U.S. patent application number 10/496676 was filed with the patent office on 2006-06-08 for device for adjusting a dual-servo drum brake with internal shoes.
Invention is credited to Gianpaolo Cortinovis, Maurizio Mascheretti.
Application Number | 20060122479 10/496676 |
Document ID | / |
Family ID | 11133753 |
Filed Date | 2006-06-08 |
United States Patent
Application |
20060122479 |
Kind Code |
A9 |
Cortinovis; Gianpaolo ; et
al. |
June 8, 2006 |
DEVICE FOR ADJUSTING A DUAL-SERVO DRUM BRAKE WITH INTERNAL
SHOES
Abstract
A device for adjusting a dual-servo brake with internal shoes
(9) being supported on a shoe-holder plate (2) so as perform
floating selfreinforcing or automatic activation movements against
a braking surface of a drum. The device comprises: adjustment
elements (30) comprising thrust surfaces (31) cooperating with
opposed counter-thrust surfaces (32) of a pyramidal end of an
actuation elements (34) provided with a threaded portion (35)
housed rotatably in a threaded through-hole (36) of a support
element (37), the threaded through-hole being arranged
substantially along an axis transverse the axis of the mutual
separation or approach movement of the ends of the shoes, the
support element further comprising support means (38) for housing
the adjustement elements slidably so as to form, with the actuation
element, a support ans thrust structure closed onto the opposed
adjustment elements, the actuation element further comprising an
operating extension which can be housed so as to float freely in a
slot provided in the shoe-holder plate so that an activation end
(41) projects from the brake.
Inventors: |
Cortinovis; Gianpaolo;
(Dalmine, IT) ; Mascheretti; Maurizio; (Lallio,
IT) |
Correspondence
Address: |
HOGAN & HARTSON LLP;IP GROUP, COLUMBIA SQUARE
555 THIRTEENTH STREET, N.W.
WASHINGTON
DC
20004
US
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20050090730 A1 |
April 28, 2005 |
|
|
Family ID: |
11133753 |
Appl. No.: |
10/496676 |
Filed: |
November 27, 2001 |
PCT Filed: |
November 27, 2001 |
PCT NO: |
PCT/IT01/00598 |
371 Date: |
May 26, 2004 |
Current U.S.
Class: |
600/407 |
Current CPC
Class: |
F16D 51/50 20130101;
F16D 65/42 20130101; F16D 65/40 20130101 |
Class at
Publication: |
600/407 |
International
Class: |
A61B 5/05 20060101
A61B005/05 |
Claims
1: A device for adjusting a dual-servo brake with internal shoes,
the device cooperating with adjacent ends of two shoes which are
constantly urged towards one another by a resilient element, the
shoes being supported for floating freely on a shoe-holder plate so
as to perform floating auto-expansion movements against a braking
surface of a drum, the device comprising: adjustment elements, each
of which cooperates with one of the adjacent shoe ends and which
are movable jointly in opposite directions so as to move the
adjacent shoe ends substantially towards one another or apart, the
adjustment elements comprising thrust surfaces cooperating with
opposed counter-thrust surfaces of a pyramidal end of an actuation
element provided with a threaded portion housed rotatably in a
threaded through-hole of a support element, the threaded
through-hole being arranged substantially along an axis transverse
the axis of the mutual separation or approach movement of the ends
of the shoes, the support element further comprising support means
for housing the adjustment elements slidably so as to form, with
the actuation element, a support and thrust structure closed onto
the opposed adjustment elements, the actuation element further
comprising an operating extension which can be housed so as to
float freely in a slot provided in the shoe-holder plate so that an
activation end projects from the brake.
2: The [[A]] device according to claim 1 in which each of the
adjustment elements comprises a spacer.
3: The [[A]] device according to claim 2 in which the spacer
comprises a portion suitable for form coupling with a portion of
the end of the shoe.
4: The [[A]] device according to claim 3 in which the portion
suitable for form coupling comprises a fork forming a seat for an
end portion of a rib of the shoe.
5: The [[A]] device according to claim 1 in which each of the
adjustment elements comprises an end face which is remote from the
shoe and a portion of which forms the thrust surface.
6: The [[A]] device according to claim 5 in which the portion of
the end face which forms the thrust surface covers a fraction of
the extent of the end face.
