Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PARKING BRAKE ASSEMBLY WITH WEAR ADJUSTMENT FOR HEAVY ROAD VEHICLE DISC BRAKE
BACKGROUND OF THE INVENTION
1. Field of the Tnvention
The present invention relates to a vehicle
brake system and, more particularly, to disc brakes
for heavy road vehicles.
2. Description of the Prior Art
United States Patent No. 5,205,380 issued
to Paquet et al. on April 27, 1993 discloses a disc
brake assembly for heavy road vehicles. The disc
brake assembly includes a parking or safety brake
which is automatically activated when the road
vehicle is parked. The parking brake comprises spring
acting on a movable plate to urge a brake shoe
against a friction surface provided on one face of a
disc. A fluid bladder is provided to overcome, when
expanded, the force of the spring in order to release
the brake shoe from the friction surface of the disc.
Although the parking brake described in the
above-mentioned patent is effective, it has been
found that there is a need for a new parking brake
which is more compact.
SUMMARY OF THE INVENTION
It is an aim of the present invention to
provide a new parking brake for a disc brake
assembly.
Tt is also an aim of the present invention
to provide a new disc brake assembly having a system
for automatically repositioning a brake shoe to
compensate for wear thereof.
It is a further aim of the present
invention to provide a compact parking brake which is
integrated with a disc brake assembly.
Therefore, in accordance with the present
invention, there is provided a disc brake assembly
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having a disc and a brake shoe movable towards and
away from a friction surface provided on one face of
the disc, and a parking brake comprising a first
pushing member for moving the brake shoe towards and
away from the friction surface of the disc, a first
movement transmitting member displaceable between a
first position wherein said first movement
transmitting member forces said first pushing member
against a biasing force acting thereon to maintain
the brake shoe in friction engagement with the disc
and a second position wherein said first pushing
member is free to move in a direction away from the
disc to release the brake shoe from the friction
surface of the disc, and a motive means to displace
said first movement transmitting member between said
first and second positions thereof.
In accordance with a further general aspect
of the present invention, there is provided a parking
brake for mechanical connection to a wheel of a
vehicle for maintaining the vehicle stationary,
comprising a disc adapted to be mounted to the wheel
and having a friction surface on a face thereof, a
brake shoe movable towards and away from said
friction surface of said disc, and a brake actuator
for normally maintaining said brake shoe against said
friction surface, said brake actuator comprising a
first pushing member biased in a direction away from
said friction surface, said brake shoe being movable
by said first pushing member, and a first cam
displaceable by a motive means between a first
position wherein said first pushing member is pushed
against a biasing force thereof by said first cam and
a second position wherein said first pushing member
is allowed to return to a rest position thereof under
the biasing force acting thereon, and wherein said
brake shoe is applied against said friction surface
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as long as said first pushing member is pushed by
said first cam against said biasing force thereof.
In accordance with a further general aspect
of the present invention, there is provided a self
adjusting brake for a wheel on a vehicle, comprising
at least one disc adapted to be mounted to the wheel
and having a friction surface on one face thereof, at
least one brake shoe movable axially towards and away
from said friction surface for friction engagement
therewith and release thereof, and a brake actuator
for displacing the brake shoe from an idle position
to a functional position in which said brake shoe is
urged against said friction surface of said disc, a
wear compensating mechanism for automatically
readjusting said idle position of said brake shoe to
accommodate wear thereof, at least two pivotally
mounted ratchet arms biased towards a closed position
wherein said ratchet arms are urged in toothed
engagement with a pawl member, said ratchet arms
having a number of axially spaced-apart level of
notches, said pawl member being loosely mounted for
limited axial movement along an axially extending
brake shoe proj ection so that when the stroke of the
brake shoe becomes greater than a permitted distance
of travel of said pawl member on said brake shoe
proj ection, said ratchet arms are pivoted to an open
position thereof by said pawl member to allow said
pawl member to fall into a next level of notches on
said ratchet arms.
