Now Scania goes automatic
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by Graham Montgomerie
BOTH of Scandinavia's truck manufacturers now provide an automatic transmission option. Scania's announcement this week comes hard on the heels of a similar version from Volvo (CM June 25) which also uses an Allison gearbox.
I drove one of the prototype automatics in Sodertalje—the LB81, which is available in rigid or tractive unit form. This is the model chosen by Scania for the automatic option.
Although Volvo offers a choice of four or five-speed automatic transmissions, Scania is putting its eggs in one basket and going for the five-speed version only. The transmission is an Allison unit, but Scania has co-operated with Detroit Diesel Allison to adapt the system to the characteristics of the turbocharged DSS engine.
One such modification concerns the cooling requirements for the oil in the torque converter. The engine's own cooling system has been modified so that the oil cooler for the transmission has full-flow cooling which Scania claims gives a temperature difference of around 50°C (122°F) between the incoming coolant and the maximum permissible oil temperature in the system. Other modifications have included a new engine flywheel and propeller shaft. The gearbox, known as the GA652, has five ratios, the first of which the Swedes aptly call an "inclining" ratio. From the second gear, which is the nor
The Allison automatic gearbox is now available in the UK on the L581 Scania. it can be equipped with a pto which is either operated hydraulically via the torque converter or by direct drive.
The GA652 transmission has five speeds with the first gear being what Scania calls an "inclining" ratio.
mal starting ratio, up to fourth gear the truck is driven by the torque converter.
At a road speed of around 50km/h (31mph) in fourth or fifth, the torque converter is automatically by-passed and a lock up clutch comes into operation giving a direct drive.
The selector level can also be used to limit the number of gears in use: for example, in heavy traffic the lever can " hold " the transmission in one of the lower gears.
In normal operation, the second to third will take place at around 20-25km/h (12-15 mph) depending on the rear axle ratio. Third/fourth will occur at around 32-40km/h (20-25mph) and direct drive through the top ratio will be engaged at between 56-69km/h (35-43mph). A power-take-off is available as an optional extra on the Allison which is driven through the torque converter when engaged. The pto shaft-speed is dependent on the loading and may be up to twice the engine speed. Direct drive of the pto may be engaged by means of a special button beside the pto engagement button. The direct drive can be used only when the truck is stationary and in this case the shaft speed is 1-2 x engine speed.
The pto is engaged by setting the selector lever to D. The turbine wheel with the driving gear for the pto will then stop allowing the pto to be engaged smoothly. The selector lever is then moved back to the neutral position. The pto may be engaged only when the vehicle is stationary. If direct drive for the pto is engaged, this will be automatically disengaged when one of the drive ratios is selected.
The automatic 81 is available immediately with the extra cost of the Allison being in the region of £2,000 over the list price of the manual version.
The prototype automatic I drove in Socierttilje had only the four-speed box). Personally I find that, although an automatic gearbox makes life easier for the driver and saves on clutch replacement costs, the transmission does not change gear at the same point I would have selected with a manual version.