US3641921A - Electric toaster - Google Patents

Abstract

An electric toaster which has in a casing thereof a stationary plane heating element disposed centrally of said casing and a pair of movable plane heating elements disposed on both sides of said stationary plane heating element in opposed relation thereto, and which is capable of browning slices of bread over their entire surfaces to the same extent by the stationary and movable plane heating elements, holding the slices of bread from both sides in direct contact therewith, irrespective of the thickness and size of the slices of bread.

Description

United States Patent Toyooka et al.

ELECTRIC TOASTER Inventors: Tadao Toyooka, Toyonaka; Hiromutsu Ueda, lbaragi; Takeo Nishida; Atsuo Ono,

both of Toyonaka, all of Japan Assignee: Matsushita Electric Industrial Co., Ltd.,

Osaka, Japan Filed: Nov. 12, 1970 Appl. No.: 88,865

Foreign Application Priority Data June 24, 1970 Japan ..45/55464 July 15, 1970 Japan 45/62378 Sept. 26, 1970 Japan ..45/842l9 Nov. 14, 1969 Japan ..44/ 108646 Apr. 11, 1970 Japan ..45/3494l U.S.Cl ....99/390, 219/521 Int. Cl. ..A47j 37/08 Field of Search ..99/390, 391, 372; 219/549,

References Cited UNITED STATES PATENTS Chandler "99/399 1 Feb. 15, 1972 2,849,946 9/1958 Palmer ..99/390 2,868,946 1/1959 Stephensonm. ..2l9/549 X 2,910,929 1 1/1959 Sorenson ..99/ 390 2,922,867 1/1960 Crump ..2l9/549 X 2,938,992 5/1960 Crump 219/549 X 3,060,303 10/ 1962 Skoglund et al. ..2l9/549 3,349,225 10/1967 Dubois ..2l9/549 X 3,349,359 10/1967 Morey ..2l9/549 X Primary Examiner-Walter A. Scheel Attorney-Stevens, Davis, Miller & Mosher [57] ABSTRACT An electric toaster which has in a casing thereof a stationary plane heating element disposed centrally of said casing and a pair of movable plane heating elements disposed on both sides of said stationary plane heating element in opposed relation thereto, and which is capable of browning slices of bread over their entire surfaces to the same extent by the stationary and movable plane heating elements, holding the slices of bread from both sides in direct contact therewith, irrespective of the thickness and size of the slices of bread.

7 Claims, 12 Drawing Figures SHEET 1 [IF 7 FIG.

ATTORNEY! PATENTEDFEB 151m SHEET 2 0F 7 FIG.

PATENTEU EB 15 I972 SHEET 4 OF 7 FIG.

PAIENTED FEB I 5 I972 SHEET 5 BF 7 FIG. 5

PATENIEnrw 15 m2 3,641,921

SHEET 6 [IF 7 ELECTRIC TOASTER The present invention relates to an electric toaster of the type in which slices of bread are toasted between heating elements in direct contact therewith.

The majority of the commercial toasters are of the type which resorts'to convection and radiation of heat for toasting slices of bread. These toasters generally comprise heating elements each consisting of an electric heating wire wound around mica or asbestos and guards disposed in front of said respective heating elements so as to define a suitable space therebetween, said heating elements being energized after a slice of bread is placed in the space between said guards, whereby the slice of bread is toasted by convection and radiation of the heat generated by said heating elements.

In this type of toasters, since the heat of the heating elements is not directly transmitted to the slice of bread, the efficiency of the toasting operation is poor and hence an undesirably long time is'required or otherwise the capacity of the heating elements is required to be increased. In addition, the toasting operation occasionally results in uneven browning of the toast or excessively deep browning of the toast due to extraction of an unnecessarily large amount of water from the bread, which spoils the taste of the resultant toast.

In order to solve such problems of the conventional toasters as described above, the present invention has for its object the provision of a simple and economic electric toaster which is capable of toasting slices of bread by holding them between heating elements in directly contact therewith.

Since the basic concept of the present invention is to toast a slice of bread by holding it between heating elements in contact therewith, the heating elements used must generally planar in shape. As a plane heating element, there can be considered one in which an electric heating wire lapped around a substrate such as mica and a Teflon-coated metal sheet are arranged withan optional insulating space therebetween; one in which an inorganic insulating material having an electric heating wire embedded therein is integrally coupled with a metal sheet or the like; or one such as is used in one embodiment of the present invention in which an electric heating wire is molded-in a heat-resistant resin material. In either case, it is of course essential that the surface to be brought into contact with bread consists of an electrically insulating material, but it is also essential fromthe standpoint of specification, safety and construction, that the effective heating area of the heating element is an optional insulating distance spaced from the peripheral edge of the heating element.

