JPH043354B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a four-wheel steering system for a vehicle.

(Prior art) An example of a four-wheel steering system for a vehicle is disclosed in Japanese Patent Application Laid-open No. 56-167562.
It is disclosed in the publication No. This four-wheel steering device is
The front wheels and rear wheels are connected by a link member, etc., and the steering angle ratio of the rear wheels to the front wheels increases as the vehicle speed increases, in other words, the rear wheels are steered more largely based on the signal from the vehicle speed sensor. However, if a vehicle speed sensor malfunctions and a signal indicating a vehicle speed higher than the actual vehicle speed is output, the rear wheels will be steered abnormally.

Further, in the conventional technology described above, the steering operation of the front wheels is mechanically transmitted to the rear axle by a link member, etc., but the steering angle of the front wheels is detected by a sensor,
It is also conceivable to electrically control the steering angle of the rear wheels based on the detection signal and the detection signal from the vehicle speed sensor. When performing such control, an abnormality in the front wheel steering angle sensor in addition to the vehicle speed sensor poses a problem. That is, if a signal indicating a larger steering angle than the actual front wheel steering angle is output, the rear wheels will be abnormally steered.

However, in response to abnormalities in the sensor system,
It is also possible to determine the maximum vehicle speed and maximum front wheel steering angle determined from the driving behavior of the vehicle, and then determine whether the signals from each sensor exceed these maximum values. However, for example, it is unthinkable in terms of vehicle operation that the steering angle of the front wheels is at its maximum when the vehicle speed is at its maximum, and although it is clear that such a situation is causing an abnormality in the sensor system, the vehicle speed signal and There is a problem in that an abnormality in the sensor system cannot be detected as long as the front wheel steering signal is within the permissible range of the output of each sensor.

(Purpose of the Invention) In view of the fact that countermeasures against sensor system abnormalities are one of the extremely important issues for safe vehicle operation in four-wheel steering systems, the present invention aims to solve the problem by grasping the relationship between vehicle speed and front wheel turning angle. The abnormality of the sensor system is determined by checking whether the driving condition specified by both the signal from the vehicle speed sensor and the signal from the front wheel steering angle sensor is possible based on the driving characteristics of the vehicle. This is intended to improve vehicle driving safety by preventing abnormal steering of the wheels.

(Configuration of the Invention) The configuration of the present invention is clearly shown in FIG. That is, the four-wheel steering device for a vehicle according to the present invention includes a steering device 2 that steers the front wheels 1 of the vehicle, a rear wheel steering device 4 that steers the rear wheels 3, and a vehicle speed sensor 5 that detects the vehicle speed. It includes a front wheel steering angle sensor 6 that detects the steering angle of the front wheels 1, and a controller 7 that controls the operation of the rear wheel steering device 4.

The controller 7 receives the outputs from the vehicle speed sensor 5 and the front wheel steering angle sensor 6, and adjusts the rear wheels 3 to the front wheels 1.
automatic control means 8 for outputting a control signal to the rear wheel steering device 4 so that the steering angle characteristics of the rear wheel steering device 4 change depending on the vehicle speed;
, a determining means 9 for determining a failure in the sensor system, and a safety control means 10 for setting the steering angle of the rear wheels 3 to zero in response to the output of the determining means 9. The determining means 9 then compares the front wheel steering angle obtained from the output from the front wheel turning angle sensor 6 with the allowable critical front wheel turning angle obtained from the output from the vehicle speed sensor 5, and determines the magnitude thereof. and front wheel steering angle sensor 6
When the front wheel turning angle exceeds the critical front wheel turning angle, an activation signal is output to the safety control means 10.

(Example) Hereinafter, an example of the present invention will be described based on FIGS. 2 to 5.

As shown in Figure 2, the left and right front wheels 1, 1 of the vehicle
The steering device 2 includes a steering wheel 11, a rack and pinion mechanism 12 that converts the rotational motion of the steering wheel 11 into linear reciprocating motion, and a tie rod 13a that transmits the operation of the rack and pinion mechanism 12 to the front wheels 1, 1. ,13
a and a transmission means 13 consisting of knuckle arms 13b, 13b.

On the other hand, a rear wheel steering device 4 that steers the left and right rear wheels 3, 3 has knuckle arms 14, 14 attached to the rear wheels 3, 3.
and a rod 16 connected via tie rods 15, 15. This rod 16 moves in the left-right direction by the rotation of a pinion 18 that meshes with the rack portion 17, thereby steering the rear wheels 3, 3. The pinion 18 is connected to a pulse motor 20 via a transmission mechanism 19 consisting of a pair of bevel gears.

