US Patent 7568460 Variable valve drive of an internal combustion engine

A variable valve drive (1) of an internal combustion engine is provided which is used to actuate a gas exchange valve (5). Displacement thereof takes place via a cam (7) generated lift and via a lift generated by a piston (14, 32) of a hydraulic force applying device (4a, 4b), which is superimposed on the cam lift and which is independent thereof. The hydraulic force applying device is connected to a hydraulic fluid line (S-P) which provides an adjustable hydraulic pressure medium and includes a pressure chamber (24a, 24b) which is limited on one side by the piston (14, 32), in addition to a hydraulic valve lash compensation device (23a, 23b) which includes a working chamber (22a, 22b) which is radially defined by a housing (13a, 13b). The housing (13a, 13b) is also used to radially define the pressure chamber (24a, 24b).