GB1573445A

GB1573445A - Spark plugs

Info

Publication number: GB1573445A
Application number: GB1018676A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-03-11
Filing date: 1977-03-11
Publication date: 1980-08-20

Description

(54) IMPROVEMENTS IN OR RELATING TO SPARK PLUGS (71) I, PETER BURGESS, of British Nationality, of 31 Fulford Road, West Ewell, Epsom, Surrey, do hereby declare the invention for which I pray that a patent may be granted to me, and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to spark plugs for internal combustion engines and more particularly to spark plugs for engines which are used in motor vehicles.

It is well known that a motor vehicle engine is expected to be able to start without difficulty under a very wide range of operational and climatic conditions and circumstances which may or may not be inter-related to each other.

Thus, for example, the driver of a motor vehicle usually expects to be able to start the engine of a vehicle without any difficulties not only during any one of the many climatic variations that occur in any locality but also after the vehicle has been left unused for various time intervals ranging from minutes to weeks; and also irrespective of the operational condition of the engine, the fuel system and the ignition system.

Some of the principal causes of difficult starting are in practice directly associated with the condition of the ignition system both in the case of factors arising from the deterioration of the system through use and also through inherenr factors arising from the actual design and construction of the system.

These various factors can include poor physical condition of the insulator and electrodes of the spark plug, incorrect settings for the actual width of the gap, insufficient high tension energy available at the plug electrodes at the instant of starting; energy leakages caused by dirty insulators, poor condition of the battery and many other factors.

In practice, any substantial departure of any part of an ignition system from its opu'- mum operational condition can result in unreliable or difficult starting of an engine, whilst relatively minor departures in combinations of a number of factors such as mentioned above can collectively lead to starting problems.

Furthermore, there are factors other than those arising from the condition of the engine and its associated components which can contribute to starting difficulties. These additional causes of difficult starting include the ambient weather conditions. For instance when the weather is very cold the starter battery functions at a greatly reduced effi- ciency; also it is more difficult for the starting motor of the engine to turn the crank shaft in view of the higher frictional drag against engine movement, caused by the higher viscosity of lubricating oils used in the engine.

This condition results in the starter motor having to work against an increased starting torque so that the energy demands by the motor are increased whereby the residual energy available for the formation of sparks at the plugs is reduced thereby introducing the possibility that the energy provided at the plugs is neither sufficient to produce a spark hot enough to ignite the petrol air mixture nor able to jump the standard spark plug gap.

Similar problems can arise if the climatic conditions are such that the engine compartment is wet or damp enough to produce voltage leakages from the ignition system to the body of the engine or body work which are sufficiently large enough to prevent formation of an adequate spark at the plugs.

It will thus be clear that any departures of a number of different atmospheric conditions from genreal average conditions in conjunction with defective or reduced operational capability of the engine and engine components can result in difficult starting of the engine.

It is an object of the present invention to provide means which is able to improve starting capability of an internal combustion engine, and also to increase ignition efficiency generally over the range of engine operating conditions.

According to the invention a spark plug for use with an internal combustion engine, comprises a metal outer casing arranged at one end for insertion into the cylinder head of the engine; an insulating body sealed into the outer casing and having a nose extending substantially to said one end of the casing; a central electrode sealed within and extending axially through the insulating body, the insulating body closely surrounding and sup porting the central electrode at least throughout that part of the outer casing arranged to lie within the cylinder head when in use, the central electrode having a free end extending beyond the nose of the insulating body; and at least one earth electrode secured to the casing at said one end thereof, the earth electrode having a free end formed to lie at a predetermined spacing from the central electrode to form a spark gap; the composition of the electrodes being selected to produce relative movement between the free ends thereof in response to temperature rise within the cylinder of the engine for which the plug is intended such that as the temperature rises the spark gap in increased in size.

For a better understanding of the invention and to show how to carry the same into effect reference will now be made to the accompanying drawings in which: Figure 1 is a sectional view of spark plug, the section showing the main components of a spark plug suitable for a motor vehicle; Figure 2 is an elevation to an enlarged scale of the electrode structure of a spark plug incorporating a first embodiment of the thermally responsive electrode of the invention; Figure 3, is an elevation to an enlarged scale of the electrode structure of a second form of a spark plug incorporating the first embodiment of the thermally responsive electrode of the invention; and Figures 4 to 7 each show an elevation of electrode structures of spark plugs, to the same scale as Figures 2 and 3, each of the Figures 4 to 7 depicting different embodiments of thermally responsive electrodes of the invention.

