DE102004004160A1 - Determining exhaust gas recirculation rate in engine combustion chamber, compares ionization test pulse response with that when recirculation is absent - Google Patents

Abstract

The invention relates to a method for determining the exhaust gas recirculation rate in the combustion chamber (2) of an internal combustion engine (1), wherein in an exhaust gas recirculation the current profile (I¶Sm¶, I¶Sh¶) of an ionization signal (I¶S¶) and its maximum value (U¶m¶) detected and the current course (I¶Sm¶, I¶Sh¶) are compared with the same maximum value (U¶m¶) having reference curve (I¶R¶) without exhaust gas recirculation. The degree of deviation of the current curve (I¶Sm¶, I¶Sh¶) from the reference curve (I¶R¶) is used as a measure of the exhaust gas recirculation rate. Alternatively, the ratio between the mean value (M¶Sm¶, M¶Sh¶) and the maximum value (U¶m¶) of the ionization curve (I¶Sm¶, I¶Sh¶) is used as a measure of the exhaust gas recirculation rate.

Description

The The invention relates to a method for determining the exhaust gas recirculation rate in the combustion chamber of an internal combustion engine, in which a during the Burning duration of a combustion process in the combustion chamber due a test pulse generated ionization signal is detected.

In particular, in direct-injection gasoline engines, the effect of external or internal exhaust gas recirculation on the reduction of nitrogen oxide emissions is known. This reduction in NO _x emission is due to a lowering of the combustion temperature, which is caused by the high specific heat capacity of carbon dioxide and water components in the combustion exhaust gas. Thus, with an exhaust gas recirculation rate of 16%, the nitrogen oxide emission can be reduced to a NO _x concentration <250 ppm. The internal exhaust gas recirculation is built up inside the engine, for example by a valve overlap of the intake and exhaust valves of an internal combustion engine of an internal combustion engine, wherein the exhaust gas comes from adjacent combustion chambers. In contrast, the external exhaust gas recirculation is realized with an exhaust gas recirculation valve.

By means of an example from the DE 196 14 388 C1 known method for controlling the combustion process of an air-fuel mixture in an internal combustion engine based on a detected during a combustion phase or a combustion process ionization signal statements about characteristic combustion variables are possible. This includes in particular the ratio of air to fuel or fuel (A / F) or the air ratio lambda (λ).

at This procedure is used during the combustion process offset in time to the combustion preliminary ignition pulse an electrical test or voltage pulse to the spark plug set the respective combustion chamber of the combus- tion engine. During the Duration of the test pulse is its influence by the respective air-fuel mixture the corresponding combustion chamber detected as an electrical parameter and evaluated therefrom Ionisationssignal. The history of the ionization signal as a function of The time or the crank angle can be mathematical, for example by determining the curve integral, the maximum or certain Curve ascents, to be evaluated.

It is recognized in exhaust gas recirculation (EGR) with increasing recirculation rate an increasing carry-over of combustion, i. a shift the Ionisationsverlaufes towards larger crankshaft angle and thus a later one Burning up. This affects a value exceeding a certain value Exhaust gas recirculation rate unfavorable on the ignition behavior and the burning speed off. In addition, there are increasing fluctuations the maximum combustion pressure has been observed, which is the engine power reduce the internal combustion engine and their efficiency.

Of the The invention is therefore based on the object, a particularly suitable Method for determining the exhaust gas recirculation rate of an internal combustion engine or specify an internal combustion engine. In particular, the provision should the recirculating rate of the exhaust gas cylinder selectively in relation to Amount of fresh gas, d. H. to the amount of the supplied air-fuel or fuel mixture allows become.

These The object is achieved by The features of claim 1. These are in existing exhaust gas recirculation the current course of the ionization signal and its maximum value detected. This maximum value will change the course of an ionization signal without exhaust gas recirculation or imaging reference history swept. From the degree of deviation the current course of the ionization signal from the reference curve the rate of exhaust gas recirculation can be determined. With others Words: The degree of deviation of the current course from the reference curve is used as a measure of the exhaust gas recirculation rate.

In appropriate training be from the time of the crossing a reference value of the reference curve by the at this time current ionization value the area contents the trajectories are determined and their relationship formed. To do this advantageously while specifiable Time intervals within the combustion time the difference of individual Area shares of Traces determined and summed the area shares. there is expediently from within the predetermined time intervals over the combustion time ascertained and accumulated area differences the gradient curves the area determined between the curves. The summation of the area contents conveniently takes place until the reference value of the reference curve equals zero is.

