Abstract:
The present invention provides a method and apparatus for adaptively controlling a closed throttle downshift in an automatic transmission wherein a transmission aberration during a shift is diagnosed and corrected during subsequent closed throttle downshifts. The invention is carried out by monitoring transmission characteristics including input speed, output speed and shift duration during a closed throttle downshift, and identifying departures from acceptable patterns. Each type of departure calls for a particular remedy, and a suitable adjustment is calculated based on the times and/or the commanded pressures at certain times, the adjustment being implemented by changing one or more initial conditions for the next shift of the same type. The adjustments may have to be large to make a full or significant partial correction at the next shift. Conversely small increments may be necessary to avoid over-correction.

Description:
TECHNICAL FIELD 
     The present invention relates to a method and apparatus for improving closed throttle downshifts of an automatic transmission. 
     BACKGROUND OF THE INVENTION 
     Generally, a motor vehicle automatic transmission includes a number of gear elements coupling its input and output shafts, and a related number of torque establishing devices such as clutches and brakes that are selectively engageable to activate certain gear elements for establishing a desired speed ratio between the input and output shafts. As used herein, the terms “clutches” and “torque transmitting devices” will be used to refer to brakes as well as clutches. 
     The input shaft is connected to the vehicle engine through a fluid coupling such as a torque converter, and the output shaft is connected directly to the vehicle wheels. Shifting from one forward speed ratio to another is performed in response to engine throttle and vehicle speed, and generally involves releasing or disengaging the clutch (off-going) associated with the current speed ratio and applying or engaging the clutch (on-coming) associated with the desired speed ratio. 
     The speed ratio is defined as the transmission input speed or turbine speed divided by the output speed. Thus, a low gear range has a high speed ratio and a higher gear range has a lower speed ratio. To perform a downshift, a shift is made from a low speed ratio to a high speed ratio. In the type of transmission involved in this invention, the downshift is accomplished by disengaging a clutch associated with the lower speed ratio and engaging a clutch associated with the higher speed ratio, to thereby reconfigure the gear set to operate at the higher speed ratio. Shifts performed in the above manner are termed clutch-to-clutch shifts and require precise timing in order to achieve high quality shifting. 
     The quality of shift depends on the cooperative operation of several functions, such as pressure changes within on-coming and off-going clutch apply chambers and the timing of control events. Moreover, manufacturing tolerances in each transmission, changes due to wear, variations in oil quality and temperature, etc., lead to shift quality degradation. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a method and apparatus for adaptively controlling a closed throttle downshift in an automatic transmission wherein a transmission aberration during a shift is diagnosed and corrected during subsequent closed throttle downshifts. 
     It is a further object to provide such a method which is capable of making both large and small corrections. 
     The method of the invention is carried out by monitoring transmission characteristics including input speed, output speed, and shift duration during a closed throttle downshift, and identifying departures from acceptable patterns. Each type of departure calls for a particular remedy, and a suitable adjustment is calculated and implemented by changing certain parameters in the shift control to alter one or more conditions for the next shift of the same type. The adjustments may have to be large to make a full or significant partial correction at the next shift. Conversely, small increments may be necessary to avoid over-correction. 
