Abstract:
A pump is disclosed, having a pumping chamber in the rotor. The rotor is rotatable between first, second, third and fourth positions. When the rotor is in the first position, an inlet cam assembly displaces a piston to draw fluid into the pumping chamber via a first housing inlet. When the rotor is in the second position, an outlet cam assembly displaces the piston to expel fluid out of the pumping chamber via a first housing outlet. When the rotor is in the third position, the inlet cam lobe assembly displaces the piston to draw fluid into the pumping chamber via a second housing inlet. When the rotor is in the fourth position, the outlet cam assembly displaces the piston to expel fluid out of the pumping chamber via a second housing outlet. A method of pumping fluid is also disclosed.

Description:
CROSS REFERENCE 
     The present application claims priority from U.S. Provisional Patent Application No. 60/976,178 filed Sep. 28, 2007, entitled FLUID PUMP, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method and apparatus for pumping fluids. 
     BACKGROUND OF THE INVENTION 
     Internal combustion engines have many moving parts, and a number of these parts slide against each other with very tight tolerances. As such, these parts require lubrication to allow them to slide against one another and prevent the parts from becoming damaged. 
     Lubrication of the pistons of the engine is particularly important. As the pistons reciprocate in the cylinders as many as several thousand times per minute, they slide against the cylinder walls. In addition, the connection between the piston and the control rod (known as the “wrist pin”) is subjected to sliding friction as the angle between the piston and the control rod changes throughout the engine cycle. It is important to deliver adequate lubricant to these sites, to ensure proper functioning of the engine. 
     A lubricant pump is typically employed to provide a regular supply of lubricant to these and other parts of the engine. The pump supplies lubricant simultaneously to suitable locations within the engine so that the lubricant reaches the sites where lubrication is required. For example, in a two-stroke engine, lubricant may be supplied to the air intake system of each cylinder, at a point upstream from the reed valve. The air intake system of the engine carries the lubricant into the combustion chamber of the cylinder, where it provides lubrication between the piston and the cylinder wall. Lubricant may also be provided to nozzles that are oriented to spray the lubricant on the wrist pin of each piston. The pump would supply lubricant to each of these locations, to ensure that they remain lubricated. 
     However, prior art pumps have a number of drawbacks. Pumps typically include check valves to ensure that the lubricant is pumped in the intended direction, toward the surfaces that require lubrication, and to restrict the flow of lubricant in the opposite direction. These check valves are susceptible to sticking at cold temperatures, resulting in irregular or insufficient supply of lubricant. In addition, lubricant must be supplied to a number of areas at the same time, particularly in engines having several cylinders, each with a piston requiring lubrication. For example, if the engine has four cylinders, the pump must supply lubricant to eight separate locations: four pistons and four wrist pins. Pumping lubricant to eight places simultaneously reduces the quantity of lubricant that can be supplied to each location, and thereby reduces the effectiveness of the lubrication. 
     Therefore, there is a need for a way of providing lubrication to portions of an engine. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to ameliorate at least some of the inconveniences present in the prior art. 
     It is also an object of the present invention to provide a pump without check valves that are susceptible to sticking at low temperatures. 
     It is also an object of the present invention to provide a pump that delivers lubricant sequentially to more than one location. 
     In one aspect, the invention provides a piston pump, comprising a housing. A rotor assembly is rotatably disposed in the housing. The rotor assembly comprises a rotor. A pumping chamber is disposed in the rotor. A piston is slidably disposed within the pumping chamber and movable between a first position and a second position therein. The housing comprises a first housing inlet and a second housing inlet selectively fluidly communicating with the pumping chamber. The housing comprises a first housing outlet and a second housing outlet selectively fluidly communicating with the pumping chamber. An inlet cam assembly is fixedly disposed in the housing. The inlet cam assembly has first and second inlet cam lobes operative to move the piston to the first position. An outlet cam assembly is fixedly disposed in the housing. The outlet cam assembly has first and second outlet cam lobes operative to move the piston to the second position. The rotor is rotatable sequentially between first, second, third and fourth positions relative to the housing. When the rotor is in the first position: the pumping chamber is in fluid communication with the first housing inlet and in fluid isolation from the second housing inlet and from the first and second housing outlets; and the first inlet cam lobe urges the piston toward the first position to draw fluid into the pumping chamber via the first housing inlet. When the rotor is in the second position: the pumping chamber is in fluid communication with the first housing outlet and in fluid isolation from the first and second housing inlets and from the second housing outlet; and the first outlet cam lobe urges the piston to the second position to expel fluid out of the pumping chamber via the first housing outlet. When the rotor is in the third position: the pumping chamber is in fluid communication with the second housing inlet and in fluid isolation from the first housing inlet and from the first and second housing outlets; and the second inlet cam lobe urges the piston toward the first position to draw fluid into the pumping chamber via the second housing inlet. When the rotor is in the fourth position: the pumping chamber is in fluid communication with the second housing outlet and in fluid isolation from the first housing outlet and the first and second housing inlets; and the second outlet cam lobe urges the piston to the second position to expel fluid out of the pumping chamber via the second housing outlet. 
