Patent Publication Number: US-10330161-B2

Title: Brake disc for a bicycle

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of Italian Application No. UA2016A004916, filed on Jul. 5, 2016, which is incorporated herein by reference as if fully set forth. 
     FIELD OF INVENTION 
     The present invention relates to a brake disc for a bicycle. In particular, the brake disc is configured to be mounted on a hub of a bicycle wheel. Preferably, the bicycle is a racing bicycle. 
     BACKGROUND 
     As known, it is now common in bicycles to use disc brakes. Such brakes are indeed often preferred to conventional brakes of different design since they ensure a high braking force and are less subject to problems caused by mud or water. 
     Typically, a disc brake comprises a caliper fixed to the frame of the bicycle and a brake disc mounted on the hub of the wheel. Inside the caliper there are two or four opposite brake pads. The brake disc rotates inside the space defined between the opposite pads. By actuating the brake lever, the pads are brought towards the brake disc, generating friction on the brake disc and, consequently, braking the wheel. 
     The brake disc comprises a braking track configured to cooperate with pads and a radially inner annular portion for coupling with the hub. 
     The braking track is made of a material that ensures good braking characteristics, for example it can be made from steel. 
     The brake disc can be made in a single piece or, in order to reduce the weight thereof, it can be made in two components. 
     In this case, the brake disc comprises a first component having the braking track and a second component having the radially inner annular portion for coupling with the hub. 
     The first component is made of a first material that ensures good braking characteristics, like for example steel, whereas the second component is made of a lighter second material, like for example aluminum or light alloys. 
     The second component has a plurality of radially outer portions for connecting to the first component at a respective plurality of connection portions of the first component. 
     In the jargon, the second component is called spider, whereas the first component is simply indicated with the expression “braking track”. 
     The connection between the radially outer connection portions of the second component and the connection portions of the first component can be fixed or, alternatively, can be such as to allow a relative radial and/or axial clearance between the first and the second component. 
     Such relative clearance is useful to stop the thermal dilations of the first component that occur during use (by the friction generated by the contact between pads and braking track) creating undesired stresses at the connection areas between first component and second component. 
     As far as the coupling with the hub is concerned, the radially inner annular portion of the brake disc (which is made in the second component, in the case of a brake disc made in two components) is provided with a grooved radially inner surface (i.e. a radially inner surface that extends longitudinally and is provided with longitudinal grooves), which is mounted on a matching grooved radially outer surface (i.e. a radially outer surface that extends longitudinally and is provided with longitudinal grooves matching those of the radially inner surface) of a portion of the hub, as is disclosed in patent application EP 1932753 to the same Applicant. 
     EP 1932753 also discloses a lock nut, which is screwed onto the hub until it comes into axial abutment on the radially inner annular portion of the brake disc, so as to define the axial portion of the brake disc on the hub. 
     The Applicant has observed that, in the case of a brake disc made in two components, it is necessary for the connection between the radially outer connection portions of the second component and the connection portions of the first component to be extremely reliable, so that a certain braking quality is guaranteed as much as possible. 
     Damage to or breaking of the connections between first and second component could result in great limitations in braking quality, even to the point of braking itself being impossible, with the obvious serious consequences in terms of safety. 
     The above becomes even more important, if such a thing is possible, in the field of racing bicycles. 
     The problem at the basis of the present invention is to make a brake disc for a bicycle that, as well as having excellent features of strength and lightness, ensures extreme certainty of braking over time. 
     SUMMARY 
     The present invention relates to a brake disc for a bicycle having a first component that is made of a first material and has a braking track configured to cooperate with brake pads. A second component is made of a second material and has (i) a radially inner annular portion for coupling with a hub of a bicycle wheel and (ii) a plurality of radially outer portions for connecting to the first component at a respective plurality of connection portions of said first component. The first component further comprises a radially inner annular portion connected to the braking track, and in that it comprises axial locking members active on the radially inner annular portions of the first and of the second component to keep said radially inner annular portions of the first and of the second component under mutual pressure. 
