Abstract:
An internal combustion engine has a fuel supply system which has a fuel pump driving mechanism that limits the relative motion between a part of the mechanism contacting a plunger of the pump and the plunger.

Description:
CROSS-REFERENCE 
       [0001]    The present application claims priority to U.S. Provisional Patent Application No. 61/299,694, filed Jan. 29, 2010 the entirety of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to internal combustion engine fuel supply systems and to engines incorporating such systems. 
       BACKGROUND 
       [0003]    Many internal combustion engines use a fuel pump which consists of a piston reciprocating inside the housing of the pump between two positions. A spring biases the piston towards one of the two positions. A plunger is connected to the piston and extends from the pump housing. In order to actuate the pump a cam connected to a rotating shaft of the engine comes into contact with the end of the plunger. As the cam rotates, the plunger reciprocates and as a result, causes the piston to reciprocate. 
         [0004]    In order to prevent wear of the cam and of the plunger due to friction between the two parts, lubricant needs to be supplied between these two parts. In four-stroke engines, this can be easily achieved since the engine is typically lubricated using pressurized lubricant, and as such, lubricant can be injected between the cam and the plunger. However, two-stroke engines do not use pressurized lubricant to lubricate the various components of the engine, which makes supplying lubricant between the cam and the plunger more difficult. 
         [0005]    In addition to causing wear of the cam and the plunger, the friction between these two parts also causes side forces to be transmitted to the piston. The side forces cause the piston to press against the inner wall of the pump which causes friction and therefore wear of these parts of the pump. 
         [0006]    Also, when the pressure at which fuel needs to be supplied increases, the forces that need to be applied to the plunger in order to cause it to reciprocate also increase. As a result, the friction between the cam and the plunger increases which accelerates the wear of the cam and the plunger. 
         [0007]    Therefore, there is a need for an internal combustion engine having a fuel supply system which has fuel pump driving mechanism that limits the wear of the parts of the mechanism and of the pump. 
       SUMMARY 
       [0008]    It is an object of the present invention to ameliorate at least some of the inconveniences present in the prior art. 
         [0009]    It is also an object of the present invention to provide an internal combustion engine having a fuel supply system which has a fuel pump driving mechanism that limits the relative motion between a part of the mechanism contacting a plunger of the pump and the plunger, thus limiting the wear of the pump, the part of the mechanism contacting the plunger and the plunger. 
         [0010]    In one embodiment, a bearing is disposed around an eccentric shaft driving the pump and an outer race of the bearing contacts the end of the plunger of the pump. 
         [0011]    In another embodiment, a lever has an end contacting the end of the plunger of the pump. A cam moves the lever such that the lever drives the pump. The cam and the lever are arranged such that the end of the lever moves generally parallel to an axis of the plunger. 
         [0012]    In one aspect, the invention provides an internal combustion engine having at least one cylinder, at least one piston disposed in the cylinder, the at least one cylinder and the at least one piston defining at least in part at least one combustion chamber, a crankshaft operatively connected to the at least one piston, at least one fuel injector fluidly communicating with the at least one combustion chamber, and a fuel pump fluidly communicating with the at least one fuel injector. The fuel pump includes a pump piston movable between a first and a second position, a plunger connected to the pump piston, and a spring biasing the pump piston toward the first position. An eccentric shaft has a first cylindrical surface having a first central axis and a second cylindrical surface having a second central axis. The second central axis is offset from the first central axis. The eccentric shaft is operatively driven by the crankshaft such that the eccentric shaft rotates about the first central axis. At least one bearing has an inner race disposed on the eccentric shaft around the second cylindrical surface and an outer race abutting an end of the plunger such that as the eccentric shaft rotates, the at least one bearing moves the pump piston between the first and the second position. 
         [0013]    In an additional aspect, the eccentric shaft has a third cylindrical surface having a third central axis. The third central axis is co-axial with the first central axis. The second cylindrical surface is disposed between the first and the third cylindrical surfaces. 
         [0014]    In a further aspect, a shaft is operatively connected to the crankshaft and is disposed generally perpendicular to the crankshaft. The eccentric shaft is operatively driven by the shaft. 
         [0015]    In an additional aspect, the eccentric shaft is coaxial with the shaft. 
         [0016]    In a further aspect, a water pump is driven by the shaft. 
