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From the Drawing Boar
Page 60
Page 61
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by Graham MontgomeriE The T45 has finally been unveiled to the world. Now known as thi Road train, Leyland's latest lorry incorporates much of the Maratha experience, but there are a lot of departures — not the leas interesting being the use of "sticky bolts" on the chassis frame.
FOR T45, READ ROADTRAIN. That is the name by which the most long-awaited model in commercial vehicle history is now known.
Although a lot of Marathon experience is incorporated in the Roadtrain concept, there are some interesting departures from previous Leyland practice.
Without getting embroiled in political discussion in a vehicle iesign feature, it is nice to be 3ble to report that Roadtrain is at ast available and that it will give _eyland Vehicles the ammuni:ion with which to get back its market share.
The chassis frame for Road:rain was designed and deveoped using a combination of _Ryland's experience and addanced computer analysis techgigues. One of the interesting 'eatures of the frame is the use 3f chemical locking nuts — or 'sticky bolts' to use the terminology of Jim Mason, chief 3ngineer, vehicle engineering. Ihere are interesting reasons for ising this method of fastening.
The design philosophy for he Roadtrain was to go metric ind, in the early prototype itages, Leyland had a lot of pro31ems using metric coarse :hreads because structural tes.ing showed a tendency to oosen.
Metric fine threads were then :hosen. This improved the situition considerably, but there were still some areas of the frame where slight slackening of the bolts occurred; To put a time scale on this, some relaxation was noticed after around 800 miles of the Leyland standard 1,000 miles pave test.
Because of the need to have a chassis frame which can accommodate a variety of engines and also be able to get at the sump without taking the frame apart, Leyland has gone for a fairly long engine bay.
It would have been easy to stick in an extra cross-member to get the required structural integ ity, but this would obviously have made access worse.
What Leyland did eventually, and with 100 per cent success, was to adopt "sticky bolts".
These are conventional bolts incorporating small capsules of adhesive in the thread. So when the nut is wound on, it breaks the capsules and produces an effective seal.
Taking the decision to adopt this novel method of fixing for full-scale production obviously caused some heart-searching at Leyland. As Jim Mason put it: "We traditional engineers were pretty cynical about all this, but we did a whole vehicle out like that and didn't get any fidgeting of the nuts and bolts at all. The structural integrity of the frame was maintained throughout the 1,000 miles of pave with no trouble."
The use of adhesive has also allowed Leyland to go back and use metric coarse threads as intended originally. The bolts themselves are described by Leyland as -snug fitting" which is not the same as a fitted bolt in a reamed hole; it merely implies that the clearance on the hole is less than the normal commercial standard.
Although the standard Roadtrain engine is basically the same TL12 unit used for Marathon, there have been a number of detail changes. These can be considered as being in three separate categories: (a) changes made to improve performance; (b) changes made to improve reliability; (c) changes made to suit installation in Roadtrain.
The most obvious change is the reduction in maximum rate( engine speed from 2,200 t( 2,000rpm. According to Ley land, this has permitted bette control of the air/fuel mixin( and given lower engine noisi levels.
Revisions in the turbocharge matching have enabled thi altitude capability of the engini to be extended while, in th■ Bosch fuel pump, double heli: elements have been specified t( give a faster injection.
The net result of thesi modifications, together with ; slightly retarded injectior timing, has been to give ar improved torque curve and ; torque back up of 18 per cent The accompanying performanci curves show this in greater de tail.
The latest version of the TL1: engine (with the type number o TL12 /41) is now known a "Flexitorque". The maximun power output is the same as thi TL12/ 10 unit to T25 Marathor specification. From a cubil capacity of 12.5 litres (761cuin it produces 203IM (270bhp et installed at 2,000rpm with a laximum torque of 1,1 80Nm 360Ibft) at 1 ,200rpm.
The lower engine speed for Flexitorque unit comes into nether improvement category, hat of reliability, as Leyland laims that the resulting lower iston speed has improved the il control in the cylinders.
An increase in air capacity 'ore the water-cooled compresDr has been made for improved raking performance. The apacity is now 20cfm ompared with the 1 3.5cfm of le earlier unit. Four bolt flanges ave been introduced for the Khaust manifold to give better 3aling, especially for exhaust rake applications.
Changes made to TL12 for stallation in the Roadtrain inude a new double fill oil sys.m (so oil can be added with the )b in the upright or the tilted osition) and new exhaust ianifolds which are necessary clear the floor for the preium cab version.
The fuel filter has been ,positioned to allow clearance r the tilt of the new cab and to mplify the pipework.
As installed in Roadtrain, the 33kW (270bhp) of the TL1 2 exitorque gives a power-toeight ratio of 6.2kW /tonne .4bhp/ton) at 32 tons and 3kW/tonne (7.2bhp /ton) at 3 tonnes. If we want to be ally optimistic, the power-toeight ratio at 40 tonnes is 1kW/tonne (6.9bhp/ton). When it became known that yland was intending to use e Spicer SST10 gearbox for 15, there was a great deal of rnment. This was not necesrily critical: more of a reflecin on the fact that the Fuller arbox on Marathon had been rticularly successful and so ly change it?
The Leyland move is linked to