WO2011125085A1

WO2011125085A1 - Energy measurement device for electric traction vehicles

Info

Publication number: WO2011125085A1
Application number: PCT/IT2011/000103
Authority: WO
Inventors: Gian Pietro Beghelli
Original assignee: Beghelli S.P.A.
Priority date: 2010-04-07
Filing date: 2011-04-05
Publication date: 2011-10-13
Also published as: IT1399429B1; ITVI20100097A1

Abstract

An energy measurement device for electric traction vehicles, suitable to continuously analyze, store and make available consumption and saving information of hybrid electric traction or pure electric traction vehicle, such an electric car (1), compared to a corresponding reference vehicle powered by fossil fuels; the electric traction vehicle essentially comprises a traction battery (3) connected with at least one energy charger (4) and, through at least a power converter or inverter (5), with at least one electric motor (9). In particular, the measurement device comprises a meter (2), provided with an electronic controller with microprocessor, which provides for counting the consumed and/or saved energy starting from the measure of instantaneous power supplied by the battery (3) to the electric motor (9), from the measure of energy supplied by the battery (3), from the measure of energy injected into the battery (3) e from the measures of instantaneous speed and distance covered by the electric traction vehicle.

Description

ENERGY MEASUREMENT DEVICE FOR

ELECTRIC TRACTION VEHICLES

The present invention generally relates to an energy measurement device for electric traction vehicles.

More specifically, the invention relates to a device that can continuously analyze, store and make available, during use, consumption and saving data of an electric traction vehicle, such as an electric car, compared to a corresponding vehicle operating with fossil fuels.

The invention also concerns a measurement device of the energy saving achieved ("saving counter"), which can be generally applied to hybrid electric cars, in which an electric engine is combined with a fossil fuel engine; in this respect, it has to be considered that the hybrid electric car is an important variant of the electric car since, thanks to the possibility of supply of conventional fuel, it allows the use without depending on the availability of electric charging points, as, in case of exhaustion of the electric autonomy, the hybrid car can continue the journey thanks to the supply of conventional fuels at a regular sale point of the existing distribution network.

The electric car is marked by a high energy efficiency in the exploitation of energy; it follows that one of the optimal synergies with the electric car is the combination with systems of electric energy generation from renewable sources, which can be used for charging the batteries.

Purpose of the present invention is indeed to create an energy measurement device for electric traction vehicles, which allows to optimize the management of the supply of energy, for example of electric cars, allowing also to continuously analyze, store and make available, during use, consumption and saving information of the electric vehicle, compared with corresponding vehicles powered by fossil fuels.

Further purpose of the invention is to provide an energy measurement device for electric traction vehicles, which practically constitutes a system of measurement and accounting of the energy saved in the operation of the electric vehicle, compared to a vehicle of equivalent performances powered by fossil fuel.

These and other purposes, according to the present invention, are achieved by implementing an energy measurement device for electric traction vehicles, according to the attached claim 1.

Other technical features of detail are described in the subsequent claims.

Advantageously, according to the present invention, a meter of the power and energy consumed by a hybrid electric car is described, which integrates an appraiser of the consumptions of the equivalent car powered by fossil fuels.

In this way, it is thus possible to calculate the saving obtained by the hybrid electric car.

The measurement device described is also provided with a radio interface and can be integrated into the hybrid electric car, object of use, by the user.

In particular, the two possible cases of application to the hybrid cars are hereinafter evaluated:

- hybrid electric car with hybrid traction (electric motor + endothermic engine contributing to the traction, such as for example in the case of the Toyota Prius® car);

- hybrid electric car with electric traction (electric motor for the traction with endothermic engine used only for generating electricity used directly by the electric motor and/or for recharging the on board battery).

Additional features and advantages of an energy measurement device for electric traction vehicles, according to the present invention, will be more evident from the description that follows, related on respective exemplifying and preferred, but not limited, embodiments and from the drawings attached, where:

- figure 1 shows a block diagram of the energy measurement device for electric traction vehicles, interfaced to a hybrid electric car with hybrid traction, according to a first embodiment object of the present invention;

- figure 2 shows a block diagram of the energy measurement device for electric traction vehicles, interfaced to a hybrid electric car with electric traction, according to a further embodiment of the present invention;

- figure 3 shows a block diagram of operation of the energy measurement device for electric traction vehicles, according to the present invention;

- figure 4 is a Cartesian diagram illustrating the characteristic curves of specific fuel consumption of an endothermic engine of hybrid electric car with electric traction.

