Space heater

Disclosed is a space heater, with an air cleaning function, that monitors combustion at a burner, and prevents the halting of combustion due to the erroneous detection of a combustion abnormality. According to the present invention, a space heater includes: a heating unit control unit, which performs a “heating operation” for igniting fuel gas at a burner to operate a heating fan; an air cleaning unit control unit, which performs an “air cleaning operation” for operating an ion generator and an air cleaning fan; a combustion forced halt unit, for monitoring the combustion state of the burner based on a thermoelectromotive force TC generated by a thermocouple, and for halting combustion at the burner when the thermoelectromotive force TC drops, from a reference value TC_b, the equivalent of a determination level TC_j or more; and a reference value setup unit for, when the mode is shifted from an “independent heating mode”, during which only the “heating operation” is performed, to a “synchronous operating mode”, during which both the “heating operation” and the “air cleaning operation” are performed, designating as the reference value TC_b the thermoelectromotive force TC, generated by the thermocouple 16, that is stabilized after mode switch.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a space heater that has an air cleaning function and that halts combustion at a burner when a combustion abnormality has occurred.

2. Related Background Art

There is, as an example, a well known gas space heater wherein a thermocouple is provided near a burner and combustion at the burner is controlled by monitoring the thermoelectromotive force generated by the thermocouple, and wherein, when the thermoelectromotive force is reduced to a predetermined reference value or lower, due to incomplete combustion at the burner or a misfire, combustion at the burner is forcibly halted. Furthermore, a gas space heater is proposed wherein such a reference value is designated based on the thermoelectromotive force generated by the thermocouple when the burner is in a stable combustion state, thereby preventing the erroneous halting of combustion at the burner when incomplete combustion or a misfire does not actually occur (e.g., Japanese Patent Laid-Open Publication No. Hei 05-223248).

Furthermore, a gas space heater having an air cleaning function has been developed in order to improve the convenience afforded users.

For a space heater having an air cleaning function, a heating fan for supplying air for combustion to a burner and an air cleaning fan for supplying air to an air cleaner must be separately provided in order to independently control the flow rate of the air supplied to the burner and the flow rate of the air supplied to the air cleaner. In addition, as the sizes of space heaters are reduced, there are cases wherein separate air intakes for the heating fan and for the air cleaning fan are located near each other, and cases wherein a single, common air intake is provided for both the heating fan and the air cleaning fan.

A space heater having an air cleaning function selectively performs, in a “synchronous operating mode”, both heating and air cleaning, or performs, in an “independent heating mode”, only heating. However, in both the “synchronous operating mode” and the “independent heating mode”, combustion at the burner must be monitored.

For a space heater wherein the air intake for a heating fan and the air intake for an air cleaning fan are located near each other, and for a space heater wherein a single air intake is provided for the two fans, the present inventors found that even when a reference value for an abnormal combustion was designated while the burner was in a stable combustion state, sometimes a combustion abnormality was erroneously detected and combustion at the burner was halted.

It is, therefore, one objective of the present invention to provide a space heater that has an air cleaning function and that can, by monitoring the combustion state of a burner, prevent combustion at the burner from being halted due to the erroneous detection of a combustion abnormality.

SUMMARY OF THE INVENTION

To achieve this objective, the present invention relates to an improved space heater, comprising:

a burner;

a heating fan for taking in air through a first air intake and supplying the air to the burner, and for propelling, through a warm air grille, air heated by the burner;

an air cleaner;

an air cleaning fan for taking in air through a second air intake located in the vicinity of the first air intake and supplying the air to the air cleaner, and for propelling, through a clean air grille, air purified by the air cleaner;

an operation controller for selectively performing either a heating operation, during which combustion occurs at the burner while the heating fan is being operated, and an air cleaning operation, during which the air cleaner and the air cleaning fan are operated, in a synchronous operating mode, or only the heating operation in an independent heating mode;

a thermocouple for generating a thermoelectromotive force consonant with the combustion state of the burner; and

a combustion forced halt unit for halting combustion at the burner when, during a heating operation, the thermoelectromotive force generated by the thermocouple is lower, by a predetermined determination level, than a predetermined reference value.

Further, provided for the space heater is a reference value setup unit for, when the mode is shifted from the independent heating mode to the synchronous operating mode and a thermoelectromotive force generated by the thermocouple is stabilized thereafter, determines that the thermoelectromotive force is the reference value (corresponds to claim1).

