Method for controlling a pedal-assisted electric motor for a vehicle with a pedal crank mechanism

Description

DOMAINE TECHNIQUE

[0001] The present invention relates to the field of control systems and methods for electrically assisted pedal-driven vehicles. The present invention relates more particularly to a method for controlling a pedal-driven vehicle motor. It is applicable to the automatic adaptation of electrical assistance in difficult starting conditions (heavy load, hill starts, etc.). ETAT DE LA TECHNIQUE

[0002] Electric bikes are generally equipped with either a pedaling (or rotation) sensor, which provides the rotation speed of the cyclist's crankset, or a torque sensor, which provides not only the rotation speed of the crankset, but also measures the effort exerted by the cyclist.

[0003] When starting the bike (with zero initial speed), different control loops can be implemented depending on the type of sensor fitted to the electrically assisted bike.

[0004] With a torque sensor, the control provides a command that is proportional to the effort provided by the cyclist. In the event of a difficult start, the cyclist instantly exerts greater effort, and the control therefore provides an equally strong assistance that will help the cyclist overcome the difficulty of starting. The presence of a torque sensor therefore allows for perfectly adapted electric assistance during a start-up phase. A disadvantage of this solution is the fact that a torque sensor incurs a significant cost. This cost issue is even more significant on the scale of a fleet of bicycles.

[0005] With a pedaling (or rotation) sensor, the regulation provides, whatever the situation (difficult start or not), an identical command aimed at trying to bring the bicycle to a defined target speed. Thus, in the case of a difficult start, this regulation is identical to the situation where the load is low and / or the start is on the flat or downhill. As a result, the starting dynamics of the bicycle are not the same for an easy start or a difficult start. In the situation of a difficult start, the acceleration may be too slow and the starting speed too low, which may result in difficulty for the cyclist to maintain balance. Document US 2017 / 151997 A1 discloses a method for controlling an electric pedal-assist motor for a pedal-driven vehicle, according to the preamble of claim 1.

[0006] An object of the present invention is therefore to propose a method for controlling an electric pedal-assist motor for a pedal-driven vehicle which makes it possible to reduce, or even eliminate, the disadvantages of known solutions.

[0007] Another object of the present invention is to propose a method for controlling an electric pedal assistance motor for a pedal-driven vehicle which makes it possible to automatically adapt the electric assistance to the difficulty of starting, without knowing the effort provided by the cyclist (therefore in the absence of a torque sensor).

[0008] Other objects, features, and advantages of the present invention will become apparent from the following description and accompanying drawings. It is understood that other advantages may be incorporated. RESUME

[0009] To achieve this objective, according to a first aspect of the invention, a method is provided for controlling an electric pedal assist motor for a pedal-driven vehicle comprising the following steps: at least as soon as a rotation of the pedal is detected, measure the instantaneous speed V of the vehicle, and if the instantaneous speed V of the vehicle is lower than a first threshold value V S1 predetermined, control the electric motor by applying a control loop comprising, or even consisting of, a process of iteration of a function f defining, at each instant n and from a torque command C n-1 applied at the moment n-1 previous, a couple order C n to be applied immediately n, said function having: as a variable, or even as the only variable, a difference between the first threshold value V S1 and the instantaneous speed Vof the vehicle, and as parameters, or even as the only parameters, a maximum torque control value C max of the engine and a so-called acceleration coefficient K defining a maximum amplitude of each iteration.

[0010] Thus, the invention according to its first aspect consists of a method of controlling by iteration a function of which one variable, or even the only variable, namely the instantaneous speed V of the pedal-driven vehicle, allows the engine torque control to be varied according to the vehicle dynamics.

[0011] The process thus allows, by adjusting the parameters of the function f of the iteration process, to guarantee the cyclist sufficient assistance allowing him to reach an equilibrium speed quickly enough not to put him in difficulty when the starting conditions are difficult.

[0012] This method provides relevant electrical assistance to the cyclist, without the need for a torque sensor. The invention therefore reduces the cost of electrically assisted bicycles. It therefore presents an even more significant advantage on the scale of a bicycle fleet.

[0013] Another aspect of the invention relates to a computer program product comprising instructions, which when carried out by at least one processor, executes at least the steps of the method as introduced above.

[0014] Another aspect of the invention relates to a control unit (or computer) of an engine, such as a microcontroller or a microprocessor, designed to carry out at least the instructions of the computer program product as introduced above.

