GB2140457A

GB2140457A - Motor vehicle having a corrosion protection device

Info

Publication number: GB2140457A
Application number: GB08411788A
Authority: GB
Inventors: Martin Earnest Parrock; Wade Edward Parrock
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-05-25
Filing date: 1984-05-09
Publication date: 1984-11-28
Also published as: GB8411788D0

Abstract

A motor vehicle has a vehicle body (21;31) to which is secured a corrosion protection device (10;20;) comprising a sacrificial anode made of a less noble material than the vehicle body, whereby in use, an electrolytic cell is created between the sacrificial anode (10;30), the body (21;31;) and moisture in electrical contact with both the sacrificial anode and the body, so that the sacrificial anode corrodes in preference to an area of the body surrounding the sacrificial anode. <IMAGE>

Description

SPECIFICATION Motor vehicle having a corrosion protection device Description of invention This invention relates to a motor vehicle having a corrosion protection device.

Corrosiion of metal parts of motor vehicles, particularly of the body and exhaust system, is a well known problem.

Motor vehicles are particularly vulnerable to corrosion in splash zones, i.e. the regions of the vehicle which are subject to spray as the vehicle moves, such as under the wings of the body, the underbody, and exhaust system for examples. The corrosion problem is aggravated in countries where salting of the roads is common.

It is an object of the present invention to provide a motor vehicle in which such corrosion is reduced.

According to the present invention, we provide a motor vehicle having a vehicle body to which is secured a corrosion protection device comprising a sacrificial anode made of a less noble material (as herein defined) than the vehicle body, whereby in use, an electrolytic cell is created between the sacrifical anode, the body and moisture in electrical contact with both the sacrificial anode and the body, so that the sacrificial anode corrodes in preference to an area of the body surrounding the sacrificial anode.

Preferably the sacrificial anode is secured to the vehicle body by releasable means, such as nut and bolt means, which extends through an opening provided in the vehicle body, although any other releasable means may be provided, such as a clip or clamp means to simplify installation and replacement once the sacrificial anode has severely corroded.

In one embodiment, the sacrificial anode comprises a head part having integral therewith a threaded shank which extends through the opening in the vehicle body, and receives a nut thereon, to trap the vehicle body between the nut and the head part of the sacrificial anode.

In another embodiment, the sacrificial anode has a recess such as a bore, to receive a bolt or other fastener which may be made of the same material as the sacrificial anode, or preferably of a more noble material (as herein defined) than both the sacrificial anode and the vehicle body.

Thus, when moisture is present, an electrolytic cell is not only formed between the sacrificial anode and the vehicle body, but also between the fastener and the vehicle body. However, the sacrificial anode will in such construction, still corrode in preference to the vehicle body and in preference to the fastener as it is the least noble of the three metals.

By more or less noble material, we mean a material lying higher or lower respectively in the electrochemical series. Thus, where the vehicle body is made, for example, predominently of steel, the sacrificial anode may be made of any metal in the electrochemical series below steel, such as zinc, cadmium, aluminium or magnesium. However, zinc is preferred to cadmium for economic reasons, and to aluminium as the aluminium tends to form a protective oxide coating which inhibits formation of an electrolytic cell, and to magnesium for safety reasons, as magnesium is prone to catch fire.

The zinc or other less noble material is preferably as pure as possible, so that impurities do not inhibit the formation of the electrolytic cell. Where a fastener of more noble material than the vehicle body is used, this is preferably copper.

It is well known that the rate of corrosion of an anode in an electrolytic cell is proportional to the ratio of cathode to anode area, amongst other parameters.

In a motor vehicle, substantially the entire vehicle body may be a cathode or earth for the purposes of the electrical services of the car, although only a limited area of the body surrounding the sacrificial anode will be protected threby as there will not be a significant flow of current from the sacrificial anode to the cathode at any substantial distance from the sacrificial anode.

Preferably however, to ensure that the sacrificial anode protects as large an area as possible, the effective surface area of the sacrificial anode is as large as possible. This may be accomplished by providing a crevice between part of the sacrificial anode and the vehicle body, in which crevice moisture may collect.

It will be appreciated that a predominently steel vehicle body for example may be chemically changed into rust through various stages, due to elements other than iron being present in the steel and any residual current flowing through the vehicle body to operate the electrical services of the vehicle.

