Abstract:
A three element fluid torque converter has a variable pitch stator. The stator blades have two principal orientations, closed and open. The blades are biased toward the closed position by a spring loaded annular piston. In the closed position, the blades block approximately 75% to 90% of the annular area between a stator core and a stator shell. An inlet angle for the stator blades is between 30 degrees and 70 degrees in the closed position. This combination reduces creep torque without any significant increase in driveline noise and vibration when the engine is idling. As engine speed and torque are increased, the blades overcome the spring bias to rotate to the open position thereby increasing the torque transmitted to effectively propel the vehicle.

Description:
This is a continuation-in-part application of U.S. Ser. No. 07/947,613, filed Sep. 21, 1992, now U.S. Pat. No. 5,263,319, issued Nov. 23, 1993. 
    
    
     TECHNICAL FIELD 
     This invention relates to a three element fluid torque converter for use between an engine and a transmission. More particularly, this invention relates to a torque converter having a variable pitch stator. 
     BACKGROUND OF THE INVENTION 
     Torque converters having variable pitch stators are desirable for reducing the tendency of the vehicle to creep when the vehicle is idling and the transmission is in a drive gear range. Reduction of creep torque offers several benefits. Fuel economy can be increased. The engine load at idle can be decreased, thereby reducing engine vibration perceived by the driver. And further, for vehicles requiring elevated idle speeds to satisfy high electrical power requirements at idle, idle speed can be increased while maintaining the same creep power. 
     Variable pitch stators are well known in the art of torque converter design. In most such stators, each stator blade is mounted for rotation about a blade axis passing through the blade. These blade axes typically intersect the torque converter axis. 
     Both active and passive means are used to provide blade rotation. U.S. Pat. No. 3,398,532, issued to Egbert et al. on Aug. 27, 1968, shows an example of active rotation with the blades being rotated to one of three positions by axial motion of a fluid driven piston. U.S. Pat. No. 2,015,300, issued to C. Dell et al. on Sep. 24, 1935, shows a passive system, wherein the blades rotate in response to fluid force against the blades. 
     The angle of the stator blades with respect to the torque converter axis changes as the blades are rotated about their respective blade axes. Generally, when the stator blades are rotated to a high inlet angle or closed position, the torque converter capacity for multiplying input torque at a given engine speed is substantially reduced. The blades are typically in the closed position when the vehicle engine is idling. This has the effect of reducing the torque transmitted to the vehicle wheels, thereby substantially reducing the tendency of the vehicle to creep. 
     However, the disruption of the fluid flow within the torque converter caused by the blades being in the closed position results in vibrations being generated within the torque converter. These vibrations are transmitted through the vehicle to the driver as audible noise and unpleasant vibrations. This condition typically occurs at idle. Also, variable pitch stators have been contributors to harshness of torque converter clutch engaging and disengaging. 
     SUMMARY OF THE INVENTION 
     It has been found that providing a variable pitch stator with a moderately open stator flow path when the blades are in the closed position will reduce creep torque by over 50% while inducing little of the vibrations, noise and harshness commonly associated with torque converters having variable pitch stators. 
     The present invention offers the advantage of creep torque reduction at idle with a minimum increase in noise over a fixed blade stator. This advantage is attained by using variable pitch stator blades with high inlet blade angles and by limiting the portion of the flow area blocked by the blades. This combination of providing the high positive inlet angle and limiting the reduction in flow area reduces the noise and harshness. 
     A spring load biases the blades to a closed position when the engine is at idle speed. As engine speed increases, the velocity of the fluid leaving the turbine and impinging against the stator blades increases, thus overcoming the spring load to rotate the stator blades to the open position. 
     As the vehicle begins to accelerate, the relative speed between the turbine and the impeller decreases, thereby shifting the direction of fluid impingement against the stator. This change in direction does not change the position of the stator blades. The blades continue to be held in the open position by the fluid. 
     The present invention both reduces noise and vibration at idle and reduces harshness of converter clutch engagement and disengagement. 
     The present invention, when both fixed and rotatable blades are employed, provides a stator with both the advantages of rotatable blades and much of the structural rigidity of a stator having all blades fixed. 
     It is an object of this invention to provide an improved torque converter having a stator with variable pitch blades, wherein the blades in a closed position provide an open area approximately 15% of the flow area of the stator, and further wherein the blades have a closed position inlet angle between 30 degrees and 70 degrees depending upon the number of stator blades, the torque converter thereby being capable of reducing creep torque at idle by approximately 50% without inducing vibrations. 
     It is also an object of this invention to provide a three element fluid torque converter having a bladed impeller rotatively fixed to the engine, a bladed turbine rotatively fixed to a transmission input element, and a bladed stator rotatively fixed to a stationary shaft when subjected to torque in a first direction, yet rotating freely about the shaft when subjected to torque in a second direction, this stator comprising a stator shell, a stator core, and a plurality of stator blades distributed around the torque converter axis between the core and the shell, the blades being rotatable between an open position and a closed position, the blades blocking approximately 75% to 90% of an annular area between the shell and the core when in the closed position, an inlet angle of the blades being between approximately 30 degrees and 70 degrees in the closed position, with this angle varying inversely with the number of stator blades, with the closed position inlet angle and the area blocked being sufficient to diminish a flow of fluid from the turbine to the impeller so as to reduce torque converter torque transmitting capacity in the closed position by approximately 50% of the torque transmitting capacity of the torque converter with the stator blades in the open position. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a top half of a section of a torque converter in an open position. 
