Technical Fferø

This invention relates to a clutch plate for use in a clutch pack assembly.

Background Art

Automatic transmissions used in motor vehicles generally employ clutch assemblies. These clutch assemblies typically include one or more clutch packs which comprise friction clutch plates typically having internal splines alternated with separator clutch plates typically having external splines. The separator and friction clutch plates are typically placed within a clutch housing which has a spline configuration designed to mate with the external splines of the separator clutch plates, thereby allowing the separator clutch plates to slide back and forth within the clutch housing. The internal splines of the friction clutch plates likewise slidably engage the mating splines of a clutch shaft or hub assembly located within the clutch housing.

The working surface of the separator clutch plate is that portion of the separator clutch plate which frictionally engages the friction clutch plate when the plates are engaged during use; i.e., a portion of the separator clutch plate excluding the splines. Likewise, the working surface of the friction clutch plate is that portion of the friction clutch plate which frictionally engages the separator clutch plates when

the plates are engaged, i.e., a portion of the friction clutch plate excluding the splines.

The clutch pack is sometimes called a wet clutch pack because a fluid, such as transmission fluid, is used to dissipate heat and minimize the frictional wear between the friction and separator plates while allowing the plates to engage and drive each other during use. When the plates are disengaged, the fric¬ tion and separator plates rotate relative to each other. Ideally, there would be no torque transmitted between the separated friction and separator plates. However, in reality, some torque is transmitted. First, while the intended space between the friction and separator plates when disengaged is quite small, typically in the range of 0.01 inch. Because of the close proximity of the plates and the transmission fluid between the plates, viscous shear forces will arise between the separator and friction clutch plates when disengaged and rotating relative to each other. The resulting "drag torque" or "parasitic spin loss" results in an energy loss thereby requiring more fuel to be spent in driving the vehicle. This drag torque may also generate heat which can decrease clutch performance and life.

Various methods have been proposed to minimize drag torque. Some such methods were disclosed in F.

Lloyd, Parameters Contributing to Power Loss in

Disengaged Wet Clutches, SAE Technical Paper No. 740676

(1974) and R. Fish, Using the SAE #2 Machine to Evaluate

Wet Clutch Drag Losses, SAE Technical Paper No. 910803 (1991) . One of the methods disclosed is to provide waved separator or friction plates in lieu of flat plates. Another method disclosed is to provide grooves in the plates.

As explained in SAE Technical Paper No. 910803, these surface irregularities — waving or grooving — may reduce drag loss for several reasons. First, they may aid in keeping the friction separator plates uniformly separated during disengagement. Because torque drag is not linear with the space between adjacent plates but is disproportionately higher between close plates, this uniform separation will reduce drag torque. Surface irregularities also serve to reduce drag torque by helping to release "stuck" plates and by providing an oil passage or receptacle from which oil might flow to fill the space left between separating plates.

However, because clutch plates are usually manufactured by punching from sheet metal, the waving or grooving of such plates adds another step to the manufacturing process. This additional step makes such plates not only more expensive to manufacture, but makes it more difficult to stay within specification tolerances.

Another prior art method proposed in the past to reduce drag torque is illustrated in Figure 1. Figure 1 shows a clutch plate comprising a separator plate 10 having an inner perimeter 12 and external splines 14. In order to decrease drag torque, small circular holes 16 in linear groups of three at equidistant spaces around the clutch separator plate 10 are employed. Such a separator plate would normally be manufactured by initially punching the separator plate 10 from a piece of sheet metal so as to define the inner perimeter 12 and the external splines 14. Because of the small size of the circular holes 16 they must be drilled and deburred before use. Like the methods of

waving and grooving, this adds additional steps to the manufacturing process, making the plates not only more expensive to manufacture but also more difficult to keep within specification tolerances.

Summary Of The Invention

An object of the present invention is to provide an improved clutch plate which reduces drag torque, which does not raise manufacturing costs, and which can easily be manufactured within specified tolerances.

In carrying out the above objects, the invention is a clutch plate comprising a plate having a spline and a plate center point, the plate defining one or more oblong holes having a hole perimeter edge where a majority portion of the hole perimeter edge is oriented at an angle to an imaginary circumferential line drawn about the plate center point.

An advantage of this invention is that the oblong hole reduces drag torque by providing an oil passage through which, or a receptacle from which, fluid can flow to fill the space between the clutch plates when the clutch assembly is disengaged. More importantly, the oblong holes also serve to create a turbulence in the fluid between the plates. This turbulence serves to reduce or break the surface tension between the fluid and the plate thereby reducing drag torque, referred to in the industry as parasitic spin loss. Because the majority portion of the hole perimeter edge is oriented at an angle to the direction of travel of the clutch plate, the turbulence is increased and consequently the drag torque is reduced.

