Method of controlling gear changes in an automatic transmission

Abstract: In an automatic transmission, clutch-to-clutch powered downshifting is controlled by filling the on-coming clutch (C1-C5) at a low pressure while ramping down the off-going clutch pressure until turbine (T) speed is pulled up due to off-going clutch slippage, and then increasing the off-going pressure stepwise to compensate for the change from static to dynamic coefficients of friction. Then the on-coming pressure (Pion) is gradually ramped up and a closed-loop profile control period starts wherein the slip speed of the on-coming clutch is measured and controlled to a slip speed profile by controlling the off-going clutch pressure. When synchronization of the on-coming clutch (C1-C5) is first detected, a closed-loop sync control period starts wherein the off-going pressure (Pioff) is controlled to minimize the slip and the on-coming pressure (Pion) is ramped up at a steeper rate to begin clutch engagement during the sync control period. Adaptive control is accomplished for the initial on-coming pressure by an iterative process which decreases that pressure stepwise until flare occurs and then increases the pressure to stop the flare and repeating the changes in smaller steps to approach the flare condition. Initial off-going pressure is modified when early slip or late slip of the off-going pressure is detected. A modification of off-going pressure step value is effected when the final pressure in the closed-loop period is greater or smaller than the initial pressure. The modifications are targeted to correct fully the respective conditions.

Description: This invention relates to a method of controlling changes in an automatic transmission for a motor vehicle from a lower speed ratio to a higher speed ratio on the basis of the quality of previous changes. 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 a downshift, a shift is made from a low speed ratio to a high speed ratio. In the type of transmission described below, the downshift is accomplished by disengaging a clutch associated with the lower speed ratio and engaging a clutch associated with the higher speed ratio thereby to 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 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. 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-0,331,523 discloses a method of preventing engine racing or flare in which, when flare is detected, the initial on-coming pressure on the on-coming torque transmitting device is increased to a level to prevent engine flare. The method includes the step of adjusting the initial on-coming pressure repeatedly, by amounts dependent upon the amount of flare detected, until flare no longer occurs. EP-A-0,327,004 discloses a method of controlling changes in an automatic transmission which provides closed loop control of the off-going clutch and in which the control time is adjusted to be proximate a preset value. According to an aspect of the present invention, there is provided a method of controlling changes in an automatic transmission for a vehicle from a lower speed ratio to a higher speed ratio as defined in Claim 1. The method can adaptively control a powered downshift in an automatic transmission, wherein a transmission aberration during a shift is diagnosed and corrected fully (or optionally, partially) on the next powered downshift between the same speed ratios. Preferably, the method is capable of making large corrections initially and is limited to small changes thereafter. In a practical embodiment, the method is carried out by monitoring transmission input and output speeds during a powered downshift, and identifying departures from acceptable speed patterns and the times during the shift when the departures occur. For closed-loop control, the relationship of commanded clutch pressures is similarly monitored. Each particular type of departure calls for a particular remedy, and in the embodiment, 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, large changes are inhibited and small increments are used instead. Preferably, the method comprises the steps of iteratively adjusting the initial on-coming pressure up and down to approach closely a desired pressure and of periodically repeating the adjustment. The present 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, graphs A and B, are graphs illustrating on-coming pressure command and off-going pressure command, respectively, for clutch-to-clutch shifting; Figure 5, graphs A and B, are slip diagrams of the on-coming clutch for closed-loop operation of the off-going clutch and of turbine speed during the closed-loop period, respectively; Figures 6 to 9 are flow diagrams illustrating an embodiment of powered downshift logic for the off-going clutch; Figure 10 is a flow diagram illustrating an embodiment of powered downshift logic for the on-coming clutch; Figures 11a and 11b are a flow diagram of an embodiment of main adaptive logic for powered downshift; Figure 12 is a graph illustrating the closed-loop increase of pressure for the off-going pressure; Figure 13 is a flow diagram of an embodiment of adaptive logic for increasing the initial step pressure; Figure 14 is a graph illustrating the adaptive increase of initial off-going pressure; Figure 15 is a graph illustrating an embodiment of iterative process for modifying the initial on-coming pressure; Figures 16 and 17 are flow diagrams of an embodiment of method for respectively decreasing and increasing the initial on-coming pressure to carry out the process shown in Figure 15; Figure 18, graphs A and B, are turbine speed curves for the cases of a short converter shift and all other shifts, respectively. 