Patent Description:
Fuel cell vehicles that travel with electric power supplied from a fuel cell have been studied and developed widely. Fuel cells produce electric power through a chemical reaction of hydrogen and oxygen. Typically, hydrogen is supplied to a fuel cell as a fuel, while oxygen is taken from surrounding air into the fuel cell. A fuel cell vehicle includes a hydrogen tank from which hydrogen is supplied to the fuel cell. When the hydrogen tank is short of hydrogen, hydrogen is supplied to the hydrogen tank of a fuel cell vehicle from a hydrogen supply apparatus installed at a hydrogen station.

It is necessary to monitor leakage of hydrogen, which is flammable gas, from fuel cell vehicles and hydrogen supply apparatuses. Hydrogen sensors are therefore widely used along with fuel cell vehicles and hydrogen supply apparatuses. The hydrogen sensors measure the concentration of hydrogen contained in air and issue an alarm in response to the hydrogen concentration exceeding a predetermined value.

For apparatuses in which fluid circulates, such as a radiator or vacuum device of automobiles, abnormality is tested for by detecting leakage of helium while allowing helium to communicate within the apparatuses. Such a test is performed with various types of helium sensors, as helium detectors. Helium sensors, similar to hydrogen sensors, measure the concentration of helium contained in air or detect the concentration of helium exceeding a predetermined value.

The <CIT>, <CIT>, <CIT> and <CIT> disclose apparatuses that measure the concentration of specific gas. The apparatuses disclosed in these patent documents measure the concentration of specific gas based on propagation properties of ultrasound, such as a propagation velocity of ultrasound, in mixture gas such as air to be measured, and may be used for measurement of the concentration of hydrogen and helium, for example.

<CIT>, <CIT>, <CIT> and <CIT> disclose gas concentration sensors having a cylindrical shape of a sensing chamber wherein ventilation holes are provided for the gas to be measured to enter the measuring chamber.

Apparatuses that measure the concentration of specific gas based on the propagation velocity of ultrasound typically include a space in which the concentration of the gas is measured. This concentration measurement space includes an ultrasonic transducer that transmits and receives ultrasound. The propagation velocity of ultrasound is determined based on a propagation time, which is a time between transmission of ultrasound from a transmitting ultrasonic transducer and reception of ultrasound having propagated within the concentration measurement space by a receiving ultrasonic transducer, and a predetermined propagation distance.

While it is necessary to allow mixture gas such as air to be measured to externally flow into the concentration measurement space, sudden inflow of the air to be measured into the space may significantly change the propagation velocity and propagation direction of ultrasound, causing an error in measurements of the gas concentration.

An object of the present invention is to measure the gas concentration with high accuracy.

The present invention provides a gas concentration sensor with the features of claim <NUM> that inter alia includes a cylindrical body; an ultrasonic transducer disposed at a first end of the cylindrical body; an ultrasonic wave reflecting surface disposed at a second end of the cylindrical body and intersecting an axial direction of the cylindrical body; and a plurality of ventilation holes disposed in a peripheral wall of the cylindrical body. The plurality of ventilation holes have corresponding through lines each extending in a direction perpendicular to an axial section of the cylindrical body, the through lines of the plurality of ventilation holes pass different locations, and each of the ventilation holes has a shape extending in the axial direction of the cylindrical body.

The present invention enables highly accurate measurements of the gas concentration.

Each embodiment of the present invention will be described with reference to the drawings. Similar elements are designated with similar numerical references throughout a plurality of drawings. The terms used herein to refer to geometric shapes such as a cylindrical shape and a column shape may also refer to modified versions of the original geometric shapes modified to emphasize the function and aesthetic appearance of members.

<FIG> illustrates a gas concentration measurement apparatus <NUM> according to a first embodiment of the present invention. The gas concentration measurement apparatus <NUM> includes a gas sensor <NUM> and a body <NUM>. The gas sensor <NUM> includes a sensor enclosure <NUM> containing an ultrasonic transducer. The sensor enclosure <NUM> has a hollow cylindrical shape, that is, a column shape with a closed top. The sensor enclosure <NUM> includes, on its peripheral wall, ventilation holes <NUM> through which mixture gas such as air is allowed to flow into the sensor enclosure <NUM>. Under the control of the body <NUM>, ultrasound is transmitted from the ultrasonic transducer to the interior of the sensor enclosure <NUM>, and the ultrasound reflected within the sensor enclosure <NUM> is received by the ultrasonic transducer. The body <NUM> determines, based on the time when the ultrasonic transducer transmits ultrasound and the time when the ultrasonic transducer receives the ultrasound, a propagation time corresponding to a round-trip propagation time of ultrasound within the sensor enclosure <NUM>, and determines, based on the propagation time, the concentration of target gas.

