Modern Hybrid
Vehicles and its uses
Hydraulic Hybrids..:
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.
Major components
• 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.
·
Lower Emissions.
·
Reduced operating costs.
·
Better acceleration performance.