7: The [[A]] device according to claim 5 in which the portion
forming the thrust surface is inclined at a predetermined angle of
inclination to a plane transverse the thrust element.
8: The [[A]] device according to claim 7 in which the angle of
inclination is between 10 degrees and 40 degrees.
9: The [[A]] device according to claim 7 in which the angle of
inclination is 20 degrees.
10: The [[A]] device according to claim 5 in which the portion
forming the thrust surface is inclined to a plane transverse the
thrust element so as to transfer a force transmitted by the
actuation element in a direction suitable for moving the ends of
the shoes apart in order to take up the wear of the friction
material.
11: The [[A]] device according to claim 1 in which the adjustment
elements are arranged opposite one another so as to form, with the
inclined portions, a V-shaped seat for the pyramidal end of the
actuation element.
12: The [[A]] device according to claim 1 in which the actuation
element comprises a pyramidal end defined by a plurality of
counter-thrust surfaces suitable for abutting the thrust surfaces
of the adjustment elements.
13: The [[A]] device according to claim 12 in which the pyramidal
end comprises counter-thrust surfaces which are identical to one
another.
14: The [[A]] device according to claim 12 in which the pyramidal
end comprises six counter-thrust surfaces.
15: The [[A]] device according to claim 12 in which opposed
surfaces of the pyramidal end are inclined so as to be arranged
parallel to the thrust surfaces facing them.
16: The [[A]] device according to claim 1 in which the actuation
element comprises a body which extends substantially longitudinally
with an axis substantially transverse the axis of the mutual
approach or separation movement of the ends of the shoes.
17: The [[A]] device according to claim 16 in which the body
comprises an externally threaded cylindrical portion which can
cooperate with the threaded through-hole of the support
element.
18: The [[A]] device according to claim 17 in which the threaded
portion is provided in the vicinity of the pyramidal end.
19: The [[A]] device according to claim 17 in which the threaded
portion has an extent sufficient to allow the pyramidal end to be
inserted between the adjustment elements so as to move the shoes
apart by a distance at least equal to the maximum wear of the
friction material.
20: The [[A]] device according to claim 16 in which the actuation
element comprises a shank of a length such as to allow an end
thereof remote from the pyramidal end to project from the
shoe-holder plate.
21: The [[A]] device according to claim 20 in which the shank
comprises an abutment element which can abut a counter-abutment
surface provided in the support element, the abutment element
defining a position of maximum insertion of the actuation element
between the adjustment elements.
22: The [[A]] device according to claim 16 in which the actuation
element comprises an activation end which projects from the brake
and can be activated in order to rotate the actuation element,
advancing it or retracting it between the adjustment elements.
23: The [[A]] device according to claim 22 in which the activation
end comprises key or nut surfaces suitable for cooperating with a
tool such as a wrench or spanner.
24: The [[A]] device according to claim 1 in which the support
element comprises a body provided with a support and guide for the
activation element and fork like arms forming opposed support means
for the support and sliding of the adjustment elements.
25: The [[A]] device according to claim 24 in which the body
comprises a plate bent so as to be U-shaped, forming a base
comprising a threaded seat for the actuation element and two
parallel arms provided with through-holes forming the means for the
support and sliding of the adjustment elements.
26: The [[A]] device according to claim 25 in which the base
comprises a cylindrical extension provided with the threaded
through-hole for the support and guiding of the actuation
element.
27: A dual-servo brake with internal floating shoes comprising an
adjustment device, said device cooperating with adjacent ends of
two shoes which are constantly urged towards one another by a
resilient element, the shoes being supported for floating freely on
a shoe-holder plate so as to perform floating auto-expansion
movements against a braking surface of a drum, the device
comprising: adjustment elements, each of which cooperates with one
of the adjacent shoe ends and which are movable jointly in opposite
directions so as to move the adjacent shoe ends substantially
towards one another or apart, the adjustment elements comprising
thrust surfaces cooperating with opposed counter-thrust surfaces of
a pyramidal end of an actuation element provided with a threaded
portion housed rotatably in a threaded through-hole of a support
element, the threaded through-hole being arranged substantially
along an axis transverse the axis of the mutual separation or
approach movement of the ends of the shoes, the support element
further comprising support means for housing the adjustment
elements slidably so as to form, with the actuation element, a
support and thrust structure closed onto the opposed adjustment
elements, the actuation element further comprising an operating
extension which can be housed so as to float freely in a slot
provided in the shoe-holder plate so that an activation end
projects from the brake.
