Toothed wheel and method for making it and hydraulic gear pump

Abstract

A toothed wheel (R), defining a longitudinal axis of rotation (L) for transmitting motion by rotation about the longitudinal axis, comprises: a number N of teeth (D), disposed around the longitudinal axis, each tooth extending longitudinally along a predetermined tooth profile (P); a plurality of discs (11), each disc defining a number N of radial protrusions (S). The discs of the plurality of discs are superposed on each other along the longitudinal axis, positioned angularly about the longitudinal axis according to a predetermined criterion, so that each tooth of the toothed wheel is formed from a corresponding plurality of longitudinally superposed radial protrusions, to define the tooth profile of that tooth, the discs of the plurality of discs being integral with each other to rotate as one and thus form the toothed wheel.

Description

[0001] DESCRIPTION

[0002] TOOTHED WHEEL AND METHOD FOR MAKING IT AND HYDRAULIC GEAR PUMP

[0003] Technical field

[0004] This invention relates to a toothed wheel and to a method for making a toothed wheel. The technical field of this disclosure regards a toothed wheel.

[0005] Background art

[0006] Toothed wheels are generally used in machines and, in particular, in pumps and motors, where a first toothed wheel, called drive wheel, transmits motion to a second wheel, called driven wheel.

[0007] In particular, in the field of toothed wheels, the toothed wheels may be spur gear wheels, where the tooth profile is substantially parallel to the axis of the wheel, or helical gear wheels, where the tooth profile is inclined with respect to the axis of the wheel. To ensure that motion between the drive wheel and the driven wheel is transmitted regularly and constantly, at least one pair of teeth (one on each of the two wheels) is meshed at any one time. The regularity and silence of motion transmission are improved if two or more pairs of teeth are meshed at any one time. The fact that the teeth are inclined relative to the axis means that during rotation, two or more pairs of teeth are meshed simultaneously at all times, thus improving the regularity of the motion transmitted. For this reason, helical gear wheels are generally preferred because they are less noisy and more regular than spur gear wheels.

[0008] Traditionally, toothed wheels are made by cutting, with reciprocating motion by means of a gear cutter or shaper, or with continuous motion by milling by means of a gear hobbing machine, etc.; since the tooth profile to be obtained must be very precise, these tools for making toothed wheels are very complex and expensive.

[0009] The disadvantage of helical gear wheels is that during operation they i generate axial thrust forces which are eventually transferred to other components of the machine, with negative effects which must be counteracted with specific mechanisms. An example of a compensating mechanism for counteracting axial thrust is provided by patent document US2016265528A1 .

[0010] In particular, therefore, there is a need to reduce the costs of gear cutting and reduce the axial thrust forces in the case of helical gears. Patent document US2018 / 372102A1 describes a toothed wheel comprising a series of superposed discs. However, on account of the thinness of the discs and the screw-like configuration of the wheel, the use of wheels of this kind in a hydraulic pump limits the maximum obtainable pressure to 100 bar. Similarly, the toothed wheel described in patent document GB564309A, when used in a hydraulic pump, does not allow obtaining pressure greater than 50 bar. Moreover, since the drive wheel is mounted to a shaft by a key, a minimum clearance is created between it and the driven wheel, allowing them to move slightly. The resulting impacts can lead to damage to the gear teeth. Patent documents US2349022A and DE3141681 A1 , which describe a key coupling, and patent document US2515201A, which describes a prismatic coupling, have similar problems.

[0011] Aim of the invention

[0012] The aim of this disclosure is to provide a toothed wheel and a method for making a toothed wheel, be it a spur gear wheel or a helical gear wheel, to overcome the above mentioned drawbacks of the prior art.

[0013] In particular, the aim of this disclosure is to provide a toothed wheel which is easy to make and which allows obtaining a precise gear (or gear tooth) profile.

[0014] This aim is fully achieved by the toothed wheel and method for making a toothed wheel of this disclosure, as characterized in the appended claims.

[0015] In particular, the toothed wheel defines a longitudinal axis of rotation for transmitting motion by rotation about the longitudinal axis.

[0016] The toothed wheel comprises a number N of teeth disposed around the longitudinal axis. Each tooth extends longitudinally along a predetermined tooth profile. Preferably, the number N of teeth of the toothed wheel is at least equal to 7.

[0017] The toothed wheel comprises a plurality of discs (that is, the toothed wheel comprises from one to a plurality of discs). Each disc defines a number of radial protrusions (that is, protrusions jutting away from the longitudinal axis of the wheel) equal to N. In other words, each disc defines a number of radial recesses (that is, protrusions extending towards the longitudinal axis of the wheel) equal to N. The radial protrusions and the radial recesses of a disc define a tooth profile of that disc. The tooth profile of the wheel is suitable for meshing with a tooth profile of another toothed wheel in order to transmit motion. In particular, the tooth profile of each disc is straight.

[0018] The discs of the plurality of discs are superposed on each other along the longitudinal axis. In particular, the discs are positioned angularly about the longitudinal axis according to a predetermined criterion, so that each tooth of the toothed wheel is formed from a corresponding plurality of longitudinally superposed radial protrusions, to define the tooth profile of that tooth.

[0019] Preferably, the discs of the plurality of discs are integral with each other to rotate as one and thus form the toothed wheel.

