JPH0992104A - pressure switch - Google Patents

Abstract

(57) [Abstract] [Purpose] To improve the reliability of the pressure sensor by reducing the change in the relative position of the permanent magnet and the reed switch due to the change in the ambient temperature of the pressure sensor mounted on the vehicle. And [Structure] Focusing on the thermal expansion coefficient between the resin material of the operating rod that holds the permanent magnet and the resin material of the housing that positions and positions the reed switch at the top, the thermal expansion coefficient of the operating rod is set to the thermal expansion coefficient of the housing. A resin material that is larger than the coefficient was used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure switch.

[0002]

2. Description of the Related Art Conventionally, there is known a pressure switch for switching on and off according to the pressure of fluid such as intake and exhaust of a hydraulic circuit or an internal combustion engine.

A general pressure switch will be described with reference to FIG. A base housing 2 having a recess 1 and an upper housing 4 containing an actuating rod 3 are joined together to form a pressure switch housing 5. The base housing 2, the operating rod 3, and the upper housing 4 are made of a resin material such as PBT (polybutylene terephthalate). At the joint between the base housing 2 and the upper housing 4, a diaphragm 6 fixed so as to cover the outer peripheral portion of the operating rod 3 is urged upward by a spring 17 to be arranged in the upper part of the drawing. The diaphragm 6 divides the inside of the housing 5 into an upper atmosphere chamber 7 and a lower pressure chamber 8 which are vertically divided into two parts. A fluid from an engine (not shown) is introduced into the pressure chamber 8 from a fluid introduction passage 9 provided in the base housing 2. On the other hand, in the atmosphere chamber 7, the tubular portion 10 of the operating rod 3 extends outside the boss portion 11 of the upper housing 4, and a ring-shaped permanent magnet is provided at the tip of the tubular portion 10 of the operating rod 3. 12 is fixed. A reed switch 13, which is on / off controlled by a permanent magnet 12, is arranged on the inner peripheral portion of the boss portion 11 of the upper housing 4. The reed switch 13 is mounted on the upper portion of the upper housing 4 by a mounting portion 16
It is attached and positioned by.

In the pressure switch having such a structure, the pressure (negative pressure) of the fluid introduced into the pressure chamber 8 through the fluid introduction passage 9 is set.
Acts on the diaphragm 6 and the operating rod 3, and this pressure (negative pressure) moves the operating rod 3 downward in the figure against the biasing force of the spring 17. Along with this, the permanent magnet 12 fixed to the tubular portion 10 of the operating rod 3 also descends, and the magnetic force of the permanent magnet 12 causes the reed switch 13 to move.
Then, the electrodes 14 and 15 are opened to turn off the reed switch 13. Further, when the pressure (negative pressure) of the fluid introduced into the pressure chamber 8 via the fluid introduction passage 9 becomes close to the atmospheric pressure, the operating rod 3 moves upward in the drawing. At this time, the permanent magnet 12 fixed to the tubular portion 10 of the operating rod 3 rises, so that the electrodes 14 and 15 of the reed switch 13 are connected and the reed switch 13 is switched on. That is, the reed switch 13 is turned off when the fluid pressure in the pressure chamber 8 reaches the preset pressure (negative pressure), and is turned on when the fluid pressure is closer to the atmospheric pressure side than the preset pressure (negative pressure). 8 can detect the magnitude of the fluid pressure.

[0005]

When the pressure switch having the above structure is used in an engine room of an automobile or the like,
Consideration should be given to the case where a car runs in an extremely cold area or in a scorching desert area. In the pressure switch, the operating rod 3 holding the permanent magnet 12 is fixed to the diaphragm 6, and the reed switch 13 is fixed to the boss portion 11 of the upper housing 4, so that the operating rod 3 is affected by the difference in ambient temperature. And the upper housing 4 have different lengths, the relative positions of the permanent magnet 12 and the reed switch 13 may change. More specifically, the position of the diaphragm 6 serving as the mounting surface is used as the reference surface, and the length from the reference surface to the mounting portion 16 of the upper housing 4 for fixing the reed switch (the length indicated by A in FIG. 1) and the reference surface From the central part of the permanent magnet 12 attached to the operating rod 3 (B in FIG. 1).
The length indicated by is different. Therefore, even if this pressure switch is adjusted to turn off the reed switch 13 at a predetermined pressure in the pressure chamber 8 at room temperature, when it is used in a place where the ambient temperature is high, the expansion due to heat is the amount by which the length A increases. However, since the length of B becomes larger than the amount of extension, the distance between the permanent magnet 12 and the reed switch 13 becomes larger than the distance adjusted in advance. Therefore, before the pressure in the pressure chamber 8 reaches a predetermined pressure, the permanent magnet 12 descends to the switching position of the reed switch 13, and the reed switch 13 is switched off.

