Abstract:
A method of controlling the delivery of fluid to an engine includes receiving a fuel flow rate signal. An electric pump is arranged to deliver fluid to the engine. The speed of the electric pump is controlled based on the fuel flow rate signal.

Description:
CLAIM FOR PRIORITY 
   This application claims the benefit of U.S. Provisional Application No. 60/458,460, filed Mar. 28, 2003. 

   U.S. GOVERNMENT RIGHTS 
   This invention was made with government support under the terms of Contract No. DE-FC04-2000AL67017 awarded by the Department of Energy. The government may have certain rights in this invention. 

   TECHNICAL FIELD 
   This invention relates generally to fluid delivery systems for internal combustion engines, and more particularly to control systems for controlling fluid delivery to internal combustion engines. 
   BACKGROUND 
   Conventional internal combustion engines are typically lubricated with a mechanical pump powered by the engine via belts or gears. The speed of the pump, and therefore the oil pressure and rate of oil flow, are a function of the engine speed. Auxiliary electrically operated oil pumps have been used to operate at engine start-up to ensure oil flow to the engine as soon as possible. 
   Oil not only lubricates engine parts, but oil is also important in engine cooling. It is important that sufficient oil pressure be provided to float the engine bearings and prevent metal-to-metal contact. With the use of a mechanical oil pump powered by the engine, the amount of lubrication and cooling of the engine is dependent on engine speed and is not relative to the work load of the engine. 
   U.S. Pat. No. 5,884,601 to Robinson discloses a variable speed electric pumping system that controls the speed of an electric oil pump based on engine load. Engine load is determined by monitoring an engine speed signal received from an engine RPM sensor. Robinson also discloses receiving an oil pressure signal from an oil pressure sensor and controlling the oil pump speed to maintain a designed specification oil pressure. Robinson discloses that this compensates for the tendency of the oil pressure to decrease as the engine wears. 
   The disclosure of Robinson, however, does not describe any method of determining engine load other than by sensing engine speed from an engine RPM sensor. Sensing engine RPM is often an inadequate method for determining the load on an engine and for determining the lubrication requirements of the engine. For example, a truck traveling up a steep hill at a given engine RPM may have a much higher torque on the engine than the same truck traveling down a hill at the same engine RPM. The torque on the truck engine traveling uphill will be much higher and, consequently, there will be more force exerted on the engine bearings and the engine bearings will be more prone to wear. Thus, an oil pump control system that controls the oil pump based solely on engine RPM will not be able to provide adequate lubrication to an engine under all load conditions without wasting a significant amount of pumping energy. 
   The present invention provides a fluid delivery control system that avoids some or all of the aforesaid shortcomings in the prior art. 
   SUMMARY OF THE INVENTION 
   In accordance with one aspect of the disclosure, a method of controlling the delivery of fluid to an engine includes receiving a fuel flow rate signal. An electric pump is arranged to deliver fluid to the engine. The speed of the electric pump is controlled based on the fuel flow rate signal. 
   In accordance with another aspect of the disclosure, an electric pump control system controls delivery of fluid to an engine. A pump is arranged to pump fluid to an engine. An electric motor is arranged to drive the pump. A controller is operatively coupled to the electric motor. The controller controls the speed of the electric motor in response to a fuel flow rate signal. 
   In accordance with another aspect of the disclosure, a method of controlling the delivery of fluid to an engine includes receiving a sensed oil pressure signal. A desired oil pressure is determined based on engine torque. An electric pump is arranged to deliver fluid to the engine. The speed of the electric pump is controlled based on the desired oil pressure and the sensed oil pressure signal. 
   In accordance with another aspect of the disclosure, a method of controlling the delivery of fluid to an engine includes determining a value representative of engine torque and controlling the speed of an electric pump arranged to deliver fluid to the engine based on the engine torque. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a graph illustrating maximum engine torque as a function of engine RPM, and also illustrating the engine oil pressure provided by a conventional mechanical oil pump; 
       FIG. 2  is a block diagram illustrating an exemplary pump control system of the present disclosure; 
       FIG. 3  is a block diagram illustrating a feedback control loop for controlling the delivery of fluid to the engine based on engine torque; 
       FIG. 4  is a block diagram illustrating a feedback control loop for controlling the delivery of fluid to the engine based on engine torque and engine speed; 
       FIG. 5  is a state diagram illustrating different modes of engine operation; and 
       FIG. 6  is a block diagram illustrating a feedback control loop for controlling the delivery of fluid to the engine during pre-lube mode. 
