The present invention relates generally to the field of stators utilized in torque converters, more specifically to one-way or unidirectional clutches for stators and still more specifically to friction one-way clutches used with stators.
In transmissions, it is common to use a one-way clutch to provide a single direction of rotational motion. One-way clutches for torque converter stators commonly use either roller or sprag clutches. Both of these designs result in high stress due to line contact between the components. As a result, the components must have a minimum length to withstand the stresses. The minimum length creates a need for larger components which increase the cost of the one-way clutch.
U.S. Pat. No. 4,341,294 to Kerr discloses a spiral type one-way clutch assembly that includes utilizing monolithic annular outer and concentrically positioned annular inner body members which have mutually opposed tangentially congruent spiral surfaces defining a spiral race positioned between them. A plurality of axially oriented abutting roller members is positioned in, and almost fills, the spiral race, with each roller member being in contact with both the inner and outer spiral surfaces. Limit springs are placed between the body members to limit the relative oscillatory movement between the body members.
U.S. Pat. Nos. 3,107,764 and 3,202,250, both to Fulton, disclose a friction one-way clutch that uses a spiral similar to that seen in Kerr. The rollers in Kerr are replaced with friction modifiers in the form of wedges. However, the clutches disclosed in the Fulton patents use multiple springs and multiple wedges which add to the cost of manufacturing. The also possess a complex geometry on the contact surfaces of the various components.
Although the clutches discussed above provide unidirectional movement to stators in torque converters, they are both complex assemblies in terms of both number of parts and length of contact components. In addition, they are relatively costly to produce.
Thus, there exists a need in the field for a friction one-way clutch for torque converter stators that is comprised of a minimum of parts that are easily and cheaply manufactured and assembled.
The present invention broadly comprises a friction one-way clutch comprising a flat outer race, the outer race having an inner circumference and an outer circumference; a flat wedge ring, the wedge ring having at least one tapered wedge that forms at least part of an inner circumference of the wedge ring and an outer circumference having a radius offset at any point on the outer circumference, wherein the wedge ring forms an interference fit with the inner circumference of the outer race; and, a flat inner race, the inner race having an inner circular perimeter and an outer perimeter, in which the outer edge is generally round and formed into at least one tapered ramp. By generally round is meant that the overall shape of the outer edge is round but may not form a perfect circle. The at least one ramp of the inner race contacts at least one of the at least one tapered wedges to form at least one friction point when the clutch rotates in one direction.
The present invention also comprises a torque converter stator—one way friction clutch assembly comprising a torque converter stator; a flat outer race, in which the outer race includes an inner circumference and an outer circumference and is attached to the stator; a flat wedge ring, in which the wedge ring possesses at least one tapered wedge that forms at least part of an inner circumference of the wedge ring and an outer circumference having a radius offset at any point on the outer circumference, wherein the wedge ring forms an interference fit with the inner circumference of the outer race; and a flat inner race, the inner race having an inner circular perimeter and an outer perimeter, wherein the outer perimeter is generally round and formed into at least one tapered ramp. The at least one ramp of the inner race contacts at least one of the at least one tapered wedges to form at least one friction point when the inner race is rotated in one direction.
The invention also comprises a method of shaping a wedge ring of a one-way clutch comprising: determining the inner radius of the wedge ring; determining the outer radius of the wedge ring; establishing the coefficient of friction between the wedge ring and an inner race of the one-way clutch; calculating the range of lock up wedge angles between the wedge ring and the inner race, wherein the lock up angle range allows the one-way clutch to break away from the lock up with negligible force; and, shaping the wedge ring to have a wedge angle within the angle range when locked up with the inner race.
One object of the present invention is to present a one-way or unidirectional friction clutch with a reduced number of parts.
A second object of the invention is to provide a one-way unidirectional clutch comprising primarily stamped components.
A third object of the invention is to supply a one-way unidirectional clutch constructed in such a way as to reduce stress caused by line contact between components.
An additional object of the invention is to reduce the over all length of the components of the friction one-way clutch needed to withstand the stresses of contact between the components.
A further object of the invention is to supply a method of shaping the wedge ring of the present invention by determining an optimal range of wedge angles based on known coefficients of friction between the outer race, the inner race and the wedge ring, and the inner and outer radii of the wedge ring.
The nature and mode of the operation of the present invention will now be more fully described in the following detailed description of the invention taken with the accompanying drawing Figures, in which:
At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical structural elements of the invention. It also should be appreciated that figure proportions and angles are not always to scale in order to clearly portray the attributes of the present invention.
While the present invention is described with respect to what is presently considered to be the preferred embodiments, it is understood that the invention is not limited to the disclosed embodiments. The present invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
Adverting to the drawings,
Outer race 30 preferably is a circular flat component having a round inner perimeter 31 and an outer perimeter 32. By flat is meant that the major surfaces of a particular component are essentially parallel and distinctly greater than the minor surfaces. Outer race 30 defines outer race holes 51b.
Wedge ring 40 is a flat generally round component that includes at least one tapered wedge 41 that projects from outer circumference 43 toward the inner space defined by inner circumference 44 to form at least part of inner circumference 44 of wedge ring 40. In one embodiment, wedge ring 40 may have a plurality of wedges 41 as seen in
Cover 60 covers the components of clutch 10 and defines holes 51c that are aligned with holes 51a and 51b during assembly to form a continuous passthrough or hole through which nut and bolt assemblies are passed to hold the clutch—stator assembly together. Cover 60 includes inner surface 61 which forms part of passage 70 with stator 20 and clutch 10.
