TECHNICAL FIELD

[1] This disclosure pertains to strain monitoring of bolts and rods and more particularly it relates to a load monitoring system for wheel studs of road vehicles.

BACKGROUND

[2] Vehicle wheel rims are commonly mounted to a hub by lug nuts fastened down on an equal number of wheel studs. Failure of wheel studs may occur when lug nuts come loose or if the material of the wheel and vehicle components gripped by the wheel studs and lug nuts diminish and disintegrate. Failure of wheel studs and runaway wheels in road vehicles causes many accidents every year. According to provincial records, 70% of wheel stud failures are due to wheel studs losing clamping force. It would be a benefit to the vehicle operator and to public safety if the operator could be alerted to these conditions while the vehicle was in operation.

[3] Wheels detach from transport trucks and trailers at a significant rate. According to

643 reported incidents in the US that were analyzed between 2000 and 2003, the reasons that wheels become detached include loose wheel fasteners (clamping force of nuts to hub) (65%), failed bearings (26%) and other causes such as axle and/or suspension structural failures (9%).

[4] Despite numerous innovations in the field, this type of roadway accident is still very high. The industry continues to use torque for defining the safety range of lug nut tightening rather than wheel stud tension, also referred to herein as clamping force or strain. However, torque is a very poor indicator of clamping force of fasteners. The condition of the surfaces of the threads, nut, and wheels can change the relationship of torque to clamping force significantly. If there is rust or paint on the wheel surface that changes in thickness during use, the clamping force will be reduced. A change of .001" thickness will reduce clamping force by approximately 15%. Furthermore, torque is largely taken up by friction and only 10% is taken up by tension. Therefore, there is not a good correlation of torque to wheel stud tension/clamping force. Wheel stud tension may vary for a given torque value depending on factors such as bolt age, condition (for example deterioration and rust) and lubrication.

[5] The most popular system in use for detecting the loosening of a wheel nut is a colored pointer that mounts to a wheel nut and is set in a specific orientation. When all pointers are aligned radially or circumferentially relative to the wheel for example, a nut that has rotated out of position can be identified at a glance. This type of pointer is described in the following publications:

US 6,158,933, issued to 0. Nicholson, on Dec. 12, 2000; and

US 6,398,312, issued to M. Marczynski et al., on June 4, 2002;

US 8,152,426, issued to M. Marczymski on April 2, 2012;

GB 2,508,152, published by A. A. Petrus de Groot, on May 28, 2014;

GB 2,536,294 issued to R E. Woods on Sept. 14, 2016.

[6] Another technology found in the prior art includes a circuit, a sensor and a transmitter mounted in a wheel nut. A signal is transmitted to the vehicle alarm system when the wheel nut is unscrewed or removed. This system is described in:

US Patent 5,552,759 issued to D. Stoyka on Sept. 03, 1996, and

WO 2016/042513 Al published by C.E. Lopes on March 24, 2016. [7] Other devices for detecting a loose lug nut include deformable washers mounted under a nut to be monitored. These washers give a visual or an electronic signal when a nut has been unscrewed or removed. Some of these devices are described in the following documents:

US Patent 3,589,234 issued to J.V.H. Trigg on June 29, 1971;

US Patent 4,636,120 issued to T.A. Brandsberg et al., on Jan. 13, 1987;

US Patent 8,872,668 issued to G.G. Schnare on Oct. 28, 2014.

[8] Other visual indicators of loose bolts are described in the publications listed below. In these documents, there are described different visual indicia, changing color or position, on the head of bolts, to indicate a degree of rotation of the bolts. US Patent 3,248,923 issued to R.H. Blakeley on May 03, 1966;

GB Patent 1,316,899 published by Gyrfalcon Inc., on May 16, 1973

US Patent 3,799,108 issued to J.E. Mosow on Mar. 26, 1974;

US Patent 3,850,133 issued to R.C. Johnson on Nov: 26, 1974;

CA Appl. 2,069,319 published by B. Walton on May 28, 1991;

US Patent 5,584,627 issued to S. Ceney et al., on Dec. 17, 1996; and

WO 2009/049060 published by C.H. Popenoe on April 6, 2009.