With particular reference to the mentioned figures 1-2, the electric traction vehicle is constituted, in the preferred embodiment of the invention, by a hybrid electric car, which includes the following components:

• a traction battery 3, constituted by a set of electrochemical cells connected in series or parallel in order to get the necessary power to ensure the autonomy of the electric car 1 ;

• a charger 4 of the battery 3, powered by a connector 17, which can be connected with the 230 Volts power system at alternating current for recharging the battery 3;

• a power converter or inverter 5, which supplies the electric motor and auxiliary services of the car, possibly through a second auxiliary battery for the services (not shown in the attached figures);

• an electric motor 9;

• a set of auxiliary electromechanical devices 10, such as a system for aiding braking, lights, control panel, heating and air conditioning system, etc.

• mechanical members 11 for transmitting motion to the wheels 12;

• a tank 36 for containing combustible fuel;

• an endothermic engine 37 which, in the case of the electric car with a hybrid traction (shown in the attached figure 1), provides mechanical energy directly to the transmission members 11 , and which, in the case of the electric car with pure electric traction (shown in the attached figure 2), provides mechanical energy to an electric generator 40, which, in turn, provides electricity to the charger 4 and thus to the battery 3.

The measurement device according to the invention also includes a meter 2, with radio interface and/or antenna 16, for counting the consumed and/or saved energy ("saving counter"), a portable terminal 18 and a control unit 19, with related antenna 50 and user interface.

With particular reference to the attached figure 3, the measurement device object of the invention consists of the following parts:

- a microprocessor controller 28,

- a radio transceiver 31 , for example of the FH-DSSS type, operating in the 2.400÷2.483 GHz band, with an antenna 32,

- a non-volatile memory 29, for example of the EEPROM or Flash type, for storing energy consumption and saving data,

- a block of supply circuits 20, which convert the voltage of the battery 3 adjusting it to the value required for the operation of the various parts of the measurement device,

- a connecting device 30 for the connection with the traction battery 3,

- a conditioning circuit 21 of the measure of the voltage of the battery 3,

- a pair of conditioning amplifiers 22, 23 of the current measured by the current sensors 13, 14,

- a conditioning circuit 24 of the encoder 15,

- a sensor 14 of direct current, of induction type, for example at Hall effect, which measures the current absorbed by the electric traction motor 9 and the auxiliary board services 10,

- a sensor 13 of direct current, of induction type, for example at Hall effect, which measures the current of recharging of the battery 3,

- a pulses-counter sensor 15 (or incremental encoder) to be keyed on the drive shaft in order to measure the revolutions number and speed of the vehicle,

- a fuel level sensor 35, inserted into the tank 36 of fuel itself, which is preferably the level sensor yet existing in the electric vehicle 1 ,

- a conditioning circuit 41 of the fuel level sensor 35, which, in case the pre-existing level sensor is used, reads the position of the sensor in parallel to the circuitry of the onboard panel of the electric car 1 (usually the fuel level sensors are of potentiometric type, therefore in this case the conditioning circuit 41 reads, at high impedance, the output voltage of the pre-existing potentiometer, whose value is proportional to the level of fuel in the tank 36),

- a flow meter 38, which measures the fuel flow (in ml/sec) flowing into the supply duct of the endothermic engine 37 (this sensor is of low insertion loss type, in order to not alter the conditions of the supply of the motor itself),

- a conditioning circuit 42 of the reading signals of the flow meter 38,

- a pulses-counter sensor 44 or incremental encoder, to be keyed on the drive shaft of the endothermic engine 37, for measuring the revolutions number and speed of the engine 37,

- a conditioning circuit 45 of the encoder 44 signal,

- a triaxial accelerometer with function of inclinometer 46,

- a CAN interface 33 for the connection with the onboard computer of the electric car 1.

The operation of the energy measurement device, according to the present invention, is substantially as follows.

