System for an electrically driven vehicle, and vehicle therewith and method therefor

A system for an electrically-driven vehicle includes at least one first energy store, which is of an accumulator type, and at least one second energy store, of a type which differs from an accumulator type. The second energy store has an energy density lower than an energy density of the first energy store, and has a power density higher than a power density of the first energy store. The first energy store and the second energy store are designed to supply electrical energy for an electric drive of the vehicle.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase Application under 35 U.S.C. § 371 of International Application No. PCT/EP2019/062125, filed on May 13, 2019, and claims benefit to German Patent Application No. DE 10 2018 111 681.0, filed on May 15, 2018. The International Application was published in German on Nov. 21, 2019, as WO 2019/219555 A1 under PCT Article 21(2).

FIELD

The present disclosure relates to the field of vehicles having an electric or hybrid drive. In particular, vehicles of this type are utility vehicles, such as heavy goods vehicles, or trailer vehicles, preferably for utility vehicles. The term “hybrid vehicle” here describes a vehicle which firstly incorporates an electric drive having one or more electric motors, and secondly incorporates a drive having a combustion engine.

BACKGROUND

According to the general concept of these vehicles, the kinetic and potential energy which is stored in the mass of the vehicle, in the event of a slow-down, i.e. upon braking, or in the event of downhill travel, is converted by one or more electric motors of the electric drive, operating in generator mode, into electrical energy and stored in an energy store. The energy thus recovered can then be employed for acceleration, in an exclusively electrically-driven vehicle, or for the support of combustion engines in a hybrid vehicle, in the event of acceleration or uphill travel, for the propulsion of the electric motor(s) of the electric drive. It is moreover possible for other electrical loads in the vehicle to be supplied by the energy store. Particularly in the case of a hybrid vehicle, this reduces the loading of the combustion engine, and fuel consumption is reduced accordingly.

A distinguishing characteristic between exclusively electrically-driven vehicles and hybrid vehicles is that hybrid vehicles require a comparatively smaller energy storage capacity, on the grounds that, during actual travel, periods in which energy can be recovered are generally limited, and regularly follow phases in which energy can be rapidly released back to the drive system.

For the storage of energy, accumulators are customarily employed, which store electrical energy by an electrochemical principle. The technology employed in these accumulators is associated with limitations of their maximum potential charging capacity. However, a maximum potential charging capacity is also dependent upon the energy storage capacity of the accumulator employed. In general, the power which can be delivered by an accumulator is significantly greater than the power at which it can be charged. Moreover, any power recovered during braking or downhill travel, particularly in the case of heavy goods vehicles, is generally significantly greater than the requisite drive power.

Consequently, it is now customary, either to limit power for the charging of the accumulator during braking or downhill travel, such that the charging power is not so high that it results in damage to the accumulator, or to provide an accumulator with an energy storage capacity which, relative to the normal drive, is over-dimensioned, such that power generated during braking or downhill travel can be employed, with no limitation of the service charging capacity of the accumulator. Accordingly, energy generated by braking or downhill travel, in some cases, is not entirely utilized or, for the full utilization thereof, a comparatively over-expensive accumulator is employed.

SUMMARY

In an embodiment, the present invention provides a system for an electrically-driven vehicle includes at least one first energy store, which is of an accumulator type, and at least one second energy store, of a type which differs from an accumulator type. The second energy store has an energy density lower than an energy density of the first energy store, and has a power density higher than a power density of the first energy store. The first energy store and the second energy store are designed to supply electrical energy for an electric drive of the vehicle.

DETAILED DESCRIPTION

The present disclosure is therefore the identification of an option by means of which, as far as possible, the full amount of energy generated during braking or downhill travel, particularly of a utility vehicle, can be subject to intermediate storage in its entirety, without the necessity for the employment of an expensive and relatively over-dimensioned accumulator for this purpose.

To this end, the present disclosure relates to a system for an electrically-driven vehicle. In particular, the vehicle is a utility vehicle, such as a heavy goods vehicle. Alternatively, the vehicle is a vehicle trailer, for example a semitrailer for a tractor which is configured as a utility vehicle. A further example of the vehicle is a passenger vehicle. The system comprises at least one first energy store and at least one second energy store, which are designed to deliver energy for the supply of an electric drive of the vehicle. The first energy store of the system is of the accumulator type. The first energy store is thus a rechargeable accumulator for storing of electrical energy on an electrochemical basis. The first energy store thus comprises one or more rechargeable storage elements, which are also described as secondary elements or secondary cells. Examples of an accumulator include, for example, a lead-acid accumulator, a lithium-ion accumulator, a lithium-polymer accumulator, or a lithium-iron phosphate accumulator.

