DE102014215906A1 - Disconnecting an electrical energy storage of a serial hybrid drive - Google Patents

Abstract

A first aspect relates to a method for decoupling a rechargeable electrical energy store of a serial hybrid drive for a motor vehicle. The serial hybrid drive comprises an electric drive machine for driving the vehicle with an upstream power electronics. Furthermore, an energy converter for generating electrical energy for the electric drive machine and for an electrical energy storage is provided. Furthermore, the coupled with the energy converter and the power electronics of the electric drive machine electrical energy storage is available. Furthermore, controllable uncoupling means for uncoupling the electrical energy storage of the energy converter and the electric drive machine are present. In addition, means for adjusting the voltage applied to the input of the power electronics DC link voltage with decoupled energy storage available. Before decoupling the energy storage device, a first value of the intermediate circuit dc voltage is present at the input of the power electronics. According to the invention it is found that for a driving task no loss or absorption of electrical power from the energy storage is required, and in dependence is decided to decouple the energy storage. In response to the decision to decouple the energy storage, the controllable decoupling means are controlled such that the electrical energy storage is decoupled from the energy converter and the electric drive machine. After decoupling the electrical energy store, a second value of the intermediate circuit DC voltage, which is modified compared to the first value, is set, which is characterized by an increased energy efficiency of the combination of energy converter and electric drive machine compared to the first value of the DC link voltage.

Description

The invention relates to serial hybrid drives.

A motor vehicle with serial hybrid drive comprises an electric traction unit with an electric drive machine for driving the vehicle and an upstream power electronics. Furthermore, an energy converter for generating electrical energy is provided. These are, for example, an internal combustion engine and an electric generator driven thereby, wherein the chemical energy of a fuel is converted by combustion into mechanical work, and the mechanical work in the generator is converted into electrical energy. Instead of a combination of internal combustion engine and generator, the energy converter may alternatively also be a fuel cell in which chemical reaction energy is converted into electrical energy. Furthermore, a rechargeable electrical energy storage is provided. The electrical energy storage can absorb electrical energy of the energy converter and provide electrical energy to the electric drive machine. The electrical energy store may be an electrochemical battery or a capacitor.

In ordinary serial hybrid drives, the electrical energy store is continuously electrically connected to the so-called intermediate circuit, the electrical circuit of the energy converter and the input of the power electronics of the electric drive machine being connected to the intermediate circuit.

It is known to electrically decouple the electrical energy storage in the event of an accident or a malfunction or in a deep discharge or overcharge of the energy storage or an overvoltage or unused vehicle. Examples of this are in the documents DE 10 2012 210 596 A1 . DE 10 2012 211 393 A1 . DE 10 2012 018 321 A1 . DE 10 2009 035 483 A1 . DE 100 50 379 A1 . WO 2011/103911 and EP 0967108 A1 described.

The value of the intermediate DC voltage prevailing in the intermediate circuit, which is present at the input of the power electronics of the drive machine, is typically determined essentially by the no-load voltage of the electrical energy store and hardly by the energy converter. The reason for this is that typically the electrical energy storage corresponds to a voltage source with very low internal resistance. In the case of energy converter in the form of an internal combustion engine with mechanically coupled generator and rectifier downstream of the energy converter corresponds approximately to a power source with high internal resistance.

If the electrical energy store is a rechargeable battery with several battery cells, the DC link voltage is essentially determined by the cell voltage, the state of charge, the number of cells and the battery current.

The energy efficiency of the cascade of energy converter and electric traction machine depends on the DC link voltage. Depending on the driving task, therefore, a voltage level of the DC link voltage deviating from the energy store can be advantageous.

It is an object of the invention to provide an operating method for a serial hybrid drive and a corresponding serial hybrid drive with improved energy efficiency of the cascade of energy converter and electric traction machine.

The object is solved by the features of the independent claims. Advantageous embodiments are described in the dependent claims.

A first aspect relates to a method for decoupling a rechargeable electric energy storage of a serial hybrid drive for a motor vehicle, in particular for a passenger car.

The serial hybrid drive comprises an electric drive machine for driving the vehicle with an upstream power electronics. The electric drive machine with power electronics is, for example, a polyphase synchronous machine (in particular a three-phase synchronous machine) with an inverter.

Furthermore, an energy converter for generating electrical energy for the electric drive machine and for an electrical energy storage is provided. This is, for example, an internal combustion engine and a generator driven therewith and configured as an electric machine with a downstream rectifier. Furthermore, the coupled with the energy converter and the power electronics of the electric drive machine electrical energy storage is available. The electrical energy store may be an electrochemical battery or a capacitor.

Furthermore, controllable decoupling means for decoupling the electrical energy storage of the energy converter and the electrical Drive machine available. With uncoupled energy storage, the energy storage therefore no longer determines the voltage level in the DC link. As decoupling preferably one or more electrically controllable switches, such as contactors or relays come into question.

Furthermore, means for adjusting the voltage applied to the input of the power electronics DC link voltage with decoupled energy storage available. For example, a variably adjustable voltage regulator is used for regulating the DC link voltage.

Before disconnecting the energy store, a first value of the intermediate circuit DC voltage is present at the input of the power electronics, which corresponds approximately (neglecting the voltage drop in the case of current flow) to the no-load voltage of the energy store, for example an intermediate circuit voltage of approximately 360 V.

