FR2712357A1 - Improved mechanical assembly and motor vehicle starter comprising such an assembly. - Google Patents

Abstract

The invention provides a mechanical assembly of the type comprising a screw (20) whose threaded body (30) is screwed into the threaded end (18, 32) of a shaft and whose head (22) has a radial face of clamping (34) which abuts against the annular radial end face (38) of the shaft, characterized in that the radial clamping face (34) of the head (22) of the screw (20) comprises a recess (40) shaped so as to prevent any flaring of the end portion (18) of the shaft when tightening the screw (20). Application to the assembly of a limit stop screw for a motor vehicle starter launcher.

Description

The present invention relates to a

  improvement of a mechanical assembly.

  The invention relates more particularly to a mechanical assembly of the type comprising a screw whose threaded body is screwed into the threaded end of a shaft and whose head has a radial clamping face which abuts against the annular radial face

end of the tree.

  According to a known design of such a type of screw connection, the radial support or tightening face of the screw which comes into contact with the annular end face of the shaft is planar. It is also known to interpose between these two faces one or more washers of various designs making it possible to improve the resistance of the assembly and making it possible to increase the resistance of the assembly to loosening and / or to unscrewing. This known type of assembly nevertheless poses various problems resulting from the initial operations

Clamping.

  In fact, in the event of excessive tightening, it can be seen that the axial pressure exerted by the tightening face of the screw on the tubular end of the shaft causes the latter to deform, resulting in a

  flaring phenomenon, as its diameter increases.

  Such deformation is not admissible in many mechanical devices incorporating such a type of assembly, and in particular in the case of a stop screw for a motor vehicle starter launcher such as

this will be explained later.

  In addition, and despite a significant initial tightening force, there are phenomena of accidental loosening of the assembly, in particular when the latter is used under severe conditions and it is subjected to vibrations, shocks, etc. Loosening can lead to unscrewing and detaching the

two components of the assembly.

  Such a type of mechanical assembly is used in particular in the production of a starter for a thermal engine of a motor vehicle of the type comprising a starter pinion which is slidably mounted on a starter shaft of which a tapped free end receives the threaded body of a stop screw which delimits the axial stroke of the pinion relative to the starter shaft. In this case, an initial deformation, resulting from the tightening, of the end part of the starter shaft is not admissible insofar as it prevents the free sliding movement of the starter pinion on its shaft and a separation accidental accident of the two components of the assembly can cause significant damage to the internal combustion engine

  and / or for some of its equipment.

  The aim of the present invention is to propose a mechanical assembly of the type mentioned above, which is of simple and economical design, and which remedies

  to the disadvantages which have just been mentioned.

  To this end, the invention provides a mechanical assembly characterized in that the radial face for tightening the head of the screw has an imprint shaped so as to prevent any flaring of the

  end portion of the shaft when tightening the screw.

  According to other characteristics of the invention: - the impression has a profile of revolution around the axis of the screw; - the imprint has a truncated cone profile; - The impression is shaped so as to cause a radial deformation towards the inside of the end portion of the shaft when the screw is tightened; - in the clamped position, the end portion of the shaft deformed radially inwards extends opposite a shoulder formed on the threaded body of the screw the shoulder axially delimits the threading of the threaded body of the screw ; the end portion of the shaft has an external chamfer which, during tightening, cooperates with the impression. The invention also provides a motor vehicle starter of the type comprising a starter pinion slidably mounted on a starter shaft whose free tapped end receives the threaded body of a stop screw which delimits the axial stroke of the pinion relative to the shaft, characterized in that the stop screw and the starter shaft constitute a mechanical assembly

  carried out in accordance with the teachings of the invention.

  Other features and benefits of

  the invention will appear on reading the description

  detailed which follows for the understanding of which reference will be made to the accompanying drawings in which: - Figure 1 is a sectional view illustrating a motor vehicle starter comprising a mechanical assembly according to the prior art; - Figure 2 is a view similar to that of Figure 1 illustrating a different operating position of the starter; - Figure 3 is an axial section view, on a larger scale, of the mechanical assembly according to the prior art forming part of the starter illustrated in Figures 1 and 2 and shown in the non-tight position; - Figure 4 is a view similar to that of Figure 3 in which the assembly is illustrated in the clamped position; - Figures 5 and 6 are views similar to those of Figures 3 and 4 which illustrate a mechanical assembly produced in accordance with the teachings of the invention; - Figure 7 is an exploded perspective view with partial cutaway of a mechanical assembly

  carried out in accordance with the teachings of the invention.

  There is shown in Figures 1 and 2 a starter 10 of a conventional and known design and which in particular comprises a starter pinion 12 which is mounted to slide axially on a starter shaft 14 and whose

  the movements are controlled by a fork 16.

  The launcher shaft 14 is a shaft, the axial end portion 18 of which is hollow and tapped and receives a stop screw 20, the head 22 of which has a radial collar 24 which is capable of cooperating with an annular stop ring 26 arranged in the internal bore

28 of the starter pinion 12.

