JPH0656743U - Combustion pressure detector - Google Patents

Abstract

(57) [Abstract] [Purpose] Even when the engine speed changes, the combustion pressure is accurately detected by following the change in the engine speed.
Improves detection accuracy and reliability. [Structure] A resistor 23 and a plurality of capacitors 24 are provided between an inverting input terminal 22A and an output terminal 22C of a differential amplifier 22.
A to 24D are connected, and the control unit 26 is
According to the engine speed N detected by the crank angle sensor 28, a predetermined electrostatic capacity is read out from the rotational speed-electrostatic capacity map, and a control signal is output to the corresponding changeover switch 25, so that the electrostatic capacity is responded to. The capacitors are selectively connected. When the engine speed N fluctuates, the changeover switch 25 opens and closes, a predetermined capacitor is connected to the differential amplifier 22, and the current signal from the piezoelectric body 19 has a time constant corresponding to the engine speed N. Are converted into voltage signals V.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a combustion pressure detecting device suitable for use in detecting the combustion pressure of an automobile engine, for example.

[0002]

[Prior art]

 A conventional combustion pressure detecting device is shown in FIGS.

In the drawing, reference numeral 1 denotes a piezoelectric body formed of a piezoelectric material such as lead titanate and attached to, for example, a cylinder head of an engine body (neither is shown) located near an ignition plug, The piezoelectric body 1 is provided with one side electrode 1A connected to a differential amplifier 2 to be described later, and another side electrode 1B grounded via the engine body. Then, when the piezoelectric body 1 receives the combustion pressure of the engine body, it generates an electric charge according to the stress change due to the combustion pressure inside the combustion chamber, and as shown by the sensor waveform in FIG. The current signal i corresponding to the pressure is output to the differential amplifier 2.

Reference numeral 2 denotes a differential amplifier provided on the output side of the piezoelectric body 1, and a resistor 3 for adjusting the time constant is provided between the output side of the differential amplifier 2 and the inverting input (minus input) side. And the capacitor 4 charged by the voltage signal V output from the differential amplifier 2 are connected, and the non-inverting input (plus input) side is grounded. The differential amplifier 2 then outputs the current signal i output from the piezoelectric body 1 by a predetermined time constant τ (τ = CR) determined by the resistance value R of the resistor 3 and the electrostatic capacitance C of the capacitor 4. By integrating, as shown as an output waveform in FIG. 5, it is converted into a voltage signal V which is a combustion pressure detection signal and output to a fuel injection control device (not shown) or the like.

The combustion pressure detecting device according to the prior art has the above-mentioned configuration, and when the engine starts and a combustion pressure is generated in the combustion chamber as shown by a pressure waveform in FIG. The combustion pressure is received via the cylinder head and a current signal i corresponding to the combustion pressure is output. Then, the current signal i is converted into a voltage signal V by the differential amplifier 2 and output to the fuel injection control device or the like.

[0006]

[Problems to be solved by the device]

 By the way, in the above-described conventional combustion pressure detecting device, the current signal i output from the piezoelectric body 1 is input to the differential amplifier 2, and this current signal i is determined by the time constant τ determined by the capacitance C of the capacitor 4. By integrating with, the voltage signal V corresponding to the combustion pressure of the engine body is obtained.

However, according to the conventional technique, the resistance value R of the resistor 3 and the capacitance C of the capacitor 4, which determine the time constant τ of the differential amplifier 2, are fixed to one value, so that a certain engine rotation speed is obtained. If the time constant τ is set in order to maximize the detection accuracy, the output level and output waveform of the voltage signal V will change as the engine speed changes, and the pressure waveform inside the combustion chamber will be accurately reproduced. However, there is a problem in that the detection accuracy and reliability of the combustion pressure are greatly reduced.

That is, as shown in FIG. 5, when the time constant τ of the differential amplifier 2 is set to detect the combustion pressure at a predetermined engine speed (cycle T), as shown in FIG. When the rotation speed shifts to high rotation (TH <T) with a short cycle TH, the time constant τ is too long compared to this short cycle TH (τ >> TH), so the output level drops significantly and the waveform collapses. There is a problem that it will end up. On the other hand, as shown in FIG. 7, when the engine speed shifts to a low speed with a long cycle TL (TL> T), the time constant τ is too short with respect to this cycle TL (τ << TL). The result is that integration is not performed and the sensor waveform of the piezoelectric body 1 is simply followed.

