JPH1054773A - Pressure measuring sensor usable in high temperature environment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure sensor capable of easily measuring pressure, which is very compact, light in weight and has a simple construction, high durability, and low in price, and requiring no additional device such as cooling device even in s high temperature environment. SOLUTION: This pressure sensor can directly measure combustion pressure P of an internal combustion engine generated by burning fuel mixture of gasificated gas at a high temperature of 1000 deg.C or higher without additional device such as cooling device and output a charge signal which is in proportion to the pressure at speed of 1μs, so that the signal is converted into a voltage signal by a charge amplifier and it signal value is read out by an induced unit Pa of the pressure and at the same time combustion waveform for determining condition of combustion (normal or abnormal) can be monitored by a self diagnostic system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

Since the sensor according to the present invention can be used at high temperatures, it can be used directly in the combustion chambers of various internal combustion engines and used as a pressure sensor for constantly measuring the combustion pressure generated during combustion. The following items can be controlled and detected. 1. Knock detection (comparison between normal combustion waveform and abnormal combustion monitor). 2. EGR (exhaust gas recirculation) control. 3. MBT (minimum advance electrical position for maximum torque) control. 4. Misfire detection (idling, engine braking). 5. Optimal mixture ratio control (lean burn control by immediate detection of torque fluctuation). 6. Exhaust gas measures. In addition to the use in an internal combustion engine, the pressure fluctuation state at a high temperature in a nuclear reactor can be directly measured without cooling a sensor.

[0002]

2. Description of the Related Art Conventionally, in order to measure pressure or force, a sensor itself is deformed by an applied mechanical load, and a so-called strain gauge for measuring an amount of the deformation, and a mechanical load is applied to a piezoelectric element to charge the piezoelectric element. Is used. In general, the former can be said to be suitable for a state where pressure or force changes slowly, that is, static measurement, and the latter is suitable for a state where pressure or force changes rapidly, ie, measurement of a continuous dynamic pressure peak. However, in both cases, the operating temperature range is limited, and particularly the operating temperature limit in the high temperature range of the piezoelectric sensor is determined by being restricted by the Curie point of the piezoelectric element itself. Usually, because of the following ranges, the sensor itself cannot be used by directly mounting it in the combustion chamber at present.

[0003]

The measurement of pressure or force in a normal temperature range by a piezoelectric sensor is often used because of excellent characteristics such as no displacement of the sensor itself, fast response speed and small size. You. However, since the sensor cannot be used beyond the Curie temperature of the sensor element, the air-fuel mixture explodes in the combustion chamber of the internal combustion engine.
The purpose of directly measuring pressure (combustion pressure) fluctuations at high temperatures exceeding 0 ° C. cannot be achieved. In this case, as a countermeasure, use a water-cooled adapter to cool the area around the pressure sensor, or install the pressure sensor in a place with a low temperature, connect the combustion chamber to the sensor with an inlet pipe, and reduce the pressure generated after lowering the temperature. A method of detecting a peak is employed. A drawback in these methods is that the water-cooled system can be used when testing the internal combustion engine on the floor due to the large size of the apparatus, but it is extremely difficult to use it in a vehicle. In addition, the method of connecting the combustion chamber to the sensor with a pressure introducing pipe has defects such as a delay in response, and the inability to perform accurate measurement due to carbon or the like adhering to the inside of the introducing pipe due to long-term use.

[0004]

