Abstract:
A disk spring assembly including a flat disk between two angled plates is used in an automatic transmission clutch application. The inner peripheral edge and the outer peripheral edge of the disk are deflected in opposite directions relative to each other by the angled plates. The maximum deflection of the disk is defined by the angled plates. The stiffness of the disk increases monotonically with the deflection of the disk resulting in smooth clutch application.

Description:
TECHNICAL FIELD 
     This invention relates to clutch applications for automatic transmissions. 
     BACKGROUND OF THE INVENTION 
     Ideally, clutches used in automatic transmissions should engage smoothly. Range clutches typically employ a filter spring to lessen the initial impact of the clutch engaging, resulting in a smoother ride. The spring is positioned between the force acting to engage the clutch and the clutch itself to lessen the impact of the force. Ideally, an impact filter spring should have a small stiffness at small deflections and a monotonically increasing stiffness during deflection (i.e., a stiffness that increases at a constant rate over the deflection range) until a fully loaded condition is reached. 
     Two kinds of washer springs are typically used in automatic transmissions: wave washer springs and Belleville washer springs. Wave washer springs have a waved surface configuration that affects the stiffness of the spring. Belleville washer springs have a cone-shaped portion that is flattened during deflection of the spring. The wave washer has a stiffness that is a constant between 20 percent and 80 percent of its deflection range. The Belleville washer has a stiffness that decreases monotonically with respect to deflection. Accordingly, neither of these types of springs have the desired characteristic of monotonically increasing stiffness over the deflection range of the spring. 
     SUMMARY OF THE INVENTION 
     A disk spring assembly for smooth clutch application may include a substantially flat ring-shaped disk having opposed faces and a hole formed in the center of the disk such that the disk has an inner peripheral edge and an outer peripheral edge. The disk may have an inner radius at its inner peripheral edge and an outer radius at its outer peripheral edge. Furthermore, the disk may have a substantially uniform thickness between its opposed faces. The disk may be steel. The assembly may also have a movable first angled plate located adjacent to one opposed face. The assembly may further include a second angled plate located adjacent to the other opposed face such that the inner and outer peripheral edges of the disk are deflected in opposite directions relative to each other when the disk moves toward the second plate during engagement of the clutch. The maximum deflection of the disk may be defined by the angled plates. 
     The first and second angled plates may each have an angled face. The angled face of the first plate may be located adjacent to a face of the disk such that an angle is formed by the first plate and the disk at the inner peripheral edge. The angled face of the second plate may be located adjacent to the opposed face of the disk such that a substantially equivalent angle is formed by the second plate and the disk at the outer peripheral edge. The first plate may be configured such that it first contacts and applies load at the inner peripheral edge of the disk when it moves toward the disk. Furthermore, the second plate may be configured such that it first contacts and applies a reaction load at the outer peripheral edge of the disk when the disk moves toward the second plate by the first plate. The angled face of each plate may have a substantially equivalent inner and outer radius. 
     The opposed faces of the disk may be in substantially complete contact with respective angled faces of the plates when the clutch is engaged. Additionally, the maximum deflection of the disk may occur when the opposed faces of the disk are in substantially complete contact with the respective angled faces of the plates. The load applied by the first plate may be uniformly distributed across the substantially completely contacted faces of the disk and the plates. 
     The stiffness of the disk may increase in proportion to the square of the deflection of the disk. Thus, the stiffness of the disk may increase monotonically with the deflection of the disk. The deflection characteristics of initially flat washer springs are discussed in Almen, J. O. and Laszlo, A., “The Uniform-Section Disk Spring,” Trans. ASME, Vol. 58, no. 4, May 1936, pp. 305-314. The stiffness of the disk may be the ratio of the change in force applied to the disk to the change in deflection of the disk. The stiffness of the disk is represented by S and may be determined in accordance with the following formula:          S   =         K   1     +     3        K   2          d   2                   wherein                   K   1         =     Nt   3         ,       K   2     =     N        t   2         ,     N   =     E       (     1   -     υ   2       )          Ma   2           ,     
            1   M     =       (         α   +   1       α   -   1       -     2     ln                 α         )            π        (     α     α   -   1       )       2         ,       and                 α     =     a   b       ,                          
     wherein a represents the outer radius of the disk, b represents the inner radius of the disk, E is Young&#39;s modulus, t represents the thickness of the disk, and υ is Poisson&#39;s ratio. See Almen and Laszlo, supra, pp. 309-312, regarding the derivation of this formula. 
