Automatic transmission control system with shift lever position sensor

Abstract

An automatic transmission control system equipped with a shift lever position sensor which includes a plurality of switches which output binary signals following a shifting motion of a gear shift lever. Patterns of combinations of the switch outputs are preselected so as to represent positions to which the gear shift lever is manually shiftable. The switches are broken down into two groups each of which produces a binary code carrying information about the position of the gear shift lever to monitor a failure in operation of the shift lever position sensor. The control system also works to perform a deemed D-position hydraulic transmission control to ensure the running of the vehicle even if the shift lever position sensor is failing.

1 . An automatic transmission shift lever position sensing apparatus comprising: 
 a lever position sensor including a plurality of sensing elements each of which produces a binary signal, each of the binary signals selectively having one of two binary values in response to a shifting motion of a gear shift lever of an automatic transmission, the sensing elements being broken down into a first and a second sensing element group, the first and second sensing element groups working to produce a first and a second binary code made up of the binary values, respectively, each of the first and second binary code carrying information about one of lever positions in which the gear shift lever is placed;    a position determining circuit which determines in which of the lever positions the gear shift lever is placed and/or determines whether the lever position sensor is failing or not based on the first and second binary codes produced by the first and second sensing element groups of the lever position sensor.    
   
   
       2 . An automatic transmission shift lever position sensing apparatus as set forth in  claim 1 , wherein the lever positions of the gear shift lever are a parking position, a reverse position, a neutral position, a drive position, and intermediate positions therebetween, and wherein the first sensing element group is made up of a given number of the sensing elements, the first binary code being formed by each of predetermined combinations of the binary signals produced by the first sensor element group which corresponds to one of the parking, reverse, neutral, drive, and intermediate positions.  
   
   
       3 . An automatic transmission shift lever position sensing apparatus as set forth in  claim 2 , wherein two of the combinations of the binary signals representing adjacent two of the parking, reverse, neutral, drive, and intermediate positions are different from each other in the binary value of the binary signal as produced by only one of the sensing elements.  
   
   
       4 . An automatic transmission shift lever position sensing apparatus as set forth in  claim 2 , wherein the first sensing element group is made up of a given number of the sensing elements, at least one of the sensing elements of the first sensing element group producing an active level signal as the binary signal thereof when the gear shift lever is placed in any of the parking, reverse, neutral, drive, and intermediate positions.  
   
   
       5 . An automatic transmission shift lever position sensing apparatus as set forth in  claim 2 , wherein the first sensing element group is made up of a given number of the sensing elements, the sensing elements of the first sensing element group all producing active level signals as the binary signals thereof when the gear shift lever is placed in the drive position.  
   
   
       6 . An automatic transmission shift lever position sensing apparatus as set forth in  claim 1 , wherein the lever positions of the gear shift lever are a parking position, a reverse position, a neutral position, a drive position, and positions intermediate therebetween, wherein the first sensing element group is made up of a given number of the sensing elements, the first binary code being formed by each of predetermined combinations of the binary signals produced by the first sensor element group which corresponds to one of the parking, reverse, neutral, drive, and intermediate positions, wherein the second sensing element group is made of one of the sensing elements, the second binary code being formed by the binary signal produced by the second sensing element group which has a first one of the binary values when the gear shift lever is placed in either of the parking and neutral positions and a second one of the binary values when the gear shift lever is placed in any of the lever positions other than the parking and neutral positions, and wherein said position determining circuit performs a determination of in which of the lever positions the gear shift lever is placed using the first binary code and determines whether said lever position sensor is failing or not using a result of said determination and the second binary code.  
   
   
       7 . An automatic transmission shift lever position sensing apparatus as set forth in  claim 6 , the first sensing element group is made up of three of the sensing elements, two of the sensing elements of the first sensing element group producing active level signals as the binary signals thereof when the gear shift lever is placed in any of the intermediate positions.  
   
