Abstract:
An electromagnetic valve for use in controlling fluid flow between first and second passageways in a hydraulic valve block includes a valve body. The valve body defines a central axis, has a central opening therethrough, and has a lower end adapted to be inserted into a bore of the valve block. A hollow valve dome is attached to an upper end of the valve body. An armature is axially moveable within the valve dome. A spring biases the armature in one axial direction. A closing element is coupled to 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 axial direction. A valve seat member is carried by a 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 that surrounds the orifice and cooperates with the closing element for selectively closing the orifice. The valve seat member is formed as a deep drawn part and includes a tubular portion having one end defining a valve seat, and an opposite end connected to the valve body.

Description:
BACKGROUND 
       [0001]    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. 
         [0002]    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. 
         [0003]    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. 
         [0004]    As used in the description of the invention and the appended claims, the phrase “analog control” is defined as the ability to control a device such that an output is proportional to the input. 
         [0005]    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. 
         [0006]    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. 
         [0007]    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. 
         [0008]    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. 
         [0009]    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 
       [0010]    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, and has a lower end adapted to be inserted into a bore of the valve block. A hollow valve dome is attached to an upper end of the valve body. An armature is axially moveable within the valve dome. A spring biases the armature in one axial direction. A closing element is coupled to 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 axial direction. A valve seat member is carried by a 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 that surrounds the orifice and cooperates with the closing element for selectively closing the orifice. The valve seat member is formed as a deep drawn part and includes a tubular portion having one end defining a valve seat, and an opposite end connected to the valve body. 
         [0011]    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 
         [0012]      FIG. 1  is a schematic diagram of a vehicle brake system having a normally open isolation valve. 
           [0013]      FIG. 2  is a cross-sectional view of the isolation valve illustrated in  FIG. 1 . 
           [0014]      FIG. 3  is an enlarged exploded view of a portion of the isolation valve illustrated in  FIG. 2 . 
           [0015]      FIG. 4  is an enlarged perspective view of a portion of the valve body illustrated in  FIGS. 2 and 3 . 
           [0016]      FIG. 5  is an enlarged perspective view of a portion of the isolation valve illustrated in  FIG. 2 , showing a second embodiment of a check valve. 
           [0017]      FIG. 6  is an enlarged perspective view of a portion of the isolation valve illustrated in  FIG. 2 , showing a third embodiment of a check valve. 
           [0018]      FIG. 7  is an enlarged cross-sectional view of a portion of the isolation valve illustrated in  FIG. 2 . 
           [0019]      FIG. 8  is an enlarged cross-sectional view of a portion of a second embodiment of the isolation valve. 
           [0020]      FIG. 9  is a graph of fluid flow force to tappet travel in the isolation valve illustrated in  FIG. 2 . 
           [0021]      FIG. 10  is an enlarged cross-sectional view of a second embodiment of the tappet illustrated in  FIGS. 2 and 7 . 
           [0022]      FIG. 11  is an enlarged cross-sectional view of a third embodiment of the tappet illustrated in  FIGS. 2 and 7 . 
           [0023]      FIG. 12  is an enlarged cross-sectional view of a fourth embodiment of the tappet illustrated in  FIGS. 2 and 7 . 
           [0024]      FIG. 13  is an enlarged elevational view of a fifth embodiment of the tappet illustrated in  FIGS. 2 and 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    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. 
         [0026]    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. 
         [0027]    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. 
         [0028]    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 . 
         [0029]    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 . 
         [0030]    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 . 
         [0031]    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. 
         [0032]    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. 
         [0033]    It will be understood that the vehicle brake system  10  may include a hydraulic control unit (HCU) (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 typically includes a hydraulic valve block or housing  2  containing the various control valves and other components described herein for selectively controlling hydraulic brake pressure at the wheel brake cylinders  28 . 
         [0034]    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. 
         [0035]    A sectional view of an exemplary embodiment of the isolation valve is indicated generally at  25  in  FIGS. 2 and 3 . The isolation valve  30  may be identical to the isolation valve  25  and will not be described in detail herein. 
         [0036]    The isolation valve  25  is received in a bore  35  formed in the housing  2 . The isolation valve  25  includes a hollow valve dome or sleeve  58  having a first or closed end  58 A and a second or open end  58 B and has a central longitudinal axis A. An armature  60  has an upper or first end  60 A and a lower or second end  60 B and is slidably received in the sleeve  58 . A valve body  62  has a generally cylindrical body portion  63  having an upper or first end  64  defining a first diameter portion and a second end or lower  66  defining a second diameter portion. In the illustrated embodiment the second diameter portion is larger than the first diameter portion. The second end  66  of the valve body  62  includes a radially outwardly extending circumferential flange  68 . The lower end  66  of the valve body  62  further includes an annular section  67 . 
