Abstract:
The invention is a planar clutch having a plurality of pawls and a related plurality of notches numerically selected so that two more pawls are engaged at substantially the same time, thus sharing and balancing the eccentric forces of engagement between the drive plate and the driven plate. The pawls have a cross-sectional design, wherein each pawl has surfaces for receiving compressive loading forces and is thicker at a middle point between the surfaces for receiving compressing loading forces. A pivot ridge is located at the thickest area of the pawl.

Description:
TECHNICAL FIELD 
     This invention relates to clutches, and more particularly to a planar ratchet one way clutch apparatus. 
     BACKGROUND OF THE INVENTION 
     Overrunning or one way clutches are commonly known today and there are various types of such clutch assemblies in use. Overrunning clutch assemblies are designed to have many different structures, including ratchet-type clutches and traction/locking clutches, such as a roller ramp clutch or sprag clutch. Traction-type clutches are generally limited in their applicability if high torque delivery is a design requisite. Therefore, ratchet-type clutches are preferred in instances where increased torque capacity is needed for transmissions containing one way clutch assemblies. Such rachet-type clutch assemblies make use of pawls carried by a drive member, which are designed to engage with notches, commonly located in a driven member. The capacity to carry increasing torque amounts and eliminate the potential for clutch backlash variously depends upon the number of pawls engaged with notches at any given point in time and the overall dimensions of the driven and drive members. 
     A typical ratchet-type clutch assembly is shown in U.S. Pat. No. 5,853,073. The &#39;073 patent discloses a radial ratchet clutch assembly having an inner radial race juxtaposed with an outer radial race. The outer radial race includes a plurality of pockets having pawls positioned in the pockets for engagement with notches located in the inner radial race. The pawls are designed to have a center of mass such that when the clutch rotates, centrifugal force acts upon the center of mass and causes the pawls to move into an engaged position with the notches of the inner radial race. Other embodiments in the &#39;073 patent make use of spring members to tilt or force the pawls toward engagement with the notches. 
     Radial ratchet clutch assemblies such as that disclosed in the &#39;073 patent can be designed for heavy torque transfer and are commonly very reliable. However, when design applications call for a lightweight clutch assembly or clutch assembly of minimized axial dimensions that remains capable of high torque transfer, radial ratchet one way clutches such as that shown in the &#39;073 patent are commonly unsuitable. 
     One solution has led to the design of a planar ratchet assembly, such as that shown in U.S. Pat. No. 5,070,978. The &#39;978 patent discloses a planar ratchet one way clutch having a planar drive member and a planar driven member positioned in close proximity to the planar drive member. A series of pockets is incorporated in the driven face and a plurality of cooperating pawls are positioned in the drive face. When the drive member is rotated in a desired direction by a suitable source of power, only one of the plurality of pawls will engage with only one of the plurality of pockets to impart drive forces to the driven member. The pawls of the &#39;978 patent are designed to have a narrow cross-section so as to provide for easy movement from a position of non-engagement to a position of engagement with a low moment of inertia. The pawl members have torsion springs disposed in recesses centrally located in the pawl which act to outwardly displace the pawl for engagement with the pocket of the driven member. However, planar ratchet assemblies such as that disclosed in the &#39;978 patent have encountered problems when heavy torsional loading is applied, such as eccentric deformation of the drive and/or driven plates and a common failure due to the buckling of the pawls. 
     Another embodiment of a planar ratchet one way clutch assembly is shown in U.S. Pat. No. 5,597,057. The &#39;057 patent again discloses a one way clutch apparatus having a planar driving member with a plurality of recesses and biasing members with pawls of thin cross-section are disposed in the recesses. A driven member having a plurality of engaging notches is juxtaposed with the driving member. The pawls are spring loaded to press engagement of the pawls into the notches of the driven member. Again, problems similar to these discussed earlier with regard to the &#39;978 patent have been encountered with clutches of the type of the &#39;057 patent when heavy torsional loading is applied. 
     Such planar clutches have small pawls, commonly of a generalized rectangular shape that are long and thin and are commonly designed so that only one pawl is engaged at a time. The use of such long thin pawls allows for the placement of an increased number of pawls and notches in the clutch, thereby reducing the potential for backlash in the clutch. However, because only one pawl is commonly available to carry the entire load, the torque capacity of the prior art planar clutches does not meet desired levels. Loading on a single thin pawl will cause high eccentric loads on the drive plate and driven plate that wear down the clutch. Further, the thinness of the pawl will increase the potential for the pawl to buckle under high static loads. 
