* * * *

Field of the invention

The present invention refers to a system for controlling the motion of an impulsive-type human-powered vehicle. The term "impulsive-type human-powered vehicle" means a vehicle operated by a driving force discontinuously applied by an user. Vehicles of this type are for example push scooters and skateboards, which are driven by discontinuous and therefore substantially impulsive thrusts, generally exerted by an user foot. Such vehicles are for example different from the bicycles because these latter are operated by exerting a substantially continuous torque by the user.

Specifically, the present invention refers to impulsive-type human powered vehicles provided with motion assisting means, in other words means adapted to supply an ancillary driving force in addition to the one supplied by the user, for example by an auxiliary motor.

Although the present description focuses on land vehicles, the system can find an application also in impulsive-type human-powered vehicles of a different type, such as for example rowboats.

Prior art

Recently, impulsive-type human-powered vehicles provided with auxiliary motors have found an increasing acceptance, mainly due to road congestions and environmental problems which have led to the demand of alternative vehicles, preferably low-cost and having a low environmental impact.

For example, push scooters provided with an auxiliary electric motor supplying a driving power in addition to the power supplied by the user, are known. The operation of the motor is usually commanded by the user via interface devices, such as levers or knobs.

Unfortunately, such vehicles have an unusual behavior with respect to the behavior which they would have without the auxiliary motors. Moreover, the presence of the interface devices for controlling the vehicle can distract the driving user.

The document WO 2012/163789 describes a system for controlling the motion of an impulsive-type human-powered vehicle (100), particularly a push scooter, wherein the presence/absence of user a thrust is detected, and based on such detection, an electric motor commanding the push scooter driving wheels is activated/deactivated. Determining the presence/absence of the user thrust is based on the detected speed plot of the vehicle, particularly assuming that, following a speed peak due to the thrust, there is a sudden deceleration, determined by the discontinuation of the same thrust. Such principle for determining the presence/absence of the thrust, based on the speed plot can however lead to erroneous assumptions when an analogous speed plot is produced by causes different from the thrust, such as for example sudden variations of the path slope, humps, etcetera, with the risk of turning on the motor by means of the system also in cases wherein this should not occur.

Summary of the invention

Therefore, the problem, from which the present invention stems, is to provide a system for controlling the motion of an impulsive-type human-powered vehicle, so that, when it is associated to the vehicle, this latter, despite the provision of auxiliary actuators reducing the user effort, has a behavior similar to the one the vehicle would have without such system, making therefor superfluous the interface devices commanding the vehicle itself by the user during the operation. A further problem, from which the present invention stems, consists of making available a system for controlling the motion of an impulse-type human-powered vehicle which is sufficiently strong, such as to avoid to operate the auxiliary actuators in erroneous circumstances, with the risk of unusual behaviors of the vehicle itself.

Such problem is solved by a system for controlling the motion of an impulsive- type human-powered vehicle according to claim 1 .

The dependent claims define possible advantageous embodiments of the invention.

Brief description of the drawings

In order to better understand the invention and appreciate the advantages thereof, some exemplifying non limiting embodiments of the invention will be described in the following with reference to the accompanying figures, wherein:

Figure 1 is a schematic view of an impulsive-type human-powered vehicle of a system according to the invention;

Figure 2 is a block diagram of a system for controlling the motion of an impulsive- type human-powered vehicle according to a possible embodiment of the invention;

Figure 3 illustrates a possible trend of the speed v of the impulsive-type human- powered vehicle equipped with a system according to the invention, and of the estimated thrust Fk of the user as a function of time t;

Figure 4 illustrates a possible comparison between the speed v when the impulsive-type human-powered vehicle equipped with a system according to the invention is started, and the same vehicle without such system, all the conditions being equal during the time t;

Figure 5 illustrates a possible comparison between the speed v of an impulsive- type human-powered vehicle equipped with a system according to the invention, and the same vehicle without such system all conditions being equal during the time t.

Detailed description of the invention

Figure 1 schematically shows an impulsive-type human-powered vehicle 1 00 with an user 200 on the same vehicle. The vehicle 1 00 shown in Figure 1 is a push scooter. Alternatively, the vehicle 1 00 can be, for example, a skateboard or similar vehicle drivable by impulsive thrusts exerted by the user foot. Alternatively, the vehicle 1 00 can be, for example, a wheelchair driven by impulsive thrusts exerted by the user on the wheels of the same, or another analogous impulsive thrust vehicle driven by the action of the arms. Alternatively, the vehicle can be a not land type vehicle, for example a rowboat.

