JPH10206256A - Pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure sensor capable of preventing surely the surface of a pressure sensitive element from dewfall and keeping preferable pressure sensing accuracy without needing the disposition of a protective film or the like. SOLUTION: A diaphragm 62 is provided near the pressure receiving surface 62a with an electrode 66a (66b) and an auxiliary electrode 67 formed of a material having the heat transfer rate higher than that of the electrode 66a (66b). Further, a waterdrop catching groove 68 consisting of a fine groove is provided right below the auxiliary electrode 67. When the temperature of a pressure medium is abruptly lowered, dewfalls are selectively generated on the auxiliary electrode 67 and water drops made of the dewfalls are actively guided into the same waterdrop catching groove 68 and held therein by the capillary action of the waterdrop catching groove 68.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor having an elastic pressure sensing element such as a semiconductor diaphragm and detecting a pressure based on an elastic displacement of the pressure sensing element.

[0002]

2. Description of the Related Art In order to measure the intake pressure in an intake pipe of an engine or the like, a pressure sensor having a pressure-sensitive element such as a diaphragm as a detection unit has been conventionally used.
And as this pressure sensor, for example, a semiconductor piezoresistive type using a semiconductor such as silicon as a pressure-sensitive element, or an elastic thin film of a semiconductor or a metal is arranged vertically close to each other,
A capacitance type or the like that detects a change in electric capacitance between the upper and lower films caused by a pressure difference between the upper and lower films is generally used.

[0003] In any case, in these pressure sensors, the absolute value of the pressure is measured by utilizing a small change in the electrical properties of the pressure-sensitive element caused by the pressure medium guided to the surface of the pressure-sensitive element. Alternatively, the relative fluctuation is measured.

[0004] The most problematic here is dew condensation generated on the surface of the pressure-sensitive element due to moisture in the intake pipe or the like.
As described above, since these sensors are precise measuring devices that detect pressure based on subtle changes in the electrical properties of the pressure-sensitive element, water droplets and contaminants condensed on the surface of the pressure-sensitive element are measured. Accuracy is easily degraded.

For this reason, a method of preventing water (steam) from entering the inside of the sensor using a waterproof filter such as Gore-Tex is usually used. However, according to this method, since the inside of the sensor covered with the filter is closed, there is a problem that water vapor originally present in the space inside the sensor is condensed due to, for example, a rapid temperature drop in the intake pipe. Was.

Therefore, conventionally, as shown in FIG. 4, for example, the surface of a diaphragm 70 as a pressure-sensitive element is coated with a gel-like insulator protective film 71 formed of silicon oxide or the like, and the surface of the diaphragm 70 is formed. Or the pressure-sensitive element surface is covered with an insulating protective film made of silicon oxide or silicon nitride, as described in JP-A-8-193899, and the pressure is transmitted thereon without fluctuation. A countermeasure has been taken such as laminating a water-resistant polymer film such as fluororesin or polyparaxylene through a soft resin layer to prevent moisture and other contaminants.

[0007]

However, in each of the above conventional sensor structures, the diaphragm is distorted due to the weight of the protective film laminated on the diaphragm and the difference in the thermal expansion coefficient between the diaphragm and the material forming the protective film. There is a problem that the pressure sensitivity of the diaphragm is easily deteriorated. Further, when the pressure sensor is used in an engine, there is a problem in that the protective film becomes a weight, and the diaphragm detects acceleration caused by vibration of the engine and the like.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to eliminate the necessity of providing a protective film or the like and to appropriately prevent the occurrence of dew condensation on the surface of the pressure-sensitive element. An object of the present invention is to provide a pressure sensor capable of maintaining a high pressure-sensitive accuracy.

[0009]

In order to achieve the above object, an invention according to claim 1 comprises a pressure-sensitive element which changes its electrical properties in response to a pressure received from a pressure medium, The gist of the present invention is to provide a dew condensation promoting means which is provided near the pressure element and is made of a member having a lower thermal resistance than at least the pressure sensitive element and which promotes the generation of dew.

