U.S. patent application number 09/884558 was filed with the patent office on 2001-10-18 for brake monitoring system.
Invention is credited to Heron, Walter E., Osterman, Paul S..
Application Number | 20010030602 09/884558 |
Document ID | / |
Family ID | 24039378 |
Filed Date | 2001-10-18 |
United States Patent
Application |
20010030602 |
Kind Code |
A1 |
Osterman, Paul S. ; et
al. |
October 18, 2001 |
Brake monitoring system
Abstract
A vehicle brake monitor for a brake actuator including a
housing, a reciprocal push rod extending through an opening in the
housing and a stone shield mounted in the housing opening. An
annular sleeve surrounds the push rod which is integrally formed of
plastic including opposed sleeve portions which are generally
semicircular in cross-section and a longitudinal integral flexible
hinge portion interconnecting the adjacent sides of the sleeve
portions, such that the annular sleeve may be received on the push
rod, and an adjustable connector element interconnecting the
opposed sides of the sleeve portions. The sleeve includes an
elongated magnet, preferably a ceramic magnet having face portions
which are magnetized with adjacent north and south poles and the
stone shield includes a Hall-effect sensor which senses the
location of the sleeve as the push rod reciprocates through the
stone shield.
Inventors: |
Osterman, Paul S.; (Eugene,
OR) ; Heron, Walter E.; (Veneta, OR) |
Correspondence
Address: |
HOWARD & HOWARD ATTORNEYS, P.C.
THE PINEHURST OFFICE CENTER, SUITE #101
39400 WOODWARD AVENUE
BLOOMFIELD HILLS
MI
48304-5151
US
|
Family ID: |
24039378 |
Appl. No.: |
09/884558 |
Filed: |
June 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09884558 |
Jun 19, 2001 |
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09512504 |
Feb 24, 2000 |
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6255941 |
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Current U.S.
Class: |
340/453 ;
340/454 |
Current CPC
Class: |
F16D 66/028 20130101;
F16D 65/28 20130101; B60T 17/22 20130101; B60T 17/08 20130101; F16D
66/025 20130101 |
Class at
Publication: |
340/453 ;
340/454 |
International
Class: |
B60Q 001/00 |
Claims
1. A vehicle brake monitor, comprising: at least one service
chamber defined by a cup shaped housing and a cover; said housing
defining an opening having a pushrod for actuating a brake slidably
inserted therethrough; a sleeve circumscribing said pushrod and
defining a pocket having an elongated magnet disposed therein
oriented generally parallel to an axis of said pushrod, wherein
said sleeve derives reciprocating movement through said opening
from said pushrod; a stone shield circumscribing said sleeve and
being positioned adjacent said housing substantially sealing said
opening around said sleeve thereby preventing stones and debris
from entering said chamber through said opening, said stone shield
comprising two interconnecting parts having a sensor disposed in
one of said parts for sensing the location of said magnet relative
to said stone shield when said sleeve is reciprocating through said
opening.
2. A vehicle brake monitor set forth in claim 1, wherein said
sleeve includes a key and said stone shield includes a keyway
guiding said sleeve in a longitudinal direction through said
opening thereby maintaining said magnet in a position proximate to
said sensor.
3. A vehicle brake monitor set forth in claim 1, wherein said
sensor comprises a Hall effect sensor potted in one of said
interconnecting parts of said stone shield proximate to said magnet
thereby determining the location of said pushrod by detecting a
change in magnetic field emitted by said magnet.
4. A method of assembling a brake monitor for monitoring the
disposition of a brake, comprising the steps of: affixing a sensor
to a stone shield utilized to seal an opening in a service chamber
of a brake actuation assembly; positioning a sleeve having a magnet
affixed thereto onto a pushrod of said brake actuation assembly;
adjusting the position of said sleeve on said pushrod thereby
positioning said magnet in a fixed location relative to said
pushrod; inserting said pushrod into said opening disposed in said
service chamber through said stone shield; and adjusting the
position of said sensor affixed to said stone shield relative to
said magnet disposed in said sleeve to monitor the location of said
pushrod.
5. A method as set forth in claim 4 further including the step of
clamping said sleeve onto said pushrod thereby affixing the
location of said magnet relative to said pushrod.
6. A method as set forth in claim 4 wherein said step of inserting
said pushrod through said stone shield is further defined by
securing semicircular sections of said stone shield around said
pushrod.