         [0037]    A longitudinally extending central opening or bore  70  is formed through the valve body  62 . The bore  70  includes a first portion  70 A at the first end  64 , a second portion  70 B at the second end  66  and a third portion  70 C between the first and second portions  70 A and  70 B. In the illustrated embodiment, the first and second portions  70 A and  70 B have substantially the same diameter and the third portion  70 C has a diameter smaller than the diameter of the first and second portions  70 A and  70 B. The second portion  70 B defines a second intermediate passageway for connecting the second passageway P2 to the orifice  96  of the valve seat member  72 . 
         [0038]    The intersection of the first and third portions,  70 A and  70 C, respectively, defines a first spring shoulder  70 D. The second end  58 B of the sleeve  58  is attached to the first end  64  of the valve body  62 . The sleeve  58  may be attached to the valve body  62  by any suitable means, such as with a single laser weld. Alternatively, the sleeve  58  may be attached to the valve body  62  by any other desired method. 
         [0039]    Referring now to  FIGS. 3 and 4 , the second end  66  of the valve body  62  is substantially cylindrical and has an outer surface  66 A. A distal end  66 B of the second end  66  defines a plurality of circumferentially spaced castellations  200 . A plurality of notches  202  are circumferentially arranged between adjacent castellations  200 . Grooves  204  are formed in the outer surface  66 A of the second end  66  and axially from the notches  202  toward the flange  68 . When the valve body  62  is assembled as part of the valve  25 , the grooves  204  and the notches  202  define a fluid flow path for fluid flowing through the brake circuit  11 A and into the valve  25 , as shown by the arrows  206 . 
         [0040]    The isolation valve  25  further includes a valve seat member  72  and a coil assembly  74  disposed about the sleeve  58 . Because the isolation valve  25  is a normally open valve, the tappet  108  (described in detail below) is biased away from contact with the valve seat member  72  by a spring  76  when the coil assembly  74  of the isolation valve  25  is not energized, thereby allowing fluid to flow through the isolation valve  25  in one of two directions. Fluid may flow in the direction of the arrows  78 , such as for example, in a traction control release mode. Alternatively, fluid may flow in the direction of the arrows  79 , such as for example, in an ABS apply mode. When the coil assembly  74  is energized, the tappet  108  is urged toward the valve seat member  72  to block fluid flow through the isolation valve  25 . 
         [0041]    In the illustrated embodiment, the sleeve  58  is formed as a single piece from ferromagnetic material in a deep drawing 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 sleeve  58  may be formed from any other desired ferromagnetic material. 
         [0042]    The valve seat member  72  includes an upper or first end  72 A and a lower or second end  72 B. The valve seat member  72  further includes a substantially cylindrical inner wall  84  defining an inner cylindrical portion and concentrically arranged within a substantially cylindrical outer wall  86 . The outer wall  86  defines an outer cylindrical portion. The inner wall  84  and the outer wall  86  are connected by a radial connecting or base wall  88  having at least one opening or fluid passage  89  formed through the base wall  88 . The inner wall  84 , outer wall  86 , and base wall  88  define an annular groove  92 . In the illustrated embodiment, an upper end  86 A of the outer cylindrical portion  86  is press fit over an outside of the annular section  67  of the valve body  62 . The annular section  67  further defines a downwardly facing axial stop surface  67 S configured for engagement with the valve seat member  72 . 
         [0043]    The valve seat member  72  includes a longitudinal fluid passage  94  that terminates at the first end  72 A in a reduced diameter orifice or opening  96  defining a valve seat  98 . The inner cylindrical portion  84  defines a first intermediate passageway  94  which connects the first passageway P1 to the orifice  96  of the valve seat member  72 . The outer cylindrical portion  86  and the annular section  67  cooperate to define a second intermediate passageway  70 B which connects the second passageway P2 to the orifice  96  of the valve seat member  72 . As best shown in  FIG. 7 , the outer (upper when viewing  FIG. 7 ) inside surface of the valve seat  98  defines a valve seal shoulder  98 S. The valve seat shoulder  98 S may have any desired radius. In the illustrated embodiment, the radius may be defined as a ratio wherein the valve seat shoulder radius  98 S r =0.08*spherical radius r4. The valve seat shoulder radius  98 S r  may also be within the range of from about 0.06*spherical radius r4 to about 0.10*spherical radius r4. Alternatively, the valve seat shoulder radius  98 S r  may be within the range of from about 0.04*spherical radius r4 to about 1.12*spherical radius r4. 
