JP2743856B2 - Air flow meter and internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention relates to air flow meter, in particular constitutes an intake system of an automobile engine, detects the intake air amount, further engine air flow suitable for control <br /> Related to the meter.

[0002]

BACKGROUND OF THE INVENTION air flow meter for a conventional internal combustion engine, JP-A-50-50520, JP-50-146369, JP
As described in JP-A-55-69021, there is an arrangement in which a straight tubular sub-flow path (branch pipe) is disposed at the center of a main flow path, and a hot-wire element is disposed therein. However, Japanese Patent Laid-Open No. 50-50
In the configuration described in Japanese Patent Application Laid-Open No. 520-520, the hot-wire element is unprotected against blow-back caused by backfire due to the ignition timing of the engine or the like.
No. 6,369, 55-69021, and the like, a structure for protecting a hot-wire element against backfire has been proposed. However, due to the non-linearity of the heat transfer coefficient, the output of a hot-wire element generally decreases when placed in a pulsating flow, despite the increased average flow velocity. In any of the above-described known examples, there is a problem that the flow rate of the pulsating flow is not accurately detected.

In addition, Japanese Utility Model Application Laid-Open No. 56-135127,
As described in JP-A-60-185118, a sub-flow path for disposing a hot-wire element is provided in a main flow path to perform the above-described countermeasures against backfire or to accurately detect a pulsating flow. The fluid resistance of the downstream sub-flow path is increased, and the outlet opening of the sub-flow path is formed parallel to or almost parallel to the main flow. In other words, against the backflow, the dynamic pressure acting on the outlet opening of the sub flow path is reduced, and the flow reaching the hot wire element is attenuated, thereby improving the backfire resistance. Since the outlet of the sub flow path is directly opened almost parallel to the main flow, the flow in the sub flow path slightly fluctuates due to the static pressure fluctuation caused by the flow mixing in this portion. This appears as noise in the output of the hot wire element. Although high-frequency noise can be cut to some extent by a circuit filter, noise caused by the above-mentioned fluctuations is a problem in system control, such as when the engine is running at a low speed. Further, in terms of hardware, there are disadvantages such as a long axial dimension, poor productivity in attaching component members such as sub-flow paths, and productivity (cost and weight) and reliability (large number of parts).

On the other hand, Japanese Patent Application Laid-Open No. 47-13557,
8-109816, 56-76012, 6
In Japanese Patent Application Laid-Open No. 1-28017, a sub-flow path in which a hot-wire element is disposed is formed outside a main flow path in order to prevent the above-mentioned backfire and stabilize the output with respect to intake pulsation. In these embodiments, as pointed out in Japanese Patent Application Laid-Open No. 56-76012, heat conduction from the engine or heat generation of the hot wire element itself, or in the case of a car, in the engine room due to heat generation of the engine and solar radiation. There is a disadvantage that the flow rate detection error increases due to thermal conditions such as a temperature rise. That is, the sub-channel portion where the hot-wire element is arranged has a large heat capacity,
In addition, a relatively narrow passage is formed inside the body wall which does not have a large heat transfer area for the intake air flow, and the air flow flowing therethrough is formed under conditions with good heat transfer characteristics. The temperature of the airflow in the flow passage is affected by the temperature of the passage wall, and the difference from the air temperature in the main flow passage becomes large. This has caused an increase in the measurement error of the intake air flow rate.

[0005]

Some of the above prior arts have a configuration that does not withstand backfire or strong blowback of the engine and that cannot be used practically in that an accurate average flow rate of pulsating flow cannot be detected. Others are
Accurate flow measurement cannot be performed for various thermal conditions to which the flow meter is exposed, and the output noise is large.As a result, the control for operating the engine at the optimum air-fuel ratio becomes incomplete, and the engine is incomplete. This has been an obstacle to purifying exhaust gas, improving fuel efficiency, and improving drivability. In some cases, no consideration has been given to the axial dimension of the flow meter body, that is, to reduce the length of the intake pipe, reduce the weight of the equipment, and reduce production costs, resulting in an increase in pressure loss in the intake pipe. However, there has been a problem that the weight of the system including the engine is increased, which causes obstacles such as improvement of fuel efficiency of the engine and space saving of the engine room. No consideration is given to improving the assemblability by configuring the probe holder block and the body separately from each other and by configuring the probe holder block and the sensor circuit unit to be detachable from the body. Was something.