7. A method as set forth in claim 4 wherein said step of adjusting
the position of said sensor relative to said stone shield is
further defined by inserting a key on said sleeve through a keyway
on said stone shield.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an improved brake
monitoring system, particularly for use on heavy vehicles, such as
a tractor and trailer combination, buses and the like, having a
spring brake actuator.
BACKGROUND OF THE INVENTION
[0002] Heavy-duty trucks, buses and other large vehicles are
typically equipped with a pneumatic brake actuating system. The
brake actuating system typically applies air under pressure to a
service chamber of a brake actuator to move a diaphragm in a first
direction. A push rod typically moves with the diaphragm and the
push rod is connected to a linkage which actuates the vehicle
brakes. An emergency chamber having a power spring and a second
diaphragm is typically mounted on the service chamber and is
operable to move the push rod and actuate the brakes in the event
that the pneumatic vehicle system fails or when the vehicle is
turned off when the vehicle is parked. Thus, the emergency chamber
serves as an emergency braking system for the vehicle and a parking
brake.
[0003] A brake actuator has a predetermined amount of available
movement of the push rod or stroke of the push rod. The amount of
movement of the push rod required to fully actuate the braking
system of the vehicle should be carefully monitored, such that it
is within the stroke of the push rod of the brake actuator.
Excessive movement of the push rod can be created by one of several
factors.
[0004] A brake actuator has a predetermined amount of available
movement of the push rod or stroke of the push rod. The amount of
movement of the push rod required to fully actuate the braking
system of the vehicle should be carefully monitored, such that it
is within the stroke of the push rod of the brake actuator.
Excessive movement of the push rod can be created by one of several
factors. Typically, excessive movement of the push rod is due to
brake lining wear. As the brakes wear, more movement of the push
rod is required to actuate the brakes. Further, as the linkages and
connections between the push rod and the linkages, et cetera, bend
or become loose or excessively worn, additional push rod movement
may be required to actuate the brakes. A combination of these
several factors may sometimes cause the amount of push rod movement
required to actuate the brakes approach the available push rod
movement or stroke available from the brake actuator. As will be
understood, this is an undesirable situation.
[0005] The prior art has proposed various methods and apparatus to
monitor the push rod movement during actuation of the brake and
provide some indication to an operator as to when there is
excessive push rod movement, which is referred to as "overstroke."
As will be understood, a determination of when there is excessive
push rod movement or overstroke is dependent upon the designed or
rated stroke of the brake actuator. For example, the push rod of a
typical brake actuator includes a brightly colored ring, which may
be painted on the push rod, which indicates an overstroke condition
when the ring extends out of the brake actuator during actuation of
the brakes. The ring may, however, be difficult to see because of
the location of the brake actuators beneath the truck or trailer
and accumulated road debris. Automatic slack adjusters located
between the push rod and the foundation brake are also
conventionally used, wherein the slack adjuster incrementally
adjusts to compensate for slack in the braking system and to
decrease the required push rod movement.
[0006] The prior art has also proposed various electronic
monitoring systems which generally monitor either the stroke of the
push rod or the movement of the linkages between the push rod and
the foundation brake including the slack adjuster. However, there
are several obstacles to be overcome. First, powering and
monitoring electronic indicators on each brake actuator of an
18-wheel vehicle is costly. Further, the hostile environment in
which the brake actuators are mounted beneath the vehicle can
damage the monitoring system, particularly where there are exposed
pistons, sleeves, sensors, et cetera. Finally, where the stroke of
the push rod is monitored by the brake monitoring system, it is
essential that the push rod stroke monitoring system be accurately
assembled on the brake actuator and be able to withstand the
hostile environment of the brake actuator. Finally, it is desirable
that the components of the brake monitoring system be easily and
accurately assembled on the brake actuator without special
tools.
SUMMARY OF THE INVENTION
[0007] The present invention relates to an improved brake
monitoring system which may include a plurality of brake monitors
mounted on each of the plurality of brake actuators of a vehicle.
As set forth above, a conventional brake actuator includes a
housing having an opening therethrough, a reciprocal rod or push
rod extending through the housing opening and typically an annular
stone shield mounted within the housing opening surrounding the
push rod preventing debris from entering the brake actuator
housing.
