Heating cooking appliance

Abstract: A heating cooking appliance includes a high frequency oscillator (22) for high frequency heating food contained in a cooking chamber (12), a heater for heating the food, a damper (21) rotatably mounted for controlling supply of outside air into the cooking chamber (12) and a motor (26) driving the damper (21) so that the damper (21) is closed and opened, a position detector (28, 29) for detecting positions of the damper (21) when the damper (21) is closed and opened and a controller (17) for controlling the motor (26) based on a position detection signal generated by the position detector (28, 29).

Description: This invention relates to a heating cooking appliance comprising a high frequency oscillator for high frequency heating food contained in a cooking chamber and a heater for heating the food and starts from US-A-4,450,344. A damper is rotatably mounted in the heating cooking appliance of the type described above for controlling supply of an outside air into a cooking chamber. The damper is driven by a motor so as to be opened and closed. The damper is opened during the high frequency heating so that the outside air is supplied into the cooking chamber while it is closed during the heating by the heater so that the outside air is prevented from entering the cooking chamber. FIGS. 18 and 19(a) to 19(d) illustrate one such conventional construction. Referring to FIG. 18, a motor 1 driving a damper (not shown) through a crank mechanism (not shown) is connected between power supply bus lines 3 and 4 both extended from an ac power source 2. Microswitches 5 and 6 and a relay switch 7 are connected between the motor 1 and the power supply bus line 4, as shown. The microswitch 5 is turned off when the damper is closed while it is turned on when the damper is opened. The microswitch 6 is turned on when the damper is closed while it is turned off when the damper is opened. The relay switch 7 is controlled by a control circuit 8 so that it is turned on when contacts c and a are closed and it is turned off when the contacts c and b are closed. The contacts c and b of the relay switch 7 are closed when the damper in the closed state as shown in FIG. 18 is opened, whereby the motor 1 is energized so that the damper is rotatively moved via the crank mechanism. When the damper is opened, the microswitch 6 is turned off to deenergize the motor 1 as shown in FIG. 19(b), thereby holding the damper in the open state. In order that the damper is closed, the contacts c and a of the relay switch 7 are closed, as shown in FIG. 19(c), whereby the motor 1 is energized to rotatively move the damper via the crank mechanism. The microswitch 5 is turned off to deenergize the motor 1 when the damper is closed, as shown in FIG. 19(d), thereby holding the damper in the closed state. In accordance with the above-described construction, two microswitches 5, 6 are employed so that the motor 1 is energized and deenergized when the damper is opened and closed. Further, two cams are mounted on a drive shaft of the motor 1 so that the microswitches are operated. Thus, the number of parts are increased and the construction is complicated. Additionally, the motor 1 is continuously energized unnecessarily when either of the microswitches is not normally operated because of failure, so that the damper is alternately opened and closed repeatedly. When such a damper malfunction occurs during cooking by the heating of the heater not by the high frequency oscillator, hot air in the cooking chamber is caused to be exhausted from the same since the outside air is supplied into the cooking chamber. Consequently, the atmospheric temperature in the cooking chamber is not sufficiently increased, which prevents execution of the normal cooking. US-A-4,450,344 discloses a combined microwave and electric heater oven including a fan system for cooling a magnetron, and a damper for selectively introducing a forced air flow generated by the fan system into an oven cavity. A damper cam is secured to a drive shaft of a damper motor, and a damper link is disposed between the damper cam and the damper to drive the damper. A microswitch is disposed near the damper cam so that the microswitch develops a first detection signal when the damper is tightly closed. In response to the first detection signal, the rotation of the damper motor is terminated to hold the damper in the tightly closed state. The microswitch develops a second detection signal when the damper is placed in the full-open state. In response to the second detection signal, the rotation of the damper motor is terminated to hold the damper in the full-open state. An object of the present invention is to provide a heating cooking appliance wherein the construction for opening and closing the damper can be simplified, the number of parts necessitating adjustment can be reduced and, yet, the damper can reliably be opened and closed. According to the present invention, there is provided a heating cooking appliance comprising a high frequency