JPS63274425A - Air cleaner - Google Patents

Abstract

PURPOSE:To contrive stabilization of detection sensitivity by inputting the output of a gas detection element to a reference voltage circuit contg. a time lag circuit, and controlling the time lag circuit in accordance with both the level change velocity of its output signal and the change direction thereof. CONSTITUTION:When a heater 11a is electrified, an electrode 11b is made to an actuated state and combustible gas is detected with a gas sensor 11. Just after starting of electrification, resistance value is made high and the gas sensor is unstable and therefore the circuit of a comparator 17 is actuated for a constant time after the starting and a transistor 14 is held at an electrification state, and also the output of the comparator 17 is connected with the reset terminal of a multivibrator 34 to actuate reset function and furthermore the trigger of the multivibrator 34 is controlled with a switch 42 and a time lag circuit is controlled thereby. The multivibrator 34 actuates the blower of a cleaner for a constant time and controls the actuation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention mainly relates to an air purifying device for automobiles, and particularly to an air cleaning device equipped with a smoke (gas) detection circuit suitable for automatic operation.

[Conventional technology]

Semiconductor gas sensors have conventionally been used as smoke detectors for cigarettes and the like, and are discussed, for example, in Detector Practical Manual, pages 638 to 644, published by the New Technology Development Center on September 20, 1976. In other words, the gas sensor is a sintered body whose main component is the semiconductor 5nO1, and has a built-in electrode and a heater coil that also serves as the electrode.In clean air, the gas sensor maintains a certain resistance value. Therefore, a constant current flows through the circuit.

The above document states that when a reducing gas such as hydrogen or carbon oxide comes into contact with this, the resistance value of the sensor decreases according to the gas concentration, and this change appears as a voltage change across the load resistor R4. It is shown.

By the way, the above sensors are generally affected by temperature, so
For example, as shown in Japanese Unexamined Patent Publication No. 60-236054, a temperature compensation circuit is added.

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

[Problem that the invention seeks to solve]

The above-mentioned gas sensor, which is commonly used as a smoke detector, has a detection sensitivity that changes depending on changes in temperature and humidity. Specifically, the resistance value of the gas sensor itself changes depending on temperature and humidity, and the resistance value is small when high temperature and humidity are high, and becomes large when low temperature and low humidity.

To solve this problem, for example, a temperature compensation circuit has been added to stabilize the detection sensitivity.

When applying such a sensor to an automotive air purifying device, (1) Fluctuations in detection sensitivity (temporarily large resistance value of the gas sensor) immediately after starting energization after being left without energization for a long time.

(2) When using air fresheners or deodorants, malfunctions may occur due to the particles filling the vehicle interior.

(3) A problem arises in that the detection sensitivity fluctuates (gas sensor resistance value change) due to sudden changes in the ambient temperature of the vehicle interior due to opening and closing of the door.

SUMMARY OF THE INVENTION An object of the present invention is to provide an air cleaning device for an automobile that can solve the above-mentioned problems, stabilize detection sensitivity, and prevent malfunctions.

Means for solving problem C] The above purpose is to detect the output signal of the gas detection element (gas sensor),
A comparator circuit inputs the output signal with a signal passed through a time delay circuit mainly composed of a resistor and a capacitor, and compares the signal levels. This is achieved by providing a pulse generating circuit that outputs a pulse with a predetermined time width, and a device that controls the cleaning ability of the air cleaner based on the pulse output of the pulse generating circuit.

[Effect]

Regarding changes in the atmosphere of the gas sensor, the rate of change in the sensor voltage is slow when the resistance of the gas sensor decreases, whereas the rate of change in the sensor voltage during smoking is very fast compared to the above-mentioned problems. Therefore, the time constant of the time delay circuit is set to be about the same as the time constant of the problem in the prior art, but much larger than the rate of change during smoking.

As a result, the potential of the time delay circuit, especially the capacitor, is not affected by changes in the output of the smoke sensor during smoking, and can maintain only changes in the smoke sensor's atmospheric conditions such as changes in temperature and humidity, thereby maintaining the atmospheric conditions of the smoke sensor. Since it functions as an element, a comparator that uses this as one reference value will not cause false detection due to the influence of the atmosphere, and the capacitor potential will always be a constant voltage value that is slightly higher than the gas sensor output potential. Since the comparator output can maintain a constant smoke detection concentration in any atmosphere.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 10
is a constant voltage circuit, which receives power from the car's battery voltage vl and supplies a stable constant voltage (Vc) to the output side.1) is a semiconductor gas sensor, with heater lla and electrode 1)b The heater Ila is supplied with power from V, the electrode 1)b is connected on one side to VC and on the other to a resistor 12, and the other end of the resistor 2 is grounded.

