A toothed gear for a transmission mechanism and a method for making it

Abstract

Described is a toothed gear (B), preferably designed to be included in a transmission mechanism (M1, M2), which includes a main body (R) made with an axial-symmetrical extension about an axis of symmetry (X) for the toothed gear (B) and which is designed to perform a rotary movement about the axis of symmetry (X). In the toothed gear (B) there are a plurality of teeth (A) distributed along a perimeter portion of the main body (R) and which extend according to a tapered geometry. The tapered geometry comprises a head portion (T), which has an arc-shaped perimeter extension defined by a head circumference (C1) defined by a head diameter (D1), a foot portion (P) which has an arc-shaped perimeter extension, defined by a foot circumference (02) defined by a foot diameter (D2), and a joining stretch (G) between the head portion (T) and the foot portion (P). The invention also relates to a method for making the toothed gear (B).

Description

[0001] A TOOTHED GEAR FOR A TRANSMISSION MECHANISM AND A METHOD FOR MAKING IT

[0002] DESCRIPTION

[0003] Technical field

[0004] This invention relates to a toothed gear designed to be used in transmission mechanisms, reducers and the like and a relative production process.

[0005] Background art

[0006] The prior art is particularly rich in examples of various types of toothed gears, including gear wheels, toothed cylinders, toothed crowns and the like used for various functions. The toothed gears are important basic mechanical parts, widely used in almost all production machinery of all traditional industrial manufacturing sectors, in the aerospace sector, rail transport, building machines, precision instruments and many others.

[0007] The use of these gears is so common that the prior art has for some time settled on the use of solutions which comprise various types of design of the teeth, including gears with a standard design, that is to say, which have a specific standard with regard to their geometry.

[0008] For example, the ISO 6336 standard for the gear wheels indicates an entire series of parameters which are suggested to be implemented as a function of the characteristics of the gear wheels and the type of connection to be obtained. The general dimensional factors of the gear include, for example, indications on the dimensions of the basic diameter of the gear, head diameter, primitive diameter and tooth geometry, but also indications on material and gear treatment, load distribution, lubrication factors and the like.

[0009] In particular, the standard toothed gears, also called unified, generally have teeth with a tapered transversal cross-section consisting of separate curves (lateral evolutions and head and foot circles), joined only by small connections, one of which, the foot one, does not participate in the contact during the meshing. The body of each of the teeth ends in a head in the form of an acute angle connection and the teeth generally have a geometry which is quite sharp, even if they are then joined in such a way as to avoid excessive concentration of forces, and therefore, risk of interference, cracks or breakages of the tooth.

[0010] Disadvantageously, this type of toothed gear has a meticulous design, since the various mechanical dimensions and parameters are interconnected, limiting combinations of the features of the gears and, above all, of the teeth. It follows that these gears are very difficult to make since they require specific production steps and processes which require specific tools, including unified milling cutters, gear making machines or gear hobs, which make the processing very costly and, consequently, the production is very expensive and time-consuming.

[0011] Despite their particular embodiment, the gears with unified teeth can in any case have interference phenomena or impacts between the teeth during the mutual coupling of two or more gears; this is even more true when the unified gears have very similar primitive diameters.

[0012] A first consequence of such interference or impacts consists in a concentration of stresses on certain specific points of the teeth during transmission of the contact forces. It is known that this type of gear provides a maximum of the concentrations of the stresses generally at the base of the tooth, where the connection of the foot has a very small radius. Such interferences, if neglected, reduce the working life of the teeth, resulting, in extreme cases, in the breakage of the tooth.

[0013] A second consequence of such interference or impacts results in the consequent noise. More specifically, this noise, which is caused by interference during gripping between coupled gear teeth, makes the gear system annoying to any operators nearby.

[0014] According to the prior art there are various alternatives with respect to the use of standard teeth with the aim of improving the efficiency of the distribution of loads and / or allowing meshes which are as free as possible from interference but which allow a different design of the gears and, in particular, of the geometry of the teeth. Patent document CN1 14704609A describes a toothed gear comprising high performance teeth for withstanding the load transmitted and received, using a curvature of the tooth which follows a quadratic curved extension.

[0015] Disadvantageously, even this geometry is not easily achieved and requires the same careful design of foot of the tooth and the relative radius of connection to the body of the gear, therefore being difficult to make since it requires specific tools, such as, for example, numerical control milling cutters.

[0016] Aims and summary of the invention

[0017] A technical purpose of the invention is to provide a toothed gear which can be implemented in transmission mechanisms which overcomes the drawbacks present in the prior art.

[0018] An aim of this invention is therefore to provide a toothed gear which is able to reduce the concentration of the forces on the teeth and obtain a greater distribution of the contact force on the entire tooth, simultaneously improving the duration of the useful life, the efficiency of the transmission of the operating torque whilst at the same time allowing a reduction in the noise value caused by the contact of the teeth.

[0019] Another aim of this invention is to provide a toothed gear which is flexible in terms of sizing the characterising parameters, allowing greater ease and reduced cost of production of the gear.

[0020] A further aim of this invention is to provide a transmission mechanism which has one or more toothed gears according to this invention, made in such a way that it improves the coupling and the distribution of the forces transmitted between the toothed gears, especially in the cases in which the primitive diameters of the toothed gears used are very similar.

