Liquid-pressure rotating device

Abstract

A cylinder block including plurality of piston chambers formed at intervals in circumferential direction; plurality of pistons fitted in respective piston chambers movable in expanding and contracting directions to reciprocate in the expanding and contracting directions; a valve plate in contact with the cylinder block rear end surface and including first and second ports communicating with piston chambers. A portion of each ports is close to a top dead center switching land formed between first and second ports as a portion having a narrow opening width in a rotation radial direction of the cylinder block. An auxiliary port is formed at the valve plate switching land. Auxiliary port pressure is maintained lower than pressure of a side port that is the first or second port. When the piston chamber lacks communication with the side port (first or second port), the piston chamber and auxiliary port communicate with each other.

1 . A liquid-pressure rotating device comprising:
 a cylinder block provided rotatably and including a plurality of piston chambers formed at intervals in a circumferential direction;   a plurality of pistons fitted in the respective piston chambers so as to be movable in an expanding direction and a contracting direction and configured to reciprocate in the expanding direction and the contracting direction; and   a valve plate provided in contact with the cylinder block and including a first port, a second port, and a switching land formed between the first port and the second port, the first and second ports communicating with the piston chambers, wherein:   a portion of at least one of the first and second ports of the valve plate which portion is located close to the switching land is formed as a narrow portion having a narrow opening width in a radial direction;   an auxiliary port is formed at the switching land of the valve plate;   pressure of the auxiliary port is maintained lower than pressure of a high pressure side port that is any one of the first and second ports; and   when the piston chamber does not communicate with the high pressure side port that is the first or second port, the piston chamber and the auxiliary port communicate with each other.   
     
     
         2 . The liquid-pressure rotating device according to  claim 1 , wherein the narrow portion is formed in an angle range from a position of a dead center to a position of not more than 45° in the circumferential direction. 
     
     
         3 . The liquid-pressure rotating device according to  claim 1 , wherein:
 openings of the piston chambers which openings face the valve plate serve as cylinder ports; and   the opening width of the narrow portion in the radial direction decreases as the narrow portion extends toward the dead center.   
     
     
         4 . The liquid-pressure rotating device according to  claim 1 , wherein:
 openings of the piston chambers which openings face the valve plate serve as cylinder ports;   each of the cylinder ports has a shape including a base portion and a convex portion projecting from the base portion outward or inward in the radial direction;   the convex portion is formed such that when the piston chamber communicates with the auxiliary port through the cylinder port, only the convex portion communicates with the auxiliary port; and   before and after the piston chamber communicates with the auxiliary port through the cylinder port, the base portion is located away from the auxiliary port by a sealing portion having a predetermined seal width in the radial direction.   
     
     
         5 . The liquid-pressure rotating device according to  claim 4 , wherein the seal width is not less than 3 mm.