Technical Field

The present invention relates to an electric motorcycle with wheel anti-lock system.

Background Art

The use is known and more and more common of electrically-propelled motorcycles.

Electric motorcycles of known type comprise an electric motor, typically consisting of a single-phase AC motor or of a brushless motor, a rechargeable electric battery and an inverter connected to the electric battery and able to control the electric motor.

In practice, the inverter receives a signal from the throttle grip of the electric motorcycle, and converts this received signal into a corresponding supply current/voltage of the electric motor. Therefore, during this phase of power supply to the electric motor, the inverter draws a predetermined current from the electric battery and appropriately converts it into power supplied to the electric motor.

Furthermore, electric motorcycles of known type can be provided with a regenerating system, i.e., a system capable of recovering energy during deceleration braking of the motorcycle in order to use it for recharging the electric battery.

Consequently, when slowing down and/or braking the recovered energy translates into a current sent to the electric motorcycle battery, to recharge the battery itself.

Nevertheless, the known type of electric propulsion systems require a number of solutions. In particular, it is known that the wheel anti-lock systems (ABS - Antilock Braking System) of conventional type are difficult to fit on electrically-propelled motor vehicles.

In fact, the known type of anti-lock braking systems are not able to handle all those driving situations wherein the locking of the drive wheel is caused by the deceleration of the motor vehicle due to the braking action of the electric motor, i.e., during the battery regeneration phase, when use is made of the energy recovered to charge the electric battery.

For example, in case of the locking of the wheel of the motor vehicle caused exclusively by the braking action of the electric motor, an anti-lock system of conventional type would operate directly on the brakes of the motor vehicle so as to decrease the braking force.

However, not only would such operation of the anti-lock system not allow the release of the wheel, but would also risk impairing a subsequent operation of the brakes controlled by the rider.

The document US 2012/138375 Al describes a wheel anti-lock system for electric motorcycles.

Nevertheless, such known system does not allow effectively preventing the wheels of an electric motorcycle from locking even after vehicle deceleration caused by the braking action of the electric motor of the motorcycle, during an electric battery regeneration phase.

Description of the Invention The main aim of the present invention is to provide an electric motorcycle with a wheel anti- lock system which allows to avoid the locking of the wheels even after deceleration of the motorcycle caused by the braking action of the electric motor, during an electric battery regeneration phase.

Another object of the present invention is to provide an electric motorcycle with a wheel anti- lock system which allows to overcome the mentioned drawbacks of the prior art within the ambit of a simple, rational, easy and effective to use as well as affordable solution.

The above mentioned objects are achieved by this electric motorcycle with a wheel anti-lock system, having the characteristics of claim 1.

Brief Description of the Drawings

Other characteristics and advantages of the present invention will become better apparent from the description of a preferred, but not exclusive, embodiment of an electric motorcycle with a wheel anti-lock system, illustrated by way of an indicative, but non-limiting, example in the accompanying drawings, wherein:

Figure 1 is a side view of a possible electric motorcycle according to the invention;

Figure 2 is a general block diagram that illustrates the wheel anti-lock system and the driving control unit of the electric motorcycle according to the invention;

Figure 3 is a block diagram that illustrates a possible embodiment of the wheel anti-lock system of the electric motorcycle according to the invention;

Figure 4 is a block diagram that illustrates a possible embodiment of a first detecting unit of the wheel anti-lock system of the electric motorcycle according to the invention;

Figure 5 is a block diagram that illustrates a possible embodiment of a second detecting unit of the wheel anti-lock system of the electric motorcycle according to the invention;

Figure 6 is a block diagram that illustrates a possible alternative embodiment of a first detecting unit and of a second detecting unit of the wheel anti-lock system of the electric motorcycle according to the invention;

Figure 7 is a block diagram that illustrates in detail the limiting means of the system of Figure

3;

Figures 8, 9 and 10 illustrate possible trends in different friction conditions of the maximum regeneration torque and the maximum limited torque obtained by means of the wheel anti-lock system of the electric motorcycle according to the invention.

Embodiments of the Invention

With particular reference to such Figures, reference number 1 globally indicates a wheel anti- lock system usable in particular on an electric motorcycle M or a similar electrically-propelled vehicle.

