Brake band for transmission assembly

Abstract: A one-piece transmission brake band (10) and the method of forming the same wherein the band is an elongated strap (11) with brackets (14,15) at the opposite ends (12,13) thereof, the brackets providing an apply end and a reaction end. Each end consists of an end portion (12,13) of the strap that is folded over upon itself onto the exterior surface of the band and suitably fastened thereto, such as by clinch fastening (25,34) or spot welding. The apply end of the band has the outer layer (12) provided with a transverse upwardly folded or crimped ridge (20) having a central depression (23) to receive the end of an apply piston (16), and the reaction end has an outwardly extending radial opening (26) formed by piercing through both layers (27,28) of material after the end (13) is folded over, with the layers being outwardly extruded in both the radial and circumferential directions. An alternative embodiment utilizes an insert (42) having a cylindrical body (43) with a circumferential base flange (44). An opening (46) is stamped in the outer layer (45) of material with a raised rim (47) therearound; the opening (46) receiving the cylindrical body (42) and the raised rim (47) receiving the base flange (44).

Description: The invention disclosed herein relates to transmission brake bands utilized in vehicle automatic transmissions. In conventional vehicle automatic transmissions of the torque converter type, a driving shaft extends from the torque converter into the transmission housing to a unit therein having one or more clutch drums around which are arranged either single-wrap or double wrap brake bands. Depending on torque requirements, one-piece bands can be utilized in low load/torque coast band or overdrive situations. It is the function of the brake bands under suitable hydraulic controls to effect gear change and control of the direction of rotation of the output or driven shaft from the transmission to the differential for the driving wheels of the vehicle. Presently manufactured brake bands of the single-wrap type are formed from a strip of sheet steel or similar material and the ends are formed from separate relatively thick forgings, castings or stampings which are suitably secured to the strap of material by spot welding or similar means. Each brake band has an actuation or apply end for an apply piston and a reaction end which is operatively connected to a reaction member in the transmission. Various types of automatic transmissions utilize different types of reaction members. Some reaction members may be of the tangential type which have a stationary plunger or stop member acting against an anchor end of the brake band, while others may be of the reaction pin type where the pin extends perpendicular to the clutch drum and strap and extends into a suitable opening in the anchor bracket for the band. Where a reaction pin is used to form a reaction member in the transmission, a "volcano" type reaction bracket is often provided which consists of an extruded opening extending radially outwardly from the reaction bracket of the band or a bushing that is secured to the bracket at an opening therein to receive the free end of the reaction pin providing the stationary end of the brake band during use of the band in the automatic transmission. The opposite or apply end of the band is provided with an apply bracket which cooperates with the end of an apply plunger in the transmission that is hydraulically controlled to urge the band ends together to tighten around the clutch drum and stop the rotation of the drum or otherwise alter the rotation of the drum or other member to change the gear ratio or alter the direction of rotation of the output shaft. Due to assembly tolerances in the transmission assembly and/or testing facilities, the reaction brackets can be subjected to high stress which may result in premature failure during testing or operation of the transmission. To overcome the possibility of any premature failures of the bands or brackets associated therewith, the present invention relates to a novel method of manufacture of the brake band and the brackets therefor such that the strength of the bracket is increased and stress reduced so that failure of the bracket will be lessened and possible rejection of the bands overcome. In accordance with one aspect of the invention as claimed, there is provided a transmission brake band for use in an automatic transmission for an automotive vehicle, wherein the brake band is formed from a single curved strap of elongated material having an apply bracket at one end and a reaction bracket at the opposite end with a friction lining secured to an interior surface of the strap, the reaction bracket being formed by folding an end of the strap backward and over on to an exterior surface of itself to form two layers of material, the reaction bracket including a reaction opening, and wherein either (a) the reaction opening is formed from the two layers of material by