The meter 2 is a device that continuously records the following parameters:

• the instantaneous power supplied by the battery 3 to the electric motor 9 through the converter 5 (the measure is performed by the sensors 4, 30)

• the energy supplied by the battery 3 (the measure is performed by the sensor 14),

• the energy injected into the battery 3 (the measure is performed by the sensors 13, 14),

• the instantaneous speed of the electric car 1 (through the sensor 15),

• the mileage covered by the electric car 1 (through the sensor 15),

• the consumption of fossil fuel through the measure of the level of the fuel tank 36 (through the level sensor 35), • the instantaneous power of the endothermic engine 37 through the measure of the flow of the fuel consumed (through the flow meter 38) and the revolutions number of the motor itself (through the sensor 44).

In practice, the meter 2 calculates the saving of the operating cost of the electric hybrid car 1 in its actual operating mode, compared to the operating cost of a virtual reference car powered by fossil fuel under the same operating conditions.

The operation saving Re of the electric hybrid car 1 is calculated by the meter 2 starting from the following equation:

Re = Cf_s - Ce_s,

where:

Ce_s = Ce/Sp = specific energy cost of the electric car (in€/km);

Cf_s = Cf/Sp = specific energy cost of the virtual car corresponding to fuel

(in€/km)

Ce = energy cost of the electric hybrid car 1 in the period of use concerned,

Cf = energy cost of the electric hybrid car 1 in the period of use concerned, Sp = space covered by the electric hybrid car 1 (in Km) in the period of use concerned.

As far as the operating cost Ce of the real hybrid car is concerned, in its use conditions, it is calculated by the measurement device 2 in the following way:

Ce = Kc^*Qc + Ee^*Ke,

where:

Kc is the cost per litre of the fuel,

Ke is the cost per kWh of electricity used to recharge the battery 3, measured at the charger 13 output,

Qc is the amount of fuel consumed in a time unit Tu (in litres) and

Ee is the electricity consumed in the time unit Tu (in kWh).

The electric energy consumed by the hybrid car 1 is measured as product of the battery voltage (Vbatt) by the current measured by the sensor 13 (Iric); then the integral of such a product, correct with the efficiency qc of the charger 4, provides the energy Ee used: Ee = nc ^* i₀ ^Tu Vbatt(t) ^* lric(t) dt.

In order to measure and calculate the saving four different methods can be used as an alternative to each other (depending on the desired degree of accuracy in determining the saving and complexity of interaction of the measurement device 2 with the hybrid car 1 concerned).

These different methods differ each other in the way of estimating the operating cost of the virtual comparison vehicle powered by fossil fuel.

In particular, according to the first measure method, the virtual fossil fuel car (equivalent to the electric car 1) is assigned the average operation consumption Qf_s_mdich declared by the manufacturer of the car; then, the saving is given by:

Re = Kc * Qf_s_mdich - Ce_s

In this case, the saving counter measurement device 2 may be simplified at a maximum extent because the measures of the flow of fuel 38, neither the revolutions number of the endothermic engine 44, nor the sensor 14 are not needed.

Indeed, in order to calculate Ce, the measure of the electricity, through the current sensor 13, the measure of fuel consumption, through the level sensor 35, and the measure of the kilometres covered by the car, through the sensor 15, are sufficient.

Alternatively, a second measure method uses the estimation of the fuel consumption of the equivalent fossil fuel car, which can be performed by measuring the speed through the counter 15, and inclination, through the built-in inclinometer 46, ignoring the effect of the possible presence of contrary wind.

The method provides for the arbitrary compensation of the underestimation due to the lack of the wind measure which is always underestimating the real evaluation.

Saving is calculated as follows.

For each value of speed Vf(t) and inclination lncl(t) of the car an approximate consumption value corresponds which takes into account of the running in standard conditions; if, for example, at 70 Km/h, with 5a gear and horizontal road, the virtual car consumption could be estimated as Q1 , in the same conditions, with uphill road and inclination of 5%, the consumption can be estimated as Q2, with Q2>Q1.

