Your first experience at the controls of an automated transmission can be a foreign feeling. Your left foot instinctively moves toward the clutch pedal that isn't there; your right hand reaches for a shift lever and finds a controller that feels l...
July 1, 2004
John G. Smith, Technical Correspondent
COMPLETELY AUTOMATIC: Truck OEM’s are still debating fuel economy on automatic transmissions; but quicker accelerations are a selling point.
Your first experience at the controls of an automated transmission can be a foreign feeling. Your left foot instinctively moves toward the clutch pedal that isn’t there; your right hand reaches for a shift lever and finds a controller that feels like it should be attached to a video game.
But it quickly becomes familiar territory.
There’s no doubt that automated equipment is easier to drive than its mechanical counterparts, and your focus quickly turns to everything else that requires attention. (There are more gauges to be watched than the tachometer, after all. And did you notice the traffic around you?)
The automation itself can come in a number of forms. Fully automatic versions, such as those offered by Allison Transmission, incorporate torque converters to deliver shifts that mimic those of a car. Eaton’s Lightning models allow truck drivers to shift without double-clutching, thanks to electronics that rev and slow engine speeds.
The ZF Meritor FreedomLine offers joystick-like controls that allow drivers to let the truck take care of all shifts, or make shifting decisions on their own.
Still, as easy as they are to drive, automatic and automated transmissions are hardly the norm in Class 8 trucks – those who build the equipment tend to estimate that fewer than one in 10 transmissions have the electronic controls.
A few years ago, ZF Meritor officials were predicting that half the transmissions in the market could be automated in five years. “We never said the start point,” jokes Charlie Allen, director of marketing and engineering for Meritor Transmissions. But the prediction is still relevant, he says. “It’s a question of when is it going to take off?”
Those who offer the transmissions continue to insist that a widespread adoption is just a matter of time. And Eaton has just announced that it’s beginning “high volume production” of its 10-speed UltraShift.
Obviously, those who struggle with shifts in the first place are the most likely to benefit from the helping hand of electronics.
“You don’t need the high level of qualified driver that once we had, that grew up with a stick in his hand,” says Peter Messeroll, Eaton’s national account manager in Canada.
“Anything downstream of the transmission is not going to have the potential to be abused by the (inexperienced) driver,” Allen adds.
“Certainly the shock load would be reduced significantly by having the transmission do the shifting.”
But other drivers can also see a benefit. Those with a smaller stature, for example, may struggle with the need to apply 60 lb. of force to release the clutch on a Class 8 truck, he says.
Without a doubt, the biggest barrier to the adoption of automated and automatic equipment is the initial purchase price.
Traditionally, an automatic transmission can be about three times the cost of manual equipment, Messeroll says. Automated models can cost about $5,000 more than their manual counterparts.
And the question of whether automated manual transmissions can actually improve a truck’s fuel economy is a matter of debate between the manufacturers.
Allen, for example, says fleets can expect to trim fuel consumption by three to five per cent, largely because of the accuracy of shifts made by computers that don’t fatigue.
“The real savings is when you push the gearing,” he adds, referring to his company’s 12- and 16-speed FreedomLine that will skip as many as four gears at a time. “It will run the engine just as slow as it can.”
But Messeroll suggests that automated-related fuel savings are negligible, if they can be measured at all.
“To stand here and say, ‘Yes, an automated transmission will save you fuel,’ that’s damn near impossible to do,” he says. And he suggests a trained driver can easily match the fuel economy that comes with electronic shifts.
Allison, meanwhile, will go so far as to admit that fuel consumption will increase with the use of a fully automatic transmission, but notes that the real benefit comes in the form of quicker accelerations. With every 10 per cent of a truck’s day that’s spent below 45 mph, route times can be improved by one per cent, says Mitch Murray, Allison’s marketing manager for North America. “If you improve your route time, you’ll use more fuel.”
But the quicker jumps to speed could mean additional deliveries for operations such as couriers that tend to gravitate to medium-duty trucks when working in urban areas.
As trouble-free as automated equipment can be, there are some maintenance-related issues that need to be considered – fluid levels and condition are the first that come to mind.
For example, Allison’s 3000 and 4000 series of transmissions that are used in on-highway service can have drains that extend as long as 150,000 miles when filled with a synthetic TranSynd fluid, he says.
But the choice of Automatic Transmission Fluid (ATF) also continues to be crucial in fully automatic models.
If you expose a clutch pack designed for ATF+3 to a Dexron III fluid, the result will be harder shifts, Chevron Texaco’s Tom Hansel says as an example, referring to a bump in the friction curve – a diagnostic chart that shows torque levels at specific points in time.
And he also questions those who claim that a simple additive will offer a one-bottle-fits-all solution.
“What you haven’t done is maintain the same capacity as the transmission was designed for,” he says. “When you start putting other products into this transmission, you’re not going to get optimum performance.
“You’re going to see it in the shift field, or you’re going to see it in long-term torque transmission and capacity.”
A 15 to 20 per cent drop in torque that accompanies an easier shift can lead to excessive wear and heat, he adds.
Transmission sumps run at temperatures from 175 to 220 Fahrenheit (79 to 104 degrees C) during normal duty cycles, but hotter temperatures can lead to dramatic cuts in ATF drain intervals.
Each fluid exerts a force to move transmission components, while lubricating parts and cooling the clutch, torque converter and retarder.
But all things change with time. The viscosity of an ATF can thin out with use, reducing the protective thickness of the lubricating film, and leading to the damage associated with higher heats.
A fluid that’s allowed to oxidize will become thicker, sticking valves and leading to a loss in clutch friction despite the variety of filters that are meant to keep everything clean and free of debris.
Electronics account for the other area to be watched, Messeroll says.
Connectors, for example, should not be allowed to carry a load, and should be regularly inspected for any signs of weakness.
However, the electronic packages themselves have improved.
“Ten years ago, electronics were a much bigger part of our warranty,” Murray says.
There was no “silver bullet” that overcame any of the issues, but connectors have improved, the computers themselves are more robust, and RF interference has been addressed to ensure fewer emissions for those who use two-way radio systems, he says.
Allison plans to unveil its next generation of electronic controls in the summer of 2005.
Still, drivers won’t see a huge difference.
Many of the changes are simply in response to the fact that microprocessors eventually become obsolete.
“They don’t make the same chip for 20 years,” Murray says.
The language of transmission specifications
Startability – Determined by the transmissions low gear and axle ratio, tire size and engine torque at 800 RPM. Startability is a measure of how easy it is to get a vehicle moving.
Cruise speed – Determined by the same factors as startability, cruise speed is a desired engine speed at a particular road speed (in high gear) for efficient operation.
Step size – Used to match the engine to the transmission. Older engines with narrow operating ranges and “steep” horsepower curves required small steps.
Overall ratio – The lowest gear ratio divided by the highest gear ratio. A transmission with
small steps requires more speeds to gain more overall ratio.