     FIG. 2 shows a stator having rotatable blades with the rotatable blades in the open position from the direction of Arrows 2 of FIG. 1. 
     FIG. 3 shows a stator having rotatable blades with the rotatable blades in the open position from the direction of Arrows 3 of FIG. 1. 
     FIG. 4 shows a stator having rotatable blades with the rotatable blades in the closed position from the direction of Arrows 2 of FIG. 1. 
     FIG. 5 shows a stator having rotatable blades with the rotatable blades in the closed position from the direction of Arrows 3 of FIG. 1. 
     FIG. 6 shows a plot of creep torque as a function of engine speed. 
     FIG. 7 shows a stator having alternate fixed and rotatable blades with the rotatable blades in the open position from the direction of Arrows 2 of FIG. 1. 
     FIG. 8 shows a stator having alternate fixed and rotatable blades with the rotatable blades in the open position from the direction of Arrows 3 of FIG. 1. 
     FIG. 9 shows a stator having alternate fixed and rotatable blades with the rotatable blades in the closed position from the direction of Arrows 2 of FIG. 1. 
     FIG. 10 shows a stator having alternate fixed and rotatable blades with the rotatable blades in the closed position from the direction of Arrows 3 of FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A three element fluid torque converter 10 has a bladed impeller or pump 12, a bladed turbine 14 and a bladed stator 16. The impeller 12 is rotatively fixed to the engine crankshaft (not shown) through a flex plate 17 in a conventional manner. The turbine 14 is rotatively fixed to a transmission input element 18. The stator 16 is rotatively fixed to a stationary shaft 20, when subjected to torque in a first direction, but rotates freely about the stationary shaft 20, when subjected to torque in a second direction. 
     The stator 16 is disposed in a flow path from the turbine 14 to the impeller 12. The stator 16 has a stator core 22 with a core surface 24 having a center 26 disposed on a torque converter axis 28. FIGS. 1-5 show the core surface 24 having a concave spherical shape. The stator 16 also has a stator shell 30 with a shell surface 32 disposed radially inward of the core surface 24 with the center thereof being disposed in common with the center 26 of the core surface 24. FIGS. 1-5 show the shell surface 32 having a convex spherical shape. 
     The stator 16 has fourteen stator blades 34 distributed around the torque converter axis 28 between the core surface 24 and the shell surface 32. The blades 34 each have a first edge surface 36 and a second edge surface 38 proximate to and complementary to the shell surface 32 and the core surface 24 respectively. Each blade 34 also has an axis of rotation 40 passing through the center 26 of the stator shell 30 and core 22. The blades 34 are rotatable between an open position, shown in FIG. 2 and FIG. 3, and a closed position, shown in FIG. 4 and FIG. 5. 
     In the closed position, the blades 34 block approximately 75% to 90% of an annular flow area 42 between the core 22 and the shell 30. The blades 34 also have a closed position inlet angle A, shown in FIG. 4, between the torque converter axis 28 and a line 43 from the axis of rotation 40 of the blades 34 through the tip of the blade 34. In the preferred embodiment, the angle A equals 64 degrees. The closed position inlet angle A is sufficiently large to diminish the flow of fluid from the turbine 14 to the impeller 12, thereby reducing torque converter transmitting capacity with the blades 34 in the closed position approximately 50% when compared with the torque transmitting capacity of the torque converter 10 when the stator blades 34 are in the open position. The difference in the torque transmitting capacity is shown in the plots in FIG. 6. 
     An open position inlet angle B of the blades 34, corresponding to the closed position inlet angle A, is shown in FIG. 2. 
     The torque transmitting capacity reduction results in low creep torque. The combination of using the inlet angle A and blocking of the flow area between the core 22 and the shell 30 being limited to 75% to 90%, results in appreciably less driveline noise and vibration when compared with a conventional variable pitch stator. 
     The rotation of the stator blades 34 is controlled by a rotary control assembly 44 which establishes the angular disposition of the stator blades 34 between the open and the closed positions. The rotary control assembly 44 includes an annular piston cylinder 46 integral with the stator core 22, an annular piston 48 axially aligned with the piston cylinder 46, a plurality of stator pivots 50--one for each stator blade 34, and a plurality of piston springs 58 disposed between the piston cylinder 46 and the piston 48. The rotary control assembly 44 biases the blades 34 toward the closed position. Fluid impinging on the stator blades 34 must overcome the bias to rotate the blades 34 to the open position. 
