Abstract:
An electromagnetic valve ( 32 ) for use in controlling fluid flow between first and second passageways (P 1 , P 2 ) in a hydraulic valve block ( 4 ), includes a valve body ( 51 ). The valve body ( 51 ) defines a central axis (A), has a central opening ( 51 A) therethrough, has a lower end ( 54 ) adapted to be inserted into a bore ( 19 ) of the valve block ( 4 ), and is provided with a lower cylindrical opening ( 70 ). An armature ( 56 ) is axially movable within the valve body ( 51 ) and is biased by a spring in one axial direction ( 57 A). A closing element ( 88 ) is carried by a lower end ( 54 ) of the armature ( 56 ). An electromagnetic coil ( 64 ) coaxially surrounds the armature ( 56 ) and is operable to effect axial movement of the armature ( 56 ) in an axial direction opposite the one direction ( 57 B). A valve seat member ( 62 ) is carried by the lower end ( 54 ) of the valve body ( 51 ) and has an orifice ( 98 ) providing fluid flow between the first and second valve block passageways (P 1 , P 2 ). The valve seat member ( 62 ) defines a valve seat ( 96 ) surrounding the orifice ( 98 ) and cooperates with the closing element ( 88 ) for selectively closing the orifice ( 98 ). The valve seat member ( 62 ) includes a cylindrical tubular portion ( 90 ) frictionally retained in the lower cylindrical opening ( 70 ) of the valve body ( 51 ). The lower cylindrical opening ( 70 ) of the valve body ( 51 ) is provided with a stop surface ( 68 ) at the upper end of thereof, and an upper part ( 92 ) of the cylindrical portion ( 90 ) of the valve seat member ( 62 ) includes a flange ( 100 ) engageable with the stop surface ( 68 ) for limiting downward movement of the valve seat member ( 62 ) relative to the valve body ( 51 ).

Description:
BACKGROUND 
     The present invention will now be described with occasional reference to the illustrated embodiments of the invention. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein, nor in any order of preference. Rather, these embodiments are provided so that this disclosure will be more thorough, and will convey the scope of the invention to those skilled in the art. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for describing particular embodiments only and is not intended to be limiting of the invention. As used in the description of the invention and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth as used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless otherwise indicated, the numerical properties set forth in the specification and claims are approximations that may vary depending on the desired properties sought to be obtained in embodiments of the present invention. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical values, however, inherently contain certain errors necessarily resulting from error found in their respective measurements. 
     Various embodiments of a control valve are described herein. In particular, the embodiments described herein are mounted in a hydraulic control unit of an electronically controlled brake system. 
     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. 
     Control valves for HCU&#39;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 respectively permitting or blocking fluid flow through the valve. 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 respectively slide from the biased open or closed position to a closed or open position. 
     Control valves mounted in a HCU are actuated by an electronic control unit (ECU) to provide desired braking functions such as anti-lock braking, traction control, and vehicle stability control. 
     To provide desired braking responses, an armature must respond quickly and in a predictable manner to an electromagnetic field generated by an energized coil assembly. 
     SUMMARY 
     The present application describes various embodiments of an electromagnetic valve for use in controlling fluid flow between first and second passageways in a hydraulic valve block. One embodiment of the electromagnetic valve includes a valve body. The valve body defines a central axis, has a central opening therethrough, has a lower end adapted to be inserted into a bore of the valve block, and is provided with a lower cylindrical opening. An armature is axially moveable within the valve body and is spring biased in one axial direction. A closing element is carried by a lower end of the armature. An electromagnetic coil coaxially surrounds the armature and is operable to effect axial movement of the armature in an axial direction opposite the one direction. A valve seat member is carried by the lower end of the valve body and has an orifice providing fluid flow between the first and second valve block passageways. The valve seat member defines a valve seat surrounding the orifice and cooperates with the closing element for selectively closing the orifice. The valve seat member includes a cylindrical tubular portion frictionally retained in the lower cylindrical opening of the valve body. The lower cylindrical opening of the valve body is provided with a stop surface at the upper end of thereof, and an upper part of the cylindrical portion of the valve seat member includes a flange engageable with the stop surface for limiting downward movement of the valve seat member relative to the valve body. 