According to the invention it is found that for a driving task no loss or absorption of electrical power from the energy storage is required, and in dependence is decided to decouple the energy storage. In order to establish that no electric power output from the energy store is required for a driving task, the absorbed power of the electric drive machine or an associated variable (eg the current measured by a current sensor from the drive machine is preferably used ). For example, the current electrical power consumption or the mechanical power output of the electric drive machine (or a variable characteristic thereof) is determined and checked whether this power together with the absorbed power of other electrical consumers (such as an air compressor), which are powered by the DC link via which energy converters can be provided.

To determine that for a driving task no loss or absorption of electrical power from the energy storage is required, the current consumption can be measured via a current sensor.

In response to the decision to decouple the energy storage, the controllable decoupling means are controlled such that the electrical energy storage is decoupled from the energy converter and the electric drive machine. For example, one or more relays or contactors that couple the energy storage to the intermediate circuit between the output of the energy converter and the input of the power electronics are opened.

After decoupling the electrical energy store, a second value of the intermediate circuit DC voltage, which is modified compared to the first value, is set, which is characterized by an increased energy efficiency of the combination of energy converter and electric drive machine compared to the first value of the DC link voltage. For example, after decoupling, the DC link voltage is reduced to 320 V.

The invention is based on the idea that the electrical energy store for driving tasks, which do not require the supply or release of electrical power from the energy store, can be decoupled, so that thereafter the DC link voltage is no longer determined by the electrical energy store. The intermediate circuit voltage then corresponds to an adjustable degree of freedom, wherein an energy efficiency optimized value for the intermediate circuit voltage can be selected to increase the energy efficiency of the combination of energy converter and electric drive machine. By decoupling the electrical energy storage so the remaining composite of energy converter and electric drive machine can be operated at a more favorable in terms of energy efficiency voltage level of the intermediate circuit voltage, for example at a low voltage level.

It can be provided that it is determined that for a driving task no decrease or absorption of electric power required by the energy storage, and thus the decision to decouple the energy storage, in any case positively met and not the presence of additional necessary conditions is checked. However, it may alternatively be provided that it is established for a driving task that no decrease or absorption of electrical power on the part of the energy store is required, and this does not necessarily mean that the energy store is decoupled. For example, it can then be checked in a second step, whether it makes sense for reasons of efficiency for the current operating point of the generator of the energy converter and the electric traction engine to decouple the electrical energy storage, since the decoupling would result in a significant increase in energy efficiency when adjusting the DC link voltage.

The determination that for a driving task no loss or absorption of electrical power from the energy storage is required, is preferably carried out in such a way that it is determined that for the respective driving task (eg constant driving with a certain driving speed or Accelerating at a certain acceleration) the power of the electric drive machine and, if applicable, the power of one or more other electrical consumers (eg the air conditioning compressor of the air conditioning system), which are supplied via the intermediate circuit, greater (or greater than) than a lower limit ( 10 kW) of the energy converter's power and less (or less than) than an upper limit (eg, 45 kW) of the power converter's power. For example, the upper limit describes the power maximum of the energy converter, and the lower limit describes, for example, a lower power limit at which sufficient efficiency of the energy converter or a part of the energy converter is achieved, for example an efficiency of greater than 30% for the internal combustion engine of the energy converter. Preferably, the performance consideration is based on the electrical power; but it would also be possible to perform the performance consideration for the mechanical performance. In the case of driving tasks that are in the energetically sensible operating range of the energy converter with regard to the power requirement, the energy storage device can be decoupled.

It is therefore preferably checked whether the power required for the driving task of the drive machine plus the power for other electrical consumers that are supplied with loss of energy storage via the energy converter with power within a power window of the energy converter. If this is the case, the power can be provided via the energy converter and there is no need for any loss or absorption of electrical power from the energy storage. In this case, it may be useful to decouple the electrical energy storage to modify the DC link voltage to increase the efficiency.

It is advantageous if it is not only verified for the uncoupling that for the driving task no loss or absorption of electrical power from the energy storage is required, but for the driving task decoupling is also useful for energy efficiency reasons. For this purpose, the value of a variable (eg efficiency or power loss) can be determined for the respective driving task at the first value of the intermediate circuit DC voltage, which corresponds to the energy efficiency of the combination of energy converter and electric drive machine or a part thereof (eg generator and electric drive machine) ). This is, for example, an efficiency indication or a power loss indication. For example, at the first value (eg, 360 V) of the intermediate circuit DC voltage, an overall efficiency of the generator and electric drive machine chain is determined. The decision to decouple the energy storage, then preferably takes place as a function of this value of the characteristic of energy efficiency size. Depending on this value, it can be determined, for example, whether decoupling is worthwhile for reasons of efficiency.

Furthermore, for the driving task at an optimum value of the intermediate circuit DC voltage, a value of the size which is related to the energy efficiency of the combination of energy converter and electric drive machine or a part thereof can be determined. Optimum value of the intermediate circuit DC voltage is to be understood as a value of the intermediate circuit voltage at which there is an optimum with regard to the quantity associated with the energy efficiency (for example an efficiency optimum).

The step of deciding to decouple the energy store then takes place as a function of the value of the variable at the first value of the DC link voltage, and the value of the variable at the optimum value of the DC link voltage. These two values can be compared with each other.

For example, it can be stated that the overall efficiency of the generator and electric drive machine chain at the first intermediate DC voltage value is less than the overall efficiency of the generator and electric drive chain at the optimum intermediate DC voltage value minus an offset value, and is decided in this case to decouple the energy storage. Otherwise the energy store will not be decoupled.

