HEAD FOR AN INTERNAL COMBUSTION RECIPROCATING ENGINE

Abstract: The present invention is concerned with a head for an internal combustion reciprocating engine, with a couple of spark-plugs for each combustion chamber, wherein the architecture of the said head is optimized in order to improve the performance of the engine, and to secure the necessary structural stiffness.

Description: Internal combustion engines, equipped with a pair of spark plugs per each combustion chamber are known, wherein a more complete, rapid, stable and gradual combustion of the mixture takes place, than in engines with one spark-plug per combustion chamber only, because the path of propagation of the flame front is shorter, and the different points of the combustion chamber are reached within shorter times. Furthermore, also the cyclic dispersion of the combustion ignition point results to be more reduced, thanks to the higher probability of having the correct mixture ratio in the nearby of at least one from the two ignition points, then in the usual single-point configuration. A head of the above type is shown in JP-A-57 183 527 and is defined according to the precharacterizing portion of claim 1. As a consequence, leaner mixtures can be used, without penalizing the torque and maximum power performance of the engine, with advantages due to the reduction in fuel consumption, and also due to the reduction of unburnt pollutants, such as carbon oxide (CO) and unburnt hydrocarbons (HC), in the exhaust gases. The more regular behaviour of the combustion in the engine improves also the drive ability of the vehicle, in particular under partial loads. Providing substantially semi-spherical combustion chambers, in order to improve the surface/volume ratio thereof, is known as well. The purpose of the present invention and of our investigations is to provide heads for internal combustion engines provided with substantially semi-spherical combustion chambers, equipped with a pair of spark-plugs which, with the barrel bore being the same, show a reduced volume and are particularly compact, with a favourable surface/volume ratio. These purposes have been achieved according to the present invention by providing a head in an internal combustion reciprocating engine, having the features claimed in claim 1. In the head, less deep combustion chambers can be provided, and pistons having a practically flat head can be used; that makes it possible the compression ratio to be increased, and the heat exchange surfaces to be reduced, with the further advantage than higher efficiencies can be obtained both under partial loads, and under conditions of full opening of the choking valve. A reduction in the pressure drop in correspondence of the inlet openings of the combustion chamber, and, consequently, a better filling of the cylinders at all revolution speeds, in particular at high revolution speeds, can be obtained. Furthermore, an increase has been obtained in the torque and in the maximum power supplied by the engine, such an increase being to be attributed both to the improvement in the filling, and to the higher combustion efficiency due to the shape of the combustion chamber. The improvement in combustion, and the increase in maximum power cause large increases in pressure inside the combustion chamber, in particular under the high loads, with consequent high mechanical and thermal stresses being applied to the engine head. To the end of preventing deformations due to tightening loads and thermal loads, besides the arising of noisiness and troublesome disturbances, and of furthermore avoiding the risk that cracks may occur, which would endager the engine life, according to the present invention, the head has been strengthened by means of stiffening wall elements, which make it possible a concentrated strength in the most stressed regions, such as the combustion chambers, and a circulation of the cooling liquid such to secure an uniform heat dispersion, to be obtained. Thus, in correspondence of the combustion chambers an adequately strong structure has been realized, which, at the same time, leaves wide passages free for the head cooling fluid to flow through. Furthermore, the head has inner walls further contributing to the structural strength of the head. Structural and functional characteristics, and advantages of the present invention will be now illustrated by referring to the following figures, wherein for exemplifying and non-limitative purposes a preferred form of practical embodiment is shown of a head in an internal combustion reciprocating engine according to the present invention. Figure 1 shows a longitudinal elevation view of an engine according to path I-I of Figure 2, Figure 2 shows a transversa l sectional view according to path II-II of Figure 1, Figure 3 shows a partial top plan view of the only structure of the head of the engine, Figure 4 shows a partial bottom plan view of the head of Figure 3, Figure 5 shows a transversal sectional view according to path V-V of Figure 3, Figure 6 shows a transversal sectional view according to path VI-VI of Figure 3, Figure 7 shows a partial sectional view of the only body of the head according to path VII-VII of Figure 2, and Figure 8 shows a partial sectional view of the only body of the head according to path VIII-VIII of Figure 2. In Figure 1, the block of an internal combustion reciprocating engine, e.g., of the straight, four-cylinder type, is generally shown by the reference numeral 10; in Figure 1, transversal walls 11, 12, 13 thereof are visible; and in Figure 2, longitudinal walls 14, 15 thereof are visible. The barrels of the cylinders, each of which is indicated by the reference numeral 16, are fastened, at the bottom, inside the engine block 10, in a known, and