CN101203819A - Heating equipment and household appliances for liquids - Google Patents

Abstract

The invention relates to a heating device for fluids, in particular for use in dishwashers, comprising a heating element (1), whose resistance is a function of its temperature and which is coupled to a current supply (200) via switching means (2). In addition, the heating device has a protective unit (300), which protects the heating element from overheating. Said protective unit is designed to actuate the switching means (2) in accordance with the temperature of the heating element. According to the invention, the protective unit (300) is configured as an integrated circuit.

Description

Heating equipment and household appliances for liquids

The invention relates to a heating device for liquids, especially for use in dishwashers, comprising a heating element whose resistance is a function of its temperature and which is coupled to a power supply via switching means; and a protection device for The heating element is prevented from overheating, the protection device being configured to actuate the switching means as a function of the temperature of the heating element.

The invention also relates to a household appliance, in particular a dishwasher, comprising a device for washing dishes and comprising a heating device for heating a liquid to be heated, in particular a treatment liquid such as washing liquid.

Heating elements used in heating elements used to heat liquids can be permanently damaged when the heating element boils dry or the water boils over. For heating water in domestic appliances such as water heaters, coffee machines, dishwashers and washing machines, in particular resistance heaters based on thick-film technology are used as heating elements. These must meet specific security requirements. For example, provisions must be made for protection against ignition, against leakage and against voltage breakdown on the heating element. In particular, protection against voltage breakdowns is not necessarily provided via existing building or household fuses according to applicable standards. To meet this requirement, a thermal protection switch, a pressure switch that detects the presence of liquid, or a safety fuse that blows and cuts out when the heating element burns dry (which in this case causes the heating element to continue to heat) is usually used heater circuit.

However, such fuses have significant disadvantages. The pressure switch described above has a relatively slow response characteristic. Safety fuses, when triggered, cause irreversible opening of the heating circuit, causing failure of the heating equipment and costly customer service incidents.

Therefore, there is a desire for a fuse system to protect heating devices of the aforementioned type in a simple, fast and economical way, and it is desired that the fuse system be independent of the control of any existing appliances.

A general heating device is disclosed in EP 0845119 B1. The heating device is configured such that it is able to adjust the heating temperature of the heating element using the pulse-pause principle. The preselection of the heating temperature is prescribed by a scaling device implemented as a voltage divider, wherein the resistance can be changed by the user.

The invention solves the problem of specifying a heating device for liquids with a simple and economical protection device for preventing overheating of the heating element of the heating device. The invention also solves the problem of specifying a household appliance in which a simple, reliable and economical way of monitoring a heating device for overheating is achieved.

These problems are solved by means of a heating device having the features of claim 1 and by means of a domestic appliance having the features of claim 10 . Preferred embodiments are obtained from the dependent claims.

According to the invention, the protection device for a heating device for liquids is implemented as an integrated circuit, especially for use in dishwashers. The integrated circuit is preferably implemented as a microcontroller, which allows an arithmetical indirect determination and monitoring of the temperature of the heating element, so that the switching device is actuated when a preset temperature is exceeded. The rejection of discretely constructed monitoring circuits and their replacement by integrated circuits has the advantage of particularly economical and above all flexible monitoring. In particular, for example, any desired monitoring algorithm can be provided in the integrated circuit, on the basis of which algorithm the temperature of the heating element can be determined arithmetically. In particular, by means of a simple modification of the program sequence, it is possible to modify the threshold temperature or to take into account time-dependent aspects of the temperature profile of the heating element. The required algorithms and thresholds can be stored in the memory of the integrated circuit. Thus, the heating device can be installed with the same structure in various types of domestic appliances, in particular dishwashers, wherein in each case only the parameters adapted according to the domestic appliance have to be stored in the integrated circuit.

A voltage derived from the current flowing through the heating element is supplied to the protective device as an input variable. This can be achieved by providing a current sensor device coupled to the heating element, at its output a (voltage) signal proportional to the current flowing through the heating element can be tapped off, wherein the current sensor device is connected by a shunt Forms are implemented as discrete components. An analog signal can be output at the branch, which is converted into a digital signal by the integrated circuit using an analog-to-digital converter for further processing by the integrated circuit. In order to evaluate this signal, it is necessary to be able to read out the comparison value, eg from the memory of the integrated circuit.

