Method of closed loop control of the air/fuel ratio of an internal combustion engine

The invention relates to a method for regulating the fuel-air ratio an internal combustion engine, wherein the output signal of a first Lambda probe, the catalyst in the exhaust passage of the internal combustion engine in front of a is arranged a regulator is supplied, which has a PI characteristic having, and the controller, a manipulated variable for the fuel-air ratio outputs, and that the controller, a further signal is fed, which downstream from the output signal of a second, the catalyst Lambda probe is obtained, and the control circuit of the first Lambda probe acts.

In order to achieve pollution-free as possible exhaust gases are usually facilities for Internal combustion engines are known in which the oxygen content in the exhaust gas channel is measured and evaluated. For this purpose, Sauerstoffmeßsonden called known lambda probes z. B. on the principle of Ioneniertung by a solid electrolyte due to an oxygen partial pressure work and in accordance with the oxygen present in the exhaust Write a voltage signal during the transition from a lack of oxygen the excess oxygen or vice versa a voltage jump having.

The output signal of the lambda sensor is evaluated by a controller, which in turn via an actuator, the fuel-air mixture adjusts.

is with the regulation of the fuel-air ratio is primarily a Reduction of harmful components of exhaust emissions from internal combustion engines sought.

With the aid of a second lambda probe positioned downstream of the catalyst , the signal from the first lambda probe as the probe aging is corrected, subject.

Despite these superimposed control, the aging of the first lambda probe is not properly corrected. this leads to Irregularities in the mixture formation.

The invention is thus based on the object to provide a method, which allows a precise and adaptive control so that the fuel-air ratio in the sense of a reduction of the exhaust emission is further improved.

According to the invention the object is achieved by the fact that the P component of the Output signal of the control loop of the first lambda probe function the output signal of the second lambda probe is changed.

The advantage of the invention is a rapid feedback of the output signal the second lambda control circuit on the control circuit of the first Lambda probe by changing the voltage jump of the output signal the first lambda probe.

Advantageously, from the control deviation between an actual value and a target value of the second lambda probe formed a correction signal, through which the P component of the first lambda control loop is increased, when the sign of the deviation of the second lambda control loop the envelope tendency of the first lambda probe and corresponds to the P component the first lambda control loop is reduced when the sign opposite to the deviation of the envelope tendency of the first lambda probe is.

Because the correction signal mulitplikativ to the P component of the control loop the first lambda probe acts, the P component of the control loop strengthened or weakened.

In one embodiment, the correction signal from the second lambda control loop the arrayed at the time of turning in front of the catalyst formed first lambda control probe and then the control loop the first lambda probe fed.

The P-component of the first control loop is thus by a correction value affected, which of the actually ongoing period of depends output of the first lambda probe.

In one development, the correction signal is a function of the air mass flow and / or the ratio of the amplitude of the second Lambda probe made to the amplitude of the first lambda probe.

About the amplitude ratio is the efficiency of the catalyst in correcting the first control loop into account.

The amplitude of both the first and the second lambda probe is determined by discrete samples of the output signal of each lambda probe, wherein one of the sampling within a time window in each case Average is calculated, determined from which the amplitude ratio becomes.

Advantageously, the correction signal in dependence on the sign of the deviation of the second lambda control loop weighted.

The invention permits numerous embodiments. One of them is based the figures shown in the drawings are explained in detail.

It shows<dl tsize="8" compact="compact"><dt>Fig. 1:</dt><dd>schematic representation of a device for regulating the Fuel-air mixture of an internal combustion engine</dd><dt>Fig. 2:</dt><dd>Control unit of a motor vehicle </dd><dt>Fig. 3:</dt><dd>Voltage characteristic of a lambda probe on the fuel-air mixture (Λ-factor)</dd><dt>Fig. 4:</dt><dd>Loop of arranged behind the catalyst oxygen sensor</dd></dl>

According to figure 1 the device consists of an internal combustion engine 1 with a catalyst 2 via a suction pipe 3 is supplied to the engine 1 air.

The fuel is injected through injectors 4 in the suction pipe 3rd

Between engine 1 and catalyst 2 a first lambda probe 5 is for detecting the engine exhaust gas is arranged. In the exhaust duct downstream of the catalyst 2 another lambda probe 6. The lambda sensors 5 and 6 measure the respective lambda value of the exhaust gas before and after the Catalyst 2. Both signals delivered by the lambda probes 5 and 6 be performed on a controller with PI characteristic 8, which is usually in Control unit (Fig. 2) is arranged in the motor vehicle.

From these signals, the controller 8 forms by means of desired values ​​a control signal, which is the injection valves 4, respectively.

This control signal results in a change in the fuel metering, which together with the air mass sucked in a specific lambda value has the exhaust gas result.

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

The controller 8 evaluates the signal of the first lambda probe 5, by the current value with a stored in the memory ROM setpoint 9 for Lambda probe 5 and determines it as the manipulated variable an injection time is, causing the fuel-air mixture is regulated. this comparison is superimposed on the evaluation of the second lambda control loop as in the Connection with FIG. 4 will be explained in detail. The result the second lambda control loop represented in the determination of Hold time TH. This hold time TH causes the action of the controller 8 on the injection valves 4, which in dependence of the comparison of the first Control loop takes place, with a time delay.