[0015] Another aspect of the invention relates to a pedal-driven vehicle comprising at least one motor and a control unit (or a computer) as introduced above. BREVE DESCRIPTION DES FIGURES

[0016] The aims, objects, as well as the characteristics and advantages of the invention will emerge more clearly from the detailed description of an embodiment thereof which is illustrated by the following accompanying drawings in which: There figure 1 graphically represents five examples of starting speed profiles. The figure 2 graphically represents a first of the five examples of starting speed profile illustrated on the figure 1 and the corresponding evolution of the torque control. The figure 3 graphically represents a second of the five examples of starting speed profiles illustrated in the figure 1 and the corresponding evolution of the torque control. The figure 4 graphically represents a third of the five examples of starting speed profiles illustrated in the figure 1 and the corresponding evolution of the torque control. The figure 5 graphically represents a fourth of the five examples of starting speed profiles illustrated in the figure 1 and the corresponding evolution of the torque control. The figure 6 graphically represents the fifth of the five examples of starting speed profiles illustrated in the figure 1 and the corresponding evolution of the torque control. The figure 7 is a flowchart of an embodiment of the first aspect of the invention.

[0017] The drawings are given as examples and are not limiting of the invention. They constitute graphic representations of principle intended to facilitate the understanding of the invention. Even if these graphic representations aim to illustrate practical applications of the invention, the scale of each of their axes is not intended to limit the field of applications of the invention. DESCRIPTION DÉTAILLÉE

[0018] Before commencing a detailed review of embodiments of the invention, optional features which may possibly be used in combination or alternatively are set out below: According to one example, the motor is a wheel motor.

[0019] In one example, before a crank rotation is detected, the torque command to the motor is zero.

[0020] According to an example, the first iteration loop is included in a loop conditioning each iteration on not exceeding the torque command C n relative to the maximum torque control value C max of the engine; said maximum torque control value C max is preferably substantially between 20 A and 50 or 60 A.

[0021] According to the invention, the acceleration coefficient is a dimensionless number substantially between 1 and 100, for example substantially equal to 30.0.

[0022] According to the invention, said function f is defined so that each iteration is of decreasing amplitude: as the instantaneous speed V of the vehicle increases and until it is zero when the instantaneous speed V of the vehicle reaches the first threshold value V S1 .

[0023] According to an example, the first threshold value V S1 is substantially between 2 and 10 km / h, preferably substantially between 4 and 8 km / h.

[0024] According to an example, if the instantaneous speed V of the vehicle is greater than a second threshold value V S2 predetermined, the control of the electric motor comprises the joint application of the first control loop and a second control loop, the second threshold value V S2 being lower than the first threshold value V S1 and preferably substantially between 2 km / h and 6 km / h, and preferably substantially equal to 4 km / h.

[0025] According to the invention, said function f takes the following form: f = P V Cmax K , Or C max is the maximum torque command value of the motor, K is the acceleration coefficient K defining the maximum amplitude of each iteration, and P(V) is defined so that each iteration is of decreasing amplitude: i. as the instantaneous velocity V of the vehicle increases and ii. until it is zero when the instantaneous speed V of the vehicle reaches the first threshold value V S1 .

[0026] According to the previous example, P V = V S 1 − V V S 1 m , with m an integer between 1 and 4, preferably with m = 2 .

[0027] For example, the instantaneous speed V of the pedal-driven vehicle is calculated, by a control unit (or a computer), based on the measurement of an engine rotation and with reference to a predetermined database stored by the control unit. The measurement of the engine rotation is preferably carried out with a high sampling rate, preferably greater than 100Hz. The instantaneous speed Vof the pedal-assisted vehicle thus obtained is of sufficient precision to allow fine and responsive control of the electric assistance.

[0028] In one example, the rotation of the crankset is detected by a pedaling (or rotation) sensor. The pedaling (or rotation) sensor also makes it possible to determine the pedaling speed.

[0029] In one example, the pedal-driven vehicle is free of a torque sensor.

[0030] A parameter that is "substantially equal to / greater than / less than" a given value means that this parameter is equal to / greater than / less than the given value, within plus or minus 20% or even 10% of this value. A parameter that is "substantially between" two given values means that this parameter is at least equal to the smallest given value, within plus or minus 20% or even 10% of this value, and at most equal to the largest given value, within plus or minus 20% or even 10% of this value.

[0031] The first aspect of the invention relates to a method for controlling an electric pedal-assist motor for a pedal-driven vehicle. The method is essentially such that it comprises the following steps, illustrated in the figure 7 : at least as soon as a rotation of the pedal is detected, measure the instantaneous speed V of the vehicle, and if the instantaneous speed Vof the vehicle is lower than a first threshold value V S1 predetermined, control the electric motor by applying a first control loop comprising a process of iteration of a function f defining, at every moment n and from a couple order C n-1 applied at the moment n-1 previous, a couple order C n to be applied immediately n.