28: The [[A]] brake according to claim 27 further comprising an
actuator acting on the ends of the shoes remote from those which
cooperate with the adjustment device, the actuation ends facing an
abutment element for discharging the braking stress directed
circumferentially by the shoes, to the shoe-holder plate.
29: The device according to claim 6 in which the portion forming
the thrust surface is inclined at a predetermined angle of
inclination to a plane transverse the thrust element.
30: The device according to claim 6 in which the portion forming
the thrust surface is inclined to a plane transverse the thrust
element so as to transfer a force transmitted by the actuation
element in a direction suitable for moving the ends of the shoes
apart in order to take up the wear of the friction material.
31: The device according to claim 13 in which the pyramidal end
comprises six counter-thrust surfaces.
Description
DESCRIPTION
[0001] The subject of the present invention is a device for
adjusting a dual-servo drum brake with internal shoes [a
self-energizing or duo/dual-servo brake].
[0002] Brakes of this dual-servo type are described, for example,
in DE-485 688, U.S. Pat. No. 6,131,711 and U.S. Pat. No.
6,302,245.
[0003] These known dual-servo brakes with internal shoes are
capable of producing a large braking force by virtue of the
provision of shoes which can perform movements such as to give rise
to an automatic activation of the brake. This efficient braking
action is also known as self-energizing action or auto-expansion
movement of the shoes and is achieved mainly by virtue of the
provision of shoes which are supported so as to float freely on a
shoe-holder plate.
[0004] In these dual-servo brakes, first ends of the shoes
cooperate with a separator device which, during the braking
operation, moves these ends away from an abutment element which
projects from the shoe-holder plate and is disposed between the
opposed activation ends of the shoes. As the shoes move apart, they
pivot about their opposite ends, between which a spacer is
disposed. As the operation continues, the shoe train widens
radially, bringing the friction material which is present on the
shoes into contact with the braking surface of the drum. At this
point, the drum tends to rotate the shoe train into abutment with
the abutment element. Any further action of the separator device
and/or of the drum tends to "wedge" the shoe train against the
braking surface of the drum and into abutment with the abutment
element to an ever greater extent.
[0005] In order to distribute the braking force uniformly on the
braking surface even with increasing wear of the friction material,
it is known to interpose an adjustable spacer between the ends of
the shoes remote from those which cooperate with the separator
device.
[0006] An example of these devices is described in U.S. Pat No.
5,076,402.
[0007] Although these known devices afford the shoes the freedom of
movement necessary to achieve the automatic activation or
floating-shoe movement, they are also imprecise because they are
difficult to adjust. In fact, in order to perform the necessary
adjustments of the relative spacing of the ends of the shoes, it is
necessary to insert a screwdriver into the brake until the end of
the screwdriver is coupled with the drive slot of a grub screw
which, when rotated, can pivot the levers which move the
above-mentioned opposed ends of the shoes apart or towards one
another.
[0008] In particular, in order to adjust the relative distance
between the ends of the shoes to compensate for wear of the
friction material, there is a great need to provide a highly
reliable and accurate device which at the same time is of simple
construction and easy to use.
[0009] Attempts to fulfil this need have already been made in the
past but solutions have been found only for drum brakes having
non-floating shoes, and these solutions are not satisfactory.
[0010] Examples of adjustment devices for non-floating (or non
dual-servo) shoes are described in the patents U.S. Pat. No.
5,456,338, GB-777,589, GB-565,088 and GB-951,381.
[0011] The problem underlying the present invention is that of
proposing a device for adjusting a dual-servo brake with internal
shoes which has structural and functional characteristics such as
to overcome the disadvantages mentioned above with reference to the
prior art.
[0012] This problem is solved by means of a device for adjusting a
dual-servo drum brake with internal shoes as described in claim 1,
as well as by a drum brake as described in claim 27.
[0013] Further embodiments are described in the dependent
claims.
