Starter/generator for an internal combustion engine, in particular a vehicle engine

The invention relates to a starter / generator for an internal combustion engine of a motor vehicle.

Motor vehicles and other vehicles equipped with internal combustion engines generally require an electric starter for starting the internal combustion engine, as well as a generator for supplying electrical loads and for charging a battery which, among other things, supplies the electrical energy required for starting. Since the early days of automotive engineering, starters and generators are usually two separate electrical machines which are particularly adapted to their respective functions. A starter must apply relatively high torques at a relatively low engine speed, and is therefore conventionally high as opposed to the internal combustion engine. It does not run continuously, but is only coupled to the internal combustion engine for the start-up process. A generator, on the other hand, runs continuously with the internal combustion engine and reaches high speeds at a relatively high ratio.

The combination of these two functions in one and the same electrical machine is an objective, since one of the two conventionally required machines can thereby be saved.

One possibility of combining both machines in spite of the different requirements for starters and generators is known from G. Henneberger: "Electric Motor Equipment", Vieweg, Braunschweig 1990, pp. 98-103. According to this proposal, the electric machine, which is an inverter-controlled rotary field machine, does not start the internal combustion engine itself, but accelerates a flywheel (decoupled initially from the internal combustion engine). When a sufficiently high rotational speed is reached, the flywheel is coupled to the crankshaft of the internal combustion engine by means of a friction clutch. The rotational energy stored in the flywheel then ejects the internal combustion engine. In generator operation, the electrical machine is permanently coupled to the internal combustion engine by the friction clutch. This solution has the advantage that the powers and torques of the electrical machine are similar during start-up and generator operation. However, the great mechanical load on the friction clutch during coupling of the fast-running flywheel, which leads to clutch wear, inter alia, as well as a dead time before each starting process, which is required in each case to accelerate the flywheel, are disadvantageous.

An electrical asynchronous machine is known from PCT / SE91 / 00272, which can alternatively operate as a generator or as a starter. It is coupled to a battery via a control unit. A further starter / generator is known, for example, from EP-A-0 569 347.

The invention provides a starter / generator for a combustion engine of a motor vehicle according to claim 1.

An "electric machine" is any kind of machine for rotary motions, which can be operated both as an electric motor and as an electric generator. In contrast to a current-reversing machine, "rotary-field machine" is understood to be, in particular, a commutatorless machine in which a magnetic rotating field, preferably 360 °, is swept.

The inverter can generate the voltages and / or currents required for the magnetic fields with (freely definable) frequency, amplitude and / or phase (within certain limits).

"Combination from the stand" means that the electric machine and the drive unit start up from the stand together, unlike the aforementioned flywheel starter.

Because of the confluence from the state<ul><li>Starting is fast and without dead time,</li><li>The starter / generator is practically wear-free,</li><li>The starter / generator achieves a relatively high efficiency (since no energy is consumed for clutch heating and wear)</li><li>The clutch between the internal combustion engine and the electric machine can be dispensed with.</li></ul>

The electric machine runs - unlike a conventional starter - permanently with the internal combustion engine. A single-track and free-wheeling device required there can therefore be dispensed with here.

The electric rotary field machine is preferably an asynchronous machine, a synchronous machine or a reluctance machine, in particular for three-phase current, for example. An asynchronous machine generally has a relatively simple rotor (eg a rotor with short-circuit windings or windings, the ends of which are connected to slip rings), in which currents are induced by the magnetic rotating fields of the stator, which precede or follow the movement of the rotor. It therefore has advantages with respect to the production costs and the mechanical load-bearing capacity, but it is more expensive to control because the magnitude and phase angle of the rotor current is load-dependent, but can not be directly measured by stator sizes. On the other hand, synchronous machines have rotors with predetermined pronounced poles, which are produced by permanent magnets or electromagnets. The electromagnets can, for example, be supplied with current via slip rings. Synchronous machines generally have higher production costs, but are easier to control because their torque is essentially dependent on the rotor angle, which is directly measurable with the aid of a rotor position encoder. They also require less effort in the field of power electronics, can be made more compact, have a lower cooling demand and achieve a better efficiency. Reluctance machines are, in the broader sense, the synchronous machines.

In particular in the case of the asynchronous machine, the electrical machine is preferably controlled on the basis of a field-oriented control (so-called vector control). In this case, starting from directly measurable instantaneous variables, such as the applied voltage, stator current and possibly rotational speed, the stator current is converted into a torque-forming component which generates the torque with the rotor flux, and a component running perpendicular to the machine flux, based on a computational dynamic machine model And the torque is determined. This control technology allows a desired torque to be set with high accuracy, although the current ratios in the rotor are not directly measurable.

The starter / generator according to the invention is an auxiliary system associated with the internal combustion engine. Because of its auxiliary character, it should occupy little space relative to the internal combustion engine, that is to say as compact as possible. In this case, the starter / generator must be able to apply relatively high torques for starting up and should have the highest possible efficiency for the generator function. The advantageous measures mentioned in the following serve, among other things, for a compact design with high torque output and high efficiency.

One measure for obtaining high compactness is that the rotating-field-generating operating unit of the electrical machine (ie, generally the stator) has at least 8 magnetic poles (relative to 360 °). Particularly advantageous are finer pole divisions, corresponding, for example, to 10, 12, 14, 16 or more poles (with circularly closed machine). For the manner in which three-phase windings are realized with a certain number of poles, reference is made, for example, to G. and H. Häberle, "Electrical Machines in Power Systems", Verlag Europa-Lehrmittel, Haan-Gruiten, 1994, pages 169-172.

A high number of poles makes it possible, inter alia, to make the winding heads of the stator small, both in the axial direction and also in the circumferential direction of the machine, so that the machine can be designed to be shorter overall in the axial direction. Preferably, the axial projection of the winding heads on each side of the stator is only 5-25 mm, in particular 10-20 mm. The axial width of the stator back is preferably 25-100 mm. For an overlap of 2 × 15 mm and a back width of 40 mm, an overall axial width of the stator of 70 mm results for example, the ratio of the back width to the total width being 0.57. This ratio is preferably between 0.4 and 0.8, particularly preferably between 0.55 and 0.8. In addition to the advantage of a more compact design of the machine, the ohmic losses are lower because of the smaller winding wire length - smaller winding heads require less non-active winding wire. Furthermore, the stray field (which essentially determines the reactive power component) is smaller since it depends on the winding head surface.

