FR2807979A1 - Hybrid electric vehicle with separate electric machines for priority regenerative braking, uses small braking generators driven by the wheels not driven by the drive motor - Google Patents

Abstract

The electric vehicle has driving wheels (10) and non-driving wheels (12). An electric motor (14) is connected to the driving wheels. A braking generator (20) is connected to each of the non-driving wheels, and is activated with priority over the drive motor during braking. Transient operation of the braking generators allows a nominal rating of a fifth or a sixth of the drive motor rating.

Description

 ELECTRIC OR HYBRID VEHICLE COMPRISING AT LEAST ONE PRIORITY BRAKE ELECTRIC MACHINE DESCRIPTION <B> TECHNICAL FIELD </ B> The invention relates to a vehicle with electric or hybrid propulsion, comprising at least one drive wheel that can be driven by a machine. electric traction, and at least one non-driving or free wheel.

The invention applies to any type of electric or hybrid vehicle and in particular to vehicles with two, three or four wheels.

Throughout the text, the term "hybrid vehicle" designates any vehicle whose propulsion can be provided, depending on the circumstances either by an electric propulsion system or another propulsion system such as a heat engine.

Furthermore, throughout the text 'expression' electrical machine 'means a reversible machine such as a synchronous or DC machine, which can operate as a motor during vehicle traction phases and as a generator during deceleration and braking phases. vehicle. This expression is used indifferently either to designate an electric machine alone, or to designate an electric machine associated with speed reduction mechanism.

The expression "electrical traction machine is used throughout the text to designate an electric machine mainly used to pull the vehicle.

The term "drive wheel" is used throughout. text, to designate a wheel driven by electric traction machine.

The expression "electric brake machine" or electric machine with priority braking "is used, throughout the text, to designate an electric machine mainly affected, or primarily, the braking of the vehicle.

Finally, the term "non-driving wheel" or "free wheel" is used, in the text set, to designate a wheel mechanically connected to an electric braking machine.

 State <B> of the </ B> technique On vehicles with electric or hybrid traction existing, the wheels are generally not all motor. Thus, an electric traction machine acts for example on each of the front wheels of a four-wheeled vehicle and on the rear wheel of a two-wheeled vehicle. This arrangement, similar to that found more frequently for vehicles with a heat engine, is due in particular to the desire to limit the mass of the vehicle and the cost of the power train.

Unlike heat engines, electrical machines can provide very high braking torque compared to their rated power. These machines are thus able to transform the mechanical energy of braking into electrical energy. However, the electrical energy recovered on electric or hybrid vehicles during braking is deliberately reduced, so as not to destabilize these vehicles during deceleration. Indeed, since the electric traction machines that equip these vehicles are not connected to all the wheels, a complete recovery of the electrical energy available during braking could translate into a loss of traction of the driving wheels on the roadway. . For this reason, only 10 to 20% of the available electrical energy is recovered.

In addition, some very particular electric or hybrid vehicles are equipped with an electric traction machine on each of their wheels. These vehicles include buses and limited-speed urban vehicles for flat terrain. In such vehicles, all the electric machines work synchronously in traction and during braking or slowing down of the vehicle. These electric machines are therefore dimensioned accordingly, which represents a sizeable mass associated with each of the drive wheels.

OBJECT OF THE INVENTION The object of the invention is precisely an electric or hybrid vehicle whose original design enables it to recover more than% of the electrical energy available during braking without destabilizing the vehicle and without increasing its mass too much. According to the invention, this result is obtained by means of a vehicle comprising at least one driving wheel, at least one non-driving wheel, and at least one electric traction machine mechanically connected to each driving wheel, said vehicle being characterized in it further comprises at least one electric braking machine mechanically connected to each non-driving wheel and having a nominal power substantially lower than that of the electric traction machine, and control means able to operate the electrical machine of regenerative braking, during a limited time, during a braking of the vehicle.

The electric braking machine acting on each non-driving wheel is a reduced bulk machine compared to the electric traction machine acting on each drive wheel. This electric braking machine operates as a generator, transiently, during braking of the vehicle. It then develops temporarily, a power comparable to that of electric traction machine. The braking is thus balanced and it becomes possible to recover more of the mechanical braking energy in the form of electric energy, without destabilizing the vehicle. In a preferred embodiment of the invention, first torque measuring means are provided for measuring a torque applied to the driving wheel and second torque measuring means are provided for measuring a torque applied to the non-driving wheel. The control means are then sensitive to signals delivered by said first and second torque measuring means to substantially equalize the torques applied to each of the wheels, during braking of the vehicle.

