EP0445127A1

EP0445127A1 - Process and device for establishing at least one threshold voltage for a lambda closed-loop control.

Info

Publication number: EP0445127A1
Application number: EP19890911535
Authority: EP
Inventors: Adolf Fritz; Juergen Zimmermann; Christian Rein
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1988-11-24
Filing date: 1989-10-19
Publication date: 1991-09-11
Anticipated expiration: 2009-10-19
Also published as: DE58903617D1; KR0147073B1; KR900702191A; EP0445127B1; BR8907785A; WO1990005840A1; JPH04501898A; DE3839634A1; US5119788A

Abstract

Dans le procédé décrit, la tension de seuil n'est plus fixée à une valeur prédéterminée avec précision, au moyen d'une source de tension de référence très précise. Au lieu de cela, une contre-tension est connectée en opposition à la tension de la sonde et mesurée, et la ou les tensions de seuil sont mises en corrélation avec la valeur mesurée dont la valeur absolue ne doit pas être nécessairement connue. Ce procédé permet de se dispenser d'une source de tension de référence très précise et de résistances de haute précision. Celles-ci sont remplacées dans le dispositif décrit par un moyen de mesure de la contre-tension et un moyen pour mettre en corrélation les tensions de seuil avec la contre-tension.In the method described, the threshold voltage is no longer fixed at a predetermined value with precision, by means of a very precise reference voltage source. Instead, a counter voltage is connected in opposition to the probe voltage and measured, and the threshold voltage (s) are correlated with the measured value, the absolute value of which need not necessarily be known. This process makes it possible to dispense with a very precise reference voltage source and high precision resistors. These are replaced in the device described by a means for measuring the counter-voltage and a means for correlating the threshold voltages with the counter-voltage.

Description

Method and device for setting at least one threshold voltage in lambda one control

The invention relates to a method for setting at least one threshold voltage in lambda one control, with a lambda probe, to which a voltage is connected, which essentially corresponds to the desired switching voltage. The invention also relates to a device for performing such a method.

State of the art

From DE 33 19 432 A1 (US 4,528,957) a structure for detecting the voltage of the lambda probe is known, which uses a counter voltage source, the voltage of which is connected to that of the lambda probe. Two threshold voltages are related to the opposing voltage, namely an upper threshold voltage U _Q and a lower threshold voltage Uy. The counter voltage is z. B. at 450 mV and the threshold voltages up and down by 50 mV. If the measured voltage reaches one of the two thresholds, the system switches from control to regulation. In closed-loop control mode, control is carried out in the lean direction as long as the measured voltage is above a changeover threshold voltage, and control is carried out in the rich direction if it is above it. The switching threshold voltage is usually close to the counter voltage, e.g. B. 10 mV above this.

In the case of the example mentioned, the counter voltage is 450 mV, the upper switch-on threshold voltage 500 mV, the lower switch-on threshold voltage 400 mV and the switchover threshold voltage 460 mV. A digital value is permanently assigned to each voltage value. In the example, these are the values 130, 143, 117 and 132.

In order to be able to set the voltage values precisely, a highly accurate reference voltage source is used, that is, not the usual voltage stabilizer, which u. a. provides the usual logic voltage of + 5 V for electronic components. The voltage of the reference voltage source is divided with high-precision, temperature-stable resistors in such a way that the desired counter voltage is set. The threshold voltages are related to this precisely set counter voltage. In addition to the coordination with the aid of the exact resistances, software-based coordination can also take place in such a way that the specified digital value for the counter voltage is set.

The object of the invention is to be able to manage without the high-precision reference voltage source and without high-precision resistors. For this purpose, a method and a device are to be specified.

Advantages of the invention

The invention is for the method by the features of claim 1 and for the device by the features of Claim 6 given. Advantageous further developments and refinements of the method are the subject of subclaims 2-5.

