METHOD FOR DETERMINING THE AERODYNAMIC DRAWBACK AREA AND / OR THE ROLL COEFFICIENT OF A VEHICLE AND ASSOCIATED MEASURING DEVICE

Description

FIELD OF INVENTION

[0001] The present invention relates to the field of devices and methods for measuring and determining the forces acting on a moving vehicle. The invention is particularly aimed at determining the aerodynamic drag area and / or the rolling resistance coefficient of a cyclist on their bicycle, with precision, reproducibility, and by implementing a simple and rapid protocol. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] Accurately measuring key cyclist friction parameters (rolling and aerodynamics) remains a major challenge for the cycling industry. Two main categories of testing can be considered: stationary tests and tests in motion.

[0003] For stationary testing, the general principle is to simulate air or ground movement while the bicycle (and potentially the cyclist) remains physically stationary. These methods require a laboratory setting with dedicated instrumentation to accurately measure specific forces. The advantage is that they allow for independent measurement of rolling resistance and aerodynamic parameters. The wind tunnel is the instrument of choice for measuring aerodynamics, while a system of moving drums is often preferred for measuring rolling resistance. The disadvantage is that this type of methodology introduces measurement biases. Wind tunnels struggle to reproduce the inherently turbulent nature of outside air; drums introduce measurement biases due to the variety of roads and temperature conditions that cyclists encounter outdoors.These laboratory methods also have the major drawback of being very expensive and not easily accessible to the general public.

[0004] Unlike stationary tests, moving tests aim to place the cyclist and their bicycle in real-world conditions. Certain parameters governing movement are then precisely measured to deduce the rolling resistance and aerodynamic coefficients of the cyclist on their bicycle. The main difficulty lies in distinguishing between rolling resistance and aerodynamic parameters, the resultant of which is an overall friction force, practically impossible to discern at constant speed.

[0005] Indeed, a cyclist in motion is subject to several forces: The force of gravity: F poids = − m g p

[0006] With m the mass of the cyclist, g the acceleration due to gravity and p the slope of the road, the average slope can be expressed from H and L, respectively the height (or elevation difference) and the length of the section of road traveled. Dry friction force (rolling force): F roulement = − m g C r

[0007] With C r the rolling coefficient (unitless). Fluid friction force (friction force with air):

[0008] With ρ the air density, v air the air speed relative to the cyclist i.e. the vehicle speed v plus the wind speed, Cx the vehicle shape factor, S the frontal area. The forward force (force exerted by the cyclist on the pedals): F avancement = P v

[0009] With P being the driving power transmitted to the wheels and v the speed of the vehicle.

[0010] According to the fundamental equation of dynamics:

[0011] In order to minimize the energy cost of the vehicle's movement, it appears particularly key to be able to accurately measure the frictions applied to the cyclist (rolling and aerodynamics) expressed through the parameters C r, rolling coefficient, and CxS, aerodynamic drag area.

[0012] However, we see that the equation which governs the movement of a cyclist involves multiple parameters m, ρ, v air , v, CxS, C r , H and L.

[0013] All the methods presented below assume a known mass m of the vehicle and a known air density ρ. However, in order to discriminate between Cr and CxS during one or more test movements, different strategies are employed to do without knowing one or more of the remaining variables (H, v air, v, CxS, Cr, L).

[0014] Document FR2725520 proposes a method consisting of performing several freewheeling tests in an enclosed space on a flat road, while very precisely recording the deceleration rate (typically using pressure strips placed on the ground, spaced 1m and 20m apart, with detection at 30µs). This protocol allows for several simplifications. Indeed, when traveling on a closed circuit that is perfectly flat and has a constant surface (such as a velodrome, a hangar, or a gymnasium, for example), the height can be assumed to be zero and the rolling resistance constant. Furthermore, by operating in an enclosed and unventilated space, vair can be considered equivalent to the cyclist's speed v. Finally, by operating in freewheeling conditions (deceleration without applying any driving force), the driving force can be assumed to be zero, and only inertia propels the cyclist forward. Based on these assumptions, an analytical equation of motion can be derived: And v0 is the initial velocity.

[0015] By measuring the movement very precisely (speed or distance and time of passage at certain points using measurement strips or speed radar), the parameters α and β can be approximated in order to deduce C r and CxS.

[0016] Relatively low variability in measurements was obtained using this method by multiplying the decelerations (standard deviations of 0.56% and 0.59% for CxS and C r respectively per series of 30 decelerations). However, the difficulty of implementation (repetition of tests, enclosed hangar, installation of measuring equipment) makes this method generally unattractive despite the reliability of the results obtained.

[0017] Document WO2007038278 proposes a similar solution based on deceleration tests, but this time outdoors, with wind and altitude measurements. It consists of closely matching a theoretical equation of motion to reality during an outdoor freewheeling test by adjusting the parameters CxS and Cr. In this protocol, the wind relative to the ground and the road incline are measured via an onboard device and are no longer assumed to be zero.

[0018] This solution does not allow for accurate results. The sources of inaccuracies are numerous. Indeed, the onboard tachometer (with a 1Hz sampling rate) introduces too many uncertainties to accurately describe a movement that is short by definition (freewheeling for less than 100m). Altitude measurement is also subject to too much inaccuracy. In fact, it relies on an inclinometer whose value can vary depending on the pressure applied to the bicycle, and whose calibration is difficult to perform under real-world conditions (bicycle + cyclist).

[0019] Another solution is based on regression tests. This involves performing multiple round trips (typically around ten), at increasing speeds, on a flat, sheltered section of road with a constant surface (typically 1 km). In the case of a velodrome, the tests require completing several laps of the track at increasing speed (J. Martin, A. Gardner, M. Barras, et al., "Aerodynamic drag area of ​​cyclists determined with field-based measures," Sportscience 10 2006 68-69). Each lap or section is completed at the most constant speed possible, and the energy expended per section or lap is measured using a wattmeter. Establishing the relationship between the energy developed and the square of the speed of the section allows for the precise calculation of CxS and Cr.

[0020] Regression tests have proven capable of measuring very small differences in CxS, on the order of 1.5%. However, they are very time-consuming to implement because they require at least ten kilometers of test routes at varying speeds. A result cannot therefore be obtained in less than 30 minutes.

[0021] Following the same principle as before, assuming Cr is known (for example, through a regression test), it is possible to determine CxS by simply performing a round trip outdoors on a flat test course at a constant speed. In this case, the wind can be assumed to be constant and not zero.

[0022] This type of protocol is currently being proposed ( https: / / www.aerotune.com / ), with recommendations for use in conditions of low wind and road gradient of less than 0.5%. It is also recommended to perform 3 round trips per test, in order to average the uncertainties, which implies relatively long procedures of at least 15-20 minutes per test.

[0023] Beyond its cumbersome implementation, a real question lies in the accuracy of this protocol if the conditions of constant wind are not respected (variation of wind or other vehicle on the route during the test, for example).

[0024] We also know the virtual elevation method on a closed circuit known as the "Chung Method" (see the publication "Estimating CdA with a power meter" by R. Chung, updated version March 2012). It consists of recalculating a so-called virtual altitude on a closed course without wind or external vehicles, run several times without braking, making assumptions about aerodynamic drag and the rolling resistance coefficient (Cr). The vehicle speed (cyclist on their bicycle), the power output of the cyclist, and potentially the wind speed are measured by sensors. The slope (p), then the elevation difference (H) at each point of the circuit can then be recalculated by making assumptions about Cr and CxS. p t = − 1 g dv t dt + P t mgv − C r − 0.5 ρ CxS mg v air t 2 H T = ∫ 0 T p t dt

[0025] The realistic values ​​of CxS and Cr are those which allow obtaining an identical virtual elevation for each of the paths taken.

