US Patent 7237517 Camshaft adjuster of an internal combustion engine

In a camshaft adjuster for an internal combustion engine comprising a control valve having a control piston slidably supported in a valve housing, an operating unit for adjusting the angular position of the camshaft relative to a crankshaft of the engine and a drive unit with an electric motor and a transmission structure for actuating the control piston, the transmission is non-self-locking so that backward movement of the valve piston can be achieved by a backward force on the valve piston.