GB2383112A

GB2383112A - High torque clamp hub

Info

Publication number: GB2383112A
Application number: GB0220646A
Authority: GB
Inventors: Robert Michael Barton
Original assignee: Reliance Gear Co Ltd
Current assignee: Reliance Gear Co Ltd
Priority date: 2001-09-05
Filing date: 2002-09-05
Publication date: 2003-06-18
Anticipated expiration: 2022-09-05
Also published as: GB2383112A8; GB0121449D0; GB2383112B; GB0220646D0

Abstract

A split type clamp for attaching a component to a shaft 20 comprises a hub body having a first diametral slit 11 through a cental bore 12 to form two body sections which are compressed together about a shaft by a bolt 16 and attached at the other end of the slit (40 Fig. 7) to a driven body. An additional slit 18 is provided in an end face of the clamp at 90 degrees to the original slit to reduce the stiffness of the clamp and thus maximising the clamp friction grip for a given fastener torque compared to a single slit clamp. The additional slit may extend to the axial centre line of the clamp and there may be two bolts or other fasteners. The clamp may be of steel, aluminium, plastics or ceramics.

Description

HIGH TORQUE CLAMP HUB Many methods of attaching components to shafts are known in the prior art. These methods include the use of set screws and various pins which transmit high torques. However these methods can permanently damage the shaft. Another method is clamp style hubs that do not damage the shafts, but they suffer from lower torque transmission.

One common type of clamp hubs use tapered components axially pulled together by a number of screws, expanding radially due to the tapers to clamp the shaft. This type of clamp hub is shown in Figures l (a)-l (d). This type of clamp exerts significant interface pressure and transmits high torques, but the high component count and complex machining required are drawbacks. Due to their intricate nature, the minimum size of the hub is often comparatively large. Also, fitting these clamps on a shaft can be problematic. During the clamping process, the screws must be tightened with torque that may cause the component to rotate on the shaft, hindering assembly.

Another common type of clamp hubs is the split type clamp. These are generally much simpler devices with a single slit and one or two screws. This type of clamp is seen in Figures 2 (a)-2 (b). The existing Reli-a-Flexo'-coupling clamp design falls into this category. These types of clamps exert pressure on two diametrically opposed contact areas. Although the resulting pressure can be high, particularly with two screws, the torque that can be transmitted is often not very large because the area over which it acts is smaller.

In the present invention, the clamp utilizes a split type of clamp for ease of manufacture and low component count, but has an important additional feature to increase the level of transmitted torque. This feature is an additional slit at 90 degrees to the original slit to reduce the stiffness of the clamp. The additional slit produces few quadrants having greater flexibility. This flexibility allows the clamp to reduce its effective diameter while still maintaining a circular cross section. The result is the ability to transmit greater torque

for the same fastener torque compared to a clamp without the additional slit.

Accordingly, the present invention a clamp for connecting components to a shaft, comprising a first and second section, each section having a first face, a second face, a perimeter wall, a first end wall and a second end wall, at least one fastener for connecting said two sections together to secure the clamp about the shaft, each section having a slit in one of said faces.

In one particular embodiment of the invention, said at least one fastener is a screw. In another embodiment, said at least one fastener is a pair of screws, each screw extending through the perimeter wall and end wall of one section and into the end wall of the other section.

Preferably, each section has a centerline located equidistant from said first and second face, said slit extending to said centerline.

Preferably, said slit is perpendicular to said first and second end wall.

Preferably, each section is semicircular.

The invention shall now be further described by way of exemplification and with reference to the following drawings in which: FIGURE la is a end view of a prior art clamp hub on a shaft.

FIGURE 1b is a side cross sectional view of prior art hub on a shaft holding a component.

FIGURE lc is a side cross sectional view of a prior art clamp hub.

FIGURE 1d is an end view of a prior art clamp hub. FIGURE 2a is an end view of a prior art device having a single screw.

FIGURE 2b is an end view of a prior art device having two screws.

FIGURE 3 is an end view of the hub of the invention.

FIGURE 4 is an side view of the invention.

FIGURE 5 is a cross section taken along line A-A of Figure 3.

