GB2088995A

GB2088995A - Timing Device for a Household Appliance

Info

Publication number: GB2088995A
Application number: GB8128141A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-10-09
Filing date: 1981-09-17
Publication date: 1982-06-16
Also published as: DE3038168C2; IT8124304A0; IT1138928B; NL8104598A; GB2088995B; FR2492013A1; DE3038168A1; FR2492013B1

Abstract

A timing device, particularly a pneumatic timing device for use in a household appliance such as an electric toaster, comprises a cylinder 10 which has a piston guide surface 60 and an adjoining enlarged end section 66, and a piston 30 having a sealing skirt 62. In operation, the sealing skirt 62 sealingly co-operates with the guide surface 60 and moves at a rate determined by orifice 68, and in the rest position is disposed unstressed in the enlarged end section 66. The cylinder bore is shaped so that the transition point between the guide surface 60 and the enlarged end section 66 is formed as an abrupt transition with a sharp edge at the end of the guide surface. Any debris which collects on the piston is wiped off by the sharp edge, each time the timer is set. <IMAGE>

Description

SPECIFICATION Timing Device for a Household Appliance The present invention relates to a timing device and has particular reference to a pneumatic timing device for use in a household appliance such as an electric toaster.

In DE-PS 26 24 578 there is described a pneumatic timing device incorporated in an electric toaster. The device comprises a piston with a sleeve which remains in a cylinder which is provided in a lower region thereof with a cylindrical slide surface co-operating with the sealing sleeve. The cylinder is enlarged in its upper region by an inclined transition so that the sealing sleeve in a rest state is able to rest unstressed in this enlarged space. Problems with irregularities of running time occur in a timing device of this kind and there is a need for a device which provides a more uniform running time.

According to the present invention there is provided a timing device for a household appliance, comprising a cylinder provided with a bore having a first portion defining a piston guide surface and an enlarged second portion connected to the first portion by an abrupt transition formed by a sharp edge of the bore wall at an axial end of the guide surface, and a piston comprising a sealing portion engaged in the cylinder bore to sealingly co-operate with the guide surface and to be displaceable against diminishing fluid pressure into an unstressed rest position in the second portion of the bore.

Compared with the known device, an appreciable improvement in the uniformity of the running time is achieved by a device of the present invention, with no increase in manufacturing effort. The guide surface of the cylinder bore and/or the co-operating surface of the piston sealing portion may be provided with a thin lubricant film, for example silicone fat, to enhance the running life. Foreign matter, for example grains of plastics material of the cylinder, which are residual from manufacture of the cylinder, can attach to this lubricant film and, in the known device, could lead to leakage between the cylinder and the sealing means or to changes in the coefficient of friction. Foreign matter of that kind can now be stripped off by the sealing means through the sharp edge and retained at the transition point of the fat also stripped off through the sharp edge.

The sudden transition is expediently formed as step which includes a sharp angle with the slide wall of the cylinder. This angle can be about 900 or less, preferably about 600.

An embodiment of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which Fig. 1 is a schematic vertical sectional elevation of part of an electric toaster with a pneumatic timing device according to the said embodiment; and Fig. 2 is a detail, to an enlarged scale and in section corresponding to that of Fig. 1, of part of the timing device showing a modification.

Referring now to the drawings, in Fig. 1 there is shown a bread toaster 1 comprising a housing part 2 which contains a control with a guide 4 for a bread stage 6 and which is provided with a top opening 8, in which a cylinder 10 of a pneumatic short-term timing device is detented. The bread stage 6 comprises a guide element 12 sliding in the guide 4 and a bread carrier 14 connected to the element 12 and arranged to carry bread slices 1 6. The bread carrier 14 extends through a guide slot 1 8 in the side of the housing part 2 facing a toasting chamber 20.

A resilient inclined latching arm 22 is formed on the guide element 12 and serves for latching the bread stage 6 in the lowered, toasting position, the arm 22 co-operating with a fixed latching projection 24 at the cylinder 10. A tension spring 28 is hooked onto the guide element 12 and to a housing projection 26 and imparts to the bread stage an upwardly directed bias.

