Two in one
While Volvo does not have a hybrid research project in the United States, says spokesman Jim McNamara, the company will benefit from research and testing done by its parent, Volvo Trucks, in Sweden. Volvo is developing a refuse vehicle hybrid similar to the Mack system in Europe.
“The goal of our hybrid is a reduction in fuel consumption,” says Daimler Trucks’ Paul Menig, chief engineer for mechatronics. The biggest potential savings will likely be in fuel conserved via recovered braking energy, although the amount saved will depend on the application. International’s Gosbee says, “Coast to coast at 65 to 70 mph, at constant speeds, you won’t be able to recover that much. But, in the East and West Coast north-south corridors, the picture gets a lot better. In some applications, significant energy can be recovered, at times doubling efficiency, which has an enormous impact on fuel economy.” n
How hybrids mesh with the drivetrain
The electronics of hybrids not only control the system but also convert the alternating current from the generator to direct current at various voltages for battery charging and vehicle use. They also convert the DC from the batteries back to AC for use in the motor as well as for hotel loads.
There are two basic types of architecture – parallel and series.
A PARALLEL HYBRID connects both the diesel engine and the electric motor to the drivetrain, usually by inserting the motor generator between the clutch and the transmission. The two power sources then share the job of moving the vehicle forward, sometimes providing torque simultaneously. They also share braking done through the drive axles – that is, the electric motor shares the job of slowing the vehicle with the engine brake.
A SERIES HYBRID resembles a diesel-electric locomotive, eliminating the solid driveline linking the diesel engine to the wheels and using the diesel only to generate electricity. Such hybrids have separate electric motors that drive the wheels. It is sometimes called a SPLIT HYBRID, or series-parallel system when the system can operate as a series hybrid under one set of conditions, and then lock the engine to the drivetrain under another and operate as a parallel system. This is the case with the ArvinMeritor design.
HVAC, microwave, TV — bring it on
Hybrid technology is ideally suited for handling hotel loads overnight in a sleeper. The combination of powerful, fast-charging batteries and a big motor-generator promises to provide a high level of auxiliary power.
Paul Menig says Daimler Trucks’ hybrid has integrated an electric air-conditioning system into the existing duct system of its cabs and sleepers, and employs a fuel-fired heater to keep the driver comfortable in cold weather.
Dmitri Kazarinoff says the maximum charging rate of Eaton’s motor-generator is 44 kilowatts at a fast idle of 1,000-1,200 rpm. An occasional 4-6 minute cycle could charge the batteries, while a 120-volt AC system is cooling the cab during a rest stop. Under these conditions, he says, “the diesel is under a significant load, and is efficient.” And, because the motor-generator can crank the engine at lightning speed, without the noise and low-rpm shake of a standard starter, drivers will be able to sleep through charging cycles.