         [0017]    In an additional aspect, the eccentric shaft and the crankshaft rotate at a same speed. 
         [0018]    In a further aspect, the fuel pump is a high pressure fuel pump adapted to pressurize fuel at a pressure exceeding 70 bar. 
         [0019]    In an additional aspect, the fuel pump is adapted to pressurize fuel between a minimum pressure of 20 bar and a maximum pressure exceeding 200 bar. 
         [0020]    In a further aspect, the engine is a direct fuel injection two-stroke engine. 
         [0021]    In an additional aspect, the at least one cylinder is at least two cylinders, the at least one piston is at least two pistons, the at least one combustion chamber is at least two combustion chambers, and the at least one fuel injector is at least two fuel injectors. A fuel rail has one inlet fluidly connected to the fuel pump and at least two outlets fluidly connected to the at least two fuel injectors. 
         [0022]    In a further aspect, the fuel pump includes an intake valve for opening and closing a fuel inlet port of the fuel pump. An amount of fuel pressure generated by the fuel pump is controlled by adjusting a closing time of the intake valve. 
         [0023]    In an additional aspect, a fuel line fluidly communicates the fuel pump with the at least one fuel injector. A control valve fluidly communicates with the fuel line. The control valve fluidly communicates the fuel line with a fuel tank when the pressure of fuel being supplied to the at least one fuel injector is above a desired fuel pressure. 
         [0024]    In a further aspect, a fuel line fluidly communicates the fuel pump with the at least one fuel injector. An other fuel injector is fluidly connected to the fuel line. The other injector pumps fuel away from the fuel line to a fuel tank when the pressure of fuel being supplied to the at least one fuel injector is above a desired fuel pressure. 
         [0025]    In another aspect, the invention provides an internal combustion engine having at least one cylinder, at least one piston disposed in the cylinder, the at least one cylinder and the at least one piston defining at least in part at least one combustion chamber, a crankshaft operatively connected to the at least one piston, at least one fuel injector fluidly communicating with the at least one combustion chamber, and a fuel pump fluidly communicating with the at least one fuel injector. The fuel pump includes a pump piston movable between a first and a second position, a plunger connected to the pump piston, and a spring biasing the pump piston toward the first position. A cam is operatively driven by the crankshaft such that the cam rotates about a first axis. A roller abuts the cam such that the cam moves the roller between a third and a fourth position as the cam rotates. A lever is rotatably connected to the roller about a second axis. The lever has a first end abutting an end of the plunger such that as the cam moves the roller between the third and the fourth position, the first end of the lever moves the pump piston between the first and the second position. 
         [0026]    In an additional aspect, the lever has a second end extending on a side of the second axis opposite the first end of the lever. The second end of the lever pushes against a surface of the engine as the cam moves the roller between the third and the fourth position. 
         [0027]    In a further aspect, a ball is disposed between the second end of the lever and the surface of the engine. 
         [0028]    In an additional aspect, the first end of the lever has a recessed portion. The end of the plunger is received in the recessed portion. 
         [0029]    In a further aspect, a balancer shaft is operatively connected to the crankshaft. The cam is disposed on the balancer shaft. 
         [0030]    In an additional aspect, the fuel pump is a high pressure fuel pump adapted to pressurize fuel at a pressure exceeding 70 bar. 
         [0031]    In a further aspect, the fuel pump is adapted to pressurize fuel between a minimum pressure of 20 bar and a maximum pressure exceeding 200 bar. 
         [0032]    In an additional aspect, the engine is a direct fuel injection two-stroke engine. 
         [0033]    In a further aspect, the at least one cylinder is at least two cylinders, the at least one piston is at least two pistons, the at least one combustion chamber is at least two combustion chambers, and the at least one fuel injector is at least two fuel injectors. A fuel rail has one inlet fluidly connected to the fuel pump and at least two outlets fluidly connected to the at least two fuel injectors. 
         [0034]    In an additional aspect, the fuel pump includes an intake valve for opening and closing a fuel inlet port of the fuel pump. An amount of fuel pressure generated by the fuel pump is controlled by adjusting a closing time of the intake valve. 
