Method of controlling gear change in an automatic transmission

Abstract: In an automatic transmission 16 upshifting is controlled by ramping down the pressure in an off-going clutch C1-CS associated with a high speed ratio and increasing the pressure in an on-coming clutch C1-CS associated with a lower speed ratio. The on-coming clutch C1-CS has commanded pressure at a maximum value for an initial fill time, a lower increasing ramp value during the ramp of the off-going clutch until the on-coming clutch starts to engage, and then a closed-loop control until the clutch reaches a synchronous speed. The closed-loop control parameter is on-coming clutch slip which is controlled to a calculated slip speed profile. Parameters for controlling the quality of a shift such as on-coming clutch initial pressure, off-going clutch initial pressure and on-coming clutch fill time are automatically adjustable during vehicle use to correct shift aberrations which degrade shift quality. A fast adjustment mode is in effect initially to calibrate the transmission control for the engine and vehicle. After a smooth shift is obtained only small adjustments are allowed.

Description: This invention relates to a method of controlling the change in an automatic transmission for a vehicle from an off-going fluid pressure operated torque transmitting device associated with a first speed ratio to an on-coming fluid pressure operated torque transmitting device associated with a second speed ratio. 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 which are selectively engageable to activate certain gear elements for establishing a desired speed ratio between the input and output shafts. The brake can be of the band-type or disc-type. Automotive engineers commonly refer to disc-type brakes in transmissions as "clutches" or "reaction clutches". 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 an upshift, a shift is made from a high speed ratio to a low speed ratio. In the type of transmission described below, the upshift is accomplished by disengaging a clutch associated with the higher speed ratio and engaging a clutch associated with the lower speed ratio, thereby to reconfigure the gear set to operate at the lower 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 and the timing of control events. Certain parameters in the shift control can be recognized as key elements in determining the shift quality. The vehicle type and the engine characteristics are very important factors in the shift operation and influence the correct selection of the parameters. In many cases, especially in truck applications, the vehicle and engine to be used with the transmission are not known to the manufacturer of the transmission. Moreover, manufacturing tolerances in each transmission, changes due to wear, variations in oil quality and temperature, etc., lead to shift quality degradation. It has been found that this can be overcome by an adaptive scheme for adjusting the parameters, whereby as the vehicle is driven, the shift quality is analyzed and the required adjustments are calculated and implemented for subsequent shifts. Large calibration adjustments may need to be made for each shift of a newly manufactured transmission. It is important to provide the capability for the transmission control to adjust itself rapidly to its system configuration when it is first operated as well as to maintain a continuous update capability. EP-A-0,327,004 discloses a shift control for an automatic transmission adapted to shift speed ranges by coupling or decoupling of the friction coupling elements mounted on the transmission mechanism. The coupling force of the friction coupling elements is subjected to feed-forward control during a preset period after a signal of instruction for shifting is given. A control value for the feed-forward control is determined in accordance with control value characteristics which vary from a given initial value at a constant change rate. After the preset period, coupling force of the friction coupling element is feedback controlled by actual revolutions of an input shaft of the transmission mechanism. A final control value for the feedback control is determined by determining a target change rate in the feedback control by an amount of change in revolutions number of the input shaft of the transmission mechanism estimated by shifting and a set time for the feed-back control. For each control cycle, the final control value is determined by comparing the actual number of revolutions of the input shaft and the target number of revolutions. EP-A-0,230,101 discloses a shift control system in which shifting from a currently engaged speed ratio to the specified speed ratio includes a completion phase during which fluid is supplied to the torque-establishing device in accordance with a predetermined pressure schedule to initiate and progressively increase the transmission of torque therethrough. The time required to complete a specified portion of the speed ratio progression is identified and compared with a reference time representative of the time required to complete the progression when the shift quality is not degraded. The predetermined pressure schedule is adjusted based on such comparison so as to compensate for sources of error which affect the increase of torque transmission through the torque-establishing device during the completion phase and cause the shift quality to be degraded. EP-A-0,331,523 discloses a method of determining and correcting engine racing during a gear shift by monitoring the input and output rotational speed ratio of an off-going or on-coming clutch. When that ratio, which is normally greater than 1.0 during a shift, either dips below 1.0, or dips below a threshold value smaller than 1.0, (and possibly, remains low for a predetermined time) engine racing is present and a correction factor is calculated and applied to the next shift. The correction may be applied to the hydraulic pressure, or the cycle timing, of the on-coming clutch in the next shift. US-A- 4 742 461 discloses, a method for calibrating an automatic transmission by altering the initial value of a pressure in accordance to