piercing through both layers of material, the piercing of the layers of material acting to extrude the material both radially and circumferentially outwardly to urge the material layers together, or (b) the reaction opening is formed by an insert which is positioned between an inner layer of the two layers of material and the outer layer thereof in an opening pierced through the outer material layer. The invention as claimed also includes a method of forming a transmission brake band from an elongated strip of material, wherein either (a) an elongated material strip is formed into a strap with a pair of brackets at the opposite ends of the strap, the ends of the strap are bent over on to the outer surface of the strap to form an apply bracket and a reaction bracket, an opening is formed to receive a reaction pin by piercing both layers of material at the folded-over end of the strap, a friction lining is secured on to the strap, and the strap is formed into a curved brake band, the step of piercing both layers of material extruding the material layers generally radially outwardly perpendicular to the strap to urge the material layers together, or (b) the strip of material forms a friction lined strap with a pair of end brackets on the opposite ends of the strap, one of the brackets being an apply bracket and the other of the brackets being a reaction bracket, and wherein the ends of the strap are bent over outwardly and backwardly on to themselves to form the brackets, a friction lining is applied on to the inner surface of the strap, the strap is formed into a curved said brake band, an outer layer of the bent-over end is pierced to provide the reaction bracket to form an opening with a raised outer rim, and an insert is located within the opening in the outer layer of material to provide a location opening for a reaction pin. Accordingly, rather than forming a separate reaction bracket and punching or piercing the "volcano" type reaction opening in the bracket as in the hereinbefore discussed presently manufactured brake bands, the present invention uses a brake band with which the reaction bracket is integral. In one preferred embodiment of the invention, the anchor embossment is extruded from double thicknesses of the base metal of the brake band to produce the "volcano" type reaction bracket at one end of the brake band. In forming the aforesaid one preferred embodiment of the brake band, a single strip of suitable metallic material is provided and both ends of the strip are bent upwardly and rearwardly over upon itself to form double thicknesses or layers of material to form the apply and reaction brackets at the ends of the strap. Once the material has been folded upon itself, the "volcano" type opening to receive the reaction pin of the transmission is formed by piercing the layers to extrude the layers to form a tapered opening that is more stress resistant. Simultaneously, the two layers of material are secured together by clinch fastening or spot welding. Similarly, a double layer of material forming the apply bracket is provided with an apply ridge by folding the outer layer of material outwardly to provide an apply surface for the end of an apply piston to engage and act to tighten the band around the clutch drum to apply the transmission band to the drum. Attention is drawn to US-A-4053032 which discloses a one-piece brake band for a brake mechanism of a compact lawn or garden tractor, the brake band being formed from a single curved strap of elongated material having an apply bracket at one end and a reaction bracket at the opposite end with a friction lining secured on to an interior surface of the strap, each of the apply and reaction brackets being formed by folding a respective end of the strap backward and over on to an exterior surface of itself to form two layers of material, the reaction bracket including a reaction opening formed from the respective two layers of material by forming an aperture through both layers of material. In order that the present invention may be well understood, the aforesaid one preferred embodiment of the invention together with another preferred embodiment, which are given by way of example, will now be described with reference to the accompanying drawings, in which: FIGURE 1 is a perspective view of a transmission brake band embodying the present invention and which is to be applied to a clutch drum; FIGURE 2 is a partial end elevational view of the same brake band with portions in cross section showing the apply and reaction brackets formed at the outer ends; FIGURE 3 is a top plan view of the apply bracket for the same, single-wrap, transmission band; FIGURE 4 is a top plan view of the reaction bracket of the same transmission band; FIGURE 5 is an enlarged cross sectional view taken on the line 5-5 of FIGURE 4 of a portion of the reaction bracket for the brake band showing the extrusion of the two layers of metal to form the reaction opening; FIGURE 6 is a partial elevational view of an alternative form of reaction