BACKGROUND OF THE INVENTION The state of the art includes bicycles equipped with a frame made entirely of elements of tubular metal, such as usually a horizontal tube, an oblique tube, a substantially vertical tube or column, a steering tube and a rear fork welded together to define a monolithic structure of a substantially trapezoid conformation.

This type of frame requires a long time to make and particular welding techniques, especially in the case of tubular elements made of light metal alloy.

Recently, there have been proposals for bicycle frames with conformations which, in some details, for example shock absorber means, are partly different from conventional frames. However, except for increased comfort for the rider, these frames do not offer substantial advantages from the point of view of simplicity and speed of assembly of the various components, such as the wheels, the motion transmission assembly, etc.: moreover, they increase the overall weight.

Due to their monolithic structure, in the event of damage or breakage, conventional frames also require the whole piece to be replaced, entailing high costs for the user. The configuration of these frames, moreover, cannot be varied to adapt them to the user's requirements.

The element which supports and contains the motion

transmission assembly is normally distinct from the frame and has no structural function; also, it is normally considerable in size and weight.

To at least partly solve these problems, bicycle frames have been proposed made in two or more autonomous parts, coupled together.

The coupling systems which have been proposed so far, and the structure of the individual parts, however, have given no advantages either from the point of view of riding comfort, or from the point of view of ease and speed of assembly/dis-assembly, both of the components to the frame, and of the frame itself.

The present Applicant has devised and embodied this invention to solve these shortcomings of conventional bicycles, and to obtain other advantages.

SUMMARY OF THE INVENTION The invention is set forth and characterized in the main claim, while the secondary claims describe other characteristics of the invention.

The main purpose of the invention is to achieve a bicycle which is simple, light, reliable, and versatile in construction and which will allow components to be maintained and replaced simply and quickly.

Another purpose of the invention is to achieve a bicycle which will allow the user to make variations in the configuration to adapt it to the specific requirements and/or the conformation of the user. A further purpose of the invention is to provide a bicycle where the coupling and removal of the wheels, particularly the rear wheel, will be simple and quick.

A bicycle according to the invention comprises a frame made in two parts, respectively front part and rear part, coupled together by constraining means able to allow them to

be dis-assembled quickly and easily.

According to a first characteristic of the invention, the front part and the rear part of the frame are arranged on different vertical and parallel planes, and the constraining means are of the type with a pin able to couple the front and rear parts together in correspondence with a zone where the parts are partly adjacent.

Said coupling zone coincides, according to the invention, with the axis of the shaft of the pedal cranks of the bicycle.

In a first embodiment according to the invention, when the bicycle is being used, the constraining means are able to allow the front and rear parts to oscillate with respect to each other, remaining on said vertical planes, to adapt to the movements and anomalous stresses to which the wheels are subjected when the bicycle is being used, for example during an uneven or cross-country ride.

According to another solution, the two parts, front and rear, are fixed in use, but their reciprocal position can be modified, by acting on appropriate adjustment means, to adapt to the conformation of the user and/or the specific use of the bicycle.

According to one characteristic of the invention, the rear part of the frame, which extends substantially at least from the zone of the shaft of the pedal cranks to the zone of the rear wheel hub, has a box-like conformation able to entirely enclose the transmission assembly which transmits motion from the pedals to said rear wheel.

According to another characteristic of the invention, the rear part has in a single piece the means to support and attach the front part of the frame and/or the rear wheel.

In a preferential embodiment, the support and attachment means consist of pin elements which protrude on at least one

side of the rear part of the frame and onto which said front part of the frame and said rear wheel can be respectively inserted and clamped.

According to a variant, the rear part of the frame consists of two half-shells, made advantageously of material with a high mechanical resistance and low specific weight, coupled together at least in correspondence with the perimeter.

In the bicycle according to the invention, the coupling of the rear wheel to the frame is extremely simple since it is carried out from the side, using the support and attachment means present in a single piece on the rear part of the frame instead of from below as happens in conventional type bicycles.

To this purpose, the support and attachment means comprise a wheel-bearing shaft and are able to be coaxially and laterally inserted into the hub of the rear wheel and clamped there by means of rapid attachment means.

According to a variant, the wheel-bearing shaft is solid with the wheel hub and can be coupled laterally to the support and attachment means which are solid with the rear part of the frame.

According to the invention, the front part of the frame has a substantially monolithic conformation made of material with a high mechanical resistance and low specific weight, and includes means to support the handlebar and the saddle of the bicycle.

BRIEF DESCRIPTION OF THE DRAWINGS These and other characteristics of the invention will become clear from the following description of some preferred forms of embodiment given as a non-restrictive example with reference to the attached drawings wherein: Figs. 1 and 2 show two side views of a bicycle according to

the invention; Fig. 3 shows a view from below of Fig. 1; Figs. 4a and 4b show two variants of the bicycle frame shown in Figs. 1 and 2; Fig. 5 shows an exploded view of the bicycle frame in Figs.

