Abstract:
A valve assembly includes a hydraulic subassembly with a valve member displaceable along a valve axis for controlling flow of fluid. The valve assembly also includes a solenoid subassembly for selectively displacing said valve member. The solenoid subassembly includes a metallic solenoid housing having an open end and a solenoid housing base. The solenoid subassembly also includes a solenoid coil assembly disposed within the solenoid housing, the solenoid coil assembly having a coil wound around a plastic spool defining a spool bore extending through the spool. The solenoid subassembly also includes a metallic solenoid housing cover closing off the open end of the solenoid housing and attached to the solenoid housing with a crimp connection. The solenoid subassembly also includes a metallic column disposed within and passing through the spool bore extending from the solenoid housing base to the solenoid housing cover.

Description:
TECHNICAL FIELD OF INVENTION 
     The present invention relates to a solenoid-actuated control valve; more particularly to a solenoid-actuated control valve which is resistant to pressure drift over time; and even more particularly to a solenoid-actuated control valve which does not place crimp assembly loads on plastic components within the solenoid. 
     BACKGROUND OF INVENTION 
     Solenoid-actuated control valves, herein after referred to as control valves, are well known to control the flow and/or pressure of a fluid. In many applications, it may be desirable that the flow and/or pressure output of the control valve be proportional to an electric current supplied to a solenoid of the control valve. In a common control valve arrangement, the electric current supplied to the solenoid of the control valve affects the position of a supply valve member and/or an exhaust valve member relative to a supply valve seat and an exhaust valve seat respectively. The position of the supply valve member relative to the supply valve seat and/or the position of the exhaust valve member relative to the exhaust valve seat affects the fluid flow and/or pressure leaving the control valve. It is therefore important that the position of the valve members relative to the valve seats for a given electric current supplied to the solenoid does not change during the life of the control valve because if the position of the valve members relative to the valve seats is not as is expected, the flow and/or pressure leaving the control valve may not be the desired magnitude. 
     The solenoid of the control valve is typically enclosed in a housing that is cylindrical and made of metal. An example of such a control valve is shown in US Patent Application Publication No. US 2007/0138422 A1. During manufacturing of the control valve, at least one end of the housing is open to allow components of the solenoid to be placed within the housing. After all of the components have been placed within the housings, a cover may be placed over the open end, and the housing may be crimped or folded over the cover to retain the cover to the housing. When the housing is crimped to retain the cover, an axial load is placed on the components within the housing and the axial load on the components within the housing is maintained by the crimp connection. However, this axial load from the crimp is known to be transmitted through plastic components, such as the spool (also known as a bobbin or coil former) around which the coil of the solenoid is wound. Over time, this crimp load may cause the plastic components to creep (i.e. change in shape and position), thereby changing the position of the valve members relative to the valve seats for a given a given electric current supplied to the solenoid. As a result, the desired flow and/or pressure leaving the control valve may not be the desired magnitude for a given electric current supplied to the solenoid. 
     One way to address the effects of creep of the plastic components and the changing of position of the valve members relative to the valve seats over time is to use closed loop feedback. In this arrangement, the actual flow and/or pressure leaving the control valve is measured with a sensor. The sensor sends a signal indicative of the flow and/or pressure to a controller. If the signal indicates that the flow and/or pressure is not the desired magnitude, the controller can alter the electric current supplied to the solenoid until the desired flow and/or pressure reaches the desired magnitude. In this way, the effects of creep of plastic components can be overcome. However, using closed loop feedback increases the cost and complexity of the system, for example by the addition of sensors, wiring, and software. 
     What is needed is a control valve in which the flow and/or pressure leaving the control valve does not change over time for a given magnitude of electric current used to actuate the control valve. What is also needed is a control valve which is not affected by creeping of plastic components of the solenoid over time. 
