Abstract:
A torque converter defines an ellipticity lower than or equal to 0.23 which is an outermost length of the torque converter in an axial direction, divided by an outermost diameter of the torque converter in a radial direction. The torque converter includes: a pump impeller connecting to an input shaft; a turbine runner opposed to the pump impeller and connecting to an output shaft; and a stator disposed between an inlet of the pump impeller and an outlet of the turbine runner, by way of a one way clutch which allows a one way rotation. The torque converter transmits a power by circulating a fluid through the pump impeller, the turbine runner and the stator. A first area ratio A is: 0.23≦A≦0.45, A second area ratio B is: 0.23≦B≦0.45, and A third area ratio C is: 0.15≦C&lt;0.23.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a torque converter used for a power transmission of a vehicle and the like. 
   2. Description of the Related Art 
   Conventionally, a torque converter is widely used in such a manner as to be disposed between an engine and a transmission. The above torque converter is of a 3-element type, namely, including a pump impeller, a turbine runner and a stator. More specifically, the above torque converter has a fluid pass construction including an inlet of the pump impeller, an outlet of the pump impeller, an inlet of the turbine runner, an outlet of the turbine runner, an inlet of the stator, and an outlet of the stator. The inlets and the outlets of each of the three elements have fluid pass areas that are substantially common. The fluid pass area is about 23% of an area of a circle defined by an outermost diameter (nominal diameter) of the torque converter. 
   The above torque converter can absorb and amplify a torque. The thus absorbed torque is commensurate with a work done by a fluid flowing in the fluid pass in the pump impeller. As a criteria, the thus absorbed torque is referred to as a torque capacity. More specifically, a torque capacity factor is defined as an input torque divided by a second power of an input speed {=input torque/(input speed) 2 }. The torque capacity smaller than its proper value for an engine torque may cause a high engine speed, resulting in a heavy fuel consumption. On the other hand, the torque capacity greater than its proper value for the engine torque may cause a heavy load to the engine. In sum, it is important to provide the torque capacity that is proper for the engine. 
   Having the fluid pass areas that are substantially “common” among the inlet inlets and the outlets of each of the three elements, the above conventional torque converter is likely to limit its torque capacity. In other words, the torque capacity has its upper limit. Thereby, the thus limited torque capacity cannot be applied to the engine that has high torque. Use of the torque converter having a low torque capacity for the high torque engine, however, may be responsible for the heavy fuel consumption. 
   Due to the substantially “common” fluid pass areas, enlarging the outermost diameter (nominal diameter) for securing the required torque capacity may involve increased weight, resulting in the heavy fuel consumption and higher cost. 
   Japanese Patent Unexamined Publication No. Heisei 11 (1999)-063149 (JP 11063149) discloses a torque converter having the following construction for securing the torque capacity factor. 
   At first, a first area ratio A, a second area ratio B and a third area ratio C are respectively defined as follows. (A) The first area ratio A is an area of an outlet of a turbine runner, divided by an area of a circle defined by an outermost diameter D; the first area ratio A is also an area of an inlet of a stator, divided by the area of the circle defined by the outermost diameter D. (B) The second area ratio B is an area of an outlet of the stator, divided by the area of the circle defined by the outermost diameter D; the second area ratio B is also an area of an inlet of a pump impeller, divided by the area of the circle defined by the outermost diameter D. (C) The third area ratio C is an area of an outlet of the pump impeller, divided by the area of the circle defined by the outermost diameter; the third area ratio C is also an area of an inlet of the turbine runner, divided by the area of the circle defined by the outermost diameter D. 
   With the above definition, the first area ratio A, the second area ratio B and the third area ratio C provide the following conditions:
         (1) The first area ratio A is in a range from 0.24 to 0.31, the second area ratio B is in a range from 0.24 to 0.31, and the third area ratio C is in a range from 0.23 to 0.31, meeting A=B&gt;C.   (2) The first area ratio A is in a range from 0.24 to 0.31, the second area ratio is in a range from 0.23 to 0.31, and the third area ratio is in a range from 0.23 to 0.31, meeting A&gt;B and A&gt;C.   (3) The first area ratio A is in a range from 0.23 to 0.31, the second area ratio B is in a range from 0.24 to 0.31, and the third area ratio C is in a range from 0.23 to 0.31, meeting B&gt;A and B&gt;C.       