     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 illustration of an automatic transmission; 
         FIG. 1A  is a schematic illustration of a valve of  FIG. 1 ; 
         FIG. 2A  is a graphical depiction of turbine speed vs. time during an optimal closed throttle downshift, and further showing the shift aberrations “slip early” and “underlap”; 
         FIG. 2B  is a graphical depiction of the on-coming clutch pressure vs. time during the optimal closed throttle downshift of  FIG. 2A ; 
         FIG. 2C  is a graphical depiction of the off-going clutch pressure vs. time during the optimal closed throttle downshift of  FIG. 2A ; 
         FIG. 3  is a block diagram illustrating a method of adjusting the off-going pressure adaptive parameter of the present invention; 
         FIG. 4  is a block diagram illustrating a method of adjusting the on-coming pressure adaptive parameter of the present invention; 
         FIG. 5  is a block diagram illustrating a method of adjusting the on-coming volume adaptive parameter of the present invention; 
         FIG. 6A  is a graphical depiction of turbine speed during the shift aberration “synchronization”; 
         FIG. 6B  is a graphical depiction of turbine speed during the shift aberration “turbine float”; and 
         FIG. 6C  is a graphical depiction of turbine speed during the shift aberrations “short shift,” “long shift,” “closed loop increase,” and “closed loop decrease.” 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The control of this invention is described in the context of a multi-ratio power transmission having a planetary gear set of the type described in the U.S. Pat. No. 4,070,927 to Polak, and having an electro-hydraulic control of the type described in U.S. Pat. No. 5,601,506 to Long et al, both of which are hereby incorporated by reference in their entireties. Accordingly, the gear set and control elements shown in  FIG. 1  hereof have been greatly simplified, it being understood that further information regarding the fluid pressure routings and so on may be found in the aforementioned patents. 
     Referring to  FIG. 1 , the reference numeral  10  generally designates a vehicle power train including engine  12 , transmission  14 , and a torque converter  16  providing a fluid coupling between engine  12  and transmission input shaft  18 . A torque converter clutch  19  is selectively engaged under certain conditions to provide a mechanical coupling between engine  12  and transmission input shaft  18 . The transmission output shaft  20  is coupled to the driving wheels of the vehicle in one of several conventional ways. The illustrated embodiment depicts a four-wheel-drive (FWD) application in which the output shaft  20  is connected to a transfer case  21  that is also coupled to a rear drive shaft R and a front drive shaft F. Typically, the transfer case  21  is manually shiftable to selectively establish one of several drive conditions, including various combinations of two-wheel-drive and four-wheel drive, and high or low speed range, with a neutral condition occurring intermediate the two and four wheel drive conditions. 
     The transmission  14  has three inter-connected planetary gear sets, designated generally by the reference numerals  23 ,  24  and  25 . The planetary gear set  23  includes a sun gear member  28 , a ring gear member  29 , and a planet carrier assembly  30 . The planet carrier assembly  30  includes a plurality of pinion gears rotatably mounted on a carrier member and disposed in meshing relationship with both the sun gear member  28  and the ring gear member  29 . The planetary gear set  24  includes a sun gear member  31 , a ring gear member  32 , and a planet carrier assembly  33 . The planet carrier assembly  33  includes a plurality of pinion gears rotatably mounted on a carrier member and disposed in meshing relationship with both the sun gear member  31  and the ring gear member  32 . The planetary gear set  25  includes a sun gear member  34 , a ring gear member  35 , and a planet carrier assembly  36 . The planet carrier assembly  36  includes a plurality of pinion gears rotatably mounted on a carrier member and disposed in meshing relationship with both the sun gear member  34  and the ring gear member  35 . 
     The input shaft  18  continuously drives the sun gear  28  of gear set  23 , selectively drives the sun gears  31 ,  34  of gear sets  24 ,  25  via clutch C 1 , and selectively drives the carrier  33  of gear set  24  via clutch C 2 . The ring gears  29 ,  32 ,  35  of gear sets  23 ,  24 ,  25  are selectively connected to ground  42  via clutches (i.e., brakes) C 3 , C 4  and C 5 , respectively. 
     The state of the clutches C 1 -C 5  (i.e., engaged or disengaged) can be controlled to provide six forward speed ratios (1, 2, 3, 4, 5, 6), a reverse speed ratio (R) or a neutral condition (N). For example, the first forward speed ratio is achieved by engaging clutches C 1  and C 5 . Downshifting from one forward speed ratio to another is generally achieved by disengaging one clutch (referred to as the off-going clutch) while engaging another clutch (referred to as the on-coming clutch). For example, the transmission  14  is downshifted from second to first by disengaging clutch C 4  while engaging clutch C 5 . 
