JP4909561B2 - Heating resistor type air flow measuring device - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating resistor type air flow rate measuring device used for measuring an air flow rate sucked into an internal combustion engine for automobiles, and in particular, to reduce an air flow measurement error due to dust or the like sucked together with air in an intake pipe. It is invention regarding.

  A heating resistor type air flow rate measuring device is known as a flow rate measuring technique for an internal combustion engine. This is based on the fact that the amount of heat taken away by the heating resistor increases monotonously with the inflow rate, and since it can directly measure the mass flow rate, it is widely used especially as an air-fuel ratio control flow meter for automobiles. Yes. In Patent Document 1, a bypass for providing a detour portion on the upstream side of the heating resistor and separating dust and air by centrifugal force is known as a known technique.

  Further, there is Patent Document 2 as a known technique closest to the configuration of the present invention. This is an improvement in the responsiveness by arranging a long heating resistor obliquely in a limited space in the sub air passage.

JP 2004-37131 A Japanese Examined Patent Publication No. 6-17809

  The heating resistor type air flow measuring device is attached to a part of the intake duct of the vehicle and has a role of measuring the intake air flow rate. The intake air flow of a vehicle usually flows in conjunction with the accelerator, and the amount of air sucked into the duct increases as the amount of depression of the accelerator increases. When the amount of intake air increases, not only air but also dust floating in the air, dust blown up by a tire of a vehicle traveling ahead, and the like are sucked together with air. Since the heating resistor is heated, it is generally considered that dust does not easily adhere to it. However, depending on the type of dust and the amount of flying dust, adhesion of dust is recognized little by little over time. If dust adheres to the heating resistor part, which is the flow rate detection unit of the heating resistor type air flow measuring device, the amount of heat released from the heating resistor changes, resulting in a measurement error of the heating resistor type air flow measuring device.

  Dust and the like can be captured by the air filter in the air cleaner, but depending on the size of the dust, the dust passes through the air filter and enters the engine. The particle size of the dust that can be captured by the air filter is generally about 10 μm, and if the particle size is smaller than that, it easily passes through the air filter.

  In recent years, especially in diesel engines, exhaust gas has been cleaned, and the emission of soot (carbon) in a size that can be seen with the naked eye has been reduced. However, due to atomization at the time of fuel injection and the like, soot with fine particle diameters that cannot be discerned visually has been discharged. These particles are several tens of nanometers, and it has recently been taken up as a problem that wrinkles of this nanoparticle diameter adhere to the heating resistor for the reasons described above.

  Because of the fineness of the soot with a nanoparticle size, it deposits at a higher density when attached, compared to the soot so far, and its deposition power is very strong. In the case of conventional soot, the density at the time of deposition is low, so the deposition force is weak. For example, the deposit may fall due to engine vibration, etc., and the change in the heat dissipation amount of the heating resistor returns to the initial state. There was also. However, it is difficult for the soot deposited at high density to drop due to engine vibration, etc., compared to the conventional soot, so that soot remains accumulated on the heating resistor indefinitely, and the amount of heat released remains unchanged. turn into. In addition, since the soot having a nanoparticle diameter is very light, there is a problem that the effect of separating dust (soot) by centrifugal separation which is effective in the prior art cannot be sufficiently exhibited.

  In order to respond to this problem, attention is paid to the heat dissipation surface of the heating resistor, the air flow, and the collision angle of dust, and improvements are made.

  First, the heat radiation surface of the heating resistor is inclined with respect to the air flow. This eliminates the water stop area (area where the air flow stays) on the heat radiating surface, and further tilting increases the shear stress due to the flow on the heat generating surface. Power works. For this reason, since an air flow always occurs on the heat radiating surface of the heating resistor, it is difficult for dust to adhere to it. The tighter the tilt angle, the less dust adheres to the heat dissipation surface. However, the surface area that the air is exposed to decreases, and the sensitivity to the flow velocity (flow rate) decreases, resulting in poor measurement accuracy as a flow meter. Resulting in. For this reason, there is a limit to the angle of inclination, and at the same time, there is a limit to preventing the adhesion of dust.

