Abstract:
An electromagnetic wet clutch system includes operation members configured to magnetically work. The system includes a set of clutch plates configured to engage by the operation members. The set of clutch plates includes first plates with first sides. Respective one of the first sides is configured to contact respective one of the operation members. At least one of the first sides is boundary-lubricative.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention relates to an electromagnetic wet clutch system.  
           [0002]    A conventional coupling includes a rotary casing, an inner shaft, a primary clutch, a ball cam, a pressure plate, a cam ring, a pilot clutch, an armature, and an electromagnet.  
           [0003]    The pilot clutch includes a multi-plate clutch of inner and outer plates. The multi-plate clutch is formed with lubrication grooves or is nitrided under a gas atmosphere or a salt-bath thereon. Neighboring inner and outer plates have air gaps of lubrication grooves or surface treatment layers (nitrided film) therebetween.  
         SUMMARY OF THE INVENTION  
         [0004]    The air gaps or layers, however, interfere or reduce the magnetic force of the electromagnet, thus deteriorating magnetic flux efficiency. The deterioration lowers the force of attraction to the armature.  
           [0005]    Specifically, both sides of the inner and outer plates are formed with the lubrication grooves or a surface treatment layers. Between an outer plate and the armature or the rotor, the air gaps of lubrication grooves or surface treatment layers cause loss of magnetic flux. This loss deteriorates magnetic flux efficiency.  
           [0006]    The present invention is directed to an electromagnetic wet clutch system with improved clutch plates durability.  
           [0007]    The present invention is directed to one with improved magnetic flux efficiency.  
           [0008]    The invention includes an electromagnetic wet clutch system. The system includes operation members configured to magnetically work. The system includes a set of clutch plates configured to engage by the operation members. The set of clutch plates includes first plates with first sides. Respective one of the first sides is configured to contact respective one of the operation members. At least one of the first sides is boundary-lubricative.  
           [0009]    According to the system, an operation member with a stable sectional area of magnetic path contacts a boundary-lubricative first side with air gaps for boundary-lubrication. This allows maximum magnetic permeability, thus further improving magnetic flux efficiency.  
           [0010]    The term of “boundary lubricative” means that a side includes minute projections and recesses, surface roughness and a basic roughness remaining due to the formation into a plate shape by pressing. The projections and recesses are not limited by a rotational and a radial direction, a dotted state and length. The term means that a surface structure of the side is essentially boundary lubricative.  
           [0011]    The operation members include, for example, an armature and a rotor.  
           [0012]    Preferably, the set of clutch plates comprises a second plate disposed between the first plates. The second plate including inner and outer peripheries defines a second side therebetween. The second side defines a hydraulic passage extends between the inner and outer peripheries. According to the system, the hydraulic passage on the second side allows secure lubrication and cooling, thus preventing wearing and seizing.  
           [0013]    Preferably, the second plate includes a boundary-lubricative second opposite side relative to the second side. According to the system, the combination of first and second plates improves magnetic flux efficiency, which increases engagement torque of the system.  
           [0014]    Preferably, the second plate includes a second opposite side relative to the second side, the second opposite side defining a hydraulic passage.  
           [0015]    Preferably, the hydraulic passage extends radially. This system enhances the hydraulic circulation on the second side, thus further improving cooling exertion. The preference allows the hydraulic fluid to be retained quickly and uniformly on a boundary-lubricative first side.  
           [0016]    Preferably, a boundary-lubricative first plate is configured to rotate integrally with an operation member. This system further prevents variation of air gaps and increases the magnetic path in the surface area, thus improving magnetic flux efficiency. The first side or a contact side requires no hardening treatment such as a heat treatment, thus allowing improvement in magnetic flux efficiency and reduction in fuel costs.  
           [0017]    Preferably, the first plate and the operation member connect to a common spline.  
           [0018]    Preferably, the set of clutch plates includes a pair of sides sliding each other. One of said pair of sides includes a hydraulic passage. Another of said pair of sides is boundary-lubricative. According to the preference, the loss of magnetic permeability due to the hydraulic passage on the one side allows the loss of magnetic force to be limited to a minimum.  
