JPH04214131A - Detector for clogging of dust filter - Google Patents

Abstract

PURPOSE:To provide a detector for the clogging of a dust filter, which is capable of detecting directly a clogged status irrespective of respective variations in a blower, a peripheral temperature and the characteristics of a dust filter. CONSTITUTION:A detection hole 10 which permits an air stream in a duct 1 to directly pass therethrough is formed in a dust filter 9 disposed in the duct 1 of an air conditioner. A first flow velocity sensor 11 for detecting the rate of flow of the air stream passing through the aforementioned detection hole 10 and a second flow velocity sensor 12 for detecting the rate of flow of the air stream passing through the dust filter 9 are arranged on the downstream side of the dust filter 9, and the clogged status of the dust filter 9 is computed on the basis of the rates of flow of the air streams, which are detected by the first flow velocity sensor 11 and the second flow velocity sensor 12.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for detecting clogging of a dust filter.

0002

2. Description of the Related Art When a dust filter becomes increasingly clogged, problems arise in automatic temperature control, such as delayed response and sometimes malfunction. For this reason, Japanese Utility Model Publication No. 42-5671 discloses an air filter clogging display device for prompting early replacement and cleaning of the dust filter. Furthermore, Japanese Patent Laid-Open No. 1-113569 discloses a clogging detection device for an air cleaner for an internal combustion engine.

0003

[Problems to be Solved by the Invention] However, the air filter clogging display device displays the degree of clogging of the air filter by the inclination of the wind receiving plate, and does not work unless the applied voltage to the blower motor is constant. The clogging detection function cannot be performed. Further, the clogging detection device for an air cleaner for an internal combustion engine detects the absolute pressure P0 on the upstream side of the air cleaner provided in the intake pipe and the pressure loss ΔP in the air cleaner, estimates the intake air amount Q0 from the absolute pressure P0, and The clogging of the air cleaner is detected by estimating the pressure loss ΔP1 that is the limit of clogging, and comparing it with the pressure loss ΔP. This is because it is airtight like the intake pipe of an internal combustion engine, the absolute pressure P0 on the upstream side of the air cleaner always corresponds to the intake air amount Q0, and the airflow velocity flowing through the intake pipe is fast, reducing pressure loss in the air cleaner. Since the amount is on the order of 100 mmAq or more, clogging of the air cleaner can be detected as described above. On the other hand, not only household air conditioners, but also automobile air conditioners are required to deal with dust pollution.
Although installation of a dust filter is considered, in the case of automobile air conditioners, the airtightness of the duct is not as high as that of an internal combustion engine's intake pipe, and the flow rate of the air flowing inside the duct is low, so dust filters are removed due to the influence of ram pressure. The absolute pressure on the upstream side of the filter and the air flow rate do not necessarily correspond, and furthermore, the absolute pressure on the upstream side of the filter is 0 to 50 mmAq.
Because of the pressure loss before and after, the device for detecting clogging of an air cleaner of an internal combustion engine cannot be used as it is as a device for detecting clogging of a dust filter of an air conditioner for an automobile. The present invention has been made in view of the above, and provides a dust filter that can directly detect the amount of clogging even if the air flow rate changes continuously, the ambient temperature changes, or the characteristics of the dust filter change. An object of the present invention is to provide a filter clogging detection device.

0004

[Means for Solving the Problems] As a specific means for achieving the above object, a detection hole is formed in a dust filter disposed in a duct of an air conditioner, through which the airflow in the duct passes as is, a first flow rate sensor that detects the flow rate of the air flow passing through the detection hole on the downstream side of the dust filter; and a second flow rate sensor that detects the flow rate of the air flow passing through the dust filter near the first flow rate sensor. clogging of the dust filter, further comprising a calculation means for calculating the amount of clogging of the dust filter based on the flow velocity detected by the first flow velocity sensor and the second flow velocity sensor. A detection device is provided. Further, the first flow rate sensor and the second flow rate sensor are each thermally responsive elements, and the heat capacity of the protective film that covers and protects the first flow rate sensor is reduced by the heat capacity of the protective film that covers and protects the second flow rate sensor. The first and second heat capacities during operation are made larger than the heat capacity of
A dust filter clogging detection device is provided in which the responsiveness of flow rate sensors to changes in ambient temperature is made substantially equal. Furthermore, there is provided a clogging detection device for a dust filter characterized in that an air flow rate control means for increasing the air flow rate according to the amount of clogging is added.

