System for determining a torque applied between two rotating parts

Abstract

The invention relates to a system for determining a torque applied between two rotating members, said system comprising a test body (5) having an inner ring (6) and an outer ring (7) concentrically connected by a deformable structure of N branches (19) each extending between an inner end (19a) and an outer end (19b), said adjacent ends (19a, 19b) being separated by an angle respectively Acou and Aban, and a device for determining an angle between the rings (6, 7) which is a function of the applied torque, each ring (6, 7) being equipped with N means (6a, 7a) for fixing a corresponding ring of the encoder, said fixing means being angularly distributed forming an angle ACint and ACext with the nearest branch end (19a, 19b), said angles being such that: 0.25*Aban ≤ ACext ≤ 0.35*Aban and 0.45*Acou ​​≤ ACint ≤ 0.55*Acou. Figure 2a

Description

Title of the invention: System for determining a torque applied between two rotating members

[0001] The invention relates to a system for determining a torque applied between two rotating members in one direction around a geometric axis of rotation.

[0002] The components may in particular be integrated into a transmission of engine torque to a vehicle, for example between the electric motor or the pedal assembly and the mechanical transmission of an electrically assisted bicycle.

[0003] To do this, it is known to use a test body having an inner ring integral in rotation with means for coupling said test body to a first of the members, and an outer ring extending around the inner ring while having means for coupling said test body to the second of the members, said rings being connected concentrically around the axis of rotation by branches which are arranged to transmit the torque between the members while allowing angular movement between said rings as a function of the torque applied between the members.

[0004] Such a test body can be instrumented with an encoder by equipping each of the rings with a ring carrying a magnetic track, respectively inner and outer, which is capable of emitting a periodic signal representative of the rotational movement of the corresponding ring. In particular, each of the tracks has a succession of pairs of North and South poles to form a multipolar magnetic track delivering a pseudo-sinusoidal magnetic signal.

[0005] The determination system then comprises a sensor having a first - respectively a second - pattern of sensitive elements arranged at a reading distance from the inner track - respectively from the outer track - to form a signal representative of the angular position of the corresponding ring.

[0006] Documents FR-2 816 051, FR-2 821 931 and FR-2 862 382 describe the use of a device for comparing such signals which is capable of determining an angular difference between the portions, and therefore the applied torque, in that it induces said angle by twisting the deformable structure.

[0007] Since the encoder rings are fixed to the rings, the problem arises of their possible deformation during the relative movement under torque of the rings. In particular, such deformations can degrade the accuracy of the torque determination, due to the variation in the primitive diameters of the ring fixings which causes triangulation of the magnetic tracks.

[0008] In addition, the deformation of the encoder rings may cause a phenomenon to appear hysteresis due to friction at the level of their attachment to the rings, which oppose the applied torque and therefore minimize deformation under load and prevent return during unloading.

[0009] Furthermore, in certain applications, particularly in relation to the transmission of an electrically assisted bicycle, the space available for installing the test body is severely limited. This results in the need to design test bodies with reduced bulk, particularly radially, which further constrains the fixing of the encoder rings to the rings.

[0010] The invention aims to improve the prior art by proposing in particular a system in which the fixing of the encoder rings on the rings is optimized to make the precision of the torque determination more reliable, and this in particular on a radially compact test body.

[0011] To this end, the invention proposes a system for determining a torque applied between two rotating members in one direction around a geometric axis of rotation, said system comprising: - a test body having an inner ring integral in rotation with means for coupling said test body to a first of the members, and an outer ring extending around the inner ring while having means for coupling said test body to the second of the members, said rings being connected concentrically around the axis by a deformable structure which is arranged to transmit the torque between the members while allowing an angular movement between said rings as a function of the torque applied between said members, said deformable structure comprising a set of N branches distributed angularly between the rings, each of said branches extending between an inner end and an outer end, said adjacent inner - respectively outer - ends being separated by an angle Acou - respectively Aban - a device for determining an angle between the rings, said device comprising: • an encoder having an inner ring and an outer ring which are fixed respectively to the inner ring and the outer ring, said rings each carrying a respectively inner and outer magnetic track which is capable of emitting a periodic signal representative of the rotational movement of the corresponding ring; • a sensor comprising a first - respectively a second - pattern of sensitive elements arranged at a reading distance from the track inner - respectively of the outer track - to form a signal representative of the angular position of the corresponding ring; • a device for comparing the signals delivered by the sensor, said device being capable of determining an angle between the rings which is a function of the torque applied;

