Abstract:
A solenoid valve comprises a sleeve having ports and through hole, a spool slidably located in the through hole of the sleeve so that an intercommunication between the ports are changed, one end of the spool being faced with outside of the sleeve, a solenoid means for driving the spool, a case fixed to the sleeve to form an inner space for accommodating the solenoid means, and a diaphragm for sealing the inner space from the through hole, wherein a passage is formed in the spool so that the inner space is fluidlically communicated with an outside of the sleeve.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is based on and claims priority under 35 U.S.C. §119 with respect to Japanese Patent Application No. 2004-041990 filed on Feb. 18, 2004, the entire content of which is incorporated herein by reference.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to a solenoid valve for switching passages of a hydraulic circuit.  
       BACKGROUND  
       [0003]     The solenoid valve comprises a cylindrical yoke, a coil wound on the yoke, a plunger located in the yoke to be movable in axial direction thereof, and a valve member to be moved in cooperation of the movement of the yoke. The solenoid valve controls fluid flow (oil flow) and possible foreign particles in the fluid enter a gap between the yoke and the plunger.  
         [0004]     According to a solenoid valve described in JP2000-39083A, a clearance is provided to allow the foreign particles pass therethrough. It is not possible to make the clearance small so as to prevent the foreign particles from stopping at the clearance. In order to make the solenoid valve small as possible, a space for accommodating the yoke and the plunger is constructed so that the foreign particles are hard to enter the space. If the space is sealed, the plunger is prevented from smooth movement since the plunger must be moved in the sealed space.  
         [0005]     According to a solenoid valve described in JP2003-329164A, a passage is provided so as to fluidlically communicate the space with outside of the space. The passage is able to be so-called labyrinth passage to prevent the foreign particles from entering the space through the passage.  
         [0006]     The labyrinth passage is provided in a case for accommodating the coil, but the case is complicatedly processed. The case is suitably manufactured by press forming of a metal plate due to cost reduction.  
       SUMMARY OF THE INVENTION  
       [0007]     In light of the foregoing, the present invention provides a solenoid valve comprising a sleeve having ports and through hole, a spool slidably located in the through hole of the sleeve so that an intercommunication between the ports are changed, one end of the spool being faced with outside of the sleeve, a solenoid means for driving the spool, a case fixed to the sleeve to form an inner space for accommodating the solenoid means, and a diaphragm for sealing the inner space from the through hole, wherein a passage is formed in the spool so that the inner space is fluidlically communicated with an outside of the sleeve. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The foregoing and additional features and characteristics of the present invention will become more apparent from the following detailed description when considered with reference to the accompanying drawings, wherein:  
         [0009]      FIG. 1  is a cross-sectional view of a solenoid valve according to the invention; and  
         [0010]      FIG. 2  is a cross-sectional view of a spool valve of the solenoid valve.  
     
    
     DETAILED DESCRIPTION  
       [0011]     Embodiments of the present invention will be explained with reference to illustrations of the drawing figures as follows.  
         [0012]     As shown in  FIGS. 1 and 2 , a solenoid valve  100  comprises a cylindrical sleeve  1  and a cup-shaped case  5  located at one end of the sleeve  1 . The sleeve with ports  1   a  through  1   c  and passage  1   d.  The number of the ports is not restricted in three. A spool  2  is located in the sleeve  1  so as to be slidably movable in axial direction thereof. A valve stopper  13  is inserted into the open end (left end) of the sleeve  1  to limit the movement of the spool  2  in leftward direction. A spring  3  is located between the spool  2  and the stopper  13  so as to urge the spool  2  in rightward direction. An opening  13   a  is formed to fluidlically communicate inside of the sleeve with outside thereof.  
         [0013]     A bobbin  11  is located in the case  5  and a coil  9  is wound around the bobbin  11 . A first yoke  6  and a second yoke  7  are coaxially located inside and each sides of the bobbin  11 , respectively. The yokes  6  and  7  are made of magnetic material. A spacer  15  made of non-magnetic material (eg. aluminum) is coaxially located between the yokes  6  and  7 . A column-shaped plunger  4  made of magnetic material is movably located in the yokes  6  and  7  as well as the spacer  15  in axial direction of the yokes  6  and  7 . A left end of the plunger  4  is located within the spacer  15  when the plunger  4  is located to be contacted with a stopper  14  that is integrally formed with the case  5 . The left end of the plunger  4  is contacted with a right end  2   a  of the spool  2 . Namely, the spool  2  and the plunger  4  are restricted by the stopper  14  in such manner that a left end of the plunger  4  is contacted with the stopper  14 . A spiral passage  4   a  is formed outer surface of the plunger  4  so as to fluidlically communicate both sides thereof. The second yoke  7  is inserted into the case  5  to be fixed each other.  