[0005]

[Operation] The operation of the dust filter clogging detection device is as follows. The flow velocity of the air flow passing through the detection hole formed in the dust filter is detected by a first flow velocity sensor, and the flow velocity of the air flow passing through the dust filter is detected by a second flow velocity sensor. Calculate the amount of clogging. Then, the heat capacity of the protective film of the first flow velocity sensor, which is a thermally responsive element, is
By making the heat capacity larger than the heat capacity of the protective film of the flow rate sensor and making the responsiveness of the first and second flow rate sensors to changes in ambient temperature substantially equal during operation, even if the ambient temperature changes, the first and second flow rate sensors To minimize fluctuations in a calculated value of the amount of clogging of a dust filter based on the flow velocity of an air flow detected by a flow velocity sensor. Further, the air flow rate control means increases the air flow rate in the duct according to the detected amount of clogging to maintain constant air conditioning performance.

[0006]

Embodiments (First Embodiment) A first embodiment of the present invention will be described with reference to FIGS. 1 to 7. The diagram shows 1 Automotive air conditioner (hereinafter referred to as air conditioner)
FIG. 1 in the figure is a ventilation duct,
An air inlet 3 with an inside/outside air switching damper 2 provided at both ends thereof and a conditioned air outlet 4 are formed,
Inside is a blower 5 for blowing air, an evaporator 6 for cooling the air, and a heater core 7 for heating the air.
and an air mix damper 8 that adjusts the mixing ratio of cooling and heating air. A dust filter 9 is arranged between the blower 5 and the evaporator 6. As shown in FIG. 2, the dust filter 9 is constructed by bending the filter medium 9a in a zigzag shape to enlarge the filtration area, and then forming the case 9b.
It is stored in. Detection holes 10 are formed at predetermined locations on the zigzag filtering surface of the filter medium 9a to allow the air blown by the blower 2 to pass through. A first flow rate sensor 11 that detects the flow rate of air passing through the detection hole 10, and a second flow rate sensor located near the first flow rate sensor 11 that detects the flow rate of air passing through the filtering surface of the dust filter 9. Place 12.

13 is a microcomputer,
It is composed of a CPU, ROM, RAM, various interfaces (all not shown), etc., and automatically controls the amount of air blown by the blower 5 and the opening degree of the air mix damper 8 according to an air conditioning control program stored in the ROM. Furthermore, the amount of clogging of the dust filter 9 is calculated by inputting each flow velocity detected by the first flow velocity sensor 11 and the second flow velocity sensor 12. Reference numeral 14 is a warning device that displays a warning in response to a signal from the microcomputer 13 when the dust filter 9 becomes clogged to a predetermined tolerance value (limit degree of clogging) or more.

[0008] The detection hole 10 is designed to have the minimum size necessary to enable the first flow rate sensor 11 to detect the flow velocity of the air passing through the detection hole 10, so as not to reduce the filtration performance of the dust filter 9 as a whole. . Also, the first and second
The flow rate sensors 11 and 12 are connected to the case 9 of the dust filter 9.
It may be placed at the corner of b (see FIG. 3). In this case, the flow rate sensors 11, 12 and the detection hole 10 are made into a unit,
Replace it when replacing the dust filter 9. Flow rate sensor 1
2 corresponds to a dust filter piece 9c having the same characteristics as the dust filter 9. Further, the flow rate sensor may be an integrated type or a separate type. In the case of a separate type, it is necessary to perform correction between each flow rate sensor.

[0009] The flowchart of FIG. 4 and FIGS. 5 to 7 are as follows.
The operation of the above embodiment will be explained with reference to the characteristic diagram. When the processing by the microcomputer 13 starts,
In step 11, the flow velocity Va of air passing through the detection hole 10 detected by the first flow velocity sensor 11 and the flow velocity Vb of air passing through the dust filter 9 detected by the second flow velocity sensor 12 are input. Next, the process proceeds to step 12, where the degree of clogging (resistance coefficient) ζb of the dust filter 9 is calculated using the formula ζb=ζa (Va/Vb)2. The pressure loss at the detection position of each flow velocity is △P=ζa・ρVa2/2
, ΔP=ζb·ρVb2/2, and the pressure loss of both becomes equal {where ζ: resistance coefficient (degree of clogging), ρ: density}. Therefore, from the above two equations, ζb=ζa(Va/
Vb) becomes 2. The above steps 11 and 12 constitute the clogging amount detection means of the present invention.