oscillator for high frequency heating food contained in a cooking chamber, a heater for heating the food, a damper rotatably mounted for controlling supply of outside air into the cooking chamber and a motor driving the damper so that the damper is closed and opened, position detecting means for detecting positions of the damper when the damper is closed and opened and control means for controlling the motor based on a position detection signal generated by the position detecting means, characterized by abnormal condition detecting means for detecting an abnormal condition of the damper closed and opened, based on the position detection signal generated by the position detecting means, heating control means for controlling the high frequency oscillator and the heater so that the high frequency oscillator and the heater are deenergized when the abnormal condition of the damper closed and opened is detected by the abnormal condition detecting means and warning means for warning of the abnormal condition of the damper when the abnormal condition of the damper is detected by the abnormal condition detecting means. Preferably, the abnormal condition of the damper is detected by the abnormal condition detecting means when the position detection signal indicative of the closed state of the damper is continuously generated by the position detecting means where the damper is driven to be opened, when the position detection signal indicative of the open state of the damper is continuously generated by the position detecting means where the damper is driven to be closed or when the position detection signals indicative of the respective closed and open states of the damper are alternately generated by the position detecting means repeatedly where the damper is driven to be opened or closed and the warning means comprises a buzzer or a display device. Preferably, the control means is arranged so that the damper is rotatively moved so as to be set to an initial position when a power supply is put to the heating cooking appliance. Preferably, the position detecting means comprises a cam rotated by the motor so that a rotative movement of the cam is interlocked with closing and opening operations of the damper and a microswitch turned on and off by the cam. The heating cooking appliance may be further characterized by an opening formed in one of walls of the cooking chamber so as to be closed and opened by the damper, a duct on which the damper is rotatably mounted through a damper shaft, the duct being provided for guiding the outside air to the opening, a tension coil spring provided between the damper and the cooking chamber wall with the opening for urging the damper in a direction that the damper is closed and that the duct has elongated grooves supporting the damper shaft, the grooves being formed so as to be elongated in a direction that a spring force of the tension coil spring acts. The heating cooking appliance may be further characterized by an opening formed in one of walls of the cooking chamber so as to be closed and opened by the damper and a duct on which the damper is rotatably mounted through a damper shaft, the duct being provided for guiding the outside air to the opening, the damper having a positioning portion for positioning the damper shaft and a caulking portion for caulking the damper shaft such that the damper shaft is secured. The invention will be described, merely by way of example, with reference to the accompanying drawings, in which: FIG. 1 schematically illustrates an electrical arrangement of a heating cooking appliance of a first embodiment in accordance with the present invention; FIG. 2 is a time chart for explaining operations of a relay switch and a microswitch employed in the appliance in the course of a cooking operation; FIG. 3 is a partial transverse sectional view of the appliance; FIG. 4 is a longitudinal sectional view of the appliance; FIG. 5 is an exploded perspective view of a damper, motor and their peripheral parts; FIG. 6 is a front view of the heating cooking appliance of a second embodiment with a door open; FIG. 7 is a transverse sectional view of a machine compartment; FIG. 8 is a perspective view of the damper; FIG. 9 is an enlarged view showing the state of the damper shaft before it is caulked; FIG. 10 is an enlarged view showing the state of the damper shaft after it is caulked; FIG. 11 is an exploded perspective view of the damper, duct and their peripheral parts; FIG. 12 is an exploded perspective view of the damper drive mechanism; FIG. 13 is a partial top plan view in the condition that the damper is opened; FIG. 14 is a partial top plan view in the condition that the damper is closed; FIGS. 15(a) and 15(b) are top plan view of a cam and a microswitch and a time chart showing changes in the output signal of the microswitch, respectively; FIG. 16 is an electrical circuit diagram of the appliance; FIG. 17 is a time chart for explaining operations of the relay switch and the microswitch in the course of the cooking operation; FIG. 