Patent Description:
As described in <CIT> entitled "One-Way Clutch Assembly Featuring Improved Strut Stability" and assigned to the assignee of the present application, clutches are used in a wide variety of applications to selectively couple power from a first rotatable "driving" member, such as a driving disk or plate, to a second, independently-rotatable "driven" member, such as a driven plate or disk. In one known variety of clutches, commonly referred to as "one-way" or "overrunning" clutches, the clutch "engages" to mechanically couple the driving member to the driven member only when the driving member seeks to rotate in a first direction relative to the driven member. Once so engaged, the clutch will release or decouple the driven member from the driving member only when the driving member rotates in a second, opposite direction relative to the driven member. Further, the clutch otherwise permits the driving member to freely rotate in the second direction relative to the driven member. Such "free-wheeling" of the driving member in the second direction relative to the driven member is also known as the "overrunning" condition.

One such known one-way clutch employs juxtaposed, nominally-coaxial driving and driven members featuring generally planar clutch faces in closely-spaced axial opposition. Such "planar" one-way clutches, as taught by Frank in <CIT> and Ruth et al. in <CIT>, typically include a plurality of recesses formed in the face of the driving member and at least as many recesses formed in the face of the driven member. A thin, flat strut is carried within each of the driving member's pockets such that a first longitudinal end of each strut may readily engage and bear against a shoulder defined by its respective recess of the driving member. The strut's second, opposite longitudinal end is urged toward and against the face of the driven member, for example, by a spring positioned beneath the strut in the recess of the driving member.

When the driving member rotates in the first direction relative to the driven member, the second end of at least one strut engages and thereafter bears against a shoulder defined by a recess of the driven member, whereupon the strut is placed in compression and the driven member is coupled for rotation with the driving member. When the driving member rotates in the second direction relative to the driven member, ramped surfaces defined by other portions of the driven member's recesses urge the second end of each strut back towards the driving member, whereupon the driving member is permitted to freely rotate in the second direction relative to the driven member.

This periodic engagement of the second end of each strut with the ramped surfaces of the driven member's clutch face during clutch overrun may generate a noise or "ratcheting" sound that is often associated with one-way clutches. Known approaches to reduce this ratcheting sound during clutch overrun include modifications to the design of the strut, including reductions in the strut's inertial mass; modifying the spring forces exerted on the strut; and the use of various motion-damping fluid in the space between the clutch faces to thereby better control the dynamics of the strut during clutch overrun. However, further improvement in noise reduction during overrun is desirable, particularly as other clutch components, such as the driven member, become fabricated from materials exhibiting different noise-transmissive characteristics, for example, powdered metal.

"Strut instability" is an unfavorable state often characterized by a strut that is extended when it should be seated in its pocket. Strut instability is a primary concern in terms of durability as it directly correlates to premature spring, strut and pocket wear and eventual failure. It is advantageous during the overrun phase that the struts descend into their respective pockets to minimize parasitic loses due to various Newtonian interactions. The minimum angular velocity of the pocket plate which keeps the strut confined to the pocket is often referred to as the strut "laydown" speed.

The mechanics effecting the descent of the strut are numerous and can be correlated to (among many other factors) rotational velocity of the pocket plate, angular acceleration of the pocket plate, strut geometry, spring coefficient, fluid interactions and pocket wall draft angle.

As previously mentioned (and as shown in <FIG>), the draft angle of the outer pocket wall can also significantly affect the strut laydown speed. Angles above zero degrees tend to increase the laydown speed, while negative angles can be used to decrease the laydown speed. However, this presents the trade-off of manufacturing complexity, higher draft angles generally represent lower manufacturing costs as they can increase the life of the press used to produce the pocket plate. Whereas zero or negative draft angles are more difficult to produce, and usually require a secondary machining operation.

<CIT> (also assigned to the assignee of the present application) provides a dynamic engagement analysis of a strut within its respective pocket wherein various forces acting upon the strut are illustrated and described as follows:.

As described in the above-noted application a "truly vertical" or "slightly negative" vertical wall improves the stability of a strut or rocker (i.e. collectively referred to as "locking members") which experiences rotational centrifugal forces during overrun. Also the "slightly negative" angle lower the rpm even further at which a strut "locks down" due to such centrifugal forces.

In other words, performance is improved when a pocket plate wall is machined vertical or slightly negative versus a cast, positively angled, surface which may have a draft such as <NUM>-<NUM> degrees or <NUM>-<NUM> degrees (i.e. the surface is angled "slightly positive").

<CIT> discloses a bi-directional overrunning pawl-type clutch. <CIT> discloses a planar overrunning coupling for transfer of torque. <CIT> discloses a selectable one-way clutch assembly for use in an automatic transmission. <CIT> and <CIT> disclose an overrunning coupling assembly. <CIT> discloses an overrunning coupling assembly. <CIT> discloses an overrunning radial coupling assembly or clutch.

