Design evolution of a novel tilting three-wheeled motorcycle for city environments

The average speed of European City traffic is less than 12 miles per hour and the vast majority of journeys are less than two miles. It seems reasonable therefore to devise an environmentally friendly vehicle with low or zero emissions to serve a market that requires safe but manoeuvrable transport with a small road footprint. Working with European colleagues in industry and academia a narrow track threewheeled vehicle with crash protection, partial enclosure, electric drive and lightweight construction has been developed to the prototype stage. In this paper the design evolution of a tilting mechanism for this narrow track vehicle which provides locking of the tilt axis at low speed and variable damping at high speed is presented. Active and passive alternatives are discussed and a passive alternative is chosen on the basis of cost and safety. A range of actuation and speed sensing mechanisms are compared and a solution identified which is simple, low power, low cost and controllable. The system uses appropriate technology with a low maintenance requirement that is both compact and lightweight. Despite the potential for good reliability the system is designed to be fail safe; it is of paramount importance that the vehicle be allowed to tilt freely rather than become locked once the speed has risen above that required to balance. The driving style required at low speed, when the tilt axis is locked, will be different to that required at higher speeds, when the handling will be similar to that of a standard motorcycle. However the low lateral accelerations associated with low speed manoeuvres should make the change in driving style imperceptible and a degree of rear wheel steering, introduced as a result of the tilt axis, should improve mid-speed manoeuvrability. Having an estimated sale cost of 7000 the vehicle would be suitable for personal transport or a carrier of light loads in city environments.