JPH0331065A - Fail safe circuit for electrically-driven power steering - Google Patents

Abstract

PURPOSE:To improve safety and reliability by resetting a microcomputer with an abnormality signal, output from a watch dog timer(W.D.T) circuit and held to a low level by a latch circuit, while actuating a fail safe circuit, in case of abnormality generated in the microcomputer. CONSTITUTION:In case of abnormality generated in a microcomputer 12, a fail safe circuit 15 is actuated by a fail signal 2, thus a power relay and a clutch relay are cut off. While simultaneously when a pulse frequency, output from the microcomputer 12, exceeds a predetermined value, an abnormality signal is output form a watch dog timer(W.D.T) circuit 13. An abnormal condition is latched by a latch circuit 14, further a reset terminal of the microcomputer 12 is held to a low level, while a fail signal 1 is output to the fail safe circuit 15. In this way, all the control circuits are stopped, while even in the case of the microcomputer 12 reset to its normal condition, careless reactuation is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a steering control system for an automobile.
In particular, the present invention relates to a fail-safe circuit that controls electric power steering (hereinafter abbreviated as electric power steering) that uses a motor to assist the driver's steering force.

BACKGROUND OF THE INVENTION In recent years, electric power steering using a motor has been increasingly used, particularly in power steering control technology for automobiles.

As shown in FIG. 4, the electric power steering includes motor 3. Reducer 4. Torque Cereza 2. The controller 1 (14) controls the torque of the motor 3 according to the steering force detected by the torque sensor 2, thereby reducing the steering force of the driver.

This system uses a motor to assist driving and steering power, and the power of the motor used is about 200 W, which is equal to or higher than the power of a human. The above-mentioned assistance must be performed at an appropriate amount and at an appropriate time based on the will of the driver. Anything other than that cannot be called an assist, and is considered abnormal as it moves in a way that is different from the driver's will. The controller has a failsafe function to prevent this abnormal operation.

A conventional electric power steering fail-safe circuit will be explained below.

FIG. 3 is a block diagram of a conventional electric power steering fail-safe circuit, in which 9 is a microcomputer, 10 is a quarter-dog timer circuit, and 11 is a fail-safe circuit.

Regarding the electric power steering fail-safe system configured as described above, the operation is explained below, and the abnormality handling method when the microcomputer is functioning normally is determined by the input from various monitoring circuits. If it is determined that there is an abnormality, the microcomputer 9 outputs a fail signal 2 to operate the fail safe circuit 11. This failsafe circuit 11 is composed of a power relay and the like that turns on and off the drive current of the motor drive circuit. Next, consider the case where the microcomputer itself becomes abnormal. First, one way to detect an abnormality in a microcomputer is to output pulses of a constant frequency from the microcomputer and monitor the frequency range of the pulses. The software that is generating this is also affected, and the frequency output from the microcontroller changes. This method captures this frequency change and uses it as an abnormality signal for the microcomputer itself. In this case, since the microcomputer itself is damaged, control must be stopped immediately.

However, since the microcomputer is already abnormal, the fail signal 2 output from the microcomputer is not a reliable signal. Therefore, in this case, the WOD1-dog timer (hereinafter referred to as WDT) circuit 10 outputs a reset pulse to the microcomputer to stop the microcomputer operation, and
A fail signal 1 is sent to the fail safe circuit 11 to perform a fail safe circuit.

Problems to be Solved by the Invention However, in the above conventional configuration, it was necessary to separately generate a reset pulse and a fail signal from the WDT circuit. Further, when the microcomputer returns to the normal state from the abnormal state, the reset of the microcomputer is naturally canceled and the fail-safe circuit also returns to its original state. However, the microcomputer is the most important part of the system, and once something goes wrong with this part, there is pressure to get it working again. In this system, re-operation of the microcomputer should be prohibited in order to protect the driver's safety, but there is a problem that this cannot be achieved with the above circuit.

In view of the above-mentioned problems, the present invention provides a fail-safe circuit that operates a fail-safe circuit in the event that a microcomputer malfunctions, and continues to maintain fail-safe processing even if the microcomputer returns to normal. It is.

Means for Solving the Problems In order to achieve this object, the fail-safe circuit of the present invention has a structure in which a latch circuit is provided to latch an abnormal signal from the microcomputer, and the output of the latch circuit is inputted to the microcomputer and the fail-safe circuit. There is.

