FR2525174A1 - BICYCLE DERAILLEUR SYSTEM - Google Patents

Abstract

IN A DERAILLEUR SYSTEM FOR A BICYCLE, A CHAIN MOVING DEVICE 5 IS MOUNTED ON A TROLLEY 3. THE TROLLEY 3 IS SUPPORTED BY A BRACKET 2. THE BRACKET 2 IS MOUNTED ON THE BICYCLE. A GUIDANCE SYSTEM 2, 6, 7, 3 IS PROVIDED TO GUIDE THE CARRIAGE 3 ON A COURSE 28 SENSITIVELY PARALLEL TO THE AXIS OF A SPROCKET SYSTEM 1, TO MOVE A CHAIN 27 ON DIFFERENT SPROCKETS 1A TO 1F. TO FACILITATE CHAIN ENGAGEMENT WITH RESPECTIVE 1A THROUGH 1F SPROCKETS, MOVEMENT OF CHAIN SHIFT 5 EXCEEDS THE DISTANCE BETWEEN SUCCESSIVE SHIFT POSITIONS DURING AN OFFSET MANEUVER. THE MOVEMENT OF THE CHAIN MOVING DEVICE 5 IS ACHIEVED BY ENGAGING A ROTARY CAM FOLLOWING DEVICE 10, 15 AND A CAM SURFACE 12 WHICH COMES INTO THE CAM FOLLOWING DEVICE 10, 15. TO OBTAIN THE MOVEMENT IN EXCESS, THE CAM TRACKER DEVICE 10, 15 INCLUDES A CAM SURFACE ENGAGER 15 WHICH IS PIVOTALLY MOUNTED ON THE CAM TRACKER 10, 15.

Description

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1 1 #J

  zt Sz Sz to allow rotation of the cam follower device relative to the second guide device in response to

  operation of the shift member in order to bring the

  said engagement engagement face with different and predetermined areas of the cam surface Des

  means are provided to bring on engagement the organ of-

  cam surface engagement with the cam surface.

  The cam surface engagement member can move over a limited distance relative to the follower device

  cam in response to the movement of the engagement backing-

  ment, starting from a pre-terminated area of the cam to reach a predetermined and following area of the cam, in at least one direction along said cam surface The movement of said cam surface engaging member by relationship to the cam follower determines

  a relative transitiomlel and modified positioning of the

  positive cam follower and Gr Ace cam at this position-

  transitional and modified relative performance, the

  chain movement is transitionally displaced

  beyond the new offset position of the slide carriage

  nir, in order to facilitate the engagement of the chain with the

  new sprocket, especially when a certain degree of u

  sure appears in the derailleur system.

  This derailleur system is known from the request for

German patent NO 29 33 361.

  In the known system, the surface engagement member

  this cam is a roller which is received in a long slot

  tudinal of the cam follower The course followed by the cam surface engagement member with respect to the cam follower is defined by the length of this elongated slot The movement of the engagement member

  of cam surface in relation to the cam follower

  me is a rolling movement along an edge of the elongated slot This known system has proven to be very effective in obtaining the excess and desired movement of the chain moving device beyond the new offset position But we found that we must respect a

  high precision for the manufacture of the engagement member

  cam surface, slot and roller in order to obtain correct movement of the roller along the

  slot In addition, the roller and the edge of the slot are exposed

  are at considerable risk of wear and therefore they must

  Be made with a material very resistant to wear.

  A main object of the invention is to propose a simplified form of the derailleur system, in particular

  with regard to the cam follower and the organ-

no cam surface engagement.

  Another object of the invention is to provide a system

  derailleur valve of the type defined above, in which less precision can be used for the manufacture of the cam follower device and of the engagement member

of cam surface.

  Yet another object of the invention is to provide a derailleur system as defined above, which is

  very reliable even after a long period of use.