[0012] each of the rings being equipped with N means for fixing respectively internal and external to the corresponding ring of the encoder, said fixing means being distributed angularly forming an angle ACint for the internal means - respectively ACext for the external means - with the closest internal - respectively external - end, said angles being such that: 0.25*Aban < ACext < 0.35*Aban and 0.45*Acou ​​< ACint < 0.55*Acou.

[0013] Other objects and advantages of the invention will appear in the following description, given with reference to the appended figures, in which:

[0014] [Fig-1] is a partial perspective representation cut transversely of the crankset of an electrically assisted bicycle equipped with a torque determination system according to the invention,

[0015] [Fig. la] reproducing [Fig.l] with an exploded representation of the assembly of the test body,

[0016] [Fig.lb] being a partial longitudinal sectional view of [Fig. la];

[0017] [Fig.2] is a perspective representation from above of the test body of the [Fig.l],

[0018] [Fig.2a] being a perspective view from above of said test body devoid of encoder;

[0019] [Fig.3a],

[0020] [Fig.3b] and

[0021] [Fig.3c] are front views of [Fig.2] showing each of the dimensions by particular features of the test body according to the invention;

[0022] [Fig.4] represents in perspective and in partial axial section the relative arrangement of the encoder and sensor of the determination system of the previous figures.

[0023] In relation to these figures, a system for determining a torque applied between two rotating members 1, 2 in one direction around a geometric axis of rotation R is described below.

[0024] In this description, the terms of positioning in space are taken with reference to the axis R of rotation. In particular, the terms "interior" and "exterior" relate to an arrangement respectively close to and at a distance from this axis R, and the terms "axial" and "radial" relate to an arrangement respectively along this axis R and moving away from or approaching it.

[0025] In particular, the system allows the determination of a torque applied between two members 1, 2 integrated in a transmission of a motor torque to a vehicle, for example between the electric motor or the pedal assembly and the mechanical transmission of an electrically assisted bicycle.

[0026] Figures 1, 1a and 1b represent a crankset of an electrically assisted bicycle comprising a crank 3 equipped with a pedal 4, said crank being mounted on a shaft driven in rotation along the axis R to form a member 1 for applying a pedaling torque M+ depending on the direction of pedaling.

[0027] The system comprises a test body 5 which makes it possible to transmit the pedaling torque M+ to the other of the members 2, which, in the figures, is represented in the form of a sleeve, for example a satellite carrier of an epicyclic train of a motorized gearbox, exerting a torque Mbv.

[0028] In this application, the pedaling force F at the end of the pedal 4 to be considered according to standard EN15194: 2017 is 1,500 N which, with a crank length Lm 3 of 165 mm, generates a torque M+ of the order of 250 Nm. In particular, the torque to be transmitted by the test body 5 is only in one direction of rotation (that represented M+ in the figures), insofar as the other direction corresponds to the freewheel of the bicycle.

[0029] The test body 5 has an inner ring 6 integral in rotation with means for coupling said test body to the first member 1, and an outer ring 7 extending around the inner ring 6 while having means for coupling said test body to the second member 2.

[0030] In relation to the figures, the inner ring 6 has a bore 8 equipped with coupling means on the shaft 1, in particular in the form of grooves 8a arranged to engage with complementary ribs 8b formed circumferentially and in relief on the periphery of said shaft.

[0031] As regards the coupling to the other member 2, the embodiment shown provides that the outer ring 7 has at least one radial lobe 9 - in particular N radial lobes - which is equipped with a means 10 for fixing said outer ring to the sleeve 2. In particular, three lobes 9 at 120° are provided, each of them having an orifice 10 for fixing by a pin 12 or by screwing into a complementary orifice 11 of the sleeve. As a variant, the outer ring 7, in particular its periphery, may have geometric means for gearing with the second member 2.