[0032] The function f has as a variable, a difference between the first threshold value V S1 and the instantaneous speed V of the vehicle. Equivalently, the function f has as variable the instantaneous speed V of the vehicle, the first threshold value V S1 being considered as a predetermined parameter of the function f.

[0033] A mathematical rewriting of the above and in accordance with the invention is given as follows: C n − C n − 1 = f V S 1 − V .

[0034] The function f also has as parameters: i. a maximum torque control value C max of the engine and ii. a so-called acceleration coefficient K defining a maximum amplitude of each iteration; as we will see below, the amplitude of each iteration is weighted according to the difference between the first threshold value V S1 and the instantaneous speed V of the vehicle.

[0035] The maximum torque control value C max of the motor corresponds to a maximum intensity value of the motor supply current. The acceleration coefficient K defines, directly or indirectly proportionally, the minimum number of iterations that the control loop will perform before reaching: be the first threshold value V S1 , or a couple order C n equal to the maximum torque control value C max .

[0036] Alternatively, but strictly equivalently, the function f can be considered as having, as variable, the instantaneous speed V of the vehicle and, for parameters, the maximum torque control value C max , the acceleration coefficient K and the first threshold value V S1 .

[0037] For purely illustrative purposes, an embodiment of the method according to the first aspect of the invention is described below with reference to figures 1 à 6 .

[0038] According to this embodiment, the maximum torque control value C max is equal to 35 A (Amperes) and the value of the acceleration coefficient K is equal to 30.0.

[0039] However, these given values of the two parameters of the function f are not limiting of the method according to the first aspect of the invention.

[0040] More specifically, the maximum torque control value C max can be provided by the motor manufacturer; it is typically between 20 A and 50 or 60 A. As for the value of the acceleration coefficient K , it can vary on a case-by-case basis, in particular depending on the frequency at which the control unit (or calculator) operates, in particular to calculate the instantaneous speed V of the pedal-driven vehicle. When the acceleration coefficient K is equal to 30.0, the maximum amplitude of each iteration is then equal to 1 / 30 of the maximum torque command value C max , and more than thirty iterations of the control loop are necessary for the torque control C n reaches the maximum torque control value C max . Note here that, as will be clear from the description of the figures below, it is possible that the control loop does not lead to the achievement of a torque command. C n equal to the maximum torque control value C max , if the instantaneous speed V of the vehicle reaches or exceeds the first threshold value V S1 for a torque command value C n less than the maximum torque control value C max .

[0041] Furthermore, according to the embodiment illustrated in the figures 1 à 6 , the first threshold value V S1 is set equal to 4 km / h. Again, this value of the first threshold value V S1 is not limiting of the method according to the first aspect of the invention. The first threshold value V S1 can in fact be substantially between 2 and 10 km / h, preferably substantially between 4 and 8 km / h.

[0042] Let us note here that, as discussed in the introduction, the pedal-driven vehicle concerned by the present invention, if it is preferably free of a torque sensor, is on the other hand equipped with a pedaling sensor, also called a rotation sensor, less expensive than a torque sensor. By means of the pedaling sensor, it is possible on the one hand to detect a rotation of the pedals, on the other hand to measure the speed of this rotation, as illustrated in the figure 7 .

[0043] Instantaneous speed Vof the vehicle can be calculated by the control unit (or equivalently the computer) of the pedal-driven vehicle. The way in which this calculation is carried out is known per se. It may involve a predetermined database stored by the control unit or consultable remotely by said unit. The measurement of the rotation of the motor is preferably carried out with a high sampling frequency. Preferably, said sampling frequency is greater than 100Hz and is not necessarily greater than 16kHz; it is typically equal to 2000 Hz. The sampling frequency of the measurement of the rotation of the motor is potentially higher than the frequency at which the calculation of the assistance is carried out; the latter being inversely proportional to the time lapse between two instants n-1 and n.More particularly, the frequency of the assistance calculation can be carried out at a much lower frequency, and for example at least ten times lower than the sampling frequency of the measurement of the rotation of the engine. Typically, the frequency of the assistance calculation can be carried out at a frequency of 100 Hz. For example, the processor of the control unit can operate at a frequency of 16 kHz. This ensures not only a sufficiently fast stabilization of the values of the instantaneous speed V of the vehicle, but still a sufficient number of assistance calculations so that the evolution of the instantaneous speed Vof the vehicle appears to be continuous, at least during the period of time when the first regulation loop is to be applied, regardless of the vehicle dynamics considered. By thus avoiding regulation jolts which could surprise the cyclist, or even destabilize him, we ensure smooth regulation of the electric assistance and comfort for the cyclist.

