Abstract:
Unit for picking up a spare wheel of a vehicle. According to one implementation the unit includes a gear assembly configure to apply a torque on a drum supporting a cable, the gear assembly having a cam that wobbles as the gear assembly transmits the torque. A rotatable stop is situated adjacent a side edge of the cam and is configured to act on the edge of the cam to limit the travel of the cam during the wobbling movement. The stop has a first contact surface and a second contact surface with the edge of the cam configured to slide along the first contact surface as the drum is rotated in at least one direction by operation of the cam. A guide surface is provided to interact with the second contact surface to limit the rotation of the stop when the edge of the cam acts on the stop.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application relates to and claims the benefit and priority to Spanish Patent Application No. P201331321, filed Sep. 11, 2013. 
     TECHNICAL FIELD 
     The present invention relates to units for picking up spare wheels in vehicles. 
     BACKGROUND 
     Units for picking up spare wheels designed for use in vehicles, and more specifically units designed for picking up or releasing a spare wheel that are arranged below the chassis (or on the underbody) of the vehicle are known in the state of the art. 
     These units generally comprise a mechanism with a transmission shaft which allows winding or unwinding a cable when the user manipulates the transmission shaft with a tool. The transmission shaft comprises a gear assembly which allows transmitting a torque which the user produces with the tool, and a drum which allows winding or unwinding the cable and to which the torque is transmitted from the gear assembly. 
     The gear assembly comprises at least one cam having a toothed area, and a hole in which an eccentric shaft operated by the tool of the user is coupled. The toothed area of the cam has one tooth less than the toothed area of the drum where it is coupled or one tooth less than the toothed area of a ring gear of the gear assembly which is intermediate between the cam and the drum. When the rotation is transmitted from the gear assembly to the drum, a wobbling movement occurs in the cam, i.e., the cam swings in time with a back and forth movement caused by the action of the eccentric shaft. This wobbling movement, also known as a pilgrim movement, along with the fact that the toothed area of the cam has one tooth less than the toothed area of the drum, causes the cam to rotate and go forward one tooth of its toothed area into the teeth of the toothed area of the drum or of the ring gear. The torque is thus transmitted, but the cam also rotates, and to limit the rotation the cam comprises a prolongation abutting with an element of the unit for picking up spare wheels. According to the unit type, the stop can directly be one of the casings of the unit, or the prolongation of the cam can comprise a groove in which a bolt of the unit is located, such that the groove of the cam slides during the wobbling movement and is supported on the abutting bolt, thus preventing rotation of the cam. 
     European Publication No. EP1352871 A2 discloses a unit for picking up spare wheels comprising a gear assembly which allows transmitting a torque, the gear assembly comprising a cam having a wobbling movement as the gear assembly transmits the torque, and at least one stop limiting the travel of the cam during the wobbling movement. 
     SUMMARY OF THE DISCLOSURE 
     According to some implementations a unit for picking up spare wheels is provided that comprises a gear assembly which allows transmitting a torque, the gear assembly comprising a cam having a wobbling movement as the gear assembly transmits the torque, and at least one stop limiting the travel of the cam during the wobbling movement. The unit comprises at least one guide surface which interacts with a contact surface of the stop and determines the travel of the stop when the cam acts on the stop, the stop acting on the cam from one side of the cam. 
     The known units for picking up spare wheels have an efficiency problem in the transmission of torque which the user produces on the transmission shaft of the unit with the tool. The transmission shafts comprise a gear assembly in which during its wobbling movement, upon transmitting the torque, the cam performs a combined movement of being supported and sliding on the stop defined in the unit to limit rotation of the cam. The cam comprises a surface that is laterally supported on the stop, the surface being either one of the casings of the unit or a groove defined in the cam which is supported on a bolt. This support produces a pressure line between the edge of the support surface of the cam and the stop, and taking into account the torques that are transmitted to assure that the wheel is irreversibly fixed in place, a crushing between the edge of the surface of the cam and the stop occurs. This crushing causes difficulties in sliding the cam on the stop and torque transmission efficiency becomes worse. 
