Abstract:
A controllable hydrodynamic torque converter is provided for use within a vehicle having a detectable throttle level, the torque converter comprising a first stator having a first outlet angle and a second stator having a higher second outlet angle. The second stator is selectively engageable with the first stator using a hydraulic clutch to thereby vary the torque converter K-factor during idle and high-throttle conditions, and is permitted to freewheel during low or part throttle conditions. The first outlet angle is at least five degrees lower than the second outlet angle. A vehicle is also provided including an engine having an engine torque and a detectable throttle level, a transmission, a torque converter operable to transmit the engine torque to the transmission and having a stator assembly with two stators, a selectively controllable clutch, and a controller configured to selectively actuate the clutch to vary the K-factor depending on the throttle level.

Description:
TECHNICAL FIELD 
     This invention relates generally to a controllable hydrodynamic torque converter, and in particular to a hydrodynamic torque converter having two controllable stators configured with different outlet angles for selectively varying the torque converter K-factor. 
     BACKGROUND OF THE INVENTION 
     Automatic power transmissions used in modern vehicles typically utilize a multi-function turbomachine or device commonly referred to as a hydrodynamic torque converter. A hydrodynamic torque converter is used to automatically disengage a rotating engine crankshaft from a transmission input shaft during vehicle idling conditions to enable the vehicle to stop and/or to shift gears without stalling. Additionally, the torque converter is used as a torque multiplier for multiplying engine torque in the lower vehicle speed range until the vehicle speed nearly matches the engine speed. 
     Within a torque converter, a number of specially constructed internal components combine to enable an efficient fluid coupling effect between the disparately rotating engine and transmission shafts. In particular, a standard or conventional torque converter consists of an engine-driven pump or impeller, which is the driving member of the torque converter giving impetus to a stream of hydraulic fluid. The pump is connected to the engine crankshaft and therefore rotates in unison with the engine, thereby accelerating a supply of hydraulic fluid and directing the accelerated fluid to the second component, the turbine. The turbine, which is driven by the accelerated fluid discharged by the pump, is typically splined to a transmission input shaft and converts the fluid energy imparted by the fluid stream into useable mechanical energy, which is transmitted to the splined transmission input shaft to propel the vehicle. Finally, a stationary member or stator is included within the torque converter for redirecting the fluid stream between the pump and turbine. The stator is connected to a fixed reaction shaft through a one-way clutch that allows the stator to free-wheel when torque multiplication is no longer possible. 
     Torque converters are designed to slip at lower vehicle speeds in order to enable the transmission to rotate at a slower rate than the coupled engine, with the slip rate gradually diminishing as the vehicle is accelerated. Effectively, the torque converter holds the engine speed nearly constant, allowing the transmission speed to gradually reach or approach the engine speed as the vehicle accelerates. The torque converter input speed, identical with the engine speed and stated in revolutions per minute, is an important design factor that is substantially affected by the outlet angle of the stator. The outlet angle is primarily determined by the configuration or construction of a plurality of stator blades within the stator. However, the torque converter input speed depends in large part on the engine output torque, and therefore a more descriptive variable, the “K-factor”, is usually used to rate or describe an individual torque converter. K-factor refers to the input speed divided by the square root of the engine torque, as measured at any torque converter operating point. The operating point of a torque converter is most conveniently defined by the ratio of the output speed to the input speed of the torque converter. This parameter or variable is known as the torque converter speed ratio. 
     Vehicle fuel economy and performance is enhanced when the operating or performance characteristics of a given torque converter are automatically optimized. While a variable-blade angle stator may be used, wherein individual piston-actuated stator blades are allowed to pivot on shafts running from shell to core in order to adjust the stator blade position and angle, such variable designs tend to be intricate and therefore may be less than optimal due in part to their relative cost and complexity. 
     SUMMARY OF THE INVENTION 
     Accordingly, a controllable hydrodynamic torque converter is provided for use within a vehicle, the torque converter having two stators each configured with a different outlet angle, with the second stator being selectively engageable with respect to the first stator for varying the torque converter K-factor depending on throttle position. 
     In one aspect of the invention, the second stator is selectively engageable using a clutch when the detectable throttle level is idle or high-throttle. 
