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Replacing a conventional automatic transmission with a high torque capacity, full-toroidal traction drive Infinitely Variable Transmission (IVT), delivers fuel economy benefits approaching those achieved by hybrid drivelines when a suitable balance between battery life and fuel economy is implemented, but with minimal additional on-cost, weight and complexity. These benefits are achieved by optimizing the engine operating conditions, eliminating the torque converter and removing torque interruptions during the gearshifts. Recent application of a non-optimal IVT to an Optare Solo bus (an 11,300kg European Midi-Bus) produced fuel savings of 19% over the standard Allison 5-speed automatic transmission. These measurements were independently performed by the internationally recognized Millbrook Proving Ground, UK.

The Torotrak full toroidal traction drive technology has been proven in a range of applications, the most familiar being a V8 SUV where double figure fuel economy improvements were delivered in a durable, smooth and refined package. Novel transmission architectures, new approaches to roller control and improvements in hydraulic design and operation have delivered significant parts count and cost reductions together with system efficiency, performance and package improvements. The result is a family of new transmission design concepts in both ‘clutch start’ Continuously Variable Transmission and ‘geared neutral’ Infinitely Variable Transmission format. Automotive applications are from high torque RWD / SUV vehicles to low torque FWD vehicles. This paper describes the new designs, transmission layouts and roller control mechanisms, with particular focus on FWD / transverse applications in the A, B and C sector vehicles.

A supercharger system which boosts the engine via a direct drive from the engine crankshaft has been identified as a possible solution to improve low-end torque and transient response for a conventional turbocharged SI engine. However, the engine equipped with a fixed-ratio supercharger is not as fuel-efficient especially at high load and low speed due to the fact that a large portion of the intake mass air flow has to recirculate through a bypass valve causing inevitable mechanical and flow losses. In addition, the fixed drive ratio of the supercharger which is mainly determined by the full-load requirements might not be able to provide sufficient over-boost during a transient. The fact that a clutch may be necessary for high engine speed operation on the fixed-ratio supercharger system is another issue from the perspective of cost and NVH performance.