Abstract:
A torque converter assembly is provided, which includes an impeller, a turbine, and a stator. The impeller and the turbine each have a plurality of passages for directing fluid. The inlet and outlet of each passage are larger in cross-sectional area than the middle portion of the passage, located between the inlet and outlet. This structure reduces energy losses, which typically occur near the midpoint of the passage due to flow separation. Additionally, reducing the flow area of the torus of the impeller and turbine permits an overall thinner torque converter, which is preferred for engine packaging purposes. The stator includes a core, a shell, and a plurality of stator blades. One end of each stator blade is fixed to the core, while the opposite end is fixed to the shell. Each stator blade has a mean camber line and an associated mean camber line length. The maximum thickness of each stator blade is approximately 20% of the mean camber line length. Each stator blade has a midsection located between the ends affixed to the core and the shell. The midsection of each stator blade has a larger cross-sectional area than either end of the blade. This stator blade structure creates a larger stator blade surface, which is more effective at re-directing fluid within the torque converter.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/576,853 filed Jun. 3, 2004, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This invention relates to torque converter assemblies having an impeller, a turbine, and a stator. 
     BACKGROUND OF THE INVENTION 
     Current automatic power transmissions generally include a hydrodynamic input device such as a torque converter or fluid coupler. A torque converter is employed mainly to provide torque multiplication in the lower speed range. A torque converter consists of an engine-driven impeller, a fluid turbine, and a fluid stator. The engine-driven impeller accelerates fluid for passage to the turbine. The turbine converts the fluid energy coming from the impeller into mechanical energy, which is transmitted to the input shaft of a transmission. 
     The stator mechanism disposed between the fluid inlet of the impeller and the fluid outlet of the turbine redirects the fluid from the turbine to the impeller thereby improving the flow efficiency and increasing the torque multiplication of the hydrodynamic torque converter. The fluid passes from the inner section of the impeller torus substantially radially outward in a toric path and then through the path in the turbine in a substantially toric path back to the stator. In constant area turbine assemblies, the flow therein can encounter energy losses when a reversal or separation in flow occurs near the center of the torus flow path adjacent the inner side wall. This flow inconsistency reduces the efficiency of the torque converter. 
     A stator is made up of a plurality of stator blades, which are connected at one end to a relatively small ring, the shell, and at the other end to a larger ring, the core. Fluid flowing through the stator passes along the stator blades. These blades force the fluid to change direction so fluid exiting the stator enters the pump flowing in the same direction as the pump is rotating, thereby conserving power. Stator blades with a larger surface area are more effective at re-directing the fluid. The core has conventionally limited the surface area of the stator blades because the sides of a standard stator blade are linearly configured between the core and the shell. This design often results in a stator blade with a relatively small surface area, and therefore a loss of potential torque. 
     The stator blade cross-sectional design is important in the overall design of a torque converter. Stator blade shapes that result in flatter input speed lines allow for engine operation at lower engine speeds, which improves vehicle fuel economy. Additionally, flatter input speed lines improve performance in some vehicle applications due to smaller changes in engine speed when the torque converter clutch is applied. 
     An example of a conventional torque converter assembly is described in U.S. Pat. No. 4,177,885 and an example of a conventional torque converter stator is described in U.S. Pat. No. 5,431,536, both of which are assigned to General Motors Corporation and are hereby incorporated by reference. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an improved torque converter having an impeller, a turbine, and a stator. 
     A torque converter assembly is provided, which includes an impeller, a turbine, and a stator. The impeller and the turbine each have a passage for directing fluid. Each passage has an inlet having an inlet cross-sectional area, an outlet having an outlet cross-sectional area, and a middle portion having a middle portion cross-sectional area. The middle portion cross-sectional area is smaller than each of the inlet cross-sectional area and the outlet cross-sectional area. The stator includes a core, a shell, and a plurality of stator blades. Each stator blade has a mean camber line, a mean camber line length, and a maximum thickness, which is less than approximately 20% of the mean camber line length. Each stator blade has a midsection defined by a mid-cross-sectional area, a first end defined by a first end cross-sectional area attached to the stator core, and a second end defined by a second end cross-sectional area attached to the stator shell. The mid-cross-sectional area is larger than each of the first cross-sectional area and the second cross-sectional area. 