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 activated 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, 3 and 6 - 11 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 described 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 and B, show respectively, the on-coming and off-going pressure commands for control of the on-coming and off-going clutches during a powered downshift. At shift initiation, the off-going clutch pressure command is stepped to an offset value for a set time, then stepped to an initial pressure value Pinitial, and is then ramped downward at a first off-going rate until turbine speed pullup occurs. This pullup is a result of the beginning of off-going clutch slip. Pullup is detected by the turbine speed Nt becoming greater than the product of the output speed No and the old or lower speed ratio SR(old) plus a constant K, or algebraically, Nt > No * SR(old) + K. During this same time interval, the on-coming pressure command is set at a low "fill" pressure level to prepare for the time when the on-coming clutch must engage. When the off-going clutch starts to slip, the coefficient of friction in the clutch changes from a static level to a dynamic level. The friction reduction and its associated decrease in clutch torque capacity is compensated for by increasing the clutch pressure in a step fashion Pstep to a level at which the torque capacity of the clutch remains nearly constant. This pressure command level is maintained for a preset hold time (HOLD) or until on-coming clutch synchronization (sync) has occurred. Synchronization is detected when the turbine speed equals the output speed times the new or high speed ratio, or Nt = No * SR(new) . If the hold time has elapsed before on-coming clutch synchronization, the off-going clutch pressure command is determined by a closed-loop control signal which attempts to maintain on-coming clutch slip on a predefined profile. This closed-loop slip profile control continues until on-coming clutch synchronization (first sync) has been detected. Beginning at the detected pullup and continuing through this interval of off-going clutch closed-loop control until synchronization is detected, the on-coming clutch pressure is ramped upward at a first ramp rate. 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 closed-loop profile control is carried out by correcting the off-going clutch command pressure by a term which is proportional to slip speed error. The effect on turbine speed is shown in Figure 5, graph B, where pullup is detected when turbine speed increases a certain amount above the lower dashed line which represents the product of output speed (NO) and speed ratio for the old range (SR OLD). Thereafter the turbine speed increases in accordance with the profile control where on-coming clutch slip speed is seen to be the difference between the turbine speed curve and the upper dashed line which represents the product of output speed (NO) and speed ratio for the new range (SR NEW). Ideally, the slip speed converges to zero but in some conditions the turbine speed exceeds the target value and turbine flare results as shown by broken lines in graphs A and B. Once the first sync has been detected, a closed-loop sync control is invoked to bring the slip speed to zero by integral-plus-proportional control, thereby to maintain on-coming clutch synchronization. Simultaneously, the ramp rate of the on-coming clutch pressure command is increased to a second ramp rate which is greater than the first (graph A of Figure 4). This closed-loop sync control and second ramp rate continues until a preset number of additional syncs are detected. Then to complete the shift, the off-going pressure is ramped toward zero at a second off-going ramp rate, and the on-coming pressure is increased at a third ramp rate which is greater than its second ramp rate. Control can return to the closed-loop sync control from the second off-going ramp phase if turbine flare is detected (indicating on-coming clutch under-fill). The closed-loop sync control is an integral/proportional control algorithm using the slip speed as an error signal and correcting the off-going clutch pressure by the sum of proportional and integral terms. The second ramp rate of the on-coming clutch continues throughout this phase. Time constraints are imposed to assure that the shift does not take too long. If a set time after first sync detection expires, or if a set time after off-going clutch slip