[0032] The rings 6, 7 are connected concentrically around the axis R by a deformable structure which is arranged to transmit the torque between the members 1, 2 while allowing angular movement between said rings as a function of the torque applied between said members.

[0033] In particular, the torque resulting from the pedal torque M+ applied to the ring in inner ring 6 and the torque Mbv applied by the sleeve 2 to the outer ring 7 induces a torsion between the rings 6, 7, and therefore a relative angular displacement of said rings according to an angle of torsion which is a function of said torque.

[0034] The system comprises a device for determining an angle between the rings 6, 7 which, in particular taking into account the stiffness of the deformable structure, is a function of the torque applied.

[0035] According to one embodiment, the determination device comprises: - an encoder produced by equipping each of the rings 6, 7 with a ring 13, 14 carrying a magnetic track, respectively inner 13a and outer 14a, which is capable of emitting a periodic signal representative of the rotational movement of the corresponding ring 6, 7; - a sensor comprising a first 15 - respectively a second 16 - pattern of sensitive elements arranged at a reading distance from the inner track 13a - respectively from the outer track 14a - to form a signal representative of the angular position of the corresponding ring 13, 14; - a device for comparing the signals delivered by the sensor, said device being capable of determining an angle between the rings 6, 7 which is a function of the torque applied.

[0036] In relation to figures 1, 1a and 1b, the axis of the pedal assembly is mounted in rotation in a casing 17 on which the sensor is implanted with the patterns 15, 16 at a reading distance from the corresponding tracks 13a, 14a.

[0037] According to one embodiment, a succession of pairs of North and South poles is magnetized on a ring 13, 14 respectively to form a multipolar magnetic track 13a, 14a capable of emitting a magnetic signal of pseudo-sinusoidal shape.

[0038] The rings 13, 14 may comprise an annular matrix, for example made from a plastic or elastomer material, in which magnetic particles are dispersed, in particular ferrite or rare earth particles such as NdFeB, said particles being magnetized to form the magnetic tracks 13a, 14a.

[0039] Each pattern 15, 16 may comprise at least two sensitive elements, in particular a plurality of aligned sensitive elements, as described in documents FR-2 792 403, EP-2 602 593 and EP-2 602 594.

[0040] The sensitive elements may be based on a magnetoresistive material whose resistance varies according to the magnetic signal of the track 13a, 14a to be detected, for example of the AMR, TMR or GMR type, or a Hall effect probe.

[0041] According to one embodiment, the angular position can be determined incrementally by means of the signal emitted by a magnetic track 13a, 14a. According to another embodiment, the angular position can be determined absolutely, that is to say with respect to a reference position, by providing a secondary magnetic track or specific coding on the ring 13, 14.

[0042] In relation to [Fig. 4], the inner ring 13 has an outer main magnetic track 13a and an inner secondary magnetic track 13a', the sensor being provided with a pattern 15 for detecting an absolute angular position by means of the main track 13a, along a reading ray RLCintl, as well as an additional pattern of sensitive elements for detecting a reference position by means of the secondary track 13a', along a reading ray RLCint2.

[0043] The system further comprises a device for comparing the signals delivered by the sensor, said device being capable of determining an angle between the rings 6, 7 which is a function of the torque applied. In relation to the figures, the sensor comprises a card 18 on which the patterns 15, 16 of sensitive elements are implanted in an electronic circuit.

[0044] According to one embodiment, the sensors deliver incremental square signals in quadrature, the comparison device comprising counting means indicating the angular position of each of the rings 13, 14 and subtraction means making it possible to calculate the difference between said angular positions, in particular as described in documents FR-2 816 051, FR-2 821 931 and FR-2 862 382.

[0045] The deformable structure comprises a set of N branches 19 distributed angularly between the rings 6, 7. In particular, the branches 19 and the rings 6, 7 are formed in a single piece, for example by cutting with a wire machine or by stamping a blank of metallic material.

[0046] Each of the branches 19 extends between an inner end 19a secured to the inner ring 6 and an outer end 19b secured to the outer ring 7.