the shift delay. According to an aspect of the present invention, there is provided a method of controlling the change in an automatic transmission as specified in claim 1. It is possible with the invention to provide a method of adaptively controlling a change in an automatic transmission wherein a transmission aberration during a change is diagnosed and fully (or optionally partially) corrected on the next change of the same type. Preferably, large corrections are made initially and then limited to small incremental changes thereafter. In a preferred embodiment, the adaptive control principles are applied to an upshift. Advantageously, transmission input and output speeds are monitored during a shift and departures from acceptable speed patterns and the times during the shift when the departures occur are identified. For closed-loop control, the relationship of commanded clutch pressures are similarly monitored. Each particular 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. Once the corrections are made, the continuing ability to make a large change is undesirable because road or system noise may distort the speed signals to give false indications of a shift aberration which would trigger a large adjustment. To avoid that problem, in an embodiment, once the initial corrections have resulted in a satisfactory shift quality, the large corrections are inhibited and only small adjustments are permitted. The invention is also directed to apparatus comprising means for carrying out the steps of the described method. An embodiment of the present invention is described below, by way of illustration only, with reference to the accompanying drawings, in which: Figure 1a is a system diagram of a fluid operated motor vehicle transmission, including several solenoid operated fluid pressure control valves, and a control unit; Figure 1b is a table illustrating the clutch engagements required to establish the various speed ratios of the transmission of Figure 1a; Figures 2, 3a and 3b are flow diagrams of an embodiment of method of controlling gear change by means of the controller of Figure 1a; Figure 4 illustrates typical turbine speed, off-going pressure command and on-coming pressure commands for a clutch-to-clutch upshift; Figure 5 is a slip diagram for the closed-loop operation of the on-coming clutch; Figures 6, 8, 10 and 12 are flow diagrams illustrating an embodiment of adaptive shift control logic; and Figures 7, 9, 11, 13, 14 and 15 are graphs of clutch pressures and turbine speeds against time for corrected shift conditions. Referring now to Figure 1a, the reference numeral 10 generally designates a motor vehicle drive train which includes a throttled internal combustion engine 12, a fluidic torque converter 14, a six-speed fluid operated power transmission 16 and a differential gear set (DG) 18. The engine 12 is connected to the torque converter 14 via shaft 20, the torque converter 14 is connected to the transmission 16 via shaft 22, the transmission 16 is connected to the differential gear set 18 via shaft 24 and the differential gearset is connected to a pair of drive wheels (not shown) via the prop shafts 26 and 28. Gear shifts are accomplished by selectively engaging and disengaging brakes and clutches, herein called torque transmitting devices or clutches. These clutches are actuated by hydraulic pressure and upon engagement require a fill time before torque is transmitted between a driving and a driven friction element. The speed and torque relationships between the engine 12 and the drive wheels of the vehicle are controlled by a fluid operated torque converter clutch, designated TCC, and five fluid operated transmission clutches, designated C1 - C5. The torque converter clutch TCC is selectively engaged by the solenoid operated control valve 30 to connect mechanically the impeller I and turbine T of torque converter 14. The clutches TCC, C1, C2, C3, C4, C5 are selectively engaged and disengaged by the solenoid operated control valves 30, 32, 34, 36, 38, 40 according to the diagram shown in Figure 1b, selectively to establish a desired transmission speed ratio. The illustrated transmission gear set provides one reverse ratio and six forward ratios, and is described in detail in U.S. Patent 4,070,927. An operator actuated accelerator pedal 41 positions the engine throttle for controlling the engine power output. The operation of the solenoid operated control valves 30 - 40 is controlled by a computer-based control unit 42, shown in dotted outline, via lines 44 - 54 in response to various input signals representative of system parameters. Such inputs include an engine throttle position signal %T on line 56, an engine output shaft speed signal Ne on line 58, a torque converter output shaft speed signal Nt on line 60, a transmission output shaft speed signal No on line 62, a system supply voltage signal Vb on line 64, a transmission fluid temperature signal Tsump on line 66 and an operator range selector position signal RS on line 68. The system voltage is supplied by the storage battery 70, and the input signals are obtained with conventional electrical transducers such as potentiometers, thermistors and magnetic speed pickups. Internally, the control unit 42 comprises a number of conventional devices including a microcomputer (uC) with internal clock and memory, an input/output device (I/O) and an array of pulse width modulated signal generators (PWM) and drivers (DR). As indicated below, a PWM generator and a driver (DR) are dedicated to each solenoid operated control valve 30 - 40. The PWM generator outputs are delivered to the respective drivers (DR) and are used to energize the respective solenoid operated control valves. The duty cycle of the PWM generator outputs determine the hydraulic pressure supplied by the solenoid operated control valves, with a low percent duty cycle yielding a low pressure and a high percent duty cycle yielding a high pressure for a normally closed valve. The hydraulic circuit of transmission 16 includes a positive displacement pump 82 for supplying pressurized hydraulic fluid from the sump or reservoir 84, to the clutches TCC and C1 - C5 through various