EP1000242B1 - Starting mode with a diesel engine and propulsion system with such an engine - Google Patents

Abstract

The invention relates to a method for starting a diesel engine (1), comprising the following steps: no thermal auxiliary starting agent needs to be used in a range of low temperatures up to the lowest acceptable temperature or at least above a low threshold temperature; the diesel engine (1) is speeded by means of an electrical starter (4) up to a sufficiently high number of TPM to ignite the fuel without preliminary use of a thermal auxiliary starting agent; the diesel engine (1) starts. The invention also pertains to a corresponding propulsion system.

Description

The present invention relates to a method for starting of a diesel engine and a drive system of a motor vehicle with a diesel engine.

The willingness of diesel engines to start takes off at low temperatures down. On the one hand, there is an increase in the frictional torque responsible. On the other hand, leakage and heat losses decrease when compressing the air the final compression pressure as well the final compression temperature. Traditionally Diesel engines therefore with thermal starting aids equipped. The temperature limit above which the jump starter must be used depends on of the engine type from. So have direct-injection diesel engines with one-piece Combustion chamber (hereinafter referred to as "DI engines") due to smaller Heat loss better starting behavior than pre-and swirl chamber engines, which have a divided combustion chamber.

Start-up aids are usually used in small-volume vehicles DI engines as well as engines with split combustion chamber glow plugs used. The glow plug of the candle protrudes into the combustion chamber or in the chamber of the engine. Besides glow plugs are also Glow plugs (in the narrower sense) common, i.e. Glow plugs with exposed Filament. In the case of large-volume diesel engines, the thermal jump start often on preheating the suction Air with the help of electrically heated spark plugs or Heating flanges (see Automotive Engineering Handbook, 22. Ed. 1995, VDI-Verlag, Düsseldorf, pp. 538-540).

JP 55-75568 describes a starter device for diesel engines known, when starting at low temperatures initially no air is let into the combustion chamber, which means the starter's workload is reduced and as a result the Starting speed increased. To preheat it then to Glow plugs are provided to start let-in air.

From DE 195 32 135 A1 a drive system with a Automatic start-stop is known, in an advantageous manner Embodiment an electric starter an internal combustion engine drives until idling speed is reached. This is used to stop the internal combustion engine after a stop electric starter directly to idle speed.

A flywheel starter is known from DE 28 53 130 A1, the before starting with the help of an electric drive is brought to such a high speed that the stored kinetic energy is sufficient to start. at low temperatures will have a greater starting energy than at high, the flywheel is correspondingly lower Temperatures brought to higher speed. The aspect of a thermal jump start is in this document in which it primarily a special type of flywheel drive goes, not mentioned.

The company publication: BOSCH Technical Instruction, Electric starting systems, 1st edition, February 1, 1994, p. 5 and 11 gives general explanations of the starting process as well Information about the lower limit temperature of different starter types.

The object of the present invention is an improved method to specify a diesel engine to start and a corresponding To provide drive system.

• die Motortemperatur wird erfaßt;
• in Abhängigkeit von der erfaßten Temperatur wird eine Drehzahl bestimmt, auf die der Dieselmotor zum Starten durch einen elektrischen Direktstarter ohne Verwendung eines thermischen Starthilfsmittels zu bringen ist, wobei diese Drehzahl bei niedriger Temperatur höher als bei hoher liegt;
• der Dieselmotor wird durch den elektrischen Starter direkt auf die bestimmte Drehzahl gebracht und dadurch gestartet.

In terms of method, this object is achieved according to claim 1 by a method for starting a diesel engine of a motor vehicle, which has no thermal starting aid, with the following steps:

• the engine temperature is recorded;
• depending on the temperature detected, a speed is determined to which the diesel engine is to be brought to start by a direct electric starter without using a thermal starting aid, this speed being higher at low temperature than at high;
• the electric starter brings the diesel engine to the specified speed and starts it.

