System for determining the torque applied between two rotating parts

Abstract

The invention relates to a system for determining the torque applied between two rotating elements, said system comprising a test body (5) having an inner ring (6) and an outer ring (7) connected concentrically by a deformable structure of N arms (19), each extending between an inner end (19a) and an outer end (19b), said adjacent ends (19a, 19b) being separated by angles Acou and Aban, respectively, 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 to form angles ACint and ACext with the nearest arm 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 the torque applied between two rotating parts

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

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

[0003] To do this, it is known to use a test body having an inner ring fixed in rotation to coupling means of said test body to a first of the members, and an outer ring extending around the inner ring having coupling means of 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 an angular deflection 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 having an inner and outer magnetic track, respectively, which is capable of emitting a periodic signal representative of the rotational displacement of the corresponding ring. In particular, each of the tracks has a succession of North and South pole pairs 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 deviation 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 bushings, the problem arises of their possible deformation during the relative movement of the bushings under torque. In particular, such deformations can degrade the accuracy of the torque determination, due to the variation in the pitch diameters of the ring fixings, which causes triangulation of the magnetic tracks.

[0008] In addition, the deformation of the encoder rings can cause a hysteresis phenomenon due to friction at the point of their attachment to the rings, which opposes the applied torque and therefore minimizes the deformation under load and prevents the return during unloading.

[0009] Furthermore, in certain applications, particularly those related to the transmission of an electric-assist bicycle, the space available for mounting the test body is severely limited. This necessitates the design of test bodies with reduced dimensions, especially radially, which further constrains the mounting of the encoder rings onto the bushings.

[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 improve the reliability of the determination of the torque, and 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 elements in one direction around a geometric axis of rotation, said system comprising: - a test body having an inner ring fixed in rotation to coupling means of said test body to a first of the members, and an outer ring extending around the inner ring having coupling means of 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 deflection 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 on the inner ring and the outer ring respectively, said rings each having an inner and outer magnetic track respectively which is capable of emitting a periodic signal representative of the rotational displacement of the corresponding ring; • a sensor comprising 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; • 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 applied torque;

[0012] each of the rings being equipped with N means of fixing respectively internal and external of the corresponding ring of the encoder, said means of fixing being distributed angularly forming an angle ACint for the internal means -respectively ACext for the external means - with the nearest 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 become apparent from the following description, made with reference to the accompanying figures, in which:

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

[0015] [Fig. 1a] reproducing [Fig. 1] with an exploded view of the proof body assembly,

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

[0017] [Fig.2] is a top perspective representation of the proof body of the [Fig.l],

[0018] [Fig.2a] being a top perspective view of said proof body devoid of encoder;

[0019] [Fig.3a],

[0020] [Fig.3b] and

[0021] [Fig.3c] are front views of [Fig.2] representing each of the dimensions specifics of the test specimen 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 system for determining 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 for positioning in space are taken with reference to the axis R of rotation. In particular, the terms "inside" and "outside" relate to an arrangement respectively close to and at a distance from this axis R, and the The terms "axial" and "radial" relate to an arrangement respectively along this axis R and moving away from or towards it.

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

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

[0027] The system includes a test body 5 which allows the pedaling torque M+ to be transmitted to the other of the organs 2, which, in the figures, is represented in the form of a sleeve, for example of 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 1500 N, which, with a crank length Lm of 165 mm, generates a torque M+ of approximately 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), since the other direction corresponds to the freewheel of the bicycle.

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

[0030] In relation to the figures, the inner ring 6 has a bore 8 equipped with the 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] Regarding the coupling to the other component 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 in the sleeve. Alternatively, the outer ring 7, in particular its periphery, may have geometric means for meshing with the second component 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 components 1, 2. by allowing angular movement between said rings as a function of the torque applied between said components.

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

[0034] The system includes 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 applied torque.

[0035] According to one embodiment, the determination device comprises: - an encoder made 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 displacement 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 able to determine an angle between the rings 6, 7 which is a function of the applied torque.

[0036] In relation to figures 1a and 1b, the crank axle is mounted for rotation in a housing 17 on which the sensor is implanted with motifs 15, 16 at reading distance of the corresponding tracks 13a, 14a.

[0037] According to one embodiment, a succession of North and South pole pairs 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 motif 15, 16 may include at least two sensitive elements, including 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 can be based on a magnetoresistive material whose resistance varies according to the magnetic signal of track 13a, 14a to be detected, for example of type AMR, TMR or GMR, 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, i.e. relative to a reference position, by providing a secondary magnetic track or a specific coding on the ring 13, 14.

[0042] In relation to [Fig. 4], the inner ring 13 has a magnetic track main 13a outer and a secondary magnetic track 13a' inner, the sensor being provided with a pattern 15 for detecting an absolute angular position by means of the main track 13a, along a reading radius RLCintl, and with an additional pattern of sensitive elements for detecting a reference position by means of the secondary track 13a', along a reading radius 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 applied torque. As shown in the figures, the sensor comprises a board 18 on which the patterns 15, 16 of sensitive elements are embedded in an electronic circuit.