     The torque converter clutch  19  and the transmission clutches C 1 -C 5  are controlled by an electro-hydraulic control system, generally designated by reference numeral  44 . The hydraulic portions of the control system  44  include a pump  46  which draws hydraulic fluid from a reservoir  48 , a pressure regulator  50  which returns a portion of the pump output to reservoir  48  to develop a regulated pressure in line  52 , a secondary pressure regulator valve  54 , a manual valve  56  manipulated by the driver of the vehicle, and a number of solenoid-operated fluid control valves  58 ,  60 ,  62  and  64 . 
     The electronic portion of the electro-hydraulic control system  44  is primarily embodied in the transmission control unit  66 , or controller, which is microprocessor-based and conventional in architecture. The transmission control unit  66  controls the solenoid-operated fluid control valves  58 - 64  based on a number of inputs  68  to achieve a desired transmission speed ratio. Such inputs include, for example, signals representing the transmission input speed TIS, a driver torque command TQ, the transmission output speed TOS, and the hydraulic fluid temperature Tsump. Sensors for developing such signals may be conventional in nature, and have been omitted for simplicity. 
     The control lever  82  of manual valve  56  is coupled to a sensor and display module  84  that produces a diagnostic signal on line  86  based on the control lever position; such signal is conventionally referred to as a PRNDL signal, since it indicates which of the transmission ranges (P, R, N, D or L) has been selected by the vehicle driver. Finally, fluid control valves  60  are provided with pressure switches  74 ,  76 ,  78  for supplying diagnostic signals to control unit  66  on lines  80  based on the respective relay valve positions. The control unit  66 , in turn, monitors the various diagnostic signals for the purpose of electrically verifying proper operation of the controlled elements. 
     The solenoid-operated fluid control valves  58 - 64  are generally characterized as being either of the on/off or modulated type. To reduce cost, the electro-hydraulic control system  44  is configured to minimize the number of modulated fluid control valves, as modulated valves are generally more expensive to implement. To this end, fluid control valves  60  are a set of three on/off relay valves, shown in  FIG. 1  as a consolidated block, and are utilized in concert with manual valve  56  to enable controlled engagement and disengagement of each of the clutches C 1 -C 5 . Valves  62 ,  64  are of the modulated type. For any selected ratio, the control unit  66  activates a particular combination of relay valves  60  for coupling one of the modulated valves  62 ,  64  to the on-coming clutch, and the other one of the modulated valves  62 ,  64  to the off-going clutch. 
     The modulated valves  62 ,  64  each comprise a conventional pressure regulator valve biased by a variable pilot pressure that is developed by current controlled force motors (not shown). Fluid control valve  58  is also a modulated valve, and controls the fluid supply path to converter clutch  19  in lines  70 ,  72  for selectively engaging and disengaging the converter clutch  19 . The transmission control unit  66  determines pressure commands for smoothly engaging the on-coming clutch while smoothly disengaging the off-going clutch to shift from one speed ratio to another, develops corresponding force motor current commands, and then supplies current to the respective force motors in accordance with the current commands. Thus, the clutches C 1 -C 5  are responsive to the pressure commands via the valves  58 - 64  and their respective actuating elements (e.g., solenoids, current-controlled force motors). 
     As indicated above, each shift from one speed ratio to another includes a fill or preparation phase during which an apply chamber  91  of the on-coming clutch is filled in preparation for torque transmission. Fluid supplied to the apply chamber compresses an internal return spring (not shown), thereby stroking a piston (not shown). Once the apply chamber is filled, the piston applies a force to the clutch plates, developing torque capacity beyond the initial return spring pressure. Thereafter, the clutch transmits torque in relation to the clutch pressure, and the shift can be completed using various control strategies. The usual control strategy involves commanding a maximum on-coming clutch pressure for an empirically determined fill time, and then proceeding with the subsequent phases of the shift. The volume of fluid required to fill an apply chamber and thereby cause the clutch to gain torque capacity is referred to as the “clutch volume.” 
