WO2022066871A1

WO2022066871A1 - Drum brake monitoring systems and methods

Info

Publication number: WO2022066871A1
Application number: PCT/US2021/051703
Authority: WO
Inventors: Weixu Chen; Frank J. Sienkiewicz; Eric C. GARDELL
Original assignee: Sensata Technologies
Priority date: 2020-09-24
Filing date: 2021-09-23
Publication date: 2022-03-31

Abstract

A braking system for a vehicle includes a cam shaft, such as an S-cam shaft, a slack adjuster, a pushrod, and a braking chamber. The braking system also includes a sensing system configured to determine a rotational displacement of the cam shaft, e.g., during application of brakes on the vehicle. A controller determines a state of the braking system based at least in part on the rotational displacement of the cam shaft.

Description

DRUM BRAKE MONITORING SYSTEMS AND METHODS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 63/082,777, filed on September 24, 2020, the entire contents of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0002] The subject disclosure relates to methods and systems for monitoring drum brakes, and more particularly to improved methods and systems for monitoring pushrod stroke, S-cam shaft for cam-over condition, and/or brake effectiveness.

2. Background of the Related Art

[0003] Commercial vehicles such as trucks and tractor-trailers are the major transportation vehicles for freight in the United States and commonly used around the world. Generally speaking, a tractor trailer may weigh 40 tons and, thus, requires more braking power than a typical vehicle, so making the brakes as simple and as cost effective as possible is very important. Approximately 85% of commercial vehicles are equipped with pneumatic or hydraulic brake systems. Such brake systems commonly have a drum assembly with a S-cam shaft as the primary braking mechanism on each wheel. Drum brakes are favored on bigger vehicles because of increased surface area in brake pads to get a heavier load slowed down more efficiently. The S-cam arrangement allows the brakes of big vehicles to be more compact with less moving parts, since only a rotating shaft is required at the wheel assembly. As a result, the bulky air cylinders of the brake chamber are located outside of the wheel.

[0004] In operation, the driver of the vehicle presses the brake pedal, which sends power to a brake chamber having a diaphragm. The power is typically compressed air. The diaphragm moves a pushrod in a linear motion. The pushrod is connected to a slack adjuster that translates the linear motion into a rotational motion applied to a shaft connected to an S- cam. As the cam rotates, two symmetrical brake pads are forced outward against the brake drum to create friction and stop the vehicle. When the driver releases the brake pedal, the pressure is released, and the brake pads return to their resting position allowing free rotation of the wheels. [0005] S-cams are very efficient at keeping brakes maintained because as the brake pad wears, the S-cam rotates more and causes the pads to still make proper contact. Since the lobes on the S-cam increase in radius when turned, the brake pads linear motion is increased. To avoid slack in the brake system, the brakes can be adjusted periodically to maintain proper responsiveness and performance. Commonly on modem vehicles, the slack adjustment is automatically performed to some extent by the slack adjuster.

SUMMARY

[0006] Despite the advancements of automatic slack adjusters, vehicles can be out of service for various reasons related to the brake systems, often at great cost. For example, the pushrod may be out of adjustment and/or there may be leakage of compressed air in the brake lines. The pushrod being out of adjustment means that the pushrod extends beyond a predefined value. For safety reasons, extension beyond the predefined value is not desired. Conversely, leakage of compressed air in the brake lines can result ineffective application of brakes despite application of pressure by the driver to the brake pedal. Commonly, these and other aspects of the braking system are checked by visual safety inspection, which is time consuming and complex. The visual inspection of the pushrod is particularly labor-intensive and difficult on vehicles with low ground clearance. Preventing an increased lag in braking and a reduced steady-state brake force due to compressed air leakage is even trickier. Another area of concern is if the brake system is worn and/or adjusted to the point that the S-cam goes into a cam-over condition. In the cam-over condition, the S-cam has been over-rotated to the point that the camp followers ‘fall off the cam lobe, and the brakes become stuck in a partially or, more likely, fully engaged position. Thus, there is a need for a brake system that provides warnings during live monitoring of these parameters during uninterrupted vehicle operation.

[0007] For efficient and continuous monitoring of the pushrod for out-of-adjustment and/or sufficient service brake pressure, one performance-based live monitoring system of the subject technology includes: a magnetic based sensor assembly measuring rotary angles of the S-cam shaft, which translates the high-pressure compressed air to actuation of the brake shoes; an automotive pressure transducer; a controller for (i) receiving the sensor assembly and pressure transducer reading, (ii) applying a first built-in algorithm to convert rotational measurements into pushrod stroke, (iii) applying a second built-in algorithm to determine brake effectiveness, (iv) warn of impending cam-over as well as other related recommended maintenance being required, and (v) estimate the state of wear of the brake shoes. [0008] In one embodiment, the sensor assembly includes a housing or shell with a geared central aperture. The central aperture mates with the S-cam shaft for rotation therewith. The housing fixedly retains and protects a magnetic ring that has a central hole axially aligned with the central aperture. Thus, the magnetic ring rotates with the housing. A stationary sensor unit includes a sensor and, optionally, control electronics, which may be mounted on a single printed circuit board. The control electronics may include application specific integrated circuits (ASICs) such as a microprocessor and other components as well as standard electronic components. The sensor may be any kind of magneto resonance sensor (e.g., xMR).

