WO2001071211A1

WO2001071211A1 - Brake monitoring system

Info

Publication number: WO2001071211A1
Application number: PCT/US2001/009281
Authority: WO
Inventors: Alan C. Lesesky; Wally V. Stegall
Original assignee: Indian Head Industries, Inc.
Priority date: 2000-03-22
Filing date: 2001-03-22
Publication date: 2001-09-27
Also published as: JP2003535739A; CA2402889A1; US6352137B1; JP4981230B2; CA2402889C; AU2001245951A1

Abstract

A vehicle brake monitor (42) for a brake actuator (20). The brake monitor includes a magnet (54) and a sensor (50) located within the magnetic field of the magnet and fixed relative to housing (22), and a shunt (58, 60) which is reciprocal with a brake actuator rod (28) between the magnet and the sensor which interrupts a signal between the sensor and the magnet when the shunt is located between the magnet and the sensor during reciprocal movement of the rod, signaling at least one position of the rod relative to the housing. The brake monitor includes a sensor sleeve (44) having two pairs of opposed magnets and sensors and a shunt sleeve (46) surrounding the brake actuator rod having a pair of circumferentially spaced shunts which reciprocates with the actuator rod between each of the pairs of sensors and magnets, sensing an overstroke condition, brake drag, failure and normal operation.

Description

BRAKE MONITORING SYSTEM

BACKGROUND OF THE INVENTION 1) TECHNICAL FIELD

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 plurality of spring brake actuators.

2) DESCRIPTION OF THE PRIOR ART

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 moves with the diaphragm and the push rod is connected to a linkage which actuates the vehicle bralces. In a piston-type brake actuator, the piston plate seals against the internal surface of the housing, eliminating the requirement for a diaphragm. 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.

A brake actuator has a predetermined amount of available movement 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 available 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, if 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 bralces approach the available push rod movement or

stroke available from the brake actuator. As will be understood, this is an undesirable situation. 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 may include a brightly colored ring, which may be painted on the push rod, indicating 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 bralce actuators beneath the truck or trailer and accumulated road debris. Automatic slack adjusters located between the push rod and the foundation bralce 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. 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 bralce 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 bralce

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 bralce actuator preferably without special tools.

SUMMARY OF THE INVENTION AND ADVANTAGES

The present invention relates to an improved bralce monitoring system which may include a plurality of bralce monitors mounted on each of the plurality of bralce actuators of a vehicle. As set forth above, a conventional bralce actuator includes a housing having an opening therethrough, a reciprocal piston 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. As set forth above, the improved vehicle brake monitor of this invention may be utilized with any bralce actuator which includes a housing and a piston or push rod reciprocable through an opening in the housing for actuation of a vehicle brake. A typical brake actuator includes a flexible cup-shaped diaphragm having a peripheral edge portion which is supported within the housing and a piston having a piston plate which is spring biased against the diaphragm by a return spring. The piston rod or push rod is reciprocable through an opening in the housing having a free end typically connected to a slack adjuster, which is connected to the foundation bralce of the vehicle. Upon actuation of the brake by the vehicle operator, the pneumatic pressure of the vehicle is received by the bralce actuator, inverting the flexible diaphragm and driving the piston rod through the opening in the brake actuator housing, actuating the braking system of the vehicle. As will be understood, however, the improved bralce monitor of this mvention may be utilized with any bralce actuator, including piston- type bralce actuators, wherein the piston plate or head is sealed against an inside surface of the brake actuator housing, eliminating the requirement for a cup-shaped diaphragm, and other types of bralce actuators. The bralce actuator may also include an emergency chamber having a power spring as is well known in the prior art.

The improved bralce actuator of this invention includes a sensor, such as a reed switch, and a generally opposed spaced magnet, which are fixed relative to the housing of the bralce actuator. As will be understood from the following description of the improved vehicle bralce monitor of this invention, the sensor is located relative to the magnet such that the sensor is within the magnetic field of the magnet, but is spaced from the magnet. Thus, the term "opposed" is not intended to limit the relative location of the magnet and sensor except as required for this application. For example, where the sensor is a reed switch, the normally open reed switch sensor is closed within the magnetic field of the magnet. The vehicle brake monitor further includes a

