JPH052549B2 - - Google Patents

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a four-wheel steering system for a vehicle.

(Prior art) Regarding a four-wheel steering device that controls the steering of the rear wheels in accordance with the steering of the front wheels of a vehicle, for example, as described in Japanese Patent Application Laid-Open No. 59-92263, there is a method of steering the front wheels. It is known that a device for steering rear wheels in conjunction with the operation of a steering device is provided with a variable steering ratio mechanism that changes the steering ratio characteristics of the front and rear wheels.

By the way, when this steering ratio variable mechanism is controlled by an actuator such as a motor depending on the driving condition of the vehicle such as vehicle speed, a separate steering ratio detection means is provided to detect the actual steering ratio required depending on the driving condition. It is preferable to correct the deviation in the steering ratio from the viewpoint of improving the accuracy of steering ratio control. However, when such a steering ratio detection means is provided, when the steering ratio detecting means malfunctions, accurate steering ratio correction cannot be performed, and there is a possibility that the steering ratio is controlled to a completely different steering ratio from the required steering ratio.

(Object of the Invention) The present invention provides a variable steering ratio mechanism that changes the steering ratio of the front and rear wheels according to the driving condition of the vehicle. The basic purpose is to detect this and control the steering ratio to zero, to ensure the drivability of the vehicle, and to improve the reliability of the four-wheel steering system.

Then, when controlling the steering ratio to zero in the event of such a failure, since the vehicle speed is zero at the time of startup, the control amount necessary to make the steering ratio zero is determined in advance, and this control amount is The steering ratio can be brought to zero by the output, but if you try to control the steering ratio to zero at restart, control will be performed using the above control amount from the zero steering ratio position that was controlled at the previous startup. There is a problem in which the steering ratio deviates significantly from the zero position. The present invention attempts to solve such problems as well.

(Structure of the Invention) As shown in FIG. 1, the steering ratio characteristics of the rear wheels 3 with respect to the front wheels 2 of the vehicle 1 are changed by a steering ratio variable mechanism 4 according to the driving condition, and this steering ratio control A failure detection means 6 is provided to detect a failure of the steering ratio detection means 5 used for such purposes at the time of startup, and in the event of a failure, the steering ratio variable mechanism 4 is controlled by the steering ratio zero control means 7 to bring the steering ratio to zero. On the other hand, when the vehicle is stopped, the variable steering ratio mechanism 4 is controlled by the steering ratio return means 8 to return the steering ratio to the state before zero steering ratio control.

(Example) Hereinafter, an example of the present invention will be described based on FIGS. 2 to 9. Note that the same reference numerals are used for components in the embodiment that correspond to those shown in FIG.

-Example 1- This example is shown in FIGS. 2 to 8, and is an example in which the steering of the front wheels 2 is mechanically transmitted to the rear wheels 3.

First, the left and right front wheels 2, 2 are connected to the Katsukuru arm 9,
9, connected to both ends of the relay rod 11 via tie rods 10,10. relay rod 11
The shaft 13 from the handle 12 is easily 1
4 and pinion 15, and when the handle 12 is rotated, the relay rod 11 moves left and right to steer the left and right front wheels 2, 2.

On the other hand, the left and right rear wheels 3 and 3 are also equipped with Natsukuru arm 1.
It is connected to both ends of a relay rod 18 via tie rods 17 and 17, and is configured to be steered by moving the relay rod 18 left and right. This relay rod 18 moves in conjunction with the movement of the front wheel side relay rod 11, and the movement is assisted by hydraulic pressure.

Specifically, the front end of an operating rod 19 extending in the front-rear direction is connected to the relay rod 11 on the front wheel side by engaging a rack 20 and a pinion 21, and the rear end of this operating rod 19 controls the rotation of the front wheels 2 and rear wheels 3. It is connected to a control rod 23 extending from a relay rod 18 on the rear wheel side via a variable steering ratio mechanism 4 that changes the steering ratio. The actuating rod 19 rotates in response to the steering of the front wheels 2, and the control rod 23 slides left and right at the steering ratio determined by the variable steering ratio mechanism 4, so that the rear wheels 3 are steered. It's getting old.

The steering ratio is changed by operating a stepping motor 22, which is connected to a control circuit 24 that outputs a control signal in response to an output from a vehicle speed sensor 32 that detects the vehicle speed.
The operation is now controlled by Also,
A steering ratio detection means 5 for detecting a steering ratio is attached to the steering ratio changing mechanism 4 to output a steering ratio signal to a control circuit 24.
4 is connected to a battery power source 26 via an ignition switch 25.

