JP2007303925A - Failure detection circuit of noncontact sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a failure detection circuit of a noncontact sensor capable of detecting existence of a failure accurately at every time. <P>SOLUTION: The first detection part 6A and the second detection part 6B are disposed respectively near a main detection part 6M, and the first detection part 6A, the second detection part 6B and the main detection part 6M output respectively each output voltage specified univocally to a control input of a brake pedal. The second, third and fourth comparators 22, 23, 24 determine whether the output voltage from the main detection part 6M is between the output voltage from the first detection part 6A and the output voltage from the second detection part 6B which are set previously or not. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a failure detection circuit for a non-contact sensor.

  Generally, a vehicle is provided with a stop lamp switch that turns on a stop lamp by depressing a brake pedal (for example, Patent Document 1). The stop lamp switch outputs an off signal when the depression amount of the brake pedal is smaller than a predetermined amount, and outputs an on signal when the depression amount of the brake pedal is larger than the predetermined amount. Thereby, lighting control according to the depression amount of the brake pedal is performed.

Such a stop lamp switch is used for lighting control of the stop lamp, and also for constant speed traveling control at a traveling speed set by the driver. The stop lamp switch outputs the ON signal to a cruise control system for executing constant speed traveling control, and cancels traveling control at the set traveling speed. This enables engine control in accordance with the accelerator pedal depression operation.
Japanese Patent Laid-Open No. 2004-9805

  By the way, the stop lamp switch binarizes the brake pedal depression amount and outputs it. For this reason, for example, if the stop lamp switch cannot be switched when the depression amount is smaller than a predetermined amount, a failure of the switch cannot be detected until the depression amount becomes larger than the predetermined amount. Similarly, if the stop lamp switch cannot be switched when the depression amount is larger than the predetermined amount, a failure of the switch cannot be detected until the depression amount becomes smaller than the predetermined amount.

However, since the stop lamp switch is used for the various controls described above, a function that can always detect a failure of the stop lamp switch is required.
An object of the present invention is to solve the above-described problems, and is to provide a failure detection circuit for a non-contact sensor that can accurately detect the presence or absence of a failure at any given time.

  The invention according to claim 1 is arranged in a non-contact manner with the detected body, and outputs an output signal having a value corresponding to a relative position with respect to the detected body, and in a non-contact manner with the detected body. And one or a plurality of sub sensors arranged at positions adjacent to the main sensor and outputting an output signal having a value corresponding to a relative position with respect to the detected object; and connected to the main sensor and the sub sensor, the main sensor The gist of the present invention is that it includes a comparison determination circuit that compares an output signal from the sensor and an output signal from the sub-sensor and determines the presence or absence of a failure of the main sensor based on the comparison result.

  According to the first aspect of the present invention, one or a plurality of sub sensors are arranged at positions adjacent to the main sensor. Therefore, when the main sensor and the sub sensor are operating normally, the magnitude relationship between the output signal of the main sensor and the output signal of the sub sensor always maintains the preset magnitude relationship. In addition, when at least one of the main sensor and the sub sensor is out of order, the magnitude relationship between the output signal of the main sensor and the output signal of the sub sensor is different from the preset magnitude relationship. Show. As a result, the failure of the non-contact sensor can be detected from time to time based on the comparison result of the comparison determination circuit.

  According to a second aspect of the present invention, the sub-sensor outputs a first sub-sensor that outputs a higher level output signal than the output signal from the main sensor during normal operation, and the output signal from the main sensor during normal operation. A second sub sensor that outputs an output signal of a low level, wherein the comparison determination circuit includes an output signal from the main sensor, an output signal from the first sub sensor, and an output signal from the second sub sensor. , It is determined that there is no failure of the main sensor, and the output signal from the main sensor is higher than the output signal from the first sub sensor, or the second sub sensor. The gist is to determine that the main sensor has a failure when the level is lower than the output signal from.

  According to the second aspect of the present invention, the failure of the main sensor depends on whether the output signal from the main sensor is at a level between the output signal from the first sub sensor and the output signal from the second sub sensor. The presence or absence of can be detected. As a result, the failure of the non-contact sensor can be detected more accurately from time to time.

The gist of the invention described in claim 3 is that each of the main sensor and the sub sensor includes a magnetoresistive element whose resistance value changes in accordance with a magnetic field exerted by the detected object.
According to the invention of claim 3, a failure of the non-contact sensor provided with the magnetoresistive element can be detected from time to time.

  The gist of the invention described in claim 4 is that the detected body is attached to a driven member interlocked with a brake pedal of a vehicle, and the main sensor is a sensor for detecting an operation amount of the brake pedal. To do.