The present invention has been made in view of the above-mentioned problems of the prior art. Even when the engine speed changes, the combustion pressure can be accurately detected by following the change in the engine speed. It is an object of the present invention to provide a combustion pressure detecting device capable of improving accuracy and reliability.

[0010]

[Means for Solving the Problems]

 In order to solve the above-mentioned problems, a configuration adopted by the present invention is a piezoelectric body that is provided in an engine body and outputs a current signal according to combustion pressure, and one input side is connected to the piezoelectric body and the other side is connected. Of the differential amplifier whose input side is grounded, a resistor provided between the output side of the differential amplifier and the one input side, and a resistor connected in parallel with the resistor and having different electrostatic capacitances, respectively. A plurality of capacitors, a switching means for selectively switching and connecting at least one of the capacitors and the resistor, a rotation speed detecting means for detecting an engine speed of the engine body, A rotational speed-electrostatic capacity storage means for storing electrostatic capacity with respect to the number of revolutions, and a predetermined electrostatic capacity from the rotational speed-electrostatic capacity storage means based on the engine rotational speed detected by the rotational speed detection means. Read, above By outputting a control signal to the switching means, and a selection control means for selecting the capacitor corresponding to the capacitance.

[0011]

[Action]

 When the engine body starts, the selection control means reads out a predetermined electrostatic capacity from the rotational speed-electrostatic capacity storage means based on the engine rotational speed detected by the rotational speed detection means, and outputs a control signal to the switching means. . When the switching means connects the capacitor corresponding to the control signal to the resistor, the current signal output from the piezoelectric body has a time constant determined by the capacitance of the selected capacitor and the resistance value of the resistor. Is integrated and converted into a voltage signal.

[0012]

【Example】

 Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

In the figure, reference numeral 11 denotes a sensor main body that constitutes a combustion pressure detecting device together with an electric circuit shown in FIG. 2 which will be described later. The casing main body 12 is formed substantially in the shape of a casing, and an upper cover 13 for covering the upper end side of the casing main body 12 and the like. The casing main body 12 has a small-diameter cylindrical portion 12B on the lower end side, which corresponds to the combustion pressure. A thin disk-shaped diaphragm 14 that is displaced is integrally provided. The sensor body 11 is attached to the cylinder head 15 so that the diaphragm 14 faces the combustion chamber (not shown) of the engine body.

Reference numeral 16 denotes a pressure receiving rod that is located inside the small-diameter cylindrical portion 12B of the casing body 12 and is displaceable in the axial direction. The lower end side of the pressure receiving rod 16 is in contact with the upper surface side of the diaphragm 14, The upper end side is in contact with a piezoelectric body 19 described later through a lower plate 17 made of an insulating material and the like. When the diaphragm 14 is bent in the axial direction by the combustion pressure, the pressure receiving rod 16 is axially displaced in the casing body 12, transmits the displacement of the diaphragm 14 to the piezoelectric body 19, and the high temperature in the combustion chamber increases. It is intended to prevent direct transmission to the piezoelectric body 19.

A contact plate 18 is provided inside the large-diameter cylindrical portion 12 A of the casing body 12 so as to face the pressure receiving rod 16, and a position 19 is provided on the outer peripheral side of the contact plate 18 and above the pressure receiving rod 16. The respective piezoelectric bodies are formed of a piezoelectric material such as lead titanate in a cylindrical shape, and an upper electrode 19A and a lower electrode 19B are formed on the upper and lower surfaces of the piezoelectric body 19, respectively. As shown in FIG. 2, the upper electrode 19A of the piezoelectric body 19 is grounded via the upper plate 20 made of a conductive material, the casing body 12 and the like, and the lower electrode 19B is connected to the contact plate 18 and the like. It is connected to an inverting input terminal 22A of a differential amplifier 22, which will be described later. When the diaphragm 14 bends and the pressure receiving rod 16 is displaced and the piezoelectric body 19 is pressed by the pressure receiving rod 16, the piezoelectric body 19 generates an electric charge according to the pressing force (stress), and a current corresponding to the electric charge. The signal i is output to the differential amplifier 22.

Reference numeral 21 denotes a set screw screwed into the large-diameter cylindrical portion 12 A of the casing body 12. The set screw 21 presses the piezoelectric body 19 with a predetermined initial load via the upper plate 20, and The piezoelectric body 19 and the like are fixed inside the casing body 12.

In FIG. 2, reference numeral 22 denotes a differential amplifier provided outside the sensor body 11. The differential amplifier 22 has an inverting input terminal 22 A (minus input side) which is one input side thereof, in the contact plate 18. Is connected to the lower electrode 19B of the piezoelectric body 19 via the like, the other input side of the non-inverting input terminal 22B (plus input side) is grounded, and the output terminal 22C is connected to the fuel injection control device (not shown). ) Etc.

