Patent Publication Number: US-9885264-B2

Title: Electronic oil pump

Description:
CROSS-REFERENCE 
     The present application is a continuation of U.S. patent application Ser. No. 13/852,564, filed Mar. 28, 2013, which is a divisional of U.S. Pat. No. 8,428,846, issued Apr. 23, 2013, which is a national phase entry of International Patent Application No. PCT/US2009/059007, filed Sep. 30, 2009, the entirety of all of which is incorporated herein by reference. 
    
    
     FIELD 
     The present invention relates to an electronic oil pump and a method of controlling an engine to which lubricant is supplied by the oil pump. 
     BACKGROUND 
     Snowmobiles conventionally have a lubrication system that uses an oil pump that is mechanically driven by an engine of the snowmobile. This type of oil pump is generally referred to as a mechanical oil pump. 
     When the engine operates on a four-stroke principle, the lubricant is stored in an oil tank that is usually connected or integrated to the engine, such as an oil pan. The mechanical oil pump pumps the lubricant from the oil tank to make it circulate through the engine. After circulating through the engine, the lubricant is returned to the oil tank. 
     When the engine operates on a two-stroke principle, the lubricant is stored in an oil tank that is usually spaced apart from the engine. The mechanical oil pump pumps the lubricant from the oil tank to the crankcase of the engine. From the crankcase, the lubricant flows to the cylinders where it is combusted with a mixture of fuel and air. Since the lubricant is combusted by the engine, the oil tank occasionally needs to be refilled with lubricant for the engine to operate properly. 
     By having the mechanical oil pump driven by the engine, the amount of lubricant being pumped is directly proportional to the speed of the engine. Therefore, the faster the engine turns, the more lubricant is being pumped by the mechanical oil pump, and the relationship between engine speed and the amount of lubricant being pumped is a linear one. However, the actual lubricant requirements of an engine, especially in the case of an engine operating on a two-stroke principle, are not linearly proportional to the engine speed. 
     Some mechanical oil pumps driven by the engine are also linked to the throttle lever that is operated by the driver of the vehicle, such that the position of the throttle lever adjusts the output of the mechanical oil pump. Although this provides for an improved supply of lubricant to the engine, it does not account for other factors which affect the actual lubricant requirements of the engine such as ambient air temperature and altitude. 
     For a two-stroke engine, the actual lubricant requirement depends, at least in part, on the power output of the engine, not only engine speed. The higher the power output, the more lubricant is required. There are instances during the operation of the two-stroke engine where the engine speed is high, but where the power output of the engine is low. In such instances, the mechanical oil pump driven by the engine provides a lot of lubricant even though the actual requirements are low. One such instance is when the track of the snowmobile is slipping on a patch of ice. In this instance the engine speed is high due to the slippage, but the actual power output is low. There are other instances where the actual lubricant requirements are lower than what would be provided by a mechanical oil pump driven by the engine. For example, at start-up, all of the lubricant that was present in the engine when it was stopped has accumulated at the bottom of the crankcase. The accumulated lubricant would be sufficient to lubricate the engine for the first few minutes of operation, however the mechanical oil pump, due to its connection to the engine, adds lubricant regardless. Therefore, in the case of an engine operating on the two-stoke principle, using a mechanical oil pump results in more lubricant being consumed by the engine than is actually required. This also results in a level of exhaust emissions that is higher than a level of exhaust emissions that would result from supplying the engine with its actual lubricant requirements since more lubricant gets combusted than is necessary. 
     The actual lubricant requirements of an engine for a snowmobile are also a function of one or more of the altitude at which the snowmobile is operating, the engine temperature, and the position of the throttle lever, to name a few. Since snowmobiles are often operated in mountainous regions and that temperatures can vary greatly during the winter, the actual lubricant requirements of the engine can be significantly affected by these factors and therefore need to be taken into account. Conventional snowmobile lubrication systems using mechanical oil pumps, due to the linear relationship between the engine speed and the amount of lubricant being pumped, cannot take these into account. 
     In the prior art, mechanisms were provided on some snowmobiles which would modify the amount of lubricant provided by the oil pump per engine rotation. These mechanisms provided two (normal/high, or normal/low) or three (normal/high/low) oil pump settings. Although these settings provided some adjustment in the amount of lubricant being provided to the engine by the oil pump, since the pump is still mechanically connected to the engine, the relationship is still a linear one, and thus does not address all of the inconveniences described above. The settings simply provide consistently more or less lubricant, as the case may be, than at the normal settings. 
     Therefore, there is a need for an oil pump that can provide an engine, such as the engine of a snowmobile, with an amount of lubricant that is at or near the actual lubricant requirements of the engine. 
     There is also a need for an oil pump that can supply lubricant to an engine, such as the engine of a snowmobile, non-linearly with respect to the engine speed and other factors. 
     Finally, since snowmobiles are used during the winter, the low ambient temperature causes the lubricant to be very viscous when the engine is first started and becomes less viscous as the engine warms up (thereby warming the lubricant), thus affecting the efficiency with which the lubricant can be pumped. Therefore, when the lubricant has a high viscosity, the oil pump may be unable to supply the amount of lubricant necessary for the proper operation of the engine under certain conditions. Also, different lubricants, at the same temperature, have different viscosities. Therefore, similar issues may be associated with lubricants having a normally high viscosity. 
     Therefore, there is also a need for an oil pump that can take into account varying lubricant viscosities and a method of use thereof. 
     SUMMARY 
     It is an object of the present invention to ameliorate at least some of the inconveniences present in the prior art. 
