EP1880200A1

EP1880200A1 - Device and method for the operation of a gas sensor, especially a lambda probe

Info

Publication number: EP1880200A1
Application number: EP06754941A
Authority: EP
Inventors: Frank Kowol; Stefan Rodewald; Cyril Verdier
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2005-05-02
Filing date: 2006-05-02
Publication date: 2008-01-23
Also published as: DE102005020363A1; JP2008541030A; CN101171510A; WO2006117357A1

Abstract

Disclosed are a device and a method for operating a gas sensor, particularly a lambda probe. Said sensor is provided with a heater and is heated before an internal combustion engine is started.

Description

Device and method for operating a sensor for gases, in particular a lambda probe

State of the art

The invention relates to a method for operating a sensor for gases, in particular a lambda probe according to the preamble of the independent claim. Furthermore, the invention relates to an apparatus for operating such a sensor.

From DE 100 52 005 Al, a sensor for gases is already known, in which after a start of an internal combustion engine to avoid thermal shock of the ceramic by condensed water, first a protective tube of the probe at a temperature in the vicinity of the evaporation temperature of water between 80 ° until 150 ⁰ C is brought. This procedure ensures that all water evaporates at the installation site of the probe in order to avoid possible deposits on the ceramic element of the probe. After a certain residence time in this so-called protective heating mode, the sensor is set to its operating temperature of, for example. 300 ° to 450 ° C or even heated above. For typical lambda probes, the operating temperature or readiness of the probe is reached from approx. 15 seconds after engine start.

This time is very long to comply with modern exhaust emission limits, because especially at start the exhaust emissions without regulation can reach high values. Furthermore, a high Aufheizgradient is necessary, whereby the sensor element undergoes a correspondingly high thermo-mechanical load. Finally, any existing condensation in the protective tube during the Schutzheizphase can not be completely evaporated. This in turn leads to an increased risk of thermal shock.

Advantages of the invention

The inventive method with the features of the independent claim has the advantage that the sensor is heated before a start of the internal combustion engine. This switch-on strategy significantly shortens the time until the sensor is ready for operation after an engine start. Compliance with the limits for modern emission standards such. As EU4 / ULEV or SULEV concepts is thus much easier. Furthermore, the thermo-mechanical robustness is increased. Furthermore, it is advantageous to heat the sensor only up to a first temperature, wherein furthermore the first temperature is to be selected maximally so that the sensor does not suffer a thermal shock. Preferably, the first temperature is set so that the protective tube and the ceramic of the sensor in the exhaust system is above a dew point, so that the risk of accumulation of condensation in the protective tube and the associated risk of thermal shock is drastically reduced.

Furthermore, it is advantageous to determine the heating depending on determined operating variables. So can advantageously the temperature profile the prevailing

Conditions, such as Temperature sensor or exhaust system, shutdown time, battery voltage, etc. can be adjusted.

In particular, it is advantageous in the presence of hot start conditions not only to heat the probe to a first temperature, but up to the required operating temperature, so that the sensor is ready for use immediately after the start of the internal combustion engine.

An expedient embodiment provides that the temperature rise of the probe is set via a variable heating voltage. So can advantageously the

Temperature gradient adjusted so that first the dew point temperature is reached in a very short time and in the further course of the temperature rise may be flatter, whereby the risk of thermal shock can be further reduced.

A further embodiment provides that the sensor initially with a first

Heating voltage and then a second heating voltage is heated to the first temperature, wherein in a further advantageous embodiment, the first heating voltage is higher than the second. This approach has the advantage that alone by varying the heating voltages, an advantageous increase in temperature can be realized. By means of a first high heating voltage, a temperature can first be advantageously reached at which water present can evaporate without the probe suffering a temperature shock. After reaching such an intermediate temperature, it is provided according to the invention, with a second heating voltage, which is lower than the first heating voltage, to realize a flatter temperature rise, in order thus to reach the first temperature, without mechanical or thermal stresses causing the sensor endanger. By doing so, the thermo-mechanical robustness of the probe is increased since, in contrast to the methods known from the prior art, lower heating gradients occur in the probe.