     SUMMARY OF THE INVENTION 
     Briefly described, a valve assembly includes a hydraulic subassembly with a valve member displaceable along a valve axis for controlling at least one of flow and pressure of fluid from a fluid source to a working device. The valve assembly also includes a solenoid subassembly for selectively displacing the valve member. The solenoid subassembly includes a metallic solenoid housing having an open end distal from the hydraulic subassembly and a solenoid housing base adjacent to and connected with the hydraulic subassembly. The solenoid subassembly also includes a solenoid coil assembly disposed within the solenoid housing, the solenoid coil assembly having a coil wound around a plastic spool defining a spool bore extending through the spool. The solenoid subassembly also includes a solenoid housing cover closing off the open end of the solenoid housing and attached to the solenoid housing with a crimp connection that creates a compressive crimp force acting along the valve axis. The solenoid subassembly also includes a metallic column disposed within and passing through the spool bore, the metallic column extending from the solenoid housing base to the solenoid housing cover. The compressive crimp forces are transferred through the metallic column from the solenoid housing base to the solenoid housing cover to isolate the compressive crimp forces from plastic components. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       This invention will be further described with reference to the accompanying drawings in which: 
         FIG. 1  is a cross section of a valve assembly in accordance with the invention shown in a position which allows full pressure and/or flow from a fluid source to a working device; 
         FIG. 2  is an exploded isometric view of the valve assembly of  FIG. 1 ; and 
         FIG. 3  is the cross section of  FIG. 1  now with the valve assembly shown in a position which prevents fluid communication from the fluid source to the working device. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     In accordance with a preferred embodiment of this invention and referring to  FIGS. 1 and 2 , solenoid-actuated control valve  10  is shown, hereinafter referred to as valve assembly  10 . Valve assembly  10  includes hydraulic subassembly  12  in fluid communication with fluid source  14  and working device  16 . Working device  16  may be, for example, a transmission clutch. Valve assembly  10  also includes solenoid subassembly  18  which is connected to hydraulic subassembly  12  and which controls the fluid communication from fluid source  14  through hydraulic subassembly  12  to working device  16  based on an electric current which is variable and which is supplied by electric current source  20 . Electric current source  20  may be, for example, an electronic controller. 
     Hydraulic subassembly  12  includes hydraulic subassembly housing  22  which may be made, for example, by injection molding a plastic material. Hydraulic subassembly housing  22  extends along valve axis A and includes attachment flange  24  at one axial end which is used to attach hydraulic subassembly  12  to solenoid subassembly  18 . Hydraulic subassembly housing  22  also includes inlet port  26  located in the axial end of hydraulic subassembly housing  22  which is distal from attachment flange  24 . Inlet port  26  is in constant fluid communication with fluid source  14 . Hydraulic subassembly housing  22  also includes working port  28  extending radially outward from hydraulic subassembly housing  22 . Working port  28  is in constant fluid communication with working device  16  and is in variable fluid communication with inlet port  26  based on input from solenoid subassembly  18 . Hydraulic subassembly housing  22  also includes exhaust port  30  which is in variable fluid communication with working port  28  based on input from solenoid subassembly  18 . 
     Hydraulic subassembly  12  also includes a supply valve member shown as ball  34  which is located within inlet port  26  and which is selectively seated and unseated with supply valve seat  36 . Supply valve seat  36  is annular, coaxial with valve axis A, and formed between working port  28  and inlet port  26  to be small in diameter than ball  34 . In order to retain ball  34  within inlet port  26 , ball retainer  38  may be provided. Ball retainer  38  may be secured, for example by press fit or welding, within an enlarged portion of inlet port  26 . A reduced diameter section of ball retainer  38  may extend further into inlet port  26  to prevent ball  34  from escaping inlet port  26  while still allowing for axial movement of ball  34  relative to supply valve seat  36  to allow for desired flow and/or pressure from fluid source  14  to working device  16  when ball  34  is not seated with supply valve seat  36 . 
     Hydraulic subassembly  12  is also provided with poppet rod  40  in order transfer linear motion produced by solenoid subassembly  18  to ball  34  to selectively seat and unseat ball  34  with supply valve seat  36 . Poppet rod  40  is coaxial with valve axis A and sized to extend through supply valve seat  36  such that a clearance is formed radially outward of poppet rod  40  to allow fluid communication radially between hydraulic subassembly housing  22  and poppet rod  40  from inlet port  26  to working port  28  when ball  34  is unseated with supply valve seat  36 . When ball  34  is to be unseated with supply valve seat  36 , poppet rod tip  42  contacts ball  34  and urges ball  34  away from supply valve seat  36 . 