[0026] This method has been popularized by its implementation in smartphone applications, enabling the collection of data from numerous sensors on the bicycle. Document GB2568885A also describes a device for implementing this method using an anemometer attached to the bicycle fork. However, Chung's method involves several constraints. First, it requires the ability to complete a closed-loop course without braking, safely and without any external vehicles: in practice, this means courses in a dip between two roundabouts without sharp turns. Such courses are very difficult to find, especially in urban areas. Furthermore, this method does not specify how to distinguish between the terms CxS and Cr. The solution found is, in fact, a possible pair (CxS, Cr). By setting a hypothesis for Cr, it is possible to observe the relative variation of CxS for different trials.However, the absolute value remains unattainable. Another drawback of this method lies in the difficulty of carrying out numerous runs under the required weather conditions (without wind, when wind is not measured) to obtain the best measurement accuracy.

[0027] From the same author, we know of document US2012 / 0221257 describing a method for determining the aerodynamic drag area (CxS) of a moving vehicle based on wind characteristics. This method relies in particular on measuring wind speed and direction during movement, which makes it complex to implement.

[0028] We finally know of a solution from document WO2017 / 055759, based on the analysis of four trips (two round trips) on an outdoor route, for example, under freewheeling conditions. The wind is assumed to be constant. Specifically, one round trip is performed at low speed and one round trip at high speed. Speed ​​values ​​are recorded very precisely for each test using an onboard device. An algorithm allows the coefficients Cr and CxS, as well as the average wind speed vwind (vair - vs), to be deduced from three equations derived from the principle of conservation of energy and based on three constraints on the elevation changes of the route. In practice, arbitrary values ​​of the parameters Cr, CxS, and vwind, initially fixed, are corrected iteratively by relating the errors made on these parameters (ΔCr, ΔCxS, and Δvwind) with the errors on the altitudes resulting from the three aforementioned constraints.The resolution of such a system can be done for example by the Cramer method and results in obtaining the corrections (ΔC r , ΔCxS and Δv vent ) to be applied to the arbitrary values ​​of the characteristic factors initially injected.

[0029] The method has the advantage of being usable outdoors, on a course exposed to wind. Furthermore, its implementation is relatively quick (2 to 5 minutes per test maximum). It also allows for the differentiation between Cr and CxS. Standard deviations of approximately 2% for CxS and 4% for Cr were recorded during repeatability tests under calm wind conditions.

[0030] The main drawback of this method lies in its reliance on a relatively strong assumption: that the wind will remain constant throughout the four movements. However, the test duration (a few minutes) is on the same order of magnitude as the characteristic wind speed variation time relative to the ground. This is why coefficients of variation exceeding 5% for CxS can be observed under strong wind conditions. SUBJECT OF THE INVENTION

[0031] The present invention aims to overcome all or part of the aforementioned drawbacks. It relates to a preparatory sequence for determining the aerodynamic drag area and rolling resistance coefficient of a vehicle, in particular a cyclist on a bicycle. The invention also relates to methods for determining one or both of these key friction parameters, based on said preparatory sequence and offering excellent reproducibility and ease of implementation. The determination methods according to the invention are particularly advantageous for short test runs, typically less than 1 km. BRIEF DESCRIPTION OF THE INVENTION

[0032] The invention concerns a preparatory sequenceFor determining the aerodynamic drag area and / or rolling resistance coefficient of a vehicle under real-world driving conditions, without braking, on a defined section of road with a starting point and an ending point, the preparatory sequence includes the following steps: a) the definition of a traffic lane with a width less than or equal to 1m, along said section of road, b) the vehicle carrying out a first movement, on the section of road, from the starting point to the arrival point, and in the traffic lane, during which the following parameters are measured: the air velocity relative to the vehicle, with an anemometer having a sampling frequency greater than or equal to 1Hz and a measurement repeatability less than (or better than) 2% RMS for a sampling frequency of 1Hz, or the dynamic air pressure, with a differential pressure sensor having a sampling frequency greater than or equal to 1Hz and a measurement repeatability better than 4% RMS for a sampling frequency of 1Hz, the speed of the vehicle at the starting and arrival points of the section of road, with a speed sensor having a repeatability better than 0.25% RMS, the motive power supplied by the vehicle along the road segment, with a power sensor exhibiting a repeatability better than 1% RMS, or the consideration of zero motive power if said movement is carried out in freewheeling.

[0033] According to other advantageous and non-limiting features of the invention, taken alone or in any technically feasible combination: the width of the traffic lane is less than or equal to 50cm, or even 30cm, or even 10cm; the road segment has a length greater than or equal to 500m when motive power is developed by the vehicle during movement on said segment; the road segment has a length less than or equal to 300m, preferably around 100m, when movement on said segment is carried out in freewheeling; the road segment has a downward gradient of around 0 to -1%, and a length less than or equal to 500m, preferably around 200m, when movement on said segment is carried out in freewheeling; the measurement of the vehicle's speed is based on counting the number of wheel revolutions of said vehicle per unit of time;the measurement of the vehicle's speed uses one or more magnet(s) placed on the wheel and a system for detecting the number of times the magnet(s) pass per unit of time, with a sampling frequency greater than or equal to 2kHz; the measurement of the vehicle's speed is obtained from at least two sensitive wheel detection strips, placed respectively at the starting point and at the ending point of the road section, capable of delivering an electrical pulse when the vehicle passes and coupled to a timing system with a sampling frequency greater than 2kHz;The movement of step b) is preceded by a momentum phase, initiated at a point of vehicle activation located at a known distance from the starting or finishing point, said distance being a multiple of one or a fraction of a wheel rotation, and a passage over the starting or finishing point of the road segment, during the movement of step b), is detected precisely by counting the number of wheel rotations from the point of activation; a passage over the starting or finishing point of the road segment is detected precisely by a satellite positioning system; a passage over the starting or finishing point of the road segment is detected precisely by a system of radio frequency beacons positioned at the starting and / or finishing points.

[0034] The invention also relates to five methods of determining the aerodynamic drag area and / or the rolling resistance coefficient.

[0035] A first method of determination of the aerodynamic drag surface implements the aforementioned preparatory sequence, and further includes the following step: c) the determination of the aerodynamic drag surface from an equation derived from the principle of conservation of energy, and from: of known parameters such as the mass of the vehicle, the acceleration due to gravity, the air density (if necessary), the length of the section, the elevation difference of the section, parameters measured during the first movement, and the rolling coefficient known or arbitrarily fixed.

[0036] A second method of determination of the rolling resistance coefficient, implements the aforementioned preparatory sequence, and includes the following step: d) the determination of the rolling resistance coefficient from an equation derived from the principle of conservation of energy, and from: of known parameters such as the mass of the vehicle, the acceleration due to gravity, the air density (if necessary), the length of the section, the elevation difference of the section, parameters measured during the first movement, and the known or arbitrarily fixed aerodynamic drag area.

[0037] A third method of determination of the aerodynamic drag surface, implements the aforementioned preparatory sequence, and includes the following steps: b') the vehicle making a second trip, on the road section, from the starting point to the arrival point, and in the traffic lane, during which the same parameters are measured as in step b), c') the determination of the aerodynamic drag area from an equation based on the principle of conservation of energy, and from: known parameters such as the mass of the vehicle, the acceleration due to gravity, the air density (if necessary), the length of the section, and the parameters measured during the first and second trips.

[0038] A fourth method of determination of the aerodynamic drag area and rolling resistance coefficient implements the aforementioned preparatory sequence, and further includes the following steps: b') the vehicle making a second trip, on the road section, from the starting point to the arrival point, and in the traffic lane, during which the same parameters are measured as in step b), e) the determination of the aerodynamic drag area and the rolling coefficient from an equation based on the principle of conservation of energy, and from: known parameters such as the mass of the vehicle, the acceleration due to gravity, the air density (if necessary), the length of the section, the elevation difference of the section, and the parameters measured during the first and second trips.

