Abstract:
A method for adaptively learning clutch volumes and fill level to compensate for build tolerances and clutch wear includes increasing a fill level of a clutch during an oncoming fill phase of a clutch to clutch transmission. A state of a regulator valve of the clutch to clutch transmission is monitored during the oncoming fill phase. Fill level of the clutch is adjusted before a next shift based on whether the regulator valve switches from a regulating state to a full feed state before elapse of a valid shift time.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention generally relates to electronic control of vehicle clutch systems, and more particularly to a control system and method for adapting oncoming clutch volume and fill level in a clutch to clutch transmission.  
       BACKGROUND OF THE INVENTION  
       [0002]     Conventional transmission control systems use a one way clutch or mechanical diode as an offgoing element to transfer torque through a powertrain. In these systems, release is controlled through a rate of an on-coming element during a shift. System compliant devices such as accumulators, wave plates, and orifices have been employed with line pressure control for shift feel to control the rate of the oncoming element. This system has physically prevented occurrence of tie-up or flare that cause undesired output torque disturbances. This system, however, is not suitable for use in a clutch to clutch transmission.  
         [0003]     A clutch to clutch transmission reduces hardware cost and envelope size by removing the mechanical system compliant devices and diodes. An electronic control system controls the oncoming and offgoing elements precisely to avoid flare and tie-up.  
       SUMMARY OF THE INVENTION  
       [0004]     In accordance with the present invention, a method for adaptively learning clutch volumes and fill level to compensate for build tolerances and clutch wear includes increasing a fill level of a clutch during an oncoming fill phase of a clutch to clutch transmission. A state of a regulator valve of the clutch to clutch transmission is monitored during the oncoming fill phase. Fill level of the clutch is adjusted before a next shift based on whether the regulator valve switches from a regulating state to a full feed state before elapse of a valid shift time.  
         [0005]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0007]      FIG. 1  is a functional block diagram of an exemplary vehicle transmission system according to the present invention;  
         [0008]      FIG. 2  is a flow diagram depicting steps of the method according to the present invention;  
         [0009]      FIGS. 3 and 4  are flow diagrams depicting switch event detection in accordance with the present invention;  
         [0010]      FIG. 5  is a flow diagram depicting evaluation of detected and recorded switch events to establish and record reasons for adapting clutch fill level;  
         [0011]      FIG. 6  is a flow diagram depicting evaluation of detected and recorded switch events to establish and record reasons for adapting estimated clutch volume;  
         [0012]      FIG. 7  is a flow diagram depicting determination of what to adapt with respect to one or more reasons for one or more adaptations in accordance with the present invention;  
         [0013]      FIG. 8  is a flow diagram depicting update of adaptive parameters to increase or decrease clutch fill level before a next shift in accordance with the present invention;  
         [0014]      FIGS. 9A and 9B  are a flow diagram depicting update of adaptive parameters to adjust clutch volume level in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]     The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar components.  
         [0016]     Referring now to  FIG. 1 , an exemplary automatic transmission  10  includes a torque converter  12 , a plurality of gear sets  14   a ,  14   b , hydraulically- actuated multiple clutches  16   a ,  16   b , a transmission control system  18 , and a hydraulic pump  20 . The hydraulic pump  20  may be driven by the engine or an electric motor. The torque converter  12  enables start-off, provides torque multiplication, and absorbs harmonic vibrations within the vehicle drivetrain.  
         [0017]     The gear sets  14   a ,  14   b  are located between an input shaft  22 , which is connected to the torque converter  12 , and an output shaft  24 . The gear sets  14   a ,  14   b  enable the output shaft  24  to be driven at multiple gear ratios. The transmission control system  18  selectively engages the multiple clutches  16   a ,  16   b . The hydraulic pump  20  supplies hydraulic fluid pressure for valve body and shift components and/or for the torque converter  12 .  
         [0018]     The transmission control system  18  defines gear selection and shift points and regulates demand-response shifting. Demand-response shifting is based on a shift program that is selected by the driver using a selector  26 , a position of an accelerator  28 , engine operating conditions, and/or vehicle speed. The transmission control system  18  is generally a combined hydraulic and electric system. The transmission control system  18  hydraulically actuates the clutches  16   a ,  16   b . The transmission control system  18  actuates gear selection and modulates the clutch pressure electronically in accordance with the torque flowing through the transmission  10 .  
