Abstract:
A drive unit includes a housing defining a rotational axis, a drive shaft supported by the housing for rotation about the rotational axis, an actuator supported by the housing for rotation about the rotational axis responsive to rotation of the drive shaft, and a coupling mechanism for coupling rotation of the drive shaft and the actuator. The coupling mechanism includes a first frictional surface rotatable with the drive shaft and a second frictional surface rotatable with the actuator. The first and second frictional surfaces are mating conical frustrum surfaces, the first frictional surface driving the second frictional surface via friction upon rotation of the drive shaft. Means are included for urging the first and second frictional surfaces together. The urging means may include a compression spring. The coupling mechanism may include a friction ring non-rotatably mounted to the drive shaft, the first frictional surface being disposed on the friction ring.

Description:
BACKGROUND OF THE INVENTION 
     The invention concerns a drive unit, and more particularly concerns a drive unit having a housing, gearing, shaft, actuator, and slip clutch. 
     In the case of a conventional drive unit of the usual type, there is provided an electric motor with a multi-step, RPM reducing drive enclosed in one housing. Between a drive shaft from the stepped down transmission and a driven component designed as a rotary actuator, a slip clutch is inserted which is comprised of several disks, i.e., a disk clutch. The disks are pressed together by a screw compressed spring, which, on the one side presses against the disks, and on the other side against the head of a screw, which is threadedly engaged in the drive shaft facility. 
     Motor-gear drive-units of this kind are installed for the activation of external mirrors on motor vehicles and particularly on trucks. The slip clutch is necessary so that the motor vehicle mirror, which is usually positioned by the motor driven actuator, can be also set by hand. The step-down gear drives are, naturally, self limiting. 
     The sliding moment, by the overstepping of which the frictional connection of the slip clutch is overcome, is not exactly defined, but varies within a non-reproducible range. In the case of a rotary movement contrary to the normal rotation, the screw will loosen itself, whereby the clutch will fail to hold. Moreover, there is a high cost of installation related to the many parts which must be handled. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     Thus the present invention has the fundamental purpose of creating a drive unit for this general application which is comprised of few parts, is simple to install, and exhibits a very exact, predictable slip moment. This purpose will be achieved by means of the features of the claimed invention. 
     By means of the measures taken in accord with the invention, the achievement has been gained, that on conical frustum shaped friction surfaces, a very exact, definable friction moment is given, so that in turn, also a very exact, definable slip moment is available, thus, inside the tolerance limits within which the slip clutch operates, the moment is generally constant. 
     Additional objects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned from practice of the invention. 
     Further features, advantages and details of the invention are to be gained from the following description of an embodiment with the assistance of drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     There is shown by: 
     FIG. 1 a profile view of a motor drive unit in accord with the present invention, 
     FIG. 2 a sectional view through the motor drive unit in accord with the section line II—II in FIGS. 1 and 3, 
     FIG. 3 a sectional view through the motor drive unit in accord with the section line III—III in FIG. 1, 
     FIG. 4 a longitudinal view of the ring gear of a drive, 
     FIG. 5 a front view of the ring gear in accord with the arrow V in FIG. 4, and 
     FIG. 6 a plan view of an annular thrust ring. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the presently preferred embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, and not meant as a limitation of the invention. For example, features illustrated or described as part of one embodiment can be used on another embodiment to yield yet another embodiment. It is intended that the present invention include such modifications and variations. 
     The motor drive unit presented in the drawings exhibits a housing under-piece  1  and a housing upper-piece  2  consisting of a thermoplastic material with weldable properties and wherein the two said housing pieces are connected with matching flanges  3 , 4 . Flange  3  of the housing under-piece  1  is provided with centering holes  5 , while flange  4  of the housing upper-piece  2  is equipped with pins  6  which are aligned with the centering holes  5 . These pins are introduced into the centering holes  5  and following the assembly and the combining of the housing under-piece  1  and the housing upper piece  2 , said pins are welded in place, so that they simultaneously also serve for a firm connection of housing under-piece  1  and housing upper-piece  2 . 
     The housing  1 , 2  is provided with a reception space  7  for an electric motor  8 , the electrical supply  9  for which is brought in through an opening  10  in said reception space  7 . The motor  8  is rotatable in either direction and hence drivable in both directions. The electric motor  8  lies in the reception space  7  against the detenting points  11 . Thus, when so inserted into the housing under-piece  1 , the motor  8  is already aligned in its position. 
     The electric motor is provided with a shaft  12 , extending unencumbered and outwardly projecting from the housing  1 ,  2 . The end  13  of said shaft remote from motor  8  is supported by a bearing seat  14  molded into the housing under-piece  1 . Encapsulating the steel shaft  12  is a cylindrical worm drive  16 , non-rotatably installed in respect to the shaft  12  by, preferably, force fit. 
     The helical cogging  17  of the worm  15  engages a corresponding toothing  18  of a worm driven gear  19 , which, together with the worm  15 , forms a worm drive  16 . 
