JP4345207B2 - Mechanical quantity detection sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a mechanical quantity detection sensor provided with a circuit (signal processing circuit) for amplifying the output of a sensor unit, and in particular, a sensor unit comprising a Wheatstone bridge circuit (hereinafter simply referred to as a bridge circuit) composed of a strain gauge. It is suitable for use in a pressure sensor provided.
[0002]
[Prior art]
In recent years, electronic control of vehicles has progressed, and various pressure sensors have been used. These are used for brake fluid pressure measurement in a brake control system and intake pressure detection in an engine control system, and high reliability is required. If these sensors fail and a normal output signal cannot be output, brake control and engine control based on the sensor output cannot be performed, so it is necessary to detect sensor abnormality.
[0003]
As sensors capable of detecting such an abnormality, there are sensors disclosed in Japanese Patent Publication No. 6-64085, Japanese Patent Application Laid-Open No. 8-247881, or Japanese Patent Publication No. 10-506718.
[0004]
[Problems to be solved by the invention]
However, in the sensor disclosed in Japanese Patent Publication No. 6-64085, abnormality detection is performed only when the engine is started, and abnormality detection cannot be performed after the engine is started.
[0005]
In addition, the sensor disclosed in Japanese Patent Laid-Open No. 8-247881 is configured to generate an output for diagnosis when performing abnormality detection, and a pressure corresponding to the pressure applied to the sensing unit during diagnosis. The signal cannot be output.
[0006]
Further, the sensor disclosed in Japanese Patent Publication No. 10-506718 includes a bridge circuit for diagnosis in addition to the bridge circuit for pressure measurement, and detects pressure and abnormality of the pressure sensor by these two systems. As a result, the sensing area is widened, the number of wire bonding locations for electrical connection with each system is increased, and the circuit configuration of the sensor becomes redundant.
[0007]
The present invention has been made in view of the above points, and it is an object of the present invention to enable detection of an abnormality of a mechanical quantity detection sensor and to output a signal corresponding to the mechanical quantity even at the time of inspection.
[0008]
It is another object of the present invention to detect an abnormality of a mechanical quantity sensor without making the circuit configuration redundant.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, the sensor unit (1) whose sensitivity changes in accordance with the applied voltage or the applied current, the output from the sensor unit, and the output from the sensor unit are processed. A signal processing circuit (3) that generates an output signal according to the first sample hold circuit (4) that holds the output signal of the signal processing circuit, and the sensor unit, the first applied voltage or the first An arithmetic processing circuit for arithmetically processing the output signal of the first sample and hold circuit when the applied current is applied and the output signal of the signal processing circuit when the second applied voltage or the second applied current is applied ( 5) and a determination circuit (6) that performs abnormality detection based on the calculation processing result of the calculation processing circuit.
[0010]
With such a configuration, the output of the first sample hold circuit that holds the output of the signal processing circuit at the time of dynamic quantity detection and the signal at the time of diagnosis by changing the applied voltage or applied current at the time of dynamic quantity detection and at the time of diagnosis. By determining whether or not the output of the processing circuit satisfies a predetermined relationship, it is possible to detect abnormality of the mechanical quantity detection sensor. Thereby, abnormality detection of the mechanical quantity sensor can be performed without making the circuit configuration redundant.
[0011]
Then, by holding the output signal of the signal processing circuit by the first sample and hold circuit, the pressure signal corresponding to the applied pressure can be output by the first sample and hold circuit even at the time of diagnosis.
[0012]
Specifically, as shown in claim 2, when the first applied voltage or the first applied current is applied to the sensor unit, the output signal of the sample hold circuit is V1, the second applied voltage, or the second applied voltage. When the applied current is applied to the sensor unit, the output signal of the signal processing circuit is V2, the second applied voltage or the second applied current is the first applied voltage or a times the first applied current, the output of the sensor unit When the offset voltage of VO is VO, the arithmetic processing circuit performs arithmetic processing based on V2 = (a * V1- (a-1) * VO).
[0013]
In the invention according to claim 3, the signal processing circuit is configured to generate an output signal in a predetermined range when the mechanical quantity is detected, and the determination circuit is detected to be abnormal based on the calculation processing result. The output signal output from the signal processing circuit is converted into an output signal that is different from the range generated by the signal processing circuit when the dynamic quantity is detected.
