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The invention relates to a domestic appliance embodied as a tumble drying device with a lifting magnet, in particular a heat pump dryer.
Tumble drying devices, which are currently of interest, are described in the documents WO 2008/119611 A1, WO 2007/093461 A1, WO 2007/093467 A1, as well as in WO 2007/093468 A1. Each of these tumble drying devices has a heat pump, which has a component loaded with dirt in the form of lint, which accumulates during a tumble drying process. This component is the heat sink, at which the heat pump absorbs heat from its passing process air stream. Fine lint deposits there, which has to be regularly removed. To this end, a cleaning device is present in each instance, which regularly cleans the loaded components and/or the region of the heat pump, in which this component is arranged, with the aid of rinsing fluid. The rinsing fluid is supplied by means of a correspondingly provided channel with the aid of a rinsing valve to be opened at a given time as well as further components which are described in detail in each instance.
Lifting magnets are frequently used as the drive to activate switching processes. To optimize cost and installation space, lifting magnets can be used, which only have a restricted on-time duration (e.g. of 10%). Exceeding the permissible on-time duration, e.g. in the event of a faulty actuation, can result in the lifting magnet being damaged, as a result of which safety requirements can in some instances not be fulfilled. To observe safety regulations, a complicated “functional safety” or a temperature protector could previously be used in the lifting magnet coil. However, these solutions are comparatively complicated and expensive. Introducing a protector into the coil may possibly represent significant additional expenses, since this is generally not provided in a production facility.
It is thus an object of the present invention to provide a cost-effective and reliable possibility of protecting a lifting magnet against an excessive power supply.
The domestic appliance embodied as a tumble drying device includes a heat pump with a lifting magnet, with a rinsing valve of the heat pump being connectable by means of the lifting magnet. The lifting magnet and a PTC resistor with a nonlinear resistance curve are connected in series, with it being possible to heat up the PTC resistor by means of a current flow and said PTC resistor being highly resistive in the case of a predetermined limit temperature being exceeded and with the limit temperature being adjusted such that it is reached before a permissible on-time duration of the lifting magnet is exceeded. As a result of the PTC resistor being able to be heated up by means of the current flow and being highly resistive if the limit temperature is exceeded, the current is limited to a degree which is noncritical to the lifting magnet.
The scope of the invention does not necessarily depend on the embodiment of the heat pump. The heat pump currently has a heat source, which is used to heat up a process air stream for the drying process and a heat sink, which is used to cool down the process air stream. In this way, heat, which the heat pump absorbs in the heat sink, is pumped to the heat source and is output there again in the event of an increase in temperature. Details relating to the embodiment of a heat pump result from the documents cited in the introduction, to which reference is made here in its entirety.
The invention is not necessarily restricted to a special function of the rinsing valve. The application of the invention to a rinsing valve is however currently of particular interest, said rinsing valve being used to this end to supply a rinsing fluid to a region of the heat pump loaded with dirt for the purpose of rinsing and removal. The dirt may be lint, such as accumulates in the region of the heat sink, at which moisture from an air stream loaded with steam and lint is condensed out, said air stream flowing around the heat sink, and correctly adheres to the heat sink as a result of the presence of moisture.
The following advantages are achieved by introducing the PTC resistor: a cost-effective lifting magnet with a reduced on-time duration can be used and a complicated safety circuit is dispensed with on the electronics system. A temperature protector in the lifting magnet coil can also be omitted.
The PTC resistor can be embodied for instance as a PTC resistor based on ceramics, e.g. with barium titanium or based on polymers, e.g. with a sooty particle-filled plastic.
It is advantageous for the simple and precise switching of the lifting magnet for the lifting magnet to be connected to an electronic controller for its actuation.
It is also advantageous if the limit temperature is adjusted such that a correct activation of the lifting magnet heats up the PTC resistor to a temperature below the limit temperature. In other words, the dimensioning of the PTC resistor is then effected such that the inrush current and the working current of the lifting magnet do not allow the PTC resistor to be highly resistive within the necessary time interval.
A domestic appliance is also preferable, in which a correct activation takes place within a period of approximately 5-10 seconds.
The domestic appliance may be present as a washer dryer or as a separate dryer.
The invention is illustrated schematically below with reference to an exemplary embodiment.
FIG. 1 shows a circuit diagram for operating a lifting magnet in a heat pump dryer.
FIG. 1 shows a tumble drying device 7 with a heat pump 8, with the heat pump 8 being equipped with a rinsing valve 9. The rinsing valve 9 is used to clear a channel through which rinsing fluid is supplied to a region of the heat pump 8 which is loaded with lint, in particular the region in which the heat sink of the heat pump 8 is arranged, for lint rinsing and removal purposes. The heat pump 8 is currently only shown schematically, since it does not essentially depend on its inner design for the present description. In any case, the heat pump 8 has a heat source, which is currently used to heat up a process air stream for the drying process and a heat sink, which is used to cool down the process air stream. In this way, heat, which the heat pump 8 absorbs in the heat sink, is pumped to the heat source and output there again in the case of an increase in temperature.
A lifting magnet 4 is used to connect the rinsing valve 9. Two alternating current power supply terminals 1, 2 are connected in series in order to actuate the lifting magnet 4:
(i) a switching relay 3 for the optional opening and closing of an associated current circuit which can be supplied by means of the alternating current power supply terminals 1, 2,
(ii) the current-controlled lifting magnet 4 and
(iii) a PTC; (“Positive Temperature Coefficient”-) resistor 5.
The switching relay 3 is activated by means of an electronic circuit 6, which has a microcontroller. The lifting magnet 4 is mechanically connected to the rinsing valve 9 for the opening and closing thereof.
The activation of the lifting magnet 4 only needs to take place for a period of approximately 5-10 s. Pause times of several minutes are then provided. To optimize cost and installation space, a lifting magnet 4 is used, which only has a limited permissible on-time duration (ED) of e.g. 10%. If the permissible on-time duration is exceeded, this may lead to the lifting magnet 4 being damaged or safety regulations not being observed.
The PTC resistor 5 has a non-linear resistance curve, whereby below a predefined limit temperature, an ohmic resistance is typically comparatively low and only changes marginally, while above the limit temperature, the PTC resistor is rapidly highly resistive. The PTC resistor 5 can be heated up by means of a current flow passing therethrough. The limit temperature is adjusted such that it is reached before a permissible on-time duration of the lifting magnet is exceeded, while, in the case of a correct activation (inrush current and working current) of the lifting magnet of approximately 5-10 seconds here, the PTC resistor is only heated up to a temperature below the limit temperature.
When the switching relay 3 is closed, current flows through the current circuit and firstly allows the lifting magnet 4 to connect and secondly heats up the PTC resistor 5. With a correct and/or proper actuation of the switching relay 3, the PTC resistor 5 remains low resistive, and the limit temperature is not reached by means of the currents. In the case of a fault, it may however occur that the switching relay 3 closes for longer. If the temperature in the PTC resistor 5 then reaches the limit temperature, which occurs before a permissible on-time duration of the lifting magnet 4 is exceeded, the PTC resistor 5 is highly resistive and limits the current flow through the current circuit, as a result of which the lifting magnet 4 is protected against damage.