Method for determining the applied torque between two rotating parts

Abstract

Method for determining a torque applied between two rotating members The invention relates to a method for determining a torque applied between two rotating members, said method comprising a calibration procedure for the determination which provides for: rotating a test body through at least one revolution under a constant calibration torque between the members and using a determination system to define calibration values ​​of the angular deviation as a function of the angle of rotation of said test body, the subsequent determination of the applied torque being obtained by correcting the angular deviation determined at a given angle with the corresponding calibration value.

Description

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

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

[0002] The invention applies in particular to the determination of a torque applied between two members 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.

[0003] To do this, it is known to use a test body having a first - respectively a second - portion integral in rotation with a first - respectively a second - of the members, said portions being connected by a deformable structure which is arranged to transmit the torque between the members while allowing angular movement between said portions.

[0004] Such a test body can be instrumented with a torque determination system comprising, for each of the portions: - an encoder carrying a track capable of emitting a periodic signal representative of the rotational movement of the corresponding portion; and - a sensor comprising a pattern of sensitive elements arranged at a reading distance from the track to deliver a signal representative of the angular position of the corresponding encoder.

[0005] 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 torque applied in that it induces said angle by twisting the deformable structure.

[0006] The limit of this solution lies in the precision of the determination of the torque, in particular in relation to test bodies having an eccentricity of the portions and / or the tracks, an inhomogeneity of the encoders or non-linearities of the sensors, which can cause an error when comparing the position signals to determine the angle which is a function of the applied torque.

[0007] The invention aims to solve the problems of the prior art by proposing in particular a method for determining a torque whose precision is improved by allowing correction of any relative defects between the portions of the test body, the encoders and / or the sensors.

[0008] To this end, the invention proposes a method for determining a torque applied between two members rotating around a geometric axis of rotation, said method providing: - to use a test body having a first - respectively a second - portion integral in rotation with a first - respectively a second - of said members, said portions being connected by a deformable structure which is arranged to transmit the torque between the members while allowing angular movement between said portions; - to equip the test body with a torque determination system comprising, for each of the portions: • an encoder carrying a track capable of emitting a periodic signal representative of the rotational movement of the corresponding portion; and • a sensor comprising a pattern of sensitive elements arranged at a reading distance from the track to deliver a signal representative of the angular position of the corresponding encoder;

[0009] said determination system comprising a device for comparing the signals delivered by each of the sensors, said device being capable of determining an angular difference between the portions which is a function of the torque applied;

[0010] said method comprising a procedure for calibrating the determination of the torque which provides for: - rotate the test body at least one revolution under a constant calibration torque between the components; - use the determination system to define calibration values ​​of the angular deviation between the portions as a function of the rotation angle of the test body;

[0011] the subsequent determination of the applied torque being obtained by correcting the angular deviation determined at a given angle with the corresponding calibration value.

[0012] Other objects and advantages of the invention will appear in the following description of different embodiments of a method according to the invention for determining a torque applied between two members rotating around a geometric axis of rotation.

[0013] In particular, the method allows the determination of a torque applied between two components 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.

[0014] To do this, the method uses a test body having a first - respectively a second - portion integral in rotation with a first - respectively a second - of the members, said portions being connected by a deformable structure which is arranged to transmit the torque between the members while allowing angular movement between said portions.

[0015] According to one embodiment, the test body may have an integral inner ring rotating means for mounting said test body on one member, and an outer ring extending around the inner ring while presenting means for mounting said test body on the other member, said rings being connected by at least one deformable arm.

[0016] Alternatively, the test body may be in the form of a torsion bar, each end of which has a portion secured to a respective member, the bar being arranged to deform in torsion as a function of the torque applied between said members.

[0017] To determine the angular movement of the portions which is a function of the applied torque, the test body is equipped with a system comprising, for each of the portions: - an encoder carrying a track capable of emitting a periodic signal representative of the rotational movement of the corresponding portion; and - a sensor comprising a pattern of sensitive elements arranged at a reading distance from the track to deliver a signal representative of the angular position of the corresponding encoder.

[0018] In particular, a succession of pairs of North and South poles is magnetized on an encoder respectively to form a multipolar magnetic track capable of emitting a magnetic signal of pseudo-sinusoidal shape, said encoder being associated in rotation with the corresponding portion.

