DESCRIPTION

[0001 ] . Field of the invention

[0002 ] . The present invention relates to a piston for a brake caliper, and to a brake caliper .

[0003] . Background art

[0004 ] . Brake calipers are known, which comprise at least one piston actuatable by both a brake fluid, to act on a brake pad as a service brake, and a mechanically or electrically actuated thrust member, to act on the brake pad as a parking brake , such as an electromechanical parking brake (EBB) , for example .

[0005 ] . Such brake calipers comprise a caliper body, in which a hollow cylinder delimited by a cylindrical wall and a bottom wall , substantially transverse to the cylindrical wall , is obtained . The bottom wall internally delimits a through-seat adapted to house in a sealed and rotational manner at least one portion of a rotating member connectable , on one side, to an actuating mechanism, such as an electric motor, and on the other side to the thrust member connectable to the piston . The piston comprises a thrust head adapted to come into contact with the brake pad and a side wall adapted to sealingly slide with respect to the cylindrical wall . Moreover, with said thrust head and said side wall , the piston delimits an open cavity on the side opposite to the thrust head, adapted to accommodate at least partially the thrust member coupled to the rotating member of the parking brake device . The thrust member is coupled to the rotating member so as to transform the rotation of the rotating member into a translation of the thrust member, which allows a displacement in the axial direction by biasing the brake pad .

[0006] . In brake calipers of this type , the brake fluid is fluid- tightly introduced between the bottom wall of the cylinder and the piston, which allows the piston to be actuated by virtue of the fluid pressure, where the rotating member and the thrust member are immersed in the brake fluid and allow the piston to be actuated as a parking brake regardless of the action of the fluid .

[0007 ] . With the operation of the brake caliper as a service brake, the interaction between brake pads and disc generates heat that reaches high temperatures , of the order of hundreds of degrees , which is transferred to caliper body and piston thus increasing the temperature of the brake fluid .

[0008 ] . As known, in the brake calipers of disc brakes , air bubbles are created in the braking system when the brake fluid becomes excessively hot approaching the boiling point . These bubbles , unlike the brake fluid being substantially incompressible, can lead to an increase in the stroke of the brake actuating device , such as a pedal or lever, for example, to compress such gas bubbles during a braking action, compromising the braking comfort and potentially compromising the braking action itself .

[0009] . In addition to such a problem, in such calipers , an excessive increase in temperature of the brake fluid can lead to the expansion of the components of the thrust member and the rotating member, which are immersed in the brake fluid, and subsequent contraction during cooling . It has been found that heating and cooling cycles , and the resulting subsequent expansions and contractions of the components immersed in the brake fluid of the parking system in the cylinder chamber, can lead to impaired operation of the parking brake until the brake caliper cools down . [0010 ] . Additionally, the excessive heating of the braking fluid adds a risk factor to the reliability of the parking brake when activated with a vehicle on a slope after the service brake has been repeatedly activated . Indeed, since the disc, the pads , as well as the thrust member and the rotating member are immersed in the braking fluid, they reduce their si ze as they cool down after the expansion due to the increase in temperature, causing the parking force initially established on the high temperature disc to be insufficient to keep the vehicle stationary on slopes after the caliper has cooled down .

[0011 ] . Therefore , the need is strongly felt to devise brake caliper solutions which allow avoiding excessive overheating of the braking fluid .

[0012 ] . In addition, one of the needs felt in the field is to manufacture a disc brake caliper which is as light as possible , so as to limit as much as possible the unsprung masses of the vehicle with which the disc brake is associated, and on the other hand, the need to ensure a necessary stiffness of the caliper body, to prevent it from deforming in use and compromising the braking action . In particular, any deformations of the caliper body can compromise the sliding thereof with respect to the bracket , and thus there can be an incorrect distribution of the thrusts acting on the pads acting on opposite faces of the braking band . Obviously, such needs for stif fness and lightness are antithetical since increased stiffness is normally achieved by increasing component thicknesses and related masses .

[0013] . Solut ion

[0014 ] . It is the obj ect of the present invention to provide a brake piston and a brake caliper which allow better resistance to the increase in temperature of the braking fluid than known so far .

[0015 ] . It is a further obj ect of the present invention to provide a piston and a brake caliper which allow obtaining high resistance to brake fluid temperature increase by limiting the space available for brake fluid in the caliper body, i . e . , by limiting the si ze of the pressure chamber delimited between piston and cylinder made in the caliper body, reducing the weight of the brake caliper and maintaining high resistance to stress .