[9] In an electronic sensor category of loose bolt indicators, technologies using various instruments are found, such as described herein below:

[10] US Patent 2,600,029 issued to A.R. Stone on June 10, 1952. This document describes a bolt with a strain gauge mounted along the central axis of the bolt. A strain on a wire at the center of the bolt changes the resistivity of that wire, and by conversion of amperage to pounds of force, the resistance of the wire indicates a degree of strain of the bolt. [11] US Patent 3,969,713 issued to R. Bossier, Jr., on July 13, 1976. This document describes a series of contacts mounted on the head of a bolt to measure head deformation corresponding to a desired pre-load of a bolt or to a no-load condition.

[12] US Patent RE. 30,183 issued to C.H. Popenoe on Jan. 08, 1980. This patent describes a passive chip mounted in the head of a bolt. A reference pin at the center of the bolt indicates the relative elongation of the bolt, and applies more or less pressure on the chip. A corresponding change in inductance or capacitance of the elements of the chip are interrogated by a remote electronic meter to detect the condition of the bolt.

[13] US Patent 5,291,789 issued to B. Walton on Mar. 8, 1994. This document discloses an instrument to measure, by electrical contact, the relative elongation between a bolt and a stem mounted at the center of the bolt. A pair of set screws and circuit contacts on the head of the stem are calibrated to indicate two different stress levels in the body of the bolt.

[14] US Patent 7,412,898 issued to J.D. Smith et al. on Aug. 19, 2008. This document also discloses a passive chip mounted in the head of a bolt. The chip includes a radio-frequency identification transponder. A stem at the center of the bolt indicates the relative elongation of the bolt and activates an on-off contact on the chip to indicate a stress condition of the bolt. The chip is interrogated periodically by preventive maintenance personnel, for example, using a portable radiofrequency (RF) transmitter/receiver.

[15] In yet another document found in the prior art, a bolt has a central cavity filled with a fluid and a pressure sensor mounted in communication with the hollow core. This technology is described in:

[16] US Patent 7,994,901 issued to C.S. Malis et al., on Aug. 09, 2011. A piezoelectric pressure sensor is mounted in the head of the bolt. This sensor measures the pressure in the fluid of the cavity and translates it to strain in the bolt. An RF transmitter is also mounted in the head of the bolt and transmits the condition of the bolt to a vehicle warning system for example. One embodiment described in this document uses a piezoelectric sensor to generate power from the movement of the wheel on which the bolt is mounted to energize the RF transmitter.

[17] Despite the advances in this field, there remains a need for a system capable of measuring a change in tension in a threaded fastener, or more specifically a wheel stud, and bearing condition and to warn a vehicle operator of a dangerous condition of that wheel stud.

SUMMARY

[18] In the present disclosure, there is described a threaded fastener load monitoring system that detects precarious conditions on that threaded fastener. These conditions can be readily transmitted to the operator of the vehicle to avoid a hazardous situation.

[19] In a first aspect of the present invention, there is provided a threaded fastener load monitoring system to monitor a clamping force of a lug nut attached to a threaded fastener, the threaded fastener load monitoring system comprising two or more separators, wherein at least one of the separators is resilient and at least one of the separators is positioned between a head end of the threaded fastener and the lug nut, a contact element mounted to one of the separators, the contact element being movable along a displacement path upon elongation and relaxation of the threaded fastener by the lug nut, and a switch element at a proximity to the contact element and along the displacement path of the contact element.

[20] In a further aspect of the present invention, there is provided a road vehicle having a wheel rotor assembly comprising a wheel rotor, a wheel stud mounted to the wheel rotor and a wheel stud load monitoring system mounted to the wheel stud to monitor a clamping force of a lug nut attached to the wheel stud, the wheel stud load monitoring system comprising two or more separators, wherein at least one of the separators is resilient and at least one of the separators is positioned between a head end of the wheel stud and the lug nut, a contact element mounted to one of the separators, the contact element being movable along a displacement path upon a change of a clamping force, a switch element at a proximity to the contact element and along the displacement path of the contact element, the switch element making calibrated contact with the contact element upon a movement of the contact element along the displacement path, and an electronic circuit interpreting a position of the switch element relative to the contact element.

[21] A more complete understanding of the wheel-stud load measuring system can be obtained by reference to the following detailed description in connection with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[22] FIG. 1 is a cross-section view of an embodiment of the load monitoring system.

[23] FIG. 2 is a cross-section view of another aspect of the load monitoring system illustrated in FIG. 1.

