JP2733795B2 - Four-wheel steering system - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a four-wheel steering device for controlling the turning angle of the rear wheels of a four-wheel steering vehicle, and in particular, to reduce costs without impairing reliability. It relates to a four-wheel steering system.

[Prior Art] An example of this kind of four-wheel steering speed is shown in FIG. FIG. 4 shows a control circuit, which has a central processing unit 1 for control and a central processing unit 2 for diagnosis for diagnosis of the central processing unit 1 in parallel. These two central processing units 1 and 2 respectively have wheel speed sensors 3 for front wheels and rear wheels,
Wheel speed data for obtaining the vehicle speed is input from the interface 4 through the interface, and turning angle data of the front and rear wheels is input from the front and rear wheel steering angle sensors 5 and 6 via the interface. Based on the data from the sensors 3, 4, 5, and 6, the central processing units 1 and 2 calculate a target steering angle of the rear wheels and output a control signal for driving the rear wheels including a direction signal and a PWM signal. Along with
Diagnosis of each sensor 3, 4, 5, 6 and both central processing units 1,
2 and outputs a failure especially a fail safe signal. The output signals from the two central processing units 1 and 2 are compared in NAND circuits 21, 22, 23, 24 and 25. Control signals are output from NAND circuits 21 to 24, and a fail-safe signal is output from NAND circuit 25. The output is output to a rear wheel drive motor.

[Problems to be Solved by the Invention] By the way, the above-mentioned device is a central processing unit 1 for control and a central processing unit 2 for diagnosis for diagnosing the central processing unit 1.
Are provided in parallel, and in both central processing units 1 and 2,
While the data from the sensors 3, 4, 5, and 6 are input in parallel, the output signals are compared via NAND circuits 21, 22, 23, 24, and 25, and then the rear wheel control signal and the fail-safe signal are output. The output is used to control the steering while ensuring the reliability of the system. However, on the input side, it is necessary to input signals from the respective sensors 3, 4, 5, 6 to both the central processing units 1, 2, so that the number of interfaces is increased, and more comparators are required on the output side. There was a problem that the manufacturing cost was increased.

Japanese Patent Application Laid-Open No. 63-162378 "Electric control device for rear wheel steering in front and rear wheel steered vehicles" incorporates abnormality detection means in the first central processing unit and the second central processing unit, respectively. When an abnormality is detected in the central processing unit, the operation program of the other central processing unit is switched from the main control program to the sub control program in which the steering control content is simpler, and is operated. There is disclosed an apparatus which eliminates blank control and allows four-wheel steering to be connected. However, this device
In normal times, the first central processing unit and the second central processing unit respectively perform the rear wheel steering control and the steering restriction control in accordance with the main control program in a role-sharing manner. Also cooperate with each other. That is, the second central processing unit does not concentrate on the abnormality determination of the first central processing unit, but both central processing units calculate and output the control signal by passing data through a common RAM or the like. Therefore, the operation program of the second central processing unit also requires complicated logic,
In addition, the configuration in which the main control unit is taken over by the remaining central processing unit when one of the central processing units fails to realize fail-safe requires more complicated logic, so the burden of software processing is very large, There is a problem that the failure occurrence probability is high. Also,
An output control circuit that shuts off the output when a failure occurs is provided outside the electronic control unit (ECU), and the output control circuit is configured to shut off the output by a signal from the central processing unit. Unlike the system that controls the direction signal and the steering angle signal required for steering angle control with a single DC motor, the hydraulic circuit is combined with the step motor, even if the size of the device seen is easily enlarged and the rear wheel steering is performed. Since the configuration is controlled by the system, there is a problem that the configuration is easily complicated.

The present invention has been made in view of the above circumstances,
It is an object of the present invention to provide a four-wheel steering device capable of reducing costs without impairing reliability.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a wheel speed sensor which is provided for each of front wheels and rear wheels and outputs vehicle speed data, and a wheel speed sensor for front wheels and rear wheels, respectively. A steering angle sensor is provided to output steering angle data of front and rear wheels, and sensor outputs of the front wheel and rear wheel speed sensors and the front wheel and rear wheel steering angle sensors are supplied. A first central processing unit that calculates a target steering angle of the vehicle and outputs a control signal including a direction signal for rear wheel drive and a steering angle signal, an output of a wheel speed sensor for the front wheel, and a signal for the front wheel and rear wheel. Each output of the steering angle sensor and a direction signal of the control signal are supplied, and the direction signal is compared with the output of each sensor to diagnose the first central processing unit and output a fail-safe signal. Characterized by having a second central processing unit It is assumed that.