     A spring assembly for enhancing clutch smoothness may include a substantially flat washer having opposing faces, a first ring-shaped plate with an angled face forming an outwardly conical shape located adjacent to one washer face and a second ring shaped plate with an angled face forming an inwardly conical shape located adjacent to the other washer face, wherein the angled faces are cooperatively configured to contact the respective adjacent faces of the washer when the first plate moves in the direction of the washer during engagement of the clutch. 
     The above features and advantages, and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration in side cross-sectional view of an automatic transmission clutch including a disk spring assembly; 
     FIG. 2 a  is a schematic illustration in plan view of a disk for use in the disk spring assembly of FIG. 1; 
     FIG. 2 b  is a schematic illustration in side cross-sectional view of the disk of FIG. 2 a;    
     FIG. 3 a  is a schematic illustration in plan view of an angled plate for use in the disk spring assembly of FIG. 1; 
     FIG. 3 b  is a schematic illustration in side cross-sectional view of the angled plate of FIG. 3 a;    
     FIG. 4 a  is a schematic illustration in plan view of another angled plate for use in the disk spring assembly of FIG. 1; 
     FIG. 4 b  is a schematic illustration in side cross-sectional view of the angled plate of FIG. 4 a;    
     FIG. 5 is a schematic sectional perspective illustration in an exploded view of the disk spring assembly of FIG. 1; 
     FIG. 6 a  is a schematic cross-sectional illustration of the disk spring assembly of FIG. 1; 
     FIG. 6 b  is a schematic cross-sectional illustration of the disk spring assembly of FIG. 1 showing contact of the angled plate of FIG. 3 a  and the angled plate of FIG. 4 a  with the disk of FIG. 1; 
     FIG. 7 is a schematic cross-sectional illustration of load forces acting upon the disk of the disk spring assembly of FIG. 6 b;    
     FIG. 8 a  is a schematic illustration in partial vertical cross-sectional view of a first alternative embodiment of a disk spring assembly; 
     FIG. 8 b  is a schematic illustration in partial vertical cross-sectional view of a second alternative embodiment of a disk spring assembly; 
     FIG. 8 c  is a schematic illustration in partial vertical cross-sectional view of a third alternative embodiment of a disk spring assembly; 
     FIG. 8 d  is a schematic illustration in partial vertical cross-sectional view of a fourth alternative embodiment of a disk spring assembly; 
     FIG. 9 is a graph of the theoretical relationship between load F and deflection d of a disk in the disk spring assembly of FIG. 1; and 
     FIG. 10 is a graph of analytical and experimental data related to load in Newtons (N) applied to the disk in the disk spring assembly of FIG. 1 versus the deflection of the disk in millimeters (mm). 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a disk spring assembly  11  used in a clutch application. The disk spring assembly includes a ring-shaped disk  13 , a first angled plate  15 , and a second angled plate  17 . The ring-shaped disk  13  is also referred to as a washer. The first angled plate  15  is also referred to as a first ring-shaped plate. The second angled plate  17  is also referred to as a second ring-shaped plate. The first angled plate  15  is moveable towards the ring-shaped disk  13  by a piston  19 . Fluid force acts upon the piston  19  to move it towards the first angled plate  15  for engaging a clutch  16 . The disk spring assembly  11  shown is in an “at rest” state and the clutch is not engaged. 
     Referring to FIG. 2 a,  wherein like reference numbers refer to like components in FIG. 1, the ring-shaped disk  13  having a face  21  is shown. The ring-shaped disk  13  also has an opposed face  23  shown in profile in FIG. 2 b  wherein like reference numbers refer to like components in FIGS. 1-2 a.  FIG. 2 b  is a cross sectional view of the disk taken at the arrows shown in FIG. 2 a.  The disk  13  has an inner peripheral edge  25  and an outer peripheral edge  27 . A hole  29  is formed in the center of the disk  13 . The disk  13  has an inner radius b measured from the center to the inner peripheral edge  25 , and an outer radius a, measured from the center to the outer peripheral edge  27 . Referring again to FIG. 2 a,  the disk  13  has extensions or fingers  31  along the outer peripheral edge  27 . The fingers  31  are for guidance in positioning the washer during assembly. The disk  13  may have fewer or more fingers  31  than shown; additionally, a continuous flange around the outer peripheral edge  27  of the disk  13  may be used in place of fingers  31 . The fingers  31  are not included within the outer radius a. The disk  13  has a thickness t. The disk  13  is substantially flat, as can be seen in FIG. 2 b.  The disk  13  is preferably made of steel. 
