JPH01213534A - Inside-cylinder pressure detector for internal combustion engine - Google Patents

Abstract

PURPOSE:To stabilize signals corresponding to inside-cylinder pressure of an internal combustion engine by correcting the signals in accordance with the output value of a temperature detector. CONSTITUTION:The output electric charge of a piezo-electric type inside-pressure sensor 1 is converted into a voltage value by the feedback control of an operational amplifier 51. An electric current is made to flow from the output of the operational amplifier 51 to the inverted input of another operational amplifier 52 through a capacitor 54 and resistance 55 and, since the electrostatic capacity of the capacity is set sufficiently largely, the electric current made to flow to the capacitor 54 is decided by the output voltage of the amplifier 51 and the value of the resistance 55. The output voltage of the amplifier 52 is proportional to the output electric charge of the sensor 1 and its output signal corresponds to the inside- cylinder pressure itself, since the resistance value of the resistance 57 is set at a high level. Since the quantity of the output electric charge increases as the temperature rises, the quantity is corrected by means of a thermistor assembled in the sensor 1 in order to obtain correct inside-cylinder pressure. When the output signal of the sensor is inputted as a current value and temperature correction is performed by integrating the signals corresponding to the current value in such way, a stable inside-cylinder pressure signal can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to cylinder pressure detection of an internal combustion engine, which measures pressure information within the combustion cylinder of an internal combustion engine.

[Conventional technology]

The pressure in the combustion cylinder is generally measured to measure the combustion state of the internal combustion engine and the previous work for each rotation cycle. A piezoelectric cylinder pressure sensor is often used as the cylinder pressure sensor used for this measurement. This piezoelectric cylinder pressure sensor outputs charged acid according to the applied pressure by directly or indirectly applying the pressure in the VC cylinder to a piezoelectric element that generates an electric charge in response to pressure. For example, an example of a piezoelectric internal pressure sensor is shown in FIG. In Fig. 4, Uυ is a piezoelectric element, an electrode that is sandwiched between IJ''ar12 piezoelectric elements and leads the output signal to lead aI131, and Q4 is a case that covers the internal beak part of the sensor.This piezoelectric cylinder pressure sensor has a ring-shaped shape, and as shown in Fig. 5rC, it is placed in a gr layer between the cylinder head 12), which forms the clay wall of the combustion cylinder of the engine, and the spark plug +31.Then, the pressure inside the combustion cylinder increases. is transmitted to the piezoelectric type cylinder pressure sensor, 11 piezoelectric elements 1υ, through the spark plug, and an electric charge corresponding to the cylinder pressure is output.

By the way, since the output signal corresponding to the cylinder pressure of the piezoelectric cylinder pressure sensor is a charged acid, this charge 1it-?
[It is necessary to convert it to an h voltage value that can be easily processed. Therefore, a charge amplifier has generally been used as a means for converting charge at a voltage value. Figure 6 shows the basic circuit of the charge amplifier. In FIG. 6, wn is an operational amplifier, and wn is a capacitor. The output of the piezoelectric cylinder pressure sensor +1+ is connected to the inverting input of the operational amplifier 14υ, and the capacitor (6) is connected between the inverting input and the output of the operational amplifier (b). Further, the non-inverting input of the operational amplifier 0υ is grounded. Now, the output is controlled so that the inverting and non-inverting input voltages to the operational amplifier lυ are at the same level, and when the charge Q is input from the piezoelectric cylinder pressure sensor 111, the operational amplifier (6) V′i voltage Qt Control operation is performed to charge all capacitors VC.

Therefore, if the capacitance rC of capacitor 4 is v -Q
A voltage of /C appears at the output of the operational amplifier. Here, since the electric charge Q is proportional to the cylinder pressure, the output voltage V of the operational amplifier (6) is a value corresponding to the cylinder pressure I/i, and during engine operation, the combustion [Problem to be Solved by the Invention] However, in the piezoelectric type cylinder pressure sensor 111 described above, the piezoelectric charge absorption property changes with temperature, and the piezoelectric element does not respond to temperature changes. has a characteristic of charge generation called the pyro effect. In particular, when it is installed near the combustion chamber as shown in Fig. 5, there is a large temperature change in each cycle due to the temperature rise of the cylinder spatula (r+21) and the spark plug 131, and the transmission of the temperature in the combustion chamber. The problem is that the output signal waveform of the charge amplifier is greatly affected by the temperature change, making accurate measurement impossible.・Now, even if you try to compensate for the temperature in some way, the charge amplifier circuit will directly transfer the output charge to the capacitor.
The problem was that it became complicated because it was converted into a voltage value.

The present invention has been made in view of these problems, and
It is an object of the present invention to realize accurate measurement of the cylinder pressure that is not affected by temperature changes of the cylinder pressure sensor when obtaining a signal corresponding to the cylinder pressure from the output signal of the cylinder pressure sensor.

[Means for Solving the Problem] [Operation] In order to achieve the above object, the cylinder pressure detection device 1 for an internal combustion engine according to the present invention detects the cylinder pressure according to the output signal of the cylinder pressure detector. The output signal of the in-cylinder pressure signal output circuit which outputs No. 11 is corrected in consideration of the output value of the temperature detector which measures the temperature of the above-mentioned in-cylinder pressure detector.