In the following step 13, it is determined whether the degree of clogging ζb is equal to or higher than the limit degree of clogging ζc, and if it is, the process proceeds to step 14, where the warning device 14 is activated to flash a clogging alarm, etc. to display a clogging indication. Further, if the degree of clogging is below the limit clogging degree ζc, in step 15, the resistance coefficient ζb0 of the dust filter 9 when new is set,
Based on the flow velocity Va detected by the first flow velocity sensor 11, from the formula Vb0=Va (ζa/ζb0) 1/2, if the dust filter 9 is not clogged, that is, the dust passes through the new dust filter 9. Air flow velocity can be calculated.

The resistance coefficient ζb0 when new is determined by the equation ζb=ζa at the first operation after replacing the dust filter 9.
(Va/Vb)2 is calculated and stored. Then, in step 16, the flow velocity Vb detected by the flow velocity sensor 12 is compared with the flow velocity Vb0 calculated by the above formula. If Vb≧Vb0, the process proceeds to step 17, where the blower voltage is slightly increased to increase the air volume. and,
After repeating steps 11 to 17 until Vb≧Vb0, the blower voltage is fixed in step 18, and even if the degree of clogging of the dust filter 9 progresses, it is always assumed that there is no clogging. Match the air volume to maintain a constant air conditioning performance. The above steps 16 and 17 are
This constitutes the air flow rate control means of the present invention.

In the above embodiment, the relationship between the blower voltage and the flow rate of air flowing through the dust filter 9 is shown in FIG. 5, and the relationship between the pressure loss ΔP and the flow rate of air flowing through the dust filter 9 is shown in FIG. In addition, there is a correlation between the degree of clogging ζb of the dust filter 9 and (Va/Vb)2 as shown in FIG.
can be directly calculated based on the flow velocities Va and Vb detected from the first flow velocity sensor 11 and the second flow velocity sensor 12.

For this reason, the device of the first embodiment is useful for detecting clogging of dust filters used in air conditioners where the air flow velocity constantly changes due to fluctuations in ram pressure, blower voltage, damper positions for selecting various outlets, etc. Ideal for Furthermore, even if the dust filter becomes clogged, using the resistance coefficient ζb0 when it is new, we can calculate the flow velocity of air passing through the dust filter when it is new, assuming that the dust filter is not clogged. Since the air volume can be increased, a constant air conditioning performance can be maintained at all times, and the occupants will not feel uncomfortable.

(Second Embodiment) FIG. 8 is a schematic diagram of the main parts of a second embodiment of the present invention. A first flow rate sensor 21 that detects the flow rate of air passing through the detection hole 10 of the dust filter 9;
The second flow rate sensor 22, which is arranged near the dust filter 1 and detects the flow rate of air passing through the filtering surface of the dust filter 9, uses a heat generating thermistor. This heat-generating thermistor is composed of a semiconductor detection element having a negative temperature coefficient and a resin protection film that encapsulates and protects the detection element. This first,
The second flow rate sensors 21 and 22 are incorporated into a bridge circuit 25 to which fixed resistors 23 and 24 are connected. If the applied voltage of this bridge circuit 25 is V0, the output voltage V is V={R
o/(Ro+Rf)-1/2}·V0. However, Ro
is the resistance of the heat generating thermistor that constitutes the first flow rate sensor 21, and Rf is the resistance of the heat generating thermistor that constitutes the second flow rate sensor 22.

The detection elements 21a and 21b are in a heat-generating state due to the applied voltage V0 of the bridge circuit 25, and the flow velocity Uo of the air passing through the detection hole 10 and the flow velocity Uf of the air passing through the filtering surface of the filter 9. Therefore, the temperature of the detection element 21a is To, and the temperature of the detection element 21b is Tf.
is balanced. Here, if the ambient temperature suddenly changes, the air flow velocity is Uo>Uf, so the first flow velocity sensor 2
The fluctuating heat amount of the first detection element 21a is larger. Therefore, if the changes from the balanced temperatures To and Tf are respectively △To and △Tf, then │△To│>│△Tf│, and from the resistance-temperature characteristics of the detection elements 21a and 21b, detection is possible. The resistance changes of the elements 21a and 21b are respectively ΔRo
, △Rf, then │△Ro│>│△Rf│. Since the detection elements 21a and 21b have negative temperature coefficients as described above, considering the formula for the output voltage V, if the ambient temperature rises suddenly, the value of the output voltage V decreases, and the ambient temperature suddenly rises. If the output voltage V decreases, the value of the output voltage V increases.

