Electrical connection arrangement

Abstract

 An electrical connection arrangement (200,300) comprises a spark plug terminal (203,303) and an ignition coil terminal (202,302). A first spring (242,348) is arranged to engage the spark plug terminal (203,303) and bias the spark plug terminal (203,303) towards the ignition coil terminal (202,302). A second spring element(246,350) is arranged to engage the spark plug terminal (203,303) and to at least partially oppose the biasing of the first spark plug terminal (203,303) by the first spring element (242,348).

Description

[0001] This invention relates to an electrical connection arrangement. More particularly, but not exclusively, the invention relates to an electrical connections arrangement between a spark plug and an ignition coil.

[0002] Current connection arrangements between a vehicle ignition coil and a spark plug comprise a number of springs that urge a terminal of the spark plug into contact with a terminal of the coil. Figure 1 is an embodiment of such an arrangement.

[0003] A problem associated with such arrangements is that during strong vibrations, typically in excess of 70G, the terminal of the spark plug and the hard metal surface of the coil's terminal undergo relative movement against one another. This relative motion generates further stresses within the springs that can cause the springs to break. The failure of one or more of the springs results in the tip of the spark plug breaking electrical contact with the ignition coil terminal.

[0004] According to a first aspect of the present invention there is provided an electrical connection arrangement comprising a first contact element and a second contact element and a first biasing element, the first biasing element being arranged to engage the first contact element and being further arranged to bias the first contact element towards the second contact element characterised by a second biasing element arranged to engage the first contact element and to being further arranged to bias the first contact element away from the and second contact element.

[0005] Such an arrangement reduces the relative motion between the first and second contact elements caused by strong vibrations by absorbing the energy associated with the strong vibrations in the second biasing element. This reduces work fatigue in the first biasing element, and prolongs the life of the first biasing element.

[0006] The second biasing element may be arranged to reduce relative motion between the first and second contact elements. The second biasing element may be arranged to dissipate energy associated with relative motion between the first and second contact elements in a controlled manner.

[0007] The first and second biasing elements may comprise portions of a resilient member. Alternatively, the first biasing element and the second biasing element may comprise respective individual resilient members.

[0008] The first biasing element may comprise an elbow formed in the resilient member. Typically the elbow is formed in a mid-portion of the resilient member.

[0009] The second biasing element may comprise a shoulder formed in the resilient member. Preferably the shoulder is arcuate. The shoulder may be arranged to abut end surfaces of both the first and second contact elements.

[0010] Alternatively, the second biasing may comprise a further elbow formed in the resilient member. The further elbow may abut a surface of the first contact element adjacent a free end thereof. The surface may be a frusto-conical surface of the contact element. A free end of the resilient member may engage an end wall of a housing containing the second contact element, adjacent the second contact element.

[0011] The second biasing element may comprise a portion of the resilient member having a greater stiffness than at least one other portion of the resilient member. The second biasing element may comprise a portion of the resilient member having either, or both, of a greater transverse width or thickness than the at least one other portion.

[0012] The resilient member may comprise a plurality of resilient fingers each of which comprises respective first and second biasing elements. The fingers may be arranged to be equiangularly spaced about the first contact element. The plurality of fingers may be conjoined by a connecting element. The connecting element may comprise a portion of the resilient member. The connecting element may comprise an annular portion of the spring. The connecting element may be arranged to be interposed between the first and second contact elements, in use.

[0013] The first contact element may comprise a spark plug terminal. The second contact element may comprise an ignition coil terminal.

[0014] The resilient member may comprise a spring. The spring may be a leaf spring.

[0015] According to a second aspect of this present invention there is provided a method of reducing failure rate in an ignition coil terminal to spark plug terminal electrical connection comprising the steps of:

(i) biasing the spark plug terminal towards the ignition coil terminal by a first biasing means; and characterised by

(ii) at least partially opposing the biasing of step (i) by a second biasing means.

[0016] The invention will now be described, by way example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic representation of an embodiment of a prior art electrical connection arrangement;

Figure 2 is a schematic representation of a first embodiment of an electrical connection arrangement in accordance with an aspect of the present invention;

Figure 3 is a schematic representation of a second embodiment of an electrical connection arrangement in accordance with an aspect of the present invention;

Figure 4 is a schematic representation of a third embodiment of an electrical connection arrangement in accordance with an aspect of the present invention; and

Figure 5 is a line graph showing a comparison of a variation of acceleration with time between the arrangement of Figure 1 and an electrical connection arrangement according to the present invention.

[0017] Referring now to Figure 2, an electrical connection arrangement 200 comprises an ignition coil contact 202, a spark plug terminal 203 and a spring 204. The contact 202 comprises a cylindrical electrically conductive housing 206 with a circular opening 208 in one end wall 210. The opening 208 has an inwardly projecting rim 212 which forms an annular recess 214 about the end wall 210 internal of the housing 206.

