JP6952577B2 - Gas sensor device - Google Patents

Description

The present invention relates to a gas sensor device including a thermal sensor element for detecting a gas concentration or the like.

Gas sensor devices that measure environmental characteristics such as gas concentration are used in various technical fields. For example, in internal combustion engines for automobiles, in order to reduce fuel consumption, the humidity, pressure, and temperature of intake air are measured. It measures and controls the optimum combustion. Furthermore, in order to operate the internal combustion engine optimally, it is required to measure environmental parameters such as humidity and oxygen concentration with high accuracy.

In the intake passage of the internal combustion engine, pulsation occurs in the air flow as the intake valve that controls the intake air to the combustion chamber opens and closes. In particular, when the rotation speed of the internal combustion engine increases, the intake valve opens and closes in a short time, so that a rapid air flow occurs. The thermal sensor element detects the humidity of the intake air based on the change in the amount of heat released from the heater and the change in temperature. Therefore, when the sensor element is arranged in the air flow, the amount of heat radiated changes depending on the air flow, so that the amount of heat radiated cannot be accurately determined and good measurement cannot be performed. Therefore, it is necessary to reduce the influence of air flow around the sensor element.

As a sensor device corresponding to such a problem, in Patent Document 1, a first cavity formed in a housing of the sensor device to protect the sensor element and communicating with the intake passage, and a first cavity communicating with the first cavity. Two cavities are provided, and the sensor element is housed in the second cavities. In this way, by configuring the sensor element so as not to be directly exposed to the air flow, the influence of the air flow is reduced, the dustproof effect, and the destruction of the sensor element due to the collision of particles are suppressed.

Further, in Patent Document 2, a lid member for covering the sensor element is provided, an introduction hole is provided in the lid member, and the introduction hole is arranged so that the measurement gas does not directly hit the sensor element.

JP-A-2015-4609 Japanese Unexamined Patent Publication No. 2014-81367

For example, a gas sensor device that measures the environment of the intake passage of an internal combustion engine needs to measure the amount of gas in real time. Therefore, a high-speed response is desired for the gas sensor device. In order to achieve a high-speed response, it is desirable to expose the sensor element directly to the intake passage. However, when the sensor element is exposed in the intake passage, the intake air flows at high speed due to the high rotation operation of the internal combustion engine, which adversely affects the gas measurement.

The sensor device for measuring the gas concentration of Patent Document 1 has an effect of protecting the sensor element, but the time for the change in gas concentration to reach from the intake passage to the sensor element is delayed. Further, although the speed of Patent Document 2 is higher than that of Patent Document 1, the measurement gas flows into the lid member, which is insufficient for high-precision measurement. Therefore, it is difficult to use it in an internal combustion engine where high-precision measurement is desired in a wide flow rate range in which the measurement gas flows from low speed to high speed.

In order to solve the above problems, the present invention includes a signal processing unit for processing a signal of the thermal sensor element in a gas concentration sensor device including a thermal sensor element having a heating element formed on a thin film portion of the substrate. , The signal processing unit outputs a signal shifted toward the minimum value of the input signal, and the signal processing unit outputs from the minimum value detecting unit that outputs the minimum value of the input signal and the minimum value detecting unit. A low-pass filter for smoothing the signal is provided, and the minimum value detection unit includes a differential device for detecting the gradient of the input signal and an integrator for attenuating the response of the input signal, and the gradient is provided. When is positive, the signal is output through the integrator, and when the gradient is negative, the signal is output without passing through the integrator .

According to the present invention, it is possible to suppress a decrease in responsiveness and improve measurement accuracy under conditions of severe environmental changes.