expires, the shift is completed by ramping both pressures to their final values, as though the preset number of syncs were detected. There are some cases where the sync control phase is bypassed and shift completion directly follows the profile control phase. Two of these cases are a near-converged converter-lockup shift and a near-converged long open-converter shift. This determination depends on the adaptive control (block 162) which calculates the amount of a shift parameter change required to achieve a high quality shift (or convergence). If only a small correction is needed, the shift is "near converged". If the torque converter is in the open-converter mode and the time between slip and first sync exceeds a preset value, it is considered to be a long converter shift. In these two cases, the off-going pressure is immediately exhausted and the on-coming pressure is ramped up at the third ramp rate. Sync control is also bypassed if the time since pullup exceeds a set value. In that case, however, the off-going clutch is ramped off at the second rate instead of being immediately exhausted. It has been found that the control technique described above has several advantages over prior techniques. The low fill command pressure for the on-coming clutch is insufficient to cause torque transfer until late in the second ramp phase. This eliminates the detrimental effect on shift quality resulting from an on-coming clutch overfill at maximum pressure and allows off-going clutch control of the shift. The multiple slopes or ramp rates of the on-coming pressure command provide significant protection from shift miscalibration due to system variations. The first slope begins the clutch fill process but ensures that no significant pressure is generated. The second slope completes the fill process and begins the on-coming clutch pull-in process. The third slope completes the clutch application. Fill (or compression) of the on-coming clutch occurs simultaneously with the reduction of on-coming clutch slip which is caused by the increased turbine speed permitted by the slipping off-going clutch. Consequently, the on-coming clutch is ready for application immediately upon the detection of synchronization. It has been found that this can shorten the holding period required for off-going clutch control and significantly reduce the energy dissipation required in the off-going clutch. Another important feature of this embodiment is the off-going clutch pressure command step which follows the detection of turbine pullup. This compensates for the change from static to dynamic friction and allows the off-going clutch to gain control of the on-coming clutch pullup rate prior to initiation of the closed-loop profile control. The delay in beginning closed-loop control after the pressure command step allows the pressure to react fully to the step command before introducing additional command changes. The use of the closed-loop on-coming clutch slip speed profile control establishes slip control before synchronization is reached and thereby brings the on-coming clutch elements to the same speed before torque transfer takes place in that clutch. The following sync control, when employed, continues to keep the clutch close to sync as the clutch engaging pressure is applied, thereby minimizing turbine speed flare and associated shift quality degradation. In addition, the slip profile itself helps to provide consistent shift timing. Additional protection from shift miscalibration is provided by constantly monitoring turbine flare during the second ramp of the off-going clutch. If flare occurs (indicating insufficient on-coming clutch capacity), the sync control phase is reestablished. This allows additional time for on-coming clutch fill and prevents additional flare. A key part of the powered downshift clutch control of this embodiment is the immediate exhaust of the off-going clutch for near-converged converter-lockup and long open-converter shifts. This significantly reduces off-going clutch heat generation due to clutch synchronization control when this task is not required to achieve desired shift quality. The flow charts of Figures 6 to 10 illustrate the control logic incorporated in the program for powered downshift control. Figure 6 shows the logic flow for the off-going clutch control 176. First, the shift time is tested 200 and if it has expired, the off-going clutch is exhausted 202 to end the shift. If the time has not elapsed, SHIFT PHASE is examined. SHIFT PHASE is a pointer indicating the stage of shift progress. If the SHIFT PHASE is OFFSET 204, and the loop is run for the first time 206, an initial pressure value, Pinitial, is set 208. If not, block 208 is bypassed. Next, the pressure offset phase is executed 210. In the offset phase, if the time since shift initiation does not exceed a set value, the off-going pressure command is set equal to the chosen initial pressure plus an offset amount, Pinitial + Offset. If the time does exceed that value, the off-going pressure command is set to the chosen initial pressure and SHIFT PHASE is set to