. In toasting a slice of bread by holding it between such plane heating elements in contact therewith, it should be avoided that the portion of the slice of bread which is opposite to the insulating portion of the heating element is not browned and remains in white color. In order to avoid such phenomenon, it is desirable to make the length of a bread inserting opening equal to the dimension of effective heating region of the heating element, but this alone is not entirely satisfactory in that the upward movement of the slice of bread upon completion of the toasting is prevented by the rim of the bread inserting opening. In the present invention, a consideration is given also in this point.

In any toaster as well as in the conventional ones, it is desirable that both surfaces of a slice of bread are browned to the same extent and evenly, and to this end it has been customary to change the capacity of the heating elements while taking the construction of the easing into account. In the toaster of the present invention, however, a special consideration is given to the construction thereof so as to obtain a better result of toasting in this respect, without changing the capacity of the heating elements used.

' Further, in the toaster of the invention the stroke of the movable heating elements relative to the stationary heating element ismade sufficiently large to ensure that slices of bread of a thickness ranging from a large to small thickness, which are being sold on the market, can be toasted. ln thiscase, a special device must be made to a bread carrier frame to be used, so that the bread carrier frame singly is capable of carrying thereon either a sliceof bread having a large thickness or a slice of bread, having a small thickness, because, if the bread carrier frame isof a dimension adapted for carrying a slice of bread having a small thickness, the slice of bread would fall into the space between the bread carrier frame and the heating element when the interval between the confronting heating elements-is largest. In this respect, the present invention also provides a simple construction.

Now, the present invention will be described in detail hereunder with reference to the accompanying drawings.

In the drawings,

FIG. 1 is a perspective view showing the internal construction of an embodiment of the electric toaster according to the present invention, as viewed from the side on which a bread carrier frameelevating mechanism is located;

FIG. 2 is a front elevational view of the electric toaster shown in FIG. 1;

FIG. 3 is a perspective view showing the internal construction of another embodiment of the electric toaster of the invention;

FIG. 4 is a front elevational view of the electric toaster shown in FIGS;

FIG. 5 is a cross-sectional view showing the arrangement for evenly toasting slices of bread;

FIGS. 6A and 6B, are perspective views of the bread carrier frame, of which FIG. 6A shows the state of the bread carrier frame with no external force imposed thereon and FIG. 6B

shows the state of the same with an external force imposed thereon;

FIGS. 7A and 7B are illustrative views showing the manner in which the bread carrier frame shown in FIGS. 6A and 6B is used;

FIG. 8 is a cross-sectional side view illustrating bread guides and means for preventing overheating of the heating elements;

FIG. 9 is a diagram showing in comparison the performances of the toaster according to the present invention and the conventional toaster with respect to the temperature rise at the center of a slice of bread; and

FIG. 10 is a diagram showing in comparison the performances of the toaster according to the present invention and the conventional one with respect to the amount of water remaining in a slice of bread at each of different wattages.

Referring to the drawings, numeral 1 designates a casing of the toaster and 2 designates plane heating elements each consisting, for example, of a glass cloth having electric heating wires incorporated therein as part of the warp threads and weft threads and molded in a heat-resistance resin, such as silicone enamel or polyimide resin. Two of the heating elements 2 are stationarily disposed centrally of the casing l and one heating element 2 is movably disposed on each side of the central heating elements 2. The central heating elements 2 are mounted on a frame 4. Numeral 5 designates a reflector for each movable heating element 2 and numeral 6 designates sideplates. Numeral 7 7 designates an elevator plate which is provided with main bread carrier frame 8, two guide rollers 10 for guiding arms 9, an operating lever 11 and a latch 12. An upward movement of the elevator plate 7 is guided by a guide rod 13 and a spring 14 is provided for causing the upward movement of the elevator plate. As shown in FIG. 1, the arm 9 pivotably supports each of movable heating element supporting frames 4 from both sides, and both of the arms 9 are constantly urged toward the center of the casing by a spring 15.

The latch 12 engages a cooperating latch 16 when the operating lever 11 of the elevator plate 7 is lowered, thereby to hold the elevator plate 7 in its lowered position. The engagement between the latches l2 and I6 is released by the action of control means, e.g., a relay 17, connected to the latch 16, and upon release of the engagement, the bread carrier frames 8 integral with the elevator plate 7 are elevated under the biasing force of the spring 14. The arms 9 are bent outwardly at the lower portions thereof as at 9'. Therefore, when the rollers 10 are shifted to the outwardly bent portions 9' of the arms 9 while rolling on said arms, the arms are set free from the rollers 10 and concurrently the movable heating ele- I ments are moved toward the center of the casing under the biasing force of the spring 15. The reverse operation will be obvious and not explained herein.

