JPS649526B2 - - Google Patents

Description

Detailed Description of the Invention The present invention automatically and continuously varies the amount of combustion depending on the load, and 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 achieve combustion stability. This invention relates to high-load gas combustion control devices used particularly in household appliances to maintain 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 to the back pressure air 7 of the pressure equalization valve, and the pressure equalization valve 4 automatically adjusts the gas pressure at the outlet of the pressure equalization valve to be equal to the pressure of the back pressure air. Here, the pressure upstream of the air-side restriction is P _A ,
If the air volume is Q _A , the pressure upstream of the gas side restriction is P _G , the gas volume is Q _G , and the pressure in the mixing section is P _M , the air ratio is
Q _A /Q _G is K1 and K2 have a constant relationship.

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 a differential pressure _of In other words, since P _G = P _A + ΔP _G becomes. In other words, the air-fuel ratio error due to the error ΔP _G is
The smaller the absolute value of P _A − P _M becomes, the larger it becomes.
Therefore, in order to increase the combustion amount control ratio within a certain air-fuel ratio error range, it is necessary to increase P _A - P _M or make the diaphragm of the pressure equalizing valve larger to decrease ΔP _G. .

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 increase the size of the equipment, and if you widen the combustion amount adjustment range and increase the differential pressure (P _A − P _M ) generated at the air side restriction, the gas It has been difficult to apply it to household combustion equipment, as it cannot be used with household gas fuels such as city gas, which have low supply pressure.

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 a gas proportional valve to adjust the combustion amount using an electric signal according to the temperature of the heated body detected by a temperature detector, and also uses a gas proportional valve provided upstream of the mixing section. The pressure upstream of the air-side restriction and the gas-side restriction is alternately measured with an absolute pressure type or relative pressure type pressure sensor via a pressure switch, and the signal from the pressure detector is switched in conjunction with the operation of the pressure switch. Each signal is stored in the air pressure memory and the gas pressure memory, and the air volume variable mechanism is controlled so that the pressure difference signal becomes zero according to the pressure difference signal obtained from the difference between the respective signals read from each memory. It is something to do.

With this configuration, the combustion amount is automatically adjusted according to the load, and the air-fuel ratio is also kept stable. Also,
By measuring two pressures with the same pressure detector and calculating the difference between the stored pressure signals, errors such as temperature drift and variation in the temperature detector itself are canceled out from the pressure difference signal.

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

FIG. 2 is a block diagram showing one embodiment of the present invention, and only the main parts are shown in detail in cross section.

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 air and gas meet, where the gas and 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 of the heat exchanger. A gas proportional valve 13 is placed in the gas passage upstream of the gas-side throttle, and a movable iron core placed in the coil continuously adjusts the opening degree of the gas valve in accordance with 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 outlet temperature control circuit, which amplifies the difference between the signals between the thermistor 12 and the temperature setting device 14, adjusts the current of the electromagnetic coil of the gas proportional valve, and automatically adjusts the gas amount so that the hot water outlet temperature becomes equal to the set temperature. do. 16 is a semiconductor diffusion type pressure sensor, and a pressure inlet 21 is connected to an output hole 22 of a pressure switching device 17. In the pressure switching device 17, by applying current to the electromagnetic coil 23, the movable iron piece 26 supported by the case 25 via the plate spring 24 is attracted to the fixed iron core 27, and the elastic valve body 28 attached to the tip of the plate spring is attached. The gas pressure introduction hole 29 is closed and the air pressure introduction hole 30 is opened. When the electromagnetic coil is de-energized, the air pressure introduction hole 30 is closed by the restoring force of the leaf spring 24, and the gas pressure introduction hole 29 is opened. The pressure upstream of the gas-side restriction is introduced into the gas pressure introduction hole, and the pressure upstream of the air-side restriction is introduced into the air pressure introduction hole. is guided to the pressure sensor 16.

31 is an air-fuel ratio control circuit, and the output of an amplifier 32 that amplifies the output signal of the pressure sensor is sent to an air pressure analog memory 34 and a gas side pressure analog memory 35 via a changeover switch that is changed over by a changeover signal generator 33. Each value is stored and updated in synchronization with the guided switching signal. From the switching signal generator, the electromagnetic coil 23 of the pressure switching device 17
Current is also supplied to the The difference between the output signals from the memories 34 and 35 is integrally and operationally amplified by the rotation speed control circuit 36, and the rotation speed of the fan motor is feedback-controlled so that the difference between the output signals from the memories 34 and 35 becomes zero.

FIG. 3 is a graph showing an example of applied pressure versus output voltage of a semiconductor diffusion type pressure sensor.

In the figure, a shows the relationship between the output and the applied pressure in steady state, and b shows the offset, which is the output voltage when the applied pressure is zero. There is variation in this value between pressure sensor products. Figure c shows an example of the characteristics of the pressure sensor when the ambient temperature changes, and the sensitivity to offset and pressure also changes. This depends on the temperature characteristics of the semiconductor element, and generally varies much more greatly than the level of the pressure difference that we are trying to measure. This can be corrected to some extent by trimming external circuits or internal elements, but it cannot be completely corrected considering the increased cost.

