Physical quantity detection device

Abstract

This disclosure provides a physical quantity detection device that can reduce the influence of sound waves generated by a turbocharger and suppress the reduction in detection accuracy of physical quantities including gas flow rate. The physical quantity detection device (100) is used to detect the physical quantity of air drawn in from the intake passage of an engine equipped with a turbocharger. The physical quantity detection device (100) includes: a secondary passage (130) that draws in a portion of air flowing from the upstream side to the downstream side of the intake passage along a first direction (D1) parallel to the centerline of the intake passage; and a flow rate detection unit that detects the flow rate of the air drawn into the secondary passage (130). The secondary passage (130) has: an inlet (114) opening towards the upstream side of the first direction (D1); an outlet (116) opening towards the downstream side of the first direction (D1); and an attenuation chamber (134) for attenuating sound waves propagating from the turbocharger to the inside of the outlet (116).

Description

Technical Field

[0001] This disclosure relates to a physical quantity detection device. Background Technology

[0002] Previously known inventions relate to devices for measuring flow rate and velocity (Patent Document 1 below). This conventional measuring device includes a flow branching path, a detection element, and a retention space. The fluid to be measured is introduced into the flow branching path. The detection element is exposed to the fluid within the flow branching path and detects fluid-related quantities such as flow rate and velocity. The retention space is located midway through the flow branching path, between the detection element and the outlet of the flow branching path, and retains at least a portion of the countercurrent introduced from the outlet. The measuring device is characterized in that, near the outlet, as the fluid to be measured flows in the forward direction towards the outlet, the flow branching path tilts in a downstream direction (Patent Document 1, paragraph 0006, claim 1). Figure 1 wait).

[0003] According to the conventional measuring device, by setting the aforementioned stagnation space in the middle of the diversion path, the influence of backflow on the measuring accuracy is reduced, and the influence of pulsation is also reduced (Patent Document 1, Paragraph 0007, etc.).

[0004] Existing technical documents

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2001-255188 Summary of the Invention

[0007] The technical problem that the invention aims to solve

[0008] With the increasing demand for vehicle miniaturization, there is a growing trend towards internal combustion engine vehicles equipped with turbochargers. However, due to vehicle miniaturization, if the engine compartment space shrinks, the distance between the physical quantity detection device used to measure physical quantities such as the airflow rate of the engine intake and the turbocharger is shortened, making it easier for sound waves generated by the turbocharger to reach the physical quantity detection device. In this case, in the aforementioned conventional measuring devices, the influence of the sound waves generated by the turbocharger can affect the detection element, potentially reducing the accuracy of flow rate and velocity detection.

[0009] This disclosure provides a physical quantity detection device that can reduce the influence of sound waves generated by a turbocharger and suppress the reduction in detection accuracy of physical quantities including gas flow rate.

[0010] Technical means for solving technical problems

[0011] One aspect of this disclosure is a physical quantity detection device that detects the physical quantity of air drawn in from the intake passage of an engine equipped with a turbocharger. The device is characterized by comprising: a secondary passage that draws in a portion of air flowing from an upstream side to a downstream side of the intake passage along a first direction parallel to the centerline of the intake passage; and a flow rate detection unit that detects the flow rate of the air drawn into the secondary passage, the secondary passage having: an inlet opening towards the upstream side in the first direction; an outlet opening towards the downstream side in the first direction; and an attenuation chamber for attenuating sound waves propagating from the turbocharger to the inside of the outlet.

[0012] Invention Effects

[0013] According to one of the above-described methods of this disclosure, a physical quantity detection device can be provided that can reduce the influence of sound waves generated by a turbocharger and suppress the reduction in detection accuracy of physical quantities including gas flow rate. Attached Figure Description

[0014] Figure 1 A schematic diagram of an engine system illustrating an embodiment of the physical quantity detection device of this disclosure is shown.

[0015] Figure 2 It is set in Figure 1 A rear view of the physical quantity detection device on the intake passage of the engine system.

[0016] Figure 3 yes Figure 2 The left side view of the physical quantity detection device.

[0017] Figure 4 yes Figure 2 The right-side view of the physical quantity detection device.

[0018] Figure 5 It means to remove. Figure 2 A rear view of the state of the cover plate of the physical quantity detection device.

[0019] Figure 6 It is along Figure 5 A cross-sectional view of the physical quantity detection device for the VI-VI line.

[0020] Figure 7 It is Figure 5 The enlarged view of the attenuation chamber of the physical quantity detection device in section VII.

[0021] Figure 8 yes Figure 7 A schematic diagram of the attenuation chamber.

[0022] Figure 9 It means Figure 8 A schematic diagram of a modified attenuation chamber.

[0023] Figure 10 It means Figure 8 A schematic diagram of a modified attenuation chamber. Detailed Implementation

[0024] Hereinafter, embodiments of the physical quantity detection device involved in this disclosure will be described with reference to the accompanying drawings.

[0025] Figure 1 This is a schematic diagram of an engine system 200 illustrating one embodiment of the physical quantity detection device of this disclosure. The engine system 200 is mounted, for example, in a vehicle such as an automobile, and generates power for driving the vehicle. The engine system 200 includes, for example, an engine 201 as an internal combustion engine, and an intake passage 202 and an exhaust passage 203 connected to the engine 201.

[0026] The intake passage 202 is equipped with, for example, a physical quantity detection device 100, a turbocharger 204, an air bypass valve 205, an intercooler 206, a boost temperature sensor 207, a throttle valve 208, an intake manifold 209, a boost pressure sensor 210, and a flow enhancement valve 211.

[0027] Engine 201 includes, for example, an intake valve 212, an exhaust valve 213, open / closed position sensors 214 and 215, a fuel injection valve 216, a spark plug 217, a knock sensor 218, a crank angle sensor 219, and a variable compression ratio mechanism 220.

[0028] The exhaust passage 203 may include, for example, an exhaust bypass valve 221, an air-fuel ratio sensor 222, an exhaust purification catalyst 223, an exhaust gas recirculation (EGR) pipe 224, an EGR cooler 225, an EGR temperature sensor 226, an EGR valve 227, and a differential pressure sensor 228.

[0029] The engine system 200 also includes, for example, a control unit 230. The control unit 230 may be, for example, an Electronic Control Unit (ECU) that controls the engine 201, or a part of an ECU. The ECU may be, for example, a microcontroller, including a Central Processing Unit (CPU) (not shown), storage devices such as ROM and flash memory, various computer programs and data stored in the storage devices, timers, and input / output units for communicating with peripheral devices.

