Diagnostic device and control device for automatic transmission

A diagnostic device for an automatic transmission to be used in a stepped automatic transmission having gear positions, the diagnostic device comprising:

• a range position determinator configured to determine a range position based on a select operation of a driver;
• a shift solenoid configured to control engagement/disengagement of each of a plurality of friction elements of a gear train;
• and
• a transmission controller configured to receive a range position signal transmitted from the range position determinator and output a control instruction to the shift solenoid, wherein
• the transmission controller is further configured to:
• output an engagement instruction/a disengagement instruction to a friction element based on the received range position signal during the select operation,
• when the received range position signal indicates that the range position is switched from a travelling range to a neutral range during travelling, output the disengagement instruction to all of friction elements that are in an engaged state in the travelling range, and then, when a vehicle speed decreases to a value lower than a predetermined vehicle speed, output the disengagement instruction to at least one friction element among a plurality of friction elements to be engaged when a predetermined gear position is to be shifted to and output the engagement instruction to the remaining friction elements,
• while the disengagement instruction is output to the at least one friction element and after the engagement instruction is output to the remaining friction elements, confirm a change in a rotation speed of a transmission input shaft, and
• when there is the change in the rotation speed, diagnose that any of the friction elements instructed to be disengaged is in an erroneously engaged state in which the any of the friction elements is not able to be disengaged.

A control device for an automatic transmission to be used in a stepped automatic transmission having gear positions, the control device comprising:

• a shift solenoid configured to control engagement/disengagement of each of a plurality of friction elements, wherein
• the control device is configured to:
• when a range position is switched from a travelling range to a neutral range during travelling, output a disengagement instruction to all of friction elements that are in an engaged state in the travelling range,
• output the disengagement instruction to at least one friction element before the disengagement instruction is output to all of the friction elements that are in the engaged state in the travelling range,
• confirm a change in a rotation speed of a transmission input shaft after the disengagement instruction is output to the at least one friction element, and
• issue a warning when there is no change in the rotation speed.

A control device for an automatic transmission to be used in a stepped automatic transmission having gear positions, the control device comprising:

• a shift solenoid configured to control engagement/disengagement of each of a plurality of friction elements, wherein
• the control device is configured to:
• when a range position is switched from a travelling range to a neutral range during travelling, output a disengagement instruction to all of friction elements that are in an engaged state in the travelling range, and then, when a vehicle speed decreases to a value lower than a predetermined vehicle speed, output the disengagement instruction to at least one friction element among a plurality of friction elements to be engaged when a predetermined gear position is to be shifted to and output an engagement instruction to the remaining friction elements,
• while the disengagement instruction is output to the at least one friction element and after the engagement instruction is output to the remaining friction elements, confirm a change in a rotation speed of a transmission input shaft, and
• issue a warning when there is no change in the rotation speed.