Systematic Approach to Finding the Best Transmission Variant

IAV advance engineering process finds optimum system solution for every application

At the moment, the European market for heavy-duty trucks still tends to be dominated by automated manual transmissions (AMT). However, in many cases an alternative solution would lead to less fuel consumption. IAV has developed an advance engineering process that starts by considering all possible variants in order to supply the optimum system solution at the end.

There is a huge choice of transmissions, from manual transmissions via AMTs through to planetary and dualc l u t c h transmissions. However, the European truck segment is still dominated by AMTs as a particularly favorable solution in terms of production costs and efficiency. "But this could change in future", predicts Rico Resch, IAV project manager for transmission/hybrid systems, synthesis/concepts. "More and more OEMs implement downspeeding, for example, to reduce fuel consumption. But the lower engine speeds in the powertrain mean that higher torque is needed at the transmission input shaft to produce the same power output at the wheel. And so, power-shifting systems such as dual-clutch transmissions are currently a hot topic."

Optimum solution for each case

The example shows that there will never be one single ideal transmission system for all commercial vehicles. Instead, it is a case of finding the best possible solution for every individual case. And that is exactly the aim of the systematic advance engineering process with which IAV tackles this task. The experts examine two to three different variants for every type of transmission and work by means of elimination to filter out the particular solution with the greatest benefits in terms of efficiency, for example.

The process begins with IAV powertrain synthesis (see page 56), which supplies the initial possible configurations for the basic powertrain structure, including suggestions for the engine and transmission together with its transmission ratio series. This is an important input parameter for the next step where IAV's transmission synthesis supplies the best compromise from millions of variants. This is followed by 2D design of several options with computation of their loss maps. These in turn are used by the developers to simulate the longitudinal dynamics with IAV's Velodyn for Com Apps tool and then to calculate fuel consumption. "This is one of the key decision criteria for development to the manufacturing readiness level", says Resch. "In addition, costs also play a major role, so that we always consult our cost assessment specialists when selecting the best concept."

Modular system for various scenarios

To demonstrate the efficiency of the systematic advance engineering process, Resch and his colleagues have developed a transmission for a heavy-duty off-road truck. "This needs high drive power and constantly available driving force, uninterrupted where possible", explains Resch. "This would indicate a dual-clutch transmission or automatic planetary transmission; on the other hand, the market also offers AMTs with special shifting programs." At the end of the advance engineering process, a ninespeed automatic planetary transmission with two reverse gears proved to be a promising option on account of its high torque density and flexible power-shifting capability.

IAV's advance engineering process goes beyond developing just one single transmission. Indeed, it also offers a modular approach to obtain lower-cost solutions for derivatives such as buses, for example. In this specific case, the nine-speed automatic planetary transmission with two reverse gears can be modified into an automatic transmission with six forward and one reverse gear, containing many carry-over parts to save costs.