A fine pole pitch makes it possible, among other things, to make the stator back for the magnetic reflux thinner (and thus also lighter), with the result that, with the same external diameter of the machine, the rotor can have a larger diameter. Larger rotor diameter leads to greater torque because of the longer air gap in the circumferential direction and the larger effective lever arm. The thickness of the back in the radial direction, which is composed of the height of teeth and the thickness of the continuous back part, is advantageously 10-50 mm, preferably 15-30 mm, and is particularly preferably less than or equal to 25 mm. The outer diameter of the back is preferably 230-450 mm and more preferably 250 mm-350 mm. The ratio of the two-fold back thickness to the back outer diameter is preferably 0.05-0.25, and most preferably 0.1-0.2. For example, a machine with a back outer diameter of 300 mm has a tooth height of 15 mm and a thickness of the continuous back part of 10 mm, in total a return thickness of 25 mm. The above ratio is then 50 mm to 300 mm, that is, 0.167.

All in all, a fine pole pitch, small wobble heads and a thin column stand lead to a more compact and lighter machine.

In high-speed rotating field machines, high pole numbers are unusual because they require a relatively high polarity frequency. A typical value for the pole-changing frequency is, for example, 120 Hz. The electrical machine used in the invention, on the other hand, advantageously has a high maximum pole-changing frequency, preferably between 300 and 1600 Hz and more, particularly preferably between 400 Hz and 1500 Hz.

In order to reduce the influence of eddy currents in the stator - which increase with increasing polarity frequency - the stator advantageously has thin stator plates, preferably with a thickness of 0.35 mm or less, particularly preferably 0.25 mm or less. As a further measure for reducing the losses, the stator plates are preferably manufactured from a material with low losses of magnetization, in particular less than 1 Watt / kg at 50 Hz and 1 Tesla.

As a further measure which contributes to a compact design, the electrical machine advantageously has an internal fluid cooling. The fluid can basically be gas (eg air) and advantageously liquid (eg oil). A cooling technique is to place the machine completely inside cooling liquid (ie, in the space accommodating the rotor). A disadvantage, however, is that above about 500 min^-1 Turbulence losses occurring above about 2000 min^-1 Can have considerable proportions. In order to counteract this, the supply of the cooling liquid is advantageously carried out with a loss of performance and / or speed, preferably with a spray liquid cooling. In the machine there is always only as much cooling liquid as is currently required to dissipate the power loss. In the case of very high power losses and / or low rotational speeds, the whole machine can be placed under cooling liquid. The spray liquid cooling ensures a highly effective heat transfer as well as a particularly good distribution of the liquid.

The electrical machine preferably has its own closed coolant circuit. In order to dissipate the heat to the outside (eg into the atmosphere), this can have an autonomous recooler (eg an air cooler). However, a parasitic recooler is also possible, which introduces the waste heat into another cooling system, which can be, for example, the internal combustion engine or transmission oil cooling circuit of a motor vehicle. The waste heat is then discharged to the outside through the recooler of the other cooling system. The parasitic recooler can be constructed very simply and compactly, for example in the form of a cooler, which is immersed in the cooling liquid of the other cooling system and requires only a relatively small surface because of the good heat transfer. However, alternatively, the electrical machine can also not have its own closed cooling circuit, but can be integrated into another cooling circuit, for example in a transmission oil cooling circuit.

In order to achieve particularly high torques, the electrical machine preferably operates strongly in the region of magnetic saturation. A measure of the magnetic saturation is the current (maximum torque) in the stator per cm of the air gap length in the circumferential direction. This dimension is preferably at least 400-1000 A / cm, particularly preferably at least 500 A / cm. Another measure of the magnetic saturation is the so-called flattening factor: It indicates how strong the sinusoidal excitation current is the ratio of the peak value to the arithmetic mean value of the magnitude of the magnetic field. It is 1.57 in the case of purely sinusoidal progression, approximately 1.35 in the case of conventional electrical machines, and 1.05-1.15 in this preferred embodiment. Working strongly in the saturation range has the further advantage that the machine can have a relatively wide air gap between the operating units (generally rotor and stator). The width of the air gap is preferably 0, 25 - 2.5 mm, preferably 0.5 - 1.5 mm, and particularly preferably 0.75 - 1.5 mm. Changes in the air gap - as occur in the case of radial oscillations of the shaft bearing the rotor - have hardly any effect because of the operation in the saturation region. In addition to the robustness against radial vibrations, this measure also permits a reduction in the precision requirements and thus a considerable simplification of the manufacture of the electrical machine.

Quantitatively, the compactness can be expressed by the magnitude "torque density". The electrical machine preferably has a high torque density, based on the maximum torque, which is particularly preferably greater than 0.01 Nm / cm 2³ Is.

A compact electric machine generally has a relatively low inductance. However, in order to achieve a smooth, sinusoidal current as possible as possible with the aid of a clocked voltage for generating the electric rotating fields, the inverter operates with a clock frequency of more than 10 kHz, in particular 20 kHz to 100 kHz and higher. A high clock frequency also has the advantage of allowing a compact design of the inverter itself. For example, in the case of a voltage intermediate circuit inverter, the capacitance in the intermediate circuit, which provides the intermediate circuit voltage to the electronic switches of the inverter, is inversely proportional to the frequency, so that at a higher clock frequency A smaller capacity is sufficient. The smaller intermediate circuit capacitors can be arranged with short line paths directly next to the electronic switches. Furthermore, a necessary EMC filtering (EMC: electromagnetic compatibility) of the inverter can be made more compact towards the outside, since the size of the filters is inversely proportional to the clock frequency.

An "intermediate circuit" is understood to mean a circuit which can supply substantially constant voltage or current, from which a subsequent inverter part (the so-called machine inverter) can form variable alternating voltages or currents through pulses or clocks. This DC voltage or this direct current must therefore be provided with a large flank slope. For this purpose, a vehicle battery is usually too slow, so, for example, a capacity is used as energy storage in the intermediate circuit. In general, an intermediate-circuit converter comprises three modules, namely an input module for supplying or removing electrical energy, an output module in the form of the machine inverter and the intermediate circuit therebetween.