Other related <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>;<CIT>; <CIT>; <CIT>; <CIT>; and the following <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>;, <CIT>; <CIT>, <CIT>; <CIT>; <CIT>; <CIT>; <CIT>;<CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>;<CIT> and<CIT>. <CIT> discloses a stator. <CIT> discloses an overrunning coupling assembly.

For purposes of this application, the term "coupling" should be interpreted to include clutches or brakes wherein one of the plates is drivably connected to a torque delivery element of a transmission and the other plate is drivably connected to another torque delivery element or is anchored and held stationary with respect to a transmission housing. The terms "coupling", "clutch" and "brake" may be used interchangeably.

A "moment of force" (often just moment) is the tendency of a force to twist or rotate an object. A moment is valued mathematically as the product of the force and a moment arm. The moment arm is the perpendicular distance from the point or axis of rotation to the line of action of the force. The moment may be thought of as a measure of the tendency of the force to cause rotation about an imaginary axis through a point.

In other words, a "moment of force" is the turning effect of a force about a given point or axis measured by the product of the force and the perpendicular distance of the point from the line of action of the force. Generally, clockwise moments are called "positive" and counterclockwise moments are called "negative" moments. If an object is balanced then the sum of the clockwise moments about a pivot is equal to the sum of the counterclockwise moments about the same pivot or axis.

An object of at least one embodiment of the present invention is to provide an improved coupling member and one-way clutch assembly wherein locking member or strut dynamics are improved with regards to strut laydown speed by angling the pocket(s) which receive and nominally retain the strut(s). The improvement in strut dynamics is achieved when the strut rotates with reference to the normal axis. This would normally be achieved by rotating the entire pocket, but could also be accomplished just by rotating the outer wall (and inner pocket ear). According to an aspect of the present invention, there is provided a coupling member according to Claim <NUM>.

The coupling member may be a pocket plate.

The coupling face may have an annular coupling face.

The coupling face may have a plurality of pockets. Each of the pockets may be sized and shaped to receive and nominally retain a corresponding locking strut.

Each pocket may have an inner recess for receiving a biasing spring wherein each pocket is a spring pocket.

The annular coupling face may be oriented to face axially along the rotational axis.

Each pocket axis may be angled with respect to the normal in a range of -<NUM> ° to <NUM>°.

While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the scope of the claims. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.

Besides the many previously described factors effecting the "laydown" or "lockdown" speed of a strut, the inventors of this application have discovered that "pocket rotation angle" (i.e. angle of the entire pocket (or the outer wall and inner pocket ear of the pocket) within the pocket plate) is another factor that affects laydown speed as shown in <FIG>. Counter-clockwise (i.e. outward) pocket rotation lowers laydown speed for a rotating pocket plate thereby allowing or compensating for relatively large draft angles which allows lower manufacturing costs. Clockwise (i.e. inward), pocket rotation raises laydown speed as also shown in <FIG>. The desired speed (i.e. RPM) at which struts laydown determines the clutches ability to engage. Therefore, if it is desired that the clutch engage at a relatively high speed (i.e. RPM), than inward pocket rotation would be used.

With the addition of a pocket rotation, the geometric composition of the strut and its pocket change, resulting in the generation of a new moment due to the centripetal force now acting on the strut. Centripetal force is the physical force causing the strut/lock wall dynamics as described herein. This new moment arises from the relative change of point of rotation about which the strut rises or descends.

Referring now to <FIG> and <FIG>, there is illustrated a coupling member, generally indicated at <NUM>, for an engageable coupling assembly. The coupling member or pocket plate <NUM> has a centerline <NUM> through a center of the coupling member <NUM>. The coupling member <NUM> includes a coupling face <NUM> having at least one pocket and, preferably, a plurality of pockets <NUM> labeled pocket # <NUM>-<NUM> in <FIG>. Each of the pockets <NUM> has a different draft angle and pocket axis angle, Φ, for illustrative purposes. However, it is to be understood that preferably the pockets <NUM> have the same draft angle and the same pocket axis angle. Each pocket <NUM> is sized and shaped to receive and nominally retain a locking member such as a locking strut <NUM> (i.e. <FIG>) that lays down in its pocket <NUM> during an overrunning condition of the assembly at a laydown angular velocity of the coupling member <NUM> about a rotational axis <NUM> of the assembly. Each pocket <NUM> has a pocket axis <NUM> (only shown for pocket #<NUM> in <FIG>) which is angled with respect to a normal <NUM> to the centerline <NUM> to improve locking member dynamics during the overrunning condition.

The pocket axis <NUM> of each pocket <NUM> is rotated outwardly or counter clockwise with respect to the normal as shown in <FIG>.

The locking member <NUM> is a locking strut.

The coupling face <NUM> is preferably an annular coupling face <NUM>. The coupling face <NUM> has the plurality of pockets <NUM> and each pocket <NUM> has a "T" shape.

Each pocket <NUM> has an inner recess <NUM> (<FIG>) for receiving a biasing spring (not shown) wherein each pocket <NUM> is a spring pocket.

The annular coupling face <NUM> is oriented to face axially along the rotational axis Splines <NUM> are provided on the inner diameter of the plate to transfer torque to or from the plate.

