DRIVING AUTOCAR'S DIESEL-HYDRAULIC HYBRID
Fuel-saving 'E3' system replaces the usual trash truck's automatic transmission with hydraulic pumps and electronic controls, but it behaves much like current vehicles.
Watch a trash truck go about its rounds, its engine roaring and brake linings shrieking as its driver and maybe a helper pause at each stop to pour garbage into the packer body, then move on to the next cluster of cans.
In your heart, you just know this type of truck could really use some kind of hybrid-drive system.
Hybrids capture the energy now burned away by brake linings and convert it to propulsion, so the more a truck stops, the more efficient it becomes. You can't buy one right this minute – but soon.
Autocar LLC, which makes the Xpeditor Class 8 low cabover formerly produced by Volvo, says it will be the first to offer a hybrid to the waste industry. Called "E3" because it's environmentally friendly, energy efficient and economical, the diesel-hydraulic product will be an option beginning next spring, said Tom Vatter, Autocar's vice president of sales and marketing. E3, a so-called series hybrid because engine power is funneled through the hydraulic system, is being adapted from a RunWise system developed by Parker Hannifin Corp.
E3 will be expensive, adding $40,000 or more to the price of an Xpeditor chassis, but it will pay for itself through savings in fuel and brake maintenance. Fuel economy of an E3-equipped truck should be 30 percent to 50 percent better than today's trucks, so the investment will be paid back in two to three years – maybe less as fuel prices continue to rise, Vatter said. And it's possible that Congress could make tax credits that are now available for buying alternative-fuel trucks also available for hybrids.
E3's driveline has three hydraulic pumps – a primary and two secondaries – to capture braking energy, explained Joe Theart, the project manager. The pumps drag the truck to a stop and use kinetic energy from the vehicle's motion to pump hydraulic fluid through lines into storage tanks, called accumulators. When the truck needs to start up again, the pressurized fluid shoots back to the pumps, which then act as motors, pushing the truck into motion. Operating pressure is 2,000 to 5,000 pounds per square inch.
Also part of the system is a Power Drive Unit, a hefty two-speed gearbox that takes engine power and feeds it through the pumps to supplement hydraulic force from the accumulators. The gearbox provides some reduction for starting out, and enables efficient high-speed cruising to the landfill. At 40 mph, the engine begins driving directly through the gearbox. This eliminates hydraulic churning losses and enhances fuel economy at highway speeds, Theart said. And of course there are electronic controls to manage the E3 operation and continuously modulate power produced by the diesel. Programming the controls for optimum operation is a project in itself.
Vatter showed me a "beta" version of E3, installed in a chassis parked in the lower level of the Autocar plant in Hagerstown, Ind. The apparatus was snuggled between the frame rails of the Xpeditor chassis, while some accessories – including a large cooler for the hydraulic system – were mounted outside the rails. The chassis was being readied for display at a trade show and was not ready for driving. The E3 system is still months away from production because Theart and his crew continue to test and refine it for its trash-collection role. The braking system also must still be certified with federal authorities.
On the day of my visit, the "alpha" truck was running on a race track near Winchester, about 30 miles northeast. So Vatter and I went there for my drive. As we arrived, the truck, a beastly looking contraption whose prototype E3 system was inelegantly stacked, strapped and bolted onto the chassis behind the cab, was stopping and starting out on the track. It had no packer body, but 20,000 pounds worth of concrete blocks were chained aboard to simulate the weight of a packer body and its load.
The truck presented an interesting audio show. The mechanism whined as the driver stepped on the brake pedal and the pumps pressurized the hydraulic fluid; it made a lower-pitch whine as the fluid coursed back through the pumps, which, as motors, helped launch the truck. The noise is quite noticeable to a bystander, but less objectionable than engine noise. Yet the engine roared with each start, because one stop generates about 70 percent of the hydraulic pressure needed to independently launch the vehicle from a dead stop, Theart said. So during most launches, the engine has to make about 30 percent less power and thus uses less fuel.
"We are chasing efficiency," he said later, and the production version, which is due out next April, should capture more energy and allow downsizing of the engine. The beta truck has an 8.3-liter Cummins ISC rated at 315 horsepower; it might be possible to use an ISB, which for 2007 will displace 6.7 liters and make close to the 350 horsepower that would be ideal for the E3.
"We don't need much torque," Theart said. "We need horsepower." The ISB, or something like it, would make enough horses but weigh less than the ISC and much less than 10- and 11-liter diesels now common in trash trucks.
On the track, the truck stopped where Vatter and I were standing and its driver, test engineer Josh Farmer, invited me to take the right-hand driver's seat while he sat on the left side – like many trash trucks, this one had dual controls – and he talked me through the simple controls.
Like a truck with an Allison automatic transmission, this one had a keypad-type selector with Drive, Neutral and Reverse buttons. Driving it was as simple as punching D, releasing the parking brake and stepping on the accelerator.
The engine revved upon launch and its noise drowned out the hydraulic whining. On level pavement, the mechanism expends its stored hydraulic energy quickly, within 10 or so seconds of the driver getting on the accelerator, and then the engine's full effort is needed. The engine's output would vary with the distance between stops and the uphill or downhill profile of the route, as would the amount of braking energy captured and converted to launching power. On level pavement, all normal stopping is done by the pumps, but service brakes apply if more forceful braking is needed.
Once a driver got accustomed to the whining sounds, he'd find that driving the E3 diesel-hydraulic hybrid is a lot like operating a normal trash truck with a diesel running through an Allison. The hybrid stops and starts like any other, and if the driver hops out each time to tip cans he'd find that he still has a physically tough job.
Before getting out of the cab he'd set the work brake, which is a parking brake that applies without the spring brakes being deployed, and thus is much quicker to release. The work brake wouldn't strain because while at a stop, this hybrid system lets the engine idle as though it were in neutral, instead of inching forward as it would with the idling engine sending some torque through an Allison. The E3's neutral effect might be convenient at a red traffic light because the driver wouldn't have to apply much pressure to the brake pedal to keep the truck from moving.
Another difference with the E3 hybrid is that its gearbox upshifts only once, sort of like an old GM two-speed Powerglide. On the alpha truck the upshift occurred at about 5 mph. After that, engine speed is constant because it is not directly geared to the driveline, but instead drives the system's hydrostatic pumps, which twist the driveline to send power to the wheels.
Upon launch, the engine responds to the mashing of the accelerator by revving to and staying near its 1,900- rpm redline; then it falls back toward idle when the driver gets off the pedal.
For test purposes the alpha truck's top speed was limited to 24 mph, Farmer said, so I didn't get to experience the system's direct drive feature, which kicks in at 40. I did make a lot of stops to simulate a trash collection route – at one point yelling at Vatter and his colleagues to "tip those cans!" – and got to enjoy the hydraulic whining, even if it was muted from the driver's perspective.
When I was done, Farmer drove the truck off the track, switched off the engine and backed the truck into a nearby garage. Hydraulic energy captured during the last stop was enough to slowly move the truck backwards until it was inside the building. Maybe he was showing off, but that nearly silent maneuver saved maybe a teaspoon of fuel. In a day's work, the hydraulic system would save many gallons of the fuel that a trash truck would normally burn, not to mention reducing exhaust emissions.
If the system proves reliable, which further testing will try to ensure, that's something operators could take to the bank instead of the landfill.
— Tom Berg, Senior Equipment Editor
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