     According to the implementations disclosed and contemplated herein, the cam acts on the stop from one side of the cam when the cam performs the supporting and sliding movement. Since the stop is located on the side and therefore outside the cam, it can be designed with more freedom since it is not limited in an inner groove, such that the side edge of the cam can be supported not on a pressure line such as that which occurs between an edge of the cam and a bolt. Furthermore, to assure that the support between the edge of the cam and the stop is in time with the wobbling movement of the cam, the unit comprises a guide surface interacting with a contact surface of the stop other than the area of contact between the stop and the side of the cam, such that the guide surface determines the travel of the stop when the cam acts laterally on the stop during its wobbling movement. 
     Torque transmission efficiency in the transmission mechanism of the unit for picking up spare wheels can thus be improved through improvements in the combination of the supporting movement for supporting the cam on the stop by locating the stop on a side and by being able to freely design the stop, and of the sliding movement by introducing a contact surface in the stop which interacts with a guide surface defined in the unit. 
     These and other advantages and features will become evident in view of the drawings and the detailed description of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exploded perspective view of a first embodiment of a unit for picking up spare wheels. 
         FIG. 2  shows a perspective view of the unit of  FIG. 1  in which the cover casing has been removed, with a guide surface which is a pin located inside the stop of the unit. 
         FIG. 3  shows a perspective view of a second embodiment of a unit for picking up spare wheels in which the cover casing has been removed, with a guide surface which is a pin located outside the stop of the unit. 
         FIG. 4  shows a perspective view of a third embodiment of a unit for picking up spare wheels in which the cover casing has been removed. 
         FIG. 5  shows a perspective view of the cover casing of the unit of  FIG. 4  with the ring gear and the eccentric assembly of the unit already assembled, with a guide surface located outside the stop of the unit and formed in the cover casing, the guide surface being in contact with the stop of the unit, and the slider of the cam being in contact with the stop of the unit. 
         FIG. 6  shows a perspective view of the stop of the unit of  FIG. 1 . 
         FIG. 7  shows a perspective view of the slider of the cam of the embodiments of the unit of  FIGS. 2, 3 and 4 . 
         FIG. 8  shows a perspective view of the stop of the unit of  FIG. 3 . 
         FIG. 9  shows a perspective view of the stop of the unit of  FIG. 4 . 
         FIG. 10  shows a detailed perspective view of a cam. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an exploded perspective view of a first embodiment of a unit for picking up spare wheels  100 , the unit  100  comprising two casings, a cover casing  150  and a housing casing  160 , a drum  40  which rotates for winding or unwinding a cable  41 , and a gear assembly  50 . The gear assembly  50 , which allows transmitting the torque which a user produces (not shown in  FIG. 1 ) by acting on a drive shaft  70  of the unit  100  with a tool, comprises in this embodiment a cam  10  and a ring gear  30 . The drive shaft  70  is assembled in an eccentric assembly  60  and the eccentric assembly  60  is coupled to the gear assembly  50 , the eccentric assembly  60  being assembled in a hole  14  of the cam  10 . The cam  10  comprises a toothed area  13  and the ring gear  30  comprises a toothed area  31 , both toothed areas  13  and  31  meshing with one another. The gear assembly  50  is coupled through the toothed area  31  of the ring gear  30  to a toothed area (not shown in  FIG. 1 ) of the drum  40 , thus allowing transmitting the torque applied by the user to the drive shaft  70  by means of the tool, and the rotation of the drum  40  in one direction or another thus being obtained. 