The spark plug shown in Figure 1 includes a body portion 1 comprising a heat resisting and electrically insulating material, and having a central bore 2 which is stepped at 3 to provide an upper bore section 4 of a larger diameter than that of the lower bore section 5. The body portion 1 has an outwardly directed flange 6 substantially at the level of the internal step 3. Below the flange 6, the body has a cylindrical part 7 merging into a tapered part 8 terminating in a nose 9 with a rounded external edge.

A second cylindrical part 10 of a larger diameter than than of the part 7, extends from the upper part of the flange 6 and merges with a tapered part 11.

The body portion is mounted in a metallic cylindrical casing 12 more commonly referred to as the shell. The body portion 1 is securely attached to the casing 12 by means of a heat resisting gas tight seal 13. The casing 12 is stepped beneath the region of the flange 6 of the body portion to provide a smaller diameter sleeve 14 which is externally threaded for mounting in the cylinder head of an engine.

A central electrode 15 is positioned within the stepped bore 2, the electrode having an annular flange 16 which co-operates with the step 3 in the bore 2. The electrode 15 is firmly secured at a suitable location within the bore 2 by a heat resisting gas tight seal 17. In practice this seal can be located within the bore at what ever position it is required to lock the electrode to the body portion. In an alternative construction the formation of the electrode 15 can be such that the step 16 does not contact the step 3 at the position shown but co-operates with a further stop at a higher position within the body. If desired this can be attained by providing the step 3 at a higher position within the bore 2.

The upper end of the electrode connects with a terminal stud 18 which is mounted in the uppermost end 19 of the body portion 1.

The lowermost end of the electrode 15 projects to a predetermined extent from the nose 9 of the body portion 1 to provide an exposed electrode tip 20.

A second electrode 21 is attached to the casing sleeve 14 and is so shaped that its free end 22 overlies the tip 20. In practice the end 22 is carefully positioned relative to the tip 20 because it is the distance between the tip 20 and the end 22 that forms the spark gap of the plug, this gap being indicated by the reference numeral 23.

Referring now to Figure 2, in accordance with a first embodiment of the invention the electrode 21 is made from a material having heat expansion characteristics which are different from that of the sleeve 14 and the electrode 15 so that when the plug is located in or subjected to change of temperature the width of the gap 23 is correspondingly varied.

Consequently when the plug is cold, that is when the engine is not operating, the gap 23 has a first width. This position is indicated in full lines in the Figure 2, and when the plug is hot, that is when the engine has attained its operating temperature, the gap has a second width value which is greater than its value when the plug is cold. The position of the electrode end 22 is shown in dashed lines in the Figure 2 for the case of the hot plug.

In practice the difference in the heat expansion characteristics is such that if the gap 23 has a width of 0.018 inches when the plug is cold the gap will increase to a width of 0.025 inches when the plug is hot.

This latter dimension is the one at which the plug is intended to function whilst the engine is operating and in fact in so far as conventional plugs are concerned this is the average general dimension to which the gap is set when the plug is cold.

Consequently it is this larger dimension for the gap which has to be bridged by the sparks at the time of starting the engine.

Hence in the event of any of the above mentioned factors leading to a reduction of the electrical energy at the plug electrodes it may not be readily possible for a spark to bridge the gap when it is within the conventionally used range of 0.025 to 0.040 inches so that starting becomes a difficult process.

However, in the case of plugs according to the invention, since the width of the gap 23 when the plug is cold is considerably smaller than the gap when the plug is hot it is possible for a reduced level of electrical energy availability at the electrodes to still be able to cause a spark of sufficient quality to cause combustion. Consequently, it is possible to effect starting when the available electrical energy is not sufficient to produce a spark across a spark gap of a larger width i.e., within the range mentioned above.

Once the engine has started to operate and the temperature within the cylinder and in the vicinity of the plugs increases ro the op- erating temperatures the differential expansion between the electrodes increases the width of the gap to the required larger value, which latter is in practice set to provide the optimum operating efficiency. Because of the relatively small dimensions of the plugs relative to the dimensions of the remainder of the cylinder components it will be appreciated that the plug will attain its operating temperature relatively quickly so that the spark gap is increased to the larger width very shortly after starting of the engine so that the operational characteristics of the engine are to all intents and purposes not disturbed.

