JP2006349687A - Air mass meter with additional heater element for reducing surface contamination - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hot film air mass meter for measuring air mass flow flowing in direction of main flow especially in the suction pipe of internal combustion engine capable of avoiding the heretofore known defect from conventional technology. <P>SOLUTION: At least one additional heater element (154 or 156), and at least one additional temperature sensor (158 or 160) is disposed on the measurement surface (114) outside of the sensor region (136). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a hot film air mass meter for measuring an air mass flow flowing in a main flow direction. This type of hot film air mass meter is used, for example, in an intake pipe of an internal combustion engine.

More particularly, the present invention is a hot film air mass meter for measuring an air mass flow flowing in a main flow direction, particularly an air mass flow in an intake pipe of an internal combustion engine,
The hot film air mass meter has a sensor chip with a chip surface through which air mass flow can flow.
The chip surface has a measurement surface and a land surface,
The sensor chip has a heat transfer property that is at least an order of magnitude less in the area of the measurement surface than in the area of the land surface,
The measuring surface is fitted with a conductor path of a central hot film air mass meter circuit comprising at least one central heating element and at least one temperature sensor,
The outer dimensions of the conductor path of the central hot film air mass meter circuit relate to a hot film air mass meter of the type that defines the sensor area of the measurement surface.

  In many processes, for example in the field of process technology, chemistry or machine tools, a gas mass, in particular an air mass, must be defined and supplied. This includes, inter alia, combustion processes that progress under controlled conditions. An important example here is the combustion of fuel in an internal combustion engine of a motor vehicle, followed by, inter alia, catalytic exhaust gas cleaning. Various types of sensors are used here for measuring the ventilation mass flow rate.

  A sensor type known from the prior art is the hot film air mass meter (HFM), which is described, for example, in the examples of DE 19601791 A1. In this type of hot film air mass meter, a sensor chip having a thin film sensor membrane, for example, a silicon sensor chip is usually used. The sensor membrane is typically provided with at least one heating resistor, which is surrounded by two or more temperature measuring resistors (temperature sensors). The temperature distribution changes in the air flow guided over the membrane, which can be detected by a temperature measuring resistor and can be evaluated by a control and evaluation circuit. For example, the air mass flow can be detected from the resistance difference of the temperature measurement resistance. Various other variations of this sensor type are known from the prior art.

  A problem known from DE 10111840C2, for example of this type of sensor, is that the sensor chip is usually caused by frequent contamination of the sensor, for example by oil, other fluids, or other impurities. Or it is used directly by the bypass to the intake pipe of an internal combustion engine. Here, during operation of the internal combustion engine, oil may deposit on the sensor chip, in particular on the sensor membrane. This oil deposition can undesirably affect the measurement signal of the sensor chip. This is because the oil film on the surface of the sensor chip acts on the heat conduction on the surface, which gives an error to the measurement signal. Oil contamination can also occur when an internal combustion engine, such as a diesel engine, is shut off or immediately after it is shut off. This is particularly the case when the overpressure present in the crank casing after the internal combustion engine is shut off is exhausted to the intake pipe of the internal combustion engine (and thus to the bypass channel of the hot film air mass meter) by crank casing ventilation. In this case, oil vapor or oil mist is frequently introduced together.

  DE 10111840C2 therefore proposes a method for avoiding contamination of the sensor chip using an additional heater. The sensor chip has a sensor area and an additional heater arranged outside the sensor area. This additional heater is heated so that a thermal gradient vortex is generated in the area of the additional heater. This thermal gradient vortex causes the flow medium contaminants to deposit away from the sensor area in the area of the additional heater.

  However, the device and the method disclosed in DE 10111840C2 are actually associated with drawbacks due to the different modes of operation of internal combustion engines. For example, as a disadvantage, it is practically impossible to determine the position of the target thermal gradient vortex by the device disclosed in DE 10111840C2. Due to the high thermal conductivity of silicon, the heat generated by the additional heater is easily spread throughout the chip. This causes a uniform temperature distribution and thus the entire chip is heated.