18 is a view similar to FIG. 1 illustrating a conventional arrangement; FIGS. 19 (a) to 19(d) are circuit diagrams for explaining operations of the relay switch and the microswitches; and FIG. 20 is a view similar to FIG. 14 showing another conventional construction. A first embodiment in which the heating cooking appliance of the invention is applied to an electronic cooking range with oven and grille functions will now be described with reference to FIGS. 1 to 5. Referring first to FIGS. 3 and 4, a cooking chamber 12 having a front opening is provided in a range cabinet 11. A door 13 is mounted on the range cabinet 11 so as to open and close the front opening of the cooking chamber 12. A machine compartment 33 is provided at the right-hand side of the cooking chamber 12, as viewed in FIG. 3. A cooling fan 14 is mounted on the rear wall of the machine compartment 33 and a printed wiring board 15 is provided at the front interior of the machine compartment 33. Electronic parts including a dc drive type relay 16 and a microcomputer 17 (see FIG. 1) are provided on the printed wiring board 15. An operation control program is stored in the microcomputer 17 so that the microcomputer 17 serves as control means, heating control means and abnormal condition detecting means, as will be described later. A right-hand partitioning wall 18 of the cooking chamber 12 has a number of openings or vent holes 19, as viewed in FIG. 3. A duct 20 is also mounted on the partitioning wall 18 at the machine compartment side. An outside air introduced by the fan 14 is guided by the duct 20 to be supplied into the cooking chamber 12 through the vent holes 19. The vent holes 19 are opened and closed by a damper 21 which will be described later. A high frequency oscillator for high frequency heating food contained in the cooking chamber, for example a magnetron 22, is provided between the cooling fan 14 and the duct 20 in the machine compartment 33. A heater (not shown) also heating the food in the cooking chamber 12 is provided in the cooking chamber 12. The damper 21 will be described in detail with reference to FIG. 5. The damper 21 is formed into the shape of a generally rectangular plate. A damper shaft 23 is extended through a hole formed through a projection 21a formed by bending the lower end of the damper 21 and an engagement portion 23a formed by bending the upper end of the damper shaft 23 at a right angle is engaged with an engagement concave portion 21c formed in a projection 21b formed by bending the left-hand upper portion of the damper 21. The damper shaft 23 is welded along the left-hand end of the damper 21 by way of the spot welding, as viewed in FIG. 5. The damper shaft 23 is rotatably mounted on a bearing (not shown) provided on the partitioning wall 18 such that the damper shaft 23 is rotatively moved with the damper 21. A coil spring 24 is interposed between an engagement strip 21d formed by bending the projection 21b and the partitioning wall 18 to usually urge the damper 21 such that the vent hole 19 is closed by the damper 21. A motor mounting plate 25 is mounted on the partitioning wall 18 below the duct 20. A motor 26 is mounted on the underside of the motor mounting plate 25. The motor 26 is equipped with a reduction gear mechanism and a drive shaft 27 of the motor 26 is upwardly extended through a hole formed in the mounting plate 25. A generally disc-shaped cam 28 is mounted on the extended end of the drive shaft 27. A high portion 28a of the cam 28 is extended over its half outer periphery. A pin 28b is projected on the upper peripheral edge of the cam 28 and a lever portion 23b formed by bending the lower end of the damper shaft 23 at a right angle is hooked by the pin 28b. The rotative movement of the cam 28 is converted to the reciprocal rotative movement of the lever portion 28b, which movement causes the damper shaft 23 and therefore, the damper 21 to rotatively move forward and backward so that the vent holes 19 are opened and closed by the damper 21. The vent holes 19 are usually closed by the damper 21 when the cooking is not executed. A microswitch 29 is mounted on the upper side of the mounting plate 25 so that an actuator of the microswitch 29 is depressed by the high portion 28a of the cam 28. The microswitch 29 is turned on when the actuator thereof is depressed by the cam high portion 28a. Damper position detecting means is thus comprised of the microswitch 29 and the cam 28. Referring now to FIG. 1 showing an electrical arrangement of the electronic range, a series circuit of the motor 26 and a relay switch 16a of the relay 16 is connected between power bus lines 31 and 32 extended from an ac power source 30. The relay switch 16a is controlled by the microcomputer 17 so as to be turned on and off. A switch signal generated by the microswitch 29 is supplied to the microcomputer 17. The operation of the electronic range will be described with reference to FIG. 2. The case where the food in the cooking chamber 12 is high frequency heated by the magnetron 