   

   DETAILED DESCRIPTION 
   Reference will now be made in detail to the exemplary embodiments of the invention which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     FIG. 1  depicts a set of curves illustrating the relationship between maximum engine torque and the engine oil pressure provided by a conventional mechanical oil pump. Maximum engine torque curve  2  illustrates the maximum engine torque that can be provided by a particular engine as a function of engine RPM. As engine RPM increases from an idle condition, the maximum engine torque initially increases until it reaches a peak and then decreases as engine RPM further increases. 
   As mentioned previously, a conventional internal combustion engine is typically lubricated with a mechanical oil pump powered by the engine via belts or gears. The mechanical oil pump speed is thus proportional to engine speed. Curve  4  illustrates the engine oil pressure provided by a conventional mechanical pump. As engine RPM increases from an engine idle condition, the mechanical pump speed increases proportionally causing a linear increase in engine oil pressure. This provides increased lubrication and cooling to the engine as engine RPM increases. When engine RPM reaches the speed at which the maximum engine torque curve  2  is at its peak, an oil pressure relief valve opens. For all engine speeds above this point, the pressure relief valve remains open. This bleeds off excess oil pressure, keeping the oil pressure at a constant level for all engine speeds above this point. Engine oil pressure curve  4  is designed so that adequate lubrication is provided to the engine when it is loaded with its maximum torque over a range of speeds. 
   Although oil pressure remains essentially constant for engine speeds greater than the point at which the pressure relief valve opens, the oil pump speed continues to increase as engine RPM increases. If not for the opening of the pressure relief valve, the oil pressure would follow dashed line  6 . Because the oil pump is turning faster than is needed to provide adequate lubrication to the engine, oil pumping power is wasted. The excess oil that is bled through the pressure relief valve represents wasted oil pumping energy. The wasted energy takes the form of heat added to the oil, which is then rejected via the engine&#39;s cooling system. 
   When the engine is running at point C (see  FIG. 1 ), the torque on the engine is less than at point B, although the engine speed is the same at the two points. The engine bearings are consequently under less pressure when the engine is running at point C than at point B, even though the engine is operating at the same speed at points C and B. A conventional mechanical pump system would provide the same oil pressure at points B and C, because the engine is operating at the same speed at points B and C. In contrast, the oil pumping system disclosed herein provides increased oil pressure at point B to account for the increase in engine torque and the consequent increase in force placed on the bearings. Thus, for example, if a truck travels down a hill and then travels up a hill, the oil pumping system will increase oil pressure when the truck travels up the hill to account for the increased torque, even if the engine speed remains constant. The increased oil pressure is needed to account for the increased force on the bearings at increased torque levels. By reducing the oil pressure when the truck travels down hill (i.e. when engine torque decreases), the oil pumping system can ensure that oil pumping power is used efficiently and not wasted, while still ensuring that adequate lubrication and cooling is provided to the engine. 
   An engine operating at point A has the same torque as at point C, but is operating at a higher speed at point A. As will be described in more detail below, in a first embodiment, the oil pumping system can provide a constant oil pressure at a given engine torque without varying oil pressure as a function of engine speed. In a second embodiment, the oil pumping system can increase oil pressure as engine speed increases—thus oil pressure will be a function of both engine torque and engine speed. 
     FIG. 2  illustrates an oil pump control system  20  according to an exemplary embodiment of the present disclosure. The pump controller can be implemented as a microprocessor  22 , which controls the speed of the electric oil pump based on various inputs. Microprocessor  22  can be the engine control unit (ECU), the processor which controls operation of the engine, or alternatively, microprocessor  22  can be implemented as a separate processor for controlling the oil pump. Alternatively, the pump controller can be implemented as multiple processors. 
