GB2472784A

GB2472784A - resistor and method of manufacture

Info

Publication number: GB2472784A
Application number: GB0914327A
Authority: GB
Inventors: Robert Alexander Blanch
Original assignee: Tyco Electronics UK Ltd
Current assignee: Tyco Electronics UK Ltd
Priority date: 2009-08-17
Filing date: 2009-08-17
Publication date: 2011-02-23
Also published as: GB0914327D0

Abstract

An electrical power resistor (4) comprises a corrugated conductive member 5 having different thicknesses. The resistor may include web portions (6) and bight portions (8) having a first thickness (Y) and relatively thicker bight portions (10) having a greater second thickness (Z). When electrical pulse loading of the resistor occurs, heat is generated in the resistor may be rapidly conducted to the relatively thicker bight portions (10) which accordingly act as heat sinks. Heat may subsequently be conducted to the relatively thinner web (6) and bight (8) portions for dissipation to atmosphere surrounding the resistor (4). The resistor (4) may be formed from a sheet blank of uniform thickness by a stamp drawing method which leaves portions of the sheet blank at least substantially undrawn to form the thicker bight portions (10) of the resistor (4). The resistor may be used in an electrical braking system in a vehicle, used as a crow-bar resistor or in a resistive load bank.

Description

RESISTOR AND METHOD OF MANUFACTURE

[0001] The present invention relates to electrical resistors and a method of manufacturing them.

[0002] In particular the present invention relates to a power resistor of the type suitable for use as braking resistor in an electrical braking system of a vehicle, for use as a crow-bar resistor (which can be used to rapidly provided a short between two electrical terminals) or for use in a resistive load bank. Such a resistor dissipates electrical energy by converting it into heat energy. If such a resistor dissipates power in a steady state situation its power rating is determined by its ability to dissipate heat energy continuously resulting from electrical heating of the resistor. In such a situation a high surface area is advantageous. Such a high surface area however provides no advantage in situations in which pulse energy needs to be absorbed. The so-called pulse power capability of a resistor represents the amount of power that the resistor can absorb in a time scale, possibly in the order of a few seconds, that is too short for significant energy to be dissipated, for example as radiant energy, to the surroundings of the resistor. The amount of pulse energy that can be absorbed by a resistor is calculated on the basis of the product of the mass, the specific heat capacity and the temperature change which takes place. The maximum temperature change in turn will be determined by the difference between ambient temperature and the maximum temperature to which the resistor can be heated without sustaining irreparable damage.

[0003] A typica] prior art power resistor is disc]osed in patent US 4551614. The resistor comprises a thin metal foil ribbon which is folded into a corrugated configuration and held between confronting surfaces of a channel support member which is provided with undercut sections to support the corrugated ribbon. A longitudinal cross-section through a typical corrugated power resistor 2 is shown in Fig. 1.

[0004] An object of the invention is to provide a power resistor which is better able to absorb pulse power than

typical prior art power resistors.

[0005] Thus according to the invention there is provided an electrical resistor including a corrugated conductive member having portions of different thicknesses. With such a resistor, heat generated in relatively thin portions of the resistor will be rapidly conducted to the relatively thicker portions which will heat up and act as heat sinks without dissipating a significant amount of heat energy to the surroundings of the resistor for the duration of an electrical pulse. Heat energy can subsequently be conducted from the relatively thicker portions to the relatively thinner portions for efficient dissipation of heat energy to the surroundings by radiation and/or conduction. The corrugated form of the conductive member allows the resistor to have a relatively high overall surface area for a given projected size and will enable the resistor to provide efficient heat dissipation when subjected to steady state electrical loading.

[0006] Preferably the portions of different thickness define a thickness distribution pattern that is repeated along a longitudinal axis of the resistor.

[0007] Preferably corrugations of the conductive member define a shape that is repeated along a longitudinal axis of the resistor.

[0008] In order to provide rapid dissipation of heat energy after the pulse has occurred, the resistor preferably includes portions of a first thickness and relatively thicker portions and wherein a first cumulative surface area of the portions having the first thickness is greater than a second cumulative surface area of the relatively thicker portions.