Alternatively, this comparison value can also be supplied to the protection device as a further input variable in the form of a reference voltage. This is preferably achieved by providing scaling means at whose output a signal proportional to the supply voltage of the heating element can be output, wherein the scaling means is implemented as a discrete component in the form of a shunt coupled to the power supply. Therefore, by measuring the resistance of the voltage divider, the desired level of the reference voltage will be permanently set. By using a reference voltage, inaccuracies due to fluctuations in the input voltage can advantageously be avoided. In this case, it is not necessary to retain the reference voltage or the reference value in the memory of the integrated circuit. Thus, this variant allows the use of an integrated circuit comprising only a memory for the algorithm evaluating the input signal.

According to a preferred variant, a switching device is provided for opening the heating circuit in the event of overheating, which is embodied as a power semiconductor switch. This advantageously allows the components necessary for monitoring to be accommodated in a small space.

In this case, it is especially preferred to implement the switching device together with the protective device in an integrated circuit.

The protective device is preferably used to detect a change in the resistance of the heating element and to compare the change in resistance with a reference value, preferably derived from the supply voltage, so that the heating circuit can be interrupted by actuating the switching device when the reference value is exceeded. According to this preferred variant, the analysis of the temperature profile of the heating element is carried out by the integrated circuit using program-based means, based on the observation of the change in the resistance value.

A household appliance according to the invention, in particular a dishwasher, comprising a device for washing dishes and a heating device for heating a liquid to be heated, in particular a treatment liquid such as washing liquid, wherein the device is heated to protect The device is characterized as being implemented in the form of an integrated circuit for monitoring and disconnecting the heating device when a specified temperature value of a heating element of the heating device is exceeded. Electronic monitoring of the heating equipment ensures reliable disconnection of the heating equipment in the event of overheating. In this case, the dishwasher can be operated again once the heating device has cooled down again. The electronic monitoring also takes into account other influencing variables for switching off the heating system. For example, monitoring of the fill-level of the washing liquid in the heating device can also be considered. If the fill level gauge emits an electronic signal indicating that the fill level is below a preset value, the electronic protection device can already switch off the heating device before the heating device reaches a critical temperature value.

The household appliance preferably comprises a heating device as described above.

The heating element of the heating device of the domestic appliance is preferably embodied as a thick-film heating entity whose resistance value is a function of its temperature. This makes it particularly easy to allow electronic monitoring, since the resistance value of the heating element can be determined mathematically by the protective device.

The basic principle of the present invention for temperature monitoring of heating equipment is based on DE10360533.3 of the applicant, the content of which is incorporated into this application document. In particular, an arithmetic determination of the resistance value can be done based on the method described in the present application. In this case, it is recommended not to rely on direct measurements of the resistance of the heating element, but to calculate the resistance indirectly via measurements of the current flowing through the heating element and the voltage across the heating element. This involves approximating the division by means of a Taylor series expansion, and removing the term after the second. Thus, division is replaced by subtraction, which is easily simulated in arithmetic. While in DE 10360553.3 the Taylor series expansion suggested the use of discrete components, according to a development of the invention a program-based analysis of the input variables in an integrated circuit is provided. In this case, apart from the described Taylor series expansion, in principle any analysis algorithm can be used. This enables an extremely precise determination of the resistance value in a simple and economical manner.

The invention will be further described below with reference to the accompanying drawings, which show the basic structure of a heating device for liquid according to the invention.

A heating element 1 embodied as a resistive heating element is connected in series between a first power supply terminal VA1 and a second power supply terminal VA2 using a switching device 2 and a current sensor device 4 in the form of a shunt. An input voltage U _E is present between the supply terminals VA1 , VA2 .

The switching device 2 can be controlled via a switch control circuit 3 . The switching device 2 can be implemented in the form of a relay, which switches conductive if the heating element 1 does not exceed a preset temperature value, and switches non-conductive as soon as a critical temperature value of the heating element 1 is exceeded. However, the switching device 2 can also be implemented in the form of a power semiconductor which is integrated together with the switching control circuit 3 in an integrated circuit.

A power supply 200 (which will not be described in further detail below) applies a supply voltage to the switch control circuit 3 and the protection device 300 implemented as an integrated circuit. The power supply 200 essentially features a rectifier circuit for rectifying the alternating voltage signal or alternating current signal present at the power supply terminals VA1, VA2 and converting it into a corresponding voltage level for feeding the switching control circuit 3 and the protection device 300 supplies energy.

