New efficient shift strategy in the city bus-automatic transmission

Shift strategy of automatic transmissions and power shift transmissions has a large influence on fuel consumption, as the engine operating point is concerned. An optimum operating point has a minimum performance. The power needed depends beside measurable figures mainly on the non measurable road gradient. Different methods to determine the road gradient are possible: gradient sensor, air pressure sensor, gradient information achieved from a map or calculation of the gradient utilize the dynamic torque balance equation of the vehicle. Advantages and disadvantages are discussed. ZF Friedrichshafen AG with TopoDyn has developed a shift strategy using the torque balance method. The results of field tests confirm that this approach is right.