     According to some implementations the toothed area  13  of the cam  10  has one tooth less than the toothed area of the drum  40  where it is coupled and one tooth less than the toothed area  31  of the ring gear  30  of the gear assembly  50 , the ring gear  30  being intermediate between the cam  10  and the drum  40 . When rotation is transmitted from the gear assembly  50  to the drum  40 , a wobbling movement occurs in the cam  10 , i.e., the cam  10  swings in time with a back and forth movement caused by the action of the eccentric assembly  60 . This wobbling movement, also known as a pilgrim movement, along with the fact that the toothed area  13  of the cam  10  has one tooth less than the toothed area of the drum  40 , causes the cam  10  to rotate and move one tooth of its toothed area  13  forward into the teeth of the toothed area of the drum  40  and of the toothed area  31  of the ring gear  30 , the torque thus being transmitted. The cam  10  comprises an arm  11  prolonging from the central body of the cam  10 , and an edge  12  limiting the outside of the cam  10 . 
       FIG. 2  shows a perspective plan view of the unit  100  of  FIG. 1  already assembled in which the cover casing  150  has been removed. The unit  100  comprises inside the housing casing  160  a housing  161  in which the drum  40  is housed, and the gear assembly  50  meshes with the drum  40 . The unit  100  comprises a sliding guide  120  which is preferably made of plastic but can also be made of another material, the sliding guide  120  being assembled in the housing casing  160  inside the housing  161 . The arm  11  of the cam  10  of the gear assembly  50  comprises a side  15  which is supported on and abuts with the sliding guide  120  when the wobbling movement of the cam  10  occurs while the torque is being transmitted. During its wobbling movement, the cam  10  performs a combined rotating or swinging movement and back and forth or sliding movement. To limit the cam&#39;s rotation, the side  15  of the arm  11  of the cam  10  abuts with and is supported on the sliding guide  120  when the drum  40  rotates, unwinding the cable. In the other direction of rotation, when the drum  40  is winding the cable, and therefore greater torque is transmitted for lifting the wheel and locking it in place, the arm  11  of the cam  10  abuts with another side  16 , opposite the side  15 , with a stop  1  arranged on a surface  162  of the casing  160  which is located at substantially the same height as the edge  12  of the cam  10 . The cam  10  acts on the stop  1 , being supported on a contact surface  3  of the stop  1  during its rotating movement and in sliding movement, the stop  1  limiting the travel of the cam  10 . 
     The unit  100  shown in  FIG. 2  also comprises a guide surface  110  which interacts with a contact surface  2  of the stop  1 , the guide surface  110  allowing a rotating movement of the stop  1  accompanied by the wobbling movement of the cam  10 , and limiting the travel thereof. The guide surface  110  is the substantially cylindrical outer surface of a pin which is arranged inside the stop  1 . In this first embodiment, the stop  1  comprises, as shown in  FIG. 6 , a body having a contact surface  3  with a parallelogram shape, the contact surface  3  facing the side  16  of the arm  11  of the cam  10  and a hole  4  traversing the body of the stop  1 , the axis of the hole  4  being substantially parallel to the drive shaft  70  of the unit  100  and to the contact surface  3 . The pin comprising the guide surface  110  is arranged in this hole  4 . The stop  1  is preferably manufactured in plastic or composite material with a low coefficient of friction, although it can also be made of metal or another material. Therefore, the support and sliding of the cam  10  through the side face  16  of the arm  11  takes place on a relatively large planar surface versus a line contact that allows it to slide without problems, improving torque transmission efficiency. 