[0039] A fifth method of determination of the aerodynamic drag area and rolling resistance coefficient implements the aforementioned preparatory sequence, and further includes the following steps: b") the vehicle making a second trip, on the road section, from the arrival point to the starting point, and in the traffic lane, during which the same parameters are measured as in step b); b‴) the vehicle making a third trip, on the road section, from the starting point to the arrival point, and in the traffic lane, during which the same parameters are measured as in step b); e') the determination of the aerodynamic drag area and the rolling resistance coefficient from an equation based on the principle of conservation of energy, and from: known parameters such as the mass of the vehicle, the acceleration due to gravity, the air density (if necessary), the length of the section, and the parameters measured during the first, second and third trips.

[0040] The invention finally concerns an integrated systemfor the implementation of one of the aforementioned methods for determining the aerodynamic drag area and / or rolling resistance coefficient of a vehicle. The integrated system includes: an anemometer, having a sampling frequency greater than or equal to 1Hz, for measuring the air speed relative to the vehicle, or a differential pressure sensor, having a sampling frequency greater than or equal to 1Hz, for measuring the dynamic air pressure, a speed sensor corresponding to a stopwatch associated with a reed switch, based on the detection of the number of passages of at least one magnet placed on a wheel of the vehicle, with a frequency greater than or equal to 2kHz, for measuring the speed of the vehicle, a calculator for determining the aerodynamic drag area and / or rolling coefficient from the measured parameters and known or arbitrarily pre-recorded parameters.

[0041] Advantageously, the integrated system includes means of remote communication with a mobile phone or a screen.

[0042] It includes, according to a preferred mode, an aerodynamic envelope in which are integrated the anemometer or one or more pressure sensing elements of the differential pressure sensor, the speed sensor and the computer, the aerodynamic envelope being located at the front of the vehicle. BRIEF DESCRIPTION OF THE FIGURES

[0043] Other features and advantages of the invention will become apparent from the detailed description of the invention which follows with reference to the accompanying figures in which: [ Fig. 1a], [Fig. 1b ] THE Figures 1a and 1bpresent a plan view and a cross-sectional view of a section of road on which the vehicle will travel for the implementation of the preparatory sequence and methods for determining the vehicle's friction coefficients, according to the present invention; [ Fig. 2 ] There figure 2 presents a result value for the aerodynamic drag area CxS and the rolling coefficient Cr, obtained from the fifth method of determination according to the invention, for a given test condition; [ Fig. 3 ] There figure 3 presents results of aerodynamic drag area (CxS) values, obtained from the first determination method according to the invention, for five different test conditions; [ Fig. 4 ] There figure 4 presents a possible implementation of an integrated system according to the present invention, on a time trial bicycle handlebar; [ Fig. 5 ] There figure 5presents results of aerodynamic drag area values ​​CxS, obtained during 16 tests carried out under identical test conditions: 8 tests (according to the invention) were carried out respecting the traffic lane and the CxS values ​​were obtained from the first method of determination according to the invention; the other 8 tests (outside the invention) were carried out without respecting the traffic lane and the CxS values ​​were obtained on the same basis of method of determination.

[0044] The figures are schematic representations which, for the sake of readability, are not necessarily to scale. DETAILED DESCRIPTION OF THE INVENTION

[0045] The present invention relates to a preparatory sequence for determining the aerodynamic drag area CxS and / or the rolling resistance coefficient Cr of a vehicle under real-world driving conditions. This sequence, which takes the form of a method, is called preparatory because it constitutes an essential step common to the aforementioned methods for determining friction coefficients, said methods also being the subject of the present invention.

[0046] The preparatory sequence and determination methods apply particularly to a bicycle-type vehicle on its bicycle 1 ( figure 1a ). They could nevertheless apply to any other vehicle moving by means of human or mechanical energy, such as a rolling, floating, sliding vehicle...

[0047] According to the invention, the aim is to determine the friction coefficients of a vehicle, namely the aerodynamic drag area CxS and the rolling resistance coefficient Cr, under real-world driving conditions, without braking, on a defined road segment T with a starting point A and an ending point B. The starting point A and the ending point B may, for example, be marked by beacons on the side of the road and / or strips glued or painted on the road. The road segment T has a length L and a height (or difference in elevation) between the starting point A and the ending point B, denoted H ( Figures 1a and 1b ). Preparatory sequence:

[0048] The preparatory sequence includes a first step a) corresponding to the definition of a traffic lane C with a width less than or equal to 1m, along the road segment T. Advantageously, the width of the traffic lane is even less than or equal to 50cm, or even 30cm, or even 10cm.

[0049] This first step can be carried out by identifying the traffic lane C, for example by adhesive strips or painted markings along the section of road T. Alternatively, the traffic lane C may be materialized by only a single strip or line, continuous or broken, which the vehicle must follow as closely as possible: in practice, the vehicle thus remains in a traffic lane C with a width of less than 50cm.

[0050] Of course, the definition of a traffic lane C can be achieved using any other technique that guarantees the vehicle travels along the road segment T in a lane less than or equal to 1 meter wide, as previously stated. In other words, the aim is to ensure that the vehicle does not deviate from its trajectory by more than 50 cm along the road segment T.

[0051] The preparatory sequence then includes a second step b) during which the vehicle makes a first movement, on the road segment T, from the starting point A to the arrival point B, and in the traffic lane C.

[0052] This movement is carried out under specific test conditions, i.e., a particular vehicle configuration. Applied to a cyclist on their bicycle, the test conditions are defined in particular by a specific bicycle (wheels, handlebars, materials, etc.), the cyclist's posture, the clothing and helmet worn by the cyclist, etc.

[0053] During the first movement, several parameters are measured. The air velocity (vair) relative to the vehicle must be measured using an anemometric sensor with a sampling frequency greater than or equal to 1 Hz, or greater than or equal to 2 Hz, or greater than or equal to 4 Hz, or greater than or equal to 6 Hz, or greater than or equal to 8 Hz, or greater than or equal to 10 Hz, and a measurement repeatability better than 2% RMS at a sampling frequency of 1 Hz. In practical terms, this means that the standard deviation of the difference between two concurrent measurements of air velocity at a sampling frequency of 1 Hz on the same moving bicycle, during the same movement, must not exceed 2.8% (2% x √2).For a sampling frequency above 1 Hz, a significantly higher measurement repeatability is acceptable: for example, for a frequency of 4 Hz, a measurement repeatability better than 4% RMS (i.e., 2% RMS times the square root of the sampling frequency) is required. Note that the air velocity vair corresponds to the vehicle velocity v, if the movement takes place in an enclosed space sheltered from the wind.

[0054] As an alternative to measuring air velocity, it is possible to measure the difference between total and static air pressure using a differential pressure sensor. This air pressure difference, measured while the bicycle is moving, corresponds to the dynamic air pressure. The differential pressure sensor must have a sampling frequency greater than or equal to 1 Hz, or greater than or equal to 2 Hz, or greater than or equal to 4 Hz, or greater than or equal to 6 Hz, or greater than or equal to 8 Hz, or greater than or equal to 10 Hz, and a measurement repeatability better than 4% RMS at a sampling frequency of 1 Hz. This means that the standard deviation of the difference between two concurrent measurements of dynamic pressure at a sampling frequency of 1 Hz on the same moving bicycle, during the same movement, must not exceed 5.6% (4% x √2).For a sampling frequency greater than 1Hz, a significantly higher measurement repeatability can be tolerated, as mentioned previously.