     In another aspect of the invention, the first outlet angle of the first stator is at least 5 degrees less than the second outlet angle of the second stator, with the first outlet angle selected from the range of 10 to 65 degrees, and the second outlet angle selected from the range of 25 to 75 degrees. 
     In another aspect of the invention, a vehicle is provided having an engine having an engine torque and a detectable throttle level, a transmission, a torque converter operable to transmit the engine torque to the transmission and also having a stator assembly with first and second stators, a selectively controllable clutch, and a controller configured to selectively actuate the clutch depending on the detected vehicle throttle level, wherein actuation of the clutch locks the first and second stators to thereby vary the K-factor of the torque converter. 
     The above objects features and advantages, and other objects, features and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic plan view of a vehicle having a controllable dual-stator, variable K-factor torque converter according to the invention; 
         FIG. 2  is cutaway side view of the torque converter of the invention; 
         FIG. 3  is a schematic representation of low and high angle stator blades usable with the variable K-factor torque converter of the invention; 
         FIG. 4  is a performance curve of a low K-factor and a high K-factor torque converter; and 
         FIG. 5  is a table describing the three vehicle operating modes or throttle positions in relation to the operation of clutch and dual stators of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , wherein like reference numerals refer to like components, a vehicle  10  is shown having a plurality of wheels  26  disposed or positioned on a pair of axles  22  and  24 , an engine or energy conversion system  12 , a hydrodynamic torque converter  14 , and a power transmission  16  having a rotatable input member (not shown) and a rotatable output member  18 . The energy conversion system  12  is preferably a gasoline or diesel internal combustion engine of the type known in the art, and is operable to generate a rotational force or torque suitable for rotating a crankshaft (not shown) that is selectively connectable or engageable with the input shaft of transmission  16  through the torque converter  14 . However, any energy conversion capable of powering the vehicle  10  is also useable with the invention, for example fuel cells. 
     By means of the torque converter  14 , torque from the energy conversion system is smoothly transferred to the transmission  16 , and ultimately to the wheels  26  for propulsion of the vehicle  10 . The torque converter  14  is preferably automatically controllable using a controller  30 , preferably part of an on-board transmission control system also configured to detect a throttle position or level represented in  FIG. 1  as “T” and in  FIG. 5  as “throttle position”, and adapted to selectively engage the energy conversion system  12  with the input shaft (not shown) of transmission  16  while also acting as a torque multiplier as needed, particularly at low or reduced vehicle speeds, as explained in more detail hereinbelow. 
     Depending on whether a front-wheel, rear-wheel, or all-wheel drive configuration is used, one or both axles  22  and  24  may be further adapted for use as drive axles suitable for powering the vehicle  10 . To this end, a front and/or rear differential  20 F,  20 R, respectively, may be employed for transmitting output torque from the transmission  16  to either or both of the axles  22 ,  24 , and/or for distributing output torque along a common axle  22  or  24 , for example to prevent slippage on slippery pavement or while the vehicle  10  is cornering. 
     Turning to  FIG. 2 , the hydrodynamic torque converter  14  of the invention is shown in cutaway side view having an outer shell or cover  32  that is bolted, welded, or otherwise rigidly attached or connected to an engine flexplate (not shown), preferably using a lag  23 , and having a centerline of rotation  11 . The engine flexplate is ultimately attached to the engine crankshaft (not shown). The torque converter  14  includes an impeller or pump  50 , a turbine  52  having a hub  33 , and a stator assembly  44  selectively connectable to a fixed stator shaft (not shown) by means of a one-way clutch  19 . The one-way clutch  19  is operable to hold torque in one direction, and may take the form of, for example, a mechanical diode, latch, or other suitable one-way clutching device. The pump  50  includes a pump housing  34  that is rigidly connected to the torque converter cover  32 , preferably using a lag  21  or other suitable faster device or fastening method such as welding so that the pump  50  rotates in conjunction with and at the rate of the energy conversion system  12  (see  FIG. 1 ). Torque converter  14  preferably includes a mechanical lock-up clutch  27  (see  FIG. 2 ) for selectively directing power from the energy conversion system  12  to the transmission  16  when torque converter function is not desired, for example during periods of relatively high vehicle speeds. Cover  32  and housing  34  may be constructed using any suitable combination of ferrous and/or non-ferrous materials, depending on the design requirements. 