<FIG> is a perspective view of the gas sensor <NUM>. The sensor enclosure <NUM> includes a front enclosure <NUM> and a rear enclosure <NUM>. The front enclosure <NUM> has an arch shaped upper part, corresponding to three-quarters of a front face of the sensor enclosure <NUM>. A rear face of the front enclosure <NUM> and a front face of the rear enclosure <NUM> are engaged with each other to form the sensor enclosure <NUM>. The front enclosure <NUM> and the rear enclosure <NUM> include a plurality of ventilation holes <NUM> for communication between the inside and the outside of the sensor enclosure <NUM>. Each ventilation hole <NUM> extends along the axis of the cylindrical shape of the sensor enclosure <NUM>. Thus, each ventilation hole <NUM> has a vertical length that is longer than a lateral length (width).

<FIG> is a front view of the gas sensor <NUM>, and <FIG> is a cross section (a cross section perpendicular to the axial direction) taken along AA line in <FIG>. As illustrated in <FIG>, the gas sensor <NUM> includes, on its front face, seven ventilation holes <NUM> arranged in three rows: two ventilation holes <NUM> arranged laterally in an upper row; three ventilation holes <NUM> arranged laterally in a middle row; and two ventilation holes <NUM> arranged laterally in a lower row. The ventilation hole <NUM> on the left in the upper row is disposed above a space between the ventilation hole <NUM> on the left in the middle row and the ventilation hole <NUM> at the center in the middle row, and the ventilation hole <NUM> on the right in the upper row is disposed above a space between the ventilation hole <NUM> on the right in the middle row and the ventilation hole <NUM> at the center in the middle row. The ventilation hole <NUM> on the left in the lower row is disposed below a space between the ventilation hole <NUM> on the left in the middle row and the ventilation hole <NUM> at the center in the middle row, and the ventilation hole <NUM> on the right in the lower row is disposed below a space between the ventilation hole <NUM> on the right in the middle row and the ventilation hole <NUM> at the center in the middle row.

<FIG> is a rear view of the gas sensor <NUM>. The gas sensor <NUM> includes, on its rear face, eight ventilation holes <NUM> arranged in three rows: three ventilation holes <NUM> arranged laterally in an upper row; two ventilation holes <NUM> laterally arranged in a middle row; and three ventilation holes <NUM> laterally arranged in a lower row. The ventilation hole <NUM> on the left in the middle row is disposed below a space between the ventilation hole <NUM> on the left in the upper row and the ventilation hole <NUM> at the center in the upper row, that is, above a space between the ventilation hole <NUM> on the left in the lower row and the ventilation hole <NUM> at the center in the lower row. The ventilation hole <NUM> on the right in the middle row is disposed below a space between the ventilation hole <NUM> on the right in the upper row and the ventilation hole <NUM> at the center in the upper row. that is, above a space between the ventilation hole <NUM> on the right in the lower row and the ventilation hole <NUM> at the center in the lower row. The ventilation holes <NUM> on the left and right and at the center in the upper row are disposed above the ventilation holes <NUM> on the left and right and at the center in the lower row, respectively, via a region where the ventilation holes <NUM> in the middle row are arranged.

Referring back to <FIG>, the positional relationship between the ventilation holes <NUM> disposed on the front enclosure <NUM> and the ventilation holes <NUM> disposed on the rear enclosure <NUM> will be described. Each ventilation hole <NUM> extends in the front-rear direction through the peripheral wall of the sensor enclosure <NUM>. <FIG> shows, with dashed and double-dotted lines, through lines <NUM> extending through the ventilation holes <NUM> and perpendicular to the axial section of the sensor enclosure <NUM>, which is a plane parallel to the front and rear faces. The through line <NUM> is a straight line extending in the same direction as the through direction of the ventilation hole <NUM>. The through lines <NUM> extending from the respective ventilation holes <NUM> pass through different locations. Therefore, the ventilation holes <NUM> disposed on the front enclosure <NUM> and the ventilation holes <NUM> disposed on the rear enclosure <NUM> do not exist on the same through lines <NUM>.

<FIG> illustrates a front view of the gas sensor <NUM> with the front enclosure <NUM> being removed. The gas sensor <NUM> includes an ultrasonic transducer <NUM> in a region below a region where the ventilation holes <NUM> are disposed in the rear enclosure <NUM>. The rear enclosure <NUM> includes, at its upper end, a top board <NUM> having a board face perpendicular to the axial direction of the sensor enclosure <NUM>. The front enclosure <NUM> is fitted to the rear enclosure <NUM> from the front, to thereby form the sensor enclosure <NUM>.

