JPH033847B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention automatically and continuously varies the amount of combustion depending on the load, and also maintains the ratio of the amount of combustion air to the amount of gas (hereinafter referred to as the air-fuel ratio) almost constant to stabilize combustion. The present invention relates to high-load gas combustion control devices used particularly in household appliances to maintain performance and high efficiency.

As a conventional combustion control device for this type of high-load combustor, the pressure equalization valve system (or zero governor system) shown in FIG. 1 is well known. That is, the combustion air sent by the blower 1 passes through the air-side throttle 2 and enters the mixing section 3, and the gas passes through the pressure equalization valve 4, passes through the gas-side throttle 5, enters the mixing section 3, and the air and gas are mixed, and then the burner 6 Burn.

The pressure upstream of the air-side throttle 2 is introduced into the back pressure chamber 7 of the pressure equalizing valve, and the pressure equalizing valve 4 automatically adjusts the gas pressure at the outlet of the pressure equalizing valve to be equal to the pressure in the back pressure chamber. Here, if the pressure upstream of the air side restriction is P _A , the air amount is Q _A , the pressure upstream of the gas side restriction is P _G , the gas amount is Q _G , and the pressure in the mixing section is P _M , then the air-fuel ratio
Q _A /Q _G is ...There is a relationship as shown in Equation 1.

If the pressure equalizing valve can ideally adjust P _G = P _A , then from the above equation Therefore, even if Q _A is changed, the air-fuel ratio will always remain constant.However, since the pressure equalizing valve receives the differential pressure between P _A and P _G at the diaphragm 8 and moves the valve 9 mechanically, the rigidity of the diaphragm , there will always be a pressure setting error △ due to changes in the effective area of the diaphragm due to displacement, etc.
P _G occurs.

In other words, since P _G = P _A + △P _G becomes. That is, the error in the air-fuel ratio due to the error ΔP _G becomes larger as the absolute value of P _A −P _M becomes smaller.
Therefore, in order to increase the combustion amount control ratio within a certain air-fuel ratio error range, either increase P _A - P _M or increase the diaphragm of the pressure equalizing valve to increase △.
_PG must be made small.

For this reason, the combustion amount adjustment ratio should be adjusted to 1/5 to 1/10.
If you try to achieve this, you will need an extremely large blower and pressure equalizing valve, which will make the equipment larger, and if you increase the differential pressure (P _A − P _M ) generated at the air side restriction in order to increase the combustion amount control ratio, It cannot be used with household gas fuels such as city gas, which have low gas supply pressure.
In addition, when the gas supply pressure decreases or when the internal static pressure of equipment increases due to strong winds, etc., the required amount of gas cannot be supplied even if the pressure equalization valve is fully opened, and the air-fuel ratio fluctuates significantly. However, it was difficult to apply it to household combustion equipment, as the combustion became unstable.

The present invention eliminates such conventional drawbacks, and aims to provide a combustion control device with a large combustion amount control ratio and good air-fuel ratio stability without increasing the size of the blower or valve device. do.

In order to achieve this objective, the present invention regulates the combustion amount with a gas proportional valve, and detects the pressure difference between the air-side throttle and the gas-side throttle, which are respectively provided upstream of the mixing section, using a differential pressure detector. The air amount variable mechanism is controlled so that the pressure difference becomes zero.

With this configuration, the differential pressure detector does not need to directly move the gas valve and only needs to generate an electrical signal, and if the control circuit includes an integral element, the differential pressure can be constantly stabilized at zero. It also becomes possible. Therefore, the differential pressure detector can achieve its purpose with a small diaphragm, and the pressure generated at both ends of the throttle can be reduced, so the blower can also be small.
Furthermore, since the amount of air is supplied in accordance with the amount of gas actually supplied, the air-fuel ratio is kept constant even when the gas supply pressure or the like decreases.

Embodiments of the present invention will be described in detail below with reference to the drawings. In the figure, parts that are the same as those in FIG. 1 are given the same numbers.

