JP6499494B2 - Air-fuel ratio sensor and imbalance determination system using the same - Google Patents

Description

  The present invention relates to an air-fuel ratio sensor used for imbalance determination for determining an air-fuel ratio imbalance between cylinders of a multi-cylinder internal combustion engine, and an imbalance determination system using the same.

In a multi-cylinder internal combustion engine having a plurality of cylinders, the injection performance of the injectors provided in each cylinder and the intake air distribution amount for each cylinder vary, and the actual air-fuel ratio varies among the cylinders. There is a risk that exhaust emissions will deteriorate. Therefore, an air-fuel ratio sensor is attached to the exhaust side of the multi-cylinder internal combustion engine, and the presence or absence of air-fuel ratio variation (air-fuel ratio imbalance) between the cylinders is determined based on the output of the air-fuel ratio sensor.
By the way, the air-fuel ratio sensor houses a detection element for detecting the concentration of gas such as oxygen in the exhaust gas in a housing, a case, etc., and a lead wire electrically connected to the detection element from the inside of the case to the outside. It has a drawn-out configuration. An external circuit (ECU) is connected to the lead wire via a connector or the like, and an output signal from the detection element is taken out to detect an imbalance abnormality.
Furthermore, the lead wire exposed to the outside of the case is covered with a protective tube to prevent damage to the lead wire or to suppress deterioration of the lead wire due to heat from the outside (see Patent Document 1).

JP 2008-3076 A (paragraphs 0002 and 0035)

By the way, as a protective tube, what coated the silicone varnish to the braided body of glass fiber is known. Such a protective tube is shipped in a state in which the lead wire drawn out of the case of the air-fuel ratio sensor is covered. However, it was found that the siloxane contained in the silicone varnish of the protective tube volatilizes and adheres to the detection portion (especially the electrode) of the detection element during shipping, and the electrode is poisoned. In this case, the sensor output is delayed when the sensor is used.
When the sensor output is delayed, as shown in FIG. 4, for example, the sensor output (air-fuel ratio) of the third cylinder of a four-cylinder engine can obtain the original output characteristic (solid line in FIG. 4) at timing t3. When the sensor output is delayed, an erroneous output characteristic (broken line in FIG. 4) is acquired at timing t4 when the sensor output (air-fuel ratio) of the fourth cylinder is detected, and the cylinder in which imbalance occurs is appropriately determined. Becomes difficult.
Therefore, the present invention prevents the poisoning of the detection element due to the influence of the protective tube, and uses the air-fuel ratio sensor used for imbalance determination capable of appropriately determining the cylinder in which the imbalance has occurred, and the same. The purpose is to provide an imbalance determination system.

In order to solve the above problems, an air-fuel ratio sensor for imbalance determination according to the present invention is connected to a detection element extending in an axial direction, a cylindrical housing surrounding the detection element, and a rear end side of the housing. A cylindrical case, a lead wire that is electrically connected to the detection element and taken out from the inside of the case, and a protective tube that covers the lead wire outside the case. In an air-fuel ratio sensor for imbalance determination that determines an air-fuel ratio imbalance between cylinders of an internal combustion engine, the protective tube is formed by applying acrylic resin to the surface of a braided body of glass fiber, or polyphenylene sulfide fiber And a polyether ether ketone fiber.
According to this air-fuel ratio sensor for imbalance determination , the protective tube is formed by coating acrylic resin on the surface of a glass fiber braid or a braid of polyphenylene sulfide fiber and polyether ether ketone fiber. . As a result, during shipping of the air-fuel ratio sensor for imbalance determination with the lead wire covered with the protective tube, since the protective tube does not contain siloxane, the siloxane volatilizes and the detection unit ( In particular, it is possible to prevent the electrode from being poisoned by adhering to the electrode. As a result, it is possible to appropriately determine the cylinder in which the imbalance has occurred without causing a delay in the sensor output. Further, by using the above-described protective tube, it is possible to prevent the lead wire from being damaged, which is the original role of the protective tube, or to suppress deterioration of the lead wire due to heat from the outside.

