Abstract:
A method of regulating operation of an automatic transmission includes identifying a tie-up condition of the automatic transmission, adjusting a pressure of a transmission element in response to the tie-up condition and determining whether a first gear ratio of the automatic transmission holds. The pressure is set to zero if the gear ratio does not hold and a faulty transmission element is identified as one associated with a second gear ratio that is lower than said first gear ratio.

Description:
FIELD 
     The present disclosure relates to a transmission that is driven by a prime mover, and more particularly to a transmission clutch control to identify a clutch that is inducing a tie-up condition. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Traditionally, vehicles include a prime mover, such as an internal combustion engine, that generates drive torque. The drive torque is transferred through a powertrain to drive a drivetrain, propelling the vehicle along a surface. Exemplary powertrain components include a transmission and a coupling device, through which the drive torque from the engine is transferred to the transmission. The transmission multiplies the drive torque by a gear ratio and further transfers the multiplied drive torque to the driveline. 
     An exemplary transmission includes an automatic transmission having a plurality of transmission elements that are hydraulically engaged to establish a desired gear ratio. Accordingly, each transmission element includes a corresponding hydraulic circuit having a variable bleed solenoid (VBS) to regulate the actuation pressure of a corresponding transmission element, as well as brake switches and pressure switches. 
     A transmission tie-up condition can occur when a transmission element engages at an inappropriate time. More specifically, in so called clutch to clutch type transmissions, a gear ratio shift is orchestrated by lowering the torque transfer capacity of an off-going (i.e., disengaging) clutch while increasing the torque transfer capacity of an on-coming (i.e., engaging) clutch. In the event that a third or redundant clutch should be applied during steady-state conditions, the vehicle decelerates at a rate that is proportional to the torque transfer capacity that the offending clutch comes on with. 
     Accordingly, traditional diagnostic routines are implemented in transmission systems to identify the offending clutch upon detection of a tie-up condition. More specifically, traditional diagnostic routines cycle through and diagnose the various control elements (e.g., VBS, pressure switches, brake switches) to identify the offending element and to correct the tie-up condition. These traditional diagnostic routines, however, can result in false detection of tie-up conditions and can induce vibrations or other phenomenon that can be sensed by the driver. 
     SUMMARY 
     Accordingly, the present disclosure provides a method of regulating operation of an automatic transmission. The method includes identifying a tie-up condition of the automatic transmission, adjusting a pressure of a transmission element in response to the tie-up condition and determining whether a first gear ratio of the automatic transmission holds. The pressure is set to zero if the gear ratio does not hold and a faulty transmission element is identified as one associated with a second gear ratio that is lower than said first gear ratio. 
     In other features, the method further includes setting a pressure of the transmission element to a value just below a slip pressure of the transmission element if the first gear ratio holds and again determining whether the first gear ratio of the automatic transmission holds. The pressure is set to zero if the gear ratio does hold and a faulty transmission element is identified as one associated with a second gear ratio that is higher than the first gear ratio. The pressure is set to an engagement pressure if the gear ratio does not hold and a no fault condition of the automatic transmission is indicated. 
     In still another feature, the adjusting of the pressure includes determining a slip pressure of the transmission element, determining an offset pressure and setting the pressure of the transmission element to the slip pressure plus the offset pressure. 
     In yet another feature, the method further includes monitoring a transmission input shaft speed, monitoring a transmission output shaft speed and identifying the tie-up condition based on the transmission input shaft speed and the transmission output shaft speed. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a functional block diagram of an exemplary vehicle powertrain that is regulated based on the transmission clutch control of the present disclosure; 
         FIG. 2  is a flowchart illustrating exemplary steps executed by the transmission clutch control of the present disclosure; and 
         FIG. 3  is a functional block diagram of exemplary modules that execute the transmission clutch control of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term module refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, or other suitable components that provide the described functionality. 
