AU607465B2 - Improvements relating to multi-cylindered two stroke cycle engines - Google Patents

Description

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607 COMMONWEALTi

PATENTS

COMPLETE

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Application Number: PI 0523 Lodged: 25th February, 1987 'o"riplete Specification Lodged: 0000 Class Int. Class S TO VALUS OF ihACHEO MAIL OFFI This document contains the amendments made under Section 49 and is correct for printing 0 0 ,P ity: 0 0 00 0 0 o 0 o o oo cRcloted Art: o 0 0 00 0 0 0 0 Accepted: Published: LOD') .C r S liSw1'iCE 2 I FEB 1988 Melbourn ~a~jM ~*a=i~i~iCi~Ls~pl~ I 0 00 00 0 0 Uame of Applicant: ORBITAL ENGINE COMPANY PROPRIETARY LIMITED 00 0 0 00 AddressofApplicant Whipple Street, Balatta, Western Australia. Australia.

AddressofApplicant: 4 Whipple Street, Balcatta, Western Australia. Australia.

ooo000 0000 o cActual Inventor: s o 0 00 Address for Service: KENNETH PHILIP SEEBER and CHRISTOPHER KIM SCHLUNKE EDWD. WATERS SONS, 50 QUEEN STREET, MELBOURNE, AUSTRALIA, 3000.

Complete Specification for the invention entitled: IMPROVEMENTS RELATING TO MULTI-CYLINDERED TWO STROKE CYCLE ENGINES The following statement is a full description of this invention, including the best method of performing it known to

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-2- IMPROVEMENTS RELATING TO MULTI-CYLINDERED TWO STROKE CYCLE ENGINES This invention relates to multi-cylinder engines operating on the two stroke cycle and incorporating exhaust ports and inlet or transfer ports in the peripheral wall of the respective cylinders.

In order to obtain the desired gas flow within the cylinder of an engine operating on the two stroke cycle, to achieve the required power output, fuel efficiency, and exhaust gas emission control, the disposition of the exhaust ro port and transfer ports is a critical factor.

t 10 It is a feature of engines operating on the two stroke cycle that the transfer ports and the exhaust port or S"oI ports are open at the same time in the engine cycle and so there is a potential for part of the fresh charge entering the cylinder through the transfer ports to travel across the cylinder and escape through the exhaust port during the period that both the exhaust and transfer ports are ,simultaneously opened. This problem can not be solved by arranging the transfer and exhaust ports so that they are not both open at the same time as the fresh charge entering through the transfer ports is required to assist in the scavenging of the exhaust gas from the cylinder through the :.0o exhaust port.

Various arrangements of transfer and exhaust ports around the periphery of a cylinder of a two stroke cycle engine have been proposed with the aim of obtaining effective scavenging of the exhaust gases from the engine with a minimum loss of fresh charge through the exhaust port. In early proposals the transfer ports were located generally on the opposite side of the engine cylinder to the exhaust port and a hump was provided on the crown of the piston of the engine to direct the fresh charge entering the cylinder through the transfer ports, upwardly in the cylinder. The upward movement of the fresh charge increased the length of the flow path thereof to the exhaust port and tg.~t 3tSZ tug S. tilt

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-3so reduced the amount of fresh charge reaching the exhaust port within the time available. Also the upward flow of the fresh charge promoted the flow of exhaust gases within the upper part of the cylinder towards and through the exhaust port.

Although the provision of the hump on the piston crown assisted in obtaining the required control of the flow of the incoming fresh charge, it introduced new problems in the effective operation of the two stroke cycle engine. In 10 particular, the hump required the provision of a somewhat complementary cavity in the cylinder head, in order to obtain an acceptable compression ratio, and thus provided a substantial restriction on the design of the cylinder head and the resultant combustion space, This restriction has 15 prevented the optimisation of the shape of the combustion space in order to obtain the desired control over the combustion process for maximum efficiency and emissions control. In addition the hump on the crown of the piston presented a substantial surface area to the combustion gases and therefore generated a high heat input to the piston giving rise to difficulties in cooling the piston and thermal stresses in the piston.

The two stroke cycle engine discussed above is generally referred to as a cross-scavenged engine and 25 engines operating on this principal a~re basically recognised by the hump on the piston crown, which is normally offset from the centre line of the piston towards the transfer ports and extends substantially across the full extent of the crown of the piston at that location. In order to overcome the problems associated with the cross-scavenged engine there was subsequently developed a con figuration of transfer ports which would establish a generally upwardly directed flow within the engine cylinder of the incoming fresh charge without the necessity to provide the hump on the crown of the piston.