[0016] . These and other obj ects are achieved by a piston according to claim 1 and by a brake caliper according to claim 8 .

[0017 ] . The dependent claims relate to preferred and advantageous embodiments of the present invention .

[0018 ] . Drawings

[0019] . In order to better understand the invention and appreciate the advantages thereof , some non-limiting exemplary embodiments thereof will be described below with reference to the accompanying drawings , in which : [0020 ] . - figure 1 is an axonometric view of a brake caliper for a disc brake according to an embodiment of the invention;

[0021 ] . - figure 2 is a side view of the brake caliper shown in figure 1 ;

[0022 ] . - figure 3 is a side view of a brake caliper, sectioned along a plane comprising an axial direction A-A and a radial direction R-R, according to an embodiment of the invention, in which a piston actuatable by a brake fluid and a thrust device can be seen, so as to brake a vehicle as a service brake and as a parking brake, where the piston delimits a ventilation chamber in the direction of a first brake pad which allows thermally insulating a septum of the piston which separates the ventilation chamber from a thrust seat delimited by the piston in which a thrust device immersed in the brake fluid is housable , where a stepped piston sidewall is also visible, which allows reducing the radial dimensions of a pressure chamber in which the brake fluid is introduced by moving the brake fluid away from the first brake pad;

[0023] . - figure 4 is an axonometric view of a piston according to the present invention, slidingly insertable into a cylinder delimited by the brake caliper in figure 3 , in which the ventilation chamber delimited by the piston can be seen;

[0024 ] . - figure 5 is an exploded axonometric view of the piston in figure 4 and a thrust device housable in a thrust seat delimited by the piston and configured to mechanically and/or electromechanically actuate the piston, according to an embodiment of the invention; [0025 ] . - figure 6 is an axonometric view of the piston according to the present invention, sectioned along a plane comprising an axial direction A-A and a radial direction R-R, according to an embodiment of the invention;

[0026] . - figure 7 is a front view of the piston according to the present invention, in which a first septum surface facing the brake pad can be seen, delimiting a bottom of the pressure chamber, having a raised central portion and two depressed peripheral portions according to an embodiment ;

[0027 ] . - figure 8 is a front view of the piston according to the present invention, in which a first surface of the septum facing the brake pad can be seen, delimiting a bottom of the pressure chamber, having a raised circular central portion and a depressed peripheral circular-crown portion according to an embodiment .

[0028 ] . Description of some preferred embodiments

[0029] . According to a general embodiment, a piston for a brake caliper 1 is indicated by reference numeral 10 .

[0030 ] . The piston 10 comprises a side wall 11 mainly extending along an axial direction A-A. The piston 10 comprises a first annular edge configured to come into contact with a first brake pad 4 . The piston 10 comprises a second annular edge 13 configured to receive a thrust from a brake fluid . The side wall 11 extends between the first annular edge 12 and the second annular edge 13 . [0031 ] . The piston 10 comprises a septum 14 extending at least along a radial direction R-R, where said radial direction R-R is transverse to said axial direction A-A. [0032 ] . Said septum 14 comprises a first pad-side surface 15 adapted to face said first brake pad 4 . Said septum 14 comprises a second brake fluid-side surface 16 adapted to face the opposite side of said first pad-side surface 15 , along said axial direction A-A.

[0033] . Said side wall 11 and said septum 14 delimit a thrust seat 18 and a ventilation chamber 17 , where said thrust seat 18 and said ventilation chamber 17 are fluidically separated along said axial direction A-A by said septum 14 .

[0034 ] . Said thrust seat 18 is open at said second annular edge 13 and is closed at said second brake fluid-side surface 16.

[0035 ] . Said thrust seat 18 is adapted to receive at least partially a thrust device 19 to mechanically actuate the piston 10 by biasing said first brake pad 4 .

[0036] . Said ventilation chamber 17 is open at said first annular edge 12 and is closed at least by said first pad-side surface 15.

[0037 ] . Advantageously, said ventilation chamber 17 is adapted to accommodate air to thermally insulate the septum 14 . Air can thus be trapped between the pad and the septum 14 , reducing the heat transfer from the pad zone to the thrust seat 18 in which the brake fluid is present when the piston is under operating conditions in a brake caliper 1 .

[0038 ] . Advantageously, said side wall 11 comprises a first side wall portion 20 having a first outer diameter Del and a second side wall portion 21 having a second outer diameter De2 , where said first outer diameter Del is greater than said second outer diameter De2 . Said first side wall portion 20 internally delimits at least said ventilation chamber 17 . Said second side wall portion 21 internally delimits said thrust seat 18 at least partially .