         [0035]    In a further aspect, a fuel line fluidly communicates the fuel pump with the at least one fuel injector. A control valve fluidly communicates with the fuel line. The control valve fluidly communicates the fuel line with a fuel tank when the pressure of fuel being supplied to the at least one fuel injector is above a desired fuel pressure. 
         [0036]    In an additional aspect, a fuel line fluidly communicates the fuel pump with the at least one fuel injector. An other fuel injector is fluidly connected to the fuel line. The other injector pumps fuel away from the fuel line to a fuel tank when the pressure of fuel being supplied to the at least one fuel injector is above a desired fuel pressure. 
         [0037]    Embodiments of the present invention each have at least one of the above-mentioned objects 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 objects may not satisfy these objects and/or may satisfy other objects not specifically recited herein. 
         [0038]    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 
         [0039]    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: 
           [0040]      FIG. 1  is a schematic illustration of a fuel system for an engine according to the present invention; 
           [0041]      FIG. 2  is a perspective view taken from a rear, left side of a portion of an engine according to the present invention; 
           [0042]      FIG. 3  is a perspective view taken from a rear, right side of a portion of the engine of  FIG. 2 ; 
           [0043]      FIG. 4  is a perspective view of a fuel pump mounting flange of the engine of  FIG. 2 ; 
           [0044]      FIG. 5  is a cross-sectional view of a fuel pressure control adaptor of the fuel system of  FIG. 1 ; 
           [0045]      FIG. 6  is a bottom view of a fuel rail of the engine of  FIG. 2 ; 
           [0046]      FIG. 7  is a cross-sectional view of a portion of the engine of  FIG. 2  taken perpendicularly to a crankshaft of the engine and through an axis of rotation of a water pump shaft of the engine showing a first embodiment of a pump driving mechanism of the engine of  FIG. 2 , an interior of a fuel pump of the engine being shown schematically; 
           [0047]      FIG. 8  is a perspective view of an eccentric shaft used in the first embodiment of the pump driving mechanism shown in  FIG. 7 ; 
           [0048]      FIG. 9  is a view of a first end of the eccentric shaft of  FIG. 8 ; 
           [0049]      FIG. 10  is a view of a second end of the eccentric shaft of  FIG. 8 ; 
           [0050]      FIG. 11  is a schematic illustration of a second embodiment of a pump driving mechanism of the engine of  FIG. 2 ; 
           [0051]      FIG. 12  is a cross-sectional view of a portion of the second embodiment of the pump driving mechanism of  FIG. 11  taken through line A-A of  FIG. 11 ; and 
           [0052]      FIG. 13  is a schematic illustration of an alternative embodiment of the pump driving mechanism of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0053]    The invention will now be described with respect to a direct injection, two-stroke engine  10  having a high pressure fuel pump  12  capable of supplying fuel at pressures in excess of 70 bar, since the above-mentioned problem are more likely to occur in such an arrangement. However, it is contemplated that the invention could also be used in four-stroke engines, with engines having a fuel pump having a lower maximum fuel supply pressure, and/or with engines having fuel supplied to its combustion chamber(s) by systems other than a direct injection system, such as a semi-direct injection system. 
         [0054]    As seen in  FIGS. 1 to 3 , the engine  10  has a crankcase  14 , a cylinder block  16 , and a cylinder head  18 . A crankshaft  20  is disposed inside the crankcase  14  to rotate therein and extends through a wall of the crankcase  14  to be operatively connected to an element to be driven by the engine  10 , such as a wheel of a motorcycle or an endless track of a snowmobile. The cylinder block  16  defines two cylinders  22  (schematically shown in  FIG. 1 ) therein. Two pistons  24  (schematically shown in  FIG. 1 ) are disposed inside the cylinders  22  to reciprocate therein. The pistons  24  are connected to the crankshaft  20  via connecting rods (not shown) to drive the crankshaft  20 . The cylinder head  18 , the cylinders  22 , and the pistons  24  define two combustion chambers  26  (schematically shown in  FIG. 1 ). Two throttle bodies  28  are connected to one side of the cylinder block  16  to supply air to the combustion chambers  26 . An exhaust manifold  30  is connected to another side of the cylinder block  16  to receive exhaust gases from the combustion chambers  26  resulting from the combustion process occurring therein. Two fuel injectors  32  (schematically shown in  FIG. 1 ) are connected to the cylinder head  18  to supply fuel to the combustion chambers  26 . A fuel rail  34  is connected to the cylinder head  18  to supply fuel to the fuel injectors  32  as described in greater detail below. As best seen in  FIG. 6 , the fuel rail  34  has a single inlet  36  connected to a center of the tube  38  and two outlets  40  connected near the ends of the tube  38 . The outlets  40  are disposed at an angle to the inlet  36 . The inlet  36  fluidly communicates with the fuel pump  12  and the outlets  40  fluidly communicate with the fuel injectors  32 . Flanges  42  are provided around the outlets  40  to permit the attachment of the fuel rail  34  to the cylinder head  18 . The engine  10  also has other components known to those skilled in the art, such as spark plugs, but since these are not believed to be necessary to the understanding of the present invention, they will not be described herein. 
