Abstract:
A dual plunger valve having nested inner and outer plungers seated within a bore in the valve housing. The valve housing has an inlet port and an outlet port fluidly connected by the bore and sealed from one another by the plungers which are biased towards respective sealing surfaces by a pair of nested biasing elements located between the inlet port and the outlet port. The outer plunger is slidable within the bore and has a lip extending inwardly therefrom. The inner plunger is slidable within the outer plunger between a sealed position and a second position wherein it is in contact with the lip. Pressure in the inlet port which is high enough to overcome the force of the biasing elements causes the inner plunger to slide within the outer plunger to its second position wherein the outer plunger will then begin to slide within the bore to remove the seal between the inlet port and the outlet port.

Description:
[0001]     This application claims priority from U.S. provisional application no. 60/706,457 filed on Aug. 9, 2005. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to pressure relief valves used in fluid systems.  
       DESCRIPTION OF THE PRIOR ART  
       [0003]     Pressure relief valves used in fluid systems are generally one-way valves designed to open at a specific pressure to prevent damage to the system. For example, a pressure relief valve is used in an engine&#39;s lubrication system to relieve excessive pressure that may develop in the oil pump as the engine speed increases or downstream of the pump if an unpredictable restriction occurs.  
         [0004]     Pumps used in fluid systems are susceptible to contamination. In the case of an engine the contamination generally originates in the engine and may comprise particles of iron, aluminum, sand etc. Although filters and inlet screens are provided, the system is designed on the assumption that some particles of contaminate will reach the pump, which therefore are designed to pass the contaminates through the pump without issue.  
         [0005]     A conventional relief valve has a seat in a bore with a valve member biased into engagement with the seat. There is a nominal clearance between the bore and the valve member to maintain a seal when the valve is closed. An effective seal is necessary to ensure priming of the pump as the engine starts, particularly where the pump is mounted in an elevated position and flow past the valve is re-circulated to the inlet. If a contaminate particle becomes lodged between the valve member and the bore, the relief valve will become wedged into an open position. With the relief valve wedged open, the pump will drain when the engine is switched off and may not prime when the engine is initially started. This can lead to premature failure of the engine. The tendency for particles to become wedged is particularly evident when the pressure drops in the pump and the valve is closing, i.e. when the engine is shut down, and thereby exacerbates the problem.  
         [0006]     U.S. Pat. No. 4,953,588 to Sands discloses a check valve assembly in which a pair of poppet valves is arranged to act independently of one another to seal a line. The purpose of this assembly is to inhibit reverse flow if one of the poppets fails. The Sands patent is directed to check valves where only a nominal resistance to flow is envisaged rather than relief at an elevated pressure. As such the independent operation of the valves is of primary concern rather than the pressure/flow characteristics of a relief valve. If used as a relief valve, the independent nature of each of the valves would require each to function as a separate relief valve in series, causing significant difficulties in matching their operation to regulate the pressure accurately.  
         [0007]     It is therefore an object of the present invention to obviate or mitigate the above mentioned disadvantages.  
       SUMMARY OF THE INVENTION  
       [0008]     In one aspect, a valve for a fluid system is provided comprising a housing, the housing having an inlet port, an outlet port, a bore fluidly connecting the inlet port to the outlet port, an inner sealing surface and an outer sealing surface at spaced locations between the inlet port and the outlet port. The valve also comprises an outer sealing member slidably located within the bore and having a sealing face biased into engagement with the outer sealing surface by an outer biasing element and a circumferential sealing surface that engages a portion of the wall of the bore extending axially between the inlet and the outlet; and an inner sealing member nested within the outer plunger and being sealingly engaged with the inner sealing surface by an inner biasing element. The outer plunger is moveable to an open position in which fluid flows between the inlet port and the outlet port. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     An embodiment of the invention will now be described by way of example only with reference is made to the appended drawings wherein:  
         [0010]      FIG. 1  is a schematic representation of a hydraulic pump with a pressure relief valve.  
