Cam phasing is accomplished with a hydraulic cam phaser. For higher power operation, hydraulic pressure is used to insert a pin to lock the middle rocker arm to the outer rocker arms for operation on the high lift cam. For light load operation, the valves are operated by the two outer, low lift cams and associated outer rocker arms. The VTEC system consists of a camshaft with a center high lift cam and outer low lift cams and associated rocker arms, as shown in Figure I.1. The Honda i-VTEC (intelligent-Variable Valve Timing and Lift Electronic Control) system provides continuous cam phasing (VVT) and discrete variable valve lift (DVVL) control using the cam profile switching (CPS) concept. The incorporation of the CPS concept in numerous production applications is described in the following sections. The low lift cam for light load operation reduces fuel consumption by transferring air flow control from the throttle to the intake valves which results in reduced pumping losses. CPS provides a means of switching the actuation of the intake valves between a standard high lift cam for maximum power operation and a low lift cam for efficient light load operation. Two-stage, or discrete, variable valve lift (DVVL) systems generally rely on the cam profile switching (CPS) concept. Several systems that have been introduced with the objective of reducing fuel consumption are described in this Appendix.ĭISCRETE VARIABLE VALVE LIFT (DVVL) SYSTEMS A variety of two-stage, or discrete, variable valve lift (DVVL) and continuously variable valve lift (CVVL) systems have recently been incorporated in production vehicles.
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