60/466,489 filed April 28, 2003.

BACKGROUND OF THE INVENTION [0001] This invention relates to vehicular brake systems, and more particularly to an improved armature for a control valve mounted in a hydraulic control unit of an electronically controlled brake system.

[0002] Electronically controlled brake systems for vehicles are well known. One type of electronically controlled brake system includes a hydraulic control unit (HCU) connected in fluid communication between a master cylinder and a plurality of wheel brakes. The HCU typically includes a housing containing control valves and other components for selectively controlling hydraulic brake pressure at the wheel brakes.

[0003] Control valves for HCU's are commonly formed as electronically actuated solenoid valves. A typical solenoid valve includes a cylindrical armature slidably received in a sleeve or flux tube for movement relative to a valve seat. A spring is used to bias the armature in an open or closed position, thereby permitting or blocking fluid flow through the valve, respectively. A coil assembly is provided about the sleeve. When the valve is energized, an electromagnetic field or flux generated by the coil assembly causes the armature to slide from the biased open or closed position to a closed or open position, respectively. A description of electromagnetic flux generated by the coil assembly of a solenoid valve is provided in U. S. Patent Application No. 10/389,459, filed March 14,2003 which is hereby incorporated by reference.

[0004] Control valves mounted in a HCU are actuated by an electronic control module to provide desired braking functions such as anti-lock braking, traction control, and vehicle stability control.

[0005] To provide desired braking responses, fluid flow must be maintained from the wheel brakes to the master cylinder during all fluid pressure conditions during brake release.

BRIEF DESCRIPTION OF THE DRAWINGS [0006] Fig. 1 is a schematic diagram of a vehicular braking system according to the present invention illustrating a hydraulic control unit having a normally open control valve, a normally closed control valve, an accumulator, and a pump.

[0007] Fig. 2 is a cross sectional view through the normally open control valve schematically illustrated in Fig. 1, showing the armature assembly according to this invention.

[0008] Fig. 2A is an enlarged partial view of the valve shown in Fig. 2.

[0009] Fig. 3 is a bottom plan view of the armature core illustrated in Fig. 2.

[0010] Fig. 4 is a cross sectional view taken along line 4-4 of Fig. 3.

[0011] Fig. 5 is a cross sectional view through an alternate embodiment of the normally open control valve schematically illustrated in Fig. 1, showing an alternate embodiment of the armature assembly according to this invention.

[0012] Fig. 6 is a bottom plan view of the armature core illustrated in Fig. 5.

[0013] Fig. 7 is a cross sectional view taken along line 7-7 of Fig. 6.

[0014] Fig. 8 is an enlarged cross sectional view of the armature illustrated in Fig. 5.

[0015] Fig. 9 is a bottom plan view of a first alternate embodiment of the armature core illustrated in Fig. 2.

[0016] Fig. 10 is a bottom plan view of a second alternate embodiment of the armature core illustrated in Fig. 2.

[0017] Fig. 11 is a bottom plan view of a third alternate embodiment of the armature core illustrated in Fig. 2.

[0018] Fig. 12 is a bottom plan view of a fourth alternate embodiment of the armature core illustrated in Fig. 2.

[0019] Fig. 13 is a flow chart showing the method of forming an armature according the method of this invention.

SUMMARY OF THE INVENTION [0020] The present invention relates to an armature assembly for a valve and a method of manufacturing the same. The method includes providing powdered metal. The powdered metal is then placed in a die having a cavity defining the shape of an armature core. Pressure is then applied to the powdered metal in the die so as to compact the powdered metal into the shape of the armature core. The powdered metal of the armature core is then heated so as to bond the powdered metal, thereby forming a paramagnetic armature core.

[0021] In another embodiment of the invention, the armature assembly includes an armature core formed from powdered metal, and an armature body attached to the armature core.

[0022] In another embodiment of the invention, the armature assembly includes an armature core formed from ultra-pure iron, and an armature body attached to the armature core.

[0023] In another embodiment of the invention, the armature assembly includes an armature core having a longitudinal passage therethrough, wherein the longitudinal passage includes a substantially longitudinal groove, and an armature body attached to the armature core.