BRIEF DESCRIPTION OF THE DRAWINGS
Having thus generally described the nature
of the invention, reference will now be made to the
accompanying drawings, showing by way of illustration
a preferred embodiment thereof, and in which:
Fig. 1 is a top view of a disc brake
assembly for heavy road vehicles in accordance with a
first embodiment of the present invention;
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Fig. 2 .is a rear plan view of the disc
brake assembly of Fig. 1;
Fig. 3 is an enlarged perspective view,
partly in section, of the disc brake assembly
illustrated in an idle position thereof;
Fig. 4 is an enlarged cross-sectional view
of a parking brake spring biased in an idle position
thereof; and
Fig. 5 is an exploded perspective view of a
pair of parking brake forming part of the disc brake
assembly of Fig. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Now referring to the drawings, an in
particular to Figs. 1 and 3, a disc brake assembly 10
suited for heavy road vehicles, such as trucks,
busses, tractors or trailers, will be described.
As illustrated in Fig. 1, the disc brake
assembly 10 comprises a housing 12 adapted to be
mounted on an axle 14 of a vehicle for housing a pair
of axially spaced-apart ventilated discs 16 and 18
adapted to be connected to the hub 20 of a wheel (not
shown) for rotative movement therewith, as described
in United States Patent 5,205,380 issued on April 27,
1993 to Paquet et al..
A pair of mechanically linked identical
parking brakes 22a, 22b are housed in respective
cylindrical shells 24a and 24b secured on opposed
sides of the housing 12. The security or parking
brakes 22a and 22b are mechanically connected with a
disc brake sub-assembly 26 (Fig. 3) which is, in
turn, operatively connected to the pedal brake (not
shown) of the vehicle to act as the main brake of the
vehicle to control the speed thereof when the latter
is in operation.
As shown in Fig. 2, the parking brakes 22a
and 22b are mechanically linked and operated by a
brake actuator including a pneumatic cylinder 28
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extending therebetween. The pneumatic cylinder 28
includes a cylindrical housing 30 and a piston rod 32
normally biased in a retracted position by a spring
(not shown) provided within the cylindrical housing
30. As shown in Fig. 5, the piston rod 32 is
pivotally connected at 34 to a cam 36a which is, in
turn, pivotally mounted at 35 to a bracket 38a
secured onto the shell 24a. Likewise, the housing 30
is pivotally mounted at 40 to a cam 36b which is, in
turn, pivotally mounted to a bracket 38b secured onto
the shell 24b. Therefore, when the biasing force of
the spring (not shown) of the pneumatic cylinder 28
is overcome by the air pressure directed into the
housing 30 via conventional fluid lines (not shown) ,
the piston rod 32 will slide axially out of the
housing 30 to an extended position thereof, thereby
causing the cams 36a and 36b to rotate in opposed
directions, as depicted by arrows 39a and 39b in Fig.
1, respectively. As seen in Fig. 5, a brace member 42
extends between the brackets 38a and 38b to
structurally unify the same and increase the rigidity
of the assembly. The brackets 38a and 38b have
respective bottom through bore 41a and 41b for
receiving corresponding tubular necks 43a and 43b
formed on respective top surfaces of the shells 24a
and 24b. The term cam is herein intended to encompass
any rotating or sliding piece of any definite shape
for imparting a desired movement to the pushing
members 44a and 44b. For instance, a sliding wedge
defining an inclined surface could also be used to
displace the pushing members 44a and 44b. It is also
contemplated to use a pantograph linkage or a pair of
scissor links in lieu of a cam to transmit a movement
to the pushing members 44a and 44b.
Referring now to Fig. 4, the action of the
carn 36b on the parking brake 22b, as well as the
structural details of the latter will now be
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described. The interaction between the cam 36a and
the parking brake 22a is similar to that of the cam
36b and the parking brake 22b and, thus, the
duplicate description thereof will be omitted. The
structural details of the parking brake 22a, which
are identical to those of the parking brake 22b, will
not be repeated for brevity.
As seen in Fig. 4, the parking brake 22b
includes a pushing member 44b mounted for axial
movement within the shell 24b and having a
cylindrical stem portion 46b extending outwardly of
the shell 24b through a cylindrical passage 48b
defined by the tubular neck 43b thereof . The cam 36b
has a curved cam surface 50b for engaging a domed-
shaped terminal distal end 52b of the cylindrical
stem portion 46b. Upon rotation of the cam 36b in the
direction indicated by arrow 54, the pushing member
44b will be pushed axially into the shell 24b due to
the curvature of the cam surface 50b.