As a further advantageous measure for achieving a compact design of the inverter, electronic switches of the inverter are fluid-cooled, preferably boiling bath-cooled. As the boiling bath coolant, for example, a fluorocarbon can be used. During the boiling bath cooling, the liquid coolant evaporates from heat sources and thereby withdraws its relatively high heat of evaporation. The steam rises and can, for example, condense in an external cooler and thereby release its heat of evaporation. This cooling system allows the most compact arrangement of the electronic switches of the inverter without any heat sinks. In addition, it has the advantage that relatively low temperature differences are sufficient to achieve even high cooling performance: whereas a temperature difference of 40 ° C. between the cooling surface and the housing of a chip to be cooled is usually necessary in air cooling C, in particular about 5 ° C. As a result, high ambient temperatures are tolerable, for example, at a chip temperature of 65 ° C., an ambient temperature of up to 60 ° C. The absence of heat sinks and the high achievable compactness also allows a high vibration resistance; In addition, the boiling bath allows the creation of an oxygen-free atmosphere in the area of ​​the electronic components of the inverter, which has a lasting effect on the lifetime. The housing forming the cooling chamber can also serve as a shield, if it is made of conductive material. Electrical intermediate circuit storage elements for providing voltage or current to be clocked (eg, the above-mentioned capacitance) can be arranged within the cooling housing, as a result of which short conductor paths can result. A separately separate electric brake energy accumulator can be arranged inside or outside the cooling housing. The relatively high supply inductances in the latter case do not interfere with the brake energy accumulator operating on a relatively "slow" time scale.

A further cooling-technically advantageous measure is to switch several electronic switches of the inverter, in particular 2 to 20 and more, in parallel. The parallel circuit leads to a distributed one. Arrangement of the heat sources and thus a relatively low power loss density.

The inverter preferably comprises a switch semiconductor switch, preferably a fast semiconductor switch, such as field effect transistors, particularly preferably metal oxide semiconductor (MOS) field effect transistors, bipolar transistors and / or bipolar transistors with insulated gate connection (IGBTs). By "fast" semiconductor switches are meant in particular those; Which allow the above clock frequencies. MOS field effect transistors have the relatively lowest losses at high clock frequencies. They have an ohmic characteristic (whereas other semiconductor devices generally have a fixed loss characteristic), so that the losses are relatively low in partial load operation.

The inverter is a pulse inverter, ie it generates the voltages and / or currents required for the magnetic fields of the electrical machine, preferably by pulses, in particular on the basis of pulse width or pulse amplitude modulation. It can do this advantageously with the aid of electronic switches which cut out the pulses from a predetermined DC or AC voltage or a predetermined direct or alternating current. For example, in the case of an intermediate-circuit inverter with a constant intermediate circuit voltage, almost sinusoidal currents of arbitrarily adjustable frequency, amplitude and / or phase can be generated by sinusoidal pulse width modulation at high clock frequencies due to the machine inductance. In pulsed amplitude modulation, for example, one proceeds from an inverter with a variable intermediate circuit voltage and thus generates pulses of different amplitudes.

In order to provide the high electrical power required for the starting process without an excessive load on the vehicle battery, an energy store is provided, which is charged with energy before the starting process and the required energy is then taken out at short notice. For this purpose, the inverter is designed as an intermediate circuit inverter, which has at least one energy store for the starting energy in the intermediate circuit. The memory may be, in particular, an electrical, magnetic and / or electrochemical memory, such as a capacitance, an inductance and / or a (fast) battery. In addition to storing the starting energy, this can also serve other tasks. For example, it can store the energy required for pulse operation of the inverter. (In the latter case it could coincide with the usual intermediate circuit memory). Moreover, the configuration of the converter as an intermediate-circuit converter can be advantageous in any case - for example even without a memory for the starting energy and possibly the brake energy.

Conventional motor vehicles, other vehicles and also stationary drive units often have auxiliary machines which, since they absorb relatively high power, are mechanically driven by the drive unit (ie by the internal combustion engine), for example via belt drives. These can be, for example, climate machines, servo drives (eg for brake and steering assistance), pumps or the like. Such a mechanical drive coupling is generally not optimal since the auxiliary machine must follow the drive unit through the speed states specified by it. On the one hand, it does not run constantly with its optimum operating variable (eg the rotational speed in the case of a rotary auxiliary machine) and, on the other hand, also has to run if this is not necessary at all in the absence of a requested auxiliary power. These disadvantages can be overcome with the starter / generator according to the invention, which can be designed as a high-performance machine. The electrical machine supplies current at a relatively high voltage level, preferably in the upper region of the low voltage, where it is not yet necessary to provide special contact protection (eg about 60 V DC voltage). Further, preferably, a range of 250-450 volts is selected. The auxiliary machines are advantageously operated electrically from the intermediate circuit at these high voltage levels. Such a high voltage level is already present in the intermediate circuit in the case of an intermediate-circuit converter, and does not need to be generated particularly for this additional purpose. An electrical rather than an auxiliary mechanical drive is possible because relatively high currents result from the high voltage level (as opposed to the 12 volt voltage level of a conventional motor vehicle network, for example). Electrically driven, the auxiliary machines can be run at their optimum rotational speed as required and otherwise switched off. This results in a significant increase in the overall efficiency. Advantageously, all the devices and auxiliary drives of a motor vehicle are operated electrically. The internal combustion engine then serves as the main drive motor for the vehicle as well as the drive motor of the generator. For low-power users, a conventional low-voltage onboard network (eg, 12 V or 24 V) may be provided. A battery can be arranged in the region of the low-voltage bus system.

Advantageously, a (further) inverter is also provided for the supply of 220 V alternating current and / or 380 V three-phase current with a common mains frequency (eg 50 Hz). The supply of this further inverter can also be effected from the (DC voltage) intermediate circuit. A vehicle designed in this way allows the supply of normal electrical power supply units and thus represents a mobile mains power generator, which can be advantageously used, for example, in external work.

The conversion of electrical energy from the intermediate circuit into alternating current can also advantageously serve to supply an alternating voltage vehicle electrical system of the vehicle. Such a network has the advantage that arbitrary voltages adapted to the respective loads can be generated from the on-board electrical system by means of transformers in the individual consumers. Particularly advantageously, the alternating voltage is high-frequency (ie, the frequency is greater than 1 kHz) since the transformers can then be particularly small and light.