     Referring now to  FIG. 1 , an exemplary powertrain  10  is illustrated and includes an engine  12  that drives a transmission  14  through a coupling device  16 . More specifically, air is drawn into an intake manifold  18  of the engine  12  through a throttle  20 . The air is mixed with fuel and the air/fuel mixture is combusted within cylinders  22  to reciprocally drive pistons (not shown) within the cylinders  22 . The pistons rotatably drive a crankshaft (not shown) to provide drive torque. Exhaust generated by the combustion process is exhausted from the engine through an exhaust manifold  26 . Although 4 cylinders are illustrated, it is appreciated that the present invention can be implemented in vehicles having any number of cylinders. 
     The drive torque drives is transferred through the coupling device  16  to drive the transmission  14 . The transmission  14  multiplies the drive torque by a desired gear ratio to provide a modified drive torque. The modified drive torque is transferred to a vehicle driveline (not shown) by a transmission output shaft  28 . The transmission  14  includes an automatic transmission that provides a plurality of pre-defined, fixed gear ratios, wherein shifting of the transmission  14  is automatically regulated based on a selected drive range (e.g., P, R, N, D, L), a vehicle speed (V VEH ) and an engine load. 
     A control module  30  regulates operation of the powertrain based on vehicle operating parameters. More specifically, the control module  30  regulates an effective throttle area (A EFF ) via a throttle actuator  32 . A throttle position sensor  34  generates a throttle position signal (TPS) based on the angular position of the throttle  20 . The control module  30  determines a requested engine torque (T ENG ) and adjusts the throttle position and other engine operating parameters to achieve T ENG . The other engine operating parameters include, but are not limited to, a fueling rate, spark timing, a camshaft phase and/or an intake/exhaust valve lift or timing. 
     The control module  30  also regulates operation of the transmission  14  based on vehicle operating parameters. More specifically, a crankshaft position sensor  36  generates a crankshaft position signal, which is used to determine an actual engine speed (RPM ENG ). A transmission output shaft speed (TOSS) sensor  38  generates a TOSS signal, which is used to determine V VEH , and a transmission input shaft speed (TISS) sensor  39  generates a TISS signal. 
     For the purpose of the present description, an exemplary 6-speed automatic transmission will be briefly described. It is anticipated, however, that the transmission slip control of the present invention can be implemented with any type of transmission know in the art. The exemplary 6-speed automatic transmission includes four clutches C 1 -C 4  and a brake element B 1 , each of which is hydraulically actuated via a corresponding hydraulic circuit. C 1 -C 4  and B 1  are selectively implemented in pairs to establish 6 forward gear ratios and a reverse ratio, in accordance with Table 1, below: 
                                                                                           TABLE 1                       1 st     2 nd     3 rd     4 th     5 th     6 th     R                                        C1   X   X   X   X                       C2       X               X           C3           X       X       X           C4               X   X   X           B1   X                       X                        
Accordingly, two transmission elements (i.e., C 1 -C 4  and B 1 ) are actuated to establish a desired gear ratio.
 
     During a gear shift, one of the two transmission elements remains actuated while the other transmission element gradually disengages (i.e., is off-going) and a third transmission element gradually engages (i.e., is on-coming). For example, in 1 st  gear, C 1  and B 1  are engaged. During an upshift to 2 nd  gear, C 1  remains engaged and is considered the primary element. B 1  gradually disengages while C 2  gradually engages. Because C 2  is the on-coming element for 2 nd  gear, it is considered the secondary element for an up-shift to 2 nd  gear. Similarly, C 1  remains engaged (i.e., is the primary element), C 2  gradually disengages and C 3  gradually engages during an upshift to 3 rd  gear. Accordingly, C 3  is the secondary element for an up-shift to 3 rd  gear. 
     The transmission clutch control of the present invention determines whether a tie-up condition exists during steady-state condition. A steady-state condition exists when there are no driver induced transients including, but not limited to, vehicle acceleration/deceleration and a gear shift. The TISS and TOSS signals are monitored while the transmission is operating in steady-state. If the both the TISS and TOSS signals remain constant, there is no tie-up condition. If the TISS signal remains constant and the TOSS signal decreases (i.e., the torque transfer to the driveline is decreasing), a tie-up condition is present. 
