Patent Description:
The present disclosure relates to vehicle braking systems, including but not limited to pneumatically-operated spring brake actuators having a push rod that engages a wheel brake.

The following U. Patents and U. Patent Application Publication disclose relevant background information.

<CIT> discloses one example of a conventional spring-brake actuator. The spring-brake actuator has a push rod assembly with a base located in a service brake chamber and a push rod extending from a service brake chamber. Pneumatic activation of the spring-brake actuator causes the push rod to further extend out of the service brake chamber to thereby engage a wheel brake with a wheel of the vehicle. Pneumatic deactivation of the spring-brake actuator causes the push rod to retract back into the service brake chamber to thereby disengage the wheel brake from the wheel of the vehicle.

<CIT> discloses a brake chamber having a chamber housing having an end, a push rod configured for reciprocal movement in the chamber housing in a first direction and a second direction over a stroke distance, a return spring disposed in the chamber housing configured to urge the push rod in the second direction and a sensor assembly having a sensor and a magnet movable relative to the sensor with movement of the push rod. The sensor is configured to detect a magnetic field strength of the magnet and output sensor data representative of the detected magnetic field strength. The sensor assembly is configured to determine a position of the push rod based on the sensor data over the entire stroke distance.

<CIT> discloses a spring brake actuator for applying a brake of a vehicle having a housing containing a diaphragm that separates the housing into first and second chambers. A clutch actuator device is for selectively compressing a compression spring such that the spring brake actuator is operable in a plurality of states including a parking state, driving state, and a braking state.

<CIT> discloses a spring brake actuator. The spring brake actuator has a push rod assembly with a base located in a service brake chamber and a push rod extending from a service brake chamber. Pneumatic activation of the spring brake actuator causes the push rod to further extend out of the service brake chamber to thereby engage a wheel brake with a wheel of the vehicle. Pneumatic deactivation of the spring brake actuator causes the push rod to retract back into the service brake chamber to thereby disengage the wheel brake from the wheel of the vehicle.

In certain examples, a system for monitoring stroke of a spring brake actuator of a vehicle comprises a spring brake actuator having a push rod, wherein pneumatic activation of the spring brake actuator causes the push rod to further extend out of the spring brake actuator to thereby activate braking of the vehicle, and wherein pneumatic deactivation of the spring brake actuator causes the push rod to retract back into the spring brake actuator to thereby deactivate braking of the vehicle. A first magnet and a second magnet are coupled to the push rod, and the second magnet is spaced apart from the first magnet. A sensor is configured to sense changes in a magnetic field created by the first magnet and the second magnet, and a controller is configured to determine stroke of the push rod based upon the changes in magnetic field.

Optionally, the first magnet is fixed relative to the second magnet such that as the push rod moves, distance between the first magnet and the second magnet remains constant. Optionally, the spring brake actuator has a chamber from which the push rod extends, and the first magnet is positioned in the chamber and the second magnet is positioned exterior of the chamber. Optionally, the second magnet is coupled to a rod end of the push rod. Optionally, a shroud is on the second magnet. Optionally, the shroud comprises a non-ferromagnetic material. Optionally, a sleeve couples the second magnet to the push rod. Optionally, the sleeve comprises a ferromagnetic material. Optionally, the sleeve has a lip and further comprising a shroud that rests on the lip to thereby protect the second magnet. Optionally, the sleeve has an end surface, and an end surface of the second magnet lies flush against the end surface of the sleeve. Optionally, the sleeve comprises a material having a high magnetic permeability. Optionally, the material comprising the sleeve has a magnetic permeability in the range of <NUM>,<NUM> to <NUM> relative permeability. Optionally, the material comprising the shroud has a magnetic permeability in the range of <NUM> to <NUM> relative permeability.

In certain examples, a spring brake actuator for braking a wheel of a vehicle comprises a first chamber, a second chamber, and a push rod extending from the second chamber, wherein pneumatic activation of the spring brake actuator causes the push rod to further extend out of the second chamber to thereby activate braking of the wheel of the vehicle, and wherein pneumatic deactivation of the spring brake actuator causes the push rod to retract back into the second chamber to thereby deactivate braking of the wheel of the vehicle. A first magnet is coupled to the push rod and a second magnet is also coupled to the push rod, the second magnet being spaced apart from the first magnet. A sensor is configured to sense changes in a magnetic field created by the first magnet and the second magnet. A controller is configured to determine stroke of the push rod based on changes in magnetic field.

Optionally, the first magnet is fixed relative to the second magnet such that as the push rod moves, distance between the first magnet and the second magnet remains constant. Optionally, the spring brake actuator has a chamber from which the push rod extends, and wherein the first magnet is positioned in the chamber and the second magnet is positioned exterior of the chamber. Optionally, the second magnet is coupled to a rod end of the push rod. Optionally, a shroud is on the second magnet. Optionally, the shroud comprises a non-ferromagnetic material. Optionally, a sleeve couples the second magnet to the push rod. Optionally, the comprises a ferromagnetic material. Optionally, the sleeve has a lip and a shroud rests on the lip to thereby protect the second magnet. Optionally, the sleeve has an end surface, and an end surface of the second magnet lies flush against the end surface of the sleeve. Optionally, the sleeve comprises a material having a high magnetic permeability. Optionally, the material comprising the sleeve has a magnetic permeability in the range of <NUM>,<NUM> to <NUM> relative permeability. Optionally, the material comprising the shroud has a magnetic permeability in the range of <NUM> to <NUM> relative permeability.

In certain examples, a system for monitoring stroke of a spring brake actuator of a vehicle includes a spring brake actuator having a push rod such that pneumatic activation of the spring brake actuator causes the push rod to further extend out of the spring brake actuator to thereby activate braking of the vehicle and pneumatic deactivation of the spring brake actuator causes the push rod to retract back into the spring brake actuator to thereby deactivate braking of the vehicle. A first magnet and a second magnet are coupled to the push rod, and the second magnet is spaced apart from the first magnet. A sensor is configured to sense a magnetic field created by the first magnet and the second magnet, and a controller is configured to determine stroke of the push rod based upon the magnetic field.

In certain examples, a system for monitoring stroke of a spring brake actuator of a vehicle includes a spring brake actuator having a push rod such that pneumatic activation of the spring brake actuator causes the push rod to further extend out of the spring brake actuator to thereby activate braking of the vehicle and pneumatic deactivation of the spring brake actuator causes the push rod to retract back into the spring brake actuator to thereby deactivate braking of the vehicle. A first magnet and a second magnet are coupled to the push rod, and the second magnet is spaced apart from the first magnet. A sensor is configured to sense a magnetic field created by the first magnet and the second magnet, and a controller configured to determine stroke of the push rod based upon the magnetic field.

