PATENT ABSTRACT
Disclosed is an electromagnetic valve in which a force due to a working fluid from an inflow hole acting perpendicularly with respect to the axis of a shut-off valve is reduced to thereby reduce the sliding resistance of the shut-off valve. An electromagnetic valve according to the present invention includes: a housing ( 10 ) having an inflow hole ( 11 ), an inner flow path ( 12 ), and a discharge hole ( 13 ); a valve seat ( 15 ) secured in position inside the housing ( 10 ); a shut-off valve ( 16 ) adapted to abut one surface of the valve seat ( 15 ) to shut off the working fluid flowing into the inner flow path ( 12 ) through the inflow hole ( 11 ); and a pressure regulating valve ( 17 ) provided coaxially with the shut-off valve ( 16 ) and adapted to control, through adjustment of the dimensions of a gap between itself and the other surface of the valve seat ( 15 ), the amount of working fluid flowing to the exterior of the housing ( 10 ) through the discharge hole ( 13 ). In the electromagnetic valve, the housing ( 10 ) is equipped with a whirling member for causing the working fluid having flowed into the inner flow path ( 12 ) through the inflow hole ( 11 ) to whirl in one direction.

PATENT DESCRIPTION
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an electromagnetic valve to be provided, for example, in a hydraulic control circuit of an automatic transmission of an automobile,  FIG. 8  is an illustration of an automatic transmission of the prior art that may be used with the inventive hydraulic valve. 
   2. Description of the Related Art 
   Conventionally, an electromagnetic valve has been known in which a spool, which is accommodated in a valve housing so as to be capable of reciprocating, rests at a position where equilibrium is attained between the following forces: the urging force of a coil spring urging the spool toward a linear solenoid, a driving force generated by a current supplied to a coil which causes a plunger to be attracted to an attracting portion to thereby cause a shaft to push the spool, and a force received by the spool from an oil chamber of a feedback chamber (see, for example, JP 2003-139261 A ( FIG. 1 )). 
   However, the housing has an input port formed so as to be perpendicular to the axis of the spool, so that working fluid having passed the input port is guided to the interior of the housing of the electromagnetic valve while perpendicularly colliding with the spool; thus, a lateral force due to the collision dynamic pressure of the working fluid acts on the spool, resulting in an increase in the sliding resistance during the operation of the spool and a sealing defect when shutting off the working fluid. 
   Further, the working fluid is divided, starting from the point at which it collides with the spool, into a plurality of flows along the outer peripheral surface thereof, and these flows join again on the opposite side of the inflow port, thus generating a complicated flow; thus, the working fluid undergoes a marked reduction in velocity and an increase in fluid resistance, resulting in a deterioration in the efficiency with which the working fluid is discharged through a discharge hole; further, foreign matter (contaminant) contained in the working fluid also enters the housing and undergoes a reduction in velocity as the working fluid is decelerated, and is liable to stay around the spool, with the result that foreign matter is caught between the sliding surfaces of the spool and the housing. 
   SUMMARY OF THE INVENTION 
   The present invention has been made with a view toward solving the above problems in the prior art. It is an object of the present invention to provide an electromagnetic valve in which a force due to a fluid from an inflow hole acting in a direction perpendicular to the axis of a first valve is reduced to thereby reduce the sliding resistance of the first valve and in which the fluid flowing in through the inflow hole flows smoothly through an inner flow path, achieving an improvement in terms of the efficiency with which the fluid is discharged through a discharge hole. 
   An electromagnetic valve according to the present invention includes: a housing having an inflow hole through which a fluid flows in, an inner flow path communicating with the inflow hole, and a discharge hole through which the fluid is discharged to an exterior; a valve seat secured in position inside the housing; a first valve adapted to abut one surface of the valve seat to shut off the fluid flowing into the inner flow path through the inflow hole; and a second valve provided coaxially with the first valve and adapted to control, through adjustment of a dimension of a gap between the second valve and the other surface of the valve seat, an amount of fluid flowing to the exterior of the housing through the discharge hole. In the electromagnetic valve, the housing is equipped with a whirling means for causing the fluid having flowed into the inner flow path through the inflow hole to whirl in one direction. 
