WO2021094944A1

WO2021094944A1 - Wheel for electric bicycles

Info

Publication number: WO2021094944A1
Application number: PCT/IB2020/060617
Authority: WO
Inventors: Adriano Zanfei
Original assignee: C R D Centro Ricerche Ducati Trento Srl
Current assignee: C R D Centro Ricerche Ducati Trento Srl
Priority date: 2019-11-12
Filing date: 2020-11-11
Publication date: 2021-05-20
Anticipated expiration: 2022-05-12
Also published as: EP4058345A1; IT201900021003A1

Abstract

The wheel (1) for electric bicycles comprises: - a fixed structure (2); - a rim structure (6) comprising: - a central box- shaped element (7); - an outer rim (11); and - a plurality of tie-rods (13) for the connection of the central box- shaped element (7) to the outer rim (11); - an electric motor (14, 15); wherein the central box-shaped element (7) comprises: - at least one shell (8, 9) provided with a main opening (16) for the access to the inside of the central box- shaped element (7); and - at least one closing cover (10) for closing the main opening (16) as sociable with the shell (8, 9); wherein the tie-rods (13) are associated with the central box-shaped element (7) only at the point where the shell (8, 9) is located.

Description

WHEEL FOR ELECTRIC BICYCLES

Technical Field

The present invention relates to a wheel for electric bicycles.

Background Art

In the context of the present discussion, the term “electric bicycles” relates to all types of bicycles provided with an electric motor associated with one of the wheels to release a driving force that is added to and/or replaces the user’s pedal stroke.

Electric bicycles are also widely referred to as pedal-assisted bicycles which, according to the definition provided by the European Directive 2002/24/CE, consist of bicycles provided with an auxiliary electric motor having the following characteristics: maximum continuous rated power of the electric motor: 0.25 kW; motor power supply progressively reduced and then cut off when it reaches

25 km/h; motor power supply cut off before 25 km/h if the cyclist stops pedaling.

The electric motor is controlled by a processing and control unit that manages the power supply thereof according to the user’s pedal stroke, thus balancing the insertion of the propulsion in a progressive manner from the beginning of the pedal stroke, in order to make it smooth and regular.

For this purpose, pedal-assisted bicycles are usually provided with a torque sensor arranged at the pedals or with a speed sensor located in the crank arm, or both.

In the traditional pedal-assisted bicycles, the electric motor is housed directly in the hub of the motorized wheel and is powered by means of a battery pack which, on the other hand, is mounted on the frame of the bicycle.

In other cases, the driving unit is housed on the frame itself, in the crankset area, with appropriate technical precautions to allow the installation thereof. This type of approach is not retro-fittable on common bicycles.

Taking into account the need to provide the bicycle with all the above mentioned components in order to perform different functions, traditional assisted pedaling systems are usually conceived since their design phase to be installed on a specific bicycle model.

Only rarely, in fact, is it possible to develop kits which are able to adapt to more than one model of bicycle, taking into account the considerable diversity among the bicycles on the market, in particular their frames which, obviously, have such different shapes and sizes to prevent a practical and complete standardization of the assisted pedaling systems.

It should also be emphasized that the application of a kit for pedal-assisted bicycles in the after-sales phase, even if possible, usually requires the execution of uncomfortable and impractical operations of adjustment and fixing to the frame of the various components, which most often cannot be performed by the end user and require the intervention of an expert technician.

In order to overcome at least in part the above mentioned drawbacks, it is known to add, in the motorized wheel, not only the electric drive motor but also the battery pack, the torque sensor and the derailleur.

Some particular types of wheels for pedal-assisted bicycles are shown in patent documents W02012/123800A1, WO2012/123801 Al, WO2012/123802A1 and WO2014/174403A1.

For the housing of the electric motor and, if necessary, of the battery pack, the torque sensor and the derailleur, the traditional wheel hubs are usually designed so as to have two hollow half- shells that can be coupled to each other in order to define a central box- shaped element which is disc- shaped or cylinder- shaped.

On the peripheral edge of the hub are mounted the spokes or tie-rods of the wheel, which connect the hub to the rim carrying the tyre; more specifically, some spokes are mounted on one of the half- shells while other spokes are mounted on the other half-shell.

Each type of wheel has its own system for fixing the spokes to the hub; the free ends of the spokes, on the other hand, are almost always connected to the rim of the wheel by means of nipples, i.e. threaded nuts that can be rotated to pull the spokes to the desired tension level.

