Electric power system of a vehicle with electric propulsion

An electric power system of a vehicle with electric propulsion having: an electric machine; a storage system provided with two chemical battery packs electrically separated from each other; an electronic DC/AC power converter, which exchanges electric energy with the storage system and controls the electric machine; a pair of electronic DC/DC power converters, each of which increases the voltage and has a low-voltage side, which is electrically connected only and exclusively to a corresponding chemical battery, and a high-voltage side, which is connected to the electronic DC/AC power converter in parallel to the high-voltage side of the other electronic DC/DC power converter; and a common container, which houses the storage system and the electronic power converters therein.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 to Italian Patent Application No. BO2014A000336, filed Jun. 17, 2014, the entirety of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an electric power system of a vehicle with electric propulsion.

The present invention is advantageously applied to a road vehicle with hybrid propulsion, to which explicit reference will be made in the following description without therefore losing in generality.

BACKGROUND OF THE INVENTION

A hybrid vehicle comprises an internal combustion thermal engine, which transmits torque to the driving wheels by means of a transmission provided with a gearbox, and at least one electric machine which is electrically connected to an electric storage system and mechanically connected to the driving wheels.

The electric power system of a hybrid vehicle comprises a storage device provided with a chemical battery pack and a two-way electronic DC/AC power converter, which is connected to the storage device on the DC side and is connected to the electric machine on the AC side, and has the function of controlling the electric machine itself.

The chemical batteries used in current road vehicles with hybrid propulsion may have high specific storable electric energy (i.e. per unit of mass and/or volume) and low specific deliverable electric power (i.e. per unit of mass and/or volume), and thus be adapted to meet the needs of a long trip traveled at constant speed (and, especially, with limited accelerations/decelerations). Alternatively, the chemical batteries used in current road vehicles with hybrid propulsion may have low specific storable electric energy (i.e. per unit of mass and/or volume) and high specific deliverable electric power (i.e. per unit of mass and/or volume), and thus be adapted to meet the needs of a short trip traveled at high speed (and, especially, with fast accelerations/decelerations).

In order to attempt to obtain an acceptable trade-off between range needs (for which chemical batteries which have high specific electric energy are required) and performance needs (for which chemical batteries which have high specific electric power are required), it has been attempted to manufacture trade-off chemical batteries which have intermediate features between the two extremes; however, it has been observed that such trade-off chemical batteries are a “second-rate” trade-off, i.e. the significant reduction of specific electric energy does not correspond to an equally significant increase of specific electric power, and vice versa.

In order to attempt to obtain an acceptable trade-off between range needs (for which chemical batteries which have high specific electric energy are required) and performance needs (for which chemical batteries which have high specific power are required), it has also been suggested to include both chemical batteries which have high specific electric energy and chemical batteries which have high specific energy in the storage system. However, the overall results (in terms of range and performance) and in particular the operative lifespan of the chemical batteries have been found not to be entirely satisfactory because the “final result” was in some way inferior to the sum of the single parts.

Italian patent application BO2012A000315 describes an electric power system of a vehicle with electric propulsion; the electric power system has: a pair of connected electric machines; a storage system comprising two chemical battery packs electrically separated from each other; a pair of electronic DC/AC power converters, each of which exchanges electric energy with the storage system and controls a corresponding electric machine; and a pair of electronic DC/DC power converters, each of which increases the voltage and has a low-voltage side, which is electrically connected only and exclusively to a corresponding chemical battery pack, and a high-voltage side, which is connected to both electronic DC/AC power converters in parallel to the high-voltage side of the other electronic DC/DC power converter. However, the electric power system described in Italian patent application BO2012A000315 has relatively high dimensions.