         [0019]     The transmission control system  18  includes a controller  30  that communicates with a plurality of sensors. A speed sensor  32  monitors engine speed and a position sensor  33  monitors selector-lever position. Load sensors  35  and speed sensor  37  monitor the torque converter load and the rotational.speed of the output shaft  24 , respectively. The controller  30  adjusts analog or digital pressure regulators  36  to control clutch pressure.  
         [0020]     Shift-quality depends upon the accuracy that the pressure of the clutches  16   a ,  16   b  is adjusted to the level of torque transmitted. The level of torque transmitted is estimated based on engine load and output shaft speed. As the automatic transmission shifts gear ratios, one clutch gradually disengages (i.e. is off-going) as another clutch gradually engages (i.e. is on-coming). The decrease and increase of pressure of the off-going and on-coming clutches, respectively, determines the operator&#39;s feel.  
         [0021]     Shifting between gear ratios occurs in two distinct phases: a torque phase and an inertia phase. During the torque phase, the speed of the input shaft  22  from the torque converter  12  remains constant. During the inertia phase, there is a response to the shift and the input shaft  22  changes speed. For an up-shift, the speed is decreased. For a down-shift, the speed is increased.  
         [0022]     In operation, a first gear  40  of the first gear set  14   a  is initially coupled to the input shaft  22  to drive the output shaft  24  at a first gear ratio. When an up-shift is signaled by the controller  30 , the clutch  16   a  gradually decreases engagement of the first gear  40  with the input shaft  22  (i.e. is off-going). The second clutch  16   b  gradually increases engagement of a second gear  42  of the second gear set  14   b  with the input shaft  22  (i.e. is on-coming). Eventually, the first clutch  16   a  completely disengages the first gear  40  from the input shaft  22  and the second clutch  16   b  couples the second gear  42  with the input shaft  22  to drive the output shaft  24  at a second gear ratio.  
         [0023]     The oncoming phase for a clutch may further be divided into an oncoming fill phase and an oncoming torque phase. The present invention in part operates by detecting when the regulating valve switches to full feed. In a preferred embodiment, the present invention also detects switch from an oncoming fill phase to an oncoming torque phase by detecting when the regulator valve switches from the full feed state to the regulating state. Thus, hydraulic sensors (not shown) are provided to regulators  36  to provide feedback to controller  30 . This feedback indicates whether a regulator valve is in a full feed state or a regulating state. Controller  30  preferably monitors this state during an oncoming phase of the transmission.  
         [0024]     The oncoming fill phase occurs when the transmission is increasing fill level of the clutch and attempting to engage the gear. The regulating valve switches to a full feed state when fill pressure reaches a certain level. The oncoming torque phase occurs when the clutch obtains torque capacity greater than zero. The regulating valve switches back to a regulating state at this point so that the clutch can engage the gear at a level appropriate to the torque. The fill level of the clutch is an important adaptive parameter. It must be properly maintained to minimize return spring stroke time while achieving a regulation pressure just above the zero oncoming capacity level for reduction in tieup.  
         [0025]     As illustrated in  FIG. 2 , the present invention performs switch event detection at step  50  to determine when a valid fill state has been achieved. It monitors switching over time of the regulator valve from a full feed state to a regulating state. It also tracks change from an oncoming fill phase to an oncoming torque phase when the regulator valve switches back to the regulating state. These sets of information are employed in step  52  to determine whether one or more reasons exist that may call for updating adaptive parameters relating to clutch fill level and clutch volume. In turn, the reasons determined in step  52  are employed in step  54  to determine what to adapt. Finally, the determinations of what to adapt are used in step  56  to update the adaptive parameters, and the reasons for the adaptation are also employed to guide and limit the update process.  
