Abstract:
A transmission control module for a vehicle transmission includes a gear determination module, a predictive shift module, and a validation module. The gear determination module commands a first shift configuration based on an actual pedal position. The predictive shift module calculates a predicted pedal position based on the actual pedal position and commands a second shift configuration based on the predicted pedal position. The validation module validates the predicted pedal position and selectively cancels the second shift configuration based on the validation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/029,596, filed on Feb. 19, 2008. The disclosure of the above application is incorporated herein by reference in its entirety. 
     FIELD 
     The present disclosure relates to control of an automatic transmission and more particularly to an accelerator pedal predictive shift point control for improved downshift response and downshift type consistency. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Motorized vehicles traditionally include a power supply (e.g. an internal combustion engine, an electric motor and/or a combination thereof) that produces a drive torque. A transmission receives the drive torque and employs various gear ratios to modify the input drive torque to obtain a desired output torque for the wheels. 
     One or more control modules regulate operation of the power supply and transmission to achieve this desired output torque. For example, an engine control module may regulate a throttle controlling air entering the internal combustion engine, while a transmission control module may regulate the various gear ratios transmitting the output drive torque. Additionally, the functions of the engine and transmission control modules may be incorporated into a single powertrain control module. The control module(s) may receive direction from a driver interface device, such as an accelerator pedal. As the accelerator pedal position is changed, the control module(s) select operating conditions to achieve a specific gear ratio corresponding to the requisite output torque. The specific gear ratio is obtained from a lookup table of current throttle versus vehicle speed. 
     In operation, a driver may require a rapid switch between specific gear ratios. This normally occurs when the transmission downshifts due to driver requested rapid acceleration (e.g. when passing another vehicle). Switching between gear ratios can occur as a stacked single-step multiple downshift (e.g. a first shift from 6-5 followed by a second shift from 5-4), a jump downshift (e.g. 6-4), or a skip downshift (e.g. 6-3). In the stacked single-step multiple downshift, an inability to abort an on-going first downshift causes a delay in initiating the second downshift. The driver may perceive this as poor downshift response or an undesirable second shift event. Further, since the downshift types are commonly determined relative to the pedal position as a function of time, rather than using an accelerator pedal position rate of change and/or an accelerator pedal velocity rate of change, the driver may also perceive inconsistent downshift types under low, medium, and high tip-in maneuvers (e.g. depression of the accelerator pedal). 
     SUMMARY 
     A transmission control module for a vehicle transmission includes a gear determination module, a predictive shift module, and a validation module. The gear determination module commands a first shift configuration based on an actual pedal position. The predictive shift module calculates a predicted pedal position based on the actual pedal position and commands a second shift configuration based on the predicted pedal position. The validation module validates the predicted pedal position and selectively cancels the second shift configuration based on the validation. 
     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 illustrating a vehicle drive system according to the present disclosure; 
         FIG. 2  is a schematic diagram illustrating an engine control module and a transmission control module of the vehicle drive system according to the present disclosure; 
         FIG. 3  is a flow diagram of a shift point control method incorporating a Predictive Shift Point Control Mode (PSHP) according to the present disclosure; 
         FIG. 4  is a flow diagram of the PSHP initiated in  FIG. 3  according to the present disclosure; and 
         FIG. 5  is a flow diagram of a validation operation of the PSHP of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 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, and/or other suitable components that provide the described functionality. 
     Referring now to  FIG. 1 , an exemplary vehicle drive system  10  is shown. The vehicle drive system  10  includes a throttle valve  12 , an engine  14 , an automatic transmission  16 , an engine control module (ECM)  18 , and a transmission control module (TCM)  20 . Air enters the vehicle drive system  10  through the throttle valve  12 . The throttle valve  12 , under direction from the ECM  18 , regulates the amount of air flowing into the engine  14 . The air is evenly distributed to N cylinders  22  located in the engine  14 . Although  FIG. 1  depicts the engine  14  having six cylinders  22  (N=6), it should be understood that the engine  14  may include additional or fewer cylinders  22 . For example, the engine  14  may include 4, 5, 6, 8, 10, 12 or 16 cylinders. The functions of the separate ECM  18  and TCM  20  could also be combined in a single powertrain control module (PCM). 