     As the pump  50  rotates in conjunction with the energy conversion system  12 , a fluid  15  such as hydraulic oil or other suitable fluid is accelerated by and through the pump  50  and discharged or expelled into the turbine  52 . The turbine  52  is operatively connected to a transmission input shaft (not shown) by means of a splined turbine hub  33 , and configured to convert the fluid energy imparted by fluid  15  discharged from pump  50  into mechanical energy suitable for driving or rotating the transmission input shaft. This conversion to mechanical energy is enhanced when the blades (not shown) of turbine  52  are configured to discharge fluid  15  with rotational velocity opposite that of the pump  50 . A stator assembly  44  is positioned between the inlet  71  of the pump  50  and the outlet  72  of the turbine  52  to receive fluid  15  discharged from the turbine  52  and conduct or redirect it back to the inlet of pump  50 . Stator assembly  44  is further configured to variably and controllably redirect the fluid  15  flowing between the pump  50  and the turbine  52  imparting more or less rotational velocity in the direction of that of the pump  50 , thereby improving the efficiency of the torque converter  14  and increasing torque multiplication. 
     Stator assembly  44  includes a first stator  45 , a second stator  46 , and a clutching mechanism or clutch  40 , with first and second stators  45  and  46  being selectively and automatically engageable or connectable with respect to each other as needed using the clutch  40 . First stator  45  is operatively connected to a fixed stator shaft (not shown) by means of a one-way clutch  19 , which allows the stator assembly  44  to automatically freewheel when redirection of fluid  15  is not necessary. Clutch  40  is preferably a controllable, hydraulically-actuated piston or other suitable clutching device adapted to selectively engage, lock, or join together the first and second stators  45  and  46  in order to controllably and variably redirect fluid  15  between pump  50  and turbine  52  to thereby affect the performance of torque converter  14 , as explained in more detail hereinbelow. 
     In accordance with the invention, fluid  15  flowing through the stator assembly  44  passes through the first stator  45 , and subsequently through the second stator  46 . The fluid  15  entering stator assembly  44  is forced to change direction and, upon exiting the first stator  45 , enters the second stator  46  flowing in the same rotational direction as the pump  50 . Depending on the position or actuation status of clutch  40 , the fluid  15  may be forced to a higher speed of rotation in the same direction as pump  50 , thereby conserving more or less power. 
     Clutch  40  is preferably powered or actuated by the pressurized fluid at  17  that is isolated or separate from fluid  15  and fed to the clutch  40  through an internal fluid passage or channel  48  from a controllable pressure source, such as a positive displacement pump (not shown) or other suitably controllable pressure source. Channel  48  is preferably cylindrical in shape and substantially circular in cross-sectional area, and adapted to efficiently conduct or direct oil or other hydraulic fluid, and may take the form of, for example, various die or sand cast channels or passages. 
     Turning now to  FIG. 3 , the plurality of first and second stator blades  60  and  62 , respectively, are shown in developed sections. Stator blades  60  are disposed within the first stator  45 , and stator blades  62  are disposed within the second stator  46 . Each of the blades  60 ,  62  are configured to substantially reverse the direction of rotation of the fluid  15  upon entering the stator assembly  44 . Fluid  15  flowing through the stator assembly  44  (see  FIG. 2 ) passes through the first stator  45  and is acted on by the blades  60 . Fluid  15  upon leaving or exiting stator  45  passes through stator  46 . When clutch  40  is actuated or engaged, the fluid  15  is acted upon by blades  62 . When clutch  40  is not actuated or engaged, blades  62  are released and are allowed to freewheel with negligible effect on the fluid  15 . When the fluid  15  is acted upon by the blades  60 , it is redirected in accordance with the geometry and construction of the blades  62 . 
