JPH01214722A - Detecting device for inner-cylinder pressure of internal combustion engine - Google Patents

Abstract

PURPOSE:To enable the implementation of an efficient signal processing being resistive to noise, by inputting an output signal of a piezoelectric type inner-cylinder pressure sensor in the form of a current and by measuring a knock signal from an output signal of LPF. CONSTITUTION:When a charge Q is outputted in accordance with an inner-cylinder pressure from the output of a piezoelectric type inner-cylinder pressure sensor 1, a current of -dQ/dt is outputted from an operational amplifier 51 to a resistance 52 by a feedback control of the amplifier 51. Due to a voltage drop of the resistance 52, an output voltage V1 of the amplifier 51 turns to be V1=-R1.dQ/dt when a resistance value of the resistance 52 is denoted by R1. This voltage V1 of the amplifier 51 is a voltage obtained by subjecting the inner-cylinder pressure to time differentiation. The voltage V is supplied to LPF 53. This LPF 53 attenuates a low frequency component caused by a change in the inner-cylinder pressure and also can output a high frequency component of pressure vibration, with a uniform frequency characteristic. By passing an output signal of the LPF 53 through BPF 54 having a characteristic of a central frequency, a knock signal can be extracted effectively from a pressure frequency component.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application] The present invention relates to a cylinder pressure detection device for an internal combustion engine that measures pressure information in a combustion cylinder of an internal combustion engine.

[Conventional technology]

BACKGROUND OF THE INVENTION Generally, the pressure within a combustion cylinder is measured to measure the combustion state of an internal combustion engine and the operation of each rotation cycle. A piezoelectric cylinder pressure sensor is often used as the cylinder pressure sensor used for this measurement. In response to this pressure 1, the pressure inside the cylinder is directly or indirectly applied to a piezoelectric element that generates an electric charge in response to pressure, and outputs an electric charge Wk corresponding to the applied W pressure. . For example, an example of a piezoelectric nodal internal pressure sensor is shown in FIG. In Figure 5, αIJ
is a piezoelectric element, ++21 is an electrode that is sandwiched between the two piezoelectric elements and leads the output signal to the lead wire, and Q41 is a case that covers the internal structural parts of the sensor. This piezoelectric cylinder pressure sensor has a ring shape, and is installed between the cylinder head (21) and the spark plug (31), which form the earthen wall of the combustion cylinder of the engine, as shown in Fig. 6. The pressure in the combustion cylinder is transmitted through the spark plug to the piezoelectric element d1J of the piezoelectric cylinder pressure sensor, 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 internal pressure sensor is a charged acid, it is necessary to convert this charged acid into a voltage value that can be easily processed electrically. Therefore, a charge amplifier has generally been used as a means for converting the charge into a charge@ft*pressure value. Figure 7 shows the basic circuit of the charge amplifier. In FIG. 7, U#-! It is an operational amplifier, and (in) is a capacitor. Piezoelectric cylinder pressure sensor 1
! ) can be connected to the inverting input of the operational amplifier (9),
A capacitor is connected between the inverting input and the output of the operational amplifier CTJ. The non-inverting input of the Mana operational amplifier is grounded. Now, the operational amplifier (incorporated) controls the output so that the inverting and non-inverting input voltages are at the ground level, and when the charge Q is input from the piezoelectric internal pressure sensor Ill, the operational amplifier i4D transfers all the charge Q to the capacitor. The control operates to charge the battery.

Therefore, if the capacitance of the capacitor (6) is C and τ, then v-
A voltage Q/c appears at the output of the operational amplifier.

Here, since the electric charge WkQ is proportional to the cylinder pressure, the value corresponds to the output voltage vB of the operational amplifier cylinder pressure VC, and during engine operation, a combustion pressure signal as shown in No. 8L%1 is output. [Problem to be Solved by the Invention] By the way, when detecting pressure vibration due to knock as combustion pressure information, the pressure vibration signal is The problem was that it was easily disturbed by noise.

The present invention has been made in view of these problems,
When obtaining a pressure vibration signal due to knock from the output signal of a piezoelectric cylinder pressure sensor, the object is to obtain a single word level with a large amplitude regarding knock.

[Means for resolving ambiguity]

In order to achieve the above objects, 1. The cylinder pressure signal iron W of an internal combustion engine according to the present invention inputs the output signal of a piezoelectric type cylinder pressure sensor in the form of a current, and incorporates a low-pass filter in the circuit for this current input. , or installed at a later stage, and the knock signal is measured from the output signal of this low-pass filter.

[Effect]

In the present invention, optimum frequency reduction characteristics can be obtained by using a low-pass filter for input circuit fil.

