Hydraulic hybrid
Encyclopedia
Hydraulic Hybrid Vehicles or HHVs are vehicles that use pressurized fluid, instead of electric power, as an additional or alternative power source along with an engine.
, pump/motor (in parallel hybrid system) or in-wheel motors and pumps (in series hybrid system), and accumulator
. In some system hydraulic transformer is also installed for converting output flow at any pressure with a very low power loss. In electric hybrid system
, electrical power is stored in the battery
and is delivered to the electric motor
to power the vehicle. During braking
the kinetic energy
of the vehicle is used to charge the battery
through the regenerative braking. In hydraulic hybrid system, the pump/motor extracts the kinetic energy
during braking
to pump the working fluid from the reservoir
to the accumulator
. Working fluid is thus pressurized. When the vehicle accelerates, this pressurized working fluid provides energy to the pump/motor to power the vehicle.
, there are also series hydraulic hybrid and parallel hydraulic hybrid.
In a parallel hydraulic hybrid vehicles, the pump/motor connects to the driveshafts through a transmission box. The role of pump/motor is to provide assistance to the engine during acceleration.
In a series hydraulic hybrid vehicle, the pump/motor directly connects to the driveshaft, or the in-wheel motors provide driving torque directly to the wheel. The internal combustion engine is set to operate in its most efficient power range to maintain the optimal hydraulic pressure in the accumulator.
because no complicated or expensive materials (such as those required for batteries
) are used.
Hydraulic hybrids recover, or harvest, the vehicle's kinetic energy during braking and decelerating significantly more efficiently than electric systems; hydraulic hybrids can recover up to 75% of the vehicle's kinetic energy compared to 25% for electric hybrids.
Technical challenges with hydraulic hybrid vehicles include noise, size, and complexity. Technical advances, such as very Large Diameter, Flat Format (LDFF) hydraulic motors which produce very high torque in limited driveline space, enable heavy vehicles like refuse trucks and city buses to be fitted with hydraulic hybrid systems.
Principle of Operation
Hydraulic Hybrid Vehicle systems consists of four main components: the working fluid, reservoirReservoir
A reservoir , artificial lake or dam is used to store water.Reservoirs may be created in river valleys by the construction of a dam or may be built by excavation in the ground or by conventional construction techniques such as brickwork or cast concrete.The term reservoir may also be used to...
, pump/motor (in parallel hybrid system) or in-wheel motors and pumps (in series hybrid system), and accumulator
Hydraulic accumulator
A 'hydraulic accumulator' is an energy storage device. It is a pressure storage reservoir in which a non-compressible hydraulic fluid is held under pressure by an external source. That external source can be a spring, a raised weight, or a compressed gas...
. In some system hydraulic transformer is also installed for converting output flow at any pressure with a very low power loss. In electric hybrid system
Hybrid electric vehicle
A hybrid electric vehicle is a type of hybrid vehicle and electric vehicle which combines a conventional internal combustion engine propulsion system with an electric propulsion system. The presence of the electric powertrain is intended to achieve either better fuel economy than a conventional...
, electrical power is stored in the battery
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
and is delivered to the electric motor
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
to power the vehicle. During braking
Brake
A brake is a mechanical device which inhibits motion. Its opposite component is a clutch. The rest of this article is dedicated to various types of vehicular brakes....
the kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
of the vehicle is used to charge the battery
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
through the regenerative braking. In hydraulic hybrid system, the pump/motor extracts the kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
during braking
Brake
A brake is a mechanical device which inhibits motion. Its opposite component is a clutch. The rest of this article is dedicated to various types of vehicular brakes....
to pump the working fluid from the reservoir
Reservoir
A reservoir , artificial lake or dam is used to store water.Reservoirs may be created in river valleys by the construction of a dam or may be built by excavation in the ground or by conventional construction techniques such as brickwork or cast concrete.The term reservoir may also be used to...
to the accumulator
Hydraulic accumulator
A 'hydraulic accumulator' is an energy storage device. It is a pressure storage reservoir in which a non-compressible hydraulic fluid is held under pressure by an external source. That external source can be a spring, a raised weight, or a compressed gas...