[0019] Advantageously, the sensors comprise a pattern of 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.

[0020] The sensitive elements may be based on a magnetoresistive material whose resistance varies according to the magnetic signal of the track to be detected, for example of the AMR, TMR or GMR type, or a Hall effect probe.

[0021] According to one embodiment, the angular position can be determined incrementally by means of the signal emitted by a magnetic track. According to another embodiment, the angular position can be determined absolutely, i.e. with respect to a reference position, by providing a secondary magnetic track or a specific coding of the track.

[0022] The torque determination system comprises a device for comparing the signals delivered by each of the sensors, said device being capable of determining an angular difference between the portions which is a function of the torque applied.

[0023] According to one embodiment, the sensors deliver incremental square signals in quadrature, the comparison device comprising counting means providing the angular position of each of the encoders and subtraction means making it possible to calculate the difference between said angular positions as a function of the rotation angle.

[0024] In particular, the torque determination system may comprise means for applying an interpolation factor fi and f2 to the signal delivered by a sensor respectively, the counting means measuring a number of edges ni and n2 in each of said interpolated signals.

[0025] In relation to tracks comprising respectively Nppi and Npp2 pairs of North and South poles, the subtraction means perform for example the operation DIFF = Npp2.f2.ni - Nppi.fi.n2 to calculate the difference between the angular positions.

[0026] In particular, the determination system comprises means for applying interpolation factors such as: f2 / fi = Nppi / Npp2. When the tracks have the same number of pole pairs (Nppi = Npp2), the calculation can be carried out by simple subtraction of the fronts ni and ne with the same interpolation factor (fi = f2).

[0027] The method comprises a torque determination calibration procedure which provides for: - rotate the test body at least one revolution under a constant, and in particular substantially zero, calibration torque between the components; - use the determination system to define calibration values ​​of the angular deviation between the portions as a function of the rotation angle of the test body.

[0028] Thus, the subsequent determination of the applied torque can be obtained by correcting the angular deviation determined at a given angle with the corresponding calibration value, so as to be able to eliminate errors originating from possible relative defects between the portions, the encoders and / or the sensors.

[0029] The method may provide for determining a reference angular position per revolution of the test body, in order to be able to initiate and / or terminate the calibration procedure as a function of the determination of said reference angular position.

[0030] To do this, at least one encoder can carry a reference track capable of emitting a signal once per revolution, the sensor arranged at a reading distance from said track delivering the reference angular position upon detection of said emitted signal.

[0031] Advantageously, the determination of the torque can be obtained, for a given angle of rotation, in particular determined using a reference angular position, by subtracting the calibration value from the difference in angular positions calculated by the subtraction means.

[0032] According to one embodiment, the calibration values ​​are defined in a table comprising the differences DIFF calculated during the calibration procedure as a function of a number of fronts counted by at least one counting means. In particular, the table begins with the reference angle.

[0033] Calibration DIFF values ​​can be defined for each counted edge, or for an integer number of fronts counted to limit the number of values ​​to be calculated.

[0034] The table can be saved in the form of a curve, in particular having been filtered beforehand, for example by a moving average in order to smooth it. Alternatively, the table can be used as is.

[0035] The curve can be recorded as is, point by point, or by being divided into angular sections to limit the space required in memory. In particular, 360 sections each corresponding to 1° of angle can be envisaged, or advantageously 4 sections per pair of magnetic poles of the encoder track.

[0036] Each of these sections can be approximated by a straight line segment, represented by two parameters, the slope and the offset, then making it possible to easily calculate the correction as a function of the angle on the section concerned: error to be corrected = (slope x angle) - offset.

[0037] The curve obtained will then be used to correct the determined angular deviation, by subtracting from it, at a given angle, in particular determined using a reference angular position, the value recorded at the end of the calibration procedure.

[0038] Thus, this calibration procedure is simple to carry out, in particular not requiring an angular sensor and / or reference torque or rotating the test body at a constant speed. The correction made during operation is also simple to implement, in particular in that it does not cause any delay in determining the torque in real time.

[0039] According to one embodiment, the determination of the applied torque is carried out in one direction of rotation of the members, the calibration torque resulting from the rotation of the members in the opposite direction of rotation.

