Actuating device for a brake disc
An actuating device for a disc brake may have a piston, and a first ramp-ball motion converter having a first ramp portion axially constrained and actuatable in rotation around and actuating axis. The device may also have a second ramp portion coupled to the piston and a plurality of rolling elements interposed in contact between ramp tracks formed by the first and second ramp portion. The device may also have a second screw and nut motion converter connected between the second ramp portion and the piston. The device may also have a torque limiter that implements a torsional connection of the first ramp portion with the second ramp portion. The torque limiter may also decouple the rotation of the first ramp portion with respect to the second ramp portion about the actuating axis when a predetermined limit torque is exceeded.
1 . An actuating device for a brake disc, comprising:
a piston slidingly supported along an actuating axis,
a first ramp-ball motion converter, having a first ramp portion axially constrained and actuatable in rotation around the actuating axis, a second ramp portion coupled to the piston and facing the first ramp portion, and a plurality of rolling elements interposed in contact between ramp tracks formed by the first and second ramp portion, so that the rotation of the first ramp portion with respect to the second ramp portion brings about a braking translation of the second ramp portion together with the piston with respect to the first ramp portion, along the actuating axis,
a second screw and nut motion converter, connected between the second ramp portion and the piston, so that a rotation of the second ramp portion with respect to the piston about the actuating axis brings about a compensating translation of the piston with respect to the second ramp portion, along the actuating axis,
a torque limiter that:
makes a torsional connection of the first ramp portion with the second ramp portion, so that they rotate together about the actuating axis, until a predetermined limit torque in said torsional connection is reached,
decouples the rotation of the first ramp portion with respect to the second ramp portion about the actuating axis when the predetermined limit torque is exceeded,
wherein the torque limiter comprises one or more jaws coupled in a rotationally fixed manner to a coupling seat of the second portion of the ramp and elastically biased in engagement with a transmission shaft formed at the first portion of the ramp.
2 . The actuating device according to claim 1 , wherein the second portion of the ramp is directly formed on a screw body of the second nut and screw motion converter.
3 . The actuating device according to claim 2 , wherein the piston forms:
a cylindrical wall with a threaded inner piston surface screwed onto the screw body such as to form a nut of the second nut and screw motion converter,
anti-rotation means which prevent rotation of the piston about the actuating axis.
4 . The actuating device according to claim 3 , wherein the screw body forms: —a cylindrical side wall, concentric with respect to the actuating axis, with an outer thread for screwing with the inner thread of the piston,
a screw front wall facing the direction of advancement of the piston and a screw rear wall opposite to the screw front wall, said screw rear wall forming one or more second rolling tracks of the ramp cam tracks,
a coupling seat extended radially and axially internally with respect to the outer thread and which houses the torque limiter.
5 . The actuating device according to claim 4 , wherein the first ramp portion is formed by a rotor body having:
a rotor front wall facing a direction of advancement of the piston and forming one or more first rolling tracks of the ramp tracks,
a drive shaft protruding from the rotor front wall, coaxial to the actuating shaft, and connected to the torque limiter, wherein the second ramp portion is rotatably supported and centered on the drive shaft.
6 . The actuating device according to claim 5 , wherein the screw rear wall forms a through-hole opening into the coupling seat, through which the drive shaft extends into the coupling seat, wherein the through-hole forms a centered and rotation permitting support of the screw body with respect to the rotor body.
7 . The actuating device according to claim 5 , wherein a bearing assembly supports the rotor body in axial abutment and concentrically with respect to the actuating axis, said bearing assembly being positioned inside the rotor body.
8 . The actuating device according to claim 5 , wherein the rolling elements are further contained by a containment cage interposed between the first ramp portion and second ramp portion and supported on the drive shaft.
9 . The actuating device according to claim 5 , wherein the first ramp portion, the second ramp portion and the rolling elements are elastically pushed into mutual contact in the direction of the actuating axis.
10 . The actuating device according to claim 9 , comprising an axial preload spring, configured to axially push the assembly of the first motion converter and the torque limiter.
11 . The actuating device according to claim 10 , wherein the axial preload spring is supported on the drive shaft and clamped between a free end portion of the drive shaft and the front wall of the screw body.
12 . The actuating device according to claim 5 , wherein the drive shaft forms an axial through-hole which accommodates a tie rod having:
an enlarged front end portion, axially resting against a front wall of the screw body, and
a portion of the rear end protruding into an inner cavity of the rotor body,
wherein an axial preload spring is clamped between the rear end portion of the tie rod and a bottom surface of the inner cavity of the rotor body through the interposition of a rolling axial bearing.
13 . The actuating device according to claim 1 , wherein the first motion converter, the second motion converter and the torque limiter are at least partially or completely housed in an inner piston cavity.
14 . The actuating device according to claim 1 , wherein the torque limiter is at least partially or completely housed in an inner cavity of a screw body of the second motion converter.
15 . The actuating device according to claim 1 , wherein the torque limiter comprises one or more jaws coupled in a rotationally fixed manner with said screw body and elastically biased in engagement with the drive shaft of the rotor body.
16 . The actuating device according to claim 15 , wherein:
the coupling seat forms two abutment surfaces that are diametrically opposite to each other with respect to the actuating axis and two lateral guiding surfaces,
the jaws are accommodated between the side guiding surfaces, and guided radially to the actuating axis,
preloaded elastic elements are arranged between the abutment surfaces and the jaws.
17 . The actuating device according to one of claim 15 , wherein the torque limiter comprises two jaws positioned mutually opposite with respect to the drive shaft.
18 . The actuating device according to claim 16 , wherein the torque limiter comprises two jaws positioned mutually opposite with respect to the drive shaft.
19 . The disc brake, comprising a caliper with two spaced apart side walls which delimit a disc space to accommodate a brake disc portion, means for fixing the caliper connects the side walls to each other, at least one pad seat formed in each of said side walls and adapted to accommodate at least one friction pad, thrust means constrained to one or both side walls and adapted to push the friction pads against the brake disc to clamp it, wherein the thrust means comprise an actuating device according to claim 1 .