Method for determining at least one friction parameter of a cyclist under real conditions of movement, and associated devices

Abstract

The invention relates to a method for determining at least one friction parameter of a cyclist under real movement conditions, on a banking section of track or road, extending longitudinally from a start line (LD) to a finish line (LA) over a length (L), each of the start line (LD) and the finish line (LA) extending transversely across a width (l). The method, based on an equation derived from the principle of conservation of energy, comprises a step of measuring a first transverse position (P1) at which the cyclist crosses the start line (LD) and a second transverse position (P2) at which the cyclist crosses the finish line (LA), each of the first and second transverse positions (P1, P2) being determined across the width (l) with an accuracy of + / -5 cm. The invention also relates to devices for measuring a transverse position at which the cyclist crosses.

Description

METHOD FOR DETERMINING AT LEAST ONE FRICTION PARAMETER OF A CYCLIST IN REAL TRAVEL CONDITIONS, AND ASSOCIATED APPARATUS FIELD OF THE INVENTION

[0001] The present invention relates to the field of devices and methods for measuring and determining resistive forces exerted on a cyclist in motion. The invention aims in particular to determine parameters characterizing the resistive forces such as the aerodynamic drag surface and / or the rolling coefficient of the cyclist on his bicycle, with precision, reproducibility and by implementing a simple and rapid protocol.

[0002] TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] There are two categories of tests for measuring key cyclist friction parameters (rolling and aerodynamics): stationary tests (wind tunnel) and in-motion tests (real-life riding conditions). Real-life tests are particularly interesting because they can take into account parameters related to the cyclist's posture during effort and movement.

[0004] As explained in document WO2022074330A1, a moving cyclist is subjected to several forces (gravity force, rolling force, friction force with the air, forward force). In order to minimize the energy cost of the vehicle's movement, it appears particularly key to know how to accurately measure the friction applied to the cyclist (rolling and aerodynamics).

[0005] The methods for determining the aerodynamic drag surface and the rolling coefficient proposed by this document, based on the principle of conservation of energy, generally offer excellent reproducibility as well as great simplicity of implementation.

[0006] It was nevertheless observed that in certain test route conditions, short and involving a sloping road (for example on a velodrome track), the level of precision for the determination of friction parameters was lower than expected.

[0007] SUBJECT OF THE INVENTION

[0008] The present invention aims to remedy all or part of the aforementioned drawbacks. It relates to a method for determining at least one friction parameter of a cyclist in real travel conditions, on a section of track or road with a slope.

[0009] BRIEF DESCRIPTION OF THE INVENTION

[0010] The invention relates to a method for determining at least one friction parameter of a cyclist in real travel conditions, on a section of track or road having a slope and extending longitudinally from a starting line to a finishing line over a length, each of the starting and finishing lines extending transversely over a width.

[0011] The method, based on an equation derived from the principle of conservation of energy, is remarkable in that it comprises a step of measuring a first transverse position of the cyclist crossing the starting line and a second transverse position of the cyclist crossing the finishing line, each of the first and second transverse positions being determined along the width with an accuracy of + / -5cm.

[0012] According to other advantageous and non-limiting characteristics of the invention, taken alone or in any technically feasible combination: the measuring step involves at least one membrane potentiometer arranged on the starting line and on the finishing line, along the width; the membrane potentiometer is held on a rigid strip, which is arranged on the starting line (respectively on the finishing line), along the width; the measuring step involves at least one time-of-flight measuring sensor, opposite each of the starting and finishing lines; each of the first and second transverse positions is determined over the width with an accuracy of + / -4cm, or even + / -3cm, + / -2cm, or even + / -1cm;the at least one membrane potentiometer arranged on the starting line (respectively the finish line) or the at least one time-of-flight measuring sensor associated with the starting line (respectively the finish line) is connected to a microcontroller capable of transmitting information relating to the first transverse position (respectively to the second transverse position), via a wireless communication protocol; the microcontrollers implemented in the method are synchronized using GNSS (global navigation satellite systems) receiver modules; the width of the starting line and / or the width of the finish line is between 0.2m and 5m; the starting line and the finish line are the same, the section of track or road defining a loop; the first and second transverse positions are precisely time-stamped when they are measured;the method involves one or more movements on the section of track or road by the cyclist, and comprises for each movement:- a measurement of the difference in kinetic energy of the cyclist between the finish line and the starting line,- a measurement of the motive energy developed by the cyclist, if applicable, during his movement on the section between the start line and the finish line,- a direct or indirect measurement of the dynamic air pressure during the movement of the cyclist on the section between the start line and the finish line, so as to plot a relationship linking the resistive force to the average dynamic air pressure, the mass of the cyclist being known and the difference in altitude between the start line and the finish line being determined from the first and second transverse positions;the relationship linking the resistive force to the average dynamic air pressure is linear and we determine an aerodynamic drag surface, the directing coefficient of the line, and a rolling coefficient, proportional to the coordinate at the origin of the line.;

[0013] The invention also relates to an apparatus for measuring a transverse position of the cyclist crossing a starting or finishing line and its time stamping, comprising:

[0014] - a resistive membrane potentiometer arranged on the start or finish line, the dimension of the potentiometer along a transverse axis being equal to a transverse extent or width of the start or finish line, the potentiometer comprising three pins and having a fixed resistance between a first pin and a third pin and a variable resistance between the second pin and a third pin, said variable resistance being proportional to the transverse position of passage of the cyclist along the dimension;

[0015] - a microcontroller to which the membrane resistive potentiometer is connected, the second pin of the membrane resistive potentiometer being connected to an analog input of the microcontroller allowing voltage variations representative of the transverse position of the cyclist to be read and timestamped.

