JPH0729020B2 - Air purifier - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air cleaner, and more particularly to an air cleaner having a smoke (gas) detection circuit suitable for automatic operation.

[Conventional technology]

Conventionally, a semiconductor gas sensor has been used as a smoke detector for cigarettes and the like, and is discussed, for example, in Practical Manuals for Detectors, pages 638 to 644, issued by the New Technology Development Sensor on September 20, 1976. That is, the gas sensor is a sintered body containing semiconductor SnO ₂ as a main component, and has a heating heater coil that also serves as an electrode and is incorporated inside.
In a clean atmosphere, a constant resistance value is maintained, so a constant current flows in the circuit. When a reducing gas such as hydrogen or carbon monoxide comes into contact with the sensor, the resistance value of the sensor decreases in accordance with the gas concentration, so that the change appears as a voltage change across the load resistance R _L. Is shown in. By the way, since the above-mentioned sensor is generally affected by temperature, a temperature compensating circuit is added as disclosed in, for example, Japanese Patent Laid-Open No. 60-236054.

However, when such a sensor is used in an air purifying device for an automobile, it is necessary to have a stable device that adapts not only to the influence of only the temperature but also to various environmental conditions described later and does not malfunction.

[Problems to be solved by the invention]

The commonly used gas sensor as the above-mentioned smoke detector has a detection sensitivity which changes with changes in temperature and humidity. Specifically, the resistance value of the gas sensor itself changes according to temperature and humidity, and the resistance value is small at high temperature and high humidity, and is large at low temperature and low humidity.

In order to solve this problem, for example, a temperature compensating circuit is added to stabilize the detection sensitivity.

When such a sensor is applied to an automobile air cleaning device, (1) fluctuations in detection sensitivity (temporarily large resistance value of gas sensor) immediately after starting energization after being left unenergized for a long time.

(2) Malfunction due to the particles filling the interior of the vehicle when using an air freshener or deodorant.

(3) There is a problem that the detection sensitivity changes (gas sensor resistance value change) due to a sudden change in the vehicle interior atmosphere temperature due to opening and closing of the door.

An object of the present invention is to solve the above problems, and to provide an air purifying device capable of stabilizing detection sensitivity and preventing malfunction.

[Means for solving problems]

In order to achieve the above object, the present invention provides a gas detection element (gas sensor) for detecting a gas concentration in room air, a reference voltage circuit for outputting a reference voltage for gas detection, and a detection signal of the gas detection element. And a comparison circuit that controls the operation of the air purifier by comparing the reference voltage from the reference voltage circuit and the reference voltage from the reference voltage circuit.

The reference voltage circuit receives the detection signal of the gas detection element and includes a time delay circuit, and the time constant of the time delay circuit, for example, changes in temperature and humidity, and the indoor atmosphere such as the use of fragrance or deodorant. It is characterized in that the reference voltage of the reference voltage circuit is made to follow the change of the indoor atmosphere by setting the same as the change rate.

[Action]

Regarding the change in the atmosphere of the gas sensor, the change rate of the sensor voltage is gradual when the resistance of the gas sensor is low in any of the problems of the above-mentioned conventional techniques, while the change rate when smoking is very fast as compared with the above. Therefore, the time constant of the time delay circuit is set to be very large depending on the rate of change during smoking, that is, set to about the same as the rate of change in the indoor atmosphere, and the reference voltage of the reference voltage circuit is changed in the indoor atmosphere. Set to follow.