According to a preferred embodiment, the energy converter comprises an internal combustion engine and a generator (in particular polyphase alternating current generator) with a downstream power electronics (rectifier). The decision to decouple the energy store is preferably made as a function of the rotational speed of the generator or of a variable dependent thereon (eg electrical power in the intermediate circuit or induced voltage) and / or depending on the rotational speed of the drive machine or a variable dependent thereon. This approach is based on the finding that often at higher speeds, a higher voltage level in the DC link in terms of energy efficiency is beneficial, and at lower speeds, a low voltage level in the DC link in terms of energy efficiency is beneficial. The speed of the generator and / or the drive machine thus has an influence on the optimum voltage position in the DC link and is therefore an influencing factor for whether the energy store should be decoupled or Not. Namely, if the optimum voltage position differs greatly from the impressed by the energy storage voltage level, it is particularly advantageous to decouple the energy storage and set the optimal voltage level.

Similar considerations apply to the torque of the generator or the torque of the electric drive machine, so that the decision to decouple the energy storage can also be made dependent on the torque of the generator and / or the torque of the electric drive machine.

It is advantageous to determine the current operating point of the generator in terms of speed and torque and the current operating point of the prime mover in terms of speed and torque, and to decide on the decoupling depending on these four sizes.

For example, for the current operating point of the generator in terms of speed and torque and for the current operating point of the prime mover in terms of speed and torque, the efficiency of the chain of generator and traction machine at the current value of the intermediate circuit voltage can be determined, and at the same operating point for Generator and prime mover efficiency can be determined at an optimal value of the DC link voltage. These two values can then be set in relation to one another and based on this, it can be decided whether the energy store is to be disconnected or not. Alternatively, instead of the values of the efficiency, the values of the power loss (or of another quantity related to the energy efficiency) can be determined and put into relation to one another.

After the energy storage has been decoupled and the DC link voltage has been adjusted, it may happen again that the power (either positive power or negative power in an energy recombination of the drive) for the respective driving task outside the power window of the energy converter falls, and a balancing stream from or to Energy storage is required. Then preferably the DC link voltage is adjusted to the open circuit voltage of the energy storage and then electrically coupled via the controllable decoupling again the energy storage with the energy converter and the electric drive machine, for example by shooting one or more switches for energy storage.

Before coupling, it is first decided to reconnect the energy store. For this purpose, it can be established, for example, that for the driving task very well a decrease or absorption of electrical power from the energy storage is required (for example, evaluation of the performance of the electric drive machine), and it can be decided in this case to couple the energy storage again. The need for the removal or absorption of electrical power from the energy storage device can be determined, for example, if the power of the electric drive machine (plus the power of further consumers to be supplied via the DC link) is outside the power converter's power window discussed above. After it has been positively decided to reconnect the energy store, the value of the intermediate circuit voltage is adjusted to a value adapted to the no-load voltage of the energy store before coupling the energy store. By adjusting the DC link voltage prevents when coupling the energy storage by the voltage difference, a high compensation current flows, which could lead to damage, for example, in the one or the decoupling used for switches or in the energy storage.

It has been described above that the electrical energy store can be decoupled in order to improve the overall efficiency in driving states in which no current flow to and from the energy store is necessary. When the energy store is disconnected, the DC link voltage can be set to an energetically more favorable voltage level.

As soon as high power dynamics require a power output (because then the power consumption of the traction machine exceeds the power output of the energy converter) or high negative dynamics, power consumption (eg in the case of recuperation of energy by operation of the traction machine as a generator) is required by the energy store , And thus a connection of the battery is necessary, the intermediate circuit voltage is preferably first adapted to the output voltage of the energy storage. This process can take several 100 ms, resulting in a noticeable delay for a positive dynamic request or a negative dynamic request.

To avoid this problem, it may be provided to allow the decoupling of the energy storage only in driving situations that can not expect high positive or negative driving dynamics, and in a driving situation ahead with high driving dynamics timely pre-tax even before the high dynamic demand decoupling of the energy storage to pick up again. To evaluate the preceding Driving situation is preferably the navigation system and / or the front camera used. However, other sources of information such as the position of a driving mode switch (eg position on "Sport") can be used to detect a driving situation with high driving dynamics. In recognized driving situations without high driving dynamics (ie with a high proportion of constant driving), the decoupling of the energy store can basically be released and, under the conditions discussed above, the energy store can then actually be decoupled. Upon detection of probable forthcoming dynamic requirements, the basic release of the decoupling of the energy storage is canceled and a possibly already decoupled energy storage coupled in time again.

It is therefore advantageous if, in the context of the method for deciding to reconnect the energy store, it is predicted that a high (positive / negative) driving dynamics is to be expected for a driving situation ahead. The setting of a value adapted to the output voltage of the energy storage value DC link voltage and the coupling of the energy storage can then take place in time so early that both takes place before the expected high driving dynamics, so that the dynamic demand can be implemented without delay.

It can be predicted for a preceding route section that a high driving dynamics is to be expected for the route section lying ahead. In the case of a high driving dynamics, this route section can be assigned a decoupling prohibition, so that the energy store can not be decoupled in this route section. In the case of no increased driving dynamics, this route section can be assigned a basic uncoupling release. Whether the energy storage is then actually decoupled in this route section, may be dependent on the achievement of the route section no loss or absorption of electrical power from the energy storage is required and optionally additionally a decoupling also for energy efficiency reasons is also appropriate.