Therefore, in general, consumption data for all the possible pairs of values Vf, Incl being known, it is possible to calculate the consumption using the formula

Cf = i₀ ^Tu Kc(t) Q(t) dt

where:

Kc is the cost per litre of fuel and

Q(t) is the fuel consumption corresponding to the pair of parameters Vf(t), lncl(t).

Then it follows:

Re = Cf/Sp - Ce_s

According to a third method of measure, it is provided for the allocation of a category of average consumption of the equivalent fossil fuel car in every different condition of actual use and, in this connection, four categories of average consumption are assigned to the equivalent fossil fuel car:

Qf_s_m_urban = average fuel consumption of the equivalent fossil fuel car in urban driving,

Qf_s_m_extra_urban = average fuel consumption of equivalent fossil fuel car in on extra urban driving,

Qf_s_m_highway = average fuel consumption of equivalent fossil fuel car in highway driving,

Qf_s_m_mountain = average fuel consumption of equivalent fossil fuel car in mountain driving.

The meter 2 uses, moment by moment, the information of the sensors 15 (sensor of the transmission shaft of the motion to the wheels 12 of the car 1), 44 (sensor of the rotation shaft of the motor) and 35 (sensor of the fuel level) in order to determine at which of the four categories mentioned it is possible to bring back the car operating speed of the hybrid car during its use.

The meter 2 measures, every 10 minutes of operation of the hybrid car 1 , the following parameters:

- fuel consumption Qc,

- electricity consumption Ee,

- space Sp covered by the electric car 1 ,

- number of accelerations Nac and number of decelerations NDC of the car 1 ,

- course of the ratio Rtc between car speed and rotation speed of the engine shaft (depending on the type of use of the speed gear),

- inclination of car 1 through the inclinometer 46 built-in in the measurement device 2.

By using an appropriate table the 2 meter assigns, for any period of time of 10 minutes, one of four categories previously defined.

For example, if, in the time period concerned, there are a high consumption of fuel Qc and electricity Ee (Qc + Ee) and simultaneously a small space Sp covered, the most likely categories are Cf_s_m_urban and Cf_s_m_mountain and the choice between these two is further performed by the meter 2 by analyzing the values of Nac and Ndc, the trend of Rtc and the information of the inclinometer 46.

Thus, in this measure method the saving is defined as follows:

Rejot =∑₀ ^Nper(Qf(category)*Kc(period) - Ce(period)), where:

Nper = number of periods of 10 minutes concerned,

Qf (category) = average consumption of the equivalent fossil fuel car of the category defined in the period concerned,

Ce (period) = actual consumption of the hybrid car in the 10 minutes period concerned,

Kc (period) = cost per litre of fuel in the 10 minutes period concerned. It finally follows the specific saving:

Re = Rejot / Spjot,

considered in the total period of use in which the space Sp_tot in kilometres has been covered.

The fourth and final measure method provides for the measure of the instantaneous power of the hybrid car 1 in the real conditions of use and, through such a measure, the determination of the instantaneous speed of the virtual operation of the engine of the corresponding fossil fuel car.

In order to measure the power of the endothermic engine the following method is used.

In the attached figure 4, by way of example, the curves of consumption of specific fuel BSFC ("Brake Specific Fuel Consumption", in g/kWh) of a typical endothermic engine of hybrid car are shown (line A in figure indicates the limit above which the hybrid system tries to maintain the operation speed of the endothermic engine in order to minimize fuel consumption).

Curves B in figure 4 illustrate each a place of points related to a given specific consumption of the engine; a series of curves for specific consumptions BSFC from 230g/kWh to 600g/kWh are indicated in the example.

For each value of n (number of revolutions per minute or RPM of the engine), the consumption depends on the output torque of the engine (C in figure 4).

Remembering that the motor torque C is uniquely linked to the power Pm from the relation: ^{' ■'} .

Pm = C * n ^* 2TT/60,

it is known then the univocal link between fuel consumption BSFC and endothermic engine power Pm at a given number of revolutions n.

Thus, by measuring the instantaneous fuel flow and the number of revolutions, the measurement device 2, the characteristic curves of figure 4 of the engine in question being known, is able to calculate for each time t the value of the mechanical power Pm(t) supplied by the endothermic engine 37.