The possibility of designing the starter / generator as a high-performance machine at a high voltage level allows its use for heating purposes in the vehicle. This can be, for example, electric heating of the internal combustion engine, for example by heating the cooling circuit (in particular for the winter operation of direct-injection turbo diesel engines), a passenger compartment, an exhaust gas catalytic converter of the internal combustion engine, a fuel filter, a windshield washer system, exterior mirrors and / or Windows of the vehicle. In conventional motor vehicles, such heating systems are either not possible, only insufficiently, or only by exhaust heat from the internal combustion engine. The electric heating system has a beneficial effect on the environmental friendliness of motor vehicles, apart from the increase in the comfort of the passenger compartment heating system. Electric engine and catalytic converter heating systems quickly bring the combustion engine or the catalytic converter up to operating temperature and also allow precise and fast control of the operating temperatures . These are important measures to meet strict emission regulations. The control and regulation of the various heaters, in particular of the engine and catalytic converter heating, can be taken over by the control of the starter / generator for controlling the inverter.

Due to its low noise and wear, as well as the lack of dead time, the starter / generator is suitable for very frequent starting. It is therefore advantageously combined with a start-stop control of the internal combustion engine in which the internal combustion engine only runs as needed and is otherwise switched off. In urban traffic, combustion engines of motor vehicles run a considerable part of their operating time during idle due to frequent stops at traffic lights and crossroads. This represents a considerable waste of resources and environmental pollution since it entails in itself a useless additional consumption of fuel with accompanying emissions of toxic, climate-active or otherwise harmful exhaust gases.

The automatic start-stop control preferably causes automatic stopping of the internal combustion engine when a stop condition (or one of several) is satisfied. For definition of a stop condition, different conditions can be used alone or in a (sub) combination, for example: zero load, shifting operation, idling, standstill of the motor vehicle (ie driving speed below a certain small value, eg 4 km / h), combustion engine is disengaged, no gear Is engaged, the operating or parking brake is actuated, actuation of a stop switch.

Accordingly, the start-stop control preferably initiates an automatic start of the internal combustion engine with the aid of the electric machine in the presence of a starting condition (or one of several). Also for the definition of the starting condition, various conditions can be used alone or in a (sub) combination, for example: actuation of the accelerator pedal, release of the operating or parking brake, actuation of the clutch, touching or moving a gear shift lever, engaging a gear, actuating a start switch.

Conventional starters bring the internal combustion engine to a relatively low starting speed (typically 80-250 rpm), which is well below its idle speed (typically 600-800 rpm), because of its high ratio. The engine speed difference between the start speed and the idling speed must then be overcome by the internal combustion engine itself. However, because of the fact that, at these speeds, it is far below its idle speed in a very unfavorable operating range, it requires a relatively large quantity of fuel which, moreover, burns incompletely. Each engine start is therefore associated with additional fuel consumption and particularly environmentally harmful emissions. Preferably, therefore, the drive system is designed in such a way that the electrical machine has a driving effect at least essentially until the idle speed of the internal combustion engine (which is between 600 and 800 rpm at an operating temperature). This measure allows the internal combustion engine to start up only when its idling speed is reached, thus eliminating the operationally unfavorable start-up on its own. It thus reduces fuel consumption and the particularly harmful emissions during start-up and also makes the start-up process faster. The measure is thus ecologically particularly advantageous for vehicles with and without start-stop automatic.

Advantageously, the electrical machine can perform other functions besides its functions as a starter and as a generator:

A first advantageous additional function is that the electrical machine accelerates and / or decelerates the shaft, for example in order to accelerate or decelerate the motor vehicle. For deceleration, the electrical machine can serve as a wear-free (retarder) brake that is advantageously regenerative for the purpose of energy recovery. In connection with a drive slip (ASR) control, the electric machine can quickly reduce the total drive torque and thus the slip of one or more drive wheels by braking. In the case of a driving additional torque for acceleration assistance, the internal combustion engine can be dimensioned weaker in the case of unchanged achievable vehicle acceleration values ​​so that it operates on average at a higher medium pressure and therefore consumes less fuel. This measure also contributes to the reduction of harmful emissions. The acceleration support can advantageously be controlled in such a way that it smoothes the torque characteristic curve of the internal combustion engine, for example by applying a correspondingly greater additional torque in a rotational speed range with relatively low torque (for example, in the so-called "turbocharger" in a turbocharger-charged engine) than in other rotational speed ranges .

A further additional function is that the electrical machine actively reduces rotational nonuniformities by generating a rapidly alternating torque in antiphase with respect to the rotational irregularities. This alternating torque may be superimposed on the constant or slowly varying torque of the generator function or possibly the braking or booster function.

The rotational nonuniformities can in particular be those which occur in the internal combustion engine (which is, in particular, a reciprocating piston engine with internal combustion) through the gas and / or mass forces of the individual reciprocating pistons acting on the crankshaft. For example, a four-cylinder four-stroke engine shows relatively large rotational irregularities in the second order (ie, two times the rotational frequency of the engine). In addition, there are rotational irregularities at higher orders as well as stochastic irregularities.

By "fast" is meant here a variation in the frequency range of the rotational nonuniformities to be reduced, ie, for example, in the rotational nonuniformity of the second order and at a rotational speed of 3000 min^-1 A variation with a frequency of 100 Hz. On the other hand, the torques associated with the generator function or other of the abovementioned functions generally vary slowly or they are constant.

They are therefore also referred to in the following as "constant torques".

If the amplitude of the changeover torque is greater than the constant or slowly varying torque, the overall torque of the electrical machine alternately shows positive and negative values, albeit offset relative to the zero line. Otherwise, the total torque is only positive or negative, with its magnitude containing a rapidly varying portion.

The energy obtained in these additional functions is advantageously temporarily stored in the above-mentioned (or another) energy storage device and is used for the generation of driving torques (for example, for the generation of driving torques), for example, in the case of vehicle braking, starting with "grinding" clutch, deceleration of gear wheels, braking with positive rotational nonuniformity Vehicle acceleration, acceleration of gear wheels, driving in a negative rotational nonuniformity) and / or fed into a vehicle vehicle network and / or a battery. For very large incidences. The energy storage device can advantageously be designed as a flywheel memory, the flywheel of which is driven and braked by an electric machine. (DE). WIPO Home services World Intellectual Property Organization Alternatively, these large amounts of energy can be fueled, for example, by an electric heating coil which is arranged parasitically in the cooling circuit of the internal combustion engine (similar to a dive plunger).

