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Abstract



Cylinder volume function for SVC engines


One of the features of the SAAB Variable Compression engine (SVC) is its possibility to change the compression by tilting the top of the engine. Due to the change in geometry, the standard equation used to calculate the cylinder volume as function of crank angle may not give sufficiently accurate result.

A new cylinder volume function, that is specially designed for the SVC, is derived and described. It is written on the form V(theta,v) = V_c(v)+V_d(theta,v), where theta is the crank angle, v the tilt angle, V_c the clearance volume, and V_d the volume displaced by the piston. It is shown that the biggest relative deviation between the standard volume function and the SVC volume function is approximately 6\%. It is also shown that by adjusting the crank angle input to the standard volume function so that the TDC coincide with the actual TDC, that is V(theta,v) = V_c(v)+V_{std}(theta-theta_{TDC}), the relative error caused by using the standard volume function is reduced by a factor 10.

Ylva Nilsson

2001

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