The connection point between electrode 1)b of gas sensor 1) and resistor 12 is P.
point, the transistor 14 is connected from the point P through the resistor 13.
and the non-inverting input terminal of an impedance matching circuit, commonly known as a voltage follower 16, which is composed of an operational amplifier and has an inverting input terminal and an output terminal connected. The output of the voltage follower 16 is centered on the resistor 23 and capacitor 27 on one side;

and the output terminal (■), a series circuit of a resistor 22 and a diode 24 from the side, and also (■). Capacitor 27 and resistor 2 from the side
6 and a series circuit of a diode 25 are connected, and a resistor 23 is further connected to the connection point between the resistor 22 and the diode 24 (point F) and the connection point between the capacitor 27 and the resistor 26 (point Q). The output of the voltage follower 29 is inputted from point Q, which is the output of the time delay circuit, to the second voltage follower 29 through a time delay circuit, and the output of the voltage follower 29 is connected to a diode 30 and a variable resistor 31.
The variable end (point R) of the variable resistor 31, which is the output of the voltage dividing circuit, is connected to the resistor 32 through a parallel circuit, and the other end of the resistor 32 is grounded. It 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 point of the voltage follower 16 is connected to the other input terminal of the voltage comparator 33. Voltage comparator 33
The output is input to a monostable multivibrator 34 (abbreviated as monostable multi), and the output pulse width of the monostable multi 34 is determined from VC by a resistor 35 and a capacitor 36. The output of monostable multi 34 is connected to resistor 37 and transistor 3.
8 to transmit the signal to the next stage. That is, the air purifier operating circuit is constructed by connecting the blower motor 40 of the air purifier and the resistor 39 in series with the battery voltage v3, and connecting the resistor 39 of the grounded circuit in parallel with the collector and emitter of the transistor 38. . In addition, the connection point of the pixel element, in which a resistor 18 and capacitor 19 are connected in series between A timer circuit consisting of a voltage comparator 17 has one output as the reset signal input of the monostable multi 34 through the switch 42, and the other side connects the emitter to the above side through the resistor 15, and the collector to the above side. i! configured to be connected to the non-inverting input of the first voltage follower 16! ! This is a circuit for measuring the initial stabilization of It. The air purifier has a filter that filters out dirt and a blower that rotates at low and high speeds, and is configured to be installed on a storage shelf or ceiling in the vehicle interior.

The operation of the apparatus having the above configuration will be explained next.

The power supply V of the automobile is normally connected to the key ON position π, and the device operates mainly when the engine is running. When electricity is applied to the heater lla of the gas sensor 1), the electrode 1)b becomes activated, and when a flammable gas such as hydrogen, carbon oxide, propane, alcohol, pensol, etc. comes into contact with the gas sensor 1), the electrode 1)b becomes activated. Resistance value decreases. Figure 2 shows examples of detection characteristics for various gases. That is, the horizontal axis represents the gas concentration, and the vertical axis represents the ratio of the detection characteristic in clean air (=Rs Air) to each gas concentration (Rs).
When taken, air (does not change), carbon oxide, ethyl alcohol, and hydrogen each exhibit the characteristics shown in Figure 2. Cigarette smoke is known to contain carbon monoxide. - The gas sensor 1) reacts with flammable gases such as carbon oxide.

FIG. 3 shows an example of actual measurement of point P in FIG. 1 when a smoking test was conducted inside a car. That is, when non-smoking, V is a constant potential balanced with the atmosphere inside the vehicle, and after smoking starts, this is detected and the resistance value of sensor Ilb decreases, so VP increases in accordance with the concentration.

Therefore, it can be seen that smoking can be detected using a gas sensor by detecting a change in the potential of VP.

FIG. 1 shows a specific example, in which the gas sensor output vP is directly input to one of the voltage comparators 33 after impedance conversion (voltage follower 16), and (2).

Smoking is detected by a circuit whose other input of the comparator 33 is the output of a reference value circuit composed of a time delay circuit and a voltage divider circuit.