For example, if one measures in a given instant of time a rotation speed of 3000 rpm and a consumption of 250g/kWh, it is obtained from figure 4 that the engine is working with a torque of 60 Nm, corresponding to a supplied power of 18.85 kW.

The instantaneous power consumed by the electric motor is measured as the product of the voltage Vbatt of the battery 3 by the current Imel measured by the continuous current induction sensor 14:

Pe = Vbatt * Imel

In order to calculate the instantaneous power consumed by the hybrid 1 it is necessary to distinguish between the two existing types of hybrid car, that one with mixed traction and that one with pure electric traction.

In the first case (mixed traction and presence of an endothermic engine 37 coupled with an electric motor 9), the instantaneous power consumed by the hybrid car 1 is:

Pib(t) = Pm(t) + Pe(t),

while, in the second case (electric traction and presence of the electric motor 9 only), the instantaneous power consumed by the hybrid car 1 is:

Pib(t) = Pe(t),

since there is no direct contribution to the traction of the endothermic engine 37.

Once measured and calculated the instantaneous power of the hybrid car Pib(t) in the real conditions of use, it is possible to determine the virtual power of fossil car under the same conditions.

Indeed, the diagram (of the type shown in the appended figure 4) characteristic of the engine of the virtual car being available, it is possible to determine for each value of Pf(t) = Pib(t) and rotation speed of the engine n, the consumption value BSFC_f(t), in litres of fuel per kWh, of the virtual engine.

The integration of the calculated values allows to calculate the operating cost Cf of the equivalent virtual car in the real conditions of use:

Cf = Io^Tu Kc(t) BSFCJ(t) Pf(t) dt

with Kc (t) = cost per litre of fuel in the period concerned.

At the basis of this measure method there is the consideration that the use speed of the virtual engine is the same of the engine group of the hybrid car, that is in each operating speed the speed gear is set on the same ratios.

This assumption is necessary in order to use the latter method of saving measure and calculation, which provides the most accurate results in the estimation of the saving itself.

It finally follows then:

Re = Cf/Sp - Ce_s

It, therefore, results that in every operation moment, thanks to the measurement device 2,

- the total operation costs Ce and Cf,

- the specific costs per kilometric unit Ce_s and Cf_s,

- the kilometres covered,

- the saving Re in€/km

are available.

Indeed, the measurement device 2 is able to associate at any time a price with the fuel consumed in a given period, thus allowing to monetize the saving.

In particular, the measurement device 2 uses in the calculation the value Kc in order to allocate the right cost to fuel used; since this value is linked to the market fluctuations, it is necessary to update it in due time and the meter 2 is able to recover from the control unit 19 the updated value Kc, since, every time the electric car 1 is placed in a garage, the measurement device 2 communicates by radio with the control unit 19, from which it is able to receive the updated value of the fuel price Kc, which the unit 19 itself receives updated by a service centre, for example connected through a telecommunications network (through, for example, a GSM/GPRS modem integrated into the unit 19).

Moreover, whenever the car 1 is placed in a garage, the measurement device 2 communicates by radio to the control unit 19 the data on the consumptions and savings recorded in the last period of use; in this way/for every access to the garage (or the place where the unit 19 is placed), the unit 19 is updated on the consumptions and savings of the electric car 1 and the user of the electric car 1 can consult the consumptions and savings and the other parameters, such as Ce, Cf, Km, by using the portable terminal 18 or accessing the display of the control unit 19. With particular reference to the attached figure 3, which illustrates a block diagram of the measurement device according to the invention, the management of the assembly is given to the controller 28, provided with microprocessor, which performs the various functions required.

In particular, the controller 28 measures:

- the voltage of the traction battery 3 through the analogue circuit 21 which transforms the battery voltage (usually of high value (100-400 V)) bringing it to the proper value for the measure and properly filtering it; - the current supplied by the battery 3 to the electric car 1 through the magnetic induction proximity current sensor 14 (for instance at Hall effect) and the analogue amplifier circuit 22 which transforms the signal of the proximity sensor 14 into a correct value for the numerical processing by the microprocessor;

- the recharging current of the battery 3, through the magnetic induction proximity current sensor 13 (for instance at Hall effect) and the analogue amplifier circuit 23, which transforms the signal of the proximity sensor 3 into a correct value for the numerical processing by the microprocessor;