Effect: With this configuration, if an abnormality occurs in the microcomputer, the microcomputer is reset by the abnormality signal held at a low level by the latch circuit, and the fail-safe circuit also operates. Furthermore, even if the microcomputer returns to normal, the latch output is held at a low level, and the microcomputer will not operate again.

EXAMPLE An example of the present invention will be described below with reference to the drawings.

FIG. 1 shows a block diagram of a fail-safe circuit for electric power steering according to an embodiment of the present invention. Also,
FIG. 2 is an example for embodying FIG. 1.

In FIG. 1, 12 is a microcomputer, 13 is a watchdog timer circuit (WDT circuit), 14 is a latch circuit,
15 is a fail-safe circuit, and in FIG. 2, 16 to 2
0 is a transistor, and 21 to 23 are NAND logics.

The operation of the electric power steering fail-safe circuit of the present invention configured as described above will be described below.

First, when the microcomputer is normal, it determines the status of other input signals. If there is an abnormality, the fail-safe circuit 15 is activated by the fail signal 2 shown in FIG. The fail-safe circuit 15 is configured so that, as shown in FIG. 2, for example, even if either of the fail signal 1 and the fail signal 2 goes to Lo- level, the power relay clutch relay and other cut-off elements are also cut off. Configure it.

Next, when the microcomputer becomes abnormal, the constant pulse frequency output from the microcomputer changes, so when the frequency exceeds a certain range, W-D-
7 circuits are configured to output abnormal signals. Then, when an abnormal signal is output, the status is latched,
The microcomputer RESET terminal is held at Lo- level, and a fail signal 1 is output to cut off the power relay, clutch loop, and other cut-off elements. Figure 2 shows
This is an example of implementing the above configuration. Microcontroller is RESE
Since the T terminal is in a low level state, the program is in a stopped state. Further, the fail-safe circuit also keeps power relays etc. cut off, so the motor does not operate and motor torque is not transmitted to the vehicle side mechanism.

As described above, according to this embodiment, the abnormal signal from the WD-7 circuit is latched and the RESET terminal of the microcomputer is set to Lo.
In addition to holding it at the W level, the fail-safe circuit is also activated, so in the event of a serious microcomputer failure, all control circuits will stop. Then, normal operation will not resume unless the controller is powered on again or the latch circuit is reset. Furthermore, the circuit can be simplified because the microcomputer's reset signal and the fail-safe circuit's operation signal can be shared.

In this embodiment, an example has been shown in which the power relay or the like is shut off at the same time as the microcomputer reset signal, but a time delay element may be added to the power relay or other shutoff circuit. This is because there is a risk that a sudden shutdown may cause the driver to panic. Further, other interrupting elements may be used, for example, to forcibly set the command of the controller to zero.

Effects of the Invention According to the present invention, when an abnormal signal occurs in the system or when the microcomputer becomes abnormal, the system for transmitting the driving force of the motor to the vehicle can be mechanically or electrically activated. When the power is shut off and an abnormality occurs in the microcomputer, turn on W-D-
Since the abnormal signal output from the T is latched and this resets the microcomputer, even if the microcomputer returns to normal, it will not be affected by the driver's intention (and if the power steering system is activated again, it will prevent the vehicle from being damaged). This can improve safety.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a fail-safe circuit of electric power steering according to an embodiment of the present invention, Fig. 2 is a circuit diagram showing a specific embodiment of Fig. 1, and Fig. 3 is a block diagram of a fail-safe circuit of electric power steering according to an embodiment of the present invention. FIG. 4 is a block diagram of the illumination safe circuit and a schematic diagram of the electric power steering system. 1... Controller, 2... Torque sensor, 3... Motor, 4... Speed reducer,
9...Microcomputer, 10...W-D-7
Circuit, 11... Fail safe circuit, 12...
...Microcomputer, 13...W-D-7 circuit,
14...Latch circuit, 15...Fail safe circuit, 16-20...Transistor,
21-23...NAND element.

Claims (1)

[Claims] The microcontroller outputs a pulse with a certain frequency, and when the frequency is outside a certain range, the watchdog timer circuit outputs a signal that recognizes an abnormality, simultaneously latches the abnormality recognition signal and sets the microcontroller's RESET terminal to a low level. At the same time, at least one of the interrupter that turns on and off the electric current to the motor drive circuit and the cutoff element that turns on and off the drive current to the clutch drive circuit that controls the transmission of the motor torque to the external mechanism is cut off. Fail-safe circuit for electric power steering.