• einem Dieselmotor, der kein thermisches Starthilfsmittel aufweist,
• einem elektrischen Direktstarter,
• Mitteln zum Erfassen der Motortemperatur und/oder der Außentemperatur, und
• einer Steuerung, die den Starter veranlaßt, den Dieselmotor auf eine, in Abhängigkeit von der erfaßten Temperatur variierte Drehzahl zu bringen, die zum Zünden des Kraftstoffs ausreicht, wobei die Drehzahl bei tiefen Temperaturen höher als bei tiefen Temperaturen liegt.

In terms of the device, this object is achieved according to claim 7 by a drive system of a motor vehicle, with

• a diesel engine that does not have a thermal starting aid,
• an electric direct starter,
• Means for detecting the engine temperature and / or the outside temperature, and
• a controller which causes the starter to bring the diesel engine to a speed which varies depending on the temperature sensed and which is sufficient to ignite the fuel, the speed being higher at low temperatures than at low temperatures.

It has been recognized that a significant part of the launch problems at low temperatures from cooling by compression heated air on the cold cylinder walls. Building on this, the invention is based on the idea that by reducing the contact time between air and cylinder walls a significant improvement in the misfire start behavior can be achieved. The shorter contact time in turn is achieved by a faster starting speed. For example is tripled compared to the starting speed the conventional starting method the contact time in the cylinder a third of the traditional value. According to the invention so the compression when starting more adiabatic Area so that for the auto-ignition of the fuel required limit temperature even at low temperatures is achieved solely by compression. The use of thermal jump starters, such as glow plugs or Air preheating devices in the intake tract can be completely or at least above a low limit temperature. In terms of the device, the diesel engine therefore has no thermal Jump starter on or it is controlled so that a any starting aid, if any, or only above the low limit temperature is used. Preferably is also used for any other indirect preheating of the engine, z. B. in the form of cooling water heating (possibly above the low limit temperature). The diesel engine therefore preferably has no such device for indirect preheating or is controlled so that such Device for starting not or only above the deep one Limit temperature is used. With some engine designs a post-heating device (e.g. an after-glow device) be provided in the first period after Start of the diesel engine is operated to warm up to bring about better combustion. Such heating after starting is not considered "using a thermal Starting aids "to understand. Accordingly, a drive system with glow plugs or the like, which is controlled so that the Glow plugs are heated only after starting, not as "Having thermal starting aids" understood. Especially no such post-heating is advantageously carried out and there is also no post-heating device.

• die herkömmlicherweise für das Vorglühen oder Luftvorwärmen erforderliche Wartezeit entfällt (zumindest oberhalb der tiefliegenden Grenztemperatur), wodurch das Starten schneller erfolgen kann. Dies dient der Verkehrssicherheit (in Gefahrensituation, in der bei abgestelltem Motor ein schnelles Losfahren erforderlich ist) und erhöht den Komfort bei Dieselfahrzeugen;
• mit der Einsparung der herkömmlich vorhandenen thermischen Starthilfsanlage geht eine beträchtliche Aufwandsersparnis einher;
• die zum Starten benötigte Energiemenge ist geringer, was eine kleinere Dimensionierung der Starterbatterie erlaubt.

The method and drive system according to the invention have the following advantages:

• the waiting time conventionally required for preheating or air preheating is eliminated (at least above the low limit temperature), which means that starting can take place more quickly. This serves traffic safety (in a dangerous situation, in which a fast start is necessary when the engine is switched off) and increases the comfort of diesel vehicles;
• the saving of the conventional thermal starting aid system is associated with a considerable saving of effort;
• the amount of energy required to start is less, which allows the starter battery to be dimensioned smaller.

Overall, the present invention thus makes a contribution on traffic safety, environmental protection and increasing the Driving comfort and to reduce effort in diesel vehicles. It can thus be used for the further spread of diesel vehicles contribute.

In the subclaims are more detailed explanations and advantageous Refinements specified:

According to claims 2 to 4, it is further defined what is advantageously to be understood by "higher speed" in the range of lower temperatures, namely a speed of 400 min ^-1 or more, preferably 600 min ^-1 or more, more preferably 800 min ^{- 1} or more. The maximum speed at the lowest temperature will typically not exceed 1500 min ^-1 .

Claims 5 and 8 relate to the point in time in the course fuel is injected during the starting process. And that is done this is advantageous only after the speed has been reached is necessary for self-ignition of the fuel. This saves Fuel and reduces smoke.

