DE19651613C1 - Method for regulating the fuel-air ratio of an internal combustion engine - Google Patents

Description

The invention relates to a method for regulating the fuel-air Ratio of an internal combustion engine according to the preamble of Pa  claim 1.

Control devices are used to achieve pollutant-free exhaust gases known for internal combustion engines in which the oxygen content in the Ab gas channel is measured and evaluated. For this purpose, oxygen measurement probes, so-called lambda probes known, the z. B. on the principle ion conduction through a solid electrolyte due to an oxygen par tial pressure difference and work according to the existing in the exhaust gas Oxygen partial pressure emit a voltage signal that occurs during the transition from lack of oxygen to excess oxygen or vice versa Has voltage jump.

The output signal of the lambda probe is output by a controller evaluates the fuel / air mixture via an actuator settles.  

The regulation of the fuel-air ratio primarily results in a Reduction of harmful portions of exhaust gas emissions from internal combustion engines seem aimed.

With the help of a second lambda sensor, which is behind the catalytic converter the signal of the first lambda probe is corrected, since the son en is subject to signs of aging.

Such generic regulations are from DE 41 17 476 C2 and DE 35 00 594 C2 is well known. To improve the control cycle ses the P component of the output signal of the control loop first lambda sensor as a function of the output signal of the second Lambda sensor changed.

Despite this superimposed regulation, the signs of aging can of the first lambda probe cannot be corrected sufficiently. this leads to irregularities in the mixture formation.

The invention is therefore based on the object of applying a method ben, which enables precise and adaptable regulation, so that the fuel-air ratio in the sense of a reduction in Exhaust emissions are further improved.

According to the invention, the object is characterized by the features of the label nes of claim 1 solved.

The advantage of the invention is a quick feedback of the Output signal of the second lambda control loop to the control loop of first lambda probe by changing the voltage jump of the Output signals of the first lambda probe.  

The control deviation between an actual value is advantageously used and a setpoint of the second lambda probe provides a correction signal Det, by which the P component of the first lambda control loop increases when the sign of the control deviation of the second lambdare circle corresponds to the changeover tendency of the first lambda probe and the P component of the first lambda control loop is reduced if that Sign of the rule deviation of the turnover tendency of the first Lambda probe is opposite (see claim 2).

The fact that the correction signal multiplicative to the P component of the rule circle of the first lambda probe, the P component of the rule circle strengthened or weakened.

The P component of the first control loop is thus determined by a correction value influenced, which of the actually lasting period of the Output signal of the first lambda sensor is dependent.

In a further development, the correction signal is dependent on the air mass flow and / or the ratio of the amplitude of the second Lambda probe for the amplitude of the first lambda probe formed (see. Claims 3 and 4).

The efficiency of the catalyst is determined by the amplitude ratio taken into account when correcting the first control loop.

The amplitude of both the first and the second lambda probe becomes by discrete samples of the output signal of each lambda probe agrees, with one from the sampling within a time window Average value is formed, from which the amplitude ratio is determined is (see claim 5).  

The correction signal is advantageously dependent on the previous Sign of the control deviation of the second lambda control loop tet (claim 6).

The invention allows numerous exemplary embodiments. One of these is said to be based on the figures shown in the drawing who explained the.

It shows

Fig. 1: schematic representation of a device for controlling the fuel-air mixture for an internal combustion engine

Fig. 2: control unit of a motor vehicle

FIG. 3 shows voltage waveform of a lambda probe over the fuel-air mixture (λ factor)

Fig. 4: Control loop of the lambda probe arranged behind the catalytic converter.

According to Fig. 1 the device consists of an internal combustion engine 1 with a Catalyst 2. Air is supplied to the engine 1 via an intake manifold 3 .

The fuel is injected into the intake manifold 3 via injection valves 4 .

A first lambda probe 5 is arranged between the engine 1 and the catalytic converter 2 for detecting the engine exhaust gas. Another lambda probe 6 is provided in the exhaust duct behind the catalytic converter 2 . The lambda probes 5 and 6 measure the respective lambda value of the exhaust gas upstream and downstream of the catalytic converter 2 . Both signals supplied by the lambda probes 5 and 6 are fed to a controller with PI characteristic 8 , which is usually arranged in the control unit ( FIG. 2) in the motor vehicle.