     Advantageously, thanks to the provision of the radially inner annular portion of the first component and of the axial locking members active on the radially inner annular portions of the first and second component, the first and second component are kept under mutual pressure even in the misfortunate case of damage to or breaking of the connection between the first and the second component at the radially outer connection portions of the second component and at the respective connection portions of the first component. 
     Furthermore, thanks to the provision of the radially inner annular portion of the first component connected to the braking track, it is also ensured that there is strengthening of the first component, so that the braking track of the first component withstands the stresses to which it is subjected during braking better than in brake discs of the prior art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING(S) 
       Further features and advantages of the invention will become clearer from the description of a preferred embodiment, made with reference to the attached drawings, where: 
         FIG. 1  is an exploded perspective view of a hub of a bicycle wheel, comprising a brake disc for a bicycle according to the present invention; 
         FIG. 2  is a perspective view of the brake disc of  FIG. 1 ; 
         FIG. 3  is a front view of the brake disc of  FIG. 1 ; 
         FIG. 4  is a perspective view of a component of the brake disc of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention therefore relates to a brake disc for a bicycle comprising: 
     a first component made of a first material and having a braking track configured to cooperate with brake pads; 
     a second component made of a second material and having (i) a radially inner annular portion for coupling with a hub of a bicycle wheel and (ii) a plurality of radially outer portions for connecting to said first component at a respective plurality of connection portions of said first component; 
     characterized in that said first component further comprises a radially inner annular portion connected to said braking track, and in that it comprises axial locking members active on the radially inner annular portions of the first and of the second component to keep said radially inner annular portions of the first and of the second component under mutual pressure. 
     Advantageously, thanks to the provision of the radially inner annular portion of the first component and of the axial locking members active on the radially inner annular portions of the first and second component, the first and second component are kept under mutual pressure even in the misfortunate case of damage to or breaking of the connection between the first and the second component at the radially outer connection portions of the second component and at the respective connection portions of the first component. 
     Indeed, the axial locking members keep the radially inner annular portions of the first and of the second component under mutual pressure, which by friction remain rotationally substantially constrained to one another even in the misfortunate case of damage or breaking outlined above, without there being a significant relative rotation between first and second component, so as to ensure a sufficient possibility of braking, even if with lower efficiency with respect to normal operation of the undamaged or unbroken brake disc. However, in the case of damage or breaking outlined above, the cyclist can take care of replacing the brake disc as soon as possible to be able to have use of normal operation of the brake disc. 
     Furthermore, thanks to the provision of the radially inner annular portion of the first component connected to the braking track, it is also ensured that there is strengthening of the first component, so that the braking track of the first component withstands the stresses to which it is subjected during braking better than in brake discs of the prior art. 
     Preferably, said radially inner annular portion of said first component is connected to said braking track through a plurality of connection arms that are distinct from said plurality of connection portions. 
     Advantageously, the provision of the radially inner portion of the first component and of the connection arms ensure a strengthening of the first component, so that the braking track of the first component withstands the stresses to which it is subjected during braking better than in brake discs of the prior art. 
     Furthermore, the connection arms of the first component that are distinct from the plurality of connection portions allow the two mutual constraint areas between the first and the second component to be mechanically and functionally decoupled. In this way, damage to or breaking of the connection between the first and the second component, at the radially outer connection portions of the second component and of the respective connection portions of the first component, does not jeopardize the rotational mechanical constraint between the first and the second component at the radially inner annular portions of the first and second component. 
     Preferably, said axial locking members are furthermore configured to axially constrain said radially inner annular portion of the second component to said hub. 
     Advantageously, the axial locking members thus also define the axial position of the brake disc with respect to the hub. 
     Preferably, the axial locking members are in abutment against the radially inner annular portion of the first component. 
     More preferably, said radially inner annular portion of said first component is provided with a knurled axially outer surface. 
     Advantageously, the knurled axially outer surface makes it possible to increase the friction with the axial locking members in abutment against the radially inner annular portion of the first component. 
     Preferably, said radially inner annular portion of the first component at least partially juxtaposes the radially inner annular portion of the second component in the axial direction. 