     In one aspect, a method of controlling an engine having an electronic oil pump supplying lubricant thereto is provided. The electronic oil pump includes at least one lubricant inlet, at least one lubricant outlet, at least one piston, and an actuator operatively connected to the at least one piston. The piston is movable between a fully retracted position and a full stroke position to pump lubricant from the at least one inlet to the at least one outlet. The actuator includes an electromagnetic coil. The method comprises: applying a current to the electromagnetic coil to move the at least one piston from the fully retracted position toward the full stroke position; sending a signal to an electronic control unit (ECU) when the at least one piston reaches the full stroke position; determining a time taken to reach the full stroke position from the fully retracted position based on the signal; determining a power-on time based on the determined time taken to reach the full stroke position from the fully retracted position; and returning the at least one piston to the fully retracted position by stopping to apply the current to the electromagnetic coil once the power-on time has elapsed. 
     In a further aspect, the method further comprises: estimating a time for returning the at least one piston to the fully retracted position from the full stroke position based on the time taken to reach the full stroke position from the fully retracted position; determining an estimated cycle time of the pump based the time taken to reach the full stroke position from the fully retracted position and the estimated time for returning the at least one piston to the fully retracted position from the full stroke position; and limiting a maximum allowable engine speed based at least in part on the estimated cycle time. 
     In an additional aspect, the method further comprises: calculating a calculated cycle time of the pump based on at least one current operating condition of the engine; and reducing the maximum allowable engine speed when the estimated cycle time is greater than the calculated cycle time. 
     In a further aspect, the method further comprises further reducing the maximum allowable engine speed until one of: the estimated cycle time is less than or equal to the calculated cycle time; and a time since stopping to apply the current to the electromagnetic coil is greater than the time for returning the at least one piston to the fully retracted position from the full stroke position. 
     In an additional aspect, the method further comprises: sensing a speed of the engine; and determining a cycle time of the pump based at least on the sensed engine speed. 
     In a further aspect, the power-on time is based on the cycle time. 
     In an additional aspect, the power-on time is longer than the time taken to reach the full stroke position from the fully retracted position. 
     In a further aspect, the power-on time is the time taken to reach the full stroke position from the fully retracted position. 
     In another aspect, a method of controlling an engine having an electronic oil pump supplying lubricant thereto is provided. The electronic oil pump includes at least one lubricant inlet, at least one lubricant outlet, at least one piston, and an actuator operatively connected to the at least one piston. The piston is movable between a fully retracted position and a full stroke position to pump lubricant from the at least one inlet to the at least one outlet. The actuator includes an electromagnetic coil. The method comprises: applying a current to the electromagnetic coil to move the at least one piston from the fully retracted position toward the full stroke position; sending a signal to an electronic control unit (ECU) when the at least one piston reaches the full stroke position; determining a time taken to reach the full stroke position from the fully retracted position based on the signal; continuing to apply the current to the electromagnetic coil when the time taken to reach the full stroke position from the fully retracted position is above a predetermined time; and stopping to apply the current to the electromagnetic coil when the time taken to reach the full stroke position from the fully retracted position is less than the predetermined time. 
     In an additional aspect, the method further comprises limiting engine performance when the time taken to reach the full stroke position from the fully retracted position is above the predetermined time. 
     In a further aspect, the method further comprises determining an estimated cycle time of the pump based the time taken to reach the full stroke position from the fully retracted position. 
     In an additional aspect, the method further comprises calculating a calculated cycle time of the pump based on at least one current operating condition of the engine. 
     In a further aspect, the method further comprises determining a power-on time based on the estimated and calculated cycle times. 
     In an additional aspect, the power-on time is a difference between the calculated cycle time and the estimated cycle time. 
     In a further aspect, the power-on time is greater than the time taken to reach the full stroke position from the fully retracted position. 
     In an additional aspect, the method further comprises returning the at least one piston to the fully retracted position by stopping to apply the current to the electromagnetic coil once the power-on time has elapsed. 
     In yet another aspect, a method of controlling an engine having an electronic oil pump supplying lubricant thereto is provided. The electronic oil pump includes at least one lubricant inlet, at least one lubricant outlet, at least one piston, and an actuator operatively connected to the at least one piston. The piston is movable between a fully retracted position and a full stroke position to pump lubricant from the at least one inlet to the at least one outlet. The actuator includes an electromagnetic coil. The method comprises: applying a current to the electromagnetic coil to move the at least one piston from the fully retracted position toward the full stroke position; determining if the at least one piston has reached the full stroke position within a predetermined time; continuing to apply the current to the electromagnetic coil after the at least one piston has reached the full stroke position if the at least one piston has reached the full stroke position after the predetermined time; and stopping to apply the current to the electromagnetic coil once the at least one piston has reached the full stroke position if the at least one piston has reached the full stroke position before the predetermined time. 
     In a further aspect, the method further comprises limiting engine performance if the at least one piston has reached the full stroke position after the predetermined time. 
     In an additional aspect, the method of further comprises determining a power-on time based on a time taken for the at least one piston to reach the full stroke position. 
     In a further aspect, the method further comprises, if the at least one piston has reached the full stroke position after the predetermined time, stopping to apply the current to the electromagnetic coil once the power-on time has elapsed. 
     Embodiments of the present invention each have at least one of the above-mentioned object and/or aspects, but do not necessarily have all of them. It should be understood that some aspects of the present invention that have resulted from attempting to attain the above-mentioned object may not satisfy this object and/or may satisfy other objects not specifically recited herein. 