The pushing member 44b has three
circumferentially spaced-apart ratchet arms 55b, 57b,
59b (Fig. 5) pivotally mounted thereto for engagement
with a pawl provided in the form of an annular ring
61b loosely fitted about a piston head 56b securely
mounted to a spring-loaded pusher or piston 58b. More
particularly, the annular ring 61b has a beveled
bottom rim 63b for mating engagement into axially
spaced-apart interdental spaces or notches 65b
defined on respective inner surfaces of the ratchet
arms 55b, 57b and 59b. The ratchet arms 55b, 57b and
59b are normally biased radially inwardly to a closed
position thereof against the annular ring 61b by an
annular spring member 66b encircling the lower ends
of the arms 55b, 57b and 59b. The piston 58b has a
stem 68b having a radially enlarged end portion 70b
from the periphery of which depends a cylindrical
skirt 72b defining an annular seat 74b about the stem
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68b for receiving one end of a compression spring
76b. The other end of the spring 76b is abutted
against a spider 77b mounted on the axle 14 to
support the housing 12 and receive the actuator of
the disc brake sub-assembly 26. An annular dish
member 78b extends about the skirt 72b and is urged
against the free terminal ends of the arms 55b, 57b
and 59b by a second compression spring 80b
concentrically disposed about the first spring 76b
and having a first end abutting against the dish
member 78b and a second opposed end received in an
annular seat 79b defined in the spider 77b. The
second spring 80b normally urges the dish member 78b
against the arms 55b, 57b and 59b to resist the axial
displacement of the pushing member 44b and, thus,
allow the radial deployment of the arms 55b, 57b and
59b when the piston 58b is drawn against the spring
76a in response to the activation of the disc brake
sub-assembly 26 to brake or control the speed of the
vehicle, as will be explained hereinafter.
The piston 58a and 58b are structurally
connected to an annular pressure plate 82 (see Fig.
3) by conventional fastening elements (not shown).
Therefore, the axial displacement imparted to the
pushing members 44a and 44b by the rotational
movement of the cams 36a and 36b and transferred from
the pushing members 44a and 44b to the pistons 58a
and 58b via the ratchet arms 55a, 55b, 57a, 57b, 59a,
59b and the annular rings 61a and 61b, will be
communicated to the pressure plate 82 which forms
part of the main brake, herein referred to as the
disc brake sub-assembly 26.
As seen in Fig. 3, a plurality of brake
shoe lining segments 84 forming a lining ring or,
alternatively, a one-piece lining ring are/is mounted
to the front surface of the pressure plate 82
adjacent a radial friction surface 86 of the disc 16.
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A second brake shoe lining ring 88 is mounted to an
axially movable intermediate annular plate 90
adjacent a second radial friction surface 92 of the
disc 16 opposite the first friction surface 86
thereof. The intermediate plate 90 is slidably
mounted to the pressure plate 82. As seen in Fig. 3,
the intermediate plate 90 includes a plurality of
axially extending fingers 94 which are slidably
receive in corresponding channels 96 formed on an
axially extending portion of the pressure plate 82. A
third brake shoe lining 98 (Fig. 1) is mounted to the
intermediate plate 90 opposite the second brake shoe
lining 88 adjacent a radial friction surface (not
shown) of the second disc 18. A fourth stationary
brake lining (not shown) is mounted within the
housing 12 adjacent a second friction surface (not
shown) of the second disc 18 opposite the first
friction surface thereof.
When the vehicle is not in operation, the
pneumatic cylinder 28 is depressurized so as to
retract the piston rod 32 and cause the rotation of
the cams 36a and 36b in the direction indicated by
arrows 39a and 39b in Fig. 1. The rotational movement
of the cams 36a and 36b will cause the pushing
members 44a and 44b to be pushed within respective
shells 24a and 24b, thereby pushing the pistons 58a
and 58b and the annular dish members 78a and 78b
against the springs 76a, 76b and 80a, 80b,
respectively. The pistons 58a and 58b will then push
on the pressure plate 82 which will, in turn, press
the movable brake shoe lining 84 against the friction
surface 86 of the first disc 15 which is mounted for
limited axial movement on the axle 14 via a spline
arrangement (not shown), as described in United
States Patent No. 5, 205, 380 issued to Paquet et al .
