Step automatic transmission

1. An automatic transmission of a motor vehicle, comprising:

a plurality of planetary gear units;

a plurality of frictional elements, the frictional elements assuming engaged/disengaged condition upon receiving a ratio change instruction thereby to establish a desired speed of the transmission with the aid of the planetary gear units;

a deceleration detecting means that detects a deceleration of the motor vehicle;

a gear ratio detecting means that detects an actual gear ratio that is actually established in the transmission; and

an interlock judgment means that judges whether or not the transmission is subjected to an interlock, the interlock being a condition wherein upon receiving the ratio change instruction, at least one of the frictional elements is brought into unintended engagement,

the interlock judgment means being configured to carry out judgment of the interlock by analyzing the deceleration of the vehicle and a relation between a gear ratio intended by the ratio change instruction and the actual gear ratio actually established by the transmission while the transmission is not under a ratio change, and

the interlock judgment means being configured to judge occurrence of the interlock when the deceleration of the vehicle is higher than a predetermined deceleration and the actual gear ratio relative to the intended gear ratio exceeds a predetermined range.

2. An automatic transmission as claimed in claim 1 , in which the interlock judgment means carries out the judgment of the interlock when a condition wherein the deceleration of the vehicle is higher than the predetermined deceleration is kept for a first predetermined time and a condition wherein the actual gear ratio is out of the predetermined range of the gear ratio intended by the ratio change instruction is kept for a second predetermined time.

3. An automatic transmission of a motor vehicle, comprising:

a plurality of planetary gear units;

a plurality of frictional elements, the frictional elements assuming engaged/disengaged condition upon receiving a ratio change instruction thereby to establish a desired speed of the transmission with the aid of the planetary gear units;

a deceleration detecting means that detects a deceleration of the motor vehicle;

a gear ratio detecting means that detects an actual gear ratio that is actually established in the transmission;

an interlock judgment means that judges whether or not the transmission is subjected to an interlock, the interlock being a condition wherein upon receiving the ratio change instruction, at least one of the frictional elements is brought into unintended engagement,

the interlock judgment means being configured to carry out judgment of the interlock by analyzing the deceleration of the vehicle and a relation between a gear ratio intended by the ratio change instruction and the actual gear ratio actually established by the transmission while the transmission is not under a ratio change,

in which the interlock judgment means carries out the judgment of the interlock when a condition wherein the deceleration of the vehicle is higher than a predetermined deceleration is kept for a first predetermined time and a condition wherein the actual gear ratio is out of a predetermined range of the gear ratio intended by the ratio change instruction is kept for a second predetermined time;

a first limp-home control means that, when the interlock judgment means judges the interlock, causes the deceleration of the vehicle to be smaller than the predetermined deceleration by issuing instruction to at least one of the frictional elements; and

a second limp-home control means that, when the deceleration of the vehicle is smaller than the predetermined deceleration and a condition wherein the actual gear ratio is out of the predetermined range intended by the ratio change instruction is kept for a third predetermined time, issues instruction to at least one of the frictional elements, that is different from the instruction issued from the first limp-home control means.

4. An automatic transmission as claimed in claim 1 , further comprises a brake operation detecting means that detects whether a brake pedal is depressed or not, and in which the interlock judgment means carries out the judgment of the interlock when the transmission is not under ratio change and the brake operation is not carried out, and in which the interlock judgment means carries out the judgment of the interlock assuming that the brake operation is not carried out, when the brake operation detecting means is not in order or when it is impossible to carry out judgment as to whether the brake operation detecting means is in order or not.

5. An automatic transmission as claimed in claim 1 , further comprises:

a first rotation speed detecting means that detects a rotation speed of an output shaft of the transmission; and

a second rotation speed detecting means that detects a rotation speed of a drive road wheel of the motor vehicle,

in which the deceleration detecting means calculates the deceleration of the motor vehicle based on values detected by the first and second rotation speed detecting means, and

in which when the second rotation speed detecting means is not in order, the deceleration detecting means calculates the deceleration of the motor vehicle based on only the values detected by the first rotation speed detecting means.

6. In an automatic transmission of a motor vehicle including a plurality of planetary gear units and a plurality of frictional elements, the frictional elements assuming engaged/disengaged condition upon receiving a ratio change instruction thereby to establish a desired speed of the transmission with the aid of the planetary gear units,

a method for judging an interlock of the transmission, comprising:

detecting a deceleration of the motor vehicle;

detecting an actual gear ratio that is actually established in the transmission; and

judging whether or not the transmission is subjected to an interlock, the interlock being a condition wherein upon receiving the ratio change instruction, at least one of the frictional elements is brought into unintended engagement, the judgment for the interlock being carried out by analyzing the deceleration of the vehicle and a relation between the gear ratio intended by the ratio change instruction and the actual gear ratio while the transmission is not under a ratio change, occurrence of the interlock being judged when the deceleration of the vehicle is higher than a predetermined deceleration and the actual gear ratio relative to the intended gear ratio exceeds a predetermined range.

7. A method as claimed in claim 6 , in which the judgment for the interlock is carried out by:

detecting that the deceleration of the vehicle is higher than the predetermined deceleration;

continuing the detection of the deceleration of the vehicle for a first predetermined time from a time on which the detection of the vehicle deceleration being higher than the predetermined deceleration is made;

judging whether or not a condition wherein the actual gear ratio is out of the predetermined range of the gear ratio intended by the ratio change instruction is kept for a second predetermined time; and

judging that the transmission is subjected to an interlock when it is judged that the actual gear ratio is out of the predetermined range of the gear ratio intended by the ratio change instruction.

8. A method as claimed in claim 7 , further comprising:

upon judgment of the interlock, issuing first instruction to at least one of the frictional elements in order to make the deceleration of the vehicle smaller than the predetermined deceleration;

and issuing second instruction to at least one of the friction elements when it is judged that actual gear ratio is out of the predetermined range of the gear ratio intended by the ratio change instruction without detected information in which the vehicle deceleration is higher than the predetermined deceleration, the second instruction being different from the first instruction.