INTERNAL COMBUSTION ENGINE WITH BEARING BEAM STRUCTURE

Abstract: An internal combustion engine (10) comprises a cy­ linder block (12) having a plurality of cylinder barrels (14) and a plurality of bearing sections (22) for the journals of a crankshaft; a bearing beam structure (26) and including a plurality of main bearing cap sections (28) each of which associates with each cylinder block bearing section (22) to form a bore (24) for rotatably receiving the crankshaft journal, each bearing cap section (28) being formed with first and second projections (30A, 30B) which are spaced from each other and located opposite to each other with respect to the axis of the bore, and first and second beam membres (32A, 32B), which are independent from but securely connected to the first and second bearing cap section projections (30A, 30B), respectively, by bolts (34), thereby greatly reducing engine noise emission and improving the pro­ ductivity of the engine.

Description: The present invention is directed to an internal combustion engine of the type as indicated in the precharacterising clause of claim 1. From SAE-Paper 770775 regarding the Off-Highway Vehicle Meeting & Exhibition, Mecca, Milwaukee, September 12-15, 1977, Figure 3 a bearing beam structure for an internal combustion engine is known including obliquely downwards and outwards extending projections integrally formed with main bearing caps, said projections terminating in integral beams which extend in parallel to the axis of the crankshaft. However, said beams have not been located spaced as far as possible from the crankshaft axis. Moreover this integral beam arrangement results in a heavy cast iron arrangement of the bearing beam structure which is undesirable from the points of view of fuel economy, assembling process conditions and natural frequency range of the bearing beam structure. Another internal combustion engine comprising a bearing beam structure is shown in FR―A―2135632. Said French patent publication shows a bearing beam structure in which a plurality of main bearing caps are securely connected with each other by means of a reinforcement member which is directly connected to a cylinder block by bolts. Another crank case and bearing structure for internal combustion engines is disclosed in US-A-3 046 954 including a plurality of individual main bearing cap sections which are either interconnected to adjacent side walls of the crank case by tie straps (Figure 8) or which are interconnected by longitudinal plate members (Figure 9). These longitudinal plate members have spaced inwardly disposed projections which are perforated to receive the cap bolts which secure the tie plates to the bolt clamping shoulders of the main bearing cap sections. The present invention aims at an improved and lighter bearing beam structure. The desired improvement is achieved by adding the features as contained in the characterising clause of claim 1 to the features as indicated in the preamble of claim 1. On the basis of integral projections formed spaced from each other at the main bearing cap sections at opposite marginal bottom portions thereof, projecting obliquely downward, the essential feature of the invention resides in the following facts: (a) beam members which engage longitudinally aligned projections in parallel to the crankshaft axis consist of two separate reinforcing struts, and (b) said struts being secured at the lowermost end portion of respective projections by bolts, engaging an installation base surface of the projections. The inventive arrangement suppresses not only the coming-down vibration of each bearing cap section in the crankshaft axis direction but also the torsional vibration of the cylinder block thereby noticeably reducing engine noise emission and improving the productivity of the engine. Moreover, this arrangement enables beams to be used consisting of a light alloy, such as aluminium, resulting in a weight saving crankcase structure. One way of carrying out the invention is disclosed in the following description of a preferred embodiment with reference to Figures showing only one embodiment of the present invention in which like reference numerals and characters designate like parts and elements, in which: Fig. 1 is a front elevation of a conventional internal combustion engine; Fig. 2 is a vertical sectional view taken in the direction of arrows substantially along the line II―II of Fig. 1; Fig. 3 is a perspective view of a conventional bearing beam structure used in the engine of Fig. 1; Fig. 4 is a vertical cross-sectional view of a preferred embodiment of an internal combustion engine in accordance with the present invention; Fig. 5 is a fragmentary side view of the engine of Fig. 4; and Fig. 6 is a fragmentary perspective view of a beam member of a bearing beam structure of the engine of Fig. 4. Detailed Description of the Invention To facilitate understanding the invention, a brief reference will be made to an engine block 1 of a conventional automotive internal combustion engine, depicted in Figs. 1 to 3. Referring to Figs. 1 and 2, the engine block 1 includes a cylinder block 2, and a bearing beam structure 3 secured to the bottom part of the cylinder block 2 by means of bolts. The bearing beam structure 3 has a plurality of main bearing cap sections 4 each of which associates with