[0020] In an embodiment, each disc defines a longitudinal thickness of between 0.1 mm and 20 mm. Preferably, the longitudinal thickness is between 0.1 mm and 10 mm, and in particular, between 0.1 mm and 8 mm. More preferably, the longitudinal thickness is between 1 mm and 5 mm. It should be noted, however, that this invention can be carried out even with different (for example, even larger) thicknesses.

[0021] It should be noted that the expression "plurality of longitudinally superposed radial protrusions" also refers to the case where the plurality of protrusions are partly superposed, that is to say, where the radial protrusions overlap, meaning that they are not completely superposed longitudinally on each other. In particular, each disc of the plurality of discs may be angularly staggered relative to the discs adjacent to it, so that the tooth profile is helical. That way, the meshing profile extends like a helical profile although it is made up of a plurality of straight, partly superposed teeth.

[0022] In this case, the plurality of superposed protrusions are only partly superposed so as to define a toothed wheel whose tooth profile (that is, meshing profile) is helical. Each disc of the plurality of discs may be angularly aligned with the discs adjacent to it, so that the tooth profile is straight. In this case, the plurality of superposed protrusions are completely superposed so as to define a toothed wheel whose tooth profile is straight. Thus, the predetermined criterion according to which the discs are mutually positioned is such that the radial protrusions can be aligned along the longitudinal axis to obtain a straight tooth profile or inclined with respect to the longitudinal axis to obtain a helical profile.

[0023] It is stressed that this disclosure allows obtaining any tooth profile, for example, bi-helical or with a helix angle which is variable along the axis of the wheel.

[0024] Generally speaking, each disc of the plurality of discs may be angularly staggered relative to the adjacent disc by a predetermined offset angle 0i. Thus, the offset angle 0i indicates the angular offset between a disc "i" and the disc "i-1 ". The offset angle 0i between one disc and the adjacent disc may be the same for each disc of the wheel (in other words, the offset angles 0i may be the same), or the offset angle 0i between one disc and the adjacent disc may be different for each disc of the wheel (in other words, the offset angles 0i may be different from each other).

[0025] The plurality of discs extends longitudinally from a first disc to a last disc. The discs of the plurality of discs may be mutually staggered so as to form a total offset angle Q between the first disc and the last disc. Preferably, the total offset angle Q between a radial protrusion of the first disc and a radial protrusion of the last disc is less than or equal to 10 degrees. In other words, the discs of the plurality of discs may be mutually offset so as to define a helical tooth profile where the rotation angle of the tooth profile is less than or equal to 10 degrees. It is thus possible to make a helical gear wheel by consecutively offsetting the discs of the wheel to obtain a helical profile.

[0026] It is noted that the total offset angle 0 is given by the sum of the offset angles between individual discs. Thus, given n discs, the total offset angle 0 is 0 = 01 + ... + 0i + ... + 0n.

[0027] It is also possible to make a gear wheel having a straight tooth profile. In particular, the straight tooth profile may be obtained by completely superposing the radial protrusions of the plurality of discs, or by staggering them slightly so that the total offset angle 0 is substantially zero.

[0028] Thus, the mutual angular stagger between the discs may be used to obtain a specific tooth profile, for example, a helical or other tooth profile, or to obtain a straight tooth profile. In the latter case, angularly staggering the discs to obtain a tooth profile which is altogether straight may be useful for a wheel in a hydraulic pump, to reduce output pressure ripple phenomena of the pump.

[0029] The total offset angle 0 is predefined (chosen, selected) based on the shape (that is, the profile) of the radial protrusions (that is, the teeth) and on the number of radial protrusions (that is, the number of teeth) so as to keep pump delivery and suction separate. The wheels of a pair of toothed wheels are configured to mesh so that the delivery and suction of a hydraulic pump are kept separate. In other words, one tooth space of a toothed wheel (for example, a helical tooth space) cannot be in contact with suction and delivery simultaneously.

[0030] It is noted that a fluid to be pumped by a hydraulic pump is moved, transported by the helical tooth spaces (where each helical tooth space is formed by a sequence of recesses of a row of discs), from a suction zone to a delivery zone. To ensure that delivery and suction remain separate, anyone (helical) tooth space moving towards the suction zone must not come into contact with the suction zone until that tooth space is isolated from the delivery zone. In particular, a radial protrusion of one wheel of the pair of wheels and a recess of the other wheel of the pair of wheels are mutually coupled so as to have two points of mutual contact. That way, delivery and suction are kept separate. The total offset angle 0 is selected so that (that is, is such that) a tooth space is in contact with suction and delivery simultaneously; in particular, the total offset angle 0 is selected so that (that is, is such that) there are two points of mutual contact between a radial protrusion of one wheel and a recess of the other wheel of the pair. The offset angles 0i of the discs are preferably determined on the basis of the total offset angle 0. Preferably, a value of the total offset angle 0 is independent of the number N of discs making up the toothed wheel (that is to say, it is independent of the length of the toothed wheel). The individual offset angles 0i are selected on the basis of the number N of discs making up the toothed wheel (that is to say, based on the length of the toothed wheel).

[0031] If the discs are mutually offset by the same quantity 0i, then each offset angle is 0i = 0 / (n-1 ).

[0032] The radial protrusions extend away from the longitudinal axis and have an end which is distal to the longitudinal axis. At the end of the radial protrusion, the radial protrusion has a profile. Each recess of the disc has a profile that corresponds (that is, matches) the profile of the radial protrusion. That way, one radial protrusion meshes with a corresponding recess of a toothed wheel.