   Microprocessor  22  receives a series of inputs from various sensors.  FIG. 2  depicts examples of inputs that may be provided to microprocessor  22 . Oil temperature sensor  24  may be located in the oil sump and provides a signal representative of the oil temperature in the oil sump. Oil pressure sensor  26  may be located in the oil gallery rail leading into the engine block. Oil pressure sensor  26  provides a signal representative of oil pressure. Engine speed sensor  28  may be coupled to the crankshaft. Engine speed sensor  28  senses engine RPM and outputs a signal representing engine speed. Operator demand sensor  30  provides a signal representing the engine demand requested by an operator of a vehicle or machinery containing the engine. Operator demand sensor  30  senses the load demand that is requested by the operator. For example, operator demand sensor  30  can sense the amount by which an operator depresses an accelerator pedal in a vehicle. Alternatively, operator demand sensor  30  can sense the demand requested by a cruise control system. 
   Electric oil pump current sensor  32  senses the current drawn by the electric motor coupled to the oil pump. Fuel flow sensor  34  senses the rate of fuel flow delivered to the engine. Air flow sensor  36  senses the rate of air flow delivered to the engine. Air pressure sensor  38  senses the air pressure at the intake manifold of the engine. Air temperature sensor  43  senses the air temperature at the intake manifold of the engine. Key position  40  senses the position of the key that is used to start the vehicle or other machinery that contains the engine. Key position  40  provides, for example, a signal representing various key positions such as Off, Accessory, Run, and Start. Start switch  42  provides a signal indicating whether the Start pushbutton has been depressed. 
   Microprocessor  22  outputs an output signal to motor driver circuit  44 . Motor driver circuit  44  provides electric power to drive electric motor  46 . Electric motor  46  is operatively coupled to drive oil pump  48 . Oil pump  48  pumps oil or other fluid to the engine thereby providing sufficient pressure to float the bearings and prevent metal-to-metal contact. Oil or other fluid is also sprayed on the engine pistons and/or other engine surfaces for the purpose of cooling the engine. 
     FIG. 3  depicts a block diagram illustrating an exemplary control algorithm of the present invention executed by the pump controller (microprocessor  22 ). Microprocessor  22  receives a fuel flow signal from fuel flow sensor  34 . The fuel flow signal represents the rate of fuel flow to the engine. Microprocessor  22  also receives an engine speed signal from engine speed sensor  28 . At block  50 , microprocessor  22  calculates engine torque. Engine torque can be determined in a number of ways. Fuel flow rate is the primary variable used to determine engine torque. Other variables, such as engine speed, air pressure at the intake manifold, and air temperature may be used to obtain a more precise value of engine torque. 
   One method of determining engine torque is to calculate engine torque as a linear function of fuel flow rate. Thus, when the engine is operating at 100% fuel flow rate, microprocessor  22  determines that engine torque is at 100% of the maximum engine torque. When the engine is operating at 50% fuel flow rate, microprocessor determines that engine torque is at 50% of the maximum engine torque. 
   Other approximations of engine torque may be used other than a linear relationship to provide a more accurate determination of engine torque. A curve showing engine torque as a function of fuel flow rate for a particular engine can be generated experimentally or based on conventional equations. This curve can be programmed into microprocessor  22 . Microprocessor  22  thereby determines engine torque based on fuel flow rate using such a curve (or using equations that represent the curve). 
   A closer approximation of engine torque can be used by determining engine torque as a function of both fuel flow rate and engine speed. An engine speed signal is received from engine speed sensor  28 . As before, a set of curves can be generated that show engine torque as a function of both fuel flow rate and engine speed. The curves can be generated experimentally for a particular engine or based on conventional equations. Microprocessor  22  uses these curves (or equations representing such curves) to calculate engine torque as a function of fuel flow rate and engine speed. Other signals may be used by microprocessor  22  to further refine the determination of engine torque. For example, air pressure at the intake manifold, air temperature, air flow, and other inputs can be used to further determine engine torque. These signals are provided by sensors shown in  FIG. 2 . 