According to this invention, when the mode is shifted from the independent heating mode to the synchronous operating mode and the air cleaning operation is started, and the air cleaning fan is operated and begins to take in air through the second air intake, the flow of air near the first air intake, which is located in the vicinity of the second air intake, fluctuates greatly momentarily, and changes continually thereafter. Because of the change in the flow of air, the flow rate is reduced for air drawn in by the heating fan, through the first air intake, and supplied to the burner. As a result, there is a case wherein the volume of the air supplied for combustion at the burner is reduced, and the thermoelectromotive force generated by the thermocouple becomes lower, by the predetermined determination level, than the reference value designated in the independent heating mode. Therefore, when the reference value designated in the independent heating mode continues to be employed following a shift from the independent heating mode to the synchronous operating mode, even though the indoor density of oxygen is not so low as to cause abnormal combustion at the burner and is sufficient to enable normal combustion, the combustion forced halt unit will erroneously detect oxygen depletion and halt combustion at the burner.

Therefore, when the mode is shifted from the independent heating mode to the synchronous operating mode, and when the thermoelectromotive force generated by the thermocouple is stabilized after the amount of air to be supplied for combustion at the burner has been reduced, the reference value setup unit defines the thermoelectromotive force as the reference value. As a result, the combustion forced halt unit can prevent the halting of combustion at the burner due to the erroneous detection of an abnormal combustion.

Furthermore, a single air intake is provided for use in common as the first air intake and the second air intake (corresponding to claim2).

According to this invention, since the heating fan and the air cleaning fan take in air through the same air intake, when the independent heating mode is shifted to the synchronous operating mode and the air cleaning fan is activated, the reduction in the volume of air supplied to the burner by the heating fan is increased. Therefore, when the mode is shifted from the independent heating mode to the synchronous operating mode, it is especially effective for the reference value setup unit to designate, as the reference value, the thermoelectromotive force, generated by the thermocouple, that is stabilized after the mode has been shifted from the independent heating mode to the synchronous operating mode.

The space heater further comprises:

a first storage unit for storing the reference value used for the independent heating mode,

wherein, immediately before the mode is shifted from the independent heating mode to the synchronous operating mode, the reference value setup unit stores, in the first storage unit, the reference value for the last independent heating mode, and when the mode is next shifted from the synchronous operating mode to the independent heating mode and then a thermoelectromotive force generated by the thermocouple is stabilized, compares the thermoelectromotive force with the reference value stored in the first storage unit,

wherein, when the thermoelectromotive force is greater than the reference value stored in the first storage unit, the reference value setup unit determines that the thermoelectromotive force is a reference value for the present independent heating mode, and updates the reference value in the first storage unit,

wherein, when the thermoelectromotive force is equal to or smaller than the reference value stored in the first storage unit, the reference value setup unit maintains the reference value in the first storage unit as a reference value for the present independent heating mode (corresponds to claim3).

According to this invention, the reference value used in the independent heating mode is stored in the first storage unit. And when the independent heating mode and the synchronous operating mode are selectively performed, e.g., when the mode is shifted from the synchronous operating mode to the independent heating mode, the reference value setup unit compares the reference value, which was used in the preceding independent heating mode and is stored in the first storage unit, with the thermoelectromotive force generated by the thermocouple, which is stabilized after the mode has been shifted.

When the thermoelectromotive force is greater than the reference value stored in the first storage unit, it is assumed that the combustion state of the burner has been rendered satisfactory because an obstacle, such as a curtain, that partially blocked the first air intake in the preceding independent heating mode has now been removed from the first air intake, and the volume of the air supplied to the burner via the first air intake is increased. At this time, the reference value setup unit designates, as a reference value for the present independent heating mode, not the reference value that was previously used in the independent heating mode and is stored in the first storage unit, but the thermoelectromotive force, generated by the thermocouple, that is stabilized after the mode has been shifted from the synchronous operating mode to the present independent heating mode, wherein the combustion state of the burner is now satisfactory. As a result, the combustion forced halt unit can halt combustion at the burner based on a new reference value that is designated in accordance with the change in the combustion state of the burner.

When the thermoelectromotive force generated by the thermocouple, which is stabilized after the mode has been shifted from the synchronous operating mode to the independent heating mode, is equal to or smaller than the reference value stored in the first storage unit, it can be determined that the combustion state of the burner is either unchanged from the preceding independent heating mode, or has been degraded. At this time, the reference value setup unit designates, as a reference value, for the present independent heating mode, the reference value, stored in the first storage unit, for the preceding independent heating mode. As a result, the combustion forced halt unit can halt combustion at the burner in accordance with the degree to which the combustion state of the burner has been degraded from the state existing when the previous independent heating mode was started.

The space heater further comprises:

a unit for changing combustion quantity for the burner at a plurality of levels,

wherein the reference value setup unit stores the reference value for the independent heating mode in the first storage unit for each of the combustion quantities for the burner at the individual levels, and

wherein, when the mode is shifted from the synchronous operating mode to the independent heating mode, the reference value setup unit compares the thermoelectromotive force generated by the thermocouple at the time that the thermoelectromotive force is stabilized after the mode shift, with the reference value that is consonant with a combustion quantity for the burner that is stored in the first storage unit at the time of the mode shift (corresponds to claim4).

