DE29723175U1 - Starter systems for an internal combustion engine - Google Patents

Description

Starter systems for an internal combustion engine

The present invention relates to starter systems for an internal combustion engine.

It is known that a combustion engine can be started using capacitors. The energy required for starting is brought to a higher voltage level from an on-board battery (with 12 volts or 24 volts) using a boosting DC-DC converter (so-called boost converter) and stored in one or more capacitors. Such starter systems are known, for example, from SU 1265388 Al (MOSC AUTOMECH) and EP 0 390 398 Al (ISUZU). In simpler systems, the capacitor storage is at the same voltage level as the vehicle battery, so no boost converter is connected in between. Examples of this are DE 41 35 025 Al (MAGNETI MARELLI) and US-PS 5 041 776 (ISUZU). In all of the above-mentioned 'S;" 25 systems, the battery is separated from the starter motor during the starting process, so that starting is carried out entirely using the energy stored in the capacitor storage.

In simple systems of the second type (without boost converter) it has also been proposed in JP 02175350 A (ISUZU) and JP 02175351 A (ISUZU) to connect the battery and the pre-charged capacitor in parallel during starting, so that both energy storage devices contribute to the starting process.

From EP 0 403 051 A1 (ISUZU) it is also known to charge a capacitor used to store the starting energy only up to a certain variable voltage level which depends on the prevailing temperature of the engine coolant.
5

In addition to the above proposals, which concern the use of capacitors as storage for starting energy, there are also proposals for other applications, e.g. as storage for the energy required by electric heaters. For example, EP 0 533 037 Bl (MAGNETI MARELLI) discloses an electric catalyst heater and EP 0 420 379 Bl discloses an electric glow plug system for a diesel engine, whereby the heating energy is stored in a capacitor storage unit.

Finally, WO93/11003 (BOSCH) and EP 0 688 698 A2 (BMW et al) disclose on-board power supply systems each with a starter battery and an on-board power supply battery, which are charged together but separated when starting. In the latter publication, the two batteries are connected via a controller unit, which controls the charging process.

The well-known starter systems with capacitor storage ensure safer starting, especially in very cold conditions, and allow a smaller design of the conventional vehicle battery, which is not really suitable for short-term discharge 5 during starting.

The present invention aims to provide improved starter systems with short-term storage, such as a capacitor storage.
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According to a first aspect of the invention, a starter system for an internal combustion engine comprises:
- an electric starter,

an electrical short-term storage device, in particular a capacitor storage device, which after charging is used to feed the.

Starters,

direct or indirect temperature measurement, and

- a control device which, before the start-up process, causes a portion of the energy stored in the short-term storage device to be withdrawn to supply one or more consumers, the size of the portion of energy withdrawn being temperature-dependent and smaller at low temperatures than at high temperatures (claim 1).

This first aspect of the invention is based on the following findings: at low temperatures of the internal combustion engine, particularly in severe frost such as -20 ⁰ C, the electrical energy required for starting is considerably greater than at high temperatures, such as operating temperature. This is essentially due to the considerably greater resistance that the internal combustion engine offers to the starter rotation due to the greater viscosity of the oil in cold weather. The starter system must be designed for the lowest temperatures that occur in practice. This means that the capacity of the capacitor is greatly over-dimensioned for the higher temperatures that usually occur. This applies in particular to designs in which the capacitor storage is intended to store all of the energy required for starting, and also applies to a somewhat lesser extent to designs in which part of the starting energy is taken from the long-term battery and only part is to be stored in the short-term storage. In order to avoid loading the capacitor with more energy than is required for starting at the higher temperatures that usually occur, the above-mentioned EP 0 403 051 Al (ISUZU) proposes storing smaller amounts of energy as the temperature increases.

The invention (first aspect), however, takes a different approach: 0 because even a temperature-dependent loading of the short-term storage device does not change the fact that it must be dimensioned for the lowest temperature that occurs - and is therefore over-dimensioned. It was recognized that - at higher temperatures, the portion of the short-term storage capacity that is not required can be used to serve other consumers (other than the starter) in order to be able to supply them with high power for a short time, preferably before the combustion engine is started. At high temperatures, such as operating temperature, these additional consumers have a relatively large energy and power value before the

Starting. As the temperature of the combustion engine decreases, this amount decreases because a larger proportion of energy must be reserved for the starting process. If the capacitor storage is dimensioned accordingly, there is no energy left for the additional consumers at the lowest temperature. Their supply can - in this relatively rare case - be postponed, for example, until immediately after starting, if a generator driven by the combustion engine supplies sufficient energy.

