The first conversion of the partnership is already underway, a MY 2002 CNG Chevrolet HD 2500 provided by Denver International Airport. The truck is used for runway checks and plowing. The hybrid system is currently being finalized, installed and tested at HHS’s shop in downtown Loveland, Colorado and the truck prototype will be put back into runway service in early October 2009.

HHS has also purchased a totaled 2008 Chevy Silverado HD 2500 that will serve as a demonstration vehicle. The truck has been stripped down almost to a bare chassis and will have a plexiglass floorboard to show the system as it works. Other vehicle platforms will be prototyped in the near future to meet the needs of current fleets.

Hydraulic hybrids have been around for a while, but there has been no reason until now to explore these kinds of technologies. Now is the time to move forward with hydraulics because of the push to cut emissions and dependence on foreign oil. Batteries just cannot address issues for fleets at the scale that we need.

—Richard LeFrancois, founder and president of EMI-Global

HHS system on the test stand. Click to enlarge.

Genesis of HHS. In late 2008 Loveland-based Lightning Hybrids began engineering a biodiesel hydraulic hybrid vehicle that combined a small biodiesel engine with a 150 hp hydraulic pump on a lightweight sports sedan. The first prototype was displayed at the Denver Auto Show in April 2009. At that show questions arose from a number of fleet managers about the prospect of applying the hydraulic hybrid as a retrofit to existing fleet vehicles.

We explored the opportunity and found a need for fuel and emissions savings in the light-duty fleet market. A hydraulic hybrid retrofit system is an excellent answer in situations where the light duty fleet vehicle does a lot of start and stop driving, such as city and state fleet vehicles, vocational and contractor trucks and vans, mining and oil field vehicles, and school buses.

—Dan Johnson, CEO of HHS

In late April 2009 Lightning Hybrids’ engineering team started the design and implementation of a hydraulic hybrid system that could be applied to fleet vehicles. Lightning Hybrids established Hydraulic Hybrid Systems, LLC in July 2009 to manage the manufacturing and distribution of the system.

The HHS system. A parallel hydraulic hybrid system is similar to many of the electric hybrid vehicles on the market today, but stores recaptured braking energy in hydraulic accumulators rather than a battery. The main components of a parallel hydraulic hybrid system are:

• Hydraulic Pump/Motor, a variable displacement, axial piston type pump. This type of closed circuit pump has been used reliably in various hydraulic applications for many years. Depending on which port is pressurized, the pump/motor can operate in both counter-clockwise and clockwise directions and as a pump or motor with the same efficiency of between 85% and 90% depending on speed. Because of this characteristic, the pump/motor can either add power to the system or be used to pump hydraulic fluid to a high pressure accumulator and store that energy for use in its opposite mode of operation.
• Hydraulic accumulator.
• The conventional automotive drivetrain.

The hydraulic pump/motor is coupled to the driveline via a belt and clutch. The pump captures braking energy and stores it in accumulator. Upon acceleration, the pump becomes a motor that uses the stored energy in the accumulators to provide torque to power the wheels. The large fuel efficiency gains are achieved by regenerating the braking energy that is normally lost to heat, and using this energy instead of (and in addition to, if needed) the internal combustion engine for acceleration.

The HHS hydraulic hybrid system includes a heavy-duty Eaton hydraulic pump and motor, an ASTM-certified high pressure accumulator tank, a low pressure reservoir, a valve block, HHS control system, brackets and associated certified hoses.