Patent Publication Number: US-2007111855-A1

Title: Engine speed-dependent pressure regulation of oil pumps

Description:
FIELD OF THE INVENTION  
      The invention concerns the regulation of the conveying pressure of hydraulic pumps. It relates particularly to a speed dependent pressure regulation for so-called oil control pumps for the lubricating oil supply of internal combustion engines which comprise a conveying capacity adjusting device and, for biasing it with pressure, a control piston for generating a control pressure, which may be biased by a device providing a variable additional force for varying the conveying pressure.  
     BACKGROUND OF THE INVENTION  
      Hydraulic pumps of controllable conveying capacity need a reduced oil pump driving power, as compared with hydraulic pumps using a by-pass regulation, and are already used with a constantly controlled conveying pressure as so-called oil control pumps for the lubricating oil supply of internal combustion engines.  
      But only by a speed-dependent pressure regulation of oil control pumps in accordance with the oil pressure need of internal combustion engines, which is speed-dependent to a large extent, the potential of improvement of oil control pumps can almost completely be utilized. As a consequence of a reduction of the hydraulic conveying power, which is considerable by then, the resulting advantages of the driving power of oil control pumps are enabled to cause a contribution worth mentioning to a consumption reduction in internal combustion engines.  
      An oil control pump having a variable oil pressure regulation is known from Patent No. DE 102 37 911 B4 and is also described in WO 03/058071. In the first case, it is constructed as an external teeth wheel pump comprising a displacement unit using an axially variable tooth engagement width that effects the adjustment of the conveying capacity. The regulation of the operational oil pressure is effected over the variable conveying capacity, the axially variable position of the displacement unit being adjusted by a control pressure acting onto it which is provided by a control piston. The control piston comprises a control spring and is biased so as to counter-act to it by the operational oil pressure and, thus, functions as an oil pressure sensor which is dimensioned for a corresponding nominal operational oil pressure. Communicating with oil bores, it comprises control grooves which generate the control pressure for biasing the displacement unit. Due to an additional variable biasing force onto the control piston by a control device, the operational oil pressure may either be adapted in steps or continuously to the oil pressure need of the internal combustion engine to be lubricated, which is speed-dependent to a large extent.  
      An embodiment of the DE 102 37 911 B4 shows changing over in two steps of the operational oil pressure by a switching valve actuated by centrifugal force acting in a speed-de-pendent manner. In another embodiment, a continuously variable regulation of the operational oil pressure is effected by an electrical adjusting device of the control piston which, in turn, is controlled by the control appliance of the internal combustion engine. A further embodiment comprises a spiral groove on a rotating shaft, where oil sharing forces dependent on the number of revolutions generate a pressure for oil pressure regulation which biases the control piston.  
      While a regulation of the operational oil pressure in steps makes only limited use of the improvement potential of an oil control pump, an advantageous continuous regulation of the operational oil pressure involves either a higher electrical control expenditure or, in the case of a spiral pressure regulation, is only usable in a limited temperature range due to the oil viscosity which varies with temperature.  
     SUMMARY OF THE INVENTION  
      The invention has the object to provide an oil pressure regulation for an oil control pump, which adapts continuously the operational oil pressure to the oil pressure needs of an internal combustion engine, which is substantially speed-dependent, without requiring an electrical control expenditure or without temperature-dependent limitations.  
