FR3112183A1 - Low stiffness high torque density torsion spring - Google Patents

Abstract

A low stiffness, high torque density torsion spring (2) for a concurrent axis gear reducer, comprising: a plurality of blades (5) evenly distributed about a Y axis and extending radially; each of said blades (5), comprising an inner edge (5a) and an outer edge (5b), parallel to the Y axis; the outer edge (5b) cooperating with a toothed pinion (3) of axis of rotation Y; the inner edge (5a) cooperating with a shaft (4) of axis of rotation Y; each of said blades (5) further comprising, on either side of the inner edge (5a), a biased face (5a1; 5a2) ) extending parallel to Y, characterized in that each of said biased face (5a1; 5a2), of said blade (5), of said plurality of blades (5), is in coplanar and aligned contact, with the biased face ( 5a1; 5a2) adjoining the adjacent blade (5), so that said plurality of blade (5) forms an annular shape with an axis of revolution Y. The plurality of said biased faces (5a1; 5a2) being attached to each other. "Figure for the abstract: Figure 1"

Description

Low stiffness torque high density torsion spring

The present invention relates to a torsion spring used in a gear reducer with intersecting axes intended for aircraft engines. Although the present invention was developed for use in a speed reducer, some applications may be outside this field.

The torsion spring with high torque density and low stiffness according to the invention is preferably used to carry out the load sharing in a speed reducer with divided torque, with gears with concurrent axes. A split-torque speed reducer, or “split-torque” (in English), allows high power density, obtained by multiplying the force paths connecting the input stage and the output stage of the reducer, and is, for example, used in an aircraft engine of the turbofan or turbofan (in English language) type, in order to reduce the speed of rotation of a fan driven by a turbomachine with a high speed of rotation.

The power density being defined as the ratio of the transmissible power per unit of weight, the advantage of such a reducer is to be as compact and light as possible while having a very high transmissible torque capacity.
With the divided torque technique, the motor torque and the rotational speed of a motive power, for example of an aircraft turbomachine, are transmitted to the input stage of the reducer, the motor torque is divided by transiting through a plurality of force paths, then recombines on the output stage of the reducer. Therefore, rather than taking a single path, the motor torque passes through the reducer via a plurality of force paths. This proportionally reduces the load on the teeth of the internal gears constituting said force paths, and consequently reduces the weight and size of the reducer, thus maximizing the power density.
In gear reducers with high power density concurrent axes, the force paths can, for example, be composed of pairs of toothed pinions coupled together in rotation.

However, due to manufacturing tolerances and structural deflections of gearbox components under load, the actual division of motor torque between each of the force paths cannot be equally distributed in a natural manner, and if left unchecked, too large gaps between each of the paths of force can cancel the advantage of this technique.
To operate optimally, a split torque gearbox must be designed to allow the most equal distribution of load possible between each of the force paths, and even more particularly in a gearbox application for aircraft engines, where the constraints of weight, size and operability are extremely severe.

In a known way, one solution consists in adding a deformable system in each of the force paths so that, under the load, the substantially identical deformation of each deformable system of each of the force paths, allows all the mesh contacts of gears to be established and to transfer the force between the input stage and the output stage of the reducer, which has the effect that the plurality of the force paths naturally tend to share the total motor torque between them, in roughly equal fractions.
However, in order not to impact the weight and size of the reducer while allowing less demanding and therefore less expensive manufacturing precision, the deformable system targeted by the present invention must have a high torque density and maximum torsional flexibility. . The torque density being defined as the ratio of the maximum transmissible torque per unit volume.

In addition, due to the very high speeds of rotation, other constraints must be taken into account, such as in particular the centrifugal effect and the inertial constraints.
Finally, in the application targeted by the present invention, it would be advantageous for a divided torque reduction gear for an aircraft engine to incorporate a torque limiter function to make it possible to separate the turbomachine and the fan, in certain extreme torque situations. exceptionally high, above those expected from normal use.

