Abstract:
A recirculation valve for a pump having a regulator spool, a first resilient biasing member and a control valve. The first resilient biasing member biases the regulator spool in a first position in which flow of a liquid from a first port of the pump to a second port of the pump is prevented. The control valve controls the force required to move the regulator spool against the first resilient biasing member to a second position in which flow of the liquid from the first port to the second port is enabled.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to GB patent application No. 1504058.7 filed on Mar. 10, 2015, the disclosure of which is hereby incorporated in its entirety by reference herein. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to a recirculation valve. More specifically, the present invention relates to an electric recirculation valve, for example an electric recirculation valve for a pump for controlling or regulating oil recirculation in internal combustion engines. 
       BACKGROUND 
       [0003]    Lubricating oil is circulated through engines in order to reduce friction between moving parts and to remove heat from pistons, bearings and shafts. 
         [0004]    Oil pumps are known to include a recirculation valve for controlling or regulating the delivery of oil to an engine. Such recirculation valves are designed to open when the pressure of oil in an engine reaches a predetermined value and prevent excess oil flow being delivered to the engine main gallery. 
         [0005]    One example of a known recirculation valve is a directional control valve having a control chamber, a spring and a spool. When the pressure of oil in the engine exceeds the pressure in the control chamber by more than the compression pressure of the spring, the spool moves beyond the break edge of the pump, allowing oil to flow from the outlet of the pump to the inlet. In this way excess oil is recirculated and not delivered to the engine main gallery or other oil consumers within the lubrication system. 
         [0006]    Since such recirculation valves only open at a single, predetermined regulation pressure, which is controlled by the compression pressure of the spring, it is only possible to regulate the engine oil pressure at a single, predetermined feedback pressure. This can result in a delivery of oil flow that is greater than the optimum amount at a given operating condition. For example, during operating conditions where the piston cooling jets are inoperable a much lower pump output can be tolerated. Reducing the pump output to the ideal optimum reduces the work that the pump must do and in turn reduces the parasitic drag on the engine, leading to increased engine efficiency. 
       SUMMARY 
       [0007]    According to a first aspect of the present invention there is provided an electric recirculation valve for a pump, the electric recirculation valve comprising a regulator spool, a first resilient biasing means and a control valve, wherein the first resilient biasing means biases the regulator spool in a first position in which flow of a liquid from a first port of the pump to a second port of the pump is prevented; and the control valve controls the force required to move the regulator spool against the first resilient biasing means to a second position in which flow of the liquid from the first port to the second port is enabled. 
         [0008]    The control valve advantageously enables the force required to move the regulator spool from the first position, in which recirculation flow is not possible, to the second position, in which recirculation flow is enabled, to be varied. 
         [0009]    The control valve may comprise a second resilient biasing means and a vent. The control valve may be an electromagnetic solenoid valve, for example an electromagnetic solenoid valve having an on/off solenoid or a proportional solenoid. 
         [0010]    The use of an on/off solenoid enables the force required to move the regulator spool to be set at a maximum and a minimum force. The use of a proportional solenoid enables the force required to move the regulator spool to be varied over a range between a maximum force and a minimum force. 
         [0011]    According to a second aspect of the present invention, there is provided a pump comprising a first port, a second port and a recirculation valve comprising a regulator spool and a first resilient biasing means, wherein the first resilient biasing means biases the regulator spool in a first position in which flow of a liquid from the first port to the second port is prevented; and the pump further comprises a control valve to control the force required to move the regulator spool against the first resilient biasing means to a second position, in which flow of the liquid from the first port to the second port is enabled. 
         [0012]    The control valve may be housed within the pump. The control valve may further include a second resilient biasing means and a vent. The control valve may be an electromagnetic solenoid valve, for example an electromagnetic solenoid valve comprising an on/off solenoid or a proportional solenoid. 
         [0013]    According to a third aspect of the present invention, there is provided a method of controlling the recirculation of a liquid between a first port and a second port, the method comprising the steps of: (a) providing a recirculation valve comprising a regulator spool and a first resilient biasing means, wherein the first resilient biasing means biases the regulator spool in a first position in which flow of a liquid from the first port to the second port is prevented; (b) providing a control valve having a second resilient biasing means and a vent; and (c) using the control valve to vary the force required to move the regulator spool against the first resilient biasing means to a second position in which flow of the liquid from the first port to the second port is enabled. 
         [0014]    The method may further comprise increasing the force acting on the regulator spool against the first resilient biasing means to enable movement of the regulator spool to the second position. 