      This object is achieved according to the invention in a second step according to the invention in a simple manner in that the control piston of an oil control pump is biased both with the operational oil pressure and with an additional centrifugal pressure which is generated in dependence upon the centrifugal force by an oil column in a rotating radial bore in a speed-dependent manner. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Details of the invention will become apparent from the following description of embodiments schematically illustrated in the drawings, in which:  
       FIG. 1 : shows an oil regulating pump with an external teeth wheel according to the invention, which comprises a control piston that is situated within a pump housing;  
       FIG. 2 : is an oil pressure plot of the oil pressure need of an internal combustion engine, and the course of oil pressure of a oil control pump according to the invention;  
       FIG. 3 : illustrates an oil regulating pump with an external teeth wheel according to  FIG. 1 , where the control piston, however, comprises a non-interacting differential pressure piston;  
       FIG. 4 : represents a detail of an oil regulating pump with an external teeth wheel comprising the arrangement of the oil pressure regulation according to the invention in its displacement unit;  
       FIG. 5 : is an arrangement, alternative to that of  FIG. 4 , of a solenoid valve for increasing the oil pressure. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a first embodiment of an oil regulating pump with an external teeth wheel according to the invention for an internal combustion engine, where an oil pressure regulation is effected by a control piston  1  arranged in a pump housing  2 . A driving shaft  4  supported in a housing cover  3  supports a first conveying wheel  5  in toothed engagement with a second conveying wheel  6 . The conveying wheel  6  is supported by a stationary journal bolt  7  which, on the right side of the conveying wheel  6 , supports a pressure piston  8  and, on the left side, a spring biased piston  9 . The assembly of the pressure piston  8 , journal bolt  7  and conveying wheel  6  as well as of spring biased piston  9  forms a displacement unit  10 . By axially displacing the displacement unit  10 , the tooth engagement width of the conveying wheels  5  and  6  can be varied by which fact a variation of the conveying capacity of the oil control pump is enabled in a known manner.  
      The axial displacement of the displacement unit  10  is effected as a function of forces which act onto it from the exterior. While the pressure piston  8  is constantly biased by the operational oil pressure acting in its chamber  11 , which in this embodiment is callipered behind an oil filter  32  as the supply pressure for the internal combustion engine, the force of a reset spring  12  and the pressure force of a control pressure prevailing in the spring chamber  13  act onto the spring biased piston  9 . The control pressure is generated to meet the needs in a known manner by the control piston  1  and is fed into the spring chamber  13  through a control bore  14 .  
      The control piston  1  is constantly biased on its front-sided effective surface  15  via its central bore by the operational oil pressure. A control spring  16 , counteracting the operational oil pressure, of the control piston  1  is dimensioned for a predetermined basic operational oil pressure of, for example, 1.0 bar. By a trunnion portion  17  of the control piston  1  and a pressure groove  18  on the left side, which is biased by the operational oil pressure, and a relief groove  19  on the right side, which communicates with ambient, an appropriate control pressure to the spring chamber  13  is adjusted through the control bore  14 , as is known per se. This control pressure adjusts the conveying capacity required for a certain nominal operational oil pressure by axial positioning of the displacement unit  10 .  
      In the case that the oil pressure deviates from the nominal operational oil pressure, for example due to a change of the number of revolutions of the internal combustion engine and the, thus, at first changing conveying capacity of the pump, the control piston  1 , working as an oil pressure sensor, answers with a corresponding axial displacement so that the control pressure prevailing in the spring chamber  13  is either increased or decreased, and an adaptation of the conveying capacity to the nominal operation oil pressure will be effected for the purpose of an oil pressure correction.  
      For changing the nominal operational oil pressure to adapt it to the speed-dependent variable oil pressure need of the internal combustion engine, the control piston  1  is biased with an additional force. To this end, it comprises, according to the invention, a differential pressure piston  20 . While a reference pressure surface  21  of the differential pressure piston  20 , through a pressure connection  22 , is constantly biased by the conveying pressure prevailing in a pressure chamber  23  of the pump housing  2 , a centrifugal pressure surface  24 , opposite the reference pressure surface  21 , communicates the pressure hydraulically through a pressure connection  25  to the inner end of a radial bore  26  of the rotating conveying wheel  5 . The radial bore  26 , which ends radial externally in a tooth head of the rotating conveying wheel  5 , in the rotational angular position shown of the conveying wheel  5 , is biased with the conveying pressure of the pressure chamber  23 .  
      The centrifugal action of the oil in the radial bore  26  generates a radial externally directed, speed-dependent centrifugal pressure so that the conveying pressure, which acts from the pressure chamber  23  onto the radial bore  26  at its radial inner end is reduced by the centrifugal pressure. The centrifugal pressure, which is effectively only acting onto the differential pressure piston  20 , because the conveying pressure which acts on both sides onto it compensates itself, exerts a speed-dependent additional force, which assists the control spring  16  and which depends also upon the dimension of the differential pressure piston  20 . This additional force enables a control function of the control piston  1  for the control pressure acting in the spring chamber  13  only with a correspondingly increased operational oil pressure biasing the effective surface  15 .  
