WO1999000199A1

WO1999000199A1 - Powershift clutch and method of forming same

Info

Publication number: WO1999000199A1
Application number: PCT/US1997/011266
Authority: WO
Inventors: Bruce A. Skaggs
Original assignee: Rockford Powertrain Inc
Current assignee: Rockford Powertrain Inc
Priority date: 1997-06-27
Filing date: 1997-06-27
Publication date: 1999-01-07
Anticipated expiration: 1999-12-27

Abstract

A method is provided for forming a clutch drum (16) having radially disposed teeth using a punch press. A blank drum is indexed on an mandrel (110) and a die (112) on the punch press forms teeth at each position. The method avoids the creation of a wave of excess material which must be accounted for in previously known methods. Also, an improved backing plate (68) is provided for use in a powershift clutch (10) which has a relief angle for reducing the bending moment created when the backing plate is loaded and which may otherwise damage the drum.

Description

POWERSHIFT CLUTCH AND METHOD OF FORMING SAME

Field Of The Invention The present invention generally relates to clutches, and more particularly relates to clutches used to transmit power along the drivetrain of a vehicle.

Background Of The Invention

Clutches are commonly used in vehicles to selectively transmit the rotation of an input member, such as a transmission shaft, to an output member, such as a gear. In the typical clutch, a drum is attached to and rotates with the shaft. A first set of driving plates operatively attached to the drum are interposed with a second set of driven plates operatively attached to the output member such as a gear. A piston may be hydraulically actuated to engage and release the plates. Accordingly, when the plates are engaged, the friction force between the plates increases and transfers the rotation of the first set of plates to the second set. The clutch is therefore used to control the gear output. The clutch drum must adequately support the driving plates so that the plates do not slip when engaged. It is therefore typical for the drum to have radially extending teeth or splines formed about the perimeter of the drum which correspond to splines on the driving plates for adequately supporting the plates on the drum.

Unfortunately, past methods for forming the teeth in the drum are excessively expensive and relatively difficult. One method, known as rack-rolling, forms the teeth by positioning a blank drum over a mandrel and rolling a linear rack with

successively larger teeth along the outside of the blank. Each successive rack tooth therefore increases the bend in the blank until the desired drum tooth shape and size are obtained. During this process, however, excess material may be pushed along the periphery of the drum so that a wave of excess material gathers or "bunches" at a point on the blank which may ruin the drum. Another known method is to machine the teeth into the drum. In this method, teeth are machined into the interior wall of a sufficiently thick cylindrical blank. The machining process, however, is not only relatively expensive, but also requires the use of a relatively thick blank to form the drum and results in wasted material.

Previously known clutches may have further problems resulting from the bending loads exerted on a backing plate of the clutch disposed behind both sets of plates. As the plates are compressed together, the backing plate provides a resisting force so that the plates engage one another. A retaining ring inserted in a groove in the drum limits movement of the backing plate in response to the clutch plates and piston. As the plates are forced against a typical backing plate, a bending moment is created which may create excessive forces on the drum which may ultimately damage the drum.

Summary Of The Invention A general aim of the present invention is to provide an easy and inexpensive method for forming a clutch drum.

In that regard, it is an aim of the present invention to provide a method for forming teeth in a drum which utilizes widely available machine tools in a manner which avoids creating a wave of excess material in the drum. Another object of the present invention is to provide a clutch which minimizes damage to the clutch drum resulting from excessive forces generated during compression of the clutch plates.

More particularly, it is an object of the present invention to provide a backing plate which reduces the bending forces exerted on the drum.

These and other objects and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

Brief Description Of The Drawings

FIGURE 1 is a partially sectioned perspective view of a powershift clutch in accordance with the present invention.

FIG. 2 is a sectional side view of the clutch taken along line 2-2 of FIG. 1 showing the declutched position. FIG. 3 is an enlarged sectional side view of the clutch taken along line 2-2 of

FIG. 1 showing the fully engaged position.

FIG. 4 is a top view of a drum made in accordance with the present invention and incorporated into the clutch of FIG. 1.

FIG. 5 is a sectional side view of the drum taken along line 5-5 of FIG. 4. FIG. 6A is a perspective view of an initial drum blank which is ultimately formed into the drum of the present invention.

FIG. 6B is a perspective view of the drum blank of FIG. 6 A having a plurality of indentations pressed into the outer periphery of the flange. FIG. 6C is a schematic illustration of the drum blank placed in a press having a die shaped to form teeth in the blank.

