Automatic and automated medium-duty transmissions will continue to increase their market dominance, slowly driving out their manual counterparts, says Darry Stuart, general chairman of the Technology & Maintenance Council (TMC).
In identifying several trends that are likely to shape design over the next several years, he points out that medium-duty transmissions also becoming more “beefed up” as part of an effort to lower maintenance costs and better match trucks' longer life cycles. Finally, more gears and more capability are being added to help improve fuel economy.
Yet it's the change in driver skills that overshadows everything, says Stuart. “The pool of drivers available…for the medium-duty segment simply don't learn how to shift gears growing up anymore,” he explains. Consequently, transmissions must be easier to use, more robust and provide better fuel economy.
“Automaticity is the most obvious medium-duty transmission trend in North America,” says Teddy Gilbert, manager-North American marketing sales and service for GM Powertrain-Allison Transmission. “The marketplace is recognizing that fully automatic transmissions have superior performance, durability, shift quality and driver retention benefits.”
Another trend is increasing ratio coverage, which allows for better overall vehicle performance and improved optimized fuel economy, Gilbert says. “An example of this is a first range of 3.5:1 or 4.5:1 and a high range (sixth gear for an Allison transmission) of .65:1,” he notes. “The lower ranges allow for greater torque multiplication and the double overdrive ratio of .65:1 results in lower engine speed during highway operation. Ultimately, this results in improved fuel usage.”
Medium-duty transmissions are also getting beefier, adds Stuart, with more gears and more muscle so they can better manage higher horsepower and torque loads, yet remain as fuel efficient as possible, as well as provide increased reliability and longevity.
“We're getting away from 5-speed transmissions in this segment, going back into 6- and 7-speed configurations to smooth out the shifts, carry the [torque] load, yet still hit the ‘sweet spot’ for maximum fuel economy as much as possible,” Stuart says. “Also, the duty cycle is changing in medium-duty: trucks are expected to work harder and last longer. That dictates more ‘meat’ within the transmission itself, so it can better handle daily pounding and vibration without affecting performance or longevity.”
That muscle is even more critical due to all the sensitive electronics packed into today's transmissions, he stresses. “Overhauling a transmission today will cost you $2,500 and up because of all those electronics, so you want to make sure that — at least over your ownership cycle — the transmission can last with minimal maintenance cost,” Stuart says.
That's one reason so many transmission manufacturers are switching to synthetic fluids for their products, adds Bill Gross, Eaton Corp.'s manager of sales support for North America.
“We factory-fill with a synthetic fluid that's got a 500,000-mile change interval — that pretty much matches the life expectancy of a medium-duty truck,” he explains. “That's because the primary ‘wants’ of the medium-truck buyer are reliability and low cost. They simply want that truck to work, day in and day out, with minimal maintenance input on their end. So our transmissions must step up and meet those standards.”
One factor driving the need for tougher, longer-lasting transmissions is that fleets are extending their ownership cycle for medium-duty trucks. According to Gross, this is a direct result of tighter emission regulations, which have made trucks more expensive.
“The engines are the real cost point in medium-duty,” he explains. “So fleets are trying to hold onto their trucks longer. That puts more wear and tear on all of the truck's components, transmissions included.”
“Since the introduction of the new low-emission technology engines, owners have been more likely to experience an engine problem,” notes Brian Etchells, senior research manager in the commercial vehicle group at J.D. Power and Associates.
“While we can't pinpoint whether the overall increase in engine problems is directly related to the new low-emission technologies, the fact that the number of problems has increased at the same time the technology was introduced would indicate a correlation. Exhaust gas recirculation valves, which are a component of the new technology, are among the top 10 most commonly mentioned engine problems,” he says.
J.D. Power, which has surveyed medium-duty truck customer satisfaction annually over the past 14 years, says four major factors rule the day in the medium-duty truck buyer's mind: vehicle performance, quality, cost of ownership and warranty coverage.
In addition, users are dissatisfied with the price of service, especially labor and parts, says Etchells, which puts even more pressure on component suppliers to minimize downtime for required maintenance. “Manufacturers have to be concerned because truck downtime translates directly into increased costs and lost revenue for truck owners,” he says.”
