Cam design by hyperbolic spline functions of fourth order

E-mail: kohaupt{at}tfh-berlin.de In this paper, cam design using splines is discussed. The splinesare of 4th order so as to guarantee the continuity of the valve-liftcurve up to the third derivative in order to obtain valves withbetter dynamic behaviour. First, ordinary polynomial splinesare investigated, and their limited potential in cam designis illustrated. Then, the reason for introducing the new hyperbolicsplines is explained, and their potential for cam design isshown. Finally, specific cam designs based on the new splinesare compared with cams developed by Kurz. It turns out thatspline cams are an interesting alternative to Kurz's designsince—in some cases—they show a better dynamic behaviourwhen compared with Kurz's cams. The spline cam has been employed,e.g. in the M103 engine of Mercedes-Benz.     

Gyroscopic forces in automotive design

The resonance frequencies (eigenfrequencies) of a car may dependsignificantly on the gyroscopic forces resulting from the steeringof the rotating wheels. For example, in the investigated carmodel, the first eigenfrequency decreases considerably withincreasing velocity, and only by taking the gyroscopic forcesinto account do the measured and calculated results match. Asa consequence, it is of great importance to have the gyroscopicforces incorporated in the respective car model. In this paper,for a wheel model with six degrees of freedom (6 DOF), the equationsof motion and eigenvalue equation are set up, where the gyroscopicforces are taken into account exactly. Then, it is shown usingadditional concepts how gyroscopic forces can be incorporatedin the MSC/NASTRAN finite-element package (FE package). Moreover,for a large-scale FE vehicle model, frequency-response calculationswith unbalanced excitation are carried out which exhibit gyroscopiceffects. The results for both the 6-DOF wheel model and theFE vehicle model are illustrated graphically. Among other things,this work has caused the MacNeal Schwendler company to extendthe FE program MSC/NASTRAN in cooperation with Mercedes-Benzso that gyroscopic effects can now be put in directly.