According to this invention, in accordance with the combustion quantity for the burner, the reference value setup unit designates the reference value for the independent heating mode. Therefore, the reference value can be determined by reflecting the relationship between the thermoelectromotive force generated by the thermocouple and the combustion state of the burner, which varies in accordance with the combustion quantity, and the combustion forced halt unit can more accurately detect a combustion abnormality at the burner and halt the combustion process.

The space heater further comprises:a unit for changing combustion quantity for the burner at a plurality of levels; and

a first storage unit for storing the reference value for the independent heating mode,

wherein, when the combustion quantity for the burner is changed in the independent heating mode, the reference value setup unit stores, for each of the combustion quantities for the burner at the individual levels, in the first storage unit, the reference value just before the change of the combustion quantity,

wherein, when the combustion quantity for the burner is next changed, the reference value setup unit compares the thermoelectromotive force generated by the thermocouple at the time that the thermoelectromotive force is stabilized thereafter, with the reference value that is consonant with the combustion quantity for the burner after the change of the combustion quantity and is stored in the first storage unit,

wherein, when the thermoelectromotive force is greater than the reference value stored in the first storage unit, the reference value setup unit determines that the thermoelectromotive force is a reference value for the present independent heating mode, and updates the reference value in the first storage unit, and

wherein, when the thermoelectromotive force is equal to or smaller than the reference value stored in the first storage unit, the reference value setup unit maintains the reference value stored in the first storage unit as a reference value for the present independent heating mode (corresponds to claim5).

According to this invention, when the combustion quantity for the burner is changed in the independent heating mode, the reference value setup unit compares with the reference value that is consonant with the preceding combustion quantity and is stored in the first storage unit, a reference value that is consonant with the combustion quantity for the burner that has newly been designated. As a result, the reference value can be determined in accordance with how combustion at the burner has been changed from the state wherein the preceding combustion quantity was effective to the state wherein the present combustion quantity is effective. Further, the combustion forced halt unit can more accurately detect a combustion abnormality at the burner and halt the combustion process.

The space heater further comprises:

a second storage unit for storing a reference value for the synchronous operating mode,

wherein, when the mode is shifted from the synchronous operating mode to the independent heating mode, the reference value setup unit stores, in the second storage unit, the reference value for the last synchronous operating mode, and when the mode is next shifted from the independent heating mode to the synchronous operating mode and then a thermoelectromotive force generated by the thermocouple is stabilized, compares the thermoelectromotive force with the reference value stored in the second storage unit,

wherein, when the thermoelectromotive force is greater than the reference value stored in the second storage unit, the reference value setup unit determines that the thermoelectromotive force is a reference value for the present synchronous operating mode, and updates the reference value in the second storage unit, and

wherein, when the thermoelectromotive force is equal to or smaller than the reference value stored in the second storage unit, the reference value setup unit maintains the reference value in the second storage unit as a reference value for the present synchronous operating mode (corresponds to claim6).

According to this invention, the reference value for the synchronous operating mode is stored in the second storage unit. When the shift from the independent heating mode to the synchronous operating mode is made, e.g., when the mode is shifted from the independent heating mode to the synchronous operating mode, the reference value setup unit compares the thermoelectromotive force generated by the thermocouple, which is stabilized following the mode shift, with the reference value that was used for the preceding synchronous operating mode and is stored in the second storage unit.

When the thermoelectromotive force is greater than the reference value stored in the second storage unit, it is assumed that for the burner a more satisfactory combustion state exists than in the preceding synchronous operating mode. Therefore, as a reference value for the present synchronous operating mode, the reference value setup unit does not designate the reference value for the preceding synchronous operating mode, which is stored in the first storage unit, but the thermoelectromotive force generated by the thermocouple, which is stabilized following the start of the present synchronous operating mode, in which the combustion state of the burner is satisfactory. As a result, the combustion forced halt unit can halt combustion at the burner by using a new reference value that is designated in accordance with the change in the combustion state of the burner.

When the mode is shifted from the independent heating mode to the synchronous operating mode, and the thermoelectromotive force generated by the thermocouple, which is stabilized thereafter, is equal to or smaller than the reference value stored in the second storage unit, it is determined that the combustion state of the burner is either unchanged or has been degraded, compared with the state that existed in the preceding synchronous operating mode. Therefore, as a reference value for the present synchronous operating mode, the reference value setup unit designates the reference value that was used for the preceding synchronous operating mode and is stored in the second storage unit. As a result, the combustion forced halt unit can halt combustion at the burner in accordance with the degree to which the combustion state of the burner has been degraded since the start of the preceding synchronous operating mode.