      Since the radial bore  26  in the rotating conveying wheel  5 , in dependence on the rotating angle, gets also into contact with regions of the pump housing  2 , which are not biased by the conveying pressure, for example with the joining cross-sections of a suction chamber  27  not shown in the drawing, the pressure connection between the radial bore  26  and the centrifugal pressure surface  24  is only possible through a transverse connection  28  of a stationary journal bolt  29  which is oriented to the pressure chamber  23 .  
      By a higher number of radial bores in the conveying wheel  5 , for example one radial bore  26  each per conveying tooth, a more effective, and with a permanent overlap with the transverse connection  28  even a maximum centrifugal effect, can be achieved on the differential pressure piston  20 .  
      The two pressure connections  22  and  25  of the differential pressure piston  20  or even the journal bolt  29  may contain filters, for example the filters  30  and filter  31 , for avoiding pollution-caused malfunctions.  
       FIG. 2  shows an oil pressure plot for an internal combustion engine having an oil supply by an oil control pump  1  illustrated in  FIG. 1 . The speed-dependent oil pressure need p B  of the internal combustion engine amounts, for example, to 1.0 bar in minimum up to an engine number of revolutions n=2000 rpm, and then increases in the shape of a parable with raising number of revolutions up to 3.7 bar at 6000 rpm.  
      The control spring  16  of the control piston  1  ( FIG. 1 ) is dimensioned for a predetermined basic operational oil pressure p 0  which, with a low number of revolutions without an effective centrifugal pressure action, amounts at the differential pressure piston  20 , for example, to p 0 =1.0 bar as the minimum admissible operational oil pressure for the internal combustion engine.  
      The centrifugal pressure p F  generated in the radial bore  26  increases with the number of revolutions of the engine in the shape of a parable, reaching, however, according to  FIG. 2  only about 0.5 bar at a maximum motor speed of n=6000 rpm due to the relative compact dimensions of the conveying wheel  5 . Due to the relative large effective area of the differential pressure piston  20  for the centrifugal pressure p F , corresponding amplifying factor of V=6.3 is achieved so that the centrifugal pressure p F  generated in the radial bore  26 , which is only small, exerts a sufficiently high additional force onto the control piston  1 . This additional force of the differential pressure piston  20 , which assists the force of the control spring  16 , adjusts finally the operational oil pressure p R  of the internal combustion engine, which is, according to the invention, regulated in a speed-dependent manner by the oil control pump, and which may be calculated with the formula 
 
 p   R   =p   0   +p   F   ×V.  
 
      The operational oil pressure p R  must always be larger than the oil pressure need p B  of the internal combustion engine.  
      A further embodiment of a control pump, shown in  FIG. 3 , comprises a modified control piston  41 , as compared with the embodiment of  FIG. 1 . It comprises a differential pressure piston  42  axially displaceable on it, which transfers the additional force resulting from the centrifugal pressure in the radial bore  26  of the conveying wheel  5 , via a spring  43  and a spring abutment  44  to the control piston  41 .  
      Due to the, now, soft coupling of the differential pressure piston  42  to the control piston  41  by the spring  43 , it is only a very small damping effect of the differential pressure piston  42  having a relative large area which is achieved so that the control piston  41  may answer to all occurring deviations form the nominal operational oil pressure, in contrast to the differential pressure piston  20  of  FIG. 1  which is rigidly coupled to the control piston  1 .  
      With a low number of revolutions without an effective centrifugal pressure, the spring  43  is almost force-less and engages the differential pressure piston in a relieved manner. With a centrifugal pressure increased with raising speed, the differential pressure piston  42  displaces under increasing tension of the spring  43  to the right, whereby a corresponding additional force is transferred to the control piston  41 . As a desired consequence, the regulation of the operational oil pressure, that biases the effective surface  45 , occurs in the above-mentioned manner only with a correspondingly raised pressure level.  
