DE102009029335A1 - Accumulator for two-battery electrical system in vehicle, particularly in micro-hybrid vehicle, is charged with electric power by generator when electrical energy supply from generator is interrupted - Google Patents

Abstract

The accumulator is charged with electric power by a generator (16) when the electrical energy supply from the generator is interrupted. The generator supplies electrical power from a high power load and a low power load. The accumulator is a lithium-ion battery. Independent claims are also included for the following: (1) a two-battery electrical system for a micro-hybrid vehicle, particularly for electrical power supply of high power load and low power load; (2) a micro-hybrid vehicle; and (3) a method for supplying a high power load with electrical power through an accumulator.

Description

State of the art

The invention relates to an accumulator for a two-battery system in a vehicle, a two-battery system for a μ-hybrid vehicle for the electrical power supply of at least one high-current consumer and a low-current consumer and a method for supplying a high-current consumer with electrical energy via a first parallel to the high-current consumer battery ,

It is becoming apparent that in the future, new battery systems will increasingly be used both in stationary applications such as wind turbines and in vehicles such as hybrid and electric vehicles. The terms battery and battery system are hereinafter - not quite correct, but adapted to the usual language - used as a replacement for the terms accumulator or accumulator system.

The block diagram of a current 14 V standard vehicle electrical system in a motor vehicle is in 6 shown. When fully charged (state of charge SOC = 100%), the lead-acid battery typically has a voltage of 12.8V. When the battery is discharged (state of charge SOC = 0%), the battery is unloaded and has a typical terminal voltage of 10.8V. The vehicle electrical system voltage is in driving mode - depending on the temperature and state of charge of the battery - in the range between 10.8 V and 15 V.

In 7 the block diagram of a so-called two-battery system is shown. Such Bordnetze be used when compared to the standard on-board network increased requirements for the availability of electrical energy. As an example, Bordnetze called, with which an electro-hydraulic brake, an electromechanically assisted steering or X-by-wire systems, such as brake by wire or steer by wire are supplied. Two-battery systems also offer advantages in seasonally used vehicles such as convertibles, as z. B. even after a prolonged shutdown a start of the vehicle can be made from the specially provided for starting battery. This starter battery is not discharged by the unavoidable quiescent currents, which occur in principle due to electrical consumers. Conventional two-battery systems, as exemplified in 7 shown today are used in luxury cars.

Another development in the field of automotive engineering is the so-called μ-hybrid vehicles, which are increasingly being introduced to the market due to the high energy-saving potential. In contrast to the normal hybrid vehicles, μ-hybrids do not provide any electrical support for the drive or even purely electric driving. In μ hybrids, the electrical machines are used, among other things, for start-stop operation or recuperation. This refers to the conversion of kinetic energy into electrical energy during braking or in sailing operation.

μ-hybrid vehicles have been introduced to counteract the loss of vehicle propulsion energy due to vehicle idling, for example, stopping at the traffic light, in front of the gate or in stop-and-go traffic. For this purpose, a start-stop function is used, which shuts down the engine at a short standstill in order to save fuel and reduce CO2 emissions.

With μ-hybrid technology, today's vehicles can save up to 8 percent of fuel consumption for city driving. If one combines the μ-hybrid technology with a brake energy recovery, as used for example in a full-hybrid vehicle, the savings potential can even be increased to up to 12 percent.

The vehicle electrical system voltage of μ-hybrid vehicles is currently still identical to today's 14 V standard on-board networks. It is expected that this will be maintained in the future, or that at least a significant part of the electrical system is a 14 V electrical system, so that electrical consumers in the vehicle, which are now supplied with the 14 V technology, can continue to be used ,

However, μ-hybrid vehicles already in production today have problems with the lifespan of lead-acid batteries, as they are exposed to a considerable additional charge throughput compared to other vehicles. The reason for this is that the electrical consumers must be supplied from the battery during the stop phases in which the internal combustion engine is switched off. As a result, the batteries in μ-hybrid vehicles sometimes have a service life of significantly less than 2 years. The frequently required replacement of batteries leads to problems with the reliability of the vehicles and inconvenience among users of the vehicles.

Disclosure of the invention

It is therefore an object of the invention to significantly increase the reliability of today's vehicles with μ-hybrid technology.