[0033] The profile of the radial protrusion has a top end surface (that is, a top land or tip). The top end surface is operatively in contact with inside surfaces of a pump casing. Similarly, the profile of the recess has a bottom surface. The profile of the radial protrusion has a first flank surface and a second flank surface, opposite the first flank surface.

[0034] In an example, the profile of the radial protrusion is rounded. Similarly, the bottom surface of the recess is rounded.

[0035] In particular, the top end surface of the protrusion may have a curved angular length (that is, a top end arc). The angular length of the top end surface may be greater than or equal to the offset angle 0i between two adjacent discs. This prevents possible leakage between adjacent discs of the same wheel caused by the fact that the discs are angularly staggered.

[0036] In particular, two adjacent discs are angularly staggered so that two corresponding adjacent protrusions have an angularly overlapped stretch. The angularly overlapped stretch between two adjacent discs is equal to the angular length of the top end surface minus the offset angle 0i between the two adjacent discs. Preferably, the angular length of the top end surface is greater than the offset angle 0i.

[0037] In an example, the profile of the top end surface is substantially straight (the profile of the flank surfaces may be slightly rounded or straight). Preferably, the angularly overlapped stretch between two adjacent discs is greater than zero. In this case too, the angular length of the top end surface may be greater than the offset angle 0i. Preferably, two protrusions of two adjacent discs are mutually superposed along the full radial length of the protrusions. This ensures that there is no leakage of liquid between one disc and the one adjacent to it. The fact that two protrusions are mutually superposed along the full radial length is ensured by the fact that the angularly overlapped stretch between two adjacent discs is greater than zero and that the profile of the top end surface is substantially straight. In other words, the profile of the top end surface of one disc and the profile of the top end surface of an adjacent disc are superposed (at least partly superposed) along an overlapped stretch which is greater than zero. Preferably, operatively, a first flank surface of one disc is in contact with a first flank surface of a conjugate disc at least at a first contact point, and a second flank surface of the disc is in contact with a second flank surface of the conjugate disc at a second contact point. Thus, during the rotation and meshing of a wheel with a conjugate wheel, there are always at least two contact points (the first contact point and the second contact point). This ensures that delivery and suction remain separate during meshing between two toothed wheels in a pump. In an example, the ratio between a diameter D between a top end surface of one protrusion and a top end surface of a diametrically opposite protrusion D and a longitudinal thickness S of the discs is between 8 and 25. A shaft diameter d may be between 0,4D and 0,6D.

[0038] In an example, the plurality of discs extends longitudinally from a first disc to a last disc, and the plurality of discs can be divided into a first group, including the first disc, and a second group, including the last disc.

[0039] The discs of the plurality of discs may be angularly staggered in such a way that the discs of the first group are progressively rotated relative to each other in a first direction and the discs of the second group are progressively rotated relative to each other in a second direction. In general, the first direction is different from the second direction. Preferably, the second direction is the opposite of the first direction, so that the tooth profile of the toothed wheel is bi-helical.

[0040] In other words, the tooth profile of the toothed wheel is helical in a first longitudinal stretch of the toothed wheel and helical in opposite direction in a second longitudinal stretch of the toothed wheel, so that, overall, the tooth profile of the toothed wheel is bi-helical.

[0041] In any case, the meshing between the teeth of the pairs of wheels which mesh to transmit motion always occurs by coupling between pairs of toothed discs with straight teeth, even if the discs of each wheel are angularly staggered to produce helical meshing. The resulting helical gear wheels made in this way do not generate axial thrust forces when they mesh.

[0042] In an example, the toothed wheel comprises a shaft. The shaft is coaxial with the longitudinal axis of the toothed wheel and the plurality of discs is fixed to the shaft.

[0043] In an embodiment, each disc comprises an internal opening, for example defining an inside diameter. Each disc defines an outside diameter, around which the plurality of radial protrusions are disposed. The outside diameter is greater than the inside diameter of the disc.

[0044] In an example, the plurality of discs is coupled to the shaft by mechanical interference. Therefore, the internal opening (that is, the inside diameter) of each disc is adapted to the shaft so it can be fixed to the shaft and can rotate as one with the shaft.

[0045] In an example, the plurality of discs may be coupled to the shaft and centred on the diameter of the shaft; therefore, the internal opening of each disc of the plurality of discs may have a diameter which is larger by a certain quantity than the diameter of the shaft. The plurality of discs may be coupled to the shaft by prismatic couplings (for example, to allow the plurality of discs to be entrained in rotation by the shaft).

[0046] In an example, the shaft includes a plurality of fastening elements disposed consecutively to each other along a stretch of the shaft. Each disc may include a groove, formed in an internal opening of the disc. The groove is configured to be engaged by a corresponding fastening element of the shaft. In particular, the fastening elements of the plurality of fastening elements may be disposed consecutively to each other and mutually staggered around the longitudinal axis so that when the grooves of the discs are engaged by the fastening elements, the tooth profile of the toothed wheel is helical. The fastening elements of the plurality of fastening elements may also be disposed consecutively to each other and mutually aligned along the longitudinal axis so that when the grooves of the discs are engaged by the fastening elements, the tooth profile of the toothed wheel is straight.