A piston 30 of rubber is displaceably arranged in the cylinder 10 and has a piston rod 32, from thelower end of which a spring fastening arm 34 extends laterally.

Hooked onto the arm 34 is one end of a tension spring 36, which extends along the outside of the cylinder 10 and is hooked at its other end into a projection 38 on the cylinder 10.

The spring 36 acts to draw the piston into the cylinder.

The piston rod 32 and the guide element 12 have drag projections 40 and 42, both of which co-operate with a common lifting lever 44 which is mounted to be vertically displaceable in the front wall of the housing part 2 and which is provided with a handle at the outside of the housing part 2.

Fig. 1 shows the component elements at the end of the lifting stroke of the lifting lever 44, through the downward motion of which the bread stage is lowered against the effect of the spring 28 and the bread is drawn fully into the chamber 22. At the same time, the timing device is stressed against the effect of the spring 36, in that the piston 30 is drawn into its lowermost position. The latching arm 22 at the end of the lifting stroke latches behind projection 24 of the cylinder. After reiease of the lifting lever 44, the piston 30 slides upwardly in the cylinder 10 under the effect of the spring 36, wherein the running speed and therefore the running time or the toasting time depend on the setting of a throttle screw 46 and an upper air exit of the cylinder 10.

The piston assembly through the drag projection 40 entrains the lifting lever 44 until, in the position illustrated in chain-dotted lines, the latching arm 28 is unlatched, whereby the spring 28 again lifts the guide element 12 and the bread stage 6 with the bread 1 6. The rest position of the piston 30 is indicated by dashed lines 31.

The cylinder is provided in its lower region with a cylindrical slide surface 60, which is lubricated by a thin film of silicone fat and during the operation of the timing device co-operates with a sealing sleeve or skirt 62 of the piston 30. An enlarged end section 66 of the cylinder adjoins the surface 62 by way of a right-angled step 64, and a throttle channel 68, which co-operates with the throttle screw 46, leads outwardly from the section 66. As soon as the skirt 62 of the piston 30 has passed the step 64, air can escape from the cylinder around the skirt 62, whereby the piston abruptly moves to its end position.In the end position, the skirt 62 rests unstressed in the enlarged end section 66 without touching the walls of the cylinder On restoring the timing device to its operative state by means of the lever 44, the skirt 62 is compressed on moving over the step 64 until it is fully engaged with the narrower cylindrical slide surface 60.

Fig. 2 shows a detail of a modification in which a cylinder 210 with a cylindrical slide surface 260, to which an enlarged end section 266 of the cylinder 210 adjoins by a transition in the form of a step 264. A piston 230, which is illustrated in the rest position, has a sealing sleeve 262 which in operation of the timing device sealingly cooperates with the surface 260. The step 264 includes an acute angle of about 750 with the slide surface 260 and meets with the surface 260 in a sharp edge 265. The piston 230 consists of a resilient plastics material or rubber.

Claims

1. A timing device for a household appliance, comprising a cylinder provided with a bore having a first portion defining a piston guide surface and an enlarged second portion connected to the first portion by an abrupt transition formed by a sharp edge of the bore wall at an axial end of the guide surface, and a piston comprising a sealing portion engaged in the cylinder bore to sealingly cooperate with the guide surface and to be displaceable against diminishing fluid pressure into an unstressed rest position in the second portion of the bore.

2. A device as claimed in claim 1, wherein the sharp edge is defined by a step in the bore wall, the step including an acute angle with the guide surface.

3. A device as claimed in claim 2, wherein the angle is close to 900.

4. A device as claimed in claim 2, wherein the angle is substantially 600.

5. A timing device for a household appliance, the device being substantialiy as hereinbefore described with reference to the accompanying drawings.

6. An electric toaster provided with a timing device as claimed in any one of the preceding claims, the device being arranged to control bread toasting means of the toaster.

7. An electric toaster substantially as hereinbefore described with reference to the accompanying drawings.