GB2074958A - Transmission for tandem bicycles - Google Patents

Abstract

In a transmission designed to reduce the size of the tandem cycle, the rear pedals 6 are mounted on a rotary shaft which has the same axis of rotation B as the rear wheel 8, and the rear wheel hub unit is freely rotatable on the shaft, a gear wheel is provided on one side of the shaft, and a free trip sprocket wheel is provided with one or more gear pinions secured to said hub on the side opposite to that provided with the gear wheel; two drive chains are respectively disposed one between a gear wheel on the front pedal unit and that on the back pedal unit, back and the other between a second gear wheel of the front pedal unit and a gear pinion of the sprocket wheel unit. <IMAGE>

Description

SPECIFICATION A propelling device for tandem bicycles and tandem bicycles thus obtained This invention relates to a propelling device for tandem bicycles and tandem bicyles thus obtained.

As well known, tandem bicycles, as generally referred to, comprise a front pedal, a back or rear pedal, a hub unit mounted on the back or rear wheel and two drive chains, of which one is disposed between the front pedal and the rear pedal, and the other is disposed between the rear pedal and the hub unit. In such a device, or propelling device, the thrust force provided by the front pedal is transmitted to the rear pedal which, by summing it to the propelling force thereby produced, transmits the resulting composite force to the rear wheel. Therefore, the two connecting chains start from the rear pedal and extend one in one direction and the other in opposite dir cation, that is one chain extends between the rear pedal and the front pedal, and the other chain extends between the rear pedal and the hub unit for the rear wheel.

This arrangement of the two chains, one chain on the extension of the other, necessarily involves an extension of the bicycle frame. Accordingly, tandem bicycles as hiterto known are rather cumbersome and heavy, whereby the use, handiness and transport thereof are difficult.

These drawbacks have been responsible of a not complete or wide diffusion of tandem bicycles.

It is the object of the present invention to provide a tandem bicycle, the frame of which is substantially the same, as to length and weight, to a normal single-seat bicycle.

It is another object of the present invention to provide a novel propelling device not requiring the use of two drive chains, of which one disposed on the extension of the other.

According to the present invention, these and further objects which will become apparent from the following description have been accomplished by a propelling device comprising a front torque, a rear torque, a hub unit secured to the rear wheel, and two drive chains, in which the front torque comprises a rotary shaft at one end provided with a pedal crank and a first gear wheel, and at the other end with a pedal crank and at least a second gear wheel; the rear torque comprises a rotary shaft, the axis of rotation of which is coincident with that of the hub unit, provided at each end with a pedal crank and a gear wheel on the side corresponding to said first gear wheel, the hub unit comprises at least two bearings keyed on said rotary shaft of the rear torque, a hub keyed on the outer surface of said bearings, and a free trip sprocket wheel unit, provided with one or more gear pinions, secured to said hub on the side opposite to that on which the gear wheel is disposed, and the two chains are respectively disposed one between the rear gear wheel and the first front gear wheel, and the other between one of said second front gear wheels and one of the gear pinions of the hub.

According to the invention, that the axes of the rear pedal and rear wheel are coincident enables to eliminate the arrangement of the two chains, of which one chain on the extension of the other chain, and accordingly to obtain tandem bicycles of substantially the same size as that of a normal single-seat bicycle.

Moreover, in a propelling device according to the present invention, the motive power provided by the rear pedal does not directly affect the driving rear wheel, but is transmitted to the front pedal which, by summing it to its own power, transmits the resulting composite motive power directly, that is without any further transmissions, to the driving rear wheel.

The connection of the front pedal to the hub of the rear wheel is carried out so that the movements of both the pedal and wheel are completely unobstructed or free, whereby the free sliding of the wheel does not involve the pedal trailing, and vice versa.

The rear pedal and hub unit of the rear wheel rotate on the same axis and the movements thereof are independent by the interposition of ball bearings keyed on the pedal shaft and within the hub, so that by holding the pedal stationary, the free turning of the hub and wheel will continue.

