Abstract:
A system includes a controller that executes a method for determining failure of the door latch sensor using both the door latch sensor and a door lock sensor. If the door latch sensor is faulty, the controller adjusts an automatic feature of the vehicle based on a door lock signal instead of a door state signal. The controller is also configured to mark the door latch signal as faulty if the door latch system is not functioning properly by using a fault counter that tracks the door lock sensor.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention pertains to the field of sensors providing information to automatic transmission controllers for motor vehicles and, more particularly, to a method and system for detecting whether a door is open or closed and if a door sensor fails. 
     2. Background of the Invention 
     A traditional automatic transmission includes a control device employed to control the transmission of a motor vehicle. In particular, the transmission control device is used to select several ranges, such as Park wherein the transmission is locked to prevent the vehicle from moving, Neutral wherein the transmission allows the vehicle to be moved freely, such as when being towed, Reverse wherein the transmission allows the vehicle to move backwards, and one or more Drive ranges that enable forward motion of the vehicle. Usually, the transmission control device is in the form of a lever connected with a mechanical connection, such as a cable or a hydraulic line, to the transmission. Typically, the lever is also connected to an indicator. As the transmission control mechanism is moved from one range to another, the mechanical connection physically shifts the transmission to the selected setting and the indicator moves to show the driver which range has been selected. Even if the vehicle is turned off, the driver is able to determine the current transmission range from the indicator and, in some cases, to move the transmission control mechanism to Neutral if for example, the vehicle is to be towed. 
     The traditional automatic transmission utilizes multiple friction elements for automatic gear ratio shifting. Broadly speaking, these friction elements may be described as torque establishing elements, more commonly referred to as clutches or brakes. The friction elements function to establish power flow paths from an internal combustion engine to a set of vehicle traction wheels. During acceleration of the vehicle, the overall speed ratio, which is the ratio of a transmission input shaft speed to a transmission output shaft speed, is reduced during a ratio upshift as vehicle speed increases for a given engine throttle setting. A downshift to achieve a higher speed ratio occurs as an engine throttle setting increases for any given vehicle speed, or when the vehicle speed decreases as the engine throttle setting is decreased. Various planetary gear configurations are found in modern automatic transmissions. However, the basic principle of shift kinematics remains similar. Shifting an automatic transmission having multiple planetary gearsets is accompanied by applying and/or releasing friction elements to change speed and torque relationships by altering the torque path through the planetary gearsets. Friction elements are usually actuated either hydraulically or mechanically based on the position of the transmission control device. 
     In a shift-by-wire transmission arrangement, the mechanical connection between the transmission control device and the transmission is eliminated. Instead, the transmission control device transmits an electrical signal along a wire to an electronic controller, which directs separate actuators to apply or release the various friction elements to obtain a desired gear ratio. The control device is no longer necessarily in the form of a lever because the control device is no longer moving a mechanical connection for controlling the transmission. Instead, the control device is typically an electro-mechanical interface (e.g., a series of buttons, lever or knob) that is used to instruct the transmission to switch between the transmission ranges. An electronic display, powered by a battery on the vehicle, is typically employed to indicate the current range for the transmission and must be on, and thus drawing power, in order for the driver to know which range has been selected. 
     Many vehicles with a shift-by-wire transmission incorporate a “Return to Park” feature to automatically shift the transmission into Park when the driver exits the vehicle or the battery supplies a voltage below a certain threshold level. Automatically shifting the transmission into Park prevents unwanted motion of the vehicle. See, for example, U.S. Pat. Nos. 3,937,105, 4,892,014 and 7,156,218. Such a feature is activated when certain triggering events occur, for example, when the system detects a seat belt being unbuckled while a driver door is opened and the vehicle is essentially stationary, or when the ignition is turned off. Sensors or switches are typically used to detect the triggering events. When these sensors, which are preferably in the form of switches, fail, the “Return to Park” functions do not operate properly and in some cases the “Return to Park” functions are disabled. Some controllers that normally use sensor inputs to control a transmission will ignore a sensor that is known to be faulty and control the transmission based on the remaining sensors. For example, when the controller detects a faulty door sensor, the controller will ignore the door sensor and control the transmission based on a seatbelt sensor. The seatbelt sensor may be a hall sensor connected to a control system incorporating diagnostic routines that determine if the sensor is sending a faulty signal. However, in the case of a driver&#39;s door latch sensor used to determine if the driver&#39;s door is open, the sensor may have two valid states, i.e., door open or door closed. Since both states are valid, determining if the sensor has failed simply by looking at its state is not possible. If the switch fails and always sends a signal indicating that the door is closed, even when it is not, then the “Return to Park” feature becomes disabled. 