     Additional and/or alternative features, aspects, and advantages of embodiments of the present invention will become apparent from the following description, the accompanying drawings, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present invention, as well as other aspects and further features thereof, reference is made to the following description which is to be used in conjunction with the accompanying drawings, where: 
         FIG. 1  is a right side elevation view of a snowmobile in accordance with the invention; 
         FIG. 2  is a perspective view from a front, right side, of an oil tank and electronic oil pump assembly to be used in the snowmobile of  FIG. 1 ; 
         FIG. 3  is a perspective view from a rear, left side, of the oil tank and electronic oil pump assembly of  FIG. 2 ; 
         FIG. 4  is a perspective view from a front, right side, of internal components of the snowmobile of  FIG. 1 , with some of the components removed for clarity; 
         FIG. 5  is a perspective view from a rear, right side, of internal components of the snowmobile of  FIG. 1 , with some of the components removed for clarity; 
         FIG. 6A  is an exploded view of a first embodiment of the electronic oil pump used in the assembly of  FIG. 2 ; 
         FIG. 6B  is an exploded view of a second embodiment of the electronic oil pump used in the assembly of  FIG. 2 ; 
         FIG. 7  is a perspective view from a rear, left side, of an alternative embodiment of the electronic oil pumps of  FIGS. 6A and 6B ; 
         FIG. 8  is a perspective view from a front, right side, of the electronic oil pump of  FIG. 7 ; 
         FIG. 9  is a schematic illustration of some of the various sensors and components present in the snowmobile of  FIG. 1 ; and 
         FIG. 10  is a logic diagram illustrating a control of the electronic oil pump. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention will be described in combination with a snowmobile. However it is contemplated that at least some aspects of the present invention could be used in other applications. 
       FIG. 1  illustrates a snowmobile  10  including a forward end  12  and a rearward end  14  which are defined consistently with a travel direction of the snowmobile  10 . The snowmobile  10  includes a frame  16  which includes a tunnel  18  and an engine compartment  20 . A front suspension  22  is connected to the frame. The tunnel  18  generally consists of one or more pieces of sheet metal bent to form an inverted U-shape. The tunnel  18  extends rearwardly along the longitudinal centerline  61  of the snowmobile  10  and is connected at the front to the engine compartment  20 . An engine  24 , which is schematically illustrated in  FIG. 1 , is carried by the engine compartment  20  of the frame  16 . A steering assembly (not indicated) is provided, in which two skis  26  are positioned at the forward end  12  of the snowmobile  10  and are attached to the front suspension  22  through a pair of front suspension assemblies  28 . Each front suspension assembly  28  includes a ski leg  30 , a pair of A-arms  32  and a shock absorber  29  for operatively connecting the respective skis  26  to a steering column  34 . Other types of front suspension assemblies  28  are contemplated, such as a swing-arm or a telescopic suspension. A steering device such as a handlebar  36 , positioned forward of a rider, is attached to the upper end of the steering column  34  to allow the rider to rotate the ski legs  30  and thus the skis  26 , in order to steer the snowmobile  10 . 
     An endless drive track  65  is positioned at the rear end  14  of the snowmobile  10 . The endless drive track  65  is disposed generally under the tunnel  18 , and is operatively connected to the engine  24 . The endless drive track  65  is driven to run about a rear suspension assembly  42  for propelling the snowmobile  10 . The rear suspension assembly  42  includes a pair of slide rails  44  in sliding contact with the endless drive track  65 . The rear suspension assembly  42  also includes one or more shock absorbers  46  which may further include a coil spring (not shown) surrounding the individual shock absorbers  46 . Suspension arms  48  and  50  are provided to attach the slide rails  44  to the frame  16 . One or more idler wheels  52  are also provided in the rear suspension assembly  42 . 
     At the front end  12  of the snowmobile  10 , fairings  54  enclose the engine  24 , thereby providing an external shell that not only protects the engine  24 , but can also be decorated to make the snowmobile  10  more aesthetically pleasing. Typically, the fairings  54  include a hood (not indicated) and one or more side panels which can be opened to allow access to the engine  24  when this is required, for example, for inspection or maintenance of the engine  24 . In the particular snowmobile  10  shown in  FIG. 1 , the side panels can be opened along a vertical axis to swing away from the snowmobile  10 . A windshield  56  is connected to the fairings  54  near the front end  12  of the snowmobile  10 . Alternatively the windshield  56  can be connected directly to the handlebar  36 . The windshield  56  acts as a wind screen to lessen the force of the air on the rider while the snowmobile  10  is moving. 
     A straddle-type seat  58  is positioned atop the frame  16 . A rear portion of the seat  58  may include a storage compartment or can be used to accommodate a passenger seat (not indicated). Two footrests  60  are positioned on opposite sides of the snowmobile  10  below the seat  58  to accommodate the driver&#39;s feet. 
     Turning now to  FIGS. 2 and 3 , the lubrication system of the snowmobile  10  includes an oil tank  70  and an electronic oil pump  72 A. The oil tank  70  is disposed in the engine compartment  20  (see  FIG. 4 ) and is shaped so as to fit between the various other components located in the engine compartment  20 . The oil tank  70  is preferably fixed to the frame  18  and is preferably positioned slightly behind the engine  24 . Since the oil tank  70  is not directly connected to the engine  24 , the oil tank  70  is partially isolated from the vibration generated by the engine  24 . The oil tank  70  is preferably made of plastic. As seen in  FIG. 3 , a portion  74  of the oil tank  70  is translucent to permit visible inspection as to the level of lubricant in the oil tank  70 . Level markers  76  provide a visual indication as to the relative level of lubricant in the tank  70 . A cap  78  is provided to open or close an oil filling opening (not shown) on the oil tank  70 . A hose  80  extends from an upper portion of the oil tank  70  to a component of the engine  24 , such as a water pump (not shown), to provide lubricant thereto. When the oil tank  70  is filled up above the level of the upper end of the hose  80 , the hose  80  is filled with lubricant. The lubricant present in the hose  80  is then gradually fed by gravity to the component to which the hose  80  is connected. The volume of lubricant in the hose  80  is preferably sufficient to provide lubricant to the component until the oil tank  70  is once again filled up above the level of the upper end of the hose  80 . 