22 with the damper 21 open will first be described. The damper 21 is closed at the cooking start time and accordingly, the microswitch 29 is turned off. Consequently, the switch signal generated by the microswitch 29 is at the low level. The motor 26 is energized to rotate the cam 28 when the relay switch 16a is turned on 0.1 sec. after the cooking start time, that is, at time t₁. The rotative movement of the cam 28 is converted to the reciprocal rotative movement of the lever portion 23b of the damper shaft 23 such that the damper shaft 23 and the damper 21 are rotatively moved in the clockwise direction, as viewed in FIG. 3 or 5. When the damper 21 reaches the open position at time t₂, the microswitch 29 is depressed by the high portion 28a of the cam 28 such that the microswitch 29 is turned on. The high level switch signal generated by the microswitch 29 is supplied to the microcomputer 17, which operates to turn off the relay switch 16a, thereby deenergizing the motor 26. The motor 26 holds the damper 21 at the open position against an urging force of the coil spring 24. The period between times t₁ and t₂ is approximately 3 seconds. The food contained in the cooking chamber 12 is high frequency heated by the magnetron 22 and the outside air is supplied by the cooling fan 14 into the cooking chamber 12 through the vent holes 19 in the condition that the damper 21 is opened. Subsequently, the damper 21 is closed when the cooking is completed at time t₃. The motor 26 is energized to rotate the cam 28 when the relay switch 16a is turned on at time t₃, as shown in FIG. 2. Consequently, the rotative movement of the cam 28 is converted to the reciprocal movement of the lever portion 23b of the damper shaft 23 such that the damper shaft 23 or the damper 21 is rotatively moved in the counterclockwise direction, as viewed in FIG. 3 or 5. The cam high portion 28a stops depressing the microswitch 29 when the damper 21 reaches the closed position at time t₄, thereby turning off the microswitch 29. The low level switch signal generated by the microswitch 29 is supplied to the microcomputer 17, which operates to turn off the relay switch 16a so that the motor 26 is deenergized. Consequently, the vent holes 19 are closed by the damper 21. The period between times t₃ and t₄ is also approximately 3 seconds. On the other hand, when the food contained in the cooking chamber 12 is heated by the heater, the cooking is executed with the damper 21 closed. More specifically, the outside air is prevented from entering the cooking chamber 12 by the damper 21 since it is held at the closed position. Consequently, the hot air in the cooking chamber 12 is prevented from leaking to the machine compartment 33 side. If the relay 16 should fail and the motor 26 should be continuously energized, for example, the damper 21 would be alternately opened and closed repeatedly. In such a case, the switch signal generated by the microswitch 29 is changed from the low level to the high level and vice versa at predetermined intervals or the position detection signals indicative of the closed state of the damper 21 and those indicative of the open state of the damper 21 are alternately generated by the microswitch 29 repeatedly. In response to such signal changes, the microcomputer 17 operates to detect the abnormal condition of the damper 21 such that the magnetron 22 and the heater are deenergized and warning means such as a buzzer (not shown) is activated. Furthermore, the above-described damper abnormal opening and closing operations can occur in the case where the low level switch signal indicative of the closed state of the damper 21 is continuously generated by the microswitch 29 when the damper 21 is moved toward its open position and such a low level signal is continuously detected for one minute, for example. The damper abnormal operations can also occur in the case where the high level switch signal indicative of the open state of the damper 21 is continuously generated by the microswitch 29 when the damper 21 is moved toward its closed position and the high level signal is continuously detected for one minute, for example. In each of the above-described damper abnormal operations, the microcomputer 17 also operates to detect the abnormality of the damper 21 to thereby deenergize the magnetron 22 and the heater and activate the buzzer as the warning means. In accordance with the above-described embodiment, the damper 21 open and closed positions are detected by the microswitch 29. The motor 26 is controlled based on the switch signal generated by the microswitch 29 so that the damper 21 is opened or closed. Thus, a single microswitch 29 is necessitated and therefore, the number of parts can be reduced as compared with the prior art (FIG. 18) in which two microswitches are necessitated, resulting in simplification of the arrangement. Since a single microswitch 29 needs to be adjusted, the number of adjusted parts is reduced as compared with the prior art. Consequently, the number of occurrences of an