WO2003014546A1

WO2003014546A1 - Slow release inhibitor-generating device for an ic engine

Info

Publication number: WO2003014546A1
Application number: PCT/AU2002/001044
Authority: WO
Inventors: Adrian James Domney; Stanley Davidenko
Original assignee: Adrian James Domney; Stanley Davidenko
Priority date: 2001-08-08
Filing date: 2002-08-08
Publication date: 2003-02-20
Also published as: NZ520674A; MY135143A

Abstract

A slow release inhibitor-generating device (10), including a pellet (16), for an IC engine (10b) having a cooling system (10a). The device (10) is installed in-line with a hose (23) of the cooling system (10a) for slowly releasing concentrated inhibitor from the pellet (16) , which is located in a perforated chamber (14). The device (10) has a bypass chamber (98) for allowing free passage of inhibitor liquid in the cooling system (10a). The action inhibitor liquid passing through the bypass chamber (98) and impinging on the perforated chamber (14) causes the perforated chamber (14) to rotate thus reducing the amount of resistance otherwise caused by the device (10) in the cooling system (10a).

Description

SLOW RELEASE INHIBITOR-GENERATING DEVICE FOR AN IC ENGINE

FIELD OF THE INVENTION

The present invention relates to a slow release inhibitor-generating device for an internal combustion (IC) engine. The inhibitor-generating device obviates the need to remove inhibitor liquid from the engine at regular services intervals. The device is installed in an IC engine having pure (de-mineralised) water in its cooling system. The inhibitor-generating device is of the inline type, being installed into a main coolant hose of the cooling system of an IC engine. The device includes a bypass chamber to reduce the chances of blockage of the device by detritus material entrained in the inhibitor. The device has a slow release table that releases a concentrated inhibitor into the water over a period of typically about 6 months or 10.000 kilometres thus maintaining relatively high concentrations of inhibitor in the cooling system and hence maintaining relatively high levels of protections to the IC engine.

BACKGROUND OF THE INVENTION

Around 60% of engine problems result from failure of the cooling system. A weakness of the modem cooling system in engines is the reliance upon an inhibitor to prevent corrosion and overheating of the engine. Over time the effectiveness of the inhibitor reduces and then the engine is prone to damage.

The problem of conventional liquid inhibitors is that they have their highest concentration when they are first introduced into the cooling system and over time their effectiveness reduces. Then it is often not possible to see the damage being done inside the engine caused by an ineffective concentration of inhibitor.

Generally inhibitor in IC engines must be removed and replaced at regular service intervals. In petrol engines this is typically required every 1 to 2 years. In heavy-duty diesel engines this can be as often as every month or every 20.000 kms. The ethylene glycol and triethanol amine used as major components of inhibitors are toxic substances and many authorities now require the disposal of spent inhibitor in proper facilities. Otherwise the ethylene glycol and triethanol amine damage the environment and poses a threat to anyone who comes into contact with it. This increases the cost of replacing the inhibitor and creates a problem with the handling and disposal the inhibitor.

nee the mid 1980's it has become well known to use inhibitor filters in diesel engines. Diesel engines are quite intolerant to deficiencies in inhibitor function due to their particular operating conditions. Such inhibitor filters are typically spin-on devices that act as a bypass filter. The bypass filter is capable of treating substantially all of the inhibitor liquid once for every 16 to 20 volumes of inhibitor pumped through the cooling system.

Such filters are a disposable item and often contain some kind of slow release additive either in liquid, powder or pellet form. Special devices are provided to ensure that there is slow release of the additives into the main coolant system - say over a period of hours in some cases, and up to about a year in other cases. The advantage of these filters is that the period between replacement of the inhibitor in the engine is greatly increased and in some cases it is not necessary to every replace the liquid in the cooling system - as in Penray^'s ® Fill-For-Life® coolant program. Although, the Fill-For-Life® program requires a phase were a special cleaning filter is applied to the IC engine to clean out any detritus material that could otherwise cause blocking of the spin- on bypass filter.

These coolant filters mechanically filter the engine inhibitor through a fine paper filter element to remove impurities, such as sand and rust particles suspended in the cooling system.

These various filters are typified by US3.348.693; US5.050.549; US5.094.745; US5.435.346; US5.662,799 and US5, 803,024. These are all spin-on filters and are designed to supplement a charge of inhibitor in the cooling system.