hydraulic and electro-hydraulic valving mechanisms. After passing through a main circuit filter 86, the fluid output of pump 82 is directed to a main pressure regulator valve 88 which develops regulated fluid pressures in lines 90 and 92. The fluid in line 90, generally referred to as converter feed pressure, is directed through the torque converter 14, as schematically designated by the converter shell 97. After passing through a cooler 100 and cooler filter 102, the converter fluid is then regulated down to a lower pressure by the regulator valve 104 and directed to the transmission lube, or lubricant circuit 106. The fluid in line 92, generally referred to as main or line pressure, is supplied as an input to the solenoid operated control valves 30 - 40, and also to the control pressure regulator valve 96. The control pressure regulator valve 96 develops a somewhat lower pressure in line 98, referred to herein as the control pressure, such pressure being directed to the solenoid of each control valve 30 - 40. The fluid in line 94, referred to as the converter clutch pressure, is supplied directly by solenoid 30 to the torque converter clutch TCC to engage the same. This pressure is also supplied to the main pressure regulator valve 88 to provide a lower regulated line pressure in the converter lock-up mode. Figures 2, 3a - 3b and 6, 8, 10 and 12 are flow diagrams representative of computer program instructions executed by the computer-based control unit 42 of Figure 1 in carrying out the shift control technique decribed below. Figure 2 represents an executive or main loop program which directs the sequential execution of various subroutines. Block 130 designates a series of instructions executed at the initiation of each period of vehicle operation for setting the various timers, registers and variable values of control unit 42 to predetermined initial values. Thereafter, the blocks 132 - 140 are sequentially and repeatedly executed as indicated by the flow diagram lines. Block 132 reads the various input signal values and outputs the required control signals to the PWM generators and drivers for solenoid controlled valves 30 - 40. Blocks 134 - 138 contain diagnostic, shift scheduling, and adaptive flag logic. The clutch control logic block 140 analyzes the various system input signals described above in reference to Figure 1a, develops pressure command signals PCMD for application to the solenoid operated control valves at the next execution of block 132, and computes adaptive corrections based on the adaptive flags at shift completion. Block 140 also effects pulse-width-modulation of the solenoid drive voltage to carry out the pressure commands for specific shift operations. Block 140 is detailed in the flow chart of Figures 3a - 3b. The flow diagram of Figures 3a - 3b sets forth the program for making decisions as to the type of range shift in progress, if any, and determines the specific control for the on-coming and the off-going clutches. The program also checks whether a shift has performed within specifications, and if not, certain shift parameters are changed at shift completion according to predefined adaptive logic to correct the shift. First, lockup clutch control is executed 142 if a lockup shift is in progress 144. Then it is determined (from the shift schedule) whether a range shift is in progress 146. If not, the clutch control logic is exited. If a range shift is in progress 146, it is determined whether it is an upshift 150, a downshift 152, a neutral shift 154, or a garage shift 156. A garage shift is a shift from neutral to either drive or reverse, or a shift from drive to reverse or from reverse to drive. The control flows from either the upshift, downshift, neutral shift or the garage shift block to the end-of-shift test 160. Once the shift is completed 160, adaptive shift parameters are changed if required 162 and the duty cycle command is output 163. If the shift has not ended 160, the duty cycle command is output 163 before returning to the main loop of Figure 2. If an upshift is indicated 150, the upshift on-coming clutch control 164 and the upshift off-going clutch control 166 are activated. If a downshift is indicated 152, it is next decided whether it is a closed throttle downshift or a powered downshift 168. If it is closed throttle, a closed throttle in progress flag is set 169, the closed throttle on-coming clutch control is activated 170 and the closed throttle off-going clutch control is activated 172. If the downshift is not at closed throttle 168, the closed throttle flag is checked 173. If the flag is not set, the powered downshift on-coming clutch control 174 and the powered downshift off-going clutch control 176 are activated. If the closed throttle flag is set 173, the throttle opened during the course of the closed throttle downshift and a transition to powered downshift may be necessary; in such case, the appropriate transition logic is invoked 178. If the shift is a neutral shift 154, the neutral shift clutch control executes shifts from drive to neutral or from reverse to neutral 155. Each control phase operates by setting pressures, pressure increments, times or other values to predefined calibrated values which are herein generally called "set", "preset", "given" or "certain" values. Each such value is chosen from a table of calibrated values for each specific transmission condition, throttle range and shift type. Thus, different values are supplied for upshift, downshift, etc. as well as each range shift, e.g., 1-2, 2-1, 4-3, 5-4, etc. Converter and lockup modes may also require separate sets of calibration values. Figure 4, graphs A, B, and C detail the controlled clutch pressure for an upshift as well as the turbine speed or input speed. Graph A depicts the turbine speed versus time, graph part B depicts the commanded pressure versus time for the off-going clutch, and graph C depicts the commanded pressure versus time for the on-coming clutch. Graph A curve is typical for the case of increasing vehicle speed prior to shift initiation and indicates the turbine speed during the first range, the speed decrease during shifting, and increase again at