[0014]
As described above, when an abnormality is detected, an abnormality signal can be detected from the sensor output by outputting an output signal outside the range that is used as an output signal when the mechanical quantity is detected. .
[0015]
Further, as described in claim 4, if the offset voltage is set to a voltage outside the range that is generated by the signal processing circuit when detecting the dynamic quantity, the output voltages V1 and V2 are not the same within the range. By the above calculation, the sensor abnormality can be reliably detected.
[0016]
The invention according to claim 5 is characterized in that a second sample hold circuit (7) for holding the output of the determination circuit is provided. In this way, by holding the output of the determination circuit by the second sample and hold circuit, it can be output that the sensor is abnormal during the holding period.
[0017]
According to a sixth aspect of the present invention, a timing generation circuit (10) for generating a timing signal is provided, and based on the timing signal, the first applied voltage or the first applied current and the second applied voltage or the second applied voltage are provided. The operation of the first sample hold circuit and the second sample hold circuit can be controlled based on the timing signal generated by the timing generation circuit (10).
[0018]
Specifically, according to a seventh aspect, the timing signal generated by the timing generation circuit holds the output signal of the previous signal processing circuit by the first sample hold circuit, the first applied voltage, or the first application. Switching between the current and the second applied voltage or the second applied current is performed in the order of holding the output of the determination circuit by the second sample and hold circuit.
[0019]
In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 1 shows a circuit configuration of a pressure sensor as a mechanical quantity detection sensor to which an embodiment of the present invention is applied. Hereinafter, based on FIG. 1, the structure of the pressure sensor in this embodiment is demonstrated.
[0021]
The pressure sensor shown in FIG. 1 is used, for example, for measuring brake fluid pressure in a vehicle. As shown in FIG. 1, the pressure sensor includes a sensor unit 1 including a bridge circuit composed of strain gauges (diffusion resistors) 1a to 1d, a constant current circuit 2 that generates a constant current I, and an output of the sensor unit 1 as a signal. A signal processing circuit 3 to be processed, a sample hold circuit (first sample hold circuit) 4 for holding an output signal of the signal processing circuit 3 at a predetermined timing, and a timing generation for generating a self-diagnosis command signal at a predetermined timing A self-diagnosis command generation circuit 10 as a circuit is provided.
[0022]
A constant current I generated by the constant current circuit 2 is applied to the sensor unit 1, and the sensitivity of the sensor unit 1 changes according to the magnitude of the applied current I.
[0023]
The applied current I flowing through the constant current circuit 2 can be switched in magnitude based on a self-diagnosis command signal from the self-diagnosis signal generation circuit 10, and when pressure is detected (hereinafter referred to as pressure detection). Is a constant current I1, and when diagnosing an abnormality in the pressure sensor (hereinafter referred to as a diagnosis), it is a current I2 for diagnosis.
[0024]
On the other hand, the potential difference at each midpoint of the bridge circuit that fluctuates according to the applied pressure is used as the output of the sensor unit 1, and this output is amplified by the signal processing circuit 3 including an amplifier, and then output through the sample hold circuit 4. Is output to the outside.
[0025]
The output voltage Vsig of the signal processing circuit 3 corresponds to the normal operating pressure range of the pressure sensor. For example, when a 5 V power source is used as the power source, an analog signal of 0.5 to 4.5 V is output from the signal processing circuit 3. It is set to output. In the present embodiment, as shown in FIG. 2, the relationship between the applied pressure P and the output voltage Vsig is indicated by a straight line A when the constant current I1 at the time of pressure detection is passed through the sensor unit 1, and the current I2 at the time of diagnosis. Is set to be indicated by a straight line B when it is passed through the sensor unit 1.
[0026]
The output of the signal processing circuit 3 outputs a voltage outside the above range (for example, near the power supply voltage or near the GND voltage) as a diagnostic signal when an abnormality to be described later is detected. The sensor output indicating the diagnosis signal confirms that the pressure sensor is abnormal on the system (not shown) side where the output signal from the pressure sensor is sent.