[0047] Advantageously, each branch 19 has an elbow formed between a convex section 20 extending from its inner end 19a and a concave section 21 extending to the outer end 19b.

[0048] As shown in the figures, for a torque M+ applied to the inner ring 6 in an anticlockwise direction, the branches 19 are inclined to the right, at an angle which depends on the maximum torque to be transmitted and the width of the branches 19.

[0049] The inclination of the branches 19 in combination with their geometric conformation in the shape of an S with two concave 21 and convex 20 sections makes it possible to satisfy the radial size constraint of the test body 5, for example in relation to an outer ring 6 with an outer radius of less than 50 mm, while increasing the length of the branches 19 in order to reduce their stiffness.

[0050] In particular, the branches 19 operate like a leaf spring and, to obtain a flexible spring while controlling the maximum stresses, it is the length of the branch 19 which is important. With the inclination, a pure tensile component is superimposed on the bending at the connection between the branch 19 and the rings 6, 7, because the branch 19 lengthens in the event of rotation of the outer ring 7.

[0051] In relation to figures 3a and 3b, each of the branches 19 extends over an angular sector SECT formed between two diametrical directions Apb and Atb passing through their respectively inner 19a and outer 19b ends. In the embodiment shown, the test body 5 comprises three branches 19 which each extend over an angular sector SECT between 50° and 90°, and in particular equal to 60°.

[0052] As shown in [Fig.3a], the adjacent outer ends 19b are separated by an angle Aban, which is measured between two adjacent directions Atb passing through respectively one of said outer ends.

[0053] Similarly, as shown in [Fig.3b], the adjacent inner ends 19a are separated by an angle Acou, which is measured between two adjacent directions Apb passing through respectively one of said inner ends.

[0054] Advantageously, the angles Acou and Aban are each equal to 360° / N, or of the order of 120° in the embodiment shown. This arrangement makes it easier to manufacture the test body 5, but also to guarantee a uniform circumferential distribution of the deformations of the structure during the relative movements of the rings 6, 7.

[0055] Each of the rings 6, 7 is equipped with respectively inner 6a and outer 7a fixing means for the corresponding ring 13, 14 of the encoder. In the embodiment shown, each ring 13, 14 is carried by an inner 13b and outer 14b frame respectively. Furthermore, each ring 6, 7 comprises fixing means in the form of orifices 6a, 7a to allow fixing by rivets 22 or by screwing into complementary fixing orifices formed for this purpose on the corresponding frame 13b, 14b.

[0056] Each ring 6, 7 comprises N fixing orifices 6a, 7a, i.e. a number identical to the number N of branches 19 of the deformable structure, said orifices being distributed angularly on the test body 5 forming an angle ACint for the internal orifices 6a - respectively ACext for the external orifices 7a - with the closest internal end 19a - respectively external 19b - said angles being such that: - 0.25*Aban < ACext < 0.35*Aban; and - 0.45*Acou ​​< ACint < 0.55*Acou.

[0057] These arrangements make it possible to angularly offset each orifice 6a, 7a towards a zone of the corresponding ring 6, 7 which is sufficiently far from the ends of adjacent branches 19a, 19b to present reduced radial deformations during the rotation of said ring and the tensile forces exerted by the branches 19 on said ring.

[0058] Thus, the risks of deformation of the rings 13, 14 during the relative rotation of the rings 6, 7 are limited, and therefore the risk of the appearance of friction and / or variation in diameter at the level of the fixing orifices 6a, 7a is limited. This makes it possible to limit the appearance of triangulation and / or hysteresis phenomena, which can affect the precision of the signals emitted by the rings 13, 14, and therefore the measurement of these signals by the sensor.

[0059] According to one embodiment, the angles are such that: 0.28*Aban < ACext < 0.32*Aban and 0.48*Acou ​​< ACint < 0.52*Acou. In particular, in the case of a test body 5 with three branches 19 as shown, the angle ACext is between 33.6° and 38°4, and the angle ACint is between 57.6° and 62.4°.