[0055] During the first movement, the vehicle speed v at the starting point A and the ending point B of the segment must also be measured with a repeatability better than 0.25% RMS. This means that the standard deviation of the difference between two competing speed measurements of the same moving bicycle, during the same movement, must not exceed 0.35% (0.25% x √2).

[0056] Finally, the motive energy (Wmot) supplied by the vehicle along the segment is also measured, with a repeatability better than 1% RMS. If the movement is performed in freewheeling mode, measurement of the motive energy is not required, and zero motive energy is assumed. Repeatability can be verified by comparing the energy measurement system used with a commercially available reference power sensor, such as an SRM or Verve Infocrank. The variability of the difference in energy measured between the energy measurement system and the reference power sensor over multiple journeys must not exceed a standard deviation of 1% x √2, or 1.4%.

[0057] According to the invention, the parameters measured during displacement must be measured under strict repeatability conditions, which imposes repeatability requirements on the sensors used. It is important to remember that random error is always present in a measurement and is closely related to the concept of sensor accuracy. The higher the accuracy of a sensor, the lower the variability of fluctuations in its measurements due to random error, and the better the sensor's measurement repeatability. Random error is caused by inherently unpredictable fluctuations in sensors. Random errors appear as different results for seemingly the same repeated measurement. These errors tend to be normally distributed due to the central limit theorem, as the stochastic error is often the sum of many independent random errors.They can be estimated by evaluating the repeatability of multiple measurements of a stable phenomenon, or when the measured phenomenon is not perfectly stable - as in the case of a cyclist set in motion by his own means - by comparing two simultaneous measurements of the same phenomenon.

[0058] Consider two sensors X and Y providing measurements Xmes and Ymes of the same parameter Z. Assume these sensors are identical and have a random error of the same magnitude, normally distributed. This means that the measurement errors Xerr = Xmes - Z and Yerr = Ymes - Z both follow a normal probability distribution N(µsysX, σ2) and N(µsysY, σ2), where µsysX and µsysY are the systematic errors and σ is the standard deviation corresponding to the random error. The repeatability of a sensor measurement, as defined in the present invention, is determined by the contribution of the random error: a measurement repeatability of the parameter Z better than 2% RMS means that σ is less than or equal to 2%, or σ ≤ 0.02 x Z.

[0059] In practice, it is sometimes simpler and more pragmatic to compare two simultaneous measurements of the same parameter Z taken by two identical sensors X and Y to evaluate the standard deviation σ representing the random error. The difference between the measurements Xmes - Ymes follows a normal probability distribution N(µsysX - µsysY, 2σ ≤ 2). By evaluating Xmes - Ymes, it is possible to find the value of the standard deviation σ of a single sensor. To do this, simply divide the standard deviation σ Δ of Xmes - Ymes by √2, which is approximately 1.4.

[0060] The repeatability of the measurement of a sensor within the meaning of the present invention can thus be appreciated from the standard deviation σ Δ of the difference (X mes - Y mes ) between two concurrent measurements X mes , Y mes , of the parameter Z. A measurement repeatability of the parameter Z better than 2%RMS therefore also means that σ Δ is less than or equal to √2 x 2%, i.e. σ Δ ≤ 0.028 x Z, the value of Z being estimated as the average of the measurements X mes , Y mes .

[0061] The air velocity vair (or dynamic pressure), in the case of travel along a stretch of road exposed to wind, can be measured by an anemometer (or a differential pressure sensor) mounted on the bicycle. A sampling frequency greater than or equal to 1 Hz ensures that the work done by the aerodynamic force Waero (expressed later in equation [equation 9], and consequently the energy balance (expressed later in equation [equation 8]) and its constituent unknowns (Cr and / or CxS and / or H), are calculated with sufficient accuracy along the stretch, even when airflow is variable and turbulent.

[0062] The anemometer (or the total pressure measurement element of the differential pressure sensor) is placed in an area where the airflow around the vehicle does not significantly interfere with the reading of the incident air. In the case of a bicycle, a zone midway between the top of the wheel and the handlebars, and 0 to 1.5 meters in front of the cyclist, is preferred. This zone is reached, for example, by means of an extension attached to a bracket fixed to the handlebars or fork ( figure 4 ).

[0063] Preferably, the air velocity (vair) or dynamic pressure (ΔP) can be measured using a differential pressure sensor connected to a Pitot tube. The air velocity is deduced from the pressure measurement using the following relationship: V air = k 2 Δ P ρ

[0064] With ΔP (dynamic pressure) the difference between total pressure and static pressure of the air at the outlets of the Pitot tube, ρ the air density and k a calibration factor which can be determined during a round trip test flight where the average wind is assumed to be zero.

[0065] More generally, the dynamic pressure ΔP can be estimated using any type of differential pressure port, provided that the two pressure ports exhibit significant differences in sensitivity to dynamic pressure. A calibration factor kp will allow adjustment of the actual dynamic pressure ΔP from the measured differential pressure ΔP using the relationship ΔP_actual = kpx / ΔP_measured. This factor will be determined based on the difference in sensitivity of the ports to dynamic pressure.

[0066] The air speed in the case of movement not exposed to wind (for example in a hangar, a velodrome, a gymnasium, etc.) can be assumed to be equal to the speed of the cyclist and measured using an on-board tachometer, for example, using the same method as that used for measuring speeds at points A and B described below.

[0067] The vehicle's speed, v, can be measured by counting the number of wheel revolutions per unit of time at the starting point, A, and the destination, B. According to an advantageous variant, the vehicle's speed is measured using one or more magnets placed on the wheel and a magnetic switch with flexible reeds, sensitive to the passage of these magnets, located, for example, on the fork in the case of a bicycle. This switch is coupled to an electronic timing system capable of detecting the open and / or closed states of the switch with a resolution of less than 500 µs (or a sampling frequency greater than 2 kHz). The speed can be easily calculated using the following relationship: v = D roue Δ top β 2 π with Δ top the time interval measured between two successive rising (or falling) voltage fronts measured across the terminals of the switch, D wheel the diameter of the wheel and β the angle between the magnet considered and its predecessor (B=2π in the case of a measurement with a single magnet).

[0068] Alternatively, the vehicle speed v can be measured using at least two pairs of sensitive wheel detection strips. Each pair is positioned to encompass the starting point A and the ending point B of the road segment T. These pairs of strips can be made of a pressure-sensitive material, laid parallel to each other on the ground at distances dA and dB respectively from points A and B (advantageously, dA and dB are less than 10 m), and placed perpendicular to the tread, covering its entire width. Each strip is capable of delivering an electrical pulse as the vehicle passes over it and is coupled to a timing system designed to receive the electrical pulses and determine the time interval between two consecutive pulses with a resolution of less than 500 µs (or a sampling frequency greater than 2 kHz).The velocities at points A and B can be calculated simply as follows: . v A = d A T A et v B = d B T B

[0069] TA and TB are respectively the time intervals between two consecutive pulses measured during the passage of the vehicle over the road segment T at points A and B.

[0070] The motor energy (Wmot) can be measured using a commercially available power sensor with the aforementioned repeatability characteristics. The data transmitted by the sensor is retrieved using the sensor's wireless transmission protocol (Bluetooth, ANT+, etc.). The sensor calibration procedures recommended by the manufacturer are applied before each test session.

[0071] In the case of a freewheel, energy can be assumed to be zero, and therefore no power meter is necessary. The cyclist can then advantageously continue to perform a virtual pedaling motion by rotating their legs without actually pressing on the pedals, thus replicating an aerodynamic position corresponding to a dynamic pedaling situation.