[0027]
The sample hold circuit 4 outputs the output voltage of the signal processing circuit 3 as it is as the sensor output Vout when pressure is detected, and during the diagnosis, that is, during the period when the self-diagnosis signal is sent from the self-diagnosis signal generation circuit 10 The output voltage of the signal processing circuit 3 at that time is held. Thus, by holding the output voltage of the signal processing circuit 3 before diagnosis by the sample hold circuit 4 at the time of diagnosis, a diagnostic output signal generated by the signal processing circuit 3 at the time of diagnosis is output to the outside of the sensor. Can be prevented.
[0028]
The pressure sensor includes an arithmetic processing circuit 5 that performs arithmetic processing based on the output signal of the sample hold circuit 4 and the output signal of the signal processing circuit 3, and abnormality of the pressure sensor based on the arithmetic processing result of the arithmetic processing circuit 5. A window comparator 6 as a determination circuit and a sample hold circuit (second sample hold circuit) 7 that holds an output signal of the window comparator 6 are provided.
[0029]
The arithmetic processing circuit 5 performs a predetermined calculation based on the output voltage Vout of the sample hold circuit 4 and the output voltage Vsig of the signal processing circuit 3. Hereinafter, this calculation will be described.
[0030]
As described above, the current flowing through the constant current circuit 2 at the time of diagnosis is switched from the constant current I1 to the diagnostic current I2, and the output voltage Vout output at this time is held in the sample hold circuit 4. As a result, the sensitivity of the sensor unit 1 is changed, and the relationship between the applied pressure P and the output voltage Vsig of the signal processing circuit 3 becomes a pressure-output voltage characteristic indicated by a straight line B in FIG.
[0031]
Here, the output voltage held in the sample hold circuit 4 is V1, the pressure applied to the sensor unit 1 immediately before diagnosis is P, the sensitivity of the sensor unit 1 is S1, and the voltage at the intersection of the straight line A and the straight line B is P1. If a certain offset voltage is VO, the output voltage V1 is expressed by the following equation.
[0032]
[Expression 1]
V1 = S1 × P + VO
Further, since the sensitivity S1 is proportional to the constant current I1, if the proportionality constant is K, Equation 1 is replaced as follows.
[0033]
[Expression 2]
V1 = K × I1 × P + VO
On the other hand, assuming that the current I2 has a relationship of I2 = a × I1 (where a is an arbitrary constant), and the output voltage Vsig of the signal processing circuit 3 at the time of diagnosis is V2, the output voltage V2 is given by It is expressed in
[0034]
[Equation 3]
V2 = K × I2 × P + VO
Therefore, the following equation is derived from Equations 2 and 3.
[0035]
[Expression 4]
V2−V1 = K × (I2−I1) × P
When this expression is replaced with the expression of the output voltage V2, the following expression is obtained.
[0036]
[Equation 5]
V2 = K × (I2−I1) × P + V1
When it is considered that I2 = a × I1 with respect to the current I2, Equation 5 can be converted as follows.
[0037]
[Formula 6]
V2 = K * (a-1) * I1 * P + V1
= (A-1) * S1 * P + V1
= (A-1) x (V1-VO) + V1
= A x V1 one (a-1) x VO
For example, when a = 0.5, V2 = 0.5 × V1 + 0.5 × VO. As is apparent from this equation, since the pressure P is not included as a function in this equation, the relationship of this equation always holds in the entire pressure range.
[0038]
Therefore, when the output voltage V1 when the constant current I1 is applied and the output voltage V2 when the diagnostic current I2 is applied deviate from the above equation 6, the sensor characteristics are abnormal. For example, when the resistance value of the strain gauge 1a fluctuates due to contamination or the like, the relationship of Equation 6 is broken. For this reason, ΔV shown in Equation 7 is obtained by the arithmetic processing circuit 5.
[0039]
[Expression 7]
ΔV = V2− (a × V1− (a−1) × VO)
The window comparator 6 compares ΔV obtained by the arithmetic processing circuit 5 with a predetermined threshold level, and determines whether ΔV is within a predetermined range. If ΔV is not within the predetermined range, the window comparator 6 generates a diagnosis command signal that the pressure sensor is abnormal. In the case of this embodiment, a Hi level signal is output.
