EP2601486A1

EP2601486A1 - Method for determining a resulting total mass flow to an exhaust gas mass flow sensor

Info

Publication number: EP2601486A1
Application number: EP11745711.9A
Authority: EP
Inventors: Andres Tönnesmann; Karsten Grimm; Sven Nigrin
Original assignee: Pierburg GmbH
Current assignee: Pierburg GmbH
Priority date: 2010-08-03
Filing date: 2011-07-05
Publication date: 2013-06-12
Also published as: KR20130055634A; US20130132003A1; CN103003674A; JP5479654B2; JP2013532831A; CN103003674B; DE102010033175B3; WO2012016775A1; KR101434808B1

Abstract

The present invention relates to a method for determining a resulting total mass flow in a defined flow direction to an exhaust gas mass flow sensor, and to an exhaust gas mass flow sensor (10) for carrying out this method. The exhaust gas mass flow sensor (10) for carrying out the method preferably comprises two sensor elements (15, 16) which are arranged in series in the flow direction, wherein the second sensor element (16) for its part has two temperature sensors (17, 18) which are arranged in series in the flow direction, and the exhaust gas mass flow sensor (10) additionally has an evaluation unit (28) in which the first and the second characteristic map (29, 30) are stored.

Description

DESCRIPTION

Method for determining a resulting total mass flow on an exhaust gas mass flow sensor

The present invention relates to a method for determining a resulting total mass flow on an exhaust gas mass flow sensor and an exhaust gas mass flow sensor for carrying out this method.

In order to meet the ever increasing demands of new emission standards in the field of motor vehicles, are a number of internal engine measures, such as

Exhaust aftertreatment systems have become integral parts of current and future engine concepts. However, the full potential of such measures, such as the cooled exhaust gas recirculation, but can only be exhausted if a correspondingly accurate vote of the imported exhaust gas mass flow to the respective engine operating conditions. Thus, increased demands are placed on the engine control and in particular on the sensors used for this purpose.

For determining the mass flow in a pipe through which hot exhaust gas flows, exhaust gas mass flow sensors which operate on the anemometric principle are frequently used.

One of the main challenges here is the detection of exhaust gas pulsations of the exhaust gas mass flow, which are mainly caused by the gas exchange processes in the internal combustion engine and the correct balance of the exhaust gas mass flow from this, which requires correct direction detection. Exhaust gas mass flow sensors are known from the prior art, by means of which an exhaust gas mass flow is to be measured as a function of the flow direction or flow direction changes.

Such an exhaust gas mass flow sensor is known from DE 10 2006 030 786 AI. The exhaust gas mass flow sensor disclosed herein has two sensor elements arranged in a row, the second sensor element again consisting of two temperature sensors arranged in series. The arranged in the flow direction first sensor element is a temperature measuring element, which is realized in the form of a platinum thin-film resistor. This first sensor element measures the temperature of the exhaust gas. The second sensor element arranged downstream in the flow direction is a heating element which is likewise realized in the form of a platinum thin-film resistor. This second sensor element is heated to an elevated temperature by means of electrical heating, so that heat is dissipated to the exhaust gas mass flow essentially by convection. By measuring the temperature change or the measurement of the required power consumption to keep the temperature of the second sensor element constant, an exhaust gas mass flow can be determined with the aid of suitable algorithms. By arranging two separate temperature sensors on the second sensor element, a direction detection of the exhaust gas mass flow is made possible.

In the prior art, however, it is not disclosed how such a direction detection is performed by means of such an exhaust gas mass flow sensor, in particular it is not disclosed how a determination is carried out in order to obtain a resulting total mass flow in the case of occurring exhaust gas pulsations. Exhaust gas mass flow sensors are typically thermally inert sensors, ie, due to the material thickness of the resistance elements used, the determination of the temperature of the exhaust gas, in particular the temperature of the exhaust gas with exhaust gas pulsations is slower than the pulsation frequency of the engine. In the case of exhaust gas pulsations with a return flow component, the average heating power of the second sensor element is thus markedly increased, without a detection of the fluctuations in the mass flow caused by the exhaust gas pulsations of the engine taking place. As a result, an incorrect exhaust mass flow value is output from the exhaust gas mass flow sensor. In addition, the temperatures occurring over a time range on the resistance elements differ depending on the backflow component.

It is therefore an object of the invention to provide a method for determining a resulting total mass flow at an exhaust gas mass flow sensor, by means of which a more accurate determination of the exhaust gas mass flow is made possible in the case of occurring exhaust gas pulsations, and to provide an exhaust gas mass flow sensor for carrying out such a method.

This object is achieved by a method according to claim 1 and by an exhaust gas mass flow sensor for carrying out this method according to claim 6.

