Abstract:
A wall-mounted microwave oven and a control method for controlling a hood motor are provided. Here, the wall-mounted microwave oven having a main body forming a cavity for accommodating foods to cook, a casing enclosing the main body and forming a hood duct having an inlet located on a bottom area and an outlet located on an upper area, and a hood fan installed in the hood duct, includes a hood motor driving the hood fan, a first switching portion for switching a current supplied from an external electrical power source to the hood motor, and a microcomputer for controlling the rotational speed of the hood motor by adjusting an on/off time of the first switching portion, based on an external control signal. Thus, since the speed of the hood fan can be varied, conveniences of users can be achieved.

Description:
CLAIM OF PRIORITY 
     This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from my two applications WALL MOUNTED TYPE MICROWAVE OVEN AND HOOD MOTOR SPEED CONTROLLING METHOD THEREOF filed with the Korean Industrial Property Office on Mar. 9, 1999 and there duly assigned Ser. No. 7718/1999, and WALL MOUNTED TYPE MICROWAVE OVENAND HOOD MOTOR SPEED CONTROLLING METHOD THEREOF filed with the Korean Industrial Property Office on Mar. 9, 1999 and there duly assigned Serial No. 7720/1999. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a wall-mounted microwave oven and a method for controlling a hood motor, and more particularly, to a wall-mounted microwave oven and a method for controlling a hood motor, to vary the speed of the hood motor. 
     2. Description of the Related Art 
     A wall-mounted microwave oven is installed on the upper wall over a gas range, and functions as a hood for inhaling vapor and fumes generated during cooking foods in the gas range and discharging the inhaled vapor and fumes to the outside. 
     As shown in FIGS. 1 and 2, the wall-mounted microwave oven includes a main body  53  and a casing  56  enclosing the main body  53 . Between the casing  56  and the main body  53  is formed a hood duct  65  as a path for discharging vapor and fumes. On the lower surface of the casing  56  is formed an inlet  58  for inhaling vapor and fumes into the hood duct  65 . On the upper surface of the casing  56  is formed an outlet  59  to which a discharging tube  61  is connected. The discharging tube  61  is connected to a discharging path  67  which penetrates the wall and communicates with the outside. Also, on the upper portion of the main body  53  adjacent to the outlet  59  is formed a hood fan  63  for discharging the vapor and fumes inhaled in the hood duct  65  via the inlet  58  to the outside via the outlet  59 , as indicated by arrow marks. 
     The hood fan  63  operates by a user&#39;s selection through a select button provided in a control panel  35 . As it being the case, a hood sensor  57  (FIG. 7) which turns on or off the hood fan  63  according to air temperature or smoke detection is provided to the inlet  58  of the hood duct  65  or the inside thereof, thereby controlling operation of the hood fan  63 . Here, the hood sensor  57  is generally made of a bimetal. 
     FIG. 7 is a circuit diagram of a hood driver for a conventional wall-mounted microwave oven. The hood motor  95  is installed on an electric power line which mutually and serially connects first and second commercial alternating voltage (AC) electric power lines  51  and  52  which extend from an external power source  55 . On the electric power line where the hood motor  95  is installed, are formed a hood fan switch  72  which turns on or off the hood motor  95  and a speed select switch  73  for selecting a driving speed of the hood motor  95  at low or high speed. Here, the speed select switch  73  has a high speed contact  73   a  and a low speed contact  73   b  for turning on the hood motor  95 , with a result that the hood motor  95  operates at high speed or at low speed, respectively. The speed selection switch  73  is normally connected to the low speed contact  73   b.    
     The hood sensor  57  is connected in parallel with the hood fan switch  72 . As described above, the hood sensor  57  detects heat or gases transferred from a gas range  100  and is turned on when heat or gases is detected. 
     By this configuration, a selection button for driving the hood fan can be selected to discharge heat and fumes emitted from foods during cooking. Here, if a user presses the selection button once, a microcomputer  60  turns on the hood fan switch  72 , in which case the speed selection switch ordinarily in contact with the low speed contact  73   b  drives the hood motor  95  at low speed. If the selection button is pressed twice, the microcomputer  60  directs the speed selection switch  73  to contact the high speed contact  73   a  to drive the hood motor  95  at high speed. If the selection button is pressed once again, the microcomputer  60  turns off the hood fan switch  72  to stop the hood motor  95 . 
     Meanwhile, although the user does not manipulate the selection button, if the hood sensor  57  detects heat or fumes during cooking, the hood sensor  57  is turned on to drive the hood motor  95  at low speed. 