According to claims 6 and 9, the diesel engine is preferably a small-volume engine with a displacement of less than 3000 cm ³ , particularly preferably less than 2000 cm ³ . This type of engine is used in particular in passenger cars and small commercial vehicles with a total weight of less than 3.5 t. In such engines, the cooling in the combustion chamber is particularly pronounced, and the omission of thermal starting aids achieved by the invention is therefore particularly advantageous here.

The starter of the drive system is a direct starter, i.e. he brings the power required to start instantaneously (i.e. without storage) by converting electrical energy into mechanical Energy on. So it's not one Flywheel starter, the drive of which is not what is required to start Can apply torque, so that the drive Start only indirectly due to the storage of kinetic energy is possible.

According to claim 10, the starter is a as Starter / generator functioning electrical machine that is permanent runs along, unlike a flywheel starter before starting but does not have a driving effect. The relative speed of electrical Machine to diesel engine is in starter and generator operation same, i.e. the transmission ratio between electrical Machine and internal combustion engine are constant. Such Machines are designed for generator operation at high speeds. For starter operation, they have to be able to, high Applying torques. They are required to achieve the required excellent starting speed. According to Claim 11 is an electric starter inverter-controlled induction machine. Under "Rotary field machine" is understood to mean a machine in which a magnetic rotating field occurs, which rotates through 360 ° and thereby takes the runner with him. The inverter provides for the generation of the rotating field alternating or three-phase with freely adjustable Frequency, amplitude and phase ready. According to claim 12 the energy required to start is at least partially a capacitor store (e.g. a so-called intermediate circuit store) removed, the subpoena according to claim 13 can take place depending on the temperature. According to claim 14, the Energy for starting at least partially taken from a battery.

Refinements and features preceding or following described in connection with the procedure apply of course also in connection with the drive system revealed (and vice versa).

Fig. 1

eine schematische Darstellung eines Anstriebssystems mit einem Dieselmotor;

Fig. 2

eine Veranschaulichung des Zusammenhangs zwischen Startdrehzahl und Temperatur;

Fig. 3

ein Flußdiagramm zum Starten des Dieselmotors im kalten Zustand bei tiefer Temperatur.

The invention will now be explained in more detail on the basis of exemplary embodiments and the attached schematic drawings. The drawing shows:

Fig. 1

a schematic representation of a drive system with a diesel engine;

Fig. 2

an illustration of the relationship between starting speed and temperature;

Fig. 3

a flow chart for starting the diesel engine in the cold state at low temperature.

The drive system according to Fig. 1 is e.g. for a motor vehicle, determined about a passenger car. It has a direct injection diesel engine with a small cubic capacity (e.g. 1500cm) 1 on, the torque via a drive shaft 2, a clutch 3 and other (not shown) parts of a drive train delivers the drive wheels of the vehicle. The diesel engine 1 is with no glow device and no preheating device equipped for the intake air. He also has no institution for heating the cooling water with the engine stopped. On the Drive shaft 2 is an electrical one serving as a starter / generator Machine 4, here an asynchronous three-phase machine, arranged. It has a seated directly on the drive shaft 2 and rotatably connected runner 5 and one e.g. supported on the housing of the diesel engine 1 stand 6. The (not shown) winding of the stator 6 is by a Inverter 7 with electrical currents and voltages fed practically freely adjustable amplitude, phase and frequency. It is a DC link inverter, which is essentially one constant DC link voltage with the help of electronic Switches e.g. sine-weighted, wide-modulated pulses cuts out the - averaged by the inductance of the electrical machine 4 - to almost sinusoidal currents desired frequency, amplitude and phase.

The inverter is essentially made up of a machine DC-AC converter 7a, one DC voltage intermediate circuit 7b and an electrical system side DC converter 7c constructed. The latter is with one Vehicle electrical system 8 and an electrical system long-term storage 9, here a conventional lead-sulfuric acid battery. The Vehicle electrical system 8 and the vehicle electrical system battery 9 are at a low level Voltage level, e.g. 12 or 24 volts. The intermediate circuit 7b on the other hand is due to an increased voltage, which is advantageous is in the range between 200 and 400 volts. With others Embodiments, the increased voltage is at the top of the low voltage range, around 36 volts. In the intermediate circuit 7b is a short-term storage, here a capacitor storage 10 switched, which also the voltage in the intermediate circuit with a steep slope increasing current draw - the when pulses are generated by the converter 7a - approximately keeps constant. In other embodiments (not shown) is the short-term storage by a short-term battery (i.e. a quick-discharge battery).