A common disadvantage to most of these spin-on filters is that they cannot be retrofitted to an engine that has been in use because the inhibitors released from the filters cannot dissolve corrosion products or gels that have already formed. Therefore, these spin-on filters can only be used on engines with special facility to receive them and must be installed at the point of manufacture of the engine. Also, these filters are not intended to replace the function of a inhibitor, they simply augment the inhibitor by adding extra inhibitors that extend the life of the inhibitor and in most cases reduce the time before which the inhibitor must be dumped from the engine and new inhibitor added. Further, these filters are solely used in diesel engines and are not intended for use in petrol engines. Still further, these filters must be thrown away once their internal inhibitor supplementing function is exhausted. ιere have also been some attempts to provide cooling systems with in-line filters for removing tritus material and thereby cleaning the cooling system for reducing the likelihood of blockage the radiator of the cooling system. Typical examples of this kind of filter are shown in

AU79859/87 and EP 0080541. This is exemplified by EP0080541. which has a V-shaped sheet mesh. A disadvantage of this filter is that the filter must be cleaned out at very regular intervals to prevent clogging of the mesh, which would then lead to blocking of the cooling system. In some cases the filter must be unblocked every few hundred kilometres.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide a slow release inhibitor-generating device for an IC engine that slowly releases inhibitor into the cooling system of an IC engine.

In accordance with one aspect of the present invention there is provided a slow release inhibitor- generating device for releasing inhibitor into the cooling system of an IC engine, the slow release inhibitor-generating device including a housing having an inlet and an outlet, means to couple the inlet and the outlet to the said cooling system, a perforated chamber located within the housing and in fluidic communication with the inlet and the outlet, a bypass chamber located within the housing allowing fluid to bypass the perforated chamber, a pellet including inhibitor agent shaped for location within the perforated chamber for slowly releasing inhibitor into the cooling system, and means located in the housing for allowing the pellet to be inserted into the perforated chamber.

In accordance with another aspect of the present invention there is provided a pellet for use in a slow release inhibitor-generating device including a housing having an inlet and an outlet, means to couple the inlet and the outlet to a cooling system of an IC engine, a perforated chamber located within the housing and in fluidic communication with the inlet and the outlet, a bypass chamber located within the housing allowing fluid to bypass the perforated chamber, and means located in the housing for allowing the pellet to be inserted into the perforated chamber for releasing inhibitor into the cooling system, the pellet including one or more inhibitor agents and one or more binding agents, the inhibitor agents being concentrated and the binding agents allowing slow dissolution of the inhibitor agents into liquid in the cooling system of the IC engine over the normal service interval of the IC engine.

In the context of the present invention "slowly" in connection with the releasing of the inhibitor into the cooling system means over a period of at least several months (such as about 6 months) up to about 10,000 kms in vehicle based IC engines, and up to about 300 hours of operation in tionary IC engines. That is, the inhibitor is released over a period that is similar in duration to ? normal service interval of the IC engine.

The slow release inhibitor-generating device is mounted in a fluid hose of the cooling system as an in-line filter.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, in which:-

Figure 1 is a perspective view, seen from above, of a slow release inhibitor-generating device for an IC engine;

Figure 2 is an end view of the slow release inhibitor-generating device of Figure 1, showing a perforated chamber and a bypass chamber;

Figures 3 and 4 are a side and plan view respectively of the slow release inhibitor-generating device of Figure 1 ;

Figure 5 is a cross-sectional side view of the slow release inhibitor-generating device of Figure 4 taken on lines AA;

Figure 6 is an exploded perspective view, seen from above, of the slow release inhibitor- generating device of Figure 1 ; and.

Figure 7 is a schematic side view of an IC engine including a cooling system fitted with the device of Figure 1.

DESCRIPTION OF AN EXEMPLARY EMBODIEMENT

In the drawings there is shown a slow release inhibitor-generator device 10 for use in the cooling system 10a of an IC engine 10b.

The device 10 has a housing 12, a perforated chamber 14 rotationally mounted in the housing 12. and an inhibitor pellet 16 located in the perforated chamber 14. e housing 12 includes an inlet port 20 and an outlet port 22 for connection into a hose 23 (as >wn in Figure 7) of the cooling system 10a. The ports 20 and 22 each have an annular lip 24 linst which two of the ends of the hose 23 can be clamped in known manner. Alternatively barbs or the like could be formed into the outer circumferential surface of the ports 20 and 22 to retain the hose 23.

