Patent Application
20060027563
1. Field of Application and Prior Art
The invention relates to an appliance for switching on and off several heating devices of a cooker, as well as to a cooker having such an appliance.
Radiant heaters with a certain diameter, which for example exceeds 230 mm, suffer in part from the problem that their energy supply through so-called energy or power control devices on the one hand and an excess temperature protection for a glass ceramic plate over the radiant heater through so-called temperature limiters on the other are limited by the maximum power levels which can be applied and by a so-called flicker standard. The flicker standard indicates how frequently in a specific time period a particular power can be switched on and off in a cooker and is intended to prevent significant network reactive effects in line with the power supply companies.
The switching capacity both of the power or energy control devices and the temperature limiters, which operate with so-called snap-action switches, such as for example described in U.S. Pat. No. 6,064,045 and U.S. Pat. No. 4,633,238, is generally limited. For the USA it is for example 12 or 13 Ampere, so that 100,000 switching cycles must be attainable.
With the conventionally predetermined mains voltage, a further increase of the power of a radiant heater is consequently impossible.
2. Problem and Solution
The problem of the invention is to provide the aforementioned appliance, together with a cooker, with which the prior art disadvantages can be avoided and in particular the activation of a further heating device for increasing the heating power of a heater of a hotplate can be brought about for minimum cost.
This problem is solved by an appliance having the features of claim 1 and a cooker having the features of claim 11. Advantageous and preferred developments of the invention form the subject matter of the further claims and are explained in greater detail hereinafter. By express reference the wording of the claims is made into part of the content of the description. In the sense of the present application the word “have” means that this feature can be inter alia provided, independently of other features.
According to the invention this problem is solved in that the appliance has a cyclic energy control device, such as is for example known from U.S. Pat. No. 6,064,045, which has a distance change for a tripping path of a first switching device contained in the power control device. The spacing change can in turn be influenced by the adjusting path covered on the energy control device, for example by a rotary movement using a rotary toggle or knob of the energy control device. In turn the tripping path defines the on or off times or their mutual ratio, with which the heating device is either deactivated or activated with full power. As a result of the timing or cyclic ratio or the length of the on and off times, the so-called averaged energy generation can take place and there is also a so-called average power. At one point of the tripping path is provided a second tripping point, where a second switching device is activated or switched on and with which a second heating device can be activated. This second heating device is advantageously an additional heater relative to the first heating device.
If the two heating devices form a hotplate, it is possible in this way for the power of the second heating device not to have to be switched by means of the same first switching device, which also switches the first heating device. This permits higher heating powers in a hotplate than have hitherto been possible.
Advantageously the spacing change is such that, at the second tripping point, it sets the tripping path for the first switching device at an initial value again for the definition of the on and off times and the mutual ratio thereof and as from this point with a further increasing adjusting path the tripping path is changed again, particularly in the same direction as previously. In other words the spacing change with an overall increasing adjusting path the tripping path rises from an initial value to the second tripping point and consequently correspondingly influences the first switching device. At the second tripping point, by means of the second switching device, the second heating device is activated in addition to the first heating device. The trip for the first heating device is reset again and therefore so is its average power output over and beyond a certain time, for example in the case of a cooker is set to a lower stage. Advantageously said second tripping point is positioned so that the average power generated up to just prior to the second tripping point by the first heating device corresponds to that which is then generated by the second heating device. The average power generated by the first heating device as from the second tripping point is once again greatly reduced and starts to rise again with an increasing adjusting path and increasing tripping path. Thus, at the second tripping point a certain constant value of the average power is produced by the second heating device. The variable part, whose level can be influenced via the energy control device at the first heating device then comes in rising manner again from the heating device. An advantage of this arrangement is that only the first heating device has to be timed, namely with a somewhat lower current than corresponds to the total produced average power.
The appliance can have a temperature limiter or can be connected thereto and this is located in the action area of the first heating device and in certain circumstances also in the action area of the second heating device. This temperature limiter can for example be constructed in the manner described in U.S. Pat. No. 4,633,238 and on exceeding a specific temperature and in particular for protecting a glass ceramic plate positioned over the heating device, switches off the first heating device. For this purpose the temperature limiter can have a switch, which is located in the connection path for the first heating device.
