Abstract:
A bleed-type proportional electromagnetic valve having an input port, output port, and ejection port is disclosed. Fluid force and pressing force, proportionate to an output pressure and a current flowing in a solenoid coil respectively, act on a bleed valve for controlling the output pressure, whereby the valve can obtain an output pressure commensurate to the flowing current by displacing the valve to a position that those forces counterbalance, wherein the valve is provided with a stop valve disposed so as to be in sliding contact with a passage between the input and output port, and in contact with or separated from a valve seat. This enable the stop valve to contact with the valve seat so as to close the input port and communicate the output port with the ejection port when controlling the output pressure to be minimum.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a three-way bleed type proportional electromagnetic valve in which the fluid force that is proportional to the output pressure and the pressing force that is proportional to the energization current of a solenoid coil act on a bleed-valve element and the bleed valve element is displaced to a position where the two kinds of force are balanced with each other, whereby the output pressure is made proportional to the energization current.  
         [0003]     2. Description of the Related Art  
         [0004]     In hydraulic circuits of electronic control type automatic transmissions (hereinafter abbreviated as ATs) for automobiles, a bleed type proportional electromagnetic valve in which the output pressure is controlled so as to be proportional to the energization current is used to change the operating oil pressure of each operating portion of an AT.  
         [0005]     First, a description will be made of a method for using a bleed type proportional electromagnetic valve in a hydraulic circuit of the AT. Automatic transmission fluid (hereinafter abbreviated as ATF) stored in an oil pan is sucked by an oil pump that is driven in synchronism with an engine. After its pressure is adjusted to a prescribed value by a regulator or the like, the ATF is compression-transported to the input port of each electromagnetic valve. The bleed type proportional electromagnetic valve can produce a prescribed output pressure by controlling the load imposed on the bleed valve element by controlling the current supplied to the solenoid coil in accordance with the automobile running state. A gear shift is effected by controlling the opening/closing of a control valve provided in the hydraulic circuit of the AT using the above output pressure. ATF that has passed the bleed valve element of the bleed type proportional electromagnetic valve is collected into the oil pan via an ejection port.  
         [0006]     The flow rate of the oil pump, which is a gear pump or the like, is always set to a maximum necessary value. Since the oil pump discharges ATF at a maximum flow rate, the reduction of the energy consumption of the oil pump is an important factor in increasing the fuel efficiency.  
         [0007]     The structure of the bleed type proportional electromagnetic valve is generally classified into two types by the relationship between the energization current and the output pressure. The first type is a normally high type (hereinafter abbreviated as “N/H type”) in which the output pressure is high in a non-energization state and decreases as the current increases. The second type is a normally low type (hereinafter abbreviated as “N/L type”) in which, conversely, the output pressure is low in a non-energization state and increases with the current.  
         [0008]      FIGS. 11 and 12  are sectional views showing a conventional N/H-type, two-way bleed type proportional electromagnetic valve. As shown in  FIGS. 11 and 12 , a solenoid coil  2  is provided inside a cylindrical case  1  that defines a main body outward shape. The solenoid coil  2  has a terminal  3  and a connector  4  for its energization from an external power source. A core (fixed core)  5  and a yoke  6  for formation of a closed magnetic path are fixed to the respective ends of the case  1  by welding so as to house the solenoid coil  2 . A housing  7  to be inserted into a valve body (not shown) of the hydraulic circuit of the AT is fixed to the yoke  6  by welding. The yoke  6  is provided with a bleed valve guide  6   a  that extends inward so as to taper.  
         [0009]     The housing  7  is provided with an ATF input port  7   a,  output port  7   b,  and ejection port  7   c.  A valve seat  8  is press-fit in the housing  7 , that is, in the flow passage connecting the input port  7   a  and the output port  7   b  to the ejection port  7   c.  The valve seat  8  is formed with a bleed valve seat portion  8   a  on its ejection port  7   c  side. A spherical bleed valve element  9  is loosely fit in the bleed valve guide  6   a  so as to be slidable. O-rings  10   a  and  10   b  are provided for sealing between the ports  7   a - 7   c.  The thus-configured bleed-type proportional electromagnetic valve is fixed to the valve body by bolts or the like via a flange (not shown) that is fixed to the housing  7  by welding.  