In certain examples, spring brake actuator for braking a wheel of a vehicle includes a first chamber, a second chamber, and a push rod extending from the second chamber such that pneumatic activation of the spring brake actuator causes the push rod to further extend out of the second chamber to thereby activate braking of the wheel of the vehicle and pneumatic deactivation of the spring brake actuator causes the push rod to retract back into the second chamber to thereby deactivate braking of the wheel of the vehicle. A first magnet is coupled to the push rod, a second magnet coupled to the push rod, and the second magnet is spaced apart from the first magnet. A sensor configured to sense a magnetic field created by the first magnet and the second magnet, and a controller configured to determine stroke of the push rod based on the magnetic field.

In certain examples, a method for monitoring stroke of a spring brake actuator includes coupling a first magnet and a second magnet to a push rod of the spring brake actuator; actuating the spring brake actuator to thereby move the push rod; sensing magnetic field created by the first magnet and the second magnet as the push rod is moved; and determining stroke of the push rod.

Optionally, the first magnet is fixed relative to the second magnet such that as the push rod moves, distance between the first magnet and the second magnet remains constant. Optionally, the spring brake actuator has a chamber from which the push rod extends, and the first magnet is positioned in the chamber and the second magnet is positioned exterior of the chamber. Optionally, the coupling the second magnet to the push rod includes using a sleeve to couple the second magnet to the push rod. Optionally, the sleeve comprises a ferromagnetic material. Optionally, the sleeve comprises a material having a high magnetic permeability. Optionally, the material comprising the sleeve has a magnetic permeability in the range of <NUM>,<NUM> to <NUM> relative permeability. Optionally, the material comprising the shroud has a magnetic permeability in the range of <NUM> to <NUM> relative permeability.

Various other features, objects, and advantages will be made apparent from the following description taken together with the drawings.

The same numbers are used throughout the Figures to reference like features and like components.

Heavy trucks, trailers, and other commercial vehicles typically use brake systems including pneumatically-operated spring brake actuators which provide the braking forces necessary to stop the vehicle. Such a system typically includes a brake pedal positioned on the floor of the driver's cab or compartment of the vehicle which, upon activation, causes pressurized air from an air reservoir to enter an air chamber of the spring brake actuator. The spring brake actuator features a push rod which is caused to extend out of the air chamber to activate a wheel brake having brake shoes with a brake lining material that is pressed against a brake drum at the vehicle wheel-end. The wheel brake often includes a slack adjustor which turns a cam roller via a camshaft to force the brake shoes to engage the brake drum to stop the vehicle. Releasing the pressurized air from the air chamber allows a spring within the air chamber to retract the push rod back to its original position. See above-referenced <CIT> for an example conventional spring brake actuator.

The present inventors have observed that the output force generated by a spring brake actuator, such as the spring brake actuator disclosed in <CIT>, can be non-linear throughout the range of motion and decreases near the full-stroke limit. Federal regulations define the maximum stroke that can be used during vehicle operations as a subset of the full range of stroke as manufactured. If brake actuator push rod movement exceeds the specified limit during inspection, the brakes are considered to be out of adjustment.

In an attempt to resolve these problems, automatic slack adjusters have been required for new trucks and tractors since <NUM> and for new trailers since <NUM>; however, brake adjustment violations continue to rank among the top five vehicle out-of-service violations in the United States. In addition to on-going mitigation efforts, improved means of detection are viewed as an important component in addressing this wide-spread safety concern.

Some conventional stroke monitoring systems, such as the systems disclosed in above-referenced <CIT>, utilize a single magnet and/or one or more sensors to determine brake stroke at fixed, predetermined positions-one of these positions frequently being the "out of adjustment" or "overstroke" position. One of the disadvantages of this approach is that it is not possible to determine brake stroke outside of the fixed positions. Other systems rely on vision-based means to determine stroke, such as <CIT> and <CIT>, but these may be susceptible to environmental contamination in over-the-road and off-road commercial vehicle applications and require special design considerations for maintaining operating conditions within the sensed area.

Accordingly, the present inventors endeavored to develop systems of the present disclosure (described herein below) that are improved systems over the prior art and resolve one or more of the disadvantages noted above.

<FIG> depicts an example system <NUM> of the present disclosure. The system <NUM> includes a spring brake actuator <NUM> for applying a wheel brake of a vehicle. The spring brake actuator <NUM> extends along a center axis <NUM> and has an axially elongated housing <NUM>. The housing <NUM> includes opposing cup-shaped end housing portions, namely a first housing portion <NUM> and a second housing portion <NUM>. The first and second housing portions <NUM>, <NUM> have perimeter flanges <NUM>, <NUM> respectively, that engage each other in a sealing relationship. The housing <NUM> defines a first chamber <NUM> and a second chamber <NUM>. The first chamber <NUM> is separated from the second chamber <NUM> by a flexible diaphragm <NUM>. The perimeter of the diaphragm <NUM> is held and compressed by the perimeter flanges <NUM>, <NUM>. A port <NUM> formed through the first housing portion <NUM> is configured to admit and release compressed air to and from the first chamber <NUM>. The pressurized air can be provided by a conventional source of pressurized air located on the vehicle. A port <NUM> formed through the second housing portion <NUM> is configured to admit and release air to and from the second chamber <NUM>.

A push rod <NUM> has a first end portion <NUM> abutting the diaphragm <NUM> and an opposite, second end portion <NUM> extending out of second chamber <NUM>. The second end portion <NUM> is pivotably coupled to a lever arm of a conventional slack adjuster or cam roller (not shown). The slack adjuster and/or cam roller is configured to translate the reciprocal movement of the push rod <NUM> to a wheel brake for the vehicle. The push rod <NUM> has a rod <NUM> located in the second chamber <NUM> and extending through a hole in an end wall <NUM> of the second housing portion <NUM>. The push rod <NUM> also includes an end flange <NUM> that abuts the diaphragm <NUM> such that as the diaphragm <NUM> flexes back and forth in the housing <NUM>, the rod <NUM> reciprocates out of and back into the second chamber <NUM>.

A return spring <NUM> is located in the second chamber <NUM> and is compressed between the end wall <NUM> of the second housing portion <NUM> and the end flange <NUM> to thereby bias the rod <NUM> into the second chamber <NUM> and oppose movement of the rod <NUM> out of the second chamber <NUM>. In certain examples, a flexible bellows (not depicted) is coupled to the end wall <NUM> of the second housing portion <NUM> and covers the return spring <NUM> and the rod <NUM>.