Thus it cannot always be guaranteed that current will flow from the sacrificial anode to the vehicle body, but a reverse current may flow which could encourage corrosion of the vehicle body. Thus, the sacrificial anode may be polarised by impressing on the sacrificial anode a positive charge whih will flow in the desired current direction to the vehicle body, to polarise the sacrificial anode correctly and promote initial electrolytic action.

This charge may be impressed as a pulse as often as necessary. In one arrangement, the vehicle has a moisture detector which, when the level of moisture detected exceeds a predetermined value, signals a current generator to impress a pulse or series of pulses on the sacrificial anode.

in an alternative arrangement, in place of a moisture detector, a pulse or series of pulses may be impressed on the sacrificial anode each time the ignition of the vehicle is switched on, or at predetermined intervals, every hour or so say, to ensure that the sacrificial anode remains correctly polarised.

It will be appreciated that any wire connecting the current generator to the sacrificial anode must be made of a more noble material than the sacrifical anode, so that the wires themselves do not corrode at their point of connection to the sacrificial anode if mosture is present. Preferably, the wires are copper, and where a copper fastener is used to secure the sacrificial anode to the vehicle body, the connecting wires are preferably connected to the copperfas- tener.

The sacrificial anode may have a head provided with a plurality of grooves or other formations to adjust, i.e. increase or decrease the surface area of the sacrificial anode which may be brought into contact with the moisture.

The head may be generally circular in crosssection and the grooves may extend circumferentially around the head. The head may be generally dome-shaped or flat, but in each case, if desired, the head may have a recess, the mouth of which in use, is uppermost so that moisture collects in the recess to ensure that the electrlytic action between the sacrificial anode and the vehicle body is continuous, even during generally dry conditions. In this event, it may not be necessary to provide polarisation by means of impressing a charge on the sacrificial anode as the anode would be always correctly polarised.

Preferably, a plurality of sacrificial anodes are provided at spaced positions over the vehicle body, particularly in splach zones. The sacrificial anodes may each be connected to the current generator.

The invention will now be described with the aid of the accompanying drawings, wherein: Figure lisa side elevation, partly in section of a sacrificial anode for use in a motor vehicle embodying the invention; Figure 2 is a plan view of the sacrificial anode of Figure 1; Figure 3 is a diagrammatic side section of a second embodiment of the sacrificial anode in accordance with the invention; Figure 4 is a side view, partly in section, of a still further sacrificial anode for use in a motor vehicle embodying the invention; Figure 5 is a diagrammatic representation of part of the electrical circuitry of a motor vehicle embodying the invention.

Referring to Figure 1, a sacrificial anode 10 comprises a generally cylindrical shank 11 having a threaded end portion 12. At the other end of the shank 11 and integral therewith is a head 13 which is generally dome-shaped and circular in cross-section, as can be seen from Figure 2, hving a flared portion 15 adjacent the shank 11.

The head 13 is provided with three circumferentially extending grooves 16 which serve to increase the surface area of the head.

The under surface 17 of the head is provided with a peripheral rebate 18 which provides a crevice approximately 0.020" (0.008 cm) deep between the surface 19 of the rebate and the adjacent surface 20 of the part 21 of the body of the motor vehicle, on which the anode is mounted. The shank 11 is received in an aperture 22 of the part 21 and a nut 23 is received on the threaded end of the shank 11,so that the part 21 of the vehicle is trapped between the head 13 of the sacrificial anode 10, and the nut 23.

The sacrificial anode 10 of this example is made by die casting a near pure zinc, but may be made of a die casting zinc alloy. Furthermore, the sacrifical anode may be made by any other suitable process and in any other suitable material which is less noble than the material from which the vehicle body is made.- For example, for steel motor vehicle bodies, the sacrificial anode 10 may be made of magnesium or one of its alloys, or even cadmium or aluminium, although pure zinc is preferred as there are no impurities to inhibit electrolytic corrosion of the sacrificial anode.

When the motor vehicle is used, for example in rain, the rainwater contacts both the anode 10 and the part 21 of the vehicle body surrounding the sacrificial anode as a result of spray from the wheels of the motor vechicle or the rainwater dripping from higher parts of the motor vehicle body, thus causing an electrolytic cell to be created so that galvanic corrosion of the sacrificial anode 10 occurs in preference to corrosion of the steel body part 21.