[0008] In the improved brake monitoring system of this invention,
an improved elongated annular sleeve is received around the push
rod which is fixed relative to the push rod and contains one of the
sensor elements. The other sensor element is fixed relative to the
brake actuator housing, preferably in the stone shield. The
improved annular sleeve in the brake monitoring system of this
invention is integrally formed of plastic, including opposed sleeve
portions, generally semicircular in cross-section, and a
longitudinal integral flexible hinge portion interconnecting the
adjacent first sides of the opposed generally semicircular sleeve
portions, thereby permitting the sleeve to be molded in one piece
and the sleeve portions to be received around the rod following
assembly of the brake actuator. In the most preferred embodiment of
the sleeve, the opposed sides of the generally semicircular sleeve
portions, spaced from the integral flexible hinge portion, include
integral connector elements for interconnecting the second sides of
the sleeve portions. Thus, the sleeve may be formed as an integral
molded plastic part which may be easily and accurately assembled on
the push rod. The sleeve assembly further includes an adjustable
locking clamp, preferably comprised of identical semicircular
plastic components, which permit adjustment of the sleeve on the
push rod following assembly and clamping of the sleeve to the push
rod. In the disclosed and preferred embodiment, the connector
element includes a plurality of opposed spaced male and female
connector elements which are integrally formed on the second sides
of the sleeve, permanently attaching the second sides of the
generally semicircular sleeve portions upon receipt of the sleeve
on the rod. The clamp includes a pair of opposed resilient clamping
members which surround the rod and the rod preferably includes a
grooved portions for receipt of the semicircular resilient clamping
members and accurate location of the sleeve relative to the push
rod.
[0009] In the most preferred embodiment of the vehicle brake
monitor of this invention, the sensing element in the sleeve is an
elongated bar-shaped magnet and the sensing element in the stone
shield is a Hall-effect sensor which may be utilized to
continuously monitor the location of the sleeve during actuation of
the brake actuator by continuously monitoring the magnetic field of
the elongated bar-shaped magnet. In the most preferred embodiment,
the magnet has a first longitudinal portion which is magnetized on
one face to define a north magnetic field and a second longitudinal
portion which is magnetized on an adjacent face to define a south
magnetic field. The most preferred magnet is a ceramic magnet able
to withstand the adverse temperature conditions experienced by
brake actuators, wherein the faces of the first and second portions
opposite the sensor in the stone shield are magnetized as set forth
above. As set forth below, a brake monitoring system having a
magnet as described and a sensor in the stone shield may be
utilized to monitor an overstroke condition, wherein the push rod
extends out of the brake actuator housing beyond the rated stroke
indicating wear of the foundation brake or misalignment or wear of
the linkages described above, a dragging brake condition, wherein
the push rod does not fully retract into the brake actuator, a
normal stroke condition and a nonfunctioning brake actuator.
[0010] As will be understood, it is necessary to maintain the
orientation of the sensing element in the stone shield opposite the
sensing element in the sleeve in the improved vehicle brake
monitoring system of this invention. This is accomplished in the
vehicle brake monitoring system of this invention by providing a
keyway slot in the stone shield and an elongated longitudinally
extending radial key on the sleeve which is slideably received in
the keyway in the stone shield, thereby maintaining the orientation
of the sleeve relative to the stone shield during actuation of the
brake. The vehicle brake monitoring system of this invention is
thus easy to assemble accurately on the brake actuator and the
brake actuator push rod stroke monitoring system of this invention
is rugged and able to withstand the adverse conditions encountered
by the brake actuator. Other advantages and meritorious features of
the vehicle brake monitoring system of this invention will be more
fully understood from the following description of the preferred
embodiments, the claims and the appended drawings, a brief
description of which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a side partially cross-sectioned view of a brake
actuator having a preferred embodiment of the vehicle brake
monitoring system of this invention;
[0012] FIG. 2 is an enlarged side partially cross-sectioned view of
FIG. 1 as indicated by the encircled portion;
[0013] FIG. 3 is a side partially cross-sectioned view of FIG. 1 as
indicated by the encircled portion;
[0014] FIG. 4 is an exploded view of the sleeve and adjusting clamp
assembly prior to assembly on the push rod; and
[0015] FIG. 5 is an exploded side elevation of the components of
the stone shield.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] As described above, the brake monitoring system of this
invention is particularly, but not exclusively, adapted for use
with a conventional brake actuator, such as the brake actuator 20
shown in FIG. 1. A brake actuator 20 includes a housing 22 which,
in the disclosed embodiment, includes a cup-shaped case 24 and a
cup-shaped cover 26. The case 24 includes a radial flange 28 and
the cover includes an opposed radial flange 30. The rim portion 31
of the flexible diaphragm 32 is received between the flange
portions 28 and 30 of the case 24 and cover 26, respectively, and
the flange portions are clamped together by a clamp 34. During
assembly of the brake actuator, the flange portions 28 and 30 are
pressed together against the rim portion 31 of the flexible
diaphragm 32 and clamped in place by the clamp 34. The clamp 34 may
be a conventional bolted clamp band as known in the prior art or a
continuous ring which is deformed in place to permanently secure
the cover 26 on the case 24 after assembly of the brake
actuator.
