JPH04254731A - Pressure sensor - Google Patents

Abstract

PURPOSE:To enable a pressure to be detected highly accurately by preventing a temperature change of a piezo-electric element and a superposition of a pyroelectricity onto a voltage signal. CONSTITUTION:A temperature switch 13 is connected to a heater 11 in series via a lead wire 12 and is formed by a PTC (positive property) type thermistor where its resistance value rapidly changes at the Curie temperature. Also, the Curie temperature of the temperature switch 13 is adjusted to a setting temperature T which is set approximately 5-6 deg.C higher than an average temperature of a piezo-electric body 9 in a constant combustion status within a combustion chamber. The temperature of temperature switch 13 is increased along with that of the piezo-electric body 9 via an upper plate 10. When that temperature reaches the setting temperature T. a current which is fed from a battery to the heater 11 is blocked by increasing the resistance value. thus enabling a heat build-up of the heater 11 to be stopped. Also, when the temperature of the piezo-electric body is decreased below the setting temperature T, the resistance value is reduced for allowing a current from the battery to be fed to the heater 11, thus enabling the piezo-electric body 9 to be retained to the setting temperature T owing to the heat build-up of the heater 11.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor suitable for use as a combustion pressure sensor for detecting combustion pressure in, for example, an automobile engine.

0002

2. Description of the Related Art Generally, a casing, a flat diaphragm provided on the distal end side of the casing and displaced in the axial direction in response to pressure acting on the distal end side of the casing from the outside, and a flat diaphragm provided within the casing. , a pressure receiving rod whose distal end side contacts the diaphragm and is displaced in the axial direction in accordance with the axial displacement of the diaphragm; and a pressure receiving rod provided at the proximal end of the pressure receiving rod and transmitting the pressure of the diaphragm through the pressure receiving rod. A combustion pressure sensor as a pressure sensor comprising a piezoelectric body that outputs displacement in the axial direction as a voltage signal corresponding to the pressure is known, for example, from Japanese Utility Model Application No. 60-535.

[0003] This type of conventional combustion pressure sensor is installed in the engine with the diaphragm facing the combustion chamber of the engine, and receives high pressure (combustion pressure) during combustion with the diaphragm. By applying axial displacement to the piezoelectric body through the pressure receiving rod, the piezoelectric body outputs a voltage signal corresponding to the combustion pressure to a control unit, etc., and the control unit determines the magnitude of the combustion pressure based on this voltage signal. This is then used to control the timing of fuel supply to the engine, ignition timing, etc.

0004

[Problems to be Solved by the Invention] By the way, although the pressure sensor according to the above-mentioned prior art detects the combustion pressure during combustion by being attached to the combustion chamber of the engine, There is a temperature difference between combustion and non-combustion, and this temperature difference causes the temperature of the piezoelectric body to change greatly in a short period of time, so pyroelectricity is generated in the piezoelectric body in response to this temperature change, and this pyroelectricity There is a problem in that the voltage signal is superimposed on the voltage signal of the piezoelectric body, making it impossible to output an accurate voltage signal corresponding to the combustion pressure.

For this reason, in the prior art described above, a temperature sensor such as a thermocouple or a thermistor is provided near the piezoelectric body, the temperature of the piezoelectric body is detected by the temperature sensor, and the control unit performs control based on this detected temperature. Although the detection signal of the piezoelectric body is corrected, the control unit must sequentially correct the voltage signal from the piezoelectric body according to the temperature of the piezoelectric body, which changes greatly in a short time. There is a problem in that the electronic circuit of the control unit, the correction program, etc. become significantly complicated, and the cost of the pressure sensor increases.

The present invention has been made in view of the above-mentioned problems with the prior art, and it is an object of the present invention to provide a pressure sensor that can prevent temperature changes in a piezoelectric body and detect combustion pressure with high accuracy. .

[0007]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the features of the configuration adopted by the present invention include a heater that heats the piezoelectric body by supplying power from a power source, and a heater connected in series with the heater. A temperature switch connected to the piezoelectric body controls the current supplied to the heater according to the temperature of the piezoelectric body to maintain the piezoelectric body at a predetermined temperature.