         [0010]     A plunger  11  as a movable core is disposed inside the solenoid coil  2 . A rod  12  is press-fit in the inner circumferential surface of the plunger  11  coaxially and hence is movable together with the plunger  11 . The rod  12  is supported by, that is, loosely fit in, non-magnetic sliding bearings  13  and  14  located on both sides with the plunger  11  interposed in between. The one sliding bearing  13  is press-fit in the bleed valve guide  6   a  of the yoke  6  and the other sliding bearing  14  is loosely fit in the inner circumferential surface of the core  5 .  
         [0011]     To prevent an operation failure due to magnetic sticking of the core  5  and the plunger  11 , an annular, non-magnetic stopper  15  is disposed around the rod  12  so as to be in contact with the end face of the plunger  11 . A spring  16  for output pressure adjustment is disposed between the end face of the stopper  15  and the sliding bearing  14 . A load adjusting member  17  such as a spring pin is press-fit in the inner circumferential surface of the core  5  so as to compress the spring  16  via the sliding bearing  14 . In this state, the rod  12  is pressed via the stopper  15  and the plunger  11  and the yoke- 6 -side end face of the rod  12  presses the bleed valve element  9 . As a result, the bleed valve element  9  rests on the bleed valve seat portion  8   a  and the valve is closed.  
         [0012]     Next, the operation of the N/H-type, two-way bleed type will be described. First, in a state that the solenoid coil  2  is not energized as shown in  FIG. 11 , as described above the compressed spring  16  presses the end face of the plunger  11  via the stopper  15  and hence the rod  12 , which is integral with the plunger  11 , presses the bleed valve element  9  against the bleed valve seat portion  8   a.  A maximum output pressure is obtained when the output pressure of ATF flowing through the output port  7   b  after passing through the input port  7   a  and the housing  7  is balanced with the pressing force acting on the bleed valve element  9  from the rod  12  (i.e., the force from the compressed spring  16 ) divided by the area S (=π(φd) 2 /4; φd: diameter of the bleed valve seat  8 ) of the bleed valve seat  8 . The maximum output pressure can be set in a range that it is lower than the input pressure by adjusting the force from the compressed spring  16  by adjusting the press fit length of the load adjusting member  17 .  
         [0013]     When the solenoid  2  is energized via the terminal  3 , a magnetic field is generated and a closed magnetic circuit is formed by the case  1 , the core  5 , the plunger  11 , and the yoke  6 . As a result, magnetic attractive force is generated between the excited core  5  and the plunger  11  in the movable direction of the plunger  11 . Since the magnetic attractive force acts against the force from the spring  16 , the pressing force acting on the bleed valve element  9  from the rod  12  is decreased ((force from compressed spring  16 )−(magnetic attractive force)). The individual parts are shaped so that the pressing force becomes proportional to the current independently of the position of the plunger  11  in its movable range. That is, when the current is constant, the pressing force is constant independently of the position of the plunger  11 .  
         [0014]     As a result, the bleed valve element  9  is separated from the bleed valve seat portion  8   a  and displaced to a position where the pressing force acting on the bleed valve element  9  from the rod  12  is balanced with the fluid force that is proportional to the output pressure at the output port  7   b.  As the current flowing through the solenoid coil  2  increases, the pressing force acting on the bleed valve element  9  from the rod  12  decreases and hence the output pressure also decreases. In a state that the output pressure is controlled to a minimum value, the input port  7   a  communicates with the ejection port  7   c  and hence part of the AFT flows from the input port  7   a  to the ejection port  7   c.    