[0060] Advantageously, the angle ACext is equal to 0.3*Aban, or of the order of 36° in the figures, the angle ACint being equal to 0.5*Acou, or of the order of 60° in the figures.

[0061] In the embodiment shown, each external orifice 7a is arranged in a sector located between two adjacent branch sectors SECT.

[0062] Furthermore, each internal orifice 6a is arranged substantially in radial alignment with the external end 19b of the branch 19 of the corresponding sector SECT, so that the angle ACint is substantially equal to the angle of the angular sectors SECT of the branch.

[0063] In the figures, the branch sectors SECT each extend at an angle of the order of 60°, being separated two by two by an intermediate sector with an angle approximately equal to 60°, in which an orifice 7a is formed respectively for fixing the outer ring 14.

[0064] Furthermore, each of the lobes 9 for attachment to the sleeve 2 is arranged in a respective angular sector SECT of the branch, extending inside the concave section 21 of the corresponding outer end 19b. In particular, each lobe 9 has a radius of curvature similar to the radius of curvature of the concave section, so as to form a reduced clearance with said concave section.

[0065] This embodiment makes it possible to limit the size and, in this position, there are only very small deformations under load and thus the relative movement of the pins 12 in the orifices 10 is reduced to a minimum, avoiding wear phenomena.

[0066] In relation to figures 3c and 4, the internal orifices 6a - respectively external orifices 7a - are distributed along a radius RCint - respectively RCext - the dimensions of which are arranged to limit the risks of radial displacements during rotations of the rings 6, 7, as well as the overall radial size of the test body 5, while ensuring a positioning of the rings 13, 14 in accordance with the implantation of the sensitive patterns 15, 16 on the electronic card 18.

[0067] To do this, as shown in [Fig.4], the radius RCint of implantation of the holes 6a is less than the reading radius RLCintl of the main inner magnetic track 13a of the corresponding ring 13.

[0068] Thus, by offsetting the fixing orifices 6a of the ring 13 inside its reading track 13a, the radial deformations at the level of said orifices during the rotation of the ring 6 are limited, which makes it possible, in combination with the angular arrangement of said orifices according to the angle ACint, to guarantee the precision of the signal emitted by the track 13a.

[0069] In order to be able to withstand the mechanical stresses generated by its coupling to the shaft 1, the inner ring 6 must retain a sufficient radial thickness, while offering a compromise with the radial position constraints of the orifices 6a described previously.

[0070] To do this, the bore 8 of the ring 6 has a radius Rcan, the radius RCint for mounting the orifices 6a being such that 2.5 mm < RCint - Rcan < 4.5 mm. In the embodiment shown, the radius Rcan is measured at the foot of the splines 8a for coupling to the shaft 1, and the inner ring 6 has a minimum radial thickness EPtMIN, measured between said radius Rcan and the radius inscribed between the inner ends of each orifice 6a, which is preferably of the order of 2.3 mm.

[0071] Thus, as shown in Figures 2a, 3a, 3b and 3c, the inner ring 6 has a substantially annular geometry with three ears 23 with a reduced radial excess thickness, which are equally distributed at 120°, and in each of which a fixing orifice 6a is formed.

[0072] Similarly, the external magnetic track 14a has a reading radius RLCext, the radius RCext of implantation of the orifices 7a being less than said reading radius RLCext.

[0073] Thus, by offsetting the fixing of the outer ring 14 inside its magnetic track 14a, its radial size is limited, which makes it possible to avoid the risks of collision of the rivets 22 fixing said ring with the internal structure of the casing 17 during rotation of the outer ring 7.

[0074] This arrangement also makes it possible to bring the outer orifices 7a radially closer to the inner orifices 6a, in order to allow the use of a sensor of reduced dimensions, with sensitive patterns 15, 16 radially close together, and thus satisfy the overall size constraints of the system.

[0075] As shown in Figures 2a, 3a, 3b and 3c, the inner ring 7 has three lobes 24 equally distributed at 120° which each extend along a radial dimension towards the inside of the test body 5, and in each of which a fixing orifice 7a is formed.