[0009] It should be appreciated that the subject technology can be implemented and utilized in numerous ways, including without limitation as a process, an apparatus, a system, a device, a method for applications now known and later developed such as a computer readable medium and a hardware device specifically designed to accomplish the features and functions of the subject technology. These and other unique features of the system disclosed herein will become more readily apparent from the following description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] So that those having ordinary skill in the art to which the disclosed system appertains will more readily understand how to make and use the same, reference may be had to the following drawings.

[0011] FIG. 1 is a perspective view of an axle assembly with an integrated sensor assembly in accordance with the subject technology.

[0012] FIG. 2 is a partially exploded perspective view of a portion of an axle assembly with the sensor assembly in accordance with the subject technology.

[0013] FIG. 3 is a reverse (e.g., looking inward) perspective view of a S-cam shaft coupled to a sensor assembly in accordance with the subject technology.

[0014] FIG. 4 is a reverse (e.g., looking inward) perspective view of a sensor assembly in accordance with the subject technology.

[0015] FIG. 5 is a perspective view of a sensor assembly in accordance with the subject technology. [0016] FIG. 6 is a perspective exploded view of a sensor assembly in accordance with the subject technology.

[0017] FIG. 7 is a flowchart for calculating pushrod stroke excessiveness in accordance with the subject technology.

[0018] FIG. 8 is a plan view illustrating two positions of an air brake chamber coupled to a slack adjuster on an S-cam shaft in accordance with the subject technology.

[0019] FIG. 9 is a chart of chamber size and maximum stroke for various brake chambers in accordance with the subject technology.

[0020] FIG. 10 is a pair of synchronized graphs of field measurements in accordance with the subject technology.

[0021] FIG. 11 is another pair of synchronized graphs of field measurements in accordance with the subject technology.

[0022] FIG. 12 is a flowchart for calculating brake effectiveness in accordance with the subject technology.

[0023] FIG. 13 is a graph of pushrod force versus stroke in accordance with the subject technology.

[0024] FIG. 14 is another replotted graph of pushrod force versus stroke in accordance with the subject technology.

[0025] FIG. 15 is a regression analysis graph of pushrod force versus stroke in accordance with the subject technology.

[0026] FIG. 16 is another regression analysis graph of pushrod force versus stroke in accordance with the subject technology.

[0027] FIG. 17 is a graph of key regions of brake effectiveness overlaid on Figure 14 in accordance with the subject technology.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0028] The subject technology overcomes many of the prior art problems associated with monitoring drum brake performance. The advantages, and other features of the systems and methods disclosed herein, will become more readily apparent to those having ordinary skill in the art from the following detailed description of certain preferred embodiments taken in conjunction with the drawings which set forth representative embodiments of the present invention. It is understood that references to the figures such as up, down, upward, downward, left, and right are with respect to the figures and not meant in a limiting sense. In particular, inward is used to describe standing outside the vehicle looking toward the center, usually from a lateral side, whereas outward is used to describe a view from within the vehicle looking away from the center, usually perpendicular to the lateral side.

[0029] FIG. 1 is a perspective view of an axle assembly 100 with an integrated sensor assembly in accordance with the subject technology. For example, the axle assembly 100 may be a part of a vehicle, such as a tractor configured to haul a trailer. The axle assembly 100 includes an axle 102 extending generally along an axis 104. The axle 102 terminates at hubs 106, on which wheels (not shown) may be coupled to the axle assembly 100. Moreover, a braking system 108 is disposed at each end of the axle 102. FIG. 1 shows two instances of the braking system 108, which may be substantially identical. For ease of reference and description, components of only a single instance of the braking system 108 is labelled in FIG. 1 and described herein, although it will be appreciated that the other braking system will have the same or similar features and attributes.

[0030] The braking system 108 includes a brake drum 110 disposed proximate each of the hubs 106. Although not illustrated in the figures, the brake drum 110 may be a conventional brake drum 110 such as the type that houses brake shoes, one or more return springs for returning the brake shoes to positions spaced from the brake drum 110, e.g., when the brakes are deactivated, and cam rollers disposed on the brake shoes. The braking system 108 also includes a cam shaft 112. The cam shaft extends from a first end 114 to a second end 116. Although not visible in FIG. 1, an S-cam is disposed on the first end 114 of the cam shaft. The S-cam interacts with the cam rollers disposed in the brake drum 110. For example, rotation of the cam shaft 112 about its axis causes the S-cam to contact the cam rollers. As the cam rollers are displaced by the S-cam, the cam rollers in turn cause the brake shoes to contact the brake drum 110, creating friction to slow the vehicle.

[0031] The braking system 108 also includes a slack adjuster 118 disposed proximate the second end 116 of the cam shaft 112. As will be appreciated, the slack adjuster 118 is coupled to the cam shaft 112 and to a pushrod 120. In turn, the pushrod 120 is coupled to a brake chamber 122. The brake chamber 122 is in fluid communication with a brake pedal (not shown) such that when a driver applies a pressure to the brake pedal, air pressure in the brake chamber 122 increases. This increase in pressure in the brake chamber 122 causes the pushrod 120 to extend relative to the brake chamber 122, e.g., via movement of a diaphragm in the brake chamber 122, thereby, causing the slack adjuster 118 and the cam shaft 112 to rotate. As noted above, rotation of the cam shaft 112 causes rotation of the S-cam, which in turn causes the brake shoes to contact the brake drum 110.