         [0015]    Alternatively, the method may further comprise reducing the force acting on the first resilient biasing means to enable movement of the regulator spool to the second position. 
         [0016]    The control valve may be an electromagnetic solenoid valve, for example an electromagnetic solenoid valve comprising an on/off solenoid or a proportional solenoid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    An example of a recirculation valve in accordance with the present invention will now be described with reference to the accompanying figures in which: 
           [0018]      FIG. 1  is a part-sectioned side view of a pump assembly having a recirculation valve according to a first embodiment of the present invention; 
           [0019]      FIG. 2  is a hydraulic circuit diagram of the pump assembly of  FIG. 1  with the electromagnetic valve and the regulator spool valve shown in the closed position; 
           [0020]      FIG. 3  is a hydraulic circuit diagram of the pump assembly of  FIG. 1  with the electromagnetic valve shown in the open position and the regulator spool valve shown in the recirculating position; 
           [0021]      FIG. 4  is a hydraulic circuit diagram of a pump assembly having a recirculation valve according to a second embodiment of the present invention; 
           [0022]      FIG. 5  is a hydraulic circuit diagram of a pump assembly having a recirculation valve according to a third embodiment of the present invention; 
           [0023]      FIG. 6  is a hydraulic circuit diagram of a pump assembly having a recirculation valve according to a fourth embodiment of the present invention; 
           [0024]      FIG. 7  is a hydraulic circuit diagram of a pump assembly having a recirculation valve according to a fifth embodiment of the present invention; and 
           [0025]      FIG. 8  is a hydraulic circuit diagram of the pump assembly of  FIG. 7  with the electromagnetic solenoid valve vented to the inlet port. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    Referring now to  FIG. 1  there is shown a pump assembly  10  comprising a pump housing  12 , a pump cover  14  and a recirculation valve  15  according to a first embodiment of the invention. The recirculation valve  15  comprises a regulator spool valve  16 , an electromagnetic solenoid valve  18  and a regulator spring  52 . 
         [0027]    The housing  12  comprises gear pocket  22 , a valve cavity  24  and a gallery cavity  26  defined therein. The housing  12  defines an inlet port  28  which is in communication with an external source of fluid ( 66  in  FIG. 2 ) and an outlet port  30  which is in fluid communication with a fluid cavity  32  for pressurized fluid to be delivered. 
         [0028]    The valve cavity  24  is generally cylindrical and has a wall  34  extending along its length. A first end  36  of the valve cavity  24  is open to the gallery cavity  26  and the other end  38  of the valve cavity  24  is open to the exterior of the housing  12 . 
         [0029]    The gallery cavity  26  is generally cylindrical and extends between the first end  36  of the valve cavity  24  and the engine main gallery (not shown) from which pressurized fluid is delivered. 
         [0030]    The generally cylindrical regulator spool valve  16  has a wall  41  and a cylindrical bore  42  that extends between a spring guide  44  at one end and an orifice  46  at the other end. The orifice  46  opens in to a fluid passage  48 , which is in communication with the gallery cavity  26 . The spring guide  44  is positioned adjacent to a control chamber  50  in which the regulator spring  52  is located. The regulator spring  52  is mounted at an opposite end  53  of the control chamber  50  to the spring guide  44 . The free end of the regulator spring  52  is positioned within the spring guide  44 . 
         [0031]    The electromagnetic solenoid valve  18  comprises a first cylindrical body  54  having an electrical connector  56  at a first end and a shoulder portion  58  which leads to a second cylindrical body  60  at an end opposite to the first end. The second cylindrical body  60  is aligned with the first cylindrical body  54 , but has a smaller diameter. The shoulder portion  58  has a vent port  62 . The electromagnetic solenoid valve  18  has a spring ( 76  in  FIG. 2 ), a pressure face (not shown), a proportional solenoid ( 78  in  FIG. 2 ), and an internal venting mechanism (not shown) having a spool (not shown), a fluid passage  82  and an orifice  64 . The fluid passage  82  is in fluid communication with the orifice  64 , which is in fluid communication with the control chamber  50  of the regulator spool valve  16 . 
         [0032]    The pump assembly  10  is assembled as follows. 
         [0033]    The regulator spool valve  16  is mounted in the valve cavity  24  such that the wall  41  of the regulator spool valve  16  is in sliding engagement with the wall  34  of the valve cavity  24 . The fluid passage  48  of the regulator spool valve  16  is connected to the gallery cavity  26 . As shown in  FIG. 1 , the outlet port  30  is in fluid communication with the fluid cavity  32 . 