1 and 2; Fig. 6 shows a view from above of Fig. 5; Fig. 7 shows a variant of Fig. 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Figs. 1 and 2 show a bicycle 10 according to the invention, comprising a frame indicated in its entirety by the reference number 11 and consisting of two parts only, front lla and rear 11b.

The front part lla supports a saddle-bearing tube 12, an attachment 13 for the handlebars and a fork 14 to which the front wheel 15 is associated in a conventional manner. To this purpose, the front part lla is equipped with a first through hole 22 inside which the fork 14 and the attachment 13 can be constrained, on opposite sides, allowing the wheel to rotate freely.

In this case, in correspondence with the zone where the front part lla and the fork 14 are coupled, there is a shock absorber element 23 able to at least partly absorb the stresses to which the front wheel 15 is subjected when the bicycle 10 is in use. The front part lla is also equipped, in a position opposite the first hole 22, with a second blind hole 24 into which the saddle-bearing tube 12 is inserted and clamped.

The rear part llb of the frame 11 consists of a closed, box-like structure, on one face of which there is, in a single piece and laterally protruding, a shaft 17 to which the rear wheel 16 is attached and a box-like support element 18 able to coaxially contain the shaft 21 of the cranks 19

of the pedals 20.

The shaft 21 is mechani. cally connected to a transmission assembly able to transmit rotary motion from the pedals 20 to the rear wheel 16; the transmission assembly is housed inside the rear part llb.

In this way, the rear part llb performs two functions at the same time: a structural function for the bicycle 10, and a containing and protective function for the transmission assembly.

The transmission assembly and other functional organs of the bicycle 10, such as the brake assembly and the gear assembly, have not been shown in the drawings for simplicity of illustration.

The two parts of the frame 11, front lla and rear llb, are laterally coupled together in correspondence with respective ends.

To this purpose, substantially in correspondence with its rear end, the front part lla has a transverse through hole 25 able to allow the support element 18 to be inserted.

In the embodiment shown in Figs. 1 and 2, the front part lla and the rear part llb are coupled together only thanks to the contact between the hole 25 and the support element 18.

According to the embodiment shown in Fig. 4a, the front part lla extends beyond the coupling zone defined by the support element 18 with two parallel fins 31 equipped with a respective through hole suitable for a clamping screw or pin 32 to be inserted.

This configuration allows to adjust the reciprocal position, or inclination, of the front part lla and the rear part llb, by tightening the screw or pin 32, arranging the parts lla and llb in the desired position and then fixing said position by acting again on the screw or pin 32 to

increase the clamping contact between the hole 25 and the support 18.

In this way the frame 11 can be adapted to the conformation of the user or the type of ride or activity performed by the user.

According to the variant shown in Fig. 4b, between the front part lla and the rear part llb there is a shock absorber element 27, which in this case consists of a curved pneumatic jack; the end of the piston 28 is solidly attached to the front part lla of the frame 11 and the cylinder 30 is solidly anchored to the rear part llb.

As can be seen in Fig. 7, the shock absorber element 27 allows to make one part (lla or llb) of the frame 11 oscillate with respect to the other, around the horizontal axis defined by the support element 18, according to the oscillations imparted by the conformation of the ground where the bicycle 10 is used.

This configuration, with the frame 11 substantially oscillating, renders the bicycle 10 extremely versatile and able to be used substantially on every type of ground, ensuring a high level of comfort for the user in all circumstances.

According to another characteristic of the invention, the rear part llb has a box-like structure defined by two half- shells, lllb and 211b, coupled at least in correspondence with the perimeter. According to a variant, inside the box- like structure there are stiffening elements.

The box-like structure is able to entirely contain the transmission assembly, associated with a gear change mechanism, able to transmit motion from the shaft 21 to the shaft 17 and thence to the rear wheel 16.

The rear part llb, in this case, has a zone 26 with a reduced section, to reduce the weight of the rear part

(llb).

As shown in Fig. 6, the parts lla and llb are coupled laterally and therefore it is extremely simple and above all quick to dismantle the frame 11.

The fact that it is possible to separate the parts lla and llb from each other, moreover, allows the user to vary the configuration of the bicycle 10 at any moment to adapt it to a specific requirement.

For example, a rear part llb equipped with a transmission assembly of a first type can be replaced by another rear part llb containing a transmission assembly of another type.

Similarly, it is possible to associate to the same rear part llb front parts lla which differ in form and size from that shown in the Figures.

In the bicycle 10 according to the invention, the dismantling of the rear wheel 16 is simplified compared with conventional bicycles since it is carried out laterally to the frame 11, using the protruding support element with which the rear part llb is equipped.

To this purpose the rear wheel 16 is equipped with a hub 29 provided with rapid coupling means, not shown here, able to constrain it to the segment of the shaft 17 which protrudes laterally from the rear part llb of the frame 11.

It is obvious that modifications and additions can be made to the invention, but these shall remain within the field and scope thereof; it is also obvious that, although the description refers to a specific example, a person of skill shall certainly be able to achieve many equivalent forms of the bicycle, all of which shall come within the field and scope of the invention.