00 0 0 0 0 0 S 00 l-CC -4- This later development is generally referred to as a loop-scavenged engine and in a typicalinodJern example the cylinder has a generally centrally located transfer port or ports opposite the exhaust port and additional transfer ports on either side of the central transfer port orientated to direct the incoming fresh charge from these side ports away from the exhaust port and towards the central transfer port. The combined effect of the central and side transfer ports is to create an upward flow of the incoming fresh 000o-0 charge on the side of the cylinder opposite to the exhaust ooo port, thereby avoiding a direct cross-over of the incoming 0600 0 0o0. charge to the exhaust port. An example of the exhaust and 0 0o090 transfer ports in a loop-scavenged engine is illustrated in 00o 0 British Patent No. 1021378, that engine being provided with o 0 0 further transfer ports 26 between the exhaust port 19 and S the respective side transfer ports 20. However, it will be noted that the additional transfer ports 26 are also 9 66:4 orientated to direct the charge entering therethrough across 00% the cylinder towards the central transfer port 23.

0. 20 The configuration of the transfer ports in the o o 0loop-scavenged engine avoided the use of a hump on the crown o °of the piston, overcoming the disadvantages associated therewith, and succeeded in obtaining the required control ame over the flow of the incoming fresh charge from the transfer 0000 25 ports so as to obtain effective scavenging of the exhaust 0o o gases from the engine and limiting the loss of fresh charge through the exhaust port. However, the provision of the transfer ports, and the required associated transfer passages between the ports and the engine crankcase, on the two opposite sides of the engine resulted in a significant increase in the overall dimension of the cylinder and associated transfer ports and passages in a direction at right angles to the axis of the exhaust port. This can be readily seen in Figure 3 of the above referred to British patent wherein the dimension across the engine between the rear walls of the respective transfer passages 21 is approximately 1.6 times the diameter of the engine bore.

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Although such an increase in the overall dimensions can be tolerated in a single cylinder engine, particularly of the cooled construction wherein the transfer passages 21 may be located within the cooling fin configuration provided on the engine, the increase in the overall dimensions of each cylinder and its transfer ports and passages is of major consideration in multi-cylinder engines, particularly of the in-line type. Other arrangements of transfer and exhaust ports in loop-scavenged engines are to be found in .o 010 Australian Patent No. 152471 and German Patent No. 590331, 0 000 the latter being a patent granted to Dr. Adolph Schneurle 0000 ooo who is credited as being the discoverer of the 0 °oo°o loop-scavenged system, which is sometimes referred to as the 0 Schneurle scavenged system.

C 0o Although the transfer port arrangements to achieve 000 00 0 loop-scavenging are operationally desirable to achieve effective scavenging of exhaust gases from the cylinder and 0O the correct location of the fresh charge, the position of 000 the side transfer ports, and the transfer passages o communicating those transfer ports with the engine 0 crankcase, present complications in the construction of multi-cylinder engines. In particular the spacing of the cylinders and the construction of the end sections of the cylinder block of a multi-cylinder engine must be sufficient oo6 25 to accommodate the transfer ports and associated transfer 00 0 0 o0 passages. It is readily seen from the above referred to prior disclosures of various loop-scavenged engine constructions that these constructions, if applied to a multi-cylinder in-line engine, would require a substantial spacing between cylinders and a resulting sustantial increase in the overall length of the engine. This increase in engine block length results in a corresponding increase in engine weight, and in automotive applications, an increase in engine compartment size and overall vehicle size and weight.

In an attempt to reduce the size of such multi-cylinder engines, it has been the practice to skew the 00 0 0 0000 00000 o 0 00 0 6 0 a 0 O 00000 o 0 0 0 0 0 00 a 0 0 0 00 00 0 0 a0 0 006 000 a0000 00 0 00 0 0 00 -6scavenging axis of each cylinder with respect to the common longitudinal plane of cylinders, to thus obtain a somewhat nesting relationship between the transfer passages of the side transfer ports of adjacent cylinders. Examples of engines with a skewed scavenge axis are disclosed in United States Patent No. 4092958 to Hale, and in German Patents Nos. 665126 to Humboldt-Deutzmotoren Akt. and 663500 to Auto-Union AG. These and similar configurations of the side transfer ports and passages does contribute to a degree of .10 reduction in the overall length of a cylinder block, but there is still the need to provide a substantial spacing between the adjacent cylinders, and to provide space at the ends of the cylinder block to accommodate the transfer ports and passages.