     Other advantages of the electromagnetic valve will become apparent to those skilled in the art from the following detailed description, when read in light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a vehicle brake system having a normally closed dump valve. 
         FIG. 2  is a cross-sectional view of the dump valve illustrated in  FIG. 1 . 
         FIG. 3  is an enlarged sectional view of the normally closed supply valve illustrated in  FIG. 1 . 
         FIG. 4  is an exploded perspective view of the dump valve illustrated in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     A hydraulic vehicle brake system is indicated generally at  10  in  FIG. 1 . The illustrated embodiment of the vehicle brake system  10  includes valves and other components described below to provide an electronic brake control capability. The vehicle brake system  10  is intended to be exemplary and it will be appreciated that there are other brake control system configurations that may be used to implement the various valve embodiments described herein. In other embodiments, the brake system  10  may include components to provide an anti-lock braking, traction control, and/or vehicle stability control function. 
     The vehicle brake system  10  has two separate brake circuits  11 A and  11 B, respectively, which are depicted on the left and right halves of  FIG. 1 . In the exemplary embodiment illustrated in  FIG. 1 , the circuits supply brake pressure to a front and rear wheel brake. The illustrated rear wheel brake is arranged diagonally to the front wheel brake. Only a left brake circuit  11 A in  FIG. 1  is described in the following in more detail, however a right brake circuit  11 B in  FIG. 1  is structured in the same manner. 
     The brake system  10  includes a driver-controlled first pressure generating unit  12  with a brake pedal  14 , a power brake unit  16  and a tandem master brake cylinder  18 , which presses the brake fluid out of a reservoir  20  into the two brake circuits  11 A and  11 B. Arranged behind an outlet of the tandem master brake cylinder  18  is a pressure sensor  22  for detecting the driver&#39;s input. 
     Under normal driving conditions, a brake fluid pressure emanating from the driver-controlled first pressure generating unit  12  continues via the block valve arrangement  24  and an anti-lock brake system (ABS) valve arrangement  26  to wheel brake cylinders  28 . The ABS valve arrangement  26  includes an ABS inlet or isolation valve  30  and an ABS discharge or dump valve  32 . The ABS inlet valve  30  is normally open, and the ABS discharge valve  32  is normally closed. Each wheel brake cylinder  28  includes an ABS valve arrangement  26  and the brake fluid pressure of both brake circuits is distributed diagonally in the vehicle to a respective pair of wheel brake cylinders  28  (front left (FL) and rear right (RR), or front right (FR) and rear left (RL)), respectively. The illustrated block valve arrangement  24  is part of a traction control or vehicle stability control system and includes an isolation valve  25  that is normally open in a currentless state. In a current-carrying state the block valve arrangement  24  is blocked from a backflow of brake fluid from the wheel brake cylinders  28  to the master brake cylinder  18 . 
     Brake fluid pressure may be built up independent of the driver-controlled first pressure generating unit  12  by an autonomous second pressure generating unit  34 . The autonomous second pressure generating unit  34  includes a pump  36  driven by a pump motor  39 , an attenuator  44 , and an orifice  38 . The attenuator  44  is in fluid communication with a pump outlet  46  and the inlet side  40  of the orifice  38 . Pulsations emanating from the pump  36  are periodic fluctuations in the brake fluid flow. The attenuator  44  takes in brake fluid during the pulsation peaks and releases it again between the pulsation peaks. As a result, the attenuator  44  levels out a temporal pressure progression on the inlet side  40  of the orifice  38 . 
     Arranged on the intake side of the pump  36  are a low pressure accumulator (LPA)  48  and a pump inlet or supply valve  50 . The illustrated pump inlet valve  50  is a normally closed valve. When the pump inlet valve  50  is currentless and closed, the pump  36  is supplied with brake fluid from the LPA  48 . When the pump inlet valve  50  is current-carrying and open, the pump  36  can also suction brake fluid from the master brake cylinder  18 . 
     The driver-controlled first pressure generating unit  12  and the autonomous second pressure generating unit  34  convey brake fluid in a common brake branch  52  of one of the two brake circuits. As a result, both pressure generating units  12 ,  34  can build up brake fluid pressure to the wheel brake cylinders  28  of the brake circuit independent of one another. 