  From the point of view of at least one of the above objects,

  the cam surface engaging member is mounted in a

  pivoting lesson on the cam follower device, on an axis

  pivoting fixed relative to the cam follower

  me and substantially parallel to the axis of rotation on which

  is mounted the cam follower, on the second u-

  guide unit The cam surface engaging member can move along a limited angular path relative to the cam follower device The position of

  the pivot axis and the position of the backing face

  pledge with respect to the axis of rotation are such that

  the radial distance from the engagement counter face with respect to

  port to the axis of rotation varies in response to movement of the cam surface engaging member relative to the cam follower along the limited angular path The cam surface engaging member is

  in a first angular position of said angular course

  area when the engagement backing is engaged

  with one of the predetermined areas of the surface of the cam.

  But when the engagement face of the engagement member

  cam surface area is moved from one of the zones

  from the cam surface to a predeter area-

  mined and following from the surface of the cam, at least in one direction along the surface of the cam, the cam surface engaging member is brought in a second

  angular position of said angular path In this se-

  in angular position, the radial distance between the

  three-face engagement and axis of rotation of the device

  cam follower is different from the radial distance

  both in the first angular position This difference

  radial distance appears when passing the counter

  engagement face of a predetermined area of the surface

  from the cam to a next area This difference in distance

  this radial determines a transitional movement in excess of the cam relative to the cam follower device Ce

  relative movement in excess translates into a tran movement

  excess of the chain shifting device beyond the new desired offset position Therefore, the engagement of the chain with the new sprocket is facilitated even after a long period of use

  and considerable wear and tear on the main derailleur system

  cipe of the invention can be applied for example to the system

  derailleur valve which is described in the patent application

  French Ne 81 18 170 in the name of the Claimant.

  The excess movement of the chain moving device beyond its new offset position is particularly advantageous when the chain has to be changed from a small diameter sprocket to a larger diameter sprocket, because during this maneuver it is more difficult to bring the chain into engagement with a new sprocket than when it is a reverse movement during which the chain must pass from a sprocket of large diameter to a sprocket of smaller diameter Because of this, it

  it is further proposed that the radial distance from the counter

  engagement face with respect to the axis of rotation is at a minimum when the cam surface engagement member is in its first angular position, and this distance

  angular increases transitionally beyond said mini

  num when the surface engagement member is brought to the second angular position because said engagement face is displaced from a predetermined area of the cam surface corresponding to a pinion of smaller diameter to an area predetermined area of the

  cam which corresponds to a pinion of larger diameter.

  In order for the shifting or shifting positions of the chain moving device to be invariable despite variations in the transmission system, such as the extension of the Bowden cable used for the transmission system, it is preferable to define the

  predetermined areas of the cam surface by plates

  ges located at a constant radial distance from the axis of rotation at least over part of their length In this

  case, provision is made for transition flanks between

  According to another characteristic of the invention, the transition flanks can come into engagement with a

  flank engagement face of said surge engagement member

  cam face when the engagement counter face is displaced

  from a predetermined range to another predefined range

  When this movement takes place, the enga-

  management of the respective transition flank with the facing face

  flank engagement creates a torque which is applied to the body

  no cam surface engagement mounted on the pivot axis

  and in order to move the engagement member of

  cam surface to the second angular position.

  The principles of the invention are applicable in a

  particular lesson but not exclusive to the mechanisms of

  timing in which the shift member is blocked in

  the various offset positions by blocking means

  ge, so that the user only has to move the

  offset gane until the locking means come

  are engaged in the respective offset position.

  These blocking means are known for example by the request

  of German patent NO 29 33 36 i They are used so that the user can easily carry out the maneuver of

  shifting However, the use of such mo-

  Locking yen makes it difficult to move the chain moving device in excess beyond the respective new shift position, by operating the shift member. The idea of the invention which consists in obtaining a movement in excess of the chain moving member beyond the new shift position which has been chosen and automatically without the use of the shift member is therefore particularly valid in

  connection with said blocking means associated with the mechanism

  shift or shift change.