         [0011]      FIG. 2  is a cross sectional view of the valve of  FIG. 1  along line II-II.  
         [0012]      FIG. 3  is a series of views showing the operation of the valve of  FIG. 2  under different conditions.  
         [0013]      FIG. 4  is a cross sectional view of an alternative embodiment of valve to that shown in  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]     Referring therefore to  FIGS. 1 and 2 , an oil supply for an engine includes a pump P having a vaned impeller V driven by the engine and rotating within a pump housing H. Oil is drawn in to the housing H by an inlet I and delivered to a supply port S. A bypass path B is provided between the supply port S and inlet I to permit oil to be re-circulated from the supply port S to the inlet I. Flow through the bypass path B is controlled by a valve  10  which opens to permit flow when the pressure in the supply port S exceeds a predetermined value and closes when the pressure of oil drops below that value. In many installations, the pump P is mounted at an elevated location on the engine and draws oil through the inlet I into the housing H from the sump below the engine.  
         [0015]     Valve  10  generally comprises a valve housing  12  with an inlet pressure port  14  connected to the supply port S and an exhaust port  16  connected to the bypass path B. The inlet port  14  and exhaust port  16  are axially spaced along a stepped bore  17 .  
         [0016]     The stepped bore  17  extends within the valve housing  12  from the inlet port  14  past the outlet port  16  to a recess  31  in the housing  12 . A pair of radial seats  24 ,  28  are formed in the bore  17  separated by an inner circumferential sealing surface  32 . The radial seat  24  is positioned adjacent the inlet port  14  and extends between the port and the inner sealing surface  32 . The radial seat  28  extends between the inner sealing surface  32  and an outer circumferential sealing surface  34  defining a major extent of the bore  17  and which is intersected by the exhaust port  16 . A retainer provided by a retaining disc  30  and secured by a pin (or other means), is located in the recess  31 .  
         [0017]     An inner sealing member or plunger  18  and an outer sealing member or plunger  20  are nested within the bore  17  and are biased towards the inlet port  14  by respective inner and outer springs  22 ,  26 . The outer plunger  20  is formed as a cylindrical sleeve with a sealing face  29  at one end and a radial lip  21  at the opposite end. The sealing face  29  is biased into engagement with the outer radial sealing surface  28  by the outer spring  26  which acts between the lip  21  and the retaining disc  30 . The outer plunger  20  is sized to provide a close sliding fit within the bore  17  between the radial face  29  and the outlet  16 . This maintains a seal between its outer surface  23  and the outer circumferential sealing surface  34  whilst it slides within the bore  17  and thus provides a pair of separate sealing bands, one radial and one circumferential (extending axially along bore), between the plunger  20  and bore  17 .  
         [0018]     The inner plunger  18  is formed as a “cup shaped” member with a sealing face  25  at one end opposed to the inner sealing face  24  in the bore  17 . The plunger  18  also is a close sliding fit within the inner circumferential sealing surface  32  to provide seal between the plunger  18  and bore  17 . The sealing face  25  is biased into engagement with the inner radial seat  24  by the inner spring  22  which is seated between the interior of the plunger  18  and the retainer  30  and nested within the outer spring  26 . The inner plunger  18  is a sliding fit within the outer plunger  20  to maintain a seal between the two plungers  18 ,  20  over the axial extent of their sliding engagement. The rear end of the inner plunger  18  abuts the lip  21  to limit relative movement between the plungers  18 ,  20 . The relationship between the plungers  18 ,  20  also helps to protect the spring  22  from hitting solid height or experiencing premature fatigue failure.  
         [0019]     The position shown in  FIG. 2  illustrates the valve under normal operating conditions wherein the pressure of the fluid in the inlet port  14  is at or below the maximum desired operating pressure of the particular component utilizing the valve  10 . In this position, a seal is provided between the plunger  18  and both the radial face  24  and circumferential seal  32  and a further pair of seals between the plunger  20  and the radial face  28  and circumferential seal  34 . In addition a sliding seal is provided between the plungers  18 ,  20 .  
