Abstract:
A strategy for controlling an electric pump and control valve in an internal combustion engine cooling system compensates for backpressure variations and maintains system operation within design parameters. The method comprises the steps of measuring the coolant temperature, measuring the electrical current and voltage to the pump motor, determining the pump speed and coolant flow, determining the desired coolant flow, determining a negative correction to the flow control valve and pump if desired flow is less than present coolant flow and determining a positive correction to the flow control valve and pump if desired flow is more than present coolant flow and undertaking this correction to coolant flow. Thus, based upon inferred back pressure in the engine coolant system from the data relating to the pump energy input, proper coolant flow, heat rejection and engine operating temperature can be maintained in spite of variations in system flow restrictions and backpressure.

Description:
FIELD 
       [0001]    The present disclosure relates to electric pumps utilized in internal combustion engine coolant circuits and more particularly to a strategy for controlling an electrically powered pump in an internal combustion engine coolant circuit. 
       BACKGROUND 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
         [0003]    The cooling circuit of an internal combustion engine and more particularly coolant flow in the cooling circuit of an internal combustion engine in a motor vehicle is critical not only from the fundamental standpoint of dissipating the heat of combustion to the ambient but also to accurately control the temperature of the engine to optimize performance and fuel economy. 
         [0004]    Significant engineering and design effort is directed to these operational parameters, especially the latter given increasingly stringent fuel economy requirements. Unfortunately, even the most sophisticated cooling system configurations are subject to variations caused by, for example, manufacturing and assembly variables and wear and aging of the components such as the pump impeller, the radiator and the hoses. These variations cause variations in system backpressure which can result in flow reduction and temperature variations that deviate from design goals. 
         [0005]    With older engines having engine driven coolant pumps (and less stringent performance expectations and requirements) such backpressure variations were of little moment. Today, an increasing number of internal combustion engines, obviously subject to today&#39;s performance expectations and requirements, utilize electrically driven coolant pumps, which, unfortunately, are highly sensitive to backpressure variations. A engine cooling system utilizing an electric pump that initially met all heat dissipation and temperature control requirements, as components wear and age and system backpressure changes, may no longer achieve the desired design goals. Because coolant flow and thus temperature and heat dissipation affect cylinder wall and cylinder head temperature, an engine operating at other than design or optimal temperature will compromise fuel economy. 
         [0006]    The present invention addresses this problem. 
       SUMMARY 
       [0007]    The present invention provides a strategy for controlling an electric pump in an internal combustion cooling circuit or system which compensates for backpressure variations and maintains system operation, especially engine temperature, within design parameters. The method of operation comprises the steps of measuring the coolant temperature, measuring the electrical voltage and current to the electric pump, determining the pump speed and the coolant flow, determining the desired coolant flow, determining a positive correction signal to the flow control valve and electric pump motor if desired flow is less than current coolant flow and determining a negative correction signal to the flow control valve and electric pump motor if desired flow is more than current coolant flow and undertaking this correction to coolant flow. Thus, based upon inferred back pressure in an engine coolant circuit from the data, engine operating temperature can be maintained in spite of short term and long term variations in system flow restrictions and backpressure and thus variations in coolant flow. 
         [0008]    It is thus an aspect of the present invention to provide a control method for a cooling system or circuit of an internal combustion engine which compensates for variations in flow restrictions. 
         [0009]    It is a further aspect of the present invention to provide a control method for a cooling system or circuit of an internal combustion engine which measures electric coolant pump voltage and current to determine pump speed and flow. 
         [0010]    It is a still further aspect of the present invention to provide a control method for a cooling system or circuit of an internal combustion engine which infers system or circuit backpressure from electric pump operational date. 
         [0011]    It is a still further aspect of the present invention to provide a control method for a cooling system or circuit of an internal combustion engine which provides a positive correction signal to the flow control valve and electric pump motor if instantaneous coolant flow is less than desired coolant flow. 
         [0012]    It is a still further aspect of the present invention to provide a control method for a cooling system or circuit of an internal combustion engine which provides a negative correction signal to the flow control valve if instantaneous coolant flow is more than desired coolant flow. 
         [0013]    It is a still further aspect of the present invention to provide a control method for a cooling system or circuit of an internal combustion engine which compensates for variations in system backpressure thereby maintaining design engine operating temperature and other parameters. 