The space heater of the invention further comprises:

a unit for changing a combustion quantity for the burner at a plurality of levels,

wherein the reference value setup unit stores the reference value for the synchronous operating mode in the second storage unit for each of the combustion quantity for the burner at the individual levels, and

wherein, when the mode is shifted from the independent heating mode to the synchronous operating mode, the reference value setup unit compares the thermoelectromotive force generated by the thermocouple at the time that the thermoelectromotive force is stabilized after the mode shift, with the reference value that is consonant with a combustion quantity for the burner and is stored in the second storage unit (corresponds to claim7).

According to the present invention, the reference value setup unit designates the reference value for the synchronous operating mode in accordance with the combustion quantity for the burner. As a result, the reference value is designated by reflecting the relationship between the combustion state of the burner, which fluctuates in accordance with the combustion quantity for the burner, and the thermoelectromotive force generated by the thermocouple. Further, the combustion forced halt unit can more accurately detect a combustion abnormality at the burner and halt the combustion process.

The space heater further comprises:

a unit for changing a combustion quantity for the burner at a plurality of levels; and

a second storage unit for storing a reference value for the synchronous operating mode,

wherein, when the combustion quantity for the burner is changed in the synchronous operating mode, the reference value setup unit stores, for each of the combustion quantities for the burner at the individual levels, in the second storage unit, a reference value used just before the change of the combustion quantity,

wherein, when the combustion quantity for the burner is next changed, the reference value setup unit compares the thermoelectromotive force generated by the thermocouple at the time that the thermoelectromotive force is stabilized, with the reference value that is consonant with the combustion quantity for the burner after the change of the combustion quantity and is stored in the second storage unit,

wherein, when the thermoelectromotive force is greater than the reference value stored in the second storage unit, the reference value setup unit determines that the thermoelectromotive force is a reference value for the present synchronous operating mode, and updates the reference value in the second storage unit, and

wherein, when the thermoelectromotive force is equal to or smaller than the reference value stored in the second storage unit, the reference value setup unit maintains the reference value in the second storage unit as a reference value for the present synchronous operating mode (corresponds to claim8).

According to this invention, when the combustion quantity for the burner is changed in the synchronous operating mode, the reference value setup unit compares the reference value consonant with the combustion quantity for the burner that is stored in the second storage unit, which is consonant with the preceding combustion quantity, with the reference value that is consonant with the present combustion quantity for the burner. Therefore, the reference value is designated in accordance with the change in the combustion state of the burner, i.e., the change between the state for the preceding combustion quantity and the state for the present combustion quantity. Furthermore, the combustion forced halt unit can more accurately detect a combustion abnormality at the burner and halt the combustion process.

The space heater further comprises:

a combustion quantity change unit for changing a combustion quantity for the burner; and

a determination level change unit for reducing the predetermined determination level as the combustion quantity for the burner is increased (corresponds to claim9).

According to the present invention, the thermoelectromotive force generated by the thermocouple varies not only in consonance with the combustion state of the burner, but also in consonance with the combustion quantity for the burner. As combustion at the burner is increased, the drop in the thermoelectromotive force generated by the thermocouple, due to the degrading of the combustion state, tends to be reduced. Therefore, as the combustion quantity for the burner is increased, the determination level change unit reduces the predetermined determination level to suppress an affect produced by a change in the combustion quantity for the burner, and the combustion forced halt unit can halt the combustion process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment and a second embodiment of the present invention will now be described while referring toFIGS. 1 to 8.FIG. 1is a front view of a gas space heater with an air cleaning function;FIG. 2is a cross-sectional view of the gas space heater inFIG. 1;FIG. 3is a control block diagram showing the gas space heater inFIG. 1;FIGS. 7(a) to7(c) are graphs showing a change in the thermoelectromotive force generated by a thermocouple during the operation of the gas space heater; andFIGS. 4 to 6and8are flowcharts showing the operation of the space heater.

First Embodiment

FIG. 1is a front view of a gas space heater1(corresponding to a space heater according to the present invention) wherein the front panel of a body case2has been removed. The gas space heater1comprises: an air cleaning unit3, a heating unit4and a controller5for controlling the operation of the gas space heater1. The air cleaning unit3includes: an ion generator6, for using plasma radiation to generate positive ions (H+) and/or negative ions (O2−); and an air cleaning fan7, of a sirocco type, for propelling outward, indoors, ions generated by the ion generator6.