According to the above structure, when dew condensation occurs in the pressure sensor due to a temperature change, the dew condensation is located near the pressure-sensitive element and has a smaller thermal resistance than the pressure-sensitive element (for example, pressure-sensitive element). It is positively generated by the dew condensation generation promoting means (made of a material having higher thermal conductivity than the element). For this reason, the occurrence of dew condensation on the pressure-sensitive element itself can be suitably avoided, and the pressure-sensitive accuracy can be well maintained.

According to a second aspect of the present invention, in the pressure sensor according to the first aspect, the dew condensation promoting means is made of a member having a smaller thermal resistance than an electrode member for transmitting and receiving signals to and from the pressure-sensitive element. Is the gist.

Since the electrode member is made of a conductive metal material, its thermal resistance is usually smaller than that of the pressure-sensitive element. Therefore, according to the same configuration in which the member constituting the dew condensation promoting means has a smaller thermal resistance than this electrode member, when dew condensation occurs on the pressure sensor due to a temperature change, the dew condensation occurs before the electrode. In the meantime, dew formation is promoted in the dew formation promoting means. For this reason, generation | occurrence | production of the dew condensation on the pressure sensitive element itself is avoided more suitably, and generation | occurrence | production of the dew condensation on the said electrode comes to be suppressed suitably.

[0013] The invention according to claim 3 is the invention according to claim 1 or 2.
The gist of the pressure sensor described above further includes a water droplet capturing unit that captures a water droplet generated by the dew condensation generation promoting unit by the dew condensation generation promoting unit.

According to the above configuration, even if the dew condensation promoting means has a small volume or surface area, the water droplets generated there are accurately captured by the water droplet capturing means. The scattering and adhesion of water droplets to itself can be properly prevented.

According to a fourth aspect of the present invention, in the pressure sensor according to the third aspect, the water droplet capturing means is a minute groove formed near the dew formation promoting means.

According to the above configuration, the water droplets captured by the water droplet capturing means can be suitably sealed by the capillary action of the micro grooves forming the water droplet capturing means, and the scattering of the captured water droplets can be more accurately performed. Is prevented.

[0017]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a pressure sensor according to the present invention.

FIG. 1 is a schematic configuration diagram showing an application example when the present pressure sensor is used as a sensor for detecting the pressure in an intake pipe of a gasoline engine. The engine 10, which is a gasoline engine, has a plurality of cylinders (only one cylinder is shown in the figure) in a cylinder block 11, and an intake port 121 corresponding to each cylinder is provided above the cylinder block 11. And a cylinder head 12 having an exhaust port 122. Cylinder head 12
The intake port 121 and the exhaust port 122 are provided with an intake valve 13 and an exhaust valve 14, respectively. The cylinder block 11 is provided with a water temperature sensor 30 for detecting a temperature (cooling water temperature) THW of the cooling water of the engine 10.

An intake pipe 15 as an intake passage is connected to each of the intake ports 121 (cylinder head 12) corresponding to each cylinder. At the end of each intake pipe 15 connected to the cylinder head 12, a fuel injection valve 16 for supplying fuel to each intake port 121 is provided for each cylinder. The surge tank 1 is connected to the other end of the intake pipe 15.
7, a throttle body 18, and an air cleaner 19 are connected. The surge tank 17 is a tank having a predetermined capacity for suppressing intake pulsation of intake air. The surge tank 17 is provided with the pressure sensor 61 according to the present embodiment as a means for detecting an intake pressure (intake pressure). I have. An output signal from the pressure sensor or the like is taken into an electronic control unit (ECU) 50 that controls an operation state of the engine 10.

FIG. 2 is a plan view showing the structure of the pressure sensor 61, and FIG. 3 is a sectional view of FIG. 2 taken along line 3-3. As shown in FIGS. 2 and 3, in the pressure sensor according to the present embodiment, a diaphragm (pressure-sensitive element) 62 is adhered to a base 64 housed in a resin housing 63. The diaphragm 62 is formed by etching the center of a thick chip of n-type silicon formed of silicon single crystal into a thin film by etching, and the bottom surface is concavely recessed.
A space 65 is formed on the base 64. Further, the space 65 is open to the outside atmospheric pressure through a passage 35 passing through the base 64.