      A stop member  46  acting for the differential pressure piston  42 , delimits, via the maximum stress of the spring  43 , the additional force to be transferred to the control piston  41  so that the maximum operational oil pressure is then limited, for example to 5 bar.  
      By the speed-dependent centrifugal pressure control of the oil control pump, the operational oil pressure is enabled to be adapted to a large extent to the oil pressure need of an internal combustion engine to be supplied so that corresponding advantages of the driving performance will result from the oil pressure minimization. In the case of an increased oil pressure need of the internal combustion engine, for example for quickly actuating a hydraulic camshaft adjuster, a pressure relief may be attained at the centrifugal pressure surface  48  of the differential pressure piston  42 , which is normally biased by the centrifugal pressure, by a solenoid valve  47 , controlled by an engine control appliance. The conveying pressure, which acts always onto the reference pressure surface  49  of the differential pressure piston  42 , shifts then the differential pressure piston  42  towards its stop  46  so that the spring  43  is in maximum stress, whereupon an increased operational oil pressure of, for example, 5 bar is regulated independently from speed. A throttle  50  situated in the pressure connection  25 , with controlled solenoid valve  47 , effects a more effective pressure reduction at the centrifugal pressure surface  48  of the differential pressure piston  42 .  
      As an alternative to the arrangement of the control piston according to the invention in a pump housing, in correspondence to the embodiments of  FIGS. 1 and 3 , in the case of a control pump with an external teeth wheel, an arrangement of the control piston within the displacement unit, which effects the change of the conveying capacity, is also possible. In this way, a very compact oil control pump comprising a simple pump housing may be realized. In this context,  FIG. 4  shows a preferred embodiment of a displacement unit  60  as an enlarged detail of an oil control pump with an external teeth wheel.  
      The displacement unit  60  comprises a conveying wheel  61  having a radial bore  62  which extends inclined to the centrifugal direction and generates the centrifugal pressure. The conveying wheel  61  is supported on a hollow journal bolt  63  which is made in one piece with a spring piston  64 . Opposite the spring piston  64 , the displacement unit  60  is completed by a pressure piston  65  fixed on the journal bolt. The axial position of the displacement unit  60  and, thus, the respective conveying capacity of the control pump with external teeth wheel, is dependent upon the operational oil pressure that acts onto the pressure piston  65  in its chamber  66 , on the one hand, and upon the opposing forces at the spring piston  64 , on the other hand, which are generated by a reset spring  67 , on the one hand, and by the control pressure that acts in its spring chamber  68 , on the other hand.  
      The control pressure, in this embodiment, is generated by an annular control piston  69  which is situated within the journal bolt  63  and is biased, at one end, by the operational oil pressure prevailing in the chamber  66 , while propping against a control spring  70  at the other end. The latter rests on a collar  71  of a pressure pipe  72  which, through its central bore  74 , feeds the control pressure generated by the control piston  69  into the spring chamber  68 . The collar  71  on the pressure pipe  72  props against a cover  73  fixed to the spring piston  64 . The pressure pipe  72  sealingly penetrates the control piston  69  with a close sliding fit. Its central bore  74 , which is closed at its end facing the chamber  66  is continuously in pressure connection with a groove  75  of the control piston  69 , for example through appropriate transversal bores in the pressure pipe  72  and in the control piston  69 .  
      The groove  75  of the control piston  69 , in the middle control position shown, overlaps slightly both a pressure bore  76  fed with the operational oil pressure from the chamber  66 , and a relief bore  78 , that communicates with a suction chamber  77 . Deviations from the nominal operational oil pressure, which acts from the chamber  66  onto the front surface of the control piston  69 , are automatically corrected in the abovementioned manner by an axial control movement of the control piston  69  and by means of the control pressure which prevails in the spring chamber  68  by an axial displacement of the displacement unit  60  that controls the conveying capacity.  