  Membrane or sensor surface contamination problems are exacerbated by thermodynamic effects. For example, it is known that a fluid drop having a gradient in surface tension receives a force in a relatively high direction of surface tension. This usually causes the droplets to move from the lower surface tension to the higher one. In particular, this gradient is caused by a temperature gradient at the surface where the fluid drop is applied. The drop usually moves from a relatively warm area of the surface to a relatively cool area due to the temperature gradient and the resulting force. This effect is described in, for example, G. Levic, “Physicochemical Hydrodynamics”, Prentice-Hall, N .; J. et al. , 1962, pp. 373-380.

As noted above, a typical hot film air mass meter is configured such that it has a low heat transfer sensor membrane (eg, a silicon membrane) and a surrounding chip land. Thus, during operation of a hot film air mass meter, a temperature gradient is usually formed at the edge of the sensor membrane, i.e. the boundary to the surrounding chipland, and a fluid wall is accordingly formed, for example in the form of oil droplets. Air flow can drag all or part of this fluid wall, so that the oil droplets can reach the sensor membrane and affect the measurement there. Furthermore, the fluid wall enhances the heat transfer at the edge of the sensor membrane. This can also cause errors and drift in the measurement signal.
DE19601791A1 DE10111840C2 V. G. Levic, “Physicochemical Hydrodynamics”, Prentice-Hall, N .; J. et al. 1962, pp. 373-380

  The object is to provide a hot film air mass meter for measuring the air mass flow flowing in the main flow direction in the intake pipe of an internal combustion engine, which can avoid the disadvantages of the devices known from the prior art.

  This hot film air mass meter can be used universally, in particular so that the flow velocity is optimized for the measurement of air mass flow between 0 and 60 m / s.

  This object is achieved according to the invention in that in the hot film air mass meter mentioned at the outset, additionally at least one additional heating element and at least one additional temperature sensor are arranged on the measuring surface outside the sensor area. Solved by configuring.

  A hot film air mass meter has a sensor chip with a chip surface through which air mass flow passes. Here, the sensor chip can be, for example, a silicon chip as described above. The chip surface further has a measurement surface and a land surface. In the area of the measuring surface, the sensor chip has a transverse heat transfer which is at least an order of magnitude smaller than the land surface.

  Reducing transverse heat transfer can be accomplished in various ways. For example, as known from the prior art and as described above, a sensor chip comprising a sensor membrane having a thickness of only a few μm can be used. Here, the fact that the heat conductivity of the air surrounding the sensor membrane is small (about 0.026 W / mK) is used. Alternatively, a porous region can be created on the chip as a measurement region having a measurement surface on the side facing the air mass flow. This is done, for example, by making the silicon chip porous. A measurement region with a transverse heat transfer of 0.1 to 2 W / mK can be produced by the closed cavity in this way. Compared to this, the heat conductivity of the silicon substrate is 156 W / nK.

  The conductor surface of the central hot film air mass meter circuit is deposited on the measurement surface. The central hot film air mass meter circuit has at least one central heating element and at least one, preferably at least two temperature sensors. For example, this can be a central heating element surrounded by two temperature sensors as described above. Other geometric shapes are also conceivable.

  The external dimensions of the conductor path of the central hot film air mass meter circuit define the sensor area of the measurement surface. Thereby, the measurement surface is divided into a sensor region and a region outside the sensor region. For example, the sensor area may take the form of a (virtual) rectangle that surrounds the conductor path of the central hot film air mass meter circuit, and this rectangle is arranged, for example, in the center in the measurement surface.

  In practice, however, the production of measuring surfaces, in particular membranes or porous regions, is cumbersome and expensive. This is in particular because corresponding semiconductor technology methods are used. Furthermore, the measuring surface is usually vulnerable to obstacles. The membrane is easily damaged. Correspondingly, the porous regions in the silicon are easily contaminated and exposed to a high risk of destruction. Therefore, efforts are made to minimize the area of the measurement surface in a conventional hot film air mass meter. Thus, in a typical hot film air mass meter, the measurement surface is usually almost completely filled by the conductor path of the central hot film air mass meter circuit. The measurement surface used here is optimally used in terms of space, and the sensor area and the measurement surface are almost identical in a normal sensor chip.