   
       8 . An automatic transmission shift lever position sensing apparatus as set forth in  claim 6 , wherein each time any one of the binary signals produced by the first sensing element group changes in the binary value, said position determining circuit performs an interruption operation to sample the binary signals outputted from the first sensing element group and also samples the binary signal outputted from the second sensing element group at a given sampling cycle.  
   
   
       9 . An automatic transmission shift lever position sensing apparatus as set forth in  claim 1 , wherein the first sensing element group is made up of a given number of the sensing elements, wherein each time any one of the binary signals produced by the first sensing element group changes in the binary value, said position determining circuit determines whether or not the lever position represented by a resulting combination of the binary signals produced by the first sensing element group is adjacent to that represented by a combination of the binary signals produced by the first sensing element group before the any one of the binary signals changes to determine whether said lever position sensor is failing or not.  
   
   
       10 . A computer executable control program for controlling an automatic transmission shift lever position sensing apparatus equipped with a lever position sensor including a plurality of sensing elements each of which produces a binary signal, each of the binary signals selectively having one of two binary values in response to a shifting motion of a gear shift lever of an automatic transmission, the sensing elements being broken down into a first and a second sensing element group, said control program including a first task to be executed to sample the binary signals produced by the first and second sensing element groups to read therefrom a first and a second binary code carrying information about one of lever positions in which the gear shift lever is placed and a second task to be executed to determine in which of the lever positions the gear shift lever is placed and/or determine whether said lever position sensor is failing or not based on a combination of the first and second binary codes made of the binary signals produced by the first and second sensing element groups.  
   
   
       11 . A computer executable control program as set forth in  claim 10 , wherein the lever positions of the gear shift lever are a parking position, a reverse position, a neutral position, a drive position, and positions intermediate therebetween, wherein when the gear shift lever is placed in one of the parking, reverse, neutral, drive, and intermediate positions, the first sensing element group works to produce the first binary code made of one of predetermined combinations of the binary signals which represents the one of the parking, reverse, neutral, drive, and intermediate positions, wherein the second sensing element group is made of one of the sensing elements, the sensing element of the second sensing element group working to produce the second binary code made of the binary signal which has a first one of the binary values when the gear shift lever is placed in either of the parking and neutral positions and a second one of the binary values when the gear shift lever is placed in any of the lever positions other than the parking and neutral positions, and wherein said second task is to perform a determination of in which of the lever positions the gear shift lever is placed using the first binary code produced by the first sensing element group and to determine whether said lever position sensor is failing or not using a result of said determination and the second binary code produced by the second sensing element group.  
   
   
       12 . A computer executable control program as set forth in  claim 11 , wherein each time any one of the binary signals produced by the first sensing element group changes in the binary value, said first task performs an interruption operation to sample the binary signals outputted from the first sensing element group and samples the binary signal outputted from the second sensing element group at a given sampling cycle.  
   
   
       13 . A computer executable control program as set forth in  claim 11 , wherein the first sensing element group is made up of a given number of the sensing elements, wherein each time any one of the binary signals produced by the first sensing element group changes in the binary value, said second task works to determine whether or not the lever position represented by a resulting combination of the binary signals produced by the first sensing element group is adjacent to that represented by a combination of the binary signals produced by the first sensing element group before the any one of the binary signals changes to determine whether said lever position sensor is failing or not.  
   
   
       14 . An automatic transmission shift lever sensor comprising: 
 a plurality of sensing elements each of which produces a binary signal, each of the binary signals selectively having one of two binary values in response to a shifting motion of a gear shift lever of an automatic transmission, the sensing elements being broken down into a first and a second sensing element group, the first and second sensing element groups working to produce a first and a second binary code made up of the binary values, respectively, each of the first and second binary code carrying information about one of lever positions in which the gear shift lever is placed.    
   