         [0015]     In an ordinary output pressure control, the magnetic attractive force is controlled by the current so as to be weaker than the force from the compressed spring  16  and hence the plunger  11  does not contact the core  5  via the stopper  15 . However, if the current is so large that the magnetic attractive force is stronger than the force form the compressed spring  16 , the stopper  15  that is attached to the plunger  11  is kept in contact with the core  5  as shown in  FIG. 12 .  
         [0016]      FIGS. 13 and 14  show a conventional N/L-type, two-way bleed type proportional electromagnetic valve, which is approximately the same in configuration as the above N/H-type two-way bleed type proportional electromagnetic valve except for the following points. The core  5  and the yoke  6  are arranged in the opposite manner. Both of sliding bearings  18  and  19  are press-fit; in particular, the sliding bearing  19  is formed with a flange and thereby given a stopper function of stopping the plunger  11 . The spring  16  for output pressure adjustment and the load adjusting member  17  are absent. The stopper  15  for preventing sticking of the core  5  and the plunger  11  is absent. Further, in a non-energization state, the bleed valve element  9  is separated from the bleed valve seat portion  8   a  by the fluid force that is proportional to the output pressure, whereby the valve is opened.  
         [0017]     Next, the operation of this type of proportional electromagnetic valve will be described. In a state that the solenoid coil  2  is not energized (see  FIG. 13 ), the fluid force that is proportional to the output pressure acts on the bleed valve element  9  and hence the bleed valve element  9  is separated from the bleed valve seat portion  8   a:  a minimum output pressure is obtained. Since the input port  7   a  communicates with the ejection port  7   c,  part of the AFT flows from the input port  7   a  to the ejection port  7   c.    
         [0018]     When the solenoid  2  is energized via the terminal  3 , a magnetic field is generated and a closed magnetic circuit is formed by the case  1 , the core  5 , the plunger  11 , and the yoke  6 . As a result, magnetic attractive force is generated between the excited core  5  and the plunger  11  in the movable direction of the plunger  11 . The magnetic attractive force acts in such a direction as to move the bleed valve element  9  closer to the bleed valve seat  8 , that is, pressing force (=magnetic attractive force) acts on the bleed valve element  9  from the rod  12 . The individual parts are shaped so that the pressing force becomes proportional to the current independently of the position of the plunger  11  in its movable range. That is, when the current is constant, the pressing force is constant independently of the position of the plunger  11 .  
         [0019]     As a result, the bleed valve element  9  is displaced to a position where the pressing force acting on the bleed valve element  9  from the rod  12  is balanced with the fluid force that is proportional to the output pressure at the output port  7   b.  As the current flowing through the solenoid coil  2  increases, the pressing force acting on the bleed valve element  9  from the rod  12  increases and hence the output pressure also increases. A maximum output pressure is obtained when the pressing force is stronger than the input pressure multiplied by the area S (=π(φd) 2 /4; φd: diameter of the bleed valve seat  8 ) of the bleed valve seat  8  and hence the bleed valve element  9  rests on the bleed valve seat portion  8   a  (the valve is closed).  FIG. 14  shows this state.  
         [0020]     As described above, in each of the N/H-type valve and the N/L-type valve, a state that the input port  7   a  and the ejection port  7   c  communicate with each other occurs when the output pressure is controlled to the minimum value. Therefore, ATF flows from the input port  7   a  to the ejection port  7   c,  which increases the necessary flow rate of the oil pump for giving input pressure to the input port  7   a  and hence increases the size of the oil pump. This results in a problem that the energy that is consumed by the oil pump is increased. To solve this problem, a three-way bleed type proportional electromagnetic valve has been proposed as disclosed in Japanese patent publication JP-A-2002-286152.  
         [0021]     In the valve disclosed in the patent publication, when the output pressure is controlled to a minimum value, a state that the input port and the ejection port are isolated from each other and a state that the output port and the ejection port communicate with each other are established, whereby ATF is prevented from flowing from the input port to the ejection port. However, the valve of patent document-1 employs a structure that a stop valve element (ball valve element  24 ) can contact and be separated from a bleed valve element (composed of a bleed valve element portion  3  and a rod portion  4 ) for controlling the output pressure. In particular, the stop valve element is a spherical poppet valve (ball valve element  24 ). Therefore, force acts on the ball valve element because of a pressure of AFT flowing around the ball valve element and only the axial component (i.e., the component toward the bleed valve element) of that force serves as a load that is imposed on the bleed valve element.  