  The first basic technical idea of the invention is that the measurement surface is not completely filled with the sensor area, but additionally at least one additional heating element and at least one additional temperature sensor are measured outside the sensor area. Is to place on the surface. A significant advantage of this arrangement, unlike DE 10111840C2, is that the heat provided by the at least one additional heating element is spatially sufficiently localized due to the low heat transfer of the measuring surface. Thus, the entire sensor chip or the entire measurement surface is not heated during the heating of the at least one additional heating element.

  Furthermore, the at least one additional temperature sensor is preferably arranged in the immediate vicinity of the at least one additional heating element, the temperature of the at least one additional heating element or the at least one additional heating element or at least one The temperature of the measuring surface in the immediate vicinity of the two additional temperature sensors can be adjusted precisely. For example, a plurality of additional heating elements can be provided, each of which is assigned, for example, one additional temperature sensor. In this way, the temperature defined in the predetermined area of the measurement surface of the sensor chip is adjusted. Thereby, the formation of the temperature gradient vortex on the chip surface can be adjusted much better than the apparatus known from the prior art.

  Another basic technical idea of the present invention uses an improved form of the structure of a hot film air mass meter. Here, the conductor path of the central hot film air mass meter circuit is connected to a control evaluation circuit for controlling and evaluating the measurement of air mass flow, wherein at least one additional heating element and at least one additional temperature sensor are Is connected to a temperature control circuit for adjusting and / or controlling the temperature Tfix. With this type of configuration, a “temperature wall” can be formed around the sensor area of the hot film air mass meter by utilizing the force effect exerted on the surface fluid drop by the temperature gradient. For example, at least one additional temperature sensor can be connected to the control input of the temperature control circuit, and at least one additional heating element can be connected to a corresponding output of the temperature control circuit (possibly indirectly, for example via a current supply). Can be connected to). In this way, a defined temperature can be applied to a predetermined area of the measurement surface without depending on the operating state of the hot film air mass meter. Thereby, for example, environmental temperature effects are blocked from the sensor area, so that the sensor area always operates under the same thermal conditions. This avoids drift of the measurement signal.

  Furthermore, the “temperature wall” acts so that, for example, an oil drop that is moved to the sensor region by an air mass flow receives a counter force based on the above-described surface tension action, and is thereby moved away from the sensor region. The temperature gradient can be adjusted as desired, and this temperature gradient influences the temperature gradient of the oil droplet as expected and the oil droplet is moved away from the sensor area.

Here, in practice, it has been shown that it is particularly effective if at least one additional heating element and at least one additional temperature sensor at least partially border the sensor area.
Here, “partial” means that a pair of the first additional heating element and the first additional temperature sensor is arranged on the upstream side of the sensor region with respect to the main flow direction of the air mass flow. It should be understood that a pair of two additional heating elements and a second additional temperature sensor is disposed downstream of the sensor region with respect to the main flow direction of the air mass flow. In particular, this configuration can be symmetric with respect to the symmetry axis of a hot film air mass meter extending perpendicular to the main flow direction. Here, the additional heating element and the additional temperature sensor can be arranged symmetrically with respect to the symmetry axis in pairs. Other geometric configurations are possible, for example using additional temperature sensors and additional heating elements.

  As already indicated, the symmetrical configuration of the sensor chip is particularly advantageous. This particularly facilitates the evaluation of the measurement signal. This is because it is not necessary to apply a correction algorithm due to asymmetry to the measurement signal. However, other asymmetrical configurations are of course conceivable as well.

  In an advantageous symmetrical configuration, the measuring surface and the sensor surface have a substantially rectangular shape, the long sides of each rectangle being arranged substantially perpendicular to the main flow direction. In particular, the sensor area rectangle can be arranged in the measurement surface rectangle substantially symmetrically with respect to an axis of symmetry perpendicular to the main flow direction. The at least one additional heating element in this case preferably extends parallel to the side of the rectangle arranged perpendicular to the main flow direction. Here, “substantially” should be understood as deviations not exceeding 10 °, preferably not exceeding 5 °.

