JP2006349688A - Hot air mass meter reduced in vulnerability of 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: The measurement surface (114) and the sensor region (136) are representing substantially rectangular geometries (116, 138), and the longer side of each rectangular geometry (116 or 138) is essentially disposed perpendicular to the main flow direction (122). <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. In particular, the proposed hot film air mass meter is suitable for the measurement of air mass flow with flow rates from 0 to 60 m / s.

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 present invention relates to a hot film air mass meter of a type in which a conductor path of a central hot film air mass meter is attached to a 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 especially the case when the overpressure present in the crank casing after the internal combustion engine is shut off is exhausted into the intake pipe of the internal combustion engine by crank casing ventilation. In this case, oil vapor or oil mist is frequently introduced together.

  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. As a result, the droplet moves from the lower surface tension to the higher surface tension. 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. In addition, the fluid wall can dissipate at the edge of the membrane and when the temperature gradient associated therewith disappears, which can cause oil to flow to the membrane.
DE19601791A1 DE10111840C2 V. G. Levic, “Physicochemical Hydrodynamics”, Prentice-Hall, N .; J. et al. 1962, pp. 373-380

  The object of the present invention is to provide a hot film air mass meter which can avoid the disadvantages of the devices known from the prior art, in particular for measuring the air mass flow flowing in the main flow direction in the intake pipe of an internal combustion engine. Is to provide. This hot film air mass meter is optimized by hydrodynamic calculations and corresponding experiments, especially for the measurement of air mass flow with flow rates between 0 and 60 m / s.

This object is achieved in a hot film air mass meter of the type mentioned at the beginning according to the invention,
The measurement surface and the sensor area have a substantially rectangular shape;
The long side of each rectangle is arranged and solved so as to be arranged substantially perpendicular to the main flow direction.

  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. For example, this can be a central heating element surrounded by two temperature sensors as described above. Other geometric shapes are also conceivable.

  In particular, the production of measuring surfaces, for example membranes or porous regions, with corresponding semiconductor technology methods, is actually cumbersome and expensive. Furthermore, the measuring surface is usually vulnerable to obstacles. The membrane is easily damaged. Thus, in a normal hot film air mass meter, the area of the measurement surface is minimized and the measurement surface is almost completely filled with conductor tracks. Usable measuring surfaces are thereby used optimally spatially.

  However, the basic technical idea of the present invention is based on the knowledge that, as mentioned above, fluid contamination due to temperature gradients adjusted during operation occurs at the transition between the measuring surface and the land surface. If this transition is located more closely adjacent to the conductor path of the central hot film air mass meter circuit, contaminants, such as oil or other fluids, can more easily reach the conductor path from this transition. The measurement signal of the film air mass meter will drift.

  The basic technical idea is therefore to place this transition between the measuring surface and the land surface as far as possible from the conductor path of the central hot film air mass meter. There are also significant disadvantages associated with the advantages achieved thereby that the contamination of the central hot film air mass meter circuit is reduced. This disadvantage is associated, inter alia, with an increase in the sensitivity of the measurement surface due to the enlargement of the measurement surface, and thus an increased failure vulnerability of the hot film air mass meter. Further, the usable area on the chip surface for the electric line and the electronic circuit element is also reduced in this way. Furthermore, if the measuring surface expands too large compared to the central hot film air mass meter circuit, the cleaning action may possibly be reversed. For example, an oil flow may cause oil droplets to separate at the transition between the measurement surface and the land surface. The oil droplets are pressed against the chip surface again after a predetermined “flight stroke” on the chip surface. This may cause oil drops to be carried back to the central hot film air mass meter circuit by the air flow, even if the temperature gradient is located sufficiently away from the central hot film air mass meter circuit.