Advantageously, the control means are also sensitive to the signals delivered by the first torque measuring means for automatically operating the electric braking machine as a generator when the braking torque measured by the first torque measuring means exceeds a predetermined safety threshold. .

Alternatively, the control means also automatically operate each electrical braking machine generator when the braking torque measured by the first torque measuring means increases at a speed greater than a predetermined velocity threshold.

The first and second torque measuring means may comprise myyens for measuring the electric current respectively flowing through each electric traction machine and each electric braking machine.

The first and second torque measuring means can also be directly implanted on each driving wheel and each non-driving wheel, respectively. In this case, the measured torque takes into account the possible action of a mechanical brake.

Alternatively or in addition to the means for measuring torque, first speed measuring means can be provided for measuring the speed of rotation of each electric traction machine, second speed measuring means can be provided for measuring the rotational speed of each electric braking machine, and the control means are responsive to signals delivered by said first and second speed measuring means to substantially equalize the speeds of rotation of the electric traction and braking machines, when braking of the vehicle.

In the preferred embodiment of the invention, temperature measuring means are advantageously provided for measuring the temperature of each electric braking machine. The control means are then sensitive to a signal delivered by temperature measuring means for operating each engine braking machine during acceleration and traction phases of the vehicle and as a generator during vehicle deceleration phases, at a speed of controlled power function of the measured temperature. This feature allows the vehicle to benefit, at least temporarily and in case of need, the benefits provided by the AWD, that is to say by all the wheels of the vehicle are driving.

Preferably, each electric braking machine has a nominal power approximately 5 to 6 times lower than that of each electric traction machine.

Moreover, each electric braking machine and each electric traction machine have substantially equal maximum pairs.

In a particularly advantageous embodiment of the invention, each electric braking machine comprises a hollow or disc-shaped rotor facilitating the integration of said machine on the corresponding drive wheel.

Brief description of the drawings will now describe, by way of non-limiting example, a preferred embodiment of the invention, with reference to the accompanying drawings, in which Figure 1 is a top view schematically illustrating the propulsion members of the invention. braking of a four-wheeled electric vehicle according to the invention; and FIG. 2 is a curve which represents, as a function of time (in seconds), the variations in the power (in watts) of an electric traction machine and an electric braking machine used on the vehicle of the figure 1.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION FIG. 1 very schematically shows a four-wheeled motor vehicle, electrically propelled, produced in accordance with the invention. Such a four-wheeled electric vehicle is only one example of possible application and should not be considered as limiting the scope of the invention. In particular, it applies to any vehicle with two or more wheels, comprising at least one driving wheel and at least one non-driving wheel. Furthermore, the invention can be used both on a fully electric propulsion vehicle or on a hybrid vehicle, the propulsion of which can be provided as appropriate by either an electric machine or a heat engine.

In the embodiment of the invention illustrated by way of example in FIG. 1, the vehicle comprises two rear-wheel-drive wheels 10 and two non-driving front wheels 12. The vehicle also comprises two electric traction machines 14, each of which is mechanically connected to the rear wheel drive 10. The electric traction machines 14 are dimensioned so as to propel the vehicle at a determined speed. Each of the electric traction machines 14 weighs, for example, approximately 30 kilograms and comprises an electric motor 16 and a reduction mechanism 18. The electric traction machines 14 comprise standard electric motors 16, which work permanently during the traction phases. and during the braking phases of the vehicle.

By way of non-limiting example, the speed of the vehicle can be set at about 130 km / h for a vehicle whose mass is about 1000 kilos. Each of the electric traction machines 14 then has, in steady state, a nominal power of about 25,000 watts. However, they can temporarily deliver a maximum power of 45,000 watts for about 25 seconds. The maximum torque delivered by each of the electric traction machines 14 is, for example, about 00 Nm.

