JP2001201413A - Pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure sensor, capable of surely detecting a failure in the case of variation of output of a bridge circuit due to the failure. SOLUTION: The pressure sensor is provided with a pressure detecting circuit, constituted of a plurality of gauge resistors RA to RD and having a plurality of output terminals and provided with a memory means 5 for recording in advance the response relation of each output in arbitrary two or more output terminals in a plurality of output terminals and determines the failure of the pressure detection circuit by whether each output of the arbitrary two or more output terminals fulfill the response relation. The pressure detection circuit can be a bridge circuit 1, and in this case, the failure of the bridge circuit can be determined, based on the two middle point electric potentials VB and VC of the bridge circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure detecting device for detecting pressure, and more particularly to a pressure detecting device capable of self-diagnosis of occurrence of a failure.

[0002]

2. Description of the Related Art Conventionally, in a pressure sensor, a thin diaphragm portion is formed on a semiconductor substrate, and two pressure detecting elements (gauge resistors) are provided at a central portion and a peripheral portion of the diaphragm portion, respectively. Is composed. When pressure is applied to the diaphragm, the resistance value of the pressure detecting element changes due to the piezoresistance effect, and as a result, a potential difference (output voltage) occurs at the midpoint potential of the central and peripheral pressure detecting elements. .
The pressure sensor performs an appropriate amplification and adjustment process on the output voltage to output an electric signal corresponding to the pressure.

[0003]

As described above, the pressure sensor merely amplifies and adjusts the potential difference output from the bridge circuit. For example, when the bridge circuit generates an erroneous potential difference due to contamination, damage, or the like. In this case, there is a possibility that an erroneous electric signal is output as it is.

As a pressure sensor having a function of detecting such an abnormality, there is a pressure sensor described in Japanese Patent Application Laid-Open No. H8-247881. This pressure sensor makes a failure determination based on the sum voltage of two output terminals of the bridge circuit. However, this pressure sensor has a problem that a part of the abnormality detection is missing.

That is, if the power supply voltage is Vcc, the output fluctuation of the output terminal due to stress fluctuation is ΔV, and the error component due to the fault is ΔVe, the output of one output terminal is Vcc / 2 +
ΔV + ΔVe, and the output of the other output terminal is Vcc /
2-ΔV−ΔVe. At this time, if the sum voltage of both output terminals is taken, the error component ΔVe is canceled out and no abnormality can be detected. Therefore, when an error component (+ ΔVe and −ΔVe) having the same magnitude and a different sign occurs at each output terminal, the result is that the abnormality cannot be detected.

In view of the above problems, an object of the present invention is to provide a pressure sensor that can reliably detect a failure when the output of the bridge circuit changes due to the failure.

[0007]

In order to achieve the above object, according to the first aspect of the present invention, a plurality of gauge resistors (R
A to RD) and a pressure sensor including a pressure detection circuit having a plurality of output terminals, wherein a correspondence relationship between respective outputs at any two or more output terminals among the plurality of output terminals is stored in advance. Storage means (5), and failure determination means for determining failure of the pressure detection circuit based on whether each output of two or more output terminals at an arbitrary pressure point satisfies the correspondence. It is characterized by.

As described above, by monitoring output fluctuations at each output terminal of the pressure detection circuit and accurately grasping the relationship between them, a highly reliable failure judgment can be made.

The pressure detecting circuit may be a bridge circuit (1), specifically, according to the second aspect of the present invention, and the two midpoint potentials (VB,
VC), the failure determination of the bridge circuit can be performed.

Further, according to the present invention, when the output (VB) of the first output terminal (B) is used as a reference, the second
The failure detection of the pressure detection circuit is performed by determining whether or not the output (VC) of the output terminal (C) is within a predetermined range based on the correspondence between the outputs stored in the storage means in advance. I have. This predetermined range can be set arbitrarily in consideration of manufacturing variations and detection accuracy of the pressure sensor.

The reference numerals in parentheses of the above-mentioned means indicate the correspondence with the concrete means described in the embodiments described later.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment to which the present invention is applied will be described below with reference to FIGS. The pressure sensor according to the present embodiment measures a pressure such as a brake fluid pressure of a brake device or a fuel pressure of a fuel injection device in a vehicle. FIG. 1 shows a schematic circuit configuration of the pressure sensor of the present embodiment, and FIG. 2 shows a change characteristic of outputs VB and VC at the output terminals B and C of the pressure sensor with respect to pressure.

As shown in FIG. 1, the pressure sensor includes a bridge circuit (pressure detection circuit) 1 in which four gauge resistors (diffusion resistors) RA, RB, RC, and RD are connected in a bridge. The bridge circuit 1 is formed in a diaphragm portion (thin portion) of a silicon substrate (not shown). When pressure is applied to the diaphragm part, a stress displacement occurs, and each resistance value of the resistances RA to RD changes in the direction of the arrow in FIG. 1 due to the piezoresistance effect. Note that the resistors RA to RD should be formed in the same process so as to have the same shape and the same resistance, respectively, so as not to be affected by patterning, temperature, and the like.

