This invention relates to internal combustion engines.

More particularly, the invention relates to internal combustion engines of the kind comprising a main combustion chamber communicating with a subsidiary combustion chamber and flow control means for controlling fluid flow between these, the control means being effective to at least provide ^' a substantial restriction to communication between the combustion, chambers, prior to ignition of a subsidiary air fuel charge introduced into the subsidiary combustion chamber in use of the engine, and to subsequently effect relief of said restriction whereby ignited said subsidiary air fuel charge is caused to pass to said main combustion chamber via a passageway extending from the subsidiary combustion chamber to effect ignition of a main working fluid charge in the main combustion chamber, the igniting working fluid charge then expanding against a movable part of the engine to effect operation thereof.

In the specification of my Australian Patent Application 35853/78 there is described an internal combustion engine of the above kind wherein the movable part of the engine comprises a piston reciprocable in a

cylinder for compressing, on a compression stroke of the engine, at least an air component of an air-fuel mixture, said main combustion chamber and said substantially closed subsidiary combustion chambers being communicable with the main combustion chamber via a passageway, and said flow control means comprising control valve means in use of the engine controlled ^' to be open to provide communication between said cortlbustion chambers via said passageway during at least a portion of said compression stroke of the engine, whereby compression of said at least said air component occurs in both said combustion chambers, means being provided for inlet of fuel whereby to cause, at least after said compression, said air—fuel mixture to be present in said main combustion chamber and in said subsidiary combustion chamber, to form main and subsidiary air-fuel charges in said main combustion chamber and in said subsidiary combustion chamber respectively, said engine being effective to ignite the air-fuel charge in said subsidiary combustion chamber, with said control valve means in a substantially closed condition at which it provides said at least substantial restriction to communication between the combustion chambers, then to cause said control valve means to be opened to effect said relief of said restriction to effect said ignition of said main working fluid charge, the expansion of the main working fluid charge acting to drive said piston on an expansion stroke of the engine occurring after said compression stroke. The main combustion chamber may be formed separately from the

cylinder volume above the piston and may communicate with the sylinder volume via a passage.

Usually, the control valve means is controlled to be closed before completion of said compression stroke whereby, by continuance of said compression stroke, said at least air component in the main combustion chamber is then compressed to a higher degree of compression than that in said subsidiary combustion chamber. The'engine may be a fuel injection engine in which case the means for inlet of fuel comprises one or more fuel injectors. The engine may however be a carburettor engine in which case the means for inlet of fuel comprises a carburettor. Engines constructed as above described have been found to be particularly effective in use. Preferred embodiments of such an engine operate on a four stroke cycle, with compression ratios in the range 12-15:1 for the main air-fuel charge and 6-8:1 for the subsidiary charge. With these engines, separate fuel injection into the two combustion chambers has been found to be effective, with air being admitted to the engine via an inlet valve to the cylinder volume only, so as to avoid air scavenging of the subsidiary combustion chamber.

These engines are capable of operation under a wide range of loads with good efficiency whilst the described "split phase" combustion process has been found to give partic larly effective burning of the air-fuel charges with minimum generation of undesirable engine emissions.

While these engines have also been found to be suitable for operation on a wide variety of fuels, a difficulty sometimes occurs in obtaining best operation

when using heavy fuel, under the condition where the engine is cold. In particular, a spark igniter for the subsidiary combustion chamber may be unable to provide adequate cold starting and running performance.

One object of the present invention is to provide an arrangement for an engine of the first above described kind and operable on heavy fuels, such as diesel fuel, wherein means is provided to lessen ^* operating difficulties under cold start and running conditions.

In accordance with this aspect of the invention there is provided an engine as first above described characterised in that heating means is provided for heating the subsidiary combustion chamber. Preferably said heating means comprises an electric heating element operable to produce heat when connected to an electric current supply. It has been found satisfactory to utilize conventional "glow plugs" as employed for preheating diesel engines. However it is preferred that said heating means be arranged to effect heating over a substantial area of the surface defining the subsidiary combustion chamber. More particularly, the heating element is preferably coupled to a heat dissipating element, a surface of which defines said substantial area of the surface of the subsidiary combustion chamber. Where the subsidiary combustion chamber is spherical, it is preferred that said heat dissipating element define said substantial area as a substantially hemispherical surface. The heat dissipating element may directly receive the heating element therein or thereon,or the heating element may be incorporated into

a conventional glow plug which is fittable into the said heat dissipating element, such as removably, in order to facilitate replacement.

