JP2526293Y2 - Sensor signal processing circuit - Google Patents

Description

[Detailed description of the invention] Outline An output signal of a sensor such as a magnetic pickup for detecting the speed of a rotating body and a result of failure diagnosis of the sensor are selectively switched by a switching circuit and input to a micro computer. .

As a result, the input terminals of the microcomputer are shared and the number of terminals is reduced.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor signal processing circuit having a failure diagnosis function of a sensor, shaping a waveform of an output signal of the sensor, and inputting the waveform to a microcomputer.

FIG. 4 is a block diagram of a typical prior art signal processing circuit 1. As shown in FIG. The sensor 2 realized by a magnetic pickup or the like is fixed to, for example, the body of an automobile,
Correspondingly, a rotating body 3 having magnetic poles formed alternately in the circumferential direction is attached to the wheel of the automobile.

The output signal of the sensor 2 is input into the signal processing circuit 1 via the connection terminal 4 and shaped into a rectangular wave pulse by the waveform shaping circuit 5, and then input from the input terminal P1 to the micro computer 6
Is input to The micro computer 6 calculates the rotational speed of the wheels, the vehicle speed, and the like based on the pulse,
Performs anti-skid control operation and the like.

The microcomputer 6 derives a failure diagnosis signal from the output terminal P3 when the internal combustion engine is started or the like. In response to the failure diagnosis signal, the failure diagnosis circuit 7 in the signal processing circuit 1 Failure diagnosis such as disconnection detection is performed, and the diagnosis result is input to the input terminal P2 of the microcomputer 6.

Problem to be Solved by the Invention In the above-described conventional technology, the microcomputer 6 includes:
Output terminal P3 for sensor 2 and two input terminals P1 and P2
And a total of three terminals are required. Also two input terminals
P1 and P2 are not used simultaneously.

Further, the sensors 2 are provided in association with all four wheels of the automobile, and a waveform shaping circuit 5 and a failure diagnosis circuit 7 are provided for each sensor 2. Therefore, in the microcomputer 6, the number of terminals necessary for detecting the wheel speed is 12.

An object of the present invention is to provide a sensor signal processing circuit capable of reducing the number of input terminals of a microcomputer.

Means for Solving the Problems The present invention provides a waveform shaping circuit for shaping a waveform of an output signal of a sensor and deriving the waveform to a micro computer, and responding to a fault diagnosis signal from the micro computer to perform fault diagnosis of the sensor. A failure diagnosis circuit that derives a diagnosis result to a microcomputer, and an output of a waveform shaping circuit in response to the failure diagnosis signal;
A signal processing circuit having a switching circuit for selectively switching any one of the outputs of the failure diagnosis circuit and inputting the output to a common input terminal of the microcomputer, wherein the failure diagnosis signal comprises: a sensor terminal; A sensor signal processing circuit which is a refresh signal for destroying an oxide film formed between the signal processing circuit and a terminal of the signal processing circuit.

According to the present invention, the output signal of the sensor through the waveform shaping circuit and the result of the failure diagnosis of the sensor by the failure diagnosis circuit are selectively switched by the switching circuit and input to the common input terminal of the micro computer. You.

The failure diagnosis circuit performs a failure diagnosis of the sensor in response to a failure diagnosis signal from a microcomputer.
The switching circuit inputs the output of the failure diagnosis circuit to the micro computer when the failure diagnosis signal is derived, and inputs the output of the waveform shaping circuit to the micro computer when the failure diagnosis is not performed.

Therefore, an output signal from the sensor and a failure diagnosis result of the sensor can be input to the microcomputer from a common input terminal.

Further, a failure diagnosis signal output from the microcomputer for performing failure diagnosis of the sensor is a refresh signal for destroying an oxide film formed between a terminal of the sensor and a terminal of a signal processing circuit of the sensor. Because
It becomes unnecessary to newly provide a terminal for outputting the refresh signal in the microcomputer.

FIG. 1 is a block diagram showing a basic configuration of a signal processing circuit 11 according to an embodiment of the present invention. A sensor 12 implemented by a magnetic pickup or the like is fixed to a vehicle body of a car, and a rotating body 13 having magnetic poles formed alternately in a circumferential direction is attached to a wheel of the car correspondingly. I have.