A sensor assembly <NUM> is in the second chamber <NUM>. The sensor assembly <NUM> is directly or indirectly coupled to the end wall <NUM> of the second chamber <NUM>. The sensor assembly <NUM> includes a housing <NUM> in which one or more sensors <NUM> (described further herein) are positioned. The housing <NUM> protects the sensor <NUM> from debris and damage. In the example depicted in <FIG>, the push rod <NUM> slidably extends through a hole <NUM> defined by the sensor assembly <NUM>. The sensor housing <NUM> may be formed of plastic or other similar, suitable material. In certain examples, the sensor assembly <NUM> includes a printed circuit board ("PCB"), to which the sensor <NUM> is operably connected. In this example, the PCB includes a memory system, a processing system, such as a microprocessor, and a communication system.

The sensor <NUM> is configured to sense one or more magnetic characteristics (e.g., magnetic field, magnetic field strength) of one or more magnets <NUM>, <NUM> (described further herein) and output sensor data corresponding to the sensed magnetic characteristics. In one example, the sensor <NUM> senses a magnetic field strength and outputs sensor data corresponding to a value of the detected magnetic field strength. The sensor <NUM> can be any suitable sensor capable of sensing magnetic characteristics, and in one example, the sensor <NUM> is a Hall-Effect sensor. An example of a commercially available Hall-Effect sensor is part number Si7210 manufactured by Silicon Labs, and another commercially available Hall-Effect sensor is part number TLV493 manufactured by Infineon. Note in certain examples, the sensor <NUM> is configured to also sense temperature of or near the spring brake actuator <NUM>. In other examples, the sensor assembly <NUM> includes a separate temperature sensor for sensing temperature of or near the spring brake actuator <NUM>.

The spring brake actuator <NUM> includes a first magnet <NUM> directly or indirectly coupled to the end flange <NUM> of the push rod <NUM>. The first magnet <NUM> faces the sensor assembly <NUM> and moves with the end flange <NUM> as the rod <NUM> reciprocates into and out of the second chamber <NUM>, as noted above. In one example, the first magnet <NUM> is embedded in the end flange <NUM>. In another example, the first magnet <NUM> is disposed on an upper or lower surface of the end flange <NUM>.

The strength of the magnetic field detected by the sensor <NUM> varies based on a distance between the first magnet <NUM> and the sensor <NUM>. For instance, the detected magnetic field strength is weaker when the first magnet <NUM> is positioned farther from the sensor <NUM> and stronger when the first magnet <NUM> is positioned nearer to the sensor <NUM>. Thus, the detected magnetic field from the first magnet <NUM> is weakest when the rod <NUM> is at a 'zero stroke position' at start portion of a fore stroke (e.g., the fore stroke is movement of the rod <NUM> out of the second chamber <NUM>) which corresponds to an end position of the return stroke (e.g., the return stroke is movement of the rod <NUM> into the second chamber <NUM>). The zero stroke position also corresponds to the position of the rod <NUM> when the spring brake actuator <NUM> is in a driving state (described hereinbelow). In contrast, the sensed magnetic field of the first magnet <NUM> is strongest when the rod <NUM> is at an end position of the fore stroke, which corresponds to a start position of the return stroke, when the spring brake actuator <NUM> is in a braking state (described herein below, see <FIG>), and applying a maximum braking force on the vehicle. Note that the sensor <NUM> may detect the strength of the magnetic field at any desired time interval or in response to a known position of the rod <NUM>, the end flange <NUM>, and the first magnet <NUM>. For example, the sensor <NUM> may continuously sense the magnetic field strength during operation of the spring brake actuator <NUM>.

The present inventors observed that conventional system for monitoring stroke of spring brake actuators using a single magnet have shortcomings in sensing changes in magnetic fields as spring brake actuators are actuated. For example, the present inventor recognized that sensors, such as Hall-effect sensors are constructed to provide magnetic field strength readings to a specified sensitivity within a defined range. As such, when relative motion between the sensor and a single magnet occurs, a field-stroke curve based on the sensed magnetic field strength relative to stroke of the push rod is relatively flat when the distance between the magnet and the sensor is large or increases.

Referring to <FIG>, an example field-stroke curve <NUM> is depicted of a conventional single-magnet system. Note that the brake stroke axis <NUM> corresponds to stroke or distance moved by the push rod, and the sensed field strength axis <NUM> corresponds to the sensed magnetic field strength. In this example, the sensor is located on the end wall of the spring brake actuator and the magnet is coupled to the end flange of the push rod. As the push rod begins the fore stroke, the distance between the sensor and the single magnet is sufficiently large such that sensor does not sense or minimally senses magnetic field strength changes. This observation can be attributed to the sensitivity, or lack thereof, of the sensor, i.e. the sensor lacks the sensitivity to detect changes in magnetic field strength as the magnet moves with the push rod and thereby cannot distinguish stroke changes as the push rod moves. As such, the field-stroke curve <NUM> is sufficiently flat during the beginning of the fore stroke (see zone <NUM> which schematically depicts the beginning of the fore stroke; e.g., the beginning of the fore stroke may correspond with the first <NUM> of movement of the push rod) due to the lack the sensitivity of the sensor. Accordingly, the measurements of the stroke logged by the system may not accurately determine distinct stroke positions and/or stroke distance from the zero stroke position during the beginning of the fore stroke. Note that the sensor may accurately determine distinct stroke positions later in the fore stroke (schematically depicted by the field-stroke curve <NUM> outside of the zone <NUM>) as the distance between the magnet and the sensor decreases. Also, note that the description relative to the beginning of the fore stroke is also true regarding the end of the return stroke.

In one example sequence of the fore stroke of the push rod, the sensor may sense the magnetic field strength to be a value of <NUM> millitesla (mT) when the push rod is at the zero stroke position. As the push rod is moved along the fore stroke, the sensor senses: (<NUM>) the magnetic field strength to be a value of <NUM> mT at a stroke of <NUM>; (<NUM>) the magnetic field strength to be a value of <NUM> mT at a stroke of <NUM>; (<NUM>) the magnetic field strength to be a value of <NUM> mT at a stroke of <NUM>; (<NUM>) the magnetic field strength to be a value of <NUM> mT at a stroke of <NUM>; and (<NUM>) the magnetic field strength to be a value of <NUM> mT at a stroke of <NUM>. As such, actual stroke and movement of the magnet may not be accurately determined by the sensor during the beginning of the fore stroke (see zone <NUM> on <FIG>).

