Abstract:
An actuator includes: at least one drive motor; an outlet ( 22 ); an adjustable torque limiter which is disposed between the/each motor and the outlet ( 22 ), the torque limiter having a mobile element ( 100 ) which is used to set the maximum torque transmitted; and a case which houses the motor and the torque limiter. The case is provided with an opening ( 110 ) for accessing the mobile element ( 100 ) used to set the maximum torque transmitted and the torque limiter is mounted in the case.

Description:
FIELD OF THE INVENTION 
   The present invention relates to an actuator of the type comprising:
         at least one drive motor;   an output member;   an adjustable torque limiter which is interposed between the or each motor and the output member, the torque limiter comprising a movable member for adjusting a maximum transmitted torque; and   a housing which contains the or each motor and the torque limiter.       

   BACKGROUND OF THE INVENTION 
   In a number of fields, it is necessary for actuators to be provided with a torque limiter. This torque limiter is constituted, for example, by friction members which are held compressed together, the compression force of these friction members defining the sliding torque between these two members. The torque transmitted is limited to the sliding torque. 
   In practice, it is advantageous for the torque limiter to be calibrated before assembly. In an actuator, the torque limiter is generally preceded and/or followed by other reduction gear members, such as an epicyclic reduction gear, or reduction steps which are provided between the drive motor(s) and the torque limiter. 
   Owing to the machining differences between the various components which can be used from one actuator to another, it is difficult to determine by means of calculation the calibration of the torque limiter in accordance with the other elements of the actuator in order to ensure a maximum predetermined torque at the output member of the actuator. 
   SUMMARY OF THE INVENTION 
   The object of the invention is to provide an actuator which allows the limit torque measured at the output member to be fixed in a precise manner, independently of the production quality of the various members which are present in the kinematic chain between the drive motor(s) of the actuator and the output member. 
   To this end, the subject-matter of the invention is an actuator of the above-mentioned type, characterised in that the housing has an opening for access to the movable member for adjusting the maximum torque transmitted whilst the torque limiter is mounted in the housing. 
   According to specific embodiments, the actuator further comprises one or more of the following features:
         the adjusting member comprises a nut and the torque limiter comprises a shaft having a threaded portion, the nut is screwed on the threaded portion, the axial position of the nut on the threaded portion defining the maximum torque transmitted, and the actuator comprises corresponding recesses which are provided in the shaft and in the nut, as well as a member for fixing the nut on the shaft, which member is engaged in the corresponding recesses, in the direction of the shaft;   the fixing member comprises a support which is arranged at the end of the shaft, which support carries at least one locking finger which is engaged in two corresponding recesses;   it comprises a screw for retaining the fixing member, which screw is engaged in a threaded hole which is provided in the shaft;   it comprises a removable plug for closing the opening; and   it comprises at least one reduction step between the or each motor and the output member.       

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood from a reading of the following description, given purely by way of example and with reference to the drawings, in which: 
       FIG. 1  is a partially cut away perspective view of an actuator according to the invention; 
       FIG. 2  is a longitudinal sectioned view of the actuator of  FIG. 1 ; 
       FIG. 3  is a partially cut away perspective view of the differential reduction gear and torque limiting mechanism of the actuator of  FIGS. 1 and 2 ; 
       FIG. 4  is an exploded perspective view of the mechanism of  FIG. 3 ; and 
       FIG. 5  is a longitudinal sectioned view of the mechanism illustrated in  FIGS. 3 and 4 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The actuator  10  illustrated in the Figures is intended for locking an undercarriage of an aircraft in a retracted position. 
   This actuator comprises a housing  12 , inside which two drive motors  14 A,  14 B are arranged, each of which is connected mechanically to a differential reduction gear and torque limiting mechanism  15 . This mechanism comprises a differential reduction gear  16  which includes a torque limiter  18 . The actuator further comprises an epicyclic reduction gear  20  which is driven by the mechanism  15  and a rotating output member  22  which protrudes from the housing  12  and which is itself driven by the epicyclic reduction gear  20 . 
   More precisely, the two motors  14 A,  14 B are constituted by electric motors whose stators  24 A,  24 B are fixedly joined to the housing  12  and whose rotors  26 A,  26 B can be rotatably moved about axes Y 1 -Y 1  and Y 2 -Y 2  which extend parallel with each other. 
   The output shafts  28 A,  28 B of the motors drive the first and second motor sun pinions  30 A,  30 B of the differential reduction gear  16 . These motor sun pinions can rotate around the same principal axis X-X which extends parallel with the axes Y 1 -Y 1  and Y 2 -Y 2  of the motors. 