In order to directly measure the state of a pressure peak generated in a combustion chamber of an internal combustion engine, it is desirable to install a pressure sensor in the combustion chamber. However, since the temperature at which the air-fuel mixture burns in the combustion chamber exceeds 1000 ° C., the sensor itself must be able to withstand high temperatures. Conventionally, the Curie point (or temperature) of a single crystal material such as quartz, lead zirconate titanate, or titanic acid, which is generally used as a piezoelectric element, is 320 to 550.
As low as ° C. The Curie point is different from the melting temperature or melting point of the substance, and refers to the temperature at which the crystal state changes due to the applied temperature and the piezoelectric effect cannot be obtained. Naturally, the high temperature generated when the air-fuel mixture burns in the combustion chamber Cannot be used inside. In the present invention, lithium niobate (LiNbO ₃ ) having a very high Curie point or langasite (La ₃ Ga ₅ Si) having no Curie point is used.
O ₁₄ ) A pressure peak generated in a combustion chamber is directly measured by using a single crystal material for a piezoelectric element. The melting point and Curie point of each single crystal material are shown below. Generally, of the three crystallographic axes X, Y, and Z of a single crystal material, two of X and Y are called electrical axes, and Z is called an optical axis. The single crystal material generates an electric charge due to a piezoelectric effect of the single crystal material under a given mechanical load. Specifically, when a mechanical load is applied in the X-axis direction with respect to the Y-axis of the crystal, the single crystal material has a Y-axis. Electric charges are generated on both sides of the axis (vertical axis effect). Similarly, when a mechanical load is applied to the X axis in the direction of the Y axis, electric charges are generated on both sides of the X axis (horizontal axis effect). FIG.
Indicates the direction in which a mechanical load F is applied to the single crystal piezoelectric element 1 cut along the crystallographic axis X and the electric charge q generated on the piezoelectric element. That is, in FIG.
Acts on the piezoelectric element 1 as a compressive force (positive direction) + F, and if a charge of positive polarity + q appears on one surface of the element, a negative polarity −q is applied on the surface on the opposite side (back side) of the element. Shows the state where appears. FIG. 2 shows that the polarity of the charge generated on the piezoelectric element when the mechanical load F acts in the pulling direction (negative direction) -F is reversed and appears at -q, and at the same time, the surface on the opposite side (back side). Shows a state where a positive polarity + q appears. Next, the nominal sensitivity in the vertical axis effect of the single crystal material used in the present invention is shown. For comparison, the nominal sensitivity in the vertical axis effect of a quartz crystal conventionally used as a piezoelectric element is shown. That is, in the vertical axis effect, the electric charge q appears on the surface of the loaded piezoelectric element in direct proportion to the total applied mechanical load, and its amount is independent of the size and shape of the piezoelectric element.
In lithium niobate (LiNbO ₃ ), a charge of 6 pico-coulombs appears per newton, in langasite (La ₃ Ga ₅ SiO ₁₄ ), a charge of 4 pico-coulombs appears per newton, and in the case of quartz, 2 pico-coulombs appear. Generates picocoulomb charges. FIG. 3 shows a basic configuration of the single crystal piezoelectric element sensor for pressure detection according to the present invention. That is, in FIG. 3, two single-crystal piezoelectric elements 1, an electrode 2 sandwiched between two single-crystal piezoelectric elements to extract a charge signal, a diaphragm 3 for transmitting force or pressure to the piezoelectric element, a piezoelectric element, and an insulating element A housing 5 containing the material 4 so that the entire sensor can be screwed into a cylinder head portion of the internal combustion engine.
The single-crystal piezoelectric element sensor for pressure detection according to the present invention arranges two single-crystal piezoelectric elements 1 in the direction in which a mechanical load acts as shown in FIG. 3, and transmits the pressure fluctuation due to combustion to the piezoelectric element by the diaphragm 3. It is characterized in that a charge signal is generated and the charge signal is taken out by the electrode 2.

[0005]

[Function] A piezoelectric sensor deforms the crystal of the element when a mechanical load acts on the piezoelectric element, and charges electric energy in accordance with the amount of deformation of the element surface. (N, Pa, Kgf, etc.) in principle, but it is difficult to directly handle the charged electric energy. In practice, it is converted into a voltage signal that can be easily handled through a charge amplifier. There must be. In order to prevent the discharge of the charged electric charge, the insulation resistance of each element constituting the whole system such as the sensor element itself, the sensor housing, the electric connector, and the connection cable leading to the charge amplifier must be kept high.
FIG. 4 shows a configuration of a single crystal piezoelectric element sensor for pressure detection and a charge amplifier according to the present invention. The two single-crystal piezoelectric elements 1 face each other with the same polarities of the charges to be charged facing each other, so that twice the charge sensitivity (2 × q) with respect to the same mechanical load can be obtained. When a mechanical load is applied, the surface of the piezoelectric element 1 is charged in an amount directly proportional to the mechanical load. The charged electric charge is once stored in the capacitor 6 and then discharged through the fixed resistor 7. In this case, whether the stored charge is positive (+) or negative (-) depends on whether the mechanical load acting on the element is in the positive pressure (compression) direction or the negative pressure (pull) direction. It is determined. The time constant of the circuit is determined by the electric capacity of the capacitor 6 and the electric resistance of the fixed resistor 7, and the discharge time is accordingly determined.
Reference numeral 8 in FIG. 4 denotes a Mos transistor, which converts the charge energy stored in the capacitor 6 into an electric quantity and outputs it as an easily handled analog voltage. The single-crystal piezoelectric element sensor for pressure detection according to the present invention is connected to the charge amplifier described above, so that a reference pressure is applied to the piezoelectric element sensor, and the electric signal output according to the reference pressure is adjusted. Can be calibrated by the reference pressure. Therefore, if this pressure sensor is directly attached to the combustion chamber, fluctuations in pressure due to combustion can be converted into electric signals that are directly proportional to the pressure and output, so measurement is performed using the value of each induction unit such as MPa or bar. it can.