[Operation] According to the configuration of the present invention, the first central processing unit controls the rear wheel drive based on the outputs of the front wheel and rear wheel speed sensors and the outputs of the front wheel and rear wheel steering angle sensors. Is output to the rear wheel drive device and the second central processing unit, while the second central processing unit outputs the output of the front wheel speed sensor and the output of the front wheel and rear wheel steering angle sensors. And comparing the direction signal with the output of each of the sensors based on the direction signal of the control signal to diagnose the first central processing unit and output a fail-safe signal.

The second central processing unit diagnoses the first central processing unit based on the control signal from the first central processing unit, and each output of the front wheel speed sensor and the front wheel and rear wheel steering angle sensors. . Since the output of the rear wheel speed sensor is not supplied to the second central processing unit, the interface is simplified.

EXAMPLES Hereinafter, the present invention will be described based on one example shown in the drawings. FIG. 1 is a block diagram showing a circuit configuration of an embodiment of a four-wheel drive device according to the present invention. FIGS. 2 and 3 show control operations of a central processing unit for control and a central processing unit for diagnosis, respectively. It is a flowchart which shows.

This system has a central processing unit for control (first central processing unit) 1 and a central processing unit for diagnosis (second central processing unit) 2 for diagnosing the central processing unit in parallel. .

The control central processing unit 1 uses a 16-bit microprocessor, and wheel speed data for obtaining vehicle speed from front and rear wheel speed sensors 3 and 4 is input via an interface. . Further, data of the direction and magnitude of the steering angles of the front and rear wheels are input from the steering angle sensors 5 and 6 for the front wheels and the rear wheels to the central processing unit 1 for control via the interface. Steering angle sensor 5,
6 is an encoder 5a, 6a, a center switch 5b,
6b and potentiometers 5c and 6c capable of obtaining the direction and magnitude of the steering angle are provided, and each output terminal is connected to an input terminal of the central processing unit 1 for control via an interface.

On the other hand, the central processing unit 2 for diagnosis uses an 8-bit microprocessor, and wheel speed data for obtaining the vehicle speed from the wheel speed sensor 3 for the front wheels is input via an interface. Unlike the central processing unit 1 for the rear wheels, no input is made from the wheel speed sensor 4 for the rear wheels. In addition, the turning angle data of the front and rear wheels from the steering angle sensors 5 and 6 for the front wheels and the rear wheels is input to the central processing unit 2 for diagnosis via an interface. In contrast to this, the input is not made from the encoders 5a and 6a, but is made only from the center switches 5b and 6b and the potentiometers 5c and 6c capable of obtaining the direction and magnitude of the steering angle.

In addition, the central processing unit 1 for control includes the above-described sensors 3,
Calculates the target steering angle of the rear wheel based on the data from 4, 5, and 6, outputs a control signal consisting of a direction signal and a PWM signal (steering angle signal) to the rear wheel drive motor, and diagnoses only the direction signal. To the central processing unit 2. Also,
The central processing unit 1 outputs a failure signal to one input terminal of the NAND circuit 7 when its own failure occurs and when each of the sensors 3, 4, 5, and 6 fails.

Further, the central processing unit 2 for diagnosis compares the direction signal from the central processing unit 1 for control with the data of each of the sensors 3, 5, and 6 except the wheel speed sensor 4 for the rear wheels. Diagnoses the central processing unit 1 for control, and outputs the diagnosis result to the other input terminal of the NAND circuit 7.

Reference numeral 8 denotes a signal line connecting between the central processing units 1 and 2, and data communication is performed via the signal line 8 so that the central processing units 1 and 2 mutually detect runaway. A current sensor 9 controls the current value of the rear wheel drive motor based on data from the current sensor 9.

Next, control operations by the central processing units 1 and 2 will be described with reference to flowcharts shown in FIGS. 2 and 3, respectively.

First, FIG. 2 (A) shows a main routine of the control central processing unit 1. First, the sensors 3, 4, 5, and 6 are diagnosed (step 101), and then an interrupt is received (step 102). ), A target steering angle is calculated based on the data provided by the sensors 3, 4, 5, and 6 (step 103), and a control signal including a direction signal and a PWM output signal is output to the rear wheel drive motor. And outputs only the direction signal to the central processing unit 2 for diagnosis (step 10).
4) Return to step 101 at an appropriate cycle, and make a diagnosis of each of the sensors 3, 4, 5, and 6 again (step 105). In step 101, the subroutine of FIG. 2B is executed. In the subroutine, first, each sensor 3, 4, 5, 6
Is checked (step 106). And
If it is determined in step 107 that a failure has occurred, step 108
Outputs a fail safe signal to the NAND circuit 7. If it is determined in step 107 that the failure has not occurred, the process returns to the main routine of FIG. 2A again, and the necessary processing is continued, and the above procedure is repeated.

