JPS62206319A - Air-fuel ratio control device of burner - Google Patents

Abstract

PURPOSE:To be able to control air-fuel ratio constantly to a target one regardless of the temp. of combustion gas by a method wherein the temp. of combustion gas generated by a burner is detected by a temp. sensor and a reference value is decreased as the temp. of this gas rises up. CONSTITUTION:A part of flames is introduced into an lead-out tube 34 and the residual oxygen concentration in combustion gas produced by the flames is detected by an O2 sensor 36. A temp. comparison circuit 54 compares a set temp. set previously by a temp. set dial 58 with the temp. of burning gas or hot wind temp. detected by a temp. sensor 44 and a deviation signal obtained by deducing the output of the dial 58 from the output of the sensor 44 is input into a fuel amount control circuit 56 and as the temp. of combustion gas rises up, the reference voltage in an air amount circuit 52 is decreased. The circuit 52 compares the output of the O2 sensor with the reference voltage and when the output of the O2 sensor is higher than the reference voltage, the revolution speed of a blower motor 18 is increased to control an air-fuel ratio by increasing the air supply amount.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an air-fuel ratio control device for a burner, and more particularly to an air-fuel ratio control device for a burner used in a hot air dryer for drying grain.

[Conventional technology]

Conventionally, grain is retained between the wire mesh that constitutes the hot air chamber and the wire mesh that constitutes the exhaust chamber, and the combustion gas generated by the burner is transferred from the combustion chamber to the exhaust chamber through the accumulated grain layer. Hot air dryers that dry grain by blowing air are known.

In such a hot air dryer, the temperature of the hot air is determined in advance by detecting the temperature of the hot air using a temperature sensor, comparing the detected hot air temperature with a preset temperature, and controlling the amount of fuel supplied to the burner. The set temperature is maintained. In addition, a part of the flame of the burner is introduced from one end of the outlet pipe so that a part of the combustion gas generated by the burner is led out through the outlet pipe, and a part of the combustion gas is introduced into the outlet pipe so as to protrude into the outlet pipe. Detects the residual oxygen concentration of 0! A sensor is installed and the air-fuel ratio is controlled to a target air-fuel ratio near the logical air-fuel ratio based on the 02 sensor output (electromotive force). That is, 0. The sensor output is
As shown in Figure 2, the stoichiometric air-fuel ratio (excess air ratio = 1.0
), the level suddenly reverses, and it is easy to obtain control information on the rich side of the stoichiometric air-fuel ratio, so it is easy to obtain control information on the rich side of the stoichiometric air-fuel ratio.
A constant reference voltage within 925 V is compared with the 02 sensor output, and when the Ot sensor output is higher than the constant reference voltage, that is, when the air-fuel ratio is richer than the target air-fuel ratio, the air supply amount is increased, and the Ot sensor output is set to the constant reference voltage. When the air-fuel ratio is lower than the voltage, that is, when the air-fuel ratio is leaner than the target air-fuel ratio, the air supply amount is decreased to control the air-fuel ratio to the target air-fuel ratio.

[Problem that the invention seeks to solve]

However, when the set temperature is changed by adjusting the temperature setting dial in order to change the temperature of the hot air, the size of the flame generated by the burner changes, and thereby the size of the flame introduced into the outlet pipe changes. As a result, the temperature of the combustion gas in the outlet pipe changes.

On the other hand, as shown in FIG. 2, the electromotive force of the O2 sensor output changes depending on the temperature, and in a region on the richer side than the stoichiometric air-fuel ratio, the electromotive force decreases as the temperature decreases. For this reason, when controlling the air-fuel ratio by comparing a constant reference voltage and the electromotive force of the O snow sensor which is the 02 sensor output, as in the past, the 0. Since the electromotive force of the sensor changes, a problem has arisen in that the air-fuel ratio cannot be controlled to the target air-fuel ratio.

The present invention has been made to solve the above problems, and an object thereof is to provide a burner air-fuel ratio control device that can control the air-fuel ratio to a target air-fuel ratio even if the temperature of combustion gas changes. do.

