JPH01213537A - Inside-cylinder pressure detector for internal combustion engine - Google Patents

Abstract

PURPOSE:To obtain stable inside-cylinder pressure waveforms by receiving the output signals of a piezo-electric type inside-cylinder pressure sensor in the form of electric currents and integrating the currents after converting them into voltage or current values. CONSTITUTION:The output electric charge of a piezo-electric inside-cylinder pressure sensor 1 is converted into a voltage value under the feedback control of an operational amplifier 51 and an electric current is made to flow from the output of the amplifier 51 to the inverted into of another operational amplifier 52 through a capacitor 54 and resistance 55. The electrostatic capacity of the capacitor 54 is sufficiently large so that the impedance can become smaller against the current changing rate caused by pressure changes. Therefore, the current at the capacitor 54 is decided by the voltage of the amplifier 51 and resistance value of the resistance 55. The value of a resistance 57 is set in such a way that the current made to flow through the resistance 57 can become smaller to a negligible degree as compared with the current at the capacitor 54. The output voltage of the amplifier 52 is proportional to the output electric charge of the sensor 1 and the output signal of the amplifier 52 corresponds to the inside-cylinder pressure itself. By inputting the output signal of the sensor 1 as current values and integrating signals corresponding to the current values in such way, stable inside-cylinder pressure waves which do not change even if a leak current is produced can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of sedentary use] This invention relates to a cylinder pressure detection system 4 for measuring pressure information in a combustion cylinder of an internal combustion engine.

[Conventional technology]

Generally, the pressure inside the cylinder is measured to measure the combustion status of the internal combustion engine and the operation of each rotation cycle. A piezoelectric cylinder pressure sensor is often used as an in-plane pressure sensor used for this measurement. This pressure-formed cylinder pressure sensor is such that the pressure inside the cylinder is directly or indirectly applied to a piezoelectric element that generates a charge in response to pressure, and outputs a subsequent charge il in accordance with the applied pressure. For example, an example of a piezoelectric cylinder pressure sensor is shown in FIG. In Figure 8, Lu1
l is a piezoelectric element, +121 is sandwiched between 8 piezoelectric elements,
This is a case that covers the internal structural parts of the 4-electrode sensor that guides the output signal to the lead surface. This pressure-molded cylinder pressure sensor has a ring-shaped shape, and as shown in Figure 4, it is a case that covers the internal structural parts of the sensor. VCG is pumped between the cylinder head 121, which forms the clay wall of the cylinder, and the spark plug 131. Then, the pressure in the combustion cylinder is transmitted through the spark plug 2 to the piezoelectric element dυ of the piezoelectric internal pressure sensor Il+, and an electric charge corresponding to the cylinder internal pressure VC is output.

By the way, since the output signal corresponding to the cylinder pressure of the piezoelectric type cylinder pressure sensor is a charge loss, it is necessary to convert this charge loss into a voltage value that can be easily processed in one step. Therefore, in the past, charge amplifiers have generally been used as means for converting the charge #t into a voltage value. FIG. 5 shows the basic IMI of a charge amplifier. In Figure 8, +41J
is an operational amplifier and the decoy is a capacitor. The output of the piezoelectric cylinder pressure sensor Il+ is connected to the inverting input of an operational amplifier (incorporated), and the capacitor is connected between the inverting input and output of the operational amplifier (6). The non-inverting input of the enclosed operational amplifier is grounded. I1, operational amplifier: 41
1r1 The output is 1ljlla so that the inverted and non-inverted input voltages are at the same level, and when the charge Q is input from the piezoelectric cylinder pressure sensor..., the operational amplifier (2)
Load Q? All capacitors lId VC act as 1 sub-operations so that the capacitance t of the capacitor sensor becomes C
Then, V = Q/C, the voltage is
appears in the output of Here, the charge @Q#':I is proportional to the cylinder pressure, so the output voltage V of the operational amplifier will be a value that corresponds to the cylinder pressure, and during engine operation, combustion will occur as shown in Figure 6. Pressure signal? Output.

[Problem to be solved by the invention]

However, in the above charge amplifier, 11M1t
It is a method that converts directly into a voltage value using a purple capacitor, and the capacitance of the capacitor area is the piezoelectric cylinder pressure sensor ill.
Since the piezoelectric element is set small to match the static capacitance of +1υ, current leakage from the pressure'1 type cylinder pressure sensor, its output signal line, or charge amplifier input circuit, etc.
Or ′, human bias of the operational amplifier 4′ [, flow, etc.
If there is a charge transfer other than the in-cylinder pressure signal, that is, a current, in the input section, the output voltage of the operational amplifier +4υ will fluctuate, making it impossible to accurately measure the in-cylinder pressure.

The present invention has been made in view of these problems,
[Means for Solving the Problems] Internal combustion according to the present invention The engine internal pressure detection device receives the output signal of the piezoelectric cedar pressure sensor in the form of current, converts it into a voltage value or current value, and then differentiates it with an integrator to obtain the cylinder pressure signal. be.

[Effect]

In the present invention, an integrator is configured via the current input port W, and the integrator at-
Can be configured.