[0024] In another embodiment of the invention, the armature assembly includes an armature core having a groove with a substantially arcuate cross-section defined in a surface thereof, and an armature body attached to the armature core.

[0025] Other advantages of this invention will become apparent to those skilled in the art from the following detailed description of the invention, when read in light of the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION [0026] An exemplary vehicular brake system having a valve according to this invention is indicated generally at 10 in Fig. 1. The brake system 10 includes valves and other components described below to provide an anti-lock braking function. In other embodiments, brake system 10 can also include components to provide traction control and/or vehicle stability control functions, and/or other brake system control functions.

[0027] The exemplary brake system 10 includes a brake pedal 12 connected to a master cylinder 14 for providing pressurized brake fluid to a plurality of wheel brakes 16, only one of which is shown. The wheel brake 16 is schematically illustrated as a disc brake. However, the wheel brake 16 may be any type of wheel brake found on vehicles, including a drum brake.

[0028] The brake system 10 also includes a hydraulic control unit (HCU) 18 connected in fluid communication between the master cylinder 14 and the wheel brake 16. The HCU 18 includes a housing 19 having bores for receiving control valves and other components described below. Fluid conduits are provided between the bores to provide fluid communication between the valves and other components.

For purposes of clarity of illustration, only one set of components is illustrated in Fig. 1. Typically, however, the HCU 18 also houses corresponding components for other brake circuits and/or wheels of the vehicle.

[0029] The HCU 18 preferably includes a normally open control valve 20, commonly known as an isolation valve, disposed between the master cylinder 14 and the wheel brake 16. The HCU further includes at least one low pressure accumulator 22, a normally closed control valve 24, commonly known as a dump valve, disposed between the wheel brake 16 and the low pressure accumulator 22.

A hydraulic pump 26 has an inlet connected to the low pressure accumulator 22, and a pump discharge connected to the fluid conduit between the master cylinder 14 and the control valve 20. The HCU 18 may also include other fluid flow devices such as an attenuator, restricted orifices, and check valves (none of which are illustrated), depending upon the system design. The control valve 20 is preferably formed as a solenoid valve switchable between two positions. The control valve 24 is also preferably formed as a solenoid valve switchable between an open and a closed position. The valves 20 and 24, as well as the pump 26, are electrically connected to an electronic control module (not illustrated) and operated to provide desired system braking in a well-known manner.

[0030] A sectional view of the control valve 20 is illustrated in Fig. 2. The control valve 20 is received in a bore 28 formed in the housing 19. The control valve 20 preferably includes a valve body 30 having a first body portion or sleeve 32 and a second body portion or valve seat 34. The valve seat 34 includes a body portion 36. The valve seat 34 further includes a radially outwardly extending flange 48 formed about an intermediate portion thereof. One or more longitudinally extending flow passage slots 49 are formed in the outer surface of the valve seat 34, including the flange 48.

[0031] An annular portion 46 of the sleeve 32 is crimped onto the flange 48 during assembly of the valve body 30 to fix the sleeve 32 to the valve seat 34. Fig.

2A shows the"as manufactured"position of the annular portion 46 relative to the flange 48, that is, the position before the annular portion 46 is crimped. A lip seal 70 can be provided in a groove 72 formed in an outer surface of the valve seat 34.

A fluid seal 74 can be provided between the sleeve 32 and the valve seat 34. Any other desired type of fluid sealing means can also be used.

[0032] The control valve 20, being a normally open control valve, further includes an armature 40 slidably received in a bore 42 of the sleeve 32, and biased away from the valve seat 34 when the control valve 20 is not energized. A coil assembly 44 is disposed about the sleeve 32. When the coil assembly 44 is energized to produce an electromagnetic field, the armature 40 is pulled toward the valve seat 34 to prevent fluid flow through the valve 20.

[0033] The armature 40 is disposed at an extreme of travel away from the valve seat 34 when the coil assembly 44 is deenergized such that the control valve 20 is in an open position, as shown in Fig 2. A spring 45 preferably engages the armature 40 to urge the armature 40 away from the valve seat 34 and toward an open position of the control valve 20. When the coil assembly 44 is energized, the armature 40 is urged by the electromagnetic force in opposition to the spring force to travel toward the valve seat 34, and thus toward the closed position. When the control valve 20 is in the closed position, fluid flow through the control valve 20 is blocked. When the control valve 20 is in the open position, fluid flow through the control valve 20 is not blocked.

