JPH0628670Y2 - Piezoelectric pressure sensor output processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a piezoelectric pressure sensor output processing device. The piezoelectric pressure sensor is used, for example, in a cylinder pressure detection system of an internal combustion engine.

[Conventional technology]

It is necessary for maintenance inspection to measure the maximum value of the in-cylinder pressure of the engine, but in recent years, it has been proposed to control the air-fuel ratio of the engine in accordance with the in-cylinder pressure. Requires very accurate pressure detection.

In order to directly detect the in-cylinder pressure of the engine described above, it is usual to provide a heat-resistant piezoelectric pressure sensor (hereinafter simply referred to as a pressure sensor) as a pressure detecting means in the engine cylinder.
Since the output of this pressure sensor is easily affected by temperature,
It is necessary to exclude output drift due to temperature fluctuations.

In order to eliminate the output drift due to temperature fluctuation, the maximum value and the minimum value of the pressure sensor of the cylinder pressure for the combustion cycle of the engine (720 ° CA) were held, and the maximum value of the cylinder pressure was determined by the difference. The output of the pressure sensor is forced to a predetermined potential, for example, the ground potential when it is not necessary to detect the pressure (refer to Japanese Patent Laid-Open No. 56-17032 and Japanese Utility Model Laid-Open No. 57-29834) or to detect the cylinder pressure. (Refer to Japanese Patent Laid-Open No. 56-119825).

[Problems to be solved by the invention]

However, in any of the above-mentioned conventional types, the detection accuracy is prioritized for the maximum value of the in-cylinder pressure, that is, the circuit sensitivity of the charge / voltage conversion circuit that converts the output charge of the pressure sensor into a voltage is determined by the circuit power supply voltage. , It is decided according to the maximum value of the cylinder pressure under the constraint of the circuit element parameter, and as a result, it is very difficult to maintain high precision detection of minute pressure under this circuit sensitivity. There was a problem. This is because the dynamic range of the charge / voltage conversion circuit is adjusted to the maximum value of the in-cylinder pressure, so that the minimum required detection accuracy is greatly reduced.

Therefore, it is an object of the present invention to provide an output processing device for a piezoelectric pressure sensor that enables highly accurate detection of minute pressure.

[Means for solving problems]

A means for solving the above problems is shown in FIG.

In FIG. 1, the charge / voltage conversion circuit accumulates the output charge of the piezoelectric pressure sensor to generate a voltage, and the reset means resets the charge / voltage conversion circuit (in this case, a capacitor) every predetermined period. The cumulative addition means cumulatively adds the output voltages immediately before the resetting of the charge / voltage conversion circuit to obtain the pressure detected by the pressure sensor.

[Action]

According to the above-mentioned means, the charge / voltage conversion circuit does not always store the generated charge, but accumulates the generated charge only for a predetermined period. Therefore, the dynamic range of the charge / voltage conversion circuit can be adjusted to a small pressure change.

〔Example〕

FIG. 2 is an overall schematic diagram showing an internal combustion engine to which the piezoelectric pressure sensor output processing device according to the present invention is applied. In FIG. 2, the intake passage 2 of the engine body 1 is provided with a fuel injection valve 3 for supplying pressurized fuel from the fuel supply system to the intake port for each cylinder. Further, the distributor 4 is provided with a crank angle sensor 5 which generates a reference position detecting pulse signal every 30 ° even if its axis is converted into a crank angle, for example. The pulse signal of the crank angle sensor 5 is supplied to the control circuit 10.
Further, the cylinder block 6 of the engine body 1 is provided with a pressure sensor 7 for detecting the in-cylinder pressure. The pressure sensor 7 generates an electric signal of an analog voltage according to the cylinder pressure.