Patent application EP2117106A1 describes an electric power system of a vehicle with electric propulsion; the electric power system comprises:

two electric machines MG1and MG2;

a storage system comprising two chemical battery packs10and20electrically separated from each other;

a first electronic DC/AC power converter INV1, which exchanges electric energy with the storage system and controls a first electric machine MG1;

a second electronic DC/AC power converter INV2, which exchanges electric energy with the storage system and controls a second electric machine MG2;

a first electronic DC/DC power converter18, which increases the voltage and has a low-voltage side, which is electrically connected only and exclusively to a first chemical battery pack10, and a high-voltage side, which is connected to both electronic DC/AC power converters INV1, INV2; and

a second electronic DC/DC power converter28, which increases the voltage and has a low-voltage side, which is electrically connected only and exclusively to a second chemical battery pack20, and a high-voltage side, which is connected to both electronic DC/AC power converters INV1, INV2in parallel to the high-voltage side of the first electronic DC/DC power converter CONV1.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide an electric power system for a vehicle with electric propulsion, which is free from the above-described drawbacks while being easy and cost-effective to be manufactured.

According to the present invention, an electric power system for a vehicle with electrical propulsion is provided as claimed in the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

InFIG. 1, reference numeral1indicates as a whole a road vehicle with hybrid propulsion provided with two front wheels2and two rear driving wheels3, which receive torque from a hybrid propulsion system4.

The hybrid propulsion system4comprises a thermal internal combustion engine5arranged in front position and provided with a drive shaft6, a transmission7which transmits the torque generated by the internal combustion engine5to the rear driving wheels3, and two electric machines8and9which are mechanically connected to transmission7and are reversible (i.e. may work as electric motor by drawing electric energy and generating mechanical torque, and as electric generator by drawing mechanical energy and generating electric energy). Alternatively, one of the electric machines8and9(or a further third electric machine) could be mechanically connected to a turbocharger of the internal combustion engine5instead of being mechanically connected to transmission7.

Transmission7comprises a propeller shaft10, which on one end is angularly integral with the drive shaft6and on the other end is mechanically connected to a gearbox11, which is arranged in rear position and transmits motion to the rear driving wheels3by means of two axle shafts12, which receive motion from a differential13.

Both electric machines8and9are mechanically connected to gearbox11. The electric machine8is controlled by an electronic DC/AC power converter14(i.e. an inverter) and the electric machine9is driven by an electronic DC/AC power converter15(i.e. an inverter). Both electronic power converters14and15are electrically connected to an electric energy storage system16provided with chemical batteries.

As shown inFIG. 2, the storage system16comprises two distinct chemical battery packs17and18, each of which consists of a plurality of chemical batteries connected to one another in series and/or in parallel; each chemical battery comprises respective electrochemical cells, which are adapted to convert the stored chemical energy into electric energy and vice versa. The chemical batteries of the two chemical battery packs17and18have different electric energy storage and delivery features: in particular, the chemical batteries of the chemical battery pack17have a higher specific storable electric energy (i.e. per unit of mass and/or volume) and a lower specific deliverable electric power (i.e. per unit of mass and/or volume) than the chemical batteries of the battery pack18.

Therefore, the chemical batteries of battery pack17are adapted to meet the needs of a long trip traveled at moderate speed (and, especially, with limited accelerations/decelerations) because they have the advantage of being able to provide a high amount of specific electric energy (i.e. per unit of mass and/or volume) but have the disadvantage of not being able to deliver a very high specific electric power (i.e. per unit of mass and/or volume), and thus allow the road vehicle1to travel considerable distances in electric mode (high range), but not to allow the road vehicle1to achieve high dynamic performance in electric mode. Instead, the chemical batteries of the battery pack18are adapted to meet the needs of a short trip traveled at high speed (and, especially, with high accelerations/decelerations) because they have the advantage of being able to deliver a very high specific electric power (i.e. per unit of mass and/or volume) but on the contrary are not able to provide a high amount of specific electric energy (i.e. per unit of mass and/or volume), and thus allow the road vehicle1to achieve high dynamic performance in electric mode, but do not allow vehicle1to travel considerable distances in electric mode. The proportion between the two chemical battery packs17and18is chosen during the step of designing as a function of the desired range/performance ratio in electric mode.

