Method and device for controlling an internal combustion engine

Abstract

The invention relates to a method and a device for controlling an internal combustion engine (1) which has a prechamber spark plug (3) and a hook-type spark plug (4) in a combustion chamber (2). In a first operating range of the internal combustion engine (1), the combustion in the combustion chamber (2) is triggered by the prechamber spark plug (3), and in a second operating range of the internal combustion engine, the combustion is triggered by the hook-type spark plug (4).

Description

[0001] Description

[0002] title

[0003] Method and device for controlling an internal combustion engine

[0004] State of the art

[0005] The invention is based on a method and a device for controlling an internal combustion engine according to the preamble of the independent patent claims. Methods and devices for controlling internal combustion engines are already known that have either a prechamber spark plug or a hook-type spark plug. The control of such internal combustion engines is adapted to the prechamber spark plug or the hook-type spark plug.

[0006] Advantages of the invention

[0007] The method and device according to the invention, with the features of the independent patent claims, each have the advantage of optimized operation of the internal combustion engine in different operating ranges. Depending on the operating range, combustion is triggered either by the prechamber spark plug or by the hook-type spark plugs. This results in optimized operation of the internal combustion engine for each operating range, resulting in fuel consumption benefits, improved performance, or reduced exhaust emissions.

[0008] Further advantages and improvements arise from the measures of the dependent patent claims. Combustion is initiated by the hook spark plugs through a corresponding ignition spark between electrodes of the hook spark plugs. Combustion is initiated by the pre-chamber spark plug through at least one ignition jet that extends into a combustion chamber of the internal combustion engine. Depending on the operating range of the internal combustion engine, combustion is initiated by the pre-chamber spark plug, after which, with a time delay after the ignition jet, an ignition spark occurs at the hook spark plug. If combustion is initiated by the ignition spark at the hook spark plug, an ignition jet follows, with a time delay, into the combustion chamber. This measure can reduce the occurrence of soot on the pre-chamber spark plug or hook spark plug and, moreover, combustion can be improved.The first operating range in which combustion is initiated by the ignition jet is characterized in particular by a high load on the internal combustion engine and operation at risk of knocking. By initiating combustion by the ignition jet, the tendency to knock is reduced compared to initiation by an ignition spark, which means that the internal combustion engine can be operated in an optimized manner with fuel consumption advantages or increased power. Alternatively, the first operating range in which combustion is initiated by the ignition jet of the pre-chamber spark plug can be defined as any range in which combustion in the combustion chamber can be reliably initiated by the pre-chamber spark plug. Accordingly, the second operating range in which combustion is initiated by the hook spark plugs is defined as the operating range in which combustion cannot be reliably initiated by the pre-chamber spark plug.This second operating range is particularly characterized by a low load or operation for heating an exhaust system of the internal combustion engine.

[0009] Drawings

[0010] Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description.

[0011] They show:

[0012] Figure 1 schematically shows an internal combustion engine with a pre-chamber spark plug and a hook spark plug, and

[0013] Figure 2 different operating ranges of the internal combustion engine according to Figure 1. Description

[0014] Figure 1 schematically shows an internal combustion engine 1 with a combustion chamber 2. The internal combustion engine 1 has a cylinder 11 in which a piston 12 is arranged. The free area above the piston 12 of the cylinder 11 defines the combustion chamber 2. Air for combustion can be supplied to the combustion chamber 2 through an air supply 13, and burnt exhaust gas is removed from the combustion chamber 2 through an exhaust line 14. Corresponding valves for controlling the supply of air or the removal of exhaust gas are not shown in the drawing for reasons of simplification. Furthermore, fuel is introduced into the combustion chamber 2 and, together with the supplied air, forms a combustible mixture. The fuel is supplied to the combustion chamber 2 by injecting fuel either into the air supply 13 or directly into the combustion chamber 2. Corresponding injection valves are not shown here for reasons of clarity.Combustion of the fuel-air mixture in combustion chamber 2 causes a pressure increase in the combustion chamber 2, which causes piston 12 to move up and down. This is therefore a conventional Otto-cycle internal combustion engine.

[0015] The fuel-air mixture in combustion chamber 2 is ignited by a spark plug. Two different spark plugs, a hook-type spark plug 4 and a prechamber spark plug 3, are provided in combustion chamber 2 in Figure 1.

