Engines & Fuel Economy
On-Board Speed Manager
A little-known cummins electronics feature can push an inefficient driver into fuel-bonus territory.
Rolf Lockwood
Contributing Editor
Engine speed has been managed electronically for years now, but a sophisticated new wrinkle on the theme may have escaped your notice. Called "Load Based Speed Control," it's a patented feature that's standard on all ISM and ISX engines built after October 2002. Not a lot of noise has been made about its capabilities and that's a shame, because it works a treat and could raise your least-efficient drivers to fleet-average fuel economy performance — or better.
CALL IT A VIRTUAL TRAINER
Some months ago, we spent a day with a pair of LBSC trucks operated by Concord Transportation out of Concord, Ontario, Canada. At the time, fleet manager Derek Varley tracked fuel economy very closely, and he'd been experimenting with this new feature for a few months to pretty good effect. (In fact Varley was so good at this stuff, he's since moved on to bigger and better things.)
The trucks we drove — my colleague Jim Park and I — were Kenworth T2000s, both with 2001-model Cummins ISX 450 ST2 engines, one mated to an Eaton Fuller 13-speed, the other to an Eaton AutoShift box. But more on our test driving later.
First, let's define "load" and then look at the technology.
IN THEORY
By "load" we mean literally everything the engine must overcome to move the truck — the rig's gross weight, aerodynamic drag, tire rolling resistance, transmission and axle parasitics, various kinds of inertia, and whatever else that conspires to keep it stationary. That includes a few items we can't talk about for proprietary reasons.
As the name suggests, LBSC continuously calculates that load and then optimizes the allowable speed range of the engine to ensure maximum efficiency. It works in conjunction with the Cummins road-speed governor and "geardown protection" features to manage engine rpm — not only in top gear and one down from top — but in all lower gears as well. In a 13- or 18-speed, for instance, LBSC will be in charge up to seventh low. In a 10-speed, it handles gears one through eight.
The logic divides the engine's operating range in two — normal and extended ranges — with a dividing line, or breakpoint, that you can set according to your own management criteria. You can have a low and a high engine speed breakpoint anywhere between 1,400 rpm and the engine's governed speed. The maximum allowed rpm will vary between those points depending on fueling demand. If the engine load is light, speed will stay closer to the low breakpoint; if the load is 100%, you'll get the higher value. And you'll get access to the extended rpm range if you add a grade or a headwind or some other such drama to the mix.
In a 2,000-rpm engine, which is where ISX motors are now governed, the default breakpoints are both 1,800 rpm, for a balance between economy and performance. In a fuel-sensitive application, the default gives you 1,500 rpm on the low side and 1,600 rpm on the high side. If performance is your game, you set both thresholds to the highest value and let 'er rip.
If activated in that 1,800-rpm default setting, the feature will let drivers access the extended range above 1,800 rpm when there's a serious load placed on the engine, but holds revs below that point when they're not needed. (See charts)
You also get access to the extended range during any out-of-gear condition to facilitate early downshifts and, when the truck's at rest, to enable PTO use, explains Cummins heavy duty product manager Cliff Putterill.
Sounds simple — and in principle it's very straightforward indeed — but LBSC took a lot of development work. In fact, Cummins engineer Steve Bellinger, whose brainchild it is, says it took two years of intensive work that had him road-testing 10-15 hours a week. That's not routine. Four patents were ultimately issued and a number of North American fleets had ISX engines reprogrammed with the LBSC feature in 2002 before it became a standard production offering.
Bellinger, who is also responsible for the Smart Torque feature on many Cummins motors, says he conceived LBSC while concentrating on an engine's fuel map. Basic physics dictates that any internal-combustion engine will operate most efficiently at low rpm under heavy load and least efficiently with light or intermediate load and high revs. He realized there was no practical justification for operating an on-highway engine in that least economical way. The driver gains nothing and the fleet loses money up the stack.
So why not try to control things, he asked himself, by essentially just moving the engine's governed speed around? Put another way, why not try to enforce progressive-shifting habits while maintaining the flexibility to extend the engine's operating range when the driver really needs it? The driver loses nothing and the fleet buys less fuel.
"This feature is designed to continuously compute the power demand or load on the engine and then move the high-speed governor around, based on how hard the engine is working," Bellinger explains. "When the engine's not working very hard we pull the high-speed governor in and limit the usable speed range of the engine. Conversely, where loads are high and there's a legitimate need for extending its operating range, such as when climbing a grade or dragging a multi-axle trailer around a tight turn, we allow it."
