The invention relates to the bicycle defined in the introductory section of patent claim 1. In the prior art there is known a bicycle composed of two parts, i.e. a front frame member and a rear frame member, which members are interconnected by a pivotal structure. Thus the front and rear frame members are turnable at the pivotal structure to meet each other when the bicycle is adjusted to transport position. In the normal riding position the pivotal structure is locked so that the front and rear members of the frame form an essentially stationary, normal bicyle frame. A generally used pivotal structure is a pivotal hinge, in which case the front frame member is turnable around a hinge pin to meet the rear frame member.

A drawback with the previously known bicycle is that in the riding position, the strain is focused directly on the axis of hinge, wherefore the hinge structure must be fairly robust. Another drawback is that the pivotal hinge is located outside the frame structure and remains totally unprotected from weather conditions and external mechanical strain. Yet another drawback of the known bicycle is that in the riding position, the front and rear frame members must be secured to each other in order to faci¬ litate transport by pulling the bicyle manually. On the whole, other type of transport than carrying the bicyle for instance in the boot of a car or in a public trans¬ port vehicle is neither practical nor convenient. The pivotal structure is cumbersome, not to mention the fact that hardly any attention has been paid to the design or weight of the frame structure itself, for instance in order to facilitate transport by pulling by the hand when walking.

The object of the invention is to eliminate

the above mentioned drawbacks. A particular object of the invention is to introduce a new type of city bicy¬ le, which is particularly well suited to riding short distances and is easily adjustable from riding position to transport position, to form an easily transportable package which is as small as possible.

The bicycle of the present invention is cha¬ racterized by the novel features of the patent claim 1. The bicycle of the invention comprises a frame composed of two parts, i.e. the front and rear frame members, which are interconnected by a pivotal structu¬ re so that the front and rear frame members are turna¬ ble from the riding position to meet each other in the transport position. According to the invention, the pivotal structure includes a cylindrical casing protec¬ ted by a sheath, and a first and second segment member, and the cylindrical casing is arranged in connection with the frame, in an essentially perpendicular positi¬ on to the lengthwise direction of the frame, and the first segment member is arranged in connection with the front frame member and the second segment member is arranged in connection with the rear frame member; both of the said segments are installed in the cylindrical casing, on opposite sides of the casing, when seen in the direction of the central axis thereof, and turnably with respect to the central axis of the cylindrical casing, so that the first side surfaces of the segment members are arranged to be supported against each other in the riding position, most advantageously above the central axis, and to be released of each other when the front and rear frame members are folded to transport position complete with their segments.

The cylindrical casing protected by the sheath can be provided in connection with either the front or rear frame member, together with either the first or second segment. Thus the cylindrical casing constitutes a cylindrical recess, part of which is covered by the

segment member of the corresponding frame member, and the segment member of the second frame member is adjus¬ table in this cylindrical casing.

In a preferred embodiment of the bicycle, the sheath of the cylindrical casing is formed as a part of a separate frame member, whereto the seat is connected. By means of the separate frame member, for instance the position of the seat can be adjusted to be suitable with respect to the front and rear frame members. More- over, the cylindrical casing can be formed as a separa¬ te space, whereto the front and rear frame members can be fitted at their segment members.

In another embodiment of the bicycle, the first segment member is arranged to protrude from the front frame member, and the second segment member is arranged to protrude from the rear frame member. This structure is particularly advantageous when employing a separate frame member, with the cylindrical casing contained in the sheath connected thereto. Thus- the pivotal structure is realized in an advantageous fashi¬ on with respect to strength calculations.

In another embodiment of the bicycle, in con¬ nection to the front and rear frame members there are provided elevation pieces which are fitted in the cy- lindrical casing. The purpose of the elevation pieces is to serve as centralizing members so that both the front and rear frame members can be safely and reliably turned around the commong turning axis.

In another embodiment of the bicycle, the pivotal structure includes locking means for locking the front and rear frame members to each other, at least in the riding position. Moreover, the locking means are advantageously used for securing the front and rear frame members to each other in the transport position.

In another embodiment of the bicycle, the locking means are arranged to pass through apertures at

the apexes of the first and second segment members of the front and rear frame member respectively, and through the central axis of the cylindrical casing in order to lock the front and rear frame members and the segment members to each other.

In another embodiment of the bicycle, the locking means comprise a stub axle, which at its first end is provided with an end flange or similar stop, and at its second end with a swinging arm including an eccentric member in order to press the front and rear frame members against each other and against the sheath in the locked-up position.