hence not displayed, way. The chambers through which the coolant for the same cylinders circulates are indicated by the reference numeral 17. In Figure 1, only two of the pistons sliding inside the barrels 16 are shown; the pistons, whose head is practically flat, are indicated by the reference numeral 18, and sets of three compression rings thereof are indicated by the reference numeral 19. The motor head, generally indicated by the reference numeral 20 is constituted by a lower structure comprising two substantially horizontal walls, i.e., a first wall, indicated by the reference numeral 21, wherein combustion chambers 22 are provided, and a second wall, indicated by the reference numeral 23. Inside each chamber 22 there are an intake valve 24, and an exhaust valve 25, visible in Figure 2, and a pair of spark plugs 26 and 27, which are visible in Figures 1 and 2. As it results from the Figures, the spark-plugs 26 and 27 are positioned with their axes lying on a plane perpendicular to the plane which contains the axes 28 and 29 of the valves, with said plane being positioned offset, by a certain distance, from the centre of the combustion chamber; in particular, the spark-plugs 26 and 27 are vertical, and equidistant from the centre of the combustion chamber. The vertical arrangement of the spark-plugs facilitates the machining of their seats, so that the total head machining costs are reduced. The valves, in their turn, are closely approached to the centre of the combustion chamber, and are positioned with their axes 28 and 29 inclined through narrow acute angles relatively to the vertical axis 30 of the same combustion chamber. Preferably, said acute angles are smaller than 25°. The substantially horizontal walls 21 and 23 are connected by substantially vertical perimetrical walls, i.e., longitudinal walls 31 and 32, and transversal walls 33 and 34, visible in Figures 1, 2, 4; the same walls 21 and 23 are also connected by the tubes which form intake ducts 35 and exhaust ducts 36. The axes of the intake ducts, one of which is indicated by the reference numeral 37 in figure 2, are inclined through an angle smaller than 70°, preferably comprised within the range of from 65° to 60°, relatively to the vertical axis 30 of the combustion chamber 22. By 38, a sealing gasket interposed between the block 10 and the head 20, is indicated. The substantially horizontal walls 21 and 23 are furthermore connected by pair of substantially vertical wells 39 and 40, wherein the spark-plugs 26 and 27 are housed. The walls 21 and 23 are furthermore connected by studs or sleeves 41, visible in Figures 5, 6, 7 and 8, whose internal bores 42 house the stud bolts, not shown, which fasten the head 20 to the block 10. Thus, the ducts 35 and 36, the wells 39 and 40, the studs 41, also perform the function of structural strengthening elements. In Figures 1 and 2, plugs 43 are visible, which close bores 44 provided on the wall 23, visible in Figures 2 and 3, for the passage of the head casting cores. Inside a chamber 45, or multi chamber, comprised between the substantially horizontal walls 21 and 23, and the vertical walls 31-34, the head 20 cooling liquid circulates, coming from the chambers 17 of the engine block 10, through passages indicated by the reference numeral 46 in figures 2 and 4. The cooling liquid leaves the head through bores indicated by the reference numeral 47 in Figures 5 and 7, whose location has been studied in order to optimize the flow of the same liquid and the heat dispersion. The head 20 shows an upper structure which is formed by substantially vertical longitudinal walls 48, high-thickness transversal walls 49, low-thickness transversal walls 50, which connect the wall 23 with the walls 31-34, as shown in the figures. The enlargements formed at the crossing of said longitudinal and transversal walls are radiused with the studs or sleeves 41, and are provided with the same inner bores 42. The walls 48 are furthermore connected with the wall 23 and with the walls 31 and 32 by means of blocks 51 and 52, inside which seats 53 and 54 for the valve guides, and seats 55 and 56 for respectively the intake and exhaust valves actuation cups, visible in Figures 2, 3 and 4, are provided. In Figure 2, valve guides 57 and 58, valve actuation cups 59 and 60, and all of the elements in engagement with the valves 24 and 25 are visible; they are not described in detail, because they are known. Shafts and cams 61 and 62, which actuate the valves, are shown in sectional view. As shown in Figures 3, 5 and 6, in the transversal walls 49, seats 63 are provided, to house the bearings of the cam shafts 61 and 62. In the same walls 49, also threaded bores 64 are provided, wherein stud bolts 65 have to be screwed down, to lock the brackets 66 supporting the cam shafts 61 and 62; also shown in Figures 1 and 2 are then threaded bores, indicated by the reference numeral 67, inside which stud bolts 68 have to be screwed down, in order to fasten to the head a cover 69, still shown in Figures 1 and 2. With the illustrated engine head, wherein the combustion chambers 22, of substantially semi-spherical shape, show a small volume, and a small surface/volume ratio, an increase in the compression ratio, and a reduction in heat exchange surfaces have been achieved. Furthermore by positioning the intake ducts in a fairly inclined position, the volumetric efficiency of the engine has been increased. An increase in engine torque and maximum power resulted. Finally, the special configuration of the elements performing functions of structural strength, made it possible to accomplish a particularly strong head, capable of withstanding the strong mechanical and thermal stresses deriving from the improvement in performance.