         [0022]     As a result, the flow of ATF around the ball valve element is unstable depending on the flow rate of the AFT and the oil passage shape and the pressure distribution on the surface of the ball valve element every moment. Therefore, the force acting on the ball valve element is also unstable and its axial component influences the behavior of the bleed valve element, resulting in a problem that the output pressure and flow rate characteristics are unstable. To solve this problem, it is necessary to stabilize the axial component of the force acting on the ball valve element. However, much time is needed to optimize the oil passage shape etc., which increases the development cost.  
       SUMMARY OF THE INVENTION  
       [0023]     The present invention has been made to solve the above problems, and an object of the invention is therefore to provide a three-way bleed type proportional electromagnetic valve that makes it possible to realize, while stabilizing the output pressure and flow rate characteristics, a structure in which operation fluid does not flow from the input port to the ejection port when the output pressure is controlled to a minimum value.  
         [0024]     The invention provides a three-way bleed type proportional electromagnetic valve comprising a solenoid coil; a core that is excited by energizing the solenoid coil; a plunger on which magnetic attractive force is exerted from the core when the core is excited; a bleed valve element that is in contact with or separated from a valve seat depending on the magnetic attractive force acting on the plunger; a housing that houses the valve seat and the bleed valve element and has an input port, an output port, and an ejection port for control subject fluid; and a stop valve element that is disposed in a flow passage between the input port and the output port so as to be in sliding contact with a wall of the flow passage and that is in contact with or separated from the valve seat, wherein in controlling an output pressure to a minimum value the stop valve element is brought in contact with the valve seat so as to close the input port and to cause the output port and the ejection port to communicate with each other.  
         [0025]     The three-way bleed type proportional electromagnetic valve according to the invention provides an advantage that in controlling the output pressure to a minimum value the operation fluid can easily be prevented from flowing from the input port to the ejection port in such a manner that the output pressure and flow rate characteristics are kept stable. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]      FIG. 1  is a sectional view of an N/H-type, three-way bleed type proportional electromagnetic valve according to a first embodiment of the present invention in a non-energization state;  
         [0027]      FIG. 2  is an enlarged view of part A in  FIG. 1 ;  
         [0028]      FIG. 3  is a sectional view of the N/H-type, three-way bleed type proportional electromagnetic valve according to the first embodiment of the present invention in an energized state;  
         [0029]      FIG. 4  is an enlarged view of part B in  FIG. 3 ;  
         [0030]      FIG. 5  is a sectional view of an N/L-type, three-way bleed type proportional electromagnetic valve according to a second embodiment of the invention in a non-energization state;  
         [0031]      FIG. 6  is a sectional view of the N/L-type, three-way bleed type proportional electromagnetic valve according to the second embodiment of the invention in an energized state;  
         [0032]      FIG. 7  is a sectional view of an N/H-type, three-way bleed type proportional electromagnetic valve according to a third embodiment of the invention which is a modification of the N/H-type, three-way bleed type proportional electromagnetic valve according to the first embodiment;  
         [0033]      FIG. 8  is a sectional view of an N/H-type, three-way bleed type proportional electromagnetic valve according to a fourth embodiment of the invention which is a modification of the N/H-type, three-way bleed type proportional electromagnetic valve according to the third embodiment;  
         [0034]      FIG. 9  is a sectional view of an N/H-type, three-way bleed type proportional electromagnetic valve according to a fifth embodiment of the invention which is another modification of the N/H-type, three-way bleed type proportional electromagnetic valve according to the first embodiment;  
         [0035]      FIG. 10  is a sectional view of an N/H-type, three-way bleed type proportional electromagnetic valve according to a sixth embodiment of the invention which is a further modification of the N/H-type, three-way bleed type proportional electromagnetic valve according to the first embodiment;  
         [0036]      FIG. 11  is a sectional view of a conventional N/H-type, two-way bleed type proportional electromagnetic valve in a non-energization state;  
