WO2008125442A1

WO2008125442A1 - Method for air mass measurement and air mass sensor

Info

Publication number: WO2008125442A1
Application number: PCT/EP2008/053541
Authority: WO
Inventors: Rudolf Bierl; Thorsten Knittel; Stefan Pesahl; Frank Steuber
Original assignee: Continental Automotive Gmbh
Priority date: 2007-04-11
Filing date: 2008-03-26
Publication date: 2008-10-23
Also published as: DE102007017058A1

Abstract

The present invention relates to a method for air mass measurement and to an air mass sensor. In order to create an inexpensive and reliable method and a corresponding device for flow measurement based on a hot film anemometer, it is proposed to use two or more hot film anemometers as measuring elements (3, 4, 5, 6) that are disposed in a cross-sectional plane in the intake pipe (2) such that the flow in different regions of the cross-section is detected by measuring and evaluated, using quasi punctiform detection of the flow conditions.

Description

description

Method for air mass measurement and air mass sensor

The present invention relates to a method for air mass measurement and an air mass sensor.

In a known manner, an air-fuel mixture is brought under compression to combustion in internal combustion engines. The power output of the internal combustion engine depends on the ratio of fuel mass to air mass. The measurement of a respective air mass is carried out with an air mass sensor, which sits in the intake tract of the internal combustion engine. Due to the high economic importance of the motor vehicle sector is discussed below without limiting the use of inventive and generally applicable flow sensors only to the application for determining a sucked or otherwise supplied to an internal combustion engine air mass.

Numerous modern internal combustion engines are today equipped with an exhaust gas turbocharger, which causes a pre-compression of the air mass. Was already at the beginning of the development of internal combustion engines, the attempt of precompression of an internal combustion engine air supplied with the aim of increasing the engine power by increasing the air flow and fuel flow per stroke performed, so today the charging of gasoline internal combustion engines is no longer primarily under the performance aspect but as a way to save fuel and reduce pollutants. In this case, in a known manner, a respective exhaust gas flow energy for pre-compression of the air mass flow through a turbine running in the exhaust gas stream with mechanically coupled fresh air compressor, so that, for example, a diesel engine no longer as a naturally aspirated engine, but as a supercharged engine with charge air pressures of up to 1 5 bar or even 2.5 bar with significant increase in output and reduced emissions. For this purpose, of course, an air mass in a predetermined ratio to admit a particular fuel mass, so that an air mass sensor plays a significant role in the economy and emission reduction of an internal combustion engine.

Since it depends on the mass ratios of fuel and air in the chemical process of combustion in any operating condition of an internal combustion engine, the mass flow of the intake / charge air is also continuously as accurately as possible to measure. Depending on the engine power of the internal combustion engine, the maximum air mass flow to be measured is in the range of 400 to approx. 1000 kg / h. Due to the low idle demand of modern internal combustion engines, the ratio of a minimum to a maximum air flow rate is between 1:90 to about 1: 100.

An air mass sensor can operate as a mass flow sensor according to a thermal principle, wherein a release of heat output of a heated by the flow of electric current sensor wire compared to a thermally insulated sensor wire is evaluated via a resistance bridge circuit as a measure of a respective flow rate. Such devices are also known as hot film anemometers.

In order to influence the air flow as little as possible and to minimize the space compared to other known arrangements, such devices are designed as very small units and, inter alia, used in protective and measuring channel arrangements, as they are known for example from WO 03/089884 Al. As a rule, such air mass sensors in principle only capture a portion of the cross-sectional distribution of the flow within the intake tract of an internal combustion engine. By application or creation of a characteristic for the specific circumstances Characteristic becomes the basic characteristic; of the sensor, which is the result of a calibration, adapted to a particular operating environment. Consequently, a mean air filter characteristic curve is formed in known devices for implementing corresponding measuring methods, ie for the specific flow conditions within a specific intake tract characteristic curve of the sensor. In such a "second adjustment", however, neither individual component scattering of the components used in the intake tract can be taken into account, nor are changes in the flow conditions detected, as described for. B. occur due to unequal contamination of an air filter mat in practice. Also, aging effects and all changes in the characteristic curve over the sensor lifetime as well as component scattering of the intake tract itself can not be taken into account in this form.

It is the object of the present invention to provide an inexpensive and reliable method and a corresponding device for flow measurement on a hot-film anemometer basis.

This object is solved by the features of the independent claims. Advantageous developments are the subject of the respective subclaims.

