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HTUF Selects Hybra-Drive to Build Three Hydraulic Series Hybrid Trucks for Testing

The hydraulic series hybrid uses the combustion engine to power a hydraulic pump/motor. Click to enlarge.

The Hybrid Truck Users Forum (HTUF), a government-corporate partnership led by CALSTART, has selected Hybra-Drive Systems LLC (HDS) to build three identical Class 6 hydraulic series hybrid delivery trucks for real-world testing by UPS, FedEx Ground and Purolator.

Under the new agreement, which is being funded by the Department of Energy, Hybra-Drive will build and deliver three hydraulic hybrid trucks over the next 9 to 12 months. UPS, FedEx Ground and Purolator then will each conduct a 6 to 9 month evaluation of the vehicle. Hybra-Drive anticipates that the evaluations will demonstrate up to a 60% cut in fuel use along with an accompanying reduction in emissions.

We are increasingly convinced that this technology offers a chance to&madsh;fairly quickly—improve the fuel mileage of large trucks. We’ve seen several innovative approaches for this type of vehicle and this is one that our team wants to test to help speed introduction.

—Bill Van Amburg, senior vice president of CALSTART

Hybra-Drive, based in Deerfield, Mich., was selected from among roughly four dozen companies that responded to a Request for Proposals issued last September.

A hydraulic hybrid truck uses hydraulic pumps and hydraulic storage tanks to store energy, similar to what is done with electric motors and batteries in hybrid electric vehicles. 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 US Environmental Protection Agency unveiled the first hydraulic diesel series hybrid urban delivery vehicle in June 2006. (Earlier post.) Since then, several vehicle manufacturers have been working on the technology. Hybra-Drive’s approach differs in that it has developed a hydraulic fluid transmission to go along with the hydraulic pumps and storage tanks that are used to store energy.

Hybra-Drive Systems, working in conjunction with Gates Corporation, Detroit Custom Chassis (a subsidiary of Spectra LMP, LLC) and Morgan Olson LLC, proposed a series hydraulic hybrid vehicle (HHV) based on a Ford chassis for the HTUF validation project.

The HDS Hydraulic Hybrid Power Train (HHPT) system combines a combustion engine with a hydraulic propulsion system that replaces the conventional drivetrain and transmission. The engine, fueled by gasoline, diesel or alternative fuel, operates a hydraulic pump that pressurizes the stored energy hydraulic system to propel the vehicle.

The HDS-HHPT system is designed to add no extra curb weight compared to the standard vehicle and includes unique, cost-effective designs for the variable displacement gear pump and fluid power accumulator system.

Although the corporate members of HTUF have direct experience with operating both hydraulic and electric hybrid parcel delivery vehicles, their objective is to explore other technology options to better understand the relative merits and benefits of different technical approaches. The Hybrid Truck Users Forum allows the corporate members to pool their resources more efficiently and work together to advance alternative fuel technologies.




We have seen quite a few annoucement about this technnogy which has the immense advantage compared to electric hybrid that it can be installed on existing truck. But we haven't seen any commercial product so far, so they should speed it up or the everything will move to electric hybrid and this technology will be useless

John Taylor

In all other applications, Hydraulic pumps and motors experience a significant efficiency penalty in power transfer. One wonders if this is in any way different?


This subject always makes me angry. Ford started testing an F-150 in 2002, by 2005 it was deemed a success. Reports cam out that it could go into production as early as 2007 model year but 2008 model for sure. Well, 2008's came out and no HH F-150. Now there is speculation for 2010 model year. For some reason ford dosen't think that with $4 gas anyone would want a PU that gets twice the MPGs

hampden wireless

Hydraulic storage can be made in the USA in almost any quantity desired big or small. There are no long term limiting factors like batteries so this is a very attractive concept. Unfortunately and in contradiction to the article these systems add a lot of weight. They also do not provide nearly the energy reserves of a battery.


from what i've read, hydralic systems are better at storing power (W/kg) but not energy (Wh/kg). Also better at storing braking energy because they can take high energy inputs over short times unlike batteries and because it is direct mechanical storage unlike electrical systems which transfer energy back and forth. I'm sure that this tech has it's own problems though. Hate to see what the system are like near their end life.

The tech certainly wouldn't be applicable as a plug in concept because of poor energy storage density but in a intensive stop/go traffic situation, it may pay for itself especially if the accumlator can store energy for the idle delivery time. It should also be noted that the accumalator could be tapped for other uses like garbage compacting.

Hydraulics is a fairly old and mature technology. New technology has shrunk the needs too. New planes use very small units for the control surfaces where before you had to have tubing all over the place.

If it works good for them. Sounds interesting that this is basically a series hydraulic system though. Wonder how long it takes to start it up though but that could be worked around with multiple accumulators. A small one that is used for fast start up and a variable valve that allows fill up of the larger one as the vehicle travels and for braking storage.

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I agree with the earlier comment about efficiency.

Infinitely variable hydrostatic transmissions (like this) have been around since the 70's. They work really nicely but they are poor for raw energy transfer (i.e. highway driving). Can't beat straight gears.

Hydraulics haven't changed much since then. I wonder what these guys did different - or are the numbers purely based on a continuous stop-and-go scenario?

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