For insight into transmission design efforts, it helps to get out on the road with an expert like Mack Trucks' Frank Steinhofer. For the past 17 years Steinhofer has worked at the OEM's test facility, giving him time behind the wheel of every kind of truck Mack makes, in almost every kind of climate and weather imaginable. “The real key to driving today is that you've got to be patient. People will do anything to get around you, so you have to watch all around the truck, checking your mirrors frequently,” he says. “It's all about taking what the truck can give you in terms of power and not pushing it.”
Steinhofer says the transmission is increasingly becoming the fulcrum for those kinds of issues: It's where making trucks safer, more fuel-efficient and more productive — all while reducing the stress of shifting gears — comes together in one package.
“Take the air-assisted clutch, for example. It takes all the physical work of shifting right out and gives you an automotive feel to driving; you can almost forget there's a 53-ft. trailer behind you,” he points out.
SIMPLICITY DRIVES DEVELOPMENT
According to David McKenna, Mack's product marketing manager for engines, transmissions and axles, what's really driving development is the desire to achieve “simplicity,” not only in terms of driving experience and emissions compliance, but also in terms of how transmissions interact with the engine and other components to produce good fuel economy, performance and power.
“First…driver skills are changing. They aren't what they once were, so transmissions have to become easier to use,” says McKenna. “Second, the transmission doesn't only have to integrate smoothly with different engine platforms; it must also integrate smoothly with low-emission platforms that are going to rapidly change and evolve from 2007 on out.”
Finally, he adds, you have to sort through the different priorities fleets have for their transmissions and make sure you can meet them. “An over-the-road LTL carrier, for example, wants fuel economy benefits above all else, with reliability a close second,” he notes. “Vocational fleets, however, demand durability and reliability above all else, with fuel economy a distant second. And both want more oomph at the bottom end of the gears for more efficient operation at low speeds. So transmissions have to meet all those demands today even before we start integrating with the engine and truck chassis designs of tomorrow.”
William Batten, manager of global product planning for Roadranger, sees tighter emissions regulations in 2007, 2010 and beyond as the biggest challenge, as well as the biggest opportunity, for transmission designs.
“Emissions compliance is driving the whole truck manufacturing industry,” he explains. “The emission rules are changing so fast that it's creating a huge learning curve in terms of the technology needed just to keep up. On the one hand, we face a huge challenge in making sure our transmissions can be integrated easily with all the changes going on in truck engines. Yet the opportunity is also there to give the customer a more optimized product, one that is at once emissions-compliant, easier to use, and a benefit to their operation.”
“Emission rules are changing the very nature of truck engines,” adds Mitch Murray, marketing director-North America for Allison Transmission. “In 2002, for example, many engine makers added variable geometry turbochargers (VGTs) to their products to better manage emission levels, yet not affect engine responsiveness. We, in turn, had to adapt our products to handle the different torque curves VGTs produced.”
BALANCING ACT
Murray notes that managing emissions while maintaining power and fuel economy through the shift can be a quite a balancing act. “Staying in the sweet spot to get the best fuel economy, power and emission compliance is a lot harder now,” he says. “But it's easier to do it correctly every single time with today's electronics.”
Adapting manual transmissions to new engine horsepower and torque outputs is relatively simple, Mack's McKenna points out. The challenge is to make sure those changes don't make the driver's job more complicated.
For its Maxitorque manual transmission line, Mack is developing multi-speed reverse models (T308 and T308M) that should be easier for drivers to use. “We're talking about having an 8-sp. transmission act like a 6-sp. when the truck is empty, yet also having 1,700 lb.-ft. of torque capacity so it can handle any engine it's linked to,” explains McKenna.
McKenna believes that over time automation will play an even bigger role. “You are going to see higher levels of automation and logic-driven systems on transmissions in order to take these ever-more complex gear selection decisions away from the driver and put them with the ECU,” he explains.
“You're going to see a lot more of that kind of interface simply to better handle the emissions control requirement with as much fuel savings as possible, along with load sensors to give the transmission more flexibility — to skip shifts when unloaded, for example,” he adds.
According to Charlie Allen, national service director for ArvinMeritor, “The electronics on AMTs [automated mechanical transmissions] will allow us to better manage all the variables. In the future, we'll need to integrate with a much wider group of engines that are going to be constantly changing as emission rules get tighter between 2007 and 2010. “We also have to manage new side effects produced by those engines — especially the higher heat levels — and other operating characteristics, yet still get fleets within reach of their fuel economy targets.”