improper adjustment can be reduced and the damper 21 can be reliably opened and closed. Heating the food is not performed with the damper 21 maintained in the above-described abnormal condition since the magnetron 22 and the heater are deenergized when the abnormality of the damper 21 is detected. Consequently, the hot air in the cooking chamber 12 can be prevented from leaking to the machine compartment 33 side when the food is heated by the heater and the cooking can be prevented from being executed in the condition that the atmospheric temperature in the cooking chamber 12 is not sufficiently high. Furthermore, since the buzzer is activated to warn of the abnormal operation of the damper 21 when it is detected, the user can readily notice the abnormal operation of the damper 21 and accordingly, a countermeasure such as repair can be quickly taken. Although the buzzer is employed as the warning means in the foregoing embodiment, a display device comprising light-emitting diodes may be employed as the warning means, instead. A second embodiment of the invention will be described with reference to FIGS. 6 to 17. Referring to FIG. 6, the cooking chamber 42 having the front opening is provided in the range cabinet 41. The door 43 is mounted on the range cabinet 41 so as to open and close the front opening of the cooking chamber 42. A heater 44 for the grille cooking is mounted on the ceiling of the cooking chamber 42. A fan (not shown) is provided on the back of the rear wall of the cooking chamber 42. The air in the cooking chamber 42 is sucked through the vent holes 45 by the fan and again fed into the cooking chamber 42 through blow holes 46, thereby circulating the air in the cooking chamber. The machine compartment 47 is provided at the right-hand side of the cooking chamber 42, as viewed in FIG. 7. The right-hand partitioning wall 48 of the cooking chamber 42 has an opening 49 in the front upper portion of the partitioning wall 48. The partitioning wall 48 comprises two heat insulation plates 50 and 51 and a heat insulating material sandwiched between the heat insulation plates. A number of vent holes 53 are formed in the cooking chamber interior side heat-insulation plate 50 by way of punching so as to correspond to the opening 49. The cooling fan 54 is mounted on the rear wall of the machine compartment 47 and the magnetron 55 is disposed between the cooling fan 54 and the opening 49. The duct 56 is extended from the sides of the cooling fan 54 and the magnetron 55 to the opening 49 so that the outside air sucked by the cooling fan 54 is supplied into the cooking chamber 42 through the duct 56 and the vent holes 53. Air in the cooking chamber 42 is exhausted outside through exhaust holes 57 formed in the left-hand side wall of the cooking chamber 42, as viewed in FIG. 6. An amount of opening of the opening 49 is controlled by the damper 58. Referring to FIG. 8, the damper 58 is formed into the shape of a generally shallow rectangular box by pressing a metal plate. The damper 58 has damper shaft insertion apertures 58d formed in the left-hand end portions of the upper and lower rising walls respectively, one of the apertures 58d being shown. The damper shaft 59 is extended through the apertures 58d such that the lower shaft end is projected downwards from the aperture 58d formed in the lower rising wall. The upper portion of the damper shaft 59 is cranked such that the upper engagement portion thereof is projected upwards. A positioning portion 58a is integrally formed on the left-hand end portion of the upper rising wall of the damper 58 so as to be projected upwards. The positioning portion 58a has an upper spring peg 58b. A caulked portion 58c is integrally formed so as to be projected upwards from the left-hand edge of the upper rising wall of the damper 58, as viewed in FIG. 8. A horizontal portion 59b of the damper shaft 59 is held between the positioning portion 58a and the caulked portion 58c so as to be positioned. The caulked portion 58c is bent in the direction of arrow in FIG. 9 so as to be caulked, thereby securing the damper shaft 59 as shown in FIG. 10. Referring now to FIG. 11, oblique notched grooves 56a and 56b are formed in the opening 49 side end portions of upper and lower walls of the duct 56 so as to correspond to the damper shaft 59, respectively. The damper shaft 59 is fitted in the notched grooves 56a and 56b so that the damper 58 is rotatably mounted on the duct 56. One of two ends of an extension coil spring 60 is fastened to another spring peg 50a integrally formed on the upper end of the heat insulation panel 50 and the other end of the spring 60 is fastened to the spring peg 58b. The damper 58 is usually urged by the coil spring 60 so as to close the opening 49. The notched grooves 56a, 56b are formed so as to be extended along the direction that the spring force of the coil spring 60 acts, as shown in FIGS. 13 and 14. Referring to FIG. 12, the drive mechanism 61 is provided for rotatively moving the damper 58 in the direction that the