An enhanced flexible dynamic model and experimental verification for a valve train with clearance and multi-directional deformations

- An enhanced dynamic model with multi-direction deformation and clearance is proposed.
- Cam lift at each time node is achieved by interpolation to avoid high frequency loss.
- Bending deformation of rocker arm is discovered much larger than radial deformation.
- Clearance impact on pushrod is weakened by the components elasticity and damping.
- Large clearance and deformations lead to decrease of valve lift and working phase.

An enhanced flexible dynamic model for a valve train with clearance and multi-directional deformations is proposed based on finite element method (FEM), and verified by experiment. According to the measured cam profile, the available internal excitations in numerical solution to the model are achieved by using piecewise cubic Hermite interpolating polynomial. The comparative analysis demonstrates that the bending deformation of the rocker arm is much larger than the radial deformation, signifying the necessities of multi-directional deformations in dynamic analysis for the valve train. The effects of valve clearance and cam rotation speed on contact force, acceleration and dynamic transmission error (DTE) are investigated. Both theoretical predictions and experimental measurements show that the amplitudes and fluctuations of contact force, acceleration and DTE become larger, when the valve clearance or cam speed increases. It is found that including the elasticity and the damping will weaken the impact between the rocker arm and the valve on the components (not adjacent to the valve) at either unseating or seating scenario. Additionally, as valve clearance or cam rotation speed becomes larger, the valve lift and the working phase decrease, which eventually leads to inlet air reduction. Furthermore, our study shows that the combustion rate improvement, input torque, and components durability can be improved by tuning valve clearance or adjustment the cam profile.

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