed V, and when the vehicle speed is low, the turning of the vehicle changes. In order to improve the steering performance, the rear wheels 2L and 2R are steered in the opposite direction to the front wheels IL and 1R, that is, in the opposite phase, and the steering ratio becomes negative, while the vehicle speed becomes far from the predetermined value. Sometimes, the steering ratio becomes zero, and the front wheel is 1L.

The steering angle θR of rear wheels 2L and 2R is 0R regardless of the steering of 1R.
=O and the vehicle enters the normal two-wheel steering state. Furthermore, when driving at high speed, the rear wheels 2L and 2 when cornering
In order to improve the R's grip and drive stability, the rear wheels 2. The wheels L and 2R are steered in the same direction as the front wheels 1L and 1R, that is, in the same phase, and the steering ratio is set to be positive. The vehicle speed (■) is compared and a target steering ratio corresponding to the vehicle speed (2) is determined.

Furthermore, after determining this target steering ratio, the stepping motor 5
The sector gear 46 is rotated by the drive of the holder 34.
By changing the inclination angle with respect to the reference plane and changing the steering angle θR of the rear wheels 2L, 2R, the steering ratio of the front and rear wheels IL, 2L is variably controlled to the target value.

Incidentally, FIG. 4 shows the characteristics of the rear wheel steering angle with respect to the steering wheel steering angle when the vehicle speed changes, and FIG. 5 shows the characteristics of the steering ratio with respect to the vehicle speed when the steering wheel steering angle is predetermined. Also, the front and rear wheels IL detected by the steering ratio sensor 101
, 2L is input to the control unit 100 as a feedback signal, and when the actual steering ratio does not match the target steering ratio, the stepping motor 51 is considered to be out of step, By opening the electromagnetic on-off valve 28 and using the urging force of the return springs 17d and 17d in the power cylinder 17 to set the steering angle θR of the rear wheels 2L and 2R to θR=O, the steering characteristics of the vehicle are forcibly changed. It maintains the two-wheel steering control characteristic and sets it to failsafe mode.

When the determination in step S1 is YES that QA≦, the pedal return speed dQA/dt is calculated from the accelerator pedal depression @QA in step S2, and the value is negative, that is, the vehicle is in a decelerating state. If the determination is YES (dQA/dt)<Q, the steering angle sensor 103 is turned on in step S3.
It is determined whether the detected steering wheel angle θH is greater than or equal to a predetermined value A. When this determination is YES (θH≧A), the process proceeds to step S4 and the two-wheel steering state (rear wheels 2L, 2R
If the determination is YES, the process advances to step S5 to interrupt the driving of the stepping motor 51, and then returns to step S1.

Further, when each determination in steps 82 to S4 is NO, that is, when (dQA/dt>≧O and the accelerator pedal is in a stationary state or depressed for acceleration etc.), the steering wheel steering angle θto1 is is smaller than the predetermined value A, the vehicle goes straight,
When the vehicle is in the two-wheel steering state and when the vehicle is not in the two-wheel steering state, the process proceeds to step s6.

Therefore, in this embodiment, steps S+ and S2 in the above-described control routine constitute the deceleration detection means 105 that detects the deceleration state of the vehicle.

Similarly, in steps S4 and Ss, anti-phase control inhibiting means 106 is configured to receive the output of the deceleration detecting means 105 and prohibit control to the opposite phase side of the target steering ratio when the vehicle is decelerating. be done.

In general, in step S3, the control means 107 is configured to operate the reverse phase control inhibiting means 106 when the steering wheel angle θH detected by the steering angle sensor 103 is equal to or greater than a predetermined value.

Next, the operation of the above embodiment will be explained.

First, when an ignition key switch is turned on to drive a vehicle that is not in use, the initial control position of the stepping motor 51 is determined accordingly. Thereafter, when the vehicle shifts to a running state, the vehicle speed (2) at that time is detected by the vehicle speed sensor 102, and a detection signal is output from the vehicle speed sensor 102 to the control unit 100. A target steering ratio corresponding to the vehicle speed (2) is calculated by comparison and verification, and a pulse signal corresponding to this target steering ratio is output to the stepping motor 51 to drive the motor 51. The sector gear 46 is rotated by the drive of the motor 51, and the swing trajectory plane of the swing arm 36 connected to the sector gear 46 is changed in inclination with respect to the reference plane.
L.