[0018] A contact pedestal 216 having a circular cross section projects from the other end wall 218. A hemispherical contact projection 219 is formed centro symmetrically upon an end surface 220 of the pedestal 216. An annular channel 221 is formed between the pedestal 216 and the housing 206.

[0019] The terminal 203 comprises a cylindrical body portion 222, a waist portion 224 and a head portion 226. The waist portion 224 lies between, and is narrower than, the body portion 222 and the head portion 226. A frusto-conical chamfer 228 links the waist portion 224 and the head portion 226. The head portion 226 has a bevelled edge 227.

[0020] The spring 204 comprises two opposing planar fingers 230, 232 linked by an annular neck section 234. Each of the fingers 230, 232 are substantially identical and will therefore be described with reference to only one of them.

[0021] The finger 230 comprises a short foot portion 236 that connects to a lower arm portion 238 via a kink 240. The kink 240 is angled such that the low arm portion 238 is inclined inwardly towards the centre of the neck section 234. An elbow 242 connects the lower arm portion 238 to an upper arm portion 244. The elbow 242 is angled such that the upper arm portion 244 is directed outwardly away from the centre of the neck section 234. A resilient curved shoulder 246 connects the upper arm portion 244 to the neck section 234.

[0022] In use, the foot portions 236 of the spring 204 locate in the channel 214 with the kink 240 locating at approximately the same height as a free end of the rim 212. An outer surface 248 of the each of the shoulders 246 abuts the end surface 220 the contact pedestal 216.

[0023] The spark plug terminal 203 locates within the housing 206 such that the spring's elbow 242 engages the chamfer 228 and urges the head portion 226 into contact with the neck section 234.

[0024] The resilient shoulder 246 acts to mediate the force exerted by the elbow 242 on the terminal 203.

[0025] The shoulder 246 buffers relative motion between the terminal 203 and the housing 206 by dissipating the energy of the motion within the spring 204. This results in a decrease in the acceleration response of the coil contact 202 relative to the spark plug terminal 203 as the energy dissipation is spread over a longer time period than in prior art arrangements. This reduces the maximum stress exerted on spring 204 with a consequential decrease in fatigue in the spring 204.

[0026] Referring now to Figure 3, the ignition coil contact and the spark plug terminal of this second embodiment of the present invention are substantially the same as those of the first embodiment and identical parts of these elements will be accorded similar reference numerals in the three hundred series.

[0027] The arrangement of this second embodiment of the present invention differs from that of the first embodiment in that there is no annular neck portion of the spring 304. Consequently, respective terminal ends 352,354 of the spring's fingers 330, 332 abut the bevelled edge 327 of the spark plug 303. The spring's elbow 342 engages the chamfer 328 and urges the head portion 326 into contact with the terminal ends 352,354.

[0028] Referring now to Figure 4, the ignition coil contact and the spark plug terminal of this third embodiment of the present invention are substantially the same as those of the first embodiment and identical parts of these elements will be accorded similar reference numerals in the four hundred series.

[0029] The spring 404 comprises two substantially identical fingers 430, 432. Accordingly, the detailed structure of the fingers 430, 432 will now be described with reference to only one of them.

[0030] The finger 430 comprises an elongate substantially w-shaped body portion 433 with end portions 434, 436 projecting away from the body portion 433 in a plane perpendicular to that containing the w of the body portion 433.

[0031] The body portion 433 comprises a relatively stiff v-shaped central section 438 connected at its free ends to respective arm section 440, 342 by respective curved elbows 444, 446.

[0032] In use, one of the end portions 434 locates in the recess 414 with the other end portion 436 locating in the channel 421. The apex of the central section 438 is directed outwardly away from a central axis of the housing 406 and the elbows 444, 446 are directed inwardly towards the central axis.

[0033] The spark plug terminal 403 locates within the housing 406. One inner surface 448 of the central section 438 engages the chamfer 428 and urges the head portion 426 into contact with the other inner surface 450 of the central section 438. The force required to deform the arm sections 440,442 is less than that required to deform the central section 438. Consequently, when small relative movements between the spark plug terminal 403 and the ignition coil contact 402 occur there is substantially no relative motion between the central section 438 of the spring 404 and the spark plug terminal 403. The relative motion between the spark plug terminal 403 and the ignition coil contact 403 is accommodated in the 440, 442 of the spring 404. Typically, there will be only minimal movement between the spark plug terminal 403 and the spring's fingers 430, 432.

[0034] Thus, the spring 404 buffers relative motion between the spark plug terminal 403 and the ignition coil contact 402 by dissipating energy associated with such motion in a controlled manner, over time. This is shown graphically in Figure 5 in which curve A represents acceleration versus time for a rigid, prior art, terminal-coil connection and curve B represents acceleration versus time for a flexible terminal-coil connection according to an embodiment of the present invention.