     The controller  66  determines the timing of the pressure commands based on an estimated on-coming clutch volume, i.e., an estimated volume of fluid required to fill the on-coming clutch apply chamber and thereby cause the on-coming clutch to gain torque capacity. An estimated on-coming clutch volume must be used because the actual on-coming clutch volume may vary over time as a result of wear, and may vary from transmission to transmission because of build variations and tolerances. 
     The controller  66  calculates an estimated volume of fluid supplied to the on-coming clutch apply chamber as the chamber is being filled based on a mathematical model of the transmission hydraulic system, and compares the estimated volume of fluid supplied to the estimated clutch volume. When the estimated volume of fluid supplied to the apply chamber equals the estimated clutch volume, then the on-coming clutch should gain capacity. A hydraulic flow model for use in estimating the volume of fluid supplied to an apply chamber is described in U.S. Pat. No. 6,285,942, issued Sep. 4, 2001 to Steinmetz et al, which is hereby incorporated by reference in its entirety. The model inputs include the fill pressure, the shift type ST (for example, a 2-1 downshift), the speed of pump  46 , and the temperature Tsump of the hydraulic fluid. The output of the model is the on-coming clutch flow rate. The flow rate is integrated by an integrator to form the estimated cumulative volume of fluid supplied to the apply chamber. In a preferred embodiment, the controller  66  subtracts the estimated volume of fluid supplied from the estimated clutch volume to determine an estimated clutch volume remaining. If the controller is accurate, the estimated clutch volume remaining will be zero at the time the on-coming clutch gains torque capacity. 
     Alternatively instead of modulated valves  62 ,  64  and relay valves  60 , the transmission may include a plurality of individual control valves each operatively connected to a respective apply chamber  91 . Referring to  FIG. 1A , an exemplary fluid control valve  90  includes a regulator  92 , a solenoid  94  and a pressure sensor  96 . Each control valve  90  is configured to provide fluid to the apply chamber  91  of its respective clutch C 1 -C 5  at either a full feed state or a regulating state. 
     The method of the present invention establishes three adaptive parameters for each closed throttle downshift. The adaptive parameters include an off-going clutch pressure adaptive parameter, an on-coming clutch pressure adaptive parameter, and an on-coming clutch volume adaptive parameter. The adaptive parameters are so named because they are monitored and may be adapted to improve subsequent downshifts. The term “closed throttle downshift” generally refers to a downshift when there is no gas pedal demand, but as used herein refers to any downshift that takes place during a period of very low input torque. Therefore a closed throttle downshift may take place while the throttle is somewhat open if the input torque is sufficiently low. 
       FIGS. 2A-2C  show a predefined optimal closed throttle downshift. More precisely,  FIG. 2A  shows torque converter turbine speed T s  transitioning from the attained gear speed A g  to the commanded gear speed C g . Those skilled in the art will recognize that the turbine and input shaft are interconnected, and, accordingly, the turbine speed is the same as the input shaft speed. Those skilled in the art will also recognize that the attained gear speed A g  is the transmission output speed multiplied by the currently selected gear ratio, whereas the commanded gear speed C g  is the transmission output speed multiplied by the commanded gear ratio. Accordingly, during a closed throttle  4 - 3  downshift, A g  is transmission output speed multiplied by the fourth gear ratio and C g  is the transmission output speed multiplied by the third gear ratio. 
       FIG. 2B  shows on-coming clutch pressure during the closed throttle downshift, including the fill time in which the on-coming clutch apply chamber is filled and wherein on-coming pressure is zero, the torque phase during which the on-coming clutch begins to generate torque, and the inertia phase. Similarly,  FIG. 2C  shows off-going clutch pressure during the closed throttle downshift. As seen in  FIGS. 2A-2C , during an optimal closed throttle downshift, off-going clutch pressure is maintained as the on-coming apply chamber is filled so that the off-going clutch does not slip and the turbine speed T s  remains at the attained gear speed A g . After the on-coming clutch apply chamber is filled and the on-coming clutch begins to generate torque, the off-going clutch pressure is reduced. The timing of an optimal closed throttle downshift is such that as the off-going clutch pressure reaches zero and is thereby released, the on-coming clutch is engaged to effect the downshift and the turbine speed T s  correspondingly shifts from the attained gear speed A g  to the commanded gear speed C g . 
