WO2014206541A1

WO2014206541A1 - Method for regulating ignition energy

Info

Publication number: WO2014206541A1
Application number: PCT/EP2014/001662
Authority: WO
Inventors: Stephan BRENDLER; Markus Raindl
Original assignee: Mtu Friedrichshafen Gmbh
Priority date: 2013-06-26
Filing date: 2014-06-18
Publication date: 2014-12-31
Also published as: DE102013010685A1

Abstract

The invention relates to a method for regulating ignition energy. The method is intended to be performed with an ignition system (1) of an internal combustion engine having spark ignition. Said ignition system (1) comprises an ignition coil (3), which has a primary circuit (5) and a secondary circuit (7), and a spark plug (11) arranged in the secondary circuit (7) on a combustion chamber of the internal combustion engine. For a current operating cycle (i+1) of the internal combustion engine, a setting (E_ZS,_i+1 = f(l_ZS,i+1, t_ZS,i+1)) is determined as a function of a determined breakdown voltage (U_{Z, i}) of the preceding operating cycle (i) and is provided for regulating the ignition energy (E_Z) in the current operating cycle.

Description

Method for controlling the ignition energy

The present invention relates to a method for controlling the ignition energy according to the preamble of claim 1.

In the prior art, a generic electronic ignition method and an ignition system for a spark-ignition internal combustion engine are known from the document DE 10 2010 015 998 A1, which in the event of a fault counteract the ignition energy, i. to a value where errors, e.g. Misfiring, effectively avoided.

Proceeding from this, the present invention has the object to provide an executable in particular with a pre-chamber spark plug method, which allows an improved energy-optimized and thus wear-optimized control of ignition.

This object is solved by the features of claim 1.

Advantageous developments and embodiments of the invention are specified in the further claims.

According to the invention, a method is proposed for regulating the ignition energy, wherein the method is provided for execution with an ignition system of an internal combustion engine with spark ignition. Preferably, the spark-ignition internal combustion engine is e.g. a gas engine. The ignition system which can be used with the method has an ignition coil with a primary (current) circuit and a secondary (current) circuit and a spark plug arranged in the secondary circuit on a combustion chamber (cylinder) of the internal combustion engine, particularly preferably a prechamber spark plug.

The method according to the invention is characterized in that, for a current working cycle of the internal combustion engine, a setting input (Ezs, i + i) = f (lzs, i + i _> tzs, i + i)) depends on a determined breakdown voltage, in particular In particular, an actual ignition energy, depending on the previous work cycle is determined and provided for the control of the ignition energy (in the current work cycle). The setting for setting a minimum ignition energy in the current working cycle is preferably provided.

In particular, by the Arbeitstpielauflösung invention can be provided over the operation of the internal combustion engine advantageously always optimized, especially minimal ignition energy, so that the wear of the spark plug significantly reduced and thus the service life is increased, woneben breakdown voltage and actual ignition energy can be determined in an advantageous simple manner, For example, be provided by commercially available ignition control devices at an output as tappable information already.

In the context of the present inventive method is further preferred, the expended ignition energy or the control target for the current cycle further depending on a molecular concentration or density (of the mixture) in the combustion chamber and the electrode gap of the spark plug and / or at least one engine operating variable load, calorific value , Burning rate and combustion air ratio, in particular each of the previous cycle to determine.

O.A. specified (engine operating) variables (density, electrode spacing, load, calorific value, burning rate and combustion air ratio), which are, for example, measured variables or can be correlated for the provision of the control input in a respective control loop, for example, with a map (which eg Test stand was generated).

According to the invention, it has been recognized in connection herewith that it is precisely the burning rate (function of pressure, temperature, fuel concentration) and the electrode spacing for the determination of the respective setting parameter (s) that represent significant quantities and are preferably taken into account. In particular, the consideration of the actual electrode spacing makes it possible to regulate the minimum energy in the respective working cycle. It has been found that the higher the breakdown voltage, the lower the spark duration requirement, ie the time required for the glow phase (which is essentially determined by a default value for tzs.i or the spark duration).

In a particularly simple manner, the breakdown voltage can be calculated, for example, from the course of the primary current or the primary voltage (each in the primary circuit). The primary current can be measured for this purpose, for example.

In the context of the proposed method, provision is made for a spark duration and / or a current (in the secondary circuit) to be set via the setting input (E _zs , i + i) = f (lzs, i + i, tzs, i + i)) for the current working cycle ) are set in the current working cycle, that is, the default setting each includes a default value for the spark duration and / or the (to be set in the secondary circuit) current. By means of the default value for the current, the mean secondary current level can preferably be predetermined. An adjustment or default values for current or spark duration can or can be determined based on a map.

