Abstract:
A band brake drum assembly ( 50 ) is provided and includes a brake band member ( 52 ), a generally round and/or cylindrical and brake drum ( 54 ) which is disposed concentric to band ( 52 ), and an input or hub shaft ( 56  which is fixedly coupled to and rotatably drives drum ( 54 ). Drum includes an interior surface having a recessed portion ( 62 ) which is effective to retain a certain amount of lubricant or oil within the drum, and several relatively large drainage holes ( 70 ) which are effective to quickly drain excess lubricant from drum ( 54 ), thereby providing a consistent amount of lubricant wit in drum ( 54 ) and improving the overall performance of the brake band assembly.

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     This invention relates to a band brake assembly and more particularly, to a band brake assembly for use in a vehicle and having a drum with improved lubrication flow control. 
     2. Background of the Invention 
     Band brakes are generally employed within automatic transmissions in order to perform gear shifts within the transmissions. For example and without limitation, shifting a “step-ratio” type automatic transmission is accomplished by selectively applying and releasing friction elements such as band brakes which are assigned to various rotating elements or gears (e.g., planetary gears) within the transmission. 
     A conventional band brake includes a band, a drum, and a hydraulic servo. The band-drum interface is lubricated with an oil. The drum is directly connected to a planetary gear or other automotive transmission component. When the band brake is actuated, it frictionally engages the drum, effective to hold connected components while altering a gear configuration for automatic shifting. Thus, the band engagement dynamics directly affect automotive transmission shift quality. Consistent band behavior in repeated engagements or under varying operating conditions is vital to providing and maintaining good shift quality. 
     However, in a conventional automotive transmission system, the band-drum engagement behavior varies significantly due to varying lubrication flow into the band-drum interface. Typically, the lubricant (e.g., oil) is first routed to the interior surface of the drum from the drum hub shaft. The rotation of the drum exerts a centrifugal force on the oil layer inside the drum. The amplitude of this force depends on the rotational speed of the drum and the oil layer thickness. The drum has small lubrication holes drilled through its shell. The centrifugal force pushes the oil through those holes into the band-drum interface. Prior art has relied upon the size, number, and location of lubrication holes to regulate the oil flow into the interface. However, the oil layer thickness inside the drum still varies widely under different operating conditions. As a result, a large variability still exists in the actual lubrication flow rate, causing widely varying engagement behavior. The band-drum engagement variability makes automatic transmission shift calibration more difficult, leading to inconsistent shift quality. 
     Referring now to FIG. 1, there is shown a sectional view of a prior art band brake assembly  10 . As shown, a conventional brake band assembly  10  typically includes a band  12 , a drum  14 , and a hub shaft  16  which receives engine generated torque which is distributed through the transmission. The drum  14  is fixedly attached to the hub shaft  16  or other rotating components (not shown). The drum  14  shown in FIG. 1 rotates with the hub shaft  16 . The drum is generally hollow and typically houses other conventional transmission components  26 . The drum includes several oil-lubrication holes  18  which are typically drilled through the drum  14 . The hub shaft  16  includes oil distribution channels  20  which are formed within the shaft  16  and which communicate with apertures  22  which release and/or discharge the oil into the inside of drum  14 . When a relatively large oil flow exists under certain transmission operating conditions, a relatively thick oil layer  24  may accumulate inside the drum  14 . This relatively thick oil layer  24  may induce an excessive lubrication at the band-drum interface unless the oil is drained elsewhere. This excessive lubrication is particularly detrimental to the engagement behavior at low oil temperatures due to strong hydrodynamic effects. It may also lead to increased parasitic torque loss when the band is not engaged. While some attempts have been made to direct the oil into a low flow resistance area for draining purposes, this has led to lubrication deficiencies at the band-drum interface at high oil temperatures. These lubrication deficiencies potentially cause a very abrupt engagement behavior, increased band-drum interface temperature, and reduced band durability. 
     There is therefore a need for a new and improved band brake drum assembly which overcomes many, if not all, of the previously delineated drawbacks of such prior vehicle band brake drum assemblies, and which provides for reduced engagement variability. 