     Solving this problem is surprisingly difficult. Proposed solutions have proved to be ineffective or costly. For example, setting a door state within the controller to “indeterminate” until a signal is received from the door latch sensor indicating a transition from open to closed or vice versa may seem promising but causes unexpected problems. With such a system, a driver might be at car wash and turn off the engine to conserve fuel, which might also power off the controller, thus setting the door state to indeterminate and causing the controller to use only the seatbelt sensor. Then later, as the driver restarts the car and drives into the carwash and selects neutral, any unbuckling of the seatbelt will cause the “Return to Park” function to operate unexpectedly. Another proposed solution replaces the simple switch to one with inherent diagnostic capabilities. However, this solution uses an expensive switch and is thus undesirable. 
     As can be seen by the above discussion, there exists a need for a method and system for detecting a door state and door sensor failures that is cost effective and does not result in the transmission control system behaving in unexpected ways. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a system for determining failure in a door sensor. The system is preferably in a vehicle that has a driver&#39;s door that includes a door latch and a door lock. The door is equipped with a door latch sensor for sending a door state signal indicating if the door is open or closed. The door is also equipped with a door lock sensor for sending a door lock signal indicating if the door is locked or unlocked. 
     The vehicle preferably includes a shift-by-wire transmission including an automatic Return to Park feature that automatically shifts the transmission to Park based on the door state signal received from the door latch sensor. The Return to Park feature is configured to automatically shift the transmission to Park if the vehicle is traveling below a low set speed threshold, i.e., substantially stationary, upon detecting a triggering event, specifically a door state being open or indeterminate and a signal from a seatbelt sensor transitioning from indicating that the seatbelt is buckled to indicating that the seat belt is unbuckled; a signal from a seatbelt sensor indicating that the seatbelt is unbuckled or the sensor has failed and the door state transitioning from closed to open; or an ignition switch being turned off. 
     The system also includes a controller for executing a method for determining failure of the door latch sensor by receiving the door state signal from the door latch sensor, receiving the door lock signal from the door lock sensor, and determining from the door state signal and the door lock signal if the door latch sensor is faulty. If the door latch sensor is faulty, the controller adjusts the automatic Return to Park feature of the transmission so that the transmission shifts to Park based on the door lock signal instead of the door state signal. The controller includes a memory and is configured to initialize the memory to remember a state of the door to be “indeterminate”. The controller is further configured to change the memory to remember the state of the door to be “closed” when the door latch signal indicates a transition from open to closed or the door lock signal indicates a transition from unlocked to locked. In addition, the controller changes the memory to remember the state of the door to be “open” when the door latch signal indicates a transition from closed to open or the door lock signal indicates a transition from locked to unlocked. 