[0034] Preferably, the sleeve 32 is retained within the bore 28 by clinching, wherein material of the housing 19 is forced into a groove 50 formed in the outer surface of the sleeve 32, as the valve body 30 is pressed into the bore 28. This occurs because the diameter of the body 32 on the side of the groove 50 adjacent to the sleeve 32 is smaller in diameter than the bore 28. While the diameter of the body 32 on the other side of the groove 50 is greater in diameter than the bore 28 as shown in Fig. 2. The combined sleeve 32 and valve seat 34 can alternately be retained in the bore 28 by any desired mechanical or chemical means operative to retain the sleeve 32 within the bore 28.

[0035] The valve seat 34 includes a longitudinal (preferably axial) fluid passage 52 that terminates in a reduced diameter bore 54. A seat 56 is formed on an outer surface of the valve seat 34. If desired, the seat 56 can be formed as a truncated cone. Preferably, the outer conical surface of the seat 56 forms an angle a within the range of from about three degrees to about five degrees, as measured from a plane 58 perpendicular to the longitudinal axis of the fluid passage 52. More preferably, the seat 56 has an angle a of about four degrees.

[0036] An end surface 60 of the armature 40 acts as a valve sealing element and engages the seat 56 when the armature 40 moves downwardly. When the end surface 60 engages the seat 56, the fluid passage 52 is blocked. A filter assembly 62 can be provided adjacent an inlet of the fluid passage 52.

[0037] The armature 40 is preferably formed as a subassembly and then assembled with the remainder of the valve 20. The armature 40 includes an armature core 100, as shown in Figs. 3 and 4, formed as a hollow cylinder from a paramagnetic material, preferably a ferromagnetic material, that is, a paramagnetic material composed at least partially of iron. Preferably, each end of the armature core 100 is a planar surface. The armature core 100 includes a longitudinal passage 102. The longitudinal passage 102 can be formed as a bore extending along a longitudinal axis L of the armature core 100, as shown in Fig. 2. In one preferred embodiment, the longitudinal passage 102 is formed with a constant diameter.

[0038] The armature 40 also includes an armature body 104. Preferably, the armature body 104 is formed of a non-magnetic material. The armature body 104 is also preferably formed from a molded material such as a plastic, ceramic, or non- magnetic metallic material. More preferably, the armature body 104 is formed from a polymeric material such as polyphenylene sulfide (PPS) or polypthalamide (PPA).

The armature core 100 can be placed in a mold. Then the desired material can be injected into the mold to form the armature body 104. The armature body 104 includes a central section 106 that fills the longitudinal passage 102 of the armature core 100. A first end section 108 and a second end section 110 are formed at opposite ends of the central section 106. Each of the first and second end sections 108 and 110 extend beyond an end surface of the armature core 100 a predetermined distance. This formation and structure can be described as an armature core 100 having an overmolded armature body 104.

[0039] The armature core 100 is, surprisingly, formed from a powdered metal.

In the past, an upper practical limit on compaction of powdered metal was about 86 percent. Therefore, known powdered metal objects had relatively high reluctance (resistance to magnetic flux) to a degree that made the use of powdered metal unsuitable for use an armature for a solenoid valve. It has been discovered however, that very high compaction of at least some paramagnetic powdered metals (described in more detail below) can produce a component suitable for use as a core of an armature for a solenoid valve. A source providing services for very high compaction of powdered metals is SG Magnets Limited, Tesla House, 85 Ferry Lane, Rainham, Essey RM139YH, United Kingdom. Depending upon the application, a compaction of about 95 percent is believed to provide objects with sufficiently low reluctance that they may be useful as armature cores in solenoid valves. To date, objects with compaction of about 98.5 percent have been produced, and these have been shown to be very suitable for use as cores for solenoid valve armatures.