     The vehicle brake system  10  described in the foregoing uses the autonomous second pressure generating unit  34  for generating brake pressure within the scope of a vehicle stability control (VSC function). Moreover, the autonomous second pressure generating unit  34  is also used for the adaptive cruise control (ACC function). In the process, the autonomous second pressure generating unit  34  can build up brake fluid pressure for autonomously braking the vehicle in the course of a stop-and-go function in frequent succession and not just in extraordinary, relatively rare driving situations. This also occurs with predominantly low to moderate driving speeds, at which the basic noise level in the vehicle interior is relatively low. Under such conditions, known pressure generating units represent a source of noise and pulsation that is annoying in terms of driving comfort. 
     It will be understood that the vehicle brake system  10  may include a hydraulic valve block or hydraulic control unit (HCU)  4  (not shown in  FIG. 1 ) connected in fluid communication between the master brake cylinder  18  and wheel brake cylinders  28 . As best shown in  FIG. 2 , the HCU  4  typically includes a housing  2  containing the various control valves and other components described herein for selectively controlling hydraulic brake pressure at the wheel brake cylinders  28 . 
     As shown at  54  in  FIG. 1 , the vehicle brake system  10  may include an electronic control unit (ECU) which receives input signals from sensors, such as yaw rate, master cylinder pressure, lateral acceleration, steer angle, and wheel speed sensors. The ECU may also receive ground speed data from the ACC system  56 . The ACC system may receive input data from a radar and the vehicle yaw rate sensor. One example of a vehicular control system adapted to control fluid pressure in an electronically-controlled vehicular braking system and an electronically-controlled ACC system is disclosed in U.S. Pat. No. 6,304,808 to Milot, which is incorporated herein by reference. 
     A sectional view of an exemplary embodiment of the dump valve  32  is shown in  FIG. 2 . The dump valve  32  is received in a bore  19  formed in the housing  2 . The dump valve  32  includes a valve body or sleeve  51  having a first end  52  (the upper end when viewing  FIG. 2 ) and a second end  54  (the lower end when viewing  FIG. 2 ). The sleeve  51  defines a central or longitudinal axis A. An armature  56  has a first end  58  and a second end  60  and is slidably received in the sleeve  51 . 
     The dump valve  32  further includes a valve seat member  62  and a coil assembly  64  disposed about the sleeve  51 . Because the dump valve  32  is a normally closed valve, the armature  56  is biased into contact with the valve seat member  62  by a spring  66  when the coil assembly  64  of the dump valve  32  is not energized, thereby blocking fluid flow through the dump valve  32 . When the coil assembly  64  is energized, the armature  56  is urged away from the valve seat member  62  to permit fluid flow between a first passageway P 1  and a second passageway P 2  and through the dump valve  32 , as indicated by the arrows  29 . 
     In the illustrated embodiment, the sleeve  51  has a central opening  51 A therethrough and is formed as a single piece from non-ferromagnetic material in a deep drawing process. An example of suitable ferromagnetic material is stainless steel. It will be understood however, that low-carbon steel is not required, and that the sleeve  51  may be formed from any other desired non-ferromagnetic material. 
     The first end  52  of the sleeve  51  defines an axially extending cylindrical portion. The second end  54  of the sleeve  51  includes a radially inwardly extending wall which defines a stop surface or shoulder  68 . The shoulder  68  further defines a lower cylindrical or sleeve opening  70 . The opening  70  includes an axially extending cylindrical portion  72 . The shoulder  68  has at least one fluid flow aperture  74  formed therein. 
     A substantially cylindrical mounting collar  76  is attached, such as by welding, about an outer surface of the second end  54  of the sleeve  51 . The illustrated collar  76  includes a radially outwardly extending circumferential flange  78  at one end (the lower end when viewing  FIG. 2 ). A magnetic core  82  is attached within the first end  52  of the sleeve  51 , thereby closing the first end  52  of the sleeve  51 . The core  82  may be attached to the first end  52  of the sleeve  51  by any suitable means, such as with a single laser weld. Alternatively, the core  82  may be attached to the first end  52  of the sleeve  51  by any other desired method. 