Further, the relay rod 18 on the rear wheel side passes through a power cylinder 27 fixed to the vehicle body, and the inside of the power cylinder 27 is divided into two hydraulic chambers 30a and 30b by a piston 28 fixed to the relay rod 18. Both hydraulic chambers 30a, 30b are connected to an oil pipe 3.
1a and 31b to a control valve 33, and the control valve 33 is connected to an oil supply pipe 35 from a reservoir tank 34 and an oil return pipe 3.
6 is connected. control valve 33
detects the direction of movement of the control rod 23, and connects the oil supply pipe 35 to one of the hydraulic chambers 30a, 30b and the oil return pipe 36 to the other of the hydraulic chambers 30a, 30b according to the direction of movement. , an oil pump 3 interposed in the oil supply pipe 35
The hydraulic pressure from the relay rod 18 is controlled to a pressure corresponding to the shifting force of the control rod 23, and the hydraulic pressure introduced into the power cylinder 27 controls the shifting force of the relay rod 18, that is, the steering force of the rear wheels 3, 3. assist.

The oil pump 37 is driven by the engine, and the hydraulic chambers 30a, 30b are provided with springs 38, 38 for biasing the relay rod 18 to a neutral position, that is, a zero rear wheel steering position.

The specific structure of the variable steering ratio mechanism 4 will be explained with reference to FIG. 3. First, the control rod 23 is supported slidably in the vehicle width direction with respect to the vehicle body 39, and The axis is designated l1. The steering ratio changing mechanism 4 includes a holder 40 rotatably supported on the vehicle body 39 about an orthogonal line l2 orthogonal to the movement axis l1, and a swing arm 41 is attached to the swing shaft 42 of the holder 40. It is held in a swingable manner. This swing shaft 42 is connected to the above-mentioned movement axis.
It is located at the intersection of l1 and orthogonal line l2, and its swing axis l3 extends in a direction orthogonal to orthogonal line l2.

One end of a connecting rod 43 is connected to the control rod 23 through a ball joint 44, and the other end of this connecting rod 43 is connected to the tip of the swing arm 41 through a ball joint 45. There is. This connecting rod 43 includes a rotation imparting arm 4 having a rotation shaft 46 on the movement axis l1.
7 is connected via a ball joint 48, and an actuating rod 19 extending from the relay rod 11 on the front wheel side is connected to the rotating shaft 46 by the bevel gear 4.
They are connected by a mesh of 9 and 50. The rotation imparting arm 47 is a cylinder 5 integrated with the rotation shaft 46.
1, and is allowed to move forward and backward in a direction perpendicular to the rotation axis 46.

A worm 52 is provided on the output shaft of the stepping motor 22, and this worm 52 meshes with a worm wheel 53 provided on the rotating shaft of the holder 40.
The steering ratio is changed by the operation of 2, and the steering ratio is detected from the rotation angle of the holder 40 by the steering ratio detection means 5 attached to the holder 40.

That is, in the variable steering ratio mechanism 4,
The front wheels 2 are steered by the swinging arm 4 via the actuating rod 19, the rotation arm 47, and the connecting rod 43.
1, and the swing arm 41 swings (rotates) around the swing axis l3. When this swing axis l3 coincides with the movement axis l1 of the control rod 23 due to the rotation angle setting of the holder 40 by the stepping motor 22, the swing locus of the tip of the swing arm 41 is the movement axis l1. Even if the front wheels 2 are steered, no force is generated to shift the control rod 23 via the connecting rod 43, so the rear wheels 3 are not steered. (The steering ratio is zero.)

On the other hand, when the swing axis l3 is tilted downward to the right with respect to the movement axis l1 as shown in FIG. However, in response to the steering of the front wheels 2, the swinging of the swinging arm 41 generates a force that moves the control rod 23 from side to side via the connecting rod 43, and the rear wheels 3 are rotated in the same phase as the front wheels 2. be steered. Furthermore, when the swing axis l3 is tilted in the opposite direction, the rear wheels 3 are steered in the opposite phase. In other words, the stepping motor 22 rotates the holder 40 to change the inclination angle of the swing axis l3 to change the swing locus of the swing arm 41, thereby changing the turning angle of the rear wheels 3 relative to the turning angle of the front wheels 2. In other words, the steering ratio is changed between minus (opposite phase) and plus (same phase).

In addition, in the case of this example, the holder 40 has a swing shaft 4
Arms 54, 54 supporting both ends of the vehicle are connected in a U-shape.
Stoppers 55, 55 are provided which come into contact with the base end of the swing shaft 42 and regulate the rotation angle of the swing shaft 42.

