Patent Publication Number: US-2022213942-A1

Title: Caliper body for a brake caliper

Description:
FIELD OF THE INVENTION 
     The present invention relates to a caliper body for a brake caliper. 
     Furthermore, the present invention relates to a brake caliper for a disc brake. 
     PRIOR ART 
     In a disc brake, the brake caliper is generally arranged straddling the outer peripheral margin of a brake disc, adapted to rotate about a rotation axis defining an axial direction (X-X). In a disc brake, a brake disc radial direction (R-R), which is substantially orthogonal to said axial direction (X-X), and a tangential direction (T-T), orthogonal to both said axial direction (X-X) and said radial direction of the disc brake (R-R), is further defined. 
     Brake pads generally comprise a pad onto which friction material is fixed, adapted to press against a facing braking surface of the braking band of the brake disc. 
     A brake caliper of known type comprises a caliper body specifically designed to offer sufficient rigidity and avoid the caliper from being deformed because of the forces with arise during the braking action. Deformations of this type are highly undesirable in the caliper because they make the braking ineffective, absorbing part of the action applied on the brake fluid, e.g. by the brake pedal, in the deformation. 
     In floating caliper bodies associated with fixed discs, a floating portion of the caliper body has a cylinder, or cylinders, adapted to accommodate hydraulic pistons capable of applying a thrust action on the friction pad facing it, abutting it against the braking surface of the disc, while sliding on the bracket, or fixed portion of the caliper, and acts on the second clutch pad abutting it against the brake disc to apply the braking action on the motor vehicle. 
     In fixed caliper bodies associated with fixed discs, a cylinder, or cylinders, is or are present on both opposed sides of the caliper body, adapted to accommodate hydraulic pistons capable of applying a thrust action on the friction pads facing it, abutting both the opposite brake pads against the opposite braking surface of the disc to apply the braking action on the vehicle. 
     Conversely, floating caliper bodies associated with fixed discs are also known, in which only one of the elongated portions of the caliper body has cylinders adapted to apply a thrust action on the friction pad facing it, making it abut against the braking surface of the disc, and by reaction it slides axially on its support, typically two supports and in turn abuts the second friction pad against the disc braking surface to apply the braking action on the vehicle. 
     Typically, in hydraulically actuated brake calipers, the pressure applied by the vehicle driver on the brake pedal applies, through a brake master cylinder, a brake fluid pressure which through a pipe is applied to the brake fluid present in the hydraulic circuit placed inside the caliper body to reach the cylinders where the pressure is applied onto the bottom surface of the pistons, thereby forcing them to be close against the pads, which in turn abut against the braking surfaces of the disc. 
     The pressure action of the brake fluid is also applied on the bottom wall of the cylinder, thereby causing a reaction in the caliper body which deforms it away from the disc surfaces. The caliper body thus deforms also as a function of the torque applied by the action of the pistons which make the pads abut against the braking surfaces of the disc, applied in directions which form torque arms with respect to the fixing points of the caliper body to its support. These torques also deform the caliper body in a tangential and radial direction with respect to the disc, as well as an axial direction. This deformation of the caliper body leads to an increase of piston stroke, and thus to an increase of brake pedal stroke. 
     Typically, in electrically actuated brake calipers, the braking control applied by the vehicle driver results in a sequence of electrical signals for the activation of an electric motor, which in turn is operationally connected to a ball screw assembly, in which the nut by moving on the screw acts as a piston which, sliding axially with respect to the caliper body applies the thrust action on the friction pad facing it. 
     When the braking action ceases, and thus when the bias which is created and deforms the caliper body away from the brake disc ceases, the caliper body returns to its undeformed resting configuration, approaching the brake disc again, and thus approaching the pads to the braking surfaces. 
     Such approaching of the pads to the brake disc is sometimes undesired because it determines a contact, albeit minor, between pad and disc, which causes continuous minor friction and thus a braking action, also known as residual braking torque, also when the braking command by the driver of the vehicle ceases. 
     The residual braking torque is often considered undesired because it generates noise, albeit minor, caused by the friction action between pads and disc braking surfaces, undesired wear of the pads and the brake disc, and implies more frequent maintenance for their replacement, and minimum fuel consumption for feeding the drive unit with the energy, even if minimum, needed to overcome this residual torque. 
