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Speed change control method for an automatic transmission

  • US 5,647,819 A
  • Filed: 08/17/1995
  • Issued: 07/15/1997
  • Est. Priority Date: 11/05/1993
  • Status: Expired due to Term
First Claim
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1. 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.

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