     In a further aspect, the housing is generally symmetric about a central longitudinal axis of symmetry. 
     In a further aspect, the rotor is rotatable about the central longitudinal axis of symmetry. 
     In a further aspect, the inlet cam is concentric with the central longitudinal axis of symmetry. 
     In a further aspect, the outlet cam is concentric with the central longitudinal axis of symmetry. 
     In a further aspect, the housing further comprises a third housing inlet selectively fluidly communicating with the pumping chamber. The housing further comprises a third housing outlet selectively fluidly communicating with the pumping chamber. The inlet cam assembly further comprises a third inlet cam lobe. The outlet cam assembly further comprises a third outlet cam lobe. When the rotor is in the first, second third and fourth positions, the pumping chamber is in fluid isolation from the third housing inlet and the third housing outlet. The rotor is further rotatable between fifth and sixth positions relative to the housing. When the rotor is in the fifth position: the pumping chamber is in fluid communication with the third housing inlet and in fluid isolation from the first and second housing inlets and from the first, second and third housing outlets; and the third inlet cam lobe urges the piston toward the first position to draw fluid into the pumping chamber via the third housing inlet. When the rotor is in the sixth position: the pumping chamber is in fluid communication with the third housing outlet and in fluid isolation from the first, second and third housing inlets and from the first and second housing outlets; and the third outlet cam lobe urges the piston to the second position to expel fluid out of the pumping chamber via the third housing outlet. 
     In a further aspect, the pumping chamber is a first pumping chamber. The piston is a first piston. The chamber inlet is a first chamber inlet. The chamber outlet is a first chamber outlet. A second pumping chamber is disposed in the rotor. A second piston is slidably disposed within the second pumping chamber and movable between a first position and a second position therein. The housing further comprises a third housing inlet and a fourth housing inlet selectively fluidly communicating with the second pumping chamber. The housing further comprises a third housing outlet and a fourth housing outlet selectively fluidly communicating with the second pumping chamber. The rotor is further rotatable between fifth, sixth, seventh and eighth positions relative to the housing. When the rotor is in the fifth position: the second pumping chamber is in fluid communication with the third housing inlet and in fluid isolation from the fourth housing inlet and from the third and fourth housing outlets; and the first inlet cam lobe urges the second piston toward the first position to draw fluid into the second pumping chamber via the third housing inlet. When the rotor is in the sixth position: the second pumping chamber is in fluid communication with the third housing outlet and in fluid isolation from the third and fourth housing inlets and from the fourth housing outlet; and the first outlet cam lobe urges the second piston to the second position to expel fluid out of the second pumping chamber via the third housing outlet. When the rotor is in the seventh position: the second pumping chamber is in fluid communication with the fourth housing inlet and in fluid isolation from the third housing inlet and from the third and fourth housing outlets; and the second inlet cam lobe urges the second piston toward the first position to draw fluid into the second pumping chamber via the fourth housing inlet. When the rotor is in the eighth position: the second pumping chamber is in fluid communication with the fourth housing outlet and in fluid isolation from the third housing outlet and the third and fourth housing inlets; and the second outlet cam lobe urges the second piston to the second position to expel fluid out of the second pumping chamber via the fourth housing outlet. 
     In a further aspect, the third housing inlet is the first housing inlet. The fourth housing inlet is the second housing inlet. 
     In a further aspect, the fifth position is the first position. The sixth position is the second position. The seventh position is the third position. The eighth position is the fourth position. 