The invention therefore provides an accumulator for a two-battery system in a vehicle. The electrical system has a generator which is provided for the electrical power supply of a high-current consumer and a low-power consumer and for charging the accumulator with electrical energy. The accumulator is provided for supplying electrical power to the high-current consumer and / or the low-current consumer when the electrical energy supply from the generator is interrupted. According to the invention, this accumulator is a lithium-ion accumulator. In contrast to conventional lead-acid batteries, lithium-ion batteries can handle a significantly higher charge throughput. This makes it possible to significantly increase the life of the battery despite its use in μ-hybrid technology. This gives him a better ability to work flawlessly over a period of time. For the consumer, the accumulator is also associated with lower costs in relation to the total cost of ownership.

The dependent claims show preferred developments of the invention.

The invention also provides a two-battery system for a μ-hybrid vehicle for the electrical power supply of at least one high-current consumer and a low-power consumer. According to the invention, the vehicle electrical system is provided for receiving electrical energy from a first accumulator according to the invention and for supplying a high-current consumer and / or a low-current consumer with the received electrical energy.

In a particular embodiment of the invention, the two-battery system may have the first accumulator, wherein the first accumulator is provided for supplying the high-current consumer and / or the low-current consumer. In this way, the accumulator can initially supply one of the two types of consumers regularly with energy and jump in as an emergency aggregate for energy supply of the other type of consumer.

In a further development of the invention, the first accumulator can be constructed from the two-battery system from a series circuit of at least two lithium-ion battery cells.

In a further particular embodiment of the two-battery system, each lithium-ion battery cell of the first battery can have at least one electrode of lithium iron phosphate. These lithium-ion battery cells have a comparatively constant course of their quiescent voltage characteristic. As a result, such a rechargeable battery can keep its output voltage constant over a large charge state range, so that the first rechargeable battery is outstandingly suitable as an energy store for supplying energy to the low-current consumers in the two-battery system.

In another or additional particular embodiment of the invention, the two-battery system may have a second accumulator, wherein the second accumulator is provided to supply the high current consumer. This type of accumulator can be perfectly adapted to the needs of the high-current consumer, taking no account of the low-current consumers.

In a further development of the invention, the second accumulator can be constructed from the two-battery system from a series circuit of at least two lithium-ion battery cells.

In a further particular embodiment of the two-battery system, each lithium-ion battery cell of the second battery can have at least one electrode of lithium-nickel-cobalt-aluminum oxide or lithium-nickel-cobalt-manganese oxide. These lithium-ion battery cells have a comparatively steep quiescent voltage characteristic. As a result, such a rechargeable battery can reach a very high output voltage in the fully charged state of charge, so that the second rechargeable battery is eminently suitable as an energy store for supplying energy to a high-current consumer in the two-battery system, such as the electric starter in a vehicle for only a short time a high output current needed.

In another or additional particular embodiment of the invention, the electrical system can have a coupling unit, via which the electrical system for electrical power supply of the high-current consumer is provided from the first accumulator. Thus, the first accumulator can contribute to the energy supply of the high-current consumer in an emergency and thus increase the reliability of the two-battery system, for example, if the second accumulator has discharged due to too long a lifetime of his vehicle.

In a further development of the invention, the coupling unit of the two-battery system can have a DC-DC converter, via which the electrical system is provided for charging the second accumulator.

In an additional or alternative embodiment of the invention, the DC-DC converter of the two-battery system for charging be provided of the first accumulator via the second accumulator.

In this case, the DC-DC converter can be provided for the conversion of large electrical power.

In another or additional particular embodiment of the invention, the first and second accumulators may each comprise a series arrangement of a predetermined number of lithium ion accumulator cells, and the number of lithium ion accumulator cells in the second accumulator may be greater than the number of lithium Ion accumulator cells in the first accumulator.

In a particular embodiment of the invention, the coupling element of the two-battery system can have an electronic component that allows a flow of current from the first accumulator to the second accumulator and locks in the other direction.

The invention also provides a μ-hybrid vehicle with an internal combustion engine for driving the μ-hybrid vehicle, wherein the internal combustion engine is started by an auxiliary unit and the auxiliary unit is operated as a high-current consumer of a vehicle electrical system according to one of the preceding claims.