- the number of revolutions and speed of the wheel 12 of the car 1 , through the sensor 15 and the analogue conditioning circuit 24;

- the level of fuel in the tank 36 of the hybrid car 1 , through the level sensor 35 and conditioning circuits 41 (in particular, the level sensor 35 can conveniently read the output signal of the existing level meter and, since the level meters used are typically of potentiometric type, in such a case, the circuit 41 may consist of a high impedance voltage meter which connects with the yet existing potentiometer in the hybrid car 1);

- the fuel flow powering the engine of the hybrid car 1 , through the flow meter 38 and the conditioning circuits 42;

- the number of revolutions of the endothermic engine 37 of the car 1 , through the counter or encoder 44 and the conditioning circuit 45.

In addition, the controller 28 manages the radio transceiver 31 , provided with antenna 32, which, through a proper radio communication protocol, allows the exchange of messages between the measurement device 2, placed inside the electric car 1 , and the external devices 18, 19.

The controller 28 also reads, in continuous mode, the accelerometer or inclinometer 46 for determining the inclination of the meter 2 itself and, consequently, of the car , inside of which it is mounted, with respect to the horizontal plane.

Finally, the controller 28 is provided with a CAN serial interface 33 for the possible interfacing to a onboard computer of the electric car 1 , in such a way that, through such an interface 33, the measurement device 2 is able to exchange information useful to refine the performed measures.

In particular, the consumption data measured by the sensors 13, 14, 15, 35, 38 and 44 can be compared with similar data recorded by the onboard computer; alternatively, in a different embodiment, the sensors 15, 35 and 38 and circuits 24, 41 and 42, or any part thereof may be eventually omitted, in case data on distance, speed, level and/or flow of fuel can be got directly from the meter 2 through the CAN interface 33, by interrogating the onboard computer of the car 1.

The induction current sensors 13 and 14 are of non-contact type and can then be applied in a non-invasive way to the electric car 1 , since they can be applied as "amperometric clamps" on the power cables

(as shown in the attached figure 1).

Finally, the microprocessor controller 28 is supplied with a very high efficiency converter included in the power circuits 20, which provides full functionality of the controller 28 with an absorption of few tens of uA from the traction battery 3; in addition, the controller 28 manages all the measure, processing and communication functionalities through energy saving strategies, in order to minimize the power consumption of the measurement device 2 and make it insignificant, and is provided with a non-volatile memory that records the conversion tables with the characteristic data of the engines and in which the controller 28 stores the saving and consumption data calculated.

Therefore, it has been proved how the energy measurement device for electric traction vehicles, according to the present invention, allows the accurate measure of the energy saving of a hybrid electric car during operation.

The measure is fully performed because both the energy saved and the cost in money corresponding to such a saving are measured, and various methods are used to estimate the consumption of the virtual equivalent car.

Moreover, the proposed device can be easily (and not so invasively) integrated in every electric car 1 , since, thanks to the radio interface, can be integrated without affecting the aesthetics of the car 1 , while the measurement device 2 is produced very compact and can be housed in a container of small dimensions (for example 80x40x20 mm) and very light weight, which easily lends itself to be inserted into the engine room or elsewhere of the diver and passenger compartment.

The measurement device 2 is then produced with very low power consumption technology, so as to slightly affect the energy balance of the electric car 1.

The features of the energy measurement device for electric traction vehicles, which is the object of the present invention, as well as the advantages, are clear from the description just made.

It is, finally, clear that many other variations may be made to the measurement device in question, without departing from the principle of novelty intrinsic in the inventive idea expressed here, as it is clear that, in the practical implementation of the invention, materials, shapes and sizes of the illustrated details can be changed, as needed, and replaced with others technically equivalent.