  The invention will now be described with reference to the attached drawings in which:

  Figure 1 is a schematic view of a derailed system A

  their according to the invention, in an offset position in which the chain is in engagement with the pinion of smaller diameter; Figure 2 shows the derailleur system of Figure 1 in an offset position in which the chain is in engagement with the sprocket of larger diameter; Figure 3 shows a form of the mechanism & derailleur in the position corresponding to that of Figure 1;

  Figure 4 shows the device of Figure 3 in a po-

  sition corresponding to that of Figure 2; Figure 5 shows a detail of Figures 3 and 4, Namely

  the engagement between a cam surface and an engagement member

  cam surface area, and Figure 6 is a side view of the derailleur mechanism of Figures 3 and 4, in the direction of arrow VI of Figure 3. In Figure 1, a sprocket system is shown in (1) and includes several sprockets (the A if) The sprocket system (1) is connected to the driven wheel of a bicycle

  or has a drive member for a gear hub, associated

  Cie To the driven wheel The driven wheel is not shown

  This driven wheel is connected by a chatle (27)

  to a pinion mounted on the pedal shaft of the bicycle.

  To obtain various transmission ratios between the pedal shaft and the driven wheel, the chain must be

  in engagement with the various individual gables (la à If).

  To move the chain (27) to the various sprockets,

  provides a chain moving member (5) on the chain

  riot (3), capable of moving in the direction of the arrow (28), in a direction substantially parallel to the axis of the sprockets (la à if) The chain movement member (5) can be a mounted sprocket rotatably on the carriage (3) and in engagement with the chain (27) A system

  chain tensioner can be combined with the sprocket (5) which

  drags the chain The course followed by the carriage (3) can

  deviate considerably from a parallel direction

  the to the pinion axis (la to If) to compensate for the differences

  rents diameters of the pinions (l A to if) The carriage (3) is supported by the support (2) which is integral with the frame of the bicycle The carriage (3) is supported by the support (2) by means of a guidance system comprising

  a first connecting rod (6) and a second connecting rod (7) The first

  connecting rod (6) is pivotally connected to both the support (2) and the carriage (3) The second connecting rod (7) is connected both to the support (2) and to the carriage (3) by means of connections pivoting and sliding The connecting rods (6 and 7) intersect and are interconnected by another connection Pivoting (11) The guide system which consists of the support (2), the carriage (3) and the connecting rods (6 and 7) allows the carriage (3) to move relative to the support (2), from the position illustrated in FIG. 1 to the

position illustrated in figure 2.

  A plate (10) constituting a cam follower is mounted

  rotated around the axis defined by the axis of

  pivoting (11) A cam (12) is fixed on the carriage (3).

  The cam (12) includes a cam surface (12 ') The surface

  this cam (12 ') comprises several areas (13 a to 13 f) and several transition flanks (14 a to 14 e) On the plate (10) constituting the cam follower is mounted a cleat

  cam follower (15) which can rotate about an axis of pi-

  vote (17) o The cam follower stop (15) can move

  angularly between moult first angular position re-

  presented in Figures i and 2 which is defined by the commitment-

  ment of a stop member (20) fixed on the plate (10) which constitutes a cam follower member and a stop face

  (18) provided on the cam follower stop (15), and a se-

  the angular position defined by the engagement of the

  stop gane (20) with a stop face (19) of the cleat

cam follower (15).

  A first biasing spring (26 a) is connected to the connecting rods (6 and 7) so as to bias these connecting rods

  (6 and 7) towards the position shown Se At the end

  gure 1 A second biasing spring (26 b) is connected to the plate forming the cam follower (O 10) and to the connecting rod (6) so as to bias the plate (10) clockwise to the position shown in

  figure 2 These springs (26 a and 26 b) hold the counter

  engagement face (15 ′) of the cam follower cleat (15) in engagement with the range (13 f) of FIG. 1 and with the range (13 a) of FIG. 2 The existing contact force

  between the engagement back face (15 ') and the pads

  pectives (13 f and 13 a) maintains the cam follower cleat

  (15) in the first position which is shown in fig.

  Figures 1 and 2, the abutment face (18) being in engagement with the abutment member (20) A Bowden target (8) is connected to the carriage (3) and to the offset member (41) of the offset (40), as shown in Figure 1 The tube (9) of the Bowden cable (8) is supported by the housing of the offset mechanism (40) and by a support arm (29) of the plate

(10) which forms the cam follower.