As a result, the potential of the capacitor of the time delay circuit in particular can hold the smoke sensor changes only in the atmospheric conditions such as temperature and humidity changes without being significantly affected by the output changes of the smoke sensor during smoking. Since it has a function as a holding element, the comparator using this as a reference value does not cause erroneous detection due to the influence of the atmosphere. Moreover, since the capacitor potential can always maintain a constant voltage value slightly higher than the gas sensor output potential, the comparator output can obtain a constant smoke detection concentration in any atmosphere.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. Reference numeral 10 is a constant voltage circuit, which is supplied with power from the battery's battery voltage V _B and supplies a stable constant voltage (= V _C ) to the output side. Reference numeral 11 denotes a semiconductor gas sensor, which is composed of a heater 11a and an electrode 11b. The heater 11a is supplied with electric power from V _C. One of the electrodes 11b is connected to V _C and the other is connected to a resistor 12, and a resistor 12
The other end of is grounded. Assuming that a connecting point P between the electrode 11b of the gas sensor 11 and the resistor 12 is a point P, an impedance matching circuit is formed by connecting the collector of the transistor 14 and the operational amplifier via the resistor 13 and connecting the inverting input end and the output end. , Commonly referred to as the voltage follower 16 connected to the non-inverting side input end. The output of the voltage follower 16 is a resistor 23 and a capacitor on one side.
A series circuit of a resistor 22 and a diode 24 is connected from V _C side to V _C and the output terminal centering on 27, and a series circuit of a capacitor 27, a resistor 26 and a diode 25 is also connected from V _C side, and After passing through a time delay circuit formed by connecting a resistor 23 to the connection point (F point) between the resistor 22 and the diode 24 and the connection point (Q point) between the capacitor 27 and the resistor 26, the time delay circuit output Q The second voltage follower 29 is input from the point, and the voltage follower 29 is input.
The output of is connected to the resistor 32 through a parallel circuit of the diode 30 and the variable resistor 31, and the other end of the resistor 32 is output to the variable resistor which is the output of the voltage divider circuit via the voltage divider circuit which is grounded. The variable end (point R) of the device 31 is connected to one input of the voltage comparator 33. The reference voltage circuit including the time delay circuit and the voltage dividing circuit has the above configuration. The other connection destination of the voltage follower 16 is connected to the other input terminal of the voltage comparator 33. The output of the voltage comparator 33 is input to the monostable multivibrator 34 (abbreviated as monostable multi) and the monostable multivibrator 34 is input.
The output pulse width of 34 is determined by the resistor 35 and the capacitor 36 from V _C. The signal of the output of the monostable multi 34 is transmitted to the next stage by the resistor 37 and the transistor 38. That is, in the purifier operating circuit, the blower motor 40 and the resistor 39 of the air purifier are connected in series from the battery voltage V _B, and the resistor 39 of the circuit grounded, the collector of the transistor 38, and the emitter are connected in parallel. is there. Note that a connection point of the two elements which are connected between V _C and the ground a resistor 18 and a capacitor 19 in series, also a dividing point which is divided between V _C and ground by a resistor 20, 21 2
The timer circuit composed of the voltage comparator 17 that receives the input has one output through the switch 42 as the reset signal input of the monostable multi 34, and the other through the resistor 15 to the emitter to the V _C side and the collector to the collector. It is a circuit for measuring the initial stabilization of energization, which is configured to be connected to the non-inverting input of the first voltage follower 16. The air purifier has a filter that filters dirt and a blower that rotates at low speed and high speed, and is installed on the Riyashi Elf in the vehicle compartment or on the ceiling.

The operation of the apparatus having the above configuration will be described below.

Power V _B of the motor vehicle is connected to the position of the regular key ON, apparatus mainly operate during engine operation. Gas sensor 11 is a heater
The electrode 11b is activated when 11a is energized, and when the gas sensor 11 is contacted with a combustible gas such as hydrogen, carbon monoxide, propane or alcohol, benzol, etc.
The resistance value of b decreases. FIG. 2 shows an example of detection characteristics of various gases. That is, the gas concentration is plotted on the horizontal axis, and the ratio Rs / Rs Air between the detection characteristics (= Rs Air) in clean air and the respective gas concentrations (Rs) is plotted on the vertical axis. Air (no change), carbon monoxide , Ethyl alcohol, and hydrogen each exhibit the characteristics shown in FIG. It is known that cigarette smoke contains carbon monoxide, and the gas sensor 11 reacts with combustible gas such as carbon monoxide.