     Partially, this phenomenon known as elastic deformation or “strain” of the brake caliper is compensated by providing rollback devices in the piston-cylinder interface, which retract the piston into its cylinder by a limited predetermined entity, moving it away from the respective pad and thus allowing the pad, biased in turn by an axial spring, to move away from the disc, reducing the undesired residual torque. 
     The amount of axial distance (X-X) of the piston from the back of the respective pad when the braking action ceases defines an axial distance called “luft”. 
     It is desirable for said axial luft distance to be kept within permissible values during the entire service life of the brake pads. 
     When the brake pad has become thinner due to prolonged use, the piston must increase its stroke by protruding further from the cylinder to compensate for the reduction in axial thickness of the brake pad friction material. 
     Furthermore, in hydraulically actuated brake calipers, the piston pulling force is biased by the pressure of the brake fluid which pushes the piston itself, and therefore the brake pad facing it, during the braking action. A prolonged braking action, e.g. necessary for major vehicle decelerations, requires a considerable increase in brake fluid pressure. It is estimated that in some cases, such pressure can activate and reach and even exceed 100 bar. 
     The drag applied on the roll-back elastic element by the piston sliding with respect to the cylinder can cause the piston to slip with respect to the roll-back elastic element, with a consequent loss of retractable capacity of the system, particularly when the pressures in play are high. 
     Such piston slip phenomena necessarily bias the axial luft distance value, as well as pad wear. 
     The elastic deformation of the caliper body also biases the axial luft distance value. Indeed, there is typically a deterioration in the retraction performance of the piston on the side of the caliper body opposite to the fixing means the brake caliper to the vehicle. 
     Typically, a roll-back elastic element is in the form of an elastomeric ring with a substantially constant section. Knock-back elastic elements are also known to apply an elastic force on the piston to bring it closer to the back of the brake pad facing it. Usually, said knock-back and said roll-back spring elements are integrated into a single spring ring and their function is determined by the geometry of the annular housing and the deformation chambers. 
     Various geometries of the annular housing which receive the roll-back elastic element have been suggested. 
     A solution of roll-back spring element received inside a dedicated annular housing surrounding the brake caliper piston is shown, for example, in document U.S. Pat. No. 6,044,936 in which a roll-back deformation chamber is made on the side of the annular housing facing the disc brake disc. Such deformation chamber accommodates a predetermined portion of the roll-back elastic element during its elastic deformation approaching the disc when fed in the axial direction (X-X) by the piston which applies the thrust action on a brake pad. The extension in the axial direction (X-X) of such deformation chamber is chosen to obtain the desired elastic retracting action. 
     For example, document U.S. Pat. No. 8,794,369 shows a housing bottom wall having a characteristic saddle shape, in which a radial relief acts as a stop element to oppose the axial deformation (X-X) of a part of the elastic element. Such a solution, however, causes a concentration of strains in the radially external peripheral portion of the body of the elastic element which is repeatedly in contact and rubbing against this radial relief which acts as a stop. In this manner, the elastic element undergoes a rapid progressive deterioration of its functionality. 
     For example, document, JP-H06249274 shows an annular deformation chamber placed radially outside of the annular housing which receives the roll-back spring element when it is in the undeformed configuration. 
     Document EP-2370707 by the Applicant shows a solution in which the deformation chamber is obtained by installing an additional annular component axially placed between the roll-back elastic element and the wall of the annular housing facing axially in the direction of the disc. 
     However, the known solutions described above are not without drawbacks, because they are not able to keep the axial luft distance value within permissible values, e.g. when the brake fluid pressure is high. 
     Furthermore, the walls of such deformation chamber form edges facing the side of the roll-back elastic element which is deformed when fed by the piston. Such edges can generate strain concentration on the elastic roll-back element during the movement of the piston towards the brake pad facing it, and thus the disc. 
     The need is strongly felt to provide a solution capable of providing an elastic retracting action of the piston with respect to the caliper body of improved effectiveness compared to known solutions, without increasing the number of components of the disc brake system. 
     The need is felt to keep the axial luft distance within a range of permissible values even during prolonged braking. 
     Solution 
     It is an object of the present invention to solve the drawbacks of the prior art and to provide a solution to the needs described hereto with reference to the prior art. 
     A further object is to reduce the residual braking torque of the caliper, reduce the noise of the disc brake in absence of braking and reduce the pads and brake disc wear. 
     These and other objects are reached by a caliper body according to claim  1 . 
     Some advantageous embodiments are the object of the dependent claims. 