[0044] According to one embodiment, the sensors deliver incremental quadrature square signals, the comparison device comprising counting means indicating the angular position of each of the rings 13, 14 and subtraction means allowing the difference between said angular positions to be calculated, 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 one piece, for example by cutting with a wire machine or by stamping a blank in metallic material.

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

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

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

[0049] The inclination of the arms 19 in combination with their S-shaped geometric conformation with two concave 21 and convex 20 sections makes it possible to satisfy the radial space 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 19 arms in order to reduce their stiffness.

[0050] In particular, the arms 19 function as a leaf spring, and to obtain a flexible spring while controlling maximum stresses, the length of the arm 19 is important. With inclination, a pure tensile component is superimposed on the bending at the connection between the arm 19 and the rings 6, 7, because the arm 19 lengthens when the outer ring 7 rotates.

[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 respective inner end 19a and outer end 19b. 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 extremities 19b are separated by an angle Aban, which is measured between two adjacent directions Atb passing through respectively one of said outer extremities.

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

[0054] Advantageously, the angles Acou and Aban are each equal to 360° / N, or approximately 120° in the embodiment shown. This arrangement facilitates the manufacture of the test body 5, and also ensures a uniform circumferential distribution of the structure's deformations during the relative displacements of the rings 6, 7.

[0055] Each of the rings 6, 7 is equipped with internal 6a and external 7a fastening means for the corresponding encoder ring 13, 14. In the embodiment shown, each ring 13, 14 is supported by an internal 13b and an external 14b frame. Furthermore, each ring 6, 7 includes fastening means in the form of holes 6a, 7a to allow fastening by rivets 22 or by screwing into additional fastening holes formed for this purpose on the corresponding frame 13b, 14b.

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

[0057] These arrangements allow each orifice 6a, 7a to be angularly offset towards an area of ​​the corresponding ring 6, 7 which is sufficiently far from the ends of adjacent branches 19a, 19b to exhibit reduced radial deformations during the rotation of said ring and the tensile forces exerted by the branches 19 on said ring.

[0058] Thus, the risk of deformation of the rings 13, 14 during the relative rotation of the rings 6, 7 is limited, and therefore the risk of friction and / or diameter variation at the mounting holes 6a, 7a is reduced. This limits the occurrence of triangulation and / or hysteresis phenomena, which can affect the accuracy 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 three-branch test body 5 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, i.e. of the order of 36° in the figures, the angle ACint being equal to 0.5*Acou, i.e. of the order of 60° in the figures.

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

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

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

[0064] Furthermore, each of the lobes 9 for attaching 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 analogous to the radius of curvature of the concave section, so as to form a reduced gap with said concave section.

[0065] This embodiment makes it possible to limit the bulk 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 - whose dimensions are arranged to limit the risks of radial displacements during rotations of rings 6, 7, as well as the overall radial size of the test body 5, while ensuring a positioning of rings 13, 14 in accordance with the placement of sensitive patterns 15, 16 on the electronic board 18.

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

[0068] Thus, by offsetting the orifices 6a for fixing the ring 13 inside its reading track 13a, radial deformations at the level of said orifices are limited during the rotation of the ring 6, which, in combination with the angular arrangement of said orifices along the angle ACint, makes it possible to guarantee the accuracy 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 maintain a sufficient radial thickness, while offering a compromise with the radial position constraints of the orifices 6a described previously.

[0070] To achieve this, the bore 8 of the ring 6 has a radius Rcan, the mounting radius RCint of 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 base 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 inscribed radius between the inner ends of each orifice 6a, which is preferably on 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 lugs 23 with a reduced radial thickness, which are equally spaced at 120°, and in each of which a fixing orifice 6a is formed.

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

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

[0074] This arrangement also allows the outer orifices 7a to be brought closer radially to the inner orifices 6a, in order to allow the use of a sensor of reduced dimensions, with sensitive motifs 15, 16 brought closer radially, 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 spaced at 120°, each extending along a radial dimension towards the interior of the test body 5, and in each of which a fixing orifice 7a is formed.

Claims

11 Demands

1. A system for determining a torque applied between two rotating members (1,2) in one direction about a geometric axis of rotation (R), said system comprising: a test body (5) having an inner ring (6) rotationally fixed to 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) 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 deflection 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 - 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 on the inner ring (6) and the outer ring (7), said rings each having a magnetic track respectively inner (13a) and outer (14a) which is capable of emitting a periodic signal representative of the rotational displacement 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 applied torque; said determination system being characterized in that each of the rings (6, 7) is equipped with N fixing means respectively internal (6a) and external (7a) of 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. A torque determination system 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. A system for determining a torque according to any one of claims 1 or 2, characterized in that the arms (19) extend over an angular sector (SECT) formed between two diametrical directions (Apb, Atb) passing through the respectively inner (19a) and outer (19b) ends, 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. A 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 sectors of branch (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 360° / N.

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

8. A torque determination system according to any one of claims 1 to 7, characterized in that the rings (13, 14) are carried by an internal (13b) and external (14b) armature respectively.

9. A 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. A torque determination system 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 any 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 arms (19) have a bend formed between a convex section (20) extending from the inner end (19a) and a concave section (21) going to the outer end (19b).

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