The heating unit4includes: a burner11, arranged in a combustion case10; and a heating fan13, for supplying air for combustion to the burner11, and for propelling indoors, through a warm air grille12, air that is heated by the burner11. A common air intake15(corresponding to a first air intake and a second air intake according to the invention) is provided in the rear face of the gas space heater1, and the air cleaning fan7and the heating fan13take in indoor air through the common air intake15. The heating unit4further includes: a thermocouple16, for detecting the combustion state of the burner11; a solenoid valve (not shown), for opening or closing a gas supply pipe (not shown) along which a fuel gas is supplied to the burner11; a proportioning valve (not shown), for adjusting the opening of the gas supply pipe; an igniter (not shown), for igniting a fuel gas at the burner11; and a room temperature sensor (not shown), for detecting room temperatures.

The controller5is an electronic unit, constituted, for example, by a microcomputer and a memory, that performs a “heating operation”, for indoor heating, and an “air cleaning operation”, for cleaning indoor air. There are three operating modes: an “independent heating mode”, for performing only the “heating operation”, an “independent air cleaning mode”, for performing only the “air cleaning operation”, and a “synchronous operating mode”, for performing both the “heating operation” and the “air cleaning operation”.

While referring toFIG. 2, a common air filter is detachably provided for the common air intake15to cover the entire face, and air drawn in through the common air filter20and the common air intake15is supplied to the air cleaning unit3and the heating unit4. An operation panel21, including various operating switches, is provided on the front of the upper face of the body case2, and a warning lamp22, for notifying a user that the air cleaning unit3or the heating unit4has been halted, and a filter lamp23, for providing notification that the common air filter20requires cleaning, are provided on the upper portion of the front face of the body case2.

When the “heating operation” is started, the controller5activates the heating fan13for the combustion of fuel gas at the burner11. Then, the fuel gas is burned using secondary combustion air, which is drawn in at the common air intake15and supplied, via a secondary combustion air inlet25, to a combustion chamber10, and primary combustion air that is drawn in at a primary combustion air inlet (not shown). Gas generated by combustion passes from above the burner11, through the upper portion of the combustion chamber10, and is discharged.

The combustion gas discharged from the upper portion of the combustion chamber10and air drawn in through the common air intake15are mixed, between a partition26and the combustion chamber10. Furthermore, to cool the body case2, part of the air drawn in through the common air intake15, by the rotation of the heating fan13, flows downward between the body case2and the partition26, whence it is supplied to the heating unit4through a slit27. Then, in the heating unit4, the air is mixed with an air mixture flowing in from the top, and the resultant mixed air is propelled indoors, at an appropriate temperature, through the warm air grille12.

When the “air cleaning operation” is started, the controller5activates the air cleaning fan7and the ion generator6. And a dust collection filter30, located behind the air cleaning unit3, captures dust particles that are not removed by the common air filter20. Together with the air supplied via the dust collection filter30, the air cleaning fan7propels out, through a clean air grille31, ions (positive ions and/or negative ions) generated by the ion generator6. The ions so dispersed are used to disinfect indoor air.

While referring toFIG. 3, the controller5is connected to the operation panel21, the thermocouple16, an igniter60, a solenoid valve61, a proportioning valve62, the heating fan13, a room temperature sensor17, the ion generator6, the air cleaning fan7, the warning lamp22and the filter lamp23. The controller5controls the operation of the air cleaning unit3and the heating unit4in accordance with control signals that the controller5receives from a heating start switch50, an air cleaning start switch51and a temperature setup switch52on the operation panel21.

The controller5further includes: a combustion forced halt unit40, a heating unit control unit41, a reference value setup unit42, an air cleaning unit control unit44and a display control unit45. A first memory70(corresponding to the first storage unit according to the invention) and a second memory71(corresponding to the second storage unit according to the invention) will be described later while referring to a second embodiment of the present invention.

During the “heating operation”, the combustion forced halt unit40monitors a thermoelectromotive force TC generated by the thermocouple16, and halts combustion at the burner11when there is a reduction, equivalent to a predetermined determination level TC_j, in the thermoelectromotive force TC, which has a predetermined reference value TC_b.

The heating unit control unit41, to perform the “heating operation”, controls the operations of the igniter60, the solenoid valve61, the proportioning valve62and the heating fan13. For the “heating operation”, the heating unit control unit41performs a “temperature adjustment” process during which the combustion quantity for the burner11is changed to one of seven levels (corresponds to a plurality of levels in accordance with the present invention), the first level (the lowest) to the seventh level (the highest), in accordance with a difference between a target temperature, designated by manipulating the temperature setup switch52, and a temperature detected by the room temperature sensor17, so that the two temperatures correspond.

The combustion quantity for the burner11is altered by changing the amount of fuel gas supplied to the burner11via the proportioning valve62and the amount of air supplied to the burner11by the heating fan13. The proportioning valve62and the heating fan13respectively correspond to the means of the invention for changing the combustion of the volume of the burner at a plurality of levels and the means of the invention for changing the combustion quantity for the burner.

The air cleaning unit control unit44controls the operations of the ion generator6and the air cleaning fan7to perform the “air cleaning operation”. And the display control unit45turns on/off the warning lamp22and the filter lamp23.