According to the invention, the four-wheeled vehicle illustrated in Figure 1 further comprises two electric braking machines 20 each of which is mechanically connected to the non-driving front wheels 12 of the vehicle. The electrical braking machines 20 are primarily designed to operate as a generator, for a limited time during braking of the vehicle. They have a power rating substantially lower than that of electric traction machines 14, so that their mass also much lower than that of these machines 14. In general, the nominal power of each of the electrical braking machines 20 is about 5 to 6 times lower than that of electric traction machines 14.

By way of non-limiting illustration in the case of the example cited above, where each electric traction machine 14 has a nominal power of approximately 25,000 watts and weighs approximately 30 kilos, each of the electric braking machines 20 has a nominal power of about 5000 watts and weighs less than 7.5 pounds. However, the electric brake machines 20 can deliver a maximum power of 28,000 watts for about 40 seconds. They deliver a high maximum torque compared to their power. This maximum torque is substantially equal to that which is provided by the electric traction machines 14, that is to say about 3000 Nm in the ciphered example mentioned above.

In practice, each of the electric brake machines 20 comprises an electric motor and a reduction mechanism (not shown). The electric motor may be a permanent magnet synchronous motor, a brushless DC motor, a DC rotor motor with a disk-shaped rotor, or an asynchronous motor. Each of the braking electrical machines 20 advantageously comprises a disk-shaped rotor or hollow rotor for easily inserting the machine inside or against the corresponding non-driving front wheel 12. Moreover, this type of machine makes it possible to obtain better couples. In addition, the machines 20 are designed to be able to withstand and rapidly evacuate high temperature rises.

FIG. 2 shows, as a function of time t (in seconds), the evolution curves of the respective power P (in watts) of the electric traction 14 and brake 20 machines. More precisely, the curve C1 represents the evolution of the power of each of the electric traction machines 14 and the curve C2 represents the evolution of the power of each of the electric braking machines 20. The upper half of FIG. 2 corresponds to the case where the machines operate as a motor and the lower half of Figure 2 in case the machines operate as generators. The preferential use zone of the electric braking machines 20, hatched in FIG. 2, corresponds to the period of time situated between the instant 0 and the instant t1. This instant t1 is substantially equal to 40 seconds in the encrypted example given above. The preferred area of use of each of the electric traction machines 14 is on the contrary beyond this time t1.

The vehicle shown schematically in Figure 1 further comprises control means 26 constituted by an electronic circuit. The electric traction machines 14 and the electrical braking machines 20 are connected to the control means. These control means 26 are also connected to the vehicle control members such as the brake and the accelerator (not shown).

In general, the electric traction machines 14 connected to the driving wheels 10 are permanently actuated by the control means 26, both during the vehicle traction phases and during the braking phases.

As regards the electric braking machines, they are actuated transiently by the control means 26, so as to operate primarily as generators for a limited time during braking phases of the vehicle. Advantageously, the electric braking machines 20 are also used in motors for a limited time during an acceleration of the vehicle. They can also be used, at reduced power, either in motors in the traction phases of the vehicle, or in generators in the slowdown phases of the vehicle.

Apart from the uses of electric braking machines 20 in generators during the braking phases of the vehicle, which have priority, all the other uses of these machines are voluntarily limited. Indeed, because of their small size, these machines accumulate a lot of heat punctually, for example in the case of a powerful braking. Then you have to give them time to cool down. Outside a braking phase, the available power is a function of the temperature of the components of the electrical braking machines 20, and mainly that of the electrical conductors (coils).

For this purpose, a temperature sensor 28 is associated with each of the electrical braking machines 20. Each of the temperature sensors 28 delivers a signal representative of the temperature of the components of the corresponding electrical braking machine 20, and in particular of the temperature of the windings of this machine. This signal is transmitted to the control means 26, as schematically illustrated in FIG.

From the measured temperature the sensors 28, the control means 26 calculate the available power on the electric braking machines 20, to perform specific acceleration or for permanent operation. In other words, the machines are controlled by the temperature. This control makes it possible to operate the electric braking machines 20, with controlled power, in motors or generators depending on whether the vehicle is in the traction phase or the deceleration phase. In all the temporary actuation of electric braking machines in generators at full power is always possible, during a braking phase of the vehicle.

Advantageously and as also schematically illustrated surfila Figure 1, the vehicle according to the invention is also equipped with first means 30 for measuring torque, able to measure the torque applied to each of the rear wheels 10 and second means 32 measuring torque, able to measure the torque applied to each of the non-driving front wheels 12.

