DE102012018730B4 - Motor vehicle electrical system with an additional energy storage and associated operating method - Google Patents

Abstract

Motor vehicle electrical system for a motor vehicle with an internal combustion engine, with a) a rechargeable electric battery (1, 2) for storing electricity, b) a starter generator (9) which can be driven by the internal combustion engine and has an integrated generator for generating electricity, the starter generator (9) optionally being the Internal combustion engine can start or is driven by the internal combustion engine to generate electricity, c) a live power line (5) for electrical contacting the battery (1, 2), the starter generator (9) and the starter (7), d) an energy storage device (11) for electricity storage, wherein the energy storage (11)d1) has a sufficiently large capacity to carry out a warm start of the internal combustion engine, andd2) is a capacitor, and mite) a start-stop system for automatically switching off the internal combustion engine during a stationary phase of the motor vehicle and for the automatic warm start of the internal combustion engine by the starter generator (9) at the end of the stationary phase, the starter generator (9) being supplied with power from the energy storage (11) during a warm start, andf) a starter (7) for a cold start of the Internal combustion engine, whereby the starter (7) is supplied with power from the battery (1, 2) during a cold start; characterized in,g) that the battery (1, 2) is connected to the live power line (5) via a main switch (4), wherein the battery (1, 2) can be connected to the live power line (5); andh) that the motor vehicle electrical system has a DC-DC converter (10) which is connected to the power line (5) in order to supply the starter generator (9) with the required electrical energy for a warm start and to supply the starter generator (9) during a warm start to supply the required electrical energy from the electrical energy storage (11) independently of the battery (1, 2).

Description

The invention relates to a motor vehicle electrical system for a motor vehicle with an internal combustion engine and start-stop operation and a corresponding operating method for such a motor vehicle electrical system.

Modern passenger cars with an internal combustion engine often have a start-stop system to save fuel. When operating such a passenger car, the start-stop system switches off the internal combustion engine during short standstill phases, for example when the passenger car stops at a traffic light. At the end of the stationary phase, the start-stop system automatically starts the combustion engine again so that the car can continue driving if, for example, the traffic light turns green. Such start-stop systems can also be used in commercial vehicles (e.g. city buses) to reduce fuel consumption. However, the problem with using a start-stop system in a city bus is the high number of start-stop cycles over the lifespan of the city bus, which puts a lot of strain on the vehicle's electrical system and in particular on the city bus's battery. Without complex additional measures, a reduced service life of the vehicle battery can therefore be expected when using a start-stop system in a city bus. In addition, the high power consumption when starting the internal combustion engine leads to a corresponding voltage drop in the vehicle electrical system, which is associated with functional restrictions (e.g. in control devices and comfort devices). The large energy requirement when the engine stops and the vehicle is stationary puts additional strain on the battery.

Out of DE 103 05 058 B3 A motor vehicle electrical system is known, which, however, only has a starter generator that carries out both a cold start and a warm start.

Out of DE 10 2010 027 828 A1 Although it is known to provide both a starter and a starter generator, the starter generator carries out a warm start, whereas the starter carries out a cold start. However, the power supply for both the starter generator and the starter motor comes from a conventional battery.

The DE 10 2009 027 931 A1 discloses an electronic control device for an electric machine. The control device may include a starter generator or a starter for an internal combustion engine in a motor vehicle. The control device can further comprise a controller and a circuit arrangement with a pulse inverter. In order to reduce material, component and assembly costs and weight, the control device includes the pulse inverter, the associated controller and a DC/DC converter in one structural unit.

The DE 10 2008 041 298 A1 relates to a support device for supporting a motor vehicle battery or an internal combustion engine of a motor vehicle, which is loaded by a motor vehicle electrical system and a motor vehicle starter or by a desire to accelerate. The support device comprises a temporary energy storage and a coupling device which is connected between the temporary energy storage and an energy delivery point which is set up for connection to the motor vehicle starter (and thus to the internal combustion engine). The temporary energy storage is set up to deliver at least a portion of the energy temporarily stored in the temporary energy storage to the motor vehicle starter via the coupling device and the energy delivery point.

Reference should also be made to the general technical background of the invention DE 10 2008 054 885 A1 , DE 10 2007 026 164 A1 , DE 103 13 081 A1 and DE 10 2012 205 824 A1 .

The invention is therefore based on the object of solving the above-mentioned problems when using a start-stop system in a city bus or other motor vehicle.

This object is achieved by a motor vehicle electrical system according to the invention with the features of the main claim or by a corresponding operating method with the features of the secondary claim. Advantageous further developments are specified in the dependent claims and the description.