[0035] It will be appreciated that due to the resilient nature of the fingers of the spring a small offset angle between the longitudinal axis of the spark plug terminal and the axis of the spring will not cause a misalignment of the terminal in the ignition coil housing.

[0036] It will also be appreciated that the stiffness of the section of the spring holding the terminal can be increased or decreased appropriately to specific requirements, this is typically achieved by varying the width, and/or the thickness, and/or the number of fingers of this section of the spring locally.

[0037] It will be further appreciated that although described with reference to a unitary spring construction having two resilient biasing regions the invention may be effected by means of two, or more, discrete springs operating to dampen relative motion between the terminal and the ignition coil, particularly under vibration.

Claims

1. An electrical connection arrangement (200,300) comprising a first contact element(203,303) and a second contact element (202,302) and a first biasing element (242,348), the first biasing element (242,348) being arranged to engage the first contact element (203,303) and being further arranged to bias the first contact element (203,303) towards the second contact element (202,302) characterised by a second biasing element (246,350) arranged to engage the first contact element (203,303) and being further arranged to at least partially oppose the biasing of the first contact element (203,303) by the first biasing element (242,348).

2. An arrangement according to Claim 1 wherein the first and second biasing elements (242,246,348,350) comprise portions of a resilient member (204,304).

3. An arrangement according to Claim 2 wherein the first biasing element (242,348) comprises an elbow formed in the resilient member (204,304).

4. An arrangement according to either Claim 1 or Claim 2 wherein the second biasing element (246) comprises a shoulder formed in the resilient member (204).

5. An arrangement according to Claim 4 wherein the shoulder (246) is arcuate.

6. An arrangement according to either Claim 4 or Claim 5 wherein the shoulder (246) is arranged to abut an end surface (220) of the second contact element (202).

7. An arrangement according to either Claim 2 or Claim 3 wherein the resilient member (304) comprises a W-shaped mid-portion (333).

8. An arrangement according to Claim 7 wherein the first and second biasing elements (348,350)comprise respective elbows of the W-shaped mid-portion (333).

9. An arrangement according to Claim 8 wherein the second biasing element (350) abuts a surface of the first contact element (303) adjacent a free end thereof.

10. An arrangement according to any one of Claims 2 to 9 wherein a free end (336) of the resilient member (304) engages an end wall of a housing (306) containing the second contact element (302), adjacent the second contact element (302).

11. An arrangement according to any one of Claims 2 to 10 wherein the second biasing element (246,350) comprises a portion of the resilient member (204,304) having a greater stiffness than at least one other portion of the resilient member (204,304).

12. An arrangement according to any one of claims 2 to 11 wherein the second biasing element (246,350)comprises a portion of the resilient member (204,304) having either, or both, of a greater transverse width or thickness than the at least one other portion of the resilient member (204,304).

13. An arrangement according to any one of Claims 2 to 12 wherein the resilient member (204,304) comprises a plurality of resilient fingers (230,232,330,332) each of which comprises respective first and second biasing elements (242,246,348,350).

14. An arrangement according to Claim 13 wherein the fingers (230,232,330,332) are arranged to be equiangularly spaced about the first contact element (203,303).

15. An arrangement according to either Claim 13 or Claim 14 wherein the plurality of fingers (230,232,330,332) are conjoined by an annular connecting element (234).

16. An arrangement according to Claim 15 wherein the annular connecting element (238) comprises a portion of the resilient member (204).

17. An arrangement according to either of Claims 15 or 16 wherein the connecting element (234) is arranged to be interposed between the first contact element (203) and the second contact element (202), in use.

18. An arrangement according to Claim 1 wherein the first biasing element (242,348) and the second biasing element (246,350) comprise respective individual resilient members.

19. An arrangement according to any one of Claims 2 to 18 wherein the resilient member (204,304) comprises at least one spring.

20. An arrangement according to any preceding claim wherein the first contact element (203,303) comprises a spark plug terminal.

21. An arrangement according to any preceding claim wherein the second contact element (202,302) comprises an ignition coil terminal.

22. An arrangement according to any preceding claim wherein the second biasing element (246,350) is arranged to reduce relative motion between the first contact element (203,303) and the second contact element (202,302).

23. An arrangement according to any preceding claim wherein the second biasing element (246,350) is arranged to dissipate energy associated with relative motion between the first contact element (203,303) and the second contact element (202,302) in a controlled manner.

24. A method of reducing failure rate in an ignition coil terminal to spark plug terminal electrical connection comprising the steps of:

(i) biasing the spark plug terminal (203) towards the ignition coil terminal (202) by a first biasing means (242,348); and characterised by

(ii) at least partially opposing the biasing of step (i) by a second biasing means (246,350).

Drawing