[0016] Finally, the invention relates to another apparatus for measuring a transverse position of the cyclist crossing a starting or finishing line and its time stamping, comprising:

[0017] - two resistive membrane potentiometers arranged parallel and side by side on the start or finish line, the dimension of each potentiometer along a transverse axis being equal to a transverse extent or width of the start or finish line, each potentiometer comprising three pins and having a fixed resistance between a first pin and a third pin and a variable resistance between the second pin and a third pin, said variable resistance being proportional to the transverse position of the cyclist passing along the dimension;

[0018] - a microcontroller to which the two resistive membrane potentiometers are connected, the second pin of the first resistive membrane potentiometer being connected to an analog input of the microcontroller for reading the transverse position of the cyclist's passage, the second pin of the second resistive membrane potentiometer being connected to an interrupt of the microcontroller so as to trigger the timestamp with an accuracy better than + / -100ms.

[0019] Advantageously, one or other of the aforementioned devices comprises wireless communication means for transmitting information relating to the transverse position of the cyclist and relating to its time stamp. BRIEF DESCRIPTION OF THE FIGURES

[0020] Other characteristics and advantages of the invention will emerge from the detailed description of the invention which follows with reference to the appended figures in which:

[0021] This is a diagram of the implementation of a method in accordance with the invention;

[0022] This is a graphical representation of the resistive force as a function of the dynamic air pressure, for 8 movements (8 points) made by a cyclist, on the section of track or road on a slope, between the start and finish lines, with different speeds, and without implementing the measurement of the first and second transverse positions of passage on said start and finish lines of the method according to the invention;

[0023] This is a graphical representation of the resistive force as a function of the dynamic air pressure, for the same 8 movements (8 points) made by a cyclist, on the section of track or road on a slope, between the start and finish lines, by applying the measurement of the first and second transverse positions of passage on said start and finish lines to correct the altitude information, in accordance with the present invention;

[0024] Presents a table of values ​​of the aerodynamic drag surface CxS, for ten similar movements (same equipment configurations and position, similar movement speeds), determined without altitude correction and with altitude correction thanks to the determination of the first and second transverse passage positions in accordance with the invention;

[0025]

[0026] Laet lapresent devices for measuring a transverse position of the cyclist's passage on a starting or finishing line and its time stamping;

[0027] This shows an example of the relationship between the value retrieved from the analog input of the microcontroller and the transverse position y detected by a membrane potentiometer;

[0028]

[0029]

[0030] Figures 7a, 7b and 7c show diagrams relating to the implementation of a method according to the invention, in which the measurement of a transverse position of passage of the cyclist on a starting or finishing line is carried out using a time-of-flight measuring sensor;

[0031] This presents an implementation variant for the time stamping of the measurement of the transverse positions of the cyclist crossing a start or finish line, using an interrupted beam barrier type sensor.

[0032] Figures are schematic representations which, for the sake of readability, are not necessarily to scale. DETAILED DESCRIPTION OF THE INVENTION

[0033] The invention relates to a method for determining at least one friction parameter of a cyclist in real travel conditions, on a section of track or road with a slope. A friction parameter is any parameter that makes it possible to characterize the resistance experienced by the cyclist during his travel; this parameter can therefore in particular be an aerodynamic drag surface CxS, a rolling coefficient Cr, an overall friction force F res which applies to the cyclist during his movement, or the work of this force per unit of time.

[0034] The section may in particular correspond to a portion (or all) of a velodrome track.

[0035] The section extends longitudinally from a starting line LD to a finishing line LA over a length L (). Each of the starting lines LD and finishing lines LA extends transversely over a width l. The cyclist is intended to move along a longitudinal axis, over the length L of the section; the width l extends along a transverse axis, substantially normal to the longitudinal axis.

[0036] Note that the start line LD and the finish line LA can possibly be confused, especially when the section of track or road defines a loop.

[0037] The starting line LD and the finishing line LA may have different widths l. However, for reasons of simplification and without this being limiting, a single width l will be considered in the remainder of this description for the starting lines LA and finishing lines LA.

[0038] The width l defines the traffic lane in which the cyclist must pass when carrying out a test in real travel conditions, on the section. Preferably, the width l is between 0.2m and 5m.