As schematically shown in figure 1, the electric motorcycle M comprises a support frame, a rear wheel RW, a front wheel FW, an electric propulsion motor E, an electronic control unit 2 for driving the electric motor E and a wheel anti-lock system 1 operatively connected to the control unit 2.

The system 1 is implemented by means of a plurality of hardware and/or software components suitably interfaced with one another.

As shown by way of example in figure 2, the system 1 can be implemented inside an electronic control unit 2 for driving an electric motor E for the propulsion of an electric motorcycle M. For example, the control unit 2 can be of the type described in the Italian patent application no. MO2014A000307. The implementation of the system 1 cannot however be ruled out within different systems and appliances for driving the electric motor of electric motorcycles.

Still with reference to the example shown in figure 2, the control unit 2 comprises an output 3 connectable to an inverter I controlling an electric motor E of the electric motorcycle M. The output 2 is able to send to the inverter I a driving signal TOUT.

The inverter I may consist of an inverter of the conventional type connected to a rechargeable electric battery B of the electric motorcycle M and able to control the electric motor E according to the driving signal TOUT.

In particular, the driving signal TOUT sent to the inverter I corresponds to a torque value delivered by the electric motor E.

The control unit 2 can be used both during an active operating phase and during a phase of regeneration of the electric battery B. In particular, during the active operating phase, the inverter I takes a predetermined electric current from the electric battery B and converts it appropriately into power supplied to the electric motor E. During the regeneration phase (generally during deceleration and/or braking of the electric motorcycle M) the recovered energy translates into a current supplied by the inverter I to the electric battery B, to recharge the battery itself.

The control unit 2 comprises a first input 4 connectable to a control device C of the acceleration of the electric motorcycle M, consisting of the throttle grip. The first input 4 is able to receive a command signal G coming from the electronics of the knob C and correlated to the angular position of the knob itself.

The control unit 2 comprises a second input 5 able to receive an output voltage value VB of the electric battery B. More specifically, such output voltage VB can vary according to the conditions of use and temperature of the electric battery B.

The control unit 2 comprises, furthermore, a third input 6 able to receive an RPM rotation speed value of the electric motor E.

The control unit 2 further comprises:

- a fourth input 7 able to receive a dynamic value of maximum deliverable current IMAX; a fifth input 8 able to receive a dynamic value of the maximum absorbable current

RIMAX. In particular, such dynamic values IMAX and RIMAX represent the maximum deliverable current that can be delivered and the maximum absorbable current that can be absorbed respectively by the electric battery B, and can be calculated e.g. by a BMS-type (Battery Monitoring System) system or similar system fitted on the electric motorcycle M, according to the temperature and/or the charge level of the electric battery B.

The control unit 2 can comprise a sixth input 9 and a seventh input 10 able to receive the signals for selecting the delivery/regeneration modes MapiN, RMapiN able to select the different operating modes of the electric motorcycle M during the active phase or during the regeneration phase, respectively.

The control unit 2 is capable to perform the dynamic generation of the delivered torque value TOUT sent to the inverter I.

In particular, during the active phase, the control unit 2 dynamically generates the delivered torque value TOUT according to the command signal G coming from the knob C and to a maximum deliverable current value IMAX of the electric battery B of the electric motorcycle M. Similarly, during the regeneration phase, the control unit 2 dynamically generates the delivered torque value TOUT according to the command signal G coming from the knob C and to the maximum absorbable current value RIMAX of the electric battery B of the electric motorcycle M.

The control unit 2 comprises a first calculation unit 11 able to calculate a maximum deliverable torque value TMAX according to the maximum deliverable current value IMAX, to the output voltage value VB and to the RPM rotation speed value.

Similarly, the first calculation unit 11 is able to calculate a maximum regeneration torque value RTMAX according to the maximum absorbable current value RIMAX, to the output voltage value VB and to the RPM rotation speed value.

Furthermore, the control unit 2 comprises a second calculation unit 12 able to calculate the delivered torque value TOUT to be sent to the inverter I according to the maximum deliverable torque value TMAX, to the maximum regeneration torque value RTMAX and to the command signal G.

Preferably, the delivered torque value TOUT varies between a maximum value equal to the maximum deliverable torque value TMAX and a minimum value equal to the maximum regeneration torque value RTMAX, while all the intermediate values are appropriately determined.

