JPH0158412B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application 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 combustion control device for high-load gas burners used in household appliances, in particular, to maintain combustion stability and high efficiency by keeping the amount of gas at a nearly constant level. Conventional Structure and Problems The pressure equalizing valve system shown in FIG. 1 is well known as a conventional combustion control device for this type of high-load gas burner. In FIG. 1, air sent by a blower 1 is guided to a mixing section 3 via an air throttle 2, while gas is guided to a mixing section 3 via a pressure equalizing valve 4 and a gas throttle 5, and the mixed gas is combusted in a burner 6. do. Here pressure equalizing valve 4
_The pressure P _A upstream of the air throttle 2 is guided to the back pressure chamber 7 _of
Adjust approximately equal to. In the above configuration, when the rotational speed of the blower 1 is adjusted to increase or decrease the amount of air, the pressure of P _A changes, and the pressure equalizing valve 4 keeps P _G almost equal to P _A. Therefore, the air throttle 2 and the gas throttle 5 The pressure difference applied to each of them is always equal, and a constant air-fuel ratio determined by the respective flow coefficients of the air restrictor 2 and the gas restrictor is maintained. However, since the pressure equalizing valve 4 operates a mechanical valve in response to the pressure difference between P _A and P _G , a pressure difference is always required to obtain the operating force, and P _A and P _G must be perfectly matched. It is not possible. Furthermore, it is difficult to achieve high accuracy due to the effects of changes in gas supply pressure, changes in pressure equalizing valve components over time, etc. For high precision, pressure equalizing valve 4
It would be possible to increase the pressure receiving area by increasing the size of the device, but this would increase the size of the device and increase the cost, making it impossible to apply it to household devices. Furthermore, when changing the combustion amount, the operation to change the gas amount starts after a change in the air amount occurs and a pressure difference occurs, so it is not possible to respond to sudden changes, and transient air-fuel ratio changes are large. In addition, increasing the precision by increasing the size of the pressure equalizing valve described above increases the mass of the pressure equalizing valve's movable part, which further slows down the response, and high precision and high-speed response are contradictory. Purpose of the invention The present invention solves such conventional problems,
The present invention provides a gas combustion control device that improves the accuracy of air-fuel ratio adjustment without increasing the size of the blower or valve device, improves the response of combustion amount adjustment and air-fuel ratio adjustment, and has excellent transient stability. Structure of the Invention In order to achieve this object, the present invention provides a blower, an air throttle, a rotation speed adjustment circuit for the blower, a gas proportional control valve and a gas throttle in the gas passage, and a downstream side of the air throttle and a gas throttle. a mixing section that joins the downstream of the , a differential pressure detector that detects the pressure upstream of the air throttle and upstream of the gas throttle, and a combustion amount calculation circuit that calculates a combustion amount adjustment signal according to the burner load. , a gas delay drive circuit that delays the combustion amount adjustment signal to drive the gas proportional control valve, an air amount calculation circuit that calculates the required air amount signal from the combustion amount adjustment signal, and an integrated differential pressure signal from the differential pressure detector. The air amount correction calculation circuit calculates an air amount correction signal by calculation including elements, and the required air amount signal and the air amount correction signal are added and input to the rotation speed adjustment circuit. With this configuration, when the combustion amount adjustment signal suddenly changes depending on the burner load, the rotation speed adjustment means is first driven by the required air amount signal calculated from the combustion amount adjustment signal, and the change is controlled by the response speed of the blower. start. The gas proportional control valve is driven by the gas amount delay drive circuit with a delay from the change in the combustion amount adjustment signal, and the gas amount changes until the air amount reaches the target value or in the middle thereof. After that, the air amount correction signal obtained by integrating the differential pressure signal is added to the air amount adjustment circuit, and the air amount is corrected until the pressure difference between the upstream of the air restriction and the upstream of the gas restriction disappears, and the air-fuel ratio is kept constant. act. DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below as shown in FIGS. 2, 3, and 4.
This will be explained using figures. In Fig. 2, the air passage has a blower 1 and an air throttle 2 downstream thereof, the gas passage has a gas proportional control valve 8 and a gas throttle 5 downstream thereof, and the air throttle 2 and the gas throttle 5 have an air throttle downstream thereof. A mixing section 3 for mixing the gas and the gas is provided, and a burner 6 is connected to the mixing section 3. The pressure P _A upstream of the air throttle 2 and the pressure P _G upstream of the gas throttle 5 are each guided to a differential pressure detector 9. A temperature detector is provided at the outlet of a heat exchanger 10 that heats water, which is an object to be heated, and its temperature signal is compared with a temperature setting signal 13 of a temperature setting circuit 12, and the difference is inputted to a combustion amount calculation circuit 14. The output, that is, the combustion amount adjustment signal 15 , is input to a gas amount delay drive circuit 16 and an air amount calculation circuit 17. The gas amount delay drive circuit 16 includes a signal delay circuit 18 and a signal delay circuit 1 that delay the combustion amount adjustment signal for a certain period of time.