FIG. 3 shows an example of actual measurement of point P in FIG. 1 when a smoking test was conducted in the interior of a car. That is, when non-smoking, V _P is a constant potential balanced in the atmosphere in the passenger compartment, and after the start of smoking, the resistance value of the electrode 11b decreases by detecting this, so the gas sensor 11
The output voltage V _P of V increases with the concentration.

Therefore, it can be seen that smoking detection using a gas sensor can be obtained by detecting a potential change of V _P.

FIG. 1 shows a specific example. The gas sensor output V _P is directly input to one of the voltage comparators 33 after impedance conversion (voltage follower 16), and a time delay circuit and voltage divider circuit with V _P as input. Smoking is detected by a circuit in which the output of the constituent reference value circuit is the other input of the comparator 33.

Here, the gas sensor is affected by temperature and humidity, and the resistance value decreases as the temperature and humidity increase, and the resistance value increases as the temperature and humidity decrease. An example is shown in FIG.
Therefore, in order to compensate for this influence, it is necessary to provide a temperature / humidity compensation circuit in the reference value circuit.

However, the current conditions for automobiles have not been put to practical use other than temperature compensation. The present invention eliminates this point without a temperature sensor, and the time delay circuit of FIG. 1 has this function. P
Since the point has a high output impedance, the voltage follower 16 measures the output voltage increase and drives the time delay circuit. resistance
If the value of 22 is sufficiently smaller than that of the resistor 23, the current from the power supply V _C is mainly due to the resistor 22, the diode 24 and the voltage follower 16
Therefore, the potential on the anode side (point F) of the diode 24 can always be kept higher than the potential V _P at the cathode end by the forward saturation voltage. In the integrating circuit composed of the resistor 23 and the capacitor 27 which receive the potential at the F point, the potential at the Q point is kept at V _P + the potential at the F point V _F when V _P is in a balanced state, and V _C
Therefore, the potential difference obtained by subtracting the potential is always held at both ends of the capacitor 27, and the potential V _{Q of the} capacitor 27 can be regarded as the reference potential when the gas sensor 11 is in equilibrium.
The output power is increased by the voltage follower 29 having the point Q as an input, and the output is connected by driving the voltage dividing circuit including the variable resistor 31. In this circuit, without the diode 30, the potentials at both fixed ends of the variable resistor 31 are proportional to V _Q ,
The potential difference between V _P and the potential V _R at the variable end R varies depending on V _Q , which causes a problem. Therefore, when the diode 30 is connected as shown in FIG. 1, the potential across the diode 30 of the voltage dividing circuit becomes approximately equal to the potential of the diode 24 described above, and the cathode side potential of the diode 30 becomes V _P at equilibrium. It becomes almost equal. Therefore, the variable resistor 31 can set an arbitrary potential from V _P to V _Q to the variable end R. As described above, the time delay circuit and the voltage dividing circuit are circuits that function as reference values when the gas sensor is in equilibrium.

Here, the rate of change of temperature and humidity in the vehicle interior during driving is
For example, when using a heater, it rises at about 0.04 V / min in V _P conversion. This is a value that takes into account both the temperature increase in the vehicle interior and the accompanying humidity decrease. The time constant of the time delay circuit is set to the same level as that when the heater is used. As a result, the potential V _Q of the capacitor 27 can correspond to the voltage increase of the sensor output V _P with respect to the temperature and humidity change when the heater is used, which is approximately 1: 1. This is an increase rate of about 0.5 V / during smoking in the example of FIG. Since it is very small compared to the minute, the time delay circuit cannot follow the change during smoking. That is, when the time delay circuit is used as described above, it is possible to follow changes in the vehicle interior atmosphere (temperature and humidity) when the heater is used and not accept smoking changes.

This means that the time delay circuit compensates the temperature and humidity of the gas sensor.

Further, there are cases where an fragrance or a deodorant is used in the passenger compartment, but in a normal circuit, the gas sensor may detect these gas components. However, since the time change rate of the gas sensor potential due to the above components is smaller than that when the heater is used, the time delay circuit can follow the atmosphere change due to the fragrance or the like and can compensate.