           [0019]    Preferably, the set of clutch plates is disposed between inner and outer rotary members. The inner and outer rotary members have a fluid sealed therebetween for lubricating the set of clutch plates. According to the system, within a limited space between the inner and outer rotary members, the lubrication, cooling and magnetic flux efficiency of the system improve. The system has large torque capacity of clutch engagement, with less variation per time and excellent durability. 
       
    
    
     BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS  
       [0020]    These and other features, aspects, and advantage of the present invention will become better under stood with reference to the following description, appended claims, and accompanying drawings where:  
         [0021]    [0021]FIG. 1 is a sectional view of a coupling according to the first embodiment of the invention;  
         [0022]    [0022]FIG. 2 is an enlarged sectional view of a pilot multi-plate clutch in FIG. 1;  
         [0023]    [0023]FIG. 3 is a perspective view of inner and outer plates in FIG. 1;  
         [0024]    [0024]FIG. 4 is a perspective view of inner and outer plates according to the second embodiment;  
         [0025]    [0025]FIG. 5 is a perspective view of inner and outer plates according to the third embodiment;  
         [0026]    [0026]FIG. 6 is an exploded sectional view of a multi-plate clutch according to the fourth embodiment;  
         [0027]    [0027]FIG. 7 is a perspective view of inner and outer plates of the multi-plate clutch in FIG. 6; and  
         [0028]    [0028]FIG. 8 is a perspective view of inner and outer plates of the multi-plate clutch according to the fifth embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    The embodiments of the invention will be described with reference to drawings.  
         [0030]    [First Embodiment] 
         [0031]    As shown in FIG. 1, coupling  1  is disposed between a rear differential to be separated and an engine (transfer). The left of FIG. 1 corresponds to the front (engine) of a vehicle.  
         [0032]    Whole coupling  1  is housed in a casing (not shown in FIGS.) fixed to the vehicle body. Coupling  1  includes clutch housing  3  or an outer rotary member. Coupling  1  includes clutch hub  9  or an inner rotary member in clutch housing  3 . Disposed between clutch housing  3  and clutch hub  9  are primary clutch  11 , ball cam  13 , pressing member  15 , cam ring  17 , and pilot clutch  19 .  
         [0033]    Clutch housing  3  of a magnetic steel is configured in a cylindrical shape as a whole. The front part of the housing connects to power transmission shaft  5 . The rear part of the housing has opening  21  provided thereto.  
         [0034]    Shaft  5  is made of a magnetic steel for a shaft. The external face  5   a  of the shaft is formed with serration  7  for serration connection with a companion flange (not shown in FIGS.). The companion flange connects to a flange of a propeller shaft to connect to the engine (transfer).  
         [0035]    Mounted to opening  21  is ring-shaped magnetic rotor  31  to rotate integrally with housing  3 . Shaft  5 , housing  3  and rotor  31  are integral with each other. They  5 ,  3 ,  31  are supported to a casing of a vehicle by bearings (not shown) on shaft  5  and rotor  31 .  
         [0036]    Clutch hub  9  is disposed within housing  3 . The front end thereof is supported to housing  3  by ball bearing  43 . Hub  9  connects to a drive pinion shaft of the rear differential.  
         [0037]    Multi-plate primary clutch  11  is disposed between housing  3  and hub  9 . Ball cam  13  is disposed between pressing member  15  and cam ring  17 . Ball cam  13  and cam ring  17  constitute a cam mechanism.  
         [0038]    Pressing member  15  is splined axially movably to hub  9 . Ball cam  13  presses primary clutch  11  to be engaged under a thrust force.  
         [0039]    Cam ring  17  is disposed on the outer peripheral face of hub  9 . Disposed between cam ring  17  and rotor  31  is thrust bearing  47  against the cam repulsion of ball cam  13 .  
         [0040]    Pilot clutch  19  includes multi-plate clutch  49 . The clutch  49  is disposed between housing  3  and cam ring  17 . Armature  53  is disposed proximate to the front of clutch  49 . The armature is connected to a spline  3   a  of housing  3 . The spline  3   a  is also connected with outer plates  75 A. Armature  53  may be splined to hub  9 .  
         [0041]    Rotor  31  is operated by electromagnet  51 . Inserted with some play in recess  57  of rotor  31  is yoke  55  of electromagnet  51 . Rotor  31  is supported rotatably to yoke  55  by seal bearing  59 .  
