GB1486102A - Variable torque drive mechanism - Google Patents

Abstract

1486102 Ratchet mechanism Z E CHASE 9 Jan 1975 914/75 Heading F2Q [Also in Division B7] A human-power driving mechanism, e.g. for a bicycle, comprises a pair of oscillatory radial shafts 3, 4 each having a pedal at one end and a respective rotatable axle at the other, means for limiting the angle through which the shafts rotate, an arm 6, a transmission 5 for oscillating the arm 6 in response to movement of the pedals and translating movement of one pedal into an oppositely directed movement of the other pedal, a freely rotatable sprocket 30, a drive sprocket 32 on a drive axle 33, a continuous drive chain 40 linking the sprockets 30, 32, first and second ratchet devices 38, 39 cooperable with the chain 40 and linked to a slide member 7 on the arm 6, and control means for moving the member 7 along the arm. In operation motion of the arm 6 to the right as viewed in the drawings causes the ratchet device 38 to engage the chain 40 and pull the latter but does not cause the devices 39 to drivingly engage the chain, and motion of the arm to the left causes the device 39 to engage the chain and push the latter but removes the device 38 from driving engagement with the chain, so that movement of the pedals results in unidirectional rotation of the drive sprocket 32. Movement of the member 7 along the arm 6 by the control means alters the effective moment arm of the arm 6 and hence varies the drive ratio between the pedals and sprocket 32. In the illustrated construction each ratchet device comprises a pair of looking jaws 43 interconnected by pivoted links 42 and biased out of driving engagement with the chair 40 by springs 44 (one only shown) but movable against the action of the springs to clamp the chain upon movement in the appropriate direction of arms 34, 35 connecting the devices to the member 7 through a cross-piece 36 and link 37. The transmission 5 comprises intermeshing gearwheels 11, 12 on the axles 13, 16 of the shafts 3, 4 and a hub 19 on the axle 16 which mounts the arm 6. A control lever 9 is connected through a Bowden cable 20, 21 to the lower end of a rod 24 axially slidable in a cavity in the arm 6 and carrying the member 7, whereby the member 7 can be moved along the arm. A stop (59) (Fig. 8, not shown) on the shaft 4 is engageable with a housing containing the gears 11, 12 to limit the angle through which the shafts 3, 4 rotate.