It does sound simple, but the key is computing "load" accurately — and often. In its first incarnation, LBSC assumed an arbitrary gross weight, but that would have limited its usefulness. Especially in Canada, because that arbitrary weight would have been somewhere between 65,000 and 80,000 pounds to fit U.S. conditions and thus wouldn't have been much help with heavier weights up there. Conversely, if actual gross were much lighter, you'd need a heck of a grade to get into extended range.
Recognizing the limitations of an assumed gross weight, Bellinger and his comrades came up with an innovative way to actually estimate the gross weight of the vehicle while it's being used — a dynamic calculation done in that little red or black electronic control module once every 20 milliseconds. It also takes into account many of the load variables mentioned earlier, and more besides, but for reasons of confidentiality, we can't go into them. The bottom line, apparently, is a computation that not only yields an accurate result but is also very responsive to sudden changes in effective weight. Though these estimates are purely theoretical, we're told that weigh-scale tests with loaded trailers show the mass estimate to be surprisingly accurate.
ON THE ROAD
That's a lot of description, but how does it work? Mighty well. And it was obvious right away that the best drivers won't notice anything. Cummins' Putterill agrees, emphasizing that LBSC aims to help inexperienced drivers maximize the engine's fuel potential.
Park took the first stint at the wheel, in the 13-speed truck set with 1,500/1,600-rpm thresholds, and we instantly realized that he always shifts sooner than the computer assumes. A natural progressive shifter after years as an owner-operator, squeezing every gallon of fuel to avoid emptying his own wallet, he had to will himself to bump against the artificial governor — it feels exactly like that — at 1,500 rpm on level ground with our light payload of some 25,000 pounds. LBSC wouldn't help him.
We were driving a simple 20-mile route on a two-lane highway running north from Concord, with a great many short, sharp hills and a couple of long ones. It was a perfect test ground for our purposes, and on those grades the Load Based feature worked as promised. On the first hill, the red box gave Park 1,800 rpm, but he said he wouldn't have let it go that high normally. The switch from normal range to extended was seamless.
We also stopped at the base of a good hill and wondered how quickly LBSC would recognize the load when we started again. For an instant — but not much more than that — it held us to 1,500 rpm, then let us go.
Not having Park's discipline or in-the-trenches experience, I've never had to care much about progressive shifting except in theoretical terms. Meaning, me and the governor are usually on pretty good terms. So when I did the 40-mile rounder up and down those hills, I knew only too well that I was being held back on occasion. That probably makes me like many drivers — most certainly like the least efficient ones.
Did I feel hemmed in, constricted? Not at all, and after just a few shifts I was pretty comfortable with LBSC. In fact, I was grateful to be given what I saw as guidelines, and the driving job was actually much easier. The engine's driveability didn't suffer in the slightest and the engine speed was there on demand when I met a grade or if I wanted to launch a downshift high on the tach.
On that point, Cummins has done surveys of drivers at several American fleets where the Load Based feature has been used for a while. Maybe a little fearful that drivers would object, they found quite the opposite. Most drivers actually preferred LBSC to the open alternative, Bellinger says, while a few didn't care one way or another, and only a small minority preferred the traditional governor route.
How did it mate with the AutoShift? Not at all, in a sense, because the transmission's own shift logic takes over in automatic mode and LBSC is shut down. Some drivers do however use these gearboxes in manual mode at least some of the time, and in that case LBSC is there to take charge of managing engine speeds.
We both ran the same route with the auto box, preferring to use it in manual to manage the hills ourselves. It was actually a pretty good combination if we let out fingers do the tapping on the up and down shift buttons.
THE REAL WORLD
At Concord, Derek Varley's figures at the time showed some remarkable gains after installing LBSC in these two long-haul, light-load tractors. We're not claiming any rigorous fuel testing here, and we don't know exactly how many variables we're dealing with, so bear that in mind. These are just company records.
Nonetheless, the AutoShift tractor went from average monthly miles-per-gallon figures in the high sevens and low eights through 2001 and early 2002, then all the way to high eights and low nines with LBSC activated, through October. Its best month was September of 2002, at 9.3 mpg, compared to 7.9 for the same month a year earlier.
The 13-speed got as high as 10.3 mpg in August of 2002, compared to 8.8 in the same month a year earlier — although it did dip down to 7.9 in October, 2002 for some unknown reason. On average, it went from high eights and low nines without LBSC to higher nines and low tens with it.
Again, there's nothing terribly scientific about these results, and in fact Putterill and Bellinger are a little dubious about them because there are unknown variables in play. That said, we're told that every fleet using LBSC so far has reported positive fuel results to some extent. Assuming your drivers are more like me than like Park, which seems probable, it sounds like easy asset management.
We'll give the last word to an executive at a huge American fleet that's gone 100% to LBSC. After testing the feature on the road he said, "That'll knock the spurs off their cowboy boots."
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