Spec'ing the Right Powertrain

An informal survey of a dozen truck sales reps suggests that the overwhelmingly most popular truck spec today is “just the same as the truck I have now.”

While that might seem like a ringing endorsement of their truck, more likely, it’s because customers are change-averse and reluctant to embrace new technology.

We asked a few fleet maintenance managers a similar question at the American Trucking Associations' Technology & Maintenance Council’s meeting earlier this year and got similar answers. They want a truck they are familiar with and that they — and their drivers — understand. New technology comes with a learning curve, and that makes some people nervous.

That said, newer technology, or upgrades from previous versions, are usually better. Here are a few points to consider when spec’ing your next powertrain.

What Does the Truck Do for a Living?

The first consideration, obviously, is the application. Vocational powertrain specs will be different from long-haul over-the-road, which be different again from short-haul regional.

However, you may still be able to use the same engine platform across different applications by tuning certain parameters, such as axle ratios and the engine’s torque and horsepower curves, to the application.

There are many economic and logistic benefits to operating a standardized fleet that share common parts, training requirements, and other characteristics, but you can take that only so far. 

You can run into performance difficulties when asking double-duty of a truck, for example a P&D truck by day and a linehaul truck at night. Tuning for one application will leave you at a disadvantage in the other. And trying to split the difference may yield unsatisfactory results in both types of service.

“We believe that every truck needs to be spec’d and purchased for the work it'll be doing,” says Len Copeland, product marketing manager, Detroit Products, Daimler Truck North America. “There's just such a diversity in applications — weight, length of haul, road speed, climate, etc. — that each truck needs to be set up specifically for how it's going to be worked.”

The other challenge with a powertrain spec is driver acceptance. Obviously, the fleet is looking for a reliable, efficient spec, while drivers like high-performance trucks that go fast. It’s a constant battle, and at this point in time drivers seem to have the upper hand.

“I would say a lot of the fuel economy fundamentals have gone by the wayside because of the driver shortage situation,” Copeland says. “Any disruption to drivers in terms of road speed or anything like that will shake up a driver and perhaps even scare him or her to leave the fleet. That is something we're hearing a lot about from fleet customers.”

Parameter Settings & Fuel Economy Features

All OEMs offer a multitude of customer-programmable powertrain parameters, and the functionality varies across the brands. Some are offered as optional performance packages, while others can be set individually. Understanding these settings can help bridge the gap between fleet and driver desires.

One such offering, from Cummins, called On Ramp Boost, can help neutralize trip time deficits.

“On Ramp Boost releases the fuel potential on an on-ramp to maximize merging speed, where predictive gear shift provides a downshift before the hill starts to maximize gradeability,” explains Kris Ptasznik, powertrain TCO and consultancy leader at Cummins. “The negative speed offsets can be counteracted by the positive speed offsets by charging an uphill to maintain speed on a grade. This speed profile provides increased fuel economy with similar trip times.”

That might take a bit of explaining to a driver, but when they begin to understand there’s a bit of give and take in the settings, they might embrace them more enthusiastically.

One common feature, generically known as predictive cruise control, uses the vehicle’s GPS and in some cases terrain maps to optimize throttling, braking, and shifting for the road conditions. Users can also bake in some flexibility to improve driveability, such as allowing the truck to run out a little on a downhill grade or throttle up as it approaches a hill.

“Beyond traditional SmartCoast, Advanced SmartCoast and SmartCoast Extensions are default-enabled with predictive road map modules to maximize the coast time," Ptasznik says of one Cummins option. The engine electronics know the truck can start coasting earlier where the vehicle may reduce speed, but the speed offset will be equalized or exceeded on the other side of the crest.

“Hill Rollout allows for a safe descent speed of the hill, while releasing engine brakes near the bottom of the hill in order to speed the truck up for the greatest duration of post-downhill coast possible back to cruise set speed, while not exceeding a fleet's max desired speed.”

If you’re unfamiliar with such offerings, talk to your dealer and make a point of getting to know everything your powertrain can do.

“The dealer is going to be the best source for learning about the available engine parameters and levers they can pull to improve efficiency,” says Sarah Abernethy, Kenworth vocational marketing manager.

Get Drivers off the Pedal

One of the greatest impediments to good fuel economy is drivers who insist on driving the truck in “manual” mode, that is, with cruise control not activated. Most of the fuel-saving features in today’s powertrains are active only when cruise control is activated.

Sometimes the problem is that the default fuel economy settings are a bit too aggressive and disliked by drivers.

