Abstract:
A method of dynamically controlling pressure to a torque converter clutch (TCC) of a torque converter coupled to a transmission is provided. The method includes: monitoring throttle position; monitoring engine speed; controlling pressure to the torque converter clutch to increase slip after the throttle position indicates a tip-in has occurred and when engine speed is low; regulating at least one of a transmission steady state pressure to the transmission and pressure to the torque converter to maintain the increased slip; and controlling pressure to the torque converter to reduce slip by engaging the torque converter clutch.

Description:
FIELD 
     The present disclosure relates to methods and systems for controlling a torque converter clutch. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Automatic transmissions use a fluid clutch known as a torque converter to transfer engine torque from the engine to the transmission. The torque converter operates through hydraulic force provided by pressurized fluid from the automatic transmission. The torque converter multiplies engine torque and directs it through the transmission. 
     A conventional torque converter includes a sealed chamber filled with hydraulic fluid. The chamber includes a pump (or impeller) driven by the engine, a turbine connected to an output shaft, and a stator that provides torque multiplication. As the impeller rotates, the centrifugal force pushes the pressurized fluid outward, causing the turbine to rotate. Fluid exiting the turbine strikes the stator. Blades of the stator act to reverse the radial direction of the fluid&#39;s motion so that the fluid is moving the same direction as the impeller when it reenters the impeller chambers. This reversal of direction greatly increases the efficiency of the impeller. The force of the fluid striking the stator blades also exerts torque on the turbine output shaft, providing additional torque multiplication equivalent to a higher numerical gear ratio. 
     A torque converter is said to “slip” when the impeller speed and the turbine speed are not equivalent. High slip rates reduce the efficiency of the torque converter and may generate excessive heat. Some converters incorporate a lockup mechanism such as a mechanical clutch that engages at cruising speeds to physically link the impeller with the turbine. The physical link causes the impeller and the turbine to rotate at the same or near the same speed, thereby reducing or eliminating slip. The clutch is applied and released via fluid supplied through a hollow shaft at the center axis of the rotating converter assembly. 
     Engaging the torque converter clutch is not desirable in all modes of vehicle operation. Lockup conditions prevent the torque converter from providing torque multiplication. Instances may occur, for example, when driving along the highway and the driver steps on the accelerator pedal to pass another vehicle (referred to below as a throttle tip-in). The vehicle is operating in a higher gear with low engine speed (i.e. less than 2000 rpm) and the torque converter clutch is locked. If the current speed is above the requisite speed to initiate a downshift, the engine will remain at the low speed and the lockup will prevent torque transfer that is sufficient to accelerate the vehicle. 
     SUMMARY 
     Accordingly, a method of dynamically controlling pressure to a torque converter clutch (TCC) of a torque converter coupled to a transmission is provided. The method includes: monitoring throttle position; monitoring engine speed; controlling pressure to the torque converter clutch to increase slip after the throttle position indicates a tip-in has occurred and when engine speed is low; regulating at least one of a transmission steady state pressure to the transmission and pressure to the torque converter to maintain the increased slip; and controlling pressure to the torque converter to reduce slip by engaging the torque converter clutch. 
     In other features, a dynamic torque converter clutch control system, for torque converters coupled to a transmission is provided. The system includes: a dynamic mode module that selects a current mode from an inactive mode, a target determination mode, a pressure regulation mode, and a pressure correction mode; a target determination module that determines target values for engine speed, engine torque and slip error based on the current mode and throttle position; and a torque convert clutch pressure control module that controls pressure to the torque converter clutch based on the current mode and the target values for engine speed, engine torque, and slip error. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a functional block diagram of a vehicle including a conventional torque converter system. 
         FIG. 2  is a dataflow diagram illustrating the torque converter clutch (TCC) dynamic control system. 
         FIG. 3  is a graph illustrating modes of the TCC dynamic control system. 
         FIG. 4  is a state transition diagram illustrating the transitions between modes of the TCC dynamic control system. 
         FIG. 5  is a table that lists conditions for each TCC dynamic control transition. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. As used herein, the term module refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
       FIG. 1  illustrates a vehicle  10  that includes a conventional torque converter system. An engine  12  combusts an air and fuel mixture to produce drive torque. Air is drawn into an intake manifold  14  through a throttle  16 . The throttle  16  regulates mass air flow into the intake manifold  14 . Air within the intake manifold  14  is distributed into cylinders  18 . Although six cylinders  18  are illustrated, it can be appreciated that the engine can have a plurality of cylinders including, but not limited to, 2, 3, 5, 6, 8, 10, 12 and 16 cylinders. 