〔Example〕

FIG. 1 shows an embodiment of the present invention. In Figure 1,
511 and Sakura are operational amplifiers, iii, 'f1. +57
1 is a resistor, and in particular, the resistor 53 is a variable resistor, and the resistance value changes depending on the voltage at the control terminal. Keita, I
Toton is capacitor% + 61 TTL thermistor, (to)
is an amplifier. The output of the piezoelectric cylinder pressure sensor il+ is connected to the inverting input of the operational amplifier IIυ, and resistively connected between the inverting input and the output of the operational amplifier 6υ. The capacitor and the resistor 111 are connected in series between the output of the operational amplifier) υ and the inverting input of the operational amplifier is5, and the resistor be) and the capacitor 111 are connected in parallel between the inverting input and output of the operational amplifier 1. Ru.

Further, the non-inverting inputs of the operational amplifier 5υ and F1a are both grounded.

Further, the output of the thermistor 161 is input to an amplifier 581, and the output of the amplifier is input to the resistive l1lal terminal.

Next, the operation of the embodiment shown in FIG. 1 will be explained. now,
Corresponding to the cylinder pressure from the output of the piezoelectric cylinder pressure sensor...
[? When 1fTQ is output, the feedback control of the operational amplifier 50 causes the resistance to become -d5a.
A current is output from the operational amplifier till. Then, due to the voltage drop across the resistor, the output voltage V of the operational amplifier 60,
is the resistance value R of the abrasive.

Then, Q V, -R, -t. In other words, the output of the piezoelectric cylinder pressure sensor is +
1 is converted into a voltage value. This operational amplifier 5
The signal shaping of the output voltage V of 9 is shown in (&1) in FIG.

This waveform corresponds to the time derivative of the cylinder pressure.

A current flows from the operational amplifier 2a7 to the inverting input VC of the operational amplifier F12+ via the capacitor I and the resistor t5119.

Here, since the space between the capacitors is used for current coupling, the capacitance is set to be sufficiently large so that the impedance becomes extremely small with respect to the rate of change in current due to pressure build-up in the cylinder. Therefore, the current flow 111- flowing there is expressed as the output voltage V of the operational amplifier core a, and the resistor 5 as shown below.
Resistance of @ (determined by iiiRx).

Then, a current of one magnitude flows from the output of the operational amplifier φ)2 due to feedback control. Here, resistance 67
1 is a resistor for returning the output voltage v1 of the operational amplifier i+'4 to the zero point with a long time constant, and the resistor 1 is R.
The capacitor s is installed in one direction with high resistance so that the current a is negligible compared to the current flowing through the capacitor rc. Therefore, the output voltage V of the operational amplifier is determined by the output current -Is and the static response tC of the capacitor as shown in the following equation.

In other words, the output voltage v3 of the five operational amplifiers is proportional to the output charge Q of the piezoelectric in-plane pressure sensor +l+,
As shown by lbl in FIG. 6, the output signal corresponds to the cylinder pressure itself.

In this way, the previous pressure 1d can be obtained by inputting the output signal of the piezoelectric in-cylinder pressure sensor as the chemical flow and performing 1g@t-complementation according to the input flow bias.

By the way, the pressure curve conversion coefficient of the piezoelectric internal pressure sensor has a positive temperature characteristic, and as the temperature decreases, the output and charge increase. Therefore, the output signal of the operational amplifier 511 increases as shown by the broken line of the second (al), and in order to obtain accurate cylinder pressure, it is safe to correct the temperature change of the cylinder pressure sensor 111. 5-'-% Example V In this case, a thermistor (6) is incorporated inside the piezoelectric internal pressure sensor mountain as shown in Fig. 3. Thermistor (III pole a in addition to 61)
4 and an insulating plate 061 are added. The amount of temperature change is detected from the amount of resistance change of the thermistor 16).

The amplifier converts the resistance value connected to its input into a voltage value, and converts the resistance change amount of the thermistor 161 into a voltage change amount. The resistance value of the feedback resistor core of the operational amplifier Ill changes according to the output voltage of the amplifier 4 cap. Therefore, as the temperature of the piezoelectric cylinder pressure sensor increases and the output charge pupil increases, the operational amplifier 5
Even if the output signal of υ tries to increase as shown by the broken line in Figure 2 (!L1), the resistance value of the thermistor (61) decreases due to the change in the resistance value of the thermistor (61). Regardless, the signal shown by the solid line IJLI in FIG. 2 can be obtained, and a stable cylinder pressure signal can always be obtained as shown in FIG. 2 1b+.

Although a thermistor was used as the temperature measuring device in the above embodiment f, other methods such as a semiconductor or a thermocouple may also be used. Moreover, the temperature measuring device can be installed adjacent to the in-cylinder pressure sensor instead of being built into the cylinder pressure sensor.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to obtain a stable cylinder pressure signal that does not change even if a temperature change occurs in the cylinder pressure sensor.

The figures are an explanatory view of the operation of one embodiment of Fig. 1, Fig. 3 is a cross-sectional structural diagram of the piezoelectric cylinder pressure sensor in the embodiment of Fig. 1, and Fig.
5 is an installation diagram of the piezoelectric cylinder pressure sensor, FIG. 6 is a circuit diagram of a conventional device, and FIG. 7 is an output waveform diagram of the conventional device.

Claims (1)

[Claims] (1) In-cylinder pressure detection means for detecting the pressure in the combustion cylinder of an internal combustion engine; in-cylinder pressure signal output means for outputting a signal according to the in-cylinder pressure from the output signal of this in-cylinder pressure detector; A cylinder pressure detection device for an internal combustion engine, comprising a temperature detection means for measuring the temperature of the pressure detection means, and a temperature correction means for correcting the output of the cylinder pressure signal output means according to the output of the temperature detection means.