Microwave oven with variable-speed turntable

Abstract: A microwave oven has a variable speed transmission for driving its turntable (16) at different speeds. The transmission comprises complementary sector gears (122, 124; 146, 148) which alternately come into play thereby varying the gear ratio of the transmission.

Description: The present invention relates to a microwave oven including a turntable and a motor for driving the turntable. Microwave ovens are well known. Referring to Figure 1, a microwave oven has a cooking chamber 12 and a electrical component chamber 14 in a body 10. The cooking chamber 12 receives food to be cooked and has a door at its front.. A turntable 16 for supporting and rotating food is mounted at the bottom of the cooking chamber 12. The electrical component chamber 14 houses various electrical components, including a magnetron 17, a high-voltage transformer 18, a waveguide, a cooling fan 19 and a control part. A control panel 30 is provided at the front of the electrical component chamber 14 so that a user to set various cooking modes and operate the microwave oven. When the electrical components in the electrical component chamber 14 are operated, microwaves generated in the magnetron 17 are guided to the cooking chamber 12 through the waveguide 17. The microwaves guided to the cooking chamber 12 directly irradiate food or indirectly irradiate food after being reflected by a wall or walls of the cooking chamber. The microwaves vibrate water molecules of food thereby raising its temperature. The food is cooked by the generated heat. In order for food to be evenly heated, it is known to provide a turntable 16 for rotating food during cooking. Referring to Figure 2, the turntable 16 is driven by a motor and gear unit 42 mounted under the floor 13 of the cooking chamber 12. A drive shaft 44 couples the motor and gear unit 42 to the turntable 16 which has a socket 43 for receiving the end of the shaft 44. The gears in the drive and gear unit 42 reduce the speed of the motor's shaft so that the drive shaft 44 rotates more slowly than the motor's shaft. During cooking, the motor and gear unit 42 is energised to rotate the turntable 16 at a constant speed. It is an aim of the present invention to provide a microwave oven that cooks more evenly. A microwave oven according to the present invention is characterised by a variable-speed transmission between the motor and the turntable for changing the speed of the turntable. Preferably, the variable-speed transmission changes the speed of the turntable periodically between predetermined speeds. Preferably, the transmission means comprises first and second gears fixed on a first shaft and third and fourth gears fixed on a second shaft for engagement with respectively the first and second gears, the first and second gears being toothed in nonoverlapping sectors and the combination of the first gear and the third gear providing a different gear ratio to the combination of the second gear and the fourth gear. More preferably, the first and second gears each carry teeth around a substantially 180° sector. The second shaft or the first shaft may extend from the turntable. Preferably, an oven according to the present invention comprises a body in which a cooking chamber is formed and a microwave generator for generating and radiating microwaves into the interior of the cooking chamber, and the turntable is mounted in the cooking chamber. Embodiments of the present invention will now be described, by way of example, with reference to Figures 3 to 5 of the accompanying drawings, in which:- Figure 1 is a perspective view of a known microwave oven; Figure 2 is a cross-sectional view of a known turntable driving apparatus; Figure 3 is a cross-sectioned view of a first turntable driving apparatus according to the present invention; Figures 4A and 4B are plan views illustrating the operation of the turntable driving apparatus of Figure 3; and Figure 5 is a cross-sectional view of a second turntable driving apparatus according to the present invention. Referring to Figures 3 to 4B, a first turntable driving apparatus includes a driving source 112 for providing a driving force, a driving shaft 114 and a driven shaft 116 for transmitting the driving force from the driving source 112 to the turntable 102, and a speed changing gear unit for changing the rotational speed of the turntable 102 disposed between the driving shaft 114 and the driven shaft 116. An electric motor is used as the driving source 112. The driving shaft 114 is connected to the rotor of the electric motor 114. The driven shaft 116 is connected to the centre portion of the underside of the turntable 102 and extends through the floor 103 of the cooking chamber. The speed changing gears include a driving gear unit 121 which is mounted to the driving shaft 114 and driven gear unit 125 which is mounted to the driven shaft 116. The driving gear unit 121 has a first driving gear 122 and a second driving gear 124, which are sector gears having complementary tooth distributions. The teeth of the first and second driving gears 122, 124 (as shown in Figure 4A), are formed along half the entire outer periphery, that is 180° along the outer periphery, of each of the gears 122, 124. The driven gear unit 125 has a first driven gear 126 and a second driven gear 128, respectively co-operating with the first driving gear 122 and the second driving gear 124. When cooking begins, the driving shaft 114 of the driving source 112 is rotated. The driving force of the driving shaft 114 is transmitted to the driven shaft 116 to rotate the turntable 102. At this time, the rotational force of the driving shaft 114 is alternately transmitted to the driven shaft 116 through the first gears 122, 126 and the second gears 124, 128 of the driving gear unit 121 and the driven gear unit 125. Accordingly, the rotational speed of the turntable 102 rotated by the driven shaft 116 is periodically changed. That is, in the state that the first driving gear 122 of the driving gear unit 121 is meshed with the first driven gear 126 of the driven gear unit 125, the second driving gear 124 is in a separated state from the second driven gear 128. Accordingly, the driving force of the driving shaft 114 is transmitted to the driven shaft 116 through the first driving gear 122 and the first driven gear 126, and the turntable 102 is rotated at a speed corresponding to the ratio of the first gears 122, 126. In the state that the first driving gear 122 is meshed with the first driven gear 126, the driving shaft 114 is rotated up to 180°, the driven shaft 116 is rotated up to an angle covered by the number of its gear teeth equal to those on one half of the outer periphery of the first driving gear 122. If the driving shaft 114 is rotated by 180°, the first driving gear 122 separates from the first driven gear 126 and, at the same time, the second driving gear 124 meshes with the second driven gear 128, so that the driving force of the driving shaft 114 is (as shown in Figure 4B) transmitted to the driven shaft 116 through the second driving gear 124 and the second driven gear 128, and the turntable 102 is rotated at a speed corresponding to the gear tooth ratio of the second gears 124, 128. The driving shaft 114 is then rotated by 180° with the second driving gear 124 meshed with the second driven gear 128, and the driven shaft 116 is rotated by an angle β corresponding to the number of teeth in region b, i.e. half of the outer periphery of the second driving gear 124. During one rotation of the driving shaft 114, drive is transmitted first via the first gears 122, 126 and then via the second gears 124, 128 of the driving gear unit 121. Consequently, the turntable is alternately rotated faster and slower. It will be appreciated that more than two sector driving gears may be provided, together with corresponding, respective driven gears so that the turntable can be rotated at more than two speeds during one rotation of the driving shaft. If will also be appreciated that a plurality of sector gears may be embodied with one gear wheel by providing groups of teeth at different locations. With such gears, the turntable speed can be driven for two periods at the same speed during one revolution of the driving shaft. Preferably, when the driving shaft 114 is rotated once, the angle by which the driven shaft 116 is rotated (i.e. n(α+β) where n is a positive integer) may or may not be 360°. Referring to Figure 5, a second turntable driving apparatus includes a driving source 132 for providing a driving force, a driving shaft 134 and a driven shaft 136 for transmitting a driving force of the driving source 132 to the turntable 102', and a speed changing gear unit for changing the rotational speed of the turntable 102' disposed between the driving shaft 134 and the driven shaft 136. The speed changing gear unit includes a driving gear unit 141 which has a first driving gear 142 and a second driving gear 144, and a driven gear unit 145 which has a first driven gear 146 and a second driven gear 148. However, in this embodiment of the present invention, the first and second driven gears of the driven gear unit 145 are sector gears. Thus, as in the first embodiment, the rotational force of the driving shaft 134 is alternately transmitted through the first gears 142, 146 and the second gears 144, 148 of the driving gear unit 141 and the driven gear unit 145. However, since the first and second gears 146, 148 of the driven gear unit 145 are sector gears, the speed changes happen for each half-revolution of the turntable. Accordingly, the rotational speed of the turntable 102' at a particular angular position is always the same. Further, it will be appreciated that, as in the case of the first embodiment, more sector gears may be provided, on separate gear wheels to provide more speeds and/or on the same gear wheels to provide more speed changes between the same speeds.

