JPH05223000A - Knocking control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To provide a knocking control device of an internal combustion engine furnished with an envelope detection circuit capable of detecting even a knocking signal which is less than 0.6V. CONSTITUTION:A knocking signal is taken out of an output signal of a knock sensor 1 by a buffer filter 2. A direct current component is removed from the taken-out knocking signal by a direct current cut condenser, and a direct current level of about 2B is given to it by a level shift circuit consisting of resistors R1 and R2. An output signal of the level shift circuit is input to a rectification integrating circuit, which consists of an integration capacitor and an emitter follower made of a transistor TR1 and a resistor R4, and the output signal is detected into an envelope. As the knocking signal passes through the level shift circuit, it is possible to detect the knocking signal of less than 0.6V, too.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a knocking control device for an internal combustion engine, and more particularly to a knocking control device for an internal combustion engine which can detect even a small knocking and perform more accurate engine control.

[0002]

2. Description of the Related Art As is well known, a conventional knocking control system for an internal combustion engine uses a circuit for envelope detection of a knocking signal which is an output of a knock sensor (for example, Japanese Patent Laid-Open No. 58-105036). See the bulletin).

An example of a conventional envelope circuit will be described with reference to FIG. In the figure, 1 is a knock sensor mounted on a cylinder block wall of an engine, 2 is a buffer filter for extracting a signal in a frequency band of about 5.5 KHz to 8.5 KHz with a center frequency of about 7 KHz, and 3 is a rectifier composed of a diode. The circuit 4 is an integrating circuit composed of a resistor and a capacitor.

In this conventional device, the signal output from the knock sensor 1 is about 5.
Signals in the frequency band of 5 KHz to 8.5 KHz are extracted. Now, assuming that the waveform of the extracted signal is as shown in FIG. 4 (a), when this signal a is rectified by the rectifying circuit 3,
The waveform is shown by the solid line in (b). As is well known, since the diode has a forward voltage drop of about 0.6V, the signal becomes smaller by about 0.6V than the magnitude of the input signal.
It is output from the rectifier circuit 3. Here, the waveform shown by the dotted line in FIG. 4 (b) is the waveform of the signal without the voltage drop of about 0.6V.

The output signal b of the rectifying circuit 3 is input to the integrating circuit 4 and subjected to integration processing. FIG. 4 (c) shows the integration circuit 4
3 shows the waveform of the output signal c of FIG. The signal c is a signal obtained by envelope-detecting the signal b.

[0006]

The conventional envelope detection circuit is composed of the rectifying circuit 3 and the integrating circuit 4 as described above, and the rectifying circuit 3 has a forward voltage drop of about 0.6V. Therefore, as shown in FIG. 4B, the signal of less than 0.6 V in the signal a is ignored by the rectifying circuit 3. Therefore, in the conventional device,
Although a large knocking signal of 0.6 V or more is detected,
There was a problem that a knocking signal smaller than 0.6V was not detected.

An object of the present invention is to provide a knocking control device for an internal combustion engine equipped with an envelope detection circuit capable of eliminating the above-mentioned problems of the conventional device and detecting a knocking signal smaller than 0.6V. Especially.

[0008]

To achieve the above object, the present invention provides a level shift of a knocking signal, which is an output of a knock sensor, so that the zero point of the signal is at least about 0.6V or more. It is characterized in that an envelope circuit including a shift circuit and a rectifying / integrating circuit connected to the level shift circuit is provided.

[0009]

According to the present invention, since the zero point of the knocking signal is level-shifted to at least about 0.6 V or more and is input to the rectification / integration circuit, the forward voltage of the diode or transistor of the rectification / integration circuit. The drop ensures that low level signals of the knocking signal are not ignored. Therefore, it becomes possible to detect even a small knocking signal of 0.6 V or less.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings. FIG. 1 is a circuit diagram illustrating an embodiment of the present invention. In the figure, reference numeral 5 indicates an envelope detection circuit, and other reference numerals indicate the same as or equivalent to those in FIG.

As is apparent from the figure, the envelope detection circuit 5 of this embodiment comprises a level shift circuit composed of resistors R1 and R2, and a rectifying / integrating circuit connected to the level shift circuit. The rectifying / integrating circuit includes an emitter follower circuit including a transistor TR1 and a resistor R4, and the resistor R4.
4 and an integrating capacitor C2 connected in parallel.

Next, the operation of this embodiment will be described with reference to the waveform chart of FIG. The signal a having the waveform shown in FIG. 2A represents the knocking signal output from the buffer filter 2. The DC component of the signal a is cut by the capacitor C1 and the zero point is shifted to the DC level of 2V by the level shift circuit. This 2V is an example, and the present invention is not limited to this. The knocking signal provided with the DC level of 2V is applied to the base of the transistor TR1.

Now, in the emitter of the transistor TR1,
If the capacitor C2 is not connected, the waveform of the emitter output signal of the transistor TR1 becomes the waveform shown in FIG. 2 (b). That is, the 0 point of the knocking signal is 1.4V
The waveform is shifted to.

However, when the capacitor C2 is connected to the emitter of the transistor TR1, when the voltage of the signal input to the base of the transistor TR1 is larger than (base-emitter voltage + charge voltage of the capacitor C2), The current flowing through the base of the transistor TR1 flows through the transistor TR1 so that the capacitor C2 is charged quickly.

When the voltage of the signal input to the base of the transistor TR1 is larger than (base-emitter voltage + charging voltage of the capacitor C2), the transistor TR1 is turned off and the electric charge charged in the capacitor C2 becomes a resistance. Slowly discharge through R4 with a predetermined time constant.

As a result, the waveform of the output signal c of the envelope circuit 5 becomes a waveform as shown in FIG. 2 (c). This waveform is shown in Figure 2.
The waveform becomes a waveform with the peak points of the signal in (b) connected, and
The signal of less than 0.6 V appears without being ignored.

Therefore, according to this embodiment, 0.6 V
It becomes possible to detect even the following small knocking signals, and it becomes possible to perform knocking control of the engine more accurately than in the conventional case.

The envelope waveform of FIG. 2 (c) is 1.4V.
The DC bias is added to this DC bias. If the signal level when the knock sensor signal is almost 0 at the time of idling, for example, is stored in the microcomputer and the difference is taken, this DC bias is added. It is obvious that the DC bias component can be easily removed by subtracting the DC bias component from the signal of FIG. 2 (c), and there is no influence on knocking detection.

[0019]

As is apparent from the above description, according to the present invention, there is an effect that even a small knocking signal of 0.6 V or less can be detected.

[Brief description of drawings]

FIG. 1 shows a circuit diagram of an embodiment of the present invention.

FIG. 2 shows a waveform diagram of signals of a main part of the circuit of FIG.

FIG. 3 shows a circuit diagram of a conventional device.

FIG. 4 shows a waveform diagram of signals of a main part of the circuit of FIG.

[Explanation of symbols]

1 ... Knock sensor, 2 ... Buffer filter, 5 ... Envelope circuit

Claims (2)

[Claims] 1. A level shift circuit for level-shifting a knocking signal which is an output of a knock sensor so that a zero point of the signal is at least equal to or more than a voltage drop of a rectifying element, and a rectifying / connecting circuit connected to the level shift circuit. A knocking control device for an internal combustion engine, comprising an envelope circuit including an integrating circuit. 2. The knocking control device for an internal combustion engine according to claim 1, wherein the rectifying / integrating circuit comprises an emitter follower circuit and an integrating capacitor connected to the output side of the emitter follower circuit.