Here is my updated write-up:
Expandable Gear CVT
Abstract:
Single front and rear gears that both expand and contract (using looped scissor-like radial expansion segments, Hoberman), inversely correlated (as one expands the other contracts), duplicating the effect of popular cone shaped variable transmissions, but with the high torque to speed conversion efficiency of a single front and rear gear setup.
Description:
- Expandable Gears:
Gear Contraction (front gear, on crank):
This will happen when the expanding circle (Hoberman) gear is held rotationally still, and the gear core in rotated. When the gear core is rotated, the curved expansion arms will rotate and move from a horizontal position to a vertical position; pulling in the expansion arms; contacting the expandable gear.
Rotating the gear cores in relation to the expanding gears will be accomplished with a clutch plate attached to a disc hard attached to the crank axis. This clutch plate, along with the crank axis, is moved inwards to connect with the gear core by way of an inner crank plate moving along screw threads into an outer crank plate.
Gear Expansion (front gear, on crank):
This will happen when the gear core is rotated in reverse. This will be accomplished with a planetary gear setup on the crank axis, on the opposite side of the gear core than the expansion clutch. The outer ring gear will be hard attached to a plate, hard attached to the crank axis. The inner sun gear will be loosely attached (oil or bearings) to the crank axis, and would have a clutch plate attached to it, to make connection with the other side of the gear core. The middle planet gears will spin on pins hard attached to the plate that the outer ring gear is hard attached to, and would be held in place with pin heads or by enclosing the planetary gear setup (minus the sun gear clutch connecting surface).
Gear Expansion and Contraction (rear gear, on rear wheel axle):
The rear expandable circle (Hoberman) gear will need to be inversely correlated to the front expandable circle gear, and will need to be perfectly synchronized. This will be accomplished by hard attaching small gears to the side of each gear core (front and rear), just outside of where the clutches connect, and connecting these gears with a standard bike chain. The rear expandable circle gear will be flipped around, so that the rotational movement of the front gear core causing expansion will cause contraction in the rear expandable circle gear.
- Drive Chain:
The inner most rotation points of the expanding circle (Hoberman) have the greatest ratio of expansion, and so the drive chain would need to be expanded/contacted based on their movement. For the drive chain to be expanded/contacted along with the circle, the rotation points would need to have expanded pins (out towards the crank plate), long enough to support the width of the drive chain, with freely spinning cylinders on which the drive chain would rest and move along like a conveyer belt.
The drive chain will have the gear "teeth", which will protrude horizontally, towards and connecting with the crank plate and the rear axle plate, which will have radial grooves that the teeth connect with. The teeth would connect in unison with the rotation of the crank plate on one half of it, but the issue would be the other half, where the chain and teeth would cause friction against the rotating crank; moving somewhat perpendicular to the rotational direction of the plate. To solve this, the "teeth" need to be able to swivel horizontally out, and then back inside the chain; so that they can come in frictional contact with the crank plate only on the one half where it is helpful. This could be done with chain "guides", one that will brush the back of the teeth causing them to open up outward just after the half way point, and then another guide to push them back into place at the other half point. This would be the same connection type on the rear axle plate.
- Automatic Transmission
The automatic transmission will be accomplished with a spring (*this could also be accomplished by filling the space between the two crank plates with compressible fluid or gas, which would be compressed when the inner plate screws inward, and would “spring” back when the torque pressure goes down). The spring will automatically expand or contract the gears, based on the torque needed to move the bicycle. This will cause the level of torque needed to move the bicycle to even out to an average-constant.
The crank arm will attach to a smaller, inset crank plate, nested in the larger crank plate, the spring connecting the two plates together, vertically. When torque is applied, the inner crank plate will start winding the spring. If low toque is needed to rotate the rear wheel axle, then the spring will wind a smaller amount before the outer crank plate/drive belt/rear axle starts to rotate, if more torque is needed (i.e. going up hill), then the spring will wind up more beforehand.
The smaller crank plate will have a hard connected protrusion (lock pin) on its vertical outer edge, which will lock it against the vertical inner edge of the larger crank plate, at the starting (0% torque) position. This will prevent the spring from pulling the crank plates into a negative torque position.
The relative difference in rotation of the smaller and larger crank plates will be translates into movement of the crank axis in and out of the bicycle frame. This will be accomplished by having screw threads connecting the small and large crank plates. As increased torque causes more relative difference in rotation between the crank plates, the smaller crank plate will begin to rotate on screw threads between its outer edge and the inner edge of the large crank plate; moving the small crank plate inward. As the small crank plate will be hard connected to the crank axis; as the crank plate moves inward, so too does the crank axis.
As torque starts at a low percentage, the planetary gear clutch will start off being connected, causing front expandable gear expansion. As torque increases to mid-range the crank axis will move and disengage the inner planetary gear core clutch, stopping expandable gear expansion and maintaining it. As torque increases to a high level, the crank axis will move in enough to engage the outer front gear core clutch, causing front expandable gear contraction.
Torque adjustment would be accomplished by “winding” or unwinding the spring.
- Manual Transmission
Two cables will be connected to the MC. One cable will rotate the MC counter-clockwise (looking at the crank side of the bicycle); engaging the GCDB (gear expansion). The other cable will rotate the MC clockwise; disengaging the brake, and then engaging the CPGSC (gear contraction). The torque spring, smaller crank plate, small disc plates and TAC connected to the MC are not needed in this version.- Stability:
The entire setup would be likely to contort under the torque pressure.
The pieces making up the expanding circular gear will need to be I-Beam shaped hinges; to avoid side to side bending.
Due to the issues of dirt and other environmental factors affecting the complex joints and pins, the entire setup will be enclosed in a thin casing (metal, clear resin?), exposed only at the rear wheel axis, this should also assist in minimizing the contortion.
Torque Adjustment Cylinder (*originally included but... needed??)
Expandable Gear CVT side slice.jpg
TAC.jpg
Basic front and rear gear setup.jpg
Hoberman expandable circle - 1.jpg
Hoberman expandable circle - 2.jpg
Hoberman expandable circle with core - 1.jpg
Hoberman expandable circle with core - 2.jpg
Basic Planetary gear setup.jpg
Compound planetary gear setup.jpg