〔Example〕

FIG. 1 shows an embodiment of the present invention. In Figure 1, +
51 and Ml are operational amplifiers, caps (to), 5''II are resistors, and capacitors are between.The output of the piezoelectric cylinder pressure sensor... is connected to the inverting input of operational amplifier 511, and the resistor - is the operational amplifier input. A capacitor (and a resistor) are connected in series between the output of the op-amp Ill and the inverting input of the op-amp Ill, and the resistor
bη and the capacitor are connected in parallel between the inverting input and output of the operational amplifier 6. Further, the non-inverting inputs of the operational amplifier 61 and s'4 are both grounded.

Next, the operation of the embodiment shown in FIG. 5 will be explained.

1/-1, when a charge Q is output from the output of the piezoelectric cylinder pressure sensor corresponding to the cylinder pressure, 1-tlQ/dt is applied to the resistance by the feedback control of 5 operational amplifiers.
A current of 5υ is output from the operational amplifier 5υ. Then, due to the voltage drop of the resistor -, the output voltage v1 of the operational amplifier 5D
If the resistance value of the resistor is R1, then it becomes ``v,''-R1π.In other words, the output current (I) of the piezoelectric cylinder pressure sensor is
Q/idt is converted into a voltage value.

The signal waveform of the output '1 voltage vl of this operational amplifier 40 is
This waveform is shown in (&1) in the figure. This waveform corresponds to the time derivative of the cylinder pressure.

Next, a current '4 flows from the output of the operational amplifier J1 to the inverting input of the operational amplifier ) through the capacitor wire and the resistor f4.

Here, since capacitor A is used as a main flow connecting table, its capacitance is set sufficiently large so that a
dffi conversion 541 (the impedance gets used to the size and becomes smaller.Then, as shown in the formula below, the output voltage v1 of the operational amplifier is
It is determined by the resistance value R1 of the resistor and the resistor.

Then, a current of XS flows from the output of the operational amplifier f1''a by feedback control. Here, resistance f1
71 is a resistor for returning the output voltage V of the operational amplifier to zero point, and its resistance value R is the capacitor 1! The resistance is set to a high value so that the current flowing through the capacitor is negligible.

Therefore, the output voltage V of the operational amplifier 4 is determined by the output current -II and the capacitance CI/in the order of the capacitors, as shown in the equation below.

That is, the output voltage Vs tfi of the operational amplifier color is proportional to the output charge QK of the piezoelectric cylinder pressure sensor 11,
As shown by lbH in the 1X2 diagram, the output signal corresponds to the cylinder pressure itself.

In this way, the in-cylinder pressure signal can be obtained by inputting the output signal r of the piezoelectric in-cylinder pressure sensor as a current value and integrating the signal obtained by dividing the input 1[Rlii K jI5.

By the way, if a steady leakage current occurs in the output line of the piezoelectric cylinder pressure sensor Il+.

The output voltage v1 of the operational amplifier 6D is V-m-C, and the output signal waveform is as shown in the dashed line (&1) in Figure @6. However, the static capacitance of the capacitor *Cs
can be set to a relatively large value, so that write breaks due to manual leakage Xa of the operational amplifier 5'IJ are reduced. Furthermore, since the input of the integrator due to the color of the operational amplifier in the next stage of VC is inputted to AC M4+ by the capacitor, the above '1/
j? The change due to the E leak - R1 is blocked here, and only the Ig component - Rμ due to the cylinder pressure change is integrated.

t Therefore, the output of the integral, that is, the output waveform of the six operational amplifiers, has a stable in-cylinder pressure waveform as shown at lb+ in FIG. 6, regardless of the presence or absence of the leakage current.

In the above practical example, the current-to-voltage conversion circuit is used as the current-to-voltage input circuit by the operational amplifier 6, but it may be a current-to-voltage converter circuit with a current output of ms. In this case, the operational amplifier, iJ The integrator by the above eliminates the need for the resistor 6θ, and can be used as a circuit that directly integrates the output current.

Also, 151! Although the coupling capacitor is inserted only between the current input circuit and the horizontal divider, if it is also inserted between the DC input circuit and the piezoelectric cylinder pressure sensor, 7 will be created.

〔Effect of the invention〕

As explained above, according to the present invention, there is a leakage t (flt) in the output signal line of the pressure ilC type internal pressure sensor.

This has the effect of being able to obtain a stable in-cylinder pressure waveform that does not fluctuate even if this occurs.

[Brief explanation of the drawing]

1v; 4 is a circuit diagram of an embodiment according to the present invention, Fig. 2 is an explanatory diagram of the operation of the embodiment of Fig. 1, Fig. 3 is a cross-sectional structural diagram of a piezoelectric cylinder pressure sensor, and Fig. 4 is a piezoelectric type FIG. 5 is a circuit diagram of the conventional 5tiIIf, and FIG. 6 is an output waveform diagram of the conventional g position.

Claims (1)

[Claims] (1) A piezoelectric pressure detector that detects the pressure in the combustion cylinder of an internal combustion engine, a current input circuit that receives the output current signal of this piezoelectric pressure detector, and an integrator that integrates the output signal of this current input circuit. A cylinder pressure detection device for an internal combustion engine.