[0039] In the context of the present invention, the section of track or road is considered to be on a slope from the moment there is a variation in altitude, between points on the starting line LD or between points on the finishing line LA, greater than or equal to 1 cm. This is the case, for example, when the traffic lane extends over a width of between 15 cm and a few meters on a conventional velodrome track.

[0040] The method of the invention is based on an equation derived from the principle of conservation of energy.

[0041] The preparatory sequence described in document WO2022 / 074330A1, as well as the methods for determining the aerodynamic drag surface CxS and / or the rolling coefficient Cr can also be implemented in the method of the invention.

[0042] Note that the content of document WO2022 / 074330A1 is incorporated into this application by reference.

[0043] The method according to the invention nevertheless proposes a significant improvement, in that it comprises a step of measuring a position (along the transverse axis) of passage of the cyclist on the starting line LD (called first transverse position of passage P1) and a position (along the transverse axis) of passage of the cyclist on the finishing line LA (called second transverse position of passage P2). The position of the cyclist along the transverse axis is assimilated either to the position of the front wheel of his bicycle, or to the position of the rear wheel of his bicycle, or to the average of the positions of the front and rear wheels.

[0044] Each of the first P1 and second P2 transverse positions is determined along the width l of each of the lines LD,LA with an accuracy of + / -5cm. Advantageously, the positions P1,P2 are determined with an accuracy of + / -4cm, or even + / -3cm, + / -2cm or even + / -1cm.

[0045] As will be explained in detail and illustrated later, precise knowledge of the first P1 and second P2 transverse positions provides access to the difference in altitude of the cyclist between the starting line LD and the finishing line LA. The applicant observed that an inaccuracy in this difference in altitude (elevation difference H) greatly affected the quality of the results and therefore the accuracy of the values ​​of the friction parameter(s) obtained.

[0046] Different measuring systems can be used to determine the first P1 and second P2 transverse positions of passage on the start line LD and finish line LA.

[0047] According to a first embodiment, the step of measuring the first P1 and second P2 transverse positions involves at least one membrane potentiometer arranged on the starting line LD and on the finishing line LA, along the width l. The dimension D of the membrane potentiometer is chosen to extend over the entire width l of the starting lines LD and finishing lines LA (D = l).

[0048] A resistive membrane potentiometer has three pins connected to electrodes spanning dimension D (). The resistance R 13 between a first and a third pin is fixed, while the resistance R 23between the second and third pins is variable and proportional to the transverse position y at which a pressing force will be applied to the potentiometer. The second pin of the potentiometer is connected to an analog input of a microcontroller allowing voltage variations representative of the transverse position of the cyclist to be read and timestamped.

[0049] We thus understand that the passage of the cyclist on the membrane potentiometer placed on the starting line LD (or finishing line LA) will generate a resistance value R 23 given; said value is associated with a precise position on the potentiometer and therefore on the starting line LD (or finishing line LA); this precise position will correspond to the first P1 (or second P2) transverse position of passage.

[0050] The membrane potentiometer can be placed directly on the ground of the section of track or road, or, advantageously, fixed on a rigid strip, easily removable and movable, which will be placed and temporarily immobilized on the starting line LD and on the finishing line LA, along the width l.

[0051] The membrane potentiometer is connected to a microcontroller capable of transmitting information relating to the first P1 and second P2 transverse positions by wired connection (to a ground computer, for example) or by a wireless communication protocol (to an on-board device, for example). The on-board device is suitable for measuring various parameters such as the speed of the cyclist, the air speed or the dynamic air pressure, the power developed by the cyclist if necessary, during the movement of the cyclist on the section of track or road, the values ​​of which are necessary for determining the friction parameter(s).

[0052] Regardless of the type of measuring system (membrane potentiometer or other), it is important to note that a time lag in receiving information relating to the first P1 and second P2 transverse positions can also affect the quality of the results: it is therefore preferable that the transmission time of information from the microcontroller to the embedded device is less than 100ms.

[0053] Of course, if it were considered to transmit information from the embedded device to the microcontroller, the same transmission time requirements would apply.

[0054] An alternative solution to this information transmission time constraint consists of time-stamp the cyclist's passages on the starting line LD and on the finishing line LA, with an accuracy better than + / -100ms. This solution also requires implementing a clock synchronization mechanism between the clock of the microcontroller of the measurement system and the clock of the on-board device, also with an accuracy better than + / -100ms. This mechanism could rely on a master device, for example one of the microcontrollers connected to the measurement system (band with membrane potentiometer), capable of emitting on one of its output ports at periodic intervals, for example every minute, an electrical pulse perfectly synchronized with its clock.The other devices, by definition slaves (for example the device on board the bicycle and the microcontroller connected to the other measuring system), will be able to connect to this port and make the necessary adjustments to their own clock. The measuring system (in particular, its microcontroller) must then be able to transmit by wired connection (to a computer on the ground, for example) or by a wireless communication protocol (to the on-board device, for example), the information relating to the first P1 and second P2 transverse positions and the timestamp of the cyclist's passage on the start LD and finish lines LA.