         [0042]    Electromagnet  51  is fixed to the casing of the vehicle body. Electromagnet  51  connects to a battery via lead wire  29 . The operation of magnetization or demagnetization is controlled by a controller.  
         [0043]    Rotor  31 , clutch  49  and armature  53  define line  61  of magnetic force (path of magnetic flux) from electromagnet  51 .  
         [0044]    Disposed in rotor  31  is ring  63  of non-magnetic stainless steel. The ring prevents the magnetic flux  61  of magnetic force from escaping. Clutch  49  includes notch  65  located in correspondence with ring  63 . Notch  65  prevents the magnetic flux  61  of magnetic force from escaping and leaking.  
         [0045]    Disposed between thrust bearing  47  and rotor  31  is spacer  73  of a washer. Spacer  73  is made of non-magnetic material such as aluminum or stainless steel. The spacer  73  prevents the leakage of the magnetic flux  61  of electromagnet  51  to cam ring  17 .  
         [0046]    Clutch  49 , as shown in FIGS. 2 and 3, includes, for example, four outer plates  75 A and three inner plates  77 A alternately stacked on each other. As to the stack, outer plates  75 A 2  are located at both ends of clutch  49 . The arrangement allows inner plates  77 A to be interposed between outer plates  75 .  
         [0047]    Outer plates  75 A are splined to housing  3 . Inner plates  77 A are splined to cam plate  17 . For the achievement of spline connection, the outer periphery of each outer plate  75 A includes arc-shaped engagement lugs  79  formed at angular intervals of 90 degrees. The inner periphery of each inner plate  77 A includes arc-shaped engagement lugs  81  formed at angular intervals of 90 degrees. Each plate  75 A,  77 A includes four arc-shaped holes  76 ,  78  for hydraulic lubrication therethrough.  
         [0048]    Neighboring plates  75 A,  77 A slide against each other. Formed on plate  77 A are lubrication grooves  85  for hydraulic lubrication.  
         [0049]    Lubrication grooves  85  are formed on one of sliding sides  75 Ab,  77 Aa. In FIG. 3, both sides  77 Aa and  77 Ab of each inner plate  77 A of the embodiment are formed with lubrication grooves  85 . The grooves include narrow grooves  85   a  and  85   b  on the both sides  77 Aa,  77 Ab of inner plate  77 A. Grooves  85   a,    85   b  transversely extend between the inner and outer peripheries of inner plate  77 A. Grooves  85   a,    85   b  cross each other at an angle of, for example, 90 degrees. The radial component of each of the grooves  85   a,    85   b  circulates a lubrication oil from the inside to the outside of inner plate  77 A. The tangential component of each groove  85   a,    85   b  retains a lubrication oil.  
         [0050]    The both sides  75 Aa,  75 Ab of outer plate  75 A are flattened without lubrication grooves. The flatting includes a minute unevenness at a surface roughness less than 10 im.  
         [0051]    The combination of outer plate  75 A and inner plate  77 A negate an air gap therebetween, the side of outer plate  75 A facing armature  53  being without lubrication grooves. On the other hand, inner plates  77 A, being interposed between outer plates  75 A, slide against outer plates  75 A. Thus, the formation of lubrication grooves is limited to a necessary minimum. This reduces air gaps due to the lubrication grooves  85 . The reduction prevents reduction in magnetic force, thus improving magnetic flux efficiency.  
         [0052]    In the structure, electromagnet  51  attracts armature  53  along magnetic flux  61  of magnetic force when magnetizing. The armature presses and engages clutch  49 . The engagement produces a pilot torque. The pilot torque allows a driving force of the engine to be applied to ball cam  13  through housing  3 , clutch  49 , and cam ring  17 . The thrust force of the cam allows pressing member  15  to press and engage primary clutch  11  under a thrust force. The engagement allows coupling  1  to be connected.  
         [0053]    The connection of coupling  1  allows the rear differential to be connected to the engine. The connection reduces the vehicle to four-wheel drive. At this time, the control of the magnetic force of electromagnet  51  in magnitude by a controller allows the pilot torque of clutch  49  to be changed due to sliding. The change allows thrust force of ball cam  13  to be changed. The change allows connecting force of primary clutch  11  and coupling  1  to be adjusted.  