FIRST OFF-GOING RAMP. If SHIFT PHASE is FIRST OFF-GOING RAMP 212, the FIRST OFF-GOING RAMP routine is executed 214. In that routine, the off-going pressure command is decremented by a preset value. If turbine pullup is then detected, the off-going pressure command is increased by a step amount and SHIFT PHASE is set to CLOSED-LOOP DELAY. If SHIFT PHASE is CLOSED-LOOP DELAY 216, the CLOSED-LOOP DELAY routine is executed 218. There, the off-going pressure command is held at its last value. The closed-loop slip speed profile is computed, and, when either a given time has elapsed or one sync (or oversync) is detected, SHIFT PHASE is set to PROFILE CLOSED-LOOP. If SHIFT PHASE equals PROFILE CLOSED-LOOP 220, the PROFILE CLOSED-LOOP routine is executed 222 as shown in Figure 7. The slip speed error is calculated from the profile (Figure 5) 224 and closed-loop pressure command is computed using proportional control 226. If sync or a value above sync is detected 228, and if the shift is a near-converged lockup shift 230 or a near-converged long converter shift 232, SHIFT PHASE is set to END 234. Otherwise, SHIFT PHASE is set to SYNC CLOSED-LOOP 236. If sync (or oversync) is not detected 228, and the time since pullup detection exceeds a set TIMEOUT value 238, SHIFT PHASE is set to SECOND OFF-GOING RAMP 240. If SHIFT PHASE is SECOND OFF-GOING RAMP 242, the SECOND OFF-GOING RAMP routine is executed 244, as shown in Figure 8. The off-going pressure command is decremented by a set amount 246 each time through the loop. If a previous TIMEOUT has been encountered 248, or if no flare is detected 250, SHIFT PHASE is set to END provided sync has been detected for a certain time and the on-coming pressure command is full on 254. If turbine flare is detected 250, the off-going pressure command is set to the last computed sync closed-loop value 256 and SHIFT PHASE is set to SYNC CLOSED-LOOP 258. If SHIFT PHASE is SYNC CLOSED-LOOP 260, the SYNC CLOSED-LOOP routine is executed 262 as shown in Figure 9. The closed-loop slip speed error is computed from sync speed 264 and the pressure command is computed using integral/proportional control 266. If a certain number of sync signals (not necessarily consecutive) have not been detected 268, it is determined whether a time from first sync 270 or a time from pullup 272 have timed out. If not timed out, the routine repeats but if either has timed out, SHIFT PHASE is set to SECOND OFF-GOING RAMP 274. If the required number of syncs have been detected 268, a delay timer is initialized 276, or if already initialized 278, it is decremented 280. Then if the delay timer times out 282, SHIFT PHASE is set to SECOND OFF-GOING RAMP 284 and if not timed out the loop repeats. The powered downshift on-coming clutch control logic program 174 is shown in Figure 10. If the shift time exceeds a preset limit value 300, the on-coming pressure command is set to its maximum value 302 to assure immediate completion of the shift. If the SHIFT PHASE is equal to INITIAL PRESSURE 304, the INITIAL PRESSURE routine is executed 306. If it is the first time through the routine 308, initial pressure and other parameters are chosen based on throttle value and shift type 310. In this and the subsequent routines, tables of calibrated values may be prepared for various throttle and transmission conditions so that the optimum pressure, pressure increment or time can be selected. The initial pressure routine sets the pressure command to an initial pressure value. The pressure command does not change as the loop repeats unless pullup is detected or the off-going pressure command equals zero. In those events, SHIFT PHASE is set to FIRST RAMP and first ramp increment is chosen based on transmission mode (lockup or converter). If the SHIFT PHASE equals FIRST RAMP 312, the FIRST RAMP routine is executed 314. There the on-coming pressure command is incremented by the chosen increment value each time through the loop. If on-coming clutch sync or an above sync condition is detected, SHIFT PHASE is set to SECOND RAMP and the pressure increment is chosen for the second ramp. If the SHIFT PHASE equals SECOND RAMP 316, the SECOND RAMP routine is executed 318. There the pressure command is incremented by the chosen value each time through the loop. If (1) a given number of syncs are detected, (2) the time from pullup exceeds a set value, or (3) the time from sync exceeds another set value, SHIFT PHASE is set to THIRD RAMP and the third ramp pressure increment is chosen. If the SHIFT PHASE equals THIRD RAMP 320, the THIRD RAMP routine is executed 322. In that routine the on-coming pressure command is incremented by the chosen value. If the maximum on-coming pressure is commanded and sync has been detected for a given time the shift is completed. Adaptive Control Adaptive control adjusts certain parameters for each type of shift independently of other types. That is, a 2-1 powered downshift is treated separately from a 4-3 powered downshift, 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 of Figure 3b sets adaptive conditions. This is accomplished in three