The electrical machine 4 and the inverter 7 are like this designed to have the required torque and the necessary Power for directly driving the drive shaft 2 (e.g. the Crankshaft) of the diesel engine 1 to the required high Apply speed.

The electrical machine 4 can, for example, after the starting process act as a generator, i.e. electrical power deliver. For this purpose, the converter 7c is a bidirectional converter educated. On the one hand, it can if the electrical machine 4 is operated as a motor and from the on-board electrical system battery 9 is fed, electrical energy from the electrical system battery 9 bring in the intermediate circuit 7b, and on the other hand if they as Generator is operated, energy from the intermediate circuit 7b for the purpose of feeding the consumers of the vehicle electrical system 8 and the vehicle electrical system battery 9 convict.

The capacitor store 10 can also be used as an energy store for all or part of that required for starter operation Serve energy. The charging of the capacitor store 10 can be done in different ways: There is one possibility therein, the capacitor storage 10 even when the To keep diesel engine 1 charged: When operating the Diesel engine 1, i.e. in generator operation of the electrical machine 4 it will be charged anyway. When the engine stops the unavoidable slight charge losses are continuously recharged from the on-board electrical system battery 9. The start can then be done without waiting. Another one Reloading is not possible. The capacitor store 10 then discharges when the engine is at a standstill, and only from the on-board electrical system battery 9 before starting charged. In both cases, the whole does not need to Start required energy stored in the capacitor store 10 his. Part of it can also be used during the startup process can be removed from the on-board electrical system battery 9. Others (not shown) Embodiments takes a separate, with the Intermediate circuit 7b coupled energy store (e.g. a capacitor store or a short-term battery) storing the all or part of the starting energy. If at deep Temperatures a thermal starting aid for use comes, it is also advantageously from the capacitor store 10 fed. In embodiments (not shown) the supply of the starter 4 and possibly the thermal Starting aids wholly or partly from a battery, e.g. the on-board electrical system battery 9.

A higher-level control unit 11 controls the starting process by it the inverter 7, namely the converter 7a and the Converter 7c controls. It gives the converter 7a amplitude, phase and frequency of the three-phase voltage to be generated. the There is converter 7c the amount of current, the current direction for motor Operation and, if applicable, the amount of voltage increase (if energy is taken from the on-board electrical system battery 9). To the Starting the diesel engine 1, the control unit 11 controls the electrical Machine 4 via the inverter 7 such that the Drive shaft 2 to a high enough to ignite the fuel Speed is driven, not by one thermal booster system is made use of.

The speed at which the diesel engine 1 from the electrical Machine 4 is driven (at least in a partial area) selected depending on temperature. To record the engine and outside temperature is an engine temperature sensor 12a and an outside temperature sensor 12 b provided.

Fig. 2 illustrates the dependence of the starting speed (ie the speed required for self-ignition, at which fuel is injected) on the temperature. To simplify matters, the engine and outside temperature are assumed to be the same; Different values of these temperatures are taken into account by a corresponding map. The dependency drawn is such that the starting speed drops from a maximum (eg 400 min ^-1 ) at the lowest temperature with increasing temperature. Above a certain temperature (here 10 ° C) it is kept constant, ie it is in this area by an amount increasing with increasing temperature above the minimum required speed value. This setting of a minimum speed serves for starting comfort. A further temperature-dependent parameter (not illustrated in more detail here) can be the starting time, ie the time with which the diesel engine 1 is driven at the starting speed until fuel is injected. The start time is longer at low temperatures than at high ones, ie their temperature dependence is similar to the relationship shown in FIG. 2. When charging the capacitor store 10, these temperature dependencies are taken into account by variably setting the charge level at least so high that a safe start is ensured at the respective temperature. Depending on whether the capacitor store 10 is continuously charged or is only charged shortly before starting, the control unit 11 provides for a permanent recharging or one-time charging from the on-board electrical system battery to the above-mentioned minimum charge level before the actual starting process. When using a battery as an energy source, its capacity and power are selected sufficiently to ensure starting with the required starter speed at all temperatures.