In order to achieve the highest possible efficiency of braking energy recovery in the case of a vehicle braking with the aid of the electric machine, the electrical machine is advantageously decoupled from the internal combustion engine, for example with an intermediate clutch, for example a friction clutch or claw clutch.

For the optimum utilization of the space available, for example, in a motor vehicle, it is advantageous that a clutch, preferably a friction clutch serving as a driving clutch, is integrated into the electrical machine, and in particular in the rotor thereof. For example, in the case of an asynchronous and synchronous machine with an internal rotor, the rotor can be functionless in its inner region and thus be designed to be hollow for receiving the coupling. As a result of this measure, it is possible for the electric machine, together with the clutch integrated in the interior of the rotor, to occupy only as much as or hardly more space in the axial direction than in a conventional motor vehicle, the clutch alone. Owing to the reduced available diameter and to minimize the moment of inertia, an embodiment as a multi-disc and / or lamellar coupling is also possible. If the integrated clutch is designed as a wet clutch, the clutch fluid can also provide cooling for the electrical machine. The actuation of the clutch can be effected mechanically, electrically, magnetically, electromagnetically, hydraulically, pneumatically or with mixing forms thereof.

In the rest of the present description, the term "x" is understood to mean "at least x", and only preferably in the sense of "exactly x".

The invention is now explained in more detail by means of exemplary embodiments and the attached schematic drawing. In the drawing: FIG.<dl id="dl0001"><dt>FIG</dt><dd>FIG. 9 is a schematic representation of a drive system with an embodiment of the starter / generator; FIG.</dd><dt>FIG</dt><dd>3 shows a schematic, exemplary illustration of the operation of the starter / generator with additional function "active oscillation damping";</dd><dt>FIG</dt><dd>3 shows a schematic sectional representation of an electrical machine with a cutting plane perpendicular to the axial direction;</dd><dt>FIG</dt><dd>3 shows a schematic sectional illustration of an electrical machine with an integrated friction clutch with a cutting plane in the axial direction;</dd><dt>FIG</dt><dd>3 is a schematic circuit diagram of an inverter used in the starter / generator.</dd></dl>

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the figures, essentially functionally identical parts bear the same reference numerals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The drive system of a motor vehicle shown in FIG. 1, for example a passenger car, has a combustion engine 1 as the drive unit, which is, for example, a four-cylinder four-stroke Otto or diesel engine. The torque generated by the internal combustion engine 1 can be transmitted to drive wheels 3 via a drive train 2. In the drive direction, an electric machine 4 serving as a starter / generator is arranged in the drive train 2 downstream of the internal combustion engine 1. These are followed by a driving clutch 5, a transmission 6 and an axle drive 7, which transmits the torque to the drive wheels 3. The clutch 5 and the transmission 6 can be a friction clutch and a shift transmission; Alternatively, for example, an automatic clutch or converter clutch, each with, for example, a manual-operated manual transmission or automatic transmission is possible.

The electric machine 4, in this case a three-phase traveling-wave machine in asynchronous or synchronous design, comprises a stator 8 and a rotor 9. The former is rotationally fixed against the internal combustion engine 1, a vehicle chassis (not shown) (Crankshaft) 10 of the internal combustion engine 1 or an extension thereof and is coupled to the latter in a rotationally fixed manner. The drive shaft 10 and the rotor 9 thus rotate together without the intermediary of a transmission.

The electrical machine 4 performs several functions: it acts as a generator for charging a vehicle battery 11 and for supplying electrical loads, and thus replaces a conventional electric machine in the motor vehicle. On the other hand, it functions as a starter, which starts the internal combustion engine 1 from the stand, and can thus also replace a starter which is conventionally provided separately in the motor vehicle. The electric machine 4 has further optional functions: a generator function with much greater torque is used to decelerate the vehicle or the internal combustion engine 1. In addition, the electric machine 4 can function as an additional booster, for example to assist the internal combustion engine in accelerating the vehicle . Also, it can serve as an active rotation uniformity reducer (Figure 2). Finally, due to the mass moment of inertia of the rotor 9, it functions as a flywheel and can thus replace the flywheel present on the crankshaft in conventional motor vehicles.

The electric machine 4 is internally cooled by a spray liquid cooler 12. After passing through a re-cooler 13 and a pump 14, the coolant-in this case a suitable oil-is sprayed onto the rotor 9, in the vicinity of its axis of rotation. Due to the rotation of the rotor, it migrates outward as a result of centrifugal force and thereby cools rotor 9 and stator 8, and then leaves a housing 15 of the electrical machine 4 in order to enter the cooler 13 again in a closed circuit. The coolant flow is dependent on the loss of performance and speed, by corresponding control of the pump 14 in such a way that in each case essentially only a minimum required quantity of the cooling fluid is located inside the housing 15. A compensating vessel (not shown) allows this variation of the cooling fluid quantity in the housing 15. In other embodiments (not shown), the cooler is used as a parasitic cooler which is, for example, inserted into the cooling circuit of the internal combustion engine. In further embodiments (not shown), the electrical machine does not have its own closed cooling system. For example, it (or only the rotor) is integrated into a clutch and / or transmission housing and is cooled by a lubricating and / or cooling fluid (eg clutch or transmission oil) therein.

In the case of simpler (not shown) embodiments in which the electric machine 4 does not have to perform additional functions with a high continuous power, the cooling can be carried out more simply. Here, for example, internal cooling with gas or only external cooling of the stator with liquid or gas is sufficient.

The electric machine 4 is also equipped with a rotary transformer 16 (so-called resolver), which preferably has more than 8 poles, eg 12 poles. It consists of two adjacent printed circuit boards one of which is fixed and the other rotating with the drive shaft 10. The printed circuit boards carry windings, which are formed by conductor tracks, on their facing surfaces, such that a rotational-angle-dependent transformer-translation ratio results. The rotary transformer 16 operates according to the transponder principle: the fixed windings (active plate) are actively supplied with current / voltage and radiate electromagnetic energy to the rotatable coils (rotatable circuit board). The latter radiate a part of this energy again, this part depending on the angle of rotation dependent on the angle of rotation. The re-radiated part generates a rotation-angle-dependent signal in the fixed windings. An evaluation of this signal supplies the instantaneous rotational angle of the drive shaft 10 with an accuracy of at least 0.5 deg. In the case of simpler embodiments, an incremental encoder is used or a corresponding encoder is dispensed with entirely.

