JPH05134899A - Runaway monitoring circuit for microcomputer - Google Patents

Abstract

PURPOSE:To detect the runaway state of a microcomputer in simple configuration. CONSTITUTION:An integration circuit 62 converts a watch dog pulse led to a line 61 by a microcomputer 51 into voltage V corresponding to its duty ratio. The level of the voltage V is discriminated by reference voltage V1. V2 in comparators 71, 72. When the microcomputer 51 is brought into the runaway state, the duty ratio of the watch dog pulse takes a value different from that in normal operation time. Accordingly, the output voltage V of the integration circuit 62 may exceed the reference voltage V1 or drop below the reference voltage V2. At this time, a low level signal is led to a line 66. The low level signal is given to a reset input terminal RESET of the microcomputer 51 as a runaway state detection signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a runaway monitoring circuit of a microcomputer which is preferably used in a so-called antilock brake system for preventing wheels from becoming locked.

[0002]

2. Description of the Related Art When a brake is suddenly applied on a wet road surface or a snowy road, the wheels stop rotating and reach a locked state. When the wheels are locked in this manner, not only the braking distance increases, but also the lateral grip force of the tire (hereinafter referred to as "cornering force") is lost and steering becomes impossible, resulting in an extremely dangerous condition. Become. In addition, the loss of cornering force can cause the vehicle to become unstable, causing it to sway and spin.

Therefore, conventionally, in order to prevent the wheels from being locked even when the brake pedal is strongly depressed to perform a sudden braking operation, a so-called anti-lock
A brake system (hereinafter referred to as "ABS") is installed in a vehicle and used. In ABS, the vehicle speed, which is the actual vehicle speed, and the wheel speed, which is the rotational speed of the wheels, are detected, and the slip ratio defined by the following equation (1) becomes a predetermined control target value. The brake pressure of each wheel is controlled so that they approach each other.

[0004]

[Equation 1]

That is, the coefficient of friction between the tire and the road surface becomes maximum not when the slip ratio is 100% (completely locked state where the wheel speed is 0), but when the slip ratio is 2.
It is known to be around 0%. On the other hand, the cornering force decreases as the slip ratio increases,
It becomes 0 at 100%. Therefore, in the ABS, the brake pressure is controlled at the time of the sudden braking operation so that the slip ratio is about 20% so that the friction coefficient between the tire and the road surface becomes maximum.

[0006] By such anti-lock control, ideal braking can be realized while the braking distance is minimized and the stability and steerability of the vehicle are secured regardless of the driving technique of the driver. The control of the brake pressure is performed by controlling the hydraulic pressure from the master cylinder connected to the brake pedal with the hydraulic unit. The hydraulic unit is provided with solenoid valves corresponding to the front and rear wheels, and these solenoid valves are used for the control unit (EC
Driven by U), the hydraulic pressure transmitted to the brake of each wheel is controlled.

The control unit used in the ABS is generally equipped with a pair of microcomputers that perform the same operation. This is because both microcomputers are monitored by software whether or not they are performing the same operation, so that the antilock control is prohibited when the microcomputers perform an abnormal operation such as a runaway state. That is, the anti-lock control is
Since the hydraulic pressure from the master cylinder is reduced and transmitted to the brakes of each wheel, if the brake pressure is excessively reduced due to the runaway of the microcomputer, the braking operation will be injured and life-threatening will occur. It can happen. Therefore, it is necessary to prohibit the antilock control when the microcomputer runs out of control.

However, even when a pair of microcomputers are provided and monitored by each other as described above, since the pair of microcomputers generally share a power source, when a surge enters the power line,
It is possible that both microcomputers will runaway at the same time. In such a case, the anti-lock control cannot be reliably stopped by software-based monitoring of the microcomputers. Therefore, it is necessary to monitor the runaway of the microcomputer also by the hardware configuration.

To monitor the runaway of the microcomputer,
A technique for monitoring a watchdog pulse output from a microcomputer has been conventionally used and is also used in an ABS control unit. The watchdog pulse is a pulse that is output one by one in one control routine of the microcomputer, and is created by causing the pulse to rise and fall at different points in the control routine. ..

When the microcomputer goes into a runaway state, the timing of the rise and fall of the pulse in one control routine will deviate from the normal operation. Therefore, in the runaway monitoring circuit of the microcomputer that has been conventionally used, the period of the watchdog pulse is monitored, and the pulse period becomes extremely long,
By detecting that it has become extremely short, the runaway of the microcomputer is detected. Runaway detection may also be performed by counting the number of watchdog pulses within a certain period of time. If the count value is extremely large or extremely small, the microcomputer is in a runaway state. To be taken.