Preferably the electrode 22 is formed from a bimetallic combination which provides the desired change in the separation between the electrodes as a result of the change in the temperature from a cold engine to the operating engine. In the Figure 2 the relative expansion movement has been indicated as a vertical shift of the electrode end 22 relative to the central electrode tip 20. It is also contemplated that the dimensional movement could be attained by a twisting or torsional movement which causes the end 22 to move away from its cold position.

It will be appreciated that by suitable shaping of the electrode 21 a substantial amount of fiexure necessary to achieve the required movement between the electrodes can be accommodated. In particular by providing bends such as shown in Figure 2 or by introducing a curved kink or curved kinks in the electrode the amount of flexure of the element at the region of the join between the electrode and casing sleeve 14 can be mini- mised. Thus to obtain increased flexare from an electrode of limited length the electrode could be corrugated.

Such kinking can include forming the electrode 21 with a generally question mark pro file, or with a C or reversed C shaped profile.

Referring new to Figure 3 this illustrates the electrode structure of the invention incorported in a second form of spark plug which is of the kind provided with an additional earth electrode 24 that is an electrode secured to the casing sleeve 14. In this construction the electrode 21 co-operates directly with the central electrode tip 20 in the manner described in relation to Figure 2. The second earth electrode 24 is such that the free end 25 thereof is at a fixed distance from the central electrode tip 20. This free end 25 overlies the free end 22 of the electrode 21 and thus effectively provides a limit stop for any outward movement of the electrode end 22.

As in the case of Figure 2 the full line position of the electrode 21 represents irs setting wfien the plug is cold and the dashed line position represents the position or setting of the electrode when the plug is hot It will be understood that the various observations made in relation to the Figure 2 construction are applicable to the arrangement of Figure 3 so that a detailed description of the mode of operation of the construction of Figure 3 is not thought necessary.

In a modified form of the plug of Figure 3 which modification is not shown as a separate Figure the second electrode 24 can be such as to form a bridge or stop which extends from diametrically opposite sides of the casing to form an electrode which bridges both the electrode end 22 and the tip 20.

To accommodate the formation of the bridging electrode the electrode 21 is mounted upon the casing sleeve 14 so that the free end is interposed between the electrode bridge and the tip 20. Conveniently the electrode is mounted at right angles to the bridging electrode so as to achieve a symmetrical relationship.

In the spark plug electrode construction shown in Figure 4 there are two earth electrodes 26 and 27 arranged in a generally side by side configuration. The electrode 26 overlies the tip 20 of the central electrode 15 of the plug and forms with the tip a permanently positioned earth electrode spaced from the tip 20 by a distance which is considerably greater than the conventional spark gap (but which is the maximum permissible high temperature gap for a particular engine).

The other earth electrode 27 is shaped so that the free end 28 is located substantially level with the electrode tip 20 but laterally displaced with respect thereto. The separation is such that the distance between the side of the electrode end 23 and the adjacent tip 20 defines the spark gap 23 of the plug. The electrode 27 is the thermally responsive electrode and as such is arranged to move in response to the heating of the plug such that the end 28 moves away from the tip 20 to increase the width of the spark gap leaving the preset electrode 26 to function as the normal working gap for the plug if the end 28 opens a gap greater than the permissible maximum.

In the Figure 4 the full line position of the electrode 27 indicates the position of the electrode when the plug is cold and the position of the electrode when the plug is hot is indicated by the dashed lines.

As in the case of the embodiments of Figures 2 and 3 the thermally responsive electrode can be a bimetallic element It will be understood that whilst the electrode 27 has been shown in the Figure 4 as being a metal strip bent over at the end to provide the free end 28 the formation of the eletcrode could be such as to include one or more bends or a curved portion so that the amount of flexure at the region of the join with the sleeve 14 is minimised.

As so far described the construction of the plug electrode formations have been such that the thermally responsive gap variation has been attained by providing a positionally movable earth electrode. In practice it is also feasible to utilise a movable or displaceable central electrode construction which makes possible the required thermally responsive gap setting. Figures 5, 6 and 7 separately illustrate embodiments of electrode formations with positionally variable central electrodes.