   Microprocessor  22  can also use a signal from operator demand sensor  30  to calculate the predicted torque on the engine. For example, if an operator of a vehicle pushes on the accelerator pedal, microprocessor  22  can predict the extent to which engine torque will increase using either conventional equations or experimentally determined response characteristics. Microprocessor  22  can then increase oil pressure to match the predicted engine torque. 
   Block  50  in microprocessor  22  outputs a percentage torque signal  52  representing the percentage of the maximum torque that the engine is capable of outputting, a value between 0 and 100 percent. The term “signal” as used herein can refer to an analog signal, a digital signal, or simply a data value determined by the microprocessor. Percentage torque signal  52  is provided to a look-up table  54  to determine a desired oil pressure signal  56 . Look-up table  54  outputs a desired oil pressure signal  56 . Look-up table  54  contains a series of values representing the desired oil pressure at different levels of engine torque ranging from 0 to 100 percent engine torque. The desired oil pressure values that are programmed into look-up table  54  are chosen based on the cooling and lubrication requirements of the engine at each percentage torque. Sufficient oil pressure must be provided at a given engine torque to prevent metal-to-metal contact of the engine bearings, and to provide adequate cooling to the engine. As an alternative to look-up table  54 , the microprocessor can execute one or more calculations that provide desired oil pressure as a function of torque. 
   Alternatively, microprocessor  22  can determine the desired oil pressure based on calculating a parameter related to engine torque, such as engine power output. For example, microprocessor can calculate the engine power output based on engine torque and engine speed. The engine power output can then be used as an input to look-up table  54  to determine a desired oil pressure. 
   Microprocessor  22  uses a feedback control loop to control operation of the oil pump  48  to produce the desired oil pressure. Microprocessor  22  receives an oil pressure signal from oil pressure sensor  26 . The oil pressure signal is provided to the negative input of summer  58 . The desired oil pressure signal  56  is provided to the positive input of summer  58 . Summer  58  outputs an error signal  60  representing the difference between the desired oil pressure and the sensed oil pressure. Microprocessor  22  outputs error signal  60  to electric motor driver circuit  44 . If the error signal  60  is a positive value, then desired oil pressure is greater than the sensed oil pressure. Motor driver circuit  44  responds to a positive error signal by increasing the speed of electric motor  46 . If the error signal  60  is a negative value, then the desired oil pressure is less than the sensed oil pressure. Motor driver circuit  44  responds to a negative error signal by decreasing the speed of electric motor  46 . Electric motor  46  drives oil pump  48  in accordance with the drive signal received from motor driver circuit  44 . 
   As an alternate feature, microprocessor  22  can determine desired oil pressure  56  based on other criteria in addition to engine torque. For example, microprocessor  22  can determine the desired oil pressure based on oil temperature and/or engine speed, in addition to engine torque. At higher engine speeds, there is more friction on the bearings and thus may require a slightly increased oil pressure even if engine torque remains constant. At high oil temperatures, the oil provides less cooling and thus may require slightly increased oil pressure to adequately cool the engine even if engine torque remains constant. Thus, the desired oil pressure determined by microprocessor  22  will increase as oil temperature increases and/or as engine speed increases, even if engine torque remains constant. In other words, oil pumping speed at a given engine torque will increase at higher oil temperatures and/or higher engine speeds. 
     FIG. 4  depicts a block diagram illustrating an alternative control architecture  106  for controlling oil pump speed based on both engine torque and engine speed. Percentage engine torque signal  70  is input to a look-up table  72 . Percentage engine torque signal  70  is calculated by the microprocessor  22 , as described previously, based on such signals representing the energy input to the engine such as air flow and fuel flow. Look-up table  72  outputs a pump speed signal  74 . At zero percent torque, look-up table  72  outputs a pump speed signal  74  representing zero pumping speed. As engine torque increases, the pump speed signal  74  output by look-up table  72  increases. When percentage engine torque signal  70  reaches 80% engine torque, the pump speed signal  74  reaches its maximum value corresponding to maximum pump speed. The relationship between percentage engine torque signal  70  and pump speed signal  74  can be linear or can be a non-linear curve based on the lubrication requirements of the engine. For percentage torque values above 80%, the pump speed signal  74  remains constant at 100% pumping speed. 