     Advantageously, the greater the juxtaposition, the greater the friction between the radially inner annular portions of the first and second component, on which the axial locking members are active. 
     Preferably, said axial locking members comprise a collar in axial abutment on the radially inner annular portion of the first component and a lock nut, which extends axially away from the collar, configured to couple with said hub. 
     More preferably, said collar and said lock nut are made in one piece. 
     Preferably, at least one of said connection arms of said first component and at least one of said radially outer connection portions of said second component are coupled together through at least one shape coupling. 
     Advantageously, thanks to the provision of shape couplings between connection arms of the first component and radially outer connection portions of the second component, the first and second component are kept coupled together even in the misfortunate case of damage to or breaking of the connection between the first and the second component at the radially outer connection portions of the second component and at the respective connection portions of the first component. 
     Indeed, the aforementioned shape couplings allow the first and second component to remain rotationally substantially constrained to one another even in the misfortunate case of damage or breaking outlined above, without there being a significant relative rotation between first and second component, so as to ensure a sufficient possibility of braking, even if with lower efficiency with respect to normal operation of the undamaged or unbroken brake disc. 
     Furthermore, the aforementioned shape couplings also ensure a strengthening of the first component, so that the braking track of the first component withstands the stresses to which it is subjected during braking better than in brake discs of the prior art. 
     Advantageously, furthermore, the shape coupling does not require further structural elements, such as bolts, rivets, screws or similar, to be able to carry out its action. 
     Preferably, said at least one shape coupling comprises at least one housing seat made on one from said at least one connection arm and said at least one radially outer connection portion and housing a portion of the other from said at least one connection arm and said at least one radially outer connection portion. 
     Advantageously, the housing seats can be made easily from the constructive point of view. 
     Preferably, said at least one connection arm and said at least one radially outer connection portion extend along directions of extension substantially crossing over one another. 
     Advantageously, the directions of extension substantially crossing over one another improve the structural characteristics of torsional strength of the brake disc, as well as also the substantial rotational constraint between the first and the second component. 
     Preferably, said at least one housing seat is made on said at least one radially outer connection portion of the second component and has an axial depth greater than or equal to half of an axial thickness of said at least one connection arm of said first component measured at said housing seat. More preferably, said at least one housing seat has an axial depth equal to the axial thickness of said at least one connection arm of said first component. 
     Advantageously, the aforementioned axial depths of the housing seat ensure a sufficient substantial rotational constraint between the first and the second component. 
     Preferably, said housing seat comprises at least one shoulder formed on said at least one radially outer connection portion of the second component abutted by a portion of said at least one connection arm of said first component, said shoulder having a direction of extension substantially parallel to a direction of extension of said at least one connection arm of said first component. 
     Preferably, said braking track, said plurality of connection arms, said plurality of connection portions and said radially inner annular portion of said first component have a substantially uniform axial thickness and are substantially coplanar. 
     Advantageously, the first component can be easily made from the constructive point of view. 
     Preferably, said first component is placed on an axially outer first mid-plane with respect to a second mid-plane of said second component, wherein said first and second planes are parallel to one another. 
     In the following description and in the following claims, the terms “axial, “axially”, “longitudinal’, “longitudinally” and similar refer to a direction substantially coinciding with or substantially parallel to a rotation axis of the brake disc, which substantially coincides with a longitudinal axis of the hub, whereas the terms “radial”, “radially” and similar refer to a direction that lies in a plane substantially perpendicular to the rotation axis of the brake disc and that passes through such a rotation axis. 
     With reference now to the figures, reference numeral  10  wholly indicates a brake disc for a bicycle according to the present invention. 
     The brake disc  10  is configured to be mounted on a hub  12  of a bicycle wheel (not illustrated). 
     In particular, in the non-limiting example of  FIG. 1  a hub  12  for a rear bicycle wheel is shown. 
     The hub  12  is mounted on the frame of the bicycle. 
     In particular, the frame comprises two opposite support arms of the rear wheel at the respective free end portions of which housing seats of opposite free end portions  12   a ,  12   b  of the hub  12  are foreseen. 
     A caliper (not illustrated) of a disc brake is fixed onto the bicycle frame. 