   By optimizing the area ratios for the fluid pass based on the above conditions, the torque converter according to Japanese Patent Unexamined Publication No. Heisei 11 (1999)-063149 (JP11063149) is supposed to increase the torque capacity. 
   BRIEF SUMMARY OF THE INVENTION 
     FIG. 5  shows a schematic of a torque converter. The torque converter has an outermost diameter D and a length L. In an axial direction of a vehicle, the length L is defined as a length between a forward end (left in  FIG. 5 ) of a pump impeller and a rearward end (right in  FIG. 5 ) of a turbine runner. An ellipticity L/D of the torque converter is defined as the length L divided by the outermost diameter D. 
   For improving mountability of the torque converter on the vehicle, the torque converter tends to be more compact, thus decreasing the length L. In this case, however, the ellipticity L/D becoming smaller (namely, the length L becoming smaller relative to the outermost diameter D) may cause the following:
         i) A curvature of each of a core of an outlet of the pump impeller and a core of an inlet of the turbine runner becomes great, thus causing a peel to the fluid flow, resulting in a lowered efficiency.   ii) The thus caused peel of the fluid flow may reduce an effective fluid pass area. Thereby, enlarging the outlet of the pump impeller and the inlet of the turbine runner may not contribute to increase in the fluid, thus failing to increase the torque capacity factor.       

   It is an object of the present invention to provide a torque converter having a small ellipticity. 
   It is another object of the present invention to provide such a proper area ratio for a fluid pass of the torque converter as to cause a proper torque capacity. 
   According to an aspect of the present invention, there is provided a torque converter defining an ellipticity lower than or equal to 0.23 which is an outermost length of the torque converter in an axial direction, divided by an outermost diameter of the torque converter in a radial direction. The torque converter comprises:
         1) a pump impeller connecting to an input shaft;   2) a turbine runner opposed to the pump impeller and connecting to an output shaft; and   3) a stator disposed between an inlet of the pump impeller and an outlet of the turbine runner, by way of a one way clutch which allows a one way rotation.       

   The torque converter transmits a power by circulating a fluid through the pump impeller, the turbine runner and the stator. 
   When a first area ratio A, a second area ratio B and a third area ratio C are respectively defined as follows:
         A. at least one of the following:
           a) a fluid pass area of the outlet of the turbine runner, divided by an area of a circle defined by the outermost diameter of any one of the pump impeller and the turbine runner, and   b) a fluid pass area of an inlet of the stator, divided by the area of the circle defined by the outermost diameter of the any one of the pump impeller and the turbine runner,   
           B. at least one of the following:
           a) a fluid pass area of an outlet of the stator, divided by the area of the circle defined by the outermost diameter of the any one of the pump impeller and the turbine runner, and   b) a fluid pass area of the inlet of the pump impeller, divided by the area of the circle defined by the outermost diameter of the any one of the pump impeller and the turbine runner, and   
           C. at least one of the following:
           a) a fluid pass area of an outlet of the pump impeller, divided by the area of the circle defined by the outermost diameter of the any one of the pump impeller and the turbine runner,   b) and a fluid pass area of an inlet of the turbine runner, divided by the area of the circle defined by the outermost diameter of the any one of the pump impeller and the turbine runner,   
           the first area ratio A is in a following first range:
 
0.23≦A≦0.45,
   the second area ratio B is in a following second range:
 
0.23≦B≦0.45, and 
   the third area ratio C is in a following third range:
 
0.15≦C&lt;0.23.
       