Taking into account the knowledge that the course of the ionization signal with increasing exhaust gas recirculation rate increasingly deviates from the ionization signal without exhaust gas recirculation can can already be deduced from the magnitude of the deviation of the surface area compared with the surface area formed under the ionization signal without exhaust gas recirculation on the rate of exhaust gas recirculation. Therefore, the area between the course of the current ionization signal and the reference curve is determined in a simple manner during the combustion period. From the relationship between this surface area and the surface area of the ionization signal without exhaust gas recirculation representing reference curve is then at least quantitatively closed on the amount of exhaust gas recirculation, ie, whether it is, for example, a high, medium or low exhaust gas recirculation rate.

alternative is from the time of the maximum value of the current ionization signal the mean value of the ionization curve is determined. From the relationship between this mean and the maximum value of the ionization can then in a simple way the rate of exhaust gas recirculation turn be determined at least quantitatively. This relationship will then as a measure of the exhaust gas recirculation rate used. In this case, a suitable time window or time interval for the Determine averaging, is conveniently the mean as long as formed until the reference value of or one of the same maximum value having reference curve of the ionization signal without exhaust gas recirculation is equal to zero.

following become an embodiment of the invention explained in more detail with reference to a drawing. Show:

1 schematically a circuit diagram for the generation and evaluation of an ionization signal,

2 in a voltage-time diagram, the course of the ionization signal as a result of a test or voltage pulse during a combustion process characterizing the working cycle of an internal combustion engine,

3 in a diagram according to 1 different curves of ionization signals at different levels of exhaust gas recirculation rates, and

4 in a diagram according to 2 a current ionization curve and an associated reference curve.

each other corresponding parts are in all figures with the same reference numerals Mistake.

According to 1 has an internal combustion engine 1 at least one below as a combustion chamber 2 designated cylinder with therein movable piston 3 and with a spark plug 4 on. An ignition coil unit 5 with a primary winding 5a and a secondary winding 5b is on the primary side of a breaker contact 6 connected. During a combustion phase referred to hereinafter as the combustion process, the spark plug is fired 4 first of the ignition coil unit 5 an ignition pulse Z and this time-delayed by a pulse generator 7 generates a test or voltage pulse P.

2 shows in a voltage-time diagram, the ignition pulse Z and the temporal this subsequent, preferably rectangular, dashed lines shown voltage pulse P. While the ignition voltage of the ignition Z at time t _{0 is} about 15kV, the amplitude U _{0 of} the rectangular voltage pulse P is between 100V and 1000V. This voltage or voltage amplitude U ₀ is by means of the pulse generator 7 held in front of a measuring resistor R _m during a pulse duration t ₂ - t ₁ = .DELTA.t to a constant value of preferably U ₀ = 600 V.

The pulse generator 7 downstream measuring resistor R _m is via a measuring line 8th to a contact point 9 with one to the spark plug 4 leading ignition cable 10 guided. As a result of during the combustion of the combustion gases in the combustion chamber 2 occurring ionization flows through the measuring resistor R _m an ionization current I _m , which leads according to Ohm's law to a corresponding voltage drop across the measuring resistor R _m (U _m = R _m · I _m ). The measured in the current flow direction behind the measuring resistor R _m measurement voltage-U _m , whose in 2 is shown below as ionization signal I _s , is proportional to the ionization current I _m . Depends on the particular composition of the air-fuel mixture (A / F) in the combustion chamber 2 over the duration of the voltage pulse P in the time interval .DELTA.t resulting time-dependent course of the measuring voltage U _m is via the measuring resistor R _m in an evaluation circuit 11 detected. At the same time that is between the pulse generator 7 and the measuring resistor R _m tapped rectangular voltage pulse P also to the evaluation circuit 11 guided.

For detecting the ignition timing t ₀ is the pulse generator 7 via a signal line 12 to the breaker contact 6 or to the ignition coil unit 5 guided. For decoupling the secondary winding 5b the ignition coil unit 5 from the voltage pulse P are in the secondary winding 5b with the spark plug 4 connecting ignition cable 10 in the embodiment, two voltage-dependent resistors R _S connected. This ensures that on the one hand the ignition pulse Z to the spark plug 4 and on the other hand, the test pulse P in time after the ignition pulse Z to the spark plug 4 arrives. The evaluation circuit 11 also receives an electrical setpoint S _L. This corresponds to a lambda desired value for the engine operation with λ = 0.8 to λ = 1.3, for example λ = 1.

The voltage level or amplitude U _{0 of} the voltage pulse P is at the dashed line indicated electrical resistance R _I within the combustion chamber 2 adjusted Ionisationsstrecke formed. In this case, the voltage amplitude U _{0 of} the voltage pulse P is selected such that in all engine or operating states, a measurement of the ionization current I _m and the ionization voltage U _m and thus the ionization I _s in the linear region resulting from the current-voltage dependence Function course takes place.