[0047] In an example, the plurality of fastening elements extends longitudinally between a first fastening element and a last fastening element and the plurality of fastening elements can be divided into a first group of fastening elements, including the first fastening element, and a second group of fastening elements, including the last fastening element. The fastening elements of the first group can be rotated relative to each other in a first direction progressively along a first stretch of the shaft, and the fastening elements of the second group can be rotated relative to each other in a second direction progressively along a second stretch of the shaft. The first direction may be the opposite of the second direction so that when the grooves of the discs are engaged by the fastening elements in the first stretch and in the second stretch of the shaft, the tooth profile of the toothed wheel is bi-helical.

[0048] In an embodiment the shaft includes a single fastening element. The single fastening element may be a protrusion extending along the axis of the shaft, for example, parallel to the axis of the shaft or around the axis of the shaft. The grooves of the discs may each be configured to be engaged by the single fastening element of the shaft. The grooves of the discs may be disposed consecutively to each other, mutually staggered or aligned along the longitudinal axis so that when the grooves of the discs are engaged by the single fastening element, the toothed profile of the wheel is respectively helical or straight.

[0049] In an example, the plurality of grooves extends longitudinally between a first groove and a last groove and the plurality of grooves can be divided into a first group of grooves, including the first groove, and a second group of grooves, including the last groove. The grooves of the first group can be rotated relative to each other in a first direction progressively along a first stretch of the toothed wheel, and the grooves of the second group can be rotated relative to each other in a second direction progressively along a second stretch of the toothed wheel. The first direction may be the opposite of the second direction so that when the grooves of the discs are engaged by the single fastening element in the first stretch and in the second stretch of the toothed wheel, the tooth profile of the toothed wheel is bi-helical.

[0050] In an example, each disc of the plurality of discs defines an inside diameter, around which the plurality of radial protrusions is disposed, for example to define a toothed wheel having an internal tooth profile. It is therefore possible to make toothed wheels having an internal toothed profile, for example, for use in epicyclic reduction gear units or for use in pumps, where a wheel having an external tooth profile is coupled to a wheel having an internal tooth profile. In effect, cutting internal teeth to make toothed wheels having an internal tooth profile is very expensive and complex, especially if the internal tooth profile to be made is helical. Superposing a plurality of discs in such a way that the protrusions of the discs are superposed (partly or completely) makes producing the tooth profile of the wheels (internal and / or external) simpler and more economical; in effect, it avoids having to make the tooth profile of the wheel in a single part.

[0051] The plurality of discs may be coupled to a cylindrical cavity. The cylindrical cavity may be coaxial with the longitudinal axis of the toothed wheel. The cylindrical cavity is configured to guide and contain the plurality of discs, where the discs are preferably attached to each other. Thus, the outside diameter of each disc of the plurality of discs may be adapted to an inside diameter of the cylindrical cavity. In this case, each disc of the plurality of discs is configured to rotate as one with the other discs and relative to the cylindrical cavity, or each disc of the plurality of discs may be attached to the other discs of the plurality and attached also to the cylindrical cavity. In an example, the plurality of discs is coupled to the cylindrical cavity by a prismatic coupling.

[0052] However, the use of prismatic couplings (for example, tongues or keys) for transmitting power between shafts and toothed wheels in a pump may lead to a number of problems; for example, since the total offset angle 0 must be kept constant for each tooth profile (hence the individual offset angles i varied as a function of the number of discs N), adopting the prismatic coupling would mean having to machine a central diameter of the discs to obtain the prismatic coupling with an angular position relative to the teeth which is different for each number N of stacked discs; moreover, machining the shaft to obtain the slot for the prismatic coupling element and mounting the prismatic coupling element are particularly arduous tasks.

[0053] The discs are therefore fixed to the shaft by mechanical interference. Since the individual offset angles i can be determined at will, costs can be reduced and greater flexibility in the construction of the toothed wheels can be obtained if discs with central opening are shrink fitted to the shaft. Advantageously, the shaft may have a smooth surface. That way, commercially available pins can be used as shafts.

[0054] In an example, each (toothed) disc is a piece of sheet metal obtained by blanking, for example, chemical or other blanking process such as mechanical blanking.

[0055] In an example, each toothed disc is a piece of sheet metal obtained by laser cutting or waterjet cutting the tooth profile.

[0056] In an example, each toothed disc is made using traditional gear cutting methods, with reciprocating or continuous motion. In an example, each toothed disc is heat treated (to improve the strength properties of the disc). In an example, the profile of a protrusion (in particular, the top end surface and / or the flank surfaces) has rounded edges (for example obtained by tumbling).

[0057] In an embodiment, for each disc, each radial protrusion has an involute, cycloidal, epicyclic or hypocyclic shape or, generally speaking, has a profile suitable for making a conjugate profile that meshes with the teeth of a homologous wheel so as to create a transmission with a predefined gear ratio.

[0058] This invention also allows making a hydraulic pump. The hydraulic pump comprises a pair of meshing toothed wheels, where each of the toothed wheels of the pair is a toothed wheel according to one or more aspects of this disclosure. It is noted that this disclosure is also applicable to a hydraulic motor, where the hydraulic motor comprises a pair of meshing toothed wheels, where each of the toothed wheels of the pair is a toothed wheel according to one or more aspects of this disclosure.

