Control apparatus and method for automatic transmission

1. A control apparatus for an automatic transmission, comprising:

a shift control section configured to perform a shift of the automatic transmission by engaging a first friction-engagement element which is in a released state, and by releasing a second friction-engagement element which is in an engaged state; and

a judder judging section configured to judge an occurrence of a judder due to self-excited vibration;

wherein the shift control section includes an inertia-phase determining section configured to judge whether or not a progress of the shift is during an inertia phase, the inertia phase being one of phases each representing a degree of shift progress under a shift control, an input speed of the automatic transmission being varied for the inertia phase;

wherein the judder judging section is configured:

to calculate a characteristic-gradient index value, the characteristic-gradient index value being a value obtained by quantifying a phenomenon that appears as a relative rotational speed of input and output of the first friction-engagement element becomes reduced with a progress of the inertia phase, the phenomenon appearing in a different way in dependence upon whether a relational characteristic of a friction coefficient of the first friction-engagement element with respect to the relative rotational speed is a positive-gradient characteristic or a negative-gradient characteristic, and

to determine that the judder has occurred, when the characteristic-gradient index value indicates that the phenomenon has appeared due to the negative-gradient characteristic.

2. The control apparatus as claimed in claim 1 , wherein the judder judging section includes a characteristic-gradient index-value calculating section configured:

to specify an ending period of the inertia phase as a period for which the relative rotational speed of the first friction-engagement element approaches 0, within an inertia phase period being defined between a start and an end of the inertia phase; and

to calculate a drive-system physical quantity which appears during the specified ending period of the inertia phase, as the characteristic-gradient index value.

3. The control apparatus as claimed in claim 1 , wherein the judder judging section includes a characteristic-gradient index-value calculating section configured:

to specify an ending period of the inertia phase as a period for which the relative rotational speed of the first friction-engagement element approaches 0, within an inertia phase period being defined between a start and an end of the inertia phase;

to calculate a first drive-system physical quantity which appears during a period between a starting region and an ending region of the inertia phase;

to calculate a second drive-system physical quantity which appears during the specified ending period of the inertia phase; and

to calculate a ratio between the first drive-system physical quantity and the second drive-system physical quantity, as the characteristic-gradient index value.

4. The control apparatus as claimed in claim 3 , wherein the characteristic-gradient index-value calculating section is configured:

to define a time point when an actual transmission ratio of the automatic transmission becomes equal to an inertia-phase start determining transmission ratio, as an inertia-phase start time;

to define a time point when the actual transmission ratio becomes equal to an inertia-phase end determining transmission ratio, as an inertia-phase end time;

to calculate the first drive-system physical quantity corresponding to a first time period between a first time point and the inertia-phase end time, the first time point being a time point when the actual transmission ratio becomes equal to a first transmission ratio by the progress of the shift from the inertia-phase start time; and

to calculate the second drive-system physical quantity corresponding to a second time period between a second time point and the inertia-phase end time, the second time point being a time point when the actual transmission ratio becomes equal to a second transmission ratio, the second transmission ratio being a transmission ratio value advanced from the first transmission ratio by the progress of the shift.

5. The control apparatus as claimed in claim 3 , wherein the characteristic-gradient index-value calculating section is configured:

to specify each of the first drive-system physical quantity and the second drive-system physical quantity by using an elapsed time period within the inertia phase, and

to calculate a ratio of a second inertia-phase period corresponding to the second drive-system physical quantity to a first inertia-phase period corresponding to the first drive-system physical quantity, as the characteristic-gradient index value; and

wherein the judder judging section is configured to determine that the judder has occurred due to self-excited vibration when the ratio of the second inertia-phase period to the first inertia-phase period is lower than or equal to a judder judgment threshold value.

6. The control apparatus as claimed in claim 1 , wherein the judder judging section includes a judder reduction-control executing section configured, in a case where it is determined that the judder has occurred due to self-excited vibration, to carry out a judder reduction control to shorten a shifting time of the automatic transmission when a shift having a shift mode same as that of the shift receiving the current determination of judder occurrence is conducted next after the current determination.

7. An apparatus for an automatic transmission, comprising:

a first friction-engagement element;

a second friction-engagement element; and

means for:

performing a shift of the automatic transmission by engaging the first friction-engagement element which is in a released state, and by releasing the second friction-engagement element which is in an engaged state,

judging whether or not a progress of the shift is during an inertia phase, the inertia phase being one of phases each representing a degree of shift progress under a shift control, an input speed of the automatic transmission being varied for the inertia phase,

calculating a characteristic-gradient index value, the characteristic-gradient index value being a value obtained by quantifying a phenomenon that appears as a relative rotational speed of input and output of the first friction-engagement element becomes reduced with a progress of the inertia phase, the phenomenon appearing in a different way in dependence upon whether a relational characteristic of a friction coefficient of the first friction-engagement element with respect to the relative rotational speed is a positive-gradient characteristic or a negative-gradient characteristic, and

determining that a judder due to self-excited vibration has occurred when the characteristic-gradient index value indicates that the phenomenon has appeared due to the negative-gradient characteristic.