     The worm drive  16  is associated with a planetary drive  20 . The planetary drive  20  includes a sun gear  21  which is non rotatably affixed as one part to the worm driven gear  19 . In the outer circumferential cogging  22  of the sun gear  21 , three planetary gears  23  (of which only one is shown) engage with their respective outer cogging. Beyond this, the planetary gears  23  support themselves on an annular interior gear  25 , which is provided with an inner cogging  26  into which the respective circumferential cogging  24  of the planetary gears  23  engage. The annular gear  25  is, in respect to the housing, non-rotary, to which effect it is provided on its outer perimeter with projections  27 , which protrude into the recess  28  of the housing  1 , 2 . The planetary gears  23  are rotatably carried by bearing pins  29  of a web under-part  30  and are positioned relative to one another at equal angular displacements. 
     The planetary gears are generally designed to be in close contact with a gear  32  of an annular drive  33 . The outer cogging of these gears  32  of the annular gear drive  33  interfit into an inner cogging  35  of a power take-off annular gear  36  of the annular gear drive  33 . 
     In the gears  32  is found a bearing pin  37  of an upper-part of the web  38 . The of under-part of the web  30  and the upper-part of the web  38  are in the middle of the constructed recesses  39  of the under-part of the web  30  and engage in the designed connection pins  40  of the web upper part  38 , to bind to each other as a housing like web. 
     The driven annular gear  36  as shown is a single piece with cylindrical bearing section  41 , which is concentric with the common rotation axis  42  of the worm drive gear  19 , the planetary drive  20  and the annular drive  33 . The annular gear  36  rests upon the bearing shell  43  which is installed on the housing upper piece  2 . The driven annular gear  36  further is secured concentric with the rotation axis  42  relative to the housing upper piece  2  by means of the detent surfaces  44 ,  45  which extend also concentric to the rotational axis. These do not interfere with the rotation of the driven annular gear  36 , but limit the play, that is, the displacement of the annular gear  36  along the rotational axis to about 0.1 mm. 
     The worm gear drive  16 , the planetary drive  20  and the and the annular drive  33  together form a step-down gear drive. 
     The worm driven gear  19  is secured on a continuous, through steel axle  46 , one end of which is set in a recess  47  in the housing under piece  1  with a force fit. The axle is non-rotating, in relation to the housing under piece  1 . The other end of the axle  46  is in a concentric, cylindrical recess  48  of the of the driven annular gear  36 , concentric to the rotation axis  42  and in great measure supported to be free of play, whereby, however, the non-rotating axle  46  does not interfere with the turning of the driven annular gear  36 . The worm gear  19  is set for free rotary motion on the axle  46  and supported concentric to the turning axis  42  counter to the front side  49  of the recess  47  toward the housing under piece  1 . Concentric with the annular gear  36 , gear  19  is axially supported on annular gear  25  of the planetary gearing  20 . 
     The driven annular gear  36 , consisting entirely of metal, for instance of cast zinc, possesses a cylindrical driving shaft  50  which is part of the bearing component  41  which exhibits at least one, but preferably two, continuous, longitudinal grooves  51  which run on mutually diametrically opposite sides parallel to the rotational axis  42 . 
     On the cylindrical driving shaft  50 , a frictional ring  52  is installed which ring is part of a slip clutch  53 , and which further engages the longitudinal grooves  51  respectively with a projection  54 A. By this means, a non-rotational connection between the annular gear  36  and the frictional ring  52  is brought about. The frictional ring  52  lies against a ring binder  55  at the transition point from the cylinder bearing component  41  to the longitudinal grooves comprising a drive section  51 , parallel to the rotational axis  42  making a firm connection. The ring  52  forms the above mentioned detent surface  45 . 
     The drive shaft  50  is surrounded by an actuator cylinder  56 , which shows a recess  57  running parallel to the rotational axis  42 , in which a bolt (not shown) can fix a swiveling part. The actuator  56  possesses a friction surface  58  which lies against a friction surface  59  of the friction ring  52 . Both friction surfaces  58 ,  59 , are shaped as conical frustums and taper themselves in a direction away from housing upper piece  2  less than a half conical angle “a”. The angle runs about 7°≦a≦15°, with a preference for a ≃10°. 
     The actuator  56  is pressed in a direction toward the tapered friction ring  52  by a pre loaded helical compression spring  60 , whereby, because of turning piece  56  and the friction ring  52 , only the frictional surfaces  58  and  59  contact one another. Between these two parts, therefore, the above mentioned slip clutch  53  is brought into being, the slip moment being defined by the friction coefficients between the frictional surface  59  of the friction ring  52  and the friction surface  58  of the turning part  56 , as well as through the force normal (90°) to the frictional surfaces  58 ,  59  and also defined by the average diameter “d”. The force active between the friction surfaces  58 ,  59  and normal to the same, is proportionately greater at a prescribed force of the compression spring  60  parallel to the rotational axis  42 , the smaller the half conical angle “a” of the frictional surfaces  58 ,  59  is. The active force between and normal to the friction surfaces  58 ,  59  is in any case about a magnitude greater than the force of the compression spring  60 . This allows the situation that the friction ring is comprised of metal, for instance cast zinc, while the actuator  56  is of common plastic. 