     Hydraulic subassembly  12  is also provided with exhaust seat  44  which is disposed within hydraulic subassembly housing  22  axially between working port  28  and exhaust port  30 . Exhaust seat  44  is substantially disk-shaped and includes exhaust aperture  46  extending axially therethrough and coaxial with valve axis A. Exhaust aperture  46  is sized to allow poppet rod  40  to pass therethrough with sufficient radial clearance with poppet rod  40  to allow fluid communication radially between exhaust aperture  46  and poppet rod  40  from working port  28  to exhaust port  30 . Exhaust valve member  48  is fixed to poppet rod  40  and sized to be larger in diameter than exhaust aperture  46 . Poppet rod  40  is moveable based on input from solenoid subassembly  18  to allow exhaust valve member  48  to be selectively seated and unseated with exhaust seat  44 . In this way, fluid communication from working port  28  to exhaust port  30  is substantially prevented when exhaust valve member  48  is seated with exhaust seat  44 . Conversely, fluid communication from working port  28  to exhaust port  30  is permitted when exhaust valve member  48  is not seated with exhaust seat  44 . It should also be noted that fluid communication from inlet port  26  to working port  28  is permitted when exhaust valve member  48  is seated with exhaust seat  44  and that fluid communication from inlet port  26  to working port  28  is substantially prevented for a portion of the travel of poppet rod  40  in which exhaust valve member  48  is not seated with exhaust seat  44 . 
     Hydraulic subassembly  12  is also provided with exhaust seat retainer  50  for retaining exhaust seat  44  within hydraulic subassembly housing  22  and for guiding poppet rod  40 . Exhaust seat retainer  50  captures exhaust seat  44  axially between a shoulder within hydraulic subassembly housing  22  and the axial end of exhaust seat retainer  50  that is distal from solenoid subassembly  18 . Exhaust seat retainer  50  is press fit or otherwise fastened within hydraulic subassembly housing  22  to prevent relative movement between exhaust seat retainer  50  and hydraulic subassembly housing  22 , thereby retaining exhaust seat  44  within hydraulic subassembly housing  22 . Exhaust seat retainer  50  is cup-shaped to define exhaust chamber  52  radially outward of poppet rod  40 /exhaust valve member  48  which allows axial movement of exhaust valve member  48  within exhaust chamber  52 . Exhaust seat retainer  50  includes exhaust seat retainer aperture  54  extending axially therethrough and coaxial with valve axis A. Exhaust seat retainer aperture  54  is sized to be a clearance fit with poppet rod  40  such that poppet rod  40  is able to move axially substantially uninhibited while radial movement of poppet rod  40  is substantially prevented. 
     Solenoid subassembly  18  includes solenoid housing  56  which is made of a magnetic metal. Solenoid housing  56  includes a substantially cylindrical section defining solenoid housing sidewall  58 . Solenoid housing  56  also includes solenoid housing base  60  which extends radially inward from solenoid housing sidewall  58  to partially close the end of solenoid housing  56  which is proximal to hydraulic subassembly  12 . Solenoid housing base  60  may be constructed as one piece with solenoid housing sidewall  58 , for example by a metal stamping process. Solenoid housing base  60  defines solenoid housing aperture  62  extending axially through solenoid housing base  60  coaxial with valve axis A. Solenoid housing  56  also includes attachment tabs  64  which are used to retain hydraulic subassembly  12  to solenoid subassembly  18 . Attachment tabs  64  extend axially from solenoid housing sidewall  58  toward hydraulic subassembly  12 . In  FIG. 2 , attachment tabs  64  are shown as phantom lines as they appear after being crimped or folded over attachment flange  24  of hydraulic subassembly housing  22  in order to retain hydraulic subassembly  12  to solenoid subassembly  18 . Attachment tabs  64  are also shown in  FIG. 2  as solid lines as they would appear prior to attachment tabs  64  being crimped over to attach hydraulic subassembly  12  to solenoid subassembly  18 . 