[0040] One skilled in the art would expect a valve, such as the valve 20, having such a powdered metal armature, to generate less output force than known steel (generally screw machined) armatures. However, when provided with the armature 40 having the core 100 formed from powdered metal, the valve 20 was shown in experiments to produce a greater than expected output force. Advantageously, the valve 20, having the armature 40 according the invention, produced an output force within the range of about 1 percent to about 4 percent higher than similar valves having known steel armatures. Further, in the armature 40 having the core 100 formed from powdered metal, it has been calculated that the valve 20 can produce an output force increase of about 9 percent higher than similar valves having known steel armatures, such as, for example an increase of from about 9. 4 N to about 10.3 N. It has been further shown in experiments that the armature 40 having the core 100 formed from powdered metal will have a magnetic permeability within the range of from about 4 percent to about 9 percent greater than typical known steel armatures.

[0041] To form the armature core 100, as best shown in Fig. 4, powdered metal is preferably disposed in a die, such as the die 101 schematically illustrated in Fig.

4. The powdered metal is then shaped by high-tonnage compacting pressure within the die 101. Such high-tonnage compacting pressure results in very high compaction. As used herein, compaction is defined as the percent of volume filled with material. Very high compaction is defined as compaction that is within the range of from about 95 percent to about 100 percent. For example, within a given volume in the armature core 100,95 percent of the volume (or more) is occupied by the powdered metal with the remaining volume, if any, consisting of voids between particles of powdered metal. Once compacted, the armature core 100 is heat- treated, such as by the process known as sintering, to fuse the powdered metal and induce optimal strength. As used herein, sintering is defined as a process whereby material in powder form is heated to a high temperature less than the melting point of the material. Such heating produces a generally porous material that is fused or bonded.

[0042] As shown in Fig. 13, a preferred method of forming a powdered metal armature, such as the armature 40, includes providing powdered metal. The powdered metal is then placed in a die having a cavity defining the shape of an armature core. A pressure is applied to the powdered metal in the die so as to compact the powdered metal into the shape of the armature core. The powdered metal of the armature core is then heated so as to bond the powdered metal.

[0043] As best shown in Figs. 3 and 4 the armature core 100 is generally cylindrical and includes a plurality of grooves 112 in an outer surface of the armature core 100. Preferably, the grooves 112 are substantially arcuate when viewed in cross section as best shown in Fig. 3. The edges 114 of the grooves 112 are also preferably arcuate or rounded, such as, for example having a radius of about 0.20 mm, as best shown in Fig. 3. Such grooves 112 provide fluid flow between the armature core 100 and the bore 42.

[0044] As would be understood by one skilled in the art, to achieve a precise outer diameter of an armature, armatures are often machined by the application of a tool. Preferably, centerless grinding is used to achieve a precise outer diameter of an armature, and such a process could be used on the armature core 100. However, such centerless grinding often results in undesirable sharp edges and undesirable sharp burrs when encountering vertical wall grooves in the surface of an armature.

The rounded edges 114 of the grooves 112 of the armature 100 formed from powdered metal and shaped by high-tonnage compacting pressure according to the method of the invention, substantially eliminate such sharp edges and sharp burrs.

[0045] It will be understood that, as used herein, machining is defined as the application of a tool to achieve a desired effect, such as polishing a surface or removing material from a surface. As described above, centerless grinding is used to achieve a precise outer diameter of an armature or armature core. It will be further understood that machining is not limited to the use of a tool in which the tool physically contacts the surface. Machining can include any other desired method for polishing a surface or removing material from a surface, such as those in which the tool is used to guide a polishing or material removal agent.

[0046] In the embodiment shown in Fig. 2, the armature core 100 includes two grooves 112. It will be understood however, that the armature core 100 can include any desired number of grooves 112, such as one groove, or more than two grooves, such as illustrated in the armature cores 100'shown in Fig. 9. It will be further understood that the armature core can include a plurality of grooves 113 formed in a surface of the longitudinal passage 102. The grooves 113 can be radially aligned with the grooves 112, as illustrated in the armature cores 100"and 100"', shown in Figs. 10 and 11, respectively. Alternately, the grooves 113 can be radially off-set relative to the grooves 112, as illustrated in the armature core 100"shown in Fig.