[0055] An apparatus for measuring a transverse position of the cyclist's passage on a start or finish line and its time stamping, may advantageously comprise two resistive membrane potentiometers (respectively named band 1 and band 2 on the diagram of the) arranged parallel and side by side on the start line LD or finish line LA, the dimension D of each potentiometer along a transverse axis being equal to a transverse extent or width l of the line. As mentioned previously, each potentiometer comprises three pins and has a resistance R 13 fixed between a first pin and a third pin and a variable resistor R 23 between a second pin and the third pin, said variable resistor R 23 being proportional to the transverse position y of the cyclist's passage along dimension D (or width l).

[0056] The apparatus also includes a microcontroller to which the two resistive membrane potentiometers are connected, the second pin of the first resistive membrane potentiometer being connected to an analog input (to analog digital converter, ADC) of the microcontroller for reading the transverse position of the cyclist's passage, the second pin of the second resistive membrane potentiometer being connected to an interrupt of the microcontroller so as to trigger the time stamp with an accuracy better than + / -100ms.

[0057] The relationship between the ADC analog input and the transverse position is slightly non-linear. An example of this relationship is for a 47kOhm PD pull-down resistor, a resistor R 13of 20kOhm and a 12-bit converter (4096 values) is illustrated in. Once the transit time and the value of the ADC analog input have been determined, the microcontroller proceeds to send the data, for example wirelessly, to the on-board device. The latter can then determine the altitude H(P1) at the first transverse transit position P1 (and similarly H(P2)), using the following relationship:

[0058] [Equ.1]

[0059]

[0060] with D the length of the strip (which is equivalent to the width l of the starting line LD), R PD pull-up resistor, ADC val the value retrieved from the microcontroller's ADC analog input, M the number of sampling bits of the analog-to-digital converter, R 13the total resistance of the band, θ the track angle at the starting line LD. Note that this track angle, shown schematically on the, may be different at the starting line LD (θ D ) and at the finish line LA (θ A ).

[0061] According to a second embodiment, the step of measuring the first P1 and second P2 transverse positions involves at least one time-of-flight measurement sensor, associated with each of the departure LD and arrival LA lines.

[0062] A Time-of-Flight sensor measures the distance between the sensor and an object with an accuracy of less than 1 centimeter. It is an advanced device consisting essentially of 3 components: a light pulse source, usually a laser diode, this one generally of the VCSEL type; a light pulse receiver, usually an avalanche photodiode, this one generally of the SPAD type; and a control unit driving the source and the receiver, this one generally a microcontroller. The distance measurement is obtained by precisely measuring the time it takes for a light pulse emitted by the source to return to the receiver after being reflected by the object; this is the time of flight of the light signal. Since the speed of light is a constant, the distance is directly proportional to this duration. A schematic diagram of a Time-of-Flight sensor is shown in the figure.

[0063] In the second embodiment, two time-of-flight sensors are arranged on the edge of the runway, respectively at the start line LD and the finish line LA, so that their field of view (FoV) points in a direction perpendicular to the runway and parallel to the start and finish lines. They are connected to a microcontroller, making it possible to record the measured distances and the timestamps of said measurements. Two reflective targets are positioned opposite the sensors, on the opposite edge of the runway. An example of the arrangement of the time-of-flight sensors and the reflectors on the runway is illustrated in.

[0064] When the start line LD and the finish line LA are not obstructed, the time-of-flight sensors continuously measure the distance separating them from the reflective target (reflector). This continuous measurement allows to confirm the operation of the time-of-flight sensor and to estimate the accuracy of the distance measurement. When one of the start line LD or the finish line LA is crossed by the bicycle, it reflects the light signal from the sensor in real time, which allows to measure the distance between the sensor and the bicycle (). We can then deduce the transverse position P1,P2 of the bicycle on the track at the instant of crossing the start line LD or the finish line LA.

[0065] Distance measurements are repeated at a frequency of several tens, even several hundred, or even more thousands of times per second (Hertz). When the measured distance is detected as less than the distance of the target placed opposite, the falling edge of this variation in distance is time-stamped, this determines the instant at which the bicycle crossed the line. The timestamping is all the more precise as the frequency of repetition of the distance measurements is high.

[0066] In a variant embodiment, the time stamping is carried out by a second sensor of the "break beam barrier" type, which complements the time-of-flight sensor. This is composed of a light source, generally infrared, generally laser, arranged opposite a receiver, generally a photodiode, generally infrared, generally of the avalanche photodiode type, so that the light signal emitted by the source is received by the receiver when the line of sight is not obstructed ().

[0067] The source and receiver are arranged on either side of the track so that the line of sight between the two coincides with the starting line LD and the finishing line LA, respectively. When the line is not obstructed, the light signal emitted by the source is continuously received by the receiver. When the bike crosses the line, the light signal is interrupted and is no longer received by the receiver. The receiver is connected to a digital input of a microcontroller, configured in interrupt mode. When the light signal is interrupted, a rising or falling edge on the voltage of the signal connected to the digital input causes an interrupt on the microcontroller. This interrupt is time-stamped by the microcontroller. This makes it possible to measure with an accuracy of less than a millisecond the instant at which the bike crosses the line.