Next, in automobiles, when passengers get on and off, the door may be temporarily opened, which causes temperature, humidity, and
The fragrance concentration may change suddenly. For example, when the outside temperature is low, when the door is lifted, the gas sensor is temporarily cooled, so that the resistance value of the sensor itself increases. Therefore, the sensor potential V _P decreases, but the decrease rate of V _{Q of the} time delay circuit is slow, so the voltage difference between P and Q temporarily increases, and P-
The potential difference between R also becomes large. This means that the detection sensitivity of the sensor is temporarily reduced.For example, when the occupant immediately starts smoking after getting on, there is a problem that the gas sensor cannot detect with a predetermined detection sensitivity. Occurs.

Therefore, in order to keep the detection sensitivity constant even if the atmosphere changes suddenly due to the opening and closing of the door, the diode 25 is provided.
Is. That is, when the potential V _{P of the} gas sensor drops sharply,
Capacitor 27, resistor 26, diode 25 and voltage follower
In the circuit consisting of 16, the capacitor potential V _Q has a small resistance 26, so if the voltage drop here is ignored, it will move parallel along V _Q ≈ V _P + (forward saturation voltage of diode 25). .

Therefore, it is possible to optimally compensate for a sudden change in the vehicle interior atmosphere when the door is opened and closed.

Next, the case of smoking in a circuit capable of absorbing the various atmosphere factors will be described with reference to FIG. When the engine is running and not smoking, after cleaning 40, the blower is operated at a low speed. When smoking starts in the passenger compartment, the gas sensor detects this and V _P begins to rise in potential as shown in Fig. 6b, and eventually V _R
This coincides with (Fig. 6a). The voltage comparator 33 outputs a coincidence signal at this coincidence point as shown in FIG. 6c. Monostable Multi 34
Is triggered by the first coincidence signal of the comparator 33, and outputs a pulse for its own set time, for example, 8 minutes (Fig. 6d). When the blower 40 of the air purifier is operated at high speed rotation during pulse output of the monostable multi 34, and is operated at low speed rotation at other times, the air purification in the passenger compartment can be efficiently performed during smoking. I can.

Next, the gas sensor 11 has a very high resistance value immediately after the power is turned on, then approaches zero, and eventually stabilizes at a certain resistance value.
This stable value is a value obtained by absorbing the above-mentioned various factors such as temperature and humidity, fragrance and other atmospheres, and this is shown in FIG. Since the time until stabilization is unstable, the monostable multi 34 may be erroneously triggered during this time, resulting in erroneous operation. Therefore, during this time, a malfunction prevention circuit described below was added.

That is, the first is the capacitor 27 in the section (Fig. 5a) in which the gas sensor-voltage V _P after the power is turned on is temporarily close to zero.
With respect to the above, since the one end V _C is established and the resistance 26 at the other end has a small value, the potential difference in the capacitor 27 suddenly becomes large and the capacitor 27 is rapidly charged to a value close to V _C. After that, V _P approaches V _{C as} shown in Fig. 5P and stabilizes at the operating value.
Since V _Q has a large time constant, it follows the characteristics as shown in Q of FIG. 5, and even if the sensor reaches the stable range, it cannot follow the operating conditions as shown in a and b of FIG. Therefore, immediately after the power is turned on, the circuit of the comparator 17 is operated for a certain period of time to output a pulse, and the transistor 14 is held in the conductive state by this output to eliminate such a problem. By doing so, the capacitor potential V _Q can be set to a value higher than V _P by a certain potential before entering the stable region, as shown in Q ′ of FIG.

Secondly, since the comparator 33 erroneously outputs in the unstable region immediately after power-on and triggers the monostable multi 34, the output of the comparator 17 is output to the reset terminal of the multivibrator 34 in order to prevent this malfunction. Connected and activated the reset function.

The present invention is further provided with a switch 42 so that the initial stable monostable multi-current
When the switch 42 is closed, the reset operation is performed. When the switch 42 is opened, the monostable multi 34 is triggered, and the blower of the purifier is forcibly operated once (about 8 minutes) at high speed. In this way, the initial down time is compensated.