Document EP 0814 281-B1 discloses a split-torque reducer of the type with concurrent axis gears, which proposes as a deformable load-sharing system, a flexible connection in torsion, coupling in rotation the pair of toothed pinions forming the path of strength.
Such a deformable system is advantageous for a gear reducer with concurrent axes, because the deformation allowing the distribution of the load being done in the natural direction of rotation of the pair of toothed pinions, no degradation of the mesh contact pattern or "contact pattern (in English), nor any vibration is generated.
In addition, in the case of a reduction gear intended for an aircraft engine, this deformable load distribution system, independent of the other components of the reduction gear, is little affected by the structural deflections undergone by the engine. This allows a certain stability of the torque division, which limits overstressing and improves the operability of the reducer.

However, the torsionally flexible devices proposed by the aforementioned patent have the disadvantage that the torsion shaft must be long to allow both a high torque and a large angular deflection. And for the second proposal concerning a flexible elastomer coupling, this requires a significant thickness of material to obtain equivalent characteristics. In addition, these types of materials can degrade over time, especially when exposed to oils and high temperatures, as is the case in most high power density transmissions.
In the two cases proposed, the useful volume, the torque density and the torsion flexibility are not optimal.

Various compact and deformable systems in torsion, coupling in rotation a shaft with a pinion, exist in the state of the art, such as for example patent WO 0104507 A1 or patent AT 516 397 A4. These propose to use cut-out tabs or inserted strips respectively, working substantially in bending with the aim of producing an angular flexibility simulating a torsion deformation.
However, because they were not designed for this purpose, none of these devices makes it possible to obtain both torsional flexibility and maximized torque density.

The energy performance and reliability of commercial aircraft engines having a constant need for improvement, the object of the invention is to propose an optimized torsion spring making it possible to remedy the aforementioned drawbacks.

To do this, the invention relates according to its most general acceptance, a high torque density torsion spring with low stiffness, preferably for a gear reducer with concurrent axes, coupling in rotation a shaft to a toothed pinion, comprising;
a plurality of blades, evenly distributed around a Y axis and extending radially;
each of said blades, comprising an inner edge, parallel and proximal to the Y axis, having a dimension, in the direction of the Y axis, equal to or greater than an outer edge, parallel and distal to the Y axis;
said outer edge, being configured to cooperate in an operational manner with a toothed pinion whose axis of rotation substantially coincides with the Y axis;
said inner edge, being configured to cooperate operatively with an axis of rotation shaft substantially coinciding with the Y axis; And
each of said blade further comprising, on either side of said inner edge, a biased face extending parallel to the Y axis;
characterized in that each of said biased face, of said blade, of said plurality of blades, is in coplanar and aligned contact with the adjoining biased face of the adjacent blade, so that said plurality of blades forms an annular shape of axis of revolution Y. The plurality of said biased face being attached to one another.

Indeed, in the application targeted by the present invention, the high torque to be transmitted, the limited size of the reducer, and the need to have the highest possible angular flexibility, requires a torsion spring consisting of many blades substantially identical, each having the greatest possible bending or bending capacity.
In addition, such an annular-shaped torsion spring is compatible with very high rotational speeds, on the one hand because the balancing of the moment of inertia is simplified because the plurality of said blades making up said spring are substantially identical, and on the other hand, because each of said blades having a low mass, said spring is not very sensitive to centrifugal force.

When a torsion spring according to the present invention is subjected to a torque, the torsional deformation generating an angular offset between the two ends of the torsion spring, is obtained by bending or bending, of a plurality of flexible blades.

In the prior art, flexible tongues cut out of the mass or flexible blades inserted into one or more connecting pieces generate, among other things, either very high stress concentrations at the foot of the tongues for the first case, or a volume not optimized for the second case, which is not optimal.
Advantageously, the torsion spring according to the invention is only composed of substantially identical blades, attached directly to each other. This allows, for a given volume, a maximum plurality of blades.

To do this, on either side of said inner edge of the blade, the thickness is bevelled on each side, parallel to the Y axis, forming two faces, biased so that each blade of the plurality of blades evenly distributed around the Y axis, being juxtaposed one after the other, biased face aligned, in contact and attached with the neighboring biased face, forms the torsion spring according to the invention of annular shape with axis of revolution Y.

In general, said blade has a shape or a profile, which can be straight or curved or even shaped, determined according to the desired angular deflection of said spring when it is subjected to a given torque.
Preferably, said biased faces are substantially symmetrical to each other with respect to a median plane passing through the Y axis and the middle of said inner edge, said blade having a constant thickness, symmetrical and parallel to said median plane and said biased faces are welded together to form a torsion spring according to the invention, comprising an inner end, formed by the plurality of said inner edges, substantially coaxial with an outer end, formed by the plurality of said outer edges.

