Electric heating – Microwave heating – With diverse-type heating
Patent
1994-03-11
1995-07-18
Leung, Philip H.
Electric heating
Microwave heating
With diverse-type heating
219746, 219750, H05B 672
Patent
active
054343917
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to microwave ovens, and in particular to such ovens having magnetrons for delivering microwave power to the oven cavities and forced hot air systems for re-circulating hot air through the cavities.
BACKGROUND OF THE INVENTION
The applicants' U.S. Pat. No. 4,691,088 discloses a microwave oven having a magnetron for delivering microwave power to the oven cavity and a forced hot air system for re-circulating hot air through the cavity. The microwave energy is delivered to the cavity through a launch area in the base of the cavity. A metal turntable is supported in the cavity above the launch area so that the oven when devoid of food provides an inefficient power match with the magnetron, whereby the dielectric load of food items placed in the oven determines the power coupled to the loaded oven from the magnetron. The oven has a hot air system which re-circulates hot air through the oven cavity by means of inlet and outlet apertures in the rear wall of the cavity. The invention stems from the realisation that advantages can be gained if the microwave energy and the hot air can be delivered into the cavity from the same site.
DISCLOSURE OF THE INVENTION
According to the invention a microwave oven comprises a cavity, a magnetron for delivering microwave power to the cavity through a launch area, a forced hot air system comprising an electrical resistance heating element and a fan for forcing air over the element and through the cavity, a metal plate supported in the cavity so that a front surface of the plate faces into the cavity and a rear surface of the plate faces the launch site, the metal plate having peripheral edges spaced from the cavity walls so that the oven when devoid of food provides an inefficient power match with the magnetron, whereby the dielectric load of food items placed in the oven determines the power-coupled to the loaded oven from the magnetron, the forced flow of air re-circulating around the plate which thereby serves as a baffle plate for the hot air system and as a mis-match plate for the microwave power.
The launch area is preferably in a rear panel of the cavity. This has the particular advantage that the base panel of the oven can be left unobstructed, making for easy cleaning. Alternatively, the launch area may be in the top panel or one of the walls of the cavity.
The fan and the electrical resistance heating element are preferably positioned between the metal plate and the rear panel of the cavity, with the fan preferably being surrounded by the heating element.
The plate is preferably centrally apertured so that air is drawn into central apertures in the plate, then passes over the heating element and around the edges of the plate to be re-circulated through the cavity.
A microwave oven according to the invention will now be described by way of example with reference to the accompanying drawings in which:
FIG. 1 is a perspective view of the oven with a front door removed, and
FIG. 2 is a sectional plan view through the oven.
The oven has a cavity 10 defined by two side walls 12, a rear panel 14, a base panel 16 and a top panel. The microwave oven has a magnetron (not shown) which delivers microwave power through a passage 18 and thence through a launch site or area 20 into the cavity. A rotatable member 22 acts as a mode stirrer to prevent the setting up of standing waves in the cavity 10.
A vertical metal plate 24 is positioned in the cavity so that it is spaced a short distance in front of the rear panel 14. The plate 24 is generally rectangular and its outer edges are spaced from the walls 12 and the base and top panels of the cavity, so that there is all-round clearance between the edges of the plate 24 and the structure defining the cavity. The positioning of the plate 24 is such that the plate 24 presents to the magnetron a load which is a poor match with respect to the magnetron. As a result, the amount of power delivered by the magnetron to the empty oven is small, and this low degree of power coupling can be demons
REFERENCES:
patent: 3235701 (1966-02-01), Duras et al.
patent: 3884213 (1975-05-01), Smith
patent: 4480164 (1984-10-01), Dills
patent: 4481396 (1984-11-01), Matsubayashi et al.
patent: 4691088 (1987-09-01), Eke
patent: 4940869 (1990-07-01), Scholtes et al.
Leung Philip H.
Microwave Ovens Limited
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