[0030] The physical quantity detection device 100 includes, for example, a temperature sensor, a flow sensor, and a humidity sensor, for measuring the temperature, flow rate, and humidity of the air drawn into the exhaust passage 203, and outputting the measurement results to the control device 230. The turbocharger 204 includes a compressor 204a and a turbine 204b. The turbine 204b rotates due to the gas flowing through the exhaust passage 203, and the rotation of the turbine 204b rotates the compressor 204a. Thus, the turbocharger 204 compresses the air drawn into the intake passage 202 and delivers it to the engine 201.

[0031] An air bypass valve 205 is provided, for example, in a bypass passage that bypasses the turbocharger 204 of the intake passage 202. This bypass passage opens and closes according to a control signal from the control device 230 to prevent excessive rise in air pressure between the compressor 204a and the throttle valve 208. For example, if the throttle valve 208 suddenly closes during boost pressure, the air bypass valve 205 opens under the control of the control device 230. As a result, compressed air downstream of the compressor 204a flows back upstream of the compressor 204a through the bypass passage, thereby reducing the boost pressure.

[0032] Intercooler 206 cools the intake air, which has been thermally compressed and heated by compressor 204a, thereby lowering its temperature. Boost temperature sensor 207 measures the temperature of the intake air cooled by intercooler 206 (boost temperature) and outputs the result to control device 230. Throttle valve 208, for example, is located downstream of boost temperature sensor 207 and its opening is controlled by control device 230, thereby controlling the amount of intake air flowing into the cylinders of engine 201. Throttle valve 208 is, for example, a butterfly valve, whose opening is controlled independently of the amount of time the driver depresses the accelerator pedal, via a control signal from control device 230.

[0033] The intake manifold 209 is located downstream of the throttle valve 208 and is equipped with a boost pressure sensor 210. The boost pressure sensor 210 measures the pressure of the intake air in the intake manifold 209, i.e., the boost pressure, and outputs the measurement result to the control device 230. The intake manifold 209 and the intercooler 206 can be integrated. In this case, the volume of the intake passage 202 from the compressor 204a to the cylinder of the engine 201 can be reduced, and the responsiveness of the vehicle's acceleration and deceleration can be improved.

[0034] A flow enhancement valve 211 is located downstream of the intake manifold 209, causing a flow deflection in the intake air, thereby enhancing the dispersion generated in the mixed airflow within the cylinders of the engine 201. Intake valve 212 and exhaust valve 213 are each controlled by a control unit 230 and include a variable valve mechanism for continuously varying the phase of the valve's open and closed positions. Open / closed position sensors 214 and 215 are respectively located in the variable valve mechanisms of intake valve 212 and exhaust valve 213, detecting the phase of the open / closed positions of the intake and exhaust valves 212 and outputting this phase to the control unit 230.

[0035] Fuel injection valve 216 is provided, for example, in the cylinder of engine 201, and is a direct injection type for injecting fuel directly into the cylinder. Fuel injection valve 216 may also be a port injection type for injecting fuel into the intake port. Spark plug 217 is provided in the cylinder of engine 201 and ignites the combustible mixture in the cylinder through a spark from an electrode portion exposed inside the cylinder head. Knock sensor 218 is provided in the cylinder block of engine 201 and detects whether knocking occurs within the combustion chamber.

[0036] A crankshaft angle sensor 219 is mounted on the crankshaft of the engine 201, and outputs a signal corresponding to the rotation angle of the crankshaft as a signal representing the rotational speed of the crankshaft to the control device 230 during each combustion cycle. A variable compression ratio mechanism 220 is provided in the crank mechanism of the engine 201, and changes the compression ratio according to the operating state of the engine 201 under the control of the control device 230, thereby increasing the maximum output while maintaining optimal thermal efficiency.

[0037] The exhaust bypass valve 221 is, for example, an electrically operated valve installed in a bypass passage for bypassing the turbocharger 204 in the exhaust passage 203, and whose opening is controlled by a control signal from the control device 230. For example, the control device 230 can adjust the opening of the exhaust bypass valve 221 based on the boost pressure measured by the boost pressure sensor 210, thereby allowing a portion of the exhaust gas to pass through the bypass passage of the exhaust passage, thus reducing the work done by the exhaust gas on the turbine 204b of the turbocharger 204. As a result, the boost pressure can be maintained at the target pressure.

[0038] For example, the air-fuel ratio sensor 222 is located downstream of the exhaust bypass valve 221 in the exhaust passage 203 to measure the oxygen concentration, i.e., the air-fuel ratio, in the exhaust gas, and outputs the measurement result to the control device 230. The exhaust purification catalyst 223 is located, for example, downstream of the air-fuel ratio sensor 222 in the exhaust passage 203, and purifies harmful exhaust gas components such as carbon monoxide, nitrogen compounds, and unburned hydrocarbons in the exhaust gas through a catalytic reaction.

[0039] EGR pipe 224 connects the portion of exhaust passage 203 downstream of exhaust purification catalyst 223 and the portion of intake passage 202 upstream of compressor 204a of turbocharger 204. A portion of the exhaust gas passing through exhaust purification catalyst 223 flows back to intake passage 202 upstream of compressor 204a. EGR cooler 225 is disposed in EGR pipe 224 and cools the exhaust gas passing through EGR pipe 224. EGR temperature sensor 226 is disposed, for example, between EGR cooler 225 and EGR valve 227, measures the temperature of the exhaust gas flowing through EGR pipe 224, and outputs it to control device 230.

[0040] EGR valve 227 is, for example, located between EGR temperature sensor 226 and intake passage 202. Its opening is controlled by control device 230 to control the flow rate of exhaust gas returning from exhaust passage 203 to intake passage 202. Differential pressure sensor 228 is located in EGR pipe 224, and is positioned upstream and downstream of EGR valve 227. It measures the differential pressure between the exhaust gas pressure upstream of EGR valve 227 and the exhaust gas pressure downstream of EGR valve 227, and outputs this differential pressure to control device 230.

[0041] For example, as described above, the control unit 230 is connected to various sensors constituting the engine system 200 and actuators driving various parts of the engine system 200. The control unit 230 controls the operation of actuators such as the throttle valve 208, the intake valve 212 and exhaust valve 213 with variable valve mechanisms, the fuel injection valve 216, and the EGR valve 227. Furthermore, the control unit 230 detects the operating state of the engine 201 based on signals input from various sensors and ignites the spark plug 217 at a timing determined according to the operating state.