     In particular, the caliper is fixed in a conventional manner to one of the support arms of the rear wheel. 
     Inside the caliper there are at least two opposite brake pads (not illustrated). 
     The brake disc  10  rotates inside the space defined between the opposite brake pads. By actuating the brake lever (not illustrated), the brake pads are brought closer to the brake disc  10 , generating friction on the brake disc  10  and, consequently, braking the wheel. 
     In particular, the hub  12  comprises a pin  13  extending along a longitudinal axis X of the hub  12  and a body  14  rotatably mounted on the pin  13 . The longitudinal axis X coincides with the rotation axis of the bicycle wheel. 
     The body  14  comprises a coupling portion  16  with the brake disc  10 . Furthermore, the body  14  comprises, in a position adjacent to such a coupling portion  16  and on the axially innermost side with respect to it, a further coupling portion  17  with a plurality of spokes of the wheel (not shown). The coupling portions  16  and  17  are preferably portions of a single body. Alternatively, the coupling portions  16  and  17  can be defined in two distinct bodies. 
     On the body  14 , on the axially opposite side with respect to the coupling portions  16  and  17 , a flange  18  is fitted comprising a coupling portion with the remaining spokes of the wheel, which are arranged on the opposite side to the aforementioned plurality of spokes with reference to a mid-plane of the rim of the wheel, such a plane being perpendicular to the rotation axis of the wheel. Such a flange  18  can be an integral part of the body  14 . 
     A pair of rolling bearings (not illustrated) is radially arranged between the pin  13  and the body  14  and allows the rotation of the body  14  with respect to the pin  13 . The bearings are mounted in a position adjacent to the opposite free end portions of the pin  13 . 
     The coupling portion  16  comprises a disc seat  16   a , for receiving and locking in rotation the brake disc  10 , and a shoulder  16   b , which provides an abutment position in the axial direction for the brake disc  10  mounted on the disc seat  16   a.    
     The disc seat  16   a  comprises a grooved radially outer surface, namely a radially outer surface that extends longitudinally and is provided with longitudinal grooves. 
     The brake disc  10  comprises a grooved radially inner surface  42   a  matching that of the disc seat  16   a  (namely a radially inner surface  42   a  that extends longitudinally and is provided with longitudinal grooves matching those of the grooved radially outer surface of the disc seat  16   a ), as will be described better hereinafter. 
     More in general, the disc seat  16   a  is shaped according to a shape coupling profile. This term is meant to indicate that the profile of the disc seat  16   a  has geometric characteristics such as to allow the transmission of a torsion between the body  14  (on which the disc seat  16   a  is formed) and the brake disc  10  mounted on such a disc seat  16   a  with a matching profile. A shape coupling profile can for example be a polygonal profile, or a circular profile with an alteration (for example, levelled along a rope), or other. In particular, the shape coupling profile of the disc seat  16   a  illustrated in the non-limiting example of the figures is a grooved profile, with projections and throats, oriented in a direction parallel to the axis X. 
     The shoulder  16   b  is provided adjacent to an axially inner side of the disc seat  16   a.    
     Adjacent to the opposite axially outer side of the disc seat  16   a  there is a threaded portion  20 , formed at a free end portion of the body  14 , for coupling with a lock nut  22 , which holds the brake disc  10  in the disc seat  16   a , against the shoulder  16   b.    
     Now with particular reference to  FIGS. 2-4 , the brake disc  10 , having rotation axis coinciding with the longitudinal axis X of the hub  12 , comprises a first component  30  and a second component  40 . 
     The first component  30  comprises a braking track  32  and the second component  40  comprises a radially inner annular portion  42  for coupling with the hub  12 . The braking track  32  has substantially annular extension. The radially inner annular portion  42  is provided with the grooved radially inner surface  42   a  described earlier. 
     The first component  30  is made of a first material that ensures good braking characteristics, like for example steel, whereas the second component  40  is made of a lighter second material, like for example aluminum or light alloys. 
