SCHWEINFURT – ZF offers a high-performance clutch module for cross country rallying. Flywheel, clutch, bellhousing including all closure plates and a clutch release mechanism are supplied as a unit. In desert rallies, like the near 10,000 kilometre Rally Dakar, the transmission is subject to extreme loads.
The 300 hp plus prototypes entered by top teams plough through seas of sand, reach the crests of the highest dunes and cross river beds and scree deserts. Turbo diesel power plants have long since set themselves at the pinnacle of cross country rallying. As a result, the transmission systems must be designed to handle high torque loadings.
To transfer this power reliably, ZF Race Engineering has developed a complete clutch module. It includes the flywheel and a three-plate clutch as well as the clutch release system and also the bellhousing – a specially sealed housing with closure plate that protects the clutch from dust and water when driving off-road and when crossing rivers. The friction discs have an outside diameter of 184 millimetres and the clutch can transmit a static torque of 1,750 Newton metres.
The operating conditions are unusual in cross country rallying. For example, the module is subject to extreme loads when the vehicle is bogged down. Sensitive modulation of the clutch is required when trying to free the vehicle. If too much slip occurs when engaging or disengaging the clutch, excessive heat is generated. While a steel-sinter friction pair was initially used, the engineers selected a particularly robust and durable ceramic-sinter combination as friction lining. The advantage of ceramic discs: they are considered particular warp resistant even in high temperatures. The sinter linings are dimensioned with sufficient reserves in order to withstand the stresses and strains encountered on desert rallies. The clutch housing also withstands high mechanical and thermal stresses as it is manufactured from high-strength tempered steel.
The clutch and release mechanism are located in a bellhousing, which is produced from high-strength aluminium alloy and is equipped with a sophisticated sealing system. As a result, the moving parts are protected effectively from dirt, water and thermal shock loading during river crossings. However, if something unforeseen happens ZF has another solution in-hand: the clutch must not be integrated between engine and gearbox as is usually the case, but can in fact be installed behind the gearbox. As a result, the possibility to change the unit quickly arises.
During the 2015 season, a ZF partner took victory in a desert rally over 5,000 kilometres in Asia. ZF is already working on the next steps for the 2016 Rally Dakar 2016. The new clutch is further optimised in the areas of installation space and weight. As a result, the drivers who rely on the ZF clutch pull away under ideal conditions in January 2016.