     In a second embodiment of the present invention, a torque converter assembly having an impeller, turbine, and stator is provided. The impeller has a predetermined flow path for directing fluid radially outward through a substantially toroidal path. The turbine has a substantially toroidal flow path for directing fluid from the impeller radially inward. The toroidal flow path through the turbine has an inlet and an outlet. The flow path in the turbine decreases in flow area from the inlet to a predetermined point having a third area along the flow path and increases in flow area from the predetermined point to the outlet. The stator has a plurality of stator blades. Each stator blade has a mean camber line length and a maximum thickness, which is less than approximately 20% of the mean camber line length. Additionally, each stator blade has a first end defined by a first end cross-sectional area, a second end defined by a second end cross-sectional area, and a midsection defined by a mid-cross-sectional area. Each stator blade becomes smaller in cross-sectional area in a direction from the midsection to the first end and becomes smaller in cross-sectional area in a direction from the midsection to the second end. Thus, the mid-cross-sectional area is larger than each of the first and second end cross-sectional areas. 
     In a third embodiment of the present invention, a torque converter assembly is provided including an impeller, a turbine, and a stator. The impeller and the turbine each have a passage for directing fluid. Each passage has an inlet having an inlet cross-sectional area, an outlet having an outlet cross-sectional area, and a middle portion having a middle portion cross-sectional area. The middle portion cross-sectional area is smaller than each of the inlet cross-sectional area and the outlet cross-sectional area. The stator includes a core, a shell, and a plurality of stator blades. Each stator blade has a mean camber line, a mean camber line length, and a maximum thickness that is less than approximately 20% of the mean camber line length. 
     In a fourth embodiment of the present invention, a torque converter assembly including an impeller, a turbine, and a stator is provided. The impeller and the turbine each have a passage for directing fluid. Each passage has an inlet having an inlet cross-sectional area, an outlet having an outlet cross-sectional area, and a middle portion having a middle portion cross-sectional area. The middle portion cross-sectional area is smaller than each of the inlet cross-sectional area and the outlet cross-sectional area. The stator includes a core, a shell, and a plurality of stator blades. Each stator blade has a midsection having a mid-cross-sectional area, a first end having a first end cross-sectional area attached to the core, and a second end having a second end cross-sectional area attached to the shell. The mid-cross-sectional area is larger than each of the first end cross-sectional area and the second end cross-sectional area. 
     In a fifth embodiment of the present invention, a torque converter assembly is provided including an impeller, a turbine, and a stator. The stator includes a core, a shell, and a plurality of stator blades. Each stator blade has a mean camber line, a mean camber line length, and a maximum thickness, which is less than approximately 20% of the mean camber line length. Each of the stator blades has a midsection having a mid-cross-sectional area, a first end having a first end cross-sectional area attached to the core, and a second end having a second end cross-sectional area attached to the shell. The mid-cross-sectional area is larger then each of the first end cross-sectional area and the second end cross-sectional area. 
     In a sixth embodiment of the present invention, a torque converter assembly including an impeller, turbine, and stator is provided. The turbine has a predetermined flow path for directing fluid radially inward through a substantially toroidal path. The impeller has a substantially toroidal flow path for directing fluid radially outward. The flow path in the impeller has an inlet and an outlet. The flow path decreases in flow area from the inlet to a predetermined point having a third area along the flow path and increases in flow area from the predetermined point to the outlet. The stator includes a plurality of stator blades. Each stator blade has a mean camber line length and a maximum thickness, which is less than approximately 20% of the mean camber line length. Each stator blade has a first end defined by a first end cross-sectional area, a second end defined by a second end cross-sectional area, and a midsection defined by a mid-cross-sectional area. Each stator blade becomes smaller in cross-sectional area in a direction from the midsection to the first end and becomes smaller in cross-sectional area in a direction from the midsection to the second end. Thus, the mid-cross-sectional area is larger than each of the first and second end cross-sectional areas. 