An imbalance determination system according to the present invention includes an air-fuel ratio sensor for imbalance determination attached to an exhaust side of a multi-cylinder internal combustion engine, and an output of the air-fuel ratio sensor for imbalance determination based on the output of the air-fuel ratio sensor for imbalance determination. An imbalance determination system comprising: a determination means for determining an air-fuel ratio imbalance between the cylinders of claim 1. The imbalance determination air-fuel ratio sensor according to claim 1 as the imbalance determination air-fuel ratio sensor. In use, the determination means is electrically connected to the lead wire.
By using an air-fuel ratio sensor for imbalance determination using the above-described protective tube in such an imbalance determination system, the sensor output is not delayed, and the cylinder in which the imbalance has occurred can be appropriately selected. Can be determined.

  According to this invention, it is possible to prevent the detection element from being poisoned by the influence of the protective tube, and to appropriately determine the cylinder in which the imbalance has occurred.

It is a schematic block diagram which shows an example of the engine to which the air fuel ratio imbalance determination system of this invention is applied. 1 is an external view of an air-fuel ratio sensor according to an embodiment of the present invention. 1 is a cross-sectional structure diagram along an axial direction of an air-fuel ratio sensor according to an embodiment of the present invention. It is a schematic diagram of imbalance determination using a conventional air-fuel ratio sensor.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 is a schematic configuration diagram showing an example of an engine 100 to which the air-fuel ratio imbalance determination system of the present invention is applied.
The engine 100 is a port injection type four-cylinder engine (spark ignition type internal combustion engine) mounted on a vehicle, and a cylinder block (not shown) constituting each cylinder # 1, # 2, # 3, # 4 A piston (not shown) is provided inside. A spark plug 103 is disposed in the combustion chamber of the engine 100. An intake passage 111 and an exhaust passage 112 are connected to the engine 100, and a part of the intake passage 111 is formed by an intake port 111a and an intake manifold (not shown). A part of the exhaust passage 112 is formed by an exhaust port 112a and an exhaust manifold 112b.
In an intake passage 111 of the engine 100, an air cleaner 107 that filters intake air, a hot-wire air flow meter 133, an intake air temperature sensor 134 (built in the air flow meter 133), a turbocharger 300, an intercooler 104, and an intake air amount of the engine 100 A throttle valve 105 and the like for adjusting the pressure are arranged. The throttle valve 105 is driven by a throttle motor 106. The opening degree of the throttle valve 105 is detected by a throttle opening degree sensor 135.

An injector (fuel injection valve) 102 capable of injecting fuel is disposed in the intake port 111 a of the intake passage 111. The injector 102 is provided for each cylinder # 1 to # 4. These injectors 102 are connected to a common delivery pipe 191, and fuel is supplied to the delivery pipe 191. Then, the fuel injected by the injector 102 is mixed with the intake air to become an air-fuel mixture, and in each cylinder # 1 to # 4, the first cylinder # 1 → the third cylinder # 3 → the fourth cylinder # 4 → the second Combustion and explosion in the order of 102 cylinder # 2. The combustion gas is discharged to the exhaust passage 112.
The operating state of the engine 100 is controlled by an ECU (Electronic Control Unit) 200.