  For this reason, the measurement accuracy of the flowmeter and the reduction of dust adhesion are both achieved by providing a difference between the angle of air contact and the angle of dust collision. This is achieved, for example, by placing the heating resistor tilted after the bending vertex of the bending path. Even in the middle of a curved passage, even if the weight is light, dust flows in the auxiliary air passage in the direction separated by the centrifugal force to the outside of the curved portion. For this reason, the angle of the collision between the heat generating resistor and the heat radiation surface and the angle of the air flow direction can be changed by the angle difference from the air flow direction caused by the centrifugal force. In other words, while maintaining the measurement accuracy of the flow meter, the air flow makes it possible to make dust more difficult to adhere by tightening the angle at which the dust collides with the heat radiating surface of the heating resistor.

  With the above configuration, it is possible to reduce the adhesion of dust to the heating resistor. In particular, it becomes possible to reduce the amount of change in characteristics over time of the heating resistor type air flow measuring device due to the adhesion of carbon with a nanoparticle diameter, which will be a problem in future diesel engines and the like. As a result, it is possible to maintain the fuel control of the engine with high accuracy for a long time, and it is possible to send a clean vehicle of exhaust gas to the market for a long time.

  The present invention reduces an air flow measurement error due to a liquid such as water sucked together with air into an intake pipe of a heating resistor type air flow measuring device used for measuring an air flow taken into an internal combustion engine for an automobile. It was devised as a method.

  Embodiments of the present invention will be described in detail with reference to the following drawings.

  First, the operation principle of the heating resistor type air flow measuring device will be described. FIG. 6 is a schematic circuit diagram of a heating resistor type air flow rate measuring device. The driving circuit of the heating resistor type air flow measuring device is roughly divided into a bridge circuit and a feedback circuit. A heating resistor 3RH for measuring the intake air flow rate and a temperature sensing resistor 4RC and R10, R11 for compensating the intake air temperature are combined to form a bridge circuit. A heating current Ih is supplied to the heating resistor 3RH so as to maintain a constant temperature difference between the temperature resistors 4RC, and an output signal V2 corresponding to the air flow rate is output. That is, when the flow rate is high, a large amount of heat is taken from the heating resistor 3RH, so that a large amount of heating current Ih flows. On the other hand, when the flow rate is low, the amount of heat taken away from the heating resistor Rh is small, so that the heating current can be reduced.

  FIG. 7 is a cross-sectional view showing an example of a heating resistance type air flow meter, and FIG. 8 is an external view as viewed from the upstream side (left side).

  Components of the heating resistor type air flow rate measuring device include a housing member 1 containing a circuit board 2 constituting a driving circuit, a sub air passage constituent member 10 formed by a non-conductive member, and the like. 10, a heating resistor 3 for detecting the air flow rate 3 and a temperature sensitive resistor 4 for compensating the intake air temperature are electrically connected to the circuit board 2 via a support 5 made of a conductive member. The housing, the circuit board, the auxiliary air passage, the heating resistor, the temperature sensing resistor, and the like are arranged as an integrated module of the heating resistor type air flow measuring device. Further, a hole 25 is formed in the wall surface of the main air passage constituting member 20 constituting the intake pipe line, and a sub air passage portion of the heating resistor type air flow rate measuring device is inserted from the outside through the hole 25 to make a sub The wall surface of the air passage constituting member and the housing member 1 are fixed with screws 7 or the like so as to maintain the mechanical strength. Moreover, the sealing material 6 is attached between the auxiliary air passage constituting member 10 and the main air passage constituting member, and the airtightness between the inside and outside of the intake pipe is maintained.

  The heating resistor 3RH installed in the auxiliary air passage has a shape as shown in FIG. 3, for example, a platinum bobbin wound around a cylindrical bobbin made of a heat-resistant insulating material such as alumina, or a platinum film. Is vapor-deposited, and both ends are electrically connected through a lead material and a support material composed of a conductive member, and at the same time, mechanical fixing is performed. In addition, the platinum wire is coated with a glass material, etc. to improve the corrosion resistance, and at the same time, the surface unevenness is eliminated to minimize the adhesion of foreign matters such as dust. .