      Within the spring piston  64  is a differential pressure piston  79 , which is axially movably supported by a guide sleeve  80  in the cover  73  and in the journal bolt  63 , and which, according to the invention, is able to transfer elastically an additional force onto the control piston  69  via a spring  81 . The conveying pressure of the oil control pump, which continuously acts in a pressure pocket  82  of the spring piston  64 , biases, in principle, both sides of the differential pressure piston  79 , i.e. through a connection  83  of the spring piston  64 , on the one hand, and through the inclined radial bore  62  of the conveying wheel  61 , an oriented transversal bore  84  in the journal bolt  63  as well as by a local radial clearance between the guide sleeve  80  and the journal bolt  63 . This conveying pressure is, however, reduced in the radial bore  62  by the centrifugal pressure acting in dependence on speed so that it is only the centrifugal pressure which generates effectively an additional force on the differential pressure piston  79 .  
      This additional force generated by the differential pressure piston  79 , when it engages a stop  85 , is by then limited by the maximum stress of spring  81  so that the adjusted maximum operational oil pressure of the control pump is then limited, for example, to 5 bar.  
      In order to achieve a perfect function of the regulation, the hollow spaces in the journal bolt  63  have to be depressurized. To this end, the pressure piston  65  comprises a suction pocket  86 , that communicates with the suction chamber  77 , which causes a pressure relief of these hollow spaces through a relief bore  87  of the journal bolt  63 .  
      With an arrangement of the control piston  69  within the displacement unit  60 , a temporal increase of the operational oil pressure, in the case of an increased oil pressure need of the internal combustion engine, is also possible. To this end, a conduit  88  which is under the operational oil pressure comprises a solenoid valve  89  which, being electrically controlled by the engine control appliance, effects an increase in pressure through a throttle bore  90 , thus being superimposed to the control pressure of the spring chamber  68 . In this way, the displacement unit  60  is shifted to the right and into a position of an increased oil conveying capacity by the reset spring  67  so that an increase of the operational oil pressure will result. However, a pressure relief valve  91  limits the pressure in the spring chamber  68  to a predetermined value so that the operational oil pressure prevailing in the chamber  66  can only rise up to a corresponding maximum value. With this maximum operational oil pressure, by then being independent from the number of revolutions, the oil control pump works further with an active regulation of conveying capacity, while the control piston  69  is then out of function.  
      As an alternative to  FIG. 4 ,  FIG. 5  shows another possibility of an embodiment of a control pump with external teeth wheel embodying a centrifugal pressure regulation integrated into the displacement unit  60 . In a supply conduit  92 , which feeds the operational oil pressure into the chamber  66 , there is a solenoid valve  93  which is closed, when the engine control appliance demands an increase of the operational oil pressure, and which, at the same time, relieves the chamber  66  from pressure through a connection piece  94 . The reset spring  67  moves then the displacement unit  60  into the position of maximum conveying capacity, which will result in an increase of the operational oil pressure. Due to the fact that the regulation of conveying capacity is then inactive, a usual by-pass regulation comprising a pressure relief valve  95  must then be provided for limiting the maximum operational oil pressure, for example to 6 bar.  
      In  FIG. 5 , and in contrast to  FIG. 4 , the control piston  69 , biased by the operational oil pressure form the chamber  66 , props against the differential pressure piston  79  only via a pre-stressed control spring  97 .  
      In comparison with the embodiment of  FIG. 4 , this simplified embodiment has, however, a somewhat different control characteristic as a consequence, because the additional force, generated by centrifugal pressure on the differential pressure piston  79 , can only influence the pressure regulation from a certain operational number of revolutions on, thereby overcoming the pre-stressing force of the control spring  96 .  
      An oil-filled throttle chamber  97 , formed between the cover  73  of the guide sleeve  80  of the differential pressure piston  79  and the collar  71  of the pressure pipe  72 , with an appropriate choice of the clearance between the guide sleeve  80  and the collar  71 , may dampen the movement of the differential pressure piston  79 . In this way, one avoids particularly a transfer of quick control movements of the control piston  69  through its elastic coupling to the differential pressure piston  79 , so that with an appropriate dampening it remains in almost unchanged position, thus enabling a stable regulation function.  
      The control device according to the invention uses the centrifugal pressure generated in oil-filled radial bores of rotating components due to the centrifugal force in order to establish a speed-dependent regulation of the oil pressure in oil control pumps. In this way, with all operational temperature, a consumption-favorable reduction of oil pump driving power for internal combustion engines is achieved.