         [0055]    It is contemplated that the engine  10  could have only one or more than two cylinders  22 . As should be understood, the engine  10  would then have a corresponding number of pistons  24 , combustion chambers  26 , throttle bodies  28  and fuel injectors  32 . In cases where the engine  10  has more than two cylinders  22 , the fuel rail  34  would have a corresponding number of outlets  40 , it is however contemplated that the fuel rail  34  could be omitted should the engine  10  have only a single cylinder  22 . It is contemplated that more than one fuel injector  32  could be provided per cylinder  22 , in which case the fuel rail  34  would have a number of outlets  40  corresponding to the number of fuel injectors  32 . It is also contemplated that the engine  10  could have less throttle bodies  28  than cylinders  22 , such that each throttle body  28  would supply air to more than one combustion chamber  26 . 
         [0056]    The fuel system of the engine  10  will now be described with reference to  FIGS. 1 to 3 . Fuel to be supplied to the engine  10  is stored in a fuel tank  44 . A pump  46  disposed inside the fuel tank  44  pumps fuel from the fuel tank  44  to the fuel pump  12 . The pump  46  supplies fuel to the fuel pump  12  at a pressure of about 3 bar, but other pressures are contemplated. The fuel pump  12  then further pressurizes the fuel. The pressure at which the fuel pump  12  pressurizes the fuel is determined by an electronic control unit (ECU, not shown) of the engine  10  based on data such as engine speed and atmospheric pressure. The manner in which the pressure at which fuel is supplied from the fuel pump  12  is controlled will be described below. As previously mentioned, the fuel pump  12  is a high pressure fuel pump capable of supplying fuel at pressures in excess of 70 bar. It is contemplated that the fuel pump  12  could supply fuel at pressures exceeding 150 or even 250 bar. It has been found that by supplying fuel to the engine  10  at higher pressures, the mixing of air and fuel in the combustion chambers  26  prior to ignition is improved, resulting in a more homogeneous combustion. This leads to reduced fuel consumption and exhaust emissions. Supplying fuel to the engine  10  at higher pressures also reduces injection time per cycle, which allows for better control and flexibility of the injection event such as by allowing multiple injections per cycle for example. From the fuel pump  12 , fuel flows in a fuel line  48  to a fuel pressure control adaptor  50 . A check valve  52  (schematically shown in  FIG. 1 ) is provided at an outlet of the fuel pump  12  to prevent fuel from returning inside the fuel pump  12  from the fuel line  48 . 
         [0057]    As seen in  FIG. 5 , the fuel pressure control adaptor  50  has a main passage  54  and a bypass passage  56  connected perpendicularly to the main passage  54 . An inlet  58  of the main passage  54  is connected to the fuel line  48 . An outlet  60  of the main passage  54  is connected to a fuel line  62  ( FIGS. 1 and 3 ). A plug  64  is screwed inside the inlet  58 . As can be seen, the plug  64  has an aperture  66 . The small size of the aperture  66  decouples the fuel line  48  from pressure fluctuations resulting from the injection of fuel by the fuel injectors  32 . However, the size of the aperture is selected to be large enough to prevent or at least minimize head loss across the aperture  66 . A pressure sensor  68  connected to the fuel pressure control adaptor  50  senses the fuel pressure downstream of the plug  64 . An outlet  70  of the bypass passage  56  is connected to one of a control valve  72  and a fuel injector  74  (schematically shown in  FIG. 1 ), which is connected to a fuel line  76 . The fuel pressure control adaptor  50  is preferably not rigidly connected to the engine  10  so as to decouple the fuel pressure control adaptor  50  from engine vibrations. For example, when the engine  10  is disposed in a vehicle, the fuel pressure control adaptor  50  could be connected to a frame of the vehicle. 