   In the electromagnetic valve of the present invention, the force due to the fluid from the inflow hole acting in the direction perpendicular to the axis of the first valve is reduced to thereby reduce the sliding resistance of the first valve, and the fluid flowing in through the inflow hole flows smoothly through the inner flow path, thus achieving an improvement in terms of the efficiency with which the fluid is discharged through the discharge hole. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
       FIG. 1  is a front sectional view of a proportional electromagnetic valve for pressure control according to Embodiment 1 of the present invention; 
       FIG. 2  is a sectional view taken in the direction of arrows A of  FIG. 1 ; 
       FIG. 3  is a front sectional view of a main portion of a proportional electromagnetic valve for pressure control according to Embodiment 2 of the present invention; 
       FIG. 4  is a sectional view taken in the direction of arrows B of  FIG. 3 ; 
       FIG. 5  is a diagram showing the relationship between lead per perimeter and the inner diameter of an inflow hole; 
       FIG. 6  is a front sectional view of a main portion of a proportional electromagnetic valve for pressure control according to Embodiment 3 of the present invention; and 
       FIG. 7  is a sectional view taken in the direction of arrows C of  FIG. 6 . 
       FIG. 8  is an illustration of an automatic transmission in an automobile that may be used with the inventive hydraulic valve. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiments of the present invention will now be described with reference to the drawings; the members and portions that are the same as or equivalent to each other are indicated by the same symbols. 
   Embodiment 1 
     FIG. 1  is a front sectional view of a proportional electromagnetic valve for pressure control according to Embodiment 1 of the present invention, and  FIG. 2  is a sectional view taken in the direction of arrows A of  FIG. 1 . 
   This proportional electromagnetic valve for pressure control (hereinafter simply referred to as the electromagnetic valve) consists of a normally-low type three-way proportional electromagnetic valve for hydraulic control in an automatic transmission. 
   In this electromagnetic valve, a coil  3  is provided inside a yoke  1  and a plate  2  forming a magnetic circuit. A plunger  4  is provided on the inner side of the coil  3 . A rod  5  extends through this plunger  4 . At the ends of the rod  5 , there are provided a first slide bearing  6  and a second slide bearing  7  supporting the rod  5  so as to allow it to move in the axial direction. Fixed to the yoke  1  is a core  8  axially opposed to the plunger  4  and surrounding the rod  5 . 
   Fixed to the lower portion of the core  8  is a housing  10  locked to a flange  22 . Inside the housing  10 , there are formed an inflow hole  11  through which working fluid flows in, an inner flow path  12  communicating with the inflow hole  11 , a discharge hole  13  through which the working fluid is discharged to the exterior, and an output hole  14 . 
   Inside the housing  10 , there is secured in position a valve seat  15  in which a through-hole  25  is formed so as to extend along the center axis. Under the valve seat  15  and inside the housing  10 , there is secured in position a cylindrical sleeve  18 . Provided inside the sleeve  18  is a shut-off valve  16  serving as a first valve which is coaxial with the rod  5  and which can vertical slide relative to the sleeve  18 . The shut-off valve  16  is urged toward the valve seat  15  by the elastic force of a spring  19 . The shut-off valve  16  has a passage  20  extending along the center axis, and, in the upper end portion of the passage  20 , there are formed a pair of holes  24  opposed to the inner wall surface of the valve seat  15 . 
   Under the core  8 , there is provided a guide portion  23  extending toward the shut-off valve  16 . A spherical pressure regulating valve  17 , guided by the guide portion  23  and serving as a second valve, is provided between the rod  5  and the shut-off valve  16 . 
   Provided in the housing  10  is a whirling means for whirling in one direction the working fluid flowing into the inner flow path  12  from the inflow hole  11 . As shown in  FIG. 2 , in this embodiment, the whirling means is formed by a circular wall surface  12   a  of the inner flow path  12  and the inflow hole  11  which is in a plane perpendicular to the axis of the rod  5  and which extends tangentially with respect to the wall surface  12   a.    
