STEPPED PISTON ENGINE

Abstract: A stepped piston engine comprises first (10), second (11) and third (12) stepped cylinders, each cylinder (10, 11, 12) having a larger diameter pumping part (10p, 11p, 12p), and a smaller diameter working part (10w, 11w, 12w), and a piston (13, 14, 15) slidable in the cylinder, each piston (13, 14, 15) being coupled to an output shaft (16) of the engine, first transfer passage means (20) to transfer the precompressed charge from the larger diameter pumping part (10p) of the first cylinder (10) to the smaller diameter working part (11w) of the second cylinder (11), second transfer passage means (21), to transfer precompressed charge from the larger diameter pumping part (11p) of the second cylinder (11) to the smaller diameter working part (124) of the third cylinder (12), and third transfer passage means (22) to transfer precompressed charge from the larger diameter pumping part (12p) of the third cylinder (12) to the smaller diameter working part (10w) of the first cylinder (10).

Description: Title: Stepped piston engine Description of Invention This invention relates to a stepped piston engine- According to the invention I provide a stepped piston engine comprising first, second and third stepped cylinders, each cylinder having a larger diameter pumping part, and a smaller diameter working part, and a piston slidable in the cylinder, each piston being coupled to an output shaft of the engine, first transfer passage means to transfer precompressed charge from the larger diameter pumping part of the first cylinder to the smaller diameter working part of the second cylinder, second transfer passage means to transfer precompressed charge from the larger diameter pumping part of the second cylinder to the smaller diameter working part of the third cylinder, and third transfer passage means to transfer precompressed charge from the larger diameter pumping part of the third cylinder to the smaller diameter working part of the first cylinder. The charge may comprise air, or a mixture of air and fuel. The invention will now be described with reference to the accompanying drawings in which: FIGURE I is an illustrative side view of an engine in accordance with the invention with the pistons shown at 90 to their true positions, so as to illustrate the phase relationship between the pistons and the operating cycle of the engine. FIGURE 2 is an illustrative plan view of an engine in accordance with the invention, showing the arrangement of transfer passage means between the cylinders. FIGURE 3 is an illustrative perspective view of part of an engine of the invention showing in perspective a possible layout of transfer passages. FIGURE 4 is a series of cross sections taken through a oractical version of a manifold which may orovide the transfer passage layout of Figure 3. Referring first to figures I to 3 of the drawings, a stepoed piston engine comprises first, second and third cylinders 10, 1 1 , 12, each cylinder being of stepped configuration having a larger diameter pumoinq part I0p_,l Ip,l2p and a smaller diameter working part lOw, 1 Iw, 12w and a respective piston 13,14,15, slidable therein. Each piston has a larger diameter part 13j>, I 4p, 15p_, generally of corresponding dimension to the larger diameter pumping part I0p_,l 1 £» i 2D, of the respective cylinders 10,11,12, with appropriate piston rings (not shown) received in grooves in the pumping parts I0p_,l l£,12g, and a smaller diameter part I3w, I4w, I5w generally of corresponding diameter to the smaller diameter working parts lOw, llw, I2w of the respective cylinders 10,11,12, again with appropriate piston rings (not shown) received in grooves in the working parts I3w,l4w,15w. Each of the pistons 13,14,15, is connected to a common crank shaft 16 which comprises an output shaft from the engine, by respective connecting rods 17, as is well known in the art. The first cylinder 10 comprises an outlet port 10a which communicates with the larger diameter pumping part I0p_ leading to a first transfer passage means 20 which comprises an inlet passage part 20^ which communicates with the port 10a, and a main passage part 20m from which a pair of branches 20a,20b, extend. The branches 20a,20b extend to opposite sides of the smaller diameter working part llw of the second cylinder II with which they communicate by respective ports I lb, I I c. The second cylinder I I comprises an outlet port I l which communicates with the larger diameter pumping part I l _ and leads to a second transfer passage means 21 which comprises an inlet passage part 2lj_ which communicates with the port I la and a main passage part 21m from which a pair of branches 2la,2lb extend. The branches 2la,2lb, extend to opposite sides of the smaller diameter working part I2w of the third cylinder 12 with which they communicate via respective ports 12b,12c. The third cylinder !2 comprises an outlet port i2a which communicates with the larger diameter pumping oart I2p_ leading to a third transfer