[0072] Advantageously, the road segment T has a length L greater than or equal to 500 m when motive power is generated by the vehicle during the first movement, or, as will be detailed later with reference to the determination methods according to the invention, during a subsequent movement on said segment. However, when the first movement (or a subsequent movement) on the road segment T is made in freewheeling mode on a flat road, said segment T has a length less than or equal to 300 m, preferably on the order of 100 m. Advantageously, a slightly sloping road with a gradient between 0 and -1% can be chosen so as to maximize the freewheeling length beyond 200 m and thus minimize the impact of uncertainties on the measurements. In this latter case, the segment is traveled in only one direction.

[0073] When the implementation methods of step b) of the preparatory sequence use measurements taken on-board (speed with detection of magnet passage on the wheel, airflow with anemometer or dynamic pressure with differential pressure sensor, motive energy with power sensor), it is important to be able to precisely synchronize the measured data with the distance traveled between the starting point A and the arrival point B of the road segment T. Several options are possible for this.

[0074] According to one option, the movement in step b) is preceded by a momentum phase, initiated at a starting point M, M' of the vehicle, located at a known distance from the starting point A or the arrival point B: in practice, for simplicity, this distance is chosen as a multiple of one wheel revolution of the vehicle or a fraction of a wheel revolution. This distance can typically be on the order of 200 m. Thus, the vehicle's passage over the starting point A or the arrival point B of the road segment T, during the movement in step b) (or any other movement), is precisely detected by counting the number of wheel revolutions from the starting point M, M'.

[0075] According to another option, the vehicle's passage over the starting point A or the ending point B of road segment T can also be precisely detected using a Global Navigation Satellite System (GNSS). According to yet another option, the vehicle's passage over the starting point A or the ending point B of road segment T is precisely detected using a system of radio frequency beacons positioned at the starting point A and / or the ending point B.

[0076] The preparatory sequence according to the invention defines optimal conditions for reconstructing the vehicle's energy balance as faithfully as possible, particularly for short test journeys (less than 1 km), where variations in kinetic and potential energy (elevation changes) play a major role. Defining a restricted traffic lane along the road segment T (step a) of the preparatory sequence ensures an excellent level of constancy in the potential energy lost or gained by gravity (W weight, expressed later in equation [eq. 10]) and possibly that lost by rolling (W rolling, expressed later in equation [eq. 11]), along the journey during the first movement (and subsequent movements, as will become apparent).

[0077] The speed measurement (v) is very precise in order to accurately determine the variations in kinetic energy. Furthermore, the required precision for the measurements of the other parameters (v air, ΔP, W mot) is also very high in order to reconstruct a faithful energy balance of the vehicle and ultimately allow the determination of representative and exact values ​​for the aerodynamic and / or rolling coefficients. Principle of conservation of energy:

[0078] From an energy perspective, along a road segment T with a length L and a difference in elevation H, equation [eq.5] stated in the introduction gives: ∫ 0 L ∑ F dx = ∑ W = ∫ 0 L m dv dt dx ,

[0079] As dx = V dt, We can deduce the following equation [eq.7]: ∑ W = ∫ 0 L m V dv = 0.5 m V final 2 − V ini 2

[0080] By decomposing the work generated by each force on a road segment T, we obtain: ∑ W = W areo + W poids + W roulement + W mat = 0.5 m V final 2 − V ini 2

[0081] With W areo = − ∫ 0 L 0.5 ρ CxS v air 2 dx , aerodynamic energy, which can also be expressed as W areo = − ∫ 0 L CxS Δ P dx .

[0082] This last expression for W aero is independent of air density. When the dynamic pressure ΔP is measured instead of the air velocity, it is therefore not necessary to know the air density in the determination methods that will be described later. W poids = − m g H , energy lost or gained through gravity W roulement = − m g C r L , the energy lost by rolling W mot = ∫ 0 L P V dx = ∫ 0 L P dx dt dx = ∫ 0 T P dt , motive power.

[0083] This gives us the following relationship linking the elevation difference H to the remaining parameters: H = 0.5 g V ini 2 − V final 2 − CxS 1 m g ∫ 0 L 0.5 ρ V air 2 dx − C r L + W mot m g

[0084] The methods for determining the friction coefficients CxS, Cr of a vehicle, which will now be detailed, implement the preparatory sequence described and the equation [eq.13] above, derived from the principle of conservation of energy. First method of determination:

[0085] The first method according to the present invention makes it possible to determine the aerodynamic drag surface CxS.

[0086] It implements steps a) and b) of the preparatory sequence and then includes step c) corresponding to the determination of the aerodynamic drag area CxS from equation [eq.13] derived from the principle of conservation of energy, and from: of known parameters such as the mass m of the vehicle, the acceleration due to gravity g, the air density ρ (if necessary), the length of the section L, the elevation difference of the section H, parameters measured during the first movement of step b), and the rolling coefficient Cr known or arbitrarily fixed.

[0087] The aerodynamic drag area CxS can be expressed as follows: CxS = K v + W mot mg − H − C r L K a with K a = 1 m g ∫ 0 L 0.5 ρ v air 2 dx = 1 m g ∫ 0 L Δ P dx , K v = 0.5 g V ini 2 − V fin 2 And W wordthe motive energy supplied by the vehicle during the first movement, V ini and V fin corresponding respectively to an initial velocity and a final velocity of the vehicle, respectively to the starting point A and the arrival point B of the section T during the first movement, ΔP corresponding to the dynamic pressure and v air corresponding to the air velocity measured during the first movement.

[0088] Advantageously, the first movement in step b) is carried out at high speed: for a cyclist on their bicycle, at a speed greater than 20 km / h, for example 45 km / h. This maximizes aerodynamic energy losses along the path and therefore minimizes the influence of uncertainty on C r; it also allows us to get closer to racing speed conditions.

[0089] This first method for determining the aerodynamic drag area CxS assumes that the elevation difference H of the section is known. It is also possible that the elevation difference H of the road section T be evaluated using a geodetic instrument such as an optical level 10 ( figure 1b ) or any other suitable topographic tool (theodolite system, for example), with an accuracy on the order of a millimeter, to then be used in equation [eq. 14] above. Note that this technique for measuring the elevation difference H of section T can be applied to other determination methods that require it.

[0090] The rolling resistance coefficient Cr is either known or arbitrarily fixed. In the first case, an absolute value of the aerodynamic coefficient CxS can be obtained using the first method of determination; in the second case, the value obtained from said coefficient will only be relative.

[0091] It is important to remember that the aerodynamic drag area (CxS) is related to the test conditions under which the vehicle first moved. Applied to a cyclist on their bicycle, the CxS coefficient is representative of the bicycle, the cyclist's posture, clothing, helmet, etc.

[0092] The first method of determination according to the invention therefore provides for the possibility of repeating steps b) and c) (new displacement) for other test conditions (namely, for example, another helmet, another cyclist posture, etc.). The (absolute or relative) values ​​of the aerodynamic coefficient CxS obtained for the different test conditions can then be compared to identify the conditions most favorable to the vehicle's aerodynamics. Second method of determination:

[0093] The second method according to the present invention allows the rolling resistance coefficient Cr to be determined. It implements steps a) and b) of the preparatory sequence and then includes step d) corresponding to the determination of the rolling resistance coefficient Cr, from equation [eq.13] derived from the principle of conservation of energy, and from: of known parameters such as the mass m of the vehicle, the acceleration due to gravity g, the air density ρ (if necessary), the length of the section L, the elevation difference of the section H, parameters measured during the first movement, and the aerodynamic drag area CxS known or arbitrarily fixed.

[0094] The turnover coefficient can be expressed as follows: with And W wordthe motive energy supplied by the vehicle during the first movement, V ini and V fin corresponding respectively to an initial velocity and a final velocity of the vehicle, respectively to the starting point A and the arrival point B of the section T during the first movement, ΔP corresponding to the dynamic pressure and v air corresponding to the air velocity measured during the first movement.