12. The grooves 112 and the grooves 113 can have any desired depth, such as the depths dl and d2, respectively, as shown in Fig. 10. It will be understood that the grooves 112 and the grooves 113 can have substantially equal depths, as shown in Fig. 10. Alternately, the grooves 113 can have a depth d3 greater that the depth d2 of the grooves 112, as shown in Fig. 11. Although not illustrated, if desired the grooves 112 can have a depth greater that the depth of the grooves 113.

[0047] The axial grooves 112 of the powdered metal armature 40 provide hydraulic damping and a flow path for hydraulic fluid. Additionally, the axial grooves 112 help to suppress eddy currents in the armature 40. The electric current in a solenoid valve coil naturally generates a magnetic field in the solenoid magnetic circuit, which cause the armature to move. See, for example, U. S. Patent Application No. 10/389, 459, which has been incorporated herein by reference.

However, as the electric current in the solenoid valve coil is terminated or rapidly decreased, the magnetic field collapses and generates a generally circular current in the armature. Such a circular current then exerts a magnetic force on the armature, thereby undesirably delaying movement of the armature.

[0048] Advantageously, the axial grooves 112, 113, and the longitudinal passage 102, increase the path length of the eddy currents, shown generally by the lines 120 in Figs. 3, and 9 through 12, inclusive, and decrease the cross-sectional area of the "conductor"in which the eddy currents are flowing, both of which increase the electrical resistance of the eddy current flow path. The magnitude of the eddy current paths 120 are therefore decreased, thereby decreasing (improving) the response time of the solenoid valve 20 to terminated or rapidly changing electric current.

[0049] Preferably, the armature core 100 is formed with very pure iron, known as ultra-pure iron. As used herein, ultra-pure iron is defined as consisting of about 99.90 percent iron, and having a carbon content of less than about 0.01 percent. If desired, small amounts of other materials such as phosphorous, silicon, binders, lubricants, and the like can be added to the ultra-pure iron. Preferably, the armature core 100 is formed from material that also includes about 0.45 percent phosphorous to improve the compaction. It has been determined for example, that such ultra- pure iron including about 0.45 percent phosphorous, allows a manufacturer to achieve compaction of about 98.5 percent. It will be understood that the armature core 100 can also be formed from any other desired powdered paramagnetic metal.

[0050] If desired, the armature core 100 can be polished or burnished, or can be coated or plated with a layer of a material suitable for reducing friction and corrosion. Electroless nickel is one such material that may be suitable. It has been determined that when covered with a layer of electroless nickel, the armature core 100 has increased resistance to corrosion, and a lower coefficient of friction.

Further, a non-magnetic coating such as electroless nickel provides a desirable non- magnetic gap between the armature core 100 and the bore 42.

[0051] A substantial cost reduction may be realized by forming the core 100 from powdered paramagnetic material. For example, in the exemplary embodiment of the valve illustrated in Fig. 2, it was shown in experiments that the cost to produce the armature 40 having the armature core 100, can be reduced by an amount within the range of from about $0.069 to about $0.186 less than a known armature.

[0052] Grooves formed in an outer surface of armatures formed according to the prior art typically have sharp lateral edges. Centerless grinding of the outer surface of such prior art armatures can generate undesirable metal burrs or debris, especially as a grinding tool contacts the sharp lateral edges of the grooves. An additional advantage of the present invention is that such metal debris is substantially eliminated during centerless grinding of an armature core 100 formed with grooves 112 having rounded edges 114 as described herein.

[0053] A sectional view of an alternate embodiment of the normally open control valve is illustrated generally at 220 in Fig. 5. The control valve 220 is received in the bore 28 of the housing 19. The control valve 220 preferably includes a valve body 230 having a first body portion or sleeve 232 and a second body portion or valve seat 234. The valve seat 234 includes a body portion 236. The valve seat 234 further includes a radially outwardly extending flange 248 formed about an intermediate portion thereof. One or more longitudinally extending flow passage slots 249 are formed in the outer surface of the valve seat 234, including the flange 248. An annular portion 246 of the sleeve 232 is crimped onto the flange 248 during assembly of the valve body 230 to fix the sleeve 232 to the valve seat 234.