     The controller is also configured to determine if the door latch is not functioning properly and, if so, mark the door latch signal as “faulty.” The controller has a fault counter that tracks the door lock sensor. The controller is configured to send a lock command signal to the door lock; determine if the door lock signal indicates that the door lock has switched to a locked position; send an unlock command signal to the door lock; determine if the door lock signal indicates that the door lock has switched to an unlocked position; increase a fault counter when the lock or unlock command signal does not change the door to the locked or unlocked position respectively; and decrease the fault counter when the lock or unlock command signal does change the door to the locked or unlocked position respectively. The controller will set a fault flag when the fault counter exceeds a threshold value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a vehicle incorporating a system for determining failure in a door sensor in accordance with the invention; 
         FIG. 2  is a basic schematic diagram of the system shown in  FIG. 1 ; 
         FIG. 3  is a flowchart showing part of a control routine employed in the system of  FIG. 1  used to determine door sensor failure; 
         FIG. 4  is a flowchart showing another part of the control routine employed used to determine door sensor failure; 
         FIG. 5  is an electrical schematic of wiring extending from the door sensors; and 
         FIG. 6  is a detailed view of a door sensor of  FIG. 1  incorporating a light emitting diode. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With initial reference to  FIG. 1 , there is shown an automotive vehicle  10  having a body  11  and an engine  12  with a battery  15 . Power from engine  12  is transmitted to a transmission  18 , then to the other portions of a powertrain  20  and eventually to drive wheels  22 . Vehicle  10  is shown as a rear wheel drive vehicle but any type of powertrain arrangement, including front wheel or all wheel drive systems, could be employed. In addition, although engine  12  is shown as an internal combustion engine, other types of drive arrangements, including hybrid drive systems, could be utilized. A controller  25  is connected to engine  12  and transmission  18  by communication lines  27  and  28  respectively. Controller  25  uses inputs from several sources to obtain information used to control engine  12  and transmission  18 . For example, controller  25  is connected to a driver door latch sensor  30 , for determining if a door latch  31  of driver door  32  is open, by communication line  35  and a driver door lock sensor  37 , for determining if a door lock  38  of driver door  32  is locked. A seat belt sensor  40  determines if a seat belt  41  is buckled or unbuckled and is also connected to controller  25  through a communication line  45 . An ignition switch  47  and a brake sensor  48  are connected to controller  25  through lines  50  and  51  respectively. 
       FIG. 2  shows more details of transmission  18 , which is an example of a multiple-ratio transmission wherein ratio changes are controlled by friction elements acting on individual gear elements. While a preferred example is disclosed, numerous different types of transmission could be employed. Engine torque from engine  12  is distributed to torque input element  110  of hydrokinetic torque converter  112 . An impeller  114  of torque converter  112  develops turbine torque on a turbine  116  in a known fashion. Turbine torque is distributed to a turbine shaft, which is also transmission input shaft  118 . Transmission  18  is shown to include a simple planetary gearset  120  and a compound planetary gearset  121 . Gearset  120  has a permanently fixed sun gear S 1 , a ring gear R 1  and planetary pinions P 1  rotatably supported on a carrier  122 . Transmission input shaft  118  is drivably connected to ring gear R 1 . Compound planetary gearset  121 , sometimes referred to as a Ravagineaux gearset, has a small pitch diameter sun gear S 3 , a torque output ring gear R 3 , a large pitch diameter sun gear S 2  and compound planetary pinions. The compound planetary pinions include long pinions P 2 / 3 , which drivably engage short planetary pinions P 3  and torque output ring gear R 3 . Long planetary pinions P 2 / 3  also drivably engage short planetary pinions P 3 . Short planetary pinions P 3  further engage sun gear S 3 . Planetary pinions P  2 / 3 , P 3  of gearset  21  are rotatably supported on compound carrier  123 . Ring gear R 3  is drivably connected to a torque output shaft  124 , which is drivably connected to vehicle traction wheels  22  through powertrain  20  shown in  FIG. 1 . Gearset  120  is an underdrive ratio gearset arranged in series with respect to compound gearset  121 . Typically, transmission  18  preferably includes a lockup or torque converter bypass clutch, as shown at  125 , to directly connect transmission input shaft  118  to engine  12  after a torque converter torque multiplication mode is completed and a hydrokinetic coupling mode begins. 