     The rotary control assembly 44 is largely disposed in a core void 52. The core void 52 is bounded by an impeller core 54, a turbine core 56 and the stator core 22. The piston cylinder 46 is principally disposed in the core void 52 as is the annular piston 48. The stator pivots 50 are rotatively fixed to the corresponding blades 34. The pivots 50 have a cam portion 60 and a shaft portion 62 which passes through the stator core 22, the blades 34 and the stator shell 30. The stator pivots 50 are rotatively supported by the stator core 22 and the stator shell 30. The cam portion 60 is disposed in the core void 52 contiguous with the annular piston 48. 
     The piston springs 58 between the piston cylinder 46 and the piston 48 press the piston 48 into contact with the pivot cam portions 60. The blades 34 are thus biased to the closed position. The stator blades 34 are rotated to the open position by fluid flow past the blades 34. The piston 48 is displaced by the cam portions 60 of the stator pivots 50 toward the piston cylinder 46. 
     A pair of double labyrinth seals or restrictions 64 impede fluid from moving into and out of the core void 52. One double labyrinth seal 64 is located between the turbine core 56 and the stator core 22. The other double labyrinth seal 64 is located between the stator core 22 and the impeller core 54. The double labyrinth seals 64 minimize fluid flow through the core void 52 to reduce fluid drag in the core void 52. 
     A torque converter clutch 66 rotatively couples and uncouples the impeller 12 and the turbine 14. 
     An alternative configuration of the variable pitch stator 16 has eighteen stator blades 34 with the closed position inlet angle A equaling 30 degrees. Other stator configurations with the number of blades 34 being between fourteen and eighteen are possible. The closed position inlet angle A for a particular stator will vary inversely with the number of stator blades 34, from approximately 30 degrees to 70 degrees. 
     In a second alternative configuration, shown in FIGS. 7-10, a stator 16 has seven rotatable blades 34 and seven fixed blades 68. The fixed blades 68 are located alternately with the rotatable blades 34. The closed position inlet angle A of the rotatable blades 34 is approximately 64 degrees. The fixed blades 68 are integral with both the stator shell 30 and the stator core 22. An inlet angle C of the fixed blades 68 is approximately equal to the inlet angle B of the rotatable blades in the open position. 
     The fixed blades 68 have a chord length W longer than a chord length X of the rotatable blades 34. The chord length is a distance from the tip to a tail of the blade. This longer chord length W enables the blades 34 and 68 to block 75% to 90% of the flow area 42 with the rotatable blades 34 in the closed position. The chord length X of the rotatable blades 34 is longer than it appears in FIGS. 7 and 9 because the axes of rotation 40 of the rotatable blades 34 are not parallel to the fixed blade 68 shown. 
     The fixed blades 68 increase the structural rigidity of the stator 16, thereby improving the durability of the stator 16. However, there seems to be an increase in difficulty in obtaining the 50% reduction in torque transmitting capacity as the number of fixed blades 68 relative to the number of rotatable blades 34 is increased. 
     As few as three fixed blades 68 provide an appreciable increase in stator stiffness. For such a stator, the fixed blades 68 would be distributed generally uniformly among a remainder of rotatable blades 34. 
     The stator shell surface 32 and stator core surface 24 are shown as having core flats 70 and shell flats 72 for interfacing with the blades 34 and 68, as opposed to the spherical surfaces shown in FIGS. 1 through 5. 
     As the engine speed is increased from idle, the force of the fluid impinging on the stator blades 34 also increases. The force on the blades 34 is transferred to the cam portions 60 through the shaft portions 62. The cam portions 60 press against the piston 48, displacing the piston 48 into the piston cylinder 46, thereby compressing the springs 58. As the piston 48 moves further into the cylinder 46, the blades 34 are able to rotate further toward the open position. 
     The effect on creep torque of the transition in blade position from closed to open is illustrated in FIG. 6. Torque is shown as a function of the rotative speed of the engine crankshaft to which the impeller 12 is rotatively locked. The turbine 14 is stalled. The torque level with the stator blades 34 locked in the closed position is less than half the torque levels with the stator blades 34 locked in the open position. The stator blades 34, when not locked, make the transition from the closed to the open position between 800 and 1200 rpm. 
     As with a conventional fixed blade stator, the variable pitch stator 16 is rotatively fixed to the stationary shaft 20 when the rotative speed of the impeller 12 is significantly greater than that of the turbine 14. This is the case when the turbine 14 is stalled. Fluid exiting the turbine 14 impinges on the stator blades 34 at an angle resulting in a rotative force being applied to the stator 16 in the first direction opposite the direction of rotation of the impeller 12, thereby rotatively fixing the stator 16 to the stationary shaft 20. When the turbine 14 is allowed to rotate, its rotative speed approaches that of the impeller 12. The direction of fluid exiting the turbine 14 is shifted to produce a rotative force on the stator 16 in the second direction, the direction of rotation of the impeller 12 and turbine 14, thereby rotating the stator 16 relative to the stationary shaft 20 in the second direction. 
     An increased harshness of clutch 66 coupling and uncoupling has been perceived with previous variable pitch stators. The present invention is effective at minimizing any such harshness. 
     Obviously, many modifications and variations of the present invention are possible in light of the above teaching. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.