Turning now to Figure 5 in the plug electrode construction illustrated the portion of the central electrode projecting from the nose 9 of the insulation body is increased as is indicated at 29 and the free end 30 of the electrode is turned to extend transversely of the axis of the central electrode. In addition the free end 31 of the earth electrode 32 is inwardly turned so as to be located beneath the end 30 thereby to provide the spark gap 23.

The central electrode is formed from a material which has a thermal expansion which is such that when the electrodes are at the operating temperature of the engine for which the plug is intended the central electrode will have expanded relative to the insulation body and the earth electrode by an amount suffi- cient for the width of the gap 23 to increase to the width specified for the optimum operation of the plugs.

In the Figure the full line represents the position of the end 30 when the plug is cold and the dashed line schematically indicates the position of the end 30 when the plug is hot. In practice, the distance variation is similar to that disclosed in relation to the previously described Figures. That is to say the cold plug gap of 0.018 inches increases to a hot plug distance of 0.025 inches.

In the embodiment of Figure 5 the central electrode is mounted within the plug body such that a length of the electrode is able freely to expand whilst maintaining the desired degree of mechanical and gas tight attachment.

For example the upper end part of the electrode can be secured to the insulating body thereby leaving substantially the full length of the electrode to expand away from the terminal end of the plug.

The formation of the central electrode portion 29 and the shape of its free end 30 together with the shaping of the associated earth electrode can be selected with a view to enhancing the expansion of the central electrode. Thus for example, Figure 6 illustrates an embodiment of the invention in which the central electrode portion 29 and the associated free end 30 are constituted by an electrode shape sornewhat similar to the shape of a question mark. In the Figure 6 the full line representation of the electrode 29, 30 represents the cold condition of the plug and the dashed lines represent the hot condition of the plug.

It will be understood that the particular shape of the electrode 29, 30 and the shape of the earth electrode 31, 32 associated therewith will be such as to attain the desired gap width at both the cold and hot conditions of the electrodes.

In the case of the electrode structure illustrated in the embodiment of Figure 7 the shaping of the electrode 29, 30 and the associated earth electrode 31, 32 is such that the end region 30 of the central electrode is inclined at substantially 450 to the axis of the central electrode, with the earth electrode being correspondingly deformed so that the tip of the free end 31 is substantially perpendicular to the plane of the end 30 of the electrode 29. In this Figure 7 the full line representations of the electrode 29, 30 represents the cold condition of the plug, whilst the dashed line representation indicates the position of the electrode 29, 30 when the plug is hot.

It will be seen that the change in temperature has produced an axial elongation of the central insulated electrode 29, 30 which has thus increased the gap width.

In the various embodiments of spark plugs discussed in relation to the Figures the central electrode for the electrode constructions of Figures 1, 2, 3 and 4 can be formed from a conventionally used non-magnetic nickel alloy. A similar material can be used for the earth electrodes of the electrode arrangements illustrated in Figure 5, 6 and 7.

In the case of the electrode constructions shown in Figures 2, 3 and 4 the temperature sensitive earth electrode 21 and 27 can be formed by a bi-metallic strip material comprising metals which will withstand both the operating temperatures and pressures arising within the cylinder of the engine. One such material which has been found suitable has been utilised in bi-metallic high temperature cut-off devices used in heater units for boilers and the like.

The temperature sensitive central electrode arrangements such as shown in Figures 5, 6 and 7 can be formed from the metal alloy which forms the principal expansion part of the bi-metallic element mentioned above. If desired, such a material can comprise a tip element fused to a main electrode part of another metal such as said nickel alloy.

It will be understood that although emphasis has been placed upon the improvements in the starting of the engines incorporating spark plugs according to the invention there are further benefits to be obtained from the use of the plugs. Such benefits arise where the normal operating width of the spark gap has to be towards the higher end of the range mentioned above or where the operating conditions of the engine would be enhanced by having a relatively wide spark gap.

An example of the latter situation is at the hot idling condition of the engine wherein a relatively weak mixture would be more satisfactorily ignited by a longer spark. Similar requirements prevail at light throttle cruising speeds of the vehicle during which the mixture is weakened and the ignition timing is fully advanced. Under these conditions the plug and cylinder temperatures tend to increase so that a long spark is required. In view of the temperature sensitivity of the plug of the invention the spark gap width can correspondingly respond.