More preferably the first cumulative surface area is at least 2.5 times the second cumulative surface area.

[0009] So as to facilitate production of the resistor and allow it to be formed from a sheet of constant thickness which is stamp drawn into a corrugated shape, preferably the corrugations include web portions of a first thickness and web-connecting bight portions of a second thickness.

[0010] Preferably the second thickness of the bight portions is greater than the first thickness of the web portions.

More preferably the second thickness of the bight portions is at least twice the size of the first thickness of the web portions in order that the bight portions provide particularly effective heat sinks. The second thickness of the bight portions may even be at least three times the thickness of the web portions.

[0011] Only a fraction of the bight portions may have the second thickness and remaining bight portions may have a thickness that is substantially equal to the first thickness of the web portions. With such an arrangement the resistor will include more web portions than relatively thicker bight portions thus increasing the proportion of the surface area of the resistor which is relatively thinner.

[0012] According to a second aspect of the invention there is provided a method of manufacturing an electrical resistor including the steps of: (a) providing a sheet of conductive material; and (b) stamping the sheet such that it is drawn into a corrugated form including portions of different thicknesses.

[0013] Preferably the stamping step involves stamping the sheet so as to form a thicknesses distribution pattern that is repeated along a longitudinal axis of the resistor.

[0014] The stamping step may involve stamping the sheet into web portions interconnected by bight portions and wherein at least some of the bight portions are at least less drawn than the web portions and have a larger thickness than the web portions.

[0015] Preferably at least some of the bight portions are substantially undrawn by the stamping step.

[0016] The stamping step preferably draws the web portions down to a first thickness which is at least half of the larger thickness of the bight portions.

[0017] The invention will now be described by way of example only with reference to the accompanying drawings in which: [0018] Fig. 1 shows a longitudinal cross-section through a

typical prior art corrugated power resistor;

[0019] Fig. 2 shows a cross-section through a sheet blank prior to forming into a resistor according to the invention; [0020] Fig. 3 shows a longitudinal cross-section through a resistor according to a first embodiment of the invention; [0021] Fig. 4 shows a perspective view of the resistor shown in Fig. 3; [00221 Fig. 5 shows a longitudinal cross-section through a second embodiment of the invention; and [0023] Fig. 6 shows a longitudinal cross-section through a third embodiment of the invention.

[0024] Fig. 3 shows a longitudinal cross-section through a corrugated power resistor 4 according to a first embodiment of the invention and Fig. 4 shows a perspective view of the resistor 4. The resistor 4 includes a corrugated member 5 having a longitudinal axis 12 and defines a repeating thickness distribution made up from portions 6 and 8 of a first thickness Y between relatively thicker portions 10 of a second thickness Z. The corrugated member 5 may be made of stainless steel, nickel-chromium alloy, cobalt-nickel-chromium alloy or any other suitable material and has a width W. The corrugated member 5 also defines a repeating shape made up from corrugations 14 having corrugation axes 16 which are perpendicular to the longitudinal axis 12 of the corrugated member 5.

[0025] Web portions 6 of the corrugated member 5 have the thinner thickness Y. Alternate bight portions 8 of the corrugated member 5 also have the first thinner thickness Y. The remaining alternate bight portions 10 have the second thicker thickness Z. The thinner and thicker portions 6, 8 and 10 of the corrugated member 5 are integral with each other and for this reason conduction of heat between the portions is rapid.

[0026] The surface area of each thinner portion, comprising an adjacent pair of web portions 6 and the thinner bight portion 8 interconnecting them, will be: (A1+A2)W (where Al and A2 are the dimensions marked as such in Fig. 3) . The surface area of each thicker bight portion 10 will be: (E1+B2)W (where El and E2 are the dimensions marked as such in Fig. 3) . The cumulative surface area of the thinner portions 6 and 8 is greater than the cumulative surface area of the thicker portions 10. In the first embodiment illustrated in Figs. 3 and 4 the cumulative surface area of the thinner portions is slightly more than double that of the thicker portions.