Further, the rod 16 passes through the power cylinder 21, and a piston 24 that partitions the inside of the power cylinder 21 into left and right hydraulic chambers 22, 23 is attached to the rod 16.
is fixed to. Each hydraulic chamber 22, 23 is connected to an oil pump 30 via hydraulic passages 25, 26, a control valve 27, an oil supply passage 28, and an oil return passage 29, and an electric motor 31 is connected to the oil pump 30.

The control valve 27 detects the rotational direction of the pinion 18 and connects the oil supply passage 28 to one hydraulic chamber 22 or 23 and the oil return passage 29 to the other hydraulic chamber 23 or 22, and also connects the oil supply passage 28 to one hydraulic chamber 22 or 23 and the oil return passage 29 to the other hydraulic chamber 23 or 22. It controls the hydraulic pressure to the pressure corresponding to the rotational force of the pinion 18, and the power cylinder 21
The hydraulic pressure introduced into moves the rod 16, that is,
Assists the steering force of the rear wheels 3, 3.

The operation of the pulse motor 20 and the electric motor 31 is controlled by control signals output from the controller 7. This controller 7 includes a vehicle speed sensor 5 that detects the vehicle speed, and a steering wheel 11 that detects the steering angle of the front wheels 1.
A front wheel steering angle sensor 6 detects the steering angle of the rear wheels 3, a rear wheel steering angle sensor 32 detects the steering angle of the rear wheels 3, a display means 33 that graphically displays the steering status of the front wheels 1 and the rear wheels 3, and a rear wheel steering angle sensor 32 that detects the steering angle of the rear wheels 3. A mode switch 34 and a battery 35 are connected to set the third steering mode. In FIG. 2, 36 is a steering angle (front wheel turning angle) detection section, 37 is a pulse motor rotation angle detection section, and the rear wheel turning angle sensor 32 detects the rotation angle of the rear wheels 3 from the rotation angle of the pulse motor 20. The steering angle is detected.

Next, the specific configuration of the controller 7 will be explained.

The controller 7 includes a determining means 9 that receives outputs from the vehicle speed sensor 5 and the front wheel steering angle sensor 6 and determines whether there is a failure in the sensor system, and a determining means 9.
The automatic control means 8 controls the operation of the rear wheel steering device 4 based on the signals from the vehicle speed sensor 5 and the front wheel steering angle sensor 6 upon receiving a determination that there is no failure in the sensor system, and the determination means 9 has a failure. The vehicle is equipped with a safety control means 10 that sets the rear wheel steering angle to zero in response to the determination.

As shown in FIG. 3, the determining means 9 determines a vehicle speed region based on a vehicle speed signal input from the vehicle speed sensor (pulse generator) 5 through an input protection section 38 and a counting section 39 that counts the number of pulses. A/A from the determination unit 40 and the front wheel steering angle sensor 6
a front wheel steering angle determination unit 43 that determines whether the front wheel steering angle signal inputted through the D conversion unit 41 and the encoding unit 42 is possible in terms of the driving characteristics of the vehicle in relation to the vehicle speed signal; We are prepared.

Specifically, in the input protection section 38, 4
4 is an integrating circuit for stabilizing the pulse signal from the vehicle speed sensor 5; 45 is an inverter with hysteresis that exhibits a buffering action;
8, noise is removed. In addition, the count section 39
Then, the vehicle speed is determined by counting the number of pulses. On the other hand, the front wheel steering angle sensor 6 uses a potentiometer, and the voltage signal from the front wheel steering angle sensor 6 is converted into a digital quantity (pulse) by the A/D converter 41, and then converted into a digital quantity (pulse) by the encoder 42. The signal is encoded using a binary code and captured as a front wheel turning angle signal.

As shown in _FIG .
It is divided into a low speed region from V _nax to V _lin or less, a medium-high vehicle speed region from V _lin to V _nax , and an abnormal vehicle speed region exceeding V _nax , and it is determined to which vehicle speed region the vehicle speed signal from the counter 39 belongs. It is something to judge. the above
V _lin is the state when the steering wheel 11 is steered to the lock position, that is, the maximum front wheel steering angle θ _Fnax
(when steering to the right), -θ _Fnax (when steering to the left) is the upper limit of the vehicle speed that can be traveled, and V _nax is the maximum value of the vehicle speed that is allowable for the vehicle's functionality. The vehicle speed region determining section 40 outputs an operation command signal to the automatic control means 8 when the vehicle speed signal from the counting section 39 belongs to the abnormal vehicle speed region, and outputs an operation command signal to the front wheel steering angle determining section 43 when it belongs to another vehicle speed region. Output the judgment result.

