Patent Grant
8038412
This invention relates to a method and apparatus for managing the temperature of a hydraulic pump that uses an electric motor.
In aircraft and other applications, electrical motor driven pumps are used to provide or supplement hydraulic power for actuators and other hydraulically or fluid powered components. In many cases, these pumps are inactive for long periods in cold environments and then are expected to startup rapidly and provide full performance in a very short period of time.
In cold environments, the hydraulic fluid becomes very viscous so that starting the pump under sustained cold conditions is difficult. To decrease the viscosity of the fluid and enable desired startup of the pump, it is typical to either run the pump continuously or to provide the pump with a continuous flow of hot gases, typically bleed air from a turbine engine. Continuously running the pump decreases the life of it and the electric motor. Providing a continuous flow of bleed air decreases the efficiency of the source providing the bleed air.
To avoid the above problems, power sufficient to provide a stall torque to the electric motor has been used to generate heat using the windings of the electric motor. Similar to the solutions described above, the power is provided to the electric motor continuously, which is inefficient. What is needed is an efficient hydraulic pump and electric motor system that reduces the viscosity of the hydraulic fluid on an as-needed basis.
A hydraulic pump system for an aircraft is provided that includes a pump driven by an electric motor. The electric motor includes windings that receive power from a power source. In one example, a temperature sensor is arranged in proximity to hydraulic fluid associated with the pump, such as at an input of the pump. The windings are used as the temperature sensor, in one example. In another example, the temperature sensor measures the ambient temperature to predict the viscosity of the pump based upon cool down rates of the system. A controller monitors a temperature at the temperature sensor and commands power to be provided to the windings to generate heat. The heat reduces the viscosity of the hydraulic fluid. Bleed air may be selectively provided to a casing associated with the hydraulic fluid in response to a command from the controller. The controller actuates a valve to regulate the flow of bleed air to the casing to provide supplemental heat to the heat provided by the windings.
In another example, the electric motor is rotated and the power to the electric motor is monitored to determine the viscosity of the hydraulic fluid. Heat is applied to the hydraulic fluid if the power consumption corresponds to an undesired viscosity. In this manner, the viscosity of the hydraulic fluid is more efficiently managed to provide desired startup of the pump in cold conditions.
Other advantages of the present invention can be understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
A hydraulic pump and electric motor system 10 is shown in
The electric motor 20 includes windings 22 that, when energized, rotate a rotor driving the pump 12, as is known in the art. Current is provided to the windings 22 from a power source 24 that passes through an inverter 26 or motor relay, for example.
A controller 28 is schematically shown in
In another example, the controller 28 can monitor an ambient temperature using temperature sensor 31 in an open loop arrangement to predict the viscosity of the hydraulic fluid based upon the temperatures and the duration of time the hydraulic system has been inoperable and exposed to the cold conditions. For example, cool down rates of the hydraulic system can be empirically determined. The cool down rates together with the ambient temperature and inoperable time is used to estimate the temperature of the hydraulic fluid. The viscosity of the hydraulic fluid can be modeled based upon this and other information.
The controller 28 provides power to the electric motor 20 by energizing the windings 22 to generate heat with the windings 22 when an undesired viscosity is predicted. In this manner, the hydraulic fluid associated with the pump 12 can be heated when it is too viscous for desired start up. In one example, the windings 22 are energized such that heat is generated, but the electric motor 20 does not rotate. In one example, a rotational sensor 33 can be connected to the controller 28 to monitor the rotation of the electric motor 20 to insure there is no undesired rotation. In another example, the pump 12 is rotated by the electric motor 20 to monitor the power consumed, which can be correlated to the viscosity of the hydraulic fluid. If the power consumption to rotate the electric motor 20 corresponds to an undesired viscosity, then rotation is stopped and the pump 12 is heated.
Under some conditions, the heat provided by the windings 22 may be insufficient to adequately reduce the viscosity of the hydraulic fluid. For example, cavitation at the inlet 14 can be a problem after extreme cold soak conditions when the inlet lines are remote from the pump 12 and not well insulated. As a result, it may be desirable to further heat the hydraulic fluid. In one example, bleed air from a bleed air source 34, such as a turbine engine 32, may be provided to a casing 36 associated with pump 12. The casing 36 can heat the fluid within the pump 12 and hydraulic fluid associated with the inlet 14. A valve 40 is arranged within a passageway 38 to selectively provide bleed air to the casing 36 using an actuator 42, which is regulated by the controller 28. In this manner, the temperature of the pump 12 is efficiently managed using heat selectively provided by the electric motor and bleed air selectively provided from a bleed air source.
Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For example, although physical connections are shown between many of the elements in
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