<FIG> and <FIG>, which fall outside the scope of the claims and are present to assist in the understanding of the invention, show a coupling member or pocket plate <NUM>' which is substantially identical to the pocket plate <NUM> of <FIG> and <FIG> and, consequently, like parts have the same reference number but a single prime designation. The pocket plate <NUM>' is substantially identical to the pocket plate <NUM> except the pockets <NUM>' have an inward rotation. Each pocket <NUM>' of pocket plate <NUM>' has the same draft angle and the same magnitude of rotation as the corresponding pocket <NUM> in pocket plate <NUM>. As previously mentioned, the pocket plate embodiment of <FIG> and <FIG> (i.e. inward pocket rotation) is used when it is desired that the resulting clutch engage at a relatively high RPM as shown in <FIG>.

Each pocket axis <NUM> is angled with respect to the normal <NUM> in a range of -<NUM>° to <NUM>° as shown in <FIG>.

A combination of the pocket plate <NUM> with a second coupling member of <FIG> and one or more locking struts <NUM> form a coupling or clutch assembly having the central axis <NUM>.

The annular notch plate <NUM> extends around the central axis <NUM> and includes notches <NUM> spaced from each other about the central axis <NUM>. The notches <NUM> are formed in a coupling face <NUM> of the notch plate <NUM>. The notches <NUM> are angled Φ which corresponds to at least one of the angles Φ of the pocket plate <NUM> or -Φ when used with the pocket plate <NUM>'.

The following equations relate to the previously described new moment on a strut due to centripetal force and other factors affecting laydown speed, wherein:.

In summary, the inventors discovered that the orientation of a locking member or strut with respect to the normal of the centerline of the pocket plate has an effect on the dynamic characteristics with regards to strut laydown speed. Counter clockwise rotation of the pocket axis tends to decrease the speed at which the strut lays down, whereas clockwise rotation tends to increase the laydown speed.

Counter clockwise rotation of the pocket(s) (i.e. with strut tip(s) towards outer diameter of the clutch) can reduce the sensitivity to oil requirements as well as aid in manufacturability by opening functional dimensional tolerances. Counter-clockwise rotation of the pocket(s) tends to decrease the strut laydown speed. This has a tendency to increase the resilience of the clutch to low oil conditions which might otherwise increase strut instability.

Conversely, clockwise rotation of the pocket(s) (i.e. with strut tip(s) towards the inner diameter of the clutch) tends to increase the strut laydown speed. This can be beneficial in clutch applications wherein the struts are required to be active at higher speeds, such as a dynamic application in which the clutch is required to be able to engage at high pocket plate and notch plate speeds.

Based on the discoveries of the inventors, instead of having the orientation of pocket primary or pocket axis normal to a center line passing through MD, the inventors made the strut's primary or pocket axis differ by an angle normal to that of the plate's center line.

The previously described "strut instabilities" and the damage it causes relates to improper dynamics of the strut. The strut dynamics are engineered such that at certain conditions (usually identified by a pocket plate RPM range as shown in <FIG> and <FIG>) the strut is no longer able to rise and remains in the pocket, compressing its biasing spring for the duration it is seated within the pocket. When these dynamics are altered the strut is allowed to leave the pocket during inappropriate circumstances, the result is strut instability which manifests as a distinct sound and vibration emanating from the component, and ultimately leads to failure.

As shown in <FIG>, rotation of the pockets significantly alters the strut dynamics of the clutches. Inward rotation of the pocket contributes to a moment that would tend to raise the strut from the pocket; conversely, an outward rotation tends to lower it, acting against the spring force.

The graphs of <FIG> shows that from the baseline laydown speed of <NUM> RPM, a - <NUM>° rotated pocket increases this speed to nearly <NUM> RPM, a <NUM>% increase. Conversely, the laydown speed can be reduced from the baseline laydown speed by nearly <NUM>% by adding a positive rotation angle as also shown in <FIG>. This rotation angle improves strut dynamics.

Claim 1:
A coupling member (<NUM>) for an engageable coupling assembly, the coupling member (<NUM>) having a centerline (<NUM>) through a center (<NUM>) of the coupling member (<NUM>), the coupling member (<NUM>) comprising:
a coupling face (<NUM>) having at least one pocket (<NUM>), each pocket (<NUM>) being sized and shaped to receive and nominally retain a locking strut (<NUM>) that lays down in its pocket (<NUM>) during an overrunning condition of the coupling assembly when an angular velocity of the coupling member (<NUM>) about a rotational axis of the coupling assembly is greater than a strut laydown speed, and characterised in that, each pocket (<NUM>) has an outer wall having a draft angle (Θ), the draft angle (Θ) being a positive draft angle (Θ) which increases the strut laydown speed, and each pocket (<NUM>) further has a pocket axis (<NUM>) angled outwardly with respect to a normal (<NUM>) to the centerline (<NUM>) which decreases the strut laydown speed thereby compensating for the increase in the strut laydown speed due to the positive draft angle (Θ).