[0021] Brief description of the invention

[0022] The technical purpose indicated and the aims specified are substantially achieved by a gear wheel comprising the technical features described in one or more of the appended claims. The dependent claims correspond to alternative embodiments. In detail, the toothed gear comprises a main body made according to an axial-symmetrical extension, that is, with a radial symmetry structure, about an axis of symmetry and designed to perform a rotary movement about the axis of symmetry, which has a plurality of teeth, distributed along a perimeter portion of the main body. These teeth extend according to a tapered geometry, oriented radially relative to the axis of symmetry.

[0023] This tapered geometry comprises a head portion and a foot portion, each of which has an arc-shaped perimeter extension, defined respectively by a head circumference, defined by a head diameter, and by a foot circumference, defined by a foot diameter. Moreover, there is a joining stretch between the head portion and the foot portion.

[0024] The foot portions connect between two successive teeth.

[0025] More precisely, the foot portions of successive teeth define connecting portions with a circumferential arc shape, defined by the foot circumference. Another aspect of the invention is due to the fact that, according to a particular embodiment, during engagement with another toothed gear, for example outside an internal gear, the teeth of the internal and external gear all pass through the primitive diameters, in such a way that the head of the internal gear (tangential to the foot of the other gear, the external gear) works with the foot of the external gear and, simultaneously, the head of the external gear works on at least two points of the foot circumference of the internal gear.

[0026] The fact that the teeth all pass through the primitive diameters of the inner and outer gears makes it possible to make gears which couple with teeth with different pitches, since the ratio between the two gears is not based on the number of teeth, but on the respective diameters.

[0027] In this way, in effect, there are always at least two resting points in the meshing and the work of each point involves both the gears.

[0028] As a result, the pressure angle is greatly reduced because there is always a push in those two points.

[0029] Therefore, advantageously, teeth of any size (even very high) can be made without coupling or meshing problems: the teeth in fact only serve the pushing step and determine a pressure angle tangential to the head circumference of the inner gear relative to the bottom diameter of the foot of the inner gear.

[0030] This contact on at least two points allows a reduction in the size of the products, allowing the production of reducers with small dimensions and, even, the profile according to the invention can be executed using traditional machines with considerable savings in production costs.

[0031] According to a variant embodiment, the main body has a lateral perimeter surface interposed between a first and a second base face, positioned preferably perpendicularly to the axis of extension.

[0032] The main body has a cavity intended for the connection on the insertion on a rotation pin, such as, for example, a shaft, by which it can transmit or receive the rotary motion.

[0033] Preferably, this gear comprises various alternative connecting means of per se known type.

[0034] Advantageously, the teeth of this gear are positioned circumferentially on a lateral perimeter surface of the main body, oriented radially relative to the axis of extension towards the outside of the main body.

[0035] The lateral surfaces of each tooth are substantially aligned in a parallel manner and are also preferably coincident, respectively, with the first and second base face.

[0036] As a result, the ridges and troughs formed by the heads and by the feet aligned with the axis form a so-called “straight-tooth” shape.

[0037] The technical purpose indicated and the aims specified are further achieved by a transmission mechanism comprising two or more toothed gears, wherein at least one toothed gear is designed to transmit the motion to a further toothed gear.

[0038] Another aspect of the invention relates to a method for making a toothed gear which comprises the following steps.

[0039] Firstly, the gear module is established and the number of teeth is obtained from the linear ratio which links these two quantities with the primitive diameter of the toothed gear, or the number of teeth is established and the module is obtained in a similar manner.

[0040] The formula is as follows:

[0041] Z=Dp / m where: m = module

[0042] Z = number of teeth

[0043] Dp = primitive diameter

[0044] Therefore, an outer arc, that is, defined outside the gear wheel, is considered on the foot circumference, defined by a foot diameter equal in size to the chord of the outer arc.

[0045] The Applicant has perceived that it is not necessary to change the number of teeth when modifying the primitive circumference of the wheel.

[0046] In effect, by means of the invention, it is possible to maintain the primitive diameter of one or both the gears being gripped by modifying the transmission ratio, that is to say, increasing or decreasing the number of teeth. More specifically, the reference module will not be a whole number.

[0047] For example, if the primitive diameter is “Dp” is 200 and the number of teeth “Z” is 50, then the module “m” will be 4.

[0048] By modifying the number of teeth, from 50 to 51 (Z = 51 ), the module “m” will be equal to 3.922.

[0049] The primitive diameter “Dp” can therefore be modified maintaining the number of teeth: Dp = 201 , Z = 50 and m = 4,020

[0050] With this type of toothing it is possible to easily modify the ratios whilst maintaining the dimensions of the reducer body.

[0051] In order to execute the modules indicated above with “traditional” toothing there would be unacceptable costs.

[0052] The head diameter of the head circumference is calculated by means of a predetermined parameter, in such a way as to eliminate the interference between the teeth during the meshing of the toothed gear when they operate in a transmission mechanism.

[0053] The ratio between the foot diameter is directly proportional to the head diameter as a function of the parameter selected.

[0054] This parameter is advantageously between 1.18 and 1 .23, preferably between 1.1 ,19 and 1 .22, inclusive, more preferably between 1 .20 and 1 .21 inclusive, even more preferably equal to 1 .20.

[0055] The centre of the foot circumference is identified as the midpoint of the linear segment which subtends the outer arc and the foot circumference is traced like the one passing through the ends of that segment.

