Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02520747 1994-11-29
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HEAVY DUTY ELECTRONIC BRAKE STROKE INDICATOR
BACKGROUND OF THE INVENTION
This application in general relates to an electronic stroke indicator which is
incorporated into the cylinder housing of a brake actuator in such a way that
it is
_ protected from damage from the other components in the brake actuator.
After routine wear, brake actuators typically begin to require adjustment, and
may have an undue amount of stroke. In such ~a condition it is said the brake
is out-
of stroke. The prior art has attempted to give warnings to operators of the
vehicle
when the brakes need adjustment. The indicators which have been incorporated
into
production units have typically been visual indicators. Thus, an indicator
such as
a colored stripe which should typically not be visual unless the brake is out
of stroke
is placed on the piston rod.
An operator would periodically check the brake, and if the colored stripe is
visible, the operator would have a signal that the brake requires adjustment.
Such
indicators, while quite valuable could still be improved. first, an indicator
that
requires visual identification positioned in the neighborhood of the brake is
~ often
exposed to mud or dirt. Thus, the visual indicator may not be readily visible.
In
addition, the visible indicators are tygicaUy positioned at the rear of the
vehicle.
An operator must periodically leave the vehicle to check the brakes. This
requires
the operator to perform periodic checks in order to insure that the brake does
not
become too far out of stroke.
Several electronic stroke indicators have been proposed, although they have
not been widely utilized in production brake or brake actuators. Typically,
these
units axe incorporated onto a piston rod and monitor the stroke of the piston
or the
piston rod. When an undue amount of stroke is sensed, a signal is sent to an
operator in the vehicle cab. While these proposed systems do address the
deficiencies in visual indicators, there have not been systems proposed which
would
~ be practically utilizable. The interior of the brake chamber includes a
number of
components which move relative to each other. ~ The proposed systems have
' typically included sensors within the chamber, in a location where they are
likely
to be damaged by other components. As one example, the sensors in a proposed
system are placed in the service brake chamber, in the general location of the
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spring. 'There has been no attempt to protect the delicate sensor and
associated
wires from being contacted by the spring and being damaged. A necessary
component of reliance on any electronic stroke indicator is a stroke indicator
system
which is reliable and operable for a relatively long period of time. The prior
art
systems which have not adequately protected the sensor and associated wires
may
not be as reliable as would be desirable. '
Other proposed sensors include indicators which are mounted on the piston
rod outwardly of the chamber away from the spring. The proposed units which
have indicators mounted on the piston rod outwardly of the chamber have not
necessarily solidly connected the indicator or the sensor to structure at a
fixed
location. As an example, in one proposed system, the sensor is mounted on a
rod
adjacent to the piston rod. An indicator is mounted on the piston rod. When
the
sensor or indicator units on the piston rod are not at fixed locations, the
reliability
of any out-of-stroke indication from the sensor is in question. This problem
is made
more severe since the outside area of the brake chamber is in a hostile
environment
exposed to dirt, rocks and other debris. Such debris could contact the sensor,
damaging the sensor, or misaligning the position of the various members.
Again,
the environment that the brake is disposed in is hostile, and a sensor placed
outside
of the brake chamber may not always function properly.
Thus, the prior art systems have been unable to provide a sensor system
which is protected from the operative elements of the brake, and which may be
relied upon to operate for a relatively long period of time.
SifMMARY OF THE INVENTION
This invention includes a sensor which is incorporated into a stone shield in
the brake chamber housing. The stone shield protects the sensor from
contacting
other operative components of the brake actuator. As an example, the stone
shield
will protect the sensor from contact by the spring.
In a disclosed embodiment of this invention, the stone shield is positioned
about the piston rod in the brake chamber housing. The shield incorporates
part of '
a sensor unit for determining an out-of stroke condition of a brake actuator.
In a
preferred embodiment of this invention, the stone shield which has a bore at
an
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inner peripheral surface extending radially inwardly from the inner peripheral
surface of a bore in the nominal brake housing. The stone shield functions to
surround the piston rod and limit the amount of debris which may enter into
the
brake chamber housing from the bore in the brake housing.
S In preferred embodiments of this invention, a wire is incozporated into the
stone shield leading from the sensor outwardly of the housing. The wire is
protected from the spring, which is typically found in the chamber housing, by
the
stone shield.
In a first preferred embodiment of this invention, a sensor is embedded into
- the stone shield, as are electric contact rings. A retainer for holding the
stone shield
within the housing has contacts which mate with contact rings in the stone
shield.
