JPS646363B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a combustion control device that variably controls the combustion amount of a combustion device.

Conventional configuration and its problems A conventional combustion control device is shown in FIG.

A gas amount control valve 3 and a combustion air supply means 4 are provided upstream of the gas throttle 1, gas differential pressure sensor 1a, air throttle 2, and air differential pressure sensor 2a, respectively, and the downstream side of the two throttle parts is They merge and are led to the combustion chamber 5. 6 is a gas amount control valve 3 or
This is a control unit that controls the combustion air supply means 4 to variably control the combustion amount according to the load.

In FIG. 1, Pg is the pressure on the outlet side of the gas amount control valve 3, that is, the pressure on the upstream side of the gas throttle 1. Pa is the outlet pressure of the combustion air supply means 4, that is, the upstream pressure of the air throttle 2. P _n is the pressure at the confluence of fuel gas and combustion air. In the above configuration, when the fuel gas flow rate Q _g and the combustion air flow rate Q _a are expressed using the pressures of P _g , P _a , and P _n , Q _g = K ₁ √ _g − _n , Q _a = K ₂ √ _a − _n . However, K ₁ and K ₂ are proportionality constants.

The theoretical air amount Q _ap is calculated as follows, with K ₃ as a constant: Q _ap = K ₃ Q _g =
It can be expressed as K ₃・K ₁ √ _g − _n . Therefore, if the air ratio is expressed as m, m=Q _a /Q _ap = (K ₂ √ _a − _n )/
(K ₃ · K ₁ √ _g − _n ), and if K ₄ = K ₂ /K ₃ · K ₁ , then m = K ₄ √ ( _a − _n ) ( _g − _n ).

As already briefly explained, the control unit 6 has the function of changing the combustion amount in response to the external load and controlling the air ratio at the same time, and the air ratio control method always satisfies P _a = P _g . That is, m= _K4√ ( _a − _n )( _g − _n )= _K4√ ( _g − _n )( _g − _n )= _K4 (constant). However, differential pressure sensors have a certain error e due to variations in output, and in reality, P _a = P _g instead of P _a = P _g ±e
Therefore, the actual value of the air ratio m is m=K ₄ √( _a − _n )( _g − _n ) = K ₄ √( _g − _n ±)( _g − _n ) = K ₄ √1±( _g − _n ).

In other words, the air ratio m is a function of (P _g −P _n ).

In Figure 2, the horizontal axis is (P _g −P _n ), that is, the gas flow rate.
This situation is illustrated by plotting the air ratio m on the vertical axis of Q _g . The fuel gas flow rate, i.e. the combustion amount, is √
Since it is proportional to (P _g −P _n ), the left side of FIG. 2 shows the low combustion region. As is clear from the figure, the error in the air ratio m suddenly increases in the low combustion range for a constant error ±e.

FIG. 3 shows both the range of good combustion indicated by rough hatching and the range of variation in the air ratio m described above superimposed on a coordinate plane having the same axis as in FIG. 2. The lower limit of the range for good combustion depends on the combustion characteristics of the burner, but is usually approximately constant at about 1.2 to 1.4.

As is clear from the figure, the limit value of the variation in the air ratio m spreads rapidly in the low combustion range, so it is necessary to set the air ratio m at a high value, that is, m=1+A. On the other hand, if the air ratio m is set as small as possible, the error in the air ratio m will rapidly increase in the low combustion range, which will deviate from the lower limit of the good combustion range. need to be narrowed down.

Therefore, under such conditions, extra combustion air is always supplied in areas other than the low combustion range, which increases the amount of heat carried away by the exhaust gas and reduces thermal efficiency. It was causing a decline. In addition, supplying surplus combustion air means that combustion air supply means such as blowers become larger.
Another problem was that it led to an increase in combustion noise.

Purpose of the Invention The present invention solves these conventional problems, and its purpose is to prevent the lower limit curve of air ratio variation from rapidly expanding downward, especially in the low combustion range. The air ratio is set to a low value over a wide combustion range, and wind resistance is improved.

Structure of the Invention In order to achieve this object, the present invention provides a gas amount adjusting means and a gas throttle in the gas side passage, and a blower for supplying combustion air and an air throttle in the air side passage. and a bypass passage in which the downstream sides of the respective air constrictors join together at a ventilate tube-shaped mixing section and are guided to the burner, and a variable throttle mechanism is provided between the upstream side of the air restriction and the throat section of the ventillary tube-shaped mixing section. The apparatus further includes differential pressure detection means for detecting a pressure difference on the upstream side of each of the gas throttle and the air throttle, and a control section for controlling the blower and the variable throttle mechanism.

