Patent Publication Number: US-2022235766-A1

Title: Variable displacement lubricant pump

Description:
CROSS REFERENCE TO PRIOR APPLICATIONS 
     This application is a U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2019/063280, filed on May 23, 2019. The International Application was published in English on Nov. 26, 2020 as WO 2020/233812 A1 under PCT Article 21(2). 
    
    
     FIELD 
     The present invention is directed to a variable displacement lubricant pump for providing a pressurized lubricant. The present invention in particular relates to a mechanical variable displacement lubricant pump for providing a pressurized lubricant for an internal combustion engine. 
     BACKGROUND 
     The lubricant pump is mechanically driven by the engine, for example, via a gear or a belt, and is fluidically coupled to the engine for pumping the pressurized lubricant to and through the engine. The variable displacement of the lubricant pump allows a controlling and/or a stabilizing of a pump discharge pressure of the lubricant pump and thereby allows, for example, a controlling and/or stabilizing of a lubricant gallery pressure in the engine. 
     WO 2018/196991 A1 describes a typical variable displacement lubricant pump for providing a pressurized lubricant for an internal combustion engine. The lubricant pump is provided with a static pump housing and is provided with a shiftable control ring which is arranged within the pump housing and which radially confines a substantially cylindrical pumping chamber. The lubricant pump comprises an outlet chamber which is partially confined by a radial outside of the control ring. The lubricant pump is provided with a rotatable pump rotor which is arranged within the pumping chamber and which is provided with several rotor vanes which define several pumping chamber compartments. The rotor vanes and, as a result, the pumping chamber compartments, rotate within the shiftable control ring. The lubricant pump comprises a pumping chamber pressure section which is defined by those pumping chamber compartments which are fluidically connected with the outlet chamber via a discharge opening. The lubricant pump comprises a slide bearing which adjoins the outlet chamber and which shiftably supports the control ring within the pump housing. The slide bearing comprises a first slide bearing surface which is defined by the pump housing and which extends in a slide plane, and comprises a second slide bearing surface which is defined by the control ring. 
     Due to the outlet chamber geometry of the above-described lubricant pump, the control ring is pushed away from the outlet chamber and towards the pump inlet if the outlet chamber is filled with the pressurized lubricant. The second bearing surface which is defined by the control ring is therefore moved away from the first bearing surface which is defined by the pump housing so that a significant bearing gap is formed. This bearing gap can provide a leakage path for lubricant, for example, from the outlet chamber into a control chamber which is located at an opposite side of the slide bearing. This undesired lubricant leakage into the control chamber can adversely affect the control of the control ring position and, as a result, can impair the pump discharge pressure control and/or the pump performance. 
     The first slide bearing is therefore provided with a seal element to avoid a lubricant leakage via the bearing gap. This seal element, however, increases the slide friction of the friction bearing and thereby reduces the lubricant pump&#39;s efficiency. The pump housing and/or the control ring must also be provided with a specific holding device to hold the seal element in place and to avoid a slipping of the seal element out of the bearing gap. 
     SUMMARY 
     An aspect of the present invention is to provide a cost-efficient, reliable and efficient variable displacement lubricant pump. 
     In an embodiment, the present invention provides a variable displacement lubricant pump for providing a pressurized lubricant. The variable displacement lubricant pump includes a static pump housing, a control ring which is arranged within the static pump housing, an outlet chamber, a rotatable pump rotor, a pumping chamber pressure section, and a slide bearing. The control ring is configured to be shiftable and to radially confine the pumping chamber which is configured to be substantially cylindrical. The control ring comprises a radial outside, an inside pressure surface, and an outside pressure surface. The outlet chamber is partially confined by the radial outside of the control ring. An interface between the outlet chamber and the control ring defines the outside pressure surface of the control ring. The rotatable pump rotor is arranged within the pumping chamber. The rotatable pump rotor comprises a plurality of rotor vanes which define a plurality of pumping chamber compartments. The pumping chamber pressure section is defined by the plurality of pumping chamber compartments which are directly fluidically connected with the outlet chamber via a discharge opening. An interface between the pumping chamber pressure section and the control ring defines the inside pressure surface of the control ring. The slide bearing is arranged to adjoin the outlet chamber and is configured to shiftably support the control ring within the static pump housing. The slide bearing comprises a first slide bearing surface which is defined by the static pump housing and which extends in a slide plane, and a second slide bearing surface which is defined by the control ring. An outside projection area is defined by an orthographic projection of the outside pressure surface onto the slide plane. A maximum inside projection area is defined by an orthographic projection of the inside pressure surface onto the slide plane. The outside projection area is smaller than the maximum inside projection area. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described in greater detail below on the basis of embodiments and of the drawings in which: 
         FIG. 1  shows a partially sectioned view of a variable displacement lubricant pump according to the present invention; 
         FIG. 2  shows a magnification of a part of the lubricant pump of  FIG. 1 ; and 
         FIG. 3  shows a schematic illustration of orthographic projection areas of control ring pressure surfaces onto a slide plane of the lubricant pump of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The variable displacement lubricant pump according to the present invention is provided with a static pump housing which defines a pump inlet and a pump outlet. The pump inlet is typically fluidically connected with a lubricant tank, and the pump outlet is fluidically connected with an engine for providing the engine with pressurized lubricant. 