     In an additional aspect, the invention provides a method of distributing fluid via a pump. The pump has a housing. A rotor is rotatably disposed within the housing. The rotor has a pumping chamber disposed therein. A piston is slidably disposed within the pumping chamber. The housing has a first housing inlet and a second housing inlet selectively fluidly communicating with the pumping chamber. The housing has a first housing outlet and a second housing outlet selectively fluidly communicating with the pumping chamber. The method comprises: rotating the rotor to a first position providing: fluid communication between the pumping chamber and the first housing inlet; fluid isolation between the pumping chamber and the second housing inlet; fluid isolation between the pumping chamber and the first and second housing outlets; and actuation of the piston to draw fluid into the pumping chamber via the first housing inlet; rotating the rotor to a second position providing: fluid communication between the pumping chamber and the first housing outlet; fluid isolation between the pumping chamber and the second housing outlet; fluid isolation between the pumping chamber and the first and second housing inlets; and actuation of the piston to expel fluid out of the pumping chamber via the first housing outlet; rotating the rotor to a third position providing: fluid communication between the pumping chamber and the second housing inlet; fluid isolation between the pumping chamber and the first housing inlet; fluid isolation between the pumping chamber and the first and second housing outlets; and actuation of the piston to draw fluid into the pumping chamber via the second housing inlet; and rotating the rotor to a fourth position providing: fluid communication between the pumping chamber and the second housing outlet; fluid isolation between the pumping chamber and the first housing outlet; fluid isolation between the pumping chamber and the first and second housing inlets; and actuation of the piston to expel fluid out of the pumping chamber via the first housing outlet. 
     In a further aspect, the housing is generally symmetric about a central longitudinal axis of symmetry. Rotating the rotor comprises rotating the rotor about an axis coaxial with the central longitudinal axis of symmetry. 
     In a further aspect, the housing further comprises a third housing inlet selectively fluidly communicating with the pumping chamber and a third housing outlet selectively fluidly communicating with the pumping chamber. The inlet cam assembly further comprises a third inlet cam lobe. The outlet cam assembly further comprises a third outlet cam lobe. Rotating the rotor to any of the first, second, third and fourth positions further provides fluid isolation from the third housing inlet and the third housing outlet. The method further comprises: rotating the rotor to a fifth position providing: fluid communication between the pumping chamber and the third housing inlet; fluid isolation between the pumping chamber and the first and second housing inlets; fluid isolation between the pumping chamber and the first, second and third housing outlets; and actuation of the piston to draw fluid into the pumping chamber via the third housing inlet; and rotating the rotor to a sixth position providing: fluid communication between the pumping chamber and the third housing outlet; fluid isolation between the pumping chamber and the first and second housing outlet; fluid isolation between the pumping chamber and the first, second and third housing inlets; and actuation of the piston to expel fluid out of the pumping chamber via the third housing outlet. 
     In a further aspect, the pumping chamber is a first pumping chamber. The piston is a first piston. The chamber inlet is a first chamber inlet. The chamber outlet is a first chamber outlet. The rotor further comprises a second pumping chamber disposed therein. A second piston is slidably disposed within the second pumping chamber. The housing further comprises a third housing inlet and a fourth housing inlet selectively fluidly communicating with the second pumping chamber. The housing further comprises a third housing outlet and a fourth housing outlet selectively fluidly communicating with the second pumping chamber. The method further comprises: rotating the rotor to a fifth position providing: fluid communication between the second pumping chamber and the third housing inlet; fluid isolation between the second pumping chamber and the fourth housing inlet; fluid isolation between the second pumping chamber and the third and fourth housing outlets; and actuation of the second piston to draw fluid into the second pumping chamber via the third housing inlet; rotating the rotor to a sixth position providing: fluid communication between the second pumping chamber and the third housing outlet; fluid isolation between the second pumping chamber and the third and fourth housing inlets; fluid isolation between the second pumping chamber and the fourth housing outlet; and actuation of the second piston to expel fluid out of the second pumping chamber via the third housing outlet; rotating the rotor to a seventh position providing: fluid communication between the second pumping chamber and the fourth housing inlet; fluid isolation between the second pumping chamber and the third housing inlet; fluid isolation between the second pumping chamber and the third and fourth housing outlets; and actuation of the second piston to draw fluid into the second pumping chamber via the fourth housing inlet; and rotating the rotor to an eighth position providing: fluid communication between the second pumping chamber and the fourth housing outlet; fluid isolation between the second pumping chamber and the third housing outlet; fluid isolation between the second pumping chamber and the third and fourth housing inlets; and actuation of the second piston to expel fluid out of the second pumping chamber via the fourth housing outlet. 
