Abstract:
A closed loop control system for a fuel pump based on characteristics of speed, pressure, and current. The pressure generated by the pump system is increased at the point in time when the pump system is working against a dead head system (i.e., coasting) to a level that a calibration valve is opened to a determined working point. By measuring the characteristic phase current as a function of the speed, the characteristic is able to be compared, with the pre-calibrated value of the hardware to perform an error compensation algorithm. The error compensation is overlaid with the standard pressure characteristic as a function of speed and phase current, and uses the pre-calibrated opening pressure value (i.e., the inflection point) of the calibration valve and/or in addition the change of the speed to the initial (first calibration), or to a sliding average therefrom.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/713,183 filed Oct. 12, 2012. The disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to a closed loop control system for a fuel pump which also includes calibration functionality. 
     BACKGROUND OF THE INVENTION 
     Fuel pumps are commonly used to transfer fuel to an injection system for an engine. It is common for a fuel pump to be driven by a type of motor, such as an electric motor. The operation of the fuel pump and motor are typically controlled by some type of closed-loop feedback system, where pressure is monitored, and the speed of the pump is adjusted based on a comparison of the measured pressure to the desired pressure. These types of closed-loop feedback control systems require a pressure sensor to monitor the pressure. The type of pressure sensor required for a closed-loop feedback system is costly and adds components to the system. 
     Other attempts have been made to control a fuel pump and motor by using an open-loop control system. An open-loop control system includes a control map which includes various speeds and flow rates which correspond to each speed, the pump operates at a particular speed to generate the correct flow. An open-loop system for a fuel pump does not provide a measurement of pressure that is used for comparison to a desired pressure. There are several speeds used to provide different flow rates, and the operation of the pump is changed to correspond to a desired flow rate. Known mapped control systems (such as open-loop control systems) exhibit a high uncertainty with regard to the real pressure and may not always take advantage of full potential energy savings, since under certain conditions high fitting pressure adversely affects the energy balance. 
     Accordingly, there exists a need for a closed-loop control system for a fuel pump which does not require a pressure sensor, and is more accurate than an open-loop control system. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a closed loop control system for a fuel pump based on characteristics of speed, pressure, and current. 
     The pressure generated by the pump system of the present invention is increased at the point in time when the pump system is working against a dead head system (i.e., coasting) to a level that the calibration valve is opened to a determined working point. By measuring the characteristic phase current as a function of the speed, the characteristic is able to be compared at the inflection point, with the pre-calibrated value of the hardware to perform an error compensation algorithm. 
     The error compensation is overlaid with the standard pressure characteristic (as a function of speed and phase current) resulting in an effective pressure which is more precise. 
     The error compensation uses the pre-calibrated opening pressure value (inflection point) of the calibration valve and/or in addition to the change of the speed (influenced in the short term by changes in viscosity, media, and in the long-term by wear) to the initial (first calibration) or to a sliding average therefrom. 
     The pump system of the present invention is more precise than a preconfigured map control (which has a total failure of the summation of component tolerances), and does not require a pressure sensor. The approach of the present invention also allows for the prediction of long term deviations caused by wear, as well as actual conditions (short term) caused by changes of fluid properties. 
     In one embodiment, the present invention is a pump system having a motor, a pump for generating a pumping action to pump fluid, where the pump is connected to and driven by the motor. The pump system also has an inlet conduit in fluid communication with the motor, allowing fluid to pass into the pump, and an outlet conduit in fluid communication with the pump, such that the fluid flowing into the outlet conduit is pressurized by the pump. A secondary conduit is in fluid communication with the outlet conduit such that a portion of the fluid pressurized by the pump flows into the secondary conduit. A calibration valve is in fluid communication with the secondary conduit, and the calibration valve changes between an open position and a closed position to limit the maximum pressure in the secondary conduit and outlet conduit. The pressure of the fluid in the outlet conduit and the secondary conduit is based on the position of the calibration valve and the current applied to the motor, such that a substantially constant pressure is maintained. 
     In one embodiment, the motor is a three-phase motor, the current applied to the motor is phase current, and the speed of the motor is based on the phase current applied to the motor. As the phase current applied to the three-phase motor changes, the speed of the motor changes, and the output of the pump changes, while maintaining substantially constant pressure. 
