Patent Publication Number: US-10330096-B1

Title: System and method for cold temperature control of an electric oil pump

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Application Ser. No. 61/773,361, filed on Mar. 6, 2013, the disclosure of which is expressly incorporated herein by reference. 
    
    
     BACKGROUND AND SUMMARY OF THE DISCLOSURE 
     The present disclosure relates to a system and method for lubricating an engine of a vehicle. More particularly, the present disclosure relates to a system and method for controlling operation of an electronic oil pump to provide improved lubrication of the engine, particularly during cold temperature conditions. 
     The lubrication system and method in the present disclosure is particularly suited for use with cold weather vehicles such as snowmobiles, but may also be used in other types of vehicles. In conventional lubrication systems, a lubricant such as oil is stored in an oil tank. The oil tank may be integral with or separate from the engine. An oil pump has an input coupled to an output of the oil tank. 
     Conventional mechanical oil pumps are driven by the engine. In contrast, electric oil pumps are controlled by a signal from an electronic control unit (ECU). In two stroke engines, the oil pump provides oil which is mixed with fuel and burned in the engine. Therefore, it is important for the oil pump to deliver a proper volume of oil to a two stroke engine to maintain the fuel/oil ratio at a desired level. 
     Vehicles such as snowmobiles are often operated at very cold temperatures. At such low temperatures, the viscosity of the oil in the oil tank and oil pump increases to a high viscosity level. Such high viscosity oil is difficult to pump, especially during initial start up of a cold engine. Both mechanical oil pumps and electric oil pumps are subject to low volumetric flow rates at cold oil temperatures with high oil viscosity. However, unlike a mechanical oil pump which is physically mounted to an engine, an electric oil pump is often remotely mounted on the vehicle. Such remote mounted electric oil pumps are not subject to much pump heating as the engine temperature increases. As such, the electric oil pump control strategy of the present disclosure controls or manipulates an oil pump command signal from the ECU to increase volumetric efficiency of the oil pump such that oil delivery from the oil pump meets the fuel/oil ratio requirements of the engine. 
     After a cold soak to low ambient temperatures, an electric oil pump volumetric output is lower for the first few oil pump actuations or “shots”. Therefore, the system and method of oil pump output conditioning of the present disclosure eliminates the first few ineffective oil pump shots from an oil volume output calculation so that oil pump efficiency is more stable. This method, used in conjunction with control signal manipulation discussed below, increases oil pump volumetric efficiency without causing an over-oiling condition. 
     The system and method of the present disclosure manipulates an oil pump command signal drive time such that the drive time is increased with decreasing temperature to increase pump volumetric efficiency of the oil pump. The drive time correction uses both a representative temperature measurement as well as the pump drive frequency which are represented by inlet air temperature and engine speed, respectively. For example, the oil pump characteristic volume is manipulated to account for a reduction in volumetric efficiency of the oil pump at low temperatures even with the increased signal drive time. This allows greater versatility in both low and high frequency pump operation with oils of varying density and kinematic viscosity. 
     In an illustrated embodiment of the present disclosure, a method is provided for controlling an electric oil pump with a pump control signal generated by an electronic control unit (ECU) of a vehicle. The pump control signal has a variable drive time portion during which the electric oil pump is actuated to supply oil to an engine of the vehicle and a variable cycle time defining a frequency of the pump control signal. The illustrated method includes determining a base pump volume of the electric oil pump; determining a temperature associated with the engine; and correcting the base pump volume using the determined temperature to provide a corrected pump volume. The method also includes determining a speed of the engine; determining a frequency of the pump control signal based on the determined engine speed and the corrected pump volume; determining a drive time of the pump control signal based on the determined engine speed and the determined temperature; and controlling the electric oil pump using a pump control signal having the determined drive time and the determined frequency. 