[Means for solving problems]

In order to achieve the above object, the present invention provides a temperature sensor for detecting the temperature of combustion gas generated in a burner, an outlet pipe for discharging a part of the combustion gas to the outside, and a combustion gas in the outlet pipe. An oxygen concentration sensor that detects the residual oxygen concentration in the combustion gas and outputs an air-fuel ratio signal compares the air-fuel ratio signal with a reference value that decreases as the temperature of the combustion gas rises to determine the air-fuel ratio as the target air-fuel ratio. This configuration includes a control circuit that controls the

[For production]

According to the present invention, the temperature of the combustion gas generated by the burner is detected by the temperature sensor, and the reference value is changed so as to decrease as the temperature of the combustion gas increases.

Since the reference value is changed in this way, even if the temperature of the combustion gas changes, the reference value always corresponds to the target air-fuel ratio. Then, the control circuit compares the reference value changed as described above and the O2 sensor output to control the air-fuel ratio to the target air-fuel ratio.

〔Effect of the invention〕

As explained above, according to the present invention, the reference value is changed to become smaller as the temperature of the combustion gas increases,
Since the reference value is always set to a value corresponding to the target air-fuel ratio, it is possible to always control the air-fuel ratio to the target air-fuel ratio regardless of the temperature of the combustion gas.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 3 is a schematic diagram of a burner of a hot air dryer equipped with an air-fuel ratio control device according to the present invention. A wind cylinder 1 communicating with an air guide path IO for supplying hot air arranged inside the body of a hot air dryer.
A burner housing 16 having a plurality of air supply holes 11 formed in the bottom thereof is supported by a support plate 14 inside the burner housing 2 . A blower motor 1 and a heating bowl motor 20 are fixed in this housing 16 in this order from the bottom to the top of the housing. A blower 22 is fixed to the output shaft of the blower motor 18, and the output shaft of the heating bowl motor 20 extends through the inside of the discharge cylinder 24. Heating bowl motor 2
A heating bowl 26 is fixed to the tip of the output shaft of 0 with a nut.

A fuel receiver 28 is fixed to the inner surface of the heating bowl 26 so that its tip protrudes into the discharge cylinder 24 .

On the heating bowl 26 side of the housing 16, the heating bowl 26 has a side surface.
A combustion dish 30 is fixed so as to surround the.

A combustion plate 32 having a large number of combustion holes 31 is disposed on the bottom side of the combustion plate 30 so as to form a cavity inside. The cavity inside the combustion disk 32 is communicated with the cavity inside the heating bowl 26. Further, the ignition plug 46 is arranged so that the ignition part protrudes inside the combustion dish 30.

A lead-out pipe 34 is arranged so that one end thereof is interposed between one of the combustion holes 31 of the combustion plate 32, and an 027 sensor 36 is arranged so that its tip protrudes inside the lead-out pipe 34. .

A fuel tank 38 storing liquid fuel such as kerosene is connected via a fuel pipe to a fuel pump 40 which is an electromagnetic pump. One end of a fuel transport pipe 48 is connected to the discharge port of the fuel pump 40, and a nozzle 50 whose tip protrudes into the fuel receiving portion 28 is attached to the other end of the fuel transport pipe 48. The fuel pump 40 is connected to a control circuit 42 so that the amount of fuel discharged can be changed. Further, the blower motor 18 is connected to a control circuit 42 so that its rotation speed can be changed. The control circuit 42 includes an air guide path lO
A thermistor-type temperature sensor 44 and an 02 sensor 36 fixed so as to protrude inside are connected.

As shown in FIG. 1, the control circuit 42 includes an air volume adjustment circuit 52 made up of an operational amplifier whose reference voltage can be changed, a temperature comparison circuit 54, and a fuel amount adjustment circuit 56. A temperature sensor 44 is connected to the input terminal of the temperature comparison circuit 54.
and temperature setting dial 58 are connected, and the output terminal of temperature comparison circuit 54 is FUEL! It is connected to the input end of the f adjustment circuit 56.

Further, the 02 sensor 36 is connected to the input end of the air volume adjustment circuit 52, and the output end of the air volume adjustment circuit 52 is connected to the blower motor 1.
8 is connected. The output end of the fuel amount adjustment circuit 56 is connected to the fuel pump 40, and is also connected to the other input end of the air flow adjustment circuit 52 so as to change the reference voltage.

