Two presenters break down various systems to benefit equipment upfitters and fleet professionals
Apr 1, 2010 12:00 PM, By Rick Weber
TRUCK technology has advanced drastically in recent years, and distributors can expect even more changes as hybrid trucks gain traction with commercial customers.
How do they work, and what do distributors need to know about them? The NTEA session titled “I Have a Hybrid Truck In The Shop: Now What?” was offered to provide answers. The session included presentations from two speakers, one speaking on hydraulic hybrids, the other a specialist in electric hybrid systems.
Leading off was Simon Baseley, director of engineering studies and applications at Bosch Rexroth, manufacturers of a system designed to use hydraulic pressure to capture and utilize the energy that otherwise is lost in stop-and-start driving.
“This system can deliver significant value when matched with the right drive cycle and emissions profile,” Basely said. “The refuse truck is one very good example. It improves fuel consumption, performance, and acceleration while providing two to four times the brake life.
Basely said that shops staffed with technicians who know hydraulics should catch on quickly to hydraulic hybrid systems.
Hydrostatic Regenerative Braking (HRB) systems for commercial vehicles and mobile equipment recapture braking energy. Instead of allowing braking energy to be lost, the HRB system converts it into hydraulic energy and stores it. The next time the vehicle is accelerated, this stored energy is fed back to the transmission. As a result, the truck's internal combustion engine does not have to work as hard.
Rexroth has developed parallel and series HRB systems for the various drive concepts in commercial vehicles and mobile equipment. The hydraulic hybrid drive works best when used on heavy vehicles and mobile equipment that brake frequently. The more intensive the start-stop cycle, the more HRB can reduce fuel consumption.
He said the parallel hybrid drive is designed for vehicles having a conventional mechanical drivetrain and powered primarily by an internal combustion engine. A gearbox links a hydraulic variable axial piston unit to the truck's drive shaft to convert kinetic into hydraulic energy when braking. As the truck brakes, the axial variable piston unit uses that energy to load a hydraulic bladder accumulator with hydraulic fluid. This process is controlled by an electronic controller that is teamed with a hydraulic valve manifold. During acceleration, the entire process is reversed: The pressurized fluid is discharged in a controlled manner from the accumulator and flows back through the variable axial piston unit. The latter is driven by the fluid flow and, acting like a motor, gives up its energy to the mechanical drive train. A pressure relief valve in the system ensures the highest level of safety for both processes.
A bonus for the vehicle operator: The HRB significantly reduces brake wear. The production of fine dust from brake wear and the CO
Modular construction means the parallel HRB is be integrated into essentially any commonly available commercial vehicle frame. This also enables retrofitting of existing vehicle fleets.
System components of the parallel HRB: A4VSO variable axial piston pump with gearbox for pump/motor operation; high-pressure bladder accumulator; HIC valve manifold; electronic controller; and sensors.
Words of caution
One thing for technicians to consider when working on trucks equipped with hydraulic hybrid systems:
“There are critical areas where there are possible high temperatures, but rarely do temperatures become high enough to cause issues,” Baseley said. “We use standardized hydraulic fittings available from general distributors. Hose assemblies are pressure-tested. The accumulator is a very strong component. It's obviously designed to handle 5000 psi.
“When temperatures within the oil fall outside established bounds, the system will not allow engagement of the pump or will only engage with limited torque and limited mode until temperatures get back within range. Experience has shown that hardly ever happens. But if we do see significant system anomalies, the system will be shut down. Because it's a power-off system, vehicle operation is not compromised. You will not get fuel savings and brake-wear reduction, but you can drive and operate the vehicle.
“We normally supply the system in the truck with the accumulator charge, but you would need to recharge occasionally because there is some diffusion of air into the oil. The equipment you need is a nitrogen bottle in 2,300 psi, fully charged. You need an intensifier that is readily available from distributors and works off shop air and takes the lower pressure of nitrogen charge boosted up so you can inject it into the accumulator through the appropriate valve. If you need to repair the accumulator because of an internal problem, then you need trained hydraulic personnel or return the unit to a supplier or distributor for repair.”
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