The vehicle 1 00 is provided with a system 1 for controlling its motion, shown by the block diagram in its possible embodiment of Figure 2. The system 1 is suitable to deliver a force in addition to the human thrust provided by the user 200 under predetermined conditions, as it will be better described in the following.

Referring again to Figure 1 , the system 1 comprises a motor 2 associated to at least one driving wheel 3 of the vehicle 1 00 (or a different power element, for example a motor provided with propellers in case of a non land vehicle) in order to provide power to the same under predetermined conditions. Obviously, plural driving wheels, if present, can be associated to the motor 2. Moreover, the system 1 comprises an energy storing system 4 supplying the motor 2 so that this latter can produce power. For example, the motor 1 can comprise an electric motor and the energy storing system 4 can comprise one or more batteries. Alternatively, the motor 2 and energy storing system 4 can be of a different type. For example, the motor 1 can comprise an internal combustion engine and the energy storing system 4 can comprise a fuel tank. Moreover, the system 1 comprises a sensor 5 for detecting the vehicle speed v, suitable for generating a signal representative of such speed. For example, the speed sensor 5 can be associated to a vehicle wheel, for example to the driving wheels 3. By means of the wheel rotation speed, it is possible to determine the vehicle longitudinal speed v, in other words the speed along the axis x of a x-y axis system integral with the vehicle 100, according to what has been shown in Figure 1 .

Further, according to a possible embodiment, the system 1 comprises an inertial measuring unit 6 suitable for measuring at least the vehicle longitudinal acceleration (in other words the acceleration according to the axis x of Figure 1 , as previously described) and for generating a signal representative of the same.

According to a possible embodiment, moreover the system 1 comprises a sensor (not shown in the figures) for detecting the slope θ of the path which the vehicle itself is moving along, suitable for generating a signal representative of the slope. The slope θ is given by the angle between the axis x in Figure 1 , integral with the vehicle, and the axis x of an absolute system not shown in the figures, so that θ is zero when the two axes x coincide.

Alternatively, the inertial measuring unit 6 can substitute the function of the slope sensor, which to this end can be further arranged in order to detect at least also the vehicle 100 vertical acceleration (in other words the acceleration according to the axis y of the axis system shown in Figure 1 ) and to generate a signal representative of the vertical acceleration.

Referring now to Figure 2, it shows a block illustrative diagram of the system 1 according to a possible embodiment of the invention.

The system 1 comprises a module 7 for controlling a main driving torque T of the electric motor 2 associated to the vehicle 100 based on the effective speed v of the same. Specifically, the vehicle effective speed v can be obtained from the signal representative of the vehicle speed generated by the speed sensor 5. As it will be illustrated in the following, preferably the control module 7 performs a closed-loop control of the vehicle speed, by acting on the main torque T.

Further, the system 1 comprises a module 8 for estimating the presence or absence of a thrust F _k of the user. For example, with reference to a push scooter, the module 8 is capable of determining if the user is exerting a thrust by his/her foot for causing the push scooter to advance. The module 8 is connected to the module 7 for controlling the main driving torque, and is configured in order to supply: - an activation signal (usually indicated by the signal 1 in Figure 2) to the module 7 controlling the main torque T, when it is estimated the absence of the thrust Fk of the user;

- a deactivation signal (usually indicated with the signal 0 in Figure 2) to the module 7 controlling the main torque T, when it is estimated the presence of the thrust F _k of the user.

