JPH06329042A - Rear wheel steering system - Google Patents

Abstract

PURPOSE:To improve the reliability of control by using two control system computing parts independently with such constitution as to make both computing parts monitor each other and to enable the continuation of rear wheel steering control by one system even if the other system is abnormal, and also comparing two control signals. CONSTITUTION:CPUs 1, 2 are respectively independent and compute on the basis of signals from sensors 3 while detecting the other party mutually to generate motor driving command signals. These two command signals are compared by a comparator 6. In the case of two signals coinciding with each other, a driving signal is outputted to a motor driving means 7, and rear wheel steering control is executed. In the case of two signals not coinciding with each other, control is interrupted to maintain the existing state. The reliability of control is thereby improved compared to a single control value instruction. The runaway of the CPU 1 or 2 is detected by a watch dog. The runaway CPU is reset, and rear wheel steering control is performed only by the normal CPU. Since there is little probability of both CPUs 1, 2 becoming simultaneously abnormal and being reset, control is hardly interrupted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called 4WS (four-wheel steering) system for controlling rear wheel steering along with front wheel steering in a vehicle or the like, and more particularly to a device for controlling rear wheel steering by an electric motor.

[0002]

2. Description of the Related Art Conventionally, in a system for steering a rear wheel using an electric motor, a CPU for driving and controlling the motor
There has been a proposal to fix the motor at its current position or return the rear wheels to the neutral position when the vehicle runs out of control and is reset (JP-A-61-108066). Also, CP
There has also been proposed a method of stopping the control and returning it to the neutral position when an abnormality occurs in the RAM of U (JP-A-61-108067).

[0003]

However, in the above means for fixing the motor to its current position or returning the rear wheels to the neutral position, the rear wheel steering is performed during the reset and after the reset and until the control is returned. Cannot be performed, and a period in which control is not performed occurs. Further, even in the method for dealing with the RAM abnormality, since the wheel is returned to the neutral position every time the RAM abnormality occurs due to the influence of the noise of the motor, the meaning of the rear wheel steering becomes meaningless, and the effect of the rear wheel steering cannot be sufficiently exerted. There is.

[0004]

In order to solve the above-mentioned problems, the structure of the present invention has four wheels of front wheels and rear wheels, and steering of rear wheel steering in response to steering of a steering handle for steering front wheels. In a rear wheel steering device having a main system, a sub system, two independent systems, and a computing unit, the control unit for controlling the rear wheel steering drive unit by a motor, in which the amount and the like are determined, includes Each of the operation units of the system independently controls and outputs a control instruction, a control comparing unit that compares the two control instructions, and a rear wheel steering unit that receives the final instruction determined by the control comparing unit. And a rear wheel steering drive means for performing, with respect to the arithmetic unit of the main system and the arithmetic unit of the sub system,
Reset generating means for independently generating a reset signal, and monitoring means for monitoring the status of each other's system,
And a fail safe means for controlling the rear wheel steering with the calculation result of the other remaining system when the calculation section of one of the systems becomes abnormal and the calculation section is reset by the reset generating means. It is characterized by

[0005]

[Operation] Two independent operation units of the control system are used to monitor each other. Even if one system becomes abnormal, the rear wheel steering control is continued in the remaining system until the abnormal system is restored to normal. Further, the two control signals are compared, and if they are the same, it is determined to be normal and the rear wheel steering is instructed. If they do not match, the control is interrupted and the current state is maintained.

[0006]

Since the plurality of CPUs control each other to monitor each other, even if any one of them is abnormal, the other one can maintain the normal control and the control is less likely to be interrupted. Further, by comparing the two control instruction values, the control reliability is sufficiently improved as compared with the case of a single control value instruction.

[0007]

EXAMPLES The present invention will be described below based on specific examples. FIG. 1 is a block diagram showing a control system of a rear wheel steering device, in which a motor 8 in a rear wheel steering mechanism 24 of a vehicle schematically shown in FIG. 2 is controlled by an ECU (electronic circuit control device) in accordance with front wheel steering. ) The rear wheel steering is performed under the control of the instruction from 20. There are two main CPUs, a main CPU1 and a sub CPU2, in the arithmetic unit, and various sensor signals 3 such as a vehicle speed sensor are input to these CPUs in parallel. Note that the names main and sub are for convenience, the main side is not prioritized, and plays an equivalent role for control. The CPUs 1 and 2 mutually detect the rise of the other party, and the CP of the other party.
The CPU past reset signal lines b and d indicating whether U has been reset are connected.

Reset generating means 4 and 5 are attached to the two CPUs 1 and 2, respectively, and watchdog signal lines e and f from the CPU and reset signal lines g and h to the CPU are connected. The motor drive commands i, j from each CPU are connected in parallel to the comparator 6, and the output priority flag signal lines k, m of each CPU are also connected to the comparator 6. The comparator 6 determines the result of comparing the command values i and j, outputs a motor drive instruction to the motor drive means 7, and drives the motor 8 to perform rear wheel steering. As the sensor used for the rear wheel steering control, in addition to the steering sensor 21, the vehicle speed sensor 22 and the motor position sensor 23 shown in FIG. 2, a wheel speed sensor (not shown) for improving the control depending on the purpose,
A yaw rate sensor, a lateral G sensor, etc. are connected.

The two CPUs 1 and 2 each generate a motor drive command signal by calculation based on the sensor signal 3 and the like, and the signal is sent to the comparator 6. The comparator 6 compares the two motor drive signals, and if the comparison results are in agreement, outputs a drive signal to the motor drive means 7 to execute rear wheel steering control. If they do not match, the drive signal is interrupted to keep the motor as it is.

