Abstract:
A circular hub containing an outside brake drum, an inside clutch drum spaced concentrically inward from the brake drum, and a plurality of circumferentially spaced supporting webs rigidly connecting the drums to each other; a plurality of spaced heat conducting fins attached to the inside of the brake drum and spaced away from the clutch drum to reduce the heat conduction from the brake drum to the clutch drum.

Description:
BACKGROUND OF THE INVENTION 
     Large machines, such as those used in earth moving applications, frequently include a hub having both a brake drum and a clutch drum that are used to operate the machine. Typical of such a machine is a Lima 2400 dragline having a brake and clutch hub. Both the brake and the clutch may function by clamping and releasing frictional bands against the respective drums. In so doing a large amount of heat is generated and must be dissipated in some fashion or the drum will become damaged, e.g. by heat stress cracking. In the prior art these drums have been designed as two concentric rings separated from each other by, and rigidly connected to each other by spaced radial webs inclined at an angle to the axis of rotation. It was anticipated that the webs would serve as fan blades to cause great volumes of air to pass through between the drums and keep them cool enough to avoid damage by heat stress cracking. This hope has not materialized, and such hubs have been found to have a relatively short life due to heat stress cracking. 
     It is an object of this invention to provide an improved brake and clutch hub for earth moving machinery. It is another object of this invention to provide a brake and clutch hub which will operate without fear of damaging heat stresses. Still other objects will appear from the more detailed description which follows. 
     BRIEF SUMMARY OF THE INVENTION 
     This invention relates to an improved circular hub having an outside drum adapted to cooperate frictionally with a brake band, and an inside drum adapted to cooperate frictionally with a clutch band; where the improvement comprises a plurality of circumferentially spaced radially oriented heat conducting fins between said outside drum and said inside drum, attached in a heat conducting relationship to said outside drum and spaced apart from said inside drum. 
     In specific preferred embodiments of the hub is rotatable about a central axis wherein said outside drum is a ring with an outside cylindrical surface adapted to cooperate with a brake band which is capable of contracting inwardly to frictionally engage said outside surface; and wherein said inside drum is a ring spaced concentrically inward from said outside drum and having an inside cylindrical surface adapted to cooperate with a clutch band which is capable of expanding outwardly to frictionally engage said inside surface. 
     In other preferred embodiments the fins are attached to the outside drum, but not to the inside drum; and there are also a plurality of circumferentially spaced air passageways between the two drums. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed to be characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which: 
     FIG. 1 is a top plan view of the hub of this invention; 
     FIG. 2 is a side elevational view of the hub of FIG. 1; 
     FIG. 3 is an enlarged view of a portion of the top plan view of FIG. 1; 
     FIG. 4 is an enlarged view of a portion of a bottom plan view of FIG. 1; 
     FIG. 5 is an enlarged cross sectional view of a portion of a side elevational view taken at 5--5 of FIG. 1 and with the outside drum removed; 
     FIG. 6 is a cross sectional view taken at 6--6 of FIG. 1; 
     FIG. 7 is a cross sectional view taken at 7--7 of FIG. 1; 
     FIG. 8 is a cross sectional view taken at 8--8 of FIG. 1; 
     FIG. 9 is a top plan view of the hub of the prior art; 
     FIG. 10 is a side elevational view of the hub of the prior art; and 
     FIG. 11 is a cross sectional view taken at 11--11 of FIG. 9. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     This invention can best be understood by reference to the attached drawings. 
     In FIGS. 1-2 there is shown a typical brake and clutch hub having an outside brake drum 21 and an inside clutch drum 22 rigidly joined to each other by a plurality of equally spaced radial supporting webs 25 and a plurality of annular supporting webs 26. Drums 21 and 22 and their supporting webs 25 and 26 are attached to a mounting flange 32 which permits the drums 21 and 22 to be attached by bolts through bolt holes 33 to a fly wheel (not shown) or other structure driven by the machine, e.g. a dragline, to which this hub is attached. Normally such a hub is either cast iron or machined steel. 