In addition, external perturbations (e.g., interference from other metallic or magnet components of the spring brake actuator or vehicle) may induce 'noise' in the magnetic field and/or mechanical movement of components of the system may cause the magnet to become misaligned relative to original calibrated positions. This 'noise' can decrease accuracy in sensing the magnetic field strength at the beginning of the fore stroke. Note that as the distance between the magnet and the sensor increases, the 'sensed magnetic field strength'-to-noise ratio increases and thus accuracy increases.

For these reasons, the present inventors endeavored to develop improved systems that can accurately determine distinct stroke positions the push rod during the beginning of the fore stroke and end of the return stroke and/or distances between stroke positions.

During research and development, the present inventors realized that certain seemingly obvious or simple solutions do not achieve the improved systems the present inventors desired to develop. For example, the constrained geometry of the spring brake actuator (without making major modifications thereto) does not permit simple increases to the size and/or shape of the single magnet to achieve increased magnetic field strength and/or variances the magnetic field strength throughout the range of stroke. This is due to physical envelope limitations within the spring brake actuator and component cost constraints that limit the size and shape of the magnet that can be used. For instance, it may not be physically or economically feasible to provide a sufficiently large magnet to create the required field variation across the full range of stroke. For example, increasing the diameter of the magnet would interfere with the return spring and increasing the thickness of the magnet would prevent full stroke as the magnet would contact the sensor of the end wall. Furthermore, there is often a trade-off between maximizing sensor sensitivity and maximizing sensor range. When sensitivity is maximized to resolve minute differences in the magnetic field, the sensor becomes more vulnerable to over-saturation as the magnet approaches the sensor because range has been sacrificed for sensitivity. This problem may be compounded by using a larger magnet.

As such, the present inventors endeavored to develop the systems <NUM> of the present disclosure that have more than one magnets to thereby advantageously address shortcomings in sensing changes in magnetic fields over distances as encountered with conventional single-magnet systems, increase accuracy of sensing changing magnetic fields, and/or provide additional improvements which maximize the ability to sense the magnetic field.

Referring back to <FIG>, the system <NUM> of the present disclosure further includes a second magnet <NUM> directly or indirectly coupled to the rod <NUM> such that the combined magnetic field strength of the magnets <NUM>, <NUM> is sensed by the sensor <NUM> as the rod <NUM> reciprocates into and out the second chamber <NUM> (as described above). The system <NUM> of the present disclosure is capable of more accurately determining the distinct stroke positions during stroke of the rod <NUM> including the during the beginning of the fore stroke and the end of the return stroke. That is, the systems <NUM> of the present disclosure have greater resolution of the magnetic field strength of the magnets <NUM>, <NUM> sensed by the sensor <NUM> during the stroke of the rod <NUM>, relative to conventional single-magnet systems.

The second magnet <NUM> is coupled to a rod end <NUM> of the rod <NUM>. In the non-limiting example depicted in <FIG>, the push rod <NUM> has an adapter <NUM> that couples the second magnet <NUM> to the rod end <NUM>. The adapter <NUM> is described in greater detail herein below. As noted above, the first magnet <NUM> is located on the end flange <NUM> and thus, the magnets <NUM>, <NUM> are on opposite sides of the sensor <NUM>. The magnets <NUM>, <NUM> are fixed relative to each other such that as the rod <NUM> reciprocates, the distance D1 between the magnets remains constant. Note that in other examples, the second magnet <NUM> is positioned between the sensor assembly <NUM> and the end wall <NUM> or between the sensor assembly <NUM> and the first magnet <NUM>. In certain examples, the second magnet <NUM> is orientated into alignment with the magnetic origination of the first magnet <NUM> such that opposite poles of magnets <NUM>, <NUM> are oriented toward each other. For instance, the north pole of the second magnet is oriented toward the south pole of the first magnet <NUM>.

Like the first magnet <NUM>, as described above, strength of the magnetic field of the of the second magnet <NUM> weaker when the second magnet <NUM> is positioned farther from the sensor <NUM> and stronger when the second magnet <NUM> is positioned nearer to the sensor <NUM>. Thus, the detected magnetic field of the second magnet <NUM> alone is strongest when the rod <NUM> is at a 'zero stroke position' at start portion of a fore stroke (e.g., the fore stroke is movement of the rod <NUM> out of the second chamber <NUM>) which corresponds to an end position of the return stroke (e.g., the return stroke is movement of the rod <NUM> into the second chamber <NUM>). However, the system <NUM> of the present disclosure includes both the first magnet <NUM> and the second magnet <NUM> such that the overlapping or collective magnetic field and/or magnetic field strength is unique and different than that only one of the magnets <NUM>, <NUM> alone.

The present inventors discovered that including the second magnet <NUM> with the first magnet <NUM> advantageously changes the magnetic field strength sensed by the sensor <NUM> such that the system <NUM> can more accurately determine distinct stroke positions of the push rod <NUM>. The magnetic fields of the magnets <NUM>, <NUM> are superimposed onto each other, and the sensor <NUM> senses the magnetic field strength of the magnets <NUM>, <NUM>. As will be described in greater detail herein below, as the rod <NUM> reciprocates the sensor <NUM> senses a different magnetic field strength as the positions of the magnets <NUM>, <NUM>, which are positionally fixed relative to each other, changes relative to the sensor <NUM>. In certain examples, as the rod <NUM> and the magnets <NUM>, <NUM> axially translate, the magnetic field of the magnets <NUM>, <NUM> also axially translates.

<FIG> depict the spring brake actuator <NUM> in various operational states. <FIG> depicts the spring brake actuator <NUM> in driving state in which the vehicle may be driven, by releasing the parking brake (e.g., manually release of a lever). Releasing the parking brake causes pressurized air to flow from the first chamber <NUM> via the port <NUM> into the second chamber <NUM> such that the air pressure in the first chamber <NUM> decreases and thereby causing the return spring <NUM> to retract the rod <NUM> in a first direction (see arrow A) into the second chamber <NUM>. Thus, no braking forces are applied to the wheels of the vehicle (e.g., the wheel brakes are not applied) and rod <NUM> is at the zero stroke position. Note that the rod end <NUM> extend a first distance R1 from housing <NUM>.

