Hybrid electric vehicles make especially good sense for taxis, buses, garbage trucks, and delivery vehicles, which run all day in stop-and-go traffic. They can shut off their internal-combustion engine while idling, and they can recapture energy through regenerative braking.
Now UPS is considering another kind of hybrid vehicle, a hydraulic hybrid vehicle:
EPA and the United Parcel Service (UPS) have developed a hydraulic hybrid delivery vehicle to explore and demonstrate the environmental benefits of the hydraulic hybrid for urban pick-up and delivery fleets. The demonstration vehicle is a 24,000 pound UPS package car, fitted with an EPA-patented full-series hydraulic hybrid drive integrated into the rear axle. The vehicle competed in the Michelin Challenge Bibendum in China with other advanced technology vehicles and received the top overall ranking among all commercial hybrid vehicles (delivery vehicles and urban buses).
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In laboratory tests, the city fuel economy of the hydraulic hybrid UPS vehicle is 60% to 70% increased miles per gallon compared to a conventional UPS truck. The CO2 emissions of the demonstration UPS vehicle are more than 40% lower than a comparable conventional UPS vehicle. The hydraulic hybrid vehicle also achieves approximately 50% lower hydrocarbon and 60% lower particulate matter in laboratory tests. This prototype vehicle has also demonstrated modest reductions in NOx emissions. Optimized production vehicles are expected to have larger NOx reductions. Hydraulic hybrids are able to capture and reuse 70-80% of the otherwise wasted braking energy.
I can’t say I’m impressed with this financial analysis:
When commercialized in high volume, EPA estimates that the additional cost of hydraulic hybrid technology has the potential to be about $7,000 for the UPS package car. In today’s dollars, the net lifetime savings of this technology in a typical UPS truck, which is used for 20 years, would be over $50,000. If fuel prices continue to increase faster than inflation, the lifetime savings would be even greater. The current data demonstrates that hydraulic hybrid vehicles have great potential not only for large commercial urban vehicles but also for personal vehicles, especially larger personal vehicles such as large SUVs, pickups, and vans.
How much is it saving in fuel costs per year? And for how many years? Are maintenance costs higher or lower than with a traditional engine and transmission? And will the salvage value be higher or lower at the end of its useful life?
Anyway, I’m sure you want to know how a hydraulic hybrid works:
A high-efficiency diesel engine is combined with a unique hydraulic propulsion system, replacing the conventional drivetrain and transmission. Hydraulic pumps and hydraulic storage tanks are used to store energy, similar to what is done with electric motors and batteries in hybrid electric vehicles.
A UPS press release explains it further:
With a diesel “series” hydraulic hybrid of the type being purchased by UPS, a high-efficiency diesel engine is combined with a unique hydraulic propulsion system, replacing the conventional drivetrain and transmission. The vehicle uses hydraulic pumps and hydraulic storage tanks to capture and store energy, similar to what is done with electric motors and batteries in a hybrid electric vehicle. In this case, the diesel engine is used to periodically recharge pressure in the hydraulic propulsion system. Fuel economy is increased in three ways: vehicle braking energy is recovered that normally is wasted; the engine is operated more efficiently, and the engine can be shut off when stopped or decelerating.The EPA estimates that when manufactured in high volume, the added costs of the hybrid components can be recouped in less than three years through lower fuel and brake maintenance costs.