     The armature  56  is slidably received in the first end  52  of the sleeve  51 . In the exemplary embodiment illustrated, the first end  58  of the armature  56  includes a spring cavity  84 . The spring  66  is disposed in the cavity  84  and engages the armature  56  and the core  82  to urge the armature  56  toward the valve seat member  62  (in the direction of the arrow  57 A) when the dump valve  32  is in the closed position. When the coil assembly  64  is energized, the armature  56  moves away from the valve seat member  62  (in the direction of the arrow  57 B) such that the armature  56  is disposed at an extreme of travel away from the valve seat member  62 , and is in an open position (not illustrated). 
     A substantially cylindrical recess  86  is formed in an end surface of the second end  60 . A spherical closing element or ball  88  is pressed into the recess  86 . In the illustrated embodiment, the ball  88  is formed from steel. Alternatively, the ball  88  may be formed from any other substantially non-deformable metal or non-metal. The ball  88  acts as a valve sealing element and engages the valve seat member  62  when the valve  32  is in the closed position (e.g. when the coil assembly  64  is not energized, as shown in  FIG. 2 ). It will be understood that the ball  88  is not required, and that a valve sealing element may be integrally formed in the armature  56  at the second end  60  of the armature  56 . 
     In the illustrated embodiment, the armature  56  is formed from ferromagnetic material in a cold forming process. An example of suitable ferromagnetic material is low-carbon steel. It will be understood however, that low-carbon steel is not required, and that the armature  56  may be formed from any other desired ferromagnetic material. 
     The valve seat member  62  includes a generally cylindrical tubular portion or body  90 , an upper part or first end  92 , and a lower part or second end  94 . The first end  92  defines a valve seat  96  surrounding an orifice or opening  98 . A radially outwardly extending circumferential flange  100  is formed at the first end  92  adjacent the valve seat  96 . 
     In the illustrated embodiment, the valve seat  96  includes a circumferential ridge  96 A surrounding the opening  98 . The illustrated ridge  96 A has a substantially rounded or toroidal surface contour such that the ball  88  sealingly engages the ridge  96 A when the dump valve  32  is in the closed position. 
     In the illustrated embodiment, the valve seat member  62  is formed as a single piece from non-ferromagnetic material in a deep drawing process. An example of suitable non-ferromagnetic material is stainless steel. It will be understood however, that stainless steel is not required, and that the valve seat member  62  may be formed from any other desired non-ferromagnetic material. In the illustrated embodiment, the valve seat member  62  is widened at a distance from the first end  92  to define the flange  100 . The illustrated flange  100  includes a crease defined between two substantially transversely extending wall portions  110  and  112 . The wall portions  110  and  112  bear against one another substantially without any space between them. 
     The body  90  may be press-fit within the cylindrical portion  72  of the sleeve opening  70 , such that the body  90  engages the lower cylindrical portion  72  of the sleeve  51 . 
     The coil assembly  64  is disposed about the sleeve  51 , armature  56 , and magnetic core  82  and selectively induces a magnetic flux in the armature  56 . 
     A circumferentially extending internal band filter  104  may be placed about the body  90  of the valve seat member  62 , although such a band filter  104  is not required. The inner surface of the filter  104  seals against the outer surface of the body  90  of the valve seat member  62 . A return flow path is defined between the outer surface of the filter  104  and the wall of the bore  19  and between the outer surface of the body  90  of the valve seat member  62  and the wall of the bore  19 . 
     The bore  19  includes a lip seal groove portion  3 . As shown in  FIG. 2 , the lip seal groove portion  3  is formed in a frusto-conical manner, as best described in WIPO Publication No. WO/2008/097534, the description of the lip seal and lip seal groove disclosed therein are incorporated herein by reference. 
     A lip seal  106  is disposed about the body  90  at the second end  94  of the valve seat member  62 . The illustrated lip seal  106  is substantially V-shaped in transverse section, and includes a resilient annular body  106 A. A resilient annular seal lip  106 B includes an outer circumferential surface and flares radially outwardly and upwardly from the body  106 A in the general direction of the valve seat member  62 . 
     During assembly of the illustrated embodiment of the dump valve  32  into the housing  2 , the sleeve  51  is disposed within the bore  19  of the housing  2  such that the flange  78  is supported on a shoulder portion  23  of the bore  19 . 
