JPS6398535A - Input processing circuit of pressure sensor in cylinder - Google Patents

Abstract

PURPOSE:To remove an error due to a drift component, by holding the output level of a pressure sensor at the time of a bottom dead point calculated from a crank angle signal as a sample and subtracting a bottom dead point level from the output of the pressure sensor. CONSTITUTION:A pressure sensor 13 is provided to the upper part of an engine cylinder 11 and the pressure in the cylinder 11 changing by the operation of a piston is detected to be inputted to the subtraction circuit 19 and sample holding circuit 17 of an input part 15. An angle-of-rotation sensor 23 to work in conjunction with a crank shaft is mounted in a distributor 25 to detect the angle of rotation of the crank shaft and the detection value is inputted to the input/output part 33 of an electronic control circuit 31. CPU 35 outputs said value through the input/output part 33 at every crank angle corresponding to a bottom dead point and the output of the pressure sensor 13 at that point of time is held by the sample holding circuit 17. This held value is subtracted from the output of the sensor 13 by the subtraction circuit 19 and converted by an A/D converter 21. By this method, a drift component is removed from the output of the sensor 13 and the pressure in the cylinder can be accurately calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an input processing circuit for a cylinder pressure sensor that removes a drift component of a pressure detection signal from a cylinder pressure sensor.

[Prior Art and its Problems] Conventionally, this type of pressure sensor has been used in a device that detects the pressure in the cylinder of an engine and determines the engine output based on this pressure detection signal.

By the way, in the above pressure sensor, noise due to drift is superimposed on the pressure detection signal due to a rise in temperature, etc.
Detection error occurs. Further, a pressure detection signal output from the pressure sensor is converted into a digital signal by an A/D converter and processed by an electronic control circuit. For this reason,
A by the amount that the pressure detection signal increases due to drift,
'It may exceed the detection range of the D converter, reducing detection accuracy. In order to deal with this, there is a problem in that the capacity of the A/D converter must be increased.

In order to solve this problem, for example,
As described in Japanese Patent No. 54671, there is a technique for removing a drift component of a pressure detection signal from a pressure sensor using an AC converter. However, this conventional technique has problems in that the output signal may be deformed and the circuit configuration becomes complicated.

The present invention has been made in order to solve the problems of the above-mentioned conventional technology, and aims to provide an input processing circuit for a cylinder pressure sensor that can detect the pressure inside a cylinder with high precision and has a simple configuration. purpose.

[Means for Solving the Problems] The present invention, which has been made to solve the above problems and achieve the above objects, includes a pressure sensor that detects the pressure in the cylinder of an engine, and a pressure sensor that detects the crank angle of the engine. A rotation angle sensor, and a sample AND circuit that samples and holds the pressure detection signal from the pressure sensor as the bottom dead center pressure signal level at the bottom dead center of the crank angle based on the crank angle signal output from the rotation angle sensor. A hold circuit; a subtraction circuit that subtracts the bottom dead center pressure signal level from the pressure detection signal of the pressure sensor and outputs a correction signal for the pressure detection signal; do.

[Operation] According to the configuration of the input processing for the cylinder pressure sensor of the present invention, the pressure in the cylinder of the engine is detected by the pressure sensor, and this detection signal is input to the subtraction circuit and the sample-and-bold circuit. The sample-and-hold circuit samples the pressure detection signal of the pressure sensor at the bottom dead center of the crank angle based on the input signal of the rotation angle sensor, and holds this as the bottom dead center signal level. Then, the bolded bottom dead center signal level is input to a subtraction circuit, where the A for the pressure detection signal of the pressure sensor is
Used as n signal. Therefore, the pressure detection signal of the pressure sensor output from the subtraction circuit is corrected at the bottom dead center signal level output at the bottom dead center of the crank angle.

This circuit configuration was based on the following idea. Since the cylinder pressure at bottom dead center is almost equal to atmospheric pressure,
Even if the pressure detection signal of the pressure sensor increases due to drift due to temperature, this increase is not due to fluctuations in the cylinder pressure;
It can be seen that it depends only on drift due to temperature.

Therefore, since the pressure detection signal at the bottom dead center can be used as a reference value, the detection signal of the pressure sensor is subtracted and corrected by the cylinder pressure at the bottom dead center.

[Effects of the Invention] As explained above, according to the present invention, the pressure detection signal of the cylinder pressure sensor is subtracted and corrected by the bottom dead center signal level at the bottom dead center of the crank angle, so that the drift of the pressure sensor is reduced. Errors due to components are removed, and accurate cylinder pressure can be determined.

