GB2138894A - Fully enclosed four speed bicycle gearbox - Google Patents

Abstract

A gearbox has a body 12 which contains a mainshaft 13 driven by pedal cranks 11. A cluster of gears 14 sliding on splines in mainshaft 13 effects three different gear ratios by engaging with gears fixed to layshaft 17. Another gear fixed to this layshaft engages with a gearwheel running on the mainshaft 13 and fixed to a sprocket 10 which is outside the gearbox and which drives the rear wheel by means of a chain. A gearwheel 16 running on a bearing on the mainshaft is in constant mesh with a gear wheel fixed to the layshaft and is brought into operation when dogs on the side of the gear cluster 14 engage with it giving the fourth gear ratio. Gear changes are effected by a normal fork and lever arrangement (not shown in diagram). <IMAGE>

Description

SPECIFICATION Gear box for bicycle This invention relates generally to bicycles, more specifically it relates to bicycle drive mechanisms.

A principal object of the present invention is to provide a four speed automotive type transmission for a pedal bicycle which can be mounted in place of a pedal crank.

Yet another object of the invention to be described is to provide a bicycle transmission wherein the present invention has the advantage over current variable speed models in that all external sprockets, except for one at the transmission comprising a pedal crank, and one at the rear wheel, are eliminated.

The invention also provides a bicycle transmission system wherein speeds can be varied without loss of motion or slippage.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure one is a side view of the bicycle according to the invention.

Figure one A is a scrap pian view of part of figure one and Figure two is a cross section of the gear box which is the subject of the invention.

A bicycle 1 has a frame 2 which has a cross bar 3 sufficiently low to be standard for both male and female. The crossbar 3 extends 1 6" backwards beyond the saddle and forms a support for a carrier 16. The end of the crossbar 3 is open and is threaded to accept an end cap 1 5 which is integral with the handle of the pump (not shown in the drawings), which is inserted into the crossbar 3.

A rear wheel 4 is located in vertical slots 5 in lugs 6 on vertical members 7 of the frame 2 and the drive from the pedals 11 to the rear wheel 4 is by means of a chain 9 from a front sprocket 10 to a rear sprocket 8. The sprockets 8 and 10 are of equal diameter; this is possible because step up gearing is provided between the pedal shaft 1 3 and the front sprocket 10, preferably in the form of a change-speed gear box 12.

A more detailed description of the gear box as shown in Fig. 2 is as follows: A cast aluminium box 1 2 contains a shaft 1 3 to which are fixed normal bicycle cranks 11. This shaft is splined for part of it's length and one the splines runs a gear cluster 14 actuated by a normal motorcycle type gear fork and lever (not shown). A layshaft 1 7 is also contained within the box and fixed to this shaft are five gear wheels, the one on the right of the diagram being in constant mesh with a gear wheel which runs freely on a bearing on shaft 13.

This gear wheel is integral with a sprocket 10 which is outside the box and which drives the chain running to the sprocket on the rear wheel of the bicycle.

In the position shown the first gear on gear cluster 14 is engaged with one of the gears on the layshaft. By moving the cluster one position to the left a neutral position is found.

By moving another position to the left the second gear of the cluster engages with the second gear on the layshaft.

Again, another movement to the left will find a neutral and the next movement to the left will engage third gear. The third neutral position is found by again moving to the left and fourth gear is engaged by moving to the left when the dogs 1 5 on gear cluster 14 will engage with sprocket 1 6 which idles on mainshaft 13, and is in constant mesh with layshaft 17.

The gears to be manufactured with the teeth shoulders slightly cut away (not shown) to allow easy engagement.

Provision for altering the tension of the chain is made by the gear box 1 2 being movable longitudinally on a bottom bracket 14 (figure one), which is provided with spaced mounting holes or slots for adjusting the gearbox position.

1 A fully enclosed four speed bicycle gearbox fitted in place of the normal bottom bracket and held to the cycle frame by studs tapped into an L shaped plate welded into the cycle frame.

2 A fully enclosed four speed bicycle gearbox as in claim 1 using only four moving parts as distinct from the mainshaft which already exists in normal bicycles and the gear change mechanism.

3 A fully enclosed four speed bicycle gearbox as in claims 1 and 2 having splines cut in the mainshaft to enable the changing of gears by means of a sliding gear cluster.

4 A fully enclosed four speed bicycle gearbox as in preceding claims having slots into which the retaining studs fit allowing forward and rearward movement of the box for chain tension adjustment.

5 A fully enclosed four speed bicycle gearbox as in all preceding claims being operated by a single lever mounted conveniently to the operators hand.

6 A fully enclosed four speed bicycle gearbox as in all previous claims being fixed to the cycle frame by studs fitted in slots which allow chain adjustment and which permit the rear wheel therefore to be mounted in vertical slots.