While referring to the flowcharts inFIGS. 4 to 6, an explanation will be given for the processing performed by the heating unit control unit41, the reference value setup unit42and the combustion forced halt unit40in the “independent heating mode” and in the “synchronous operating mode”. The processing inFIG. 4is performed by the heating unit control unit41. When a user turns on the heating start switch50at STEP1, the “heating operation” is started at STEP2, and the heating unit control unit41ignites the fuel gas at the burner11.

At STEP2, the heating unit control unit41starts the revolution of the heating fan13at a predetermined ignition speed. When at STEP3the heating fan13is revolving normally, at near the predetermined ignition speed, the igniter60is turned on at STEP4, the solenoid valve61is opened at STEP5, the opening of the proportioning valve62is adjusted in accordance with a predetermined amount of gas to be ignited at STEP6, and the gas at the burner11is ignited. When the heating fan13is not revolving normally, program control branches to STEP30to halt the “heating operation”. At this time, an abnormal operation notification is provided by the display control unit45using the warning lamp22.

At STEP7, the heating unit control unit41starts a forced hold timer to determine whether ignition at the burner11has occurred, and performs the loop at STEPs8and40. At STEP8, a check is performed to determine whether the thermoelectromotive force TC generated by the thermocouple16has attained a predetermined ignition detection or higher level. When the thermoelectromotive force TC has attained the ignition detection or higher level, at STEP9the igniter60is turned off. When at STEP8the thermoelectromotive force generated by the thermocouple16has not reached the ignition detection level, program control branches to STEP40to determine whether the time designated for the forced hold timer has expired.

When the time designated for the forced hold time has not expired, program control returns to STEP8. When the time designated for the forced hold timer has expired, i.e., when at STEP8ignition at the burner11is not detected within the period (e.g., thirty seconds) set for the forced hold timer, at STEP41, the heating unit control unit41halts the “heating operation”. At this time, an abnormal operation notification is provided by the display control unit45using the warning lamp22.

When ignition at the burner11is detected, at STEP10, the heating unit control unit41starts a stable combustion wait timer. When the time designated for the stable combustion wait timer has expired at STEP11, at STEP12, the heating unit control unit41starts the “temperature adjustment” process and program control advances to STEP13inFIG. 5.

The processing at STEPs13to17inFIG. 5is performed by the reference value setup unit42. At STEP13, the reference value setup unit42starts a combustion quantity unchanged timer, and performs the loop at STEPs14to16. That is, the reference value setup unit42determines at STEP14whether the air cleaning start switch51has been manipulated, determines at STEP15whether the combustion quantity for the burner11has been changed, and waits at STEP16until the time designated for the combustion quantity unchanged timer has expired.

When the air cleaning start switch51has been manipulated at STEP14, or when the combustion quantity for the burner11has been changed at STEP15, program control branches to STEP13, and the combustion forced halt unit40restarts the combustion quantity unchanged timer. As a result, when the mode is shifted from the “independent heating mode” to the “synchronous operating mode”, or from the “synchronous operating mode” to the “independent heating mode” through manipulation of the air cleaning start switch51, following the mode shift, there is a wait until the period (e.g., thirty seconds) set for the combustion quantity unchanged timer has elapsed.

When the combustion quantity for the burner11is changed, following the change there is a wait until the period set for the combustion quantity unchanged timer has elapsed. When the time designated for the combustion quantity unchanged timer has expired at STEP16, at STEP17the combustion forced halt unit40designates, as the reference value TC_b, the present thermoelectromotive force TC_s generated by the thermocouple16.

The processing at STEPs18to23and STEP50is performed by the combustion forced halt unit40. When the combustion quantity for the burner11at STEP18is at the first or second level, at STEP19, the combustion forced halt unit40designates the determination level TC_j as TC_lo for a small combustion quantity. When the combustion quantity for the burner11at STEP18is at a third to seventh level, program control branches to STEP50, and the combustion forced halt unit40designates the determination level TC_j as TC_hi (<TC_lo) for a large combustion quantity.

Then, the combustion forced halt unit40performs the loop at STEPs20to23to monitor the combustion state of the burner11. When, at STEP20, the present thermoelectromotive force TC_s generated by the thermocouple16is reduced from the reference value TC_b by an amount equivalent to the determination level TC_j or more (TC_s≦TC_b−TC_j), program control is shifted to STEP60inFIG. 6.

