Most of you know that hybrid engine use a combination of an engine and an electric motor. They work by charging batteries while braking, through a process called regenerative braking. But another hybrid technology called the Hydraulic Hybrid System uses pressurized fluid instead of batteries to store energy as an alternative power source. It was developed by The U.S. Environmental Protection Agency (EPA) and its partners which include Army’s National Automotive Center, Hannifin Corporation, Eaton Corporation and Ford Motor Company back in 2004.
The technology wasn't much in focus for a long time, it has become more refined over the years. Around a weeks ago the city of Ann Arbor, Michigan got its first four garbage trucks powered by HLA (Hybrid Launch Assist) which is a type of Parallel Hydraulic Hybrid System developed by Eaton Corporation, it promises to be 30% more fuel efficient than conventional trucks. Ann Arbor was among the first to receive funding through the U.S. Department of Energy's Clean Cities Program for these Hybrid trucks. It's great news for Hydraulic Hybrid Systems and for its future.
How Hybrid Launch Assist Works?
Now there are two type of Hydraulic Hybrid Systems A Parallel hybrid and a Series hybrid system.
|Parallel Hybrid system|
Parallel hybrid system actually supplements the existing conventional power train which consists of engine and transmission so it is like an add on to existing systems, it utilizes a pump and 2 storage tanks which store high pressure and low pressure fluid to save excess energy and utilize it when available/necessary. They are cheaper to manufacture providing significant improvement in efficiency figures and can be added to existing automobiles.
|Parallel Hybrid system layout By Eaton Corporation|
Series hybrid system also utilize a pump and 2 storage tanks but there is no transmission the automobile is driven by hydraulic fluid completely. A pump is connected to the Engine. The engine turns ON and OFF as required. When the engine is ON, the excessive power generated is stored in the form of high pressure fluid (Mostly Nitrogen) and utilized during acceleration and charged during braking (Regenerative Braking). It provides a great increase in fuel efficiency, reduction in emission and maintenance cost as there are fewer moving parts and no transmission. This video should help you understand better.
Now Hybrid Launch Assist is a Parallel hybrid system which works in two stages. Regeneration and Launch Assist
Regeneration basically stores the kinetic energy during braking. Instead of wasting energy during braking, the energy is used to transfer hydraulic fluid from the low pressure reservoir(tank) to a high pressure accumulator(tank). This provides braking as well as energy storage.
Launch Assist on the other hand utilizes the stored energy in the high pressure accumulator by pushing out the high pressure fluid to drive the pump/motor as a motor. The system moves the vehicle by transmitting torque to the driveshaft. The launch assist system by Eaton Corporation provides a 15-30% increase in fuel efficiency, Thus reducing fuel requirement and emissions this system is best suited for heavy vehicles like garbage trucks buses etc which are more into start and stop driving.
Overall the hydraulic hybrid technology has not been explored by the automobile industry to it full potential it requires more attention. Public promotion like the Ann Arbor hybrid garbage truck launch definitely helps.
Source- Technology Review
Source- Technology Review