7/25/2023 0 Comments Sequential transaxleBy 1961, when it was replaced by a ZF unit, it had been adapted for mid-engine use, the final drive had been changed to a spiral form after lubrication issues with the hypoid, and the change had been modified so that the lever now migrated as gears were selected, two racks being required in the system to achieve this.īut Chapman never completely gave up on his original transmission concept. The ‘box was notoriously variable in its reliability, gaining the nome de plume of ‘Lotus Queerbox’ something that has been put down variously over the years to poor lubrication, undersized gears, and reuse of out of life parts in what was still an organisation that existed on the margins of viability. Bronze spacers between each gear formed a neutral position, with the cockpit lever always returning to the same, central, neutral position after down- or up-changes. On this was formed a six sided spline which engaged with similar splines formed on the inner annulus of each gear. Rather than using a rotating drum, selection was by a sliding sleeve that sat over the first motion shaft. One set of gears was permanently splined to the pinion shaft and the other free to rotate about the first motion shaft. In its original form the manually operated unit was fully sequential. Shaft centres were 99 mm with a further 30 mm step up available from a hypoid final drive. It was, in effect, a scaled up motorcycle unit, with five forward speeds occupying no more than 80 mm in length, and an all up weight of just 22,5 kg. For his first tentative steps into single seater racing, Chapman boldly commissioned a bespoke unit that was typically somewhat in advance of anything else available ‘off the shelf’ at the time – of which there was precious little in any case. This was never raced, but in 1956 a similar system was adopted for the first single seater Lotus, the front engine type 12 Formula Two car. The historical ancestor of the concept – in the racing world – is the gearbox designed for the Cisitalia GP car for which Porsche was responsible, immediately post war. As it does so it will sequentially pick up conventional selector forks that will move face dogs into engagement with the next gear. Depending on the type of system fitted to the car, as the driver pulls at his steering wheel paddles, an actuator will be operated either by pneumatic, hydraulic, or fully electric means, which will in turn move a peg or lever that engages in the track of the drum, and so rotates it. In the modern box this normally takes the form of a drum, with a pathway machined into it, whose axis is parallel to that of the actual gear shafts. In previous Monitor features we have touched upon the automated gearshift of a modern race car and attempted to put it into historical context, but how many of its mechanical design features represent new thinking ?Ĭentral to its function has been the move from a H-gate to sequential gear selection, for with this it is much easier to provide powered control of the actual selection mechanism. Categories: Archive, transmission Sequential gearbox origins
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