     The unit for picking up spare wheels  100  can work with the features described until now, but in order to further improve torque transmission efficiency, the cam  10  may further comprise, as shown in  FIG. 2 , a slider  17  coupled to the side  16  of the cam  10 . This slider  17  comprises, as shown in  FIG. 7 , a body having a contact surface  18 , which according to one implementation has a parallelogram shape, the contact surface  18  facing the contact surface  3  of the stop  1  which may also have a parallelogram shape. This configuration of the slider  17  of the cam  10  and of the stop  1  of the unit  100  assures that when the cam  10  acts on the stop  1  during its wobbling movement, the support during rotation and sliding takes place between two planar surfaces with sufficient support surface so that when the force derived from the transmitted torque is applied, the pressure of the cam  10  on the stop  1  decreases, and torque transmission efficiency increases significantly. The slider  17  can be coupled with the side  16  of the arm  11  of the cam  10  in different manners, the coupling shown in  FIG. 2  being done by means of inserting a groove  19  of the body  17  into a section  20  of the edge  12  of the side  16 . To improve the coupling of the body  17  with the side  16 , the section  20  of the edge  12  of the cam  10  is reduced, as shown in a detailed view of the cam  10  in  FIG. 10 , such that the ends of the body  17  fit into the ends of the section  20  of the edge  12 . The coupling can also be done by means of screwing, clamping, welding or another similar mode. The slider  17  is manufactured in plastic or composite material with a low coefficient of friction, although it can also be made of metal or another material. Torque transmission is therefore further improved since the contact surfaces  18  of the slider  17  and the contact surface  3  of the stop  1  have a very low coefficient of friction. 
     In this first embodiment of the unit  100 , the cover casing  150  and the housing casing  160  are attached to one another by means of four rivets  130  having different lengths, these rivets  130  having a pin-shaped central body with a cylindrical outer surface and two heads at the ends of the central body which allow riveting between the cover casing  150  and the housing casing  160 . 
     The guide surface  110  is the surface of the central body of one of the rivets  130  of the unit  100 . This rivet  130  projects from the surface  162  of the housing casing  160 , the stop  1  being able to pivot about the rivet  130 . The contact surface  2  of the stop  1  is the inner surface of the hole  4  of the stop  1 , the contact surface  2  of the stop  1  contacting with the guide surface  110  of the rivet  130 . Therefore, when the wobbling movement of the cam  10  occurs, when the transmitted torque is for winding the cable, the contact surface  18  of the slider  17  of the cam  10  is supported and slides on the contact surface  3  of the stop  1 , and this stop  1  accompanies this supporting and sliding movement by rotating about the rivet  130  which is in contact with the stop  1 , the contact surface  2  of the stop  1  being supported on the guide surface  110  of the rivet  130 , the guide surface  110  limiting the travel of the stop  1 . 
     The dimension of the rivet  130  performing the function of a pin in contact with the stop  1  is in accordance with the dimension of the unit  100  and with the need of the torque to be transmitted from the drive shaft  70  to the drum  40 . The rivets  130  of the unit  100  can be replaced by bolts with a cylindrical central body and a threaded end section allowing the threaded attachment of the cover casing  150  and of the housing cover  160 . One of the threaded bolts would be located inside the stop  1 , traversing the hole  4 , and comprising the guide surface  110 . Other similar attachment elements can be used to perform the same function. Therefore, the guide surface  110  is obtained, without adding more elements to the unit  100 , by making one of the rivets  130  project from the surface  162  of the housing casing  160 , the surface of the central body of the projecting rivet  130  forming the guide surface  110 . 
     Since the stop  1  is located on the side and therefore outside the cam  10 , it can be designed with more freedom, such that the side  16  of the cam  10  acting on the stop  1  can be supported not on a pressure line such as that which occurs between an edge of the cam and a bolt, but in a space demarcated by a planar contact surface  18  of the slider  17  of the cam  10  and a planar contact surface  3  of the stop  1  in which it is supported. 
     In another embodiment (not shown in the drawings), the cam  10  comprises a second slider with the same features as the slider  17  of the cam  10  of the unit  100  of  FIG. 7 , this second slider being coupled to the side  15  of the arm  11  of the cam  10 , and a contact surface of this second slider of the cam  10  being supported, in the direction of rotation of the unit  100  for unwinding the cable from the drum  40 , on a contact surface of the second stop of the unit  100  during rotation supporting movement and sliding movement of the cam  10 . The coupling of the second slider of the cam  10  to the side  15  has the same features as the coupling of the slider  17  with the cam  10  shown in  FIGS. 2, 7 and 10 . Therefore, if the unit  100  comprises a second slider of the cam  10 , a second stop, and a second guide surface of the unit  100 , the support and sliding of the bodies during the wobbling movement of the cam  10  when the cable is unwound is similar to that described above for the wobbling movement of the cam  10  when the cable is wound, although the torque transmitted in this second case is less. 