Claims

1. Energy measurement device for electric traction vehicles which continuously analyzes, stores and makes available energy consumption and saving data of at least one hybrid electric traction or electric traction vehicle such as an electric car (1), compared to a corresponding reference vehicle powered by fossil fuels, said electric traction vehicle essentially comprising a traction battery (3) connected with at least one energy charger (4) and, through at least one power converter or inverter (5), at least one electric motor (9), characterized in that said device comprises a meter (2), provided with an electronic controller (28) with microprocessor, which provides for counting the consumed and/or saved energy starting from a measure of instantaneous power supplied by said battery (3) to said electric motor (9) and from a measure of energy supplied by said battery (3) and from a measure of energy injected into said battery (3), said power and said energy being measured by current sensors (13, 14, 30), as well as starting from a measure of instantaneous speed and distance covered by said vehicle which is made by means of a counter or an encoder (15).

2. Energy measurement device as claim 1 , characterized in that said meter (2) measures said consumption of the fossil fuel through a measurement (35) of a fuel level in a tank (36) of said vehicle, said meter (2) also measuring the instantaneous power delivered by an endothermic engine (37), which is associated with said electric motor (9), through a measurement of fuel flowing in a feeding pipe of said endothermic engine (37), said meter (2) also measuring the number of turns of said endothermic engine (37) through at least one pulse counter (44) which is fitted on a drive shaft (11) of said endothermic engine (37).

3. Energy measurement device as claim 1 , characterized in that said meter (2) is able to estimate savings in operating costs of said electric vehicle, compared with operating costs of a reference vehicle powered by fossil fuel under the same employment conditions, starting from an energy specific cost of said reference vehicle powered by fossil fuel and starting from an energy specific cost of said electric vehicle, said costs depending on fuel and electricity costs and on the amount of fuel and electricity consumed in a fixed period of time.

4. Energy measurement device as claim 3, characterized in that said energy specific cost of said electric vehicle is calculated starting from a measurement of electricity and from a measurement of fuel consumption and from a measurement of distance traveled by said electric vehicle.

5. Energy measurement device as claim 3, characterized in that said energy specific cost of said reference vehicle powered by fossil fuel is measured starting from an estimate of fuel consumption of said reference vehicle, which is made through a speed measure and an inclination measure, by means an accelerometer or inclinometer (46), of said reference vehicle, said speed and said inclination corresponding to at least one value of fuel consumption.

6. Energy measurement device as claim 3, characterized in that said energy specific cost of said reference vehicle powered by fossil fuel is measured starting from an assignment of a category of average consumption of said reference vehicle, depending on the fact that said reference vehicle is used on urban path, on extra-urban path, on highway path or on mountain path, and starting from a measure, for a fixed period of time, of fuel consumption, electricity consumption, distance traveled, number of accelerations, number of decelerations, status of the relationship between vehicle speed and speed of rotation of the drive shaft, vehicle inclination.

7. Energy measurement device as claim 3, characterized in that said energy specific cost of said reference vehicle powered by fossil fuel is measured starting from a measure of instantaneous power of said electric vehicle during the use and of instantaneous power supplied by an endothermic engine (37) of said reference vehicle, through measurement of an instantaneous flow of fuel and of the number of turns of said endothermic engine (37).

8. Energy measurement device as claim 1 , characterized in that said meter (2) provides, at each prefixed time intervals, the total operating costs, the specific costs per unit of distance traveled and the distance traveled by said electric vehicle and by said reference vehicle supplied with fossil fuels.

9. Energy measurement device as claim 1 , characterized in that said meter (2) is connected via radio to a control unit (19), from which said meter (2) receives the fuel prices and to which said meter (2) sends data about the consumption and savings recorded in a fixed period of time.

10. Energy measurement device as claim 1 , characterized in that said electronic controller (28) measures the voltage of said traction battery (3), the current delivered by said battery (3), the charging current of said battery (3), the number of turns and the wheel speed (12) of said electric vehicle, the fuel level in the tank (36) of said electric vehicle, the fuel flow supplying an endothermic engine (37) of said electric vehicle, the number of turns of said endothermic engine (37), the inclination of said meter (2) and of said electric vehicle with respect to a horizontal plane.

11. Energy measurement device as claim 1 , characterized in that said electronic controller (28) has a serial interface (33) for connection to an on-board computer of said electric vehicle.

12. Energy measurement device as claim 1 , characterized in that said device is integrated in the electric vehicle and said meter (2) is housed in the engine compartment and/or in other parts of the driver and passenger compartment of said electric vehicle.