(1) Field of the Invention
This invention relates to a solenoid valve for controlling the flow of pressurized fluid in, e.g., an antilock control device of an automotive brake.
This type of solenoid valve is provided in a pressure oil passage to open and close the passage according to instructions from a computer.
(2) State of the Prior Art
FIG. 2 shows a conventional solenoid valve of this type. It comprises a cylindrical frame 21, a valve seat 23 fitted in a small-diameter hole 22 formed in the upper part of the frame 21, an armature 25 mounted in an intermediate-diameter hole 24 formed in the frame 21 under the small-diameter hole 22, and an electromagnetic coil 27 mounted on the inner wall of a large-diameter hole 26 formed in the frame 21 under the intermediate-diameter hole 24. Also, a sleeve 28 having an inner diameter larger than the diameter of the armature 25 is mounted on the armature in the intermediate-diameter hole 24. A yoke 29 is inserted in the sleeve 28 from its bottom.
The contact portions between the small-diameter hole 22 and the valve seat 23, between the intermediate-diameter hole 24 and the sleeve 28 and the between the sleeve 28 and yoke 29 (designated a, b and c in FIG. 2) are sealed, e.g. by welding. Thus, a pressure oil chamber 31, in which is mounted the armature 25, is sealed except for an inlet/outlet port for pressure oil and a hole 32 formed through the side wall of the frame 21.
The armature 25 is movable up and down in the pressure oil chamber 31 and is urged upwards by a coil spring 45. Thus, the pressure oil inlet/outlet port of the valve seat 23 is normally closed by a valve body 33 provided on the top end of the armature 25.
The frame 21, armature 25 and yoke 29 are made of a magnetic material. These magnetic parts and the electromagnetic coil 27 form a magnetic circuit. When the electromagnetic coil 27 is excited, the armature 25 descends, separating the valve body 33 from the valve seat 23. The pressure oil inlet/outlet port is now opened.
On the other hand, the frame 21 is inserted in a hole 35 formed in a housing 34, which may be a component part of an antilock control device. The yoke 29 is in contact with a housing cover 36. In this way, the solenoid valve is mounted on an antilock control device.
The housing 34 has a first pressure oil inlet/outlet port 37 communicating with the small-diameter hole 22 of the frame 21 and a second pressure oil inlet/outlet port 38 communicating with the hole 32 formed in the frame 21. Thus, a pressure oil passage is formed between the first and second pressure oil inlet/outlet ports 37 and 38, extending through the pressure oil chamber 31. This pressure oil passage is closed while the oil pressure inlet/outlet port of the valve seat 23 is closed. It is opened when the electromagnetic coil 27 is excited and the pressure oil inlet/outlet port of the valve seat 23 opens.
The frame 21 has on the outer peripheral surface thereof two grooves 41 and 42 carrying O-rings 43 and 44, respectively. The O-ring 43 serves to close the fluid communication between the first pressure oil inlet/outlet port 37 and the small-diameter hole 22. The communication between the second pressure oil inlet/outlet port 38 and the hole 32 is closed by both O-rings 43 and 44. The other ring 44 serves to seal the passage between the second pressure oil inlet/outlet port 38 or the hole 32 and the outside.
Another solenoid valve of this type is disclosed in Japanese Unexamined Utility Model Publication 63-99081 filed by the present applicant.
Such conventional solenoid valves require many seals such as seals for portions a), b) and c) and O-rings 43 and 44. Thus, such conventional valves need O-rings for a liquid-tight seal or an additional welding step. Otherwise, a finishing step has to be added so that a sufficiently liquid-tight seal is obtainable simply by press-fitting. This increases the cost and makes it difficult to reduce the size of the valve.