In another aspect, the invention is concerned with the valve means incorporated into engines of the above described kind. More particularly, in the engine described in the specification of Australia Patent.' ^* Application No. 35853/78 there is specifically shown a valve means in the form of a reciprocable element. ^' It has now been found that especially satisfactory operation can be obtained by use of a rotary valve of specific configuration. Thus, in accordance with this aspect of the invention there is a provided an engine as first above described characterised in that said flow control means means comprises chamber means defining a cylindrical chamber extending transversely of said passageway and having opposed or otherwise peripherally spaced first and second ports communicating with portions of said passageway leading, respectively, to the subsidiary combustion chamber and to the main combustion chamber, and a valve element rotatable about the axis of said cylindrical chamber and retained within said cylindrical chamber, said valve element having a surface portion of part cylindrical configuration which is arranged to move in close proximity to the surface of said cylindrical chamber during rotation of said element and being of sufficient dimension so as, when directly opposed to said first port, to at least partially block that port and when directly opposed to said second port, to at least partially block that port, the periphery of the valve element being relieved over a relieved portion thereof adjacent said surface

portion to a sufficient extent as to permit flow from one said port to the other through the cylindrical chamber and around said relieved portion, when the valve element is positioned at a location at which it does not block either said port. Preferably, said relieved portion extends over the whole of the periphery of the valve element save for the part occupied by said surface portion, whereby, by appropriate positioning of the valve element in relation to either said port, flow may occur through said cylindrical chamber from one said port to the other selectively around either of two sides of the valve element. In a preferred construction, drive means is provided for driving the valve element, such as from the cam shaft of the engine, to effect rotation of said valve element in such a fashion as to cause said surface portion to be opposed directly to one said port to effect blocking of said passageway during said compression stroke and to remove obstruction from the passageway to effect communication between said combustion chambers as said valve element moves to cause said surface portion to be no longer directly opposed to said one port.

The invention is further described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a fragmentary axial cross section of one cylinder of an internal combustion engine constructed in accordance with the invention;

Figure 2 is a sectional view approximately on the line 2-2 in figure 1;

Figure 3 is a fragmentary side view taken in the direction indicated by arrow "A" in figure 1 and partly sectioned on line 3-3 in figure 1.

The engine 10 shown in the drawings is, aside from details of the cylinder head and auxiliary equipment as described hereinafter, of generally conventional construction having a piston 12 which moves in a closed cylinder 14 in the cylinder block 16 of the engine. The piston 12 is substantially flat topped but with a recess 22 for a purpose described later.

The cylinder head 15 of the engine has formed therewithin a main combustion chamber 26 which communicates with the top of the cylinder 14 via a short passageway 28. Main combustion chamber 26 is interconnected with a smaller subsidiary combustion chamber 30, also formed in cylinder head 15, via a passageway 32, this passageway having a flow control means (in the form of a rotary valve 34) associated therewith for controlling flow through the passageway and between the combustion chambers 26 and 30. Main combustion chamber 26 has a fuel injector 38 associated therewith and arranged for direct injection of fuel thereinto. Subsidiary combustion chamber 30 likewise has a fuel injector 40 associated therewith and arranged for direct injection of fuel thereinto. Combustion chamber 30 is also provided with a spark plug 44 (figure 3). The cylinder head 15 defines an inlet port 18 having an inlet valve 20 for admission of air to the cylinder 14. An exhaust port and exhaust valve are also provided in the cylinder head, for exhaust of gases from cylinder 14. These are not shown in the drawings, but

the location of the exhaust port is shown diagrammatically in figure 2 by phantom line 50.

The operation of the engine 10 is generally the same as described in relation to the engine of application 35853/78 and reference may be made to that specification for a full description of the principles of the engine. For the present purposes it is however sufficient to note that the engine operates on a four stroke cycle and that operation is essentially characterised by the following:

(1) On the induction stroke of the engine with the piston 12 moving away from the top of the cylinder 14, the valve 20 is opened to admit air into the volume in the cylinder 14 above piston 12, which air is free to flow ^' through the passageway 28 into the main combustion chamber 26 and, during at least some part of such stroke, along the passageway 32 via the then open valve 34 to the subsidiary combustion chamber 30.

(2) On the following compression stroke, with inlet valve 20 closed, air in the volume above the piston 12, as well as air in the combustion chambers 26 and 30 is compressed as piston 12 moves toward top dead centre. Initially, the valve 34 is arranged to be open so that equal compression occurs in the aforementioned cylinder . volume above the piston as well as in the two combustion chambers.