Such control principle causes, after the application of the user thrust Fk, in other words when the thrust is determined as ceased and therefore absent, the module 7 controlling the main torque T to start operating so that the motor 2 supplies such main torque T to the driving wheel 3. As it will be described in the following, the main torque T is preferably supplied in a non impulsive mode. Instead, when the module 8 determines the user thrust Fk is in progress, the main torque T control by the module 7, is deactivated and therefore the torque T is preferably equal to zero. The thrust estimating module 8 can be differently configured because the thrust can be determined according to plural modes. Particularly, the thrust determining module 8 receives, at the input, at least one signal representative of the vehicle longitudinal acceleration Ax. This latter signal can be supplied to the module 9 for determining the vehicle longitudinal acceleration, configured, for example, for determining the acceleration by inferring the speed, known from the signal representative of the longitudinal speed supplied by the speed sensor 5. Alternatively, if an inertial measuring unit 6 is present, it is possible to obtain such signal representing the longitudinal acceleration Ax from a measured longitudinal acceleration signal A _X | _M u generated by the inertial measuring unit 6 itself, preferably pre-processed by the module 9 itself, as it will be better explained in the following. Further, the thrust estimating module 8 receives, at the input, preferably the signal representative of the speed v supplied by the speed sensor 5.

Moreover, the thrust estimating module 8 optionally can receive, at the input, one signal representative of the path slope θ if the system is provided with the corresponding slope sensor.

In addition, the module 8 can relate the user thrust to the overall mass M of the vehicle and user. Such parameter can be determined in a fixed way, in a predetermined way or alternatively, can be determined by a module for determining the vehicle mass + user mass, not shown in the figures.

Further, the module 8 can relate its estimate of the user thrust to a signal representing the driving force F _mo t exerted by the motor 2. Such parameter is known and is obtainable from the driving torque supplied by the motor, which is controlled by the system itself, for example by the current supplying the motor if this latter is an electric one.

According to a possible embodiment, the system 1 further comprises a thrust amplifying module 10 adapted to generate an auxiliary torque command T" which must be supplied by the motor in addition to the main torque T, which is instead commanded by the module 7. The total torque T supplied by the motor is therefore given by the sum of the main torque T, commanded by the module 7, and the auxiliary torque T", commanded by the thrust amplifying module 10. Such optional module 1 0 has the function of partially changing the trend of the vehicle generated by the combined contribution of the human thrust and the main torque T in the different motion steps. For example, the thrust amplifying module 10 can require the motor an additional torque in the presence of path upgrades, and/or can amplify the effect of the thrust Fk in a time period when this is supplied. The thrust amplifying module 1 0 can therefore optionally receive, at the input, the signal representative of the path slope θ, if the corresponding sensor is available, and the signal representative of the user thrust F _k as determined by the module 8. The amount of the torque amplification can be adjusted by the user by regulating one or more operative parameters of the module 1 0 itself. Traditionally, such parameters are indicated by the parameter k in Figure 2, which indicates just a parameter adjustable by the user. The parameter k adjustment can be made by an user interface device (not shown) or alternatively by a cellular phone or smartphone, connectable to the system 1 by a communication module not shown in Figures.

Now, a detailed description of the preferred embodiments of the single modules of the system 1 will be given.

Module 7 for controlling the motor main torque T'

Advantageously, the module 7 for controlling the motor driving torque T comprises a module 1 1 generating the reference speed v _re f and a module 1 2 controlling the vehicle speed by a closed loop.

The module 1 1 generates the reference speed v _re f which the vehicle should follow as precisely as possible following the thrust applied by the user. The reference speed v _re f plot can be selected in several different ways. Preferably, the reference speed v _re f is such to be equal to the effective speed v detected by the speed sensor 5 at the instant when the main torque control module 7 is activated by the module 8. In this way, the electric motor starts operating gradually, avoiding sudden vehicle accelerations. Advantageously, to this end, the reference speed v _re f generating module 1 1 receives, at the input, the signal representative of the vehicle speed v.

The reference speed v _re f can be set as a curve gradually decreasing with the time from the effective speed v detected at the activation time of the control module 7, in order to simulate a condition of limited frictions for the vehicle motion.

The time (t) - speed (v) diagram of Figure 4 shows a comparison between the reference speed v _re f in case the control module is activated (curve 1 3) and the effective speed of the vehicle in case the control module is not activated (curve 14) in a time interval of the vehicle moving from a standing start. Initially, in the time period wherein the thrust F _k is applied by the user, the two curves coincide from the instant wherein the control module has been deactivated. After such time interval, in case the vehicle is not provided with the control module or in case the control module is deactivated, the speed curve exhibits a variable trend which can for example depend on terrain unevenness or on the presence of downgrades and upgrades. Vice-versa, the reference speed, set in the figure as gradually decreasing, is independent from the effective conditions encountered by the vehicle during its path.