     SUMMARY OF INVENTION 
     A first non-limiting advantage of the invention is that it provides a band brake drum assembly which overcomes at least some of the previously delineated drawbacks of prior assemblies and which effectively controls the oil layer thickness inside the drum under all operating conditions, thereby providing a consistent oil flow into the band-drum interface and consistent engagement behavior. 
     A second non-limiting advantage of the invention is that it provides a band brake drum assembly having lubrication flow control attributes which are effective to reduce the variability in lubrication flow within the band interface. 
     A third non-limiting advantage of the invention is that it provides a band brake drum assembly for use in an automatic transmission system which reduces the variability in engagement and shifting characteristics. 
     A fourth non-limiting advantage of the invention is that it provides a band brake drum assembly having reduced parasitic torque loss at the band-drum interface due to regulated lubrication flow. 
     A fifth non-limiting advantage of the invention is that it provides a band brake drum assembly with improved oil draining flow which is effective to reduce parasitic torque loss in the rotating components of the assembly. 
     According to a first aspect of the present invention, a drum is provided for use within a band brake assembly. The drum includes interior surface which receives lubricant, a shoulder which is disposed upon the interior surface and which forms a lubricant retention area for holding an amount of the lubricant, at least one lubricant hole formed within the lubricant retention area, the hole communicating with a band-drum interface exterior to the drum and allowing at least a portion of the lubricant to be communicated from the drum to the band-drum interface, and at least one lubricant draining hole which is formed outside of the lubricant retention area and which is effective to drain excess lubricant from the drum. 
     According to a second aspect of the present invention, a band brake assembly is provided and includes a selectively actuatable brake band member; a selectively rotatable shaft having at least one channel which selectively distributes an amount of lubricant and an aperture which communicates with the channel and which selectively discharges the lubricant; and a generally cylindrical rotating drum which is fixedly coupled to the selectively rotatable components such as a shaft, the drum including an interior surface which receives an amount of lubricant, a recessed lubricant retention portion which is formed upon the interior surface and which selectively receives and holds an amount of the discharged lubricant, a plurality of lubricant holes formed within the lubricant retention portion, the lubricant holes communicating with an exterior portion of the drum which is selectively engaged by the brake band member and allowing at least a portion of the lubricant to be communicated to the exterior portion of the drum, and a plurality of lubricant draining holes which are formed outside of the lubricant retention portion and which is effective to drain excess lubricant from the drum. 
     According to a third aspect of the present invention, a method is provided for controlling the amount of lubricant within a transmission band brake drum. The method includes the steps of: forming a lubricant retention area on the inside surface of the transmission band brake drum, effective to retain a certain amount of lubricant; and draining excess lubricant from the band brake drum which flows outside of the lubricant retention area. 
     These and other features, aspects, and advantages of the invention will become apparent by reading the following specification and by reference to the following drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a sectional view a band brake assembly which is made in accordance with the teachings of the prior art. 
     FIG. 2 is a sectional view of a band brake assembly which is made in accordance with the teachings of the preferred embodiment of the invention. 
     FIG. 3 is a perspective view of a drum used within the band brake assembly shown in FIG.  2 . 
     FIG. 4 is a graph of torque verses time for several band brake engagements utilizing a conventional band and drum. 
     FIG. 5 is a graph of torque versus time for several band brake engagements utilizing the band brake assembly of the present invention. 
     FIGS. 6A-6D are partial sectional views illustrating various embodiments of band brake drums which are made in accordance with the teachings of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring now to FIG. 2, there is shown a band brake assembly  50  which is made in accordance with the teachings of the preferred embodiment of the invention and which is adapted for use in combination with a vehicle of the type having an engine which operatively provides torque to an automatic transmission assembly. In the preferred embodiment, assembly  50  is operatively disposed within the vehicle&#39;s automatic transmission assembly. While the following discussion relates to a band brake assembly for use within an automatic transmission, it should be appreciated that assembly  50  may be used in virtually any other apparatus, device or assembly in which a brake band assembly may be useful or desirable. 
     Band brake assembly  50  includes a brake band member  52 , a generally round and/or cylindrical band brake drum  54  which is disposed concentric to band  52 , and an input or hub shaft  56  which is fixedly coupled to and rotatably drives drum  54 . 