Wires lead from those contacts to a location outwardly of the housing.
In a second preferred embodiment a Hall Effect sensor is embedded into the
stone shield, when the stone shield is molded. A Iip at the outer peripheral
surface
of the stone shield receives the brake chamber spring such that the spring is
maintained in a position where the spring will not be likely tv contact any of
the
wires of the -sensor system.
In a third preferred embodiment, the stone shield incorporates a pair -of
contact switches, with a first inner contact switch actuating a first warning
indicator
as the brake begins to approach an out-of stroke condition. When a second
contact
switch contacts the structure on the piston, a second indicator light would
typically
be actuated which would give a warning that the brake is now fully out of
stroke.
In this third preferred embodiment, a contact member is preferably mounted
on the piston rod and has a contact portion extending radially outwardly from
the
outer surface of the piston rod. The contact switches are formed at
circumferentially spaced positions on the stone shield, and extend to varying
heights
to provide the two stroke indication levels.
In a fourth preferred embodiment of this invention, a load cell sensor is
incorporated into the stone shield to monitor the compression in the spring.
As the
- 30 brake approaches an out-of stroke condition, the piston moves beyond its
normal
position, thus compressing the spring beyond typical compression. This is
sensed
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by the load cell which then provides a signal to the operator that the brake
is
approaching an out-of stroke condition.
These and other features of the present invention can be best understood
from the following specifications and drawings, of which the following is a
brief
description.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross-sectional view through a first embodiment stroke indicator
according to the present invention.
Figure 2A is a perspective view of one portion of the stroke indicator
illustrated in Figure 1.
Figure 2B is a perspective view of a second portion of the stroke indicator
shown in Figure 1.
Figure 3 is a cross-sectional view through a second embodiment stroke
indicator.
Figure 4 is a cross-sectional view through a third embodiment stroke
indicator.
Figure 5 is a perspective view of a portion of the embodiment shown in
Figure 4.
Figure 6 is a cross-sectional view through a fourth embodiment stroke
indicator according to the present invention.
DETAILED DESCRIPTION OF THE PREFF~tRED EMBODllVIENT
Figure 1 shows a spring brake actuator 20, having a service side housing 22.
As shown, a piston 24 moves with a piston rod 26 through an opening 28 in the
housing 22. As also shown, a stone shield 30 has an inner peripheral bore 32
extending radially inwardly from the innermost extent of bore 28. Stone shield
30
functions to limit the amount of dirt or debris which may enter. the chamber
of the
housing 22.
A sensor 34 is embedded into the stone shield 28, and monitors the position
of a magnetic tape 36 molded onto piston rod 26. By monitoring the position of
magnetic tape 36, sensor 34 can determine if there is an undue amount of
stroke,
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WO 95116149 PCTNS94113616
thus indicating that the brake needs readjustment. A spring 38 abuts piston 24
at
one end, and abuts a stone shield retainer 40 at an opposed end. An outer
radial
surface 42 of retainer 40 receives spring 38. Retainer 40 includes a radially
inner
portion 44, which extends axially and then radially inwardly from the outer
portion
40. Contacts in inner portion 44 connect to contact rings 46 and 48 in stone
shield
30. The contact rings 46 and 48 connecting through the contacts provide an
electric
circuit from sensor 34 to a wire 50 extending outwardly of the housing. Wire
50
is connected to an appropriate control 51 to provide a signal to aw operator
in the
vehicle cab when an out-of stroke condition is sensed. Such indication can be
a
light, an audio warning, or any other known or typical warning signal.
As shown in Figure 2A, a stone shield 30 incorporates a sensor 34 which is
embedded into the molded stone shield over a portion of its circumferential
extent.
Contact rings 46 and 48 preferably extend around the entire circumference of
the
stone shield 30.
Figure 2B shows a detail of the retainer 40. A contact strip 52 is radially
aligned with the location of contact ring 46 and a second contact strip 54 is
radially
aligned with contact ring 48. Contacts strips 52 and 54 are each connected to
electrical connections 56, which are connected to wire 50. Since contact rings
46
and 48 extend around the entire circumference of the stone shield 30, the
relative
circumferential relationships of the retainer 40 and the stone shield 30 need
not be
carefully monitored. Rather, whatever the circumferential relationship, the
contact
strips 52 and 54 will contact the rings 46 and 48, respectively, thus
providing
electrical connection from the sensor 34 to the wire 50, and thus to control
51.