In another embodiment of the bicycle, the sheath of the cylindrical casing comprises annular stop faces, and the segment members are surrounded by annu¬ lar friction faces of the front and rear frame members, matched with the said stop faces. The purpose of the stop faces and friction faces is to render a maximum amount of contact surface in between the separate mem- bers, in order to make them remain in the desired posi¬ tion against each other.

In another embodiment of the bicycle, the annular stop faces of the sheath and the friction faces of the front and rear frame members are conical surfa- ces. Thus there are not needed high pressures in order to secure the front and rear frame members to each other and to the sheath, particularly in the riding position, and consequently the locking means may be fairly light in structure. In another embodiment of the bicycle, in bet¬ ween the stop faces and the friction faces, there are arranged friction rings. By means of these friction rings, the maintenance of the bicycle is made easier, and a high friction is created in between the surfaces resting against each other. The friction rings can be manufactured for example of some suitable plastic, such as elastomer, in which case the friction ring functions

in the pivotal structure like a cup spring.

An advantage of the invention is that the bicycle of the invention is easy to use; it is easily folded into transport position and opened back to ri- ding position. The bicyle is easily adjusted to trans¬ port position by a couple of manual steps, whereafter it is ready to be carried or pulled from the handlebar. When collapsed, the bicycle also fits in the boot of a car and does not take up a lot of space in storage, for instance.

Another advantage of the invention is that the pivotal structure is simple, reliable and easily reali¬ zed.

Yet another advantage of the invention is that the elements conneceted to the pivotal structure are merged in the front and rear frame members, so that there are no protruding or easily breaking parts. The riding, transport by pulling and maintenance of the bicycle is easy. Yet another advantage of the invention is that the frame and pivotal hinge can be made of for instance composite plastic, in which case the frame becomes light and durable. The manufacturing techique of plas¬ tics also allows for providing all necessary functional elements in the frame members and in connection with the sheath of the cylindrical casing. Thus the amount of separate elements in the whole frame construction of the bicycle can be reduced.

In the description below, the invention and other connected advantages are explained in more detail with reference to the appended drawings, wherein figure 1 is a side-view illustration of the bicycle of the invention, seen in riding position; figure 2 is a side-view illustration of the bicycle of figure 1, seen in transport position; figure 3 is an exploded view of the pivotal structure of a bicycle of the invention;

figure 4 is an exploded view of the locking means of the pivotal structure of figure 3; figure 5 is a cross-sectional illustration of the pivo¬ tal structure of figure 3; figure 6 illustrates the configuration of the segment parts of the pivotal structure of figure 3 in riding position; and figure 7 respectively illustrates the configuration of the segment parts in transport position. The bicycle of the invention is illustrated in the riding position in figure 1. The bicycle comprises a frame 1 formed of two parts, i.e. the front frame member 2 and the rear frame member 3. The front frame member 2 has a front wheel 4 and the rear frame member 3 has a rear wheel 5. The means for moving the bicycle, i.e. the pedals 6, the cog wheels 7, 8 and the chain 9 are arranged in a normal fashion in connection with the rear frame member 3 and the rear wheel 5. The handlebar 10 is connected to the front frame member 2. The ^" seat 11 is connected to the frame member 12 separate from the front and rear frame members, this separate frame member 12 also constituting part of the frame 1.

The front and rear members 2 and 3 of the frame 1 are interconnected by a pivotal structure 13. Owing to this pivotal structure 13, the front frame member 2, the rear frame member 3 and the separate frame member 12 are turnable to the transport position illustrated in figure 2. In this position, the front 2 and rear 3 frame members are arranged in a roughly parallel, but slightly crosswise configuration, so that the front wheel 4 and the rear wheel 5 are roughly adjacent. The seat 11 is turned, by means of the sepa¬ rate frame member 12, to a position deviant from the riding position, towards the front wheel 4 and the rear wheel 5. Now the protruding part of the bicyle is the handlebar 10, from which the collapsed bicycle can be pulled by the hand for instance when walking. Alterna-

tively, the bicycle can be easily fitted for instance in the boot of a car.