         [0058]    In an embodiment using the control valve  72 , when the fuel pressure sensed by the pressure sensor  68  is at or below a desired fuel pressure to be supplied to the fuel injectors  32  determined by the ECU, the valve  72  is closed, preventing fuel from flowing out of the adaptor  50  via the outlet  70 . Fuel flows from the fuel pressure control adaptor  50  to the fuel line  62 , then to the fuel rail  34  and fuel injectors  32 , and finally to the combustion chambers  26 . When the fuel pressure sensed by the pressure sensor  68  is above the desired fuel pressure to be supplied to the fuel injectors  32  determined by the ECU, the valve  72  is opened. Fuel then flows out of the adaptor  50  via the outlet  70  to the fuel line  76  which returns fuel to the fuel tank  44 , thus relieving the excess fuel pressure. 
         [0059]    In an embodiment using the fuel injector  74 , when the fuel pressure sensed by the pressure sensor  68  is at or below the desired fuel pressure to be supplied to the fuel injectors  32  determined by the ECU, the fuel injector  74  is not operated, preventing fuel from flowing out of the adaptor  50  via the outlet  70 . Fuel then flows to the combustion chambers  26  as described above. When the fuel pressure sensed by the pressure sensor  68  is above the desired fuel pressure to be supplied to the fuel injectors  32  determined by the ECU, the fuel injector  74  is operated. The fuel injector  74  pumps fuel out of the adaptor  50  (and fuel lines  48 ,  62 ) via the outlet  70  to the fuel line  76  which returns fuel to the fuel tank  44 , thus relieving the excess fuel pressure. Since the fuel injector  74  actively permits the removal of fuel from the adaptor  50  (i.e. by pumping), this embodiment relieves the excess fuel pressure faster than the embodiment using the valve  72 . It is contemplated that the fuel injector  74  could be replaced by a pump. 
         [0060]    In an alternative embodiment (not shown), the valve  72  or injector  74  is replace by a valve disposed at the outlet of the fuel pump which, depending on the fuel pressure sensed by the pressure sensor  68 , selectively allows fuel to flow from the fuel pump  12  to the adaptor  50  or back to the fuel tank  44 . 
         [0061]    Turning now to  FIGS. 2 to 4 , and more specifically  FIG. 7 , the fuel pump  12  will be described. As can be seen in  FIG. 7 , the fuel pump  12  has a housing  80  defining therein a pump chamber  82 . A fuel inlet port  84  of the fuel pump  12  is disposed on top of the housing  80  and a fuel outlet port  86  (best seen in  FIG. 2 ) defined on a side of the housing  80 . A pump piston  88  is disposed inside the pump chamber  82  to reciprocate therein. A spring  90  biases the pump piston  88  away from the fuel inlet port  84 . A plunger  92  is connected to the bottom of the pump piston  88 . The plunger  92  is driven by the pump driving mechanism described below. As it is being driven, the plunger  92  moves up and down which causes the pump piston  88  to also move up and down. An intake valve  94  is disposed inside the fuel inlet port  84 . As the pump piston  88  moves down, the intake valve  94  is opened to let fuel enter the pump chamber  82 . As the pump piston  88  moves up, the intake valve  94  is closed. This causes the fuel pressure to increase as the pump piston  88  moves up. A pressure regulator  96  connected to the pump housing  80  controls the opening and closing of the intake valve  94  based on a signal received from the ECU. The signal sent by the ECU to the pressure regulator  96  indicates to the pressure regulator  96  when the intake valve  94  should be closed as the pump piston  88  moves up in order to obtain the desired fuel pressure to be supplied to the fuel injectors  32  determined by the ECU. As the pump piston  88  moves up, the intake valve  94  is initially opened, thus allowing fuel in the pump chamber  82  to exit the pump chamber  82  via the fuel inlet port  84  and preventing the fuel pressure from increasing, at least not significantly, as the pump piston  88  moves up. The pressure regulator  96  then closes the intake valve  94  at the time determined based on the signal received from the ECU and fuel pressure increases as the pump piston  88  completes its upward stroke. Therefore, the amount of fuel pressure generated by the fuel pump  12  can be controlled to be at any value (within the fuel pump&#39;s operating parameters) by adjusting a closing time of the intake valve  84 . As should be understood, the maximum fuel pressure that can be generated by the fuel pump  12  is obtained by maintaining the intake valve  14  closed for the entire upward stroke of the pump piston  88 . In one embodiment, the maximum fuel pressure that can be generated by the fuel pump  12  per stroke is about 15 bar. From the fuel pump  12 , fuel is supplied to the fuel line  48  via the fuel outlet port  86 . The fuel pressure to be supplied to the fuel injectors  32  can be any pressure between a minimum pressure of 20 bar and a maximum pressure exceeding 200 bar. This pressure is achieved over multiple strokes of the fuel pump  12 . 
