GET IN GEAR WITH ZF
Page 20
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ZF GEARS showed off its semi-automatic Transmatic transmission, comprising a gearbox plus torque converter, at the Public Works Exhibition in Birmingham.
Bearing in mind that the function of a gearbox is to provide a range of torque bands that can be applied to the road wheels, the purpose of a torque converter is to extend the torque range for each of the gears.
ZF claims that its transmission system is particularly suited to vehicles having an on/off road capability such as those used in the construction industry.
For demonstration purposes. ZF had fitted its semiautomatic system to a MAN 26-320 6X6 tipper truck loaded to 24.4 tonnes (24 tons) gross weight.
However, we used the 6x4 drive option for the duration of the brief test drive, in which it was possible to see how it performed both on and off the road.
Once in the cab the engine could be started both in neutral or any gear selected with out the use of the clutch.
No sudden surge was evident from engine torque, which must have been absorbed within the converter. The extra torque available enabled the vehicle to be driven away from standstill without fuss, using third gear. The clutch was needed only during gear changes.
The gearbox had full synchromesh for the forward gears, enabling changes to be made without the need to doubledeclutch. Sixth gear provided a very useful speed band and pulled well from as low as 40km /h up to a maximum of around 90km /h.
The actuation of the converter is governed by a sensor measuring the difference in torque delivered by the engine before and after the ZF's transmission.
With engine speeds above 1,000rpm the vehicle can be driven in the normal manner.
Between 1,000 rpm and 1,500rpm a kick-down facility, which requires a very positive action, is available and extends the useful torque range of that gear.
Above 1,500rpm the converter becomes locked out, below 1,000rpm the converter automatically comes into play. A one-way clutch fitted within the converter provides for full engine braking right down to stall conditions, also making it possible to bump start the vehicle from very low speeds in any gear.
Off the road we did not get above third gear, but even so it was possible to try the versatility of the gearbox in wet and muddy conditions.
Approaching a gradient, and allowing the truck to slow down and come to a stop about halfway up, without any use of the clutch pedal relying solely on the accelerator, it is possible to hold at a standstill or inch forwards with absolute control.
Also fitted to the 26-320 MAN was ZF power steering which gave a nice and smooth response and feel, even off the road.
General impressions of the ZF gearbox and torque converter were good.