Alternatively, the reference speed v _re f can be selected as a gradually increasing curve, in order to simulate a behavior of the vehicle along a downgrade.

According to more sophisticated models, the reference speed v _re f trend is not determined in a fixed way, but can change as a function of the effective conditions encountered by the vehicle during its motion. For example, it is possible to generate a reference speed v _re f simulating, and simultaneously reducing the effort by driver, the presence of upgrades and downgrades, in order to provide to the vehicle a behavior as natural as possible. To this end, the reference speed v _re f can be determined as a function of the signal representative of the path slope θ, generated by the corresponding slope sensor or from the signal representative of the longitudinal acceleration Ax (or also possibly from the vertical acceleration) Ay, if the associated sensors are provided.

Advantageously, the closed-loop speed control module 12 modulates the motor main torque T so that the vehicle will follow the reference speed v _re f generated by the reference speed generating module 1 1 . For example, the module 12 can comprise a controller PID, or alternatively, more sophisticated controllers, for example fuzzy-logic controllers. The module 1 2 receives, at the input, a signal representative of the difference Δν between the vehicle effective longitudinal speed v, measured by the speed sensor 5, and the reference speed v _re f as generated by the module 1 1 , and determines the main torque T so that such speeds tend to be coincident to each other.

Module 9 for determining the longitudinal acceleration Ax

The longitudinal acceleration Ax determining module 9 has the function of generating a signal representative of the vehicle longitudinal acceleration Ax and can be differently configured according to the available sensors in the system.

In case the inertial measuring unit 6 is not present, the module 9 can be configured for determining the vehicle longitudinal acceleration Ax from the signal representative of the longitudinal speed v from the speed sensor 5, by deriving the speed itself. Preferably, the module 5 comprises, in this case, a high-pass filter for filtering the signal from the speed sensor.

In case the inertial measuring unit 6 is provided, the signal representative of the acceleration Ax provided by this latter, can be directly used, at the input, in the other modules, according to what has been previously described. In such case, the module 9 does not perform any processing of the signal. Alternatively, preferably, the module 9 comprises a filter, still more preferably a complementary filter. In this way, by means of the signal representative of the measured longitudinal acceleration A _X | _M u from the inertial measuring unit 6, it is obtained the signal representative of the longitudinal acceleration Ax which is used, at the input, by the other system modules.

Module 8 for determining the user thrust

The module 8 is configured for determining the presence or absence of the thrust F _k by the user. By determining the presence or not of such thrust, the module 8 supplies a deactivation or activation signal to the module 7 for controlling the main torque T, particularly to the reference speed generating module 1 1 .

A possible principle for determining such thrust Fk can be based on a balance of the forces acting on the vehicle 1 00, according to the following formula:

Mv = -77(v) + F _k + - Mg sin(5) ( 1 )

M is the mass of the user-vehicle unit. As previously said, the mass can be considered as a fixed and known parameter, by knowing the vehicle mass to which a mass of an average user is added.

Alternatively, the mass M can be calculated in a mass estimating module (not shown in the figures) by known algorithms, for example by Kalman filters. Further known systems for determining the vehicle mass M from signals representative of cinematic and/or dynamic magnitudes of the vehicle are for example described in the following articles:

- Xiaobin Zhang; Liangfei Xu; Jianqiu Li; Minggao Ouyang, "Real-Time Estimation of Vehicle Mass and Road Grade Based on Multi-Sensor Data Fusion," Vehicle Power and Propulsion Conference (VPPC), 2013 IEEE, vol., no., pp.1 ,7, 15-18 Oct. 2013

- Rhode, S.; Gauterin, F., "Vehicle mass estimation using a total least-squares approach," Intelligent Transportation Systems (ITSC), 2012 15th International IEEE Conference on, vol., no., pp.1584,1589, 16-19 Sept. 2012

- Fathy, H.K.; Dongsoo Kang; Stein, J.L., "Online vehicle mass estimation using recursive least squares and supervisory data extraction," American Control Conference, 2008, vol., no., pp.1842,1848, 1 1 -13 June 2008

- doi: 10.1 109/ACC.2008.4586760

- Mclntyre, M.L.; Ghotikar, T.J.; Vahidi, A.; Xubin Song; Dawson, D.M., "A Two- Stage Lyapunov-Based Estimator for Estimation of Vehicle Mass and Road Grade,"

Vehicular Technology, IEEE Transactions on, vol.58, no.7, pp.3177,3185, Sept. 2009

- doi: 10.1 109/TVT.2009.2014385

v is the vehicle acceleration obtainable according to the previously described modes with reference to the module 9 for determining the signal representative of the vehicle longitudinal acceleration Ax.