         [0037]      FIG. 12  is a sectional view of the conventional N/H-type, two-way bleed type proportional electromagnetic valve in an energized state;  
         [0038]      FIG. 13  is a sectional view of a conventional N/L-type, two-way bleed type proportional electromagnetic valve in a non-energization state; and  
         [0039]      FIG. 14  is a sectional view of the conventional N/L-type, two-way bleed type proportional electromagnetic valve in an energized state. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     Embodiment 1  
       [0040]      FIGS. 1-4  are sectional views of an N/H-type, three-way bleed type proportional electromagnetic valve according to a first embodiment of the present invention.  FIG. 1  shows states of individual members in a non-energization state, and  FIG. 2  is an enlarged view of part A in  FIG. 1 . Members in  FIGS. 1-4  having the same or corresponding members in  FIGS. 11 and 12  are given the same reference symbols as the latter and will not be described. The following description will be mainly directed to novel features.  
         [0041]     According to the first embodiment of the invention, a stop valve element  20  is disposed in the flow passage between the input port  7   a  and the output port  7   b  of the housing  7 . The stop valve element  20  is generally shaped like a cylinder and is stepped, that is, consists of a large-diameter portion  20   a  and a small-diameter portion  20   b.  The stop valve element  20  is loosely fit in a stop valve guide  7   g  (that is formed inside the housing  7  adjacent to the above flow passage) in such a manner that the large-diameter portion  20   a  can slide on the stop valve guide  7   g  in the axial direction. The radial clearance and the sealing length (in the axial direction) of the sliding contact portion are set to such values that the flow passage between the input port  7   a  and the output port  7   b  is closed there. The valve seat  8  is formed with a stop valve seat portion  8   b  so that a stop valve sealing edge  20   d  that is an edge of the stop valve element  20  can rest thereon. The small-diameter-portion  20   b  of the stop valve element  20  is inserted in a valve seat communication hole  21  and the end of the small-diameter-portion  20   b  can contact and be separated from the spherical bleed valve element  9 .  
         [0042]     A flow passage that is sufficiently wide for the output pressure control is secured between the outer circumferential surface of the small-diameter portion  20   b  of the stop valve element  20  and the wall of the valve seat communication hole  21 . A spring  22  is disposed between the other end of the stop valve element  20  and a brim that is formed at the output port  7   b  of the housing  7 . The compressed spring  22  generates force in such a direction as to cause the stop valve sealing edge  20   d  of the stop valve element  20  to rest on the stop valve seat portion  8   b  of the valve seat  8 . A stop valve element communication hole  23  is formed in the stop valve element  20 . The stop valve element communication hole  23  has one opening at the output-port- 7   b -side end of the stop valve element  20 . At the other end, the stop valve element communication hole  23  communicates with bleed valve element communication holes  20   c  that are formed through the side wall of the small-diameter portion  20   b.    
         [0043]     The maximum displacement of the stop valve element  20  is set longer than that of the bleed valve element  9  that can control the output pressure in a necessary range.  
         [0044]     As is apparent from the above configuration, unlike in the conventional two-way bleed type proportional electromagnetic valve, the three-way bleed type proportional electromagnetic valve according to this embodiment can be attached without the need for changing the attachment shape including the port positions, the internal components, etc.  
         [0045]     Next, the operation of the first embodiment will be described. In a state that the solenoid coil  2  is not energized, as shown in  FIGS. 1 and 2  the bleed valve element  9  rests on the bleed valve seat portion  8   a  because it receives force from the compressed spring  16 : the flow passage between the input port  7   a  and the ejection port  7   c  is closed. On the other hand, the stop valve element  20  is in contact with the bleed valve element  9  and the stop valve sealing edge  20   d  of the stop valve element  20  is separated from the stop valve seat portion  8   b  of the valve seat  8 . Therefore, the input port  7   a  and the output port  7   b  communicate with each other. In this state, the input pressure at the input port  7   a  is applied to the output port  7   b  via the stop valve element communication hole  23  and hence the output pressure is at the maximum.  