An inverter 17 supplies the windings of the stator 8 of the electrical machine 4 at a very high clock frequency (for example, 10-100 kHz) sinusoidal pulse-width-modulated voltage pulses which give essentially sinusoidal three-phase currents whose amplitude, frequency and phase free under the effect of the machine inductance Preselectable.

The inverter 17 is a voltage intermediate circuit inverter and comprises an electrical intermediate circuit storage 19, a DC voltage converter 18 (input module) which converts DC voltage from a low level (here 12 V) to a higher intermediate circuit level (here 350 V) and in the opposite direction , A capacitor or an arrangement of parallel-connected capacitors, and a machine inverter 20 (output module), which can generate the (pulsed) three-phase alternating voltage of variable amplitude, frequency and phase from the intermediate circuit direct voltage Engine 4 can convert such arbitrary alternating voltages into the intermediate-circuit direct voltage. In other embodiments (not shown), the intermediate circuit level is located at the upper edge of the low-voltage range, which is permissible without special protection against contact, here 60 V.

The three assemblies 18, 19, 20 of the inverter 17 are hermetically enclosed in a shielding housing 21, which is filled with a suitable boiling coolant. This is, for example, a fluorocarbon which has a suitable boiling point, for example at 60 ° C., at a suitable pressure (approximately between 50 mbar and 3 bar). Evaporated boiling coolant can condense in a condensation cooler 22 and return to the housing 21 in liquid form in a hermetically closed circuit.

The direct voltage converter 18 is connected on the low side to the vehicle battery 11 and various low voltage consumers 23, such as, for example, lighting and electronic devices. The inverter 17 can, on the one hand, provide current at a low voltage level for charging the vehicle battery 11 and supplying the low-voltage consumers 23; on the other hand, it can extract the current from the vehicle battery 11 at a low voltage level for starting the internal combustion engine 1. In other embodiments (not shown), the vehicle battery is at intermediate circuit level and is directly coupled to the intermediate circuit.

The intermediate circuit memory 19 is connected to an external additional memory 24, which is an electrical memory, here an additional capacitance 25. The additional accumulator 24 relieves the vehicle battery 11 during the starting process of the internal combustion engine 1 in that energy is removed only relatively slowly and stored in the additional accumulator 24 before starting. This is then available for a quick removal during the start process. In addition, it can also be used to store the energy which is generated during braking processes mediated by the electrical machine 4. Finally, it has the task of temporarily storing the energy gained during a rotational uniformity reduction in a braking phase and outputting it again for the subsequent drive phase. For large energies to be stored, supplementary memory 24 may include a flywheel memory 26 as a complement or alternatively.

On the other hand, the (inner) intermediate circuit store 19 essentially has the task of supplying the machine inverter group 20 with voltage with the high edge steepness necessary for the clocking, ie rapidly. He does not need a very high capacity (he has eg 2<i>μ</i>F), are rather low in feed inductances, which is ensured by the arrangement in the interior of the inverter 17 (preferably on the same printed circuit board on which the electronic switches of the machine inverter 20 are also arranged). The additional memory 24, on the other hand, can operate relatively slowly, so that the supply capacitances do not interfere with the external arrangement. The additional capacitance 25 can be, in particular, 50 to 10,000 times greater (for example, 4.7 mF for the storage of the rotational nonuniformity energy) than that of the intermediate circuit store 19.

Even larger storage s are serviced by a flywheel 26 which comprises its own invertor-controlled electric machine 27 and a gyrating mass 28 coupled comprises here. The latter can be formed by a separate flywheel or integrated into the rotor of the electrical machine 27. The moment of inertia of the inertia mass 28 is preferably 0.05 to 2 kgm². It is also possible to store a multiplicity of the energy required for starting the internal combustion engine 1 in the flywheel store 26, and to take it off quickly (ie, in less than one second) from the required starting energy.

The intermediate circuit with its high voltage level (here 60 V or 350 V) supplies various auxiliary drives 29, such as a climate machine and servo drives, as well as various heating devices 30, such as motor and catalyst heaters with electrical energy. While such high-performance consumers are conventionally driven by mechanical coupling from the internal combustion engine 1 or are heated by exhaust heat from the internal combustion engine 1, the high voltage level available here permits an efficient, more efficient, purely electric drive.

A control device 31 provides the inverter 17 with appropriate control, its semiconductor switch at any time, which amplitude, frequency and phase is to have the alternating voltage to be generated by it. The control device 31, which can be formed, for example, by a correspondingly programmed microcomputer system, determines in a first step the amount and the direction of the torque which the electric machine 4 is intended to produce at a particular point in time. It can do this, for example, with the aid of a characteristic map control, by receiving the angular position of the drive shaft 10 as the input information from the rotary transformer 16, the instantaneous mean rotational speed, and possibly other operating parameters, such as the throttle position. To start the internal combustion engine 1, the desired torque can be determined on the basis of stored values ​​which specify the desired time profile of the rotational speed or the torque of the electrical machine 4 during the starting process, possibly supplemented by a measurement of these variables and a feedback control , Which ensures compliance with the requirements. A power consumption control device (not shown) indicates how much energy is required to charge the vehicle battery 11 to supply the low voltage consumers 23 and the high-power consumers 29, 30 so that the control device 31 can cause a corresponding braking torque. A motor control unit 33 instructs the control unit 31 whether and to what extent the electric machine 4 is to act in addition to the vehicle acceleration or deceleration so that it has a corresponding torque, for example, for smoothing the moistening characteristic of the internal combustion engine 1 (eg for filling a "turbo hole "At lower speeds). Correspondingly, an ASR control unit 34 (ASR = drive-slip control) of the control device 31, in the presence of drive slip, provides that the electric machine 4 is to act temporarily as a regenerative brake, possibly before the ASR control unit is operated as a more massive measure Braking of the affected drive wheels is caused by the wheel brake. In addition, the ASR controller may transfer its slip information to the engine controller 33 to also cause a reduction in the internal combustion engine torque. The engine control unit 33 can also carry out an automatic start-stop control and provide the control unit 31 with a decision as to whether the electric machine 4 is to start the internal combustion engine 1.