Figure 3 shows a second embodiment electronic stoke indicator 60. In
electronic stroke indicator 60, a single stone shield 62 incorporates a
radially outer
lip 63 holding ari end of spring 64. A Hall Effect switch 66 is embedded into
the
molded stone shield 62 and monitors the stroke of a piston and 67. As shown,
piston rod 67 incorporates a magnetic tape portion 68, and a nonmagnetic
section
70. The Hall Effect switch can sense as the portion 68 approaches, and can
provide
a signal of an out-of stroke condition. Switch 66 is connected by an embedded
wire
65 to wire 69 which Ieads from stone shield 62 outwardly through an opening 70
in the brake housing 61. Lip 63 provides an assurance that spring 64 is
maintained
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at a position where it is unlikely to contact wire 69. Thus, wire 69 is
protected
from damage from the spring 64.
As shown in Figure 4, a third embodiment indicator 80 incorporates a stone
shield 82 also having a radially outer lip 83 catching a spring 84. A radially
inner
end 86 of the spring 84 abuts piston contact member 88 having an end face 90
abutting piston 92. An outer contact portion 94 extends radially outwardly
from
surrounding portions of contact member 88. A first set of contact switches 96
is
positioned on stone shield 82 at an axially inner location and a second set of
contact
switches 98 is positioned on stone shield 82 at a relatively axially outer
location.
An inner peripheral surface 100 on contact switches 96 and 98 is formed jagged
to
ensure a good connection between the contact switches 96 and 98 and the
contact
portion 94 when it is at a location such as shown in phantom at 102. Contact
plugs
104 are connected to each contact switch 96 and 98 through an embedded
connector
and extend outwardly of the stone shield 82. The contact plugs 104 are connect
through a wire 106 to extend outwardly of the housing 81 through a plug member
108. The base of shield 82 is preferably a non-conductive plastic. The contact
switches are preferably steel or other conductive material. Again, lip 83
insures that
spring 84 is unlikely to contact any of the contact members 104, or wire 106.
In operation, as the piston approaches an out-of stroke condition, contact
portion 94 will initially contact the first set of contact switches 96. This
may be at
80 percent of the stroke. A signal would then be provided to the operator in
the
vehicle, such as described above. As the brake moves more out-of stroke,
portion
94 will eventually approach the second set of contact switches 98. At that
time, a
second more urgent signal will preferably be given. As an example, switch 96
may
actuate a yellow light whereas switch 98 may actuate a red light and an audio
warning. By providing the two indicators, one gives an operator advance notice
that
the brake actuator is approaching a condition that requires adjustment.
As shown in Figure 5, stone shield 82 incorporates lip 83, and contact plugs
104 connected with each contact switch 96 and 98 by embedded portions 105. The
contact 96 and 98 are preferably circumferentially spaced.
Figure 6 shows a fourth embodiment electronic stroke indicator 110
incorporated into the housing 111 of a brake actuator. Again, a spring 112
contacts
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a piston 113 having a piston rod 114 extending through a stone shield 116. In
the
instant case, the stone shield is incorporated into the bore 118 of the
housing 111.
Embedded into the stone shield 116 is a load cell 119, shown schematically.
The
load cell monitors the amount of compression in spring 112. As the piston 113
approaches an out-of stroke condition, the compression in spring 112
increases.
Load cell 119 senses such undue compression and is connected through an
embedded wire to provide a signal through wire 120. If compression beyond a
preset limit is sensed, a warning is sent. Wire 120 is molded into an end
surface
121 of the housing 11 I, and extends outwardly through a plug 122 in the outer
wall
of end wall 121. Thus, when the load cell l I9 senses undue stress in spring
112
a signal is sent to the operator.
The stone shields can be made of any material which is suitable for the
function of the stone shield. Preferably, a non-conductive material which may
be
molded to have the embedded sensors and electrical connections utilized. Tough
plastics would be suitable materials. The sensor elements themselves and the
other
electronics are all known electronic components.
The several embodiments all have in common that the sensor units are
somehow incorporated into a stone shield- member to protect the sensitive
sensor
elements from the other components in the brake, and in particular the spring.
Due
to the incorporation of the electronics into the stone shield, a sensor unit
is typically
provided with a long operating life. In addition, the units also are
ogeratable to
provide indications of levels of out-of stroke condition, as well as
monitoring the
load in the spring, which provides a good indication of an out-of stroke
condition.
Although preferred embodiments of this invention have been disclosed, a
worker of ordinary skill in the art would recognize that certain modifications
would
come within the scope of this invention. For that reason the following claims
should be studied in order to determine the true scope and content of this
invention.
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