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Eaton Launches Hydraulic Hybrid Retrofit Program for Refuse Trucks

The HLA system. Click to enlarge.

Diversified industrial manufacturer Eaton Corporation will begin offering retrofit versions of its Hydraulic Launch Assist (HLA) hybrid power system (earlier post) for refuse trucks later this year. The Refuse Retrofit Program will be offered through select qualified partners and installers. Eaton is currently seeking partners for the program.

The Eaton Hydraulic Launch Assist system is a parallel hybrid system, in which the conventional powertrain is supplemented by the addition of the hydraulic system that captures braking energy to use to propel the truck forward and helps to slow it down. The system is best suited for vehicles that operate in stop and go duty cycles such as refuse trucks—the initial commercialization target.

The HLA system has two parts: regeneration and launch assist.

  • Regeneration. During braking, the vehicle’s kinetic energy drives the hydraulic pump/motor as a pump, transferring hydraulic fluid from the low-pressure reservoir to a high-pressure accumulator. The fluid compresses nitrogen gas in the accumulator and pressurizes the system. The regenerative braking captures about 70% of the kinetic energy produced during braking.

  • Launch Assist. During acceleration, fluid in the high-pressure accumulator is metered out to drive the pump/motor as a motor. The system propels the vehicle by transmitting torque to the driveshaft. The Launch Assist has two different settings, the economy mode and the performance mode.

  • Economy Mode. When the Hydraulic Launch Assist System is operating in Economy Mode, the energy stored in the accumulator during braking is used alone to initially accelerate the vehicle. Once the accumulator has emptied, the engine will begin to perform the acceleration. This process results in increased fuel economy.

  • Performance Mode. When the Hydraulic Launch Assist System is operating in Performance Mode, acceleration is created by both the energy the stored in the accumulator and the engine. Once the accumulator has emptied, the engine is completely responsible for acceleration. While fuel economy improvements are seen in Performance Mode, the greatest benefit is increased productivity

Benefits of the system include 20 to 30% improvement in fuel economy, longer brake life, and increased productivity due to the extra power the HLA system provides.

By retrofitting existing trucks, Eaton is giving our customers a best-of-both-worlds scenario. Until now, our refuse market customers in North America have been frustrated in their efforts to improve fuel efficiency and reduce emissions in fleets of newer trucks with many years of service left in them. The have been asking for a hybrid solution that does not require the purchase of a new truck, and we’re pleased to deliver the retrofit option.

—Seth Deutsch, manager – Hybrid Market Planning

Eaton offers the most complete line-up of hybrid systems for commercial vehicle applications. Eaton hybrid electric, plug-in hybrid electric and two hybrid hydraulic power systems, parallel (HLA) and series, are available or in development on truck models including International, Peterbilt, Kenworth, Freightliner, Iveco, DAF, Daimler, and Ford and on bus models from Foton, Zhongtong, Yutong, JNP, King Long, Shen Long, Heng Tong, BCI and Solaris. Eaton hybrid power systems have accumulated more than 30 million miles of road-tested service around the world.



Wouldn't this system be able to charge the pressure tanks anytime the vehicle slowed down even at highway speeds. You don't necessarily have to come to a complete stop right?

Nick Lyons

Great idea. I hope this pencils out for lots of trash collectors.


"Wouldn't this ... charge the pressure tanks anytime the vehicle slowed down even at highway speeds. .. don't .. have to come to a complete stop .?"

Exactly - unless it was simpler somehow to make it automatic or .. ? .

The huge savings is from the many, many stop - starts.
An occasional decel and accel while at speed would make this feature a minor savings.

Henry Gibson

The hydraulic hybrid idea has been sucessfully tested in various vehicles. This retrofitting with a parallel system for existing vehicles will cut costs. Any case where start stop operation is used, hydraulic operation is suitable and cheaper than batteries or ultra-capacitors. The Artemis system was very successful in its conversion of a car. INNAS NOAX invented hydraulic system components that are very efficient. The 1920s steam-diesel Kitson-Still locomotive remains an example of a very efficient hybrid vehicle. The parry people movers with hydraulic hybrid flywheels are quite efficient. ..HG..


The hydraulics in this system are coupled only to the driveshaft.  When the vehicle is stopped, the engine is still idling with no load; this is the least-efficient mode of operation.  One way to improve this system would be to add a second hydraulic pump on the engine, to boost the accumulator to full pressure while the vehicle is stopped.  This would allow the maximum launch assist with relatively low additional fuel consumption due to the low engine speed.


In theory a hydraulic hybrid should have an efficiency advantage over any other scheme because the state of energy remains the same, kinetic...braking force becomes hydraulic pressure becomes acceleration. With any change in state of energy, there is some inefficiency, for example ICE engine powering a generator has frictional losses, line losses, heat losses, etc. The question I have is whether hydraulic is practical as a series hybrid, ie can hydraulic motors power a vehicle at speed?



There are concerns about efficiency losses in freeway operation for a pure hydraulic transmission, which a series hybrid would likely have.

There is a kind of cool engine "Free Piston" design used for hydraulic forklifts and the like which apparently is quite efficient. You might look for examples of that and share what you find.

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