     The shift aberrations, i.e., deviations, from the predefined optimal shift that are correctable by adjusting the off-going pressure adaptive parameter are also graphically represented in  FIG. 2A . Turbine speed T s1  represents the shift aberration “slip early” and turbine speed T s2  represents the shift aberration “underlap.” Slip early and underlap are both attributable to inadequate off-going clutch pressure. The characteristic defining the difference between the two aberrations is the relative engine speed during a particular closed throttle downshift. More precisely, slip early is the case wherein engine speed E s1  is greater than attained gear speed Ag such that turbine speed T s1  prematurely, in comparison to the optimal shift, deviates therefrom by increasing. Similarly, underlap is the case wherein engine speed E s2  is less than attained gear speed Ag such that turbine speed T s2  prematurely, in comparison to the optimal shift, deviates therefrom by decreasing. 
     The optimal off-going clutch pressure during a closed throttle downshift is that which is just enough to prevent premature slip of the off-going clutch. If premature slip is observed, the off-going pressure adaptive parameter is incrementally increased during subsequent shifts until the premature slip condition no longer exists. In this manner, the off-going pressure adaptive parameter is self-correcting when the estimated value thereof is too low. To correct the adaptive parameter when the estimated value is too high, the off-going pressure adaptive parameter is revised after a predetermined number of shifts without premature slip. More precisely, if a predetermined number of shifts occur without premature slip, the off-going pressure adaptive parameter is incrementally reduced during subsequent shifts until premature slip is observed and thereafter is incrementally increased until the premature slip condition no longer exists. In this manner, the off-going pressure adaptive parameter is maintained at the optimal value, which is just above the premature slip threshold. 
     A method of adjusting the off-going clutch pressure adaptive parameter is depicted in  FIG. 3 . With reference to  FIGS. 2A-C  and  3 , premature deviation of turbine speed T s  from attained gear speed A g  is monitored by the control unit to determine the occurrence of slip early or underlap during fill (Step  100 ). If turbine speed T s  falls more than a predetermined amount, e.g., 50 rpm, below attained gear speed A g , underlap is indicated. Similarly, if turbine speed T s  prematurely rises more than a predetermined amount, e.g., 50 rpm, above attained gear speed A g , slip early is indicated. If either slip early or underlap during fill is detected, the off-going clutch pressure adaptive parameter (P OFF ) is increased at step  102 . At step  104 , a counter is monitored. The counter is set to a predetermined integer value after P OFF  is increased in step  102 , and is decreased by one at step  110  when premature slip is not detected at step  100 . If the counter equals zero, and the slip is observable, then the off-going clutch pressure is reduced for each subsequent shift at step  106  until premature slip is observed. Slip is not observable when engine speed is near, e.g., +/−50 rpm, the attained gear speed A g . Steps  108  and  110  reduce the counter by one each time the transmission downshifts without premature slip. Thereafter the steps of the off-going pressure adaptive described hereinabove are repeated. 