The at least one second energy store is of a type which differs from an accumulator type. Consequently, the second energy store is thus a store which is not an accumulator. Moreover, the second energy store has an energy density which is lower than the energy density of the first energy store. The second energy store further has a power density which is higher than the power density of the first energy store.

The system thus comprises two different energy store types, wherein one of the store types has a higher power density, but thus a lower energy density than the other energy store.

It is thus possible for one energy store, namely the second energy store, in the event of a slow-down, i.e. upon braking, or in the event of downhill travel, to be employed for charging to a high capacity, and for the energy thus stored to be employed thereafter for the supply of the motor and the charging of the first energy store. To this end, the second energy store has a correspondingly higher power density than the first energy store. This means that the second energy store can be charged to a higher capacity than the first energy store, wherein, for the continuous operation of the electric drive, the first energy store has a higher energy density, such that the latter is designed with a higher energy storage capacity than the second energy store.

A significantly higher power generated in the event of a slow-down or downhill travel can thus be subject to short-term intermediate storage in the second energy store in its entirety, with no limitation of capacity. Additionally, a first energy store can be configured with a lower power density than the second energy store, in order to provide a comparatively cost-effective energy store, the essential function of which is the supply of the electric drive during routine travel.

According to a first form of embodiment of the system, the energy density of the second energy store is less than one half the energy density of the first energy store, and the power density of the second energy store corresponds to at least five times the power density of the first energy store. As a result, preferably in particularly heavy vehicles, such as loaded heavy goods vehicles and/or trailer vehicles thereof having a dedicated electric drive, a particularly high power which is generated by a slow-down or by downhill travel can undergo intermediate storage, in its entirety, in the second energy store.

According to a further form of embodiment, the second energy store is a capacitor, particularly a supercapacitor. A supercapacitor of this type is available as a standardized component, and can thus be employed as an energy store with a high power density which is comparatively cost-effective. Alternatively or additionally, the second energy store is a flywheel, to which an electric motor-generator set and a converter are assigned. By means of the converter and the electric motor-generator set, operating in a motor mode, a flywheel is set in rotary motion by the energy which has been generated by a slow-down or by downhill travel, in order to store said energy. This energy can then be retrieved, wherein the rotation of the flywheel, with the electric motor-generator set operating in a generator mode, by the reverse operation of the converter, is converted into power again for the supply of the electric drive. Energy stores of this type are particularly suitable for the intermediate storage of power, and feature a particularly high power density.

According to a further form of embodiment, the system comprises a DC voltage connection, which is designed to deliver electrical energy to an electric drive from the first energy store and/or the second energy store for the supply of an electric drive. The DC voltage connection is moreover designed to store energy from the at least one electric drive, during operation in a generator mode, in the first and/or second energy store. The DC voltage connection is moreover designed to transmit energy from the second energy store to the first energy store.

The DC voltage connection thus constitutes a connection, which is specifically routed via further electrotechnical components, between the first energy store, the second energy store and an electric drive. Thus, for example, a transmission of energy is possible from one region of a vehicle, in which the system is employable, to another region of the vehicle, such that it is not necessary for the energy stores to be arranged in the immediate vicinity of the electric drive.

According to a further form of embodiment, the system comprises a DC voltage converter, by means of which the second energy store is detachably connected to the DC voltage connection. The DC voltage converter is, for example, a flyback converter, a forward converter or a buck/boost converter. If the DC voltage converter is configured as a buck/boost converter, the latter particularly comprises a half-bridge and a power inductance. The DC voltage converter is designed for detachable connection, such that the latter, for example, particularly if it is configured as a flyback converter or a forward converter, permits a galvanic isolation of the DC voltage converter from the DC voltage connection. In this case, however, the term “detachably connected” does not refer exclusively to galvanic isolation, such that a buck/boost converter, also described as an inverting converter, in an out-of-service mode, also describes an interruption of the connection. In any event, the function of the DC voltage converter is the delivery of an essentially constant voltage on the DC voltage connection by means of the second energy store, in the event that the second energy store is configured as a capacitor or a supercapacitor. This is based upon the knowledge that a capacitor assumes a terminal voltage which is proportional to the energy stored in the capacitor. Upon the discharging or charging of the second energy store, there is a corresponding variation in the voltage which is delivered directly on the output of a second energy store, which is compensated by the DC voltage converter.