     Upon identifying the tie-up condition, the transmission clutch control reduces the pressure of the secondary element (P SEC ) to a learned clutch slipping pressure (P SLIP ) plus an offset (P OFFSET ). P SLIP  is just insufficient to maintain the secondary element in the fully-engaged state, resulting in clutch slip. P OFFSET , however, maintains P SEC  sufficiently above P SLIP  to prevent slipping of the secondary element. P SLIP  can be determined from a look-up table based on the particular secondary element. The look-up table is preferably continuously updated throughout the lifetime of the transmission to account for component wear. P OFFSET  is provided as a pre-stored value. 
     If the gear ratio does not hold upon decreasing P SEC  (i.e., the TOSS continues to decelerate), the offending element is one that is associated with a lower gear ratio. P SEC  is reduced to zero (i.e., 0 kPA), which effectively results in a gear ratio shift to a lower gear ratio. The transmission clutch control can identify the offending element. More specifically, when P SEC  is rapidly dropped, the faulted gear ratio is sought. Upon stable input/output speed information the gear ratio can accurately assessed. From this gear ratio, it is known which offending clutch is involved with the primary clutch. If the gear ratio does hold upon decreasing P SEC , P SEC  is set to a value just below P SLIP , enabling the secondary element to start slipping. 
     If the gear ratio holds upon decreasing P SEC  to just below P SLIP , (i.e., the TOSS stops decelerating), the offending element is one that is associated with a higher gear ratio. P SEC  is reduced to zero (i.e., 0 kPA), which effectively results in a gear ratio shift to a higher gear ratio. The transmission clutch control can identify the offending element, as discussed above. If the gear ratio does not hold upon decreasing P SEC  to just below P SLIP , there is no fault and PSEC is set equal to the normal engagement pressure (P ENGAGE ). 
     The transmission clutch control sets a diagnostic trouble code (DTC) corresponding to a particular transmission element or elements deemed to be defective. A technician can readily identify the defective component by reading the DTCs. In this manner, the transmission can be easily and effectively repaired, decreasing warranty and other associated costs. 
     Referring now to  FIG. 2 , exemplary steps that are executed by the transmission clutch control of the present invention will be described in detail. In step  200 , control monitors TISS and TOSS. In step  202 , control determines whether a tie-up condition exists. If a tie-up condition does not exist, control ends. If a tie-up condition does exist, control continues in step  204 . In step  204 , control sets P SEC  equal to P SLIP  and P OFFSET . 
     Control determines whether the gear ratio is holding in step  206 . If the gear ratio is not holding, control continues in step  208 . If the gear ratio is holding, control continues in step  210 . In steps  208  and  210 , control sets P SEC  equal to zero and identifies the offending clutch element and control ends. In step  210 , control sets P SEC  to a value just below P SLIP . 
     Control determines whether the gear ratio is holding in step  214 . If the gear ratio is holding, control continues in step  216 . If the gear ratio is not holding, control continues in step  218 . In steps  216  and  220 , control sets P SEC  equal to zero and identifies the offending clutch element and control ends. In step  218 , control sets P SEC  equal to P ENGAGE . Control indicates that there is no fault in step  222  and control ends. 
     Referring now to  FIG. 3 , exemplary modules that execute the transmission slip control will be described in detail. The exemplary modules include a tie-up determining module  300 , a hold determining module  302 , a P SEC  setting module  304  and a fault identifying module  306 . The tie-up determining module  300  determines whether a tie-up condition exists based on RPM TISS  and RPM TOSS . The hold determining module  302  determines whether the gear ratio holds during the various steps of the transmission clutch control based on RPM TISS  and RPM TOSS  and a tie-up condition signal from the tie-up determining module. The P SEC  setting module selectively sets P SEC  in accordance with the transmission clutch control based on the tie-up condition signal and a hold signal. The fault identifying module  306  identifies a fault condition or a no fault condition in accordance with the transmission clutch control based on the hold signal. 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.