     Thus, it is an object of the invention to provide for a one way planar ratchet clutch capable of carrying and transmitting heavy torque loads. 
     Yet another objective of the present invention is to provide for a planar ratchet one way clutch, wherein the components are minimized in size without impairing the ability of the clutch to transmit heavy torque loads without incurring eccentric deformation and failure or buckling of the pawls. 
     Yet another object of the present invention is to provide a planar ratchet one way clutch, wherein at least one of the planar juxtaposed driven members has a flat backing surface capable of utilization as a backing plate for a friction plate of the clutch. 
     Yet another objective of the present invention is to provide for compact pawls having a cross-section, wherein high torque loading on the pawls will not cause the pawl to buckle. 
     SUMMARY OF THE INVENTION 
     The present invention solves these problems and meets the objectives of the invention by providing a planar ratchet clutch assembly having a plurality of pawls and a related plurality of notches numerically selected so that two or more pawls are engaged at substantially the same time. Thus, two or more notches will be engaged by the pawls and share the static load, thereby balancing the eccentric forces of engagement. The pawls of the present invention have a unique shape into which is designed a pivot ridge which serves a dual purpose. The pivot ridge is used to control the pawl motion during transfer from a free wheeling mode to engaged mode. Further, the pawl is designed to be thickest at the pivot ridge, thereby providing for better load carrying capacity and thereby reducing the potential for failure of the pawl during high static loading. The shape of the pawls are further designed such that the compressive surfaces of each pawl that is engaged with a notch are angled from the perpendicular to the line of action of the load on the pawl to provide for positive engagement between each pawl and its respective notch. Thus, if a situation occurs where the pawl is not completely engaged with its respective notch, the compressive load bearing on the pawl will force it rapidly into full engagement with the notch. In one embodiment of the invention, a reduction in the failure rate of the pawl due to buckling can be achieved by maintaining the perpendicular orientation of the compressive load bearing surfaces of the pawl to the line of action of the load. 
     The pawls incorporated in the present invention are unique in planar ratchet assemblies in that they are shaped to provide a ridge about which the pawls pivot. Prior art planar ratchet assemblies most commonly use an axle as the pivot axis which is attached to the pawl. Thus, an unnecessary structural feature is eliminated in the complex structures of the planar ratchet patents. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the planar clutch assembly of the present invention with a cutaway to show a pawl, spring and notch assembly. 
     FIG. 2 is a detail view of FIG. 1 showing a close up view of the engagement between the pocket plate and notch plate with the pawl in an engaged position between the pocket plate and the notch plate. 
     FIG. 3 is a detail view of the cutaway of FIG. 1 of a pocket plate and a notch plate showing the pawl in a disengaged position with the notch plate. 
     FIG. 4 is a side cutaway detail view of a pocket plate and a notch plate showing the pawl in a disengaged position with the notch plate. 
     FIG. 5 is a side cutaway detail view of a pocket plate and a notch plate showing the pawl in an engaged position with the notch plate. 
     FIG. 6 is a detail view of the notch plate of the present invention. 
     FIG. 7 is a detail view of the pocket plate of the present invention. 
     FIG. 8 is a perspective view of a pawl as used in the present invention. 
     FIG. 9 is a perspective view of a preferred embodiment of a spring as used with the pawl in the present invention. 
     FIG. 10 is a schematic cutaway view of a friction clutch having the pocket plate in use as a backing plate. 
     FIG. 11 is a schematic cutaway view of a friction clutch having the pocket plate and the retaining plate each in use as a backing plate. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a perspective view of the planar ratchet clutch assembly of the present invention which is generally indicated by the reference numeral  10 . This clutch assembly is designed to be in engagement with an input shaft having a longitudinal axis which is adapted to be connected to a source of power (not shown) for rotating the shaft about its longitudinal axis. The power input shaft commonly includes a series of circumferentially spaced splines which are engaged with the inner radial splines  12  of a driven plate or notch plate  14 . The input shaft through its engagement with the splines  12  of the notch plate  14  will serve as the drive member for the clutch assembly  10  by providing clockwise and counterclockwise rotation to the driven plate or notch plate  14 . The drive plate or pocket plate  16  forms a shell-like structure which radially encloses the notch plate  14  and creates a close tolerance interface between the outer diameter  18  of the notch plate  14  and the adjacent inner diameter  20  of the pocket plate  16 . Thus, the close tolerance between the outer diameter  18  and the inner diameter  20  serves to radially support and center the pocket plate  16 . A retainer plate  17  is fixed to the notch plate  14  to axially enclose the pocket plate  16  by known means such as welding, riveting, or a screw-on type structure. 