:15 The skewing of the sc 'avenging axis also necessitates the exhaust port of each adjacent cylinder being located so that the axis of the exhaust port is inclined to the common longitudinal plane of the cylinders.

This inclined attitude of the axis of the exhaust port 20 introduces complications if it is desired to provide a valve to regulate the timing and/or extent of opening of the exhaust port, as a means of improving the power output and/or controlling exhaust emissions and fuel consumption.

In multi-cylinder engines, with the axis of each exhaust 25 port inclined to the common longitudinal plane of the cylinder block, the valve associated with each port is mounted on a respective pivot axis transverse to the axis of the exhaust port. It is consequently necessary to provide individual coupling of each valve to a suitable actuator device, or to provide a form of flexible coupling between the valves of each exhaust port of the engine. Both of these forms of construction are relatively complex and are therefore expensive to manufacture and maintain.

There is disclosed in United States Patent Application No. 866426 and corresponding Australian Patent Application No. 57898/86 an exhaust port valve in a skew i rii -7scavenged axis engine wherein the pivot axis of the valve is inclined to the exhaust port axis. This construction enables the valves of a number of exhaust ports in a multi-cylinder engine to be mounted on a single actuating shaft. However, in this construction there is a substantial area of the valve located within the exhaust port and hence exposed to the high temperature exhaust gases. This results in some operational problems due to clearance that must be provided for the moving valve, and carbon build-up on the exposed surface of the valve and the exhaust port areas over which the valve moves when in operation. The manufacture of these valves is also complex and hence expensive.

_o It is the object of the present invention to provide an improved arrangement of the exhaust and transfer oo ports in a multi-cylinder two stroke cycle engine to provide ooo 15 the required gas flow within the cylinders of the engine, o00 0 0o °o while also permitting the overall length of the cylinder ooooo block to be reduced, and the installation of simple exhaust port controls.

With this object in view there is provided according to the present invention a multi-cylinder engine ooa block for a two stroke cycle internal combustion engine 00o0 .o operating on the Schneurle loop-scavenged system and having 0 0 00 two or more adjacent cylinder bores in said block with the oo axes of the bores parallel and in a common longitudinal 00lane, each cylinder bore having a respective exhaust o port, an exhaust passage extending from each exhaust port to an external surface of the block in a direction generally at Si right angles to said common longitudinal plane, each cylinder bore having two first transfer ports located one on either side of the exhaust port of that cylinder bore, each first transfer port communicating with a respective first transfer passage, each cylinder bore having at least one second Disk 0081/1 .74 -8transfer port located on the opposite side of said common longitudinal plane to the exhaust port of that cylinder bore, each second transfer port communicating with a respective second transfer passage, one of said first transfer ports and the associated first transfer passage of each of two adjacent cylinder bores being located on the same side of said longitudinal plane in a portion of the cylinder block between the respective exhaust ports and passages of said adjacent cylinder bores and on opposite sides of a transverse plane i0 substantially at right angles to said common longitudinal 0Dd plane and midway between said two adjacent cylinder bores, oo said one first transfer port and associated first °0 transfer passage of each of said adjacent cylinder bores 9000 being configured and located to direct the charge entering o o 15 o the cylinder therethrough across the cylinder bore in a 0 0 o 00 direction towards the second transfer port, and so the axes o0 0 of the two adjacent cylinder bores are spaced apart not more than 1.22 times the diameter of the cylinder bores.

20 Preferably each of the two adjacent cylinder bores 2O is provided wi'th two second transfer port in that portion of 0000 o00 the cylinder bore on the opposite side of the common o° °o longitudinal plane to that where the exhaust port is 0 a provided. The second transfer ports on said opposite side ooo0 of the commcn longitudinal plane are also preferably oo 25 a arranged so' that they do not extend beyond the above oooooo000000 90 referred to transverse plane between said two adjacent 00. 0 cylinder bores.

00 Conveniently, the transfer port arrangement may iio include a central port diametrically opposite the exhaust port and two further side ports, one on either side of the central transfer port. The central transfer port may be in the form of a single port with an upright divider, the two ports so formed communicating with a common transfer passage. Alternatively there may be two central transfer with respective transfer passages. ports with respective transfer passages.

