Patent Publication Number: US-8994484-B2

Title: Linear solenoid

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on and incorporates herein by reference Japanese Patent Application No. 2013-26178 filed on Feb. 14, 2013. 
     TECHNICAL FIELD 
     The present disclosure relates to a linear solenoid. 
     BACKGROUND 
     For example, JP4569371B2 (corresponding to US2006/0243938A1) recites a linear solenoid, which includes a plunger made of a magnetic material, a yoke made of a magnetic material and a stator core. The stator core includes a magnetically attracting core, a slide core and a magnetic shield portion, which are formed integrally. 
     In this linear solenoid, the plunger is placed on a radially inner side of a coil and is movable in an axial direction. The yoke is configured into a cup form and includes an opening, a bottom wall portion and a peripheral wall portion. The peripheral wall portion covers an outer peripheral portion of the coil, and the bottom wall portion covers one axial end of the coil. 
     The magnetically attracting core of the stator core is made of a magnetic material and magnetically attracts the plunger toward the other axial side, which is opposite from the one axial end of the coil, with a magnetic flux generated through energization of the coil. The slide core is made of the magnetic material and is configured into a tubular form. The slide core is placed on the radially inner side of the coil and covers an outer peripheral portion of the plunger. The slide core axially slidably supports the plunger and conducts the magnetic flux between the slide core and the plunger in a radial direction. The magnetic shield portion limits flow of the magnetic flux between the magnetically attracting core and the slide core. 
     The stator core is inserted into an inside of the yoke from one axial side of the stator core where the slide core is located, and the stator core is fixed to the yoke at the opening of the yoke. A distal end of the slide core is inserted into a hole formed in the bottom wall portion of the yoke such that a predetermined size of an installation gap is formed between the bottom wall portion of the yoke and the distal end of the slide core, so that the distal end of the slide core forms a free end that is not fixed to the yoke. 
     In the linear solenoid of JP4569371B2 (corresponding to US2006/0243938A1), a ring core is axially installed between the coil assembly and the bottom wall portion of the yoke to limit a reduction in the amount of the magnetic flux between the slide core and the yoke, caused by the presence of the installation gap. Here, the ring core is installed such that the ring core covers an outer peripheral portion of the slide core and is slidable relative to the slide core. Also, the ring core conducts the magnetic flux between the ring core and the slide core in the radial direction. The ring core contacts the bottom wall portion of the yoke and conducts the magnetic flux between the ring core and the bottom wall portion of the yoke in the axial direction. 
     However, due to the installation of the ring core, an axial size of the linear solenoid of JP4569371B2 (corresponding to US2006/0243938A1) is disadvantageously increased. Therefore, in order to meet a demand of increasing the number of winding turns of the coil and a demand of reducing the axial size without deteriorating the advantage of enhancing the conduction of the magnetic flux with the ring core, additional measures are required. 
     SUMMARY 
     The present disclosure is made in view of the above disadvantages. According to the present disclosure, there is provided a linear solenoid, which includes a coil, a plunger, a yoke, a stator core, a stepped portion, and a ring core. The plunger is made of a magnetic material. The plunger is placed on a radially inner side of the coil and is movable in an axial direction. The yoke is made of a magnetic material and is configured into a cup form. The yoke includes an opening and a bottom wall portion and covers an outer peripheral portion of the coil. The stator core includes a magnetically attracting core and a slide core. The magnetically attracting core is made of a magnetic material and magnetically attracts the plunger in the axial direction with a magnetic flux generated through energization of the coil. The slide core is made of a magnetic material and is configured into a tubular form. The slide core is placed on a radially inner side of the coil and covers an outer peripheral portion of the plunger. The slide core axially slidably supports the plunger and conducts the magnetic flux between the slide core and the plunger in a radial direction. The magnetically attracting core and the slide core are integrated with each other along with a magnetic shield portion, which is interposed between the magnetically attracting core and the slide core in the axial direction. The stator core is inserted into an inside of the yoke from one axial side of the stator core where the slide core is located. The stator core is fixed to the yoke at the opening. The stepped portion is formed in an outer peripheral portion of the slide core and is stepped to reduce an outer diameter of one portion of the slide core located on one axial side of the stepped portion, which is axially opposite from the magnetically attracting core, in comparison to another portion of the slide core located on another axial side of the stepped portion where the magnetically attracting core is placed. The ring core is made of a magnetic material and includes a first conducting portion and a second conducting portion. The first conducting portion covers an outer peripheral surface of the one portion of the slide core and is slidable along the outer peripheral surface of the one portion of the slide core. The first conducting portion conducts the magnetic flux between the first conducting portion and the slide core in the radial direction. The second conducting portion is configured into a form of a flange and radially outwardly extends from the first conducting portion. The second conducting portion conducts the magnetic flux between the second conducting portion and the bottom wall portion of the yoke in the axial direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a longitudinal cross-sectional view of a hydraulic pressure control valve including a linear solenoid according to an embodiment of the present disclosure; 
         FIG. 2A  is a partial enlarged longitudinal cross-sectional view showing a main feature of the linear solenoid according to the embodiment; and 
         FIG. 2B  is a transverse cross-sectional view of the linear solenoid taken along line IIB-IIB in  FIG. 2A  according to the embodiment, showing a cross section of a peripheral wall portion of a yoke and a bottom surface of a ring core while eliminating a plunger and a slide core for the sake of simplicity. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of the present disclosure will be described with reference to the accompanying drawings. 