     The variable displacement lubricant pump according to the present invention is also provided with a shiftable control ring which is arranged within the pump housing and which radially confines a substantially cylindrical pumping chamber. The control ring can, for example, be linearly shiftable with respect to the pump housing. The control ring is in any case not pivotably hinged within the pump housing. The pumping chamber is typically provided with an exactly circular radial cross section. The pumping chamber can, however, also be provided with a non-exactly circular radial cross section, for example, with a slightly elliptical cross section, to improve the pump efficiency and/or the pump pressure control. 
     The variable displacement lubricant pump according to the present invention is also provided with an outlet chamber which is fluidically connected with the pump outlet. The outlet chamber is located to directly adjoin the control ring and is partially confined by a radial outside of the control ring. The outlet chamber is filled with pressurized lubricant during pump operation. An interface between the outlet chamber and the control ring, i.e., the part of the radial outside surface of the control ring which is in direct fluidic contact with the outlet chamber, defines an outside pressure surface of the control ring. 
     The variable displacement lubricant pump according to the present invention is also provided with a rotatable pump rotor which is arranged within the control ring and which is in particular arranged within the pumping chamber. The pump rotor comprises several rotor vanes which define several pumping chamber compartments. The rotor vanes and, as a result, the pumping chamber compartments, rotate within the control ring and thereby pump the lubricant from an inlet chamber into the outlet chamber. The pump rotor is mechanically driven by the engine, for example, via a belt drive or a gearing. The pump rotor axis of rotation is static so that shifting the control ring changes the eccentricity of the pump rotor with respect to the surrounding control ring to thereby control the displacement and thereby the volumetric performance of the pump. 
     The variable displacement lubricant pump according to the present invention is also provided with a pumping chamber pressure section which is defined by those pumping chamber compartments which are located to adjoin a discharge opening of the control ring and which thereby are fluidically connected with the outlet chamber via the discharge opening. The pumping chamber pressure section is filled with pressurized lubricant during pump operation. As a result of the rotation of the pumping chamber compartments, the extent of the pumping chamber pressure section varies between a minimum and a maximum extent during pump operation. An interface between the pumping chamber pressure section and the control ring, i.e., the part of the radial inside surface of the control ring which is in direct fluidic contact with the pumping chamber pressure section, defines an inside pressure surface of the control ring. 
     The variable displacement lubricant pump according to the present invention is also provided with at least one slide bearing which is located to adjoin the outlet chamber and via which the control ring is shiftably supported within the pump housing. The slide bearing comprises a first slide bearing surface and a corresponding second slide bearing surface. The first slide bearing surface is defined by the pump housing and extends in a slide plane. The second slide bearing surface is defined by the control ring and is provided opposite and parallel to the first slide bearing surface. 
     During pump operation, the outlet chamber and the pressure region of the pumping chamber are both filled with pressurized lubricant so that the inside pressure surface as well as the outside pressure surface of the control ring are loaded with the same hydraulic pressure, in particular with the hydraulic pressure of the pressurized lubricant. The strength and in particular the direction of a total hydraulic load force (generated by the lubricant pressure and affecting the control) is as a result only determined by the geometry of the pressure surfaces. A strength and a direction of an effective load force fraction which is effective perpendicular to the slide plane is in particular defined by the ratio of projection areas being defined by the orthographic projection of the pressure surfaces onto the slide plane. 