     As can also be seen in  FIGS. 2 and 3  the electronic oil pump  72 A is disposed externally of the oil tank  70 . An inlet  82  of the electronic oil pump  72 A is connected directly to a bottom of the oil tank  70  on a side of the oil tank  70  opposite the side of the oil filling opening. The inlet  82  is preferably connected to the lowest point of the oil tank  70 . The electronic oil pump  72 A has four outlets  84 ,  86 . The two outlets  84  are connected to hoses  88 . As seen in  FIG. 4 , the hoses  88  are connected to the two exhaust valves  90  of the engine  24  (one exhaust valve  90  per cylinder  92 .) to supply lubricant thereto. One possible construction of the exhaust valves  90  is described in U.S. Pat. No. 6,244,227, issued Jun. 12, 2001, incorporated herein by reference. It should be understood that other constructions of the exhaust valves  90  are contemplated which would not deviate from the present invention. The two outlets  86  are connected to hoses  94 . As seen in  FIG. 4 , the hoses  94  are connected to the crankcase  96  of the engine  24 . Each hose  94  fluidly communicates with a crank chamber (not shown) inside the crankcase  96  (one crank chamber per cylinder  92 ) to supply lubricant to the crankshaft bearings (not shown) and the other components located therein. It should be understood that should the engine  24  have more or less cylinders  92 , that the electronic oil pump  72 A would have a number of outlets  84  and  86  that correspond to the number of cylinders. For example, should the engine  24  have three cylinders  92 , then the electronic oil pump  72 A would have three outlets  84  and three outlets  86 . It is also contemplated that two electronic oil pumps  72 A could be used should the number of outlets become too great for a single electronic oil pump  72 A. It is also contemplated that the electronic oil pump  72 A could provide lubricant only to the cylinders  92  (via the crankcase  96 ) and that the exhaust valves  90  would be lubricated in some other way. In this case, an electronic oil pump  72 C having only two outlets  86  (for an engine  24  having two cylinders  92 ) as shown in  FIGS. 7 and 8  would be used. It is also contemplated that the electronic oil pump  72 A could provide lubricant to other components and parts of the engine  24 . 
     Turning now to  FIGS. 4 and 5 , a cooling system, an exhaust system, and a positioning of the electronic oil pump  72 A relative to these systems will be described. The cooling system has a coolant tank (not shown) that supplies coolant to the remainder of the system via pipe  98 . Coolant can also flow back to the coolant tank via the pipe  98  when the coolant expands in the cooling system as the temperature of the coolant increase. Similarly, gas bubbles in the coolant system can flow to the coolant tank via pipe  98 . Coolant in the system flows in coolant hose  100  to T-connector  102 , and from T-connector  102  to coolant hose  104 . From coolant hose  104 , coolant enters coolant passages (not shown) inside the engine  24  thereby absorbing heat from the engine  24 . The coolant then exits the engine  24  via coolant hose  106 . From coolant hose  106 , the coolant enters a thermostat  108 . When the temperature of the coolant is below a predetermined temperature, the thermostat directs the coolant back to coolant hose  100 , and from there the coolant is re-circulated through the engine  24  as described above. When the temperature of the coolant is above the predetermined temperature, the thermostat  108  prevents the coolant from entering coolant hose  100  and redirects the coolant to coolant hose  110 . It is contemplated that the thermostat  108  could redirect only a portion of the coolant to coolant hose  110  and let a remainder of the coolant flow to coolant hose  100 . From coolant hose  110 , the coolant flows to a first heat exchanger  112  to be cooled. The first heat exchanger  112  forms the upper central part of the tunnel  18 . From the first heat exchanger  112 , the coolant flows to coolant hose  114 . From coolant hose  114 , the coolant flows to a second heat exchanger  116  (the majority of which is hidden by engine  24  in  FIG. 4 ) located in the rear portion of the engine compartment  20  to be further cooled. It is contemplated that the first and second heat exchangers  112 ,  116  cooled be located elsewhere on the snowmobile  10  and that only one of the first and second heat exchangers  112 ,  116  could be used. From the second heat exchanger  116 , coolant flows to coolant hose  118 . From coolant hose  118 , coolant flows to T-connector  102 , to coolant hose  104 , to the engine  24  to coolant hose  106  and back to thermostat  108  as described previously. The thermostat  108  causes the coolant to flow through the first and second heat exchangers  112 ,  116  until the temperature of the coolant is once again below the predetermined temperature. 
     The exhaust system receives exhaust gases from the exhaust ports  120  ( FIG. 4 ) of the engine  24 . The exhaust valves  90  regulate the flow of the exhaust gases through the exhaust ports  120 . An exhaust manifold (not shown) is connected to the exhaust ports  120 . The exhaust gases flow from the exhaust ports, through the exhaust manifold to a muffler  122  ( FIG. 5 ). From the muffler  122  the exhaust gases flow through an exhaust pipe (not shown) to the atmosphere. 
     As can be seen in  FIGS. 4 and 5 , the electronic oil pump  72 A is disposed in proximity to heat generating components of the snowmobile  10 . These heat generating components include coolant hoses  110  and  114 , heat exchanger  116 , muffler  122 , and engine  24 . The coolant hoses  110  and  114 , and heat exchanger  116  generate heat due to the hot coolant flowing through them. The muffler  122  generates heat due to the hot exhaust gases flowing through it. The engine  24  generates heat due to the combustion events taking place inside the cylinders  92 . The electronic oil pump  72 A is located proximate enough to these heat generating components that the heat generated by them, when the snowmobile  10  is in operation, heats up the lubricant contained in the electronic oil pump  72 A. Therefore, by being heated, the lubricant maintains a viscosity level that allows it to be easily pumped by the electronic oil pump  72 A. It is contemplated that locating the electronic oil pump  72 A in proximity to at least one of these heat generating components could be sufficient to maintain the viscosity level of the lubricant in the electronic oil pump  72 A. 