     The second component  40  comprises a plurality of radially outer portions  44  for connecting to the first component  30  at a respective plurality of connection portions  34  of the first component  30 . In the non-limiting example illustrated in the figures, the radially outer portions  44  and the connection portions  34  are circumferentially equally spaced and are six in number. In the figures, so as not to complicate the graphical representation, reference numerals are only indicated on some of the radially outer portions  44  and the connection portions  34 , as well as only some of other elements described hereinafter. 
     The connection between the radially outer connection portions  44  of the second component  40  and the connection portions  34  of the first component  30  can be fixed or, alternatively, be such as to allow a relative radial and/or axial clearance between the first component  30  and the second component  40 . In the non-limiting example illustrated in the figures, such a connection is made through caulked pins  50 , received in respective holes formed in the radially outer portions  44  and in the connection portions  34 . 
     The braking track  32  is configured to cooperate with the brake pads. 
     Advantageously, the first component  30  comprises a radially inner annular portion  36  connected to the braking track  32 . The radially inner annular portion  36  could comprise a grooved radially inner surface, analogous to the grooved radially inner surface  42   a  of the second component  40 . In the embodiment illustrated in the attached figures such a grooved radially inner surface of the radially inner annular portion  36  of the first component  30  is not provided. 
     In particular, the radially inner annular portion  36  is connected to the braking track  32  through a plurality of connection arms  38  distinct from the plurality of connection portions  34 . In the non-limiting example illustrated in the figures, the connection arms  38  are circumferentially equally spaced and are six in number. 
     On the radially inner annular portions  36 ,  42  of the first  30  and of the second component  40  axial locking members are active, which keep the radially inner annular portions  36 ,  42  of the first  30  and of the second component  40  under mutual pressure. 
     In the non-limiting example illustrated in the figures, the axial locking members comprise the lock nut  22  described above. 
     In general, the axial locking members are furthermore configured to axially constrain the radially inner annular portion  42  of the second component  40  to the hub  12 . 
     The axial locking members are in abutment against the radially inner annular portion  36  of the first component  30 . 
     The radially inner annular portion  36  of the first component  30  is provided with a knurled axially outer surface  36   a.    
     The radially inner annular portion  36  of the first component  30  at least partially juxtaposes the radially inner annular portion  42  of the second component  40  in the axial direction. In the non-limiting example illustrated in the figures, the radially inner annular portion  36  substantially entirely juxtaposes the radially inner annular portion  42  in the axial direction. 
     The axial locking members preferably comprise a collar in axial abutment on the radially inner annular portion  36  of the first component  30  and the lock nut  22 , which extends axially away from the collar, configured to couple with the hub  12 . 
     In the non-limiting example illustrated in  FIG. 1 , the collar is made in one piece with the lock nut  22 . 
     Advantageously, the connection arms  38  of the first component  30  and the radially outer connection portions  44  of the second component  40  are coupled together through shape couplings  60 . 
     In the non-limiting example illustrated in the figures, shape couplings  60  are provided on all of the connection arms  38  and on all of the radially outer connection portions  44 . Alternatively, shape couplings  60  can be provided only on one or some of the connection arms  38  and radially outer connection portions  44 . 
     In particular, the shape coupling  60  comprises one or more housing seats  62  made on the radially outer connection portion  44  and housing a portion of the connection arm(s)  38 . Alternatively, vice-versa, one or more housing seats  62  can be made on the connection arms  38  and house a portion of the radially outer connection portion(s)  44 . 
     In the non-limiting example illustrated in the figures, on each radially outer connection portion  44  there are two housing seats  62  for two consecutive connection arms  38  of the first component  30 . 
     Preferably, the housing seats  62  are provided on axially outer surfaces of the radially outer connection portions  44 . 
     In particular, the housing seats  62  comprise shoulders  62   a  formed on the radially outer connection portion  44  of the second component  40  abutted by a portion of the connection arm  38  of the first component  30 . The shoulders  62   a  have directions of extension substantially parallel to directions of extension of the connection arms  38  of the first component  30  that are housed in the respective housing seats  62 . 