(3) At a time prior to the piston 12 reaching top dead centre, the valve 34 closes, whereupon continued

compression of air occurs only in the cylinder volume above the piston and in the main combustion chamber 26. The piston 12 moves with very little clearance above the top of the cylinder 12 at top dead centre. Thus, essentially, the bulk of the air in the volume above the piston is ultimately forced into the two combustion chambers. A consequence of the closing of the va ^' ve 34 prior to completion of compression is, however, that the ultimate compression ratio reached in the combustion chamber 26 is higher than that in subsidiary combustion 30.

(4) At suitable times, fuel is injected into the two combustion chambers 26 and 30 by operation of the fuel injectors 38 and 40. Injection is arranged so that there is an air-fuel mixture in the chamber 30 before closing of valve 34 on the compression stroke, whilst injection from the injector associated with chmaber 26 occurs after such closing.

(5) The resultant air-fuel charge in chamber 30 is ignited by operating spark plug 44, usually somewhere before top dead centre, and usually just after commencement of fuel injection into chamber 26 from injector, 38 when the engine is operating at high speed.

(6) The valve 34 is then opened, whereupon the igniting air fuel charge in chamber 30 is energetically transferred to the chamber 26 via passageway 32 to effect combustion of the air-fuel charge in chamber 26.

(7) Burning air fuel charges from chambers 26 and 30 pass into cylinder 14, via passageway 28, to be expanded on the subsequent expansion stroke of the engine as piston 12 moves away from top dead centre.

(8) On the following exhaust stroke, as piston 12 again moves towards top dead centre, the exhaust valve is ^' opened to exhaust gases from the cylinder 14.

In order to improve the cold starting and running performance of the engine 10, the chamber 30 is provided with heating means. More particularly, as shown specifically in figures 1 and 3, the chamber 30 is of substantially spherical shape. One half of the defining surface thereof, being a surface portion 30a, is formed at the inner end of a recess 35 formed in cylinder head 15. The other half of the surface defining the chamber 30 is formed as a hemispherical surface portion 30b, being formed on an element 52 which is inserted into the recess 35 and held by means of a threaded clamping member 54 which is engaged in a threaded outer end of the recess 35. Element 52 has a generally cup shaped end portion 52b, on which surface 30b is defined, and a stem 52a extending therefrom and coaxially arranged within a central bore in member 54. The rim of the end portion 52b abuts a step 37 formed in recess 35 and it is against step 37 that the element 52 is clamped by member 54, retaining force being applied to the element 52 via an annular heat insulating member 39 between the end portion 52b and the member 54. Member 54 has on its innermost transverse face an annular ridge 39a. Ridge

39a is of "V" shaped cross-section whereby form an edge ' at the outer portion of the cross-section. The ridge 39a is forced into an adjacent surface of recess 35, being a step in the recess, by the action of screwing member 54 into the recess 35. Thus, the ridge 39a provides a seal between recess 35 and member 54. Stem 52a is hollow and is lengthwise split so as to receive and resiliently retain the end portion of a conventional glow plug 56 which is threaded received in an interior bore in member 54. Element 52 is formed of material of good heat conductivity and good resistance to degradation or distortion when heated.

By operating the glow plug 56, the end portion thereof is heated to thereby effect heating of the element 52 and of the surface portion 30b thereof. This heating has been found to very much facilitate operation of the engine 10 under cold start and run conditions where heavy fuel is used.

It is preferred that the glow plug 56 be connected to suitable control circuitry operating to cause the glow plug to be heated only for a short period prior to starting operation of the engine. Heat sensing means may be provided sensitive to inhibit operation of the glow plug when a predetermined temperature of the chamber 30 or surrounding part of head 15 is reached. This may be arranged to prevent heating of the glow plug at all where the engine is still hot from a previous operation.