  Therefore, the sensor chip geometry must be carefully optimized. Corresponding optimization calculations were performed for flow rates between 0 and 60 m / s. Correspondingly, the hot film air mass meter of the present invention has a chip surface divided in three. In addition to the land surface, a measurement surface is arranged on the sensor chip as described above. The measurement surface further has a sensor area. This sensor area is defined by the outer dimensions of the conductor path of the central hot film air mass meter circuit. Here, the line to the conductor track can usually be ignored and need not be considered. In many cases the sensor area has, for example, a rectangular geometry. Depending on the optimization calculations and experimental results, the sensor area of the proposed hot film air mass meter of the present invention has an overall measurement surface with a factor of 1.5 to 4.5, preferably 2 to 4, particularly preferably. Is configured to be larger than the sensor region by a factor of 3. With this configuration, the contamination vulnerability of the hot film air mass meter is minimized with respect to the flow velocity. This minimizes the signal drift of the hot film air mass meter, which significantly improves the air mass flow measurement and thus provides improved engine control.

  The configuration of the hot film air mass meter of the present invention can be advantageously improved in various ways. For example, for reasons of symmetry that favors the measurement electronics, it is advantageous if the measurement surface and the sensor area have a substantially rectangular shape. Here, the long side of each rectangle is preferably arranged perpendicular to the main flow direction. For example, the sensor area rectangles can be arranged substantially symmetrically within the measurement surface rectangle. For example, the measurement surface rectangle and the sensor region rectangle have the same axis of symmetry, preferably perpendicular to the main flow direction.

  The sensor area perpendicular to the main flow direction should use the measuring surface substantially completely. This means, for example, that the sensor area has a maximum extent perpendicular to the main flow direction (eg the long side of the rectangle that limits the sensor area), which is the maximum extent of the measurement surface (eg the measurement surface). 80% to 100% of the long side of the rectangle.

  If a rectangular measuring surface and a rectangular sensor area are used, the rectangular short side of the measuring surface (ie parallel to the main flow direction) has a factor of 1.5 to 4.5, preferably a factor of 2 To 4, particularly preferably a factor of 3 longer than the rectangular short side of the sensor area (also parallel to the main flow direction). In particular, it has proved advantageous in terms of manufacturing technology if the rectangular short side of the sensor area has a length of between 250 and 640 μm, preferably between 350 and 550 μm, particularly preferably of 440 μm. The rectangular short side of the measuring surface has a length between 1100 and 1900 μm, preferably between 1300 and 1700 μm, particularly preferably 1500 μm.

  Based on calculations and hydrodynamic considerations, the optimal spacing between the sensor area (ie, the boundary upstream of the sensor area) and the measurement surface boundary (ie, the upstream boundary of the measurement surface toward the tipland) is about 540 μm. It turned out to be. This is approximately satisfied by the geometric length.

  In the configuration of the invention described above, the measurement surface remains rarely used outside the sensor area. However, advantageous embodiments of hot film air mass meters that additionally use a measuring surface that has not been used so far are also conceivable. This embodiment has, for example, at least one additional heating element and at least one additional temperature sensor in this area of the measuring surface outside the sensor area. For example, this means that 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 in the sensor area of the hot film air mass meter. Done. The at least one additional heating element and the at least one additional temperature sensor arranged on the measurement surface outside the sensor area advantageously regulate and / or control the predetermined temperature in the area of the at least one additional heating element Connected to a temperature control circuit for

  In this way, for example, a constant temperature is adjusted at a predetermined interval from the sensor area on the measurement surface outside the sensor area. This temperature is only slightly changed by the temperature control circuit during operation of the hot film air mass meter. Here, a great advantage of the arrangement in which at least one additional heating element is arranged on the measuring surface (not on the chip land) is that the measuring surface has a small heat transfer. This means that the heat provided to the measurement surface by the additional heating element is not again discharged to the surrounding sensor chip in the same way, but a constant temperature is maintained without significantly heating the surrounding sensor chip. Ensure that it can be maintained.