     In the illustrated embodiment, the flange  78  of the collar  76 , and therefore the dump valve  32  to which the collar  76  is attached, is retained and sealed within the bore  19  by clinching, wherein material of the housing  2  is forced into engagement with a first surface (an upwardly facing surface when viewing  FIG. 2 ) of the flange  78 . The collar  76  of the may also be retained in the bore  19  by any desired mechanical means operative to retain the dump valve  32  within the bore  19 . 
     A sectional view of an exemplary embodiment of the supply valve is indicated generally at  50  in  FIG. 3 . The supply valve  50  is received in a bore  5  formed in the housing  2  and controls fluid flow between a first passageway P 1  and a second passageway P 2 . The supply valve  50  includes a valve body or sleeve  200  having a first end  202  (upper end when viewing  FIG. 3 ) and a second end  204  (lower end when viewing  FIG. 3 ) and defining a central axis B. An armature  206  has a first or upper end  208  and a second or lower end  210  and is slidably received in the sleeve  200 . The supply valve  50  further includes a coil assembly (not shown) disposed about the sleeve  200 . 
     In the illustrated embodiment, the sleeve  200  has a central opening  201  therethrough and is formed as a single piece from non-ferromagnetic material in a deep drawing process. An example of suitable non-ferromagnetic material is stainless steel. It will be understood however, that stainless steel is not required, and that the sleeve  200  may be formed from any other desired non-ferromagnetic material. 
     The sleeve  200  includes a first or upper body portion  212  having a first diameter, a second or intermediate body portion  214  having a second diameter, and a third or lower body portion  216  having a third diameter. The second end  204  of the sleeve  200  includes a radially inwardly extending first shoulder  218  extending between the second body portion  214  and the third body portion  216 , and defining a valve seat  218 . The second end  204  further defines a lower cylindrical opening  207 . A plurality of fluid passages  205  are formed in the sleeve  200 . A core  220  is attached to the first end of the sleeve  200 , thereby closing the first end  202  of the sleeve  200 . In the illustrated embodiment, the core  220  is pressed into the sleeve  200  with an interference fit. The core  220  may be further hydraulically sealed to the first end  202  of the sleeve  200  by any suitable means, such as with a single laser weld. Alternatively, the core  220  may be sealed to the first end  202  of the sleeve  200  by any other desired method. In the illustrated embodiment, the core  220  is formed from ferromagnetic material, such as low carbon steel. 
     The armature  206  is slidably received in the sleeve  200 . In the exemplary embodiment illustrated, the first end  208  of the armature  206  includes a spring cavity  222 . The first spring  224  is disposed in the cavity  222  and engages the armature  206  and the core  220  to urge the armature  206  and the poppet  226  (described in detail below) toward the valve seat  218  (in the direction of the arrow  57 A) when the supply valve  50  is in the closed position. When the coil assembly, represented by the phantom line  64 ′, is energized, the armature  206  and the poppet  226  are disposed at an extreme of travel away from the valve seat  218 , such that the supply valve  50  is in an open position (not shown). 
     A recess  228  is formed in an end surface of the second end  210  of the armature  206 . A closing element or ball  230  is pressed into the recess  228 . In the illustrated embodiment, the ball  230  is formed from steel. Alternatively, the ball  230  may be formed from any other substantially non-deformable metal or non-metal. In the illustrated embodiment, the armature  206  is formed from ferromagnetic material in a cold forming process. An example of suitable ferromagnetic material is low-carbon steel. It will be understood however, that low-carbon steel is not required, and that the armature  206  may be formed from any other desired ferromagnetic material. 
     The poppet  226  is disposed between the armature  206  and the valve seat  218  and includes a generally cylindrical body  232  having a first end  234  (upper end when viewing  FIG. 3 ), a second end  236  (lower end when viewing  FIG. 3 ), and a bore  238  therethrough. The first end  234  defines a seat portion  240 . A radially outwardly extending circumferential shoulder  242  is defined in an outer surface of the poppet  226  intermediate the first end  234  and the second end  236 . A second spring  244  extends between the second end  210  of the armature  206  and the shoulder  242 . A radially outwardly extending circumferential flange  245  is also formed in an outer surface of the poppet  226 . 