When the runaway of the microcomputer is detected, the reset signal is input to the reset terminal of the microcomputer, the power supply to the solenoid valve of the hydraulic unit is stopped, and the antilock control is performed. prohibited.

[0012]

However, the above-mentioned conventional techniques require a circuit having a complicated function of monitoring the pulse period and counting the pulses.
The circuit scale becomes large. This causes a problem that the cost of the control unit increases. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above technical problem and to provide a runaway monitoring circuit of a microcomputer capable of monitoring the runaway of a microcomputer with a simple configuration.

[0013]

According to another aspect of the present invention, there is provided a runaway monitoring circuit for a microcomputer according to claim 1, wherein a watchdog pulse output from the microcomputer is set to a duty ratio of the watchdog pulse. The level of the output voltage of the integrating circuit and the output voltage of this integrating circuit are determined by the reference voltage,
And a means for outputting a runaway state detection signal indicating that the microcomputer is in a runaway state when the output voltage of the integrating circuit is out of a predetermined range.

According to a second aspect of the present invention, there is provided a runaway state monitoring circuit for a microcomputer, which includes an integrating circuit for converting a watchdog pulse output by the microcomputer into a voltage corresponding to a duty ratio of the watchdog pulse, and the integrating circuit. Output voltage of the upper limit and lower limit of 2
When the output voltage of the integrating circuit exceeds the upper limit value or the output voltage of the integrating circuit falls below the lower limit value, the runaway state is detected, which indicates that the microcomputer is in a runaway state. And means for outputting a signal.

When the microcomputer is operating normally, the watchdog pulse output from the microcomputer has a substantially constant duty ratio. Therefore, when the duty ratio of the watchdog pulse is extremely large or extremely small, it can be said that the runaway of the microcomputer is occurring.

Therefore, in the present invention, the duty ratio of the watchdog pulse is converted into a voltage signal by an integrating circuit,
By discriminating the output voltage of the integrating circuit at a predetermined voltage level, a change in the duty ratio of the watchdog pulse is detected, and a runaway of the microcomputer is detected through this. That is, when the output voltage of the integrating circuit is a value outside the predetermined range, it is determined that the microcomputer has runaway, and a runaway state detection signal indicating this is output.

In response to the runaway state detection signal,
Preferably, means for resetting the microcomputer are further included. Further, it is preferable to further include means for making a system including the runaway monitoring circuit of the microcomputer into a fail safe state in response to the runaway state detection signal.

Further, in response to the runaway state detection signal,
It is preferable that a means for temporarily or completely stopping the power supply to the microcomputer is further included. These configurations prevent the system including the runaway monitoring circuit from performing an undesired operation due to the runaway of the microcomputer.

[0019]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 2 is an anti-lock brake system (hereinafter referred to as "ABS") to which a runaway monitoring circuit of a microcomputer according to an embodiment of the present invention is applied.
It is a conceptual diagram showing an outline of. ABS is based on the output of the wheel speed sensor 21 provided on each wheel, and the brake 2 of each wheel is
By electronically controlling the brake pressure of No. 2, it is a device that avoids the locked state of the wheels at the time of sudden braking operation and realizes an optimum slip ratio. That is, when the brake pedal 23 is strongly depressed, the hydraulic pressure from the master cylinder 24 is controlled by the hydraulic unit 25 and is transmitted to the brake 22 of each wheel. In this hydraulic unit 25,
Four channels are provided for individually controlling the hydraulic pressure for each wheel, and at least one solenoid valve for controlling the hydraulic pressure is provided for each channel. This solenoid valve drive control monitors the output of the wheel speed sensor 21 by a control unit (EC
U) 26. Reference numeral 27 is a warning lamp for notifying the driver of this when the antilock control is prohibited due to a runaway of the microcomputer in the control unit 26 or the like.

FIG. 3 is a block diagram showing the electrical construction related to the driving of the solenoid valve. Electric power from the battery 31 is supplied to the control unit 26 via the ignition switch 32, and the hydraulic unit 2
5 is applied to the relay coil 34b of the relay 34 that controls the power supply to the solenoid valve 33 inside the vehicle. Relay 3
4 switches the electric power from the battery 31 given via the line 35 to the line 36. Further, the electric power via the ignition switch 32 is given to the warning lamp 27.

Further, the electric power from the battery 31 is supplied to the motor 40 in the hydraulic unit 25 from the line 35 through the contact 39a of the relay 39. The motor 40 drives a pump (not shown) for returning the excess liquid generated in the hydraulic unit 25 to the master cylinder 24 for controlling the hydraulic pressure. The relay coil 39b of the relay 39 is supplied with power from the battery 31 via the contact 34a of the relay 34.