Of course, where salt is applied to the road, the potential corrosion effect of the salt laden water is greater than with non-salted water, butthis is countered by the greater efficiency ofthesalted water as an electrolite in the electrolytic cell formed between the sacrificial anode 10 and the vehicle body part 21 so that greater protection is achieved.

By providing the crevice 18 between the surfaces 19 and 20, a region of increased potential is provided to facilitate initiate corrosion of the sacrificial anode.

The extent and size or pattern of the grooves 16 or ribbing provided in the surface of the dome-shaped head 13 may be adjusted to adjust the surface area of the sacrificial anode as required.

It has been found that current does not always flow from the sacrificial anode 10 to the vehicle body, due to the presence of impurities in the steel from which the vehicle body is made, and/or residual electrical current flowing in the vehicle body which operates the electrical services ofthe vehicle.

Thus if desired, a charge may be impressed on the sacrificial anode to polarise the sacrificial anode, and to ensure that current always flow from the sacrificial anode to the vehicle body. This is described hereinafter in more detail with reference to Figure 5.

In this event however, it would be necessary to connect wires or the like to the sacrificial anode to connect the sacrificial anode to a current generator.

Of course, if the wires were less noble than the sacrificial anode, these would corrode, particularly at the point where the wire is connected to the sacrificial anode.

Preferably, such wires would be made of a more noble material than the zinc sacrificial anode shown, and more noble than the vehicle body. On such suitable material is copper. Thus any electrolytic cell formed between the copper and the zinc would merely encourage electrolytic corrosion of the zinc anode.

Referring now to Figure 3, an alternative sacrificial anode 30 is shown in which there is a third metal present, i.e. copper. The sacrificial anode comprises a generally spherical shaped head 33, again having a plurality of circumferential grooves 34 in the surface thereof to increase the surface area as necessary, and a recess 35 therein, the mouth 36 thereof extending generally upright in use.

Within the recess 35 there is a bore 37 which extends through the head 33 of the scrificial anode and receives a fastening 38 made of a more noble material than either the vehicle body part 31 to which the sacrificial anode 30 is secured, or the sacrificial anode 30 itself, i.e. a copper bolt.

Moisture, for example from spray, is retained in the recess 35 in the head 33 so that the electrolytic action is continuous even in dry conditions. As shown, a connecting wire 39 is secured to the copper fastening 38 and may extend to a current generator so that a charge may be imposed on the sacrificial anode 30 as described hereinbefore to ensure correct polarisation.

It will be appreciated that an electrolytic cell will be formed between the copper bolt 38 and the part 31 of the vehicle body, although the zinc sacrificial anode 30 will still tend to corrode in preference to either the bolt 38 or part 31 of the vehicle body as a maximum potential difference will still be formed between the copper and the zinc. In this arrangement, it can be seen that a crevice C is naturally formed between the dome-like head 33 of the anode 30 and the vehicle body part 31, due to the rounded shape of the head 33.

Referring now to Figure 4, a still further embodiment of the invention is shown.

A sacrificial anode 40 has a head 43, which is generally flat, but has a recess 44 in the upper surface thereof to entrap moisture therein to ensure that the electrolytic process proceeds continuously.

Again, a copper fastener 45 is provided comprising a threaded shank 46 which is fixed to the head of the anode and extends through an opening 47 in the vehicle body part 41 and receives a nut 48 thereon to trap the vehicle body 41 between the nut 48 and the head 43.

In Figure 4 device, an annular rebate 49 is cut in the underside of the head to provide a crevice around the threaded fastener.

Referring now to Figure 5, a diagrammatic representation of an electrical circuit using several sacrificial anodes is shown.

The vehicle body is indicated generally at 50 and a plurality of sacrificial anodes 10' are secured thereto by copper fastenings as hereinafter described with reference to Figure 3 or Figure 4.

Each of the sacrificial anodes 10' acts over an active area surrounding the sacrificial anode as indicted by dotted lines. as shown, the sacrificial anodes are spaced so that their active areas overlap.

The sacrificial anodes 10' are electrically connected together by connecting wires Wand are connected to a current generator indicated at G by a further connecting wire W'. Each of the wires Wand W' are made of copper and are secured to the copper fastening of the sacrificial anode 10' as described with reference to Figure 3.