The invention also provides a method for supplying a high-current consumer with electrical energy via a first accumulator connected in parallel with a high-current consumer, which is connected in parallel to a second accumulator via a coupling unit, the first accumulator being provided directly to the high-current consumer for delivering the electrical energy and has a dependent on its state of charge output voltage. According to the invention, in this method, the power supply of the high current load is switched to the second accumulator when the output voltage of the first accumulator falls below a predetermined value.

In a particular embodiment of the method, the predetermined value results from the output voltage of the second accumulator minus the blocking voltage of a diode which is connected in series with the parallel connection of the first accumulator and the high current consumer such that current from the second accumulator to the first accumulator and is locked in the opposite direction.

drawings

Hereinbelow, non-limiting embodiments of the invention will be described in detail with reference to the accompanying drawings. In the drawings show:

1 a circuit diagram for a first embodiment of a two-battery system according to the present invention;

2 a circuit diagram for a second embodiment of a two-battery system according to the present invention;

3 a circuit diagram for a third embodiment of a two-battery system according to the present invention;

4 a characteristic curve for the open-circuit voltage as a function of the state of charge for a rechargeable battery according to the invention;

5 a characteristic curve for the rest voltage as a function of the state of charge for a further accumulator according to the invention;

6 a circuit diagram for a conventional single-battery system; and

7 a diagram of a conventional two-battery system.

Preferred embodiments of the invention

Hereinafter, with reference to the figures, preferred embodiments of the invention will be described in detail.

In 1 a circuit diagram for a first embodiment of a two-battery system according to the present invention is shown. According to the invention, this battery system is a two-battery system 2 in which lithium-ion batteries are used as a replacement for lead-acid battery. This in 1 illustrated two-battery board network 2 is suitable for use in vehicles where the launch is via a separate starter 4 takes place or can take place, ie does not necessarily have to be done via a starter generator.

The starting battery 6 is to supply a first subnetwork 7 in two-battery system 2 provided and designed as a lithium-ion battery. It becomes the supply of the starter 4 and possibly further high-current consumers used. The starting battery 6 must therefore be designed for high performance requirements. The voltage 8th the starting battery 6 may be replaced by the The voltage level of today's standard on-board electrical system in 14 V technology or 42 V technology differ.

The electrical system battery 10 is to supply a second subnet 11 in two-battery system 2 provided and also designed as a lithium-ion battery. It serves to supply the low-current consumers 12 . 14 of the two-battery system 2 and must therefore comply with the current requirements for the corresponding technology, such as 14 V technology or 42 V technology in terms of voltage. The electrical system battery 10 must be the low-current consumer 12 . 14 also during the stop phases, in which supply a generator 16 to the actual power supply of the low-current consumers 12 . 14 no electrical energy for the two-battery system 2 can deliver. It must therefore be designed as a storage battery, ie for high energy requirements.

The two sub-networks 7 . 11 are via a so-called coupling unit 18 connected with each other. The coupling unit 18 allows an energy flow between the two sub-board networks 7 . 11 , This is required as the generator 16 in this embodiment of the invention, only the second sub-board network 11 can supply directly with electrical energy.

In 2 a circuit diagram for a second embodiment of a two-battery system according to the present invention is shown. Same elements 1 be in 2 provided with the same reference numerals and not described again extra.

The electrical system battery 10 is designed to be suitable in terms of their voltage level to the low-current consumers 12 . 14 in the appropriate technology to provide electrical energy. For example, for a two-battery system 2 in 14 V technology four lithium-ion battery cells with a voltage characteristic according to the in 5 voltage characteristic connected in series with each other in order to achieve suitable voltages. Such lithium-ion battery cells can preferably be realized, in which is used as the material for its cathode lithium iron phosphate.

For the starter battery 6 High-performance lithium-ion battery cells are used, as used for example in hybrid vehicles. As an example of a concrete execution, the starter battery 6 from a series connection of four lithium-ion cells 22 exist, each cell has a capacity of 5 Ah. The voltage level of each individual cell can be selected between 4.2V in the fully charged state and 2.7V in the fully discharged state. Such a voltage characteristic is in 4 shown and can be achieved if for each individual lithium-ion cell 22 As the material for its cathode lithium-nickel-cobalt-aluminum oxide is used. These lithium-ion cells 22 So you can endure a peak performance for a 10 s load of 1000 W. Such lithium-ion battery cells 22 are suitable for use in the starter battery 6 because they can achieve a high performance with a suitable design to the high starting currents 24 for the starter 4 already noted. In addition, they have a low self-discharge. This is for example a significant advantage over the conventionally used double layer capacitors (DLC). They are also smaller in their volume and have a lower weight.