From these signals, the controller 8 uses setpoints to form an actuating signal which is fed to the injection valves 4 .

This control signal leads to a change in the fuel metering, wel together with the intake air mass a certain lambda value of the exhaust gas.

The controller 8 is, as shown in Fig. 2, a microcomputer consisting of a central processor unit CPU, a RAM and egg nem ROM. The controller 8 evaluates both the signals of the first lambda probe 5 and the signals of the second lambda probe 6 , which are fed to it via its input / output unit I / 0, and processes them further.

The controller 8 evaluates the signal of the first lambda probe 5 by comparing the current value with a target value 9 stored in the memory ROM for the lambda probe 5 and an injection time is determined therefrom as a manipulated variable, thereby regulating the fuel-air mixture. The evaluation of the second lambda control loop is superimposed on this comparison, as will be explained in detail in connection with FIG. 4. The result of the second lambda control loop is represented in the determination of the holding time TH. This holding time TH has the effect that the action of the controller 8 on the injection valves 4 , which takes place as a function of the comparison of the first control loop, is delayed.

The controlled system 11 is the combustion process in the engine 1, which is controlled via the injection time as a manipulated variable and the injection valves as actuators.

Each lambda sensor delivers a signal curve as shown in FIG. 3 via the λ factor representing the respective fuel-air mixture. Depending on the type of lambda sensor used for the control, either the resistance or the voltage across the λ factor can be considered.

The following explanations refer to the signal voltage.

If the probe is active, it has a signal voltage that is outside of the range (ULSU, ULSO). Delivers during the lean rash the lambda probe has a minimal output signal that is below ULSU lies. A maximum voltage signal appears during the fat rash measured above ULSO in a range of 600-800 mV. This maximum value is subject to due to manufacturing tolerances and old certain scatter caused by a probe correction door factor to be corrected.

In order to compensate for the long-term drift of the lambda probe 5 in front of the catalytic converter, a second control circuit is present which contains the second lambda probe 6 behind the catalytic converter 2 and which is explained in more detail in FIG. 4.

The controlled system 11 contains the engine 1 , which is supplied by the controller 8 , as described in FIG. 1, the control signal in the form of the changed injection time of the injection valves.

The lambda probe 6 arranged in the exhaust gas duct behind the catalytic converter 2 supplies a lambda value in the form of a signal voltage. At the beginning of each control cycle, it is checked whether the probe is active. This happens because it is determined whether this signal voltage is outside a voltage range (ULSU, ULSO). If this is the case, a correction signal is formed in which the U _6IST measured by the lambda probe 6 is compared at a summing point 12 with a setpoint U _6SOLL stored in the memory ROM of the control device. This target value U _6SOLL is formed from the mean value measured by the lambda probe 6 when the lambda probe 5 arranged in front of the catalytic converter works without problems.

The control difference formed in point 12 from the setpoint and actual value of the output signal from the second lambda probe 6 is fed to a limiter 13 , which compares the amount of the control difference with a threshold value 14 , which is also stored in the memory ROM of the control unit. Only if the amount of the control difference is greater than this threshold value 14 , the control difference is passed to a comparator 15 which, depending on the sign of the difference between the actual value U _{6IST of} the second lambda probe 6 and the target value U _{6SOLL of} the second lambda probe 6, is a 1 or Outputs -1. Depending on this output value, a Signum integrator 16 is advanced or reset.

The Signum integrator 16 increments when the actual value U _{6IST is} greater than the setpoint U _6SOLL . It decrements by 1 if the actual value U _{6IST is} smaller than the setpoint U _6SOLL . If both values are the same, the counter reading is not changed.

The Signum integrator 16 is processed with each envelope 17 of the first lambda probe 5 arranged in front of the catalytic converter and is thus clock-controlled by the latter.