Generally, it is provided according to the invention that the method is carried out iteratively. For the start of the method, a start parameter set can be provided, which is predetermined by the motor parameter set, for example. A parameter set which contains a start specification can be determined, for example, at the (engine) test bench.

The invention also proposes an ignition system for carrying out the method described above. The ignition system preferably has an ignition energy regulator, which may furthermore preferably be provided in the form of the engine controller (ECU). In addition, an ignition control device may be provided, which cooperates with the ignition energy regulator.

Alternatively, the ignition energy regulator may also have the functionality of the control unit according to the invention. For example, the controller may provide the ignition controller with information about the secondary voltage or breakdown voltage for the control, and in particular also the ignition energy used. The ignition energy regulator in turn can transmit the control variable determined therefor for the current working cycle to the ignition control device for the provision of the ignition energy by the same.

The method proposed according to the invention can be carried out in particular with a multi-cylinder internal combustion engine such that the ignition energy is regulated individually for each cylinder. For this purpose, a setpoint can be determined for each cylinder for a respective working cycle. Such a setting specification comprises in particular a cylinder-individual specification for the spark duration, in particular also the current, for example - as described above - for the mean secondary current level.

Further features and advantages of the invention will become apparent from the following description of embodiments of the invention, with reference to the figures of the drawings, which show details essential to the invention, and from the claims. The individual features can be realized individually for themselves or for several in any combination in a variant of the invention.

Exemplary embodiments of the invention are explained below with reference to the accompanying drawings. Show it:

1 shows an example and schematically an ignition system of an internal combustion engine for carrying out the method according to a possible embodiment of the invention;

2 shows by way of example and schematically a diagram for illustrating the method sequence according to a possible embodiment of the invention.

In the following description and the drawings elements of the same or comparable function correspond to the same reference numerals. 1 illustrates by way of example and greatly simplified an ignition system 1 for carrying out the method according to the invention. The ignition system 1, which is provided for an internal combustion engine (not shown), has an ignition coil 3 with a primary (current) circuit 5 and a secondary där (current) circuit 7, wherein the ignition coil 3 acts as an energy storage and transformer.

The primary side 5 of the ignition coil 3 can be supplied via an ignition controller 9 with a current or primary current, which primary current for generating a high voltage on the secondary side 7 is suitably interrupted, for example via a switch of the primary side 5 (not shown). The switch is, for example, an IGBT or generally a transistorized switch, which may be part of the control unit 9 in particular.

The induction-based generated high voltage on the secondary side 7 is intended to generate at a secondary circuit 7 to a combustion chamber or cylinder of the internal combustion engine (not shown) arranged spark plug 11, in particular in the form of a Vorkammerzündkerze, a spark, ie. between the electrodes 11a, 11b. Successful energy transfer from the spark to the fuel-air mixture to be ignited requires a minimum ignition energy.

With the ignition control unit 9, which provides an adjustment for the spark duration and preferably also of the power supply, for example in the form of a PWM output capability (PWM pulse width modulation), furthermore, an ignition energy regulator 13 cooperates, which is preferably formed by an engine controller (ECU) of the internal combustion engine is. The ignition regulator 13 is e.g. connected to one or more sensors (not shown), which provide provided for the method engine operating information to the controller 13.

2 illustrates by way of example the method according to the invention for regulating the ignition energy, which can be carried out with the above-described ignition system 1 of an internal combustion engine. In the method, for a current working cycle i + 1 of the internal combustion engine, an actuating input E _zs , i + i = f (lzs, i + i, tzs, i + i) = f (U _z , i, Hu, i, λ, , Ρ ,, v _B j) depending on a detected breakdown voltage Uz, in particular also an actual ignition energy E _Z i, each of the previous cycle i determined and provided for the control of the ignition energy E _z in the current working cycle, ie handed over to the control unit 9 , The control unit 9 accordingly sets current lzs, i + i and spark duration tzs, i + i at the spark plug 11 via ignition coil 3 according to lzs, i + i and tzs, i + i (it should be noted here that the indexing I is an actual value, the indexing S should be a target value and Z should designate an ignition process).