〔Example〕

Fig. 1 shows the first embodiment of the present invention? show. In Fig. 1, +111i piezoelectric cylinder pressure sensor, 511 operational amplifier, 5? In resistance, 531 is low pass filter 1, ) 41
is a bandpass filter. Piezoelectric cylinder pressure sensor Il
The output of I is connected to the inverting input of the operational amplifier fil, and the resistive surface is VC connected between the output and the inverting input of the operational amplifier SI1. Furthermore, a low-pass filter FIJ is connected to the output of the operational amplifier 5Il, and the output of the low-pass filter 53 is input to the band-pass filter I.

Next, the operation of the embodiment shown in FIG. 1 will be explained. now,
When a charge Q is output from the output of the piezoelectric cylinder pressure sensor Ill in accordance with the cylinder pressure shown in FIG. 8, the operational amplifier t
Due to the feedback control of 5a, the resistance group has -aQ
A current /at is output from the operational amplifier 5Il. Then, due to the voltage drop on the resistor surface, the output voltage v1 of the operational amplifier 5υ becomes V, assuming that the resistance value of the resistor +52 is R1.
= -R,・kit, that is, pressure [output current dQ of the internal pressure sensor
/dt is converted into a voltage value.

The output voltage v of this operational amplifier 5a corresponds to the time differentiation of the Fi cylinder pressure.

Here, regarding the pressure vibration component such as knocking, the output signal of the piezoelectric cylinder pressure sensor Ill due to pressure vibration is Q = Qo'' (kft) for the frequency I, then the output IJLEE Vl of the operational amplifier 611 is V, = -2πf −RtQa −=+n (2πft)
becomes. From the above equation, the frequency characteristic of the output voltage V□ of the operational amplifier bυ is fixed to the frequency as shown by tal in FIG. Furthermore, among the cylinder pressure signals shown in Fig. 8, the low frequency component signal indicating the pressure change in the cylinder is attenuated, and the level of the pressure fluctuation due to pressure vibration is reduced as shown in tal in Fig. 3. becomes larger. Therefore, when measuring pressure vibrations such as knocks, the signal level is large, which is advantageous against noise.

However, if the characteristic of monotonically increasing frequency remains unchanged, the signal level of a frequency that is better than the knock frequency will become larger, making accurate measurement of the knock signal impossible. Therefore, the cutoff frequency fc, which is sufficiently lower than the knock frequency fK, is installed after the operational amplifier 5υ as shown in fb+ in Fig. 6.
By installing the filter, the output frequency characteristics of the operational amplifier 5rJ are set as shown in Figure 2 (0), which attenuates the low frequency components caused by in-plane pressure changes and attenuates the high frequency components of pressure vibrations. can output with uniform frequency characteristics. Stone, Figure 2 1
By passing the output signal of the low-pass filter layer through a band-pass filter having the characteristic of center frequency fK as shown in dl, the knock signal can be effectively extracted from the pressure vibration component as shown in bI in Fig. 3. can do.

A long time ago, the second implementation by uninvention f! Shown in Figure AJ k 51. The difference from the first embodiment in FIG.
A capacitor 5υ is added in parallel with .

The output voltage of the operational amplifier 6υ is V, and the capacitance of the capacitor θ is C.

Then, the frequency characteristic becomes a high-pass type characteristic with a cutoff frequency fc as shown at +O1 in FIG. That is, capacitor 5
By adding .about. to the circuit of the operational amplifier 6υ with one layer of low-pass filter in FIG.

In this way, by processing the output signal of the piezoelectric cylinder pressure sensor as a chemical optical input and passing it through a low-pass filter, the low frequency components caused by changes in the cylinder pressure are attenuated, and the high frequency components caused by pressure image movement etc. are uniformed. By using a band-pass filter to extract only the frequency component unique to knocking, it is possible to efficiently measure the knocking signal.

〔Effect of the invention〕

As explained above, according to the present invention, when measuring a pressure vibration component such as a knock signal from an output signal of a piezoelectric cylinder pressure sensor, it is possible to perform efficient signal processing that is resistant to VC and noise.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of the first example according to the present invention, FIG. 2 is a frequency characteristic diagram of the valley part of the embodiment of FIG. 1, and FIG. 3 is an operation waveform diagram of the embodiment of FIG. 1. Fig. 4 is a configuration diagram of a second embodiment of the present invention, Fig. 5 is a sectional structural diagram of a piezoelectric cylinder pressure sensor, Fig. 6 is an installation diagram of the piezoelectric cylinder pressure sensor, and Fig. 7 is a diagram of a conventional device. The circuit diagram and FIG. 8 are cylinder pressure waveform diagrams.

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 a current input circuit that is built in or installed in the subsequent stage of this current input circuit. A cylinder pressure detection device for an internal combustion engine, comprising a low-pass filter and a knock measuring device for measuring a knock signal of the internal combustion engine from an output signal of the low-pass filter.