Reference numeral 41 is a stop lamp which is turned on by being supplied with electric power through a switch 42 which is turned on by operating the brake pedal 23. The operation state of the brake pedal 23 is monitored by the control unit 26 via the line 43. The warning lamp 27 is turned on when the control unit 26 grounds the line 44. When the contact 34a of the relay 34 is connected to the ground side, a current flows from the line 45 through the diode 46, and the warning lamp is turned on at this time as well. The control unit 26 includes the ignition switch 3
In the period immediately after 2 becomes conductive, the relay coil 3
4b is demagnetized, the contact 34a is connected to the ground side, and the warning lamp 27 is turned on. Then, the relay coil 34b is excited, and the solenoid valve 33 and the relay coil 39b can be supplied with electric power. Then, when the signal ALT-L indicating this is given when power generation by a generator (not shown) is started, the warning lamp 27 is turned off.

The control unit 26 has a pair of microcomputers 51 therein, and each microcomputer 51
Runaway monitoring circuit 52 for detecting the runaway state for each
Is equipped with. The voltage Vcc from the stabilized power supply circuit 53 is commonly supplied to such a pair of microcomputers 51. This pair of microcomputers 51
Operates according to the same control program,
Whether or not the other microcomputers 51 are performing the same operation is monitored by software. When the other microcomputer 51 performs a different operation, the warning lamp 27 is turned on and the antilock control is prohibited.

FIG. 1 is an electric circuit diagram showing the internal configuration of the runaway monitoring circuit 52. The microcomputer 51 derives one watchdog pulse to the line 61 during the execution of one control routine. The watchdog pulse is converted into a voltage corresponding to the duty ratio of the watchdog pulse by the integrating circuit 62 including the resistors R1 and R2 and the capacitor C1. A voltage corresponding to the duty ratio of the watchdog pulse is derived from the line 63.

The output voltage V of the integrating circuit 62 is applied to the inverting input terminal of the comparator 71 via the resistor R3. A voltage appearing at a voltage dividing point 64 obtained by dividing the power supply voltage Vcc by the resistors R4 and R5 and R6 is applied to the non-inverting input terminal of the comparator 71 as the reference voltage V1. The output voltage V of the integrating circuit 62 is further supplied to the non-inverting input terminal of the comparator 72 via the resistor R7. The voltage appearing at the voltage dividing point 65 obtained by dividing the power supply voltage Vcc by the resistors R4 and R5 and the resistor R6 is input to the inverting input terminal of the comparator 72 as the reference voltage V2 (V2 <V1).

The outputs of the comparators 71 and 72 are commonly connected to the line 66 connected to the reset input terminal RESET of the microcomputer 51. Therefore, when at least one of the comparators 71 and 72 outputs a low level signal, the potential of the line 66 becomes low level. This line 66 is connected to the power supply voltage V through the resistor R8.
cc is given. This is because the comparators 71 and 72 are of open collector output type.

With the above configuration, when the output voltage V of the integrating circuit 62 is V2 <V <V1 (2), the outputs of the comparators 71 and 72 are both at the high level. On the other hand, when the output voltage V of the integrating circuit 62 is V <V2 ... (3), the output of the comparator 71 becomes high level and the output of the comparator 72 becomes low level. As a result, the resistance R
Since a current flows through 8 and is absorbed by the comparator 72, the line 66 becomes the ground potential. The low-level signal derived on this line 66 is used as the runaway state detection signal as the reset input terminal RESE of the microcomputer 51.
When applied to T, the microcomputer 51 responds to this and performs a reset operation.

Further, when the output voltage V of the integrating circuit 62 is V1 <V (4), the output of the comparator 71 becomes low level and the output of the comparator 72 becomes high level. As a result, the line 66 becomes the ground potential, so that the microcomputer 51 is reset as in the above case.

FIG. 4 is a waveform diagram for explaining the operation. The microcomputer 51 performs rising and falling of the pulse at different locations in one control routine, so that during normal operation, the watch with a duty ratio of approximately 50%, as indicated by reference numeral A1. Output dog pulse. At this time, the output voltage V of the integrating circuit 62 becomes a value between the reference voltage voltages V1 and V2.

