GB801901A - Improvements in or relating to automatically controlled gearboxes - Google Patents

Abstract

801,901. Change-speed control. REGIE NATIONALE DES USINES RENAULT. Nov. 23, 1955 [Dec. 9, 1954], No. 33618/55. Class 80 (2). In an automatic motor vehicle changespeed gear wherein a gear change is effected through means not shown by a circuit 8 controlled by a relay 4 whose energizing current 1 varies both with a transmission shaft speed and with engine load so that the relay contacts 6 are closed and upshift occurs at a vehicle speed V while the contacts 6 open and downshift occurs at a lower speed v, a manual override device according to the invention allows the driver to cause a downshift only when the relay current is between its upshift and downshift values, the device thereby preventing a manual downshift at high vehicle speeds. Upshifts are effected automatically, irrespective of the condition of the manual override device. The current 1 may be provided by a generator or by a shaft-driven contact breaker. The speeds V and v are distinctly different to avoid " hunting," the speed V being the optimum for an upshift. If the driver desires to cause a downshift before the vehicle speed drops to v (at which speed the automatic downshift occurs) he actuates a switch 9-either manually or by pressing the accelerator pedal beyond the fully-open position. A condenser 11, which is normally connected to a voltage source 17 and is thus normally charged, is thereby discharged through a demagnetizing coil 15 so that the relay flux is decreased for a short period and the contacts 6 open. Provided the vehicle speed is less than V the contacts 6 remain open and the desired downshift is effected. If, however, the driver operates the switch 9 and causes the contacts 6 to open when the vehicle speed is greater than V, the contacts are re-closed as soon as the condenser has discharged and the vehicle remains in high gear, since the gear-changing means in the circuit 8 is so designed that the short period during which the contacts 6 are open is insufficient to cause a gear change. The coil 15 may be mounted on a separate core and act directly on the relay armature, or on a member connected thereto. In a modification dispensing with the coil 15 a driver-operated switch connects the relay 4 in parallel with a. condenser so that the relay current is decreased during the condenser-charging time and allows the contacts 6 to open. In further modifications the relay coil 4 is supplied through, or alternatively may be short-circuited by, a " time delay switch " which when actuated by the driver de-energizes the relay for a very short period.