The cross-sectional view which shows the structure of the sensor element of Example 1 of this invention. The plan view which shows the structure of the sensor element of Example 1 of this invention. The figure for demonstrating the operation and effect of the gas sensor apparatus of Example 1 of this invention. The figure for demonstrating the operation and effect of the gas sensor apparatus of Example 1 of this invention. The block diagram which shows the signal processing means of Example 1 of this invention. The block diagram which shows the signal processing means of Example 1 of this invention. The figure for demonstrating the operation and effect of the signal processing means of Example 1 of this invention. The figure for demonstrating the operation and effect of the signal processing means of Example 2 of this invention. The figure for demonstrating the operation | effect of the signal processing means of Example 3 of this invention. The figure for demonstrating the operation | effect of the signal processing means of Example 3 of this invention. The figure for demonstrating the operation | effect of the signal processing means of Example 3 of this invention. The figure for demonstrating the system suitable for application of this invention. The figure for demonstrating the system suitable for application of this invention. Block diagram showing signal processing in Example 2 of the present invention

Hereinafter, an embodiment of the gas sensor device according to the present invention will be described.

The thermal gas sensor of the present invention in the first embodiment will be described with reference to FIGS. 1 to 7.

The sensor element 1 has a substrate 2 made of single crystal silicon. A cavity 3 is formed in the substrate 2, and a first heating element 4 and a second heating element 5 are laid on the cavity 3. The thin film supports 6a and 6b that support these heating elements 4 and 5 are formed so as to cover the cavity 3 of the substrate 2.

Here, the thin film supports 6a and 6b are composed of an insulating film laminated on the upper surface of the substrate 2, and the heating elements 4 and 5 are interposed and supported between the thin film supports 6a and 6b. There is. The heating element 5 is arranged so as to surround the heating element 4.

The heating element 4 dissipates heat by transferring heat to air, which is a measurement medium. Since the thermal conductivity of air changes depending on the humidity and the amount of heat radiated changes, a signal corresponding to the humidity can be obtained by measuring the voltage value or the current value based on the amount of heat radiated by the heating element 4. The heating element 5 has an effect of keeping the ambient temperature of the heating element 4 constant, and can eliminate the influence of the heat radiation amount of the heating element 4 on the environmental temperature.

In the present embodiment, the second heating element 5 is provided around the first heating element 4, but the second heating element 5 is provided for temperature compensation and is not necessarily the present invention. It is not essential in the configuration. The effect of the present invention can be obtained even in a configuration using only the first heating element 4.

FIG. 2 shows a plan view of the sensor element 1. The heating elements 4 and 5 are fine-width resistors extending along the plane of the thin film supports 6a and 6b and having a plurality of folded portions. Electrodes 7a, 7b, 7c, and 7d are formed in the sensor element 1 for connection with a drive circuit (not shown) for supplying a heating current to the heating elements 4 and 5.

As the heating elements 4 and 5, it is desirable to use a material stable at high temperature (a material having a high melting point), for example, platinum (Pt), tantalum (Ta), molybdenum (Mo), silicon (Si) and the like. Be selected. As the thin film supports 6a and 6b, a single layer or a laminate of silicon oxide (SiO2) and silicon nitride (Si3N4) is selected. Further, as the thin film supports 6a and 6b, a resin material such as polyimide, ceramic, glass or the like can be selected in a single layer or laminated structure. Further, aluminum (Al), gold (Au), or the like is selected for the electrodes 7a, 7b, 7c, and 7d.

The sensor element 1 is formed by using a semiconductor microfabrication technique using photolithography and an anisotropic etching technique. The cavity 3 is formed by anisotropic etching of the substrate 2.

FIG. 3 (a) and FIG. 3 (b) are used to show the mechanism of occurrence of measurement error caused by the air flow around the sensor element. The thermal humidity sensor in this embodiment utilizes the fact that the amount of heat radiated from the first heating element 4 changes depending on the humidity. In this embodiment, in order to detect a change in the amount of heat radiation, a method of controlling the first heating element 4 to a constant temperature is used. In this way, the heating power for holding the first heating element 4 at a constant temperature changes according to the amount of heat radiated, and the humidity can be measured by detecting this.