[0042] The physical quantity detection device 100 is inserted into the interior of the intake passage 202 through a mounting hole provided on the passage wall of the intake passage 202, and is used while fixed to the passage wall of the intake passage 202. The physical quantity detection device 100 draws in a portion of the air that is drawn in through an air filter (not shown) and flows from the upstream side to the downstream side of the intake passage 202 along a first direction D1 parallel to the center line 202a of the intake passage 202.

[0043] The physical quantity detection device 100 detects the physical quantity of the intake air and outputs it to the control device 230. The physical quantity detection device 100 protrudes radially from the passage wall of the intake passage 202 toward the centerline 202a of the intake passage 202. That is, the protruding direction of the physical quantity detection device 100 in the intake passage 202 is, for example, a second direction D2 orthogonal to a first direction D1 parallel to the centerline 202a of the intake passage 202.

[0044] The control device 230 calculates the fuel injection quantity and ignition timing, for example, based on the physical quantity of intake air output by the physical quantity detection device 100 and the engine speed of the engine 201 measured based on the output of the crank angle sensor 219. Based on the above calculation results, the control device 230 controls the fuel injection quantity of the fuel injection valve 216 and the ignition timing of the spark plug 217.

[0045] In fact, the control device 230 also precisely controls the fuel supply and ignition timing based on the intake air temperature, the change in the opening of the throttle valve 208, the change in the engine speed of the engine 201, and the air-fuel ratio of the exhaust gas. The control device 230 also uses an idle air control valve (not shown) to control the amount of air bypassing the throttle valve 208 when the engine 201 is idling, and to control the engine speed of the engine 201 when idling.

[0046] The fuel supply and ignition timing, which are the main control quantities of the engine 201, are calculated using the output of the physical quantity detection device 100 as the main parameter. Therefore, improving the measurement accuracy of the physical quantity detection device 100, suppressing changes over time, and improving its reliability are crucial for improving the control accuracy and ensuring the reliability of the vehicle.

[0047] In recent years, in particular, expectations for vehicle fuel efficiency and exhaust gas purification have been very high. To meet these expectations, improving the detection accuracy of the physical quantities of the intake air detected by the physical quantity detection device 100 is extremely important. Furthermore, maintaining high reliability of the physical quantity detection device 100 is also crucial. In addition, vehicles equipped with the physical quantity detection device 100 are used in environments with significant temperature or humidity variations. Preferably, consideration is also given to the physical quantity detection device 100's ability to cope with temperature and humidity changes in its operating environment, as well as its ability to handle dust and contaminants.

[0048] With the increasing demand for vehicle miniaturization, there is a growing trend of internal combustion engine vehicles equipped with turbochargers 204. However, due to vehicle miniaturization, if the space in the engine compartment is reduced, the distance between the physical quantity detection device used to detect physical quantities such as the intake air flow of the engine 201 and the turbocharger 204 is shortened, and the sound waves generated by the turbocharger 204 can easily reach the physical quantity detection device 100.

[0049] Therefore, for the physical quantity detection device 100, it is very important to reduce the influence of the sound waves generated by the turbocharger 204 and suppress the reduction in the detection accuracy of physical quantities, including gas flow rate.

[0050] Although described in detail later, the physical quantity detection device 100 of this embodiment is characterized by having the following structure, thereby reducing the influence of the sound waves generated by the turbocharger 204 and suppressing the decrease in the detection accuracy of physical quantities including gas flow rate (see reference). Figure 5 and Figure 6 -{}-

[0051] The physical quantity detection device 100 of this embodiment detects the physical quantity of air drawn in from the intake passage 202 of the engine 201 equipped with a turbocharger 204. The physical quantity detection device 100 includes: a secondary passage 130 that draws in a portion of air flowing from the upstream side to the downstream side of the intake passage 202 along a first direction D1 parallel to the centerline 202a of the intake passage 202; and a flow rate detection unit 151 that detects the flow rate of the air drawn into the secondary passage 130. The secondary passage 130 has: an inlet 114 opening towards the upstream side of the first direction D1; an outlet 116 opening towards the downstream side of the first direction D1; and an attenuation chamber 134 for attenuating sound waves propagating from the turbocharger 204 to the inside of the outlet 116.

[0052] The following will refer to Figures 2 to 10 The physical quantity detection device 100 of this embodiment will be described in more detail. In the above figures, a device parallel to... Figure 1 The diagram shows a rectangular coordinate system comprising the X-axis of the protruding direction of the physical quantity detection device 100 in the air intake passage 202, the Y-axis parallel to the center line 202a of the air intake passage 202, and the Z-axis parallel to the thickness direction of the physical quantity detection device 100. Furthermore, in the following description, the air drawn into the air intake passage 202 through the air filter flows from the upstream side to the downstream side (positive Y-axis direction) of the air intake passage 202 along a first direction D1 parallel to the center line 202a (Y-axis) of the air intake passage 202.

[0053] Figure 2 It is set in Figure 1 Rear view of the physical quantity detection device 100 in the intake passage 202 of the engine system 200. Figure 3 yes Figure 2 The left side view of the physical quantity detection device 100. Figure 4 yes Figure 2 The right side view of the physical quantity detection device 100.

[0054] The physical quantity detection device 100 includes, for example, a housing 110 and a cover plate 120. The housing 110 is manufactured, for example, by injection molding of a synthetic resin material. The cover plate 120 is, for example, a plate-shaped component made of metal or synthetic resin. The cover plate 120 can be, for example, a molded article made of synthetic resin material. The housing 110 and the cover plate 120 constitute the outer casing of the physical quantity detection device 100 disposed within the air intake passage 202.

[0055] The housing 110 includes, for example, a flange 111, a connector 112, and a measuring section 113. The flange 111, when viewed from above along the second direction D2, has a generally rectangular plate shape and a pair of fixing portions 111a at its diagonal corners. The fixing portions 111a have cylindrical through holes 111b (see reference). Figure 6 The through hole 111b passes through the flange 111 in the center and a fixing screw is inserted therein.