     In accordance with the invention, blades  60  and  62  have different respective geometrical sections and physical features that are selected to optimize the performance of the torque converter  14  under different vehicle operating conditions, for example, during idling, light-to-moderate or low/part throttle, and heavy throttle. Stator blades  60  of first stator  45  are constructed or configured to provide a relatively low fluid outlet angle, denoted as “L” for “low” herein and represented in  FIG. 3  as θ L . Likewise, stator blades  62  of second stator  46  are constructed or configured to provide a relatively high fluid outlet angle, denoted as “H” for “high” herein and represented in  FIG. 3  as θ H . Stator blades  62  of second stator  46  are preferably constructed or configured so as to admit fluid  15  discharged or expelled from first stator  45  at substantially the same angle, i.e. θ L , thereby minimizing losses and improving efficiency. In other words, the inlet angle of the second stator should match the outlet angle of the first stator. Once admitted into the second stator  46 , the fluid  15  is redirected at the relatively high outlet angle θ H , with the terms “relatively low/high” referring to the angular relationship between the variables θ L  and θ H . 
     Turning now to  FIG. 4 , which shows a representative set of curves  70  that collectively describe torque converter efficiency, torque ratio, i.e. the output torque divided by the input torque, and K-factor, as explained previously hereinabove, in terms of its speed ratio, i.e. the output speed divided by the input speed. In general terms, if the outlet angle of a stator is relatively high, such as with θ H  of blades  62  (see  FIG. 3 ), the torque converter  14  will have a proportionately higher K-factor. Such a torque converter is also referred to as a “loose” torque converter or, said differently, a loose converter has a relatively high K-factor. Loose torque converters also generally multiply torque to a relatively high speed ratio. Loose torque converters generally reduce fuel consumption at idle by reducing the amount of engine power absorbed by the torque converter as a consequence of the relatively high K-factor, while enhancing vehicle performance by multiplying torque to a higher vehicle speed. 
     Conversely, if the outlet angle of a stator is relatively low, such as with θ L  of blades  60 , the K-factor will also be relatively low. Such a torque converter is also referred to as a “tight” converter, i.e. one having a low K-factor. Tight torque converters improve fuel economy during part throttle acceleration by reducing engine speed as a consequence of the relatively low K-factor. Accordingly, loose and tight torque converters are each optimal under different underlying vehicle operating conditions. 
     As shown in  FIG. 4 , the set of performance curves denoted with the subscript “L” describe the general performance of a “loose” torque converter, and the set of performance curves denoted with the subscript “T” describe the general performance of a “tight” torque converter, as described previously hereinabove. Referring to  FIGS. 1 ,  4 , and  5 , during mode  1 , i.e. when the throttle position or level T (see  FIG. 1 ) as detected by the controller  30  indicates a vehicle “idle” condition, clutch  40  is automatically actuated or engaged (i.e. “X” in  FIG. 4 ), thereby locking the second stator  46  with respect to the first stator  45 . The variable K-factor of stator assembly  44  is increased to the value of the “loose” or L-curve (see  FIG. 4 ), reducing the idle fuel consumption of the energy conversion system  12 . 
     During mode  2 , i.e. when the throttle position or level T indicates light or low/part throttle driving conditions, the clutch  40  is released or disengaged, thereby permitting the second stator  46  to rotate freely or freewheel without effect. In other words, the torque converter  14  will operate as if second stator  46  were not present, thus performing as a tight converter along the “T” curve collectively described by Torque Ratio T , Efficiency or E T , and K-Factor T  in  FIG. 4 . The energy conversion system  12  (see  FIG. 1 ) will operate at a reduced speed, thereby decreasing the engine brake specific fuel consumption (BFSC) and increasing fuel economy. 
     Finally, during mode  3 , i.e. when the throttle position or level T indicates a “high” throttle driving condition, clutch  40  is once again engaged to lock the second stator  46  with the first stator  45 , resulting in the torque converter  14  once again operating on the “loose” or L-curve. Vehicle  10  will then accelerate at a faster rate due to the higher torque multiplication afforded by the torque ratio L-curve at high speed ratios and the additional engine power permitted by the higher engine speed as a consequence of the higher K-factor L-curve. In this manner, torque converter  14  performance is optimized as the torque converter  14  is permitted to operate at its most efficient point across all three modes or throttle positions, levels, or conditions. 
     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.