The present invention relates to a solenoid-controlled valve and, more particularly, to a solenoid-controlled valve capable of achieving changeover and control at three positions by exciting only one particular solenoid.
Two types of solenoid-controlled valves are conventionally well known as those which can achieve changeover and control at three positions. The first has two solenoids, and it is intended to achieve changeover and control at three positions by exciting the solenoids independently. The second has only one solenoid, and it is intended to achieve changeover and control at three positions by changing the value of current by which the solenoid is excited, as disclosed in Japanese Utility Model Publication No. 58-17169.
The above-mentioned two types of solenoid-controlled valves have the following drawbacks. Since the first type uses two solenoids, it naturally needs two magnetic circuits in which heavy yokes must be included. Therefore, as a whole it becomes large and heavy.
On the contrary, the second type needs only one magnetic circuit because it has only one solenoid. Therefore, it can be smaller and lighter when compared with the first type. However, the second type includes a slider, which is successively moved to first, second and third positions by a magnetic attraction force generated by the solenoid, and two valve members, arranged at both ends of the slider, which independently open and close at each position of the slider. In the case of this solenoid-controlled valve, the valve members become complicated in construction, and high accuracy is needed to assemble these valve members on the slider. Therefore, it cannot be prepared easily and its cost becomes high.