The present invention is based on the finding that a significant disadvantage of known solutions is in an only quasi-point-specific detection of the flow conditions and thus a flow velocity distribution over the entire pipe cross-section remains unconsidered. In an air mass sensor constructed according to the invention, more than two measuring elements are used which are very small in construction. Two or more such measuring elements are arranged in an intake tract in a cross-sectional plane such that different regions of the cross section are detected. A changing distribution of the flow velocities across the cross-section at constant mean value leads to a substantial lesser error measurement than the same change with only one point measurement with one measurement element. An arrangement of a plurality of measuring elements thus has an integrating effect over the cross-sectional area.

In an advantageous embodiment of the invention, micromechanically produced measuring elements are used which contain as so-called single-chip solutions both the measuring bridge and the evaluation electronics. Micromechanical sensor elements are particularly favorable because of their small size. Single-chip solutions require no further evaluation electronics, which would also occupy a lot of space in the measuring tube.

In a preferred embodiment of the invention, the single-chip measuring elements are constructed such that a measuring element is connected as a central unit or ECU in a type of master / slave configuration and other measuring elements as satellites. The signals that are generated in each individual measuring element are then transmitted to the central unit via a connecting line system, which is designed in particular in the form of a leadframe.

In such a central unit, depending on the embodiment, either an averaged, possibly alternatively or additionally also differently weighted measured value is generated and output to the central unit and output on a data line or via a data bus, the measurement signals of all measuring elements for further billing in the ECU, or the data are issued on separate lines for further billing in the ECU. In these embodiments of the invention, compact sensor designs with almost identically short signal lines are realized in each case.

Due to the velocity distribution within the tube, roughly two flow regions can be distinguished: an edge flow which is limited to the region of the tube wall and a center flow which is the region of a tube cross section. Schnitt fills. From the pipe wall with the interface condition v = 0, the flow velocity in the edge region increases sharply. The flow velocity in the middle flow is the strongest and almost the same everywhere. By the arrangement described above, an average of the flow velocity distribution over the entire pipe cross-section is not possible. In order to increase the reliability of the measurement results, in one embodiment of the invention a computational compensation via characteristic fields and / or calibration is used.

In any case, the integrating effect of averaging single point results provides greater accuracy, less susceptibility to flow change, and redundancy in the failure of a single sensing element. The entire sensor retains its almost full functionality, so no emergency operation must be activated.

Further features and advantages of the invention are given below with description of embodiments with reference to the figures of the drawing. In the drawing show in a schematic representation:

FIGS. 1a and 1b:

Cross sections through an intake pipe with four or two arranged in a plane and via a mechanical mounts interconnected measuring elements;

FIG. 2: an arrangement of four measuring elements in the form of a central cross, which arrangement is alternative to the exemplary embodiment according to FIG.

Figures 3a and 3b: a plan view and a perspective view of an alternative design of a measuring element in a housing with a bypass solution and FIGS. 4a and 4b:

Signal flow patterns of the embodiments according to FIGS. 1a and 2 in a cross-sectional plane of the intake pipe.

Throughout the various illustrations of exemplary embodiments, the same reference numerals and designations are used below for the same functional or assembly groups and method steps.

The figure of Figure Ia shows a simplified cross section through a device 1 with an intake pipe 2, in which four measuring elements 3, 4, 5, 6 are provided in the form of hot-film anemometers in an approximately star-shaped arrangement. For this purpose, the measuring elements 3, 4, 5, 6 via a respective flow inlet 7 to the actual measuring element mechanical support 8 are connected to each other, through which a fixation within the intake pipe 2 is effected. Furthermore, the holder 8 also assumes the tasks of an electrical supply and derivation of the sensor output signals, as will be explained in more detail below.

The measuring elements 3, 4, 5, 6 are designed as micromechanically produced measuring elements. In the special design as so-called single-chip solutions, they include both a measuring bridge and a required evaluation electronics in a very compact component. On a separate display of bridge and transmitter has been omitted for reasons of clarity in the drawing. Micromechanical sensor elements are particularly favorable because of their small size, since they perform quasi-point measurements and influence the flow conditions in a reasonably small extent. This will be detected by the measuring elements 3, 4, 5, 6 different areas of the cross section. A changing distribution of the flow velocities over the cross section at a constant average result in the averaging shown here on the measurement results of four measuring elements 3, 4, 5, 6 to a much smaller incorrect measurement than the same change in only punctual measurement with a measuring element. An arrangement of a plurality of measuring elements thus has an integrating effect over the cross-sectional area.