  The constant “temperature barrier” around the sensor area, which can be adjusted in this way, makes the hot film air mass meter much more robust against temperature drift. In particular, the action of the fluid barrier occurring at the transition between the measuring surface and the tip land is blocked from the original sensor area. Therefore, the change in heat transfer at the measurement surface edge, easily caused by the fluid film or fluid barrier that collects, only has a very greatly prolonged effect on the temperature distribution in the sensor area. This greatly improves the reliability of air mass measurements with the hot film air mass meter of the present invention, is robust against failures, and is subject to very little drift.

  For example, as described above, the sensor region can be configured in a substantially rectangular shape. The rectangle has two sides arranged perpendicular to the main flow direction and at least one additional heating element is substantially parallel to the side arranged perpendicular to the main flow direction. Can stretch. Here, “substantially” should be understood as a deviation not exceeding 5 °, for example. For example, the at least one first additional heating element and the first additional temperature sensor are arranged upstream of the sensor region with respect to the main flow direction, and the at least one second additional heating element and at least one The second temperature sensor is disposed on the downstream side of the sensor region with respect to the main flow direction. In this way the sensor area is shielded from the influence of obstacles on both sides. Alternatively or additionally, the at least one additional heating element can be configured around the sensor area as a frame (fully closed or partially open). In this way, the shielding efficiency is additionally increased.

  The present invention will be described in detail below with reference to the drawings.

  FIG. 1 shows (schematically) 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. 1A 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 0.1 to 2 W / mK in the region of the measurement surface 114, compared to the heat transfer property of the surrounding lands 156 W / mK. This can be achieved by making the silicon porous in the region of the measurement surface 114. Alternatively, a sensor membrane having a heat transfer property equivalent to that of ambient air of 0.026 W / mK can be used.

  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. Conductor track 128 limits sensor area 136 at its outer dimensions at 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. 1A.

  In an embodiment corresponding to the prior art of FIG. 1A, 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. 1A 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. 1A, 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. 1A show the temperature distribution along the main flow direction 122 of the measurement surface 114. When there is no concentration of oil drops 148 (curve 150, solid line), oil drops 148 Are collected (curve 152, broken line). Here, it can be seen that the heat drop is enhanced by the oil droplets 148 and / or that the temperature drops in the region of the temperature sensors 132 and 134 due to the above-described flow effect. Accordingly, the temperature sensor 132.134 measures a temperature that is 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. 1B 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. 1A. However, in the present invention of FIG. 1B, the dimensions of rectangles 116 and 138 of measurement surface 114 or sensor area 136 are significantly different from the configuration of FIG. 1A. In this embodiment, the rectangle 138 of the sensor region 136 has a short side ls of 440 μm, whereas the short side of the rectangle 116 of the measurement region 114 has a length of 1M = 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 ratio to the short sides lM, ls is 3.4, and the ratio to the long sides LM, LS is 1.1.

  As can be seen from the approximately scaled representation of the oil drop 148 in FIG. 1B, in this embodiment, the oil drop 148 moves away from the sensor area 136 and hence the conductor track 128 at the transition between the measurement area 114 and the land surface 112. 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.

  Further, in the upper part of FIG. 1B, the temperature course when the central heating element 130 is heated in a predetermined manner is shown. Again, the solid line curve 150 represents the case where there is no oil contamination, and the broken line curve 152 represents the temperature course when there is contamination due to the oil droplets 148. It is clear that the curves 150 and 152 differ only slightly in this embodiment. This is the region of the temperature sensors 132 and 134, and the measurement difference ΔTmes between the temperature measurement in the absence of oil contamination and the temperature measurement in the presence of oil contamination is much smaller than in the case of FIG. 1A corresponding to the prior art. Because. The measurement difference depending on the operating point is reduced by about 80 to 90%. This is because the temperature measured by the temperature sensors 132 and 134 is higher than in the case of FIG. 1A, so that the relative measurement error is reduced as a whole. Furthermore, the signal drift of the hot film air mass meter due to contamination is also greatly reduced. Therefore, the reliability of the measurement signal of the hot film air mass meter and the long-term stability of this signal are greatly improved by the configuration of FIG. 1B. Signal drift is also greatly reduced.