[0016] The hook-shaped spark plugs 4 have two (or more) electrodes 5 that protrude into the combustion chamber 2. Between the two electrodes 5 of the hook-shaped spark plugs 4, an ignition spark can be triggered, which is in direct contact with the combustible fuel-air mixture in the combustion chamber 2 and thus triggers combustion in the combustion chamber 2. Since one of the electrodes 5 is designed as a hook, such spark plugs, with an ignition spark in direct contact with the combustible mixture in the combustion chamber, are referred to as hook-shaped spark plugs. However, alternative designs of the electrodes 5 that deviate from this hook-shaped electrode design are also conceivable. In the following, the term hook-shaped spark plugs therefore refers to all spark plugs in which an ignition spark is in direct contact with the combustible mixture in the combustion chamber 2. The prechamber spark plug 3 also has electrodes between which an ignition spark can be triggered.However, this ignition spark is not in direct contact with the combustible mixture in the combustion chamber 2, but rather these electrodes are surrounded by a cap 7. The cap 7 has openings through which a combustible fuel-air mixture enters the interior of the cap 7, which is ignited by an ignition spark between the electrodes of the pre-chamber spark plug 3. Combustion of the fuel-air mixture in the interior of the cap 7 then causes an increased pressure in the interior of the cap 7, so that at least one ignition jet 6 extends from the cap 7 into the combustion chamber 2. The ignition jet 6 consists of a burning fuel-air mixture, which causes ignition, i.e. the start of combustion, of the fuel-air mixture in the combustion chamber 2.

[0017] Figure 1 shows a pre-chamber spark plug with three ignition jets. However, any other number of ignition jets is also conceivable. There is a time offset between the ignition spark inside the cap 7 and the at least one ignition jet. This must be taken into account when controlling the pre-chamber spark plug 3. This at least one ignition jet 6 then triggers the combustion of the fuel-air mixture in the combustion chamber 2. This combustion is triggered simultaneously at many points in the combustion chamber 2 and not in a point-like manner, as with a hook-type spark plug. Such combustion, which is triggered at multiple points in the combustion chamber 2, results in an improved conversion of the combustion energy into mechanical power, i.e. combustion is more efficient than when combustion is triggered locally using a hook-type spark plug.The use of pre-chamber spark plugs thus enables advantageous operation of the internal combustion engine 1. It is therefore advantageous to initiate combustion in the combustion chamber 2 preferably using the pre-chamber spark plug 3. Furthermore, such combustion, which is initiated simultaneously at several points in the combustion chamber, is significantly more effective against knocking. If knocking does occur, the usual procedures for reducing the frequency of knocking can also be used with a pre-chamber spark plug. In particular, the time at which combustion is initiated can be shifted to a later time in order to avoid knocking. Figure 1 shows an internal combustion engine 1 which has two spark plugs, a hook spark plug 4 and a pre-chamber spark plug 3. Depending on the operating ranges of the internal combustion engine 1, the two spark plugs can be used differently.Figure 2 shows schematically the operating ranges of the internal combustion engine.

[0018] Figure 2 illustrates the operating ranges of internal combustion engine 1 relative to the operating parameters of engine speed (n) and load (L). The operation of internal combustion engine 1 is limited in terms of speed such that operation of the internal combustion engine is not possible below a speed n0 and above a speed n1.

[0019] With regard to the load, curve 21 shows a full-load curve. Depending on the speed, this full-load curve 21 represents the maximum possible load conditions of the internal combustion engine.

[0020] A knock curve 22 is also shown. The operating range between the full-load curve 21 and the knock curve 22 is the operating range at risk of knocking, in which knocking can occur depending on other operating parameters of the internal combustion engine 1. The determination of this knock curve 22 is a design question that depends on the percentage of knocking combustions (knock events) that is permissible. The knock curve 22 is shifted accordingly if, for example, one knock event per 100,000 combustions or one knock event per 1,000,000 combustions is used as a criterion. In this operating range at risk of knocking, combustion is initiated by the ignition jets 6 of the prechamber spark plug 4, since this achieves particularly effective operation of the internal combustion engine 1.Furthermore, the initiation of combustion by the pre-chamber spark plug 4 generally reduces the tendency to knock, which is also advantageous in this operating range. If knocking does occur, the tendency to knock can be further reduced by a time delay of the ignition jets 6. In addition to initiating combustion by an ignition jet 6, an ignition spark can also be triggered at the hook spark plug 4. However, this occurs with a small time delay in order to ensure ignition by the pre-chamber spark plug 3. The time offset between the ignition in the chamber 7 of the pre-chamber spark plug 3 and the occurrence of the ignition jet 6 must be taken into account accordingly. This additional ignition spark at the hook spark plug prevents the deposit of soot particles on this hook spark plug 3.Furthermore, combustion is generally promoted by a large number of ignition sources, so that a further small improvement in combustion can be achieved by the additional ignition spark at the hook spark plug 3.