On the other hand, the upper surface of the diaphragm 62 is a pressure receiving surface 62a having a planar shape for measuring a pressure to be measured. Strain gauges R1, R2, R3, and R made of p-type silicon are provided at the center of the pressure receiving surface 62a in the thin film shape.
4 (both not shown) are pn-joined on the n-type silicon thick chip. The strain gauges R1 to R4
Constitute a Wheatstone bridge as four resistance layers, and are connected to a constant voltage input terminal ((electrode) 66a) and an output terminal (electrode) 66b.

In the pressure sensor 61 of the present embodiment, an auxiliary electrode 67 shown in FIGS. 2 and 3 is provided separately from the electrodes 66a and 66b.
The auxiliary electrode 67 is a dummy electrode electrically, and is made of a material having a higher thermal conductivity than each of the electrodes 66a and 66b. That is, assuming that, for example, an alloy of chromium (Cr) and iron (Fe) is used as the electrodes 66a and 66b, a material such as aluminum (Al) or copper (Cu) is used as the auxiliary electrode 67. Will be done. Further, the auxiliary electrode 6
A water droplet capture groove 68 which is a space depressed in a concave shape is formed in a part of the housing 63 directly below the housing 7.

The pressure receiving surface 62a of the diaphragm 62 configured as described above communicates with the space in the intake pipe via the pressure passage 69 shown in FIG. The pressure sensor 6
In the vicinity of the entrance from 1 to the pressure passage 69, a fiber filter (not shown) having excellent waterproofness and air permeability is provided to protect the diaphragm 62 from water vapor and minute contaminants existing in the intake pipe.

Next, the operation of the pressure sensor of the present embodiment configured as described above will be described. In the engine control system illustrated in FIG. 1, when the engine 10 is started, air flows into the intake pipe 15 through the throttle body 18. And the surge tank 17
In the process of passing through, the pressure of the intake air is transmitted to the diaphragm 62 of the pressure sensor 61 via the pressure passage 69.

In the pressure sensor 61, the electric resistance is changed in accordance with the pressure applied to the surface of the silicon single crystal constituting the diaphragm 62. This change in electric resistance (attributable to the piezo effect of the semiconductor) is detected using the Wheatstone bridge constituted by the above-described strain gauges R1 to R4, and is sent to the ECU 50 as an output signal of the pressure sensor 61.

Here, when the temperature in the pressure sensor 61 decreases due to, for example, a decrease in the temperature of the intake air flowing into the surge tank 17, the space between the waterproof and breathable fiber filter and the diaphragm 33. The water vapor trapped in the liquid liquefies.

In the conventional pressure sensor, condensation occurs on the surface of the diaphragm or its protective film due to the liquefaction of the water vapor. However, in the pressure sensor 61 of the present embodiment, dew condensation first occurs in the auxiliary electrode 67 having the highest thermal conductivity in the vicinity of the pressure receiving surface 62a of the diaphragm due to the temperature drop. That is, the auxiliary electrode 67 functions to positively promote the occurrence of dew condensation in the pressure sensor 61 of the present embodiment. The generated dew (water droplets) flows into a water droplet capturing groove 68 provided immediately below the auxiliary electrode 67 and is stored in the water droplet capturing groove 68. By the way, in such a semiconductor pressure sensor,
Since the size is at most several tens of mm, the width of the short side of the water droplet capturing groove 68 is also about 1 mm. For this reason, the stored water droplets are confined by capillary action, and even if the pressure sensor 61 vibrates, it does not scatter. Thus, the diaphragm 62 as a pressure-sensitive element can transmit a signal corresponding to the intake pressure in the surge tank 17 to the ECU 50 with stable sensitivity based on protection from dew condensation.