     Turning now to  FIG. 6A , details of the electronic oil pump  72 A will be described. The electronic oil pump  72 A is what is know as a reciprocating solenoid pump. The electronic oil pump  72 A has a body  124  having the inlet  82  and the outlets  84 ,  86  integrally formed, over-molded, or press fit therewith. The body  124  is preferably made of plastic or other electrically insulating material. It is contemplated that the body could be made of an electrically conductive material covered with an electrically insulating material. Alternatively, the body could be made of an electrically conductive material and be provided with a sleeve therein made of electrically insulating material. As can be seen, the outlets  86  are larger than the outlets  84 . This is because more lubricant needs to be supplied to the cylinders  92  by the outlets  86  than needs to be supplied to the exhaust valves  90  by the outlets  84 . Two O-rings  126  are provided around the outlet  82  to prevent lubricant present in the oil tank  70  to seal the connection between the outlet  82  and the oil tank  70 . A filter  128  is disposed in the outlet  82  to prevent debris from entering the electronic oil pump  72 A. A stopper  130  is inserted in the body  124  centrally of the outlets  84 ,  86 . A first electrical lead  131  electrically connects the stopper  130  to the ECU  160 . It should be understood that the first electrical lead  131  may not connect the stopper  130  directly to the ECU  160 . An O-ring  132  disposed around the stopper  130  seals the connection between the stopper  130  and the body  124 . Check valves  134  are disposed in the passage of the outlets  84  to prevent lubricant from entering the body  124  via the outlets  84 . Similarly, check valves  136  are disposed in the passage of the outlets  86  to prevent lubricant from entering the body  124  via the outlets  86 . The check valves  134 ,  136  are sized according to the size of their corresponding outlets  84 ,  86 . A piston carrier  138  has four pistons  140 ,  142  thereon. As can be seen the pistons  142  are larger than the pistons  140 . The pistons  142  are used to pump lubricant through the larger outlets  86 , and the pistons  140  are used to pump lubricant through the smaller outlets  84 . A spring  144  is disposed between the piston carrier  138  and the stopper  130 . A cap  145 , made of plastic or other electrically insulating material, is disposed at the end of the spring  144 , between the spring  144  and the stopper  130 . The piston carrier  138  is connected to a plunger  149  of an armature  150 . The plunger  149  extends through a pole  146 . An O-ring  148  is provided around the pole  146  to prevent lubricant present in the body  124  from leaking into the section of the electronic oil pump  72 A that is opposite the side of the pole  146  where the piston carrier  138  is connected (i.e. to the left of the pole  146  in  FIG. 6A ). The armature  150  is made of magnetizable material such as iron. The armature  150  is slidably disposed inside a sleeve  152 . The sleeve  152  is disposed in the center of a coil bobbin  154  and is press-fitted over the pole  146 . The coil bobbin  154  has a coil  156  wound around it. The ends of the coil  156  are connected to connector  158  which is used to connect the electronic oil pump  72 A to the electronic control unit (ECU)  160  (see  FIG. 4 ). The coil bobbin  154  is disposed inside a solenoid housing  162 . The solenoid housing  162  is made of electrically conductive material. A washer  164  is disposed between the coil bobbin  154  and the end of the solenoid housing  162 . A spring  166  is disposed between the armature  150  and the sleeve  152 . Three threaded fasteners  168  are used to fastened the solenoid housing  162  to the body  124 . When the solenoid housing  162  is fastened to the body  124 , all of the components shown therebetween in  FIG. 6A , except connector  158 , are housed inside the volume created by the solenoid housing  162  and the body  124 . A second electrical lead  169  electrically connects one of the fasteners  168  to the ECU  160 . It should be understood that the second electrical lead  169  may not connect the one of the fasteners  168  directly to the ECU  160 . 
     The electronic oil pump  72 A operates as follows. Lubricant enters the body  124  via inlet  82 . Current is applied to the coil  156  via the ECU  160 , as will be described in greater detail below. The current applied to the coil  156  generates a magnetic field. The armature  150  slides towards the body  124  (to the right in  FIG. 6A ) under the effect of the magnetic field. The piston carrier  138  and the pistons  140 ,  142  move together with the armature  150 . This movement of the armature also causes spring  144  to be compressed between the piston carrier  138  and the cap  145  and stopper  130 . The movement of the pistons  140 ,  142  towards the body  124  compresses the lubricant contained in the body  124  and causes the lubricant to be expelled from the electronic oil pump  72 A through the outlets  84 ,  86 , via the check valves  134 ,  136 . When the portion of the piston carrier  138  which houses the spring  144  makes contact with the stopper  130 , an electrical path is created between the leads  131  and  169 , thus closing the circuit formed by the leads  131  and  169 , the pump  72 A and the ECU  160 . This signals the ECU  160  that the pump  72 A has reached its full stroke position. Thus, the ECU  160  can determine the time it takes to reach the full stroke position by calculating the time elapsed between the time when current is applied to the coil  156  to the time when the electrical path between the leads  131  and  169  is closed. When the piston carrier  138  reaches this position, the lubricant has been expelled from the electronic oil pump  72 A. The ECU  160  then stops applying current to the coil  156  which then no longer creates a magnetic field. Since the armature no longer applies a force to compress the spring  144 , the spring  144  expands, thereby returning the pistons  140 ,  142 , the piston carrier  138 , and the armature  150  to their initial positions (towards the left in  FIG. 6A ) and opening the electrical path between the leads  131  and  169 . The cap  145  provides electrical insulation between the stopper  130  and the spring  144 , thereby preventing electrical connection between the leads  131  and  169  when the pump  72 A is not in its full stroke position. The spring  166  prevents the armature  150  from hitting the end of the sleeve  152 , which would generate noise and potentially damage the armature  150 , and counteracts the force of the spring  144  to place the armature  150  in the correct initial position. By returning to their initial positions, the pistons  140 ,  142  create a suction inside the body  124 . The suction  124 , along with gravity, causes more lubricant to flow inside the body  124  via the inlet  82 . The check valves  134 ,  136  prevent the lubricant that was expelled from the electronic oil pump  72 A from re-entering the body via outlets  84 ,  86 . Once the armature  150  returns to its initial position, the ECU  160  applies current to the coil  156  and the cycle is repeated. 