[0056] The physical quantity measuring device 100 is fixed to the passage wall of the intake passage 202, for example, by the following steps: First, the measuring part 113 of the physical quantity measuring device 100 is inserted into the intake passage 202 through the mounting hole provided on the passage wall of the intake passage 202, and the flange 111 abuts against the passage wall of the intake passage 202. Next, the fixing screw inserted into the through hole 111b of the flange 111 of the physical quantity measuring device 100 is screwed into the screw hole of the passage wall of the intake passage 202 and tightened. Thus, as Figure 1 As shown, the physical quantity detection device 100 is fixed to the air intake passage 202.

[0057] Connector 112 protrudes from flange 111 and is connected to control device 230 via a connector and cable disposed outside air intake passage 202, for example, not shown in the figure. Figure 4 As shown, multiple external terminals 112a and calibration terminals 112b are provided inside the connector 112. The external terminals 112a include, for example, output terminals for physical quantities such as flow rate, temperature, and humidity, which are the measurement results of the physical quantity detection device 100; and power supply terminals for providing DC power to operate the physical quantity detection device 100.

[0058] The calibration terminal 112b is used to measure physical quantities after manufacturing the physical quantity detection device 100, determine calibration values ​​for each physical quantity detection device 100, and store the calibration values ​​in the memory inside the physical quantity detection device 100. When measuring physical quantities subsequently by the physical quantity detection device 100, calibration data based on the calibration values ​​stored in the aforementioned memory is used, instead of using the calibration terminal 112b.

[0059] The measuring section 113 extends from the flange 111 fixed to the passage wall of the intake passage 202 toward the centerline 202a of the intake passage 202, and protrudes radially (second direction D2) in the intake passage 202 orthogonal to the centerline 202a. The measuring section 113 has a flattened angular shape that is approximately cuboid in shape. The measuring section 113 has a length in the protruding direction (second direction D2) in the intake passage 202, and a width in the mainstream airflow direction (first direction D1) in the intake passage 202. In addition, the measuring section 113 has a thickness in a direction orthogonal to the protruding direction (second direction D2, X-axis direction) and the width direction (first direction D1, Y-axis direction) (Z-axis direction). As a result, since the measuring section 113 has a flattened shape along the mainstream airflow direction of the intake air flowing through the intake passage 202, the fluid resistance of the intake air can be reduced.

[0060] The measuring section 113 has a front surface 113a, a back surface 113b, an upstream side surface 113c, a downstream side surface 113d, and a lower surface 113e. The front surface 113a and the back surface 113b have larger areas than the other surfaces of the measuring section 113 and are substantially parallel to the protruding direction (second direction D2) of the measuring section 113 and the centerline 202a (first direction D1) of the intake passage 202. The upstream side surface 113c and the downstream side surface 113d have elongated shapes with smaller areas than the front surface 113a and the back surface 113b and are substantially orthogonal to the centerline 202a (first direction D1) of the intake passage 202. The lower surface 113e has a smaller area than the other surfaces of the measuring section 113, is substantially parallel to the centerline 202a (first direction D1) of the intake passage 202, and is substantially orthogonal to the protruding direction (second direction D2) of the measuring section 113.

[0061] The measuring unit 113 has an inlet 114 for a secondary passage (described later) on its upstream side 113c and an outlet 116 for a secondary passage on its downstream side 113d. Alternatively, the measuring unit 113 may also have a foreign matter outlet 115 for the secondary passage on its downstream side 113d. The inlet 114, outlet 116, and foreign matter outlet 115 for the secondary passage are located at the front end of the measuring unit 113, further forward than the center in the protruding direction (second direction D2). This allows air near the center of the intake passage 202, away from the inner wall of the intake passage 202, to be drawn in through the inlet 114. Therefore, the physical quantity detection device 100 can suppress the decrease in measurement accuracy caused by the heat of the engine 201.

[0062] Figure 5 It means it has been removed. Figure 2 A rear view of the state of the cover plate 120 of the physical quantity detection device 100. Figure 6 It is along Figure 5A cross-sectional view of the physical quantity detection device 100 for the VI-VI line in this embodiment. The physical quantity detection device 100 in this embodiment includes, for example, a secondary path 130, a circuit board 140, and a chip package 150.

[0063] Figure 4 The external terminal 112a of the connector 112 shown is, for example, via... Figure 6 The bonding wire 143 shown is connected to the pads of the circuit board 140. For example, in the circuit board 140, a protection circuit 144 is mounted on the surface connected to the bonding wire 143. The protection circuit 144 stabilizes the voltage in the circuit and eliminates noise. The bonding wire 143 and the protection circuit 144 are covered and sealed by a sealing material (not shown). As a sealing material, for example, silicone gel or an epoxy-based sealing material with higher rigidity than silicon-based sealing materials can be used.

[0064] like Figure 5 As shown, the housing 110 has a concave secondary passage groove 117 and a concave circuit chamber 118 on the back side 113b of the measuring section 113. The opening of the secondary passage groove 117 is... Figure 2 The cover plate 120 shown is closed, thereby forming a secondary passage 130 between the cover plate 120 and the secondary passage 130.

[0065] The secondary passage 130 has, for example, an inlet 114, an inlet-side passage 131, an outlet-side passage 132, an outlet 116, a foreign matter discharge passage 133, and a foreign matter discharge outlet 115. For example, the secondary passage 130 draws in a portion of the air flowing through the intake passage 202 from the inlet 114, which opens to the upstream side facing the first direction D1, and allows it to pass through the inlet-side passage 131, the outlet-side passage 132, and the foreign matter discharge passage 133, and returns to the intake passage 202 from the outlet 116 and the foreign matter discharge outlet 115, which open to the downstream side facing the first direction D1.

[0066] The secondary passageway 117, for example, has a first secondary passageway 117a, a second secondary passageway 117b, and a third secondary passageway 117c. Figure 5 As shown, the first secondary passage groove 117a extends from the inlet 114, which opens to the side 113c on the upstream side of the measuring section 113, in the first direction D1, and then bends from the first direction D1 to the second direction D2, and bends and extends along the second direction D2 to the flange 111 at the base end of the measuring section 113.

[0067] The inlet-side passage 131 of the secondary passage 130 is formed between the first secondary passage groove 117a and the cover plate 120. The upstream end of the inlet-side passage 131 is connected to the inlet 114. The inlet-side passage 131 has, for example, an upstream inlet-side portion 131a extending from the inlet 114 along a first direction D1, and an inlet-side downstream portion 131b extending from the upstream inlet-side portion 131a along a second direction D2 orthogonal to the first direction D1 and having a flow detection unit 151 disposed at its downstream end.

