| 摘要 |
A valve system is disclosed for an internal combustion engine which allows a secondary valve event, serving for example to provide internal EGR, to be selectively disabled. The system comprises two valve 10 and 22, a first cam 20 acting on the first valve 10 by way of a rocker 12 pivotable about a fixed pivot axis and a second cam 36 having at least two lobes and acting on the second valve 22 by way of a second rocker 24 pivotable about an eccentric 26. The second of the two lobes of the second cam 36 is arranged to open the second valve 22 at a time that the first valve 10 is opened by the first cam 20. A selectively operable latching mechanism 50 latches the eccentric 26 in a fixed position in which each of the cam lobes of the second cam causes the second valve to open. When the latching mechanism 50 is released, a coupling between the eccentric 26 and the first rocker 12 causes or permits the eccentric 26 to move during the opening of the first valve 10 in a sense to oppose the lifting of the second valve 22 by the second lobe of the second cam.
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