     The pocket plate  16  has an inner drive face  22  which incorporates a series of uniformly circumferentially spaced pockets  24 , as best shown in FIGS. 4,  5  and  7 . In the preferred embodiment, the pockets  24  are spaced at 90° intervals to provide for a plurality of four pockets  24  equidistantly spaced within the drive face  22 . Each pocket is designed to contain a pawl  26  and spring  28 , as best shown in FIGS. 1-5. 
     The driven face  30  of the notch plate  14  includes a series of uniformly circumferentially spaced notches  32 , greater in number than the number of pockets  24 , which extend radially and are equally spaced about the driven face  30 . Preferably, there are eighteen notches  32  on the driven face  30  of the notch plate  14 . Thus, when the pocket plate  16  and notch plate  14  are in their respective engaged positions, two of the pockets  24  containing their respective pawls  26  and two of the notches  32  will comprise the coupling arrangement of the clutch assembly  10 . 
     Since the preferred embodiment of the pocket plate  16  has four pawls  26  and the preferred embodiment of the notch plate  14  has eighteen notches  32 , there will always be an engagement of two pawls  26  with notches  32  during the engaged rotation of the pocket plate  16  with the notch plate  14 . Of course, the number of pawls  26  and number of notches  32  can be varied depending upon the design required for varying torque loads and static forces so that a differing number of pawls  26  can be engaged with notches  32  at any given time. The number of pawls and notches is selected such that the two numbers have only one common factor, other than one. For instance, if the designer wished for all four pawls  26  to be engaged with notches  32 , the designer could design the notch plate  14  to have eight, twelve, sixteen or twenty notches. It has been found that the more notches  32  provided, the less opportunity for backlash in the clutch assembly  10 . Therefore, a number of notches  32  close to twenty is preferable. In the preferred embodiment of the present invention, it is intended that two pawls  26  be engaged with the notches at any given time and the preferred number of notches  32  for the notch plate  14  is eighteen and the preferred number of pawls  26  is four. This design permits the clutch assembly to be somewhat lightweight, compact, and yet sustain heavy torque loads and provide for the elimination of the eccentric forces which create deleterious wearing on the clutch assembly. 
     Referring to FIGS. 2 and 5, engagement between the pawls  26  and notches  32  is provided when the pocket plate  16  is rotated clockwise, thus causing the notch plate  14  to also rotate with the pocket plate  16 . Adversely, when the pocket plate  16  is rotated counterclockwise, all of the pawls  26  functionally remain in their respective pockets  24  and do note engage the notches  32  as shown in FIGS. 3 and 4. As a result, the pocket plate  16  rotates freely in the counterclockwise direction and the notch plate  14  is not engaged. 
     Referring now to FIGS. 4,  5  and  8 , each of the pawls  26  is designed for use in the preferred embodiment of the invention, to have opposed compressive load bearing surfaces  34 ,  36  which are substantially parallel to each other. The cross-section of the pawl  26  is thicker in the region  38  midway between the two compressive load bearing surfaces  34 ,  36 , which provides a greater resistance to failure as a result of high compressive load bearing forces. The pawl  26  has a peak or ridge  40  at its thickest region  38  which serves as a pivot for rotation of the pawl  26  in the pocket  24 , as shown in FIGS. 4 and 5. Each pawl  26  has an axial width greater than the circumferential length and the circumferential length of the pawl  26  is greater than the radial thickness of the pawl  26  at region  38 . The pocket  24  is designed to provide a compressive load bearing surface  42  which is angled from the perpendicular to the line of action of the load. The compressive load bearing surface  44  of the notch  32  is angled from the perpendicular to the line of action of the load to provide for positive engagement between each pawl  26  and its respective notch  32 , as shown in FIG.  5 . Thus, if a situation occurs where the pawl is not completely engaged with its respective notch, the compressive bearing load on the pawl  26  will force it rapidly into full engagement with the notch  32 . The load bearing surfaces  34 ,  36  of the pawl  26  are designed to engage the load bearing surfaces  42 ,  44  respectively and provide for a compressive load bearing line of action as shown in FIG. 5 which extends angularly the length of the pawl  26  between load bearing surface  42  of the pocket  24  and load bearing surface  44  of the notch  32 . Further, the pocket  24  is shaped to provide an indentation  46  which retains the spring member  48 , preferably a Z-shaped spring as shown in FIG.  9 . However, springs and resilient members of any variety may be used in accordance with design specifications. 