     In another illustrated embodiment of the present disclosure, a method is provided of controlling an electric oil pump with a pump control signal generated by an electronic control unit (ECU) of a vehicle. The pump control signal has a variable drive time portion during which the electric oil pump is actuated to supply oil to an engine of the vehicle and a variable cycle time defining a frequency of the pump control signal. The illustrated method includes determining a speed of the engine; determining a volume of oil to deliver from the electric oil pump to the engine based on the determined engine speed; and determining a temperature associated with the engine. The method also includes determining a number of initial ineffective oil pump actuations after start up of the engine due to a high oil viscosity based on the determined temperature; ignoring the determined number of initial ineffective oil pump actuations when determining the volume of oil delivered from the electric oil pump to the engine; determining a frequency of the pump control signal and a drive time of the pump control signal based on the determined temperature and determined engine speed to deliver the determined volume of oil from the electric oil pump to the engine; and controlling the electric oil pump using a pump control signal having the determined drive time and the determined frequency. 
     Additional features of the present disclosure will become apparent to those skilled in the art upon consideration of the following detailed description of illustrative embodiments exemplifying the best mode of carrying out the invention as presently perceived. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and additional features of the present system and method will become more readily appreciated and become better understood by reference to the following detailed description when taken in conjunction with the accompanying drawings. 
         FIG. 1  is a block diagram illustrating a lubrication system for an engine of a vehicle in accordance with the present disclosure; 
         FIG. 2  is a graph showing an oil mass output from electric oil pump measured during cold temperature at engine idle; 
         FIG. 3  is a graph showing a base drive time voltage supplied to an electric oil pump by an electronic control unit (ECU) of the present disclosure; 
         FIG. 4  is a graph showing an increased drive time voltage supplied to the electric oil pump by the ECU under cold temperature operating conditions; 
         FIG. 5  is a graph showing volumetric efficiency of the electric oil pump during cold temperature performance at three different oil pump drive times; and 
         FIG. 6  is a flow chart illustrating control of the electric oil pump by the ECU. 
     
    
    
     Although the drawings represent embodiments of various features and components according to the present disclosure, the drawings are not necessarily to scale and certain features may be exaggerated in order to better illustrate and explain the present disclosure. 
     DETAILED DESCRIPTION OF THE DRAWINGS 
     For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the drawings, which are described below. The embodiments disclosed below are not intended to be exhaustive or limit the invention to the precise form disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may utilize their teachings. It is understood that no limitation of the scope of the invention is thereby intended. The present invention includes any alterations and further modifications in the illustrated devices and described methods and further applications of the principles of the invention which would normally occur to one skilled in the art to which the invention relates. 
     Referring more to the drawings,  FIG. 1  illustrates a lubrication system  10  of the present disclosure for providing lubrication to an engine  12  of a vehicle. Illustratively, the engine  12  is mounted to a vehicle chassis or frame  14 . In the illustrated embodiment, an oil tank  16  is coupled to the frame  14  spaced apart from the engine  12 . An electric oil pump  18  is also coupled to a frame spaced apart from the oil tank  16 . Oil pump  18  is illustratively controlled by an electronic control unit (ECU)  20 . ECU  20  also provides output controls for engine  12  in a conventional manner. 
     ECU  20  is coupled to outputs from a plurality of different sensors including, but not limited to, an idle state sensor  22 , an air temperature sensor  24 , an engine speed sensor  26 , a coolant temperature sensor  28  and a throttle position sensor  30 . ECU  20  is also coupled to outputs from a chassis voltage sensor  32  and an air pressure sensor  34 . The ECU  20  also receives inputs to determine whether the engine is in a break-in mode  36  and to determine a characteristic pump volume  38  of the oil pump  18 . 
     Electric oil pumps  18  used in vehicles such as snowmobiles typically allow for increased packaging capability compared to a crankshaft driven mechanical oil pumps. However, because oil pump  18  is mounted remotely from oil tank  16  and engine  12 , the oil pump  18  is not subject to much heating as the temperature of the engine  12  increases. The system and method of the present disclosure provides cold temperature correction for the electric oil pump  18  control from ECU  20  to promote high viscosity oil flow within the operating conditions of the engine to reduce the likelihood of cold temperature piston scuffing. In other words, the control strategy of the present disclosure controls the oil pump command signal from ECU  20  to increase volumetric efficiency of the oil pump  18  with the high oil viscosity caused by cold temperatures. 
