JPS62168762A - Four-wheel steering gear for vehicle - Google Patents

Abstract

PURPOSE:To reduce a change in steering ratio at any troubles for improving safety by providing a means for setting the steering ratio to an intermediate predetermined value in the same phase when the trouble in a system for controlling the ratio (steering ratio) of steering angle of rear wheels to that of front wheels is detected. CONSTITUTION:A rear wheel steering mechanism 12 comprises a power steering mechanism 16 in which a piston 17a is moved by controllably supplying and discharging pressurized oil to and from hydraulic chambers 17b, 17c in a power cylinder 17 through a control valve 20 to assist a drive force for a relay rod 15. This valve 20 is controllably interlocked with the operation of a front wheel steering mechanism 3 through a rotary shaft 28 and a steering ratio controlling mechanism 29 which in turn controls the steering ratio by controlling a stepping motor 50 through a controlling unit 100. In this case, when any troubles in a steering ratio controlling system are detected by a trouble detecting section 103, the steering ratio is adapted to be set to an intermediate predetermined value in the same position by a controller section 104 in failure time.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a four-wheel steering device for a vehicle, that is, a device that steers the rear wheels as well as the front wheels. This invention relates to troubleshooting for a four-wheel steering system that is controlled by changing the ratio of the steering angle of the rear wheels to the steering angle (steering ratio).

(Prior Art) A four-wheel steering device has been developed that controls the rear wheels as well as the front wheels, and changes the steering ratio of both wheels according to the driving state of the vehicle. This is generally done by setting the steering ratio in opposite phases at low speeds and in the same phase at high speeds, thereby increasing the steering response at low speeds and improving stability at high speeds. The opposite phase is changed to the same phase at the boundary, and thereafter, as the traveling speed increases, the steering ratio of the same phase is increased to a predetermined maximum (direction).

In such a four-wheel steering system, the running state of the vehicle (
For example, a vehicle speed sensor is used to detect vehicle speed (for example, vehicle speed), but if this vehicle speed sensor fails, the signal will indicate zero vehicle speed. Normally, at zero vehicle speed, the steering ratio is set to a value with a large opposite phase, so the specified steering ratio is The steering ratio of a vehicle running at the same steering ratio suddenly changes to a large opposite phase, which is unfavorable in terms of running stability. In addition, not only the vehicle speed sensor but also the same problem as described above may occur if a part of the control system breaks down, such as runaway of the CPU used for control.

Therefore, a system has been proposed in which the steering ratio is set to the highest value of the same phase in the event of a failure. (Unexamined Japanese Patent Publication No. 60, 850γ
No. 7) This is a safety measure in which the steering ratio is set to the maximum value of the same phase when the hydraulic system used for four-wheel steering fails, but the maximum value of the same phase In reality, this is the value when the steering ratio is almost saturated at a vehicle speed of about 130/la/hour, and is quite far from the steering ratio at normal vehicle speeds, so it is unlikely that a malfunction will occur. It is considered that there are many cases in which the change in the steering ratio at the time of switching is relatively large and is not necessarily the best in practice. In addition, since it is necessary to continue driving at the fixed steering ratio for a while after a failure, it is not necessarily the steering ratio that is the easiest to drive, and this point requires further refinement and improvement. By the way.

(Object of the Invention) Based on the above considerations, the present invention is designed to change the steering ratio at the time of a failure so that the amount of change is small, and even if it is fixed, the steering ratio is easy to drive. The object of the present invention is to provide a four-wheel steering device with a steering ratio of .

(Structure of the Invention) The four-wheel steering device according to the present invention sets the steering ratio to a predetermined value between the same phases when a failure occurs in the control system that controls the steering ratio according to the driving state. It is characterized by the fact that

Here, failure in the control system naturally refers to failure in parts of the auxiliary system other than those that have the function of setting the steering ratio to a predetermined value between the same phases (for example, the vehicle speed sensor, (failures in electrical systems, control units, etc. that operate in response to output) and do not include failures that make it impossible to set the above-mentioned predetermined value due to the failure.

