EP1568113A1

EP1568113A1 - Circuit for a motor vehicle power supply network and corresponding operating method

Info

Publication number: EP1568113A1
Application number: EP03773526A
Authority: EP
Inventors: Stephan Bolz; Rainer Knorr; Günter LUGERT
Original assignee: Siemens AG
Current assignee: Continental Automotive GmbH
Priority date: 2002-12-04
Filing date: 2003-10-14
Publication date: 2005-08-31
Also published as: US20060164033A1; DE10256704B3; US7477040B2; WO2004051820A1

Abstract

The invention relates to an operating method for an electrical circuit with an energy store (5), made from several storage elements (C2-C5) and a charge-equalisation circuit (6), for charge equalisation between the individual storage elements (C2-C5) of the energy store (5), comprising the following steps: charging the energy store (5) and charge equalisation between the individual storage elements (C2-C5) of the energy store (5) by means of the charge equalisation circuit (6). The invention further relates to a corresponding electrical circuit for carrying out said operating method.

Description

description

Circuit for a vehicle electrical system and associated operating method

The invention relates to an electrical circuit for a vehicle electrical system according to the preamble of claim 1 and an associated operating method according to the preamble of claim 10.

Multi-voltage motor vehicle electrical systems are known which, for example, have operating voltages of 12 and 42 volts and are supplied with electrical energy by an integrated starter generator (ISG).

As is known, a double-layer capacitor can be used here as an electrical energy store, the energy stored in the double-layer capacitor allowing the internal combustion engine to start safely even after the motor vehicle has come to a temporary standstill.

For example, an engine starting system for a motor vehicle is known (DE 196 01 241 AI), in which a double-layer capacitor of a lead battery is connected in parallel. This double-layer capacitor is charged by the lead battery and discharges when the engine is started. In this way, the load on the lead battery when the engine is started is reduced.

Commercial double-layer capacitors, however, have a relatively large self-discharge, so that the double-layer capacitor must be charged from the vehicle battery at intervals of several days when the vehicle is stationary for a longer period of time in order to enable the internal combustion engine to be started safely later. This recharging of the double-layer capacitor takes place, for example, via a DC voltage converter from the 12 V vehicle battery, but this is associated with various disadvantages.

On the one hand, the DC / DC converter is usually designed for electrical loads with an output of 1 to 3 kW, so that large electrical losses occur when the double-layer capacitor is recharged while the vehicle is at a standstill.

On the other hand, in addition to the double-layer capacitor, the intermediate circuit capacitor must also be charged, which, with its large capacitance of several 10,000 μF, has the task of smoothing out the ripple that occurs when rectifying the three-phase alternating current generated in the ISG. The additional charging of the intermediate circuit capacitor also increases the energy consumption when the vehicle is at a standstill. This is particularly serious because the intermediate circuit capacitor has a high self-discharge due to its large capacitance, which necessitates frequent recharging.

Finally, the known type of recharging requires a switching operation, which leads to further losses in the case of electromechanical relays due to the excitation current and in the case of power semiconductors due to the control current.

The invention is therefore based on the object of recharging a capacitor stack - also referred to as a double-layer capacitor - in a motor vehicle electrical system while the vehicle is at a standstill with as little energy loss as possible.

Starting from a known circuit according to the preamble of claim 1, this object is achieved by the characterizing features of claim 1 and speaking operating method - solved by the features of claim 10.

The invention encompasses the general technical teaching of charging the double-layer capacitor by means of the charge compensation circuit which is present anyway.

However, the invention is not limited to the recharging of double-layer capacitors. Rather, it is also conceivable that instead of double-layer capacitors, other types of energy stores are used that have multiple storage elements. In the following, however, for the sake of simplicity, only the term of a double-layer capacitor is often used, although other types of electrical energy stores can also be used instead.

Charge balancing circuits of the type mentioned above are known per se and are described, for example, in EP 0 432 639 A2, so that the content of this publication can be attributed to the present description. However, the invention is not limited to the types of charge equalization circuits described therein, but can also be implemented with different types of charge equalization circuits.