[0014] Further characteristics and the advantages of the adjustment
device according to the invention will become clear from the
following description of a preferred embodiment thereof, provided
by way of non-limiting example with reference to the appended
drawings, in which:
[0015] FIG. 1 is a perspective view of a dual-servo drum brake,
without the drum,
[0016] FIG. 2 is a further perspective view of the brake of FIG.
1,
[0017] FIG. 3 is a front view of the brake of FIG. 1,
[0018] FIG. 4 is a section through the brake of FIG. 1, taken on
the arrows IV-IV of FIG. 3,
[0019] FIG. 5 is a section through the brake of FIG. 1, taken on
the arrows V-V of FIG. 3,
[0020] FIG. 6 is a perspective view of an adjustment device,
[0021] FIG. 7 is a perspective view of the device of FIG. 6 with
parts separated, and
[0022] FIG. 8 is a view of the adjustment device of FIG. 6,
substantially from above.
[0023] With reference to the above-mentioned drawings, a unit
comprising elements of a disk service brake and of a drum parking
brake is generally indicated 1. In particular, the unit comprises a
shoe-holder plate 2 suitable for supporting a caliper, not shown,
of the disk service brake and also for supporting the non-rotating
components of the drum parking brake.
[0024] "Service brake" is intended to define a brake which can slow
down or stop, for example, a moving axle or shaft of a vehicle,
whereas "parking brake" is intended to define a brake suitable for
keeping, for example, an axle or a shaft of a vehicle locked when
it is not in motion.
[0025] The non-limiting embodiment described below is a dual-servo
drum parking brake but the present invention may equally well be
applied to a dual-servo drum service brake.
[0026] The shoe-holder plate 2 is substantially toroidal, with an
outer surface 3. The plate comprises, internally, a flange-shaped
portion 4 for fixing to an axle of a vehicle. The flange 4 has a
plurality of holes 5, preferably eight holes (FIG. 3) disposed
along arcs of a circle and diametrally opposed in pairs with
respect to the axis s-s of the braking surface or brake axis (FIGS.
1 and 2). Substantially radial projections 6 for the fixing of the
caliper extend outwardly from the outer surface 3. The shoe-holder
plate 2 has, on its surface 7 which faces outwardly relative to the
vehicle when installed, a plurality of projections 8, preferably
six projections, arranged along arcs of a circle, diametrally
opposed in pairs with respect to the axis s-s of the brake and,
according to one embodiment, aligned with two of the fixing holes
5. Shoes 9 can bear on these projections 8. The shoe-holder plate
has an abutment element 10 circumferentially spaced from the holes
and from the projections, for the discharge of the braking stress.
In the vicinity of the abutment element, there is an opening 11
(FIG. 5), for example, a substantially rectangular opening,
suitable for housing an actuator device, for example, a
shoe-separator or spreader device, generally indicated 12. For
example, the actuator is a lever actuator of known type which can
separate the shoes at one end in order to bring them into contact
with the braking surface of the drum (not shown).
[0027] Each shoe 9 comprises a plate 13 shaped as an arc of a
circle and reinforced by a flat rib 14, for example, disposed
centrally relative to the depth of the shoe. Each plate 13 is
provided with friction material 15 suitable for contacting the
braking surface of the drum in order to exert the required braking
force (FIG. 5). Each rib 14 has, at an end 16, a bearing surface 17
suitable for abutting the abutment element 10 in order to discharge
the braking stress. The end 16 also has a seat 18 for housing the
actuator 12. Each rib 14 has, at its end 19 remote from the
actuator 12, a seat 20 for coupling with an adjustment device,
generally indicated 21, which, amongst other things, acts as a
spacer between the two ends 19 of the floating shoes 9.
[0028] The shoes 9 are arranged opposite one another with edges 22
of the plates 13, and possibly of the friction material, arranged
bearing on the plurality of projections 8 (FIG. 5). The shoes are
held in position axially by resilient means 23, one for each shoe,
associated with a corresponding number of pins 24 fixed axially to
the shoe-holder plate 2. The shoes 9 are restrained purely on the
resilient means, for example, flexion spring-like members, and do
not come into contact with the respective pins 24 during their
movement, by virtue of the fact that each pin is housed freely in a
slot 25 provided in the rib 14 of the shoe.
