Method and apparatus for detecting clutch tie-up

Abstract: The disengagement of the off-going clutch C1-C5 is monitored to determine as early as possible if there is a clutch tie-up due to failure to disengage. Beginning at the initial clutch release command, the turbine speed Nt and output speed No are used to determine if clutch slip has occurred and a pass signal is given if slip occurs in several consecutive control loops. Beginning a preset time after the command to exhaust fully the clutch C1-C5, the number of no-slip conditions are counted. A fail signal is given when a set number of no-slip conditions are counted.

Description: This invention relates to a method and apparatus for determining whether there is clutch tie-up during shifting of an automatic transmission. 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 range to another or to reverse generally involves releasing or disengaging the clutch (off-going) associated with the current range and applying or engaging the clutch (on-coming) associated with the desired range. Shifting from a range to neutral also involves disengaging an off-going clutch. 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. To ensure success of the clutch-to-clutch shifts as well as shifts to neutral, it is desirable to monitor the progress of the shift. If an off-going clutch experiences "tie-up", or fails to disengage at the desired time, the shift will not succeed and it is undesirable to attempt completion of the shift. It has been found that timely information on shift progress can be used to determine whether a shift should be aborted. According to an aspect of the present invention, there is provided a method of detecting failure of disengagement of a torque transmitting device as defined in claim 1. The invention can provide a method of detecting whether clutch tie-up is occurring during a shift. Preferably the method attains a decision on tie-up as soon as possible in the shift progress. In an embodiment, the method determines from turbine and output speeds whether off-going clutch slip occurs after an initial clutch release command and issues a pass indication if a number of consecutive slips are detected, and determines whether slip fails to occur after a command for complete pressure exhaust and issues a tie-up indication if slip fails to occur a set number times. According to another aspect of the present invention, there is provided apparatus for detecting failure of disengagement of a torque transmitting device as defined in claim 6. 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 a method of controlling gear changes by means of the controller of Figure 1a; Figure 4 graphs A, B and C are graphs illustrating turbine speed, on-coming pressure command and off-going pressure command, respectively, for clutch-to-clutch closed throttle downshifting; Figure 5 is a flow diagram of an embodiment of tie-up test logic incorporated in a downshift control logic; and Figure 6 is a flow diagram illustrating an embodiment of the tie-up test logic. 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, 3, 5 and 6 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 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 analyses 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. The clutch tie-up test logic is applied as a part of the off-going clutch control 166, 176 and 172 for each type of range shift. For the purposes of illustration only, the following description of the tie-up logic is given for the case of a closed-throttle downshift. Figure 4, graphs A, B and C, show respectively the turbine speed and the on-coming and off-going pressure commands for control of the on-coming and off-going clutches during a closed throttle downshift. At shift initiation, the on-coming pressure command is set to maximum for a fill time to prepare the on-coming clutch to accept torque. Also, at shift initiation, the off-going clutch release command is given. Then the off-going clutch pressure command is stepped to an intermediate value Pint for a set time and is then stepped to a lower value Pioff until a preset time before the end of the fill time. Thus, the fill time less the preset time determines the off-going clutch period. Then the off-going clutch is exhausted of operating fluid so that the on-coming clutch can take over when it is ready. The on-coming clutch pressure command is set to an initial closed-loop pressure Picl and then ramped up until slip of the off-going clutch (or turbine pullup) is detected. Turbine pullup is a result of the beginning of off-going clutch slip and is determined to have occurred when the turbine speed becomes greater than the product of the output speed and the old or lower speed ratio plus a constant. The off-going clutch slip triggers closed-loop control of the on-coming clutch pressure. The on-coming clutch slip is monitored and controlled to a calculated slip profile. This closed-loop slip profile control continues until on-coming clutch synchronization has been detected several consecutive times within the control period. Then maximum on-coming clutch pressure is commanded to complete the shift. Figure 5 is a flow diagram which illustrates how the tie-up detection logic is incorporated in the closed-throttle downshift off-going clutch control logic 172. A SHIFT PHASE pointer is used to indicate the shift progress through different phases. If SHIFT PHASE equals INITIAL PRESSURE 200, the Initial Pressure routine is run 200. This entails setting the command pressure to the value Pint for a short preset period, and then to the value Pioff for a period which expires before the fill time runs out. When that period expires, SHIFT PHASE is set to EXHAUST so that the Exhaust Off-going Clutch command is implemented 204 and the off-going pressure command is set to zero to cause the off-going clutch to empty and lose torque capacity as soon as possible. Each time through the clutch control loop, the program flows to block 206 which queries whether the TIE-UP flag is set to PASS, TEST or FAIL. If it is set to TEST, the Tie-up Detection Logic is executed 208. If the flag is set to FAIL, a Tie-up Diagnostic Response is executed 209. The diagnostic response is generally involved with aborting the shift, i.e., returning to the previous range, and recording a code for diagnosis purposes. If the TIE-UP flag is set to PASS 206, the tie-up detection is bypassed and the program flows to the main loop. The tie-up detection logic is arranged to provide a definitive test result as soon as possible. Beginning at the off-going clutch release command, the logic looks for off-going clutch slip in a set number of consecutive loops and sets the TIE-UP flag to PASS when it occurs. This is indicated by a pass test region in graph C of Figure 4. The clutch slip is defined by the turbine speed being outside a speed window which is the product of the output speed and the speed ratio of the initial range plus or minus a constant K1, or Nt outside of (No * SR) + K1. The TIE-UP flag is also set to PASS whenever turbine flare is detected during an upshift, flare being defined as Nt (No * SR) + K2. The test is terminated when the flag is set to PASS. Another test looks for a failure of clutch slip and is defined as turbine speed being within the same speed window, or Nt within (No * SR) ± K1 for a set number of times. If that test is satisfied, the TIE-UP flag is set to FAIL. This test occurs only after the off-going pressure has had an opportunity to reach a sufficiently low pressure to release the off-going clutch. It is implemented a preset time after the off-going pressure command goes to zero and is shown as the fail test region in graph C of Figure 4. The clutch tie-up detection logic 208 as shown in Figure 6 begins by inquiring whether the preset delay time has elapsed after the exhaust command of the off-going clutch 210. If it has, the failure test is initiated by determining if the slip failure has been detected a set number of times 212. If it has, the TIE-UP flag is set to FAIL 214. Then, the test pass logic routine is executed 216-220. The TIE-UP flag is set to PASS 216 if the set number of consecutive slips have been detected 218 or turbine flare is detected 220; if neither, the program returns to the main loop. It will thus be seen that the pass testing makes a determination of no tie-up as soon as possible so that the on-coming clutch control can proceed without further regard to tie-up potential and that the fail testing provides a certain determination that off-going clutch release is not progressing properly and that the shift should not be completed. Reference is made to our co-pending applications EP-A-435 376 (RJ/3422), EP-A-435 377 (RJ/3423), EP-A-435 372 (RJ/3424), and EP-A-436 978 (RJ/3425) filed and published the same day as this application.