Based on the magnitude of the (cylinder-specific) breakdown voltage Uz, the new spark duration tzs, i + i can be determined in the proposed method, wherein the new or current spark duration tzs, i + i is set the lower, the higher the breakdown voltage Uz in the previous work game is. Furthermore, the height of the (feed) current Izs is correlated with the ignition time (ZZP) and the burn rate estimable from the calorific value, lambda, pressure and temperature in the combustion chamber. In this case, the (feed) current Iz can be reduced with increasing burning speed and later ZZP. The adjustment limits for the parameters spark duration t _z and supply current l _z are given upwards by the performance of the ignition control unit 9 and down, for example, from the requirement for engine running rest.

The breakdown voltage Uz and the actual ignition energy Ezi, ie that of the respective working cycle, is preferably reported by the ignition controller 9 to the controller 13, s. Feedback path or interface 15 in Figs. 1 and 2. Preferably, the breakdown voltage Uz of the respective working cycle is estimated, in particular advantageously calculated inexpensively from a primary current profile of the working cycle. The control unit 9 can be suitably designed for this purpose. Alternatively, the breakdown voltage Uz may be measured, for example. For the first working cycle, indicated i = 0 in FIG. 2, a parameter set determined on the engine test bench with starting specifications for the initial spark duration tzs, i = o and the current to be set in the secondary circuit lzs, i = o is used as setting for Ez, s. FIG. 2. The starting values can be stored in the controller 13.

In the context of the control method, the ignition energy E _z to be expended for the current working cycle (i + 1) is furthermore preferably dependent on a density in the combustion chamber and the electrode spacing of the spark plug 11 and / or at least one engine operating variable from load P, calorific value H _u and combustion air ratio λ je 2, according to which the setting input (s) E _Z s, i + i or -zs, tzs) i + i is / are determined as a function of H _u , λ, P and Uz.

This will be discussed in more detail below, in particular in conjunction with FIG. 2.

According to the invention, it has been recognized that the electrode spacing EA at the spark plug 11, in particular also the calorific value Hu, the combustion air ratio λ and the instantaneous power output P (all influencing variables of the combustion speed) are determined from a multiplicity of chemical and physical influencing factors which could be considered in the context of the ignition energy application ), are considered as essential. Their influence can be compensated in the context of the method according to the invention for optimized ignition energy supply or is corrected.

Generally applies to the applied minimum energy of each ignition (combustion rate VB = f (P, λ, Hu)):

E _Z , Min = f (P, λ, Hu, EA) (1)

Furthermore, it must be considered that the following applies to the ignition energy:

Ez = ί U (t) _z l (t) dt (2) Based on the laws (1) and (2) can in the context of the inventive method per cycle an adjustment (Ezs, i + i in Fig. 2) for the energy Ez, in particular for a corresponding adjustment of the current lz and / or the Spark duration tz can be determined. Depending on the respective engine operating situation, however, the disturbances P, λ, Hu, EA are to be regarded as differentiated with regard to their effect as such.

In this case, the following relationships were identified as essential and the regulation for the determination of the setting Ezs of a respective work cycle is based on:

P † then U _Z T †, Izll and t _z || = f (U _z )

A † then U _z †, lz † and t _z † = f (v _B )

Then hat Uzi, Izi and t _z | = f (v _B )

EA † then U _Z † T, Iz and t _z || = f (U _z )

It can be seen that the burning speed v _{B of} the compressed mixture and the breakdown voltage Uz are significant. In the course of test series, it was recognized that the influence of the calorific value Hu in a gas engine and the use of fuel in the form of natural gas is relatively low. It has also been found that the air ratio λ is not significant in natural gas applications, but could be relevant to off-gas applications such as biogas or hydrogen.

Furthermore, E _Z s is taken into account in the context of the method for the determination of a respective setting input, which may apply

U _z = c * pz (ZZP) * EA (3) with

Uz breakdown voltage [V]

c Proportionality constant [Vm ² / kg]

Pz (ZZP) Density of the mixture in the Cylinder at the ignition point [kg / m ³ ]

EA electrode gap of the spark plug [m] wherein the density pz (ZZP) can be determined, for example, based on the engine operating point.

With knowledge of Uz and p _z (ZZP), according to the invention, both the electrode spacing EA and the spark duration tzs to be set for the ignition energy E _Z s or the mean secondary current Izs to be set can be estimated. In the context of the present invention proposed control method is to adjust the spark duration t _z, and the current I _z (primary or secondary current) or of the expended ignition energy E _z preferably also the burning rate as a function of pressure, temperature, heating value and lambda of the mixture in the combustion chamber taken into account as far as than at a certain

Uz / EA (4) a certain average secondary current lz or a specific spark duration t _z (lz and t _z = f (E _z , min)) is required for a successful ignition. The latter relationship can be determined empirically by means of an experimental test, but can also be correlated on the basis of an estimate of the burning rate and spark volume.