Claims: Head in an internal combustion reciprocating engine, provided with cylinders (16) located inside an engine block (10), with pistons (18), and with a circuit for the cooling liquid, wherein the engine head (20) is provided with combustion chambers (22) of substantially semispherical shape, and each combustion chamber (22) is provided with a piston (18), with a pair of spark-plugs (26, 27) and at least an intake valve (24) and at least an exhaust valve (25), located inside relating ducts (35, 36), said intake valves (24) and said exhaust valves (25) being positioned with their axes (28, 29) which are inclined through an angle smaller than 25° relatively to the vertical axis (30) of the respective combustion chamber (22), characterized in that it comprises a lower and an upper structure, wherein said lower structure is formed by first and second substantially horizontal walls (21, 23) which are connected by substantially vertical perimetral walls (31, 32, 33, 34), by tubes forming said intake (35) and exhaust (36) ducts, and by wells (39, 40) inside which said spark-plugs (26, 27) are housed, said combustion chambers (22) being provided in said first horizontal wall (21), and said upper structure is formed by substantially vertical longitudinal walls (48), high-thickness transversal walls (49) and low-thickness transversal walls (50) which connect also said second horizontal wall (23) with said vertical perimetral walls (31, 32, 33, 34). Head in a reciprocating engine according to claim 1, characterized in that said substantially horizontal walls (21, 23) are also connected by studs (41), whose inner bores (42) house stud bolts for the fastening of the head (20) to the engine block (10). Head in a reciprocating engine according to claim 1, characterized in that each pair of spark-plugs (26, 27) is disposed aligned in a longitudinal direction inside said wells (39, 40) provided between two successive low-thickness transversal walls (50) and two vertical longitudinal walls (48). Head in a reciprocating engine according to claim 3, characterized in that said wells (39, 40) are sustantially vertical. Head in a reciprocating engine according to claim 1, characterized in that said pair of spark-plugs (26, 27) for each combustion chamber (22) are positioned with their axes lying on a plane perpendicular to the plane containing said axes (28, 29) of said intake and exhaust valves (24, 25), and offset relatively to the centre of said combustion chamber (22). Head in a reciprocating engine according to claim 5, characterized in that said spark-plugs (26, 27) are positioned with their axes being substantially vertical. Head in a reciprocating engine according to claim 5, characterized in that each pair of spark-plugs (26, 27) are substantially equidistant from said axis (30) of said combustion chamber (22). Head in a reciprocating engine according to claim 1, characterized in that said upper structure comprises blocks (51, 52) wherein first seats (53, 54) for valve guides and second seats (55, 56) for valve actuation cups are provided, said blocks (51, 52) connecting said longitudinal walls (48) with said perimetral walls (31, 32) and with said second horizontal wall (23). Head in a reciprocating engine according to claim 2, characterized in that enlargements are formed at the crossing of said longitudinal walls (49) and transversal walls (49) and are radiused with said studs (41). Head in a reciprocating engine according to claim 1, characterized in that each intake duct (35) is positioned with its axis (37) being inclined through an angle smaller than 70° relatively to the vertical axis (30) of said related combustion chamber (22). Head in a reciprocating engine according to claim 10, characterized in that said angle between said axis (37) of said intake duct (35) and said vertical axis (30) is comprised within the range of from 65° to 60°.

Inventors: CICCARONE, ANGELO, OLDANI, EMILIO, SCAPECCHI, PIER LUIGI
Applicants: ALFA LANCIA S.P.A.
Application year: 1987
Main classification: F02F1
IPC codes: F02F1, F01L1, F02B1