         [0026]      FIGS. 3 and 4  illustrate one implementation of switch event detection in accordance with step  50  ( FIG. 2 ). For example,  FIG. 4  illustrates switch event detection during, for example, an oncoming torque phase, while  FIG. 3  illustrates switch event detection during an oncoming fill phase. Accordingly, accumulated clutch volume is calculated at step  60  based on a predetermined flow rate and accumulated shift time. This accumulated clutch volume is an elapsed shift time that tracks the amount of time since the beginning of an oncoming fill phase. During the oncoming fill phase as at  62 , the accumulated volume is compared to a mask volume calibration as at  64  and  66 . This mask volume is a temporal threshold that governs when the controller begins to monitor the state of the regulator valve during the oncoming fill phase. In part, this mask volume marks the end of a mask window during which switch to the full feed state is not detected because it did not last long enough.  
         [0027]     The accumulate volume is also compared to a validation volume as at  66 . The mask volume marks the beginning of a validation window, and the calibration volume marks the end of the validation window. During recursive loops of this switch event detection, the accumulated volume is increased until it enters the validation window and the controller begins looking at the state of the regulator valve. If the regulator valve is detected to be in a full feed state during the validation window, possibly because it entered the full feed state during the mask window, then the process begins to recursively follow branch  72 .  
         [0028]     Branch  72  records that the full feed state existed during the validity window, and further whether the full feed state existed at the start of the validity window. If the valve switches back to the regulating state after having reached full feed, then the oncoming fill phase is exited as at  68  and step  70 . However, if the regulator valve does not switch back to the regulating state within the validity window, then the process begins recursively taking branch  74 .  
         [0029]     Branch  74  records that the regulator valve did not switch back to the regulating state before exiting the validity window. It also records in which state the regulator valve exited the mask window. Thus, separate validity flags are maintained by loop branches  72  and  74  to indicate three observations: whether the full feed state was noted after the beginning of the validity window, whether it was initiated before or after the beginning of the validity window, and whether a switch back to the regulating state was observed before the end of the validity window.  
         [0030]      FIG. 4  illustrates the switch detection procedure that occurs when the transmission is not in an oncoming fill phase. For example, the process determines and records whether an oncoming torque phase is in process at  76  and steps  78  and  80 . Also, the process determines and records the position of the regulator valve as at  82 ,  84 ,  86 , and steps  78  and  80 . Further, the process determines and records whether the regulator valve changed position from regulating to full feed during the torque phase ramp. In addition, the amount of accumulated volume during the full feed fill stage until the first instance of regulating is encountered. The result is employed at  90  and  92  to record at steps  94  and  96 , whether the switch indication of full feed is long enough to allow an eventual decrease of pressure. An iteration through one path of these processes completes step  50  ( FIG. 2 ), and the method of the present invention continues to step  52 , one example of which is described below with reference to  FIGS. 5 and 6 .  
         [0031]      FIG. 5  illustrates evaluation of detected and recorded switch events as at  98 - 102  to establish and record reasons for adapting clutch fill level at steps  110 - 120 . Each of steps  110 - 120  records information about conditions surrounding a regulator switch event, and each of steps  110 - 118  further records an amount of calculated volume remaining when the switch event occurred. This information records detected-circumstances that may indicate whether and in what manner clutch fill level needs to be adjusted. Also, the amount of clutch volume remaining when these circumstances occur may be further useful in determining whether and in what manner to adjust clutch volume as explained below with reference to  FIG. 6 . Thus, part of the information needed for adapting clutch volume is recorded during an evaluation of reasons for adapting clutch fill level.  
         [0032]      FIG. 6  illustrates evaluation of detected and recorded switch events as at  122 - 128  to establish and record reasons for adapting estimated clutch volume at steps  130 - 134 . In particular, each of determinations  122 - 128  compares the calculated volume remaining when the regulator valve switched to regulating from full feed to predetermined thresholds to determine whether an increase or decrease in estimated clutch volume may be needed. An estimated remaining clutch volume is determined and recorded at the point when the regulator valve switches from the full feed state to the regulating state, thus exiting the oncoming fill phase. This estimation is accomplished by counting down clutch volume over time during the shift based on a flow rate until the switch from full feed to regulating is detected. The remaining volume is then compared to high and low thresholds straddling zero volume to define a volume window. Similar procedures are employed with respect to clutch fill level as shown in  FIG. 5  to determine and record whether clutch fill level should be increased or decreased. Information relating to whether engine flare occurs during a torque ramp phase may be used to justify an adjustment of fill level. Also, non-switch of the regulator valve to full feed during the oncoming fill state can be used to justify an adjustment of fill level. Further, remaining volume level can be correlated with whether a valid fill is achieved to mitigate and affect one another. An iteration through the process illustrated in  FIGS. 5 and 6  completes step  52  ( FIG. 2 ), and the method of the present invention continues with step  54 , one implementation of which is illustrated in  FIG. 7 .  