FIG. 2 is a block diagram showing the configuration of one embodiment of the present invention.

In the figure, reference numeral 1 denotes a blower that supplies combustion air, and here a variable air volume mechanism is constructed by controlling the rotational speed of the blower. Reference numeral 2 denotes an air-side throttle provided in the air passage, which generates a pressure difference between both ends of the throttle in accordance with the amount of air. Reference numeral 5 denotes a gas-side throttle provided in the gas passage, which generates a pressure difference between both ends of the throttle in accordance with the amount of gas. 3 is a mixing part where the air passage and the gas passage meet, where gas and combustion air are mixed and the mixed gas is introduced to the burner 6. 11 is a heat exchanger which heats the water passed through the pipe. 12 is a thermistor that generates an electric signal according to the hot water temperature at the outlet of the heat exchanger. 13 is a gas proportional valve, and a movable iron core placed in the coil continuously adjusts the opening degree of the gas valve according to the current flowing through the electromagnetic coil. Reference numeral 14 denotes a temperature setting device, and the hot water temperature is set by manually rotating a variable resistor. 15 is a hot water temperature control circuit;
The difference between the signals between the thermistor 12 and the temperature setting device 14 is amplified and the current of the electromagnetic coil of the gas proportional valve 13 is adjusted to automatically adjust the gas amount so that the hot water temperature becomes equal to the set temperature. A differential pressure detector 16 detects the pressure difference between the upstream side of the air-side throttle 2 and the upstream side of the gas-side throttle 5, and generates an electric signal proportional to the differential pressure.
17 is an air-fuel ratio control circuit which receives a signal from the differential pressure detector 16, and when the differential pressure becomes positive (P _A > P _G ), the rotation speed control circuit 19 decreases the rotation speed of the blower 1 to reduce the differential pressure. When becomes negative (P _A < P _G ), it works to increase the rotation speed of the blower. Further, the air-fuel ratio control circuit has an integral element 18 and functions to reduce the steady-state deviation of the differential pressure to zero.

Here, a relationship similar to Equation 3 described in the conventional example is established, and an air amount proportional to the gas amount adjusted by the gas proportional valve is supplied. Here, the error corresponding to △P _G in Equation 3 can be brought as close to zero as possible by the integral element of the air-fuel ratio control circuit, so even if the differential pressure generated between the air side and gas side throttles at the rated time is selected to be small. , the combustion amount adjustment ratio can be increased.

Here, we take as an example an all-primary system in which gas and combustion air are mixed in advance in a mixing section and supplied to the burner, but the mixing section and burner are integrated and the combustion air is divided into multiple stages and converted into gas. It can be carried out in almost the same way even in a mixed type. Further, the air amount variable mechanism may be configured by a damper provided in the air passage.

FIG. 3 is a sectional view showing the detailed structure of a differential pressure detector according to an embodiment of the present invention. The upper case 21, the lower case 22, and the diaphragm 23 form a pressure chamber A2.
4 and a pressure chamber B25 are formed, and the pressure introduction hole A2
6 and pressure introduction hole B27, the air side throttle upstream pressure and the gas side throttle upstream pressure are respectively introduced. The diaphragm is sandwiched between a pressure receiving plate A28 and a pressure receiving plate B29 and fixed at the center by a fixing pin 30, and the pressure chambers A and B are sealed. A cylindrical core guide 31 made of non-magnetic material is integrally provided on the upper case 21, and the core 3 in contact with the fixing pin 30
2 and also serves as a seal between the differential transformer and the outside air. A coil 33 of a differential transformer is fixed to the outside of the core guide 31. The weight of the diaphragm part and core is lower case 2.
The core is supported by the spring 36 between the adjusting screw 34, the spring receiver 35, and the pressure receiving plate B29, which are threadedly connected to the 2, and the core is at the midpoint of the differential transformer when the pressure difference is zero. In other words, the output signal of the differential transformer is adjusted to zero.