     Brake band  52  is generally cylindrical and is manufactured from a durable resilient material, such as a metal material. Band  52  is coupled to and actuated by a conventional actuating mechanism (not shown) which selectively “squeezes” band  52 , thereby reducing the diameter of the band  52  and causing the band  52  to constrict in the directions of arrows  58 . The inner surface  60  of band  52  is coated and/or covered with a conventional friction material (e.g., friction paper) which selectively engages the outer surface  59  of drum  54  when band  52  is actuated, thereby slowing and/or stopping the rotational movement of drum  54 . 
     Drum member  54  is generally hollow and cylindrical and houses other conventional transmission components  72 . The drum member  54  includes an annular recessed portion  62  which is formed on the interior surface  64  of drum  54  and which defines a lubricant retention area. A raised shoulder portion  66  is formed at and/or defines an end of recessed portion  62  and assists in retaining lubricant or oil within portion  62 . Drum  54  further includes a plurality of relatively small lubrication apertures  68  which are formed in the recessed area  62  and which pass through the drum  54 , thereby allowing for communication between the interior and exterior of the drum  54  (i.e., the band-drum interface). In the preferred embodiment, drum  54  includes about four lubrication apertures  68  which are disposed in a “ring” or circular configuration around drum  54 . The apertures  68  and recessed area  62  are aligned with band  62 , such that when band  62  engages drum  54 , it engages the portion of the outer surface  59  of drum  54  which includes apertures  68  (i.e., the band-drum interface). Drum  54  further includes a plurality of relatively large draining apertures  70  which are formed immediately or close to outside of the recessed area  62  and which pass through the drum  54 , thereby allowing for further communication between the interior and exterior of the drum  54  without interfering a part of the outer surface  59  where the band  52  makes a contact during the engagement. In the preferred embodiment, drum  54  includes approximately twelve draining apertures  70  which are disposed in a “ring” or configuration around drum  54 . It should be appreciated that the exact number and/or size of apertures  68 ,  70  may depend on the various desired structural and/or functional attributes of assembly  50 . 
     Hub shaft  56  is a conventional cylindrical hub shaft including several internal oil distribution channels  74  which are communicatively coupled to a conventional source of pressurized lubricating oil or fluid (not shown). Several apertures  76  are formed within hub shaft  56  and communicate with channels  74 . Particularly, apertures  76  receive pressurized lubricant from channels  74  and emit or discharge the lubricant inside drum  54 , thereby lubricating the drum and transmission components  72 . In the preferred embodiment of the invention, discharge apertures  76  are formed along a portion of the length of shaft  56  that is aligned with recessed area  62 . In this manner, the majority of lubricant discharged by apertures  76  is discharged into the recessed area  62 . 
     Drum member  54  is generally hollow and cylindrical and houses other conventional transmission components  72 . Th drum member  54  includes an annular recessed portion  62  which is formed on the interior surface  64  of drum  54  and which defines a lubricant retention area. A raised shoulder portion  62  is formed at and/or defines an end of recessed portion  62  and assists in retaining lubricant or oil within portion  62 . Drum  54  further includes a plurality of relatively small lubrication apertures  68  which are formed in the recessed area  62  and which pass through the drum  54 , thereby allowing for communication between the interior and exterior of the drum  54  (i.e., the band-drum interface). In the preferred embodiment, drum  54  includes about four lubrication apertures  68  which are disposed in a “ring” or circular configuration around drum  54 . The apertures  68  and recessed area  62  are aligned with band  52 , such that when band  52  engages drum  54 , it engages the portion of the outer surface  59  of drum  54  which includes apertures  68  (i.e., the band-drum interface). Drum  54  further includes a plurality of relatively large draining apertures  70  which are formed immediately or close to outside of the recessed area  62  and which pass through the drum  54 , thereby allowing for further communication between the interior and exterior of the drum  54  without interfering a part of the outer surface  59  where the band  52  makes a contact during the engagement. In the preferred embodiment, drum  54  includes approximately twelve draining apertures  70  which are disposed in a “ring” or configuration around drum  54 . It should be appreciated that the exact number and/or size of apertures  68 ,  70  may depend on the various desired structural and/or functional attributes of assembly  50 . 
