The manufacture of bicycles according to conventional methods comprises a number of production steps. The bicycle frame for example, can be manufactured with as many as 17 work stations. The number of work stations or steps will of course be very significant for an efficient production and thereby for the costs. Therefore simplification of the usually rather complicated manufacturing process, has great economical interest. This invention aims at a novel cycle design which involves significant advantages in this respect.

As far as the actual bicycle frame is concerned, rationalisation gains are obviously obtained by casting the frame instead of welding or brazing it from steel or aluminum tubes. The manufacture of frames and other bicycle parts by casting, however, leads to various problems:

The appearance of the bicycle may be quite strongly modified in relation to what is conventional and considered to be normal and pleasing, cast structural parts depend on a shape which allows the production tool to have a slip with respect to the cast product, which makes it difficult to cast closed profiles and thus torsion-rigid constructions, and the actual frame or middle section of a bicycle during its use is subjected to large torque stresses which call for a good torsional rigidity as just mentioned.

Previously there have been set forth various proposals for bicycle designs having improved properties with respect to manufacturing, in which there are partly included essential main parts consisting of die cast light metal components or injection moulded plastics composite compo¬ nents. Examples of such earlier designs may be found in German patent 807.487, European patent application 84306319.9 and British patent application 8520378. These among other things, show structures in which the complete bicycle frame is cast in one piece, but with the frame parts

subjected to torque stress as mentioned, having an I-shaped cross section, which means a poor torsional rigidity when the dimensions shall not be prohibitive, in particular when bicycles for adult users are concerned, as these must be able to withstand much higher stresses than bicycles for children.

Another example is found i German patent application 3,145.634, which shows that the appearance of a bicycle may- become rather unconventional and probably inacceptable by the use of uncommon manufacturing methods, including die- casting of the main parts of the bicycle. The same in part applies to the bicycle frame according to British patent 1.281.731, which describes a frame composed of two cast shells, so that there is obtained a closed cross-section at the highly stressed frame parts.

A problem with the latter design is that the two assembled shells must be rigidly connected to each other in the joint along the central plane of symmetry in order that torsional stresses may be transferred therethrough. Such a joint requires a high degree of dimensional accuracy in both cast parts. Injection or die-cast parts however, are often subject to crimping during the production process as well as tolerance deviations and dimensional differences, depending inter alia, on the moulding time, possible alloy elements, the temperature and wear of the moulding tool and so forth. In particular cast bicycle frames for adult bicycles therefore involve very substantial problems when a fully cast design in the form of two shells is attempted in practice, because of problems of joining two shells of such large dimensions as being of interest here.

On the above background the present invention provides a.new and improved bicycle design the novel and specific features of which consist in the combination of: a cast rear section with bearings for a rear wheel and a crank as well as integrated details, such as a baggage rack and a mud-guard, a front fork cast in one piece with

integrated details, in particular bearings for the steering movement and a front wheel, a middle section comprising two frame tubes bent to shape from a continuous length of tube and being at two rear ends rigidly connected to the rear section, said frame tubes having a common intermediate portion which constitutes an anchoring piec extending substantially parallel to the front fork for coupling thereto and pivoting thereof.

The structure described here implies that those parts of the bicycle frame, namely the rear part or rear section, which do not need to have any particular tortional rigidity, can be efficiently produced by moulding. Besides this rear section advantageously can be an integrated structure in which various details may be formed in one manufacturing step by moulding. The middle section or the actual frame however, is based on a tubular component which in view of the tubular cross section gives the required torsional rigidity at the same time as this results in an appearance being more in compliance with that which is conventional and accepted, The front fork is moulded or cast in one piece with integrated details.

As will be seen from the following description there is an additional important feature of the bicycle according to the invention, that the intermediate portion of the frame tubes has an internal reinforcement member and possibly a co-operating external attachment member having bearing parts for journalling the front fork.

As far as the rear section is concerned, this can either be formed by complementary shells as mentioned above, or it can be cast in one piece as a whole.

The invention also comprises a specific method for manufacturing said frame tubes which constitute essential components in the bicycle design described here. This form of frame tubes in co-operation with the other cast main parts, give the bicycle high strength in the highly stressed and critical area where the front fork is connected to and

ournalled at the frame.

Additional particular features and advantages of the bicycle according to the invention will be apparent from the following description with reference to the drawings, in which:

Fig. 1 shows in elevation a bicycle built according to this invention.