     In the non-limiting example illustrated in the figures, the connection arms  38  and the radially outer connection portion  44  extend along directions of extension substantially crossing over one another. Preferably, the angle formed between a connection arm  38  and a radially outer connection portion  44  is comprised between 45° and 110°, more preferably comprised between 70° and 100°, for example about 80°. 
     In particular, the connection arms  38  of the first component  30  extend from the radially inner annular portion  36  along substantially tangential directions and, in the front view of the brake disc  10  illustrated in  FIG. 3 , are directed in the counter-clockwise direction. Vice-versa, the radially outer connection portions  44  of the second component  40  extend from the radially inner annular portion  42  along substantially tangential directions and, in the front view of the brake disc  10  illustrated in  FIG. 3 , are directed in the clockwise direction. 
     Preferably, the housing seats  62  have an axial depth greater than or equal to half of an axial thickness of the connection arms  38  of the first component  30 , measured at the housing seat  62 . 
     Preferably, the first component  30  has a substantially uniform axial thickness, for example comprised in a range of between about 1.8 mm and 2 mm. 
     Preferably, the braking track  32 , the connection arms  38 , the connection portions  34  and the radially inner annular portion  36  are substantially coplanar. 
     The first component  30  is arranged on an axially outer first mid-plane with respect to a second mid-plane of the second component  40 , wherein such first and second planes are parallel to each other. 
     Preferably, at the area of juxtaposition between the radially inner annular portion  36  of the first component  30  and the radially inner annular portion  42  of the second component  40 , the second component  40  comprises a groove directed axially having a depth equal to the depth of the housing seats  62 . 
     In this way it is possible to ensure a uniform thickness of the first component  30 , the contact of the radially inner annular portion  36  of the first component  30  on the radially inner annular portion  42  of the second component and the insertion of the connection arms  38  in the housing seats  62 . 
     In the non-limiting example illustrated in the figures, the connection arms  38  have a shorter transverse width than the transverse width of the connection portions  34  of the first component  30 , which have a transverse width substantially equal to that of the radially outer connection portions  44  of the second component  40 . 
     The ratio between the transverse width of the connection arms  38  and that of the connection portions  34  is for example comprised in a range of between about 0.4 and 0.7. 
     In terms of sizing of the brake disc  10 , the following considerations are valid. 
     During braking, the brake pads act on the braking track  32  as a heat flow source, which is in part conveyed away by convection, in part transmitted by conduction towards the center of the brake disc  10  and to the hub  12 . 
     A radial temperature gradient is created in the brake disc  10  from the hottest point (outer edge of the brake disc  10 ) to the least hot point (inner edge of the brake disc  10 ). Such a gradient generates a deformation of the brake disc  10  and a relative inner tensional state, since the brake disc  10  is constrained to the hub  12 . 
     The brake disc  10  of the invention comprises the connection arms  38  made entirely in the first material of the first component  30  and other arms formed from the connection portions  34 , made in the first material of the first component  30 , connected through caulked pins  50  to the radially outer connection portions  44 , made in the second material of the second component  40 . 
     In order to obtain the maximum thermal stability of the brake disc  10 , it is suitable to size the length of the connection arms  38 , of the connection portions  34  and of the radially outer connection portions  44  so that the radial deformation is as uniform as possible during braking. 
     Such lengths can be changed independently within a finite range, by modifying the angle of extension of each connection arm  38  and of each arm formed from the connection portions  34  connected to the radially outer connection portions  44  with respect to the radial direction. 
     Furthermore, for the connection portions  34  and the radially outer connection portions  44  it is possible to establish the point where the connection with the caulked pin  50  is made, namely the percentage of the total length made in the first material of the first component  30  (the remaining length is, consequently, made in the second material of the second component  40 ). Such a percentage of the total length made in the first material of the first component  30  can for example be comprised in a range between about 10% and 60%. 
     The sizing can be further improved by considering the contact heat resistance of the connections between first  30  and second component  40 ; in this way, the sizing can be made using a more realistic temperature profile. 
     Of course, those skilled in the art can bring numerous modifications and variants to the brake disc for a bicycle of the present invention, in order to satisfy specific and contingent requirements, all of which are in any case encompassed by the scope of protection defined by the following claims.