It's synchro for ZF at higher weights
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HNRADFABRIK FRIEDRICHSHAFEN (ZF) is confident that the ind towards synchromesh rather than constant mesh gearboxes top weight vehicles in Europe will continue, writes BRYAN RVIS.
4ccording to ZF, there has en a steady increase in delnd for synchromesh transssions and this is borne out by a fact that.92 per cent of its osplit range built in 1982 was ecified in this form, and the ntinuing increase in sales sugsts a similar trend for 1983.
So convinced is ZF that synchroesh gearboxes with splitters economically essential for iavy vehicle fleets that it has troduced a medium duty transission range into the UK.
This is the S6-36, which is degned for a maximum gearbox put to torque of 540Nm (398 ft) and is aimed at vehicles up 25 ton gvw for on-road use or r 18ton gvw tipping vehicles nployed on site work.
Two sets of ratios are avail1e with either overdrive or rect drive on sixth gear. The rect-drive version can also inade an optional 7.4 close ratio 9.0 wide ratio first gear. It is so available in splitter form to ve 12 speeds.
Both Leyland and Daf specify is gearbox and other manufacirers currently have it under raluation.
But ZF is also convinced that for better fuel economy transport managers and fleet engineers should concentrate their attentions on synchromesh gearboxes, particularly for 32.5tonne and the impending 38tonne vehicles.
Over the past decade, rising fuel prices have made a vehicle's fuel consumption one of the most important factors of fleet operations and as a result of recent development, modern diesel engines have been designed to produce higher torque figures at lower engine speeds.
From its own research, ZF maintains that the driver of a modern heavy haulage vehicle can cope, with the majority of driving conditions within the 1,200 to 1,800rpm speed range but without high revving or excessive fuel consumption. It is also the range of the highest torque output and vehicle manufacturers indicate this as a "green zone" on the rev counter.
To make maximum use of this green range, a gearbox with close ratio steps is required together with a carefully chosen rear-axle ratio to allow driving at maximum legal speeds within the green zone. Research by ZF into power train efficiency has shown that the higher the steps in ratio between the gears, the longer the time lapse before synchronising the speeds of the gearbox input and mainshafts. As gear change time is vital to keep the engine speed within the green zone, a close ratio gearbox with an easy gear shift action is a necessary requirement for heavy haulage operations.
Its tests are also said to show that each time a 38-tonne vehicle decellerates on a straight road from 80km/h to a stop and then accelerates back to 80km/h it consumes on average 1.5 litres of diesel fuel.
With these points in mind, ZF developed its eight-speed Ecosplit gearbox with integral splitter and advises that its five rules are essential guidelines which will enable the driver to develop the desired technique that will lead to fuel savings, improved journey times, and less wear and tear of drive line components.
ZF introduced sintered metal synchromiser rings and molydenum coating to overcome its problems of the past. It also altered its design to eliminate the tortional vibrations which were previously created through the drive line, especially at low engine speeds.