same is opened. The motor mounting plate 63 is mounted on the ceiling 62 of the cooking chamber 42 so as to be positioned above the duct 56. The motor 64 is mounted on the underside of the mounting plate 63. The motor 64 is equipped with a reduction gear mechanism and the drive shaft 64a of the motor 64 is upwardly extended through a hole formed in the mounting plate 63. The disc-shaped cam 65 is mounted on the extended end of the drive shaft 64a. The high portion 65a of the cam 65 is extended over its half outer periphery. The pin 66 is projected on the upper peripheral edge of the cam 65 and fitted in an elongated slit 67a formed in one end of the lever 67. The lever 67 is rotatably mounted on the mounting plate 63 by a screw 68. An engagement concave portion 67b formed in the other end of the lever 67 is engageable with the engagement portion 59a. Upon energization of the motor 64, the rotational movement of the cam 65 is converted to the forward and reverse movement of the lever 67, which movement of the lever 67 causes the damper shaft 59 and that is, the damper 58 to be moved forward and backward such that the opening 49 and accordingly, the vent holes 53 are opened and closed, as shown in FIGS. 13 and 14. The microswitch 69 is mounted on the upper side of the mounting plate 63 so that the actuator of the microswitch 69 is brought into contact with the cam 65. The damper position detecting means is thus comprised of the microswitch 69 and the cam 65. The microswitch 69 is turned on when the actuator thereof is depressed by the high portion 65a of the cam 65, thereby generating a high level signal, as shown in FIGS. 15(a) and 15(b). Referring now to FIG. 16 showing an electrical arrangement of the electronic range, the power bus lines 71 and 72 are extended from the ac power source 70. A primary winding 73a of a high voltage transformer 73, a heater 74, a pilot lamp 75, a door switch 76, a short switch 77 and relays 78 to 80 are connected between the power bus lines 71 and 72, as shown in FIG. 16. The magnetron 55 and a rectifier circuit 81 are connected to the transformer secondary winding 73b side. A series circuit of the motor 64 and the relay switch 82 is connected between power bus lines 71 and 72. A primary winding 84a of a transformer 84 for applying a voltage to the control means 83 is also connected between the power bus lines 71 and 72. The control means 83 comprises a rectifier circuit and a microcomputer. A secondary winding 84b of the transformer 84 is connected to the control means 83. The switch signal generated by the microswitch 69 and switch signals generated by various operation switches (not shown) provided in an operation section 85 are supplied to the control means 83. The control means 83 controls the relay switches 78-80 and 82 in accordance with the stored control program so that each relay switch is turned on and off and the display section 86 is activated and deactivated. The operation of the electronic range will be described with reference to FIG. 17. The damper 58 is rotatively moved so as to be set to the initial or closed position, for example, when the electrical power is supplied to the electronic cooking range. Setting the damper 58 to the initial position will be described in detail. The relay switch 82 is turned on so that the motor 64 is energized when the electrical power is supplied to the range or a power supply plug (not shown) is connected to the plug socket. Consequently, the cam 65 is rotatively moved. The high level signal is supplied from the microswitch 69 to the control means 83 in the case where the microswitch 69 is depressed by the high portion 65a of the cam 65 upon supply of electrical power to the electronic range. The cam 65 is rotatively moved in the direction of arrow C in FIG. 13 or 15(a). When the cam 65 is moved so that the damper 58 reaches the open position at time t₂ in FIG. 17, the cam high portion 65a stops depressing the microswitch 69, which then generates the low level signal. Subsequently, when the cam 65 is further rotatively moved in the direction of arrow C, the damper 58 is rotatively moved in the direction of its closed position via the pin 66, lever 67, damper shaft 59 and the like. The microswitch 69 is again depressed by the cam high portion 65a as shown in FIG. 14 when the damper 58 is rotatively moved to the closed position at time t₃, whereby the microswitch 69 generates the high level signal. Rise of the high level signal is detected so that the relay switch 82 is turned off to deenergize the motor. Consequently, the damper 58 is set to the closed position. In accordance with the second embodiment, the damper 58 is set to the initial or closed position when the electrical power is supplied to the electronic range. Consequently, the opening and closure of the damper 58 can readily be performed in the subsequent heating operation. In this embodiment, too, the damper 58 is opened so that the outside air is delivered into the cooking chamber 42 during the high frequency heating operation while