JPH0159495B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in combustion control devices for combustion equipment such as water heaters.

In recent years, water heaters have been used to detect the temperature of hot water coming out of a heat exchanger, perform PID calculations to determine a predetermined control amount from the deviation from the arbitrarily set target temperature, and then control the amount of fuel according to this control amount. By adjusting the valve opening of the flow rate control valve installed in the supply path and controlling the combustion state in the burner so that it is low combustion when the amount of hot water coming out is low, and high combustion when the amount of hot water coming out is high, the temperature of the hot water used can be controlled. Some models have appeared that are equipped with a combustion control device that operates to maintain the water temperature at a target temperature regardless of changes in water temperature.

In this way, this type of water heater performs feedback control so that the detected temperature matches the set temperature, so it is different from the conventionally widely used water heaters in which the combustion state is constant or can only be changed in stages. Unlike the conventional method, it has the great effect of always providing hot water at the desired temperature regardless of changes in water temperature or amount of hot water, and is oriented toward energy conservation.

However, in conventional combustion control devices, only the amount of fuel supplied to the burner is controlled based on the above deviation, and the supply of combustion air is always a constant amount regardless of the combustion state in the burner. Since combustion air is supplied by a fan motor, there is an excess or deficiency in the amount of combustion air supplied, reducing combustion efficiency.
The significance of introducing PID control is being undermined.

Therefore, in order to match the air-fuel ratio and improve combustion efficiency, the rotation speed of the fan motor must be adjusted to the above control amount.
In other words, it is only necessary to control the output signal of the PID calculation circuit, and for this purpose, a switching means for changing the rotational speed of the fan motor step by step, and a control means for outputting a switching signal to the switching means according to the output level of the PID calculation circuit. It is conceivable to provide

As is well known, in response to the step input of the deviation signal shown in Fig. 1a, the PID calculation circuit calculates a signal A proportional to the deviation, a signal B integrating the deviation, and a change rate of the deviation as shown in Fig. 1b. A signal D is output by combining the differentiated signal C. Therefore, a problem when adopting such a configuration is that the output signal of the PID calculation circuit includes a differential signal.
That is, since the control means creates the switching signal according to the level of the output signal of the PID calculation circuit, the switching signal is naturally output in response to this differential signal as well. However, since the fan motor has inertia, the switching signal responsive to this differential signal simply opens and closes the contacts of the switching means, and the switching signal at this time results in wasting the life of the contacts. This is expected to have an adverse effect on the lifespan and reliability of the combustion control device itself.

This invention was developed in light of these problems, and its purpose is to make it possible to vary the rotational speed of the fan motor according to the combustion state without adversely affecting the lifespan or reliability of the combustion control device itself. An object of the present invention is to provide a combustion control device.

In order to achieve the above object, the present invention includes a deviation detection circuit that generates a deviation signal from a temperature sensor and a target temperature setter, a proportional-integral circuit that performs proportional-integral calculation based on the output of this deviation detection circuit, and A differential circuit that performs differential calculations based on the output of the circuit, and a valve drive circuit that operates in response to the sum of the outputs of the proportional-integral circuit and the differential circuit to drive a flow control valve that adjusts the amount of fuel supplied to the burner. , a switching element that changes the rotational speed of the fan motor that supplies combustion air to the burner step by step, and the output of the proportional-integral circuit that is level-discriminated into multiple levels, and the switching element is operated with this discrimination output to control the fan motor. The present invention is characterized by comprising a fan motor speed control circuit that changes the rotational speed of the motor in steps.

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

FIG. 2 is a diagram showing the basic configuration of a water heater equipped with a combustion control device according to the present invention.

In the figure, the fuel supply path leading to the burner 2 in the main body 1 of the water heater is provided with an electromagnetic switching valve 3 that turns on/off the supply of fuel, a governor 4, and a flow control valve 5 that adjusts the fuel flow rate. , an igniter 6 that generates an ignition spark in connection with the burner 2, and a flame detector 7 that detects whether or not the ignition is normally ignited by the ignition operation. It is equipped with an alarm device 8 that issues an alarm in the event of an abnormality. A flow switch 10 is installed at the water inlet leading to the heat exchanger 9 to detect the water flow passing through the heat exchanger 9.
However, a temperature sensor 11 such as a thermistor for detecting the temperature of the tapped water is provided on the hot water outlet side. Further, a fan motor 12 is provided in the upper opening of the main body 1, and a wind pressure switch 13 detects that the fan motor 12 has started to rotate.

Further, the combustion control device 14 that controls the hot water output temperature of the water heater to be constant is composed of a combustion sequence control circuit 15 and a hot water temperature control circuit 16, and the combustion sequence control circuit 15 includes an electromagnetic switching valve 3, Elements such as an igniter 6, a flame detector 7, an alarm 8, a flow switch 10, and a wind pressure switch 13 are connected. Further, various elements such as a flow rate control valve 5, a temperature sensor 11, a temperature setting device 17, etc. are connected to the hot water temperature control circuit 16, and the fan motor 1 is connected to the hot water temperature control circuit 16.
2 are connected to a combustion sequence control circuit 15 and a hot water temperature control circuit 16, respectively.