FIG. 9 shows the detection element 21 of the first flow velocity sensor 21.
The heat capacity of the protective film 21b that protects the flow rate sensor 21a and the heat capacity of the protective film 22b that protects the detection element 22a of the second flow velocity sensor 22 are the same, and both detection elements 21a and 2 have negative temperature coefficients.
2 shows actual measured values of the temperature transient characteristics of the output voltage V of the bridge circuit 25 when the resistance-temperature characteristics of the bridge circuit 2a are made equal. For example, if the ambient temperature of the first and second flow rate sensors 21 and 22 suddenly drops, the temperature transient characteristics of the output voltage will cause an overshoot of about 5 to 6 mV,
Further, when the voltage rises rapidly, an undershoot of about 5 to 6 mV occurs. It takes about 2 to 10 minutes for the overshoot or undershoot to converge.

The above phenomenon occurs when the first and second flow velocity sensors 21,
Even if the air flow velocity detected by the bridge circuit 22 does not change, the output voltage V of the bridge circuit 25 will deviate significantly from the normal value due to a change in the ambient temperature. This is because when the heat capacities of the protective films 21b and 22b are made equal as described above, the first flow velocity sensor 21 placed in a faster air flow has a faster resistance-temperature characteristic response than the second flow velocity sensor 22. This is due to the fact that the time constant becomes faster, that is, the time constant becomes smaller.

Therefore, the protective film 21 of the first flow rate sensor 21
If the heat capacity of b is made larger than the heat capacity of the protective film 22b of the second flow rate sensor 22 and the time constant is increased to slow down the response speed of the resistance-temperature characteristic, the ambient temperature will suddenly change and the output voltage V of the bridge circuit 25 will be reduced. It is possible to prevent the inconvenience that the value deviates significantly from the normal value. In order to increase the heat capacity of the protective film 21b, the material of the protective film 21b may be changed from metallic glass to resin, or the volume of the protective film 21b may be increased.

FIG. 10 shows the bridge when the ratio Cpo/Cpf of the heat capacity Cpo of the protective film 21b and the heat capacity Cpf of the protective film 22b is set to 1.00, 1.17, 1.25, and 1.33, respectively. It shows the temperature transient characteristics of the output voltage V of the circuit 25. According to this, the heat capacity ratio Cpo
When /Cpf=1.25, the fluctuation in the output voltage V is the smallest. Further, FIG. 11 shows the heat capacity ratio Cpo/Cpf
This shows the relationship between the maximum fluctuation range of the output voltage V and the maximum fluctuation range of 0 when the heat capacity ratio Cpo/Cpf=1.26.
becomes. From the above, the heat capacity ratio of the protective film Cpo/Cpf=
By setting it to about 1.2, the fluctuation range of the output voltage V can be significantly reduced. This numerical value is not significantly affected even if the amount of dust attached to the dust filter 9 changes or the air flow velocity or air volume changes.

FIG. 12 shows how, in the operation of the second embodiment, the clogging limit voltage VR is set and the bridge circuit 2
5 is a flowchart showing a process of lighting a clogging alarm based on comparison with the output voltage V of No. 5 to notify clogging of the dust filter 9. FIG. When the amount of clogging of the dust filter 9 increases and the flow velocity of the air detected by the second flow velocity sensor 22 becomes slower, the output voltage V of the bridge circuit 25 increases. ,
Blinks the clogging alarm.

In the case of the second embodiment, as in the case of the first embodiment, the amount of clogging is calculated from the output voltage V of the bridge circuit 25, and the air flow control means controls the amount of air in the dust according to the amount of clogging. It is possible to maintain a constant air conditioning performance by increasing the air flow rate. In the above embodiment, by changing the heat capacity of the protective film of the flow rate sensor, the response speeds, that is, the time constants of the resistance-temperature characteristics of the two flow rate sensors placed in air flows with different flow rates are made to be substantially the same. However, it is also possible to electrically change the time constant of each flow rate sensor. In this case, the time constant may be automatically changed by detecting a change in ambient temperature using a temperature sensor or a circuit.