     Oil pump  18  pumps oil to the engine  12  in a conventional manner. Oil pump receives oil from an outlet of oil tank  16 . In two stroke engines, oil pump  18  pumps oil to engine  12  which is mixed with fuel and burned in the engine  12 . Therefore, oil is not recirculated back to oil tank  16  in two stroke engines. 
     As discussed above, during cold ambient temperatures, the initial actuations of the electric oil pump produce a reduced amount of oil mass flow upon initial start up of the engine  12 .  FIG. 2  illustrates an example of the oil mass flow from oil pump  18  at cold temperatures. During the first initial actuations or “shots” of the oil pump  18 , little or no oil flow occurs from the oil pump  18  as shown at location  40  in  FIG. 2 . The duration of the “no flow” period  40  varies depending upon the type of oil used, the ambient temperature, and the operating specifications of the particular oil pump  18 . 
       FIG. 3  illustrates an exemplary control signal supplied to the oil pump  18  by ECU  20 . The signal from ECU  20  includes drive time or pump “ON” time portions  50  in which a voltage is supplied to the oil pump  18  to cause oil pump  18  to pump oil from oil tank  16  to the engine  12 .  FIG. 3  shows an example of a base drive time  50  or pump “ON” time for the oil pump  18 . A cycle time for the oil pump  18  is equal to the time between successive drive pulses  50 . Cycle time is illustrated by dimension  52  in  FIG. 3 . Cycle time  52  is adjustable to change a frequency of operation of the oil pump  18 , thereby changing the volume of oil delivered over time. 
     In the system and method of the present disclosure, the drive time  50  and frequency or cycle time  52  are adjustable by the ECU  20  depending upon operating conditions of the engine as described below to control the oil pump  18 . Specifically, the system and method of the present disclosure adjusts the drive time signal to oil pump  18  and provides cold temperature volume compensation. For example,  FIG. 4  illustrates a modified drive time illustrated by dimension  54  which has been increased by the ECU  20 . The cycle time  52  remains the same in the illustrated embodiment of  FIG. 4 . 
     As shown in  FIG. 5 , volumetric efficiency of oil pump  18  increases, especially during initial actuation of the oil pump  18  at cold temperatures with high oil viscosity as the drive time  54  of the control signal increases.  FIG. 5  is a graph showing pump volumetric efficiency percentage for three different drive times  60 ,  62  and  64  supplied to the oil pump  18  by ECU  20 . In the illustrated embodiment, drive time  62  is greater than drive time  60 . Drive time  64  is greater than drive time  62 . Therefore, the longer drive time  54  of the control signal, the more efficient the oil pump  18  operates, especially during initial shots of the oil pump  18  at cold temperatures. 
     One embodiment of operation of the lubrication system  10  and control method of the present disclosure is illustrated in  FIG. 6 . The ECU  20  uses a known base pump volume as illustrated at block  70  and a base drive time  50  for the oil pump  18  illustrated at block  71 . The base pump volume  70  is a volume of oil typically pumped by oil pump  18  during each stroke or shot of the oil pump  18  at a normal engine operating temperature which is in the range of about 100-140° F. ECU  20  receives a characteristic pump volume input  38  which is a variable that defines the nominal or base volume of the pump. The base oil pump volume is illustratively determined by an actual measurement of oil pump volume during the manufacture of the oil pump. The oil pumps are sorted by the supplier according to volumetric flow rate. This flow rate represents the pump volume in volume per actuation and is identified as block  70  in  FIG. 6 . 
     The base drive time  50  is a length of time for a full stroke of a piston of the oil pump  18 . The base pump volume at block  70  and base drive time at block  71  vary depending upon the particular characteristics of the oil pump  18 . 
     The system and method of the present disclosure further include a conditioning drive time or pump “ON” time input parameter illustrated at block  72  and a conditioning frequency input parameter illustrated at block  74 . The conditioning drive time at block  72  is illustratively longer than the base drive time at block  71 . For example, drive time  50  of  FIG. 3  illustratively represents the base drive time  71  while drive time  54  of  FIG. 4  illustratively represents the conditioning drive time  72 . Drive time during output conditioning at block  72  is taken from block  100  in  FIG. 6  and incorporates corrections by air temperature, engine speed and chassis voltage as discussed herein. The conditioning frequency at block  74  is illustratively a fraction of a maximum operating frequency at cold temperatures established and recommended by pump suppliers, although other frequencies may be used. In an illustrative example, the conditioning frequency at block  74  may be set at about 1 Hz. 