         [0046]     When a current that is necessary to control the output pressure in an ordinary range is supplied to the solenoid coil  2 , the bleed valve element  9  is separated from the bleed valve seat portion  8   a  (this state is not shown in any drawings): the input port  7   a  and the ejection port  7   c  communicate with each other. On the other hand, the stop valve element  20  is displaced together with the bleed valve element  9  while kept in contact with the bleed valve element  9 . However, since the stop valve sealing edge  20   d  is still separated from the stop valve seat portion  8   b,  the input port  7   a  and the output port  7   b  communicate with each other. In this state, the output pressure varies in proportion to the energization current. And force originating from pressure that is generated by ATF flowing inside and outside the stop valve element  20  acts on the stop valve element  20 . However, since the output pressure acts on the ends of the stop valve element  20  on both sides of the sliding contact portion, the axial components (i.e., the components toward and going away from the bleed valve element  9 ) of the force cancel out each other and hence no effective axial component remains. That is, only the force originating from the compressed spring  22  acts from the stop valve element  20  to the bleed valve element  9 . Stable force that does not depend on the AFT flow state acts on the bleed valve element  9 . Therefore, the output pressure and flow rate characteristics are very stable and the problem of the conventional valve is solved.  
         [0047]     An operation in a case that a current that is larger than the above current and is so large that the magnetic attractive force acting on the plunger  11  is stronger than the force from the compressed spring  16  will be described with reference to  FIGS. 3 and 4 .  FIG. 3  shows states of the individual members in an energized state, and  FIG. 4  is an enlarged view of part B in  FIG. 3 . In this state, the stopper  15  that is located at the top of the plunger  11  is in contact with the core  5  (i.e., the plunger is located at its highest position in  FIG. 3 ). The stop valve sealing edge  20   d  of the stop valve element  20  rests on the stop valve seat portion  8   b  because of the force from the compressed spring  22 . On the other hand, whereas the bleed valve element  9  is separated from the rod  12 , the bleed valve element  9  is kept in contact with the stop valve element  20  and is most distant from the bleed valve seat portion  8   a.    
         [0048]     Therefore, the flow passages between the input port  7   a  and the other ports  7   b  and  7   c  are closed, which prevents ATF from flowing from the input port  7   a  to the ejection port  7   c.  At the same time, the output port  7   b  and the ejection port  7   c  communicate with each other and hence the output pressure is at the minimum. Since the flow passage between the input port  7   a  and the ejection port  7   c  is closed in the state that the output pressure is at the minimum, AFT does not flow from the input port  7   a  to the ejection port  7   c.  Therefore, the flow rate of AFT that is output from the oil pump to produce a necessary input pressure at the input port  7   a  can be reduced and the capacity of the oil pump can be optimized and the energy consumption of the oil pump can be reduced.  
       Embodiment 2  
       [0049]      FIGS. 5 and 6  show an N/L-type, three-way bleed type proportional electromagnetic valve according to a second embodiment of the invention. This valve is similar in configuration to the N/H-type three-way bleed type proportional electromagnetic valve according to the first embodiment and has the same differences from it as the differences between the conventional N/L-type and N/H-type, two-way bleed type proportional electromagnetic valves that were described in the background section. The principle of operation of this N/L-type valve is similar to that of the N/H-type valve according to the first embodiment and hence will be described below only briefly. In a state that the solenoid coil  2  is not energized, as shown in  FIG. 5  the stop valve sealing edge  20   d  of the stop valve element  20  rests on the stop valve seat portion  8   b  because of the force from the compressed spring  22 .  