The operation of this embodiment will be explained below. When the power switch is turned on, the heating bowl motor 20 is rotated to rotate the heating bowl 26, the blower motor 18 is rotated to rotate the blower 22, and the fuel pump 40 is operated to supply fuel. Fuel is injected from the nozzle 50 onto the inner wall surface of the fuel receiving portion 28 via the transport pipe 48 . As the fuel receiver 28 is rotated, the fuel injected into the inner surface of the fuel receiver 28 adheres to the inner wall surface of the fuel receiver 28 in a thin film form and is vaporized, and is mixed with the air supply supplied by the blower 22. The air-fuel mixture passes through the cavity in the heating bowl 26 and the cavity in the combustion disk 32 and is injected from the four holes 31, and the injected air-fuel mixture is ignited by the spark plug 46. A portion of the flame generated by the ignition is introduced into the outlet pipe 34, and the residual oxygen concentration in the combustion gas caused by the flame is detected by the OT sensor 36.

The temperature comparison circuit 54 compares the set temperature preset by the temperature setting dial 58 and the temperature of the combustion gas detected by the temperature sensor 44, that is, the hot air temperature.
A deviation signal obtained by subtracting the output of the temperature setting dial 58 from the output of the temperature sensor 44 is input to the fuel Wi11 node circuit 56. fuel! The 11-node circuit 56 controls the fuel pump 40 to decrease the fuel discharge amount when the deviation signal is positive, and controls the fuel pump 40 to increase the fuel discharge amount when the deviation signal is negative. do. When the temperature setting dial 58 is adjusted to increase the set temperature of the hot air, the temperature comparison circuit 5
A negative deviation signal is output from the fuel Il1 node circuit 56.
As a result, the amount of fuel discharged from the fuel pump 40 is increased, the amount of fuel burned increases, and the flame of the burner becomes larger.

As a result, the amount of flame introduced into the outlet pipe 34 increases, and the temperature of the combustion gas in the outlet pipe 34 increases. Conversely, when the set temperature of the hot air is lowered, a positive deviation signal is output from the temperature comparison circuit 54, the amount of fuel discharged from the fuel pump 40 is reduced, and the amount of fuel burned is reduced. As a result, the amount of flame introduced into the outlet pipe 34 decreases, and the temperature of the combustion gas within the outlet pipe 34 decreases.

As described above, the output signal of the fuel amount v4 node circuit 56 corresponds to the combustion gas temperature in the outlet pipe 34, and the fuel amount adjustment circuit 56 inputs this output signal to the air volume adjustment circuit 52.
As the fuel discharge amount increases, that is, as the temperature of the combustion gas increases, the reference voltage of the air volume adjustment circuit 52 is lowered. The wind 1lf1 node circuit 52 compares the Ox sensor output with the reference voltage changed as described above, and if the 0□ sensor output is higher than the reference voltage, that is, if the air-fuel ratio is richer than the target air-fuel ratio, the blower motor 18 The air-fuel ratio is controlled to be lean by increasing the rotational speed of the engine and increasing the intake air amount. On the other hand, if the O2 sensor output is lower than the reference voltage, that is, if the air-fuel ratio is leaner than the target air-fuel ratio, the air-fuel ratio is controlled to be rich by lowering the rotation speed of the blower motor 18 and reducing the amount of air supply. do.

As described above, the reference voltage of the air volume adjustment circuit 52 is lowered as the temperature of the combustion gas increases, so that even if the temperature of the combustion gas changes, the reference voltage always remains at a value corresponding to the target air-fuel ratio, and the air-fuel ratio can be controlled to a target air-fuel ratio near the stoichiometric air-fuel ratio.

In addition, above we have explained an example in which the reference value is changed by the output of the air volume adjustment circuit, but since the temperature sensor output and the output of the temperature setting dial correspond to the combustion gas temperature, the reference value can be changed by the output of the temperature sensor or the temperature setting dial. The reference voltage as the reference value may be changed.