[0068] For these last two embodiments of the time stamping, by time-of-flight measurement sensor or by beam interruption barrier type sensor, the time stamping is carried out by dedicated microcontrollers arranged at the edge of the runway, respectively associated with the departure LD and arrival LA lines. As for the first embodiment, by resistive potentiometer, it is necessary to synchronize the clocks of the microcontrollers of these measurement systems with the clock of the on-board device, with an accuracy better than + / -100ms.

[0069] Advantageously, synchronization between these different microcontrollers can be achieved by GNSS receiver modules (Global Navigation Satellite System). This requires visibility of the sky, which is applicable when the runway is located outdoors.

[0070] The synchronization principle is based on the use of precise time signals provided by GNSS satellites. The GNSS receiver captures the signals from the satellites, which contain extremely precise time synchronization information. This information is processed by the receiver to extract a reference time signal. The microcontroller to be synchronized is connected to the GNSS receiver via a digital communication interface (I2C, UART, SPI) allowing it to receive a timestamp message (i.e. containing the date and hours, minutes, and seconds) from the GNSS module. The microcontroller is also connected via a digital input to a digital output of the GNSS receiver (generally called the PPS signal for "Pulse Per Second" in English). The GNSS receiver generates a change of state (rising or falling edge) on the PPS output at each instant of passage of a whole second.The microcontroller adjusts its internal clock registers based on the received time stamp message and then initiates the next cycle of the clock at the instant the PPS signal edge change is detected. This synchronization ensures time accuracy of less than one millisecond between the microcontrollers of the different components of the system.

[0071] As stated previously, the preparatory sequence and the methods for determining the aerodynamic drag surface CxS and / or the rolling coefficient Cr presented in document WO2022 / 074330A1 can be implemented in the method of the invention which aims, in addition, to precisely measure the difference in altitude (or gradient) between the cyclist's point of passage on the starting line LD and his point of passage on the finishing line LA, this thanks to the knowledge of the first P1 and second P2 transverse positions, when moving on a section of track or road on a slope.

[0072] The present invention also proposes a protocol for testing and determining at least one friction parameter, different from those proposed by document WO2022074330A1.

[0073] Let us recall the fundamental equation of dynamics:

[0074] [Equ.2]

[0075]

[0076] With

[0077] fluid friction force (friction force with air):

[0078] [Equ.3]

[0079] the force of gravity:

[0080] [Equ.4]

[0081] dry friction force (or rolling force):

[0082] [Equ.5]

[0083] the forward force (force exerted by the cyclist on the pedals):

[0084] [Equ.6]

[0085] In which:v air , P air are respectively the air speed and the dynamic air pressure,m is the mass of the cyclist + bicycle couple,g is the acceleration of gravity,p = H / L his the slope of the road defined as the ratio between the elevation H of the section (difference between the altitude H(P1) at the crossing of the starting line LD and the altitude H(P2) at the crossing of the finishing line LA) and its length projected on a horizontal plane L h ,E m is the driving energy produced by the cyclist,L is the length of the path,CxS is the aerodynamic drag surface of the cyclist on his bicycle,C r is the rolling coefficient, I, the sum of the moments of inertia of the two wheels, and R, their radius.

[0086] From an energy point of view this gives:

[0087] [Equ.7]

[0088]

[0089] gold,

[0090] [Equ.8]

[0091] From where

[0092] [Equ.9]

[0093]

[0094] With

[0095] V final and V ini, respectively the speeds at the arrival and departure of the cyclist, or the speeds of the cyclist respectively at the crossing of the finish line LA and at the crossing of the start line LD.

[0096] By breaking down the work generated by each force on a section, we obtain:

[0097] [Equ.10]

[0098]

[0099] With

[0100] W res the energy lost by aerodynamic friction and rolling on the section of track or road.

[0101] This can be expressed using the fluid friction parameters CxS (aerodynamic coefficient) and dry friction C r (rolling coefficient):

[0102] [Equ.11]

[0103]

[0104]

[0105]

[0106]

[0107]

[0108] The variation of kinetic energy ΔE c can be defined as being equal to:

[0109] [Equ.12]

[0110]

[0111] This variation in kinetic energy is calculated between the two positions which are the first transverse position of passage P1 (passage of the cyclist on the starting line LD) and the second transverse position of passage P2 (passage of the cyclist on the finishing line LA).

[0112] We thus obtain the following relationship between the height difference (or gradient) H and the rest of the parameters CxS, Cr, v and P air :

[0113] [Equ.13]

[0114]

[0115] The difference in height H is calculated between the first transverse position of passage P1 and the second transverse position of passage P2. These positions are precisely determined on the starting lines LD and finishing lines LA, and knowing the slope of the section (track angle on the starting line and track angle on the finishing line), it is easy to go back to the difference in height H.