         [0050]     On the other hand, the bleed valve element  9  is in contact with the stop valve element  20  and is most distant from the bleed valve seat portion  8   a.  Therefore, the flow passages between the input port  7   a  and the other ports (i.e., the output port and the ejection port)  7   b  and  7   c  are closed, which prevents ATF from flowing from the input port  7   a  to the ejection port  7   c.  At the same time, the output port  7   b  and the ejection port  7   c  communicate with each other and hence the output pressure is at the minimum. Since the flow rate of AFT that is output from the oil pump to produce a necessary input pressure at the input port  7   a  can be reduced, the capacity of the oil pump can be optimized and the energy consumption of the oil pump can be reduced.  
         [0051]     When a current that is necessary to control the output pressure in an ordinary range is supplied to the solenoid coil  2 , the bleed valve element  9  is displaced in such a direction that it will rest on the bleed valve seat portion  8   a.  The stop valve element  20  that is in contact with the bleed valve element  9  is displaced together with the bleed valve element  9  and the stop valve sealing edge  20   d  is separated from the stop valve seat portion  8   b.  Therefore, the input port  7   a  communicate with both of the ejection port  7   c  and the output port  7   b.  In this state, the output pressure varies in proportion to the energization current.  
         [0052]     Force originating from pressure that is generated by ATF flowing inside and outside the stop valve element  20  acts on the stop valve element  20 . However, since the output pressure acts on the ends of the stop valve element  20  on both sides of the sliding contact portion, the axial components (i.e., the components toward and going away from the bleed valve element  9 ) of the force cancel out each other and hence no effective axial component remains. That is, only the force originating from the compressed spring  22  acts from the stop valve element  20  to the bleed valve element  9 . Stable force that does not depend on the AFT flow state acts on the bleed valve element  9 . Therefore, the output pressure and flow rate characteristics are stable.  
         [0053]     When a current that is large enough to cause the bleed valve element  9  to rest on the bleed valve seat portion  8   a  is applied to the solenoid coil  2 , as shown in  FIG. 6  the flow passage between the input port  7   a  and the ejection port  7   c  is closed and the input port  7   a  and the output port  7   b  communicate with each other. Since the input pressure at the input port  7   a  is applied to the output port  7   b  via the stop valve element communication hole  23 , the output pressure is at the maximum.  
       Embodiment 3  
       [0054]      FIG. 7  is a sectional view of an N/H-type, three-way bleed type proportional electromagnetic valve according to a third embodiment of the invention which is a modification of the N/H-type, three-way bleed type proportional electromagnetic valve according to the first embodiment. In this embodiment, a guide member  24 , which is employed as the stop valve guide  7   g  of the housing  7 , is press-fit in the inner circumferential surface of the housing  7 . In the first embodiment, the flow rate of leakage between the input port  7   a  and the output port  7   b,  that is, the sealability and the slidability, can be set properly by changing the settings of the radial clearance and the sealing length (i.e., axial length) of the sliding contact portion that consists of the outer circumferential surface of the stop valve element  20  and the stop valve guide  7   g  of the housing  7 . However, the housing  7  should be re-produced each time, which is costly. In contrast, in this embodiment, by virtue of the use of the guide member  24  which is a separate component, the above items can be set arbitrarily merely by changing the specifications (the dimensions and the material) of the guide member  24  without changing the housing  7 . As such, the third embodiment is superior in utility and advantageous in cost.  
       Embodiment 4  
       [0055]      FIG. 8  is a sectional view of an N/H-type, three-way bleed type proportional electromagnetic valve according to a fourth embodiment of the invention which is a modification of the N/H-type, three-way bleed type proportional electromagnetic valve according to the third embodiment. In this embodiment, the valve seat  8  and the guide member  24  are integrated into a member  25  and lateral, ATF inflow holes  25   a  are formed through the member  25 . The integral member  25  is press-fit in the inner circumferential surface of the housing  7 .  
