Power plants – Combustion products used as motive fluid – With lubricators
Reexamination Certificate
1999-06-21
2001-05-29
Freay, Charles G. (Department: 3746)
Power plants
Combustion products used as motive fluid
With lubricators
Reexamination Certificate
active
06237322
ABSTRACT:
TECHNICAL FIELD
The invention is directed to an oil pump driven by a hydraulic motor, that is itself driven by the motion of fuel pumped by a remote fuel pump through the engine fuel line, particularly for use in a gas turbine engine.
BACKGROUND OF THE ART
Conventional engines include a fuel circuit which conducts fuel with a fuel pump from a fuel tank to the combusters. In general, a separate lubricating oil system is provided to circulate oil between bearings and other moving components and an oil tank through an oil pump, oil filter and optionally through a heat exchanger in a continuous cycle.
To heat the fuel sufficiently to avoid icing of the fuel filter, in gas turbine engines the oil and fuel circuits are both conveyed to a heat exchanger whereby the hot oil withdrawn from the bearings is cooled and cold fuel from the fuel tank is heated simultaneously. Conventionally, the fuel pump and oil pump are mechanical driven by an auxiliary gearbox mechanically connected to a rotating engine shaft. The engine shaft includes a gear which drives a radially extending power take-off shaft to the auxiliary gearbox. The auxiliary gearbox, in addition to driving the oil and fuel pumps, is used to drive a hydraulic pump for the aircraft hydraulic system, connects the starter/generator to the engine shaft and drives the oil/air separator as well as other oil and fuel system components.
The conventional auxiliary gearbox has proven reliable, however, due to the weight of gears and shafts, and the overall mechanical complexity, it represents a significant cost in engine weight and performance as well as increasing the cost of engine assembly and maintenance.
The speed of the auxiliary gearbox is necessarily dependent upon the rotation speed of the engine shaft. There is very little freedom for individual control of driven components and adaptability. If different components driven by the auxiliary gearbox would be optimally driven at different speeds at different times during engine operation, such optimum efficiency is sacrificed in order to keep the auxiliary drive system simple and avoid further weight penalties, or complexity in mechanisms and control systems.
The auxiliary gearbox therefore represents a significant drain on engine performance and it is not necessary the most efficient manner of powering these engine components. The current trend is to eliminate parts or reduce the number of separate parts, improve performance, reduce weight and reduce overall cost of the engine in design, manufacture, assembly and operation.
Regarding conventional oil pumps, the supply of oil is directly dependent on the speed of the engine since the oil pump is driven by the auxiliary gearbox that is driven by the engine shaft. The rotational speed of a conventional oil pump is much lower than the rotational speed at which the engine shaft rotates since oil would cavitate the oil pump otherwise. The stepping down of the rotational speed with mechanical gears involves significant cost in manufacture, maintenance and performance.
Further, there is no direct correlation between the engine rotational speed and the need for oil to cool and lubricate the bearings. During aircraft take-off the engine speed is high, the engine thrust is high. Consequently the load on the bearings and need for oil cooling of the bearings is also high. However, at cruising speed and altitude, the aircraft's airspeed is high and therefore the engine speed is high as well. During cruising, the engine thrust is much lower than at takeoff. Due to the lower thrust and the cooler ambient air temperature at cruising altitude the demand for oil is much lower as well. However, since the conventional oil pump is driven at a rate dependant on the engine speed, unnecessarily large volumes of oil are circulated during cruising. As a result, energy is wasted in pumping the oil, and oil system components are subjected to unnecessary wear. Further, the temperature of oil withdrawn from the bearings is lower, due to shorter residence times within the bearing gallery, and as a result the exchange of thermal energy to the fuel is reduced thereby increasing the risk of ice buildup on the fuel filter.
It is an object of the present invention to eliminate or substantially reduce the dependence on an auxiliary gearbox; thereby improving engine efficiency and reducing weight and cost.
It is a further object of the invention to reconfigure the oil system of a gas turbine engine to combine various components together in a compact easily manufactured unit.
It is a further object of the invention to reduce the amount of energy wasted or unnecessarily consumed in driving the oil and fuel components with an auxiliary gearbox.
Further objects of the invention will be apparent from review of the disclosure and description of the invention below.
DISCLOSURE OF THE INVENTION
The invention relates to an oil pump driven by a hydraulic motor, that is itself driven by the motion of fuel pumped by a remote fuel pump through the engine fuel line.
The hydraulic fuel-driven oil pump is particularly advantageous for use in a gas turbine engine, to reduce dependence on or completely eliminate the auxiliary gearbox (AGB) conventionally used to mechanically connect various engine systems with an engine shaft.
Conventionally the AGB connects a starter/generator to rotate the engine shaft and initiate combustion, and thereafter the rotating engine shaft through the AGB mechanically drives the fuel pump, oil pump, oil/air separator, hydraulic pump, and other oil and fuel system components.
To avoid cavitation in a conventional positive displacement oil pump, the AGB must include gears to reduce the speed of rotation substantially increasing the weight and mechanical complexity of the AGB. However the fuel pump, starter/generator, oil/air separator can be run at high speeds directly connected to an engine shaft without gear reduction. The weight penalty and mechanical complexity of the AGB can be completely eliminated by directly connecting the starter/generator and oil/air separator to an engine shaft and driving the slower oil pump with a hydraulic motor itself driven by the motion of the flow of fuel in the fuel line.
The hydraulic system pump and fuel pump can be positioned within the fuselage or elsewhere driven by separate electric motors. Separating the oil pump and other fuel/oil system components from the AGB enables the rationalization of these systems and allows designers to reconfigure systems into a compact modular unit including the oil pump, oil/air separator, oil tank, heat exchanger, fuel filter and oil filter. Using pressurized fuel to hydraulically drive the novel centrifugal oil pump, frees the oil pump from location restraints and operating limitations.
Prior to takeoff and during takeoff a large portion of the fuel circulated by the fuel pump is diverted from the combustors through the fuel bypass circuit. Fuel is thereby readily available for takeoff but is held in a standby mode by rapidly circulating in the bypass circuit. The use of a hydraulically driven motor for the oil pump driven by the motion of fuel in the bypass circuit permits recovery of otherwise wasted energy from the fuel bypass circuit during idling and takeoff. Since engine thrust is highest during takeoff, the need for oil is also highest. The high fuel bypass flow and pressure at takeoff correlates to the need for oil flow therefore a fuel-driven hydraulic motor recovers otherwise wasted energy and reduces the need to cool the rapidly circulating bypass fuel.
The close correlation between fuel flow and oil requirements eliminates the energy wasted in conventional systems which pump oil at rates dependant on the speed of the AGB and engine rotation. Conventionally, the engine speed dictates the supply of oil however the need for oil is dependant on engine thrust not speed. At cruising altitude, the engine speed is very high due to the low air density and high aircraft airspeed, however the oil requirement is relatively low due to lower thrust and cooler air temperature. Pumpin
Astle Jeffrey W.
Freay Charles G.
Pratt & Whitney Canada Corp.
Rodriguez William
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