Disk 0083/1.13 -9- Conveniently the transfer ports on the same side of the common longitudinal plane as the exhaust port do not extend in the circumferential direction around the cylinder bore beyond the common longitudinal plane. Further it is desirable that the transfer passages associated with those transfer ports do not extend from the port in the direction of said common longitudinal plane a distance greater than the thickness of the wall of the cylinder at that location.

That portion of the transfer passage which is immediately adjacent the transfer port on the exhaust port side of the engine, preferably extends generally in the tangential direction with respect to the bore of the associated 000 cylinder at the common longitudinal plane. This portion of 000 the transfer passage directs the charge entering the 9000 QooOo S15 cylinder in a direction toward the opposite side of the eoo~15 0 cylinder preferably in a direction generally at right angles 00 0 0 0o 0o o to the common longitudinal plane.

The transfer passages associated with the central o 0 ports, and with the two second transfer ports on the side of 20 the bore .opposite to the exhaust port, are shaped so that 2O the charge entering the cylinder through these ports is o000o directed upwardly in the cylinder. This upward movement is 0000 0 further promoted by the upward movement of the piston in the oo engine cylinder to thereby establish the required upward 0 2 flow of the incoming gases as the initial part of the o 25 25loop-scavenge movement of the incoming gases. In contrast, o the charge entering the cylinder through the transfer ports on either side of the exhaust port is generally directed 0o0 o across the cylinder bore towards the central transfer port 00 0 o Soo 30 or ports so that that charge is directed away from the exhaust port and the general flow of exhaust gases towards that exhaust port.

The above arrangement of the transfer ports and associated passages, so that the transfer ports, on the exhaust port side of the engine, do not extend through the Disk 0081/1.74 -9atransverse plane between two adjacent cylinders, enables the centre distance between the respective cylinder bores to be substantially reduced so that the distance between the bores, measured in said longitudinal plane is not substantially more than the required wall thickness of the two cylinders. This construction substantially reduces the overall length of a multi-cylinder engine cylinder block, as compared with previously known cylinder blocks wherein the cylinder bores are spaced a substantial distance apart so to accommodate transfer passages in the area between any two cylinders.

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0 000 a 6000.)o 0 a 00 0o a aa a 09 6 00 t *000 4 0 a *o a To t (00 tt 0 0(0 0C* 000 to a t C a to C Disk 0081/1.74 A space reduction is also possible at each end of the multi-cylinder block, as the transfer ports at the outer side of the end cylinder bores do not require additional space beyond that required for the normal cylinder wall thickness, and water jacket or other cooling provision as requi red.

The above described positioning of the transfer ports and associated passages between the exhaust ports of adjacent cylinders, enables the centre distance between adjacent cylinder bores to be reduced to the order of a range of 1.08 to 1.22 times the diameter of the cylinder bore, and preferably about 1.19 times the cylinder bore, for 01.0 an engine bore in the range of about 75 to 110mm diameter.

The relation of cylinder bore size to cylinder spacing is influenced by bore size as the required wall thickness about 11. the bores increases with bore diameter to maintain the 0oOO tensile loading in the wall within allowable limits.

In addition, the locating of the exhaust ports and associated passages to extend in a direction generally normal to the common longitudinal plane of the axes of the o cyind er bores, simplifies the construction of exhaust valves and actuating mechanisms for such exhaust valves when fitted 00 to the exhaust ports.

*0 0 The invention will be more readily understood from the following description of one construction of the "a cylinder block with reference to the accompanying drawings.

.060 In the drawings: Figure 1 is a plan view of the cylinder block of a three cylinder two-stroke engine with portion thereof in section along line 1-1 in Figure 3 being a cylinder diametral plane passing thrdugh the exhaust and transfer ports of that cylinder; Figure 2 is a view from the exhaust port side of the cylinder block shown in Figure 1; Figure 3 is a view of the induction side of the cylinder block shown in Figure 1; ~1 -11- Figure 4 is a sectional view on the line 4-4 in Figure 3; Figure 5 is a sectional view on the line 5-5 in Figure 3; Figure 6 is a sectional view on the line 6-6 in Figure 3; Figure 7 is a sectional view of the cylinder block along line 7-7 in Figure 1, being the longitudinal plane of the cylinder block.

Figure 8 is a sectional view on line 8-8 in Figure 0 1.

Referring now to Figures 1, 2 and 3 of the 0 Cleo drawings, the cylinder block 50 has three cylinders 10, 11 and 12 provided therein with the axes of the cylinders 015 parallel and located in a common longitudinal plane 25. The top face 51 of the block is at right angles to the common longitudinal plane 25 and is planar so that a cylinder head io may be fitted thereto in the conventional manner.