[24] FIG. 3 is a cross-section view of a further embodiment of the load monitoring system.

[25] FIG. 4 is a cross-section view of a further embodiment of the load monitoring system.

[26] FIG. 5 is a detail view of the load monitoring system illustrated in FIG. 4. [27] FIG. 6 is a perspective top cutaway view of the embodiment of the load monitoring system illustrated in FIG. 4.

[28] FIG. 7A is a perspective bottom view of an embodiment of the load monitoring system.

[29] FIG. 7B is a perspective top view of the embodiment of the load monitoring system illustrated in FIG 7A.

[30] FIG. 8 is a schematic diagram of an embodiment of a signalling system for the load monitoring system.

[31] The drawings presented herein are presented for convenience to explain the functions of the elements included in the described embodiments of the threaded fastener load monitoring system. Elements and details that are obvious to the person skilled in the art may not have been illustrated. Conceptual sketches have been used to illustrate elements that would be readily understood in the light of the present disclosure. Some details have been exaggerated for clarity. These drawings are not fabrication drawings and should not be scaled.

DETAILED DESCRIPTION

[32] The following description and drawings are illustrative of the disclosure and are not to be construed as limiting the disclosure. Numerous specific details are described to provide a thorough understanding of various embodiments of the present disclosure. However, in certain instances, well-known or conventional details are not described in order to provide a concise discussion of embodiments of the present disclosure.

[33] The following description refers to a wheel stud load monitoring system. It will be understood by those skilled in the art that the disclosure provided may be applied to monitor load in other threaded fasteners, for example pipe fittings. In the load monitoring system, the clamping force is monitored, where the clamping force is the force supplied by a lug nut on a threaded fastener to hold two components together.

[34] An embodiment of the present disclosure is presented in FIG. 1. A threaded fastener 100, also referred to herein as a stud, has a head end 110 and an elongated threaded portion 120. A lug nut 130 is threaded onto the elongated threaded portion 120 of the stud 100 to fasten a wheel rim 140 to a wheel hub 150. A first separator 160 and second separator 170 are positioned between the wheel rim 140 and lug nut 130. The first separator 160 is comprised of resilient material such that, as the lug nut 130 is tightened on the stud 100, the first separator 160 is compressed by the force of the lug nut 130. In an embodiment, the first and second separators 160, 170 may each be comprised of resilient material. In a further embodiment, the first and second separators 160, 170 may each be comprised of resilient material having different Young's moduli, such that as the lug nut 130 is tightened on the stud 100, the first and second separators each compress with a different strain or clamping force. A contact element 180 is fixed to the second separator 170 and is movable along a displacement path as the lug nut 130 is tightened on the stud 100. A switch element 190 is located at a proximity to the contact element 180, such that as the contact element is displaced with the lug nut 130 tightening, the contact element makes contact with the switch element. The contact element 180 and the switch element 190 may be gold plated for efficient contact. The switch element 190 is resilient or may be mounted on a resilient connector (not shown) so that the switch element returns to its original position when the lug nut 130 load is relaxed.

[35] The first and second separators 160, 170 may be comprised of plastic or metal. As illustrated in FIG. 2, the first separator 160 may be a metal spring, in a donut or C-shape, to accommodate high loads provided by the clamping force of the lug nut 130 on the stud 100.

[36] FIG. 3 illustrates another embodiment of the present invention. In this embodiment, the first separator 160 comprises a resilient material, such as a plastic spring 310, and the second separator 170 comprises a recessed washer 320 overlapping the plastic spring. The recessed washer 320 may be comprised of metal. A gap 325 between the recessed washer 320 and the wheel rim 140 is preferably between 0.005 to 0.010 inches. The surface area of overlap between the recessed washer 320 and plastic spring 310 should be sufficiently large and the gap 325 between the recessed washer and the wheel rim 140 large enough so the plastic spring will deflect enough to provide resolution for the contact between the contact element 180 and the switch element 190. As the lug nut 130 is tightened on the stud 100, the lug nut load compresses the plastic spring 310 thereby moving the contact element 180 along the displacement path to come into contact with the switch element 190. As the lug nut 130 is further tightened, the recessed washer 320 closes the gap 325 and abuts the wheel rim 140. Further tightening of the lug nut 130 on the stud 100 elongates the stud. The switch element 190 is mounted in a resilient manner so that when the load provided by the lug nut 130 is relaxed by loosening the lug nut from the stud 100, the switch element 190 returns to its original position. As further illustrated in FIG. 3, the contact element 180 may comprise a set screw 330 traversing the recessed washer 320.