Wedge 40 provides the advantage of distributing stress evenly inside of outer race 30. Friction is provided at one or more friction or contact points between wedge ring 40 and outer race 30 by offsetting outer perimeter 43 at any point on wedge ring 40. The offset creates an interference fit that creates the friction between outer race 30 and wedge ring 40. By adjusting the width of gap 42 the interference fit can be adjusted. Similarly, stress from friction between wedge ring 40 and inner race 50 is also evenly distributed inside of wedge ring 40 and inner race 50. Because this stress on all three components of clutch 10 is distributed throughout the body of each component, clutch 10 provides the advantage of enabling the manufacture of a friction one-way clutch using a less expensive method, such as stamping, as opposed to casting or forging and also allows for fewer parts to be fabricated and installed in the complete assembly.
Wedge ring 40 provides friction between outer race 30 and wedge ring 40 by using a spiral to create an offset angle. The outer diameter of wedge ring 40 is larger than the inner diameter of outer race 30 to stop the wedge ring from rotating in one direction. Preferably, the spiral on wedge ring 40 is an equal angular spiral which creates a constant angle across the entire surface. The constant angle is preferred for longer arcs to ensure proper contact is maintained at any given contact point. However, as the number of wedges 41 in wedge ring 40 increases, the amount of error in a non-equal angular spiral decreases which allows for the use of different shapes for wedges 41 as they get shorter in length.
One problem that may be encountered with clutch 10 is that wedge ring 40 may become frictionally wedged with outer race 30 in the lock up mode such that force may be necessary to dislodge wedge ring 40 from outer race 30 when clutch 10 enters the counterrotational or freewheeling mode. In a preferred embodiment, wedge ring 40 becomes dislodged without a minimal amount of force, meaning only negligible force, if any, is applied to enable “wedge ring” clutch 10 to begin to rotate in the opposite or freewheeling direction. Consequently, it is preferred that minimal or negligible force is used to lodge or “lock up” wedge ring 40.
The relation of the frictional force (Ffo) of wedge ring 40 to the torque on outer race 30 and wedge angle θ can be seen as follows:
where μo is the coefficient of friction between outer race 30 and wedge ring 40, θ is the wedge angle as seen in
Ffi<Fno sin θ 5.
Fno cos θμi<Fno sin θ 6.
μi<sin θ/cos θ 7.
μi<tan θ 8.
It can be seen that to achieve a free break away, the tangent of the wedge angle θ must be greater than the coefficient of friction μ between wedge ring 40 and inner race 50.
This shows that with a lower coefficient of friction μ, wedge angle θ can be reduced. For example, in the case of a stator for a torque converter, the radial area available to contain clutch 10 can be a limiting factor in terms of the size and configuration of the clutch. In order to adjust to a limited radial area, a shallow angle θ is preferred. This can be achieved using materials together that have a low coefficient of friction. Low coefficients of friction can be achieved using hardened materials that are coated using physical vapor deposition (PVD), chemical vapor deposition (CVD), nitride processes, or other suitable processes well known to those skilled in the art.
It will be recognized that clutch 10 may be adapted for use in a variety of contexts where use of a one-way clutch is desired. In automotive components, for example stators in torque converters, coefficients of friction μ may range from about 0.05 to about 0.25, inner radius ri may range from about 25 mm to about 150 mm, and outer radius ro may range from about 50 mm to about 175 mm. It will be recognized however, that clutch 10 may be sized beyond these ranges when necessary to provide unidirectional control in a variety of automotive and other types of settings.
In this example, the coefficient of friction μ is 0.2. This is similar to coefficients of friction found with typical materials that may be used in one-way clutches for stators, such as steel. As per equation 8, wedge angle θ must be greater than 11.31° (0.2<tan 11.31°). This will be the angle θ in lock up equation 4. To can be removed as To is larger than Ti because it is at the outer radius. In addition, Fpre, the force generated by the wedge ring—outer race interference fit, is essentially zero as it is minimally sufficient to move wedge ring 40 into contact at all surfaces. Using the equation ri<μro/tan θ, 0.2 will be μ, ro is known to be 40.0 mm (a hypothetical but typical outer radius for wedge ring 40), and 11.5° for θ because it is larger than tan−1μ. This gives an inner wedge radius ri of less than 39.32 mm. Therefore to ensure clutch 10 breaks free with no torque applied, the wedge angle θ must be greater than 11.31° and to ensure the clutch locks we will have an outer wedge radius ro of 40.0 mm and an inner wedge radius of less than 39.32 mm.
It will be readily seen that a wedge angle range enabling both lock-up and “force-free” break away can be calculated from a revision of the equation to μi<tan θ<μoro/ri inserting the relevant inner radius and outer radius.
Because of the friction that develops between the components of clutch 10, it is preferred that harder materials be used in fabricating the components. For manufacturing purposes, a medium carbon steel, for example 1035 or 4140, hardened to about 40-65 Rockwell C is preferred for outer race 30 and inner race 50, while a high carbon, prehardened steel, such as 1075, is preferred for wedge ring 40.
Thus it is seen that the objects of the invention are efficiently obtained, although changes and modifications to the invention should be readily apparent to those having ordinary skill in the art, which changes would not depart from the spirit and scope of the invention as claimed.
This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 61/008,285 filed on Dec. 19, 2007 and is incorporated herein by reference.
Number | Date | Country | |
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61008285 | Dec 2007 | US |