The wheels for electric bicycles of traditional type do have some drawbacks. First of all, we would like to point out that, whenever maintenance work is required on the electric motor or on the electronic circuitry of the wheel, it is inconveniently necessary to separate one half-shell from the other to access the inside of the hub. This operation is very complex and time consuming.

The operation is particularly slow because it is necessary to remove the spokes from the wheel; in other words, to open the half-shells it is necessary to remove all, or almost all, the spokes first, and then reassemble these once the operation inside the hub is finished. In addition, the systems for fixing the spokes to the hub are not always practical and functional.

These fixing systems, in fact, must necessarily ensure a high degree of clamping of the spokes and mechanical resistance, to withstand the tensioning of the spokes themselves. It follows that traditional hubs are usually made of robust materials (i.e. metal), have rather high manufacturing costs and are particularly heavy, worsening the rideability of bicycles and making the wheels of known type less attractive to customers.

Description of the Invention The main aim of the present invention is to devise a wheel for electric bicycles in which the maintenance operations inside the wheel can be carried out in a practical, easy, functional manner and in a very short time.

A further object of the present invention is to devise a wheel for electric bicycles that is strong and resistant but also very light. Another object of the present invention is to devise a wheel for electric bicycles that is cheap, highly rideable and appreciated by customers.

Another object of the present invention is to devise a wheel for electric bicycles that allows overcoming the above mentioned drawbacks of the prior art within a simple, rational, easy and effective solution, as well as of simple and quick assembly.

The above mentioned objects are achieved by the present wheel for electric bicycles having the characteristics of claim 1.

Brief Description of the Drawings

Other characteristics and advantages of the present invention will be more evident from the description of a preferred, but not exclusive, embodiment of a wheel for electric bicycles, illustrated by way of an indicative, yet non-limiting example, in the attached tables of drawings in which:

Figure 1 is an axonometric view of the wheel according to the invention;

Figure 2 is an axonometric, partly broken view, from another angle, of the wheel according to the invention;

Figure 3 is an exploded view of the central box- shaped element of the wheel according to the invention;

Figure 4 is an axonometric view of a detail of the wheel according to the invention;

Figure 5 is a sectional view of a barrel element of the wheel according to the invention;

Figure 6 is a sectional view of a barrel element and of a tie-rod of the wheel according to the invention;

Figure 7 is an axonometric view of an alternative embodiment of the barrel elements of the wheel according to the invention.

Fmbodiments of the Invention

With particular reference to these figures, reference numeral 1 globally indicates a wheel for electric bicycles.

The wheel 1 comprises at least one fixed structure 2, provided with attachment means for attaching to the frame of a bicycle.

The fixed structure 2, e.g., consists of an axle provided with a first end 3 and with a second end 4 that can be attached to the fork of the bicycle in a familiar way.

The wheel 1 also comprises at least one rim structure 6 comprising: a central box-shaped element 7, assembled on the fixed structure 2 in a rotatable manner around a main axis of rotation R; an outer rim 11, supporting a tyre 12 for the running of the bicycle onto the ground; and a plurality of tie-rods 13, or spokes, for the connection of the central box shaped element 7 to the outer rim 11.

Inside the central box- shaped element 7 at least one electric motor 14, 15 is housed for the motorization of the rim structure 6 with respect to the fixed structure 2; as better described below, inside the central box-shaped element 7 there can also be other electric and electronic components required for the operation of the electric motor 14, 15.

The central box-shaped element 7 comprises: - at least one shell 8, 9 provided with a main opening 16 for the access to the inside of the central box-shaped element 7; and at least one cover 10 for covering and closing the main opening 16, which is associable with the shell 8, 9 between a closure configuration and an opening configuration. The tie-rods 13 are associated with the central box-shaped element 7 only at the shell 8, 9; in other words, the cover 10 is not directly associated with the tie- rods 13 and it is possible to separate it from the shell 8, 9 to access to the inside of the central box- shaped element 7 without removing the spokes of the wheel

1. Advantageously, the central box-shaped element 7 is substantially disc-shaped, with axis of symmetry coinciding with the main axis of rotation R and lying on a substantially median lying plane of the wheel 1; in other words, when the cover 10 is arranged in a closure configuration, the shell 8, 9 and the cover 10 take on the shape of a disc, which allows making optimal use of the space inside it to house the electric motor 14, 15 and, at the same time, ensuring an aerodynamic shape to the wheel 1.

