Hydraulic Hybrids
Using Fluid Power to Increase Fuel Economy on Commercial Vehicles
The answer to reducing emissions and increasing fuel economy may be Hydraulic Hybrids; a relatively unknown technology. Hydraulic Hybrid technology can dramatically reduce emissions and increase fuel economy on commercial vehicles. The high power density of the hydraulics allows both performance increases as well as fuel economy.
Hydraulic hybrids use fluid power in the form of hydraulics to help propel the vehicle. Using hydraulics is a clean, reliable and efficient way to reduce emissions, fuel consumption and wear. Hydraulic Hybrids can also increase productivity, conserve resources, help protect the environment and decrease maintenance.
How do Hydraulic Hybrids Work?
Like electric hybrids, hydraulic hybrids use regenerative braking. Instead of capturing the braking energy in a battery pack, hydraulic hybrids store the braking energy in a hydraulic accumulator. The pressure then drives a pump/motor assembly which drives the wheels.
Hydraulic hybrids combine a hydraulic system with a diesel engine. The engine runs very efficiently because it doesn’t have a conventional transmission or drivetrain. The pump/motor drives the wheels which are powered by the hydraulic accumulator. This allows the engine to be shut off when the hydraulic system is propelling the vehicle.
How well do Hydraulic Hybrids Perform?
The regenerative braking system used in hydraulic hybrids is very efficient. The EPA stated that hydraulic hybrids are able to recover up to 70% of the braking energy that would usually be lost in a conventional vehicle.
This could potentially save 70% of the fuel and emissions of a conventional vehicle. Gas/electric hybrid vehicles also use regenerative braking but are much less efficient, only recovering up to 30% of the braking energy.
The high power density of the hydraulic system also improves acceleration and performance as well as fuel economy and emissions. In 2004, a Ford Expedition Hydraulic Hybrid was unveiled at the SAE World Congress. This vehicle was retrofitted as a Hydraulic Hybrid, the hydraulic powertrain was patented by the EPA. These are the fuel economy and performance details:
Fuel Economy (MPG):
- Stock: 12 city, 17 highway
- Hydraulic Hybrid: 32 city, 22 highway
Performance (0 – 60 mph):
- Stock: 15 seconds
- Hydraulic Hybrid: 8.9 seconds
Application of Hydraulic Hybrids
Hydraulic hybrids need large accumulators to store the energy which is not practical in smaller vehicles unless lighter and more efficient accumulators are developed. The EPA has been researching how to design accumulators to meet those needs. Weight, cost and size is a challenge in smaller vehicles.
Commercial vehicles are ideal for hydraulic hybrid applications, such as: utility, telecomm, refuse, delivery and municipality vehicles as well as transit and city buses. This is because of the high power density which improves vehicle acceleration and because of the highly efficient regenerative braking.
UPS has plans to deploy delivery trucks using the technology developed and manufactured by the EPA and Eaton Corp. along with other partners.
According to Eaton Corp., “The EPA estimates that a hydraulic hybrid delivery truck could save 1000 gallons of gasoline per vehicle per year.” This would largely reduce fuel costs and vehicle emissions. There is a great potential market for hydraulic hybrids in commercial vehicles.
2004 Ford Expedition
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