Numeral l8 designates grooves for guiding the vertical movement of the bread carrier frame 19, a bottom cover of the casing having air passage holes as formed. therein, bread guides which will be described hereinafter, 21 auxiliary bread carrier frames cooperating with the main bread carrier frame 8 respectively, 22 leaf springs coupling the main bread carrier frame 8 and the auxiliary bread carrier frames 21 with each other and stretching or contracting incident to the movement of the movable heating elements toward or away from the stationary heating elements, and 23 pins which connect the leaf springs 22 with the bread carrier frames 21 and are slidably received in guide slots 24 respectively.

When a slice of bread 25 is inserted into one of the toasting chambers, the heating elements of both toasting chambers are prepared to'be energized. In this case, the auxiliary bread carrier frames 21 are widely spaced from the main bread carrier frame 8 by'the action of the springs 22 as shown in FIG. 6A and the slice of bread is not allowed to drop off the bread carrier frame 8 as seen in FIG. 7A. When the slice ofbread is held from both sides by the movable heating element and the stationary central heating element, the main bread carrier frame and the auxiliary bread carrier frames are placed in the state as shown in FIG. 7B and, as seen, the thickness of the slice of bread poses no problem at all. Then, the operating lever 11 is while being carried on the bread carrier frame 8, and at the same time the rollers 10 on both sides of the elevator plate 7 move down while rolling on the respective arms 9. When the rollers 10 reach the outwardly bend portions 9 of the arms 9, the arms are set free from the rollers 10 and the movable heating elements are moved toward the center of the casing under the biasing force of the'compression spring 15, so that the slice of bread in each toasting chamber is held from both sides by the-movable heating element and the stationary heating element. At the same time, the latch 12 is brought into engagement with the latch 16, when a source switch is actuated to conduct a current through the respective heating elements 2.

Since the heat generated by the respective plane heating elements is directly transmitted to the slice of bread, the heating efficiency is high and the temperature at the center of the bread rises very quickly. Such features of the toaster are shown in FIG. 9. Moreover, since the slice of bread is held in plane contact with the heating elements, the amount of water removed from the slice of bread is not so large as in the conventional toaster and the surfaces of the slice of bread are browned, with a suitable amount of water remaining in the bread, so that a toast can be obtained which gives a good feeling of touch to the teeth. Further, because of the plane contact, the surfaces of the slice of bread are browned evenly over the entire areas thereof and hence the resultant toast has an appearance stimulating ones appetite. The amount of water remaining in the bread is illustrated in FIG. 10.

As will be seen in FIG. 5, the central stationary heating elements have only a small portion thereof exposed to the outside air and define a box-shaped compartment by reason of their arrangement, in which heat tends to be trapped. The movable heating elements are more easily brought into contact with the outside air through the spaces between they and the casing the space surrounding the movable heating element is large to provide for the movement of said movable heating element. Further, the bread carrier frame guiding grooves 18 provide for movement of air. Under such conditions, it is impossible to brown the surfaces of the slice of bread evenly. Namely, the surface in contact with the central heating element will be browned deeper than the surface on the other side. While such unevenness may of course be avoided, for example, by differentiating the capacities of the movable heating element and the central stationary heating element, it will be more pushed down, whereupon the'slice of bread 25 is lowered economical, from the overall standpoint of production and management of the toaster, to solve such problem structurally without differentiating the capacities of the respective heating elements. Further, by so doing, the occurrence of an unevenness in degree of toasting between both surfaces of a slice of bread can be prevented economically and in addition, where it is desired to provide a temperature sensing element in the toaster, a smooth return movement of control means in a continuous toasting operation can be ensured owing to the cooling effect of the air passing through the toaster. According to the present invention, the problem is solved simply by forming a suitable size of hole a, b in the bottom cover 19 and the central heating element supporting frame 3, as shown in FIG. 5, to provide for the passage of air in the directions of the arrows through the compartment formed between the central heating elements.

If thecompressive force of the heating elements is too weak, the heating efficiency is degraded by the airgap formed between the slice of bread and the heating elements, whereas if it' is too strong, a smooth upward movement of the bread carrier frame cannot be obtained unless the biasing force of the spring 14 is increased. It has been confirmed through experiment that the surfaces of the slice bread can be browned evenly and a smooth upward movement of the carrier frame can be obtained when the compressive force of the spring 15 is within the range of0.1 to 0.2 g./cm.