         [0020]     As the pressure in the inlet port  14  rises, the force imparted on the sealing face  25  will cause the inner plunger  18  to compress the inner spring  22  and begin to slide within the outer plunger  20 . During this movement, a seal is maintained between the plunger  18  and the circumferential face  32 . The biasing force of the inner spring  22  is chosen to respond to changes in pressure such that at a predetermined value, below the crack or opening pressure, it will have overcome the biasing force imparted by the inner spring  22  on the inner plunger  18  which then abuts the lip  21 .  
         [0021]     Upon abutment of the plunger  18  with the lip  21 , further increase in the pressure causes a corresponding conjoint movement of the plungers  18 ,  21  against the bias of both springs  22 ,  26  with the pressure acting on the entire face of both plungers.  
         [0022]     A seal is maintained between the inlet port  14  and the exhaust port  16  until the sealing face  29  of the outer plunger  20  uncovers the exhaust port  16 . Upon exposure of the port  16 , fluid present in the inlet port  14  may pass through the exhaust port  16  to maintain pressure in the supply port S at a predetermined value.  
         [0023]     It will be appreciated that the outer plunger  20  may also be designed to move without requiring the inner plunger  18  to engage the lip  21 . For example, the sealing face  29  may be designed to be partially exposed such that a predetermined pressure (and corresponding spring) will also move the outer plunger  20 .  
         [0024]     The plungers  18 ,  20  will regain the position seen in  FIG. 2  when the pressure in the inlet port  14  falls below the maximum desired pressure. The biasing forces imparted by the springs  22 ,  26  will cause the plungers  18 ,  20  to slide back into position when these forces are able to overcome the force imparted on the sealing faces  25 ,  29  by the fluid pressure in the inlet port  14 . Initially the inner and outer plungers  18 ,  20  move in unison until the outer plunger  20  engages the radial face  29 . Thereafter, the inner plunger  18  extends from the outer plunger  20  until the end face  25  seats against the seat  24 . It will be noted that the plungers  18 ,  20  act in unison against a common bias during opening, thereby facilitating control of relief pressure.  
         [0025]     As noted above, the oil in the sump of the engine may carry contaminants that interfere with the normal operation of the valve. If the valve  10  is lodged in an open position, a direct connection between the supply port s and inlet port I is provided that inhibits the priming of the pump when the engine is restarted. The provision of the multiple sealing surfaces and the independent operation of the plungers mitigates the impact on the operation of the valve and permits priming of the pump in all but the most extreme situations.  
         [0026]     As shown in  FIG. 3   a , contaminant  44  may become lodged between the plungers  18 ,  20  to inhibit relative sliding movement. If the inner plunger  18  is held within the plunger  20 , the outer plunger  20  is operable to move to a closed position with a seal on the radial face  28  and circumferential seal  34 . Thus an effective seal is provided that allows rejoining of the pump. Moreover, the valve  10  will continue functioning to relieve pressure.  
         [0027]     If the plunger  18  is wedged so that it partially extends from the plunger  20 , an additional seal is provided between the plunger  18  and circumferential face  32 .  
         [0028]     Alternatively, the plunger  18  may be wedged whilst partially extended as shown in  FIG. 3   b . In that position, the plunger  18  will seat against radial face  24  and seal against inner circumferential seal  32  although the outer plunger  20  is held away from its sealing position. The valve is therefore operable to seal the pump cavity and re-prime the pump.  
         [0029]     Typically, the wedging by the contaminant is a transient condition and is freed at the next operation of the pump by flow of fluid under pressure.  