The sensor enclosure <NUM> formed from the front enclosure <NUM> and the rear enclosure <NUM> includes a cylindrical body <NUM>, as a cylindrical member, having an upper end closed with the top board <NUM>. The ultrasonic transducer <NUM> is disposed toward the lower end of the cylindrical body <NUM>, and an ultrasound propagation path along which ultrasound propagates is formed between the ultrasonic transducer <NUM> and the top board <NUM>. The sensor enclosure <NUM> further includes a plurality of ventilation holes <NUM> on the peripheral wall of the cylindrical body <NUM>.

The ratio of the area of openings of all the ventilation holes <NUM> with respect to the area of the peripheral face of the sensor enclosure <NUM> may be <NUM>% or greater and <NUM>% or less, and preferably <NUM>% or greater and <NUM>% or less. A belt-shaped ventilation region surrounding the peripheral face of the sensor enclosure <NUM>, where the ventilation holes <NUM> are disposed, may have an area which is <NUM>% of the area of the peripheral face of the sensor enclosure <NUM>. The number of ventilation holes <NUM> in the ventilation region may be, for example, one or more and six or less per <NUM><NUM>, and preferably two or more and five or less per <NUM><NUM>.

Assuming that <FIG> is an axial cross section of the gas sensor <NUM>, operation of the gas sensor <NUM> will be described. The ventilation holes <NUM> disposed in the sensor enclosure <NUM> ventilate the internal space of the sensor enclosure <NUM> serving as a concentration measurement space. Specifically, the air outside the sensor enclosure <NUM> flows through the ventilation holes <NUM> disposed in the sensor enclosure <NUM> into the sensor enclosure <NUM>. The air inside the sensor enclosure <NUM> flows through the ventilation holes <NUM> disposed in the sensor enclosure <NUM> out of the sensor enclosure <NUM>. To facilitate ventilation of the air, a user may move the gas concentration measurement apparatus <NUM> (see <FIG>) in the air.

The ultrasonic transducer <NUM> transmits ultrasound based on a transmitting signal output from a controller included in the body <NUM> illustrated in <FIG>. The ultrasound transmitted from the ultrasonic transducer <NUM> propagates along the ultrasound propagation path formed by the cylindrical body <NUM> and is reflected by a lower face (an ultrasonic wave reflecting surface <NUM> intersecting the axial direction of the cylindrical body <NUM>) of the top board <NUM>. The ultrasound reflected by the ultrasonic wave reflecting surface <NUM> propagates along the ultrasound propagation path toward the ultrasonic transducer <NUM>, and is then received by the ultrasonic transducer <NUM>. The ultrasonic transducer <NUM> converts the reflected ultrasound to a received signal and outputs the received signal to the controller. The controller determines, based on a time when the controller outputs the transmitting signal and a time when the ultrasonic transducer <NUM> outputs the received signal, a round-trip propagation time which the ultrasound takes to propagate between the ultrasonic transducer <NUM> and the ultrasonic wave reflecting surface <NUM>. The controller further determines a propagation velocity of the ultrasound along the ultrasound propagation path based on the distance between the ultrasonic transducer <NUM> and the ultrasonic wave reflecting surface <NUM> and the round-trip propagation time, and then further determines the concentration of target gas to be measured based on the propagation velocity.

As illustrated in <FIG>, in the gas sensor <NUM> of this embodiment, each ventilation hole <NUM> extends in the front-rear direction through the peripheral wall of the sensor enclosure <NUM>. The ventilation holes <NUM> disposed in the front enclosure <NUM> and the ventilation holes <NUM> disposed in the rear enclosure <NUM> do not exist on common through lines <NUM>. The flow of air flowing into the gas sensor <NUM> through the ventilation holes <NUM> disposed in the front enclosure <NUM> and attempting to flow out through the ventilation holes <NUM> disposed in the rear enclosure <NUM> is therefore blocked by a region of the rear enclosure <NUM> where the ventilation holes <NUM> are not disposed. Similarly, the flow of air flowing into the gas sensor <NUM> through the ventilation holes <NUM> disposed in the rear enclosure <NUM> and attempting to flow out through the ventilation holes <NUM> disposed in the front enclosure <NUM> is blocked by a region of the front enclosure <NUM> where the ventilation holes <NUM> are not disposed. This configuration maintains ventilation of the interior of the sensor enclosure <NUM> and simultaneously prevents rapid inflow of the air to be measured into the sensor enclosure <NUM>, thereby reducing a change in the propagation velocity and propagation direction of ultrasound within the sensor enclosure <NUM>. This prevents an error in the time in which the ultrasound makes a round-trip within the concentration measurement space, thereby reducing an error in gas concentration measurement. Further, the ventilation holes <NUM> extending along the axial direction of the cylindrical shape of the sensor enclosure <NUM> facilitate ventilation of the interior of the sensor enclosure <NUM> which is axially elongated.