the damper 58 is closed during the heating by the heater such that the hot air in the cooking chamber 42 can be prevented from leaking out to the machine compartment 47 side. Conventionally, the dampers have not been placed at a predetermined position in the stage that assembly of the electronic ranges have been completed. Accordingly, the positions of the dampers differ from product to product at the time of shipment. Consequently, in some cases, the tension coil spring urging the damper in the direction of its closed position is fully extended at the time of shipment, which reduces the spring force, resulting in occurrence of failure. In the above-described embodiment, however, the damper 58 can be set to the initial or closed position only when the electrical power is supplied to the products of the electronic ranges at the final stage of assembly. Thus, all the products can be shipped with the tension coil springs 60 contracted. Consequently, occurrence of failure can be prevented in opening and closing the damper. Furthermore, since the damper shaft 59 is positioned by the positioning portion 58a and the caulked portion 58c formed on the damper 58, specific jigs for the positioning are not necessitated and the positioning can be performed with ease. Moreover, the caulked portion 58c of the damper 58 is caulked so that the damper shaft 59 is secured. Since a spot welding machine is not necessary, the equipment expense for manufacturing of the electronic ranges can be saved. Since the damper shaft 59 can be readily positioned and secured as described above, the assembly efficiency can be improved and the manufacturing cost can be reduced as compared with the prior art. Further, since the damper shaft 59 is not welded to the damper 58, a deficiency that a weld is corroded can be eliminated, resulting in improvement of quality of the products. Although the spring peg 58b is integrally formed on the positioning portion 58a of the damper 58 in the foregoing embodiment, these parts may be separately formed. Additionally, a plurality of caulked portions 58c may be formed and the shape of the damper shaft 59 may be changed. FIG. 20 illustrates a conventional damper mounting structure. An opening (not shown) is formed in a wall or heat insulation panel 92 of the cooking chamber 91. A duct 93 is provided for introducing the outside air to the opening. A damper shaft 95 of the damper 94 is inserted in and supported by a slender notched portion 93a formed in the duct 93 with a semi-circular inner face. A tension coil spring 96 is provided between the damper 94 and the heat insulation panel 92 of the cooking chamber 91 for urging the damper 94 in the direction of the damper closed position. The damper shaft 95 is supported by the notched portion 93a in the above-described conventional structure and the reason for this will be described. Difference in the thermal expansion coefficiency between the duct 93 and the heat insulation panel 92 causes variations in the dimensions of these parts when they are thermally deformed. In this case a gap is formed between the duct 93 and the heat insulation panel 92. To cope with occurrence of such a gap, the damper shaft 95 is allowed to be moved in the notched portion 93a such that the opening of the heat insulation panel 92 can always be closed by the damper 94. However, since the direction that a spring force of the tension coil spring 96 acts differs from the direction that the damper shaft 95 is moved, the spring force does not act effectively, resulting in non-smooth movement of the damper shaft 95. Consequently, the damper 94 is insufficiently closed such that the outside air is unnecessarily delivered into the cooking chamber 91 and the hot air is caused to leak out of the cooking chamber 91 such that the atmospheric temperature in the cooking chamber 91 is not sufficiently increased, resulting in a disadvantage of a large amount of heat loss. In accordance with the above-described second embodiment of the invention, however, the notched portions 56a and 56b formed in the duct 56 for supporting the damper shaft 59 is extended in the direction that the spring force of the tension coil spring 60 acts, as shown in FIG. 13. Since the damper shaft 59 is thus moved in the same direction that the spring force of the tension coil spring 60 acts, the spring force effectively acts such that the damper shaft 59 is smoothly moved. If a gap should be formed between the duct 56 and the heat insulation panel 51, the damper 58 could sufficiently be closed. Consequently, the external air can be prevented from being unnecessarily delivered into the cooking chamber 42 and the hot air can be prevented from leaking out of the cooking chamber 42. Accordingly, variations in the atmospheric temperature in the cooking chamber 42 and the amount of heat loss can be reduced. Although the two notched portions 56a and 56b are formed in the duct 56 in the foregoing embodiment, an elongated aperture may be formed in the duct 56 instead of the lower notched portion 56b.