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

Each oxygen sensor provides over which the particular fuel-air mixture representing λ factor a waveform as shown in Figure 3 is. Depending on what type of lambda probe used for control is, either the resistance or the voltage across the λ factor can to be viewed as.

The following statements relate to the signal voltage.

If the probe is active, it has a signal voltage which outside the range (ULSU, ULSO) lies. During the lean rash supplies Lambda probe a minimum output of the below ULSU lies. During the fat-deflection is a maximum voltage signal above ULSO in a range of 600 - 800 mV measured. This maximum value is subject to due to manufacturing tolerances and aging phenomena certain variations, by a probe correction factor Getting corrected.

In order to compensate for the long-term drift of the lambda sensor 5 before the catalytic converter, a second control loop exists, the second lambda probe 6 contains behind the catalytic converter 2 and which further illustrated in Figure 4 is.

The controlled system 11 containing the motor 1, which by the controller 8 as shown in Fig. 1 described, the control signal in the form of the altered injection time of the injectors is supplied.

The arranged in the exhaust passage downstream of the catalyst Lambda probe 2 6 provides 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 is done by that it is determined whether this signal voltage is out of a Voltage range (ULSU, ULS0) is. Is of the case, a correction signal formed, in which the measured value of the oxygen sensor 6 U_6is to a summing junction 12 with a memory in the ROM of the control unit stored setpoint U_6SOLL is compared. This setpoint U_6SOLL is formed from the measured by the lambda probe 6 mean, when arranged in front of the catalyst Lambda Sensor 5 interference is working.

The control difference formed in point 12 of setpoint and actual value of the output signal the second oxygen sensor 6 is supplied to a limiter 13, of the amount of deviation with a threshold value 14, the is also stored in the memory ROM of the control unit, compares. Only if the amount of the control deviation is larger than this threshold value 14, the error signal is routed to a comparator 15, the function the sign of the difference between the actual value U_6is second Lambda probe 6 and the target value U_6SOLL the second lambda probe 6 a 1 or -1 outputs. In response to this output value is a Signum integrator 16 upstream or reset.

The Signum integrator 16 is incremented by 1 if the actual value U_6is greater than the target value U_6SOLL, It is decremented by 1 if the actual value U_6issmaller than the desired value U_6SOLL is. If both values ​​are equal, the Count does not change.

The Signum integrator 16 is in each envelope 17 of the catalyst prior to arranged first lambda probe 5 edited and is therefore of This clocked.

At a first Multiplizierpunkt 18 the count by a proportionality constant is 19 worth (0.5 - some 100) ms / probe cover the first lambda probe 5 multiplied, ensuring absolute retention time TH_raw is determined. The thus obtained holding time TH_raw , in a second Multiplizierpunkt 20 rated by a weighting factor WF, which in point 23 by dividing the actually measured period 21 of the first lambda probe 5 is determined by a constant 22nd The constant 22 is a function of the period duration of the first Lambda probe 5 at idle.

In comparison to commonly used at this point characteristic fields, wherein where the weighting factor may be a maximum value of 1, Now the disturbance compensated regardless of their size, since a kind of self-amplification is achieved by the larger factor. The so gained hold time TH as a control variable to the controller 8 to adjust the control system 11 is supplied.

In addition to the hold time TH of the controlled system 11 is supplied to a correction signal, the following is formed.

The control difference formed in the summing junction 12 of the second lambda probe 6 a change-over switch 24 is supplied, which depending on the sign of the votes from the comparator 15 signals on. If the signal negative, a first evaluation factor KM is composed of a first characteristic curve 25 taken, the signal is positive, a second characteristic of a second factor KL taken for the deviation. This Factor KM or KL is the point 27 a from a map 28 formed third factor KF multiplied. The map 28 is the amplitude ratio averaging 29 of the two lambda probes 5 and 6 and the reading of the mass air flow sensor 7 air mass flow 30 certainly.

The characteristic value formed at point 27 KPF is at point 31, depending the probe cover 17 of the first lambda probe 5 and of the sign the deviation of the second lambda probe 6, which by the Comparator is won 15, weighted.

Are the signals of both probes in the fat area is a positive Sign accepted. Working both probes in the lean range is a negative sign accepted.

The weighting of the correction factor PCF is as follows. Work both probes 5, 6 at the same time in the rich or lean in the same area, the correction factor is increased by KPF. 1 Does the first probe fats and the second probe in the lean region or vice versa, the Correction Factor KPF stripped of Figure 1. The weighting factor as contained as dimmensionslose size is independent of the hold time TH the Controller 8 is fed into the control path 11th It is in like-minded Tendency of the output signal of the oxygen sensor 5, 6 of the P component the controller 8 increases and decreases in opposite directions tend to what Entails that a quick and direct action of the second lambda control loop takes place on the first lambda control loop.