Typically the housing 12 is made from plastics materials, which are resistant to temperatures below about 200 °C, more preferably to temperatures below 400 °C. It is also preferred that the material be resistant to attack or deterioration from contact with petrol, diesel and other oils, as well as radiator inhibitor. For example, the housing 12 could be made from glass filled nylon. It i to be noted that some plastics materials are not suitable because they become brittle or warp or the like in the environment of the IC engine 10b.

The device 10 could be made from metal materials, including stainless steel or other non- corrosive metals.

The housing 12 also has a body 26 upon which the ports 20 and 22 are mounted on substantially opposite sides. There is fluidic communication possible from one of the ports 20 and 22 to the other port 22 and 20 through the body 26. Typically, the ports 20 and 22 are located on opposite sides of the body 26. Preferably, the ports 20 and 22 are disposed off axis to a diameter of the body 26, particularly as shown in Figures 2 and 4 - for reasons that will be explained.

The body 26 has a cavity 28 that is substantially cylindrical, with its axis at 90 degrees to the axes of the ports 20 and 22 and intended to be disposed substantially upright with respect to the IC engine 10b. An upper end 30 of the cavity 28 terminates with an externally threaded annular wall 32 upon which is threaded an inspection cap 34. A lower end 36 of the cavity 28 terminates with an externally threaded annular wall 38 upon which is threaded a sump cap 40.

Each cap 34 and 40 is sealed to its end 30 and 36 of the cavity 28 with a respective O-ring 42.

The cavity 28 has a base wall 50 proximate the lower end 36. which defines a sump 52 with the sump cap 40. The base wall 50 has a plurality of apertures, typically in the form of holes 54, for communication of fluid and detritus material from the port 20 as described hereinafter.

The base wall 50 has a central hole 56 that is substantially coaxial with the axis of the cavity 28 to provide a journal for the perforated chamber 14. e inspection cap 34 has a centre post 60 with a hole 62 formed partway into it and arranged for position inside and coaxial with the cavity 28 when the inspection cap 34 is threaded onto the per end 30 of the cavity 28.

The inspection cap 34 and/or the body 26 could have a transparent portion to allow inspection of the cavity. The inspection cap 34 is intended to allow inspection of the colour of the inhibitor liquid in the cooling system 10a and thereby give a quick check as to operation of the inhibitor. In the event of little or no inhibitor colour new pellets 16 need to be added into the perforated chamber 14.

The perforated chamber 14, particularly as shown in Figure 6. has a spindle 70. a screen 72 and a retainer 74. The spindle 70 includes a base plate 76 with a plurality of apertures, conveniently in the form of holes 78. and a shaft 80 disposed upwardly from the base plate 76. The base plate 76 also has an annular groove 81 located proximate its outer circumference. The shaft 80 has a pair of vanes 82 and a stub 84 proximate its distal end. The spindle 70 has another stub 86 on the underside of the base plate 76.

The screen 72 is substantially cylindrical and has a diameter large enough to receive the pellet 16. The screen 72 is perforated with many holes 88. The screen 72 is typically made from plastics materials, although it could be made from metals materials, such as. for example. stainless steel. Optionally, the perforations 88 of the screen 72 are provided with small ribs on one side, not shown in the drawings. It is intended that such ribs be disposed from proximate an upper most extent of each perforation 88 to a lowermost extent of each perforation 88 so that liquid passing by the screen 72 can impinge against the ribs and thereby induce the perforated chamber 14 to rotate in the body 26 of the housing 12. Although, it is to be understood that the ribs are not essential to achieving rotation of the perforated chamber 14. It is the offset of the ports 20 and 22, which is primarily responsible for inducing rotation of the perforated chamber 14. Any ribs used are intended to increase the rate of that rotation for a given flow rate of inhibitor liquid through the cooling system 10a and thereby reduce any likelihood of the device 10 of the present invention leading to clogging of the cooling system 10a in the event that the perforate chamber 14 becomes completely clogged with detritus material entrained in the inhibitor liquid.