         [0062]    As can be seen in  FIG. 2 , the fuel pump  12  is connected to a side of the crankcase  14  via a pump mount  98 . As best seen in  FIG. 4 , the pump mount  98  has an upper flange  100  to which the fuel pump  12  is fastened and a crankcase mounting face  102  facing the crankcase  14  when the pump mount  98  is connected to the crankcase  14 . The upper flange  100  has apertures  104  to receive the fasteners used to connect the fuel pump  12  to the pump mount  98 . The upper flange  100  also defines an aperture  106  that receives the plunger  92  of the fuel pump  12  (see  FIG. 7 ). The crankcase mounting face  102  has apertures  108  to receive the fasteners used to connect the pump mount  98  to the crankcase  14 . The crankcase mounting face  102  also defines an aperture  110  to receive the pump driving mechanism described below (see  FIG. 7 ). 
         [0063]    Turning now to  FIGS. 7 to 10 , a first embodiment of the pump driving mechanism will be described. The first embodiment of the pump driving mechanism includes an eccentric shaft  112  and a pair of ball bearings  114 . It is contemplated that only one or more than two ball bearings  114  could be used. As best seen in  FIGS. 8 to 10 , the eccentric shaft  112  has five cylindrical surfaces  116 ,  118 ,  120 ,  122  and  124  each having different diameters. It is contemplated that the eccentric shaft  112  could have more or less than five cylindrical surfaces and that at least some of the surfaces could have the same diameter. The cylindrical surfaces  116 ,  118 ,  120 , and  124  have a common central axis  126 . The cylindrical surface  122  has a central axis  128  which is offset from the central axis  126 . The ball bearings  114  are disposed on the eccentric shaft  112  such that their inner races are disposed around the cylindrical surface  122 . The outer races of the ball bearings  114  abut the end of the plunger  92 . As seen in  FIG. 7 , the eccentric shaft  112  is supported in the pump mount  98  by a ball bearing  129  disposed between the cylindrical surface  118  and the aperture  110 . 
         [0064]    A groove  130  is defined in the end of the eccentric shaft  112 . As seen in  FIG. 7 , the groove  130  is engaged by a tongue  132  defined in an end of a water pump shaft  134 . It is contemplated that other types of connections could be provided between the eccentric shaft  112  and the water pump shaft  134 , such as a splined or conical connection for example. The water pump shaft  134  is disposed perpendicularly to the crankshaft  20  and is coaxial with the central axis  126  of the eccentric shaft  112 . The water pump shaft  134  is driven by the crankshaft  20  via helical gears  136  and  138  disposed on the water pump shaft  134  and the crankshaft  20  respectively. As such, the water pump shaft  134  drives the eccentric shaft  112  and, as its name suggests, a water pump  140  disposed in the crankcase  14 . It is contemplated that the eccentric shaft  112  could be driven by any other rotating shaft of the engine  10  such as the crankshaft  20  or the balancer shaft (not shown). 