As shown in FIG. 3A, it is desirable that the air around the heating element 4 is in a stationary state. If the humidity of the environment in which the sensor element 1 is placed increases in this state, the heating power of the first heating element 4 increases. However, due to the influence of the air flow in the intake passage of the internal combustion engine, a flow velocity V is generated around the sensor element 1 as shown in FIG. 3 (b), which increases the heat radiation amount of the first heating element 4. Therefore, when heat dissipation increases due to air flow, the heating power for holding the first heating element 4 at a constant temperature increases.

Such a MEMS type thermal humidity sensor detects that the thermal conductivity of air changes with humidity from the change in the amount of heat released from the heating element. Therefore, when placed in the flow of air, heat is dissipated by the air flow. Since it changes, it is not possible to distinguish between heat dissipation due to air flow and heat dissipation due to humidity, and good measurement cannot be performed. Therefore, it is necessary to reduce the influence of the air flow around the sensor element 1. In particular, when it is installed in the intake passage of an internal combustion engine, it is important because the flow velocity of air in the intake passage changes greatly depending on the operating condition of the internal combustion engine.

A MEMS type element such as the sensor element 1 can reduce the heat capacity of the detection unit and improve the responsiveness. On the other hand, since the heat capacity is small, measurement errors are likely to occur due to minute air flow. Therefore, it is important to reduce the measurement error due to the air flow around the sensor element.

On the other hand, if a cover or a filter is provided in order to reduce the air flow around the sensor element, the air permeability is deteriorated and the responsiveness to a change in humidity is impaired. Therefore, in this embodiment, the configuration is as follows.

As shown in FIG. 4A, pulsation occurs in the air flow V as the intake valve that controls the intake air into the combustion chamber of the internal combustion engine is opened and closed. The illustrated waveform is an example of a case where the rotation speed of the internal combustion engine is gradually increased. As shown in the figure, in the low rotation range in the first half, the fluctuation is gradual, but in the second half, a rapid air flow occurs because the intake stroke becomes shorter as the rotation speed increases.

FIG. 4B shows the sensor output waveform in the above air flow V. The dotted line Din in the figure shows the output waveform in a form to which the present invention is not applied. It is desirable that the sensor output be constant in a constant humidity environment, but a spike-like measurement error occurs in the sensor output Din because the peak value of the air flow V increases in the high rotation range. The solid line Df in the figure is a waveform averaged to the dotted line Din by low-pass filtering. Since the measurement error that occurs on the dotted line Din is only a positive error, an offset error remains in the average value when low-pass filtering is performed.

The solid line Dout in FIG. 4B shows a signal waveform obtained by applying this embodiment. The solid line Dout in this embodiment is a waveform that follows the minimum value Dmin of the signal Din. As shown in FIG. 4A, the timing at which the signal Din becomes the minimum value coincides with the timing Vmin at which the air flow V decreases. Therefore, even if spike-like errors are superimposed in the high speed region of the engine, if the minimum value of the signal Din is acquired, the sensor output in a state where the air flow is stationary can be obtained.

The error caused in the thermal humidity sensor by the air flow is only a positive error as shown in FIG. 4 (b). This is because the effect of air flow is only an increase in the amount of heat radiated from the first heating element of the sensor element 1. That is, by acquiring the minimum value of the signal obtained from the sensor element 1, it is considered that the signal is a conditioned signal in which air flow is not occurring or is insignificant. Can be extracted.

In this embodiment, when a high frequency fluctuation occurs in the signal Din, the output Dout is shifted to the minimum value side of the signal Din. That is, it shifts in the direction of canceling the signal that changes due to the air flow. The shift direction may differ depending on the output form of the sensor signal. Since the change in the sensor output signal due to the increase in humidity and the change in the signal due to the error due to the air flow are in the same direction, the correction unit of the present invention is shifted to the low humidity side when the output signal of the sensor is converted into humidity. It will be.

The sensor element 1 as in this embodiment is manufactured by the MEMS process, has a small heat capacity, and has a high-speed response. Therefore, it is a sensor element suitable for the present invention because it can follow the pulsating air flow and can capture the signal when the air flow stops momentarily.