"Short-term storage" is preferably understood to mean any storage device for electrical energy in which the largest part (e.g. 97%) of the maximum stored energy can be removed without causing damage within 60 seconds, preferably within 30 seconds and particularly preferably within 15 seconds. In addition to capacitors, this can also include chemical energy storage devices for high power consumption, e.g. so-called alkaline secondary systems, e.g. alkaline nickel/cadmium systems or nickel/iron systems, which can contain e.g. sintered electrodes or fiber structure electrodes. "Long-term storage", on the other hand, is a storage device from which the entire stored energy can only be removed for periods longer than 10 minutes after it has been fully charged.

The consumer is advantageously an electric heater, preferably a catalyst heater (claim 2). In order to meet future strict exhaust emission regulations, it will probably be necessary to electrically heat the exhaust catalysts in Otto engines before the combustion engine is started. This ensures that the catalyst is already at its operating temperature during the first ignitions and thus works effectively. The invention allows rapid preheating of the catalyst with practically no additional construction effort, as the - otherwise oversized - short-term storage device serves as an intermediate storage device for the catalyst heating energy when the combustion engine is not too low. Unlike when powered by a conventional long-term battery (which typically has minimal discharge times of more than 30 minutes), the short-term storage device is used with little power consumption.

The battery is slowly charged or - in the case of an earlier driving cycle - from the vehicle electrical system and then discharged almost suddenly to heat up the catalyst (claim 2). In contrast to a conventional lead-acid battery, the heating takes place with high electrical power and is therefore very fast, within one or a few seconds. Other heating systems, e.g. window heating systems, can also be advantageously supplied with high power before starting.

A second aspect of the invention relates to a starter system for an internal combustion engine, with

an electric starter;

a short-term electrical storage device, in particular a capacitor storage device, which, after charging, serves to supply the starter;

- a long-term electrical storage system; and

a coupling circuit which, when starting, allows simultaneous energy withdrawal from the short-term storage and the long-term storage, whereby the proportion of energy and/or power withdrawn from the long-term storage and/or the short-term storage can be actively controlled (claim 3).

This second aspect is based on the idea of not making the short-term storage so large that it can start the combustion engine on its own even at very low temperatures, but rather of drawing energy from the short-term storage and the long-term storage (e.g. in the form of a conventional sulphuric acid lead accumulator) at the same time. Simple parallel connections of battery and capacitor storage are - as mentioned above - known from the Japanese publications 02175350 A (ISUZU) and 02175351 A (ISUZU). However, these are very simple starter systems. Known systems that are more advanced in development, on the other hand, have a boost converter from the battery to the capacitor storage, which keeps the two storage units separate from each other when starting (see, for example, the SU 1265388 Al (MOSK AUTOMECH) mentioned at the beginning). It is used to charge the capacitor storage unit to a higher voltage level than the long-term storage unit.

The invention (second aspect) takes a different approach by providing an actively controllable coupling between the two energy storage devices not (only) when charging the short-term storage device, but also when discharging during the start-up process. The involvement of both energy storage devices allows the short-term storage device to be dimensioned smaller while at the same time adapting the relative power consumption to the generally different characteristics of the two different storage types. "Actively controllable" does not (only) mean the possibility of switching the long-term storage device and/or short-term storage device on and off, but the possibility of continuously displaying the proportion of energy and/or power that is taken from the long-term storage device and/or the short-term storage device when starting.

Advantageously, only as much power is taken from the long-term storage as is required for starting with full use of the short-term storage (claim 4). As explained above, the power required for starting depends, among other things, heavily on the temperature of the combustion engine. The amount of power taken from the long-term storage can therefore be controlled on the basis of a measurement of the current temperature value using a known temperature dependency function. This design leads to a minimal short-term load on the long-term storage.

In another advantageous embodiment, only as much power is taken from the short-term storage device as is required for starting when the long-term storage device is fully utilized (claim 5). This allows the maximum possible proportion of the energy stored in the short-term storage device at the respective temperature to be used for purposes other than starting, in particular for supplying other consumers before starting, such as the heaters mentioned in connection with claim 2 (in particular catalyst heaters).