The invention includes the general technical teaching of providing an energy storage device (e.g. Ultracap) in a motor vehicle electrical system for power supply in addition to the conventional battery in order to maintain the electrical system voltage in the motor vehicle electrical system, in particular during a warm start of the internal combustion engine initiated by the start-stop system to stabilize and supply the on-board electrical system when the engine stops. Furthermore, the energy storage can also be used in normal operation to power the vehicle electrical system in order to save fuel, with the energy storage being charged in overrun phases by recuperation, so that the generator requires less mechanical drive power on average over time, which leads to corresponding fuel savings .

The motor vehicle on-board electrical system according to the invention initially has, in accordance with conventional motor vehicle on-board electrical systems, a rechargeable electric battery for storing electricity, the battery usually being an electro-chemical battery, such as a conventional lead accumulator.

In addition, the motor vehicle electrical system according to the invention also has a conventional starter in accordance with the prior art in order to start the internal combustion engine, such starters being known from the prior art and therefore need not be described in more detail. This conventional starter is used for cold starts.

In addition, the motor vehicle electrical system according to the invention, in accordance with the prior art, has a generator, which is also referred to as an alternator and is used to generate electricity. According to the invention, the generator is a so-called integrated starter generator (ISG), wherein the integrated starter generator can either start the internal combustion engine or is driven by the internal combustion engine to generate electricity. In a “generator” operating mode, the starter generator works as a generator to generate electricity, whereas in a “starter” operating mode, the starter generator works as a starter to start the internal combustion engine.

In addition, the motor vehicle electrical system according to the invention has a live power line to which the battery, the generator and the starter are or can be connected.

In addition, the motor vehicle electrical system according to the invention also has a start-stop system which automatically switches off the internal combustion engine when the motor vehicle is stationary and automatically restarts the internal combustion engine at the end of the stationary phase. Such start-stop systems are known from the prior art and therefore do not need to be described in more detail.

In the preferred embodiment, the starter generator works with 24V voltage and is magnet-free, i.e. the starter generator has no permanent magnets. This is advantageous because it means that no safety precautions regarding contact protection are required, since even in the event of a fault, no electrical voltages above the legal limit values can occur. For example, the starter generator can be designed as a reluctance motor, in particular as a switched reluctance machine.

The energy storage device provided according to the invention is a capacitor, for example a so-called supercapacitor, in particular in the form of a double-layer capacitor. However, the invention is not limited to these exemplary embodiments with regard to the design and functionality of the energy storage device. However, the energy storage preferably has a large capacity in order to be able to store enough electrical energy. In general, it can be said that the energy storage device has a sufficiently large capacity to store the electrical energy required for a warm start of the internal combustion engine and for supply during the stop phases.

Furthermore, the motor vehicle electrical system according to the invention comprises a DC-DC converter. The DC-DC converter can connect the energy storage device to the power line and/or directly to the starter generator, with the DC-DC converter providing the mains voltage on the network side.

In the preferred exemplary embodiment, the motor vehicle electrical system has an electrical system voltage that is so low that no contact protection is required. For example, the motor vehicle electrical system can have an electrical system voltage of 24 volts, since contact protection is only required when the electrical system voltage is more than 60 volts DC. In addition, it should be mentioned that the motor vehicle electrical system is preferably free of high voltage without high-voltage components with a voltage that requires protection against contact, in particular without high-voltage components with more than 60 volts DC or 25 volts AC.

Furthermore, it should be noted that the invention does not only claim protection for the motor vehicle electrical system described above, regardless of the associated motor vehicle. Rather, the invention also claims protection for a complete motor vehicle with such a motor vehicle electrical system, which can be, for example, a truck or a city bus or another commercial vehicle.

Finally, the invention also includes a corresponding operating method for such a motor vehicle on-board electrical system, wherein the live power line of the motor vehicle on-board electrical system is fed from the energy storage, in particular when the internal combustion engine is started, in order to support the on-board electrical system voltage during the starting process of the internal combustion engine and when the engine is switched off to supply the on-board electrical system.

According to the invention, the motor vehicle electrical system has both a starter and a starter generator. As part of the operating method according to the invention, the internal combustion engine is always started by means of the starter generator during a warm start, whereas the internal combustion engine is always started by the conventional starter during a cold start.

In addition, there is also the possibility that the energy storage device is charged from the vehicle electrical system when the internal combustion engine is operating in overrun mode and does not produce any mechanical power, which is known from the prior art under the term recuperation.

• 1 ein schematisches Schaltbild eines erfindungsgemäßen Kraftfahrzeug-Bordnetzes,
• 2 eine Abwandlung des Kraftfahrzeug-Bordnetzes aus 1 für einen Betrieb in einem Stadtbus,
• 3 ein Flussdiagramm zur Verdeutlichung des Startens des Verbrennungsmotors bei einem Kaltstart,
• 4 ein Flussdiagramm zur Verdeutlichung von Start und Abschalten des Verbrennungsmotors durch das Start-Stopp-System, sowie
• 5 ein Flussdiagramm zur Verdeutlichung der Rekuperation zum Aufladen des Energiespeichers.