         [0014]    It is a still further aspect of the present invention to provide a control method for a cooling system or circuit of an internal combustion engine which compensates for short term and long term variations in system backpressure thereby maintaining design engine operating parameters such as temperature. 
         [0015]    Further aspects, advantages and areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0016]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0017]      FIG. 1  is a schematic diagram of an internal combustion coolant system or circuit incorporating the present invention; 
           [0018]      FIG. 2  is a diagrammatic map of control valve spool position versus flows of the coolant control valve illustrated in  FIG. 1 ; 
           [0019]      FIG. 3  is a graph presenting current to the electric pump of  FIG. 1  on the X (horizontal) axis versus pump flow in liters per minute in the Y (vertical axis) for several speed (r.p.m.) conditions of the electric pump between 1000 r.p.m. and 5900 r.p.m.; and 
           [0020]      FIG. 4  is a flow chart of the method of operating an internal combustion engine cooling system or circuit having an electrically driven coolant pump according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0022]    With reference to  FIG. 1 , an internal combustion engine and cooling system or circuit is illustrated and generally designated by the reference number  10 . The engine and cooling system  10  includes an internal combustion engine  12  having an engine block  14  including cylinders and pistons, a head  16  including valves and an integrated exhaust manifold  18 . These components of the internal combustion engine  12  are surrounded by a cooling jacket  20  through which a liquid coolant is circulated by an electric pump  24 . The coolant pump  24  is driven by an electric motor  26 . From the electric pump  24 , the liquid coolant is circulated in a coolant supply line  28  to the components of the internal combustion engine  12 , a turbocharger  32 , a surge tank  34  and a heater core  36 . 
         [0023]    The coolant passing through the components of the internal combustion engine  12  exits in a coolant line  42  which includes an engine outlet temperature sensor  44 . The coolant then enters a first inlet port  48  of a two section coolant control valve  50 . A first section  52  of the coolant control valve  50  receives coolant flow from the internal combustion engine  12  through the first inlet port  48  and directs it to either a first exhaust port  54  connected through a line  56  to a radiator  60  or a second (bypass) exhaust port  62  connected to a line  64  which bypasses the radiator  60  and returns coolant to the inlet or suction side of the electric pump  24 . 
         [0024]    A second section  68  of the coolant control valve  50  receives coolant flow in a second inlet port  72  from both the integrated exhaust manifold  18  and the turbocharger  32  in a line  74  which also communicates with the inlet port  48  of the first section  52  of the coolant control valve  50 . A third inlet port  76  of the second section  68  of the coolant control valve  50  is connected to the electric pump  24  through the fluid supply line  28 . The second section  68  of the coolant control valve  50  also includes two exhaust ports: a third exhaust port  82  which directs coolant flow to an engine oil heater  84  and a fourth exhaust port  86  which directs coolant flow to a transmission oil heater  88 . Return coolant flows from the engine oil heater  84  and the transmission oil heater  88  are carried in the line  64  which communicates with the inlet or suction side of the electric pump  24 . The coolant control valve  50  also includes a single, i.e., tandem, spool or flow control element  92  which is linearly and bi-directionally translated by an electric or hydraulic actuator or operator  94 . 
         [0025]    Both the electric motor  26  of the coolant pump  24  and the linear actuator or operator  94  of the coolant control valve  50  are under the control of an engine control module (ECM)  96  or other, similar global or dedicated electronic control module have I/O devices, static and transient memories and processors or microprocessors as well as associated electronic components. 
         [0026]    Turning now to  FIGS. 1 and 2 , a diagrammatic map of the position of the spool or flow control element  94  of the coolant control valve  50  is illustrated and designed by the reference number  100 . The upper portion  102  of the map  100  relates to the first section  52  of the coolant control valve  50  and the lower portion  112  relates to the second section  68  of the coolant control valve  50 . While the map  100  presents two portions  102  and  112  relating specifically to the two respective sections  52  and  68  of the coolant control valve  50 , it should be understood that since there is but a single linear operator  94  and a single (tandem) spool or flow control element  92 , the action of one section relative to the other is always the same. Stated somewhat differently, at any given position of the spool or flow control element  92 , the actions or flow control conditions of the two section  52  and  68  will always be the same. 