On the other hand, FIG. 3 shows a routine of the central processing unit 2 for diagnosis. First, input data from each of the sensors 3, 5, and 6 excluding the wheel speed sensor 4 for the rear wheel and a signal from the central processing unit 1 are shown. The input data of the direction signal is compared, and the failure of the central processing unit 1 is diagnosed based on the comparison (step 201). And
If it is determined in step 202 that a failure has occurred, a fail-safe signal is output to the NAND circuit 7 in step 203. On the other hand, if it is clear in step 202 that there is no failure, the process returns to step 201 again, and the above procedure is repeated.

As described above, the control central processing unit 1 receives all the data from the sensors 3, 4, 5, and 6, but the diagnostic central processing unit 2 includes the control central processing unit 1 and the rear wheel. The data of each of the sensors 3, 5, and 6 except the wheel speed sensor 4 is input while the central processing units 1, 2 on the output side.
By outputting only the fail-safe signal from the NAND circuit 7 and outputting the control signal of the rear wheel target steering angle without comparison, the interface on the input side and the NAND circuit 7 on the output side are reduced. Therefore, the cost can be significantly reduced while ensuring the reliability.

In the above embodiment, data is input to the central processing unit 2 for diagnosis only from the center switches 5b and 6b and the potentiometers 5c and 6c among the steering angle sensors 5 and 6, and data is input from the encoders 5a and 6a. Since no input is made, the number of interfaces can be further reduced.

[Effects of the Invention] As is clear from the above description, according to the present invention, the first central processing unit includes the front wheel and rear wheel speed sensors and the front wheel and rear wheel steering angle sensors. Based on the sensor output, a target steering angle of the rear wheels is calculated and a control signal including a direction signal and a steering angle signal for driving the rear wheels is output, while the second central processing unit controls a wheel speed sensor for the front wheels. Diagnosing the first central processing unit by comparing the output and each output of the steering angle sensor for front wheels and rear wheels and the direction signal of the control signal,
Since it is configured to output a fail-safe signal, all data is supplied from each sensor to the first central processing unit, but the second central processing unit is provided with the minimum necessary for diagnosing the first central processing unit. Only information, that is, the output of the front wheel speed sensor, the outputs of the front and rear wheel steering angle sensors, and only the direction signal of the control signals are supplied, and the output of the rear wheel speed sensor is supplied. Therefore, the interface on the input side is simplified, and in the output measurement, the fail-safe signals of the first central processing unit and the second central processing unit are compared, but the control signals such as the direction signal and the steering angle signal are not compared. Therefore, it is possible to greatly reduce the number of comparators on the output side, and to achieve excellent effects such as a great reduction in manufacturing cost while ensuring reliability.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a circuit configuration of an embodiment of a four-wheel steering apparatus according to the present invention, and FIGS.
FIG. 4 is a flowchart showing the control operation of the central processing unit for control and the central processing unit for diagnosis shown in FIG. 4, and FIG. 4 is a block diagram showing a circuit configuration of an example of a conventional four-wheel steering device. (Description of reference numerals in the drawings showing main parts) 1, 2, central processing unit 3, 4, wheel speed sensor 5, 6, steering angle sensor 7, NAND circuit

Claims (1)

(57) [Claims] A wheel speed sensor provided for a front wheel and a rear wheel and outputting vehicle speed data, and a steering angle sensor provided for a front wheel and a rear wheel and outputting steering angle data of front and rear wheels, respectively. And the respective sensor outputs of the front wheel and rear wheel speed sensors and the front wheel and rear wheel steering angle sensors are supplied to calculate the target steering angle of the rear wheels and the direction signal for driving the rear wheels. And a first central processing unit that outputs a control signal consisting of a steering angle signal, an output of the wheel speed sensor for the front wheel, each output of the front and rear wheel steering angle sensors, and a direction of the control signal. And a second central processing unit for receiving a signal, comparing the direction signal with each of the sensor outputs, diagnosing the first central processing unit, and outputting a fail-safe signal. Wheel steering device.