[0029] The shoes 9 are constantly urged towards one another by
resilient elements 26 and 27 disposed at the two ends 16 and 19,
respectively, and engaged in suitable holes 28 provided in the ribs
14, so that the ends are constantly in abutment with the actuator
12 and with the adjustment device 21, respectively.
[0030] A further resilient means, for example, a wire spring 29,
constantly urges the shoes 9 away from the abutment element 10. The
action of this spring and the frictional force produced between the
shoes and the projections prevent the shoes from moving towards the
surface of the drum as a result of the stresses and/or vibrations
produced during the movement of the vehicle and under their own
weight. For example, the wire spring has its ends wrapped around
two projections 8 remote from the actuator 12 and has an arcuate
portion which abuts the angle formed between the rib and the plate
of each shoe, urging it away from the drum and/or from the abutment
element in a radial direction so as to compensate for the effect of
the stresses, the vibrations, and the weight of the shoes.
[0031] The actuator 12, a first shoe 9, the adjustment device 21
acting as a spacer, and the second shoe 9 form a kinematic train or
chain which abuts the abutment element 10 during the braking
operation.
[0032] Advantageously, the adjustment device comprises adjustment
elements 30 each cooperating with one of the adjacent ends of the
shoes 9. The adjustment elements 30 can be moved jointly in
opposite directions so as to move the adjacent ends 19 of the shoes
substantially towards one another or apart. The adjustment elements
30 comprise thrust surfaces 31 cooperating with opposed
counter-thrust surfaces 32 of a pyramidal end 33 of an actuation
element 34. The actuation element 34 has a threaded portion 35
housed rotatably in a threaded through-hole 36 of a support element
37 (FIG. 7). The threaded through-hole 36 is arranged substantially
along an axis b-b transverse the axis a-a of the mutual separation
and approach movement of the ends 19 of the shoes. The transverse
axis b-b is preferably substantially parallel to the axis s-s of
the braking surface of the drum, or brake axis or, more
advantageously, is slightly inclined away from the axis s-s, to
facilitate manipulation. The support element 37 also comprises
support means 38 for slidably housing the adjustment elements 30 so
as to form, with the actuation element 34, a support and thrust
structure closed onto the opposed adjustment elements. The
actuation element 34 also comprises an operating extension 39 which
can be housed so as to float freely in a slot 40 provided in the
shoe-holder plate 2 in manner such that an activation end 41
projects from the brake (FIGS. 4 and 5).
[0033] According to one embodiment, each of the adjustment elements
30 comprises a spacer which can abut the end 19 of the shoe 9 in
order to transmit the tangential components of the braking force
from one shoe to the other of the kinematic chain which is in
abutment with the abutment element. In particular the spacer
comprises an end portion 42 suitable for form coupling with the end
portion of the shoe forming the seat 20. The portion 42 suitable
for form coupling comprises a fork 43 forming a coupling seat 44
for the end portion of the rib 14 of the shoe 9 that forms the base
of the seat 20 of the shoe.
[0034] According to one embodiment, each of the adjustment elements
30 comprises an end face 45 remote from the shoe 9 and having a
portion which forms the thrust surface 31. The portion of the end
face 45 forming the thrust surface 31 advantageously covers a
fraction of the extent of the end face 45. For example, the thrust
surface is slightly more than half of the extent of the end face,
preferably a fraction of between 45% and 70% of the extent of the
end face. Tests performed on the device have shown that an extent
of between 60% and 65% of the end face and, in particular of 63% of
the end face provides a strong thrust surface for withstanding and
transmitting even the most severe braking forces. For example, for
cylindrical spacer adjustment elements having an outside diameter
of 13 mm, it has been found particularly advantageous to have a
thrust surface which has an extent of 8.2 mm transverse the
spacer.
[0035] According to one embodiment, the portion forming the thrust
surface is inclined to a plane transverse the adjustment element
and parallel to the axis b-b of the actuation element, with a
predetermined angle of inclination Z (FIG. 8). The portion forming
the thrust surface is advantageously inclined to a plane transverse
the adjustment element so as to transfer the force transmitted by
the actuation element in a direction suitable for moving the ends
of the shoes apart in order to take up the wear of the friction
material. For example, the angle of inclination is between 10
degrees and 40 degrees and preferably between 15 degrees and 30
degrees. It has been found from tests carried out on the adjustment
device that, with an angle of inclination Z of 20 degrees, highly
accurate adjustment, as well as a more than adequate bearing
surface, are achieved.
