Patent Application
20070196213
This application relates generally to a metering pump for gas turbine engine that includes a method of self-calibration and health-monitoring.
A demand flow system traditionally includes a controller, a motor and a pump. The demand flow system functions as a metering system to regulate fuel delivery to, for example, a gas turbine engine. Fuel regulation is traditionally accomplished by direct control of the pump, also known as a metering pump. The metering pump includes a motor, where speed is varied to provide a desired flow. The effectiveness of the demand flow system is dependent on the accuracy of the control of the motor and the tolerances of the pump.
Known demand flow systems are typically calibrated only upon initial manufacture. However, a primary problem associated with known demand flow systems is system accuracy, which includes both determining system accuracy at an initial system start-up and monitoring system accuracy or “health” throughout the life of the system. Because the systems are calibrated at initial manufacture, and due to system variations based on allowable system tolerances and changes in the system operating environment, the demand flow system may not meet desired operational requirements throughout the life of the product.
Accordingly, it is desirable to provide a metering pump that is operable to self-calibrate at initial start-up and which includes a health-monitoring system that allows the system to monitor performance and re-calibrate to compensate for performance losses.
A metering pump of the present invention incorporates a method of relating inner loop current to pump output pressure for a demand flow system. It has been determined that a system current is proportional to a pump delivered pressure. Because each pump by design has pre-defined characteristics of backpressure and flow at a given speed, a relationship can be developed that can determine the operating condition or the “health” of the system by utilizing information such as the pump/motor speed, an operating temperature, and the system current, for example.
The pump/motor speed is measured and controlled by a system controller. A system temperature is also measured by the system controller. The controller monitors the measured system temperature and provides for compensation for system losses, including inductive-resistive (IR) losses, and for density and viscosity shifts, within a pre-determined allowable system temperature operating range. For demand flow systems including a metering pump of the present invention, the system controller uses a root mean square (RMS) method of current measurement to measure the current through an inner loop of the system. This is accomplished through either direct measurement or indirect measurement of the current by the system controller.
An initial calibration of the system is conducted using a “shut-off” test where the pump is at a very slow known speed while the system is shut-off. Under these conditions, the pump is “dead-headed” and the only “flow” is leakage. This allows the system to generate a base flow map. By incorporating a health-monitoring feature at this point, the base flow map can be adjusted, i.e. pump speed is increased or decreased from a flow request, to account for the measured leakage. After the appropriate adjustment has been made, the current is directly proportional to the pump performance.
After initial start-up, the health-monitoring feature continues to monitor the current as an indicator of pump performance and continuously adjusts motor speed to maintain a desired level of pump performance. This provides the system with the ability to compensate for performance losses, including performance losses due to variations in operating conditions, and to compensate for pump wear.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
An amount of current transmitted to the motor 16 is directly related to a speed of the motor 16. The speed of the motor 16 is proportional to a pressure of a fluid delivered by the pump 18 to the gas turbine engine 20. The pressure of the fluid delivered by the pump 18 correlates to a flow of fluid from the pump 18 to the gas turbine engine 20. As such, a relationship exists between the amount of current transmitted to the motor 16 and the flow of fluid from the pump 18.
An initial calibration of the system is conducted using a “shut-off” test where the pump 18 is run at a very slow known speed while the system is shut-off. Under these conditions, the pump 18 is “dead-headed” and the only “flow” is leakage from the pump 18. This allows the system to generate a Base Flow Map (BFM). A health-monitoring feature is used to adjust the BFM by increasing or decreasing pump speed from a flow request, to account for the measured leakage. After the appropriate adjustment has been made, the current is directly proportional to the pump performance. Therefore, subsequent monitoring of the current is indicative of pump performance.
As such, after initial start-up, the health-monitoring feature continues to monitor the current as an indicator of pump performance and continuously adjusts motor speed to maintain a desired level of pump performance. This allows the system the ability to compensate for performance losses, including performance losses due to variations in operating conditions, and to compensate for pump wear. For example, when an actual measured pump leakage is greater than an expected pump leakage, the controller 12 will increase the current delivered to the motor 16, which in turn increases an actual flow delivered from the pump 18 to the gas turbine engine 20, to accommodate for the additional pump leakage. Conversely, when the actual measured pump leakage is less than the expected leakage, the controller 12 will decrease the current delivered to the motor 16, which in turn decreases the actual flow delivered from the pump 18 to the gas turbine engine 20. This adjustment is reflected in an adjusted BFM. The health-monitoring process is repeated continuously throughout the daily operation of the system 10 and throughout the life of the system 10.