  The starter is illustrated at rest in FIG. 1 and in the actuated position in FIG. 2 in which it can be seen that the radial collar 24 of the head 22 of the screw is in abutment against the stop ring 26 so as to limit the stroke axial, to the left when considering FIG. 2, of the pinion with respect to the starter shaft 14. The mechanical assembly constituted by the screw 20 and the shaft 14, according to the state of the art, is illustrated more in detail in FIGS. 3 and 4 in which it can be seen that the threaded body 30 of the screw 20 is screwed into a tapping 32 produced in the end portion

tubular 18 of the shaft 14.

  The bearing or tightening face 34 of the head 22 of the screw 20 is a flat radial face in the form of an annular sector which is separated from the threaded body 30 by a

radial groove 36.

  The radial end face 38 of the tubular portion 18 of the shaft 14 is a flat annular face which, during tightening, cooperates with the flat face

  34 of the head 22 of the screw 20.

  Before tightening, the outside diameters of the tubular end portion 18 and of the body of the head 22 of the screw 20 are substantially equal so as to constitute a set of constant diameter to allow the passage of the rod 26 in sliding along the connection zone between these two diameters during the axial movement of the starter pinion 12 relative to

to the shaft 14 of the launcher.

  In the event of excessive tightening, and as illustrated in FIG. 4, there is a phenomenon of radial flaring towards the outside of the portion

  tubular end 18 of the shaft 14.

  This flaring phenomenon has the drawback on the one hand of increasing the diameter of the portion 18 and, on the other hand, of reducing the length engaged between the

thread 30 and internal thread 32.

  The increase in the outside diameter of the portion 18 can affect the proper functioning of the launcher by limiting the axial stroke of the pinion relative to the shaft 14 by the coming into contact of the rod 26 with the flared portion 18, and the reduction of the assembly length

  threaded in night grip & its resistance to loosening.

  The mode of operation of the invention illustrated in FIGS. 5 to 7 will now be described in which elements identical or similar to those illustrated in FIGS. 3 to 4 are designated by the same

reference figures.

  According to the invention, the clamping face 34 of the head 22 of the screw 20 has an imprint 40 which, in the example illustrated in the figures, is an imprint in the form of a truncated cone centered on the axis of

the opinion.

  The cavity 40 is thus shaped so as to oppose on the one hand to any phenomenon of flaring of the tubular end portion 18 of the shaft 14 and, on the other hand, to cause a radial tightening towards

  inside the end portion 18 during tightening.

  In fact, as can be seen in FIG. 6, the cavity 40 acts during tightening like a guide chamfer which causes the penetration of the tubular end portion inside the cavity 40 by causing a phenomenon deformation

radial inward.

  It can be seen that there is therefore no longer any phenomenon of flaring of the tubular end portion 18 and that the outside diameter of the assembly constituted by the end portion 18 of the shaft 14 and by the body of the head 22 of screw 20, is substantially

  constant over the entire length of the assembly.

  In addition, the end portion 18 constricted radially inwards, and in particular the annular end face 38, extends opposite the shoulder 42 which axially delimits the threaded body of the screw 20. This cooperation constitutes an axial stop which later prevents any loosening

  accidental mechanical assembly.

  FIG. 7 is a perspective representation of the assembly illustrated in FIGS. 5 and 6 and on which, in accordance with an improvement of the invention, an external chamfer 44 has been shown formed in the vicinity of the end of the tubular portion 18 of the shaft 14, chamfer which improves the phenomenon of inward radial tightening during the operation

  tightening, in cooperation with the conical impression 40.

Claims (8)

  1. Mechanical assembly of the type comprising a screw (20) whose threaded body (30) is screwed into the threaded end (18, 32) of a shaft and whose head has a radial clamping face (34) which is in abutment against the annular radial end face (38) of the shaft (14), characterized in that the radial tightening face (34) of the head (22) of the screw (20) has an imprint (40 ) shaped so as to prevent any flaring of the end portion (18) of the shaft (14) when tightening the screw (20).   2. Mechanical assembly according to claim 1, characterized in that the imprint (40) has a profile   of revolution around the axis of the screw.   3. Mechanical assembly according to claim 2, characterized in that the imprint (40) has a profile in truncated cone.   4. Mechanical assembly according to any one   of the preceding claims, characterized in that   the cavity (40) is shaped so as to cause a radial deformation towards the inside of the end portion (18) of the shaft (14) when the screw (20).   5. Mechanical assembly according to claim 4, characterized in that, in the clamped position, the end portion (18) of the radially inwardly deformed shaft extends opposite a shoulder (42) formed   on the threaded body (30) of the screw.   6. Mechanical assembly according to claim 5, characterized in that the shoulder (42) axially delimits the thread of the threaded body (30) of the screw (20). 7. Mechanical assembly according to any one   of the preceding claims, characterized in that the   end portion (18) of the shaft (14) has an external chamfer (44) which, during tightening, cooperates with the imprint (40).   8. Motor vehicle starter (10) of the type comprising a starter pinion (12) slidably mounted on a starter shaft (14) of which a tapped free end (18) receives the threaded body of a stop screw (20, 24) which delimits the axial stroke of the pinion (12) relative to the shaft (14), characterized in that the stop screw (20) and the starter shaft (14, 18) constitute a conforming mechanical assembly & any of previous claims.