a lower level after shifting. The peak of the turbine speed is due to the slowing action of the on-coming clutch, causing slip of the off-going clutch, and is indicative of "turbine pulldown". Turbine pulldown is detected by sensing when the turbine speed falls a set amount below the output speed multiplied by the higher speed ratio. The speed after shifting is "synchronous speed", i.e., the turbine speed (Nt) equals the output speed (No) times the lower speed ratio (SR) or Nt = No * SR. Referring to graphs B and C, it may be observed that initially, at the time of the shift command, the off-going pressure is reduced to an intermediate value, Pint, for a brief time and is then reduced to an initial value, Pioff, and then ramps down until off-going clutch slip (or turbine pulldown) is detected and then drops to zero. The brief intermediate value, Pint, is effective to reduce clutch pressure undershoot caused by solenoid dynamics. For the on-coming clutch, graph C shows that maximum pressure is commanded for a fill time. The fill time allows nearly complete stroking of the clutch plates and obtains clutch torque capacity. Then the command pressure drops to an initial value, Pion, and ramps up slowly until it causes turbine pulldown. The combination of the on-coming upward ramp and the off-going downward ramp results in a torque transition from the off-going to the on-coming clutch. Then the off-going clutch is released, and the on-coming clutch control enters a closed-loop control period wherein the pressure is adjusted to maintain the on-coming clutch slip close to a calculated slip profile. When the turbine speed, Nt, reaches synchronous speed, the pressure command is increased to maximum value to engage the clutch fully and complete the shift. The upshift process of this embodiment has several features which contribute to smooth and efficient operation. The on-coming and off-going pressure ramp commands reduce clutch timing sensitivity to the initial pressure commands. Thus, variations in clutches due to temperature or other factors do not impose critical demands on the timing of torque transition because the two ramps can continue for a variable time, subject to a limit value, so that the actual assumption of torque by the on-coming clutch determines the time of transition. Also, the immediate release of the off-going clutch following pulldown detection reduces clutch tie-up which might result in a braking action. The closed-loop control of the on-coming clutch reduces shift variation and the end-of-shift torque disturbance. The closed-loop profile control is better explained with reference to Figure 5, graph A, which shows the on-coming clutch slip speed profile in solid lines and actual slip speed in dashed lines. Slip speed is determined by comparing the turbine speed to the output speed. Specifically, slip speed is the absolute value of the difference (times a conversion factor K) between turbine speed and the product of the output speed and the speed ratio of the higher or new range, or algebraically, SLIP = ABS |K*[Nt- (No * SR(new))]|. Thus, as soon as a shift command is issued, there is slip in the on-coming clutch. The initial slip speed, SLIPI, is the slip value at the initiation of closed loop. The slip speed profile begins at that point and decreases at a fixed rate, called the first slope. Then at a determined point, the rate reduces to a second slope. The slopes are chosen so that, ideally, the actual slip speed can be made to go to zero smoothly within a given time period. The second slope is less steep than the first slope and reduces end of shift torque disturbance by more closely matching the acceleration rates on both sides of the on-coming clutch. By using slip speed as the control target, both turbine and output speeds are taken into account when controlling the shift duration. To determine the slopes of the slip profile, three constants C1, C2 and C3 are defined. The constant C1 is a fraction of SLIPI at which the second slope begins; i.e., if SLIP = C1 * SLIPI, the slope changes to slope 2. The constant C2 is the desired time to utilize the first slope. The constant C3 is the desired overall closed-loop time. The constants C2 and C3 are used only for the slope calculation and not for direct timing purposes. The first and second slopes SLOPE1, SLOPE2 are defined as: SLOPE1 = [SLIPI-(C1*SLIPI)]/C2; and SLOPE2 = C1*SLIPI/(C3-C2). The arrival at synchronization speed is determined by making several measurements in consecutive control loops. This assures that true synchronization has been achieved and maintained. If synchronization is assured, full clutch pressure is immediately applied. In the event the turbine speed goes below the synchronization speed, as shown in dashed lines in Figure 4, it is smoothly pulled up to synchronization speed by ramping the pressure up over a fixed period. This feature prevents full application of the on-coming clutch (during closed throttle shifts) when the on-coming clutch is not completely stroked. The "below sync" condition can only result when turbine pulldown is achieved through a "neutral" condition caused by lack of on-coming clutch capacity. The ramp application of the on-coming clutch will significantly reduce end-of-shift torque disturbance. Adaptive Control Adaptive control adjusts certain parameters for each type of shift independently of other types. That is, a 1-2 upshift is treated separately from a 3-4 upshift, and the shift quality of each is separately monitored and the parameters for each type are individually adjusted and stored. The process of adapting the parameters for a particular type of shift is on-going, and proceeds during each shift of that type independently of the other types of shifts. At the end of each completed shift, the block 162 sets adaptive parameters. This is accomplished in three phases: (1) diagnosing the shift to identify shift aberrations (generally recognized through aberrations in input and/or output speed and pressure commands), (2) determining whether fast or slow adaptive adjustment is appropriate, and (3) calculating new parameter values for the next shift. If fast adaptive adjustment is