     Solenoid subassembly  18  also includes spool  66  which is made of a material which does not conduct electricity, for example, plastic. Spool  66  includes spool cylinder  68  which is coaxial with valve axis A and spool bore  70  which extends axially through spool cylinder  68  coaxial with valve axis A. Spool  66  also includes spool rims  72 ,  74  which extend radially outward from the ends of spool cylinder  68 . Spool rim  72  extends radially outward from the end of spool cylinder  68  which is proximal to solenoid housing base  60  while spool rim  74  extends radially outward from the end of spool cylinder  68  which is distal from solenoid housing base  60 . Electrically conductive wire is wound around spool cylinder  68  between spool rims  72 ,  74  to form coil  76  which is connected to terminals  78  which are connected to electric current source  20 . Spool  66  and coil  76  together define a solenoid coil assembly. 
     Solenoid subassembly  18  also includes primary pole piece  80  and secondary pole piece  82  which are each made of a magnetic material. Primary pole piece  80  and secondary pole piece  82  are sized to fit within spool bore  70  such that primary pole piece  80  and secondary pole piece  82  may be inserted within spool bore  70  without restriction. Primary pole piece  80  may be disposed proximal to solenoid housing base  60  while secondary pole piece  82  may be disposed distal from solenoid housing base  60 . It should be noted that primary pole piece  80  and secondary pole piece  82  are part of the magnetic circuit of solenoid subassembly  80  which function to control the magnetic flux distribution. 
     Primary pole piece  80  includes primary pole piece bore  84  which extends axially through primary pole piece  80  coaxial with valve axis A. Primary pole piece bushing  86  is fixed within primary pole piece bore  84 , for example, by press fit. Primary pole piece bushing  86  is made of a non-magnetic material, for example, bronze or plastic and includes primary pole piece bushing bore  88  which extends axially through primary pole piece bushing  86  coaxial with valve axis A. Primary pole piece  80  is fixed to solenoid housing base  60 , for example, by press fit within solenoid housing aperture  62 . 
     Secondary pole piece  82  includes secondary pole piece bore  90  which extends axially through secondary pole piece  82  coaxial with valve axis A. Secondary pole piece bushing  92  is fixed within secondary pole piece bore  90 , for example, by press fit. Secondary pole piece bushing  92  is made of a non-magnetic material, for example, bronze or plastic and includes secondary pole piece bushing bore  94  which extends axially through secondary pole piece bushing  92  coaxial with valve axis A. 
     Primary pole piece  80  may be fixed to secondary pole piece  82  with alignment ring  96 . Alignment ring  96  is cylindrical and made of a non-magnetic material, for example, brass or stainless steel. Alignment ring  96  is fixed to primary pole piece  80 , for example, by press fit with primary pole piece reduced diameter section  98 . Alignment ring  96  axially abuts primary pole piece shoulder  100  which is defined by primary pole piece reduced diameter section  98 . Similarly, alignment ring  96  is fixed to secondary pole piece  82 , for example, by press fit with secondary pole piece reduced diameter section  102 . Alignment ring  96  axially abuts secondary pole piece shoulder  104  which is defined by secondary pole piece reduced diameter section  102 . Alignment ring  96  is sized to fit within spool bore  70  such that alignment ring  96  may be inserted within spool bore  70  without restriction. Alignment ring  96  is also sized to axially space primary pole piece  80  from secondary pole piece  82 . 
     Solenoid subassembly  18  also includes armature  106  which is at least partly disposed within secondary pole piece bore  90  in a clearance fit such that armature  106  is able to slide within secondary pole piece bore  90  without restriction and such that radial movement of armature  106  within secondary pole piece bore  90  is substantially prevented. Armature  106  is made of a magnetic material and includes armature bore  108  which extends axially through armature  106  and coaxial with valve axis A. Armature  106  may also be partially received within enlarged section  110  of primary pole piece bore  84 . Enlarged section  110  is sized to allow unrestricted movement of armature  106  within enlarged section  110 . The axial position of armature  106  along valve axis A is variable based on electric current supplied to coil  76  by electric current source  20 . 