<FIG> depicts the spring brake actuator <NUM> in several different braking states as the operator depresses a brake pedal (not depicted) to thereby apply the wheel brake to slow or stop the vehicle. When depressing the brake pedal, pressurized air is provided via the port <NUM> to the first chamber <NUM> such that the air pressure in the first chamber <NUM> moves the diaphragm <NUM> is the second direction (arrow B) against the bias of the return spring <NUM>. As such, the rod <NUM> moves in the second direction (arrow B) out of the second chamber <NUM> such that the distance between the rod end <NUM> and the housing <NUM> increases to a second distance R2 (<FIG>) and thereby causing the wheel brakes to be applied. The second distance R2 is greater than the first distance R1 (<FIG>), and <FIG> sequentially depict the second distance R2 between the rod end <NUM> and the housing <NUM> increasing as the brake pedal is depressed further causing the spring brake actuator <NUM> to further actuate and further extend the rod <NUM> in the second direction (arrow B). <FIG> depicts the between the rod end <NUM> and the housing <NUM> at a maximum third distance R3 that is greater than the second distance R2. Note that in the example depicted on <FIG> the first magnet <NUM> contacts the sensor assembly <NUM> such that rod <NUM> stops moving in the first direction (arrow A). In other examples, bolts (not depicted) used to secure the spring brake actuator <NUM> in place on the vehicle extend into the chamber <NUM> and thereby prevent excessive movement of the push rod <NUM> in the first direction (arrow A) such that when the push rod <NUM> contacts the bolts there is a 'space' between the sensor assembly <NUM> and the first magnet <NUM> and these components do not damage each other. When the operator releases the brake pedal, the pressurized air in the second chamber <NUM> is released or exhausted and the spring brake actuator <NUM> returns to the driving state noted above (<FIG>).

In a non-limiting example, the first distance R1 (<FIG>) that the rod end <NUM> extends from the housing <NUM> is in the range of <NUM>-<NUM> millimeters (mm). When the rod <NUM> moves in the second direction (arrow B) out of the second chamber <NUM> to thereby initially cause the wheel brakes to be applied, the second distance (R2; e.g. see <FIG>) is in the range of <NUM>-<NUM>. Note that if the spring brake actuator <NUM> is in the driving state (<FIG>) and a control system <NUM> (described further herein) determines (based on the sensed magnetic field strength) that the distance between the rod end <NUM> and the housing <NUM> is greater than <NUM>-<NUM>, the control system <NUM> may further determine and/or alert the operator that the spring brake actuator is inadvertently applying braking to the vehicle (e.g., the spring brake actuator is 'dragging'). As the pedal is further depressed and/or over time as components of the spring brake actuator <NUM> wear, the second distance (R2; e.g., see <FIG>) between the rod end <NUM> and the housing <NUM> as the pedal is depressed may increase and result in a second distance R2 in an 'acceptable' range of <NUM>-<NUM>. Note that when the second distance R2 is within the 'acceptable' range, the spring brake actuator <NUM> is still considered to be functioning normally and within acceptable operational parameters for applying braking forces. However, once the distance between the rod end <NUM> and the housing <NUM> increases past the 'acceptable' range (e.g., to a 'unacceptable' position between the position of the push rod <NUM> depicted in <FIG> and the position of the push rod <NUM> depicted in <FIG>) in the range of <NUM>-<NUM> (when the maximum third distance R3 is <NUM> <FIG>), the spring brake actuator <NUM> is considered to be 'out of adjustment' and requires servicing or replacement.

Referring to <FIG> which depicts an example field-stroke curve when utilizing the two-magnet system <NUM> of the present disclosure, the sensor <NUM> advantageously senses greater variations in magnetic field strength during the beginning of the fore stroke and the end of the return stroke. As such, the system <NUM> accurately determines distinct stroke positions of the rod <NUM>, relative to conventional single-magnet systems, as illustrated by the field-stroke curve <NUM> depicted in <FIG>. In the example depicted on <FIG>, the field-stroke curve <NUM> is not flat during the beginning of the fore stroke (see zone <NUM> which schematically depicts the beginning of the fore stroke) to the magnetic field strength sensed by the sensor <NUM>. As such, measurements of stroke logged by the system <NUM> accurately distinguish distinct stroke positions during the beginning of the fore stroke and the end of the return stroke. Note that while <FIG> depicts the upper half of sensed field strength axis <NUM> exemplarily and schematically being positive field strength (+) and the lower half of the sensed field strength axis <NUM> exemplarily and schematically being negative field strength (-), this distinction is arbitrary and merely illustrative of relative changes in magnetic field strength sensed by the sensor <NUM> of the system <NUM> such that a clearer comparison can be made to magnetic field strength sensed by the sensor <NUM> of conventional systems (such as the system depicted in <FIG>).

In one example sequence of the fore stroke of the piston rod, the sensor <NUM> senses the magnetic field strength to be a value of -<NUM> when the rod <NUM> initially moves from the zero stroke position. As the rod <NUM> is actuated along the fore stroke, the sensor senses: (<NUM>) the magnetic field strength to be a value of -<NUM> at a stroke of <NUM>; (<NUM>) the magnetic field strength to be a value of -<NUM> at a stroke of <NUM>; (<NUM>) the magnetic field strength to be a value of -<NUM> at a stroke of <NUM>; and (<NUM>) the magnetic field strength to be a value of -<NUM> at a stroke of <NUM>; (<NUM>) the magnetic field strength to be a value of - <NUM> at a stroke of <NUM>; and (<NUM>) the magnetic field strength to be a value of -<NUM> at a stroke of <NUM>. As such, actual stroke of the rod <NUM> during the beginning of the fore stroke (see zone <NUM> on <FIG>) is determined by the system <NUM> due to the variations in the magnetic field strength sensed by the sensor <NUM>.

Referring now to <FIG>, an example adapter <NUM> of the present disclosure is depicted in greater detail. As noted above the adapter <NUM> couples the second magnet <NUM> to the rod end <NUM>. The adapter <NUM> has a sleeve <NUM> that is generally cylindrical with an open first end <NUM> and an opposite open second end <NUM>. A bore <NUM> is defined between the ends <NUM>, <NUM>, and the sleeve <NUM> has an inner first surface <NUM> and an opposite outer second surface <NUM>. The rod end <NUM> of the rod <NUM> is received into the bore <NUM> and engages the first surface <NUM> thereby securing the adapter <NUM> to the rod end <NUM>. In certain examples, the first surface <NUM> has threads that engage with threads of the rod end <NUM>. The second end <NUM> is configured to coupled to a lever arm of a conventional slack adjuster or cam roller (not shown) to thereby translate the reciprocal movement of the push rod <NUM> to a wheel brake for the vehicle.