Fig. 2 shows in enlarged longitudinal section important details of the common intermediate portion of the frame tubes,

Fig. 3 shows a reinforcement member in a subtantially rectilinear condition before insertion into and bending together with the frame tubes,

Fig. 4 shows a rear section based on two shells, for the bicycle in Fig. 1, somewhat more in detail and in elevation, as welll as accompanying cross sections in Fig. 4A - 4E,

Fig. 5 shows one of the two shell castings which are incorporated in the frame of Fig. 4, and in end elevation.

Fig. 6 shows another embodiment of the rear section based on casting as one piece and seen in elevation,

Fig. 7 shows an end elevation of the rear section of Fig. 6, and

Fig. 8 shows a front fork cast in one piece and being with advantage incorporated in the bicycle of Fig. 1, with accompanying cross sections in Fig. 8A - 8C.

The main parts of the bicycle design shown in Fig. 1 are as follows: a middle section formed by two frame tubes 1 and 2 which have a common intermediate portion 4, the frame tubes being bent to shape from a continuous length of tube, taking into account particularly the critically stressed intermediate portion 4 which extends generally in parallel to the adjacent part of the front fork 3. The rear section of the bicycle consists of the parts 6, 7, 8 and 9 which are manufactured by casting, for example either die- cast light metal or injection moulded plastic composite

material. At their rear ends 11 and 12 respectively the frame tubes 1 and 2 are rigidly connected to the rear section. In the usual manner the rear section has a bearing piece 18 for the rear wheel axle of the bicycle. Besides the bicycle has other necessary parts and components, such as a handle-bar 10 and a seat 13 with a supporting seat tube 15 and a seat tube clamp memeber 16 which constitutes a part of the rear section.

The specific design of the frame tubes leads to advantages both with respect to an efficient manufacture and with respect to mechanical strength conditions. The rigidity of the tubes is maintained through the common intermediate portion 4 as mentioned, which besides has an interior reinforcement which will be explained below with reference to Fig. 2 and 3. The conventional manner of design based on two separate tubes which at the region of the front fork are interconnected by means of sleeves or the like, involves highly stressed and critical joints at this region. Such points of weakness are avoided with the design accor¬ ding to the invention.

Fig.2 shows more in detail the intermediate portion 4 at the transition region between the frame tubes 1 and 2. In the interior of the tube length and before bending to shape there is introduced a reinforcement member 14 which is bent together with the tube to the shape shown. Initially the member 14 has a shape as shown in Fig. 3, so that it can easily be inserted into the initially straight length of tube which is going to form the frame tubes 1 and 2 with the common intermediate portion 4. As will appear from Fig. 2 and 3 the member 14 has a main portion which extends in the longitudinal direction and projecting transverse portions, of which one portion 14C is indicated in Fig. 3, so that the member 14 can easily take part in the bending operation so as to fill the inner tube cross section at the intermediate portion 4 as shown in Fig. 2. During bending this tube cross section thus becomes somewhat reduced in relation to

the cross section of the remaining length of the frame tubes

1 and 2.

At one end the reinforcement member 14 has a tongue- like extension which is in conformity with the transitional region between the frame tube 1 and the intermediate portion 4 having a reduced cross section. Thus the tongue 14D has a particular reinforcement effect at this location. A similar tongue or extension possibly may also be provided at the opposite end of the member 14. This member moreover has anchoring holes 14A and 14B at its ends. According to Fig.

2 these holes receive bolts 21 and 22 for the attachment of an exterior anchoring member 24 having a contour adapted to the bent shape of the intermediate portion 14. The anchor¬ ing member 24 has bearing pieces 25 and 26 for journalling of the front fork 3, which is also shown in Fig. 1.

In the light of the above explanation there is obtained a double function with the interior reinforcement member 14, i.e. in the first place to form anchoring points or holes for threaded bolts 21 and 22 from the outside and with an exact position. In the second place the member 14 exerts a counterforce during the plastic deformation of the bent intermediate portion 4, which is effected by means of a tool acting from the outside. With the illustrated reduction or narrowing of the tube cross section at the intermediate portion 4, brought about by pressing this portion exterial- ly, the radii of curvature of the actual bending regions can be made very small. This makes it possible to satisfy a critical factor of appearance. Moreover it is an important factor that the forces occuring at this region of the structure during use of the bicycle, will be absorbed in an advantageous manner. Thus the forces from the bearing pieces 25 and 26 will be transferred into the inner reinforcement member 14 through the bolts 21 and 22. The member 14 engages the inner tube wall along a large surface so that these forces are evenly distributed and points of peak stress are avoided.

Fig. 4 and 5 with accompanying cross sections in fig. 4A to 4E shows an embodiment of the rear section of the bicycle, based on two shells or halves, of which one is shown in Fig. 5. In compliance with Fig. 1, Fig. 4 and 5 show main parts 6, 7, 8 and 9, of which the latter part constitutes or carries a baggage rack and completely or in part can form the rear mud-guard of the bicycle. However there is also indicated a retractable rear mud-guard member 19, which when its use is not desired, can be hidden in a retracted position in the interior of the baggage rack structure.

From a mechanical strength standpoint it is important that the frame tubes with their ends 11 and 12 are rigidly and securely connected to the main parts of the rear section shown. Cross sectional Fig. 4A and 4B show how the two shell parts 31 and 32 clamp the respective frame tubes and how anchoring takes place by means of transverse bolts. The attachment holes of the tubes, for example 33, are flanged as shown at 39 (Fig. 4A) in order to distribute the tighten¬ ing forces. Like Fig. 4B, Fig. 4C and 4D show the cross section of one shell at the central portion of the respec¬ tive stays or main parts 8 and 7. The basic main part 6 has a cross section as shown more in detail in Fig. 4E, which in particular illustrates a groove- and tongue connection 31A -

32A having great significance for the joining of the two shell parts 31 and 32 as regards a maximum of mechanical strengt and in paraticular torsional rigidity. Thus from Fig. 4E and besides from the cross section of Fig. 4A it is seen that the groove- and tongue connection extends along the front edge of the main part 6 and further in the extension 16 thereof, which constitutes the seat tube clamp. With such an arrangement of these connection means tolerance problems are avoided during assembly of the two shells, which apparently is advantageous from a manufacturing point of view.

Another possible embodiment of the rear section as

shown in Fig. 6 and 7, is based on the casting or moulding of the whole section as one piece. This requires that the design must make possible the pulling out of the moulding tool parts, which is obtained here by means of a substan¬ tially U-shaped cross section being open downwardly and rearwardly, so that the direction of pulling out the moulding tool will be as indicated with arrow T in Fig. 6. In this connection it is of significance to note that the angle of inclination of the supporting stay 58 from the seat tube and baggage rack region 66/59 to the wheel bearings at 68, involves a sufficient draft angle in order that a tool core can be pulled out in spite of a slight narrowing of the stay in the direction towards the wheel bearings. The remaining main parts 56 and 57 of this rear section are provided with stiffening ribs 55A, 55B, 55C and so forth, having such an orientation that they coincide with the pull- out direction T.

The configuration of the main parts 56, 57, 58 and 59 in the rear section 50 of Fig. 6 and 7 correspond substan¬ tially to the arrangment of Fig. 4, except that the embodi¬ ment of Fig. 6 and 7 is moulded in one piece. At 62 in Fig. 6 there is shown a hole and attachment means for an upper frame tube (not shown) .

The design of the front fork as illustrated in Fig. 8 is also based on moulding as one piece, having essentially U-shaped cross sections the open side of which is directed rearwardly with respect to the longitudinal direction of the bicycle. The cross sectional shape at various places is shown in particular in Fig. 8A, 8B and 8C. With such a design the front fork will have an attractive appearance at the same time as its properties with respect to mechanical strength are good. This also applies to the pivot or coupling region 41 which through the bearing pieces 25 and 26 (see Fig. 1 and 2) shall co-operate with the remaining parts of the bicycle frame. This region 41 is relatively wide, this inter alia, in view of the forming of an inte-

grated cavity 42 which faces forwardly and shall serve to receive a light and possible batteries. The cavity 42 is then closed with a suitable cover which can also comprise a light glass.

For manufacturing the main components of. metal for the bicycle described, die casting is mentioned in the first place, but it may also be possible to employ chilled casting or sand-casting. Injection moulded plastic composite parts can also be an attractive alternative, depending on among other things, material prices and manufacturing technology employed at the production plant concerned. As it has appeared from the preceding description with accompanying drawings, this new bicycle design can be made to have an appearance being very similar to present conventional bicycles, at the same time as at essential points involves advantages with respect to manufacturing and mechanical strength, which in part to a very substantial extent are distinguished in relation to bicycle designs as known hitherto. Moulding makes it possible in an advantageous way to integrate various details in the design, in particular various cavities which inherently turn out in moulded structures, for example cavities in the front fork for a light, batteries, etc. and in a like manner in the baggage rack for a pump, a mud-guard and so forth.