Patent ID: 6301538
Filing Date: 2001-10-09
Classification: F16H

Abstract:
An automatic transmission and control system comprising a first multiple ratio gear unit and a second gear unit with two gear ratios, the gear units being arranged in series in a powertrain torque flow path from an engine to a driven member during operation in at least four overall underdrive ratios;a first reaction brake for anchoring a reaction element of the second gear unit to effect an overdrive ratio of the second gear unit during operation in one overall underdrive ratio;a second reaction brake for anchoring a reaction element of the first gear unit to effect an underdrive ratio of the first gear unit during operation in another overall underdrive ratio higher than the one overall underdrive ratio;a pressure operated clutch for connecting together two elements of the first gear unit to effect a direct drive ratio of the first gear unit during operation in an overall direct drive ratio;each reaction brake having an operating servo with a piston and apply and release pressure chambers on opposite sides of the piston;control means including pressure distributor valves for selectively pressurizing and exhausting actuating pressure to the pressure chambers and to the clutch;the control means including an electronic controller and a valve circuit, the controller establishing control signal pressures in the valve circuit in response to powertrain operating variables whereby the brake for the first gear unit is applied in advance of release of the brake for the second gear unit during a ratio change from the one underdrive ratio to the other underdrive ratio whereby the reaction element for the first gear unit is decelerated before completion of the ratio change by applying first reaction brake;the valve circuit defining a clutch pressure passage extending to the pressure operated clutch and a pressure exhaust flow path for the release pressure chamber of the second reaction brake that is separate from the clutch pressure passage whereby drifting of the clutch to an apply state is avoided during the ratio change.