When a pressure difference occurs between pressure chambers A and B, the diaphragm is displaced, and an electric signal corresponding to the amount of displacement is output from the secondary coil of the differential transformer 33.As mentioned above, the air-fuel ratio Since the control circuit performs feedback control so that the pressure difference is always zero, the amount of displacement of the diaphragm can be small, so it is less affected by the rigidity of the diaphragm and the effective area due to displacement. Furthermore, the performance required of a differential pressure detector is that only the output when the differential pressure is zero is stable, and the linearity of the output signal with respect to the differential pressure,
Changes in gain, etc. do not need to be highly accurate. The zero point output position of the differential transformer is the coil 33 and core 32.
It is almost determined by the mechanical positional relationship with the coil, and is almost unaffected by fluctuations in the excitation current and frequency, fluctuations in the coil resistance, etc. Therefore, the differential pressure detector can be constructed by combining a small diaphragm and a differential transformer with a simple structure.

With the above configuration, even if the flow rate and inlet water temperature of the water that loads the burner fluctuate, the gas amount can be automatically adjusted to keep the outlet hot water temperature stable and the air-fuel ratio stable.

Furthermore, if the gas supply pressure decreases or if the internal static pressure increases due to strong winds or the like, the required amount of gas cannot be supplied even if the gas proportional valve 13 is fully opened. Even at this time, the rotation speed of the blower is controlled so that the differential pressure is zero, and the amount of air is supplied according to the amount of gas actually supplied, so the air-fuel ratio is stable and the combustion is kept stable.

As described above, according to the gas combustion control device of the present invention, an air-side restriction and a gas-side restriction are provided upstream of the air-gas mixing section, and the differential pressure between the upstream of the air-side restriction and the upstream of the gas-side restriction is controlled. The differential pressure is detected by the differential pressure detector, and the variable air volume mechanism is controlled by the signal via the integral element to bring the differential pressure to zero, so the air-fuel ratio is stabilized with high precision even when the combustion amount adjustment ratio is increased. can be converted into
Since the pressure generated by the air and gas side throttles can be reduced, the blower can also be made smaller, and it can also be used with household gas fuel, which has a low gas supply pressure. Furthermore, since the differential pressure detector only needs to be able to stably detect when the differential pressure is zero, it can be realized with a simple configuration using a small diaphragm and a differential transformer, thereby reducing the size and cost of the device. Furthermore, the combustion amount is adjusted by a gas proportional valve, and the variable air volume mechanism is controlled according to the signal from the differential pressure detector mentioned above to keep the air-fuel ratio constant. Even if the internal static pressure increases due to the influence of strong winds, etc., the air-fuel ratio is always kept constant and combustion does not become unstable.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a conventional gas combustion control device, Fig. 2 is a block diagram showing the structure of a gas combustion control device according to an embodiment of the present invention, and Fig. 3 is a differential pressure diagram of an embodiment of the present invention. It is a fir cross-sectional view showing the configuration of a detector. 1...Blower, 2...Air side throttle, 3...Mixing section, 5...Gas side throttle, 13...Gas proportional valve, 1
9... Rotation speed control circuit, 16... Differential pressure detector, 1
1... Heat exchanger, 12... Thermistor, 14...
Temperature setting device, 15... Hot water temperature control circuit, 17...
Air-fuel ratio control circuit, 18... Integral element, 23... Diaphragm, 33... Differential transformer coil, 32
……core.

Claims (1)

[Claims] 1. A blower that supplies combustion air, a mixing part that mixes gas and combustion air, a burner, an air passage and a gas passage upstream of the mixing part, respectively, and an air side and a gas side, and a gas passage. A gas proportional valve that continuously varies the gas supply amount in response to an electrical signal, an air volume variable mechanism that continuously varies the air volume in response to an electrical signal, and a pressure difference between the upstream side of the air side and the upstream side of the gas side. and a differential pressure detector that outputs an electric signal according to the pressure difference, and controls the air amount variable mechanism so that the differential pressure becomes zero based on the signal from the differential pressure detector.