In addition, the predetermined value in the middle of the same phase mentioned above means a value that is about the middle of the maximum value and the minimum value among the same phase values of the steering ratio that change depending on the driving condition, and is usually In the case of an automobile, the steering ratio is preferably set for a vehicle speed of about 80-90 degrees/hour, assuming that the steering ratio changes from opposite phase to same phase at 50 degrees/hour.

In addition, the speed at which the steering ratio changes from the previously set value to the predetermined value at the time of a failure is compared to the speed at which the steering ratio changes in response to normal driving conditions. The later the better. This is because a sudden change in the steering ratio at the time of a failure is undesirable for the driving operation of a running vehicle. Furthermore, the rate of change is faster when changing the steering ratio from a value in the same phase that is larger than the predetermined value to the predetermined value than when changing the steering ratio from a value smaller than the predetermined value in the opposite phase or in the same phase to the predetermined value. It is preferable to set it so that it is slower. This is because when the steering ratio changes from a large value of the same phase to a value of the opposite phase, the retrospective performance of the vehicle increases, so the responsiveness to steering increases, and this has a large effect on driving.

(Effects of the Invention) According to the present invention, when the steering ratio control system in the four-wheel steering device fails, the steering ratio is set and fixed at an intermediate value of the same phase, so no matter what speed the vehicle is traveling. However, the change in the steering ratio is small, and the effect of the change on the steering is small, making it possible to realize four-wheel steering that is easy to drive.

Particularly at high speeds, changes in the steering ratio have a large effect on driving, so setting the same phase to an intermediate value provides a greater sense of stability.

Although it is conceivable to switch to two-wheel steering in the event of a failure, it is considered preferable for drivers who are accustomed to four-wheel steering to maintain four-wheel steering with a somewhat in-phase steering ratio.

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a relationship graph between vehicle speed and steering ratio showing an example of a predetermined value of the steering ratio that is set in the event of a failure according to the present invention. As shown in Figure 1, with a four-wheel steering system, the vehicle generally speeds up (horizontal axis).
The steering ratio (vertical axis) is changed from the opposite phase to the same phase with a boundary of approximately 50-/hour in accordance with the change in the steering ratio. In the illustrated example, when the control system fails, the same-phase steering ratio a1 is set when the vehicle speed is 80KJn/hour, and the same-phase steering ratio a2 is set when the vehicle speed is 90KJn/hour. It is set to the value in the area in between (shown with diagonal lines). This region is neither extremely in-phase nor out-of-phase, but shows an intermediate value of in-phase, and in fact provides a steering ratio that is just above easy to drive.

Next, a second example of the basic mechanism of the four-wheel steering system of the present invention will be described.
This will be explained with reference to FIGS. 3 and 4.

In Figures 2 and 3, IL, 1R, 2L, 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 2+1 are linked by a rear wheel steering mechanism 12, respectively.

The front wheel steering mechanism 3 includes a pair of left and right knuckle arms 4L.
, 4g, tie rods 5L, 5R, and a relay rod 6 that connects the left and right tie rods 5L, 5+1. In addition, a steering wheel 1 is connected to the front wheel steering mechanism 3 via a rack and pinion type steering mechanism 7.
0 is linked. That is, the relay rod 6 has a rack 8 formed thereon, and a steering shaft 11 with a steering wheel 10 connected to its upper end.
A binion 9 that engages with the rack 8 is attached to the lower end of the vehicle, and the left and right front wheels IL and 1R are steered in accordance with the operation of the steering wheel 10.

On the other hand, the rear wheel steering mechanism 12, like the front wheel steering mechanism 3, includes left and right knuckle arms 13L, 13R, tie rods 14L, 14R, and the tie rod 14L.
.

It has a relay rod 15 that connects the 14Rs, and is further provided 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 connects the relay rod 15 as a piston rod. Inside the power cylinder 17, two hydraulic chambers are formed by a piston 17a that is integrally attached to the relay rod 15. Sections 17b and 17c are formed,
A hydraulic chamber 17b within this cylinder 17.