     Referring to FIG. 3 a,  wherein like reference numbers refer to like components in FIGS. 1-2 b,  the second angled plate  17  is shown having a surface  33  that is away from the washer  13  when assembled as in FIG.  1 . The second angled plate  17  has an inner peripheral edge  35  and an outer peripheral edge  37 . The inner and outer peripheral edges  35 ,  37  are at the same inner and outer radii b, a as the inner peripheral edge  25  and the outer peripheral edge  27  of the disk  13  in FIG. 2 a.    
     Referring to FIG. 3 b,  wherein like reference numbers refer to like components in FIGS. 1-3 a,  a cross-sectional view of the second angled plate taken at the arrows shown in FIG. 3 a  is shown. The second angled plate  17  is tapered from its inner peripheral edge  35  to its outer peripheral edge  37  such that it is thicker at its outer peripheral edge  37  than at its inner peripheral edge  35 . The distance along an axis through the center of the second angled plate  17  from the beginning of the taper to the end of the taper is shown as d max . Referring again to FIG. 3 a,  the second angled plate  17  has fingers  39  used for guidance during assembly. The second angled plate  17  may have fewer or more fingers  39  than shown; additionally, a continuous flange around the circumference of the second angled plate  17  may be used in place of the fingers  39 . The fingers  39  are not part of the taper of the second angled plate  17 . 
     Referring to FIG. 4 a,  wherein like reference numbers refer to like components in FIGS. 1-3 b,  a face  41  of the first angled plate  15  having an inner peripheral edge  43  and an outer peripheral edge  45  is shown. Referring to FIG. 4 b,  wherein like reference numbers refer to like components in FIGS. 1-4 a,  a cross-sectional view of the first angled plate  15  taken at the arrows shown in FIG. 4 a  is shown. The first angled plate  15  has substantially the same inner and outer radii b, a as the disk  13 . Referring again to FIG. 4 a,  the first angled plate  15  has fingers  47  at its outer peripheral edge  45  for guidance during assembly. The first angled plate  15  may have fewer or more fingers  47  than shown; additionally, a continuous flange around the circumference of the first angled plate  15  may be used in place of the fingers  47 . The first angled plate  15  is tapered such that the inner peripheral edge  43  is thicker than the outer peripheral edge  45 . Thus the face  41  is angled. The difference in thickness between the inner peripheral edge  43  and the outer peripheral edge  45  is d max . The fingers  47  are part of the taper of the first angled plate  15 . 
     Referring to FIG. 5, wherein like reference numbers refer to like components in FIGS. 1-4 b,  an exploded view of the second angled plate  17  with the substantially flat ring-shaped disk  13  and the first angled plate  15  in assembled positions (as shown in FIG. 1) relative to one another is shown. The second angled plate  17  has an angled face  49  located adjacent to the face  21  of the ring-shaped disk  13 . The second angled plate  17  is shown rotated slightly upward in order to expose the angled face  49 . The angled face  49  is angled due to the taper of the second angled plate  17  between its inner peripheral edge  35  and its outer peripheral edge  37 . The angled face  49  has an inwardly conical shape defined by the difference in thickness, d max , shown in FIG. 3 b,  of the inner peripheral edge  35  and the outer peripheral edge  37  of the second angled plate  17 . 
     The moveable first angled plate  15  has angled face  41  which has an outwardly conical shape defined by the difference in thickness d max , shown in FIG. 4 b,  between the inner peripheral edge  43  and the outer peripheral edge  45  of the first angled plate  15 . The angled face  41  of the first angled plate  15  is adjacent to an opposed face  23  of the flat ring-shaped disk  13 . 
     Referring to FIG. 6 a,  wherein like reference numbers refer to like components in FIGS. 1-5, a cross-sectional view of the disk spring assembly  11  in an “at rest” position without deflection of the disk  13  is shown. An angle theta θ is formed at the outer peripheral edge  27  of the disk  13  between the second angled plate  17  and the disk  13 . A substantially equivalent angle θ′ is formed at the inner peripheral edge  25  of the disk  13  between the first angled plate  15  and the disk  13 . An imaginary line drawn opposite θ between the inner peripheral edge  35  of the angled face  49  of the second angled plate  17  and the inner peripheral edge  25  of the face  21  of the disk  13  has a length d max . An imaginary line drawn opposite the angle θ′ between the outer peripheral edge  27  at the opposed face  23  of the disk  13  and the outer peripheral edge  45  of the angled face  41  of the first angled plate  15  also has a length d max . 