As described above, according to the pressure sensor of the present embodiment, the following effects can be obtained. (A) When the temperature of the outside air (pressure medium) near the diaphragm 62, which is a pressure-sensitive element, drops, the electrodes 66a and 66b, the auxiliary electrode 67, and the diaphragm 62
The temperature of the main body also starts to drop. Here, according to this embodiment, the auxiliary electrode 67 having the highest thermal conductivity has the fastest temperature drop rate and reaches the dew point (the temperature at which dew condensation occurs) first. Then, dew condensation is selectively generated on the auxiliary electrode 67, and the water droplet is captured in the water droplet capturing groove 63. For this reason, the occurrence of dew condensation on the diaphragm 62 itself can be suitably avoided, and the pressure-sensitive accuracy can be maintained well.

(B) In the present embodiment, the water droplet capturing groove 6
Since 3 is a sufficiently fine groove, water droplets condensed on the auxiliary electrode 67 can be actively captured and contained based on the capillary phenomenon. Therefore, it is possible to preferably prevent the water droplets once captured from spilling or scattering and reaching the surface of the diaphragm 62 due to vibration of the engine 10 or the vehicle body.

(C) In this embodiment, the diaphragm 62 is exposed to the outside air without being coated with another material such as a protective film. For this reason, a physical quantity that is not directly attributable to the intake pressure such as the acceleration or vibration of the vehicle body is not erroneously detected. Further, even when a temperature change occurs, due to a difference in thermal expansion coefficient between the material constituting the protective film and
No wrinkles or distortions occur in the diaphragm 62.

The above embodiment can be modified and embodied as follows. (A) The combination of the materials forming the electrodes 66a and 66b and the auxiliary electrode 67 is arbitrary, as long as the material of the auxiliary electrode 67 has a relatively higher thermal conductivity than the material of the electrodes 66a and 66b. Any combination may be selected.

For example, iron (F) is applied to the electrodes 66a and 66b.
e), nickel (Ni), silicon (Si), phosphorus (P)
Various elemental elements or compounds composed of the above can be used. Further, for the auxiliary electrode 67, various single metals or alloys made of gold (Au), silver (Ag), or the like can be used other than the above-described aluminum (Al) and copper (Cu).

Further, any physicochemical characteristics such as specific heat may be used as a criterion for selecting the material as long as it can be a criterion for the tendency of dew formation according to a change in outside air temperature.

(B) In the present embodiment, the electrodes 66a, 66
b and the auxiliary electrode 67 are made of materials having different thermal conductivities, but the point is that the thermal resistance of the auxiliary electrode 67 is
If the heat resistance is not smaller than the thermal resistances a and 66b, the same operation as the above embodiment can be obtained. That is, even if the two electrodes are made of the same material or a material having the same thermal conductivity, the thermal resistance of the auxiliary electrode 67 is higher than that of the electrode 66a.
If the shape and size are selected so as to be relatively small as compared with the thermal resistance of 66b, the same effect as in the present embodiment can be obtained. For example, of the two electrodes, the auxiliary electrode 67 may have a relatively large cross-sectional area and a short length.

(C) Diaphragm 62 as pressure-sensitive element
In order to prevent the occurrence of dew condensation on the auxiliary electrode 6
As 7, it is sufficient to use a member having a lower thermal resistance than at least the diaphragm 62.

(D) Means for promoting the formation of dew need not be electrodes, such as the auxiliary electrode 67. (E) A polymer absorber may be inserted into the water droplet capturing groove 68.

(F) Two or more water droplet capturing grooves 68 may be provided. Further, the shape is not limited to this embodiment, and may be, for example, an elliptical shape. (G) Even if the means for promoting the occurrence of dew condensation by using the water droplet capturing means, such as the water droplet capturing groove 68, is small in volume or surface area, it is impossible to accurately capture the water droplets generated there. Although it is possible, it is not always necessary to dispose such a water droplet capturing means in the sense of preventing the dew condensation on the diaphragm 62 as a pressure sensitive element.