Claims

Claims

1. System for determining a torque applied between two rotating members (1, 2) in one direction around a geometric axis of rotation (R), said system comprising: - a test body (5) having an inner ring (6) integral in rotation with means (8a) for coupling said test body to a first of the members (1), and an outer ring (7) extending around the inner ring (6) while having means (10) for coupling said test body to the second of the members (2), said rings being connected concentrically around the axis (R) by a deformable structure which is arranged to transmit the torque between the members (1, 2) while allowing an angular movement between said rings as a function of the torque applied between said members, said deformable structure comprising a set of N branches (19) distributed angularly between the rings (6, 7), each of said branches extending between an inner end (19a) and an outer end (19b), said adjacent inner ends - respectively outer ends - being separated by an angle Acou - respectively Aban -; - a device for determining an angle between the rings (6, 7), said device comprising: • an encoder having an inner ring (13) and an outer ring (14) which are fixed respectively to the inner ring (6) and the outer ring (7), said rings each carrying a magnetic track respectively inner (13a) and outer (14a) which is capable of emitting a periodic signal representative of the rotational movement of the corresponding ring (6, 7); • a sensor comprising a first (15) - respectively a second (16) - pattern of sensitive elements arranged at a reading distance from the inner track (13a) - respectively from the outer track (14a) - to form a signal representative of the angular position of the ring (13, 14) cor- corresponding; • a device for comparing the signals delivered by the sensor, said device being capable of determining an angle between the rings (6, 7) which is a function of the torque applied; said determination system being characterized in that each of the rings (6, 7) is equipped with N means for fixing, respectively internal (6a) and external (7a), the corresponding ring (13, 14) of the encoder, said fixing means being distributed angularly, forming an angle ACint for the internal means (6a) - respectively ACext for the external means (7a) - with the nearest internal end (19a) - respectively external (19b), said angles being such that: 0.25*Aban < ACext < 0.35*Aban and 0.45*Acou ​​< ACint < 0.55*Acou.

2. System for determining a torque according to claim 1, characterized in that the angles ACint and ACext are such that: 0.28*Aban < ACext < 0.32*Aban and 0.48*Acou ​​< ACint < 0.52*Acou.

3. System for determining a torque according to one of claims 1 or 2, characterized in that the branches (19) extend over an angular sector (SECT) formed between two diametrical directions (Apb, Atb) passing through the inner (19a) and outer (19b) ends respectively, the angle Acou being measured between two adjacent directions (Apb), the angle Aban being measured between two adjacent directions (Atb).

4. A torque determination system according to claim 3, characterized in that the external fixing means (7a) are arranged between the angular branch sectors (SECT).

5. System for determining a torque according to claims 3 or 4, characterized in that the angle ACint is substantially equal to the angle of the angular branch sectors (SECT).

6. A system for determining a torque according to any one of claims 1 to 5, characterized in that the angles Acou and Aban are each equal to 3607N.

7. System for determining a torque according to any one of claims 1 to 6, characterized in that the fixing means (6a, 7a) of the rings (13, 14) are in the form of orifices.

8. System for determining a torque according to any one of claims 1 to 7, characterized in that the rings (13, 14) are carried by an inner (13b) and outer (14b) frame respectively.

9. System for determining a torque according to any one of claims 1 to 8, characterized in that the internal fixing means (6a) are distributed along a radius RCint.

10. System for determining a torque according to claim 9, characterized in that the inner ring (6) has a bore of radius Rcan, the radius RCint being such that: 2.5 mm < RCint - Rcan < 4.5 mm.

11. A torque determination system according to one of claims 9 or 10, characterized in that the inner magnetic track (13a) has a reading radius RLCintl, the radius RCint being less than said radius RLCintl.

12. System for determining a torque according to any one of claims 1 to 11, characterized in that the external fixing means (7a) are distributed along a radius RCext.

13. A torque determination system according to claim 12, characterized in that the outer magnetic track (14a) has a reading radius RLCext, the radius RCext being less than said radius RLCext.

14. A torque determination system according to any one of claims 1 to 13, characterized in that the branches (19) have an elbow formed between a convex section (20) extending from the inner end (19a) and a concave section (21) extending to the outer end (19b).

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