Accumulator control for hydraulic actuating pressure of automatic transmission friction clutch or brake.

摘要

The time rate at which pressure increases in a friction element (96, 74, 98) engaged to produce a gear shift is controlled through operation of an accumulator (256, 260, 262). Shift valves (232, 236) in a hydraulic circuit produce selectively a connection between hydraulic lines associated with the friction elements to be engaged and a source of line pressure. A first control pressure has a magnitude that varies according to a required torque transmitting capacity of the friction element. A line modulator valve (220) produces a second control pressure having a magnitude that varies with the magnitude of the first control pressure but at a different rate. An accumulator includes a piston movable within a cylinder defining a first volume connected to the second control pressure output by the line modulator valve, and a first volume communicating with line pressure. The accumulator control valve directs this pressure to the second volume of the accumulator through an orifice having a predetermined diameter that controls the flow rate of fluid into the second volume of the accumulator. When line pressure is removed from the accumulator control valve to disengage the friction element, the clutch or brake is vented through the shift valve.