shunt having a predetermined length which is reciprocal with the bralce actuator rod between the magnet and the sensor. The shunt, for example, may be a ferrous metal or ferrous alloy strip which projects radially from the rod and reciprocates with the rod between the sensor and the magnet, interrupting the signal between the sensor and the magnet when the shunt is located between the sensor and the magnet during reciprocal movement of the rod signaling at least one position of the rod relative to the housing. Although in the preferred embodiment of the vehicle brake monitor, the shunt is located in a sleeve fixed to the rod and the opposed sensor and magnet are located in a sensor sleeve surrounding the rod, the entire assembly of sensor, magnet and shunt may be separate from the rod, provided the sensor and magnet are fixed relative to the housing and the shunt reciprocates with the rod. The vehicle bralce monitor of this invention may thus be utilized to indicate at least one condition of the bralce actuator, such as an overstroke condition, wherein the brake actuator is nearing or exceeds an overstroke condition, or a dragging bralce, wherein the brake actuator rod does not return to a "zero stroke" condition following actuation of the brakes.

In the most preferred embodiment of the bralce actuator of this invention, the brake monitor includes two pairs of generally opposed space magnets and sensors, which are fixed relative to the housing, and two shunts, each having a predetermined length or position relative to the longitudinal axis of the rod, which reciprocate with the push rod between each of the opposed pairs of sensors and magnets. By utilizing two pairs of magnets, sensors and shunts, several conditions of the brake actuator may be identified and monitored, including a dragging bralce, an overstroke condition, normal operation and a failure of the vehicle brake monitor for each brake actuator on the vehicle. As described more fully in a copending application Serial No. 09/091,057, filed November 30, 1998, assigned to the assignee of this application, each bralce monitor may include an RF transmitter which periodically transmits the condition of each bralce actuator to a controller. Alternatively, the bralce actuator monitor may be hardwired to the controller. The controller then signals the condition of each bralce actuator to the vehicle operator by conventional display, such as a heads up display in the vehicle cab or a conventional display panel.

In the preferred embodiment of the vehicle bralce monitor of this invention, the magnet and sensor are located in a sensor sleeve generally surrounding the bralce actuator rod. fn the most preferred embodiment, the sensor sleeve is a stone shield located within the bralce actuator housing opening surrounding the rod of the bralce actuator. In this preferred embodiment of the vehicle bralce monitor of this invention, the shunt is located hi a sleeve fixed to the brake actuator rod, wherein the shunt extends radially between the magnet and sensor during reciprocal movement of the sleeve on the rod. hi the most preferred embodiment, the shunt sleeve on the rod of the brake actuator includes two circumferentially spaced radially extending shunts which reciprocate with the push rod between each of the pairs of sensors and magnets. Because the shunts are of different lengths and/or spaced along the longitudinal axis of the rod, the bralce momtor can detect multiple positions of the rod relative to the brake actuator as described above. The most preferred embodiment of the shunt sleeve further includes a key or radially projecting rib and the sensor sleeve includes a radial slot or keyway which slideably receives the key on the shunt sleeve positioning the shunt sleeve relative to the sensor sleeve during reciprocal movement of the shunt sleeve and the bralce actuator rod. The vehicle brake monitoring system of this invention is thus relatively simple in design, rugged in construction and able to withstand the harsh environment required of brake actuators. Further, the bralce actuator monitor of this invention may be utilized to monitor various conditions of the bralce actuator including a dragging brake, overstroke, normal operation and a malfunctioning bralce actuator monitor, particularly where the sensor is a reed switch as described above. Other advantages and meritorious features of the vehicle brake monitor of this invention will be more fully understood from the following description of the preferred embodiments, the appended claims and the drawings, a brief description of which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a partial side partially cross-sectioned view of a preferred embodiment of a vehicle bralce monitor of this invention;

Figure 2 is a side elevation of the embodiment of the brake monitor shown in

Figure 1 without the bralce actuator; Figure 3 is a bottom view of the embodiment of the sensor sleeve shown in

Figures 1 and 2 prior to assembly;

Figure 4 is a side cross-sectional view of the brake momtor shown in Figure 4 in the direction of view arrows 4-4; Figures 5 and 6 are side elevations of the shunt sleeve shown in Figures 1 and 2 illustrating a preferred position of the shunts in the shunt sleeve; and