Here, this gas sensor is affected by temperature and humidity, and has a characteristic that 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. 4.
Therefore, in order to compensate for this influence, it is necessary to provide a temperature and humidity compensation circuit in the reference value circuit.

However, at present, nothing other than temperature compensation has been put to practical use in automobiles.The present invention solves this problem without using a temperature sensor, and the time delay circuit shown in FIG. 1 is provided with this function. P
Since the point has high output impedance, the voltage follower 16
If the output voltage increase is measured at , and the value of the zero resistor 22 that drives the time delay circuit is set to a sufficiently smaller value than the resistor 23, the current from the power supply V will mainly flow through 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 vP on the cathode end by the forward saturation voltage. An integrating circuit consisting of a resistor 23 and a capacitor 27 which inputs the potential at point F has a potential of V when VF is in equilibrium.
+V, and the potential difference obtained by eliminating this potential from ■ is constantly held across the capacitor 27, and the potential V of the capacitor 27 can be regarded as the reference potential at equilibrium of the gas sensor 1). I can do it. The output power is increased by a voltage follower 29 which receives the Q point as an input, and its output drives and connects a voltage dividing circuit including a variable resistor 31. In this circuit, if there is no diode 30, the variable resistor 31
Both fixed end potentials of are V.

Since it is proportional to , a problem arises in that the potential difference between ■, v, and l changes depending on V. Therefore, diode 3
0 as shown in Figure 1, the potential across the diode 30 of the voltage divider circuit becomes approximately equal to the potential of the diode 24 described above, and the potential on the cathode side of the diode 30 is approximately equal to V at equilibrium. Therefore, the variable resistor 31 has vP
Any potential from to vo can be set at the variable end R. As described above, the time delay circuit and the voltage dividing circuit are circuits that function as reference values during equilibrium of the gas sensor.

Here, the rate of change in temperature and humidity inside the car during driving is:
For example, when using the heater, the vP value increases at a rate of Q, approximately 04 cm/min. This value takes into account both the increase in temperature inside the vehicle and the accompanying decrease in humidity. The time constant of the time delay circuit is set to be approximately the same as that when the heater is used. As a result, the potential V of the capacitor 27 is approximately 1:1 with the voltage increase of the sensor output ■ due to changes in temperature and humidity when the heater is in use.
This corresponds to +! in the example in Figure 3. 3! ! Since the rise rate is very small compared to the approximately 0.5 V/min when the heater is in use, the time delay circuit cannot follow the changes during smoking. (Temperature and humidity) changes can be followed, but changes in smoking can be ignored.

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

Further, although air fresheners or deodorizers are sometimes used in the vehicle interior, there is a risk that the gas sensor may detect these gas components in a normal circuit. However, since the rate of time change in the gas sensor potential due to the above components is smaller than when the heater is used, the time delay circuit can also follow and compensate for changes in the atmosphere caused by aromatic agents and the like.

Next, in cars, when passengers get on and off the vehicle, the doors may be opened temporarily, which causes the temperature and humidity inside the car to change.
For example, when the outside temperature is low, the gas sensor is temporarily cooled rapidly when the door is opened, and the resistance value of the sensor itself increases. Therefore, the sensor potential Vp decreases, but since the V of the time delay circuit decreases at a slow rate, the voltage difference between P and Q temporarily increases.
The potential difference between P and R also increases. This means that the detection sensitivity of the sensor temporarily decreases,
For example, if a passenger starts smoking immediately after getting into the vehicle, the gas sensor may not be able to detect the gas with a predetermined detection sensitivity.

Therefore, in order to keep the detection sensitivity constant even in the case of sudden changes in the atmosphere due to the opening and closing of the door, the diode 2 is installed as an element.
It is 5. That is, when the potential VP of the gas sensor suddenly drops, the potential V of the capacitor in the circuit consisting of the capacitor 27, resistor 26, diode 25, and voltage follower 16 is reduced because the resistor 26 is small, so the voltage drop here is ignored. When you do it, ■. # It is necessary to move in parallel along Vp+ (forward saturation voltage of diode 25).

Therefore, it is possible to optimally compensate for sudden changes in the air inside the vehicle when the door is opened or closed.