     The pump system also has closed loop functionality, where the pump operates at a plurality of speeds, and the current is measured at each of the speeds. A first rate of change is based on a first difference in measured current between two of the commanded speeds, a second rate of change is based on a second difference in measured current between two more commanded speeds, and the first rate of change is greater than the second rate of change. The first rate of change occurs when the valve is closed, and the second rate of change occurs when the valve is open. 
     The pump system also includes a calibration function. A third rate of change is based on a third difference in measured current between another two of the commanded speeds, and a fourth rate of change is based on a fourth difference in measured current between yet another two of the commanded speeds. The third rate of change is greater than the fourth rate of change, and the third rate of change occurs when the valve is open, and the fourth rate of change occurs when the valve is closed. 
     The pump may be different types of pumps, such as a gerotor pump, an impeller pump, or the like. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is diagram of a pump system, according to embodiments of the present invention; 
         FIG. 2  is a first chart having speed and the corresponding phase current for a pump system according to the present invention; 
         FIG. 3  is a second chart having speed and the corresponding phase current for a pump system according to the present invention; 
         FIG. 4  is a third chart having speed and the corresponding phase current for a pump system according to the present invention; 
         FIG. 5  is a fourth chart having speed and the corresponding phase current for a pump system according to the present invention; and 
         FIG. 6  is a fifth chart having speed and the corresponding phase current for a pump system according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     A diagram of a pump system according to the present invention is shown at  10 . The pump system  10  includes a motor  12  and a device  14  for generating a pumping action, such as, but not limited to, a gerotor pump, an impeller pump, or any other mechanism suitable for creating a pumping action. The motor  12  is in fluid communication with an inlet conduit  16 . The motor  12  is also connected to the device  14  through a mechanical connection  18 . The device  14  is in fluid communication with an outlet conduit  20 , and the outlet conduit  20  is in fluid communication with a secondary conduit  22 . In fluid communication with the secondary conduit  22  is an internal calibration valve, shown generally at  24 . The pump system  10  is controlled by a control unit  26 . The input signal into the control unit  26  determines the nominal pressure, by using the phase current and/or speed of the pump system  10  (and more specifically, the motor  12 ) in a way such that the pressure requirement is met. 
     In operation, fuel flows through the inlet conduit  16  and through the motor  12 , a pumping action is created by the motor  12  driving the device  14 , which draws the fuel from the inlet conduit  16 , through the motor  12 , the device  14 , and out of the outlet conduit  20 . A portion of the fuel also flows into the secondary conduit  22 , and the fluid in the outlet conduit  20  and the secondary conduit  22  is allowed to reach a maximum value as determined by the calibration valve  24 . The calibration valve  24  is capable of changing between an open position and a closed position. The calibration valve  24  remains in a closed position until a predetermined pressure level is met in the secondary conduit  22  and the outlet conduit  20 . 
     In this embodiment, the motor is a three-phase motor  12  having three windings. The speed of the motor  12  is a function of current, more particularly phase current. The engine requires different amounts of fuel based on the different speeds at which the engine operates. The phase current of the motor  12  is proportional with the pressure generated by the device  14  for one dedicated engine speed. As the pressure in the outlet conduit  20  and the secondary conduit  22  generated by the motor  12  remains constant, the current of the motor  12 , speed of the motor  12 , and the flow rate of the pump  14  change accordingly. By knowing at least the phase current of the motor  12 , information regarding the pressure may be obtained, and the pressure readings are more accurate by compensation of the slope over the speed of the motor  12 . 
     Referring to  FIGS. 2-6 , various charts are shown representing the correlation between the phase current and speed of the motor  12 , and the corresponding pressure generated by the pump  14 . Referring to the first chart  28 A in  FIG. 2 , the second chart  28 B in  FIG. 3 , and the third chart  28 C shown in  FIG. 4 , the current (in Amps), indicated generally at  30 , is located along a Y-axis, shown generally at  32 , and the speed (in revolutions per minute (RPM)), indicated generally at  34 , is located along an X-axis, shown generally at  36 . There are also several curves plotted on the charts  28 A, 28 B, 28 C with each curve representing a different pressure of the fuel flowing through the system  10 . 
     A first curve  38  represents pressure at 2.0 Bar, a second curve  40  represents pressure at 3.0 Bar, a third curve  42  represents pressure at 4.0 Bar, a fourth curve  44  represents pressure at 5.0 Bar, and a fifth curve  46  represents pressure at 6.0 bar. In order to maintain a specific pressure level, the speed  34  and current  30  are changed, which varies the output flow rate of the pump  14 . The fuel flows out of the outlet conduit  20  and to the other fuel system components, such as a fuel rail  48  having one or more injectors  50 . 