Claims: A heating cooking appliance comprising a high frequency oscillator (22) for high frequency heating food contained in a cooking chamber (12), a heater for heating the food, a damper (21) rotatably mounted for controlling supply of outside air into the cooking chamber (12) and a motor (26) driving the damper (21) so that the damper (21) is closed and opened, position detecting means (28, 29) for detecting positions of the damper (21) when the damper (21) is closed and opened and control means (17) for controlling the motor (26) based on a position detection signal generated by the position detecting means (28, 29), characterized by abnormal condition detecting means (17) for detecting an abnormal condition of the damper (21) closed and opened, based on the position detection signal generated by the position detecting means (28, 29), heating control means (17) for controlling the high frequency oscillator (22) and the heater so that the high frequency oscillator (22) and the heater are deenergized when the abnormal condition of the damper (21) closed and opened is detected by the abnormal condition detecting means (17) and warning means for warning of the abnormal condition of the damper (21) when the abnormal condition of the damper (21) is detected by the abnormal condition detecting means (17). A heating cooking appliance according to claim 1, characterized in that the abnormal condition of the damper (21) is detected by the abnormal condition detecting means (17) when the position detection signal indicative of the closed condition of the damper (21) is continuously generated by the position detecting means (28, 29) where the damper (21) is driven to be opened, when the position detection signal indicative of the open condition of the damper (21) is continuously generated by the position detecting means (28, 29) where the damper (21) is driven to be closed or when the position detection signals indicative of the respective closed and open conditions of the damper (21) are alternately generated by the position detecting means (28, 29) repeatedly where the damper (21) is driven to be opened or closed and the warning means comprises a buzzer or a display device. A heating cooking appliance according to claim 1, characterized in that the control means (17) is arranged so that the damper (21) is rotatively moved so as to be set to an initial position when a power supply is put to the heating cooking appliance. A heating cooking appliance according to claim 1, characterized in that the position detecting means (28, 29) comprises a cam (28) rotated by the motor (26) so that a rotative movement of the cam (28) is interlocked with closing and opening operations of the damper (21) and a microswitch (29) is turned on and off by the cam (28). A heating cooking appliance according to claim 1, further characterized by an opening (49) formed in one of walls of the cooking chamber (42) so as to be closed and opened by the damper (58), a duct (56) on which the damper (58) is rotatably mounted through a damper shaft (59), the duct (56) being provided for guiding the outside air to the opening (49), a tension coil spring (60) provided between the damper (58) and the cooking chamber wall with the opening (49) for urging the damper (58) in a direction that the damper (58) is closed and characterized in that the duct (56) has elongated grooves (56a, 56b) supporting the damper shaft (59), the grooves (56a, 56b) being formed so as to be elongated in a direction that a spring force of the tension coil spring (60) acts. A heating cooking appliance according to claim 1, further characterized by an opening (49) formed in one of walls of the cooking chamber (42) so as to be closed and opened by the damper (58) and a duct (56) on which the damper (58) is rotatably mounted through a damper shaft (59), the duct (56) being provided for guiding the outside air to the opening (49), the damper (58) having a positioning portion (58a) for positioning the damper shaft (59) and a caulking portion (58c) for caulking the damper shaft (59) such that the damper shaft (59) is secured.

Inventors: ENDO MASAAKI NAGOYA WORKS K K, KONDO TOMOYUKI NAGOYA WORKS K, NISHIMURA NOBUICHI NAGOYA WORK, ONO ATSUHIKO NAGOYA WORKS K K, OZAKI MASAAKI NAGOYA WORKS K K, SUZUKI YUKIO NAGOYA WORKS K K, TAKAGI MINORU NAGOYA WORKS K K, ENDO, MASAAKI, NAGOYA WORKS, K.K.TOSHIBA, KONDO, TOMOYUKI, NAGOYA WORKS, K.K.TOSHIBA, NISHIMURA, NOBUICHI, NAGOYA WORKS, K.K.TOSHIBA, ONO, ATSUHIKO, NAGOYA WORKS, K.K.TOSHIBA, OZAKI, MASAAKI, NAGOYA WORKS, K.K.TOSHIBA, SUZUKI, YUKIO, NAGOYA WORKS, K.K.TOSHIBA, TAKAGI, MINORU, NAGOYA WORKS, K.K.TOSHIBA
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1991
Main classification: H05B6
IPC codes: H05B6