Abstract:
A transmission control system for regulating operation of an automatic transmission of a vehicle includes a first module that provides a predetermined shift schedule including upshift and downshift lines and a second module that offsets each of the upshift and downshift lines by an offset amount to provide modified upshift and downshift lines when a deceleration of the vehicle exceeds a threshold deceleration. A third module regulates operation of the automatic transmission based on the modified upshift and downshift lines.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/815,147, filed on Jun. 20, 2006. The disclosure of the above application is incorporated herein by reference. 
     
     FIELD 
       [0002]    The present disclosure relates to a powertrain having an automatic transmission driven by an internal combustion engine through a torque converter, and more particularly to a deceleration dependent shift control for an automatic transmission. 
       BACKGROUND 
       [0003]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0004]    Vehicle powertrains typically include a prime mover, such as an internal combustions engine, that drives a transmission through a coupling device. In some cases, the transmission includes an automatic transmission that is driven by the prime mover through a torque converter. The transmission multiplies the engine drive torque by a desired gear ratio and transfers the multiplied drive torque to a driveline to propel the vehicle. 
         [0005]    A control module regulates operation of the transmission based upon vehicle operating parameters including, but not limited to, vehicle speed and throttle position. More specifically, the control module includes predetermined shift lines that are used to command upshift and downshifts. 
         [0006]    In some instances, the vehicle is rapidly decelerated, for example, to avoid a collision or to otherwise come to a rapid stop. As the vehicle decelerates, several events can simultaneously occur including, but not limited to, suspension movement, axle wind-up and a transmission downshift. Under certain conditions, a transmission downshift can result in undesired driveline disturbances in the form of noise (e.g., an audible clunk) and/or driveline oscillations. 
       SUMMARY 
       [0007]    Accordingly, the present invention provides a transmission control system for regulating operation of an automatic transmission of a vehicle. The transmission control system includes a first module that provides a predetermined shift schedule including upshift and downshift lines and a second module that offsets each of the upshift and downshift lines by an offset amount to provide modified upshift and downshift lines when a deceleration of the vehicle exceeds a threshold deceleration. A third module regulates operation of the automatic transmission based on the modified upshift and downshift lines. 
         [0008]    In one feature, the transmission control system further includes a fourth module that determines the offset amount based on at least one of a current gear ratio of the automatic transmission and the deceleration. 
         [0009]    In another feature, the offset amount is a fixed, predetermined amount. 
         [0010]    In another feature, the second module stores a base downshift line vehicle speed, and sets the offset amount to zero when a current vehicle speed falls below the base downshift line vehicle speed. 
         [0011]    In another feature, the second module initiates a timer upon executing the step of offsetting, and sets the offset amount to zero when the timer achieves a threshold time. 
         [0012]    In still another feature, the second module sets the offset amount to zero when a throttle position exceeds a threshold throttle position. 
         [0013]    In yet other features, the second module monitors a vehicle speed, and decays the offset amount towards zero when the vehicle speed accelerates back through the upshift lines. The second module decays the offset amount based on a decay rate. The decay rate is a predetermined, fixed value. Alternatively, the decay rate is determined based on an acceleration of the vehicle. 
         [0014]    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 
         [0015]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0016]      FIG. 1  is a functional block diagram of an exemplary vehicle powertrain that is regulated based on the deceleration dependent shift control of the present invention; 
           [0017]      FIG. 2  is a graph illustrating exemplary shift lines for an exemplary automatic transmission; 
           [0018]      FIG. 3-5  are graphs illustrating the exemplary shift lines of  FIG. 2  including exemplary offset shift lines in accordance with the deceleration dependent shift control of the present invention, and exemplary vehicles maneuvers executed during an offset mode; 
           [0019]      FIG. 6  is a flowchart illustrating exemplary steps executed by the overspeed protection control of the present invention; and 
           [0020]      FIG. 7  is a functional block diagram of exemplary modules that execute the overspeed protection control of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    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. 
