US 5,647,819 AGranted

Speed change control method for an automatic transmission

AssigneeMitsubishi Jidosha Kogyo Kabushiki Kaisha

InventorsKenjiro Fujita, Katsutoshi Usuki, Tetsuya Tashiro

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Abstract

A speed change control method for an automatic transmission is provided, which is capable of reducing a shift shock and a required shifting time period. A skip down-shift from a first shift position to a second shift position is effected by way of a third shift position which is not used in a normal shifting. If it is determined that a difference (N.sub.TM -N.sub.T) between the present turbine rotation speed N.sub.T and the synchronous rotation speed N.sub.TM for the third shift position becomes smaller than a threshold value .DELTA.N.sub.FM during the shifting from the first shift position to the third shift position, a control for releasing a friction engaging element 23, corresponding to a releasing side speed-changing element of the third shift position, is started prior to establishment of the third shift position, whereby a time period for establishing the third shift position is shortened, so that a shift shock and a required shifting time period are reduced.

Claims11

Dependent claims

A speed change control method for an automatic transmission including a first transmission mechanism for establishing a plurality of gear positions, and a second transmission mechanism for establishing a plurality of gear positions, said first and second transmission mechanisms being connected in series with respect to a power transmission, the automatic transmission establishing an arbitrary one of a plurality of shift positions, including first and second shift positions, by a combination of a speed position established in the first transmission mechanism and a gear position established in the second transmission mechanism, a speed ratio of the second shift position being lower than a speed ratio of the first shift position, comprising:

(a) starting a speed-changing operation of the second transmission mechanism to establish a gear position, corresponding to the second shift position, in the second transmission mechanism when a speed change command for instructing a speed change from the first shift position to the second shift position is output;
and
(b) reducing an engagement force of a first friction element provided in said first transmission mechanism to a predetermined value prior to an initiation of a speed-changing operation in the first transmission mechanism to establish a gear position, corresponding to the second shift position, in the first transmission mechanism before said speed-changing operation in step (a) is completed, said first friction element being engaged when establishing, in the first transmission mechanism, a gear position corresponding to the first shift position, and released when establishing, in the first transmission mechanism, the gear position corresponding to the second shift position.

Dependencies are inferred from the claim text.