In the particular embodiment shown in the figures, the shell 8, 9 comprises: at least a first half- shell body 8 provided with the main opening 16 and with a first connecting edge 17; - at least a second half-shell body 9 provided with a second connecting edge

18 which couples substantially mating to the first connecting edge 17, to define the shell 8, 9.

In the particular embodiment shown in the figures, the shell 8, 9 is made of only two pieces (i.e. the first half-shell body 8 and the second half-shell body 9) intended to be assembled with each other; this embodiment is particularly convenient from the productive point of view, because, this way, it is possible to manufacture the shell 8, 9 in a practical, easy and extremely cheap manner. Alternative embodiments cannot however be ruled out wherein the shell 8, 9 is made in a single body piece or by assembly of three or more parts.

Conveniently, when paired together, the first connecting edge 17 and the second connecting edge 18 lie on the substantially median lying plane of the wheel 1 orthogonal to the main axis of rotation R.

In other words, the first connecting edge 17 and the second connecting edge 18 are circular and mate from opposite sides of the substantially median plane of the wheel 1.

For the connection of the first connecting edge 17 to the second connecting edge 18, the wheel 1 is provided with threaded linking means 19.

The threaded linking means 19 consist e.g. of screws that can be inserted in through holes made on the first half- shell body 8 and screwed inside blind holes 20 made on the second half- shell body 9.

Advantageously, the main opening 16 is circular, it is substantially concentric to the main axis of rotation R and has a diameter that is more than 50% of the outer diameter of the central box- shaped element 7, preferably more than 65%, better still more than 90%; it follows that the first half-shell body 8 has a substantially ring shape and the main opening 16 is very large compared to the outer diameter of the central box- shaped element 7.

This way, when the cover 10 is opened, it is possible to easily access to almost all the space inside the central box- shaped element 7.

The second half- shell body 9 comprises a secondary opening 21 which is placed around the fixed structure 2, e.g. in the proximity of the first end 3 of the axle (Figure 1).

The secondary opening 21 is circular, is substantially concentric to the main axis of rotation R and has a diameter which is less than 50% of the outer diameter of the central box-shaped element 7, preferably less than 30%, better still less than 15%.

It follows that the secondary opening 21 is rather narrow compared with the outer diameter of the central box- shaped element 7 and, at the secondary opening 21, the second half- shell body 9 can advantageously lean on one or more turning bearings of small size and particularly cheap, not shown in the figures.

The cover 10 is substantially shaped as a circular plate and comprises an outer circular edge 22 which can couple substantially mating to the main opening 16 and an inner circular edge 23 which, in the closure configuration, is substantially concentric to the main axis of rotation R and can be placed around the fixed structure 2, e.g. in the proximity of the second end 4 of the axle (Figure 2). The outer circular edge 22 has substantially the same diameter as the main opening 16.

The inner circular edge 23, on the other hand, has a diameter that is less than 50% of the outer diameter of the central box-shaped element 7, preferably less than 30%, better still less than 15%. It follows that also the inner circular edge 23 is rather narrow compared to the outer diameter of the central box- shaped element 7 and, when the cover 10 is in the closure configuration, it can advantageously lean on one or more small-sized and particularly cheap turning bearings, not shown in the figures.

Conveniently, the wheel 1 also comprises threaded joining means 24 for the removable connection of the cover 10 to the shell 8, 9.

The threaded joining means 24 consist, e.g., of screws that can be inserted in through holes obtained on the cover 10 and screwed inside the blind holes 25 made on the first half- shell body 8.

After the threaded linking means 19 have been removed, the cover 10 can be separated from the shell 8, 9, in particular from the first half-shell body 8, by pulling the inner circular edge 23 out of the second end 4 of the axle. The central box- shaped element 7 is advantageously made of plastic.

In other words, the first half-shell body 8, the second half-shell body 9 and the cover 10 are made of plastic, which makes the central box- shaped element 7 and, more generally, the wheel 1 very light. As said, inside the central box- shaped element 7 is housed the electric motor 14, 15 and, if necessary, also other electric and electronic components required for the operation of the electric motor 14, 15.

The electric motor 14, 15 comprises a stator 14 and a rotor 15.