appropriate, a parameter value is calculated, which is generally targeted to correct the aberration fully in the next shift. If slow adaptive adjustment is appropriate, the existing parameter is changed by a set increment. The system is capable of being programmed to make a partial correction in the fast adaptive mode and this is sometimes employed to avoid over-correction. The distinction between fast and slow adaptive adjustment is based on the need to make potentially large adjustments when a new or rebuilt transmission is initially operated in a given vehicle/engine combination, as opposed to the need to make small updates due to clutch plate wear, engine performance degradation, oil viscosity degradation and the like during the life of the transmission. Initially, the electronic control is set to make fast adaptive adjustments for each type of shift. As soon as all the parameters are correctly adjusted for that type of shift, as evidenced by a shift in which substantially no aberrations are detected, the shift calibration is said to be "converged" to an optimal solution and a memory flag is set to restrict future shifts of that type to the slow adaptive mode. Once the controller 42 enters the slow mode, the correction authority is such that a misleading speed signal caused by road or system noise cannot trigger large adjustment of a control parameter. In this embodiment, the diagnosis of shift aberrations is accomplished by monitoring key shift quality indicators during the shift, and setting a memory flag whenever a certain speed change occurs under given conditions, a certain change of command pressure takes place, or certain corrective action has already been taken. Thus, the shift pattern of the transmission is embodied in these indicators. Then, by a logical assessment of the states of the several flags, the presence of a given aberration is determined and a suitable adjustment can then be calculated. These flags are described below. Adaptive Flags The following flags are set if the conditions associated with them apply. They are used in the adaptive adjustment described with reference to Figures 6a and b. PULLDOWN EARLY: Turbine speed pulldown is detected prior to a set time after the end of the fill period for a given number of times. PULLDOWN LATE: Turbine speed pulldown is not detected prior to a greater set time from the end of the fill period. FLARE DURING FILL: Flare is detected prior to another set time after the end of the fill period. Flare is defined for an upshift as the turbine speed exceeding the product of the output speed and the previous speed ratio plus a threshold constant or Nt > (No * SRold) + K. FLARE AFTER FILL: Flare is first detected within a time window beginning a set time after the end of the fill period. CLOSED-LOOP INCREASE: A closed-loop increase occurs when the commanded on-coming pressure at the first detected sync exceeds the initial closed-loop pressure command by a threshold amount. CLOSED-LOOP DECREASE: A closed-loop decrease occurs when the commanded on-coming pressure at the first detected sync is below the initial closed-loop pressure command by a threshold amount. CLUTCH OVERLAP: A decrease in turbine speed a threshold amount below the maximum turbine speed is detected before turbine pulldown for a set number of consecutive shifts. BELOW SYNC: Turbine speed is below sync speed for a set number of times. Sync speed is defined for an upshift as the turbine speed being within a window below the product of the output speed and the target speed ratio. HIGH TURBINE DECEL: Turbine acceleration is less than a set amount for a certain number of consecutive times prior to a set time following the fill period. FILL TIME DECREASED: A memory flag that indicates that the fill time has been decreased. The flag is set when the fill time is decreased and is reset when the set number of shifts occur as determined by a shift cycle counter, SCC. FAST ADAPT OVERFILLS: A memory flag that indicates that corrections to overfills will use the fast adaptive calculation. SHIFT CONVERGED: A memory flag set when a shift is completed which requires no adjustment and that indicates that the shift calibration has converged to an optimal solution. CLOSED THROTTLE: A flag that is set when the throttle setting is less than a threshold amount at the time of the range shift command. SHORT SHIFT: The time period between the detection of sync speed and the detection of off-going clutch slip is less than a threshold amount. LONG SHIFT: The time period between the detection of sync speed and the detection of off-going clutch slip is greater than a threshold amount. Fast Adaptive Algorithms The parameters to be adjusted in this embodiment for converging an upshift quickly to the optimal calibration are: fill time, initial on-coming pressure, and initial off-going pressure. Each of these parameters may be increased or decreased in accordance with the detected nature of the previous shift. A brief overview of the techniques used in this embodiment for calculating the fast adaptive adjustments of the shift parameters are as follows: FILL TIME: If turbine speed flare is observed, the correction is based on the time of maximum turbine speed flare, Tnmax. If flare is not observed, the correction is based on the time of turbine speed pulldown Tpd. In each case, the measurement is an estimate of the actual on-coming clutch fill time. INITIAL ON-COMING PRESSURE MODIFICATION: The correction is based on the closed-loop error signal, which is an estimate of the change in the on-coming clutch pressure required to achieve the desired pulldown rate. INITIAL OFF-GOING PRESSURE: If turbine speed flare is observed, the correction is based on the off-going pressure level where the flare was first observed. If flare is not observed, the correction is based on the off-going pressure level which allowed turbine pulldown to occur. In each case, the measurement is an estimate of the desired off-going pressure at the end of the on-coming clutch fill time. Upshift Logic The flow diagram of Figure 6 details the CHANGE ADAPTIVE SHIFT PARAMETERS block 162 of Figure 3b. If the shift cycle counter, SCC, is zero 200, the