     However, the conventional hood motor  95  can be controlled only at two levels, that is, at low speed and high speed. Thus, if a user wishes the hood motor  95  to be driven faster than at high speed, or wishes the hood motor  95  to be driven at intermediate speed, such user needs cannot be met. That is, the driving speed of the hood motor  95  cannot be adaptively controlled according to the degree of heat or fumes emitted. 
     To solve these problems, the winding number of coils is increased to enlarge the capacity of the hood motor  95 , thereby controlling the rotational speed of the hood motor  95  in multiple steps. In the case that the winding number of coils is increased, the volume of the hood motor  95  also increases. In addition, as the number of steps are increased, the number of contacts in the speed selection switch  73  should be increased. As a result, a production cost increases and an assembling work is complicated. 
     SUMMARY OF THE INVENTION 
     To solve the above problems, it is an object of the present invention to provide a wall-mounted microwave oven which is adaptively controlled according to a cooking condition under which the speed of a hood motor is diversified. 
     It is another object of the present invention to provide a hood motor speed controlling method in a wall-mounted microwave oven which is adaptively controlled according to a cooking condition under which the speed of a hood motor is diversified. 
     To accomplish the above object of the present invention, there is provided a wall-mounted microwave oven having a main body forming a cavity for accommodating foods to cook, a casing enclosing the main body and forming a hood duct having an inlet located on a bottom area and an outlet located on an upper area, and a hood fan installed in the hood duct, the wall-mounted microwave oven comprising: a hood motor driving the hood fan; a first switching unit for interrupting a supply current supplied to the hood motor, a hood sensor connected in parallel with the first switching unit, said hood sensor detecting whether or not the hood fan need to be turned on or off; a microcomputer for controlling the rotational speed of the hood motor by controlling an on and-off time of the first switching unit, in response to an external control signal; and a second switching unit transmitting a control signal supplied from the microcomputer to the first switching unit. 
     Preferably, the wall-mounted microwave oven further comprises a rectifying unit rectifying the supply current supplied from a power unit. 
     Preferably, the wall-mounted microwave oven further comprises a filtering unit connected between the first switching unit and the hood motor, each end of the filtering unit connected to the rectifying unit, the filtering unit filtering rectification current rectified in the rectifying unit. 
     Preferably, the first switching unit comprises a transistor. 
     The wall-mounted microwave oven further comprises a second switching unit for transmitting a control signal supplied from the microcomputer to the first switching unit. The second switching unit comprises a first transistor connected to the microcomputer and turned on or off according to a driving signal supplied from the microcomputer and a second transistor operating reversely to the on-and-off operation of the first transistor and transmitting a driving signal to the first switching unit. 
     Preferably, when the speed of the hood motor is increased, the first switching unit is controlled to have a short duty cycle. 
     Preferably, the wall-mounted microwave oven further comprises a selection switch connected serially to said hood sensor, having a first pole connected to said hood sensor and a second pole connected to said first switching unit. 
     Also, the wall-mounted microwave oven further comprises a speed control button for controlling the speed of the hood motor externally. The wall-mounted microwave oven preferably comprises a hood sensor provided on an electrical line connected in parallel with the first switching unit, for detecting whether or not the hood fan needs to operate, and a selection switch serially connected to the hood sensor on the electrical line, having a first contact connected to the hood sensor and a second contact connected to the first switching unit. Preferably, the selection switch is set to contact the first contact in a normal case, and to contact the second contact if a user selects a hood fan speed button when the hood fan is turned on by a detection signal supplied from the hood sensor. 
     Meanwhile, the wall-mounted microwave oven further comprises a rectifying unit for rectifying a supply current supplied from the power supply unit, and a first filtering unit disposed in parallel between the rectifying unit and the hood motor, for filtering the rectification current rectified in the rectifying unit by increasing the rectification current by a predetermined level. The wall-mounted microwave oven further comprises a second filtering unit disposed in parallel between the rectifying unit and the first filtering unit, for filtering the rectification current rectified in the rectifying unit, and speed change switch disposed between the first filtering unit and the hood motor, for selecting a filtering current from the second filtering unit to be transferred to any one of the first filtering unit or the hood motor. 
     Here, the first and second filtering units are formed of a capacitor, respectively, in which it is preferable that a capacity of the first filtering unit is larger than that of the second filtering unit. It is also preferable that the speed change switch transfers the rectification current from the rectifying unit to one of the first and second filtering units. 