7 A fully enclosed four speed bicycle gearbox as in all previous claims having a layshaft to which are fixed four gear wheels for the purpose of gear changing and a further gear wheel fixed on the layshaft which is in constant mesh with another gearwheel which transmits the drive to the rear wheel.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Gear box for bicycle This invention relates generally to bicycles, more specifically it relates to bicycle drive mechanisms. A principal object of the present invention is to provide a four speed automotive type transmission for a pedal bicycle which can be mounted in place of a pedal crank. Yet another object of the invention to be described is to provide a bicycle transmission wherein the present invention has the advantage over current variable speed models in that all external sprockets, except for one at the transmission comprising a pedal crank, and one at the rear wheel, are eliminated. The invention also provides a bicycle transmission system wherein speeds can be varied without loss of motion or slippage. An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure one is a side view of the bicycle according to the invention. Figure one A is a scrap pian view of part of figure one and Figure two is a cross section of the gear box which is the subject of the invention. A bicycle 1 has a frame 2 which has a cross bar 3 sufficiently low to be standard for both male and female. The crossbar 3 extends 1 6" backwards beyond the saddle and forms a support for a carrier 16. The end of the crossbar 3 is open and is threaded to accept an end cap 1 5 which is integral with the handle of the pump (not shown in the drawings), which is inserted into the crossbar 3. A rear wheel 4 is located in vertical slots 5 in lugs 6 on vertical members 7 of the frame 2 and the drive from the pedals 11 to the rear wheel 4 is by means of a chain 9 from a front sprocket 10 to a rear sprocket 8. The sprockets 8 and 10 are of equal diameter; this is possible because step up gearing is provided between the pedal shaft 1 3 and the front sprocket 10, preferably in the form of a change-speed gear box 12. A more detailed description of the gear box as shown in Fig. 2 is as follows: A cast aluminium box 1 2 contains a shaft 1 3 to which are fixed normal bicycle cranks 11. This shaft is splined for part of it's length and one the splines runs a gear cluster 14 actuated by a normal motorcycle type gear fork and lever (not shown). A layshaft 1 7 is also contained within the box and fixed to this shaft are five gear wheels, the one on the right of the diagram being in constant mesh with a gear wheel which runs freely on a bearing on shaft 13. This gear wheel is integral with a sprocket 10 which is outside the box and which drives the chain running to the sprocket on the rear wheel of the bicycle. In the position shown the first gear on gear cluster 14 is engaged with one of the gears on the layshaft. By moving the cluster one position to the left a neutral position is found. By moving another position to the left the second gear of the cluster engages with the second gear on the layshaft. Again, another movement to the left will find a neutral and the next movement to the left will engage third gear. The third neutral position is found by again moving to the left and fourth gear is engaged by moving to the left when the dogs 1 5 on gear cluster 14 will engage with sprocket 1 6 which idles on mainshaft 13, and is in constant mesh with layshaft 17. The gears to be manufactured with the teeth shoulders slightly cut away (not shown) to allow easy engagement. Provision for altering the tension of the chain is made by the gear box 1 2 being movable longitudinally on a bottom bracket 14 (figure one), which is provided with spaced mounting holes or slots for adjusting the gearbox position. CLAIMS

1 A fully enclosed four speed bicycle gearbox fitted in place of the normal bottom bracket and held to the cycle frame by studs tapped into an L shaped plate welded into the cycle frame.

2 A fully enclosed four speed bicycle gearbox as in claim 1 using only four moving parts as distinct from the mainshaft which already exists in normal bicycles and the gear change mechanism.

3 A fully enclosed four speed bicycle gearbox as in claims 1 and 2 having splines cut in the mainshaft to enable the changing of gears by means of a sliding gear cluster.

4 A fully enclosed four speed bicycle gearbox as in preceding claims having slots into which the retaining studs fit allowing forward and rearward movement of the box for chain tension adjustment.

5 A fully enclosed four speed bicycle gearbox as in all preceding claims being operated by a single lever mounted conveniently to the operators hand.

6 A fully enclosed four speed bicycle gearbox as in all previous claims being fixed to the cycle frame by studs fitted in slots which allow chain adjustment and which permit the rear wheel therefore to be mounted in vertical slots.

7 A fully enclosed four speed bicycle gearbox as in all previous claims having a layshaft to which are fixed four gear wheels for the purpose of gear changing and a further gear wheel fixed on the layshaft which is in constant mesh with another gearwheel which transmits the drive to the rear wheel.

8 A fully enclosed four speed bicycle gearbox substantially as described herein with reference to Figs. 1-2 of the accompanying drawings.