Claims: A microwave oven including a turntable (102; 102') and a motor (112; 132) for driving the turntable, characterised by a variable-speed transmission (121, 125; 141, 145) between the motor and the turntable for changing the speed of the turntable. A microwave oven according to claim 1, wherein the transmission means comprises first and second gears (122, 124; 146, 148) fixed on a first shaft (114; 136) and third and fourth gears (126, 128; 142, 144) fixed on a second shaft (116; 134) for engagement with respectively the first and second gears, the first and second gears being toothed in nonoverlapping sectors (a, b) and the combination of the first gear and the third gear providing a different gear ratio to the combination of the second gear and the fourth gear. A microwave oven according to claim 2, wherein the first and second gears each carry teeth around a substantially 180° sector (a, b). A microwave oven according to claim 2 or 3, wherein the second shaft (116) extends from the turntable (102). A microwave oven according to claim 2 or 3, wherein the first shaft (136) extends from the turntable (102'). A microwave oven according to any preceding claim, comprising a body in which a cooking chamber is formed and a microwave generator for generating and radiating microwaves into the interior of the cooking chamber, wherein the turntable (102) is mounted in the cooking chamber.

Inventors: CHOI WON-WOO, CHOI, WON-WOO
Applicants: SAMSUNG ELECTRONICS CO LTD, SAMSUNG ELECTRONICS CO., LTD.
Application year: 1999
Main classification: H05B6
IPC codes: A47J43, H05B6, F24C7