     It is contemplated that other types of electronic oil pumps could be used. For example, the armature  150  of the reciprocating electronic oil pump  72 A described above could be replaced with a permanent magnet. In this embodiment, applying current in a first direction to the coil  156  causes movement of the permanent magnet, and therefore of the pistons  140 ,  142 , in a first direction, and applying current in a second direction to the coil  156  causes movement of the permanent magnet in a second direction opposite the first one. Therefore, by being able to control the movement of the permanent magnet in both direction, this type of pump provides additional control over the reciprocating motion of the pump when compared to the solenoid pump  72 A described above. 
       FIG. 6B  illustrates an alternative embodiment of the pump  72 A, pump  72 B. The pump  72 B has all of the elements of the pump  72 A with the addition of a cap  151  and a third lead  139 . The third lead  139  electrically connects the piston carrier  138  to the ECU  160 . It should be understood that the third electrical lead  139  may not connect the piston carrier  138  directly to the ECU  160 . The cap  151 , which is made of plastic or other electrically insulating material, is disposed at the end of the plunger  149 , between the plunger  149  and the piston carrier  138 . When the piston carrier  138  makes contact with the pole  146 , an electrical path is created between the leads  139  and  169 , thus closing the circuit formed by the leads  139  and  169 , the pump  72 A and the ECU  160 . This signals the ECU  160  that the pump  72 B has reached its fully retracted position. The cap  151  provides electrical insulation between the piston carrier  138  and the plunger  149 , thereby preventing electrical connection between the leads  139  and  169  when the pump  72 B is not in its fully retracted position. Thus, the ECU  160  can determine the time it takes to reach a full stroke by calculating the time elapsed between the time when the electrical path between the leads  139  and  169  is opened to the time when the electrical path between the leads  131  and  169  is closed. Similarly, the ECU  160  can determine the time it takes to reach the fully retracted position by calculating the time elapsed between the time when the electrical path between the leads  131  and  169  is opened to the time when the electrical path between the leads  139  and  169  is closed. 
     As described above, the ECU  160  is electrically connected to the connector  158  of the electronic oil pump  72 A to supply current to the coil  156  and the ECU  160  also receives a feedback from the oil pump  72 A via leads  131  and  169 . The ECU  160  is connected to a power source  161  ( FIG. 9 ) and, based on inputs from one or more of the various sensors described below with respect to  FIG. 9 , regulates when current from the power source  161  needs to be applied to the electronic oil pump  72 A such that the proper amount of lubricant is supplied to the cylinders  92  of the engine  94 . As seen in  FIG. 9 , an engine speed sensor (RPM sensor)  170  is connected to the engine  24  and is electrically connected to the ECU  160  to provide a signal indicative of engine speed to the ECU  160 . The engine  24  has a toothed wheel (not shown) disposed on and rotating with a shaft of the engine  24 , such as the crankshaft (not shown) or output shaft (not shown). The engine speed sensor  170  is located in proximity to the toothed wheel (see  FIG. 4  for example) and sends a signal to the ECU  160  each time a tooth passes in front it. The ECU  160  then determines the engine rotation speed by calculating the time elapsed between each signal. An air temperature sensor (ATS)  172  is disposed in an air intake system of the engine  24 , preferably in an air box (not shown), and is electrically connected to the ECU  160  to provide a signal indicative of the ambient air temperature to the ECU  160 . A throttle position sensor (TPS)  174  is disposed adjacent a throttle body or carburetor (not shown), as the case may be, of the engine  24  and is electrically connected to the ECU  160  to provide a signal indicative of the position of the throttle plate inside the throttle body or carburetor to the ECU  160 . An air pressure sensor (APS)  176  is disposed in an air intake system of the engine  24 , preferably in an air box (not shown), and is electrically connected to the ECU  160  to provide a signal indicative of the ambient air pressure to the ECU  160 . A coolant temperature sensor (CTS)  178  is disposed in the cooling system of the engine  24 , preferably in one of coolant hoses  100 ,  104 , or  106 , and is electrically connected to the ECU  160  to provide a signal indicative of the temperature of the coolant to the ECU  160 . It is contemplated that the CTS  178  could be integrated to the thermostat  108 . A counter  180  is electrically connected to the ECU  160 . The counter  180  can be in the form of a timer and provide a signal indicative of time to the ECU  160 . The counter  180  could also count the number of times the electronic oil pump  72 A has been actuated. The counter  180  could also be linked to the engine  24  to provide a signal indicative of the number of rotations of a shaft of the engine  24  to the ECU  160 . It is contemplated that the RPM sensor  170  could integrate the function of the counter  180  to provide a signal indicative of the number of rotations of a shaft of the engine  24  to the ECU  160  in addition to the signal indicative of engine speed. It is also contemplated that there could be two (or more) counters  180 , one acting as a timer, and the other counting the number of rotations of the engine  24  or the number of times the electronic oil pump  72 A has been actuated. 