Often, drivers simply don’t understand the feature’s purpose and so don’t see the advantage. Getting drivers over this hump usually requires a combination of training on how the system works and incentives to improve utilization.

“We recommend settings that balance efficiency and performance, and that feel intuitive and expected for the driver,” says Laura Ricart, Navistar senior chief engineer for vehicle performance integration. “Training the driver in terms of what to expect in different situations will give them confidence on the features, enhanced with messaging on the instrument panel that feature is active.”

And in this case particularly, driver training should be more than a recommendation that they read the manual sometime while they are waiting for a load.

Joe Scarnecchia, Mack Trucks’ powertrain sales development manager and a former driver trainer, says education makes a major difference in drivers' understanding of the equipment and how to drive it for best fuel economy and/or performance.

“You need the right venue where you can have the driver’s attention without interruption and distractions,” he says. “If it’s a large group or you’re unable to have a face-to-face training session with the driver, the next best option is to train the trainer.

"There is nothing more frustrating than when the driver has complaints and concerns and 99% of them are because nobody held a driver training session.”

DTNA’s Copeland says the fuel savings associated with cruise control are just too great to ignore, especially when you get into predictive and adaptive cruise control.    

“We think that using cruise control can get you up to 6% better fuel economy [than the pedal alone], and you can add to that with a predictive cruise mechanism,” he says. “I think most of the OEMs are deploying predictive cruise now, and that is only available in cruise control. With ACC, we figure you can achieve up to 11% better fuel economy than with cruise control alone.”

Any fleet that has ever tried will tell you it’s difficult to establish fuel-economy incentive programs because of the drivers’ perception of fairness. They, correctly, see heavy loads and urban driving, even weather, as factors that conspire against best-in-class fuel economy. Some OEMs now advocate incentivizing correct driving behavior and technique rather than hard mpg.

“We're hearing from customers that set an average cruise usage target,” says Copeland. “That involves establishing a metric and having a highly transparent dashboard so drivers can see and learn to trust the metric.”

And if else fails, try setting the pedal road speed slower than the cruise-on road speed.

“Setting the vehicle pedal speed slightly lower than the vehicle's cruise speed will encourage drivers to use cruise control if they would like faster road speeds,” suggests Duane Tegels, powertrain product marketing manager, Volvo Trucks North America.

In addition, Tegels recommends fleets look at scheduling, where possible, to minimize time spent in congested areas or heavy traffic.

“Plan routes that involve highways or long stretches of road with steady traffic flow,” he says. “This creates more opportunities for drivers to engage cruise control.”

The Hardware Spec               

The current trend in driveline spec’ing is downspeeding. We are seeing taller rear axle ratios (lower numeric values) than ever before, but this has a limiting effect on the number of suitable applications. Superfast ratios like 2.15-2.17:1, for example, allow the engine to operate at low rpm during moderate terrain, reducing engine pumping loss.

“Faster ratios require an integrated quick-shifting transmission that allows the top three gears to be used at road speed while keeping the engine at peak torque or horsepower, depending on the terrain,” says Tegels.

Such ratios, however, wouldn't work well for fleets that put trucks into mixed service doing local and regional work.

“Generally, the lowest cruise rpm at speed will provide the best fuel economy,” says Cummins’ Ptasznik. “However, being too aggressive for a fleet that spends significant time on two-lane operation or speeds slower than the normal 65 mph results in additional gear down time.”

Such specs are usually subject to an engineering review before approval, so the OEM has a bit of a say in how the product should be used.

Spec’ing Outside the Box

There are options available for fleets with specific duty cycles, such as loaded one way, empty back, or with diminishing loads, such as food service delivery.

Mack and Volvo offer a 6x2 liftable pusher axle for such applications. When empty or less than 60,000 GVW, the pusher axle will lift off the ground and will use less fuel and save highway tolls than when the axle is off the ground.

Navistar’s new S13 Integrated Powertrain is designed to be matched as Direct Drive Optimized (to cruise in 13th gear or direct drive). However, the overdrive gear is always available to use in the T14 transmission. The Low RPM Cruise feature engages when the powertrain senses the vehicle is hauling light. It calculates whether it would be more efficient to run in the overdrive gear (though overdrive is usually less efficient than direct.) This action moves the engine into a more efficient point of lower rpm and higher torque, ultimately optimizing for the overall efficiency of the entire powertrain, not the engine or transmission individually.

With all the options available today, choosing one or a few can be daunting. It would be easy to say just load up on technology, but that can get pricey. Talk to dealers to see what’s new in the portfolio of options, or how the technology you’ve come to love and understand has evolved.

You won’t get the same truck you have now. Chances are, it will be better.