[0006]

FIG. 5 shows a pressure sensor according to the present invention mounted in a combustion chamber 10 of a cylinder head 9 of an internal combustion engine.
The pressure sensor according to the present invention uses a piezoelectric element having a very high Curie point or having no phase transition, thereby exposing the pressure-sensitive portion, that is, the diaphragm 3 of the pressure sensor into the combustion chamber 10 from the cylinder head 9 as shown in FIG. The operation can be performed in a state where the pressure is applied, and the pressure load P generated at the time of combustion can be directly transmitted to the piezoelectric element. This configuration has the advantages that the change in mechanical load is transmitted through an extremely short vibration system, so that the resonance frequency of the sensor itself is high, the response speed is fast, and a wide dynamic range can be obtained. Therefore, it is possible to accurately measure the pressure peak, monitor the combustion waveform, and determine the torque fluctuation. As for the mechanical load generated in the combustion chamber 10 and applied to the pressure sensor, the pressure load P due to combustion is considered to be the largest, but a large combustion pressure is not generated during idling rotation, rotation during engine braking, and the like. It is difficult to distinguish from pressure fluctuations that occur during exhaust. Therefore, in order to accurately measure only the pressure fluctuation due to combustion, this system measures the rotation angle of the crankshaft, and rotates the rotation angle detection rotary so that the charge amplifier circuit is reset and the combustion pressure signal is read at a specific angle. An encoder 11 is provided to output an operation signal.

[0007]

The pressure sensor according to the present invention is extremely small and lightweight, has a simple structure, is durable, is inexpensive, and can easily measure pressure even in a high temperature environment without requiring additional equipment such as cooling. It is characterized by. The mechanical strength or pressure resistance of the single-crystal piezoelectric element for pressure detection used here is 150 bar for an area of 10 mm ² of the element, and this value corresponds to the combustion pressure in an engine with a displacement of about 2,000 cc normally. I do. Therefore, this pressure sensor can be downsized. In particular, the screw outer diameter of the mounting portion can be equivalent to M10. In actual use, the sensor can be mounted only by machining a screw hole of about M10 in the cylinder head portion of the engine. Therefore, the measurement of the combustion pressure in the combustion chamber of the internal combustion engine and the monitoring of the combustion waveform can be performed while the vehicle is mounted on the vehicle. Since the pressure sensor according to the present invention can monitor the combustion waveform simultaneously with the measurement of the combustion pressure, this function can be used as knocking detection. That is, knocking is a state in which the ignition timing does not follow the torque fluctuation accompanying the load fluctuation, abnormal combustion occurs in the combustion chamber, and the entire engine abnormally vibrates. In the conventional knock detection, abnormal vibration is detected by an acceleration sensor. However, since the engine itself constantly generates vibrations such as rotation of the crankshaft and camshaft, opening and closing of valves (valve driving vibration), intake, explosion, exhaust, etc., the acceleration sensor detects only abnormal vibration due to abnormal combustion. It is difficult. Generally, a rotation angle encoder is mounted on a crankshaft to receive a signal from an acceleration sensor at a timing when the crankshaft angle enters a stroke of explosion. Since the pressure sensor according to the present invention can directly monitor the combustion waveform, it detects abnormal combustion due to torque fluctuation as an abnormality in the combustion waveform. In particular, in a lean-burn internal combustion engine with the aim of conserving energy, torque fluctuations are directly detected using a combustion pressure sensor, and MBT (minimum advance electrical position for maximum torque) control for lean combustion limit is performed. It can be done easily. It is necessary to cope with an increase in the displacement or an increase in the mechanical load (increase in the combustion pressure) such as an internal combustion engine with a feeder by increasing the element area, that is, increasing the size of the combustion pressure sensor.

[Brief description of the drawings]

FIG. 1 shows electric charges generated on the element surface when a mechanical load (+ F) in a compression direction acts on a single crystal piezoelectric element 1 and its polarity + q. + X, + Y, + Z indicate the orientation of the crystal.

FIG. 2 shows electric charges generated on the element surface when a mechanical load (−F) in a tensile direction acts on the single crystal piezoelectric element 1 and its polarity −q. + X, + Y, + Z indicate the orientation of the crystal.

FIG. 3 shows a configuration of a single crystal piezoelectric element 1, a metal thin film electrode 2 for extracting electric charge q, and a sensor housing 3 in the present invention. In this configuration, the two single-crystal piezoelectric elements 1 face each other (one pair = one pair) and the metal thin-film electrode 2 is interposed therebetween, so that a mechanical load (+ F) in the compression direction acts. In this case, the charge q generated on each element surface can be taken out with twice the charge sensitivity.
That is, if 2x-q is printed on the metal thin-film electrode 2, 2x + q is printed on the sensor housing 3.