According to a further form of embodiment, the electric drive comprises an intermediate DC voltage circuit, at least one inverter, at least one electric motor and at least one motor controller for the actuation of the at least one inverter. The intermediate DC voltage circuit is connectable to the DC voltage connection, in order to compensate and/or smooth voltage fluctuations on the DC voltage connection. The inverter is configured, from the power delivered to the intermediate DC voltage circuit, to deliver power for the at least one electric motor. The inverter is actuated by the motor controller, in order to generate a desired electric motor torque. The motor controller is further employed for the actuation of the inverter in a reverse direction, in order to connect the electric motor, which is operated in a generator mode, to the DC voltage connection via the intermediate DC voltage circuit, such that energy which is generated in the electric motor operating in a generator mode can be stored as energy in the first energy store and/or in the second energy store.

According to a further form of embodiment, the system comprises an energy management circuit, which is designed to control or regulate power and/or energy which is exchanged between the DC voltage connection and the first energy store, and between the DC voltage connection and the second energy store. To this end, the energy management circuit is preferably designed to control the DC voltage converter, and to control an accumulator management circuit of the first energy store.

Accordingly, a central element, namely the energy management circuit, is provided as a superordinate authority for the control, organization and regulation of energy and power within the system.

According to a further form of embodiment, a first switch is provided, which is preferably a semiconductor switch. The function of the first switch is the interruptible connection of the first and second energy stores to the electric drive. The energy management circuit is moreover designed to actuate the first switch. By means of the first switch, disconnection of the electric drive from the first energy store and the second energy store, i.e. from the energy supply, is possible. This is of particular use in the event that, additionally, a combustion engine is present in a vehicle having the system, and an acceleration is executed exclusively by means of the combustion engine, when the electric drive is not required in a transitional period. During this transitional period, energy can be charged from the second energy store to the first energy store via the DC voltage connection such that, insofar as possible, the full capacity of the second energy store is available in the event of a subsequent slow-down or downhill travel.

According to a further form of embodiment, the system comprises a second switch, which is also preferably a semiconductor switch. The function of the second switch is the interruptible connection of the first energy store to the DC voltage connection. The energy management circuit is moreover designed to actuate the second switch. As a result—provided that the first energy store is essentially fully charged—energy can be exchanged with the electric drive exclusively by the charging and discharging of the second energy store, with no necessity for the actuation of the first energy store, particularly by means of its accumulator management circuit.

According to a further form of embodiment, the energy management circuit is designed to be operated in a first mode. In the first mode, the first switch and the second switch are closed, in order to store electrical energy, which is generated by the electric drive, in the first energy store and/or the second energy store. Alternatively, both switches are closed, in order to employ energy from the first energy store and/or the second energy store for the supply of the electric drive. The energy management circuit is preferably designed to switch over to the first mode, if a charge of the first energy store lies below a predefined first threshold value. Accordingly, a mode other than the first mode is then preferably employed, provided that the charge of the first energy store lies on or above the predefined first threshold value.

The circumstance is thus exploited whereby energy generated by the drive is only employed for the recharging of the first energy store if sufficient energy storage capacity is available in the latter. By the actuation of the accumulator management circuit, the energy management circuit preferably limits the charging capacity of the first energy store, such that the latter is not destroyed.

According to a further form of embodiment, the energy management circuit is designed, in the event that the second energy store assumes a charge in excess of a second predefined threshold value, to limit the power delivered by the electric drive. In this case, namely wherein the second energy store already assumes a charge which exceeds a second threshold value, which is preferably selected to represent an essentially full charge of the second energy store, electric power which is supplied by the drive is limited accordingly. It is thus ensured that the first energy store, which is still capable of being charged, is not charged to a capacity which damages the latter.

Protection of the first energy store in the event of an essentially fully-charged second energy store is ensured accordingly.

According to a further form of embodiment, the energy management circuit is designed to be operated in a second mode, in which the first switch is closed and the second switch is open. In this mode, the system is designed only to store energy which is delivered by the electric drive in the second energy store, or to only employ energy from the second energy store for the supply of the electric motor. The energy management circuit is designed to switch over to the second mode, particularly if a charge of the first energy store exceeds the predefined first threshold value. Accordingly, if the first energy store is essentially fully-charged, or is fully charged, said first energy store, for the protection of the DC voltage connection, is disconnected by the opening of the second switch. An energy exchange is then only possible between the drive and the second energy store.