FIG. 6D is a perspective view of a completed drum. FIG. 7 is an enlarged side view of a backing plate of the clutch of FIG. 1. FIG. 8 is a schematic illustration showing the loading of a backing plate in accordance with the present invention.

FIG. 9 is a schematic illustration showing the loading of a conventional backing plate.

While the invention is susceptible of various modifications and alternative constructions, certain illustrative embodiments thereof have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions and equivalents falling within the spirit and scope of the invention as defined by the appended claims.

Detailed Description Of The Preferred Embodiment Referring to FIGS. 1-3, a clutch 10 mounted on a transmission shaft 12 for selectively operating left and right gears 14 is shown incorporating the clutch drum 16 in accordance with the invention. FIGS. 1-3 illustrate a transmission shaft 12 having symmetrical left and right clutch drums and associated components. Reference will be made to the left drum clutch and associated components.

Referring to FIGS. 4 and 5, the drum 16 has an integral wall separated into small and large diameter walls 18, 20 by a flange 22. The first end 24 of the drum forms an inwardly disposed base 26 and the second end 25 of the drum 16 defines a second end of a cavity 28. The first end 24 has an opening 30 for slidably engaging the shaft 12 during assembly and is welded to the middle gear 14 generally at point 32 (FIG. 2). The middle gear 14 is also welded to the shaft 12 at point 34 so that the drum 16 rotates in unison with the shaft 12. The large diameter drum wall 20 defines a plurality of teeth or splines 36. The splines 36 are adapted to receive corresponding splines 38 of a plurality of annular driving clutch plates 40 for forming a spline connection which permits the driving clutch plates 40 to rotate in unison with the transmission shaft 12. For reference purposes, the teeth 36 define a plurality of alternating troughs 42 and crests 44. As best shown in FIGS. 4 and 5, a circular slot 46 is formed near the second end 25 of the drum 16. The slot 46 comprises a series of slot portions 47 formed in the troughs 42 and is sized to accommodate a portion of a retaining ring 48.

The gear 14 provides output from the transmission shaft 12 when the clutch is engaged. As best shown in FIGS. 2-3, the gear 14 has a central bore 15 supported on the transmission shaft 12 using bearings 50. Oil seals, retainer rings, bearings, and

the like are shown in the drawings, but will not be described in great detail since one of ordinary skill in the art will recognize the structure and functionality of such elements from there appearance in the figures. The left and right gears 14 have a sleeve 52 concentric with the transmission shaft 12 which projects into the cavity 28 of the drum 16. The outer diameter of the sleeve 52 has a plurality of splines 54. A plurality of driven clutch plates 56, which extend outwardly from of the sleeve 52, have a plurality of splines 58 which engage the sleeve spline 54 to form a spline connection. The driven clutch plates 56 are interposed between the driving clutch plates 40 to form a series of alternating driving and driven clutch plates 40, 56.

It will be appreciated that the interposed clutch plates 40, 56 may be selectively compressed and released to control the output of the gear 14. In the illustrated embodiment, a conventional oil actuated piston 60 may be used to compress and release the clutch plates 40, 56 as the piston 60 is positioned between a disengaged or declutched position shown in FIG. 2 and an engaged or fully clutched position shown in FIG. 3. As shown in FIGS. 2-3, the piston 60 has a recessed wall 62 which, in conjunction with the walls 12a, 14a, 16a of transmission shaft 12, middle gear 14 and drum 16, respectively, form an annular cavity 64. Oil may be selectively supplied in a conventional manner to the cavity 64 through oil port 66 which is in fluid communication with an oil line 67 in the transmission shaft 12. It will be appreciated that as oil flows into the cavity 64, the oil pressure in the cavity 64 increases and ultimately pushes the piston 60 toward the clutch plates 40, 56. As the clutch plates 40, 56 are forced together in response to the piston 60, the plates 40, 56 are compressed and the rotation of the driving clutch plates 40 is transferred to the driven clutch plates 56, thereby rotating the gear 14.