Reference numeral 23 is a resistor provided by connecting between the inverting input terminal 22A and output terminal 22C of the differential amplifier 22, and 24A, 24B, 24C and 24D are capacitors connected in parallel with the resistor 23, respectively. The capacitors 24A, 24B, 24C and 24D are set to have different electrostatic capacities C1, C2, C3 and C4.

Reference numerals 25, 25, ... Depict changeover switches as changeover means connected in series to the capacitors 24A, 24B, 24C, 24D, respectively. The changeover switches 25 are, for example, switching elements such as diodes or so-called analog. It is configured as a switch. Each of the change-over switches 25 is connected to a control unit 26, which will be described later, and is opened or closed in response to a control signal from the control unit 26 to select at least one of the capacitors with respect to the resistor 23. Are to be connected.

Reference numeral 26 denotes a control unit as selection control means, which is configured as a microcomputer from an arithmetic processing circuit such as a CPU, a storage circuit such as a ROM or a RAM (none of which is shown), and the like. A memory area 26A is formed in the memory circuit, and in the memory area 26A, the number of revolutions-the number of revolutions-capacitance map 27 as an electrostatic capacity storing means shown in FIG. 3 is stored. Further, the control unit 26 is connected at its input side with a crank angle sensor 28 as a rotational speed detecting means for detecting the engine rotational speed, and at its output side with respective changeover switches 25.

Here, the rotational speed-electrostatic capacity map 27 is a stepwise map of the relationship between the engine rotational speed N and the electrostatic capacity C, as shown in FIG. The capacitance C is gradually reduced as is increased. That is, as an example, when the resistance value R of the resistor 23 is 1 GΩ, the capacitance C1 is 10 nF in the engine speed N range of 0 to 1000 rpm and the engine speed N is 1000 to 2000 rpm. The capacitance C5 of 5 nF, the capacitance C3 of 2.5 nF when the engine speed N is in the range of 2000 to 4000 rpm, and the capacitance C4 of 1.25 nF when the engine speed N is 4000 rpm or more, respectively. It has a capacity of C.

Based on the engine speed N detected by the crank angle sensor 28, the control unit 26 uses the engine speed-electrostatic capacity map 27 to determine a predetermined electrostatic capacity C corresponding to the current engine speed N. Is read out, a control signal is output to the changeover switch 25 connected to the capacitor corresponding to the electrostatic capacitance C, the changeover switch 25 is closed, and a capacitor having a predetermined electrostatic capacitance C is connected to the resistor 23. It is the one to connect.

The combustion pressure detecting device according to the present embodiment has the above-mentioned structure, and its operation will be described below.

First, when the engine body is started, the control unit 26 reads out the electrostatic capacity C1 corresponding to the idling state from the rotational speed-electrostatic capacity map 27 based on the engine rotational speed N from the crank angle sensor 28. By closing the changeover switch 25 connected to the capacitor 24A having this electrostatic capacity C1, the time constant τ1 (= C1R) at idling is set.

When the diaphragm 14 is bent by the combustion pressure of the engine body and the displacement of the diaphragm 14 is transmitted to the piezoelectric body 19 via the pressure receiving rod 16, the piezoelectric body 19 produces a current signal corresponding to the combustion pressure. i is output, and this current signal i is integrated with the time constant τ1 at the time of idling and converted into a voltage signal V.

When the engine speed N exceeds 1000 rpm, the control unit 26 reads the next electrostatic capacity C2 from the rotational speed-electrostatic capacity map 27 and is connected to the capacitor 24B having this electrostatic capacity C2. The changeover switch 25 is closed to set a new time constant τ2 (= C2R), and the current signal i is integrated with this time constant τ2.

Hereinafter, similarly, the control unit 26 detects the engine speed N that sequentially changes according to the running state and the like through the crank angle sensor 28, and the optimum electrostatic speed for the current engine speed N is detected. The capacitance C is read and the time constant τ is adjusted stepwise.

Thus, according to this embodiment, the predetermined electrostatic capacitance C is obtained from the rotational speed-electrostatic capacity map 27 according to the engine rotational speed N detected by the crank angle sensor 28, and the corresponding changeover switch 25 is obtained. Since a control signal is output to and closed to selectively connect only the capacitor having the predetermined electrostatic capacitance C among the capacitors 24A to 24D to the differential amplifier 22. , An optimum time constant τ according to the engine speed N can be obtained.

