This application is related to Japanese Patent Application No. 2007-186781 filed on Jul. 18, 2007, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a gas sensor mounted on an exhaust system or the like of an internal engine to measure a concentration of a specific gas contained in a gas under measurement.
2. Description of Related Art
To perform combustion control of an internal combustion engine such as a vehicle engine on the basis of an air-fuel ratio of the engine, as shown in
The exhaust gas G flowing through an exhaust pipe of the exhaust system enters inside the element cover 93 through the vent holes 933, and reaches the gas sensor element 92. By the exhaust gas G contacting the gas sensor element 92, it is possible to measure an oxygen concentration in the exhaust gas G. Incidentally, when the engine is cold-started, it may occur that moisture contained in the exhaust gas G is condensed to waterdrops when it contacts an inner wall surface of the cold exhaust pipe. If the engine is started up in this state, the waterdrops are blown off the inner wall surface and enters inside the element cover 93 together with the exhaust gas G, particularly during a period in which the temperature of the exhaust gas G is still low, and accordingly the waterdrops are not vaporized.
On the other hand, for the gas sensor element 92 to perform measurement, it is necessary to keep the gas sensor element 92 constituted by a solid electrolyte body at a high temperature, higher than 400 degrees C. so that it is kept in an active state. Accordingly, if the waterdrops W which have entered inside the element cover 93 adhere to a surface of the gas sensor element 92, cracks may occur in the gas sensor element 92 due to thermal shock.
To cope with this problem, in the system shown in
If this happens, cracks may occur in the gas sensor element 92 due to the waterdrops W adhering to the gas sensor element 92.
To cope with this problem, as shown in
As shown in
The present invention provides a gas sensor comprising:
a gas sensor element for measuring a concentration of a specific gas contained in a measurement gas;
a housing through which the gas sensor element is inserted in a longitudinal direction of the gas sensor; and
an element cover fixed to a front end portion of the housing;
the element cover including an inner cover and an outer cover located around the inner cover,
the outer cover being formed with a plurality of outer openings at a side surface thereof, and including a front end portion formed with a discharge opening, the discharge opening being located more closely to a front end side of the gas sensor than the outer openings,
the inner cover being formed with a plurality of inner openings at a side surface thereof, the inner openings being located more closely to the front end side of the gas sensor than the outer openings,
an opening direction of each of the inner openings extending from an inner side to an outer side of the inner cover having a direction component extending in the longitudinal direction towards a base end side of the gas sensor,
wherein, when a clearance between the outer and inner covers at a longitudinal position of the outer openings is A, and an inner diameter of the outer cover at the longitudinal position is B, a ratio of A/B is equal to or larger than a predetermined value.
According to the present invention, it is possible to provide a gas sensor having a high response speed, and a capability of preventing cracks from occurring therein due to moisture contained in a measurement gas.
Other advantages and features of the invention will become apparent from the following description including the drawings and claims.
In the accompanying drawings:
As shown in
As shown in
As shown in
When the distance of a clearance 43 between the outer cover 42 and the inner cover 41 at a longitudinal position of the outer openings 421 is A, and an inner diameter of the outer cover 42 at the same longitudinal position is B, the relationship of A/B≧0.083 holds.
In this embodiment, the distance A is equal to or larger than 1 mm.
In the following, the gas sensor 1 of this embodiment is explained in more detail. As shown in
The inner cover 42 includes a first inner diameter-varying portion 413a located on the front end side, and a second inner diameter-varying portion 413b located on the base end side, each having a tapered shape in which the diameter thereof reduces towards the front end side. As shown in
The inner cover 41 includes a front end portion formed with a front end opening 412 which opens to the outside. The front end opening 412 may have a diameter of 2 mm. The inner cover 41 also includes an opposite side portion 415 formed so as to be opposite to the outer openings 421 and extend in parallel with the longitudinal axis of the gas sensor 1. The opposite side portion 415 is located more closely to the base end side of the gas sensor 1 than the first and second inner diameter-varying portions 413a and 413b.
The outer cover 42 includes a front end portion formed with a large-diameter opening 424 whose inner diameter (6 mm, for example) is larger than an outer diameter (5 mm, for example) of the front end portion of the inner cover 41. By inserting the front end portion of the inner cover 41 into the large-diameter opening 424, there is formed the discharge opening 422 having a width of 0.5 mm, for example, between an outer wall of the front end portion and an inner wall of the large-diameter opening 424.