  In FIG. 1, the engagement counter face (15 ′) is in engagement with the range (13 f) which corresponds to the pinion (if) In FIG. 2, the engagement counter face (15 ′)

  is in engagement with the range (13 a) which corresponds to the pi-

gnon (la).

  When we start from the position of FIG. 1, the shifting member (41) has passed from position (f) to position (a), the Bowden cable (8) is released: the plate (10) constituting the cam follower is turned clockwise by the second spring (26 b) toward the position shown in Figure 2, and the connecting rods (6, 7)

  pass from the position shown in FIG. 1 to the posi-

  tion represented 6 e in figure 2 under the action of the counter

  engagement face (15 ') which slides along the surface of

  cam (12 '), this movement being carried out against the ac-

  tion of the first spring (26 a) which maintains the engagement of the engagement backing (15 ') with the cam surface (12') Starting from the position shown in FIG. 2,

  the Bowden cable (8) is pulled and the gold-

  gane for shifting (41) from position (a) In position (f), the plate (10) constituting the cam follower rotates anticlockwise until the counter face d commitment (15 t) comes in engagement with

  the range (13 f) and that the connecting rods (6, 7) pass from the po-

  sition shown In Figure 2 at the position shown

  In Figure 1 under the action of the first spring (26 a).

  Note that the radial distance between the counter

  engagement face (15 ') and the axis of rotation (11) is at mid

  minimum in the first angular position of the cam follower stop (15), defined by the stop member (20) and the face

  when the shift member (41) is readjusted

  tee from position (f) of figure 1 to position (a)

  and when the plate (10) which forms the cam follower begins

  this to turn clockwise under the action of the second spring (26 b), an engagement face of

  side (15 ") of the cam follower stop (15) engages

  with the transition flank (14 e) Consequently, the cam follower stop (15) is tilted around the pivot axis (15) until the abutment face (19) comes into contact with the stop member (20) Thus, the cleat

  cam follower (15) reaches its second position an-

  gulaire It is only when the engagement counter face (15 ′) has exceeded the edge defined by the transition flank (14 e) and the area (13 e) that the cam follower stop (15) is tilted back to Fa first angular position

  defined by the abutment face (18) and the abutment cam (20).

  When the cam follower stop (15) is in its se-

  second angular position defined by the abutment face (19) and the abutment member (20), the radial distance between the engagement counter face (15 ′) and the axis of rotation (11)

  exceeds the radial distilce existing between the first po-

  angular section shown in Figures 1 and 2 This if

  means that during the transition phase during the

  which the engagement face (15 v) exceeds the edge located between the track (13 e) and the transition flank (14 e), the carriage (12) is moved to the left beyond the position which is in alignment between the chain moving member (5) and the pinion (the), so that the chain

  is brought reliably into engagement with the pinion (the).

  It is only after the engagement counter face (15 X) has come into engagement with the track (13 e) that the cam follower stop (15) returns to the position defined by the stop face ( 18) and the stop member (a 0), so

  the chain moving member (5) is aligned

with the pinion (the).

  It should be noted that the relative position of the axis of

  pivot (17), the axis of rotation (11) and the counter

  engagement face (15) which are represented in FIG. 1

  are responsible for the operating mode described above

above.

  When the guidance system and the movement device

  chain cement (5) are moved from the position shown

  tée in Figure 2 to the position shown in Figure 1, the cam follower stop (15) always remains in the first angular position which is defined by the stop member (20) and by the stop face (18) , so that the radial distance between the engagement counter face (15 ') and the axis of rotation (15) is always constant This

  means that there is no excess movement of the device

  tif of chain movement (5) beyond the new il

  offset position reached However, this is acceptable

  ble of the fact that the engagement of the chain with a pinion

  small diameter is less critical.

  The embodiment shown in Figures 3 to 6 corresponds to that of Figures 1 and 2 both from the point of view of the basic principles of its constitution and its

  but some details of construction sup-

  are shown, the loading springs

  tion (26 a and 26 b) being replaced by a single spring

(126).