[0056] Subsequently, the centre of the head circumference is found on the line joining the centre of the toothed gear with the centre of the foot circumference, knowing that it is tangential to the foot circumference at the meeting point between the latter and the above-mentioned joining line.

[0057] Moreover, the centre which is being sought has a distance from the latter point equal to half of the head diameter.

[0058] The two circumferences thus created, head and foot, are joined by two straight segments tangential to both (double tangency).

[0059] In this way, there is a double contact between the corresponding head and foot in the toothing and, consequently, a considerable increase in the thrust: the effect will be to have a double thrust on the tooth and on the foot of the driven wheel, where the motor gear pushes simultaneously with the corresponding head and foot.

[0060] In practice, the designer may reduce the size with the same torque of the “traditional” gears since the latter have a single thrust point on the side of the tooth.

[0061] In addition, the tooth is always gripped even in the presence of radial clearance.

[0062] This aspect is highlighted by the fact that, as shown in Figures 10 (and 11 ), the drive wheel pushes in the driven wheel by means of a contact which occurs simultaneously at least in two points: on the meshing tooth but also on the next tooth. The foot of the drive wheel pushes the head of the driven wheel at two or more different points and in sequence with each other relative to the transmission of the motion.

[0063] Therefore, the two teeth act simultaneously in the bottom of the foot and, without a break, the contact between the drive wheel and the driven wheel lasts and continues.

[0064] Yet another advantage of the invention is due to the fact that the gears made in this way are executed by milling or wire cutting machines, without the need to use gear cutting machines.

[0065] That is to say, the construction of the toothing of this type of gear is carried out on machining centres, avoiding gear making machines even with material already hardened and tempered.

[0066] Moreover, the use of the wire electrical discharge machining technique creates the teeth after hardening with very low tolerances: with suitable tolerances and hot assembly (working temperature), it is possible to obtain absence of radial clearance because the head works on the bottom of the corresponding foot.

[0067] Detailed description of the actuation of invention

[0068] Further features and advantages of the invention are more apparent in the non-limiting description which follows of a non-exclusive embodiment of toothed gear and of distribution mechanism comprising a plurality of these toothed gears.

[0069] The description is set out below with reference to the accompanying drawings which are provided solely for purposes of illustration without restricting the scope of the invention and in which:

[0070] Figure 1 is a front view of a toothed gear made in the form of a disc with the teeth oriented towards the outside;

[0071] Figure 2 shows the detailed content of the detail Det. 1 shown in Figure 1 ;

[0072] Figure 3 is an accidental perspective view of a toothed gear and relative detail of the teeth illustrated in Figure 1 .

[0073] Figure 4 is a front view of a toothed gear made in the form of a crown with the teeth oriented towards the inside;

[0074] Figure 5 shows the detailed content of the detail Det. 2 shown in Figure 4;

[0075] Figure 6 is a front view of a transmission mechanism comprising two toothed gears made as in Figure 1 .

[0076] Figure 7 shows the detailed content of the detail Det. 3 shown in Figure 6;

[0077] Figure 8 is an accidental perspective view of a toothed gear illustrated in Figure 6;

[0078] Figure 9 is a front view of a transmission mechanism comprising a first toothed gear made as in Figure 1 and a second toothed gear made as in Figure 4;

[0079] Figure 10 shows the detailed content of the detail Det. 4 shown in Figure 9; Figure 1 1 is an accidental perspective view of a toothed gear and relative detail of the teeth illustrated in Figure 9;

[0080] Figure 12 illustrates the method for making a toothed gear B.

[0081] Figures 13A and 13B show two successive positions of the notch between the gears B and B’, respectively an inner gear and an outer gear, both alternative profiles according to the invention.

[0082] With reference to the drawings, the reference “B” denotes a toothed gear comprising a main body “R” made with axial-symmetrical extension about an axis “X” and designed to perform a rotary movement about the axis “X” and by a plurality of teeth “A” distributed along a perimeter portion of the main body “R”.

[0083] The teeth “A” extend according to a tapered geometry.

[0084] More specifically, the tapered geometry comprises: a head portion “T”, which has a first circumferential arc extension defined by a head diameter “D1 ”; a foot portion “P”, having a arc-shaped perimeter circumferential arc extension defined by a foot diameter “D2”; and by a joining stretch “G” between the head portion “T” and the foot portion “P”.

[0085] The gear “B” further comprises that the foot portions “P” of the successive adjacent teeth “A” form connecting portions with a circumferential arc shape having the above-mentioned foot diameter “D2”. In other words, and with reference to the accompanying drawings, two adjacent teeth “A” have respective foot portions “P” constituting a single circular arc having the same value of the diameter equal to the foot diameter “D2”.

[0086] The parameter used for the coupling between a plurality of gears is given by the module, that is to say, the value obtained by dividing the primitive diameter “Dp” and the number of teeth.

[0087] As is known, amongst the parameters characterising a toothed gear there are the base diameter or foot diameter “Db”, that is to say, the diameter of the base circumference or foot circumference “Cb”, ideal, defined by the main body “R” traced at the base of the teeth “A”; the head diameter “Dt”, that is to say, the diameter of the head circumference “C1 ”, ideal, defined by the main body “R” traced at the top of the teeth “A”; and the primitive diameter “Dp” defining the primitive circumference “C2” of the toothed gear, that is to say, the circumference, interposed between the head circumference “C1 ” and the foot circumference “C2”, arranged in such a way that it passes where the width of the teeth is equal to the width of the compartments formed between two successive teeth “A”.