A backing plate 68 is attached to the drum 16 near the second end 25 to provide a surface against which the driving and driven clutch plates 40, 56 are compressed. The backing plate 68 has a body portion 69 extending between the interior face of the drum wall 20 and the exterior face of the sleeve 52. The body portion 69 has an elongated top face 71 which slidably engages a seal 73 in the sleeve 52 to prevent oil leakage therethrough. Like the driving clutch plates 40, the backing

plate 68 (FIG. 7) has a plurality of teeth or splines 70 adapted for slidably engaging the drum spline 36 to form a spline connection. The backing plate 68 has a generally flat engaging surface 72 disposed towards the clutch plates (FIG. 7). The slot 46 in the drum 16 (best shown in FIGS. 4-5) is located on the rear or left side of the backing plate 68 (as shown in FIG. 2) and carries the retaining ring 48 which limits the leftward movement of the backing plate 68 and resists the forces exerted on the backing plate 68 by the clutch plates 40, 56 and the piston 60. Accordingly, the piston 60 compresses the clutch plates 40, 56 against the backing plate 68 to thereby engage the clutch 10.

When the oil pressure in the piston cavity 64 is decreased below a predetermined level, a spring member 76 disposed about the circumference of the transmission shaft 12 overcomes the oil pressure and returns the piston 60 to the disengaged position, wherein the clutch plates 40, 56 are disengaged from each other. As illustrated in FIG. 2, the spring 76 is disposed inside the sleeve 52 between a retaining ring 78 disposed in a shaft slot 80 and a cut-off ring 82 adjacent to the piston 60. The strength of the spring 76 is selected so that it overcomes a predetermined pressure level in the cavity 64 and thereby pushes the piston 60 to the disengaged position.

In the preferred embodiment, oil is directed through the driving and driven clutch plates 40, 56 to cool the heat generated from friction between the plates 40, 56. A cooling oil inlet 84, in fluid communication with the lubrication line 86 inside the shaft 12, discharges inside the drum 16 near the spring 76. The oil flows radially from the shaft 12 towards the drum wall 20 in response to centrifugal forces. The clutch plates 40, 56 preferably have arcuate grooves (not shown) on their surfaces which facilitate the flow of oil from the center to the periphery of the plates 40, 56 and the drum 16. Axially aligned outlet holes 88 are located periodically throughout the drum 16 for allowing the oil to exit the drum 16. In the preferred embodiment, the drum 16 has four lines of holes 88 spaced radially about the drum every 90 degrees. The cut-off ring 82 controls the flow of cooling oil. As best shown in FIGS.

2-3, the cut-off ring 82 slidably engages the transmission shaft 12 and is located between the spring 76 and the piston 60. As the piston 60 moves toward the engaged position, the cut-off ring 82 is moved along the surface of the transmission shaft 12 (leftward in FIGS. 2-3) to expose the cooling oil inlet 84 as shown in FIG. 3 and allow oil to flow into the drum 16. When the piston 60 is positioned to the declutched position, the spring 76 positions the cut-off ring 82 (rightward in FIGS. 2- 3) over the inlet as shown in FIG. 2 to restrict, without entirely stopping, oil flow. As a result, maximum cooling oil flows through the clutch 40, 56 when the plates are engaged and most likely to generate heat. In accordance with one aspect of the present invention, the backing plate 68 is configured to reduce the bending moment Fj_. resulting from loads applied from the clutch plates 40, 58 on the backing plate 68. Referring to FIG. 9 which schematically illustrates the loading of a conventional backing plate 90 supported by a retaining ring 92, the clutch plates exert a load F₂ on the backing plate 90 which, in turn, exerts a load F₃ on the retaining ring 92. Since the load F₂ from the conventional backing plate 90, on the retaining ring 92 is greatest at a point furthest from an axis of bending 94, a relatively large bending moment is created which may damage the retaining ring 92 and the drum 16. As best shown in FIG. 7, the backing plate 68 in accordance with the present invention, however, has a rear face 96 disposed at a relief angle 98. The relief angle

98 is preferably inclined V«, to I 2 degrees from a radial plane of the drum 16. The relief angle positions the load F₃ from the backing plate 68 on the retaining ring 48 closer to the axis of bending 94, minimizing the bending moment on the retaining ring

48 and the drum 16 as schematically shown in FIG. 8.

In accordance with the present invention, the drum 16 may also be formed in accordance with a novel and relatively inexpensive manufacturing method.