In the case of the regulation of the ignition energy E _z according to the method, (a) the secondary voltage or breakdown voltage Uzj is fed back via the interface 15 from the ignition control unit 9 to the ignition energy regulator 13. Together with further variables such as P ,, H _Uii and λ, (b) the transmitted breakdown voltage Uzj is used to recalculate E _Z s, i + i in the controller 13. After (c) calculation of E _Z s, i + i, this determined setting is reported back to the ignition controller 9 via the communication interface 15 (d).

As a result, (e) E _Z s, i + i = f (lzs, i + i, tzs + i) implemented in the control unit 9 and immediately (f) in the primary circuit 5 and via the ignition coil 3 in the second - därkreis 7 fed, whereby the spark plug 11 receives a changed secondary current lz and a changed spark duration tz. Hereinafter, steps (a) to (f) are repeated as part of the iterative process execution.

By means of the method, the spark plug 1 is supplied with energy as required as a function of power, calorific value, emission of the engine and the state of wear of the spark plug 11. Opposite to e.g. constant Zündparametereinstellung thereby the Kerzenverschleiß is significantly reduced and thus achieved a significant operating cost reduction for the engine operator.

Furthermore, very small spark plug electrode distances can be operated with this method, without having to drive the disproportionately high ignition energies over the entire service life of a spark plug 11, since the wear state of the plug 11 can be estimated at any time via the secondary voltage. Furthermore, a service or replacement recommendation can be issued to the engine operator via the engine controller 13 and a connected alarm communication interface, whereby the wear can also be optimized application-related - this applies individually for each cylinder, each operating load of the engine and any chemical stress from the main combustion chamber, all of which determine the wear of the spark plug 11.

REFERENCE CHARACTERS

I ignition system

3 ignition coil

5 primary circuit

7 secondary circuit

9 ignition controller

I I spark plug

11a, b electrode

13 ignition regulator

15 interface

Claims

claims

1. A method for controlling the ignition energy, wherein the method of execution with an ignition system (1) of an internal combustion engine with

Ignition system is provided, which ignition system (1) an ignition coil (3) having a primary circuit (5) and a secondary circuit (7) and a secondary circuit (7) arranged on a combustion chamber of the internal combustion engine spark plug (11), characterized in that a current working cycle (i + 1) of the internal combustion engine an actuating input (Ezs, i + 1 = f (lzs, i + i> tzs, i + i)) as a function of a determined breakdown voltage (Uz,), depending on the previous working cycle (i) determined and provided for the control of the ignition energy (Ez) in the current work cycle.

2. The method according to claim 1, characterized in that the setting (E _Z s, i + i) for the current cycle (i + 1) further in dependence of a density (pZ (ZZP)) in the combustion chamber and the electrode spacing (EA) the spark plug (11) and / or at least one engine operating variable of load (P), calorific value (H _u ), burning rate (v _B ) and combustion air ratio (λ) is determined depending on the previous cycle (i).

3. The method according to claim 1 or 2, characterized in that the breakdown voltage (Uz) is calculated.

4. The method according to claim 3, characterized in that the breakdown voltage (Uz) from the course of the primary current (lz) and or the primary voltage is calculated.

5. The method according to any one of the preceding claims, characterized in that on the setpoint (Ezs, i + 1 = f (lzs, i + i, tzs, i + i)) a current (Izs) and / or a spark duration (tzs ) in the current work cycle (i + 1).

6. The method according to any one of the preceding claims, characterized in that the respective control setting (E _Z s, i + i = f (lzs, i + i, tzs, i + i)) is determined based on a map.

7. The method according to any one of the preceding claims, characterized in that the method is carried out iteratively.

8. ignition system (1) for carrying out the method according to one of claims 1 to 7.

9. ignition system (1) according to claim 8, characterized in that the ignition system (1) comprises an ignition energy regulator (13) and an ignition control device (9), wherein the setting (E _Z s + i = f (lzs, i + i, tzs, i + i)) is provided by the ignition regulator (13) to the ignition controller (9).

10. The method according to any one of claims 1 to 7 or ignition system (1) according to any one of claims 8 and 9, characterized in that the spark plug is a Vorkammerzündkerze and / or the internal combustion engine is a gas engine.