     Brake drum 20 preferably is a cylindrical ring having an outside cylindrical face 23 with a lateral width 30. Surface 23 is engaged by a brake band (not shown) which can be contracted upon outside surface 23 to provide a frictional force tending to stop or prevent the rotation of the hub. Brake bands, as is well known, are designed to be contracted upon or released from the brake drum 21 as desired by the operator. 
     Clutch drum 22 is operationally similar to brake drum 21. Inside surface 24 faces inwardly and has a lateral width 31 designed to cooperate with a clutch band (not shown) which may be expanded to press against inside surface 24 to provide a frictional force tending to cause the clutch band and any machinery attached thereto to rotate with the rotation of clutch drum 22. In the same manner as with brake bands and brake drum 21, the operator may as desired engage the clutch by expanding the clutch band against inside surface 24 or disengage the clutch by releasing the clutch band. 
     In the prior art as shown in FIGS. 9-11 the hub included brake drum 121, clutch drum 122, radial supporting webs 125, flange 132, and bolt holes 133. Between adjacent webs 125 there was open space 128 for air flow. Webs 125 were included at an angle of about 30° to the centerline 129 of the hub for the purpose of blowing air through spaces 128 after the fashion of rotating fan blades. It was anticipated that such air flow would be sufficient to keep drums 121 and 122 cool enough to operate without interruption, except for ordinary wear and tear. This did not prove to be the case, however. The tremendous heat build-up in brake drum 121 was conducted to the clutch drum 122, and eventually caused destruction of the hub because of heat stress cracking of clutch drum 122. The present invention has eliminated such destructive heat build-up. 
     In the present design heat conducting fins 27 oriented in a radial direction, and circumferentially spaced apart from each other, have been positioned between brake drum 21 and clutch drum 22. Fins 27 are included between adjacent radial supporting webs 25, and are attached to brake drum 21 but not to clutch drum 22. Fins 27 are also attached to annular webs 26. Thus, there is much cross sectional area, principally due to fins 27, for heat conduction away from drum 21 which, in the normal operation of the machine, has a large heat build-up due to the slippage of the brake band thereon. The cross sectional area for heat conduction from brake drum 21 through radial webs 25 and annular webs 26 to clutch drum 22 is considerably less, although about the same as in the prior art machine. 
     Furthermore, there is a plurality of air passageways 24 to provide as much cooling air flow as possible. This 28 extending the widths of outside surface 23 and inside surface arrangement of fins 27 and air passageway 28 has been found to provide sufficient cooling to permit brake drum 21 to be made thinner and while clutch drum 22 retains the same thickness as before. The arrangement of annular webs 26 and radial webs 25 provides a better structural strength and heat stress stability to the brake and clutch hub, which translates into a substantially greater usable life. 
     In FIGS. 3-8 there are shown the preferred arrangements for fins 27. It may be seen that fins 27 extend laterally outward in opposite directions from both sides of annular web 26. The preferred arrangement for maximum structural strength is for fins 27 to be staggered on opposite sides of annular web 26. This may best be seen in FIG. 5 where an enlarged view of fins 27, annular webs 26, passageways 28, and radial webs 25 is shown. Fins 27 on the right half of FIG. 5 are staggered with respect to fins 27 on the left half of FIG. 5. This arrangement provides a maximum of structural strength around annular web 26, and at the same time provides a maximum in heat conduction from brake drum 21 to fins 27, and thence to the surrounding air. It should be noted that two radial webs 25, one annular web 26 and a plurality of fins 27 (in this case four on each side for a total of eight) and air passageway 28 form a repeating unit that fills the annular space between outside brake drum 21 and inside clutch drum 22. In this instance (as shown in FIGS. 1-2) each repeating unit occupies a 10° space, which means there are 36 such units in a complete hub. Of course, other sizes of units can be employed, such as 8°-15° spaces which is equivalent to 45-24 repeating units. One annular web 26 and two radial webs 25 are preferably joined together to make one integral supporting web having a stairstep shape. Annular web portion 2 lies midway between the two edges of drum 21 and drum 22 perpendicular to axis 29. A radial web 25 is attached at each end of annular web 26 and extending in opposite directions parallel to axis 29. Fins 27 are attached to annular web portion 26. 