An object of the present invention is to provide a sub-flow path having a heating element.
Air flow meter with a main flow in the main flow path for improved assemblability
And to enable accurate flow rate detection .

Another object of the present invention is to provide an auxiliary device having a heating element.
For internal combustion engines using an air flow meter with a flow path in the main flow path
In addition to improving the assemblability of the air flow meter,
It is to enable accurate flow rate detection .

[0008]

In order to solve the problems] order to achieve the above purpose
In addition, the air flow meter of the present invention provides an intake air flow path for an internal combustion engine.
A main flow path, a heating element for measuring intake air,
A sub-element provided inside the main flow path with
And an air flow meter having a flow path,
It has an inlet opening on the flow side and is formed in the axial direction of the main flow path
Bent in the axial flow path and the downstream side of the axial flow path.
With a bent flow path turned back to the flow side,
The probe holder block, which is configured inside the block,
Comprises a circuit unit for the heating element,
Inserted into the main flow channel from an opening provided in the wall of the
Cantilever supported detachably to main flow path
Things.

Further , in order to achieve the above object, the present invention
Internal combustion engine has a speed sensor that detects the rotational speed of the engine
And a fuel injection device that injects fuel, an air flow meter,
Intake air amount detected by the air flow meter and the speed
Respond based on the rotational speed detected by the sensor
Calculate the fuel injection amount and inject the calculated amount of fuel
A control device for outputting a command to the fuel injection device.
In the internal combustion engine, the air flow meter is provided for controlling the intake of the internal combustion engine.
A main flow path that forms the air flow path and a source that measures the amount of intake air
A heating element, having the heating element therein, and
And a sub-flow path provided on the upstream side.
An axial direction having an opening and formed in the axial direction of the main flow path
Channel and bends downstream of this axial channel to fold upstream
Probe holder block
The probe holder block is configured inside,
It has a circuit unit of the heating element, and on the wall surface of the main flow path
It is inserted into the main channel from the opening provided, and is inserted into the main channel.
It is designed to be cantilevered and detachable.
You.

[0010]

With this configuration, the main flow path body
With the heating element incorporated in the intake system of the internal combustion engine.
Insert the sensor with the sub flow path from the outside of the body
It can be a standing structure. Also disassemble the main flow path
Remove the sensor from the main flow path together with the sub flow path without performing
It becomes possible. Therefore, the assemblability of the air flow meter is improved.
In addition, replacement and maintenance of the sensor are facilitated. Also,
The entire sub flow path including the bent flow path from the main flow path together with the sensor
Because it can be attached and detached, it smells like calibration of the sensor
Thus, the configuration of the sub flow path does not change from that at the time of mounting. Therefore,
When the intake air volume is measured in the main flow path,
It is possible to reduce an error caused by twisting.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

FIG. 1 is a system embodiment of an internal combustion engine equipped with an electronically controlled fuel injection device to which a hot-wire air flow meter for an internal combustion engine according to the present invention is applied.

The air to the internal combustion engine (cylinder) 500 is
Inhaled by the air filter 503, the connection pipe 504,
It is supplied through the flow meter 1 and the intake manifold 501. The flow meter 1 is formed with a sub flow path 22 protruding from the main flow path 11, and a hot wire element 2 a and a temperature compensation element 2 b formed integrally with the circuit unit 2 are provided in the sub flow path 12. By detecting the air flow velocity in this portion, an output for the total intake air amount is obtained. In the passage of the flow meter 1, a throttle valve 3 for controlling the amount of intake air interlocking with an accelerator pedal of the vehicle is provided. Further, the flow meter 1 is provided with an idle speed control (ISC) valve 8 for controlling the flow rate when the throttle valve is fully closed (idling).

On the other hand, fuel is injected from a fuel tank 505 by a pump 506 into an intake manifold 501 from an injector 507 and supplied to the engine 500 together with air.

In the control unit 510, an output signal of the hot-wire element circuit unit 2, a rotation angle signal of the throttle valve 3, an output signal of the oxygen concentration sensor 508 installed in the exhaust manifold 507, an output signal of the engine rotation speed sensor 509, and the like. Is input, the fuel injection amount, ISC
The valve opening and the like are calculated. The injector 507, the ISC valve 8, etc. are controlled according to the result.