     As can be seen when looking at the charts  28 A, 28 B, 28 C, the first curve  38  represents pressure at 2.0 Bar, and as the phase current  30  is increased, the speed of the motor  12  is also increased. In order to maintain the desired pressure of 2.0 Bar, as the speed  34  and therefore the phase current  30  of the motor  12  is increased, a larger amount of fuel passes through the injectors  50 , and therefore the flow rate is increased. Conversely, as the speed  34  and therefore the phase current  30  of the motor is decreased, the smaller amount of fuel passes through the injectors  50 , and therefore the flow rate is decreased to maintain the desired pressure of 2.0 Bar. The flow rate is also changed as the phase current  30  and the speed  34  are changed, and a desired pressure is maintained as indicated by the other curves  40 , 42 , 44 , 46  in the charts  28 A, 28 B, 28 C. 
     The phase current  30  is also known because the phase current  30  is measured; the speed  34  of the motor  12  is controlled, and the phase current  30  needed to obtain the desired speed  34  is measured, and therefore the speed  34  is of the motor  12  corresponds to the required phase current  30  input to the motor  12 . Because the motor  12  is a three-phase motor, the motor  12  therefore has three coil pairs, and only one coil pair is needed to monitor the phase current  30 . 
     When the pump system  10  is assembled, the system  10  is calibrated to function correctly using the speed  34  and measured phase current  30 . Referring to the fourth chart  28 D shown in  FIG. 5  and the fifth chart  28 E shown in  FIG. 6 , a pressure calibration curve  52  is generated using the current  30  and speed  34  of the motor  12 , and the pump  14 . The calibration valve  24  is designed to open when the pressure of the fluid in the secondary conduit  22  approaches a predetermined value, which in this embodiment is about 6.5 Bar. Once the pressure level of 6.5 Bar is reached, the system  10  is coasting to a level such that the valve  24  is opened to a predetermined working point. 
     As shown in  FIGS. 5-6 , the calibration curve  52  has two different slopes, a first portion  54  having a first slope, and a second portion  56  having a second slope. The first portion  54  of the curve  52  represents the operation of the motor  12  and pump  14  when the valve  24  is closed, and the second portion  56  of the curve  52  represents the operation of the motor  12  and pump  14  when the valve  24  is open. To generate the curve  52 , the motor  12  is commanded to operate at various speeds, and the phase current  30  is then measured at each speed. There is no sensor used for detecting whether the valve  24  is open or closed. 
     In this embodiment, and as shown in  FIG. 6 , when the motor  12  is commanded to operate at a first speed, which in this embodiment is about 1100 rpm, the measured current  30  is about 4.0 Amperes, and when the motor  12  is operating at a second speed, about 1500 rpm, the current  30  is about 6.1 Amperes. Furthermore, when the motor  12  is operating at a third speed, about 2500 rpm, the current  30  is about 8.9 Amperes, and when the motor  12  is operating at a fourth speed, about 3000 rpm, the current  30  is about 9.1 Amperes. Along the first portion  54  of the curve  52 , the current  30  increases about 2.1 Amperes as the speed  34  increases from the first speed of 1100 rpm to the second speed of 1500 rpm, a difference of 400 rpm (a rate of change of about 0.525 Amperes for every increase in 100 rpm). Along the second portion  56  of the curve  52 , the current  30  increases about 0.2 Amperes as the speed  34  increases from the third speed of 2500 rpm to the fourth speed of 3000 rpm, a difference of 500 rpm (a rate of change of about 0.04 Amperes for every increase in 100 rpm). 
     To increase the speed 400 rpm along the first portion  54  of the curve  52 , the current increased 2.1 Amperes, and to increase the speed 500 rpm along the second portion  56  of the curve  52 , the current  30  increased only 0.2 Amperes. The current  30  increases (as the speed  34  is increased) at a different rate along the first portion  54  of the curve  52  compared to the second portion  56  of the curve  52 . Therefore, the first portion  54  of the curve  52  has a first rate of change (of current  30  versus speed  34 ) of about 0.525 Amperes for every increase in 100 rpm, and the second portion  56  of the curve  52  has a second rate of change (of current  30  versus speed  34 ) of about 0.04 Amperes for every increase in 100 rpm. 