[0032] As also illustrated, a sensing system 124 (or sensor assembly) is disposed proximate the second end 116 of the cam shaft 112. As detailed further herein, the sensing system 124 is coupled to the axle assembly 100 near the slack adjuster 118. As a result of this positioning, the sensing system 124 is desirably remotely located from the wheel. Also, as a result, the sensing system 124 is physically spaced from high temperatures occurring at the brake pads and the brake drum 110. As detailed further herein, the sensing system 124 is generally configured to determine a rotational displacement of the cam shaft 112, and thus the S-cam disposed on the cam shaft 112.

[0033] FIG. 1 also illustrates, schematically, a controller 126. The controller 126 is illustrated as being communicatively coupled to the sensing system 124 associated with each of the wheels. For instance, the controller 126 is configured to receive sensor data from the sensing system 124 and perform processes associated with drum brake monitoring, as detailed further herein. For example, the controller may be configured to determine alarm states associated with the braking system 108. Although the controller 126 is illustrated as remote from the sensing system 124, this is for illustration only. In some implementations, aspects of the controller 126 may be implemented by components of the sensing system 124. Without limitation, and as discussed herein, the sensing system can include a sensor with integrated processing components that implement the controller 126.

[0034] FIG. 2 is a partial, exploded perspective view of a portion of the axle assembly 100. Specifically, in FIG. 2, only a single side (e.g., associated with only a single wheel) of the axle assembly 100 and the corresponding instance of the braking system 108 is shown, and portions of the sensing system 124 are separated from the cam shaft 112. As can be seen, the cam shaft 112 has a plurality of splines 202 spaced about its circumference at the second end 116. The sensing system 124 has a rotating portion 204 having a plurality of teeth 206 (more clearly shown in FIGS. 4-6). The sensing system 124 is coupled to the cam shaft 112 such that the teeth 206 engage with the splines 202. As detailed further below, through this arrangement, rotation of the cam shaft 112 cause the rotating portion 204 of the sensing system 124 to also rotate. As also discussed further below, the rotating portion 204 may act as, or incorporate, a magnetic target. As will be appreciated, in addition to being used to couple the rotating portion 204 of the sensing system 124 to the cam shaft 112, the splines 202 may also promote coupling of the slack adjuster 118 to the cam shaft 112.

[0035] Although the example of FIG. 2 shows the rotating portion 204 of the sensing system 124 having the teeth 206 for cooperating with the splines 202 on the cam shaft 212, this disclosure is not limited to that arrangement. For instance, other mechanical arrangements that couple the rotating portion 204 of the sensing system 124 to the cam shaft 112 may be used. Without limitation, the rotating portion 204 may be coupled to the cam shaft 112 via an interference or press fit, using one or more keys, via a threaded engagement, or otherwise. In still further examples, epoxies, adhesives, or the like may also or alternatively be used to secure the rotating portion 204 to the cam shaft 112. Other example arrangements that couple the rotating portion 204 to the cam shaft 112 such that the rotating portion 204 rotates with the cam shaft 112 also may be used and will be appreciated by those having ordinary skill in the art with the benefit of this disclosure.

[0036] FIG. 3 is a perspective view of a portion of the braking system 108. Specifically, the view of FIG. 3 is opposite that of FIGS. 1 and 2 and shows the cam shaft 112 coupled to the sensor system 124 in accordance with the subject technology. Specifically, FIG. 3 shows an S-cam 302 coupled to the first end 114 of the cam shaft 112. The S-cam 302 is a conventional S-cam, having two arcuate surfaces 304 that contact cam rollers, as described herein. The arcuate surfaces 304 may have a varied radius about an axis 306 of the cam shaft 112. As discussed above, and as generally known in the art, the cam shaft 112 rotates with application of a braking force (as transmitted by the pushrod 120) to cause the arcuate surfaces 304 of the S-cam 302 to contact cam rollers.

[0037] As also illustrated in FIG. 3, the braking system 108 includes a bracket 308 with a hole (not visible in FIG. 3) through which the cam shaft 112 passes. In examples, a stationary sensor unit 310 may be mounted to the bracket 308. The stationary sensor unit 310, aspects of which are detailed further below, is positioned to determine a rotation of the cam shaft 112, via the rotating portion 204 of the sensing system 124. As illustrated, aspects of the slack adjuster 118 also may be secured to the axle assembly 100 via the bracket 308. As will be appreciated, the size, shape, and/or other aspects of the bracket 308 may vary from the illustrated embodiment.

[0038] FIGS. 4 and 5 are perspective views of the sensor system 124 in accordance with the subject technology, and FIG. 6 is an exploded view corresponding to the view shown in FIG. 5. Together, FIGS. 4-6 show aspects of the sensor system 124, including the rotating portion 204, in more detail. Specifically, the rotating portion 204 of the sensing system 124 includes a housing 402 or shell with a central aperture 404. The teeth 206 are disposed in the central aperture 404, e.g., to extend generally radially inwardly from the central aperture 404. As noted above, the teeth 206 in the central aperture 404 mate with the splines 202 on the cam shaft 112, such that rotation of the cam shaft 112 causes corresponding rotation of the housing 402. In the illustrated example, the housing 402 generally includes a boss 406 circumscribing a portion of the central aperture 404, and the teeth 206 are disposed only on the boss 406 of the housing 402. In other examples, the teeth 206 may be formed over more, including substantially all, or less, of the axial length of the central aperture 404. The housing 402 also includes an annular lip 408 disposed about an outer circumference of the housing 402. In examples, the housing may be a molded, cast, and/or machined part.