[0036] The adjustment elements 30 are arranged opposite one another
so as to form, with their inclined thrust surfaces, a V-shaped seat
for the pyramidal end 33 of the actuation element 34.
[0037] According to one embodiment, the actuation element 34
comprises the pyramidal end 33 defined by a plurality of
counter-thrust surfaces 32 suitable for abutting the thrust
surfaces 31 of the adjustment elements 30. The opposed surfaces of
the pyramidal end 33 are inclined so as to be arranged parallel to
the thrust surfaces facing them. The pyramidal end 33
advantageously comprises identical counter-thrust surfaces 32. For
example, the pyramidal end 33 comprises six counter-thrust (or
opposing thrust) surfaces 32. In particular, the formation of a
pyramidal end with six counter-thrust surfaces has been found
highly advantageous during tests since, in combination with the
angle of inclination or aperture (twice Z) of the pyramidal end,
this shape prevents excessively accentuated jumping of the spacer
adjustment elements, biased by the spring acting between the ends
19 of the shoes, as they pass over the angles between two adjacent
counter-thrust surfaces during the rotation of the actuation
element. At the same time, this solution enables the counter-thrust
surface to have an extent such as to withstand in an optimal manner
the load generated by braking.
[0038] According to a further embodiment, the actuation element 34
comprises a body which extends substantially longitudinally with an
axis b-b substantially transverse the axis a-a of the mutual
approach or separation movement of the ends of the shoes. The body
advantageously comprises an externally-threaded cylindrical portion
35 which can cooperate with the threaded through-hole 36 of the
support element 37. With further advantage, the threaded portion 35
is provided in the vicinity of the pyramidal end 33. The threaded
portion has an extent sufficient to allow the pyramidal end 33 to
be inserted between the adjustment elements 30 in a manner such as
to move the shoes 9 apart by a distance equal to the maximum wear
of the friction material. It was found in tests carried out on the
adjustment device that an M12.times.1.75 thread, in combination
with the angle of inclination of the thrust and counter-thrust
surfaces, as well as in combination with the number of
counter-thrust surfaces of the pyramidal end, achieved optimal
precision and safety in the adjustment of the distance between the
ends of the shoes.
[0039] According to one embodiment, the actuation element 34
comprises a shank 46 of a length such as to allow an end 41 thereof
remote from the pyramidal end 33 to project from the shoe-holder
plate 2. The shank advantageously comprises an abutment element 47,
for example, an annular rim or projection, which can abut a
counter-abutment surface 48 provided in the support element 37. The
abutment element defines the position of maximum insertion of the
actuation element 34 between the adjustment elements 30.
[0040] According to yet a further embodiment, the actuation element
34 comprises an activation end 41 projecting from the brake and
suitable for being operated by hand or by a tool for rotating the
actuation element, advancing it or retracting it between the
adjustment elements 30. For example, the activation end 41
comprises key or nut surfaces 49 for cooperating with a tool such
as a wrench or spanner.
[0041] According to one embodiment, the support element 37
comprises a body provided with a support and guide 50 for the
activation element 34 and fork-like arms 51 forming opposed support
means 38 for the support and sliding of the adjustment elements 30.
In particular, the body comprises a plate bent so as to be
U-shaped, forming a base 52 comprising a threaded seat 36 for the
actuation element 34 and two parallel arms 51 provided with
through-holes 38 forming the means for the support and sliding of
the adjustment elements 30. According to one embodiment, the base
52 comprises a cylindrical extension 53 provided with the threaded
through-hole 36 for supporting and guiding the actuation element
34. According to a further embodiment, the cylindrical extension is
formed by an internally threaded sleeve fixed by force-fitting or
interference-fitting in a suitable hole provided in the base 52 of
the body.
[0042] When the shoe brake is activated in order to brake the
vehicle, the separator actuator moves apart the ends of the shoes
which face it so that the shoes are pressed into contact with the
braking surface of the brake drum. The frictional force which is
developed between the shoes and the drum causes a first shoe (the
shoe which is the first depends on the direction of rotation of the
drum or on the direction of the force exerted by the drum on the
shoes, if the drum is stationary) to press against the adjustment
device which in turn presses against the second shoe, which is kept
pressed into contact with the drum by the actuator. The drum in
turn tends to rotate and the entire unit formed by the drum and the
kinematic chain of the shoes, the actuator and the adjustment
device, rotates until the bearing surface of the second shoe abuts
the corresponding surface of the abutment element so as to develop
the braking force.