[0068] Additionally, the third secondary passageway 117c branches off from the first secondary passageway 117a and extends along the first direction D1 to a foreign matter discharge port 115 that opens to the downstream side 113d of the measuring section 113. A foreign matter discharge passage 133 is formed between the third secondary passageway 117c and the cover plate 120, extending from the upstream portion 131a of the inlet side toward the foreign matter discharge port 115 and along the first direction D1. The foreign matter discharge passage 133 returns a portion of the air drawn in from the inlet 114, along with foreign matter such as dust drawn in from the inlet 114, from the foreign matter discharge port 115 back to the intake passage 202. The foreign matter discharge port 115 opens toward the downstream side of the first direction D1 at a position where it passes the downstream end of the outlet 116 beyond the downstream portion 132b of the outlet side and moves away from the outlet 116 along the second direction D2.

[0069] Furthermore, the second secondary passageway 117b is bent into a U-shape, causing it to fold back from the downstream end of the first secondary passageway 117a in the opposite direction of the second direction D2, and extend along the second direction D2 towards the outlet 116 at the front end of the measuring section 113. An outlet-side passageway 132 of the secondary passageway 130 is formed between the second secondary passageway 117b and the cover plate 120. The outlet-side passageway 132, for example, has an upstream outlet-side portion 132a and a downstream outlet-side portion 132b.

[0070] The upstream portion 132a on the outlet side is bent into a U-shape, for example, so that its front end, which extends from the downstream portion 131b on the inlet side, is turned back in the opposite direction to the second direction D2, i.e., in the protruding direction of the measuring portion 113. For example, the downstream portion 132b on the outlet side extends from the downstream end of the upstream portion 132a on the outlet side toward the outlet 116 along the second direction D2, and an attenuation chamber 134 is provided at its downstream end. Furthermore, the downstream end of the downstream portion 132b on the outlet side extends, for example, beyond the outlet 116 toward the second direction D2, and a concave portion 134a is formed in the attenuation chamber 134.

[0071] In the concave portion 134a, for example, only the upstream end of the downstream portion 132b on the outlet side is open, and the bottom of the downstream end of the downstream portion 132b on the outlet side and the sidewall portion surrounding the bottom are closed. That is, the concave portion 134a is the end point or dead end of the downstream end of the downstream portion 132b on the outlet side. The open end of the concave portion 134a is adjacent to one end of the outlet 116 that opens in the first direction D1.

[0072] Figure 7 It is formed in Figure 5 An enlarged view of section VII of the attenuation chamber 134 at the downstream end of the downstream portion 132b on the outlet side of the secondary passage 130 shown. Figure 8 yes Figure 7 The diagram shows an attenuation chamber 134. The attenuation chamber 134 is formed, for example, by making the downstream end of the outlet-side downstream portion 132b larger than its upstream side. More specifically, for example, the cross-sectional area of ​​the attenuation chamber 134, which is orthogonal to the second direction D2, is increased compared to the outlet-side downstream portion 132b on its upstream side.

[0073] The attenuation chamber 134, for example, attenuates sound waves having a frequency corresponding to the resonant frequency of the secondary passage 130. The resonant frequency ω of the secondary passage 130 can be calculated, for example, by setting the sound velocity as c, the opening area of ​​the outlet 116 as S, the flow path length of the secondary passage 130 from the outlet 116 to the inlet 114 as L, and the volume of the secondary passage 130 from the outlet 116 to the inlet 114 as V, based on the following equation (1).

[0074] [Mathematical Expression 1]

[0075]

[0076] The flow path length L in equation (1) above is, for example, the sum of the length of the centerline from the downstream end to the upstream end of the outlet-side passage 132 and the length of the centerline from the downstream end to the upstream end of the inlet-side passage 131. Similarly, the volume V in equation (1) above is, for example, the sum of the volume of the outlet-side passage 132 and the volume of the inlet-side passage 131. The flow path length L may, for example, include the length of the centerline from the center of the foreign matter discharge port 115 to the upstream end of the foreign matter discharge passage 133, and similarly, the volume V may, for example, include the volume of the foreign matter discharge passage 133. Furthermore, the resonant frequency ω of the secondary passage 130 may, for example, be determined experimentally or through computer simulation.

[0077] The attenuation chamber 134 has, for example, a reflective wall 134b that causes sound waves propagating from the turbocharger 204 to the inside of the outlet 116 to pass through the center of the outlet 116 and be reflected toward the outlet centerline 116a, which is parallel to the first direction D1. The reflective wall 134b is positioned opposite to the outlet centerline 116a.

[0078] More specifically, in Figure 7In the example shown, the reflector wall 134b is tilted relative to the second direction D2 and is opposite to the outlet centerline 116a. More specifically, the reflector wall 134b is tilted outward of the downstream portion 132b on the outlet side, that is, the reflector wall 134b is tilted towards the side 113d downstream of the measuring portion 113 in the intake passage 202, so that the downstream portion 132b on the outlet side extending along the second direction D2 extends from the upstream side to the downstream side.

[0079] like Figure 8 As shown, the reflector wall 134b can be parallel to the outlet centerline 116a and the first direction D1, and orthogonal to the second direction D2. That is, the reflector wall 134b can be stepped, such that the downstream portion 132b on the outlet side extends from the upstream side to the downstream side. Furthermore, multiple reflector walls 134b can be arranged in a stepped manner within the attenuation chamber 134, such that the downstream portion 132b on the outlet side gradually expands from the upstream side to the downstream side. In this case, each reflector wall 134b can be inclined relative to the outlet centerline 116a or parallel to the outlet centerline 116a.

[0080] Additionally, for example, such as Figure 8 As shown, in the reflector wall 134b, the distance d1 from the center line 116a of the outlet in the direction of reflection of the sound wave propagating inside the outlet 116 is one-quarter wavelength of the reflected sound wave. That is, if the wavelength of the sound wave reflected by the reflector wall 134b and the re-reflector wall 134c is set as λ, then the following equation (2) holds.

[0081] d1=λ / 4…(2)

[0082] Here, for example, such as Figure 8 As shown, the incident direction and reflection direction of the sound wave on the reflector wall 134b are parallel to the extension direction of the downstream portion 132b on the outlet side, i.e., the second direction D2, and are orthogonal to the outlet centerline 116a. For example, the incident direction of the sound wave on the reflector wall 134b and the reflection direction of the sound wave on the reflector wall 134b can be determined by computer simulation.