Therefore, the first disc 16 will also be pushed
against the second brake shoe lining 88 which will,
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in turn, push the intermediate plate 90, and the
third brake shoe lining 98 against the second disc 18
which will move axially against the stationary brake
shoe lining (not shown).
When the pneumatic cylinder 28 is
pressurized, the springs 76a and 76b act on the
pistons 58a and 58b to maintain the brake shoe
linings 84, 88 and 98 out of engagement with the
discs 16 and 18, thereby allowing the discs 16 and 18
to rotate freely with the associated wheel (not
shown) .
When the vehicle is operated, the parking
brakes 22a and 22b are disabled, i.e. the pneumatic
cylinder 28 is pressurized, and the speed of the
vehicle is controlled by a pneumatic brake actuator
100 (Fig. 3) mounted within the spider 77b for
selectively pushing the pressure plate 82 towards the
discs 16 and 18 to engage the movable brake shoe
linings 84, 88 and 98 and the stationary brake shoe
lining (not shown) with the radial friction surfaces
of the discs 16 and 18, as described hereinbefore
with respect to the parking brakes 22a and 22b. As
the pressure plate 82 is pushed by the pneumatic
brake actuator 100, the pistons 58a and 58b are
pulled against the springs 76a and 76b thereof. As
seen in Fig. 4, the piston head 56b has a flange 102b
which is axially spaced from the annular ring 61b to
define therewith a play 104b when the piston 58b is
at rest, i.e. when the piston 58b is not solicited by
external axial forces. It is understood that a
similar play exist between the piston head 56a and
the annular ring 61a. These plays correspond to the
play existing between the brake shoe linings 84, 88
and 98 and the discs 16 and 18 when the brake
assembly 10 is not operated and the discs 16 and 18
are free to rotate.
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Therefore, when the pneumatic actuator 100
is activated to displace the pressure plate 82, the
pistons 58a and 58b will travel with the pressure
plate 82 over an axial distance corresponding to the
play 104b. Accordingly, the annular rings 61a and 61b
will remain trapped in the first level of notches 65a
and 65b. However, when the brake shoe linings 84, 88
and 98 will become worn, the thickness thereof will
reduce and consequently the displacement of the
pressure plate 82 and the pistons 58a and 58b
necessary to effect braking will increase. At a
certain level of wear of the brake shoe linings 84,
88 and 98, the displacement of the pressure plate 82
and the pistons 58a and 58b under the governed of the
pneumatic operator 100 will be such that the annular
rings 61a and 61b will be drawn by the piston heads
56a and 56b, thereby causing the radial deployment of
the arms 55a, 55b, 57a, 57b, 59a and 59b which are
retained against axial movement by the spring loaded
dish members 78 and 78b, to allow the annular rings
61a and 61b to move axially relative to the arms 55a,
55b, 57a, 57b, 59a and 59b beyond the first level of
notches 65a and 65b thereof. V~lhen the pressure
exerted by the pneumatic actuator 100 is released,
the springs 76a and 76b will urge the pistons 58a and
58b and the annular rings 61a and 61b towards their
original position but the respective beveled rims 63a
and 63b of the annular rings 61a and 61b will fall
into the second level of notches 65a and 65b of the
arms 55a, 55b, 57a, 57b, 59a and 59b, which tend to
return to their original closed position under the
biasing force of the annular spring 66a and 66b,
thereby preventing the p~.stons 58a and 58b from
returning to their original resting position.
When the brake shoe linings 84, 88 and 98
will become further worn, the annular rings 61 and
61b will automatically fall in the next level of
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notches 65a and 65b and so on. This mechanism allows
to automatically compensating for the wear of the
brake shoe linings 84, 88 and 98 to maintain the
original adjustment of the parking brakes 22a and 22b
irrespectively of the condition of the brake shoe
linings 84, 88 and 98.
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