According to a further form of embodiment, the energy management circuit is designed to be operated in a third mode. In the third mode, the first switch is open and the second switch is closed, in order to charge the first energy store with energy from the second energy store. This case will occur where a vehicle with the system, for example having no electric drive, is driven by a combustion engine only, wherein the system is employed for the transfer of charge from the second energy store to the first energy store, such that the availability of the full capacity of the second energy store, for a further braking process or for downhill travel, is restored.

According to a further form of embodiment, the present disclosure provides a vehicle, particularly a utility vehicle, a vehicle trailer or similar, which incorporates a system according to one of the above-mentioned forms of embodiment. The present disclosure further provides a method for operating a system according to one of the above-mentioned forms of embodiment, or a vehicle having the system according to one of the above-mentioned forms of embodiment.

FIG.1shows a vehicle10, which is a utility vehicle. The vehicle10comprises an electric drive12, by means of which wheels14on a drive axle16are drivable. The drive axle16is moreover drivable by a combustion engine drive18. The combustion engine drive18represented here comprises an engine controller20and a combustion engine22for actuating the drive axle16. The electric drive12comprises an intermediate DC voltage circuit24, via which electrical energy for the electric drive12can be delivered to the input26. The function of the intermediate DC voltage circuit24is the smoothing and intermediate storage of electrical energy. The electric drive12further comprises an electric motor28, which can be supplied with energy from the intermediate DC voltage circuit, which is converted into an AC voltage32by means of an inverter30. The inverter30is actuated by means of a motor control device34, in accordance with a desired torque of the electric motor28. The electric motor28can also be operated in a generator mode for the braking of the drive axle16, wherein energy from the electric motor28is then injected via the inverter30into the intermediate DC voltage circuit24, which can then be delivered as an output via the terminal26of the electric drive12.

For the supply of the electric drive12with energy13, or for the storage of energy13delivered by the electric drive12, the vehicle comprises a system36. The system36comprises a first energy store38and a second energy store40. The first energy store38is connected via an accumulator management circuit42, and the second energy store40via a DC voltage converter44to a DC voltage connection46. The function of the DC voltage connection46is the connection of the first energy store38and the second energy store40to the electric drive12. Electrical energy47for the electric drive12is thus delivered from the first energy store38and the second energy store40via the DC voltage connection46. Electrical energy43from the first energy store38, and electrical energy45from the second energy store40is thus available.

The DC voltage connection46comprises a first switch48and a second switch50. Additionally, an energy management circuit52is provided, which controls the first switch48, the second switch50, the motor control device34, the DC voltage converter44and the accumulator management circuit42, via control lines49. The second energy store40assumes an energy density54which is lower than an energy density56of the first energy store38. The second energy store40moreover assumes a power density58which is higher than a power density60of the first energy store38. The first energy store38is an accumulator and the second energy store40is a supercapacitor51.

FIG.2shows a further vehicle10, which is a vehicle trailer63. The vehicle trailer is towed by an exemplarily represented tractor vehicle62. The vehicle10inFIG.2comprises the same components as the vehicle10inFIG.1, wherein the vehicle10inFIG.2comprises no combustion engine drive18. Accordingly, the same reference numbers identify the same features.

FIG.3shows the torque of an electric drive12, which can be delivered according to a vehicle speed. To this end, the vehicle speed is plotted on the axis70. The torque of the electric drive12during positive acceleration is represented on the curve72and, up to the “transition speed”79, is essentially constant. The same applies to a negative torque74which, in the event of braking, is delivered by the electric drive12in a generator operating mode, and is represented by the curve74. Depending upon the torque, correspondingly, the energy required by the electric drive12for acceleration is represented by the curve76, and the energy delivered by the electric drive12in a generator operating mode is represented by the curve78. It will be seen that an electric drive12assumes its maximum efficiency in a region80. This, for example, is a region which, in utility vehicles, is essentially selected between 40 km/h 75 and 80 km/h 77.