   The other objects and features of the present invention will become understood from the following description with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a cross section of a torque converter, according to an embodiment of the present invention. 
     FIG.  2 ( a ) shows a schematic of a torque converter, according to a prior art using a conventional area ratio, while FIG.  2 ( b ) shows a schematic of the torque converter, according to the embodiment of the present invention. 
       FIG. 3  shows a graph plotting an efficiency, a stall torque ratio and a torque capacity factor, relative to a third area ratio C, according to the embodiment of the present invention. 
       FIG. 4  shows a graph plotting the efficiency, the stall torque ratio and the torque capacity factor, relative to the first area ratio A and the second area ratio B, according to the embodiment of the present invention. 
       FIG. 5  shows a schematic of a torque converter. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   In the following, a certain embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
   For ease of understanding, the following description will contain various directional terms, such as, left, right, upper, lower, forward, rearward and the like. However, such terms are to be understood with respect to only a drawing or drawings on which the corresponding part of element is illustrated. 
     FIG. 1  shows a cross section of a torque coverter, according to an embodiment of the present invention. 
   There is provided a pump impeller  20  connected to an engine (not shown in  FIG. 1 ) by way of a casing  21 . The pump impeller  20  has the following construction. A shell  22  (fixed to the casing  21 ) and a core  23  (of the pump impeller  20 ) are so formed as to define an operation fluid pass by way of a blade  24 . 
   There is provided a turbine runner  25  opposed to the pump impeller  20 . The turbine runner  25  has the following construction. A shell  26  and a core  27  (of the turbine runner  25 ) are so formed as to define an operation fluid pass by way of a blade  28 . 
   The turbine runner  25  connects to an input shaft (not shown in  FIG. 1 ) of a transmission (not shown in  FIG. 1 ) by way of an inner race  29 . 
   There is provided a stator  30  interposed between the pump impeller  20  and the turbine runner  25 . The stator  30  has the following construction. A plurality of vanes  33  are arranged between an inner ring  31  and an outer ring  32  (core ring), in such a manner that the stator  30  can be supported to a predetermined rigid shaft (not shown in  FIG. 1 ) by way of a one way clutch  34  which is rotatable only in one direction. 
   Moreover, there is provided a lock up clutch  36  between the shell  26  (of the turbine runner  25 ) and the casing  21 . The lock up clutch  36  is disconnectable. 
   An outlet  40  of the turbine runner  25  has an operation fluid pass area (ratio) which is the same as that of an inlet  41  of the stator  30 . An outlet  42  of the stator  30  has an operation fluid pass area (ratio) which is the same as that of an inlet  43  of the pump impeller  20 . An outlet  44  of the pump impeller  20  has an operation fluid pass area (ratio) which is the same as that of an inlet  45  of the turbine runner  25 . With the above construction, the operation fluid passes between the elements, namely, the turbine runner  25 , the stator  30  and the pump impeller  20  are so formed as to connect with each other smoothly. 
   Hereinabove, the torque converter has an outer diameter, in other words, an outermost diameter D of any one of the pump impeller  20  and the turbine runner  25  which two members are the same in diameter. Moreover, the torque converter has a length L, as shown in FIG.  5 . An ellipticity L/D which is defined as the length L divided by the outer diameter D is smaller than or equal to 0.23. Moreover, a first area ratio A, a second area ratio B and a third area ratio C are respectively defined as follows. (A) The first area ratio A is an operation fluid pass area of the outlet  40  of the turbine runner  25 , divided by an area of a circle defined by the outermost diameter D. The first area ratio A is also an operation fluid pass area of the inlet  41  of the stator  30 , divided by the area of the circle defined by the outermost diameter D. Hereinafter, the first area ratio A is, as the case may be, referred to as “stator area ratio”. (B) The second area ratio B is an operation fluid pass area of the outlet  42  of the stator  30 , divided by the area of the circle defined by the outermost diameter D. The second area ratio B is also an operation fluid pass area of the inlet  43  of the pump impeller  20 , divided by the area of the circle defined by the outermost diameter D. Hereinafter, the second area ratio B is, as the case may be, referred to as “stator area ratio”. (C) The third area ratio C is an operation fluid pass area of the outlet  44  of the pump impeller  20 , divided by the area of the circle defined by the outermost diameter D. The third area ratio C is also an operation fluid pass area of the inlet  45  of the turbine runner  25 , divided by the area of the circle defined by the outermost diameter D. 