The method according to the invention is characterized in that the counter voltage is measured and threshold voltages are related to the measured counter voltage. Is that _. measured counter voltage z. B. 450 mV instead of 450 mV, the upper switch-on threshold voltage U _{Q is set} to 510 mV instead of 500 mV. It is pointed out that, strictly speaking, it is not known whether the counter voltage is 455 mV or 465 mV, since there is no highly accurate reference voltage source for comparison. Exact knowledge is also not important, since other tensions that are important, e.g. B. the switch-on threshold voltages are related to the measured voltage. This ensures that, for. B. the two switch-on threshold voltages are always symmetrical to the counter voltage, regardless of what the exact value of the counter voltage is. For digital. Value of the measured counter voltage are z. For example, 13 units are always added to obtain the value for the upper switch-on threshold voltage, or 13 units are subtracted to arrive at the lower switch-on threshold voltage. Other distances or asymmetrical distances can also be set accordingly.

In addition to the switch-on threshold voltages, the switchover threshold voltage is advantageously also related to the measured voltage.

Because threshold voltages are related to the measured countervoltage, it is no longer necessary to set the countervoltage to a precisely specified value with the aid of a highly precise reference voltage source and with the aid of highly accurate resistors. Rather, the voltage from the usual voltage stabilizer can be used and normal-precise resistors can be used. If only the switch-on threshold voltages are corrected, it is sufficient to measure the counter voltage when the lambda probe is cold. This is the case in particular when starting an internal combustion engine on which the lambda probe is used, but also after prolonged overrun phases.

Should changes in the switching threshold voltage be detected, such as z. B. due to temperature or aging-related changes in resistance values or gain factors, it is advisable to measure the counter voltage at regular intervals and to relate the switching threshold voltage to the measured counter voltage.

A device for carrying out the method mentioned has a means for measuring the counter-voltage and a means for relating Schwel 1 voltages to the counter-voltage.

drawing

The invention is explained in more detail below on the basis of exemplary embodiments illustrated by figures. It shows:

1 shows a circuit diagram of a probe loaded with a counter voltage, the counter voltage being generated with the aid of the voltage of a conventional voltage stabilizer;

FIG. 2 shows a flow chart for explaining a method according to which threshold voltages are related to a measured counter voltage; and

3 and 4 circuit diagrams for explaining possibilities for measuring the counter voltage. Description of exemplary embodiments

1 has, inter alia, a lambda probe 10, which is represented by its equivalent circuit diagram, namely by a direct voltage source 11 with the probe voltage U _< . and a resistor 12 with the internal resistance value R _ς . The probe voltage is connected across a load resistor 13 with the resistance value R, a counter voltage U _β . This is generated by dividing the + 5 V voltage of a voltage stabilizer 14. In the exemplary embodiment, it should be 450 mV. However, this value fluctuates by a good 5% up and down, since the output voltage from the voltage stabilizer 14 depends on its input voltage, that is to say the battery voltage, on the load on the stabilizer and on the effects of temperature and aging. In addition, there is a spread from circuit to circuit with respect to the output voltages of the voltage stabilizers due to manufacturing tolerances. Further causes for the fluctuation range of the counter voltage U _G are manufacturing tolerances of the voltage divider resistors 15.1 and 15.2 and changes in their resistance values due to temperature and aging effects.

The probe voltage U_ and the counter voltage U _G are composed of the input voltage U _E at a differential amplifier 16 as follows:

E = ^U G ^{+ R} L ^(U S ^"U G ^{) (R} L ⁺ V

This voltage is fed to an A / D converter 17, the digital output values of which are processed by a microcomputer 18 for lambda control purposes.

In particular, the microcomputer 18 checks whether the input voltage U - has exceeded an upper switch-on threshold voltage U _Q or has fallen below a lower switch-on threshold voltage U. These threshold voltages are off ^ exemplary embodiment no longer at precisely predetermined values, but instead lie around predetermined count values above or below the count value which arises at the output of the A / D converter 17 when the counter voltage U _{β is} measured with the aid of the differential amplifier 16.

The process just mentioned is shown in the flow chart of FIG. 2. The counter voltage U _{G is} measured in a step s1. In a step s2, a difference value 4U _Q is added to the measured voltage in order to achieve the value for the upper switch-on threshold voltage U _Q , a difference 4Uy is subtracted in order to obtain the lower switch-on threshold voltage Uy, and a voltage ^ U added in order to provide a switching threshold voltage U _UM . If the latter threshold voltage is exceeded or undershot by the input voltage U _f , the control direction is reversed in each case.