As a result, even when the engine speed N changes in accordance with the running state or the like, the current signal i from the piezoelectric body 19 can be converted into the voltage signal V with the time constant τ that is optimal for this engine speed, By eliminating the dependence on the number of revolutions, the waveform of the combustion pressure can be accurately reproduced, and the detection accuracy and reliability of the combustion pressure can be greatly improved.

In the above embodiment, the case where the four capacitors 24A to 24D are selectively switched and connected has been described as an example, but the present invention is not limited to this, and may be, for example, two or three. May use five or more capacitors.

Further, in the above-mentioned embodiment, it has been described that four capacitors 24A to 24D corresponding to predetermined electrostatic capacitances C1 to C4 are used and any one of them is selectively connected. Instead of this, for example, four capacitors of 1nF, 2nF, 3nF, and 4nF may be used, and a predetermined capacitance may be obtained by combining the capacitors. In this case, it is possible to obtain 10 kinds of capacitances of 1 to 10 nF with four capacitors.

Further, in the above-described embodiment, the combustion pressure detecting device for transmitting the displacement of the diaphragm 14 to the piezoelectric body 19 through the pressure receiving rod 16 has been described as an example, but the present invention is not limited to this, and for example, the piezoelectric body It can also be used in other combustion pressure detecting devices such as a combustion pressure detecting device in which the body is directly provided on the diaphragm and the displacement of the diaphragm is directly transmitted to the piezoelectric body.

[0033]

[Effect of device]

 As described above in detail, according to the present invention, a predetermined electrostatic capacity is read from the rotational speed-electrostatic capacity storage means according to the engine speed detected by the rotational speed detection means, and a control signal is output to the switching means. By doing so, the capacitor corresponding to this predetermined electrostatic capacity is selectively connected to the resistor, so that it corresponds to the engine speed by the electrostatic capacity of the selected capacitor and the resistance value of the resistor. The optimal time constant can be obtained.

As a result, even if the engine speed of the engine body changes, it is possible to quickly follow this engine speed and convert the current signal from the piezoelectric body into a voltage signal by a differential amplifier or the like. By accurately reproducing the combustion pressure waveform, it is possible to improve detection accuracy and reliability.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a sensor body of a combustion pressure detecting device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a circuit configuration of a combustion pressure detecting device.

FIG. 3 is an explanatory diagram showing a rotation speed-capacitance map stored in a control unit in FIG.

FIG. 4 is a circuit diagram showing a circuit configuration of a combustion pressure detecting device according to a conventional technique.

FIG. 5 is a waveform diagram showing a correlation between a pressure waveform of combustion pressure, a sensor waveform detected by a piezoelectric body, and an output waveform output as a combustion pressure detection signal.

FIG. 6 is a waveform diagram similar to FIG. 5 showing changes in each waveform when the engine speed is increased.

FIG. 7 is a waveform diagram similar to FIG. 5 showing changes in each waveform when the engine speed becomes low.

[Explanation of symbols]

Reference Signs List 19 piezoelectric body 22 differential amplifier 23 resistance 24A to 24D capacitor 25 changeover switch (switching means) 26 control unit (selection control means) 27 rotational speed-electrostatic capacity map (rotational speed-electrostatic capacity storage means) 28 crank angle sensor (Rotation speed detection means)

Front page continued (72) Inventor Masahiko Shimamura 1671, Kasukawa-cho, Isesaki-shi, Gunma Nippon Electric Equipment Co., Ltd. (72) Hideki Ueoka 1671 1 Kasukawa-cho, Isesaki-shi, Gunma Nippon Electric Equipment Co., Ltd.

Claims (1)

[Scope of utility model registration request] 1. A piezoelectric body provided in an engine body for outputting a current signal according to combustion pressure; a differential amplifier having one input side connected to the piezoelectric body and the other input side grounded; A resistor provided between the output side of the dynamic amplifier and the one input side, a plurality of capacitors connected in parallel with the resistor and having different electrostatic capacities, and at least one of the capacitors. Switching means for selectively switching and connecting the condenser and the resistor, and a rotation speed detecting means for detecting an engine speed of the engine body,
A rotation speed-electrostatic capacity storage means that stores the electrostatic capacity with respect to the rotation speed, and a predetermined electrostatic capacity is read from the rotation speed-electrostatic capacity storage means based on the engine speed detected by the rotation speed detection means. A combustion pressure detecting device comprising a selection control means for selecting a capacitor according to the electrostatic capacity by outputting a control signal to the switching means.