  Next, a change in characteristics when the heating resistor is soiled will be described. In the case of a bobbin-like heating resistor as shown in FIG. 4, heat generation is most promoted on the front surface where the air hits, and heat generation on this front surface becomes dominant particularly at a high flow rate. On the other hand, since the air flow is stagnant at the point A shown in the figure, it is a position where the shearing force due to the air flow is the weakest and also a place where dust is likely to adhere. That is, when dust or the like enters the intake air and adheres to the point A in the figure, dust accumulates around the point A as a base point, and eventually adheres to a triangular mountain shape. For this reason, since the part with the largest amount of heat generation is covered with dust, the amount of heat generation decreases, and the characteristic change amount shows a negative characteristic change. If the horizontal axis is the flow velocity and the vertical axis is the characteristic change amount, as shown in FIG. 5, the characteristic change is a downward-sloping characteristic that becomes negative as the flow velocity increases, and it is detected that the air amount is smaller than the actual air amount. To do. For this reason, when this phenomenon occurs in an internal combustion engine, less fuel is injected than the actual amount of air, the air-fuel ratio becomes thin, the combustion temperature rises, and in the worst case, problems such as engine burning It will cause.

Next, the specific sub air passage and the installation position of the heating resistor of the present invention will be described with reference to FIG. The sub air passage 120 disposed in the main air passage 101 constituted by the main air passage constituting member 100 is formed by the sub air passage constituting member 102, and the sub air passage inlet 121, the curved passage 122, and the curved downstream straight portion 123 are formed. , The auxiliary air passage outlet 124. Further, the curved passage 122 has a shape that makes a detour of about 180 ° from the downstream side to the upstream side of the main air passage, and the most downstream side of the bypass portion becomes the apex 125 of the curved passage. The heating resistor 110 serving as a flow rate measuring unit is installed at the end of the bent passage or near the starting point of the bent downstream straight portion 123, and is integrated with the lead material 111 via the support member 103 to drive a circuit (not shown). Are electrically connected. Although the temperature sensitive resistor that constitutes a part of the drive circuit should be illustrated in the original, the position of the temperature sensitive resistor is not particularly important in the present invention. It is omitted in this illustration as it should be.

A configuration in the vicinity of the heating resistor 110 and a streamline in the sub air passage 120 are shown in FIG. A streamline through which air flows indicates a streamline direction substantially along the shape of the passage, and both the heating resistor 110 and the lead material 111 are attached to be inclined with respect to the streamline of air in the sub air passage. On the other hand, the dust 150 that has flowed into the auxiliary air passage 120 together with the air becomes a streamline that tends to travel outside the bend due to centrifugal force when passing through the bend passage 122 of the sub air passage 120. For this reason, air strikes the heating resistor 110 at an angle that is substantially inclined by the heating resistor 110, but the angle that the dust strikes becomes even tighter. In other words, the dust 150 tries to collide with the heat generating resistor 110 at an angle close to parallel to the heat radiating surface of the heat generating resistor 110, so that the energy at the time of collision is dispersed and hardly adheres to the heat generating resistor 110. Since the flow flows along the heat radiating surface of the heat generating resistor 110, a shearing stress that peels off the dust to be attached acts and makes it difficult to attach the dust. In this embodiment, the heating resistor has been described at the position where it is installed at the downstream end of the curved passage 122. However, if the heating resistor is too far away from the downstream end of the curved passage, the effect cannot be exhibited sufficiently. As a range where the effect can be expected, the effect can be expected as long as the distance is within the radius of the curved path from the downstream end. In addition, although a cylindrical bobbin-shaped heating resistor is taken as an example this time, the same effect can be obtained even if it is a structure in which a resistor is deposited on a plate material.

  Needless to say, the same effect can be obtained by installing a heating resistor in the middle of the bending passage 122. However, in order to fully exhibit the effect of centrifugal separation, it is desirable that it is downstream of the bending vertex 125 of the bending passage 122.

