Fly-by-wire clutch cuts automotive fuel consumption

Schaeffler E-Clutch

Intelligent clutch system for manual transmission vehicles automatically disengages clutch when coasting to reduce engine speed, fuel consumption and emissions.

Schaeffler has developed intelligent, automatic clutches for previously purely mechanical or hydraulic clutch systems. Depending on the development stage, the new E-Clutch system from Schaeffler either operates the clutch only under specific driving situations or completely automates all clutch operations. This enables fuel saving driving strategies, from “sailing” to electrically supported driving, to be integrated into vehicles with manual transmissions.

“The E-Clutch from Schaeffler paves the way for hybridisation of manual transmissions, thereby opening up new markets and market segments,” said Uwe Wagner, Vice President Automotive R&D at Schaeffler.

Up until now, this has been possible only in combination with automatic transmissions. The E-Clutch is therefore a significant step forward in the market. This type of transmission is far and away the most commonly used in many growing economies as well as in the lower and middle market segments in the European market. Today, approximately 50% of all vehicles have a manual transmission, even as global production continues to increase.

One Idea, three concepts

Schaeffler has developed three stepped concepts for the E-Clutch for manual transmissions depending on the level of automation required. In the MTplus version, the basic principle of transmitting forces hydraulically is maintained but with the addition of an actuator directly in the pressure line. The advantage in this arrangement is that the demands on actuation times and the number of actuations are lower, resulting in reduced demands on performance. “By using this method, Schaeffler has managed to keep the on-costs of the MTplus to a minimum compared to a classic clutch operating system,” explained Markus Kneißler, E-Clutch System Development Manager for Schaeffler’s LuK brand.

Even partial automation makes a significant contribution to reducing fuel consumption when “sailing”. During continuous driving, the engine is disconnected from the transmission and is either completely switched off or idles. The MTplus system disconnects the transmission. The driver provides the signal for this indirectly by taking his foot off the accelerator pedal. Tests conducted using the up-and-coming WLTP consumption measurement cycle and realistic customer cycles have recorded reductions in fuel consumption from two per cent (engine goes to idle) to six percent (engine switches off).

Using a 1.2 litre petrol engine demonstration vehicle, Schaeffler has shown that it is possible to achieve savings of up to eight percent in urban driving conditions. The function of “sailing” not only helps in the future consumption cycle, but can also be claimed today as an “eco-innovation” for the approval of reduced CO2 emissions.

Intelligent clutch pedal

In the clutch-by-wire concept, the mechanical or hydraulic connection between the pedal and the clutch release system is replaced completely. The opposing force on the pedal from the clutch release system, which is no longer required, is now generated by a new pedal force adjuster developed by Schaeffler. This contains an additional sensor that sends a signal on the pedal position to a clutch actuator. The driver is therefore not immediately aware of the automatic engagement but continues to drive as normal with a manual transmission. A recently developed, intelligent actuator undertakes the actual opening and closing of the clutch in all driving situations. This consists of a basic actuator that includes all the electronics, the e-motor and a spindle drive. The connection to the clutch actuation is either mechanical or hydraulic depending on the application. The modular design means that it is universally applicable, which reduces the development time and overall system costs. This is an important factor in order to maintain the cost advantages of manual transmissions over automatic transmissions.

Clutch-by-wire is much more powerful than MTplus: the functionality of this clutch release system means that it can accommodate driving conditions with very high dynamic requirements, such as rapid gear shifting or emergency braking. The option of electrically tuning the transfer from pedal travel to clutch travel is considered particularly convenient. This makes it possible to have gear-related adaptation or a sport mode option, previously only reserved for automatic transmissions.

The performance of this technology can be clearly seen in the “Gasoline Technology Car” (GTC) co-developed by Schaeffler, Ford and Continental, where reductions in fuel consumption and CO2 emissions of 17 per cent were achieved with the automatic clutch making a significant contribution to this.

No pedal at all

Electronic Clutch Management (ECM) is technically based on the same system as clutch-by-wire, but without a clutch pedal. A sensor provides the signal for disengagement when the driver changes gear. Engagement follows automatically once the gear is selected. The high degree of automation in the ECM provides a good basis for integrating an electric motor into the drive train. By using a suitable battery in a 48V on-board electrical system, this system is used to drive the vehicle in all instances when the engine is running inefficiently, for example, when parking, in stop/start traffic or at low-speed urban driving conditions.

“ECM provides a technically elegant and economical step up to mild hybridisation, which could not be achieved with an automatic transmission,” explains Kneißler.

The E-Clutch system from Schaeffler not only opens up new prospects for manual transmissions, but this configuration also provides a way into new markets and market segments for hybrid transmissions.

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