JPH0231287B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention continuously varies the combustion amount according to the load, and also changes the ratio of the combustion air amount (hereinafter simply referred to as the air amount) to the gas amount (hereinafter referred to as the air-fuel ratio). This invention relates to a gas combustion control device used particularly in household appliances to achieve almost constant combustion stability and high efficiency.

Configuration of Conventional Example and its Problems As a conventional gas combustion control device of this type, the one shown in FIG. 1 is known.

In FIG. 1, the air passage is provided with a blower 1 and an air throttle 2, the gas passage is provided with a gas proportional control valve 3 and a gas throttle 4, and a mixing section 5 is provided downstream of the air throttle 2 and gas throttle 4. It will be done. air aperture 2
The pressure Pa upstream of the gas throttle 4 and the pressure Pg upstream of the gas throttle 4 are guided to a differential pressure detector 6. A burner 7 and a heat exchanger 8 are provided downstream of the mixing section 5, and a thermistor 9 is provided at the outlet of the heat exchanger 8.

Furthermore, the signal of the temperature setting device 10 and the thermistor 9
The difference between the signals is input to the temperature control calculation circuit 11,
Rotation speed minimum value regulation circuit 12, rotation speed adjustment circuit 13
It is connected to the blower 1 through. On the other hand, the signal from the differential pressure detector 6 is connected to the gas proportional control valve 3 via the air-fuel ratio control circuit 14.

With the above configuration, the signal of the temperature setting device 10 and the signal of the thermistor 9 are compared, and if the temperature of the thermistor 9 is low, the rotation speed of the blower 1 is increased by the rotation speed adjustment circuit, and the amount of air to the burner 7 is increased. do.

Due to the increase in the amount of air, the air pressure Pa increases, and the signal from the differential pressure detector 6 increases. The signal from the differential pressure detector 6 is amplified by the air-fuel ratio control circuit 14 to increase the current of the gas proportional control valve 3, thereby increasing the gas amount. Balance occurs when gas pressure Pg becomes approximately equal to air pressure Pa.

When Pa and Pg are approximately equal, the ratio of air to gas becomes a constant ratio determined by the fluid resistance of the air restrictor 2 and the gas restrictor 4. In this way, a so-called air-leading type air-fuel ratio control device is constructed in which the gas amount follows changes in the air amount and the combustion amount changes while keeping the air-fuel ratio constant.

Here, the air-fuel ratio control circuit 14 increases the amplification factor so that the signal of the differential pressure detector 6 is always zero, that is, Pa.
Although Pg is controlled to be equal, the differential pressure detector 6 has an offset error, and if the signal of the differential pressure detector 6 is controlled to be zero, a differential pressure between Pa and Pg remains by the offset error. .

FIG. 2a is a graph showing the relationship between the amount of gas and the amount of air using the offset error of the differential pressure detector 6 as a parameter, and FIG. 2b is a graph showing the relationship between the amount of air and the air-fuel ratio. a is when there is no offset error, and the gas amount changes in proportion to the air amount,
The air-fuel ratio becomes constant at d. b is a case where the offset error is positive, that is, Pa<Pg, and the signal from the differential pressure detector 6 becomes zero, the gas amount becomes larger than the optimum value, and the air-fuel ratio becomes e. As the amount of air decreases, the differential pressure across the air throttle 2 decreases as a result of the square relationship.On the other hand, the offset error remains constant regardless of the amount of air, so the error in the air-fuel ratio increases with acceleration.

c has a negative offset error, that is, Pa<
When the signal from the differential pressure detector 6 becomes zero at Pg, the gas amount becomes less than the optimum value, which is the opposite of the above, and the air-fuel ratio changes by e. Since the gas amount is smaller than when the offset error is positive, the differential pressure at the gas throttle 4 is small, so the air-fuel ratio error becomes larger for the same absolute value of offset error, and the same air amount Qa1
When the air-fuel ratio is positive, it is at point g, and when it is negative, it is at point h.

The air amount Qa1 is determined by the rotational speed minimum value regulation circuit 12, but if it is set to the gas amount Qg1 corresponding to the minimum combustion amount of the burner when there is no offset error, a negative offset error will occur as described above. If this occurs, the amount of gas will be Qg2, which is less than the minimum combustion amount Qg1 of the burner, and there is a risk of misfire. In addition, the air-fuel ratio becomes abnormally high, exceeding the burner air-fuel ratio upper limit i, and there is a risk of lift combustion and generation of CO.