         [0054]    The adjustment of the connecting force of coupling  1  allows the torque distribution ratio between front and rear wheels of the vehicle to be adjusted.  
         [0055]    When electromagnet  51  demagnetizes, the pilot torque of clutch  49  disappears. The disappearance allows primary clutch  11  to be disengaged. The disengagement allows coupling  1  to be disconnected. The disconnection of coupling  1  allows the rear differential to be separated from the shaft  5 . The vehicle becomes a two-wheel drive with front-wheel drive.  
         [0056]    An oil is poured into shaft  5 , housing  3  and rotor  31  through oil hole  67  provided to housing  3 . After pouring the oil, ball  68  seals oil hole  67 .  
         [0057]    Disposed between housing  3  and hob  9  is X-ring  37 . Between the housing  3  and rotor  31 , O-ring  39  is disposed. Between rotor  31  and hub  9 , X-ring  41  is disposed. The respective rings prevent the leakage of oil to the outside.  
         [0058]    The sealed oil is stored in oil reservoir  33  provided to hub  9 . Hub  9  has radial oil passage  69  in communication with reservoir  33 . When hub  9  rotates, the oil flows from reservoir  33  through passage  69 . The oil lubricates primary clutch  11  and ball bearing  43 . In addition, the oil lubricates ball cam  13 , thrust bearing  47 , clutch  49 , X-rings  37 ,  41 .  
         [0059]    In the above-embodiment, the both sides  77 Aa,  77 Ab of inner plates  77 A are formed with lubrication grooves  85 . Both sides of each outer plates  75 A are formed without lubrication grooves. Inner plates  77 A, being interposed between outer plates  75 A slide against outer plates  75 A,. The formation allows grooves  85  to be limited to a necessary minimum. The formation of grooves  85  reduces air gaps needed to be produced. This reduction prevents the lowering of magnetic force, thus improving magnetic flux efficiency.  
         [0060]    The improvement of magnetic flux efficiency allows magnetic flux to be guided efficiently to armature  53 , thus obtaining pilot torque by clutch  49 .  
         [0061]    The loss of exciting power to electromagnet  51  reduces remarkably. The reduction reduces load of a battery, thus improving fuel costs of the engine. The electromagnet  51  is small-sized, and the whole coupling  1  becomes lighter and more compact.  
         [0062]    The formation of lubrication grooves  85  on the both sides  77 Aa,  77 Ab of all inner plates  77 A allows for their use as common inner plate components.  
         [0063]    [0063]FIG. 4 shows the second embodiment. Corresponding identical members to the first embodiment are attached with identical reference characters. The description omits repetition.  
         [0064]    [Second Embodiment] 
         [0065]    The second embodiment differs in the formation of lubrication grooves and is identical to the first embodiment in other structures.  
         [0066]    Respective inner and outer plates  77 B,  75 B include lubrication grooves  85 ,  87  formed on one side  77 Ba,  75 Ba thereof. The opposite side  77 Bb,  75 Bb are flattened without lubrication grooves. The sides  77 Ba,  75 Ba with lubrication grooves  85 ,  87  contact with the neighboring flat sides  75 Bb,  77 Bb, thus allowing the stacking of outer and inner plates  77 B,  75 B each other.  
         [0067]    According to the stacked plates, lubrication grooves are not provided to both of facing sides  77 Bb and  75 Ba or  77 Ba and  75 Ab of neighboring plates, but to one of the facing sides (one side)  77 Ba and  75 Ba for hydraulic lubrication. The formation of lubrication grooves on one side  77 Ba,  75 Ba at siding portions allows the lubrication grooves to be limited to a necessary minimum. This reduces air gaps produced due to the formation of lubrication grooves  85 ,  87 . This reduction prevents the lowering of magnetic force, thus improving magnetic flux efficiency.  
         [0068]    [Third Embodiment] 
         [0069]    The third embodiment will be described with reference to FIG. 5. The third embodiment has outer plates  75 C of clutch  49  formed with lubrication grooves.  