FIG. 3 is a detailed circuit diagram of the control circuit of FIG. Third
In the figure, 101 is a charge / voltage conversion circuit, which includes an operational amplifier 1010, a capacitor 1011, and a switch for accumulating charges.
Switch that resets (discharges) 1012 and capacitor 1011
Consisting of 1013. The switch 1012 is a normally closed switch, and the switch 1013 is a normally open switch. 102 is an A / D converter, 103 is a flip-flop, 104 is a single multivibrator with time τ, 105 is a CPU, 106 is a ROM for storing programs, fixed constants, etc., 107 is RAM for storing temporary data, and 108 is It is an input / output interface.

Next, the circuit operation of FIG. 3 will be described with reference to the timing chart of FIG. 4 and the flowchart of FIG.

Here, the output P of the pressure sensor 7 using the piezoelectric element is the fourth
It changes as shown in FIG. In the illustrated state, the electric charge of the output P of the pressure sensor 7 is accumulated in the capacitor 1011 via the switch 1012, so that FIG.
As shown in, the voltage V ₁ changes. Fig. 4 (B)
As shown in, when the output signal (30 ° CA) of the crank angle sensor 5 is generated at the times t ₁ , t ₃ , ..., The falling edge of this signal sets the flip-flop 103 to turn off the switch 1012, Therefore, the charge / voltage conversion circuit 101 is in the hold state. At the same time, the A / D converter 102 outputs A / D of the output voltage V ₁ of the charge / voltage conversion circuit 101.
Start D conversion. When the A / D conversion is completed at the times t ₂ , t ₄ , ...
A D conversion end signal is generated in the CPU 105, and as a result, the A / D conversion end routine of FIG. 5 starts.

In step 501 of FIG. 5, V ₁ is fetched from the A / D converter 102, the cumulative addition is updated in step 502, and this routine ends in step 503.

At the same time, at times t ₂ , t ₄ , ..., The single multivibrator 104 operates to generate the rectangular wave signal shown in FIG. 4 (C). As a result, the switch 1013 of the charge / voltage conversion circuit 101 is turned on and the capacitor 1011 is reset. That is, as shown in FIG. 4 (D), the capacitor 1011 of the charge / voltage conversion circuit 101 is reset every predetermined period (in this case, a crank angle of 30 °). Further, the flip-flop 103 is reset by the falling edge of the rectangular wave signal, the switch 1012 returns to the ON state, and the capacitor 1011
Charging resumes.

Note that the reset period (τ) is the charge / voltage conversion circuit 101.
It is set to be smaller than the charge storage time of the capacitor 1011, and therefore the amount of charge storage during that period is negligible.

In this way, the capacitor 1011 of the charge / voltage conversion circuit 101 is
The charge accumulation of is adapted to a small pressure change of the pressure sensor 7, and the maximum value of the pressure sensor 7 is obtained by cumulative addition according to the routine of FIG.

FIG. 6 is a modification of FIG. In FIG. 6, 2
Two charge / voltage conversion circuits 101 and 101 'are provided, and accordingly, a multiplexer 109 is added to the preceding stage of the A / D converter 102. Further, flip-flops 110 and 111 are provided in place of the flip-flop 103 and the single multivibrator 104. Further, the switch 1 of the charge / voltage conversion circuit 101 '
012 'is a normally open switch.