         [0044]    In the illustrated embodiment, the valve seat member is a deep drawn part 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 valve seat member  72  may be formed from any other desired ferromagnetic material. The second end  66  of the valve body  62  may be press-fit within the annular groove  92  of the valve seat member  72 . 
         [0045]    The armature  60  is slidably received in the sleeve  58 . In the exemplary embodiment illustrated, at least one longitudinal groove  100  is formed in an outer surface of the armature  60 . A longitudinal bore  102  is formed through the armature  60  and includes a first portion  102 A at the first end  60 A and a second portion  102 B at the second end  60 B. The first portion  102 A has a diameter smaller than a diameter of the second portion  102 B. 
         [0046]    A spherical valve part or ball  106  is pressed into the first portion  102 A of the bore  102 . In the illustrated embodiment, the ball  106  is formed from steel. Alternatively, the ball  106  may be formed from any other substantially non-deformable metal or non-metal. 
         [0047]    A first embodiment of a closing element or tappet  108  includes a first end  108 A, a second end  108 B, and a third or central portion  108 C between the first and second portions  108 A and  108 B. In the illustrated embodiment, the first end  108 A and the second end  108 B have diameters smaller than a diameter of the central portion  108 C. The intersection of the second end  108 B and the central portion  108 C defines a second spring shoulder  108 D. The first end  108 A of the tappet  108  is disposed in the second portion  102 B of the armature bore  102  and the second end  108 B and the central portion  108 C are disposed in the bore  70  of the valve body  62 . The tappet  108  may be formed from any desired material such as polyphenylene sulfide (PPS), polythalamide (PPA), polyetheretherketone (PEEK), stainless steel, and other metal and non-metal material. 
         [0048]    A distal portion of the second end  108 B is rounded and acts as a valve sealing element and engages the valve seat  98  when the valve  25  is in the closed position (e.g. when the coil assembly  74  is energized). It will be understood that the second end  108 B may have any shape suitable for creating a sealing engagement with the valve seat  98 . 
         [0049]    The spring  76  is disposed about an outer surface of the second end  108 B of the tappet  108  between the first and second spring shoulders  70 D and  108 D, respectively. The spring  76  urges the tappet  108  in a first one axial direction (in the direction of the arrow  57 B) away from the valve seat member  72  when the isolation valve  25  is in the open position. When the coil assembly  74  is energized, the tappet  108  moved axially in a second axial direction opposite the first axial direction (in the direction of the arrow  57 A) toward the valve seat member  72 , such that the isolation valve  25  is in a closed position (not shown). 
         [0050]    In the open position, as shown in  FIG. 2 , the armature  60  is spaced a longitudinal distance G from the valve body  62 . When the coil assembly  74  is energized and the tappet  108  moves axially toward the valve seat member  72  and the closed position, it is desirable to maintain a minimum air gap G. In the illustrated embodiment, the minimum air gap G is about 0.10 mm. 
         [0051]    During manufacture, the ball  106  is pressed into the bore  102  at a depth chosen to ensure a desired position of the tappet  108  relative to the armature  60  to achieve the desired minimum air gap G during actuation of the valve  25 . It will be understood that the minimum air gap G may vary and that the position of the ball  106  may be adjusted during manufacture to ensure the desired position of the tappet  108  relative to the armature  60  to achieve the desired minimum air gap G. 
         [0052]    In the illustrated embodiment, the armature  60  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  60  may be formed from any other desired ferromagnetic material. An electrical coil  112  is disposed about the sleeve  58  and armature  60  and selectively induces a magnetic flux in the armature  60 . 
         [0053]    A first embodiment of a check valve and filter assembly  114  is illustrated in  FIGS. 2 and 3 . The check valve and filter assembly  114  includes a first end  116  and a second end  118 . The first end  116  defines a segmented annular positioning member having at least one notch  144 N in an outer surface  144  of the annular positioning member  116 . The check valve and filter assembly  114  further includes a substantially cylindrical body  120 , and a substantially cylindrical inner wall  122  concentrically arranged within a substantially cylindrical outer wall  124 . The inner wall  122 , outer wall  124 , and body  120  define an annular groove  126 . 
         [0054]    The outer wall  124  has a plurality of fluid outlet openings  128  formed therein. The inner wall  122  defines a first longitudinal fluid passage  130  which is in fluid communication with the longitudinal fluid passage  94  of the valve seat member  72 . The first longitudinal fluid passage  130  may have any desired diameter or combinations of diameters and may thus may control fluid flow based on the fluid flow requirements of the valve in which the check valve and filter assembly  114  is installed. For example, a plurality of check valve and filter assemblies, each having a different size fluid passage  130  may be used for a valve. The fluid passage  130  may have any desired diameter, such as a diameter within the range of from about 0.35 mm to about 0.85 mm. 