As shown inFIG. 2, the road vehicle1is provided with an electric power system20, which comprises the storage system16provided with two chemical battery packs17and18, the two electronic power converters14and15which control the two electric machines8and9, and two electronic DC/DC power converters21and22(e.g. of the “buck-boost” type) which are interposed between the chemical battery packs17and18of the storage system16and the two electronic power converters14and15and have the function of increasing the voltage. The nominal voltage of the chemical battery pack17is 380 Volt (obviously, it could also be different, according to different alternative embodiments), the nominal voltage of the chemical battery pack18is 200 Volt (obviously, it could also be different according to alternative embodiments), while the nominal voltage of the electronic power converters14and15is 700 Volt (obviously, it could also be different according to alternative embodiments); therefore, the function of the electronic power converters21and22is to increase the voltage supplied by the chemical battery packs17and18to the values required by the electronic power converters14and15(it is apparent that the two electronic power converters14and15have different nominal increase ratios, because they receive differentiated electric input voltages and supply the same electric output voltage).

The electronic power converter21has a low-voltage side, which is connected only to the chemical battery pack17(i.e. is completely isolated from the chemical battery pack18) and a high-voltage side, which is connected in parallel to a high-voltage side of the electronic power converter22. Similarly, the electronic power converter22has a low-voltage side which is connected only to the chemical battery pack18(i.e. is completely isolated from the chemical battery pack17) and a high-voltage side, which is connected in parallel to a high-voltage side of the electronic power converter21. The two electronic power converters14and15are both connected in parallel to the high-voltage sides of the two electronic power converters21and22(i.e. the DC sides of the two electronic power converters14and15are connected to each other in parallel). Thereby, electronic power converter21on low-voltage side exchanges electric energy only with the chemical battery pack17(i.e. not with the chemical battery pack18) and on high-voltage side exchanges electric energy with both electronic power converters14and15; similarly, electronic power converter22on low-voltage side exchanges electric energy only with the chemical battery pack18(i.e. not with the chemical battery pack17) and on high-voltage side exchanges electric energy with both electronic power converters14and15.

It is worth noting that the two electronic power converters21and22could be integrated in a single physical unit, i.e. could both be arranged inside a single container, and could thus have auxiliary components in common. Furthermore, it is worth noting that electronic power converter21must be optimized as a function of the features of the chemical battery pack17(i.e. relatively high energy and low power), while electronic power converter22must be optimized as a function of the chemical battery pack18(i.e. relatively low energy and high power).

Each electronic power converter21or22is adapted to provide always the same constant voltage on high-voltage side (i.e. towards the electronic power converters14and15) independently from the voltage present on low-voltage side (i.e. at the terminals of the corresponding the chemical battery pack17or18). In other words, the transformation ratio of each electronic power converter21or22is continuously varied to maintain the voltage on high-voltage side always constant and equal to a nominal value. Furthermore, each electronic power converter21or22is adapted to filter (i.e. block, compensate) the high-frequency current/voltage oscillations generated by the electronic DC/AC power converters14and15.

The electric power system20comprises an electronic DC/DC power converter23which supplies a low-voltage section24(having a nominal voltage of 12 Volt) to which part of the auxiliary services of the road vehicle1are connected; furthermore, the electric power system20comprises an electronic DC/DC power converter25which supplies a low-voltage section26(having a nominal voltage of 48 Volt) to which the remaining part of the auxiliary services of the road vehicle1are connected. In other words, the auxiliary services of the road vehicle1which require electric power supply are divided between low-voltage sections24and26; for example, the auxiliary services of the road vehicle1which require electric power supply may comprise an electric starter motor of the thermal engine5, an electric motor which actuates a pump of a power steering system, an electric motor which actuates a circulation pump of a cooling system of the thermal engine5and/or of the electric machines8and9, a radio, a lighting and indicating system etc. The electronic power converters23and25are normally of the one-way type (i.e. capable of transferring electric energy only towards the low-voltage sections24and26and not vice versa). The low-energy consumption electric/electronic devices (radio, satellite navigator, interior passenger compartment lighting, etc.) are generally connected to the low-voltage section24, while the electric/electronic devices with higher energy consumption (pumps, light clusters etc.) are connected to the low-voltage section26. The low-voltage section24is generally provided with a buffer chemical battery19(obviously operated at 12 Volt and having a modest energy capacity compared to the chemical battery packs17and18), which is arranged downstream of the electronic power converter23, while the low-voltage section26is free from electric energy storage systems provided with chemical batteries (i.e. does not have any chemical battery) and receives electric energy only through the electronic power converter25.