With this configuration, in a region where the combustion amount is equal to or higher than a predetermined value, the air ratio remains constant even if the combustion amount changes in response to the burner load (however, the error of the differential pressure detection means is zero). ), and in a region below a predetermined value, the air ratio can be controlled by changing the air ratio.

Therefore, the air ratio can be increased in the region where the combustion amount is below a predetermined value, and the lower limit curve of the air ratio variation can be prevented from rapidly expanding downward, so even if the air ratio is set low overall. , it is possible to have the effect that the air ratio does not go below the lower limit curve of the good combustion range.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 4 to 7.

In FIG. 4, a gas amount adjusting means 2 and a gas throttle 3 are provided in the gas side passage 1, and a blower 5 and an air throttle 6 are provided in the air side passage 4. After the gas and the combustion air are combined in a ventilate tube-shaped mixing section 7, they pass through a mixed gas passage 8 and are led to a burner 9. 10 is differential pressure detection means such as a differential pressure sensor that detects the pressure difference on the upstream side of the gas throttle 3 and the air throttle 6 (hereinafter the differential pressure detection means will be referred to as a differential pressure sensor);
1 is a differential pressure sensor detection circuit, 12 is a bypass passage that communicates the upstream of the air throttle 6 and the throat part of the ventilate tube-shaped mixing section 7, and 13 is a bypass passage 1.
This is a variable diaphragm mechanism located at 2. Reference numeral 14 denotes a secondary air passage, and 15 variably controls the blower 5 with the variable throttle mechanism 13 kept fully closed in the range from the maximum combustion amount to a predetermined combustion amount, and in the region below the predetermined combustion amount. Here, the control section is configured to control the blower 5 to maintain a constant air amount corresponding to a predetermined combustion amount, and to variably control the variable throttle mechanism 13. 16 is a temperature setting device, and 17 is a temperature detection circuit.

In the above configuration, it is assumed that the maximum rated combustion amount is currently reached. When in such a state,
When the temperature setting device 16 is reset to lower the hot water temperature, that is, when the load is reduced, the temperature setting device 16 and the temperature detection circuit 17
The deviation signal is processed by the control unit 15 to control the blower 5 so that the amount of air decreases. Therefore,
When the amount of air decreases, a differential pressure is generated in the differential pressure detection means 10, and this differential pressure output is sent to the differential pressure sensor detection circuit 11.
The gas amount adjusting means 2 is controlled to decrease the gas amount so that the differential pressure output becomes zero. Further, if the load is increased from such a state, the air amount and gas amount are controlled to increase. That is, even if the load fluctuates, the gas amount changes to follow the air amount, so the air ratio m is maintained at a substantially constant value. In this state, the predetermined combustion amount (for example, 1/3 of the maximum rated combustion amount) is still being reached.
value).

In this state, the variable diaphragm mechanism 13 is held in a fully closed state by the control section 15.

Next, the load is further reduced from this state, and in the range below the predetermined combustion amount (for example, from 1/3 of the maximum rated combustion amount to the minimum combustion amount), the control unit 15 At the same time that the circuit that maintains the amount of air sent out by the built-in blower 5 (the amount of air at 1/3 of the maximum rated combustion amount) is activated, the deviation signal of the temperature setting device 16 and temperature detection circuit 17 is activated. The variable aperture mechanism 13 is then variably controlled.

To make the above operation easier to understand, differential pressure sensor 1
Figure 5 shows the changes in the air-fuel ratio assuming that the error in the control system such as the differential pressure sensor detection circuit 11 is zero, and the combustion amount (gas amount Q _G )
FIG. 6 shows the relationship between the air ratio m and the air ratio m.
Next, we will consider the actual case where control system errors occur in the differential pressure sensor 10, etc. within the range of good combustion determined by the combustion characteristics of the burner 9, that is, the change situation of the air ratio m taking into account control system variations. What is shown is FIG. Note that in FIGS. 5 to 7, a, b, and c indicate the maximum rated combustion amount, the predetermined combustion amount, and the minimum combustion amount, respectively. Further, A and B in FIG. 7 represent the upper and lower limits of the good combustion range, respectively.

In the above configuration, if the air ratio m at the maximum rated combustion rate is determined as is clear from FIG. become. However, as in one embodiment of the present invention, the air amount is reduced from point b to point c.
By fixing it to the same value as point and varying only the gas amount, the air ratio m is increased, and by making sure that it does not reach the lower limit of the good combustion range of burner 9, the combustion amount variable range can be changed from point b to point c. It can be expanded to.