  According to the fourth aspect of the present invention, a failure of the non-contact sensor that detects the operation amount of the brake pedal can be detected from time to time.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a stop lamp switch 1 having a failure detection circuit for a non-contact sensor.
In FIG. 1, a stop lamp switch 1 is disposed on the right side of the brake pedal P (in the direction of the arrow X in FIG. 1). The stop lamp switch 1 is provided with a switch case 2 formed in a box shape, and a plunger 3 as a driven member extending in the anti-X arrow direction is slid in the X arrow direction and the anti-X arrow direction. It is prepared to be movable.

  A magnetic body 4 as a detected body is fitted to the base end portion of the plunger 3 and the end portion located in the switch case 2. A coil spring SP that urges the plunger 3 always toward the brake pedal P is interposed between the base end portion of the plunger 3 and the switch case 2. When the brake pedal P is not depressed (at the position indicated by the solid line in FIG. 1), the plunger 3 is pressed by the pressing portion Pa of the brake pedal P and retracts inward of the switch case 2 so that the magnetic body 4 is moved. It is arranged on the X arrow direction side (solid line position in FIG. 1). On the other hand, the plunger 3 is urged by the coil spring SP when the brake pedal P is depressed (at the position of the two-dot chain line in FIG. 1) and protrudes outward from the switch case 2 so that the magnetic body 4 can Arranged on the arrow direction side (two-dot chain line position in FIG. 1).

  In the present embodiment, the position of the magnetic body 4 when the brake pedal P is not depressed in FIG. 1 is defined as the reference position. Further, the displacement amount along the anti-X arrow direction of the magnetic body 4 and the displacement amount based on the reference position is defined as the operation amount G.

  A magnetic sensor S as a non-contact sensor is disposed in the switch case 2 and below the plunger 3 (magnetic body 4). The magnetic sensor S is provided with a circuit board 5, and on the circuit board 5, three detection parts 6 constituting a failure detection circuit are formed along the sliding direction of the plunger 3 (magnetic body 4). .

  In the present embodiment, the detection unit 6 located closest to the reference position among the three detection units 6 is defined as the first detection unit 6A constituting the first sub sensor. Moreover, the detection part 6 located in the anti-X arrow direction side most among the three detection parts 6 is defined as the 2nd detection part 6B which comprises a 2nd sub sensor. Moreover, the detection part 6 located between 6 A of 1st detection parts and the 2nd detection part 6B is defined as the main detection part 6M which comprises a main sensor.

  The first detection unit 6A, the second detection unit 6B, and the main detection unit 6M are each composed of a plurality of semiconductor magnetoresistive elements (MR elements). The first detection unit 6A, the second detection unit 6B, and the main detection unit 6M each detect a magnetic field exerted by the magnetic body 4, convert it to a resistance value, and output an output signal having a level corresponding to the detected magnetic field. The first detection unit 6A and the second detection unit 6B are used to determine whether or not the main detection unit 6M has failed (whether or not it is in a predetermined failure mode). The main detection unit 6M is used to determine whether or not the brake pedal P is depressed.

  A permanent magnet MG is disposed below the circuit board 5 and below each detector 6. The permanent magnet MG increases the detection sensitivity of the magnetic field detected by the first detection unit 6A, the second detection unit 6B, and the main detection unit 6M when the plunger 3 (magnetic body 4) slides.

The magnetic sensor S is electrically connected to a stop lamp 8 and an alarm device 9 such as a buzzer or a horn through an electronic control unit (ECU 7).
When the magnetic sensor S determines that the brake pedal P is depressed, the magnetic sensor S sends a high-potential signal (H-level output signal Vo1) to the ECU 7 to turn on the stop lamp 8 or cancel the cruise control. Output. The ECU 7 controls the lighting of the stop lamp 8 when the magnetic sensor S outputs the H level output signal Vo1.

  Further, the magnetic sensor S outputs a high-potential signal (H-level output signal Vo2) for operating the alarm 9 to the ECU 7 when the main detection unit 6M determines that it is in the predetermined failure mode. The ECU 7 operates the alarm 9 when the magnetic sensor S outputs the H level output signal Vo2.

  Next, the electrical configuration of the stop lamp switch 1 (magnetic sensor S) will be described with reference to FIGS. FIG. 2 shows an electric circuit of the stop lamp switch 1. FIG. 3 shows output signals of the first detection unit 6A, the second detection unit 6B, and the main detection unit 6M. FIG. 4 shows the output signal of the main detection unit 6M in each failure mode.