     Preferably, the pawl  26  is of a generally cylindrical cross-sectional shape as shown in FIG. 8, having flat ends and the same cross-sectional cylindrical shape throughout its axial width. Thus, the pawl  26  can be easily manufactured by either an extrusion or, preferably a drawing process. The thicker cross-section of the pawl  26  further allows for manufacture of the pawl from a lower grade less expensive material. The pawls are preferably constructed from 52100 bearing steel and the notch plate  14  and pocket plate  16  are constructed from a low alloy bearing stock, powdered metal (steel) or aluminum. 
     Referring now to FIG. 10, an alternative embodiment of a friction clutch incorporating the present invention are shown. The friction clutch includes a drum or casing  50  which encloses the friction clutch components and a hub  52  which is engaged by splines  12  to the driven plate or notch plate  14 . The drum or casing  50  is engaged with the drive plate or pocket plate  16  by splines  13  which are located on the outer radial surface of the pocket plate  16 . The notch plate  14  is held in proper radial orientation by its interface with the pocket plate  16  as described earlier herein and is held in proper axial orientation by retaining plate  17 . The retaining plate  17  serves to counter any axial thrust that occurs when the clutch is engaged. Snap ring  19  seals the pocket plate  16  in a fixed axial position. The friction clutch is composed of series of interleaved friction plates  56  engaged with the hub  52  and separation plates  54  engaged with the drum  50 . The friction plates  56  carry friction material  58  for engagement with the separation plates  54 . The friction clutch can be engaged by applying a force as indicated by the arrow in FIG.  10 . The force is reacted by the drive plate or pocket plate  16 . Use of the drive plate  16  in this manner eliminates the need for an additional backing plate in the clutch, thereby allowing the clutch to more easily meet the objectives of compactness and being lightweight. 
     Another alternative embodiment of a friction clutch incorporating the present invention is shown in FIG. 11, which provides for two friction clutches which are independently engageable by the forces indicated by the opposed arrows. The friction clutch includes a drum or casing  50  that encloses the friction clutch components and two independently rotating hubs  52 A,  52 B, one of which,  52 B engaged by splines  12  to driven plate or notch plate  14 . The drum or casing  50  is engaged with the drive plate or pocket plate  16  by splines  13  which are located on the outer radial surface of the pocket plates  16 . The notch plate  14  is held in proper radial orientation by its interface with the pocket plate  16  as described earlier herein and is held in proper axial orientation by retaining plate  17 . The retaining plate  17  serves to counter any axial thrust that occurs when the clutch is engaged. Snap rings  19 A,  19 B locate the pocket plate  16  and notch plate  14  in a fixed axial position. The two independent friction clutches are each composed of a series of interleaved friction plates  56 A,  56 B engaged respectively with the hubs  52 A,  52 B and separation plates  54  engaged with the drum  50 . The friction plates  56 A,  56 B carry friction material  58 A,  58 B for engagement with the separation plates  54 . The friction clutches can be independently engaged by application of the forces shown by arrows in FIG.  11 . The force of the first friction clutch (B) is reacted by the drive plate or pocket plate  16 . The force of the second clutch (A) is reacted by the retaining plate  17 . Use of the drive plate  16  and retaining plate  17  in this manner eliminates the need for additional backing plates in the clutch, thereby allowing the clutch to more easily meet the objection of being compact and relatively lightweight. 
     In operation, as shown in FIGS. 4 and 5, when the pawl  26  is not in alignment with the notch  32 , the spring  48  is compressed and the pawl is retained within the pocket  24  so that the pocket plate  16  and notch plate  14  rotate counter to each other without engagement. In FIG. 5, the pawl  26  has aligned with the notch  32  and the spring  28  has pressed the pawl  26  about its pivot  40 , such that the load bearing surfaces  34 ,  36  of the pawl  26  engage the load bearing surface  42 ,  44  of the pocket plate and notch plate  14  respectively, thereby providing for engagement between the two plates and successful torque carrying capacity. 
     The above description of the preferred embodiment of the present invention is intended to be illustrious in nature and not intended to be limiting upon the scope of the following claims.