[0039] . Said piston 10 comprises a third annular edge 22 mainly extending along said radial direction R-R, where said third annular edge 22 externally connects said first side wall portion 20 and said second side wall portion 21 in an undercut manner to receive a thrust from said brake fluid . In other words , the third annular edge 22 forms a shoulder of said side wall 11 which extends along said radial direction .

[0040 ] . According to an embodiment , said septum 14 , on the side of said first pad-side surface 15, comprises a central portion 23 and a peripheral portion 24 , where said central portion 23 is raised with respect to said peripheral portion 24 . According to an embodiment, said peripheral portion 24 is depressed with respect to said central portion 23 . This allows ensuring the air trapping in the ventilation chamber . Moreover, when air enters the ventilation chamber, the geometry of the central portion 23 and the peripheral portion 24 allows increasing a turbulent motion of the air present in the ventilation chamber, avoiding an excessive overheating of the septum 14 .

[0041 ] . According to an embodiment, said central portion 23 has a circular shape , and said peripheral portion 24 has a circular-crown shape about said central portion 23 . According to an embodiment, said central portion 23 is bone-shaped, and said peripheral portion 24 is formed by two crescent-shaped portions , separated by said central portion 23 .

[0042 ] . According to an embodiment , said first annular edge 12 comprises at least one contact tooth 25 and at least one dip 26, where said at least one contact tooth 25 is raised along said axial direction A-A or a direction parallel to said axial direction A-A with respect to said at least one dip 26 so that when said at least one tooth 25 is in contact with said first brake pad 4 , said dip 26 forms a radial window with said side wall 11 , adapted to allow a passage of air into and out of the ventilation chamber 17 and reduce a contact surface between the first annular edge 12 and the first brake pad 4 .

[0043] . According to an embodiment , said first annular edge 12 comprises a plurality of said at least one contact tooth 25 and a plurality of said at least one dip 26, arranged circumferentially alternating along said first annular edge 12 .

[0044 ] . According to an embodiment, said first side wall portion

20 comprises a first tubular portion 27 . According to a first embodiment, the first tubular portion 27 has a first thickness SI and a first axial length Al . According to an embodiment , said first tubular portion 27 internally delimits said ventilation chamber 17 . [0045 ] . According to an embodiment, said second side wall portion

21 comprises a second tubular portion 28 connected to said first tubular portion 27 . According to an embodiment, said second tubular portion 28 has a second thickness S2 and a second axial length A2 . According to an embodiment, said second tubular portion 28 at least partially delimits said thrust seat 18 .

[0046] . According to an embodiment, said first axial length Al is at least equal to said second axial length A2 .

[0047 ] . According to an embodiment, said first thickness SI is at least equal to said second thickness S2 . According to an embodiment, said second thickness S2 is less than said first thickness S I .

[0048 ] . According to an embodiment, said first side wall portion 20 comprises a third tubular portion 29 interposed between said first tubular portion 27 and said second tubular 29. According to an embodiment, the third tubular portion 29 is connected to the second tubular portion 28 with said third annular edge 22 .

[0049] . According to a first embodiment , the third tubular portion 29 has a third thickness S3 and a third axial length A3 .

[0050 ] . According to an embodiment, said third thickness S3 is at least double said first thickness S I .

[0051 ] . According to an embodiment, said third axial length A3 is at least double said first thickness SI .

[0052 ] . According to an embodiment, said first axial length Al is greater than said third axial length A3 .

[0053] . According to an embodiment, said first tubular portion 27 and said septum 14 form a cup-shaped portion .

[0054 ] . According to an embodiment, said second tubular portion 28 and said third tubular portion 29 and said septum 14 form a T-shaped portion . According to an embodiment , said third tubular portion 29 forms a restricted shank of said T-shaped portion and said third tubular portion 29 connected to said septum 14 forms a head of said T-shaped portion .

[0055 ] . Advantageously, the provision of said third tubular portion 29 of greater thickness than said first tubular portion and said second tubular portion, and having a length equal to at least half the outer diameter of the first wall portion 20 , allows slowing down the overheating and heat transfer from the pad side to the third annular edge 22 facing the brake fluid .

[0056] . According to an embodiment, said first pad-side surface 15 and said second brake fluid-side surface 16 are diametrically opposite to each other along said axial direction A-A.