Now, the configuration of the control circuit 24 that controls the operation of the stepping motor 22 of the variable steering ratio mechanism 4 is as follows.
As shown in the figure.

That is, the control circuit 24 includes the characteristic switching means 56,
It includes a central processing unit 57, a stepping motor drive circuit 58, and an energization control means 59. The characteristic switching means 56 receives the output from the vehicle speed sensor 32 and outputs a steering ratio characteristic switching signal (vehicle speed signal) to the central processing unit 57. The central processing unit 57 includes a steering ratio calculation means, a failure detection means for detecting a failure of the steering ratio detection means 5 at the time of starting the four-wheel steering device (at the time of starting the engine), and a steering ratio calculation means for detecting a failure of the steering ratio detection means 5 when there is no failure. A correction means for making the actual steering ratio match the required steering ratio at zero vehicle speed based on the detection signal; a steering ratio zero control means for controlling the steering ratio to zero when there is a failure; When the control is performed, the steering ratio is returned to the state before the zero control when the four-wheel steering device is stopped (when the engine is stopped). A stepping motor rotation direction signal S ₀₁ and a drive pulse signal S ₀₂ for control are output.

Further, the energization control means 59 controls the battery power supply 26
A first relay switch 60 switches the energization from the ignition switch 25 on and off to the central processing unit 57 and the stepping motor drive circuit 58, and a first relay switch 60 that switches the energization to the central processing unit 57 and the stepping motor drive circuit 58 by turning the ignition switch 25 on and off; a second relay switch 61 that is held for a predetermined time;
a transistor 62 for controlling the operation of the transistor 1;
Also, a start signal is sent from the ignition switch 25.
S ₀₃ and a stop signal S ₀₄ are sent to the central processing unit 57. In this case, an on/off signal is sent to the transistor 62 from the central processing unit 57.

Then, the steering ratio calculation means of the central processing unit 57 calculates one of the pre-stored steering ratio characteristic lines shown in FIG. 6 based on the vehicle speed signal for switching the steering ratio characteristic. A selection calculation is performed and a control signal is output to the stepping motor drive circuit 58 for changing the steering ratio according to the vehicle speed.

The failure detection means operates in response to a starting signal S ₀₃ (ON) from the ignition switch 25 when the engine is started, and operates upon receiving a signal from the steering ratio detection means 5. Determine whether or not there is a failure. That is, as shown in FIG. 7, the steering ratio detection means 5 operates at a first position where the output signal switches between H (high) and L (low) when the swing shaft 42 comes to the steering ratio position where the vehicle speed is zero. The signal and the second signal in which the signal is switched at the zero steering ratio position are output to the central processing unit 57, and furthermore, if there is a disconnection of the coupler, a signal (H, H) is output.
In other words, if the combination of the first and second signals is (H, L), the steering ratio will be in the out-of-opposite phase region, if (L, L), it will be in the anti-phase region, and if (L, H), the steering ratio will be in the in-phase region. It turns out that there is. Furthermore, when the vehicle speed decreases to zero, the above signal switches from (L, L) to (H, L), so when the vehicle speed is zero, the signal (H, L) is output from the steering ratio detection means 5. be done. Therefore, as shown in the processing flow in FIG. 8, the failure detection means reads the steering ratio signal, and if the signal is (H, L) when the engine is started, that is, when the vehicle speed is zero, the steering ratio is determined. It is determined that the detection means 5 is normal, and if the signal is other than (H, L), it is determined that the steering ratio detection means 5 is malfunctioning (steps S ₁ and S ₂ ).

When the failure detection means determines that there is no failure (YES in step _S2 ), the correction means performs stepping until the signal of the steering ratio detection means 5 switches from (H, L) to (L, L). A drive pulse signal S ₀₂ is output one pulse at a time to the motor drive circuit 58 to make the actual steering ratio match the steering ratio position at zero vehicle speed (step S ₃ ). After that, the steering ratio calculation means starts steering ratio control according to the vehicle speed in an open loop.

When the failure detection means determines that there is a failure (determination NO in step _S2 ), the steering ratio zero control means controls the steering ratio from the zero vehicle speed position because the actual steering ratio is currently at the zero vehicle speed position. The signal S ₀₂ is outputted at the preset number of drive pulses required for steering ratio control up to the zero steering ratio position, and the actual steering ratio is set to the zero steering ratio position. Prevent control (steps S ₄ , S ₅ ).

The steering ratio return means holds a failure signal by the failure detection means, and upon receiving the ignition switch off, that is, the stop signal _S04 , controls the steering ratio from the zero steering ratio position to the zero vehicle speed position. A signal S ₀₂ is output with the number of driving pulses required for (step S ₄ reverse pulse), and the actual steering ratio is set to the zero vehicle speed position (steps S ₆ , S ₇ ).

