That’s how the gears are changed in a DTM car
It’s a permanent up and down: up to 40 times per lap, a DTM driver shifts gears with the two paddles placed behind the steering wheel. At the Norisring, the shortest circuit on the DTM calendar, only 18 gear changes are necessary per lap but at the end of the 78 lap-race, every driver will have shifted about 1332 times. And every time a driver presses one of the two paddles this results in rather complex procedures. The times of having to step on the clutch pedal and long gear linkages have been history in DTM for quite a while. We explain what happens when a driver is changing gears.
For the driver, the perfect point in time is of major importance: the perfect revs per minute for the gear change. In addition to a classic rev counter, an LED display also informs the driver on the revs his engine is running at. Should the lights switch from the green to the red area, it’s time for the driver to execute the gear shift by dint of one of the two paddles. To do so, any driver has got different preferences. Some of them prefer the right paddle for shifting up, other favour the left.
The procedures that are activated by pressing the paddle, however, are virtually the same in every DTM racer. After all, all the components involved in the gear change – up to the six-speed Hewland gearbox – are so-called control parts. This means they have to be identical in very DTM car.
Is the gear-shift paddle pressed, the ECU (Engine Control Unit) simultaneously reduces the current torque of the eight-cylinder engine, thus making for a slight rpm drop. The gearbox control unit detects this sequence and sends a control command to the valves of the gearbox pneumatics right away. Thanks of a blow of compressed air in the direction of the controller cylinder it begins to turn. This results in movement of the shift forks, disengaging the cog wheels currently used while the following cog-wheel pair is engaged by dint of the so-called dog clutches.
When this procedure has been completed, the ECU cedes its short-time control over the engine performance. Now, the right foot of the driver re-gains full control over the accelerator and the power delivered by the engine.
What looks like a long function chain if you read it is executed at lightning speed and nearly imperceptible, in reality. A complete gear change in a DTM car needs just 80 milliseconds. In other words: For all the 1332 gear changes during a DTM race at the Norisring, a driver and his car need just one and a half minutes. .