GB2315925A

GB2315925A - Resilient contact for a resistive heating track

Info

Publication number: GB2315925A
Application number: GB9712665A
Authority: GB
Inventors: John Crawshaw Taylor; Ath Lawrence De
Original assignee: Strix Ltd
Current assignee: Strix Ltd
Priority date: 1996-06-14
Filing date: 1997-06-16
Publication date: 1998-02-11
Anticipated expiration: 2017-06-16
Also published as: GB9712665D0; GB9612462D0; GB2315925B

Abstract

A heater assembly, comprises an electric heater 2 having a resistive heating track 8 provided on an electrically insulating substrate 6, the track having at least one terminal portion 8a for electrical connection to the heater, further comprising an axially compressible, electrically conductive, resilient contact member 14 sandwiched between the terminal portion and an electrical terminal 16. The contact member may be push-fitted into an electric terminal of a power supply such as spade terminal. The contact member may also be provided within a carrier means.

Description

Electric Heaters The present invention relates to electric heaters, and in particular to contact arrangements for heaters of the type comprising a resistive heating track provided on an electrically resistive substrate.

Heaters of the above type have been proposed for use in liquid heating vessels, such as kettles.

Typically they comprise a thick film printed heating track provided on a ceramic layer which is itself provided on a metallic substrate, which may, for example, form the base of the vessel. One such "thick film" heater is shown in EP-A-485211. In that document, electrical connection is made to a terminal of the heating track through an electrically conductive solder.

In another proposal, disclosed in EP-A-651936, a wire is heated and pushed into the track material to melt the same, and thereafter allowed to cool to solidify and effect an electrical connection.

The present invention seeks to provide a simplified electrical connection to a heater of the above type, and thus from a first aspect provides a heater assembly comprising an electric heater of the type comprising a resistive heating track provided on an electrically insulating substrate, said track having at least one terminal portion for electrical connection to the track, for example to a power supply for the heater, further comprising an axially compressible, electrically conductive, resilient contact member sandwiched between said terminal portion and an electrical terminal, for example a power supply terminal.

Thus, according to the invention, an electrically conductive, resilient and compressible contact member is sandwiched between an electrical terminal and a terminal portion of the heater track. The resilience of the contact member allows the requisite contact force to be generated and, at the same time, accommodates assembly tolerances between these components.

The contact member may take a number of forms. For example, in one embodiment, it may comprise a coil spring, whilst in an alternative embodiment it may comprise a C-spring.

Although discrete electrical contacts, for example copper or silver contacts may be provided at respective ends of the contact member, this is not preferred, as it increases cost. However, if required for a particular application, such contacts may be used. Preferably, therefore the respective ends of the contact member make direct electrical contact with the electrical terminal and the heater track terminal portion.

The heater track terminal portion may take any suitable form. For example, a contact pad may be formed on a particular section of the track, or a section of the track material itself exposed.

Whilst the electrical terminal may be mounted for example in a cover for the heater, preferably it is provided on a thermally sensitive control for the heater, which is mounted in a face to face relationship with the heater. In the case of a power supply terminal, the electrical supply to the heater flows through the control, so as to be disconnected in the event, for example, that the heater temperature moves above a predetermined temperature. Such a control is disclosed, for example, in WO 95/34187.

Preferably the control is provided with a guide, for example a plastics bore, to receive and guide the contact member.

The control of WO 95/34187 has been described in the context of an underfloor sheathed element heater, but it is also suitable for use with thick film heaters as described herein. Moreover, in that control, power supply terminals of the control are formed as push-fit, in particular spade terminals, which can be connected to the cold tail of the sheathed element by an appropriate lead or conductor. However the spade connector will also provide a substantial planar surface for engagement with a spring contact member and such a terminal is thus particularly preferred in this invention. It also means that the control may easily be adapted for connection to different types of heater, for example either by a lead or by a spring contact as described above.

The control of the heater may be an electronic control, for example mounted on a printed circuit board (PCB). In this case, the resilient contact member may provide an electrical connection between an electrical terminal on the PCB and the terminal portion of the heater. The electrical terminal on the PCB may be simply a region of conductive material such as tinned copper or silver. Alternatively, the electrical terminal may be a spade terminal or the like. The electrical connection between the PCB and the heater need not be a power supply connection to the heater, but may be used to tap the voltage at the terminal portion of the heater, for example to monitor the operation of the heater or to supply power from the heater to an electronic control.