Abnormalities in the CPUs 1 and 2 are caused by, for example, the data in the RAM being changed by the influence of noise of the motor, a writing error, or radiation in the natural world.
Therefore, this abnormality occurs stochastically. Therefore, if this abnormality occurs, the motor drive command value will become an abnormal value, and the control will cause a large error, so if the data of any CPU is an abnormal value, the control output above will not be deviated. To prevent control abnormalities.

When an abnormality occurs in the program part, the CPU
Runs out of control. Therefore, the watchdog program monitoring method detects the runaway of the CPU, and normal C
The PU sends an abnormal signal (watchdog reset signal) to the reset generating means, and uses the reset means to make a runaway C.
The PU is reset, the normal CPU is also made to detect the occurrence of the reset, the normal output priority flag signal of the CPU is sent to the comparator, and the drive signal is not compared but controlled by the drive command of the priority CPU. Then, a past reset generation signal indicating that it has been reset is issued to the runaway CPU. The runaway CPU starts from the beginning of the program by a reset, so it starts to function normally again.
If no instruction is given, the initial check will be executed again. To avoid this, check the past reset generation signal from the CPU that continues normal control, and if there is this signal, avoid the initial processing. Immediately shift to control.

If both CPUs 1 and 2 function normally, the same motor drive command value should be output, so that the comparator 6 also outputs a normal motor drive signal, and the rear wheel steering control is continued. . Since the probability that both CPUs become abnormal at the same time and is reset is extremely small, it is unlikely that the steering position of the rear wheels will be fixed due to interruption of control, and the probability that the same abnormal value will be output at the same time is extremely high. It is small, so even if a part of the control system malfunctions, control continues.

The operation of each CPU will be described with reference to the flow charts shown in FIGS. 3 is a flow chart of the main CPU, and FIG. 4 is a flow chart of the sub CPU, but the flow is exactly the same, and the only difference is that the monitoring partners are replaced with each other. In FIG. 3, after starting, the main CPU first performs an initial process at step 100, sets a flag to inform the sub CPU side that the main has started at step 102, waits for the sub CPU side to start, and waits for the current CPU of this program. In step 106, it is checked whether or not the rising edge of the execution is due to a reset. If it is due to the reset, the initial check in step 108 is skipped. When the power is turned on to start up and perform an initial check, check the sensor connection status and measurement system.

Next, in step 110, the signal value of each sensor is read, and in step 112 the target value of the motor is calculated. Then, in step 114, the current motor position is checked, and in step 116, the required motor movement amount is calculated and output as a motor drive command value. Thereafter, in step 118, processing for a watchdog for detecting a program runaway abnormality is performed, and in step 120 it is detected whether the sub CPU is reset. Step if reset
In step 122, the flag of the sub CPU past reset occurrence signal is set, and in step 124, the main output priority signal flag is set and the process returns to step 110 which is the start of control again. If it is not reset, it is confirmed in step 126 whether the sub CPU is booted up. If it is booted, the main output priority flag which may be output is set in step 12.
Press 8 to go back to step 110.

If the main CPU 1 is reset for some reason, the main program restarts from step 100. Therefore, since the signal from the sub CPU side has been generated that the previous reset was performed in step 106, the step of initial check is omitted. Normally, the flow chart of this control is repeated for several tens of ms.
The order is ec, and the initial check takes a time on the order of seconds.Therefore, an abnormality occurs during the rear wheel steering control and reset occurs, and if the initial check is executed, the control becomes unstable. I will end up. Therefore, the unnecessary steps are skipped, and the flow chart is set so that the control can be executed more safely.

The flow chart of the sub CPU side in FIG. 4 is also the same as the flow of processing, and the other party is the main C.
The description is omitted because it is only PU.

The relationship between each means and the main constituent elements of this embodiment is as follows. Control instruction means: Two CPUs, each sensor signal line, motor drive command line, steps 116 and 216 Control comparison means: Comparator Rear wheel steering drive means: Motor, motor drive means, rear wheel steering Mechanism Reset generating means: reset signal line, watchdog signal line, steps 118, 218 Monitoring means: CPU rising signal line, reset signal line Failsafe means: reset signal line, each output priority signal line, step 120-128, 220-228

As described above, the rear wheel steering control system is constituted by the two arithmetic processing units, and the mutual states are monitored,
By responding to abnormal conditions and continuing stable control,
The reliability of the rear wheel steering system could be improved.

[Brief description of drawings]

FIG. 1 is a block diagram of a rear wheel steering system control system (ECU).

FIG. 2 is a schematic system diagram of a rear wheel steering device.

FIG. 3 is a control flowchart of the main system.

FIG. 4 is a control flowchart of a sub system.

[Explanation of Codes] 1 main CPU 2 sub CPU 3 sensor signal 4 reset means (main side) 5 reset means (sub side) 6 comparator 7 motor drive means 8 motor 20 ECU 21 steering sensor 22 vehicle speed sensor 23 motor position sensor

Claims (1)

[Claims] 1. A control having four wheels, a front wheel and a rear wheel, wherein a steering amount for rear wheel steering is determined in accordance with steering of a steering wheel for steering front wheels, and a rear wheel steering drive section is controlled by a motor. In a rear wheel steering device in which the device has a main system, a sub system, two independent systems, and a computing unit, a control in which each of the computing unit of the main system and the computing unit of the sub system independently calculates and outputs a control instruction. An instruction means, a control comparison means for comparing the two control instructions, and a rear wheel steering drive means for steering the rear wheels in response to the final instruction determined by the control comparison means. Section and the operation unit of the sub system, reset generating means for independently generating a reset signal, monitoring means for monitoring the status of each other system, and the operation unit of one of the systems becomes abnormal. , The reset generation means When Ri該 calculating section is reset, rear wheel steering apparatus, characterized in that it has a fail-safe means for controlling the rear wheel steering operation result of the remaining other strains, the.