Advantageous possibility: the / greatest possible power is taken from the long-term storage (claim 6). This is achieved by the coupling circuit loading the long-term storage with optimal adaptation, i.e. that the effective internal resistance of the coupling circuit

resistance is approximately equal to the internal resistance of the long-term storage. In this adaptation, resistances between the long-term battery and the coupling circuit must be taken into account (by adding them either to the input resistance of the coupling circuit or to the internal resistance of the long-term storage). This design assigns a comparatively larger share of the total power to the long-term storage and thus allows a comparatively smaller dimensioning of the short-term storage. In modifications to this design, only a certain fraction of the greatest possible power is taken from the long-term storage, e.g. fractions in the range of 50 to 100%, advantageously 65 to 100%, preferably 75 to 100% and particularly preferably 90 to 100% of the greatest possible power.

Preferably, the short-term storage device operates at a different, in particular a higher voltage level than the long-term storage device (claim 7). Preferably, the coupling circuit then comprises a voltage converter, e.g. a boost converter, which can bring current from one voltage level to the other. The different voltage levels can advantageously be adapted to the different technical characteristics of the two different storage types. For example, a capacitor storage device generally achieves its greatest energy storage density at a relatively high voltage level (e.g. at 300 volts), while an accumulator battery - depending on the type of battery used and the number of cells connected in series - generally delivers lower voltages, which generally correspond to the voltage of a low-voltage vehicle electrical system (e.g. 12 volts or 24 volts). The coupling circuit is, for example, a boost converter based on an induction pump circuit. One such device is made up of a series circuit of an inductance and an electronic switch, for example, through which current from the long-term storage flows when the switch is closed. Between these two elements there is a branch to the short-term storage, which is at a higher voltage level and is equipped with a backflow-preventing diode. By opening the switch, a voltage peak (in principle of any size) is created by induction, which allows the current to flow briefly to the high voltage level and thus increases it. By increasing or

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By reducing the switching frequency of the switch, the boosted current can be increased or reduced accordingly.

The starter is advantageously fed by an inverter with a DC intermediate circuit, whereby the short-term energy storage is at the voltage level of the DC intermediate circuit (claim 8). A DC intermediate circuit inverter cuts out width-modulated pulses from a constant DC intermediate circuit voltage using electronic switches (e.g. field effect transistors or IGBTs), which - averaged by the inductance of the generator - lead to almost smooth direct currents of the desired voltage or alternating currents of the desired frequency, amplitude and phase. It is therefore particularly advantageous for the starter to be designed as a three-phase machine (also called a rotating field machine). In contrast to a commutator machine, this is understood to mean a machine without a commutator, in which, for example, the stator generates a magnetic rotating field that rotates by 3 60° and takes the rotor with it. The starter can be designed in particular as an asynchronous machine, e.g. with a squirrel-cage rotor, or as a synchronous machine, e.g. with a rotor with distinct magnetic poles. The squirrel-cage rotor in the asynchronous machine can, for example, be a cage rotor with short-circuit bars in the axial direction. In other designs of the asynchronous machine, the rotor has windings which, for example,

can be short-circuited externally via slip rings. The distinctive magnetic poles of the rotor in the synchronous machine are implemented, for example, by permanent magnets or by electromagnets, which can be fed with excitation current, for example, via slip rings. The starter can be indirectly coupled to the combustion engine shaft, for example via pinions, gears, etc. It is advantageous, however, for part of the starter, in particular the rotor, to be located directly on the engine shaft and preferably to be or can be coupled to it in a rotationally fixed manner. The rotor can, for example, be located on the shaft leading to the gearbox, or on the other side of the combustion engine on the blind-ending shaft stub there. Another part of the starter, in particular the stator, is rotationally fixedly connected to a non-rotatable part or can be detachably connected, e.g. the engine or gearbox housing.

·

In addition to the starter function, an inverter-controlled three-phase machine can advantageously have one or more additional functions, e.g. the function of a generator for the on-board power supply, an additional vehicle drive motor, an additional vehicle brake and/or an active smoothing device for rotational irregularities that occur in combustion engines due to their discontinuous operation. The switch from motor to generator operation is carried out by appropriate switch of the magnetic fields using appropriate inverter control.