     In a seventh embodiment of the present invention, a torque converter assembly is provided including an impeller, a turbine, and a stator. The impeller has a predetermined flow path for directing fluid radially outward through a substantially toroidal path. The turbine has a substantially toroidal flow path for directing fluid from the, impeller radially inward. The flow path in the torque converter turbine has an inlet and an outlet. The flow path decreases in flow area from the inlet to a predetermined point having a third area along the flow path and increases in flow area from the predetermined point to the outlet. The stator includes a plurality of stator blades. Each stator blade has a mean camber line length and a maximum thickness, which is less than approximately 20% of the mean camber line length. 
     In an eighth embodiment of the present invention, a torque converter assembly including an impeller, a turbine, and a stator is provided. The turbine has a predetermined flow path for directing fluid radially inward through a substantially toroidal path. The impeller has a substantially toroidal flow path for directing fluid radially outward. The flow path in the torque converter impeller has an inlet and an outlet. The flow path decreases in flow area from the inlet to a predetermined point having a third area along the flow path and increases in flow area from the predetermined point to the outlet. The stator includes a plurality of stator blades. Each stator blade has a mean camber line length and a maximum thickness, which is less than approximately 20% of the mean camber line length. 
     In a ninth embodiment of the present invention, a torque converter assembly is provided including an impeller, a turbine, and a stator. The impeller has a predetermined flow path for directing fluid radially outward through a substantially toroidal path. The turbine has a substantially toroidal flow path for directing fluid from the impeller radially inward. The flow path in the torque converter turbine has an inlet and an outlet. The flow path decreases in flow area from the inlet to a predetermined point having a third area along the flow path and increases in flow area from the predetermined point to the outlet. Each stator blade has a first end defined by a first end cross-sectional area, a second end defined by a second end cross-sectional area, and a midsection defined by a mid-cross-sectional area. Each stator blade becomes smaller in cross-sectional area in a direction from the midsection to the first end and becomes smaller in cross-sectional area in a direction from the midsection to the second end. Thus, the mid-cross-sectional area is larger than each of the first and second cross-sectional areas. 
     In a tenth embodiment of the present invention, a torque converter assembly including an impeller, a turbine, and a stator is provided. The turbine has a predetermined flow path for directing fluid radially inward through a substantially toroidal path. The impeller has a substantially toroidal flow path for directing fluid radially outward. The flow path in the torque converter impeller has an inlet and an outlet. The flow path decreases in flow area from the inlet to a predetermined point having a third area along the flow path and increases in flow area from the predetermined point to the outlet. Each stator blade has a first end defined by a first end cross-sectional area, a second end defined by a second end cross-sectional area, and a midsection defined by a mid-cross-sectional area. Each stator blade becomes smaller in cross-sectional area in a direction from the midsection to the first end and becomes smaller in cross-sectional area in a direction from the midsection to the second end. Thus, the mid-cross-sectional area is larger than each of the first and second end cross-sectional areas. 