Next, the circuit operation of FIG. 6 will be described with reference to the timing chart of FIG. Also in this case, the output P of the pressure sensor 7 changes as shown in FIG. 7 (A). In the state shown in the figure, in the charge / voltage conversion circuit 101, the charge of the output P of the pressure sensor 7 passes through the switch 1012 and the capacitor 10
In the charge / voltage conversion circuit 101 ', the capacitor 1011' is reset by the switch 1013 '. That is, the charge / voltage conversion circuits 101, 101 ′
The two states of the charge / voltage conversion circuit 101 are alternately selected and operated by the flip-flops 110 and 111.
The output V ₁ of the output changes as shown in FIG. 7 (C), while
The output V ₂ of the charge / voltage conversion circuit 101 'changes as shown in FIG. 7 (D). In addition, the crank angle sensor 5 converts the selected charge / voltage conversion circuits 101 and 101 'into the A / D converter 102.
The multiplexer 109 is operated so that it is connected to. Therefore, when the output signal (720 ° CA) of the crank angle sensor 5 is generated at times t ₃ , t ₇ , ..., The A / D converter 1
02 starts A / D conversion of the output voltage V ₁ of the charge / voltage conversion circuit 101. Then, at times t ₄ , t ₈ , ...
When the A / D conversion is completed, the A / D converter 102 generates an A / D conversion end signal to the CPU 105, and as a result, A / D conversion in FIG.
The D conversion end routine starts. On the other hand, at time t ₁ ,
At t ₅ , ..., The output signal of the crank angle sensor 5 (3
0 ° CA), the A / D converter 102 starts A / D conversion of the output voltage V ₂ of the charge / voltage conversion circuit 101 '. When the A / D conversion is completed at the times t ₂ , t ₆ , ..., The A / D converter 102 generates an A / D conversion end signal to the CPU 105, and as a result, the A / D conversion shown in FIG. The termination routine starts.

As described above, the circuit of FIG. 6 has the advantage that the reset period of each charge / voltage conversion circuit 101, 101 'can be made longer than that of the circuit of FIG.

The switches 1012, 10 of the charge / voltage conversion circuits 101, 101 'are
The mode of 13,1012 'and 1013' is not limited to the one shown in the figure. For example, all the same type transistors are used and switches 1012 (1012 ') and 1013 (1013') are appropriately added with inverters. May be. In addition, the A / D converter 102
As for the start timing of, the other synchronizing signal generating means having a cycle of the output P of the pressure sensor 7, for example, a cycle smaller than 720 ° CA may be used.

[Effect of device]

As described above, according to the present invention, the output drift due to the temperature change of the pressure sensor can be removed by resetting the charge / voltage conversion circuit, and by adjusting the reset period (the operation period of the charge / voltage conversion circuit), It is possible to detect a very small pressure with high accuracy, and further, because the accumulating means can secure a substantially large dynamic range without being limited by the dynamic range of the charge / voltage conversion circuit, the cylinder internal pressure, for example, the maximum detection accuracy can be detected. Can hold.

[Brief description of drawings]

FIG. 1 is a block diagram showing the basic configuration of the present invention, FIG. 2 is an overall schematic diagram showing an internal combustion engine including a piezoelectric pressure sensor processing device according to the present invention, and FIG. 3 is a detail of the control circuit of FIG. FIG. 4 is a timing diagram showing the operation of the control circuit of FIG. 3, FIG. 5 is a flowchart showing the operation of the control circuit of FIG. 3, and FIG. 6 is a circuit showing a modification of FIG. 7 and 8 are timing charts showing the operation of the control circuit shown in FIG. 1 ... Engine main body, 4 ... Distributor, 5 ... Crank angle sensor, 7 ... Pressure sensor, 10 ... Control circuit, 101, 101 '... Charge / voltage conversion circuit, 102 ... A / D converter, 104 …… Single multivibrator, 109 …… Multiplexer.

Claims (3)

[Scope of utility model registration request] 1. A charge / voltage conversion circuit (101) for accumulating output charges of a piezoelectric pressure sensor (7) to generate a voltage, and reset means (103) for resetting the charge / voltage conversion circuit at predetermined intervals. ), And a cumulative addition means for cumulatively adding the output voltages immediately before the resetting of the charge / voltage conversion circuit to obtain the pressure detected by the pressure sensor. 2. A piezoelectric pressure sensor output according to claim 1, wherein two charge / voltage conversion circuits are provided and the charge / voltage conversion circuits are alternately switched to operate. Processing equipment. 3. The A / D means for A / D converting the output of the charge / voltage conversion circuit by the cumulative addition means.
2. The piezoelectric pressure sensor output processing device according to claim 1, further comprising a converter and means for cumulatively adding digital outputs of the A / D converter.