Hydraulic Hybrid Vehicles

The hydraulic hybrid technology has become the talk of the town of late, with vehicles purely based on this technology being pitched as the vehicles of the future. It is one of the most inexpensive and environment friendly power utilization method, and hence appreciated by the whole world.

Hydraulic Hybrid Technology

The hydraulic hybrid technology is a hybrid system which uses pressurized fluid as an alternative source of power to the engine. Unlike the electrical hybrid system, it doesn't require a battery, and therefore keeps the environment free from toxic chemicals which are used in the electrical hybrid system. The hydraulic hybrid system is made up of four components.

• The working fluid
• The reservoir
• The pump or motor
• The accumulator

The pump or motor installed in the system extracts kinetic energy during braking. This in turn pumps the working fluid from the reservoir to the accumulator, which eventually gets pressurized. The pressurized working fluid then provides energy to the pump or motor to power the vehicle when it accelerates. There are two types of hydraulic hybrid systems:-

• Parallel hydraulic hybrid system wherein the pump is connected to the drive-shafts through a transmission box.
• Series hydraulic hybrid system wherein the pump is directly connected to the drive-shaft.

Hydraulic Hybrid Vehicles

A hybrid vehicle is a vehicle that uses more than one source of power for functioning or movement. In some of these cars, fluid (hydraulic technology) is used as an additional source of power along with diesel or gas - these are referred to as hydraulic hybrid vehicles. This technology seems to be an apt replacement for battery technology which is relatively expensive, bulky and hazardous for the environment. Owing to its advantages, this technology has lately been utilized as an alternative power source for vehicles. In these vehicles, the energy is stored in high pressure hydraulic accumulators, which are generally charged in excess of 3000 psi. An ideal accumulator is required to possess the density of approximately 500 KW/kg.

In hydraulic hybrid vehicles, the engine of the car, run by diesel or gas, powers the hydraulic pump, which eventually charges the high pressure accumulator. This accumulator drives one or more pump motors which are connected to the wheels. Based on the design, there can be a single pump motor to drive a pair of wheels or one pump motor for each wheel (mostly seen in all wheel drive version). The hydraulic circuit is completed by the second accumulator, which has relatively low pressure.

Researchers have started to evaluate the feasibility of using hybrid hydraulic technology in smaller vehicles. The United States Environmental Protection Agency has been working on such a concept involving the designing and testing of hydraulic hybrid vehicles. A hydraulically driven UPS truck was showcased at the International Fluid Power Exposition in Las Vegas, stressing the need for utilizing the alternative source of power, the fluid power.

Some hydraulic hybrid designs, such as full-series hybrid, are still in prototype stage. Allowing full-series hybrids to capture braking losses, and permitting engine-off operations for significant periods can enhance its capacity. Though hybrid hydraulic technology has made decent development in various aspects, it still has to pass some more tests in order to make it feasible for high volume production in the automobile industry. Introducing these systems will definitely help to completely eliminate mechanical transmission, and thus help the economy as well as the environment.