Abstract:
A variable displacement lubricant pump for providing a pressurized lubricant for an internal combustion engine includes a control ring configured to be shiftable, a pump rotor comprising a plurality of slidable vanes which are configured to rotate in the control ring, a hydraulic control chamber configured to directly actuate the control ring, a valve bore, and a temperature control valve configured to connect or disconnect the temperature control opening to an atmospheric pressure. The hydraulic control chamber comprises a side wall comprising a temperature control opening arranged therein. The temperature control valve comprises a switching strip which comprises a switching temperature. The switching strip is configured to be in an open position if a temperature is below the switching temperature, and to be in a closed position if the temperature is above the switching temperature so as to close the valve bore.

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/EP2012/072135, filed on Nov. 8, 2012. The International Application was published in English on May 15, 2014 as WO 2014/071976 A1 under PCT Article 21(2). 
     FIELD 
     The present invention relates to a variable displacement lubricant pump for providing pressurized lubricant for an internal combustion engine. 
     BACKGROUND 
     The mechanical pump comprises a pump rotor with radially slidable vanes rotating within a shiftable control ring, whereby the control ring is pushed by a plunger which pushes the control ring into high pumping volume direction. The plunger is shiftably arranged in a control chamber. The pump comprises a pressure control system for controlling the discharge pressure of the pressurized lubricant leaving the pump. The pump&#39;s discharge pressure is controlled by controlling the position of the shiftable control ring by controlling the pressure in the hydraulic control chamber, thereby moving the plunger. 
     Variable displacement vane pumps have previously been described in WO 2005/026553 A1. The pump is provided with a pressure control system for controlling the discharge pressure of the lubricant. The pressure control system comprises a first pressure control chamber, wherein a first plunger is provided so as to be axially movable. The first pressure control chamber is connected via a pressure conduit with the pump outlet port. The pressure control system also comprises a separate control element which is realized as a cylinder-piston-element which keeps the pressure of the pressurized lubricant provided by the pump at a more or less constant level independent of the rotational speed of the pump rotor. This is realized by opening and closing a control outlet of the first pressure control chamber, thereby moving the control ring into a low pumping volume direction or pushing the control ring into a high pumping volume direction. 
     The lubricant pressure demand of the engine and the mechanical stress of the pump is, however, dependent on working conditions, such as the engine&#39;s and the lubricant&#39;s temperature. 
     SUMMARY 
     An aspect of the present invention is to provide a simple and reliable variable displacement lubricant vane pump with different lubricant pressures levels which are dependent on the lubricant temperature. 
     In an embodiment, the present invention provides a variable displacement lubricant pump for providing a pressurized lubricant for an internal combustion engine which includes a control ring configured to be shiftable, a pump rotor comprising a plurality of slidable vanes which are configured to rotate in the control ring, a hydraulic control chamber configured to directly actuate the control ring, a valve bore, and a temperature control valve configured to connect or disconnect the temperature control opening to an atmospheric pressure. The hydraulic control chamber comprises a side wall comprising a temperature control opening arranged therein. The temperature control valve comprises a switching strip which comprises a switching temperature. The switching strip is configured to be in an open position if a temperature is below the switching temperature, and to be in a closed position if the temperature is above the switching temperature so as to close the valve bore. 
    
    
     
       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 schematic representation of a variable displacement lubricant pump including a temperature control valve, the pump being arranged in a lubricant circuit including an internal combustion engine; 
         FIG. 2  shows a cross section of an embodiment of a temperature control valve in the closed position; 
         FIG. 3  shows the temperature control valve of  FIG. 2  in the open position; 
         FIG. 4  shows an embodiment of a simpler temperature control valve in the open position; and 
         FIG. 5  shows the temperature control valve of  FIG. 4  in the closed position. 
     