The resilient contact member may be received in guide means, such as a bore, channel or recess, for example, of moulded plastics. The bore etc. may be provided integrally in a control for the heater or in a separate carrier arranged between the control and the heater. The carrier with at least one resilient contact member may be pre-mounted to the control or the heater before assembly of the contact to the heater.

To facilitate assembly, preferably, the guide means is provided with retaining means for the resilient contact member. This in itself is considered a novel arrangement, and thus from a third aspect the invention provides an electrical contact carrier locatable between an electric heater and a control for the heater, the carrier comprising guide means for receiving a resilient contact member for forming an electrical connection between an electrical terminal of the control and a terminal portion of the electric heater, wherein the guide means is provided with retaining means for retaining the resilient contact member in the guide means.

The contact carrier may be formed integrally with or attached to the control or the heater. In one arrangement it is formed integrally with the control unit, so that the contact may be mounted in the control unit during manufacture of the latter. In another arrangement, the carrier may be a separate component sandwiched between the control and the heater, and which effectively and more easily locates the contact during assembly. All these arrangements considerably facilitate assembly of the spring contact.

The retaining means may comprise a projection which engages with the resilient contact member to retain it in the guide means. Preferably, the retaining means does not hold the contact member fast, but allows some movement when a sufficient force is applied to the contact member. For example, the retaining means may be an internal projection in a bore which acts as the guide means. In this example, if the contact member is a helical spring, when the spring is inserted into the bore, the projection will engage between successive windings of the spring and retain it in the bore. When the carrier is located between the control and the heater and the carrier and heater are mounted to the control, the pressure exerted by the terminal portion of the heater or the electrical terminal of the control on the spring will overcome the force applied by the projection and the spring will tend to assume a position in the bore in which the spring force acting on each of the terminal portion and the electrical terminal is substantially equal.

As an alternative to the axially compressed spring discussed above, an appropriately shaped resilient contact member, for example a leaf spring, may be pushfitted on to a terminal of the control. This is itself a novel arrangement in general terms and from a second aspect, therefore, the invention provides a heater assembly comprising an electric heater of the type comprising a resistive heating track provided on an electrically insulating substrate, said track having at least one terminal portion for electrical connection to a power supply for the heater, said power supply having a push-fit terminal, and a resilient contact member fitted onto said terminal for engagement with the terminal portion of the track.

This arrangement also allows a control to be adapted easily from one application to another.

The contact member in this embodiment may, for instance be generally C-shaped with one limb pushed onto the power supply terminal and a contact mounted on the opposed limb for contact with the track. The contact member may for example be formed by bending a strip of conductive material, such as BeCu.

Some preferred embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a schematic sectional view of a first embodiment of the invention; Fig. 2 is a schematic sectional view of a second embodiment of the invention; Fig. 3 is a schematic sectional view of a third embodiment of the invention; and Fig. 4 is a schematic sectional view of a fourth embodiment of the invention.

With reference to Fig. 1, a heater comprises a metallic, for example a stainless steel, plate 4 upon which is deposited in a known manner a ceramic insulating layer 6, upon which in turn is screen printed, again in a know manner, a resistive heating track 8. The track 8 may be of whatever length and configuration is required to give a desired heating effect and distribution. A protective overglaze 10 is provided over the track 8, although this can be omitted if the track material is corrosion and oxidation resistant.

The track 8 has a terminal portion 8a, to which an electrical connection can be made. In this embodiment, the terminal portion 8a is formed merely by a portion of the track exposed through a window 12 in the overglaze 10, although a contact pad, for example of palladium silver, may be provided on the track at that location.

The electrical connection to the track 8 is made via a coil spring 14 which is sandwiched and axially compressed between the terminal portion 8a, and a spade connector 16 of a thermally sensitive control 18 for the heater, which is mounted against the heater, for example by mounting studs (not shown). The spring 14 is constrained laterally by a guide bore 20 formed in a moulding of the control body. Electrical power is thus conducted to the heater track via the control 18 and the spring 14.

It will be seen that the compression of the spring 14 will generate a contact pressure at both ends thereof, and will also allow for mounting tolerances to be accommodated.

If necessary, contacts, e.g. silver or copper contacts, may be provided at one or both ends of the spring 14 to improve the contact with the track 8 and/or terminal 16.

A modification of the embodiment of Fig 1 is shown in Fig. 2. The only difference between these two embodiments is that in the embodiment of Fig 2., the spring comprises an axially compressible C-spring 14'.