Next, another embodiment of the present invention will be described with reference to FIGS. 4 to 6. In this embodiment, a microcomputer is used to control the air-fuel ratio. As shown in FIG. 4, a temperature sensor 60 is attached near the 0□ sensor 36 attached to the outlet tube 34 to detect the temperature T1 of the combustion gas inside the outlet tube 34. As shown in FIG. The multiplexer 62 constituting the control circuit includes an Ozz sensor 6. Temperature sensor 6
0, a temperature sensor 44 for detecting the hot air temperature T2 in the air guide path IO and a temperature setting dial 58 for manually setting the set temperature T0 are connected. The multiplexer 62 is connected to the human port 6 via an analog-to-digital converter (ADC) 62. The input port 6 is connected to a central processing unit (CPU) 68 and a random access memory (RAM) 7 via buses such as a data bus and a control bus.
0, a read-only memory (ROM) 72, and an input port door 4. The output port door 4 is connected to the blower motor 1B via a drive circuit 76 and to the fuel pump 40 via a drive circuit 78. And ROM? 2 stores in advance a control routine program to be described below and a map of reference value v0 shown in FIG.

The map of the reference value V is determined to be a value that decreases as the degree T1 of the combustion gas increases and corresponds to the target air-fuel ratio, based on the characteristics of the Ot sensor shown in FIG.

FIG. 5 shows the control routine of this embodiment. In step 100, the current Ot sensor output V is AD converted and stored in the RAM.

Combustion gas temperature T+, hot air temperature T! , the hot air set temperature To is taken in, and in step 102 a reference value V corresponding to the current combustion gas temperature T is calculated from the map of reference value V in FIG.
The sensor output color reference value v0 is compared, and if V≧v0, the rotational speed of the blower motor 18 is increased in step 106, thereby increasing the air supply amount and controlling the air-fuel ratio to be lean. On the other hand, in step 104, v■■.

If it is determined that the blower motor 1 is
Control is performed so that the air-fuel ratio becomes rich by decreasing the air supply amount by lowering the rotational speed of the engine 8.

In the next step 110, the temperature T2 of the hot air is compared with the set temperature T0 of the hot air, and if T≧T, step 112
The fuel pump 40 is controlled at T to reduce the fuel discharge amount.
If z < T o, in step 114, the fuel pump 4
0 to increase the fuel discharge amount.

As a result of the above, the air-fuel ratio is always controlled to the target air-fuel ratio and the hot air temperature is controlled to the set temperature regardless of the temperature change of the combustion gas.

In addition, above we have explained an example in which the air-fuel ratio is controlled by controlling the rotation speed of the blower motor, but it is also possible to provide a damper that opens and closes the air supply hole drilled in the bottom of the housing, and to drive this damper with a step motor. Alternatively, the air-fuel ratio may be controlled by controlling the opening degree of the air supply hole and changing the amount of air supply by controlling the step motor while keeping the rotation speed of the blower motor constant.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a control circuit according to an embodiment of the present invention, FIG. 2 is a diagram showing output characteristics of an Ot sensor, and FIG. 3 is a schematic diagram of a burner equipped with an air-fuel ratio control device according to the present invention. figure,
FIG. 4 is a block diagram of a control circuit according to another embodiment of the present invention;
FIG. 5 is a flowchart showing the control routine of the type control circuit shown in FIG. 4, and FIG. 6 is a diagram showing a reference value map. DESCRIPTION OF SYMBOLS 10... Air guide path, 12... Wind barrel, 18... Blower motor, 20... Heating bowl motor, 22... Blower, 26... Heating bowl, 28... Fuel receiving part, 34...4 outlet pipe, 36...02 sensor, 40... fuel pump, 42... control circuit, 44... temperature sensor, 46... spark plug, 52... wind filt adjustment circuit, 54...temperature comparison circuit, 56...fuel amount adjustment circuit, 58...temperature setting dial. Fig. 1 6 ships 臥8yo I) Takashi' (enter Fig. 6 mass *T

Claims (1)

[Claims] (1) A temperature sensor that detects the temperature of the combustion gas generated by the burner, a discharge pipe for discharging a part of the combustion gas to the outside, and a residual oxygen concentration in the combustion gas in the discharge pipe. an oxygen concentration sensor that outputs an air-fuel ratio signal, and a control circuit that controls the air-fuel ratio to a target air-fuel ratio by comparing the air-fuel ratio signal with a reference value that is decreased as the temperature of the combustion gas increases. Includes burner air-fuel ratio control device.