A conventional control method is carried out in a subroutine in accordance with step s3. The subroutine according to step s3 is executed repeatedly. This repeated procedure can be preceded by a new measurement of the counter-voltage and the establishment of threshold voltages. This is shown by the dashed return line in FIG. 2. You can return to step s1 after each step of step s3. However, it is not necessary to go through steps s1 and s2 so often, since the counter voltage changes only slowly due to temperature and aging effects and load-dependent effects hardly play a role when the internal combustion engine is running. It is therefore normally sufficient to measure the countervoltage only once when the internal combustion engine is started up. In order to increase the accuracy, however, can also be at predetermined times, for. B. at intervals of a few seconds, or when predetermined operating conditions occur. An operating state which triggers the measurement can be overrun operation which lasts for a few seconds. In this case it cools the probe off, and so far during extended overrun that it is even no longer ready for control when the overrun is ended. Sufficient time is available to carry out steps s1 and s2 during overrun operation, since no control processes take place. When the overrun operation ends, the values determined in step s2 can be used to check whether the probe is ready for control.

It can be seen from the equation given above that with a very high internal resistance R _{s of} the probe, the input voltage U _£ corresponds to the counter voltage U _fi . At a probe temperature of around 250 ° C, the internal resistance value is Rς. over 1 MOh, while the load resistance value R is only in the order of a few 100 ohms. At the start of the internal combustion engine, that is when the probe is still completely cold, or in the case of extended overrun operation when the probe temperature falls below about 300 ° C., the counter voltage can thus be measured in a very simple manner in that it is equated to the measured input voltage U_.

If the probe is warm, the measurement method just mentioned fails. The voltage can then be measured, however, as illustrated in FIGS. 3 and 4.

According to FIG. 3, to measure the counter voltage, the probe voltage is disconnected by opening a switch 19, so that the input voltage U _E is identical to the counter voltage U ". In the variant according to FIG. 4, there is a tap directly at the positive pole of the counter voltage source and the voltage value present at this tap is applied to the positive input of the differential amplifier 16 by a changeover switch 20. 3 and 4, the counter voltage is generated by a counter voltage source 21. How this is designed is irrelevant. The switch 19 in the circuit diagram according to FIG. 3 and the changeover switch 20 in the circuit diagram according to FIG. 4 together with the differential amplifier 16, the A / D converter 17 and the microcomputer 18 serve as means for measuring the counter voltage. In ^¬ the variant according to FIG. 1, is to measure the counter-chip voltage controlled thereby, that the microcomputer 18 initiates the measurement process upon the occurrence of a predetermined condition, eg. B. at the start of the internal combustion engine or after prolonged overrun operation or when the internal resistance of the probe is measured, when this internal resistance exceeds a certain threshold value. It is pointed out that if the measurement is taken when the internal combustion engine starts, it is expedient to wait until it has completed a few revolutions. If measurement were carried out earlier, in the worst case even when the starter was still actuated, a counter voltage could be measured which no longer exists in later operation. This is because during the starting process and shortly thereafter, the output voltage from the voltage stabilizer 14 has dropped to a value which is no longer present during the entire further operation. ,

The microcomputer 18 is not only part of the means for measuring the counter voltage, but it is also a means for relating threshold voltages to the measured counter voltage. It also has a memory, which either stores the measured countervoltage or stores threshold voltages calculated with the aid of it.

Claims

Expectations

1. Method for determining at least one threshold 1 voltage in lambda one control, with a lambda probe to which a counter-voltage is connected, so that the counter-voltage is measured and threshold voltages are related to the counter-voltage.

2. The method of claim 1, d a d u r c h g e k e n n z e i c h ¬ n e t that the counter voltage is measured when the lambda probe is cold.

3. The method of claim 2, d a d u r c h g e k e n n z e i c h ¬ n e t that the switch-on threshold voltage, which serve to recognize readiness for control of the probe, are related to the measured counter voltage.

4. The method according to any one of claims 1-3, d a d u r c h g e k e n n z e i c h n e t that the switching threshold voltage, which serves to switch the control direction, is related to the measured counter voltage.

5. The method according to any one of claims 1-4, characterized in that the counter voltage is measured at regular intervals.

6. Device for determining at least one threshold voltage in lambda one control, characterized by a lambda probe to which a counter voltage is connected

- A means (19; 20; 16, 17, 18) for measuring the counter voltage, and

- A means (18) for relating Schwellspanπungen to the counter voltage.