For example, when the power supply voltage Vcc is 5V,
When the output voltage of the integrating circuit 62 is 2.5V with respect to the watchdog pulse having the duty ratio of 50%, the resistors R4, R5 are set so that the reference voltage V1 becomes 3V and the reference voltage V2 becomes 2V, for example. It suffices to set each resistance value of R6. When the microcomputer 51 goes into a runaway state and the duty ratio of the watchdog pulse becomes, for example, 20% as indicated by reference numeral A2, the integrating circuit 6
2 is lower than the reference voltage V2 (for example, 1
V). As a result, the output of the comparator 72 becomes low level, and the microcomputer 51 is reset.

Further, the duty ratio of the watchdog pulse increases due to the runaway state of the microcomputer 51, and as shown by reference numeral A3, for example, 8
It may be about 0%. At this time, the integration circuit 6
The output voltage V of 2 exceeds the reference voltage V1 (for example, 4
V), and as a result, the output of the comparator 71 becomes low level. As a result, the microcomputer 51 is reset.

In this way, when the duty ratio of the watchdog pulse becomes excessively large or excessively small, a low level signal is input to the reset input terminal RESET of the microcomputer 51. In response to the input of this low level signal, the microcomputer 51 is forcibly reset. As a result, the microcomputer 51 recovers from the runaway state, so that the antilock control is temporarily prohibited.
After that, the antilock control continues to be satisfactorily performed.

As described above, in this embodiment, the output voltage V of the integrating circuit 62 for converting the watchdog pulse into a voltage corresponding to its duty ratio is discriminated based on the reference voltages V1 and V2, whereby the microcomputer 5
The runaway condition of 1 is detected. in this way,
Since the runaway state of the microcomputer 51 can be detected with an extremely simple configuration, the circuit configuration of the control unit 26 can be remarkably simplified, which can contribute to a reduction in ABS cost.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the microcomputer is reset when the runaway state is detected, but when the runaway state is detected, the power supply to the solenoid of the hydraulic unit is forcibly released. In this way, the antilock control may be prohibited.

Further, in the above embodiment, the case of being used for the ABS is taken as an example, but the runaway monitoring circuit of the microcomputer of the present invention is widely applied to any device using the microcomputer other than the ABS. It can be applied. In addition, various design changes can be made without changing the gist of the present invention.

[0036]

As described above, according to the runaway monitoring circuit of the microcomputer of the present invention, the voltage signal corresponding to the duty ratio of the watchdog pulse output by the microcomputer is created by the integrating circuit having a simple structure. The runaway of the microcomputer is detected by discriminating the level of the output voltage of the integrating circuit. Therefore, it becomes possible to detect the runaway of the microcomputer with an extremely simple configuration, which can contribute to cost reduction.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram of a runaway monitoring circuit of a microcomputer according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram showing an outline of an antilock brake system.

FIG. 3 is a block diagram showing an electrical configuration of an antilock brake system to which the runaway monitoring circuit of the microcomputer of the above embodiment is applied.

FIG. 4 is a waveform diagram for explaining the operation of the runaway monitoring circuit.

[Explanation of symbols]

 26 Control Unit 51 Microcomputer 52 Runaway Monitoring Circuit 62 Integration Circuit 71 Comparator 72 Comparator V1 Reference Voltage V2 Reference Voltage V Output Voltage of Integration Circuit

Claims (5)

[Claims] 1. An integrator circuit for converting a watchdog pulse output from a microcomputer into a voltage corresponding to a duty ratio of the watchdog pulse, and a level of an output voltage of the integrator circuit is discriminated by a predetermined reference voltage, And a means for outputting a runaway state detection signal indicating that the microcomputer is in a runaway state when the output voltage of the integrating circuit is out of a predetermined range. 2. An integrating circuit for converting a watchdog pulse output from a microcomputer into a voltage corresponding to a duty ratio of the watchdog pulse, and an output voltage of the integrating circuit having two reference voltages of an upper limit value and a lower limit value. When the output voltage of the integrator circuit exceeds the upper limit value or the output voltage of the integrator circuit falls below the lower limit value, a runaway state detection signal indicating that the microcomputer is in a runaway state is output. And a runaway monitoring circuit of a microcomputer. 3. The runaway monitoring circuit for a microcomputer according to claim 1, further comprising means for resetting the microcomputer in response to the runaway state detection signal. 4. The micro computer according to claim 1, further comprising means for responding to the runaway state detection signal to bring a system including a runaway monitoring circuit of the microcomputer into a fail safe state. Computer runaway monitoring circuit. 5. The device according to claim 1, further comprising means for temporarily or entirely stopping the power supply to the microcomputer in response to the runaway state detection signal.
The runaway monitoring circuit for a microcomputer according to 2, 3, or 4.