Fluid pressure cylinder with boosting mechanism

1. A fluid pressure cylinder with a booster mechanism,

wherein a main cylinder chamber and a booster cylinder chamber that are separated by a partition wall are provided in a cylinder body,

wherein a main piston is disposed in the main cylinder chamber so as to be slidable in a direction along an axial line, and the main cylinder chamber is divided by the main piston into a first main pressure chamber and a second main pressure chamber,

wherein a booster piston is disposed in the booster cylinder chamber so as to be slidable in the direction along the axial line, and the booster cylinder chamber is divided by the booster piston into a first sub-pressure chamber and a second sub-pressure chamber,

wherein a first port that communicates with the first main pressure chamber and a second port that communicates with the second main pressure chamber and the second sub-pressure chamber are provided in the cylinder body,

wherein a piston rod is coupled to the main piston, and the piston rod extends to an outside through the partition wall, the booster piston, and an end wall of the booster cylinder chamber,

wherein a communication path, one end of which communicates with the first main pressure chamber and at the other end of which a check valve is disposed, is provided in the main piston and the piston rod, and the check valve allows the first main pressure chamber and the first sub-pressure chamber to communicate with each other by opening the communication path by being pressed by the booster piston when the piston rod reaches a booster start position before a forward stroke end,

wherein a coupling-member containing chamber is formed in the booster piston so as to surround the piston rod, and a coupling member is disposed in the coupling-member containing chamber so as to surround the piston rod, and

wherein an engagement surface and an engagement groove are formed in the coupling-member containing chamber and an outer peripheral surface of the piston rod, and, when the booster piston moves forward by an action of a pressure fluid supplied to the first sub-pressure chamber through the communication path, the engagement surface and the engagement groove engage with the coupling member and thereby the booster piston and the piston rod are coupled to each other.

2. The fluid pressure cylinder according to claim 1 , wherein a pressing member is provided on the booster piston, and the pressing member serves as both of valve opening means that opens the check valve by pressing the check valve when the piston rod performs a forward stroke and release means that releases coupling of the booster piston and the piston rod by pressing the coupling member when the booster piston performs a backward stroke.

3. The fluid pressure cylinder according to claim 2 , wherein the pressing member is displaceable relative to the booster piston in the direction along the axial line, maintains the check valve in an open state by protruding from the booster piston by being pressed by the coupling member when the booster piston moves forward and the piston rod and the booster piston are coupled to each other by the coupling member, and releases coupling of the booster piston and the piston rod by entering an inside of the booster piston and pushing the coupling member when the booster piston moves backward to a backward stroke end.

4. The fluid pressure cylinder according to claim 1 , wherein the piston rod includes, in order from a back end thereof connected to the main piston toward a front end thereof, a first collar portion having a largest diameter, a second collar portion having a smaller diameter than the first collar portion, and a rod body having a smaller diameter than the second collar portion; and a part of the communication path and the check valve are provided in the first collar portion, and the engagement groove is provided in the second collar portion.

5. The fluid pressure cylinder according to claim 4 , wherein a valve chest of the check valve is formed in a front end portion of the first collar portion so as to communicate with the communication path; an annular valve seat that surrounds the communication path, a poppet valve body that contacts or separates from the annular valve seat, and a valve spring that presses the poppet valve body against the annular valve seat are disposed in the valve chest; the poppet valve body includes a push rod that protrudes to an outside of the valve chest; and, when the push rod is pushed by the booster piston, the poppet valve body separates from the annular valve seat and the communication path opens so as to communicate with the first sub-pressure chamber.

6. The fluid pressure cylinder according to claim 4 , wherein a ring-shaped rod packing is provided on an inner periphery of a center hole of the partition wall, the first collar portion of the piston rod has an outside diameter that allows the first collar portion to gas-tightly fit into the rod packing and to slide, and the first collar portion fits into the rod packing when the piston rod reaches the booster start position and thereby the first sub-pressure chamber is shut off from the second main pressure chamber.

7. The fluid pressure cylinder according to claim 1 , wherein the coupling member includes a plurality of steel balls.

8. The fluid pressure cylinder according to claim 1 , wherein the coupling member includes an elastic ring whose diameter is variable.