[0059] In an embodiment, the toothed wheel of the pair of toothed wheels is a drive wheel; the other toothed wheel of the pair of toothed wheels is a driven wheel, driven by the drive wheel. In particular, the plurality of discs of the drive wheel are coupled to a shaft by mechanical interference. More particularly, the plurality of discs of the drive wheel are coupled to a shaft by mechanical interference so as to rotate as one with the shaft. The plurality of discs of the driven wheel may be coupled to another shaft by mechanical interference, preferably weaker than the mechanical interference by which the drive wheel is coupled.

[0060] In an example, the hydraulic pump comprises a bushing, configured to fix the discs of the driven wheel and of the drive wheel. The bushing is used to fix the discs of the driven wheel and of the drive wheel to respective shafts. In particular, the bushing may comprise a gasket; the gasket may have the function of absorbing axial play so as to give the hydraulic pump an axial play compensation feature. The hydraulic pump may have a single bushing, fixed at one end of the toothed wheels; the hydraulic pump may have an additional bushing which is fixed at an opposite end.

[0061] In an embodiment, the number N of teeth of each of the wheels of the pair of toothed wheels is at least 7. The plurality of discs (of the drive wheel and of the driven wheel) extends longitudinally from a first disc to a last disc and a total offset angle 0 between a protrusion of the first disc and a radial protrusion of the last disc is less than or equal to 10 degrees. Preferably, the longitudinal thickness of each disc of the drive wheel and of the driven wheel is between 1 and 5 mm.

[0062] This disclosure also provides a method for making a toothed wheel defining a longitudinal axis of rotation. The toothed wheel may be made according to one or more aspects of this disclosure. Preferably, this disclosure provides a method for making a toothed wheel comprising a number N of teeth disposed around the longitudinal axis, where each tooth extends longitudinally along a predetermined tooth profile.

[0063] The method comprises a step of providing a plurality of discs, each disc defining radial protrusions equal to N in number. The method comprises a step of superposing the discs of the plurality of discs on each other along the longitudinal axis and positioned angularly about the longitudinal axis according to a predetermined criterion, so that each tooth of the toothed wheel is formed from a corresponding plurality of radial protrusions which are superposed (or at least partly superposed) longitudinally to define the tooth profile of that tooth. The method also comprises making the discs of the plurality of discs integral with each other so they rotate as one and thus form the toothed wheel.

[0064] The method may also comprise axially spacing each disc from the adjacent discs.

[0065] The discs may be made by blanking. In other words, the method may comprise a step of forming the discs by blanking, for example, chemical or other blanking process such as mechanical blanking. The method may comprise a step of forming the discs by milling or other method known in the industry concerned.

[0066] In an example, the method may comprise a step of heat treating each disc. An inside diameter of the disc may be centred and calibrated on a shaft after the step of heat treating it.

[0067] In an example, the method may comprise a step of disposing the discs in the same plane and a step of grinding or planing the discs so that all the discs have the same thickness S.

[0068] In an example, the method may comprise a step of tumbling the profile of a protrusion (in particular, the top end surface and / or the flank surfaces) so as to round the edges of the profile of the protrusion.

[0069] In an example, the method comprises a step of fixing the plurality of discs to a shaft which is coaxial with the longitudinal axis of the toothed wheel.

[0070] In an example, the step of fixing is by mechanical interference. In an example, the step of fixing is by prismatic coupling.

[0071] In an example, the method comprises a step of fixing the plurality of discs to a cylindrical cavity which is coaxial with the longitudinal axis of the toothed wheel. The method may comprise a step of fixing each disc of the plurality of discs to each other and inserting the plurality of discs, which are fixed to each other, into a cylindrical cavity.

[0072] In an embodiment, the method comprises a step of providing a template. The template includes a plurality of housings to receive the plurality of discs, each housing defining a plurality of abutment surfaces configured to come into abutment against a respective plurality of radial protrusions of a corresponding disc.

[0073] The template may be divided into a first and a second portion movable relative to each other between an open position, where it allows the discs to be inserted into the housings, and a closed position, where it allows the discs to be clamped in the template. The method may comprise a step of positioning the plurality of discs inside a template so that the discs have internal openings which are aligned along an axis.

[0074] The method may comprise a step of boring an inside diameter of the internal openings of the plurality of discs which are preferably aligned in the template. In particular, the step of boring is performed so that the inside diameter is less than a diameter of the shaft by a predetermined quantity to allow making a mechanical interference fit between the shaft and the discs. In addition, or alternatively, the method may comprise a step of turning a diameter of the shaft so that the diameter of the shaft is greater than an inside diameter of the internal openings of the plurality of discs.

[0075] The method may comprise a step of inserting the shaft into the internal openings of the discs, preferably while the discs are clamped in the template.

[0076] The method may comprise a step of inserting the discs into a cylindrical cavity, for example while the discs are clamped in the template.

[0077] In an example embodiment, in the step of superposing the discs, each disc of the plurality of discs is angularly aligned with the adjacent discs so that the tooth profile is straight.

[0078] In another example, in the step of superposing the discs, each disc of the plurality of discs is angularly staggered with respect to the adjacent discs so that the tooth profile is helical.