For example, the command signal G may consist of a signal variable between 0 and 1, where zero corresponds to the minimum rotation angle of the throttle grip C, while 1 corresponds to the maximum rotation angle of the throttle grip C.

Preferably, the wheel anti-lock system 1 of the electric motorcycle M is interposed between the first calculation unit 11 and the second calculation unit 12 and is able to receive at input the maximum regeneration torque value RTMAX and to return at output the same maximum regeneration torque value RTMAX or a maximum limited torque value RTMAX L, according to whether or not a slippage condition SLP occurs of the front and rear wheels RW, FW of the electric motorcycle M.

The system 1 also comprises:

a first input 13 able to receive an instantaneous speed value F SPD of the front wheel FW; a second input 14 able to receive an instantaneous speed value R SPD of the rear wheel

RW;

a third input 15 able to receive a pressure value PI of the front brake (in bar);

- a fourth input 16 able to receive an instantaneous torque value T IN of the electric motor E to the wheel RW;

a fifth input 17 able to receive a wheel locking signal EVENT_IN coming from a conventional ABS system fitted on the electric motorcycle M.

Preferably, the system 1 also comprises a sixth input 51 able to receive a pressure value P2 of the rear brake (in bar).

A possible embodiment of the wheel anti-lock system 1 is illustrated in detail in Figure 3 and is described below.

In particular, the system 1 comprises detecting means 18 able to detect a slippage condition SLP of at least one of the wheels FW and RW of the electric motorcycle M.

Advantageously, moreover, the system 1 comprises limiting means 19 operatively connected to the detecting means 18 and able to limit the maximum regeneration torque RTMAX of the electric motor E of the electric motorcycle M in the event of detection of the slippage condition SLP.

Preferably, moreover, the system 1 has verification means 20 of the friction conditions of the wheels RW, FW of the electric motorcycle M on the road surface.

In particular, such verification means 20 are able to verify the presence or not of a high friction condition HIGH MU or of a low friction condition LOW MU.

Advantageously, therefore, the limiting means 19 are operatively connected to the verification means 20 and, in case of detection of the slippage condition SLP, they are able to limit the maximum regeneration torque RT _MAX according to the high friction condition FIIGH MU or to the low friction condition LOW MU detected.

With reference to the preferred embodiment shown in figure 3, the detecting means 18 comprise a first calculation unit 21, made up e.g. of a subtraction element (hardware circuit or software component), able to calculate the speed difference AV between the front wheel FW and the rear wheel RW starting from at least an instantaneous speed value F SPD of the front wheel FW and from at least an instantaneous speed value R SPD of the rear wheel RW.

Preferably, the detecting means 18 provide for: - a second calculation unit 22, made up e.g. of a mediator element (hardware circuit or software component), able to calculate an average speed value F AV SPD of the front wheel FW starting from a plurality of instantaneous speed values F SPD;

- a third calculation unit 23, made up e.g. of a mediator element (hardware circuit or software component), able to calculate an average speed value R AV SPD of the rear wheel RW starting from a plurality of instantaneous speed values R SPD.

Usefully, therefore, the first calculation unit 21 determines the speed difference AV as the difference between the average speed value F_AV_SPD and the average speed value R AV SPD.

For example, these average speed values F AV SPD and R AV SPD can be calculated considering two instantaneous speed values F SPD and R SPD consecutive the one to the other. This way any speed peaks can be eliminated.

Advantageously, moreover, the detecting means 18 comprise a comparison unit 24 for comparing the speed difference AV and a predefined threshold value SPD TH, wherein:

- if said speed difference is greater than (or equal to) said threshold value SPD TH, then said slippage condition SLP is present;

- if said speed difference is less than said threshold value SPD TH, then said slippage condition SLP is absent.

Preferably, the detecting means 18 comprise calculation means 25, 26 of the threshold value SPD TH according to the average speed of the front wheel F AV SPD and to the average speed of the rear wheel R AV SPD.

In particular, such calculation means 25, 26 comprise at least a fourth calculation unit 25 able to calculate the average speed AV_SPD of the electric motorcycle M as average between the average speed of the front wheel AV_F_SPD and the average speed of the rear wheel AV_R_SPD.