[0095] Advantageously, the first movement in step b) is carried out at low speed: i.e., in the case of a cyclist on their bicycle, at a speed less than or equal to 20 km / h, for example 15 km / h. This makes the energy equation primarily dependent on rolling resistance losses and thus minimizes the influence of uncertainty in other parameters.

[0096] This second method of determining the rolling coefficient Cr requires that the elevation difference H of the section be known or measured as mentioned previously.

[0097] The aerodynamic coefficient CxS is either known or arbitrarily fixed. In the first case, an absolute value of the rolling coefficient Cr can be obtained by the second method of determination; in the second case, the value obtained from said coefficient will only be relative.

[0098] It's worth remembering that the rolling resistance coefficient (Cr) is linked to the test conditions under which the vehicle first traveled. Applied to a cyclist on their bicycle, the Cr coefficient is representative of the bicycle's tires, the type of road on the stretch, etc.

[0099] The second method of determination according to the invention therefore provides for the possibility of repeating steps b) and d) (new displacement) for other test conditions (namely, for example, other tires...). The (absolute or relative) values ​​of the rolling resistance coefficient Cr, obtained for the different test conditions, can then be compared to identify conditions more favorable to the vehicle's rolling resistance. Third method of determination :

[0100] The third method according to the present invention makes it possible to determine the aerodynamic drag surface CxS.

[0101] It implements steps a) and b) of the preparatory sequence and additionally includes a step b') in which the vehicle makes a second movement, on the road segment T, from the starting point A to the arrival point B, i.e., in the same direction as the first movement in step b). The second movement is also carried out in the traffic lane C and under the same test conditions as the first movement. The same parameters as in step b) are measured, namely the air velocity vair or the dynamic pressure ΔP, the vehicle speed v, particularly at the starting point A and the arrival point B, and the motive energy Wmot if the movement is not performed in freewheeling mode. The third method then includes a step c') which corresponds to the determination of the aerodynamic drag area CxS from equation [Eq. 13] derived from the principle of conservation of energy, and from: of known parameters such as the mass m of the vehicle, the acceleration due to gravity g, the air density ρ (if necessary), the length of the section L and parameters measured during the first and second trips.

[0102] The aerodynamic drag area CxS can be expressed as follows: with And And W motn the motive energy supplied by the vehicle, V ini_n and V fin_n corresponding respectively to an initial velocity and a final velocity of the vehicle for each displacement, ΔP n corresponding to the dynamic pressure and v air_n corresponding to the air velocity, during displacement n, with n=1,2 corresponding respectively to the first and second displacement.

[0103] Advantageously, one of the first and second displacements is performed at low speed, for example, a speed less than or equal to 20 km / h, and the other is performed at high speed, for example, a speed greater than 20 km / h. This reduces the influence of uncertainties in the measurements vair or ΔP, Wmot, and v on the discrimination of the coefficients Cr and CxS.

[0104] This third method for determining the aerodynamic drag area CxS eliminates the need to know the elevation difference H of the segment T due to the implementation of a second displacement. Indeed, the elevation differences H expressed according to equation [eq. 13], respectively for the first and second displacements, cancel each other out when the two expressions for the elevation differences H are identical. The rolling resistance coefficient Cr is also eliminated, as it is likewise removed when the two expressions for the elevation differences are subtracted, as can be seen in equation [eq. 16].

[0105] The third method of determination according to the invention naturally provides for the possibility of repeating steps b), b' and c'), for other test conditions (namely, for example, another helmet, another cyclist posture, etc.). The absolute values ​​of the aerodynamic coefficient CxS obtained for the different test conditions can then be compared to identify the conditions most favorable to the vehicle's aerodynamics. Fourth method of determination:

[0106] The fourth method according to the present invention makes it possible to determine the aerodynamic drag area CxS and the rolling coefficient Cr.

[0107] It implements steps a) and b) of the preparatory sequence and includes an additional step b') in which the vehicle performs a second movement, on the road segment T, from the starting point A to the arrival point B, i.e., in the same direction as the first movement in step b). The second movement also takes place in the traffic lane C and under the same test conditions as the first movement. The same parameters as in step b) are measured, namely the air velocity vair or the dynamic pressure ΔP, the vehicle speed v, particularly at the starting point A and the arrival point B, and the motive energy Wmot if the movement is not performed in freewheeling mode.

[0108] The fourth method then includes a step e) corresponding to the determination of the aerodynamic drag area CxS and the rolling resistance coefficient Cr, from equation [eq.13] derived from the principle of conservation of energy, and from: of known parameters such as the mass m of the vehicle, the acceleration due to gravity g, the air density ρ (if necessary), the length of the section L, the elevation difference of the section H, parameters measured during the first and second trips.

[0109] The aerodynamic drag area CxS and the rolling resistance coefficient Cr can be expressed as follows: CxS = K v 1 + W mot 1 mg − K v 2 − W mot 2 mg K a 1 − K a 2 C r = K v 1 + W mot 1 mg − H − K a 1 CxS L with K a n = 1 m g ∫ 0 L 0.5 ρ v air n 2 dx = 1 m g ∫ 0 L Δ P n dx , K v n = 0.5 g V ini n 2 − V fin n 2 And W motnthe motive energy supplied by the cyclist, V ini_n and V fin_n corresponding respectively to an initial velocity and a final velocity of the vehicle, ΔP n corresponding to the dynamic pressure and v air_n corresponding to the air velocity, during the displacement n with n=1,2 corresponding respectively to the first and second displacement.

[0110] Advantageously, one of the first and second displacements is performed at low speed, for example, a speed less than or equal to 20 km / h, and the other is performed at high speed, for example, a speed greater than 20 km / h. This reduces the influence of uncertainties in the measurements vair or ΔP, Wmot, and v on the discrimination of the coefficients Cr and CxS.

[0111] This fourth method of determining the aerodynamic drag area and the rolling coefficient Cr assumes that the elevation difference H of the section T is known or measured, for example by optical level as already stated.

[0112] It also allows for the repetition of steps b) and / or b') and e) under different test conditions: for example, with reference to the cyclist, using different tires to test rolling resistance, and / or different handlebars, helmets, clothing, or riding posture to test aerodynamics. The absolute values ​​of the aerodynamic coefficient CxS and rolling resistance Cr, obtained for the different test conditions, can then be compared to identify conditions more favorable to the vehicle's aerodynamics and rolling resistance. Fifth method of determination :

[0113] The fifth method according to the present invention makes it possible to determine the aerodynamic drag area CxS and the rolling coefficient Cr.

[0114] It implements steps a) and b) of the preparatory sequence and includes an additional step b") in which the vehicle performs a second movement, on the road segment T, from the arrival point B to the departure point A, i.e., in the opposite direction to the first movement in step b). The second movement also takes place in the traffic lane C and under the same test conditions as the first movement. The same parameters as in step b) are measured, namely the air velocity vair or the dynamic pressure ΔP, the vehicle speed v, particularly at the departure point A and the arrival point B, and the motive energy Wmot if the movement is not performed in freewheeling mode.

[0115] The fifth method further includes a step b) in which the vehicle makes a third movement, along the road segment T, from the starting point A to the arrival point B, i.e., in the same direction as the first movement in step b). The third movement is carried out in lane C and under the same test conditions as the first and second movements. The same parameters as in step b) are measured.

[0116] The fifth method then includes a step e') corresponding to the determination of the aerodynamic drag area CxS and the rolling coefficient Cr, from equation [eq.13] derived from the principle of conservation of energy, and from: of known parameters such as the mass m of the vehicle, the acceleration due to gravity g, the air density ρ, the length of the section L, parameters measured during the first, second and third trips.