[0079] Alternatively, in the step of superposing the discs, each disc in a first group of discs may be angularly staggered with respect to the adjacent discs of the same group so that the tooth profile is helical in a first direction of rotation about the longitudinal axis, and each disc in a second group of discs may be angularly staggered with respect to the adjacent discs of the same group so that the tooth profile is helical in a second direction of rotation about the longitudinal axis. The first direction may be the opposite of the second direction so as to define a bi-helical profile. In an example, the method comprises a step of fixing by mechanical interference, where the protrusions of the discs are completely superposed (that is, where all the offset angles are zero, that is to say, where the discs are in mutual phase); the method may comprise a step of finishing the tooth profile of the wheel (for example by deburring or grinding); the method may comprise a (subsequent) step of mutually staggering the discs so that the tooth profile is, for example, helical. That way, it is possible to perform finishing processes on a straight profile (which is much easier to machine) and then stagger the discs to obtain a different profile. In effect, when performing finishing processes on a tooth profile, machining is much easier when the tooth profile is straight. In an example, the method comprises a step of fixing the plurality of discs of a toothed wheel to a shaft by mechanical interference with predetermined offset angles (in particular, zero or greater than zero), the wheel defining a drive wheel (in other words, the wheel is fixed to a shaft by mechanical interference so that each disc of the wheel rotates as one with the shaft); the method may comprise a step of fixing an additional wheel to an additional shaft by mechanical interference, where the mechanical interference of the additional wheel is weaker than the mechanical interference of the wheel (in other words, the additional wheel is fixed to an additional shaft by mechanical interference such that each disc of the additional wheel is free to rotate relative to the additional shaft). The additional wheel may define a driven wheel. The method may comprise a step of rotating the drive wheel about its axis of rotation (preferably by an angle at least equal to 360 degrees) and meshing each protrusion of the drive wheel with a corresponding recess of the driven wheel so as to rotate the discs of the driven wheel relative to the additional shaft. Preferably, during meshing of the driven wheel, the additional shaft remans fixed (that is to say, it does not rotate with the driven wheel). Thus, the wheel (that is, the drive wheel) is used as a template to assign the angular offset of the additional wheel (that is, of the driven wheel). Next, the method may comprise a step of forcing the discs of the additional wheel onto the additional shaft so as to make them integral with the additional shaft (and with the angular offset assigned thereto). The step of forcing the discs of the additional wheel onto the additional shaft may be carried out by means of a bushing configured to fix the discs of the additional wheel to the additional shaft; in other words, the method may comprise a step of connecting the discs of the additional wheel to the additional shaft by means of a bushing. Thus, creating the angular offset during meshing between a wheel that is fixed by (strong) interference and an additional wheel that is fixed by weaker interference has the advantage of allowing the protrusions of the two wheels to be meshed precisely independently of the specific value of the offset angle of the drive wheel. Thus, not having to necessarily fix the discs of the drive wheel with precision allows reducing productions costs.

[0080] Brief description of the drawings

[0081] This and other features will become more apparent from the following description of a preferred embodiment of the invention, illustrated by way of non-limiting example in the accompanying drawings, in which:

[0082] - Figures 1 A and 1 B show a disc according to one or more aspects of this disclosure;

[0083] - Figures 2A, 2B and 2C show a wheel according to one or more aspects of this disclosure;

[0084] - Figures 3A-3D show a pump comprising a wheel according to the prior art and Figure 3E shows an exploded view of a pump comprising a wheel according to the prior art;

[0085] - Figures 4A-4D show a pump comprising a wheel according to this disclosure and Figure 4E shows an exploded view of a pump comprising a wheel according to this disclosure;

[0086] - Figures 5A and 5B show a wheel according to one or more aspects of this disclosure. Detailed description of preferred embodiments of the invention

[0087] In the drawings, the letter R denotes a toothed wheel. The toothed wheel R defines a longitudinal axis of rotation L for transmitting motion by rotation about the longitudinal axis L.

[0088] The toothed wheel R comprises a number N of teeth D, disposed around the longitudinal axis L. Each tooth D extends longitudinally along a predetermined tooth profile P.

[0089] The toothed wheel R comprises a plurality of discs 1 1 . Each disc 1 1 defines radial protrusions S equal to N in number. Each disc 1 1 also defines a number of recesses equal to N in number, so that the radial protrusions S and the radial recesses define a conjugate profile of the disc 1 1 .

[0090] Each disc 1 1 of the wheel R defines a thickness of between 0.1 mm and 20 mm.

[0091] Preferably, the radial protrusions S have an involute, cycloidal, epicyclic or hypocyclic shape, that is to say, a shape such as to make a conjugate profile that meshes with the teeth of other wheels.

[0092] The discs 1 1 of the plurality of discs 1 1 are superposed on each other along the longitudinal axis L of the wheel, positioned angularly about the longitudinal axis L according to a predetermined criterion. In effect, each tooth D of the toothed wheel R is formed from a corresponding plurality of longitudinally superposed radial protrusions S, to define the tooth profile P of that tooth D.

[0093] The discs 1 1 of the plurality of discs 1 1 are integral with each other so they rotate as one and thus form the toothed wheel R.

[0094] In an embodiment, the radial protrusions S are completely superposed longitudinally so as to define a straight tooth profile P of the toothed wheel R.

[0095] In another embodiment, the radial protrusions S are partly superposed longitudinally so as to define a helical tooth profile P of the toothed wheel R.

