Hydraulic Hybrid Vehicles

The hydraulic hybrid vehicle technology uses the engine to charge the pressure accumulator to power the wheels by the hydraulically driven units. These vehicles are purely based on hydraulic hybrid technology and hydraulic components. 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 - the parallel hydraulic hybrid system and the series hydraulic hybrid system. In the parallel hydraulic hybrid, the pump is connected to the drive-shafts through a transmission box, while in series hydraulic hybrid, 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. Hydraulic hybrid cars use fluid (hydraulic technology) as an additional source of power, along with diesel or gas. Hydraulic hybrid technology seems to be the replacement for battery technology which is relatively expensive, bulky and hazardous for the environment. Owing to its advantages, hydraulic hybrid technology has lately been utilized as an alternative power source for vehicles. In the vehicles using hydraulic hybrid technology, the energy is stored in high pressure hydraulic accumulators, which are generally charged in excess of 3000 psi. An ideal accumulator is required to posses 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. The pump motors on the wheels reverse themselves while braking, and thus recharge the accumulator and capture the energy.

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 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.