[0088] The number of teeth is a value that depends on the choice of the geometry of the teeth.

[0089] According to the toothed gear “B” the ratio between the foot diameter “D2” and the head diameter “D1 ” is defined by a predetermined parameter “c”, in such a way as to eliminate the interference between the teeth during meshing of the toothed gear B in a transmission mechanism.

[0090] The parameter “c” which expresses the ratio between the foot diameter (D2) and the head diameter (D1 ) is between 1.18 and 1.23, preferably between 1.1 ,19 and 1 .22, inclusive, more preferably between 1 .20 and 1 .21 inclusive, even more preferably equal to 1 .20.

[0091] The choice of intervals is verified experimentally to guarantee that the coupling between a plurality of gears “B” made according to this invention is not only feasible but minimises the possible interference between the corresponding teeth “A”. In other words, when the parameter “c” falls below the “ideal” value of 1 .20, for example to 1.19 or 1.18, then it will have more thrust in the side and greater precision, but less interference.

[0092] Vice versa, for higher “c” values, for example equal to 1 .22 or 1 .23, there will be a greater interference and a lower precision.

[0093] The height of the tooth “L” is the measurement obtained by subtracting the value of the base diameter “Db” from the value of the total diameter “Dt”.

[0094] With reference to these drawings, each tooth “A” extends with a height “L” having the same extension as the foot diameter “D2”.

[0095] Preferably, the joining stretch “G” between a head portion and a foot portion has a linear extension.

[0096] It should be noted that the value of the joining stretch “G” is obtained as a function of the value of the head diameter “D1 ” and of the foot diameter “D2”.

[0097] In particular, the stretch “G” has a regular and continuous geometry, in other words without forming angles, obtained from a stretch tangential simultaneously both to the circular arc defining the head “T” and to the circular arc defining the foot “P”.

[0098] According to alternative embodiments, the joining stretch “G” can have other geometries, such as, for example, curvilinear or broken.

[0099] According to the embodiment illustrated in these drawings, each tooth comprises an engagement surface “Si”, having an undulating shape defined by the above-mentioned tapered geometry, and two lateral surfaces “S1 ” and “S2” facing each other and perpendicular to the above-mentioned axis “X” about which the main body “R” extends.

[0100] The teeth “A” lie and extend in a lying plane defined by the main body “R” along an arc of a circumferential portion of the main body “R”.

[0101] The set of engagement surfaces “Si” of the plurality of teeth “A” is a regular and parallel succession of crests and troughs, corresponding, respectively, to the heads “T” and to the feet “P” of the teeth “A” around the main body “R”. The crests and troughs are substantially oriented parallel to the axis “X”.

[0102] More specifically, the main body “R” with an axially-symmetric shape preferably has a circular lateral perimeter surface “Sp” with a diameter equal to the base diameter “Db” on which the teeth “A” are positioned.

[0103] Preferably, the teeth “A” are positioned along the entire extension of the lateral perimeter surface “Sp”.

[0104] According to some alternative embodiments, not illustrated in the drawings, the teeth “A” can be positioned only along a partial portion of the base circumference “Cb” of the toothed gear “B”.

[0105] According to a first possible embodiment, illustrated in Figures 1 and 3, the main body "R" has the shape of a disc or cylinder.

[0106] Figure 2 shows a detail of a first variant of the profile of the teeth “A”.

[0107] In addition to the lateral perimeter surface “Sp”, the main body “R” has a first base face “Sb1 ” and a second base face “Sb2”, positioned preferably perpendicularly to the axis of extension “X”. The lateral perimeter surface “Sp” is between the two base surfaces “Sb1 ” and “Sb2”.

[0108] According to this embodiment, the main body “R” has a cavity “H” dedicated to be used for the connection or for inserting on a rotation pin, such as, for example, a shaft, by which it can transmit or receive the rotary motion.

[0109] Generally speaking, the gear “B” may comprise various alternative connecting means commonly known in the prior art.

[0110] According to this embodiment, the teeth “A” are arranged circumferentially on the lateral perimeter surface “Sp” of the main body “R”, oriented radially relative to the axis “X” towards the outside of the main body “R”.

[0111] The lateral surfaces “S1 ” and “S2” of each tooth “A” are therefore positioned substantially aligned, substantially in a parallel manner, and preferably coincident, respectively, with the first and the second base faces “Sb1 ” and “Sb2”.

[0112] As a result, the ridges and troughs formed by the heads and by the feet aligned with the axis “X” form a so-called “straight-tooth” shape.

[0113] With reference to Figures 4 and 5, according to a further embodiment, the main body “R” has a crown shape.

[0114] The term “crown shape” means that the main body “R” consists of an extension axial-symmetrical about the axis “X” and equipped with the above-mentioned cavity “H” wherein the cavity “H” is preferably designed to receive at least one further toothed gear.

[0115] The cavity “H” has an axial-symmetrical extension about the axis “X”.

[0116] However, according to a different embodiment, the cavity “H” may be positioned in an eccentric manner relative to the axis “X”, in such a way as to allow the gear “B” to be connected and to rotate eccentrically relative to the axis “X”.

[0117] The main body “R” comprises an inner perimeter surface “Spi” defining the cavity “H”.