IMPROVING SHIFT MANAGEMENT
Transmission makers cite two reasons for the expected increase in the used of AMTs and fully-automatic gearboxes over the next few years. The primary reason is improved shift management, resulting in better fuel economy and emissions control, as well as longer service life. The second involves the safety benefits of taking shifting away from drivers.
“Look at the diesel engine itself. It's producing much greater levels of torque today than in the past, so fewer shifts are required,” says ArvinMeritor's Allen. “You get the ability to lug down now and work at lower speeds, so you can get back with fewer gears, using a 10-sp. transmission where a 13 or even 18-sp. was required for the job.”
Add in emission controls and things change even more, he says. “Spec'ing the right gears is more critical than ever because for '07 and beyond you really have to optimize every shift for the best power and fuel economy,” Allen notes. “That means you can't shift gears in the future the way you learned to do it 15 or even 5 years ago; you're going to have to do it the way the engine and transmission OEM recommend to get the performance and fuel efficiency you want.”
ENGINE SPEED CRITICAL
Allison's Murray notes that maintaining the right engine speed is critical for getting emission control devices to work properly, and drivers may not be in a position to manage that all the time. “For example, if an engine doesn't get run hard enough, it won't produce the heat necessary to clean out particulate filters,” he explains. “That causes them to plug up with soot. Now you have a maintenance item to take care of.”
“That's the thing about electronics: There's no need to think about any of this when shifting,” adds ArvinMeritor's Allen. “An automated system simply grabs a shift when it needs to, based on the output of the engine. That leaves the driver free to pilot the vehicle and respond to traffic conditions.”
“The automated path allows you to do two things,” says Roadranger's Batten. “First, it's going to bring all of your drivers, especially the less skilled ones, up to the same level as your veterans in terms of getting the best fuel economy. Then it maintains that level across the work day, because after eight or nine hours behind the wheel, even a veteran driver isn't going to be as disciplined in terms of shifting at the correct points. A computer, however, is going to make the right shift at the right time all day long.”
Freeing drivers from the physical task of shifting gears will also have a positive impact on safety. “Driving a truck is so much harder today that it was five years ago,” says Allison's Murray. “There is much more traffic out there; drivers need to focus their concentration on [the traffic], not on what gear they're in.”
“Drivers are at the saturation point in terms of what they need to do behind the wheel,” says ArvinMeritor's Allen. So taking the shifting away isn't necessarily the negative many drivers think it is.
“Teaching someone to drive a commercial vehicle is a big task in and of itself — and that's before they get out on the road and start to deal with traffic congestion and shifting at the same time,” he points out.
TOUGH, BUT NOT IMPOSSIBLE
In the end, says Roadranger's Batten, developing transmission packages that meet all these needs will be tough, but not impossible. “Can we pull a rabbit out of the hat? It's a steep learning curve and the final solutions for ‘07 engines haven't been mapped out yet,” he says. “We're going to be very busy over the next few years, but our goal is to make sure the customer comes out ahead at the end of the game.”
Tech talk
Changes in the engine-transmission matrix mean that spec'ing transmissions in the future may not be business as usual. Charlie Allen, national service director for ArvinMeritor, suggests that fleet managers keep several key terms close at hand as they map out transmission specs.
Cruise speed. A desired engine speed at a particular road speed (in high gear) for efficient operation; calculated by the same factors as startability.
Horsepower. Derived from torque, it's a measure of an engine's ability, i.e. the rate, of doing work over a given amount of time.
Overall ratio. Lowest gear ratio divided by the highest gear ratio. A transmission with small steps requires more speeds to gain more overall ratio.
Startability. Determined by the transmission's low gear and axle ratio, tire size and engine torque at 800 rpm. A measure of how easy it is to get a vehicle moving.
Step size. Used to match the engine to the transmission. Since today's engines have much wider operating ranges than older engines, and almost constant horsepower available throughout the operating range, the need for close-stepped transmissions has diminished.
Torque. A twisting force applied to an object that makes the object turn about its axis of rotation. Measured in lb.-ft., or foot-pounds?, torque is important in helping vehicles accelerate. Higher torque is necessary when a vehicle is towing a large load or working in rugged conditions.
Source: ArvinMeritor