. Working fluid is thus pressurized. When the vehicle accelerates, this pressurized working fluid provides energy to the pump/motor to power the vehicle.
Types of Hydraulic Hybrid Vehicles
Like the electric hybrid systemHybrid electric vehicle
A hybrid electric vehicle is a type of hybrid vehicle and electric vehicle which combines a conventional internal combustion engine propulsion system with an electric propulsion system. The presence of the electric powertrain is intended to achieve either better fuel economy than a conventional...
, there are also series hydraulic hybrid and parallel hydraulic hybrid.
In a parallel hydraulic hybrid vehicles, the pump/motor connects to the driveshafts through a transmission box. The role of pump/motor is to provide assistance to the engine during acceleration.
In a series hydraulic hybrid vehicle, the pump/motor directly connects to the driveshaft, or the in-wheel motors provide driving torque directly to the wheel. The internal combustion engine is set to operate in its most efficient power range to maintain the optimal hydraulic pressure in the accumulator.
Advantage and Disadvantages of Hydraulic Hybrid Vehicles
In some cases hydraulic hybrid systems may be more cost-effective than electrical hybrid systemsHybrid electric vehicle
A hybrid electric vehicle is a type of hybrid vehicle and electric vehicle which combines a conventional internal combustion engine propulsion system with an electric propulsion system. The presence of the electric powertrain is intended to achieve either better fuel economy than a conventional...
because no complicated or expensive materials (such as those required for batteries
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
) are used.
Hydraulic hybrids recover, or harvest, the vehicle's kinetic energy during braking and decelerating significantly more efficiently than electric systems; hydraulic hybrids can recover up to 75% of the vehicle's kinetic energy compared to 25% for electric hybrids.
Technical challenges with hydraulic hybrid vehicles include noise, size, and complexity. Technical advances, such as very Large Diameter, Flat Format (LDFF) hydraulic motors which produce very high torque in limited driveline space, enable heavy vehicles like refuse trucks and city buses to be fitted with hydraulic hybrid systems.
See also
- regenerative braking
- Hydraulic Launch Assist (HLA)Hydraulic Launch AssistHydraulic Launch Assist is a hydraulic hybrid regenerative braking system produced by the Eaton Corporation.It also is referred to as the HLA system.- Background:...
- hybrid electric vehicleHybrid electric vehicleA hybrid electric vehicle is a type of hybrid vehicle and electric vehicle which combines a conventional internal combustion engine propulsion system with an electric propulsion system. The presence of the electric powertrain is intended to achieve either better fuel economy than a conventional...
- hydraulic accumulatorHydraulic accumulatorA 'hydraulic accumulator' is an energy storage device. It is a pressure storage reservoir in which a non-compressible hydraulic fluid is held under pressure by an external source. That external source can be a spring, a raised weight, or a compressed gas...
External links
- Hydraulic Hybrid Vehicles - Research, United States Environmental Protection Agency Hydraulic Hybrid Research Page
- Hydraulic Hybrid Technology - A Proven Approach, United States Environmental Protection Agency, March 2004
- HYDRAULIC LAUNCH ASSIST (HLA) Video, Eaton Corporation (Requires QuickTime plug-in to view)
- HyDrid, Innas BV
- EPA Innovates Hydraulic Hybrid System, autoMedia.com
- Hydraulic hybrid retrofits KersTech Vehicle Systems
- Eaton To Develop Digital Hydraulic Hybrid Drive System For U.S. Army Vehicles, News Release December 21, 2007, Eaton Corporation
- IFPE High Efficiency Hydraulic Hybrid Drive System, NRG Dynamix (Formerly Hybra-Drive Systems LLC), December 12, 2007
- NRG Dynamix Web Site