     The air entering the engine  14  combusts with fuel, reciprocally driving pistons  24  located within the cylinders  22 . The reciprocating pistons  24  rotatably drive a crankshaft  26 , which provides a drive torque to the transmission  16 . The transmission  16  translates the drive torque through a series of gears  28  utilizing a plurality of gear ratios (e.g. 3-speed, 4-speed, 5-speed, 6-speed, etc.) to an output driveshaft  30 . The driveshaft  30  then distributes the drive torque to vehicle wheels  32 . Specifically, the transmission  16  may include a plurality of solenoid-actuated hydraulic valves (not shown) that shift the transmission  16  between the various gear ratios. For example, a combination of two or three electro-hydraulic solenoids shuttle the hydraulic valves to achieve a fixed gear state corresponding to each of the gear ratios. The TCM  20  manages the shifting pattern of the solenoid-actuated hydraulic valves based on a commanded gear ratio when information relayed from various vehicle sensors indicates the need for an increase or decrease in vehicle acceleration. 
     Referring now to  FIG. 2 , the various vehicle sensors may include engine sensors  50 , transmission sensors  52 , and driver interface sensors  54 . The engine sensors  50  may include, but are not limited to, a throttle sensor  60  that monitors current position and operation of the throttle valve  12 ; a crank sensor  62  that monitors the position and rotational speed of the crankshaft  26 ; and a vehicle speed sensor  64  that monitors the rate at which the crankshaft  26  is spinning. The ECM  18  uses information received from the engine sensors  50  to manage parameters, such as fuel injection timing and ignition timing, to obtain desired drive torque values. In some instances, the ECM  18  controls the position of the throttle valve  12 , creating a feedback loop between the throttle valve  12  and the ECM  18 . 
     Typical transmission sensors  52  may include, but are not limited to, a turbine speed sensor  70  that monitors rotational speed on the input side of the transmission  16 ; one or more solenoid position sensors  72  that monitor the position of the solenoid actuated hydraulic shift valves; and a transmission speed sensor  74  that monitors the rotational speed of the driveshaft  30 . It should be understood that the solenoid position sensors  72  may, instead, be pressure switches for indirect monitoring of the shifting valves. 
     The information relayed to the TCM  20  from the transmission sensors  52  assists the TCM  20  in determining the current operating conditions of the transmission  16 , such as, whether the transmission  16  is shifting between two ranges. This information, in conjunction with data obtained from the vehicle speed sensor  64 , is then used to calculate how and when to change the gears  28  to achieve optimum vehicle performance, fuel economy and shift quality at the desired drive torque value. 
     Driver interface sensors  54 , such as a pedal sensor  80  associated with an accelerator pedal  82 , also provide signals to the ECM  18 . For example, the pedal sensor  80  may signal a change in position of the accelerator pedal  82 , which indicates a driver&#39;s need for increased vehicle speed during driving maneuvers (e.g. passing another vehicle). The ECM  18  interprets this request and may adjust the throttle valve  12  to regulate airflow into the engine  14 . The ECM  18  also provides feedback to the TCM  20 , which in turn, generates instructions to downshift the transmission gear ratio from current parameters to obtain the desired output torque. The output torque ultimately transmits to the vehicle wheels  32 , affecting the desired acceleration. 
     The ECM  18  includes a pedal position module  84 , which receives data from the throttle sensor  60 , the crank sensor  62 , the vehicle speed sensor  64 , and the pedal sensor  80 . The pedal position module  84  interprets the driver intent based on information received from these signals and calculates accelerator effective position (AEP). The AEP calculation may then be transmitted from the ECM  18  to the TCM  20  via a serial datalink (e.g. CAN). 
