TURNALE DRIVING MOTOR FIXNG STRUCTURE OF MICRWAVE OVEN

Abstract: In a microwave oven in which a motor rotates a turn­ table through a coupling detachably mounted on the outer bottom center of the turntable , a motor-fixing structure comprises a cylindrical bearing (15) for covering the power transmission shaft (14) around the portion near the motor (13) in such a manner as to allow the shaft to be rotatable and permit the coupling (12) to be mounted on the shaft end, threads (16) formed on the outer circumferential surface of the bearing, a through-hole, for insertion of the bearing, formed in the microwave oven bottom wall (11) in the area facing the coupling mounting position, and a nut (18) with top and bottom faces having larger areas than the opening of the through-hole, which nut is made engaged with the threads of the bearing inserted through the through-hole and projecting into the oven, thereby fixing the motor.

Description: The present invention relates to a structure for fixing a turntable driving motor of a microwave oven, or more specifically to a simplified structure for fixing a turntable driving motor. Conventionally, as shown in Figs. 3 and 4, a motor (5a) or (5b) which drives, through a coupling (4a) or (4b), a turntable (3a) or (3b) rotatably supported by a roller (2a) or (2b) in an oven chamber (1a) or (1b) is fixed to the outer bottom of the oven chamber (1a) or (1b) by using a fixing bracket (6a) or (6b). The fixing bracket (6a) or (6b) and the motor (5a) or (5b) define a closed (or choked) space (8a) or (8b) around the portion of the coupling (4a) or (4b) projecting outside the oven chamber (1a) or (1b). The closed space (8a) or (8b) communicates with the oven chamber (1a) or (1b) via a through hole (7a) or (7b) formed in the bottom wall of the oven chamber (1a) or (1b), whereby microwave energy leaking through the gap around the coupling (4a) or (4b) passing through the through-hole (7a) or (7b) is trapped within the oven. Conventional devices such as these involved complicated construction, and therefore high manufacturing costs because the central portion of the bottom wall of the oven chamber (1a) or (1b) must be raised relative to the remainder of the bottom wall to form the closed space (8a) or (8b). BE-A-845849 describes a microwave oven in which the lower wall of the oven is substantially flat and is in capactitative contact with the motor housing. Electromagnetic losses via the motor spindle are reduced by the trapping of microwaves in the suppressor condenser. The present invention aims to provide a turntable driving motor fixing structure for a microwave oven which, in addition to fixing the motor, also prevents microwave leakage, whilst comprising a simple and low cost construction. According to the invention there is provided a mounting arrangement for a turntable motor in a microwave oven, wherein the drive motor disposed beneath the floor of the heating chamber of the oven includes a shaft which extends upwardly into the chamber through a bearing sleeve, said bearing sleeve projecting through a hole in said floor and being secured relative to said floor, means being provided for coupling the turntable to be driven by said motor shaft, characterised in that said bearing sleeve is fixed to the motor case, thereby fixing the motor to the oven. In a preferred embodiment of the invention the motor drives the turntable in the heating chamber of the microwave oven via a coupling which is detachably mounted on the central portion of the lower surface of the turntable. The motor is preferably provided with a cylindrical bearing sleeve which surrounds the power transmission shaft around the portion near the motor so as to allow the shaft to be rotatable and permit the coupling to be mounted on the shaft end, the outer circumferential face of the bearing being threaded. The bottom wall of the main body of the microwave oven has a through-hole in the region opposed to the coupling mounting position, for insertion of the motor shaft and bearing sleeve into the oven. A plate nut, whose top and bottom faces have surface areas greater than that of the through-hole, is arranged to engage with the threads of the bearing sleeve projecting into the oven, thereby fixing the motor to the microwave oven main body. In order that the present invention may be more fully understood a detailed description will be given of an embodiment thereof, by way of example, with reference to the accompanying drawings wherein: Fig. 1 shows a half section of a microwave oven turntable driving motor fixing structure according to the present invention; Fig. 2 is a sectional view of the motor bearing in the microwave oven turntable driving motor fixing structure of Fig. 1; and Figs. 3 and 4 show half sections of conventional structures for fixing a turntable driving motor to a microwave oven. An object (usually food) to be heated is placed on a turntable (9) in a heating chamber (11). When the oven switch is turned ON, the turntable (9) is rotated by means of a motor (13) while the object (or food) is heated by energy supplied from a heating source. The turntable (9) is rotatably supported by rollers (10) in the heating chamber or oven (11). A coupling (12) is detachably mounted on the central portion of the bottom surface of the turntable (9) which is driven via the coupling (12) by the motor (13). The motor (13) has a cylindrical bearing (15) which surrounds the power transmission shaft (14) around the portion close to the motor (13) so as to allow the shaft (14) to be rotatable and permit the coupling (12) to be mounted on the end of the shaft (14). Threads (16) are formed in the outer circumferential face of the bearing (15). A round through-hole (17) through which to insert the bearing (15) is formed in the bottom wall of the oven (11) in the area facing the coupling mounting position. (18) is a disc nut to be engaged with the threads (16). The disc nut (16) has a larger diameter than the through-hole (17). The nut (18) may be of square shape provided that its top and bottom faces have larger area than the opening of the through-hole (17). The method of fixing the motor (13) by using the fixing structure of the present invention is described now. First, the bearing (15) is inserted into the through-hole (17) so that the threaded portion (16) of the bearing (15) projects into the oven (11). Then, the nut (18) is made engaged with the threads (16) whereby the motor (13) is fixed by the nut (18) supported by the oven inner bottom surface. After the motor (13) is fixed, the coupling (12) is mounted on the power transmission shaft (14) and then the turntable (9) is placed on the coupling (12). As understood from the above, the motor (13) is fixed simply by engaging the nut (18) with the threads (16). Not only fixing the motor (13), but the nut (18) also closes the through-hole (17), thus preventing microwave from leaking outside the oven. Moreover, since the motor (13) can be fixed by the nut (18) alone, the motor-fixing structure of the present invention requires decreased number of parts compared with the conventional fixing structure. As a result, a simple and low cost fixing structure is realized. As described above, the present invention enables the motor to be fixed to the oven and microwave to be prevented from leaking by the simple and low cost structure. In the above embodiment of the invention, the motor power transmission shaft is connected through the coupling with the turntable. Alternatively, it may be connected directly with the turntable.