In a variant embodiment, not shown, the first and second torque measuring means are replaced or supplemented by first and second means for measuring rotational speeds of the electric traction and braking machines. The control means then receive the signals. delivered by said speed measuring means and control the motors 14 and 20 as a function of the difference between these signals, so as to substantially equalize the speeds of the machines 14 and 20, during braking of the vehicle.

In the embodiment illustrated in FIG. 1, the first and second means 30, 32 for measuring torque comprise current measuring means capable of measuring electrical current respectively passing through the windings of the electric traction and braking machines 20.

In an embodiment not shown, the first and second means 30, 32 of torque measurement are located directly on each of the driving wheels 10 and non-driving respectively. They then take into account both the torque exerted by the electric machines 14 and corresponding and the torque exerted by the conventional brakes (not shown) which also equip each of the wheels 10 and 12 of the vehicle.

The torque measuring means 30 and 32 deliver signals which are transmitted to the control means 26, as schematically illustrated in FIG.

The information thus transmitted by the first torque measurement means 30 to the control means 26 is used, during a slowing down phase of the vehicle, to automatically control the implementation of the electrical braking machines 20 either when the torque exerted on the driving wheels 10 exceed a predetermined safety threshold, ie when the braking torque applied to the drive wheels 10 increases at a speed greater than a predetermined velocity threshold.

The safety threshold of the torque applied to the drive wheels 10 corresponds to a threshold beyond which the threshold of adhesion of these wheels on the. soil may be exceeded.

The velocity threshold limiting the rate of increase of the braking torque applied to the driving wheels 10 corresponds to a risk of skidding of these wheels.

In either case, the proposed system makes it possible to slow down the vehicle rapidly by braking the non-driving wheels 12. Simultaneously, satisfactory traction conditions of the drive wheels 10 can be restored.

Furthermore, the torques measured by the torque measuring means 30 and 32 on the electric traction machines 14 and on the electric braking machines 20 allow the control means 26 to manage the power shift between the driving wheels 10 and the driving wheels 10. non-drive wheels 12, especially during braking. In other words, the electric traction 14 and brake 20 machines are continuously controlled so as to substantially equal the braking torques applied to the different wheels during a braking phase of the vehicle. It is thus possible to recover more than 50% and up to 90% of available braking energy, without destabilizing the vehicle without significantly increasing its weight.

The arrangement which has just been described makes it possible to produce a four-wheeled vehicle whose rear wheels are driving and the front wheels non-driving, without compromising the handling of this vehicle. The mechanical design of the vehicle. can be very simplified. Indeed, the gimbals are removed and the steering equipment and the body are simplified. This also allows a better seal of the vehicle to dust, cold and noise. Indeed, all the electrical machines are mounted outside the box, under the trunk for the traction machines and in the front wheels for the braking machines. Only electrical conductors, used to transmit power from the inside to the outside, pass through the box. The overall design of the vehicle is thus greatly simplified.

In case of very high braking power, all available electrical energy is not necessarily recovered in the batteries of the vehicle. Indeed, to protect them, some of this electrical energy can / be removed in resistors. Furthermore, the differential function can be provided by the control means 26, electronically, according to techniques known to those skilled in the field of electric propulsion vehicles.

As already mentioned, traditional mechanical brakes remain useful for heavy braking as well as for the complete stopping of the vehicle. However, the significant recovery of the braking energy in the electrical machinery equipping the vehicle, obtained by the invention, can greatly reduce the wear of these traditional brakes.

The operation of the vehicle according to the invention will now be briefly described in four particular uses which are displacement in urban cycle, displacement in road and highway cycle, displacement on slippery ground and braking on steep slope.

The movement of a vehicle in the urban cycle is characterized by frequent acceleration and frequent braking. The electric braking machines 20 then participate actively in the acceleration and braking of the vehicle, as previously described.

When the vehicle is traveling on a road on a highway, accelerations and braking are few. On the contrary, the vehicle operates mainly in traction at a substantially constant speed. The relatively high speed of the vehicle thus ensures a good cooling of the electric machines and these are not heated much because of the scarcity of braking. The permanent power that can be used in traction of the electric braking machines 20 can therefore be relatively large. This traction power provided by the electric braking machines 20 is then adjusted by the control means 26 so as to maintain the temperature of the electrical machines 20 below a maximum permissible temperature threshold for these machines. The performance of the vehicle is increased.

