Clutches and gearbox units are operated hydraulically. This function is performed by the gearbox mechatronics, housed in the DSG. The term “mechatronics” is derived from a combination of mechanics and electronics. And this is exactly how the mechatronics module is structured: the electronic transmission control unit, various sensors and the hydraulic control unit form one compact unit.
The control unit uses information such as engine speed, road speed, accelerator position and driving mode to select the optimum gear and to determine the ideal shift point. The hydraulic control unit then implements the shift commands in a complex sequence of individual, precisely coordinated actions.
Two clutches – eleven sensors – one control unit
The double-clutch transmission consists of two subgearboxes, each with its own clutch, that work together to shift the gears. The integrated electronic control unit that Temic developed for this transmission comprises 11 sensors and 11 actuators (e.g. valves) in one single component whose main function is to open one of the clutches and to close the other at the right moment. This results in smooth shifting without interruption of the tractive force. The electronic unit processes the sensor signals, measures the rpm’s, the speed and the load on the transmission, ascertains the positions of the mechanical components and electromagnetically operates the valves and slides of the hydraulic gear mechanism.
Such highly integrated mechatronic parts are only possible with the use of high-performance engineering plastics: Only a material that can be freely shaped is able to protect the electronic components while combining actuation and sensor technology in an extremely small space and in a single part. The wiring is simplified, the number of cables and plugs is drastically reduced, and interfaces are rendered unnecessary, thus yielding a component that is small, lightweight and reliable.
One plastic – two uses
Ultradur® B4300, a PBT made by BASF, fulfils a number of mechatronic functions in the control unit produced by Temic. The standard variant, B4300G6, containing 30 percent glassfibres, has all of the mechanical and chemical properties, for instance, dimensional stability, needed to withstand hot transmission oil. Semiconductor sensors secured in place with this plastic must not shift their position, even when exposed to high temperatures and oil. In contrast, type B4300K6, which is reinforced with glass beads, has to be highly isotropic, so that no oil can get into the structures. The Swoboda company located in Wiggensbach in the Allgäu region of Germany is in charge of the injection moulding of this plastic.