WO2001023770A1

WO2001023770A1 - Transmission brake band with sockets

Info

Publication number: WO2001023770A1
Application number: PCT/US2000/026430
Authority: WO
Inventors: Paul A. Hildebrand; David Ike, Jr.; Richard T. Popchock; Omar P. Ozust
Original assignee: Raytech Automotive Components Co
Current assignee: Raytech Automotive Components Co
Priority date: 1999-09-29
Filing date: 2000-09-26
Publication date: 2001-04-05
Anticipated expiration: 2002-03-29

Abstract

A brake band (32) and a method for making the band include a metal strap forming an arcuate band. At least one end of the metal strap is return bent (36) to form a socket for receiving an engagement member (22, 24), the socket being formed in a return bent strap portion. The return bent strap portion is spaced apart from the arcuate band at a position aligned with an engagement contact area. The arcuate portion of the strap contains a friction lining (12) and portions of the strap may be perforated for fluid communication and head dissipation in the structure forming the socket. The return bent portion may include ribs and a pinch wall for strengthening the perimeter of the socket at the contact area.

Description

TRANSMISSION BRAKE BAND WITH SOCKETS

TECHNICAL FIELD

The present invention relates to automatic transmission brake band formed from a metal strap configured to define a socket for receiving an engagement pin.

BACKGROUND ART

Transmission bands are often formed of a metal strap bent in an arc to wrap around a drum or a rotating member. The strap is tightened against the outer surface of the rotating member by engagement members that displace the ends of the strap toward each other to encircle and tighten the strap against the rotating member. Typically, the engagement members include both an apply member received in a socket carried at one end of the strap and a reaction member carried in a socket at the other end of the strap. The apply member, for example, an apply pin, strut, lever, rod or the like is displaced to tighten the band around the rotating member during actuation and return during release. The reaction member, that may also be in the form of pins, levers, struts, rods or the like, is fixed in position with respect to the transmission housing to retain the strap end from displacement as the apply member is displaced and moves the other end of the strap. For strength and resisting the deformation or other direction movement of the strap with respect to the engagement members, the sockets were often formed in separate brackets that were separately fabricated and then mounted to the ends of the thin metal strap.

To reduce processing time, material, and cost of assembling separate brackets to the straps, bands have been formed from elongated straps whose ends are bent and configured to carry sockets that receive engagement members. However, the thinner material of the strap compared to the previous conventional brackets may not provide sufficient resistance to the forces exerted by the engagement pins throughout the service life of the transmission. Moreover, the friction layer is subjected to deterioration and wear due to heat stresses, temperature cycling and repeated mechanical forces including stresses upon the strap material imposed by the engagement members. Moreover, a double layer of strap material adjacent the friction layer may increase the heat build up in the friction layer near the area of the sockets and may further affect the damage resulting from stresses imposed upon the sockets as forces are applied by the engagement members. As a result, such structures may substantially reduce the working life of the transmission bands when compared with previously known multiple piece band and bracket structures.

DISCLOSURE OF INVENTION

The present invention overcomes the above-mentioned disadvantages by providing a one-piece band construction in which the sockets are formed by looped end portions of the strap forming the band. The loop at the end of the band positions at least a portion of the strap in alignment with the displacement direction of a contact area in the socket to be engaged by an engagement member. At least one of the apply bracket and the reaction bracket are formed in this manner, although it is preferred that both ends be formed according to this process and with this structure.

Preferably, a substantial portion of the return bent strap portion remains spaced apart from the arcuate band portion to improve fluid flow and heat dissipation from the end where the engagement members apply the forces. In addition, the arcuate strap portion may include openings for fluid communication between a return bent leg at the end of the strap and the arcuate band portion supporting the friction layer. In addition, the return bent portion preferably includes reinforcement ribs that resist displacement and deformation of the strap material surrounding the socket.

In the preferred embodiment, the contact area, which may be a point, a line or an expanded surface area, is formed by a pinch wall, in which adjacent overlying portions of the strap joined by a crease resist deformation at the contact area. In addition, the pinch wall is reinforced by ribs that also resist displacement of the strap material forming the socket at the end of the band. In addition, the preferred embodiment also includes return bent strap portion forming a first leg that terminates at a mating portion that lies flat against the surface of the arcuate band, and the leg may include reinforcement ribs. Preferably, the rib is aligned with said engagement member contact area and preferably the top of the rib reinforces the contact area on the structural wall by alignment with the engagement member contact area.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will be more clearly understood by reference to the following detailed description of a preferred embodiment when read in conjunction with the accompanying drawing and which like reference characters refer to like parts throughout the views and in which:

FIGURE 1 is a sectional view of a portion of an automatic vehicle transmission in which a brake band surrounds a clutch drum for engagement with the drum in response to displacement of an apply pin toward an anchor pin;

FIGURE 2 is a perspective view of the band shown in Figure 1 ;

FIGURE 3 is an enlarged perspective view of a bent end band showing a modified construction for the reaction bracket at the end of the band;