In addition, said inner edge is attached directly or indirectly to said shaft, by welding, keying or splines and preferably directly welded to the shaft;
and said outer edge operatively co-operates with said sprocket such that force or moment can be transmitted between said sprocket and said blade.

Preferably, said outer edge has a convex rounded shape, fitting substantially into a groove of said toothed pinion, in the form of a concave hollow, of substantially identical dimensions, in order to cooperate together operationally.
In addition, each of said concave recessed groove cooperating with said plurality of blades, is connected with the adjacent groove, by a boss of rounded convex shape, a distance H separating the bottom of a groove and the top of an adjacent convex boss .

Each blade being made in one piece from one edge to the other, stress concentrations at the foot of the blade are thus avoided and the mechanical resistance is maximized.
Furthermore, said inner end and outer end of the torsion spring of the present invention, cooperating directly with respectively, said shaft and said toothed pinion, allows the volume as well as the deformable length of said blades to be maximized, which makes it possible to obtain both torsional flexibility and optimum torque density in a given volume.

When a torque or a moment, less than a predefined value, is applied between said shaft and said toothed pinion, said blades deform elastically, substantially in bending, said outer edges remaining in engagement and cooperating with said groove, thus producing an offset angular, reversible, between the shaft and the toothed pinion remaining coupled in rotation.
When a torque or a moment, greater than said predefined value, is applied between said shaft and said toothed pinion, said blades deform, substantially in bending, said outer edges not remaining in engagement and no longer cooperating with said groove, breaking thus the rotational coupling between the shaft and the toothed pinion.

The present invention further relates to a gear speed reducer with concurrent axes, characterized in that it comprises at least one device as described above.

The invention will be better understood, and other characteristics, details, aims, and advantages thereof will appear more clearly during the detailed explanatory description which follows, of an embodiment of the invention given as purely illustrative and non-limiting example, with reference to the accompanying schematic drawings.

DESCRIPTION OF FIGURES

In these drawings:
- is a perspective view of an exemplary implementation of the torsion spring according to one embodiment of the invention, shown in the rest state

- is a transverse detail view according to figure 1

- is a longitudinal sectional view AA according to figure 1

- is a perspective view of the torsion spring according to figure 1

- is a perspective view of a blade of the torsion spring according to figure 4

- is a detail view of the torsion spring according to figure 2, shown in the normal working state

There is an arrangement (1) representing an example of implementation of the torsion spring (2) with high torque density and low stiffness according to a preferred embodiment of the invention, coupling in rotation, in a torsionally flexible manner, a toothed pinion (3) and a shaft (4). The torsion spring (2), the toothed pinion (3) and the shaft (4) then pivot substantially together, around the Y axis.

Said arrangement (1) is, here in this preferred embodiment, but not limited to, representative of a deformable load distribution system such as that covered by the present invention, in which the torsion spring (2) couples in rotation , a pair of toothed pinions of a force path of a gear reducer with concurrent axes.
For example, a toothed wheel, not shown, transmits a speed of rotation and a drive torque C1 to the toothed pinion (3)
A second toothed pinion, not shown, forming with said toothed pinion (3), said pair of toothed pinions of a path of force, is attached to the shaft (4) and exerts on the latter a resistive torque C2.

In the arrangement (1) of the present example, the toothed pinion (3) transmits flexibly in torsion, via the torsion spring (2) according to the invention, the speed of rotation and the torque of drive C1 to the shaft (4), as follows:
As illustrated on the and the , on a diameter located closest to the gear teeth (3d), the toothed pinion (3) comprises a substantially circular inner wall (3a) coaxial with the Y axis, provided with a plurality of grooves (3b) s 'extending parallel to the Y axis, and evenly distributed around it.

Each groove (3b) of said plurality of grooves has a shape, preferably but not limited to, substantially of a concave hollow semicircle and each pair of adjacent grooves (3b) is connected by a shape, preferably but not limited to, of a boss convex (3c) substantially in the shape of a semicircle, so that said circular inner wall (3a) is undulated by the alternation of said concave recessed groove (3b) and said convex boss (3c), a difference in radius H separating the bottom of a groove (3b) and the top of an adjacent convex boss (3c).