  The corresponding parts are designated by the

  same reference numbers increased by 100.

  FIG. 3 represents a derailleur system comprising:

  nant a junction head (102) which is integral with the frame and a movable junction head (103) The two parts are

  pivotally attached to each other by means of

  re of a connection with five joints, known in the art an-

  tieur This connection with five articulations can be na-

  replaced by a parallelogram, which does not

  does not modify the functioning The link to five articulations

  tions consists, in known manner, of a guide piece

  ge (106) and a bent lever (107) The guide piece (106) is pivotally mounted by bearings both in the junction head (102) integral with the frame and in the movable junction head (103) The crank lever (107)

  is shorter than the guide piece (106) The lever

  thimble (107) and the guide piece (106) are interconnected by a junction pin (111) T 4 e bent lever (107) is

  in engagement, at its two ends and through

  re of slotted type swivel connections with head

  junction (102) which is integral with the frame and with the

  mobile junction te (103) Thanks to this connection with five articulations, it is possible to obtain a parallel displacement of the mobile junction head (103) relative to the junction head (102) which is integral with the frame On the junction head mobile (103) is mounted a chain displacement device and a tensioning device (104), which supports inter alia the pinion (105) which drives the chain The chain (127) which is shown in broken lines rotates around

  sprocket system (101), which includes sprockets

  different mensions and mounted side by side To operate the derailleur system, a Bowden cable (108) is provided

  passing through a tube (109) and fixed to the modular junction head

  bile (103) The cable tube (109) is supported on the plate

  that (110) constituting a cam follower and which is pivotally mounted on the axis of rotation (111) One end of the spring (126) is attached to the plate (110) constituting the cam follower and its other end is inserted in the guide plate (106) This spring exerts a force which tends to move the movable junction head (103) in

  the direction of the arrow (128), for the execution of a

  offset between a larger gear to a smaller gear in the pinion system (101) This force of the

  spring is absorbed by the cam disc (112), by the ta-

  quet (115) of the plate (110) forming a cam follower, comprising

  me we see it particularly in figure 5 This figure

  re shows the essential parts of the group made up of

  the cam plate and by the cam follower.

  The cam disc (112) comprising the various areas (113) and the respective transition flanks (114) between

  individual tracks (113) is integral with the rush head

  movable tion (103), while being able to be adjusted in position relative thereto The plate (110) constituting the cam follower can rotate about the axis of rotation (111) which coincides with the central junction of the bond to five

  joints This is however not compulsory and only

  in this case so that a single spring

  (126) is sufficient for the whole derailleur system.

  that (110) forming the cam follower could also be

* fixed to another component A cam follower stop (115) is in this case still mounted on the plate (110), on a pivot axis (117) extending parallel to the axis of rotation (111) The cleat (115) includes abutment faces (118 and 119) which can abut against a dowel

  stop (120) The cleat (115) comprises a nose (116) orientable

  tee to the cam disc (112) and an engagement backing-

  ment (115 ') This nose comes into engagement with the pads (113) Each of the pads (113) is located at a different distance from the axis of rotation (111), and the positions of

  individual offset of the pinion (105) which causes the cat-

  are thus not determined in relation to the pinion system

  (101), with a view to transferring the chain (127) to the individual sprockets If as shown in FIGS. 3 and 4, the nose (116) is

  applied against one of the pads (113), the transmission of force takes place between the pad (113) and

  the nose, in the direction of the arrow (124) in FIG. 5.

  This arrow is exactly on the perpendicular passing through the contact point, as shown in Figures 3 and 4 A torque is thus exerted on the cleat (115) clockwise so that the abutment face (118 ) of the cleat (115) rests on the stop pin (120) Thus, the minimum distance between the cam disc (112) and the plate (110) constituting the cam follower is obtained, in relation to the corresponding range (113 ) for each case If an offset maneuver must then take place between a smaller gear towards a larger gear, the Bowden cable (108) is released by means of the gear change lever (not shown), which brings the spring (126) moving the plate (110) forming

  the cam follower clockwise.

