Abstract:
A peristaltic piston pump driven by a dedicated pump cam disposed on a camshaft of an engine. A plurality of valve-opening cams are also disposed along the camshaft. The pump cam has a plurality of lobes equal in number to the number of valve cams and each pump lobe is disposed at 180° from a valve cam lobe such that the camshaft valve torque and secondary oil pump camshaft torque partially cancel, reducing overall camshaft torque oscillation. The pump includes a lost-motion shuttle and spring to permit continuous response of the pump to the cam.

Description:
TECHNICAL FIELD 
     The present invention relates to oil pumps for internal combustion engines; more particularly, to a secondary oil pump for boosting oil pressure when the output pressure of the primary engine oil pump is low; and most particularly, to a secondary oil pump driven by a cam on the engine&#39;s camshaft wherein pump-actuating cam lobes are out of phase with valve actuating cam lobes. 
     BACKGROUND OF THE INVENTION 
     Oil pumps for internal combustion engines are well known. A primary engine oil pump may be, for example, a mechanically-driven positive-displacement gear pump fed from the engine&#39;s crankcase and driven by rotation of the engine&#39;s camshaft or crankshaft. Oil pump output flow is typically a direct function of the rotary speed of the engine. Because of engineered oil leaks between lubricated components in the oil pathway, and because of wear in those components during the lifetime of the engine, oil pressure also may be relatively low during periods of low engine speeds such as at idle and increases only as engine speed increases. Also, as engine temperature increases, oil viscosity decreases in known fashion, causing increased flow through the leaks and consequent reduced line pressure. In addition to insufficient engine lubrication, low oil pressure can result in slow or faulty actuation of oil-driven auxiliary engine devices, for example, camshaft phasers and variable valve actuators. 
     It is known to use an electrically-driven auxiliary pump to increase oil pressure for oil being supplied to a variable valve actuation mechanism. 
     What is needed is an inexpensive, reliable, mechanical means for maintaining a minimum oil pressure and flow in an internal combustion engine. 
     Another problem in an internal combustion engine is the amplitude of torque oscillation of the engine&#39;s camshaft(s). During operation of the engine, while each valve is closed, the follower for the associated cam rides on the base circle portion of the cam. To open the valve, the follower rides up the front side of the eccentric lobe. The resistance caused by the opposing force of the valve return spring places a torque on the camshaft in a direction counter to the rotational direction of the camshaft. After the peak of the lobe is passed and the valve is closing, the direction of torque is reversed as the follower rides down the back side of the lobe, urged by the force of the valve spring. The camshaft is thus subjected to relatively violent torque reversals for each engine valve actuation resulting in oil pressure fluctuation (especially within the camshaft phaser), undesirable vibration, wear, and energy loss in the form of heat. 
     What is needed is a means for reducing the amplitude of torque oscillation of an engine camshaft. 
     It is a principal object of the present invention to reduce the amplitude of torque oscillation of an engine camshaft. 
     SUMMARY OF THE INVENTION 
     Briefly described, a secondary oil supply pump augments oil flow from a primary supply pump in an internal combustion engine. The secondary pump is a peristaltic piston pump driven by a dedicated cam disposed on a camshaft of the engine. Preferably, the pump cam is formed having a plurality of lobes equal in number to the number of valves actuated by the camshaft, and further, that each pump cam lobe is disposed at 180° from a valve cam lobe such that the torque exerted by the closing valve assists in providing a pumping pulse to the secondary oil pump; and the torque exerted by termination of the pumping pulse assists in opening the next valve. In this way, the net amplitude of the camshaft torque oscillation is substantially reduced. A three-way valve responsive to inline pressure and, preferably, an engine control module governs the flow of oil either around the secondary pump at acceptably high primary pump pressures or through the secondary pump when primary pressure is unacceptably low. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a schematic diagram of an oil circulation system for an internal combustion engine in accordance with the invention; 
     FIG. 2 is an elevational cross-sectional view of a secondary oil supply pump actuated by a camshaft cam in accordance with the invention, showing the pump on a base circle portion of the cam; 
     FIG. 3 is an elevational cross-sectional view like that shown in FIG. 2, showing the pump in cam-actuated mode; 
     FIG. 4 is an elevational cross-sectional view like that shown in FIGS. 2 and 3, showing the pump in non-pumping lost-motion mode; 
     FIG. 5 is a graph of camshaft torque as a function of rotational angle of a camshaft for a three-cylinder application, showing a reduction in camshaft torque oscillation as a result of the invention; and 
     FIG. 6 is an view of a camshaft in accordance with one embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, in a schematic diagram for an oil circulation system  10  for an internal combustion engine, an oil sump  12 , such as an engine crankcase, supplies oil to a conventional primary oil pump  14 . Pump  14  supplies oil under pressure to the rest of the system via a three-way valve  16  disposed at the exit of a secondary oil supply (booster) pump  18  in accordance with the invention. Oil from primary pump  14  may flow either around or through secondary pump  18  via lines  19 , 20 , as selected by valve  16  in accordance with conditions described below. 
