Abstract:
A method for controlling a transmission includes using actuation of a button of a shift module to produce a signal representing a desired gear, using the signal and a second signal commanding a park range to determining a priority range, using a shift mechanism to attempt engagement of the transmission in the priority range, and if the priority range is park and park is not engaged, engaging a park brake.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to electrical shift-by-wire selection of a desired transmission operating range. 
     2. Description of the Prior Art 
     In a conventional automatic transmission system for a motor vehicle, a direct mechanical linkage connects a driver operated gear shift lever, whose movement actuates the transmission gear shift mechanism through a cable. 
     In a shift-by-wire system, this direct linkage is separated and an electronic system that includes solenoids or motors may be used to produce the intended position of the gear shift mechanism. 
     In a shift-by-wire system that uses a push button or multiple discrete input driver interfaces, several opportunities and challenges exist in providing gear shifting that is intuitive to the operator and delivers safe vehicle operation. 
     A need exists in the industry for a shift-by-wire system that uses in combination hardware that produces the shift-by-wire function, such as a vehicle operator interface and push buttons, and a method for controlling the system. 
     SUMMARY OF THE INVENTION 
     A method for controlling a transmission includes using actuation of a button of a shift module to produce a signal representing a desired gear, using the signal and a second signal commanding a park range to determining a priority range, using a shift mechanism to attempt engagement of the transmission in the priority range, and if the priority range is park and park is not engaged, engaging a park brake. 
     The manually operated push button interface is controlled by software without physical locks of the buttons that prevent actuation by the operator. The interface has multiple discrete inputs without need for mechanical lock-outs providing design and package space flexibility. 
     All of the interlocks are managed in software of three modules: a Gear Shift Module, the driver&#39;s interface; a Powertrain Control Module, which manages all of the interlocks for the shift system; and a Transmission Range Control Module, which executes the driver&#39;s request to shift the transmission to the appropriate gear or a preemptive command to engage the Park range. 
     The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of a shift-by-wire range selection system for an automatic transmission; and 
         FIG. 2  is a logic diagram showing the steps of an algorithm that controls the system of  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1 , a shift-by-wire system  10  for an automatic transmission  12  includes a gear shift module (GSM)  14 , powertrain control module (PCM)  16 , transmission range control module (TRCM)  18 , and instrument cluster and message center  20 . The GSM  14 , located in the passenger compartment of a vehicle, is the driver interface operated manually by the vehicle operator, who selects the desired transmission range by actuating a button corresponding to the desired range: Park (P), Reverse (R), Neutral (N), Drive (D) and Low (L). These input commands are translated by the system  10  to produce signals representing the vehicle operator&#39;s requests for the desired transmission gear or range. The PCM  16  is the decision maker, managing all of the interlocks for the shift system  10 . The TRCM  18  executes the operator&#39;s requests to shift the transmission  12  to the appropriate gear or range and can trip its default-to-park mechanism causing transmission  12  immediately to produce the Park range. 
     The modules  14 ,  16 ,  18  and instrument cluster and message center  20  communicate over a communication area network (CAN). The operator&#39;s requests represented by signal  22  are carried from GSM  14  on the CAN to PCM  16 , which sends signal  24  representing the current transmission range to GSM  14  where the current range is displayed or illuminated. Information and warning messages are carried from PCM  16  to the instrument cluster and message center  20 , which sends requests, such as a request for the transmission to enter neutral-tow to the PCM. 
     PCM  16  transmits a signal  26  representing the commanded transmission range selected by the operator on the CAN to the TRCM  18 . The TRCM  18  includes electric motors, which pivot a manual lever  28  connected by a shift cable  29  to the manual valve  30  of transmission  12 . The transmission  12  produces the range that corresponds to the P, R, N and D position of the manual valve  30 . TRCM  18  transmits a signal  32  representing the P, R, N and D position its manual lever  28  to the PCM  16 . 
     Information related to the state of the vehicle&#39;s ignition switch and battery voltage is carried on lines  34  to PCM  16 . Information related to the applied and released state of the vehicle&#39;s brake is carried on line  36  to PCM  16 . A signal  38  produced by a speed sensor  40  representing the rotational speed of the transmission output shaft is transmitted to PCM  16 . A signal  42  representing the current transmission range and produced by a transmission range sensor  44  is transmitted to PCM  16 . 