     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 cross-sectional comparison of a torque converter assembly with a controlled area thin torus turbine in accordance with the present invention and a torque converter with a standard torus turbine; 
         FIG. 2  is a graphical illustration showing the gross torus flow area ratio versus torus length fraction for a standard torus turbine and a controlled area thin torus turbine; 
         FIG. 3  is a schematic cross-sectional view of a flow path through a torque converter controlled area torus portion; 
         FIG. 4  is a schematic cross-sectional blade to blade view of one dimensional flow through a torque converter torus, illustrating toroidal velocity (F) versus relative velocity (W) through the torque converter torus path; 
         FIG. 5  is a top plan view of a stator for use with the torque converter assembly of  FIG. 1  with a controlled area thin torus turbine or with the torque converter assembly of  FIG. 13  with a controlled area thin torus turbine and pump; 
         FIG. 6  is a side view of the stator of  FIG. 5 ; 
         FIG. 7  is a bottom plan view of the stator of  FIG. 5 ; 
         FIG. 8  is a schematic cross-sectional view of a stator blade airfoil; 
         FIG. 9  is a schematic cross-sectional view of a stator blade in accordance with the present invention; 
         FIG. 10  is a graphical illustration showing input speeds corresponding with the stator blade of  FIG. 9  compared with a standard or conventional stator blade over speed ratios ranging from 0.0 to 1.0; 
         FIG. 11  is a schematic perspective surface illustration of a stator blade in accordance with the present invention; 
         FIG. 12  is a perspective end view of the stator blade of  FIG. 11 ; 
         FIG. 13  is a cross-sectional comparison of a torque converter assembly with a controlled area thin torus turbine, a controlled area thin torus impeller, and a stator with blades defined by 3 sections in accordance with the present invention and a torque converter assembly with a standard or conventional torus turbine, a standard or conventional torus impeller, and standard or conventional stator; and 
         FIG. 14  is a graphical illustration comparing torque converter performance data for the torque converter assembly of the present invention and a prior art thin torus torque converter assembly. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and 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 spirit and scope of the invention. 
     Referring to the drawings, there is seen in  FIG. 1  a diagrammatic representation of a torque converter assembly  10 ′ including a conventional impeller (or pump)  12  and a controlled area thin torus turbine  14 . Also shown in  FIG. 1  in dashed lines is a torque converter turbine  16 , which has a conventional or standard torus. The stator  15 ,  15 ′ of the torque converter, shown in  FIG. 13 , has been eliminated from  FIG. 1  for clarity. The controlled area thin torus turbine  14  reduces the overall width of the torque converter  10 ′ thereby reducing the overall length requirement for a transmission in which the controlled area thin torus turbine  14  is employed. 
     As seen in  FIG. 1 , the turbine  14 ,  16  has a plurality of spaced blades to which flow from the impeller  12  is delivered. Thus, the torque converter impeller  12  has an outlet cross-sectional area  18  that is equivalent to the inlet cross-sectional area  20 ,  20 ′ of the turbine  14 ,  16 . 
     Referring to  FIGS. 1 and 4  (when the torus portion  21  in  FIG. 4  is a turbine  14 ,  16  portion), fluid flows through a predetermined passage or path  25  through the torus portion  21 . The conventional or standard turbine  16  has a constant flow area from the turbine inlet cross-sectional area  20 ′, which is equal to the area of the impeller outlet cross-sectional area  18 , to the turbine outlet cross-sectional area  28 ′ as defined in  FIG. 1 . The controlled area thin torus turbine  14  also has an inlet cross-sectional area  20  equal to the area of the impeller outlet cross-sectional area  18 . The flow area of the controlled area thin torus turbine  14 , which is a controlled area torus  33  as illustrated in  FIG. 3 , decreases at the middle portion  30 , where it has a middle portion cross-sectional area  31 , and thereafter increases toward an outlet  32  having an outlet cross-sectional area  28 . In a preferred embodiment of the present invention, the ratio of the inlet cross-sectional area  20  to the middle portion cross-sectional area  31  to the outlet cross-sectional area  28  is approximately 1:0.8:1. 
     As seen in  FIG. 4 , the flow into the torus portion  21 , which may be a turbine  14 ,  16  from  FIG. 1 , may be divided into a toroidal velocity F and a relative velocity W. These two velocities are related or proportional to each other through a function of the cosine of the blade angle θ. As the flow passes between the blades of the torus portion  21 , the relative velocity W and toroidal velocity F coincide essentially at the approximate flow path midpoint  24  and are separated by the blade angle θ at the outlet  26 . 