The sensor 12 generates an AC signal by rotation of the rotating body 13, and outputs a waveform shaping circuit 15 in the signal processing circuit 11 from a connection terminal 14.
To enter. The waveform shaping circuit 15 performs level discrimination of the output signal from the sensor 12 at a predetermined discrimination level, and derives a rectangular wave pulse to the input terminal T1 of the microcomputer 17 via the switching switch 16.

The microcomputer 17 is in a safe state in which it is not necessary to detect the vehicle speed when the power of the microcomputer 17 is turned on when the internal combustion engine is started, when the power is turned off, or when the vehicle is stopped when the shift lever is in the neutral position. Then, a high-level failure diagnosis signal is derived from the output terminal T2. In response to the failure diagnosis signal, the failure diagnosis circuit 18 performs a failure diagnosis of the sensor 12 as described later, and outputs the diagnosis result via the switching switch 16 to the microcomputer 17.
To the input terminal T1.

When the failure diagnosis signal is derived, the switching switch 16 connects the common contact 16a to the individual contact 1 on the failure diagnosis circuit 18 side.
When the failure diagnosis signal is not derived, the common contact 16a is conducted to the individual contact 16c on the waveform shaping circuit 15 side, and thus the input to the input terminal T1 of the microcomputer 17 is selected.

FIG. 2 is a block diagram showing a specific configuration of the signal processing circuit 11, and portions corresponding to the above-mentioned FIG. 1 are denoted by the same reference numerals. The waveform shaping circuit 15 includes a comparison circuit 21 and a reference voltage source 22, and performs level discrimination of an AC signal having a frequency corresponding to the rotation speed of the rotating body 13 derived from the sensor 12 with the reference voltage Vref. The rectangular wave pulse as the discrimination result is led out to the individual contact 16c of the switching switch 16.

The failure diagnosis circuit 18 includes a comparison circuit 23, a reference voltage source 24, a switch 25, a constant current source 26, and a transistor 27.
, A resistor 28, and a diode 29.

When detecting the wheel speed at which the failure diagnosis signal has not been derived, the switch 25 is turned off and the transistor 27 is turned off,
As a result, the resistor 28 is connected to the non-inverting input terminal of the comparison circuit 23.
, A high-level voltage Vcc is applied. Accordingly, the voltage level of the non-inverting input terminal is equal to or higher than the voltage level of the inverting input terminal to which the reference voltage source 24 is connected, and a high-level output is derived from the comparison circuit 23 to the individual contact 16b of the switching switch 16. Is done.

On the other hand, when the failure diagnosis signal is being derived, the switch 25 conducts, whereby the base current of the transistor 27 flows through the constant current source 26, and the transistor 27 conducts. At this time, when the sensor 12 is normal,
A current flows through the path of 28-transistor 27-diode 29-sensor 12, and the voltage drop at the resistor 28 lowers the input voltage level at the non-inverting input terminal of the comparison circuit 23. Becomes In contrast, the sensor
When the line 12 is disconnected, the input voltage level of the comparison circuit 23 remains at the high level.

Further, at the time of this failure diagnosis, a current larger than the electromotive current generated by the sensor 12 at the time of detecting the wheel speed is supplied, so that at this time, the oxide film formed on the surface of the connection terminal 14 is destroyed. As a result, the contact resistance of the connection terminal 14 can be kept low. As described above, the oxide film destruction operation and the failure diagnosis operation can be performed at the same time. Therefore, the microcomputer 17 uses a so-called refresh signal derived for destruction of the oxide film as a failure diagnosis signal.

FIG. 3 is a waveform diagram for explaining the wheel speed detection and failure diagnosis operation described above. Time in Fig. 3 (1)
As shown before t1, when the output terminal T2 of the microcomputer 17 is at the low level, that is, when the failure diagnosis is not performed, the wheel speed detection is performed by the sensor 12, and the second speed is detected from the sensor 12. An AC signal having a frequency corresponding to the wheel speed as shown in FIG. 3 (2) is derived. This AC signal is subjected to waveform shaping by the waveform shaping circuit 15 as shown in FIG. 3 (3), and is led out to the individual contact 16c of the switching switch 16.