[0040]
The sample hold circuit 7 receives the diagnosis command signal from the self-diagnosis signal generation circuit 10 and holds the output of the window comparator 6 until the next diagnosis command signal is sent. When a diagnosis command signal (Hi level signal) indicating that the pressure sensor is abnormal as described above is input to the sample hold circuit 7, the transistor 8 is turned on for a predetermined period. When the transistor 8 is turned on in this way, the output voltage Vout is in the vicinity of the GND voltage, and becomes a voltage outside the range that the sample hold circuit 4 outputs at the time of pressure detection. Thereby, it is confirmed that the pressure sensor is abnormal on the system side to which the output signal from the pressure sensor is sent.
[0041]
Next, FIG. 3 shows a timing chart of the diagnostic command signals S1, S2, and S3 that the self-diagnosis signal generation circuit 10 causes the sample hold circuit 4, the constant current circuit 2, and the sample hold circuit 7 to generate. The operation of the pressure sensor will be described.
[0042]
As shown in FIG. 3, at the time of diagnosis, diagnosis command signals S1, S2, and S3 are sent to each unit in this order. First, a diagnosis command signal S1 is sent to the sample hold circuit 4. Thereby, the sample hold circuit 4 holds the output voltage Vout generated at that time. The output voltage Vout at this time corresponds to the voltage V1.
[0043]
Thereafter, a diagnostic command signal S2 is sent to the constant current circuit 2, and the constant current circuit 2 changes the constant current I1 to a diagnostic current I2. As a result, the output voltage Vsig of the signal processing circuit 3 changes to the diagnostic voltage V2, and the arithmetic processing circuit 5 performs arithmetic processing based on the voltages V1 and V2.
[0044]
The window comparator 6 detects an abnormality based on the calculation result in the calculation processing circuit 5. At this time, the diagnosis command signal S3 is sent to the sample hold circuit 7, and the output of the window comparator 6 is held in the sample hold circuit 7.
[0045]
Thus, when it is detected that the pressure sensor is abnormal, the output voltage Vout is in the vicinity of the GND potential, and when it is not abnormal, the output voltage Vout is a voltage corresponding to the applied pressure before diagnosis. .
[0046]
Note that the pulse widths of the diagnostic command signals S1 to S3 generated by the self-diagnosis signal generation circuit 10 may be determined individually, but the pulse width of the diagnostic command signal S2 is short enough that the output of the sensor unit 1 does not fluctuate. It is preferable to set to. Assuming that the voltage V1 and the voltage V2 are outputs of the signal processing circuit 3 at the same pressure, an abnormality is detected by comparing these voltages V1 and V2, so that the pressure applied to the sensor unit 1 This is because it is necessary to make the time so short that it does not change.
[0047]
As described above, the value of the current flowing through the constant current circuit 2 is changed between pressure detection and diagnosis, and the output voltage of the signal processing circuit 3 at pressure detection and the output voltage of the signal processing circuit 3 at diagnosis are By determining whether or not the predetermined relationship is satisfied, the abnormality of the pressure sensor can be detected. Further, since the abnormality of the pressure sensor can be detected by such a one-system circuit configuration, the circuit does not become redundant.
[0048]
Further, the pressure signal before diagnosis is held by the sample hold circuit 4 even at the time of diagnosis, so that the abnormality of the pressure sensor can be detected at the time of pressure detection, and the pressure signal corresponding to the applied pressure can be output even at the time of diagnosis. At the same time, the output voltage for diagnosis can be prevented from being output to the outside of the sensor.
[0049]
In this embodiment, the pressure-voltage characteristics at the time of pressure detection and diagnosis are set to have the relationship shown in FIG. 2, but in order to obtain such a relationship, output is performed in the normal operating pressure range of the pressure sensor. The offset voltage is set to a voltage outside the voltage range used as the voltage. This is because when the offset voltage is set within the above voltage range, the straight lines A and B overlap within the normal use pressure range of the pressure sensor. In such a case, the output voltage V1 at the intersection pressure This is because the output voltage V2 becomes the same (V1 = V2 = VO) and abnormality detection cannot be performed.
[0050]
Further, the generation timing of the self-diagnosis command signal from the self-diagnosis signal generation circuit 10 may be generated at regular intervals by providing the pressure sensor itself with a clock function, or as a request signal from the outside of the sensor. It may be generated based on this.
