Abstract:
A device for displaceably actuating, in both directions along a longitudinal direction, a crown wheel includes an actuator for actuating the crown wheel to engage and lock a differential. The actuator includes an electromagnetic actuator that provides advantages of pneumatic devices.

Description:
BACKGROUND 
       [0001]    1. Technical Field of the Invention 
         [0002]    The present invention relates to an electromagnetically operated device for displaceably actuating a member for locking a rotating body. 
         [0003]    2. Description of the Prior Art 
         [0004]    It is known, for example in the technical sector of vehicles, to use differentials associated with rotating shafts which are controlled and associated with means able to cause locking of the said differentials when predetermined relative rotation conditions of the connected shafts exist. 
         [0005]    It is also known that locking of the differential is performed by means of engagement between front teeth, associated with the axially fixed rotating crown wheel, of the differential and the front teeth of a rotationally fixed, but axially movable, locking crown wheel, displacement of which is controlled by means of pneumatic pistons. 
         [0006]    Although fulfilling its function, this solution results in the need for a complicated and costly arrangement of fluid conveying pipes and headers as well as means for keeping under pressure the piston actuating fluid, which are also subject to possible losses in head resulting in malfunctioning of the locking engagement system. 
       SUMMARY 
       [0007]    The technical problem which is posed, therefore, is to provide a device for displaceably actuating a rotating crown wheel, in particular, but not exclusively, of a system for locking a differential, which is able to overcome the drawbacks of the prior art, being reliable and secure. 
         [0008]    In connection with this problem it is also required that this device should have small dimensions, be easy and inexpensive to produce and assemble and be able to be applied easily also in combination with pre-existing installations. 
         [0009]    These results are obtained according to the present invention by a device for displaceably actuating, in both directions along a longitudinal axis, a locking crown wheel, which device comprises an electromagnet actuator for displacing the crown wheel along the longitudinal. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0010]    Further details may be obtained from the following description of a non-limiting example of embodiment of the subject of the present invention provided with reference to the accompanying drawings in which: 
           [0011]      FIG. 1  shows a schematic cross-section along an axial plane of the operating device according to the present invention; 
           [0012]      FIG. 2  shows a front view of the actuating electromagnet of the device according to the present invention; 
           [0013]      FIG. 3  shows a schematic cross-section of the electromagnet according to  FIG. 2 ; 
           [0014]      FIGS. 4   a - 4   d  show schematic cross-sections illustrating the operating sequence of the device according to the invention; 
           [0015]      FIG. 5  shows a schematic cross-section of a further embodiment of the electromagnet in the rest position; 
           [0016]      FIG. 6  shows a cross-section similar to that of  FIG. 5  with the electromagnet excited; and 
           [0017]      FIG. 7  shows a schematic cross-section of a further variation of embodiment of the electromagnet according to  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0018]    As shown in  FIG. 1  and solely for the sake of convenience of the description and without limiting the present invention, a set of three reference axes with a longitudinal direction X-X, a transverse direction Y-Y and a vertical direction Z-Z as well as a front part corresponding to the axially fixed part  10   a  of the differential  10  and a rear part, opposite to the front part, the operating device according to the present invention acts on the crown wheel  20  for locking a differential  10 , which crown wheel  20  comprises front teeth  20   b  able to mesh with corresponding front teeth  10   b  of the differential  10 . 
         [0019]    In greater detail, the embodiment shown in  FIG. 1  comprises:
       a bell member  1030  rigidly connected to the fixed part  10   a  of the differential via a locking nut  12 ; said bell member  1030  is provided internally with:   a first substantially axial seat  1030   a  able to house an electromagnet  1121  for recalling an armature  1112 ;   second longitudinal seats  1030   b  able to house respective longitudinal guide pins  1111 , the rear ends  1111   a  of which co-operate with the armature  1112 , as will emerge more clearly below; and   third seats  1030   c  for housing respective second longitudinal springs  1116 , the rear ends of which exert an axial thrust on the said armature  1112 , reacting with the opposite end on the bottom of the respective seat of the bell member.       
 