As described above, during the detection of the wheel speed, the switching switch 16 is conducting to the individual contact 16c side, and therefore, the input terminal T1 of the microcomputer 17 has a waveform as shown in FIG. A rectangular pulse from the shaping circuit 15 is input. At this time, the switch 25 of the failure diagnosis circuit 18 is shut off, so that a high-level output is derived from the failure diagnosis circuit 18 as shown in FIG. 3 (4).

At time t1, when a failure diagnosis signal is derived as shown in FIG.
The input signal level becomes high as shown in FIG. 3 (2), whereby the output from the waveform shaping circuit 15 becomes low as shown in FIG. 3 (3).

As shown between time t1 and time t2 during the failure diagnosis operation, when the sensor 12 is normal, the output level of the failure diagnosis circuit 18 shown in FIG. 3 (4) and the output level of FIG. Is at a low level.

On the other hand, as shown after time t2, the sensor 12
Is disconnected, the output level of the failure diagnosis circuit 18 and the input level of the input terminal T1 become high level.

The sensors 12 for detecting the wheel speeds are provided in association with all four wheels of the automobile.
15. A failure diagnosis circuit 18 and a switching switch 16 are provided for each of these sensors 12, so that the microcomputer 17 can reduce the number of four input terminals as compared with the prior art.

As described above, the signal processing circuit 11 according to the present invention includes the sensor 12
Waveform shaping circuit 15 for shaping the output signal of the
The output from a failure diagnosis circuit 18 for diagnosing a failure of the microcomputer 17 is selectively switched by a switching switch 16 to provide a microcomputer 17
, And the input terminal T1 is shared, so that the number of input terminals of the microcomputer 17 can be reduced. Further, since the refresh signal is used as the failure diagnosis signal, it is not necessary to newly provide a terminal for outputting the refresh signal in the microcomputer, and the number of output terminals of the microcomputer can be reduced. In addition, the failure diagnosis and the refresh of the connection terminal 14 of the sensor 12 can be performed at the same time, and the failure diagnosis can be performed efficiently.

According to the present invention, as described above, the output signal of the sensor and
The result of the failure diagnosis of the sensor is selectively switched by the switching circuit and input to the microcomputer.
The input terminals of the microcomputer can be shared, and the number of terminals can be reduced. Further, since the refresh signal is used as the failure diagnosis signal, it is not necessary to newly provide a terminal for outputting the refresh signal in the micro computer, and the number of output terminals of the micro computer can be reduced. The fault diagnosis and the destruction of the oxide film formed between the terminal of the sensor and the terminal of the sensor signal processing circuit can be performed at the same time, which has the effect that the fault diagnosis can be performed efficiently.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of a signal processing circuit 11 according to an embodiment of the present invention, FIG. 2 is a block diagram showing a specific configuration of the signal processing circuit 11, and FIG. FIG. 4 is a block diagram showing the configuration of a signal processing circuit 1 according to the prior art. 11: Signal processing circuit, 12: Sensor, 14: Connection terminal, 15: Waveform shaping circuit, 16: Switching switch, 17: Microcomputer, 18: Failure diagnosis circuit, T1, T2: Terminal

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-55-117932 (JP, A) JP 58-48580 (JP, Y2) JP 61-33531 (JP, Y2)

Claims (1)

(57) [Scope of request for utility model registration] A waveform shaping circuit for shaping a waveform of an output signal of a sensor and deriving the waveform to a microcomputer; performing a fault diagnosis of the sensor in response to a fault diagnosis signal from the microcomputer; and transmitting the diagnosis result to the microcomputer. A fault diagnosis circuit to be derived, and in response to the fault diagnosis signal, selectively output one of an output of the waveform shaping circuit and an output of the fault diagnosis circuit to input to a common input terminal of the micro computer. A signal processing circuit having a switching circuit, wherein the failure diagnosis signal is a refresh signal for destroying an oxide film formed between a terminal of the sensor and a terminal of the sensor signal processing circuit. Sensor signal processing circuit.