[0117] The aerodynamic drag area CxS and the rolling resistance coefficient Cr can be expressed as follows: CxS = K v 1 + W mot 1 mg − K v 3 − W mot 2 mg K a 1 − K a 2 C r = 1 2 L − K v 1 − K v 3 K a 1 − K a 2 K a 1 + K a 2 + K v 1 + W mot 1 mg + K v 2 + W mot 2 mg with K a n = 1 m g ∫ 0 L 0.5 ρ v air n 2 dx = 1 m g ∫ 0 L Δ P n dx And K v n = 0.5 9 V ini n 2 − V fin n 2 And W motn the motive energy supplied by the cyclist, V ini_n and V fin_n corresponding respectively to an initial velocity and a final velocity of the vehicle, ΔP n corresponding to the dynamic pressure and v air_n corresponding to the air velocity, during the displacement n with n=1,2,3 corresponding respectively to the first, second and third displacement.

[0118] Advantageously, the first or second movement is performed at low speed, for example, at 20 km / h or less. The third movement is performed at high speed (for example, at a speed greater than 20 km / h) if the first movement was performed at 20 km / h or less; or the third movement is performed at low speed (for example, at 20 km / h or less) if the first movement was performed at a speed greater than 20 km / h. This reduces the influence of uncertainties in the measurements of air velocity (vair) or pressure gradient (ΔP), wind speed (Wmot), and velocity (v) during the journeys, thus improving the discrimination of the coefficients Cr and CxS.

[0119] This fifth method for determining the aerodynamic drag area CxS also allows us to determine the elevation difference H of the segment T by performing a second and a third displacement. H is then expressed as follows: H = K v n − CxS K a n − C r L with n corresponding to one of the three displacements of choice.

[0120] It also allows for the repetition of steps b") or b‴) and e'), for other test conditions: for example, with reference to the cyclist, other tires to test rolling resistance, and / or other handlebars, helmets, clothing, or posture to test aerodynamics. The absolute values ​​of the aerodynamic coefficients CxS and rolling resistance Cr, obtained for the different test conditions, can then be compared to identify conditions more favorable to the vehicle's aerodynamics and rolling resistance.

[0121] Note that measurements of pressure, temperature, and possibly humidity can be taken during step b) of the preparatory sequence to evaluate the air density ρ in real time. Optionally, these measurements can also be taken during steps b'), b"), or b‴) of the third, fourth, and / or fifth determination methods described. These measurements can also be omitted in the case of a direct measurement of dynamic pressure.

[0122] Advantageously, the movements during steps b), b'), b") and b‴) of the third, fourth and / or fifth determination methods are performed in freewheeling mode. This limits the duration of each step and provides excellent accuracy and reproducibility for the determination of the friction coefficients CxS, Cr. Examples of implementing methods according to the invention for a cyclist:

[0123] Before conducting a series of tests, the user defines a route and marks a lane on the ground using spray paint. They place visual markers at the starting point A and the finishing point B, exactly 48 wheel rotations apart. They also mark two lines 91 wheel rotations upstream and downstream of the starting point A and finishing point B, respectively: these are points M and M'. The user then installs a magnet on their front wheel and a magnetic switch to detect its passage on the bicycle's fork. The device, equipped with its Pitot tube for measuring airspeed, is mounted on the handlebars of the bicycle. The user ensures that the tube is perfectly horizontal and calibrated. Recalibration is only necessary if the tube's position on the vehicle is changed.

[0124] The user then steps onto a scale with all the equipment they will use during the tests to determine the vehicle's mass. The circumference of the wheel on which the speed is measured (typically the front wheel) is also determined.

[0125] The length of the test course – 48 wheel rotations – and the distances of the lines located upstream and downstream of the start and finish lines – 91 wheel rotations – are fixed. With the bicycle positioned facing forward, the user aligns the bicycle with point M so that the wheel is in contact with the line drawn on the ground while the magnet is positioned midway across the magnetic switch, ensuring that the first detection of the magnet's passage occurs half a wheel rotation from point M. This allows for perfect alignment of the outbound and return journeys. The fifth determination method described above is then initiated.

[0126] The cyclist sets off towards point A at approximately 15 km / h. Just before passing point A, they coast. They are careful not to change their chosen position (test conditions) and to remain within the marked lane. Once past point B, they resume pedaling towards point M'. They then repeat this sequence, starting from point M' and heading towards point B. After this second low-speed coasting, they realign their wheel with point M. They can then proceed towards point A at a speed of approximately 45 km / h, maintaining the same position as in the test. Just before passing point A, they coast. Between points A and B, they are careful not to change their position and to stay within the marked lane C.

[0127] Once point B has been passed, the values ​​of the coefficients Cr and CxS can be determined (step e' of the fifth method) as well as the height H of the path ( figure 2 ).

[0128] If the user wishes to perform a new test, they can, for example, implement the first determination method described or repeat steps b") or b‴) and e) of the fifth method. They then set off towards point A at approximately 45 km / h. Just before passing point A, they coast. They take care not to change their chosen position and to stay within the lane C marked on the road. Once point B is passed, the CxS value representing the new test conditions is determined. They can then repeat the procedure, starting from point M' and heading towards point B, and so on for a plurality of test conditions.

[0129] There figure 3This gives an example of 22 freewheeling tests that allowed for testing 5 different configurations. The series of tests shows that helmet 2 has an aerodynamic surface area approximately 0.006 m² larger than helmet 1, and that position 2 is less favorable than position 1 by approximately 0.005 m². It is clear from this that the determination methods according to the present invention allow for the comparison and differentiation of different test conditions thanks to excellent sensitivity and high precision, while maintaining a simple, quick, and undemanding operating procedure in the selection of the road segment T.

[0130] There figure 5 shows the effect of respecting the traffic lane defined in the present invention. The table of the figure 5The results present aerodynamic drag area (CxS) values ​​obtained from 16 tests conducted under identical conditions: 8 tests (according to the invention) were performed within the designated traffic lane C, and the CxS values ​​were obtained using the first determination method according to the invention; the other 8 tests were performed outside the designated traffic lane (therefore outside the scope of the invention), and the CxS values ​​were obtained using the same determination method. It is clear that the dispersion of results is three times greater for the tests outside the scope of the invention compared to the tests according to the invention. The technical effect of adhering to the designated traffic lane is to ensure consistency of the following parameters during travel along the road segment T: elevation difference, distance traveled, and also rolling resistance coefficient when determining the aerodynamic drag area (CxS) is the objective.Respecting this band ensures that the energy variations measured during the different tests are not related to variations in these parameters.

[0131] Conversely, failure to respect the traffic lane implies variations in these parameters, which are assumed to be constant in several prior art methods. These variations are likely to affect the reproducibility of the measurements, as stated with reference to the figure 5 . Integrated system:

[0132] The invention also relates to an integrated system 100 for implementing a method for determining the aerodynamic drag area CxS and / or the rolling resistance coefficient C r of a vehicle, as described above.

[0133] The integrated system 100 includes an anemometer 101, having a sampling frequency greater than or equal to 1 Hz and a measurement repeatability better than 2% RMS for a sampling frequency of 1 Hz, for measuring the air velocity vair relative to the vehicle. Alternatively, the integrated system 100 includes a differential pressure sensor, having a sampling frequency greater than or equal to 1 Hz and a measurement repeatability better than 4% RMS for a sampling frequency of 1 Hz. It also includes a speed sensor, based on detecting the number of times at least one magnet disposed on a wheel of the vehicle is passed over it, at a frequency greater than or equal to 2 kHz and having a repeatability better than 0.25% RMS, for measuring the vehicle speed v.Finally, the integrated system 100 includes a calculator to determine the aerodynamic drag area CxS and / or the rolling coefficient C r from the measured parameters and known or arbitrarily pre-recorded parameters.