[0008]

[Operation] With the above configuration, the temperature switch detects the temperature of the piezoelectric body, controls the current supplied from the power supply to the heater according to the detected temperature, and maintains the piezoelectric body at a predetermined temperature.
It is possible to prevent the piezoelectric body from changing in temperature.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to FIGS. 1 to 3, taking as an example the case where the present invention is applied to a combustion pressure sensor for detecting the combustion pressure of an engine.

In the figure, 1 indicates a casing, and 2 indicates a casing body that constitutes the casing 1 together with a diaphragm 3 and an upper cover 4, which will be described later.The casing body 2 has an upper end covered by the upper cover 4. , a large-diameter cylindrical portion 2A that accommodates a contact plate 7, a piezoelectric body 9, etc., which will be described later, and a small-diameter cylindrical portion 2B that is integrally formed on the lower end side of the large-diameter cylindrical portion 2A and accommodates a pressure-receiving rod 5 that will be described later. It is formed into a stepped cylindrical shape, and a diaphragm 3 is integrally provided on the lower end side of the small diameter cylindrical portion 2B. The casing body 2 is attached to a cylinder head (none of which is shown) of the engine body, with the diaphragm 3 facing into the combustion chamber of the engine body.

Reference numeral 3 designates a thin disk-shaped diaphragm integrally formed on the lower end side of the small-diameter cylindrical portion 2B of the casing body 2. When the diaphragm 3 receives the pressure (combustion pressure) in the combustion chamber, it absorbs this pressure. Accordingly, the pressure receiving rod 5 is bent in the axial direction (vertical direction) to displace the pressure receiving rod 5 in the axial direction.

Reference numeral 4 designates a stepped cylindrical upper cover fixed to the upper end side of the large diameter cylindrical portion 2A of the casing body 2 using means such as laser welding. A reduced diameter portion 4A that protrudes upward is formed,
Lead wires 8 and 12, which will be described later, are provided inside the reduced diameter portion 4A and extend upward.

Reference numeral 5 designates a stepped rod-shaped pressure receiving rod that is located inside the small diameter cylindrical portion 2B of the casing body 2 and is displaceable in the axial direction. The upper end side is in contact with the piezoelectric body 9 via a lower plate 6 formed of an insulating material into a disk shape. When the diaphragm 3 is bent in the axial direction due to combustion pressure, the pressure receiving rod 5 is axially displaced within the casing body 2, transmits the displacement of the diaphragm 3 to the piezoelectric body 9 in the axial direction, and This prevents high temperatures from being directly transmitted to the piezoelectric body 9.

Reference numeral 7 denotes a contact plate made of a conductive material provided in the large diameter cylindrical portion 2A of the casing body 2 facing the pressure receiving rod 5, and a disk-shaped contact is provided on the lower end side of the contact plate 7. A portion 7A is formed, the upper surface side of the contact portion 7A contacts a lower electrode 9B of a piezoelectric body 9, which will be described later, and the upper end side of the contact plate 7 extends into the reduced diameter portion 4A of the upper cover 4 to lead. It is caulked and fixed to line 8. The contact plate 7 is configured to transmit a voltage signal from the piezoelectric body 9 to a control unit 18, which will be described later, via a lead wire 8.

Reference numeral 9 denotes a piezoelectric body formed in a cylindrical shape from a piezoelectric material such as lead titanate, which is located inside the large-diameter cylindrical portion 2A of the casing body 2 and provided above the pressure receiving rod 5. On the upper and lower surfaces of the piezoelectric body 9, sheet-like upper electrodes 9A and lower electrodes 9B made of conductive paste or the like are formed. Further, the upper electrode 9A of the piezoelectric body 9 is grounded to the casing body 2 via the disc-shaped upper plate 10 made of a conductive material, and the lower electrode 9B is in contact with the contact portion 7A of the contact plate 7. and are electrically connected. Then, when the diaphragm 3 is bent in the axial direction, the pressure receiving rod 5 is displaced in the axial direction, and the piezoelectric body 9 is pressed in the axial direction by the pressure receiving rod 5, compressive strain occurs and electric charge is generated. The charge (voltage signal) is outputted from each electrode 9A, 9B to the control unit 18 via the contact plate 7, lead wire 8, etc. as a combustion pressure detection signal corresponding to the combustion pressure.