One end side (power supply side) of the bridge circuit 1
A constant voltage Vcc is applied between a terminal A of the other end and a terminal D of the other end (ground side), and a middle point B of the resistors RA and RB and a resistor R
The middle point C of C and RD is configured as an output terminal. When no pressure is applied to the diaphragm, the output (midpoint potential) is VB = VC = V at the output terminals B and C, respectively.
cc / 2. When pressure is applied to the diaphragm, a change in resistance occurs at each of the resistors RA to RD. As a result, VB = Vcc / 2 + Δ at each of the output terminals B and C.
V, VC = Vcc / 2−ΔV. The potential difference between the two output terminals B and C is amplified by the amplifier circuit 2 and adjusted by the adjustment circuit 3, and then the sensor output Vout is output. The pressure applied to the diaphragm of the silicon substrate can be measured based on the sensor output Vout.

Further, the pressure sensor according to the present embodiment includes a failure determination circuit (failure determination means) 4 for performing failure determination based on the respective outputs VB and VC of the output terminals B and C, A storage circuit 5 for storing the outputs of the output terminals B and C at the minimum and maximum times, and a switch circuit 6 for outputting the power supply voltage Vcc as the sensor output Vout when a failure occurs.

Hereinafter, failure detection in the pressure sensor of the present embodiment will be described. First, the output values VB and VC of the two output terminals when the pressure applied to the diaphragm unit is minimum and maximum are stored in the storage circuit 5 in advance. As these values, those which the pressure sensor has as a product standard may be used. This allows VB and VC
Can be accurately obtained. That is, as shown in FIG. 2, each terminal output VB at a certain pressure point,
VC has a fixed relationship, and a constant relationship (VB + Voff = VC, where Voff is a variable value with an offset voltage) is always maintained between VB and VC.

Therefore, when the pressure sensor is operating,
At an arbitrary pressure point, the terminal outputs VB and VC are directly compared to determine whether or not the above relationship (VB + Voff = VC) is established. If not, it can be determined that a failure has occurred. Specifically, for example, based on VB, it may be determined whether VC is within a predetermined range (dashed line in FIG. 2). This predetermined range can be set arbitrarily in consideration of manufacturing variations and detection accuracy of the pressure sensor.

In the pressure sensor of this embodiment, when it is determined that a failure has occurred, the failure determination circuit 4 issues a signal to the switch circuit 6. As a result, the switch circuit 6 is configured to output the power supply voltage Vcc as it is to the external device (for example, an ECU) as a sensor output to notify that an abnormality has occurred in the pressure sensor.

In each of the output terminals B and C, error components having the same magnitude and different signs (for example, + ΔVe and −ΔV
If e) occurs, a failure can be determined by exceeding the output value range stored in the storage circuit when the outputs VB and VC are at the maximum or minimum applied pressure.

As described above, there is provided a pressure sensor capable of performing highly reliable failure determination by monitoring output fluctuations at each output terminal of the bridge circuit and accurately grasping the relationship between them as in the present embodiment. can do.

Further, according to the configuration of the pressure sensor of the present embodiment, it is only necessary to change a part of the circuit pattern, and it is not necessary to change the general manufacturing method of the conventional pressure sensor. It can respond to miniaturization.

In the above-described embodiment, a bridge circuit having two output terminals is used as a pressure detection circuit. However, the present invention is not limited to this, and a circuit having more output terminals can be used. In this case, the failure determination of the pressure detection circuit may be performed based on the output at any two or more of the plurality of output terminals.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a schematic configuration of a pressure sensor according to an embodiment.

FIG. 2 is a characteristic diagram showing a change characteristic of outputs of two output terminals B and C of a bridge circuit.

[Explanation of symbols]

1. Bridge circuit, 2. Amplifier circuit, 3. Adjustment circuit, 4.
Failure determination circuit, 5: storage circuit, 6: switch circuit.

Claims (3)

[Claims] 1. A pressure sensor comprising a plurality of gauge resistors (RA to RD) and including a pressure detection circuit having a plurality of output terminals, wherein an output of any two or more of the plurality of output terminals is provided. A storage means (5) for preliminarily storing a correspondence relation of each output at a terminal; and a pressure detection circuit according to whether each output of the two or more output terminals at an arbitrary pressure point satisfies the correspondence relation. And a failure determination means for performing failure determination of the pressure sensor. 2. The pressure detection circuit is a bridge circuit (1) composed of four gauge resistors (RA to RD), and the failure determination means includes two output terminals (B, C) of the bridge circuit. 2. The pressure sensor according to claim 1, wherein the failure determination of the pressure detection circuit is performed based on the outputs (VB, VC) in (1). 3. The failure judging means according to claim 2, wherein an output (VC) of a second output terminal (C) is set to correspond to the output (VC) based on an output (VB) of the first output terminal (B). 3. The pressure sensor according to claim 2, wherein the failure detection of the pressure detection circuit is performed based on whether the pressure is within a predetermined range based on the relationship.