The active reduction of rotational nonuniformities can be controlled in such a way that the instantaneously expected rotational uniformity is determined from a stored characteristic map as a function of the abovementioned operating parameters. Another possibility is to determine the actual instantaneous rotational uniformity, for example by calculating the instantaneous rotational speed on the basis of the information provided by the rotary transformer 16 and / or by evaluating the gas pressures currently present in the internal combustion engine 1 which are detectable with the aid of gas pressure sensors 32 , Or by detecting the instantaneous torque of the internal combustion engine 1 by means of a torque hub (not shown) in the drive train. A combination of regulation and control is also possible. A corresponding (antiphase) value for the rapidly varying desired torque of the electrical machine 4, which is superimposed on the braking (or possibly driving) constant torque, is derived from the thus determined value for the instantaneous rotational nonuniformity.

In a second step, the control device 31 determines which amplitude, frequency and phase of the voltage or the current must be provided by the inverter 17 so that the electrical machine 4 produces this desired total torque. This determination is made in the electrical asynchronous machine on the basis of a field-oriented control which is based on a model calculation of the electrical machine 4 and uses as input information essentially the measurable electrical stator variables (amplitude, frequency and phase of current and voltage) and the instantaneous mean rotor speed Is derived from electrical quantities.

In FIG. 1, the control device 31 is shown as arranged outside the inverter housing 21. However, in order to participate in the boiling bath cooling, it is arranged in the interior of the inverter housing 21 in other embodiments (not shown).

The control device 31 can divide various sensor information or sensor data derived from it for the purpose of fulfilling its control tasks with the engine control unit 33 for controlling the internal combustion engine 1. It can be, for example, the rotary transformer 16 (angular position sensor), the gas pressure sensors 32, sensors (not shown) for detecting the mean rotational speed, the load state of the internal combustion engine 1 (eg via the throttle valve position) and its torque (eg with the aid of a torque hub) .

The energy obtained by braking in the additional functions is temporarily stored in the additional memory 24 in order to be reused for the later driving of the electrical machine 4 or to be supplied to the vehicle battery 11.

FIGS. 2a-2c illustrate the generator operation together with the additional function "active vibration damping". FIG. 2a shows (with solid line) the rotational speed n of the crankshaft 10 as a function of the crankshaft angle φ. The shaft, by means of an average rotational speed (here 3000 revolutions per minute), periodically produces rotational speed fluctuations to smaller and larger rotational speeds, which in this idealized example have a generally sinusoidal course. These are rotational irregularities resulting from the gas and mass forces, which occur here in the second order (ie at a frequency of 100 Hz). For illustrative purposes, the angular interval required for one revolution of the shaft is also shown. Substantially proportional to the rotational irregularities are fluctuations of the torque Mv of the internal combustion engine by an average torque. The solid line in FIG. 2a thus also illustrates the course of the motor torque Mv as a function of the crankshaft angle φ.

2b shows the torque Me produced by the electrical machine 4 as a function of the shaft angle φ. For the sake of better clarity, the braking torque component belonging to the generator function is not yet shown. The course of the machine torque Me is essentially antiphase in equal measure to the nonuniformity of the motor torque Mv. As a result, the rotational uniformity - and the fluctuation of the torque Mv - which is proportional thereto - is substantially reduced or even disappears practically as illustrated by the dashed line in FIG. 2a.

In FIG. 2b, the negative and positive torque parameters are of equal magnitude. The energy obtained in a braking phase is therefore essentially equal to the energy to be applied in the following driving phase. The energy flow to the outside is therefore zero, only braking energy is temporarily stored in the interior of the system. 2b, the system operates as a pure rotational uniformity reducer with rapidly varying torque, without a generator function.

FIG. 2c shows the superimposition of both functions: The generator function shifts the torque according to FIG. 2b globally by a certain amount ΔMe (the so-called stroke) in the negative direction. The stroke ΔMe varies slowly, in the short period of time of approximately one revolution period shown here, it is constant in a good approximation. It is smaller than the amplitude of the rapid variation of the torque for the generator power required usually so that the total torque Me alternately assumes positive and negative values. Based on the rapid torque variation, a constant torque - ΔMe is obtained. The combustion engine is thus, on the average, deprived of mechanical energy which is converted into electrical energy and removed from the system for charging the vehicle battery 11 and / or for operating electrical consumers 23, 29, With a pure generator function without vibration damping, the electric machine 4 generates a constant torque corresponding to the dash-dotted line ΔMe in FIG. 2c.

If, for example, the stroke ΔMe becomes greater than the amplitude for reducing the rotational nonuniformity during vehicle braking, the electric machine 4 acts only as a braking and no longer driving. The global torque profile can also be shifted in the positive direction (positive stroke). The electric machine then operates as a (driving) motor, eg to assist the internal combustion engine in a vehicle acceleration.

A small and very large generator power can be set by an appropriate setting of the (software) control of the electrical machine without any constructive (hardware) changes. The size of the electrical machine and the power electronics is limited. Thus, one and the same type of machine can be used, for example, for small and large types of motor vehicle without any structural adaptation.

The electrical machine 4 shown in more detail in FIG. 3 is free of brushes and / or grinders and thus is free of wear. It has an outer diameter of about 300 mm and a length in the axial direction of 70 mm and provides a continuous torque of about 50 Nm with a weight of 10-15 kg and a maximum torque of approx. 150 Nm. It can reach speeds which correspond to the peak speeds of conventional combustion engines (approx. 6000 to 10000 rpm) and is speed-resistant up to 14000 rpm. The electric machine 4 has an external stator 8 which has grooves 35 in the direction of the drive shaft 10 (axial direction). The stator 8 carries a three-phase winding 36, which is designed such that, when three-phase current is applied, it forms twelve magnetic poles. Three poles 35 are provided per pole, ie a total of thirty-six grooves 35 are provided. (In the case of other embodiments (not shown), at least six, preferably nine, grooves are present for the purpose of reducing scattering effects per pole.) The poles are rotated with the three-phase oscillation in a circular movement in the stator. For a given time, their current position is indicated by arrows bearing the reference signs "S" (for South Pole) and "N" (for North Pole). A back part 37, which terminates the grooves 35 to the outside and runs in the circumferential direction, is relatively thin in the radial direction, its thickness being 3-25 mm (at the location of a groove 35). The stator 8 is constructed of thin stator plates (the thickness is here 0.25 mm) of a material with low losses of magnetization (in this case less than 1 W / kg at 50 Hz and a Tesla), with sheet planes running perpendicular to the axial direction.