A drive circuit 2 that amplifies the output signal of 8, that is, the gas proportional valve drive signal 19, and drives the gas proportional control valve 8.
Consists of 0. The signal delay circuit 18 can be realized by using a BBD element (bucket brigade device) or by using microcomputer software, and delays the signal by a certain period of time without changing the signal waveform. On the other hand, the differential pressure signal 21 of the differential pressure detector 9 enters the air amount correction calculation circuit 22 including integral calculation, and its output, that is, the air amount correction signal 23, is sent to the air amount calculation circuit 17.
The output, ie, the required air amount signal 24, is led to the air amount adjustment circuit 25, and the output signal, ie, the rotation speed setting signal 26, is input to the rotation speed adjustment circuit 27.
The rotation speed adjustment circuit 27 adjusts the rotation speed of the blower 1 in proportion to the input signal thereof, and the rotation speed adjustment circuit 26 and the blower 1 constitute air amount adjustment means. In the above configuration, the temperature signal from the temperature detector 11 is compared with the temperature setting signal 13, and the difference therebetween is subjected to PID calculation in the combustion amount calculation circuit 14, thereby obtaining the combustion amount adjustment signal 15 that provides the required combustion amount. The combustion amount adjustment signal 15 is guided to a gas amount delay drive circuit 16 , and the signal delay circuit 18 outputs the combustion amount adjustment signal 15 for a certain period of time.
is delayed and transmitted to the drive circuit 19. Drive circuit 20
amplifies the gas proportional valve drive signal 19 and supplies current to the electromagnetic coil of the gas proportional control valve 8 to control the gas amount, that is, the combustion amount. On the other hand, the combustion amount adjustment signal 15 is transmitted to the air amount calculation circuit 1.
7, where it is amplified or divided at a constant ratio to obtain a required air amount signal 24 that is proportional to the combustion amount adjustment signal 15. The required air amount signal 24 is the differential pressure signal 2
The air amount correction signal 23 obtained by integrating 1 is added in the air amount adjustment circuit 25 to obtain the rotation speed setting signal 26 to the rotation speed adjustment circuit 27. The rotation speed adjustment circuit 27 controls the amount of air by adjusting the rotation speed of the blower 1 according to the rotation speed setting signal 26. In FIG. 3, 28 is the combustion amount adjustment signal 15.
, 29 represents the gas proportional valve drive signal 19, 30 represents the rotation speed setting signal 26, and 31 represents the differential pressure signal 21, respectively, with respect to time on the horizontal axis. Now at time T ₁ , the combustion amount adjustment signal 15 is at point 32.
When there is a sudden change from point 33 to point 33, the required air amount signal 24 changes at the same time, so the rotation speed setting signal 26 also changes at the same time.
It changes from point 34 to point 35 at T ₁ . The rotation speed adjustment circuit 27 immediately increases the voltage supplied to the motor of the blower 1 to try to increase the rotation speed, but the blower 1 has inertia and the rotation speed does not increase rapidly. FIG. 36 shows the change in the rotation speed of the blower over time, which gradually increases from time _T1 .
The amount of air is approximately proportional to the rotation speed of the blower 1 unless there is a change in the resistance of the air passage. On the other hand, the gas proportional valve drive signal 19 that has passed through the signal delay circuit 18 changes from point 37 to point 38 at time _T2 . Since the gas proportional control valve 8 does not have a large inertia, it has a much faster response than the blower 1, and the gas amount changes at almost the same speed as the gas proportional valve drive signal 19.