   As illustrated in  FIG. 2 , the output shaft  28 A of the motor is coupled to the motor sun pinion  30 A in order to be caused to rotate by means of a reduction step  32 A which is constituted by two coaxial and fixedly joined pinions  34 A,  36 A which have different diameters. 
   Similarly, as illustrated in  FIG. 1 , the output shaft  28 B of the motor is coupled in terms of rotation to the motor sun pinion  30 B by means of a reduction step  32 B which is constituted by two coaxial pinions  34 B,  36 B which have different diameters and which are fixedly joined by a shaft  38 . 
   The speed differential reduction and torque limiting mechanism  15  is illustrated alone in  FIGS. 3 to 5 . It has an output shaft  40  which extends along axis X-X. This shaft has, at a first end, an output pinion  42  which can drive the epicyclic reduction gear  20 . 
   The two motor sun pinions  30 A,  30 B are mounted so as to rotate freely about the output shaft  40 . The axes of the pinions  30 A,  30 B and the output shaft  40  are identical. The pinions  30 A,  30 B are supported by this shaft and are guided in rotation about the shaft by sliding bearings or rolling bearings  44 A,  46 A and  44 B,  46 B having lateral shoulders for axial retention. 
   Clamping jaws  48 A,  48 B are arranged between these bearings and the shaft  40 . These jaws are constituted by sleeves  50 A,  50 B which are extended at the facing ends thereof by integral collars  52 A,  52 B. The jaws  48 A,  48 B are connected in terms of rotation to the shaft  40  but are free to slide in translation along the length thereof. To this end, complementary profiles, such as flat portions, are provided on the outer surface of the shaft  40  and on the inner surface of the jaws  48 A,  48 B. 
   The differential reduction gear  16  comprises, between the two motor sun pinions  30 A,  30 B, a planet carrier  60  which is constituted by two end-plates  62 A,  62 B which are fixedly joined to each other in terms of rotation by means of pins and screws  63 . Between the two end-plates  62 A,  62 B of the planet carrier, there are mounted pairs of planet pinions  64 A,  64 B which engage with each other and each of which engages with a small driving sun pinion  70 A,  70 B which is fixedly joined to the motor sun pinion  30 A and  30 B, respectively. 
   Each planet pinion is in fact formed by two identical coaxial and integral gears which are carried by a shaft  72 , with which they are integral. 
   The shafts  72  can rotate about themselves relative to the end-plates  62 A,  62 B, between which they are held by means of bearings  74 . The shafts  72  extend parallel with each other and parallel with the axis X-X of the output shaft  40 . The axes of the shafts  72  are different from the axis X-X so that the planet pinions  64 A,  64 B can rotate together as an assembly about the axis X-X. 
   A hub  80  is fixedly joined in terms of rotation to the planet carrier  60  by means of the pins  63 . This hub is mounted so as to be able to rotate about the shaft  40 . It is arranged between the two motor sun pinions  30 A,  30 B. The hub  80  can be seen more clearly in  FIG. 4 . It is of planar form with a generally annular core which is extended by two diametrically opposed lateral lugs  80 A, through which the pins  63  extend. The pinions  64 A,  64 B are arranged around the core in the openings provided between the lateral lugs  80 A. 
   The hub  80  comprises two friction discs  82 A,  82 B which are attached by means of adhesive bonding at the opposing planar surfaces thereof. They are held compressed between the collars  52 A,  52 B of the jaws  48 A,  48 B, these collars forming friction members which can co-operate with the friction discs over planar annular surfaces. 
   The output shaft  40  is supported by means of ball bearings  90 A,  90 B which are arranged at one side and the other of the mechanism  15 . These ball bearings are supported by the housing  12 . The shaft  40  has a collar  92  which can be axially supported on the ball bearing  90 B which is axially supported on a shoulder of the housing  12 . 
   The hub  80  is axially clamped between the two jaws  48 A,  48 B. The jaw  48 B is supported on the collar  92  by means of a stack of Belleville washers  94 B and a rigid washer  96 B. 
   The jaw  48 A is pressed by means of a rigid washer  96 A and a stack of Belleville washers  94 A. This stack carried by the shaft  40  is kept clamped by means of a nut  100  which is screwed and centered on the second end of the shaft  40  opposite that which presses against the pinion  42 . The ball bearing  90 A is engaged around this nut  100  over a length of the nut which has a smooth surface at the outer side. 
