Two step hydraulic breaker with automatic stroke adjustment

A two-step hydraulic breaker having a long stroke mode and a short stroke mode, comprising:

• a cylinder including a high-low pressure chamber at an upper portion thereof, a high pressure chamber at a lower portion thereof, and a pressure converting chamber which is disposed between the high-low pressure chamber and the high pressure chamber and includes a pilot port, a high pressure connecting port connected to the high pressure chamber, a sensing port, an oil tank port, a long stroke port, and a short stroke port;
• a piston movably disposed inside the cylinder to move along a longitudinal direction of the cylinder, and including small diameter portions corresponding to the high-low pressure chamber and the high pressure chamber, a large diameter portion disposed between the small diameter portions to correspond to the pressure converting chamber, the large diameter portion including upper and lower large diameter portions and a sensing fluid groove disposed between the upper and lower large diameter portions;
• a fluid circuit unit configured to control a supply direction of the fluid to the cylinder, and to generate a fluid pressure to selectively change a stroke mode according to fluid pressures of the pilot port, the sensing port, the long stroke port, and the short stroke port;
• and
• a chisel configured to break a bedrock when a lower portion of the piston descends along a longitudinal direction of the piston to impact the chisel during a descending operation,
• wherein when the sensing fluid groove of the piston is disposed to connect a high pressure connecting port of the high pressure chamber of the cylinder to the sensing port of the cylinder, the upper large diameter portion of the piston is disposed to block the pilot port of the cylinder, and the lower large diameter portion of the piston is disposed to block the oil tank port, the long stroke port, and the short stroke port of the cylinder.