A pivotal structure 13 of the bicycle of the invention is illustrated in the exploded figure 3. The pivotal structure comprises a cylindrical casing 15 protected by a sheath 14, a first segment member 16 and a second segment member 17. In this case the sheath 14 of the cylindrical casing 15 is formed as a part of the separate frame member 12, which in turn is connected to the seat 11 as is seen in figure 1. Thus the cylindri¬ cal casing 15 is arranged in connection with the sepa¬ rate frame member 12, most advantageously so that the casing 15 and particularly its central axis A-A is essentially perpendicular to the lengthwise axis of the bicycle, i.e. to the longitudinal direction of the frame 1. The lengthwise axis passes via the hubs of the front wheel 4 and the rear wheel 5 when the wheels 4, 5 are in parallel position. Moreover, the cylindrical casing 15 is open at both sides, i.e. it is arranged to pass through the sheath 14.

The first segment member 16 is arranged in connection with the front frame member 2, so that it protrudes from the surface thereof. Respectively the second segment member 17 is arranged in connection with the rear frame member 3, so that it also protrudes from the surface of the frame. In addition to this, the segments 16, 17 protrude in an essentially perpendicu¬ lar fashion to the lengthwise axis of the bicycle, and at the same time to the longitudinal direction of the frame 1.

The segment members 16, 17 are formed of parts resembling circle sectors with a center angle α, β advantageously 120°; the curved arcs of these sectors constitute the outer surfaces 16c, 17c of the segments, and the radial parts constitute the side surfaces 16a, 16b; 17a, 17b of the segments.

At the segment members 16, 17, the front 2 and

rear 3 frame members are fitted in the cylindrical casing 15, so that the segment members 16, 17 are loca¬ ted on opposite sides of the cylindrical casing 15, when seen from the direction A-A of the central axis of the casing 15. Now the outer surfaces 16c, 17c of the segment members 16, 17 rest against the inner surface 15a of the casing 15, and the apexes are located on the central axis A-A. The front 2 and rear 3 frame members, together with their segment members 16, 17 can now be turned with respect to the central axis A-A of the casing 15.

In connection with the segment members 16, 17 there are advantageously provided elevation pieces 18, 19. These elevation pieces are circular in cross-secti- on and their diameters correspond to the diameter of the cylindrical casing 15. When the segment members 16, 17 are fitted in the cylindrical casing 15, the eleva¬ tion pieces 18, 19 centralize the segment members 16, 17 to correct locations in the cylindrical casing 15, particularly in relation to the central axis A-A there¬ of.

The pivotal structure 13 comprises locking means for securing the front 2 and rear 3 frame members and their respective segment members 16, 17 to each other in the riding position of the bicycle, and advan¬ tageously in the transport position, too. The locking means may be provided outside the pivotal structure 13 proper, somewhere in between the front and rear frame members 2, 3. By means of them, the front and rear frame members 2, 3, as well as the possible separate frame member 12, are pressed immovably together at the pivotal structure 13, both in the riding and transport positions. When the position of the bicycle is wished to be changed, the pivotal structure 13 is released from the compression of the locking means.

In a preferred embodiment of the invention, the locking means 20 are arranged to pass through the

apertures 33, 34 at the apexes of the first and second segment members 16, 17 and via the central axis A-A of the cylindrical casing 15. As is seen in figure 4, the locking means 20 include a stub axle 21, which is pro- vided with an end flange 22 at its first end and with a swinging arm 23 at its second end. The swinging arm 23 is attached to the stub axle 21 by a pin 24. The swin¬ ging arm 23 has an eccentric member 25, such as a sui¬ table protrusion, at a distance from the turning axis formed by the pin 24. The position of the stub axle 21 and the end flange 22 in relation to each other in the direction of the central axis A-A can be adjusted by means of the threaded joint provided therein.

The locking means 20 are operated as follows. When the swinging arm 23 is essentially parallel to the central axis A-A, position B in figure 5, there is looseness in between the elements of the pivotal struc¬ ture 13, and consequently the elements are movable; thus the position of the frame members 2, 3 and 12 in relation to each other can be changed. The bicycle can be folded from riding position to transport position and back again. When the swinging arm 23 is turned in the direction of the frame, into position C in figure 5, the eccentric member 25 presses, at a point adjacent to the stub axle 21 and the central axis A-A, the rear frame member 3, and further the sheath 14 and the front frame member 2 against the end flange 22, so that these members 2, 3 and 14 are compressed (dotted lines in figure 5) tightly against each other in the locked-up position. By means of the swinging arm 23 and the con¬ nected eccentric member 25, there is thus obtained sufficient pressure in a simple and effective fashion. In connection with the rear frame member 3, there is provided a slot 26 for the swinging arm 23, into which slot the swinging arm 23 is fitted in a position conforming to the shape of the frame 1 after the frame members 2, 3 and 12 are secured to each ot-

her. In the opened-up configuration B (figure 5) the swinging arm 23 can be used as a hand support when moving and particularly lifting the bicycle.