FIGS. 2 to 5 show a first embodiment of a hot-wire flow meter according to the present invention.

The body 20 includes a flow meter body 20a, a throttle valve body 20b, and an ISC valve body 20C.
Are integrally formed by die-casting. The inlet of the flow meter body 20a, provided with a gold netting 40 for rectification, the inlet portion 21a of the flow channel is formed to be bell-mouth-shaped. Downstream of the bell mouth, a probe holder block 30 in which a sub flow path 31 is formed is inserted from the outside of the body 20a, and the probe holder block 30 includes a sensor circuit unit 2 and a hot wire element 2a.
The temperature compensating element 2b is connected to the sub flow path 31b parallel to the main flow by screw members 40a and 40b as shown in the drawing. With such a configuration, the probe holder block 30 is detachable from the outside of the body 20. That is, with such a configuration, the probe holder block 30 can be assembled by inserting the probe holder block 30 from the outside of the body 20a, the assemblability of the hot wire air flow meter can be improved, and the sub flow path can be provided in the main flow path. Can be provided, the heat exchange area between the sub-flow channel wall and the main flow can be increased, and the temperature of the sub-flow channel wall is maintained at a temperature close to the intake air temperature, thereby improving the temperature characteristics.

In the portion of the throttle body 20b, a throttle valve 3 for controlling the amount of air and a valve shaft 4 for driving the throttle valve 3 are provided in the flow passage 21c so as to pass through the body 20b. A lever mechanism 5 for driving the shaft 4, a spring 6, and a throttle position sensor for detecting the rotation angle of the shaft 4 are provided outside the body 20 b in such a manner as to be coupled to the shaft 4. ISC
An ISC valve 8 for controlling the air flow when the throttle valve 3 is fully closed, that is, when the engine is idling, and an air passage 2 to the nuclear valve 8 are provided in the valve body 20c.
3, 24 and 25 are provided. The plugs 26, 2
Numeral 7 blocks unnecessary holes which do not become flow paths since the passages 23 and 25 are formed from the outside of the body 20c. The pipe 9 is provided with the throttle valve 3
This is to extract the downstream negative pressure.

Upper part 30a of probe holder block 30
In parallel with the main flow path 21, an axial sub-flow path 31 b having a smaller diameter and a circular cross-section than the main flow path having a bell mouth-shaped opening 31 a in the upstream portion of the flow meter body 20 a and a right angle thereto. A sub flow path 31c having an outlet opening surface 31d parallel to the main flow and a flow path whose length is equal to or larger than the radius of the main flow path is formed. Thereby, the main flow path 21 and the sub flow path 31 are provided in the flow meter.
To form a branching / mixing channel system. Sub flow path 31
Due to the fluid resistance element and the frictional resistance element of the passage which are responsible for the two-dimensional L-shaped right angle bend, the passage resistance, that is, the pressure loss of the flow is formed larger than the main passage. The heating element 2a and the temperature compensating element 2b
And a holder part 2c integral with the probe holder block 30 is provided in the sub-flow path 31b. With such a configuration, first, most of the outer wall of the probe holder block 30 flows in contact with the main flow, so that the flow path wall of the sub flow path 31b is always maintained at a temperature substantially equal to the intake air temperature. The flow rate is measured with a small error with respect to heat intrusion. In addition, it is possible to reduce the invasion of the backflow of the engine or the like into the sub-flow path 31 and protect the hot-wire element 2a and the like.
Since the passage resistance of the sub flow passage 31 has a pulsation damping effect,
Output abnormalities can be prevented when intake pulsation is large.

As described above, the axial sub-flow path 31b has a throttle at the inlet 31a and has a length from the inlet to the hot-wire element 2a about twice the inner diameter. These configurations, with gold mesh member 40 and the diaphragm of the flow meter inlet 21a, to reduce the turbulence of the flow coming from the flow recorded stream, it has secured basic low noise.