While, the known system operating characteristics are dictated by the original system design, they can vary within the allowable design tolerances. As such, once the BFM has been determined and upon initial system start-up, a First System Dynamic Compensation (SDC1) is conducted. The SDC1 is an initial calibration stage conducted using the “shut-off” test as described above. Under these conditions, the pump 18 is “dead-headed” and the only “flow” is pump leakage. During the SDC1 calibration stage, the controller 12 adjusts the FR based upon a Dynamic Constant (DC1) to accommodate for a variation in system operating conditions. This allows the system 10 to conduct an initial self-calibration that includes adjusting the BFM based upon the actual system operating conditions by compensating for actual component tolerances, i.e. compensation for a tight pump or a loose pump.
In this example, the DC1 is initial pump leakage and the controller 12 adjusts the FR to account for deviation of an actual measured leakage measured from the initial pump leakage expected based upon the original FR. The original FR, which was generated based upon known system characteristics, is used to generate the BFM. However, as a result of design tolerances associated with assembly of the pump 18, the known system characteristics can vary within an allowable tolerance range based upon actual dimensions of the pump 18. The SDC1 calibration stage accommodates for this variation by determining the initial pump leakage, which is indicative of the tightness or looseness of the pump 18 as discussed above, and adjusting the BFM respectively by increasing or decreasing the pump speed associated with a desired flow request to account for the initial pump leakage and provide the desired flow regardless of the initial pump leakage.
Further, the system includes a Second System Dynamic Adjustment (SDC2) that operates continuously throughout system operation and functions as a health-monitoring system feature throughout the life of the system to accommodate for changes in the system operating conditions including component wear and environmental factors, e.g. temperature variation.
The SDC2 incorporates a health-monitoring relationship into the system. The health-monitoring relationship monitors an operating characteristic associated with the system and adjusts the operating characteristic to achieve and maintain a desired system operating function level. In the example system, the monitored operating characteristic is RMS current and the desired system operating function level is Normal System Function.
A relationship is defined between the RMS Current and the pump leakage. A Nominal Characteristic line (NCL) is determined based upon the relationship and a Nominal Characteristic Range (NCR) is defined based as a function of system temperature variation. System Operating Function Levels (SOFL) are defined along the NCL. In this example system, the SOFL's include: Strong System, Normal System Function, Weak Pump, and System Ready to be Removed.
An initial SOFL is determined during initial calibration of the system. The initial SOFL is based upon the RMS current required to produce a desired flow at a nominal temperature and is adjusted during initial calibration to account for pump leakage associated with initial pump tolerances. The RMS current is directly related to motor speed. As such, if the initial SOFL is Strong System, then the controller will reduce the motor speed to produce the desired flow and reduce the SOFL to Normal System Function. Conversely, if the initial SOFL is below Normal System Function, then the controller will attempt to increase the motor speed to produce the desired flow and bring the SOFL up to Normal System Function.
An actual motor speed, system temperature and, the RMS current are continuously monitored throughout the daily operation of the system and throughout the life of the system. However, throughout the life of the system, pump wear is inevitable. As the pump 18 begins to wear, the pressure produced by the pump 18 decreases as does the flow delivered by the pump resulting in the pump 18 operating at the decreased SOFL of Weak Pump.
Because the pressure produced by the pump 18 is proportional the RMS current, as the RMS current decreases so does the pressure produced by the pump 18. As such, based upon the measured system operating temperature, the controller 12 will increase the motor speed to accommodate for pump wear to ensure the desired flow and the SOFL of Normal System Function are achieved. The increase in motor speed generates an increase in the current provided to the motor 16, and the increase in current is proportional to the pressure produced by the pump 18.
However, at some point during the life of the system, the SOFL will reach the last level—System Ready to be Removed, which indicates that the pump 18 has reached a critical wear level and the system is unable to accommodate for the losses at this level. That is, pump leakage within the system has reached a critical level and the pump should be replaced.
When the system encounters a SOFL other than Normal System Function, the system will notify the user and accommodate where possible. However, once the system reaches the last level—System Ready to be Removed, the system will shut-down and notify the user that the pump must be replaced.
Further, while the method of the present invention is discussed in relation to metering pumps, the method of the present invention is not limited to metering pumps, it may also be applied to pumps including other types of motors, for example, a switch-reluctance (SR) motor or “stepper” motor. In systems including the SR motor, phase current would be measured instead of RMS current. As such, 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 that reason, the following claims should be studied to determine the true scope and content of this invention.
