Field of Invention

[0001] The present invention generally finds application in the field of drive members for human-propelled vehicles, and particularly relates to a crank assembly for bicycles and pedal-operated machines.

Background art

[0002] Drive members have been long known, which are operated by a user to transfer a torque to one of the wheels of the vehicle, generally the rear wheel.

[0003] Typically a drive mechanism or assembly is used, in which a pair of levers or radial cranks are provided at the ends of pedals designed to be powered by a user. The cranks are mutually connected by an element, typically known as bottom bracket, having an axial spindle mechanically connected to the cranks.

[0004] The axial spindle is designed to be inserted into a cylindrical bushing associated with the bicycle frame and is supported by one or more ball bearings, which allow its free rotation about its axis.

[0005] One or more chainrings are typically fixed to the same spindle at one of the cranks, and are designed to interact with a chain for transferring the torque generated by the user to a cogset which attaches to the drive wheel of the vehicle.

[0006] A result of this arrangement is that the torque applied to the cranks exerts a considerable torsional stress on the spindle, which may cause friction and reduce the life of the assembly.

[0007] This torsional stress is also increased by the relatively small diameter of the spindle of the bottom bracket, and further affects the efficiency of the assembly.

[0008] In an attempt to obviate these drawbacks, bicycle crank assemblies have been developed which have no bottom bracket and no spindle.

[0009] Particularly, crank assemblies are known, in which each crank has tubular end portions inserted in the bore of the frame. [0010] The tubular end of each crank has coupling members, i.e. pins designed to be introduced into appropriate holes formed at the tubular end of the other crank, which are adapted to transfer to the ring gear the rotational motion generated by applying torque to the cranks.

[0011] Since the coupling members are at a relatively small distance from the axis of the hole, this solution only partially reduces the efficiency loss caused by the torsional stress applied at the connection of the tubular ends.

[0012] Furthermore, these crank assemblies are composed of a great number of parts, and require relatively long manufacturing times and a particularly accurate assembly process, which will increase manufacturing and maintenance costs.

[0013] Also, the drive chainring is fixed to one of the portions by a bushing located outside the corresponding tubular end.

[0014] As a result, the presence of this bushing makes chainring replacement difficult, whenever the chainring is broken or has to be replaced to change gear ratios.

Disclosure of the invention

[0015] The object of the present invention is to overcome the above drawbacks, by providing a crank assembly for bicycle and pedal-operated machines that is highly efficient and relatively cost-effective.

[0016] A particular object is to provide a crank assembly for bicycles and pedal-operated machines that is particularly strong and capable of resisting torsional stresses and wear.

[0017] A further object is to provide a crank assembly for bicycles and pedal-operated machines that has a particularly simple structure, affording very quick assembly.

[0018] A particular object is to provide a crank assembly for bicycles and pedal-operated machines that is composed of a very small number of parts, to reduce manufacturing and maintenance costs.

[0019] Another important object of this invention is to provide a crank assembly for bicycles and pedal-operated machines, whose parts are easily replaceable as needed by the user. [0020] These and other objects, as better explained hereafter, are fulfilled by a crank assembly for bicycles and pedal-operated machine as defined in claim 1 , which comprises a pair of substantially identical cranks, each having a substantially tubular hub with a substantially radial lever extending therefrom, at least one chainring fixed to a drive crank of said pair, and wherein said cranks are coupled by means of tubular hubs that are concentric with a common axis of rotation and with said radial levers extending on opposite sides from said common axis.

[0021 ] The assembly is characterized in that each of the hubs has a substantially annular connecting portion along a peripheral rim, which is uniformly and integrally joined with a respective lever. The connecting portion of said drive crank is designed to fix said at least one chainring, such that the torque applied to said levers is directly transferred to said at least one chainring exclusively through said connecting portion, thereby reducing torsional stresses and increasing the stiffness of the assembly.

[0022] Thanks to this combination of features, the crank assembly of the invention will be stiffer than prior art assemblies, thus considerably reducing the efficiency loss caused by the torsional stresses generated at the connection between the hubs.

[0023] The small number of parts will facilitate assembly and maintenance, as well as chainring replacement.

[0024] Advantageous embodiments of the invention are defined in accordance with the dependent claims.