     The suggested solutions can be applied to cars, race cars, as well as race cars, motorcycles, as well as motorcycles, scooters, motorbikes, motorcycles or scooters with three or more wheels and other three-wheel motor vehicles as well as snowmobiles. 
    
    
     
       FIGURE 
       Further features and advantages of the caliper body will be apparent from the description provided below of preferred embodiments thereof, given for illustrative but not limiting purposes, with reference to the accompanying drawings, in which: 
         FIG. 1  is an axonometric view of a disc brake according to a further embodiment, 
         FIG. 2  is an axonometric cross-section view of a caliper body, according to an embodiment, with which thrust means are associated; 
         FIGS. 3, 4  are diagrammatic views illustrating the braking action; 
         FIG. 5  diagrammatically shows the axial luft distance; 
         FIG. 6  is a cross-section view of a portion of a brake caliper comprising a caliper body, according to an embodiment, wherein an elastic retraction element is shown in an undeformed condition; 
         FIG. 7  shows the portion of the brake caliper in  FIG. 6  wherein the elastic retraction element is in a deformed condition; 
         FIG. 8  shows a portion section of the caliper body in  FIGS. 6 and 7 ; 
         FIG. 9  is a graph which shows the pattern of the axial luft distance in a brake caliper in  FIGS. 6 and 7  as a function of the brake fluid pressure; 
         FIG. 10  is a cross-section view of a portion of a brake caliper comprising a caliper body, according to an embodiment, wherein an elastic retraction element is shown in an undeformed condition; 
         FIG. 11  shows the portion of the brake caliper in  FIG. 10  wherein the elastic retraction element is in a deformed condition; 
         FIG. 12  shows a portion section of the caliper body in  FIGS. 10 and 11 ; 
         FIG. 13  is a graph which shows the pattern of the axial luft distance in a brake caliper in  FIGS. 10 and 11  as a function of the brake fluid pressure; 
         FIG. 14  is a cross-section view of a portion of a brake caliper comprising a caliper body, according to an embodiment, wherein an elastic retraction element is shown in an undeformed condition; 
         FIG. 15  shows the portion of the brake caliper in  FIG. 14  wherein the elastic retraction element is in a deformed condition; 
         FIG. 16  shows a portion section of the caliper body in  FIGS. 14 and 15 ; 
         FIG. 17  is a graph which shows the pattern of the axial luft distance in a brake caliper in  FIGS. 14 and 15  as a function of the brake fluid pressure; 
     
    
    
     DESCRIPTION OF SOME PREFERRED EMBODIMENTS 
     According to a general embodiment, a caliper body  1  for a brake caliper  2  for disc brake  3  is provided. 
     In a disc brake  3  an axial direction X-X is defined either coinciding with or parallel to the rotation axis A-A- of the disc  4  of the disc brake  3 , a brake disc radial direction R-R orthogonal to the axial direction X-X, and a tangential direction T-T, orthogonal to both the axial direction X-X and to the brake disc radial direction R-R. 
     The axial direction X-X defines an inner axial direction XI, directed towards the disc  4 , and an outer axial direction XO, opposite with respect to said inner axial direction XI. 
     Said caliper body  1  is adapted to straddle the disc  4 . 
     Said caliper body  1  comprises a first elongated portion  5  adapted to face, either directly or indirectly through the interposition of at least one brake pad  11 , a first braking surface  6  of the disc  4 , and a second elongated portion  7 , opposite to said first elongated portion  5  and adapted to face, either directly or indirectly through the interposition of at least one brake pad  11 , a second braking surface  8  of the disc  4  opposed to said first braking surface  6 . 
     Said caliper body  1  further comprises at least one caliper bridge  9  to connect said first elongated portion  5  and said second elongated portion  7  to each other arranged straddling the disc  4 . 
     At least either said elongated portion  5  or said second elongated portion  7  comprises at least one thrust device housing  10 , or cylinder  10 , adapted to receive at least one portion of a thrust device  13  or piston  13 , adapted to apply a thrust action  14  directed in inner axial direction XI on at least one facing brake pad  11  to abut said at least one facing brake pad  11  against a braking surface  6 ,  8  of the disc  4 . 
     Said at least one thrust device housing  10  extends about a thrust axis a-a, parallel to the axial direction X-X, and defines a radial thrust direction r-r orthogonal to said thrust axis a-a and incident thereto. Said radial direction r-r defines an outer radial direction rI directed towards said thrust axis a-a and an outer radial direction rO, opposite to said inner radial direction rI. A circumferential direction of thrust device c-c, orthogonal to said thrust axis a-a, and said radial direction r-r, is also defined. 
