Schaeffler will present its all-wheel drive (AWD) disconnect clutch developed to support automakers optimize drive trains to reduce fuel consumption and emissions by up to six percent during the 2013 North American International Auto Show (NAIAS) in Detroit. The market for AWD vehicles is growing in popularity. As technologies for these vehicles evolve, the traction and driving safety advantages are offset by the additional weight and increased frictional resistance associated with new AWD drive trains. This is where Schaeffler’s innovation comes into play: the AWD disconnect clutch decouples the AWD drive train to minimize friction losses.
“A conventional AWD system can increase the fuel consumption of a vehicle by up to ten percent if the friction losses in the drive train and the mass of the components are taken into consideration,” explains Prof. Peter Gutzmer, CTO of Schaeffler AG. “Our AWD disconnect clutch reduces this additional friction by more than half by decoupling the secondary drive train and to improve its energy efficiency. Suppliers and the automotive industry have been working to uncover the smallest potential for optimization for many years. The AWD disconnect clutch makes a significant contribution to optimizing the drive train, which, in turn, helps automotive manufacturers meet the increasingly stringent fuel consumption standards.” Modern AWD vehicles typically have permanent all-wheel drive, in which the drive power for the rear axle is transferred to the wheels via the rear differential by means of a power transfer unit (PTU). In real driving conditions, one driven axle is sufficient to ensure safe and comfortable driving in most situations. During normal driving, the secondary axle is also engaged without transferring any force to the road via the rear wheels. However, a significant proportion of the energy is lost due to friction. The Schaeffler AWD disconnect clutch decouples the drive train from the rear axle at the PTU. A second disconnection point is located in the rear axle to prevent torque from being transferred via the rotating rear wheels to the drive train, which is decoupled at the front of the vehicle. The AWD disconnect clutch comprises a hydraulically operated synchronizer clutch integrated in the input shaft on the PTU and electrically operated dog clutches on the rear axle. The clutch located on the PTU has two functions: axial disk surfaces with a high friction coefficient are used to absorb synchronization energy; while a self-energizing, bi-directional wedge clutch supports high drive train torques. The disconnect clutch system includes continuous monitoring of driving conditions and the drive train environment to ensure lightning fast switches to AWD mode if required.
“Our system offers potential fuel savings to enable AWD vehicles to achieve similar fuel consumption as front-wheel drive vehicles without impairing driving behavior,” explains Jeff Hemphill, CTO of Schaeffler North America. “The Schaeffler AWD disconnect clutch can be integrated in conventional all-wheel drive trains without major modifications.”