The stator 14 is composed, e.g., of a series of electric windings fixed to a support 26 keyed onto the fixed structure 2.

The rotor 15, on the other hand, is composed, e.g., of a series of permanent magnets fixed to the inner surface of the shell 8, 9; Figure 3 shows some of the permanent magnets as examples.

The electric windings are powered by an electric current generated by a series of batteries 27, also mounted on the support 26 and housed inside the central box shaped element 7; the excitation of the electric windings generates a magnetic field that induces a force on the permanent magnets which sets the rim structure 6 in rotation around the main axis of rotation R.

For the switching on and off of the electric motor 14, 15 and, more generally, for the management of the various electronic functions of the wheel 1 , the latter comprises a processing and control unit 28, which is operationally connected to the electric motor 14, 15, is housed inside the central box-shaped element 7 in the proximity of the main opening 16 and is accessible from the outside when the cover 10 is arranged in the opening configuration. In the particular embodiment shown in the figures, the processing and control unit 28 advantageously consists of an electronic plate- shaped board.

The electronic board is fixed to the support 26 so that it lies on a plane substantially orthogonal to the main axis of rotation R on one side of the wheel 1 facing the main opening 16 and the cover 10. After the cover 10 has been removed, therefore, the processing and control unit 28 is easily accessible from the outside, which is considerably advantageous in the light of the fact that the processing and control unit 28 is one of the components that may require maintenance and updating operations.

The processing and control unit 28 is conveniently associated with at least one light signal source 29 which is housed inside the central box- shaped element 7 and which, for example, is adapted to signal the operating status of the wheel 1 ; the central box-shaped element 7, therefore, comprises at least one at least partly transparent window 30 which is adapted to allow the display of the light signal source 29 outside the central box- shaped element 7.

The light signal source 29 consists, e.g., of a LED; the switching on and off of the LED, its possible intermittence and/or its coloring (in case of LED able to change color) allow signaling whether the system is working and/or other operating conditions thereof.

Preferably, the wheel 1 comprises a plurality of light signal sources 29 and a plurality of windows 30, the light signal sources 29 and the windows 30 being sized and arranged at such mutual distances to always allow displaying at least one of the light signal sources 29.

In the particular embodiment shown in the figures, the light signal sources 29 are present in a number of three and the windows 30 are arranged in succession along a circumference which is concentric to the main axis of rotation R. During the setting in rotation of the wheel 1, in actual facts, the windows 30 allow looking at a corresponding circumference inside the central box-shaped element 7 along which the light signal sources 29 are arranged.

The windows 30 are interspersed with each other with non-transparent portions 31, which prevent the light signal sources 29 from being viewed. The extension of the windows 30 is substantially double the mutual distance between two consecutive light signal sources 29 while the extension of the non transparent portions 31 is less than the mutual distance between two consecutive light signal sources 29; this means that at least two light signal sources 29 are always visible from the outside. It is easy to understand, however, that alternative embodiments are possible in which there is a different number of light signal sources 29. The first half- shell body 8 and the second half- shell body 9 comprise outer peripheral surfaces 32, 33 to which the tie-rods 13 are connected.

In particular, a first group of tie-rods 13 is associated with the outer peripheral surface 32 of the first half-shell body 8, while a second group of tie-rods 13 is associated with the outer peripheral surface 33 of the second half-shell body 9. The tie-rods 13 comprise an enlarged head 34 for the connection to the central box-shaped element 7, a nipple element 35 for the connection to the outer rim 11, and a small rod 36 connecting the enlarged head 34 to the nipple element 35. The nipple elements 35 couple to the outer rim 11 and can be rotated to set the tie-rods 13 in tension in a familiar manner.

To join the enlarged heads 34 to the central box-shaped element 7, on the other hand, the wheel 1 comprises a plurality of barrel elements 37, which can be coupled to the enlarged head 34 of the tie-rods 13 and which comprise an outer lateral surface 38, the central box-shaped element 7 comprising a plurality of hollow seats 39 provided with an inner lateral surface 40 wherein the barrel elements 37 can be housed with the lateral surfaces 38, 40 substantially mating each other.

Advantageously, the outer lateral surface 38 of the barrel elements 37 and the inner lateral surface 40 of the hollow seats 39 are substantially cylindrical with a circular cross-section.