     Torque from the engine  12  is supplied to a transmission  20  through a torque converter (TC)  22 . The torque converter may be any known lockup converter including a turbine, a stator, and a torque converter clutch (TCC). The transmission includes a hydraulic pump  26  that regulates pressurized fluid within the transmission and controls fluid flow to and from the TC  22  via at least one solenoid-operated valve  30 . The engine  12  drives the hydraulic pump  26 . A current and/or pulse width modulated signal is commanded by a controller  32  to the solenoid in order to vary the supply of pressurized fluid to the torque converter  22 . A slip rate of the TC  22  is varied based on control of the pressurized fluid. 
     The controller  32  determines the appropriate signal based on inputs received from the TC  22 , the engine  12 , and the transmission  20 . Inputs to the controller  32  may include: an engine speed signal received from an engine speed sensor  34 ; a turbine speed signal received from a turbine speed sensor  36 ; a throttle position signal received from a throttle position sensor  38 , and a transmission oil temperature signal received from a transmission oil temperature sensor  40 . During normal operating conditions, the controller  32  determines the appropriate pressure to be supplied to the TC  22  based on conventional methods and commands the signal to the solenoid  30  accordingly. During low engine speed conditions (i.e. less than 2000 RPM) after a throttle tip-in occurs, the controller commands the signal to the solenoid  30  according to the TCC dynamic control method of the present disclosure. 
     Referring to  FIG. 2 , a dataflow diagram illustrates various embodiments of a TCC dynamic control system  44  that implements the TCC dynamic control method. The TCC dynamic control system operates to command hydraulic pressure to the TCC. More specifically, the dynamic control system operates to apply the TCC via the pressurized fluid at low engine speeds (i.e. less than 2000 rpm) and after throttle tip-in operating conditions occur. Various embodiments of TCC dynamic control systems according to the present disclosure may include any number of sub-modules embedded within the controller  32  of  FIG. 1 . 
     In various embodiments, the TCC dynamic control system  44  of  FIG. 2  includes a dynamic mode module  46 , a target determination module  48 , a TCC pressure control module  50 , and a steady state (SS) pressure control module  52 . The sub-modules shown may be combined and/or further partitioned to provide similar control of hydraulic pressure to the TC  22 . After throttle tip-in conditions occur, the modules act collectively to control TCC pressure  56  to increase TCC slip, regulate a transmission steady state pressure  54  and TCC pressure  56  to control the higher slip, and then control TCC pressure  56  to reduce slip to meet the TCC on mode requirements. 
     In order to control slip in this manner, the TCC dynamic control system  44  transitions through a plurality of modes. The dynamic mode module  46  determines a current mode  57  based on inputs such as throttle position  58 , engine speed  60 , transmission temperature  62 , turbine speed  64 , and a TCC mode request  66 . The current mode  80  can be at least one of an inactive mode, a target determination mode, a maintain mode, a pressure correction mode, and a pressure regulation mode. Based on the current mode, the target determination module  48  determines a target value for engine speed  68 , slip error  70 , and engine torque  72 . Each target valve is determined based on an evaluation of throttle position  58 . The target values ( 68 – 72 ) and the current mode  57  are used by the TCC pressure control module  50  and the SS pressure control module  52  to control hydraulic pressure to the torque converter  22  ( FIG. 1 ) and the transmission  20  ( FIG. 1 ) respectively. 
     The TCC pressure control module  50 , more specifically, calculates a dynamic TCC pressure  56  as a function of target engine torque  72  and target engine speed  68 . When in the target determination mode, TCC pressure is set equal to a minimum of the dynamic TCC pressure and the TCC pressure estimated for normal conditions. When in the maintain mode, TCC pressure remains equal to the dynamic TCC pressure calculated at the transition into the maintain mode. When in the pressure correction mode, TCC pressure is set equal to the dynamic TCC pressure. When in the TCC pressure regulation mode, TCC pressure is set equal to the dynamic TCC pressure plus a ramp offset. The ramp offset is determined based on the target slip error  70 . 
     The SS pressure control module  52  determines a SS pressure  54  to be supplied to the transmission  20  ( FIG. 1 ). When in the target determination mode, the maintain mode, and the pressure correction mode, the SS pressure  54  is set to a maximum of a plurality of determined values. The SS pressure  54  can be set equal to the maximum of a determined steady state pressure, a steady state line pressure at time T−1, a base pressure plus a throttle modifier, and a base pressure plus a TCC throttle modifier. When in the pressure regulation mode, the SS pressure  54  is determined by the following two steps: during time T 1  SS pressure  54  equals the SS pressure determined at the transition to the TCC pressure regulation mode; during time T 2  SS pressure  54  is decreased according to a determined time ratio. 
     Referring to  FIG. 3  in view of  FIG. 2 , a graph illustrates the various modes of the TCC dynamic control system  44  and their sequential execution. The current mode is illustrated along the y-axis at  80 . Time is illustrated along the x-axis at  82 . TCC dynamic operation begins in the inactive mode  84 . While in the inactive mode  84  TCC operation is controlled based on conventional TCC control methods. From the inactive mode  84 , TCC dynamic operation transitions to the target determination mode  86  upon which the target determination module  48  determines target values for controlling TCC pressure. Based on the target values, the TCC pressure control module  50  commands TCC pressure such that slip is increased. 
