GKN Viscodrive, the world's leading producing company of viscous couplings, announces a new limited slip differential (LSD) that is the first that can be tuned to optimize both traction and handling. The new Visco Lok LSD features an uniquely designed self contained viscous shear pump that provides tremendous freedom in specifying the level of torque transfer that is provided at any particular speed difference. Small torque transfers can be provided at very low speed differences to improve handling while high torque transfer with immediate response reaction is available at higher slip speeds due to its new progressive characteristic. Conventional LSD's are generally capable of providing either traction or handling improvement but not both. The Visco Lok LSD is currently in the advanced prototype stage at two U.S. automotive manufacturers with targeted 1998 model year axle and transfer cases applications.
While the orignal purpose of an LSD was to improve traction, in recent years it has been discovered that equally great benefits apply to handling and stability if the LSD is capable of transferring torque at low speed differences. The Visco Lok can be tuned to provide torque transfer at slip speed of just a few revolutions per minute. The Visco Lok automatically transfers appropriate torque to the wheel with the best traction conditions at any given moment.
The Visco Lok consist of a wet clutch pack, a pump unit, piston with seals, and a counter load belleville spring washer. Viscodrive has developed a highly durable steel clutch pack with plates as thin as 0.6mm which enables large numbers of plates to be packaged as compared with conventional clutch plates. The increased number of plates translates to increased torque capacity.
The clutch pack is engaged by an unique patented viscous shear pump which is a self contained silicone fluid pump which generates a pressure against the pistion based on a speed difference across the pump unit. The pump is 100% filled with silicone fluid and requires no servicing. The self contained viscous shear pump provides significant benefits in packaging and durability as well as not requiring any external oil source or control.
The Visco Lok provides substantial improvement relative to other self regulating hydraulic LSD's. The Visco Lok weighs less because the viscous shear pump is substantially lighter than conventional vane type or gerotor [note wj: Gerodisc?] type pumps. The physical properties of the silicone fluid used in the Visco Lok provide minimal temperature sensitivity. The Visco Lok is self contained and can be externally mounted. Finally, self regulating hydraulic LSD's raise durability concerns regarding possible contamination of shared fluid supply, check valves and orifices. The technology used in the Visco Lok LSD has been proven in production applications to maintain original specifications beyond 200,000 miles of use.
GKN Viscodrive is the world leader in viscous coupling technology as well as the world's highest volume producer of viscous couplings and viscous differentials with 1.1 million units produced in 1994. GKN Viscodrive currently has production facilities in Bruneck, Italy and Tochigi, Japan. Viscodrive's R&D facilities are located in Lohmar, Germany and in Tochigi, Japan. Additional R&D support is provided by R&D centers of the GKN Automotive Driveline Division Auburn Hills, Michigan and Wolverhampton, England.