In a more preferred embodiment, no portion of the perimeter edge of the oblong hole is parallel to an imaginary circumferential line about the plate center point. This ensures that all portions of the perimeter edge of the oblong hole are creating turbulence thereby reducing drag torque.

In an alternative embodiment, the clutch plate comprises a plate having a working side surface and a spline, the plate defining one or more oblong holes, the total area of the one or more oblong holes being less than approximately 5% of the working side surface.

An advantage of this alternative embodiment is that the size of the holes will not interfere with the structural integrity of the plates, nor their ability to operate as heat sinks.

In yet another alternative embodiment, the clutch plate comprises a plate having a spline and a plate center point, the plate defining one or more oblong holes, the one or more oblong holes having a hole center point and a longitudinal axis, the longitudinal axis being oriented at an angle of less than 90° to an imaginary straight line drawn from the plate center point to the hole center point.

An advantage of this embodiment is that turbulence is maximized by those perimeter edge portions which are angled as widely as possible from an imaginary circumferential line about the center point of the clutch plate. The more perpendicular the perimeter edge portion of the oblong hole is to the imaginary circumferential line, the more turbulence that is created, and the more drag torque is reduced. With

regard to this embodiment, it is especially preferred that the longitudinal axis of the oblong hole be oriented at an angle of 60° or less to an imaginary straight line drawn from the plate center to the hole center point.

In all of these embodiments, the oblong hole may be shaped as having straight sides and semi-circular shaped ends. Furthermore, in any of these embodiments, it is preferred that the plate have two or more oblong holes which are set equidistant apart around the clutch plate. This will help to ensure that the plate is properly balanced about the plate center point.

Further objects and advantages of this invention will be apparent from the following description, reference being had to the accompanying drawings wherein an embodiment of the present invention is shown.

BriefDescription OfThe Drawings

While an embodiment of this invention is illustrated, the particular embodiment shown should not be construed to limit the claims. It is anticipated that various changes and modifications may be made without departing from the scope of this invention.

FIGURE 1 is a side view of a prior art clutch plate;

FIGURE 2 is a side view showing one embodiment of the invention; and

FIGURE 3 is a blow up of the circled portion of the bottom of FIGURE 2.

BestMode For Carrying Out The Invention

Figures 2 and 3 show one embodiment of this invention comprising a clutch plate 100 having an inner perimeter 102 and outer perimeter 103 defining external splines 104. Such a clutch plate 100 may be used in any appropriate clutch assembly, such as a wet clutch pack of an automatic transmission. Drag torque is reduced in this embodiment by oblong holes 106 spaced equidistantly around the clutch plate 100. While four such oblong holes 106 are shown, it may be desirable to use more or less holes.

For a clutch plate having an inside diameter A equal to approximately 145.28 mm, a minor outside diameter B equal to approximately 166.82 mm, and a major outside diameter C equal to approximately 175.05 mm, the following preferred dimensional parameters have been developed and tested to reduce drag torque and maximize manufacturing efficiency.

Parameter Preferred Parameter D 3.18 mm ± 0.13 mm E 7.92 mm ± 0.13 mm F 156.424 mm G 60.0 ^* ± 1.0 ^*

Note that while the oblong hole 106 of the embodiment shown has straight sides and circular ends, the shape of the oblong hole may comprise any shape which is of sufficient size to be punched and which lacks corners. Corners are undesirable because during

the punching process, die break protrusions are larger in magnitude at such corners and harder to finish off. Such protrusions can have the negative effect of eroding the friction surface of adjacent clutch plates within a clutch assembly.

Plates may be easily manufactured in accordance with this invention by simply punching out the oblong holes 106 at the same time the inner diameter 102 and splines 104 are punched from sheet metal. Because no additional steps are necessary, such a separator plate may be manufactured as efficiently and inexpensively as clutch plates not having such drag torque features.

The surface irregularities of the clutch plate of this invention, those being the oblong holes 106, serve to reduce drag torque by helping to release

"stuck" plates by providing an oil passage through which, or receptacle from which, fluid can flow to fill the space between clutch plates when the transmission is disengaged. More importantly, the oblong holes also serve to reduce drag torque, or parasitic spin loss, by creating a turbulence between the plates which serves to reduce or break the surface tension between the fluid and the plate. The turbulence which reduces drag torque is created by those perimeter edge 108 portions of the oblong hole which are not parallel to a circumference drawn about a center point "H" of the clutch plate.