In this embodiment, the processing unit 10 that processes the signal of the sensor element 1 detects the minimum value for the sensor signal under air pulsation, and after processing so that it becomes this minimum value under air pulsation. Is outputting the signal of. Since the minimum value, which is the signal when the air stops momentarily, is extracted and used from the signal on which the air pulsation error is superimposed, the influence of the pulsation error can be reduced. According to this embodiment, the humidity can be measured accurately even in the case of pulsation without using a filter or the like, so that the accuracy can be improved without impairing the responsiveness.

Although the signal processing unit 10 is provided on a semiconductor substrate different from the semiconductor substrate on which the sensor element 1 is formed, it may be formed on the same semiconductor substrate.

FIG. 5 shows an example of a specific embodiment of the means for reducing the measurement error. In this embodiment, the humidity sensor element 1, the pressure sensor element 9 arranged in the same environment as the humidity sensor element 1, the pressure correction unit 8 for applying pressure correction to the signal obtained from the humidity sensor element 1, and the pressure sensor element 8. It is composed of a signal processing unit 10. The signal processing unit 10 is an element for realizing the operation of the present invention.

The pressure compensator 8 is not an essential element for obtaining the effect of the present invention. When used in an environment where pressure fluctuations are severe, it is desirable to provide the signal processing unit 10 of the present invention after the pressure compensating unit 8. The amount of heat radiated from the first heating element 4 formed on the sensor element 1 also changes depending on the atmospheric pressure. Therefore, the air pressure fluctuates as the intake valve of the internal combustion engine opens and closes, so that the sensor output pulsates periodically. This is to prevent the signal processing of the present invention from being applied to this pulsation, and to perform pressure correction in the stage prior to the signal processing unit of the present invention to remove the pulsating component accompanying the pressure fluctuation.

The signal processing unit 10 includes a minimum value detecting unit 11 and a low-pass filter 12 that smoothes the signal.

As shown in FIG. 6, the minimum value detection unit 11 includes a differentiator 13 for detecting the gradient of rising or falling of the input signal Din, and an integrator 14 for attenuating the response of the input signal Din.

The minimum value detection unit 11 selects and outputs whether to output the input signal Din through the integrator 14 or to output the input signal Din as it is, according to the positive or negative of the gradient of the signal detected by the differentiator 13.

The minimum value detection unit 11 outputs a signal through the integrator 14 when the gradient of the signal detected by the differentiator 13 is positive, and sets the integrator 14 when the gradient of the signal detected by the differentiator 13 is negative. Output the signal without passing it.

The output signal Db of the minimum value detection unit 11 is input to the low-pass filter 12. The advantages of providing the low-pass filter 12 will be described below.
FIG. 7 shows the input / output waveform of the signal processing unit 10. The input signal Din is a signal including a spike-shaped measurement error obtained from the sensor element 1 by pulsation. When this input signal Din is passed through the minimum value detection unit 11, a waveform Db that follows the minimum value of Din is obtained. The minimum value detection unit 11 has an action of lowering the rising speed with respect to the signal Din, so that a saw-shaped waveform including the minimum value of the input signal Din as shown in the figure is obtained. When this signal Db is smoothed by the low-pass filter 12, the output signal Dout is obtained, and the waveform follows the minimum value of the input signal Din.

Further, in the minimum value detecting unit 11 shown in this embodiment, the response speed to the humidity change differs between the rising edge and the falling edge of the signal. Therefore, there is an advantage that the response speeds of the falling edge and the rising edge of the signal are matched by passing the low-pass filter 12 after the minimum value detecting unit 11. However, the low-pass filter 12 may not be necessary depending on the system using the present sensor device, and therefore is not necessarily an essential configuration in the practice of the present invention.

Example 2 of the present invention is shown with reference to FIGS. 8 and 14. The main difference from Example 1 is the method of detecting the minimum value.