In order to prevent these, if the minimum value of the air amount is set to Qa2 so that the lower limit of the combustion amount and the upper limit of the air-fuel ratio are not exceeded even in the worst case of the offset error, the combustion amount often cannot be reduced to the minimum value Qg1. , the minimum combustion amount increases to j, and the combustion amount adjustment ratio becomes small. If the resistance of the air restrictor 2 and the gas restrictor 4 is increased to increase the differential pressure, the effect of offset error can be reduced, but the blower 1 becomes larger,
Furthermore, a high gas supply pressure is required, which is not practical.

Furthermore, this problem can be solved by improving the accuracy of the differential pressure detector 6 and reducing the offset error, but improving the accuracy increases the cost of the differential pressure detector, and there is a limit.

Purpose of the Invention The present invention solves the above-mentioned problems.It is an object of the present invention to solve the above-mentioned problems. An object of the present invention is to provide a combustion control device.

Structure of the Invention In order to achieve this object, the present invention provides an air amount adjusting means having a minimum air amount regulating means in the air passage and a gas proportional control valve in the gas passage, a differential pressure detector that generates an electric signal according to the pressure difference with the upstream of An air-fuel ratio control circuit that controls the air-fuel ratio so that the minimum value of the drive signal of the gas proportional control valve is set between the air-fuel ratio control circuit and the gas proportional control valve to be the minimum value of the air amount regulated by the minimum air amount regulating means. A minimum value regulation circuit is provided to regulate the value to a value that provides the gas amount that provides the optimum air-fuel ratio. With this configuration, the minimum value of the air amount is regulated, and even if there is a pressure adjustment error of _P It acts to prevent the value from becoming smaller than a certain value determined by the value regulation circuit.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be explained as shown in FIGS. 3, 4, and 5.
This will be explained in detail using diagrams.

Note that the same parts as in FIG. 1 are given the same reference numerals.

A blower 1 and an air throttle 2 are provided in the air passage, a gas proportional control valve 3 and a gas throttle 4 are provided in the gas passage, and a mixing section 5 is provided downstream of the air throttle 2 and the gas throttle 4. Pressure Pa upstream of air restriction 2
and the pressure Pg upstream of the gas throttle 4 are guided to a differential pressure detector 6. A burner 7 and a heat exchanger 8 are provided downstream of the mixing section 5, and a thermistor 9 is provided at the outlet of the heat exchanger 8.

Furthermore, the signal of the temperature setting device 10 and the thermistor 9
The difference between the signals is input to the temperature control calculation circuit 11,
Rotation speed minimum value regulation circuit 12, rotation speed adjustment circuit 13
It is connected to the blower 1 through. On the other hand, the signal from the differential pressure detector 6 is connected to the gas proportional control valve 3 via an air-fuel ratio control circuit 14 and a minimum drive current value regulation circuit 15. Further, a minimum value setting signal is sent from the rotation speed minimum value regulation circuit 12 to the drive current minimum value regulation circuit 15, and the minimum value of the drive current is set in accordance with the setting of the minimum value of the rotation speed.

In the above configuration, the drive current minimum value regulation circuit 1
5 regulates the optimum gas amount as the minimum value with respect to the minimum value of the air amount set by the rotation speed minimum value regulating circuit 12.

4a is a graph showing the relationship between the electromagnetic coil current of the gas proportional control valve 3 and the gas amount, and Ic1 is Qg1 corresponding to the minimum combustion amount of the burner 7. Figure b is a graph showing the relationship between the output current and the input signal of the minimum drive current regulation circuit 15 from the air-fuel ratio control circuit 14. When the input signal becomes below k, the output current is kept at a constant value of Ic1. configured.

FIG. 5a is a graph showing the relationship between the amount of gas and the amount of air using the offset error of the differential pressure detector 6 as a parameter, and FIG. 5b is a graph showing the relationship between the amount of air and the air-fuel ratio. In the figure, m is the characteristic when the offset error is zero, n is the characteristic when the offset error is positive, and p is the characteristic when the offset error is negative. The rotational speed minimum value regulation circuit 12 is set so that the gas amount Qg1 corresponding to the minimum combustion amount of the burner 7 becomes the air amount Qa1 that provides the optimum air-fuel ratio.
On the other hand, the drive current minimum value regulation circuit 15 is set in conjunction with the minimum setting value of the rotation speed minimum value regulation circuit 12 so that the minimum current becomes Qg1. Since this is an air-leading type air-fuel ratio control device, the minimum combustion amount is first regulated by regulating the amount of air.

When the offset error is zero or positive, the operation is similar to that of the conventional example, and the air-fuel ratio has the characteristics q and r in the figure. In these cases, the gas amount does not try to become smaller than Qg1, so the regulation by the minimum drive current regulation circuit 15 does not work.