     A structure of a linear solenoid  1  of the present embodiment will be described with reference to  FIGS. 1 to 2B . 
     For example, the linear solenoid  1  is used as an actuator that generates an axial thrust force for driving a spool  3 , which serves as a valve element of a hydraulic pressure control valve  2 . 
     The hydraulic pressure control valve  2  controls a hydraulic pressure (also referred to as an oil pressure) of a control subject by supplying hydraulic oil to the control subject or draining the hydraulic oil from the control subject. The hydraulic pressure control valve  2  is installed in, for example, a hydraulic pressure control apparatus of an automatic transmission of a vehicle (e.g., an automobile) such that the hydraulic pressure control valve  2  is immersed in the hydraulic oil. 
     The spool  3  is axially slidably received in an inside of a sleeve  5 , which is configured into a tubular form and has various ports  4 . The linear solenoid  1  is integrally installed to one end side (also referred to as one axial end side or one axial side) of the spool  3  and the sleeve  5 . A spring  6  is installed in the inside of the sleeve  5 . The spring  6  urges the spool  3  in a direction that is opposite from a direction of the thrust force outputted from the linear solenoid  1 . The spool  3  is driven to change a communication state between each corresponding ones of the ports  4  based on a balance of the thrust force outputted from the linear solenoid  1 , the urging force of the spring  6  and a feedback force of the hydraulic pressure. 
     Now, the linear solenoid  1  will be described in detail. 
     The linear solenoid  1  generates the thrust force by magnetically attracting the plunger  10  to a magnetically attracting core  9  toward the other end side (also referred to as the other axial end side or the other axial side), which is opposite from the one end side, upon generation of a magnetic flux through energization of the coil  8 . The generated thrust force is conducted to the spool  3  through a shaft  11 . 
     The linear solenoid  1  includes the plunger  10 , a yoke  13 , a stator core  14 , a stepped portion  15 , a ring core  26  and an urging member (urging means)  17 . 
     The plunger  10  is a magnetic metal body, which is made of a ferromagnetic material and is configured into a generally cylindrical form. The plunger  10  directly slidably contacts an inner peripheral surface of the stator core  14 . The plunger  10  is axially movable at a location, which is on a radially inner side of the coil  8 . 
     An end surface (the other end surface) of the plunger  10 , which is located on the spool  3  side in the axial direction, contacts a distal end of the shaft  11 . The plunger  10  is urged along with the spool  3  by the urging force of the spring  6  conducted to the spool  3  in the axial direction. A through-hole  19  extends through the plunger  10  in the axial direction. The through-hole  19  functions as a first breathing passage  20 , through which fluid is moved between the one end side of the plunger  10  and the other end side of the plunger  10 . 
     The coil  8  has a conductive wire (e.g., an enamel wire), which is covered with a dielectric cover and is wound multiple times around a bobbin  21  made of a resin material. The coil  8  and the bobbin  21  form a coil assembly  22 . 