[0021] Figure 2 shows an additional curve, the ignition curve 23, which defines a region in which reliable ignition by the pre-chamber spark plug 4 cannot be ensured. Particularly at low loads, the injected fuel quantities are so small that there is not enough ignitable fuel-air mixture in the chamber 7 of the pre-chamber spark plug 4, or the charge in the pre-chamber spark plug is so small that the resulting ignition jets are too small to ignite the main combustion chamber. Therefore, in a load range below the ignition curve 23, too many combustion processes are not triggered solely by the pre-chamber spark plug 4, but misfires occur. The precise definition of this ignition curve 23 is a design issue that depends on the percentage of unsuccessful combustions (misfires) that are permissible due to triggering by a pre-chamber spark plug 4.The curve 23 is shifted accordingly if, for example, one misfire out of 1,000 combustions or one misfire out of 100,000 combustions is used as a criterion. In the operating range below the ignition curve 23, operation therefore takes place with the hook spark plugs 3, i.e. combustion is triggered by the hook spark plugs 3. In addition, an ignition jet 6 can also occur from the pre-chamber spark plug 3 in order to reduce soot deposits on the pre-chamber spark plug 3 or to improve the quality of combustion. This additional ignition jet 6 should have a smaller time offset to the triggering of combustion by the ignition spark, so that the actual definition of the starting point of combustion is carried out by the hook spark plugs 3. Here, too, the time offset between the ignition point within the pre-chamber spark plug and the emergence of the ignition jet must be taken into account.

[0022] In the operating range between knock curve 22 and ignition curve 23, combustion can be triggered by both the hook spark plugs 3 and the prechamber spark plug 4. However, since more efficient combustion is generally achieved by triggering combustion by the prechamber spark plug 4, triggering combustion by the prechamber spark plug 4 is also preferred for this operating range. Depending on other operating parameters of the internal combustion engine, a more differentiated operating strategy can also be provided for this range.

[0023] A further operating range is defined by heating an exhaust system of the internal combustion engine 1. Such operation for heating the exhaust system preferably uses very late ignition angles. These late ignition angles increase the temperature of the exhaust gas and achieve effective heating of the exhaust system. In such operation, ignition by the hook spark plugs 3 is advantageous because an ignition spark allows for later initiation of combustion than by an ignition jet from the prechamber spark plug. Furthermore, this operating range is deliberately ineffective in order to achieve greater heating of the exhaust system. In this heating operation, combustion is therefore initiated by the hook spark plugs 3.

[0024] Here, the optimal ignition timing is determined by the firing of the hook spark plug. The ignition timing of the prechamber spark plug is set with an offset selected to improve the smoothness of the internal combustion engine. The ignition timing of the hook spark plug and the offset to the prechamber spark plug are set depending on engine parameters (speed, load, fuel charge, temperature, etc.). For coking reasons, the prechamber spark plug is preferably always fired "at the same time," even if no advantage in terms of combustion stability is achieved. This must be specifically investigated and measured for each engine.

[0025] Another special operating state of an internal combustion engine 1 is the start of the internal combustion engine 1. During start-up, combustion is triggered simultaneously by an ignition jet 6 and an ignition spark. This is intended to ensure a reliable start of the internal combustion engine. Only then are the different operating strategies implemented, in which ignition occurs either via the hook spark plugs 4 or the prechamber spark plug 3.

Claims

Claims 1 . Method for controlling an internal combustion engine (1) which has a pre-chamber spark plug (3) and a further hook spark plug (4) in a combustion chamber (2), characterized in that in a first operating range of the internal combustion engine (1) the combustion in the combustion chamber (2) is triggered by the pre-chamber spark plug (3) and in a second operating range of the internal combustion engine the combustion is triggered by the hook spark plug (4).

2. Method according to claim 1, characterized in that the triggering of the combustion by the hook spark plug (4) is triggered by an ignition spark and the triggering of the combustion by the pre-chamber spark plug (3) is triggered by at least one ignition jet (6) which extends from the pre-chamber spark plug (3) into the combustion chamber (2).

3. Method according to one of the preceding claims, characterized in that during operation in the first operating range, in which the triggering takes place by the pre-chamber spark plug, an ignition spark occurs at the hook spark plug (4) with a time offset after the ignition jet (6) and that during operation in the second operating range, in which the triggering of the combustion takes place by the ignition spark at the hook spark plug (4), an ignition jet (6) occurs in the combustion chamber (2) with a time offset after the ignition spark.

4. Method according to one of the preceding claims, characterized in that the first operating range is characterized by an operation of the internal combustion engine at risk of knocking, in particular by a high load of the internal combustion engine.

5. Method according to claim 4, characterized in that when knocking occurs, the time at which combustion is initiated by the pre-chamber spark plug is shifted towards a later combustion. Method according to claims 1 to 3, characterized in that the first operating range is characterized in that combustion in the combustion chamber can be reliably triggered by the prechamber spark plug (3). Method according to one of the preceding claims, characterized in that the second operating range is characterized in that initiation of combustion in the combustion chamber (2) cannot be reliably triggered by the prechamber spark plug (3). Method according to claim 7, characterized in that the second operating range is characterized by a low load or an operation for heating an exhaust system of the internal combustion engine (1).Device for controlling an internal combustion engine (1) which has a pre-chamber spark plug (3) and a hook spark plug (4) in a combustion chamber (2), characterized in that the device triggers the combustion in the combustion chamber by the pre-chamber spark plug (3) in a first operating range of the internal combustion engine and the combustion by the hook spark plug (4) in a second operating range of the internal combustion engine.

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