At STEP60, the combustion forced halt unit40starts an oxygen depletion timer to prevent an erroneous detection due, for example, to electric noise, and performs the loop at STEPs61to63and STEP70. The period set for the oxygen depletion timer is, for example, ten seconds. When the air cleaning start switch51has not been manipulated at STEP61, when the combustion quantity for the burner11has not been changed at STEP62, when at STEP70, the thermoelectromotive force TC_s generated by the thermocouple16is lower than the reference value TC_b by an amount equivalent to the determination level TC_j, or more, and when the time set for the oxygen depletion timer has expired at STEP63, program control advances to STEP64and the combustion forced halt unit40halts combustion at the burner11to stop the heating operation.

Through this processing, combustion at the burner11is prevented from continuing in the degraded combustion state. At this time, the display control unit45uses the warning lamp22to provide an error notification.

When, At STEP61, the air cleaning start switch51is manipulated to start/halt the “air cleaning operation”, and when at STEP62the combustion quantity for the burner11is changed, the combustion condition for the burner11is also changed, so that program control branches to STEP13inFIG. 5and the reference value TC_s and the determination level TC_j are redesignated. Then, when at STEP70, the present thermoelectromotive force TC_s generated by the thermocouple16is higher than a level that is lower than the reference value TC_b by the determination level TC_j (TC_s>TC_b−TC_j), program control branches to STEP20inFIG. 5to again perform the loop at STEPs20to23.

When the air cleaning start switch51is manipulated at STEP21inFIG. 5, and when the combustion quantity for the burner11is changed at STEP22, the combustion condition at the burner11is also changed, so that program control branches to STEP13, and the reference value TC_b and the determination level TC_j are redesignated. Thereafter, when the heating start switch50is turned off at STEP23, program control advances to STEP24and the “heating operation” is terminated.

FIGS. 7(a) to7(c) are graphs showing a change in the thermoelectromotive force TC generated by the thermocouple16after the reference value TC_b and the determination level TC_j have been decided. The vertical axis represents the thermoelectromotive force TC, and the horizontal axis represents the time t. Shown inFIG. 7(a) is an example wherein the stable reference value TC_b and the determination level TC_j are decided in the “independent heating mode”; thereafter, this mode is continued. In this example, the thermoelectromotive force TC begins to drop at a time t10, whereat a reduction in the indoor oxygen density is begun, and at a time t11, whereat the thermoelectromotive force TC is reduced, from the reference value TC_b, by the determination level TC_j, combustion at the burner11is halted by the combustion forced halt unit40.

InFIG. 7(b) is shown an example wherein the stable reference value TC_b and the determination level TC_j are decided in the “independent heating mode”, and thereafter, the “air cleaning operation” is started and the mode is shifted to the “synchronous operating mode”. As is shown inFIG. 2, since the heating fan13and the air cleaning fan7take in air through the common air intake15, at a time t20, whereat the “air cleaning operation” is begun, the volume of the air drawn in through the common air intake15by the heating fan13and supplied to the burner11is reduced.

As a result, the thermoelectromotive force TC generated by the thermocouple16is reduced, and when the combustion state of the burner11is monitored using the stable reference value TC_b and the determination level TC_j that have been decided in the “independent heating mode”, combustion at the burner11is halted by the combustion forced halt unit40at a time t22whereat the reduction in the thermoelectromotive force TC, from a time t21whereat the thermoelectromotive force TC is leveled off and stabilized is smaller than the determination level TC_j. In this case, even though the indoor oxygen density is not yet low enough to require the halting of combustion at the burner11, it is determined that the oxygen density is low, and combustion at the burner11is halted, i.e., an “early stop” occurs.

InFIG. 7(c) is shown an example wherein the processing inFIG. 5is performed. When the stable reference value TC_b and the determination level TC_j are decided in the “independent heating mode”, and thereafter, the “air cleaning operation” is started and the mode is shifted to the “synchronous operating mode”, at STEP21, inFIG. 5, program control branches to STEP13.

At a time t30, whereat the time designated at the combustion quantity unchanged timer is up at STEP16, at STEP17, the reference value TC_b is redesignated, and at STEP19or STEP50, the determination level TC_j is redesignated. As a result, at a time t31, whereat the thermoelectromotive force TC generated by the thermocouple16drops, from the redesignated reference value TC_b, the equivalent of the determination level TC_j or more, combustion at the burner11is halted by the combustion forced halt unit40. In this case, combustion at the burner11can be halted while the occurrence of an “early stop”, described above, can be prevented.

Second Embodiment

A second embodiment of the present invention will now be described. The configuration of a space heater for this embodiment is the same as that for the first embodiment, with the exceptions that, while referring toFIG. 3, a first memory70(corresponding to the first storage unit according to the invention) and a second memory71(corresponding to the second storage unit according to the invention) are provided, and that a reference value setup unit42employs a different method for designating a reference value TC_b.