The node formed between the heating element 1 and the current sensor device 4 forms the output 41 of the current sensor device 4 . A voltage U _S is present between the output 41 and the supply terminal VA2. The output 41 is coupled to a first input 63 of the protection device 300 . This stands for Microprocessor. A second input 62 of the protection device 300 is connected to scaling means 5 formed by a voltage divider comprising resistors 51 , 52 . More precisely, the node 53 formed between the resistors 51 , 52 is connected to the second input 62 of the protection device 300 . The output 106 of the protection device 300 is coupled to the control input 31 of the switch control circuit 3 . When a corresponding control signal is present at output 106, the switch control circuit 3 is sensed to switch the switch device 2 from its closed state (where power is supplied to the heating element 1) to an open state in order to interrupt the heating circuit.

The heating device according to the present exemplary embodiment has the current sensor means 4 and the scaling means 5 as discrete components. Analog signals can be output at these components, which are converted into digital signals in the protective device 300 via analog-to-digital converters connected to the inputs 63 , 62 in order to allow arithmetic processing of the corresponding input variables. Depending on these input variables, as described in the applicant's document DE 103 60 553.3, the resistance value corresponding to the temperature value of the heating element 1 is compared with a reference value, wherein the reference value is set by the scaling device 5 . From the determined resistance value of the heating element 1 , it can be determined whether the temperature of the heating element 1 is in a temperature range outside the specification, which can indicate a malfunction of the heating device or of the appliance in which the heating device is installed. In this case, the protection device 300 emits a signal at its output 106 which causes the switch control circuit 3 to open the switch device 2 .

Electronic monitoring of the temperature of the heating element 1 based on the determination of the resistance value and the arithmetic analysis of the acquired signals allows a particularly simple, economical and reliable monitoring of the heating device, which is especially suitable for use in dishwashers. Thus, a particularly reliable heating device for liquids is provided, wherein mechanical damage to the heating device can be avoided in the event of dry firing.

List of reference signs

1 heating element

2 switch device

3 switch control circuit

31 input terminal

4 Current sensor device

41 output

5 zoom device

51 resistance

52 resistance

62 input

63 input

106 output

200 Power

300 Protection equipment

U _E input voltage

_US voltage

U _V voltage

VA1 power terminal

VA2 power terminal

Claims (12)

1. A heating device for liquids, especially for use in dishwashers, comprising a heating element (1), the resistance of which is a function of its temperature, and said heating element (1) is coupled via a switching device (2) to a power supply (200); and a protection device (300) for preventing overheating of said heating element (1), said protection device configured to actuate said heating element (1) as a function of said temperature of said heating element (1) The switching device (2), characterized in that the protection device (300) is implemented as an integrated circuit. 2. The heating device according to any one of the preceding claims, characterized in that the protective device (300) is implemented to determine the temperature of the heating element (1 ) indirectly arithmetically, and in excess of The switching device (2) is actuated at a preset temperature. 3. Heating device according to claim 1 or 2, characterized in that a voltage derived from the current flowing through the heating element (1) can be supplied to the protection device (300) as an input variable. 4. Heating device according to claim 3, characterized in that a current sensor device (4) coupled to the heating element (1) is provided at its output capable of outputting and flowing through the heating element (1) A signal proportional to said current, said current sensor device (4) is implemented as a discrete component in the form of a shunt. 5. The heating device according to any one of the preceding claims, characterized in that a reference voltage can be supplied to the protection device (300) as a further input variable. 6. Heating device according to claim 5, characterized in that scaling means (5) are provided, at the output of which a signal proportional to the supply voltage of the heating element (1) is able to be output, said scaling means ( 5) Implemented as a discrete component in the form of a voltage divider coupled to the supply voltage. 7. The heating device as claimed in claim 1, characterized in that the switching device (2) is embodied as a power semiconductor switch. 8. The heating device according to claim 7, characterized in that the switching means are implemented in an integrated circuit together with the protection device (300). 9. The heating device according to any one of the preceding claims, characterized in that the protection device (300) is implemented for detecting changes in the resistance value of the heating element (1 ) and for switching the The change in resistance is compared with a reference value, preferably derived from the supply voltage, so that the heating circuit can be interrupted by actuating the switching device (2) when the reference value is exceeded. 10. A household appliance, especially a dishwasher, comprising a device for washing tableware, and a heating device for heating a liquid that needs to be heated, especially a treatment liquid such as washing liquid, characterized in that the heating The device has a protection device (300) implemented in the form of an integrated circuit for monitoring and disconnecting said heating device in case a specified temperature value of a heating element of said heating device is exceeded. 11. Household appliance according to claim 10, characterized in that the heating device is implemented according to any one of claims 1-9. 12. Household appliance according to claim 10 or 11, characterized in that the heating element (1) of the heating device is implemented as a thick-film heating entity whose resistance value is a function of its temperature.

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