Auto Power

Allison has renamed and realigned its automatic truck transmission ranges, relaunching them as the Highway Series (HS) and Rugged Duty Series (RDS). The main difference is the power take-off for the vocational RDS transmission.

The company conducted a test drive for journalists and customers to compare the relative performance and driving ease of the torque-converter Allisons against automated mechanical and manual transmissions. Additionally, drag-race type acceleration demos were set up, teaming automatics with relatively conservatively rated–and lighter–engines against multi-speed manuals with high -performance big-bore power.

The object was to show how, in many urban and vocational situations with a lot of stop-start driving, that the Allison more pleasing to drive and in most cases it will outperform higher-powered equipment with manual or even automated shift.

Mitch Murray, Allison’s manager of North American market development, said because the Allison will deliver more of the engine’s performance during acceleration, the use of the torque-converter transmission can deliver improved fuel consumption over the manual.
Available for the on-highway demonstration were more than 30 heavy-duty vehicles ranging from medium straight trucks to 475-horsepower tractor-trailer combinations. Transmissions varied from Eaton 6-speeds, Meritor 10-speeds, and the ZF-Meritor FreedomLine and Eaton Ultrashift automated mechanical transmissions to compare with Allison 2500, 3000, 4000, and 4500 automatics, all rated HS for the non-PTO, on-highway applications.

In a series of convincing acceleration runs, the 5- and 6-speed Allisons consistently beat higher-horsepower manual outfits. Murray explained that the torque-converter transmissions let the engine operate for more of the time at or close to its rated speed, thereby making better use of the available horsepower.

Additionally, the torque multiplication in the converter increases the available torque to accelerate the vehicle, masking the relatively few ratios in the transmission.

On the extended course, a climb took in a 5-per-cent grade before the turn-around, giving drivers an opportunity to check out the Allison retarder on the return downgrade. Certainly, in comparison to the 13-speed-equipped Freightliner with 475 Cat C15 on hand, a Kenworth T800 with the Allison transmission/retarder setup easily was the most satisfactory combination on the stop-start course. This combo required no more than the ability to keep it pointed in the right direction, despite the many stop signs planted at regular intervals along the test centre’s roads.

The point of the demonstration was well made: The fully automatic transmission has a place in any distribution application where lots of time is spent accelerating a load up to speed. The automatic is kinder to the driver–also allowing for better, safer, vehicle control–and its performance leads to shorter journey times and greater vehicle utilization, offsetting the higher price option of the Allison.

See www.allisontransmission.com for product details, or contact your dealer.