[0040] This solution is particularly advantageous in relation to the transmission of a bicycle, in that it is easy to make a rotation of the pedals under zero torque thanks to the freewheel, by backpedaling. Furthermore, the real-time determination of the applied torque is important in this application in relation to the control of the electric assistance motor using this determination.

[0041] The calibration procedure can be initiated by means of an interface with a user, for example at the level of the assistance controller of an electric bicycle.

[0042] According to one embodiment, the calibration procedure is initiated, directly or by requesting an action from the user, by detecting a state of rotation of the organs.

[0043] The state to be detected may correspond to a rotation under a calibration torque, known or substantially zero, for example corresponding to a direction of rotation of the members by detecting backpedaling for a bicycle. The state may also correspond to a time (since the last calibration or after a revision), to a fault in determining the torque or to a combination of these parameters.

Claims

Claims

1. Method for determining a torque applied between two members rotating around a geometric axis of rotation, said method providing: - to use a test body having a first - respectively a second - portion integral in rotation with a first - respectively a second - of said members, said portions being connected by a deformable structure which is arranged to transmit the torque between the members while allowing angular movement between said portions; - to equip the test body with a torque determination system comprising, for each of the portions: • an encoder carrying a track capable of emitting a periodic signal representative of the rotational movement of the corresponding portion; and • a sensor comprising a pattern of sensitive elements arranged at a reading distance from the track to deliver a signal representative of the angular position of the corresponding encoder; said determination system comprising a device for comparing the signals delivered by each of the sensors, said device being capable of determining an angular difference between the portions which is a function of the torque applied; said method being characterized in that it comprises a procedure for calibrating the determination of the torque which provides for: - rotate the test body at least one revolution under a constant calibration torque between the components; - use the determination system to define calibration values ​​of the angular deviation between the portions as a function of the angle of rotation of the test body; the subsequent determination of the applied torque being obtained by correcting the angular deviation determined at a given angle with the corresponding calibration value.

2. A method of determining a torque according to claim 1, ca- characterized in that the calibration torque is substantially zero.

3. Method for determining a torque according to one of claims 1 or 2, characterized in that it provides for the determination of the torque in one direction of rotation of the members, the calibration torque resulting from the rotation of the members in the opposite direction of rotation.

4. Method for determining a torque according to any one of claims 1 to 3, characterized in that it provides for determining a reference angular position per revolution of the test body, the calibration procedure being initiated and / or terminated as a function of the determination of said reference angular position.

5. Method for determining a torque according to claim 4, characterized in that it provides that at least one encoder carries a reference track capable of emitting a signal once per revolution, the sensor arranged at a reading distance from said track delivering the reference angular position upon detection of said emitted signal.

6. Method for determining a torque according to any one of claims 1 to 5, characterized in that the calibration procedure is initiated by means of an interface with a user.

7. Method for determining a torque according to any one of claims 1 to 6, characterized in that the calibration procedure is initiated by detecting a state of rotation of the members.

8. Method for determining a torque according to claim 7, characterized in that the state of rotation of the members corresponds to a time, a direction of rotation of the members, a failure to determine the torque or a combination of these parameters.

9. Method for determining a torque according to any one of claims 1 to 8, characterized in that the comparison device comprises counting means providing the angular position of each of the encoders and subtraction means making it possible to calculate the difference between said angular positions as a function of the angle of rotation, the determination of the torque being obtained, for a given angle of rotation, by subtracting the calibration value from the calculated difference in angular positions.

10. Method for determining a torque according to claim 9, characterized in that the torque determination system comprises means for applying an interpolation factor fi and f2 to the signal delivered by a sensor respectively, the counting means measuring a number of fronts ni and n2 in each of said signals in- terpolated.

11. Method for determining a torque according to claim 10, characterized in that the calibration values ​​are defined in a table comprising the differences calculated during the calibration procedure as a function of a number of fronts counted by at least one counting means.

12. Method for determining a torque according to claim 11, characterized in that the calibration values ​​are defined for each counted edge, or for an integer number of counted edges.

13. Method for determining a torque according to one of claims 11 or 12, characterized in that the table is recorded in the form of a curve.

14. Method for determining a torque according to claim 13, characterized in that the recorded curve is filtered

15. Method for determining a torque according to one of claims 13 or 14, characterized in that the recorded curve is divided into angular sections.