Accordingly, while the oblong hole 106 shown in ^: Figures 2 and 3 have perimeter points 110 and 112 which are tangential to imaginary circumferential lines

114 and 116 respectively which are drawn about the center point "H," the oblong holes 106 do not have any

perimeter edge 108 portion parallel to any imaginary circumferential line about the plate center point "H." In fact, an oblong hole having a major portion of the perimeter edge parallel to an imaginary circumferential line about the center point of the clutch plate is undesirable because the turbulence and resulting drag torque reduction will be minimal or nonexistent. As a result, it is preferred that the oblong holes have a hole perimeter edge where a majority portion of the hole perimeter edge is oriented at an angle to an imaginary circumferential line drawn about the plate center point. Of course, more preferred is the embodiment shown in Figures 2 and 3, where no portion of the perimeter edge 108 of the oblong hole 106 is parallel to an imaginary circumferential line about the plate center point.

Furthermore, it is desirable to maximize the dimension, such as the dimension "I" shown in Figure 3, of the perimeter edge 108 of the clutch plate which causes turbulence in the surrounding fluid when the clutch plate is rotating. The distance "I" is determined by drawing the line 114 about the center point "H" of the plate 100 tangential to the point 110 of the oblong hole 106 closest to the center point "H," and the second line 116 about the center point "H" tangential to the point 112 on the perimeter of the oblong hole 106 farthest from the center point "H." Dimension "I" is then determined by measuring the distance between the inner line 114 and the outer line 116 along a straight line extending from the center point "H."

Similarly, because turbulence is maximized by perimeter edge 108 portions of the oblong hole which are angled as widely as possible from a circumferential line

about the center point "H" of the clutch plate 106, it is also desirable that the angle "G" between the longitudinal axis "J" of the oblong hole 106 and a line drawn from the center point "H" and intersecting the center point "K" of the oblong hole 106 be as close to zero as possible. This will place the straight side edges 120 and 122 of the oblong holes 106 in a less parallel relationship to the direction of travel of the plate 100 about the center point ^W H," thereby maximizing turbulence and reducing drag torque. Accordingly, it is preferred that the longitudinal axis "J" of the oblong hole 106 be oriented at an angle of 60° or less to an imaginary straight line drawn from the plate center point "H" through the hole center point "K." However, the achievement of this desirable angle is limited by other constraints. For example, while it is desirable to have the angle "G" be as small as possible, it is also necessary that the inner point 110 and outer point 112 of the oblong hole 106 be far enough from the inner perimeter 102 and outer perimeter 103 of the clutch plate 100 respectively so as to not structurally weaken the clutch plate 100. At the same time, it is necessary to maintain the size of the oblong hole 106 such that it may be easily manufactured by the punch and die method. Accordingly, in the embodiment shown in Figures 2 and 3, the angle "G" of 60° ± 1.0 degrees has been found to be suitable.

For the same reason, the preservation of structural integrity, there is also a preferred limitation on the area of the oblong holes in relation to the working area of the clutch plate 100. If the oblong holes are made too large, or too many in number, they may structurally weaken the clutch plate, thereby decreasing use life. Such weakening might cause the

clutch plate to warp or fail during use. Furthermore, holes which are excessive in size or number may interfere with the frictional engagement between adjacent separator and friction plates within the clutch assembly, i.e., the friction capacity of the clutch assembly will be reduced. Not only will there be less surface area available for frictional engagement which will reduce the friction capacity of the clutch assembly, holes which are too large in size may allow the adjacent plate to protrude into the holes to some extent, both interfering with operation and increasing wear between the plates. Lastly, the individual clutch plates within a clutch pack operate as miniature heat sinks, the body of the clutch plate retaining any heat generated during normal operation until it is dissipated by the surrounding fluid. If the clutch plate has insufficient mass, it will be incapable of absorbing and retaining the heat generated without being heated beyond desired limits. As a result, the clutch plate could overheat and fail.

Accordingly, it is desirable that the ratio of the area of the oblong holes 106 as compared to the working side surface of the clutch plate 100, that being normally the area of one side of the clutch plate 100 minus any splines, be 0.05 or less such as in the embodiment shown.

While only a clutch plate having external splines has been illustrated to show this invention, this invention includes the use of such torque drag reducing holes in clutch plates having internal splines.

Furthermore, while particular embodiments of the invention have been illustrated and described, it

will be obvious to those skilled in the art that various changes and modifications may be made without departing from the invention. It is intended that the following claims cover all such modifications and all equivalents that fall within the true spirit and scope of this invention.