In addition, the calculation means 25, 26 comprise a fifth calculation unit 26 able to multiply the average speed value AV SPD determined by a predefined proportionality coefficient KV. Consequently, the threshold value SPD TH so determined corresponds to a predefined percentage of the calculated average speed AV_SPD.

For example, the calculated threshold value SPD TH may correspond to 4% of the average speed value AV_SPD of the electric motorcycle M.

Usefully, the detecting means 18 comprise a calibration means 27 operatively interposed between the first calculation unit 21 and the comparison unit 24, able to receive at input the speed difference AV and a calibration value SPD CAL and able to return at output a calibrated speed difference value AVc.

In particular, the system 1 can have determination means 28 for determining the calibration value SPD CAL according to the instantaneous torque value T IN of the electric motor E to the drive wheel (e.g., the rear wheel RW) of the electric motorcycle.

Furthermore, the determination means 28 can receive at input the wheel locking signal EVENT_IN coming from a conventional ABS system.

In particular, the determination means 28 can comprise a sixth calculation unit 29, made up e.g. of a mediator element, able to calculate an average torque value starting from a plurality of instantaneous torque values T IN.

The determination means 28 also have a verification block 30, connected to the output of the sixth calculation unit 29, able to check the riding conditions of the electric motorcycle M.

In particular, the verification block 30 is able to verify the presence or absence of a stationary riding condition or of a critical riding condition by comparing different detected values relating to the current riding state of the electric motorcycle M with a series of predefined parameters.

For example, these predefined parameters may comprise predetermined threshold values relating to the delivered torque and to the pressure in the brake cylinder.

A calculation block 31 of the calibration value SPD CAL has its input connected to the verification block 30 and to the first calculation unit 21 and is connected at output to the calibration unit 27. The calculation block 31 is able to calculate the calibration value

SPD CAL according to a plurality of speed difference values AV calculated at different moments and in the presence of a stationary riding condition.

Still in Figure 2 a possible embodiment of the verification means 20 of the friction conditions is illustrated in detail.

In particular, the verification means 20 comprise a derivation unit 32 able to calculate an acceleration value F ACC of the front wheel FW and an acceleration value R ACC of the rear wheel RW according to the average speed values F_AV_SPD and R_AV_SPD, respectively. Usefully, the verification means 20 comprise a conversion unit 33 connected downstream of the derivation unit 32 and able to perform a conversion of the unit of measurement of the acceleration values F ACC and R ACC from (km/h)/s to m/s ² .

Furthermore, the verification means 20 have a determination unit 34 connected downstream of the conversion unit 33 and able to determine an average acceleration value AV ACC of the electric motorcycle M starting from the acceleration values F ACC and R ACC of the front wheel FW and of the rear wheel FW.

Alternative embodiments cannot however be ruled out wherein the acceleration value of the electric motorcycle M is determined by means of an accelerometer fitted on board the motorcycle itself.

Advantageously, the verification means 20 comprise a first detecting unit 35 able to detect a high friction condition HIGH MU according to the average acceleration value AV ACC, to the pressure value PI of the front brake of the electric motorcycle M and to the instantaneous torque value T_IN. Preferably, the first detecting unit 35 is able to also detect such high friction condition HIGH MU according to the pressure value P2 of the rear brake of the electric motorcycle M. In particular, this way it is possible to obtain a more effective detection of the high friction condition HIGH MU.

A possible embodiment of the first detecting unit 35 is schematically illustrated in Figure 4. In particular, the first detecting unit 35 comprises first comparison means 52 able to compare at least the average acceleration value AV ACC, the pressure value PI of the front brake and the instantaneous torque value T IN with respective predefined threshold values P THl, P TH2, T THl , T TH2, T TH3, ACC_TH.

Specifically, these threshold values may comprise: a first pressure threshold value P THl, a second pressure threshold value P TH2, a first torque threshold value T THl, a second torque threshold value T TH2, a third torque threshold pressure value T TH3, an acceleration threshold value ACC TH.

In this regard, it should be noticed that the torque threshold values T THl, T TH2 and T TH3 are negative torque values.

For example, possible values attributable to the predefined threshold values are the following:

P THl = 14.5 bars;

P_TH2 = 11 bars;

T THl = -43 Newton meter;

T TH2 = -33 Newton meter;

T TH3 = -21 Newton meter;

ACC_TH = -8.5 m/s ² .