Dσssage means 22 which comprises an inlet passage part 22j_ which communicates with the port 12a and a main passage part 22m from which a pair of branches 22a,22b extend. The branches 22a_,22b, extend to opposite sides of the smaller diameter working part lOw of the first cylinder 10 with which they communicate via respective ports iOb Oc. The engine comprises α crank case 25 and a cylinder block 26 common to all three cylinders 10,11,12, although if desired, a separate cylinder block may be provided for each of the cylinders. The crank case 25 and cylinder block 26 or blocks, are connected at an interface 27 at a junction between the larger diameter pumping parts I Og, I 1 p_, 12p_, and the smaller diameter working parts lOw, I Iw, I2w of the cylinders 10,11,12. In the example described, the outlet ports I0a,ll ,l2£ are at the interface 27 with the inlet passage parts 20^2 I ^221_ extending upwardly into the cylinder block 26, then down again across the interface 27 to the respective main passage part 20rn,21 m,22m_ each of which, in this example, is contained wholly within the crank case 25. It can be seen from figures 2 and 3 that the inlet passage part 2OJ_ crosses the interface 27 with the branches 22a,22b either side, whilst the inlet passage part 2 Ij_ crosses the interface 27 with the branches 20a,20b either side, and the inlet passage part 22 ^ crosses the interface 27 with the branches 21 a,2 lb either side. The cylinders 10,11,12, also each have an inlet port lOj^l l| 2j_ which communicates with a respective larger diameter pumping part IOD, 11£, I2p, to which parts charge is supplied from a respective supply passage 30. each of the respective supply passages 30 containing a one-way valve such as a reed valve 31, so that charge may be drawn into the cylinder part 10p_,l !p,l2p during downward movement of the respective piston 13,14,15, but is prevented from passing back into the supply passage 30 during pre- compression i.e. when the respective piston 13,14,15, is moving upwardly. It will be noted from figure I, that the pistons 13,14,15, are 120 out of phase with one another. The working cycle of the engine will now be described. Piston 13 is shown in figure I in cylinder 10 moving upwardly at a position just before reaching top dead-centre. Charge, comprsing a mixture of air and fuel, during the upward movement of the piston 10, has been compressed in the larger diameter pumping part I0p_ aι~d transferred via the first transfer passage means 20 to the smaller diameter working part I Iw of cylinder I I, when the iniet ports of the branches 20a,20b are uncovered by piston 14 in the second cylinder I I. At the same time, precompressed charge, previously introduced into the smaller diameter working part lOw of cylinder 10 is further compressed by the upward movement of the piston 13, once the piston has passed and hence blocked the inlet ports !0b, !0c (only one of which is shown in figure I ) which communicate with the branches 22a,22b of the third transfer passage means 22. When piston 13 reaches top dead-centre, ignition will occur. In a diesel engine, such as that shown, the charge will spontaneously ignite, but in a petrol engine, a spark plug would be reauired to initiate combustion. When piston 13 is in the position shown, piston 14 will just be commencing its upward movement. While piston 14 is below the inlet ports I l b, 1 1 c, from the branches 20a,20b of the first transfer passage means 20, the precompressed charge from the larger diameter pumping part I0p_ is pumped into the smaller diameter working part I I , but when the ports l ib, l i e are blocked as the piston 14 continues to move upwardly, the precompressed charge in the smaller diameter working part I I will be further compressed by the further upward movement of the piston 14, until the piston 14 reaches top dead-centre when ignition will occur in cylinder 1 1. Whilst pistons 13, 14, are in the positions shown, piston 15 is moving downwardly by virtue of fully compressed charge in smaller diameter working part I2w of cylinder 12 having been previously ignited. As piston 15 continues to move downwardly, an exhaust port 12d of the cylinder 12 will be unblocked, as will the inlet ports 12b, 12c connected to the branches 2l a,2 lb, of the second transfer passage means 2 ! , so that charqe precompressed by the upward movement of piston 14 can be pumped into the smaller diameter working part I 2w of cylinder 12 at the same time flushing the combustion products from the smaller diameter working part I 2w via the exhaust port 12d. Further, whilst piston 15 is moving downwardly, charqe will be drawn into the larger diameter pumping part I 2p_ via the inlet port ! 2J_ connected to the supply passage 30. Thus in each case, as the pistons 13, 14, 1 5. move downwardly fresh charge is drawn into the larger diameter pumping part i 0p_, ! I D, ! 