As stated hereinbefore, the cyclic energy control device can be constructed in such a way that the adjusting path is influenced by a linear movement or preferably a rotary movement. In the case of a rotary movement it should be somewhat less than 360°. By means of the spacing change the rotary movement is transformed into a substantially linear tripping path. For this purpose the energy control device or the spacing change can for example have a rotary spindle with a non-circular disk, on whose outer edge engages part of a switching device or the first switching device, whose switching behaviour with respect to the on and off times or their mutual ratio is dependent on the variable tripping path, that is the variable radius of the disk. For the second tripping point a similar trip can be provided, in particular once again constituted by a non-circular disk or a type of cam. AT the second tripping point said disk or cam activates the second switching device in order to connect in the second heating device. However, here there is no need for a continuously modified radius, because no increasing path is needed.
The second tripping point, where the second heating device separates the generation of the heating power from the first heating device is preferably such that the average power of the first heating device at this point is less than half the maximum, total power, for example roughly a third. At such a point during cooking processes there is normally the transition between the boiling, for example of liquids, and the frying of for example meat in a pan. The particularly high heating power levels at a hotplate advantageously producible by means of the invention are particularly advantageous for such high power frying processes, in addition to the rapid parboiling of saucepans with water.
In the case of a cooker according to the invention, there can be two heating devices for a hotplate, the cooker having a hob with a glass ceramic plate and radiant heaters below the same, together with several such hotplates. The second heating device has a maximum continuous output power corresponding to a power density of approximately 2.5 W/cmý. At this value the second heating device can generally be operated without any temperature monitoring with respect to the overheating of the glass ceramic plate. Thus, for the second heating device or the operation thereof, there is no need for temperature monitoring with respect to overheating of the glass ceramic. The power density can also be chosen above 2.5 W/cmý, if this is allowed or can be gathered from the glass ceramic manufacturer's specifications or tests.
The two heating devices are advantageously electrically separated from one another. In particular, they are contained in a so-called single circuit heater, as opposed to two-circuit heaters, which permit a size increase of a hotplate for larger cooking vessels. The first and second heating devices can comprise elongated heating resistors, particularly in flat band form, which are installed on a surface in spiral or meander-like form. The two heating devices in the form of heating strips are parallel in each case and cover the same overall surface. Thus, in the case of such a hotplate of a hob the second heating device does not give rise to a larger heating surface and instead there is a greater heating power for the same heating surface.
These and other features can be gathered from the claims, description and drawings and the individual features, in each case singly or in the form of subcombinations, can be implemented in an embodiment of the invention and in other fields and can represent advantageous, independently protectable constructions for which protection is claimed here. The subdivision of the application into individual sections and the subheadings in no way limit the general validity of the statements made thereunder.
Embodiments of the invention are described hereinafter relative to the diagrammatic drawings, wherein show:
Both heating devices 13 and 15 can be so-called radiant heaters, such as are for example described in U.S. Pat. No. 5,498,853 to which express reference is made. They are operated at mains voltage, that is in Germany for example 230V and in the USA 120 to 240 V. They are normally operated cyclically, so that a heating device is either applied to the supply voltage and operates at full power or is isolated from the supply voltage and consequently deactivated. The level of the energy generation over and beyond a certain time period does not take place by lowering the supply voltage for continuous operation, but instead by cycles with on times and off times. Through the cyclic ratio or the length of the on and off times, it is possible to obtain so-called averaged energy generation or so-called average power is obtained.
In the present example the first heating device 13 is to be operated cyclically in order to determine the level of the average continuous output power and this also applies to the second heating device 15. An energy control device 21 is provided for controlling the heating devices in the aforementioned cyclic manner with on and off times. A similar energy control device 21 is for example described in U.S. Pat. No. 6,064,045 or DE 102 004 020 977 A, to which reference is expressly made. Through a rotary movement on a toggle 22 by an operator, it is possible to set a particular cooking stage, which determines the level of the average power of the heating devices or the hotplate 19 over and beyond a long period of time. The toggle 22 is located on a rotary spindle 23. As a function thereof, the energy control device 21 switches the first heating device 13 on and off using the first switching device 24.
As can be gathered from
On the rotary spindle 23 is also provided a cam disk 34, on which engages a slider 32 of a second switching device 30 with contacts 31, which switches on and off the second switching device 15. The precise path of the cam disk 34 is also described in detail hereinafter.
The sensor 41 covers a certain area of the hotplate 19 and runs preferably over a type of free zone between the paths of the first heating device 13 and second heating device 15. However, the temperature limiting switch 42 may only interrupt the supply of the first heating device 13. Thus, it admittedly detects the temperature of the complete hotplate 19, but it only interrupts the energy supply to the first heating device 13 in the case of an excessive temperature or a temperature considered harmful for a covering glass ceramic plate 18 in accordance with
According to the invention, the second heating device 15 is constructed for a continuous output power not exceeding a value of approximately 2.5 W/cmý on covered surface. For this value it is possible and permitted to permanently operate the second heating device 15 without any possibility of an excess temperature at the glass ceramic plate 18. Thus, no temperature limiter 40 is needed here. The power of the second heating device 15, in addition to the power of the first heating device 13, can give a desired overall power.