     Solenoid subassembly  18  also includes connecting rod  112  which is received within primary pole piece bushing bore  88 , secondary pole piece bushing bore  94 , and armature bore  108  coaxial with valve axis A. Connecting rod  112  is sized to form a slip fit with primary pole piece bushing bore  88  and secondary pole piece bushing bore  94  such that connecting rod  112  is able to move axially without restriction and such that radial movement of connecting rod  112  is substantially prevented. Connecting rod  112  is fixed to armature  106 , for example by press fit or staking such that connecting rod  112  moves axially with armature  106  as a single unit. Connecting rod  112  includes rod spring seat  114  which is formed by a reduced diameter end of connecting rod  112  that is proximal to hydraulic subassembly  12 . The end of connecting rod  112  that is proximal to hydraulic subassembly  12  is fixed to poppet rod  40 . In this way, axial movement of armature  106 /connecting rod  112  is translated to axial movement of poppet rod  40 . 
     Return spring  116  radially surrounds a portion of poppet rod  40  and a portion of connecting rod  112 . Return spring  116  is disposed axially between exhaust seat retainer  50  and rod spring seat  114  to bias poppet rod  40 /connecting rod  112 /armature  106  away from hydraulic subassembly  12 . 
     Solenoid subassembly  18  also includes solenoid housing cover  118  made of a magnetic metal for closing the end of solenoid housing  56  which is distal from solenoid housing base  60 . Solenoid housing cover  118  includes alignment tabs  120  that extend radially outward from solenoid housing cover  118 . Alignment tabs  120  fit within solenoid housing notches  122  formed in solenoid housing sidewall  58  of solenoid housing  56  (only one solenoid housing notch  122  is visible in  FIG. 2 ). Attachment tabs  124  extend axially away from solenoid housing sidewall  58  to define solenoid housing notches  122 . In  FIG. 1 , attachment tab  124  is shown as a solid line as it appears after assembly and being crimped (i.e. folded over) to retain solenoid housing cover  118 . Also in  FIG. 1 , attachment tab  124  is shown as a phantom line as it would appear prior to the folding or crimping operation. In  FIG. 2 , attachment tabs  124  are shown only as they would appear prior to the folding or crimping operation. Solenoid housing cover  118  includes recessed section  126  which may be formed, for example, by a stamping operation. Recessed section  126  is formed with a diameter to receive a portion of secondary pole piece  82  therewithin. 
     After attachment tabs  124  have been crimped to retain solenoid housing cover  118 , an compressive crimp load exists on solenoid housing cover  118  along valve axis A. This crimp load is counteracted at the outer edge of solenoid housing cover  118  by solenoid housing sidewall  58 . This crimp load is also counteracted radially inward of the outer edge of solenoid housing cover  118  by a metallic column which may be formed by the combination of primary pole piece  80 , alignment ring  96 , and secondary pole piece  82 . It should be noted that if primary pole piece  80  is attached to solenoid housing base  60  by a press fit within solenoid housing aperture  62 , the force required to move primary pole piece  80  relative to solenoid housing base  60  must be greater than the axial force acting on primary pole piece  80 /alignment ring  96 /secondary pole piece  82  as a result of attachment tabs  124  being crimped over to retain solenoid housing cover  118 . In this way, the crimp load is isolated from plastic components and consequently the crimp load is not supported by any plastic components which could creep over time due to the crimp load. Creep of plastic parts over time due to the crimp load may cause a change in the position over time of poppet rod  40 /connecting rod  112 /armature  106  for a given electric current applied to coil  76  compared to the position of poppet rod  40 /connecting rod  112 /armature  106  at the same given electric current applied to coil  76  when valve assembly  10  is first manufactured. 