Conventionally, the charge equalization circuit is connected in parallel to the double-layer capacitor, the double-layer capacitor consisting of several capacitors connected in series. In this case, the voltage equalization circuit is supplied with voltage by the double-layer capacitor itself, so that only charge equalization between the individual capacitors of the double-layer capacitor is possible, whereas charging the double-layer capacitor as a whole is not possible.

In a preferred embodiment of the invention, however, the charge equalization circuit optionally enables charge equalization between the individual capacitors of the double pel-layer capacitor or a charge of the double-layer capacitor as a whole. For this purpose, the charge equalization circuit is connected to a first voltage supply by a first switching element and to the energy store by a second switching element. Depending on the switching state of the two switching elements, either a charge equalization or a charging of the double-layer capacitor takes place.

If the second switching element is closed while the first switching element is open, the charge equalization circuit is connected to the double-layer capacitor and disconnected from the first voltage supply, the charge equalization circuit being supplied with current by the first voltage supply. In this case, the charge equalization circuit only enables a charge equalization between the individual capacitors of the double-layer capacitor, but no charging of the double-layer capacitor as a whole.

For charging the double-layer capacitor, on the other hand, the second switching element is opened and the first switching element is closed, so that the charge equalization circuit is electrically separated from the double-layer capacitor and connected to the first voltage supply. In this case, the voltage supply to the charge equalization circuit is no longer provided by the double-layer capacitor, so that recharging of the double-layer capacitor as a whole is possible. In this case, however, there is an additional charge equalization between the individual capacitors of the double-layer capacitor.

In an advantageous variant of the invention, the double-layer capacitor can be charged either from the first voltage supply or from an additional second voltage supply. This is advantageous, for example, in multi-voltage electrical systems of motor vehicles, which, for example, have a 12V battery and additionally a 36V battery. Have a battery for a 42V electrical system. The double-layer capacitor can then be recharged by the battery with the better charge state. In this variant of the invention, the charge equalization circuit is therefore connected to the first voltage supply (for example the 12V battery) by the first switching element and additionally to a second voltage supply (for example 36V battery) by means of a third switching element. In order to charge the double-layer capacitor from the first voltage supply, the first switching element is closed while the third switching element is open. To charge the double-layer capacitor from the second voltage supply, on the other hand, the third switching element is closed while the first switching element is open.

It can already be seen from the above statements that the term “power supply” used in the context of the invention is not limited to the lead accumulators customary in motor vehicles, but also encompasses other types of accumulators.

The control of the individual switching elements is preferably carried out by a control unit, which is preferably connected to a timer, in order to check the double-layer capacitor at regular time intervals and to recharge it if necessary.

This control unit preferably has a first comparator unit which compares the state of charge of the double-layer capacitor with a first minimum value in order to recharge the double-layer capacitor when the value falls below the first minimum value. The first comparator unit preferably compares the state of charge of the energy store during recharging with a first maximum value in order to avoid excessive recharging of the double-layer capacitor. The double-layer capacitor is preferably only recharged when the first voltage supply (eg 12V battery) or the second voltage supply (eg 36V battery) is sufficiently charged.

In a preferred embodiment, a second comparator unit is therefore provided, which measures the state of charge of the first voltage supply and controls the first switching element as a function of the measured state of charge. The first switching element is preferably only switched through when the charge state of the first voltage supply is sufficient to enable the double-layer capacitor to be recharged.

A third comparator unit is preferably additionally provided, which measures the state of charge of the second voltage supply (e.g. 36V battery) and controls the third switching element as a function of the measured state of charge. In this case, the first switching element is preferably only switched through when the state of charge of the second voltage supply is sufficient to enable the double-layer capacitor to be recharged.