According to the invention it is further proposed that the heating of the sensor is triggered by a wake-up function of a control device. Furthermore, the triggering can be triggered by activation of a door contact, a heater, a seat contact and / or other controls. The activation of these user elements is either registered by the control unit as a user event and triggers a so-called wake-up function of the control unit, via which in turn the

Sensor is caused to heat up or the user elements is designed such that an activation acts directly on the probe and causes a heating.

Finally, according to the invention is a device for operating a sensor for

Gases provided, in which the device acts on the heating of the sensor before starting the engine with a heating voltage.

Description of the embodiment

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. Show

Figure 1 is a schematic diagram of a device according to the invention. FIG. 2 shows a temperature profile of a measuring sensor according to the invention and a temperature profile known from the prior art.

Essentially, the invention aims to preheat a sensor, in particular a lambda probe, before an engine start in order to reach an operating temperature as quickly as possible after starting the engine and thus a control capability of the sensor. For this purpose, it is provided to bring the probe and in particular the ceramic of the probe to a first temperature of about 80 ° C to about 300 ° C. These temperatures do not lead to a thermal shock in the presence of water, but significantly facilitate the further heating of the probe. Furthermore, an optionally existing protective tube of the probe is warmed up to the extent that existing condensate evaporates, - A -

or that no further condensate precipitates near the sensor.

Figure 1 shows an example of a possible embodiment of the invention. According to FIG. 1, it is provided to control the lambda probe 10 both directly via a control unit 30 or to supply it with voltages or currents, as well as indirectly via an output stage 20, in which case the output stage 20 is controlled by the control unit 30. The controller 30 also receives user events 40 and, in response to these user events, controls the lambda probe 10 either directly or indirectly via the power amplifier 20. It may also be contemplated that certain events of the user may occur directly, i. without adding the control unit, act on the sensor and cause the sensor to heat up.

Control units with a so-called wake-up function are capable of external events even in a switched-off state of the internal combustion engine, and in particular

Capture user events and respond appropriately. In particular, provision may be made for the control unit to activate at least the control of the measuring sensor by activating certain operating elements. For example, it may be provided to start the preheating procedure by activating a door contact as soon as a driver opens the car door by radio remote control or by a car key. However, the preheating procedure can also be activated by activating the auxiliary heating via radio or timer. Furthermore, it is conceivable to provide activation via a seat contact, which is activated, for example, as soon as the driver sits down on the driver's seat. Further activation options via further operating elements are conceivable.

In order to optimally utilize the time during the possibly short preheating phase, it is provided according to the invention to achieve a rapid increase in temperature with a higher initial voltage, in order then to continue to heat continuously with a lower voltage until the engine starts.

FIG. 2 shows by way of example a temporal temperature profile of a measuring sensor known from the prior art in a curve 100 and a temperature profile 200 according to the invention. In a typical procedure, the heating of the measuring probe does not become a starting time until or after the starting of the internal combustion engine t_S turned on, so that an operating temperature t_B typically only after about 15 s after the engine start is reached. According to the invention, it is now intended to heat up the sensor even if there is a user event at an event time t_E. The curve 200 shows an example of a heating with variable heating voltage. At event time t_E is first by applying a first high

Heating voltage a steep temperature gradient shown to heat the probe as quickly as possible. The temperature hereby preferably remains below a first temperature in order to avoid thermal shocks at the sensor. After reaching a certain intermediate temperature or due to other criteria, a second heating voltage is applied, which slows down the heating of the sensor. The second heating voltage is smaller than the first heating voltage. The second heating voltage may be selected, for example, so that the first temperature is reached asymptotically. At start-up time t_S, the sensor is already preheated to the first temperature, so that the heating up to operating temperature t_B takes place within a short time, and thus the operational readiness and controllability of the sensor is much faster in time available than with a conventionally operated sensor.

Alternatively, the heating can also be carried out by a control or regulation and so individually adapted to the prevailing conditions. In particular, provision may also be made for hot start conditions.