     According to the present invention, the control ring and the pump housing are designed so that an outside projection area defined by the orthographic projection of the outside pressure surface onto the slide plane is smaller compared to a maximum inside projection area defined by the orthographic projection of the inside pressure surface onto the slide plane. During pump operation, an effective hydraulic load force is as a result generated which is effective perpendicular to the slide plane and towards the outlet chamber so that the second slide bearing surface of the control ring is pressed against the first slide bearing surface of the pump housing. This reduces a bearing gap between the slide bearing surfaces and thereby avoids or at least significantly suppresses a lubricant leakage via the slide bearing without requiring any separate sealing element in the slide bearing. The variable displacement lubricant pump according to the present invention provides a reliable and efficient control of the control ring position and thereby of the volumetric pump performance. Since no sealing element is required within the slide bearing, the variable displacement lubricant pump according to the present invention can be realized very cost-efficiently. 
     In an embodiment of the present invention, the projection area of the outside pressure surface onto the slide plane can, for example, be smaller compared to a minimum projection area of the inside pressure surface onto the slide plane. The effective load force which presses together the slide bearing surface is thereby generated independently of the rotational position of the motor rotor. This minimizes the bearing gap and as a result provides a very efficient and reliable lubricant pump. 
     The outside pressure surface can, for example, be arranged completely at an outlet-sided lateral side of a pumping chamber centerline which extends parallel to the slide plane. The outside pressure surface can, for example, be arranged within an angular range of 45° to 135° with respect to a pumping chamber center and starting at the pumping chamber centerline. The outside pressure surface thereby generates a hydraulic load force which is effective substantially completely perpendicular to the slide plane and, as a result, does not significantly affect the control of the control ring position. This provides a reliable and efficient lubricant pump. 
     In an embodiment of the present invention, a control chamber can, for example, be provided for hydraulically controlling the control ring position. The control chamber is typically provided at a front side of the control ring and circumferentially adjacent to the outlet chamber. The control chamber is provided with an interface with the control ring which extends substantially perpendicular to the slide plan so that the hydraulic pressure within the control chamber loads the control ring in a direction which is parallel to the slide plane. The control chamber surrounds a large circumferential section of the control ring and in particular extends to the slide bearing so that the control chamber is fluidically separated from the outlet chamber only by the slide bearing. The control chamber is thereby provided with a relatively large interface with the control ring which allows the generating of a relatively high hydraulic actuation force with a relatively low hydraulic control chamber pressure. 
     An embodiment of the present invention is described below under reference to the enclosed drawings. 
       FIGS. 1 and 2  show a variable displacement lubricant pump  10  for providing a pressurized lubricant to an internal combustion engine  12 . The lubricant pump  10  is provided with a static pump housing  14 , with a shiftable control ring  16 , and with a rotatable pump rotor  18 . The control ring  16  is arranged within the pump housing  14  and radially confines a substantially cylindrical pumping chamber  20 . 
     The lubricant pump  10  comprises an inlet chamber  22  which is fluidically connected with a lubricant tank  24  and which is filled with lubricant substantially having atmospheric pressure during pump operation. The inlet chamber  22  is fluidically connected with the pumping chamber  20  via a suction opening  26  of the control ring  16 . 
     The lubricant pump  10  comprises an outlet chamber  28  which is fluidically connected with the engine  12  and which is filled with pressurized lubricant during pump operation. The outlet chamber  28  is located at a lateral side of the pumping chamber  20  substantially opposite with respect to the inlet chamber  22 . The outlet chamber  28  is partially confined by a radial outside of the control ring  16 , wherein an interface between the outlet chamber  28  and the control ring  16  defines an outside pressure surface  30  of the control ring. The outside pressure surface  30  is completely located at an outlet-sided lateral side of the pumping chamber  20 . The outside pressure surface  30  is in particular located within a circle sector S which extends over an angular range of 45° to 135° with respect to a pumping chamber center C and starting at a pumping chamber centerline L which extends parallel to a slide plane P of the control ring  16 . The outlet chamber  28  is fluidically connected with the pumping chamber  20  by a discharge opening  31  of the control ring  16 . 
     The lubricant pump  10  comprises a control chamber  32  which is located circumferentially between the inlet chamber  22  and the outlet chamber  28  at a front side of the control ring  16 . The control chamber  32  is filled with lubricant during pump operation. The lubricant pressure within the control chamber  32  is controllable to thereby hydraulically control the position of the control ring  16  and, as a result, the volumetric pump performance. 
     The lubricant pump  10  comprises a slide bearing  42  via which the control ring  16  is shiftably supported within the pump housing  14 . The slide bearing  42  is located adjoining the outlet chamber  28  and the control chamber  32  and fluidically separates the control chamber  32  and the outlet chamber  28 . The slide bearing  42  comprises two corresponding slide bearings surfaces  44 ,  46  which are in touching contact with each other. The first slide bearing surface  44  is defined by the pump housing  14 , and the second slide bearing surface  46  is defined by the control ring  16 . The first slide bearing surface  44  extends in the slide plane P, and the second slide bearing surface  46  is parallel with respect to the first slide bearing surface  44  so that the control ring  16  is shiftable within the pump housing  14  parallel to the slide plane P. 