       FIG. 2  graphically illustrates the gross torus flow area ratio over the torus length fraction for a torque converter  10 ″ with a conventional turbine  16  and a torque converter  10 ′ with a controlled area thin torus turbine  14 , as defined in  FIG. 1 . The gross torus flow area ratio is representative of the area at a specific design point along the torus flow length  34  divided by the torus inlet cross-sectional area  38 , as defined in  FIG. 3 . For example, a torus length fraction of 0.2 represents a point along the torus length  34 , at a distance equal to twenty percent of the torus length  34 , inward from the torus inlet  40 . 
     As shown at  43  in  FIG. 2 , the controlled area thin torus turbine  14  of  FIG. 1  has a ratio of inlet cross-sectional area  20  to middle portion cross-sectional area  31  to outlet cross-sectional area  28  of approximately 1:0.9:1. It can be seen at  45  in  FIG. 2  that the gross torus flow area ratio versus torus length fraction for a conventional torque converter  10 ″ is constant; that is, the gross torus flow area ratio is one for the entire conventional torus flow length. 
     As seen in  FIG. 2 , the gross torus flow area ratio for a controlled area torus  33  decreases from the torus inlet  40  to the approximate center of the torus length fraction, or middle portion,  41  and then increases to the torus outlet  42 , as defined in  FIG. 3 . This change in gross flow area ratio reduces or eliminates the energy losses which otherwise might occur within the turbine flow path. In a conventional torque converter  10 ″, an area of fluid separation tends to form near the midpoint  41  of the torus passage due to decelerating flow. 
       FIG. 4 , as previously stated, schematically defines the toroidal velocity F versus relative velocity W through the torus flow path  25 . If small leakages along the path  25  are ignored, the mass flow rate {dot over (m)} through the passage and the toroidal velocity F are constant. The relative velocity W in a direction tangent to the blade is proportional, as previously stated, to the toroidal velocity F as represented by the cosine of the angle θ. At the approximate flow path midpoint  24 , the two velocities F, W are equal. This indicates that the relative velocity W decreases relative to the toroidal velocity F toward the approximate flow path midpoint  24  and then increases relative to the toroidal velocity F as the fluid passes to the torus outlet  26 . Also, the relative velocity W is flowing into a region of increasing pressure as the fluid flows from the inlet  22  to the approximate flow path midpoint  24 . 
     Under these conditions, flow separation and flow reversal can occur at the approximate midpoint  24  of the torus flow path  25 . The present invention establishes a flow path  25  in which the relative velocity W is more uniform in relation to the toroidal velocity F because of the reduction in the flow area toward the midpoint of the flow path  24 . By reducing the torus flow area near the flow path midpoint  24 , the deceleration of the flow is reduced or diminished. Limiting the flow deceleration reduces the fluid separation in the passage  25  and thereby controls associated energy losses. 
     The thin torus turbine  14  of the present invention is similar to a thin torus turbine described in U.S. Ser. No. 10/765,690, entitled “Torque Converter with a Thin Torus Turbine,” filed Jan. 26, 2004, which is assigned to General Motors Corporation and is hereby incorporated by reference in its entirety. 
     The present invention also contemplates that the torque converter impeller  12  may have a controlled area thin torus structure as described hereinabove with respect to the torque converter turbine  14 . Thus, the torus portions illustrated in  FIGS. 3 and 4  may be representative of impeller torus portions. In this embodiment, both the impeller  12  and the turbine  14  may have the above-described structure. Referring to  FIGS. 3 and 13 , in this structure, both the turbine  14  and the impeller  118  have a torus structure where the inlet, which is  40  for the turbine and  42  for the impeller, and the outlet, which is  42  for the turbine and  40  for the impeller, of the passage  27  are larger in cross-sectional area than the middle portion cross-sectional area  31 ,  35 . 