   
       15 . An automatic transmission shift lever position sensor as set forth in  claim 14 , wherein the lever positions of the gear shift lever are a parking position, a reverse position, a neutral position, a drive position, and intermediate positions therebetween, and wherein the first sensing element group is made up of a given number of the sensing elements, the first binary code being provided by each of predetermined combinations of the binary signals produced by the first sensor element group which corresponds to one of the parking, reverse, neutral, drive, and intermediate positions.  
   
   
       16 . An automatic transmission shift lever position sensor as set forth in  claim 15 , wherein two of the combinations of the binary signals representing adjacent two of the parking, reverse, neutral, drive, and intermediate positions are different from each other in the binary value of the binary signal as produced by only one of the sensing elements.  
   
   
       17 . An automatic transmission shift lever position sensor set forth in  claim 15 , wherein the first sensing element group is made up of a given number of the sensing elements, at least one of the sensing elements of the first sensing element group producing an active level signal as the binary signal thereof when the gear shift lever is placed in any of the parking, reverse, neutral, drive, and intermediate positions.  
   
   
       18 . An automatic transmission shift lever position senor as set forth in  claim 15 , wherein the first sensing element group is made up of a given number of the sensing elements, the sensing elements of the first sensing element group all producing active level signals as the binary signals thereof when the gear shift lever is placed in the drive position.  
   
   
       19 . An automatic transmission shift lever position sensor as set forth in  claim 14 , wherein the lever positions of the gear shift lever are a parking position, a reverse position, a neutral position, a drive position, and positions intermediate therebetween, wherein the first sensing element group is made up of a given number of the sensing elements, the first binary code being formed by each of predetermined combinations of the binary signals produced by the first sensor element group which corresponds to one of the parking, reverse, neutral, drive, and intermediate positions, and wherein the second sensing element group is made of one of the sensing elements, the second binary code being formed by the binary signal produced by the second sensing element group which has a first one of the binary values when the gear shift lever is placed in either of the parking and neutral positions and a second one of the binary values when the gear shift lever is placed in any of the lever positions other than the parking and neutral positions.  
   
   
       20 . An automatic transmission shift lever position sensor apparatus as set forth in  claim 19 , the first sensing element group is made up of three of the sensing elements, two of the sensing elements of the first sensing element group producing active level signals as the binary signals thereof when the gear shift lever is placed in any of the intermediate positions.  
   
   
       21 . An automatic transmission control system comprising: 
 a lever position sensor designed to produce signals each of which represents one of a parking position, a reverse position, a neutral position, and a drive position to which a gear shift lever is shifted manually by an operator;    a plurality of hydraulic control valves working to control hydraulic pressures to be supplied to frictional elements of an automatic transmission;    a manual selector valve which selectively establishes hydraulic supply circuits leading to said hydraulic control valves following a shifting motion of the gear shift lever, said manual selector valve working to establish predetermined ones of the hydraulic supply circuit to achieve a selected one of forward gears of the automatic transmission only when the gear shift lever is placed in the drive position; and    a gear change controller which monitors a position of the gear shift lever using the signal produced by said lever position sensor and operates said hydraulic control valves to hydraulically control engagement of the frictional elements of the automatic transmission to establish a selected one of gears of the automatic transmission, when the signal from said lever position sensor represents the position of the gear shift lever other than the drive position, and a predetermined condition is encountered, said gear change controller deeming the gear shift lever to be placed in the drive position and performing a deemed D-position hydraulic transmission control to establish a given one of the forward gears of the automatic transmission.    
   
   
       22 . An automatic transmission control system as set forth in  claim 21 , wherein each of a given number of the signals produced by said lever position sensor carries a binary code made of a combination of a plurality of binary signals, each of the binary codes representing one of the parking, reverse, neutral, and drive position, and intermediate positions therebetween to which the gear shift lever is shiftable, and wherein two of the combinations of the binary signals representing adjacent two of the parking, reverse, neutral, drive, and intermediate positions are different from each other in a binary value of only one of the binary signals.  
   