         [0024]    The armature  1112  is mounted on a bearing  1113  mounted in the axial direction on a rear sleeve  20   a  rigidly connected to the locking crown wheel  20 . 
         [0025]    As shown, the bearing  1113  is mounted on said sleeve  20   a  so as to leave an annular gap  1113   a  between the inner race of the bearing and the sleeve itself; the latter also has, mounted thereon, a ring  30   b  able to form a rear end-of-travel stop for the bearing  1113 . 
         [0026]    The armature  1112  also has seats  1112   a  with a bottom hole  1112   b  able to allow the insertion, in the longitudinal direction, of the said guide pins  1111  which are prevented from coming out towards the front by the respective head  1111   a  having a diameter larger than that of the hole  1112   b.    
         [0027]    First springs  1115  are arranged between the bearing  1113  and the locking crown wheel  20 , said springs being axially arranged and inserted inside a respective seat  20   c  of the locking crown wheel  20 ; in the configuration shown in  FIG. 1  where the differential is open, said first springs extend in the rest condition. 
         [0028]    As shown in  FIGS. 2 and 3 , the electromagnet  1121  is formed with a circular shape having a cross-section substantially in the form of an “overturned E” and has alternating N/S windings  1121   b  along the circumference, so that the magnetic flux lines are closed without passing through the longitudinal axis, thus resulting in the absence of stray magnetic fluxes which cause magnetization of various parts of the differential, said magnetization resulting in accumulation of metallic dust on the bearings which with time tend to operate inefficiently. 
         [0029]    According to a preferred embodiment, it is also envisaged that the electromagnet  1121  is formed by a plurality of packed laminar elements  1121   a  so as to increase the force of attraction with respect to the armature  1112 . 
         [0030]    With this configuration and with reference to  FIGS. 4   a  to  4   d , locking/unlocking of the differential is performed in the following sequence:
       in the rest condition ( FIG. 4   a ) the electromagnet  1121  is deactivated, the armature  1112  is detached from the electromagnet  1121 , pushed by the second springs  1116 ; in this condition the first springs  1115  are fully extended in the rest condition and the locking crown wheel  20  is disengaged from the front teeth  10   b  of the differential, which is free to rotate;   when the differential must be locked ( FIG. 4   b ), the electromagnet  1121  is activated so as to recall displaceably the armature  1112  which, guided by the pins  1111 , moves forwards until it comes into contact against the electromagnet; during this stage, displacement of the armature causes the total compression of the second springs  1116  and the first springs  1115  which, reacting against the bearing  1113 , push towards the front the locking crown wheel  20 , the teeth  20   b  of which are able to bear frontally against the teeth  20   a  of the differential;   when rotation of the differential causes alignment of a gully of the teeth  10   b  with the teeth  20   b  of the locking crown wheel  20  ( FIG. 4   c ), the latter is able to move axially towards the differential pushed by the first springs  1115 , which extend again;   in order to unlock the differential ( FIG. 4   d ) the electromagnet  1121  is deactivated, allowing the first springs  1115  to react against the locking the crown wheel  20  so as to push backwards the armature  1112  until it comes into contact with the end-of-travel stop  30   b , in which position the springs  1115  no longer exert their thrusting force;   at this point the locking crown wheel  20  is free to move, but remains in position until the residual torque which is exerted between the two sets of teeth  10   b ,  20   b  decreases to a value less than the thrusting force of the second springs  1116  which, only in this condition, are able to push the armature  1112  and therefore the locking crown wheel  20  backwards, releasing the differential  10  which is able to start rotating again;   the thrust of the second springs  1116  moves the assembly consisting of locking crown wheel  20 /armature  1112  to the rear end-of-travel stop and restores operation for subsequent renewed actuation ( FIG. 4   a ).       
 
         [0037]    According to the invention, moreover, that activation of the electromagnet  1121  for recalling the armature  1112  is performed with a brief overcurrent transient so as to obtain a recall force sufficient to bring the armature  1112  into contact against the said electromagnet, this condition allowing the power supply current to the electromagnet to be reduced to normal values since the force required to keep the armature in contact is much less than that required for initial recall thereof. 
         [0038]    As shown in  FIGS. 5 and 6 , the magnetic core  1121 B of the electromagnet  1121  is provided with an axial extension  1121 C able to reduce the air gap existing between the electromagnet  1121  and the armature  1112 . 
         [0039]    With this solution it is possible to obtain an improved performance of the clutch system since the reduction in the air gap also allows a reduction in the initial overcurrent for recalling the armature. 
         [0040]    As shown in detail in  FIG. 6 , the axial extension  1121 C is arranged inside a seat  1112 C of the armature  1112 , said seat having suitable dimensions able to allow insertion of the extension  1121 C without mutual contact when the armature  1112  is recalled ( FIG. 6 ). 
         [0041]    Preferably the axial extension  1121 C and the corresponding seat  1112 C of the armature have a frustoconical shape so as to favour insertion, but, as shown in  FIG. 7 , the axial extension  1121 C may also be formed with a rectangular cross-section. 
         [0042]    It can therefore be seen how, with the axial actuating device according to the present invention, it is possible to achieve secure and reliable engagement/disengagement of the two sets of front teeth, which in the example described form part of a locking differential, avoiding the need for fluid conveying pipes and the associated problems for example due to possible losses in head and the like and ensuring safe operation due to the fact that duplication of the thrusting springs ensures safe recall of the armature and preparation of the crown wheel for engagement which can occur at any useful moment without damaging the electromagnet which otherwise would have to be kept in a condition where it is supplied with an overcurrent for long periods of time. 
         [0043]    Moreover, owing to the particular characteristics of the electromagnet, which can be excited with an overcurrent transient, it is possible to reduce the dimensions and house completely the locking device inside the box of the differential, avoiding the need for parts and associated volumes outside of it. 
         [0044]    Also, owing to the particular form of the bearing  1113  supporting the armature, which moves coaxially on the locking crown wheel without contact, it is possible to avoid wear from frictional contact as well as wear of the armature which, rotating on the outer race of the said bearing, is not subject to frictional forces resulting from contact in the axial direction with the end-of-travel stops.