     The electronic oil pump  72 A has an inherent time delay that is determined by an elapsed time from the time an electric current is received by the electronic oil pump  72 A from the ECU  160  to the time that lubricant is actually initially expelled from the electronic oil pump  72 A. Due to manufacturing tolerances, this time delay varies from one electronic oil pump  72 A to the other. Therefore, the electronic oil pump  72 A has a specific time delay  182  associated therewith. The time delay  182  is stored on a computer readable storage medium, such as a bar code or a RFID tag, associated with the electronic oil pump  72 A. The time delay  182  is provided to the ECU  160  and is taken into account when regulating the application of current to the electronic oil pump  72 A such that the actual operation of the electronic oil pump  72 A corresponds to the desired operation of the electronic oil pump  72 A as calculated by the ECU  160 . An example as to how this is achieved for fuel injectors, and which could be adapted for use on electronic oil pumps, is described in U.S. Pat. No. 7,164,984, issued Jan. 16, 2007, the entirety of which is incorporated herein by reference. In oil pump  72 B, this time delay does not need to be provided since the time at which lubricant is actually initially expelled from the electronic oil pump  72 B corresponds to when the electrical path between the leads  139  and  169  is opened. 
     Due to manufacturing tolerances, the amount of lubricant being expelled per stroke by the electronic oil pump  72 A varies from one electronic oil pump  72 A to the other. Therefore, the electronic oil pump  72 A has a specific pump output  183  associated therewith that corresponds to the actual amount of lubricant being expelled per stroke by the electronic oil pump  72 A. The pump output  183  is stored on a computer readable storage medium, such as a bar code or a RFID tag, associated with the electronic oil pump  72 A. The computer readable storage medium could be the same as the one used for the time delay  182  or could be a different one. The pump output  183  is provided to the ECU  160  and is taken into account when regulating the application of current to the electronic oil pump  72 A such that the actual operation of the electronic oil pump  72 A corresponds to the desired operation of the electronic oil pump  72 A as calculated by the ECU  160 . It is contemplated that only one of the time delay  182  and the pump output  183  may be provided for the electronic oil pump  72 A. 
     Turning now to  FIG. 10 , a method of controlling the electronic oil pump  72 A will be described. A method of operating the electronic oil pump  72 B is the same as the method of operating the electronic oil pump  72 A, unless specifically explained otherwise below. 
     The method is initiated at step  200 , once the key (not shown) is inserted in the snowmobile  10  or once the engine  24  is started. In the present method, a boolean variable called “Cold Limit” is used to indicate whether the lubricant being used by the pump  72 A has a viscosity which is higher than expected during normal operation of the snowmobile  10 . A “Cold Limit” which is set to “true” indicates such a higher viscosity. A “Cold Limit” which is “false” indicates that the lubricant has a viscosity within a range which is expected during normal operation of the snowmobile. As previously explained, a low lubricant temperature would result in a high viscosity of the lubricant (herein the name “Cold Limit”). Although the name of the boolean variable “Cold Limit” suggests a relationship with temperature, it should be understood that using a lubricant which has a high viscosity, even at normal operating temperatures of lubricant in a snowmobile  10 , could also result in the boolean variable “Cold Limit” being set to “true” during the present method. At step  202 , the boolean variable “Cold Limit” is set to false since no data is available at this point to determine otherwise. Then at step  204 , the ECU limits the maximum engine speed to a value of A RPM, which corresponds to an engine speed limit during normal operation of the snowmobile  10 . 
     At step  206 , the ECU  160  then applies current to the coil  156  of the oil pump  72 A. Then at step  208 , the ECU  160  determines if a signal which indicates that the circuit including the leads  131  and  169  is closed is received within a predetermined time limit t 1 . As previously described, this signal is indicative that the pump  72 A has reached its full stroke position. If the signal is not received within t 1 , then at step  210  the ECU  160  stops applying current to the coil  156  of the oil pump  72 A to return the oil pump  72 A to its fully retracted position. Since not receiving a signal within t 1  at step  208  indicates that the oil pump  72 A is unable to reach its full stroke position, and therefore unable to efficiently pump lubricant, at step  212  the ECU  160  enters a fault operation mode. The problem could be that one of the components of the pump  72 A is faulty or that the lubricant inside the oil pump  72 A is too viscous for the oil pump  72 A to pump the lubricant. The fault operation mode limits the performance of the engine  24  so as to prevent damaging the engine  24 . It is contemplated that the ECU  160  could also enter a fault mode if a signal which indicates that the circuit including the leads  131  and  169  is closed is received in less than another predetermined time limit, which would indicate that there is no lubricant present in the oil pump  72 A. If at step  208 , a signal is received within the time t 1 , then the ECU  160  continues to step  214 . 
     At step  214 , the ECU  214  determines the estimated cycle time (ECT). The estimated cycle time corresponds to the sum of the time it took the pump  72 A to reach its full stroke position (full stroke time, FST) and of the estimated time it will take the pump  72 A to reach it fully retracted position (estimated return time, ERT). The full stroke time is determined from the time it took to receive the signal from the circuit including the leads  131  and  169  that the circuit is closed as described above. The estimated return time is determined from various experimentally determined maps stored in the ECU  160  or other electronic storage devices accessible by the ECU  160 . The maps provide estimated return times for various full stroke times. Should the full stroke time not correspond to a value in the maps, the ECU  160  can interpolate the estimated return time from two known values in the maps. As previously described, a long full stroke time is indicative of a high lubricant viscosity. A high lubricant viscosity, as should be understood, makes it more difficult for the pump  72 A to suck lubricant back inside the pump  72 A. Therefore, the longer the full stroke time is, the longer the estimated return is. In a method using the oil pump  72 B, the estimated return time only needs to be determined in this manner (i.e. using maps) the first time step  214  is performed. When the step  214  is subsequently performed, the estimated return time used is the time elapsed between the circuit including the leads  131  and  169  becoming opened and the circuit including the leads  139  and  169  becoming closed. As should be understood, the estimated cycle time determined at step  214  determines the maximum frequency at which the pump  72 A can be used. 
