Solenoid operated control valve

Abstract: A solenoid operated control valve having a plastic housing (62) that supports a coil winding (18). A valve plunger (28) and a stop member (38) both of which are formed of magnetic material carry magnetic flux developed by energization of the coil winding. Opposed end faces of the valve plunger and stop member are spaced from each other to form an air gap (87) that is traversed by the magnetic flux. The length of the air gap can be adjusted. To accomplish this, the stop member has a threaded portion (44) that is threaded into a portion (64) of the plastic housing. An end cap (78), formed of plastic material, is provided that is coupled to the stop member in a manner that prevents relative rotation between the end cap and stop member. After the air gap is adjusted, the end cap is ultrasonically welded to the housing.

Description: This invention relates to solenoid operated control valves and more particularly to such a solenoid valve that is provided with means for adjusting its operating characteristic as, for example, shown in US-A-4,463,332 and DE-A-2,559,323. One of the objects of this invention is to provide an improved solenoid valve that includes means for adjusting the operating characteristic of the solenoid valve so that after adjustment the solenoid valve will have a predetermined precision operating characteristic. To this end, a solenoid operated control valve in accordance with the present invention is characterised over DE-A-2,559,323 by the features specified in the characterising portion of Claim 1. More specifically, the solenoid valve of this invention includes a coil winding that is encapsulated with plastic material that forms an outer housing. The solenoid valve has a reciprocable magnetic valve plunger and a stop member that is formed of magnetic material. The valve plunger and stop member are located within the coil winding and opposed end faces of the plunger and stop member are separated to provide an air gap. When the coil winding is energized, it generates magnetic flux that passes through or traverses the air gap. The length of the air gap can be adjusted. The adjustment of the air gap is accomplished by providing the stop member with a threaded portion that is threaded into a portion of the plastic housing. Accordingly, as the stop member is rotated it is moved axially to vary the length of the air gap. After the stop member has been rotated to an adjusted position it is fixed from rotation by an end cap which is formed of plastic material. The end cap has a hexagonal portion that is located in a complementary hexagonal bore formed in the stop member. When the air gap has been adjusted to the desired length, the end cap is assembled to the stop member and the end cap is then welded to the outer housing to thereby fix the end cap and stop member from rotation and from any further adjustment. The air gap is adjusted in a manner that has been described, while the solenoid valve is controlling fluid flow in a manner that simulates actual operating conditions of the solenoid valve. Thus, when the air gap is being adjusted, the coil winding is energized with pulse-width modulated direct current and the amount of fluid flow is measured. The air gap is adjusted until the desired amount of fluid flow is attained. Another object of this invention is to preferably provide a solenoid valve, of the type described, that has sealing means for excluding salt spray, water and other contaminants from entering the solenoid valve. More specifically, the weld between the end cap and outer housing serves as a secondary sealing means. A primary seal is provided by an elastomeric O-ring that is compressed between a portion of the outer housing and a portion of the end cap. The present invention is now described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a view, partly in section, illustrating a solenoid operated control valve made in accordance with this invention; Figure 2 is a sectional view taken along line 2--2 of Figure 1; and Figure 3 is a perspective view of a cap member that is used in the solenoid valve shown in Figure 1. Referring now to the drawings, the solenoid valve of this invention comprises a one-piece moulded part generally designated by reference numeral 10 which is formed of a moulded plastics material. The part 10 has a tubular portion 12 and a pair of annular walls 14 and 16. The outer surface of tubular portion 12 and the annular walls 14 and 16 form a coil spool which supports a coil winding 18 that is formed of a plurality of turns of wire. The internal surface of tubular portion 12 supports a stop member 38, which will be described below. The part 10 has tubular pipe or conduit portions 20 and 22 which define passages 24 and 26. As will be more fully described hereinafter, passage 24 is adapted to be connected to a source of vacuum such as the intake of an internal combustion engine and passage 26 is adapted to be connected to a charcoal canister. The tubular portion 12 of part 10 slidably supports a valve plunger 28 that is formed of steel. Since valve plunger 28 is formed of steel, it is formed of a magnetic material. The valve plunger 28 has a valve head 30 that carries an annular part 32 that is formed of rubber. The other end of valve plunger 28 carries another annular part 34 which is formed of rubber and which operates as a bumper. The annular parts 32 and 34 can be formed by moulding rubber to an axially extending internal bore (not illustrated) that extends entirely through valve plunger 28. The annular parts 32 and 34 are joined by the portion of the rubber material that is located in the bore of valve plunger 28. The annular part 32 cooperates with an annular valve seat 36. When annular part 32 engages valve seat 36 the valve is closed so that there will be no flow between passages 24 and 26. The internal surface of tubular portion 12 supports the stop member 38 that is formed of steel. Since stop member 38 is formed of steel it is