Reference numeral 11 indicates a heater fitted on the inner circumferential side of the piezoelectric body 9. The heater is formed into a cylindrical shape by winding, for example, a nichrome wire, and the outside of the nichrome wire is made of an insulating material such as ceramic. It is coated. Then, the heater 1
1 is connected to a battery 16 (described later) via a lead wire 12 consisting of a positive lead wire 12A and a negative lead wire 12B as shown in FIG. 2, and generates heat in response to the current supplied from the battery 16. The piezoelectric body 9 is heated.

Reference numeral 13 indicates a temperature switch placed on the upper surface side of the upper plate 10 and connected in series with the heater 11 via the lead wire 12. The temperature switch 13 has a Curie temperature as shown in FIG. It is formed into a short cylindrical shape from a PTC (positive characteristic) type thermistor or the like whose resistance value changes rapidly between resistance values Ra and Rb, and the outside thereof is covered with a conductive metal material. In addition, the temperature switch 1
3 is connected in series with the heater 11 via a lead wire 12, and its Curie temperature is set approximately 5 to 6 degrees Celsius higher than the average temperature of the piezoelectric body 9 in the steady combustion state of the combustion chamber (for example, about 145 to 150 degrees Celsius). The temperature is adjusted to a set temperature T as a predetermined temperature. The temperature switch 13 is
The temperature rises together with the piezoelectric body 9 via the upper plate 10,
When the temperature reaches the set temperature T, the resistance value is rapidly increased from the resistance value Ra to the resistance value Rb, and the current supplied from the battery 16 to the heater 11 is cut off (off state),
When the temperature of the piezoelectric body 9 decreases below the set temperature T, the resistance value is decreased from the resistance value Rb to the resistance value Ra, and the current from the battery 16 is allowed to be supplied to the heater 11 (on state). It is something.

Reference numeral 14 indicates a set screw screwed into the large diameter cylindrical portion 2A of the casing body 2, and the set screw 14 is in contact with the upper surface side of the temperature switch 13 via a washer 15. The set screw 14 presses the piezoelectric body 9 from above with a predetermined load via the washer 15, the temperature switch 13, and the upper plate 10, and fixes the piezoelectric body 9 etc. within the casing body 2. There is.

Reference numeral 16 indicates a battery as a power source mounted on the vehicle, and reference numeral 17 indicates a relay located between the battery 16 and the temperature switch 13 and provided in the middle of the positive lead wire 12A. For example, driving an engine,
It is designed to open and close in conjunction with an ignition switch (not shown) that is turned off.

Reference numeral 18 denotes a control unit configured as a microcomputer including a CPU and the like, and a piezoelectric body 9 is connected to the input side of the control unit 18 via a lead wire 8. When the ignition switch is turned on, the control unit 18 reads the combustion pressure detection signal from the piezoelectric body 9, determines the magnitude of this combustion pressure, and controls the timing of fuel supply to the engine, ignition timing, etc. It is.

The pressure sensor according to this embodiment has the above-mentioned configuration, and its operation will be explained next.

First, when the ignition switch is turned on and the air-fuel mixture in the combustion chamber is ignited, the diaphragm 3 receives this combustion pressure and bends in the axial direction, and the pressure receiving rod 5 is displaced in the axial direction and the piezoelectric body 9 Press in the axial direction. As a result, the piezoelectric body 9 generates an electric charge (voltage) corresponding to the pressure applied from the pressure receiving rod 5, and uses this voltage signal as a combustion pressure detection signal to the control unit via the contact plate 7, lead wire 8, etc. Output to 18. Further, when the ignition switch is turned on, the relay 17 is closed and current from the battery 16 is supplied to the heater 11.