Relays or semiconductor switches, for example, can be used as switching elements in the context of the invention. However, so-called transfer gates are preferably used as switching elements, since the polarity of the differential voltage between the double-layer capacitor and the first voltage supply (e.g. 12V battery) or the second voltage supply (e.g. 36V battery) can be arbitrary. Such transfer gates are known per se and consist of two transistors connected in series, which are preferably designed as MOSFETs.

In addition, the invention also includes a corresponding operating method for such an electrical circuit. Other advantageous developments of the invention are contained in the subclaims or are explained below together with the description of the preferred embodiment of the invention with reference to the drawings. Show it:

1 shows a circuit according to the invention for a vehicle electrical system, FIG. 2 shows a control unit for the circuit from FIG. 1, FIG. 3 shows the operating method of the circuit from FIG. 1 and

FIG. 4 shows a preferred exemplary embodiment of the switching elements in the circuit from FIG. 1.

The circuit diagram in FIG. 1 shows in simplified form a multi-voltage vehicle electrical system of a motor vehicle with two mains voltages of 12V and 42V. The structure of the multi-voltage on-board electrical system is first described below, in order to then explain its mode of operation with reference to FIG. 3.

The electrical energy is generated in the multi-voltage electrical system by an integrated starter generator ISG, which is driven by the crankshaft of an internal combustion engine.

The integrated starter generator ISG is connected on the output side to an electrical converter 1, which generates a DC voltage of 42V, the output of the converter 1 being connected to ground via an intermediate circuit capacitor C1 for smoothing the DC voltage.

The output of the converter 1 is connected via a switching element S1 to a 3βV battery 2, which is thus charged when the switching element S1 is closed.

In addition, the output of the converter 1 is connected to a 12 V battery 4 via a DC voltage converter 3, the DC voltage converter 3 being connected to the output of the converter. ters 1 provided mains voltage of 42V converted to a voltage of 14V. The 12V battery 4 is charged during operation of the internal combustion engine via the DC converter 3.

Furthermore, the multi-voltage on-board electrical system has a double-layer capacitor 5 as an electrical energy store, which can be connected to the integrated starter-generator ISG via a switching element S2 and which enables the internal combustion engine to be started safely after a long standstill. In this exemplary embodiment, the double-layer capacitor 5 consists, for simplification, of only four capacitors C2-C5 connected in series. In a 42V electrical system, however, 24 capacitors with a maximum voltage of 2.3V are normally connected in series, which results in a maximum total voltage of 55.2V. On the one hand, this total voltage enables a reliable supply of the mains voltage of 42V and on the other hand it is below the limit of 60V, up to which no special insulation measures are required in electrical systems.

In addition, the multi-voltage electrical system has a conventional charge compensation circuit 6, which effects charge compensation between the individual capacitors C2-C5 of the double-layer capacitor 5. The charge equalization circuit 6 has a primary circuit which is connected to ground via a switching element S3 and to the positive connection of the double-layer capacitor 5 via a switching element S4, a primary winding L1 being arranged in the primary circuit. Furthermore, the charge equalization circuit 6 has four secondary circuits, each of which is connected in parallel with the individual capacitors C2-C5. A diode D1-D4 and a secondary winding L2-L5 are connected in series in each secondary circuit. The mode of operation of the charge equalization circuit 6 is described in detail in EP 0 432 639 A2, so that a detailed description of the function of the charge compensation circuit 6 can be omitted.

The charge equalization circuit 6 can via a switching element

55 with the 12V battery 4 and another switching element

56 can be connected to the 36V battery 2. These connections enable the double-layer capacitor 5 to be recharged via the 12V battery 4 or via the 36V battery 2, as will be described in more detail.

The switching elements S3-S6 are controlled by a control unit 7, which is shown in a highly simplified manner in FIG.

The control unit 7 has a logic unit 8, which receives the voltage at terminal 15 of the vehicle electrical system and the switching position of the switching element S2 via a level converter 9, in order to control the switching elements S1 and S3-S6 as a function thereof, as will be described in detail below.