formed of a magnetic material. The stop member 38 has an annular flange 40. A compression spring 42 is interposed between the annular flange 40 and an annular surface on valve plunger 28. The spring 42 urges or forces the valve to a closed position, that is, it forces valve plunger 28 to a position where annular part 32 engages valve seat 36. The stop member 38 has an integral externally threaded portion 44 and a bore 46 that is hexagonally shaped in cross section. The threaded portion 44 can be formed as a 5/16-32 UNEF-2A thread. The stop member 38 has an annular groove that accommodates an elastomeric O-ring seal 48. The O-ring seal 48 engages the internal surface of tubular portion 12. A portion of the stop member 38 is disposed within an opening 50 formed in an end wall 52 of a steel part 54. The steel part 54 has two axially extending and circumferentially spaced straps, one of which is shown in Figure 1 and identified by reference numeral 56. The steel part 54 being formed of magnetic material (steel) forms part of a magnetic circuit for the flux developed by coil winding 18. The magnetic circuit for the solenoid valve further includes steel parts 58 and 60. Steel part 58 may be generally U-shaped and can have an internal arcuate wall. Although only one steel part 60 is shown it is preferred that two steel parts 60 be used which abut each other. The steel parts 60 are semi-circular. The steel parts 58 and 60 cooperate with the two straps, like strap 56, to form a magnetic circuit. The outer housing of the solenoid valve, which has been generally designated by reference numeral 62, is formed of a thermoplastic material such as 13% glass filled nylon. The outer housing 62 is moulded to the internal parts that have been described and it encapsulates these parts. During this overmoulding operation a pin is inserted into the bore of tubular portion 12 to prevent collapsing of the spool portion of part 10. This pin is shaped such that during the moulding operation, three radially inwardly extending lobes 64 are formed. The outer housing 62, after being moulded to shape, includes a tubular portion 66 having a bore 68, outer wall 70, portion 72 and outer portions 74 and 76 disposed respectively about conduit portions 20 and 22 of part 10. The solenoid valve has an end cap generally designated by reference number 78, which is shown in Figure 2 and in the perspective view of Figure 3. The end cap 78 is formed of a plastic material and can be formed of the same material as outer housing 62 (13% glass filled nylon). The end cap 78 has a hexagonal stud portion 80 which is complementary to the hexagonal bore 46 of the stop member 38. The end cap 78 further has a triangular-shaped bore 82 and an annular portion 84. The cap 78 has an annular V-shaped portion 86 which is shown in Figure 1. The intended use for the solenoid valve, that has been described, is in an evaporative emission control apparatus for a motor vehicle. In such an apparatus, fuel vapour from the vehicle fuel tank is supplied to a charcoal canister. This fuel vapour is purged from the charcoal canister by connecting the canister to the intake manifold or intake side of an internal combustion engine. The solenoid valve of this invention controls the amount of flow between the charcoal canister and the engine. Thus, the conduit portion 20 is connected to the intake of the engine and conduit portion 22 is connected to the charcoal canister. The passage 24 is accordingly connected to a vacuum and causes vapour to be pulled into the engine by control of valve plunger 28. During use, the coil winding 18 is supplied with a pulse-width modulated direct current having a variable duty cycle. This causes the valve to open and close at the frequency of the pulse-width modulated direct current and the relative time periods that the valve is open and closed depends upon the duty cycle. As duty cycle increases, the amount or volume of flow per unit time will increase and vice-versa. The purpose of stop member 38 and end cap 78 and how they are assembled to outer housing 62 will now be described. When the stop member 38 is assembled into the tubular portions 12 and 66, it is rotated to cause the threaded portion 44 to cut or roll threads into the three lobes 64. The stop member 38 now has a threaded connection with tubular portion 66 so that rotation of stop member 38 will cause it to move axially in tubular portion 12 of part 10. It can be seen in Figure 1 that there is an air gap 87 between the right end face of valve plunger 28 and the left end face of stop member 38. The air gap 87 is adjustable and may be in a range of about 0.8 mm (0.032 inches). The flux generated by coil winding 18 passes axially through valve plunger 28 and stop member 38 and passes through the air gap 87. Further, there is a gap between the end face of annular part 34 and the end face of stop member 38 which may be about 0.3 mm (0.012 inches). The gaps that have been described are both adjustable as to length by rotating stop member 38. The air gap 87 that has been described is adjusted by rotation of stop member 38. When it is desired to adjust stop member 38 an adjusting tool (not illustrated), which has a hexagonal portion, is moved into the complementary hexagonal bore 46 of stop member 38. Accordingly, rotation of the tool will now rotatably drive stop member 38. As stop member 38 rotates, the threaded portion 44 causes the stop member 38 to move axially to adjust the air gap 87 that has been described. In order to set the air gap 87, the passage 24 is connected to a source of vacuum and the coil winding 18 is energized with a pulse-width modulated current at a duty cycle of, for example, 30%. When coil winding 18 is energized, the flux developed will cause valve plunger 28 to move to a position where annular part (bumper) 34 engages the end face of stop member 38. When coil winding 18 is deenergized, the spring 42 forces the valve plunger 28 to a position where annular part 32 engages valve seat 36. The