   Next, the operation of the electromagnetic valve constructed as described above will be illustrated. 
   First, at the time of non-energization, that is, when no current is flowing through the coil  3 , the pressure regulating valve  17  is at the maximum lift position, and a shoulder portion  26  of the shut-off valve  16  is caused to abut the lower surface of the valve seat  15  by the elastic force of the spring  19 . Thus, at this time, the working fluid, which enters the housing  10  through the inflow hole  11 , is shut off by the shut-off valve  16 , and the output hole  14  and the discharge hole  13  communicate with each other through the passage  20  and the holes  24  of the shut-off valve  16 , with the pressure on the output hole  14  side being equal to the pressure on the discharge hole  13  side. 
   When an electric current is supplied to the coil  3  through a terminal  21 , a magnetic line of force is generated in the coil  3 , and a magnetic flux flows through the magnetic circuit formed by the plunger  4 , the plate  2 , the yoke  1 , and the core  8 , generating a magnetic attracting force between the plunger  4  and the core  8 . As a result, the plunger  4  is attracted toward the core  8 , and the rod  5 , which is integral with the plunger  4 , moves downwards, and the pressure regulating valve  17 , which is in contact with the rod  5 , also moves downwards against the repulsive force from the shut-off valve  16 . At this time, the magnetic attracting force from the core  8 , the elastic force of the spring  19 , and the fluid force applied through the output hole  14  act on the pressure regulating valve  17 , which moves downwards to a position where these forces are in equilibrium with each other. 
   At the same time, the shut-off valve  16 , which is pressurized by the pressure regulating valve  17 , also moves downwards, and the shoulder portion  26  of the shut-off valve  16  is separated from the lower surface of the valve seat  15 , with the result that the working fluid is guided from the inflow hole  11  to the discharge hole  13  through the inner flow path  12 , and, at the same time, from the inflow hole  11  to the output hole  14  through the inner flow path  12  and the passage  20 . 
   The dimension of the gap between the lower surface of the valve seat  15  and the shoulder portion  26  of the shut-off valve  16  is proportional to the electric current flowing through the coil  3 , and the output pressure applied through the output hole  14  is controlled linearly. 
   Further, when the shut-off valve  16 , which is pressurized by the pressure regulating valve  17 , moves downwards, the pressure regulating valve  17  abuts a shoulder portion  27  of the valve seat  15 , and the working fluid is guided solely to the output hole  14  from the inflow hole  11  through the inner flow path  12  and the passage  20 . 
   In the electromagnetic valve of this embodiment, the inflow hole  11  is provided so as to be in a plane perpendicular to the axis of the rod  5  and as to extend tangentially with respect to the wall surface  12   a  of the inner flow path  12 , so that the working fluid flows in a whirl around the center axis of the shut-off valve  16 , and the lateral force applied to the shut-off valve  16  is mitigated. Thus, the sliding resistance of the shut-off valve  16  inside the sleeve  18  is reduced, and it is possible to prevent a sealing defect, a characteristic defect, or adhesion of the working fluid to the inner surface of the sleeve  18  at the time of working fluid shut-off due to defective sliding. 
   Further, the supplied working fluid having passed the inflow hole  11  flows smoothly in the inner flow path  12  along the wall surface  12   a  thereof, and a reduction in velocity and pressure loss in the inner flow path  12  are mitigated. Thus, the efficiency with which the working fluid is discharged through the discharge hole  14  is improved, so that any foreign matter, which passes through the inflow hole  11  and enters the housing  10  together with the working fluid, is smoothly discharged through the discharge hole  13  together with the working fluid, and the amount of foreign matter staying in the vicinity of the shut-off valve  16  is reduced. 
   Embodiment 2 
     FIG. 3  is a front sectional view of a main portion of a proportional electromagnetic valve for pressure control according to Embodiment 2 of the present invention, and  FIG. 4  is a sectional view taken in the direction of arrows B of  FIG. 3 . 