Figure 7 is an exploded side elevation of the components of the embodiment of the brake monitor illustrated in Figures 1 and 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As set forth above, the vehicle bralce monitor of this invention is particularly useful for monitoring the bralces of large or heavy vehicles having a plurality of brake actuators, such as the brake actuator 20 illustrated in Figure 1. The bralce actuator 20 illustrated in Figure 1 includes a housing 22 having a reciprocable piston 24. The piston 24 mcludes a piston head or plate 26, a piston rod or push rod 28 which is reciprocable through an opening 30 in the housing for actuation of the vehicle bralcing system. The rod 28 is conventionally threadably attached to a clevis 32 and the clevis 32 is conventionally attached to the slack adjuster of the vehicle braking system (not shown). The bralce actuator housing 22 is conventionally attached to a bracket (not shown) on the undercarriage of the vehicle, cab or tractor adjacent the vehicle axles by a plurality of mounting bolts 34 which threadably receive nuts 36 and washers 38. Upon actuation of the vehicle bralce by the operator, the piston 24 is driven by air pressure from the pneumatic bralcing system of the vehicle to drive the push rod 28 through housing opening 30 to actuate the bralcing system of the vehicle. A conventional brake actuator of the type illustrated includes a flexible diaphragm 40 and the pressurized air received in the brake actuator housing 22 inverts and drives the flexible diaphragm 40 against the piston plate 26, driving the rod 28 through the opening 30 in the housing to actuate the bralcing system of the vehicle. Upon deactivation of the bralce, such as release of the bralce pedal, the pressure in the housing 22 returns to zero and the piston 24 is moved upwardly in Figure 1 by a return spring (not shown) which reacts against the piston plate 26. The above description of the brake actuator 20 is conventional. As will be understood by those skilled in this art, the bralce monitor of this invention may be utilized with any brake actuator, including, for example, piston-type bralce actuators wherein the piston plate is sealed against the internal surface of the housing 22, eliminating the requirement for a diaphragm 40. The bralce monitoring system of this invention is specifically adapted to monitor the position of the push rod 28 as it reciprocates through the opening 30 in the housing 22. More specifically, the brake monitoring system of this invention is adapted to monitor several conditions of the bralce actuator, including an overstroke condition, wherein the push rod 28 extends beyond the intended or rated limit of the piston stroke, indicating, for example, a worn bralce, a dragging bralce condition, wherein the push rod does not return to the ready or zero position, a nonfunctioning bralce monitor and a normal stroke condition. It should also be understood that the bralce monitor must be able to withstand the extreme conditions encountered by bralce actuators located under a vehicle or trailer, including extreme temperature variations and road debris including water, salt and ice.

The illustrated preferred embodiment of the brake monitor 42 includes a sensor sleeve 44, which is fixed relative to the housing 22 and a shunt sleeve 42, which is fixed relative to the rod 28 by lock ring 44 during reciprocal movement of the piston rod 28 as described above. The sensor sleeve includes a sensor 50 connected by wire 52 to a monitor (not shown) and a magnet 54, such that the sensor 50 is located within the magnetic field of the magnet 54. The sensor 50 and magnet 54 may be potted in chambers or recesses defined in the sensor sleeve 44 by potting material 56 as described below. The shunt sleeve 46 includes magnetic shunts 58 and 60 which are received between the sensor 50 and magnet 54 interrupting a signal between the sensor and the magnet when a shunt is located between the sensor and the magnet during reciprocal movement of the push rod 28, thereby signaling at least one position of the rod 28 relative to the housing 22 as described below. A preferred embodiment of the sensor sleeve 44 will now be described with reference to Figure 1 to 4 and 7. As best shown in Figures 3 and 4, the sensor sleeve 44 is comprised of two generally semi-circular parts 62 and 64 each having a semicircular recess 66 defined by the semi-circular rim portion 68. As will be understood, one of the generally semi-circular parts or components 62 and 64 may be slightly greater than one half of a circle or semi-circle, such that the larger component snaps on the push rod 28 or the components may be semi-circular as shown. The semi-circular recess 66 further includes radial integral web portions 70 which define two sensor pockets 72 each of which receive a sensor 50 as shown in Figure 1 and described above and two magnet pockets 74 each of which receive a magnet 54. As will be understood, each sleeve component 62 and 64 may have one sensor 50 and one magnet 54, provided the sensors and magnets are generally opposed in the assembled sensor sleeve 44. One of the generally semi-circular parts 62 further includes a radial lceyway 76 which receives the radial projecting end portions 90 and 92 of the shunt sleeve 46 -l i¬