In the context of the present description, the expression “substantially cylindrical” means that the lateral surfaces 38, 40 are perfectly cylindrical unless small variations (i.e. less than 10%) with respect to a reference diameter. Figure 4, for example, shows a first embodiment of the barrel elements 37 in which the outer lateral surface 38 is perfectly cylindrical, as well as the inner lateral surface 40 of the hollow seats 39; the barrel elements 37 are coupled by interlocking in the hollow seats 39 with a slight interference.

Figure 7, instead, shows an alternative embodiment of the barrel elements 37 wherein the outer lateral surface 38 has protruding ribs 41 and, in accordance with what has been said above, it is still considered substantially cylindrical and coupled substantially mating with the inner lateral surface 40 of the hollow seats 39 shown in Figure 4; the protruding ribs 41, in actual facts, facilitate and improve the coupling by interlocking between the lateral surfaces 38, 40. Alternative embodiments cannot however be ruled out wherein the lateral surfaces 38, 40 are not substantially cylindrical with a circular cross-section but rather have a prismatic shape.

Conveniently, the barrel elements 37 comprise: a central axis A1 of the outer lateral surface 38; and a transverse passage 42, 43 which is made from one side to the other of the outer lateral surface 38 transversely to the central axis A1 of the outer lateral surface 38 and in which one of the tie-rods 13 can be inserted.

In the embodiments of the barrel elements 37 shown in the figures, wherein the outer lateral surfaces 38 are substantially cylindrical with a circular cross- section, the central axis A1 of the outer lateral surface 38 coincides with the axis of symmetry of the cylinder.

Advantageously, the barrel elements 37 also comprise: a through hole 44 extending along the central axis A1 of the outer lateral surface 38; and two inlets 42, 43 formed from parts which are diametrically opposite with respect to the central axis A1 of the outer lateral surface 38 and defining the transverse passage 42, 43.

In other words, the barrel elements 37 are internally hollow, which makes it possible to obtain a particularly lightweight construction solution, the mechanical strength of the barrel elements 37 being equal.

Different technical solutions cannot however be ruled out wherein the through hole 44 is not present and the barrel elements 37 are full, unless the transverse passage 42, 43.

Conveniently, the inlets 42, 43 comprise: a first inlet 42 provided with a resting surface 45 which is adjacent to the outer lateral surface 38 and adapted to receive and hold the enlarged head 34 of the tie-rods 13; a second inlet 43 adapted to allow the passage of the small rod of the tie- rods 13.

The enlarged head 34 of the tie-rods is substantially conical in shape and the resting surface 45 is at least partly conical- shaped and substantially complementary to the enlarged head 34.

In the context of the present description, the expression “substantially conical” means that the enlarged head 34 is perfectly conical unless small variations (i.e. less than 10%) with respect to a perfectly conical surface.

Preferably, the enlarged head 34 has one or more reliefs 46 protruding from the conical surface and the tie-rods 13 are made of a harder material than the barrel elements 37; thus, when the tie-rods 13 are set in tension by means of the nipple elements 35, the reliefs 46 sink into the softer material of the barrel elements 37 and make corresponding grooves in the resting surface 45.

The reliefs 46 and the grooves thus obtained, in actual facts, define an anti- rotational system that prevents the tie-rods 13 from rotating around their longitudinal direction, allowing them to continue tensioning the tie-rods 13 by rotating the nipple elements 35.

Preferably, both the tie-rods 13 and the barrel elements 37 are made of metal; the tie-rods 13, for example, are made of steel while the barrel elements 37 are made of a softer material than steel, e.g. aluminum or brass.

Conveniently, the hollow seats 39 comprise a central axis A2 of the inner lateral surface 40 defining a direction of insertion and removal of the barrel elements 37 in the hollow seats 39.

In the embodiment of the hollow seats 39 shown in the figures, in which the inner lateral surfaces 40 are substantially cylindrical with a circular cross- section, the central axis A2 of the inner lateral surface 40 coincides with the axis of symmetry of the corresponding cylinder.

To insert the barrel elements 37 into the hollow seats 39 correctly, in actual facts, it is sufficient to align the central axes Al, A2 to each other and to couple the lateral surfaces 38, 40 by interlocking.

The hollow seats 39 are advantageously obtained on the central box- shaped element 7 so that the central axes Al, A2 of the inner lateral surfaces 40 are all substantially parallel to the main axis of rotation R.

