Hydraulic feed-rate control apparatus

A hydraulic feed-rate control apparatus comprising:

• a cylindrical body;
• a cylinder provided inside the body;
• a main piston reciprocally arranged in the cylinder;
• a main-piston rod coupled to the main piston and movably arranged in front and rear directions;
• a fluid pressure chamber provided at a front of the main piston and in which a fluid is reserved;
• a reservoir chamber provided at a rear of the main piston and in which the fluid is reserved;
• flow passages configured to communicate with the reservoir chamber and to be provided between the body and the cylinder;
• feed-rate adjustment mechanisms configured to be provided at front ends of the cylinder, to control a flow rate of the fluid flowing into the flow passages from the fluid pressure chamber, and to adjust a moving speed of the main piston;
• and
• a differential piston configured to be arranged at a rear of the reservoir chamber and to be movably provided in the front and rear directions with slidingly contacting an inner peripheral face of the body and the main-piston rod,
• the feed-rate adjustment mechanisms comprising a first throttle valve and a second throttle valve configured to be provided at the front ends of the cylinder and to respectively adjust flow rates of the fluid flowing into the flow passages from the fluid pressure chamber,
• the main piston comprising an auxiliary piston integrally moving, and
• opening and closing the second throttle valve,
• the auxiliary piston comprising:
• an outer peripheral portion configured to be fitted in the second throttle valve and to be closed;
• a concave portion formed between a front portion and rear portion of the outer peripheral portion;
• a circulation hole formed at an inner peripheral portion of the auxiliary piston;
• rear-portion escape holes configured to communicate the rear portion of the outer peripheral portion with the circulation hole;
• and
• concave-portion escape holes configured to communicate the concave portion with the circulation hole.