as described below. The generally semi-circular part 62 further includes opposed alignment tabs 78 which are received in slots 80 in the other part 64 when the generally semi-circular parts are assembled. Further, the generally semi-circular parts 62 and 64 include frustoconical tabs 82 which receive the support ring 128 shown in Figures 1 and 2 described below. The frustoconical tabs 82 define a groove bordered by annular radial rib 85. Upon assembly, the right angled portions define an inwardly opening slots 79 which receive the radial shunt holders 100 on the shunt sleeve 46 as described

below.

The illustrated embodiment of the shunt sleeve 46 is best described with

reference to Figure 7. As shown, the illustrated embodiment of the shunt sleeve includes two generally semi-circular parts 86 and 88. Each part includes a radially projecting end portion or flange 90 and 92. The radially projecting flange 90 and the opposed end portion 91 includes slots 94 which receive locking tabs 96 on the other part 88 having a hook-shaped or inclined barb 98. Upon assembly, the tabs 96 are received through slots 94 and locked in place by the hooked or barbed end portion 98. The shunt sleeve 46 further includes longitudinally extending radial shunt holders 100 each having a longitudinally extending radial slot 102 which receive the shunts 58 and 60 shown in Figures 1, 5 and 6 and described below. The internal surface 106 of the shunt sleeve components 86 and 88 is generally cylindrical to receive the cylindrical push rod 28 as shown in Figure 1.

The lock ring 48 shown in Figures 1 and 7 also includes generally semi-circular ' parts 108 and 110. The internal surface 112 is threaded to threadably receive the external threaded end portion 104 of the shunt sleeve as described below. One of the generally semi-circular parts 108 of the lock ring includes opposed locking tabs 114 having a wedge-shaped end portion 116 which are received in slots 118 on the generally semi-circular part 110 and locked in place against transverse surface 120. The disclosed embodiment of the lock ring further includes gripping surfaces 124 for use during assembly of the lock ring on the shunt sleeve 46 as described below.

Having described preferred embodiments of the components of the bralce momtor 42 of this invention, the assembly of the components on the brake actuator 20 may now be described. First, the sensor sleeve 44 is assembled by inserting the tabs 78 into the slots 80. Next, the support ring 128 is snapped over the frustoconical tabs 82 into the slot 84 shown in Figure 4. The supporting 128 includes radial notches 129 which receive the inclined tabs 82. The assembly is then inserted into the opening 30 in the brake actuator housing 20 as shown in Figure 1. The shunt sleeve 46 is assembled on the brake actuator rod 28, prior to threaded attachment of the device 32 on the brake actuator rod 28 and the piston 24 is then received in the bralce actuator housing 22. As described above, the components of the shunt sleeve 46 are assembled by snapping the locking tabs 96 into the slots 94 around the bralce actuator rod 28. The radial key on the shunt sleeve formed by radial flanges 90 and 92 is slidably received in the radial eyway 76 in the sensor sleeve 44, accurately aligning the radial shunt holders 100 in the inwardly opening slots 79 formed upon assembly of the sensor sleeve 44 and the support ring 128, as best shown in Figure 2. The shunt sleeve 46 is then accurately positioned on the push rod 28 by lock ring 48. First, the shunt sleeve 46 is accurately positioned on the push rod 28 by measuring the distance between the piston plate 26 and the predetermined position of the shunt sleeve, such that the shunts 58 and 60 are accurately located relative to the sensors 50 and the opposed magnets 54 in the sensor sleeve 44. The lock ring 48 is then assembled on the threaded portion 104 on the end of the shunt sleeve by receiving the locking tabs 114 into the slots 118 where the wedge-shaped end portions 116 are received behind the transverse surface 120 as shown in Figure 7. The internal thread 112 on the lock ring 48 then mates with the threads 104 on the end of the shunt sleeve and the lock ring is then tightened by threading the lock ring on the shunt sleeve, fixing the position of the shunt sleeve 46 on the push rod 28 as shown in Figure 1.