(H) In addition to the strain gauge type, the pressure sensitive element of the pressure sensor 61 may be a capacitance type, a surface elastic type using a SAW resonator, or the like. Any kind that changes the physical properties may be used. In addition, even when a strain gauge type is adopted, a half bridge configuration or the like can be appropriately adopted in addition to the Wheatstone bridge.

In the present embodiment, the pressure sensor of the type in which the surface of the diaphragm 62 opposite to the pressure receiving surface on the pressure medium side is released to the atmospheric pressure and the relative pressure with respect to the atmospheric pressure is detected, The present invention is similarly applicable to a type in which the space in contact with the opposite surface is a vacuum chamber and the absolute pressure of the pressure medium is detected.

The pressure sensor 61 is not limited to the one for measuring the intake pressure in the intake pipe, but may be a negative pressure applied to the brake booster, a turbocharging pressure, a gasoline vapor pressure in a fuel tank, an atmospheric pressure, or the like. , Can also be used to detect the pressure of other pressure media. Further, in various environments other than the internal combustion engine of an automobile, it is possible to operate the pressure medium as a precise pressure detecting means.

[0041]

The present invention is configured as described above, and has the following effects. In order to achieve the above object, according to the first aspect of the present invention, when dew condensation occurs in the pressure sensor due to a temperature change, the dew condensation occurs.
In the vicinity of the pressure-sensitive element, the dew-condensation-promoting means having a lower thermal resistance than the pressure-sensitive element (for example, made of a material having a higher thermal conductivity than the pressure-sensitive element) is positively generated. For this reason, the occurrence of dew condensation on the pressure-sensitive element itself can be suitably avoided, and the pressure-sensitive accuracy can be well maintained.

In the second aspect of the present invention, since the electrode member is made of a conductive metal material, its thermal resistance is usually smaller than that of the pressure-sensitive element. Therefore, according to the same configuration in which the member constituting the dew condensation promoting means has a smaller thermal resistance than this electrode member, when dew condensation occurs on the pressure sensor due to a temperature change, the dew condensation occurs before the electrode. In the meantime, dew formation is promoted in the dew formation promoting means. For this reason, generation | occurrence | production of the dew condensation on the pressure sensitive element itself is avoided more suitably, and generation | occurrence | production of the dew condensation on the said electrode comes to be suppressed suitably.

According to the third aspect of the present invention, even if the dew condensation promoting means has a small volume or surface area, the water droplets generated there are accurately captured by the water droplet capturing means, so that the water droplets are present in the vicinity thereof. The scattering and adhesion of water droplets to the pressure-sensitive element itself can be accurately prevented.

According to the fourth aspect of the present invention, the water droplets captured by the water droplet capturing means can be suitably contained by the capillary action of the micro grooves forming the water droplet capturing means, and the scattering of the captured water droplets can be improved. Precisely prevented.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an application example of a pressure sensor according to the present invention.

FIG. 2 is a plan view showing an embodiment of the pressure sensor according to the present invention.

FIG. 3 is a sectional view taken along line 3-3 in FIG. 2;

FIG. 4 is a sectional view showing an example of a conventional pressure sensor.

[Explanation of symbols]

61 pressure sensor, 62 diaphragm, 62a pressure receiving surface, 63 housing, 64 base, 65 space, 66
a, 66b: electrodes, 67: auxiliary electrodes, 68: water droplet capturing grooves.

Claims (4)

[Claims] A pressure-sensitive element that changes its electrical properties in response to a pressure received from a pressure medium; and a member that is disposed near the pressure-sensitive element and that has at least a lower thermal resistance than the pressure-sensitive element. And a dew condensation promoting means for promoting the formation of dew. 2. The pressure sensor according to claim 1, wherein the dew condensation promoting means is made of a member having a smaller thermal resistance than an electrode member for transmitting and receiving signals to and from the pressure-sensitive element. 3. The pressure sensor according to claim 1, further comprising a water droplet capturing unit that captures a water droplet generated by the dew formation promoting by the dew formation promoting unit. 4. The pressure sensor according to claim 3, wherein said water droplet capturing means is a minute groove formed near said dew formation promoting means.