         [0055]    The second end  118  of the check valve and filter assembly  114  includes a substantially cylindrical filter cavity  134 . A second longitudinal fluid passage  136  is formed within the body  120  radially outwardly of the first longitudinal fluid passage  130  and is in fluid communication with the annular groove  126 . The second longitudinal fluid passage  136  defines a check valve seat  138 . A check valve closing element or ball  139  is disposed in the second longitudinal fluid passage  136 . 
         [0056]    A filter housing  140  is substantially cylindrical and is mounted within the cavity  134  of the check valve and filter assembly  114  in a snap fit or interference fit connection. A substantially disk-shaped filter portion (not shown) may be attached to an outboard end surface  140 B of the filter housing  140 . An inboard end surface  140 A of the filter housing  140  closes the second longitudinal fluid passage  136  and retains the ball  139  within the passage  136 . 
         [0057]    The check valve and filter assembly  114  also define two fluid seals. The first seal  154  is defined between an outer surface  142  of the body  120  and the bore  35 . The second seal  156  is defined between an outer surface  123  of the inner wall  122  and an inner surface of the longitudinal fluid passage  94  of the valve seat member  72 . The check valve and filter assembly  114  and the filter housing  140  may be formed from any desired material such as polyphenylene sulfide (PPS), polythalamide (PPA), and the like. 
         [0058]    During assembly of the illustrated embodiment of the isolation valve  25  into the housing  2 , the valve  25  is disposed within the bore  35  of the housing  2  such that the flange  68  is supported on a shoulder portion  4  of the bore  35 . 
         [0059]    In the illustrated embodiment, the flange  68  of the valve body  62 , and therefore the isolation valve  25  to which the valve body  62  is attached, is retained within the bore  35  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  68 . The valve body  62  may also be retained in the bore  35  by any desired mechanical or chemical means operative to retain the isolation valve  25  within the bore  35 . 
         [0060]      FIG. 5  illustrates a second embodiment of the check valve assembly  214 . The check valve assembly  214  is similar to the check valve and filter assembly  114  and includes a first end  216  attached to the valve body  262  and a second end  218 . The check valve assembly  214  further includes a substantially cylindrical body  220 , and a substantially cylindrical inner wall  222  concentrically arranged within a substantially cylindrical outer wall  224 . The inner wall  222 , outer wall  224 , and body  220  define an annular groove  226 . 
         [0061]    The outer wall  224  has a plurality of fluid outlet openings  228  formed therein. The inner wall  222  defines a first longitudinal fluid passage  230  which is in fluid communication with the longitudinal fluid passage  94  of the valve seat member  72 . The second end  218  of the check valve assembly  214  includes a substantially cylindrical filter cavity  234 . A second longitudinal fluid passage  236  is formed within the body  220  radially outwardly of the first longitudinal fluid passage  230  and is in fluid communication with the annular groove  226 . An annular seal groove  238  is formed at the second end  218  adjacent the filter cavity  234 . An annular lobe seal  239  is disposed in the seal groove  238 . The lobe seal  239  allows fluid flow outward of the check valve assembly  214  through the second longitudinal fluid passage  236  (in the direction of the arrow  241 ), but not into the check valve assembly  214  through the second longitudinal fluid passage  236 . 
         [0062]    A filter housing  240  is substantially cylindrical and is mounted within the cavity  234  of the check valve assembly  214  in a snap fit or interference fit connection. An inboard end surface  240 A of the filter housing  240  closes the annular seal groove  238  and retains the lobe seal  239  within the annular seal groove  238 . 
         [0063]      FIG. 6  illustrates a third embodiment of the check valve assembly  314 . The check valve assembly  314  is similar to the check valve assembly  214  and includes a first end  316  attached to the valve body  362  and a second end  318 . The check valve assembly  314  further includes a substantially cylindrical body  320 , and a substantially cylindrical inner wall  322  concentrically arranged within a substantially cylindrical outer wall  324 . The inner wall  322 , outer wall  324 , and body  320  define an annular groove  326 . 
         [0064]    The outer wall  324  has a plurality of fluid outlet openings  328  formed therein. The inner wall  322  defines a first longitudinal fluid passage  330  which is in fluid communication with the longitudinal fluid passage  94  of the valve seat member  72 . The second end  318  of the check valve assembly  314  includes a substantially cylindrical filter cavity  334 . A second longitudinal fluid passage  336  is formed within the body  320  radially outwardly of the first longitudinal fluid passage  330  and is in fluid communication with the annular groove  326 . An annular seal groove  338  is formed at the second end  318  adjacent the filter cavity  334 . 