         [0027]    Turning next to the upper portion  102  of the map  100 , as noted, it relates to the first section  52  of the coolant control valve  50 . At the full left position of travel of the spool or flow control element  92 , all of the coolant flow is directed to the second (bypass) exhaust port  62  connected to the line  64  as indicated by the area  104 . As the spool  92  translates to the right, flow through the (bypass) second exhaust port  62  decreases while flow through the first exhaust port  54  connected through a line  56  to the radiator  60  increases. The latter flow is represented by the area  106 . At approximately the mid or center position of the spool or flow control element  92  all coolant flow from the first inlet port  48  of the first section  52  of the coolant control valve  50  is directed to the radiator  60 . As the spool or flow control element  92  continues to translate to the right, flow through the first inlet port  48  and the radiator  60  begins to decrease while flow through the second (bypass) exhaust port  62  and the line  64  begins to increase, as represented by the area  108 , until the limit of travel to the right is reached and all coolant flow bypasses the radiator  60  and flows through the second exhaust port and the line  64 . 
         [0028]    Referring now to the lower portion  112  of the map  100 , it will be appreciated that for a short distance of travel of the spool or flow control element  92  neither of the inlet ports  72  and  76  are open. After this region, the second inlet port  72  from the integrated exhaust manifold  18  and the turbocharger  32  opens rapidly, represented by the area  114 , and stays open until the center point of the region or area  106  in the upper portion  102  is reached. At this center point, the second inlet port  72  is closed and the third inlet port  76  connected by the supply line  28  to the electric pump  24  is opened as represented by the area  116 . This condition persists for the remainder of translation to the right of the spool or flow control element  92 . When opened, the flows from the second inlet port  72  and the third inlet port  76  are provided to both the engine oil heater  84  and the transmission oil heater  88 . 
         [0029]    With reference now to  FIG. 3 , a graph presents current in amps (A) to the electric motor  26  of the pump  24  of  FIG. 1  on the X axis versus pump flow in liters per minute (lpm) in the Y axis for several speed (r.p.m.) conditions of the electrically powered pump  24  between 1000 r.p.m. and 5900 r.p.m., which are labelled from left to right 1000, 2000, 3000, 4000, 5000, and 5900. Note that at the slower pump speeds, particularly 1000 r.p.m. to 3000 r.p.m., the locus of points is nearly vertical meaning that the relationship between pump current and flow cannot be utilized to accurately infer pump flow from current draw and voltage. Contrariwise, at the higher speeds, such as 5000 and 5900 r.p.m., the slope of the locus of points provides a readily utilized and accurate relationship between current flow and pump flow. The ability to accurately infer pump flow (output) from current flow is an important aspect of the present invention, and as  FIG. 3  illustrates, is most reliable and accurate when the electric motor  26  and the pump  24  are rotating at speeds above 4000 r.p.m. and preferably 5000 r.p.m. or higher. 
         [0030]    Turning now to  FIGS. 1 and 4 , a flow chart of a program, sub-routine or flowchart of the method of operating an electrically driven pump and control valve such as the pump  24  in an internal combustion engine cooling system or circuit  10  is illustrated and designated by the reference number  150 . Preferably, the program or sub-routine embodying the method  150  may be contained within the control module  96  or a similar electronic device. The program or method  150  begins with a start or initializing step  152  of a continuous loop program and moves to a process step  154  which reads the current or instantaneous coolant temperature from the engine outlet temperature sensor  44 . Next, a decision point  156  is encountered which determines whether the current coolant temperature is at or above a predetermined or design threshold temperature. This temperature will typically be engine and application specific. If the current temperature is below the predetermined threshold temperature, the decision point  156  is exited at NO and the method  150  terminates at a stop or exit step  160  and repeats, as noted, in a continuous loop. If the current temperature is at or above the predetermined threshold temperature sensed in the process step  154 , the decision point  156  is exited at YES and the method moves to a process step  162  which infers from the current draw or senses or reads the present speed (r.p.m.) of the electric motor  26  of the coolant pump  24 . 