The time profile of the ionization signal I _S resulting from this ionization measurement is in 2 for a lambda value of λ ≅ 1 shown. The associated ionization current I _m then results according to the relationship I _m = U _m * L, where L is the conductance of the ionized fuel gas corresponding to the reciprocal electrical resistance R _I (L = R _I ^-1 ).

With a current ionization measurement during the time interval Δt, this functional relationship results from that of the evaluation circuit 11 recorded temporal course of the voltage drop caused by the measuring resistor R _m due to the ionization current I _m flowing through the ionization path. The ionization path is through the series connection of the measuring resistor R _m and the spark plug 4 and the electrical resistance R _I in the combustion chamber 2 ionized fuel formed. The voltage pulse P is applied to this ionization path.

The evaluation circuit or device 11 compares the respective actual value of the Ionisationsssignals I _S with the preset electrical setpoint S _L and be calculated for the following ignition a number of variables S _{1 ... n} . For example, a manipulated variable S ₁ for a supply of air A in the combustion chamber 2 adjusting throttle 13 , a manipulated variable S ₂ for a supply of fuel F in the combustion chamber 2 adjusting injection system 14 and / or a further manipulated variable S ₃ determined, which via a signal line 15 for adjusting the ignition timing to the breaker contact 6 is guided. By means of an ignition distributor 16 the ignition pulses Z and the voltage pulses P are successively in time to another existing combustion chambers 2 of the internal combustion engine 1 placed.

3 illustrates the dependence of the course of the ionization signal I _S on the presence of exhaust gas recirculation (EGR). In this case, the time profile of the ionization signal I _{S represents} an undisturbed combustion cycle without exhaust gas recirculation. The ionization _signal I _Sm represents the time course at a mean exhaust gas recirculation rate, while the ionization _signal I _{Sh represents} the typical curve at a high exhaust gas recirculation rate. It can be seen that with increasing exhaust gas recirculation, the time profile of the ionization signals I _S changed such that at the end of a combustion cycle, ie at time t _e after the expiration of the combustion time an increasing with increasing exhaust gas recirculation rate residual ionization is measurable, which can also vary. The dashed lines in 3 represent mean values M _S = M _R , M _Sm and M _{Sh of} the typical ionization curves I _S , I _Sm and I _Sh , respectively.

To determine the exhaust gas recirculation rate in each considered combustion chamber 2 is in 4 by way of example, the curve of the ionization _signal I _Sh representing a comparatively high exhaust gas recirculation is used. This ionization _signal I _Sh is the current profile of the ionization measured cyclically during combustion over the combustion time t. Subsequently, the maximum value U _{m of} the ionization or of the ionization _signal I _{Sh is} detected. By this maximum value U _m , a reference curve I _{R is} laid, the course of which corresponds to the expediently idealized ionization signal I _S without exhaust gas recirculation or is approximated.

From the time t ₁ , from which the subsequently measured ionization value U _{a of} the ionization _signal I _{Sh is} greater than the reference value U _{R of} the reference curve I _R , the surface area b in the time interval dt = t _n - t _n-1 by forming the difference between the area or area fraction under the curve of the ionization I _Sh and the surface area or area fraction under the curve of the reference curve I _R determined. It is a prerequisite or restriction that the value U _{a of} the ionization _signal I _{Sh is} greater than the value U _{R of} the reference curve I _R at the same time t ₀ (U _a (t _n )> U _R (t _n )).

The surface portions b determined in this way within the following time intervals dt = t _{n + 1} -t _n are summed up to the surface area B between the curve of the measured ionization _signal I _Sh and the reference curve I _R. Subsequently, the area A under the reference curve or the Reverenzverlauf I _R and the determined surface area B between the course of the measured ionization _signal I _Sh and the Reverenzverlauf I _R are set in relation to each other. As the exhaust gas recirculation rate increases, the surface area or area ratio B increases or increases in comparison to the surface area or area ratio A. The ratio of area contents or proportions A / B is thus a measure for the exhaust gas recirculation rate in this combustion chamber 2 ,

The increase of the area fraction B with increasing exhaust gas recirculation rate becomes clear when considering the different courses of the ionization _signal I _Sm with average exhaust gas recirculation compared to the ionization _signal I _{Sh of} a high exhaust gas recirculation. It can be seen here that the area between the course of the ionization signal I _s without exhaust gas recirculation and the course of the ionization signal I _{Sm is} smaller than the area between the course of the ionization I _s and the course of the ionization I _Sh with high exhaust gas recirculation.

The comparison of the curves of the currently measured ionization _signal I _Sh or I _Sm with the reference curve I _R taking into account the respective same maximum value U _m is expediently carried out in the evaluation circuit or evaluation device 11 , For this purpose, this preferably has a corresponding processor or μ-controller, which executes the described curve comparisons, evaluations and calculations according to a corresponding algorithm.