[0044] The embodiment illustrated on the figures 1 à 6 further considers the following form of the function f : f = P V Cmax K , où P V = V S 1 − V V S 1 2

[0045] However, this form of the function f indicated above is not limiting of the method according to the first aspect of the invention. More generally, the function f, and more particularly the function P(V), can be defined so that each iteration is of decreasing amplitude: as the instantaneous speed Vof the vehicle increases and until it is zero when the instantaneous speed V of the vehicle reaches the first threshold value V S1 .

[0046] In addition, the function P(V) is preferably normalized, in the sense that it evolves between a maximum value equal to 1 and a minimum value equal to 0.

[0047] A more general expression of the function P(V) relative to that given above is as follows: P V = V S 1 − V V S 1 m , where m is an integer between 1 and 4.

[0048] The function P(V) acts as a weighting function of the maximum amplitude of each iteration given by Cmax K , depending on the instantaneous speed V of the vehicle and relative to the first threshold value V S1 . It therefore allows the evolution of the torque control to be modified according to the dynamics of the pedal vehicle.

[0049] There figure 1 shows precisely five different dynamics of the pedal-driven vehicle. Each of these five dynamics is considered to be consistent with a change in the speed profile actually observable during use of the pedal-driven vehicle. However, these five dynamics are theoretical; considering them makes it possible to illustrate the corresponding response of the method according to the first aspect of the invention for each of them.

[0050] There figure 1 illustrates more specifically five speed profiles, with different dynamics in terms of shape and acceleration; the profiles corresponding to starting sequences, with a speed evolving from 0 km / h (vehicle stopped) to 4 km / h (i.e. the value given for the first threshold value V S1 which may correspond to or be proportional to the equilibrium speed of the cyclist on the vehicle, in particular when the latter has two wheels).

[0051] Apart from the linear velocity profile, two of the five illustrated velocity profiles reflect the assumption of a logarithmic evolution of the velocity, and two others reflect the assumption of an exponential evolution of the velocity. Of the two logarithmic velocity profiles, one can be called 'slow' (it is located below the other of the two logarithmic velocity profiles) and the second can be called 'fast' (it is located above the other of the two logarithmic velocity profiles). The same is true of the two so-called 'exponential' velocity profiles.

[0052] THE figures 2 à 6 show the evolution of the torque control C n (curves with Greek cross symbols) for each of the speed profiles illustrated on the figure 1 Each profile is more specifically illustrated by a thin, continuous curve without a symbol.

[0053] There figure 2 shows the evolution of the torque control C n for a speed profile reflecting the hypothesis of a linear evolution of the speed.

[0054] Note that, on each of these figures 2 à 6 , the evolution of the function is also illustrated P(V) called maximum iteration amplitude weighting Cmax K (curves with square symbols).

[0055] There figure 3 shows more specifically the evolution of the torque control C n for the so-called 'logarithmic' and 'fast' speed profile; and the figure 4 shows the evolution of the torque control C n for the 'logarithmic' and 'slow' speed profile. We can first observe that neither of these two evolutions leads to the achievement of the maximum torque command value C max (= 35 A). A comparison of these two developments shows that the pedal-driven vehicle reaches the first threshold value more quickly V S1 when the speed profile is 'fast', but the torque command increases more quickly when the speed profile is 'slow'.

[0056] There figure 5 shows the evolution of the torque control C n for the so-called 'exponential' and 'fast' speed profile, while the figure 6 shows the evolution of the torque control C n for the 'exponential' and 'slow' speed profile. Again, we observe that the torque command increases more rapidly when the speed profile is 'slow'. Furthermore, if, for the 'exponential' and 'fast' speed profile, the torque command reaches almost asymptotically a value close to the maximum torque command value C max (= 35 A), reaching the latter is much faster for the 'exponential' and 'slow' speed profile. Indeed, in the latter case, the instantaneous speed V of the pedal-driven vehicle remaining relatively low over a relatively long time (of the order of one second) following the detection of the rotation of the pedal-driven vehicle, the amplitudes of the first iterations of the control loop are relatively close to the maximum amplitude of each iteration, thus bringing the torque control very quickly (in less than three-quarters of a second) to its maximum value.

[0057] It is clear from this last example that, as illustrated in the figure 7 , the first iteration loop is included in / or further includes a loop conditioning each iteration on not exceeding the torque command C n relative to the maximum torque control value C max of the engine.