     For the purposes of this application, the terms “radial”, “axial” and “tangential” are defined with respect to the axis of rotation of the rotor. Thus, “radial” refers to a direction toward or away from the axis of rotation and perpendicular to the axis of rotation, “axial” refers to a direction along or parallel to the axis of rotation, and “tangential” refers to a direction perpendicular to the radial direction and not along or parallel to the axial direction. 
     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. 
     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 perspective view of pump according to a first embodiment of the present invention; 
         FIG. 2  is an exploded view of the pump of  FIG. 1 ; 
         FIGS. 3A and 3B  are cross-sectional perspective views of a rotor for the pump of  FIG. 1 , showing different positions of the piston; 
         FIG. 4  is a perspective view of a piston for a pump according to a first embodiment of the present invention; 
         FIG. 5  is a perspective view of an inlet plate for the pump of  FIG. 1 ; 
         FIG. 6  is a perspective view of a cover for the pump of  FIG. 1 ; 
         FIG. 7A  is a partial exploded view of a pump according to a second embodiment of the present invention; 
         FIG. 7B  is a perspective view of a rotor for the pump of  FIG. 7A   
         FIG. 8  is a partial exploded view of a pump according to a third embodiment of the present invention; and 
         FIGS. 9A and 9B  are schematic views of an inlet plate, a rotor and an outlet cam ring for a pump in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring generally to  FIGS. 1 and 2 , a pump  10  in accordance with a first embodiment of the present invention will be described. 
     The pump  10  includes a housing  11  composed of a base plate  12  and a cover  14 . The pump  10  is driven by an electric motor  16  via an adapter plate  15  (seen in  FIG. 2 ) that is mounted to the base plate  12  via fasteners (not shown). The pump  10  may alternatively be driven by the crankshaft of an engine (not shown), or any other suitable source of power. Lubricant (not shown) enters the housing  11  via an aperture  17  (seen in  FIG. 2 ) in the lateral wall of the cover  14  and fills the interior of the housing  11 . Referring to  FIG. 2 , a rotor  20  is disposed inside the housing  11  such that it is free to rotate when driven by the motor  16 . The rotor  20  houses a piston  22  consisting of a piston body  24  and a piston follower  26  (best seen in  FIG. 4 ). The piston body  24  reciprocates within a bushing  34  to pump lubricant through the housing outlets  32  in the cover  14 , as will be discussed below in further detail. Hose connectors  18  join the housing outlets  32  to hoses (not shown) to transmit the lubricant to a location where lubrication is desired. For example, the present embodiment with six housing outlets  32  could supply lubricant to up to six different locations, which can be suitable for lubricating a three-cylinder two-stroke engine (not shown). The lubricant output from three of the housing outlets  32  could be transmitted to a location upstream of each of the intake reed valves (not shown), and the lubricant output from the other three housing outlets  32  could be transmitted to the three wrist pins (not shown) of the respective pistons (not shown) of the engine. It is contemplated that the lubricant may instead be transmitted to any other location where lubrication is desired. 
     Referring to  FIG. 2 , an inlet plate  28  is positioned inside the housing  11 , on the side of the rotor  20  opposite the housing outlets  32 . When the pump  10  is assembled, the inlet plate  28  is biased against the rotor  20  by springs  30  positioned between the inlet plate  28  and the base plate  12 . The springs  30  also bias the rotor  20  against the inside of the cover  14 . The inlet plate  28  includes pins  36  that align with the apertures  38  (two of which can be seen in  FIG. 6 ) in the cover  14 , to preserve the relative orientation of the cover  14 , base plate  12  and the inlet plate  28 . The functioning of the inlet plate  28  and the cover  14 , to respectively control lubricant flow into and out of the pumping chamber  40 , will be described below in further detail. 
     Referring now to  FIGS. 3A and 3B , the operation of the rotor  20  will be described. As the motor  16  causes the rotor  20  to rotate within the housing  11 , the piston body  24  of the piston  22  reciprocates within the bushing  34 , as will be described in further detail below. The piston body  24  reciprocates between a first position (shown in  FIG. 3A ) and a second position (shown in  FIG. 3B ). The piston body  24  and the bushing  34  together define a pumping chamber  40  (best seen in  FIG. 3A ). The pumping chamber  40  is in selective fluid communication with the housing inlets  50  via a chamber inlet  42  and in selective fluid communication with the housing outlets  32  via a chamber outlet  44 . As the rotor  20  rotates within the housing  11 , the reciprocating movement of the piston body  24  draws lubricant into the pumping chamber  40  via the chamber inlet  42  when the piston body  24  moves toward the first position shown in  FIG. 3A , and expels the lubricant out of the pumping chamber  40  through the chamber outlet  44  when the piston body  24  moves toward the second position shown in  FIG. 3B , as will be described below in further detail. 