FILL TIME DECREASED flag is reset 202; otherwise SCC is decremented 204. If the BELOW SYNC flag is set 206, the initial on-coming pressure Pion is increased by a preset increment K1 208 and the adaptive process ends for this shift. The below sync condition occurs when the on-coming clutch is underfilled and no engine power is present. When the off-going pressure is dropped, the transmission goes to neutral and the turbine speed will float down to engine idle speed. As it passes sync speed, the BELOW SYNC flag is set and the adaptive logic causes the on-coming pressure to be incremented at the next shift. When the BELOW SYNC flag is not set 206 and the PULLDOWN EARLY flag is set 210, the CLOSED THROTTLE flag is tested 212. If it is not set, the Decrease Fill Time program 214 is entered. If CLOSED THROTTLE is set and HI TURBINE DECEL flag is set 216, the Decrease Fill Time program is run, but if HI TURBINE DECEL is not set, the increase Pioff program 218 is run. If the PULL DOWN EARLY flag is not set 210, the FAST ADAPTIVE OVERFILLS flag is reset 220 and the adapt Pion program 222 is run. Then, if the throttle is closed 224, the adaptive loop ends; if the throttle is not closed, the FLARE DURING FILL flag is tested 226. If FLARE DURING FILL is set, the increase Pioff program is run 218 but if not set, FLARE AFTER FILL is tested 228. If the latter is set and FILL TIME DECREASED is set 230, the initial off-going pressure Pioff is incremented by the value K1 232. If the fill time had not been decreased 230, the Increase Fill Time program is run 234. When there is no flare after fill 228, and the OVERLAP flag is set 236 or PULL DOWN LATE is set and CLOSED-LOOP INCREASE (CLI) is not set 238, the decrease Pioff program is run 240. Figure 7 graphs A and B show commanded and actual on-coming pressure Pon and turbine speed Nt, respectively, for a condition of early pulldown. The pulldown occurs at time Tpd, prior to the end of the fill period Tfill. The actual pressure goes high within the fill period to cause the early pulldown. The correction is made by reducing the fill time term Tfill to Tpd less an offset K7 to be sure of avoiding an overfill. A minimum amount K8 of fill time reduction is programmed to insure a minimum change in fill time. Thus, Tfill is updated according to the lesser of: Tfill - Tpd - K7 or Tfill - K8 Figure 8 is the flow chart for the decrease fill time routine 214 of Figure 6b. If the FAST ADAPTIVE OVERFILLS (FAO) flag is not set 250, the fill time is decremented by a small set amount K2 to carry out the slow adaptive mode. The same is true if the SHIFT CONVERGED FLAG is set 254. When the FAO flag is set but the shift has not converged, the new fill time Tfill is calculated 256 as described above in reference to Figure 7 to carry out the fast adaptive mode. Finally, regardless of whether fast or slow adaptive mode is chosen, the shift cycle counter SCC is set to a calibrated value K9, the FILL TIME DECREASED flag is set and the FAO flag is set 258. In the logic depicted in Figure 6, the flare condition is dealt with in block 218 and blocks 226 through 234. If flare occurs during clutch fill time 226, Pioff is too low and should be increased 218. If flare occurs after fill time 228, the fill time is too low and generally should be increased 234. To prevent an overfill for borderline flare times (just after fill), a fill time increase soon after a decrease 214 is not allowed 230 and instead the initial off-going pressure Pioff is incremented 232 to manage the flare. This feature is implemented by the shift cycle counter, SCC, which is set to a predetermined value K9 by the decrease fill time routine 214 and sets the FILL TIME DECREASED (FTD) flag 258. Thereafter the increase fill time routine 234 can not be accessed until SCC is decremented to zero 200 - 204. Over time, noise disturbance could cause the detection of an overfill and the targeting of a large decrease in the fill time. In this embodiment, the FAST ADAPTIVE OVERFILLS (FAO) flag has been provided to guard against erroneously decreasing the fill time and then requiring a number of shifts to reset the FTD flag to allow the correction of the fill time. Initially, the FAO flag is set so that overfills will be adapted using the fast adaptive algorithm. However, once a shift is done where an overfill is not detected through the PULL DOWN EARLY flag 210, then the FAO flag is reset 220. If an overfill is detected after the FAO flag has been reset, then only a small decrease to the fill time is allowed. The FAO flag will then be set so that if a second consecutive overfill is detected, the fast adaptive change will be used. Figure 9, graphs A and B, show commanded and actual on-coming pressure Pon and turbine speed Nt, respectively, for a condition of turbine speed flare after the fill period Tfill. The turbine speed Nt increases above that required to maintain the upper speed ratio and reaches a peak at time Ntmax. The difference DT between Tfill and Ntmax, is reduced by an offset, K5, multiplied by a fractional constant K4, and used as the fill time increase. The constant K4 is needed to prevent an over correction. A minimum adjustment is assured by using DT = K3, where K3 is a preset value. Thus, Tfill is updated according to the greater of: Tfill + K4*(DT - K5) or Tfill + K4*(K3 - K5) Figure 10 shows the flow diagram for the increase fill time routine 234. If the shift has converged 260 the slow adaptive mode is used 262 but if it has not converged, DT is calculated 264 and the next Tfill is calculated 266. Figure 11, graphs A and B, show commanded on-coming pressure Pon and turbine speed Nt, respectively. Traces corresponding to a condition of low initial on-coming pressure Pion are shown in solid lines and traces corresponding to a condition of high Pion are shown in dashed lines. If Pion is too low, the shift may be too long, and Pion should be increased. Likewise, a high Pion yields a short shift and Pion should be decreased. Even in the absence of a long or short shift, a closed-loop decrease reveals that the closed-loop operation had to lower the pressure; accordingly, it is desirable to reduce the initial on-coming pressure