     In the illustrated embodiment, the poppet  226  is formed as a single piece from plastic material. An example of suitable plastic material is polyether ether ketone (PEEK). Alternatively, the poppet  226  may be formed from nylon, such as nylon  136 . It will be understood that the poppet  226  may also be formed from any other desired material. 
     A substantially cup-shaped cage  246  includes a first end  248  (upper end when viewing  FIG. 3 ), a second end  250  (lower end when viewing  FIG. 3 ), and a central opening  251  formed therethrough. The second end  250  of the cage  246  includes a radially inwardly extending shoulder  252  defining a cage opening  254 . A plurality of fluid passages  255  are formed in the cage  246 . In the illustrated embodiment, the cage  246  is formed as a single piece in a deep drawing process. An example of suitable material is low-carbon steel. It will be understood however, that low-carbon steel is not required, and that the cage  246  may be formed from any other desired ferromagnetic or non-ferromagnetic material. 
     The flange  245  of the poppet  226  is slidably received within the cage  246 . The second end  236  of the poppet  226  extends through the opening  254  of the cage  246  and further sealingly engages the valve seat  218 . 
     A substantially cylindrical mounting collar  276  is attached, such as by welding, about an outer surface of the second end  204  of the sleeve  200 . The illustrated collar  276  includes a radially outwardly extending circumferential flange  278  at one end (the lower end when viewing  FIG. 3 ). 
     An electrical coil (shown schematically at  64 ′) is disposed about the sleeve  200 , armature  206 , and core  220  and selectively induces a magnetic flux. The magnetic flux induced by the coil will run through the core  220 , the armature  206 , and through the cage  246  when the cage  246  is formed from ferromagnetic material. Because the supply valve  50  is a normally closed valve, the first spring  224  urges the armature  206  and the poppet  226  into contact with the valve seat  218  when the coil assembly of the supply valve  50  is not energized, thereby blocking fluid flow through the supply valve  50 . When the coil assembly is energized, the armature  206  and the poppet are urged away from the valve seat  218  to permit fluid flow through the supply valve  50 . 
     A circumferentially extending internal band filter  256  includes a first end  258  and a second end  260  and may be placed about the second body portion  214  of the sleeve  200 . In the illustrated embodiment, the second end  260  includes an opening  261  through which the third body portion  216  extends. The second end  260  of the filter  256  further engages the first shoulder  218 . It will be understood however, that such a band filter  256  is not required. A lip seal  262  is disposed about the third body portion  216  of the poppet  226  between the filter  256  and the second end  236  of the poppet  226 . 
     The ball  230  acts as a valve sealing element and engages the seat portion  240  of the poppet  226  when the valve  50  is in the closed position (e.g. when the coil assembly  134  is not energized). 
     If a pressure difference between the inlet side (see the arrow  264 ) and the outlet side (see the arrow  266 ) of the housing  2  is relatively small, and if the closing force acting on the poppet  226  is lower than the force exerted by the second spring  244 , then the valve seat  218  is opened without movement of the poppet  226  relative to the armature  206 . 
     When the pressure difference between the inlet side  196  and the outlet side  266  of the housing  2  is relatively large, then the hydraulic closing force acting on the poppet  226  may be greater than the sum of the magnetic force exerted on the armature  206  and the force of the second spring  244  as it attempts to pull the poppet  226  off of the sleeve  200 . 
     The magnetic force, which is low at the beginning of the armature  206  stroke (upward as viewed in  FIG. 3 ), will, upon movement of the armature  206  toward the core  220 , overcome the pre-stressing force of the first spring  224  and the hydraulic closing force acting on the armature  206 , in order to open the poppet  226  (by moving the ball  230  of the armature  206  away from the seat portion  240  of the poppet  226 ). 
     Opening the seat portion  240  of the poppet  226  over the course of armature  206  movement, fluid may flow through the bore  238  of the poppet  226  to the outlet side  266 . As a result of the opening of the seat portion  240 , the pressure difference is reduced, at which point the poppet to sleeve seal (at the valve seat  218 ) is opened for increased fluid flow, specifically second stage flow, relative to flow rates only through the seat portion  240  of the poppet  226 . 
     The principle and mode of operation of the control valve have been described in its various embodiments. However, it should be noted that the control valves described herein may be practiced otherwise than as specifically illustrated and described without departing from its scope.