Buyers of commercial vehicles will have more choices than consumers when contemplating a hybrid powertrain for their next vehicles (parallel or series, with electric or hydraulic energy storage), according to ABI Research. Each system has its advantages and disadvantages depending on the duty cycle, and a single hybrid technology will not prove to be best for all commercial vehicles.
Passenger transit buses have led the way toward hybrid drive for heavy commercial vehicle use, thanks to generous subsidies from the federal government; the technology used is split almost equally between series and parallel electric drive.
"Energy storage and retrieval demands for heavier vehicles are a challenge for today's batteries, and the economics are difficult to justify without subsidies," says ABI Research principal analyst David Alexander. "But the emerging development of hydraulic hybrid drive technology appears to deliver real benefits and an attractive ROI."
The larger mass of commercial vehicles means that power density is of greater importance than energy density. The prime example is a garbage-collection truck. Typically Class 8, this vehicle can be made significantly more efficient if its kinetic energy can be stored and reused during its multiple stop-start duty cycle. A large amount of energy must be captured quickly as the vehicle comes to a halt, and that energy must be reused efficiently to get the heavy vehicle moving again. A pressurized hydraulic accumulator can handle this high-energy transfer cycle better than a battery, and it is more cost-effective than an ultracapacitor system.
Additional benefits for such a hydraulic system include greatly reduced brake maintenance and the potential to use the hydraulic reservoir to power the compactor equipment, rather than driving a separate hydraulic pump as is done on conventional garbage trucks.
Conversely, production hybrid vehicles for consumers today are exclusively electrically assisted, and so far have all used a form of parallel configuration. The much-anticipated Chevrolet Volt (coming to market in 2010, according to General Motors) may be the first series hybrid-electric car for consumers. Manufacturers appear more interested in hybrid-electric drive for consumer vehicles as a step toward plug-in capability. Ford presented a concept hydraulic-hybrid Expedition in 2004, but cancelled the program.