It is envisaged that the ribs could be up to about 2 mm high and be disposed substantially parallel to a rotational axis of the perforated chamber 14. It is also envisaged that 10 to 20 ribs could be used disposed evenly about the circumferential surface of the perforated screen 72. ιe perforations 88 of the screen 72 typically have a diameter in a range from 0.25 to 1.0 mm for hides having cooling systems 10a with a capacity of up to about 20 litres of inhibitor liquid. It envisaged that in the case of truck and other engines having a cooling system capacity of between 50 and 200 litres, the perforations 88 would have a diameter of up to about 3 mm. That is to say that cooling systems 10a of larger liquid capacity require larger perforations 88.

The retainer 74 is circular in plan and has a central hole 90 and an annular flange 92 disposed downwardly about the hole 90, particularly as shown in Figure 5. The annular flange 92 is dimensioned to receive the vanes 82 of the shaft 80 so that the retainer 74 is attached to the spindle 70. The retainer 74 also has an annular groove 94. which matches and overlays the groove 81 of the base plate 76.

In the present embodiment the shaft 80 of the spindle 70 tapers from its lowermost end towards its distal end. The tapering is used to inhibit the pellet 16 from touching the base plate 76 and hence inhibits the pellet 16 from blocking the flow of detritus material from falling into the sump 52. It is to be understood that other means could be used to create a displacement between the pellet and the base plate 76. For example an annular flange could be provided around the shaft 80 proximate the base plate 76. Such a flange could be formed integral with or separate to the shaft 80.

It is to be noted that the perforated chamber 14 is centrally journalled in the body 26 of the housing 12 (by the stubs 84 and 86), and thereby is off axis to the ports 20 and 22. Hence, liquid fiowing through the ports 20 and 22 impinges more on one side of the screen 72 than the other. This is particularly apparent in Figure 2 where a bypass chamber 98 can be seen though the outlet port 22. The bypass chamber 98 is situated inside the cavity 28 along side the perforated chamber 14 and allows the liquid in the cooling system 10a to pass around the perforated chamber 14 and thereby not unduly restrict the flow of the inhibitor liquid.

The perforated chamber 14 is assembled with the screen 72 inserted over the shaft 80 and located in the annular groove 81. The pellet 16 is then inserted into the screen 72 about the shaft 80. The retainer 72 is then placed over the distal end of the shaft 80 and the stub 84 inserted into the hole 90 until the vanes 82 engage with the annular flange 92. The engagement of the vanes 82 with the flange 92 that keeps the perforated chamber 14 assembled as one piece.

Particularly as shown in Figures 2 and 5. the perforated chamber 14 fits in the cavity 28 of the body 26. The stub 86 fits into the hole 56 of the base wall 50 and the stub 84 fits into the hole 62 the inspection cap 34 to journal the perforated chamber 14 to the body 26 of the housing 12.

irticularly as shown in Figure 6, the inhibitor pellet 16 is conveniently formed in two parts, each of a half cylindrical annular shape. The inhibitor pellet 16 is sized to fit in the perforated chamber 14 around the shaft 80.

The inhibitor pellet 16 includes a concentrated inhibitor agent, and a binding agent. The inhibitor agent is sufficiently concentrated so as to be able to partly dissolve in de-mineralised water to form an inhibitor liquid in the cooling system 10a and to continue to slowly dissolve over the normal service interval of the IC engine 10b whilst maintaining a concentration of inhibitor in the liquid that will protect the IC engine 10b from corrosion. The binding agent of the inhibitor pellet 16 is designed to slow the rate of dissolution of the pellet 16 so that instead of dissolving in a matter of a few hours the pellet dissolves gradually over the normal service interval of the IC engine 10b - which is typically 6 months of 10.000 kms travelled.

In the context of the present invention the term "slowly^" in relation to the dissolving of the pellet 16 means that the pellet 16 dissolves over a period of time approximately equal, or similar to. the normal service interval of the IC engine 10b. This period could be 6 months, or 10.000 kms travelled for a vehicle engine 10b or about 300 hours of operation of a stationary IC engine 10b.

It is envisaged that the inhibitor pellet 16 could also include concentrated anti-freeze agents that arc slowly released by the binding agents.