At a first multiplication point 18 , the count value is multiplied by a proportionality constant 19 in the value of (0.5 - a few 100) ms / changeover of the first lambda probe 5 , whereby an absolute holding time TH _{raw is} determined. The holding time TH _raw obtained in this way is evaluated in a second multiplication point 20 with a weighting factor WF, which is determined in point 23 by dividing the period 21 actually measured for the first lambda probe 5 by a constant 22 . The constant 22 is a function of the period of the first lambda probe 5 at idle.

In comparison to characteristic maps usually used at this point, in which the weighting factor can assume maximum values of 1, the actual disturbance is now corrected regardless of its size, since the larger factor achieves a kind of self-reinforcement. The holding time TH obtained in this way is fed as a controlled variable to the controller 8 to adapt the controlled system 11 .

In addition to the holding time TH, the controlled system 11 is fed a correction signal, which is formed as follows.

The control difference formed in the summation point 12 of the second lambda probe 6 is fed to a changeover switch 24 which switches depending on the sign of the signals output by the comparator 15 . If the signal is negative, a first evaluation factor KM is taken from a first characteristic curve 25 ; if the signal is positive, a second evaluation factor KL for the control deviation is taken from a second characteristic curve 26 . This evaluation factor KM or KL is multiplied in point 27 by a third evaluation factor KF formed from a characteristic field 28 . The characteristic diagram 28 is determined by the mean amplitude ratio value 29 of the two lambda probes 5 and 6 and the air mass flow 30 measured by the air mass meter 7 .

The characteristic value KPF formed in point 27 is weighted in point 31 as a function of the probe envelope 17 of the first lambda probe 5 and the sign of the control difference of the second lambda probe 6 , which is obtained by the comparator 15 .

If the signals of both probes are in the fat range, a positive one Sign accepted. If both probes work in the lean area, one will negative sign accepted.

The correction factor KPF is weighted as follows. If both probes 5 , 6 work simultaneously in the rich or simultaneously in the lean region, the correction factor KPF is increased by 1. If the first probe works in the rich region and the second probe in the lean region or vice versa, the correction factor KPF is subtracted from 1. The weighting factor thus contained as a dimensionless variable is supplied to the controller 8 in the controlled system 11 independently of the holding time TH. In this case, with a like-minded tendency of the output signal of the two lambda probes 5 , 6, the P component of the controller 8 is increased and, in the opposite direction, is reduced, with the result that the second lambda control circuit acts quickly and directly on the first lambda control loop.

Claims (6)

1. A method for regulating the fuel-air ratio of an internal combustion engine, the output signal of a first lam dasonde, which is arranged in the exhaust duct of the internal combustion engine upstream of a catalytic converter, being fed to a controller which has a PI characteristic and the controller is a manipulated variable for gives the air-fuel ratio, and that a further res signal is supplied to the controller. which is won from the output signal of a second lambda probe downstream of the catalytic converter, and acts on the control loop of the first lambda probe, so that the P jump of the controller, which is determined by the control loop of the first lambda probe, as a function of the control loop of the second Lambda probe is changed, characterized in that a correction value of the second lambda control loop is formed at the time of the reversal of the first lambda probe arranged in front of the catalytic converter and is fed to the control loop of the first lambda probe independently of a holding time. 2. The method according to claim 1, characterized in that the Correction value from the control deviation between the actual value of the second lambda probe and setpoint of the second lambda probe is formed, the P jump of the first lambda control loop  is increased if the sign of the control deviation with the Transhipment tendency of the first lambda sensor matches and the P jump of the first lambda control loop is reduced if the sign of the rule deviation of the turnover tendency of the first lambda probe is opposite. 3. The method according to claim 1 or 2, characterized in that the correction signal depending on the air mass flow det. 4. The method according to claim 1 or 2, characterized in that the correction signal depending on the amplitude ratio the amplitude of the second lambda probe to the amplitude of the first Lambda probe is formed. 5. The method according to claim 3 or 4, characterized in that the amplitude of both the first and the second lambdason de by discrete samples of the output signals each Lambda probe is determined and from the sampling within egg nes time window an average of the amplitude of each Lambda probe is formed, from which the amplitude ratio nis is determined. 6. The method according to any one of the preceding claims, characterized characterized in that the correction signal depending on the Sign of the control deviation of the second lambda control loop is weighted.