As described above, it is possible to realize a circuit that does not malfunction even immediately after the power is turned on.

Further, according to the present invention, if the voltage dividing circuit as shown in FIG. 7 is used, the accuracy is further improved. In the circuit of Fig. 1, V _F is a diode rather than V _P
The forward saturation voltage (V _FD ) of 24 is equilibrated at a potential as high as about 0.7V. By the way, a diode generally has a temperature characteristic, and an example is shown in FIG. -1.6 mV / ° C when forward current is 5 mA
It becomes a coefficient of degree and changes by 80 mV when the temperature changes by 50 ° C. Since V _R -V _P is set to a value of about 0.1 to 0.5 V when not smoking, the temperature has a great influence when the set voltage is low. Therefore, as shown in Fig. 7, the circuit of Fig. 1 is modified so that the output of the voltage follower 29 is changed from the power source V _C to the resistor 5
1.Connect the diode 52,30 and the resistor 32 to the connection point of both diodes of the circuit grounded in series, and place the resistor 55, thermistor 56, and variable resistor 31 at the anode of the diode 52 and the cathode end of the diode 30. It is a circuit that was set up.

That is, a temperature compensation circuit using a thermistor was added, but the cathode end of the diode 30 when not smoking is V _P
Since V _R can be set 0.1 to 0.5 higher than V _P, it cannot be realized simply by inserting a thermistor circuit into the diode 30 shown in FIG. In addition, the thermistor 56, the resistor 55, and the variable resistor 31 are arranged in a series circuit of two diodes. FIG. 9 shows V _R -V _{P in} the circuit of FIG. 7, that is, the differential potential characteristic of the comparator 33.

FIG. 9 shows that it becomes constant regardless of temperature.

According to the present embodiment, the temperature and humidity peculiar to the gas sensor in the automobile air cleaner using the smoke sensor as the gas sensor, the fluctuation in the initial stage of energization, and the influence of the fragrance and the deodorant without being affected by the cigarette are always low. The effect is to obtain an air purifier that operates by detecting smoke.

〔The invention's effect〕

As described above, according to the present invention, the influence of temperature and humidity on the practical use of the cigarette smoke sensor using the gas sensor, the influence of the use of the fragrance, etc., absorbs other atmosphere-inhibiting factors, and is sensitive to the detection sensitivity. There is an excellent effect that it is possible to realize an air purifying device with a smoke detector having a high performance that can be constantly set to a constant value.

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit connection of an embodiment of the present invention, FIG. 2 is a functional characteristic diagram of a gas sensor, FIG. 3 is a diagram showing gas sensor detection characteristics during smoking, and FIG. 4 is a temperature and humidity of the gas sensor. FIG. 5 is a diagram showing the characteristics, FIG. 5 is a diagram showing the characteristics of the gas sensor circuit at the initial stage of power-on, FIG. 6 is a diagram showing the operation in one embodiment of the present invention, and FIG. 7 is another embodiment of the present invention. FIG. 8 is a diagram showing such a circuit connection, FIG. 8 is a diagram showing temperature characteristics of a diode, and FIG.
The figure shows the differential potential characteristics of the comparator in FIG. 10 …… Constant voltage circuit 11 …… Gas sensor 16,29 …… Voltage follower 27 …… Capacitor 31 …… Variable resistor 17,33 …… Voltage comparator 34 …… Monostable multivibrator 40 …… Air purifier blower

Claims (1)

[Claims] 1. A gas detection element for detecting a gas concentration in indoor air, a reference voltage circuit for outputting a reference voltage for gas detection, a detection signal of the gas detection element, and a reference voltage from the reference voltage circuit. And a comparison circuit for controlling the operation of the air purifier by comparing with the above, the reference voltage circuit receives the detection signal of the gas detection element and includes a time delay circuit, and the time delay circuit The air cleaning apparatus is characterized in that the time constant of is set to be approximately the same as the change rate of the indoor atmosphere, and the reference voltage of the reference voltage circuit is made to follow the change of the indoor atmosphere.