[0083] The wavelength λ of the sound wave in equation (2) above is, for example, the wavelength corresponding to the resonant frequency ω of the secondary passage 130. That is, the distance d1 between the reflector wall 134b and the outlet centerline 116a can be expressed, for example, by setting the speed of sound as c, using the following equation (3).

[0084] d1=c / 4ω…(3)

[0085] The attenuation chamber 134 also has, for example, a re-reflecting wall 134c that reflects the sound waves reflected by the reflecting wall 134b again. The re-reflecting wall 134c is arranged, for example, parallel to the reflecting wall 134b and opposite to the reflecting wall 134b. The distance d2 from the re-reflecting wall 134c to the opposite reflecting wall 134b is an integer multiple of more than twice the quarter wavelength of the sound wave. That is, if the wavelength of the sound wave reflected by the reflecting wall 134b and the re-reflecting wall 134c is λ, and n is an integer greater than or equal to 1, then the following equation (4) holds.

[0086] d2=(n+1)·λ / 4…(4)

[0087] The wavelength λ of the sound wave in equation (4) above is, for example, the wavelength corresponding to the resonant frequency ω of the secondary path 130. That is, the distance d2 between the reflecting wall 134b and the re-reflecting wall 134c can be expressed, for example, by setting the speed of sound as c, using the following equation (5).

[0088] d2=(n+1)·c / 4ω…(5)

[0089] exist Figure 7 and Figure 8 In the example shown, a reflective wall 134b is formed on the inner wall of the attenuation chamber 134, which is provided with the outlet 116. However, the structure of the attenuation chamber 134 is not limited to this. Figure 7 and Figure 8 The example shown. See below for reference. Figure 9 and Figure 10 ,illustrate Figure 7 and Figure 8 A modified example of the attenuation chamber 134 shown.

[0090] Figure 9 Is along Figure 8 A schematic cross-sectional view of a modified example of the attenuation chamber 134 corresponding to the cross-section of the IX-IX line. For example, in the attenuation chamber 134, a reflective wall 134b may be provided on the wall surface of the measuring section 113 of the physical quantity detection device 100, which is orthogonal to the first direction D1 and the second direction D2, in the thickness direction (Z-axis direction). That is, the reflective wall 134b may be formed, for example, on the bottom surface of the second secondary passage groove 117b provided in the measuring section 113 of the housing 110 or on the inner surface of the cover plate 120.

[0091] Figure 10 It shows Figure 8A schematic diagram of a modified version of the attenuation chamber 134. In this modified version, the attenuation chamber 134 includes multiple reflecting walls 134b and 134d corresponding to multiple sound waves of different wavelengths. That is, if the wavelength of the sound wave reflected by the reflecting wall 134d is set as λ′, the distance d3 between the reflecting wall 134d and the outlet centerline 116a can be calculated by the following equation (6).

[0092] d3=λ′ / 4…(6)

[0093] Although Figure 10 Two reflectors 134b and 134d corresponding to two different wavelengths of sound waves are shown, but it is also possible to provide three or more reflectors corresponding to three or more different wavelengths of sound waves.

[0094] like Figure 5 As shown, on the back side 113b of the measuring section 113 of the housing 110 and on the base end side of the measuring section 113 connected to the flange 111, the circuit chamber 118 is provided in a concave shape and houses the circuit board 140. The circuit chamber 118 is disposed adjacent to the base end side of the measuring section 113, which is further upstream of the inlet side of the inlet side passage 131 than the upstream side of the inlet side passage 131 in the first direction D1, and is disposed adjacent to the downstream side of the inlet side passage 131b and the upstream side of the outlet side passage 132a.

[0095] like Figure 6 As shown, the chip package 150 includes a flow detection unit 151, electronic components 152, a lead frame 154, and a resin sealing portion 155. The flow detection unit 151 is, for example, a thermal flow sensor. The flow detection unit 151 includes, for example, a semiconductor substrate, a thin film portion formed on the surface side of the semiconductor substrate and exposed from the resin sealing portion 155, and a recess formed on the back side of the semiconductor substrate and forming the thin film portion. In addition, the flow detection unit 151 includes a pair of temperature sensors disposed on the surface side of the thin film portion and a heater disposed between the pair of temperature sensors, and is mounted on the lead frame 154.

[0096] Electronic component 152 is mounted on lead frame 154 and drives flow detection unit 151. Lead frame 154 has connection terminals protruding from resin sealing portion 155. The connection terminals are mounted on circuit board 140 via bonding material such as solder. Resin sealing portion 155 is formed, for example, by transfer molding of thermosetting resin, and integrally seals flow detection unit 151, electronic component 152, and lead frame 154.

[0097] For example, such as Figure 6As shown, the flow detection unit 151 detects the flow rate of gas flowing through the flow detection passage 131c formed between the grooves of the circuit board 140 and the chip package 150. The flow detection passage 131c is formed, for example, in the downstream portion 131b of the inlet side of the sub-passage 130.

[0098] In addition, such as Figure 5 As shown, in addition to the chip package 150 including the flow detection unit 151, at least one of a temperature sensor 160, a pressure sensor 170, and a humidity sensor 180 is mounted on the circuit board 140. The connection terminals of each sensor are sealed, for example, by a sealing material 141. In this embodiment, the temperature sensor 160, the pressure sensor 170, and the humidity sensor 180 are mounted on the circuit board 140, but any one of the sensors may be omitted.

[0099] Temperature sensor 160 is, for example, a surface-mount temperature sensor mounted on circuit board 140. Temperature sensor 160 is, for example, disposed at the front end of extension 140c of circuit board 140 extending toward the front end of measuring section 113 in the protruding direction (second direction D2). Figure 2 As shown, the temperature sensor 160 is disposed in the temperature detection passage 190 of the measuring unit 113, and measures the temperature of the gas drawn into the temperature detection passage 190 from the intake passage 202.

[0100] The temperature detection passage 190 has an inlet on the side 113c upstream of the measuring unit 113, and outlets on both the front 113a and the back 113b of the measuring unit 113. The temperature detection passage 190 draws in air flowing through the intake passage 202 from the inlet on the side 113c upstream of the measuring unit 113, and discharges air into the intake passage 202 from the outlets on the front 113a and the back 113b of the measuring unit 113. This structure improves the heat dissipation of the temperature sensor 160.