As shown in FIG. 8, the signal Din obtained from the sensor element 1 is tc-sampled for a predetermined period and stored in the memory. This is a method of extracting the minimum value data from the sampled data (P1, P2 ...) and outputting it. By making the sampling period TC longer than the generation period of the spike waveform of the input signal Din, it is possible to obtain the output signal Dout that follows the minimum value of the input signal Din. The number of samplings in the sampling period TC is appropriately set according to the generation period of the spike waveform.

FIG. 14 is a block diagram showing the above signal processing. The signal Din obtained from the sensor element 1 is converted into a digital value by the sample hold circuit 23 and the AD converter. The data (P1, P2 ...) Converted into digital values is stored in the memory 24. Data (P1, P2 ...) For a predetermined period (TC) is held in the memory 24, and the minimum value detecting unit 25 detects the minimum value from the held data and outputs it as an output signal Dout. The sampling period tc and the number of samplings n are determined by the capacity of the memory 24 and the clock CLK that determines the update cycle of the memory, and are appropriately set according to the spike waveform generated by the air pulsation.

As shown in FIGS. 6 and 8, in the above embodiment, the minimum value of the input signal Din is acquired, but it is not always necessary to acquire only the minimum value. That is, the effect is obtained when the output signal approaches the minimum value side of the input signal, and how close it is to the minimum value can be designed according to the error range allowed in the system to which the sensor device is applied. ..

Example 3 will be described with reference to FIGS. 9 to 11. The description of the same configuration as in Examples 1 and 2 will be omitted.

FIG. 9 shows the frequency characteristics of the signal processing unit 10. When an input signal Din having a constant amplitude and a different frequency is input to the signal processing unit 10, the average value Dave of the output signal has a characteristic of approaching the minimum value of the input signal Din on the high frequency side. Let ΔDave be the difference between the average value of the input signal Din and the average value Dave of the output signal. As shown in FIG. 10, ΔDave gradually shifts in the negative direction as the frequency rises. Finally, the absolute value of ΔDave matches the amplitude of the input signal Din. That is, the average value Dave of the output signal has a characteristic approaching the minimum value of the input signal Din.

The frequency at which ΔDave is generated is determined by the frequency of the spike-like error superimposed on the sensor element 1. That is, the spike-like error depends on the ease with which air flow occurs, that is, the structure around the sensor element. The spike-shaped error waveform also depends on the responsiveness of the sensor element 1. As shown in FIG. 11, at the air flow V having a frequency faster than the responsiveness of the sensor element, the signal Din obtained from the sensor element 1 cannot follow the air flow. Then, the minimum value of the signal obtained in the first or second embodiment cannot be said to be a sufficient minimum value, and an error ΔE is left.

Therefore, in this embodiment, focusing on the fact that the frequency of the fluid, which is the medium to be measured, in which the minimum value detection functions most effectively is equal to or lower than the response speed of the sensor element 1, air having a frequency equal to or lower than the response speed of the sensor element 1. In the case of flow, the output is based on the minimum value. On the other hand, in the case of air flow with a frequency higher than the response speed, the average value Dave is output.

The response speed of the sensor element 1 is a value that changes depending on the element structure because it is determined by the heat capacity of the heating element 4. In this embodiment, if the size of the cavity 3 is 0.5 to 1.0 mm and the thicknesses of the thin film supports 6a and 6b are 1 to 5 um, the responsiveness is 100 Hz to 200 Hz. Therefore, if a signal of at least 100 Hz or higher is input to the signal processing unit 11, the average value Dave of the output signal has a characteristic of approaching the minimum value of the input signal Din. Shift to the minimum value side.

12 and 13 show an internal combustion engine system suitable for a sensor device to which the present invention is applied. The intake pulsation in the intake passage of the internal combustion engine is generated by opening and closing the intake valve 17. On the upstream side of the throttle valve 15, pulsation is suppressed by the throttle valve 15. Therefore, since the pulsation of the air flow is small on the upstream side of the throttle valve 15, it is easy to install the sensor element 1 as in this embodiment.