       FIG. 2  also shows a Transmission Range Control Module  151 , a Powertrain Control Module  152  and a Gear Shift Module  156  that collectively define part of controller  25 . Transmission Range Control Module  151  is connected to transmission  18  by a shift cable (not labeled), rather than transmission  18  being connected directly to a driver operated mechanical shifter. A transmission control mechanism, such as Gear Shift Module  156 , is provided to select a transmission shift range. One possible implementation would be various buttons  158 , each representing a different transmission range. In this type of implementation, Gear Shift Module  156  is used to select several ranges, such as Park where the transmission output is locked to prevent the vehicle from moving, Neutral where the transmission allows vehicle  10  to be moved freely, such as when being towed, Reverse where transmission  18  allows the vehicle to move backwards, and one or more Drive ranges that enable forward motion of the vehicle. Gear Shift Module  156  is also shown to include a Sport range. The Sport range is similar to the Drive range but will cause transmission  18  to shift forward ratios based on inputs from upshift and downshift switches (not shown) actuated by the driver. Gear Shift Module buttons  158  are labeled with letters generally corresponding to the several transmission ranges “P”, “R”, “N”, “D”, and “S” as shown in  FIG. 2 . Once transmission  18  has entered one of the ranges, a message center  160  shows the driver which range was entered. Each of the control modules  151 ,  152  and  156  is connected to a local communication network generally indicated at  180  and has a respective non-volatile memory  181 ,  182 ,  186 . 
     The Park range can preferably be entered in many ways. In particular, the driver can select Park by pushing the “P” button to cause the Powertrain Control Module  152  to check to see if vehicle  10  is traveling below an extremely low speed (essentially stationary) and, if so, instructs Transmission Range Control Module  151  to shift transmission  18  into Park. Alternatively, controller  25  may respond to a triggering event. For example, when driver ignition switch  47  is turned to an off position, Powertrain Control Module  152  automatically instructs Transmission Range Control Module  151  to shift transmission  18  into Park, thus enabling a “Return to Park” feature. Similarly, when the driver opens door  32  after unbuckling belt  41 , sensors  30  and  40 , if working properly, will signal Powertrain Control Module  152  which automatically instructs Transmission Range Control Module  151  to shift transmission  18  into Park, thus once again enabling a “Return to Park” feature. The Reverse range is entered by pushing the button labeled “R”, at which point Powertrain Control Module  152  automatically instructs Transmission Range Control Module  151  to shift transmission  18  into Reverse, thus enabling vehicle  10  to move backward. In the exemplary transmission embodiment shown, the Reverse range is established by applying low-and-reverse brake D and friction element B. The Neutral range is entered by a single push of the “N” button on Gear Shift Module  156  or by a push of the “P” button when vehicle  10  is traveling too fast to safely enter the Park mode. In either case, Powertrain Control Module  152  instructs Transmission Range Control Module  151  to shift transmission  18  into Neutral and transmission  18  allows wheels  22  to rotate freely. 
     The Drive or Sport ranges are entered by a single push of the “D” or “S” buttons respectively. Optionally, a Low or “L” range (not shown) can be made available to keep transmission  18  in low gears during forward motion of vehicle  10 . When in Drive, in the exemplary transmission shown, during operation in the first four forward driving ratios, carrier P 1  is drivably connected to sun gear S 3  through shaft  126  and forward friction element A. During operation in the third ratio, and fifth ratio, direct friction element B drivably connects carrier  22  to shaft  127 , which is connected to large pitch diameter sun gear S 2 . During operation in the fourth, fifth and sixth forward driving ratios, overdrive friction element E connects turbine shaft  118  to compound carrier  123  through shaft  128 . Friction element C acts as a reaction brake for sun gear S 2  during operation in second and sixth forward driving ratios. During operation of the third forward driving ratio, direct friction element B is applied together with forward friction element A. The elements of gearset  121  then are locked together to effect a direct driving connection between shaft  128  and output shaft  126 . The torque output side of forward friction element A is connected through torque transfer element  129  to the torque input side of direct friction element B during forward drive. The torque output side of direct friction element B, during forward drive, is connected to shaft  127  through torque transfer element  130 . More details of this exemplary type of transmission arrangement are found in U.S. Pat. No. 7,216,025, which is hereby incorporated by reference. 