On the other hand, an upstream catalyst 181 and a downstream catalyst 182 are arranged in series in the exhaust passage 112 of the engine 100. These upstream catalyst 181 and downstream catalyst 182 together constitute a three-way catalyst. An air-fuel ratio sensor (A / F sensor) 1 is provided in the exhaust passage 112 upstream of the upstream catalyst 181 (upstream of the exhaust flow). An O 2 sensor (oxygen sensor) 138 is disposed in the exhaust passage 112 on the downstream side (downstream of the exhaust flow) of the upstream catalyst 181. The O2 sensor 138 is an oxygen concentration sensor whose output value changes stepwise in the vicinity of the theoretical air-fuel ratio (stoichiometric).
The air-fuel ratio sensor 1 will be described later. The air-fuel ratio sensor 1 includes a lead wire 64 and a protective tube 68 that covers the lead wire 64 (see FIG. 2), and the air-fuel ratio sensor 1 is electrically connected to the ECU 200 via the lead wire 64. The air-fuel ratio sensor 1 corresponds to an “air-fuel ratio sensor” in the claims. The air-fuel ratio sensor 1 and the ECU 200 correspond to the “imbalance determination system” in the claims, and the ECU 200 corresponds to the “determination means” in the claims.
The output signals from the air-fuel ratio sensor 1 and the O2 sensor 138 are input to the ECU 200. The ECU 200 executes air-fuel ratio feedback control (stoichiometric control) based on the outputs of the air-fuel ratio sensor 1 and the O2 sensor 138.

The ECU 200 includes a known CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and the like. The ROM stores various control programs, maps that are referred to when the various control programs are executed, and the like. The CPU executes various arithmetic processes based on various control programs and maps stored in the ROM. In addition, the RAM temporarily stores calculation results in the CPU, data input from each sensor, and the like.
Then, ECU 200 executes the above-described air-fuel ratio feedback control in addition to the various controls of engine 100 based on the detection signals of the various sensors described above. Further, the ECU 200 determines the air-fuel ratio imbalance.
The air-fuel ratio imbalance determination is performed when an abnormality that affects all cylinders # 1 to # 4 of the engine 100 occurs in the fuel supply system such as the injector 102 and the air system such as the air flow meter 133. Since the absolute value of the feedback control correction amount increases, this can be detected by monitoring with the ECU 200. For example, when the charge injection amount is deviated from the stoichiometric amount by a predetermined amount as a whole, correction is performed with a correction amount that corrects the deviation amount. When the feedback correction amount becomes equal to or greater than a predetermined determination threshold, it can be detected that the fuel supply system or the air system is abnormal.
Further, as described above, since combustion and explosion occur in the order of the first cylinder # 1, the third cylinder # 3, the fourth cylinder # 4, and the 102nd cylinder # 2, as shown in FIG. Since the output characteristics of the air-fuel ratio sensor 1 are obtained for each cylinder in this order, the stoichiometric amount for each cylinder can be acquired based on these output characteristics.

Next, the air-fuel ratio sensor 1 will be described with reference to FIGS.
FIG. 2 is an external view of the air-fuel ratio sensor 1 according to the embodiment of the present invention. The air-fuel ratio sensor 1 is connected to a detection element 10 (see FIG. 3), a cylindrical metal shell (corresponding to “housing” in the claims) 50 surrounding the detection element 10, and a rear end side of the housing. Outer cylinder 65 (corresponding to “case” in claims), lead wire 64 taken out from the inside of case 65, protective tube 68 covering lead wire 64 outside case 65, lead And a connector 69 connected to the end of the line 64. And the connector part 69 (for example, male connector) is electrically connected to the pair connector (for example, female connector; not shown) of ECU200.
FIG. 3 shows a cross-sectional structure along the axis O direction of the air-fuel ratio sensor 1 according to the embodiment of the present invention. In this embodiment, the air-fuel ratio sensor 1 is inserted into the exhaust pipe of an automobile, the tip (arrow F side in FIG. 3) is exposed to the exhaust gas, and the entire area is empty to detect the air-fuel ratio from the oxygen concentration in the exhaust gas. It is a fuel ratio sensor. The detection element 10 is a known detection element that constitutes an oxygen concentration cell in which a pair of electrodes are stacked on an oxygen ion conductive solid electrolyte body and outputs a detection value corresponding to the amount of oxygen.
The lower side (arrow F side) in FIG. 3 is the front end side of the air-fuel ratio sensor 1, and the upper side in FIG.