     According to a preferred embodiment, at least either said elongated portion  5  and said second elongated portion  7  comprises a first annular housing  15  which radially opens into said thrust device housing  10 . 
     According to a preferred embodiment, said first annular housing  15  is adapted to receive an elastic retraction element  30  or elastic roll-back element  30 , adapted to apply a retracting action in outer axial direction XO on said thrust device  13 . 
     According to an embodiment, said first annular housing  15  is delimited at least partially in outer radial direction rO by a first bottom wall  16 . 
     According to a preferred embodiment, said first annular housing  15  is delimited at least partially in inner axial direction XI by a second axial wall  17 . 
     According to a preferred embodiment, said first annular housing  15  is delimited at least partially in outer axial direction XO by a third axial wall  18 . 
     According to a preferred embodiment, at least either said first elongated portion  5  and said second elongated portion  7  further comprises a second annular housing  20  which radially opens into said first annular  15 . 
     According to a preferred embodiment, said second annular chamber  20  is delimited in radial outer direction rO by a chamber bottom arched wall  19  having a chamber bottom arched wall concavity R 19  facing in radial inner direction rI which joins in an axial inner portion thereof to said second axial wall  17  and in an axial outer portion thereof to said first bottom wall  16  of said first annular housing  15 . 
     In this manner, said second annular chamber  20  is adapted to receive at least a portion of said elastic retraction element  30  at least when said thrust device  13  applies the thrust action  14 . 
     According to a preferred embodiment, said chamber arched bottom wall  19  has a substantially constant radius of curvature. 
     According to a preferred embodiment, said first bottom wall  16  of the first annular housing  15  extends substantially along a straight line. 
     According to a preferred embodiment, said first bottom wall  16  of the first annular housing  15  is tapered in the outer axial direction XO, in other words away from the disc  4 . Preferably, said first bottom wall  16  of the first annular housing  15  tapers in outer axial direction XO, forming a first bottom wall angle γ comprised between 6° and 8°, and preferably equal to 7°15′. 
     According to an embodiment, the chamber bottom arched wall  19  sweeps an arched wall angle α between 170° and 220°. Preferably, said arched wall angle α is comprised between 175° and 200°. According to a preferred embodiment, said arched wall angle α is substantially equal to 180°. According to an embodiment, said arched wall angle α is evaluated on a plane parallel to the axial direction X-X and the radial thrust direction r-r. 
     According to an embodiment, said chamber bottom arched wall  19  joins the first bottom wall  16  by means of a first connection  22  having first connection concavity R 22  opposite with respect to said bottom wall chamber concavity R 19 . According to an embodiment, said concavity of first connection R 22  is directed in outer radial direction rO. 
     According to an embodiment, said first connection wall  22  sweeps a first connection wall angle δ comprised between 96° and 98°, and preferably substantially equal to 97°15′. 
     According to an embodiment, said second axial wall ( 17 ) extends substantially in thrust device radial direction r-r, preferably tapering in the outer radial direction rO by effect of the draft angles. 
     Preferably, said caliper body  1  is made of metal using foundry techniques, e.g. sand casting or shell casting. According to an embodiment, said caliper body  1  is made in one piece, e.g. with a single casting. 
     According to an embodiment, said second axial wall  17  joins said chamber bottom arched wall  19  in thrust device radial direction r-r. 
     According to an embodiment, said thrust device housing  10  is delimited at least partially in outer radial direction rO by at least one thrust device housing wall  23 . 
     According to an embodiment, said thrust device housing wall  23  joins to said second axial wall  17  by means of an inner axial stretch  24  parallel neither to the thrust device radial direction r-r nor to the axial direction X-X. 
     According to an embodiment, said inner axial stretch  24  forms an inner axial stretch angle β comprised between 54° and 56° with said second inner axial wall  17 . Preferably, said inner axial stretch angle β is substantially equal to 55°. 
     According to an embodiment, said inner axial stretch  24  forms an inner axial stretch angle β comprised between 54° and 56°, and preferably substantially equal to 55° with the thrust device radial direction r-r. 
     According to an embodiment, said thrust device housing wall  23  joins to said third axial wall  18  by means of an inner axial stretch  25  parallel neither to the thrust device radial direction r-r nor to the axial direction X-X. 
