Instantaneous water heater and temperature sensor for an instantaneous water heater

Abstract

A flow heater with an inlet (2) and an outlet (3), a housing (1) in which a flow channel (9) for liquid to be heated runs from the inlet (2) to the outlet (3), an electrical heating element to heat liquid in the flow channel (9), a circuit board (8) with control electronics for controlling the power of the heating element and a temperature sensor (10) connected to the control electronics, characterized in that the temperature sensor (10) has a plastic body (11) in which a measuring element (13) connected to supply lines (12) is arranged, the plastic body (11) projects into the flow channel (9), and the ends of the supply lines (12) facing away from the measuring element (13) are inserted into openings in the circuit board (8).

Description

The invention relates to an instantaneous water heater with the features specified in the preamble of claim 1. Such an instantaneous water heater is known from DE 10 2020 123 996 A1. Instantaneous water heaters are used in vehicles, for example, to heat various liquids, especially water or aqueous solutions. These heaters typically contain one or more temperature sensors connected to control electronics. Key requirements for temperature sensors in automotive instantaneous water heaters include, on the one hand, the fastest and most precise possible measurement of the liquid temperature within the heater, and on the other hand, cost-effective manufacturing and ease of installation. The object of the invention is to demonstrate a way in which the temperature of liquid in a flow channel of an instantaneous water heater can be measured cost-effectively using a temperature sensor. This problem is solved by an instantaneous water heater with the features specified in claim 1. Advantageous embodiments of the invention are the subject of dependent claims. In an instantaneous water heater according to the invention, a temperature sensor is used which has a plastic body in which a measuring element connected to leads is arranged. The measuring element can be, for example, a diode or a measuring resistor, such as an NTC resistor or a PTC resistor. The plastic body of the temperature sensor projects into the flow channel of the instantaneous water heater, thus enabling a precise measurement of the temperature of the liquid in the flow channel. The plastic body of the temperature sensor can be manufactured, for example, by overmolding the measuring element and its leads, for example with polybutylene terephthalate (PBT), polyphthalamide (PPA), or an epoxy resin. The ends of the leads facing away from the measuring element are inserted into openings in the circuit board. The ends of the connecting leads can be designed as press-fit contacts or soldered into these openings in the circuit board.The press-fit contacts can be solid or, to increase their compressibility, provided with an opening, for example using needle-eye technology. A further advantageous embodiment of the invention provides that the plastic body has an annular groove in which a seal, for example an O-ring, is arranged. In this way, an opening in a wall of the instantaneous water heater can be sealed, through which the temperature sensor projects into the flow channel and is surrounded by liquid. A further advantageous embodiment of the invention provides that the plastic body has a pin at one of its ends, which is inserted into a corresponding opening in the printed circuit board. Preferably, the plastic body has two pins that fit into openings in the printed circuit board. This facilitates assembly. The pins, especially those tapering towards their free end, can facilitate the correct positioning of the temperature sensor relative to the printed circuit board, so that the ends of the leads can be more easily inserted into corresponding openings in the printed circuit board. Preferably, the ends of the leads protrude from the plastic body between two pins. A further advantageous embodiment of the invention provides that the leads are designed as stamped sheet metal parts. In this way, the leads can be easily connected to the measuring element, such as a ceramic or metallic resistance sensor, for example by soldering, creating a manageable unit that can be readily overmolded with plastic to form the plastic body. Preferably, only a single component is used for overmolding, thus avoiding a two-part manufacturing process for the plastic body. Further details and advantages of the invention are explained using an exemplary embodiment with reference to the accompanying drawings. These show: Fig. 1 an exemplary embodiment of an instantaneous water heater according to the invention; Fig. 2 a further view of the instantaneous water heater; Fig. 3 a sectional view along section line AA of Fig. 2; Fig. 4 a detail of a sectional view along section line BB of Fig. 2; Fig. 5 a view of the temperature sensor of the instantaneous water heater; and Fig. 6 a sectional view of the temperature sensor. The flow heater shown in Figures 1, 2, 3 to 4 is used to heat liquids in vehicles. The flow heater has a housing 1 with an inlet 2 and an outlet 3, as well as connectors 4 and 5 for power supply and connection to a vehicle control unit. A flow channel for the liquid to be heated runs through the housing 1 from the inlet 2 to the outlet 3. The flow channel runs alongside a heating plate 6, which has an electrical heating element on its side facing away from the flow channel to heat the liquid in the flow channel. This heating element can, for example, be formed by electrical conductors printed onto the heating plate. To improve heat dissipation, the heating plate 6 can be provided with corrugated fins 7 that project into the flow channel. The instantaneous water heater also includes a circuit board 8 with control electronics for controlling the power of the heating element. A temperature sensor 10 is connected to these control electronics; this sensor protrudes into the flow channel 9 and is shown in various views in Figures 5 to 6. The temperature sensor 10 has a plastic body 11 in which a measuring element 13, for example a ceramic NTC resistor, is arranged and connected to leads 12. The plastic body 11 can be manufactured by overmolding the leads 12 and the measuring element 13. Ends of the leads 12 protrude from the plastic body 11 and, as shown in Fig. 4, are inserted into openings in the circuit board 8. The ends can be designed as press-fit contacts or soldered to the circuit board 8. To facilitate insertion of the ends of the leads 12 into the circuit board 8, the plastic body 11 can have one or more pins 13 that extend beyond the ends of the leads 12 and are inserted into corresponding openings in the circuit board 8. In the illustrated embodiment, the ends of the leads 12 are arranged between the pins 13. The temperature sensor 10 is inserted into a mounting hole of the instantaneous water heater. To seal this mounting hole, the temperature sensor 10 has one or more sealing rings 15, for example O-rings, which sit in annular grooves on the outside of the plastic body 11. The leads 12 are stamped sheet metal parts, each with a U-shaped receptacle at one end into which the measuring element 13 is soldered. Leads in the form of stamped sheet metal parts advantageously possess good mechanical stability, which facilitates the overmolding of the leads 12 and the measuring resistor 13 to form the plastic body 11. Reference symbol list 1 Housing 2 Inlet 3 Outlet 4 Connector 5 Connector 6 Heating plate 7 Corrugated fins 8 Circuit board 9 Flow channel 10 Temperature sensor 11 Plastic body 12 Leads 13 Measuring resistor 14 Pin 15 Sealing ring QUOTES INCLUDED IN THE DESCRIPTION This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature DE 10 2020 123 996 A1