FIG. 4 shows a single-crystal piezoelectric element sensor 1 for pressure detection according to the present invention.
1 shows a configuration of a charge amplifier that takes out charges generated by two pairs (one pair = one pair) and electrodes 2 and converts them into analog signal voltages that are easy to handle. The charge amplifier is capacitor 6,
It is composed of a fixed resistor 7 and a Mos transistor 8. The figure shows a state in which a positive pressure + F is applied to the piezoelectric element sensor 1 and charges 2x−q are charged to the electrodes 2.

FIG. 5 shows a state in which a pressure sensor is attached to a combustion chamber 10 of a cylinder head 9 of an internal combustion engine, and a combustion pressure and combustion waveform detection system provided with a rotary encoder 10 for detecting a rotation angle on a crankshaft. In the combustion chamber 10 of the cylinder head 9, the combustion pressure load P
Occurs, the piston 12 and the diaphragm 3 of the pressure sensor
Shows a state in which the pressure of + F acts on.

[Description of sign]

DESCRIPTION OF SYMBOLS 1 Single crystal piezoelectric element 2 Electrode 3 Diaphragm 4 Insulation material 5 Housing 6 Capacitor 7 Fixed resistance 8 Mos transistor 9 Cylinder head of internal combustion engine 10 Combustion chamber 11 Encoder for rotation angle detection 12 Piston + F Mechanical load in compression direction (this -F mechanical state in the tensile direction (mainly pressure)
+ Q Charge with positive polarity -q Charge with negative polarity P Combustion pressure load generated by combustion of air-fuel mixture

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[Procedure amendment]

[Submission date] July 15, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Fig. 6

[Correction method] Added

[Correction contents]

FIG. 6 shows a mechanical load (+
The state of the charge generated on the side surface of the element and the polarity + q thereof and the polarity -q of the charge generated on the opposite surface when F) acts are shown. Scientifically, it is called a piezoelectric phenomenon due to the horizontal axis effect. + X, + Y, + Z indicate the orientation of the crystal. 1 and 2 refer to a piezoelectric effect due to the vertical axis effect, in which charge appears on the surface of the device in direct proportion to the total applied mechanical load, and the amount of charge (nominal charge sensitivity) is the size and shape of the device. 6 pC / N for lithium niobate,
In Langasite it is 4 pC / N. On the other hand, unlike the vertical axis effect, the charge sensitivity due to the horizontal axis effect is related to the size and shape of the element and depends on the ratio of the Y dimension to the X dimension. Generally, the charge sensitivity of the horizontal axis effect is 50 times greater than that of the vertical axis effect.
Double or more is obtained.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] Fig. 7

[Correction method] Added

[Correction contents]

FIG. 7 shows the relationship between the electric charge generated on the side surface of the piezoelectric element 1 when a mechanical load (−F) is applied to the piezoelectric element 1 and its polarity −q and the polarity + q of the electric charge generated on the opposite side surface. Indicates the status. In academic terms, it is called a piezoelectric phenomenon due to the horizontal axis effect. + X, + Y, + Z indicate the orientation of the crystal.

[Procedure amendment 4]

[Document name to be amended] Drawing

[Correction target item name] Fig. 6

[Correction method] Added

[Correction contents]

FIG. 6

[Procedure amendment 5]

[Document name to be amended] Drawing

[Correction target item name] Fig. 7

[Correction method] Added

[Correction contents]

FIG. 7

Claims (2)

[Claims] 1. A lithium niobate (LiNbO ₃ ) or langasite (La ₃ G _a5 SiO ₁₄ ) characterized by having a very high Curie point or no Curie point until the melting point of the substance is reached. Is cut along the crystallographic coordinate axis X,
A piezoelectric element formed in a chip shape having two correctly parallel surfaces. 2. A machine such as pressure or force is applied to the surface of a piezoelectric element formed by cutting a single crystal material such as lithium niobate (LiNbO ₃ ) or langasite (La ₃ Ga ₅ SiO ₁₄ ) in accordance with a coordinate axis X. When a mechanical load is applied, the charge is printed in direct proportion to the total applied mechanical load. When a mechanical load in the positive direction (load in the compression direction) is applied to both surfaces of the parallel piezoelectric element, if a positive charge is generated on one surface, a negative charge appears on the opposite parallel surface,
Conversely, when a mechanical load in the negative direction (pulling direction) is applied, the polarity is inverted and a negative charge appears, and a positive charge is printed on the opposite surface. Using this characteristic, the piezoelectric elements are aligned in the direction in which a mechanical load acts, and when a mechanical load is applied within the Curie point or melting point of these single-crystal electronic materials, the amount of charge and polarity generated there are measured. A pressure or force sensor that converts the magnitude and direction of a mechanical load into various induction units such as Newton (N), Pascal (Pa), or Kgf.