     According to an embodiment, said outer axial stretch  25  forms an angle comprised between 44° and 46°, and preferably substantially equal to 45° with the thrust device radial direction r-r. 
     According to an embodiment, said thrust device housing  10  is delimited in outer axial direction XO by a housing back wall  29 . 
     According to an embodiment, said thrust device housing  10  is substantially cup-shaped. 
     According to an embodiment, said third axial wall  18  joins to said first bottom wall  16  by means of a radial stretch  26  inclined and parallel neither to the radial direction r-r nor to the axial direction X-X. Preferably, said radial stretch  26  forms an angle comprised between 44° and 46°, and preferably substantially equal to 45° with the thrust device radial direction r-r. 
     According to a preferred embodiment, said second axial wall  17  of the first annular housing  15  joins to said thrust device housing wall  23  by means of an inner axial stretch  24  which forms an inner axial stretch angle β with the thrust device radial direction r-r, to form an axially inner deformation chamber  37  for said elastic retraction element  30 . 
     According to a preferred embodiment, said inner axial deformation chamber  37  has a wedge-shaped section of a tapering in inner axial direction XI. 
     According to a preferred embodiment, said inner axial stretch  24  comprises an arched stretch  36  having an inner arched axial stretch concavity R 36  facing radial outer direction rO. 
     The provision of said arched section  36  adapted to abut against an axially inner face of the elastic retraction element  30  makes it possible to reduce the amount of the strains arising on the body of the retraction device  30  during the thrust action  14 . 
     According to a preferred embodiment, said inner axial stretch angle β is comprised between 55° and 75°. 
     According to an embodiment, e.g. shown in  FIG. 12 , said inner axial stretch angle β is substantially equal to 60°. 
     According to an embodiment, e.g. shown in  FIG. 16 , said inner axial stretch angle β is substantially equal to 70°. 
     According to a preferred embodiment, said arched stretch  36  connects said inner axial stretch  24  with said second axial wall  17 . 
     According to an embodiment, the radius of curvature of said arched stretch  36  is comprised between 0.25 and 1.30. 
     According to an embodiment, e.g. shown in  FIG. 12 , the radius of curvature of said arched stretch portion  36  is substantially equal to 0.30. 
     According to an embodiment, e.g. shown in  FIG. 14 , the radius of curvature of said arched stretch portion  36  is substantially equal to 1.25. 
     According to an embodiment, said first bottom wall  16  connects to said second axial wall  17  by means of an outer radial connection  38 . According to an embodiment, said outer radial connection  38  has a radius of curvature comprised between 0.2 and 0.3, and preferably substantially equal to 0.25. 
     According to an embodiment, a brake caliper  2  comprises a caliper body  1  according to any of the embodiments described above. 
     According to a preferred embodiment, said brake caliper  2  further comprises at least one pair of brake pads  11 , each brake pad  11  comprising friction material  34 , adapted to press against a facing braking surface  6  or  8  of the disc  4 , and a support plate  33  which supports said friction material  34 . 
     According to a preferred embodiment, said brake caliper  2  further comprises at least one thrust device  13  received in said at least one thrust device housing  10  so that it can slide axially with respect to said thrust device housing  10 . 
     The thrust axis a-a, parallel to the axial direction X-X, the radial thrust direction r-r orthogonal to said thrust axis a-a and incident to it, and the inner radial direction rI directed towards said thrust axis a-a, outer radial direction rO, opposite to said inner radial rI direction, and the circumferential direction of thrust device c-c, are understood to be also defined on said thrust device  13  when at least partially accommodated in said thrust device housing  10 . 
     According to a preferred embodiment, said support plate  33  comprises a back plate  35  or pad back  35  facing opposite with respect to the friction material  34  and adapted to face such a thrust device  13 . 
     According to a preferred embodiment, said thrust device  13  further comprises a thrust surface  32 , adapted to abut against said back plate  35  of said brake pad  11 , to apply the thrust action  14 . 
     According to a preferred embodiment, at least said one thrust device  13  is in form of a piston having substantially cylindrical geometry which extends about the thrust axis a-a. 
     According to a preferred embodiment, at least one thrust device  13 , comprises an outer wall or skirt  28  directed in axial direction X-X. Preferably, said skirt  28  is also directed in the thrust device circumferential direction c-c. 