The ventilation holes <NUM> need not extend perpendicularly to the axial cross section, or the through lines <NUM> need not extend from the corresponding ventilation holes <NUM> toward the same direction. In other words, the depth direction of each ventilation hole <NUM> need not be normal to the axial cross section, or the through lines <NUM> need not extend in the same direction from the ventilation holes <NUM>. For example, each ventilation hole <NUM> may extend in a direction perpendicular to the peripheral face of the sensor enclosure <NUM>.

The ventilation hole <NUM> in the rear enclosure <NUM> may be disposed at locations out of the line of sight directed from the ventilation holes <NUM> in the front enclosure <NUM> toward the rear face. Similarly, the ventilation holes <NUM> in the front enclosure <NUM> may be disposed at locations out of the line of sight directed from the ventilation holes <NUM> in the rear enclosure <NUM> toward the front face. In other words, the plurality of ventilation holes <NUM> may be disposed such that a first side of the sensor enclosure <NUM> is not visible from an opposite second side of the sensor enclosure <NUM> through the ventilation holes <NUM> viewed from the peripheral wall.

Experimental results for the gas sensor <NUM> will be described. In an experiment in which the ventilation holes <NUM> had the same shape as those illustrated in <FIG>, <FIG>, the aperture ratio of a single ventilation hole <NUM> was in the range from <NUM>% to <NUM>%, the aperture ratio of all ventilation holes <NUM> was <NUM>%, and the number of ventilation holes <NUM> per <NUM><NUM> was <NUM>, a detection time was <NUM> seconds, and an exhaust time was <NUM> seconds. Here, the detection time refers to a time between when the gas sensor <NUM> was placed in air containing <NUM>% of helium and when <NUM>% of the convergence value of concentration measurements was reached. The exhaust time refers to a time starting from a state where the gas sensor <NUM> was placed in air containing <NUM>% of helium and the concentration measurement corresponded to the convergence value to when the gas sensor <NUM> was placed in air containing no helium and the concentration measurement was <NUM>. Further, in an experiment in which the aperture ratio of a single ventilation hole <NUM> was in the range from <NUM>% to <NUM>%, the aperture ratio of all ventilation holes <NUM> was <NUM>%, and the number of ventilation holes <NUM> per <NUM><NUM> was <NUM>, the detection time was <NUM> seconds and the exhaust time was <NUM> seconds.

<FIG> illustrates a perspective view of a gas sensor <NUM> according to an example that serves to explain certain aspects of the present invention. <FIG> illustrates a front view of the gas sensor <NUM>, and <FIG> illustrates a cross section along a line BB in <FIG>. The gas sensor <NUM> includes a lattice-shape rib structure <NUM> on a peripheral face of a sensor enclosure <NUM>. The rib structure <NUM> includes circumferential protrusions <NUM> surrounding the sensor enclosure <NUM> and vertical protrusions <NUM> which are linear protrusions extending vertically, and has a lattice shape. A plurality of circumferential protrusions <NUM> are formed on the peripheral face of the sensor enclosure <NUM> at predetermined intervals, and adjacent circumferential protrusions <NUM> are coupled by a plurality of vertical protrusions <NUM> arranged in the circumferential direction at predetermined intervals. The plurality of vertical protrusions <NUM> are arranged vertically in straight lines and disposed at predetermined intervals in the circumferential direction. As illustrated in <FIG>, the vertical protrusions <NUM> protrude from the peripheral face of the sensor enclosure <NUM> in the same direction as the through direction of the ventilation holes <NUM>. The openings of the ventilation holes <NUM> are located in a region enclosed by adjacent circumferential protrusions <NUM> and adjacent vertical protrusions <NUM>. The circumferential protrusions <NUM> and the vertical protrusions <NUM> may traverse the openings of the ventilation holes <NUM>.