In this embodiment, when detecting the pressure difference between the applied pressures d and e, the same pressure sensor detects them by switching them alternately over a short period of time, so the difference between the output signals of the memory circuit is f and g in the figure, and the offset b is also The fluctuations are also canceled out. Further, since f and g are controlled to be as small as possible by the air-fuel ratio control circuit having an integral element, they are almost unaffected by fluctuations in the pressure applied to the pressure sensor, fluctuations in linearity, etc.

With the above configuration, the accuracy of differential pressure detection can be increased, and the air-to-heat ratio can be kept stable even when the combustion amount adjustment ratio is increased, without increasing the pressure difference between the air and gas side throttles.

Furthermore, in this embodiment, the amount of gas is supplied according to the load, and the amount of air is supplied according to the amount of gas, so the gas supply pressure may decrease or the static pressure inside the equipment may increase due to strong winds. Even if the required amount of gas cannot be supplied, only the amount of air corresponding to the amount of gas actually supplied is supplied, so the air-fuel ratio is stable and combustion does not become unstable.

As described above, according to the gas combustion control device of the present invention, an air-side throttle and a gas-side throttle are provided upstream of the air-gas mixing section, and the pressure upstream of each throttle is adjusted to the same pressure via a pressure switch. By controlling the air flow control mechanism to alternately detect the pressure signals with the detector, store each pressure signal in memory, and make the difference between the output signals zero, (1) the error component of the pressure detector can be reduced. Since they are canceled out, highly accurate air-fuel ratio control is possible using an inexpensive pressure detector that does not perform error correction, and a large combustion amount control ratio can be achieved. The pressure detector does not need to be a differential pressure type, so the structure can be simplified.

(2) Since the pressure generated by the restriction of the air and gas passages can be reduced as described above, the air converter can be downsized and can also be applied to household gas fuels with low gas supply pressure.

(3) The above effect is further enhanced by adding an integral element.

For the above-mentioned reasons, since a semiconductor pressure sensor with large characteristic fluctuations can be used, the dimensions of the pressure sensor can be extremely small, allowing the device to be downsized and increasing the degree of freedom in arranging components. The gas proportional valve is controlled according to the temperature of the heated object, and the air amount variable mechanism is controlled according to the pressure difference signal upstream of the air and gas side throttles. Even if the required amount of gas cannot be supplied when the static pressure inside the equipment increases, the air amount corresponding to the amount of gas actually supplied will be supplied, so the air-fuel ratio will be stable and combustion will not occur. It doesn't become unstable.

[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 a gas combustion control device according to an embodiment of the present invention, and Fig. 3 is a semiconductor diffusion diagram used in an embodiment of the present invention. 2 is a graph showing applied pressure versus output voltage characteristics of a type pressure sensor. 1...Blower, 3...Mixing section, 2...Air side throttle, 5...Gas side throttle, 6...Burner, 11...
Heat exchanger, 13... Gas proportional valve, 12... Thermistor, 16... Pressure sensor, 17... Pressure switch, 34... Air pressure memory, 35... Gas pressure memory, 36... Rotation speed control circuit.

Claims (1)

[Claims] 1. A blower that supplies combustion air, a mixing section that mixes gas and combustion air, a burner, and a heat exchanger that heats an object to be heated; The air passage and the gas passage have an air side restriction and a gas side restriction, respectively, and the gas passage has a gas proportional valve that continuously varies the amount of gas supplied in response to an electrical signal, and an air valve that continuously varies the amount of air supplied in response to an electrical signal. a variable amount mechanism, an absolute pressure type or relative pressure type pressure detector,
A pressure switch that alternately switches the pressure upstream of the air-side throttle and the gas-side pressure and guides it to the pressure detector; and a pressure switch that alternately switches the pressure upstream of the air-side throttle and the gas-side pressure and guides it to the pressure detector; and the air-side throttle upstream pressure signal and the gas-side throttle upstream pressure in conjunction with the operation of the pressure switch. an air pressure memory and a gas pressure memory that electrically store signals, a temperature detector that detects the temperature of the heated body at the outlet of the heat exchanger, and a temperature setting device that sets the temperature of the heated body at the heat exchanger outlet. and controlling the gas proportional valve according to the difference between the signal of the temperature sensor and the temperature signal, and adjusting the difference to zero according to the difference between the signal of the air pressure memory and the signal of the gas pressure memory. A combustion control device that controls the air amount variable mechanism so that the amount of air changes. 2. The combustion control device according to claim 1, wherein the pressure detector is a semiconductor diffusion type pressure sensor. 3. The combustion control device according to claim 1 or 2, wherein the air amount variable mechanism is controlled via an integral element.