The hot water temperature control circuit 16 includes a deviation detection circuit 18 which generates a deviation signal from the temperature signal detected by the temperature sensor 11 and the target temperature by the target temperature setting device 17.
, a proportional-integral circuit 19 that performs a proportional-integral calculation based on this deviation signal, a differential circuit 20 that performs a differential calculation based on the deviation signal, and operates in response to the sum of the outputs of the proportional-integral circuit 19 and the differential circuit 20. and a valve drive circuit 21 that adjusts the valve opening degree of the flow control valve 5 to a predetermined opening degree, and the proportional integral circuit 19.
A switching element 22 that differentiates the output into multiple levels and switches the rotational speed of the fan motor 12.
The fan motor speed control circuit 23 operates the fan motor 12 and changes the rotational speed of the fan motor 12 in steps.

FIG. 3 is a diagram showing a specific configuration of the hot water temperature control circuit. The deviation detection circuit 18 is composed of a bridge circuit including the temperature sensor 11 and the target temperature setter 17 on one side, and the output of this bridge circuit is an impedance The signal is input to the proportional-integral circuit 19 and the differential circuit 20 via the conversion circuit 24. The output of the proportional-integral circuit 19 is the fan motor speed control circuit 23.
is input to the adder circuit 25, and the output of the differentiator circuit 20 is input to the adder circuit 25.

The switching element 22 is composed of a relay, and in this specific embodiment, the rotational speed of the fan motor 12 is switched between two stages: low-speed rotation during low combustion and high-speed rotation during high combustion by switching its contacts. be.

Next, the operation of the water heater equipped with the combustion control device configured as described above will be explained. Now, when the faucet is opened and water flow is detected by the flow switch 10, the combustion sequence control circuit 15 is activated and the fan motor 12 starts rotating. The wind pressure caused by the rotation of the fan motor 12 is applied to the wind pressure switch 1.
3, the combustion sequence control circuit 15
opens the solenoid switching valve 3. At the same time, the deviation between the water temperature detected by the temperature sensor 11 and the target temperature determined by the target temperature setting device 17 is determined by the deviation detection circuit 18, and is outputted to the proportional-integral circuit 19 and the differential circuit 20. The valve drive circuit 21 is operated by the sum of the outputs of the proportional integral circuit 19 and the differential circuit 20, and the opening degree of the flow rate control valve 5 is adjusted to an appropriate opening degree, so that a predetermined flow rate of fuel is supplied to the burner 2. Since the fuel is supplied, the combustion sequence control circuit 15 operates the igniter 6 to generate an ignition spark. As a result, the burner 2 is normally ignited, and when combustion starts, this is detected by the flame detector 7, and if there is an ignition error, the alarm 8 is activated.

On the other hand, since the fan motor speed control circuit 23 outputs a switching signal to the switching element 22 according to the output level of the proportional-integral circuit 19, the rotational speed of the fan motor 12 is adjusted, and the combustion air matching the above-mentioned combustion of the burner 2 is adjusted. is supplied.

As the burner 2 is normally ignited and enters a normal combustion state, heat exchange in the heat exchanger 9 progresses and hot water is dispensed from the faucet. The temperature and deviation are determined again by the deviation detection circuit 18. Based on this newly determined deviation, the proportional integral circuit 19 and the differential circuit 2
0 performs a predetermined calculation, and the valve opening degree of the flow rate control valve 5 is adjusted so that the deviation is small even with the sum of these outputs.

Thereafter, the above-mentioned operation is repeated, and feedback control is performed so that the detected hot water temperature matches the set temperature, so that the desired hot water with a stable temperature is obtained, and combustion air that matches the combustion state is stably supplied. Ru.

As explained in detail above, according to the present invention, combustion air that matches the combustion state can be supplied with a simple configuration without impairing the lifespan or reliability of the combustion control device, thereby significantly improving combustion efficiency. It is possible to provide a combustion control device that can

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing deviation signals and PID calculation waveforms, Fig. 2 is a basic configuration diagram of a water heater equipped with a combustion control device according to the present invention, and Fig. 3 shows a specific example of the combustion control device. It is a schematic configuration diagram. 2... Burner, 5... Flow rate control valve, 11... Temperature sensor, 12... Fan motor, 14... Combustion control device, 17... Target temperature setter, 18... Deviation detection circuit, 19... Proportional Integrating circuit, 20... Differentiating circuit, 22... Switching element, 23... Fan motor speed control circuit.

Claims (1)

[Claims] 1. A deviation detection circuit that generates a deviation signal from the temperature sensor and target temperature setter, a proportional-integral circuit that performs proportional-integral calculations based on the output of this deviation detection circuit, and a differential calculation based on the output of the deviation detection circuit. A differential circuit, a valve drive circuit that operates in response to the sum of the outputs of the proportional-integral circuit and the differential circuit to drive a flow control valve that adjusts the amount of fuel supplied to the burner, and a fan that supplies combustion air to the burner. A switching element that changes the rotational speed of the motor stepwise and the output of the proportional-integral circuit are level-discriminated into multiple levels, and the switching element is operated with this discrimination output to change the rotational speed of the fan motor in steps. A combustion control device characterized by comprising a fan motor speed control circuit.