[0039] The sensing system 124 also includes amagnetic ring 410 affixed to the housing 402. Specifically, the magnetic ring 410 has a central hole axially aligned with the central aperture 404. Because the magnetic ring 410 is fixed to the housing 402, the magnetic ring 410 rotates with the housing 402, when the cam shaft 112 rotates. As best shown in FIG. 4, the housing 402 can include a receptacle 412, e.g., formed as an annular groove or seat, in a planar surface 414. In this arrangement, an exposed surface 416 of the magnetic ring 410 is substantially flush or coplanar with the planar surface 414 of the housing 402. Of course, this arrangement is for example only. In other examples, some or all of the magnetic ring 410 may protrude relative to the planar surface 414 and/or the exposed surface 416 of the magnetic ring 410 may be recessed relative to the planar surface 414. As noted above, the magnetic ring 410 is fixed to the housing 402. For instance, when the receptacle 412 is provided, the magnetic ring 410 may be press fit or molded into the receptacle 412. In some examples, the magnetic ring 410 may be affixed via other known fastening means and/or mechanisms. Moreover, in some examples, the housing 402 may be formed to at least partially encapsulate the magnetic ring 410, e.g., by being at least partially molded or formed around the magnetic ring 410. [0040] The sensing system 124 also includes a sensor 418. In this example, the sensor 418 is a stationary sensor unit and may include control electronics as well as one or more sensing components. In some examples, the control electronics and the sensing components may be mounted on a single printed circuit board. For instance, the control electronics may be formed as an application-specific integrated circuit (ASICS), which may include a processor and/or memory as well as standard electronic components. Without limitation, the control electronics may also or alternatively include a system-on-a-chip. The control electronics may form a portion of the controller 126. The sensor may be any kind of magneto resonance sensor (e.g., xMR). As best seen in Figure 4, the sensor 418 is an xMR sensor that aligns with the magnetic ring 410 to generate a signal indicative of the cam shaft 112 rotation.

[0041] As also illustrated in FIGS. 4-6, the sensing system 124 includes a guide 420 that includes a slot 422. As shown best in FIGS. 5 and 6, the annular lip 408 is at least partially received in the slot 422. More specifically, the slot 422 may be an arcuate slot having a substantially continuous radius sized to receive the annular lip 408 therein and to allow the annular lip 408 (and thus the housing 402) to rotate relative thereto. In examples, the slot 422 may guide the rotation of the housing 402, e.g., by inhibiting axial movement of the housing 402 along the cam shaft 112.

[0042] The guide 420 is mounted to a stationary surface, e.g., to maintain the sensor 418 in a stationary position (e.g., stationary relative to the rotational movement of the cam shaft 112). For instance, the guide 420 may be mounted to the bracket 308. In the example of FIGS. 4, 5, and 6, mount wings 424 are disposed for coupling the guide to the bracket 308. In the illustrated examples, each of the mount wings 424 is a generally elongate member having a first end 426 affixed to the guide 420 and a second end 428 configured for securement to the bracket 308. The second end 428 is illustrated as including a slotted opening 430. Although not illustrated, a fastener may pass through the slotted opening 430 and attach to the bracket 308, e.g., via threaded engagement. For example, the slotted opening 430 may allow for adjustment of the guide 420 upon securement to the bracket 308, e.g., to facilitate alignment of the slot 422 with the housing 402. The illustrated embodiment shows the sensing system 124 as including two mount wings 424, although more (or only a single) may be provided. Moreover, the mount wings 424 are shown for example only. In other embodiments the sensor 418 may be otherwise secured in a fixed position, as those having ordinary skill in the art will appreciate with the benefit of this disclosure. [0001] Figure 7 is a flowchart showing a process 700 for calculating pushrod stroke excessiveness in accordance with the subject technology. Pushrod stroke excessiveness may correspond to a state of the braking system that indicates whether the brake assembly is out of adjustment. A brake assembly that is out of adjustment may result in improper wear and/or performance of the braking system. The process 700 is illustrated as a logical flow graph, with each operation representing a sequence of operations that can be implemented in hardware, software, or a combination thereof. In the context of software, the operations represent computer-executable instructions stored on one or more computer-readable storage media that, when executed by one or more processors, perform the recited operations. Generally, computer-executable instructions include routines, programs, objects, components, data structures, and the like that perform particular functions or implement particular abstract data types. The order in which the operations are described is not intended to be construed as a limitation, and any number of the described operations can be combined in any order and/or in parallel to implement the processes. Without limitation, the process 700 may be performed by a controller, such as the controller 126, integrated into the sensor 418 and/or otherwise associated with the braking system(s) described herein. For instance, aspects of the process 700 may be performed on the printed circuit board of the sensor assembly in whole or in part, or on a separate controller in communication with the sensor assembly as well as other components. The controller may also have memory and one or more processors to perform the necessary operations as well as other functions for the vehicle.