phases: diagnosing the shift to identify shift aberrations which are generally recognized through input and/or output speed aberrations, determining whether fast or slow adaptive adjustment is permitted, and calculating new parameter values for the next shift. If fast adaptive adjustment is permitted, a parameter value is calculated which is generally targeted to correct fully the aberration in the next shift or if slow adaptive adjustment is required, changing the existing parameter 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 a possible "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 control future shifts of that type in the slow adaptive mode. Once the controller 42 enters the slow mode, provision is made to assure that a misleading speed signal caused by system noises can not trigger a large adjustment when little, if any, adjustment is appropriate. In this embodiment, in the case of initial on-coming pressure, flare occurs when pressure is too low but there is no convenient diagnosis available for the pressure being too high. Here, the pressure is decreased in steps until flare occurs and then the pressure is increased by a set amount and again decreased in smaller steps. This procedure is continued with progressively smaller steps. Thus, an iterative adaptive correction process is used to control that pressure value instead of a full correction in one step. 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 detected 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. The state of the flags is then used in the adaptive adjustment step 162; as is described below with reference to Figures 11a and 11b. SLIP EARLY: Off-going clutch slip is detected within a set time from shift initiation for a given number of times. SLIP LATE: Off-going clutch slip is not detected within a set time from shift initiation. TURBINE FLARE (Short Converter Shift): During converter mode, time from slip to first detection of sync or past sync is less than a constant value. In this condition, flare is detected after a set number of nonconsecutive syncs or past syncs have been achieved. TURBINE FLARE (Long Converter or Lock-Up Shift) In the absence of the short converter shift condition or for lock-up mode, flare is detected after the first sync or past sync has been achieved. CLOSED-LOOP INCREASE: A closed-loop increase occurs when Pfinal - Picl - Poffset > Pcli, where Picl = The initial closed-loop clutch pressure. Pfinal = The final closed-loop clutch pressure. For short converter shifts, the pressure is measured at the end of the sync control period. For long converter or lock-up shifts, the pressure is measured at the first sync or past sync. Poffset = A constant to define a programmed amount of closed-loop change. Pcli = A constant to define the amount of closed-loop change required to flag a closed-loop increase. CLOSED-LOOP DECREASE: A closed-loop decrease occurs when Pfinal - Picl -Poffset < Pcld, where Pcld = A constant to define the amount of closed-loop change required to flag a closed-loop decrease. SHORT SHIFT: Time from first slip to first sync or past sync is less than a set value (different from the value used to determine the short converter shift). FAST ADAPT MODE: A memory flag which indicates that the shift calibration has not converged to an optimal solution. Adaptive Logic A powered downshift is adapted by adjustment of the initial on-coming pressure, Pion, the initial off-going pressure, Pioff, and an off-going step pressure, Pstep. The adjustment of each is undertaken in accordance with the flag settings as set forth in the flow diagram of Figures 11a-11b. First, a shift cycle counter, SCC, is decremented 350. A separate counter is used for a powered downshift to each range. Then if the SLIP EARLY flag is set 352, indicating that the pressure on the off-going clutch is too low, the Increase Pioff routine is executed 354. If the TURBINE FLARE flag is set 356, the program ends, but if it is not set, the Decrease Pion routine is run 358 to decrease the initial on-coming pressure. If the SLIP EARLY flag is not set 352 and there is a closed-loop increase (CLI) 360, the Increase Pstep routine is run 362 to increase the starting pressure of the closed-loop. If there is a closed-loop decrease (CLD) 364, the Decrease Pstep program is run 366. If the CLD flag is not set and there is a SHORT SHIFT flag 368, Pstep is set to Pstep + K1 370 to increment the step pressure by a small amount. If the SLIP LATE flag is set 372, the Decrease Pioff routine is run to lower the initial off-going clutch pressure 374. Then, if there is no turbine flare 376, the program ends; if there is flare, and the SHORT SHIFT flag is not set 378, the Increase Pion routine is run 380. If the SLIP LATE flag is not set 372 and there is no turbine flare 382 the Decrease Pion routine 358 is run; if there is turbine flare 382, the program flows to the Short Shift block 378, as in the case of SLIP LATE with flare. Figure 12 illustrates the closed-loop increase condition in the off-going clutch. In the illustration, the closed-loop control begins immediately