         [0022]    Referring now to  FIG. 1 , an exemplary powertrain  10  is illustrated and includes an engine  12  that drives a transmission  14  through a torque converter  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. 
         [0023]    The drive torque is transferred through the torque converter  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  can includes an automatic transmission that is automatically shifted based on a vehicle speed (V VEH ) and a throttle position, as discussed in further detail below. 
         [0024]    A control module  30  regulates operation of the powertrain based on vehicle operating parameters. More specifically, the control module  30  regulates a throttle opening or throttle position (TPS) corresponding to an effective throttle area (A EFF ) via a throttle actuator  32 . A throttle position sensor  34  generates a throttle position signal based on the angular position of the throttle  20 . The control module  30  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 ). 
         [0025]    Referring now to  FIG. 2 , the control module  30  adjusts a gear ratio of the transmission  14  based on the throttle position (i.e., TPS) and V VEH . More specifically, the control module  30  includes a plurality of pre-programmed upshift and downshift lines based on V VEH  and TPS, which is measured as a percentage of throttle opening. When the TPS and/or V VEH  cross one of the shift lines, the control module  30  commands a corresponding shift. In the exemplary graph of  FIG. 2 , upshift and downshift lines are provided for an exemplary 4-speed automatic transmission. The exemplary downshift lines include 2-1, 3-2 and 4-3 downshift lines. The exemplary upshift lines include 1-2, 2-3 and 3-4 upshift lines. The lines also include torque converter clutch (TCC) apply and release lines. For example, if the V VEH  is 20 kilometers per hour (kph) and the TPS is 25%, the automatic transmission is in 2 nd  gear. If V VEH  decreases past the 2-1 downshift line, while the %Throttle decreases or remains constant, a downshift from 2 nd  gear to 1 st  gear is commanded. Similarly, if V VEH  increase past the 2-3 upshift line, an upshift from 2 nd  gear to 3 rd  gear is commanded. 
         [0026]    Referring now to  FIG. 3 , the deceleration dependent shift control of the present invention temporarily offsets the shift lines based on a deceleration of the vehicle (i.e., V VEH ). More specifically, the acceleration of the vehicle (a VEH ) is determined based on the transmission output shaft signal (TOSS) and is continuously monitored. If a VEH  is negative, the vehicle is deemed to be decelerating. Furthermore, if a VEH  is less than a threshold acceleration (a THR ) (i.e., is more negative than a THR ), the deceleration dependent shift control enters an offset mode and offsets the downshift and upshift lines (see phantom lines). For example, at point A of  FIG. 3 , V VEH  is approximately 32 kph and the transmission is in 4 th  gear. The vehicle is rapidly decelerated towards point B. In response to the rapid deceleration, the shift lines are offset. It should be noted that although only a single offset downshift line is illustrated, it is anticipated that all of the upshift and downshift lines are offset. 
         [0027]    The offset amount can be a predetermined, fixed value (e.g., 4 kph) or can be determined based on a VEH  and/or the current gear. For example, if the deceleration is very rapid, the offset is greater than if the deceleration is slower. Alternatively or additionally, the offset can be based on the current gear ratio. For example, the offset is greater if the vehicle is decelerating and the transmission is in a higher gear than if the transmission is in a lower gear. 
         [0028]    Upon entering the offset mode, the deceleration shift control stores the original or base downshift line (e.g., 2-1) and an offset timer t OFFSET  is initiated. The offset mode can be exited upon t OFFSET  achieving a threshold time (t THR ) (e.g., 5 seconds), upon TPS exceeding a TPS threshold (TPS THR ) or upon V VEH  falling below the base downshift line (e.g., the original 2-1 downshift line). For example, as V VEH  moves towards point B in  FIG. 3 , and crosses the base 2-1 downshift line, the offset mode is exited and all of the offsets are set equal to zero (i.e., all of the upshift and downshift lines go back to normal). With particular reference to  FIG. 4 , the offset mode is exited upon TPS exceeding TPS THR , even though the base 2-1 downshift line is not crossed. 