04 Along one side of the block, as seen in Figure 2, 0 20 there are provided three exhaust passages 21 which project inwardly from the external side face 22 of the block to the exhaust ports 20 in the engine cylinders as will be described further hereinafter. On either side of the exhaust port of the centre cylinder 11 there is provided oo- 25 respective outwardly convex surfaces at 60 and 61 which .e .0 effectively increase the width of the cylinder block at those locations to provide for two transfer passages through the block as hereinafter described. Similar, but of lesser width in the longitudinal direction, outwardly convex portions 62 and 63 are provided at either end of the block, outwardly of the exhaust ports of the end cylinders 10 and 12, which provide for a single internal transfer passage.

Two series of stiffening webs 70 and 71 are provided on the sidewall of the block 50 as seen in Figure 2 extending upwardly from the flange 52 along the lower marginal edge of the block. The flange co-operates with a suitably ;i.

-12constructed crankcase lower portion, (not shown) which, together with a cavity area within the lower portion of the block, provides the conventional two stroke cycle engine crankcase.

Figure 3 of the dravings shows the block from the opposite side to that shown:in Figure 2, wherein there are provided three air intake or induction passages 73, 74 and which communicate respectively with the crankcase area associated with each of the cylinders 10, 11 and 12. This particular engine in use is fitted with direct fuel injection through the head, so no fuel enters the crankcase in this region. However, the invention in its broad sense is not limited to direct injected engines. As can be seen in the sectional drawing Figure 4, the air intake passages project a substantial distance laterally from the main portion of the cylinder block. The lower end of transfer passages 32 and 33 open through the upper wall 40 of the air intake passage of each cylinder in the central area thereof.

The further transfer passages 37 and 38 similarly i communicate with the air induction passage towards either side thereof. The apparent difference in dimensions of the passages 32 and 33 relative to passages 37 and 38, is caused by the transfer passages 32 and 33 breaking through a portion of the upper wall 40 that is less inclined to the vertical than the portion where the passages 37 and 38 break 02 through. Also the transfer passages 37 and 38 break through the side walls of the intake passage which are not shown in the drawings. This gives the impression that the latter two passages are of a narrower height, however, as can be seen in the various cross sectional views through the cylinder block as in Figures 4 and 5 all these four transfer passages are of comparable size.

Referring now to Figure 1 of the drawings, each of the three cylinders 10, 11 and 12, are defined by cylinder walls 13, 14 and 15. The cylinder walls are connected at various locations to the unitary outer casing 16 of the

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-13cylinder block 50 and define therebetween respective cooling water passages some of which are shown at 17, 18 and 19.

More specifically the cylinder walls 13, 14 and 15 are integral with the outer casing 16 at the lower end of the cylinder walls as can be seen in Figure 4, to form a complete water barrier therebetween. The cylinder block is substantially open at the upper end to provide passageways for the flow of water into a detachable cylinder head when installed.

As can be seen from the sectioned portion of the cylinder 12 in Figure 1, the exhaust port 20 communicates the bore of the cylinder 12, with the exhaust passage 21 0000 fO which extends to the external face 22 of the outer casing 16 S of the cylinder block. The exhaust passage 21 extends oo o 15 generally in a direction normal to the longitudinal plane oo o o 25, which is common to the axes of the three cylinders 11 and 12. On either side of the exhaust passage 21 are transfer passages 23 and 26 which communicate respectively with the transfer ports 28 and 27. It will be noted that the ports 27 and 28 do not extend in the circumferential 0 on 0 direction of the cylinder 12 beyond the common longitudinal 0 plane 25, and the port 27 and associated transfer passage 26 o o does not extend beyond the transverse plane 29, at right S o angles to the common longitudinal plane 25 and located midway between the axis of the cylinder 12 and the adjacent On the opposite side of the common longitudinal o D plane 25 there is provided in the cylinder 12 two central transfer ports 30, 31 each communicating with a respective transfer passages 32, 33. On either side of the central transfer ports 30, 31 there are further transfer ports and 36 communicating with respective transfer passages 37 and 38. It will be noted that the transfer port 35 and associated passage 37 again do not extend beyond the transverse plane 29 at right angles to the longitudinal plane i

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-14- As can be seen in Figure 1, the transfer passages 23 and 38 do not extend, in the longitudinal direction of the cylinder block, beyond the thickness of the wall of the cylinder 12. Accordingly the cylinder block is not required to provide significant additional length in the longitudinal direction to accommodate the transfer ports and passages of the ends of the cylinder block.