bracket utilizing an insert forming the reaction pin opening; and FIGURE 7 is an enlarged partial cross sectional view of the same alternative reaction bracket taken on a similar aspect to FIGURE 5. Referring first to Figure 1, there is shown a one-piece brake band 10 for use in an automotive vehicle automatic transmission (not shown) which is formed from an elongated strip of material to form a curved strap of a determinate length. The opposite ends 12 and 13 of the strap 11 are folded back upon themselves to provide brackets 14 and 15 for an apply piston 16 and a reaction pin 17, respectively. The brake band 10 includes a friction lining 18 suitably secured thereto, such as by a suitable adhesive, and the strip is formed into a curved strap such as shown in Figure 1. The improvement of the present invention resides in the bracket ends 14 and 15 of the brake band 10. As seen in Figures 2 and 3, the apply end 14 is formed by folding the end 12 upwardly and backwardly upon itself, the end being provided with an upwardly folded ridge 20 which has a strengthening rib 21 on the back side 22 of the fold located below the contact point for a piston or pin on the bracket and a depressed area forming a pocket 23 in the central area on the opposite side 24 of the fold adapted to receive the free end of the apply piston 16 acting in a generally tangential direction to the clutch drum. The folded end portion 12 is secured to the strap simultaneously with the folding and forming operation by several clinched fasteners 25. With respect to the anchor bracket 15, the end 13 is folded upwardly and rearwardly upon itself and a reaction pin opening 26 is formed in both layers 27, 28 of the strap by piercing both layers from the interior strap surface 29 with a suitable tool to form an extruded opening with an inner slightly tapered surface 30 and an outer tapered surface 31; the inner layer of material 27 being urged upwardly and outwardly to form the inner tapered surface 30 of the opening. As seen in Figure 2, the reaction pin 17 may be provided with a tapered end 32 that is received in the opening 26 of the anchor bracket 15. As more clearly seen in Figure 5, the inner layer of material terminates short of the outer layer at 33 in the opening 26 and, simultaneously with the piercing operation, the end is fastened to the strap by clinched fasteners 34 similar to the fasteners 25 in the apply bracket. Although clinched fasteners are shown, the layers could also be spot welded together if desired. As seen in Figure 2, the reaction pin 17 is received in the opening 26 to a certain depth 35 to prevent generation of excessive stress within the opening. Figure 6 and 7 discloses an alternative embodiment of the reaction bracket 41 for the one-piece brake band 10'. In this embodiment of the brake band, a separate insert 42 is formed with a generally cylindrical body 43 having a flange 44 integral with the body 43 to provide a base for the insert; the insert body being received into an opening 46 formed in the folded over layer 45 of the strap with a circular raised rim 47 encompassing the opening 46 to receive the base positioning flange 44. In this embodiment, the inner layer 48 of the strap does not have an opening formed therein. The insert has an inner tapered surface 48 and an outer tapered surface 49 for the "volcano" opening to receive the reaction pin (not shown) for the transmission. In both embodiments, the stresses are lower and the strength increased for the apply and reaction brackets compared to the brackets presently in use.

Claims: A one-piece transmission brake band for use in an automatic transmission for an automotive vehicle, wherein the brake band (10) is formed from a single curved strap (11) of elongated material having an apply bracket (14) at one end and a reaction bracket (15) at the opposite end with a friction lining (18) secured on to an interior surface (29) of the strap (11), the reaction bracket (15) being formed by folding an end (13) of the strap (11) backward and over on to an exterior surface of itself to form two layers (27, 28) of material, the reaction bracket (15) including a reaction opening (26) formed from the two layers (27, 28) of material by piercing through both layers (27, 28) of material, wherein the piercing of the layers (27, 28) of material acts to extrude the material both radially and circumferentially outwardly to urge the material layers (27, 28) together. A one-piece brake band as claimed in claim 1, wherein the opening (26) in the reaction bracket (15) receives a reaction pin (17) positioned in the transmission perpendicular to the reaction bracket (15). A one-piece transmission brake band as claimed in claim 1 or claim 2, wherein the reaction opening (26) has an inner tapered surface (30) and an outer tapered surface (31). A one-piece transmission brake band as claimed in claim 1 or claim 2, wherein the folded-over end (13) of the strap (11) is fastened to an inner layer (27) of the two layers (27, 28) of material by clinch