     The yoke  13  is made of a ferromagnetic material and is configured into a cup form. Specifically, the yoke  13  includes an opening  13   a , a bottom wall portion  13   b  and a peripheral wall portion (also referred to as a lateral wall portion)  13   c . The peripheral wall portion  13   c  is configured into a tubular form and covers an outer peripheral portion of the coil  8 . The bottom wall portion  13   b  covers one axial end portion of the coil assembly  22  located on one axial side. The yoke  13  conducts a magnetic flux, which is generated through energization of the coil  8 . A claw  13   d  is formed at the other axial end of the yoke  13 , which forms the opening  13   a . The claw  13   d  is plastically deformed against and is thereby secured to one axial end portion of the sleeve  5  after installation of the plunger  10 , the stator core  14  and the coil assembly  22  into the inside of the yoke  13 . 
     The stator core  14  is placed on the radially inner side of the coil assembly  22  and also on the other axial side of the coil assembly  22 . The stator core  14  includes a magnetically attracting core  9 , a magnetic shield portion  25  and a slide core  24 , which are integrated together such that the magnetic shield portion  25  is interposed between the magnetically attracting core  9  and the slide core  24  in the axial direction. 
     The magnetically attracting core  9  is made of a ferromagnetic material. The magnetically attracting core  9  magnetically attracts the plunger  10  toward the other end side that is axially opposite from the one end side with the magnetic flux generated through energization of the coil  8 . The magnetically attracting core  9  includes a flange portion  9   a  and an attracting portion  9   b . The flange portion  9   a  is located on the other end side of the coil assembly  22  and is magnetically coupled with the opening end of the yoke  13 . The attracting portion  9   b  is placed on the radially inner side of the coil assembly  22  and is axially opposed to the plunger  10 . The attracting portion  9   b  axially slidably supports the shaft  11 . 
     The slide core  24  is made of a ferromagnetic material and is configured into a cylindrical tubular form. The slide core  24  is connected to the one end of the magnetically attracting core  9  through the magnetic shield portion  25 . The slide core  24  is placed on the radially inner side of the coil assembly  22  and covers the outer peripheral portion of the plunger  10  along the entire circumferential extent and the entire axial extent of the plunger  10 . The slide core  24  axially slidably supports the plunger  10  and conducts the magnetic flux between the slide core  24  and the plunger  10  in the radial direction. One of an outer peripheral surface of the plunger  10  and an inner peripheral surface of the slide core  24  is surface treated to form a non-magnetic coating or layer thereon, so that stucking of the plunger  10  to the slide core  24  is limited. 
     The magnetic shield portion  25  limits direct flow of the magnetic flux between the magnetically attracting core  9  and the slide core  24  and is formed as a thin wall portion, which has a large magnetic resistance. 
     The stator core  14  is inserted into the inside of the yoke  13  from one axial side of the stator core  14  where the slide core  24  is located. The stator core  14  is fixed to the yoke  13  at the flange portion  9   a  through the plastic deformation of the claw  13   d  against the end portion of the sleeve  5 . 
     The stepped portion  15 , which is configured into a form of a step, is formed in an outer peripheral portion of the slide core  24 . The stepped portion  15  is stepped to reduce an outer diameter of one portion of the slide core  24  located on one axial side of the stepped portion  15  in comparison to the other portion (another portion) of the slide core  24  located on the other axial side (another axial side) of the stepped portion  15 . Specifically, the outer diameter of the one portion of the slide core  24  located on the one axial side of the stepped portion  15 , which is axially opposite from the magnetically attracting core  9 , is reduced in comparison to the other portion of the slide core  24  located on the other axial side of the stepped portion  15  where the magnetically attracting core  9  is placed. 
     The ring core  26  is made of a ferromagnetic material and is formed as a cylindrical body having a flange at one axial end of the cylindrical body. The ring core  26  has a first conducting portion  27  and a second conducting portion  28 . The first conducting portion  27  covers the outer peripheral part of the one portion (hereinafter referred to as a reduced diameter portion  29 ) of the slide core  24  located on the one axial side of the stepped portion  15 . Furthermore, the first conducting portion  27  is slidable relative to the reduced diameter portion  29 . The first conducting portion  27  conducts the magnetic flux between the first conducting portion  27  and the slide core  24  in the radial direction. The second conducting portion  28  is the flange, which is configured into a ring plate form and radially outwardly projects from the first conducting portion  27 . The second conducting portion  28  contacts the bottom wall portion  13   b  and conducts the magnetic flux between the second conducting portion  28  and the bottom wall portion  13   b  in the axial direction. 