[0118] According to the embodiment illustrated in Figures 4 and 5, the teeth “A” are positioned circumferentially on the inner perimeter surface “Spi”, radially relative to the axis “X” and facing the inside of the cavity “H”.

[0119] According to a further possible embodiment, not illustrated in the drawings, the main body may be equipped with two sets of teeth, a first set of teeth facing the inside of the main body and a second set of teeth facing the outside of the main body, positioned, respectively, on the lateral perimeter surface outside the main body and the inner perimeter surface of the main body inside the inner cavity.

[0120] A transmission mechanism comprises two or more toothed gears, wherein at least a first toothed gear is designed to transmit the motion to a further toothed gear.

[0121] Another example embodiment of the toothed profile is illustrated in Figures 13A and 13B. According to this variant, the gear B (or B’) is such that, when two of these gears B and B’, for example, respectively an internal gear B and an external gear B’, mesh together, the teeth A and A’ of the two gears B and B’ all pass through the primitive diameters of said teeth (A, A’).

[0122] In practice, the teeth A and A’ of the two gears B and B’ are made in such a way that the head T of the gear B works with the foot P’ of the other gear B’ and, simultaneously, the head T of the other gear B’ works on (at least) two points of the foot circumference C2 of the gear B1 .

[0123] According to this invention, more than one embodiment of transmission mechanisms may be provided using a plurality of toothed gears made according to the invention.

[0124] By way of example, some examples of transmission mechanisms comprising toothed gears made according to the invention will be provided below.

[0125] With reference to Figures 6, 7 and 8, according to a first possible embodiment a first transmission mechanism “M1 ” comprises at least a first gear “B1 ” and a second gear “B2” each comprising a first main body “R1 ” and a second main body “R2” in the form of a disc or cylinder, wherein each between the first gear “B1 ” and the second gear “B2” extend in an axially- symmetrical manner about a relative first axis “X1 ” and a second axis “X2” and rotating, respectively, axially about the relative axes “X1 , X2”.

[0126] The first gear B1 comprises a first plurality of teeth “A1 ” and a first perimeter surface “Sp1 ”, wherein the first plurality of teeth “A1 ” is positioned on the first perimeter surface “Sp1 ”.

[0127] The second gear B2 comprises a second plurality of teeth “A1 ” and a second perimeter surface “Sp1 ”, wherein the second plurality of teeth “A2” is positioned on the second perimeter surface “Sp2”. and the second gear B2 comprises a second plurality of teeth “A2”.

[0128] The teeth belonging to the first plurality “A1 ” and the second plurality “A2” grip each other.

[0129] Both the axes “X1 , “X2” are fixed.

[0130] A further example of an embodiment is illustrated in Figures 9, 10 and 1 1. This embodiment comprises a transmission mechanism “M2” comprising a third toothed gear “B3” and a fourth gear “B4” made according to this invention, wherein a first gear “B3” is made in the form of a disc or cylinder and a second gear “B4” is made in the form of a crown, each of which extends in an axially-symmetrical manner about, respectively, its own axis “X3, X4”.

[0131] The axes “X3” and “X4” are fixed.

[0132] The first gear “B3” comprises a main body “R3”, a third plurality of teeth “A3” and a third lateral perimeter surface “Sp3” on which the third plurality of teeth “A3” are positioned facing towards the outside of the main body “R3”. The second gear “B4” comprises a main body “R4”, a fourth plurality of teeth “A4”, an inner cavity “H4” about which an inner perimeter surface “Spi4” extends.

[0133] The inner cavity “H4” receives internally the first gear “B3”.

[0134] The fourth gear “B4” has the fourth plurality of teeth “A4” positioned on the relative inner perimeter surface “Spi4” facing the inside of the relative main body “R4”.

[0135] The teeth “A4” of the first gear “D3” mutually grip the teeth “A4” of the second gear “D4”.

[0136] Preferably, the third gear "B3" and the fourth gear "B4" are sized in such a way that the distance "Z" of the maximum movement away of the primitive circumference "C23" of the third gear "B3" relative to the primitive circumference "C24" of the second gear "B4" is greater than or equal to the value of the module of the first gear "B3" and of the second gear "B4".

[0137] This parameter is necessary to allow the coupling between the gears “B3 and B4”.

[0138] Further examples of alternative embodiments are possible.

[0139] Some of these possible alternative embodiments, not illustrated in the drawings, are described briefly below.

[0140] According to an example of an alternative embodiment, the transmission mechanism comprises at least two toothed gears each comprising a main body in the shape of a disc or cylinder, with an axial-symmetrical extension relative to a corresponding axis, and the teeth are positioned on the lateral perimeter surface of the body, having the corresponding teeth which grip each other.

[0141] Substantially, this embodiment follows a configuration similar to the embodiment illustrated in Figures 6, 7 and 8.

[0142] A first gear is arranged stationary whilst at least a second gear rotates about the first gear, or, in other words, achieving a roto-translational motion about the first gear.

[0143] According to a further alternative embodiment, the transmission mechanism comprises at least two toothed gears, wherein the first gear is made in the form of a disc or cylinder having the teeth positioned on a relative lateral perimeter surface of the main body, and the second gear is made in the form of a hollow crown having the teeth positioned on an inner perimeter surface and having the corresponding teeth which grip each other.