In use, the slow release inhibitor-generating device 10 of the present invention is inserted into either the upper or lower radiator hose 23 of an engine cooling system 10a as shown in Figure 7. The hose 23 is conveniently clamped in two places to ensure no leakage of liquid from the cooling system 10a during installation of the device 10. The hose 23 is then typically cut transversely between the clamps and the ports 20 and 22 inserted into the ends of the cut hose 23. Conventional hose clamps are then used to secure the device 10 into the hose 23 so as to avoid leakage.

The inspection cap 34 is then unthreaded from the wall 32 and the perforated chamber 14 removed from the cavity 28 of the housing 12. The retainer 74 is pulled off the shaft 80 and a pellet 16 placed in the screen 72 over the shaft 80. The pellet 16 slides down the shaft 80 until it wedges against the shaft 80 and is thereby prevented from falling further and so it held above the base plate 76. The retainer 74 is then replaced on the stub 84 to retain the pellet 16 in the :rf orated chamber 14.

te perforated chamber 14 is then reinserted into the cavity 26 so that the stub 86 is journalled in the hole 56 in the base wall 50. The inspection cap 34 is then rethreaded onto the wall 32. making sure that the O-ring seal 42 sits neatly on the wall 32 and seals the inspection cap 34 to the body 26.

The sump cap 40 is similarly threaded onto the wall 38 with the O-ring seal 42 to prevent leakage of the liquid from the cooling system 10a.

The clamps are then removed from the hose 23 and the IC engine 10b can be run.

^'When the device 10 is first installed into an IC engine 10b the existing inhibitor must be removed and disposed of. The cooling system 10a is then filled with mineral free water and the device 10 installed into the radiator hose 23.

When in operation, liquid is pumped around the cooling system 10a in known manner. The liquid flows into the device 10 via the inlet port 20 and impinges on the screen 72. Some of the liquid flows through the screen 72 and comes into contact with the pellet 16 and causes the pellet 16 to dissolve a little. The rate of dissolution of the pellet 16 is controlled by the binding agents and is such that the pellet 16 will take most of the regular service interval of the IC engine 10b before it completely dissolves.

Because the ports 20 and 22 are offset with respect to the perforated chamber 14 the impinging of the inhibitor liquid on the screen 72 causes the perforated chamber 14 to rotate. This is very important since it has the effect of drawing the inhibitor through the housing 12 from the inlet port 20 to the outlet port 22. If the perforated chamber 14 was not able to rotate in the chamber 26 it would present a partial blockage to the flow of inhibitor liquid in the cooling system 10a and would thereby reduce the effectiveness of the cooling system 10a in removing heat from the IC engine 10b. Hence, the rotation of the perforated chamber 14 has the effect of reducing the restriction to flow of inhibitor liquid that the perforated chamber 14 would otherwise make.

Entrained in the liquid are inhibitor and some detritus material. Some of the detritus material will come into contact with the spinning screen 72. This tends to break-up the detritus material until it is small enough to enter the perforated chamber 14 and then flow through the holes 78 and 54 and into the sump 52. the regular service interval for the IC engine 1 Ob the hose 23 is again clamped on either side the device 10. A container is placed underneath the device 10 and the sump cap 40 is removed d the detritus material collected therein is removed by knocking the cap 40 on a hard surface or blown out with compressed air or by other cleaning means. The sump cap 40 is then rethreaded onto the wall 38 with the O-ring seal 42 to prevent leakage. It may also be necessary to replace the O-ring seal.

The inspection cap 34 is then removed and the perforated chamber 14 lifted out of the cavity 28. The retainer 74 is removed from the shaft 80 and the perforated chamber 14 disassembled and cleaned. After cleaning the perforated chamber 14 is reassembled with a new pellet 16 located around the shaft 80. The clamps are then removed and the IC engine 10b can be safely run until the next service interval.

Between regular service intervals the inspection cap 34 can be removed, without the need to clamp the hose 23, and the liquid inspected to see if it has a sufficient concentration of inhibitor agent. This can be determined by the colour of the liquid in the cavity 28. Typically, the inhibitor liquid is a green colour when in sufficient concentrations to protect the IC engine 10b. When the inhibitor concentration is below that required to protect the IC engine 10b the colour of the liquid typically changes from say green to a muddy brown colour. It is to be understood that other colour changes could be used without departing from the spirit of the present invention.