     From the target determination mode  86 , TCC dynamic operation transitions to the maintain mode  88 . In the maintain mode  88 , TCC pressure control module  50  commands the TCC pressure determined in the target determination mode in order to maintain the increased slip. The higher slip will increase torque output. Thus, causing the engine to accelerate according to the throttle tip-in request (high TCC slip leads to low hydraulic torque). From the maintain mode  88 , TCC dynamic operation may transition to the pressure correction mode  90  or the pressure regulation mode  92 . The pressure correction mode  90  is optional. The pressure correction mode  90  is activated to allow the TCC pressure control module  50  to correct TCC pressure based on a comparison of actual engine torque  94  and target engine torque  72 . If the actual engine torque  94  is greater than target engine torque  72 , the TCC pressure control module  50  commands TCC pressure such that slip is reduced. While in the pressure regulation mode  92 , the TCC pressure control module  50  controls TCC pressure such that slip is reduced over time, until static regulation is reached. This causing a progressive acceleration of the vehicle. 
     Referring now to  FIGS. 4 and 5 , the dynamic mode module  46  of  FIG. 2  determines when to transition between the five modes. The transitions are governed by a rule set including a plurality of conditions. A first transition occurs between the inactive mode  84  and the target determination mode  86  labeled as A in  FIG. 4 . Control transitions from the inactive mode  84  to the target determination mode  86  based on throttle position, transmission temperature, and engine speed. Table 1 of  FIG. 5  lists conditions for transitioning from the inactive mode to the target determination mode. 
     The filtered throttle gradient listed in Table 1 is determined from the following equation: 
                     TG   Filt     =         (       K   ⁢           ⁢   1   *   TG     +     K   ⁢           ⁢   2   *     TG   prev         )       (       K   ⁢           ⁢   1     +     K   ⁢           ⁢   2       )       .             (   1   )               
K1 and K2 are predetermined constants. TG is a throttle gradient calculated based on throttle position at time T (T T ) and throttle position at time T−1 (T T−1 ) and the following equation:
 
                   TG   =           T   T     -     T     T   -   1           Loop   ⁢           ⁢   Rate       .             (   2   )               
TG prev  is a previously calculated throttle gradient.
 
     A second transition occurs between the target determination mode  86  and the maintain mode  88  labeled as B in  FIG. 4 . Control transitions from the target determination mode  86  to the maintain mode  88  based on time, throttle position, and engine torque. Table 1 of  FIG. 5  lists conditions for transitioning from the target determination mode  86  to the maintain mode  88 . 
     A third transition occurs between the maintain mode  88  and the pressure regulation mode  92  labeled as C in  FIG. 4 . Control transitions from the maintain mode  88  to the pressure regulation mode  92  based on time, throttle position, and engine speed. Table 1 of  FIG. 5  lists exemplary conditions for transitioning from the maintain mode  88  to the pressure regulation mode  92 . A fourth transition occurs between the pressure regulation mode  92  and the inactive mode  84  labeled as D in  FIG. 4 . Control transitions from the pressure regulation mode  92  back to the inactive mode  84  based on slip error, throttle position, engine speed, turbine speed, and a TCC On mode request. Table 1 of  FIG. 5  lists conditions for transitioning from the pressure regulation mode  92  to the inactive mode  84 . 
     A fifth optional transition occurs between the maintain mode  88  and the pressure correction mode  90  labeled as E in  FIG. 4 . Control may transition from the maintain mode  88  to the pressure correction mode  90  based on time and engine speed. Table 1 of  FIG. 5  lists conditions for transitioning from the maintain mode  88  to the pressure correction mode  92 . A sixth transition occurs between the pressure correction mode  90  and the pressure regulation mode  92  labeled as F in  FIG. 4 . Control transitions from the pressure correction mode  90  to the pressure regulation mode  92  based on throttle position and engine speed. Table 1 of  FIG. 5  lists conditions for transitioning from the pressure correction mode  90  to the pressure regulation mode  92 . 
     As can be appreciated, all comparisons made in Tables 1 of  FIG. 5  can be implemented in various forms depending on the selected values for the minimums, the maximums, the ranges, and the threshold values. For example, a comparison of “greater than” may be implemented as “greater than or equal to” in various embodiments. Similarly, a comparison of “less than” may be implemented as “less than or equal to” in various embodiments. A comparison of “within a range” may be equivalently implemented as a comparison of “less than or equal to a maximum threshold” and “greater than or equal to a minimum threshold” in various embodiments. 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present disclosure can be implemented in a variety of forms. Therefore, while this disclosure has been described in connection with particular examples thereof, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification, and the following claims.