     The above-described structure, including  FIGS. 1 through 4 , is the preferred embodiment for one aspect of the present invention, however the gross torus flow area ratio may be varied within the scope of the present invention. 
     Referring now to  FIGS. 5 through 7 , a stator  15  for use with the torque converter of  FIG. 1  is comprised of a shell  50 , a core  52 , and a plurality of blades  54 .  FIG. 1  illustrates the turbine  16  and impeller  12  (stator not shown) arranged in a conventional torque converter configuration, such as that shown in U.S. Pat. Nos. 4,177,885 and 5,431,536, both of which are assigned to General Motors Corporation and are hereby incorporated by reference in their entirety. A conventional torque converter stator is shown as  15 ′ in  FIG. 13 .  FIGS. 5 and 7  illustrate the stator  15  of the present invention from the top and bottom, respectively.  FIG. 6  shows a side profile of the stator  15 . 
       FIG. 8  shows a cross-sectional schematic view of a straight stator blade airfoil  60  and cross-sectional schematic view of an alternate stator blade airfoil  60 ′. An airfoil is the basic cross-sectional shape of a stator blade  54 , as shown in  FIG. 9 , before forming the angle  62  between the inlet  56  and outlet  58 . Referring back to  FIG. 8 , the length of the stator blade airfoil  60 ,  60 ′ is referred to as the mean camber line length  66 ′. The stator blade airfoil  60 ,  60 ′ of the present invention may or may not be symmetrical about the mean camber line  64 . Thus, it is important to note that in the present invention the mean camber line  64  may not lie exactly equidistant from the uppermost  61 ,  61 ′ and lowermost  63  points of the airfoil  60 ,  60 ′, and is therefore an approximation of a true mean camber line. The uppermost  61 ,  61 ′ and lowermost  63  points of the airfoil lie on the suction surface  68 ,  68 ′ and pressure surface  70 , respectively. The maximum distance  72 ,  72 ′ from the mean camber line  64  to the suction surface  68 ,  68 ′ and the maximum distance  74  from the mean camber line  64  to the pressure surface  70 , in summation, form the maximum thickness  76 ,  76 ′ of the airfoil. 
     As shown in  FIG. 8 , in one embodiment of the present invention, the maximum distance  72  from the mean camber line  64  to the suction surface  68  is 7.5% of the mean camber line length  66 ′ and the maximum distance  74  from the mean camber line to the pressure surface  70  is 10% of the mean camber line length  66 ′, whereby the maximum thickness  76  of the airfoil is 17.5% of the mean camber line length  66 ′. 
       FIG. 9  is a schematic cross-sectional view of a stator blade  54 , which is the airfoil  60 ′ of  FIG. 8  that has been modified by the incorporation of an angle  62  between the inlet  56  and the outlet  58 . The stator blade inlet  56  is located near the foremost point of the stator blade  54  and the outlet  58  is located near the rearmost point. The maximum thickness  82  of a stator blade  54  is measured with respect to the mean camber line length  66 . In one embodiment of the present invention, shown in  FIG. 9 , the maximum thickness  82  of the stator blade  54  is approximately 15–18% of the mean camber line length  66 . A stator blade  54  has two distinct surfaces. The suction surface  68 ″ of the stator blade is the convex surface of the blade where pressures are lower. The pressure surface  70 ′ is the concave surface of the blade where pressures are higher. The angle  62 , which is the difference between the inlet  56  and the outlet  58 , of each said stator blade  54  in the present invention is relatively small in comparison to the angle used in a conventional stator blade. In one embodiment of the present invention the angle  62  is between approximately 37° and 43°. In the embodiment of the present invention depicted in  FIG. 9 , the angle  62  is approximately 40°. 
