Device for securing balancing weights to a shaft

A shaft balancing device for insertion into a shaft including a generally flat cylindrical band having an outer surface, an inner surface and a set of two crush points thereon. A balancing weight is attached to the outer surface of the band between the set of crush points. The device is inserted into the shaft and the crush points are plastically deformed radially outward creating spring force which holds the balancing weight to the inner surface of the shaft. The band has a curved connecting portion between the two crush points having a radius of curvature slightly greater than the curvature of the shaft. The balancing weight has a radius of curvature slightly greater than the radius of curvature of the curved connecting portion and slightly less than the radius of curvature of the shaft.

FIELD OF THE INVENTION

The present invention relates to a device for securing balancing weights to the inside surface of a shaft. More specifically, this invention relates to an improved device for securing balancing weights to the inside surface of a shaft used in the assembly of a driveshaft.

BACKGROUND OF THE INVENTION

Motor vehicle drivetrain assemblies typically include a tubular driveshaft and one or more axles. Balancing the driveshaft aids in improving the overall performance of the drivetrain assembly. An unbalanced driveshaft can induce vibrations and noise in the drivetrain assembly. Reducing or removing excessive vibrations and noise in the driveshaft contributes to increased life of the components of the driveshaft and drivetrain assembly.

Driveshafts are preferably manufactured from tubing in the shape of a perfectly round cylinder having a uniform wall thickness throughout. A perfectly shaped driveshaft tube would be precisely balanced for rotation and would not generate any undesirable noise or vibration during use. However, the cost of a driveshaft made from materials with uniform wall thickness is often prohibitive. Lower cost commodity materials can be used to control overall costs of driveshafts; however, using such materials will often result in excessive variations in wall thickness, etc. This variation creates a difference in the mass radially around the driveshaft creating an excessive static imbalance. When this driveshaft is built into a drivetrain assembly, the static imbalance causes the assembly's dynamic balance to be excessive.

To prevent such unbalances from generating undesirable noise or vibration balancing weights are often used to counteract such imbalances. The balancing weights are sized and attached to selected portions of the driveshaft tube to balance the rotation during use.

A need exists for a device and method to balance driveshafts prior to using the shafts in other drivetrain assemblies which decreases the static imbalance of the shaft and, therefore, decreases the initial dynamic imbalance of the driveshaft assembly.

SUMMARY OF THE INVENTION

A shaft balancing device for insertion into a shaft including a generally flat cylindrical band having an outer surface, an inner surface and a set of two crush points thereon. The outer diameter of the band is slightly smaller than the inner diameter of the shaft it is inserted into. A balancing weight is attached to the outer surface of the band between the two crush points. The crush points project radially inward from the inner surface of the band and can be plastically deformed radially outward bringing the two ends of the band in contact creating a spring force which holds the balancing weight to the inner surface of the shaft. The band has a curved connecting portion between the two crush points with a radius of curvature slightly smaller than the curvature of the shaft. The balancing weight has a radius of curvature slightly greater than the radius of curvature of the curved connecting portion and slightly smaller than the radius of curvature of the shaft.

The generally flat cylindrical band can be formed by rolling a generally rectangular flat band into a cylinder with a diameter less than the diameter of the unbalanced shaft. The generally flat cylindrical band is placed inside the shaft and then released allowing the outer surface of the band to make contact with the inner surface of the shaft. The crush points are then deformed radially outward supplying a spring force to hold the balancing weight in place in the shaft.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to a device for securing balancing weights to the inside surface of a shaft.

Referring now toFIGS. 1-2, a shaft balancing device10includes a balancing weight12secured to a band14. Band14is a generally flat band made from plastically deformable material including, but not limited to, spring steel. The dimensions of band14can be chosen to suit a particular application such that band14can be inserted into a shaft. In one preferred embodiment, as shown inFIGS. 1-2, band14is generally rectangular in shape having a width14a, a length14band a thickness14c. The thickness14cof band14is uniform throughout band14. Preferably, thickness14cis relatively small compared to the thickness of the unbalanced shaft it is being inserted into. In one preferred embodiment, band14is 20.5 inches long, 1 inch wide and 0.015 inches thick.

As shown inFIGS. 1-3, band14has an inner surface14dand an outer surface14e. Balancing weight12is attached to the outer surface14eof band14. In one preferred embodiment, balancing weight12is welded to the outer surface14eof band14. In other embodiments, balancing weight12can be attached using mechanical means such as using fasteners or staking or secured through the use of adhesive. Balancing weight12can be made to any predetermined weight and size as needed in a particular application. Balancing weight12may be made of any known material suitable for an application including, but not limited to high density metals including steel, brass or copper and aluminum or plastic. In one preferred embodiment balancing weight12is substantially square in shape and has inner surface12aand outer surface12b. Balancing weight12is welded to band14such that the outer surface14eof band14is in contact with the inner surface12aof balancing weight12. In one preferred embodiment, balancing weight12has a width and/or length that is larger than the width of band14such that balancing weight12extends beyond the width14aof band14as shown inFIGS. 1-2. In one preferred embodiment balancing weight12has a thickness12cthat is larger than the thickness14cof band14.