Furthermore, the control unit 7 has a comparator unit 10, which measures the battery _voltage U _BATI2 at the output of the 12V battery 4 and compares it with a predetermined minimum value U _BATI2 , _MIN . When the minimum value U _BATI2 , _MIN is _exceeded , the comparator unit 10 _transmits a high level to the logic unit 8, the high level indicating a sufficient charge state of the 12 V battery 4.

Furthermore, the control unit 7 has a comparator unit 11, which measures the battery _voltage U _BAT36 at the output of the 36V battery 2 and compares it with a predetermined minimum value U _BAT36 , _MIK . When the minimum value U _BAT36 , _MIN is _exceeded , the comparator unit 11 _transmits a high level to the logic unit 8, the high level indicating an adequate charge state of the 36V battery 2. In addition, a comparator unit 12 is provided, which detects the voltage U _{c of} the double-layer capacitor 5 and compares it with a predetermined minimum value U _C , _MIN . If the value falls below the minimum value U _C , _MIN , the comparator unit 12 then outputs a high level to the logic unit 8 in order to indicate that the double-layer capacitor 5 must be recharged.

Furthermore, the control unit 7 has a comparator unit 13, which compares the voltage U _{c of} the double-layer capacitor 5 with a predetermined maximum value U _C , _AX . If the maximum value is exceeded, the comparator unit 13 passes a high level to the logic unit 8, the high level indicating that the charging process of the double-layer capacitor 5 should be ended.

Finally, the control unit has a timer 14 which emits a trigger signal to the logic unit 8 daily in order to stimulate the implementation of the operating method according to the invention.

The control unit 7 recognizes the driving operation from the fact that the line voltage of 14 V is present at terminal 15. In this operating state, switches S1 or S2 and S4 are closed, while switches S5 and S6 are open. The charge equalization circuit 6 is then electrically connected to the double-layer capacitor 5 via the switching element S4, but is separated from the 12V battery 4 and from the 36V battery 2. By pulsing the switching element S3, a charge equalization between the individual capacitors C2-C5 of the double-layer capacitor 5 can then take place. However, charging the double-layer capacitor 5 as a whole is then not possible because of the opened switching elements S5 and S6, since the charge equalization circuit 6 is separated from the 12V battery 4 and from the 36V battery 2. However, no charge equalization should take place between the individual capacitors C2-C5 of the double-layer capacitor 5 if the double-layer capacitor 5 is connected to the integrated starter generator ISG and is subjected to high dynamic loads. The control unit 7 therefore also evaluates the switching state of the switching element S2 and blocks the switching element S3 of the charge compensation circuit 6 when the switching element S2 is closed.

In contrast, when the vehicle is at a standstill, the switching elements S1, S2 and S4 are open, so that the double-layer capacitor 5 is electrically separated from the charge equalization circuit 6. This separation enables the double-layer capacitor 5 to be recharged, since the charging voltage is not limited by the capacitor voltage U _c .

The operating method shown in FIG. 3 is carried out in order to maintain the charge stored in the double-layer capacitor 5 and thereby enable the internal combustion engine to start safely.

At the beginning of the operating method according to the invention, the timer 14 is first reset and then incremented in a loop until a predetermined time period T _{MX has} expired, wherein the time period T _AX can correspond to one day, for example.

The voltage U _c is then measured at the positive connection of the double-layer capacitor 5 in order to be able to check whether the double-layer capacitor 5 has to be recharged.

The measured voltage U is therefore compared with a minimum value UC, _M IN, the operating method being ended when the voltage U exceeds the minimum value U _C , _MI N, since the double-layer capacitor 5 then does not have to be recharged. If, on the other hand, the voltage U _{c of} the double-layer capacitor 5 has dropped below the minimum value U _C , _MIN due to the self-discharge of the double-layer capacitor 5, the double-layer capacitor 5 must be recharged in order to ensure a reliable start of the internal combustion engine.

In the next steps it is then checked whether the state of charge of the 36V battery 2 or the 12V battery 4 is sufficient to recharge the double layer capacitor 5.