2p and at least when the respective inlet ports I 0b, 10c; I l a, I I c; 12b, 1 2c are uncovered by the pistons 13, 14,1 5, precompressed charge is pumped into the smaller diameter working parts lOw, l l w, I 2w Q1 the same time flushing combustion products from the cylinders !0,l I , I 2, via exhaust ports I0d, l I d, l 2d. As the pistons 13, 14, 15, move upwardly, charge in the larger diameter pumping part I0p_, l l 2 ? ' 2g is precompressed, and a1 least when the respective inlet I0b, l0c; I lb, l ie, 12b, 12c and exhaust ports 10d; I Id; 12d are closed by the pistons 13, 14, 1 5, the precompressed charge is further compressed until the pistons I 3, 14, 15, reach top dead-centre when ignition will occur. It will be appreciated from figures 2 and 3 that the main passage part 22m at least is considerably longer than the main passage parts 20rπ,2 l rn, which are of generally equal length, and so the third transfer passage means 22 would appear to have a greater volume than each of the first and second transfer passage means 20,21. However this would lead to inefficient transfer of precompressed charge from cylinder 12 to cylinder 10, and result in engine imbalance. Hence the first, second and third transfer passage means 20,21 ,22, are arranged to have generally equal volumes, or at least volumes within a variation of 25% of each other, more preferably within a variation of 15% of each other, and yet more preferably within a variation of 10% of one another. This arrangement has been found to allow for efficient charqe transfer overall, and a balanced engine. Generally equal volumes may be achieved by reducing the average cross sectional area of the third transfer passage means 22 by reducing the actual cross sectional area over at least part of its length, but this can lead to engine imbalance. Alternatively, the lengths of the branches 20a,20b,21 a,21 b mav be made longer than the branches 22a,22b, the longer branches relatively increasing the volumes of the first and second transfer passage means 20,21 , to allow for the longer main passage part 22m of the third transfer passage means 22 so that the combined lengths of the main passage parts (20m,21 m,22m) and branches (20a,20;2 l a,2 l b:22a,22b) and the inlet passage parts (20;2 ! .22^ of all the transfer passage means 20,21 ,22 are generally equal, so that the transfer passage means 20,21 ,22 each have generally the same volume. !n a preferred embodiment, the branches 20a,20b: 2 l a,2 ! b: 22a,22b, are all of generally equal length, or at least have lengths within a variation of 25%. or more preferably within 15% of each other, and the main pcssaae parts 20m,2 l m, being of generall y equal length and necessarily shorter than the main passage part 22m. Thus to ensure generally equal volumes within the first, second and third transfer passage means 20,21 ,22, the inlet passage parts 20j,2 M_ and 22j_are of differing lengths. It can be appreciated from figures 2 and 3 that the main passage part 22m lies alongside the cylinders 10,1 1 , 12, so that inlet passage part 22i ^ is considerably shorter than each of the inlet passage parts 20^ and 2 !j_. In the example shown, the second transfer passage means 21 is nested between the first and third transfer passage means 20 and 22. Of course, other transfer passage means arrangements are possible. For example the average cross sectional area of the third transfer passage means 22 may be slightly reduced and the branches 20a,20b,21 a,21 b of the first and second transfer passage means 20,21 , may be made longer than the branches 22a,22b of the third transfer passage means 22, whereby the volumes of the first, second and third transfer passage means 20,21 ,22, may be made generally equal. Various other modifications may be made without departing from the scope of the invention. For example, the inlet ports ! 0b, l 0c; I l b, l l c; l I b, l 2c for the smaller diameter working parts I0w, l lw, !2w of each of the cylinders 10, 1 1 and 12 are shown in the example described, generally opposite one another, with the exhaust outlet ports I 0a, l !a, ! 2a and inlet ports 10, M , I 2, qenerally on opposite sides but spaced 90° from the inlet ports 10b.1 c, M b, ! ! c. l 2b, 12c. This port arrangement has been found to provide for efficient scavenging of combustion products from the engine, although other port configurations are no doubt possible. In the example described, the main passage parts 20m,2 l m_ and 22m of the first, second and third transfer passage means 20,21 ,22, are all contained within the crank case 25 but need not be in an alternative arrangement. For example, referring to figure 4, a manifold 35 is provided which bridges the interface 27 between the crankcase 25 and the cylinder block or blocks 26. The manifold 35 wholly contains each of the main passage parts 20rn.21 m_,22m of the transfer passage means 20,21 ,22. and contains portions of each of the branches 20a,20b; 2 l a,2 i b; 22a.22b and further portions of each of the inlet passage means 20^,2 l].22j_. The remaining portions of the branches 20a,20b:2 l a,2 l b:22a,22b, are contained in the or the respective cylinder block 26, whereas the remaining portions of the inlet passage parts 20j_,2 i u22j_ are contained within the crankcase 25, so that the respective passage parts extend to the ports I l b, I I c: 12b, 12: ! 