fastening simultaneously with the reaction opening (26) being pierced through the two material layers (27, 28). A transmission brake band for use in an automatic transmission for an automotive vehicle, wherein the brake band 10' is formed from a single curved strap (11) of elongated material having an apply bracket (14) at one end and a reaction bracket (15) at the opposite end with a friction lining (18') secured on to an interior surface (29) of the strap (11), the reaction bracket (15) being formed by folding an end (13) of the strap (11) backward and over on to an exterior surface of itself to form two layers (45, 48) of material, the reaction bracket (15) including a reaction opening (48, 49), wherein the reaction opening (48, 49) is formed by an insert (42) which is positioned between an inner layer (48) of the two layers (45, 48) of material and the outer layer (45) thereof in an opening (46) pierced through the outer material layer (45). A transmission brake band as claimed in claim 5, wherein the insert (42) includes a generally cylindrical body (43) having a flat circular flange (44) forming a base for the insert (42). A transmission brake band as claimed in claim 6, wherein the opening (46) in the outer material layer (45) of the reaction bracket (15) has an encompassing raised rim (47), the opening (46) receiving the generally cylindrical body (43) of the insert (42) and the base flange (44) thereof being received by the raised rim (47). A transmission brake band as claimed in claim 7, wherein the inner material layer (48) of the reaction bracket (15) is imperforate opposite the reaction opening (48, 49). A transmission bracket band as claimed in any of claims 5 to 8, wherein the insert (42) has an inner tapered surface (48) and an outer tapered surface (49) forming a "volcano" said reaction opening (48, 49) to receive a reaction pin for the transmission. A method of forming a one-piece transmission brake band from an elongated strip of material, comprising the steps of forming an elongated material strip into a strap (11) with a pair of brackets (14, 15) at the opposite ends of the strap (11), bending the ends (12, 13) of the strap (11) over on to the outer surface of the strap (11) to form an apply bracket (14) and a reaction bracket (15), forming an opening (26) to receive a reaction pin (17) by piercing both layers (27, 28) of material at the folded-over end (13) of the strap (11), securing a friction lining (18) on to the strap (11), and forming the strap (11) into a curved brake band (10), wherein the step of piercing both layers (27, 28) of material extrudes the material layers (27, 28) generally radially outwardly perpendicular to the strap (11) to urge the material layers (27, 28) together. A method of forming a one-piece transmission brake band as claimed in claim 10, wherein the inner and outer layers (27, 28) of the strap (11) are clinch fastened (34) simultaneously with the piercing of the reaction pin opening (26). A method of forming a one-piece transmission brake band as claimed in claim 10 or claim 11, wherein the piercing operation forms the opening (26) with a slight internal outward taper (30) to locate a reaction pin (17). A method of forming a one-piece transmission brake band as claimed in any of claims 10 to 12, wherein the extruded layers (27, 28) forming the opening (26) have an external taper (31) as the material is extruded both radially and circumferentially outwardly. A method of forming a transmission brake band from an elongated strip of material wherein the strip of material forms a friction lined strap (11) with a pair of end brackets (14, 41) on the opposite ends of the strap (11), one of the brackets (14, 41) being an apply bracket (14) and the other of the brackets (14, 41) being a reaction bracket (41) comprising the steps of bending the ends (12, 13) of the strap (11) over outwardly and backwardly on to themselves to form the brackets (14, 41), applying a friction lining (18') on to the inner surface of the strap (11), forming the strap (11) into a curved said brake band (10'), piercing an outer layer (45) of the bent-over end providing the reaction bracket (41) to form an opening (46) with a raised outer rim (47), and locating an insert (42) within the opening (46) in the outer layer (45) of material to provide a location opening for a reaction pin (17). A method of forming a transmission brake band as claimed in claim 14, wherein the insert (42) is formed from a cylindrical member (43) with a circumferential flange (44) received in the raised rim (47). A method of forming a transmission brake band as claimed in claim 14 or claim 15, wherein the inner layer (48) of material of the strap (11) at the bendover end providing the reaction bracket (41) does not have an opening in that layer.

Inventors: GRZESIAK ANTHONY J, GRZESIAK, ANTHONY J.
Applicants: BORG WARNER AUTOMOTIVE, BORG-WARNER AUTOMOTIVE TRANSMISSION AND ENGINE COMPONENTS CORPORATION
Application year: 1991
Main classification: F16D49
IPC codes: F16D65