The shaft of the rear pedal is supported by two bearings in boxes secured to the end of the rear fork of the frame. Therefore, a propelling device according to the present invention assembles all of the movements and compositions of propelling forces on two shafts.

This enables to make a much compacted tandem bicycle, in which the second saddle, that is the rear saddle, can be disposed about on the same direction of the axis of rotation of the rear wheel, with considerable advantages as far as the total bicycle overall size is concerned. The second saddle can be secured adjustably in height to the end of a supporting tube arranged on the extension of the rear vertical fork and connectad to the supporting tube for the first saddle, that is the front saddle, by a pipe fitting. On said pipe fitting for the two saddle supporting tubes, the dummy handle bar for the second cyclist is secured.

A further advantage of a tandem bicycle provided with a propelling device according to the present invention is that it can be converted to a normal single-seat bicycle by removing the connecting tube, the supporting tube for the second saddle and the two rear pedal cranks.

The functional and constructive characteristics of the propelling device according to the present invention, and also the advantages provided thereby when applied to a tandem bicycle, will be better understood from the following detailed description, in which reference is made to the figures of the accompanying drawing showing a preferred but not restrictive embodiment of the present device, and in which: Fig. 1 is a side perspective view of a tandem bicycle provided with the propelling device according to the present invention; and Fig. 2 is a schematic view of the cross-section of the inventive propelling device taken along a plane parallel with the road plane.

Referring to Fig. 1, a tandem bicycle according to the present invention comprises a front saddle (1) mounted adjustably in height to the upper end of the slightly inclined vertical front tube (35) of the frame, and a rear saddle (2) mounted adjustably in height to the end of a second tube (11) disposed on the extension of the rear fork (12) and parallel with the front tube (35). At the top a tube (10) connects the two parallel supporting tubes (11) and (35) respectively for said saddles (1) and (2). The guide or steering handle bar (3) is disposed on the extension of the front fork, while the dummy handle bar (4) is secured on the connecting tube (10).

The front wheel (9) is conventionally fastened to the front fork and the rear wheel (8) is fastened to the rear fork (12). The axle base H, that is the distance between the axis of rotation for the front wheel (9) and that for the rear wheel (8) is nearly the same as that of a normal single-seat bicycle.

Referring to Fig. 2, a propelling device according to the present tandem bicycle, comprises a first front torque rotating about an axis A, a second rear torque rotating about an axis B, and a hub unit for the rear wheel (8) rotating about said axis B. Thus, said axis B is the axis of rotation for the rear wheel (8), hub unit and second torque.

The first front torque comprises a shaft (33) provided at each end with a pedal crank (7) having pedals (5). At one end of said shaft (33) a gear wheel (20) is secured, whereas one or more gear wheels (13) of different diameter are secured at the other end. Said shaft (33) freely rotates in a tubular housing (31) formed at the connection location for the frame tubes (35), (36) and (28). At the two ends said tubular housing (31) is closed by threaded caps (30) and is internally provided with balls (29), said shaft (33) rotating thereon.

Said second rear torque comprises a shaft (32) provided at the side corresponding to the gear wheel (20) of the first torque with a second gear wheel (21) and at each free end with a pedal crank (7) having pedals (6). This shaft (32) rotates about said axis B by means of two ball bearings (22) accommodated within boxes (23) provided with threaded extensions (24). Each of said boxes (23) are secured at each end (27) of the horizontal fork the frame tube (28) is provided with. Said ends (27) are also provided with grooves (26), in which said threaded extensions (24) are arranged and act as chain stretchers (34) by adjustment of nuts (25) screwed to said extensions (24) and gripping on said ends (27).