In the asynchronous machine, the internal rotor 9 is designed as a cage rotor with cage rods extending essentially in the axial direction, which are each connected on the face side to a short-circuit ring 38. In the synchronous machine, the rotor 9 carries the same number of poles as the stator 8 (here 12 poles), which may be constituted by permanent magnets or correspondingly excited coils. The synchronous machine is also illustrated in FIG. 3, in that the rotor poles (reference numeral 39) present in it are schematically indicated. Power for feeding the rotor winding (not shown) which produces these poles is fed to the rotor via slip rings.

The air gap 40 between rotor 9 and stator 8 is relatively large; Its width is 1 mm.

In other embodiments (not shown), the rotor is outboard and the stator is inboard.

In the embodiment according to FIG. 4, the clutch 5 is virtually completely integrated in the electrical machine 4. Within the stator 8 mounted, for example, on the motor housing or gearbox housing, the rotor 9 is non-rotatably connected at its periphery to the drive shaft 10 of the internal combustion engine 1 via an axially laterally projecting cage 54. The rotor 9 is hollow on the inside and has essentially the shape of a flat circular cylinder jacket. In the cavity, the clutch 5 - in this case a lamellar clutch (multi-surface friction disc clutch) acting as a driving clutch is arranged. It can produce a force connection between the drive shaft 10 with the rotor 9 and an output shaft 55, which projects into the cavity, to the transmission 6. For this purpose, the rotor 9 is internally toothed and the output shaft 55 is externally toothed in the region of the cavity 55. A disk pack 56 is arranged in the space therebetween, the disks 57 of which are alternately externally and internally toothed so that alternately one disk is connected to the rotor 9 (outer disk 57a) alternately and the next disk is positively connected to the output shaft 55 (inner disk 57b). Without axial pressure, the outer and inner lamellae 57a, 57b can rotate virtually freely against each other, the shafts 10, 55 are then uncoupled. If the outer and inner lamellae 57a, 57b are pressed together in the axial direction by means of a pressure device (not shown) (for example, an angle lever), the frictional forces produced bring about the crosstalk between the shafts 10, 55 so that the pressure generated by the internal combustion engine 1 and the Electrical machine 4 to the output shaft 55. The force-locking part (ie here the disk pack 56) of the clutch 5 is located completely in the rotor 9, so it does not protrude laterally out of the axial direction. The clutch 5 is designed as a wet clutch. The coupling oil simultaneously serves to cool the electrical machine 4. In other embodiments (not shown), other switchable, non-positive couplings are integrated, for example a single disc clutch in dry or wet construction.

FIG. 5 shows a schematic circuit diagram of the inverter 17. One recognizes the intermediate circuit storage 19 in the form of a capacitance, which is connected in parallel with the additional memory 24 (not shown here). The capacitance symbolizes a parallel connection of several capacitors.

The machine inverter 20 is formed by three parallel-connected (but independently switchable) switch groups 42, each of the switch groups 42 being responsible for the generation of one of the three three-phase voltages. Each of the switch groups 42 is a series connection of two (independently switchable) switches 43 between the positive and negative poles of the intermediate circuit. The series circuit is connected centrally (ie, between the switches 43) to one side of one of the three windings 36a, 36b, 36c of the three-phase winding 36, respectively; On the other side, the three windings 36a, 36b, 36c are connected to each other.

A free-floating diode 44 is connected in parallel with the switches 43. It is polarized such that it normally blocks and, only when the opposing switch is opened, allows a short-term current flow due to self-induction to pass through.

Each switch 43 symbolizes a parallel connection of several (eg five) MOS field effect transistors, which are directly controlled by the control device 31 to form a three-phase current of desired amplitude, frequency and phase.

The DC converter 18 comprises two subassemblies, one which can bring electrical energy from the low voltage level (12V) to the high intermediate circuit voltage level (60V and 350V), respectively, and vice versa From the high voltage level (60 V and 350 V) to the low voltage level (12 V). In the case of embodiments with a vehicle battery arranged in the intermediate circuit, the first-mentioned subassembly can be omitted.

The first sub-assembly is, for example, a step-up actuator 45. This is formed by a series connection of an inductor 46 connected to the positive pole of the vehicle battery 11 and a switch 47 connected to the negative pole thereof and the negative pole of the intermediate circuit A high-setting diode (which is polarized in the forward direction) is connected to the positive pole of the intermediate circuit. When the switch 47 is closed, a circulating current flows from the positive to the negative pole of the vehicle battery 11. After opening the switch 47, a self-induction voltage is used to prevent a breakdown of this current, with the result that the high intermediate circuit voltage level (350 V) is briefly exceeded Through the (otherwise blocking) step-up diode 48 and charges the intermediate circuit storage 19. By periodically opening and closing the switch 47, a quasi-stationary charging current is obtained, for example, in preparation of the starting process. The switch 47 is a semiconductor switch, which is controlled directly by the control device 31.

The second subassembly is, for example, a voltage reducer 49, which functions similarly to a switching power supply. It comprises two series circuits of switches 50 between the positive and negative poles of the intermediate circuit, each having parallel-connected freewheeling diodes 51. The ends of a primary winding of a high-frequency (RF) transformer 52 are each connected to the centers of these series circuits. The secondary winding of the HF transformer 52 feeds a rectifying and smoothing unit 53 which, in turn, feeds the vehicle battery 11 and possibly the low voltage consumer 23. The switches 50 symbolize semiconductor switches, which are controlled directly by the control device 31. By periodically opening and closing the switches, a high-frequency alternating current can be generated which induces a corresponding alternating voltage in the secondary winding of the HF transformer 52 at a lower voltage level, which is rectified and smoothed by the unit 53. The exact value of the resulting DC voltage can be precisely adjusted by means of the switches 50 by varying the switching frequency.

In embodiments with a synchronous machine, no actively controlled semiconductor switches are required in the generator mode, in this case, voltage-controlled valves are sufficient to form a rectifier function. With actively controlled switches, however, higher performance is achieved.