In FIG. 2, the first detection unit 6A, the main detection unit 6M, and the second detection unit 6B are connected in parallel to each other between the power supply line Vcc and the ground line Vss.
Each of the first detection unit 6A, the main detection unit 6M, and the second detection unit 6B includes a bridge circuit 11 including the MR elements 10 and a difference circuit 12 connected to the output terminal of each bridge circuit 11. Each bridge circuit 11 constituting the first detection unit 6A, the main detection unit 6M, and the second detection unit 6B has a different resistance ratio, and when the same magnetic field is supplied, via the corresponding difference circuit 12 Outputs output voltages with different potentials.

More specifically, as shown in FIG. 3, the first detection unit 6A, the main detection unit 6M, and the second detection unit 6B each output an output voltage having a high potential as the operation amount G increases, and An output voltage uniquely defined for each manipulated variable G is output. Moreover, since the arrangement positions are arranged in a predetermined order in a predetermined direction, the first detection unit 6A, the main detection unit 6M, and the second detection unit 6B are always in the entire range of the operation amount G. An output voltage having a higher potential is output in the order of the first detection unit 6A, the main detection unit 6M, and the second detection unit 6B.

  In the present embodiment, the output voltage that is output by the main detection unit 6M and is the output voltage when the operation amount G becomes the threshold Gth for lighting the stop lamp 8 is defined as the threshold voltage Vth.

  In FIG. 2, the main detection unit 6 </ b> M is connected to the non-inverting input terminal of the first comparator 21. A predetermined reference potential (the threshold voltage Vth) is supplied to the inverting input terminal of the first comparator 21. The first comparator 21 outputs an output signal Vo1 having a low potential (L level) when the main detection unit 6M outputs an output voltage having a potential lower than the threshold voltage Vth. On the other hand, the first comparator 21 outputs a high potential (H level) output signal Vo1 when the main detection unit 6M outputs an output voltage having a potential higher than the threshold voltage Vth.

  When the first comparator 21 outputs the L level output signal Vo1, the ECU 7 waits in a state where the stop lamp 8 is not lit until the first comparator 21 outputs the H level output signal Vo1. On the other hand, when the first comparator 21 outputs the H level output signal Vo1, the ECU 7 turns on the stop lamp 8 until the first comparator 21 outputs the L level output signal Vo1.

Therefore, the stop lamp switch 1 can light the stop lamp 8 when the operation amount G becomes larger than the threshold value Gth.
In FIG. 2, the main detection unit 6M is connected to the non-inverting input terminal of the second comparator 22 constituting the comparison determination circuit and the non-inverting input terminal of the third comparator 23 constituting the comparison determination circuit. The first detection unit 6A and the second detection unit 6B are connected to the inverting input terminal of the second comparator 22 and the inverting input terminal of the third comparator 23, respectively.

  The second comparator 22 is low when the main detection unit 6M outputs an output signal having a lower potential than the first detection unit 6A (when the main detection unit 6M and the first detection unit 6A are normal). Output the output signal. On the other hand, the second comparator 22 outputs an H level output signal when the main detection unit 6M outputs an output signal having a higher potential than the first detection unit 6A (when the main detection unit 6M is in the failure mode). Output.

  The third comparator 23 outputs an L-level output signal when the main detection unit 6M outputs an output signal having a lower potential than the second detection unit 6B (when the main detection unit 6M is in the failure mode). . On the other hand, when the main detection unit 6M outputs an output signal having a higher potential than the second detection unit 6B (when the main detection unit 6M and the second detection unit 6B are normal), the third comparator 23 is H. A level output signal is output.

  In FIG. 2, the output terminal of the second comparator 22 is connected to the non-inverting input terminal of the fourth comparator 24 constituting the comparison determination circuit, and the output terminal of the third comparator 23 is connected to the inverting input terminal of the fourth comparator 24. It is connected.

  The fourth comparator 24 outputs the output signal Vo2 at L level when the output voltage of the second comparator 22 is lower than the output voltage of the third comparator 23. On the other hand, the fourth comparator 24 outputs the H level output signal Vo2 when the output voltage of the second comparator 22 is the same as or higher than the output voltage of the third comparator 23.

  In other words, the fourth comparator 24 outputs an L level output signal Vo2 when the second comparator 22 outputs an L level output signal and the third comparator 23 outputs an H level output signal. . That is, the fourth comparator 24 outputs the L level output signal Vo2 when the first detection unit 6A, the main detection unit 6M, and the second detection unit 6B are normal (if the main detection unit 6M is not in the failure mode). judge).