The invention will now be explained in more detail using exemplary embodiments and the attached schematic drawing. The drawing shows:

Fig. 1 is a diagram of the relative energy available to a consumer as a function of temperature (first aspect);

Fig. 2 a diagram of the power shares supplied by the short-term storage and the long-term storage as a function of the 0 temperature (second aspect);

Fig. 3 is a schematic representation of the main functional units of the starter systems (first and second aspects);

Fig. 4 is a flow chart of a method for starting (first aspect);

5 Fig. 5 is a flow chart of another method for starting i|B: (second aspect).

Fig. 1 illustrates the energy ratios in an embodiment of the first aspect of the invention. The proportion e _v of the energy stored in the capacitor that is diverted to the consumer is plotted as a function of the temperature of the combustion engine. The proportion e _v is defined as the ratio of the

the amount of energy E _v diverted to the consumer and the amount of the total energy E, _oul stored in the capacitor. At one extreme value, the lowest occurring temperature T _IIlin , the consumer energy component e _v is zero. All of the stored energy is required for starting, i.e. the starting energy component ^e st*rt/kait ^is equal to one. At the highest occurring temperature T _niax , e.g. the operating temperature of the internal combustion engine, only part of the stored energy is required for starting, i.e. the starting energy component e _SurtAvami is significantly less than one. The remaining amount of energy can be used to feed a consumer before starting, i.e. the consumer energy component e _Wwann is equal to the difference between one and e _SUrtAvami . Fig. 1 schematically illustrates e _v for all values between T _min and T _max . Due to the decreasing resistance of the combustion engine to the starter with increasing temperature and the decreasing starting speed, the dependency shown is a continuous and only increasing (or constant) function.

Fig. 2 illustrates the power ratios in an embodiment according to the second aspect of the invention. The total power required (for a specific moment) when starting is plotted as a function of temperature. According to the above, the total power is maximum at the lowest temperature T _min and decreases as the temperature rises up to the highest temperature T _max . The maximum power draw from the short-term storage is shown in dashed lines, which is independent of temperature - and is therefore a horizontal straight line in the illustration. Since in the second aspect of the invention the short-term storage and battery work together when starting, the maximum short-term storage power is below the maximum total power at the lowest temperature T _min , thus forming a kind of base. Energy is only drawn from the battery in the temperature range (shown in hatched form) at which the total power curve is above this base. This is shown in Figure 2 as an example for a temperature slightly above T _min . At medium temperatures the total power curve falls below the base. This means that at temperatures above the intersection point, starting takes place exclusively from the

Short-term storage, the battery does not contribute here. At other times (not shown) the maximum short-term storage power can also fall below the required total power at T, _1MX , so that the battery must then contribute. In other embodiments (not shown) the maximum short-term storage power can at all times be below the required total power at T _1111x , so that at all times the battery contributes to starting.

According to Fig. 3 (for a motor vehicle, e.g. a passenger car), a starter system has an internal combustion engine 1, which delivers torque to the drive wheels of the vehicle via a drive shaft 2 (e.g. the crankshaft of the internal combustion engine 1), a clutch 3 and other (not shown) parts of a drive train. In the starter function of interest here, the clutch 3 is open. An electrical machine 4, here an asynchronous three-phase machine, which serves as a starter, is located on the drive shaft 2. It has a rotor 5 that sits directly on the drive shaft 2 and is connected to it in a rotationally fixed manner, as well as a stator 6 that is supported, e.g., on the housing of the internal combustion engine 1. The starter 4 (as well as the devices for supplying it and storing energy, described in more detail below) are dimensioned so that the combustion engine 1 can preferably be started directly (i.e. without a flywheel function or similar) and preferably no step-up or step-down gear is arranged between the starter 4 and the combustion engine 1, so that both can run together permanently. The winding (not shown) of the stator 6 is fed by an inverter 7 with electrical currents and voltages of practically freely adjustable amplitude, phase and frequency. This is, for example, a DC intermediate circuit inverter, which, with the help of electronic switches, cuts out sinusoidal-weighted, width-modulated pulses from an essentially constant DC intermediate circuit voltage, which - averaged by the inductance of the electrical machine 4 - lead to almost sinusoidal currents of the desired frequency, amplitude and phase. The inverter is essentially made up of a machine-side DC-AC converter 7a, an intermediate circuit 7b and a DC-DC converter 7c on the vehicle network side. A