Therefore, the present invention is intended to solve the above problems, and an object of the present invention is to provide a pressure switch having a simple structure, low cost, and stable operation even when the operating environment is changed. To do.

[0007]

In order to solve the above-mentioned problems, in the first invention, a diaphragm which is mounted inside a housing made of a resin material and divides the inside of the housing into an atmospheric chamber and a pressure chamber, and a permanent member. Positioned by the working rod that holds the magnet and is fixed to the atmosphere chamber side of the diaphragm and moves up and down in the housing, and by the upper part of the housing that is farther from the diaphragm than the permanent magnet, the working rod moves the diaphragm by the pressure of the fluid in the pressure chamber. In the pressure sensor composed of a reed switch that is turned on / off by moving through, the resin material of the operating rod is made of a resin material having a thermal expansion coefficient larger than that of the resin material of the housing. By combining the operating rod, which is the member of the pressure sensor, and the resin material of the housing in this way, even if the atmospheric temperature of the pressure sensor rises, it operates more than the housing due to the difference in the coefficient of thermal expansion based on the diaphragm position. The elongation of the rod can be increased and the difference in thermal expansion due to the difference in length of the member can be absorbed.

In the second aspect of the invention, the operating rod is made of PBT (polybutylene terephthalate) and the housing is made of PPS (polyphenylene sulfide). PBT and PPS are both toughness at room temperature,
By using a PBT material having excellent rigidity and a large thermal expansion coefficient for the operating rod and a PPS material having a small thermal expansion coefficient for the housing, even if the atmospheric temperature of the pressure sensor rises, Due to the difference, the extension of the operating rod can be made larger than that of the housing.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the following table which summarizes data together with comparative examples.

[0010]

[Table 1]

Table 1 shows the ambient temperature from -10 ° C to 120 ° C.
The change in dimensions of C and D shown in FIG. 1 when the temperature was changed to ℃ was measured by appropriately changing the material of the upper housing 4 of the pressure sensor and the material of the operating rod 3 with PPS and PBT. . However, in this experiment, for convenience of measuring the length, the C dimension is adopted instead of the A dimension shown in FIG. 1, and the D dimension is adopted instead of the B dimension. The relative position change indicates the absolute value of the numerical value obtained by subtracting the D dimension change amount from the C dimension change amount.

The C and D dimensions are each 18 m.
The experiment was carried out using a m and 7.5 mm one.

As is apparent from Table 1, PPS material is used for the upper housing 4, which is a new product, and P is used for the operating rod 3.
It is clear that the one using BT has a smaller change in relative position than the one using PPS material and PBT material in each of the upper housing 4 and the operating rod 3.

In order to eliminate the change in the relative position,
Logically, the ratio of the length of the A dimension to the length of the B dimension should be equal to the ratio of the coefficient of thermal expansion of the resin material used for the upper housing 4 and the coefficient of thermal expansion of the resin material used for the operating rod 3. It can be solved by selecting a resin material. However, when selecting a resin material, it is necessary to consider not only the coefficient of thermal expansion but also various physical properties and characteristics according to the application. It is difficult to select.

[0015]

According to the first aspect of the invention, the resin material of the actuating rod holding the permanent magnet has a larger thermal expansion coefficient than the resin material of the housing holding the reed switch. Even if the length of the operating rod changes, the relative position of the permanent magnet and the magnet can be changed less, and even if the pressure switch is operated in a place where the ambient temperature changes drastically, the fluid pressure must not reach the specified pressure. For example, it is possible to provide a highly reliable pressure switch that can switch the reed switch on and off.

According to the second aspect of the invention, the operating rod is a PBT.
And the housing is made of PPS,
Due to the difference in the thermal expansion coefficient between PBT and PPS, it is possible to suppress the relative change between the reed switch and the magnet due to the change in the ambient temperature, and it is possible to provide a highly reliable pressure switch having excellent toughness and rigidity.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a pressure switch used in an experiment of a conventional technique and an embodiment of the present invention.

[Explanation of symbols]

 2 Base housing 3 Actuating rod 4 Upper housing 6 Diaphragm 7 Atmosphere chamber 8 Pressure chamber 12 Permanent magnet 13 Reed switch

Claims (2)

[Claims] 1. A diaphragm, which is mounted inside a housing made of a resin material and divides the inside of the housing into an atmospheric chamber and a pressure chamber, holds a permanent magnet, and is fixed to the atmospheric chamber side of the diaphragm to fix the inside of the housing. Positioned at the upper part of the housing, which is farther from the diaphragm than the actuating rod that moves up and down, and the actuating rod is turned on and off by moving through the diaphragm by the pressure of the fluid in the pressure chamber. A pressure sensor including a reed switch, wherein the resin material of the operating rod is made of a resin material having a thermal expansion coefficient larger than that of the resin material of the housing. 2. The pressure sensor according to claim 1, wherein the actuating rod is made of PBT and the housing is made of PPS.