GB587604A - Improvements in or relating to preselector mechanisms for use with change speed gear - Google Patents

Abstract

587,604. Controlling change-speed gearing. VICTORIA MACHINE TOOL CO., Ltd., SELBY, J., and FRYE, J. Nov. 13, 1944, No. 22351. [Class 80 (ii)] A change-speed preselector, for a machine tool, comprises rockshafts 46, 47, 48 operating, as through rack-and-pinion 43 &c. gear shift forks 38, 39, 40 respectively, controlling individual ratios operating in series so that the overall ratio is the product of the individual ratios, each rockshaft being turned, through a pair of racks 52, 52 (one only shown in Fig. 4) ; 53, 53 ; 54, 54, engaging opposite sides of pinion-teeth on the rockshafts, by a preselector disc 55, or shaft, which is turned to bring selectively-positioned profile variations, e.g., holes 56, under the rackends (Fig. 4 position), and moved bodily axially to operate the racks and introduce a preselected gear-combination (Fig. 7 position). In the case of the rack-pair 54 only, shallow holes 56 (Fig. 7, left) move the racks to a central position whilst a through-hole together with the disc-surface (Fig. 7, right) move the racks to opposite extremes, giving three effective ratio-positions of the shifter rockshaft 48. The shallow holes are not used for the other rack-pairs which have two extreme positions only, making twelve ratios in all. The disc 55 is splined to a preselectorknob with an indicating dial 58, and is moved bodily to execute a shift, by axial movement of a central rod 62, linked to a rockshaft 73 carrying an operating handle. A spring-detent 75 retains the indicator dial 58 in selected gearpositions and, to prevent axial executive movement of the pre-selector disc 55 in intermediate positions and also to prevent rotation of the disc during executive movement, a fixed peg 78 comes into engagement with one of a series of holes 77 only in gear-positions of the dial. In a modification, Figs. 1-3 (not shown) the preselector is a shaft having radially-projecting pegs of varying lengths to operate the racks when the shaft is moved bodily by cam means in a guided transverse direction to execute a shift. Two pairs of racks only are used, one having three set positions, the other two, giving six ratios in all. The preselector dial turns the shaft through a helical gear which disengages during the executive movement, a drift-pin interlock being provided between the preselector-dial and the executive rockshaft to prevent operation of the latter in intermediate gear-positions of the dial and to prevent dephasing rotation of the dial during executive movement of the selector shaft, rotation of which latter is prevented by a fixed peg such as 78, Fig. 4.