    
    
     DETAILED DESCRIPTION 
     The variable displacement lubricant vane pump according to the present invention is provided with a temperature control opening in a wall of the control chamber. A temperature control valve is provided downstream of the temperature control opening which connects or disconnects the temperature control opening to the atmospheric pressure dependent on the lubricant temperature T. The temperature control valve is provided with a switching strip with a switching temperature, whereby the switching strip is in the open position if the lubricant temperature T is below a switching temperature T s  and is in the closed position if the lubricant temperature T is above of the switching temperature T s  of the switching strip. 
     In an embodiment of the present invention, the switching strip can, for example, be provided as a bimetal strip. A bimetal switching strip is a simple, cost-effective, and reliable valve concept which allows two different lubricant discharge pressure levels to be defined dependent on the lubricant temperature. 
     In an embodiment of the present invention, the temperature control valve can, for example, be provided with a separate closing body strip. The closing body strip is actuated by the switching strip. The valve bore is directly closed and left open by the closing body strip, and not directly by the switching strip. 
     In an embodiment of the present invention, the closing body strip can, for example, be preloaded in its closing position so that the closing body strip defines a non-return reed valve. The closing body strip can, for example, be realized as a flexible tongue body. The temperature control valve is a unidirectional non-return reed valve in the open position of the switching strip. In the closed position of the switching strip, the closing body strip is forced and kept in its closing position so that the temperature control valve is closed in both flow directions. 
     In an embodiment of the present invention, a stop strip can, for example, be provided to limit the opening angle of the switching strip. The stop strip is stiff and remains in the same position and angle independently of the lubricant temperature, and limits the maximum opening movement of the switching strip. 
     In an embodiment of the present invention, the strips can, for example, be provided as a strip packet which can, for example, be held together by one single screw. The strips defining the strip packet generally have the same contour so as to define a rectangular strip packet. 
     In an embodiment of the present invention, the switching temperature T s  of the switching strip is between 60° C. and 100° C., for example, between 70° C. and 90° C. 
     In an embodiment of the present invention, the temperature control opening can, for example, be provided at a side wall of the control chamber, and a plunger element of the control ring can, for example, shift along the side wall to thereby cover or not cover the control opening. 
     The present invention is hereinafter further described with a detailed description of an embodiment of the present invention under reference to the drawings. 
       FIG. 1  shows a variable displacement lubricant pump  10  as a part of a pumping system  100  for supplying an internal combustion engine  70  with pressurized lubricant. From the internal combustion engine  70 , the lubricant flows back via a flow-back conduit  86  to a lubricant tank  50  with more or less atmospheric pressure. 
     The lubricant pump  10  comprises a pump housing  11  having a cavity  16  in which a radially shiftable control ring  12  translates. The shiftable control ring  12  encircles a pump rotor  13  which is provided with numerous radially slidable vanes  14 , whereby the vanes  14  rotate inside the shiftable control ring  12 . The pump housing  11  comprises two pump side walls  15  of which one is not shown in  FIG. 1  so that the inside of the lubricant pump  10  can be seen. The pump side walls  15 , the vanes  14 , the pump rotor  13 , and the shiftable control ring  12  define five rotating pump chambers  17 . One of the side walls  15  is provided with a pump chamber inlet opening  18  and with a pump chamber outlet opening  19 . 
     The shiftable control ring  12  is provided with a first plunger  24  housed in part in a first hydraulic control chamber  25 , and with a second plunger  22  housed in part in a second hydraulic control chamber  23  opposite to the first hydraulic control chamber  25 . 
     A pretensioned spring  28  inside the first hydraulic control chamber  25  exerts a pushing force on the first plunger  24 . Both hydraulic control chambers  25 ,  23  are formed inside and by the pump housing  11 . The pump housing  11  also comprises a pump intake port  20  to suck the lubricant from the lubricant tank  50 , and a pump outlet port  21  to feed lubricant with a discharge pressure to the internal combustion engine  70 . A conduit  80  extends from the pump outlet port  21  to supply the internal combustion engine  70 . 
     The lubricant which is supplied to the internal combustion engine  70  is conducted to the second hydraulic control chamber  23  via a pressure conduit  81 , and the lubricant is fed to the first hydraulic control chamber  25  via pressure conduits  82 ,  87 . More specifically, the lubricant in pressure conduit  82  is finally fed to the first hydraulic control chamber  25  via pressure conduit  87  through a pressure throttle valve  67  in which a calibrated pressure drop occurs as the lubricant flows through. 
