Readers letters
The history of the Torotrak transmission (Tata tries "Spin on the Spot" in City Car, April PE) is longer and more varied than could be covered in your article. Indeed the first drawings of the basic mechanical layout date back to the 19th century.
In the 1930s Austin fitted several of their models with what was then known as the Hayes transmission - Hayes, in America, having devised a means to balance the torque reaction forces on the intermediate rollers within the toroidal cavities: a vital technical advance.
In 1960, a British engineer, Forbes Perry, having refined the Hayes system and demonstrated substantial fuel saving, approached the National Research Development Corporation (NRDC) for assistance. A research programme followed to investigate such things as stability and the relationship between normal and tangential forces on the thin fluid film between the rollers and the discs. Prof. Duncan Dowson, later President of the Institution, brought to bear his knowledge of thin films in rolling contacts - the new science of elastohydrodynamics. Another brick in the wall.
English Electric/Lucas then acquired a licence from NRDC. Using the discovery that the ratio of normal to tangential forces was substantially constant over a wide range of conditions, they designed a neat, mainly hydraulically controlled, constant speed alternator drive for the Harrier jump jet. This earned the company the Queen's Award for Industry.
Meanwhile, Leyland Vehicles began to investigate the suitability of the transmission for commercial vehicles. Several experimental units were made driving, variously, a 16 tonne truck, a bus with flywheel energy storage - for which the transmission is ideal, and even an armoured personnel carrier.
The engineering team at Leyland formed the core of Torotrak Development Ltd. (TDL), a subsidiary of the British Technology Group (BTG, successor to NRDC) which was later floated on the London Stock Market. Its purpose was to develop and exploit the technology. Subjects tackled included special traction fluids (working in conjunction with the oil industry); a reduction of the parts count and a two regime arrangement which allowed clutchless starting in forward and reverse and a shock free regime change with high overdrive. A true Infinitely Variable Transmission (IVT).
The development of electronic control systems enabled TDL to match the transmission to the characteristics required by vehicle manufacturers. Conventional management of gear ratio is, however, normally replaced by hydraulic control of torque reaction : a characteristic which can be exploited in a variety of ways. The ingenious Tata Pixel demonstrates that the range of applications is far from exhausted. The recent confirmation by Allison of its continuing interest in the transmission is encouraging and illustrates the attraction to the commercial vehicle sector, in times of inexorably rising fuel costs, of an efficient system capable of handling high powers.
Tom Fellows, Oxford
Next letter: Rampant negativity