Hydraulic Launch Assist_image

Hydraulic Launch Assist

In a parallel hybrid hydraulic system, the conventional vehicle powertrain is supplemented by the addition of the hybrid hydraulic system.

The hybrid hydraulic system is best suited for vehicles that operate in stop-and-go duty cycles, including refuse and buses, where fuel economy and emissions reductions are typical.

Eaton plans to commercialize its HLA system in refuse trucks in 2009. Other applications will soon follow.
Hydraulic Launch Assist_image

The Eaton Hydraulic Launch AssistT (HLA®) System utilizes regenerative braking and is being initially targeted at refuse trucks.

Eaton''s Hydraulic Launch Assist System has two parts: regeneration and launch assist.


During braking, the vehicle's kinetic energy drives the 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

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.

In addition, the parallel hydraulic hybrid system offers the flexibility of two operating modes: economy and performance.

Economy 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

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.