In the same manner when the operating conditions are such that the instantaneous temperatures of the cylinder tend to fall so that ideally a narrower spark gap is to be desired, the temperature responsive plugs of the invention can respond to the temperature decrease.

In further embodiments of the invention which are not shown in the drawings both the earth electrode and the central electrode could be thermally sensitive and responsive in such manner that the relative electrode movemnet produces the required temperature variation in the width of the spark gap.

It will be understood that the various earth electrode and central electrode constructions shown in the Figures could be variously combined to produce the double thermally responsive electrode arrangements.

In addition, the shaping of the electrodes could be such that in the various embodiments disclosed above the temperature respensive electrode or electrodes using bimetallic strips arrangements the metal with the greater coefficient of heat expansion is positioned so as to be on the outside of any curve provided in the electrode so that on heating the free end thereof curls inwardly in such manner that the free end moves away from the other electrode. If desired, electrode combinations could be provided in which the bimetallic strips are such that one electrode curls or deforms outwardly, whilst the other electrode curls or deforms inwards, the relative movement being such that desired variation in the width of the gap is obtained.

It will he understood that the actual electrode sizes relative to the remainder of the plugs depicted in the Figures are essentially exaggerated for the sake of illustration, since in practice it is not, usually, a desirable feature of any spark plug to have electrodes of small cross-sectional dimensions protruding into the engine combustion chamber. Such projection can, in practice, result in the electrodes becoming so hot that ignition of the mixture occurs without (i.e., before) the production of the spark.

Also in practice it is desirable that the electrodes should be as thick as possible to aid the condition of heat away from the electrodes to the cooled cylinder block by way of the body of the plug.

WHAT I CLAIM IS:- 1. A spark plug for use with an internal combustion engine, comprising a metal outer casing arranged at one end for insertion into the cylinder head of the engine; an insulating body sealed into the outer casing and having a nose extending substantially to said one end of the casing; a central electrode sealed within and extending axially through the insulating body, the insulating body closely surrounding and supporting the central electrode at lesat throughout that part of the outer casing arranged to lie within the cylin der head when in use, the central electrode having a free end extending beyond the nose of the insulating body; and at least one earth electrode secured to the casing at said one end thereof, the earth electrode having a free end formed to lie a predetermined spacing from the central electrode to form a spark gap; the composition of the electrodes being selected to produce relative movement between the free ends thereof in response to temperature rise within the cylinder of the engine for which the plug is intended such that as the temperature rises the spark gap is ini creased in size.