     The off-going pressure adaptive parameter is preferably increased or decreased in steps  102  and  106  by a corrective value obtained by the following equation: (full correction)(scalar)(gain). Full correction is either a calibration or measured signal, such as from turbine speed, that gives a term to correct the adaptive problem. The scalar is a function of the shift aberration type, since some shift aberrations require more aggressive corrective action than others. The gain is related to an adaptive error counter that tracks the direction the off-going pressure adaptive parameter is moving. If the off-going pressure adaptive parameter increases during consecutive downshifts, the adaptive error counter is increased by one to a predetermined maximum value, e.g., seven. Similarly, if the off-going pressure adaptive parameter decreases during consecutive downshifts, the adaptive error counter is decreased by one to a predetermined minimum value, e.g., negative seven. The gain is established based on the adaptive error counter value such that the magnitude of the gain is proportional to the absolute value of the adaptive error counter. In other words, each consecutive increase or decrease in the adaptive error counter gives rise to a larger gain. In this manner the degree of adaptive correction can be increased if the off-going pressure adaptive parameter has been commanded to change in one direction, i.e., increased or decreased, during consecutive downshifts. Thus, the corrective value varies in response to the quantity of consecutive monitored downshifts in which a shift aberration occurs. If the off-going pressure adaptive parameter is increased and then subsequently decreased, or vice versa, the adaptive error counter is reset to zero and the gain becomes its minimal value. Additionally, it should be appreciated that the on-coming pressure and volume adaptive parameters are increased and decreased in a similar manner. 
     The transmission control unit uses the offgoing clutch pressure adaptive parameter to determine the appropriate offgoing clutch pressure command in order to achieve a desired offgoing clutch torque. Torque applied by the off-going clutch is related to off-going clutch pressure according to the equation T=(P offcmd −P off )G off , where T off  is the off-going clutch torque, P offcmd  is the on-corning pressure command, P off  is the offgoing clutch pressure adaptive parameter, and G off  is a multiplication factor for the off-going clutch. The off-going clutch pressure adaptive parameter represents the pressure applied by the on-coming clutch return spring, and is adapted and adjusted as described above with reference to  FIG. 3  to account for system variations. The optimal off-going clutch torque is based on a predefined mathematical model that describes what the torque should be to result in desired shift quality using such factors as time and input torque. In an exemplary embodiment, the optimal off-going clutch torque is defined in terms of an optimal torque profile during a shift. In order to generate an actual off-going clutch torque profile that most closely resembles the optimal off-going torque profile, the equation T off =(P offcmd −P off )G is solved for commanded pressure P offcmd . 
     This pressure to torque relationship also applies to the on-coming clutch, i.e., T on =(P oncmd −P on )G on , wherein T on  is the on-coming clutch torque, P oncmd  is the commanded on-coming clutch pressure, P on  is the oncoming clutch pressure adaptive parameter, and G on  is a multiplication factor for the on-coming clutch. As with the off-going clutch, the equation T on =(P oncmd −P on )G on  is solved using an optimal on-coming clutch torque obtained from a mathematical model to determine the commanded on-coming clutch pressure. 
     The on-coming pressure is maintained within a pressure range defined between that which is low enough to avoid a full feed state and high enough to start the ratio change in the expected time. Additionally, the on-coming pressure adaptive parameter is monitored to prevent the turbine speed from floating toward engine speed after the optimal time, and to prevent the turbine speed from floating at the engine speed for extended periods of time. Once these priorities are adhered to, the ratio change duration and the amount of closed loop offset is monitored to give an indication of how much torque exists on the on-coming element. 
     A corresponding method of adjusting an on-coming clutch pressure adaptive parameter is shown in  FIG. 4 . At step  112 , if the control valve, shown at  90  in  FIGS. 1 and 1A , corresponding to the on-coming clutch is at full feed, then the on-coming clutch pressure adaptive parameter (P ON ) is decreased at step  114 . Subsequent to step  114 , the method returns to step  112 ; thus, the on-coming clutch pressure adaptive parameter is decreased during subsequent shifts until the control valve is no longer at full feed. If, during a shift, the control valve is not at full feed, then the method includes determining whether shift aberrations “slip late,” “underlap after fill,” “past sync” and “turbine float,” which are all potentially attributable to inadequate on-coming clutch pressure, occur (step  116 ). 
     Referring to  FIG. 6A , slip late is a shift aberration wherein on-coming clutch capacity occurs more than a predetermined duration later than in the predefined optimal downshift T S . If, for example, the on-coming clutch optimally gains capacity 50 milliseconds (ms) after the fill stage is complete, a delay resulting in the on-coming clutch gaining capacity more than 100 ms after the fill stage would be indicative of slip late. On-coming clutch capacity is indicated by turbine speed T s  rising more than a predetermined amount, e.g., 50 rpm, above attained gear speed A g . 
