Patent ID: 6491604
Filing Date: 2002-12-10
Classification: F16H,Y10T

Abstract:
A method of performing hydraulic-pressure control in a speed change mechanism comprising a plurality of speed-changing hydraulic clutches, each of which is engaged according to hydraulic-pressure-increase effects and is disengaged according to hydraulic-pressure-decrease effects,wherein a piston of each of the clutches remains neutral regardless of the quantity of supplied hydraulic oil when a hydraulic pressure therein is less than a piston-holding pressure, and is operated at a stroke corresponding to the quantity of supplied hydraulic oil when the hydraulic pressure therein is not less than the piston-holding pressure, wherein while each of the clutches that has been disengaged is engaged by supplying hydraulic oil, the hydraulic pressure therein that has been less than the piston-holding pressure is gradually increased to a normal engaging-pressure above the piston-holding pressure, wherein the speed of increasing hydraulic pressure for engaging the clutch is increased correspondingly to the increase of an engine revolution frequency, and wherein, during a speed-changing operation such as to disengage one of the clutches from an engaged state and to engage another from a disengaged state, at least either a time difference between an operating-hydraulic-pressure-decrease start time for a disengagement-objective clutch and an operating-hydraulic-pressure-increase start time for a engagement-objective clutch or a time-transitional decrease property of hydraulic pressure in the disengagement-objective clutch is controlled to vary correspondingly to variations in the engine revolution frequency so that a time-transitional pressure region where the hydraulic pressures in both the engagement-objective clutch and the disengagement-objective clutch are equal to or more than the piston-holding pressure is maintained to be constant regardless of variations in the increase-speed of hydraulic pressure in the engagement-objective clutch caused by the variations in the engine revolution frequency.