[0017] The push rod 36 includes a piston plate 38 which is biased
against the central portion of the diaphragm 32 by return spring
48. The free end 40 of the push rod 36 includes a clevis 42 for
attachment of the push rod 36 of the brake actuator to a linkage or
slack adjuster attached to the foundation brake (not shown). The
brake actuator is rigidly secured generally to a bracket 59 by
mounting bolts 50. The mounting bolts 50 include a head portion 52
and a shank portion 54 which extend through openings 56 in the case
24. The case is then secured to the bracket 59 by nuts 58 which are
threadably received on the threaded end portion of the shank 54.
The case 24 includes an opening 60 which receives the reciprocal
push rod 36 and a stone shield 62 is located in the case 24
surrounding the opening 60 as described hereinbelow.
[0018] A pneumatic connector 44 is connected to the pneumatic
braking system of the vehicle (not shown) by line 46. Upon
actuation of the vehicle brakes, air under pressure is received
through line 46, which applies pressure through port 45, driving
the diaphragm 32 upwardly in FIG. 1 against the piston plate 38 and
the return spring 48. The cup-shaped diaphragm 32 inverts (as shown
in phantom) against the piston plate 38, driving the push rod 36
through the opening 60 in the case 24, actuating the foundation
brakes of the vehicle (not shown). In a typical heavy-duty vehicle,
the depression of the brake pedal (not shown) pressurizes the line
46, which drives the diaphragm to invert and actuate the foundation
brake of the vehicle (not shown). Upon release of the brake pedal,
the pressure in line 46 returns to zero and the return spring 48
pushes the piston plate 38 downwardly in FIG. 1 to return the
diaphragm to the position shown in FIG. 1. As will be understood,
brake actuators 20 of the type shown in FIG. 1 may be mounted in
any orientation, generally beneath a truck or the trailer, wherein
each axle includes a brake actuator as shown. In a typical
application, however, the brake actuator assembly may also include
an emergency chamber (not shown) generally mounted in piggyback on
the service chamber shown. In such applications, the cover 26 may
be replaced by a flange case which defines a service chamber 64 and
an emergency chamber (not shown) and the emergency chamber is
enclosed by a separate cover as disclosed more fully in U.S. Pat.
No. 4,960,036 assigned to the assignee of this application. As will
be understood, however, the brake monitoring system of this
invention is not limited to the type or configuration of the brake
actuator. For example, the brake actuator may be a double diaphragm
brake actuator, a piston-type brake actuator having annular seals
or a rolling diaphragm.
[0019] As set forth above, the brake monitoring system of this
invention is specifically adapted to monitor the position of the
push rod 36 as it reciprocates through the opening 60 in the
housing 22. More specifically, as described below, the brake
monitoring system of this invention is adapted to monitor several
conditions of the brake actuator including overstroke, wherein the
push rod 36 extends beyond the intended or rated limit of the
stroke indicating, for example, a worn brake, a dragging brake
condition, wherein the push rod does not return to the ready
position shown in FIG. 1, a nonfunctioning brake actuator and a
normal stroke condition. The brake monitoring system of this
invention may also be utilized to monitor the continuous movement
of the push rod 36 during its braking cycle.