[0101] Pressure sensor 170 is mounted on circuit board 140 and disposed within circuit chamber 118. Circuit chamber 118 is connected to upstream portion 132a of the outlet side of secondary passage 130, which is bent into a U-shape near flange 111. Thus, the pressure of gas flowing through secondary passage 130 can be measured by pressure sensor 170 disposed in circuit chamber 118.

[0102] The humidity sensor 180 is mounted on the circuit board 140, for example, and is disposed in a defined area further from the front end of the measuring section 113 than the circuit chamber 118. The humidity sensor 180 detects, for example, the humidity of the gas drawn into the sub-passage 130 from the intake passage 202.

[0103] The function of the physical quantity detection device 100 in this embodiment will be explained below.

[0104] As described above, the physical quantity detection device 100 of this embodiment is a device for detecting the physical quantity of air drawn in from the intake passage 202 of the engine 201 equipped with a turbocharger 204. The physical quantity detection device 100 includes: a secondary passage 130 that draws in a portion of air flowing from the upstream side to the downstream side of the intake passage 202 along a first direction D1 parallel to the centerline 202a of the intake passage 202; and a flow rate detection unit 151 that detects the flow rate of the air drawn into the secondary passage 130. The secondary passage 130 has: an inlet 114 opening towards the upstream side of the first direction D1; an outlet 116 opening towards the downstream side of the first direction D1; and an attenuation chamber 134 for attenuating sound waves propagating from the turbocharger 204 to the inside of the outlet 116.

[0105] With this structure, the physical quantity detection device 100 of this embodiment can attenuate the sound waves propagating from the turbocharger 204 to the inside of the outlet 116 of the secondary passage 130 through the attenuation chamber 134 of the secondary passage 130. Therefore, by suppressing the vibration of the air in the secondary passage 130 caused by the influence of the sound waves propagating to the inside of the outlet 116 of the secondary passage 130, the decrease in the accuracy of the airflow detection unit 151 in detecting the airflow can be suppressed. Therefore, according to the physical quantity detection device 100 of this embodiment, for example, even when the distance to the turbocharger 204 is shortened compared to the prior art, the influence of the sound waves generated in the turbocharger 204 can be reduced, thereby suppressing the decrease in the detection accuracy of physical quantities including gas flow.

[0106] Furthermore, in the physical quantity detection device 100 of this embodiment, the attenuation chamber 134 has a reflective wall 134b, which causes sound waves propagating to the inside of the outlet 116 to be reflected through the center of the outlet 116 towards the outlet centerline 116a, which is parallel to the first direction D1. The reflective wall 134b is disposed opposite to the outlet centerline 116a, and the distance d1 from the outlet centerline 116a in the direction of sound wave reflection is one-quarter wavelength of the sound wave.

[0107] According to this structure, in the physical quantity detection device 100 of this embodiment, the sound wave that propagates from the turbocharger 204 to the inside of the outlet 116 and is reflected by the reflector wall 134b to reach the outlet centerline 116a is deflected by half its wavelength. As a result, the sound wave newly propagating from the turbocharger 204 to the inside of the outlet 116 and the sound wave reflected by the reflector wall 134b cancel each other out. Therefore, the sound wave propagating to the inside of the outlet 116 can be attenuated in the attenuation chamber 134.

[0108] In the physical quantity detection device 100 of this embodiment, the attenuation chamber 134 may include multiple reflective walls 134b and 134d corresponding to multiple sound waves of different wavelengths. With this structure, the physical quantity detection device 100 of this embodiment can selectively attenuate multiple sound waves of different specific wavelengths in the attenuation chamber 134.

[0109] Furthermore, in the physical quantity detection device 100 of this embodiment, the attenuation chamber 134 has a re-reflecting wall 134c that reflects the sound waves reflected by the reflecting wall 134b again. The distance d2 from the re-reflecting wall 134c to the opposing reflecting wall 134b is set to an integer multiple of more than twice the quarter wavelength of the reflected sound wave. With this structure, in the physical quantity detection device 100 of this embodiment, the sound waves reflected again by the re-reflecting wall 134c cancel each other out with the sound waves reflected by the reflecting wall 134b or the sound waves newly propagating to the inside of the outlet 116. Therefore, the sound waves propagating to the inside of the outlet 116 of the secondary passage 130 can be attenuated more effectively in the attenuation chamber 134.

[0110] Furthermore, in the physical quantity detection device 100 of this embodiment, the secondary passage 130 includes an inlet-side passage 131 connected to the inlet 114, and an outlet-side passage 132 connected to the inlet-side passage 131 and the outlet 116. The inlet-side passage 131 has an upstream inlet portion 131a extending from the inlet 114 along a first direction D1, and an inlet-side downstream portion 131b extending from the upstream inlet portion 131a along a second direction D2 orthogonal to the first direction D1 and on which a flow detection unit 151 is disposed. The outlet-side passage 132 further includes: an upstream outlet portion 132a, which bends back from the downstream inlet portion 131b in the opposite direction to the second direction D2; and an downstream outlet portion 132b, which extends from the upstream outlet portion 132a toward the outlet 116 along the second direction D2 and on which an attenuation chamber 134 is disposed at its downstream end.

[0111] With this structure, the physical quantity detection device 100 of this embodiment can reduce the detection error of the flow detection unit 151 caused by air backflow or pulsation in the air intake passage 202 by using the curved shape of the secondary passage 130 from the inlet 114 to the outlet 116.

[0112] Furthermore, in the physical quantity detection device 100 of this embodiment, the downstream end of the downstream portion 132b of the outlet side of the outlet side passage 132 of the secondary passage 130 extends beyond the outlet 116 in the second direction D2, thereby forming a concave portion 134a in the attenuation chamber 134. With this structure, the physical quantity detection device 100 of this embodiment can attenuate sound waves by repeatedly reflecting them within the concave portion 134a of the attenuation chamber 134.

[0113] In addition, Figure 7 In the example shown, the wall of the attenuation chamber 134 opposite to the outlet 116 is formed into a smooth curved shape that bulges outward from the portion opposite to the outlet 116 to the bottom surface of the concave portion 134a. With this structure, sound waves can be easily reflected repeatedly within the concave portion 134a of the attenuation chamber 134.