     Referring to  FIG. 5 , the inlet plate  28  includes a hexagonal inlet cam ring  46  including six equally-spaced inlet cam lobes  48 . The inlet plate  28  also has six housing inlets  50 , the purpose of which will be described below. Referring to  FIG. 6 , the cover  14  includes an outlet cam ring  52  including six equally-spaced outlet cam lobes  54 , four of which are visible in  FIG. 6 . The cover  14  also has six housing outlets  32 , the purpose of which will be described below. Each housing inlet  50  has a corresponding inlet cam lobe  48 , and each housing outlet has a corresponding outlet cam lobe  54 . It is contemplated that there may be more or fewer housing inlets  50 , each with a corresponding inlet cam lobe  48 , and an equal number of housing outlets  32 , each with a corresponding outlet cam lobe  54 . The inlet cam lobes  48  and the outlet cam lobes  54  cause the piston to reciprocate as will be described below in further detail. 
     Referring to  FIGS. 9A and 9B , the operation of the pump  10  will now be described. 
     Referring generally to  FIGS. 9A and 9B , the cover  14 , the rotor  20  and the inlet plate  28  are shown schematically in a superimposed arrangement, as they are oriented when the pump  10  is assembled. As the rotor  20  rotates inside the housing  11 , the chamber inlet  42  comes into alignment with each of the housing inlets  50  in turn, providing fluid communication between that housing inlet  50  and the pumping chamber  40 . The contact between the rotor  20  and the inlet plate  28  blocks the housing inlets when they are not aligned with the chamber inlet  42 , providing fluid isolation between the pumping chamber  40  and the remaining housing inlets  50 . Similarly, as the rotor  20  rotates, the chamber outlet  44  comes into alignment with each of the housing outlets  32  in turn, providing fluid communication between that housing outlet  32  and the pumping chamber  40 , and providing fluid isolation between the pumping chamber  40  and the remaining housing outlets  32 . 
     In  FIG. 9A , the rotor  20  is in a first position wherein the chamber inlet  42  is aligned with a first one of the housing inlets  50 . In this position, the pumping chamber  40  is in fluid communication with the first housing inlet  50  and in fluid isolation from the remaining housing inlets  50  and from all of the housing outlets  32 . The inlet cam lobes  48  are positioned relative to the housing inlets  50  such that when the rotor  20  is in the first position, one of the inlet cam lobes  48  abuts against the piston follower  26  and urges the piston follower  26  radially outward, thereby moving the piston body  24  to the first position to increase the volume of the pumping chamber  40  as shown in  FIG. 9A . The movement of the piston body  24  draws lubricant from the inside of the housing  11  through the housing inlet  50  that is aligned with the chamber inlet  42 , into the pumping chamber  40  via the chamber inlet  42 . 
     Referring to  FIG. 9B , as the rotor  20  continues to rotate, it enters a second position wherein the chamber outlet  44  is aligned with a first one of the housing outlets  32 . In this position, the pumping chamber  40  is in fluid communication with the first housing outlet  32  and in fluid isolation from the remaining housing outlets  32  and from all the housing inlets  50 . The outlet cam lobes  54  are positioned relative to the housing outlets  32  such that when the rotor  20  is in the second position, one of the outlet cam lobes  54  abuts against the piston follower  26  and urges the piston follower  26  radially inward, thereby moving the piston body  24  to the second position to decrease the volume of the pumping chamber  40  as shown in  FIG. 9B . The movement of the piston body  24  expels lubricant from the pumping chamber  40  out of the housing  11  through the housing outlet  32  that is aligned with the chamber outlet  44 , via the chamber outlet  44 . 