In line with each of said concave hollow groove (3b), a plurality of blades (5) extend radially from an outer edge (5b) of said blade (5), parallel to the Y axis and cooperating with said groove (3b), at an inner edge (5a) of said blade (5), parallel to the Y axis and cooperating with an outer cylindrical wall (4a) of the shaft (4).

Said outer edge (5b) is of convex rounded shape and of substantially identical dimensions to said hollow concave groove (3b) of the toothed pinion (3), so as to fit into one another and to cooperate together operational way.

In the present example, but not limited to, the length of the inner edge (5a) of the blade (5) is greater than that of the outer edge (5b), and the lengths of said edges (5a; 5b) are substantially centered one relative to the other.

Said blades (5) converge radially from said outer edge (5b) to said inner edge (5a), in contact with said outer cylindrical wall (4a) of the shaft (4).
In the vicinity of the latter, to avoid interference with the adjacent blades (5), the thickness of each of the blades (5) of said plurality of blades (5) is bevelled, parallel to the Y axis, on either side and on the other side of said inner edge (5a), thus generating two biased faces (5a1; 5a2), so that each of said biased faces (5a1; 5a2), of each of said blades (5), is in coplanar contact and aligned with the biased face (5a1; 5a2) adjoining the blade (5) adjacent.

Here, in this preferred embodiment, but not limited to, as shown in the and the , the blade (5) extends radially with a constant thickness, symmetrical and parallel to a median plane passing through the Y axis and the middle of said inner edge (5a), that is to say that said median plane passes also through the middle of said outer edge (5b), and said biased faces (5a1; 5a2) are substantially symmetrical with respect to said median plane.

Furthermore, the plurality of said biased faces (5a1; 5a2) are joined together, for example, in this preferred embodiment, but not limited to, by electron beam welding, in order to form the torsion spring (2) according to the present invention, as illustrated in , of substantially annular shape with an axis of revolution Y, comprising an inner end, formed by the plurality of said inner edges (5a), substantially coaxial with an outer end, formed by the plurality of said outer edges (5b).

In this preferred embodiment, but in a non-limiting manner, said toothed pinion (3), said torsion spring (2) and said shaft (4) are made of metallic materials. In order to attach the torsion spring (2) to the shaft (4), said inner end of the torsion spring (2), in contact with the outer cylindrical wall (4a) of the shaft (4), is attached to the latter, for example, but not limited to, by welding by electron beams.

In variant embodiments not shown, said inner end of the torsion spring (2) can, for example, be welded to a grooved ring, or even be directly grooved, so that the torsion spring (2) is coupled in rotation with the shaft (4), by means of splines, keying or any other means of attaching the torsion spring (2) to the shaft (4).

In this preferred embodiment of the invention, when a driving torque C1 is applied to the toothed pinion (3), the latter, via the grooves (3b) in concave hollows, cooperating with the said outer edges (5b) in convex rounding of said plurality of blades (5), transmits the torque and drives the torsion spring (2) in rotation around the Y axis.
The force of torque C1 then passes, in each of the blades (5) of said plurality of blades (5), from the torsion spring (2), to said inner edge (5a) attached to the outer cylindrical wall (4a) of the shaft (4).
The shaft (4) resistant to rotational drive with a torque C2, forces a torque C1, which may be large enough to deform said blades (5) in bending, all in a substantially identical manner and in proportion to the amplitude of the exerted effort.

Advantageously, the large quantity of blade (5) of the torsion spring (2) makes it possible to transmit a high torque C1 with blades (5) of low unit stiffness, and therefore of high bending capacity.

As illustrated on the , when the present rotational coupling works normally, that is to say when a torque C1 is applied and the resistive torque C2 is less than a predefined value, said blades (5) flex, said outer edges (5b) convex rounded, roll and pivot, each in their respective concave recessed groove (3b), of the toothed pinion (3), remaining in engagement therewith, which has the effect of producing an angular offset D between the shaft (4) and the toothed pinion (3), with respect to an angular position at rest, shown in dotted lines on the .

