Incremental variable transmission

A variable transmission machine, comprising:

• guide idlers which are spaced apart by a gap;
• an input drive which is rotatable at a first speed about an input axis;
• an output drive which is rotatable at a second speed about an output axis, the output drive including axially aligned opposing spaced apart first and second conical discs, the first disc including a first plurality of grooves, the second disc including a second plurality of grooves which oppose the first plurality of grooves, the discs being rotatable about the output axis whereby the first and second plurality of grooves are rotated through a position at which they are not clear of the gap;
• a drive chain which passes in a loop around and between the discs and through the gap, between the guide idlers, and which includes formations which are engaged with the grooves thereby to transfer rotational drive from the input drive to the output drive;
• a controller which is operable to vary the second speed;
• a cam arrangement which is continuously driven by the output drive and which is synchronised to the output drive and which, in response to rotation of the output drive, is oscillated between first and second positions through a reference position;
• and
• an actuating mechanism which is selectively operable when the cam arrangement is at the first position to cause operation of the controller to increase a spacing between the discs by a fixed incremental amount and so increase the second speed by an increment and which is selectively operable when the cam arrangement is at the second position to cause operation of the controller to decrease the spacing between the discs by a fixed incremental amount and so decrease the second speed by an increment, and wherein the spacing between the discs is increased, or decreased, only when the first and second plurality of grooves are clear of the gap.