[0020] The improved sleeve assembly of the vehicle brake monitor
system of this invention can best be understood from the exploded
view of FIG. 4. The integral sleeve 66 includes opposed sleeve
portions 68 and 70, which are generally semicircular in
cross-section, and an integral flexible hinge portion 72 which
extends longitudinally and integrally joins the adjacent sides 67
and 69 of the sleeve portions 68 and 70, respectively. As will be
understood from the following description of the assembly, one or
the other of the opposed sleeve portions 68 and 70 may extend
slightly greater than one half of a circle (semicircular), such
that one of the sleeve portions snaps on the push rod 36, provided
the combination of the two sleeve portions define an annular sleeve
which surrounds the push rod. Each of the generally semicircular
sleeve portions 68 and 70 include a generally semicircular body
portion 74 and radial generally semicircular ribs 76 which are
longitudinally spaced and integral with the body portion 74. A
longitudinally extending pocket 78 is defined in one of the opposed
sleeve portions 70 which receives the magnet 80 described more
fully herein below. One of the sleeve portions 68 and 70 further
includes integral male connectors 82 and the other of the sleeve
portions 70 include socket-like female connectors 84. The male
connectors 82 each include an enlarged head 86 and a groove 88
beneath the head and the female connectors each include internal
ribs 89 which receive and lock the head portions 86 in the female
connectors 84, such that the male and female connectors 82 and 84
permanently interconnect the open sides of the sleeve portions 68
and 70 when the sleeve 66 is received around the push rod 36 as
shown by arrow 90 and in FIG. 1.
[0021] The sleeve is accurately located on the push rod by an
adjustable clamp 91 (see FIG. 1) by identical generally
semicircular clamp members 92 best shown in FIG. 2. The clamp
members each include an integral male connector 94 and a female
socket or connector 96. The male connectors 94 each include an
enlarged head portion 98 and a groove 100 adjacent the head. The
female connectors each include a plurality of ribs 102 which
receives the head 98 of the male connectors 94 to permanently
connect the clamp members. Each of the identical clamp members 92
also include generally semicircular pockets 106 which receive the
generally semicircular locking inserts 108. As shown in FIG. 4,
each of the locking inserts includes flat end portions 110 which
are slideably received and aligned in the slots 114 of the
semicircular pockets 106, accurately aligning the locking inserts
108 in the pockets 106. The clamp members 92 further include
gripping pockets 116 used during assembly of the clamp members 92
on the push rod as described below.
[0022] The stone shield 62 includes a radial portion 118 which
overlies the inside surface of the cup-shaped case 24 as best shown
in FIG. 3. In the preferred embodiment, the stone shield 62 is
formed of two generally semicircular components 122 and 124 as
shown in FIG. 5. One of the components 124 includes integral male
connector portions 126 and the other of the components 122 includes
female connector portions 128. Further, one of the components of
the stone shield 62 includes a longitudinal slot or keyway 130 and
the sleeve includes a radial longitudinally extending rib or key
132 as shown in FIG. 4. As described below, the longitudinally
extending key 132 of the annular sleeve 66 is slideably received in
the keyway 130 of the stone shield 62. The other component includes
a slot 134 which receives the male connector 136 of the sensor as
shown in FIG. 1. As described above, the sensor in the stone shield
is preferably a Hall-effect sensor 138 shown in FIG. 3. The sensor
is connected to the monitoring system of the vehicle by wire
140.
[0023] Having described a preferred embodiment of the components of
the brake monitoring system, the assembly and operation of the
brake monitoring system can now be described. First, the magnet 80
is assembled in the pocket 78 of the sleeve as shown in FIG. 4. In
the disclosed embodiment, the magnet is slip fit into the pocket 78
which is dimensioned slightly larger than the external dimensions
of the magnet. As described below, the magnet is magnetized to
define north and south face poles or fields which are maintained
opposite the sensor 138 as shown in FIG. 3. The sleeve 66 is then
assembled on the push rod 36 by closing the opposed sleeve portions
around the integral flexible hinge portion 72 around the push rod
as shown by arrow 90 and sliding the longitudinal key 132 on the
sleeve 66 into the keyway 130 of the stone shield, see FIGS. 4 and
5. As set forth above, in the preferred embodiment, the receipt of
the male connectors 82 on the sleeve in the female sockets or
connectors 84 permanently attaches the free sides of the sleeve,
preventing tampering or loosening of the connections. Generally,
the stone shield 62 will be assembled in the brake actuator 20 when
the brake actuator is assembled. That is, the components 122 and
124 are first preassembled and then received in the opening 60 of
the case member 24 prior to receipt of the return spring 48 and the
push rod 36, piston plate 38 and stone shield retainer 120
assembly. The diaphragm 32 is then received in the chamber 64 and
the cover 26 is assembled on the peripheral edge 31 and the
clamping member 34 is attached, clamping the diaphragm 32 as
described above.