   
       23 . An automatic transmission control system as set forth in  claim 22 , at least one of the binary signals is an active level signal when the gear shift lever is placed in any of the parking, reverse, neutral, drive, and intermediate positions.  
   
   
       24 . An automatic transmission control system as set forth in  claim 21 , wherein each of a given number of the signals produced by said lever position sensor carries a three-bit code made of a combination of a plurality of binary signals, each of the three-bit codes representing one of the parking, reverse, neutral, and drive position, and intermediate positions therebetween to which the gear shift lever is shiftable, and wherein two of the binary signals of the three-bit code representing each of the intermediate positions are in an active level.  
   
   
       25 . An automatic transmission control system as set forth in  claim 21 , wherein each of the signals produced by said lever position sensor carries a code made up of binary values, all of the binary values are active level values when the gear shift lever is placed in the drive position.  
   
   
       26 . An automatic transmission control system as set forth in  claim 21 , further comprising a failure determining circuit working to monitor a failure in operation of said lever position sensor, and wherein each of the signals produced by said lever position sensor carries a binary code made up of a combination of binary values, each time any one of the binary codes changes in the binary value, said failure determining circuit determines whether or not the position of the gear shift lever represented by a resulting combination of the binary values is adjacent to that represented by a combination of the binary values group before the any one of the binary codes changes to determine whether said lever position sensor is failing in operation or not.  
   
   
       27 . An automatic transmission control system as set forth in  claim 21 , wherein the deemed D-position hydraulic transmission control is performed when the gear shift lever is monitored as being placed in an R-N position intermediate between the reverse and neutral positions.  
   
   
       28 . An automatic transmission control system as set forth in  claim 21 , wherein the deemed D-position hydraulic transmission control is performed when the gear shift lever is monitored as being kept in an N-D position intermediate between the neutral and drive positions for a given period of time.  
   
   
       29 . An automatic transmission control system as set forth in  claim 21 , wherein the deemed D-position hydraulic transmission control is performed immediately when the gear shift lever is monitored as being shifted from the drive position to an N-D position intermediate between the drive and neutral positions, and wherein the deemed D-position hydraulic transmission control is performed when the gear shift lever is monitored as being shifted from the neutral position to and kept in the N-D position for a given period of time.  
   
   
       30 . An automatic transmission control system as set forth in  claim 27 , further comprising an input shaft speed sensor which measures a speed of an input shaft of the automatic transmission and provides a signal indicative thereof, and wherein said gear change controller monitors a gear change action of the automatic transmission using the signal provided by said input shaft speed sensor during execution of the deemed D-position hydraulic transmission control to determine whether said lever position sensor is failing in operation or not.  
   
   
       31 . An automatic transmission control system as set forth in  claim 27 , wherein said gear change controller works to determine a gear ratio of the automatic transmission, and wherein said gear change controller monitors a gear change action of the automatic transmission using the determined gear ratio during execution of the deemed D-position hydraulic transmission control to determine whether said lever position sensor is failing in operation or not.  
   
   
       32 . An automatic transmission control system as set forth in  claim 27 , wherein said gear change controller works to determine the hydraulic pressures acting on the frictional elements of the automatic transmission, and wherein said gear change controller monitors a gear change action of the automatic transmission using the determined hydraulic pressures during execution of the deemed D-position hydraulic transmission control to determine whether said lever position sensor is failing in operation or not.  
   
   
       33 . An automatic transmission control system as set forth in  claim 26 , wherein when it is determined that the lever position sensor is failing, said gear change controller performs a fail-safe function to control the hydraulic control valves so as to establish a given gear in a drive range of the automatic transmission.  
   
   
       34 . An automatic transmission control system as set forth in  claim 30 , wherein when it is determined that the lever position sensor is failing, said gear change controller performs a fail-safe function to control the hydraulic control valves so as to establish a given gear in a drive range of the automatic transmission.