     The pump rotor  18  is arranged within the pumping chamber  20  and comprises nine rotor vanes  33   a - i  defining nine pumping chamber compartments  34 a-i. During pump operation, the rotor vanes  33   a - i  and, as a result, the pumping chamber compartments  34   a -I, rotate within the pumping chamber  20  and thereby pump lubricant from the inlet chamber  22  into the outlet chamber  28 . The pump rotor  18  is mechanically driven by the engine  12 , for example, via a belt drive or a gearing, so that the pump rotor  18  always rotates with a rotational speed which is directly proportional to a rotational speed of the engine  12 . 
     Those of the pumping chamber compartments  34 a-i which are presently located adjoining the discharge opening and, as a result, which are fluidically connected with the outlet chamber  28  via the discharge opening  31 , define a pumping chamber pressure section  36 . For the exemplary pump rotor position shown in  FIG. 1 , the pumping chamber pressure section  36  is defined by the pumping chamber compartments  34   a - d.  An interface between the pumping chamber pressure section  36  and the control ring  16  defines an inside pressure surface  40  of the control ring. As a result of the rotation of the pump rotor  18  and thereby of the pumping chamber compartments  34   a - i,  the actual circumferential extent of the pumping chamber pressure section  36  and, as a result, of the inside pressure surface  40 , varies between a minimum extent E 1  and a maximum extent E 2  during pump operation. 
     The orthographic projection of the outside pressure surface  30  onto the slide plane P defines an outside projection area A 1 . Depending on the present rotational position of the pump rotor  18 , the orthographic projection of the inside pressure surface  40  onto the slide plane P defines a present inside projection area A 2 , wherein the extent of the present inside projection area A 2  varies between a minimum inside projection area A 2 - min  and a maximum inside projection area A 2 - max.    FIG. 3  shows a schematic illustration of the outside projection area Al and the present inside projection area A 2  for the exemplary rotor position shown in  FIGS. 1 and 2 , as well as of the minimum inside projection area A 2 - min  and the maximum inside projection area A 2 - max.  According to the present invention, the pump housing  14  and the control ring  16  are designed so that the outside projection area A 1  is smaller compared to the maximum inside projection area A 2 - max.  In the shown embodiment of the present invention, the outside projection area A 1  is smaller compared to the minimum inside projection area A 2 - min.    
     During pump operation, the outlet chamber  28  and the pumping chamber pressure section  36  are both filled with the pressurized lubricant so that the outside pressure surface  30  and the inside pressure surfaces  40  are loaded with the same hydraulic pressure. Since the outside projection area A 1  is smaller than the minimum inside projection area A 2 - min,  the control ring  16  is constantly hydraulically loaded with an effective load force F during pump operation, wherein the effective load force F is effective perpendicular to the slide plane P and towards the outlet chamber  28 . The second slide bearing surface  46  of the control ring  16  is thereby constantly pressed against the first slide bearing surface  44  of the pump housing  14  during pump operation so that the gap between the slide bearing surfaces  44 , 46  is minimized. 
     The present invention is not limited to embodiments described herein; reference should be had to the appended claims. 
     LIST OF REFERENCE NUMERALS 
       10  Variable displacement lubricant pump 
       12  Internal combustion engine 
       14  Pump housing 
       16  Control ring 
       18  Pump rotor 
       20  Pumping chamber 
       22  Inlet chamber 
       24  Lubricant tank 
       26  Suction opening 
       28  Outlet chamber 
       30  Outside pressure surface 
       31  Discharge opening 
       32  Control chamber 
       33   a - i  Rotor vanes 
       34   a - i  Pumping chamber compartments 
       36  Pumping chamber pressure section 
       40  Inside pressure surface 
       42  Slide bearing 
       44  First slide bearing surface 
       46  Second slide bearing surface 
     A 1  Outside projection area 
     A 2  Present inside projection area 
     A 2 - min  Minimum inside projection area 
     A 2 - max  Maximum inside projection area 
     C Pumping chamber center 
     E 1  Minimum extent 
     E 2  Maximum extent 
     F Effective load force 
     L Pumping chamber centerline 
     P Slide plane 
     S Circle sector