| 摘要 |
PCT No. PCT/JP96/01029 Sec. 371 Date Jun. 12, 1997 Sec. 102(e) Date Jun. 12, 1997 PCT Filed Apr. 12, 1996 PCT Pub. No. WO96/32228 PCT Pub. Date Oct. 17, 1996A vibration generating apparatus comprises a cylinder assembly (6) having a cylinder and a piston (3) slidably inserted in a cylindrical bore (2) of the cylinder for defining a first pressure receiving chamber (4) with a small pressure receiving area and a second pressure receiving chamber (5) with a large pressure receiving area. The piston (5) is selectively movable in one direction and in the other direction responsive to pressures in the pressure receiving chambers. A switching valve (9) has a first pressure chamber (13) with a large diameter, a second pressure chamber (14) with a small diameter, a pump port (10), an auxiliary port (23), a principal port (11) and a tank port (12). The switching valve (9) takes a first position under a pressure within the first pressure chamber and takes a second position under a pressure within the second pressure chamber. When the switching valve (9) is in the first position, the pump port is allowed to communicate with the auxiliary port and the principal port is allowed to communicate with the tank port. When the switching valve (9) is in the second position, the pump port is allowed to communicate with the principal port and the auxiliary port is allowed to communicate with the tank port. A servo valve (19) is responsive to a movement of the piston for establishing a communication of the first pressure chamber with a fluid pressure source (21) or a tank.
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