         [0031]    A decision point  164  is then encountered which determines whether the speed of the electric motor  26  is at or above a predetermined or design threshold value. If the speed of the electric motor  26  is below the predetermined or design threshold, the decision point  164  is exited at NO and the method  150  terminates at the stop or exit step  160  and repeats. If the speed of the electric motor  26  is at or above the predetermined or design threshold, the decision point  164  is exited at YES and the method  150  moves to a process step  166 . It should be appreciated that optimum control is achieved by the present method  150 , utilizing current sensing to infer motor speed, when the speed of the electric motor  26  and the pump  24  is at least 4000 r.p.m. and preferably 5000 r.p.m. or higher, as noted above, which is the optimal pump accuracy range. 
         [0032]    The process step  166  then determines the pump output or coolant flow which is a function of the speed (r.p.m.) of the pump  24 , the electric current drawn or consumed by the electric motor  26  driving the pump  24 , the voltage supplied to the electric motor  26 . From this data, and utilizing an application specific look up table or similar computational or memory device or application, the present coolant flow is determined. The position of the coolant control valve  50  is also monitored by the control module  96  which may be achieved without feedback by reading the signal provided to the linear actuator or operator  94  or may be provided by feedback from a linear sensor (not illustrated) associated with the actuator or operator  94 . 
         [0033]    Next, in a decision point  168 , the desired coolant flow is compared to the present coolant flow. The desired coolant flow is found in, for example, a look up table or read only memory which is engine specific and based upon prior dynamometer tests. The primary factors utilized to determine the desired coolant flow are engine speed, engine temperature and engine mode as well as other, optional, secondary factors. If the desired coolant flow is less than the present coolant flow such that more heat is being transported out of the engine  12  and its temperature is lower than is optimal, the decision point  168  is exited at NO and the method  150  moves to a process step  172 . If the desired coolant flow is greater than the present coolant flow such that less heat is being transported out of the engine  12  and its temperature is higher than is optimal, the decision point  168  is exited at YES and the method  150  moves to a process step  174 . 
         [0034]    Since the process step  172  is executed when, in the decision point  168 , it is determined that the desired coolant flow is less than the present coolant flow and the process step  174  is executed when, in the decision point  168 , it is determined that the desired coolant flow is greater than the present coolant flow, it should be appreciated that the two process steps  172  and  174  provide closed loop feedback in opposite directions: the former ( 172 ) reducing the coolant flow to the desired level or rate and the latter ( 174 ) increasing the coolant flow to the desired level or rate. 
         [0035]    Turning first to the process step  172 , a flow correction factor F C  is computed which is the difference between the desired and currently measured coolant flow. A flow learn value F L  which represents all previous corrections as a function of coolant valve position is also computed. Then, a flow multiplier F M  which is a correction factor for coolant backpressure based on present coolant valve position is computed by subtracting the flow correction factor F C  from the flow learn value F L . The corrected or new pump flow is then computed as the open loop (unrestricted) pump flow times the just computed flow multiplier F M . The computed corrected pump flow signal is then provided to the coolant control valve  50  by the control module  96  to adjust its position and to the electric motor  26  of the coolant pump  24  to provide an appropriate reduction in the coolant flow. The method ends at the stop or exit step  160  and then repeats. 
         [0036]    Similar though inverse activity occurs in the process step  174  wherein a flow correction factor F C  is computed which is the difference between the desired and currently measured coolant flow. The flow learn value F L  which represents all previous corrections as a function of coolant valve position is also computed. Then, a flow multiplier F M  which is a correction factor for coolant backpressure based on present coolant valve position is computed by adding the flow correction factor F C  to the flow learn value F L . The corrected or new pump flow is then the open loop (unrestricted) pump flow times the just computed flow multiplier F M . The computed corrected or new pump flow is then provided to the coolant control valve  50  by the control module  96  to adjust its position and to the electric motor  26  of the coolant pump  24  to provide an appropriate increase in the coolant flow. The method ends at the stop or exit step  160  and then repeats. 
         [0037]    It will thus be appreciated that an internal combustion engine cooling system of circuit having an electrically driven pump and coolant control valve which is operated according to the just described method is capable of not only matching coolant flow to varying operating conditions of the engine such as speed and ambient temperature but is also capable of compensating for short and long term variations in system backpressure that would otherwise interfere with attaining and maintaining optimal system operating temperatures. 
         [0038]    The description of the invention is merely exemplary in nature and 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.