     Furthermore, as the speed  34  is increased, the pressure in the system  10  is increased. However, the increase in pressure as the speed  34  is increased is limited by the calibration valve  24 . Once the pressure in the system  10  reaches 6.5 Bar, the valve  24  opens, maintaining the pressure at 6.5 Bar, even as the speed  34  continues to increase; the valve  24  opens further to allow for an increase in flow and a constant pressure to be maintained. The change in current  30  required to increase the speed  34  of the motor  12  when the valve  24  is closed is greater than the change in current  30  required to increase the speed  34  of the motor  12  when the valve  24  is opened. Therefore, the increase in unit of current  30  per increase in unit of speed  34  is greater along the first portion  54  of the curve  52  (i.e., the first rate of change) compared to the second portion  56  of the curve  52  (i.e., the second rate of change). 
     The area of the calibration curve  52  where the first portion  54  ends and the second portion  56  begins is an inflection point  58 . The inflection point  58  also represents the point during operation when the calibration valve  24  opens. After the calibration valve  24  opens, less current  30  is required to increase the speed  34 , because the valve  24  opens further to allow for an increase in flow, while maintaining the maximum allowed pressure, which as previously mentioned in this example is 6.5 Bar. Along the second portion  56  of the curve  52 , if the speed  34  is increased, the flow is increased, and the current  30  increases as well. 
     In addition to having closed loop functionality, the system  10  also includes tolerance compensation capability, or a calibration function, as well. Referring to  FIG. 6 , to compensate for the tolerance in the pump system  10 , the calibration curve  52  is generated when the motor  12  and pump  14  are new. During the life of the system  10 , a second curve, or operation curve  60  is generated also having a first portion  62 , a second portion  64 , and an inflection point  66 . The second curve  60  is created by commanding the motor  12  to operate at a specific speed  34 , and the phase current  30  is then measured as the motor  12  operates at each speed  34 . 
     To obtain a measurement of current  30  of about 4.0 Amperes along the operation curve  60 , the motor  12  is commanded to operate at a fifth speed, which in this embodiment is about 1200 rpm, and to obtain a measurement of current  30  of about 6.1 Amperes, the motor  12  is commanded to operate at a sixth speed of about 1600 rpm. The first portion  62  of the curve  60  has a third rate of change (of current  30  versus speed  34 ), of about 0.525 Amperes for every increase in 100 rpm, which is similar to the first rate of change. However, while the first rate of change and third rate of change are substantially similar, the measurements of current  30  occur at different speeds, which is a result of a change in the operation of the system  10  over time due to wear, changes in fluid viscosity, or other factors. 
     To obtain a measurement of current  30  of about 8.9 Amperes along the operation curve  60 , the motor  12  is commanded to operate at a seventh speed, about 2600 rpm, and to obtain a measurement of current  30  of about 9.1 Amperes, the motor  12  is commanded to operate at an eighth speed, about 3100 rpm. The second portion  64  of the curve  60  has a fourth rate of change (of current  30  versus speed  34 ) of about 0.04 Amperes for every increase in 100 rpm, which is similar to the second rate of change. However, while the second rate of change and fourth rate of change are substantially similar, the measurements of current occur at different speeds, which is a result of a change in the operation of the system  10  over time due to wear, changes in fluid viscosity, or other factors. 
     It is shown in  FIG. 6  that the calibration curve  52  is different from the operation curve  60 . The calibration curve  52  represents the operation of the system  10  when the system  10  is new, and the operation curve  60  represents the operation of the system  10  after a period of time has passed, and the various components of the system  10  have undergone some level of wear, or other factors may have occurred which affect the operation of the system  10 . The operation curve  60  provides an indication of how the operation of the system  10  has changed over time. A new operation curve  60  may be generated based on specific time intervals, such as daily, monthly, or yearly, or may be generated under specific conditions, such as upon vehicle start up, when there is a significant temperature change, or the like. The operation curve  60  provides a different operation functionality to the pump system  10 . This allows for the system  10  to not only provide closed loop functionality, but also provides for compensation for tolerances and variations in the function of the system  10  over time. 
     In alternate embodiments, it is also possible to have the pump system  10  operate without the use of the calibration valve  24 . The phase current and/or speed of the motor  12  is used such that the pressure requirement is met. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.