In principle, it can be provided to predict for a route section lying ahead that for this section the removal or absorption of electrical power from the energy storage is required, in particular that for the route section, the expected performance of the electric drive machine (optionally plus the power consumption further via the DC link to supplying electrical load) is less than or equal to a lower limit of the power of the power converter or greater than or equal to an upper limit of the power of the power converter. In the case of this prognosis, this route section can be assigned a decoupling prohibition, so that the energy store can not be uncoupled in this route section. In the event that, according to the prognosis, it is probably not necessary for this section to absorb or absorb electrical power from the energy store, this route section can be assigned a basic decoupling allowance. Whether the energy store in this route section is then actually decoupled, may be dependent on the fact that when reaching the route section actually no loss or absorption of electrical power required by the energy storage and optional additional decoupling also for energy efficiency reasons is appropriate.

A second aspect relates to a serial hybrid drive of a motor vehicle, which has already been explained in connection with the first aspect of the invention. A control device is provided for controlling the controllable decoupling means. The control device is set up to determine that for a driving task no decrease or absorption of electrical power on the part of the energy store is required and to decide in dependence therefrom to decouple the energy store. In response to this decision, the control unit directly or indirectly controls the controllable decoupling means such that the electrical energy store is decoupled from the energy converter and the electric drive machine. After disconnecting the electrical energy storage device, the control unit gives the means for adjusting the DC link voltage present at the input of the power electronics a second value of the DC link voltage which is different from the first value with increased energy efficiency of the composite of the energy converter and the electric drive machine compared to the first DC link voltage value Then set the means for adjusting the DC link voltage present at the input of the power electronics.

The above statements on the method according to the invention according to the first aspect of the invention also apply correspondingly to the hybrid drive according to the invention according to the second aspect of the invention. At this point, not explicitly described advantageous embodiments of the hybrid drive according to the invention correspond to the described advantageous embodiments of the method according to the invention.

The invention will be described below with reference to the accompanying drawings with reference to an embodiment. In these show:

1 an exemplary serial hybrid drive;

2 an embodiment of a method according to the invention;

3 a first embodiment for testing the efficiency-related decoupling criterion; and

4 A second embodiment for testing the efficiency-related decoupling criterion.

In 1 an exemplary serial hybrid drive is shown. This includes an electric drive machine eAM for driving the vehicle with upstream power electronics LE2. This is, for example, a multi-phase synchronous machine with an upstream inverter.

Furthermore, an electrical energy converter for generating electrical energy is provided. The energy converter comprises an internal combustion engine VM, which has a torque M _VM and an engine speed n _VM and generates a mechanical power P _MECH1 = 2π * M _VM * n _VW , and an electric generator GEN with a downstream power electronics LE1 in the form of a rectifier _receives this mechanical power P _MECH1 and, under certain losses, _converts P _{V_GEN} into an electrical power P _EL1 <P _MECH . The electrical power P _EL1 can be _{fed in the DC link} ZK in a rechargeable electric battery BAT and / or in the electric drive machine eAM with the upstream power electronics LE2. Depending on whether the electric battery BAT is charged or discharged, the electric battery BAT _receives or outputs an electric power P _EL2 . Depending on whether the electric drive machine eAM accelerates the vehicle with a positive drive torque M _tract acting in the desired direction of travel or decelerates with a negative torque M _Trak acting counter to the desired direction of travel, the electric drive machine eAM receives electrical power P _EL3 (and converts it into a mechanical power P _MECH2 = 2π · M _tract · n _tract under the additional power loss P _{V, eAM} ) or outputs this electric power P _EL3 . Furthermore, the on-board network BN is coupled with many other electrical consumers (eg air conditioning compressor) for supply to the DC link ZK via one or more DC-DC voltage converters DCDC and receives the electrical power P _EL4 .

The battery BAT is coupled via a Abkoppeleinheit AKE with one or more electrically controllable switch, such as contactors or relays to the DC link ZK; If necessary, the battery BAT can be electrically disconnected from the DC link ZK. In the coupled state of the switch or are closed, in the disconnected state of the or the electrical switch are open. The switch position of the one or more switches is controlled by a control unit SE via a control signal S. In 1 two switches are shown: a switch for disconnecting the battery BAT from the node ZK + of the intermediate circuit ZK and a switch for disconnecting the battery BAT from the node ZK- the intermediate circuit ZK. However, it would also be conceivable to use only one switch (eg the switch for the node ZK +) to disconnect the battery BAT.

The DC link voltage U _ZK in the DC link ZK is determined when coupled battery BAT essentially by the voltage of the battery BAT. The intermediate circuit ZK comprises two nodes: the node ZK + with a high potential and the node ZK- with a low potential. The potential difference between the two nodes ZK + and ZK- corresponds to the intermediate circuit DC voltage U _ZK .

Furthermore, a voltage regulation UR is provided for regulating the _{DC link} voltage with an upper limit value U _{ZK, GWo} for the intermediate _{circuit voltage} U _ZK and a lower limit value U _{ZK, GWu} for the intermediate _{circuit voltage} U _ZK . The voltage regulation UR monitors whether the intermediate _{circuit DC} voltage U _{ZK is} within the voltage range between the upper limit value U _{ZK, GWo} and the lower limit value U _{ZK, GWu} . If this is the case, the voltage regulation UR is passive and does not intervene. However, if the intermediate circuit DC voltage U _ZK leaves this voltage range, the voltage regulation UR intervenes in the power electronics LE1 of the generator GEN in such a way that the intermediate circuit DC voltage U _{ZK is} again guided into the predetermined voltage range.