On the other hand, the sub flow passage 31c is slightly lower than the downstream throttle valve shaft 4 so that the length of the sub flow passage 31c is equal to or larger than the radius of the main flow passage, that is, in the portion 21b where the main flow passage 21 has the almost smallest area. And are formed in parallel with the mainstream. Further, the outlet opening 31d is an eave member extending wall 30b of the probe holder block, more vertical wind wall 30d to flow wall surfaces of the downstream side of the main flow, the main flow is prevented from mixing directly Have been.
The outlet opening is located in the smooth main flow which is relatively unaffected by the movement of the throttle valve 3, and the eaves member prevents mixing of flows immediately after the sub flow passage outlet 31d. Is minimized to further reduce noise. The sectional shape of the sub flow path 31c is circular, and the shape of the wall 30b and 30d of the probe holder block on the upstream side with respect to the main flow, and the shape of the wall 30c on the downstream side are also circular. This also contributes to lower noise.

A throttle 22 provided at the boundary of the throttle body 20b, which is slightly delayed from the sub flow path outlet opening 31d, is provided.
Stabilizes the flow in the sub flow path 31 with respect to the movement of the throttle valve 3, that is, the flow distribution between the main flow path 21 and the sub flow path 31, thereby enabling the throttle valve 3 to be provided close to the flow meter. I have.

Therefore, according to the present embodiment, a hot wire air flow meter which can accurately measure the intake air amount of the engine and has high reliability can be realized with a short axial dimension at low cost. Also,
Since the throttle valve can be integrated in close proximity, the weight can be reduced, and as a whole, exhaust gas purification of the engine, improvement of fuel efficiency, space saving of the engine room, and the like are achieved.

FIG. 6 shows a second embodiment of the hot-wire flow meter according to the present invention. In the present embodiment, a sub flow path having a larger fluid resistance is realized by a configuration in which the axial dimension does not increase. The body 150 is separate from the circuit unit 2
In the probe holder block 153 combined with the sub flow path 152 b parallel to the main flow path 151,
2c, a sub flow path 152d is formed at right angles to the sub flow path 152c and upstream from the main flow, and a sub flow path 152e is formed at right angles to the sub flow path 152e and extends in the radial direction. Each of the sub-flow paths has a circular cross section, and a portion that does not become a flow path is filled with a plug 155. In addition, a portion 154 of the block 153 in which the wall on the upstream side with respect to the main flow is further extended into the main flow with respect to the outlet of the sub flow path 152e is provided as a windproof wall.

The fluid resistance of the sub-channel 152 formed in this way is composed of a pipe-shaped resistance element consisting of three right-angled bends and a frictional resistance proportional to the long passage length, and the resistance is increased. Therefore, this is also effective for an engine in which backfire easily occurs and in which intake pulsation is large. Also,
In particular, since the flow distribution of the sub flow path to the main flow path in the high flow rate region can be reduced, that is, the maximum value of the flow velocity applied to the hot-wire element 2a can be suppressed to a small value, it is advantageous against contamination due to dust adhesion in a long term.

FIG. 7 shows a third embodiment of the hot wire type flow meter according to the present invention. The probe holder daloc 163 is the body 16
0 and separate from the circuit unit 2 and detachable from the body.

The outlet opening surface 162d of the sub flow path 162c perpendicular to the main flow is formed to be inclined with respect to the main flow as shown in the figure. For this reason, in this state, a check valve 165 made of a thin steel plate or the like is attached because the backflow easily enters the sub flow passage. The check valve 165 is fixed to the probe holder block 163 by bolts 167 while being backed up by a retainer 166. Check valve 165
Normally, as shown in the figure, the flow of the auxiliary flow path outlet 162d is set to be open so as not to obstruct the flow extremely and to make the flow downward, and a dynamic pressure acts at the time of the backflow to open the outlet hole 162d. It is formed so as to block and prevents the backflow from entering the sub-flow passage. When the dynamic pressure is removed, the state returns to the illustrated state. Since the exit surface of the sub flow path is inclined, the role of the windbreak wall is that the wall on the upstream side of the main flow among the walls forming the sub flow path 162c plays a role.

FIGS. 8 and 9 show a fourth embodiment of the hot-wire flow meter according to the present invention. Probe holder block 203
The main flow of the block 203 is separated from the main flow of the block 203 by a sub flow passage 202b inside the body 200 and parallel to the main flow, and a radial sub flow passage 202c slightly longer than, for example, the first embodiment. Side cross-sectional groove and cover 205
Is formed. The outlet 202d of the sub flow path is provided with a windbreak wall 204 which is an extension wall of the probe holder block 203.
On the upstream side with respect to the mainstream, and also on the downstream side, a windbreak wall 206 as an extension of the cover 205.
In the present embodiment, the width of the windbreak wall 206 is formed to be smaller than the width of the sub-channel 202c.