  When the fourth comparator 24 outputs the output signal Vo2 at the L level, the ECU 7 waits without operating the alarm 9 until the fourth comparator 24 outputs the output signal Vo2 at the H level. Further, the ECU 7 continues the cruise control until the fourth comparator 24 outputs the H level output signal Vo2.

  On the other hand, the fourth comparator 24 outputs the H level output signal Vo2 when the second comparator 22 outputs an H level output signal or when the third comparator 23 outputs an L level output signal. .

  For example, as shown in FIG. 4A, when the main detection unit 6M has an abnormality in output sensitivity and the output voltage becomes higher than the output voltage of the first detection unit 6A, the second comparator 22 is set to the H level. The output signal is output. Alternatively, when the output voltage of the main detection unit 6M becomes lower than the output voltage of the second detection unit 6B, the third comparator 23 outputs an L level output signal. Then, the fourth comparator 24 outputs an H level output signal Vo2.

  As shown in FIG. 4B, when the main detection unit 6M has an offset abnormality and its output voltage becomes higher than the output voltage of the first detection unit 6A, the second comparator 22 outputs an H level output. Output a signal. Alternatively, when the output voltage of the main detection unit 6M becomes lower than the output voltage of the second detection unit 6B, the third comparator 23 outputs an L level output signal. Then, the fourth comparator 24 outputs an H level output signal Vo2.

  Further, as shown in FIG. 4C, when the output voltage of the main detection unit 6M is fixed and the output voltage becomes higher than the output voltage of the first detection unit 6A, the second comparator 22 is set to the H level. The output signal is output. Alternatively, when the output voltage of the main detection unit 6M becomes lower than the output voltage of the second detection unit 6B, the third comparator 23 outputs an L level output signal. Then, the fourth comparator 24 outputs an H level output signal Vo2.

That is, the fourth comparator 24 outputs the H-level output signal Vo2 when the main detection unit 6M is in the failure mode (determines that the main detection unit 6M is in the failure mode).
When the fourth comparator 24 outputs the H level output signal Vo2, the ECU 7 operates the alarm 9 until the fourth comparator 24 outputs the L level output signal Vo2. Further, the ECU 7 cancels the cruise control.

  As a result, the stop lamp switch 1 is always in a range in which the output voltage of the main detection unit 6M is preset in relation to the operation state of the brake pedal P (the output voltage of the first detection unit 6A and the second detection unit 6B). It can be determined whether or not the output voltage is between. Therefore, the stop lamp switch 1 can detect the presence / absence of the failure of the stop lamp switch 1 from time to time.

Next, effects of the present embodiment configured as described above will be described below.
(1) According to the above embodiment, the first detection unit 6A and the second detection unit 6B are disposed in the vicinity of the main detection unit 6M, and the first detection unit 6A, the second detection unit 6B, and The main detection unit 6M outputs an output voltage that is uniquely defined for each operation amount G. Then, the second, third, and fourth comparators 22, 23, and 24 are provided between the output voltage of the first detection unit 6A and the output voltage of the second detection unit 6B, in which the output voltage of the main detection unit 6M is set in advance. It is determined whether or not there is. As a result, the failure of the magnetic sensor S (stop lamp switch 1) can be detected from time to time based on the comparison determination results of the second, third, and fourth comparators 22, 23, and 24.

  (2) Moreover, the first detection unit 6A, the main detection unit 6M, and the second detection unit 6B are always connected to the first detection unit 6A, the main detection unit 6M, and the second detection unit 6B in the entire range of the operation amount G. Output voltage with higher potential in order. As a result, the output voltage of the main detection unit 6M can be monitored with higher accuracy. Therefore, the failure of the magnetic sensor S (stop lamp switch 1) can be detected from time to time and with higher accuracy.

In addition, you may change the said embodiment as follows.
In the above embodiment, the comparison determination circuit is configured by the second comparator 22, the third comparator 23, and the fourth comparator 24. For example, as shown in FIG. 5, the comparison determination circuit may be configured by a circuit including a NAND circuit (NAND circuit) 25.

  That is, the main detection unit 6M and the first detection unit 6A are respectively connected to the inverting input terminal and the non-inverting input terminal of the second comparator 22, and the output terminal of the second comparator 22 and the output terminal of the third comparator 23 are connected. However, the configuration may be such that each is connected to the NAND circuit 25.