Each of the transfer passages 23 and 26, extend downwardly through the cylinder block as seen in Figure 5 to open through the lower part of the wall 15 of the cylinder to communicate with the crankcase 42 of the engine.

Similarly the transfer passages 32, 33, 37 and 38 from the other transfer ports 30, 31, 35 and 36 also extend down and open through the upper face 40 of the intake passage to communicate with the crankcase 42.

SIn accordance with conventional two stroke cycle engine construction each cylinder has an independent crankcase compartment and the air charge is drawn into each compartment, through the respective intake passages 73, 74 and 75, controlled by reed or other valves (not shown), by ,1 the movement of the piston, (not shown) reciprocating in the a 00 cylinder. The air is subsequently compressed in the o° oo crankcase as the piston moves down the cylinder to thereby o displace the air charge from the crankcase through the various transfer passages and through the transfer ports into the engine cylinder.

ooo Figure 4 is a sectional view along the line 4-4 in .0oo Figure 2, the section being taken through the rear, and S portion of the next to rear, cylinders 11 and 12 of the engine. It will be noted from Figure 7, wherein the level of the section line 4-4 is noted at L4, that the section 4-4 extends through the cylinder block at the level where the lower ends of transfer passages 23 and 26 communicate with the cylinders. It will further be noted that the level L4 is below that at which the transfer passages 32, 33, 37 and 38 communicate with the main induction passage 75 of cylinder 12. As can be seen in Figures 4 and 7 the transfer passages 23 and 26 open through the cylinder wall 15 into the cylinder 12 at a location spaced upwardly from the lower end of the cylinder. Accordingly, as is known in the art of two stroke cycle engines, suitable openings are provided in the skirt of the piston (not shown) reciprocating in the cylinder 12 to permit a charge from the engine crankcase 42 to enter the transfer passages 23 and 26, as the piston moves down in the cylinder bore.

Figure 5 is a section similar to that shown in Figure 4, but at a higher level in the cylinder block, being at level L5, shown in Figure 7. At this level the section c is taken a short distance below the upper wall 40 of the intake passage 75 from which the transfer passages 32, 33, o" ,15 37 and 38 communicate with the engine crankcase 42. It will o:°Oo: be further noted that at this level the transfer passages 23 o and 26 have extended outwardly with respect to the common t 00 o longitudinal plane 25 of the cylinders and are now located within the outwardly convex portions 61 and 63 of the cylinder block previously referred to in the description 0,0 relating to Figure 1 of the drawings. The provision of S00o .oOo these outwardly projecting convex portions in the side of So the block enable the transfer passages 23 and 26 to be made o00 of a sufficient cross-section for the free flow of the 0 00 charge from the crankcase to the cylinders, without requiring the centre distance between the cylinders to be 0ooo enlarged to accommodate such transfer passages. It will 0000 further be noted from Figure 5 that the transfer passages 37 00 and 38 are of a substantial cross-section, and have been extended somewhat in the longitudinal direction of the engine. In this regard it must be understood that only part of the lower end of the transfer passages 37 and 38 are seen in Figure 4, as previously explained, and the true effective cross-sectional area of the transfer passage is considerably greater than the area as seen in Figure 4.

-16- The cross-section as shown in Figure 6 is at a level slightly below the level of the exhaust passage 21 and is indicated as level L6 in Figure 7. This view shows the true cross-sectional area of each of the transfer passares 23, 26, 32, 33 37 and 38 as they pass upwardly through the engine block to communicate with the respective ports in the wall 13 of the cylinder bore The approximate areas of the respective groups of transfer passages at level L6 are:- Transfer Passages Combined Area (mm 2 23 26 820 32 33 580 37 38 860 1 It will be appreciated from a consideration of the 5 areas of the respective groups of transfer passages that 0 approximately 26% of the incoming charge will enter the 0.o cylinder through the two central transfer ports located 0 0 o directly opposite the exhaust port and approximately a O o further 38% nf the charge will enter through the two side transfer ports located one on either side of the central o00 transfer ports. The remaining approximate 36% of the charge 0 00 S00 will enter the cylinder through the two transfer ports 00 located one on either side of the exhaust port with this oo part of the charge being directed generally towards the 0250" centre transfer ports on the opposite side of the cylinder along a path which will intersect the common longitudinal plane of the engine at substantially a right angle. The 00 directing of this not insignificant portion of the fresh S. i charge from the exhaust port side of the engine towards the opposite side where the central and side transfer ports are provided assists in controlliilg the movement of the charge entering through the central and side transfer ports against flowing across the cylinder to escape through the exhaust port. Also the flow of charge from the transfer ports on either side of the exhaust port assists in promoting the upward movement of the incoming fresh charge along the wall -17of the cylinder opposite to the exhaust port to establish the required loop-scavenge motion of the incoming fresh charge.