Claims: A mounting arrangement for a turntable motor (13) in a microwave oven, wherein the drive motor (13) disposed beneath the floor (11) of the heating chamber of the oven includes a shaft (14) which extends upwardly into the chamber through a bearing sleeve, said bearing sleeve projecting through a hole (17) in said floor (11) and being secured relative to said floor, means (12) being provided for coupling the turntable (9) to be driven by said motor shaft, characterised in that said bearing sleeve (15) is fixed to the motor case, thereby fixing the motor to the oven. A mounting arrangement according to claim 1 wherein the outer surface of said bearing sleeve (15) is screw-threaded and receives a tightened threaded nut (18) disposed above the floor so as to hold the motor (13) fixed beneath the floor, said nut providing a seal against microwave leakage through the hole around the sleeve. A mounting arrangement according to claim 2 wherein the nut (18) is provided with upper and lower faces having surfaces larger than the hole (17) to enable holding of the motor when the nut (18) is received on the bearing sleeve (15). A mounting arrangement according to any preceding claim wherein said coupling means (12) is mounted on the end of the shaft (14) and is detachably fixed to a central portion of the lower surface of the turntable (9).

Inventors: OTANI, AKIRA
Applicants: SHARP KABUSHIKI KAISHA
Application year: 1987
Main classification: F24C7
IPC codes: F24C7, H05B6, F24C15