     Underlap after fill is detected when turbine speed falls more than a predetermined amount, e.g., 50 rpm, below attained gear speed A g  after the fill stage. If the turbine speed remains at or near (e.g., +/−50 rpm) engine speed for more than a predetermined acceptable period of time, turbine float is indicated. Referring to  FIG. 6B , turbine float is therefore identified by comparing turbine speed and engine speed, and recognizing that if turbine speed T s4  is at engine speed E s4  for an excessive duration, i.e., longer than a predetermined duration, turbine float occurs. The turbine speed T s4  during turbine float is graphically depicted in  FIG. 6B . 
     The turbine speed T s3  during synchronization is graphically depicted in  FIG. 6A  and is contrasted by the solid line representation of turbine speed T s  during the predefined optimal closed throttle downshift. Referring to  FIG. 6A , it can be seen that during synchronization, the turbine speed T s3  deviates from the commanded gear speed C g  and goes toward engine speed E s3  when engine speed E s3  is greater than the commanded gear speed C g . Synchronization or “past sync,” is identified by comparing the turbine speed T s3  and the commanded gear speed C g . If turbine speed T s3  rises more than a predetermined amount, e.g., 50 rpm, above commanded gear speed C g , then synchronization is indicated. The shift aberrations slip late, underlap after fill, past sync and turbine float identified at step  116  are addressed at step  118  by increasing the on-coming clutch pressure adaptive parameter P ON . 
     The turbine speed during a short shift and a long shift are graphically depicted by line T s5  and line T s6  of  FIG. 6C , respectively, and are contrasted by the solid line representation of turbine speed T s  during the predefined optimal closed throttle downshift. A short shift or long shift is identified at steps  120  and  124 , respectively, by comparing the duration of the inertia phase of the on-coming clutch with a predetermined optimal shift time. The duration of the inertia phase is the period of time beginning when the turbine speed is a predetermined amount, e.g., 50 rpm, greater than the attained gear speed A g  and ending when the turbine speed is a predetermined amount, e.g., 50 rpm, less than the commanded gear speed C g . Insufficient inertia phase duration, i.e., in comparison to the predetermined optimal shift time, is indicative of a short shift, and the on-coming clutch pressure adaptive parameter is decreased at step  122  in response. Excessive inertia phase duration is indicative of a long shift and the on-coming clutch pressure adaptive parameter is increased in response at step  126 . 
     The controller is configured for closed-loop control of commanded pressure. Accordingly, the controller is configured to recognize deviation between intended pressure and actual pressure based on deviation between actual turbine speed and intended turbine speed. Previously addressed shift aberrations are detected by the controller comparing the actual characteristics of a shift to a predefined optimal shift. When the controller performs steps  112 ,  116 ,  120 , and  124  with no shift aberrations from optimal detected, the controller is configured to analyze information obtained from the closed loop control to adjust the oncoming pressure adaptive parameter accordingly. 
     The turbine speed during a closed loop increase and a closed loop decrease is graphically similar to a short shift and long shift, respectively. Therefore, referring to  FIG. 6C , the turbine speed during a closed loop increase is graphically depicted by line T s5 , and the turbine speed during a closed loop decrease is graphically depicted by line T s6 . As error between actual turbine speed profile and intended turbine speed profile increases, the closed loop control causes the commanded pressure to proportionally increase to correct the error. A “closed loop increase” or a “closed loop decrease” occurs when the commanded pressure increases or decreases by more than a predetermined maximum threshold. A closed loop decrease is identified at step  128  and, in response, the on-coming pressure adaptive parameter is decreased at step  130 . Similarly, a closed loop increase is identified at step  132  and, in response, the on-coming pressure adaptive parameter is increased at step  134 . 