FIG.4shows exemplary energy values, which are typically generated during the braking of an articulated truck82. For exemplary purposes, the tractor vehicle62has a weight of 8 tonnes, and the trailer vehicle63has an unladen weight of 7 tonnes, wherein a load86of 20 tonnes has been loaded therein. A distribution of forces acting on the axles is such that 64 kilonewtons83act on each of the three axles88of the trailer vehicle63, 75 kilonewtons85act on the drive axle90of the tractor vehicle62, and 55 kilonewtons87act on the front axle92. Assuming a variation in acceleration of one meter per second, at a total weight of 35 tonnes, the resulting force94is 35 kilonewtons. In the event of braking with a negative acceleration of one meter per second, this is distributed such that 7 kilonewtons96act on each of the axles88of the trailer vehicle63, 8 kilonewtons98act on the drive axle90of the tractor vehicle62, and 6 kilonewtons100act on the front axle92of the tractor vehicle62. At a speed of 80 km/h, in this case, the resulting power is 775 kilowatts, corresponding to an energy, during a braking maneuver from 85 km/h to 70 km/h, of the order of 3,250 kilowatt-seconds. If, for example, a generator drive is employed on only one axle of the vehicle trailer86, approximately 465 kilowatts and, during the above-mentioned braking from 85 km/h to 70 km/h, 1,300 kilowatt-seconds can thus be recovered. In the case of a tractor vehicle62which is braked by an electric drive12, approximately 1,950 kilowatt-seconds can be recovered from braking.

FIG.5shows an exemplary embodiment of the method.FIG.5shows a first mode112of the energy management circuit52. In the first mode112, in one step114, the first switch48and the second switch50are closed. In one step115, the first energy store38and the second energy store40are then employed for the supply of the electric drive12, or energy which is generated by means of the electric drive12is stored in the energy stores38,40. If, in a step116, a charge of the second energy store40in excess of a second threshold value118is detected, in a step120, in which the electric drive12operates in a generator mode119, power delivered by the electric drive12is limited accordingly.

FIG.6shows a further step121in the first mode112. In this case, in the first mode112, additionally, in step121, a charge of the first energy store38is compared with a first threshold value122. If the charge lies below the predefined first threshold value122,124, the energy management circuit52remains in the first mode112. If the first threshold value122is exceeded by the charge of the first energy store38,126, the energy management circuit52switches over to a second mode128in which, in one step130, the second switch50is opened. Electrical energy which is delivered by the electric drive12is thus only stored in the second energy store40, or energy from the second energy store40is employed for the supply of the electric drive12.

FIG.7shows a third mode132in which, in one step134, the first switch48is opened and the second switch50is closed. In this mode132, in a step136, energy is then charged from the second energy store40to the first energy store38.

FIG.8shows the steps of an exemplary embodiment of the method. In step138, energy is generated by means of an electric drive12and, in step140, is stored in the second store40. Thereafter, in a step142, a vehicle10having the system36is accelerated by means of a combustion engine drive18and, in a step144, energy is charged from the second energy store40to the first energy store38.

FIG.9shows an alternative exemplary embodiment of a second energy store40, which is configured as a supercapacitor51. InFIG.9, accordingly, a second energy store40is represented which comprises a flywheel150, to which an electric motor-generator set152is connected, in order to store kinetic energy generated from electrical energy in the flywheel150or, in a generator operating mode, to retrieve electrical energy from the kinetic energy stored in the flywheel150. To this end, the electric-motor generator set152is provided with a converter154, in order to convert an AC voltage32of the motor into a DC voltage for the DC voltage connection46, or vice versa.

LIST OF REFERENCE CHARACTERS

10Vehicle12Electric drive13Energy supplied by the electric drive14Wheels16Drive axle18Combustion engine drive20Motor controller22Combustion engine24Intermediate DC voltage circuit26Input28Electric motor30Inverter32AC voltage34Motor control device36System38First energy store40Second energy store42Accumulator management circuit43Energy supplied by the first energy store44DC voltage converter45Energy supplied by the second energy store46DC voltage connection47Electrical energy supplied48First switch49Control lines50Second switch51Supercapacitor52Energy management circuit54Energy density of the second energy store56Energy density of the first energy store58Power density of the second energy store60Power density of the first energy store62Tractor vehicle63Trailer vehicle70Axis of vehicle speed72Torque curve of electric drive74Negative torque7540 km/h76Curve of energy required for acceleration7780 km/h78Curve of energy delivered during braking79Transition speed80Region82Articulated truck8364 kN8575 kN86Load8755 kN88Axles of trailer vehicle90Drive axle of tractor vehicle92Front axle94Force96kN acting on the axles98kN acting on the drive axle100kN acting on the front axle112First mode of the energy management circuit114-116Steps of the method118Second threshold value119Generator operating mode120-121Steps of the method122First threshold value124Charge below the first threshold value126Charge exceeding the first threshold value128Second mode of the energy management circuit130Step of the method132Third mode of the energy management circuit134-144Steps of the method150Flywheel152Electric motor-generator set154Converter