     In addition, the wall-mounted microwave oven comprises a turbo selection button for selecting the speed of the hood motor to be driven at a predetermined level or higher, in which the microcomputer controls the speed change switch to be connected to the first filtering unit when the turbo selection button is selected, and the microcomputer controls the on-and-off time of the first switching unit to control the speed of the hood motor. 
     Here, the wall-mounted microwave oven preferably comprises a hood sensor provided on an electrical line connected in parallel with the first switching unit, for detecting whether or not the hood fan needs to operate, and a selection switch serially connected to the hood sensor on the electrical line, having a first contact connected to the hood sensor and a second contact connected to the first switching unit. Preferably, the selection switch is set to contact the first contact in a normal case, and to contact the second contact if a user selects a hood fan speed button when the hood fan is turned on by a detection signal supplied from the hood sensor. 
     According to another aspect of the present invention, there is also provided a hood motor speed controlling method in a wall-mounted microwave oven having a main body forming a cavity for accommodating foods to cook, a casing enclosing the main body and forming a hood duct having an inlet located on a bottom area and an outlet located on an upper area, a hood fan installed in the hood duct, and a hood motor for driving the hood fan, the hood motor speed controlling method comprising the steps of: generating a driving signal to be supplied to the hood motor based on an external control signal; and controlling a duty cycle of the current to be supplied to the hood motor according to the driving signal to thereby control the speed of the hood motor. 
     Here, the step of controlling the speed of the hood motor further comprises of the step of lengthening the duty cycle in the case that the speed of the hood motor is increased. 
     Also, the hood motor speed controlling method further comprises the step of amplifying the current to be supplied to the hood motor from the external electrical power source. The step of supplying the current to the hood motor is preferably a step of controlling a duty cycle of the amplified current to be supplied to the hood motor. 
     Preferably, the hood motor speed controlling method further comprises the steps of filtering the current to be supplied to the hood motor, amplifying the filtered current, and selecting the filtered current so as to be directly supplied to the hood motor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein: 
     FIG. 1 is a schematic view of a wall-mounted microwave oven installed above a gas range; 
     FIG. 2 is a partially exploded perspective view of a wall-mounted microwave oven; 
     FIG. 3 is a circuit diagram of a hood driver in a wall-mounted microwave oven according to a first embodiment of the present invention; 
     FIG. 4 is a control block diagram of the wall-mounted microwave oven of FIG. 3; 
     FIG. 5 is a circuit diagram of a hood driver of a wall-mounted microwave oven according to a second embodiment of the present invention; 
     FIG. 6 is a control block diagram of the wall-mounted microwave oven of FIG. 5; and 
     FIG. 7 is a circuit diagram of a conventional wall-mounted microwave oven. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     The wall-mounted microwave oven according to the present invention has the same configuration as those of FIGS. 1 and 2 in external appearance. Thus, the detailed description thereof will be omitted. 
     FIG. 3 is a circuit diagram of a hood driver  20  in a wall-mounted microwave oven according to the present invention, and FIG. 4 is a control block diagram of the wall-mounted microwave oven of FIG.  3 . As illustrated, the hood driver  20  includes a hood motor  30  formed of a direct current (DC) motor, a switching unit for interrupting a power supply for the hood motor  30 , and a microcomputer  10  for providing a control signal to the switching unit to control speed of the hood motor  30 . Here, the hood motor  30  is supplied with a rectified and filtered current via a rectifier  21  disposed on an electrical power line serially connecting first and second commercial electrical power lines  1  and  2  which extend from an electrical power source  5  and a filtering unit  22  connected in parallel with the rectifier  21 . 
     Meanwhile, the switching unit includes a first switching unit  24  which is turned on or off according to a driving signal supplied from the microcomputer  10 , and a hood sensor  7  connected in parallel with the first switching unit  24 , for detecting heat and/or fumes within a hood duct in which the hood sensor  7  is turned on or off according to a detection result. 
     The first switching unit  24  is formed of an npn type transistor whose base electrode is connected to the microcomputer  10  in order to receive a driving signal from the microcomputer  10 . A second switching unit  40  for transferring the driving signal from the microcomputer  10  to the first switching unit  24  is connected between the microcomputer  10  and the first switching unit  24 . The second switching unit  40  includes a first transistor  40   a , which is connected to the microcomputer  10  and is turned on or off according to a signal from the microcomputer  10  and a second transistor  40   b  for transferring a driving signal to the first switching unit  24  when the first switching unit  40   a  is turned on. Here, both the transistor of the first switching unit  24  and the first transistor  40   a  are formed of an npn type transistor, respectively so as to be turned on or off according to an identical signal and the second transistor  40   b  is formed of a pnp type transistor. 