[0144] This embodiment follows a configuration similar to the embodiment illustrated in Figures 9, 10 and 1 1 .

[0145] The first and the second gear are axially-symmetrical relative to a corresponding first axis and a corresponding second axis.

[0146] The first and the second axes are fixed.

[0147] The second gear receives internally the first gear.

[0148] The first toothed gear rotates axially in an eccentric manner relative to its axis, forming a roto-translational motion relative to a second toothed gear, positioned stationary relative to its axis.

[0149] Preferably, the first gear and the second gear are designed in such a way that the distance of the maximum movement away of the primitive circumference of first gear relative to the primitive circumference of the second gear is greater than or equal to the value of the module of the first gear and of the second gear.

[0150] According to a further embodiment not illustrated in the drawings, the transmission mechanism comprises at least three toothed gears.

[0151] A first gear is made in the form of a disc or cylinder having the teeth positioned on a relative lateral perimeter surface of the main body.

[0152] A second gear is made in the form of a hollow crown having the teeth positioned on an inner perimeter surface.

[0153] A third gear is made in the form of a disc or cylinder having the teeth positioned on a relative lateral perimeter surface of the main body. The third gear is positioned in an intermediate fashion between the first and the second gears.

[0154] The first, second and third gears are axially-symmetrical relative to a corresponding first axis, second axis and third axis and have corresponding teeth which grip each other.

[0155] The first gear has a fixed axis about which it rotates.

[0156] The second gear has a fixed axis and is positioned stationary relative to the second axis.

[0157] The third gear is arranged movable according to a rotary motion relative to its axis and a roto-translational motion relative both to the first gear and to the second gear.

[0158] Alternatively, the first gear may be positioned stationary relative to its axis. The second gear is arranged in rotary motion relative to its axis and relative to the first gear.

[0159] The third gear is arranged movable according to a rotary motion relative to its axis and a roto-translational motion relative both to the first gear and to the second gear.

[0160] Gears comprise teeth with a circular profile according to this invention comprise various numerous advantages with respect to the other types, and in particular compared with gears using unified teeth.

[0161] The geometrical shape of the teeth may be made without using specific tools, and the use of a cylindrical cutter with a diameter less than the foot diameter “D2” is sufficient.

[0162] In this way, with a single machining operation, the milling cutter can create the complete toothing.

[0163] The specific ratio between the diameter of the circular arc of the foot “D1 ” and between the diameter of the circular arc of the head “D2” is experimentally obtained and makes it possible to optimise the grip of the teeth of two gears during the operating step.

[0164] This choice makes it possible to couple gears “B” having primitive diameters “Dp” and / or numbers of teeth “A” which are very similar, drastically reducing the interference phenomenon between the teeth “A” and, consequently, the noise produced. At the same time, it is possible to obtain a number of teeth “A” gripped for each gear “B” which is up to three times greater than a coupling of gears with unified teeth.

[0165] Further, the teeth “A” are not subject to the limitations of the modules available according to the standards, allowing a greater flexibility to be obtained in the choice of the lateral dimension of the tooth, the length “L” and its pitch.

[0166] The profiles of the foot “P”, of the head “T” and of the joining stretch “G” of the tooth “A” are very regular and well connected. When the teeth “A” are gripping, the passage of the point of contact from the head “T”, to the joining section “G” and lastly to the foot “P” occurs in a very regular and continuous fashion. This feature makes the toothing with round teeth very silent during operation because the impacts are avoided of the teeth characterising the unified teeth, which consist of separate curves joined only by small connections, one of which, the foot one, does not participate in the contact during the meshing.

[0167] Since the maximum concentration of the stresses in the unified teeth is found at the base of the tooth, this is usually the main cause of tooth breakage following a certain number of work cycles.

[0168] On the other hand, the gripping of the teeth “A”, as they have a circular arc profile, distributes along the entire engaging surface “Si”, using the head tooth “T”, the foot tooth “P” as well as the joining segment “G”.

[0169] Consequently, since the point of contact is distributed over the entire length of the engagement surface “Si”; the contact force is distributed over time and is not concentrated in a single point as occurs for the unified profiles. This feature generates a reduction in the surface contact stresses during meshing, which contributes to increasing the operating life of the tooth and therefore of the overall gear.

[0170] A transmission mechanism using gears according to this invention is, advantageously, particularly suitable for using toothed gears according to this invention when the primitive diameter of the coupled toothed gears is relatively similar. The arrangement of the gears allows a coupling with low interference values whilst at the same time it allows a greater number of teeth being gripped, up to three times with respect to a transmission mechanism comprising standard gears. Consequently, the transmission mechanism may be used in certain processes where the transmission mechanisms using normal toothed gears cannot be used.

[0171] In order to make the gear wheel B, firstly a module “m” of the toothing is established and the number of teeth “Z” is calculated by knowing the primitive diameter “Dp”, by means of the ratio:

[0172] Z = Dp / m

[0173] Similarly, it will be possible to predetermine the number of teeth “Z” of the gear B and obtain the module: m = Dp / Z

[0174] Once module “m” and the number of teeth “Z” have been determined, an outer arc oc is considered, relative to the wheel B, on the foot circumference

[0175] C2, which has a foot diameter D2 equal to the chord of the outer arc oc (Figure 12).