On the other hand, the front wheel turning angle determining section 45
The maximum allowable front wheel steering angle at the vehicle speed V corresponding to the output signal of 9, that is, the critical front wheel steering angle f _(V) is determined, and the absolute value of the front wheel steering angle corresponding to the output signal of the encoder 42 | It is determined whether θ _F | exceeds the critical front wheel steering angle f _(V) , and if it exceeds, an operation command signal is output to the safety control means 10, and if it does not, an operation command is issued to the automatic control means 8. It outputs a signal.

The critical front wheel steering angle f _(V) is the maximum front wheel steering angle in the low vehicle speed region, that is, f _(V) = θ _Fnax , and in the medium and high vehicle speed region, the critical front wheel steering angle f (V) is the above-mentioned θ _Fnax , the critical vehicle speed V _lin , the maximum vehicle speed V _nax ,
It is determined by the following formula using the maximum front wheel steering angle θ _Flin allowed by this V _nax .

f _(V) = k〓V+K〓 K〓=θ _Fnax −θ _Flin ／V _lin −V _nax K〓=θ _Fnax・V _nax −θ _Flin・V _lin ／V _nax −V _linThis critical front wheel turning angle The characteristics with respect to vehicle speed V are shown in FIG.

The automatic control means 8 receives the operation command signal from the front wheel turning angle determining section 43 and determines the front wheel 1 based on the vehicle speed detected by the vehicle speed sensor 5 and the front wheel turning angle detected by the front wheel turning angle sensor 6. The vehicle is equipped with a calculation unit that calculates the optimum turning angle of the rear wheels 3 relative to the turning angle of the steering wheel. An example of the characteristics of the steering angle ratio θ _R /θ _F of the rear wheel steering angle θ R and the front _wheel steering angle θ _F stored in this calculating section with respect to the vehicle speed V is shown in FIG. Accordingly, the rear wheel turning angle θ _R is calculated, and a control signal is output to the pulse motor 20.

On the other hand, the safety control means 10
0 or an operation command signal from the front wheel steering angle determining section 43, the relay 4 transmits a signal to cut off the transmission of the control signal from the automatic control means 8 to the rear wheel steering device 4.
6, and the rear wheel 3 has a return spring attached to the knuckle arm 14, so that the steering angle becomes zero.

A program for operating the controller 7 with respect to the determining means 9 is shown in a flowchart in FIG. That is, in the step, it is determined whether the vehicle speed V is smaller than the maximum vehicle speed V _nax or not.
That is, it is determined whether or not the abnormal vehicle speed region does not belong. If YES, the process proceeds to step; if NO (an abnormality exists in the vehicle speed sensor 5), the process proceeds to step, where the safety control means 10 performs safety control. In the above step, it is determined whether the vehicle speed V is greater than the critical vehicle speed V _lin , that is, whether it belongs to the medium to high vehicle speed region (belongs to the low vehicle speed region),
If YES, proceed to step; if NO, proceed to step.

In the step, it is determined whether the absolute value of the front wheel steering angle |θ _F | is smaller than the critical front wheel steering angle f _(V) = k〓V+K〓 in the medium and high vehicle speed range, and if YES, the process proceeds to the step. Automatic control is carried out by the automatic control means 8 at step 8, and if NO (there is an abnormality in at least one of the vehicle speed sensor 5 and front wheel turning angle sensor 6), the process advances to step and safety control is carried out. On the other hand, in the step, it is determined whether the above |θ _F | is smaller than the critical front wheel steering angle f _(V) = θ _Fnax in the low vehicle speed region. , in the case of NO (there is an abnormality in the front wheel turning angle sensor 6), the process advances to the step and safety control is performed.

In FIG. 2, the display means 33 is a transmissive liquid crystal display means provided on the driver's seat side, and includes a turning direction display segment 47 that graphically displays the turning directions of the front wheels 1 and the rear wheels 3; The vehicle behavior display segment 48 graphically displays the behavior of the vehicle. The operation of the display means 33 is controlled by the controller 7 based on signals from the front wheel steering angle sensor 6 and the rear wheel steering angle sensor 32.

The mode switch 34 also operates at low vehicle speeds (e.g.
30km/h or less), the rear wheel 3 is steered in the opposite phase to the front wheel 1.
Club mode that steers in the same phase as the rear wheel 3
This switch allows the driver to select and manually set three modes: a two-wheel mode in which the steering angle of the vehicle is always zero. A signal from the mode switch 34 is input to the controller 7, and the controller 7 operates according to the mode selected by the code switch 34. In this case, the controller 7 operates the automatic control means 8 by selecting the automatic mode.