     As the rotor  20  continues to rotate, it enters a third position wherein the chamber inlet  42  is aligned with a second one of the housing inlets  50 . In this position, the pumping chamber  40  is in fluid communication with the second housing inlet  50  and in fluid isolation from the remaining housing inlets  50  and from all of the housing outlets  32 . The inlet cam lobes  48  are positioned relative to the housing inlets  50  such that when the rotor  20  is in the third position, a second one of the inlet cam lobes  48  abuts against the piston follower  26  and urges the piston follower  26  radially outward, thereby moving the piston body  24  to the first position to increase the volume of the pumping chamber  40  as shown in  FIG. 9A . The movement of the piston body  24  to the first position draws lubricant from the inside of the housing  11  through the second housing inlet  50  that is aligned with the chamber inlet  42 , into the pumping chamber  40  via the chamber inlet  42 . 
     As the rotor  20  continues to rotate, it enters a fourth position wherein the chamber outlet  44  is aligned with a second one of the housing outlets  32 . In this position, the pumping chamber  40  is in fluid communication with the second housing outlet  32  and in fluid isolation from the remaining housing outlets  32  and from all of the housing inlets  50 . The outlet cam lobes  54  are positioned relative to the housing outlets  32  such that when the rotor  20  is in the fourth position, a second one of the outlet cam lobes  54  abuts against the piston follower  26  and urges the piston follower  26  radially inward, thereby moving the piston body  24  to the second position to decrease the volume of the pumping chamber  40  as shown in  FIG. 9B . The movement of the piston body  24  expels lubricant from the pumping chamber  40  out of the housing  11  through the housing outlet  32  that is aligned with the chamber outlet  44 , via the chamber outlet  44 . 
     In the event that the pump  10  has more than two housing inlets  50  and more than two housing outlets  32 , each of the housing inlets  50  and each of the housing inlets  32  will sequentially come into fluid communication with the pumping chamber  40  as the rotor  20  continues to rotate. In this manner, the piston  22  will sequentially draw lubricant into the pumping chamber  40  from each housing inlet  50 , and expel the lubricant out of the pumping chamber  40  via a respective housing outlet  32 . 
     Referring now to  FIGS. 7A and 7B , a pump  110  will be described according to a second embodiment of the invention. A number of components of the pump  10  of  FIG. 1 , such as the base plate  12 , the motor  16 , the springs  30  and the pins  36 , have corresponding components in the pump  110  that perform a similar function. These components of the pump  110  are not shown in  FIG. 7  and will not be discussed in detail. 
     The pump  110  includes a housing (not shown) composed of a base plate and a cover  114 . The pump  110  is driven in the same manner as the pump  10  of  FIG. 2 . Lubricant (not shown) enters the housing via the aperture  117  and fills the interior of the housing in the same manner as the pump  10  of  FIG. 1 . The cover  114  has housing outlets  132  and  133  and hose connectors  118  and  119  that function similarly to the housing outlets  32  and hose connectors  18  of  FIG. 2 . The inlet plate  128  has housing inlets  150  and  151  that function similarly to the housing inlets  150  of  FIG. 2 . As the rotor  120  rotates within the housing, the respective piston followers  126  and  127  of the pistons  122  and  123  sequentially abut against the inlet cam lobes  148  and the outlet cam lobes  154 , causing the piston bodies  124  and  125  to reciprocate in their respective bushings  134  and  135  to pump lubricant respectively through the housing outlets  132  and  133  in the cover  114 , similarly to the reciprocation of the pistons  22  of the pump  10  of  FIG. 2 . 
     The rotor  120  functions similarly to the rotor  20  of  FIG. 2 . As the rotor  120  rotates, the pistons  122  and  123  are caused to reciprocate. The piston bodies  124  and  125  reciprocate within the respective bushings  134  and  135  between a first position and a second position (not shown). Each piston body  124 ,  125  and its respective bushing  134 ,  135  together define a pumping chamber (not shown). 
     Each of the pistons  122 ,  123  is actuated when the inlet cam lobes  148  of the inlet cam ring  146 , and the outlet cam lobes (not shown) act on the piston followers  126 ,  127  as will be described below in further detail. Each of the six inlet cam lobes  148  and each of the six outlet cam lobes actuates both pistons  122  and  123  via the respective piston followers  126  and  127 . It is contemplated that each piston  122  and  123  may alternatively be actuated by a separate set of inlet and outlet cam lobes. 