     The helical compression spring  60  lies below the interposed annular disk serving as pressure disk  61  which disk bears also on the actuator  56 . This pressure disk is likewise held non-rotatable in respect to driven annular gear  36  by means of projections  54 B into the longitudinal groove  51 . The friction moment acting between the pressure plate  61  and the actuator  56  is at least one tenth less than the slip moment of the slip clutch  53 . 
     The compression spring  60  lies further in the area of the free end  64  of the drive shaft  50  against a further ring disk serving as detent  62 , which, along with said drive shaft  50  is locked by means of a bayonet closure means  63 . The two ring disks are composed of metals, for instance, steel. The are identical in structure and exhibit the projections  54  is which fit into the longitudinal grooves  51 , which are identical in cross-section to the projections on friction ring  52 . 
     As may be inferred from the FIGS. 4 to  6 , in combination with FIG. 3, for the bringing about of the bayonet clamp  63  in the area of the free end of  64  of the driven annular gear  36  on the drive shaft  50  respectively, a partial circumferential groove  65  is placed, which, on the one side runs into a longitudinal groove  51 . Each partial circumferential groove is open on one end  66  to a longitudinal groove. Otherwise, the other end  67  to the respective other longitudinal groove  51  is shut. Each partial circumferential groove  65  shows a recess  68  directed to the free end, which corresponds to the projections  54 C of the counter ring disk  62 . 
     All gear wheels, with the exception of the driven annular gear  36 , consist of plastic and are turnable around the rotational axis  42  or an axis parallel thereto. 
     The assembly proceeds in such a manner, that the electric motor  8  is installed in its receiving space  7  in the housing under-piece  1  and the electric leads  9  are brought in through the opening  10 . The free end  13  of the shaft  12 , which is already provided with the worm  15  is then placed in the bearing seat  14 . First, or later, the axle  46  is pressed into the recess  47 . Then the worm gear wheel  19  of the planetary drive  20  is slipped onto the axle  46 , until it comes against the detent on the front side  49  of the recess  47 . 
     Subsequently thereto, the annular gear  25  of the planetary gear drive  20  is pushed onto the axle. Then the premounted unit from web under-part  30 , planetary gears  23  with gears  32  and web upper part  38  are so inserted into the annular gear  25 , that the outer cogging  24  of the planetary gears  23  come into working contact with the inner cogging  26  of the annular gear  25 . Thereafter, the driven annular gear  36  is slipped on the axle  46 , whereby simultaneously the outer cogging  34  of the gears  32 , along with the inner cogging  35  of the driven annular gear  36  come into working contact. Beyond this, the axle  46  is accepted in the recess  48  of the driven annular gear  36  and supported concentric to the rotational axis  42 . Subsequently to this, the housing upper-piece  2  is set upon the housing under-piece  1 , whereby the drive shaft  50  is brought through the bearing shell  43 . The pins  6  of the housing upper-piece  2  fit, as this is done, in the centralizing holes  5  of the housing under-piece  1  and, along with said lower piece, are then welded by ultra-sonic means. The driven annular gear  36  is now concentrically secured with its bearing section  41  in the bearing shell  43  of the housing upper-piece  2 . At the conclusion of this, the friction ring  52  of the slip clutch  53  is pushed on to the drive shaft  50  and then set upon the actuator  56 , so that the two friction surfaces  58 ,  59  lie one on the other. Then the compression disk  61  is placed on the drive shaft  50  and the helical compression spring  60  also installed on the drive shaft  50 . The helical compression spring  60  is preloaded against the frictional ring  52  by means of counter ring disk  62  and the disk  62  locked in place on the driving shaft  50  by means of the bayonet lock  63 . As this is done, the counter ring disk  62  is forced on to the free end  64  by the compression of the spring  60  on the free end  64  of the driving shaft  50 , and upon reaching the partial circumferentially grooves  65  so turned, that the projections  54  enter into in these partial circumferential grooves  65  to the extent that they meet the detents at the closed end  67 . Now, when the counter bearing ring disk  62  is released, it will be pushed so far in the direction toward the free end  64  until its projections come to rest in the recesses  68 . In these recesses  68  then, the counter bearing ring disk is non-rotatable in respect to the driving shaft  50 . 
     Also, disk  62  will not be released from shaft  50  due to rotation of the shaft in either direction, due to the seating of the projections  54  on the disk in recesses  68  on the shaft. 
     The finished and assembled motor drive unit can be mounted by means of designed fastening openings  69  on the housing  1 , 2  for its intended use. Such a use occurs, for instance, in external mirrors of motor vehicles and particularly for external mirrors provided on trucks. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope and spirit of the invention. It is intended that the present invention include such modifications and variations as come within the scope of the appended claims and their equivalents.