An end surface <NUM> is at the first end <NUM> of the sleeve <NUM>, and the second magnet <NUM> coupled to the end surface <NUM> such that the second magnet <NUM> is secured to the rod <NUM>. The second magnet <NUM> can be coupled to the end surface <NUM> in any suitable manner such as with adhesives, welds, mechanical fasteners, and/or the like.

A shroud <NUM> encircles the first end <NUM> of the sleeve <NUM> and the second magnet <NUM> to thereby prevent damage to the second magnet <NUM>. The shroud <NUM> is coupled to the sleeve <NUM> and/or the second magnet <NUM> by any suitable means such as adhesives, welds, mechanical fasteners, and/or the like. In certain ax maples, the shroud <NUM> is integrally formed with the sleeve <NUM>. In certain examples, the shroud <NUM> is compression fit onto the sleeve <NUM> and/or the second magnet <NUM>. In certain examples, the shroud <NUM> holds the second magnet <NUM> on the end surface <NUM> of the sleeve <NUM> by compressing the second magnet <NUM> against the end surface <NUM> or having ribs that extend radially to prevent axial movement of the second magnet <NUM> away from the end surface <NUM>. In certain examples, the end surface <NUM> of the second magnet <NUM> lies flush with and makes continuous contact with the end surface <NUM>. This origination of the second magnet <NUM> relative to the sleeve advantageously increases the magnetic field strength in the direction toward the sensor <NUM> (<FIG>). In certain examples, the shroud <NUM> rests on a lip <NUM> of the sleeve <NUM>.

The material forming the sleeve <NUM> can vary, and in certain examples, the sleeve <NUM> is formed of plastic, metal, alloy, and/or ceramic. In one example, the sleeve <NUM> is formed of ferromagnetic material having high magnetic permeability. An example of a ferromagnetic material with high magnetic permeability is steel, such as <NUM> steel. The present inventors discovered that forming the sleeve <NUM> from ferromagnetic material with high magnetic permeability advantageously focuses the magnetic field toward the sensor <NUM> and/or enhances the magnetic field strength of the second magnet <NUM>. As such, the changes to magnetic field strength sensed by the sensor <NUM> as the rod <NUM> reciprocates are more apparent. In certain examples, the sleeve <NUM> is preferably formed of highly-ferromagnetic material with high magnetic permeability such as steel (e.g., <NUM> steel), to thereby maximize enhancement of the magnetic field of the second magnet <NUM> such that the changes to the magnetic field strength sensed by the sensor <NUM> as the rod <NUM> reciprocates is more apparent. In certain examples, the sleeve <NUM> is formed with a material with magnetic permeability in the range of <NUM>,<NUM> to <NUM> relative permeability (µr). In other examples, the sleeve <NUM> is formed with a material with magnetic permeability in the range of <NUM>,<NUM> to <NUM>µr. In other examples, the sleeve <NUM> is formed with a material with magnetic permeability in the range of <NUM> to <NUM>µr.

Similarly, the material forming the shroud <NUM> can vary, and in certain examples, the shroud <NUM> is formed by plastic, metal, alloy, and/or ceramic. In one example, the shroud <NUM> is formed by non- ferromagnetic materials such as aluminum, glass-filled nylon, and carbon fiber. Note that in certain examples, non-ferromagnetic materials are non-magnetic and/or contain no iron. In another example, the shroud <NUM> is formed of weak-ferromagnetic materials having relatively low magnetic permeability. In certain non-limiting examples, weak-ferromagnetic materials having relatively low magnetic permeability include stainless steel such as stainless steel <NUM> and stainless steel <NUM>. In certain examples, the shroud <NUM> is formed with a material with magnetic permeability in the range of <NUM> to <NUM>µr. The present inventors discovered that form the shroud <NUM> with non- or low ferromagnetic materials with no or low magnetic permeability advantageously does not or minimally disrupt or mask the magnetic field of the second magnet <NUM>. As such, the changes to magnetic field strength sensed by the sensor <NUM> as the rod <NUM> reciprocates are more apparent. In certain examples, the shroud <NUM> preferably comprises weak-ferromagnetic or non-ferromagnetic material such as stainless steel <NUM>, stainless steel <NUM>, and aluminum <NUM>.

In certain examples, the present inventors observed that forming both the sleeve <NUM> and the shroud <NUM> of ferromagnetic materials disadvantageously reduces the magnetic field of the second magnet <NUM> and thereby reduces the effect of the second magnet <NUM> on the sensor <NUM> and the collective magnetic field strength sensed by the sensor <NUM>. For illustrative purposes, <FIG> depicts the field-stroke curve <NUM> of the system <NUM> of the present disclosure when both the sleeve <NUM> and the shroud <NUM> are formed of ferromagnetic materials. In this example, the sensor <NUM> only minimally senses changes to magnetic field strength caused by the magnets <NUM>, <NUM> and as such, the field-stroke curve <NUM> is flatter during the beginning of the fore stroke (see zone <NUM>) than the field-stroke curve <NUM> depicted in <FIG>, albeit not as flat at the field-stroke curve <NUM> depicted in <FIG>. As such, while the above-noted composition of the sleeve <NUM> and the shroud <NUM> does slightly improve the ability of the system <NUM> to sense changes in the magnetic field strength of the magnets <NUM>, <NUM>, relative to a conventional single-magnet system (see <FIG>), the changes to the magnetic field strength are not as apparent to the sensor <NUM> when the shroud <NUM> is preferably formed of ferromagnetic material and the shroud <NUM> is formed with non-ferromagnetic material (as exemplarily noted above).

As described above, the example systems <NUM> of the present disclose sure are capable of sensing changes in the magnetic field strength accurately during the beginning of the fore stroke and end of the return stroke of the rod <NUM>. This accuracy is important for determining problems with the spring brake actuator <NUM> during this these areas of anticipated movement of the rod <NUM>. When the spring brake actuator <NUM> is in the driving state (<FIG>), the rod <NUM> is normally and preferably is in a zero stroke position such that the rod <NUM> is not causing braking forces are not applied to the vehicle. It is possible, however, that while the driving state (<FIG>) rod <NUM> does cause braking forces to be applied to the vehicle (commonly called 'dragging') due to wear of the components of the spring brake actuator <NUM> or other problems. If the spring brake actuator is in fact dragging, the vehicle and/or the spring brake actuator <NUM> should be taken out of service for repair or replacement. The system <NUM> of the present disclosure is capable of sensing changes to the magnetic field strength while the push rod is near the zero stroke position including during the beginning of the fore stroke and the end of the return stroke.