         [0065]    As the eccentric shaft  112  rotates about the central axis  126 , the ball bearings  114  move up and down since they are disposed on the cylindrical surface  122 . This causes the plunger  92  to move up and down with the ball bearings  114 , which operates the fuel pump  112 . As mentioned above, the end of the plunger  92  abuts the outer races the ball bearings  114 . As the eccentric shaft  112  rotates, the inner races of the ball bearings  114  rotate with the cylindrical surface  122 , but the friction forces between the end of the plunger  92  and the outer races of the ball bearings  114  are sufficient to maintain the outer races rotationally stationary. It is contemplated that some rotation of the outer races of the ball bearings could occur, however the speed of rotation of the outer races would be much less than a speed of rotation of the eccentric shaft  112 . Since there is no, or very little, relative motion between the end of the plunger  92  and the outer races of the ball bearings  114 , the fuel pump  12  can be driven with no, or very little, wear of the end of the plunger  92  and with no or very little side forces applied to the plunger  92 . 
         [0066]    As seen in  FIG. 13 , it is contemplated that a tappet  142  could be disposed between the end of the plunger  92  and the outer races of the bearings  114 , thus preventing wear of the end of the plunger  92 . Also, since the tappet  142  is held in a guide  144  which prevents lateral movement of the tappet  142 , the application of side forces to the plunger  92  is prevented. 
         [0067]    In order to be able to properly control the opening and closing of the intake valve  94  of the fuel pump  12  as described above, the ECU needs to determine the position of the pump piston  88  inside the pump chamber  82 . As such, the gears  136  and  138  are preferably selected such that the crankshaft  20  and the pump shaft  134  rotate at the same speed, and therefore the eccentric shaft  112  rotates at the same speed as the crankshaft  20 . In this manner, the position of the pump piston  88  inside the pump chamber  82  can be determined using the sensor (not shown) used to sense a speed of rotation of the engine  10 . Alternatively, a dedicated sensor could be provided to determine the position of the pump piston  88 . Alternatively, it is contemplated that the gears  136  and  138  could be selected such that the pump shaft  134  rotates at half or double speed of the crankshaft  20 . 
         [0068]    Turning now to  FIGS. 11 and 12  a second embodiment of the pump driving mechanism will be described. The second embodiment of the pump driving mechanism drives a fuel pump  12 ′. The fuel pump  12 ′ is similar to the fuel pump  12  except that its fuel exhaust port  86  is disposed on the top of the pump housing  80  and has the check valve  52  disposed in the fuel exhaust port  86 . As such the fuel pump  12 ′ operates in the same manner as the fuel pump  12  and, for simplicity, its operation will therefore not be described again. Also for simplicity, the components of the fuel pump  12 ′ similar to those of the fuel pump  12  have been labelled with the same reference numerals as those of the fuel pump  12  and will not be described again. 
         [0069]    The second embodiment of the pump driving mechanism includes a generally V-shaped lever  150  rotatably mounted on a roller  152  via a shaft  154  defining an axis  156 . As seen in  FIG. 12 , one end  158  of the lever  150  has a recessed portion  160  that receives the end of the plunger  92  therein. A ball  162 , preferably made of steel, is disposed between the other end  164  of the lever  150  and a surface  166  of the crankcase  14 , or of another portion of the engine  10 . The roller  152  abuts a cam  168  disposed on a balancer shaft  170  of the engine  10  having an axis of rotation  172 . The balancer shaft  170  is driven by and is disposed parallel to the crankshaft  20 . It is contemplated that the cam could be disposed on any other rotating shaft of the engine  10  such as the crankshaft  20  or the water pump shaft  134 . 
         [0070]    As the cam  168  rotates with the balancer shaft  170 , the roller  152  moves up and down, which moves the end  158  of the lever  150  up and down and as a result, operates the pump  12 ′. The shaft  154  moves inside a groove (not shown) in order to control the movement of the roller  152 . Since the plunger  92  pushes down on the end  158  of the lever due to the bias of the spring  90 , the end  164  of the lever  150  pushes up on the ball  162 , thus retaining the ball  162  between the end  164  of the lever  150  and the surface  166  and maintaining contact between the plunger  92  and the end  158 . The movement of the end  158  of the lever  150  resulting from this arrangement provides very little relative motion between the end of the plunger  92  and the end  158  of the lever  150 . As a result the fuel pump  12 ′ can be driven with very little wear of the end of the plunger  92  and with very little side forces applied to the plunger  92 . It is contemplated that a tappet similar to the tappet  142  described above with respect to  FIG. 13  could be disposed between the end of the plunger  92  and the end  158  of the lever  150  to prevent side forces from being applied to the plunger  92 . 
         [0071]    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.