Next, another embodiment of the present invention will be described using FIGS. 8 to 10. For clarity, differential pressure sensor 1
The eighth figure is illustrated assuming that the control system error such as 0 is zero.
9, the difference from the above embodiment is that the predetermined combustion amount is divided into two, b ₁ and b ₂ , and the air ratio m is kept constant from the predetermined combustion amount b ₂ to the minimum combustion amount c. The structure was designed so that it could be controlled without changing the position. That is, when the variable diaphragm mechanism 13 is fully opened at b ₂ , c
The control unit 15 is configured so that the air blower 5 is held fully open until the point is reached, and the deviation signal from the temperature setting device 16 and the temperature detection circuit controls the blower 5 in turn.

According to this configuration, the upper limit of the range of good combustion determined by the combustibility of the burner is horizontal in the vicinity of a low combustion amount, and it is extremely useful as a control means when the air ratio m is required to be a constant value in this vicinity. Effective. FIG. 10 shows this relationship in an actual case where errors occur in the control system of the differential pressure sensor 10 and the like.

Note that C and D in FIG. 10 represent the upper and lower limits of the range of good combustion, respectively.

Effects of the Invention As is clear from the above description, the gas combustion control device of the present invention provides the following effects.

(1) A differential pressure detection means is installed to detect the difference between the pressure between the gas amount adjustment means and the gas throttle, and the pressure between the blower and the air throttle, and the downstream sides of each are joined by a ventilate tube-shaped mixture. and a control section that communicates the air throttle upstream side with the throat section of the ventilated tube-shaped mixing section through a bypass passage having a variable throttle mechanism therebetween, and controls the blower and the variable throttle mechanism. Therefore, in a region where the combustion amount is greater than a predetermined value, when the air amount changes in response to load fluctuations, the differential pressure detection means adjusts the gas amount adjustment means until the differential pressure reaches zero (or a predetermined value).
Since it operates so that the air ratio becomes constant, the air ratio can be controlled at a constant level. In addition, when the combustion amount falls below a predetermined value, the amount of air sent out by the blower becomes a constant value, and the variable throttle mechanism is activated in response to load fluctuations, so the air ratio can be set as low as possible. The combustion amount variable range can be expanded. Therefore, it is possible to realize a combustion device with high thermal efficiency and low combustion noise.

(2) In the region of low combustion amount, the air ratio is controlled to increase regardless of whether the fixed error of the differential pressure detection means is positive or negative, so there is an advantage that the wind resistance performance of the combustion equipment can be improved. 3) In addition, by configuring the control unit to keep the variable throttle mechanism fully open and operate the blower in response to load fluctuations, it is possible to control the air ratio to be constant, thereby controlling the burner combustion. This also has the effect that even when the characteristics (range of good combustion) are complex, the air ratio can be controlled in accordance with the combustion characteristics.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a conventional combustion control device, FIGS. 2 and 3 are explanatory diagrams of the same operation, FIG. 4 is a configuration diagram showing an embodiment of the gas combustion control device of the present invention, and FIG.
6 and 6 are control characteristics diagrams when there is no error in the control system such as the differential pressure detection means, and FIG. Figure 8 shows the relationship between the combustion characteristics of
9 and 9 are control characteristic diagrams when there is no error in the control system such as the differential pressure detection means in the second embodiment of the present invention, and FIG. 10 is a control characteristic and burner combustion characteristic in an actual case where there is an error. FIG. 1...Gas side passage, 2...Gas amount adjustment means, 3
...Gas throttle, 4...Air side passage, 5...Blower, 6...Air throttle, 7...Venture tube shape mixing section, 9...Burner, 10...Differential pressure detection means,
12... Bypass passage, 13... Variable throttle mechanism,
15...Control unit.

Claims (1)

[Scope of Claims] 1. A gas amount adjusting means and a gas throttle are disposed in the gas side passage, and a blower and an air throttle for supplying combustion air are disposed in the air side passage, and the downstream side of each is disposed. a bypass passage which joins at a ventilate tube shape mixing section and leads to the burner, and has a variable throttle mechanism inserted between the upstream side of the air restriction and the throat section of the ventuille tube shape mixing section; and the gas amount. A differential pressure detection means is provided for detecting a pressure difference between the pressure between the adjustment means and the gas throttle and the pressure between the blower and the air throttle, and further, in a region where the combustion amount is equal to or higher than a predetermined value, a control unit that controls the combustion air by maintaining the variable throttle mechanism in a fully closed state, and controls the variable throttle mechanism by maintaining the combustion air at a constant value in a region below a predetermined value; A gas combustion control device consisting of: 2. The gas combustion control device according to claim 1, wherein the variable throttle mechanism is configured to operate by electromagnetic force.