         [0014]     A connector  10  having terminals  12  is fixed to the bobbin  11 . Both ends of the coil  9  are electrically connected to the terminals  12 . When the coil  9  is energized through the terminal  12 , the coil  9  generates a magnetic field in cooperation with the yokes  6  and  7 . A solenoid means comprises the plunger  4 , the case  5 , the yokes  6  and  7 , the coil  9  as well as the bobbin  11 .  
         [0015]     An inner circumference of a diaphragm  8  is fixed to a circumferential groove of the spool  2  at the rightward portion thereof. An outer circumference of the diaphragm  8  is fixed between the right end of the sleeve  1  and the left end of the yoke  6 . The outer circumference is able to be fixed another portion of the sleeve  1  and/or yoke  6 . The diaphragm  8  seals an inner space  16  of case  5  from another inner space (through hole)  17 . The second inner space  16  is formed by the first yoke  6 , plunger  4  and the diaphragm  8  while the inner space  17  is formed by the sleeve  1 , the spool  2  and the diaphragm  8 . A flange  6   a  of the first yoke  6  is projected from the left end of the first yoke  6  to the sleeve  1  so that the right end of the sleeve  1  and the flange  6   a  are overlapped each other and welded by laser.  
         [0016]     An axial hole  2   b  and a radial hole  2   c  are provided in the spool  2 . The hole  2   b  is elongated in the sleeve in axial direction thereof. The hole  2   c  intersects the hole  2   b  to fluildlically communicate each other. Namely, a L-shaped passage is comprised by the holes  2   b  and  2   c.  The passage  18  fulidlically communicates the left end of the spool  2  and the second inner space  16 . The hole  2   b  is provided with steps  2   d  and  2   e  so that the inner diameter of the hole  2   b  gradually becomes narrower in rightward direction. The right end of the spring  3  is supported by the step  2   d.  The number of the steps is not restricted in two.  
         [0017]     When the coil  9  is not energized, the spool  2  and the plunger  4  are urged by the spring  3  in rightward direction. The right end of the plunger  4  is at rest on the stopper  14 . The fluid communication between the ports  1   a  and  1   b  is established by the spool  2 . When the coil  9  is energized, the magnetic flux is generated through the coil  9 , the first yoke  6 , plunger  4  and the second yoke  7  so that the plunger  4  is urged in leftward direction. The spool  2  and the plunger  4  are uniformly urged against the spring  3  in leftward direction. The fluid communication between the ports  1   a  and  1   b  is terminated by the spool  2 . The coil  9  is energized in duty-ratio manner so that the solenoid valve  100  functions as linear solenoid valve. The spool  2  is able to be stopped at an intermediate portion in the sleeve  1 . The spool  2  is able to be rapidly moved so that a variable orifice is achieved between the ports  1   a  and  1   b.    
         [0018]     The plunger  4  is smoothly moved in axial direction of the solenoid valve  100  since the passage  4   a  communicates both sides of the plunger  4  as well as the second inner space  16  is communicated with the outside of the solenoid valve  100  through the passage  18  and the hole  13   a  of the stopper  13 . A possible foreign particles in the fluid enter the holes  1   a,    1   b  and  1   c,  but the diaphragm  8  prevents the foreign particles from entering the second inner space  16 .  
         [0019]     While the plunger  4  moves in the case  5 , fluid flow is established between the second inner space  16  and the outside of the solenoid valve  100  through the passage  18 . A possible foreign particles existing around the hole  13   a  would not enter the second inner space  16  through the passage  18  because of the following reasons. Firstly the length of the passage  18  is sufficiently long against the movement length of the plunger  4  and the secondly the passage  18  is bent at the connecting portion of the holes  2   b  and  2   c.  Even if the foreign articles enter the passage  18 , the foreign articles stop at the connecting portion. Additionally the step  2   e  of the passage  18  is useful so that the foreign articles stop thereat.  
         [0020]     The case  5  is made by press forming of metal plate. The passage  18  is processed by boring of the spool  2  and the steps  2   d  and  2   e  are processed by plural boring. The stopper  14  is uniformly formed as part of the case  5  so that number of parts is able to be reduced.  
         [0021]     The principles, preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents that fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.