   The control architecture  106  shown in  FIG. 4  also controls the speed of the oil pump based on engine speed. An engine speed signal  76  is received from an engine RPM sensor. Engine speed signal  76  is input to a look-up table  108  that outputs a desired oil pressure  78  based on the input engine speed signal  76 . Desired oil pressure  78  increases as engine speed  76  increases. Desired oil pressure  78  is input to a positive input of summer  80 . A sensed oil pressure signal  82  received from an oil pressure sensor is provided to a negative input of summer  80 . The summer outputs an error signal  84 . Error signal  84  is provided to proportional and integral (PI) control block  104 . A typical PI control block is described in detail later with respect to  FIG. 6 . The PI control block  104  integrates the error signal  84  so that the history of error signal  84  is taken into account when controlling the speed of the oil pump. This helps the feedback control loop achieve the desired oil pump speed. 
   PI control block  104  outputs a pump speed signal  86 , which is input to a positive input of summer  88 . Summer  88  sums pump speed signal  74  with pump speed signal  86 . The output of summer  88  represents the pumping speed signal that is provided to motor driver circuit  44 . 
   If the engine torque increases significantly, the engine oil pressure will increase due to the increased pump speed signal  74 . This may cause error signal  84  to become negative for a relatively long time, and a large negative pump speed signal  86  can get built up on the output of PI control block  104  due to the integration of the error signal  84 . This problem can be corrected by including anti-windup in the PI control block  104 . The anti-windup feature limits the output of the integrator in PI control block  104 . 
   An additional control algorithm  102  can be included to prevent damage to the pump by ensuring the oil pumping speed does not exceed the rated capability of the pump. Control algorithm  102  acts to slow the pump whenever the input current to the pump exceeds the maximum current rating of the pump. A sensed oil pump current signal  90  is received from an oil pump current sensor that senses the current drawn by the oil pump&#39;s electric motor. The sensed oil pump current signal  90  is provided to a negative input of summer  92 . A maximum oil pump current value  94  is input to a positive input summer  92 . Maximum oil pump current value  94  is a constant value that represents the maximum input current rating for the oil pump&#39;s electric motor. Summer  92  subtracts the sensed oil pump current signal  90  from the maximum oil pump current value  94 . Summer  92  outputs an error signal  100  to saturation block  96 . Saturation block  96  outputs a zero value when it receives a positive signal. When saturation block  96  receives a negative signal, it passes the negative signal through to its output. When oil pump current signal  90  is less than the maximum oil pump current value  94 , error signal  100  is positive and the output off saturation block is zero. When sensed oil pump current signal  90  is greater than the maximum oil pump current value  94 , error signal  100  is negative and the output of saturation block  96  is equal to error signal  100 . The output of saturation block  96  is provided to amplifier  98 , which has a scalar gain P. The output of amplifier  98  is input to a negative input of summer  88 . Thus, when the oil pump current signal  90  exceeds the maximum oil pump current signal  94 , control algorithm  102  acts to decrease the pumping speed of the oil pump until the speed is below the pump motor&#39;s rated current. 
   INDUSTRIAL APPLICABILITY 
     FIG. 5  depicts a state diagram  120  illustrating examples of various modes of engine operation for an engine in a truck. The control algorithm for controlling the oil pump can be changed based on an engine mode of operation. The engine is initially in an Off state  124 . The microprocessor determines that the engine is in Off state  124  when the truck key is in the Off position. An operator can start the engine by turning the key to Run position and then depressing a “Start” pushbutton. This starts a pre-lube mode of operation  128 . The pre-lube mode of operation  128  is a mode of operation where the oil pump is operated to provide lubrication to the engine before the engine is started. If the operator turns the key to Off while the engine is in pre-lube mode, the engine returns to Off mode of operation  124 . The pre-lube mode of operation  128  may last for 20 seconds and then the engine automatically may go into cranking mode  130 . 