In particular, the sensor region is bordered by at least one additional heating element and at least one additional temperature sensor (ie at least upstream and / or downstream with respect to the main flow direction). It has proved advantageous if the temperature Tfix is adjusted to a predetermined value by means of at least one additional heating element at the location of at least one additional temperature sensor. For example, if at least one central heating element of the central hot film air mass meter circuit is operated at temperature Tmax and the land surface of the sensor chip has an average temperature To, it has proven advantageous to adjust the temperature Tfix as follows: did:
Tfix = To + k (Tmax−To)
Here, k is a Hebel coefficient, preferably taking a value of 0.1 to 0.7, particularly preferably 0.2 to 0.6, particularly preferably approximately 0.5. With this selection of the fixed temperature Tfix, if at least one additional heating element is approximately centered between the edge of the sensor area and the edge of the measurement area, the blocking of the sensor area will occur. It has been shown to be achieved particularly efficiently. The fixed temperature Tfix thus adjusted is usually slightly higher than the temperature that would be adjusted at this point without the use of an additional heating element, i.e. only with at least one central heating element. The temperature Tfix in this region is therefore adjusted by simply turning on / off at least one additional heating element. However, this fixed temperature Tfix is not high enough to significantly affect the measurement of the central hot film air mass meter circuit. However, it is also possible to adjust the temperature Tfix in other ways.

  One configuration of the above embodiment effectively avoids signal drift, especially due to contamination. The above configuration of the fluid film along the edge of the measurement surface can change the heat transfer as the hot film air mass meter operates. Accordingly, the temperature distribution of the measurement surface formed based on the operation of the at least one central heating element changes. This affects signal drift. By using a fixed temperature that is regulated by at least one additional heating element and at least one additional temperature sensor, this drift, in particular changes in temperature distribution due to contamination, are actively compensated. The signal quality of the proposed hot film air mass meter is therefore far superior to the devices known from the prior art.

  FIG. 1 shows the configuration of a sensor chip 110 of a hot film air mass meter corresponding to the prior art. The sensor chip 110 can be used, for example, in an intake pipe of an internal combustion engine or a bypass channel to the intake pipe of the internal combustion engine. A device of this kind is known, for example, from DE 19601791 A1. The sensor chip according to the configuration of FIG. 1 has a chip land with a land surface 112 in the drawing plane (only a part is shown). In this embodiment, it is assumed that the sensor chip 110 is a silicon sensor chip.

  Furthermore, the sensor chip 110 has a measurement area with a measurement surface 114 in the drawing plane. In this embodiment, the measuring surface 114 is configured as a rectangle 116, and the long pieces LM 118, 120 are perpendicular to the main flow direction 122 of the air mass flow. The short side IM of the rectangle 116 is indicated by reference numerals 124 and 126 and is arranged in parallel to the main flow direction 122.

  The sensor chip 110 has a heat transfer property of 0.5 to 2 W / mK in the region of the measurement surface 114, compared to the heat transfer property of the surrounding land is 156 W / mK. This can be achieved, for example, by making silicon porous in the region of the measurement surface 114.

  In the region of the measurement surface 114, the conductor path of the central hot film air mass meter circuit 128 is arranged. The conductor path 128 includes one central heating element 130 and two temperature sensors 132 and 134. Here, the temperature sensor 132 is disposed upstream of the central heating element 130, and the temperature sensor 134 is disposed downstream. The conductor track 128 defines a sensor area 136 at its outer dimensions at the measurement surface 114. The sensor region 136 is similarly configured as a rectangle 138 in this embodiment, and has long pieces 140 and 142 and short sides 144 and 146. The connection side short side 144 of the rectangle 138 is on the connection side short side 124 of the rectangle 116 of the measurement surface. The side length of the rectangle 138 of the sensor region 136 is indicated by Ls and Is in FIG.

  In the embodiment corresponding to the prior art of FIG. 1, the conductor path 128 of the central HFM circuit extends substantially to the outer rectangle 116 of the measurement surface 114. Typically, the long sides 118, 120 of the rectangle 116 have a length LM of about 1600 μm, and the short sides 124, 126 of the rectangle 116 have a length of IM = 450-500 μm. Here, the rectangle 138 of the sensor region 136 is configured to be slightly smaller, for example, LS is about 0.9 to 0.95 × LM, and IS is about 0.7 × IM.

