| 摘要 |
A variable camshaft timing arrangement for an internal combustion engine in which a camshaft, for example, an intake valve operating camshaft in a dual camshaft engine, is advanced or retarded in its position relative to the crankshaft and to the exhaust valve operating camshaft in reaction to torque pulsations in such intake valve operating camshaft. The camshaft has a sprocket oscillatingly mounted thereon, or on the other camshaft of a dual camshaft system. The camshaft carrying the oscillatingly mounted sprocket also has a bracket or another sprocket keyed thereto, and the bracket or other sprocket is chain driven by the rotation of the crankshaft. A pair of single acting hydraulic cylinders interconnect the oscillating sprocket and the bracket or other sprocket, with the piston ends of the cylinders pivotably attached to the oscillating sprocket and with the body ends of the cylinders pivotably attached to the other sprocket or bracket. The cylinders act in opposite directions and are hydraulically interconnected so that one extends as the other retracts and vice versa. The hydraulic system includes a control valve which is controlled by an engine controller to selectively permit one of the cylinders to extend, and the other to retract, in reaction to torque pulsations in the camshaft which is being advanced or retarded to provide desired engine operating characteristics. The camshaft which is being advanced or retarded can either be the camshaft which carries the oscillatingly mounted sprocket, or, in a dual camshaft system, it can be the other camshaft or both camshafts. In an engine having cam followers of the friction type, the unidirectionally acting torque on the camshaft which results from the friction between the camshaft and the followers can be offset by providing resilient means to act on one of the opposed cylinders to introduce a countertorque into the camshaft which is oppositely directed to the frictional torque.
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