     When electric current source  20  applies an electric current of sufficient magnitude to coil  76 , a magnetic field is generated through a magnetic circuit which includes primary pole piece  80 , armature  106 , secondary pole piece  82 , solenoid housing cover  118 , and solenoid housing  56 . The magnetic field creates an attractive force between armature  106  and primary pole piece  80 , thereby causing armature  106  to move toward primary pole piece  80  and compressing return spring  116 . The magnitude that armature  106  moves may be proportional to the magnitude of electric current applied to coil  76  in order to precisely control the axial position of armature  106 . When the electric current applied to coil  76  is decreased or stopped, return spring  116  urges armature  106  in the upward direction as viewed in  FIG. 1 . 
     In operation and referring to  FIG. 1 , valve assembly  10  is shown in an operational state in which maximum flow and/or pressure is permitted to be supplied from fluid source  14  to working device  16 . This is accomplished by electric current source  20  applying a current to coil  76  sufficient to axially move armature  106 /poppet rod  40 /connecting rod  112  until exhaust valve member  48  contacts exhaust seat  44 . When this occurs, return spring  116  is compressed and ball  34  is unseated with supply valve seat  36  by poppet rod tip  42 . Ball  34  may be moved further away from supply valve seat  36  by fluid from fluid source  14  until ball  34  contacts ball retainer  38 . In this way, the maximum amount of flow and/or pressure of the fluid from fluid source  14  is applied to working device  16 . Arrows S are used to illustrate the pressure and/or flow fluid supplied by fluid source  14 . 
     In operation an now referring to  FIG. 3  valve assembly  10  is shown in an operational state in which flow and pressure is prevented from being supplied from fluid source  14  to working device  16 . This is accomplished by stopping electric current source  20  from applying a current to coil  76  or decreasing the current to a magnitude such that return spring  116  axially urges armature  106 /poppet rod  40 /connecting rod  112  to a position that prevents poppet rod tip  42  from interfering with ball  34  from seating with supply valve seat  36 . When this occurs, exhaust valve member  48  is lifted from exhaust seat  44  to allow fluid to exit valve assembly  10  through exhaust port  30 . This allows ball  34  to seat against supply valve seat  36  by the flow and/or pressure of fluid from fluid source  14 , thereby preventing fluid communication from fluid source  14  to working device  16 . Arrows E are used to illustrate the exhaust of fluid from working device  16  to exhaust port  30 . 
     While not shown, it should now be understood that electric current source  20  may apply a current to coil  76  sufficient to axially move armature  106 /poppet rod  40 /connecting rod  112  to positions that are intermediate of the positions shown in  FIGS. 1 and 3 . This allows some flow and/or pressure of fluid from fluid source  14  to escape to exhaust port  30  in order to decrease the flow and/or pressure of fluid supplied to working device  16 , thereby achieving a desired flow and/or pressure of fluid to working device  16 . 
     Valve assembly  10  has been illustrated as preventing fluid communication from fluid source  14  to working device  16  when coil  76  is not supplied with an electric current and has also been illustrated as preventing fluid communication from working device  16  to exhaust port  30  when a maximum electric current is applied to coil  76  which is commonly referred to as a “normally low” valve because the default operation (i.e. no electric current) of valve assembly  10  results in low flow and/or pressure to working device. It should now be understood that valve assembly  10  may also be configured to be a “normally high” valve by reversing the positions of primary pole piece  80  and secondary pole piece  82  and repositioning return spring  116  to urge poppet rod  40 /armature  106 /connecting rod  112  toward hydraulic subassembly  12 . This arrangement would make the default operation (i.e. no electric current) to allow maximum flow and/or pressure of fluid to working device  16  from fluid source  14 . 
     While solenoid subassembly  18  has been shown in the context of actuating a valve, it should now be understood that the use of solenoid subassembly  18  need not be limited to actuating valves, but may be used in other applications where linear motion generated by a solenoid is commonly used. It this way, the magnitude of linear motion produced by solenoid assembly  18  may be precisely controlled over time for a given electric current since creeping of plastic components within solenoid assembly  18  due to crimp forces is eliminated. 
     While this invention has been described in terms of preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.