   When the engine speed exceeds a determined value such as 550 RPM, it is determined that the engine has exited cranking mode  130  and has entered a Run mode of operation  132 . When the engine is in Run mode  132 , it is either in cold oil run mode  134  or hot oil run mode  136 . In certain embodiments, when the sensed oil temperature is above 40° C. the engine is in hot oil run mode  136 . When the sensed oil temperature is below 40° C. the engine is in a cold oil run mode  134 . When the engine is in a Run mode of operation  132 , and the operator turns the key switch to Off, the engine enters a post-lube mode of operation  138 . Post-lube mode of operation  138  is a mode of operation where the oil pump is operated to provide lubrication to the engine after the engine has been turned off. After the engine is in post-lube mode of operation for a predetermined period of time, the engine returns to the Off mode  124  of operation. In the Off mode of operation  124 , the oil pump is shut off. 
   The pump controller can use different algorithms for controlling the pump in different engine modes of operation.  FIG. 6  depicts a block diagram illustrating a feedback control loop for controlling the oil pump during pre-lube mode of operation. When the engine is in pre-lube mode of operation, microprocessor  22  controls the oil pump by maintaining a fixed current to the oil pump&#39;s electric motor. 
   Feedback control loop  150  is a proportional and integral (PI) control loop. I sensor  is a sensed current signal received from the electric oil pump current sensor  32  and is representative of the current input to the oil pump&#39;s electric motor. I sensor  is input to a negative input of summer  152 . I ref  is a constant reference current level. I ref  can be experimentally determined by determining the optimal amount of lubrication for the engine during pre-lube. 
   Summer  152  outputs an error signal  154  which is the difference between I ref  and I sensor . Error signal  154  is multiplied by a scalar gain P and provided to summer  160 . Error signal  154  is also provided to integrating block  158  and then scaled by a scalar gain G and input to summer  160 . Summer  160  sums the two inputs and outputs a pump speed control signal  162 . Feedback control loop  150  thereby controls the speed of the oil pump&#39;s motor so as to maintain a constant input current equal to I ref . 
   When the engine is in cranking mode  130 , the oil pump is shut off. When the engine is in hot oil run mode  136 , the oil pump is controlled with respect to engine torque and/or engine speed as illustrated in  FIGS. 3  or  4 , described previously. When the engine is in cold oil run mode  134 , the oil pump is controlled by the same method as during pre-lube mode; i. e. the pump controller maintains a constant oil pump current I ref . When the oil is cold it is more viscous and requires more pumping power to pump the oil. By controlling the speed of the pump to maintain a constant oil pump current I ref , the controller ensures that sufficient lubrication is provided to the engine when the oil is cold and viscous. 
   When the engine is in post-lube mode of operation  138 , the engine is off and the pump control system continues to temporarily operate the oil pump to cool down the engine and especially to cool down the turbocharger bearings. During this mode of operation, the pump controller (e.g. microprocessor  22 ) senses oil temperature and controls oil pump speed based on sensed oil temperature. When the oil temperature is greater than or equal to 50° C. the oil pump is controlled to maintain a constant pump speed of 3000 RPM. When the oil temperature drops below 50° C. the oil pump speed is controlled linearly based on temperature. Thus, oil pump speed will decrease linearly as the oil temperature drops until the oil temperature reaches 20° C. at which point the oil pump speed will be maintained at 500 RPM. After 30 seconds of post-lube operation, the oil pump is turned off. 
   The disclosed pump control system can also be used in a lubrication system that uses a combination of a mechanical oil pump and an electrical oil pump connected in parallel—i.e., the pump outlets connected to a common passage. The mechanical pump is connected to the engine via belts or gears, and thus the speed of the mechanical pump is proportional to the speed of the engine. The electric pump is controlled by the pump controller of the present invention. The values used in the look-up tables of the various control embodiments may take into account the presence of the mechanical pump so that the electric pump provides an amount of oil to sufficiently lubricate the engine without wasting pumping energy. 
   Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the invention being indicated by the following claims.