Patent Application
20080226411
This invention is related to threaded mechanical fasteners and more particularly to tension control wheel bolts and studs.
The purpose of tightening bolts (for example, on lug nuts when attaching a wheel to a hub) is to create tension in the bolt or stud. This tension, in turn, creates clamping forces that hold the different pieces together.
The clamping force is actually friction at the interface that restricts movement of the joined surfaces relative to one another. Since clamping force is impractical to measure accurately in the field, torque of the fasteners is measured to approximate the desired clamping force.
Tightening vehicle wheel nuts to their specified torque is extremely important. When a wheel nut is under tightened, the wheel is loose which can damage the wheel, stud and wheel hub and can result in wheel loss during vehicle operation.
One cause of wheel failure is due to an installer's improper application of the correct amount of torque on the wheel nuts. This may result from inattention or to mis-calibrated tools. It is therefore desirable to eliminate the likelihood of misapplied torque with a fastener that provides immediate visual evidence that the fastener is tightened to the correct amount of torque.
Once a tire and wheel assembly has been installed on a vehicle, a period of “settling-in” occurs where the clamped/bolted assembly loses some clamp load. This clamp loss is often due to dust, dirt, paint and/or corrosion on wheel faces, nuts and stud threads settling or moving during operation. The amount of clamp loss is dependent upon the condition of the components, the method of installation used, the number of times the wheels have been installed using the same fasteners, the amount and condition of paint on wheels and the fasteners and lubrication used in the installation process.
Even new wheels and fasteners will lose clamp load. New components can lose torque as a result of loss or compression of fastener coatings on the working surfaces of the hub, brake drum, and disc wheels. Therefore retorquing is necessary to ensure the proper amount of clamp load is attained to keep the tire and wheel assembly safely coupled to the vehicle. Normally, it is recommended in the heavy-trucking industry that wheel nuts be retorqued after 50-100 miles of driving to account for this settling in.
This requisite retorquing will also benefit from a “fool-proof” system of visual inspection that the retorqued fasteners have been set to the desired level.
Currently, tension control bolts are used in the construction of static structures using structural steel framing. These prior art tension control bolts include a bolt and nut that provide immediate visual feedback to an installer that the fastener has been set to the correct torque setting. The bolt includes a breakaway section at the end of the threaded portion of the bolt. A groove is formed in the bolt between the threads and the breakaway section. The breakaway section is designed to break off, at the reduced diameter groove, when a tension above a pre-determined design level is induced in the bolt during installation. An installation tool, commonly referred to as a shear wrench, grips the breakaway section with a conforming chuck and tightens the nut until the breakaway sections twists off at the groove. These prior art tension control bolts, being designed for static structure construction that do not suffer from the settling-in of vehicle fasteners, have the inherent drawback that after their initial installation they do not provide a means for visually ensuring that a retorquing operation has properly occurred.
The broad purpose of the present invention is to provide a tension control fastener that includes at least two breakaway sections that twist free from the fastener at a predetermined amount of torque. The tension control fastener is preferably adapted as a wheel nut or stud having a threaded shank that receives a nut. The end of the threaded shank includes the multiple breakaway sections which are adjacent and axially coextensive to each other along the fastener's shank.
One advantage of the present invention is that it ensures that the fastener is tightened to a first predetermined torque level and is then able to ensure that the same fastener is tightened to a second predetermined torque level.
Another advantage of the present invention is that it provides a user with a fool-proof visual reference that the fastener has been tightened to a first predetermined torque level.
Still another advantage of the present invention is that it provides a user with a fool-proof visual reference that the fastener has been re-tightened to a second predetermined torque level.
Still further objects and advantages of the invention will become readily apparent to those skilled in the art to which the invention pertains upon reference to the following detailed description.
The description refers to the accompanying drawings in which like reference characters refer to like parts throughout the several views, and in which:
As shown best in
In this embodiment, head 18 is located at one end of the shank and body 20 is adjacent to head 18. In other non-limiting embodiments, the body 20 may be eliminated and the threaded portion may run along the entire length of the shank.
Bolt 12 differs from conventional wheel bolts in that the end 23 opposite to bolt head 18 includes a pair of breakaway sections 24 and 26. Each breakaway section includes a plurality of longitudinally running ribs or splines 27 that are gripped by a specially designed shearing chuck 28 of an installation tool 30 (shown in
Each breakaway section 24, 26 includes an adjacent breakaway groove 32, 34. The grooves 32, 34 are formed into the shank such that the grooves present the two narrowest cross-sections of the shank 16. The outermost groove 34 being slightly deeper (i.e., presenting the narrowest section in the shank) than the inner groove 32.
It should be appreciated that the splines 27 shown on the breakaway sections 24, 26 are for illustrative purposes only and that any equivalent gripping surface and complementary shear wrench chuck 28 may be used for the purpose of removably coupling the installation tool to the breakaway sections while a torsional force is applied to the fastener.
In operation, the outermost breakaway section 26 is gripped by shear chuck 28 of installation tool 30. The installation tool mates with and turns the nut 14 relative to bolt 12 (i.e., relative to breakaway section 26). As shown in
The greater depth of groove 34 presents the weakest section along shank 16 and ensures that the torque applied to nut 14 and bolt 12 will cause the outermost breakaway section 26 to break away leaving breakaway section 24 at the end of shank 16.
As shown in
Referring now to
Installation begins in
In
Once the torque applied to fastener 10 exceeds a predetermined level, breakaway section 26 shears off of the fastener at groove 34, as shown in
If a user desires to retighten or retorque fastener 10, such as after a “settling-in” period of time, the second or inner breakaway section 24 remains and provides immediate visual feedback confirming that a second retorquing process will exceed a second predetermined torque level as designed into the fastener 10.
In
Referring now to
A second cylindrical body 120 is intermediate to threaded section 118 and body 20. An enlarged annular collar or shoulder 124 is intermediate to the two bodies 20,120 and projects radially from the longitudinal axis of the stud.
It should be appreciated that the bolt 12 and stud 112 provided herein are exemplary and that various configurations of threaded fasteners may be used with the dual breakaway sections 24, 26.
As shown in
As shown in
While the present invention has been described with particular reference to various preferred embodiments, one skilled in the art will recognize from the foregoing discussion and accompanying drawing and claims that changes, modifications and variations can be made in the present invention without departing from the spirit and scope thereof as defined in the following claims.