Next, to explain the operation of the embodiment, when the steering wheel 11 is steered while the vehicle is running, the front wheels 1,
1 is steered, and when the determination means 9 determines that there is no abnormality in the sensor system, the automatic control means 8 is activated and the rear wheel steering device 4 is controlled. That is, the vehicle speed sensor 5
The signals from the front wheel steering angle sensor 6 are input to the automatic control means 8, and based on these signals, the rear wheel steering angle θ _R is calculated according to the characteristics shown in FIG _.
A pulse signal corresponding to is output to the pulse motor 20. As a result, the output shaft of the pulse motor 20 rotates at an angle corresponding to the pulse signal, the rod 16 moves in the axial direction via the transmission mechanism 19, pinion 18, and rack part 17, and the rear wheels 3, 3 rotate. be steered. At this time, the power cylinder 21 operates to assist in steering the rear wheels 3, 3.

When the determination means 9 determines that there is an abnormality in the sensor system, the safety control means 10 is activated and the steering angle of the rear wheels 3 becomes zero. In this case, in the medium to high vehicle speed region, it is determined whether the driving state of the vehicle specified by both the vehicle speed V and the front wheel turning angle θ _F is a state that should be possible in terms of vehicle functionality. Even if the output signals of the front wheel steering angle sensor 6 and the front wheel steering angle sensor 6 do not exceed V _nax and θ _Fnax , the absolute value of the front wheel steering angle |θ _F | is the critical front wheel steering angle.
If f _(V) is exceeded, it is determined that there is an abnormality in the sensor system.
Even if there is a slight abnormality in the sensor system, the rear wheels 3 will not be abnormally steered.

In the above embodiment, the critical front wheel steering angle was taken as a linear function of the vehicle speed V, but the critical front wheel steering angle characteristic with respect to the vehicle speed V was determined through a vehicle running test, and the vehicle speed V was determined from the characteristic. and front wheel steering angle θ _F
It is also possible to create a map for sensor system failure determination regarding the above, and to determine whether or not there is a failure based on the signals from the vehicle speed sensor 5 and the front wheel steering angle sensor 6. Alternatively, the critical front wheel steering angle may be approximated to a multidimensional function of the vehicle speed V based on the above characteristics, and the critical front wheel steering angle may be calculated by inputting a signal of the vehicle speed V.

Further, in the above embodiment, the safety control means 10 cuts off the signal from the automatic control means 8 to the rear wheel steering device 4 (turns off the power), but it also cuts off the signal sent from the automatic control means 8 to the rear wheel steering device 4, but it also cuts off the signal sent from the automatic control means 8 to the rear wheel steering device 4, but it also cuts off the signal sent from the automatic control device 8 to the rear wheel steering device 4. A signal may be sent to forcibly drive the rear wheels 3 so that the steering angle becomes zero.

Furthermore, the oil pump 30 in FIG. 2 may be driven by an engine.

(Effects of the Invention) According to the present invention, the critical front wheel turning angle that is functionally permissible for the vehicle with respect to the vehicle speed is determined by the output from the vehicle speed sensor, and the A failure in the sensor system is determined by comparing the wheel steering angle with the critical front wheel steering angle and the rear wheel steering angle is set to zero, so failures in the sensor system are accurately detected and abnormal rear wheel steering is prevented. This increases the safety of vehicle driving.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the present invention, Fig. 2 is a block diagram of an embodiment, Fig. 3 is a block diagram of the portion related to the determination means of the controller, and Fig. 4 shows the relationship between vehicle speed and critical front wheel turning angle. FIG. 5 is a characteristic diagram showing the relationship between vehicle speed and steering angle ratio, and FIG. 6 is a flowchart showing the mode of control related to the determination means. 1...Front wheel, 2...Steering device, 3...
Rear wheel, 4... Rear wheel steering device, 5... Vehicle speed sensor,
6...Front wheel steering angle sensor, 7...Controller,
8... Automatic control means, 9... Judgment means, 10...
Safety control measures.

Claims (1)

[Claims] 1 A steering device for steering the front wheels, a rear wheel steering device for steering the rear wheels, a vehicle speed sensor for detecting vehicle speed, a front wheel steering angle sensor for detecting the steering angle of the front wheels, a vehicle speed sensor and a front wheel steering device. and a controller that controls the rear wheel steering device in response to the output signal of the steering angle sensor, and the controller sends a control signal to the rear wheel steering device so that the rear wheel steering angle characteristic with respect to the front wheel steering angle changes depending on the vehicle speed. a control means for outputting a front wheel steering angle; a determining means for comparing and determining a front wheel steering angle obtained from an output from a front wheel steering angle sensor and an allowable critical front wheel steering angle obtained from an output from a vehicle speed sensor; A four-wheel steering system for a vehicle, comprising: safety control means that receives an output from a determining means and sets a rear wheel steering angle to zero when a front wheel steering angle determined by a sensor exceeds the maximum front wheel steering angle. .