The paper describes the design and development of a five speed gearbox for the Royal Enfield ‘Bullet’ range of motorcycles and a four speed + reverse variant for industrial, light car and similar applications.
The design specification for the five speed gearbox called for a directly interchangeable unit with the sting Bullet four speed gearbox, providing either right or left-hand gear shifting, to meet local market preferences/statutory requirements worldwide. Provision was also required for either ‘up-for-up’ or ‘up-for-down’ gear shift patterns, with the minimum of special-to-option parts.
Within these demanding spatial and functional requirements, the design produced is not materially heavier and has greater load capacity than the current four speed gearbox. The four speed + reverse variant utilises the same major castings and has all but a few components common or very similar to the parent five speed gearbox.
The design ethos and techniques used are described and various methods of assessing gear load capacity discussed and compared. Material choice and production methods are also considered, The philosophy adopted for prototype testing and reliability assurance is outlined.
Prototype gearboxes of the five speed version have now been extensively tested and a pilot-production batch manufactured, prior to build-up to full commercial production. The gearbox has also been homologated with the Indian authorities.
This is the first time that such a gearbox has been designed specifically for production by an Indian two-wheeler manufacturer. It is aimed to complement Enfield's new generation of engines in premium segments of the international and domestic markets.
Close collaboration between Enfield and their consultants, including the involvement of suppliers, production engineers and service personnel from the earliest stages, has contributed to the successful implementation of this important new product.