The moving direction and moving distance of the control rod 33 change with respect to the movement of the connecting rod 39 that rotates around the movement axis 11 in conjunction with the steering of the steering wheel 1R, and the rear wheels 2L and 2R change in accordance with the movement of the control rod 33. The front wheels IL and 1R are steered while being assisted by the power cylinder]7 of the power steering mechanism 16 so that the calculated target steering ratio is achieved. As a result, the four wheels 1L to 2 of the vehicle are controlled so that the steering ratios are in opposite phases when the vehicle speed is low, and the steering ratios are in the same phase when the vehicle speed is high.

In addition, in parallel with such steering ratio control, the steering angle sensor 10
3, the steering angle θ of the vehicle is detected, and the deceleration detection means 105 of the control unit 100 detects whether the vehicle is in a deceleration state based on the return operation of the accelerator pedal. When the vehicle is in a decelerating state, the magnitude of the steering wheel steering angle θH with respect to a predetermined value A is also determined, and when the steering wheel steering angle θH is greater than or equal to the predetermined value A, the vehicle starts turning while decelerating. Therefore, the control means 107 operates the reverse phase control prohibition means 106, and the front and rear wheels IL is activated.

The steering ratio of 2L is controlled to the opposite phase side. As a result, it is possible to reduce the squeezing phenomenon when the vehicle decelerates and turns.

On the other hand, even if it is determined that the vehicle is in a deceleration state, when the steering wheel angle θH is smaller than the predetermined value A, the operation of the anti-phase control inhibiting means 106 is stopped. Therefore, when a vehicle decelerates while traveling straight and then turns, the steering ratio is quickly controlled to the opposite phase without any delay during the turn, and as a result, the vehicle turns. It is possible to improve the performance and realize smooth cornering.

In the above embodiment, the case where the steering ratio of the front and rear wheels 1L and 2L of the vehicle is variably controlled in accordance with the vehicle speed V has been exemplified. The present invention can also be applied to a four-wheel steering system that is driven directly by a stepping motor according to the steering angle of the steering wheel.

Further, in the above embodiment, the stepping motor 51 was used as an actuator to control the steering ratio of the front and rear wheels IL and 2L, but in the present invention, the steering ratio is controlled by another actuator such as a DC motor. It can also be applied to wheel steering devices.

(Effects of the Invention) As explained above, according to the present invention, in a four-wheel steering system for a vehicle that steers the front and rear wheels, the steering ratio of the front and rear wheels is adjusted to a preset steering ratio characteristic. The vehicle is controlled by the operation of an actuator such as a stepping motor, and the deceleration state of the vehicle and the steering wheel angle are detected respectively, and the vehicle is in a decelerating state and the steering wheel angle is at least a predetermined value and the vehicle is turning. By prohibiting control of the steering ratio to the opposite phase side only when it is considered that the steering ratio is in the opposite direction, and allowing control to the opposite phase side under other conditions, the vehicle can turn while decelerating. This eliminates the delay in shifting the steering ratio to the opposite phase side when turning the steering wheel after decelerating while driving straight, improving the turning performance of the vehicle. It is something that can be maintained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the present invention. 2 to 6 show embodiments of the present invention, FIG. 2 is a plan view schematically showing the overall configuration of a four-wheel steering device, and FIG. 3 shows a rear wheel steering mechanism and a steering ratio control mechanism. Fig. 4 is a characteristic diagram illustrating the characteristics of the rear wheel steering angle with respect to the steering wheel angle that changes when the vehicle speed changes, and Fig. 5 shows the steering ratio with respect to the vehicle speed at a given steering wheel angle. FIG. 6 is a flowchart showing the control procedure for the stepping motor processed by the control unit. 1L, 1R...front wheel, 2L, 2R...rear wheel, 3...
- Front wheel steering mechanism, 12... Rear wheel steering mechanism, 32...
Steering ratio control mechanism, 51...stepping motor, 10
0... Control unit, 103... Rudder angle sensor, 104... Accelerator sensor, 105... Deceleration detection means, 106... Opposite phase control inhibiting means, 107...
- Control means, θH...handle steering angle, A...predetermined value. Figure 6 Y stop and step

Claims (1)

[Claims] (1) A four-wheel steering system for a vehicle that sets a target steering ratio for the front and rear wheels based on predetermined steering ratio characteristics, and controls the steering ratio of the front and rear wheels to the target steering ratio using an actuator. deceleration detection means for detecting a deceleration state of the vehicle; and anti-phase control prohibition for receiving the output of the deceleration detection means and prohibiting control of the target steering ratio to the opposite phase side for the actuator when the vehicle is decelerated. a steering angle detecting means for detecting a steering angle of the vehicle; and a control means for operating the reverse phase control inhibiting means when the steering angle detected by the steering angle detecting means is equal to or greater than a predetermined value. A four-wheel steering device for a vehicle, which is characterized by: