Field of application of the invention

The present invention refers to vehicles driven by muscular propulsion, and more specifically to a tricycle with doubly-articulated drawn-rope propulsion ac- tuator.

Review of the prior art

Cycles have been known for some time in which the chain drive of common bicycles is not moved by pedals, but rather by rope actuators driven by the arms and legs of the user, simulating the action carried out by a rower. For example, the patent US 6708996 B1 describes a cycle driven by muscular power, comprising:

- a frame with a longitudinal bar, equipped with a front steering wheel and a rear drive wheel,

- actuation means with a handle grippable by the user in a back-and-forth rowing movement,

- a drive mechanism for transforming said back-and-forth movement into a rotation motion of the rear wheel, and

- means for guiding the front steering wheel in rotation,

wherein the drive mechanism includes: a maintenance device formed by a back-and-forth actuation system formed by tubes articulated in parallelograms which are deformable in the longitudinal direction of the bar, and axial centering means coupled to said parallelograms to maintain the axis of the handle con- stantly in the vertical half-plane passing through the longitudinal axis of the bar. The drive mechanism includes a traction cable having one end fixed to the handle, from which it continues longitudinally until it meets the series of two counter-pulleys placed at the front end of the frame for sending the cable back to- wards the rear end, sliding inside the tubular bar of the same; the other end of the cable draws a chain that engages a freewheel toothed sprocket. A derailleur makes possible the selection of the pinion for the gear change. The user grips the handle seated on a seat slidable along the frame with his feet set against two fixed footrests, and draws the handle in order to make the cycle advance during the lengthening of the telescopic actuator produced by the extension of the legs together with the return of the arms. The cable is drawn in the opposite direction by the action of return means acting during the shortening of the telescopic actuator following the return of the legs and the extension of the arms of the user. The return means are not specified; the most well-known are those used in common rolling shutters and comprise a torsion spring with flat spiral coupled to the winding pulley of the rope. The steering mechanism comprises a first pulley fixed to the handle, a second pulley pivoted to the stem of the fork of the front wheel, and a cable windable on the two pulleys along a zigzag path between vertices of the telescopic actuator. For steering the cycle, the handle is rotated around the central pin as if it was the handlebar of a common bicycle, and such rotation is transmitted to the fork by means of the cable. The telescopic actuator can be tilted upward by raising the handle, so as to allow greater maneuvering ease without affecting the drawing of the rope.

The patent EP 0197569 differs from the preceding mainly for the fact that the actuator is constituted by a rigid bar slidable inside a short horizontal tube integral with the apex of the front fork. At the ends of the bar, a tensioned cable is horizontally connected and wound several times around a drive pulley pivoted to an arm of the front fork. Such pulley is coupled to a chain kinematic mechanism which moves the front wheel by means of a unidirectional rotation joint. The rigidity of the bar simplifies the steering mechanism and makes the use of cable return means superfluous, since these are always tensioned for both back-and-forth movements. Problems of the prior art

The vehicles described in the mentioned patents have drawn-rope propulsion mechanisms that are not capable of optimizing the transformation of the muscular work into mechanical work available to the hub of the wheels, since in order to translate the thrust exerted by the legs against the footrests into drive power, such thrust must load the other muscles, thus tiring them.

In addition, the aforesaid propulsion mechanisms employ clearly bulky and possibly dangerous actuators, since in the case of collision against an obstacle, the user would be thrust due to inertia against the nearly horizontal actuators di- rected against the thorax, impacting against the handlebar in a fairly violent manner.

Objects of the invention

Therefore, the object of the present invention is to indicate a vehicle capable of optimizing, for propulsion purposes, the use of the muscular power generated by the joint exertion of the user's arms and legs.

Another object of the invention is to limit the danger of the drawn-rope actuator in the case of impact against an obstacle.

Another object of the invention is to indicate a vehicle capable of attaining the previous objects by mainly utilizing the components of present-day bicycles and the internal spring pulleys for rewinding the belt of common rolling shutters. Summary of the invention

In order to attain such objects, the present invention has as subject a vehicle with muscular propulsion, comprising:

- a frame supported by wheels, of which at least one is a steering wheel; - a seat slidable on a longitudinal member of the frame;

- a pair of footrests mounted on the longitudinal member;

- propulsion means equipped with a longitudinal handle with two grips grip- pable by the user in a back-and-forth rowing motion drawing a rope for advancing the vehicle;

- means for tensioning the rope that are coupled, via a unidirectional rotation joint, to the shaft of a mechanism for transmitting the rotary motion to at least one drive wheel, the aforesaid tensioning means being capable of rewinding the rope during the idle motion of the handle;

- steering means actuatable by rotating the handle around a vertical axis; wherein according to the invention said propulsion means include:

- a first and a second rod, the second shorter than the first, of which:

- a first end of the first rod is connected to said longitudinal member in a pivoting manner in the vertical plane in front of a point of maximum advancement of the seat,

- a first end of the second rod is connected to the second end of the first rod in a pivoting manner in the vertical plane,

- the second end of the second rod is fixed to the handle, allowing said rotation thereof;

- means for fixing said rope to the handle;

- mean for fixing an additional rope section between the handle and the seat, the additional section having a length such that it is already tensioned when configuration of said rods and seat is that of full-forward rowing configuration, such that said additional segment remains constantly tensioned during the translation of the seat backward due to the thrust of the legs, as described in claim 1.

Further characteristics of the present invention deemed innovative are de- scribed in the dependent claims.

Advantageously, the footrests are common bicycle pedals equipped with quick- release means suitable for immobilizing the driver's shoes.

Advantageously, said robe is a belt and said fixing means include one or more screws and belt-press washers.

Advantageously, the constant length of said additional rope segment is adjustable based on the build of the user.

Advantageously, the vehicle is equipped with brakes actuatable by means of respective Bowden cables terminating at the respective levers on the handle. According to one aspect of the invention, said additional rope segment is the continuation of said rope.

According to one aspect of the invention, said drive wheel and said steering wheel coincide with the front wheel of a bicycle or a tricycle. According to one aspect of the invention, said rope tensioning means include a hollow pulley on which the rope is wound, containing a box integral with the pulley in coaxial position, the box containing a torsion spring coiled as a spiral in the same direction as the winding direction of the rope, the ends of the spring being respectively fixed to the box and to an element that is externally fixed with respect to the box, said spring in such a manner being compressed by drawing the rope such that the elastic return of the spring can impart a rotation in opposite direction that rewinds the rope.

According to one aspect of the invention, said pulley is supported inside a hous- ing fixed to the upper end of the stem of the fork which supports the hub of said front steering wheel.

According to one aspect of the invention, the housing comprises two opposite plates integral with a first spacer pin positioned close to the lower end of the plates.

For the purposes of the present invention, a plate is defined as a structural element having predominant length and width with respect to the thickness, and whose surface is flat.

According to one aspect of the invention, the housing includes a rope guide device comprising:

- a second spacer pin integral with the two plates of the housing;

- a third pin crossing a hollow shaft that is free to rotate driven by the rope;

- two support elements for the third pin that are parallel to each other and fixed to respective ends of the second pin outside the hollow shaft, orthogonally thereto and upwardly directed.

According to one aspect of the invention, the housing, close to the upper end of said plates, houses the seats for respective ball bearings which support the shaft of the drive mechanism, said shaft having at least one tapered prismatic end integral with a sprocket wheel outside the housing, belonging to a chain kinematic mechanism that moves the drive wheel.

Advantageously, said sprocket wheel belongs to a crankset with multiple sprocket wheels selectable by means of a relative derailleur of the chain driven by a cable of Bowden type controlled by a lever on the handle. Advantageously, the chain drive also comprises a pinion pack integral with the front wheel, selectable by means of a relative derailleur of the chain driven by a cable of Bowden type controlled by a lever on the handle.

According to one aspect of the invention, the vehicle comprises a chain deflec- 5 tor device including:

- a support with elongate shape projectingly fixed to the arm of the fork, said support being placed on the same side as the sprocket wheel with respect to the housing;

- a pinion pivoted to the free end of said support with the possibility to transit) late on its pin, the pinion engaging the chain on the external side, deflecting it towards the interior of the ring that it forms;

- two shells integral with the pinion on both sides thereof for containing two ball bearings, slidable on the pin together with the pinion in order to support the angular deflections of the chain during steering maneuvers.

15 According to one aspect of the invention, said steering means include:

- a bushing rigidly connected to the second end of the second rod;

- a pin integral with the handle, centrally and orthogonally thereto, and free to rotate inside said bushing;

- a longitudinal cable guide support centrally integral with the second rod, par- 0 allel to the handle and crossed by the tension wires of two Bowden type cables symmetrically positioned with respect to the center of the cable guide support; first ends of the tension wires being fixed to the handle at symmetric points with respect to the rotation pin, the second ends of the tension wires being fixed to respective arms of the fork close to the head, and the 5 ends of the respective sheaths being immobilized with respect to the tension wires.

According to one aspect of the invention, the seat is supported by a carriage formed by an upper plate rigidly and orthogonally connected to two lateral plates that are parallel to each other to form a seat for the insertion of said lon- 30 gitudinal member, of parallelepiped shape, each lateral plate being equipped with first rollers pivoted to the plate in a manner so as to roll against a respective lateral wall of the longitudinal member, and second rollers pivoted between the two lateral plates in contact with the upper wall of the longitudinal member. According to one aspect of the invention, the front end of the carriage is equipped with anti-overturning means consisting of two bars fixed to the two lateral plates, projecting beyond the lower margin of said plates for the support of the rotation pin of a small wheel.

The handle also includes all the controls of a common bicycle handlebar, no longer inserted on the stem of the fork but rather remotely situated on the propulsion actuator side; this is allowed by the use of Bowden cables of length such to support the maximum extension of the two rods articulated together. Generally, it would be possible to use only one rod instead of two: the single rod would have one end connected to the longitudinal member, as stated above for the first rod, and the coupling bushing of the handle pin would be fixed to the other end, with suitable slope. However, such solution would not allow optimal actuation of the pivoting rod and could cause problems in maneuvering the steering; this is explained in the comment of figure 10. It will be anticipated herein that the maximum forward tilt of the single rod must be less than 90°, so as to prevent an advancement of the seat such to make it impossible to collect the legs together. If one wishes to obtain the same seat travel as in the embodiment with two articulated rods, the length of the single rod must be equal to the sum of the lengths of the two preceding articulated rods. The result is that the user would be obliged to assume an unnatural position for his arms due to the higher grips, tiring himself more and having more difficulty in the steering maneuver.

Advantages of the invention

The vehicle of the invention has a bivalent propulsion mechanism capable of optimizing the transformation of the muscular work into mechanical work available to the hub of the drive wheel. This is due to the fact that the thrust of the legs while drawing the seat backward also contributes to drawing the handle, better distributing the dynamic load between the various muscles engaged in the propulsion - which will work with less fatigue and hence for a longer period. The use of two rods articulated with each other rather than one rod increases the angular width within which it is possible to exert the propulsion with back- and-forth motion, allowing a position more similar to that assumed by a rower. Also the drawbacks in case of collision against an obstacle placed in front of a vehicle are effectively reduced, since the driver thrust forward due to inertia against the handle causes the downward tilt of the two articulated rods, giving arms and legs the opportunity to dampen the impact.

Brief description of the figures

Further objects and advantages of the present invention will be clearer from the detailed description of an embodiment thereof and from the attached drawings given as a mere non-limiting example, in which:

- figure 1 shows a tricycle obtained according to the present invention in perspective view from the right side with respect to the user;

- figure 2 shows the upper part of the tricycle of figure 1 in perspective view from the left side;

- figure 3 shows, in exploded view, the frame, the fork and two rods articulated to each other belonging to the tricycle of the preceding figures, where several details are enlarged in the encircled areas;

- figure 4 is an enlargement of the front part of the tricycle of figure 1 ;

- figure 5 shows the tricycle of figure 1 in the maximum forward bending configuration of the lower rod;

- figure 6 shows the tricycle of figure 1 in the maximum backward bending configuration of the lower rod compatible with the extended posture of the user;

- figure 7 shows the posture assumed by the user of the tricycle of figures 1 and 2 at the end of the step of curling up the legs for bringing the propulsion mechanism back into the initial position;

- figure 8 shows the posture at the end of the propulsion step;

- figure 9 is a diagram of four kinematic configurations assumed by the two rods articulated with each other and by the rope segment between the handlebar and the seat at four different positions of the user in passing from the posture of figure 7 to that of figure 8;

- figure 10 compares the preceding diagram with that of a hypothetical mechanism with only one propulsion rod; - figure 11 is a perspective view of the set of parts constituting a so-called "bottom bracket" and relative chain drive, as seen by the user;

- figure 12 is an enlargement of a detail of figure 11 ;

- figure 13 is an enlargement of the sprocket wheel of figure 1 ;

- figure 14 is an enlargement of the spring pulley of figure 2;

- figure 15 is an enlargement of the chain deflector visible in figure 1 ;

- figure 16 is an enlargement of the front part of the frame at the connection of the lower rod and the foot rest pedals;

- figure 17 is the fork arc seen from the front side of the tricycle;

- figure 18 is a top view which shows the steering linkage and relative connections;

- figure 19 is a perspective view of the remote handlebar obtained via a top view of the tricycle in front of the user;

- figure 20 is a perspective view of the remote handlebar obtained via a bot- torn view of the tricycle in front of the user;

- figure 21 is a side perspective view of the translation carriage of the seat;

- figure 22 is a bottom view of the translation carriage of the seat;

- figure 23 is an in-scale exploded view of the bottom bracket of figure 1 1 and relative chain drive;

- figure 24 is the reassembly of the exploded view of figure 23.

Detailed description of several preferred embodiments of the invention

In the following description, equivalent elements which appear in different figures can be indicated with the same symbols. In the illustration of one figure it is possible to refer to elements not expressly indicated in that figure but in preced- ing figures. The scale and the proportions of the various depicted elements might not necessarily correspond to the actual scale and proportions. Below, the terms belt and rope are used as synonyms.

With reference to figures 1 - 4, a tricycle is observed whose frame is constituted by a tubular longitudinal member 1 with parallelepiped shape, on the front part joined to an oblique strut 2, with the same tubular shape, which supports a head tube 3 where the stem 4 of a fork 5 is inserted, entirely similar to that of a common bicycle. The tricycle has a single front wheel 6 of spoked type whose rotation pin is anchored to the lower end of the fork 5. A lower 7 (figure 3) and upper 8 steering series allow the rotation of the stem 4 inside the head tube 3. A joint 9 of "pipe" type is fixed to the end of the stem 4 coming out from the head tube 3; the joint 9 is of the type normally used for attaching the handlebar to the stem of the fork in common bicycles. Close to the rear end of the longitudinal member 1 , two supports are rigidly connected for the hubs of the rear right 13 and left 14 wheels, also spoked. The perspective figure shows the single support 10 of the hub 11 of the right rear wheel 10. A carriage 15 supports a seat 16, free to translate in the two directions on the longitudinal member 1 , remaining fixed thereto. Two footrest pedals 17 are connected close to the front end of the longitudinal member 1. On the longitudinal member 1 , not far from the foot- rests 17, a half-joint 18 is fixed comprising a U-shaped seat for housing the articulation pin of the lower end of a cylindrical rod 19, whose upper end is articu- lated with a first end of a shorter upper cylindrical rod 20. The rods 19 and 20 constitute two "arms" articulated with each other that are used in the propulsion of the tricycle, and will therefore be named arms or articulated arms hereinbe- low. The other end of the arm 20 provides an annular seat 21 (a large bushing) for the insertion of a pin 22 free to rotate in its seat. The pin 22 is rigidly and or- thogonally connected to a handle 23, in the center and lower part thereof. The latter is partly similar to the handlebar of a common bicycle due to the presence of two grips, levers of the brakes, and levers of two derailleurs of a chain 31 that moves the front wheel 6, and due to the fact that the aforesaid levers and derailleurs give rise to the same number of Bowden cables connected to the respec- tive actuation mechanisms. The handle 23 differs substantially from conventional handlebars due to the fact that it is a propulsion member and due to the fact that the steering action is remotely exerted via a pair of tie-rods anchored to the two arms of the fork, also called fork blades, as will be better illustrated below in the subsequent figures. Another novelty consists of the fact that the seat 16 is also a propulsion member of the tricycle. The propulsion due to the joint driving of the handle 23 and seat 16 is exerted by drawing a strong belt functionally divided into two segments 24 and 25. The segment 24 has one end fixed to the carriage 15, at the front thereof, and the other end fixed to the handle 23, centrally and above such handle. The segment 25 has one end coinciding with the end of the segment 24 fixed to the handle 23, or superimposed or contiguous if the two segments do not belong to a single belt, and the other end fixed to a pulley 26 (figure 2) on which the belt segment 25 is wound. The pulley 26 is hollow and houses therein a coaxial box containing a flat spiral spring 27, also called torsion spring, to which the pulley is coupled in order to allow the rewinding of the belt 25 following the elastic return of the spring 27. The pulley 26 is placed inside a housing 28 integral with the joint 9, thus sharing the rota- tion motion of the fork 5 on the axis of the head tube 3. The pulley 26 is coupled to its rotation pin 69 (figure 11) by means of a unidirectional rotation joint, preferably of freewheel bearing type (156 of figure 23). Such pin 69 crosses the housing 28 supported by ball bearings in order to transmit the rotation of the pulley 26, in its active phase, to a sprocket wheel 29 fixed to the common pin 69 by means of the spokes 29a. The sprocket wheel 29 belongs to a crankset comprising another sprocket wheel 30 of smaller size (figure 4). The sprocket wheel 29 meshes with the chain 31 which descends until it meshes with a pinion of a pinion pack 32 integral with the hub of the front wheel 6, passing through the small sprocket wheel 33 of a derailleur 34 whose actuation allows the selection of the pinion in the change of ratio; from here, the chain 31 rises towards the sprocket wheel 29, meshing with the small sprocket wheel 35 of a deflector, then passing through the chain guide cage of a second derailleur 37 for the selection of the sprocket wheel 29 or 30 in the change of ratio. The housing 28 is tilted forwarded with respect to the stem 4 of the fork 5 and close to the upper end it is crossed by the pin 69.

Figure 1 shows a set of flexible cables that lead from the handle 23 towards the longest arm 19 and run along the latter, held by clips; such cables continue along the oblique strut 2, also held here by clips, in the end reaching their destination on the front wheel 6 side of the tricycle. These cables, which will be bet- ter described in figure 4 and in other figures, are constituted by intertwined metal wires contained in suitable sheaths, constituted by a steel spiral coated with PVC; such sheaths allow the sliding of the tie-rods at their interior when the same are locked at the two ends. Such cables are called "Bowden cables" in the art and their merits are quite clear. Figures 5 and 6 show that the aforesaid cables are bent together in order to support the movement of the two articulated arms 19 and 20. The configuration of figure 5, the maximum theoretical ad- vancement of the seat, involves an acute angle between the two arms 19 and 20, with the articulation between the two nearly in contact with the oblique strut 2; in such case, the loop formed by the cables between the arm 19 and the strut 2 is the narrowest. The configuration of figure 6 is the maximum backward configuration of the seat, in which the handle 23 reaches the maximum distance from the housing 28 and the two articulated arms 19 and 20 are nearly aligned; in such case, the loop formed by the cables between the arm 19 and the strut 2 is the widest.

With reference to figure 4, the following cables are observed, all originating on the handle 23 and anchored to the strut 2 by means of a clip: a cable 40 for driving a brake 41 of V-brake type, whose sliding blocks act against the sides of the rim of the front wheel 6; a cable 42 whose tension wire 42' drives the caliper of a disc brake (with corrugated rim) 43 coaxial with the pinion pack 32; a cable 44 whose tension wire 44' drives the lever of the lower derailleur 34; a cable 45 whose tension wire 45' drives the lever of the upper derailleur 37 passing through the body of the deflector 36; a cable 46 whose sheath has the visible end anchored to a block 47 screwed to the strut 2 and whose tension wire 46' has the end coming out from the sheath fixed to a small cylinder 48 welded to an arm of the fork 5 in the upper part close to the curved head. A cable entirely identical to 46 and similarly connected to the strut 2 and to the other arm of the fork 5 completes the remote steering.

Greater details regarding the articulations present at the ends of the two arms 19 and 20 are provided in the exploded views of figure 3. In the bottom exploded view in the figure, it can be noted that the lower end of the cylindrical arm 19 has a segment of smaller thickness 50 in which a hole 51 is present that comes to be aligned with two holes 52 and 53 of the same number of hardened, ground bushings (not shown) inserted in the opposite walls of the half-joint 18 at a U-shaped seat obtained in the upper part for the insertion of the segment 50. The holes 52, 51 and 53 are aligned with each other transverse to the longitudinal member 1 and are crossed by a pivoting pin 54, so as to complete the lower articulated joint constituted by the elements 18, 50, 54. The half-joint 18 has a short stem 18a integral with a circular base 18b fixed with screws to the longitu- dinal member 1. One screw crosses from below the longitudinal member 1 and penetrates into a threaded hole present in the stem 18a for an improved fixing of the lower articulation. In the top left exploded view in the figure, the end of the shorter cylindrical arm 20 is connected to a half-joint 55 that has, in the terminal part, a U-shaped seat with two holes 56 and 57 in the opposite walls; the holes are aligned with each other orthogonal to the arm 20. The upper end of the cylindrical arm 19 has a segment with smaller thickness 58 in which a hole 59 is present belonging to a hardened, ground bushing (not shown). After insertion of the segment 58 in the U-shaped seat of the half-joint 55, the hole 59 is aligned with the two holes 56 and 57 for the crossing by a pivoting pin 60, so as to complete the upper articulated joint constituted by the elements 55, 58, 60.

Figures 7 and 8 show the posture assumed by the user respectively at the start and at the end of a single rowing action of the tricycle of figure 1 , the configurations of the vehicle being those shown in figures 5 and 6. The two arms 19 and 20 are moved on a substantially vertical surface passing through the longitudi- nal member 1. The user continuously passes from the first to the second posture and from the second to the first posture, repeating such alternation during the entire travel. In the curled up posture of figure 7, the seat is in a position closer to the front end of the longitudinal member 1 , the legs are completely bent, the arched back brings the trunk forward towards the raised knees, the arms are also bent and project over the knees, and the hands grip the handle 23 and push it forward. The spring 27 inside the pulley 26 is unloaded and the belt segment 25 exiting therefrom has its minimum length. In the posture of figure 8, the seat is in a more distant position with respect to the front end of the longitudinal member 1 , the legs are completely extended, the trunk brought backward, the arms extended, and the hands grip the handle 23 and pull it backward. The spring 27 is loaded and the belt segment 25 exiting from the pulley 26 has its maximum length. The passage from the second to the first pos- ture is facilitated by the fact that the footrests 17 immobilize the shoes of the user during the bending of the knees, which returns the seat forward. In the passage from the curled up configuration of figure 7 to the extended configuration of figure 8, the hands exert a traction on the handle 23 communicated to the belt segment 25 and the accompanying backward motion of the seat 16 due to the thrust of the legs keeps the belt segment 24 fixed to the carriage 15 under traction. In such a manner, the joint traction force exerted on the handle 23 from arms and legs is transferred to the belt segment 25, whose lengthening ensures that pulley 26 rotates a corresponding unwinding angle in counter- clockwise direction (as seen by the user), compressing the spiral spring 27. By means of the freewheel bearing, the rotation of the pulley 26 is transferred to the chain drive 31 for the movement of the front wheel 6. During the opposite passage, the belt segment 24 in any case remains tensioned, since it has constant length and the distance between the handle 23 and the carriage 15 re- mains substantially unchanged; the belt segment 25, meanwhile, is slackened, allowing the elastic return of the spiral spring 27 which places the pulley 26 in clockwise rotation for the rewinding of the belt segment 25, and the freewheel bearing decouples such rotation from the chain drive. With regard to the return movement lacking propulsion, it does not matter if the belt segment 24 is ten- sioned or not.

Figure 9 illustrates four configurations assumed by the two articulated arms 19, 20 and by the seat 16 during the movement that imparts the propulsion to the front wheel 6. The four configurations are indicated with letters A, B, C, D, of which A corresponds to the configuration of figure 7, while D corresponds to that of figure 8. In a non-limiting embodiment, the actual length of the arm 19 measured between the centers of the two articulation pins is 486 mm; the length of the arm 20 measured between the center of the articulation pin and the center of the fixing hole of the annular seat 21 is 140 mm, and the ratio between the lengths is therefore 3.47. The fixed length of the belt segment 24 is 554 mm. In configuration A, the angle a formed between the arm 19 and the longitudinal member is 137°, the angle β formed between the two arms 19 and 20 is 67°, the distance δ between the lower articulation pin of the arm 19 and the front end of the seat 16 is 172 mm. In configuration B, the angle a is 90°, the angle β is 103°, the distance δ is 337 mm. In configuration C, the angle is 59°, the angle β is 133°, the distance δ is 714 mm. In configuration D, the angle a is 30°, the angle β is 180°, the distance δ is 1002 mm. The arm 19 has a safety screw in- serted close to the upper end in order to prevent possible configurations in which the angle β can exceed 180°, causing the loss of synchronism in the rowing. The translation Δ = δο - 6A carried out overall by the seat is 830 mm. In the passage from the configuration A to configuration D, we can observe a progressive diminution of the angle a and a progressive increase of the angle β as in a kind of compensation.

In order to simplify the comparison, Figure 10 reports in its upper part three configurations L, M, N of a hypothetical tricycle that uses only one articulated arm 19' instead of two articulated arms 19 and 20. In the lower part of the same figure, the four configurations A, B, C, D are reported for the purpose of com- parison with the preceding figure. The comparison requires keeping both the minimum distance δ of 172 mm (case A) and the maximum distance δ (case D) of 1002 mm unchanged, since such distances of the seat 16 from the articulation of the arm fixed to the longitudinal member 1 are close to the limits of the possible postures assumable by a user of average build. The length of the arm 19' is 626 mm and corresponds to the sum of the length of the arms 19 and 20, as results in the configuration D. The rope segment 24' will be longer than the segment 24 since it must have the same length as the arm 19' in order the seat 16 respect the constraint to the longitudinal member 1. In the proximal configuration L, the angle a is 82°; in the intermediate configuration M the angle a is 65°; in the distal configuration N the angle a is 37°. The difference in the values of the angle a between the configurations L and N is 45° with respect to 107° of the configurations D and A. The greater height of the vertex of the arm 19' with respect to the arm 19 can be inferred from the dashed lines that report the heights of the upper end of the arm 19 on the configurations L, M, N. The size of the forward projection of the handle 23 supported by the pin 22, orthogonally thereto, is visible at the initial and final configurations A, D and L, N. As can be observed in figure 10, also considering the postures shown in figures 7 and 8, the greater height of the arm 19' with respect to the arm 19 negatively affects the user, who is obliged to row by gripping the higher-placed handle, and thus tires himself more. In addition, the smaller tilt of the handle 23 with respect to the horizontal plane allows a greater vision of the drive levers of the brakes and the derailleurs together with a more facilitated control of these levers, as well as of the remote steering. Overall, the configuration with two articulated arms has clear advantages with respect to that with a single arm.

With regard to the muscular power required by the user, given the same speed for the vehicle, it must be clearly the same in the two configurations; the modes of supplying such power nevertheless vary. In the two-arm configuration, the active angle a is greater than that of the single arm configuration. In a first approximation, we assume that the energy necessary for rowing is proportional to the angle a, hence the single rowing action will require more energy per stroke in the two-arm configuration. For each configuration, it is possible to divide the average energy W _M supplied on the segment of pre-established path, during the pre-established time T, into the same number of identical contributions as there are n rowing actions carried out during time T. Under the given conditions, the sum of such contributions will be equal for the two different configurations. With R = n/T the rowing rhythm, the average power will be W _M /T. Since the single rowing actions are characterized by the same energy, the average power will be equal to the power R W, of the i-th stroke characterized by the energy W, ; from this, one infers that by increasing W,, one must decrease R. In conclusion, the two-arm configuration allows slower rowing, as the energy is supplied with more continuity with respect to the single arm configuration; the latter is characterized by a faster and discontinuous rowing, overall more "abrupt" action.

Figure 11 shows the housing 28 as seen by the user. The housing 28 is constituted by two opposite rectangular plates 28a and 28b spaced from each other by means of the interposition of a strong pin 64, whose cylindrical body has a greater diameter than that of the abutment holes present at the lower end of the plates 28a and 28b. The two ends of the pin 64 are threaded and locked by two threaded ring nuts 65 and 66 (and ring nut-locking screws) against the two plates 28a and 28b. The pin 64 is tightened against the front jaw of the joint 9. The upper 8 and lower 7 steering series depends on the type of joint 9 provided, which can be a conventional joint for threaded fork shanks or a joint of Ahead- set type. A second pin 67 crosses through the housing 28 at a short distance from the pin 64. The pin 67 is fixed to the plate 28b by means of a threaded ring nut 68 in order to prevent any residual possibility of rotation of the plates 28a and 28b around the pin 64, in such a manner making it possible to mount inside the housing 28 a so-called "bottom bracket" supported by the pin 69 which crosses through the housing 28 in its upper part. The bottom bracket comprises the pulley 26 at whose interior a circular box 70 is visible open towards the out- side for the containment of the spiral spring 27 (figure 14). By means of a freewheel bearing (156 of figure 23), the pulley 26 is coupled to the pin 69, whose prismatic ends 69a and 69b (figure 23) are tapered. The crankset of the two sprocket wheels 29, 30 is axially mounted on the pin 69, rigidly connected to one end of the pin exiting from the housing 28. Without limiting the invention, the crankset is connected to the right end 69b in the figure.

Figure 12 shows, within the housing 28, two cylindrical supports 71 and 72 parallel to the plates 28a, 28b, spaced from each other by a little more than the width of the traction belt 25, locked to the base against the pin 67 by two screws 73 and 74 which cross the thickness thereof. The cylindrical supports 71 and 72 are transversely perforated close to their upper end for the screwing of a pin 75 (figure 23) parallel to the pin 67. The pin 75 crosses a hollow shaft 75a free to rotate on it. The belt 25 slides inside the space comprised between the cylindrical supports 71 and 72, the hollow shaft 75a and the pin 67, driving the shaft 75a in rotation so as to prevent friction. The contact of the belt 25 with the shaft 75a is facilitated by the external tilt of the housing 28.

Figure 13 is an enlargement of the upper part of figure 4 where the external side of the crankset is shown, constituted by the two sprocket wheels 29 and 30. The wheel 29 is a disc equipped with windows spaced from each other so as to form spokes 29a centrally integral with the pin 69; the wheel 30 is fixed to the spokes 29a. The plate 28b shows the threaded ring nut 65 and the hexagonal head of the pin 67. Figure 14 is an enlargement of the upper part of figure 4 which shows the external side of the pulley 26, coupled to the pin 29 by means of the freewheel bearing (not visible). The figure shows the box 70 containing the flat spiral spring 27, one end B of which is fixed to the box 70 while the other end (not visible) is fixed to an external point integral with the housing 28. One end of the belt 25 abuts against a bracket integral with one side of the pulley 26; a screw 76 crosses bracket and belt, a nut with washer immobilizes the end of the belt 25 against the bracket.

Figure 15 shows the deflector of the chain 31 whose function is to push the chain segment (user side) towards the opposite segment, spacing the chain even more from the frame so as to prevent impact of the user feet or the frame during steering towards the right, and more generally towards the direction corresponding to the position of the sprocket wheels 29, 30 with respect to the housing 28 as seen by the user. The deflector is essentially composed of the following elements: a longitudinal support 36 having one end thereof fixed to the right arm of the fork 5 in the upper part, projecting forward in the direction of the chain 31 ; a ground pin 78 screwed to the free end of the support 36; the small sprocket wheel 35 which engages the chain 31 ; two half-shells fixed by means of screws to the small sprocket wheel 35, on opposite sides; two ball bearings contained within respective seats present in the two half-shells and capable of sliding therewith and with the small sprocket wheel 35 on the ground pin 78 in order to support the angular deflections of the chain during steering maneuvers; a screw with washer fixed to the free end of the pin 78 in order to prevent the exit of the small sprocket wheel 35.

Figure 16 shows the lower articulation of the long arm 19, after reassembling the elements visible in the exploded view of figure 3. The figure also shows the two footrests 17 and 17b, respectively left and right, fixed to two strong and short pins 80 and 80b aligned with each other and screwed to the two sides of the longitudinal member 1 in front of the base 18b of the aforesaid articulation. The two footrests are common bicycle pedals, of quick release type 81 and 81 b, each rotatable on its own pin.

Figure 17 shows the upper part of the fork 5, comprising the arched head 5a in which the two fork blades 5b and 5c converge, and from which the stem 5d rises. Two bored cylindrical supports 48 and 48b are integral with the two sides of the head 5a for locking the ends of the two respective tension wires of the remote steering system shown in the partial top view of figure 18, in which the housing 28 including contents was removed. With reference to such figure, the front wheel 6 is observed between the blades of the fork 5, whose tubular stem 5d is inside the head tube 3. On the opposite side, one notes the handle 23 centrally fixed against the top of the pin 22 placed inside the bushing 21 , in turn immobilized on the periphery of the non-articulated end of the shortest arm 20. First ends of two steering tension wires 46' and 46b' are immobilized by two blocks 85 and 86 connected to the handle 23 at both sides of the central pin 22. The tension wires 46' and 46b' are directed towards the two ends of a parallelepiped bar 84 centrally screwed to the short arm 20, transversely thereto, in a position adjacent to the base of the half-joint 55 belonging to the articulation between the two propulsion arms 19 and 20; such half-joint reported in the enlargement shown to the right respects the actual proportions, which are also respected by the arm 19 and by the elements connected thereto. The enlargement shows that the half-joint 55 has a blind longitudinal hole terminating before the U-shaped seat; inserted in the hole is the articulated arm of the short arm 20, which also centrally crosses the bar 84. A screw 61 crosses the half-joint 55 at the arm 20 and a nut with washer is tightened at the exiting end. A second screw 62 penetrates the arm 20 orthogonally to the screw 61. A screw 63 penetrates the bar 84 and immobilizes it against the end of the arm 20.

The pin 60 has a threaded end which crosses the U-shaped seat of the half- joint 55 and is screwed into a bushing inserted in the wall of one of the two arms of the U-shaped seat, beyond which the screw is locked with nut and washer. The unthreaded part of the pin 60 is ground in order to articulate the head 58 of the long arm 19.

The tension wires 46', 46b' and the respective sheaths form two Bowden cables 46, 46b for controlling the steering wheel. For such purpose, close to the two ends of the bar 84 two through holes are present respectively crossed by the tension wires ods 46', 46b'. The two holes have a conical inlet and a cylindrical outlet with the vertex of the cone contiguous to the cylindrical segment; from such vertex, the sheaths originate of the respective cables 46, 46b running as indicated in the preceding figures. The sheaths terminate at the blocks 47 screwed to the two sides of the strut 2 close to the head tube 3, while the tension wires 46', 46b' continue towards the stop blocks 48 and 48b welded to the two sides of the head 5a of the fork 5. The aforesaid tension wires are tenioned as needed such that a rotation towards the right of the handle 23 with respect to the arm 20, even by a small angle, makes the front wheel 6 rotate to the right, while a left rotation of the handle 23 makes the front wheel 6 rotate to the left. Figures 19 and 20 complete figure 18 with regard to the missing elements and also provide a perspective view from two different angles. With reference to the top view of figure 19, the handle 23 has a central body fixed to the upper end of the pin 22 (figure 20) and two lateral arms equipped with fixed grips 91 , 92 gripped by the user both in the propulsion maneuver (and freewheel return) and for steering the front wheel 6. In the straight line movement of the tricycle, the user pulls the handle 23 forward and pushes it back, always maintaining it or- thogonal to the two articulated arms 19 and 20, while in the right or left steering the handle 23 is rotated towards the right or towards the left. The two maneuvers can be completed together for imparting the propulsion during a curve or steering the freewheel tricycle. Adjacent to the fixed grips 91 and 92, two knurled grips 87 and 88 are present on the handle 23; such grips can rotate with sequential clicks for controlling the two derailleurs 37 and 34. Two levers 89, 90 of the two brakes acting on the front wheel 6 follow in the sequence, without excluding the possibility of alternatively using one of the two brakes on the rear wheels. The two fixing blocks 85 and 86 are more internally connected to the handle 23 with respect to the levers of the brakes. Such blocks can be disman- tied into three elements, two of which tighten with screws the respective arm of the handle 23 like a clamp, while the third element tightens, with four screws, the respective tension wires 46', 46b' against the more internal element of the clamp. Also noted in the figure are the ends of all the Bowden cables departing from the handle 23 which, by crossing each other (with the exception of the steering cables), reach the respective destination on the front wheel 6. Such cables complete those already described in figure 6 by constituting the following pairs therewith: 44, 45 (derailleurs); 46', 46b' (steering tension wires); 46, 46b (steering sheaths from plate 84); 40, 42 (brakes). The belt segment 25 unwound from the pulley 26, and then rewound, is fixed to the center of the handle 23 by means of two screws 94 and 95 which cross through a compression cover 93. The belt segment 25 of variable length continues beyond the fixing point in the fixed length segment 24 fixed to the carriage of the seat. The bottom view of figure 20 reports with greater three-dimensional emphasis the same elements of the preceding figure, where one notes in particular the mutual arrangement of the two articulated arms 19 and 20, the upper half-joint 55, the belt-press block 93, and a clip 96 that fastens around the articulated arm 19 and the Bowden cables running along it. Further clips fasten around the same cables running along the strut 2.

Figures 21 and 22 respectively show side and bottom views of the seat 16 and the carriage 15 that supports it and allows the translation thereof along the longitudinal member 1. With reference to both figures, one can note that the car- riage 15 is formed by two opposite rectangular plates 100 and 101 rigidly connected to the edges of an upper rectangular plate 102 of equal length; an anti- overturning structure 103 is also connected to the front end of the carriage 15. Six brackets inside the carriage 15, two-by-two adjacent, form three pairs of brackets respectively arranged on the two sides and at the center of the car- riage. The brackets type 104-105 of each pair are screwed to the upper plate 102, one to the lateral plate 100 and the other to the plate 101. At least two further screws 106 and 107 screw the seat 16 to the upper plate 102. The seat 16 is a table covered by a padding, arranged transverse to the carriage 15. Two external brackets 108, 109 connect the lateral plates 100 and 101 to the seat 16 by means of screws. Each of said plates has two rectangular windows obtained by milling, spaced from each other along the longitudinal axis, open towards two small external frames fixed with screws, respectively 1 1 1-112 for the plate 100, and 113-1 14 for the plate 101. The small frames support the vertical rotation pins of the same number of radial ball bearings, respectively 1 15, 1 16, 1 17, 1 18, which roll in contact with the lateral walls of the longitudinal member 1 during the movement of the carriage 15. Two ground pins 120 and 122 cross both the plates 100 and 101 at a short distance from the two ends and not far from the upper plate 102. The pins are maintained in place by rings of Sieger type. Each pin 120, 122 supports a series of four radial ball bearings rolling in contact with the upper wall of the longitudinal member 1 during the movement of the carriage 15. The seat 16 with the carriage 15 can then translate forward and backward on the longitudinal member 1 experiencing low friction and constantly maintaining the longitudinal trajectory. The problem of the separation of the carriage 15 from the longitudinal member 1 following abrupt rowing movements is resolved by the front anti-overturning structure 103. The latter comprises two opposite shoulders 126 and 127 laterally screwed to the plates 100 and 101 , respectively. The shoulders 126, 127 are two short bars that extend beyond the lateral plates 100, 101 towards the bottom. The projecting ends have greater thickness and are crossed by a fixed pin 128, at the center of which a radial ball bearing 129 is inserted placed between two cylindrical thicknesses 130 and 131. A screw 1 10 crosses through the upper plate 102 not far from the shoul- ders 126 and 127, also crossing through the end of the corresponding belt segment 24, at the continuation of the segment 25 beyond the handle 23 fixing point. A nut screwed to the screw 1 10 presses a washer against the belt segment 24, locking it against the small carriage 15. A certain margin should be left between the hole for the screw 1 10 and the end of the belt segment 24, so as to allow the possible execution of other holes beyond the first in order to accommodate users with different stature. As an alternative to the screw 1 10, it is possible to fix a pin between the lateral walls 100, 101 of the carriage 15 in order to enclose the end of the belt segment 24 by 180° and then fix the two parts by means of clips and screws, rivets or crimped connectors.

The connection between the seat 16 and the handle 23 is subject to several variants. A first variant consists of the use for connecting the seat to a belt physically separate from that used for the drawing exerted on the pulley 26. A first belt is equivalent to the current segment 25, a second shorter belt is equivalent to the current segment 24; the "free" ends of each of the two segments are su- perimposed on each other and are crossed [¾j the screws 94 and 95, which fix both ends to the handle 23. The advantage of this variant is that of allowing the substitution of the single shorter belt in case of wear. A second variant consists of the physical separation of the belt or belt segment which extends from the handle 23 to the carriage 15 into two pieces, and in joining together the two pieces by means of a buckle which allows the regulation of the length of the connection to the seat. The advantage of this variant is to be able to easily adapt the length of the seat connection to the height of different users.

The subsequent and final figures 23 and 24 are a detailed description of that part of the tricycle visible in figure 11. Figure 23 is an exploded view of a section along a plane passing through the center line of the housing 28 of figure 11 where, in order to simplify the drawing, both the belt 25 and the chain 31 were omitted, as was the pipe joint 9 that mounts the housing 28 on the stem 4 of the fork 5. Figure 24 reassembles on the pin 69 all the axial elements shown in figure 23. With reference to both figures, one can observe that the ends 69a and 69b of the pin 69 are of nearly frusto-pyramidal shape with blind holes threaded in axial direction for the screwing of a tightening screw with hexagonal head, respectively 140 and 141 with interposed washers 142 and 143. In the lower part of the housing 28 between the two plates 28a and 28b, the strong spacer pin 64 is observed, whose threaded ends 64a and 64b have a smaller diameter than the diameter of the remaining part. In the assembly of the housing 28, the two threaded ends 64a and 64b exit outward from respective holes 144 and 145 present close to the lower end of the plates 28a and 28b. The internally threaded ring nuts 65 and 66 are screwed to the aforesaid ends 64a and 64b, such that the shoulders of the spacer pin 64 inside the housing 28 abut against each other for the tightening. The ring nuts 65 and 66 are fixed with screws to the respective plates 28a and 28b, so as to prevent any possibil- ity of unscrewing. The pin 67, enlarged at the bottom of the figure, is a screw pin with hexagonal head that penetrates through two holes 146 and 147 present in the plates 28a and 28b just above the holes 144 and 145. The stem of the pin 67 is ground, except for a short segment at the end 67c which is threaded. Such stem has two suitably spaced sections 67a and 67b of smaller diameter for fa- cilitating the abutment and the transverse screwing of the vertical cylindrical supports 71 and 72. The threaded end 67c of the pin 67 exits from the relative hole in the plate 28a. The internally threaded ring nut 68 is screwed to the exit- ing end 67c and further locked by means of screws. Above the axis of the pin 67, the pin 75 is visible constituted by a screw whose stem is smooth except for a short segment at the end which is screwed inside the vertical cylindrical support 71. The hollow shaft 75a is free to rotate on the pin 75. The tightening of ring nuts and screws completes the assembly of the housing 28 for the drawing belt and the belt guide system which rests on the pin 67; after this, it is possible to complete the assembly of the remaining elements visible in figures 23 and 24.

In the upper part of the housing 28, the hardened steel pin 69 crosses the pulley 26 contained between the two plates 28a and 28b. The pulley is similar to a flat sprocket whose bases extend beyond the cylindrical wall welded between them; such wall encloses a cavity therein delimiting an external space for containing the belt 25 in the groove formed with the projecting shoulders, and an internal space for containing the circular box 70. The latter has the flat spring 27 at its interior, spiral-coiled on itself in the same winding direction as the belt 25. The box 70 is coaxial with the pulley 26 and it too is crossed by the pin 69. One base of the pulley 26 has a wide circular opening that allows the entrance of the box 70 into the internal cavity, while the other base is mainly closed. The circular box 70 is open on one side to allow the placement and coiling of the spring 27, while the base wall has a wide axial hole for the insertion of a freewheel bearing 156, it too inserted on the pin 69, and other elements that will be mentioned hereinbelow.

The ground cylindrical body of the pin 69 is supported by radial ball bearings, respectively 148 and 149, inside two respective ring nuts 150 and 151 that are externally threaded for the entire length and screwed inside two respective cylindrical boxes 152 and 153 and equipped with a flanged end, 152a and 153a, forming a single body with the remaining cylindrical body of smaller diameter. The cylindrical boxes 152 and 153 are inserted in two respective holes 154 and 155 present close to the upper end of the plates 28a and 28b, with their project- ing edge placed inside the housing 28 and locked with screws against the plates 28a and 28b. The pin 69 has a collar 69c between the cylindrical body and the prismatic end 69b. On said cylindrical body of the pin 69, at a pre- established distance from the collar 69c, there is an edge in relief 69d acting as an abutment for the freewheel bearing 156. Collar 69c and edge 69d are integral parts of the pin 69. The freewheel bearing 156 is housed inside a suitable cylindrical container 157 coaxial with the pin 69. The container 157 has a flanged end 157a forming a single body with the remaining cylindrical part of smaller diameter. The container 157 is placed inside the pulley 26 with its flanged end 157a between the base of the pulley 26 and the base of the box 70, and the remaining portion inside the box 70. Pulley 26, flanged end 157a, and box 70 are tightened together by means of screws and nuts. A cylindrical spac- er 158 is inserted on the central pin 69 between the freewheel bearing 156 and the radial bearing 148, so as to prevent the residual chance of axial sliding of the bearing 156. In order to prevent friction, the spacer 158 interposed between the two bearings does not touch them.

The pin 69 and the internal ring of the bearing 156 are coupled together in a very precise manner, such that the unidirectional rotation of the internal ring is transmitted to the shaft 69 without any loss due to friction. Similarly, the external ring of the bearing 156 is coupled in a very precise manner to its seat in the cylindrical container 157, such that the bidirectional rotation of the pulley 26 is transmitted to the external ring of the bearing 156 without losses via friction. It will be the coupling between the two rings to select a single rotation direction at the outlet of the bearing 156 on the shaft 69, and specifically the counterclockwise direction (as seen by the user) of the rotation imparted to the pulley 26 by drawing the belt segment 25 so as to extract it from the groove containing it. The opposite (clockwise) rotation of the pulley 26 occurs freewheel, since it has no affect on the transmission of the motion to the front wheel 6. Such rotation is imparted by the flat spring 27 that has the more external end (movable point B) fixed to the box 70 and the more internal end (fixed point A) fixed to the box 152 inserted in the plate 28a of the housing 28. One such connection of the spring 27, coiled in the same direction as the winding of the belt 25, allows load- ing the spring during the unwinding of the belt 25 by the pulley 26, and coupling the elastic return of the spring 27 to the pulley 26 in order to make it rotate in the opposite direction, rewinding the belt 25. The details of the spring 27 con- nection just described will be illustrated further on, while the parts outside the housing 28 are illustrated in the following paragraphs.

As can be observed in figures 23 and 24, the bearing 149 on the chain drive side, unlike the radial bearing 148 on the opposite side, lacks internal and ex- ternal rings and therefore the housing is the only ball containment element. The use of a free bearing has advantages in cases like the present, in which the radial loads do not prevail with respect to the axial loads (which are particularly manifested during curves). In order to be coupled to the bearing 149, the edge between the collar 69c and the tapered end 69b of the pin 69 has a concave profile complementary to the convex profile of the balls, and the same concave profile is applied to the internal edge of the ring nut 151.

The crankset of the sprocket wheels 29, 30 is inserted on the end 69b of the pin 69; for such purpose, the spokes 29a converge in a hub having an axial hole 29b of the same tapered prismatic shape as the end 29b but shorter. The screwing of the screw 141 axially pushes the crankset of the sprocket wheels 29, 30 inward, until it is locked against the end 69b, making the crankset integral with the pin 69 also with regard to rotation. The opposite end 69a of the pin 69 supported by the radial bearing 148 does not provide for any coupling; it projects from the cylindrical box 152 for about half the length of the tapered profile, making it available for future uses.

Returning to the connection points of the spring 27, one notes in figure 23 that the spring has a hole B close to one end and a longitudinal slot A close to the opposite end. In association with the hole B, the lateral wall of the box 70 has a slot 160 parallel to the axis and open on the edge, on the spring 27 inlet side. With reference to the enlargement on the top right, the fixing of a first end of the spring 27 to the box 70 requires the presence of an element 161 simultaneously inside the hole B of the spring and the slot 160 of the box 70. The element 161 is a small internally-threaded bushing, of diameter nearly equal to the diameter of the hole B except for the upper edge exceeding the width of the slot 160. A circumferential slot 162 is obtained at the opposite end of the small bushing 161 for the insertion of the spring 27. A screw tightens the edge of the small bushing 161 against the wall of the box 70 at the slot 160, locking the more external end of the spring (movable point B) against the rotatable box 70.

The fixing of the other end of the spring 27 (fixed point A) to the housing 28 employs two small cylinders 163 and 164, the second inside the first, placed inside the box 70 in a non-aligned position and not fixed thereto. Two short screws with flared head 166 and 167 transversely penetrate the two small cylinders, locking them together. The small internal cylinder 164 is beveled and has an axial through hole threaded for the passage of a screw 170 that fixes the box 152 to the plate 28a. The small external cylinder 163 has two adjacent tabs 165 that are detached from a lateral wall and diverge on opposite sides transverse to the longitudinal axis, bending up to about 180° in order to create a seat within which the slot A at the fixed end of the spring 27 comes to be fit.

The assembly procedure of the bottom bracket and the crankset of the sprocket wheels 29, 30 employs the following steps:

1 . The two plates 28a and 28b are tightened against the two ends of the lower fixed pin 64 and the pin 67 is assembled with the belt-guide mechanism. In such a manner, the housing 28 is ready for the abovementioned assembly.

2. The cylindrical boxes 152 and 153 are mounted on the respective plates 28a and 28b.

3. The unidirectional bearing 156 is pressed into its container 157, making sure not to damage it in the process.

4. The spring 27 is mounted in the box 70. First, the movable end of the spring 70 (point B) is fixed to the box 70 as stated above; then, the spring 27 will be completely coiled in anticlockwise direction and the other end of the spring (fixed point A) will be joined to the body of the two small cylinders 163, 164 which will subsequently be fixed to the housing 28.

5. The following are fixed to each other by means of screws and nuts to form a single body: the box 70 containing the spring 27 and the small cylinders 163 and 164, the container 157 with the freewheel bearing 156 therein, and the pulley 26. The assembly thus formed is inserted between the plates 28a and 28b in axial alignment with the boxes 152 and 153.

6. The pin 69 of the bottom bracket is inserted in the box 153 and it is made to continue through the freewheel bearing 156 until it abuts against the edge 69d.

7. The spacer 158 is inserted on pin 69.

8. The left and right bearings 148 and 149 are inserted on the pin 69.

9. The two respective ring nuts 150 and 151 are screwed into the boxes 152 and 153.

10. The small cylinders 163 and 164 are screwed to the box 152, such cylinders connected to the fixed end of the spring 27 by means of the tongues 165.

11. The crankset of the sprocket wheels 29, 30 is inserted on the end 69b of the pin 69 and it will be locked by tightening the screw 141 with interposed washer 143.

12. The screw 140 with interposed washer 142 is tightened to the other end 69a of the pin 69.

Based on the description provided for a preferred embodiment, it is clear that some changes can be introduced by the man skilled in the art, without departing from the scope of the invention as results from the following claims.