[0058] Another advantage of the method according to the first aspect of the invention comes from considering that the application of the first control loop described above with reference to the figures 1à 7 is not exclusive of the application of another regulation loop, complementing the first, before possibly replacing it when the instantaneous speed V exceeds the first threshold value V S1 . So, if the instantaneous speed V of the vehicle is greater than a second threshold value V S2 predetermined, the control of the electric motor may comprise the application, together with the first control loop, of a second control loop. The second threshold value V S2 is then defined lower than the first threshold value V S1 Without this, the first control loop would finish being applied before the second control loop could be applied; the latter case being entirely conceivable. For example, the second threshold value V S2 is substantially between 2 km / h and 6 km / h, and preferably substantially equal to 4 km / h.

[0059] To the extent that the various parameters mentioned above are correctly adjusted, such adjustment being judged to be within the competence of a person skilled in the art and being able to be carried out uniformly on a fleet of identical bicycles, it is clear from the above that the method according to the first aspect of the invention makes it possible to obtain pleasant behavior of the pedal-driven vehicle for the cyclist, this behavior being characterized by: acceleration that is not too abrupt, when starting is not difficult (such as starting on the flat); sufficient acceleration to quickly bring the pedal vehicle to an equilibrium speed corresponding or proportional to the first threshold value V S1 , when starting is difficult, particularly regardless of the type of load encountered (such as starting on a hill and / or with a heavily loaded vehicle and / or in a headwind).

Claims

1. A method for controlling a pedalling-assist electric motor for a vehicle having a pedal crank mechanism and comprising the following steps: • at least when rotation of the pedal crank mechanism is detected, of measuring the instantaneous speed V of the vehicle, and • if the instantaneous speed V of the vehicle is below a first threshold value VS1 , of operating the electric motor by applying a control loop comprising a process of iterating a function f defining, at each instant n and from a torque command Cn-1 applied at the preceding instant n-1, a torque command Cn that is to be applied at the instant n, said function having: • by way of variable, a difference between the first threshold value VS1 and the instantaneous speed V of the vehicle, and • as parameters: i. a maximum torque command value Cmax of the motor and ii. a so-called acceleration coefficient K defining a maximum amplitude of each iteration, and the process characterised by the following formulations: wherein said function f takes the following form: f = P V Cmax K , où Cmax is the maximum torque command value of the motor, K is the acceleration coefficient defining the maximum amplitude of each iteration, and P(V) is defined such that each iteration is of decreasing amplitude: • as the instantaneous speed V of the vehicle increases until it is zero when the instantaneous speed V of the vehicle reaches the first threshold value VS1, and wherein P V = V S 1 − V V S 1 m , with m an integer between 1 and 4, preferably with m = 2, wherein said function f is defined such that each iteration is of decreasing amplitude: • as the instantaneous vehicle speed V increases and • until it is zero when the instantaneous vehicle speed V reaches the first threshold value VS1, - wherein the acceleration coefficient K is a dimensionless number substantially between 1 and 100, and wherein the first control loop comprising a following iteration process: C n − C n − 1 = f V S 1 − V .

2. Method according to any one of the preceding claims, wherein said function has, as the only variable, the difference between the first threshold value VS1 and the instantaneous speed V of the vehicle.

3. Method according to any one of the preceding claims, wherein, before a rotation of the pedal crank mechanism is detected, the torque command of the motor is zero.

4. Method according to any one of the preceding claims, wherein the first iteration loop is included in a loop conditioning each iteration to a non-exceedance of the torque command Cn relative to the maximum torque control value Cmax of the motor.

5. Method according to the preceding claim, wherein said maximum torque command value Cmax is substantially between 20 A and 50 or 60 A.

6. Method according to any one of the preceding claims, wherein the acceleration coefficient K is substantially equal to 30.0.

7. Method according to any one of the preceding claims, wherein the first threshold value VS1 is substantially between 2 and 10 km / h, preferably substantially between 4 and 8 km / h.

8. Method according to any one of the preceding claims, wherein, if the instantaneous speed V of the vehicle is greater than a second predetermined threshold value VS2, the control of the electric motor comprises the joint application of the first control loop and a second control loop, the second threshold value VS2 being lower than the first threshold value VS1 and preferably substantially between 2 km / h and 6 km / h, and preferably substantially equal to 4 km / h.

9. Computer program product comprising instructions which, when carried out by at least one processor, executes at least the steps of the method according to any one of the preceding claims.

10. A motor control unit designed to perform at least the instructions of the computer program according to the preceding claim.

11. A vehicle having a pedal crank mechanism comprising at least one motor and a control unit according to the preceding claim.