         [0034]    The second body  60  of the electromagnetic solenoid valve  18  is mounted in the open end  38  of the valve cavity  24 . As described above, the orifice  64  is in fluid communication with the control chamber  50  of the regulator spool valve  16 . 
         [0035]    Turning now to  FIG. 2 , there is shown the pump assembly  10  of  FIG. 1  with an external source of fluid  66 , a pump  68 , an engine cooler and filter orifice  70  and the electromagnetic solenoid valve  18  shown in diagrammatic form. The electromagnetic solenoid valve  18  is a normally-closed two-way valve. The electromagnetic solenoid valve  18  has two positions: a closed position  72  and an open position  74 . 
         [0036]    Fluid pressure acting on the pressure face (not shown) of the electromagnetic solenoid valve spool (not shown) opposes force from the electromagnetic solenoid valve spring  76  to move the electromagnetic solenoid valve  18  from normally closed position  72  to open position  74 . Applying voltage to the proportional electromagnetic solenoid  78  changes the pre-load on the electromagnetic solenoid valve spring  76  in order to change the pressure required to move the electromagnetic solenoid valve  18  between the two positions  72 ,  74 . 
         [0037]    The electromagnetic solenoid valve  18  has:
   a first port  80  in communication with a first side of the electromagnetic solenoid valve  18  and fluid passage  82 ; and   second port  84  in communication with a second side of the electromagnetic solenoid valve  18  and the external source of fluid  66 .   
 
         [0040]    Operation of the recirculation valve when no voltage is applied to the electromagnetic solenoid valve  18  will now be described. 
         [0041]    With the electromagnetic solenoid valve  18  in normally closed position  72 , the pressure of fluid in the control chamber  50  equals the pressure of fluid in the gallery cavity  26  (the feedback pressure). 
         [0042]    When the pressure of fluid in the fluid passage  82  is below lower vent limit of the electromagnetic solenoid valve spring  76 , the force exerted on the electromagnetic solenoid valve spool (not shown) is not sufficient to move it far enough to cause the vent port  62  to be opened, and so the electromagnetic solenoid valve  18  remains in first position  72 . 
         [0043]    The forces acting on the regulator spool valve  16 , due to the pressure of fluid in cavities  26  and  50 , are equal and opposite and the force from the regulator spring  52  prevents movement of the regulator spool valve  16 . Under these conditions, the regulator spool valve  16  remains in the position shown in  FIGS. 1 and 2  with the outlet port  30  in fluid communication with the fluid cavity  32  and the inlet port  28  isolated from the fluid cavity  32 . As such, there is no recirculation flow from the outlet port  30  to the inlet port  28 . 
         [0044]    When the feedback pressure is increased, the control chamber pressure and the pressure of fluid in the fluid passage  82  is increased. When the pressure of fluid in fluid passage  82  exceeds the lower vent limit of the electromagnetic solenoid valve spring  76 , the electromagnetic solenoid valve spool (not shown) compresses the electromagnetic solenoid valve spring  76  and moves beyond the break edge of the vent port  62 . As the vent port  62  starts to open, a flow of fluid is created through the orifice  46 , which creates a pressure differential between cavities  26  and  50 . This imbalance of fluid pressures creates a net force on the regulator spool valve  16  that opposes the force from regulator spring  52  and causes the regulator spool valve  16  to begin to move. The net force acting on the regulator spool valve  16  is not sufficient to enable it to move beyond the break edge of the inlet port  28  in the pump housing  12 . Under these conditions, there is no recirculation flow from the outlet port  30  to the inlet port  28  and the inlet port  28  remains isolated from the fluid cavity  32 . 
         [0045]    When the feedback pressure is further increased, the pressure of fluid in the control chamber  50  and the fluid passage  82  is further increased, causing vent port  62  to open fully. When the vent port  62  is fully opened the flow of fluid through the orifice  46  increases, causing an increase in the pressure differential between cavities  26  and  50 . This increased imbalance of fluid pressures leads to an increase in the net force on the regulator spool valve  16  that opposes the force from the regulator spring  52 . Under these conditions, the regulator spool valve  16  compresses the regulator spring  52  further and the regulator spool valve  16  moves beyond its break edge, causing the inlet port  28  to be in fluid communication with the fluid cavity  32  and enabling recirculation flow from the outlet port  30  to the inlet port  28 , as shown in  FIG. 3 . 
         [0046]    When no voltage is applied to the electromagnetic solenoid valve  18 , it performs as a mechanical vent to control movement of the regulator spool valve  16  against the regulator spring  52 . 