after the pressure step Pstep (which sets the initial closed-loop pressure Picl) and ends at Pfinal. The difference Dp = Pfinal - Picl is positive if there is no offset as described below. The Increase Pstep routine, as shown in Figure 13, uses predetermined constants K1 for a slow adaptive change, K6 for percentage of the increase Dp to be added to Pstep, K7 for an offset pressure to which the adaptive algorithm is programmed to converge, K8 for the maximum increase allowed, and K9 for the maximum value for Pstep. As set forth in block 388, Pstep is updated to the minimum of: Pstep + K6 * (Dp - K7), Pstep + K8, or K9. For the closed-loop algorithm used by the power downshift clutch control logic, the pressure command will be driven to a value that yields a constant error to the commanded clutch slip speed profile when Pstep is uncalibrated. It can be shown that if the step pressure command is adjusted by the amount of the error Dp as shown by the equation above, the result will yield a shift with zero error relative to the commanded clutch slip speed profile. The offset value, K7, will allow the adaptive algorithm to converge to a solution where the closed-loop pressure change Dp will be equal to K7. This will allow a preset amount of increase or decrease to be programmed to the closed-loop pressure response if desired. In Figure 13 the Increase Pstep routine 362 first calculates the value of Dp 384. If the FAST ADAPT MODE flag is set 386 the value of Pstep is selected 388 as described above. If the FAST ADAPT MODE flag is not set 386, the slow adapt constant K1 is used to increment the step and Pstep = Pstep +K1 390. The Decrease Step routine 366 is essentially the same except that different constants are used. In that case, the value of Dp will be negative, provided the offset pressure K7 is zero. Off-going pressure is adapted up or down according to the detection of SLIP EARLY or SLIP LATE, respectively. A slip early condition is illustrated in Figure 14. By knowing the actual time of slip detection, the slope of the off-going clutch pressure command, and the desired time of slip detection (Tdesired), a required increase in Pioff may be computed. The term Pext is extrapolated from the open loop off-going ramp to the time Tdesired. The pressure command for the time Tslip at which slip is detected is Pslip. The difference Dp is defined as (Pslip - Pext). The increase Pioff routine 354 is capable of increasing Pioff by the amount Dp so that the new off-going ramp command will reach Pslip at the time Tdesired. If K2 is the percentage of the calculated increase Dp to be added to Pioff, and K3 is the minimum increase in Pioff for the fast adaptive algorithm, the adapted value of Pioff is the maximum of: Pioff = Pioff + K2 * Dp, and Pioff = Pioff + K3. If the FAST ADAPT MODE flag is not set, the slow adapt calculation Pioff = Pioff + K1 will be used. The Decrease Pioff routine 374 is essentially the same except the value Pext does not have to be extrapolated since Tdesired occurs during the commanded ramp. In this case, Pext is simply the command pressure occurring at Tdesired. The adapted values for Pstep and Pioff are targeted to correct the aberration in one shift period if the percentage values, e.g. K2 and K6, are set to 100%. Smaller percentage values may be chosen where desired. On the other hand, the adaptive adjustment for Pion employs an iterative process wherein Pion is increased by the step amount Ds when the FLARE flag is set and decreased when FLARE is not set. The calibration constants used with this process are: K14 = the increase pressure scale factor; K15 = the minimum pressure change value; K16 = the pressure increase after convergence; K17 = the initial value of SCC; and K18 = the delta pressure scale factor. The iterative process is illustrated in Figure 15, which is a diagram of Pion versus shift number. Depending on operating conditions, there exists an value of Pion below which flare will occur. The object is to adjust quickly Pion close to that value and to maintain it there. In the fast adjustment phase, starting with a relatively high value of Pion (no flare), the pressure Pion is adjusted in each shift. First, it is reduced by relatively large steps Ds0 until flare is reached, and then it is increased by a step (K14 * Ds0) to return to a no flare condition. In the illustration, the factor K14 is unity and the increase is the same size as the last decrease. Then the step size is reduced by the scale factor K18 to Ds1 and the pressure is again reduced, the process repeating, hunting about the flare/no flare threshold with successively smaller steps until the step size reaches a limit value K15. The step size progression is Ds1 = K18 * Ds0 , Ds2 = K18 * Ds1 , etc. This achieves rapid convergence to the desired value near the threshold pressure. Once the threshold pressure is achieved, a maintenance phase is initiated in which Ds is increased by a small value K16 and the shift cycle counter SCC is set to a value K17. SCC is decremented by one during subsequent shifts of the same kind until it reaches zero; in