Solenoid actuator

A solenoid actuator for attaching to a hydraulic equipment, comprising:

• a shaft for connecting to the hydraulic equipment, the shaft having a center axis;
• a plunger made of a magnetic material and fixed to the shaft;
• a coil which magnetically chives the plunger in a direction of the center axis;
• a first bearing and a second bearing which support the shaft, the first bearing and the second bearing being located on both sides of the plunger in the direction of the center axis such that the first bearing is nearer to the hydraulic equipment than the second bearing;
• a plunger-front chamber formed between the first bearing and the plunger;
• a plunger-rear chamber formed between the plunger and the second bearing;
• a plunger-exterior oil passage formed on the outside of the plunger to connect the plunger-front chamber and the plunger-rear chamber;
• a second-bearing-rear chamber formed on the opposite side of the second bearing to the plunger-rear chamber, the second-bearing-rear chamber performing contraction/enlargement according to a stroke of the shaft;
• a second-bearing oil passage formed through the second bearing to connect the plunger-rear chamber and the second-bearing-rear chamber;
• and
• a shaft-penetrating oil passage penetrating the shaft in the direction of the center axis to introduce working oil from the hydraulic equipment to the second-bearing-rear chamber.