8. A control method for an automatic transmission, comprising:

performing a shift of transmission ratio by engaging a first friction-engagement element which is in a released state, and by releasing a second friction-engagement element which is in an engaged state; and

judging an occurrence of a judder due to self-excited vibration, by operations of:

judging whether or not a progress of the shift is during an inertia phase, the inertia phase being one of phases each representing a degree of shift progress under a shift control, an input speed of the automatic transmission being varied for the inertia phase;

calculating a characteristic-gradient index value, the characteristic-gradient index value being a value obtained by quantifying a phenomenon that appears as a relative rotational speed of input and output of the first friction-engagement element becomes reduced with a progress of the inertia phase, the phenomenon appearing in a different way in dependence upon whether a relational characteristic of a friction coefficient of the first friction-engagement element with respect to the relative rotational speed is a positive-gradient characteristic or a negative-gradient characteristic; and

determining that the judder has occurred when the characteristic-gradient index value indicates that the phenomenon has appeared due to the negative-gradient characteristic.

9. An apparatus for an automatic transmission, comprising:

a controller configured to perform a shift of the automatic transmission by engaging a first friction-engagement element which is in a released state, and by releasing a second friction-engagement element which is in an engaged state; and

wherein the controller is further configured to:

judge whether or not a progress of the shift is during an inertia phase, the inertia phase being one of phases each representing a degree of shift progress under a shift control, an input speed of the automatic transmission being varied for the inertia phase;

calculate a characteristic-gradient index value, the characteristic-gradient index value being a value obtained by quantifying a phenomenon that appears as a relative rotational speed of input and output of the first friction-engagement element becomes reduced with a progress of the inertia phase, the phenomenon being a function of whether a relational characteristic of a friction coefficient of the first friction-engagement element with respect to the relative rotational speed is a positive-gradient characteristic or a negative-gradient characteristic, and

determine that a judder due to self-excited vibration has occurred when the characteristic-gradient index value indicates that the phenomenon is caused by the negative-gradient characteristic.

10. The apparatus as claimed in claim 9 , wherein the controller is further configured to:

specify an ending period of the inertia phase as a period for which the relative rotational speed of the first friction-engagement element approaches 0, within an inertia phase period being defined between a start and an end of the inertia phase; and

calculate a drive-system physical quantity which appears during the specified ending period of the inertia phase, as the characteristic-gradient index value.

11. The apparatus as claimed in claim 9 , wherein the controller is further configured to:

specify an ending period of the inertia phase as a period for which the relative rotational speed of the first friction-engagement element approaches 0, within an inertia phase period being defined between a start and an end of the inertia phase;

calculate a first drive-system physical quantity which appears during a period between a starting region and an ending region of the inertia phase;

calculate a second drive-system physical quantity which appears during the specified ending period of the inertia phase; and

calculate a ratio between the first drive-system physical quantity and the second drive-system physical quantity, as the characteristic-gradient index value.

12. The apparatus as claimed in claim 11 , wherein the controller is further configured to:

define a time point when an actual transmission ratio of the automatic transmission becomes equal to an inertia-phase start determining transmission ratio, as an inertia-phase start time;

define a time point when the actual transmission ratio becomes equal to an inertia-phase end determining transmission ratio, as an inertia-phase end time;

calculate the first drive-system physical quantity corresponding to a first time period between a first time point and the inertia-phase end time, the first time point being a time point when the actual transmission ratio becomes equal to a first transmission ratio by the progress of the shift from the inertia-phase start time; and

calculate the second drive-system physical quantity corresponding to a second time period between a second time point and the inertia-phase end time, the second time point being a time point when the actual transmission ratio becomes equal to a second transmission ratio, the second transmission ratio being a transmission ratio value advanced from the first transmission ratio by the progress of the shift.

13. The apparatus as claimed in claim 11 , wherein the controller is further configured to:

specify each of the first drive-system physical quantity and the second drive-system physical quantity by using an elapsed time period within the inertia phase, and

calculate a ratio of a second inertia-phase period corresponding to the second drive-system physical quantity to a first inertia-phase period corresponding to the first drive-system physical quantity, as the characteristic-gradient index value; and

wherein the judder judging section is configured to determine that the judder has occurred due to self-excited vibration when the ratio of the second inertia-phase period to the first inertia-phase period is lower than or equal to a judder judgment threshold value.

14. The apparatus as claimed in claim 9 , wherein the judder judging section includes a judder reduction-control executing section configured, in a case where it is determined that the judder has occurred due to self-excited vibration, to carry out a judder reduction control to shorten a shifting time of the automatic transmission when a shift having a shift mode same as that of the shift receiving the current determination of judder occurrence is conducted next after the current determination.

15. The apparatus as claimed in claim 9 , further comprising the first friction-engagement element and the second friction-engagement element.