  According to this, when the main detection unit 6M outputs an output signal having a lower potential than the first detection unit 6A (when the main detection unit 6M and the first detection unit 6A are normal), the second comparator 22 ), An H level output signal is output. On the other hand, when the main detection unit 6M outputs an output signal having a higher potential than the first detection unit 6A (when the main detection unit 6M is in a failure mode), the third comparator 23 outputs an L level output signal. Output. As a result, the NAND circuit 25 outputs the L level output signal Vo2 when the main detection unit 6M is normal, and outputs the H level output signal Vo2 when the main detection unit 6M is in the failure mode.

Therefore, also in this configuration, the stop lamp switch 1 can detect the presence or absence of failure of the stop lamp switch 1 from time to time.
In the above embodiment, the failure detection circuit of the non-contact sensor is mounted on the stop lamp switch 1 (magnetic sensor S). For example, the failure detection circuit of the non-contact sensor may be mounted on the ECU or may be configured to be mounted outside the stop lamp switch 1.
In the above embodiment, the first detection unit 6A, the second detection unit 6B, and the main detection unit 6M are configured to output different levels of output voltages for the same operation amount G. Not limited to this, the first detection unit 6A (or the second detection unit 6B) and the main detection unit 6M are configured to output the same level of output voltage with respect to the same operation amount G, and the main detection unit 6M When a predetermined potential difference is detected between the output voltage and the output voltage of the first detector 6A (or the second detector 6B), an H-level output signal Vo2 may be output. .
In the above embodiment, the non-contact sensor is configured by a magnetoresistive element. For example, the non-contact sensor may be constituted by a magnetic Hall element or a ferromagnetic magnetoresistive element.
In the above embodiment, the sub sensor is configured by two detection units (first detection unit 6A and second detection unit 6B). However, the present invention is not limited to this, and it may be configured by one detection unit (first detection unit 6A or second detection unit 6B) or may be configured by three or more detection units.
In the above embodiment, the detection target is embodied as the magnetic body 4. For example, the object to be detected may be embodied as a magnet, as long as it applies a magnetic field that can be detected by each of the detection units 6A, 6B, and 6M.

Explanatory drawing explaining the stop lamp switch which actualized this invention. Similarly, the electrical circuit diagram which shows the electrical structure of a stop lamp switch. Similarly, the explanatory view explaining the output signal of each detection part. Similarly, explanatory drawing explaining the output signal of each detection part at the time of various failures ((a), (b), (c)). The electric circuit diagram which shows the electrical structure of the stop lamp switch in the example of a change.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Stop lamp switch, 3 ... Plunger as driven member, 4 ... Magnetic body as to-be-detected body, 6A ... 1st detection part which comprises a 1st sub sensor, 6B ... 2nd detection part which comprises a 2nd sub sensor, 6M: main detection unit constituting main sensor, G: operation amount, P: brake pedal, S: magnetic sensor as non-contact sensor, Vo2: output signal.

Claims (4)

A main sensor that is arranged in non-contact with the detected object and outputs an output signal having a value corresponding to a relative position with respect to the detected object;
One or a plurality of sub-sensors that are arranged in a non-contact manner with the detected object and adjacent to the main sensor, and output an output signal having a value corresponding to a relative position with respect to the detected object;
A comparison determination circuit that is connected to the main sensor and the sub sensor, compares an output signal from the main sensor with an output signal from the sub sensor, and determines whether or not the main sensor has failed based on the comparison result. When,
A failure detection circuit for a non-contact sensor, comprising: In the failure detection circuit of the non-contact sensor according to claim 1,
The sub-sensor is
A first sub sensor that outputs an output signal of a level higher than the output signal from the main sensor during normal operation; a second sub sensor that outputs an output signal of a level lower than the output signal from the main sensor during normal operation; With
The comparison determination circuit includes:
When the output signal from the main sensor is at a level between the output signal from the first sub sensor and the output signal from the second sub sensor, it is determined that there is no failure of the main sensor, and the main sensor When the output signal from the sensor is at a higher level than the output signal from the first sub sensor, or at a lower level than the output signal from the second sub sensor, it is determined that there is a failure in the main sensor. A failure detection circuit for a non-contact sensor. In the non-contact sensor failure detection circuit according to claim 1 or 2,
The non-contact sensor failure detection circuit, wherein each of the main sensor and the sub sensor includes a magnetoresistive element whose resistance value changes in accordance with a magnetic field exerted by the detected object. In the failure detection circuit of the non-contact sensor according to any one of claims 1 to 3,
The detected body is attached to a driven member interlocked with a brake pedal of a vehicle,
The failure detection circuit for a non-contact sensor, wherein the main sensor is a sensor for detecting an operation amount of the brake pedal.

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