When the vehicle moves on a slippery ground, the fact that all the wheels of the vehicle become motor is only really interesting when there is a speed imbalance between the driving wheels 10 and the non-driving wheels 12. normal conditions of adhesion, the speeds of these wheels are normally the same. If there is a difference in speed between the wheels, it means * that some wheels are spinning. In this case, that is to say for example if there is a difference in speed between the driving wheels 10 and non-driving 12 greater than three rev / min, it becomes useful to operate the electric braking machines 20 motor in order to provide the non-drive wheels 12 with a torque as close as possible to that which is present on the drive wheels 10.

However, in the absence of such a speed imbalance between the driving and driving wheels, the electric braking machines 20 advantageously operate at low power in traction or in slowdown, permanently, in order to apply this small power to the non-driving wheels. 12, which significantly improves the road holding. The non-driving wheels 12 are no longer, in fact, a load for the drive wheels 10. Thus, the non-driving wheels are no longer a brake, for example when driving in the snow or in a puddle of water. so that vehicle handling is improved.

When a vehicle is traveling downhill on a steep slope, the electrical braking machines 20 are not sized to provide the prolonged and relatively intense slowdowns imposed by these conditions. The electric traction machines 14 then provide most of the slowing down of the vehicle (for example about 90% of the power to be dissipated). This allows the electric brake machines 20 to cool sufficiently to allow more powerful braking and short-term, if necessary. This limitation of the power dissipated in electrical braking machines 20 is ensured by virtue of the temperature measurements made by the sensors 28, under the action of the control means 26 which permanently limit the heating of the electric braking machines 20, outside the braking periods.

Because the slowing down of the vehicle is mainly ensured by the drive wheels 10, the high torque applied to these wheels induces a risk of skidding thereof. Therefore, as already described above, the control means 26 automatically trigger / the implementation of electrical braking machines 20 generators or when the torque dissipated on the drive wheels 10 exceeds a predetermined safety threshold when the rate of increase of this torque exceeds a predetermined velocity threshold. It should be noted that the second of these thresholds must generally make it possible to trigger the braking of the non-driving wheels 12 by the electric braking machines 20 more rapidly than the safety threshold. Furthermore, the latter threshold is programmed in the control means 26, or selected and passed by the driver according to the state of the road.

In the example given above, corresponding to a vehicle of about 1400 kg (including passengers) equipped with four wheels of 20 cm radius, two electric traction machines of 2500 W -and 3000 Nm, weighing about 30 kg each and two electrical braking machines of 5000 W and 3000 Nm, each weighing less than 7.5 kg, it is calculated that the time required for braking is 9.3 seconds, if the vehicle is launched at 50 km / h. This time is 30 seconds if the vehicle is traveling at 90 km / h. Conventional brakes should therefore be used for faster braking and for complete stopping.

Based on electrical machines having the aforementioned characteristics, an overall nominal power of 60 kW can be obtained permanently, on a motorway cycle. In addition, a maximum power of 112 kW, balanced on all four wheels, can be obtained for 40 seconds. Finally, a maximum power of 146 kW (90 kW front and 56 kW rear) can be obtained for 25 seconds.

In a complementary manner, the driver of the vehicle advantageously has a warning light or an alarm system making it possible to display a message in the event of overheating of the electrical braking machines 20 or in the event of exceeding the safety threshold of the vehicle. torque applied to the drive wheels 10 of the vehicle. This message prompts the driver to reduce speed or use conventional brakes.

Safety can also be provided to prevent any acceleration of the vehicle if the temperature of the electrical braking machines 20 reaches a predetermined temperature threshold.

The foregoing description has been made with reference to a four-wheeled vehicle. However, as already indicated, the invention is not limited to this type of vehicle and also relates, for example, a scooter-style two-wheeled vehicle.

In this case, for a vehicle weighing 100 kilos with a maximum speed of 45 is equipped the rear wheel of an electric traction machine having for example a nominal power of about 2500 watts and able to provide a power of up to 4500 watts for about 25 seconds. The weight of this electric traction machine is about 8.5 kilos.