If the offset error is negative, the air-fuel ratio is s
It is a characteristic of When the offset error is negative, that is, Pa<Pg, and the signal from the differential pressure detector 6 becomes zero, the air-fuel ratio control circuit 14 controls the gas proportional control valve 3 so that the signal from the differential pressure detector 6 becomes zero. ing. As the amount of air decreases from a large amount, the gas amount reaches Qa1 at point t, and the drive current minimum value regulation circuit 15 operates to maintain the current of the gas proportional control valve 3 at Ic1 even if the amount of air decreases. , as a result, the gas amount maintains Qa1. The air-fuel ratio corresponding to point t is u, which is less than the air-fuel ratio upper limit value i. Furthermore, blower 1
The rotational speed decreases and at point v, the rotational speed minimum value regulation circuit 12 operates and the air amount is regulated at Qa1. From point t to point v, the gas amount is constant at Qg1, so as the air amount decreases, the air-fuel ratio decreases, and at point w, the air amount and gas amount are the minimum rotational speed regulation circuit 12 and the minimum drive current value, respectively. This is the minimum value regulated by the regulation circuit 15. These minimum values are set to be the optimum air-fuel ratio at the minimum combustion amount of the burner, so naturally the air-fuel ratio at point w is the optimum air-fuel ratio.
It can be m1.

As is clear from the figure, the fluctuation of the air-fuel ratio assuming the entire range of offset errors is in the range from g to h in the conventional example, but in the present example it is in the range from g to i, especially in the air-fuel ratio that causes lift combustion. A high fuel ratio region can be effectively prevented.

Further, fluctuations in the minimum combustion amount are also reduced, and the gas amount does not fall below Qg1, which is the minimum combustion amount of the burner 7, so there is no risk of misfire. Therefore, the combustion amount can be adjusted over a wide range while maintaining the safety and security of combustion, so the combustion appliance using the combustion control device of this embodiment can maintain a stable temperature over a wide range of the flow rate and set temperature of the heated object. This is how the control becomes.

Effects of the Invention As described above, the combustion control device of the present invention includes a blower provided in the air passage, an air amount adjusting means having a minimum value regulation circuit, a gas proportional control valve provided in the gas passage, an air throttle and a gas A differential pressure detector that detects the pressure difference between each upstream side of the throttle, an air-fuel ratio control circuit that amplifies the signal of the differential pressure detector and controls the signal of the differential pressure detector to become zero, and gas proportional control. By being configured with a minimum value regulation circuit that regulates the minimum value of the valve drive signal, it acts to prevent an increase in the air-fuel ratio and an excessively small combustion amount due to the offset error of the differential pressure detector at the minimum air amount. A safe and stable combustion device without the risk of CO generation, lift combustion, or misfire can be realized at a low cost. Furthermore, it is possible to widen the combustion amount adjustment range.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of a conventional gas combustion control device, Fig. 2 is a characteristic diagram showing changes in gas amount and air-fuel ratio with respect to air amount in the conventional example, and Fig. 3 is a gas combustion control according to an embodiment of the present invention. FIG. 4 is a diagram showing the configuration of the device, FIG. 4 is a characteristic diagram of the gas proportional control valve of the same embodiment, and FIG. 5 is a characteristic diagram showing changes in gas amount and air-fuel ratio with respect to air amount in the same embodiment. 1...Blower, 2...Air throttle, 3...Gas proportional control valve, 4...Gas throttle, 5...Mixing section, 6...
... Differential pressure detector, 12 ... Minimum rotational speed regulation circuit,
13... Rotation speed adjustment circuit, 14... Air-fuel ratio control circuit, 15... Drive current minimum value regulation circuit.

Claims (1)

[Claims] 1. A blower for supplying combustion air provided in an air passage, an air amount adjusting means having a minimum value regulating means for air amount, an air throttle, a gas proportional control valve and a gas throttle provided in the gas passage, and the air restrictor. and a mixing unit that mixes air and gas downstream of the gas throttle; and a differential pressure detector that generates an electrical signal in accordance with the differential pressure between the pressure upstream of the air throttle and the pressure upstream of the gas throttle. , an air-fuel ratio control circuit that amplifies and calculates a signal from the differential pressure detector and controls the gas proportional control valve so that the signal from the differential pressure detector becomes zero; the air-fuel ratio control circuit and the gas proportional control valve; a minimum value regulation that regulates the minimum value of the drive signal of the gas proportional control valve to a value that provides a gas amount that provides an optimal air-fuel ratio with respect to the minimum value of the air amount regulated by the air amount minimum value regulating means; A gas combustion control device consisting of a circuit.