     Automotive torque converters normally produce a climbing input speed characteristic relative to speed ratio (the ratio of output speed to input speed). However, a constant input speed extending across a range of speed ratios is beneficial in improving fuel economy. As illustrated in  FIG. 10 , the present stator blade  54  of  FIG. 9  maintains a nearly constant input speed from 0.0 to 0.70 speed ratio, as shown at  88 . The conventional stator blade, as shown at  88 ′, produces a noticeably increasing input speed characteristic. Thus,  FIG. 10  illustrates the improved input speed constancy resulting from a stator with the present stator blade design  54  of  FIG. 9 , as shown at  88 , over a conventional stator blade, as shown at  88 ′. 
     Referring to  FIGS. 5–6  and  11 , each stator blade  54  has a first end  100  affixed to the stator shell  50 , a midsection  104 , and a second end  106  affixed to the stator core  52 . The cross-sectional area of the midsection, the mid-cross-sectional area  110 , is larger than the either the first end cross-sectional area  112  or the second end cross-sectional area  114 . In one embodiment of the present invention, shown in the perspective surface drawing of  FIG. 11 , each stator blade  54  is linearly tapered between the mid-cross-sectional area  110  and both the first end cross-sectional area  112  and the second end cross-sectional area  114 .  FIG. 12  illustrates an approximate end view of the stator blade  54  illustrated in  FIG. 11  from the perspective of the shell  50  looking out radially toward the core  52 .  FIGS. 5 through 7  illustrate a stator  15 , which has a plurality of the stator blades  54  described above united with a stator shell  50  and core  52 . These illustrations also depict the characteristically large stator blade mid-cross-sectional area  110  and the smaller first end cross-sectional area  112  and second end cross-sectional area  114  of the present invention. 
       FIG. 13  illustrates a scaled comparison of a torque converter with a controlled area thin torus turbine  14  and a controlled area thin torus impeller  118  as opposed to a torque converter with a conventional torus turbine  16  and a conventional torus impeller  12 . The torque converter  10  with the controlled area thin torus turbine  14  and controlled area thin torus impeller  118  illustrated has been scaled to the approximate diameter of a conventional torque converter  10 ″ to provide for an accurate comparison of torque converter width  122 ,  122 ′.  FIG. 13  clearly illustrates the reduction in torque converter width  122  attained by a torque converter  10  having a controlled area thin torus turbine  14  and controlled area thin torus impeller  118 . A reduced torque converter width  122  reduces the overall packaging length requirement for a transmission in which the torque converter  10  is employed. 
     The present invention contemplates a torque converter  10  with a controlled area thin torus turbine  14 , controlled area thin torus impeller  118 , stator blades  54  having a reduced thickness, and a stator blade  54  design as shown in  FIG. 11 . A comparison of performance data collected from the torque converter  10  as contemplated by this invention with a prior art thin torus torque converter (not shown) is graphically illustrated in  FIG. 14 . The torque converter performance parameters displayed are 
               K_Factor   100     ,         
torque ratio, speed ratio, and efficiency where:
 
             KFactor   =       N   p         T   p                     TorqueRatio   =       T   t       T   p                   SpeedRatio   =       N   t       N   p             Efficiency=Torque Ratio×Speed Ratio and where: N p =pump rotational speed (rpm) N t =turbine rotational speed (rpm) T p =pump torque (Nm) T t =turbine torque (Nm) Stall=operating condition when speed ratio is 0.0 
     In  FIG. 14 , the solid lines are representative of a torque converter  10  having a stator  15  as shown in  FIGS. 5–7 , a plurality of stator blades  54  as shown in  FIGS. 9 and 11 , a controlled area thin torus turbine  14 , and a controlled area thin torus impeller  118  as shown in  FIG. 13 . The dashed lines represent a prior art thin torus torque converter (not shown). 