It will also be seen from Figure 8 of the drawings that the portion of the transfer passage 26 immediately downstream from the transfer port 27 is generally at right angles to the common longitudinal plane 25 passing through the axes of the cylinders of the engine so that the incoming fresh charge entering the cylinder through the transfer port 23 will have a generally horizontal trajectory so that it will pass directly across the cylinder towards the transfer ports on the opposite side of the cylinder bore and will not become entrained in or interfere with the flow of exhaust S gases entering the exhaust port 20 adjacent to the transfer port 27. It will further be noted from Figure 8 that the 0:00*: portion of the transfer passage 37 immediately upstream of o the port 35 has a generally upwardly inclined direction to a.00. impart an upward trajectory to the fresh charge entering the cylinder through the transfer port 35. It will further be noted from Figure 1 that the wall portion 37a of the .o0 transfer passage 37 will promote a flow of the incoming 00 charge from the port 35 in a direction generally across the cylinder towards the transfer port 36 so that that incoming o000 charge will not be directed directly towards the exhaust 021° port 20. It is also to be noted, although it is not illustrated in the accompanying drawings that the transfer o*o passages 32 and 33 are similarly inclined upwardly at the 0000 ports 30 and 31 so that the fresh charge entering through these ports will also be directed upwardly in the cylinder.

The above discussed direction of flow of the incoming fresh charge from the"respective groups of transfer ports establish that the incoming fresh charge is generally all directed to that part of the cylinder on the side of the common longitudinal plane 25 opposite from the side where the exhaust port 20 is located. This establishes within the cylinder, during the period that the transfer ports and -18exhaust ports are simultaneously open, a loop-scavenge flow of the incoming gases to effect discharge of the exhaust gases through the exhaust port with a minimum loss of fresh charge with that exhaust gas. This desired flow of the gases in the cylinder is obtained without the need to arrange the exhaust port with its axis inclined to the common longitudinal plane of the engine so that the scavenge axis of the engine is in a skewed relationship to the common longitudinal plane. Further, this desired scavenging action is obtained whilst also achieving a substantial reduction in the overall length of the cylinder block of the Wes multi-cylinder engine as compared with the overall length 0000 0 required for a loop-scavenged engine with a skewed scavenge a000 axis.

oo~oooo a °15 By way of comparison, it is to be noted that the 00 0 ao 0 engine in accordance with the present invention was 0.o developed to replace a prior construction in which the skewed scavenge axis was incorporated. The prior engine was of a three cylinder in-line construction having a nominal cylinder bore of 84 mm and an overall cylinder block length o0 0o of 337 mm. This prior engine had a total transfer passage a 0 cross-sectional area of 1840 mm 2 measured at a location corresponding to that in Figure 6.

The comparable engine constructed in accordance with the present invention and still having a nominal engine 0.0 bore of 84 mm, has an overall engine block length of 305 mm, 0 S representing a reduction of about 10% in the overall length of the engine. In the prior engine the centre distance between cylinders was 1.25 times the cylinder bore, whereas in the engine according to the present invention the ratio is 1.19. This reduction in overall length was achieved with a substantial increase in total transfer passage cross-section to 2260 mm 2 Measurements have also been made of multi-cylinder in-line engine assemblies wherein a three cylinder engine with a 79 mm bore had an overall length of 353 mm, and one -19with an 82 mm bore had an overall length of 337 mm. These same engines had a cylinder centre distance to diameter ratio of 1.4 and 1.28 respectively.

The engine block described herein is constructed for a spark ignited engine operating on the crankcase compression principle and accordingly the transfer passages communicate the transfer ports with the engine crankcase.

It is to be understood that the arrangement of transfer ports on each side of the exhaust port as herein disclosed may also be incorporated in a super-charged engine, where the transfer ports would communicate by suitably located t,,0 transfer passages to a source of pressurised air or air and fuel mixture.