The environment of the sensor device in which the present invention works particularly effectively is an environment in which the air flow pulsates. That is, it is particularly effective in an environment in which air repeatedly flows and stands still. Such an environment is likely to occur on the downstream side of the throttle valve 15 in the intake passage of the internal combustion engine. On the downstream side of the throttle valve 15, the pulsation of the air flow becomes intense due to the pressure change accompanying the opening and closing of the intake valve 17. As a result, when the thermal sensor element 1 as in the present embodiment is installed, a measurement error due to pulsatile flow occurs, but by applying the present invention, it is possible to obtain a good measured value even in a place where air flow is intense. Is.

Further, as a suitable internal combustion engine system, as shown in FIG. 13, in an intake manifold 21 in which an intake passage is branched into each combustion chamber, a gas sensor device to which the present invention is applied to the downstream side of the first branch point 22. It is preferable to arrange. In the example of the 3-cylinder engine shown in FIG. 13, the gas sensor device equipped with the sensor element 1 is arranged at the branch point toward the cylinder 18c farthest from the throttle valve 15. The intake valves provided in the cylinders 18a to 18c open and close in order. For example, when the intake valve of the cylinder 18a is opened, an air flow toward the cylinder 18a is generated, but since the intake valve of the cylinder 18c is closed, the timing at which the air flow around the sensor element 1 becomes small can be obtained. A good measured value can be obtained by securing a period in which the air flow is small by opening and closing the intake valve and acquiring the measured value at this time.

The gas sensor device of the present invention can be applied to other than the internal combustion engine of an automobile, and can be applied to measure the concentration of gas in various environments other than the internal combustion engine.

Each of the above-described embodiments is merely exemplified as a preferred embodiment, and the above-described embodiments can be combined as appropriate, and can be appropriately modified based on the gist of the invention.

1 ... Sensor element, 2 ... Substrate, 3 ... Cavity, 4 ... First heating element, 5 ... Second heating element, 6a, 6b ... Thin film support, 7a to 7d ... Electrode, 8 ... Pressure compensator, 9 ... Pressure sensor, 10 ... Signal processing unit, 11 ... Minimum value detection unit, 12 ... Low-pass filter, 13 ... Differential, 14 ... Integrator, 15 ... Throttle valve, 16 ... Intake, 17 ... Intake valve, 18 ... Combustion Chamber, 19 ... Piston, 20 ... Controller, 21 ... Intake manifold, 22 ... First branch point, 23 ... Sample hold circuit, 24 ... Memory, 25 ... Minimum value detector, 26 ... AD converter

Claims (5)

A sensor element having a substrate having a cavity, a thin film covering the cavity, and a heating element provided in the thin film.
In a gas sensor device including a signal processing unit for processing an input signal input from the sensor element.
At the time of pulsation, the signal processing unit outputs a signal based on the minimum value of the signal input from the sensor element.
The signal processing unit
A minimum value detection unit that outputs the minimum value of the input signal, and
A low-pass filter that smoothes the signal output from the minimum value detection unit is provided.
The minimum value detection unit includes a derivative that detects the gradient of the input signal and an integrator that attenuates the response of the input signal, and outputs a signal through the integrator when the gradient is positive. A gas sensor device that outputs a signal without passing through the integrator when the gradient is negative. Pressure sensor element and
A pressure correction unit for inputting signals from the pressure sensor element and the sensor element and outputting a corrected signal is provided.
The gas sensor device according to claim 1 , wherein the signal input to the signal processing unit is a corrected signal output from the pressure correction unit. The signal processing unit
The gas sensor device according to claim 1 or 2, which outputs a signal based on the minimum value of the input signal with respect to an input signal having a frequency lower than the response speed of the sensor element. An internal combustion engine system in which the gas sensor device according to any one of claims 1 to 3 is installed downstream of a throttle valve provided in an intake passage of the internal combustion engine . An internal combustion engine system in which the gas sensor device according to any one of claims 1 to 3 is installed downstream of the first branch point of a plurality of branch passages branched in a manifold of an internal combustion engine.

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