Electricity: circuit makers and breakers – Fluid pressure – Piston
Patent
1998-11-02
1999-11-23
Friedhofer, Michael
Electricity: circuit makers and breakers
Fluid pressure
Piston
73745, H01H 3538
Patent
active
059904283
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a pressure switch for a hydraulic pump, and in particular relates to improvements to a pressure switch of a vane pump which is most suitably used as an oil pressure source for vehicle power steering devices.
BACKGROUND TECHNIQUE
Conventionally, vehicles such as automobiles are provided with a power steering device using oil pressure. A vane pump is used as an oil pressure source for such power steering devices.
In an engine functioning as a drive source for such a vane pump, there is a possibility of stalling due to load rise caused by steering when idling. In order to prevent this, a pressure switch is used to detect the variation of discharge pressure (supply pressure) due to steering when idling and to increase the idle rotation speed of the engine. An example of such a pressure switch is shown in FIG. 9.
An electrically grounded body 100 of this pressure switch houses a vane pump cartridge. A depression 100A in the body 100 is connected to a pump discharge (high pressure) side via a high pressure passage 120, and connected to a pump intake (low pressure) side via a low pressure passage 130 respectively. A plug 102 screws into the depression 100A via a threaded part which is formed in the circumference of the plug 102.
The plug 102 is provided with a throughhole 102A effectively in its central part. On the inner circumference of this throughhole 102A, a conducting terminal 103 is supported in an insulated state via insulation members 105, 107 and O ring 106. The terminal 103 is fixed to the plug 102 by a push nut 104.
In a small diameter part 100B of depression 100A is housed a conducting piston 110 and plunger 109 that can displace in an axial direction facing the aforesaid terminal 103. A spring 111 to push the plunger 109 and terminal 103 apart from each other is interposed between the plunger 109 and terminal 103.
The piston 110 receives a thrust due to oil pressure of the high pressure passage 120 at its base end, displaces, and its tip comes in contact with the plunger 109. When the oil pressure applied to the high pressure passage 120 exceeds a predetermined value, the plunger 109 pressed by the piston 110 displaces to the upper part of the figure against the pushing force of the spring 111, and the terminal 103 comes in contact with the plunger 109. Due to this, the terminal 103 changes into a conducting state via the body 100, piston 110 and plunger 109. A circuit connected to the terminal 103 switches ON, and it is detected that the supply pressure of the vane pump has exceeded a predetermined value.
In this pressure switch, an oil chamber 101 formed between the plunger 109 and plug 102 connects with the low pressure passage 130 of the vane pump.
However, the conventional pressure switch shown in FIG. 9 is associated with the following problems.
Firstly, this pressure switch, terminal 103, spring 111, plunger 109 and piston 110 are each comprised of different parts. Therefore, when the pressure switch is assembled, these parts need to be assembled in a predetermined order. Hence, the number of assembly steps increases and there is a possibility of assembly errors.
Moreover, the long, narrow high pressure passage 120, and the small diameter part 100B housing the small diameter piston 110 and plunger 109 with guide flange, have to be machined inside the body 100. It is also necessary to machine the slanting low pressure passage 130 relative to the axis of the high pressure passage 120. Therefore, the number of machining steps increases, and production cost increases.
Also to improve the operating performance of the plunger 109 and piston 110, the holes for guiding these parts must be machined with higher precision and the parts themselves have to fit together more precisely, which again requires more machining steps and higher cost.
Further, when the spring 111 has low orthogonality, engaging or other assembly defects occur when the plug 102 is tightened, and the production line may have to be temporarily shut down which leads to lower pr
REFERENCES:
patent: 4724289 (1988-02-01), Heissler
patent: 4752658 (1988-06-01), Mack
patent: 4827093 (1989-05-01), Strzodka
patent: 5187337 (1993-02-01), Fujie et al.
patent: 5321220 (1994-06-01), Sekiguchi
Hayashi Tetsuji
Kuga Kenichi
Friedhofer Michael
Kayaba Kogyo Kabushiki Kaisha
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