   The torque converter has such a construction that the first area ratio A is in the following range: 0.23≦A≦0.45, the second area ratio B is in the following range: 0.23≦B≦0.45, and the third area ratio C is in the following range: 0.15≦C&gt;0.23. 
   FIG.  2 ( a ) shows a schematic of a torque converter defining a small ellipticity of lower than or equal to 0.23, according to a prior art using a conventional area ratio, while FIG.  2 ( b ) shows a schematic of the torque converter, according to the embodiment of the present invention. 
   More specifically, the torque converter in FIG.  2 ( a ) has a first area ratio A in the following range: 0.24≦A≦0.31, a second area ratio B in the following range: 0.24≦B≦0.31, and a third area ratio C in the following range: 0.23≦C&gt;0.31. In addition, the first area ratio A and the second area ratio B (the same as the first area ratio A) are greater than the third area ratio C in FIG.  2 ( a ), according to the prior art. 
   Compared with a mean diameter (radius) of the operation fluid pass according to the prior art in FIG.  2 ( a ), a mean diameter (radius) of the operation fluid pass according to the embodiment of the present invention in FIG.  2 ( b ) is greater on the outlet  44  of the pump impeller  20  and on the inlet  45  of the turbine runner  25 . 
   According to the embodiment of the present invention, dimensions and the like of the blade  24  (see  FIG. 1 ) and the blade  28  (see  FIG. 1 ) can be defined in accordance with the mean diameter (radius) of the operation fluid pass. 
   More specifically, defining the third area ratio C in the following range: 0.15≦C&gt;0.23 according to the embodiment of the present invention can allow the operation fluid to flow along the core  23  (of the pump impeller  20 ) and the core  27  (of the turbine runner  25 ), even when the ellipticity L/D is small and thereby a curvature becomes great. The construction of the torque converter according to the embodiment of the present invention can reduce a peel {see shaded area in FIG.  2 ( a )} according to the prior art. Thereby, the above construction according to the embodiment of the present invention can improve efficiency. 
   Moreover according to the embodiment of the present invention, an effective operation fluid pass area of each of the pump impeller  20  and the turbine runner  25  does not decrease, thus preventing reduction in quantity of the operation fluid. According to the embodiment of the present invention, the mean radius of the operation fluid pass which is rather greater than its counterpart mean radius according to the prior art can increase torque capacity factor. 
   With this, the torque converter even having the small ellipticity can increase the torque capacity in accordance with engine characteristic, when the torque converter according to the embodiment of the present invention is the same in outer diameter as the torque converter according to the prior art. 
   Described hereinafter are parameters which are of importance when designing the torque converter. The parameters can be ordered sequentially in terms of importance as follows: the efficiency, a stall torque ratio, and the torque capacity factor. (1) Efficiency (most important): The efficiency is responsible for fuel consumption. The lower the efficiency is, the more increased the fuel consumption of the vehicle is. Adjusting the efficiency by other parameters (i.e., configuration, angle and the like of the blade  24  and the blade  28 ) is of difficulty. Therefore, designing the torque converter is supposed to determine a way of obtaining the high efficiency (lower design limit of 85%). (2) Stall torque ratio (second most important): The stall torque ratio can greatly contribute to startability. The stall torque ratio is inversely proportional to the efficiency. More specifically, the higher the efficiency is, the more deteriorated the startability is, while the lower the efficiency is, the more improved the startability is. Hereinabove, the stall torque ratio has a lower design limit of 1.7 for operation. (3) Torque capacity factor (third most important): The higher the torque capacity factor is, the easier the tuning is. Adjusting the torque capacity factor by other parameters (i.e., configuration, angle and the like of the blade  24  and the blade  28 ) is possible to a certain extent, rendering the torque capacity factor to be less important. More specifically, allowing the vanes  33  (forming the outlet  42  of the stator  30 ) to become aligned (i.e., in parallel with) the operation fluid flow can increase the torque capacity factor to a certain extent. Moreover, varying an angle of the pump impeller  20  can vary the torque capacity factor to a certain extent. 
     FIG. 3  shows a graph plotting the efficiency, the stall torque ratio and the torque capacity factor, relative to the third area ratio C. 
   (1) Efficiency 
   The smaller the third area ratio C is, the greater the efficiency is. This is for the following cause:
         The operation fluid flowing along the core  23  (of the pump impeller  20 ) and the core  27  (of the turbine runner  25 ) can reduce the peel {see FIG.  2 ( a )}.       