This comprises a strip of material, for example BeCu, bent into a shallow C such that it can be compressed generally along its longitudinal axis. A line edge contact 32 is effectively formed with the track terminal portion 8a.

In Fig. 3, a further form of connection in accordance with the invention is disclosed. In this embodiment, a thermally sensitive control 40 for a heater 2, has a spade terminal 44. A generally C-shaped spring contact 46 made of strip material, such as BeCu has a socket 48 provided at one end for push-fitting over the terminal 44 with a spring tang 50 engaging in a hole 52 in the terminal 44 to prevent removal of the contact. A silver or copper contact 54 is mounted, for example rivetted, to the other end of the contact member 46, for engagement with the terminal portion 8 of the heater 2. The contact member 46 is sufficiently resilient to accommodate mounting tolerances and to generate the requisite contact pressures on mounting the contact 40 to the heater 2.

Figure 4 shows a further embodiment of the invention similar to that of Fig. 1. However, in this case, the control 18 for the electric heater is an electronic control on a PCB 56. The PCB is provided with a silver or tinned copper contact 58 on its underside which abuts a spring contact 14 received in a bore 60 in a carrier 62. The other end of the spring 14 abuts a contact pad 8a of the heater track 8. The bore 60 of carrier 62 is provided with an internal projection (not shown) which retains the spring 14 in the bore 60.

the carrier 62 is also provided with a mounting block 64 for attaching the carrier 62 to the PCB 56, as shown.

In assembly of the above, the spring contact 14 is pushed into the bore 60 over the retaining means so as to project from both ends of the bore 60. The carrier 62 is then secured to PCB 18 via the mounting block 64, so that one end of the spring 14 makes resilient contact with the pad 58 on the PCB 18. The PCB 18 and contact carrier 62 are then mounted together to the heater, so that the other end of the spring makes resilient contact with the heater terminal portion 8a.

It will be clear in the embodiments above that the invention allows an electrical connection to be made simply to a heater track, and at the same time allows the electrical connections of, for example, a thermally sensitive control to be easily adapted to different heater types without extensive re-design of components.

Also, the use of a compression spring contact also facilitates the electrical connection between two planar surfaces e.g. a thick film heater and a PCB.

Claims

CLAIMS:

1. A heater assembly comprising an electric heater of the type comprising a resistive heating track provided on an electrically insulating substrate, said track having at least one terminal portion for electrical connection to the heater, further comprising an axially compressible, electrically conductive, resilient contact member sandwiched between said terminal portion and an electrical terminal.

2. A heater as claimed in claim 1 wherein said contact member comprises a coil spring.

3. A heater assembly as claimed in claim 1 wherein said contact member comprises a C-spring.

4. A heater assembly as claimed in any preceding claims wherein said electrical terminal is provided on a thermally sensitive control for the heater.

5. A heater assembly as claimed in claim 4 wherein said control is provided with guide means for said contact.

6. A heater as claimed in claim 4 or 5 wherein said control is provided with means for retaining said contact member.

7. A heater assembly as claimed in any preceding claim wherein said electrical terminal is a push-fit connector.

8. A heater assembly as claimed in claim 7 wherein said electrical connector is a spade connector.

9. A heater assembly as claimed in any preceding claim wherein said electrical terminal is generally planar.

10. An electrical contact carrier locatable between an electric heater and a control for the heater, the carrier comprising guide means for receiving a resilient contact member for forming an electrical connection between an electrical terminal of the control and a terminal portion of the electric heater, wherein the guide means is provided with retaining means for retaining the resilient contact member in the guide means.

11. A carrier as claimed in claim 10, wherein the guide means is in the form of a bore through the carrier and the retaining means is in the form of an internal projection in said bore.

12. A heater assembly comprising an electric heater of the type comprising a resistive heating track provided on an electrically insulating substrate, said track having at least one terminal portion for connection to a power supply for the heater, said power supply having a spade terminal, and a contact member push-fitted into said terminal for engagement with the terminal portion of the track.

13. A heater assembly as claimed in claim 12 wherein said contact member is generally C-shaped, with one limb fitted on the terminal and the other limb having a contact for engagement with the track.

14. A heater assembly as claimed in any preceding claim wherein said heater is a thick film printed heater.

15. A heater assembly substantially as hereinbefore described with reference to Figure 1.

16. A heater assembly substantially as hereinbefore described with reference to Figure 2.

17. A heater assembly substantially as hereinbefore described with reference to Figure 3.

18. A heater assembly substantially as hereinbefore described with reference to Figure 4.