[37] The set screw 330 may be placed through a transverse opening 340 in the recessed washer 320. The switch element 190 may be set into a recess 360 in the plastic spring. The set screw 330 and switch element 190 may be accommodated in a cavity 350. The load monitoring system may be sealed with a thin film of plastic 370 on the wheel side to reduce corrosion of the electronic components.

[38] The position of the set screw 330 within the recessed washer 320 may be calibrated to correspond to a specific load on the stud 100 as follows: A load is applied to the stud 100 that approximates a minimum recommended load, below which a warning situation would exist, for example a load of 30,000 lbs. The set screw 330 is threaded into the transverse opening 340 in the recessed washer 320 so that the end of the set screw abuts the switch element 190. The set screw 330 is locked into place using, for example, a thread-locking glue. Thus, when the load would become less than 30,000 lbs, the contact between the set screw 330 and the switch element 190 would be lost, sending a signal as described in more detail below.

[39] More than one contact element 180 and switch element 190 may be utilized to monitor a range of loads. Each contact element 180 can be calibrated to make contact with a switch element 190 at a specific load, so that for example a minimum load, warning situation and maximum load value could be indicated by a set of three contact and switch elements. The multiple contact and switch elements 180, 190 may be located in the same cavity 350 or in different cavities in the circumference of the plastic spring 310. [40] FIG. 4 illustrates a further embodiment of the present invention as shown in FIG. 3, wherein the base of the recessed washer 320 is shaped as a conical spring washer 420. A gap 425 between the recessed washer 420 and the wheel rim 140 is preferably between 0.005 to 0.010 inches and is greater at the outer periphery of the base of the recessed washer 420. The set screw 330 may be placed through a transverse opening 430 in the recessed washer 420. The switch element 190, for example a rivet, may be set into a recess 450 within the cavity 440 in the plastic spring 310. A clearance 460 may be provided under the switch element 190 so that imperfections in the surface of the wheel rim do not cause the switch element to move up and make contact with the contact element 180.

[41] In this example, the lug nut 130 is tightened against the recessed washer 420 and plastic spring 310. The load from the lug nut 130 tightening on the stud 100 is shared between the first separator 160 (the plastic spring 310 in FIG. 4) and the second separator 170 (the recessed washer 420 in FIG. 4). The load or clamping force provided by the lug nut 130 is equal to the load on the plastic spring 310 plus the load on the recessed washer 320. This arrangement reduces stress on the plastic spring 310 and increases the force capability of the threaded fastener load monitoring system.

[42] FIG. 5 is a higher magnification of FIG. 4. The gap 425 between the recessed washer 420 and the wheel rim 140 with no clamping force applied is preferably between 0.005 to 0.010 inches. The size of the gap 425 increases radially outward between the recessed washer 420 and the wheel rim 140. As the lug nut 130 is tightened onto the stud 100, the outer edge of the lug nut first makes contact with the recessed washer 420. As the lug nut 130 is tightened further, it continues to make contact with the recessed washer 420 and pushes it down, so the plastic spring 310 is compressed. The plastic spring 310 is compressed before the recessed washer 420 due to the gap 425 between the recessed washer 420 and the wheel rim 140. As the lug nut 130 continues to be tightened further, it eventually compresses the plastic spring 310 enough that the gap 425 between the recessed washer 420 and the wheel rim 140 at the inner periphery of the recessed washer 420 is closed. As the lug nut 130 continues to be tightened down, the desired load on the stud 100 is reached and the contact element 180 makes contact with the switch element 190. Still further tightening of the lug nut 130 deforms the recessed washer until the recessed washer bottoms out. At that point, continuing to tighten the lug nut 130 on the stud 100 stretches the stud and there is no further movement of the contact element 180 and the switch element 190 to each other. Thus, the recessed washer 420 is shaped so when it first touches the wheel rim 140, only the inner periphery of the recessed washer touches the wheel rim, and as the lug nut 130 is further tightened, it deforms the recessed washer to close the gap 425, so the recessed washer acts as an additional spring to the plastic spring 310. This provides resilience from the second separator 170 (in this example the recessed washer 420) in addition to resilience from the first separator 160 (in this example the plastic spring 310).