FIGURE 6 is a cross section of a view taken along line B-B of Figure 3; FIGURE 7 is a cross section of a view taken along line C-C of Figure 4; and FIGURE 8 is a cross section view similar to Figure 6 showing an alternative embodiment having straight sides.

Referring to Figure 3, the hub clamp includes a main clamp hub body 10, and a first slit 11 from the bore 12 to the outside peripheral surface 14 to form two sections. These sections are joined to one another by a screw 16 or other tension-providing fastener to secure the clamp to a shaft. A second slit 18 is formed in one of the end faces of the clamp at a position ninety degrees offset from the first slit. This second slit 18 extends from the bore to the periphery, but only to the centerline between the two end faces of the clamp. The second slit forms two quadrants 32,34 in each half of the clamp.

The hub may be integral with the component typically attached in the attachment area 40. A screw or similar tensionproviding devices deflects the sections of the clamp, uniformly reducing the bore 12 and applying pressure on the mating shaft 20. The overall effect of this is to produce several advantageous effects.

As the screw is tightened the two quadrants 32,34 tilt significantly inwardly. The diameter of the bore 12 at any section of the clamp reduces very uniformly in all radial directions. A more consistent interface pressure improving the effectiveness of the clamp is produced. In comparison, a standard clamp can only nominally reduce around the axis of its single slit. The bore reduces in diameter in one direction, but not in the other, resulting in an oval shape and inconsistent interface pressure. Consequently, less torque can be transmitted. The difference between the clamp of the invention and a clamp not having the second slit is summarized in the following table:

SCREW TORQUE STANDARD CROSS SLIT 0.6 1.6 1.9 0.7 2 2.6 0.8 2.5 3.1 0.9 2.9 3.7 1.0 3.2 4.3 1. 1 3.6 4.7 1.2 3.8 5.3 1.3 4.1 5.8 1.4 4. 6 6.3 1.5 4. 9 6. 8 All Figures in Nm.

The overall stiffness of the clamp is less. Less force provided by the screw is wasted in deflecting the clamp and more is used to generate contact pressure on the shaft. Another limiting factor for some clamps can be the torque that can be applied to the screw before the head is damaged or the screw is torqued to its maximum allowable stress. With the reduced stiffness of the clamp, a greater clamping force results for the same torque applied to the screw. A stiffer prior art clamp cannot achieve the same levels of efficiency.

Reduced clamp stiffness also has another advantage. As the clamp moves more readily for a given screw force, larger clearances between the clamp and the shaft may be accommodated. The advantage is that a larger range of shaft sizes can be used with the same clamp.

Moreover, the stress at the interface between the clamp and component is reduced. With a standard clamp, high stresses

occur at this interface and, during operation, additional stresses are produced from the movement of the component. This causes premature failure at this interface. The advantage of this clamp of the invention is most of the clamping motion takes place on the additional slit, less stress is introduced at the point were the clamp is attached to the component. Therefore, the life of the component is increased.

The preferred material for this invention is metal, particularly steel, but other materials, including aluminum alloys, plastics, ceramics and almost any other machinable material could be used.

Claims

Claims:

1. A clamp for connecting components to a shaft, comprising a first and second section, each section having a first face, a second face, a perimeter wall, a first end wall and a second end wall, at least one fastener for connecting said two sections together to secure the clamp about the shaft, each section having a slit in one of said faces.

2. The clamp of claim 1, wherein said at least one fastener is a screw.

3. The clamp of claim 1, wherein said at least one fastener is a pair of screws, each screw extending through the perimeter wall and end wall of one section and into the end wall of the other section.

4. The clamp of claim 1, wherein each section has a centerline located equidistant from said first and second face, said slit extending to said centerline.

5. The clamp of claim 4, wherein said slit is perpendicular to said first and second end wall.

6. The clamp of claim 1, wherein said slit is perpendicular to said first and second end wall.

7. The clamp of claim 1, wherein each section is semicircular.

8. A clamp substantially as described herein.

9. A clamp substantially as described herein with reference to the drawings in Figures 3 to 8.