[0043] At an operation 702, the process 700 includes receiving a rotational displacement of a cam shaft. In examples described herein, the cam shaft 112 is selectively rotated, e.g., in response to application of force to a brake pedal, to apply brakes to slow or stop a vehicle. As also detailed in the examples above, aspects of this disclosure include the sensing system 124 configured to measure the rotational displacement of the cam shaft 112. For example, the sensing system 124 can include a magnetic target, e.g., the magnetic ring 410, configured to rotate with the cam shaft, and a magneto resonance sensor, e.g., the sensor 418, configured to detect the magnetic component and determine a rotational displacement based on the detection.

[0044] At an operation 704, the process 700 includes receiving a slack adjuster arm length. In the examples illustrated in FIGS. 1-4, the slack adjuster 118 is fixed at one end to the cam shaft 112, and the pushrod 120 is fixed proximate an opposite, second end of the slack adjuster 118. In examples, the slack adjuster arm length received at the operation 702 is the distance between the points of attachment to the cam shaft 112 and the pushrod 120. More generally, the slack adjuster arm length received at the operation 702 generally represents a distance, e.g., a radial distance, from the cam axis of the cam shaft 112 to any point of attachment of the pushrod 120, e.g., to the slack adjuster 118 or to some other attachment mechanism. Stated differently, the length received at the operation 702 is a distance between the axis of rotation of the cam shaft and a location at which a force is applied to cause rotation of the cam shaft.

[0045] At an operation 706, the process 700 includes determining a pushrod stroke based on the rotational displacement of the cam shaft and the slack adjuster arm length. In examples discussed herein, the cam shaft 112 rotates about the cam shaft axis as a result of a force applied via the pushrod 120. More specifically, the pushrod 120 applies a force to the slack adjuster 118, which is fixed to the cam shaft 112. In aspects of this disclosure, the stroke may be determined using Equation 1 : d = 2 r sin(«/2) Eqn. 1

Equation 1 is a trigonometric equation in which d is the pushrod stroke, r is the slack adjuster arm length, and a is the sensed rotational displacement.

[0046] FIG. 8 includes a diagram of the cam shaft 112, the slack adjuster 118, and the pushrod 120 to illustrated Equation 1. Specifically, FIG. 8 illustrates an example in which the pushrod 120, slack adjuster 118, and cam shaft 112 are moved from a first position 802 (shown in dashed lines) to a second position 804 (shown in solid lines). For example, the first position 802 may correspond to a scenario in which a vehicle is driving without brakes applied, and the second position 804 may correspond to a scenario in which the brakes of the vehicle have been applied, e.g., via application of pressure to a brake pedal. In FIG. 8, the slack adjuster arm length, r, is constant, the rotational displacement, a, is measured, e.g., via the sensing system 122 as described herein, and the travel of the pushrod, d, is determined using the Equation 1.

[0047] Conceptually, Equation 1 determines a linear distance corresponding to an arc at the length, r, resulting from the rotational displacement, a. As noted above, the slack adjuster arm length is used as the radius component for Equation 1, but the distance may vary if other linkages, mounts, or the like are used in addition to or instead of the slack adjuster 118. The operation 706 generally determines a travel of the pushrod 120 based on the measured rotational displacement. [0048] Returning now to FIG. 7, at an operation 708, the process 700 includes receiving information about a pushrod stroke limit. As is understood in the art, different brake chambers are rated for different applications and have varying specifications. One common type of specification relates to one or more attributes associated with stroke of the pushrod. For instance, different types of chambers have different regulation stroke limits, or strokes beyond which the pushrod 120 should not exceed. FIG. 9 is a table 900 including columns showing regulation stroke limits for differently-sized and/or configured braking chambers. In examples of this disclosure, data from the table 900 may be stored as a lookup table, e.g., accessible by the controller.

[0049] At an operation 710, the process 700 includes determining whether the pushrod stroke exceeds a pushrod stroke limit. For example, the operation 710 can include comparing the pushrod stroke determined at the operation 706 to the pushrod stroke limit received or build- in program at the operation 708, e.g., to determine if the pushrod travel d is excessive or out of adjustment. For example, the pushrod stroke may reach the allowable limit but not be automatically adjusted by the slack adjuster.

[0050] If, at the operation 710, it is determined that the pushrod stroke does exceed the pushrod stroke limit, at an operation 712 the process 700 determines an alarm state. For example, because the stroke of the pushrod 120 exceeds the pushrod stroke limit, the braking system may be operating outside of safe operating parameters. In examples, the operation 712 may include the controller generating a warning and/or error signal, optionally, with more detailed information such as the underlying live readings and resulting calculations. The warnings and error signals may be presented, e.g., as alarms or alerts, to the driver of the vehicle via a dashboard light, a visual or textual display, a haptic output, or the like. Also, or alternatively, the signal(s) may be sent to a remote computing device, e.g., associated with fleet operations, maintenance, or the like, by a network communication device on the vehicle and/or otherwise associated with the sensing system 124. In some examples, the remote computing device and/or an operator associated therewith may analyze the information and provide operational instruction to the driver in real-time or near real-time.

[0051] Alternatively, if, at the operation 710, it is determined that the pushrod stroke does not exceed the pushrod stroke limit, at an operation 714 the process 700 includes determining a normal state of operation. For instance, if the pushrod stroke is equal to or less than the pushrod stroke limit, the braking system may be functioning properly. In examples, the normal state of operation may be communicated to the driver and/or a remote computing device, e.g., via a normal state signal, which may include more detailed information as described above. In other examples, such detailed information can include a percentage or other metric determined based on the comparison of the determined pushrod stroke to the pushrod stroke limit.