The coupling unit 18 consists of a diode 28 and a parallel-connected DC / DC converter 26 , At startup, the startup battery becomes 6 through the starter current 24 discharged. After the startup process, the startup battery will start 6 over the DC / DC converter 26 reloaded. The voltage 8th the starting battery 6 may have higher values than the on-board battery 10 , Breaks the tension 8th For example, in the case of a cold start at -30 ° C, the starting battery is so strong that it is approx. 0.3 V below the voltage 30 the electrical system battery 10 falls, the starting current 24 partly also from the on-board battery 10 provided if the diode 28 the coupling unit 18 is designed as a Shottky diode and thus a forward voltage 32 of about 0.3V. The electrical system battery 6 supports the start battery 6 thus at takeoffs where an extremely high starting current 24 is required. When starting with a warm engine, such as in the start-stop operations, the starting current 24 completely or at least predominantly from the starting battery 6 provided what the design of the two-battery system 19 is dependent. In this way, it succeeds, the on-board battery 10 largely from the loads caused by the starting current 24 to relieve. The electrical system battery 10 can thus be specific to the supply of low-current consumers 12 . 14 of the two-battery system 19 , that is designed as a storage battery. It can so in spite of the high charge throughput through the starting current 24 , which occurs during the stop phases, the requirements for those for the low-current consumer 12 . 14 necessary life span. Therefore, offers itself, the on-board battery 6 to run as a lithium-ion battery.

In 3 is a circuit diagram for a third embodiment of a two-battery system 34 represented according to the present invention. Same elements 1 be in 2 provided with the same reference numerals and not described again extra.

In contrast to the first embodiment, there is the starting battery 6 from a series circuit of more than four lithium-ion battery cells 22 , The number of lithium-ion battery cells 22 in the starter battery 6 is thus higher than the number of lithium-ion battery cells 24 in the electrical system battery 10 , The use of a diode 28 in the coupling unit 18 makes no sense in this embodiment, since the voltage 8th the starting battery 6 due to the higher number of lithium-ion battery cells 22 Even with cold starts, it is not allowed to sink to such low values due to the system. This must be guaranteed technically, as the cells would otherwise fall below their permissible voltage range downwards. Thus, the on-board battery 10 due to their lower number of lithium-ion battery cells 24 are no longer used to support the startup process.

Due to the now higher voltage level of the starter battery 6 , which is characterized by the high number of lithium-ion battery cells 22 gives the required starting power at much lower starting currents 24 to be provided. The two-battery system 34 experiences no load and thus no voltage dips during startup. This is an advantage over the two-battery system 19 according to 3 represents.

In further embodiments, the DC / DC converter 26 the coupling unit 18 , which in the previously described two-battery on-board networks 2 . 19 . 34 only unidirectional for charging the starter battery 6 is used as a bidirectional DC / DC converter 26 be executed. This could also cause a flow of energy from the starting battery 6 in the second section 11 of the two-battery system 2 . 19 . 34 with the electrical system battery 10 respectively. This would support the on-board battery 10 enable. This could also be the second section 11 of the two-battery system 2 . 19 . 34 be carried out with high availability of electrical energy. However, the DC / DC converter needs 18 be designed for high performance in this case. In the embodiments with a unidirectional DC / DC converter for energy transport exclusively from the second sub-board network 7 in the first sub-board network 11 can be the DC / DC converter 18 be designed for low power, since the entire period between two starts for the energy transport can be used in the starter battery.