  The air-fuel ratio sensor 1 includes a cylindrical metal shell 50 having an external thread portion 51 formed on the outer surface for fixing to an exhaust pipe, an outer cylinder 65 connected to the rear end of the metal shell 50, and the metal shell 50. , A detection element 10 having a plate shape extending in the direction of the axis O, and a cylindrical flange portion 24 disposed in the metal shell 50 so as to surround the circumference of the detection element 10 in the radial direction. The sealing material 26 and the ceramic sleeve 27, the separator 60 surrounding the rear end of the detection element, the holding metal fitting 70 holding the separator 60, and the connection terminal 61 electrically connected to the rear end of the detection element 10, And a grommet 75 that closes the rear end of the outer cylinder 65.

  The detection element 10 has a detection unit 11 (an electrode of the above-described oxygen concentration cell) at the tip, and a heater (not shown) is laminated. An electrode portion 12 provided with five electrode pads 16 (two are shown in FIG. 3) for taking out a detection value output from the detection portion 11 and operating the heater is formed at the rear end of the detection element 10. Has been.

The metal shell 50 is formed in a substantially cylindrical shape, and in order from the front end side to the rear end side, the front end engaging portion 56, the male screw portion 51, the hexagon wrench, etc., are expanded in diameter, and the rear end portion. 57 and a caulking portion 53. In addition, a gasket 55 that prevents gas escape when attached to the exhaust pipe is fitted into a step portion between the front end surface of the flange portion 52 and the rear end of the male screw portion 51.
Further, the metal shell 50 has a through hole 58 that penetrates in the direction of the axis O, and the shelf 54 protrudes radially inward of the through hole 58, and the shelf 54 is inclined with respect to a plane perpendicular to the axis O direction. Is formed as an inwardly tapered surface.

Inside the through hole 58 of the metal shell 50, an annular ceramic ring 21, sealing materials 22 and 26 made of talc, and the above-mentioned ceramic sleeve 27 are arranged in this order in a state surrounding the circumference of the detection element 10 in the radial direction. It is laminated from the rear end side. A metal cup 20 is disposed between the ceramic ring 21 and the sealing material 22 and the metal shell 50, and the metal cup 20 is locked to the shelf 54. When the sealing material 22 is crushed, the ceramic ring 21, the sealing material 22, and the metal cup 20 become an integral flange portion 24 to hold the detection element 10 and maintain airtightness.
Accordingly, the detection element 10 is held by the metal shell 50 in a state where the front end side of the detection element 10 protrudes from the front end side of the through hole 58 and the electrode pad 16 protrudes from the rear end side of the through hole 58.
A caulking packing 29 is disposed along the shoulder 28 of the ceramic sleeve 27 between the ceramic sleeve 27 and the caulking portion 53 of the metal shell 50, and the caulking portion is interposed via the caulking packing 29. The ceramic sleeve 27 is pressed to the front end side by crimping 53 downward (front end side), and the sealing materials 22 and 26 are crushed.

  On the other hand, the outer periphery of the front end engaging portion 56 of the metal shell 50 covers the protruding portion of the detection element 10 and has a bottomed cylindrical shape having a plurality of holes 85 and 95 (for example, stainless steel) double. The outer protector 80 and the inner protector 90 are attached by welding or the like.

