Abstract:
A method of managing slip in a transmission that is driven by a prime mover includes determining whether a slip condition of the transmission is present based on a slip value and reducing a torque output of the prime mover based on a torque reduction value when the slip condition is present. The method further includes storing the torque reduction value in an array if the slip condition is resolved as a result of the step of reducing and identifying a faulty component within the transmission based on the array.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/819,005, filed on Jul. 6, 2006. The disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to a transmission that is driven by a prime mover, and more particularly to a transmission slip control for detecting and managing transmission slip. 
     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. 
     A transmission slip condition can occur when a transmission element is defective and/or worn or the corresponding hydraulic circuit is providing insufficient pressure to fully engage the particular transmission element. The transmission slip condition can damage transmission components and detrimentally affects the vehicle drivability. 
     Accordingly, traditional transmission slip control routines determine whether a slip condition is present and commands a transmission shift if the slip condition remains for a predetermined time period. By executing a shift and monitoring whether a slip condition exists in the next gear ratio, the traditional transmission slip control can identify which transmission element and/or hydraulic circuit is the source of the slip condition. However, if the vehicle operator changes the vehicle operating conditions (e.g., steps into the accelerator pedal changing the engine torque request), another transmission shift may be executed. As a result, the traditional slip control can inaccurately identify a particular transmission element and/or hydraulic circuit as being defective, which results in increased warranty costs and customer dissatisfaction. 
     SUMMARY 
     Accordingly, the present invention provides a method of managing slip in a transmission that is driven by a prime mover. The method includes determining whether a slip condition of the transmission is present based on a slip value and reducing a torque output of the prime mover based on a torque reduction value when the slip condition is present. The method further includes storing the torque reduction value in an array if the slip condition is resolved as a result of the step of reducing and identifying a faulty component within the transmission based on the array. 
     In other features, the method further includes incrementing the torque reduction value if the slip condition is not resolved. A shift of the transmission is initiated if the torque reduction value exceeds a maximum torque reduction value. 
     In another feature, the method further includes initiating a self-correction routine if the slip condition is present. 
     In another feature, the slip value is determined based on a transmission input shaft speed and a transmission output shaft speed. 
     In another feature, the torque reduction value is determined based on the slip value. 
     In still another feature, the method further includes setting a diagnostic trouble code based on the array. 
     In yet another feature, the array includes a plurality of torque reduction values that are associated with a corresponding plurality of clutches of the transmission. 
     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 slip control of the present invention; 
         FIG. 2  is a flowchart illustrating exemplary steps executed by the transmission slip control of the present invention; and 
         FIG. 3  is a functional block diagram of exemplary modules that execute the transmission slip control of the present invention. 
     
    
    