  FIG. 2 shows a particularly advantageous refinement of the sensor chip 110 of the hot film air mass meter. The sensor chip 110 is configured substantially as in the embodiment of FIG. 1B. That is, the sensor chip 110 again has a measurement surface 114 with a sensor area 136 with a conductor path 128 of the central HFM circuit. The dimensional configuration of the rectangle 116 of the measurement surfaces 114, 138 in the sensor area 136 is the same in this embodiment of FIG. 2 as in the embodiment of FIG. 1B.

  However, in addition to the conductor path 128 of the central HFM circuit in the sensor area 136, another conductor path is located on the measurement surface 114 outside the sensor area 136 in the embodiment of FIG. 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. 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. 1B. 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 so as to remain at the predetermined value Tfix. Ideally, this constant temperature Tfix will be adjusted at the location of 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. Higher than. This ensures that only the additional heating elements 154, 156 can control the temperature to the value Tfix.

As shown in the temperature course in the upper region of FIG. 2, the contamination due to the oil droplets 148 is caused only by the temperature course on the upstream side of the temperature sensor 158 on the upstream side and the temperature course on the downstream side of the temperature sensor 160 on the downstream side. Influencing (see the course of curves 152, 154). 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. 1B 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. 1A is a diagram showing a configuration of a measurement surface of a sensor chip corresponding to the prior art. FIG. 1B shows an advantageous embodiment of the configuration according to the invention of a sensor chip. FIG. 2 shows an advantageous second embodiment of the configuration according to the invention of the 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 (10)

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),
In a hot film air mass meter of the type in which a conductor surface (128) of a central hot film air mass meter is attached to the measurement surface (114),
The outer dimension of the conductor path (128) of the central hot film air mass meter defines the sensor area (136) of the measurement surface (114);
Hot film air mass meter characterized in that the measuring surface (114) is larger than the sensor area (136) by a factor of 1.5 to 4.5, preferably a factor of 2 to 4, particularly preferably a factor of 3. . The hot film air mass meter according to claim 1,
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 of each rectangle (116, 138) is arranged substantially perpendicular to the main flow direction (122). In the hot film air mass meter according to claim 1 or 2,
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 3,
The short side (124, 126) of the rectangle (116) of the measuring surface (114) has a factor of 1.5 to 4.5, preferably a factor of 2 to 4, particularly preferably a factor of 3 of the sensor area (136). A hot film air mass meter that is longer than the short sides (144, 146) of the rectangle (138). In the hot film air mass meter according to any one of claims 1 to 4,
The short side (144, 146) of the rectangle (138) of the sensor area (136) has a length lS of between 250 and 640 μm, preferably between 350 and 550 μm, particularly preferably 440 μm,
The short side (124, 126) of the rectangle (116) of the sensor area (114) has a length of 1M between 1100 and 1900 μm, preferably between 1300 and 1700 μm, particularly preferably 1500 μm. Mass meter. In the hot film air mass meter according to any one of claims 1 to 5,
The sensor area (136) is perpendicular to the main flow direction (122) and is 80% to 100% of the maximum spread LS of the measurement surface (114) perpendicular to the main flow direction (122) LS. A hot film air mass meter. In the hot film air mass meter according to any one of claims 1 to 6,
Having at least one additional heating element (154, 156) and at least one additional temperature sensor (158, 160);
A hot film air mass meter, wherein at least one additional heating element (154, 156) and at least one additional temperature sensor (158, 160) are located on the measurement surface (114) outside the sensor area (136) . The hot film air mass meter according to claim 7,
The conductor path (128) of the central hot film air mass meter circuit is connected to a control evaluation circuit (162) for controlling and evaluating air mass flow measurements;
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. The hot film air mass meter according to claim 7 or 8,
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 sides (140, 142) arranged perpendicular to the main flow direction (122) Air mass meter. In the hot film air mass meter according to any one of claims 7 to 9,
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.

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