  Finally, FIG. 9 shows an embodiment in which the product of the present invention is applied to an electronic fuel injection type internal combustion engine. The intake air 67 sucked from the air cleaner 54 passes through the intake manifold 59 including the body 53, the suction duct 55, the throttle body 58, and the injector 60 to which fuel is supplied in the heating resistance type air flow rate measuring device, and then enters the engine cylinder 62. Inhaled. On the other hand, the gas 63 generated in the engine cylinder is discharged through the exhaust manifold 64.

  The air flow rate signal output from the circuit module 52 of the heating resistance air flow rate measuring device, the intake air temperature signal from the temperature sensor, the throttle valve angle signal output from the throttle angle sensor 57, and the oxygen concentration provided in the exhaust manifold 64 The control unit 66 for inputting the oxygen concentration signal output from the meter 65 and the engine rotational speed signal output from the engine rotational speed meter 61, etc., sequentially calculates these signals to obtain the optimum fuel injection amount and idle air. The control valve opening is obtained, and the injector 60 and the idle air control valve 56 are controlled using the values.

  Engine control in a vehicle is the main use, but it can be used for control using a diesel engine such as a ship or a generator.

The longitudinal cross-sectional view of the subchannel | path which shows one Example of this invention. FIG. 2 is a detailed view of the vicinity of a heating resistor in FIG. 1. The structure of a heating resistor is shown. The figure which shows the dust accumulation on a heating resistor. The characteristic change when dust adheres to the heating resistor is shown. Approximate drive circuit for heating resistor type air flow measuring device. 1 is a cross-sectional view of a typical heating resistor type air flow measuring device. The figure which looked at FIG. 7 from the upstream. The system schematic using a heating resistor type air flow measuring device.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Housing member, 2 ... Circuit board, 3,110 ... Heat generating resistor, 4 ... Temperature-sensitive resistor, 5 ... Conductive support body, 6 ... Sealing material, 7 ... Screw member, 10,102 ... Sub air passage structure Member, 14, 120 ... sub air passage, 20,100 ... main air passage constituent member, 22,101 ... main air passage, 25 ... sub air passage insertion hole, 51 ... intake air temperature sensor, 52 ... module, 53 ... body, 54 ... Air cleaner, 55 ... Duct, 56 ... Idle air control valve, 57 ... Throttle angle sensor, 58 ... Throttle body, 59 ... Intake manifold, 60 ... Injector, 61 ... Tachometer, 62 ... Engine cylinder, 63 ... Gas, 64 ... Exhaust manifold, 65 ... Oxygen concentration meter, 66 ... Control unit, 67 ... Intake air, 103 ... Support material, 111 ... Lead material, 121 Auxiliary air passage inlet, 122 ... curved passage, 123 ... straight portion, 124 ... auxiliary air passage outlet, 125 ... bending vertices, 150 ... dust.

Claims (3)

A heating resistor type air flow measurement device that generates heat by flowing a heating current and measures the air flow rate based on heat radiation to the intake air, and has a sub air passage having an opening for taking in a part of the air flow of the main air passage In the heating resistor type air flow rate measuring device having a heating resistor for measuring the air flow rate in,
The heating resistor consists of a cylindrical bobbin in which lead materials having conductivity are attached to both ends of the heating resistor,
The sub air passage has at least one bent portion, has a straight passage portion on the downstream side of the bent portion, and the heating resistor is arranged in the straight passage portion,
When the axial direction of the straight passage portion is the x direction and the direction orthogonal to the x direction is the y direction on the plane defined by the bent portion, the heating resistor and the lead material are on the xy plane. And a heating resistor type air flow rate measuring device characterized by being inclined with respect to the y-axis . 2. The heating resistor type air flow measuring device according to claim 1, wherein an installation angle of the heating resistor and the lead material is in a range of approximately 20 to 50 degrees with respect to the y-axis . Heating resistor type air flow measuring device.   A fuel injection system for an internal combustion engine, characterized in that the heating resistor type air flow rate measuring device according to claim 1 or 2 is used.

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