The upper limit value U_{ZK, GWo} for the intermediate circuit voltage U_ZK and the lower limit U_{ZK, GWu} for the intermediate circuit voltage U_ZK are determined by the control unit SE and the voltage regulation UR given, and are for example at a battery voltage U_Bat from 360 V at U_{ZK, GWo}  = 390V and U_{ZK, GWu} = 290 V.

In 2 an embodiment of an inventive method is shown, the flow is controlled by the control unit SE.

In step 100 the current electric power P _{EL3 of} the electric drive machine eAM is determined. For this purpose, for example, the current flowing into the power electronics LE2 and the intermediate circuit DC voltage U _ZK can be measured and from this the recorded electrical power P _EL3 can be calculated. Alternatively, the mechanical drive power P _MECH2 = 2π · n _tract · M _{Trak of} the electric drive machine eAM can also be determined from the speed n _tract and the torque M _{tract of} the electric drive machine eAM and, assuming a specific efficiency, η _eAM = P _MECH2 / P _EL3 the electric drive machine eAM based on the mechanical drive power P _MECH2 and the efficiency η _eAM the electric power P _{EL3 are} determined.

Further, in the step 110 determines the electrical power P _EL4 supplied via the _{DC link} ZK electrical consumers. For this purpose, for example, the current flowing into the voltage converter DCDC and the intermediate circuit DC voltage U _ZK can be measured and from this the absorbed electrical power P _EL4 can be calculated.

• (a) die Summe aus der aktuellen elektrischen Leistung P_EL3 und der elektrische Leistung P_EL4 der über den Zwischenkreis ZK versorgten elektrischen Verbraucher kleiner gleich als ein oberer positiver Leistungsgrenzwert P_EL1,max für die Leistung P_EL1 des Generators GEN ist, und
• (b) die Summe aus der aktuellen elektrischen Leistung P_EL3 und der elektrische Leistung P_EL4 der über den Zwischenkreis ZK versorgten elektrischen Verbraucher größer gleich als ein unterer positiver Leistungsgrenzwert P_EL1,min für die Leistung P_EL1 des Generators GEN ist.

In the query 120 is checked as a basic requirement for disconnecting the BAT battery, whether

• (a) the sum of the current electric power P _EL3 and the electric power P _{EL4 of} the electrical consumers supplied through the intermediate _circuit ZK is less than _or equal to an upper positive power _limit P _{EL1, max} for the power P _{EL1 of} the generator GEN, and
• (b) the sum of the current electric power P _EL3 and the electric power P _{EL4 of} the electric consumers supplied through the intermediate _circuit ZK is greater than _or equal to a lower positive power _limit P _{EL1, min} for the power P _{EL1 of} the generator GEN.

If the sum of the current electrical power P _EL3 and the electrical power P _{EL4 of} the supplied via the _{DC link} ZK electrical load is greater than _or equal to the positive value P _{EL1, min} , the electric drive machine eAM does not work as a generator in the recuperation, since otherwise a negative electric power P _{EL3 of} the electric drive machine eAM would result.

The upper limit value P _{EL1, max} describes the power _{maximum of} the generator GEN (at the output of the power electronics LE1) and the lower limit value P _{EL1, min} describes a lower power limit at which still a sufficient efficiency is achieved, for example an efficiency of> 30% for the Internal combustion engine VM.

Unless in the query 120 shows that the sum of the power P _EL3 and P _{EL4 is} within the power _{band defined} by P _{EL1, min} and P _{EL2, max} , a basic requirement for disconnecting the battery BAT is met (but it is required that there are still other requirements query 130 and query 140 must be fulfilled). Thereupon, in the query 130 Verified that there is no high dynamics in the drive power. In this case, it is checked, for example, that no kickdown function was triggered by pressing a kickdown switch on the accelerator pedal, and as driving mode, for example, no sport mode (for a sporty driving style with higher power dynamics) was selected by the driver. On the query 130 could also be dispensed with in a modification of the embodiment.

If there are no signs of high drive dynamics, will be in step 140 Checked whether an additional Abkoppelkriterium related to the efficiency of the combination of generator GEN and engine eAM is met. This will later be related to the 3 and 4 explained.

If the efficiency-related decoupling criterion is fulfilled, unless the BAT battery is already decoupled (see query 150 ) - a decoupling of the battery BAT triggered (see step 160 ). For this purpose, a decoupling of the battery BAT from the DC link ZK is triggered by the control unit SE by appropriate control of the decoupling unit AKE, wherein the controllable switches of the decoupling unit AKE are opened. In addition, after disconnecting the battery BAT in step 170 an optimized value U _{ZK, opt} for the DC link voltage U _ZK set, which is characterized by a higher energy efficiency of the combination of generator GEN (including the downstream power electronics LE1) and electrical drive machine eAM (including the upstream power electronics LE2).

Before disconnecting the battery BAT, the upper limit value U _{ZK, GWo} for the voltage regulation UR is preferably reduced to a value above the current intermediate _circuit voltage U _ZK predetermined by the battery voltage, e.g. B. U _{ZK, GWo} = 365 V, and under limit U _{ZK, GWu} for the voltage control UR increased to a value below the current, predetermined by the battery voltage _{intermediate circuit} voltage U _ZK , z. B. U _{ZK, GWu} = 355 V. This has the advantage that at later uncoupling the voltage UR can react faster. If then in step 160 the battery BAT is decoupled, runs the intermediate _{circuit voltage} U _ZK (for example, starting from 360 V) to one of the two set limits U _{ZK, GWo} or U _{ZK, GWu} . After it is determined that the intermediate circuit voltage U _ZK one of the reaches the two limit values U _{ZK, GWo} or U _{ZK, GWu,} both limits U _{ZK, GWo} or U _{ZK, GWu} the intermediate circuit voltage is set by the control unit SE to an optimum value U _{ZK, opt} U _ZK such that the voltage regulation UR adjusts the intermediate circuit voltage U _ZK to the optimum value U _{ZK, opt of} the intermediate circuit voltage U _ZK .