Brief description of the drawings

[0025] Further features and advantages of the invention will become more apparent from the detailed description of a few preferred, non-exclusive embodiments of a crank assembly for bicycles and pedal-operated machines according to the invention, which are described as non limiting examples with the help with the accompanying drawings in which:

FIG. 1 is a front view of a first embodiment of the crank assembly of the invention;

FIG. 2 is a lateral sectional view of the assembly of FIG. 1 , as taken along a plane //-//;

FIG. 3 is a lateral sectional view of the assembly of FIG. 2 when it has not been assembled yet;

FIG. 4 is a front view of a first detail of FIG. 1 ;

FIG. 5 is a sectional view of the detail of FIG. 4, as taken along a plane IV-IV;

FIG. 6 is a front view of a second detail of FIG. 1 ;

FIG. 7 is a sectional view of the detail of FIG. 6, as taken along the axial plane VI-VI;

Figure 8 is an axial sectional view of a third detail of the assembly of

FIG. 1 ;

FIG. 9 is an axial sectional view of a crank assembly of the invention, mounted to a frame of a bicycle or a pedal-operated machine.

Detailed description of a preferred embodiment

[0026] The above mentioned figures show a crank assembly for bicycles or pedal-operated machines according to the invention, generally designated by the numeral 1 , which is designed to be housed in a cylindrical sleeve or bushing S associated with the frame T of a pedal-operated vehicle, not shown.

[0027] The assembly 1 basically comprises a pair of substantially identical cranks 2, 3, each having a substantially tubular hub 4, 5 with a substantially radial lever 6, 7 extending therefrom, and a substantially annular chainring 8 having peripheral teeth.

[0028] The chainring 8 is designed to be encircled by a torque transferring chain, whereby the crank 2 with the chainring 8 attached therewith will be referred to hereinafter as drive crank.

[0029] A second chainring 8', concentric with and similar to the former and having a larger diameter may be fixed to the drive crank 2, as well as other chainrings, not shown, as needed by the user and without departure from the scope of the invention.

[0030] Both chainrings are fixed to the drive crank 2 by appropriate known connection members, such as screws or pins. [0031] The radial levers 6, 7 may have respective axial through holes 9, 10 at their ends 1 1 , 1 2 for pivotal attachment of the axis of a pedal, not shown, which is designed to be powered by a user's foot.

[0032] The cranks 2, 3 are coupled by means of the tubular hubs 4, 5 which are arranged concentrically with a common axis of rotation R, such that the radial levers 6, 7 extend on opposite sides from said axis R.

[0033] When the crank assembly 1 is mounted to the frame T of the bicycle of pedal-operated machine, the axis of rotation R of the tubular hubs 4, 5 will coincide with the axis X of the cylindrical seat S of the frame T.

[0034] The outer peripheral surfaces 1 3, 14 of the tubular hubs 4, 5 may have a substantially cylindrical shape, and may have respective outside diameters Φι ₃ , Φ which are slightly smaller than the diameter O _s of the seat S.

[0035] In the exemplary embodiments as shown in the figures, the outer peripheral surfaces 1 3, 14 of the tubular hubs 4, 5 have substantially identical outer diameters Φι ₃ , Φ-ι ₄ .

[0036] A peculiar feature of the invention is that each of the tubular hubs 4, 5 has a substantially annular connecting portion 17, 1 8 along a peripheral rim 15, 1 6, which is uniformly and integrally joined to a respective lever 6, 7.

[0037] The connecting portion 1 7 of the drive crank 2 is adapted to fix the chainrings 8, 8', such that the torque applied to the levers 6, 7 is only directly transferred to the chainrings 8, 8' through the connecting portion 1 7, 1 8, thereby reducing torsional stresses and increasing the stiffness of the assembly 1 .

[0038] The tubular hubs 4, 5 may have substantially equal shapes and sizes such that, assuming a stress exerted on the respective levers 6, 7 by the user, substantially the same torque is transferred to the chainrings 8, 8' through the connecting portion 1 7, 18.

[0039] The chainrings 8, 8' have an annular shape and have an inner circular rim 1 9, 1 9' with an inside diameter Φ-ig, ΦΊ ₉ .

[0040] Furthermore, each lever 6, 7 has a radial length L ₆ , L ₇ that may be appropriately selected to change its ratio to the inside diameter Φ ₉ , Φ' ₉ of the chainrings 8, 8' as needed by the user.

[0041 ] In a preferred embodiment, as shown in FIG. 3, the diameter Φ ₃ , Φ ₄ of the outer peripheral surface 1 3, 14 of the tubular hubs 4, 5 is almost equal to the inside diameter Φ-ig, ΦΊ9 of the chainring 8, 8' and to the axial length l_6, L ₇ of the levers 6, 7.