  Further illustrated in FIG. 1 is the problem of oil droplets 148 collecting along the rectangle 116 of the measurement surface 114. Therefore, these oil droplets 148 exist in the immediate vicinity of the conductor path 128. For example, the oil droplet 148 reaches the conductor path 128 by a slight external force action caused by the air mass flow. Furthermore, the collection of the oil droplets 148 also changes the heat conductivity of the sensor chip 110 in the edge region of the rectangle 116 of the measurement surface 114. In particular, the oil drop 148 may increase the heat transfer at the transition between the measurement surface 114 and the land surface 112. This significantly affects the temperature distribution at the measurement surface 114. In addition, oil droplets 148 often form an adhesion to dust and soot. In addition, in many cases, an “oil wall” with a height of about 30 μm is formed in the edge region of the rectangle 116 of the measuring surface, which causes an air vortex in this region. And this air vortex calms down only after moving a predetermined area. This adds further error to the measurement signal. Both the thermal effect and the flow effect caused by the oil droplet 148 often work together and commonly change the measurement signal.

  In the upper region of FIG. 1, the temperature distribution is shown parallel to the main flow direction 122 of the measurement surface 114. Here, it is assumed that central heating element 130 is heated to temperature Tmax. The surrounding chip land having the land surface 112 has an environmental temperature To. Curves 150 and 152 in the upper region of FIG. 1 indicate the temperature distribution along the main flow direction 122 of the measurement surface 114. When there is no concentration of oil droplets 148 (curve 150, solid line), oil droplets 148 are obtained. Are collected (curve 152, broken line). Here, it can be seen that the temperature drops in the region of the temperature sensors 132 and 134 because the heat conductivity is increased by the oil droplets 148. Accordingly, the temperature sensors 132 and 134 measure a temperature lower by the absolute value ΔTmess than the measurement when there is no contamination of the oil droplets. This has negative effects in various ways. As a function, if a relatively low temperature is measured, a relatively large measurement error occurs. Another effect is that contamination variation due to oil droplets 148 causes the temperature drop in ΔTmes to vary. This causes a signal drift of the hot film air mass meter.

  FIG. 2 shows the configuration of the sensor chip 110 according to the present invention. Basically, the configuration of the sensor chip 110 corresponds to the configuration of the embodiment of the prior art shown in FIG. However, in the present invention of FIG. 2, the dimensions of the rectangles 116 and 138 of the measurement surface 114 or sensor area 136 are significantly different from the configuration of FIG. In this embodiment, the rectangle 138 of the sensor region 136 has a short side Is of 440 μm, whereas the short side of the rectangle 116 of the measurement region 114 has a length of about IM = 1500 μm. The lengths of the long sides of the rectangles 116 and 138 are LM = 1800 μm and Ls = 1600 μm. Accordingly, the area of rectangle 116 of measurement surface 114 is larger by a factor of 3.8 than the area of rectangle 138 of sensor area 136 in this advantageous embodiment. The total area ratio is preferably in the region from 1.5 to 4.5. The ratio to the short sides IM and Is is 3.4, and the ratio to the long sides LM and Ls is 1.1.

  As can be seen from the approximate scale representation of the oil drop 148 in FIG. It is further separated. It should be understood that “further” means that the distance between the oil drop 148 and the conductor track 128 is many times greater than the diameter of the oil drop 148. This definition may not apply in all cases, because in any case, discrete oil drops 148 may not be formed, but a continuous fluid film or fluid barrier may be formed.

  Through calculation and hydrodynamic considerations, the optimum spacing between the sensor region 136 (ie, the side 140 of the rectangle 138) and the boundary of the measurement surface 114 (ie, the boundary of the measurement surface facing the tipland, eg, the side 118 of the rectangle 116). Was found to be about 540 μm. This is approximately satisfied by the geometric length.