     Operation of the system and method starts at block  76 . ECU  20  senses coolant temperature from coolant temperature sensor  28  as illustrated at block  78 . ECU  20  uses the coolant temperature to determine a corrected pump volume for oil pump  18  as illustrated at block  80 . As discussed above, viscosity of the oil increases at cold temperatures thereby decreasing the efficiency of the oil pump  18 . In an illustrated embodiment, ECU  20  uses a look up table to adjust the base pump volume  70  based upon the coolant temperature sensed at block  78 . For example, as the coolant temperature decreases, the viscosity of the oil increases, thereby reducing the volume of oil pumped during each shot. Therefore, suitable correction is made at block  80  to account for the reduced oil volume from each shot of the oil pump  18 . 
     ECU  20  detects whether the engine state is an idle condition using the idle state sensor  22  as illustrated at block  82 . If the engine is idling at block  82 , a counter is initiated at block  84  based on a predetermined number of conditioning shots (N) necessary to clear the ineffective first oil pump shots. If the counter value is less than the predetermined number of conditioning shots (N) at block  84 , ECU  20  operates the oil pump  18  using the conditioning drive time  72  and conditioning frequency  74 . The ECU  20  continues in a loop at block  84  until the number of oil pump actuations exceeds the predetermined number of conditioning shots (N). Therefore, the ECU  20  eliminates the first ineffective shots of oil pump  18  after start up. These first few shots from the oil pump  18  at cold temperature start up produce little or no flow volume as illustrated at location  40  in  FIG. 2 . 
     The variable (N) is illustratively determined using a calibratable one-dimensional table with the ordinates of engine temperature in which the values outline the number of shots which are actuated upon first entry into idle mode. The system operates on a decrementing counter at block  84  which is reset only on first start but is not reset after a PERC actuation. This characteristic “Dead Time/Count” is accommodated in the ECU control strategy at block  84  such that the ECU  20  commands a calibratable number of actuations (N) which are accepted to be of such a low volumetric efficiency that they are not factored into the total oil delivery requirements and, as such, are completed upon first start up. In one illustrated embodiments, a typical number (N) of ineffective oil pump shots is about 25. This strategy commands the shots on first entry into idle state such that once these shots are completed, the pump volumetric efficiency is increased via input control signal manipulation. These first actuations are not factored into total oil delivery requirements of the engine as it is assumed that the pump will operate at negligible volumetric efficiency. 
     If the counter value at block  84  is greater than the predetermined number of conditioning shots (N), ECU  20  senses a speed of the engine  12  from engine speed sensor  26  as illustrated at block  86 . Next, ECU  20  senses a throttle position from throttle position sensor  30  as illustrated at block  88 . ECU  20  then calculates a base frequency for the oil pump  18  as illustrated at block  90  using the engine speed and throttle position as well as the corrected pump volume at block  80 . ECU  20  uses the engine speed and throttle position to determine the necessary amount of oil to be delivered to engine  12  to provide the proper fuel/oil ratio in two stroke engines, for example. Once this desired volume is known, ECU  20  used the corrected pump volume  80  which provides an actual amount of oil delivered by the oil pump  18  to calculate the base frequency at block  90 . 
     Next, ECU  20  senses air temperature from air temperature sensor  24  at block  92 . The air temperature sensed at block  92  is used to correct both the drive time or pump “ON” time of oil pump  18  at block  94  and to correct the frequency (cycle time) of the oil pump control signal at block  102 . In other words, referring to  FIG. 3 , the sensed air temperature is used to correct the length of the drive time portion  50  of the control signal for oil pump  18 . The engine speed sensed at block  86  is also used to correct the drive time  50  of the control signal from ECU  20 . 
     In addition, the frequency or cycle time  52  of the oil pump signal is also corrected using the sensed air temperature as illustrated at block  102 . Again, when air temperature is low and oil viscosity is high, a higher frequency control signal is needed to supply the desired volume of oil to the engine. 
