Improve Economy By 20%?
Sounds incredible, but this Ohio-based company claims "SuperDrive" system also cuts pollutants and weight.
Tom Berg
Equipment Editor
Can one product deliver a 20% improvement in fuel economy? That and more, claims a small Ohio-based company, which is marketing a system where a low-speed engine runs through a hydrostatic, continuously variable transmission, or CVT. The company guarantees the 20% improvement, and also claims lower exhaust emissions and significant weight savings.
SuperDrive — the name of the company as well as the product — is not a simple add-on. It requires major alterations to a truck's drivetrain and modifications to its engine. Retrofitting is expensive and time-consuming, at least for each newly handled vehicle, which requires designing, fitting and fabrication of new brackets and other parts. But the system has been successfully tested in labs and on highways, where dyno and snap-idle tests have shown substantial reductions in particulates, NOx and other pollutants.
The U.S. Department of Energy is enthusiastic about its fuel-saving potential and may back it with funding. DOE and the company see its future in transit buses and long-haul big rigs, but it seems just as suited for medium- and light-duty urban delivery and on/off-road trucks.
SuperDrive is the brainchild of Herman Mitchell, a prolific inventor who founded the firm in Piqua, Ohio, and is now its vice president for research & development. Ray Fleming, vice president of operations, says the company has strong financial backing, and is getting orders from transit bus operators and talking seriously with several truck operators. Among those is Kirk NationaLease of Sidney, Ohio, which is set to order 100 Volvo tractors with SuperDrive.
"We don't buy fuel," says Tom Vondenhuevel, Kirk's vice president of purchasing, "but our leasing customers do. Some of them have been operating the new engines and have seen their fuel economy go down. 'Give us back our fuel economy,' they're saying, and that's the main reason we're looking at this."
Up to now, SuperDrives have been retrofitted to existing trucks and buses at prices ranging from $14,000 for a light truck to $35,000 for a heavy. But the Kirk order will probably be done in a modification shop at Volvo's plant near Dublin, Va. Powered glider kits, produced with everything but a drivetrain, would be rolled from the plant to the Fontaine-run mod center, where SuperDrive components would be installed. This would cut the per-unit cost on the VN tractors to about $15,000, Fleming said.
Out With The Old
Retrofitting involves removing a vehicle's clutch and clutch linkage, transmission and driveshaft, then installing SuperDrive components. These include a hydraulic pump and driveline motor connected by hoses and fittings, which comprise the hydrostatic CVT. There's also a smaller pump that supplies compressed air for injection into the exhaust stream, and a compact electronic control module. The ECM works with engine controls to regulate fuel and RPMs, and controls operation of the pumps and motor.
Removal of the conventional drivetrain saves about 1,000 pounds in a Class 8 vehicle, even accounting for weight of the SuperDrive components, Fleming says. But the system's main claimed benefits are its fuel savings and reduced tailpipe emissions, plus its easy operation.
The main pump, mounted directly behind the engine and driven by it, is an axial type with five cylinders arrayed around a swash plate. The plate moves to alter the cylinders' displacement, and therefore the flow of hydraulic fluid. This in turn constantly changes the drive ratio. Pressurized fluid runs through hoses to and from the motor that's mounted ahead of the rear axle's differential; a truck with a live tandem has two motors, one ahead of each diff.
Operating pressure is generallyabout 3,500 psi, but goes up to 5,000 psi when the system encounters high loads, such as when launching from a dead stop or beginning to climb a hill. The ECU notes the situation and orders more power from the engine and adjustments of the swash plate inside the axial pump. Fleming says the ECU's programming includes 48 ratio-type "steps" for the swash plate, but they are so closely spaced that changes are not noticeable to a driver.
Low-RPM Operation
The operating range of a Class 8 diesel is about 800 to 1,300 RPM, which is 300 to 500 less than usual. This takes advantage of a diesel's torque peak, which is usually 1,000 to 1,200 RPM. And it yields "fewer combustion events per mile," while allowing more time for more complete combustion, which is largely responsible for the fuel economy gains, Fleming explains.
What about the "sweet spot" of most big diesels — the speed at which combustion is most efficient — which is 1,500 to 1,600 RPM?
"We've extended the sweet spot" downward by keeping turbocharger boost up in light-load conditions, he answers. It's done by injecting compressed air into the exhaust manifold upstream of the turbo. This also lowers exhaust temps to reduce formation of NOx. Air comes from the hydraulically driven air pump, which is also controlled by the ECU.