         [0070]    Outer plates  75 C are stacked on neighboring inner plates  77 C and are located in the middle of the stacked plates. Both sides  75 Ca,  75 Cb of outer plates  75 C are formed with lubrication grooves  87 . Another outer plates  75 D are located at both ends in the stacked plates. The outer plates  75 D each have lubrication grooves  87  on a side  75 Da facing inner plate  77 C. The opposite side  75 Db thereof is flat without a lubrication groove. The flat sides  75 Db face armature  53  and rotor  31  to rotate integrally with outer plates  75 D, and they does not slide each other. The both sides  77 Ca,  77 Cb of inner plates  77 C are flattened without lubrication grooves.  
         [0071]    The outer plates  75 C,  75 D allow lubrication grooves  87  to be limited to a necessary minimum.  
         [0072]    [Fourth Embodiment] 
         [0073]    The embodiment employs outer plates  75 C,  75 D as outer plates and inner plates  77 A as inner plates. Both sides  77 Aa,  77 Ab of inner plates  77 A and both sides  75 Ca,  75 Cb of intermediate outer plates  75 C, and one side  75 Da of outer plates  75 D located at both ends in FIG. 7, have lubrication grooves  85 ,  87  formed thereon. The sides each slide against the neighboring plate to form sliding faces. The formation of lubrication grooves  85 ,  87  allows hydraulic lubrication for smooth rotation.  
         [0074]    On the other hand, the opposite sides  75 Db of outer plates  75 D are formed without lubrication grooves. One opposite side  75 Db faces rotor  31 . The other opposite side  75 Db faces armature  53 .  
         [0075]    The outer plates  75 D, or a clutch plate, rotate integrally with armature  53  and rotor  31 , with one side  75 Db not sliding against armature  53  and rotor  31 . Thus, lubrication grooves for hydraulic lubrication are unnecessary.  
         [0076]    The contact area between outer plate  75 D and rotor  31 , or armature  53  is enlarged. The enlargement enhances magnetic permeability, thus improving the attraction force of electromagnet  51 , thus increasing the engagement force of pilot clutch  19 . The result is the increased engagement force of primary clutch  11 , thus allowing stable power transmission.  
         [0077]    No forming lubrication grooves on a side  75 Db of outer plate  75 D allows rotor  31  and outer plate  75 D not to rub together when rotor  31  screws into housing  3 , thus preventing the surface of rotor  31  from damage.  
         [0078]    Side  75 Db of one of both outer plates  75 D may be formed with lubrication grooves. This improves magnetic permeability, thus allowing the engagement force of pilot clutch  19  to increase.  
         [0079]    [Fifth Embodiment] 
         [0080]    The embodiment will be described with reference to FIG. 8. The embodiment has pilot clutch  19  with sliding sides that are surface treated. Regarding the surface treatment, clutch plates are gas or salt-bath nitrided. The surface treatment allows the surfaces of the clutch plates to be hardened. This hardening improves the efficiency of friction, sliding ability and durability of the sliding sides of the clutch plates.  
         [0081]    The surface treatment is applied to both sides  77 Ea,  77 Eb of all inner plates  77 E, both sides  75 Fa,  75 Fb of the intermediate outer plates  75 F, and the sides  75 Ga of both end outer plates  75 G, and not to the opposite sides  75 Gb.  
         [0082]    The outer plates  75 G, or a clutch plate, rotate integrally with armature  53  and rotor  31 , with the sides  75 Gb not sliding on armature  53  and rotor  31 . This does not need improved friction efficiency, and surface treatment is unnecessary  
         [0083]    Without surface treatment to the sides  75 Gb of outer plates  75 G, the dispersion and interruption of magnetic flux does not occur due to the treatment layer. This improves magnetic permeability. The improvement of magnetic permeability allows the attraction force of electromagnet  51  to increase. This increases the engagement force of pilot clutch  19 . The result increases the engagement force of primary clutch  11 , thus allowing stable power transmission.  
         [0084]    Side  75 Gb of one of both outer plates  75 G may be formed with a surface treatment. This improves magnetic permeability, thus allowing the engagement force of pilot clutch  19  to increase.  
         [0085]    The entire contents of Japanese Patent Applications P2001-194892 (filed on Jun. 27, 2001) and P2001-64752 (filed on Mar. 8, 2001) are incorporated herein by reference.  
         [0086]    While preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purposes, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.