     In FIGS. 9-11 there is shown the prior art hub for a Lima 2400 dragline. The general shape and arrangement of brake drum 121, clutch drum 122 mounting flange 132 and bolt holes 133 is generally the same as that described above. The principal differences lie in the structure of the repeating units in the annular space between brake drum 121 and clutch drum 122. In FIG. 11 it may be seen that brake drum 121 and clutch drum 122 are supported by inclined supporting webs 125. Between adjacent webs 125 is an open space 128 for air passage. In the design of this hub, brake drum 121 and clutch drum 122 are both of the same thickness (1.25 inches) for a hub diameter of 69 inches. As a result of the enhanced cooling of the improved hub of this invention, brake drum 21 has been thinned to 1.0 inch while clutch drum 22 remains at 1.25 inches of thickness. 
     While it is not intended to limit this invention, but merely to be illustrative, the comparison of a prior art hub and a hub of this invention reveals very interesting data as shown in the following tabulation. 
     
         ______________________________________        Prior Art  Invention        Ref. No.               Area    Ref. No. Area______________________________________Cross sectional area, sq.          125      14.8    25 and 12.5in. of supporting web at        26brake drumCross sectional area, sq.          --       0       27     15.0in. finsTotal Cross sectional   14.8           27.5area, sq. in.Surface area, sq. in. of          125      114.4   26     84.6supporting webSurface area, sq. in. of          --       0       27     154.0finsTotal surface area, sq. in.                   114.4          238.6Length of supporting web,          125      13.9    25 and 15.5inches                          26______________________________________ 
    
     It may be seen that there is approximately twice as much cross sectional area in the present hub structure as compared to the prior art for conducting heat away from brake band 21. There also is approximately twice as much surface area in the present hub structure as compared to the prior art for cooling by convection and radiation. Observations on two hubs, one representing the prior art of FIGS. 9-11 and the other representing the invention of FIGS. 1-8 determined that the brake drum in the hub of this invention was approximately 50% cooler, i.e., approximately 50% more heat was dissipated by the hub of this invention as compared to the prior art hub. In addition to the better heat transfer properties, there also is a better structural support in the present invention as compared to the prior art. In the prior art structure one supporting web 125 extends for 13.9 inches under brake drum 121. In the present invention the supporting webs are a combination of one annular web 26 and two radial webs 25 forming a stairstep shape (as seen in FIG. 5). The total length of that web combination under brake drum 21 is 15.5 inches. 
     Stress cracking of the clutch drum in the prior art hub was found to occur near the edges of the supporting webs 125 generally in a line parallel to the web 125. It is believed that this was due to the presence of very hot zones in clutch drum 122 where the webs 125 joined clutch drum 122 next to considerably cooler zones in the portions of clutch drum 122 between adjacent webs 125. The very hot brake drum 121 and very hot webs 125 tend to expand outwardly away from clutch drum 122. Similarly, stresses are produced between the very hot zones of clutch drum 122 near webs 125 and the cooler zones between adjacent webs 125. These stresses cause the cracking to occur. The design of the present hub eliminates the linear supporting webs and substitutes the stairstep design of one annular web 26 and two radial webs 25, effectively spreading the hot zones out over a greater area and not having such well defined alternating linear zones of hot and cold that caused the problem in the prior art. Furthermore, fins 27 transfer heat to the surrounding air and materially reduce the heat conduction to clutch drum 122, making the resulting hot and cold zones in clutch drum 122 not so widely divergent. 
     The combination of a better heat transfer and better structural support has permitted the hub of the present invention to employ a thinner brake drum 21 (1.0 inch) as compared to brake drum 121 (1.25 inch) of the prior art. 
     While the invention has been described with respect to certain specific embodiments, it will be appreciated that many modifications and changes may be made by those skilled in the art without departing from the spirit of the invention. It is intended, therefore, by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the invention.