17c are each connected to a control valve 20 via a pipe 18, 19. 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 constructed of a known spool valve type, and is integrally attached to the relay rod 15 via a connecting member 25.
0a, and a spool valve (not shown) fitted in the valve casing 20a, and one hydraulic pressure '11 of the power cylinder 17 is adjusted according to the movement of the spool valve.
7b (17c) is supplied with pressurized oil equivalent to the pressure of a hydraulic pump 24 to assist the driving force for the relay rod 15. Furthermore, turn springs 17d and 17d are installed in the power cylinder 17 to urge the rear wheels 2L and 2R to a neutral position where the steering angle θk is zero.

The relay rod 6 of the front wheel steering mechanism 3 is equipped with a rack 2 other than the rack 8 constituting the steering mechanism 7.
6 is formed, and a binion 27 attached to the front end of a rotating shaft 28 extending in the longitudinal direction of the vehicle body is engaged with the rack 26, and the rear end of the rotating shaft 28 is connected to the rear wheel rotation through a steering ratio control II mechanism 29. It is linked to the rudder @12.

As shown in detail in FIG. 4, the steering ratio control 1m mechanism 29 has a control rod 30 that is slidably held on movement axes Q and x in the vehicle width direction with respect to the vehicle body. One end of the control rod 30 is connected to the control valve 20.
is connected to the spool valve. In addition, the steering ratio control mechanism 29 has an end portion 11 attached to a support pin 3 in a U-shaped holder 31.
The holder 31 has a support 1jll135 having a rotation axis 9J2 orthogonal to the movement axis 1 of the control rod 30 on a casing 34 fixed to the vehicle body. It is rotatably supported through. Support bin 3 of the swing arm 33
2 is the above both axes 9J! .

9J2 and extends in a direction perpendicular to the rotation axis 2, and by rotating the holder 31 around the support lN135 (rotation axis 9J2), the support pin 32 at the tip and the control valve are 30 movement axis 9, r
The inclination angle formed by the movement axis 9., that is, the swing locus plane of the swing arm 33 with the support bin 32 as the center is the movement axis 9. The angle of inclination made with respect to a plane perpendicular to s (hereinafter referred to as a reference plane) is changed.

Further, one end/portion of a connecting rod 37 is connected to the tip of the swing arm 33 via a ball joint 36, and the other end of the connecting rod 31 is connected to the control rod 30 via a ball joint 38.
The fourth end at the tip of the swing arm 33 is connected to the other end.
The control rod 30 is displaced in the left-right direction in response to displacement in the left-right direction in the figure.

The connecting rod 37 is slidably supported by a rotation imparting arm 40 via a ball joint 41 at a portion thereof close to the ball joint 36 . This rotation imparting arm 40 is connected to the movement axis 9. The bevel gear 43 is provided integrally with a large-diameter bevel gear 43 rotatably supported on the support shaft 42, and the bevel gear 43 is attached to the rear end of the rotating shaft 28 as shown in FIG. A bevel gear 44 is meshed with each other to transmit the rotation of the steering wheel 10 to the rotation imparting arm 40. For this reason,
The rotation imparting arm 40 and the connecting rod 37 rotate around the movement axis Lt by an amount corresponding to the rotation angle of the steering wheel 10, and the swing arm 33 rotates accordingly.
is swung around the support pin 32, the pin 32
When the axis of the control rod 30 coincides with the movement axis 9,1 of the control rod 30, the ball joint 36 at the tip of the swing arm 33 only swings on the reference plane, and the control rod 30 is held stationary. However, the axis of the pin 32 is inclined with respect to the movement axis 1, and the swing fl of the swing arm 33 is
If the IvI trace surface deviates from the reference plane, the ball joint 3G will be displaced in the left-right direction in FIG. 4 as the swing arm 33 swings about this pin 32, and this displacement will cause Control rod 3 through 37
0, and the control rod 30 moves along the axis of movement 9.
It is configured to move along J1 and operate the spool valve of the 21st control valve 20. That is, even if the swinging angle of the swinging arm 33 about the axis of the pin 32 is the same, the displacement of the control rod 30 in the left-right direction changes with the change in the inclination angle of the pin 32, that is, the rotational angle of the holder 31. and change.