0b, 10c: and Ϊ Oa, l l a, 12a. The manifold 35 is made up of a main part 36 ( cross hatched for claritv and a cover plate 37 (stippled for clarity) with a sandwich plate 38 therebetween. The main part 36 and sandwich plate 38 together provide a recess comprising parts of branches 22a,22b, part of main passage part 22m, and part of the inlet passage means 22j_ of the transfer passage means 22. Between the sandwich plate 38 and cover plate 37, a further recess is provided comprising part of the main passage part 2 l rn of the transfer passage means 21. Between the main part 36 and cover plate 37, a yet further recess is provided, which is divided by the sandwich plate 38 to provide part of inlet passage part 2Q\ j main passage part 20m and parts of branches 20a.20b of the transfer passage means 20, part of inlet passage part 2 ! _. part of main passage part 21 m and parts of branches 2 l a,2 l b of transfer passage means 21 , and part of main passage part 22rn. The manifold joint face 40 is preferably inclined at about 45 as shown. Such a construction is preferred because manufacture of the manifold 35 by diecasting is facilitated as it is possible to provide draft on each side face of the main passage parts 20m,2 l m.22m, and portions of the other passage parts, in the manifold 35. Preferably, at least a proportion of the main part 36 of the manifold is an integral part of the crankcase 25 of the engine. The engine in the example described has only three cylinders i O, I ! , I 2 but may have more than three cylinders arranged in groups of three, eithe all in line, or in a V configuration with the three cylinders of each group o three all on one side of the V, but preferably all of the pistons 1 3, ' 4, 1 5 withi the or the groups of three cylinders 10, 1 1 , 12 are connected to a commo output shaft 1 . In the example described, charge introduced into the larger diamete pumping parts I0p_, I I p, ! 2ρ_ of the cylinders 1 , ! 1 , 1 2, comprises a mixture o air and fuel but could in a dif ferent arrangement comprise air alone, wit fuel or a mixture of air and fuel being injected or otherwise introduced int the smaller diameter working parts I w, l I w, l 2w of the cylinders 10, 1 1 , 12 by an injector means, just prior to ignition. In a further modification, if desired there may be more than two inlet branches 20a,20b, 2 ! a,2 !b,22b for each cylinder, leading to more than two inlet ports in each cylinder. Instead of the engine having an interface as indicated at 27 between the or each cylinder block 26 and the crank case 25, the various passages may be cast without having to cross such an interface. The features disclosed in the foregoing specification or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, or a class or group of substances or compositions, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims: CLAIMS 1. A stepped piston engine comprising first, second and third stepped cylinders, each cylinder having a larger diameter pumping part, and a smaller diameter working part, and a piston slidable in the cylinder, each piston being coupled to an output shaft of the engine, first transfer passage means to transfer precompressed charge from the larger diameter pumping part of the first cylinder to the smaller diameter working part of the second cylinder, second transfer passage means to transfer precompressed charge from the larger diameter pumping part of the second cylinder to the smaller diameter working part of the third cylinder, and third transfer passage means to transfer precompressed charge from the larger diameter pumping part of the third cylinder to the smaller diameter working part of the first cylinder. 2. An engine according to claim I characterised in that the first, second and third transfer passage means have volumes within a variation of 25% of each other. 3. An engine according to claim 2 characterised in that the first, second, and third transfer passage means have volumes within a variation of I 5% of each other. 4. An engine according to claim 3 characterised in that the first, second, and third transfer passage means have volumes within a variation of ! 0% of each other. 5. An engine according to any one of claims I to 4 characterised in that each of the first, second and third transfer passage means comprises an inlet passage part which extends from the respective larger diameter pumpinq part, to a main passage part from which a pair of branches extend, each branch communicating with the respective smaller diameter working pert. 6. An engine according to claim 5 characterised in that the branches communicate with the respective smaller diameter working part generally oppositely of the respective cylinder. 