In the case, not shown, where the resistant torque C2 is exceptionally high and greater than the torque expected from normal use, that is to say greater than said predefined value, said blades (5) flex excessively, to the point that said outer edges (5b) do not remain in engagement and disengage from said concave hollow groove (3b) of the toothed pinion (3), thus uncoupling in rotation the shaft (4) and the toothed pinion (3). This uncoupling thus allowing a torque limiter function for the deformable load sharing system targeted by the present invention.

Depending on the desired design objectives, such as, in particular, the ratio between the torque density and the desired flexibility, various variants of the torsion spring (2) according to the present invention, can be provided by those skilled in the art, the details of the embodiment disclosed here by way of example, which may influence a particular configuration not shown, such as, for example, curved or shaped blades (5) having a constant thickness or not, a particular contour or profile, or even a grooving of the toothed pinion (3) of different shape.

It should therefore be understood that within the scope of the appended claims, the present invention may be practiced other than as specifically described above.

Claims (11)

Torsion spring (2) high torque density with low stiffness, preferably for gear reducer with concurrent axes, coupling in rotation a shaft (4) to a toothed pinion (3), comprising;
a plurality of blades (5), evenly distributed around a Y axis and extending radially;
each of said blades (5), comprising an inner edge (5a), parallel and proximal to the Y axis, having a dimension, in the direction of the Y axis, equal to or greater than an outer edge (5b), parallel and distal to the Y axis;
said outer edge (5b), being configured to cooperate operatively with a toothed pinion (3) whose axis of rotation substantially coincides with the Y axis;
said inner edge (5a), being configured to cooperate operatively with a shaft (4) whose axis of rotation substantially coincides with the Y axis; And
each of said blades (5) further comprising, on either side of said inner edge (5a), an angled face (5a1; 5a2) extending parallel to the Y axis;
characterized in that each of said biased face (5a1; 5a2), of said blade (5), of said plurality of blades (5), is in coplanar and aligned contact, with the biased face (5a1; 5a2) adjoining the blade (5) adjacent, so that said plurality of blade (5) forms an annular shape of axis of revolution Y. The plurality of said biased face (5a1; 5a2) being attached to each other. Torsion spring according to Claim 1, characterized in that the said biased faces (5a1; 5a2) are substantially symmetrical to each other with respect to a median plane passing through the Y axis and the middle of the said inner edge (5a ), said blade (5) having a constant thickness, symmetrical and parallel to said median plane. Torsion spring according to Claim 1, characterized in that the said blade (5) has a shape or a straight, curved or shaped profile, determined according to the angular deflection desired for a given torque. Torsion spring according to claim 1, characterized in that the plurality of said biased faces (5a1; 5a2) are joined together by welding. Torsion spring according to the preceding claims, characterized in that said outer edge (5b), operatively cooperates with said toothed pinion (3), so that a force or a moment can be transmitted between said toothed pinion (3) and said blade (5). Torsion spring according to Claim 5, characterized in that the said outer edge (5b) has a convex rounded shape, fitting substantially into a groove (3b) of the said toothed pinion, in the form of a concave hollow, of substantially identical dimensions, in order to cooperate together in an operational way. Torsion spring according to Claim 6, characterized in that each of the said hollow concave grooves (3b) cooperating with the said plurality of blades (5) is connected with the adjacent groove (3b) by a boss (3c) of rounded shape. convex, a distance H separating the bottom of a groove (3b) and the top of an adjacent convex boss (3c). Torsion spring according to the preceding claims, characterized in that the said inner edge (5a) is attached directly or indirectly to the said shaft (4), by welding, keying or splines. Torsion spring according to the preceding claims, characterized in that when a torque or a moment, lower than a predefined value, is applied between said shaft (4) and said toothed pinion (3), said blades (5) deform elastically , substantially in bending, said outer edge (5b) remaining in engagement and cooperating with said groove (3b), thus producing an angular shift, reversible, between the shaft (4) and the toothed pinion (3) remaining coupled in rotation. Torsion spring according to the preceding claims, characterized in that when a torque or a moment, greater than said predefined value, is applied between said shaft (4) and said toothed pinion (3), said blades (5) deform, substantially in flexion, said outer edge (5b) not remaining in engagement and no longer cooperating with said groove (3b), thus breaking the rotational coupling between the shaft (4) and the toothed pinion (3). Gear reducer with concurrent axes, characterized in that it comprises at least one device according to one of the preceding claims.