[0024] The annular sleeve 66 is then adjusted on the push rod 36
prior to receipt of the annular clamp 91. As discussed below, the
sensor 138 in combination with the magnet 80 is adapted to monitor
and sense several conditions of the brake actuator, including an
overstroke condition, a dragging brake, a nonfunctioning brake
actuator and a normal stroke condition. Therefore, it is essential
that the sleeve 66 and the magnet 80 be accurately located on the
push rod and the location will depend upon the rated stroke of the
push rod 36. Following adjustment of the sleeve 66 on the push rod,
which is accomplished by sliding the sleeve on the push rod, the
sleeve is clamped on the push rod by the clamp members 92 as now
described. As best shown in FIG. 2, the push rod 36 includes a
plurality of spaced radial grooves 142 which are located on the
push rod approximately where the clamp ring 91 should be attached.
The generally semicircular clamp members 92 include a radial groove
142 and the free end of the sleeve includes a rib 144. The
generally semicircular clamp members 92 are then secured by forcing
the male connector portions 94 into the female sockets or
connectors 96, which permanently interconnects the clamp members
92. The radial grooves 142 then bite into the resilient locking
inserts 108, securing the clamp to the push rod and accurately
locating the sleeve 66 on the push rod as shown in FIG. 2.
[0025] The integral sleeve 66 is preferably formed by injection
molding a suitable plastic. The plastic must have sufficient
flexibility to permit closure of the sleeve portions 68 and 70
around the integral hinge portion 72. Further, the plastic must be
selected to withstand the adverse conditions encountered by a brake
actuator, particularly the wide range of temperature variations. A
brake actuator is typically rated for use in temperatures varying
from -40.degree. F. to +185.degree. F. A suitable plastic for this
application is a polypropylene copolymer, available from Amoco
Corporation, No. 10-3434. The adjustable locking clamp 91 may also
be formed of the same plastic material. However, the locking
inserts 108 should be formed of a resilient material able to
withstand the above-referenced temperature variations and
preferably a plastic material which has no memory, such that the
locking inserts will maintain clamping force against the push rod.
A suitable material for the locking inserts is Krayton.TM.
available from Shell Corporation. The stone shield may also be
formed of an elastomeric or plastic material, including the
above-referenced polypropylene copolymer. As set forth above, the
most preferred sensor 138 is a Hall-effect sensor which is
available from several sources, including Allegro of Worchester,
Mass.
[0026] Having described the preferred embodiments of the components
of the brake monitoring system of this invention, the operation of
the components may now be described. The magnet 80 may be a
continuous bar magnet, wherein the Hall-effect sensor continuously
senses a magnetic field of the magnet to determine the position of
the magnet in the annular sleeve 66. That is, each magnet has a
specific magnetic profile from its north pole to its south pole and
the Hall-effect sensor can determine the position of the magnet and
sleeve by sensing the changing magnetic field. The data received by
the Hall-effect sensor can then be processed through a computer and
the visual indicators can then be used to provide a direct readout
of the stroke of the push rod 36 on a continuous basis. In a
disclosed embodiment, however, the need for a complex computer
program for analyzing the location of the push rod and magnet has
been eliminated by utilizing a unique magnet in this application
which provides the data necessary to determine overstroke and
dragging brake conditions as set forth below.
