A self-resetting single-valve double-piston hydraulic drive device for an overhead cam engine, the hydraulic drive device comprising:
- a rocker arm assembly including:
- a rocker arm body defining a driving oil passage,
- a drive control valve configured to selectively open the driving oil passage,
- a primary driving piston arranged at a first end of the rocker arm body, and
- a first elephant foot assembly arranged at a second end of the rocker arm body;
- an integrated cam arranged below the primary driving piston, the integrated cam configured to rotate the rocker arm body;
- an exhaust valve assembly including an inner-side exhaust valve and an outer-side exhaust valve;
- a valve bridge assembly including:
- a valve bridge body arranged below the first elephant foot assembly, the valve bridge body defining an oil drain passage, and
- a secondary driving piston configured to engage one of the inner-side exhaust valve or the outer-side exhaust valve, the secondary driving piston selectively connected to the driving oil passage via the oil drain passage;
- and
- a limit assembly arranged above the oil drain passage,
- wherein the driving oil passage is configured to connect the primary driving piston to the secondary driving piston,
- wherein an engine drive solenoid is configured to control the drive control valve such that:
- when the drive control valve opens the driving oil passage, (i) during a drive lift of the integrated cam, the limit assembly is in contact with the valve bridge body so as to seal the oil drain passage and form a hydraulic linkage between the primary driving piston and the secondary driving piston, the drive lift of the integrated cam moves the primary driving piston within the rocker arm body so as to drive the secondary driving piston to open the one of the inner-side exhaust valve or the outer-side exhaust valve in such a way that the rocker arm body and the valve bridge body do not move;
- and (ii) during a positive-power exhaust lift of the integrated cam, the limit assembly is separated from the valve bridge body so as to open the oil drain passage and reset the secondary driving piston, the primary driving piston and the rocker arm body are rigidly connected as the rocker arm body rotates so as to drive the valve bridge body to open the inner-side exhaust valve and the outer-side exhaust valve, and
- when the drive control valve closes the driving oil passage, (i) during the drive lift of the integrated cam, the primary driving piston absorbs the drive lift of the integrated cam within the rocker arm body such that the rocker arm body does not move and the exhaust valves do not open, and (ii) during the positive-power exhaust lift of the integrated cam, the primary driving piston and the rocker arm body are rigidly connected as the rocker arm body rotates so as to drive the valve bridge body to open the inner-side exhaust valve and the outer-side exhaust valve, and
- wherein, the driving oil passage comprises a primary piston oil passage configured to connect the primary driving piston to the drive control valve, a secondary piston oil passage configured to connect the secondary driving piston to the drive control valve, and a control valve oil supply passage configured to connect the engine drive solenoid to the drive control valve.