     High turbine deceleration is also identified at step  128  by monitoring the deceleration rate of the turbine. Turbine deceleration is calculated by subtracting the turbine speed at the end of the shift from the turbine speed at the beginning of the shift and dividing the resultant product by elapsed time. The on-coming pressure adaptive parameter is decreased at step  130  to adjust for excessive, i.e., in comparison to a predetermined maximum allowable, turbine deceleration. 
     The on-coming clutch volume adaptive parameter works in coordination with the on-coming pressure adaptive parameter. The first priority is to decrease the on-coming clutch volume adaptive parameter when an unexpected ratio change occurs. An unexpected ratio change indicates that the on-coming clutch prematurely gains capacity. The premature on-coming capacity may be attributable to the on-coming apply chamber filling too early, and therefore the on-coming clutch volume adaptive parameter is decreased. Another indicator of early fill occurs when the regulator valve changes to a regulating state earlier than the volume adaptive logic expects, and again such an indication is addressed by decreasing the on-coming clutch volume adaptive parameter. The next priority is to make sure the on-coming element gains capacity when expected. Much like the on-coming pressure adaptive, on-coming clutch volume is monitored to start the ratio change in the expected time, not float toward engine speed after the expected time, and not float at the engine speed for extended periods of time. An upper learned, or estimated, volume limit approximates a maximum possible fill chamber volume, i.e., the designed clutch apply chamber volume plus a maximum clutch apply chamber volume variation to account for manufacturing tolerances, wear, etc. Finally, once all the above volume criteria have been met, the on-coming volume adaptive is iteratively decreased until the above actions are not met once again. The iterative action is only allowed if a slip differential can be observed or engine speed is at the synchronization speed. 
     A method of adjusting the on-coming clutch volume adaptive parameter is shown in  FIG. 5 . If on-coming clutch capacity is detected (e.g., turbine speed is more than 50 rpm above A g , and more than 50 rpm above engine speed) during the fill phase or the torque phase, it may be attributable to an excessive calculated volume such that the apply chamber of the on-coming clutch fills prematurely. The torque phase is defined for purposes of this invention as the period of time beginning with the on-coming clutch volume reaching zero (end of the fill phase) and ending with the on-coming clutch gaining capacity (beginning of the inertia phase). Therefore, if initial on-coming clutch capacity is detected during the fill phase or the torque phase at step  136 , the oncoming volume adaptive parameter (V ON ), used in calculating the estimated oncoming clutch volume for subsequent shifts, is decreased at step  138 . Similarly, slip early may be indicative of an excessive calculated volume and, if detected at step  136 , the oncoming volume adaptive parameter is decreased at step  138 . Step  136  further monitors the duration during which the control valve corresponding to the on-coming clutch is at a full feed state. If the control valve is at full feed for a period greater than a predetermined threshold, the on-coming clutch volume adaptive parameter is decreased at step  138 . 
     The aberrations slip late, underlap after fill, past sync and turbine float described hereinabove in the context of the on-coming pressure adaptive may be attributable to either inadequate pressure or inadequate calculated volume. Any of the aforementioned aberrations identified at step  140  are addressed by increasing the on-coming volume adaptive parameter at step  142 . However, the on-coming volume adaptive parameter is increased at step  142  if and only if long fill delay is not indicated. “Long fill delay” occurs when the estimated volume computer by the controller exceeds the predefined upper learned volume limit. Any of the aberrations including slip late, underlap after fill, past sync and turbine float that suggest an increase of the learned volume above the upper learned volume limit are likely attributable to on-coming pressure rather than volume, and the problem is therefore addressed by the on-coming pressure adaptive described hereinabove. In this manner the on-coming pressure and volume adaptives work together to identify which is responsible for the aberration and thereafter address the aberration in the appropriate manner. 
     If on-coming torque capacity or engine speed synchronization is detected at step  144  and all other conditions above do not exist, the on-coming volume adaptive parameter is iteratively reduced at step  146  to address the aberration during subsequent closed throttle downshifts. 
     While the best mode for carrying out the invention has 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.