     Oil flows from valve  16  via line  21  to other lubricated elements, such as a control valve  22  for controlling the action of camshaft phaser  24 , a variable valve actuation mechanism  26 , and general lubrication of engine  28 , via an optional oil accumulation reservoir  30 . All lubrication paths lead eventually back to sump  12 . 
     Referring to FIG. 2, peristaltic secondary oil pump  18  includes a pump body  32  having a transverse bore  34  and a blind bore  36  orthogonal to transverse bore  34 . Blind bore  36  preferably is provided with a vent opening  38 . Within transverse bore  34  on opposite sides of blind bore  36  are disposed first and second check valves  40 , 42  for permitting oil flow only in the direction from line  20  to line  21  and not the reverse. A lost-motion shuttle  44  having a length shorter than the depth of blind bore  36  is slidingly disposed in blind bore  36  and is captured therein by plate  46 . A lost-motion spring  48  is disposed in compression in a second well  50  in shuttle  44  to bias shuttle  44  toward plate  46 . A cam follower  52  is slidingly disposed in a first well  54  in shuttle  44  and extends through an opening in plate  46  for engaging a cam  56  fixedly disposed on a camshaft  58  of engine  28 . Of course, cam follower  52  may be a roller follower as is well known in the art. A cam follower return spring  60  is disposed in compression in a third well  62  in cam follower  52  for biasing the cam follower into continuous contact with cam  56 . In FIG. 2, cam follower  52  is in contact with a base circle portion  64  of cam  56 . A transverse bore  53  in shuttle  44  provides an oil flow path between first and second check valves  40 , 42 . Shuttle transverse bore  53  further communicates with third well  62  via an axial passage  55  in shuttle  44 . 
     Three-way valve  16  includes a valve body  66  mounted for convenience onto pump body  32 . A first bore  68  is provided preferably coaxial with transverse bore  34  in body  32  for flow of oil through body  66 . Of course, valve  16  may be mounted apart from pump  18  as desired and connected thereto via an additional line. A spool  70 , controllable as by a conventional solenoid or stepper motor or other means (none shown), is slidingly disposed in a second bore  72  in valve body  66 . In a first control position, when oil pressure output from primary pump  14  is unacceptably low, spool  70  permits oil flow through pump  18 , as shown in FIGS. 2 and 3. In a second control position, when oil pressure output from primary pump  14  is acceptably high, spool  70  permits oil flow only from line  19  through orifices  70 a and prevents oil flow through pump  18 , as shown in FIG.  4 . 
     The peristaltic pumping action of pump  18  is as follows. After initial filling, shuttle transverse bore  53  between the check valves, passage  55 , and well  62  remain filled with oil at all times. When camshaft  58  causes cam  56  to present a base circle portion  64  to follower  52 , spring  60  urges follower  52  away from the bottom of well  54 , creating a space  73  and thereby drawing oil from line  20  through check valve  42  to fill space  73 , the volume of which represents the per-stroke volume of the pump. 
     Referring to FIG. 3, when camshaft  58  rotates to cause cam  56  to present an eccentric lobe  74  to follower  52 , the follower is urged axially of bore  54 , overcoming return spring  60  (but not the stronger lost-motion spring  48 ), eliminating space  73 , and expressing an equal volume of oil from shuttle transverse bore  53  through check valve  40  into line  21 . Further rotation of camshaft  58  causes the follower to return to the next base portion circle  64  of cam  56 , refilling space  73  in preparation for the next stroke of the pump. 
     Since the pump must respond continuously to the action of cam  56 , whether or not oil is to be pumped into line  21 , a lost motion mechanism must be provided. Referring to FIG. 4, when valve  16  is closed to pump  18 , oil flow from the pump is deadheaded. Because oil is substantially incompressible, space  73  is not eliminated but rather follower  52  and shuttle  44  are displaced as a unit axially within blind bore  36  by a distance  71  equal to the height of space  73 , overcoming lost-motion spring  48 . Thus, when flow is shut off, shuttle  44  simply cycles within pump body  32  to follow in lost motion the action of cam  56 . 
     Cam  56  is shown in FIGS. 2-4 as having three base circle portion segments  64  and three eccentric lobes  74 . Thus one rotation of the camshaft produces three strokes of the pump. Referring to FIGS. 5 and 6, an added advantage of a peristaltic secondary oil pump is shown. Curve  76  represents the torque, both in the direction of camshaft rotation (+) and against the direction of camshaft rotation (−), exerted on camshaft  58  in opening and closing three intake or exhaust valves of a three-cylinder engine, or one bank of a V-6 engine. Curve  78  represents the torque exerted on camshaft  58  by one rotation of cam  56  in actuating the oil pump three times. By angularly orienting cam  56  on camshaft  58  such that the pump-actuating lobes  74  are rotationally interspersed between the valve-actuating lobes  75 , and preferably that each lobe  74  is exactly 180° from one of the three valve cam lobes  75  (FIG.  6 ), the torque resulting from the valve lobes and the pump lobes partially cancel, the net camshaft torque oscillation being represented by curve  80 . 
     While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.