As shown inFIGS. 1-3, inner surface12aof balancing weight12has a concave curved surface. The radius of the curvature provided by the concave inner surface12ais such that when band14is rolled to form a cylinder and placed inside a shaft, the radius of curvature of balancing weight12(r2) is slightly smaller than the radius curvature of the shaft (r1) allowing the outer surface12bof balancing weight12to contact the inner surface the shaft as shown inFIG. 8.

Referring now toFIGS. 1-2, band14has a set of two crush points16a,16bformed therein protruding upward from the inner surface14dof band14. Crush points16a,16bare positioned along band14such that balancing weight12is attached to band14between crush points16a,16b. Crush points16a,16bcan be of any shape or size as needed in a particular application as to provide a surface which can be deformed when a force is applied thereto and when deformed increases an “effective length” of band14to a length greater than the actual length14b. As used herein, the term “effective length” refers to length of band14if unrolled when crush points16a,16bare deformed. For example, in one preferred embodiment the length of band14is 20.5 inches as shown inFIGS. 1-2. When crush points16a,16bare deformed the “effective length” of band14is greater than 20.5 inches bringing ends14f,14gof band14into contact with one another and, thus, forcing the outer surface14eof band14radially outward against the inner surface of a shaft20as shown inFIG. 8. In one preferred embodiment, crush points16a,16bare peaks as shown inFIGS. 1-2.

The portion of band14between crush points16a,16bis a curved connecting portion18. The curvature of connecting portion18matches the curvature of the inside surface12aof balance weight12. Curved connecting portion18has an inner surface18a, outer surface18band a length18cas shown inFIGS. 1-2.

As shown inFIGS. 1-4, in one preferred embodiment band14has a single balancing weight12attached thereto. In certain embodiments, more than one balancing weight12can be added to band14to counteract imbalances in a shaft. In one preferred embodiment, as shown inFIG. 9the additional balance weights12d,ecan be added to curved connecting portion18between crush points16a,16b. The length18cof curved connecting portion18is longer than the total length of the balance weights12.

Referring now toFIG. 1, band14has two ends14f,14gon each end thereof. Band14can be rolled such that ends14f,14gmeet creating a generally cylindrical shape as shown inFIGS. 3-4. The cylindrical shaped band14has a maximum diameter14h. Curved connecting portion18provides band14with a second diameter14ias shown inFIG. 4. The difference between maximum diameter14hand second diameter14iis equal to the thickness12cof balancing weight12.

When band14is rolled such that ends14f,14gof band14overlap, band14forms a cylindrical shape such that the maximum outer diameter14hof band14is smaller than the inner diameter of shaft20which band14is to be positioned inside.

Shaft20has an inner surface20aand outer surface20b. To insert band14into a shaft20, band14is rolled to form a generally cylindrical shape having a maximum outer diameter14his smaller than diameter of the inner surface20aof shaft20and then inserted into shaft20. Band14can be positioned inside shaft20in any position as needed to counterbalance the imbalances in shaft20. As shown inFIG. 5, more than one band14can be placed inside shaft20if needed to balance shaft20. Once band14is inserted into shaft20, band14can be released allowing the outer surface14eband14to contact inner surface20aof shaft20as shown inFIG. 6. When band14is released, ends14f,14gare aligned with one another and a small gap may exist between ends14f,14g.

To provide a more secure connection between balance weight12and inner surface20aof shaft20, crush points16a,16bcan be plastically deformed by applying a force downward toward the inner surface20aof shaft20elongating band14. Prior to applying a force to crush points16a,16b, a gap may exist between the outer surface12bof balancing weight12and the inner surface20aof shaft20as shown inFIG. 6. By deforming crush points16a,16ba maximum outward spring force is created on inner surface20aof shaft20forcing the outer surface12bof balance weight12to make contact with the inner surface20aof shaft20as shown inFIGS. 7-8. During deformation, ends14f,14gof band14meet. The spring force holding balancing weight12in place is sufficient under low loads and speeds to hold balancing weight12to the inner surface20aof shaft20.FIG. 7depicts a tool17applying a force to crush points16a,16bcreating a maximum outward spring force.

However, under high loads and speeds the spring force created by the deformation of the crush points16a,16bmay not be sufficient to hold balancing weight12in place against the inner surface20aof shaft20and additional means of attachment may be needed. In one preferred embodiment, band14is further secured to the inner surface20aof shaft20using an adhesive. The adhesive is applied to the outer surface14eof band14prior to placement in shaft20. The adhesive material may be any desired adhesive material including epoxies. In another preferred embodiment, band14can be fastened to the inner surface20aof shaft20by mechanical means including, but not limited to staking. In another preferred embodiment, a coating can be applied to shaft20and band14after insertion of band14into shaft20to seal and adhere band14to inner surface20aof shaft20. The coating can be, but is not limited to, an atomized ultraviolet light curing material.

As shown inFIG. 5, additional bands14can be inserted into shaft20and positioned as needed to counter balance the imbalance of shaft20. As previously discussed, in certain embodiments, band14can also include more than one balancing weight12and be positioned in shaft20to counter balance the imbalance of shaft20as required for a particular application.