     Referring to FIG. 6 b,  wherein like reference numbers refer to like components in FIGS. 1-5, FIG. 6 b  is a cross-sectional view of the second angled plate  17 , the disk  13 , and the first angled plate  15 , when the angled face of the second angled plate  17  and the angled face of the first angled plate  15  are in substantially complete contact with the respective faces  21 ,  23  of the disk  13 . Substantially complete contact occurs when the clutch  16  of FIG. 1 is in an engaged state with the first angled plate  15  moves towards the second angled plate  17 . The maximum deflection of the disk  13  is defined by the angled faces  41 ,  49  of the plates  15 ,  17 . The maximum deflection of the disk  13  occurs when the opposed faces  21 ,  23  of the disk  13  are in substantially complete contact with the respective angled faces  49 ,  41  of the plates  15 ,  17 . Thus, the maximum deflection of the disk is d max . The disk is deflected at the angles θ, θ′ shown in FIG. 6 a,  when it is deflected to d max , as shown in FIG. 6 b.  Accordingly, an advantage of the disk spring assembly is that the maximum deflection of the disk and the maximum angle of deflection are controlled by the design of the assembly. When the angled faces  41 ,  49  of the plates  15 ,  17  and the faces  23 ,  21 , respectively, of the disk  13  are in substantially complete contact, load applied by the first angled plate  15  is uniformly distributed across these contacted faces. 
     Referring to FIG. 7, wherein like reference numbers refer to like components in FIGS. 1-6 b,  the deflection of the disk  13  when load is applied at the inner peripheral edge  25  and the outer peripheral edge  27  is depicted. The load is applied in the direction of an axis through the center of the flat disk  13 . The disk  13  is shown in a first undeflected position  51 . The disk  13  is also shown in a second deflected position  53 . The angled plates  15 ,  17  are not shown in FIG.  7 . The arrows shown at the inner peripheral edge  25  of the disk  13  in the first position  51  represent the load applied to the disk  13  by the first angled plate  15 . The triangular shapes shown at the outer peripheral edge  27  of the disk  13  represent the reaction load applied by the second angled plate  17  when load is applied to the disk  13  by the first angled plate  15 . 
     The invention contemplates a disk spring assembly design in which load may be applied by the second angled plate  17  at the outer peripheral edge  27  of the disk  13  and an equal reaction load would be applied at the inner peripheral edge by the  25  of the disk  13  by the first angled plate  15  as the deflection of the disk  13  would be the same. 
     “Angled plates,” as used herein, means any pair of plates having initial contact points (i.e., the points where the plates first contact the disk) that are axially displaced relative to one another such that the initial contact point of one of the plates is at the inner peripheral edge of the disk and the initial contact point of the other plate is at the outer peripheral edge of the disk. Any such pair of plates may be considered a first angled plate and a second angled plate within the scope of this invention. For instance, in the spring assembly shown in FIGS. 5-6 b,  the first angled plate  15  has an initial contact point at which it first contacts and applies force to the disk  13  at the inner peripheral edge  25  of the disk  13 . The second angled plate  17  has an initial contact point at which it first contacts and applies force to the disk  13  at the outer peripheral edge  27  of the disk  13 . 
     In FIGS. 8 a - 8   d,  wherein like reference numbers refer to like components in FIGS. 1-7, some alternative designs for angled plates within the scope of the invention are depicted. Referring to FIG. 8 a,  a first angled plate  15 A is tapered such that its outer peripheral edge  45 A is thicker than its inner peripheral edge  43 A and the initial contact point at which it first contacts and applies force to the disk  13  is the outer peripheral edge  27  of the disk  13 . A second angled plate  17 A is tapered such that its inner peripheral edge  35 A is thicker than its outer peripheral edge  37 A and the initial contact point at which it first contacts and applies force to the disk  13  is the inner peripheral edge  25  of the disk  13 . The plates  15 A,  17 A would cause the same maximum deflection d max  and would define the same angles θ, θ′ as the plates  15 ,  17  in FIG.  1  and FIGS. 3 a - 6   b.    
     Referring to FIG. 8 b,  a first angled plate  15 B is shown that has an angled arm  59  with an angled edge  60  that initially contacts the disk  13  at the outer peripheral edge  27  of the disk  13 . A second angled plate  17 B is shown that has an angled arm  61  with an angled edge  62  that initially contacts the disk  13  at the inner peripheral edge  25  of the disk  13 . Equivalent angles θ, θ′ that are substantially the same as those defined by the plates  15 ,  17  are formed between the disk  13  and lines shown extending from the angled edges  60 ,  62  of the angled arms  59 ,  61  on the respective plates  15 B,  17 B. The plates  15 B,  17 B would cause the same maximum deflection d max  as the plates  15 ,  17  in FIG.  1  and FIGS. 3 a - 6   b.    
