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Old 09-14-2009, 06:26 PM   #5 (permalink)
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Or how about a hydraulic electric hybrid?

And its not a hydrostatic setup. The original transmission is used.

Hydraulic Pump/Motor - The main hydraulic component of a parallel hydraulic hybrid vehicle is a hydraulic pump/motor. The pump/motor is a variable displacement, axial piston type pump. This type of closed circuit pump has been used reliably in various hydraulic applications for many years. Depending on which port is pressurized, the pump/motor can operate in both counter-clockwise and clockwise directions and as a pump or motor with the same efficiency of between 85% and 90% depending on speed. Because of this characteristic, the pump/motor can either add power to the system or be used to pump hydraulic fluid to a high pressure accumulator and store that energy for use in its opposite mode of operation.

An in-line configuration where the pump is added after the engine and torque converter but before the transmission would allow the pump to operate through a greater range of speeds before requiring assistance from the engine. This configuration would also allow the engine to drive the pump and charge the accumulator at very low flow rates. The amount of power that the pump requires from the engine comes from the equation HP = PSI X GPM / 1714, where HP is the horsepower required from the
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engine, PSI is the system pressure in pounds per square inch, GPM is the pump flow rate in gallons per minute, and 1714 is a constant. As mentioned above the pump is a variable displacement type which allows the pump to pump any amount of fluid between zero gallons per minute and its maximum value which is dependent on the physical size of the pump. While the main pump can be made to pump no fluid at all, there is an integrated gear pump within the unit that allows the pump to operate, and keeps it lubricated. This pump has a constant flow rate of .53 gallons per minute at a pressure-relieved pressure of 300 psi. This pump also powers the hydraulic logic controls. If the pump is not pumping any fluid at all, the pump losses can be calculated according to the equation: 300 psi X .53 gpm / 1714 = .092 HP or roughly one tenth of a horsepower. This is a very small amount of power, comparable to a standard alternator or air-conditioning unit used on a vehicle. The advantage of this configuration is that the pump can be made to pump fluid at the optimum rate for the engine’s fuel use maps with the transmission in neutral and the vehicle at a stop. That energy is stored in the accumulator and allows the vehicle to make a full acceleration cycle using the pump only. The accumulator can be charged in the same way while the vehicle is moving, and the system is now behaving very similarly to a series system.
For increased performance, the pump and internal combustion engine can be used simultaneously to
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