     As a result, if a low signal is generated from the microcomputer  10 , the second transistor  40   b  is turned on and both the first transistor  40   a  and the first switching unit  24  are turned off, so that a current supply is cut off toward the hood motor  30 . Reversely, if a high signal is generated from the microcomputer  10 , the second transistor  40   b  is turned off and both the first transistor  40   a  and the first switching unit  24  are turned on, so that a current is supplied to the hood motor  30 . 
     In this manner, if a duty cycle is altered by adjusting a time during which the first switching unit  24  is turned on or off, in accordance with the signal supplied from the microcomputer  10 , the magnitude of the current supplied to the hood motor  30  is varied according to the duty cycle. That is, if a time during which the first switching unit  24  is turned on is lengthened, the magnitude of the current supplied to the hood motor  30  becomes larger, so that the rotational speed of the hood motor  30  becomes faster. On the contrary, if a time during which the first switching unit  24  is turned on is shortened, the magnitude of the current supplied to the hood motor  30  becomes smaller, so that the rotational speed of the hood motor  30  becomes slower. Meanwhile, a speed control button  31  for adjusting the rotational speed of the hood motor  30  is provided in an external control panel  35 . The speed control button  31  can be formed of a knob according to the specification of the wallmounted microwave oven. 
     Meanwhile, on an electrical power line where the hood sensor  7  is installed is provided a selection switch  25  having a first contact  25   a  connected to the hood sensor  7  and a second contact  25   b  connected to the first switching unit  24 . The selection switch  25  is selectively connected to one of the hood sensor  7  and the first switch  24 . Accordingly, if the hood sensor  7  is turned on, an electrical power is supplied to the hood motor  30  to be rotated. If a user selects the speed control button  31  while the hood motor  30  is driven according to the activation of the hood sensor  7 , the microcomputer  10  controls the selection switch  25  to contact the second contact  25   b  and controls a current supply to the first switching unit  24 , with a result that the speed of the hood motor  30  can be adjusted. 
     As shown in FIG. 4, the microcomputer  10  in the microwave oven having the hood motor  30  controls a connection between the first switching unit  24  and the selection switch  25  according to a user&#39;s control of the control panel  35  at the time when an electric power is applied from the electric power supply  5 . Accordingly, the rotational speed of the hood motor  30  is controlled. 
     By the above configuration, if a user selects the speed control button  31  in order to drive the hood fan during using of a gas range, the microcomputer  10  sends the driving signal to the first switching unit  24 . Then, the microcomputer  10  controls the on-and-off time of the first switching unit  24  according to the control of the speed control button  31 , to thereby control a quantity of current applied to the hood motor  30 . As a result, the rotational speed of the hood motor  30  is changed. 
     Although a user does not select the speed control button  31 , if the hood sensor  7  detects heat or fumes, the hood sensor  7  is turned on, accordingly the current is supplied to the hood motor  30 . Thus, the hood motor  30  is driven. Here, when the hood sensor  7  is turned on, the hood motor  30  rotates at an appropriate speed which is preset in the microcomputer  10 . Even though the hood motor  30  is driven by the hood sensor  7 , if the user selects the speed control button  31 , the microcomputer  10  controls the selection switch  25  to contact the second contact  25   b  to apply the current to the first switching unit  24 . By so doing, the hood motor  30  can operate at a user&#39;s desired rotational speed according to control of a user. 
     As described above, the present invention is provided with the first switching unit  24  to control the rotational speed of the hood motor  30 , and the speed control button  31  for selecting the rotational speed of the hood motor  30  in the control panel  35 . Thus, the rotational speed of the hood motor  30  can be linearly varied within the speed interval between a high speed and a low speed. 
     Accordingly, since a user can drive the hood fan at a desired speed according to a degree of heat and/or fumes to be discharged, ventilation and exhaust can be accomplished within an optimal time, to thereby provide users with conveniences. 
     FIG. 5 is a circuit diagram of a hood driver of a wall-mounted microwave oven according to a second embodiment of the present invention, and FIG. 6 is a control block diagram of the wall-mounted microwave oven of FIG. 5. A hood driver  20  for driving a hood motor in a wall-mounted microwave oven according to a second embodiment of the present invention shown in FIG. 5 is the same as the basic configuration of the first embodiment shown in FIG.  3 . Thus, the detailed description of the elements which are assigned with the same reference numerals as those of the first embodiment will be omitted. 
