Patent GB-655531-A (GB)
Title: Improvements in change speed gears
IPC: F16H61/02
Filed: 1948-12-02
Abstract: 655,531. Change-speed control. WELLS. J. E. Dec. 2, 1948, No. 31189. [Class 80(ii)] Two double-acting pistons 3, Fig. 1, respectively operating reverse/first speed and second/high speed gear selectors (not shown), in a synchromesh or other gear box, are actuated by pressure liquid such as oil applied to one or other end of their cylinders 1, and are neutralized mechanically when changing gear by balls 9 projecting loosely through the cylinder walls and co-acting both with cam surfaces 10 on the pistons and with recesses 8 on the faces of a cam drum 4a, rotatable in quarter-turn steps, through a ratchet and pawl 4, 6, Fig. 2, from an arm 5 linked by cables or rods to a main clutch pedal so as to be operable upon depression thereof past the position of clutch disengagement. The arm 5 is acted upon by a light return spring (not shown). With a synchromesh box, each operative stroke of the arm 5 causes the balls 9 to pass from one to the next of the recesses 8, such action pressing the balls temporarily into the cylinders to centralize the pistons 3 via the cam surfaces 10. Subsequent further depression of the main clutch pedal, allowed for by elongation of the recesses 8, acts through rods or cables to depress a piston 22 in a master cylinder 11 and send pressure oil to a selected side of a selected piston 3 to engage the appropriate gear. The distribution of the oil is controlled by a rotary preselector valve 15 working in an oil reservoir 12 and turned through its pivot shaft 17 from an external arm 18 connected by a lever or cable mechanism to a control arm which, where the gear box is mounted on a motor vehicle, may be arranged near the steering wheel thereof. The valve 15 is pressed by a spring 16 against the inner surface of the reservoir 12 and is bored as shown so as to provide communication, according to its angular position, between an outlet 20 from the cylinder 11 and one or other of four bores 14 arranged in a semi-circle and communicating with the cylinders 1. A one-way valve 21 allows replenishment of the cylinder 11 when a spring 23 returns the piston 22 after gear establishment. Upon gear neutralization, oil forced out of the cylinders 1 is returned to the reservoir 12, a pipe 24 and non-return valve 25 allowing this to be effected via the cylinder 11 in the case of a bore 14 covered by the arm 15. When placed in a "neutral" position intermediate any pair of bores 14, the arm 15 is forced back against the spring 16 to allow escape of oil if the clutch pedal on neutralization is depressed far enough to actuate the piston 22, the consequent reaction on the clutch pedal indicating that. neutralization is complete. As used with a non-synchromesh gear box, only two diametrically opposed recesses 8 are provided, necessitating double depression of the clutch pedal to change gear. The invention can be applied to a gear box having four forward speeds and reverse by providing an additional cylinder 1 and drum 4a controlling the reverse gear selector. 'The cylinders 1 are supplied at each-end with bleed-screws which can be replaced by non-return ball valves during filling. According to the Provisional Specification, neutralization of the cylinders 1 is effected by a hydraulic cylinder connected to the master cylinder and having a piston the rod of which forms a pawl to operate the cam drum ratchet.