         [0065]    The annular seal groove  338  includes a lip seal groove portion  337 . As shown in  FIG. 6 , the lip seal groove portion  337  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. 
         [0066]    An annular lip seal  339  is disposed in the seal groove  338 . The lip seal  339  allows fluid flow outward of the check valve assembly  314  through the second longitudinal fluid passage  336  (in the direction of the arrow  341 ), but not into the check valve assembly  314  through the second longitudinal fluid passage  336 . 
         [0067]    A filter housing  340  is substantially cylindrical and is mounted within the cavity  334  of the check valve assembly  314  in a snap fit or interference fit connection. An inboard end surface  340 A of the filter housing  340  closes the annular seal groove  338  and retains the lip seal  339  within the annular seal groove  338 . 
         [0068]      FIG. 7  includes an alternate embodiment of the tappet  458 . The tappet  458  includes a rounded or substantially semi-spherical portion  458 S at the nose of the tappet  458 , a substantially cylindrical portion  458 C extending from the semi-spherical portion  458 S a distance D C  (extending upwardly when viewing  FIGS. 7 and 13 ), and a tapered portion  458 T (also illustrated by the phantom line  808 T′ in  FIG. 13 ) extending from the substantially cylindrical portion  458 C (extending upwardly when viewing  FIGS. 7 and 13 ). 
         [0069]    In the embodiments illustrated in  FIGS. 7 and 8 , the semi-spherical portion  458 S has a radius r4. The radius r4 may be any desired length, such as about 0.634 mm. The radius r4 may also be within the range of from about 0.620 mm to about 0.648 mm. Alternatively, the radius r4 may be within the range of from about 0.600 mm to about 0.660 mm. 
         [0070]    It will be understood that the axial length of the substantially cylindrical portion  458 C may be varied to achieve a desired brake performance, such as a desired base brake performance. It will be further understood that the tappet  458  may be formed without the substantially cylindrical portion  458 C. For example, the tappet  808  illustrated in  FIG. 13  includes the substantially semi-spherical portion  808 S and the tapered portion  808 T, wherein the tapered portion  808 T intersects the substantially semi-spherical portion  808 S at 0 degrees and 180 degrees of the arc of the semi-spherical portion  808 S. 
         [0071]    If desired, the tappet may be formed wherein the tapered portion of the tappet  808  may also extend tangentially at the angle α 1 , described in detail below, from the substantially semi-spherical portion  808 S as illustrated by the phantom line  808 T″ in  FIG. 13 . As illustrated in  FIG. 13 , the tapered portion  808 T″ intersects the substantially semi-spherical portion  808 S at an angle α3, which is less than 180 degrees of the arc of the semi-spherical portion  808 S (below the 0°-180° degree line in  FIG. 13 ). 
         [0072]    It will be understood that although the valve seat member  472  illustrated in  FIG. 8  may be machined and the valve seat member  72  illustrated in  FIGS. 2 ,  3 , and  7  is cold formed, the relative dimensions and relative shapes between the valve seat  98 , the tappet  458 , and the valve body  62  may be substantially the same as the valve seat  498 , the tappet  408 , and the valve body  462 , respectively. It will be further understood that although the valve seat member  472  is a machined part, the valve seat member and the valve seat may be formed as a deep drawn part, similar to the valve seat member  72  shown in  FIG. 7 , but wherein the upper portion of the valve seat member may be formed radially inwardly and downwardly to define the valve seat. 
         [0073]    Referring now to  FIG. 8 , a portion of a second embodiment of an isolation valve is indicated generally at  425  in  FIG. 8 . The portion of the isolation valve  425  illustrated in  FIG. 8  includes a portion of the tappet  408 , a portion of the valve body  462 , and a portion of the valve seat member  472 . A longitudinally extending central opening or bore  470  is formed through the valve body  462  and includes a central longitudinal axis B. 
         [0074]    The bore  470  of the valve body  462  includes a first cylindrical portion  470 A, a second cylindrical portion  470 B, and a radially inwardly extending flange  402  between the first and second cylindrical portions  470 A and  470 B defining a third cylindrical portion  470 C. The third cylindrical portion  470 C has a third radius r3. The third radius r3 may be any desired length, such as about 1.375 mm. The radius r3 may also be within the range of from about 1.35 mm to about 1.40 mm. Alternatively, the radius r3 may be within the range of from about 1.20 mm to about 1.55 mm. 
