EP1464831B1 - Method for starting an internal combustion engine - Google Patents

Description

The invention relates to a method for starting an internal combustion engine and an internal combustion engine arranged to carry out such a method.

In order to improve fuel economy in internal combustion engine vehicles, complete engine shutdown rather than idling often occurs when no drive power is needed. The engine must then be restarted when its power is needed again. For starting, conventional internal combustion engines have special auxiliary units, such as a starter motor or a generator which can be used as a motor (so-called starter generator). These are relatively large and expensive devices, since a high electrical power is required for starting the internal combustion engine.

Moreover, it is known to start an internal combustion engine by triggering combustion. This is possible in particular with internal combustion engines with spark ignition and direct injection. The injected directly into the combustion chamber fuel is thereby ignited by a spark, and the subsequent explosion of the air-fuel mixture moves the piston and starts the engine without the crankshaft would have to be moved by an additional auxiliary unit.

In a combination of the above methods takes place during the starting of an internal combustion engine by a starter motor early or from the beginning of an injection and combustion in the cylinders, thereby supporting the starter.

Direct or assisted starting of the engine by early combustion requires certain constraints in order to be successful. For example, it is necessary or advantageous for the crankshaft to be in or near a certain position at the start of cranking. Furthermore, it must be ensured that a sufficient force for driving the internal combustion engine can be obtained from the combustion. The latter in turn requires the provision of a sufficient amount of fresh air during the launch phase. In this regard, in the DE 199 47 784 A1 proposed the arrangement of an air storage space in which air is to be stored under an increased pressure, so that it can be fed in a direct start of the internal combustion engine in the cylinder and there provides for increased boost pressure.

From the US 2002/0026769 A1 discloses a method for injecting nitrogen monoxide into an internal combustion engine for improving the efficiency during engine operation, but not specifically for improving the starting behavior, wherein the gas is withdrawn from an externally replenished storage tank.

Against this background, it was an object of the present invention to provide alternative means for efficiently ensuring the prerequisites for the start of an internal combustion engine with the aid of early burns during the starting phase, in which a replenishment of a storage tank with nitrogen monoxide is not required.

This object is achieved by a method having the features of claim 1 and by an internal combustion engine having the features of claim 3.

Advantageous embodiments are contained in the subclaims.

The method according to the invention serves to start an internal combustion engine, fuel combustion already taking place during the starting phase in at least one combustion chamber of the internal combustion engine. By the early fuel combustion, the starting can be supported by means of an auxiliary unit, so that the latter can be designed easier and thus cheaper. Preferably, with the combustion even a direct start of the internal combustion engine is performed, which manages completely without additional auxiliary unit. The method is characterized in that during the starting phase in at least one combustion chamber of the internal combustion engine relative to the relative oxygen concentration in normal air (about 21 vol .-%) increased relative oxygen concentration prevails (wherein fuel gases and / or residual gases in the determination of the relative Concentration are not taken into account) by nitrogen monoxide is introduced as oxygen donor in at least one combustion chamber of the internal combustion engine during the starting phase, wherein the nitrogen monoxide is produced in the motor vehicle and cached. An oxygen donor is a preferably gaseous or liquid substance which contains oxygen chemically bound and under certain conditions, for example above a temperature threshold, can release it or release it to other chemical substances.

By the method described can be achieved that during the starting phase of the internal combustion engine, a larger amount of oxygen in at least one combustion chamber is present, so that there more fuel can be burned as in a corresponding filling of the chamber with ambient air under comparable pressure conditions. This ensures that from the beginning of the starting phase to a sufficient engine power for a supported starting or a direct start is available.

The increased oxygen concentration in the combustion chamber could alternatively be added to the path proposed by the present invention by supplying a gas containing oxygen in a concentration increased in excess of the normal air ratios, or even pure oxygen (hereinafter called "oxygen feed gas") Leaking of the internal combustion engine, during the stoppage of the internal combustion engine and / or generated during the starting phase of the internal combustion engine. The supply can be done in addition to or instead of the normally aspirated fresh air. In a similar manner, the oxygen donor according to the invention can also be supplied to the internal combustion engine during the run-out, the standstill and / or the starting phase. In all the mentioned types of supply it is ensured that the oxygen or the oxygen donor is available during the starting phase.

According to the method of the invention, the oxygen donor is produced during operation of the internal combustion engine on board the motor vehicle containing the internal combustion engine and temporarily stored for starting the internal combustion engine. The type of production depends on the substance used as oxygen donor.