It is however pointed out that these parameters are determined according to the specific characteristics of the electric motorcycle M. The use of different threshold values cannot therefore be ruled out.

In particular, the first detecting unit 35 is able to detect a high friction condition HIGH MU in the case at least one of the following conditions occurs:

- T_IN≤T_TH1;

- T IN≤ T TH2 and PI > P THl ;

- T IN≤ T TH3 and PI > P TH2;

- AV_ACC≤ ACC_TH.

Conveniently, as illustrated in the preferred embodiment of Figure 4, in the case the pressure value P2 of the rear brake is also considered, the high friction condition HIGH MU occurs if at least one of the following conditions is present:

- T IN - (P2 x Gp)≤ T THl ;

- T IN - (P2 x Gp)≤ T TH2 and PI > P THl ;

- T IN - (P2 x Gp)≤ T TH3 and PI > P TH2; - AV_ACC≤ ACC_TH.

where Gp is a normalization factor determined according to the specific characteristics of the rear brake and of the rear wheel (e.g. pad size, disc diameter, wheel diameter).

With particular reference to the embodiment illustrated in Figure 4, the first comparison means 52 comprise:

a first comparison unit 53 able to check if T IN - (P2 ^χ Gp) < T THl;

a second comparison unit 54 able to check if PI > P THl;

a third comparison unit 55 able to check if T IN - (P2 ^χ Gp) < T TH2;

a fourth comparison unit 56 able to check if PI > P TH2;

- a fifth comparison unit 57 able to check if T IN - (P2 ^χ Gp)≤ TH3 ;

a sixth comparison unit 58 able to check if AV ACC < ACC TH.

The first comparison means 52 also comprise:

- a first verification unit 59 able to verify the truth of both conditions at output from the second comparison unit 54 and from the third comparison unit 55;

- a second verification unit 60 able to verify the truth of both conditions at output from the fourth comparison unit 56 and from the fifth comparison unit 57;

- a third verification unit 61 able to verify the truth of at least one of the conditions at output from the first comparison unit 53 and from the sixth comparison unit 58, from the first verification unit 59 and from the second verification unit 60.

Finally, the first detecting unit 36 comprises a multiplication unit 62 for multiplying the pressure value P2 of the rear brake by the normalization factor Gp, and a subtraction unit 63 for subtracting the output of the multiplication unit 62 from the instantaneous torque value T IN.

Furthermore, the verification means 20 comprise a second detecting unit 36 able to detect a low friction condition LOW MU according to the pressure value PI of the front brake of the electric motorcycle M and to the instantaneous torque value T IN.

Preferably, the second detecting unit 36 is able to also detect such low friction condition LOW MU according to the pressure value P2 of the rear brake of the electric motorcycle M. In particular, this way, more effective detection can be obtained of the low friction condition LOW MU.

A possible embodiment of the second detecting unit 36 is shown schematically in figure 5. In particular, the second detecting unit 36 comprises second comparison means 64 able to compare at least the pressure value PI of the front brake and the instantaneous torque value T IN with respective predefined threshold values P TH2, P TH3, T TH2, T TH3, T TH4. Specifically, these threshold values may comprise: a second pressure threshold value P TH2, a third pressure threshold value P TH3, a second torque threshold value T TH2, a third torque threshold value T TH3, a fourth torque threshold pressure value T TH4. In this regard, it should be noticed that the torque threshold values T TH2, T TH3 and T TH4 are negative torque values.

For example, possible values attributable to the predefined threshold values are the following: P_TH2 = 11 bars;

P TH3 = 7 bars;

T TH2 = -33 Newton meter;

T TH3 = -21 Newton meter;

T TH4 = -16.5 Newton meter.

It is however pointed out that these parameters are determined according to the specific characteristics of the electric motorcycle M. The use of different threshold values cannot therefore be ruled out.

In particular, the second detecting unit 36 is able to detect a low friction condition LOW MU in case at least one of the following conditions occurs:

- PI < P TH2 and T_IN > T TH2

- Pl < P TH3 and T TH3 < T IN≤ T TH4.

