|The hydraulic system provides a high power-density energy storage option. Click to enlarge. Source: EPA|
After two years of road-testing of a prototype, UPS has placed its first order for hydraulic diesel series hybrid delivery vehicles (HHV), becoming the first in its industry to do so.
Disclosing the results of its road testing on Detroit routes for the first time, UPS and the US Environmental Protection Agency (EPA) said the prototype vehicle had achieved a 45-50% improvement in fuel economy compared to conventional diesel delivery trucks. UPS believes similar fuel economy improvements and a 30% reduction in CO2 are achievable in daily, real-world use.
The hydraulic series hybrid, originally developed in a laboratory of the US Environmental Protection Agency (EPA), uses a diesel engine/pump to pressurize and transfer hydraulic fluid to the rear drive pump/motor and/or high pressure accumulator. The hydraulic drivetrain replaces the conventional drivetrain and eliminates the need for a conventional transmission.
|Hydraulic series hybrid truck configuration. Click to enlarge. Source: EPA|
The hydraulic system also handles regenerative braking and energy storage. When stopping the vehicle, the hybrid controller uses the energy from the wheels by pumping fluid from the low pressure reservoir into the high pressure accumulator. When the vehicle starts accelerating, this stored energy is used to accelerate the vehicle. This process recovers and reuses more than 70% of the energy normally wasted during braking. (Earlier post.)
UPS is ordering seven HHVs. The company will deploy the first two in Minneapolis during the first quarter of 2009. Eaton, which helped develop and refine the vehicle’s hydraulic hybrid power system, will monitor the vehicle’s fuel economy performance and emissions in the Minneapolis area. The additional five HHVs will be deployed later in 2009 and early 2010.
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.
Eaton began working with the EPA in October 2001 under a Cooperative Research and Development Agreement involving hydraulic hybrid systems and components. As part of Eaton’s role in designing and developing hybrid technologies, the company’s engineers were co-located at the EPA’s Ann Arbor facility. Eaton also earned a number of hybrid power system patents and continues to work on a number of other hybrid vehicles initiatives with UPS and others.
The EPA believes the technology can perform equally well in other applications such as shuttle and transit buses and refuse pick-up trucks. In 2007, the agency launched a project to develop hydraulic series hybrid systems for Class 6 port yard hostlers—the heavy-duty diesels that move goods and products from ships to trucks at ports. (Earlier post.)
For the longer term, the EPA is interested in exploring a number of different high-efficiency engines for use in the series-hybrid architecture, including optimized diesel or spark ignition engines with biofuels; HCCI gasoline engines; and free-piston engines.
Hydraulic Hybrid Vehicles 101 (EPA, 2007)