The oxygen donor used in the invention is the gas nitrogen monoxide N ₂ O ("nitrous oxide"). This gas can either be carried in a store or generated aboard a motor vehicle in a suitably equipped reactor from suitable starting substances or, for example, by biotechnological processes.

The nitrogen monoxide N ₂ O could be obtained during operation of the internal combustion engine in a arranged in the exhaust path of the internal combustion engine exhaust gas catalyst. In conventional catalytic converters, the formation of N ₂ O is suppressed by special measures. By an appropriate adjustment of the catalysts can thus be achieved in a simple manner that they produce during operation of the motor vehicle N ₂ O, which can then be separated and cached.

The invention further relates to an internal combustion engine, preferably an internal combustion engine with direct injection and spark ignition, which is characterized in that it comprises means for providing an oxygen donor in at least one combustion chamber of the internal combustion engine, wherein the internal combustion engine is arranged for carrying out a method of the type described above. The provision of an oxygen donor can thus take place for the starting phase of the internal combustion engine, in order to thus support the start by early fuel burns or to effect a direct start.

According to a further development of the internal combustion engine, this contains a storage reservoir for an oxygen donor, wherein the storage reservoir is connected via supply lines with at least one combustion chamber of the internal combustion engine. Such a storage device may be provided with a refueling device, so that it can be refilled at regular intervals, for example when refueling the motor vehicle with fuel.

The internal combustion engine could also have an exhaust gas aftertreatment device arranged in the exhaust gas path, which is set up to generate and / or separate N ₂ O from the exhaust gas coming from the internal combustion engine. In this case, the internal combustion engine is autonomous, since it generates the oxygen donor itself and in this respect no regular refueling od. Like. Needed.

Fig. 1

eine erfindungsgemäße Brennkraftmaschine mit einem Sauerstoff- bzw. N₂O-Speicher, und

Fig. 2

eine Brennkraftmaschine mit einem N₂O-Speicher und einer N₂O-Erzeugung durch einen Abgaskatalysator.

In the following, the invention will be explained by way of example with the aid of the figures. Show it:

Fig. 1

an internal combustion engine according to the invention with an oxygen or N ₂ O memory, and

Fig. 2

an internal combustion engine with a N ₂ O storage and a N ₂ O generation by an exhaust gas catalyst.

The internal combustion engine 2 shown in the figures is, in particular, one with direct injection of fuel into the cylinders and spark ignition. The internal combustion engine is provided via an intake manifold or an intake system 1 fresh air. The combustion exhaust gases are discharged via an exhaust manifold and an exhaust path 4. In the exhaust path 4 is at least one exhaust aftertreatment device 3, z. B. a three-way catalyst.

In order to start the internal combustion engine 2 directly, ie without an additional auxiliary unit such as a starter motor, or to support such an auxiliary unit and therefore easier to interpret, during the starting phase of the internal combustion engine 2 already from each first power stroke of a cylinder to a fuel injection and combustion take place. Important for the success of such a procedure is that the combustion process provides a sufficiently high force for the startup of the internal combustion engine 2. The maximum achievable force is limited during the start-up phase, however, by the relatively small amount of oxygen available in the cylinders for combustion, since the filling gas of the cylinders is uncompressed only at atmospheric pressure.

In order to increase the combustion power of the internal combustion engine 2 during the starting phase, it is proposed to provide for an increased (relative) oxygen concentration during the starting phase. According to FIG. 1 To increase the oxygen content in the cylinders of the internal combustion engine 2, they are filled with pure oxygen O ₂ instead of fresh air or in addition to the fresh air. Another possibility is to fill the cylinders with an oxygen donor, ie, gases or liquids that contain oxygen chemically bound and can release it in the cylinders. The oxygen donor is preferably introduced into the cylinders in addition to the normal fresh air.

According to FIG. 1 is the pure oxygen O ₂ and / or the oxygen donor, which may be, for example, nitrogen monoxide N ₂ O stored in a storage tank 6 on board the motor vehicle and introduced via supply lines 5 as needed in the cylinder of the internal combustion engine. This supply of oxygen or an oxygen donor can during the running of the internal combustion engine (ie in the time from switching off the ignition and / or fuel supply to engine standstill), during engine stall (zero speed) and / or during the starting phase (ie from the engine standstill until reaching a predetermined minimum speed, for example, the idling speed). The provision of pure oxygen gas O ₂ or oxygen released from an oxygen donor in the combustor increases the total available amount of oxygen in the combustor. Therefore, an additional amount of fuel can be provided by the direct injection and completely burned, so that a larger energy is obtained from the combustion process. This ensures that the internal combustion engine 2 can be started directly by the combustion "on its own".