[0052] Figures 10 and 11 are synchronized graphs of field measurements in accordance with the subject technology. More specifically, FIG. 10 includes a first graph 1000 and a second graph 1002, and FIG. 11 includes a first graph 1100 and a second graph 1102. The graphs 1000, 1100 include an adjustment period 1004, 1104 and a subsequent, normal operation period 1006, 1106 with a desired horizontal operational band 1008, 1108. More specifically, the first graphs 1000, 1100 illustrate the output of the sensor assembly, e.g., the absolute angle corresponding to the rotational displacement in degrees. The second graphs 1002, 1102 show the determined pushrod stroke, e.g., determined according to the Equation 1, above. The spikes in the graphs 1000, 1002, 1100, 1102 represent braking activity. In the measurements shown, testing was started with the slack adjusters out of adjustment. During the adjustment period, the slack adjuster performed adequately and brought the system into acceptable performance. However, if the slack adjuster had not performed adequately, it can be seen that the out of adjustment condition would have been identified so that corrective action could be undertaken quickly and without undue delay or inspection by the live monitoring.

[0053] In the example of the process 700 of FIG. 7, the state of the braking system is determined based on stroke length. Other examples may determine the state of the braking system using other metrics, which metrics may also be based at least in part on the cam shaft rotation measured by the sensing system 124, according to the systems and techniques described herein. For example, if there is excessive brake drum depth and/or very thin lining of the brakes, the brakes can cam over. Typically, in the cam-over condition, the S-cam rotates too far and wedges against the brake pads against the drum. Thus the brakes are engaged (e.g., locked up) and will not allow movement of the trailer. The subject technology allows computing the rotation of the S-cam or S-cam shaft to determine if the position of the S-cam shaft is close to an over-cam condition. If so, again fleet operations and/or the driver can be notified with warnings so that immediate corrective action may be taken. A stroke of the pushrod 120 or a position corresponding to the over-cam condition may be a predetermined value based on the brake system configuration and may be stored in memory of the vehicle electronics, e.g., in memory associated with the controller 126, for reference and comparison. The over-cam condition position or stroke may be updated based upon thickness of the brake linings, based upon calculations using mileage, and/or other indicators of brake lining wear. The over-cam condition position may also be determined empirically during operation of the brake system.

[0002] Another example of a technique for determining a braking system state will be discussed in connection with FIG. 12. Specifically, FIG. 12 is a flowchart illustrating a process 1200 for calculating brake effectiveness in accordance with the subject technology. For example, poor brake effectiveness can be an indication of air leakage in the pneumatic system, such as via the air lines, or an indication of inadequate stroke (of the pushrod 120). As with the process 700, the process 1200 is illustrated as a logical flow graph, with each operation representing a sequence of operations that can be implemented in hardware, software, or a combination thereof. In the context of software, the operations represent computer-executable instructions stored on one or more computer-readable storage media that, when executed by one or more processors, perform the recited operations. Generally, computer-executable instructions include routines, programs, objects, components, data structures, and the like that perform particular functions or implement particular abstract data types. The order in which the operations are described is not intended to be construed as a limitation, and any number of the described operations can be combined in any order and/or in parallel to implement the processes. Without limitation, the process 1200 may be performed by a controller, such as the controller 126. In implementations, the controller may be integrated into the sensor 419 and/or otherwise associated with the braking system(s) described herein. For instance, aspects of the process 1200 may be performed on the printed circuit board of the sensor system 124 in whole or in part, or on a separate controller in communication with the sensor assembly as well as other components. The controller may also have memory and one or more processors to perform the necessary operations as well as other functions for the vehicle.

[0054] At an operation 1202, the process 1200 includes determining a pushrod stroke based on a rotational displacement of the cam shaft and the slack adjuster arm length. For example, the operation 1202 may correspond to the operation 706 discussed above in connection with FIG. 7. Without limitation, the operation 1202 may include using the Equation 1 to determine the pushrod stroke. [0055] At an operation 1204, the process 1200 includes determining a service brake pressure. As detailed herein, the braking system 108 may be operable in response to a driver applying pressure to a brake pedal. As is conventionally known, the brake pedal may be coupled to the brake chamber 122 via one or more air lines, hoses, conduits, or the like. The operation 1204 includes receiving a pressure or force corresponding to the driver-applied air pressure to the brake chamber 122. For example, a pressure sensor may be disposed proximate the brake pedal, the brake chamber 122, or otherwise, to sense a pressure corresponding to the force applied by the driver, e.g., as the service brake pressure.

[0056] At an operation 1206, the process 1200 includes receiving information about the braking system. For example, the information about the braking system can include characteristics of the braking chamber, e.g., the chamber size, a pushrod stroke limit, a nominal pushrod stroke length, and/or other details. Without limitation, the information received at the operation 1206 can include information shown in the table 900 in FIG. 9 and/or other information. For example, the information can be stored in one or more lookup tables.

