Automatic transmission control method and system having fail-safe function

An automatic transmission control system, comprising:

• a transmission gear train which perform multiple gear stages by combination of engagements of a plurality of friction elements;
• a detection means for detecting occurrence of fault-induced disengagement in any of the friction elements to be engaged at a current gear stage;
• a determination means for determining the friction element which is undergoing the fault-induced disengagement;
• and
• a command means for outputting a command to establish another gear stage different from the gear stage at the time of occurrence of the fault-induced disengagement by combination of engagements of the friction elements other than the friction elements to be engaged at the time of occurrence of the fault-induced disengagement,
• wherein the command means further simultaneously outputs a plurality of commands to establish a plurality of gear stages corresponding to combination of engagement of the friction elements to be engaged at the gear stage at the time of occurrence of the fault-induced disengagement, and engagement of the friction elements to be disengaged at the gear stage at the time of occurrence of the fault-induced disengagement to thereby establish any one of the plurality of gear stages by combination of engagement of the friction element free from the fault-induced disengagement among the friction elements to be engaged at the gear stage at the time of occurrence of the fault-induced disengagement, and engagement of the friction elements to be disengaged at the gear stage at the time of occurrence of the fault-induced disengagement, when the gear stage at the time of occurrence of the fault-induced disengagement is a predetermined gear stage which is established by combination of engagements of the friction elements which independently constitute an essential friction element to be engaged for establishing any of gear stages other than the predetermined gear stage, and the friction element undergoing the fault-induced disengagement is not determined by the determination means.

A method of controlling an automatic transmission, the automatic transmission including a transmission gear train which perform multiple gear stages by combination of engagements of a plurality of friction elements, the method comprising:

• detecting occurrence of fault-induced disengagement in any of the friction elements to be engaged at a current gear stage;
• determining the friction element which is undergoing the fault-induced disengagement;
• determining whether the gear stage at the time of occurrence of the fault-induced disengagement is a predetermined gear stage which is established by combination of engagements of the friction elements which independently constitute an essential friction element to be engaged for establishing any of gear stages other than the predetermined gear stage;
• conducting a first control in abnormal condition by outputting a command to establish another gear stage different from the gear stage at the time of occurrence of the fault-induced disengagement by combination of engagements of the friction elements other than the friction element which is undergoing the fault-induced disengagement when the friction element undergoing the fault-induced disengagement is determined;
• conducting a second control in abnormal condition by simultaneously outputting a plurality of commands to establish a plurality of gear stages corresponding to combination of engagement of the friction elements to be engaged at the gear stage at the time of occurrence of the fault-induced disengagement, and engagement of the friction elements to be disengaged at the gear stage at the time of occurrence of the fault-induced disengagement to thereby establish any one of the plurality of gear stages by combination of engagement of the friction element free from the fault-induced disengagement among the friction elements to be engaged at the gear stage at the time of occurrence of the fault-induced disengagement, and engagement of the friction elements to be disengaged at the gear stage at the time of occurrence of the fault-induced disengagement, when the gear stage at the time of occurrence of the fault-induced disengagement is the predetermined gear stage and the friction element undergoing the fault-induced disengagement is not determined;
• and
• conducting a third control in abnormal condition by outputting a command to establish another gear stage different from the gear stage at the time of occurrence of the fault-induced disengagement by combination of engagements of the friction elements other than the friction elements to be engaged at the time of occurrence of the fault-induced disengagement, when the gear stage at the time of occurrence of the fault-induced disengagement is any of gear stages other than the predetermined gear stage and the friction element undergoing the fault-induced disengagement is not determined.