When the slices of bread have been toasted for a predetermined period in the manner described and the control means is actuated, the latch 12 is disengaged from the cooperating latch 16 and the elevator plate 7 and the bread carrier frame 8 are elevated under the biasing force of the spring 14. lt is to be noted that in the toaster of the invention an arrangement is made such that the heating elements in one toasting chamber only can be energized.

As stated previously, it is generally essential from the standpoint of specification, safety and constructional requirement, that the heat generating portion of the plane heating element is an optional distance spaced from the peripheral edge thereof for the sake of insulation. In FIG. 8, numeral 2' indicates the effective heating area of the heating element 2. If

the length of the bread inserting opening formed in the casing,

is substantially equal to and in register with the distance between the opposite sidewalls 6, or substantially equal to the length of the heating elements 2, the portion of the slice of bread which is held between the insulating areas of the heating elements will not be browned and remain white. Therefore, the bread inserting opening should be formed in a length equal to the horizontal length of the effective heating area 2 of the heating elements 2, Le, in the length and at the location as shown in FIG. 8. This alone, however, is not entirely satisfactory because, if the slice of bread 25 inserted into the toasting chamber is displaced even sightly in the longitudinal direction of the toaster, the upward movement thereof upon completion of the toasting operation will be prevented by the transverse edge of the bread inserting opening and the slice of bread will not emerge from the toaster. In order to avoid such problem, according to the present invention a metal guide 20 is connected to each sidewall 6 at a location adjacent the stationary heating element, projecting inwardly from said sideplate nearly to the edge'of the effective heating area of the heating element, as shown'in FIGS. 1 and 8, the width of said metal guide 20 being slightly smaller than the thickness of the thinnest possible slice of bread being sold on the market. The provision of such metal guides 20 has an additional advantage that, even if the heating elements should be energized with no slice of bread therebetween by any chance, the central stationary heating element and the cooperating movable heating element are spaced from each other at least by a distance equal to the width of-said metal guides and overheating of said heating elements can be avoided.

Now, another type of the elevating mechanism will be described with reference to FIGS. 3 and 4 wherein similar parts as those shown in FIGS. 1 and 2 are indicated by the same numerals. This type of elevating mechanism differs from that shown in FIGS. 1 and 2 in that the arms 9 are straight and do not have the outwardly bent portions as shown in FIGS. 1 and 2, and also in that the elevator plate 7 has a relatively narrow portion 7' and a relatively wide portion 7 formed integrally with and successively to said relatively narrow portion 7'. The inwardly bent-ends of the arms 9 are in engagement with the opposite sideedges of the elevator plate 7. Therefore, when the elevator plate 7 is moved up and down, the arms 9 are caused to make a pivotal movement by the edges of the narrow portion 7 or the wide portion 7" of the elevator plate. This type of elevating mechanism is more adapted for mass production than the type of FIGS. 1 and 2, since the dimensional control of the narrow portion 7 and the wide portion 7" of the elevator plate 7 is easier than the latter.

What we claim is:

1. An electric toaster comprising a stationary plane heating element disposed in the center of a casing, a pair of movable plane heating elements provided on both sides of said stationary heating element in opposed relation thereto, a spring for constantly urging said movable heating elements toward said stationary heating element, a pair of arms for operating the movable heating elements against the biasing force of said spring, elevator means which moves said arms against the biasing force of said spring on its upward stroke and thereby moves said movable heating elements away from said stationary heating element respectively, a spring for constantly urging said elevator means upwardly, a bread carrier frame connected to said elevator means for vertical movement between said movable heating elements and said stationary heating element, a guide rod for guiding the vertical movement of said elevator means, means for latching said elevator means in its lowered position, and means for releasing the elevator means from the latching means upon completion of the toasting operation.

2. An electric toaster as defined in claim 1, wherein said elevator means comprises an elevator unit having a relatively narrow portion and a relatively wide portion formed successively downwardly of said relatively narrow portion, and said arms are held in engagement with the opposite edges of said elevator unit.

3. An electric toaster as defined in claim 1, wherein said elevator means comprises an elevator unit provided thereon with rollers for rolling engagement with the inner surfaces of said arms, while said arms are bent outwardly at their lower portions.

4. An electric toaster as defined in claim 1, wherein said stationary heating element is mounted on a supporting frame which is open at the upper end, and a bottom plate provided below said supporting frame is formed with an air passage opening for communicating the interior of said supporting frame with the outside of the toaster through said air passage opening.