     In this embodiment, the piston  122  draws lubricant from the housing inlets  150  and expels the lubricant through the housing outlets  132 ; the piston  123  draws lubricant from the housing inlets  151  and expels the lubricant through the housing outlets  133 . It is contemplated that the inlet plate  128  may alternatively have only the housing inlets  150 . In this alternative embodiment, the chamber inlets  142  and  143  would be appropriately positioned to align with the housing inlets  150  as the rotor  120  rotates. It is further contemplated that the cover  114  may alternatively have only the housing outlets  132 . In this alternative embodiment, the chamber outlets  144  and  145  would be appropriately positioned to align with the housing outlets  132  as the rotor  120  rotates. 
     It is further contemplated that there may be more or fewer housing inlets  150 ,  151 , more or fewer housing outlets  132 ,  133 , more or fewer inlet cam lobes  148  and more or fewer outlet cam lobes, as long as whenever any piston is actuated by an inlet cam lobe, its corresponding chamber inlet is in alignment with a housing inlet, and whenever any piston is actuated by an outlet cam lobe, its corresponding chamber outlet is in alignment with a housing outlet. 
     It should be understood that the pump  110  is capable of delivering lubricant to as many as twelve different locations, which can be suitable for a six-cylinder two-stroke engine (not shown). The lubricant output from each of the six housing outlets  132  could be transmitted to a location upstream of each of the intake reed valves (not shown) of the respective pistons, and the lubricant output from each of the six housing outlets  133  could be transmitted to nozzles (not shown) aimed at the six wrist pins (not shown) of the respective pistons (not shown). It is contemplated that the lubricant may instead be transmitted to any other location where lubrication is desired. It is further contemplated that the two pistons  122  and  123  can have different dimensions, such that each piston pumps different volumes of lubricant. In this manner, different locations that require different quantities of lubricant can be supplied accordingly. 
     The functioning of the pump  110  is similar to the functioning of the pump  10 , and will not be described separately in detail. 
     Referring now to  FIG. 8 , a pump  210  will be described according to a third embodiment of the invention. A number of components of the pump  10  of  FIG. 1 , such as the base plate  12 , the motor  16 , the springs  30  and the pins  36 , have corresponding components in the pump  210  that perform a similar function. These components of the pump  210  are not shown in  FIG. 7  and will not be discussed in detail. 
     The pump  210  includes a housing (not shown) composed of a base plate (not shown) and a cover  214 . The pump  210  is driven in the same manner as the pump  10  of  FIG. 2 . Lubricant (not shown) enters the housing via an axial channel  217  in the rotor  220  and fills the six housing inlet channels  250  on the inside of the cover  214 . The cover  214  has housing outlets  232  that function similarly to the housing outlets  32  of  FIG. 2 . The rotor  220  functions similarly to the rotor  20  of  FIG. 2 . As the rotor  220  rotates within the housing, the respective piston followers  226  of the pistons  222  sequentially abut against the inlet cam lobes  248  and the outlet cam lobes (not shown), causing the piston bodies  224  to reciprocate in their respective bushings  234 . The piston bodies  224  reciprocate between a first position and a second position (not shown). Each piston body  224  and its respective bushing  234  together define a pumping chamber (not shown). The reciprocation of the piston bodies  224  draws lubricant from the respective housing inlet channels  250  into the respective pumping chambers (not shown) via the chamber inlets  244 . The reciprocation of the piston bodies then pumps the lubricant out of the respective pumping chambers via the chamber inlets  244 , which also function as chamber outlets, through the respective housing outlets  232  in the cover  214 . In this embodiment, the pistons  222  reciprocate in an axial direction, parallel to the axis of rotation of the rotor  220 . 
     Each of the pistons  222  is actuated when the inlet cam lobes  248  of the inlet cam ring  246 , and the outlet cam lobes (not shown) act on the piston followers  226 . Each of the six inlet cam lobes  248  and each of the six outlet cam lobes actuates each of the pistons  222  via the respective piston followers  226 . 
     In this embodiment, each piston  222  draws lubricant from the housing inlets  250  and expels the lubricant through the housing outlets  232 . It is contemplated that there may be more or fewer housing inlets  250 , more or fewer housing outlets  232 , more or fewer inlet cam lobes  248  and more or fewer outlet cam lobes, as long as whenever any piston is actuated by an inlet cam lobe, its corresponding chamber inlet is in alignment with a housing inlet, and whenever any piston is actuated by an outlet cam lobe, its corresponding chamber outlet is in alignment with a housing outlet. 
     The functioning of the pump  210  is similar to the functioning of the pump  10 , and will not be described separately in detail. 
     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.