Under the name “ZF ECOnnect”, ZF has recently developed a variety of AWD driveline solutions with an available AWD disconnect function. The ZF AWD disconnect systems are mainly designed for FWD-based AWD architectures and greatly help to solve the conflict between AWD performance the additional fuel consumption caused by AWD in comparison to FWD. AWD disconnect means that when no AWD function is required, there will be no torque transfer to the secondary axle. Therefore, the speed-dependent losses due to friction and oil churning are avoided by bringing the normally rotating elements to a standstill, while the vehicle is still driving. Compared to a conventional hang-on AWD system, the disconnect system therefore reduces the friction losses in the AWD driveline by up to 90% in the disconnected mode. This is achieved by the overall design of the units including special features and optimized coupling elements resulting in very low drag torque. The mode change between 2WD and AWD is performed according to an operation strategy and takes place on the move - fast and seamless for the driver, while still providing full AWD-performance when needed. The ZF developed products include PTUs with different type and style of disconnect features, Single- and Twin-Clutch RDUs as well as the control strategies and software required to ensure the disconnect- and AWD function. The coupling and decoupling processes are realized with the help of precisely controlled electro-mechanical or electro-magnetic actuators which are tuned for the right balance between rapid shifting action and good comfort during the shifting process. In addition to the fuel economy improvement, the Twin-Clutch RDU also provides enhanced traction and driving dynamics as the drive torque can be distributed between the rear wheels as appropriate for specific conditions.
With the ZF ECOnnect solutions, different customer requirements in terms of costs, utility, and function are covered. Based on initial bench testing, demonstrator vehicles have been established to validate and tune the function and performance of the developed solutions. This paper describes the different solutions including their specific design elements, performance and control as well as specific information regarding actual test results.