[0027] A longitudinal cross-section through a sheet blank 18 from which the corrugated member 5 shown in Fig. 3 is formed is shown in Fig. 2. The sheet blank 18 has a thickness Z which corresponds to the thickness Z of the thicker bight portions 10 of the corrugated member 5. A stamp drawing process is used to form the sheet blank 18 into the corrugated member 5. The thicker bight portions 10 are at least substantially undrawn and preferably completely undrawn. The drawing process accordingly draws parts of the sheet blank 18 down to the thinner thickness Y to form the required thickness distribution. The thickness distribution and also preferably the overall shape form a pattern which is repeated along the longitudinal axis of the corrugated member 5. The stamp drawing process may reduce the thickness of the sheet blank in regions forming the thicker bight portions and reduce the thickness of other portions still further to form the required thickness distribution.

[0028] Fig. 5 shows a longitudinal cross-section through a corrugated power resistor 20 according to a second embodiment of the invention which comprises a corrugated member 22. The second embodiment differs from the first in that each bight portion 26 has the same thicker thickness W. These thicker bight portions 26 are interconnected by relatively thinner web portions 24 having a thickness V. The resistor 20 will be formed in a similar stamp drawing process to that used to form the resistor 4.

[0029] Fig.6 shows a longitudinal cross-section through a corrugated power resistor 30 according to a third embodiment of the invention which comprises a corrugated member 32. The third embodiment differs from the first in the each bight portion 36 has the same thicker thickness U. These thicker bight portions 36 are interconnected by relatively thinner web portions 34 having a thickness T. The resistor 30 also differs from the resistors 4 and 20 in that the web portions are curved as opposed to being straight. The resistor 30 will be formed in a similar stamp drawing process to that used to form the resistor 4.

[0030] While various embodiments of the invention have been described with reference to the accompanying drawings, it will be clear to a skilled person in the art that various modifications would be possible which would still fall within the scope of the accompanying claims.

Claims

CLAIMS1. Electrical resistor including a corrugated conductive member having portions of different thicknesses.
2. The resistor of claim 1 wherein the portions of different thickness define a thickness distribution pattern that is repeated along a longitudinal axis of the resistor.
3. The resistor of claim 1 or 2 wherein corrugations of the conductive member define a shape that is repeated along a longitudinal axis of the resistor.
4. The resistor of claim 1, 2 or 3 including portions of a first thickness and relatively thicker portions and wherein a first cumulative surface area of the portions having the first thickness is greater than a second cumulative surface area of the relatively thicker portions.
5. The resistor of claim 4 wherein the first cumulative surface area is at least 2.5 times the second cumulative surface area.
6. The resistor of any preceding claim wherein the corrugations include web portions of a first thickness and web-connecting bight portions of a second thickness.
7. The resistor of claim 6 wherein the second thickness of the bight portions is greater than the first thickness of the web portions.
8. The resistor of claim 7 wherein the second thickness of the bight portions is at least twice the size of the first thickness of the web portions.
9. The resistor of claim 8 wherein the second thickness of the bight portions is at least three times the thickness of the web portions.
10. The resistor of any of claims 6 to 9 wherein only a fraction of the bight portions have the second thickness and remaining bight portions have a thickness that is substantially equal to the first thickness of the web portions.
11. A method of manufacturing an electrical resistor including the steps of: (a) providing a sheet of conductive material; and (b) stamping the sheet such that it is drawn into a corrugated form including portions of different thicknesses.
12. The method according to claim 11 wherein the stamping step involves stamping the sheet so as to form a thicknesses distribution pattern which is repeated along a longitudinal axis of the resistor.
13. The method of claim 11 or 12 wherein the stamping step involves stamping the sheet into web portions interconnected by bight portions and wherein at least some of the bight portions are at least less drawn than the web portions and have a larger thickness than the web portions.
14. The method of claim 13 wherein at least some of the bight portions are substantially undrawn by the stamping step.
15. The method of claim 13 or 14 wherein the stamping step draws the web portions down to a first thickness which is at lease half of the larger thickness of the bight portions.