The next case where smoking is performed using a circuit that can absorb the various atmospheric factors mentioned above will be explained with reference to FIG. While the engine is running, the purifier 40 operates the blower at low speed when not smoking. When smoking starts inside the vehicle, the gas sensor detects this, and the potential of vP begins to rise as shown in Figure 6, and eventually matches V (Figure 6a). The voltage comparator 33 outputs a coincidence signal as shown in FIG. 6C at this coincidence point. The 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). By operating the blower 40 of the air purifier at high speed when the monostable multi 34 is outputting pulses, and operating at low speed at other times, the air inside the vehicle interior can be efficiently purified when smoking. I can do it.

Next, the gas sensor 1) 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 that absorbs various atmospheric factors such as the above-mentioned temperature, humidity, and fragrance, and is shown in FIG. Since the operation is unstable during this time until stabilization, the monostable multi 34 may be erroneously triggered during this time, resulting in erroneous operation.

Therefore, during this time, we added a malfunction prevention circuit as described below.

That is, the first is the gas sensor voltage V immediately after the power is turned on,
In the section where V is temporarily close to zero (Fig. 5a), V is established at one end of the capacitor 27, and the resistance 26 at the other end is a small value, so there is a sudden potential difference in the capacitor 27. becomes large, and is rapidly charged to a value close to ■. After that, V approaches <VC as shown in Fig. 5 P and stabilizes at the operating value, but on the other hand, vo has a large time constant, so as shown in Fig. 5 Q
Even if the sensor reaches a stable region, the 6th
It is not possible to follow the operating states shown in a and b in the figure.

Therefore, the circuit of the comparator 17 is operated to output a pulse for a certain period of time immediately after the power is turned on, and this output maintains the transistor 14 in a conductive state to eliminate this problem. In this way, the capacitor potential ■. can be set to a value higher than VP by a certain amount of potential before entering the stable region, as shown in Q' in FIG.

Second, the comparator 33 incorrectly outputs an output in the unstable region immediately after the power is turned on, triggering the monostable multi 34, so in order to prevent this malfunction, the output of the comparator 17 is transferred to the multivibrator 3.
I connected it to the reset terminal of No. 4 and activated the reset function.

The present invention further provides a switch 42, and when the switch 42 is closed, the 1lrITi initial monostable multi 34 is reset, and when the switch 42 is opened, the monostable multi 34 is triggered, and the monostable multi 34 is forcibly cleaned. The blower of the vessel was operated at high speed for one time (approximately 8 minutes) to compensate for the initial non-operation time.

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

Furthermore, the accuracy of the present invention can be further improved by using a voltage dividing circuit as shown in FIG. In the circuit of FIG. 1, V is balanced at a potential higher than VP by about 0.7 V, the forward saturation voltage (Vym) of the diode 24. By the way, diodes generally have temperature characteristics; an example is shown in Figure 8, where the forward current is 5m.
At time A, the coefficient is about -1.6 mV/℃, and the temperature is 50 mV/℃.
A change in temperature will result in a change of 80 mV. V * −
Since V p is set to a value of about 0.1 to 0.5 V during non-smoking, if the set voltage is low, temperature will have a great effect. Therefore, as shown in FIG. 7, the circuit in FIG. 1 is changed to connect the output of the voltage follower 29 from the power supply VC to the resistor
, a diode 52, 30, and a resistor 32 are connected in series to the connection point of both diodes of a grounded circuit, and a resistor 55, a thermistor 56, and a variable resistor 31 are arranged at the anode of the diode 52 and the cathode end of the diode 30. This is the circuit.

In other words, a temperature compensation circuit using a thermistor was added, but since the cathode end of the diode 30 during non-smoking is approximately equal to V, V can be set 0.1 to 0.5 higher than V. cannot be achieved by simply inserting a thermistor circuit into the circuit of 30.1 diodes shown in Figure 1. Therefore, a resistor 51 and a diode 52 are added, and a thermistor 56, a resistor 55, and a variable resistor are added to the series circuit of two diodes. 131 was installed. FIG. 9 shows v*-VP in the circuit of FIG. 7, that is, the differential potential characteristic of the comparator 33.

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

According to this embodiment, in an automobile air purifier using a gas sensor as a smoke detector, cigarettes can be detected at a constant sensitivity without being affected by the temperature/humidity characteristic of the gas sensor, fluctuations in the initial stage of energization, or even by air fresheners and deodorizers. This has the effect of providing an air purifier that operates by detecting smoke.