In the energization control means 59, when energization is applied from the battery power source 26 via the first relay switch 60, an on signal is output from the central processing unit 57 to the transistor 62, the second relay switch 61 is turned on, and the ignition is turned on. Tension switch 25
Even if it is turned off, control of the steering ratio return means 8 is ensured by energizing through the second relay switch 61, and an end signal (off signal) of this control is output from the central processing unit 57 to the transistor 62. Power to the central processing unit 57 is cut off.

Therefore, in this embodiment, when the engine is started, the failure detection means determines whether there is a failure based on the signal from the steering ratio detection means 5, and if there is no failure, the vehicle speed is zero at the steering ratio. After the correction is made, the steering ratio is calculated according to the vehicle speed by the steering ratio calculating means, and the steering ratio is changed by open loop control so that the required steering ratio is achieved by driving the stepping motor 22. be done. In other words, as the front wheels 2 are steered, the rear wheels 3 are steered at a steering ratio corresponding to the vehicle speed, and the vehicle is driven with four-wheel steering. On the other hand, if there is a failure, the steering ratio is immediately fixed at zero by the steering ratio zero control means, and subsequent control is stopped, and the vehicle is driven so that the rear wheels 3 are parallel to the longitudinal direction regardless of the steering of the front wheels 2. It will be operated with two-wheel steering as it is.

Then, when the engine is stopped, the steering ratio returns from the zero steering ratio position to the zero vehicle speed position, and when the engine is restarted, zero steering ratio control is performed from this zero vehicle speed position.

Incidentally, for zero steering ratio control, a method can be considered in which the holder 40 of the variable steering ratio mechanism 4 is once applied to the stopper 55 and the set number of pulses from there to the zero steering ratio position is output. In this case, the occurrence of abnormal noise at the time of contact with the stopper becomes a problem, but in the case of this embodiment, the swing shaft 42 is directly transferred from the steering ratio position of zero vehicle speed to the zero steering ratio position, so the above-mentioned There is no need to worry about abnormal noises. and,
Such direct position transition control is possible because the steering ratio is returned to the zero vehicle speed position when the vehicle is stopped. Then, there is also a method of separately remembering that zero steering ratio control was performed at startup, and prohibiting zero steering ratio control at restart, without performing steering ratio return control at stop. Although it is possible, in this case, an expensive storage means would be required, but in the case of this example,
Such storage means becomes unnecessary.

In addition, when the steering ratio detecting means 5 fails, a warning may be issued by lighting a warning lamp or the like to notify the driver that he must drive with two-wheel steering.

Moreover, even if the signal input from the steering ratio detection means 5 in the failure detection means is (H, L), even if the correction means outputs several pulses when the vehicle speed is zero and the steering ratio is corrected, the signal is (L, L). If the steering ratio does not change, it may be determined that the steering ratio detection means 5 is malfunctioning, and the steering ratio control may be immediately shifted to zero. In this case, the position in zero steering ratio control is shifted by an amount corresponding to several pulses during zero vehicle speed steering ratio correction, but this is a small error and can be tolerated without interfering with driving.

-Example 2- This example is shown in FIG. 9, and is an example in which the steering control of the rear wheels 3 in conjunction with the steering of the front wheels 2 is performed electrically.

That is, the four-wheel steering system of this example receives a steering wheel steering angle sensor 71 provided with the steering shaft 13, a steering wheel steering angle signal from the steering wheel steering angle sensor 71, and a vehicle speed signal from the vehicle speed sensor 32, and performs stepping. It includes a control circuit 72 that outputs a control signal to the motor drive circuit 58, and a stepping motor 22 that steers the rear wheels 3 using the drive signal from the stepping motor drive circuit 58.

In the case of this example, in the variable steering ratio mechanism 4, the stepping motor 22 is linked to a pinion 75 that meshes with a rack 74 of the rear wheel side relay rod 18 via a transmission mechanism 73 consisting of a pair of bevel gears. The hydraulic control valve 33 is the pinion 7
The oil passage and oil pressure are changed by detecting the rotational direction and rotational force of 5. Further, a rear wheel turning angle sensor 76 is attached to the stepping motor 22 and outputs a rear wheel turning angle signal to the control circuit 72. In addition, the control circuit 7
2 includes a display means 77 for graphically displaying the steering mode of the front wheels 2 and rear wheels 3, a control mode changeover switch 78 for setting the steering mode of the rear wheels 3, and an operation for supplying electricity from the battery via the ignition switch. energizing wire 79 and energizing wire 8 for storing steering wheel angle
0 is connected.