7. An engine according to any one of the preceding claims characterised in that the first, second and third cylinders are arranged generally in line with their respective cylinder axes contained or substantially contained within a common plane. 8. An engine according to claim 7 characterised in that the average cross sectional area of the third transfer passage means is reduced compared with the average cross sectional area of the first and second transfer passage means, such that the first, second and third transfer passage means have volumes within a variation of 25% or less, of each other. 9. An engine according to claim 8 where appendant to claim 5 characterised in that the inlet passage part of the third transfer passage means is shorter than the inlet passage parts of the first and second transfer passage means but the branches of each of the first, second and third transfer passage means have generally the same length within a variation of less than 25%, preferably, less than 15%. 10. An engine according to any one of claims 5 to 9 where appendant to claim 5 characterised in that where the three cylinders are in line, the main passage part of the third transfer passage means runs closer to the cviinders than the main passage parts of each of the first and second transfer passage means. 1 1. An engine according to any one of the preceding claims characterised in that the engine comprises a crank case and a cylinder block for each of the cylinders, or a common cylinder block for all of the cylinders, the crank case and cylinder block or blocks being connected together at an interface, the interface being arranged at or adjacent the junction between the larger and smaller diameter parts of all of the cylinders. 12. An engine according to claim I I characterised in that the first, second and third transfer passage means each cross the interface, with at least a major portion of each main passage per* contained wholly within the crank case. 13. An engine according to claim I I characterised in that an interface is provided between the cylinder block or blocks and the crankcase, but a manifold is provided which wholly contains the main passage parts of the first, second and third passage parts, and preferably also at least a portion of each of the inlet passage parts, and a portion of each of the branches of each of the trans er passage means. 14. An engine according to claim 12 or claim 13 wherein the or the remaining portions of each of the inlet passage parts are contained within the crankcase, and the, or the remaining portions of each of the, branches are contained within the, or the respective, cylinder block. 15. An engine according to claim 13 or claim 14, characterised in that the manifold comprises a main part having a recess which is closed on one side by a first external cover plate, and on another side by a sandwich plate, to provide the main passage part of the third transfer passage means, and a second cover plate with the sandwich plate, provides the main passage parts of the first and second transfer passage means. 16. An engine according to any one of claims 13 to 15 characterised in that where the manifold and cylinder block or blocks join, parts of the inlet passage parts and branches of all of the transfer passage means, are arranged along a line parallel with a plane containing the cylinder axes of all three cylinders. 17. An engine according to any one of claims 13 to 16 characterised in that the branches of the third transfer passage means are arranged to cross the interface or join, either side of the inlet passage part which provides for precompressed charge to leave the first cylinder and enter the main passage part of the first transfer passage means, and the branches of the first transfer passage means are arranged to cross the interface or join either sid of an inlet passage part which provides for precompressed charge to leσve th second cylinder and enter the main passage part of the second transfe passage means, and the branches of the second transfer passage means ar arranged to cross the interface or join either side of an inlet passage par which provides for precompressed charge to leave the third cylinder an enter the main passage part of the third transfer passage means. 18. An engine according to any one of the precedinq claims characterised in that the engine comprises a multiple of three cylinders arranged in line in groups of three or in a V formation, with the three cylinders of each group on one side of the V only, with ail of the respective pistons connected to a common output shaft of the engine. 19. An engine according to any one of the preceding claims characterised in that the pistons of the three cylinders, or each group of three cylinders, are arranged to operate 120 out of phase with each other. 20. An engine substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

Inventors: HOOPER BERNARD, HOOPER, BERNARD
Applicants: HOOPER BERNARD, HOOPER, BERNARD
Application year: 1990
Main classification: F02B23
IPC codes: F02B1, F02B3, F02B25, F02B33, F02B75