     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. B 1  gradually disengages while C 2  gradually engages. Similarly, C 1  remains engaged, C 2  gradually disengages and C 3  gradually engages during an upshift to 3 rd  gear. 
     The transmission slip control of the present invention determines whether a transmission slip condition is present based on the TISS and TOSS signals. More specifically, the transmission slip control monitors the rotational speed of the transmission input shaft (RPM IS ) and that of the transmission output shaft (RPM OS ), and determines a theoretical input shaft speed (RPM ISTHR ) by multiplying RPM OS  by the current gear ratio. If RPM ISTHR  is less than RPM IS , a slip condition is present. A slip condition indicates that at least one of the transmission elements for the particular gear ratio is not fully engages and slip is occurring across the transmission element (s). The slip condition can result from a defective or worn transmission element or a low pressure condition of the corresponding hydraulic circuit(s) (e.g., a fluid blockage), that inhibits the transmission element(s) from fully engaging. 
     In the event that the slip condition is present, the transmission slip control reduces T ENG  by a torque reduction value (T RED ). It is also anticipated, however, that a self-correction routine can be executed in an attempt to clear the associated hydraulic circuits (i.e., corresponding to each of the two engaged transmission elements) prior to reducing T ENG . In general, the self-correction routine flushes the associated hydraulic circuits with little or no detriment to the vehicle drivability. That is to say that the hydraulic circuits can be flushed without the vehicle operator noticing any fluctuation in driving performance. If the source of the slip condition is a blockage in the hydraulic circuit, the self-correction routine could resolve the slip condition without requiring further action. 
     In the event that the slip condition is not resolved, the transmission slip control reduces T ENG  based on T RED . T RED  can be a predetermined, fixed value or can be determined based on the slip value (i.e., the difference between RPM IS  and RPM ISTHR ). If the slip condition is not resolved via the initial T ENG  reduction, T RED  can be incremented or otherwise increased in an effort to further reduce T ENG  to resolve the slip condition. However, if the continuous T ENG  reduction still fails to resolve the slip condition and T RED  has achieved a maximum torque reduction value (T REDMAX ) (e.g., 10-15% of the original T ENG ), a transmission shift is initiated. The transmission shift preferably includes an upshift, but it is anticipated that a downshift can be executed (e.g., if the transmission is in 6 th  gear, for example). If the slip condition is resolved without T RED  achieving T REDMAX , the transmission continues to operate in the same gear ratio with the reduced T ENG , until a transmission shift is commanded using the normal shift logic (i.e., based on V VEH  and other operating parameters). 
     T RED  values associated with each gear ratio are stored in an array. An exemplary array is provided as provided in Table 2 below: 
                                                                                       TABLE 2                       1 st     2 nd     3 rd     4 th     5 th     6 th     R                                    T RED     T RED1     T RED2     T RED3     T RED4     T RED5     T RED6     T REDR                      
A faulty transmission element and/or hydraulic circuit can be identified based on the array values. More specifically, and as discussed in detail above, two transmission elements are engaged for any particular gear ratio. Accordingly, if the T RED  value is greater than zero for two different gear ratios in which the same transmission element is engaged, that particular transmission element and/or the hydraulic circuit associated therewith is defective. For example, if T RED1 , and T RED3  are both greater than zero, C 1  and/or its associated hydraulic circuit are most likely defective, because C 1  is the only transmission element that is engaged in both 1 st  and 3 rd  gears.
 
     The transmission slip control sets a diagnostic trouble code (DTC) corresponding to a particular transmission element or elements deemed to be defective. It is anticipated, however, that the DTC may only be set if the slip condition is particularly sever. For example, if the slip value is marginal for a particular gear ratio, the transmission slip control may wait for the slip condition to become more sever before setting the DTC. 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 slip control of the present invention will be described in detail. In step  200 , control monitors TISS and TOSS. In step  202 , control determines whether transmission slip for the particular gear ratio is present. If transmission slip is not present, control ends. If transmission slip is present, control initiates the self-correction routine in step  204 . In step  206 , control determines whether transmission slip is still present. If transmission slip is not still present, control ends. If transmission slip is still present, control continues in step  208 . 
     Control determines T RED  based on the slip value in step  208 . In step  210 , control reduces T ENG  by T RED . In step  212 , control determines whether the slip condition is resolved. If the slip condition is resolved, control stores T RED  in the array in step  214 . If the slip condition is not resolved, control determines whether T RED  is greater than or equal to T REDMAX  in step  216 . If T RED  is not greater than or equal to T REDMAX , control increments TRED in step  218  and loops back to step  210 . If T RED  is greater than or equal to T REDMAX , control executes a transmission shift in step  220 . In step  222 , control identifies a faulty transmission components (e.g., transmission element and/or associated hydraulic circuit) based on the array values. Control sets a corresponding DTC in step  224  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 slip determining module  300 , a T RED  determining module  302 , an engine control module  304 , a transmission control module  306 , a self-correction module  308  and a DTC module  310 . The slip determining module  300  generates a slip value based on the TISS and TOSS signals. The slip value is output to the T RED  determining module  302  and the self-correction module  308 . The T RED  determining module  302  determines T RED  based on the slip value and the current gear ratio. The self-correction module  308  selectively generates a self-correction routine signal that is output to the transmission control module  306 . 
     The engine control module  304  regulates operation of the engine (e.g., T ENG ) based on T RED . Similarly, the transmission control module  306  regulates operation of the transmission based on T RED . The DTC module  310  selectively generates a DTC or DTCs based on the array, which is output from the T RED  determining module  302 . 
     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.