the meantime, Pion is maintained constant. When SCC reaches zero, step decreases of K15 are employed to reinitiate flare. Then Pion is again increased by K16, SCC is reset, and the maintenance phase is repeated. Thus, the hunting is permitted only occasionally to assure that the pressure is just above the flare condition. It should be noted that in Figure 11, turbine flare is always tested 376, 382, 356 each time through the program and Pion is increased 380 or decreased 358 except for two cases: early slip and turbine flare, and late slip and no flare. Thus, the Decrease Pion routine and the Increase Pion routine work together to carry out the iteration shown in Figure 15. The Decrease Pion routine 358 shown in Figure 16 uses a flag DEC Ds which is set to TRUE when Ds may be decreased. If DEC Ds is TRUE 392, Ds is set to the larger of (K18 * Ds) or K15 394 and DEC Ds is set to FALSE 396. Then Pion is set to (Pion - Ds) 398. If DEC Ds is not TRUE at block 392, and SCC is not zero 400, the program exits, but if SCC is zero, the program goes to block 398 to decrease the pressure Pion. The Increase Pion routine 380 shown in the flow diagram of Figure 17 first increases the pressure by setting Pion = Pion + (K14 * Ds) 402 , and if Ds does not equal K15 404, the flag DEC Ds is set to TRUE 406. If Ds = K15 and SCC = 0 408, Pion is increased by K16 410 and SCC is set to K17 412. If SCC is not zero, the pressure increase is bypassed. In most cases (for long converter shifts and lock-up shifts), the iterative method will adjust the initial pressure Pion so that the turbine speed will conform to the pattern shown in Figure 18, graph B, except for occasional excursions into flare territory after sync is attained. For such shifts, the first sync is detected after the set period which starts at off-going clutch slip. In the case of a short converter shift, which occurs for downshifts between certain ranges, the first sync is detected within the set period. In those shifts, there is insufficient time in the closed-loop control period for the off-going clutch to achieve the capacity to hold synchronism, and flare results as shown in graph A of Figure 18. By defining the TURBINE FLARE flag for the short converter shift condition according to the detection of flare only after several sync or past sync detections, the actual flare is allowed to occur for a limited duration without setting the FLARE flag. The result is that the Figure 18, graph A turbine speed pattern is the normal adapted condition for a short converter shift. Reference is made to our co-pending applications EP-A-0,435,375, EP-A-0,435,373, EP-A-0,435,374 and EP-A-0,435,377 filed and published the same day as this application.

Claims: A method of controlling changes in an automatic transmission for a vehicle from a lower speed ratio to a higher speed ratio, which automatic transmission (16) comprises an input (22), an output (24), a turbine (T) connected to the input to couple driving torque thereto, an off-going torque transmitting device (C1-C5) associated with the lower speed ratio, and an on-coming torque transmitting device (C1-C5) associated with the higher speed ratio, and turbine speed and output speed sensing means (60,62) wherein the off-going torque transmitting device is disengaged substantially concurrently with the engagement of the on-coming torque transmitting device; the method comprising the steps of applying an initial on-coming pressure (Pion) on the on-coming torque transmitting device (C1-C5) and thereafter progressively increasing the on-coming pressure; applying a progressively decreasing off-going pressure on the off-going torque transmitting device (C1-C5) to allow slip thereof; initiating a closed-loop control period of the off-going torque transmitting device (C1-C5), wherein flare occurs at the end of the closed-loop period when the initial on-coming pressure (Pion) applied to the on-coming torque transmitting device (C1-C5) is below a threshold level; detecting the occurrence of flare; and adjusting the initial on-coming pressure (Pion) toward the threshold level in subsequent changes by increasing the initial on-coming pressure when flare is detected and decreasing the initial on-coming pressure when flare is not detected, wherein the magnitude of the adjustment made is progressively smaller from one change to the next. A method according to Claim 1, wherein the step of adjusting the initial on-coming pressure (Pion) toward the threshold level in subsequent changes comprises the steps of decreasing the initial on-coming pressure by predetermined steps until flare is detected, increasing the initial on-coming pressure when flare is detected, and decreasing the initial on-coming pressure by successively smaller steps when no flare is detected following a pressure increase until a predefined minimum size of step is reached. A method according to Claim 2, wherein in the step of decreasing the initial on-coming pressure by smaller sized steps, the size for a step is determined by decreasing the size of the previous step by a fixed percentage. A method