As in FIG. 1 is indicated schematically, the oxygen gas O ₂ and / or the oxygen donor can be refilled by a tank means 7, if necessary again in the memory 6.

FIG. 2 shows a modification of the system of FIG. 1 , The memory 6 'is specifically a N ₂ O memory, which is connected on the input side via a line 8 to the exhaust gas catalyst 3. Nitric oxide N ₂ O is an oxygen carrier with about 1.5 times the density of air. N ₂ O dissociates at temperatures above 300 ° C into oxygen and nitrogen according to the formula

2N ₂ O → 2N ₂ + O ₂ .

N ₂ O can be introduced into the cylinders of the internal combustion engine 2 together with fresh air for a direct start. With the fresh air and a fuel injection, a combustion can be initiated in a cylinder that is responsible for this Purpose is in the correct working position. When the temperature rises above 300 ° C due to combustion, oxygen is released from the N ₂ O, which then participates in the combustion. Due to the additional amount of oxygen provided by this release, a corresponding additional amount of fuel can be reacted in the combustion chamber. As a result, the available energy for starting the internal combustion engine increases accordingly, so that a direct start is more likely to be successful or more robust under critical boundary conditions.

As in FIG. 1 is shown, the N ₂ O gas can be stored in the motor vehicle in a storage device 6 such as a pressure bottle, which is refilled if necessary. Another possibility is that N ₂ O is generated on board the motor vehicle in a suitable reactor for this purpose. For example, N ₂ O can be generated under the action of heat from solid ammonium nitrate NH ₄ NO ₃ . Furthermore, N ₂ O can be produced by denitrification in a biotechnological process by specific nitrate bacteria and fungi. The nitrate is from time to time replenished in the reactor.

In the FIG. 2 shown further possibility of N ₂ O generation in the motor vehicle is particularly preferable because it manages with the fewest additional devices. In this method, the N ₂ O is generated in the exhaust catalyst 3 from the exhaust emissions of the internal combustion engine 2 or separated. Normally, large amounts of N ₂ O are formed in catalysts during reduction processes in an oxygen-rich atmosphere on the platinum metal of the catalyst. To avoid this formation of N ₂ O in the catalyst usually appropriate additional measures must be taken. In the present case, however, the formation process of N ₂ O is exploited in order to build up an N ₂ O storage medium on board the motor vehicle, which can then be used during a direct start. The advantage of this approach is that no replenishment of special substances (such as N ₂ O itself or ammonium nitrate) is required.

Furthermore, it is possible to produce on board the motor vehicle N ₂ O in a device suitable for this purpose from the natural nitrogen content in air, which likewise has the advantage of getting along without having to fill special substances.

Claims (4)

1. Method for starting an internal combustion engine (2) of a motor vehicle, at least one fuel combustion process taking place in at least one combustion chamber of the internal combustion engine as early as during the starting phase,
   characterized in that
   during the starting phase an oxygen donor is present in said combustion chamber, which comprises nitrogen monoxide (N₂O), the nitrogen monoxide (N₂O) being produced during the operation of the internal combustion engine (2) in the motor vehicle and temporarily stored and being introduced into the at least one combustion chamber of the internal combustion engine (2) to start the internal combustion engine (2).
2. Method according to Claim 1,
   characterized in that
   the oxygen donor is fed in during the running down, the standstill and/or the starting phase of the internal combustion engine (2).
3. Internal combustion engine (2) of a motor vehicle, having means (5, 6, 6') for supplying an oxygen donor into at least one combustion chamber of the internal combustion engine (2),
   characterized in that
   the means for providing the oxygen donor have

   - means for producing nitrogen monoxide (N₂O) in the motor vehicle during the operation of the internal combustion engine,

   - means for the intermediate storage of the nitrogen monoxide which is produced, and

   - means for introducing the nitrogen monoxide into the at least one combustion chamber of the internal combustion engine (2) during starting of the internal combustion engine.
4. Internal combustion engine (2) according to Claim 3,
   characterized in that
   it comprises a supply reservoir (6, 6') for the abovementioned oxygen donor, the supply reservoir (6, 6') being connected to at least one combustion chamber via feed lines (5).

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