A Continuous Variable Valve Event and Lift Control Device (VEL) for Automotive Engines 2001-01-0244
This paper describes a new variable valve control device called VEL (Variable Valve Event and Lift Control Device), which enables continuous control of both valve events (opening duration) and valve lifts, from the lowest lift or deactivation state (0) to a long event and high lift state.
VEL is composed of two subsystems. One is a mechanical valve train system, which converts crankshaft rotation into output cam oscillation via a transmission mechanism involving a rocker arm. The valves are moved by the output cam oscillation. The other is an electric powered actuator system, which varies valve events and lifts according to driving conditions by controlling the angular positions of a control shaft. This control shaft has a eccentric control cam inserted into the fulcrum cylinder of the rocker arm, so as to change the state of the transmission mechanism and the output cam.
In VEL, the combination of a unique transmission mechanism and state change mechanism, make it possible to gain a great adjustment range of events and lifts. In addition, it involves a compact system that can be installed on existing DOHC direct acting valve train engines without the need for any major cylinder head modifications. Furthermore, the adoption of the so-called desmodromic (forced drive) principle for the transmission mechanism makes it possible to avoid additional springs or spring loads other than the existing DOHC valve train, so as to realize a simpler system structure. In addition, this principle and the improvement of the cam profile of the output cam make it possible to achieve smooth valve motion even at high speed, so as to increase the maximum power. Low valve spring loads based on this principle and low energy loss of the output cam oscillating make it possible to reduce driving friction at low speed in combination with small valve lift control, thus reducing fuel consumption.
VEL was actually applied to a V6 engine. Test results verified that the characteristics mentioned above are possible and that the actuator system provides excellent response for controlling valve events and lifts.
This paper gives a concrete technical explanation, along with an account of verification results as well as evaluation results regarding VEL. In addition, the accompanying paper (1) also gives an account of the effect of VEL on engine performance.