This is a condition necessary to prevent the outlet flow of the sub flow path from being largely disturbed by the cover 206, and is a condition necessary for not losing the effect of the upstream windbreak wall. The windbreak wall 204 on the upstream side with respect to the mainstream of the outlet opening 202d is
As described above, it is effective in reducing noise during normal operation, that is, during forward flow. On the other hand, the downstream wall 206 greatly reduces the intrusion force into the backflow and the backflow sub-flow path of the blowback. That is, the flow is divided into two by the windbreak wall 206, and then the two flows interfere with each other in front of the sub flow path outlet 202d, so that the invasion force is weakened. Such a configuration also has a good intake pulsation damping property for an engine that frequently blows back.

FIG. 10 shows an example of a minor change of the fifth embodiment of the hot-wire flow meter according to the present invention. Cover 225
Are the outlet openings 222 of the cut-off sub-channel 222c with the side walls 223a and 223b forming the radial sub-channel 222c.
The same width is formed up to the portions d and 222e. Therefore, the width of a portion corresponding to the windbreak wall 204 in FIG. 20 is formed to be large, and 224a and 224b are formed as windbreak walls for the sub flow passage outlets 222d and 222e.

FIG. 11 and FIG. 12 are structural diagrams of models in which the effect of windbreak wall dimensions on noise is tested. Therefore, it can be said that this is also one embodiment of the present invention. FIG. 13 shows an example of the experimental result.

The experimental method and the like will be described with reference to a structural diagram and the like. Probe holder block 253 coupled to circuit unit 2
Is separate from the body 250. Inside the block 253, a sub flow path 252 formed of an axial sub flow path 252b and a radial sub flow path 252c parallel to the main flow path 251 is formed. Before the radial sub-channel 252c is incorporated, the sub-channel 252c has a width d and a depth w that are machined from the direction of the throttle valve 3 by an end mill.
A cover 256 fixed by bolts 257 is added. On the other hand, the axial flow path is a circular cross-sectional flow path having an inner diameter φd, and has a long axial distance by adding a pipe 255 in order to reduce upstream turbulence.

The example of the experimental result shown in FIG.
Upstream of the standard rounder air filter (donut type)
The test was carried out under conditions of relatively small drift without providing a net at the inlet of the flow meter. Flow rate is 10
g / sec, 40 g / sec, and 140 g / sec are shown. The flow rate is changed by the height h of the windbreak wall 254 changed by the sonic test stand and the width in the axial direction of the outlet of the sub flow path. In order to see the correlation with w, several windproof walls 254 having different heights h were prepared, and experiments were performed by changing these. In this experimental result example, the ratio b / d of the width b of the windbreak wall and the width d (radial direction) of the sub-flow passage is 1.5. The horizontal axis in FIG. 13 is h / w. As shown in the experimental result example of FIG. 13 , the flow rate, that is, the magnitude of the flow velocity is slightly different, but at least h / w compared to the case where the windbreak wall is not provided.
It was found that the noise was reduced by providing a windbreak wall of about 0.5 or more. In addition, it can be seen that in the range of h / w ≒ 0.5 to 1.0, the noise is rapidly reduced as the height h of the windbreak wall is increased, and the noise reduction is further reduced when the height h is further increased. Therefore, the effective noise reduction effect is
h / w> 0.6 and the sufficient noise reduction effect is h
/W>1.0w.

On the other hand, the ratio b / d of the width d of the sub flow path outlet to the width b of the windbreak wall also affects the noise reduction effect, and 1.3 <b / d <2.
About 0 is qualitatively effective. That is, when b / d is small, the main flow is wrapped around the side surface, so even if h / w is good, the effect is reduced. On the other hand, if it is too large, the resistance of the main flow path becomes unfavorable from the viewpoint of overall pressure loss and the like.

[0035]

According to the present invention, a sensor having a heating element is provided.
And the sub flow path and the main flow path
This improves the assemblability of the air flow meter and replaces the sensor.
And maintenance becomes easier.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an internal combustion engine using a hot wire air flow meter of the present invention.