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Claims

Instantaneous water heater with an inlet (2) and an outlet (3), a housing (1) in which a flow channel (9) for liquid to be heated runs from the inlet (2) to the outlet (3), an electrical heating element to heat liquid in the flow channel (9), a circuit board (8) with control electronics for controlling the power of the heating element and a temperature sensor (10) connected to the control electronics, characterized in that the temperature sensor (10) has a plastic body (11) in which a measuring element (13) connected to supply lines (12) is arranged, the plastic body (11) projects into the flow channel (9), and the ends of the supply lines (12) facing away from the measuring element (13) are inserted into openings in the circuit board (8). Instantaneous water heater according to claim 1, characterized in that the measuring element (13) is an NTC resistor. Instantaneous water heater according to one of the preceding claims, characterized in that the plastic body (11) is produced by overmolding the measuring element (13) and the supply lines (12). Instantaneous water heater according to one of the preceding claims, characterized in that the plastic body (11) has a pin (14) at one of its ends which is inserted into a suitable opening of the circuit board (8). Instantaneous water heater according to one of the preceding claims, characterized in that the plastic body (11) has an annular groove in which a sealing ring (15) is arranged. Instantaneous water heater according to one of the preceding claims, characterized in that the supply lines (12) are designed as stamped sheet metal parts. Instantaneous water heater according to claim 6, characterized in that the stamped sheet metal parts form a U-shaped receptacle at one of their ends in which the measuring element (13) is seated. Instantaneous water heater according to one of the preceding claims, characterized in that the supply lines (12) are soldered to the measuring element (13). Temperature sensor for an instantaneous water heater, comprising a plastic body (11), a measuring element (13), and connecting leads (12) to the measuring element (13), wherein the plastic body (11) is manufactured by overmolding the measuring element (13) and the connecting leads (12), characterized in that the plastic body has a pin (14) for insertion into an opening of a circuit board (8). Temperature sensor according to claim 9, characterized in that the ends of the leads (12) protruding from the plastic body (11) are designed as press-fit contacts.

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