The valve seat 234 is preferably formed from a ferromagnetic material, such as steel. The valve seat 234 can also be formed from any other desired ferromagnetic or non-ferromagnetic material. A lip seal 270 can be provided in a groove 272 formed in an outer surface of the valve seat 234. A fluid seal 274 can be provided between the sleeve 232 and the valve seat 234. Any other desired type of fluid sealing means can also be used.

[0054] The control valve 220, being a normally open control valve, further includes an armature 240 slidably received in a bore 242 of the sleeve 232, and biased away from the valve seat 234 when the control valve 220 is not energized. A coil assembly 244 is disposed about the sleeve 232. When the coil assembly 244 is energized to produce an electromagnetic field, the armature 240 is pulled toward the valve seat 234 to prevent fluid flow through the valve 220.

[0055] The armature 240 is disposed at an extreme of travel away from the valve seat 234 when the coil assembly 244 is deenergized such that the control valve 220 is in an open position, as shown in Fig 5. A spring 245 preferably engages the armature 240 to urge the armature 240 away from the valve seat 234 and toward an open position of the control valve 220. When the coil assembly 244 is energized, the armature 240 is urged by the electromagnetic force in opposition to the spring force to travel toward the valve seat 234, and thus toward the closed position.

When the control valve 220 is in the closed position, fluid flow through the control valve 220 is blocked. When the control valve 220 is in the open position, fluid flow through the control valve 220 is not blocked. Preferably, the sleeve 232 is retained within the bore 28 by clinching, as herein described above.

[0056] The valve seat 234 includes a longitudinal (preferably axial) fluid passage 252 that terminates in a reduced diameter bore 254. A seat 256 is formed on an outer surface of the valve seat 234. If desired, the seat 256 can be formed as a truncated cone. Preferably, the outer conical surface of the seat 256 forms an angle a within the range of from about three degrees to about five degrees, as measured from a plane 258 perpendicular to the longitudinal axis of the fluid passage 252.

More preferably, the seat 256 has an angle a of about four degrees. A filter assembly 262 can be provided adjacent an inlet of the fluid passage 252.

[0057] The armature 240 is preferably formed as a subassembly and then assembled with the remainder of the valve 220. As best shown in Fig. 8, the armature 240 includes an armature core 270, as shown in Figs. 6 and 7, formed from a ferromagnetic material. The armature core 270 is generally formed as a hollow cylinder having a first end 271 and a second end 273. Preferably, the first end 271 of the armature core 270 is a planar surface. The second end 273 is preferably stepped, and includes a first stepped portion 273A and a second stepped portion 273B. The armature core 270 includes a longitudinal (preferably axial) passage 272. The longitudinal passage 272 can be formed as a bore. Preferably, the longitudinal passage 272 is formed having a first diameter 272A at the first end 271 and a second or increased diameter 272B at the second end 273.

[0058] As best shown in Figs. 6 and 7 the armature core 270 includes a plurality of grooves 282 in an outer surface of the armature core 270. Preferably, the grooves 282 are substantially arcuate when viewed in cross section as best shown in Fig. 6. The edges 284 of the grooves 282 are also preferably arcuate or rounded, as herein described above.

[0059] The armature 240 also includes an armature body 274. Preferably, the armature body 274 is formed from materials similar to those of the armature body 104 described above, and preferably from a molded non-magnetic material such as polyphenylene sulfide (PPS) or polypthalamide (PPA). The armature core 270 can be placed in a mold. Then the desired material can be injected into the mold to form the armature body 274. The armature body 274 includes a central section 276 that fills the longitudinal passage 272 of the armature core 270. A first end section 278 and a second end section 280 are formed at opposite ends of the central section 276. The first end section 278 extends beyond an end surface of the first end 271 of the armature core 270 a predetermined distance. In the exemplary embodiment illustrated in Fig. 8, a recess 275 is formed in an end surface of the first end section 278. As best shown in Fig. 8, the second end section 280 extends slightly beyond an end surface of the second end 273 of the armature core 270 a predetermined distance. This formation and structure can be described as an armature core 270 having an overmolded armature body 274.

[0060] An end surface 280A of the second end section 280 of the armature body 274 acts as a valve sealing element and engages the seat 256 when the armature 240 moves downwardly. When the end surface 280A engages the seat 256, the fluid passage 252 is blocked.

[0061] In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiments. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.