Analogously to the representation of FIG. 1a, FIG. 1b shows a cross section through an intake pipe 2 with only two measuring elements 3, 4 arranged in a plane and interconnected via an adapted mechanical support 8. Here, too, an improvement of the output signal precision is achieved by averaging. In addition, redundancy is created, so that already in this simple embodiment, the failure of one of the measuring elements 3, 4 does not mean the failure of the entire device 1 and thus a downgrading of a connected internal combustion engine in a Notlauf- state.

FIG. 2 shows an arrangement of four measuring elements 3, 4, 5, 6 which is alternative to the exemplary embodiment according to FIG. 1 a, in which the flow feeders 7 are each designed as separate housings 9 with a feed of a partial flow in the form of an air guide channel 10. It thus results in the intake pipe 2 an arrangement of gehausten measuring elements

3, 4, 5, 6 in the form of a central cross 11, which is connected only via a mechanical support 8 in the form of a short web.

In the figures 3a and 3b is a plan view and a perspective view of the alternative design of a measuring element 3 in a housing 9 is shown with a bypass solution, as has been used in the embodiment of Figure 2. Accordingly, each of the four measuring elements 3,

4, 5, 6 arranged in a separate housing 9, which comprises an inlet 12, a guide or air duct 10 and an outlet 13. Each of the measuring elements 3, 4, 5, 6 is arranged protected in the region of the outlet 12, as in Figure 3a shown. An associated flow profile is indicated in the perspective view of this alternative design in Figure 3b.

FIGS. 4a and 4b illustrate signal flow patterns of the mirror-symmetric or point-symmetrical embodiments according to FIGS. 1a and 2 in a cross-sectional plane of the intake manifold. On the basis of these figures, two different forms of signal processing and processing in the region of the device 1 are illustrated: In the exemplary embodiment according to FIG output signals of the satellites in the measuring element 3 are calculated as the central element ECU together with the signal of the measuring element 3 and output via a data line. According to the embodiment of Figure 4b, the signals of the satellite measuring elements 4, 5, 6 and signal of the central element ECU are output via separate data lines. In both cases, the mechanical holder 8 also serves as a carrier for the electrical lines.

Claims

claims

1. A method for air mass measurement in an intake manifold to an internal combustion engine, characterized in that at least two or more hot-film anemometer as measuring elements (3, 4, 5, 6) are arranged in a cross-sectional plane in the intake pipe (2) arranged such that the flow in different areas of the cross-section under quasi-selective detection of flow conditions is metrologically recorded and evaluated.

2. Method according to the preceding claim, characterized in that as measuring elements (3, 4, 5, 6) micromechanical sensor elements in the design of so-called single-chip solutions are used, in which both the tasks of a measuring bridge and a sensor signal evaluation are carried out.

3. The method according to any one of the preceding claims, characterized in that the measuring elements (3, 4, 5, 6) are operated in a kind of master / slave configuration, so that output signals a plurality of sensors acting as a central unit (ECU) measuring element be supplied.

4. Method according to one of the preceding claims, characterized in that the measuring elements (3, 4, 5, 6) via a mechanical support

(7) are arranged in the intake pipe (2) and are supplied with electrical power.

5. Air mass sensor with a measuring element on a hot-film anemometer base, characterized in that two or more similar measuring elements arranged in an intake tract in a cross-sectional plane such are that the measuring elements are provided in different areas of the cross section for quasi-point detection of the flow conditions.

6. Air mass sensor according to the preceding claim, in that at least one of the measuring elements is designed as a so-called single-chip solution and includes both the measuring bridge and the evaluation electronics.

7. Air mass sensor according to the preceding claim, in that each of the measuring elements (3, 4, 5, 6) arranged in a separate housing (9) having an inlet (11), a Führungsbzw. Air duct (10) and an outlet (12) comprises, wherein a measuring element (3, 4, 5, 6) is arranged protected in the region of the outlet (12).

8. Air mass sensor according to one of the three preceding claims, d a d u r c h e c e n e c e s in that a measuring element is connected as a central unit (ECU) in a type of master / slave configuration and other measuring elements as satellites.

9. Air mass sensor according to one of the four preceding claims, in that a connecting line system, which is embodied in particular in the form of a leadframe, for transmitting the output signals of each individual measuring element is formed.

10. Air mass sensor according to one of the four preceding claims, characterized in that the system (6) in an area of the tube center axis (M) ange- is,