Pion so that the closed-loop control will not have to make that correction. Similarly, a closed-loop increase indicates that the initial on-coming pressure Pion should be increased. The difference Dp between initial and final closed-loop pressures, or Dp = Pfcl - Picl is, in this embodiment, the basis for calculating the correction. An offset value K11 is subtracted from Pion to control the closed-loop pressure change to the value K11, thereby allowing the closed-loop increase or decrease to be programmed to the desired shape of the closed-loop pressure response. Routine 222 of Figure 6a for adapting the initial on-coming pressure Pion is shown in further detail in Figure 12. If the SHORT SHIFT flag is set and the PULL DOWN LATE (PDL) flag is not set 270, and the CLOSED-LOOP DECREASE (CLD) flag is not set 272, the slow adaptive mode is used to decrement Pion 274 by the constant K1. If CLOSED-LOOP DECREASE is set and the shift has converged 276, the same slow adaptive mode is used. If the shift has not converged, the fast adaptive value is applied 278 as described above in reference to Figure 11. If the LONG SHIFT flag is not set 280 and the CLOSED-LOOP INCREASE (CLI) flag is set 282, the slow adaptive mode is used to increment Pion 284 by K1. If the CLOSED LOOP INCREASE flag is set and the shift has converged 286, the same slow adaptive mode 284 is used, but if the shift has not converged, the fast adaptive is used 278. Finally, if there is neither a short shift 270 nor a long shift 280 and there is a closed-loop decrease 288, control passes to the shift converged block 276 to choose either a fast or slow adaptive decrease. If there is no closed-loop decrease 288 but there is a closed-loop increase 290, the shift converged block 286 determines whether to make a fast or slow adaptive pressure increase. An appropriate event occurring at the wrong time is a type of aberration which is used to diagnose a shift problem. The time that the off-going clutch releases is important since it results in flare if too early, or in excessive clutch overlap if too late. These events are all reflected in the turbine speed Nt. When the initial off-going pressure, Pioff, is too low and engine power is present, the off-going clutch releases too early and flare during fill time results. When no engine power is present, early pulldown occurs without HIGH SPEED TURBINE DECEL. The remedy is to increase the initial off-going pressure, Pioff. Figure 13 graphs A, B and C, show off-going pressure Poff, on-coming pressure Pon, and turbine speed Nt, respectively. In graph C, flare is shown in solid lines and early pulldown is shown in dashed lines. The time of release Trel is the point the flare or the pulldown begins. The constant K12 is an offset after fill time Tfill such that (Tfill + K12) is the desired clutch release point. The controller 42 records the off-going pressure Prel at the release time. The actual pressure, Pact, at the desired release point is subtracted from the stored release pressure, Prel so that Dp = Prel - Pact. Dp is assigned a minimum value K13. If the shift has not converged, a correction is made by increasing the initial off-going pressure Pioff by Dp to obtain a higher ramp pressure as shown by the dotted line in graph A. If a conservative correction is desired, a fraction of Dp may be used as the correction to assure that an over-correction does not occur. If the shift has converged, a small pressure increment is added to the initial off-going pressure Pioff. When the initial off-going pressure Pioff is too high, the on-coming clutch cannot overcome the off-going clutch. As the off-going pressure continues to drop, it eventually reaches a value, Poff(Tpd), where the on-coming clutch can overcome the off-going clutch pressure and cause turbine pulldown. The adaptive algorithm will decrease the initial off-going pressure Pioff such that the next time the same type of shift occurs, the off-going pressure will be at this value when the on-coming clutch has gained capacity. For clutch overlap, the on-coming clutch capacity occurs at the time when overlap was detected. However, if late pulldown is detected, then on-coming clutch capacity is assumed to occur just after the end of fill at t = Tfill + K15, where K15 is an offset. Figure 14, graphs A, B and C, show the off-going commanded pressure Poff, the on-coming commanded pressure Pon and the turbine speed Nt respectively, for the case of late pulldown. The pressure at the pulldown time Poff(Tpd) is subtracted from the pressure at the desired pulldown time Poff(Tfill+K15) to obtain the pressure difference Dp which is used to calculate the target correction for the fast adaptive mode. Figure 15, graphs A, B and C, show the off-going commanded pressure Poff, the on-coming commanded pressure Pon and the turbine speed Nt, respectively, for the case of clutch overlap. The overlap occurs at time Tovlp while pulldown occurs at Tpd. The difference of pressures at those times Dp = Poff (Tovlp) - Poff(Tpd) is used to establish the target correction of the initial off-going pressure Pioff for the fast adaptive mode. The decrease Pioff routine 240 of Figure 6b calculates the pressure difference in accordance with the state of the OVERLAP flag and requests at least a minimum value for fast adaptive mode; it then calculates the new initial pressure Pioff for the fast adaptive mode. The slow adaptive mode is selected if the shift has converged. In each of the described fast adaptive routines, the correction value is calculated such that it will correct the related aberration fully on the next shift. As a design convenience, a percentage multiplier (such as the fractional constant K4 in Figure 10) may be provided in each calculation to allow adjustment of the correction value. This is useful, for example, if the calculated correction for a particular type of transmission actually results in an over-correction. Then a percentage of the correction could be specified rather than using the whole value. Reference is made to our co-pending applications EP-A-0,435,375, EP-A-0,435,378, EP-A-0,435,373 and EP-A-0,435,376, filed and published the same day as this application.