After performing the step 170 the procedure is repeated (see jump to step 100 ).

Unless one of the requirements in the queries 120 . 130 or 140 is not fulfilled, is - if the battery BAT is not already disconnected (s 180 ) - no disconnection of the battery BAT is triggered and the procedure is repeated. Unless in the query 180 on the other hand shows that the battery BAT is already decoupled, in step 190 the DC link voltage U _{ZK set} to the open circuit voltage of the battery BAT. For this purpose, the no-load voltage of the battery BAT is determined, whereupon the control unit SE _sets the limit values U _{ZK, GWo} and U _{ZK, GWu} to this no-load voltage of the battery BAT. The voltage regulation UR thereby regulates the intermediate circuit voltage U _ZK to the open circuit voltage of the battery BAT. After the intermediate circuit voltage U _{ZK has been set} to the value of the open circuit voltage of the battery BAT, the controller SE is triggered by appropriate control of the decoupling unit AKE coupling the battery BAT to the DC link ZK, wherein the controllable switch the decoupling unit AKE are closed. After reaching the battery _voltage , the upper limit value U _{ZK, GWo is} again slightly raised and the lower limit value U _{ZK, GWu} is lowered again before the battery BAT is _switched on.

An exemplary embodiment for testing the efficiency-related decoupling criterion in step 140 is in 3 shown. In step 300 the current mechanical operating point of the generator GEN, ie the current speed n _{GEN of} the generator and the current torque M _{GEN of} the generator GEN, determined. Further, in step 301 the current mechanical operating point of the electric drive machine eAM is determined, ie the current speed n _{tract of} the drive machine eAM and the current torque M _{tract of} the drive machine eAM are determined. In step 310 is based on a stored efficiency map η _GEN (M _GEN , n _GEN , U _ZK ) for the efficiency η _GEN P _EL1 / P _{MECH1 of} the generator GEN an efficiency _curve η _GEN (U _ZK ) for the efficiency η _{GEN of} the generator GEN with respect to determines the current operating point of the generator GEN (ie, n _GEN , M _GEN ). Analog will be in step 311 based on a stored efficiency _map η _eAM (M _tract , n _tract , U _ZK ) for the efficiency η _eAM = P _MECH2 / P _{EL3 of} the electric drive machine eAM an efficiency _curve η _eAM (U _ZK ) for the efficiency η _{eAM of} the prime mover eAM with respect to the current operating point (ie n _tract , M _tract ) of the prime mover eAM determined. The two efficiency characteristics η _GEN (U _ZK ) and η _eAM (U _ZK ) are in step 320 for determining an efficiency characteristic η _{GEN EAM} (U _ZK) = η _GEN (U _ZK) · η _eAM (U _ZK) η to the Efficiency = P _MECH2 / P multiplied _{GEN EAM MECH1} of the composite of generator GEN and engine IOM.

Based on the efficiency _curve η _{GEN, eAM} (U _ZK ) is determined in step 330 the efficiency η _{GEN EAM} (U _ZK = U _{ZK, akt)} in the current intermediate circuit voltage U _{ZK, nude} determined, where the current intermediate circuit voltage U _{ZK, akt} is determined by the battery.

Further, in step 340 the absolute maximum η _{GEN, eAM, max} (U _{ZK, opt} ) of the efficiency characteristic η _{GEN, eAM} (U _ZK ) and the associated value U _{ZK, opt of} the intermediate _{circuit voltage} U _ZK searched. The value U _{ZK, opt} corresponds to the optimum value of the intermediate _circuit voltage U _ZK with respect to the efficiency η _{GEN, eAM of} the _combination of generator GEN and electric drive machine eAM. The value η _{GEN, eAM, max} (U _{ZK, opt} ) at the optimum value U _{ZK, opt of} the intermediate _{circuit voltage} U _ZK corresponds to the optimum efficiency.

In the query 350 is checked whether the current efficiency η _{GEN, eAM} (U _ZK = U _{ZK, akt} ) at the current _{DC link voltage} U _{ZK, akt} by more than the value Δ (eg, with Δ = 1%) is smaller than the maximum possible Efficiency η _{GEN, eAM, max} , ie η _{GEN, eAM} (U _ZK = U _{ZK, act} ) <η _{GEN, eAM, max} (U _{ZK, opt} ) - Δ.

If this is the case, the efficiency-related additional decoupling criterion from the query is 140 in 2 Fulfills. If this is not the case, the efficiency-related additional decoupling criterion from the query is 140 in 2 not fulfilled. In order to prevent frequent switching back and forth of Abkoppeleinrichtung AKE, an additional hysteresis can be provided.