[0116] Let us note F res = W res / L the average resistive force by aerodynamic friction and by rolling along the route on the section of track or road:

[0117] [Equ.14]

[0118]

[0119] In the event that CxS and C r are constant, we can write the following relation:

[0120] [Equ.15]

[0121]

[0122] With <P air> corresponding to the average dynamic air pressure along the course (between the starting line LD and the finishing line LA).

[0123] By precisely measuring ΔE c , E m , <P air >, and knowing m, H and L, it is possible to draw the relation F res = f( <P air >) to determine the coefficients CxS and (mgC r ), by linear regression.

[0124] The method for determining at least one friction parameter according to the present invention may therefore involve one or more movements on the section of track or road by the cyclist, between the starting line LD and the finishing line LA (or vice versa) and comprise for each movement:

[0125] 1) a measure of the difference in kinetic energy of the cyclist between the finish line LA and the start line LD,

[0126] 2) a measure of the driving energy developed by the cyclist, during his movement on the section between the starting line LD and the finishing line LA, except of course if there is no driving energy because the movement on the section is done in freewheel mode,

[0127] 3) a direct or indirect measurement of the average dynamic air pressure during the cyclist's movement on the section between the start line LD and the finish line LA.

[0128] When several movements are made, the measurements stated above make it possible to trace a linear relationship linking the resistive force F res and the dynamic air pressure P air , which makes it possible to determine the aerodynamic drag surface CxS, the directing coefficient of the line, and the rolling coefficient C r, proportional to the coordinate at the origin of the line. The cyclist's speed of movement varies with each movement, all other test conditions remaining identical (bicycle, cyclist's clothing and posture, rolling properties, etc.). Each point on the line F res = f( <P air >) corresponds to a movement of the cyclist, at a given speed, therefore at a given average dynamic air pressure.

[0129] The measurement of kinetic energy can be carried out using one or more magnets positioned on one of the wheels of the bicycle and a Hall effect magnetic switch positioned on an element of the frame or fork close to the passage of the magnet(s) and connected to an on-board electronic device capable of recording with an accuracy better than + / -100ms the electrical pulses t nat each passage of magnet n in front of the switch. In the case of a single magnet, prior knowledge of the mass m of the cyclist, the circumference C of the wheel on which the magnet is positioned and the inertia I of the wheels will make it possible to accurately estimate the kinetic energy at the average point n+N / 2 between the passages of magnet n and n+N using the following relationship:

[0130] [Equ.16]

[0131]

[0132] With N a number of wheel revolutions, typically between 1 and 10, advantageously between 1 and 6.

[0133] The measurement of the driving energy developed by the cyclist may be based on the reading of a power sensor present on the cyclist's bicycle via an "ANT+" or "Bluetooth Low Energy" communication protocol.

[0134] The measurement of the dynamic air pressure will be made possible: either indirectly from the ground speed, calculated between several wheel passages N, and thanks to the magnetic switch and knowledge of the air density ρ via the relationship:

[0135] [Equ.17]

[0136]

[0137] in the event that the tests are carried out indoors without air movement relative to the ground; or directly by a differential pressure sensor connected to a structure present on the front of the bicycle of the “Pitot probe” type having an air inlet sensitive to total pressure and another sensitive to static pressure. In this case, the dynamic pressure can be compensated so as to eliminate the air blocking factor induced by the presence of the cyclist.

[0138] In both cases, the average dynamic air pressure <P air> is obtained by averaging the values ​​of P air along the stretch.

[0139] Lamontre the results F res = f( <P air >) for eight movements with different speeds, without correction of the difference in level H in the equation [Equ.14], that is to say without using the first P1 and second P2 transverse positions of passage of the cyclist on the starting lines LD and finishing lines LA.

[0140] The coefficient “R 2 » which reflects the quality of the linear regression is lower than on flat terrain without slopes (0.975 vs. 0.999 usually). The coefficients Cr and CxS cannot therefore be determined very precisely.

[0141] Lamontre the results F res = f( <P air>) for these same eight movements, using the first P1 and second P2 transverse positions of the cyclist passing on the starting lines LD and finishing lines LA to precisely determine the difference in altitude H. The linear regression is then perfect (coefficient close to 1) and we determine with very good precision a value of the aerodynamic drag surface, the directing coefficient of the line F res = f( <P air >).

[0142] The rolling coefficient is determined from the coordinate at the origin of the said line which corresponds to the term mgC r , with m and g known.

[0143] Under the test conditions of the invention, that is to say by determining the first and second transverse positions of passage of the cyclist on the starting and finishing lines, we also note an excellent reproducibility of the value obtained from the aerodynamic drag surface CxS, for the different displacements (considering Cr known): the standard deviation is 0.9% whereas it is 5.4% without correction of the difference in level (see table in the).

[0144] Example of implementation:

[0145] The tests are conducted on an indoor velodrome track. The objective is to evaluate a cyclist's friction parameters under given conditions (specific bicycle, clothing, helmet, posture).