[0057 ] . According to an embodiment, said first pad-side surface 15 and said second brake fluid-side surface 16 comprise respective central portions mainly extending along directions parallel to said radial direction R-R .

[0058 ] . According to an embodiment, said first annular edge 12 and said second annular edge 13 mainly extend along directions parallel to said radial direction R-R and form opposite axial ends of said piston 10 .

[0059] . According to an embodiment, said first annular edge 12 and said second annular edge 13 mainly extend along a respective circumferential direction C-C punctually orthogonal to said axial direction A-A and said radial direction R-R .

[0060 ] . According to an embodiment , said piston 10 has a ventilation chamber depth Pl and a thrust seat depth P2 . Said ventilation chamber depth Pl is defined by a first distance along said axial direction A-A between the central portion of said first pad-side surface 15 and an orthogonal proj ection of said first annular edge 12 on said axial direction A-A. Said thrust seat depth P2 is defined by a distance along said axial direction A-A between the central portion of said second brake fluid-side surface 16 and an orthogonal proj ection of said second annular edge 13 on said axial direction A-A. Said ventilation seat depth Pl is at least half the thrust seat depth P2 .

[0061 ] . According to an embodiment, on the side of said second brake fluid-side surface 16, said septum 14 delimits an undercut seat to house an end portion of the thrust device . The undercut seat forms a narrowing of said thrust seat 18 .

[0062 ] . According to an embodiment, said thrust seat 18 has a polygonal shape .

[0063] . According to an embodiment, said piston 10 has a piston axis A parallel to said axial direction A-A about which it extends symmetrically .

[0064 ] . According to an embodiment, said side wall 11 comprises an outer side surface which externally delimits said piston 10 with respect to said ventilation chamber 17 and said thrust seat 18 . According to an embodiment, said outer side surface is a substantially cylindrical surface .

[0065 ] . According to an embodiment, said side wall 11 comprises a first inner side surface 30 and a second inner side surface 31 , which delimit said piston 10 by internally facing said ventilation chamber 17 and said thrust seat 18 , respectively .

[0066] . According to an embodiment, said first inner side surface

30 has a first inner diameter Di l and said second inner side surface

31 has a second inner diameter Di l .

[0067 ] . According to an embodiment, said first inner diameter Dil is equal to at least one third more than said second inner diameter Di l . According to an embodiment , said first inner diameter Di l is at least double said second inner diameter Di l .

[0068 ] . According to an embodiment, said first inner side surface

30 is a substantially cylindrical surface .

[0069] . According to an embodiment, said second inner side surface

31 is a polygonal surface, such as a parallelepiped side surface, for example with a square base , with rounded corners .

[0070 ] . The present invention further relates to a brake caliper for a disc brake, generally indicated by reference numeral 1 .

[0071 ] . The brake caliper 1 comprises at least one piston 10 according to at least one of the previously described embodiments .

[0072 ] . The brake caliper 1 comprises a caliper body 2 adapted to be arranged straddling a brake disc 32 . Said brake disc 32 has a first braking surface 33 and an opposite second braking surface 34 , said brake disc 3 being adapted to rotate about a rotation axis X-X which defines a direction parallel to said axial direction A-A.

[0073] . Said caliper body 2 comprises a first caliper body portion 6 adapted to face said first braking surface 33 either directly or indirectly . Said caliper body 2 comprises at least one connecting bridge 8 supported by said first caliper body portion 6 and which proj ects straddling said brake disc 32 . Said caliper body 2 comprises a second caliper body portion 7 supported so as to be cantilevered with respect to said at least one floating element bridge 12 and adapted to face said second braking surface 4 either directly or indirectly .

[0074 ] . Said first caliper body portion 6 internally delimits a piston or cylinder seat 9 adapted to slidingly house said at least one piston 10 in a fluid-tight manner .

[0075 ] . According to an embodiment, said first caliper body portion 6 comprises a cylindrical wall 35 and a bottom wall 36 which define said piston or cylinder seat 9. The bottom wall 36 is transverse to the cylindrical wall 35 extending parallel to said radial direction R-R and is made in one piece with said cylindrical wall 35 .

[0076] . According to an embodiment, said cylindrical wall 35 comprises a first cylindrical portion 37 and a second cylindrical portion 38 connected by a cylinder shoulder 39 mainly extending substantially parallel to said radial direction R-R .