On the other hand, when the temperature of the piezoelectric body 9 is low and the temperature of the temperature switch 13 is lower than the set temperature T, the temperature switch 13 has a low resistance value Ra, so that the current from the battery 16 flows through the heater. As a result, the heater 11 generates heat and heats the piezoelectric body 9.

Then, when the piezoelectric body 1 is heated and the temperature of the temperature switch 13 reaches the set temperature T, the resistance value of the temperature switch 13 rapidly increases from the resistance value Ra to the resistance value Rb, and the battery 16 The current supplied to the heater 11 from the heater 11 is cut off to stop the heater 11 from generating heat.

Thus, according to this embodiment, the temperature switch 13 changes its resistance value between the resistance values Ra and Rb depending on the temperature of the piezoelectric body 9, and this resistance value change causes the heater to be removed from the battery 16. It is possible to control the current supplied to the piezoelectric body 9 by controlling the heat generation of the heater 11.
can be maintained at the set temperature T. As a result, temperature changes in the piezoelectric body 9 can be prevented, and pyroelectricity caused by temperature changes can be effectively prevented from being superimposed on the combustion pressure detection signal output from the piezoelectric body 9, and the combustion pressure in the combustion chamber can be maintained for a long time. can be detected accurately over the entire range. Furthermore, since the pressure sensor according to this embodiment controls the current supplied to the heater 11 by the temperature switch 13 without going through the control unit 18, the program and electronic circuit of the control unit 18 can be simplified and costs can be reduced. can be significantly reduced.

In the above embodiment, the heater 11 was described as having a cylindrical shape formed by winding a nichrome wire, but instead of this, other heaters such as a film heater may be used. .

Furthermore, in the above embodiment, the temperature switch 13
has been described as a short cylindrical thermistor of the PTC (positive characteristic) type, whose resistance value changes rapidly between resistance values Ra and Rb at the Curie temperature, but instead of this, a bimetallic Other temperature switches may also be used.

Further, in the above embodiments, the case where the pressure sensor is used as a combustion pressure sensor has been described as an example, but the present invention is not limited to this, and the present invention is not limited to this, but can be applied to gases such as air, industrial gas, fuel, water, etc. It can also be applied to pressure sensors that detect the pressure of liquids such as.

[0029]

As detailed above, according to the present invention, there is provided a heater that heats a piezoelectric body by supplying power from a power source, and a heater that is connected in series with the heater and supplies power to the heater according to the temperature of the piezoelectric body. Since a temperature switch is provided to control the current flowing through the piezoelectric body and maintain the piezoelectric body at a predetermined temperature, it is possible to prevent the temperature of the piezoelectric body from changing and to prevent pyroelectricity from being superimposed on the voltage signal output from the piezoelectric body. It is possible to effectively prevent external pressure and accurately detect external pressure over a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a pressure sensor showing an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram showing a circuit of a pressure sensor.

FIG. 3 is a characteristic diagram showing the relationship between temperature and resistance value of a temperature switch.

[Explanation of symbols]

1 Casing 3 Diaphragm 5 Pressure receiving rod 9 Piezoelectric body 11 Heater 13 Temperature switch 16 Battery (power supply)

Claims (1)

[Claims] 1. A casing, a diaphragm disposed at one end of the casing and displaced in response to pressure applied from the outside to the one end of the casing, and a diaphragm disposed within the casing such that its tip side abuts the diaphragm. a pressure receiving rod, and a piezoelectric body located within the casing and provided on the proximal end side of the pressure receiving rod, and outputting the displacement of the diaphragm transmitted via the pressure receiving rod as a voltage signal corresponding to the pressure. In the pressure sensor, the casing includes a heater that heats the piezoelectric body by supplying power from a power source, and a heater that is connected in series with the heater and that supplies current to the heater according to the temperature of the piezoelectric body. A pressure sensor comprising a temperature switch that controls the piezoelectric body and maintains the piezoelectric body at a predetermined temperature.