JPH033848B2 - - 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 and enters the mixing section 3 via the gas-side throttle 5, where the air and gas are mixed and sent to the burner. Burns at 6.

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 throttle is P _A , the air volume is Q _A , the pressure upstream of the gas-side throttle is P _G , the gas volume is Q _G , and the pressure in the mixing section is P _M , then the air ratio Q _A /Q _G is There is a relationship between

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 .
Since the valve 9 is mechanically moved in response to differential pressure _of 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, increase P _A - P _M or enlarge the diaphragm of the pressure equalizing valve to increase △P _G
must be made smaller.

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 widen the combustion amount adjustment range, It has been difficult to apply this method to household combustion equipment, as it cannot be used with household gas fuels such as city gas, which have low gas supply pressures.

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 controls an air amount variable mechanism to adjust the amount of combustion air according to the required combustion amount, and also controls the air amount and gas side restrictions provided upstream of the mixing section. The pressure difference between the upstream and downstream sides is detected by a differential pressure detector, and the gas proportional valve 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 since the pressure generated at both ends of the throttle can be reduced, the blower can also be small.

Embodiments of the present invention will be described in detail below with reference to the drawings. Note that the same parts in the figure as 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. Reference numeral 3 denotes a mixing section where the air passage and the gas passage join together, where gas and combustion air are mixed and the mixed gas is guided to the burner 6. A heat exchanger 11 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. Reference numeral 15 denotes a hot water temperature control circuit which amplifies the difference between the signals between the thermistor 12 and the temperature setting device 14 and controls the rotation speed of the blower 1 by means of a rotation speed control circuit 19. 16 is a differential pressure detector that outputs an electric signal according to the differential pressure between the upstream side of the air-side throttle 2 and the upstream side of the gas-side throttle 5. 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 _G > P _A ), it reduces the current of the gas proportional valve 13 and makes the differential pressure negative (P _G <P _A ), it works to increase the current of the gas proportional valve. Further, the air-fuel ratio control circuit 17 has an integral element 18, which 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 amount of gas is supplied that is proportional to the amount of air supplied by the blower. Here, air-fuel ratio control circuit 1
Since the error corresponding to △P _G in equation 3 can be brought as close to zero as possible by the integral element 18 of 7,
Even if the differential pressure generated between the air side and gas side throttles at rated time is selected to be small, the combustion amount control ratio can be increased.

Here, an all-primary system is used as an example where gas and combustion air are pre-mixed in a mixing section and supplied to the burner, but the mixing section and burner are integrated, dividing the combustion air into multiple stages and mixing it with the gas. It can be carried out in almost the same way even if the model is Further, the air amount variable mechanism may be constituted by a damper provided in the air passage.

FIG. 3 is a longitudinal 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 the lower case 22.
It is supported by a spring 36 between an adjusting screw 34, a spring receiver 35, and a pressure receiving plate B29, which are threadedly connected to each other, so that when the pressure difference is zero, the core is at the midpoint of the differential transformer. 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 susceptible to changes in the rigidity of the diaphragm and 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 simple differential transformer.

With the above configuration, even if the flow rate and inlet water temperature of the water that loads the burner fluctuate, the amount of air is automatically adjusted and the amount of gas is supplied according to the amount of air.
As a result, the air-fuel ratio remains constant, the combustion amount is automatically adjusted, and the hot water temperature can be 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 a differential pressure detector, and the signal is used to control the gas proportional valve to bring the differential pressure to zero through an integral element. Since the fuel ratio can be stabilized and the pressure generated at the air and gas side throttles can be reduced, the blower can also be made smaller and can be used with household gas fuel, which has a low gas supply pressure. In addition, the differential pressure detector only needs to stably detect when the differential pressure is zero, so it can be realized with a simple configuration using a small diaphragm and a differential transformer, which has the effect of reducing the size and cost of the device. is obtained.

[Brief explanation of the drawing]

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. FIG. 3 is a longitudinal 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 section that mixes gas and combustion air, a burner, an air passageway and a gas passageway upstream of the mixing section, respectively, and an air side restriction and a gas side restriction, and a gas passageway. 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 of the air-side restriction and the upstream of the gas-side restriction. and a differential pressure detector that outputs an electric signal according to the pressure difference, and controls the gas proportional valve so that the differential pressure becomes zero based on the signal from the differential pressure detector.