   The third area ratio C becoming too small, however, may be responsible for a rapid expansion and/or reduction of the operation fluid pass, thus lowering the efficiency as plotted on a left side of a peak P 1  in FIG.  3 . 
   (2) Stall Torque Ratio 
   The smaller the third area ratio C is, the smaller the stall torque ratio is. This is for the following cause:
         Reducing the third area ratio C increases the mean radius of the fluid pass {as can be assumed by FIG.  2 ( b )}, thus decreasing a stator radius ratio (see below).   # Definition of the stator radius ratio:
           =(Radius R)/(Mean radius of fluid pass)   For the radius R, refer to FIG.  5 .   
               

   As a result, the stall torque ratio shows a decrease on a left side of a peak P 2  in FIG.  3 . Reducing the third area ratio C, however, may be responsible for only a minor decrease in the stall torque ratio. 
   (3) Torque Capacity Factor 
   The smaller the third area ratio C is, the greater the torque capacity factor is. This is for the following cause:
         The mean radius of the operation fluid pass of the outlet  44  (of the pump impeller  20 ) and the inlet  45  (of the turbine runner  25 ) becomes great, with the quantity of the operation fluid substantially unchanged.       

   As a result, description of the third area ratio C can be summarized as below: 
   (Third Area Ratio C&lt;0.15) 
   The efficiency and the torque capacity factor are high. On the other hand, the stall torque ratio is lower than the lower design limit of 1.7. 
   (0.15≦Third Area Ratio C&lt;0.23) 
   The greater the third area ratio C is, the more reduced the efficiency is with the peak P 1 . The reduction in the efficiency is, however, modest, thus meeting the lower design limit of 85%. The stall torque ratio shows a modest increase, thus meeting the lower design limit of 1.7. The torque capacity factor can remain in such a range that the torque capacity factor is adjustable by other parameters (i.e., configuration, angle and the like of the blade  24  and the blade  28 ). 
   (0.23≦Third Area Ratio C) 
   The stall torque ratio reaches the peak P 2  at the third area ratio C of 0.23. On the other hand, the efficiency reaching the peak P 1  at the third area ratio C of 0.15 is reduced at the third area ratio C of 0.23 and over, thus failing to meet the lower design limit of 85%. 
   In sum, “0.15≦third area ratio C&lt;0.23” is preferred. 
   According to the embodiment of the present invention, the third area ratio C is defined 0.19 for the following causes: 
   
     
       
             
             
             
           
         
             
                 
             
           
           
             
               i) 
               Efficiency: 
               Substantially the peak P1 is 
             
             
                 
                 
               obtainable. 
             
             
               ii) 
               Stall torque ratio: 
               Substantially the peak P2 is 
             
             
                 
                 
               obtainable. 
             
             
               iii) 
               Torque capacity factor: 
               Adjustable by other parameters (i.e., 
             
             
                 
                 
               configuration, angle and the like of 
             
             
                 
                 
               the blade 24 and the blade 28). 
             
             
                 
             
           
        
       
     
   
     FIG. 4  shows a graph plotting the efficiency, the stall torque ratio and the torque capacity factor, relative to the first area ratio A (stator area ratio) and the second area ratio B (stator area ratio). 
   (1) Efficiency 
   The efficiency is unlikely to change in an area defined by the first area ratio A and the second area ratio B smaller than 0.4. The efficiency reduces, however, in the area defined by the first area ratio A and the second area ratio B of 0.4 or over, for the following cause:
         The operation fluid pass shows the rapid expansion and/or reduction.
 