     Referring to FIG. 8 c,  a first angled plate  15 C is tapered such that the outer peripheral edge  45 C is thicker than the inner peripheral edge  43 C. The first angled plate  15 C initially contacts the disk  13  at the outer peripheral edge  27  of the disk  13 . A second angled plate  17 C is shown that has an angled arm  63  with an angled edge  64  that initially contacts the disk  13  at the inner peripheral edge  25  of the disk  13 . Equivalent angles θ, θ′ that are substantially the same as those defined by the plates  15 ,  17  are formed between the disk  13  and a line shown extending from the angled edge  64  of the angled arm  63  on the plate  17 C and between the disk  13  and the first angled plate  15 C, respectively. The plates  15 C,  17 C would cause the same maximum deflection d max  as the plates  15 ,  17  in FIGS. 1,  3   a - 6   b.    
     Referring to FIG. 8 d,  a first angled plate  15 D is shown that has an angled arm  65  with an angled edge  66  that initially contacts the disk  13  at the outer peripheral edge  27  of the disk  13 . A second angled plate  17 D is tapered such that its inner peripheral edge  35 D is thicker than its outer peripheral edge  37 D. The plate  17 D initially contacts the disk  13  at the inner peripheral edge  25  of the disk  13 . Equivalent angles θ, θ′ that are substantially the same as those defined by the plates  15 ,  17  are formed between the disk  13  and the second angled plate  17 D and between the disk  13  and a line shown extending from the angled edge  66  of the angled arm  65  of the first angled plate  15 D, respectively. The plates  15 D,  17 D would cause the same maximum deflection d max  as the plates  15 ,  17  in FIGS. 1,  3   a - 6   b.    
     The invention contemplates that, in each of FIGS. 5-6 b  and  8   a - 8   d,  the first angled plate may be a piston that moves toward the disk  13  by an hydraulic force and applies a force to the disk  13  at either the inner peripheral edge  25  of the disk  13  or the outer peripheral edge  27  of the disk  13 , depending upon which edge the first angled plate first contacts, as depicted in the above referenced Figures. In FIG. 1, the invention contemplates that the piston  19  and the first angled plate  15  may be integral. 
     FIG. 9 is a graph representing the theoretical relationship between load F applied to the disk  13  and deflection d of the disk. The theoretical relationship is:          F   =           K   1        d     +       K   2          d   3                   wherein                   K   1         =     Nt   3         ,       K   2     =     N        t   2         ,     
          N   =     E       (     1   -     υ   2       )          Ma   2           ,       1   M     =       (         α   +   1       α   -   1       -     2     ln                 α         )            π        (     α     α   -   1       )       2         ,       and                 α     =       a   b     .                              
     In the above equations, the outer radius of the disk  13  is a, the inner radius of the disk  13  is b and the thickness of the disk is t. E is the modulus of elasticity, known as Young&#39;s Modulus, which is 206,900 N/mm 2  for steel. E is the ratio between stress and strain in a metal during elastic deformation. Poisson&#39;s ratio, or υ, is the negative ratio between lateral strain and direct tensile strain when load is applied to a metal. For steel, υ=0.3. 
     The stiffness of a flat washer like the disk  13  is the ratio of the change in force, F, applied to the disk to the change in deflection, d, of the disk in the direction of application of the force, F. The stiffness, S, can be derived from the above equation relating load, F, to deflection, d, as:        S   =         δ                 F       δ                 d       =       K   1     +     3        K   2          d   2                                  
     wherein K 1  and K 2  are as described above. Thus, the stiffness of the washer  13  increases in proportion to the square of the deflection d. This monotonically increasing stiffness with deflection is ideal for automotive clutch applications as the clutch will be engaged smoothly, rather than abruptly, as force applied to the disk is met with increasing resistance (stiffness) during deflection of the spring. 
     Referring to FIG. 10, wherein like reference numbers refer to like components in FIGS. 1-9, a plot of analytical data (represented by a solid line) and experimental data (represented by a dashed line with data points) showing the relationship between the load F applied to the disk and the deflection d of the disk. The load F is measured in Newtons (N) and the deflection d is measured in millimeters (mm). As shown in FIG. 10, a good correlation is achieved between the experimental data and the theoretical relationship between load F and deflection d over the deflection range 0-2.2 mm. The experimental data was achieved using a steel disk having an outer radius a of 65.5 mm, an inner radius b of 42.5 mm and a thickness t of 1 mm. In a preferred embodiment, the maximum deflection d max  of the disk  13  would be about 2.2 mm. 
     As set forth in the claims, various features shown and described in accordance with the different embodiments of the invention illustrated may be combined. 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternatives designs and embodiments for practicing the invention within the scope of the appended claims.