amount of flow from passage 26 to passage 24 is now measured as the stop member 38 is rotated to adjust the air gap 87. When the amount of flow is equal to a desired amount, the rotation of stop member 38 is stopped or terminated. After stop member 38 has been adjusted the end cap 78 and an elastomeric O-ring 88 are assembled. This is accomplished by inserting hexagonal stud portion 80 into hexagonal bore 46 of stop member 38. The end cap 78 is now ultrasonically welded to the end of tubular portion 66 of outer housing 62. This weld is between the end face of tubular portion 66 and end face of annular portion 84 and the weld is formed by the melting of engaged portions of the end faces. The weld is a continuous annular weld. This ultrasonic weld positively locks the end cap 78 to outer housing 62 and this positive lock serves to positively lock the stop member 38 in place. In this regard, when hexagonal stud portion 80 is inserted into hexagonal bore 46, stop member 38 and end cap 78 cannot rotate relative to each other. This, of course, prevents the air gap 87 from varying during use of the solenoid valve. The ultrasonic weld also forms a seal or barrier to prevent salt spray, water and the like from entering the solenoid valve. The V-shaped portion 86 of end cap 78 is used as an aid for the ultrasonic welding. In regard to the adjusting of the air gap 87, it will be appreciated that the spring 42 forces the valve closed and that the magnetic force developed to open the valve against the force of the spring will depend upon the length of the air gap 87. Further, the adjustment of stop member 38 sets a limit as to how far the valve can open, that is, valve plunger 28 is stopped in its movement when annular part (bumper) 34 engages the end face of stop member 38. The adjustment of stop member 38 compensates for differences or variations in the response characteristic of the solenoid valve that may occur from one solenoid valve to another solenoid valve during the manufacture of the solenoid valve. The purpose of O-ring seal 88 is to provide a primary seal. Thus, in most cases, the welding of end cap 78 to tubular portion 66 will provide a continuous seal. However, in the event that the weld is not entirely continuous the O-ring seal 88 will prevent entry of unwanted substances. It can be seen, in Figure 1, that the O-ring seal 88 is tightly compressed between a portion of end cap 78 and an internal surface of tubular portion 66. The bore 82 of end cap 78 is adapted to receive a tool for applying torque to end cap 78 after it is welded to the end of tubular portion 66. Torque is applied to test the strength of the weld.

Claims: A solenoid operated control valve comprising, a housing (62) having a tubular portion (66); a coil winding (18) supported by the housing and having an internal bore (12); a control valve comprising a valve plunger (28) disposed within the internal bore (12); a stop member (38) formed of magnetic material having a portion thereof disposed within the internal bore (12), the valve plunger (28) and stop member (38) having opposed spaced end faces that define an air gap (87), the coil winding (18) when energized generating magnetic flux that traverses the air gap (87); the stop member (38) having an integral external threaded portion (44) threaded into internal wall means (64) of the tubular portion (66) of the housing (62) whereby rotary movement of stop member (38) causes the stop member to be moved axially in the internal bore to adjust the air gap (87); an end cap (78) closing an open end of the tubular portion (66) of the housing (62); and coupling means (46,80) connecting the end cap (78) and the stop member (38) and which is operative to prevent relative rotation between the stop member (38) and the end cap (78); characterised in that the housing (62) and the end cap (78) are both formed of plastic material; and in that the end cap is welded to the tubular portion (66) of the housing by a substantially continuous weld that is operative to prevent rotation of the end cap relative to the housing and operative to provide a seal. A solenoid operated control valve according to claim 1, wherein the coupling means comprises a bore (46) in the stop member (38) and wherein the end cap (78) has a portion (80) thereof located in the bore (46) in the stop member (38), the bore (46) in the stop member (38) being defined by at least one flat wall and the portion (80) of the end cap (78) having at least one flat wall that engages the flat wall in the bore (46) in the stop member (38). A solenoid operated control valve according to claim 1 or claim 2, wherein an elastomeric O-ring (88) is compressed between an internal wall of said tubular portion (66) of the housing (62) and a portion of the end cap (78). A solenoid operated control valve as claimed in any one of claims 1 to 3, wherein the valve plunger (28) has valve means (32) that engages a valve seat (36) in a closed position of the valve, a spring (42) engages the valve plunger (28) and is operative to force the valve means (32) against the valve seat (36) in a closed position of the valve, a spring (42) engages the valve plunger (28) and is operative to force the valve means (32) against the valve seat (36) to close the valve, the valve plunger (28) being shiftable against the force of the spring (42) to a position wherein the valve means (32) moves away from the valve seat (36) to open the valve when the coil winding (18) is energized, the valve plunger (28) having means (34) engaging the end face of the stop member (38) when the coil winding (18) is energized to limit the opening movement of the valve plunger (28). A solenoid operated control valve according to claim 4, wherein the spring is a compression spring (42) that is interposed between the valve plunger (28) and the stop member (38).

Inventors: WATSON RICHARD D, WATSON, RICHARD D.
Applicants: GEN MOTORS CORP, GENERAL MOTORS CORPORATION
Application year: 1989
Main classification: F16K31
IPC codes: F16K31