The positioning of the shunts 58 and 60 in the longitudinal slots 102 in the radial shunt holders 100 of the shunt sleeve will depend upon the conditions of the bralce actuator 20 to be measured. As will be understood from the following description of the operation of the bralce monitor 42 of this invention, the shunts 58 and 60 may be of different lengths and/or different longitudinal positions along the longitudinal axis of the shunt sleeve 46 and push rod 28. Having described the assembly of one embodiment of the bralce monitor 42 of this invention, the operation of the bralce monitor may now be described. As set forth above, a conventional bralce actuator includes a piston 24 having a rod 28 which reciprocates through an opening 30 in the bralce actuator housing 22 to actuate the bralcing system of a vehicle (not shown). A bralce actuator of this type has a predetermined amount of available movement or stroke of the push rod 28. Therefore, the reciprocal movement of the push rod required to fully actuate the bralcing system of the vehicle should be carefully monitored, such that it is wimin the available stroke of the push rod 28. Typically, excessive movement of the push rod is due to brake lining wear; however, excessive stroke may also be caused by wear or damage to the linkages between the push rod and the foundation bralce. When the reciprocal movement of the push rod 28 through the opening 30 in the housing exceeds the rated limit of the bralce

actuator, this is referred to as an "overstroke" condition. Thus, it would be desirable to monitor the reciprocal movement of the bralce actuator to signal an overstroke condition. Another condition which should be momtored is a dragging bralce, wherein the bralce actuator rod 28 does not return to a zero stroke condition within the housing following release of the brakes. A dragging brake condition may, for example, occur when the emergency bralce is released during start-up of the vehicle and the piston 24 does not retract into the brake actuator housing to the ready or zero stroke position. As described above, when the pneumatic pressure acting against the flexible diaphragm 40 is returned to zero, a return spring (not shown) normally reacts against the piston plate 26 to retract the piston rod 28 into the housing. However, where the vehicle foundation brake fails to release either during start-up or during operation of the bralcing system, this is a dragging bralce condition. It would also be desirable to momtor the components of the bralce monitor to signal a failure. The disclosed embodiment of the brake monitor of this invention will monitor each of these conditions as now described.

As will now be understood, the preferred embodiment of the brake monitoring system of this invention includes two pair of magnets 54 located in the magnet pockets 74 of the sensor sleeve 44 and two sensors 50 located in the sensor pocket 72 within the magnetic field of the magnets, h one preferred embodiment, the sensors 50 are normally open reed switches commercially available from various sources. However, when this type of sensor is located within the magnetic field of the magnet 54, the reed switch is closed. A signal that the reed switch has closed may be transmitted to a control module by wire 52. Alternatively, an RF transmitter (not shown) may be embedded in the sensor sleeve adjacent each of the reed switches which transmits a signal to a conventional receiver indicating that the reed switch has closed or is open. The RF transmitter may be a single chip RF transmitter including a battery having a useful life longer than that of the bralce actuator. However, to extend the battery life, the RF transmitter may enter a "sleep" mode until an event occurs at which time it would transmit a signal. Alternatively, the RF transmitter may be a passive RF transmitter as is known in the art which receives energy via a transmitted RF signal from a controller or other source as disclosed in the above-referenced copending patent application.

Upon actuation of the bralce actuator by the vehicle pneumatic bralcing system, as described above, the piston 24 moves downwardly in Figure 1, extending the push rod 28 through the opening 30 in the housing. The shunts 58 and 60 are then received between the generally opposed sensors 50 and magnets 54 terrupting or blocking a signal between the sensor and the magnet, hi the described embodiment, wherein the sensor is a normally open reed switch, the switch is closed when located within the magnetic field of the adjacent magnet and open when a shunt is received between the adjacent magnet and sensor, blocking the magnetic field. Thus, in the disclosed embodiment, the shunts may be formed of any ferrous material, such as a strip of iron, steel or iron alloy, which blocks the magnetic field of the magnets 54. Stated another way, the shunts interrupt a signal between the sensor and the magnet when the shunt is located between the sensor and the magnet. Thus, the length and longitudinal position of the shunts on the shunt sleeve 46 will determine the condition of the brake actuator monitored.