FIG. 2 is a sectional view showing a first embodiment of a hot-wire air flow meter according to the present invention.

FIG. 3 is a sectional view taken along line II of FIG. 2;

FIG. 4 is a view taken in the direction of arrows II-II in FIG. 2;

FIG. 5 is a cross-sectional view of FIG.

FIG. 6 is a longitudinal sectional view showing a second embodiment of the present invention.

FIG. 7 is a longitudinal sectional view showing a third embodiment of the present invention.

FIG. 8 is a longitudinal sectional view showing a fourth embodiment of the present invention.

FIG. 9 is a longitudinal sectional view showing a fourth embodiment of the present invention.

FIG. 10 is a longitudinal sectional view showing a fifth embodiment of the present invention.

FIG. 11 is a structural diagram of a model in which an effect of a windbreak wall on noise is tested.

FIG. 12 is a structural diagram of a model in which an effect of a windbreak wall on noise is tested.

FIG. 13 is a view showing an experimental result.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Air flow meter, 11 ... Main flow path, 12 ... Sub flow path, 2a ...
Hot wire element.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mitsukuni Tsutsui 2520 Oji Takaba, Katsuta-shi, Ibaraki Co., Ltd.Sawa Plant, Hitachi, Ltd. Hitachi, Ltd., Sawa Plant (72) Inventor, Tadao Osawa, 2520, Oji Takaba, Katsuta, Ibaraki, Ltd.Hitachi, Ltd. Inside the Sawa Plant (56) References Japanese Utility Model Showa 60-174828 (JP, U)

Claims (5)

(57) [Claims] 1. A main flow path constituting an intake air flow path of an internal combustion engine, a heating element for measuring intake air, and a sub flow path having the heating element therein and provided in the main flow path. In the air flowmeter provided, the sub-flow path has an inlet opening on the upstream side and an axial flow path formed in the axial direction of the main flow path, and is bent to the downstream side of the axial flow path. A probe holder block provided inside the probe holder block, wherein the probe holder block includes a circuit unit for the heating element, and is provided with an opening provided in a wall surface of the main flow path. An air flow meter, which is inserted into the inside and is cantilevered so as to be detachable from the main flow path. 2. The probe holder block according to claim 1, wherein the probe holder block has an outlet opening surface of the sub flow path substantially along the axial direction of the main flow path, and the upstream side protrudes from the downstream side. An air flow meter having an outlet opening. 3. The sub-flow path according to claim 1, wherein an axial flow path having an entrance opening of the sub-flow path is provided eccentrically with respect to a center axis of the main flow path, and is provided downstream of the sub-flow path. When the throttle valve is rotated around its rotation axis and opened, an inlet opening of the sub-flow path is provided on a side of the throttle valve that is displaced upstream from the rotation axis, and the throttle valve is rotated. An air flow meter, wherein an outlet opening of the sub-flow path is provided on a side displaced downstream from a moving shaft. 4. The apparatus according to claim 1, wherein the sub flow path has an outlet opening surface substantially along the axial direction of the main flow path, and the probe holder block is provided on an upstream side of the outlet opening surface.
An air flow meter having a member for preventing a flow of the main flow path from joining with a flow of the sub flow path immediately after the outlet opening. 5. A speed sensor for detecting a rotation speed of the engine,
A fuel injection device for injecting fuel, an air flow meter, and a corresponding fuel injection amount are obtained based on the intake air amount detected by the air flow meter and the rotation speed detected by the speed sensor. A control device for outputting a command for injecting an amount of fuel to the fuel injection device, wherein the air flow meter measures a main flow path forming an intake air flow path of the internal combustion engine, and an intake air amount. A heating element, and a sub-flow path having the heating element therein and provided in the main flow path, wherein the sub-flow path has an inlet opening on the upstream side and has an axial direction of the main flow path. An axial flow path formed in the probe, a bent flow path bent downstream of the axial flow path and turned back upstream, is configured inside a probe holder block, the probe holder block, Heating element circuit unit Includes the door, said is inserted into the main channel through an opening provided in the wall of the main channel, removably cantilevered be that the internal combustion engine, wherein with respect to said main passage.