In order to change the inclination angle of the support pin 32 with respect to the movement axis, that is, the inclination angle of the holder 31 with respect to the reference plane, the support shaft 35 of the holder 31 is equipped with a sector gear as a worm wheel, as shown in FIG. 45 is attached, and a worm gear 47 on a rotating shaft 46 is meshed with this sector gear A745.

Further, a bevel gear 48 is attached to the rotating shaft 46, and this heavy vehicle! 1248 is meshed with an umbrella/gear 49 disposed on the output shaft 50a of the stepping motor 50 as an actuator.
By operating and rotating the sector gear 45,
By changing the inclination angle of the holder 31 with respect to the reference plane, the rear wheel 2L
, 2R, and move the sector gear 45 to a neutral position where its center line is perpendicular to the center line of the rotating shaft 46 of the worm gear 47 (at this time, the ball joint 36 at the tip of the swing arm 33 is at the reference rotates on the surface, rear wheels 2L, 2
When the steering angle θR of R becomes θR = 0), the front and rear wheels IL, 2L (1R
, 2R) (rear wheel steering angle θR/front wheel steering angle θF
) to the opposite phase in which the rear wheels 2L and 2R face in the opposite direction to the front wheels 1L and 1R, and on the other hand, when the rear wheels 2L and 2R rotate counterclockwise, the steering ratio is changed so that the rear wheels 2L and 2R face the front wheels I
It is configured to be controlled to have the same phase and direction in the same direction as L and IR.

Furthermore, the casing 34 that supports the holder 31 includes:
Stopper members 51 and 52 on the opposite phase side and the same phase side, which are made of pins that restrict the rotation range of the sector gear 45, are attached to the left and right sides of the sector gear 45, and are shown on the lower side of FIG. As shown, when the sector gear 45 rotates toward the opposite phase side, when the rotation angle from the neutral position reaches, for example, -17.5'', the sector gear 45 comes into contact with the opposite phase side stopper member 51 and rotates no further than that. On the other hand, when the sector gear 45 rotates toward the same phase side, when the rotation angle from the neutral position reaches, for example, 20 degrees, the sector gear 45 comes into contact with the stopper member 52 on the same phase side and moves. The control position of the stepping motor 50 when the sector gear 45 comes into contact with the stopper member 51 on the opposite phase side is set as its initial position. In FIG. 3, 39 is a rod stopper that restricts the maximum movement range of the relay rod 15 in the rear wheel steering mechanism 12.

- As shown in FIG. 2, the stepping motor 50 is configured to be operated and controlled by the output from a control unit 100 as a control means with a built-in microcomputer, and this control unit 100 has a device that detects the running speed SPD of the vehicle. Two vehicle speed sensors A
101a, a detection signal from vehicle speed sensor B 101b is input.

“Of these two vehicle speed sensors 101a and 101b, one vehicle speed sensor 101a is directly attached to the transmission,
The other vehicle speed sensor 101b is installed in the speedometer, and when the outputs of both sensors are equal, both sensors are normal, and when they are significantly different, it is determined that at least one is malfunctioning, and the malfunction of the vehicle speed sensor is detected. It is designed to be detected. Note that both sensors may be provided in the transmission or meter to detect the output from the same object, but if they are provided separately, there is an advantage that failures on the object side can also be detected.

The outputs from both sensors 101a and 101b are input to a control unit 102 that performs normal control, and this control unit 50 calculates a steering ratio according to the vehicle speed, and uses the calculated steering ratio to steer the rear wheels. Stepping motor 5 to steer
A drive signal is output at 0.

The outputs of both vehicle speed sensors 101a and 101b are further input to a failure detection unit 103, and the difference between the two outputs is 1 or more than a predetermined value.
-, a failure signal is output, a control stop signal is output to the control unit 102 that performs the normal control, and at the same time, the control unit 1 that performs control in the case of fail (at the time of failure of the control system)
A control start signal is output at 04.