         [0047]    In this way, when the pressure of oil in an engine (not shown) exceeds the pressure in the control chamber  50 , with the regulator spring  52  compressed and the regulator spool valve  16  moved beyond its break edge, oil is pumped from the outlet  30  to the inlet  28  and the engine circuit is bypassed. As described above, because the regulator spool valve  16  only opens at a single, predetermined regulation pressure, which is controlled by the spring rate of the regulator spring  52  and the rate of venting from the control chamber  50  by vent port  62 , it is only possible to regulate the engine oil pressure at a single, predetermined feedback pressure. 
         [0048]    Operation of the recirculation valve according to the invention, when voltage is applied to the electromagnetic solenoid valve  18 , will now be described. 
         [0049]    Direct Current (DC) voltage is supplied to the electromagnetic solenoid valve  18  by pulse width modulation so that the supply voltage is switched on and off at a given frequency for a modulated period of time (duty cycle). The duty cycle is the time the voltage is “on” and is expressed as a percentage of the time period, for example at 50% duty cycle, the voltage is “on” for 50% of the time period and “off” for 50% of the time period. In this way the time averaged voltage is only 50% of the maximum supply voltage and the current to the solenoid is only 50% of the maximum. In this way, the pulse width modulation signal controls the solenoid. 
         [0050]    At 100% duty cycle, the maximum voltage is supplied to the electromagnetic solenoid valve  18  causing the pre-load of the electromagnetic solenoid valve spring  76  to be reduced to a minimum. In this way, the pressure of fluid in the passage  82  necessary to cause the electromagnetic solenoid valve spool (not shown) to move to its break edge and open the vent port  62  is reduced to a minimum required pressure. Similarly, the pressure differential required to cause the regulator spool valve  16  to open the re-circulation path from  30  to  28  will occur at the minimum gallery feedback pressure. 
         [0051]    At zero duty cycle no voltage is supplied to the electromagnetic solenoid valve  18 , and so the electromagnetic solenoid valve  18  performs as a mechanical vent as described above. 
         [0052]    By varying the duty cycle of the electromagnetic solenoid valve  18  between 0% and 100%, the pre-load of the spring  76  can be varied between a minimum and a maximum force, enabling the feedback pressures at which recirculation occurs to be varied within a range depending on the requirements of the engine, thereby reducing the drive power of the pump  68 . As the pump  68  is engine driven, this reduces the parasitic loss and improves the engine efficiency. 
         [0053]    Referring now to  FIG. 4 , there is shown the pump assembly  10  of  FIG. 1  with a recirculation valve  115  according to a second embodiment of the present invention. Like reference numerals depict like features, which will not be described further. 
         [0054]    The electromagnetic solenoid valve  118  of this embodiment differs from that of the first embodiment as the electromagnetic solenoid valve  118  has an on/off solenoid  178 . The electromagnetic solenoid valve  118  of this embodiment only operates at 100% duty cycle or zero duty cycle and so the pre-load of the electromagnetic solenoid valve spring  76  is either a minimum or maximum force (and cannot be varied between these values). Accordingly the recirculation valve  115  can be set such that recirculation occurs only at one of two feedback pressures. 
         [0055]    Referring now to  FIG. 5 , there is shown an alternative pump assembly  210  having a recirculation valve  215  according to a third embodiment of the present invention. Like reference numerals depict like features and will not be described further. In this embodiment, the electromagnetic solenoid valve  218  is not mounted in the open end  38  of the valve cavity  24 . The electromagnetic solenoid valve  218  is fluidly connected to the control chamber  50  by fluid passage  282 . Plug member  290  is mounted in the open end  38  of the valve cavity  24 . Operation of the recirculation valve  215  to enable recirculation flow from the outlet port  30  to the inlet port  28  is as described above in relation to the recirculation valve  15  of the embodiment shown in  FIG. 1 . 
         [0056]    Referring now to  FIG. 6 , there is shown an alternative pump assembly  310  having a recirculation valve  315  according to a fourth embodiment of the present invention. Like reference numerals depict like features, which will not be described further. In this embodiment of the invention, the feedback pressure in the gallery cavity  26  is generated by fluid supplied from the outlet port  30  as depicted by line A and so does not pass through the engine cooler and filter orifice. 
         [0057]    Referring now to  FIG. 7 , there is shown an alternative pump assembly  410  having a recirculation valve  415  according to a fifth embodiment of the present invention. Like reference numerals depict like features, which will not be described further. 
         [0058]    The recirculation valve  415  of this embodiment has a control chamber  450  that is positioned between the gallery cavity  26  and the regulator spool valve  16 . The electromagnetic solenoid valve  418 , the regulator spool valve  16  and the gallery cavity  26  are in fluid communication with the control chamber  450 . 