The front end portion of the inner cover 41 may protrude from or recede from the front end portion of the outer cover 42. As shown in
As described above, in this embodiment, the distance A of the clearance 43 between the outer cover 42 and the inner cover 41 at the longitudinal position of the outer openings 421, and the inner diameter B of the outer cover 42 at the same longitudinal position are in the relationship of A/B≧0.083. As shown in
As shown in
The gas sensor element 2 includes a solid electrolyte body consisting primarily of zirconia at one surface thereof, and a reference gas side electrode and a measurement gas side electrode at the other surface thereof. The gas sensor element 2 also includes therein a heater. The heater heats the gas sensor element 2 at a high temperature of over 400 degrees C. to keep the gas sensor element 2 in an active state while the gas sensor 1 is in operation.
Next, the operation and advantages of the gas sensor 1 are explained. The element cover 4 is provided with the outer openings 421 and the discharge opening 422 at its outer cover 42, and provided with the inner openings 411 at its inner cover 41. The inner openings 411 are located more closely to the front end of the gas sensor 1 than the outer openings 421. Accordingly, as shown in
As described above, the sensing portion of the gas sensor element 2 is located more closely to the front end than the inner openings 411, and the inner openings 411 are formed such that the opening direction X includes a direction component which is parallel to the longitudinal axis of the gas sensor 1, and extends to the base end of the gas sensor 1. Accordingly, of the flow of the measurement gas G introduced into the inside of the outer cover 42 through the outer openings 421, the flow G1 heading to the discharge opening 42 is flowing in a comparatively rectilinear flow, while, the flow G2 heading from the inner openings 411 to the inside of the inner cover 41 is flowing in a comparatively curvilinear flow.
Accordingly, waterdrops flowing together with the measurement gas and introduced between the outer cover 42 and the inner cover 41 head to the discharge opening 422 and are discharged therethrough due to inertial force. That is, since the waterdrops have a large specific gravity compared to the measurement gas, the waterdrops move along the rectilinear flow G1, and are discharged from the discharge opening 422. On the other hand, the measurement gas having a small specific gravity compared to the waterdrops can move along the curvilinear flow G2 to enter inside the inner cover 41 other than along the rectilinear flow G1.
This makes it possible to prevent the waterdrops contained in the measurement gas from entering inside the inner cover 41, to thereby prevent the gas sensor element 2 from being flooded. Accordingly, the gas sensor element 2 can be prevented from cracking due to moisture contained in the measurement gas.
In addition, since the outer openings 421 and the inner openings 411 are formed in such positions that the waterdrops are prevented from entering inside the inner cover 41, the measurement gas can be introduced inside the element cover 4 in a sufficient quantity. This makes it possible for the gas sensor 1 to have a high response characteristic. Furthermore, since the gas sensor element 2 is not provided with any protection layer at its surface, and accordingly, the time needed for the measurement gas to reach the sensing section of the gas sensor element 2 is not prolonged, there is no lowering of response speed of the gas sensor 1. Also, since there is not increase in the heat capacity of the gas sensor element 2 due to provision of a protection layer, the time needed for the gas sensor element 2 to enter an active state does not become long.
In the gas sensor 1, the distance A of the clearance 43 between the outer cover 42 and the inner cover 41 at the longitudinal position of the outer openings 421, and the inner diameter B of the outer cover 42 at the same longitudinal position are in the relationship of A/B≧0.083. This makes it possible for a sufficient amount of the measurement gas introduced between the outer cover 42 and the inner cover 41 to easily enter inside the inner cover 41 from the inner openings 411. Accordingly, the measurement gas flowing through an exhaust pipe or the like can be smoothly and sufficiently supplied to the gas sensor element 2. As a result, a time lag between the change of an air-fuel ratio and the change of a sensor output can be made sufficiently small, to thereby improve the response characteristic of the gas sensor 1.
Furthermore, the distance A of the clearance 43 is made 1 mm or longer. This also makes it possible to sufficiently introduce the measurement gas between the outer cover 42 and the inner cover 41. Accordingly, the response characteristic of the gas sensor 1 can be further improved.
As shown in
Next, results of evaluation on the response characteristic of the gas sensor of the invention are explained with reference to
The measurement was performed in the following manner. One of these gas sensors was mounted on an exhaust pipe of a 3-liter in-line 6-cylinder engine. An internal combustion engine was run at a speed of 2000 rpm. As shown by the curve L1 in
The present invention is applicable to an air-fuel sensor mounted on an exhaust pipe of an internal combustion engine of a vehicle to perform exhaust gas feedback control, an O2 sensor for measuring an oxygen concentration of an exhaust gas, a Nox sensor used for detecting degradation of a ternary catalyst provided in an exhaust pipe to measure concentration of NOx as atmospheric pollutant, etc.
The above explained preferred embodiments are exemplary of the invention of the present application which is described solely by the claims appended below. It should be understood that modifications of the preferred embodiments may be made as would occur to one of skill in the art.
Number | Date | Country | Kind |
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2007-186781 | Jul 2007 | JP | national |