FIGURE 4 is a sectional view taken substantially along the line 4-4 in Figure 3 ;

FIGURE 5 is a fragmentary sectional view of a band having a modified band end construction for forming engagement pin sockets;

FIGURE 6 is a perspective view of the band ends shown in Figure 5; and FIGURE 7 is a perspective view of one of the band ends shown in

Figure 6.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring first to Figure 1, a transmission 10 includes numerous rotary parts including for example, clutch drum 12, whose rotation is resisted by tightening of a brake band 14. Preferably, the band 14 is formed by a strap 30 carrying a friction layer 34 that rubs against the outer surface of the drum 12 as the band 14 is wrapped around and tightened against the drum. The ends 16 and 18 of the band 14 are located and positioned by engagement members such as the apply pin 20 and the anchor pin 22, although other structures may be employed as engagement members without departing from the invention. The apply pin 20 is displaced in a direction aligned with an axis 24 into a socket 26 of the end 16 to displace the end 16 toward the end 18 that is retained in position by the anchor pin 22 extending into socket 28 (Figure 2) to tighten the band 14 against the drum. Similarly, retraction of pin 20 loosens the band and disengages the friction layer from the drum surface.

In the preferred embodiment, the strap 14 comprises a flat metal strap

30 having an arcuate portion 32 supporting a friction lining 34. Each socket 26 and

28 (Figure 2) at the ends of the band 14 are formed by return bent portions 36 of the strap 30. The return bent portions 36 form or at least support the sockets 26 and 28 at each end of band 14.

As best shown in Figure 2, each socket 26 and 28 of the preferred embodiment is integrally formed with the return bent portion 36 at each band end. Preferably, the socket includes a pocket that conforms with the shape of the engagement pin and provides a contact area 38. Preferably, the contact area 38, that may be as small as a point or as long as an expanded wall surface, is aligned with a wall of the return bent portion. As shown in Figure 1, a leg portion 40 is aligned with the contact area 38 at the end 16, and the contact area 42 is aligned with the leg 44 at the band end 18. Moreover, the contact area 42 may be a point or substantially larger than a point and may form a contact line or contact surface of expanded area within the socket 28 that resists the force of the reaction pin 22. Similarly, the engagement between the apply pin 20 and its receiving socket 26 may be similarly configured.

As also shown in Figure 2, the contact area 42, regardless of whether it is a point, a line, or an expanded surface, is preferably positioned on a reinforced surface such as the pinch wall 48 formed at an end of the leg 44. In addition, the pinch wall 48, preferably made of overlying wall portions joined by a crease, is supported by spaced ribs 50 and 52 adjacent to pinch wall 48. A shoulder 54 extends outwardly from the socket 28 and terminates at tapering legs 56 surrounding the socket. The remote end 58 of the return bent portion 36 lies flat against the outer surface of the arcuate portion 32 of the strap 30 and may be mechanically, adhesively or otherwise bonded to the outer surface of the arcuate portion 32. For example, as shown in Figure 2, mechanical connections 60 such as B.T.M. Company's Tog-L-Loc between the metal pieces being joined, secure the remote end 58 of the return bent portion to the arcuate portion 32 of the band 14, but alternative fasteners, such as pinch welds, rivets, other welds, or the like may be used without departing from the present invention.

Referring now to Figure 3, the reaction end 18 of the band 14 is there shown including return bend strap portion 36 having substantially different configuration 60. A socket 28 including the contact point 42 is formed as a confined recess 62 in a leg 64 spaced from the arcuate portion 32. The recess 62 includes a chamfered opening 66 that reinforces a cylindrical wall 68 forming a part of the socket. As best shown in Figure 4, a leg 64 is aligned with the contact surface 42 that extends from the outer surface of the leg 64 to the bottom of the cylindrical wall portion 68 engaged against the outer surface of the arcuate strap portion 32.

Reinforcement bends 76 support the return bent portion above the arcuate wall portion 32 and couple the leg 64 to the remote end flange 70. The remote end flange

70 lies flat against the outer surface of the arcuate strap portion 32 over an extended surface area, and is secured as described in reference to the other embodiments but preferably, for example, as shown by the plurality of mechanical connections 72. Referring now to Figure 5, a further modification of the band ends 16 and 18 are shown formed by similar structures 78 and 80. Like the band ends previously discussed, the structures 78 and 80 are similar to each other except for the angle at which the contact surfaces are aligned for mating with the respective engagement pin. The structure 80 includes a return bent leg 84 similar to the wall 44 discussed earlier but including a return bent radius 86 smaller than the radius in the return bent leg 44 in Figure 1. Nevertheless, the pinch wall 82 and its socket forming contact area 38 is aligned with a rib 88 carried on the return bent wall 84. Preferably, the top of the rib 88 is aligned with the contact point 38. Shoulders 90 extending outwardly from the socket 26 are substantially shorter than in the embodiment shown in Figures 1 and 2 to reduce the circumferential distance along the band occupied by the socket structure. Such a construction reduces the packaging area required for the apply pin actuator, and thus the overall size and weight of the transmission. Nevertheless, the sharply inclined tapered legs 96 terminate at a wall 100 engaging a large outer surface area of the arcuate strap portion 32, and may be bonded to the surface by mechanical connections, pinch welds or other fasteners as previously discussed.