Note that problems with the spring brake actuator <NUM> normally do not occur when the rod <NUM> is in the middle of the stroke (e.g., stoke positions between the beginning of the fore stroke / end of the fore stroke and the end of the fore stroke / beginning of the return stroke). As such, in the event that the changes of the magnetic field strength in the middle of the stroke are not or minimally sensed by the sensor <NUM> (see zone <NUM> of <FIG> schematically corresponding to the magnetic field strength in the middle of the stroke on the example field-stroke curve <NUM>), the system <NUM> does loss its ability to determine problems with the spring brake actuator <NUM> at the ends/beginnings of the fore and return strokes.

Referring now to <FIG>, an example control system <NUM> of the present disclosure is depicted. The control system <NUM> determines the stroke position of the rod <NUM> (<FIG>) based on signals from the sensor <NUM> that correspond to the sensed magnetic field strength of the system <NUM>. The control system <NUM> can also determine if the rod <NUM> is dragging on the vehicle and/or if the push rod <NUM> has exceeded a maximum stroke and further alert the operator of the vehicle to inspect and/or replace the spring brake actuator <NUM> or other brake components (<FIG>). The control system <NUM> can also be configured to report different determinations to the operator including dragging of the spring brake actuator <NUM>, non-functioning service brake, non-functioning parking brake, overstroke of the push rod <NUM>, slow brake actuation, slow brake release, same-axle stroke imbalance, same-axle brake actuator mismatch, no signal, and/or sensor error. In certain examples, the control system <NUM> determines an overstroke condition by comparing the sensed stroke against a predetermined maximum allowable stroke. In certain examples, the control system <NUM> determines application of braking forces to the vehicle by the spring brake actuator <NUM> by comparing the active stroke during a known brake application (determined by activation of the brake light and/or sensed brake air pressure) to determine if the braking stroke application value exceeds an engagement threshold. In certain examples, the control system <NUM> determines a same-axle stroke imbalance by comparing the maximum stroke for spring brake actuators <NUM> associated with an axle of the vehicle. The control system <NUM> alerts the operator or generates a log data if the difference between the maximum strokes exceeds a predetermined threshold value which may be indicative of improper wear of one or both of the spring brake actuators <NUM>. In certain examples, the control system <NUM> determines a 'slow release' of the push rod <NUM> of the spring brake actuator <NUM> when a brake release command has been issued (e.g., brake light or brake pressure) and a determined moment of the push rod <NUM> is below a predetermined time engagement threshold. If the time difference exceeds a predetermined time value, a 'slow release' is indicated. Note that the control system <NUM> can be positioned remote from the spring brake actuator <NUM> (such as on the vehicle) and/or include the control system included with certain example sensor assemblies <NUM> (as noted above).

Certain aspects of the present disclosure are described or depicted as functional and/or logical block components or processing steps, which may be performed by any number of hardware, software, and/or firmware components configured to perform the specified functions. For example, certain embodiments employ integrated circuit components, such as memory elements, digital signal processing elements, logic elements, look-up tables, or the like, configured to carry out a variety of functions under the control of one or more processors or other control devices. The connections between functional and logical block components are merely exemplary, which may be direct or indirect, and may follow alternate pathways.

In certain examples, the control system <NUM> communicates with each of the one or more components of the system <NUM> via a communication link <NUM>, which can be any wired or wireless link. The control system <NUM> is capable of receiving information and/or controlling one or more operational characteristics of the system <NUM> and its various sub-systems by sending and receiving control signals via the communication links <NUM>. In one example, the communication link <NUM> is a controller area network (CAN) bus; however, other types of links could be used. It will be recognized that the extent of connections and the communication links <NUM> may in fact be one or more shared connections, or links, among some or all of the components in the system <NUM>. Moreover, the communication link <NUM> lines are meant only to demonstrate that the various control elements are capable of communicating with one another, and do not represent actual wiring connections between the various elements, nor do they represent the only paths of communication between the elements. Additionally, the system <NUM> may incorporate various types of communication devices and systems, and thus the illustrated communication links <NUM> may in fact represent various different types of wireless and/or wired data communication systems.

The control system <NUM> may be a computing system that includes a processing system <NUM>, memory system <NUM>, and input/output (I/O) system <NUM> for communicating with other devices, such as input devices <NUM> (e.g., user interface panel <NUM>, the sensor <NUM>, an accelerometer, ) and output devices <NUM> (e.g., user interface panel <NUM> may also be utilized as an output device), either of which may also or alternatively be stored in a cloud <NUM>. The processing system <NUM> loads and executes an executable program <NUM> from the memory system <NUM>, accesses data <NUM> stored within the memory system <NUM>, and directs the system <NUM> to operate as described in further detail below.

The processing system <NUM> may be implemented as a single microprocessor or other circuitry, or be distributed across multiple processing devices or sub-systems that cooperate to execute the executable program <NUM> from the memory system <NUM>. Non-limiting examples of the processing system include general purpose central processing units, application specific processors, and logic devices.

The memory system <NUM> may comprise any storage media readable by the processing system <NUM> and capable of storing the executable program <NUM> and/or data <NUM>. The memory system <NUM> may be implemented as a single storage device, or be distributed across multiple storage devices or sub-systems that cooperate to store computer readable instructions, data structures, program modules, or other data. The memory system <NUM> may include volatile and/or non-volatile systems, and may include removable and/or non-removable media implemented in any method or technology for storage of information. The storage media may include non-transitory and/or transitory storage media, including random access memory, read only memory, magnetic discs, optical discs, flash memory, virtual memory, and non-virtual memory, magnetic storage devices, or any other medium which can be used to store information and be accessed by an instruction execution system, for example.

In certain examples, the control system <NUM> records calibration data related to the spring brake actuator <NUM> on the memory system <NUM>. During the manufacturing process of the spring brake actuator <NUM> according to the present disclosure, the sensor <NUM> is calibrated to thereby associate a given magnetic field strength with one or more actual stroke positions of the rod <NUM>. For example, the rod <NUM> is placed into the zero stroke position (see <FIG>) and the sensor <NUM> senses the corresponding magnetic field strength. The sensor <NUM> then outputs a signal corresponding first threshold magnetic field strength to the control system <NUM>. The control system <NUM> stores this first magnetic field strength value on the memory system <NUM>. The rod <NUM> is then placed into a maximum stroke position (see <FIG>) and the sensor <NUM> senses the corresponding magnetic field strength. The sensor <NUM> then outputs a signal corresponding second threshold magnetic field strength to the control system <NUM> which is also stored on the memory system <NUM>. As such, calibration data corresponding to the magnetic field strength while the rod <NUM> is at determined outer extents are defined for the specific spring brake actuator <NUM> being calibrated.

