GB1272793A - Gear train - Google Patents

Abstract

1,272,793. Change-speed gear. G.M. CROOK. 8 July, 1969, No. 34359/69. Heading F2D. A binary coded variable-ratio gear comprises at least four stages, each including a planetary differential gear, labelled " mechanical converter " in Fig. 1, the differential gears being arranged as a series in which the output O 2 , O 3 &c. of one stage drives one input B 1 , B 2 &c. of the next succeeding stage, the other input A 1 , A 2 , A 3 of the differentials being either clutched to a common main input or to separate inputmotors through a clutch-brake CB1 &c. and preliminary fixed-ratio gear R 1 &c., to provide one ratio contribution to the series or braked by a brake CB1 &c., to provide a different ratio contribution to the series. The output O 1 of the final stage 1 drives the final output and one input B 3 of the third stage is permanently fixed. The clutch-brakes are controlled by a binary code in which the digit 1 indicates clutch engagement in the " Truth Table," Fig. 5, whilst 0 indicates brake engagement, the position of the digit in the series representing the stage. Taking a particular example, the differential gear which, in its simplest form comprises an equal sun and intermeshed planet gear, Fig. 2 (not shown), here comprises a three-element sun-ring train, Fig. 4 (not shown), with the sun and ring forming the two inputs A, B and the planet-carrier the output O. The sun-ring ratio is such that, with the ring B 1 &c. held, the ratio Ra, of the output carrier to the input sun is 0À6; and with the sun A 1 &c. held the output-carrier to input ring ratio, Rb, is 0À4; Ra+Rb always being equal to 1. The preliminary gear-ratios R 1 are determined from the relation where n is the stage number, which, for the example in Fig. 1, gives values 0À1; 1À25; and 1À5625 respectively. In stage 3, the input ring B 3 is permanently fixed, giving this train a ratio Ra of 0À6. Thus, continuing the above example and taking line b in the " Truth Table," Fig. 5, the binary code 001 implies that in stages 1 and 2 the clutches of CB1, CB2 are disengaged and their brakes engaged, whilst the clutch CB3 of stage 3 is engaged and its brake disengaged. The overall output speed per unit input speed is then the product of the preliminary ratio of stage 3, the Ra ratio of stage 3 and the two Rb ratios of stages 1 and 2, as follows: 1À5625 (0À6) (0À4) (0À4) =0À15. (Fig. 5 shows a different output ratio as explained below.) For line c, binary code 010, the clutch of stage 2 and brakes of the other stages are engaged. Stage 3 is now locked stationary, holding B 2 , which changes stage 2 ratio from Rb to Ra, i.e. 0À4 to 0À6, which, with its preliminary ratio 1À25, gives an overall ratio of 1À25 (0À4) (0À4)=0À3. For line e, code 100, the first stage clutch and remaining brakes are engaged, upshifting the first stage to Ra, 0À6, which acts alone, giving overall ratio 0À6. The output ratios can then be arranged in discrete equal steps numbering 2<SP>n</SP>-1, where n is the number of stages. In the " Truth Table," Fig. 5, the values of output ratio do not correspond with those given above as examples using a sun-ring differential train, but are values obtained using the equal sun and intermeshed planet train, Fig. 2 (not shown), this arrangement being in Fig. 6 (not shown). In this equal-sun differential, Ra and Rb are both equal to 0À5. In stage 3 of Fig. 1, in which input B 3 is permanently fixed, the differential is replaced by a simple 2 to 1 reduction gear and the output carriers of the remaining differentials drive one input of the following differentials through an idler. Using three stages, this results in the output ratios # ... # as shown in the " Truth Table," Fig. 5. Fig. 7 (not shown) modifies this arrangement by restoring the third stage differential and providing coaxial input drives without the idlers. In Fig. 8 (not shown), three sun-ring differential gears are coaxially arranged side-by-side on a common axis and their ring gears are driven through toothed or chain pairs at the preliminary gear ratio by clutch-brake units on a parallel input shaft. The permanently grounded third stage differential of Fig. 1 may be used to measure final output torque, by measuring the torque reaction T at the grounding point B 3 , the final output torque being (Rb)<SP>n</SP>.T. Four, ten and fifteen stages are specified and control may be automatic. Separate braked motors may replace the clutch-brake units and common input. A system responding to a binary coded decimal input is referred to, the differential stages being separated into groups of four, commanded by a 1-2-4-8 binary coded decimal code to represent a decimal digit.