〔Effect of the invention〕

As described above, according to the present invention, in putting a cigarette smoke sensor using a gas sensor into practical use, it is possible to absorb the influence of temperature and humidity, the influence of the use of aromatics, and other atmospheric disturbing factors, and to increase the detection sensitivity. This has the excellent effect of realizing a high-performance air purifying device with a smoke detector for automobiles that can always be set to a constant value.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the circuit connection of an embodiment of the present invention, Fig. 2 is a functional characteristic diagram of the gas sensor, Fig. 3 is a diagram showing the gas sensor detection characteristics during smoking, and Fig. 4 is the temperature and humidity of the gas sensor. 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. FIG. 7 is a diagram showing the operation in another embodiment of the present invention. FIG. 8 is a diagram showing the temperature characteristics of the diode, and FIG. 9 is a diagram showing the circuit connection.
This figure is a diagram showing the differential potential characteristics of the comparator in FIG. 7. 10... Constant voltage circuit 1)... Gas sensor 16.29... Voltage follower 27... Capacitor 31... Variable resistor 17.33... Voltage comparator 34... Monostable multivibrator 40... Air purifier blower 2nd figure Power supply 3-K) El 1) ('c) '') Figure 5 Figure 6

Claims (7)

[Claims] (1) A gas detection element that detects gas concentration in the air,
In an air purifying device that compares the detection signal of the element with a reference voltage in a comparison circuit and controls an air purifier based on the output signal of the comparison circuit, the reference voltage circuit inputs the output of the gas detection element. An air purifying device comprising: a time delay circuit, and the time delay circuit is controlled according to a rate of change in the output signal level of the gas detection element and a direction of the change. (2) The air cleaning device according to claim (1), comprising: a comparison circuit that inputs the output signal of the gas detection element and the output of the reference voltage circuit and compares signal levels; and the gas detection element. It is characterized by comprising an initial stabilization circuit that disables the signal for a predetermined period of time in the initial stage of energization, and a purifier operating circuit that increases the purifying ability of the air purifier for a predetermined period of time based on the comparison circuit output signal. Air purification device. (3) In the air cleaning device according to claim (1), the time delay circuit connects the gas detection element to the impedance matching circuit (16) and from the power supply line to the resistor (2).
2) and a diode (24) are connected in series and connected to the output of the matching circuit (16), and a resistor (23) is connected to the connection point between the resistor (22) and the diode (24) and the power line. and a capacitor (27) are connected in series so that the capacitor is connected to the power supply line, and the resistor (23) and capacitor (27) are connected in series so that the capacitor is connected to the power supply line.
) is a time delay circuit in which a resistor (26) and a diode (25) are connected in series from the connection point to the capacitor (27).
) and the resistance (23) is an output. (4) In the air purifying device according to claim (1), the reference voltage circuit further includes an impedance matching circuit (29) from the output of the time delay circuit and inputs the impedance matching circuit (29). ) from the output of the diode (3
0) and both fixed ends of a variable resistor (31) are connected in parallel, and the circuit is further grounded via a resistor (32), and the variable end of the variable resistor (31) is the output. An air purifying device characterized by being equipped with a voltage dividing circuit. (5) The air purifying device according to claim (2), wherein the initial stabilization circuit closes the input terminal of the impedance matching circuit (16) and the power supply line for a predetermined period of time. Purification device. (6) In the air purifier according to claim (2), the purifier operating circuit receives the output of the initial stabilization circuit via a switch, and is reset by the switch for a predetermined period of time at the initial stage of energization. 1. An air cleaning device characterized in that the air cleaning device is operated for a predetermined period of time or at the initial stage of energization. (7) In the air purifying device according to claim (1), the time delay circuit further includes an impedance matching circuit (29) for inputting the circuit output terminal according to claim (3); The output of the matching circuit (29) is connected from the power line to the resistor (51), diode (52), and diode (53).
, a resistor (54) is arranged in series and connected to the midpoint between both diodes of a circuit that is grounded and the diode is in the forward direction,
Anode end of diode (51) and diode (30)
The variable end of the variable resistor consists of a circuit in which both fixed ends of a resistor (55) and a variable resistor (31) are arranged in series, and a thermistor is arranged in parallel with the resistor (55). An air purifying device characterized by having a voltage dividing circuit whose output is .