For this purpose, the voltage U _{BAT36 of} the 36V battery 2 is first measured and compared with a minimum value U _BA T ₃₆ , _MIN .

If the voltage U _{BAT36 of} the 36V battery 2 exceeds the predetermined minimum value U _BAT36 , _MIN , the energy for recharging the double-layer capacitor 5 can be taken from the 36V battery 2. In this case, the switching element S6 is closed in order to connect the charge equalization circuit 6 to the 36V battery 2, while the switching element S5 remains open.

In contrast, if the voltage U _BA T _{36 of} the 36V battery 2 falls below the predetermined minimum value U _BA T ₃₆ , _MIN , the double-layer capacitor 5 should not be recharged from the 36V battery 2, since its charge state is not sufficient for this. This prevents damage to the 36V battery.

In a next step, the voltage U _{BATI2 of} the 12V battery 4 is then measured in order to check whether the electrical energy for recharging the double-layer capacitor 5 can be drawn from the 12V battery.

The measured voltage U _{BATI2 of} the 12V battery is therefore compared with a predetermined minimum value U _BAT I2, MI _N. If the voltage U _BAT I _{2 of} the 12V battery 4 falls below the predetermined minimum value U _BA T _I2 , _MI N, then the double-layer capacitor 5 should not be recharged from the 12V battery 4, since its state of charge is not sufficient for this. In this case, the double-layer capacitor 5 is not recharged and the operating method according to the invention is ended.

If, however, the voltage U _{BATI2 of} the 12V battery 4 _exceeds the predetermined minimum value U _BA T _I2 , _MI N, the energy for recharging the double-layer capacitor 5 can be taken from the 12V battery 4. In this case, the switching element S5 is closed to connect the charge balancing circuit 6 to the 12V battery 4 while the switching element S6 is opened.

Both when recharging from the 12V battery 4 and when recharging from the 36V battery 2, the switching element S3 is then pulsed in order to charge the double-layer capacitor 5.

During the charging of the double-layer capacitor 5, the voltage U _{c of} the double-layer capacitor 5 is continuously measured and compared with a maximum value U _C , _MAX , in order to avoid excessive recharging of the double-layer capacitor 5.

The charging process is therefore interrupted when the voltage U _{c of} the double-layer capacitor 5 exceeds the predetermined maximum value U _C , _MAX . For this purpose, the two switching elements S5 and S6 and the switching element S3 are opened.

The timer 14 is then reset and the method steps described above are carried out again in a loop. Finally, FIG. 4 shows a so-called transfer gate 15, which can be used to implement the switching elements S1-S6 in terms of circuitry. The transfer gate 15 consists essentially of two series-connected MOSFET transistors T1 and T2 with two parasitic diodes D5 and D6 and a resistor R1. When a positive voltage of approximately U _G s = + 10V is applied between the gate and source of the transfer gate 15, both MOSFET transistors T1 and T2 become conductive and the transfer gate 15 is switched on. In contrast, if the gate-source voltage U _{Gs is} 0V, the transfer gate 15 is switched off. In the switched-off state, only one of the two MOSFET transistors T1, T2 blocks, since the other MOSFET transistor T1 or T2 is operated with reverse polarity and conducts its parasitic diode D5 or D6.

Claims

1.5 Claims

1. Electrical circuit for a vehicle electrical system, in particular for charge maintenance in a double-layer capacitor (5), with

a first power supply (4),

an electrical energy store (5) consisting of a plurality of storage elements (C2-C5) and chargeable by the first voltage supply (2) and

a charge compensation circuit (6) for charge compensation between the individual storage elements (C2-C5) of the energy store (5),

characterized

that the charge equalization circuit (6) is connected to the first voltage supply (4) by a first switching element (S5) and to the energy store (5) by a second switching element (S4) in order to, depending on the switching state of the switching elements (S4, S5) to effect the charge balance and / or to charge the energy store (5).

2. Electrical circuit according to claim 1, characterized in that the charge equalization circuit (6) is additionally connected by a third switching element (S6) to a second voltage supply (2) in order to selectively store the energy store (5) from the first voltage supply (4) or to charge from the second voltage supply (2).