[0146] The following steps are applied: Place two rigid strips, each equipped with a membrane potentiometer, along a starting line LD and a finishing line LA extending transversely over a width l; these lines LD, LA are spaced longitudinally by approximately 20m (length L of the section) and substantially positioned on one of the two straight track segments (i.e. without bends) of the velodrome (). Align the strips transversely with one of the height reference lines of the velodrome (black line, red line, Côte d'Azur, etc.) or with a floor slat or with a height reference given by an optical level. Measure the slope of the velodrome (with an inclinometer or an optical level) or have data relating to this slope, at the level of the starting line LD and at the level of the finishing line LA, and record this value in the parameters of the on-board device.Optionally synchronize the clocks between the device on board the bicycle and the microcontrollers on the ground (connected to the membrane potentiometers). Start a measurement sequence as described previously (steps 1), 2) and 3)). The air speed can be assumed to be equal to the ground speed and determined using the Hall effect magnetic switch. The parameters relating to the speed of movement are time-stamped and recorded at each wheel revolution. Detect and optionally time-stamp the passage of the cyclist on the starting line LD via the detection of a voltage change (membrane potentiometer connected to an analog input of the microcontroller) and / or via the detection of an interrupt on the microcontroller (membrane potentiometer directly connected to an "interrupt" input of the microcontroller).Capture information relating to the transverse position P1 of the cyclist on the track as he passes over the starting line LD using the membrane potentiometer connected to the analog input of the microcontroller or, in the case where the membrane potentiometer is connected to the interrupt of the microcontroller, using a second membrane potentiometer connected to the analog input of the microcontroller (in this case, a device such as previously described including two membrane potentiometers in parallel may be used). Immediately after detecting the passage, the microcontroller reads the analog input and detects the maximum value reached in a time period of about fifty milliseconds. Transmit the information relating to the first transverse position P1 and possibly the timestamp of the passage over the starting line LD, to the on-board device, by "wifi" or "bluetooth".Convert the information relating to the transverse position P1 into altitude of the cyclist at the time of his passage on the starting line LD thanks to the knowledge of the slope of the track at the starting line LD and the relationship between the position of the cyclist on the strip and the voltage at the terminals of the analog / digital converter of the microcontroller. This step can also be carried out before step h), by the microcontroller. Detect and optionally timestamp the passage of the cyclist on the finish line LA (similar to step f). Capture information relating to the second transverse position P2 of the cyclist at his passage on the finish line LA (similar to step g). Transmit the information relating to the second transverse position P2 and possibly to the timestamp of the passage on the finish line LA, to the on-board device (similar to step h).Convert the transverse position data into altitude difference or elevation difference H (can be done either by the microcontroller connected to the membrane potentiometer or in the on-board device). Calculate the resistive force F. res associated with the measured elevation difference H (can be done in the on-board device) optionally using the timestamp data to best match the data measured by the on-board device on one side (kinetic energy and air pressure data), and the data measured at the strips on the other (altitudes H(P1), H(P2) or lateral position). Extract a value of aerodynamic coefficient CxS, or rolling coefficient Cr; and / or carry out several tests on the section, under the given conditions to construct a straight line connecting the resistive force F res depending on the average dynamic air pressure <P air> (each test being carried out at a different speed), and extract the slope coefficient of the curve (CxS) and the coordinate at the origin (mgC r ), so as to deduce the friction parameters CxS and Cr, under the given conditions. Repeat steps a) to o), for new conditions to be tested (particular bicycle, clothing, helmet, posture).

[0147] The method according to the invention makes it possible to access, in a simple and efficient manner, the values ​​of friction parameters of a cyclist, in real conditions of movement; these values ​​are precise and the high reproducibility of the results makes it possible to evaluate in a few tests, over a very short distance, therefore in a short time, a large number of conditions (particular bicycle, clothing, helmet, posture).

[0148] Of course, the invention is not limited to the embodiments and examples described, and variant embodiments may be made without departing from the scope of the invention as defined by the claims.

