Patent ID: 8434451

Claim:
An engine brake unit, comprising: a rocker shaft having, therein, an oil passage through which oil flows to lubricate engine parts and to open or close an exhaust valve when an engine braking is in operation; an exhaust rocker arm rotatable about the rocker shaft inserted into the exhaust rocker arm, wherein the exhaust rocker arm includes, therein, a supply oil passage communicating with the oil passage and the outside, and a recess connected to the supply oil passage and having an open lower portion; an actuator disposed in the recess of the exhaust rocker arm, wherein the actuator includes a piston that selectively moves downwards through the open lower portion of the recess by oil supplied from the supply oil passage to press the exhaust rocker arm while oil pressure in the oil passage has a predetermined pressure or more; and an oil control valve connected to the oil passage of the rocker shaft and controlling the oil pressure; wherein the actuator further includes: a control screw defining a hydraulic oil passage therein and having a through-hole connecting the hydraulic oil passage to the supply oil passage; a check valve received in the hydraulic oil passage of the control screw, wherein the check valve includes a check ball that selectively opens an entrance of the hydraulic oil passage according to the oil pressure; and a control valve received in an storage hole formed in an inner upper portion of the control screw and including a control piston, the control piston slidably received in the storage hole and selectively pressing the check ball according to the oil pressure so that the check ball closes or opens the entrance of the hydraulic oil passage, wherein the piston of the actuator is slidably disposed in the recess of the exhaust rocker arm, and a storage recess slidably receiving a lower portion of the control screw is formed inside the piston of the actuator, the piston of the actuator being displaced downwards from the control screw by oil supplied through the hydraulic oil passage to press the exhaust valve when the oil pressure is equal to or higher than the predetermined pressure.