The advantage of this subdivision of the total power Pges over the two heating devices is that by means of the energy control device 21 or the two switching devices 24 and 30 contained therein, it is possible to switch on both heating devices 13 and 15 with respect to their cooking stage predetermined by an operator. As the total power of the hotplates 19 is distributed over the two switching devices 24 and 30, no problems arise here with excess currents to be switched or overloads. The temperature limiter 40 or its switch 42 only has to switch the power of the first heating device 13 or interrupt it if an excess temperature threatens. As the maximum average power for the second heating device 15 is in a range for which no temperature limitation is necessary, it can still be operated if the first heating device 13 had to be switched off due to an otherwise excessive temperature.
Function
A detailed explanation has been given hereinbefore of the control of the individual heating devices 13 and 15, the on and off times for obtaining an average power and the case of a threatening excess temperature for the glass ceramic plate 18. The heating devices must be constructed and controlled in such a way that this is as simple as possible for the operator and the desired heating functionalities are ensured. In this connection details are given of the precise form of the drum controller 27 and cam disk 34, which are significant in this connection.
In the position shown in
In a first area 27a extending from 0° to approximately 140°, there is a continuous decrease in the radius of the controller drum from the highest value. To the increase area 27a bringing about the off state is connected a second area 27b, where the radius increases again to the extent that it corresponds to the radius in area 27a, where the lowest cooking stage is reached, that is the lowest average continuous output power generated by the first heating device 13 across the energy control device 21. This is just behind the outermost point of the controller drum 27 in area 27a. As from this increase there is once again a decrease in the radius in area 27a over substantially the entire remaining angular range up to somewhat before 3600, where once again the area 27a with the strong increase commences.
At the point or angle where the area 27b commences, the cam disk 34 has the start of area 34b. The latter extends from the same angle a of approximately 140° up to approximately 360°, where the radius is increased compared with the radius in area 34a and is roughly constant. The area extends roughly over an angle from approximately 0° to approximately 140°. If the slider 32 of the second switching device 30 engages on area 34a, then the contacts 31 are opened and the second heating device 15 switched off. An energy generation at the hotplate 19 only takes place via the first heating device 13. If by means of the second switching device 30 the full power of the second heating device 15 is switched, then it is recommended that it be constructed as a snap-action switch for an improved switching behaviour.
The graph of
At angle 140° through the second area 34b at cam disk 34, the second switching device 30 is switched on and the second heating device 15 is activated. As is apparent from the graph, even with an increasing angle the power P2 is constant. The total power Pges results from the addition of P1 and P2. By the reduction of P1 roughly by the value of P2 at the angle 140°, there is overall a roughly constant, through path for the total power Pges. The value for P2 can be chosen as roughly 1100 Watt. P1 can be max. 2,100 Watt, so that in all at hotplate 19 a heating power of 3,200 Watt can be produced, which is clearly above the present maximum heating powers. In the case of an excess temperature of the glass ceramic plate 18, via switch 42 the temperature limiter 40 only separates the first heating device 13. However, the second heating device 15 continues to operate without any excess temperature risk.
The size of the hotplate 19 can be roughly 230 mm or can correspond to a conventional hotplate. For a voltage of 240 V, this normally represents a power of only 2,500 Watt, so that a heating power rise of more than one quarter is possible.
It is also noteworthy here that the cyclic operation of the energy control device 21 does not apply to the second heating device 15. This is switched on or off exclusively as a function of the angular position at the rotary spindle 23. This must be borne in mind when dimensioning the heating devices for a specific, average power.
Through the subdivision of the powers to be switched in accordance with
The covering of also the second heating device 15 by the sensor 41 of the temperature limiter 40 does not influence or disturb the function here. Although the second heating device 15 helps to raise the temperature, due to the choice of its maximum heating power as approximately 2.5 W/cm2, even on reaching an excess temperature and subsequent switching off of the first heating device 13, it can continue to be operated without any problem. For some cooking processes continuous heating can even be advantageous, because it is more uniform.
In a variant of an energy control device construction it is possible by means of the cam disk 34 not to directly control the power switch for the second heating device 15 and instead to provide a signal switch, which only switches a low power. As a result a power relay can be controlled as the second switching device and switches on and off the second heating device 15. Thus, the energy control device casing only has to contain one high power switch, which improves the construction with respect to the insulation gaps or the like.