Short-term energy storage 8, e.g. a capacitor storage, is located electrically in the intermediate circuit 7b. The converter 7c is coupled to a vehicle electrical system 9 and a long-term energy storage system, here an on-board electrical system battery 10. The on-board electrical system 9 and the battery 10 are at a low voltage level, e.g. 12 or 24 volts. The intermediate circuit 7b, on the other hand, is at an increased voltage, which is advantageously in the range between 48 and 350 volts. After the start-up process, during which it requires electrical energy, the electric machine 4 can function as a generator, i.e. supply electrical energy. The converter 7c is therefore designed as a bidirectional converter in order to be able to bring electrical energy from the on-board network battery 10 into the intermediate circuit 7b for the starting process or its preparation, and to transfer energy from the intermediate circuit 7b to the low-voltage side during generator operation in order to supply consumers of the on-board network 9 and charge the on-board network battery 10. In motor operation, the converter 7a converts the direct voltage of the intermediate circuit 7b into alternating voltage; in generator operation, it feeds the energy supplied by the electric machine 4 into the intermediate circuit 7b after rectification. The capacitor storage 8 is able to deliver voltage pulses with a high pulse frequency (advantageously in the range of 20 kHz to 100 kHz) with the required edge steepness. It also serves as an energy store for the energy required for starting, possibly in conjunction with the battery 10. In other (not shown) embodiments, a separate, particularly quickly dischargeable capacitor store is provided for the provision of steep-edge pulses, which only needs to have a lower capacity. The capacitor store 8 can be charged either in generator mode by the electric machine 4 via the converter 7a, or when the vehicle is stationary from the battery 10 via the converter 7c. A high-performance consumer 11, e.g. an electric catalyst heater, is electrically coupled to the intermediate circuit 7b via a consumer control unit 12. The high-performance consumer 11 is advantageously supplied at a high voltage level, e.g. the voltage level of the intermediate circuit 7b. In this case, the consumer control unit 12 does not serve as a voltage converter, but only as a current control unit. In other embodiments

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it also has the function of a voltage converter for higher or lower voltages. A higher-level control unit 13 controls the inverter 7, namely the converter 7a and the converter 7c, as well as the consumer control unit 12. It specifies the amplitude, phase and frequency of the three-phase current to be supplied to the starter 4 for the converter 7a. It specifies the current amount, the current direction and the amount of the voltage increase or decrease for the converter 7c. Finally, it specifies the consumer control unit 12 which current amount it should take from the intermediate circuit 7b and, if necessary, which voltage difference must be overcome in the process. The control unit 13 receives input signals from a temperature sensor 14, which provides information, for example, about the coolant temperature of the combustion engine 1. It also receives input signals from a rotary encoder (not shown), from which it can determine the current speed of the drive shaft 2. It can also receive a range of other information, e.g. concerning the position of the throttle valve of the combustion engine 1, the ignition timing, etc.

The function of the starter system of Fig. 3 according to the first aspect of the invention is explained below using the flow chart according to Fig. 4: In step S1, the capacitor storage 8 is charged. The charging takes place to a fixed, predetermined value, which is specified, for example, by the target value of the intermediate circuit voltage. If possible, the capacitor storage 8 is charged while the combustion engine is running from the electric machine 4, which then functions as a generator. If the vehicle is stationary for a longer period, however, the capacitor storage 8 gradually discharges, so that it must then be charged in whole or in part by drawing energy from the on-board battery 10. In step S2, the control unit 13 determines the current temperature of the combustion engine based on the measurement information provided by the temperature sensor 14. In step S3, the control unit 13 determines, for example, based on a stored characteristic map, the amount of energy that is expected to be required for starting at the temperature determined in the previous step. On the basis of the determined amount of energy required and the known value of the amount of energy stored in the capacitor storage, the control unit determines in step S4 the part of the energy stored in the capacitor storage.

memory 8, which is not required for starting at the current temperature. In step S5, the control unit 13 checks whether a command to start the combustion engine has been given - for example by operating the ignition key. If this is not the case, the control unit 13 carries out steps S2 to S5 repeatedly. If, however, a start command has been given, it proceeds to the following step S6. (In other (not shown) embodiments, the program is in a passive waiting state; only after receiving a start command does it carry out actions in accordance with steps S2 and S4). In step S6, the control unit 13 causes the high-performance consumer 11, here a catalyst heater, to be fed with the part of the energy that is not required at a very high power for a short time. The catalyst is therefore immediately switched off, e.g.

to operating temperature and is therefore ready for the material conversion of harmful exhaust gases from the first ignitions. In step S7, the combustion engine 1 is finally started using the energy remaining in the capacitor storage 8.