[0134] The integrated system is typically capable of displaying on a 102 screen the information presented on the figure 2 .

[0135] According to one variant, the integrated system 100 includes means of remote communication with a mobile phone or a screen, giving real-time access to results.

[0136] According to another advantageous variant, the system comprises an aerodynamic housing in which the anemometer or the total pressure sensing element of the differential pressure sensor, the speed sensor, and the control unit are integrated. The aerodynamic housing is positioned at the front of the vehicle. The housing is preferably placed in a pressure zone that is not, or only minimally, influenced by the vehicle, for example, between the top of the front wheel and the handlebars in the case of a bicycle, via a mounting fixed to the frame, fork, or handlebars, as illustrated in the following: figure 4 In this figure, system 100 includes a Pitot tube anemometer 101 and a computer capable of guiding the user in implementing one of five methods for determining the aerodynamic drag area and / or the rolling resistance coefficient of the cyclist on their bicycle, as well as displaying the information presented on the figure 2 .

Claims

1. Preparatory sequence for determining the aerodynamic drag surface area (CxS) and / or the rolling coefficient (Cr) of a vehicle (1) under actual movement conditions, without braking, on a defined road section (T) having a starting point (A) and an end point (B), the preparatory sequence comprising the following steps: a) defining a traffic lane (C) with a width less than or equal to 1 m, along said road section (T), b) carrying out by the vehicle (1) a first movement, on the road section (T), from the starting point (A) to the end point (B), and in the traffic lane (C), during which the following parameters are measured: - the air speed (vair) relative to the vehicle (1), with an anemometer having a sampling frequency greater than or equal to 1 Hz and a measurement repeatability better than 2% RMS for a sampling frequency of 1 Hz, or the dynamic air pressure, with a differential pressure sensor having a sampling frequency greater than or equal to 1 Hz and a measurement repeatability better than 4% RMS for a sampling frequency of 1 Hz, - the speed of the vehicle (v) at the starting (A) and end (B) points of the road section (T), with a speed sensor having a repeatability better than 0.25% RMS, - the driving energy (Wmot) supplied by the vehicle (1) along the road section (T), with a power sensor having a repeatability better than 1% RMS, or taking into account a zero driving energy if said movement is performed with freewheeling.

2. Preparatory sequence according to the preceding claim, wherein the width of the traffic lane (C) is less than or equal to 50 cm, or even 30 cm, or even 10 cm.

3. Preparatory sequence according to one of the preceding claims, wherein the road section (T) has a downward slope in the range of 0 to -1%, and a length (L) less than or equal to 500 m, preferably in the range of 200 m, when the movement on said section (T) is performed with freewheeling.

4. Preparatory sequence according to one of the preceding claims, wherein the measurement of the vehicle speed (v) implements one or more magnet(s) disposed on the wheel and a system for detecting the number of passages of said magnet(s) per unit of time, with a sampling frequency greater than or equal to 2 kHz.

5. Preparatory sequence according to one of claims 1 to 3, wherein the measurement of the vehicle speed (v) is obtained based on at least two wheel detection sensing bands, disposed respectively at the starting point (A) and at the end point (B) of the road section (T), capable of issuing an electrical pulse when the vehicle (1) passes through and coupled with a timing system having a sampling frequency higher than 2 kHz.

6. Method for determining the aerodynamic drag surface area (CxS), implementing the preparatory sequence according to one of the preceding claims, the method further comprising the following step: c) determining the aerodynamic drag surface area (CxS) based on an equation derived from the principle of conservation of energy, and based on: - known parameters such as the mass (m) of the vehicle, the acceleration of gravity (g), the air density (ρ) (where necessary), the length of the section (L), the height difference of the section (H), - the parameters measured during the first movement, and - the known or arbitrarily set rolling coefficient (Cr).

7. Method for determining the rolling coefficient (Cr), implementing the preparatory sequence according to one of claims 1 to 5, the method further comprising the following step: d) determining the rolling coefficient (Cr) based on an equation derived from the principle of conservation of energy, and based on: - known parameters such as the mass (m) of the vehicle, the acceleration of gravity (g), the air density (ρ) (where necessary), the length of the section (L), the height difference of the section (H), - the parameters measured during the first movement, and - the known or arbitrarily set aerodynamic drag surface area (CxS).

8. Method for determining the aerodynamic drag surface area (CxS), implementing the preparatory sequence according to one of claims 1 to 5, and further comprising the following steps: b') carrying out by the vehicle a second movement, on the road section, from the starting point to the end point, and in the traffic lane, during which the same parameters as in step b) are measured, c') determining the aerodynamic drag surface area (CxS) based on an equation derived from the principle of conservation of energy, and based on: - known parameters which are the mass (m) of the vehicle, the acceleration of gravity (g), the air density (ρ) (where necessary), , the length of the section (L) and - the parameters measured during the first and second movements.

9. Method for determining the aerodynamic drag surface area (CxS) and the rolling coefficient (Cr), implementing the preparatory sequence according to one of claims 1 to 5, and further comprising the following steps: b') carrying out by the vehicle a second movement, on the road section, from the starting point to the end point, and in the traffic lane, during which the same parameters as in step b) are measured, e) determining the aerodynamic drag surface area (CxS) and the rolling coefficient (Cr) based on an equation derived from the principle of conservation of energy, and based on: - known parameters such as the mass (m) of the vehicle, the acceleration of gravity (g), the air density (ρ) (where necessary), the length of the section (L), the height difference of the section (H), - the parameters measured during the first and second movements.

10. Determination method according to one of claims 6 to 9, wherein the height difference of the road section is assessed thanks to an optical level or any other suitable topographical tool, with an accuracy in the range of one millimetre.

11. Method for determining the aerodynamic drag surface area (CxS) and the rolling coefficient (Cr), implementing the preparatory sequence according to one of claims 1 to 5, and further comprising the following steps: b") carrying out by the vehicle a second movement, on the road section, from the end point to the starting point, and in the traffic lane, during which the same parameters as in step b) are measured, b‴) carrying out by the vehicle a third movement, on the road section, from the starting point to the end point, and in the traffic lane, during which the same parameters as in step b) are measured; e') determining the aerodynamic drag surface area (CxS) and the rolling coefficient (Cr) based on an equation derived from the principle of conservation of energy, and based on: - known parameters which are the mass (m) of the vehicle, the acceleration of gravity (g), the air density (ρ) (where necessary), the length of the section (L), and - the parameters measured during the first, second and third movements.

12. Determination method according to one of claims 6 to 11, wherein a measurement of the pressure, the temperature and optionally the moisture level is carried out during step b) of the preparatory sequence, in order to assess the air density () in real time.

13. Integrated system for implementing a method for determining the aerodynamic drag surface area (CxS) and / or the rolling coefficient (Cr) of a vehicle according to one of claims 6 to 12, the integrated system comprising: - an anemometer, having a sampling frequency greater than or equal to 1 Hz, for measuring the air speed relative to the vehicle, or a differential pressure sensor, having a sampling frequency greater than or equal to 1 Hz, for measuring the dynamic air pressure, - a speed sensor, based on detecting the number of passages of at least one magnet disposed on a wheel of the vehicle at a frequency greater than or equal to 2 kHz, for measuring the vehicle speed, - a computer for determining the aerodynamic drag surface area (CxS) and / or the rolling coefficient (Cr) based on the measured parameters and pre-recorded known or arbitrarily set parameters.

14. Integrated system according to the preceding claim, comprising means of remote communication with a mobile phone or a screen.

15. Integrated system according to one of the two preceding claims, comprising an aerodynamic envelope wherein the anemometer or a total air pressure sampling element connected to the differential pressure sensor, the speed sensor and the computer are integrated, the aerodynamic envelope being disposed at the front of the vehicle.