What is surprising about the slow release inhibitor-releasing device 10 of the present invention is that it can be used with an IC engine 10b cooling system 10a containing nothing but water. The pellet 16 then provides all the inhibitor required for the protection of the IC engine 10b over a relatively long period of time relating substantially to the normal service intervals of the IC engine 10b. During this time the pellet 16 slowly dissolves to maintain the inhibitor level in the IC engine 10b at a sufficiently high level to provide good protection to the IC engine 10b against over-heating and/or corrosion.

The slow release inhibitor-generating device 10 of the present invention has advantages including; a substantial reduction in the risks of corrosion in the cooling system 10a; improved cooling of the IC engine 10b and thus increased engine efficiency, power and performance; greatly reduced need for servicing of the cooling system 10a; substantial reduction in engine contaminants (through filtering of detritus material and removal via the sump); greatly reduced impact on the environment (through reduced dumping of coolant); and safer to handle than conventional liquid inhibitors. iodifications and variations such as would be apparent to a skilled addressee are considered ithin the scope of the present invention. For example, the pellet could be formed onto a metal ^• plastic former, thereby obviating the need to make the pellet in two halves. Also, the housing 1 could be attached directly to or formed integrally with the cooling system 10a or with the IC engine 10b. Such an arrangement could be formed at the time of construction of a radiator of the cooling system 10a or at the time for formation of a block of the IC engine 10b.

Claims

CLAIMS DEFINING THE INVENTION

] . A slow release inhibitor-generating device for releasing inhibitor into the cooling system of an IC engine, the slow release inhibitor-generating device including a housing having an inlet and an outlet, means to couple the inlet and the outlet to the said cooling system, a perforated chamber located within the housing and in fluidic communication with the inlet and the outlet, a bypass chamber located within the housing allowing fluid to bypass the perforated chamber, a pellet including inhibitor agent shaped for location within the perforated chamber for slowly releasing inhibitor into the cooling system, and means located in the housing for allowing the pellet to be inserted into the perforated chamber.

2. A slow release inhibitor-generating device according to Claim 1. in which the inlet port and the outlet port are coaxial and in which the axis of the inlet and outlet ports is off-axis with respect to the perforated chamber whereby inhibitor flowing through the housing from the inlet port to the outlet port impinges a part only of the perforated chamber for inducing rotation thereof.

3. A slow release inhibitor-generating device according to Claim 2. in which the perforated chamber includes a central shaft with a base plate proximate one end and a removable retainer plate at its distal end, and a screen located between the base plate and the retainer plate, the volume bounded by the base plate, the screen and the retainer plate defining a receptacle for the pellet wherein liquid can pass through the perforated chamber for dissolving the pellet.

4. A slow release inhibitor-generating device according to Claim 3, in which the pellet is formed in with a central aperture for receiving the central shaft, and the shaft including means for displacing the pellet from the base plate.

5. A slow release inhibitor-generating device according to Claim 3, in which the screen is perforated with apertures having a diameter of between 0.25 and 3 mm. more particularly between 0.25 and 2 mm, such as about 1 mm.

6. A slow release inhibitor-generating device according to Claim 3. in which the screen has a plurality of ribs disposed generally along a longitudinal axis of the screen, the ribs being oriented to catch impinging inhibitor liquid in the housing for generating further rotation of the perforated chamber.

7. A slow release inhibitor-generating device according to Claim 1. in which the housing has a sump located below the perforated chamber, the perforated chamber having apertures for allowing detritus material entrained in the inhibitor liquid to pass into the sump, and a sump cap for allowing removal of the detritus material from the sump.

8. A slow release inhibitor-generating device according to Claim 1. in which the housing also has a removable inspection cap for allowing removal and insertion of the perforated chamber with the pellet.

9, A pellet for use in a slow release inhibitor-generating device according to Claim 1 , the pellet including one or more inhibitor agents and one or more binding agents, the inhibitor agents being concentrated and the binding agents allowing slow dissolution of the inhibitor agents into liquid in the cooling system of the IC engine over the normal service interval of the IC engine.

10. A pellet according to Claim 9. having a central aperture for locating upon a central shaft of l he perforated chamber and the pellet being formed in two parts each with a curved inner surface for mating with a part of the shaft, the two parts substantially meeting at respective edges to form a whole.