  The sensor chip 110 of the present invention according to the embodiment of FIG. 2 has another conductor track on the measurement surface 114 outside the sensor area 136 in addition to the conductor path 128 of the central HFM circuit in the sensor area 136. Furthermore, the measuring surface 114 has two additional heating elements 154 and 156 and two additional temperature sensors 158 and 160. Additional heating elements 154, 156 and additional temperature sensors 158, 160 are disposed substantially parallel to conductor path 128 of the central HFM circuit. These additional heating elements 154, 156 and additional temperature sensors 158, 160 extend perpendicular to the main flow direction, but extend over the conductor path 128 to almost the short side 126 opposite the terminal of the rectangle 116. It is stretched. As shown schematically in FIG. 2, the conductor path 128 of the central HFM circuit is connected to a control evaluation circuit 162 for controlling and evaluating air mass flow measurements. Such a control evaluation circuit 162 is known from the prior art. In contrast, the additional heating elements 154 and 156 and the additional temperature sensors 158 and 160 are connected to the temperature control circuit 164.

  The upper region of FIG. 2 shows the temperature course on the measurement surface 114 of the sensor chip 110 when the air mass flow is measured as in FIG. Again, the dashed curve 152 indicates the case of measurement when contaminated by the oil drop 148, and the solid line 150 indicates the case of measurement without contamination.

  Here, the temperature control circuit 164 controls the temperature of the additional temperature sensors 158 and 160 by the additional heating elements 154 and 156 according to the present invention so that the temperature remains at the predetermined value Tfix. Advantageously, this constant temperature Tfix is greater than the temperature that would be adjusted at the additional temperature sensors 158, 160 when the additional heating elements 154, 156 are shut off and only the central heating element 130 is driven. Is also expensive. This ensures that only the additional heating elements 154, 156 can control the temperature to the value Tfix. As mentioned above, in practice it has been found that the temperature value for Tfix is advantageously higher than the environmental temperature To by about 0.5 of the difference between the environmental temperature To and the operating temperature Tmax of the central heating element 130. . Typically, the environmental temperature To is about 20 ° C. and the operating temperature Tmax is about 160 ° C. Accordingly, the fixed temperature Tfix is preferably selected to be about 90 ° C. and controlled to this value.

  As shown in the temperature course in the upper region of FIG. 2, the contamination by the oil droplets 148 is only caused by the upstream temperature course of the temperature sensor 158 on the upstream side and the downstream temperature course of the temperature sensor 160 on the downstream side. Influencing (see curve 150, 152 course). The measured temperature Tmess of the temperature sensors 132 and 134 is hardly affected by oil contamination. Thus, the inventive configuration of sensor chip 110 not only eliminates oil contamination 158 in areas away from sensor area 136, but also provides additional heating elements 154, 156 and additional temperature sensors 158, 160. A “temperature barrier” is formed around the sensor region 136. This makes air mass measurement substantially unaffected by oil contamination. Thus, the configuration of the present invention according to FIG. 2 almost eliminates contamination effects and signal drift due to oil droplets 148.

  Finally, it should be noted that the configuration of the sensor chip 110 according to the embodiment of FIGS. 1 and 2 is symmetric with respect to the symmetry line 166. This symmetry line 166 is arranged perpendicular to the main flow direction 122 of the air mass flow. Thus, by arranging the conductor path 128 and the additional heating elements 154 and 156 and the additional temperature sensors 158 and 160 symmetrically, the evaluation of the measurement signal of the hot film air mass meter is remarkably facilitated. In this case, the final correction of the measurement signal based on the asymmetry artifact can be omitted. This facilitates evaluation. However, of course, it is also conceivable that the sensor chip 110 and the measuring surface 114 are configured asymmetrically.

FIG. 1 is a diagram showing the configuration of the measurement surface of a sensor chip corresponding to the prior art. FIG. 2 shows an advantageous embodiment of the configuration according to the invention of a sensor chip of a hot film air mass meter.