Conveniently, with reference to the embodiment of Figure 5, if also the pressure value P2 of the rear brake is considered, the low friction condition LOW MU occurs in case at least one of the following conditions is present:

- PI < P TH2 and T IN - (P2 ^χ Gp) > T TH2

- Pl < P TH3 and Τ ΊΉ3 < T IN - (P2 ^χ Gp)≤ T TH4.

where Gp is a normalization factor determined according to the specific characteristics of the rear brake and of the rear wheel (e.g. pad size, disc diameter, wheel diameter).

With particular reference to the embodiment illustrated in Figure 5, the second comparison means 64 comprise:

- a first comparison unit 65 able to check if PI < P TH2;

a second comparison unit 66 able to check if T IN - (P2 ^χ Gp)> T TH2;

a third comparison unit 67 able to check if PI < P TH3;

a fourth comparison unit 68 able to check if T IN - (P2 ^χ Gp) < T TH4;

a fifth comparison unit 69 able to check if Τ ΊΉ3 < T IN - (P2 ^χ Gp).

The second comparison means 64 also comprise:

- a first verification unit 70 able to verify the truth of both conditions at output from the first comparison unit 65 and from the second comparison unit 66;

- a second verification unit 71 able to verify the truth of both conditions at output from the third comparison unit 67, from the fourth comparison unit 69 and from the fifth comparison unit 69;

- a third verification unit 72 able to verify the truth of at least one of the conditions at output from the first verification unit 70 and from the second verification unit 71. Finally, the second detecting unit 36 comprises a multiplication unit 73 for multiplying the pressure value P2 of the rear brake by the normalization factor Gp, and a subtraction unit 74 for subtracting the output of the multiplication unit 73 from the instantaneous torque value T_IN.

By way of example, figure 6 shows a possible alternative embodiment of the first and second detecting units 35 and 36. More specifically, in this case the first and second detecting units 35 and 36 are made by means of a single logic circuit.

In particular, several limiting units 75, 76, 77 are able to receive at input and limit the maximum and minimum values of the pressure value PI of the front brake, of the pressure value P2 of the rear brake and of the torque value T IN respectively.

A subtraction unit 80 is able to subtract the torque value T IN (which is a negative torque value) from the pressure value P2 of the rear brake.

Usefully, respective normalization units 78, 79, 81 are able to multiply the pressure value PI of the front brake, the pressure value P2 of the rear brake and the value at output from the subtraction unit 80 by respective normalization factors Nfp, Nrp and Nt. Such normalization factors depend on the dynamics of the vehicle and are determined by experimental tests.

A multiplication unit 82 is able to multiply together the pressure value PI of the front brake and the value at output from the subtraction unit 80.

A first comparison unit 83 is able to check whether the signal at output from the multiplication unit 82 is greater than or equal to a maximum threshold value TH HIGH. In this case, a high friction condition HIGH MU occurs.

A second comparison unit 84 is able to check whether the signal at output from the multiplication unit 82 is lower than a minimum threshold value TH LOW. In this case, a low friction condition LOW MU occurs.

Furthermore, a third comparison unit 85 is able to check whether the average acceleration value AV ACC is lower than or equal to an acceleration threshold value ACC TH.

In particular, a verification unit 86 is able to check whether there is at least one of the conditions at output from the multiplication unit 82 and from the third comparison unit 85.

In conclusion, then, according to the logic diagram shown in Figure 6 it is possible to detect the presence of a high friction condition HIGH MU when at least one of the following conditions is present:

(PI x (P2 - T IN)) > TH HIGH;

AV_ACC≤ ACC_TH.

Similarly, according to the logic diagram shown in Figure 6 it is possible to detect the presence of a low friction condition LOW_MU when: (PI ^χ (P2 - T IN)) < TH LOW.

Usefully, a debounce circuit 37 is arranged downstream of the first and of the second detecting units 35 and 36 and is connected to the limiting means 19. In particular, such debounce circuit 37 allows maintaining the outputs stable in the presence of variations of the inputs with duration lower than a predefined time interval. For example, such predefined time interval may be equal to 2 seconds.

Figure 7 shows in detail a possible embodiment of the limiting means 19.

Advantageously, the limiting means 19 comprise first selection means 38 between:

the maximum regeneration torque value RTMAX in the absence of slippage condition SLP; a limited torque value RTMAX L in the presence of the slippage condition SLP.