[43] FIG. 6 is a bottom view of the load monitoring system of FIG. 4. Isolation grooves

670 in the plastic spring 310 on either side of the switch element 190 isolate the switch element from distortion as the lug nut is tightened on the stud (not shown).

[44] FIG. 7A and 7B illustrate a further embodiment of the present invention. The load monitoring system may be provided as a ring 710 with an array of load monitoring elements 720 arranged to align with the studs (not shown). The load monitoring elements 720 each comprise the first and second separators (in FIG. 7B illustrated as the plastic spring 310 and recessed washer 320), contact element (not shown) and switch element 190 for monitoring the load on the wheel stud. The first separator as illustrated is a plastic spring 310, which is part of and continuous with the ring plastic. The recessed washers 320 may be press-fit into the ring 710. The ring 710 includes an electronic circuit, including PC boards 730 for electronic connection to the switch elements 190 and batteries 740 for powering the load monitoring system. The ring 710 may also incorporate recessed channels for electronic connecting wires.

[45] Referring to FIG. 8, for each stud on a wheel hub, designated STUD 1 to STUD 10, a wire leads from each switch element to a PC board 78. Two switch elements may be provided per stud to monitor two different stud loads. Thus, there may be two wires per stud, 10 studs per wheel hub and one PC board 78 per wheel hub. Loss of contact between the switch elements and the contact elements 180 opens a switch, represented as Sl.l to S10.2, and which is sensed by the PC board 78. The PC board 78 is capable of determining which switch element is at issue in case of an open switch. The condition of the switch element can be interpreted by the PC board 78 and transmitted to the vehicle's warning system to inform the vehicle's operator of a lost nut, a broken stud or an over-tightened stud. To transmit a signal, the PC board 78 may communicate by radio frequency 91 to a signal light or beacon 82. The signal light or beacon 82 may have a tri-colour LED light 89 mounted within view of the vehicle operator, for example on the side of a truck trailer. The condition of contact between switch element and contact element could be communicated to the beacon 82 resulting in a yellow light, providing a warning signal to the vehicle operator, or a red light thereby communicating to the vehicle operator that a hazardous situation exists and the vehicle should be pulled over. The beacon 82 can display a green light when both switch elements and contact elements for a given stud are closed, indicating the load monitoring system is operating correctly, for example that the wheel hub transmitters are all communicating with the beacon, all contacts are closed and the temperature of the bearings are fine. If any faulty condition is detected, the beacon 82 will flash the appropriate colour in a code of short and long flashes, that identifies which wheel hub and stud is at fault. For example, yellow flashes of three long flashes followed by two short flashes repeatedly represents a warning that hub number three and stud number two is below the recommended tension. The beacon 82 communication to the vehicle operator occurs while the vehicle is in motion, so the vehicle does not have to be stopped to inspect the wheel stud condition.

[46] The PC board 78 is preferably powered by batteries 80. The PC board 78 is grounded through an attachment to the wheel hub, for example by a bracket or with a ring connector under the head of one of the studs connected by wire to the PC board (not shown). The PC board 78 also has a transmitter 84 to transmit, by radio signal or otherwise, the conditions of the contact and switch elements as interpreted by the PC board 78 to the beacon 82.

[47] The PC board 78 may also be connected to a thermistor 86. The thermistor 86 is mounted to the wheel hub in proximity of the wheel bearings, in order to detect temperature changes due to bearing failure, in advance of failure. The PC board 78 monitors the resistance of the thermistor 86 to interpret the temperature of the hub near the bearings. If the PC board 78 interprets the temperature of the hub near the bearings to exceed a predetermined maximum acceptable value, the PC board transmits a signal to the beacon 82 to alert the vehicle operator that a hazardous condition exists due to bearing failure and overheating.

[48] While embodiments of the wheel stud load monitoring system have been illustrated in the accompanying drawings and described herein above, it will be appreciated by those skilled in the art that various modifications, alternate constructions and equivalents may be employed. It should be further understood that the claims are not intended to be limited to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure. [49] Therefore, the above description and illustrations should not be construed as limiting the scope of the invention, which is defined in the appended claims.