         [0056]     In the third embodiment, if the concentricity between the stop valve seat portion  8   b  of the valve seat  8  and the inner circumferential surface of the guide member  24  (in the first and second embodiments, the stop valve guide  7   g  of the housing  7 ) becomes low, the resting performance of the sealing edge  20   d  of the stop valve element  20  on the stop valve seat portion Bb of the valve seat  8  is impaired and the sealability is lowered. As a result, in controlling the output pressure to the minimum value, the input port  7   a  may communicate with the ejection port  7   c  to cause a flow of ATF from the former to the latter.  
         [0057]     Integrating the valve seat  8  and the guide member  24  increases the concentricity between the stop valve seat portion  8   b  of the valve seat  8  and the inner circumferential surface of the guide member  24  and hence can further stabilize the output pressure and flow rate characteristics.  
       Embodiment 5  
       [0058]      FIG. 9  is a sectional view of an N/H-type, three-way bleed type proportional electromagnetic valve according to a fifth embodiment of the invention which is another modification of the N/H-type, three-way bleed type proportional electromagnetic valve according to the first embodiment. In this embodiment, the shapes of the bleed valve element and the stop valve element are changed. A bleed valve element  9 A according to this embodiment has a mortar-like shape rather than a spherical shape, and has a cylindrical projection  9 Aa that extends toward a stop valve element  20 A. The projection  9 Aa is inserted in the valve seat communication hole  21  and the end face of the projection  9 Aa is in contact with the stop valve element  20 A. The projection  9 Aa is formed with bleed valve element communication holes  9 Ab that has openings in the end face and the side surface of the projection  9 Aa. The stop valve element  20 A has a shape as obtained by cutting off the small-diameter portion  20   b  of the stop valve element  20  of the first embodiment, and is formed with a stop valve element communication hole  23 A having openings in both end faces of the stop valve element  20 A. Whereas in the first embodiment the bleed valve element communication holes  20   c  are formed in the stop valve element  20 , in this embodiment, the bleed valve element communication holes  9 Ab are formed in the bleed valve element  9 A. The bleed valve element communication holes  9 Ab of this embodiment has substantially the same function as the bleed valve element communication holes  20   c  of the first embodiment.  
       Embodiment 6  
       [0059]      FIG. 10  is a sectional view of an N/H-type, three-way bleed type proportional electromagnetic valve according to a sixth embodiment of the invention which is a further modification of the N/H-type, three-way bleed type proportional electromagnetic valve according to the first embodiment. In this embodiment, the shapes of the bleed valve element and the stop valve element are changed differently than in the first embodiment. A bleed valve element  9 B has a mortar-like shape and has a solid projection  9 Ba that extends toward a stop valve element  20 B and is inserted in the valve seat communication hole  21 . The end face of the projection  9 Ba is in contact with the stop valve element  20 B. The stop valve element  20 B has a shape as obtained by cutting off the small-diameter portion  20   b  of the stop valve element  20  of the first embodiment. The top end face of the stop valve element  20 B is formed with an elliptical groove  20 Ba whose width is smaller than the outer diameter of the projection  9 Ba of the bleed valve element  9 B. The stop valve element  20 B is formed with a stop valve element communication hole  23 B having openings in the output-port- 7   b -side end face of the stop valve element  20 B and the bottom surface of the elliptical groove  20 Ba.  
         [0060]     Therefore, in this embodiment, ATF flows into the stop valve element  20 B through the openings adjacent to the regions where the bleed valve element  9 B and the stop valve element  20 B are in contact with each other (see the inset enlarged sectional view taken along line A-A). The elliptical groove  20 Ba has the same function as the bleed valve element communication holes  9 Ab of the fifth embodiment.  
         [0061]     It goes without saying that each of the structures of the third to sixth embodiments can also be applied to the N/L-type, three-way bleed type proportional electromagnetic valve according to the second embodiment and, when so applied, provides the same advantages as the advantages of each of the third to sixth embodiments. The above-described structures according to the invention can be applied to not only bleed-type proportional electromagnetic valves for AT hydraulic circuits but also general electromagnetic valves for hydraulic control that are used in various machines.