     In this manner, the band brake assembly  50  and novel drum design provides for reduced engagement variability. The assembly  50  effectively controls the oil layer thickness inside the drum  54  under substantially all operating conditions. The consistent lubricant or oil layer thickness leads to a consistent lubrication flow into the band-drum interface and a consistent engagement behavior. 
     In operation, pressurized lubricant or oil is pumped or otherwise introduced into channels  74  of shaft  56 . The lubricant exits the shaft  56  through apertures  76  and coats the interior surface  64  of drum  54 . Due to the oil flow control attributes of the drum  54 , the amount of this lubricant or oil which is fed into the drum  54  does not need to be accurately regulated. As the lubricant is discharged, it may flow through other transmission components  72  positioned inside the drum  54  before reaching the interior surface  64  of drum  54 . The majority of the lubricant flows into and is retained by the lubricant-capturing or retention area  62 . The depth  78  of area  62  or the height of shoulder  66  determines the amount of lubricant retained and the magnitude of centrifugal force generated by the rotating lubricant or oil layer. This centrifugal force pushes some of the lubricant or oil to the exterior of drum  54  and into the band-drum interface through the lubrication holes  68 . When the amount of lubricant inside drum  54  is excessive, the excess lubricant flows over the raised shoulder  66  into the relatively large draining holes  70 . In this manner, the present invention allows for excess lubricant to be relatively quickly removed from the system, thereby eliminating the potential adverse effects (i.e., parasitic torque loss) which may be caused by such excess lubricant. When the amount of lubricant within drum  54  is relatively small, substantially all of the lubricant is effectively trapped in the lubricant-capturing area  62  and is fed to the band-drum interface. Particularly, the raised shoulder  66  substantially prevents this oil from escaping are  62 , thereby maintaining a substantially consistent lubricant or oil layer thickness within drum  54 . The consistent lubricant or oil layer thickness, determined by the depth  78  of the lubricant-capturing area  62  (or by the height of shoulder  166 ), provides a substantially consistent lubrication flow rate at the band-drum interface, thereby desirably reducing engagement variability. In the preferred embodiment of the invention, the precise geometry (e.g., shape, size and position) of the lubrication holes  68 , the lubricant-capturing area  62 , and the draining holes  70  are designed to meet the lubrication requirements of the band friction material and/or by other desired attributes or applications of assembly  50 . In one non-limiting embodiment, the width  80  of lubricant retention area  62  is approximately 19 mm, the depth  78  of area  62  is approximately 0.5 mm, and drainage holes  70  are approximately 10 mm in diameter. 
     FIGS. 6A-6D illustrate various drum embodiments for use in the present invention. FIG. 6A illustrates the afore-described drum  54  which includes a recessed portion  62 , which may be machined or otherwise conventionally formed on the interior surface  64  of drum  54 . FIG. 6B illustrates an alternative embodiment of the drum  154  which is substantially identical to drum  54  with the following differences. Recessed portion  62  has been replaced with includes a relatively thin annular groove  161  which houses an annular ring or member  165 , which is fixedly disposed (i.e., press-fitted) within groove  161  and which forms a oil retention shoulder  166 . Particularly, ring  165  extends inward a certain length  178  from the inner surface  164  of drum  154 , thereby forming retention shoulder  166 . It should be appreciated that shoulder  166  serves a substantially similar function as shoulder  66  in forming an oil or lubricant capturing area  162 . Lubrication apertures  168  and draining apertures  170  are substantially identical to apertures  68  and  70 , respectively. FIG.  6 C illustrates another non-limiting drum embodiment  54   a . Drum  54   a  is substantially identical in structure and function to drum  54  with the exception that an additional “ring” or set of lubrication apertures  68   a  have been formed in a configuration which is substantially parallel to the ring of apertures  68 . Apertures  68   a  provide for improved oil distribution within the band-drum interface. FIG. 6D illustrates yet another non-limiting drum embodiment, drum  154   a . Drum  154   a  is substantially identical in structure and function to drum  154  with the exception that an additional “ring” or set of lubrication apertures  168   a  have been formed in a circular configuration which is substantially parallel to the ring of apertures  68 . Apertures  168   a  provide for improved oil distribution within the band-drum interface. 
     It is to be understood that the invention is not to be limited to the exact construction and/or method which has been illustrated and discussed above, but that various changes and/or modifications may be made without departing from the spirit and the scope of the invention.