[0042] This size of the cranks 2, 3 and the chainrings 8, 8' was experimentally found to allow a considerable reduction of the torsional stresses transferred by the user to the assembly 1 during application of the torque.

[0043] Appropriately, the drive crank 2 may have at least two annular steps 20, 21 in the proximity of the connecting portion 1 7, with respective inside diameters that are used as centering seats for the chainrings 8, 8'.

[0044] Each annular step 20, 21 has a front surface 22, 23 that is designed for abutment against a flat face 24, 24' of a respective chainring 8, 8'.

[0045] Also, the drive crank 2 may comprise first connection means 25 for fixation of the chainring 8, 8', which are located at the annular step 20, 21 .

[0046] Particularly, the chainring 8, 8' may be removably fixed to the annular step 20, 21 by means of a plurality of threaded screws 26, which are designed for engagement in respective reversely threaded holes formed along the circumferential extension of each annular step 20, 21 .

[0047] Conveniently the tubular hubs 4, 5, as best shown in FIGS. 4 to 7 may have an approximately conical or frustoconical shape and may have lightening through holes 27, 27'.

[0048] Furthermore, the tubular hubs 4, 5 may have annular flanges 28, 29 at the longitudinal end opposite to the connecting portion 1 7, 1 8, which radially projects inwards and have substantially flat outer surfaces 28', 29', as clearly shown in FIGS. 2, 3, 5, 7, 9.

[0049] As the cranks 2, 3 are coupled, the respective flat surfaces 28', 29' are in mutual contact along a plane of symmetry π perpendicular to the axis of rotation R and coinciding with the center plane ττ' of the seat S formed in the frame T.

[0050] Each annular flange 28, 29 may have a plurality of holes 30 and 31 that are evenly arranged along respective circumferences C30, C31 having equal diameters Φ ₃₀ , Φ31 for receiving second connection means 32 which are designed to lock together the tubular hubs 4, 5.

[0051 ] The second connection means 32 may include cylindrical pins 33 that are received in holes 30, 31 of the flanges 28, 29 and are designed to be coupled to corresponding bushings 34.

[0052] Conveniently, the tubular hubs 4, 5 may have annular cylindrical tracks 37, 38 for respective end bearings 39, 40.

[0053] Advantageously, the average diameter of the bearings Φ39, Φ ₄ ο as well as the radial length L ₆ , L ₇ of the levers 6, 7 and the inside diameter Φ19,

Φ'19 of the chainrings 8, 8' may be selected as needed by the user.

[0054] The end bearings 39, 40 are used to pivotally support the assembly 1 in a cylindrical body 41 , as better shown in FIG. 8 which may be associated with the frame T of the bicycle or pedal-operated machine.

[0055] In a particular configuration of the invention, as shown in FIG. 2 and

FIG. 3, the cylindrical body 41 may be integral with the frame T of the bicycle or pedal-operated machine.

[0056] Alternatively, as best shown in FIG. 9, the cylindrical body 41 may be distinct from the frame T of the bicycle or pedal-operated machine and may be designed to at least partially fit into the seat S.

[0057] Furthermore, the cylindrical body 41 may be formed of one piece or, alternatively, of two or more portions, each having complementary anchor means for mutual fixation.

[0058] In both cases, the cylindrical body 41 has annular housings 42, 43 for end bearings 39, 40.

[0059] The annular housings 42, 43 for the end bearings 39, 40 may be placed at the ends 44, 45 of the cylindrical body 41 , which may have an inwardly recessed intermediate portion 46.

[0060] Conveniently, the pair of cranks 2, 3 and the cylindrical body 41 may be formed of respective high-mechanical strength and low-specific weight materials, that may be selected from the group comprising aluminum and alloys thereof, carbon and alloys thereof, titanium and alloys thereof and polymeric materials.

[0061] The above disclosure clearly shows that the assembly of the invention fulfills the intended objects and particularly meets the requirement of increasing the stiffness of the assembly, thereby reducing the torsional stresses thereon, improving its efficiency and extending its life. Furthermore, the assembly has a highly simple structure, with a very small number of parts, whereby manufacturing and maintenance costs are reduced.

[0062] The crank assembly of the invention is susceptible to a number of changes and variants, within the inventive principle disclosed in the appended claims. All the details thereof may be replaced by other technically equivalent parts, and the materials may vary depending on different needs, without departure from the scope of the invention.

[0063] While the crank assembly has been described with particular reference to the accompanying figures, the numerals referred to in the disclosure and claims are only used for the sake of a better intelligibility of the invention and shall not be intended to limit the claimed scope in any manner.