         [0075]    The rounded shoulder S may have any desired radius. In the illustrated embodiment, the radius may be defined as a ratio wherein the shoulder radius S r =1.32*spherical radius r4. The shoulder radius S r  may also be within the range of from about 1.07*spherical radius r4 to about 1.57*spherical radius r4. Alternatively, the shoulder radius S r  may be within the range of from about 0.95*spherical radius r4 to about 1.69*spherical radius r4. In the illustrated embodiment, the second cylindrical portion  470 B has a diameter larger than the diameter of the third cylindrical portion  470 C. The first cylindrical portion  470 A has a diameter larger than the diameter of the second and third cylindrical portions  470 B and  470 C. 
         [0076]    The tappet  408  includes a first end (not shown in  FIG. 8 ), a second end  408 B, and an outer surface  409 . As shown in  FIG. 8 , the outer surface of the second end  408 B of the tappet  408  is tapered at an angle α 1  measured from a line C parallel with the axis B. The intersection of the line C and the outer surface of the second end  408 B of the tappet  408  defines an intersection Y. The angle α1 may be any desired angle, such as about 7.5 degrees. The angle α 1  may also be within the range of from about 7.0 degrees to about 8.0 degrees. Alternatively, the angle α 1  may be within the range of from about 5.0 degrees to about 10.0 degrees. 
         [0077]    The illustrated valve seat member  472  includes a substantially cylindrical wall  484  defining a longitudinal fluid passage  494  that terminates at a first end  472 A of the valve seat member  472  in a reduced diameter orifice or opening defining a valve seat  498 . The valve seat  498  includes a first cylindrical wall  404  having a first radius r1 and a first axial length or height h1, a second cylindrical wall  406  having a second radius r2 and a second axial length or height h2, and a tapered intermediate wall  414  between the first cylindrical wall  404  and the second cylindrical wall  406 . The intersection of the second cylindrical wall  406  and the tapered intermediate wall  414  defines an intersection z. The annular space  410  between the second cylindrical portion  470 B and the cylindrical wall  484  defines an intermediate fluid flow outlet passageway. 
         [0078]    The height h1 may be any desired length. In the illustrated embodiment, the height h1 may be defined as a ratio wherein the height h1=0.55*spherical radius r4. The height h1 may also be within the range of from about 0.47*spherical radius r4 to about 0.63*spherical radius r4. Alternatively, the height h1 may be within the range of from about 0.32*spherical radius r4 to about 0.78*spherical radius r4. The height h2 may be any desired length. In the illustrated embodiment, the height h2 may be defined as a ratio wherein the height h2=0.32*spherical radius r4. The height h2 may also be within the range of from about 0.32*spherical radius r4 to about 0.47*spherical radius r4. Alternatively, the height h2 may be within the range of from about 0.32*spherical radius r4 to about 0.63*spherical radius r4. 
         [0079]    The rounded shoulder S may have any desired radius. In the illustrated embodiment, the radius may be defined as a ratio wherein the shoulder radius S r=1.32 *spherical radius r4. The ratio shoulder radius S r  may also be within the range of from about 1.07*spherical radius r4 to about 1.57*spherical radius r4. Alternatively, the shoulder radius S r  may be within the range of from about 0.95*spherical radius r4 to about 1.69*spherical radius r4. 
         [0080]    The first radius r1 may be any desired length. In the illustrated embodiment, the first radius r1 may be defined as a ratio wherein the first radius r1=1.16*spherical radius r4. The first radius r1 may also be within the range of from about 1.14*spherical radius r4 to about 1.18*spherical radius r4. Alternatively, the first radius r1 may be within the range of from about 1.07*spherical radius r4 to about 1.25*spherical radius r4. The second radius r2 may be any desired length. In the illustrated embodiment, the second radius r2 may be defined as a ratio wherein the second radius r2=0.67*spherical radius r4. The second radius r2 may also be within the range of from about 0.66*spherical radius r4 to about 0.68*spherical radius r4. Alternatively, the second radius r2 may be within the range of from about 0.65*spherical radius r4 to about 0.69*spherical radius r4. The third radius r3 may be any desired length. In the illustrated embodiment, the third radius r3 may be defined as a ratio wherein the third radius r3=2.17*spherical radius r4. The third radius r3 may also be within the range of from about 2.13*spherical radius r4 to about 2.21*spherical radius r4. Alternatively, the third radius r3 may be within the range of from about 1.89*spherical radius r4 to about 2.45*spherical radius r4. 