[0051]
(Other embodiments)
In the above embodiment, the sample and hold circuit 7 holds the state until the next self-diagnosis signal is sent to the sample and hold circuit 7. However, the state may be changed according to the application. For example, when the pressure sensor becomes abnormal, the abnormal value may be kept, or when a reset signal is sent to the sample and hold circuit 7 separately. The state may be reset.
[0052]
In the above embodiment, the case where the constant current I is applied to the sensor unit 1 has been described. However, the present invention can be similarly applied to the case where a constant voltage is applied.
[0053]
In the above embodiment, an example in which the sensor abnormality is output to the outside by using the output voltage Vout as a diagnostic output, that is, an example in which the sensor abnormality is output from the output terminal that sends the pressure detection signal has been described. Alternatively, a terminal for sending sensor abnormality may be provided.
[0054]
Moreover, the present invention can be used for other mechanical quantity detection sensors, for example, acceleration sensors, regardless of the pressure sensor. In this case, the pressure P is replaced with the acceleration G.
[0055]
The present invention is not limited to a mechanical quantity detection sensor having a bridge-type sensor unit 1, but may be a mechanical quantity detection sensor having another type of sensor unit as long as the sensor sensitivity changes according to current or voltage. It is also possible to apply to.
[Brief description of the drawings]
FIG. 1 is a diagram showing a circuit configuration of a pressure sensor according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a relationship between a pressure P and an output voltage Vsig in each case of a constant current I1 and a diagnostic current I2.
FIG. 3 is a timing chart showing generation timings of diagnostic command signals S1 to S3.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Sensor part, 2 ... Constant current circuit, 3 ... Signal processing circuit,
4 ... sample hold circuit, 5 ... arithmetic processing circuit, 6 ... window comparator, 7 ... sample hold circuit, 8 ... transistor, 10 ... self-diagnosis signal generation circuit.

Claims (7)

A sensor unit (1) whose sensitivity changes according to an applied voltage or an applied current;
A signal processing circuit (3) for processing an output from the sensor unit and generating an output signal corresponding to the output from the sensor unit;
A first sample and hold circuit (4) for holding an output signal of the signal processing circuit;
The output signal of the sample and hold circuit when the first applied voltage or the first applied current is applied to the sensor unit, and the signal when the second applied voltage or the second applied current is applied. An arithmetic processing circuit (5) for arithmetically processing the output signal of the processing circuit;
A mechanical quantity detection sensor comprising: a determination circuit (6) that performs abnormality detection based on a calculation processing result by the calculation processing circuit. When the first applied voltage or the first applied current is applied to the sensor unit, the output signal of the sample and hold circuit is V1, and the second applied voltage or the second applied current is applied to the sensor unit. The output signal of the signal processing circuit when applied is V2, the second applied voltage or the second applied current is a times the first applied voltage or the first applied current, and the output of the sensor unit. If the offset voltage is VO,
2. The mechanical quantity detection sensor according to claim 1, wherein the arithmetic processing circuit performs arithmetic processing based on V2 = (a * V1- (a-1) * VO). The signal processing circuit is configured to generate an output signal in a predetermined range when a mechanical quantity is detected,
When it is detected that the determination circuit is abnormal based on the calculation processing result, the output signal output from the signal processing circuit is different from the range in which the signal processing circuit generates the dynamic quantity at the time of detection. The mechanical quantity detection sensor according to claim 2, wherein the mechanical quantity detection sensor is converted into a signal. 4. The mechanical quantity detection sensor according to claim 3, wherein the offset voltage is set to a voltage outside a range that is generated by the signal processing circuit when the mechanical quantity is detected. The mechanical quantity detection sensor according to any one of claims 1 to 4, further comprising a second sample hold circuit (7) that holds an output of the determination circuit. A timing generation circuit (10) for generating a timing signal;
Based on the timing signal, switching between the first applied voltage or the first applied current and the second applied voltage or the second applied current is performed,
6. The mechanical quantity detection sensor according to claim 5, wherein the first sample hold circuit and the second sample hold circuit are configured to operate based on the timing signal. By the timing signal generated by the timing generation circuit,
Holding the output signal of the previous signal processing circuit by the first sample-and-hold circuit, switching between the first applied voltage or the first applied current and the second applied voltage or the second applied current, The mechanical quantity detection sensor according to claim 6, wherein the determination is performed in the order of holding the output of the determination circuit by a second sample hold circuit.

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