In 3 became the efficiency-related decoupling criterion of the step 140 tested on the basis of the efficiency η _{GEN, eAM of} the _combination of generator GEN and drive unit eAM. In the context of an alternative embodiment, the efficiency-related decoupling criterion of the step 140 based on the power loss P _{V, GEN, eAM} (= P _{V, GEN} + P _{V, eAM} ) of the _combination of generator GEN and prime mover eAM are checked. An embodiment is in 4 shown. The steps 300 and 301 in 3 and 4 correspond to each other. The steps 310 ' . 311 ' . 320 ' and 330 ' in 4 correspond to the steps 310 . 311 . 320 respectively. 330 , however, in 4 instead of the respective efficiency, the respective power loss occurs. Accordingly, in step 340 ' unlike step 340 in 3 the minimum P _{V, GENeAM, min} (U _{ZK, opt} ) of the power loss characteristic P _{V, GEN, eAM} (U _ZK ) of the power loss P _{V, GEN, eAM of} the _combination of generator GEN and prime mover eAM and the associated value U _{ZK, opt} the DC _link voltage U _ZK searched. The value U _{ZK, opt} corresponds to the optimum value of the intermediate _circuit voltage U _ZK with respect to the power loss P _{V, GEN, eAM of} the _combination of generator GEN and electric drive machine eAM.

In the query 350 ' It is checked whether the current power loss P _{V, GEN, eAM} (U _ZK = U _{ZK, akt} ) at the current _{DC link voltage} by more than the value Δ (eg Δ = 0.1 · P _{V, GEN, eAM, min} ) is greater than the minimum possible power loss P _{V, GEN, eAM, min} , ie P _{V.GEN, eAM} (U _ZK = U _{ZK, akt} )> P _{V, GEN, eAM, min} (U _{ZK, opt} ) + Δ. If this is the case, the efficiency-related additional decoupling criterion from the query is 140 in 2 Fulfills. If this is not the case, the efficiency-related additional decoupling criterion from the query is 140 in 2 not fulfilled. In order to prevent frequent switching back and forth of Abkoppeleinrichtung AKE, an additional hysteresis can be provided.

In addition, the disconnection function described above can be extended by a look-ahead. For this purpose, the properties of the preceding route can be evaluated by using the data provided by the navigation system. These are, for example, the gradient and the gradient, the curve, possible speed limits or traffic obstructions. A prerequisite for this is that the probable route of the vehicle is known.

For example, a static electrical power consumption P _{EL3 of} the electric drive machine eAM can be predicted in each case on the basis of such data of the navigation system with respect to the route _ahead for the individual route sections lying ahead. The static mechanical drive power P _{MECH2 of} the electric drive machine eAM in the individual road sections can be determined, for example, with the aid of the known driving resistances of the vehicle (air resistance, rolling friction), the current weight of the vehicle and the navigation data of the individual road sections (eg gradient / slope, anticipated Driving speed, track limits). From the static mechanical drive power P _{MECH2 of} the electric drive machine eAM, assuming an efficiency η _eAM, a static electrical drive power P _EL3 for the individual road sections can be calculated therefrom.

If a static electrical drive power P _EL3 plus a predicted electrical power consumption P _{EL4 of} the other consumers supplied via the _{DC link} ZK lies in the line region of the generator GEN defined by P _{EL1, min} and P _{EL1, max} , a decoupling _enable is issued to the respective route section, otherwise it is maintained this a decoupling prohibition. A decoupling release does not necessarily mean that the battery is decoupled later in this section; For this purpose, the requirements in the queries will be present later 120 . 130 and 140 checked. In a decoupling prohibition but means that in this section of the route energy storage can not be decoupled (even if later the requirements in the queries 120 . 130 and 140 are fulfilled).

Alternatively or additionally, high-dynamic sections of the route lying ahead of the vehicle based on the data of the navigation system can be identified. For example, if an in-vehicle bend is detected, which is expected to reduce speed, or is likely to be recuperated, then this link will be decoupled. If a curve is found in front of the vehicle, according to the expected accelerated more, this section will be issued a decoupling. Analogously, it is possible to proceed before or after speed limits or traffic obstructions (eg congestion).

If the road sections lying ahead of the vehicle were evaluated with regard to a decoupling prohibition or a decoupling release, preferably a harmonization takes place in which several consecutive sections are assigned a common decoupling prohibition or a decoupling release in order to prevent a frequent change between decoupling prohibition and decoupling release.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102012210596 A1 [0004]
• DE 102012211393 A1 [0004]
• DE 102012018321 A1 [0004]
• DE 102009035483 A1 [0004]
• DE 10050379 A1 [0004]
• WO 2011/103911 [0004]
• EP 0967108 A1 [0004]

Claims (11)