  The nose (112) then slides along one of the transition flanks (114). Due to the inclination of these transition flanks (114), which can be clearly seen in FIG. 5, a force is exerted on the cleat (115) along the perpendicular (123) which is oriented in the direction of the arrow (25), which causes the cleat to pivot

  (115) around the pivot axis (117) in the reverse direction

  clockwise, so that the abutment face (119) of the cleat (115) abuts against the ankle

  stop (120) But at the same time, the spacing of-

  is more important between the cam disc (112) and the axis t 4 of rotation (111), which means that at the start of the sliding of the

  nose (116) to reach the next track (113), the head

  te de Junction mobile (103) covers a greater distance

  bearing in the direction of the pinion system (101) than that which corresponds to the next pinion But when the gearshift lever (not shown) remains in the

  next position and when the nose (116) abuts

  tre the next range (113), a new force exerts on the cleat (115) in the direction of the perpendicular (122) and therefore of the arrow (124), which means that a couple is exerted on the stopper (115) clockwise and so that this stopper pivots again until the abutment face (118) abuts against the abutment peg (120) Thus, the offset position corresponding is correctly adjusted and the chain movement device as well as the tensioning device (104) and the wheel (105) align with the chain

  (127) and the respective pinion of the pinion system (101).

  In the case where the d 6 timing is performed in the opposite direction, that is to say from a larger pinion to a smaller pinion, the cleat (115) remains in the position it occupies in the figures 3 and 4, because during this shifting operation, it only supports torques in the direction

  clockwise according to figure 5.

  FIG. 6 simply shows an elevation view la-

  t 6 rale corresponding to Figures 3 and 4, and illustrating the

  three-dimensional structure form 6 e by the rush heads

  tion (102 and 103), the guide piece (106), the bent lever (107), the spring (126) and the plate (110) forming a cam follower, with the cam disc (112) and the cleat

(115).

  In FIGS. 3 to 6, the tube (109) of the Bowden cable (108) is support 6 in the support (109) which is part of the plate (110) forming a cam follower In principle, however, it is always possible to insert 6 rer the tube (109) of the cable in the cleat (115) which allows to realize an excess movement of the pinion (105) which drives the chain

  in both directions of the offset In this case, it is necessary to

  how to ensure that the force exerted by the cable tube

  is only slightly greater than the opposite force exerted by

  created by the cam disc (112) on the cleat (115) Thus, during an offset maneuver and in both directions of the offset, a force is exerted on the cleat (115) to

temporarily move it.

  The embodiment of the derailleur system which is

  described above is not linked to a five-link

  lations, and it can be easily used also for a

  derailleur system guided by a parallelogram.

  While specific embodiments of the in-

  vention have been shown and described in detail with a view

  to illustrate the application of the inventive principle, we understand

  dra that the invention can be implemented in any

  otherwise without departing from these principles.

  The various references appearing in the claims

  cations are in no way limiting, but given

  simply for a better understanding of these claims

cations.

Claims (4)