Figure 1 actually illustrates an overstroke condition of the brake actuator, wherein the shunt 60 is located between a sensor and a magnet. When the piston 24 is fully retracted into the housing 22 of the brake actuator, the shunt 60 is located above the adjacent sensor and magnet and the sensor is therefore closed because it is located within the magnetic field of the adjacent magnet. The fully retracted position of the piston is referred to in the art as the "zero stroke" position. When the bralces are applied, the piston begins to move downwardly in Figure 1 and the piston rod 28 extends through the opening 30 in the bralce actuator housing 20 to actuate the bralcing system of the vehicle as described above. The shunt sleeve 46 then moves through the sensor sleeve 20 and during normal operation of the bralce actuator, the shunt 60 is not received between the adjacent magnet 54 and sensor 50 because there is a space 61 between the end 104 and the shunt 60 as best shown in Figure 6. That is, the sensor 50 is within the magnetic field of the magnet 54 and the reed switch remains closed. However, when the piston 28 and the shunt 60 of the shunt sleeve 46 is received between the adjacent sensor 50 and magnet 54 as shown in Figure 1, the sensor 50 closes because the shunt 60 interrupts the magnetic field. This is an "overstroke" condition for the bralce actuator and a signal is then sent to the controller through line 52, indicating an overstroke condition. As will be understood from the above description, it is necessary for the controller to know when the brakes are applied to determine whether there is an overstroke condition and therefore the control circuit is preferably wired to the brake light. That is, an overstroke condition is when the brake is applied and the piston rod 28 extends beyond a rated condition for the bralce actuator 20. Therefore, the disclosed embodiment of the brake monitor 42 will signal an overstroke condition.

A dragging bralce is indicated by shunt 58 and the associated sensor and magnet. At the zero stroke position, the shunt 58 is located above the adjacent sensor 50 and magnet 54 and therefore the sensor is located within the magnetic field of the magnet and the reed switch is closed. During the initial movement of the piston rod 28, the shunt holder 100 has an open space 59 as shown in Figure 5. Thus, the reed switch remains closed. However, when the shunt 58 is received between the associated sensor and magnet 54 and the bralce is not actuated, this indicates a dragging brake condition. That is, when the bralce is not on, but the piston 24 has not returned to zero stroke, the brake monitor 42 will indicate a dragging bralce condition. Thus, the monitor must also know when the bralce is actuated to indicate a dragging bralce condition and the sensor 50 associated with the shunt 58 may also be wired into the brake light of the vehicle. Finally, the disclosed embodiment of the brake monitor 42 will also sense and indicate a failure of the brake momtor. For example, if a wire breaks or a sensor is not operating, the circuit will sense an open sensor condition,

indicating a failure. The bralce monitor of this invention may thus be utilized to sense and indicate an overstroke condition of the brake actuator 20, wherein the piston rod 28 extends beyond the rated stroke for the bralce actuator. Further, the bralce monitor will also indicate a dragging bralce condition as described above. Finally, the bralce monitor will indicate a failure in the system or a normal operating condition. Thus, the bralce monitor of this invention will actually sense and indicate five functions of each of the bralce actuators, including an overstroke condition, a dragging bralce, a non-functioning brake actuator, normal stroke and sensor fault. These conditions may, for example, be easily monitored by the vehicle operator by flashing lights at the front of the trailer, opposite the back window the tractor truck, such as green for normal stroke operation, red for overstroke, flashing red for dragging bralce, etc. Alternatively, the sensors may be connected to a heads up display in the cab or a monitor in the cab. As set forth above, the sensors 50 may be hardwired to a controller by wires 52 or the wires may be eliminated by use of passive RF transmitters, as described above, which may be potted in the recess 66 in the sensor sleeve 44.

The components of the bralce monitor 44 may be formed of various materials. However, the sensor sleeve 44, shunt sleeve 46, lock ring 48 and the support ring 128 for the sensor sleeve are preferably fonned of a polymer or plastic able to withstand the hostile enviromnent of a brake actuator, as described above. A suitable plastic is Nylon 6 which is available, for example, from BASF Corporation under the trade name 'Ultramid B3ZG3," which is a high impact glass filled Nylon. As set forth above, the sensors in the preferred embodiment are reed switches, such as reed switches available from Old Electric Industry Co. Ltd. of Tokyo, apan. However, various sensors may be utilized including, for example, Hall-effect sensors. The magnets 54 may be any conventional magnetic material; however, a Neodynium 35 magnet has been found suitable for this application. The shunt material may be any suitable ferrous material which will interrupt the magnet field, such as a nickel iron alloy, preferably having high permeability. A suitable material is "Hymu80" available from National Electronic Alloys of Oakland, New Jersey.