Claims (15)

Battery for a two-battery system ( 2 . 19 . 34 ) in a vehicle, the on-board network ( 2 . 19 . 34 ) a generator ( 16 ) for the electrical power supply of a high current consumer ( 4 ) and a low-power consumer ( 12 . 14 ) and for charging the accumulator ( 6 . 10 ) is provided with electrical energy and wherein the accumulator ( 6 . 10 ) for the electrical power supply of the high-current consumer ( 4 ) and / or the low-power consumer ( 12 . 14 ) is provided when the electrical power supply from the generator ( 16 ) is interrupted, characterized in that the accumulator ( 12 . 14 ) is a lithium-ion battery. Two-battery system for a μ-hybrid vehicle for the electrical power supply of at least one high-current consumer ( 4 ) and a low-power consumer ( 12 . 14 ), whereby the electrical system ( 2 . 19 . 34 ) for receiving electrical energy ( 24 ) from a first accumulator ( 6 . 10 ) according to claim 1 and for supplying a high current consumer ( 4 ) and / or a low-current consumer ( 12 . 14 ) with the received electrical energy ( 24 ) is provided. Two-battery-battery according to claim 2 with the first accumulator ( 10 ), the first accumulator ( 10 ) for the supply of the high current consumer ( 4 ) and / or the low-power consumer ( 12 . 14 ) is provided. Two-battery-battery according to claim 3, wherein the first accumulator ( 10 ) from a series connection of at least two lithium-ion battery cells ( 20 ), each lithium-ion battery cell ( 20 ) preferably comprises at least one lithium iron phosphate electrode. Two-battery onboard network according to claim 3 or 4, with a second accumulator ( 6 ) for the supply of the high current consumer ( 4 ). Two-battery onboard network according to claim 6, wherein the second accumulator ( 6 ) from a series connection of at least two lithium-ion battery cells ( 22 ), each lithium-ion battery cell ( 22 ) of the second accumulator ( 6 ) in particular at least one electrode of lithium-nickel-cobalt-aluminum oxide or lithium-nickel-cobalt-manganese oxide. Two-battery network according to one of claims 2 to 6, wherein the electrical system ( 2 . 19 . 34 ) a coupling unit ( 18 ) via which the electrical system ( 2 . 19 . 34 ) for the electrical power supply of the high-current consumer ( 4 ) from the first accumulator ( 10 ) is provided. Two-battery system according to claim 7, wherein the coupling unit ( 18 ) a DC-DC converter ( 26 ) via which the electrical system ( 2 . 19 . 34 ) for charging the second accumulator ( 6 ) is provided. Two-battery system according to claim 8, wherein the DC-DC converter ( 26 ) for charging the first accumulator ( 10 ) via the second accumulator ( 6 ) is provided. Two-battery onboard network according to claim 8 or 9, wherein the DC-DC converter ( 26 ) is provided for the conversion of large electrical power. Two-battery on-board network according to one of claims 2 to 8, wherein the first and second accumulator ( 6 . 10 ) each a series circuit of a predetermined number of lithium-ion battery cells ( 22 . 20 ), and wherein the number of lithium-ion battery cells ( 22 ) in the second accumulator ( 6 ) is greater than the number of lithium-ion battery cells ( 20 ) in the first accumulator ( 10 ). Two-battery onboard network according to one of claims 7 to 9, wherein the coupling unit ( 18 ) an electronic component ( 28 ), that a current flow from the first accumulator ( 10 ) to the second accumulator ( 6 ) and locks in the other direction. μ hybrid vehicle with an internal combustion engine for driving the μ-hybrid vehicle, wherein the internal combustion engine of an auxiliary unit ( 4 ) and the auxiliary unit ( 4 ) as a high current consumer of a vehicle electrical system ( 2 . 19 . 34 ) is operated according to one of the preceding claims. Method for supplying a high-current consumer ( 4 ) with electrical energy via a first high-current consumer ( 4 ) parallel connected accumulator ( 6 ), which via a coupling unit ( 18 ) in parallel with a second accumulator ( 10 ), the first accumulator ( 6 ) for the delivery of electrical energy ( 24 ) directly to the high-current consumer ( 4 ) is provided and one of the state of charge of the first accumulator ( 10 ) dependent output voltage ( 8th ), characterized in that for energy supply ( 24 ) of the high current consumer ( 4 ) the second accumulator ( 10 ) is switched on when the output voltage ( 8th ) of the first accumulator ( 6 ) falls below a predetermined value. The method of claim 14, wherein the predetermined value is from the output voltage ( 30 ) of the second accumulator minus the blocking voltage ( 32 ) of a diode connected in series with the parallel connection of the first accumulator ( 6 ) and the high-current consumer ( 4 ) is switched such that current from the second accumulator ( 10 ) to the first accumulator ( 6 ) and locked in the opposite direction.

Images