Patent GB-721668-A (GB)
Title: Improvements in and relating to automatic transmissions, particularly for motor vehicles
Filed: 1950-03-21
Abstract: 721,668. Controlling variable-speed gearing and clutches. ROCHE, C. R. March 21, 1950 [May 14, 1949], No. 6974/50. Class 80 (2). In automatically-variable gearing for motor vehicles in which control is by output speed modified by throttle opening, the gear is at all times free to change up but change down to first speed is prevented until the accelerator is fully depressed. As applied to a three-speed and reverse gear in which changes between low, intermediate and high speeds are effected by successive operation of two friction clutches, a shaft 4, Fig. 2, geared to the output shaft 130 carries a centrifugal governor G, the slidable collar 11 of which is connected by a plate 28 to a piston valve 30 controlling supply and exhaust of pressure oil to and from the clutches through pipes 46, 47, the oil being supplied to the valve through a pipe 40 from a gear pump P driven from shaft 4. The position of the governor collar 10 is determined through a lever 19 by the accelerator 25, the governor assembly and valve 30 being moved bodily to the right as the accelerator is depressed while increase of speed of shaft 4 moves valve 30 to the left. With valve 30 in the extreme rightward position shown, both clutches are disengaged and low speed is operative. With valve 30 in an intermediate position, one clutch is engaged giving intermediate speed, while with valve 30 in its extreme leftward position both clutches are engaged giving high speed. A pivoted pawl 53 co-operating with a part 55, Fig. 3, of the plate 28 is controlled through a spring-loaded lever 56 by a slidable cam rod 58 connected to the accelerator 25 so that when the accelerator is either released or fully depressed the pawl is held raised, allowing the valve 30 to move freely in either direction, while in intermediate positions of the accelerator the pawl is free to drop whereby it prevents movement of valve 30 to the right from intermediate to low speed positions while allowing free movement of the valve to the left or from high to intermediate speed position. A manuallycontrolled rod 75, Fig. 7, may co-operate with a rearward extension of the pawl so that the latter may be raised when desired. The pawl may be lengthened so as to obstruct movement of the valve from its extreme leftward position, and the rod 58 may be such that the pawl is held raised only when the accelerator is fully depressed. As shown in Fig. 7, the lengthened pawl 53 has a shoulder 301 and the rod 58 is so shaped that when the accelerator is in any intermediate position the pawl is free to drop so as to obstruct any shift down, when the accelerator is in released position the pawl is held partially raised so that the shoulder 301 prevents shift from intermediate to low speed, while when the accelerator is fully depressed the pawl is fully raised. In a modification, the pawl is replaced by a spring-loaded plunger which acts on the valve to prevent movement of the latter to the right from intermediate position unless the accerator is fully depressed. As shown in Fig. 10, a plunger 330 slidable in a cylinder 326 connected to the pipe 47 engages against the plate 28 to augment the leftward shifting influence on the valve 30 in high speed position, so ensuring that downshift from high to intermediate speed takes place only at a speed considerably below that at which upshift took place. Specification 649,290, [Group IX], is referred to.