This device makes it possible to orient all the hollow seats 39 in the same direction and without undercuts, which is a necessary condition to allow the manufacture of the half-shell bodies 8, 9 inside plastic injection molding moulds.

The hollow seats 39 also conveniently comprise a lateral groove 47 connected to the inner lateral surface 40 and wherein the small rod 36 of the tie-rods 13 can be partly housed.

The lateral grooves 47 are oriented along directions that deviate from the main axis of rotation R and define the direction of exit of the tie-rods 13 from the barrel elements 37 and from the hollow seats 39, i.e. the connecting direction of the tie-rods 13 between the central box- shaped element 7 and the outer rim 11.

It has in practice been ascertained that the described invention achieves the intended objects. In this regard, it should be noted that the particular device of providing a shell and a cover, in which the tie-rods are associated only with the shell and not with the cover, allows opening the central box-shaped element without removing the spokes from the wheel and then carrying out the maintenance work inside it in an extremely fast and practical manner. In addition to this, the particular device of providing the barrel elements and the hollow seats to which the present invention relates, makes it possible to distribute the tensioning force of the tie-rods on their lateral surfaces and thus to obtain a particularly strong and resistant central box- shaped element even if made of a very light material such as plastic.

Claims

1) Wheel (1) for electric bicycles, comprising: at least one fixed structure (2), provided with attachment means for attaching to the frame of a bicycle; at least one rim structure (6) comprising: a central box-shaped element (7), assembled on said fixed structure (2) in a rotatable manner around a main axis of rotation (R); an outer rim (11), supporting a tyre (12); and a plurality of tie-rods (13) for the connection of said central box- shaped element (7) to said outer rim (11); at least one electric motor (14, 15) housed inside said central box- shaped element (7) for the motorization of said rim structure (6) with respect to said fixed structure (2); characterized by the fact that said central box-shaped element (7) comprises: at least one shell (8, 9) provided with a main opening (16) for the access to the inside of said central box-shaped element (7); and at least one cover (10) for closing said main opening (16) associable with said shell (8, 9); wherein said tie-rods (13) are associated with said central box-shaped element (7) only at the point where said shell (8, 9) is located.

2) Wheel (1) according to claim 1, characterized by the fact that said central box-shaped element (7) is made of plastic.

3) Wheel (1) according to one or more of the preceding claims, characterized by the fact that said central box- shaped element (7) has a substantially disc shaped conformation.

4) Wheel (1) according to one or more of the preceding claims, characterized by the fact that said shell (8, 9) comprises: at least a first half-shell body (8) provided with said main opening (16) and with a first connecting edge (17); at least a second half- shell body (9) provided with a second connecting edge (18) which can be coupled substantially mating to said first connecting edge (17).

5) Wheel (1) according to one or more of the preceding claims, characterized by the fact that said first half-shell body (8) and said second half-shell body (9) comprise outer perimeter surfaces (32, 33) to which said tie-rods (13) are connected.

6) Wheel (1) according to one or more of the preceding claims, characterized by the fact that said second half- shell body (9) comprises a secondary opening (21) which can be placed around said fixed structure (2).

7) Wheel (1) according to one or more of the preceding claims, characterized by the fact that said cover (10) is shaped substantially like a circular plate and comprises a circular outer edge (22) which can be coupled substantially mating to said main opening (16) and a circular inner edge (23) that can be positioned around said fixed structure (2).

8) Wheel (1) according to one or more of the preceding claims, characterized by the fact that it comprises a processing and control unit (28) which is operationally connected to said electric motor (14, 15), is housed inside said central box- shaped element (7) in the proximity of said main opening (16) and is accessible from the outside when said cover (10) is arranged in an opening configuration. 9) Wheel (1) according to one or more of the preceding claims, characterized by the fact that said processing and control unit (28) is associated with at least one light- signaling source (29) housed inside said central box-shaped element (7), said central box-shaped element (7) comprising at least one small window (30) at least partly transparent adapted to allow the display of said light- signaling source (29) outside of said central box-shaped element (7).

10) Wheel (1) according to one or more of the preceding claims, characterized by the fact that it comprises a plurality of said light- signaling sources (29) and a plurality of said small windows (30), said light- signaling sources (29) and said small windows (30) being sized and arranged at such mutual distances so as to always permit the display of at least one of said light- signaling sources (29).