Pt,, In either of the above referred to forms of the o °15 engine the fuel may be provided by carburettor or injection 0 0 means, including injection means that delivers the fuel .0ooo directly into the engine cylinders.

The engine block herein disclosed may be incorporated in engines for any use, including motors for 0 00 o 0oo20 vehicles such as automobiles and outboard marine engines.

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Claims (6)

1. A multi-cylinder engine block for a two stroke cycle internal combustion engine operating on the Schneurle loop-scavenged system and having two or more adjacent cylinder bores in said block with the axes of the bores parallel and in a common longitudinal plane, each cylinder bore having a respective exhaust port, an exhaust passage extending from each exhaust port to an external surface of the block in a direction generally at right angles to said common longitudinal planie, each cylinder bore having two first transfer ports located one on either side of the exhaust port of that cylinder bore, each first transfer port communicating with a respective first transfer passage, each cylinder bore having at least one second transfer port located on the opposite side of said common longitudinal plane to the exhaust port of that cylinder bore, each second transfer port communicating with a respective segond transfer passage, one of said first transfer ports and the associated first transfer passage of each of two adjacent cylinder bores being located on the same side of said longitudinal plane in a portion of the cylinder block between the respective exhaust ports and passages of said adjacent cylinder bores and on opposite sides of a transverse plane substantially at right angles to said common longitudinal plane and midway between said two adjacent cylinder bores, said one first transfer port and associated first transfer passage of each of said adjacent cylinder bores being configured and located to direct the charge entering the cylinder therethrough across the cylinder bore in a direction towards the second transfer port, and so the axes of the two adjacent cylinder bores are spaced apart not more than 1.22 times the diameter of the cylinder bores. I

2. 1, c asso cyli tran

3. or 2 trans passa longi 4 ports *9 enter on sa 0 4 4. 1, 2 port exten ft 40 1,2 o passa porti exten cylin cylin ca~ 400 0 0044 044 0 0 0 0044 0040) 0 4444' 0044 4 40s 44 0 00' 0 04 04 00 44 0.' 0S 00 0 00( O 44 40 0 0 04o 0 04 44 0 4 00a 0 00 10 0 4 I f I 01

6. 1, 2 passa( respec direcl substi bore Disk Disk 0083/1.13 I -21- 2. A multi-cylinder engine block as claimed in claim 1, characterised in that said second transfer port and associated second transfer passages of said two adjacent cylinder bores are located on opposite sides of said transverse plane. 3. A multi cylinder engine block as claimed in claim 1 or 2, characterised in that each cylinder has two second transfer ports communicating with respective transfer passages located on the opposite side. of said common longitudinal plane to the exhaust port, said second transfer ports and passages being arranged to direct the charge entering the cylinder therethrough upwardly in the cylinder on said opposite side of the common longitudinal plane. o 0 o 4. A multi-cylinder engine block as claimed in claim 1 i, 2 or 3, characterised in that said one first transfer port of each of said two adjacent cylinder bores does not extend beyond said common longitudinal plane. o*°a 5. A multi-cylinder engine block as claimed in claim 1,2 or 3, characterised in that said one first transfer passage of each of said two adjacent cylinder bores has a portion adjoining the associated first transfer port that extends in a direction substantially tangential to the cuo S" cylinder bore substantially at the intersection of the o cylinder bore with said common longitudinal plane. *0 0 S6. A multi-cylinder engine block as claimed in claims i, 2 or 3, characterised in that both the first transfer passages of each cylinder each have a portion adjoining the respective associated transfer port that extends in a direction substantially tangential to the cylinder bore at substantially the respective intersections of the cylinder bore with said common longitudinal plane. Disk 0083/1.13 WC -22-

7. A multi-cylinder engine block as claimed in claim 3, characterised in that each first transfer passage has a portion that adjoins the associated first transfer port that is shaped to direct charge fluid entering the cylinder bore through said first transfer port generally across the cylinder bore to combine with the upwardly directed charge entering through the second transfer ports.

8. A multi-cylinder engine block as claimed in claims 3 or 7, characterised in that each cylinder bore has at least one further transfer port communicating with the cylinder bore at a location generally opposite to the exhaust port and between the two second transfer ports of that cylinder bore. 0 DATED this 10th day of October, 1990. ORBITAL ENGINE COMPANY PTY. LIMITED i WATERMARK PATENT TRADE MARK ATTORNEYS i| o SUITE 18, 159 ADELAIDE TCE EAST PERTH WA 6004. S.: iiI Disk 0081/L.74