     The pressure conduits  82 ,  88  are connected to a control port of a first pressure control valve  60  by a conduit. The first pressure control valve  60  comprises a cylinder  65  housing a piston  61 . More specifically, the piston  61  comprises a first portion  62  and a second portion  64  connected to each other by a rod  63 . The piston portions  62  and  64  are equal in cross section to the cross section of the cylinder  65 , whereas the rod  63  is smaller in cross section than the cylinder  65 . The cylinder  65  is provided with an inlet port  66  connected hydraulically to the first hydraulic control chamber  25  by a conduit  83  and is provided with an outlet port which is hydraulically connected to the lubricant tank  50  by a conduit  84 . Another conduit  88  transfers the discharge pressure in conduit  82  to the front surface of the first portion  62  of piston  61 . The dashed line in  FIG. 1  shows the situation when the inlet port  66  of the first pressure control valve  60  is closed by the second portion  64  of the piston  61 . 
     The first hydraulic control chamber  25  is provided with a temperature control opening  26  connected hydraulically to a temperature control valve  30 . The temperature control opening  26  is provided in a side wall  27  of the first hydraulic control chamber  25  so that the first plunger  24 , sliding along the side wall  27 , thereby covers and closes the temperature control opening  26  or leaves the temperature control opening  26  open, dependent on the position of the first plunger  24  inside the first hydraulic control chamber  25 . If the temperature control valve  30  is open, the first hydraulic control chamber  25  is connected to the lubricant tank  50  having atmospheric pressure. 
     An embodiment of the temperature control valve  30  is shown in  FIGS. 2 and 3 . The temperature control valve  30  is arranged downstream of the temperature control opening  26  and connects or disconnects, dependent on the lubricant temperature T, the temperature control opening  26  to the atmospheric pressure of the lubricant tank  50  via a lubricant conduit  89 . The temperature control valve  30  is provided with a switching strip  31  with a switching temperature T s , whereby the switching strip  31  is in the open position if the lubricant temperature T is below the switching temperature T s  and is in the closed position if the lubricant temperature T is above of the switching temperature T S  of the switching strip  31 . The switching temperature T s  of the switching strip is around 80° C. The switching strip  31  is provided as a bimetal strip consisting of two different metal strips  34 ,  35  of different thermal expansion coefficients. 
     The side of the switching strip  31  orientated to a valve bore  40  could be provided with a rubber layer  36  in order to improve the sealing when the switching strip  31  closes the valve bore  40 . The rubber layer  36  could be co-molded or assembled, as a separate part, with the switching strip  31 . 
     The temperature control valve  30  is provided with a separate closing body strip  32  consisting of a single metal strip body  39  of which the side orientated to a valve bore  40  is provided with a rubber layer  36 . The rubber layer  36  is co-molded or assembled, as a separate part, with the single metal strip body  39  of the separate closing body strip  32 . The valve bore  40  is directly covered by the separate closing body strip  32 , and is not directly covered by the switching strip  31 . The separate closing body strip  32  is preloaded into its closing position so that the separate closing body strip  32  defines a non-return reed valve. In the open position of the switching strip  31 , as shown in  FIG. 3 , the temperature control valve  30  works as a unidirectional non-return reed valve so that the lubricant from first hydraulic control chamber  25  can flow to the lubricant tank  50 . In the closed position of the switching strip  31 , as shown in  FIG. 2 , the temperature control valve  30  is totally closed in both flow directions. 
     A stop strip  33  is provided opposite to the separate closing body strip  32 , with respect to the switching strip  31 , to limit the maximum opening angle of the switching strip  31 . The stop strip  33  is made out of a metal strip body  38  and is stiff at every lubricant temperature. The stop strip  33  limits the opening movement of the switching strip  31  to a maximum opening angle. 
     The three strips  32 ,  31 ,  33  are provided as a strip packet  42  which is held together and mounted to the pump housing  11  by one single assembling screw  37 . The three strips  32 ,  31 ,  33  defining the strip packet  42  have the same contour so that they define a strip packet  42  which is rectangular. 
     An embodiment of a temperature control valve  30 ′ is shown in  FIGS. 4 and 5 . This temperature control valve  30 ′ is simpler than the temperature control valve  30  of the above embodiment, and is only provided with the switching strip  31 , of which the side orientated to the valve bore  40  is provided with the rubber layer  36 . 
     The present invention is not limited to embodiments described herein; reference should be had to the appended claims.