   This embodiment differs from Embodiment 1 in that the inner flow path  12  has a bottom portion  28  formed in a spiral configuration; otherwise, it is of the same construction as Embodiment 1. 
   In this embodiment, the whirling means is formed by the wall surface  12   a  of the inner flow path  12  formed in a circular configuration, the inflow hole  11  in a plane perpendicular to the axis and extending tangentially with respect to the wall surface  12   a , and the spirally formed bottom portion  28  of the inner flow path  12 . 
   In this embodiment, the bottom portion  28  of the inner flow path  12  is spiral, so that the working fluid flowing in through the inflow hole  11  can, upon making a round along the wall surface  12   a , reduce the amount thereof colliding with working fluid newly flowing in through the inflow hole  11 , whereby it is possible to further stabilize the whirl flow of working fluid in the inner flow path  12 . 
   When an inclination angle a of the bottom portion  28  with respect to the plane perpendicular to the axis is a value larger than that obtained from the equation in  FIG. 5 , tan α=d/π×D (where d is the inner diameter of the inflow hole, and D is the inner diameter of the inner flow path  12 ), the lead per perimeter of the inner flow path  12  is larger than the inner diameter dimension of the inflow hole  11 , so that it is possible to further stabilize the whirl flow of working fluid in the inner flow path  12 . 
   It is to be noted that, from the viewpoint of workability, it is desirable to adopt a resin material for the housing  10  of Embodiment 2. 
   Embodiment 3 
     FIG. 6  is a front sectional view of a main portion of a proportional electromagnetic valve for pressure control according to Embodiment 3 of the present invention, and  FIG. 7  is a sectional view taken in the direction of arrows C of  FIG. 6 . 
   This embodiment differs from Embodiment 1 in that the inflow hole  11  is inclined with respect to the plane perpendicular to the axis; otherwise, it is of the same construction as Embodiment 1. 
   In this embodiment, the whirling means consists of the wall surface  12   a  of the inner flow path  12  formed in a circular configuration and the inflow hole  11  inclined with respect to the plane perpendicular to the axis and extending tangentially with respect to the wall surface. 
   In this embodiment, it is possible to obtain the same effect as that of Embodiment 1; further, since the inflow hole  11  is inclined with respect to the plane perpendicular to the axis, the working fluid having flowed in through the inflow hole  11  can, upon making a round along the wall surface  12   a , reduce the amount thereof colliding with working fluid newly flowing in through the inflow hole  11 , making it possible to further stabilize the whirl flow of working fluid in the inner flow path  12 . 
   When an inclination angle β of the inflow hole  11  with respect to the plane perpendicular to the axis is a value larger than the value obtained by the equation: tan β=d/π×D (where d is the inner diameter of the inflow hole, and D is the inner diameter of the inner flow path  12 ), the lead per perimeter of the inner flow path  12  is larger than the inner diameter dimension of the inflow hole  11 , so that it is possible to further stabilize the whirl flow of working fluid in the inner flow path  12 . 
   It is to be noted that, from the viewpoint of workability, it is desirable to adopt a metal material for the housing  10  of Embodiment 3. 
     FIG. 8  is an illustration of an automatic transmission  30  in an automobile  34  that may be used with the inventive hydraulic valve of the above-noted embodiments. 
   While the above-described embodiments are applied to a normally-low type electromagnetic valve, which is a three-way type proportional electromagnetic valve to be used for hydraulic control in an automatic transmission, they are also applicable to a normally-high type electromagnetic valve, in which the operating direction of the plunger upon energization is reversed. 
   Further, the present invention is also applicable to a so-called flow rate switching valve. 
   Further, while in the above-described embodiments the inflow hole  11  extends tangentially with respect to the wall surface  12   a  of the inner flow path  12  formed in a circular configuration, this should, of course, not be construed restrictively. For example, by forming the inflow hole in the housing so as to direct it between a radial axis of the shut-off valve and the wall surface of the inner flow path, it is possible to cause the working fluid flowing into the inner flow path through the inflow hole to whirl in one direction.