[0057] At an operation 1208, the process 1200 also includes determining a pushrod force. Additional parameters used in the calculation of brake effectiveness can include a pushrod force and a nominal pushrod force. In examples, the pushrod stroke is related to pushrod force for a given applied pressure. An example of this relationship for a Type 30 brake chamber is illustrated in graph 1300 of Figure 13. More specifically, the graph 1300 shows a correspondence between pushrod stroke (on the x-axis) and pushrod force (on the y-axis) for various applied pressures, e.g., service brake pressures. The graph 1300 also illustrates a first vertical line 1302 corresponding to the nominal pushrod stroke (1.75 inches in the example) and a second vertical line 1304 corresponding to the “legal” stroke, e.g., the stroke limit (2.0 inches in the example). Corresponding to FIG. 13, FIG. 14 illustrates a replotted graph 1400 of pushrod force versus stroke, modified so that a mostly linear relationship between pushrod force and brake chamber pressure is shown. Also corresponding to FIG. 14, FIGS. 15 and 16 are regression analysis graphs 1500, 1600 of pushrod force versus stroke based on Figure 14. The legal limit for a Type 30 brake chamber is shown on the graphs. From the regression analysis graph 1500, one can determine the slope (m), and from the regression analysis graph 1600 one can determine the intercept (b). Equation 2 describes FIG. 14:

F = m(P) + b Eqn. 2 wherein m = polyfit m(ST) (shown in FIG. 15) and b = polyfit b(ST) (shown in FIG. 16). Pushrod force is preferably computed based on pushrod travel.

[0058] Returning to FIG. 12, an operation 1210 includes determining a brake effectiveness based on the pushrod force. In one embodiment, brake effectiveness is computed by dividing the value computed from measurements and chamber characteristics, by the nominal values for the specific chamber. The system will operate at values >100% when adjusted properly and with sufficient brake air pressure. Brake effectiveness may also use measured values for the denominator in the effectiveness calculation. Brake effectiveness may also be set to use a user determined or regulatory driven cut-in pressure. Again, the electronics (e.g., controller and printed circuit board(s)) store, intake and process the information on the vehicle but may also communicate with fleet operations where these and other calculations may be performed to generate warnings and/or instructions for the driver and maintenance personnel. Without limitation, the process 1200 can, like the process 700, include determining an alarm state and/or a normal state of operation for the braking system based on the braking effectiveness.

[0059] FIG. 17 illustrates aspects of brake effectiveness, as determined according to the process 1200. Specifically, FIG. 17 includes a graph 1700 illustrating key regions of brake effectiveness overlaid on the graph 1400 of FIG. 14. If the combination of sufficient pressure and stroke are present, the system performs adequately at the upper right region 1702 of Figure 17. In other words, brake effectiveness is equal to or above a target effectiveness when the slack adjuster is within the functional range and air pressure is good. In one example, the nominal force F is 2268 lbs., based on a pressure of 80 psi and stroke of 1.75 inches. A second region 1704 just below the upper right region 1702 indicates that the air pressure is good, but the slack adjuster is out of adjust with the brake force still being sufficient. A lower right region 1706 is characterized by the braking force not being sufficient due to out of adjust by the slack adjuster with the air pressure being good. As you move to the left in the upper region of FIG. 17, a fourth region 1708 is characterized by the brake force being in sufficient due to low pressure (e.g., air pressure below specification) even though the slack adjuster is within tolerance. A lower left region 1710 of FIG. 17 indicates that the brake force is not sufficient due to low pressure (e.g., air pressure below specification) and the slack adjuster is out of adjust tolerance.

[0060] As will be appreciated from the foregoing, the present disclosure provides improved systems and techniques for determining braking system states, e.g., based on rotational displacements of the cam shaft 112. More specifically, aspects of this disclosure include providing a target, e.g., a magnetic target, fixed to the cam shaft 112, and a sensor, e.g., an xMR sensor, to determine rotational displacement of the target. In techniques described herein, the measured rotational displacements may be used to determine a stroke of a pushrod that causes the rotation. The pushrod stroke can be compared to a pushrod stroke limit to ensure that the pushrod is not over-stroking. Moreover, the pushrod stroke can be used, along with other information about the braking system, the brake chamber, or the like, an over-cam condition and/or a brake effectiveness. The systems and techniques described herein can improve functioning of the braking system by identifying, in real-time or near real-time, braking systems failure that can lead to further damage to the vehicle. The systems and techniques described herein can also improve safety outcomes, by identifying unsafe operating conditions in vehicles.

[0061] All orientations and arrangements of the components shown herein are used by way of example only. Further, it will be appreciated by those of ordinary skill in the pertinent art that the functions of several elements may, in alternative embodiments, be carried out by fewer elements or a single element. Similarly, in some embodiments, any functional element may perform fewer, or different, operations than those described with respect to the illustrated embodiment. Also, functional elements shown as distinct for purposes of illustration may be incorporated within other functional elements in a particular implementation.

[0062] While the subject technology has been described with respect to preferred embodiments, those skilled in the art will readily appreciate that various changes and/or modifications can be made to the subject technology without departing from the spirit or scope of the subject technology. For example, each claim may depend from any or all claims in a multiple dependent manner even though such has not been originally claimed.