         [0081]    In the illustrated embodiment, the intermediate wall  414  is formed at an angle α2 of about 40.5 degrees relative to the axis B. The angle α2 may also be an angle within the range of from about 40.0 degrees to about 41.0 degrees. Alternatively, the angle α2 may be within the range of from about 38.0 degrees to about 43.5 degrees. 
         [0082]    Referring again to the valve body  462  illustrated in  FIG. 8 , the intersection x is axially spaced apart from the intersection z a distance b. The distance b may be any desired distance, such as about 1.25 mm. The distance b may also be within the range of from about 1.20 mm to about 1.30 mm. Alternatively, the distance b may be within the range of from about 1.10 mm to about 1.40 mm. 
         [0083]    A first or converging fluid flow path within the longitudinal fluid passage  472  is indicated by the arrow F1. A second or divergent fluid flow path is indicated by the arrows F2 and further defines an intermediate outlet flow path. 
         [0084]    As fluid is forced upward (indicated by the arrows F2) along an outer surface  409  of the tappet  408 , fluid pressure along the tappet outer surface  409  is reduced. The tapered shape of the tappet  408  causes a reduction of the upward flow pressure force relative to a similar tappet without the illustrated taper. 
         [0085]      FIG. 9  illustrates an exemplary plot of increasing hydraulic flow force to increasing distance traveled by the tappet  408  at five representative pressure differential levels (measured in bar). As shown, and as a result of the taper angle α1, a relatively steep drop in hydraulic flow force occurs during valve opening until the valve opens to a first or minimum open position. It has been shown that increasing the taper angle α 1  will maximize the benefit, described below, of the steep drop in the flow force illustrated in  FIG. 9 . 
         [0086]    The combined shapes of the valve seat  498 , the tappet  408 , and the valve body  462  cause fluid to flow along a path generally illustrated by the arrows F2. Fluid is caused to separate or flow radially outwardly of the tapered surface  409  of the tappet  408  after the fluid has moved beyond the intersection Y (upward of the intersection Y when viewing  FIG. 8 ) a distance. The region, indicated generally by the circle  412 , where the fluid is caused to flow radially outwardly of the tapered surface  409  of the tappet  408  will vary based on the positions of the outlet passageway  410  and the valve seat  498 . For example, the greater the distance between the intersection x and the intersection z (i.e. the greater the distance h), the smaller the third radius r3, and the larger the roundness or the radius of the shoulder S, the further the fluid may flow along the tapered surface  409  of the tappet  408  (upwardly when viewing  FIG. 8 ) before flowing radially outwardly of the tapered surface  409  and toward the outlet passageway  410 . As the region  412 , where the fluid is caused to flow radially outwardly of the tapered surface  409 , moves further from the intersection Y, a region of low pressure on the tappet surface  409  increases. This increased region of low pressure on the tappet surface  409  may be represented by the relatively steep negative slope of the force to travel curve as the valve  425  opens, as shown in  FIG. 9 . The increased region of low pressure on the tappet surface  409  may be increased by increasing the height h1 and decreasing the first radius r1. The increased region of low pressure on the tappet surface  409  may also be increased by increasing the height h2, or changing the distance d between the intersection x and the first end  472 A. 
         [0087]    The distance d may be any desired length. In the illustrated embodiment, the distance d may be defined as a ratio wherein the distance d=0.85*spherical radius r4. The distance d may also be within the range of from about 0.77*spherical radius r4 to about 0.93*spherical radius r4. Alternatively, the distance d may be within the range of from about 0.62*spherical radius r4 to about 1.08*spherical radius r4. 
         [0088]    The steep drop in flow force experienced as the valve  425  moves between a closed position and a minimum open position M can be varied by adjusting the shapes and the dimensions of the valve seat  498 , the tappet  408 , and the valve body  462 . It will be understood that the minimum open position M may be any desired amount of tappet travel and may be determined by the desired characteristics of the valve  425 . 
         [0089]    Advantageously, the steep negative force to travel curve as shown in  FIG. 9 , is indicative of significantly improved valve control. As used herein, improved valve control is defined as a very small change in valve opening with a relatively large change in balancing or controlling magnetic force level when the magnetic force is applied to close the valve to a desired position, also known as control resolution. 
         [0090]    In embodiments of similar valves having a flatter (more horizontal) force to travel curve, the tappet is caused to move more and may undesirably oscillate with each small change in the magnetic force level. Accordingly, the structure of the valve  425  as shown in  FIG. 8  and described herein, provides the improved and decisive valve control, or control resolution required in ABS operation. The structure of the valve  425  also improves NVH, and ensures proper valve flow metering in ABS operation. 
