Stoves and furnaces – Hot-air furnaces – Compressed air
Reexamination Certificate
2000-02-18
2001-05-22
Clarke, Sara (Department: 3743)
Stoves and furnaces
Hot-air furnaces
Compressed air
C126S11600A, C431S020000
Reexamination Certificate
active
06234164
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a combustion device of the forced intake and discharge type for introducing combustion air into a burner and discharging combustion gases from the burner with a fan, and more particularly to a closure detector for detecting an unwanted closure of an intake or discharge tube of the combustion device prior to abnormal combustion.
2. Description of the Related Art
Combustion devices of the forced intake and discharge type, which are widely used as FF (forced flue)-type air heaters, for example, introduce combustion air from the outdoors and discharge combustion gases with a fan (combustion fan). Therefore, these combustion devices are capable of burning a fuel to heat rooms without contaminating the indoor air.
In order to detect an unexpected closure such as a clogging of the intake or discharge tube of a combustion device, the combustion device may have a closure detector which comprises, for example, an orifice disposed in the intake tube and a pressure sensor for detecting the value of a pressure difference between the air pressure upstream of the orifice and the air pressure downstream of the orifice.
When an unwanted closure of the intake tube occurs, the intensity of an air flow passing through the orifice while the fan is in operation is reduced, resulting in a reduction in the pressure difference between the air pressure upstream of the orifice and the air pressure down-stream of the orifice. Therefore, while the fan is in operation, the value of the pressure difference detected by the pressure sensor is monitored, and when the detected pressure value becomes smaller than a predetermined threshold value, it is judged that the intake tube is undesirably closed, and the burner can be turned off.
However, the value of the pressure difference detected by the pressure sensor may suffer an error because of an individual characteristic difference or aging of a pressure detecting element, such as a thin-film semiconductor device, of the pressure sensor. If the detected value suffers such an error, then an unwanted closure of the intake tube cannot accurately be detected by comparison between the value of the pressure difference detected by the pressure sensor and the predetermined threshold value.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a closure detector for detecting an unwanted closure of an intake or discharge tube of a combustion device of the forced intake and discharge type for introducing combustion air into a burner through the intake tube discharging combustion gases from the burner through the discharge tube with a fan, comprising an orifice disposed in the intake or discharge tube, a pressure detector for detecting the value of a pressure difference between a pressure upstream of the orifice and a pressure downstream of the orifice, memory means for storing a pressure value detected by the pressure detector before the fan operates, as a pressure value prior to operation, change detecting means for comparing a pressure value in operation, detected by the pressure detector while the fan is in operation, with the pressure value prior to operation stored by the memory means, for thereby detecting a change between the pressure value prior to operation and the pressure value in operation, and combustion stopping means for initiating the suspension of at least combustion by the burner if the absolute value of the change detected by the change detecting means is smaller than a predetermined threshold value.
The combustion stopping means stops combustion by the burner if the change, detected by the change detecting means, from the pressure value prior to operation from the pressure value in operation becomes smaller than the threshold value. Even if the pressure value detected by the pressure detector varies or suffers an error due to an individual characteristic difference or aging of the pressure detector, the variation or error is canceled out when the change detecting means detects the change from the pressure value prior to operation from the pressure value in operation. Therefore, the combustion stopping means is capable of accurately detecting an unwanted closure of the intake or discharge tube without being affected by an individual characteristic difference or aging of the pressure detector, and of stopping combustion by the burner.
The combustion stopping means may comprise means for setting the threshold value to a greater value as the rotational speed of the fan is higher.
With the above arrangement, even when the rotational speed of the fan changes, resulting in a change in the intensity of an air flow in the intake and discharge tubes, an unwanted closure of the intake or discharge tube can be determined accurately in change from the pressure values prior to operation to the pressure values during operation, depending on variations in the intensity of the air flow. Consequently, the combustion by the burner can reliably be stopped before it suffers abnormal combustion, and the burner is prevented from stopping combustion due to an erroneous detection of an unwanted closure of the intake or discharge tube.
The combustion device of the forced intake and discharge type may have room temperature detecting means for detecting the temperature of a room in which the combustion device is installed, and temperature-dependent operation control means for stopping and resuming combustion by the burner and operation of the fan based on the temperature detected by the room temperature detecting means. The memory means may comprise means for storing again the pressure value detected by the pressure detector immediately before the fan resumes its operation thereby to update the stored pressure value prior to operation, when combustion by the burner and operation of the fan are resumed by the temperature-dependent operation control means.
With the above arrangement, after the combustion by the burner and the operation of the fan are stopped, the pressure value prior to operation is updated each time the burner resumes the combustion and the fan resumes its operation. After the burner resumes the combustion and the fan resumes its operation, the change detecting means compares the pressure value in operation with the pressure value prior to operation immediately before the fan operates, for thereby detecting the change from the pressure value prior to operation to the pressure value in operation. Therefore, the change detecting means can accurately detect the change without being essentially affected by an error due to aging, etc. of the pressure detector.
The closure detector may further comprise a bypass pipe extending between portions of the intake or discharge tube which are positioned upstream and downstream of the orifice, and the pressure detector may comprise a heating resistance element having a resistance variable depending on the intensity of an air flow passing through the bypass pipe, for detecting the value of the pressure difference from the resistance of the heating resistance element.
The heating resistance element, which is relatively inexpensive, may be used as the pressure detector for detecting the pressure difference.
The closure detector may further comprise a temperature sensor for detecting the temperature in the bypass pipe, and means for correcting the value of the pressure difference detected from the resistance of the heating resistance element, based on the temperature detected by the temperature sensor.
The temperature sensor allows the pressure difference to be detected accurately without being affected by the temperature of an air flow passing through the bypass pipe.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.
REFERENCES:
patent: 4419898 (1983-12-01), Zanker et al.
patent: 4478077 (1984-10-01), Bo
Birch & Stewart Kolasch & Birch, LLP
Clarke Sara
Rinnai Kabushiki Kaisha
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