JPH0227573B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a combustion control device for a water heater that has a pre-purge operation sequence before igniting fuel.

Normally, water heaters equipped with a blower are equipped with a start/stop switch that is linked to the water faucet, and when this switch is closed, the blower motor is operated to perform a pre-purge operation to scavenge air and unburned gas in the combustion chamber. After that, the ignition operation begins. Therefore, even if the faucet is opened and the start/stop switch is closed, hot water will not come out but water will come out during the pre-purge period where air is scavenged.
However, with water heaters used at home, there are periods when the water heater starts and stops frequently depending on the time of use, and the combustion operation time is short, and hot water does not come out every time the faucet is opened. Water coming out is extremely uncomfortable for the user. The reason for this is that, as shown in Figure 1a, the combustion operation sequence of the water heater is: combustion start signal 1, prepurge period 2, ignition trial period 3.
This is because it has a fixed operation sequence in which it enters normal combustion period 4 through
This is because situations occur where the temperature of the water drops.

This invention was made to eliminate the above-mentioned drawbacks, and by shortening the pre-purge operation sequence as the frequency of starting and stopping water heaters increases, explosion accidents due to residual gas may occur. It is an object of the present invention to provide a combustion control device that can obtain good hot water discharge temperature characteristics without any problems.

Next, one embodiment of the present invention will be described with reference to the drawings. In FIG. 2, 10 is a combustion flame detection circuit;
The diode 11 is supplied with an output signal from a flame rod type flame detector or the like that utilizes flame rectification. A time constant circuit 1 further includes a charging circuit including a resistor 12 and a capacitor 13, and a discharging circuit for discharging the charge of the capacitor 13 via a resistor 14.
6 is provided on the cathode side of the diode 11. Further, 15 is a level detection circuit, and 20 is a prepurge timer circuit.

In such a configuration, once the water heater performs normal operation and shifts to the combustion operation state, the flame detection circuit 10 detects the combustion flame, and the diode 11 detects the combustion flame.
Current flows into the time constant circuit 16 via the resistor 12 and charges the capacitor 13. When this charging voltage rises to a level equal to or higher than a predetermined reference voltage of the level detection circuit 15, an output signal 22 is sent to the prepurge timer circuit 20. Prepurge
The timer circuit 20 normally receives a combustion start signal 2 from a start/stop switch (not shown) provided in conjunction with a faucet.
1 and starts its operation, but the output signal 22
If you receive a message, you can fast-forward and shorten the timer's time. Such a timer circuit 20 is
Since it is a well-known circuit that is composed of an analog circuit or a digital circuit, a description of its configuration will be omitted. Furthermore, when the combustion operation is stopped, the charge in the capacitor 13 is discharged via the resistor 14, but
For a certain period of time, the output signal continues to be sent to the timer circuit 20 because it is maintained at or above the reference voltage of the level detection circuit 15. Therefore, if the period between the stop of the previous combustion operation and the start of the next combustion operation is short, that is, the frequency of starting and stopping increases, the pre-purge operation sequence will be shortened, and the ignition operation will start in a short time, resulting in As shown in FIG. 2b, there is no drop in hot water temperature in the hot water supply characteristics, and good characteristics are obtained.

FIG. 3 shows a circuit configuration that further embodies the principle of the invention shown in FIG. In the figure, the combustion flame detection signal of flame detection circuit 10 is applied to transistor 25. Further, the level detection circuit 15 is
It is composed of a comparison circuit 19, voltage dividing resistors 17 and 18 for generating a reference voltage, and output resistors 23 and 24. In this embodiment, a level detection circuit 15 having a time constant circuit 16 including a capacitor 13 and a voltage comparison circuit 19 was explained as an example. - May be configured with a level detection circuit.

Furthermore, although this embodiment has been described for a water heater that has only a pre-purge operation sequence performed before fuel ignition, it can also be applied to a water heater that has a post-purge operation sequence after the completion of combustion. By applying the output signal of the circuit 15 to a post-purge timer circuit, it is also possible to shorten the post-purge operation sequence.
In this case as well, good hot water tapping characteristics can be obtained.

As described above, according to the present invention, when the frequency of starting and stopping of the combustion operation is high, in response to this, it is possible to eliminate the discomfort caused by the drop in the temperature of hot water discharged from the water heater. Since the pre-purge operation sequence is shortened and controlled, the pre-purge operation is performed even if it is short during the combustion operation, making it possible to reliably prevent explosion accidents caused by residual gas without adding special equipment. effective.

[Brief explanation of drawings]

1A and 1B are respectively an explanatory diagram of the operation sequence of a conventional water heater and its hot water output characteristic diagram, and FIGS. The hot water tapping characteristic diagram, FIG. 3, is a circuit diagram that further embodies the conceptual circuit configuration shown in FIG. 2a. 10... Combustion flame detection circuit, 15... Level detection circuit, 16... Time constant circuit, 19... Comparison circuit,
20...Timer circuit.

Claims (1)

[Claims] 1. In a water heater combustion control device that has a pre-purge operation sequence before fuel ignition, a time constant circuit that performs charging and discharging depending on the presence or absence of a combustion flame detection signal;
A hot water bath equipped with a comparison circuit that compares the output signal of this time constant circuit with a predetermined reference voltage signal, and a timer circuit that controls the counting speed according to the level of the output signal of this comparison circuit and performs a prepurge operation sequence. Boiler combustion control device.