Patent ID: 7529607

Claim:
A method for controlling selection of a gear reduction ratio of a stepped-ratio or continuously variable automatic transmission for a vehicle, provided with a pilot-control for inhibiting/authorizing lengthening of the gear reduction ratio or for initiating shortening of the gear reduction ratio, the method comprising: measuring a current engine speed of a vehicle engine; determining an engine speed that the vehicle engine would have if the gear reduction ratio of the transmission were lengthened, causing the current gear reduction ratio to shift to a higher ratio; calculating a resisting load exerted on the vehicle, permitting minimum power that must be delivered by a motive power group to maintain a speed setpoint to be determined, including calculating current power being delivered by the motive power group, a mass of the vehicle, and the vehicle's acceleration; determining a first threshold for a variable representative of a minimum power that must be delivered by the motive power group in the current ratio to maintain the setpoint vehicle speed, the power being increased by a first margin; determining a second threshold for the variable representative of the minimum power that must be delivered by the motive power group in the higher ratio to maintain the setpoint vehicle speed, the power being increased by a second margin, the first threshold being lower than the second threshold; demanding shortening of the gear reduction ratio of the transmission if the variable representative of the power that can be delivered by the motive power group at the current speed is lower than the first threshold; inhibiting lengthening of the gear reduction ratio of the transmission if the variable representative of the power that can be delivered by the motive power group at the determined engine speed is lower than the second threshold; and authorizing shifting from the current ratio to the higher ratio if the variable representative of power that can be delivered by the motive power group at the determined engine speed is higher than the second threshold, wherein, during braking phases, the calculating the resisting load includes determining a value of brake power produced by a brake system, the value being obtained from an information stream representative of brake pressure and a model establishing a correspondence between the brake pressure and the brake power.