         [0029]    Referring now to  FIG. 5 , the offset can decay to zero over time if there is a sudden reversal in a VEH  and V VEH  increases. In the exemplary maneuver illustrated in  FIG. 5 , a VEH  is sufficient to enter the offset mode, however, after V VEH  crosses the offset 2-1 downshift line and downshifts to 1 st  gear, V VEH  suddenly increases. As V VEH  moves towards the offset upshift lines, the offset value decays. In other words, as V VEH  moves towards the offset upshift lines, the offset value decays so that the offset upshift lines are effectively moving toward V VEH . For example, an upshift from 1 st  to 2 nd  gear is commanded at the fully offset 1-2 upshift line (e.g., offset by 4 kph). An upshift from 2 nd  to 3 rd  gear is commanded at the less than fully offset 2-3 upshift line (e.g., the offset has decayed to less than 4 kph). The offset continues to decay at a predetermined decay rate until the offset is 0 kph. It is anticipated that the decay rate can be a predetermined fixed amount or can be determined based on a VEH  as V VEH  accelerates back through the upshift lines. 
         [0030]    Referring now to  FIG. 6 , exemplary steps executed by the deceleration dependent shift control will be described in detail. In step  600 , control determines whether a VEH  is less than an acceleration threshold (a THR ). If a VEH  is less than a THR , the vehicle is sufficiently decelerating to enter the offset mode, and control continues in step  602 . If a VEH  is not less than a THR , the vehicle is not sufficiently decelerating to enter the offset mode, and control loops back. In step  602 , control enters the offset mode and offsets the upshift and downshift lines. As discussed in detail above, the shift lines can be offset by a fixed amount, or the offset amount can be determined based on the current gear ratio and/or a VEH . Control initiates t OFFSET  in step  604 . 
         [0031]    In step  606 , control determines whether V VEH  has crossed the original or base 2-1 downshift line (V BASE2-1 ). If V VEH  has crossed V BASE2-1 , control continues in step  608 . If V VEH  has not crossed V BASE2-1 , control determines whether TPS is greater than TPS THR  in step  610 . If TPS is greater than TPS THR , control continues in step  608 . If TPS is not greater than TPS THR , control determines whether t OFFSET  is greater than t THR  in step  612 . If t OFFSET  is greater than t THR , control continues in step  608 . If t OFFSET  is not greater than t THR , control continues in step  614 . In step  608 , control exits the offset mode by setting the offsets to zero, and control ends. 
         [0032]    In step  614 , control determines whether V VEH  is accelerating back through the upshift lines (see  FIG. 5 ). If V VEH  is not accelerating back through the upshift lines, control increments t OFFSET  in step  616  and loops back to step  604 . If V VEH  is accelerating back through the upshift lines, control exits the offset mode by decaying the offsets to zero at a predetermined decay rate, and control ends. As discussed above, the decay rate and be a fixed amount or can be determined based on a VEH  as the vehicle accelerates. 
         [0033]    Referring now to  FIG. 7 , exemplary modules that execute the deceleration dependent shift control will be described in detail. The exemplary modules include a shift line schedule module  700 , an offset module  702 , an offset amount module  704  and a transmission control module  706 . The shift line schedule module  700  includes the predetermined or normal shift lines. The offset module  702  offsets the shift lines based on inputs from the various modules and provides the offset shift line information to the transmission control module  706 , which regulates operation of the transmission. The offset amount module  704  determines the offset value based on a VEH  and the current gear, which is provided by the transmission control module  706 . 
         [0034]    The deceleration dependent shift control of the present invention inhibits driveline disturbances during rapid vehicle deceleration, by executing transmission downshifts earlier in the deceleration. In this manner, the deceleration event does not occur concurrently with other vehicle events (e.g., axle wind, suspension dynamic events and the like). Other advantages of the deceleration dependent shift control are that it is functional for any gear ratio, and that there are various exit criteria, providing improved flexibility in implementing the control. 
         [0035]    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.