       FIG. 2  is a logic diagram showing the steps of an algorithm that controls system  10 . At step  50 , a test is made to determine whether any of the P, R, N, D, and L buttons of the GSM  14  is pressed. If the result of test  50  is logically false, at step  52  a test is made to determine whether system  10  is in Park, Neutral Hold or Neutral Tow. Neutral Hold is a special operating mode selected by the vehicle operator in situations where maintaining the transmission in Neutral is desired, e.g., when running the vehicle through a car wash. In the Neutral Hold mode, the Return to Park functions that require the driver&#39;s presence in the vehicle are disabled and the gear indication is maintained. Neutral Tow is a special operating mode selected by the vehicle operator for long term towing, e.g., when towing the vehicle behind a motor home. In the Neutral Tow mode, the return to Park functions that require the driver&#39;s presence in the vehicle are disabled, gear indication is shut down, and all gear selections are ignored until the Neutral Tow exit procedure is executed. 
     If the result of test  52  is logically true, the control returns to start and the algorithm is re-executed. 
     If the result of test  52  is false, at step  54  a test is made to determine whether the ignition switch is off or a door is open and the corresponding seat belt is unlatched. 
     If the result of test  54  is false, at step  56  a test is made to determine whether the vehicle&#39;s battery voltage is less than nine volts. 
     If the result of test  56  is false, the control returns to start and the algorithm is re-executed. If the result of test  56  is true, at step  57  TRCM  18  trips its default-to-park mechanism, causing transmission  12  to produce the Park range. 
     If the result of test  50  is true, at step  58  GSM  14  debounces the pressed button. A debounce procedure verifies that a button has been pressed by monitoring the three output contacts associated with a single activated button to determine that two of the three contacts indicate that the button has been depressed for a period whose length is at least equal to that of a reference period. 
     At step  60 , a test is made to determine whether the pressed button is held activated longer than a reference period, or two of the contacts are made. 
     If the result of test  60  is false, the control returns to step  58 . If the result of test  60  is true, at step  62  GSM  14  transmits the operator&#39;s transmission range request to PCM  16 , which request is received by the PCM at step  64 . 
     At step  66  a test is made to determine whether certain vehicle conditions are present such that a range change can be executed. The requisite conditions requires a check of the operational condition of some or all of the following vehicle components and the magnitude of vehicle parameters: vehicle speed, brake shift interlock, status of the ignition switch, open and closed state of the operator&#39;s door, battery voltage, operation of the CAN, PWM inputs to the shift-by-wire system in the TRCM  18 , presence of a neutral-tow request, status of the neutral tow, latched status of the operator&#39;s seatbelt, operating status of the GSM&#39;s park override subsystem, operating status of the GSM button stuck subsystem, and operating status of the TRCM&#39;s default-to-park system. 
     If the result of test  66  is false, the control returns to start and the algorithm is re-executed. If the result of test  66  is true, indicating that the necessary conditions are present for a transmission range change, at step  68  PCM  16  sends command signal  26  to TRCM  18 . 
     If the result of test  54  is true, at step  70  PCM  16  sends a Park command signal  26  to TRCM  18 . 
     At step  72 , TRCM  18  moves manual lever  28  to the commanded position. 
     At step  74 , PCM  16  reads signal  42  produced by the transmission range sensor  44 . 
     At step  76  a test is made to determine whether transmission  12  has performed a range change to the range commanded in step  72 . If the result of test  76  is true, at step  78  the current range is displayed by the instrument cluster and message center  20 . 
     If the result of test  76  is false, indicating that the commanded transmission range is not engaged, at step  80  the instrument cluster and message center  20  indicates a ‘shift system fault’ message. 
     At step  82  a test is made to determine whether the transmission range commanded at step  72  is the Park range. If the result of test  82  is true, at step  84  PCT  16  issues a command that produces electrical engagement of the park brake. 
     If the result of test  82  is false or following execution of step  84 , control returns to start and the algorithm is re-executed. 
     In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.