Moreover, since the drift component is removed from the pressure detection signal of the pressure sensor, the output level of the detection signal decreases and the A/
It is possible to make maximum use of the range of the D converter, and it is possible to simplify the 1 m configuration of the A/D converter etc. to be processed later.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings. 6 Fig. 1 is a diagram showing an input processing circuit of an in-cylinder pressure sensor according to the embodiment. A well-known pressure sensor 13 made of a semiconductor device is mounted on the upper part, and an output signal of this pressure sensor 13 is input to an input section 15. This input section 1
5 is a sample and bold circuit 17, a subtraction circuit 19
and an A7/D converter 21, and the input voltage range of the A/D converter 21 is set between 0■ and 5■. A pressure detection signal from the pressure sensor 13 is input to the sample-and-hold circuit 17 and the subtraction circuit 19 . The subtraction circuit 19 subtracts the pressure detection signal of the pressure sensor 13 by the output signal of the sample-and-hold circuit 19, and outputs this output signal to the A/D converter 21. In the A/D converter 21, an analog signal is converted into a digital signal using a sampling signal of a predetermined period from an electronic control circuit 31, which will be described later, and this digital signal is input to the electronic control circuit 31.

A rotation angle sensor 23 is linked to the engine crankshaft and is provided in the distributor 25 to generate a pulse signal at every predetermined crank angle. is input.

The electronic control circuit 31 is composed of a well-known microcomputer, that is, an input/output section 33, a CPU 35, an RA
It consists of M'37, ROM39, etc.

Next, the operation of the input processing circuit of the above embodiment will be explained with reference to the waveform diagram of FIG. 2.

The cylinder pressure of the engine is converted by the pressure sensor 13 into a detection signal proportional to the pressure (FIG. 2(a)).
This detection signal is input to one subtraction circuit and a sample-and-hold circuit 17.

On the other hand, the crank angle signal from the rotation angle sensor 23 is input to the CPU 35 via the input/output section 33.
5, the crank angle is counted and a bottom dead center signal is output to the sample and hold circuit 17 at a crank angle of 0° corresponding to the bottom dead center immediately after the suction stroke (FIG. 2(b)). When the bottom dead center signal is input, the sample and hold circuit 17 samples the pressure detection signal of the pressure sensor 13 at that time and holds it as the bottom dead center signal level until the next bottom dead center signal is input. (FIG. 2(c)), this bottom dead center signal level is output to one subtraction circuit, where the bottom dead center signal level is subtracted from the pressure detection signal of the pressure sensor 13, and the bottom dead center signal level is calculated. is output to the A/D converter 21 (FIG. 2(d)). And electronic control circuit 31
At predetermined intervals, for example, as shown in FIG. 3, A/
A sampling signal is output to the A/D converter 21, and an A/D converted output signal is input to the electronic control circuit 31, where it is processed as a pressure detection signal. and,
These in-cylinder pressure signals are used to detect the output torque of the engine and the combustion state in the cylinder.

Therefore, according to the above input/output circuit, from 1 atm to 10
When the pressure sensor detects the cylinder pressure that changes to about 0 atmospheres, even if a drift amount is superimposed on the pressure detection signal of the pressure sensor due to temperature, it is subtracted at the bottom dead center signal level at the bottom dead center of the crank angle. Since it is corrected, pressure sensor 1
The drift component in the detection signal of 3 is removed,
Accurate cylinder pressure can be determined.

Moreover, since the drift component is removed from the detection signal of the pressure sensor, the detection level of the A/D converter 21 can be reduced to 5V.
The output level of one subtracting circuit is lowered, and the range of the A/D converter can be used to the maximum, simplifying the configuration of the A/D converter 21 etc. that will be processed later. It can be done.

In the above embodiment, the crank angle position used as the reference for drift is set at the bottom dead center at a crank angle of 0°.
Of course, it is also possible to set the crank angle to be approximately equal to atmospheric pressure near bottom dead center.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an input/output circuit of a cylinder pressure sensor according to an embodiment of the present invention, Fig. 2 is a waveform diagram of the input/output circuit according to the embodiment, and Fig. 3 shows the sampling period of the embodiment. FIG.

Claims (1)

[Claims] A pressure sensor that detects the pressure in the cylinder of an engine; a rotation angle sensor that detects the crank angle of the engine; and a crank angle based on a crank angle signal output from the rotation angle sensor. a sample-and-hold circuit that samples and holds the pressure detection signal from the pressure sensor as the bottom dead center pressure signal level, and a sample and hold circuit that samples and holds the pressure detection signal from the pressure sensor as the bottom dead center pressure signal level; An input processing circuit for an in-cylinder pressure sensor, comprising: a subtraction circuit that outputs a correction signal for a detection signal;