       FIG. 3  is a flow chart showing a preferred method  200  of determining if door latch sensor  30  and door lock sensor  37  are functioning properly, which is implemented by controller  25 , and starts at step  210 . Next at step  220 , controller  25  initializes memory  186  on start up and sets both a door latch state and a door lock state to “indeterminate.” Preferably, the states of door latch  31  and door lock  38  are remembered by storing information about remembered states in memory  186  of Gear Shift Module  156  but the state information may also be stored in memory  181  or  182  of Transmission Range Control Module  151  or Powertrain Control Module  152 . Controller  25  then waits at step  225  for signals from door latch sensor  30  and door lock sensor  37  to determine how to change the remembered state. If door latch  31  transitions from unlocked to locked at step  230 , the door state is switched from “indeterminate” or “open” to “closed” at step  235 . If the answer at step  230  is “No”, controller  25  proceeds to step  240 . If door lock  38  transitions from unlocked to locked at step  240 , the door state is switched from “indeterminate” or “open” to “closed” at step  235 . If the answer at step  240  is “No”, controller  25  proceeds to step  250 . If door latch  31  transitions from “closed” to “open” at step  250 , the door state is switched from “indeterminate” or “closed” to “open” at step  255 . If the answer at step  250  is “No”, controller  25  proceeds to step  260 . If door lock  38  transitions from locked to unlocked at step  260 , controller  25  proceeds to step  265  and checks to see if there was an electronic command to unlock door  32 . If not the door state is switched from “indeterminate” or “closed” to “open” at step  255 . If the answer at step  265  is yes then controller  25  checks for evidence of a door latch fault at step  270 . If there is no evidence controller  25  goes to step  225 , if there is evidence controller  25  goes to step  235 . If the answer at step  260  is “No”, controller  25  returns to step  225 . After steps  235  and  255 , controller  25  returns to wait for the next signal at step  225 . 
       FIG. 4  is a flow chart showing more details of a strategy for setting a fault flag to indicate a failed door latch sensor. Controller  25  starts at step  310  and proceeds to step  315  to wait until a lock engage or disengage command is sensed at step  320  or door  32  opens as sensed by latch  31  transitioning from closed to open at step  330 . If door lock  38  does not engage or disengage as door lock  38  should do when the command is received then controller  25  increments a fault counter at step  332 . Similarly, if door lock  38  does not disengage when door  32  is opened manually at step  330  then the fault counter is incremented at step  332 . Specifically, controller  25  determines if door lock  38  remains engaged when door latch  31  transitions from closed to open. After step  332 , controller  25  determines if the fault counter is above a threshold and, if so, a fault flag is set at step  336 . Otherwise, the fault counter is checked to determine if the counter is below zero at step  338 , in which case the fault flag is cleared at step  339 . However, if door lock  38  functions properly at steps  320  and  330 , the fault counter is decremented at step  340  and controller  25  proceeds to step  334 . From method  200  set forth in  FIG. 3 , controller  25  has a method to determine a door state from two sensors  30 ,  37  and, from strategy  300  set forth in  FIG. 4 , controller  25  knows when door latch sensor  30  is not functioning properly. With this information, controller  25  will be able to assuredly perform controller features that require a door state signal even if one door sensor  30 ,  37  fails. 
       FIG. 5  is a wiring diagram showing the connection between controller  25  and both a door latch operator  402  and a door lock operator  404 . Commands to door lock operator  404  are sensed, as before, leaving controller  25 . Controller  25  is also connected to door latch sensor  30  and door lock sensor  37 .  FIG. 6  shows an embodiment where the state of door lock  38  is signaled by an LED  450  rather than the position of a sensor. In this case, a housing  460  receives current through a pin  1  that travels through two resistors  467 ,  464 , a diode  466  and then LED  450  to an electrical source at pin  3 . A resistor  468  in parallel with LED  450  reduces the current traveling though LED  450  when LED  450  is lit, signaling that door is locked. Door lock sensor  37  is connected between pins  3  and  2 . Controller  25  is connected to pin  2  and through a diode  470  to a line  475  between two resistors  462 ,  464 . Diode  470  enables controller  25  to sense the position of door lock  38  without lighting up LED  450  at the wrong time. 
     Although described with reference to preferred embodiments of the invention, it should be readily understood that various changes and/or modifications could be made to the invention without departing from the spirit thereof. For instance, the system functions with manual or electronic locks and the controller features using this system do not need to be limited to Return to Park feature but could also include other features such as a feature that automatically stops and starts the engine to save fuel. In general, the invention is only intended to be limited by the scope of the following claims.