Other advantageous developments of the invention are characterized in the subclaims or are explained in more detail below together with the description of the preferred exemplary embodiments of the invention with reference to the figures. Show it:

• 1 a schematic circuit diagram of a motor vehicle electrical system according to the invention,
• 2 a modification of the vehicle electrical system 1 for operation in a city bus,
• 3 a flowchart to illustrate starting the internal combustion engine during a cold start,
• 4 a flowchart to illustrate starting and switching off the internal combustion engine by the start-stop system, as well as
• 5 a flowchart to illustrate the recuperation for charging the energy storage.

1 shows a motor vehicle electrical system according to the invention for a commercial vehicle or a passenger car.

The motor vehicle electrical system according to the invention has two conventional rechargeable lead batteries 1, 2, which are connected in series and can be designed, for example, as so-called AGM batteries (AGM: absorbent glass mat).

The ground-side lead battery 1 is connected to a ground point 3 of the motor vehicle, while the voltage-side lead battery 2 is connected to a live power line 5 via a main switch 4.

On the one hand, the so-called “terminal 15” is connected to the power line 5 via a switch 6, whereby the “terminal 15” is also referred to as “ignition plus” or “switched plus” and refers to the positive pole connected to the ignition lock of the motor vehicle. The consumers (e.g. radio, headlights, electric heater, etc.) are then connected to “Terminal 15”.

On the other hand, a conventional starter 7 is connected to the power line 5 and is used to start the internal combustion engine of the motor vehicle, especially during a cold start. The starter 7 is designed in a conventional manner.

In addition, an integrated starter generator 9 (ISG: integrated starter generator) is connected to the power line 5 via a DC/AC converter 8. On the one hand, the starter generator 9 serves as a generator in a “generator” operating mode and is driven by the internal combustion engine in order to generate electricity and supply the motor vehicle electrical system with the required electrical energy. On the other hand, the starter generator 9 enables the internal combustion engine to be started in a “starter” operating mode, in particular during a warm start at the end of a stationary phase in which the internal combustion engine was temporarily switched off by a start-stop system.

Finally, a DC-DC converter 10 is connected to the power line 5 and is connected to a so-called ultracap 11, which is a capacitor with a very large capacity, so that the ultracap 11 is suitable for storing electricity. The capacity of the ultracap 11 is so large that the ultracap 11 can store enough electrical energy to supply the starter generator 9 with the required electrical energy during a warm start, regardless of the lead batteries 1, 2.

The Ultracap 11 supports the vehicle electrical system voltage on the power line 5 both during a cold start and a warm start, with the support during a warm start being particularly important since warm starts occur very frequently when a start-stop system is used.

On the one hand, the support of the vehicle electrical system voltage by the Ultracap 11 prevents the service life of the lead batteries 1, 2 from being reduced by the frequent warm starts when using a start-stop system.

On the other hand, the support of the vehicle electrical system voltage by the Ultracap 11 also prevents voltage drops in the vehicle electrical system voltage on the power line 5 during a cold start or a warm start due to the then large operating current. This also prevents disruptive functional restrictions from occurring due to a voltage drop during a cold start or a warm start.

It should be mentioned here that the starter generator 9 is magnet-free, ie the starter generator 9 has no permanent magnets. This is advantageous because it means that no further safety precautions regarding contact protection are required, since even in the event of a fault, no voltages above the legal limit values can occur.

2 shows a modification of the vehicle electrical system 1 , so that to avoid repetition, reference is made to the above description, with the same reference numbers being used for corresponding details.

A special feature of this exemplary embodiment is that the battery current is measured by means of a current measuring resistor 12, the electrical voltage falling across the current measuring resistor 12 forming a measure of the battery current and being detected by a control unit 13. In addition, the DC-DC converter 10 is also connected directly to the DC/AC converter 8, so that the cold or emergency start can also take place without affecting the conventional on-board electrical system.

3 shows in a very simplified form the starting of the internal combustion engine during a cold start, with a check being made in a step S1 as to whether a cold start should take place. If this is the case, the internal combustion engine is started in a step S2 by the conventional starter 7, the power supply to the starter 7 being guaranteed by the two lead batteries 1, 2.

4 shows the operation of the start-stop system in a very simplified form. In a step S3, it is checked whether a stationary phase begins, for example when stopping in front of a red traffic light. If this is the case, the internal combustion engine is switched off in a step S4. In a step S5 it is then checked whether a warm start should take place because the stationary phase has ended, for example when the traffic light switches from red to green. If this is the case, the internal combustion engine is then started in a step S6 by the starter generator 9, the vehicle electrical system voltage on the power line 5 being supported by the Ultracap 11.