The front wheel of the vehicle is then equipped with an electric brake machine having for example a nominal power of 400 watts, up to 2500 watts for about seconds. The weight of such a machine is less than 2 kilos. This machine advantageously has the form of a disc-shaped motor integrated on the front fork in the axis of rotation of the wheel. In the case of an asynchronous motor or a DC motor, the differential function is not necessary. In the case of a synchronous motor or a brushless DC motor, this function is performed by electronic control means, according to techniques well known to those skilled in the field of electric vehicles.

The maximum torque of each of the two electrical machines is equivalent and equal to approximately 300 Nm. For a wheel with a radius of 20 cm, the maximum braking force is therefore 150 kg / wheel. The braking power of the engines is limited to 00 watts for the front wheel and 4500 watts for the rear wheel, totaling 7000 watts.

The kinetic energy accumulated by a 100 kg scooter supporting a 70 kg passenger, launched at 30 km / h, is 59,000 joules. The time required for braking is therefore about 8.5 seconds. The time required for braking is proportional to the square of the speed, it will take about 19 seconds to brake the scooter to 45 km / h. Faster braking and complete stopping can be achieved by using conventional brakes together.

Of course, the various examples should not be considered as limiting the scope of the invention. Thus, the invention applies, for example, to a three-wheeled vehicle and regardless of the location of the drive and non-drive wheels on the vehicle.

Claims (1)

A vehicle comprising at least one driving wheel (10), at least one non-driving wheel (12), and at least one electric traction machine (14) mechanically connected to each driving wheel (10), said vehicle being characterized in that it further comprises at least one electric braking machine (20) mechanically connected to each non-driving wheel (12 and having a nominal power substantially lower than that of the electric traction machine (14, and control means (26) adapted to operate the electric braking machine (20) as a generator for a limited period of time during braking of the vehicle A vehicle according to claim 1, wherein first torque measuring means (30) are provided for measuring a torque applied to each driving wheel (10), second torque measuring means (are provided for measuring a torque applied to each non-driving wheel (12), and the control means 6) are sensitive to signals delivered by said first and second torque measuring means (3, 32) for substantially equalizing the torques applied to the driving and non-driving wheels (10, 12) during braking of the vehicle. 3. Vehicle according to claim 2, wherein the control means (26) are responsive to the signals delivered by the first torque measuring means (30) for automatically operating each electric braking machine (20) as a generator when the torque braking rate measured by the first torque measuring means exceeds a predetermined safety threshold. 4. Vehicle according to any one of claims 2 and 3, wherein control means (26) are responsive to the signals delivered by the first torque measuring means) for automatically operating each electric braking machine (20) as a generator when the braking torque measured by the first torque measuring means (30) increases at a speed greater than a predetermined velocity threshold. The vehicle according to any one of claims 2 to 4, wherein the first and second torque measuring means (30, 32) comprise means for measuring the electrical current flowing through each electric traction machine (14) and each electric braking machine (20), respectively. A vehicle according to any one of claims 2 to 4, wherein first and second torque measuring means (30,32) are located on each drive wheel (10 and each non-driving wheel (12), respectively. A vehicle according to any one of the preceding claims, wherein first speed measuring means are provided for measuring the rotational speed of each electric traction machine (14), second speed measuring means are provided for measuring the rotational speed of each electric brake machine (20), and the control means (26) are responsive to signals delivered by said first and second speed measuring means to substantially equalize the rotational speeds of the electrical machines of traction (14) and braking (20), when braking the vehicle 8. A vehicle according to any one of the preceding claims, wherein means temperature measuring means (28) are provided for measuring the temperature of each electric brake machine (20), the control means (26) being responsive to a signal delivered by said temperature measuring means (28) for operating each braking machine (20) during engine operation. .phases of acceleration and traction vehicle and generator during slowdown phases of the vehicle, a controlled power function of the measured temperature. 9. Vehicle according to any one of the preceding claims, wherein each electric braking machine (20) has nominal power approximately 5 to 6 times lower than that of each electric traction machine (14). 10. Vehicle according to any one of the preceding claims, wherein each electric braking machine (20) each electric traction machine (14) have substantially equal maximum torque. Vehicle according to any one of the preceding claims, wherein each electric braking machine (20) comprises a hollow or disc-shaped rotor.