     The TCM  20  includes a gear determination module  86 , a predictive shift module  88 , and a validation module  90 . The gear determination module  86  receives the AEP from the ECM  18 , along with inputs from the turbine speed sensor  70 , the one or more solenoid position sensors  72 , the transmission speed sensor  74 , and the vehicle speed sensor  64 . The gear determination module  86  may then use the AEP to calculate AEP velocity (i.e. the rate at which the accelerator pedal  82  changes position) and AEP acceleration (i.e. the rate at which the accelerator pedal  82  changes velocity). These AEP calculations may be used to determine and command an appropriate gear ratio. 
     The TCM  20  also determines whether to initiate the predictive shift module  88  based on various factors. For example, the predictive shift module  88  is not active at all times during vehicle operation. Under certain operating conditions, such as when the throttle valve  12  experiences a fault or when accelerator pedal maneuvering is at steady state, the TCM  20  bypasses the predictive shift module  88  and allows the gear ratio from the gear determination module  86  to execute without modification. However, when the predictive shift module  88  is activated, the gear ratio from the gear determination module  86  may be modified. 
     The predictive shift module  88  receives inputs from the gear determination module  86  and the vehicle speed sensor  64 . For example, the predictive shift module  88  uses the calculated AEP rate and AEP acceleration to determine a predicted AEP (P-AEP). The predictive shift module  88  then uses the P-AEP, along with inputs from the turbine speed sensor  70 , the one or more solenoid position sensors  72 , the transmission speed sensor  74 , and the vehicle speed sensor  64 , to command an alternate P-AEP gear ratio in lieu of the previously commanded AEP gear ratio. 
     When a downshift is triggered as a result of using the predictive shift module  88 , the P-AEP is stored in the validation module  90  and a prediction timer is initiated. The validation module  90  monitors and stores the highest attained AEP during a predetermined time period corresponding to an abort shift time. The abort shift time is the amount of time available to cancel a currently commanded downshift and execute an alternate command. 
     Referring now to  FIG. 3 , a shift point control method  100  will be described in detail. The shift point control method  100  calculates the AEP rate of change (velocity) and acceleration, commands the appropriate gear ratio based on the AEP, and determines whether a Predictive Shift Point Control Mode (PSHP)  200  (as shown in  FIG. 4 ) should be entered. If the shift point control method  100  determines that the PSHP  200  should be entered, then a validation operation  300  (as shown in  FIG. 5 ) validates the P-AEP and corrects for any overprediction. This validation occurs within the corresponding downshift abort time window, thereby preventing the execution of unwanted downshifts. The shift point control method  100  then executes the appropriate gear ratio based on one of AEP or P-AEP. 
     The shift point control method  100  starts when the gear determination module  86  receives the calculated AEP from the pedal position module  84  in step  102 . The gear determination module  86  calculates the AEP velocity and acceleration in step  104 . An appropriate gear ratio corresponding to the AEP calculations and inputs from the turbine speed sensor  70 , the one or more solenoid position sensors  72 , the transmission speed sensor  74 , and the vehicle speed sensor  64 , is then determined by looking to a shift map in step  106 . The gear determination module  86  then commands the selected gear ratio in step  108 . 
     The shift point control method  100  next determines whether initiation of the predictive shift module  88  should occur in step  110 . The predictive shift module  88  is only active during certain driving maneuvers. When initiated, the predictive shift module  88  follows a Predictive Shift Point Control Mode (PSHP)  200  ( FIG. 4 ) that increases downshift availability and improves the consistency in downshift types. When the shift point control method  100  bypasses the PSHP  200  (i.e. step  110  is evaluated as “NO”), the commanded gear ratio executes in step  112 . For example, entrance criteria for the PSHP  200  may include: 1) no active throttle faults; 2) inactive PSHP  200 ; 3) AEP velocity above an entry threshold; 4) previous commanded downshift status; 5) previously active shift delay status; and 6) previously active gear override status. 
     Referring now to  FIG. 4 , when the shift point control method  100  meets all the necessary entrance criteria (i.e. step  110  is evaluated as “YES”), the predictive shift module  88  initiates and the PSHP  200  begins. However, the PSHP  200  may exit at any time if any of the following exit criteria are satisfied: 1) active PSHP  200 ; 2) a throttle fault occurs; 3) accelerator pedal maneuvering is deemed to be a steady state; 4) AEP is decreased below an exit threshold; 5) currently active shift delay status; or 6) currently active gear override status. 