Looking at the change in the differential pressure signal 21 during this time, it is found that at time T ₁
From to T ₂ , the gas amount does not change and only the air amount increases, so a positive differential pressure signal is generated. During this time, the air-fuel ratio becomes in excess of the target value. When the air amount does not reach the target value at time _T2 , the gas amount changes to the target value, so the air-fuel ratio becomes insufficient and the differential pressure signal 21 takes a negative value. After T ₂ , as the rotation speed of the blower 1 approaches the target value, the air amount correction signal 23 obtained by integrating the differential pressure signal 21 is added to the rotation speed setting signal 26 to correct the rotation speed of the blower 1, and the differential pressure signal 21 becomes zero and becomes stable, and the air-fuel ratio is maintained at the target value. For comparison, FIG. 4 39 shows the change in the differential pressure signal when the gas proportional control valve 8 is driven by the combustion amount adjustment signal 15 without using the signal delay circuit ₁₈ . Since the amount of air changes suddenly and the amount of air cannot change rapidly, a large negative differential pressure occurs. This means that the air-fuel ratio deviates significantly in the direction of air shortage, which worsens the combustibility of the burner 6. Especially when there is a lack of air, soot and CO ₂ are more likely to be generated. In this embodiment, since the change in the gas amount is delayed as described above, the change in the air-fuel ratio can be kept small. If the delay time (T ₂ −T ₁ ) is selected near the startup time constant of the blower, changes in the air-fuel ratio can be minimized. The operation when the gas amount increases rapidly has been described above, but the same operation occurs when the gas amount suddenly decreases, but in the opposite direction. Due to the above action, the signal delay circuit 1 is activated when the combustion amount suddenly changes.
8 delays the operation of the gas proportional control valve 8 and immediately transmits the change in combustion amount to the rotational speed adjustment circuit 27 via the air amount calculation circuit 17 to operate the blower 1. Therefore, the response delay of the blower can be corrected. Fluctuations in the air-fuel ratio can be suppressed. Furthermore, in order to correct the rotational speed of the blower 1 until P _G and P _A become equal using the differential pressure detector 9 and the air amount correction calculation circuit 22 including an integral element, the current vs. gas amount characteristic of the gas proportional control valve 8 is adjusted. This has the effect of keeping the air-fuel ratio constant by absorbing non-linearities and variations in the rotational speed vs. air amount characteristic of the blower 1, changes in resistance of the air passage, and the like. Effects of the Invention As described above, the gas combustion control device of the present invention provides the following effects. A blower, a rotation speed adjustment means, an air throttle provided in an air passage, a gas proportional control valve and a gas throttle provided in a gas passage, and differential pressure detection for detecting the difference in pressure upstream of each of the air throttle and gas throttle. a combustion amount calculation circuit that calculates a combustion amount adjustment signal according to the load; an air amount calculation circuit that calculates the required air amount from the combustion amount adjustment signal; an air amount adjustment circuit that adds the air amount correction signal calculated by the correction calculation circuit to drive the rotation speed adjustment means; and a gas proportional control valve that delays the combustion amount adjustment signal for a certain period of time. (1) When changing the combustion amount, the rotation speed control circuit is first driven by the combustion amount adjustment signal, and the gas proportional control valve is driven after a certain time delay by the delay circuit. Transient air-fuel ratio changes can be suppressed by correcting the response delay of the blower. Furthermore, since the gas proportional control valve and the blower are each given a roughly proportional relationship between the drive signal, the gas amount, and the air amount, the air-fuel ratio control can be performed stably with good responsiveness through open control. (2) By adding feedback correction based on air-fuel ratio detection consisting of a gas throttle, air throttle, and differential pressure detector, the air-fuel ratio accuracy during steady state is improved, and when used in combination with the open control described in (1) above, Since the gain of the feedback system can be set small, feedback control with response delay can be stably performed.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional gas combustion control device, Fig. 2 is a block diagram showing an embodiment of the gas combustion control device of the present invention, and Fig. 3 is a block diagram showing the operation of the embodiment of Fig. 2. FIG. 3 is a characteristic diagram showing changes in a signal over time. 1... Blower, 2... Air throttle, 3... Mixing section, 5... Gas throttle, 6... Burner, 8... Gas proportional control valve, 9... Differential pressure detector, 14... Combustion amount calculation Circuit, 16 ...Gas amount delay drive circuit, 17...
...Air amount calculation circuit, 22... Air amount correction calculation circuit, 25... Air amount adjustment circuit, 27... Rotation speed adjustment circuit.

Claims (1)

[Claims] 1. A blower and an air throttle provided in the air passage, a rotation speed adjustment circuit for the blower, a gas proportional control valve and a gas throttle provided in the gas passage and in which the driving current and the gas flow rate are in a roughly proportional relationship, and the air throttle. and a mixing unit that mixes gas and air 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. , a combustion amount calculation circuit that calculates a combustion amount adjustment signal according to the burner load, an air amount calculation circuit that calculates a required air amount signal from the combustion amount adjustment signal, and an integrated differential pressure signal of the differential pressure detector. an air amount correction calculation circuit that calculates an air amount correction signal by calculating the air amount correction signal including the elements, and adds the required air amount signal and the air amount correction signal to input the rotation speed adjustment circuit; A gas combustion control device comprising a gas amount delay drive circuit that delays a quantity adjustment signal for a predetermined period of time, and the gas proportional control valve is driven by an output of the gas amount delay drive circuit.