[0114] Furthermore, in the physical quantity detection device 100 of this embodiment, the secondary passage 130 has a foreign matter discharge port 115, which opens from the outlet 116 across the downstream end of the outlet-side downstream portion 132b and toward the downstream side of the first direction D1 at a position away from the outlet 116 in the second direction D2. Additionally, the secondary passage 130 has a foreign matter discharge passage 133 extending from the inlet-side upstream portion 131a toward the foreign matter discharge port 115 and along the first direction D1.

[0115] According to this structure, the physical quantity detection device 100 of this embodiment can discharge foreign matter such as dust sucked into the secondary passage 130 from the inlet 114 through the foreign matter discharge outlet 115 via the upstream part 131a on the inlet side and the foreign matter discharge passage 133. As a result, the amount of foreign matter included in the air flowing from the upstream part 131a on the inlet side to the downstream part 131b on the inlet side can be reduced, and the anti-fouling properties of the flow detection unit 151 can be improved.

[0116] Furthermore, in the physical quantity detection device 100 of this embodiment, the attenuation chamber 134 attenuates sound waves having a frequency corresponding to the resonant frequency ω of the secondary passage 130. With this structure, the physical quantity detection device 100 of this embodiment can prevent air resonance inside the secondary passage 130 due to the influence of sound waves propagating to the inside of the outlet 116 of the secondary passage 130, and can reduce the error in the airflow detection unit 151 detecting the airflow.

[0117] While the embodiments of the physical quantity detection device involved in this disclosure have been described in detail above with the aid of accompanying drawings, the specific structure is not limited to these embodiments, and design changes without departing from the spirit of this disclosure are also included in this disclosure.

[0118] For example, in the above embodiment, the attenuation chamber 134 has a reflective wall 134b that reflects sound waves propagating from the turbocharger 204 to the inner side of the outlet 116 of the secondary passage 130 toward the outlet centerline 116a. The reflective wall 134b is disposed opposite to the outlet centerline 116a, and the distance from the outlet centerline 116a in the direction of sound wave reflection is one-quarter wavelength of the sound wave. However, the physical quantity detection device of this disclosure is not limited to this embodiment. That is, the attenuation chamber 134 may not have a reflective wall 134b. In this case, for example, by providing uneven or sound-absorbing material on the inner wall surface of the attenuation chamber 134, or by enlarging the cross-sectional area of ​​the attenuation chamber 134 to be larger than the cross-sectional area of ​​the downstream portion 132b on the outlet side, sound waves can be attenuated.

[0119] Label Explanation

[0120] 100 physical quantity detection device

[0121] 114 entrance

[0122] 115 Foreign Object Discharge Outlet

[0123] 116 Export

[0124] 116a Exit Centerline

[0125] 130 secondary pathways

[0126] 131 Entrance Side Passage

[0127] 131a Inlet side upstream section

[0128] 131b Downstream section of the inlet side

[0129] 132 Exit Side Passage

[0130] 132a Upstream section of the outlet side

[0131] 132b Downstream section of the export side

[0132] 133 Foreign Body Discharge Channel

[0133] 134 Attenuation Chamber

[0134] 134a concave part

[0135] 134b Reflector

[0136] 134c re-reflecting wall

[0137] 134d reflective wall

[0138] 151 Flow Detection Department

[0139] 201 engine

[0140] 202 intake passage

[0141] 202a centerline

[0142] 204 turbocharger

[0143] d1 distance

[0144] d2 distance

[0145] d3 distance

[0146] D1 First Direction

[0147] D2 Second Direction

[0148] ω resonant frequency.

Claims

1. A physical quantity detection device for detecting the physical quantity of air drawn in from the intake passage of an engine equipped with a turbocharger, the physical quantity detection device being characterized by comprising: A secondary passage that draws in a portion of the air flowing from the upstream side to the downstream side of the intake passage in a first direction parallel to the centerline of the intake passage; as well as The flow detection unit detects the flow rate of the air drawn into the secondary passage. The secondary pathway has: An inlet facing the upstream side opening in the first direction; An outlet facing the downstream side opening in the first direction; as well as An attenuation chamber for attenuating sound waves propagating from the turbocharger to the inside of the outlet.

2. The physical quantity detection device as described in claim 1, characterized in that, The attenuation chamber has a reflective wall that causes the sound waves to pass through the center of the outlet and be reflected toward an outlet centerline parallel to the first direction. The reflective wall is disposed opposite to the outlet centerline, and the distance from the outlet centerline in the direction of sound wave reflection is set to one-quarter wavelength of the sound wave.

3. The physical quantity detection device as described in claim 2, characterized in that, The attenuation chamber includes a plurality of reflective walls corresponding to a plurality of sound waves of different wavelengths.

4. The physical quantity detection device as described in claim 2, characterized in that, The attenuation chamber includes a re-reflecting wall that reflects the sound waves that have already been reflected by the original reflecting wall again. The distance between the re-reflecting wall and the opposite reflecting wall is set to an integer multiple of more than twice the quarter wavelength of the sound wave.

5. The physical quantity detection device as described in claim 2, characterized in that, The secondary pathway includes: An entrance-side passage connected to the entrance; and An outlet-side passage connects the inlet-side passage and the outlet. The inlet-side passage includes: An upstream portion on the inlet side, extending from the inlet along the first direction; and The downstream portion on the inlet side extends from the upstream portion on the inlet side along a second direction orthogonal to the first direction and is equipped with the flow detection unit. The outlet-side access includes: The upstream portion on the outlet side is curved to fold back in the opposite direction from the downstream portion on the inlet side toward the second direction; and The downstream portion of the outlet side extends from the upstream portion of the outlet side toward the outlet in the second direction, and the attenuation chamber is provided at the downstream end.

6. The physical quantity detection device as described in claim 5, characterized in that, The downstream end of the downstream portion on the outlet side extends beyond the outlet in the second direction and forms a concave portion in the attenuation chamber.

7. The physical quantity detection device as described in claim 5, characterized in that, The secondary pathway includes: A foreign object discharge port that opens from the downstream end of the outlet, beyond the downstream portion of the outlet side, and towards the downstream side in the first direction at a location away from the outlet along the second direction; and A foreign object discharge passage extends from the upstream portion of the inlet side toward the foreign object discharge outlet along the first direction.

8. The physical quantity detection device as described in claim 1, characterized in that, The attenuation chamber attenuates the sound wave having a frequency corresponding to the resonant frequency of the secondary path.

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