[0176] In practice, the diameter of the foot circumference D2 is calculated, considering the arc oc on the primitive equal to:

[0177] As can be seen, replacing Dp with the value Dp = Z-m, gives:

[0178] The diameter of the foot circumference is equal to the chord of the arc oc.

[0179] The head diameter D1 is then calculated which is equal to:

[0180] D2 = D1 / c where “c” is a parameter predetermined by dynamic simulations performed on the teeth during the meshing step and aimed to eliminate the interference between the teeth during the meshing of the toothed gear B in a transmission mechanism.

[0181] Its value can be assumed substantially equal to 1 .20.

[0182] With reference to Figure 12, the centre of the foot circumference C2 is at the midpoint M of the linear segment KW which subtends the outer arc oc and obviously passes through the end points K and W of that segment.

[0183] The centre 01 of the head circumference C1 is therefore identified as a point belonging to the line Q joining the centre of the toothed gear B with the foot circumferences C2, and is positioned at a distance equal to half the head diameter D1 from the meeting point between the foot circumference C2 and the above-mentioned joining line Q.

[0184] The centre of the head circumference 01 is on the joining line Q and is tangential to the foot circumference C2 at the point D (meeting point of joining line Q with circumference C2); its diameter is D1 .

[0185] Lastly, the foot circumference C2 and the head circumference C1 are connected by two rectilinear segments simultaneously tangential to both the circumferences C1 and C2.

[0186] The points E, F, B and H have the particular feature of being in pairs belonging to a straight line doubly tangential to the foot circumference C2 and head circumference C1 . The circumferences C2 and C1 are therefore joined by two straight segments EF and BH, simultaneously tangential to both of said above-mentioned circumferences C1 and C2.

[0187] In practice, it is assumed that there two gear wheels which mesh with each other, that is to say, an inner drive wheel and an outer driven wheel (crown), having, respectively, the primitive diameters Dpm and Dpc and a transmission ratio “i”.

[0188] A motor moment M1 acts on the inner wheel, which rotates at the angular speed col and the contact between the wheels is assumed to occur on one tooth at a time.

[0189] In this case, the tooth of the inner wheel, in contact with the driven wheel, applies a contact force F1 on the respective tooth of the outer wheel which is being gripped at that moment.

[0190] Following a structural analysis carried out on the teeth of the two wheels, it is decided that the toothing module must be “m”.

[0191] As mentioned above, the number of teeth of the drive wheel Zm and driven wheel Zc is:

[0192] Zm = Dpm / m Zc = Dpc / m

[0193] Obviously, Zm and Zc must be whole numbers, being equal to the number of teeth respectively of the drive wheel and of the driven crown.

[0194] It should be noted that the value of “m”, common to both the wheels, does not necessarily have to be chosen from among the values established by the standards, but can be any rational number, as well as the values of Dpm and Dpc.

[0195] This feature makes the toothing according to the invention much more versatile to design than the unified one, because the available values of the unified modules limit more the choice of primitive diameters and therefore the number of teeth.

[0196] In other words, the greater possibility of choice for the values of the module “m” makes it possible with the round teeth to create gears without interference where this would not be possible with the unified teeth.

[0197] In order to make the external toothing of the drive wheel, having established the number of teeth Zm, distributed on a circumference with primitive diameter Dpm, the pitch p between the teeth will be: p = m n.

[0198] By dividing the primitive circumference into 2-Zm equal parts equal circles 2-Zm are created centred on the chord joining two consecutive points, for example A and B of Figure 12. These circles are defined as original circles. The diameter of each original circle created is equal to the diameter of the foot circle D2.

[0199] In order to determine the diameter of the head circle of the tooth, which will therefore allow its sides to be defined, a parameter c is introduced, which is basically a shape ratio of the tooth according to the invention, defined as: c = D2 / D1

[0200] The Rf ratio must be greater than 1 (D2>D1 ) to allow the meshing and must be chosen in such a way as to guarantee the absence of interference of assembly and of operation of the gear.

[0201] As mentioned, the recommended value is 1 .20 or 1 .21 .

[0202] Having previously determined D2 (equal to the diameter of the original circles), the diameter of the head circle is determined:

[0203] D1 = D2 / c

[0204] The head circle, therefore, will be tangential to the original circle and will be centred between two alternating original circles (Figure 12).

[0205] Once the foot and head circumferences of the teeth have been defined, a side of the tooth is created with a straight segment tangent to both the head and foot circumferences. Obviously, the other side will be the symmetrical of the first relative to the radial direction joining the centre of the wheel with the centre of the head circumference.

[0206] The round tooth will be the joining of the two rectilinear sides and of the circular head and foot arcs which start and end in the points of tangency with the sides.

[0207] In order make the inner toothing of the crown with primitive diameter Dpc, which meshes with the inner wheel with primitive diameter Dpm, the same procedure described above is followed for the inner wheel taking care to use the same value of the module “m”. In this case, the primitive circumference with diameter Dpc will be divided into 2-Zc parts and the positions of the head circumference with the foot circumference will be inverted (the head circumference for the crown is positioned inside the hole of the crown whilst for the outer wheel it is positioned towards the outside of the wheel).

[0208] The design of a tooth set and in particular the sizing of the tooth must take into account the structural resistance of the tooth to the contact force; in order to design the tooth, it is possible to perform an iterative procedure as described below.

[0209] After determining, by means of kinematic analysis, the diameters Dpm and Dpc, a first value of the module m’ is selected for both the wheels, taking care that the values of Zm and Zc are whole numbers.