2. A spark plug as claimed in Claim 1, in which the free end of one electrode remains substantially static.

3. A spark plug as claimed in Claim 2, in which the earth electrode remains sub stan- tially static and in which the free end of the central electrode is bent to lie adjacent the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. shown in Figures 2, 3 and 4 the temperature sensitive earth electrode 21 and 27 can be formed by a bi-metallic strip material comprising metals which will withstand both the operating temperatures and pressures arising within the cylinder of the engine. One such material which has been found suitable has been utilised in bi-metallic high temperature cut-off devices used in heater units for boilers and the like. The temperature sensitive central electrode arrangements such as shown in Figures 5, 6 and 7 can be formed from the metal alloy which forms the principal expansion part of the bi-metallic element mentioned above. If desired, such a material can comprise a tip element fused to a main electrode part of another metal such as said nickel alloy. It will be understood that although emphasis has been placed upon the improvements in the starting of the engines incorporating spark plugs according to the invention there are further benefits to be obtained from the use of the plugs. Such benefits arise where the normal operating width of the spark gap has to be towards the higher end of the range mentioned above or where the operating conditions of the engine would be enhanced by having a relatively wide spark gap. An example of the latter situation is at the hot idling condition of the engine wherein a relatively weak mixture would be more satisfactorily ignited by a longer spark. Similar requirements prevail at light throttle cruising speeds of the vehicle during which the mixture is weakened and the ignition timing is fully advanced. Under these conditions the plug and cylinder temperatures tend to increase so that a long spark is required. In view of the temperature sensitivity of the plug of the invention the spark gap width can correspondingly respond. In the same manner when the operating conditions are such that the instantaneous temperatures of the cylinder tend to fall so that ideally a narrower spark gap is to be desired, the temperature responsive plugs of the invention can respond to the temperature decrease. In further embodiments of the invention which are not shown in the drawings both the earth electrode and the central electrode could be thermally sensitive and responsive in such manner that the relative electrode movemnet produces the required temperature variation in the width of the spark gap. It will be understood that the various earth electrode and central electrode constructions shown in the Figures could be variously combined to produce the double thermally responsive electrode arrangements. In addition, the shaping of the electrodes could be such that in the various embodiments disclosed above the temperature respensive electrode or electrodes using bimetallic strips arrangements the metal with the greater coefficient of heat expansion is positioned so as to be on the outside of any curve provided in the electrode so that on heating the free end thereof curls inwardly in such manner that the free end moves away from the other electrode. If desired, electrode combinations could be provided in which the bimetallic strips are such that one electrode curls or deforms outwardly, whilst the other electrode curls or deforms inwards, the relative movement being such that desired variation in the width of the gap is obtained. It will he understood that the actual electrode sizes relative to the remainder of the plugs depicted in the Figures are essentially exaggerated for the sake of illustration, since in practice it is not, usually, a desirable feature of any spark plug to have electrodes of small cross-sectional dimensions protruding into the engine combustion chamber. Such projection can, in practice, result in the electrodes becoming so hot that ignition of the mixture occurs without (i.e., before) the production of the spark. Also in practice it is desirable that the electrodes should be as thick as possible to aid the condition of heat away from the electrodes to the cooled cylinder block by way of the body of the plug. WHAT I CLAIM IS:-

1. A spark plug for use with an internal combustion engine, comprising a metal outer casing arranged at one end for insertion into the cylinder head of the engine; an insulating body sealed into the outer casing and having a nose extending substantially to said one end of the casing; a central electrode sealed within and extending axially through the insulating body, the insulating body closely surrounding and supporting the central electrode at lesat throughout that part of the outer casing arranged to lie within the cylin der head when in use, the central electrode having a free end extending beyond the nose of the insulating body; and at least one earth electrode secured to the casing at said one end thereof, the earth electrode having a free end formed to lie a predetermined spacing from the central electrode to form a spark gap; the composition of the electrodes being selected to produce relative movement between the free ends thereof in response to temperature rise within the cylinder of the engine for which the plug is intended such that as the temperature rises the spark gap is ini creased in size.

free end of the earth electrode in such a position that linear axial expansion of the central electrode in response to a rise in temperature tends to increase the size of the spark gap.

4. A spark plug as claimed in Claim 2, in which the earth electrode remains substantially static and in which the free end of the central electrode extending beyond the nose of the insulating body includes a bimetallic combination and is shaped to incorporate at least one bend, the shape allowing the free end of the central electrode to lie adjacent the free end of the earth electrode and the bimetallic combination being chosen so that the free end of the central electrode moves away from that of the earth electrode in response to a rise in temperature.

5. A spark plug as claimed in Claim 2, in which the central electrode remains substantially static and in which the earth electrode is formed from a bimetallic combination and has a shape incorporating at least one bend, the bimetallic combination being chosen so that the earth electrode tends to straighten with a rise in temperature.

6. A spark plug as claimed in Claim 5, in which the earth electrode is bent to lie across the free end of the central electrode and in which movement of the free end of the earth electrode is substantially in line with the longitudinal axis of the central electrode.

7. A spark plug as claimed in Claim 5, in which the earth electrode is formed su that its free end lies alongside the free end of the central electrode and in which movement of the free end of the earth electrode is substantially perpendicular to the longitudinal axis of the central electrode.

8. A spark plug as claimed in Claim 7, in which an additional static earth electrode is provided shaped to lie across the end of the central electrode spaced therefrom by a distance corresponding to a required maximum spark gap, the composition of the additional electrode being chosen substantially to preserve its spacing from the central electrode throughout the temperature range for which the plug is intended, whereby the maximum spark gap is preserved in the event that the effective gap between the central electrode and the moveable earth electrode exceeds said maximum.

9. A spark plug constructed and arranged to operate substantially as described with reference to any one of Figures 2 to 7 of the accompanying drawings.