GB2325839A

GB2325839A - Ignition wire choke in gas/microwave combination oven

Info

Publication number: GB2325839A
Application number: GB9711014A
Authority: GB
Inventors: Christopher Douglas Parker; Gordon Thomas Andrews
Original assignee: Stoves PLC
Current assignee: Stoves PLC
Priority date: 1997-05-28
Filing date: 1997-05-28
Publication date: 1998-12-02
Anticipated expiration: 2017-05-28
Also published as: GB9711014D0; GB2325839B

Abstract

A microwave cooking oven is provided with an electrical lead, e.g. an ignition wire 2, which extends from the oven cavity and which is provided with a choke assembly 5 for minimising microwave energy leakage from the oven cavity where it extends through the wall thereof.

Description

Cooking Appliances This invention relates to cooking appliances and relates more especially to microwave cooking appliances. The invention has particular application to socalled gas combination microwave ovens which incorporate a microwave and a gas cooking facility.

In gas combination microwave ovens, the gas burner has usually been positioned external of the cooking cavity and normally only the products of combustion from the gas burner are circulated in the cooking cavity. It has now been proposed to position the gas burner within the oven cooking cavity and this requires that the gas burner be provided with an electric (spark) ignition system for igniting the gas burner when required. This necessarily requires an electrical lead to extend into the oven cavity from a spark ignition circuit located outside the oven cavity. In such an arrangement it must be ensured that there is no substantial leakage of microwave energy at the point where the electrical lead enters the oven cavity and great difficulty has been experienced in ensuring that acceptable limits are not exceeded.

It is an object of the present invention to provide a gas combination oven as aforesaid in which the microwave energy leakage is reduced to acceptable limits.

According to the present invention there is provided a microwave cooking appliance comprising an oven cavity, a microwave energy source for said oven cavity and an electrical lead which extends through the wall of said oven cavity, said electrical lead having a microwave energy choke arrangement where it extends from said oven cavity for minimising microwave energy leakage thereat.

A preferred appliance according to the present invention takes the form of a gas combination microwave oven, having a gas burner arrangement located within said oven cavity, a spark ignition arrangement located externally of said oven cavity, said electrical lead extending from the vicinity of said gas burner arrangement through the wall of said oven cavity to said spark ignition arrangement.

In carrying out the invention it may be arranged that said choke arrangement comprises a metallic tube through which said electrical lead extends, and also a choke chamber immediately adjacent the wall of said oven cavity and into which said metallic tube extends.

It may be arranged that the relative positions of said tube and said choke chamber are determined by the frequency of the microwave energy of said microwave energy source, and advantageously, the relative positions of said tube and said choke chamber are adjustable for microwave energy tuning purposes.

An exemplary embodiment of the invention will now be described reference being made to the accompanying single figure drawing which depicts part of the wall of an oven cavity of a gas combustion microwave oven together with an interconnecting lead and associated microwave choke assembly.

For convenience only those parts of a gas combination microwave oven relevant to the present invention will be described, it being assumed that the oven is otherwise of conventional form with a gas burner disposed within the oven cooking cavity.

In the drawing the oven wall 1, e.g. the rear wall, of the oven cooking cavity is shown, with an electrical ignition wire 2 extending through a hole 3 in the wall 1 via an insulator 4. Although not shown in the drawing, the ignition wire 2 extends from the vicinity of the gas burner disposed within the oven cavity, through the oven wall 1 of the oven cavity to a spark ignition device located external of the oven cavity.

If steps are not taken to prevent it, when the gas combination microwave oven is operated in its microwave mode, there could be a huge leakage of microwave energy from the oven cavity, in the region of the hole 3 where the electrical ignition wire 2 extends from the oven cavity and this would cause an unacceptable hazard to a user of the oven.

In order to minimise the leakage of microwave energy from the oven cavity a microwave choke assembly 5 is provided as will be described.

To the outside surface of the oven wall 1 is attached a rectangular metallic structure 6, the open side of which is closed by a face plate 7, the metallic structure 6 and the face plate 7 together forming a choke chamber 8. A metallic tube 9, conveniently of circular cross-section, is provided which extends through the face plate 7 outwards from the choke chamber 8, and through which the ignition wire 2 extends. The sizing of the tube 9 and its relative position in the choke chamber 8 is chosen to minimise the leakage of microwave energy from the oven cavity. In some applications it may be convenient to arrange that the position of the tube 9 is adjustable so that microwave energy leakage may be "tuned" to a minimum. If necessary ferrite beads may be threaded on the ignition wire 2 to further reduce microwave energy leakage.

Although the arrangement which has been described is particularly applicable to gas combination microwave ovens, it may also be applicable to other forms of microwave cooking oven where one or more electrical leads are required to extend into the oven cavity. For example, an otherwise conventional microwave oven may be provided with a temperature sensing probe which is inserted in a food item to be cooked, an electrical lead from which extends from the oven cavity to a display which enables an electrical readout of the temperature to be obtained and displayed on the oven control panel.

Claims

1. A microwave cooking appliance comprising an oven cavity, a microwave energy source for said oven cavity and an electrical lead which extends through the wall of said oven cavity, said electrical lead having a microwave energy choke arrangement where it extends from said oven cavity for minimising microwave energy leakage thereat.

2. An appliance as claimed in claim 1, in the form of a gas combination microwave oven, having a gas burner arrangement located within said oven cavity, a spark ignition arrangement located externally of said oven cavity, said electrical lead extending from the vicinity of said gas burner arrangement through the wall of said oven cavity to said spark ignition arrangement.

3. An appliance as claimed in claim 1 or claim 2, in which said choke arrangement comprises a metallic tube through which said electrical lead extends.

4. An appliance as claimed in claim 3, in which said choke arrangement comprises a choke chamber immediately adjacent the wall of said oven cavity and into which said metallic tube extends.

5. An appliance as claimed in claim 4, in which the relative positions of said tube and said choke chamber are determined by the frequency of the microwave energy of said microwave energy source.

6. An appliance as claimed in claim 5, in which the relative positions of said tube and said choke chamber are adjustable for microwave energy tuning purposes.

7. A microwave cooking appliance substantially as hereinbefore described with reference to the accompanying drawing.