Sequential gearbox halves weight… and cost

A racing type gearbox, which replaces the usual three selector shafts with a single cam track or bar, weighs in at around half the weight of the conventional variety and has been ruggedised to the extent that it looks an attractive alternative for mainstream car design. The gear changing mechanism is sequential: 1 to 2 to 3 to 4, etc : which is the favoured technique in most motorsport sectors, making the box particularly suited to semi-automatic and automatic shifting. Patented by a small design company, Speed Dynamics, the new gearbox effects shifts by moving a ratcheted slide bar acting on pushrods that in turn act on wedges. The conventional technique used in sequential motorsport gearboxes is to have a very much less robust barrel-mounted cam track acting on a single 7 or 8mm diameter pin. The function of the pushrods and wedges, or cam tracks and pins, is to act on forks that push gears in and out of engagement with dog rings. In racing gearboxes, the dog teeth are generally located on the faces of the rings, making for fairly brutal gear changes. In the case of ordinary car gearboxes, gears are pushed on and off dog rings on the shafts, with cone clutches to help match relative speeds. But the new mechanism is suitable for either approach, and is currently being trialled on a Ford Sierra. The reason that conventional car gearboxes have three selector shafts is to allow direct changes from, say 4th directly to 1st when stopping at traffic lights. In a racing car, this has to be guarded against at all costs as it will usually result in stripping the box. Instead, gear changes are made through the box by a semi-automatic mechanism as quickly as possible. It seems that the only reason why racing boxes use a cam track and pin approach is that it is an idea brought over from motorcycles, where loads are relatively small. And designers of racing boxes are reluctant to try anything different, provided the box is robust enough to last for the duration of a race. Conventional car and truck gearboxes, however, need something capable of surviving company representatives making careless gear changes for at least 100,000 miles over three years or more. The demonstration box has an aluminium sliding bar and mild steel push rods, and is based on the transmission in a Rover 600. However, it seems to be man enough for its intended task. The big potential advantage as the basis of an automatic transmission is that it is much smaller and lighter. Current trends in automatic transmission development involve doing away with energy wasting torque converters, and when combined with a suitable electronic control system and an automatic clutch, another idea perfected in motorsport, this new gearbox looks to be the simplest, lightest and cheapest way seen so achieve to do this. Pointers New gearbox replaces the usual three selector shafts with a single cam track or bar and is about half the weight and likely to be less than half the cost of a conventional car gearbox Based on the sequential gearboxes increasingly favoured in motorsport, it uses a much more robust gear changing mechanism