[0043] As the thickness of the friction material of the shoes
decreases or, in other words, as the shoes become worn, the travel
of the separator actuator in order to place the shoes against the
braking surface of the drum increases or, in other words, this
travel of the separator actuator becomes excessive, requiring, for
example, a large travel to operate the brake. In order to keep the
travel within predetermined and low values, the shoes are moved
apart by the adjustment device, moving the friction material
remaining on the shoes towards the braking surface of the drum.
This operation is usually performed during programmed maintenance
of the vehicle and, by virtue of this adjustment device, is
performed quickly but very precisely and safely.
[0044] If the activation end 41 of the actuation element which
projects from the brake is rotated, for example, by coupling a
spanner (a socket spanner or wrench) with the key surfaces 49 of
the activation end 41, the actuation element is screwed into the
threaded hole of the support element 37, bringing about an axial
movement thereof. The pyramidal end 33 penetrates between the
spacer adjustment elements 30, bringing successive faces 32 of the
pyramid into abutment with the inclined thrust surfaces 31. The
spacers are thus moved apart, moving the shoes apart precisely.
[0045] The constant force produced by the resilient means which
bias the shoes acts on the spacers so as to bring the thrust
surface into abutment with the counter-thrust surface of the
pyramidal end. This force is discharged onto the pyramidal end by
the adjustment elements, by means of the inclined thrust surfaces,
and hence onto the actuator element, which discharges it onto the
base of the support element, which discharges it transversely
relative to the spacer adjustment elements, by means of the arms.
This structure produces a closed force loop which leaves the
adjustment device free to float, without needing to be restrained
on separate supports such as the shoe-holder plate. In other words,
the proposed adjustment device avoids the use of support elements
on the shoe-holder plate.
[0046] The angle which delimits two adjacent counter-thrust
surfaces of the pyramidal end advantageously prevents the biasing
action on the shoes produced by the resilient means, together with
stresses induced by the movement of the vehicle, from bringing
about unscrewing of the actuator element.
[0047] As can be seen from the foregoing description, the
adjustment device floats, together with the shoes, preventing
obstruction of the correct operation of the dual-servo brake and at
the same time, its activation end projects from the brake,
facilitating precise, sensitive and safe operation thereof.
[0048] In this device, the cooperation between the support element,
the adjustment elements, and the actuation element forms a closed
structure in the working position or, in other words, a dynamically
closed structure which does not discharge to the exterior the
stresses which are directed transversely relative to the axis of
the mutual separation or approach movement of the ends of the
shoes, so that it does not require a further external structure
such as the shoe-holder plate as a fixed support structure for the
adjustment device.
[0049] Particularly advantageously, the adjustment device does not
modify the precise working position set by the operator since,
between counter-thrust surfaces, there is a position in which a
further separation movement of the adjustment elements is imposed
by the angle between adjacent faces of the pyramidal end.
[0050] The travel limit of the actuation element is advantageously
set by the annular projection 47 which constitutes a safety
abutment.
[0051] A further advantage is that the fork-like structure of the
support element is simple and easy to produce. For example, it can
be produced from a rectangular plate in which a hole is formed in
the base portion. The plate is then bent so as to be U-shaped and
aligned holes are formed in the ends. The threaded sleeve can then
be fitted with force or with interference, ensuring
perpendicularity between the axis a-a of the adjustment elements
and the axis b-b of the actuation element.
[0052] The device proposed has spacer adjustment elements which are
identical to one another and are easy to produce.
[0053] By virtue of the fact that only a portion of the end face of
each adjustment element is inclined, a small and compact device is
produced, so that the device can be fitted even in small
brakes.
[0054] In order to satisfy contingent and specific requirements, a
person skilled in the art may apply to the above-described
preferred embodiment of the adjustment device many modifications,
adaptations and replacements of elements with other functionally
equivalent elements without, however, departing from the scope of
the appended claims.
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