Claims

WE CLAIM:

1. A braking system for a wheel of a vehicle, the braking system comprising: a cam shaft extending along a cam shaft axis between a first end a second end and having a cam surface disposed proximate the first end of the cam shaft; a slack adjuster coupled to the cam shaft proximate the second end of the cam shaft; a pushrod coupled to the slack adjuster; a brake chamber in communication with the pushrod, the brake chamber configured to selectively cause the pushrod to move relative to the brake chamber, movement of the pushrod relative to the brake chamber causing the slack adjuster to rotate the cam shaft about the cam shaft axis; and a sensing system configured to sense a rotational displacement of the cam shaft.

2. The braking system of claim 1, further comprising a controller configured to: receive data associated with the rotational displacement of the cam shaft; and determine, based at least in part on the rotational displacement of the cam shaft, a status of the braking system.

3. The braking system of claim 2, wherein the controller is further configured to: determine, based at least in part on the rotational displacement of the cam shaft and a distance associated with the slack adjuster, a computed stroke of the pushrod; compare the computed stroke of the pushrod to a stroke limit of the brake chamber; and determine, based at least in part on the computed stroke of the pushrod meeting or exceeding the stroke limit, an over-cam condition as the status of the braking system.

4. The braking system of claim 2, wherein the controller is further configured to: determine, based at least in part on the rotational displacement of the cam shaft and a distance associated with the slack adjuster, a computed stroke of the pushrod; receive a measured brake pressure; receive information about the brake chamber; determine, based at least in part on the computed stroke of the pushrod, the measured brake pressure, and the information about the brake chamber, a pushrod force; and determine, based at least in part on the pushrod force and a nominal pushrod force, a brake effectiveness as the status of the braking system.

5. The braking system of claim 2, the controller further configured to: generate an alert based at least in part on the status of the braking system; and transmit the alert to a computing system for presentation to a driver or a fleet manager.

6. The braking system of claim 1, wherein the sensing system comprises: a magnetic ring fixed relative to the cam shaft; and a stationary sensor configured to detect movement of the magnetic ring.

7. The braking system of claim 6, wherein the sensing system further comprises: a housing having a central aperture configured to couple to the cam shaft, wherein the magnetic ring is secured to the housing about the central aperture; and a guide comprising an arcuate slot, the guide disposed such that a portion of the housing is movable relative to the guide in the arcuate slot, wherein the stationary sensor is affixed to the guide to detect the magnetic ring.

8. The braking system of claim 7, wherein the stationary sensor is a magneto resistance sensor.

9. The braking system of claim 1 , wherein the cam shaft comprises an S-cam shaft having two cam surfaces configured to contact cam rollers.

10. A method of determining a state of a braking system, the braking system comprising: a cam shaft extending along a cam shaft axis; a slack adjuster coupled to the cam shaft; a pushrod coupled to the slack adjuster, wherein extension of the pushrod causes the slack adjuster to rotate the cam shaft about the cam shaft axis; and a sensing system configured to sense a rotational displacement of the cam shaft, the method comprising: determining, based on sensor data generated by the sensing system, a rotational displacement of the cam shaft about the cam shaft axis, determining, based at least in part on the rotational displacement of the cam shaft, a stroke of the pushrod, and determining, based at least in part on the stroke of the pushrod, the state of the braking system.

11. The method of claim 10, further comprising: comparing the stroke of the pushrod to a stroke limit, wherein the determining the state of the braking system comprises determining an overcam state based at least in part on the stroke of the pushrod being greater than the stroke limit or determining a normal state of operation based at least in part on the stroke limit being equal to or less than the stroke limit.

12. The method of claim 10, further comprising: receiving a measured brake pressure; and determining, based at least in part on the stroke of the pushrod, the measured brake pressure, and characteristics of a brake chamber, a pushrod force.

13. The method of claim 12, further comprising: determining, based at least in part on the pushrod force and a pushrod nominal force associated with a brake chamber, a brake effectiveness metric as the state of the braking system.

14. The method of claim 10, further comprising: generating, based at least in part on the state of the braking system, a braking system alert; and transmitting a signal corresponding to the braking system alert to a computing device, the signal configuring the computing device to generate an alarm corresponding to the braking system alert.

15. A braking system comprising: a cam shaft extending along a cam shaft axis; a slack adjuster coupled to the cam shaft; a pushrod coupled to the slack adjuster; a brake chamber configured to selectively extend the pushrod, extension of the pushrod causing the slack adjuster to rotate the cam shaft about the cam shaft axis; and a senor configured to sense a rotational displacement of the cam shaft.

16. The braking system of claim 15, wherein: the cam shaft extends from a first end to a second end; the cam shaft includes an S-cam proximate the first end; and the sensor is coupled to the cam shaft proximate the second end.

17. The braking system of claim 15, wherein the sensor comprises a magneto resistance sensor, the braking system further comprising a magnetic target.

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18. The braking system of claim 17, wherein: the magneto resistance sensor is fixed relative to the braking system such that the cam shaft rotates relative to the magneto resistance sensor; and the magnetic target comprises a magnetic ring fixed relative to the cam shaft to rotate with the cam shaft.

19. The braking system of claim 17, further comprising: a housing having a central aperture configured to couple to the cam shaft, wherein the magnetic ring is secured to the housing about the central aperture; and a guide comprising an arcuate slot, the guide disposed such that a portion of the housing is movable relative to the guide in the arcuate slot.

20. The braking system of claim 15, further comprising: a controller configured to determine, based on the rotational displacement of the cam shaft, a state of the braking system.

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