[0096] In an embodiment, the plurality of discs 1 1 extends longitudinally from a first disc 1 1 A to a last disc 1 1 B and the plurality of discs is divided into a first group 1 1 ' of discs 1 1 , comprising the first disc 1 1 A, and a second group 1 1 " of discs 1 1 comprising the last disc 1 1 B. In this case, the discs 1 1 of the first group 1 1 ' are rotated progressively relative to each other in a first direction and discs 1 1 of the second group 1 1" are rotated progressively relative to each other in a second direction, opposite of the first direction, so as to define a bi-helical tooth profile P of the toothed wheel R.

[0097] The toothed wheel R comprises a shaft 12 which is coaxial with the longitudinal axis L of the toothed wheel R. The discs 1 1 comprise an internal opening 1 1 1 having an inside diameter.

[0098] In an example, the inside diameter of the internal opening 1 1 1 is less than the diameter of the shaft 12, by a certain quantity so that the discs 1 1 are fixed to the shaft 12 by mechanical interference.

[0099] In the drawings, the letters PI denote a hydraulic pump. The hydraulic pump PI comprises a pair of toothed wheels R which are meshed with each other. In particular, the pair of toothed wheels R includes a drive wheel RA and a driven wheel RB, driven by the drive wheel RA; the drive wheel RA and the driven wheel RB are toothed wheels according to one or more aspects of this disclosure.

[0100] It is noted that the substantial difference between the pump PI according to this disclosure, illustrated purely by way of example in Figures 4A-4E, and a pump PI according to the prior art, illustrated in Figures 3A-3E, lies in the toothed wheels RA and RB.

[0101] The hydraulic pump PI comprises a pair of shafts 12. In particular, the pair of shafts 12 includes a drive shaft 12A and a driven shaft 12B; the drive shaft 12A and the driven shaft 12B are shafts 12 according to one or more aspects of this disclosure.

[0102] In an example, the discs 1 1 of the drive wheel RA are coupled by mechanical interference to the drive shaft 12A and the discs 11 of the driven wheel RB are coupled by mechanical interference to the driven shaft 12B.

[0103] The hydraulic pump PI comprises a shim 13 and a plurality of gaskets 14 and sealing rings 15. The hydraulic pump PI comprises a casing 16 and a cover 17 which can be coupled to the casing 16 to enclose the drive wheel RA, the driven wheel RB, the drive shaft 12A, the driven shaft 12B, the shim 13, the gaskets 14 and the sealing rings 15.

[0104] To make a toothed wheel R according to one or more aspects of this disclosure, the plurality of discs 1 1 are made by blanking. The discs 1 1 are housed in a template which includes a plurality of housings for receiving the plurality of discs 11 . The housings define a plurality of abutment surfaces for coming into abutment against a respective plurality of radial protrusions S of a corresponding disc 1 1 which are superposed on each other along the longitudinal axis L. The template is divided into a first and a second portion, movable relative to each other between an open position and a closed position. Thus, the discs 1 1 are placed inside the template so that the internal openings 1 11 are aligned along an axis when the template is in the open configuration. When the template is in the closed configuration, the discs 1 1 are clamped inside the template.

[0105] The template allows each disc 1 1 to be superposed on the adjacent discs 1 1 in aligned fashion or in angularly staggered fashion so that the tooth profile P of the toothed wheel R to be made is straight, helical or bi-helical. In particular, the abutment surfaces of the template are made and adapted to obtain a certain type of tooth profile P.

[0106] The method may comprise a step of boring an inside diameter of the internal openings 11 1 of the plurality of discs 1 1 while keeping them aligned inside the template, so that the inside diameter is greater than the diameter of the shaft 12 they have to be coupled to by interference.

[0107] After that, the shaft 12 is inserted into the internal openings 11 1 of the discs 1 1 while the discs 1 1 are still clamped inside the template.

Claims

CLAIMS1. A toothed wheel (R), defining a longitudinal axis of rotation (L) for transmitting motion by rotation about the longitudinal axis (L), comprising:- a number N of teeth (D), disposed around the longitudinal axis (L), each tooth (D) extending longitudinally along a predetermined tooth profile (P);- a plurality of discs (11 ), each disc (1 1 ) defining radial protrusions (S) equal to N in number, wherein the discs (1 1 ) of the plurality of discs (1 1 ) are superposed on each other along the longitudinal axis (L), positioned angularly about the longitudinal axis (L) according to a predetermined criterion, so that each tooth (D) of the toothed wheel is formed from a corresponding plurality of longitudinally superposed radial protrusions (S), to define the tooth profile (P) of that tooth (D), the discs (1 1 ) of the plurality of discs (1 1 ) being integral with each other to rotate as one and thus form the toothed wheel (R).

2. The toothed wheel (R) according to claim 1 , wherein each disc (1 1 ) defines a longitudinal thickness of between 0.1 mm and 20 mm.

3. The toothed wheel (R) according to either of the preceding claims, wherein each disc (1 1 ) of the plurality of discs (1 1 ) is angularly staggered relative to the discs (1 1 ) adjacent to it so that the tooth profile (P) is helical.

4. The toothed wheel (R) according to claim 3, wherein the plurality of discs (1 1 ) extends longitudinally from a first disc (1 1 A) to a last disc (11 B) and, within that plurality of discs (1 1 ), a first group (1 T), including the first disc (1 1 A), and a second group (1 1"), including the last disc (11 B), can be identified, the discs (1 1 ) of the plurality of discs (1 1 ) being angularly staggered so that the discs (1 1 ) of the first group (1 T) are rotated progressively relative to each other in a first direction, and the discs (1 1 ) of the second group (1 1") are rotated progressively relative to each other in a second direction, opposite of the first direction, so that the tooth profile (P) of the toothed wheel is bi-helical.