[0210] Therefore, the teeth are sized with the procedure just described.

[0211] By knowing the input power, angular speeds and primitive diameters of the wheels, the contact force which the wheels exchange during meshing is calculated.

[0212] A structural analysis of the tooth subjected to the contact force is therefore performed using, for example, the finite element method (FEM).

[0213] It is checked whether the structural analysis is satisfied; if not, a value m” is assigned to the module with m”>m’ and the procedure is repeated as explained above: the procedure stops when the structural analysis is satisfied.

[0214] The example described above of two wheels, an inner wheel and an outer wheel (or crown wheel), is also valid for gears with two or more wheels; this is the case, for example, of epicyclic gears where the presence of satellite gears forces the designer to use the same module also for wheels which do not mesh directly with each other.

[0215] In this case, the possibility of using a greater number of values for the module, not linked to the unified ones, makes it possible to select a greater number of combinations of diameters for the wheels so as to obtain a certain transmission ratio; amongst these combinations of diameters there will also be those which in the case of unified teeth would create interference.

[0216] The invention can be modified and adapted in several ways without thereby departing from the scope of the inventive concept.

[0217] Moreover, all the details of the invention may be substituted by other technically equivalent elements.

[0218] In practice, the materials used, as well as the dimensions, may be of any type, depending on requirements, provided that they are consistent with their production purposes.

Claims

CLAIMS1. A toothed gear (B) comprising: a main body (R) made according to an axial-symmetrical extension about an axis of symmetry (X) for the toothed gear (B) and designed to perform a rotary movement about the axis of symmetry (X); a plurality of teeth (A) distributed along a perimeter portion of the main body (R) and extending according to a tapered geometry; the tapered geometry comprising: a head portion (T) having an arc-shaped perimeter extension, defined by a head circumference (C1 ) defined by a head diameter (D1 ); a foot portion (P) having an arc-shaped perimeter extension, defined by a foot circumference (C2) defined by a foot diameter (D2); a joining stretch (G) between the head portion (T) and the foot portion (P)-2. The toothed gear (B) according to claim 1 , wherein the foot portions (P) connect between two successive teeth (A).

3. The toothed gear (B) according to claim 2, wherein, during the engagement with another toothed gear (B’), the teeth (A, A’) of the two gears (B, B’) all pass through the primitive diameters of said teeth (A, A’), in such a way that the head (T) of the gear (B) works with the foot (P’) of the other gear (B’) and, simultaneously, the head (T’) of the other gear (B’) works on the foot circumference (C2) of the gear (B1 ).

4. The toothed gear (B) according to claim 2 or 3, wherein the ratio between the foot diameter (D2) and the head diameter (D1 ) is between 1.18 and 1.23, preferably between 1.19 and 1.22, inclusive, more preferably between 1 .20 and 1 .21 inclusive, even more preferably equal to 1 .20.

5. The toothed gear (B) according to claim 4, wherein each tooth (A)extends in height with a measurement substantially equal to the measurement of the second diameter (D2).

6. The toothed gear (B) according to claim 5, wherein the joining stretch (G) has a substantially linear extension.

7. The toothed gear (B) according to claim 5 or 6, wherein each tooth has an engaging surface (Si) with an undulating shape, defined by the tapered geometry, and also has two lateral surfaces (S1 , S2) facing each other and perpendicular to the axis of symmetry (X);8. The toothed gear (B) according to any one of claims 1 to 7, wherein the teeth (A) lie and extend along a lying plane defined by the main body (R) and along a lateral perimeter surface (Sp) of the same main body (R).

9. A transmission mechanism (M1 , M2) comprising two toothed gears (B1 , B2 or B3, B4) according to any one of claims 1 to 5, wherein a toothed gear (B1 , B2 or B3, B4) is designed to transmit the motion to a further toothed gear (B1 , B2 or B3, B4).

10. A method for making a toothed gear (B) according to any one of claims 1 to 7, comprising the following steps:- one is established between module (m) and number of teeth (Z) of the toothing of the toothed gear (B) and the other is calculated from the primitive diameter (Dp) of the toothed gear (B) by means of the ratio:Dp = Z ■ m- an outer arc (a) on the foot circumference (C2) is considered, having a foot diameter (D2) equal to the chord of the outer arc (a),- the head diameter (D1 ) of the head circumference (C1 ) is calculated by means of a predetermined parameter (c), in such a way as to eliminate the interference between the teeth during the meshing of the toothed gear (B)in a transmission mechanism:D1 = D2 / c- the centre of the foot circumference (C2) is identified as the midpoint of the linear segment underlying the outer arc (cc);- the foot circumference (C2) is passed through the ends of said linear segment,- the centre of the head circumference (C1 ) is identified as a point belonging to the line (Q) joining the centre of the toothed gear (B) with the foot circumference (C2), and has a distance equal to half the head diameter (D1 ) from the meeting point between the foot circumference (C2) and said joining line (Q),- the foot circumference (C2) and the head circumference (C1 ) are connected by two rectilinear segments simultaneously tangential to both said circumferences (C1 , C2).1 1 . The method according to claim 10, wherein the parameter (c) has a value of between 1.18 and 1.23, preferably between 1.1 ,19 and 1.22, inclusive, more preferably between 1.20 and 1.21 inclusive, even more preferably equal to 1 .20.

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