By the method according to the invention for determining a resulting total mass flow at an exhaust gas mass flow sensor, in a first method step the determination of the specific heating power is carried out on an exhaust gas mass flow sensor operating according to the anemometric principle with two sensor elements successively arranged in the flow direction. From a stored first map, an amount of a summed mass flow M sum = determined, where M _{BE BEFORE} the mass flow in the defined flow direction of the exhaust gas and Μ _ΛΛ the mass flow is opposite to the defined flow direction of the exhaust gas. In this first map the specific heat output is defined as a function of this amount. In a next method step, a normalized temperature gradient is determined, wherein the temperature gradient is defined as the ratio of the temperature difference between a temperature measurement value of a second and a first temperature sensor of the second sensor element to the temperature difference between a temperature value determined from the temperature measurement values of the second sensor element and a temperature measurement value of the first sensor element is. From a stored second map, a backflow ^component γ = ^{Mräck is} determined. The reverse flow component is one

Function of the specific heating power and is also dependent on the

(Ί -Ύ) normalized temperature gradient. According to the formula M _resGes = M _Sum x ---

(1 + γ) can be determined in a final process step, the resulting total mass flow of the exhaust gas mass flow sensor.

The method makes possible a more accurate and reliable determination of the exhaust gas mass flow when exhaust gas pulsations occur.

The object is further achieved by an exhaust gas mass flow sensor for carrying out the method, which consists of two consecutively arranged in the flow direction sensor elements, the second sensor element in turn two flow directionally arranged one behind the other temperature sensors, and the exhaust gas mass flow sensor also has an evaluation, in which the first and the second map are stored.

The twofold arrangement of the temperature sensors on the second sensor element is a determination of the temperature distribution allows so that caused by the exhaust gas pulsations of the engine fluctuations in the exhaust gas mass flow can be detected. With the characteristic field stored in the evaluation unit of the exhaust gas mass flow sensor, a measured value correction can take place as a function of the backflow component of the exhaust gas mass flow value, so that a more accurate exhaust gas mass flow value can be determined. Furthermore, with the evaluation unit of the exhaust gas mass flow sensor, the determined variables can be used together with state variables of the engine, such as the air ratio lambda or the gas pressure, in order to ensure optimized engine control.

According to a preferred embodiment of the method determines the determination of the specific heating power, the first sensor element, the temperature of an exhaust gas, and the second sensor element arranged behind it, based on the temperature of the passing exhaust gas, heated to an elevated temperature, so that the passing past this second sensor element Exhaust gas causes heat loss. The specific heating power is defined as the ratio of a power output from the second sensor element to the temperature difference between the second and the first sensor element. With this exhaust gas mass flow sensor constructed according to the anemometric principle, an exhaust gas mass flow can be determined with the aid of suitable algorithms.

The temperature value on the second sensor element is preferably formed from an arithmetic mean value of the respective temperature measured values of the first and the second temperature sensor. This makes sense physically if the two temperature sensors are designed symmetrically on the second sensor element.

Preferably, the first map is determined by the specific heating power is determined experimentally from a defined summed mass flow. For this purpose, the exhaust gas mass flow in a Device adjusted so that the measured exhaust gas without backflow, ie there is a pure flow, flows through the device. By the predetermined in the experiment different exhaust gas mass flows then the dependence of the specific heating power of the summed mass flow can be determined. The summed mass flow is therefore an amount of the pre-flow component and the reverse flow component.

Preferably, the second map is determined by the specific heating power is determined experimentally as a function of the temperature gradient for a defined backflow component. In this case, it is true that with a pure pulsation flow, i. the resulting total mass flow is zero, there is no temperature gradient between the two temperature sensors on the second sensor element, i. the difference is zero, so that the backflow component has the value one. By contrast, in the case of a pure pre-flow, i. the backflow rate is close to zero, the temperature gradient is maximized, i. this becomes greater zero. All states in which the resulting total mass flow is greater than zero, can be specified by a corresponding device by the backflow component is set in the exhaust gas mass flow, so that said dependence can be determined by the obtained temperature difference between the two temperature sensors and the specific heating power obtained.

Hereinafter, an embodiment of a

Exhaust gas mass flow sensor illustrated with reference to a drawing which is suitable for carrying out the method according to the invention. Furthermore, diagrams are shown which show essential functions of the method according to the invention.

FIG. 1 shows a schematic view of an exhaust gas mass flow sensor. FIG. 2 shows a plot of an exhaust gas mass flow with a backflow component as a function of time.

FIG. 3 shows a function of a first characteristic map.

FIG. 4 shows a function of a second characteristic map.

FIG. 1 shows an exhaust gas mass flow sensor 10 for carrying out the method according to the invention. The exhaust mass flow sensor 10 has two in the flow direction, i. E., At its sensor head 14 arranged in an exhaust gas channel 12. according to the arrow 11, successively arranged sensor elements 15, 16.

The first sensor element 15 is a pure temperature measuring element, with which the temperature of the exhaust gas is determined. The second sensor element 16 essentially consists of two separate temperature sensors 17, 18 arranged one behind the other in the flow direction, via which the measurement of the temperature change or the determination of the required power consumption takes place.