     In the second embodiment of the present invention, a filtering unit  22  includes a second filter  22   b  for filtering the rectified current into an average current and a first filter  22   a  connected in parallel with the second filter  22   b , for increasing the magnitude of the rectified current by a predetermined level or higher and filtering the rectified current. Here, the second filter  22   b  is connected with the second switching unit  40   b . Also, a speed change switch  45  is provided between the first filter  22   a  and the hood motor  30 . The speed change switch  45  interrupts a power supply to the first filter  22   a.    
     As a result, an electric current from the electrical power source  5  is supplied only to the second filter  22   b  in a normal case. If the speed change switch  45  is turned on, the electrical power from the electrical power source  5  is supplied to the first filter  22   a  via the second filter  22   b . The current after passing the first filter  22   a  is instantly and sharply increased and then supplied to the hood motor  30 , to thereby sharply increase the rotational speed of the hood motor  30 . 
     A switching unit of the second embodiment of the present invention has the same configuration as that of the first embodiment. Thus, the detailed description of the elements which are assigned with the same reference numerals as those of the first embodiment will be omitted. 
     Meanwhile, a control panel  35  is provided with a speed control button  31  which can vary the rotational speed of the hood motor  30  by adjusting the magnitude of the current supplied to the fist switching unit  24  and a turbo selection button  33  for turning on or off the speed change switch  45 . The speed control button  31  and the turbo selection button  33  can be formed of a knob according to the specification of the wall-mounted microwave oven. 
     As shown in FIG. 5, the microcomputer  10  in the microwave oven having the hood motor  30  controls a connection between the first switching unit  24  and the speed change switch  45  according to a control of the speed control button  31  and the turbo selection button  33  from the control panel  35 . Accordingly, the rotational speed of the hood motor  30  is controlled. 
     By the above configuration, if a user selects the speed control button  31  in order to drive the hood fan during using of a gas range, the microcomputer  10  controls the selection switch  25  to contact the second contact  25   b  at the side of the hood motor  30 , to thereby send the driving signal to the first switching unit  24 . Then, the microcomputer  10  controls the on-and-off time of the first switching unit  24  according to the control of the speed control button  31 , to thereby control a quantity of current applied to the hood motor  30 . As a result, the rotational speed of the hood motor  30  is changed within a conventional speed range. 
     If the user selects the turbo selection button  33  while the hood motor  30  is driven within the conventional speed range, the microcomputer  10  controls the speed change switch  45  to be turned on. Accordingly, the magnitude of the current to be supplied to the hood motor  30  is sharply increased to thereby sharply increase the rotational speed of the hood motor  30 . Here, if a user controls the speed using the speed control button  31 , the rotational speed of the hood motor  30  can be controlled. 
     Although a user does not select the speed control button  31 , the hood sensor  7  is turned on if the hood sensor  7  detects heat or fumes. Accordingly, the current is supplied to the hood motor  30 . Thus, the hood motor  30  is driven. Here, when the hood sensor  7  is turned on, the hood motor  30  rotates at an appropriate speed which is preset in the microcomputer  10 . Even though the hood motor  30  is driven by the hood sensor  7 , if the user selects the speed control button  31 , the microcomputer  10  controls the select [selection] switch  25  to contact the second contact  25   b  to apply the current to the first switching unit  24 . Also, the hood motor  30  can be driven at an ultra-speed according to a user&#39;s selection of the turbo selection button  33 . 
     As described above, the present invention is provided with the first switching unit  24  for controlling the on-and-off time of the current to vary the rotational speed of the hood motor  30 . The present invention is also provided with the first filter  22   a  for filtering the current by increasing the current by a predetermined level or higher, to thereby select the rotational speed of the hood motor  30  to a normal speed or an ultra-high speed. 
     As a result, according to the user&#39;s control of the control panel  35 , the rotational speed of the hood motor  30  can be linearly varied. The hood motor  30  can be also driven at an ultra-high speed. Thus, ventilation and exhaust can be accomplished within an optimal time, to thereby provide users with conveniences. 
     Meanwhile, in the second embodiment, the current passing through the second filter is supplied to the first filter. However, the current from the rectifier can be supplied to either of the first and second filters. 
     As described above, the rotational speed of the hood motor  30  can be linearly varied. The hood motor  30  can be also driven at an ultra-high speed. Thus, ventilation and exhaust can be accomplished within an optimal time, to thereby give conveniences to users. 
     In the embodiments described above, the speed control button  31  and the turbo selection button  33  are provided in the control panel  35 . However, they can be also provided in the other parts of the microwave oven than the control panel  35 . 
     Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, modifications, substitutions and deletions not specifically described may be made without departing from the spirit and scope of the invention as defined in the appended claims.