   In this manner, the nut  100  brings about axial retention of the hub  80  which is clamped between the two jaws  48 A,  48 B. The jaws are urged towards each other by the Belleville washers  94 A,  94 B, by means of the support washers  96 A,  96 B. The Belleville washers are held compressed at one side by the collar  92  and, at the other side, by the nut  100 . 
   Depending on the tightening of the nut  100 , the Belleville washers are compressed to a greater or lesser extent and the pressure which they apply to the jaws  48 A,  48 B can be adjusted in such a manner that the friction force between the jaws  48 A,  48 B and the friction discs  82 A,  82 B is modified. 
   In order to adjust the friction force, the housing  12  has an opening  110  which is provided in the extension of the output shaft  40  and which allows access to the nut  100  and allows it to be operated with a spanner. In order to bring about the fixing of the nut, the shaft  40  has, at the second end thereof which carries the nut, transverse recesses  112  which open at the end of the shaft. There are, for example, three recesses. Corresponding recesses  112 ,  114  are provided in the nut  100 . They also open at the end of the nut. 
   A locking member  120  constituted by a collar  122  which carries two locking fingers  124  is engaged at the end of the shaft in such a manner that the fingers are received in corresponding radial recesses which are provided at the end of the shaft  40  and in the nut  100 . 
   A screw  126  is engaged in a threaded hole  128  which is arranged axially at the end of the shaft. Screw  126  extends through the locking member  120  and brings about the retention of screw  126 . 
   The opening  110  is closed by means of a removable and leak-tight protection plug  140 . 
   The actuator operates in the following manner. 
   When the two motors rotate at the same speed, the two motor sun pinions  30 A,  30 B are driven in the same direction. In this manner, the associated planet pinions  64 A,  64 B of the same pair are stationary relative to each other. The planet carrier  60  is caused to rotate by the planet pinions which are themselves caused to rotate about the shaft X-X by means of the driving sun pinions  70 A,  70 B. 
   The hub  80  is then caused to rotate with the planet carrier  60 . 
   The torque which is provided by the motors is transmitted from the hub  80  to the shaft  40 , as long as the friction force applied between the clamping jaws  48 A,  48 B and the friction discs  82 A,  82 B is greater than the torque supplied by the motors. 
   If this torque provided by the motor is greater than the friction force applied by friction, the friction discs slide over the friction surfaces of the jaws in such a manner that only a portion of the torque is transmitted. Therefore, the hub clamped between the clamping members  48 A,  48 B forms a torque limiter which is interposed between the two motor sun pinions  30 A,  30 B. 
   If one of the motors rotates at a different speed relative to the other motor, or if one of the motors is stopped, the two driving sun pinions  70 A,  70 B rotate at different speeds so that the planet pinions  64 A,  64 B are caused to rotate about themselves in opposite directions, which compensates for the difference in the speed of rotation of the two motors. The planet carrier  60  is then driven at a mean speed between the speeds of the two motor sun pinions  30 A,  30 B, which thus drives the shaft  40  at this speed as long as the torque provided by the motors is less than the friction torque applied by the friction surfaces which are in contact. 
   As known per se, the shaft  40  drives the control member  22  via the epicyclic reduction gear  20 . 
   Since the torque limiter is interposed between the two motor sun pinions  30 A,  30 B, the space taken up by the reduction gear and torque limiting mechanism is reduced, which allows an actuator to be produced which generally takes up a small amount of space. 
   In order to bring about the adjustment of the torque limiter, the plug  140  is removed, thus allowing access to the screw  126 . The screw  126  is removed as well as the locking member  120 . The nut  100  is screwed or unscrewed in order to bring about a suitable clamping force for the two jaws  48 A,  48 B on the friction discs  82 A,  82 B. 
   After the position of the nut has been adjusted, the locking member  120  is engaged once more in corresponding recesses  112 ,  114  of the nut and the end of the shaft, and the screw  126  is retightened in order to bring about axial retention of the locking member  120 . The plug  140  is finally repositioned in order to ensure the leak-tightness of the housing. 
   It will thus be appreciated that, in an actuator of this type, the torque limiter can be calibrated after the actuator assembly has been assembled, thereby allowing friction and losses of efficiency caused by the various engaged elements which constitute the actuator, and in particular the pinions of the epicyclic reduction gear  20 , to be taken into account. In this manner, the maximum output torque of the actuator measured in the region of the output member  22  can be defined in a precise manner regardless of the machining quality of the various moving elements of the actuator.