How to

How Hydraulic Hybrids Work

Regenerative braking solutions

By Gabriel Gache, Science News Editor

29th of May 2008, 12:44 GMT

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Vehicle equipped with a hydraulic hybrid engine

Fossil fuel reserves, petrol in special, are becoming increasingly scarce around the world with rapid economical development of poor countries, which greatly influences petrol prices in areas all over the world. Not only that, but burning fossil fuel increases the pollution of the planet, thus accelerating the climate change and the global warming effects that are now on the verge of taking over the Earth.

There are a lot of alternatives to internal combustion engines, which could decrease the gas prices and reduce the pollution, amongst which fuel cell technologies, biofuel, electric vehicles and hybrids. Some of the most popular hybrids today combine traditional internal combustion engines with alternative power plants, such as electric motors.

Now, a new type of hybrid technology is catching up, the hydraulic hybrids, which replace the electric motors in typical hybrid vehicles with a lightweight hydraulic system that has proven extremely efficient for low speed vehicles in particular.

Electric hybrids

Hybrid vehicles work by relying on a process known as regenerative braking. The idea is that the inertial momentum of the vehicle as it travels can be recuperated in some form of energy, to be later used to put the vehicle in motion again. In electric hybrids for example, mechanical energy from the wheels is converted into electric energy with the help of electric motors, slowing down the vehicle at the same time. The energy is then stored in Li-ion batteries and used later to power the vehicle to speeds up to 48 kilometers per hour.

Once the vehicle gathered enough momentum, the petrol engine takes over again. The problem with electric hybrids is that they cannot harness efficiently the energy from the regenerative braking system while at low speeds in order to charge the batteries.

Hydraulic hybrids

Basic schematic of a simple hybrid hydraulic system

However, hydraulic hybrid systems are perfect for vehicles running at relatively low speeds. The hydraulic component of the engine consists of a low pressure reservoir, a hydraulic pump and a high pressure accumulator. The working fluid is generally nitrogen.

When a hydraulic hybrid is in motion and needs to stop, the kinetic energy from the braking system is passed to the hydraulic pump - connected to the driveshaft - which uses it to pressurize nitrogen gas in the high pressure accumulator. The pressure of the stored gas can then be used to power the hydraulic pump that rotates the driveshaft, thus putting the vehicle in motion again.

TAGS:

gas | internal combustion | pollution | global warming | hybrids

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