In the embodiment shown inFIG. 2, the electronic power converters23and25are connected only to the chemical battery pack17and to the corresponding electronic power converter21(i.e. receive electric energy from the chemical battery pack17and/or from the electronic power converter21).

The electric power system20comprises a DC recharging socket27, which is connected only to the chemical battery pack17by means of the interposition of an electronically controlled switch28; the switch28is normally open and is closed only when the recharging socket27is connected to a recharging circuit. Obviously, the chemical battery pack17is recharged directly by using the recharging socket27, but the chemical battery pack18can also be recharged indirectly by using the electronic power converters21and22(i.e. the electric energy is converted firstly by the electronic power converter21and then by the electronic power converter22to reach the chemical battery pack18starting from the recharging socket27).

The electronic power system20comprises an AC recharging socket29which is connected to the electronic DC/AC power converter14(but the recharging socket29could be connected indifferently also to electronic DC/AC power converter15) so as to use the electronic DC/AC power converter14to convert the AC coming from the recharging socket29into DC which through the electronic power converters21and22reaches the chemical battery packs17and18to recharge the chemical battery packs17and18themselves.

The electronic power system20comprises a common container31which houses the accumulation system16(i.e. both chemical battery packs17and18) and all the power electronics, i.e. the electronic power converters14,15,21,22,23and25therein. In other words, the storage system16(the chemical battery packs17and18) and all the power electronics (the electronic power converters14,15,21,22,23and25) is housed in the same common container31. According to a preferred (but not binding) embodiment, the buffer chemical battery19of the low-voltage section24is housed inside the common container31.

As shown inFIG. 3, a lubrication system32of the electric machines8and9is provided to feed an adequate flow of lubrication oil to the electric machines8and9themselves. The lubrication system32is provided with a lubrication circuit comprising a tank33for the lubricant oil, a radiator34for cooling the lubricant oil, and a circulation pump35, which is normally electrically actuated (i.e. actuated by an electric motor in DC at low voltage, preferably having a nominal voltage of 48 Volt, i.e. belonging to the low-voltage section26). In the embodiment shown inFIG. 3, the two electric machines8and9are connected in parallel in the lubrication circuit of the lubrication system32, but alternatively the two electric machines8and9could be connected in series in the lubrication circuit.

As shown inFIG. 4, a cooling system36, which uses a compression refrigeration cycle for cooling all the components of the electric power system20(i.e. the storage system16, the electronic power converters14,15,21,22,23and25, and the electric machines8and9) is provided. The cooling system36comprises a refrigeration circuit37, which implements a compression refrigeration cycle, contains a refrigeration fluid (e.g. HCFC or hydrochlorofluorocarbons) and comprises, in turn, a compressor38, a condenser39, an expansion valve40(or lamination valve), and an evaporator41.

According to a preferred embodiment, compressor38is of the rotary type and is electrically actuated (i.e. is actuated in DC by an electric motor); the electric motor of compressor38is preferably supplied directly by the chemical battery pack17(as shown inFIG. 2). Alternatively, compressor38is operated by the shaft of the electric machine8or by the shaft of the electric machine9; according to a preferred embodiment, an electrically actuated release device is interposed between the compressor38of the cooling system36and the shaft of the electric machine8or9which is controlled to connect and disconnect compressor38from/to the shaft of the electric machine8or9in a selective manner so as not to feed compressor38when the electric components do not need to be cooled.

An air radiator (known and not shown) is thermally coupled to condenser39which is struck by a flow of air when vehicle1is moving so as to disperse the heat present in condenser39into the environment; according to a preferred embodiment, such a radiator is also provided with a fan controlled by a thermostat to achieve a forced cooling of the radiator itself if required.