While referring toFIG. 3, reference values TC_m1(1) (for first level) to TC_m1(7) (for seventh level) are stored in the first memory70in consonance with the individual combustion quantities (first level to seventh level) for a burner11in the “independent heating mode”. Further, reference values TC_m2(1) (for first level) to TC_m2(7) (for seventh level) are stored in the second memory71in consonance with the combustion quantities (first level to seventh level) for the burner11in the “synchronous operating mode”. When the “heating operation” is started by manipulating the heating start switch50, an initial value of 0 is set as the reference values TC_m1(1) to TC_m1(7) in the first memory70and the reference values TC_m2(1) to TC_m2(7) in the second memory71.

A reference value setup unit42performs the processing in the flowchart inFIG. 8to designate a reference value TC_b. Processes other than the designation of the reference value TC_b are the same as those for the first embodiment shown inFIGS. 4 to 6.

First, at STEP100, the reference value setup unit42substitutes, into a variable n, the present combustion quantity (one of first level to seventh level) for the burner11. When the present mode is the “synchronous operating mode” at STEP101, program control branches to STEP110, or when the present mode is the “independent heating mode”, program control advances to STEP102. At STEP102, the reference value TC_m1(n) for the nth level in the “independent heating mode” is read from the first memory70, and is substituted into a variable TC_m. On the other hand, at STEP110, the reference value TC_m2(n) for the nth level in the “synchronous operating mode” is read from the second memory71, and is substituted into the variable TC_m.

At STEP103, the reference value setup unit42compares the present thermoelectromotive force TC_s generated by a thermocouple16with the variable TC_m. When the present thermoelectromotive force TC_s is equal to or greater than the variable TC_m, program control advances to STEP104, and the reference value setup unit42designates as the reference value TC_b the present thermoelectromotive force TC_s. Whereas when at STEP105the present mode is the “synchronous operating mode”, program control branches to STEP130and the reference value TC_b is stored in the second memory71to update the value TC_m2(n). When, however, the present mode is the “independent heating mode”, program control advances to STEP106and the reference value TC_b is stored in the first memory70to update the value TC_m1(n).

When, at STEP103, the present thermoelectromotive force generated by the thermocouple16is smaller than the variable TC_m, program control branches to STEP120and the reference value setup unit42designates the variable TC_m as the reference value TC_b. In this case, the reference values TC_m1(1) to TC_m1(7), in the first memory70, and TC_m2(1) to TC_m2(7), in the second memory71, are not updated.

When, at STEP103, the present thermoelectromotive force TC_s generated by the thermocouple16is smaller than the preceding stable value TC_m for the combustion quantity that is currently designated, it can be assumed that the combustion state of the burner11is either unchanged or has been degraded (the indoor oxygen density is either unchanged or reduced). In this case, at STEP120, the preceding stable reference value TC_m is determined to be a stable reference value TC_b, and the reduction in the thermoelectromotive force TC generated by the thermocouple16, which is continued from the state having the preceding combustion quantity, can be monitored.

When, at STEP103, the present thermoelectromotive force TC_s generated by the thermocouple16is equal to or greater than the preceding stable reference value TC_m that is held for the present combustion quantity, it can be assumed, for example, that the space wherein the gas space heater1is located is well ventilated and that the indoor oxygen density has been increased, so that the combustion condition is changed and the combustion state of the burner11is satisfactory.

In this case, program control advances to STEP104, and the reference value setup unit42designates the present thermoelectromotive force TC_s generated by the thermocouple16as a new reference value TC_b. Thus, based on the new reference value TC_b that is designated in accordance with the altered combustion condition, the combustion forced halt unit40can detect a combustion abnormality and halt combustion at the burner11.

In the “independent heating mode”, at STEP106, the reference value TC_b that is stored as the value TC_m1(n) in the first memory70, in consonance with the nth speed, is updated, or in the “synchronous operating mode”, at STEP130, the reference value TC_b that is stored as the value TC_m2(n) in the second memory71, in consonance with the nth speed, is updated. As a result, a value (TC_m) is obtained that is required at STEP103for comparison with the reference value in the next “heating operation” at the nth speed.

In the first embodiment, at STEPs13to16inFIG. 5, the elapse of the time allocated for the combustion quantity unchanged timer is awaited in order to determine whether combustion at the burner11has been stabilized. As another method, when the change in the thermoelectromotive force generated by the thermocouple16is continued within a predetermined range and for a predetermined period of time, it can be determined that combustion at the burner11has been stabilized.

Further, for the above embodiments, the gas space heater has been employed as a space heater according to the invention. However, the present invention can also be applied for a space heater that employs another fuel, such as kerosene.

Furthermore, for the gas space heater in the above embodiments, the air intake is used in common for the air cleaning fan and the heating fan. However, when an air intake is provided separately in the vicinity of the air intake for the air cleaning fan, the volume of the air drawn in by the heating fan may be changed as the air cleaning fan is started or halted. Also in this case, the present invention is effective.