(2) Stall Torque Ratio
       

   The greater the first area ratio A and the second area ratio B are, the greater the stall torque ratio is. This is for the following cause:
         Increasing the first area ratio A and the second area ratio B increases the mean diameter (radius) of the operation fluid pass of the stator  30 , thus increasing torque of the stator  30 .
 
(3) Torque Capacity Factor
       

   The greater the first area ratio A and the second area ratio B are, the greater the torque capacity factor is. This is for the following cause:
         Resistance of the operation fluid pass of the stator  30  reduces and resistance of absorbing the operation fluid at the pump impeller  20  also reduces, resulting in increase in the quantity of the operation fluid.       

   As a result, description of the first area ratio A and the second area ratio B can be summarized as below: 
   (First Area Ratio A&lt;0.23, and Second Area Ratio B&lt;0.23) 
   The efficiency is high. However, the torque capacity factor is low, and the stall torque ratio is lower than the lower design limit of 1.7. 
   (0.23≦First Area Ratio A≦0.45, and 0.23≦Second Area Ratio B≦0.45) 
   With a peak P 3 , the efficiency reduces in accordance with an increase in the first area ratio A and the second area ratio B. The reduction in the efficiency is, however, modest, thus meeting the lower design limit of 85% with “0.23≦first area ratio A≦0.45” and “0.23≦second area ratio B≦0.45”. 
   The stall torque ratio shows a modest increase, thus meeting the lower design limit of 1.7 with “0.23≦first area ratio A≦0.45” and “0.23≦second area ratio B≦0.45”. 
   Moreover, the torque capacity factor can remain in such a range that the torque capacity factor is adjustable by other parameters (i.e., configuration, angle and the like of the blade  24  and the blade  28 ). 
   (0.45&lt;First Area Ratio A, and 0.45&lt;Second Area Ratio B) 
   The stall torque ratio is on the increase, otherwise as great as a peak P 4 . The torque capacity factor is also on the increase, otherwise as great as its peak (not shown in FIG.  4 ). On the other hand, the efficiency reduces, thus failing to meet the lower design limit of 85%. 
   In sum, “0.23≦first area ratio A≦0.45” and “0.23≦second area ratio B≦0.45” are preferred. 
   According to the embodiment of the present invention, each of the first area ratio A and the second area ratio B is defined 0.31 for the following causes: 
   
     
       
             
             
             
           
         
             
                 
             
           
           
             
               i) 
               Efficiency: 
               Substantially the peak P3 is 
             
             
                 
                 
               obtainable. 
             
             
               ii) 
               Stall torque ratio: 
               Substantially the peak P4 is 
             
             
                 
                 
               obtainable. 
             
             
               iii) 
               Torque capacity factor: 
               Adjustable by other parameters (i.e., 
             
             
                 
                 
               configuration, angle and the like of 
             
             
                 
                 
               the blade 24 and the blade 28). 
             
             
                 
             
           
        
       
     
   
   In sum, the torque converter according to the embodiment of the present invention has the ellipticity L/D smaller than or equal to 0.23 which contributes to compactness of the torque converter. More specifically, the ellipticity L/D is defined 0.19. Moreover, the torque converter according to the embodiment of the present invention has the first area ratio A of 0.31, the second area ratio B of 0.31 and the third area ratio of 0.19, thus preferably balancing the parameters including the efficiency, the stall torque ratio and the torque capacity factor. 
   Although the present invention has been described above by reference to the certain embodiment, the present invention is not limited to the embodiment described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, in light of the above teachings. 
   This application is based on a prior Japanese Patent Application No. P2001-395185 (filed on Dec. 26, 2001 in Japan). The entire contents of the Japanese Patent Application No. P2001-395185 from which priority is claimed is incorporated herein by reference, in order to take some protection against mis-translation or omitted portions. 
   The scope of the present invention is defined with reference to the following claims.