     A groove  30  is formed in one end surface of the second conducting portion  28  and radially extends in the direction, which is from the central axis of the linear solenoid  1  to the upper side immediately above the central axis of the linear solenoid  1  in  FIG. 2B . The groove  30  communicates between a space  31   a  and a space  31   b . The space  31   a  is formed on the one end side of the plunder  10  and is defined by the reduced diameter portion  29 , the first conducting portion  27  and the bottom wall portion  13   b . Furthermore, the space  31   b  is defined between the coil assembly  22  and the second conducting portion  28  in the axial direction. 
     A communication hole  33  is formed in the peripheral wall portion  13   c  and communicates between the inside and an outside of the yoke  13  in the radial direction. The communication hole  33  extends through the peripheral wall portion  13   c  in the radial direction, which is from the central axis of the linear solenoid  1  to the lower side immediately below the central axis of the linear solenoid  1  in  FIG. 2B . The communication hole  33  overlaps with the space (also referred to as a gap)  31   b  in the axial direction. In other words, an axial extent of the communication hole  33  overlaps with an axial extent of the space  31   b . In this way, the communication hole  33  functions as a second breathing passage  34 , which communicates the space  31   a , the space  31   b  and a space formed around one axial end portion of the plunger  10  to the outside of the yoke  13  to enable flow of fluid therebetween. 
     The first breathing passage  20  is configured to conduct the fluid between the one end side and the other end side of the plunger  10 , and the second breathing passage  34  is configured to conduct the fluid between the inside and the outside of the yoke  13  in the radial direction. Therefore, the first breathing passage  20  and the second breathing passage  34  enable the smooth movement of the plunger  10  in the axial direction in response to the starting and stopping of the energization of the coil  8 . 
     The urging member  17  urges the second conducting portion  28  against the bottom wall portion  13   b . The urging member  17  may be, for example, a rubber, a Belleville spring or a wave washer. 
     Now, advantages of the present embodiment will be described. 
     The linear solenoid  1  of the embodiment includes the stepped portion  15  and the ring core  26 . 
     The stepped portion  15  is formed in the outer peripheral portion of the slide core  24 . The stepped portion  15  is stepped to reduce the outer diameter of the one portion of the slide core  24  located on the one axial side of the stepped portion  15  to form the reduced diameter portion  29 . The ring core  26  includes the first conducting portion  27 , which is configured into the cylindrical tubular form, and the second conducting portion  28 , which is configured into the form of the flange. The first conducting portion  27  covers the outer peripheral part of the reduced diameter portion  29  of the slide core  24  located on the one axial side of the stepped portion  15 . Furthermore, the first conducting portion  27  is slidable relative to the reduced diameter portion  29 . The first conducting portion  27  conducts the magnetic flux between the first conducting portion  27  and the slide core  24  in the radial direction. The second conducting portion  28  contacts the bottom wall portion  13   b  and conducts the magnetic flux between the second conducting portion  28  and the bottom wall portion  13   b  in the axial direction. 
     In this way, an additional space can be provided on the radially outer side of the first conducting portion  27  and on the other end side of the second conducting portion  28 . Thereby, when the coil assembly  22  is placed in this space, it is possible to meet the demand for increasing the number of winding turns of the coil  8  and the demand for reducing the radial size of the coil  8  without sacrificing the advantage of enhancing the conduction of the magnetic flux with the ring core  26 . 
     Furthermore, the linear solenoid  1  includes the urging member  17 , which urges the second conducting portion  28  against the bottom wall portion  13   b . The urging member  17  enhances the conduction of the magnetic flux between the yoke  13  and the ring core  26 . 
     Now, modifications of the above embodiment will be described. 
     In the hydraulic pressure control valve  2 , which has the linear solenoid  1  of the above embodiment, the spool  3  is configured to change the communication state between each corresponding ones of the ports  4  based on the balance of the thrust force outputted from the linear solenoid  1 , the urging force of the spring  6  and the feedback force of the hydraulic pressure (oil pressure). Alternatively, the linear solenoid of the present disclosure may be applied to a hydraulic pressure control valve, in which the feedback force of the hydraulic pressure is not applied to the spool. 
     Furthermore, the linear solenoid  1  of the above embodiment is formed as the component of the hydraulic pressure control valve  2 . Alternatively, the linear solenoid  1  may be used as a component of any other suitable devices, which are other than the hydraulic pressure control valve  2 .