In a preferred embodiment of the invention, the sheath 14 of the cylindrical casing 15 is provided with annular stop faces 27, 28 fitted around the ca¬ sing. Respectively, around the segment members 16, 17 there are provided annular friction faces 29, 30 of the front and rear frame members, the said friction faces 29, 30 being matched to the said stop faces 27, 28. Advantageously these stop faces 27, 28 and friction faces 29, 30 are conical surfaces as is apparent from figure 5. On the sides of the front and rear frame members 2, 3, these surfaces are advantageously conical to opposite directions, in which case their securing effect is intensified.

When locked in place, the pivotal structure 13 must be absolutely rigid, particularly in the riding position of the bicycle. Then the elements of the pivo- tal structure 13 must fit smoothly to each other, even when, they are slightly worn. The conical shape of the friction faces 29, 30 of the frame members 2, 3, as well as the corresponding shape of the stop faces 27, 28, allows the elements to be locked tightly in place against each other. Thus a strong static friction is achieved in the pivotal structure 13. It is also poin¬ ted out that these elements are rubbed against each other, in which case wearing is inevitable. Now in between the said stop faces 27, 28 and the said fricti- on faces 29, 30 there can advantageously be fitted friction rings 31, 32. When necessary, the worn fricti¬ on rings 31, 32 can be replaced. They can be made of plastic or other suitable material. In addition to this, they serve in between the separate surfaces ad- vantageously as spring-like power transmission means and thus strengthen the rigidity of the pivotal struc¬ ture.

The operation of the pivotal structure 13 of the bicycle of the invention is illustrated in figures 6 and 7. Let us suppose that the swinging arm 23 in figure 5 is in open position B, in which case the locking means 20 are not in locked-up position and there is looseness in the pivotal structure. The front 2 and rear 3 frame members, as well as the first seg¬ ment member 16 and the second segment member 17 in the cylindrical casing 15 are now turnable with respect to each other. The front and rear frame members 2, 3 can be turned into the riding position in figure 1, in which case the radial side surfaces 16a, 17a are pres¬ sed together and thus supported against each other, advantageously above the central axis A-A, on a level essentially perpendicular to the longitudinal axis of the bicycle and the lengthwise direction of the frame. When the swinging arm 23 of the locking means 20 is turned into position C, i.e. the locked-up position, the eccentric member 25 presses, by intermediation of the stub axle 21 and with the help of the end flange 22, the annular stop faces 27, 28 tightly against the friction faces 29, 30. Now the pivotal structure 13 is stiffened up to form a fixed unity. It is pointed out that in the riding position, the pressure strain is particularly directed against the radial side surfaces 16a, 17a of the segment members 16, 17, and through them to the frame members 2 , 3 (cf. figure 6).

The locking means 20 are unfastened when the bicycle is desired to be folded to the transport posi- tion in figure 2. The swinging arm 23 is turned from position C to position B in figure 5, whereafter the front and rear frame members 2, 3 can be turned in relation to each other in a fashion illustrated in figure 2. The separate frame member 12, whereto the seat 11 is attached, can also be turned to the desired position. The front and rear frame members 2, 3 can be turned with respect to the axis A-A, in this case 90°,

so that the second radial side surfaces 16b, 17b of the segment members 16, 17 meet, as is illustrated in figu¬ re 7. This position corresponds to the bicycle trans¬ port position of figure 2. Again, by turning the swin- ging arm 23 of the locking means 20 from position B to position C, the front and rear frame members, 2, 3 can be locked in this position so that they cannot move with respect to each other. At the same time, the sepa¬ rate frame member 12 is locked in a desired bent trans- port position.

It is pointed out that the separate frame member 12 can be moved fairly freely in between the front and rear frame members 2, 3 while adjusting the position of the bicycle. The trajectory of the separate frame member 12 around the central axis A-A is over 200°.

The invention is not restricted to the above described embodiments, but several modifications are possible within the scope of the inventional idea de- fined in the appended patent claims.