     According to a preferred embodiment, said skirt  28  of the thrust device  13  cooperates with said thrust housing wall  23  of the thrust device housing  10  to guide the movement in axial direction X-X of the thrust device  13  with respect to the caliper body  1 . In this manner, said thrust action  14  is applied. 
     According to an embodiment, said brake caliper  2  further comprises at least one elastic retraction element  30 . According to a preferred embodiment, said at least one elastic retraction element  30  has an annular shape and is received in said first annular housing  15 . 
     In operating conditions during the thrust action  14 , said at least one elastic retraction element  30  deforms elastically as a result of the inner axial direction XI applied by thrust device  13  towards the disc  4 . When the thrust action  14  ceases, the elastic retraction element  30  applies a retracting action on said thrust device  13 , moving it away from the plate back  35  by an axial luft distance  31 . 
     According to a preferred embodiment, said brake caliper  2  further comprises at least one axial spring  21  adapted to bias at least one brake pad  11  away from the disc when the retracting action ceases, in other words when the braking action ceases. In this manner, the axial spring  21  carries said plate back  35  against said thrust surface  32  of the thrust device  13 . 
     Fixing means of the vehicle  12 , e.g. threaded, may be provided on said caliper body  1 , e.g. on said second extended portion  7 . 
     By virtue of the provision of said deformation chamber  37 , according to an embodiment, the body of the retraction device  30 , during the thrust action  14 , deforms elastically in the inner axial direction XI in contact with the skirt  28  of the thrust device  13 . 
     By virtue of the provision of said at least a second chamber  20 , according to a preferred embodiment, the body of the retraction device  30 , during the thrust action  14 , deforms elastically occupying said second chamber  20 , thus reducing its axial deformation in said chamber  37 , which can, therefore, be made smaller the retracting action being equal, compared to known solutions. 
     By virtue of the suggested solutions, it is possible to reduce the variability of the axial distance of luft  31 , even in prolonged use. 
     By virtue of suggested solutions, it is possible to reduce the wear of the elastic retraction element  30  by extending its service life. 
     According to a general embodiment, a disc brake  3  comprises at least one brake caliper  1  according to any one of the embodiments described above. 
     According to a preferred embodiment, said disc brake  3  comprises at least one disc brake disc  4 . 
     The person skilled in the art may make many changes and adaptations to the embodiments described above or may replace elements with others which are functionally equivalent to satisfy contingent needs without however departing from the scope of the appended claims. 
     LIST OF REFERENCES 
     
         
           1  Caliper body 
           2  Brake caliper 
           3  Disc brake 
           4  Disc brake disc 
           5  First elongated portion of the caliper body 
           6  First braking surface of the disc 
           7  Second elongated portion of the caliper body 
           8  Second braking surface of the disc 
           9  Caliper bridge 
           10  Thrust device housing or cylinder 
           11  Brake pad 
           12  Fixing means to the vehicle 
           13  Thrust device or piston 
           14  Thrust action 
           15  First ring housing 
           16  First bottom wall of the first annular housing 
           17  Second axial wall of the first annular housing 
           18  Third axial wall of the first annular housing 
           19  Chamber bottom arched wall 
           20  Second annular chamber 
           21  Axial spring of the brake caliper 
           22  First connection, or connection 
           23  Thrust device housing wall 
           24  Inner axial stretch 
           25  Outer axial stretch 
           26  Inclined radial stretch 
           27  Dust cuff 
           28  Thrust device skirt 
           29  Housing bottom wall 
           30  Elastic retraction element 
           31  Axial luft distance, or luft 
           32  Piston thrust surface 
           33  Brake pad supporting plate 
           34  Brake pad friction material 
           35  Brake pad back, or plate back 
           36  Arched connection stretch 
           37  Deformation chamber 
           38  Outer radial connection 
         α Arched wall angle 
         β Inner axial stretch angle 
         γ First back wall angle 
         δ First connection wall angle 
         R 19  Chamber bottom arched wall concavity 
         R 22  First connection concavity 
         R 36  Arched axial stretch concavity 
         A-A Disc rotation axis 
         X-X Disc brake axial direction 
         XI Inner axial direction 
         XO Outer axial direction 
         R-R Disc brake radial direction 
         T-T Disc brake tangential direction 
         a-a Thrust axis 
         r-r Radial direction, or thrust device radial direction 
         rI Inner radial direction 
         rO Outer radial direction 
         c-c Thrust device circumferential direction