CLAIMS -   1 In a bicycle derailleur system or   analogous, said bicycle comprising a battery system   gnons (1) with several pinions (la, If) of different diameters   and a chain (27) for driving a wheel of the bicycle, this chain (27) being able to come into engagement with any one of the pinions (la, If), said derailleur system comprising:   a) a support (2) intended to be mounted on the bicy-   lette; b) a mobile carriage (3) comprising a chain displacement device (5) mounted on it in order to shift   selectively the chain (27) to come in individual engagement   vuel with the pinions (la, If); c) a guide system (2, 6, 7, 3) intended to guide the movement of the carriage (3) relative to the support (2) the   along a route (28) followed by the movement device   chain, in order to pass the chain (27) between individual sprockets (la, If), the guide system (2, 6, 7, 3) comprising several guide units (2, 6, 7, 3 ), said guide units comprising said support   (2) and the carriage (3), at least a first guide unit   dage (3) and a second guide unit (6) which can be detached   place one in relation to the other; d) a shift or shift mechanism   (40) comprising a shift member (41) allowing the   setting the carriage (3) to several offset positions corresponding to respective individual pinions (la, If);   e) a cam (12) mounted on the first guide unit;   dage (3) and comprising a cam surface (12 ');   f) a cam follower device (10, 15) mounted in a   rotating part around an axis of rotation (11) provided on the   second guide unit (6) and comprising a drive member   cam surface engagement (15) carrying a cam counter face (151) for engagement with the cam surface (12 ') in a series of predetermined areas along   of said cam surface (12 '), said predeter-   mined J (13 a, 13 f) of the cam surface corresponding to different offset positions of the carriage (3) relative to the support unit (2); g) transmission means (8, 9) connected to the offset mechanism (40) on the one hand and to the cam follower device (10, 15) on the other hand, to allow rotation   of the cam follower (10, 15) in response to the function   actuation of the shifting member (41) in order to bring the engagement counter face (15 ′) into engagement with different and predetermined zones (13 a, 13 f) of the cam surface; h) means (26 a, 26 b) determining the engagement of the cam surface engagement member (15) with said cam surface (12 '); i) said cam surface engaging member (15)   able to move along a limited course compared to   port to the cam follower device (10, 15) when the engagement counter face (15 ') is moved from a predetermined area (13 f) of the cam surface to a predetermined and following area (13 e) of the cam surface in at least one direction along said cam surface (12 '), this movement of the cam surface engaging member   (15) relative to the cam follower device (15) deter-   undermining a modified relative and transitional positioning of the cam follower device (10, 15) and of the cam (12),   improvement characterized in that the engagement member   cam surface ment (15) is pivotally mounted on the cam follower (10, 15) on a pivot axis (17) substantially parallel to the axis of rotation (11), along a path limited angular, the radial distance of the engagement counter face (15 ') relative to the axis of rotation (11) being variable as a function of said angular movement, said cam surface engagement member being in a first angular position   on said angular path when the engagement face   gement (15 ') comes into engagement with one of said predetermined areas (13 a, 13 fú) of the cam sumface and transiently reaching in a second angular position along said angular course when said engagement counter face (15 ') is moved from one (13 f) of said predetermined areas (13 a, 13 f) of the cam surface to a predetermined and next area (13 e) of the cam surface in at least one direction along the cam surface (12 ').   2 derailleur system according to claim 1,   characterized in that the radial distance between said con-   tre-engagement face (15 ') and the axis of rotation (41) is at a minimum when said surface engagement member of   cam (15) is in its first angular position, and aug-   lies transiently beyond said minimum when   said cam surface engagement member (15) is   placed towards its second angular position when said con-   tre-engagement face (15 ') is moved from a zone near & 6-   terminated (13 f) from the cam surface which corresponds to a pinion (if) of small diameter towards a predetermined zone (13 e) from the cam surface which corresponds to a pinion (1 l) larger diameter.   3 derailleur system according to claim 1,   characterized in that the first angular position is d & -   finished by a first pair of stop means & e (18, 20) and in that the second angular position is defined by   a second pair of stop means (19, 20).   4 Derailleur system according to any one of   claims I to 3, characterized in that the member for   cam surface engagement (15) is biased towards   of said first angular position by the force of engagement   gement exerted between the predetermined zone 6 e respective   (13 f) of the cam surface and said engagement face   gement (15 t), which force is substantially perpendicular to   area in the predetermined and respective area (13 f) of the cam surface.   Derailleur system according to one of the claims   tions I to 4, characterized & in that said zones predeter-   mined (13 a, 13 f) of the cam surface are defined by ranges (13 a, 13 f) and by transition flanks (14 a, 14 e) provided between successive ranges (13 a, 13 f), said transition flanks (14a, 14e) coming into engagement with a flank engagement face (15 ') of said engagement member-   cam surface ment (15) when the reverse side engages   gement (15 ') is moved from a predetermined range (13 f) to a next predetermined range (13 e), the engagement of a respective transition flank (13 e) and said flank engagement face ( 15 ") creating a torque which is applied to the cam surface engagement member (15) rotating around the pivoting member (17) so as to move   said cam surface engagement member (15) toward the said second angular position.