[0027] The preferred embodiment of the magnet 80 in this
application is a magnet, wherein the face of the magnet opposite
the sensor may be magnetized, such as a ceramic or ferrite magnet,
such as a Grade 8 ceramic magnet available from Adams Magnetics of
Elizabethtown, N.J. By using suitable jigs, as known in the art, a
portion of one face may be magnetized with one magnetic field and
the adjacent face may be magnetized with the opposite magnetic
field. In the disclosed embodiment, one face 80N is magnetized with
a north magnetic field and the adjacent face 80S is magnetized with
a south magnetic field as shown in FIG. 4. The transition line 81
has no magnetic field. As will be understood by those skilled in
this art, the face opposite face 80N will have a south magnetic
field and the face opposite the face 80S will have a north magnetic
field. Thus, the Hall-effect sensor 138 shown in FIG. 3, which is
opposite the faces 80N and 80S of the magnet, can easily identify
the magnetic fields 80N and 80S and the transition line 81 as the
push rod 36 and the sleeve 66 reciprocate through the opening 60 of
the housing. The length of the magnetic faces 80N and 80S and the
transition line 81 will depend upon the stroke of the brake
actuator. In a typical brake actuator having a 2.5 inch stroke, for
example, the face 80S should be about 2 inches and the face 80N
should be about 1/2 inch. Brake actuators of the type disclosed in
this application generally have a stroke ranging from about 2.25 to
3 inches, wherein the face 80S should be approximately 3/4 of the
total length of the magnetic. In the fully retracted position of
the push rod 36 and sleeve 66 shown in FIG. 1, the sensor 138 (see
FIG. 3) is just off or above the end of the magnet 80. The
preferred Hall-effect sensor is a ratio metric linear Hall-effect
sensor, wherein the output is proportional to the input voltage and
the applied magnetic field. In a disclosed embodiment, the input
voltage is five volts. Thus, the output from the Hall-effect
without the magnetic field is 50 percent or 2.5 volts. Thus, the
output from the sensor in the fully retracted or rest position
shown in FIG. 1 is 2.5 volts. Then, when the operator depresses the
brake and the stoplight is on, pneumatic pressure through line 46
begins to invert the diaphragm 32, driving the piston plate 38,
push rod 36 and the magnet 80 in the sleeve 66 through the opening
60 in the housing and the output voltage increases up to a maximum
of 5 volts indicating a normal stroke condition. However, when the
sensor is located opposite the transition line 81 between the faces
having a south magnetic field and 80N having a north magnetic
field, the output voltage from the sensor again decreases to 2.5
volts or less in the north magnetic field, indicating an overstroke
condition. The output voltage drops further in the face 80N having
a north magnetic field. Thus, the brake monitoring system of this
invention can then indicate either a normal stroke condition or an
overstroke condition. As will be understood, the sensor must also
be connected to the brake light wiring.
[0028] The brake monitoring system of this invention can also sense
a dragging brake condition, wherein the brake actuator does not
fully retract to the position shown in FIG. 1. As set forth above,
when the operator releases the brake pedal, the pneumatic pressure
through line 46 returns to zero and the return spring 48 urges the
piston plate 38 downwardly in FIG. 1, withdrawing the push rod and
the sleeve 66 to the position shown. If the brake light is not on
and the return voltage from the sensor is 2.5 volts or less, the
system indicates a dragging brake. A dragging brake is also
indicated when the return voltage is greater than 2.8 volts. That
is, the brake actuator did not return to its ready position.
Further, the system may also be utilized to indicate a brake
actuator failure. That is, if the system receives a signal that the
brake light is on and the output voltage from the sensor is 2.5
volts or less, this indicates a brake failure. Finally, the sensor
will also indicate a sensor fault, wherein the output voltage is 1
volt or less. Thus, the brake monitoring system of this invention
will actually sense and indicate five functions of each brake
actuators, including an overstroke condition, a dragging brake, a
nonfunctioning brake actuator, normal stroke and sensor fault.
These conditions may, for example, be easily monitored by the
vehicle operator by flashing lights on the front of the trailer
opposite the back window of the tractor or truck, such as green for
normal stroke operation, red for overstroke, flashing red for
dragging brake, et cetera. Alternatively, the sensors may be
connected to a heads up display in the cab or a monitor in the cab.
Thus, this embodiment of the invention including a single magnet
having face portions opposite the sensors with opposite magnetic
fields eliminates the requirement for a complex computer system,
but simultaneously measures several conditions of each of the brake
actuators.
[0029] Thus, the brake monitoring system of this invention is
relatively simple to install, yet accurate, reliable and rugged.
Further, the brake monitoring system of this invention is able to
withstand the adverse conditions encountered by brake actuators,
including extreme temperature variations, without failure. For
example, Hall-effect sensors of the type described above are able
to withstand extreme temperature variations from -40.degree. F. to
+302.degree. F. The deviation of the ceramic magnet described above
is about 0.1% per .degree. C. and therefore experiences only about
12% decrease in the residual magnetic flux density or field
strength at 185.degree. F. and a 13% decrease at -40.degree. F. The
preferred polypropylene copolymer used for the sleeve 66,
adjustable clamp ring 91 and the stone shield 62 will also
withstand extreme temperature variations and road debris. Further,
as described above, the sleeve 66 is preferably molded in one
piece, eliminating errors in assembly and the sleeve may be
accurately adjusted before receipt of the clamp ring 91. As will be
understood, however, various modifications may be made to the
disclosed preferred embodiment of the brake monitoring system of
this invention within the purview of the appended claims. For
example, various sensors and magnets may be utilized and various
modifications may be made to the sleeve and clamp ring.
* * * * *