     Referring to  FIG. 14 , the positive results attained by the present torque converter  10  are displayed by an increase in efficiency  126 ,  126 ′ and a lower K Factor  136 ,  136 ′ at high speed ratio while maintaining torque ratio  128 ,  128 ′ and efficiency  126 ,  126 ′, and torque multiplication greater than 1 to a higher speed ratio  138 ,  138 ′. The values of K Factor  130 ,  130 ′ displayed in  FIG. 14  are values of 
             K_Factor   100         
to allow for condensed plotting on the same axes as the torque ratio  128 ,  128 ′. In  FIG. 14  it is clear that the efficiency  126  for the torque converter  10  having a stator  15  as shown in  FIGS. 5–7 , a plurality of stator blades  54  as shown in  FIGS. 9 and 11 , a controlled area thin torus turbine  14 , and a controlled area thin torus impeller  118  as shown in  FIG. 13  is higher, particularly at speed ratios of approximately 0.85, shown at  132 ,  132 ′, than the efficiency  126 ′ of the prior art thin torus torque converter (not shown). Higher efficiency  126 ,  126 ′ is related,to higher fuel economy. K Factor  130 ,  130 ′ is a measure of engine rotational speed and torque. Torque ratio  128 ,  128 ′ measures output to input torque multiplication. Both K Factor  130 ,  130 ′ and torque ratio  128 ,  128 ′ are used to compare torque converter performance. It is preferred to have a K Factor  130 ,  130 ′ that remains relatively low over a longer range of speed ratios. More specifically, a K Factor  130 ,  130 ′ with a minimal increase in value from stall  134 ,  134 ′ to a speed ratio of approximately 0.7, shown at  136 ,  136 ′, is favored over a K Factor  130 ,  130 ′ that has a larger increase over the same interval. It is apparent in  FIG. 14  that the K Factor for the prior art thin torus torque converter  130 ′ is slightly higher at a speed ratio of 0.7, shown at  136 ′, than at stall  134 ′, whereas the K Factor  136  for the torque converter  10  having a stator  15  as shown in  FIGS. 5–7 , a plurality of stator blades  54  as shown in  FIGS. 9 and 11 , a controlled area thin torus turbine  14 , and a controlled area thin torus impeller  118  as shown in  FIG. 13  is nearly identical to its K Factor  130  at stall  134 .
 
     It is preferred for a torque converter  10 ,  10 ′,  10 ″ to reach a torque ratio of one at a higher speed ratio than at a lower speed ratio. As shown in  FIG. 14 , the torque converter  10  having a stator  15  as shown in  FIGS. 5–7 , a plurality of stator blades  54  as shown in  FIGS. 9 and 11 , a controlled area thin torus turbine  14 , and a controlled area thin torus impeller  118  as shown in  FIG. 13  reaches a torque ratio of one, shown at  138 , at a slightly higher speed ratio than the prior art thin torus torque converter (not shown), at  138 ′. 
     The invention contemplated is any combination of the three torque converter structures described above. It may be a torque converter  10  wherein the impeller  118  and turbine  14  have passages  27 , as defined in  FIG. 3 , that are smaller in cross-sectional area in the middle than at either end of the passage  27 , as shown in  FIG. 13 , and where the maximum thickness of each stator blade  82 , as shown in  FIG. 9 , is less than approximately 20% of the mean camber line length  66 . The invention herein may be a torque converter  10  wherein the impeller  118  and the turbine  14  have passages  27 , as defined in  FIG. 3 , that are smaller in cross-sectional area in the middle than at either end of the passage  27 , as shown in  FIG. 13 , and each stator blade mid-cross-sectional area  110  is larger than both the first end cross-sectional area  112  and the second end cross-sectional area  114  as shown in  FIGS. 5 ,  7 , and  11 . The invention may also be a torque converter  10 ,  10 ′,  10 ″ wherein the maximum thickness of each stator blade  82  is less than approximately 20% of the mean camber line length  66 , as shown in  FIG. 9 , and each stator blade mid-cross-sectional area  110  is larger than both the first end cross-sectional area  112  and the second end cross-sectional area  114 , as shown in  FIGS. 5 ,  7 , and  11 . Accordingly, the various features described may be implemented in different combinations within the scope of the present invention. 
     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 alternative designs and embodiments for practicing the invention within the scope of the appended claims.