In addition, as shown in Figure 6, the arcuate portion 32 is perforated, preferably as shown by openings 98, to improve fluid flow communication and heat dissipation from the structure in the harsh conditions of the operating transmission. Moreover, the transmission fluid is received in the area surrounding the socket so as to cool the band and reduce the stress levels at both the apply and reaction ends of the band.

As a result of the features discussed above, transmission fluid flows off of the friction material quicker than with the conventional designs without sacrificing bracket strength, since the holes extend through the strap rather than the bracket. Such structures improve the shift characteristics due to quicker engagement of the band. As a result, shorter engagements result in lower temperatures at the interface between the friction material and the drum surface. Moreover, the bands have less tip wear due to shorter engagements. Moreover, the improved strength of the bracket, due to the looped section which is in line with the apply load, or due to alignment with the angled support ribs, improve the strength of the bracket. In addition, reinforcement ribs add strength to the socket of the integral one-piece bracket formed by the flat strap.

Having thus described the present invention, many modifications thereto will become apparent to those skilled in the art to which it pertains without departing from the scope and spirit of the present invention as defined in the appended claims. For example, the number of holes and slots in the strap and in the friction material may vary depending upon dimensional constraints. Moreover, while one of the preferred constructions may be applied at at least one end of the bracket, other constructions may be employed at the other end of the band without departing from the scope of the invention. Moreover, the holes can be configured as slots, or in other shapes, to control fluid communication and heat dissipation.

Claims

WHAT IS CLAIMED IS:

1. A brake band for transmissions comprising: a metal strap forming an arcuate band, at least one end of said metal strap having a socket for receiving an engagement member, said socket being formed by return bent strap portion of said strap spaced apart from said arcuate band at a position aligned with an engagement member contact area, and a friction layer lining the inner circumferential surface of said arcuate band.

2. The invention as defined in claim 1 wherein said engagement pin is an apply pin displaceable along an actuation path, the actuation path containing the contact area and wherein said strap portion position is aligned with the actuation path.

3. The invention as defined in claim 1 wherein said strap portion terminates at a mating portion that lies flat against the surface of said arcuate band.

4. The invention as defined in claim 3 wherein said portion is joined to said arcuate band.

5. The invention as defined in claim 1 wherein said return bent strap portion is spaced apart from said arcuate band by a curved end wall.

6. The invention as defined in claim 5 wherein said curve is radiused.

7. The invention as defined in claim 1 wherein said return bent strap portion includes a pinch wall.

8. The invention as defined in claim 7 wherein said return bent strap portion is spaced apart from said arcuate band by a curved portion to form a first leg the return bent portion terminates at a mating portion that lies flat against the surface of said arcuate band, and said pinch wall is formed intermediate said leg and said mating portion.

9. The invention as defined in claim 8 wherein said first leg includes reinforcement ribs.

10. The invention as defined in claim 1 wherein said arcuate band is perforated beneath said return bent strap portion.

11. The invention as defined in claim 10 wherein said bent strap portion includes ribs.

12. The invention as defined in claim 10 wherein lining is perforated beneath said return bent strap portion.

13. The invention as defined in claim 1 wherein said return bent strap portion includes at least one reinforcement rib and wherein said reinforcement rib is aligned with at least one engagement pin contact point.

14. The invention as defined in claim 13 wherein the top of said reinforcement rib is aligned with said at least one engagement pin contact point.

15. A method for forming an engagement member socket on a transmission brake band, the band having an arcuate band portion of strap including a friction surface, the method comprising: forming said strap at a length longer than the friction surface; return bending at least one end of said strap to form a return bent portion spaced apart from said arcuate band portion including the friction surface; aligning at least a portion of said return bent portion with at least one engagement member contact point, and forming an engagement member receptacle at said at least one engagement member contact point.

16. The invention as defined in claim 15 and further comprising reinforcing said return bent portion by forming a rib in said return bent portion.

17. The invention as defined in claim 16 wherein said aligning step comprises aligning a portion of said rib with said at least one engagement member contact point.

18. The invention as defined in claim 17 wherein said rib portion is a top of said rib.

19. The invention as defined in claim 15 and further comprising perforating said friction surface below said return bent portion.

20. The invention as defined in claim 15 wherein said forming function includes forming a pinch wall in said return bent portion.

21. A method for extending the working life of automatic transmissions having brake bands in the form of straps having an arcuate portion carrying a friction material layer, each strap having an end with a socket for receiving an engagement member, the method comprising: forming a strap end by return bending a terminal portion of said strap to a position spaced apart from said arcuate portion; forming a socket on said return bent terminal portion; perforating the strap beneath said return bent terminal portion; and providing said strap end for installation in a transmission carrying heat dissipating medium.