Hot start conditions are usually present when an internal combustion engine has reached its operating temperature only for a short time. In such a condition, the exhaust system, so that it can be assumed in a restart of the internal combustion engine that the exhaust system is free of condensate. Furthermore, it can be considered as a hot start condition, if the wall of the exhaust line before the installation of the probe heats up sufficiently quickly at the start of the internal combustion engine, so that only small amounts of water (wall film) are formed by condensation; o- if it is ensured by design measures that a possibly resulting wall film can not be atomized by the exhaust gas flow of the internal combustion engine, so that drops of water can not hit the sensor; or if it is ensured by design measures that no water reservoirs (eg siphons) can occur in front of the probe installation site. In a further embodiment, it is conceivable to heat the probe not only to a first temperature T l, but to the operating temperature TB. Such heating up to the operating temperature before a start can take place, for example, when the exhaust gas system has a sufficiently high temperature due to a short shutdown time of the internal combustion engine, so that it can be assumed that there is no condensation water in the exhaust gas line. In particular, it may also be provided to determine further operating variables of the vehicle and to heat the measuring sensor as a function of the determined operating variables. For example, can completely be omitted or shortened at a low battery voltage on the preheating. Depending on the stopping time of the internal combustion engine or temperatures in the exhaust line, certain heating or preheating strategies can be defined.

The preheating strategy according to the invention leads to a rapid operational readiness of the sensor or of the lambda probe after engine start.

Such preheating increases the thermal robustness and eventually leads to a reduction of condensation in the area of the ceramic and a possibly existing thermowell of the probe.

Furthermore, such a method avoids the disadvantages of a so-called lei-frost phenomenon, which occurs when a sensor is heated very quickly. Touched z. As a drop of water is a hot ceramic element, the result is a water vapor zone with reduced thermal conductivity at the point of contact, which attenuates the local cooling of the ceramic and thus allows a certain thermal protection. However, this effect does not completely prevent cooling, so at too high temperatures of the ceramic element, for. B. at operating temperatures greater than 500 ° C, however, thermoelectric voltages that cause the destruction of the element.

In a further embodiment, it is provided that the heating voltage is applied via a pulse

Wide modulation to vary. Thus, it can be assumed in a simple manner directly from a supply voltage, such as a battery voltage and be selected by the choice of the pulse pause ratios of the modulation, a corresponding effective voltage or heating power for the probe heater. In order to avoid an excessive load on the battery, it may be provided to limit the Auflieizung time or provide additional criteria to stop the heating. In particular, provision may be made for preheating to be interrupted by renewed actuation of a closing contact or closing of the vehicle or the like. The preheating of the measuring element is then only at renewed

Activation of the intended controls or a re-user event activated again. This ensures that a preheat phase of the sensor precedes each time the engine is started. In the case of a hot start, so at a start of the internal combustion engine with a hot exhaust tract, for example in a renewed on let the internal combustion engine, for example, via an exhaust gas temperature or a

Shutdown be recognized that a new preheat phase is not required. This prevents overheating of the already hot sensor.

Furthermore, it is conceivable that the temperature of the measuring sensor is measured directly and a preheating phase is activated according to the detected temperature at the measuring sensor.

Claims

claims

1. A method for operating a sensor for gases, in particular a lambda probe, wherein the sensor has a heater, in which at least one operating variable of the vehicle is determined, and the sensor is heated in dependence of the determined operating variable. characterized in that the sensor is heated before starting the internal combustion engine to a first temperature which is selected to be maximum so that the sensor does not suffer thermal shock, and that is heated in the presence of hot start conditions, the sensor before starting the internal combustion engine to operating temperature ,

2. The method of claim 1, wherein a temperature rise is set via a variable heating voltage.

3. The method according to at least one of the preceding claims, wherein the sensor is first heated with a first heating voltage and then with a second heating voltage.

4. The method of claim 3, wherein the first heater voltage is higher than the second heater voltage.

5. The method according to at least one of claims 3 to 4, wherein at least one heating voltage is set via a pulse-width modulation.

6. The method according to at least one of the preceding claims, characterized in that the heating of the sensor is triggered by a wake-up function of a control device, and / or activation of a control element.

7. A device, comprising means for operating a sensor according to one of claims 1 to 6, characterized in that the device acts on a heating of the sensor before starting an internal combustion engine with a heating voltage, that a detection means determines an operating size of the vehicle, the device heats up the sensor as a function of the determined operating variable, characterized in that the device heats the sensor to a first temperature before starting the internal combustion engine, which is selected to be maximum so that the sensor does not undergo a thermal shock, and that in the presence of hot start conditions the device heats the sensor to operating temperature.