Claims

Method for determining at least one friction parameter of a cyclist in real travel conditions, on a section of track or road with a slope and extending longitudinally from a starting line (LD) to a finishing line (LA) over a length (L), each of the starting lines (LD) and finishing lines (LA) extending transversely over a width (l), the method being based on an equation derived from the principle of conservation of energy expressed as follows: ΔE c = -W res – mgH + E m with ΔE c the change in kinetic energy, W res the energy lost by aerodynamic friction and by rolling on the section, m the mass of the cyclist-bicycle couple, g the acceleration of gravity, H the difference in altitude and E mthe driving energy produced by the cyclist on the section, and being characterized in that:- it comprises a step of measuring a first transverse position of passage (P1) of the cyclist on the starting line (LD) and a second transverse position of passage (P2) of the cyclist on the finishing line (LA), each of the first and second transverse positions (P1, P2) being determined along the width (l) with an accuracy of + / -5cm,- the variation in kinetic energy (ΔE c ) and the difference in level (H) are calculated between two positions: the first transverse passage position (P1) and the second transverse passage position (P2). Method for determining at least one friction parameter according to the preceding claim, in which the measuring step involves at least one membrane potentiometer arranged on the starting line (LD) and on the finishing line (LA), along the width (l). Method for determining at least one friction parameter according to the preceding claim, wherein the membrane potentiometer is held on a rigid strip, which is arranged on the starting line (LD) and on the finishing line (LA), along the width (l). Method for determining at least one friction parameter according to claim 1, in which the measuring step involves at least one time-of-flight measuring sensor, opposite each of the departure (LD) and arrival (LA) lines. Method for determining at least one friction parameter according to one of the preceding claims, in which each of the first (P1) and second (P2) transverse positions is determined over the width (l) with an accuracy of + / -4cm, or even + / -3cm, + / -2cm, or even + / -1cm. Method for determining at least one friction parameter according to one of the four preceding claims, in which the -at least one- membrane potentiometer or the -at least one- time-of-flight measurement sensor associated with the starting line (LD) (respectively the finishing line (LA)) is connected to a microcontroller capable of transmitting information relating to the first transverse position (P1) (respectively to the second transverse position (P2)), via a wireless communication protocol. Method for determining at least one friction parameter according to the preceding claim, in which the microcontrollers implemented in the method are synchronized using GNSS receiver modules. Method for determining at least one friction parameter according to one of the preceding claims, wherein the width (l) of the starting line (LD) and / or the width (l) of the finishing line (LA) is between 0.2m and 5m. Method for determining at least one friction parameter according to one of the preceding claims, in which the starting line (LD) and the finishing line (LA) are the same, the section of track or road defining a loop. Method for determining at least one friction parameter according to one of the preceding claims, in which the first (P1) and the second (P2) transverse positions are time-stamped when they are measured. Method for determining at least one friction parameter according to one of the preceding claims, involving one or more movements on the section of track or road by the cyclist, and comprising for each movement:- a measurement of the difference in kinetic energy of the cyclist between the finish line (LA) and the start line (LD),- a measurement of the driving energy developed by the cyclist, if applicable, during his movement on the section between the start line (LD) and the finish line (LA),- a direct or indirect measurement of the dynamic pressure of the air during the movement of the cyclist on the section between the start line (LD) and the finish line (LA), so as to trace a relationship linking a resistive force (F res ) at an average dynamic air pressure ( <P air>), the mass of the cyclist being known and the difference in altitude (H) between the starting line (LD) and the finishing line (LA) being determined from the first (P1) and second (P2) transverse positions. Method for determining at least one friction parameter according to the preceding claim, in which the relationship linking the resistive force (F res ) at the average dynamic air pressure ( <P air >) is linear and we determine an aerodynamic drag surface (CxS), the directing coefficient of the line, and a rolling coefficient (C r ), proportional to the coordinate at the origin of the line. Apparatus for measuring a transverse position (P1, P2) of the cyclist passing over a starting line (LD) or finishing line (LA) and its time stamp, intended to be implemented in a method for determining at least one friction parameter according to claim 10, comprising:- a resistive membrane potentiometer arranged on the starting line (LD) or finishing line (LA), the dimension (D) of the potentiometer along a transverse axis being equal to a transverse extent or width (l) of the starting line (LD) or finishing line (LA), the potentiometer comprising three pins and having a fixed resistance between a first pin and a third pin and a variable resistance between the second pin and a third pin, said variable resistance being proportional to the transverse position (y) of the cyclist passing along the dimension (D);- a microcontroller to which the resistive membrane potentiometer is connected, the second pin of the resistive membrane potentiometer being connected to an analog input of the microcontroller allowing voltage variations representative of the transverse position (P1, P2) of the cyclist's passage to be read and timestamped.; Apparatus for measuring a transverse position of passage of the cyclist on a starting line (LD) or finishing line (LA) and its time stamp, intended to be implemented in a method for determining at least one friction parameter according to claim 10, comprising:- two resistive membrane potentiometers arranged parallel and side-by-side on the starting line (LD) or finishing line (LA), the dimension (D) of each potentiometer along a transverse axis being equal to a transverse extent or width (l) of the starting line (LD) or finishing line (LA), each potentiometer comprising three pins and having a fixed resistance between a first pin and a third pin and a variable resistance between the second pin and a third pin, said variable resistance being proportional to the transverse position (y) of passage of the cyclist along the dimension (D);- a microcontroller to which the two resistive membrane potentiometers are connected, the second pin of the first resistive membrane potentiometer being connected to an analog input of the microcontroller for reading the transverse position of the cyclist's passage, the second pin of the second resistive membrane potentiometer being connected to an interrupt of the microcontroller so as to trigger the time stamp with an accuracy better than + / -100ms.; Apparatus according to one of claims 13 and 14, comprising wireless communication means for transmitting information relating to the transverse position (P1, P2) of the cyclist's passage and relating to its time stamp.

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