         [0033]      FIG. 7  illustrates a procedure for determining what adaptive parameters to update, and this process is facilitated in the case where it has already been determined whether to increase or decrease certain adaptive parameters as detailed above. Thus, if the transmission is not in a torque phase with the regulating valve in full feed position as at  138 , then determination and recordation of whether to adapt clutch volume and/or fill level simply corresponds to checking whether the volume or fill level should be increased or decreased, regardless of the reason underlying the decision as at  140 . Also, if the regulator valve enters full feed during the oncoming torque phase as at  138  and the oncoming element does not pull turbine speed down early during the torque phase ramp as at  142 , then a record that fill level needs to be adjusted is made at step  144 . An iteration through this process completes step  54  ( FIG. 2 ), and the method of the present invention continues with step  56 , an implementation of which is illustrated in  FIGS. 8-10 .  
         [0034]      FIG. 8  illustrates update of fill adaptive parameters. For example, modules  146 - 152  receive four types of information: measured information  154  by which to compute an adaptive parameter in the form of a full correction  156 ; an adaptive error counter  158 A by which to calculate an adaptive gain  160  for the adaptive parameter; one or more recorded reasons  162  for adapting the parameter in question by which an adaptive factor  164  is determined, and adaptive error counter  158 B by which to calculate a maximum change factor  166 . Adaptive gain  160  and adaptive factor  164  are applied to full correction  156  at  168  to obtain a proposed correction  170 . Adaptive factor  164  is also used with maximum change factor  166  to produce maximum change  172  at  174 . Proposed correction  170  is limited in turn at  176  and  178  based on maximum change  172  and minimum change  180 . A five by five place calibration for each fill adaptive cell is applied at  184  to determine adaptive weighting. The fill adaptive parameter is a function of line pressure command and temperature, and this process is run for all cells in a three by three adaptive matrix. Thus, the weighted and limited adaptive parameter is applied to a previous adaptive parameter for fill level  186  at  188 . Whether the application at  188  results in an increase or decrease is governed by recordation of adaptive reasoning as previously discussed. A maximum fill level  190  is further applied at  192  to obtain a new adaptive parameter for fill level  194 .  
         [0035]      FIG. 9  illustrates a similar process for updating clutch volume adaptive parameters, but with some alternative procedures for limiting the adaptation. For example, maximum change  172  is determined at  174  based on a volume for a one loop change  196 , which is determined at  198  as a function of flow rate  200  over an iteration time  202 . Also, this volume for a one loop change  196  is further combined at  204  with a minimum volume correction factor  206  to arrive at minimum change  180 . The minimum change  180  is still employed at  178  to limit proposed correction  170 , but is also communicated to conditional control block  208 , which selects between the output of block  178  and minimum change  180  based on criteria relating to whether a current torque level is within a predetermined range, and whether a valid fill has been achieved. Control block  208  is also adapted to select an iterative decrease  210  computed by block  212  based on volume for a one loop change  196 . Iterative decrease  196  is further employed at  178  to limit proposed correction  170 . The output of block  208  has a confidence value  213  applied at  184  to obtain volume decrease backoff protection  214 . The correction is then applied to a previous adaptive volume parameter  216  to decrease the parameter  216 , and the change in the parameter is limited at  218  according to a minimum adaptation limit  220 .  
         [0036]      FIG. 10  illustrates the process of  FIG. 9  adapted for increase of the volume. For example, an iterative decrease is not required at  78  or block  208 , and no backoff protection is needed. Also, multiple confidence values  222  are employed at  184 . Further, parameter  216  is increased as a result of the update, and limited according to a maximum adaptation limit  224 .  
         [0037]     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the current invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.