Finally shows 5 In a greatly simplified form, recuperation, ie charging of the ultracap 11 during overrun operation when the internal combustion engine does not have to provide any mechanical power, for example when rolling down a slope. In a step S7 it is checked whether such an overrun operation is present. If this is the case, the Ultracap 11 is charged by the starter generator 9.

List of reference symbols:

1

Lead battery

2

Lead battery

3

ground point

4

Main switch

5

Power line

6

Switch

7

Starter

8th

DC/AC converter

9

Starter generator

10

DC-DC converter

11

Ultracap

12

Current measuring resistor

13

Control unit

Claims (9)

Motor vehicle electrical system for a motor vehicle with an internal combustion engine, with a) a rechargeable electric battery (1, 2) for storing electricity, b) a starter generator (9) which can be driven by the internal combustion engine and has an integrated generator for generating electricity, the starter generator (9) being optional can start the internal combustion engine or is driven by the internal combustion engine in order to generate electricity, c) a live power line (5) for electrically contacting the battery (1, 2), the starter generator (9) and the starter (7), d) one Energy storage (11) for storing electricity, wherein the energy storage (11) d1) has a sufficiently large capacity to carry out a warm start of the internal combustion engine, and d2) is a capacitor, and with e) a start-stop system for automatically switching off the internal combustion engine during a stationary phase of the motor vehicle and for the automatic warm start of the internal combustion engine by the starter generator (9) at the end of the stationary phase, the starter generator (9) being supplied with power from the energy storage (11) during a warm start, and f) a starter (7) for a cold start of the internal combustion engine, wherein the starter (7) is supplied with power from the battery (1, 2) during a cold start; characterized in that g) the battery (1, 2) is connected to the live power line (5) via a main switch (4), wherein the battery (1, 2) can be connected to the live power line (5); and h) that the motor vehicle electrical system has a similar voltage converter (10), which is connected to the power line (5) in order to supply the starter generator (9) with the required electrical energy for a warm start and to make the starter generator (9) independent of the battery (1, 2) during a warm start ) to supply the required electrical energy from the electrical energy storage (11). Motor vehicle electrical system Claim 1 , characterized in a) that the starter generator (9) is magnet-free, and / or b) that the starter generator (9) is a reluctance motor, in particular a switched reluctance machine. Motor vehicle electrical system according to one of the preceding claims, characterized in that a) that the energy storage (11) is a supercapacitor, in particular a double-layer capacitor, and / or b) that the energy storage (11) has a sufficiently large capacity to provide the required electrical energy in order to supply the on-board electrical system during the standstill phases of the start-stop system and then carry out the warm start of the combustion engine. Motor vehicle on-board electrical system according to one of the preceding claims, characterized in that a) that the motor vehicle on-board electrical system has an on-board electrical system voltage that is so low that no protection against contact is required, in particular an on-board electrical system voltage of 24 V, and/or b) that the battery ( 1, 2) has an electrochemical battery (1, 2), in particular a lead accumulator, and / or c) that the motor vehicle electrical system is free of high voltage without high-voltage components with a voltage that requires contact protection, in particular without high-voltage components with more than 60V DC or 25V AC voltage. Motor vehicle, in particular commercial vehicle, in particular truck or city bus, with a motor vehicle electrical system according to one of the preceding claims. Operating method for a motor vehicle electrical system according to one of the preceding claims, wherein - the live power line (5) of the motor vehicle on-board electrical system is fed from the energy storage (11), in particular when the internal combustion engine is started, in order to provide the energy required when the internal combustion engine is started and to supply the consumers in the motor vehicle on-board electrical system during stationary phases take care of, - the internal combustion engine is automatically switched off by the start-stop system when the motor vehicle is stationary, - the internal combustion engine is automatically restarted at the end of a stationary phase by the start-stop system as part of a warm start, - the internal combustion engine is started by the starter generator (9) during the warm start, - the internal combustion engine is started by the starter (7) during a cold start, and - The starter (7) is supplied with power from the battery (1, 2) during a cold start. Operating procedures Claim 6 , characterized in that the motor vehicle electrical system is supplied by the energy storage device during stationary phases of the start-stop system. Operating procedure according to one of the Claims 6 until 7 , characterized in that the energy storage (11) is charged from the motor vehicle electrical system when the internal combustion engine is operating in overrun mode and does not produce any mechanical power. Operating procedures Claim 8 , characterized in that the energy storage (11) supplies the motor vehicle electrical system with the previously recuperated electrical energy during a stationary phase of the start-stop system with the internal combustion engine switched off.

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