Furthermore, the cooling system36comprises a cooling circuit42, which contains a coolant fluid (typically water mixed with an antifreeze additive) and comprises, in turn, a heat exchanger43thermally coupled to evaporator41to release heat to the evaporator41itself, an electrically actuated circulation pump44(i.e. operated by an electric motor in DC at low voltage, preferably having a nominal voltage of 48 Volt, i.e. belonging to the low-voltage section26), and a tank45of the coolant fluid. The cooling circuit42firstly extends through the common container31which houses the storage system16(i.e. both chemical battery packs17and18) and all the power electronics (i.e. the electronic power converters14,15,21,22,23and25) therein, and then the cooling circuit42extends through both electric machines8and9(in the embodiment shown inFIG. 4, the two electric machines8and9are connected in the cooling circuit42in parallel, but alternatively the two electric machines8and9may be connected in the cooling circuit42in series). There may be heat exchangers in the common container31, each of which is thermally coupled to the corresponding electric/electronic component to adsorb heat from the electric/electronic component itself. Instead, corresponding cooling labyrinths in which the coolant fluid flows are obtained in the electric machines8and9(generally in the stator pack).

According to a possible embodiment, shown inFIG. 5, the coolant fluid in the common container31firstly flows through the chemical battery packs17and18, then flows through the electronic power converters21,22,23and25, and finally flows through the electronic power converters14and15. In other words, in the common container31, the chemical battery packs17and18, the electronic power converters21,22,23and25, and the electronic power converters14and15are arranged in series (in this order) along the cooling circuit42. According to a preferred (but not binding) embodiment, bypass circuits are provided in the common container31with electronically controlled solenoid valves to adjust the cooling of the single parts (i.e. to adjust the amount of cooling of the chemical battery packs17and18, the amount of cooling of the electronic power converters21,22,23and25, and the amount of cooling of the electronic power converters14and15). According to the variant shown inFIG. 6, the tank45of the coolant fluid and the electrically operated circulation pump44are housed in the common container31.

According to a preferred embodiment, the cooling circuit42does not concern the buffer chemical battery19of the low-voltage section24(even though such a chemical battery19is housed in the common container31in all cases).

The efficiency of the electric machines8and9and the electronic power converters14,15,21,22,23and25is higher if their temperature is lower (obviously within given limits, particularly for the electronic components) because the lower the temperature of the conductors, the lower the electric resistance of the conductors themselves. Instead, the chemical battery packs17and18of the storage system16optimally work within a given temperature range: if the chemical battery packs17and18are too cold, their discharge capacity decreases (i.e. less energy is delivered), while if the chemical battery packs17and18are too hot, the self-discharge (i.e. the energy which is lost during processes inside the chemical batteries) increases; therefore, in order to maximize the efficiency and efficacy of the chemical battery packs17and18, the temperature of the chemical battery packs17and18must be controlled, thus avoiding the chemical battery packs17and18from being cooled when the chemical battery packs17and18are too cold (which event is however rare and bound to particularly cold external temperatures) and cooling the chemical battery packs17and18when the chemical battery packs17and18are too hot.

In use, a control unit determines the temperature of each electric/electronic component by means of indirect estimates, e.g. based on electric resistance measurements or by means of a specific temperature sensor. According to the temperatures of the electric/electronic components, the control unit decides whether to generate cold in the refrigeration circuit37and thus whether to actuate compressor38. Furthermore, according to the temperatures of each electric/electronic component, the control unit decides the amount of cooling of the electric/electronic component.

According to a preferred (but not binding) embodiment shown inFIG. 4, the refrigeration circuit37is also used by the climate control system of the passenger compartment of vehicle1; in other words, the refrigeration circuit37is shared by the cooling system36of the electric power system20and the climate control system of the passenger compartment of vehicle1. Therefore, the refrigeration circuit37comprises a further expansion valve46(or lamination valve) connected in parallel to the expansion valve40and a further evaporator47thermally coupled to the climate control system of the passenger compartment of vehicle1.