η(ν) is the so called "coasting down" function of the vehicle, and represents the value of the frictions acting on the vehicles as a function of its longitudinal speed.

F _mot is the total force of the motor, which is a known parameter because, as explained before, the total torque T of the motor is controlled by means of the modules 7 and 10, if present.

Mg sin(d) is the contribution of the gravity, wherein g is the gravitational acceleration and θ is the path slope along which the vehicle moves. If the system is not provided with a sensor suitable for determining the path slope, the term Mg sin(d) can be disregarded, and the formula for calculating the thrust exerted by the user can be simplified as follows:

Mv = -^v) + F _k + F _nwt (2)

The user thrust Fk in a determined instant can be obtained by inverting the formula (1 ) or formula (2).

Obviously, also the friction term η(ν) and/or the driving force F _mot can possibly be disregarded. In such case, the estimation of the thrust F _k will be less accurate.

With reference to the coasting down function η(ν), it can be experimentally determined for example by letting the vehicle freely move along a downgrade until it spontaneously stops. According to this approach, the coasting down function is set only one time and varies only as a function of the detected vehicle speed v. However, such type of approach does not consider some factors such as the configuration of the road and/or the wear of the tyres, which affect the friction and therefore such function, modifying it during the vehicle operation.

According to a different approach, therefore, the coasting down function can be adaptively calculated during the vehicle operation, so that the estimate accounts for the variation of the conditions causing the friction, according to what has been discussed beforehand.

According to this approach, since a human-powered vehicle travels at low speeds the aerodynamic contribution (varying as the square of the speed) can be disregarded, so that the friction force as a function of the speed v can be obtained by the relation:

η{ν) = βν + γ (3)

wherein β and y are parameters which should be determined and vary during the vehicle operation.

By introducing the formula (3) into the formula (1 ), assuming there is a step in which the user thrust Fk has ended and therefore the vehicle moves following the reference speed v _re f as determined by the module 1 1 , which has low accelerations and therefore negligible, it is obtained:

0 = -fr-r + F _mot -Mg s S (4)

It is observed that in the formula (4), it is assumed that the term dependent on the slope is known, for example because it is available a slope sensor. Without such sensor, the formula (4) is: 0 = -fl, - _{r + Fmt} (5)

In this case, the unknown slope term is included in the term y to be determined.

The formulas (4) or (5) can be rewritten in a matrix form by the following linear relation:

Υ = -[β χ]χ (6)

wherein Y and X include the known terms (the driving force F _mo t, the possible gravitational contribution Mgsind, the vehicle speed v).

Such equation, whose unknowns are the time-varying parameters β and γ, can be solved, for example, with the mathematical approach known as "the least- squares method". Such approach determines the parameters β and γ at the considered instant k as a function of the parameters β and γ determined at the previous instant k-1 and also as a function of the known parameters as measured at the instant k (the driving force F _mo t, the possible gravitational contribution Mgsin , the vehicle speed v).

In order to prevent road disturbances, such as humps or user brakings, from affecting the estimate of the coasting down function, as described, they are excluded from the data calculation obtained when the vehicle effective speed v falls outside a predetermined range of the reference speed v _re f as determined by the module 1 1 . In other words, the detected data are accepted if v _re f-a < v < v _re f + b, wherein a and b are predetermined constants, while the data obtained in the opposite case are excluded. In other words, when the speed v falls in the range, called reference speed, it is activated the estimate of the parameters β and γ, viceversa is deactivated and is maintained the estimate at the previous instant.