Then, the control circuit 72 includes a steering angle calculating section that calculates a rear wheel turning amount from the front wheel turning amount calculated from the steering wheel steering angle signal and the steering ratio calculated from the vehicle speed signal, and outputs a control signal. , a steering ratio detection section that detects a steering ratio from a steering wheel steering angle signal and a rear wheel steering angle signal; failure detection means for detecting whether or not there is a failure in the detection section; correction means for correcting the actual steering ratio to a vehicle speed zero steering ratio position upon receiving a steering ratio detection signal when there is no failure; Steering in which the number of drive pulses required for control from a zero steering ratio position to a zero steering ratio position is calculated according to the steering wheel angle and outputted to the stepping motor drive circuit 58 to make the steering ratio zero. Holds the ratio zero control means and the failure signal,
In order to achieve a steering ratio of zero vehicle speed when the engine is stopped, the number of drive pulses corresponding to the steering wheel angle at that time is output to the stepping motor drive circuit 58, and the rear wheels 3 are steered to a steering ratio of zero vehicle speed. and a rudder ratio return means.

In addition, the control mode changeover switch 78 has an auto mode in which the rear wheels 3 are steered in the opposite phase to the front wheels 2 in a low vehicle speed range, and a club mode in which the rear wheels 3 are steered in the same phase as the front wheels 2. This is a switch for the driver to select and manually set the mode, and the steering ratio changes depending on the vehicle speed in each mode.

In each of the above embodiments, the steering ratio is changed depending on the vehicle speed and the vehicle speed and setting mode, but the steering ratio can be changed by combining these factors with other factors such as lateral acceleration acting on the vehicle body. Change control may also be performed. Furthermore, the steering ratio may be changed by controlling only one of the lateral acceleration, the control mode changeover switch 78, and the steering wheel angle, or by a combination of these.

Further, in each of the above embodiments, a stepping motor is used to drive the variable steering ratio mechanism 4, but other driving means such as a normal DC motor may be used. In this case, steering ratio zero control, steering ratio return control, etc. can be performed based on the operating time of the drive means.

(Effects of the Invention) According to the present invention, since the steering ratio detecting means is checked for failure at the time of startup and the steering ratio is set to zero if there is a failure, the rear wheels adjust to the driving state even in the event of failure. It is possible to prevent the vehicle from being steered with a steering ratio different from the required steering ratio, thereby ensuring the operability of two-wheel steering in which only the front wheels are steered, and improving the reliability of the four-wheel steering system. can be improved. Once the steering ratio is controlled to zero due to a failure in the steering ratio detection means, the steering ratio is returned to the state at the time of failure detection when the steering ratio is stopped, so when restarting, the same control as at the previous start is performed. By simply performing this, the steering ratio can be set to zero, and even if starting and stopping are repeated, the drivability of the vehicle can be ensured with simple patterned control without using expensive storage means.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the present invention, Figs. 2 to 8 are related to Embodiment 1, Fig. 2 is an overall block diagram of a four-wheel steering device, and Fig. 3 shows a part of the steering ratio changing mechanism. 4 is a sectional view taken along line A-A in FIG. 3, FIG. 5 is a control system diagram, FIG. 6 is a steering ratio characteristic diagram, and FIG. 7 is a steering ratio detection signal characteristic. 8 is a diagram showing the flow of processing in the central processing unit, and FIG. 9 is an overall configuration diagram of a four-wheel steering system according to a second embodiment. 1...Vehicle, 2...Front wheel, 3...Rear wheel, 4...
Steering ratio variable mechanism, 5... Steering ratio detection means, 6...
Failure detection means, 7... Steering ratio zero control means, 8...
Steering ratio return means.

Claims (1)

[Claims] 1. A four-wheel steering system that is equipped with a variable steering ratio mechanism that changes the steering ratio characteristics of the rear wheels with respect to the front wheels, and that controls the steering ratio change mechanism according to the driving condition of the vehicle. A steering ratio detection means for detecting a steering ratio, a failure detection means for detecting a failure of the steering ratio detection means at the time of startup, and a failure detection means for detecting a failure of the steering ratio detection means by the failure detection means. A steering ratio zero control means for controlling the variable steering ratio mechanism so that the steering ratio becomes zero, and a steering ratio variable mechanism that controls the variable steering ratio mechanism when the vehicle is stopped to be in a state at the time of failure detection before zero steering ratio control. A four-wheel steering system for a vehicle, comprising a steering ratio return means for returning the steering ratio.