Both sensor elements 15, 16 are each connected via an electrical connection 20, 21 to a control unit 22, which in turn may be connected via an electrical connection 24 with an on-board electronics (not shown). At the same time, heating of the second sensor element 16 or of the two temperature sensors 17, 18 takes place via the electrical connection 21. The temperature value output by the second sensor element 16 becomes extinct an arithmetic mean of the respective temperature measured values of the first and the second temperature sensor 17, 18 is formed. An evaluation unit 28 is likewise connected to the control unit 22 via an electrical connection 26, wherein maps 29, 30 are stored in the evaluation unit 28. The first map 29 is shown by way of example in FIG.

Here, the specific heating power in mW / K as a function of the summed mass flow M _SUM = shown in kg / h. The second map 30, which is stored in the evaluation unit 28, is shown by way of example in FIG. In this second map 30 is the

^{Backflow share} γ = ^Mräck depending on the specific

^M before

Heating power in mW K as a function of the normalized

Temperature gradient g shown.

FIG. 2 shows, by way of example, a time profile in ms of an exhaust gas mass flow in kg / h with a pre-flow component 32 and a backflow component 34.

Hereinafter, the method according to the invention is shown by way of example at a temperature of the exhaust gas of 95 ° C.

The exhaust gas flows through the exhaust passage 12 according to the arrow 11. At the first sensor element 15, which is a pure temperature measuring element, for example, the temperature of the exhaust gas T _SM = 95 ° C is determined.

In a next step, the second sensor element 16 arranged behind it is heated to an elevated mean temperature, based on the temperature of the exhaust gas flowing past T _SM = 95 ° C.

T _SE2 = 240 ° C, so that the flowing past this second sensor element 16 exhaust gas causes heat loss. The power output by the second sensor element 16 is, for example P = 2.6 \ 6W. This results in the specific heating power p

ps _pez ⁼ = \ 8.04 \ mW / K. From a stored first map 29, see Figure 3, the amount of the summed mass flow

_{Ι 8ιιη} = \ be determined . This results in M _Sum = 33kg / h. Furthermore, the normalized temperature gradient is determined, wherein the temperature gradient is determined as the ratio of the temperature difference between a temperature measured value of a second and a first temperature sensor 18, 17 of the second sensor element 16 to the temperature difference between a temperature value determined from the temperature measured values of the second sensor element 16 and a temperature measured value of the first Sensor element 15 is defined. This

T - T 253 - 227

g = 0.18 and is on line 36 in FIG. 4. Off

the stored second map 30, see Figure 4, the

^{Backflow share} γ = ^Mräck determined. This is then γ = ^Mräck = 0. In

. ". M ..

a final step can thus be the resulting total mass flow

(Ί -Ύ)

according to the formula M _resGe = M _Sum ^■ --- be determined. This is

(1 + γ)

M _resGes = 33 - ^ ± = 33kg / h.

Claims

Pierburg GmbH, 41460 Neuss PATENT APPLICATIONS

A method for determining a resulting total mass flow on an exhaust gas mass flow sensor (10), comprising the steps of:

Determining a specific heating power on an exhaust gas mass flow sensor (10) operating according to the anemometric principle with two sensor elements (15, 16) arranged behind one another in the flow direction,

Determining an amount of a summed mass flow M _SUM = from a stored first map (29), where M _VOR the mass flow in the defined

Flow direction is and Μ _ΛΛ the mass flow is opposite to the defined flow direction, the specific heating power is a function of this amount,

Determining a normalized temperature gradient, wherein the temperature gradient as the ratio of the temperature difference between a temperature measurement of a second and a first temperature sensor (18, 17) of the second sensor element (16) to the temperature difference between one of the Te m pe ra tu rameter of the second sensor element (16) defined temperature value and a temperature measurement value of the first sensor element (15) is defined,

Determining a return flow ^component γ = ^Mräck from a stored second map (30), wherein the backflow component is a function of the specific heat output as a function of the normalized temperature gradient, and

Determining the resulting total mass flow according to the formula

M. ^{■ ■} M -γ)

(1 + γ)

2. The method of claim 1, wherein for determining the specific heating power, the first sensor element (15) determines the temperature of an exhaust gas, and the second sensor element arranged behind (16) is heated to a, based on the temperature of the passing exhaust gas, elevated temperature, such that the exhaust gas flowing past this second sensor element (16) brings about a heat loss, the specific heating power being defined as the ratio of a power output by the second sensor element (16) to the temperature difference between the second and the first sensor element (16, 15) ,

3. The method of claim 1 or 2, wherein the temperature value at the second sensor element (16) from an arithmetic mean of the respective temperature measured values of the first and the second temperature sensor (17, 18) is formed.

4. The method according to any one of the preceding claims, wherein the second characteristic field (30) is determined by the specific heating power is determined experimentally as a function of the temperature gradient for a defined backflow component.

5. The method according to any one of the preceding claims, wherein the first map (29) is determined by a defined summed mass flow, the specific heating power is determined experimentally.

6. exhaust gas mass flow sensor (10) for carrying out a method according to one of the preceding claims, consisting of

- Two successively arranged in the flow direction sensor elements (15, 16), wherein the second sensor element has at least two in the flow direction successively arranged temperature sensors (17, 18), and

- An evaluation unit (28) in which the first and second map (29, 30) are stored.