Having described a preferred embodiment of the bralce monitor of this invention, it will be understood by those skilled in this art that various modifications may be made to the disclosed embodiment within the purview of the appended claims. For example, it may be preferred to close the free end of the radial shunt holders 100 and insert the shunts 58 and 60 through longitudinal slots in the inside surface 106 of the shunt sleeve 46 shown in Figure 7. This would protect the shunts from the environment of the bralce actuator. Various lock ring designs may also be utilized which fix the shunt sleeve 46 relative to the piston rod 28. hi the preferred embodiment of the bralce monitor 42, however, the components may be assembled without special tools and the components are designed to avoid improper assembly of the components as described. Further, as described above, the shunts 58 and 60 may be of different lengths and configurations to sense and indicate various positions of the push rod 28 as it reciprocates through the opening 30 in the housing 22 of the bralce actuator 20. Further, the number of sensors, magnets and shunts will depend upon the bralce actuator conditions to be monitored. For example, it would be possible to use only one shunt and pair of generally opposed magnets and sensors to sense and indicate one condition of the bralce actuator. Alternatively, it would also be possible to utilize more than two shunts and two pairs of sensors and magnets to sense and indicate multiple positions of the bralce actuator piston rod 28. More than one shunt may also be included in each longitudinal slot 102 in the radial shunt holders 100. Finally, in the preferred embodiment of the bralce actuator, the sensor sleeve 44 is mounted in the opening 30 in the bralce actuator housing as shown in Figure 1, such that the sensor sleeve 44 also serves as a stone shield, preventing entry of road debris into the bralce actuator housing 22. As described above, the sensor sleeve 50 is preferably assembled in the housing opening 30 during assembly of the brake actuator. However, it would also be possible to utilize the brake monitor of this invention as an aftermarket component, wherein a sensor and a magnet is fixed relative to the housing by any suitable means and the shunt is reciprocal with the bralce actuator rod without fixing the shunt in a shunt sleeve fixed to the piston rod of the bralce actuator.

Having described preferred embodiments of the vehicle brake momtor of this invention, the invention is now claimed, as follows:

Claims

CLAIMSWhat is claimed is:

1. A vehicle bralce monitor, comprising: a brake actuator including a housing and a rod reciprocable through an opening in said housing for actuation of a vehicle brake; a sensor and a generally opposed spaced magnet fixed relative to said housing; a shunt having a predetermined length reciprocal with said bralce actuator rod

between said magnet and said sensor; and said shunt inteirupting a signal between said sensor and said magnet when said shunt is located between said sensor and said magnet during reciprocal movement of said rod signaling at least one position of said rod relative to said housing.

2. The vehicle brake monitor defined in Claim 1, wherein said magnet and sensor are located in a sensor sleeve generally sureounding said rod.

3. The vehicle brake monitor defined in Claim 2, wherein said sensor sleeve is an annular stone shield located within said housing opening surrounding

said rod.

4. The vehicle brake monitor defined in Claim 1, wherein said bralce monitor includes two pairs of generally opposed spaced magnets and sensors and at least two shunts, said shunts having different predetermined lengths or longitudinal positions along said rod and reciprocable with said rod between each of said pairs of generally opposed magnets and sensors, said shunts interrupting a signal between each of said pairs of magnets and sensors at different reciprocal positions of said rod as said rod reciprocates through said opening of said housing, said sensors thereby sensing different positions of said reciprocable bralce actuator rod relative to said housing.

5. The vehicle brake momtor defined in Claim 1, wherein said shunt is located on said rod.

6. The vehicle bralce monitor defined in Claim 5, wherein said shunt is located on a sleeve fixed to said rod.

7. The vehicle brake momtor defined in Claim 1, wherein said sensor is a reed switch.

8. A vehicle bralce monitor, comprising: a bralce actuator including a housing and a rod reciprocable through an opening in said housing for actuation of a vehicle bralce; a sensor sleeve generally surrounding said rod and fixed relative to said housing having a magnet and a generally opposed sensor located within the magnetic field of said magnet; a magnet shunt having a predetermined length less than the length of said rod mounted on said rod to reciprocate with said rod between said sensor and said

magnet; and said magnet shunt interrupting a signal between said magnet and said sensor when said magnet shunt is located between said magnet and said sensor during reciprocable movement of said rod, thereby signaling a reciprocal position of said rod.