In order to reduce the computational and memory costs required for this, an alternative method can also be carried out. For this purpose, the actual course of the ionization _signal I _Sh or I _Sm is again measured in an exhaust gas recirculation. In turn, the maximum value U _{m of} this signal I _Sh or I _{Sm is} determined. In addition, the time t _{m of} this maximum value U _{m is} detected. From this point in time t _m , the mean value M _Sh or M _{Sm is} determined.

How out 3 As can be seen, this mean value M _S , M _Sm , M _Sh shifts towards higher values with increasing exhaust gas recirculation rate. Thus, the mean value Ms of the ionization signal I _S without exhaust gas recirculation - or else the mean value M _{R of} a corresponding reference signal I _R - is smaller than the mean value M _{Sm of} a mean exhaust gas recirculation rate. This mean value M _Sm is in turn smaller than the mean value M _{Sh of} a currently measured ionization _signal I _Sh at comparatively high exhaust gas recirculation. The ratio M _Sm / U _m or M _Sh / U _{m of} this mean value M _Sm or M _Sh to the respective maximum value U _m is in turn a measure of the exhaust gas recirculation rate.

1

internal combustion engine

2

Combustion chamber / cylinder

3

cylinder piston

4

spark plug

5

ignition unit

5a

primary

5b

secondary winding

6

Breakpoint

7

pulse generator

8th

Measurement line

9

contact point

10

Ignition

11

evaluation

12

signal line

13

throttle

14

injection

15

signal line

16

distributor

I _S

ionization

I _R

reference course

M

Average

P

Test / voltage pulse

S _n

manipulated variable

U _m

maximum value

Z

ignition pulse

Claims (8)

Method for determining the exhaust gas recirculation rate in the combustion chamber ( 2 ) of an internal combustion engine ( 1 ), in which a during the combustion time (t) of a combustion process in the combustion chamber ( 2 ) ionization signal (I _S ) generated as a result of a test pulse (P) is detected, characterized in that - in an exhaust gas recirculation, the current profile (I _Sm , I _Sh ) of the ionization _signal (I _S ) and its maximum value (U _m ) are detected, and - that the current profile (I _Sm , I _Sh ) is compared with a reference curve (I _R ) having the same maximum value (U _m ) without exhaust gas recirculation, wherein the degree of deviation of the current profile (I _Sm , I _Sh ) from the reference curve (I _R ) is used as a measure of the exhaust gas recirculation rate. A method according to claim 1, characterized in that from the time (t ₁ ) of exceeding a reference value (U _R ) of the reference curve (I _R ) by the at this time (t ₁ ) current ionization value (U _a ) the area (A, B) of the curves (I _R , I _Sm , I _Sh ) determined and their ratio (A / B) is formed. A method according to claim 2, characterized in that within predefinable time intervals (dt) of the combustion time (t) the area differences of the curves (I _R , I _Sm , I _Sh ) added up and the area (B) between the curves (I _R , I _Sm , I _Sh ). A method according to claim 3, characterized in that the area differences are added up until the reference value (U _R ) of the reference curve (I _R ) is equal to zero. Method according to one of claims 1 to 4, characterized in that - during combustion duration (t) a first area (A) of the reference course (I _R ) and a second area (B) between the current course (I _Sh , I _Sm , ) and the reference profile (I _R ), and - that the ratio (A / B) between these two areas (A, B) is determined. Method for determining the exhaust gas recirculation rate in the combustion chamber ( 2 ) of an internal combustion engine ( 1 ), in which a during the combustion time (t) of a combustion process in the combustion chamber ( 2 ) Generated as a result of the test pulse (P) ionisation signal (I _s) is detected, characterized in that - the current waveform (I _Sm, I _Sh) of the ionisation signal (I _S) is detected at a flue gas recirculation, the maximum value (U _m), - that the mean value (M _sm , M _Sh ) of the ionization curve (I _Sm , I _Sh ) is determined, and - that the ratio between the mean value (M _Sm , M _Sh ) and the maximum value (U _m ) of the ionization curve (I _Sm , I _Sh ) is used as a measure of the exhaust gas recirculation rate. A method according to claim 6, characterized in that the mean value (M _Sm , M _Sm ) of the ionization curve (I _Sm , I _Sh ) from the time (t _m ) of the maximum value (U _m ) is determined. A method according to claim 6 or 7, characterized in that the mean value (M _Sm , M _Sh ) is formed until the reference value (U _R ) of the same maximum value (U _m ) having reference curve (I _R ) is zero without exhaust gas recirculation ,