Claims: A method of detecting in an automatic transmission for a vehicle failure of disengagement of a torque transmitting device (C1-C5) associated with a first speed ratio, the transmission comprising an input (22), an output (24), a turbine (14) connected to the input (22) to couple driving torque thereto, turbine speed (Nt) and output speed (No) sensing means, and a controller (42) coupled to the outputs of the turbine speed (Nt) and output speed (No) sensing means, the controller being adapted to initiate disengagement of the torque transmitting device by generating an initial disengaging command for reducing the pressure applied to the torque transmitting device and to terminate disengagement by generating an exhaust command for exhausting the torque transmitting device of operating fluid; the method comprising the steps of detecting whether there is slip of the off-going torque transmitting device by comparing the turbine speed to the product of the first speed ratio and the output speed (No), and determining whether there is disengagement failure on the basis of the presence or absence of slip during the change. A method according to claim 1, wherein the step of detecting the occurrence of slip includes the step of determining that slip has occurred when turbine speed is outside a predetermined range of values related to the product of the output speed and the first speed ratio, and the step of determining whether there is disengagement failure comprises the step of periodically detecting whether there is slip from the initial disengaging command and determining that there is no disengagement failure when a predetermined number of consecutive detections of slip is reached. A method according to claim 1 or 2, comprising, when the change is from a higher-speed ratio to a lower speed ratio, the steps of detecting the occurrence of turbine flare by determining when turbine speed exceeds the product of output speed and the first speed ratio by a predetermined amount, and determining that there is no disengagement failure when turbine flare is detected. A method according to claim 1, 2 or 3, wherein disengagement failure is determined to have occurred when turbine speed is inside a predetermined range of values related to the product of the output speed and the first speed ratio, and the step of determining whether there is disengagement failure includes the step of periodically determining whether there is slip after generation of the exhaust command, and determining that there is disengagement failure when no slip is detected within a predetermined number of periods. A method according to claim 4, wherein the step of periodically determining whether there is slip begins a predetermined time after generation of the initial disengaging command. Apparatus for detecting in an automatic transmission for a vehicle failure of disengagement of a torque transmitting device (C1-C5) associated with a first speed ratio, the transmission comprising an input (22), an output (24), and a turbine (14) connected to the input (22) to couple driving torque thereto; the apparatus comprising turbine speed (Nt) and output speed (No) sensing means (42), and a controller (42) coupled to the outputs of the turbine speed (Nt) and output speed (No) sensing means; the controller being adapted to initiate disengagement of the torque transmitting device by generating an initial disengaging command for reducing the pressure applied to the torque transmitting device and to terminate disengagement by generating an exhaust command for exhausting the torque transmitting device of operating fluid, to detect whether there is slip of the off-going torque transmitting device by comparing the turbine speed to the product of the first speed ratio and the output speed (No), and to determine whether there is disengagement failure on the basis of the presence or absence of slip during the change. Apparatus according to claim 6, wherein the controller (42) is adapted to determine that slip has occurred when turbine speed is outside a predetermined range of values related to the product of the output speed and the first speed ratio, and periodically to detect whether there is slip from the initial disengaging command and to determine that there is no disengagement failure when a predetermined number of consecutive detections of slip is reached. Apparatus according to claim 6 or 7, wherein when the change is from a higher-speed ratio to a lower speed ratio, the controller being adapted to detect the occurrence of turbine flare by determining when turbine speed exceeds the product of output speed and the first speed ratio by a predetermined amount, and to determine that there is no disengagement failure when turbine flare is detected. Apparatus according to claim 6, 7 or 8, wherein the controller (42) is adapted to determine that disengagement failure has occurred when turbine speed is inside a predetermined range of values related to the product of the output speed and the first speed ratio, and to determine periodically whether there is slip after generation of the exhaust command, and to determine that there is disengagement failure when no slip is detected within a predetermined number of periods. Apparatus according to claim 9, wherein the controller (42) is adapted to determine periodically whether there is slip a predetermined time after generation of the initial disengaging command.

Inventors: HIBNER JOHN ANTHONY, HUBER JON MICHAEL, LENTZ CARL ALBERT, WILES CHRISTOPHER RUSSELL, HIBNER, JOHN ANTHONY, HUBER, JON MICHAEL, LENTZ, CARL ALBERT, WILES, CHRISTOPHER RUSSELL
Applicants: GEN MOTORS CORP, GENERAL MOTORS CORPORATION
Application year: 1990
Main classification: F16H61
IPC codes: F16H59, F16H61