The Over-Head Cam (OHC) Valve Train Computer Model

Josef Bozek Research Center of Engine and Automotive Engineering

The Over-Head Cam (OHC) Valve Train Computer Model Radek Tichanek, David Fremut Robert Cihak Czech Technical University in Prague Faculty of Mechanical Engineering Technická 4, 166 07 Praha 6 [email protected]

Josef Bozek Research Center of Engine and Automotive Engineering Content Introduction Work Objectives Model Description Cam Design Results Conclusion

Work Objectives ¾ The development of a partly flexible multi-body model of an OHC valve train. ¾ The determination of its dynamic behavior. ¾ The development of a spring model. ¾ Model usage for the optimization of cam profiles. ¾ The measurement of valve lift.

Czech Technical University in Prague Faculty of Mechanical Engineering Technická 4, 166 07 Praha 6 [email protected]

Josef Bozek Research Center of Engine and Automotive Engineering Model Description – OHC Valve Train Flexible parts: ¾ Springs ¾ Rocker arm ¾ Camshaft

Rigid parts: ¾ Cam lobe ¾ Roller follower ¾ Roller’s shaft ¾ Spring retainers ¾ Valve lash adjusters ¾ Valves

Part

Number of elements

Spring

123

Rocker arm

177

Camshaft

60


Josef Bozek Research Center of Engine and Automotive Engineering Model Description – Valve Spring Valve Spring CAD Model

Coordinates of Valve Spring Markers


Valve Spring Model in Simpack

Josef Bozek Research Center of Engine and Automotive Engineering Cam Design Cam Design Method: ¾ Based on valve lift design. ¾ Used multiple-polynomial scheme with 16 zones. ¾ The polynomial profile in each of the zones. ¾ The solution of a system of linear equations. ¾ The computation of cam profile coordinates.

Kinematical Cam Follower Mechanism Cam Profiles Schemes Theoretical valve acceleration

Cam Design Objectives: ¾ Smooth acceleration rise. ¾ Small theoretical peak acceleration. ¾ Small dynamic spring load.


Josef Bozek Research Center of Engine and Automotive Engineering Results The comparison of computed valve acceleration for Cam A and Cam B at 5000 camshaft rpm. The valve train model with a valve lash. Both non-uniformity in angular velocity and gas force acting on the valves were not taken in to account.


Josef Bozek Research Center of Engine and Automotive Engineering Results Displacement Order Spectra

The theoretical and computed order spectra of valve acceleration for Cam B at 5000 camshaft rpm. The valve displacement order spectra shows that the amplitudes of higher orders are too small and do not excite the valve train mechanism.


Acceleration Order Spectra

Josef Bozek Research Center of Engine and Automotive Engineering Results The comparison of the computed order spectra of valve acceleration for Cam A to the case when Cam B was used at 5000 camshaft rpm. Figure shows that the valve has the lower amplitudes of acceleration when Cam B is used as could be expected from the theoretical acceleration curve as well.

Acceleration Order Spectra


Josef Bozek Research Center of Engine and Automotive Engineering Test setup for measurement of valve lift

Optical Sensors TCST1000

Dynamometer MS 1713-4 (max. power 25 kW at 6000 rpm)

¾ Both contact and contactless measurement of valve displacement. ¾ The measurement of camshaft angular position.


Data Acquisition Cards: • ČVUT - FEL • KEITHLEY iiiSTA-300 Lešikar Contactless Position Sensor Incremental Position Sensor LARM MSL 30

Josef Bozek Research Center of Engine and Automotive Engineering Conclusion ¾ The flexible valve train model was developed. ¾ There were two various cam shapes used in the model and the analysis of computation results was done. This analysis was focused on valve movement in the first step. ¾ The model is prepared for a cam and a spring design, it is possible to insert various springs as substructures into the model. ¾ The building of a valve train test stand has been started which allows to motor a valve train.

Next Tasks

¾ The completion of the valve train test stand. ¾ The comparison results of computation with measured data. ¾ Model parameters setup.

Acknowledgement

The work was supported by the Josef Bozek Research Center II, No. 1M68400770002. This help is gratefully appreciated.


The Over-Head Cam (OHC) Valve Train Computer Model

Recommend Documents