Daimler Trucks North America has referred to its $40 million, five-year SuperTruck program that concluded earlier this year as “a playground for our engineers.” Overseeing this playground’s development and integration activities was Derek Rotz, the Principal Investigator who was hired in 2010 when the program kicked off. “They [U.S. Department of Energy] wanted us to look at technologies that could be implemented in say the next 5 to 7 years, but also technologies that were 10 years or plus out,” Rotz said. “We were able to work on very high-risk, high-reward technologies, and provide functional demonstration on a line-haul program.” The team leveraged the knowledge and expertise of the global Daimler organization to accelerate development. For example, among other responsibilities, Freightliner experts in Portland, OR, took the lead on base vehicle development, aerodynamics/cooling, lightweighting, and vehicle integration; engineers at Detroit Diesel concentrated on base engine development, high-voltage controls, and waste heat recovery (WHR); Mercedes-Benz in Stuttgart, Germany, also worked on WHR as well as predictive hybrid control and powertrain electronics; while Fuso engineers in Japan focused on the hybrid-electric powertrain. In the end, the company “far exceeded” its expectations, achieving 115% freight efficiency improvement, 12.2 mpg, and 50.2% brake thermal efficiency. “Some of our trucks on the road already have the lessons learned from SuperTruck,” Rotz shared during an interview with SAE Magazines. “Some of the early learnings went directly into the development of the Cascadia Evolution, and products we have coming in the next couple years have been heavily influenced as well by the SuperTruck program.”
What were some of the program’s main challenges or trade-offs?
In some cases, there are conflicting goals that had to be resolved. For example, cooling the engine and improving aerodynamic performance are typically at odds with each other in terms of how they handle the airflow. This was one of many trade-offs that needed to take place. The answer in this case was to create the articulating grille; while at slower speeds and while climbing a grade when the engine loads increase, the grille louvres open up to provide airflow through the engine compartment and the cooling package; at higher speeds when aerodynamics is more important, the grille bars close to maximize those benefits. Also with aerodynamics and cooling, we actually have the cooling package tilted back by 20°. We have a nice, round aerodynamic hood and a very square cooling package, so we tried to find numerous ways to adjust the cooling package to make it better fit with the aerodynamic hood. We settled on keeping the cooling package as is and we just tilted it.
Another example: We have a hybrid-electric powertrain on board that we basically use for regen braking, like when you’re going downhill, and essentially we’re using that to intelligently manage the kinetic energy of the vehicle as it goes up and down the hill. The system worked—it’s still pretty expensive, still pretty heavy, it’s not commercially available—but we ended up identifying other ways of managing that kinetic energy, essentially through complicated software. We have an application called eCoast, which allows you to shift the transmission into neutral under zero engine torque conditions. The engine has this friction torque when it’s not being motored so you decouple that and then you can drive more efficiently. And secondly, we introduced predictive technologies—the use of 3D digital maps and GPS to provide the vehicle with knowledge of the road ahead—hills, curves, etc. With that we’re able to adjust the cruise control speed, the shifting, and essentially manage the kinetic energy that way without having used the hybrid. Essentially, we discovered that the hybrid and the predictive [technologies] were competing for the same inefficiencies, and one is sort of a vague and heavy system and the other is software. So that was another case.
Additionally, there were questions on how do we develop a safe and efficient high-voltage power distribution system, not only for the hybrid but also for the waste heat recovery systems as well. High-voltage systems are things that we had not looked at in the past. Along the way, we also had to look at making trade-offs between efficiency, weight, and cost—hundreds of decisions have had to be made along the way.
Any technical breakthroughs that really stand out?
On the vehicle side, the aerodynamics plays a big role. We really took a clean-sheet approach and started with what we call basic shape analysis, just looking at basic shapes and seeing the aerodynamic properties. What is the coefficient of drag at 0 and 6 degrees yaw? And understanding what shapes contribute to overall drag. We found a good amount of savings through that, and as it turns out the aerodynamics ended up playing a really large part. The contribution of trailer aerodynamics was certainly a very surprising thing to us. We looked at the nosecone, trailer side skirts, and the boat tail—over two-thirds of the [aerodynamic] benefit actually come from the trailer.