The system's components can be sized to work in all classes of turboed diesels. Technicians recently installed a system in a Chevrolet 3500 with a Duramax V-8 diesel. The truck is owned by APS Energy in Phoenix, Ariz., which wants to try it out before committing to more buys. The system will also work in non-turbocharged engines, such as the gasoline Triton V-10 in a Ford Excursion, now being converted at SuperDrive's home facility.
Axle gearing is not nearly as critical as with a ratio-step manual or automatic transmission. Because of hydraulics, "the engine is uncoupled from wheel speed," Fleming explains. The ECU can be programmed and the pump and motor adjusted to work with an existing axle ratio, as was done with the Chevy 3500. Or the axle can be changed to enhance performance, as on a Kenworth T800 demonstration tractor.
The differential of one of the KW's driving axles stayed at the stock 3.73, while the ring and pinion gears in the other diff were changed to a 5.29 At low speeds, more fluid goes to the motor coupled to the "slow" 5.29 diff; as the truck accelerates, fluid is split between the two differentials, and at highway speeds, most fluid goes to the motor at the 3.73 diff.
Driving It
Operating a SuperDrive-equipped truck is really easy because there's nothing to think about but steer and brake. And the system is very smooth. The KW T800 demo tractor I drove reminded me of a 1950s Buick with Dynaflow, but without the slushiness — or a garden tractor with a hydrostatic transmission, but with far more power.That's because it had a 425-hp Caterpillar C-12 under the hood.
Following instructions from the truck's regular driver, I started the engine, then twisted a dash-mounted selector knob from N (neutral) to F (forward), released the parking brakes and stepped on the accelerator. The engine revved and off we went. There was no rising and dropping of RPMs because there are no perceptible ratio steps to climb. The C-12 revved to about 1,300 during acceleration, then dropped back to less than 1,000 as cruising speed was approached. Revs climbed slightly as I nudged the tractor toward 60 mph; there, engine speed was about 1,100. At 65 mph it cruises at about 1,150, which of course is about 500 less than what's normal practice in heavy trucks.
We were running bobtail and the truck was as fast from a traffic light as most cars. There are no gear-change interruptions, just smooth power. I wish we'd had a heavy trailer to tell me how the system felt under load. But the driver, Phil Moser, said it pulls very well.
"With a loaded trailer, it's a little bit slower [than bobtail] on takeoff, but once you get moving it just picks up," he said. "It's a lot faster than a standard truck on takeoff. With two trucks, both at 80,000 pounds, you'd have [what amounts to] a 6-second head start with the SuperDrive, if you were drag racing. With a manual transmission you have five gear changes before 20 mph, but with this you don't have that."
Moser, who runs a small truck line out of Piqua, likes the SuperDrive because it cushions the driveline, is easy to drive and greatly improves fuel economy. "From the owner of a company's standpoint, there's maintenance, and there's the driver shortage out there. We've got a lot of guys coming right out of school, and they're frankly very hard on the drivetrain. I know because I've hired a few of them, and I've spent a lot of money on drivetrain repairs — clutches, U-joints, and two complete transmissions."
"From the driver's standpoint — and I've got 25 years and 3 million miles of experience — every once in a while you miss a gear, and you fumble around to try to find one and you can't remember which one you came out of. If you go down a steep grade, you can miss a gear while trying to downshift to get the Jake Brake working right and now you're going downhill in neutral. With the SuperDrive, that will never happen because it's always in gear, and it's got what they call the hydraulic brake on it."
The retarder works by reversing the hydraulic motor, which then drags against the differential and axles. In the KW, two motors produce a lot of drag, and will completely stop the truck with no help from service brakes. The retarder begins working as soon as the driver takes his foot off the accelerator. Its output can be raised or lowered using the truck's original Jake Brake switches, with levels 1, 2 or 3. Moser said the retarder's strength and its point of actuation can be programmed to suit the truck's owner or driver.
The system could become a hybrid if pressurized fluid from the motors' braking action were stored in accumulator tanks, then sent back to the motors during launch from a stop. SuperDrive has no immediate plans to offer this, but patents on the system cover hybrid operation.
Because it's fully automatic, SuperDrive is easy to operate in traffic and while maneuvering in yards and loading-dock areas. There's no hopping of the tractor's front end and no gear-shifting work. Guys who enjoy going through the gears might find it boring because there's nothing to do but steer and brake the truck, and the engine's more or less constant speed is a little unsettling to somebody accustomed to the rise and fall of revs.
Fleming says he and some colleagues have explained SuperDrive to people at one transmission builder, but have heard nothing since. However, he says two major diesel manufacturers are intrigued with the idea, and one will begin testing it at Argonne National Laboratories if a DOE grant comes through. So it appears there is, indeed, a future for this revolutionary concept.