     From step  214 , the ECU  160  continues to step  216  and determines if the “Cold Limit” variable has a value of “true”. The first time step  216  is performed, the value of the “Cold Limit” variable is “false” and the method continues to step  222  where the ECU  160  stops applying current to the coil  156  of the oil pump  72 A to return the oil pump  72 A to its fully retracted position. When step  216  is subsequently performed, if the value of the “Cold Limit” variable is “true” as a result of step  230  described below, then the ECU  160  continues to step  218 . As previously described, when the “Cold Limit” variable is “true”, it is as a result of the lubricant having a high viscosity, which can be caused by the lubricant being at a low temperature. As should be understood, the viscosity of the lubricant can therefore be reduced by heating the lubricant. As described in more detail in PCT application no. PCT/US2008/055477, published as WO 2009/002572 A1 on Dec. 31, 2008, the entirety of which is incorporated herein by reference, by continuing to apply current to the coil  156  after the pump  72 A has reached its full stroke position, the coil  156  generates heat which can help reduce the viscosity of the lubricant. At step  218 , the ECU  160  determines a maximum amount of time (power-on time, POT) for which the current can be applied to the coil  156  of the pump  72 A before having to return the oil pump  72 A to its fully retracted position in order to initiate the next pumping cycle. The power-on time corresponds to the difference between the calculated cycle time (CCT) and the estimated cycle time (ECT) determined at step  214 . The calculated cycle time is the cycle time at which the pump  72 A needs to be operated in order to supply the amount of lubricant required by the engine  24  at the current operating conditions. The ECU  160  uses the signals received from at least some of the sensors described above with respect to  FIG. 9 , including the engine speed sensor  170 , to calculate the calculated cycle time. International publication WO 2009/002572 A1 describes some methods in which the cycle time can be calculated by the ECU  160 , but other methods are contemplated. Generally, the faster the engine speed is, the shorter the calculated cycle time will be, however the relationship between the engine speed and the calculated cycle time does not need to be a linear one. From step  218 , the ECU  160  continues to step  220  where it determines if the amount of time elapsed since the current has been applied to the coil  156  of the pump  72 A (time t 2 ) is greater than or equal to the power-on time. If it is not, then the ECU  160  will continue to loop back to step  220  until that is the case. Once the time t 2  is greater than or equal to the power-on time, the ECU  160  continues to step  222  where the ECU  160  stops applying current to the coil  156  of the oil pump  72 A to return the oil pump  72 A to its fully retracted position. 
     From step  222 , the ECU  160  continues to step  224 . At step  224  the ECU  160  determines if the amount of time elapsed since step  222  (time t 3 ) is greater than the estimated return time determined at step  214 . As should be understood, the time t 3  also corresponds to the amount of time elapsed since the circuit including the leads  131  and  169  has been opened. If at step  224 , the time t 3  is greater than the estimated return time, then the ECU  160  continues to step  232 . If at step  224 , the time t 3  is not greater than the estimated return time, then at step  226  the ECU  160  determines if the estimated cycle time determined at step  214  is greater than the calculate cycle time (which is calculated as described above with respect to step  218 ). If the estimated cycle time is not greater than the calculated cycle time, then the pump  72 A can adequately supply lubricant to the engine  24  under the current operating conditions (i.e. the pump  72 A can perform a complete pumping cycle faster than what is required) and the ECU  160  returns to step  224 . If however, the estimate cycle time is greater the calculated cycle time, then the pump  72 A cannot adequately supply lubricant to the engine  24  (i.e. the pump  72 A cannot perform a complete pumping cycle within the required amount of time) and the ECU  160  continues to step  228 . At step  228  the ECU reduces the maximum allowable engine speed by an amount of B RPM (10 RPM for example), and then sets the “Cold Limit” variable to “true” such that when the method subsequently comes to step  216 , steps  218  and  220  will be performed to warm the lubricant as described above. From step  230 , the ECU  160  returns to step  224  and if the time t 3  is not greater than the estimated return time, then step  226  is performed again. If the engine  24  was previously operating at a speed greater than the maximum allowable engine speed calculated at step  228 , then the engine speed has been reduced and therefore the calculated cycle time should have increased. If at step  226  the estimated cycle time is still not greater than the calculated cycle time, then step  228  is repeated. Step  228  will continue to be performed until either the time t 3  is greater than the estimated return time (step  224 ) or the estimated cycle time is greater than the calculated cycle time (step  226 ), whichever occurs first. 
     In a method using the oil pump  72 B, step  224  could be replaced by a step where the ECU  160  determine if a signal indicative that the circuit including the leads  139  and  169  has been closed has been received. If this circuit is opened, then the ECU  160  continues to step  226  and if it is closed the ECU  160  continues to step  232 . 
     Once it is determined at step  224  that the time t 3  is greater than the estimated return time, then at step  232  the ECU determines if the maximum allowable engine speed is less than the engine speed limit during normal operation of the snowmobile  10  of A RPM. If it is not less than A RPM, then the ECU  160  continues to step  236 , set the value of the variable “Cold Limit” to false, and then returns to step  206  where it will apply current to the coil  156  of the pump  72 A at the beginning of the next pumping cycle. If the maximum allowable engine speed is less than A RPM, the ECU will increase the maximum allowable engine speed by a predetermined amount of C RPM (but without exceeding A RPM), so as to gradually increase the maximum allowable engine speed each time step  234  is performed. From step  234  the ECU  160  returns to step  206  where it will apply current to the coil  156  of the pump  72 A at the beginning of the next pumping cycle. 
     Modifications and improvements to the above-described embodiments of the present invention may become apparent to those skilled in the art. The foregoing description is intended to be exemplary rather than limiting. The scope of the present invention is therefore intended to be limited solely by the scope of the appended claims.