New Kinematic Design Methodology and Dynamic Simulation of Continuously Variable Valve Lift (CVVL) System 2010-01-1202
Mechanical variable valve systems are being increasingly used for modern combustion engines. It is typical for such systems that the cam and valve are connected via intermediate levers. Different maximum valve lifts and duration can be achieved with the same cam profile. The intermediate levers increase the system inertia and reduce the overall stiffness. Such systems offer more flexibility, but it is more complex to create optimal design compared to the conventional systems.
In this paper a new kinematic design methodology for a CVVL (Continuously Variable Valve Lift) system is presented. Additionally, dynamic analysis of the valve train system is performed. The investigated valve train is completely developed and patented by OEM.
The main characteristic of the CVVL system is a set of intermediate levers between the cam and the finger follower like (
). One cam drives two intake valves over a set of levers. The eccentric control shaft can change the position of the intermediate levers and by that, changes the transmission ratio between the cam and the final lever. With a different position of the control shaft, different maximum valve lifts and valve lift durations can be achieved.
Within its software EXCITE Timing Drive, AVL developed new features, required by OEM that can perform a kinematic design of the CVVL system. Valve lift curve, cam profile and intermediate lever (shoe lever) profile are targets of the kinematic design. Two out of these three curves can be specified as independent inputs. Based on the geometry of the system and the two known curves, the kinematic design tool calculates the third curve. The curves are evaluated and further improved within an iterative process by repeating the previous design step.
In the dynamic simulation a detailed model of the CVVL valve train for one cam that drives two valves is calculated for various speeds and lever positions. The dynamic model considers component stiffness, clearance and hydraulic lash adjuster. The dynamic simulation results are compared with measured data from the valve train test rig.
The paper presents the problem definition, the applied simulation workflow, the modeling technique, the obtained results and the main conclusions of the investigation for this specific design.