5. An electric toaster as defined in claim 1, wherein said bread carrier frame is composed of a main carrier frame and auxiliary carrier frames coupled with said main carrier frame by a spring respectively, said spring being stretched or contracted incident to the movement of said movable heating elements toward or away from said stationary heating element to vary the width between the main carrier frame and the auxiliary carrier frame, so that said bread carrier frame may carry slices of bread irrespective of the thickness of said slices of bread.

6. An electric toaster as defined in claim 1, wherein the compressive force of said spring is selected within the range of 0.1-0.2 g./cm. with respect to the surfaces of said heating elements.

7. An electric toaster as defined in claim 2, wherein metallic elements projecting to the opposite vertical edges of the effective heating areas of said heating elements respectively are provided adjacent the central stationary heating element for guiding a slice of bread and for preventing overheating of the heating elements.

UNITED STATES P TENT OFFICE I CERTIFICATE OF CORRECTION Patent No. 3 ,641, 921 I Dated February 15, 1972 Inventor(s) Tadao TOYOOKA et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Claim for Convention Priority, one of the six Japanese applicationsis omitted and should be included as follows:

Japan, Patent Appln. N-45/97543 filed Sept. 30, 1970-- Signed and sealed this Lith day of July 1972.

(SEAL) Attest:

EDWARD I LFLETCHER, JR. ROBERT GOTTSCHALK Attesting ()fficer Com issioner of Patents FORM po'wso (10'69) USCOMM-DC seam-ps9 Q U S. GOVERNMENT PRINTING OFFICE I969 0-306-33-1 UNITED STATES P TENT OFFICE I CERTIFICATE ()F CORREQTION Patent N 3,641,921 Dated February 15, 1972 Inventor(s) Tadao TOYOOKA et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Claim for Convention Priority, one of the siX Japanese applications is omitted and should be included as follows:

Japan, Patent Appln. N 45/975413 filed Sept. 30, 1970-- Signed and sealed this 414th day of July 1972.

(SEAL) Attest:

EDWARD MELETCHER, JR. 1 ROBERT GOTTSCHALK Attesting Officer Com issioner of Patents

Claims (7)

1. An electric toaster comprising a stationary plane heating element disposed in the center of a casing, a pair of movable plane heating elements provided on both sides of said stationary heating element in opposed relation thereto, a spring for constantly urging said movable heating elements toward said stationary heating element, a pair of arms for operating the mOvable heating elements against the biasing force of said spring, elevator means which moves said arms against the biasing force of said spring on its upward stroke and thereby moves said movable heating elements away from said stationary heating element respectively, a spring for constantly urging said elevator means upwardly, a bread carrier frame connected to said elevator means for vertical movement between said movable heating elements and said stationary heating element, a guide rod for guiding the vertical movement of said elevator means, means for latching said elevator means in its lowered position, and means for releasing the elevator means from the latching means upon completion of the toasting operation.

2. An electric toaster as defined in claim 1, wherein said elevator means comprises an elevator unit having a relatively narrow portion and a relatively wide portion formed successively downwardly of said relatively narrow portion, and said arms are held in engagement with the opposite edges of said elevator unit.

3. An electric toaster as defined in claim 1, wherein said elevator means comprises an elevator unit provided thereon with rollers for rolling engagement with the inner surfaces of said arms, while said arms are bent outwardly at their lower portions.

4. An electric toaster as defined in claim 1, wherein said stationary heating element is mounted on a supporting frame which is open at the upper end, and a bottom plate provided below said supporting frame is formed with an air passage opening for communicating the interior of said supporting frame with the outside of the toaster through said air passage opening.

5. An electric toaster as defined in claim 1, wherein said bread carrier frame is composed of a main carrier frame and auxiliary carrier frames coupled with said main carrier frame by a spring respectively, said spring being stretched or contracted incident to the movement of said movable heating elements toward or away from said stationary heating element to vary the width between the main carrier frame and the auxiliary carrier frame, so that said bread carrier frame may carry slices of bread irrespective of the thickness of said slices of bread.

6. An electric toaster as defined in claim 1, wherein the compressive force of said spring is selected within the range of 0.1-0.2 g./cm.2 with respect to the surfaces of said heating elements.

7. An electric toaster as defined in claim 2, wherein metallic elements projecting to the opposite vertical edges of the effective heating areas of said heating elements respectively are provided adjacent the central stationary heating element for guiding a slice of bread and for preventing overheating of the heating elements.

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