According to a different embodiment (not shown, but perfectly equivalent), a greater number of chemical battery packs are provided, each of which is electrically connected to its own DC/DC electronic power converter which has a low-voltage side connected only to its own chemical battery pack and a high-voltage side which is connected in parallel to the high-pressure sides of the other electronic DC/DC power converters.

According to a different embodiment (not shown but perfectly equivalent), a lower number (one) or a higher number (e.g. three or four) of electric machines, each of which is controlled by a corresponding electronic power converter which is connected at the input and in parallel to the electronic power converters14and15. Such electric machines may be mechanically connected to transmission7, may be mechanically connected to the drive shaft6of the internal combustion engine5, may be mechanically connected to a turbocharger of the internal combustion engine5, or may be also connected to auxiliary services of vehicle1(cooling, lubrication etc.).

The above-described electric power system20has many advantages.

Firstly, the two chemical battery packs17and18are managed in a completely independent manner because the low-voltage sides of the two electronic power converters21and22are entirely isolated (separate). Therefore, the voltages at the terminals of the two chemical battery packs17and18may be different in terms of nominal value and variation in use, because it is the task of the electronic power converters21and22to “equalize” the voltage on high-voltage side (i.e. towards the electronic power converters14and15). This aspect is very important because, as mentioned above, the chemical battery packs17and18have very different features and thus require different managements in order to operate in an optimal manner.

Furthermore, the chemical battery packs17and18do not exchange electric energy directly with the electronic power converters14and15which control the electric machines8and9, but on the contrary the chemical battery packs17and18exchange electric energy with the electronic power converters21and22, which, by filtering the high-frequency current/voltage oscillations generated by the electronic power converters14and15, allow the chemical battery packs17and18to be operated in the best manner possible. In other words, the electronic power converters21and22filter the high-frequency current/voltage oscillations generated by the electronic power converters14and15and thus prevent such high-frequency current voltage oscillations from discharging on the chemical battery packs17and18which cause an early wear of the chemical battery packs17and18themselves.

Another positive function of the electronic power converters21and22is to maintain constant the voltage on high-voltage side, i.e. towards the electronic power converters14and15which control the electric machines8and9independently from the actual voltage at the terminals of the chemical battery packs17and18. In other words, the actual voltages at the terminals of the chemical battery packs17and18may be mutually different and especially change greatly as a function of the charge state (also of 20-30% from full charge to discharged); the electronic power converters21and22can self-adjust to have always the same voltage value on the high-voltage side, i.e. towards the electronic power converters14and15(also in the case of failure of a chemical battery pack17or18with consequent disconnection of the faulty chemical battery pack17or18). With this regard, it is worth noting that the electronic power converters14and15cannot modify the voltage value and therefore would not be able to compensate for the voltage differences determined by the chemical battery packs17and18.

The two electric machines8and9may exchange their electric energy (through the electronic power converters14and15) without passing through the chemical battery packs17or18of the storage system16; thereby, the exchange of electric energy between the two electric machines8and9do not cause any type of wear in the storage system16or any energy dissipation in the storage system16.

By virtue of the presence of the electronic power converters21and22, the nominal voltage of the electrical machines8and9may be much higher than the nominal voltage of the chemical battery packs17and18of the storage system16; thereby, the nominal voltage of the electric machines8and9can be optimized independently from the nominal voltage of the chemical battery packs17and18(the nominal voltage of the chemical battery packs17and18cannot be too high because of the technological and constructional limits of the electrochemical cells). It is worth noting that, by increasing the nominal voltage of the electric machines8and9, the section of the electric conductors of the electric machines8and9may be reduced, as well as, ultimately, the overall dimension and weight of the electric machines8and9and of the wires which connect the electronic power converters14and15to the electric machines8and9.

Finally, since the chemical battery packs17and18and the electronic power converters14,15,21,22,23and25are housed in the same common container31, the overall dimensions of the electric system may be reduced, the length and dimension of the electric wiring may be minimized, and the operation of cooling may be considerably simplified, thus making it more efficient and effective.