5. The toothed wheel (R) according to any one of the preceding claims, comprising a shaft (12) that is coaxial relative to the longitudinal axis (L) ofthe toothed wheel (R), wherein the plurality of discs (1 1 ) is fixed to the shaft (12).

6. The toothed wheel (R) according to claim 5, wherein the plurality of discs (1 1 ) is coupled to the shaft (12) by mechanical interference.

7. The toothed wheel (R) according to claim 5, wherein at least one of the following conditions is true: i) the shaft (12) includes a plurality of fastening elements disposed consecutively to each other along a stretch of the shaft (12) and each disc (1 1 ) includes a groove, formed in an internal opening (1 1 1 ) of the disc (1 1 ) and configured to be engaged by a corresponding fastening element of the shaft (12); ii) the shaft (12) includes a single fastening element consisting of a protrusion, extending along the axis of the shaft (12) and each disc (1 1 ) includes a groove, formed in an internal opening (1 11 ) of the disc (1 1 ) and configured to be engaged by the single fastening element of the shaft; iii) the plurality of discs (1 1 ) is coupled to the shaft (12) by a prismatic coupling.

8. The toothed wheel (R) according to any one of the preceding claims, wherein each disc (1 1 ) is a piece of sheet metal obtained by blanking.

9. The toothed wheel (R) according to any one of the preceding claims, wherein, for each disc (1 1 ), each radial protrusion (S) has an involute, cycloidal, epicyclic or hypocyclic shape.

10. A hydraulic pump (PI) comprising a pair of meshing toothed wheels (R), wherein each of the toothed wheels (R) of the pair is a toothed wheel (R) according to any one of the preceding claims.

11. The hydraulic pump (PI) according to claim 10, wherein:- one toothed wheel (R) of the pair of toothed wheels (R) is a drive wheel and the other toothed wheel (R) of the pair of toothed wheels (R) is a driven wheel, driven by the drive wheel;- the plurality of discs (1 1 ) of the drive wheel are coupled to a shaft (12) by mechanical interference;- the number N of teeth (D) of each of the wheels of the pair of toothed wheels (R) is at least 7;- the plurality of discs (1 1 ) extends longitudinally from a first disc (1 1 A) to a last disc (11 B) and a total offset angle 0 between a protrusion (S) of the first disc (1 1 A) and a radial protrusion (S) of the last disc (1 1 B) is less than or equal to 10 degrees;- the longitudinal thickness of each disc (D) is between 1 and 5 mm.

12. The hydraulic pump (PI) according to claim 1 1 , comprising a bushing, configured to fix the discs (D) of the driven wheel and of the drive wheel to respective shafts.

13. A method for making a toothed wheel (R) defining a longitudinal axis of rotation (L), the toothed wheel (R) comprising N teeth (D), disposed around the longitudinal axis (L), each tooth (D) extending longitudinally along a predetermined tooth profile (P), the method comprising the following steps:- providing a plurality of discs (1 1 ), each disc (1 1 ) defining radial protrusions (S) equal to N in number;- superposing the discs (1 1 ) of the plurality of discs (1 1 ) on each other along the longitudinal axis (L), positioned angularly about the longitudinal axis (L) according to a predetermined criterion, so that each tooth (D) of the toothed wheel (R) is formed from a corresponding plurality of longitudinally superposed radial protrusions (S), to define the tooth profile (P) of that tooth;- making the discs (11 ) of the plurality of discs (1 1 ) integral with each other so they rotate as one and thus form the toothed wheel (R).

14. The method according to claim 13, wherein the discs (1 1 ) are made by blanking.

15. The method according to claim 13 or 14, comprising a step of fitting the plurality of discs (1 1 ) by mechanical interference to a shaft (12) that is coaxial relative to the longitudinal axis (L) of the toothed wheel (R).

16. The method according to claim 14, comprising the following steps:- providing a template including a plurality of housings for receiving the plurality of discs (1 1 ), each housing defining a plurality of abutmentsurfaces, configured to come into abutment against a respective plurality of radial protrusions of a corresponding disc (1 1 ), the template being divided into a first and a second portion movable relative to each other between an open position, where it allows the discs (1 1 ) to be inserted into the housings, and a closed position, where it allows the discs (1 1 ) to be clamped in the template;- positioning the plurality of discs (1 1 ) inside a template so that the discs (1 1 ) have internal openings (1 1 1 ) aligned along an axis;- boring an inside diameter of the internal openings (1 1 1 ) of the plurality of discs (1 1 ) aligned in the template, so that the inside diameter is less than a diameter of the shaft (12) by a predetermined quantity to allow making a mechanical interference fit between the shaft (12) and the discs (11 );- inserting the shaft (12) into the internal openings (11 1 ) of the discs (1 1 ) while the discs (1 1 ) are clamped inside the template.

17. The method according to any one of claims 13 to 16, wherein in the step of superposing the discs (1 1 ), each disc (1 1 ) of the plurality of discs (1 1 ) is angularly staggered relative to the discs (1 1 ) adjacent to it so that the tooth profile (P) is helical.

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