         [0030]     Contaminants may also become lodged against the radial seats  24 ,  28  as illustrated in  FIGS. 3   c  and  3   d  respectively. The independent movement of the plungers  18 ,  20  permits an effective seal to be obtained to provide priming. Where the contaminant to present against the radial seat  24 , as shown in  FIG. 3   c  a seal will be established on the circumferential wells  32 ,  34  and the radial seat  28 .  
         [0031]     Similarly, where a contaminant is present on the radial seat  28 , a seal will be established at the circumferential walls  32 ,  34  and the radial seat  24 .  
         [0032]     In both cases the pump will be able to re-prime and the valve will function as a relief valve upon restarting of the pump.  
         [0033]     A further potential failure made is shown in  FIG. 3   e  where contaminant is lodged at the outlet  16  and prevents the outer plunger  20  from reseating. In this condition, the inner plunger is free to move to a sealing position under the bias of the spring so that a seal is established at the radial face  24  and the circumferential seal  32 . Again therefore, repriming of the pump is facilitated and pressure can be built up in the hydraulic circuit once the pump is re-primed.  
         [0034]     Should one of the springs fail, the independent operation of the plunger will again ensure effective sealing and continued operation under the influence of the remaining spring.  
         [0035]     Accordingly, it can be seen that a redundancy is integrated in the valve to accommodate potential failure modes.  
         [0036]     A further embodiment of the valve  10  is shown in  FIG. 4  where like reference numerals will be used to denote like components with a suffix a added for clarity. In the embodiment of  FIG. 4 , the outer plunger  20   a  is modified to provide a pair of part spherical seats  50 ,  52  at axially spaced locations within the plunger  20   a . A cross port  54  is provide in the plunger  22   a  between the seats  50 ,  52  the cross port  54  is located on the plunger  22   a  such that it is not aligned with the exhaust port  16   a  when the plunger  22   a  is against the seat  24   a  but will be moved in to alignment as the plunger  22   a  slides away from the seat  24   a.    
         [0037]     Inner plunger  18  is replaced with a ball  56  of a diameter corresponding to the diameter of the seats  50 ,  52 . A spring  22   a  acts against the ball  56  to hold it against the seat  50  and inhibit flow from the supply port S to the inlet I. When the pressure in the supply port S exceeds the bias of spring  22   a , the ball  56  is moved towards the seat  52 , and, as the pressure increases, the entire face of the plunger  20   a  and ball  56  is subjected to hydraulic pressure. The plunger  20   a  acts against the bias of the spring  26   a  and moves axially within bore  17   a  until the cross port  54  is aligned with exhaust port  16   a . Re-circulating flow can then occur through the seat  50  and the cross port  54 . If the pressure drops, the ball  54  is held against the seat  52  until the plunger  22   a  has again closed the exhaust port  16   a , and, as the pressure continues to drop, the ball  54  will be moved in to engagement with the seat  50 .  
         [0038]     It will be apparent that if the ball  54  is held off the seat  50  due to contaninants, the outer plunger  22   a  will again provide a seal at the radial seat  24   a  and the circumferential seal  34   a  to permit re-priming of the pump P. If the plunger  22   a  is held open, the ball  54  will seat against the seat  50  and close the flow path through the seat  50  to the exhaust port  16   a . Again therefore redundancy is provided to mitigate the potential for the valve  10  to be held in an open position and inhibit re-priming of the pump P. Although the two “cracking” pressures, namely for the ball  54  and plunger  22   a , are typically different, this would still protect the engine from a “no prime” condition.  
         [0039]     If a chip or contaminate particle becomes stuck between the ball  54  and the face of the plunger  22   a , the ball  54  will re-align itself and still provide a partial circumferential seal. This will aid in engine priming since the leak path is smaller.  
         [0040]     The ball  54  also provides the advantage of a smoother flow path as fluid passes over the face of the ball  54  and exits the valve  10 . This encourages contaminate particles to exit the system.  
         [0041]     Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention as outlined in the claims appended hereto.