9. The vehicle bralce monitor defined in Claim 8, wherein said sensor

sleeve is an annular stone shield located within said housing opening surrounding

said rod.

10. The vehicle brake monitor defined in Claim 8, wherein said sensor sleeve includes two pairs of generally opposed spaced magnets and sensors and said rod includes two longitudinally and radially extending shunts each having different predetermined lengths or longitudinal positions along said rod mounted on said rod in circumferentially spaced relation and reciprocal with said rod between each of said pairs of magnets and sensors, said shunts interrupting a signal between each of said pairs of magnets and sensors at different positions of said rod as said rod reciprocates through said housing opening, thereby indicating different positions of said reciprocable rod.

11. The vehicle bralce monitor defined in Claim 8, wherein said shunt is located on a sleeve fixed to said rod.

12. The vehicle bralce monitor defined in Claim 8, wherein said sensor is a reed switch.

13. The vehicle brake monitor defined in Claim 8, wherein said monitor includes a shunt sleeve surrounding said rod, fixed relative to said rod and reciprocable with said rod through said housing opening, and said magnet shunt fixed to said sleeve and extending longitudinally and radially from said sleeve between said magnet and said sensor through a radial opening in said shunt sleeve.

14. A vehicle brake monitor, comprising: a brake actuator including a housing and a rod reciprocable through an opening in

said housing for actuation of a vehicle bralce; a sensor sleeve mounted on said housing surrounding said rod having a radial

opening; a magnet and a sensor in said sensor sleeve on opposed sides of said radial opening; a shunt sleeve mounted on said rod and fixed to said rod for reciprocal movement with said rod; a magnet shunt mounted on said shunt sleeve having a predetermined length extending radially into said radial opening in said sensor sleeve between said magnet and said sensor as said shunt sleeve reciprocates with said rod through said housing

opening; and said magnet shunt interrupting a signal between said magnet and said sensor when said shunt is located between said magnet and said sensor during reciprocal movement of .said shunt sleeve, thereby signaling a position of said rod relative to

said housing.

15. The vehicle bralce monitor defined in Claim 14, wherein said sensor sleeve is an annular stone shield mounted within said housing surrounding said shunt sleeve.

16. The vehicle bralce monitor defined in Claim 14, wherein said shunt sleeve is an annular sleeve surrounding said rod and fixed to said rod by a separate connector permitting adjustment of said shunt sleeve on said rod prior to fixing a position of said shunt sleeve on said rod.

17. The vehicle bralce monitor defined in Claim 14, wherein said sensor' sleeve includes two circumferentially spaced radial openings, a sensor and a magnet on opposed sides of each of said radial openings, and said shunt sleeve including two circumferentially spaced magnetic shunts extending radially into said radial openings in said sensor sleeve between said magnets and said sensors on opposed sides of each of said openings having different predetermined lengths or longitudinal positions, wherein said sensors sense different positions of said rod.

18. The vehicle bralce monitor defined in Claim 14, wherein one of said shunt sleeve and said sensor sleeve includes a radial keyway and the other of said shunt sleeve and said sensor sleeve includes a radial key slideably received in said keyway fixing the relative rotational orientation of said sleeves.

19. The vehicle bralce momtor defined in Claim 14, wherein said shunt sleeve includes a radial projecting portion slideably received in said radial opening in said sensor sleeve and said magnetic shunt is fixed in said radial projecting portion of said shunt sleeve.

20. The vehicle brake monitor defined in Claim 14, wherein said sensor is a reed switch.

21. The vehicle brake monitor defined in Claim 14, wherein said sensor sleeve includes two circumferentially spaced radial openings and a sensor and a magnet on opposed sides of each of said radial openings and said shunt sleeve including two circumferentially spaced fenous metal shunts having different predetermined lengths or longitudinal positions along said shunt sleeve, spaced longitudinally on said shunt sleeve and reciprocable with said shunt sleeve between said magnets and said sensors interrupting a signal between said magnets and said sensors at different positions of said rod as said rod reciprocates through said housing opening.