Patent ID: 7681542

Claim:
An adjustment device for adjusting the phase position of camshaft ( 1 ) with respect to a crankshaft of an internal combustion engine which includes a hydraulic system ( 40 ) for supplying hydraulic fluid to the adjustment device, comprising: an adjustment structure including operating chambers ( 4 a - 4 d , 5 a - 5 d ), a control arrangement ( 42 ) including a control valve ( 6 ) for controlling the flow of hydraulic fluid to, and from, the operating chambers ( 4 a - 4 d , 5 a - 5 d ), and a flow passage interconnecting the various operating chambers under the control of the control valve ( 6 ), said hydraulic system ( 40 ) including a pressurized hydraulic fluid supply line with a first check valve ( 10 ) arranged in a pressurized hydraulic fluid supply line ( 9 ) and the flow passage interconnecting the operating chambers ( 4 a - 4 d , 5 a - 5 d ) including a second check valve ( 15 ), and a serial valve ( 19 ) connected to the control valve ( 6 ) for switching the adjustment device between a first operating mode, in which the camshaft is adjusted passively by changing camshaft torques, and a second operating mode, in which the camshaft is adjusted actively by controlling the admission of pressurized hydraulic fluid from a pressurized hydraulic fluid source to, and the release of the hydraulic fluid from, the operating chambers ( 4 a - 4 d , 5 a - 5 d ).