     In one example, the incremental P-AEP is calculated in step  214 . The incremental P-AEP is the product of a defined calibratable gain as a function of AEP velocity, a defined modifier as a function of AEP acceleration, and the amount of time in the future for which the P-AEP shall be computed as a function of the current commanded gear. The incremental P-AEP is limited to a positive value in step  216  to ensure that the prediction only applies to increasing throttle maneuvers. If the incremental P-AEP is not a positive value, the PSHP  200  may exit to step  112  of the shift point control method  100 . 
     If the incremental P-AEP is a positive value, beginning in step  218  three defined regions for the P-AEP characteristics are determined so that the downshift events are proportional to the driver&#39;s intended accelerator pedal tip-in maneuver. Each region is defined based on the AEP rate and includes a low range (MIN), a medium range (MID), and a high range (MAX). For example only, a hysteresis method may be used to determine the thresholds of the regions to avoid oscillation among the regions due to noise found in the AEP signal. 
     When the AEP rate is in the low range (i.e. less than MID), the incremental P-AEP is confined to a MIN limit table in step  220 . For example, the MIN limit table may only permit the scheduling of single-step downshifts. If the AEP rate is not in the low range, the AEP rate is checked to determine whether it falls in the medium range (i.e. greater than or equal to MID, but less than MAX) in step  222 . If the AEP rate is in the medium range, the incremental P-AEP is confined to a MID limit table in step  224 . For example, the MID limit table may force the scheduling of jump downshifts. Otherwise, the AEP rate falls in the high range and the incremental P-AEP is confined to a MAX limit table in step  226 . For example, the MAX limit table may force the scheduling of skip downshifts. 
     In step  228 , the limited, incremental P-AEP is added to the AEP to obtain the P-AEP. The predictive shift module  88  determines an appropriate gear ratio corresponding to the calculated P-AEP in step  230  and commands the selected gear ratio in step  232 . 
     When a downshift is triggered as a result of the PSHP  200 , the gear ratio determined from the calculated P-AEP is validated in step  234  as will be described further below. If the PSHP gear ratio is validated, the PSHP gear ratio remains as the commanded gear ratio. The PSHP  200  then exits to step  112  of the shift point control method  100  where the commanded gear ratio is executed by the gear determination module  86 . Conversely, if the PSHP gear ratio is determined to be invalid, the PSHP  200  continues to step  236  where the commanded PSHP gear ratio is cancelled. After cancelling the commanded PSHP gear ratio, the PSHP  200  exits to step  112  of the shift point control method  100  where the AEP gear ratio is executed by the gear determination module  86 . 
     Referring now to  FIG. 5 , the PSHP gear ratio validation operation  300  will be described in greater detail. In step  338 , the commanded PSHP gear ratio and associated P-AEP from step  230  are sent to the validation module  90  and stored for further evaluation. A prediction timer, located in the validation module  90 , is set in step  340 . In step  342 , the validation operation  300  monitors and stores the highest AEP achieved during a prediction time calculated to be slightly less than the abort shift time. Until the prediction time has elapsed in step  344 , the validation operation  300  continues to monitor and store the highest AEP. 
     When the prediction time has elapsed, the validation operation  300  compares the stored P-AEP to the highest value of the AEP attained during the prediction time in step  346 . If the difference between the P-AEP and the highest value of the AEP reached during the prediction time is less than a calibration threshold, as determined in step  348 , the PSHP gear ratio is considered to be valid. Conversely, if the difference between the P-AEP and the highest value of the AEP reached during the prediction time is greater than the calibration threshold, the PSHP gear ratio is considered to be invalid. The validity or invalidity of the PSHP gear ratio is output to step  234  of the PSHP  200 . As the validation operation  300  takes place within the abort shift time window, any corrections take place before unwanted downshifts are actually executed. 
     This description is merely exemplary in nature and, thus, variations that do not depart from the gist of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.