The lattice-shape rib structure <NUM> disposed on the peripheral face of the sensor enclosure <NUM> provides the following advantages. Specifically, the air attempting to flow into the sensor enclosure <NUM> from diagonally upward or diagonally downward is directed by the circumferential protrusions <NUM> in a direction perpendicular to the periphery of the sensor enclosure <NUM>. This reduces the flow of air flowing into the sensor enclosure <NUM> from diagonally upward or downward through the ventilation holes <NUM> disposed in the front enclosure <NUM> and flowing out through the ventilation holes <NUM> disposed downward or upward in the rear enclosure <NUM>. This configuration similarly reduces the flow of air flowing into the sensor enclosure <NUM> diagonally upward or downward through the ventilation holes <NUM> disposed in the rear enclosure <NUM> and flowing out through the ventilation holes <NUM> disposed downward or upward in the front enclosure <NUM>. Thus, the circumferential protrusions <NUM> reduce passage of the diagonally upward or downward air with respect to the sensor enclosure <NUM> through the sensor enclosure <NUM>.

The air to flow into the sensor enclosure <NUM> from the right or left of the ventilation hole <NUM> is directed by the vertical protrusion <NUM> in a direction perpendicular to the peripheral face of the sensor enclosure <NUM>. This prevents the flow of air flowing into the ventilation holes <NUM> disposed on the front enclosure <NUM> from diagonally forward right or left and flowing out of the ventilation holes <NUM> on the left or right disposed in the rear enclosure <NUM>. This configuration similarly prevents the flow of air flowing into the ventilation holes <NUM> disposed on the rear enclosure <NUM> from diagonally rearward right or left and flowing out of the ventilation holes <NUM> on the left or right disposed in the front enclosure <NUM>. The vertical protrusions <NUM> thus reduce passage of the air in the diagonally right and left directions with respect to the front face or the rear face of the sensor enclosure <NUM>.

The rib structure <NUM> formed on the peripheral face of the sensor enclosure <NUM> prevents rapid flow of the mixture gas such as air to be measured into the sensor enclosure <NUM> to reduce a change of the propagation velocity of ultrasound within the sensor enclosure <NUM>. More specifically, the circumferential protrusions <NUM> prevent the flow of air passing through the ventilation holes <NUM> having an axial length greater than its lateral width, diagonally upward or downward. The vertical protrusions <NUM> prevent the flow of air passing through the ventilation holes <NUM> having a lateral width greater than its axial length, from diagonally forward left or rearward right, or from diagonally rearward left or forward right. This results in a reduction in an error of time during which the ultrasound propagates the concentration measurement space to thereby reduce an error in the gas concentration measurements. The rib structure <NUM> formed on the peripheral face of the sensor enclosure <NUM> further enhances the mechanical strength of the sensor enclosure <NUM>.

While in the above embodiments and examples the sensor enclosure (<NUM>, <NUM>) has a hollow cylindrical shape, the sensor enclosure (<NUM>, <NUM>) may have a shape of a hollow polygonal cylinder or a hollow elliptical cylinder, for example. In the above embodiments, the ventilation hole <NUM> has a shape extending along the axis of the sensor enclosure (<NUM>, <NUM>), but the ventilation hole <NUM> may have a shape of an ellipse, or a rectangle, for example. Further, the cylindrical body may include, on its inner peripheral face corresponding to the peripheral face, a gas-liquid separation membrane formed of a hollow fiber membrane such as PTFE, PP, PE, silicone resin, for example, attached to the inner peripheral face, to thereby prevent entrance of water droplets and dust into the gas concentration measurement space within the cylindrical body.

Claim 1:
A gas concentration sensor (<NUM>) comprising:
a sensor enclosure (<NUM>) that includes a cylindrical body (<NUM>);
an ultrasonic transducer (<NUM>) disposed at a first end of the cylindrical body (<NUM>);
an ultrasonic wave reflecting surface (<NUM>) disposed at a second end of the cylindrical body (<NUM>), the ultrasonic wave reflecting surface (<NUM>) intersecting an axial direction of the cylindrical body (<NUM>); and
a plurality of ventilation holes (<NUM>) disposed in a peripheral wall of the cylindrical body (<NUM>), wherein
the plurality of ventilation holes (<NUM>) have corresponding through lines each extending in a direction perpendicular to an axial section of the cylindrical body (<NUM>), the through lines of the plurality of ventilation holes (<NUM>) passing through different locations,
characterized in that
each of the ventilation holes (<NUM>) has a shape extending in the axial direction of the cylindrical body (<NUM>) and has a length in the axial direction that is longer than a lateral length, and
the ratio of the area of openings of all the ventilation holes (<NUM>) with respect to the area of a peripheral face of the sensor enclosure (<NUM>) is <NUM>% or greater and <NUM>% or less.