[0022] Since the convergence time for undershoot or overshoot of the bridge circuit 25 due to a sudden change in ambient temperature is about 10 minutes, the sampling period is set to 10 minutes or more, so that an abnormality exceeding the clogging limit voltage VR can be detected. It is also possible to determine that the blockage is not clogged unless the value continues a predetermined number of times.

[0023]

[Effects of the Invention] The present invention has the above configuration, and the flow rate of the air flow passing through the detection hole formed in the dust filter is determined by the first flow rate sensor, and the flow rate of the air flow passing through the dust filter is determined by the second flow rate sensor. Since the amount of clogging of the dust filter can be directly calculated based on the detected flow velocity, it is ideal as a device for detecting clogging of the dust filter when the air flow rate constantly changes. Also,
The first flow velocity sensor and the second flow velocity sensor are each thermally responsive elements, and the heat capacity of the protective film that encloses and protects the first flow velocity sensor is determined from the heat capacity of the protective film that encloses and protects the second flow velocity sensor. is also made larger, and the first and second
By making the responsiveness of the flow rate sensors approximately equal to changes in ambient temperature, even if the ambient temperature changes, the calculated value of the amount of clogging of the dust filter based on the flow rate of the air flow detected by the first and second flow rate sensors will fluctuate. can be made as small as possible. Furthermore, the air flow rate in the duct can be increased according to the amount of clogging detected, and the air conditioning performance can always be maintained constant.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an air conditioner for an automobile.

FIG. 2 is a perspective view of the dust filter showing the arrangement of a first flow rate sensor and a second flow rate sensor.

FIG. 3 is a perspective view of a part of the dust filter showing another arrangement position of the first flow rate sensor and the second flow rate sensor.

FIG. 4 is a flowchart showing the operation of the first embodiment.

FIG. 5 is a characteristic diagram showing the relationship between voltage and the flow rate of air flowing through the dust filter.

FIG. 6 is a characteristic diagram showing the relationship between pressure loss ΔP and the flow rate of air flowing through the dust filter.

[Figure 7] Dust filter clogging degree ζb and (Va/V
b) It is a characteristic diagram showing the relationship with 2.

FIG. 8 is a schematic configuration diagram of main parts of a second embodiment.

FIG. 9 is a diagram showing actual measured values of the temperature transient characteristics of the output voltage V of the bridge circuit.

FIG. 10 is a diagram showing the relationship between the heat capacity ratio Cpo/Cpf and the temperature transient characteristics of the output voltage V of the bridge circuit.

FIG. 11 is a diagram showing the relationship between the heat capacity ratio Cpo/Cpf and the maximum fluctuation width of the output voltage V.

FIG. 12 is a flowchart showing a process for notifying the amount of clogging in the second embodiment.

[Explanation of symbols]

1. ．． ．． Ventilation duct, 5. ．． ．． Blower, 7. ．．
．． heater core, 8. ．． ．． Air mix damper, 9.
．． ．． Dust filter, 10. ．． ．． Detection hole, 11
,21. ．． ．． First flow rate sensor, 12, 22. ．． ．． second flow rate sensor, 13. ．． ．． microcomputer,
Steps 11 and 12. ．． ．． Calculation means, step 1
6 and 17. ．． ．． Air flow rate control means, 21a, 22
a. ．． ．． Detection element, 21b, 22b. ．． ．． Protective film,
25. ．． ．． bridge circuit.

Claims (3)

[Claims] 1. A detection hole is formed in a dust filter disposed in a duct of an air conditioner, through which the air flow in the duct passes as is, and the air flow passing through the detection hole is formed on the downstream side of the dust filter. A first flow velocity sensor that detects the flow velocity and a second flow velocity sensor that detects the flow velocity of the air flow passing through the dust filter are disposed near the first flow velocity sensor, and the first flow velocity sensor and the second flow velocity A clogging detection device for a dust filter, comprising a calculation means for calculating the amount of clogging of the dust filter based on the flow velocity detected by the sensor. 2. The first flow velocity sensor and the second flow velocity sensor are each thermally responsive elements, and the heat capacity of a protective film that covers and protects the first flow velocity sensor is protected by encasing the second flow velocity sensor. 2. The dust filter clogging detection device according to claim 1, wherein the heat capacity is larger than that of the protective film to make the responsiveness of the first and second flow rate sensors to changes in ambient temperature substantially equal during operation. . 3. The dust filter clogging detection device according to claim 2, further comprising air flow rate control means for increasing the air flow rate according to the amount of clogging of the dust filter.