Claims: A method of controlling the change in an automatic transmission for a vehicle from an off-going fluid pressure operated torque transmitting device (C1-C5) associated with a first speed ratio to an on-coming fluid pressure operated torque transmitting device (C1-C5) associated with a second speed ratio, wherein the off-going torque transmitting device is disengaged substantially concurrently with the engagement of the on-coming torque transmitting device, the automatic transmission including an input (22) and an output (24); the method comprising the steps of establishing a desired pattern of input speed function for the change; disengaging the off-going torque transmitting device (C1-C5) by reducing ist pre-change operating pressure (Pioff) on the basis of a first initial value, and engaging the on-coming torque transmitting device (C1-C5) by supplying it with an initial on-coming pressure (Pion) on the basis of a second initial value, the initial values affecting the input speed function and being calibrated to approximate the desired pattern; monitoring the transmission input speed and comparing a measured input speed with the desired pattern to detect any aberration; on first-time detection of an aberration, carrying out a first adjustment on a stored parameter (Tfill, Pion, Pioff) related at least to the first initial value (Pioff) responsible for such aberration by calculating the change required substantially to eliminate the aberration and altering the stored parameter on the basis thereof, thereby to effect an adaptive adjustment of the transmission in respect of the initial value to its operating environment; and on subsequent detection of such an aberration in a subsequent change, carrying out a subsequent adjustment of the stored parameter by a predetermined amount (K₁, K₂) thereby to effect a corrective adjustment thereof. A method according to claim 1, wherein the first adjustment is made in a plurality of stages and wherein once the first stage of first adjustment of the stored parameter is carried out and no aberration is detected in a subsequent change, a further stage of first adjustment is only carried out following the detection of an aberration in at least two consecutive subsequent changes. A method according to claim 1, wherein for a change from an off-going fluid pressure operated torque transmitting device (C1-C5) associated with a higher speed ratio to an on-coming fluid pressure operated torque transmitting device (C1-C5) associated with a lower speed ratio, the method includes the step of engaging the on-coming torque transmitting device (C1-C5) by supplying it with on-coming pressure for a predetermined on-coming period and thereafter controlling the on-coming pressure to effect a progressive engagement of the on-coming torque transmitting device, the stored parameter being related to the predefined initial off-going pressure so as to increase the initial off-going pressure in response to the occurrence of flare in the transmission input speed during the on-coming period, indicative of the initial off-coming pressure being too low, and being adjusted so as to decrease the initial off going pressure in response to the occurrence of an input speed change, indicative of the initial off-going pressure being too high. A method according to claim 3, wherein the step of adjusting the stored parameter comprises the step of adjusting the stored parameter to the first initial value, being a relatively large amount calculated from the times of occurrence of a plurality of aberrations during previous changes, prior to an non-aberrant change so as to obtain a non-aberrant change, and to another value, being a relatively smaller amount after the occurrence of a non-aberrant change. A method according to claim 3 or 4, wherein the step of adjusting the stored parameter so as to decrease the initial off-going pressure includes the steps of detecting a decrease in transmission input speed after the on-coming period and prior to pulldown, or detecting pulldown more than a prescribed time after the on-coming period, wherein pulldown occurs when the input speed is reduced to substantially less than the product of the transmission output speed and the higher speed ratio. A method according to claim 3, 4 or 5, wherein an amount by which the stored parameter is decreased is calculated as a function of the difference between the controlled on-coming pressure at the time of the aberration occurring during a predefined event and the controlled on-coming pressure at the desired time of the predefined event. A method according to claim 3, 4 or 5, wherein an amount by which the stored parameter is increased is calculated as a function of the difference between the controlled on-coming pressure at the time of the aberration occurring during a predefined event and the controlled on-coming pressure at the desired time of the predefined event. A method according to any one of claims 3 to 7, including the step of adjusting a further stored parameter related to the predefined on-coming period so as to increase the on-coming period in response to the occurrence of input speed flare during the change and after the on-coming period. A method according to claim 8, wherein the amount by which the on-coming period is increased is calculated from the difference between the time at which input speed is at a maximum and the end of the on-coming period. A method according to any one of claims 3 to 9, wherein following the occurrence of an adjustment which decreases the predefined on-coming period, the stored parameter related to the predefined initial off-going pressure is increased so as to increase the initial off-going pressure. A method according to any one of claims 3 to 10, wherein when the input speed change occurs during a closed throttle condition and is accompanied by input deceleration, decrease of the stored parameter related to the initial off-going pressure is inhibited and the stored parameter related to the on-coming period is adjusted so as to decrease the on-coming period. A method according to any one of claims 3 to 11, including the steps of detecting pulldown during the on-coming period, wherein pulldown is determined to have occurred when the input speed is substantially less than the product of the transmission output speed and the higher speed ratio; and in response to the detection of pulldown, the stored parameter related to the on-coming period is adjusted so as to decrease the on-coming period. A method according to claim 12, wherein the amount by which the on-coming period is decreased is related to the difference between the time of pulldown and the end of the on-coming period.

Inventors: HUNTER JOSEPH HENRY, LENTZ CARL ALBERT, RUNDE JEFFREY KURT, WILES CHRISTOPHER RUSSELL, HUNTER, JOSEPH HENRY, LENTZ, CARL ALBERT, RUNDE, JEFFREY KURT, WILES, CHRISTOPHER RUSSELL
Applicants: GEN MOTORS CORP, GENERAL MOTORS CORPORATION
Application year: 1990
Main classification: F16H61
IPC codes: F16H61, F16H59