GB1196130A - Improvements in Drive Transmission Devices - Google Patents

Abstract

1,196,130. Controlling friction clutches. FRANCAISE DU FERODO S.A. 30 June, 1967 [2 Aug., 1966; 20 April, 1967], No. 30386/67. Headings F2C and F2L. In a friction clutch which is engaged by a diaphragm spring and disengaged by an hydraulic servo piston acting on the inner periphery of the spring, a residual pressure is maintained in the servo cylinder when the clutch is engaged in order to maintain a thrust member carried by the piston in contact with the diaphragm spring. In embodiments in which the servo cylinder and piston rotate with the input parts of the clutch, the residual pressure may be provided by centrifugal force acting on the liquid remaining in the cylinder, and the piston is provided with vanes to assist in inducing the centrifugal pressure. In constructions in which the servo piston and cylinder are non-rotary, the residual pressure is produced by a backpressure valve in the exhaust line from the cylinder and the thrust member is mounted on the piston by way of a ball bearing. As shown, a control system for a clutch following an hydraulic torque converter 55 and having a rotating servo piston 33 comprises a control valve 85 positioned by a solenoid operated pilot valve 78. Liquid is supplied to the control valve 85 by a pump 72 at pressure determined by a valve 99, and in the clutch disengaged position shown liquid at this pressure is supplied to the clutch servo cylinder 31. On de-energizing the pilot valve solenoid, the pilot valve is shifted to the right by a spring and liquid is directed to the right hand chamber of the valve 85 to shift it to the left so that liquid is supplied to the torque converter 55 at a pressure determined by a valve 98, and the clutch engages. The rate of clutch engagement is controlled by a restriction 94 and a by-pass valve 95 which allows initial fast exhaust of fluid from the clutch servo cylinder until the valve 95 closes and the restriction 94 thereafter controls the rate of exhaust from the cylinder 31. A residual pressure is maintained in the cylinder by centrifugal force. In a modification (Fig. 6, not shown) the control valve is actuated directly by a solenoid, and the restriction and by-pass valve are incorporated in the control valve.