The current generator G includes a source of electrical current such as battery B and a control means C which ensures that a pulse of current is impressed on each of the sacrificial anodes 10', either at regular intervals or each time the ignition of the vehicle is switched on, or when a moisture detector (not shown) detects a moisture level above a predetermined value, as required.

The vehicle body part 50 shown may comprise the underside of a wing, the underbody, part of the exhaust or any other part of the body which may be particularly prone to splash and hence corrosion.

If desired, instead of copper wires secured to the copper fastenings of the sacrificial anodes 10', graphite wires similar to those used in spark plug high tension leads may be used, which will not form an electrolytic cell with the remainder of the sacrificial anode.

It can be seen from Figure 5 that the spacing of the sacrificial anodes 10' is not regular. The active area over which each sacrificial anode 10' will give protection will depend, amongst other things, on the grain of the metal, the area of the sacrificial anode 10' and the potential difference formed in the electrolytic cell. Thus the spacing of the anodes 10' must be determined empirically.

Many other designs of sacrificial anode are no doubt possible, but in each case, preferably the anode is eadily removable from the vehicle body, to facilitate replacement.

Claims

1. A motor vehicle having a vehicle body to which is secured corrosion protection device comprising a sacrificial anode made of a less noble material (as herein defined) than the vehicle body, whereby in use, an electrolytic cell is created between the sacrifical anode, the body and moisture in electrical contact with both the sacrificial anode and the body, so that the sacrificial anode corrodes in preference to an area of the body surrounding the sacrificial anode.

2. A vehicle according to Claim 1 wherein the sacrificial anode is secured to the vehicle body by releasable means, which extend through an opening provided in the vehicle body.

3. A vehicle according to Claim 2 wherein the sacrificial anode comprises a head part having integral therewith a threaded shank which extends through the opening in the vehicle body, and receives a nut thereon, to trap the vehicle body between the nut and the head part of the sacrificial anode.

4. A vehicle according to Claim 2 wherein the sacrificial anode has a recess to receive a fastener which extends through an opening in the vehicle body.

5. A vehicle according to Claim 4 wherein the fastener is made of the same material as the sacrificial anode, or a more noble material (as herein defined) than both the sacrificial anode and the vehicle body.

6. A vehicle according to any one of the preceding claims wherein the vehicle body is made predominently of steel, and the sacrificial anode is made of a metal in the elctrochemical series below steel.

7. A vehicle according to Claim 6 wherein the sacrificial anode is made of zinc.

8. A vehicle according to any one of Claims 5 to 7 where appendant to Claim 5 wherein the fastener is made of copper.

9. A vehicle according to any one of the preceding claims wherein a crevice is provided between part of the sacrificial anode and the vehicle body.

10. A vehicle according to any one of the preceding claims wherein the sacrificial anode is polarised by impressing on the sacrificial anode a positive charge which will flow in the desired current direction to the vehicle body, and promote initial electrolytic action.

11. A vehicle according to Claim 10 wherein the charge is impressed as a pulse.

12. A vehicle according to Claim 11 wherein a moisture detector is provided which, when the level of moisture detected exceeds a predetermined value, signals a current generator to impress a pulse or series of pulses on the sacrificial anode.

13. A vehicle according to Claim 11 wherein a pulse or series of pulses are impressed on the sacrificial anode by a current generator each time the ignition of the vehicle is switched on, or at predetermined intervals.

14. A vehicle according to Claim 12 or Claim 13 wherein wires connecting the current generator to the sacrificial anode are made of a more noble material than the sacrificial anode.

15. A vehicle according to any one of the preeding claims wherein the sacrificial anode has a head provided with a plurality of grooves or other formatins to adjust the surface area of the sacrificial anode which may be brought into contact with the moisture.

16. A vehicle according to Claim 15 wherein the head is generally circular in cross-section, the grooves extending circumferentially around the head.

17. A vehicle according to Claim 15 or Claim 16 wherein the head has a recess, the mouth of which in use, is uppermost so that moisture collects in the recess to ensure that the electorlytic action between the sacrificial anode and the vehicle body is continuous, even during generally dry conditions.

18. A vehicle substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

19. Any novel feature or novel combination of features disclosed herein and/or shown in the accompanying drawings.