A cylindrical outer cylinder 65 is fixed around the outer periphery of the rear end portion 57 of the metal shell 50, and the outer cylinder 65 accommodates the rear end side of the detection element 10. A separator 60 surrounding the electrode portion 12 of the detection element 10 is disposed inside the outer cylinder 65. The separator 60 has a cylindrical shape having a contact insertion hole 60a penetrating in the axial direction, and the connection terminals 61 provided on the inner surface of the contact insertion hole 60a are electrically connected to the electrode pads 16 of the detection element 10, respectively. It has become. Then, five lead wires 64 (only three in FIG. 3) connected to the connection terminal 61 are drawn out to the rear end side of the outer cylinder 65 through the contact insertion hole 60a.
A cylindrical metal holding metal fitting 70 is disposed between the separator 60 and the outer cylinder 65, and the rear end of the holding metal fitting 70 is bent inward to form the support portion 71. Then, the enlarged diameter flange portion 62 provided on the rear end side of the separator 60 is locked to the support portion 71, and the separator 60 is held by the holding metal fitting 70. The holding metal fitting 70 is swaged inward together with the outer cylinder 65 and fixed to a predetermined position of the outer cylinder 65.
Further, the grommet 75 closes the rear end opening of the outer cylinder 65, and each lead wire 64 is airtightly inserted through the lead wire insertion hole 76 that penetrates the grommet 75 in the axial direction, and is drawn out. The grommet 75 is crimped inward together with the outer cylinder 65 to be fixed to the rear end of the outer cylinder 65, and further presses the rear surface of the separator 60 toward the front end side.
In FIG. 3, the protection tube 68 is not shown.

In the present invention, the protective tube 68 is formed by coating an acrylic resin on the surface of a braided body of glass fiber or a braided body of polyphenylene sulfide fiber and polyetheretherketone fiber, and siloxane is used as a component of the protective tube 68. Is not included.
For this reason, since the protective tube 68 does not contain siloxane in the middle of shipping the air-fuel ratio sensor 1 with the lead wire 64 covered with the protective tube 68 described above, the siloxane is volatilized and the detection element 10 is detected. It adheres to a part (especially electrode) and can prevent that an electrode is poisoned. As a result, it is possible to appropriately determine the cylinder in which the imbalance has occurred without causing a delay in the sensor output. Further, by using the protective tube 68 described above, it is possible to prevent damage to the lead wire 64, which is the original role of the protective tube 68, or to suppress deterioration of the lead wire 64 due to heat from the outside.
The acrylic resin is applied to the glass fiber braid as long as the acrylic resin is applied to at least the surface of the glass fiber braid, but the glass fiber braid is impregnated with the acrylic resin. More preferably.
In addition, by using the air-fuel ratio sensor 1 using the above-described protective tube 68 in such an imbalance determination system, the sensor output is not delayed, and the cylinder in which the imbalance has occurred is appropriately determined. be able to.

  It goes without saying that the present invention is not limited to the above-described embodiment, but extends to various modifications and equivalents included in the spirit and scope of the present invention.

1 Air-fuel ratio sensor 10 Detection element 50 Metal shell (housing)
64 Lead wire 65 Outer cylinder (case)
68 Protective tube 100 Multi-cylinder internal combustion engine (engine)
# 1 to # 4 Cylinder 200 Determination means (ECU)
O Axial direction

Claims (2)

A sensing element extending in the axial direction;
A cylindrical housing surrounding the detection element;
A cylindrical case connected to the rear end side of the housing;
A lead wire electrically connected to the detection element and taken out from the inside of the case;
A protective tube for covering the lead wire outside the case; and an air-fuel ratio sensor for imbalance determination for determining an air-fuel ratio imbalance between cylinders of a multi-cylinder internal combustion engine.
The protective tube is an air-fuel ratio sensor for imbalance determination , in which an acrylic resin is applied to the surface of a glass fiber braid or a braid of polyphenylene sulfide fiber and polyether ether ketone fiber. An air-fuel ratio sensor for imbalance determination attached to the exhaust side of the multi-cylinder internal combustion engine;
An imbalance determination system comprising: a determination unit that determines an imbalance of the air-fuel ratio between the cylinders of the multi-cylinder internal combustion engine based on an output of the air-fuel ratio sensor for determining the imbalance.
2. An imbalance determination system in which the air-fuel ratio sensor for imbalance determination according to claim 1 is used as the air-fuel ratio sensor for imbalance determination, and the determination means is electrically connected to the lead wire.

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