The flow chart according to Fig. 5 explains a modification of the functioning of the starter system of Fig. 3 according to the second aspect of the invention: With regard to steps S11, S12 and S13, reference is made to the above statements on steps S1, S2 and S3, which also apply here in full. In step S14, on the basis of the result in step S13 and the known value of the amount of energy stored in the capacitor storage 8, the proportion of energy that must be taken from the capacitor storage 8 for the starting process at the current temperature of the on-board network battery 10 is determined. In step S15 - in accordance with the above statements on step S5 - it is checked whether a start command was given. (In this embodiment, too, the start command query can be carried out before steps S12, S13 and S14 are carried out.) In step S16, the control unit 13 finally initiates the starting 5 of the internal combustion engine 1 by drawing energy from the capacitor storage 8 and, if necessary, from the on-board battery 10 in accordance with the proportion determined in step S14. In another embodiment (not shown), steps S14 and S16 are frequently repeated in the course of the starting process in order to

to take into account any temporal change in the proportion of energy to be drawn during the start-up process. Such a time dependency can occur, for example, because the capacitor storage 8 discharges during the charging process and can only supply less energy towards the end of its discharge process, so that the proportion to be drawn from the on-board power supply battery 10 increases. Strictly speaking, in this embodiment, the proportion of power that must be drawn from the on-board power supply battery 10 at the current temperature and at the relevant time during the start-up process is determined in step S14. In step S16, a corresponding power draw is then carried out from the capacitor and the battery in accordance with the proportion of power determined in step 14.

In summary, the invention is based on the idea of taking into account the temperature dependence of the amount of energy required for starting, not when charging the short-term storage device, but during the discharge and/or starting process. This is particularly advantageous for starter systems in which the short-term storage device is to have a predetermined voltage level, such as the level of the intermediate circuit of an inverter used to supply the starter.

Claims (8)

16 Protection claims 1. Starter system for an internal combustion engine (1), comprising:
- an electric starter (4), an electrical short-term storage device (8), in particular a capacitor storage device, which after charging serves to supply the starter (4); - direct or indirect temperature measurement; - a control device (13) which causes a part of the energy stored in the short-term storage device to be taken to supply one or more consumers (11) before the start-up process, the size of this part being temperature-dependent and being smaller at low temperatures than at high temperatures. 2. Starter system according to claim 1, in which the consumer (11) is an electric heater, in particular a catalyst heater. 3. Starter system for an internal combustion engine (1), with - an electric starter (4); an electrical short-term storage device (8), in particular a capacitor storage device, which after charging for storing 5 sen of the starter (4); - an electrical long-term storage device (10); and a coupling circuit (7c) which allows simultaneous energy withdrawal from the short-term storage (8) and the long-term storage (10) during start-up, wherein the 0 Share of the long-term storage (10) and/or the short-term time storage (8) and/or power can be actively controlled. 4. Starter system according to claim 3, wherein only as much power is taken from the long-term storage device 5 (1°) as is required for starting under the maximum output power of the short-term storage device (8). 5. Starter system according to claim 3, wherein only as much power is taken from the short-term storage (8) as is required for starting under the maximum output power of the long-term storage (10). 6. Starter system according to one of claims 3 to 5, wherein the greatest possible power or a certain fraction thereof is taken from the long-term storage (10) in optimal adaptation. 7. Starter system according to one of claims 3 to 6, wherein the short-term storage (8) operates at a different, in particular higher voltage level than the long-term storage (10), and the coupling circuit (7c) comprises a voltage converter. 8. Starter system according to one of claims 1 to 7, wherein the starter is fed by an inverter (7) with a DC voltage intermediate circuit (7b), and the short-term storage (8) is located in the DC voltage intermediate circuit (7b).