Modern Hybrid Vehicles and its uses
A hydraulic-diesel hybrid powertrain allows for the use of a less powerful and more fuel efficient diesel engine operating at its optimal setting and less frequently to obtain the same power as a less efficient engine directly powering the wheels. There are two accumulators; one high-pressure and the other low-pressure. Inside the accumulators are nitrogen bladders. When hydraulic fluid accumulates, the nitrogen bladders are compressed, and energy is stored. The low pressure accumulator acts like a reservoir containing hydraulic fluid.
During braking, energy that is usually dissipated through heat is used to operate a pump that takes hydraulic fluid from the low-pressure accumulator to
pressurize the high pressure accumulator. This energy stored in the high-pressure nitrogen bladder is then used to accelerate the vehicle. During acceleration, the pressurized fluid leaves the high pressure accumulator and powers the pump/motor. The fluid then returns to the low pressure accumulator. The diesel engine is used when the high-pressure accumulator is depressurized and the vehicle is running at steady state.
• A high-pressure accumulator stores energy, as a battery would in a hybrid electric vehicle, by using hydraulic fluid to compress nitrogen gas stored inside each accumulator.
• A low-pressure reservoir stores hydraulic fluid after it has been used by the pump/motor.
• A rear drive pump/motor converts high-pressure hydraulic fluid into rotating power for the wheels and transmits braking energy back to the high-pressure accumulator.
• An engine pump transmits pressurized hydraulic fluid to the rear drive pump/motor, the high-pressure accumulator, or both.
• A hybrid controller monitors the driver's acceleration and braking actions and commands the hybrid system components.
Regenerative braking — When stopping the vehicle, the hybrid controller uses the energy from the wheels by pumping fluid from the low pressure reservoir into the high pressure accumulator. When the vehicle starts accelerating, this stored energy is used to accelerate the vehicle. This process allows hydraulic hybrids to recover and reuse over 70% of the energy normally wasted during breaking.
Optimum engine control — The engine pump pressurizes and transfers fluid from the low pressure reservoir to the rear drive pump/motor, and under certain operating conditions, to the high pressure accumulator. In the full series hybrid design, there is no conventional transmission and drive shaft connecting the engine to the wheels, which frees the engine to be operated at its "best efficiency" speed, to achieve optimum vehicle fuel.
Shutting off the engine when not needed — The unique full series hybrid design not only allows the engine to be operated most efficiently, but also enables the engine to be completely shut off during certain stages of operation — such as when decelerating and when not moving at a stop. As a result, in certain stop-and-go urban city driving, engine use is cut almost in half.
Benefits of Hydraulic Hybrid Technology…:
· Hydraulic drivetrains are particularly attractive for vehicle applications that entail a significant amount of stop-and-go driving, such as urban delivery trucks or school buses.
· A major benefit of a hydraulic hybrid vehicle is the ability to capture and use a large percentage of the energy normally lost in vehicle braking.
· Hydraulic hybrids can quickly and efficiently store and release great amounts of energy due to a higher power density.
· This is a critical factor in maximizing braking energy recovered and increasing the fuel economy benefit. While the primary benefit of hydraulics is higher fuel economy, hydraulics also increases vehicle acceleration performance.
· Hydraulic hybrid technology cost-effectively allows the engine speed or torque to be independent of vehicle speed resulting in cleaner and more efficient engine operation.
· In a system hydraulic energy can be easily reversed but in case of other systems it cannot be reversed without stopping and also causes damage to the system.
· Reduced operating costs.
· Better acceleration performance.