In the method according to FIG. 3, the first step in step S1 is to ask whether a command to start the diesel engine 1 is given has been. When operating with continuous recharging is ensured by preceding process steps (not shown), that the capacitor storage 10 is sufficiently charged is to the diesel engine 1 at the present temperature conditions without using thermal starting aids to be able to start safely. These process steps include one Measurement of temperatures, a determination of the safe Start at the required charge level measured temperature values e.g. with the help of a stored in the control unit 11 Map similar to Fig. 2, and a recharge of the capacitor store 10 to the required level. This episode of Process steps are ongoing during engine shutdown repeated. When operating with a single charge this sequence executed once after the start command. in the Step S2 then measures the temperatures (if this did not happen immediately before) and one Determination of the safe start at the measured temperature values required starting speed and duration, e.g. With With the help of a map stored in the control unit 11. Without Then use thermal starting aids (step S3) in step S4 the crankshaft 2 of the diesel engine 1 from the electric starter 4 with the predetermined starting speed driven. After the predetermined start time has elapsed The injection of fuel begins in step S5. In the following Step S6 starts the diesel engine by auto-ignition, without a thermal jump starter Would have been used, even at the deepest occurring operating temperatures.

Claims (14)

1. A method for starting a Diesel engine (1) of a motor vehicle, which has no thermal starting devices, having the following steps:

   the engine temperature is recorded;

   in dependence on the recorded temperature a speed is determined to which the Diesel engine (1) is to be brought for starting by an electric direct starter (4) without using a thermal starting device, with this speed being higher at low temperatures than at high temperatures;

   the Diesel engine (1) is directly brought to the determined speed by the electric starter (4) and is started thereby.
2. A method according to Claim 1, in which the electric starter (4) drives the Diesel engine (1) in the low-temperature range to a speed of 400 min^-1 or above.
3. A method according to Claim 2, in which the electric starter (4) drives the Diesel engine (1) in the low-temperature range to a speed of 600 min^-1 or above.
4. A method according to Claim 3, in which the electric starter (4) drives the Diesel engine (1) in the low-temperature range to a speed of 800 min^-1 or more.
5. A method according to one of Claims 1 to 4, whereby the injection of the fuel into the combustion chamber of the Diesel engine (1) takes place only after a determined speed has been reached.
6. A method according to one of Claims 1 to 5, whereby a Diesel engine (1) is used which has a small volume and is designed in particular for use in passenger vehicles and low-usage vehicles.
7. A drive system of a motor vehicle, having

   a Diesel engine (1) comprising no thermal starting devices,

   an electric direct starter (4),

   means (12a, 12b) for recording the engine temperature and/or the external temperature, and

   a control unit (11) which causes the starter (4) to bring the Diesel engine (1) to a speed which is varied in dependence on the recorded temperature which is sufficient to ignite the fuel, with the speed being higher at low temperatures than at low temperatures.
8. A drive system according to Claim 7, whereby the injection of the fuel into the combustion chamber of the Diesel engine (1) take place only after the speed which is sufficient to ignite the fuel has been reached.
9. A drive system according to Claim 7 or 8, in which the Diesel engine (1) has a small volume and is designed in particular for use in passenger vehicles and low-usage vehicles.
10. A drive system according to one of Claims 7 to 9, in which the electric direct starter (4) is constructed as a starter/generator which permanently runs along with the Diesel engine (1).
11. A drive system according to one of Claims 7 to 10, in which the electric direct starter (4) is a three-phase machine controlled by anverter.
12. A drive system according to one of Claims 7 to 11, in which the energy required for starting is taken at least to some extent from a capacitor store (10).
13. A drive system according to Claim 12, in which the preliminary charging of the capacitor store (10) takes place as a function of temperature.
14. A drive system according to one of Claims 7 to 13, in which the energy required for starting is taken at least to some extent from a battery.

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