         [0059]    The regulator spring  52  is located in chamber  451 , which has a vent  492  to prevent fluid or air locks. A plug  490  is positioned in the opening  38  of the valve cavity  24 . 
         [0060]    The electromagnetic solenoid valve  418  of this embodiment is a normally-open two way valve. The electromagnetic solenoid valve  418  has two positions: a closed position  472  and an open position  474 . 
         [0061]    Fluid pressure acting on the pressure face (not shown) of the electromagnetic solenoid valve spool (not shown) opposes force from the electromagnetic solenoid valve spring  476  to move the electromagnetic solenoid valve  418  from normally open position  474  to closed position  472 . Applying voltage to the proportional electromagnetic solenoid  478  changes the pre-load on the electromagnetic solenoid valve spring  476  in order to change the pressure required to move the electromagnetic solenoid valve  418  between the two positions  474 ,  472 . 
         [0062]    When the pressure of fluid in the fluid passage  482  is below the lower vent limit of the electromagnetic solenoid valve spring  476 , the force exerted on the electromagnetic solenoid valve spool (not shown) is not sufficient to move it far enough to cause the vent port  462  to be closed, and so the electromagnetic solenoid valve  418  remains in open position  474 . 
         [0063]    The force acting on the regulator spool valve  16  due to pressure of fluid in the control chamber  450  opposes the force from the regulator spring  52  prevents movement of the regulator spool valve  16 . Under these conditions, the regulator spool valve  16  remains in the position shown in  FIG. 7  with the outlet port  30  in fluid communication with the fluid cavity  32 . As such, there is no re-circulation flow from the outlet port  30  to the inlet port  28 . 
         [0064]    When the feedback pressure is increased, the control chamber pressure and the pressure of fluid in the fluid passage  482  is increased. When the pressure of fluid in the fluid passage  482  exceeds the lower vent limit of the electromagnetic solenoid valve spring  476 , the electromagnetic solenoid valve spool (not shown) compresses the electromagnetic solenoid valve spring  476  and moves back towards the break edge of the vent port  462 . As the vent port  462  starts to close, the flow of fluid through the orifice  46  is slowed, which creates a pressure increase in the cavity  450 . This increased fluid pressure creates a net force on the regulator spool valve  16  that opposes the force of the regulator spring  52 . The net force acting on the regulator spool valve  16  is not sufficient to enable it to move beyond the break edge of the inlet port  28  in the pump housing  12 . Under these conditions, there is no re-circulation flow from the outlet port  30  to the inlet port  28  and the inlet port  28  remains isolated from the fluid cavity  32 . 
         [0065]    When the feedback pressure is further increased, the pressure of fluid in the control chamber  450  and the fluid passage  482  is further increased, causing vent port  462  to close fully. When the vent port  462  is fully closed the flow of fluid through the orifice  464  stops, causing an increase in the pressure in cavity  450 . This increased fluid pressure leads to increase in the net force on the regulator spool valve  16  that opposes the force from the regulator spring  52 . Under these conditions the regulator spool valve  16  compresses the regulator spring  52  further and the regulator spool valve  16  moves beyond its break edge, causing the inlet port  28  to be in fluid communication with fluid cavity  32  and enabling re-circulation of flow from the outlet port  30  to the inlet port  28 . 
         [0066]    Using proportional solenoid  478 , the duty cycle of the electromagnetic solenoid valve  418  may be varied between 0% and 100% and so the pre-load of the spring  476  can be varied between a minimum and a maximum force, enabling the feedback pressures at which re-circulation occurs to be varied within a range depending on the requirements of the engine. 
         [0067]    Referring now to  FIG. 8 , there is shown an alternative pump assembly  510  having a re-circulation valve  515  according to a sixth embodiment of the present invention. Like reference numerals depict like features and will not be described further. This embodiment is similar to the fifth embodiment, except that the electromagnetic solenoid valve  518  has a port  584  that is in fluid communication with a second side of the electromagnetic solenoid valve  518  and the inlet port  28 . Operation of the re-circulation valve  515  is as described for the fifth embodiment. 
         [0068]    Variations fall within the scope of the present invention, for example the electromagnetic solenoid valve of any of the embodiments of the invention may either employ a proportional solenoid or an on/off solenoid. 
         [0069]    The electromagnetic solenoid valve of any of the embodiments of the invention may be housed within or outside of the pump assembly. 
         [0070]    The feedback pressure may be the engine gallery pressure or the outlet port pressure. The recirculation valve may vent to the sump or the inlet port.