A method for decoupling a rechargeable electric energy storage (BAT) of a serial hybrid drive of a motor vehicle, wherein the serial hybrid drive - an electric drive machine (eAM) for driving the vehicle with an upstream power electronics (LE2), - an energy converter (VM, GEN, LE1) for Generation of electrical energy for the electric drive machine and for the electrical energy storage, - coupled to the energy converter and the power electronics of the electric drive machine electrical energy storage (BAT); - Controllable decoupling means (AKE) for electrically decoupling the electrical energy storage of the energy converter and the electric drive machine; and - means (UR, SE) for adjusting the voltage applied to the input of the power electronics DC link voltage (UZK) with uncoupled energy storage; and, before disconnecting the energy store, a first value (U _{ZK, akt} ) of the DC link voltage (U _ZK ) is applied to the input of the power electronics (LE2), comprising the steps of: - detecting ( 120 ) that for a driving task no loss or absorption of electrical power from the energy storage is required and in response to decide to decouple the energy storage; - in response to this, triggering ( 160 ) of the controllable decoupling means such that the electrical energy storage is decoupled from the energy converter and the electric drive machine; and - after disconnecting the electrical energy store, setting ( 170 ) of the second value (U _{ZK, opt} ) of the _{DC link voltage} (U _ZK ) compared to the first value (U _{ZK, akt} ) of the _{DC link voltage} (U _ZK ) increased energy efficiency of the composite of energy converter and electric drive machine. The method of claim 1, wherein the determination that for a driving task no loss or absorption of electrical power required by the energy storage takes place in such a way that it is determined that for the driving task, the power (P _EL3 ) of the electric drive _machine , optional plus the power (P _EL4 ) of other electrical consumers which are supplied with electrical power via the intermediate circuit (ZK), - greater than or equal to a lower limit value (P _{EL1, min} ) of the power of the energy converter and - less than or equal to is an upper limit (P _{EL1, max} ) of the power of the power converter. Method according to one of the preceding claims, wherein - for the traveling object at the first value (U _{ZK, akt)} of the intermediate circuit DC voltage (U _ZK) of the value (η _{GEN EAM} (U _ZK = U _{ZK, akt)} P _{V, GEN, eAM} (U _ZK = U _{ZK, act} )) of a magnitude related to the energy efficiency of the composite of energy converter and electric drive machine or a part thereof; and - the step of deciding to decouple the energy storage takes place in dependence on this value of the variable. The method of claim 3, wherein the magnitude is efficiency or power dissipation. Method according to one of claims 3-4, wherein - for the driving task at an optimum value (U _{ZK, opt} ) of the _{DC link voltage} (U _ZK ) a value (η _{GEN, eAM, max} ; P _{V, GEN, eAM, min} ) of Magnitude related to the energy efficiency of the composite of energy converter and electric drive machine or any part thereof; and - the step of deciding to decouple the energy store as a function of the value (η _{GEN, eAM} (U _ZK = U _{ZK, act} ); P _{V, GEN, eAM} (U _ZK = U _{ZK, act} )) of the magnitude the first value of the intermediate _{circuit DC voltage} , and the value (η _{GEN, eAM, max} , P _{V, GEN, eAM, min} ) of the variable at the optimum value of the _{DC link voltage} . Method according to one of the preceding claims, wherein - the energy converter comprises an internal combustion engine (VM) and a generator (GEN) with a downstream power electronics (LE1), and - the step of deciding to decouple the energy storage, depending on - the speed (n _GEN ) of the generator or of a variable dependent thereon, - the rotational speed (n _tract ) of the prime mover or a variable dependent thereon, - the torque (M _GEN ) of the generator or a variable dependent thereon and / or - the torque (M _tract ) of the prime mover or a dependent there size. Method according to one of the preceding claims, comprising the steps taken after deciding to decouple the energy store: - deciding to reconnect the energy store; - before coupling the energy store, setting ( 190 ) one to the output voltage of the Energy storage adapted value of the DC link voltage; and - driving ( 200 ) of the controllable decoupling means such that the electrical energy store is again electrically coupled to the energy converter and the electric drive machine. The method of claim 7, wherein the step of deciding to reconnect the energy store comprises: Predict that a high driving dynamics is to be expected for an underlying driving situation and the setting of a value adapted to the output voltage of the energy storage value of the DC link voltage and the coupling of the energy storage takes place even before the expected high driving dynamics. Method according to one of the preceding claims, wherein It is predicted for a preceding route section that increased driving dynamics are to be expected for the route section lying ahead, and - In the case of increased driving dynamics this route section is assigned a decoupling prohibition, so that in this route section of the energy storage can not be decoupled. Method according to one of the preceding claims, wherein - it is predicted for a preceding route section that the power consumption is required to be absorbed or absorbed, in particular that for the route section the anticipated power (P _EL3 ) of the electric drive _machine , optionally plus the anticipated Power (P _EL4 ) of other electrical loads supplied with electrical power via the intermediate circuit, - less than or equal to a lower limit (P _{EL1, min} ) of the energy converter's output or - greater than or equal to an upper limit (P _{EL1, max} ) is the power of the energy converter, and - in the case of this forecast, this route section is assigned a decoupling prohibition, so that in this route section of the energy storage can not be decoupled. Hybrid serial drive of a motor vehicle, wherein the serial hybrid drive - an electric drive machine (eAM) for driving the vehicle with upstream power electronics (LE2), - an energy converter (VM, GEN, LE1) for generating electrical energy for the electric drive machine and for the electric Energy storage, - the coupled with the energy converter and the power electronics of the electric drive machine electrical energy storage (BAT), - controllable decoupling means (AKE) for electrically decoupling the electrical energy storage of the energy converter and the electric drive machine, - means (UR) for adjusting the input The power electronics applied DC bus DC voltage with uncoupled energy storage and - a control device (SE) for controlling the controllable decoupling comprises, and before disconnecting the energy storage, a first value (U _{ZK, akt} ) of the intermediate _{circuit DC voltage} (U _ZK ) is present at the input of the power electronics (LE2), wherein the control device (SE) is set up, - determine that for a driving task no loss or absorption of electrical power from the energy storage is required and in dependence decide to decouple the energy storage, in response, to control the controllable decoupling means such that the electrical energy storage is decoupled from the energy converter and the electric drive machine, and - after disconnecting the electrical energy storage a second value (U _{ZK, opt} ) of the _{DC link voltage} compared to the first value first value of the intermediate circuit DC voltage increased energy efficiency of the composite of energy converter and electric drive machine to specify the means for adjusting the voltage applied to the input of the power electronics DC link voltage.

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