Conventional techniques may be used to obtain a drum blank 100 as shown in FIG. 6 A. The drum blank 100 has smooth small and large diameter walls 102, 104 connected by a radially projecting flange 101. The blank 100 forms the cavity 107 having the nearly closed first end 103 and open second end 105. Before forming the teeth 36, a plurality of angled indentations 108 are pressed into the periphery of the flange 101 using a die at points corresponding to the troughs 42 located between adjacent teeth 36, as illustrated in FIG. 6B. The indentations 108 permit the flange 101 to remain substantially flat and planar after the teeth 36 are formed, thereby avoiding the creation of bulges in the flange 101 typically formed in conventional rack rolling methods, which cause stress concentrations and points of failure in the flange 101 and teeth 36.

After pressing the angled indentations 108 in the periphery of the flange 101, the teeth 36 are formed in the large diameter wall 104 of the blank 100. In one embodiment of the present invention, the blank 100 is indexed on a mandrel 110 resembling a spur gear, and at least one tooth 36 is formed in the blank 100 at each indexed position. The preferred method for accomplishing this step is to use a punch press (illustrated schematically in FIG. 6C and indicated by reference numeral 112) carrying a die 114 shaped to form at least one tooth. With this apparatus, it will be appreciated that the blank 100 is positioned over the mandrel 110 and the die 114 is brought to the outside face of the large diameter wall 104 to form at least one tooth 36. The die 114 is shaped so that it forms troughs 42 which extend radially inward from the large diameter wall 104 of the blank 100 to define each tooth 36. The blank

100 is then indexed on the mandrel 110 to present a cylindrical, unformed portion of the large diameter wall 104 toward the die 114, and the die 114 is again brought into contact with the blank 100 to form additional troughs 42. The process is repeated until teeth 36 are uniformly formed around the entire periphery of the large diameter wall 104 without creating the excess wave of material typically formed in conventional rack rolling methods (FIG. 6D). In a preferred embodiment, the die 114 is sized so that it forms three teeth during each cycle, as best shown in FIG. 6C. It will, however, be appreciated that a die having more or less than three teeth may also be used.

In an alternative method for the tooth forming step, the drum blank 100 is positioned over a mandrel and a cam die is forced against the outside of the blank 100. The cam die is shaped to simultaneously form troughs 42 around the entire periphery of the blank 100. As a result, a single operation using the cam die can form all of the teeth.

After the teeth 36 have been formed, the slot 46 for securing the retaining ring 48 is formed through each of the troughs 42. The slot 46 is preferably formed using a punch press carrying a die which forms one slot portion 47 at a time in respective troughs 42 (FIG. 5). The slot portions are formed so that they pass only partially into the thickness of the large diameter wall 104. The slot portions 47 do not extend completely through the large diameter wall 104 which would create through holes which may otherwise increase stress concentrations in the wall 104. It will, of course, be appreciated that the punch press may be used to shear the slot 46 entirely through the wall 104. The shear cut may, however, result in the drum having undesirable stress concentrations in the areas of the through slots. It will therefore be appreciated that the formed slot portions 47 result in greater drum strength.

After forming the slot 46, the punch press may again be used to punch a hole

116 in the base 26 having a predetermined diameter which is sized to permit the drum to slidably receive the shaft 12. Finally, the oil outlet holes 88 are formed in some of the teeth 36. According to the illustrated embodiment, the holes 88 are formed in four teeth which are radially spaced at 90 degree intervals. The number of holes in a drum, however, may be adapted to the oil flow of the particular application.

From the foregoing, it will be appreciated that the present invention provides a new and improved powershift clutch and a method for making the same. The

clutch of the present invention advantageously incorporates a backing plate which minimizes the bending forces exerted on the retaining ring and the drum by creating an angled rear face to reduce the bending moment. In addition, the present invention provides a relatively easy and inexpensive method for forming the drum of a clutch. The method may be carried out using a conventional punch press and therefore does not require expensive tooling. Furthermore, the improved method does not create a wave of excess material created during many conventional methods. Instead, the present invention uses a mandrel and die to form a portion of the teeth and then indexes the drum to form more teeth.

Claims

What Is Claimed Is:

1. A method for making a clutch drum for housing a plurality of clutch plates using a mandrel and a die having a predetermined shape corresponding to at least one spline tooth, the method comprising: forming a blank having an integral cylindrical wall defining small and large diameter walls joined by an annular flange, forming a plurality of uniformly spaced teeth in the large diameter wall wherein each tooth defines a trough and crest by pressing a plurality of radially spaced indentations in the flange at locations corresponding to the troughs, positioning the blank over the mandrel and bringing the die into contact with the large diameter wall to form at least one tooth, and indexing the blank and bringing the die into contact with the large diameter to form additional teeth until the desired number of teeth are formed in the blank.