[0077 ] . According to an embodiment , said first cylindrical portion 37 slidingly accommodates said first side wall portion 20 of said piston 10 . Said second cylindrical portion 38 slidingly accommodates said second cylindrical wall portion 21 of said piston 10 . [0078 ] . According to an embodiment , said third annular edge 22 faces said cylinder shoulder 39 , and said second annular edge 13 and said thrust seat 18 indirectly face said bottom wall 36 delimiting a pressure chamber in which a brake fluid is inj ected through a conduit 40 passing through said cylinder shoulder 39 to hydraulically bias said piston 10 at least during a service braking action .

[0079] . According to an embodiment, said brake caliper 1 comprises a thrust device 19 adapted to mechanically bias said piston 10 at least during a parking braking action .

[0080 ] . According to an embodiment, said thrust device 19 is partially housed in said thrust seat 18 and within said second cylindrical portion 38 between said bottom wall 36 and said second annular edge 22 of said piston 10 .

[0081 ] . According to an embodiment, said thrust device 19 comprises at least one rotating member 41 coupled to a thrust member 42 , where a rotation of said rotating member 41 corresponds to a translation of said thrust member 42 integrally with said piston 10 . [0082 ] . According to an embodiment, said rotating member 41 being rotatably accommodated in a sealing manner inside a rotation seat 43 formed in the bottom wall 36 of the cylinder 9 and passing through said bottom wall 36 so that the rotating member 41 is rotatable about a rotation axis substantially parallel to the axial direction A-A in connection with an electric motor 44 , constrainable to the caliper body 2 . [0083] . According to an embodiment, said thrust device 19 comprises a screw-nut screw assembly . According to an embodiment, said rotating member 41 is a screw, and said thrust member 42 is a nut screw housed in said thrust seat 18 . According to an embodiment, said nut screw comprises a threaded hollow body having a substantially cylindrical shape and a plurality of petals proj ecting radially outward from the hollow body so as to fit into the thrust seat 18 thus allowing the piston 10 to slide forward with respect to said plurality of petals when biased by the brake fluid and allowing the screw nut to advance integrally with the piston when the thrust device 19 biases the piston 10 .

[0084 ] . According to an embodiment, said thrust device 19 comprises a ball-in-ramp device , which connects said rotating member 41 to said thrust device 42 . For example, the ball-in-ramp device is known from document US20150323026A1 .

[0085 ] . According to an embodiment, said brake caliper 1 comprises a motor unit connected to said caliper body 2 , where said motor unit comprises an electric motor 44 and a reduction gear 45 , where said reduction gear 45 is connected to said rotating member 41 .

[0086] . According to an embodiment, said brake caliper l is a floating type caliper .

[0087 ] . According to an embodiment, the brake caliper 1 comprises a bracket 3 adapted to connect to a caliper support provided in a vehicle . According to an embodiment , the caliper body 2 is slidingly supported by said bracket 3 so as to move with respect to the bracket 3 along said axial direction A-A.

[0088 ] . According to an embodiment, said bracket 3 slidingly supports said first brake pad 4 and said second brake pad 5.

According to an embodiment, said brake caliper 1 is a single-piston caliper .

[0089] . According to an embodiment, said first caliper body portion 6 has a caliper body shoulder 46 , which externally reduces the radial dimension of the caliper body between the first cylindrical portion 37 and the second cylindrical portion 38 , outside the piston or cylinder seat 9 according to an embodiment .

[0090 ] . According to an embodiment, said brake caliper 1 comprises at least one electromechanical parking brake (EPB) .

[0091 ] . Obviously, those skilled in the art will be able to make changes or adaptations to the present invention, without however departing from the scope of the following claims .

LIST OF REFERENCE SIGNS ad pad body portion or first elongated portion ted portion or second caliper body portion idge inder seat edge or thrust edge r edge nsverse septum e surface fluid-side surface hamber ll portion all portion edge m portion ptum portion portion r portion portion ide surface side surface 33. First braking surface

34 . Second braking surface

35 . Cylindrical wall

36. Bottom wall

37 . Fi rst cylindrical portion

38 . Second cylindrical portion

39. Cylinder shoulder

40 . Conduit

41 . Rotating member

42 . Thrust member

43. Rotation seat

44 . Electric motor

45 . Reduction gear

46. Caliper body shoulder

Del First outer diameter

De2 Second outer diameter

Dil First inner diameter

Di2 Second inner diameter

51 First thickness

52 Second thickness

53 Third thickness

Al First axial length

A2 Second axial length

A3 Third axial length

Pl Ventilation chamber depth

P2 Thrust seat depth

A Piston axis

X-X Disc axis

Del First outer diameter