The valve 34 comprises a hollow cylindrical member 58 which is arranged with its axis normal to the axis of the piston 12 and so as to extend transversely across

the passageway 32. The member 58 has opposed ports 60, 62 which are aligned with and communicate with opposite end portions of the passageway 32. A rotatable cylindrical valve element 64 is coaxially arranged in member 58, being carried on bearings 66, 68 supported by a part 15a of the cylinder head 15. The bearings 66, 68 as well as member 58 may be received in a bore 81 i ^' h part 15a. Part 15a may (as shown) be formed separately from the remainder of the cylinder head or may be integrally formed. Over most of its exterior, the periphery of the element 64 is of circular cross-section and of only slightly less diameter than the interior diameter of member 58, whereby to provide substantially sealing engagement between the element 64 and the member 58. This sealing is completed by two annular seals 67, 69 carried in bore 81 of head 15 and engaging the periphery of the element 64 at locations axially spaced one to either side of ports 60, 62. The periphery of the element 64 has, however, a relieved portion 65 extending over a substantial part of its circumference at a location intermediate the length of element 64 and adjacent the lengthwise positions of the ports 60 and 62. This relieved portion causes the periphery of the element 64 at this lengthwise location to have a surface portion 64a which is of relatively reduced diameter, so as to provide a clearance between the element 64 and the member 58. At this lengthwise location too, that portion of the element 64 which is not relieved presents a surface portion 64b of part circular cross section and which provides substantial sealing engagement with the interior surface of the member 58.

The element 64 is driven (by means not shown) from the cam shaft of the engine 10 so as to execute one rotation for every complete back and forth reciprocatory movement of the piston 12.

Figure 1 shows valve 34 with element 64 positioned at a condition at which it obstructs flow along the passageway 32 by virtue of the surface portion 64b ^' thereof being aligned with the port 62. This condition corresponds to the condition where the valve closes the passageway 32 during the aforedescribed compression stroke of the engine 10. As the valve element 64 rotates from the postion shown, however, the surface portion 64b no longer is directly opposed to the port 62 but, rather, the portion 64a becomes so aligned The length, around the periphery, of the surface portion 64b is arranged so that non-alignment of surface portion 64b occurs at the desired time of opening of the valve 34 after ignition of the air-fuel charge in chamber 30,. for effecting transfer to chamber 26. This transfer may then occur around the valve element over the surface portion 64a from port 60 to port 62.

The described driving of the element 64 such that it executes one rotation for every back and forth reciprocatory motion of the piston 12 has the result that the valve 34 closes twice for each such reciprocation, once, whilst surface portion 64b is opposite port 62 and once whilst it is opposite port 60. However, the following closing by obstruction of port 60 is not material to the operation of the engine since it occurs for a brief interval only during the expansion stroke of the engine. It is also the case that the

valve will momentarily close twice during the following back and forth reciprocatory motion of the piston 12, once during the expansion stroke and once during the exhaust stroke, but again these closings have no effect on the operation of the engine. It is, however, possible to arrange that the element 64 rotates only one half turn for every full cycle of operation of the . ^'" engine, i.e. for every two back and forth reciprocations of the piston 12, so that the desired closing motion of the element 34 would occur at port 60 and at port 62 on respective alternate full cycles of operation. Also, by driving the element 64 at a rate such that ports 62 and 60 were each closed once each during each full cycle of operation, only one non-operative closing of the valve 34 would occur during each complete cycle of operation of the engine.

The arrangement specifically described with reference to the drawings is however preferred because it provides more rapid opening and closing of the valve, which is important for efficient operation of the engine. The recess 22 in the piston 12 is of a configuration best seen from figure 2. More particularly, when viewed in plan it comprises two overlapping shallow circular lobes 22a, 22b connected with a shallow protrusion 22c which extends away therefrom, the protrusion 22c terminating at a location immediately below passageway 28 (figure 1) . The arrangement is such that flow from chamber 26 after ignition of air-fuel charge therein is directed directly from the chamber 26 through the passageway 28 into the recess 22, flowing first along the protrusion 22c and

thence into the lobes 22a, 22b. When viewed in transverse section (figure 1) , the passageway 28 as offset to one side of axis of piston 12 and is, as shown in figure 1, somewhat angled downwardly from the chamber 26, and radially inwardly, towards the axis of the piston 12. Protrusion 22c has a terminal edge' 70 which is angled and, at top dead centre, aligned in correspondence with the angling and positioning of the radially outermost surface of passageway 28, to facilitate flow from the chamber 26 into the recess 22. The provision of the recess 22 ensures that air fuel mixture as ignited, and as passing from the chamber 26, is directed cleanly into the cylinder 14 above the piston 12, thus to ensure that it is able to flow easily into a position above the piston 12 for performance of useful work without inhibition as might be caused if the flow were to be directed into a very thin space which would otherwise exist between the piston and cylinder top at top dead centre.

Whilst the described engine operates on a four-stroke cycle the invention is equally applicable to engines operating on a two-stroke cycle.

The described construction has been advanced merely by way of example and many modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.