Said shaft (32) has two bearings (18) keyed thereon and spaced apart by a spacing tubing (37), closed at one side of the cover (38) and blocked on the side opposite to that fitted with the cover by a second spacing tubing (39) disposed between the bearing (18) and box (23). The outer surface of the bearings (18) has keyed thereon the hub (19) externally provided with two annular protrusions, on which the ends of the spokes (17) for the rear wheel (8) are secured. By screwing a normal free trip sprocket wheel unit (15) provided with one or more gear pinions (16) is secured to said hub (19) on the side opposite to that of the gear wheel (21). The sector gears (20) and (21) respectively of the front pedal crank and rear pedal crank are interconnected by a chain (34), the tension of which is adjusted by the threaded nuts (25).One of the sector gears (13) of the front pedal crank is connected to a pinion (16) of said hub (19) by a chain (14). The tension of this chain (14) is adjusted by conventional spring stretchers similar to those of.which the known transmission devices are provided with. In the above shown propelling device, the power or force exerted on the rear pedal by the second cyclist is transmitted by the chain (34) to the gear wheel (20) of the front pedal and adds to the force or power exerted on the front pedal by the first cyclist. The torque consisting of the sum of the two separate powers or forces is transmitted by one of the gear wheels (13) to the rear trailing wheel (8) by the chain (14) and one of the gear pinions (1 6) of the free trip sprocket wheel unit (1 5). The connecting tube (10), the supporting tube (11) for the second saddle (2) and the rear pedal cranks (7) can be easily removed, converting the tandem bicycle in a conventional one-seat bicycle.

As above described, the frame may be formed of metal tubes in cast or die-cast structure, or of pressed drawn metal plates.

Variations, modifications and changes can be made to the propelling device and tandem bicycle shown by illustrative but not restricted example in the figures of the accompanying drawing within the spirit of the present invention and without departing from the covering scope thereof.

Claims (9)

1. A propelling device for tandem bicycles, comprising a front torque, a rear torque, a hub unit secured to the rear wheel, and two drive chains, wherein said front torque comprises a rotary shaft provided at one end with a pedal crank and a first gear wheel, and at the othr end with a pedal crank and at least a second gear wheel; the rear torque comprises a rotary shaft, of which the axis of rotation is coincident with that of said hub unit, at each end provided with pedal crank and a gear wheel at the side corresponding to said first front gear wheel; the hub unit comprises at least two bearings keyed on said rotary shaft of the rear torque, a hub keyed on the outer surface of said bearings and a free trip sprocket wheel unit provided with one or more gear pinions, secured to said hub at the side opposite to that on which the gear wheel is disposed; and the two claims are respectively disposed one between the rear gear wheel and the first front gear wheel, and the other between one of the second front gear wheels and one of the gear pinions of the hub.

2. A propelling device according to Claim 1, wherein the motive power for the second torque is transmitted to the first torque and the resulting composite force or power is transmitted from the first torque to the hub unit of the trailing rear wheel.

3. A propelling device according to Claim 1, wherein the rotary shaft of the rear torque or pedal is supported or carried by two bearings, each of which accommodated within a box provided with a threaded extension and secured to each end of the horizontal rear fork of a bicycle frame.

4. A propelling device according to Claim 3, wherein the ends of the horizontal rear horizontal fork are provided with grooves in which the threaded extensions of the boxes are arranged; threaded nuts screwed on said extensions enable to adjust the tension of the drive chain.

5. A propelling device according to any of the preceding claims, wherein the bearings keyed on the rotary shaft of the rear torque are spaced apart from one another by a first spacing tubing, closed at one side by a cover and blocked at the side opposite to that provided with a cover by a second spacing tubing disposed between the bearing and the box secured to the fork end.

6. A tandem bicycle provided with a propelling device according to any of the preceding claims and a rear fork arranged at the axis of rotation of the rear wheel, parallel with the supporting tube for the front saddle and on the extension of which the supporting tube for the rear saddle is secured.

7. A tandem bicycle according to Claim 6, wherein the supporting tubes for the front and rear saddles are interconnected by a connecting tube having the dummy handle bar secured thereto.

8. A propelling device for tandem bicycles as above described and shown in Fig. 2 of the accompanying drawing.

9. A tandem bicycle as above described and shown in Fig. 1 of the accompanying drawing.