       FIG. 3  shows a perspective view of a second embodiment of the unit  100  of the invention, the configuration of which is similar to the unit  100  of the first embodiment shown in  FIGS. 1 and 2 , and in which the casing  150  has been removed. This second embodiment of the unit  100  has the same features as the unit  100  of  FIGS. 1 and 2 , with the difference that in this second embodiment the guide surface  110  is also the substantially cylindrical surface of the central body of a pin coinciding with one of the rivets  130  of the unit  100 , but the pin is located outside the stop  1  of the unit  100 . The stop  1  of this second embodiment of the unit  100 , as shown in  FIG. 8 , is therefore similar to the stop  1  of the first embodiment of the unit  100 , the contact surface  2  of the stop  1  in this second embodiment being a circular surface located on the surface of the stop  1  opposite the contact surface  3 , and with the same radius as the cylindrical body the guide surface  110  is part of, the contact surface  2  of the stop  1  being supported on the guide surface  110  of the rivet  130  located close to the stop  1 . 
     In another embodiment of the unit  100  (not shown in the drawings), similar to the first and second embodiments of the unit  100  shown in  FIGS. 2 and 3 , the guide surface  110  is not the surface of the central body of one of the rivets  130  joining the cover casing  150  and the housing casing  160  of the unit  100 , but rather is the side surface of an independent bolt of the rivets  130  which is fixed to one of the casings  150  or  160 , or to both. 
     In other embodiments similar to the first and second embodiments of the unit  100 , the pin comprising the guide surface  110  is formed on the surface of one of the casings of the unit  100 , either the cover casing  150  or the housing casing  160 . 
       FIG. 4  shows a perspective view of a third embodiment of the unit for picking up spare wheels  100  in which the cover casing  150  has been removed.  FIG. 5  shows a perspective view of the cover casing  150  of the unit  100  of  FIG. 4  with the ring gear  30  and the eccentric assembly  60  of the unit  100  already assembled, with a guide surface  110  located outside the stop  1  of the unit  100  and formed in the cover casing  150 , the guide surface  110  being in contact with the stop  1  of the unit  100 , and the slider  17  of the cam  10  being in contact with the stop  1  of the unit  100 . This third embodiment of the unit  100  has the same features as the unit  100  of the first and second embodiments shown in  FIGS. 1, 2 and 3 , with the difference that in this third embodiment the guide surface  110  is not a pin, but rather is formed on the surface of the cover casing  150  and has a substantially circular shape. The stop  1  of this third embodiment of the unit  100  therefore comprises, as shown in  FIG. 9 , a body having a contact surface  3  with a parallelogram shape, the contact surface  3  facing the side  16  of the arm  11  of the cam  10 , and a contact surface  2  having a substantially circular shape and located opposite the contact surface  3 . This contact surface  2  has a radius substantially equal to the radius of the guide surface  110 , the contact surface  2  of the stop  1  being in contact with the guide surface  110 , this contact allowing the stop  1  to accompany the wobbling movement of the cam  10  and limiting its travel. 
     In this third embodiment, the guide surface  110  of the unit  100  is a surface generated by stamping on a surface  151  of the cover casing  150 . This guide surface  110  comprises a wall  111  that is substantially vertical with respect to the surface  151 , the wall  111  having an at least partially circular shape which is adapted to the contact surface  2  of the stop  1 . When the stop  1  is assembled on the surface  151  of the cover casing  150 , it is trapped between the side  16  of the arm  11  of the cam  10  and the guide surface  110 . Obviously, the guide surface  110  can be formed in the housing casing  160 . 
     In any of the embodiments, the stop  1  and slider  17  are preferably manufactured in plastic or composite material with a low coefficient of friction, although they can also be made of metal or another material.