         [0091]    The spring  76  is disposed between and engages the valve body  62  and the tappet  108 . As a further advantage of the illustrated valves  25 ,  425 , fluid flows along the intermediate outlet flow path F2 between the valve seat  98  and the closing element  108 , radially outward of the closing element  108  to the intermediate fluid flow outlet passageway  410  defined by the annular space between the valve seat member  72  and the valve body  62 , such that the intermediate outlet flow path F2 does not flow through and is not altered by, the spring  76 . 
         [0092]    Referring again to  FIG. 9 , the force to travel curve indicates an increase in hydraulic or fluid flow force at a valve opening mark or a point of tappet travel greater than the minimum open position M (illustrated as a hump in the graph). This hump is caused by flow separation from the tappet surface  409  at a point closer to the intersection Y relative to smaller tappet travel distances (i.e., the valve having a smaller opening). The illustrated increase in force represented by the hump may be beneficial during normal braking and during large valve opening and large fluid flow situations. For example, in normal braking an upward force is desirable to prevent tappet pull-down due to a large pressure differential (such as from sudden stop or an apply spike). Such a large pressure differential may cause valve shut-off and an undesirable loss of brakes. Without the illustrated hump, the valve may experience a negative or pull-down force at larger valve opening values, and the inability to brake normally. The valve  425 , and its resultant force to travel curve, ensures that a positive force is maintained for larger valve opening values, and ensures excellent ABS operation without compromising normal braking. 
         [0093]    Significantly, the valves  25  and  425  described and illustrated herein provide significantly improved analog control or the ability to ensure that valve output or response is proportional to the input command. Specifically, the valve output, as defined by fluid flow through the valve is proportional to the valve input, as defined by current at the coil assembly  74 , for a specified pressure differential. In the illustrated embodiments, the analog control of the valves  25  and  425  approaches optimal, or 1:1, proportionality. 
         [0094]    In another embodiment, the valve  425  may be assembled without the spring  76 , which applies a pre-load the tappet  408 . In the embodiment of the valve  25  illustrated in  FIG. 2 , the spring  76  urges the tappet  108  away from the valve seat member  72  and keeps the valve  25  open until a pull-down force of about 1 N is reached in normal braking. As shown in  FIG. 9 , a positive push-up force acts on the tappet  408  of the valve  425  across the range of typical operating pressure differentials, shown by lines A through E in  FIG. 9 . For example, at a pressure of about 200 bar, the push-up force acting on the tappet  408  is above 1 N from 0 to about 0.250 mm of tappet travel. Accordingly, the push-up force acting on the tappet  408  increases with an increase in pressure differential, even at larger valve opening values. Thus, the illustrated valve  425  provides improved performance relative to other known tappet-type solenoid valves in ABS and in normal braking operation by providing improved analog control, performance, and NVH characteristics. 
         [0095]    Referring now to  FIGS. 10 through 12 , alternate embodiments of the tappet are illustrated. In  FIG. 10 , a conical shaped cavity  502  is formed in the second end  508 B of the tappet  508 . 
         [0096]    In many solenoid valves having a round-nose tappet used in ABS applications, a pull-in (toward the valve seat) force may occur due to Bernoulli forces acting on the tappet when the valve is opened. Such a pull-in force can occur during base brake apply, spike apply, or when there is a sudden high fluid flow, and a when a large pressure differential. Advantageously, in a valve with the tappet  508  having the conical shaped cavity  502 , there is an increase in the fluid flow force at the second end  508 B of the tappet  508  when the tappet  508  is in a fully opened position. Conversely, the conical shaped cavity  502  has substantially no effect in a metered flow position, such as during an ABS event, and there is an increase in the fluid flow force at the second end  508 B of the tappet  508  when the tappet  508  is in a fully opened position. 
         [0097]    It will be understood that the second end  508 B of the tappet  508  may have a cavity of any desired shape. For example,  FIG. 11  illustrates a cavity  602  formed in the second end  608 B of the tappet  608 . The illustrated cavity  602  has a substantially square shaped opening and each of the interior walls of the cavity  602  are also squares, thus defining a cube shaped cavity. Alternatively, the cavity  602  may have substantially rectangular shaped opening and each of the interior walls of the cavity  602  may also be rectangular. 
         [0098]      FIG. 12  illustrates a concave cavity  702  formed in the second end  708 B of the tappet  708 . In the embodiments illustrated in  FIGS. 10 through 12 , the cavities  502 ,  602 , and  702  are substantially symmetrical. Alternatively, other substantially symmetrical and non-symmetrical cavities may be formed in the rounded second end of the tappet. 
         [0099]    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.