With uptime, cost and quality as a backdrop, transmission makers are focusing on ways to make their products most cost-effective for the medium-duty user. That's one reason Freightliner LLC began offering the Mercedes-Benz Automated Gear Shift (AGS) transmission for its Business Class M2 trucks four years ago.
Built off a rugged 6-speed manual Class 8 transmission platform, the AGS model uses a hydraulic shift actuator and long-lasting components like heat-treated steel alloy gears and sealed bearings packed into a lightweight aluminum alloy housing with an integrated bell housing to improve fuel economy and reduce required maintenance, says Mark Lampert, senior vp-sales for Freightliner.
“This transmission allows drivers to focus their attention on what's most important — the driving task and the road ahead,” he notes. “In addition, the transmission helps optimize vehicle efficiency for owners by limiting wear and tear and helping to increase fuel efficiency.”
Eaton's Gross says the same thinking permeates the medium-duty version of its Fuller UltraShift HV (Highway Value) heavy-duty transmission. “What makes it more robust and long lasting is that we took a Class 8 transmission and drove it down into the Class 6 and 7 arena,” he explains. “It uses the same technology, but it's tailored specifically to produce benefits for the medium-duty user.”
Saving money is also behind the growing use of synthetic transmission fluids, says Allison's Gilbert. “We recommend TES295 approved fully synthetic fluids because the increased time between service intervals helps drive down overall life cycle costs,” he says. “Depending on the Allison transmission model and vehicle application using [them], our fluid change intervals can be increased to as much as 300,000 miles.”
Improvement in fuel economy is another big piece of the cost-saving puzzle, notes Gross. Testing conducted by an independent firm in accordance with SAE/TMC procedures measured the UltraShift HV in an urban setting requiring numerous stops and starts. Matched against a fully automatic transmission, the UltraShift HV automated unit helped deliver fuel economy savings of 7% to 19%, primarily because of the lock-up between the clutch and transmission at approximately 3 mph, as compared to lock-up at about 24 mph with a conventional automatic, says Gross.
“Until lock-up is achieved, the truck is wasting power and fuel,” he explains. “With the ever increasing cost of fuel and raw materials, companies throughout the trucking industry are looking for ways to reduce costs, so providing significant improvement in fuel economy, particularly in stop-and-go operation, is a must.”
“Understanding all of the vehicle and environmental factors that figure into the equation is the first step a customer can take to optimize fuel economy,” says Allison's Gilbert. “The driver is the single biggest factor. Engine horsepower and torque are critical, [while] weight, tires, wind resistance, transmission ratios and shift points are other factors. Fuel economy starts in the driver's seat and ends at the tires, and everything in between plays a role.”
Gearing up
Spec'ing the right transmission for your medium-duty operation is more complicated today than in the past. Not only are there more transmissions to choose from, but there are more engine ratings to match them to. Here are some tips from International Truck & Engine Co.
Selecting the engine rating is the first step. Since all transmissions are rated to a maximum input torque, this will determine which transmissions are compatible. The higher the input torque, the larger the transmission required — and the more costly that transmission might be. In addition, some transmissions have GVWR limits that must be taken into consideration.
Next comes transmission choice. An automated manual transmission is a manual transmission with a clutch and an electronic automated control system, allowing it to do the clutching and shifting. Three-pedal versions that require clutching for stops and starts and two-pedal versions with no clutch pedal are available. Automateds can be less expensive and more fuel efficient. Shifting is not as crisp, however. While automatic transmissions have no clutch, they do have a torque converter that helps with shifting and smooths the flow of power from the engine to the drive wheels.
Choosing between a 5-speed and a 6-speed automatic or automated is an important decision because the extra gear provides more efficiency at cruising speeds. However, unlike a manual transmission, gears 1 thru 5 have the same ratios in both the 5-speed and 6-speed versions, so there's no benefit to spec'ing a 6-speed unless you expect to be operating primarily at highway cruising speeds.
Engine rating also dictates how many gears to spec when you're choosing a manual transmission. More gears can translate into a better driving experience and more starting power.