     Once the drive time is corrected using the sensed air temperature and engine speed at block  94 , the ECU determines a chassis voltage from chassis voltage sensor  32  as illustrated at block  96 . Typically, a chassis voltage remains at a constant voltage unless a problem exists, such as with a voltage regulation system. If necessary, ECU  20  then corrects the drive time of the oil pump  18  control signal based on the sensed chassis voltage as illustrated at block  98  to provide the final drive time or pump “ON” time for driving the oil pump  18  as illustrated at block  100 . A one dimensional table is illustratively used to adjust the drive time at block  98  based on changes in the chassis voltage. As the chassis voltage decreases, the drive time increases to keep the force and the power consumed constant. 
     ECU  20  determines an air pressure from air pressure sensor  34  as illustrated at block  104 . The frequency of the oil pump control signal is adjusted based on the sensed air pressure as illustrated at block  106 . For example, at high altitudes and low pressure, the frequency of the drive signal is decreased since less oil is required at high altitudes with lower fuel flow rates. If the air pressure is high, such as at low altitudes, then the frequency is increased at block  106 . 
     Next, ECU  20  determines whether the engine  12  is in a break-in mode using break-in information  36 . If the engine  12  is in break-in mode, ECU  20  again corrects the frequency of the oil pump control signal as illustrated at block  110 . For example, the frequency is adjusted to increase the amount of oil delivered by oil pump  18  by about 10-20 percent when the engine  12  is in break-in mode. In the illustrated embodiment, the break-in mode information  36  is determined by the total amount of time that the engine has been operated regardless of engine speed. If the engine has been operated less than a predetermined amount of time, then the engine is considered to be in break-in mode. It is understood that other factors may be used to determine when the engine is in a break-in mode. 
     If the engine is in break-in mode at block  108 , the corrected frequency at block  110  is used for the final frequency of the oil pump control signal as illustrated at block  112 . If the engine is not in break-in mode at block  108 , the corrected frequency from block  106  is used as the final frequency at block  112 . 
     The final frequency at block  112  and final drive time at block  110  are used by ECU  20  to generate the control signal for the oil pump  18  such as by setting the drive time  54  and cycle time  52  in  FIG. 4  for example. The frequency and drive times are then reset and ECU  20  returns to block  76  to start the process again. Therefore, the system and method of the present disclosure continuously calculates the drive time, corrected pump volume and frequency of the control signal for the electric oil pump  18 . 
     In one embodiment, the control system and method of  FIG. 6  is used from start up until the engine temperature reaches a predetermined temperature such as about 100° F. to 140° F. Once the engine approaches its normal operating range, the volumetric correction is reduced until the pump is operating normally. The base pump volume  70  and base pump drive time  71  are then used by ECU  20  to drive the electric oil pump  18 . 
     The system and method of the present diclosure controls operation of the electric oil pump  18  without the need to monitor a stroke position of a piston of the oil pump  18  to provide feedback to the ECU  20 . Instead, the system and method of the present disclosure uses information on the flow characteristics of different oils with a characteristic pump volume of the electric oil pump  18  adjusted for varying temperatures and frequencies. The system and method of the present disclosure accommodates the reduction in oil pump volumetric efficiency as a function of increased oil viscosity and manipulates commanded signal to provide increased pump output at critical cold temperatures and low drive frequencies. The system and method of the present disclosure conditions an electric oil pump output rather than manipulating a pump command signal in an attempt to warm the pump to increase efficiency. 
     Drive time manipulation alone does not guarantee pump volumetric efficiency. Instead of compromising the fuel oil ratios to provide adequate oil deliver at cold temperatures which may over oil at warm temperatures, the present system and method uses volume manipulation by ambient air temperature to accommodate the reduction in pump volumetric efficiency without requiring manipulation of target fuel/oil ratio. The combination of drive time manipulation and volume compensation allows both increased performance and compensation for the pump volumetric efficiency as a function of temperature while maintaining consistent fuel/oil ratio targets. 
     While embodiments of the present disclosure have been described as having exemplary designs, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.