Smart actuation of a dual-clutch transmission

Getrag PowerShift transmissions combine the convenience of an automatic transmission with higher efficiency. One important aspect to meet improved efficiency is a low power demand for automatic actuation. Since 2009, the Getrag 6DCT250 with on-demand clutch and shift actuation has been produced in series. Compared to the first generation, its power consumption has been reduced from roughly 250 W to less than 40 W in the NEDC. The next step is to make Smart Actuation’ available for dual-clutch transmissions with wet clutches as well: The forerunners will be the new models 7DCT300 and 6DCT150.GETRAG Smart Actuation efficiency Chart

Smart Actuation reduces fuel consumption

In the first generation of Getrag’s dual-clutch transmissions, actuation was accomplished by means of a fully hydraulic system with a mechanically driven pump – being powered by the combustion engine. However, Getrag applied directly controlled hydraulics rather than the pilot-controlled hydraulics that have been typical of most automatic transmissions to date. Thus the actuation power could be reduced from roughly 500 W to 250 W in the NEDC (New European Driving Cycle). On-demand actuation is more efficient: In the 6DCT250 with a dry dual-clutch, shift operations are managed via shift drums, which are actuated by electric motors. The dry clutches are actuated electro-mechanically as well. Thanks to this completely “dry” on-demand actuation, the 6DCT250 requires a maximum of 40 W in the NEDC.

But can this frugal value be achieved with a wet dual-clutch as well? For specific applications, wet clutches can be appropriate: They are designed for higher thermal loads, while being smaller and showing less inertia. For example, this can be useful in connection with high-torque downsizing engines or in heavy vehicles with less powerful engines. The Getrag engineers met this task with a new type of electro-hydraulic actuation that operates virtually without loss. The so-called pump actuation system provides oil pressure for shift operations and clutch cooling. As a development result, power consumption of the 7DCT300 is 31 W in the NEDC, thus having hardly any impact on fuel consumption.The new dual-clutch transmission 7DCT300

A modular transmission family

The new electro-hydraulic Smart Actuation will be launched in the new dual-clutch transmission 7DCT300, which goes into series production in early 2015 in mid-size cars. Alongside on-demand actuation, it offers seven gears and a higher gear spread of up to 8.6. Whereas the 6DCT250 provides a fuel consumption advantage of roughly 6 per cent compared to a modern torque converter transmission, this advantage increases to 8 to 9 per cent with the new 7DCT300. The more compact 6DCT150, being primarily designed for small cars, will compete against CVT and automatic transmissions with four to six gears in its segment. Thanks to the low actuation power needed, consumption advantages of over 10 per cent are possible in this market environment, compared to competitors.The compact dual clutch transmission 6DCT150Getrag

Romain’s opinion:

Having such design improvements is meaningless if the interaction between engine and transmission is not appropriate in terms of control system. I mean that the transmission can be designed with intrinsic efficiency features, but if the gear shifting strategy is not optimized, then the gains are lost. Do you think that when Getrag supply these gearboxes to OEMs, they ask for a shared development for the control algorithm or the calibration?

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Romain Nicolas

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  1. I have driven two Renault products fitted with six-speed Getrag dual clutch transmissions (EDC). Neither one could be made to kick down when rapid acceleration was needed. The only way to downshift was by using the manual override. Is this normal or were both gearboxes just poorly adjusted / set up?

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