The first selection means 38 comprise, e.g., a first selector element 39 able to receive at input the maximum regeneration torque value RTMAX, the limited torque value RTMAX L and the slippage condition value SLP (preferably made up of a binary value 0 or 1). The first selector element 39 then returns at output the maximum regeneration torque value RTMAX or the limited torque value RTMAX L according to the detected slippage condition SLP.

Advantageously, still according to the preferred embodiment shown in Figure 4, the limited torque value RTMAX L can be selected according to the detected high friction condition HIGH MU or low friction condition LOW MU.

For this purpose, the limiting means 19 comprise second selection means 40 operatively connected to the first selection means 38 and able to select the limited torque value RTMAX L between:

a high friction torque value RTHIGH MU in case of the presence of the high friction condition fflGH MU;

a low friction torque value RTLOW_MU in case of the presence of said low friction condition LOW_MU;

an indeterminate friction torque value RTINT in case of the absence of both the high friction condition fflGH MU and the low friction condition LOW MU.

In particular, the second selection means 40 comprise at least a second selector element 41 able to receive at input the high friction torque value RTHIGH MU, the indeterminate friction torque value RTINT and the high friction condition value fflGH MU (preferably made up of a binary value 0 or 1). The second selector element 41 returns at output the high friction torque value RTHIGH MU or the indeterminate friction torque value RTINT according to the presence or not of the high friction condition fflGH MU.

Furthermore, the second selection means 40 comprise a third selector element 42 able to receive at input the low friction torque value RTLOW_MU, the torque value at output from the second selector element 41 and the low friction condition value LOW MU (preferably made up of a binary value 0 or 1). The third selector element 42 returns at output the low friction torque value RTLOW_MU or the torque value at output from the second selector element 41 according to the presence or not of the low friction condition LOW MU. Usefully, the first selection means 38 are connected downstream of the third selector element 42 and comprise a comparison element 43 able to select the lower between the maximum regeneration torque value RTMAX and the torque value at output from the third selector element 42.

Advantageously, the limiting means 19 comprise third selection means 44, 45 for the selection of the angles of variation of the torque value over time.

In particular, according to the preferred embodiment illustrated in Figure 4, the third selection means 44, 45 comprise a first selection block 44 of a first variation angle a from the maximum regeneration torque value RTMAX to the limited torque value RTMAX_L between:

a first high friction angle ( HIGH MU in case of the presence of the high friction condition fflGH MU;

a first low friction angle ( LOW_MU in case of the presence of the low friction condition LOW_MU;

a first indeterminate friction angle ( INT in case of the absence of both the high friction condition HIGH MU and the low friction condition LOW MU.

In addition, the third selection means 44, 45 comprise a second selection block 45 of a second variation angle β from the limited torque value RTMAX L to the maximum regeneration torque value RTMAX between:

a second high friction angle PHIGH MU in case of the presence of the high friction condition fflGH MU;

a second low friction angle PLOW_MU in case of the presence of the low friction condition LOW_MU;

a second indeterminate friction angle βΐΝτ in case of the absence of both the high friction condition fflGH MU and the low friction condition LOW MU.

In particular, the first selection block 44 has a fourth selector element 46 able to receive at input the value of the first low friction angle ( LOW_MU, the value of the first indeterminate friction angle ( INT and the low friction condition value LOW MU (preferably made up of a binary value 0 or 1). The fourth selector element 44 returns at output the value of the first low friction angle ( LOW_MU or the value of the first indeterminate friction angle ( INT according to the presence or not of the low friction condition LOW MU.

Furthermore, the first selection block 44 has a fifth selector element 47 able to receive at input the value of the first high friction angle ( HIGH MU, the value at output from the fourth selector element 46 and the high friction condition value fflGH MU (preferably made up of a binary value 0 or 1). The fifth selector element 47 returns at output the value of the first high friction angle ( HIGH MU or the value at output from the fourth selector element 46 according to the presence or not of the high friction condition fflGH MU. Similarly, the second selection block 45 has a sixth selector element 48 able to receive at input the value of the second low friction angle PLOW_MU, the value of the second indeterminate friction angle βΐΝτ and the low friction condition value LOW MU (preferably made up of a binary value 0 or 1). The sixth selector element 48 returns at output the value of the second low friction angle LOW_MU or the value of the second indeterminate friction angle βΐΝτ according to the presence or not of the low friction condition LOW MU.