A control unit 104 that performs control in the event of a failure receives the output from the steering ratio sensor 105, and converts it to the above-mentioned intermediate predetermined value of the same phase (the value in the region between the steering ratios a1 and a2 in FIG. 1). )
A drive signal is outputted to control the stepping motor 50 so that the stepping motor 50 is controlled.

Note that when the control unit 104 that performs control in the event of a failure is activated, it is preferable to generate a warning signal such as a warning sound or lighting of a warning lamp to notify the driver of the failure.

The flow of the operation of the control unit 100 is shown in the flowchart of FIG. In the flow of Figure 5,
The difference in output between the vehicle speed sensors A and B is 10 km/hour, which is used as a criterion for failure determination, but this can be determined as appropriate in consideration of the output error of both sensors.

In the above embodiment, the failure of the vehicle speed sensor was taken as an example of a failure of the control system, but this is an example of a failure of the CPU in the control unit.
It can also be replaced with a runaway.

・In other words, a runaway detection circuit 81 is connected to the CPIJ (not shown) used in the normal control unit 102, and the output of this circuit is used like the failure detection unit 703 in the above example. For example, in exactly the same way, when the CPU runs out of control, the steering ratio can be fixed to an intermediate value of the same phase. That is, in the flowchart of Figure @5, vehicle speed sensor A,
The part of reading B and determining the magnitude of the vehicle speed difference is replaced with CPU runaway detection, and YES when the CPU is normal and N when runaway.

By doing so, the intended purpose of the present invention can be achieved by treating CPU runaway as one of the control system failures.

[Brief explanation of drawings]

FIG. 1 is a characteristic diagram showing the relationship between vehicle speed and steering ratio in a four-wheel steering system according to an embodiment of the present invention, and FIG. 2 is a schematic diagram showing the overall configuration of a four-wheel steering system according to an embodiment of the present invention. FIG. 3 is a perspective view of the P type, similarly showing its mechanical configuration, FIG. 4 is a vertical sectional view similarly showing its steering ratio control mechanism, and FIG. 5 is a flowchart similarly showing its control flow. 1L, IR...Front wheel 2L, 211...Rear wheel 3.
...Front wheel steering mechanism 7...Steering mechanism 10.
...Steering wheel 12...Rear wheel steering mechanism 16...Power steering mechanism 17...Power cylinders 17b, 17c...
Hydraulic chamber 20...Control valve 22...Oil supply pipe 24...Hydraulic pump 29
... Steering ratio controller @ 30 ... Control rod 33 ... Swinging arm 37 ... Connecting rod 40 ... Rotation imparting arm 50 ... Stepping motor 53 ... Pilot piping 54 ...・Hydraulic switching valve 10
0, 110...control unit 101a,
101b, 111... Vehicle speed sensor 102... Control section 103 during normal control... Failure detection section 104... Control section 105 during failure... Steering ratio sensor Fig. 1 Fig. 3 Figure 5

Claims (1)

[Scope of Claims] 1) In a four-wheel steering system that steers the rear wheels in response to the steering of the front wheels at a steering ratio according to the running state of the vehicle and in a range including at least the same phase, the steering ratio is controlled. It is characterized by comprising a failure detection means for detecting a failure in the system, and means for receiving the output of the failure detection means and setting the steering ratio to a predetermined value between the same phases when the control system fails. A four-wheel steering system for vehicles. 2) In the event of a failure in the control system, the speed at which the steering ratio is changed from the value immediately before the failure to the predetermined value is made slower than the speed during normal control in which the steering ratio is changed in accordance with changes in driving conditions. A four-wheel steering system for a vehicle according to claim 1. 3) When changing the steering ratio to the predetermined value in the event of a failure of the control system, the speed of change of the steering ratio when changing from a steering ratio of the same phase that is larger than the predetermined value is set to be in an opposite phase or from the predetermined value. 3. The four-wheel steering system for a vehicle according to claim 2, wherein the speed of change in the steering ratio is slower than the speed at which the steering ratio changes from a small in-phase steering ratio. 4) The vehicle according to claim 1, wherein the predetermined value of the steering ratio is a steering ratio that is set when the vehicle speed is in the range of 80 km per hour to 90 km per hour in normal control. 4-wheel steering device.