2. The method of claim 1 comprising using a punch press to position the die into contact with the large diameter wall.

3. The method of claim 2 comprising positioning the die into contact with an exterior face of the large diameter wall.

4. The method of claim 3 wherein the die forms the spline by pressing the trough into the large diameter wall adjacent the indentation.

5. The method of claim 1 further comprising forming an annular groove on an interior face of the large diameter wall for receiving a retaining ring using a groove die.

6. The method of claim 5 comprising sequentially forming the groove in the interior face of each trough.

7. The method of claim 6 comprising forming the groove partially through the wall of the trough.

8. The method of claim 6 comprising forming the groove entirely through the wall of the trough.

9. The method of claim 1 further comprising punching a plurality of holes through at least one of the teeth for permitting oil to exit the drum.

10. A clutch drum for housing a plurality of clutch plates, the drum comprising an integral wall defining a small and large diameter wall joined by a

flange, the large diameter wall having a plurality of radially disposed teeth disposed for receiving a plurality of splines of the clutch plates, wherein the teeth define a plurality of alternating troughs and crests and the teeth are formed in the large diameter wall by pressing a plurality of radially spaced indentations in the flange at locations corresponding to troughs in an initial drum blank, positioning the blank

over a mandrel and bringing a die into contact with an exterior face of the large diameter wall to form at least one radially disposed tooth in the blank, and repositioning the blank on the mandrel and bringing the die into contact with the outside face until teeth are formed around an entire periphery of the large diameter wall.

11. The clutch drum of claim 10 comprising an annular groove on an interior face of the large diameter wall for receiving a retaining ring.

12. The clutch drum of claim 11 comprising the groove passing partially through the wall of the trough.

13. The clutch drum of claim 11 comprising the groove passing entirely through the wall of the trough.

14. The clutch drum of claim 10 comprising a plurality of holes through at least one of the teeth for permitting oil to exit the drum.

15. A clutch for transmitting power from an input shaft to an output gear, the clutch comprising: a generally cylindrical drum defining a cavity having first and second ends, the first end operatively fixed to and rotating in unison with the shaft, the drum having an integral wall defining a small and large diameter joined by a flange and a plurality of splines in the large diameter wall, a plurality of driving clutch plates adapted for engaging the drum cavity, each plate having a plurality of splines for slidably mating with the drum splines to form a spline connection, the gear having a sleeve projecting into the drum, the sleeve having a plurality of splines extending radially outward, a plurality of driven clutch plates adapted for fitting into the drum cavity and having a plurality of splines for slidably mating with the sleeve splines, a backing plate having a plurality of splines for slidably mating with the drum splines, an engaging face adjacent the clutch plates, and a rear face spaced from the clutch plates wherein the rear face forms a relief angle with respect to a radial plane of the drum at a relief angle for reducing a bending moment caused by the forces exerted on the backing plate, a fluid-actuated piston disposed inside the drum cavity capable of moving between a retracted position in which the output member gear is stationary, and an fully engaged position in which the piston compresses the clutch plates together against the backing plate so that the output gear rotates in unison with the input

shaft, a retaining ring attached to the drum and disposed adjacent to the rear face of the backing plate for limiting the movement of the backing plate so that piston may compress the clutch plates may be against the backing plate.

16. The clutch of claim 15 in which the relief angle is between about VΛ and about VΛ degrees.

17. The clutch drum of claim 15 comprising an annular groove on an interior face of the large diameter wall for receiving the retaining ring.

18. The clutch drum of claim 17 comprising the groove passing partially through the wall of the trough.

19. The clutch drum of claim 17 comprising the groove passing entirely through the wall of the trough.

20. A backing plate for limiting movement of a plurality of clutch plates in a clutch wherein the clutch includes a drum having drum splines, the backing plate comprising a body portion having a plurality of splines for slidably mating with the drum splines, an engaging face adjacent the clutch plates, and a rear face spaced from the clutch plates wherein the rear face forms a relief angle with respect to a radial plane of the drum for reducing a bending moment caused by the forces exerted on the backing plate.

21. The backing plate of claim 20 in which the relief angle is between about V* and 1 A degrees.