Moreover, the second selection block 45 has a seventh selector element 49 able to receive at input the value of the second high friction angle PHIGH MU, the value at output from the sixth selector element 48 and the high friction condition value HIGH MU (preferably made up of a binary value 0 or 1). The seventh selector element 49 returns at output the value of the second high friction angle PHIGH MU or the value at output from the sixth selector element 48 according to the presence or not of the high friction condition HIGH MU.

The limiting means 19 also comprise a torque variation unit 50 operatively connected to the output of the first selector element 39, to the output of the fifth selector element 47 and to the output of the seventh selector element 49 and able to vary over time the torque value at output between the maximum regeneration torque RTMAX and the limited torque value RTMAX L, according to the selected first variation angle a and the second variation angle β.

In Figures 8, 9 and 10 are illustrated, by way of example, possible trends of the maximum limited torque RTMAX L according to the friction conditions.

Specifically, in Figure 8 is illustrated a possible trend of the maximum limited torque RTMAX L in high friction conditions HIGH MU, in which the maximum limited torque RTMAX L has an amplitude equal to the high friction torque value RTHIGH MU and varies from and to the maximum regeneration torque value RTMAX with a first high friction angle ( HIGH MU and with a second high friction angle HIGH MU, respectively.

Figure 9 shows a possible trend of the maximum limited torque RTMAX L in low friction conditions LOW MU, in which the maximum limited torque RTMAX L has an amplitude equal to the low friction torque value RTLOW_MU and varies from and to the maximum regeneration torque value RTMAX with a first low friction angle (XLOwjvru and with a second low friction angle LOW_MU, respectively.

Finally, figure 10 shows a possible trend of the maximum limited torque RTMAX L in an indeterminate friction condition, when none of the high friction condition HIGH MU or low friction condition LOW MU occur, wherein the maximum limited torque RTMAX L has an amplitude equal to the indeterminate friction torque value RTINT and varies from and to the maximum regeneration torque value RTMAX with a first indeterminate friction angle ( INT and a second indeterminate friction angle βΐΝτ, respectively.

In particular, such indeterminate condition occurs in the case in which the first and second detecting units 35 and 36 are not able to provide a univocal result, e.g., in the case in which the locking condition is in an intermediate friction speed or for reasons due to the connection of the road surface or the vehicle dynamics. Therefore, the system 1 provides for such indeterminate condition to meet all those situations where, in fact, it is not possible to determine unambiguously the coefficient of friction.

In this regard, moreover, it is pointed out that according to the particular solution shown in Figure 10, the indeterminate friction torque RTINT, the first indeterminate friction angle INT and the second indeterminate friction angle βΐΝτ have values which are intermediate with respect to the torque values RTHIGH MU and RTLOW_MU and to the values of angles HIGH MU, HIGH MU, LOW_MU and LOW_MU used in high friction HIGH_MU and low friction LOW_MU conditions.

The use cannot however be ruled out of different values in indeterminate friction conditions.

In particular, it is pointed out that the values attributable to the high friction torque value

RTHIGH MU, to the low friction torque value RTLOW_MU, to the indeterminate friction torque value RTINT, to the first high friction angle HIGH MU, to the second high friction angle HIGH MU, to the first low friction angle LOW_MU, to the second low friction angle LOW_MU, to the first indeterminate friction angle INT and to the second indeterminate friction angle βΐΝτ depend on the specific characteristics of the electric motorcycle M.

For example, possible values attributable to these angles are the following:

RTHIGH MU = 22 Newton meter;

RTLOW_MU = 10 Newton meter;

RTINT = 17 Newton meter;

HIGH MU = 140 Newton meter per second;

HIGH MU = 50 Newton meter per second;

LOW_MU = 100 Newton meter per second;

LOW_MU = 30 Newton meter per second;

INT= 120 Newton meter per second;

INT =40 Newton meter per second.

It has in practice been ascertained how the described invention achieves the intended objects. In particular the fact is underlined that the wheel anti-lock system according to the invention allows avoiding the locking of the wheels of an electric motorcycle even after vehicle deceleration caused by the braking action of the electric motor of the motorcycle, during an electric battery regeneration phase.