With the calibration data stored to the memory system <NUM>, the control system <NUM> can determine the actual stoke position of the rod <NUM> during operation based on additional signals from the sensor <NUM>. For instance, if the sensor <NUM> senses the magnetic field strength to be equal to or within an acceptable range of the first threshold magnetic field strength, the control system <NUM> will determine that the rod <NUM> is at the zero stoke position. In another instance, if the sensor <NUM> senses the magnetic field strength that is greater than the second threshold magnetic field strength, the control system <NUM> will determine that the rod <NUM> has exceeded the maximum stroke alert the operator to inspect or replace the spring brake actuator <NUM>. In certain examples, the control system <NUM> may apply one or more algorithms stored on the memory system <NUM> to the signals and/or corresponding values received from the sensor <NUM> to determine the stroke of the rod <NUM>. In certain examples, the control system <NUM> compares the signals and/or corresponding values received from the sensor <NUM> to data on the memory system <NUM>, for example a look-up table, which correlates the sensed magnetic field strengths or sensed change to the magnetic field strength to a specific stroke of the rod <NUM>. Note that in certain examples, the sensor <NUM> is configured to compensate and/or adjust the signals corresponding to the sensed magnetic field strength value based on a sensed temperature. In certain examples, the control system <NUM> is further configured to receive signals from a brake light circuit sensor such that the control system <NUM> determines if the operator is actively depressing the brake pedal. Whether or not the operator is actively depressing the brake pedal may be considered by the control system <NUM> when determining the stroke position of the rod <NUM> and/or further determinations such as dragging of the brake or damaged sensor <NUM>.

In certain examples, the control system <NUM> is configured to record and store or log the data received from the sensor <NUM>. For instance, when the data corresponding to the sensed magnetic field strength is received from the sensor <NUM>, the control system <NUM> records a timestamp, which can comprise a date and a time, when the data is received. As such, a fleet manager can access this data log to observe operation and wear of the spring brake actuator <NUM>. Furthermore, the data log may provide a method for determining if the spring brake actuator <NUM> has been properly cared for and inspected. In certain examples, the control system <NUM> includes an electronic control unit (ECU).

<FIG> depicts an example control method <NUM> for operating an example system <NUM> described above. The example method included includes at step <NUM> in providing the rod <NUM> with the first magnet <NUM> and the second magnet <NUM> coupled thereto such that the spring brake actuator <NUM> has a magnetic field. At step <NUM>, the spring brake actuator <NUM> is actuated such that the rod <NUM> is moved. The sensor <NUM>, at step <NUM>, senses the magnetic field strength at the rod <NUM> and outputs a corresponding signal to the control system <NUM>. At step <NUM>, the control system determines the stroke position of the rod <NUM>.

In certain examples, a spring brake actuator for braking a wheel of a vehicle comprises a first chamber, a second chamber, and a push rod extending from the second chamber, wherein pneumatic activation of the spring brake actuator causes the push rod to further extend out of the second chamber to thereby activate braking of the wheel of the vehicle, and wherein pneumatic deactivation of the spring brake actuator causes the push rod to retract back into the second chamber to thereby deactivate braking of the wheel of the vehicle. A first magnet is coupled to the push rod and a second magnet is also coupled to the push rod, the second magnet being spaced apart from the first magnet. A sensor is configured to sense changes in a magnetic field created by the first magnet and the second magnet. A controller is configured to determine stroke of the push rod based on changes in the magnetic field.

Optionally, the first magnet is fixed relative to the second magnet such that as the push rod moves, distance between the first magnet and the second magnet remains constant. Optionally, the spring brake actuator has a chamber from which the push rod extends, and wherein the first magnet is positioned in the chamber and the second magnet is positioned exterior of the chamber. Optionally, the second magnet is coupled to a rod end of the push rod. Optionally, a shroud is on the second magnet. Optionally, the shroud comprises a non-ferromagnetic material. Optionally, a sleeve couples the second magnet to the push rod. Optionally, the sleeve comprises a ferromagnetic material. Optionally, the sleeve has a lip and a shroud rests on the lip to thereby protect the second magnet. Optionally, the sleeve has an end surface, and an end surface of the second magnet lies flush against the end surface of the sleeve. Optionally, the sleeve comprises a material having a high magnetic permeability. Optionally, the material comprising the sleeve has a magnetic permeability in the range of <NUM>,<NUM> to <NUM> relative permeability. Optionally, the material comprising the shroud has a magnetic permeability in the range of <NUM> to <NUM> relative permeability.

Citations to a number of references are made herein. In the event that there is an inconsistency between a definition of a term in the specification as compared to a definition of the term in a cited reference, the term should be interpreted based on the definition in the specification.

In the present description, certain terms have been used for brevity, clarity, and understanding. No unnecessary limitations are to be inferred therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. The different apparatuses, systems, and method steps described herein may be used alone or in combination with other apparatuses, systems, and methods. It is to be expected that various equivalents, alternatives and modifications are possible within the scope of the appended claims.

The functional block diagrams, operational sequences, and flow diagrams provided in the Figures are representative of exemplary architectures, environments, and methodologies for performing novel aspects of the disclosure. While, for purposes of simplicity of explanation, the methodologies included herein may be in the form of a functional diagram, operational sequence, or flow diagram, and may be described as a series of acts, it is to be understood and appreciated that the methodologies are not limited by the order of acts, as some acts may, in accordance therewith, occur in a different order and/or concurrently with other acts from that shown and described herein. For example, those skilled in the art will understand and appreciate that a methodology can alternatively be represented as a series of interrelated states or events, such as in a state diagram. Moreover, not all acts illustrated in a methodology may be required for a novel implementation.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claim 1:
A system for monitoring stroke of a spring brake actuator of a vehicle, the system comprising:
- a spring brake actuator having a push rod, wherein pneumatic activation of the spring brake actuator causes the push rod to further extend out of the spring brake actuator to thereby activate braking of the vehicle, and wherein pneumatic deactivation of the spring brake actuator causes the push rod to retract back into the spring brake actuator to thereby deactivate braking of the vehicle;
- a first magnet and a second magnet coupled to the push rod, the second magnet spaced apart from the first magnet;
- a sensor configured to sense a magnetic field strength created by the first magnet and the second magnet; and
- a controller configured to determine stroke of the push rod based upon the magnetic field strength.