Explanation of symbols

110 Sensor chip 112 Land surface 114 Measurement surface 116 Measurement surface rectangle 118 Long side of rectangle 116 120 Long side of rectangle 116 122 Main flow direction 124 Short side of rectangle 116 126 Short side of rectangle 116 128 Central hot film air mass meter Conductor path 130 Central heating element 132 Temperature sensor 134 Temperature sensor 136 Sensor area 138 Rectangle of sensor area 136 140 Long side of rectangle 138 142 Long side of rectangle 138 144 Short side of rectangle 138 146 Short side of rectangle 138 148 Oil drop 150 Temperature course without oil contamination 152 Temperature course with oil contamination 154 Additional heating element 156 Additional heating element 158 Additional temperature sensor 160 Additional temperature sensor 162 Control evaluation circuit 164 Temperature control circuit 166 Symmetry axis

Claims (8)

A hot film air mass meter for measuring an air mass flow flowing in a main flow direction (122), in particular an air mass flow in an intake pipe of an internal combustion engine,
The hot film air mass meter has a sensor chip (110) with a chip surface through which air mass flow can flow,
The chip surface has a measurement surface (114) and a land surface (112),
The sensor chip (110) has a heat transfer in the region of the measurement surface (114) that is at least an order of magnitude less than the region of the land surface (112),
Mounted on the measurement surface (114) is a conductor path (130, 132, 134) of a central hot film air mass meter circuit comprising at least one central heating element (130) and at least one temperature sensor (132, 134). And
In a hot film air mass meter of the type that defines the sensor area (136) of the measurement surface (114), the outer dimensions of the conductor path (130, 132, 134) of the central hot film air mass meter circuit,
In addition, at least one additional heating element (154, 156) and at least one additional temperature sensor (158, 160) are arranged on the measuring surface (114) outside the sensor area (136). Features a hot film air mass meter. The hot film air mass meter according to claim 1,
The conductor path (130, 132, 134) of the central hot film air mass meter circuit is connected to a control evaluation circuit (162) for controlling and evaluating the measurement of air mass flow,
At least one additional heating element (154, 156) and at least one additional temperature sensor (158, 160) are connected to a temperature control circuit (164) for adjusting and / or controlling to a predetermined temperature Tfix. Is a hot film air mass meter. In the hot film air mass meter according to claim 1 or 2,
The control evaluation circuit (162) is configured to control the temperature of the at least one central heating element (130) to a temperature Tfix during operation of the hot film air mass meter,
The temperature control circuit (164) adjusts the temperature Tfix at the location of the at least one additional temperature sensor (158, 160) to the value To + k (Tmax-To) by the at least one additional heating element (154, 156). Is configured as
Where To is the average temperature of the land surface (112), k is a value between 0.1 and 0.7, preferably between 0.2 and 0.6, particularly preferably approximately 0.5. There is a hot film air mass meter. In the hot film air mass meter according to any one of claims 1 to 3,
The measurement surface (114) and sensor area (136) have a substantially rectangular shape (116, 138);
A hot film air mass meter in which the long side (118, 120, 140, 142) of each rectangle (116, 138) is arranged substantially perpendicular to the main flow direction (122). In the hot film air mass meter according to any one of claims 1 to 4,
The rectangle (138) of the sensor area (136) is within the rectangle (116) of the measurement surface (114) substantially symmetrically with respect to the symmetry axis (166) perpendicular to the main flow direction (122). Arranged, hot film air mass meter. In the hot film air mass meter according to any one of claims 1 to 5,
The sensor area (136) is substantially rectangular (138) shaped,
The rectangle (138) has two sides (140, 142) arranged perpendicular to the main flow direction (122),
The hot film, wherein the at least one additional heating element (154, 156) extends substantially parallel to the side (154, 156) arranged perpendicular to the main flow direction (122) Air mass meter. In the hot film air mass meter according to any one of claims 1 to 6,
At least one first additional heating element (154) and at least one first additional temperature sensor (158) are arranged upstream of the sensor area (136) relative to the main flow direction (122). ,
At least one second additional heating element (156) and at least one second additional temperature sensor (160) are disposed downstream of the sensor region (136) relative to the main flow direction (122). , Hot film air mass meter. In the hot film air mass meter according to any one of claims 1 to 7,
The hot film air mass meter has an axis of symmetry (166) arranged perpendicular to the main flow direction (122),
The hot film air mass meter, wherein the additional heating element (154, 156) and the additional temperature sensor (158, 160) are each paired and arranged symmetrically with respect to the axis of symmetry (166).

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