according to Claim 2 or 3, wherein the adjustment is maintained by the steps of increasing the on-going pressure by a set amount to raise it above the threshold level and inhibiting further adjustments for a predefined number of changes, when the minimum size of step is reached and flare is detected. A method according to Claim 4, wherein the step of inhibiting further adjustments comprises the steps of setting a counter to a preset value, decrementing the counter at each subsequent change, and inhibiting further adjustments until the counter is decremented to zero. A method according to any preceding Claim, including the steps of detecting the occurrence of an increase in the off-going command pressure in excess of a predetermined amount during the closed-loop control period, incrementing a stored parameter following completion of the change when such an increase is detected, wherein the parameter is effective to set the initial off-going pressure to a value which minimizes the off-going pressure increase during the closed-loop period, and the parameter increment is based on the amount of increase in the off-going command pressure during the closed-loop period. A method according to any one of Claims 1 to 5, including the steps of detecting the occurrence of a decrease in the off-going command pressure in excess of a predetermined amount during the closed-loop control period, decrementing a stored parameter following completion of the change when such a decrease is detected, wherein the parameter is effective to set the initial off-going pressure to a value which minimizes the off-going pressure decrease during the closed-loop period, and the parameter decrement is based on the amount of decrease in the off-going command pressure during the closed-loop period. A method according to any preceding claim, including the steps of establishing a desired time at which slip of the first torque transmitting device is to occur, applying an initial off-going pressure on the off-going torque transmitting device at initiation of the change, detecting when slip of the first torque transmitting device occurs after initiation of the change, increasing a stored parameter following completion of the change when slip is detected before the desired time, increasing a stored parameter following completion of the change, the parameter being effective to increase the initial off-going pressure to a value which causes slip to occur substantially at the desired time. A method according to Claim 8, including the steps of extrapolating the off-going command pressure at the same rate of decrease of the off-going pressure to the point of slip, determining from the extrapolation the command pressure which would be applied to the first torque transmitting device at the desired time, calculating the difference between the extrapolated command pressure and the off-going command pressure at the actual time of slip, and increasing the stored parameter to increase the initial off-going command pressure by the calculated difference. A method according to any one of Claims 1 to 7, including the steps of applying an initial off-going pressure on the off-going torque transmitting device at initiation of the change, establishing a desired time at which slip of the off-going torque transmitting device is to occur, detecting whether or not slip of the off-going torque transmitting device occurs within a preset time after initiation of the change, decreasing a stored parameter following completion of the change when slip of the first torque transmitting device fails to occur within the preset time, the parameter being effective to decrease the initial off-going pressure to a value which causes slip to occur substantially at the desired time. A method according to Claim 10, wherein the step of decreasing the stored parameter comprises the steps of calculating the difference between the off-going command pressure which was being applied to the off-going torque transmitting device at the desired slip time and the actual command pressure being applied at the time of slip, and decreasing the stored parameter to decrease the initial off-going pressure by the calculated difference. A method according to any preceding Claim, wherein during a short change condition when the time from slip of the off-going torque transmitting device to substantial synchronization of the on-coming torque transmitting device with the turbine is less than a predetermined value, the step of detecting the occurrence of flare at the end of the closed-loop control period comprises the steps of sensing the occurrence of flare after synchronization of the on-coming torque transmitting device or after a preset number of previous synchronizations, and delaying the increase in initial on-coming pressure to allow extended flare to occur; and during other change conditions the step of detecting the occurrence of flare comprises the step of sensing the occurrence of flare after the first detection of synchronization of the on-coming torque transmitting device.

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