How important is it to consider the tractor and trailer as a cohesive whole?
This was our first time being able to do that, because normally we say, ‘Well, let’s focus on the tractor because that’s what we build.’ To really bring in the trailer and have the design freedom to make changes to it for the program, we showed how those integration benefits can come together. Also because you reduce the aerodynamic drags, reduce the rolling resistance, you improve the driveline efficiencies, and you can get by with a smaller engine, so we have an 11-L engine [in the SuperTruck]. It’s a lower rating and it’s optimized for a very efficient vehicle like this. So essentially you get engine improvements through the systems we develop [for the engine], but you also get engine improvements with the reduced aerodynamics because they work together as a system. And you get other benefits by integrating the transmission...I honestly think that’s where the SuperTruck program was unique because normally an R&D program would be systems-level—‘Okay, I’ll focus on this system or that system.’ This is really the first time to look at the whole vehicle and put all the systems on a vehicle and see on the vehicle level how they work together and what integration possibilities there are.
What were some of the ‘high-risk, high-reward’ technologies and what’s their feasibility?
By starting with a clean-sheet approach and with new ideas, we recognized that some technologies would make it into a highway tractor quicker than other technologies. In some cases, some of the systems we developed on SuperTruck are not currently feasible. Some of the technologies may not be fully mature yet; some of the technologies have a longer payback period than our customers would expect; and in other instances such as the rearview camera, regulations that mandate the use of mirrors actually impede progress. But there are a number of technologies which had immediate transfer potential to our current product line, and customers today are already experiencing those benefits. Examples include the aerodynamic packages on the current Cascadia Evolution, the integrated Detroit powertrain including technologies such as downspeeding with a 2.28 rear axle ratio, eCoast, predictive shifting, and direct drive AMTs (automatic manual transmissions). We still continue to push forward with new and improved benefits for the vehicles: aerodynamic benefits such as drive wheel fairings, underbody covers, and the active grille—things that we’re still looking at. And we also are looking to make improvements to the base engine efficiencies as well as the auxiliary systems such as the power steering, air conditioning, and air compressor systems. Currently, there are limited feasibilities with hybrid-electric technology and waste heat recovery; however, SuperTruck did give us the opportunity to explore those technologies to truly understand both the potential and the obstacles needed to introduce these challenging technologies into the product. From that we have a much better understanding.
What about the use of lightweight materials?
Firstly on the chassis, we looked at different types of materials early on; we did a lot of different concept work. We actually built up a set of carbon-fiber frame rails—really lightweight, going from around 400 lb to about 100 lb. In fact, we had the engineer who designed it pick it up on his own showing how lightweight it was. And it worked, but we knew it was really expensive so that wasn’t what we wanted to focus on in the end. So we looked at aluminum design. We have aluminum C-channel rails, some reinforcements underneath, and then cross members are also made of aluminum. What we still don’t know is, long term, how the fatigue effects are going to come to play with that design. Obviously it works great right now, it’s lightweight, it achieves the [program] goals, but there’s still some concern that after 5 or 10 years, how are the fatigue properties going to be? And that’s really where our challenge is because that’s long-term development work and it’s still with a lot of uncertainties at this point.
Now that the program’s finished, where do you go from there?
We continue to look at some designs that show promise. For example, we have the drive wheel fairings that have good aerodynamic benefit. On the SuperTruck they’re still a little heavy, a little expensive, but our engineers took that design and further evolved it [to create] a lightweight variant. As we identify technologies like that, which show promise, we’ll spin them off into the product line. We also have a good chance to improve our engineering skills, introduce new tools we haven’t had before, and really build up our capabilities in analysis as well as testing and design. That’s knowledge that we can keep moving forward, and we certainly will use that to press forward on further enhancements.