3. Electrical circuit according to claim 1 and / or claim 2, gekennzeic hn et du rch a control unit (7) for controlling the first switching element (S5) and / or the second switching element (S4) and / or the third switching element (S6).

4. Electrical circuit according to claim 3, so that the control unit (7) is connected to a timer (14) in order to initialize the recharging of the energy store (5).

5. Electrical circuit according to claim 3 and / or claim 4, dadurchgekennzeichn et that the control unit (7) has a first comparator unit (12) to the state of charge of the energy store (5) with a predetermined first minimum value (U _C , _MIN ) and / or compare with a specified maximum value (U _C , _MAX ) ZU.

6. Electrical circuit according to at least one of the claims 3 to 5, that means that the control unit (7) has a second comparator unit

(10), which compares the voltage (U _BA τi2) of the first voltage supply (4) with a second minimum value (U _BATI2 , _MIN ) and the first switching element (S5) only when the second minimum value (U _BA TI ₂ , _MIN ) switches through.

7. Electrical circuit according to claim 6, d a d u r c h g e k e n n z e i c h n e t that the control unit (7) a third comparator unit

(11), which compares the voltage (U _BAT36 ) of the second voltage supply (2) with a third minimum value (U _BAT36 , _MIN ) and the third switching element (S6) only when the third minimum value is exceeded (U _BA T ₃₆ , _MIN ) turns on.

8. Electrical circuit according to at least one of the preceding claims, characterized in that the first switching element (S5) and / or the second switching element (S4) and / or the third switching element (S6) is a relay or a semiconductor switch.

9. Electrical circuit according to at least one of the preceding claims, since you rchgek characterized that the first switching element (S5) and / or the second switching element (S4) and / or the third switching element (S6) is a transfer gate (15) ,

10. Operating method for an electrical circuit with an electrical energy store (5) consisting of several storage elements (C2-C5) and a charge equalization circuit (6) for charge equalization between the individual storage elements (C2-C5) of the energy store (5), with the following steps:

- charging the energy store (5), - charge equalization between the individual storage elements (C2-C5) of the energy store (5) by the charge equalization circuit (6), characterized in that the charging of the energy store (5) by the charge equalization circuit (6 ) he follows.

11. Operating method according to claim 10, so that the charge compensation circuit (6) for charging the energy store (5) is connected to a first voltage supply (4) or a second voltage supply (2).

12. Operating method according to claim 11, g e k e n n z e i c h n e t d u r c h the following steps:

- Measurement of the output voltage (U _BATI2 ) of the first voltage supply (4) - Comparison of the measured output voltage (U _BA τi ₂ ) with a first minimum value (U _BAT I ₂ , _MIN )

- Connection of the charge equalization circuit (6) to the first voltage supply (4) only when the first minimum value is exceeded (U _BA TI2, MIN) •

13. Operating method according to claim 12, characterized by the following steps: - Measurement of the output voltage (U _BA τ ₃₆ ) of a second voltage supply (2)

- Comparison of the measured output voltage (U _BAT36 ) with a second minimum value (U _B AT36, MIN)

- Connection of the charge equalization circuit (6) to the second voltage supply (2) only when the second minimum value is exceeded (U _B AT36, MIN) •

14. Operating method according to at least one of claims 10 to 13, characterized in that the energy store (5) in normal operation with the first voltage supply (4) and / or the second voltage supply (2) connected and at a standstill of the first voltage supply (4) and the second power supply (2) is disconnected.

15. Operating method according to at least one of claims 10 to 14, characterized in that the charge state of the energy store (5) in each case after a predetermined period of time (T _MAX ) checks and the energy store (5) when falling below a predetermined third minimum value (UC.M _IN ) is charged.

16. Operating method according to at least one of claims 10 to 15, characterized in that the energy store (5) is charged up to a predetermined maximum value (U _C , _MAX ).