Advantageously, the module 8 is configured for estimating the presence of the user thrust F _k only when the thrust F _k value determined for example by the preceding modes, exceeds a first predetermined threshold value and for estimating the absence of such thrust Fk when the thrust Fk value falls below a second predetermined threshold value less than the first threshold value. Consequently, the signal activating the control module 7, particularly the reference speed generating module 1 1 , is output when the determined value of the thrust F _k falls below the second predetermined threshold value. Analogously, the signal deactivating the control module 7, particularly the reference speed generating module 1 1 , is output when the determined thrust Fk value exceeds the first predetermined threshold value. The previous discussion is illustrated in Figure 3, wherein a possible speed plot of the vehicle provided with the system 1 (curve 15) and a possible plot of the user thrust F _k determined by the module 8 (curve 16) are drawn as a function of time t. The first thrust predetermined threshold value is indicated by the reference 18', while the second predetermined threshold value is indicated by reference 18".

The thrust F _k plot has an impulsive trend characterized by peaks in the time intervals wherein the user exerts the thrust. In the lengths 16' where the thrust F _k exceeds the first threshold value 18', the main torque controlling module 7 is deactivated, and also the speed exhibits sudden accelerations caused by the user thrust. In the lengths 17' wherein instead the estimated thrust F _k goes again below the second threshold value 18", the main torque controlling module 7 is deactivated and the speed has a trend tending to follow a reference speed which in the shown example has a gradually decreasing trend.

Thrust amplifying module 10

The thrust amplifying module 10 supplies an auxiliary torque T" command which is added to the primary torque T' as determined by the control module 7. The module 10 is configured for intervening, in other words supplies the auxiliary torque T" command, independently from the control module 7. Therefore, the module 10 can intervene both during the thrust step and when the user does not apply any thrust.

The auxiliary torque T" can be for example used also during the transient step when the user exerts the thrust, and the module 7 is deactivated, in order to enable the vehicle to reach accelerations greater than the ones it would reach by the user thrust alone. Therefore, the auxiliary torque T" can be determined:

- based on the thrust F _k as determined by the module 8. For example, the secondary torque T" can increase as such thrust increases; and/or

- based on the path slope θ, if it is available the sensor for determining it. For example, if the thrust is exerted when the vehicle goes along an upgrade, the torque T" can supply a support greater than the one which it would supply on a level surface.

Optionally, as previously discussed, the auxiliary torque T" can be further determined as a function of a parameter k adjustable by the user. For example, modifying the parameter k enables to select whether eliminating or increasing the contribution of the auxiliary torque T", all conditions being equal. Figure 5 shows a comparison between the speed of a vehicle without the control system according to the invention (curve 19) and the speed of a vehicle provided with the control system 1 all conditions being equal, wherein however, the amplifying module 10 is absent and therefore it is not present the contribution of the auxiliary torque T". During the thrust step, the acceleration in both cases is the same. Instead, when the thrust is absent, the control system 1 enables to extend the deceleration step with respect to the case without the control system. Therefore, in correspondence of each following thrust step, speeds greater than the ones without control are obtained since the starting speeds when the thrust is applied are increasingly greater.

In case the amplifying module 10 is present, generally in correspondence of each thrust step, the accelerations will be greater, and therefore during such steps the speed slope curve will be greater.

A person skilled in the art, from the above description, could appreciate how the system according to the invention enables to provide an assistance to the motion of an impulsive-type vehicle without requiring specific user interfaces. In fact, the system is capable of determining the presence or absence of the user thrust and is capable of activating therefore the motor control. So the user can use his/her vehicle without worrying about intervening on particular commands. Therefore, the vehicle can be driven in a way completely similar to the same vehicle without such system. Consequently, despite the assistance, the driver has the feeling of driving a vehicle without any supports.

Since the presence/absence of a thrust is determined as a function of a balance of the forces acting on the same vehicle, instead of a simple analysis of the vehicle speed plots for example, the system is reliable and capable of avoiding erroneous activations, caused for example by particular configurations of the road surface, which could cause sudden accelerations and decelerations.

Moreover, the system is also capable of recognizing negative forces - and therefore brakings - and consequently is capable of managing the activation/deactivation without requiring for example sensors for measuring the braking.

Despite the fact that in the present description it has been made reference to a driving torque of the motor, it is observed that in case of motors of different type, for example linear motors, the control can be applied to the motor driving force rather than to the driving torque.

A person skilled in the art, in order to satisfy specific contingent needs, can introduce several additions, modifications, or substitutions of the elements with other operatively equivalent, to the embodiments, without falling out from the scope of the accompanying claims.