each of bearing sections 5 or main bearing bulkheads of the cylinder block 2, as shown in Fig. 3. The thus associated bearing cap section 4 and cylinder block bearing section 5 rotatably support the journal of a crankshaft (not shown). The bearing cap sections 4 are securely or integrally connected with each other through a beam section 6 extending along the axis of the crankshaft, so that the rigidity of the cylinder block can be increased. Therefore, the cylinder block 2 is improved in flexural rigidity against the flexural vibration indicated by dot-dash curves I in Fig. 1, and the bearing cap sections 4 are also improved in flexural rigidity against the vibration in the axial direction of the crankshaft or in the forward-and-rearward direction which vibration so acts on each bearing cap section so as to cause it to come down. As discussed above the cylinder block 2 and the bearing cap sections 4 are improved in their mechanical strength. However, it has been confirmed that a desired engine noise reduction cannot be attained. Inventor's studies have showed that, in the above-mentioned conventional bearing beam structure in which only one beam section 6 is disposed at the bottom central portions of the main bearing cap sections 4, a sufficient suppression effect cannot be obtained against the twist vibration of each bearing cap section 4 in the direction X indicated in Fig. 3, thereby contributing to noise generation. Additionally, inventor's recent experiments have revealed that the lateral vibration in the open-and-close manner of a cylinder block skirt section 7 is mainly caused by the torsion of the main bearing sections 4 and the main bearing bulkheads 5 around the axis of the crankshaft. The thus vibrationing cylinder block skirt section not only emits noise therefrom but also excites the vibration of an oil pan (not shown) secured to the skirt section, thereby further emitting noise from the oil pan. As a result, a sufficient noise reduction cannot be achieved by the conventional bearing beam structure. Furthermore, in view of the fact that the beam section 6 is integral with the main bearing cap sections 4 in the conventional bearing beam structure 3, even if only a defective part such as porosity has been made during casting, the whole the cast bearing beam structure must be discarded, thereby deteriorating productivity and contributing to waste of materials. Besides, the conventional bearing beam structures are considerably bulky and are liable to get entangled with each other during their transportation, thereby rendering difficult their storage and treatment. In view of the above description of the automotive internal combustion engine provided with the conventional bearing beam structure, reference is now made to Figs. 4 to 6, wherein a preferred embodiment of an internal combustion engine of the present invention is illustrated by the reference numeral 10. The engine 10 in this embodiment is for an automotive vehicle and comprises a cylinder block 12 which is formed with a plurality of cylinder barrels 14 each of which defines therein a cylinder bore (no numeral). The cylinder block 12 includes a skirt section 16 which is bulged outwardly and extends downwardly to define thereinside the upper part of a crankcase (no numeral). The skirt section 16 is integrally connected through a lower block deck 18 with the cylinder barrels 14. A plurality of main bearing bulkheads 20 are parallelly disposed inside of the skirt section 16. Each bearing bulkhead 20 is located below and connected to a portion between the adjacent two cylinder barrels 14. The bearing bulkhead 20 is integrally connected at its top part with the lower block deck 18 and at its side parts with the inner wall of the skirt section 16. Each bearing bulkhead 20 is provided at its bottom central portion with a bearing section 22 for rotatably receiving the journal of a crankshaft (no numeral). A bearing beam structure 26 is securely connected to the bottom section of the cylinder block 12 and includes a plurality of main bearing cap section 28. Each bearing cap section 28 is secured at its top portion onto each bearing bulkhead 20 by means of cap bolts 29A, 29B so as to associate with the bearing section 20a of the bearing bulkhead 20, thereby defining a cylindrical bore 24 in which the journal of the crankshaft is rotatably supported. In this instance, the bearing cap section 28 is generally in the shape of a rectangular plate and accordingly is formed with the opposite side portions or surfaces 28a, 28b which are located symmetrical with respect to an imaginary vertical plate containing the crankshaft axis. As shown, each bearing cap section 28 is integrally formed with first and second projections 30A, 30B or installation bases for first and second beam sections 32A, 32B, respectively, which will be discussed hereinafter. The first and second projections 30A, 30B are located at and project from the opposite bottom corner portions, respectively, of each bearing cap section 28, which bottom corner portions are located outside of the cap bolts 30A, 30B, respectively. The bottom corner portions are located opposite, in the vertical direction, to the top corner portions which fit in the cylinder block bearing section 22. In other words, the first and second projections 30A, 30B are positioned symmetrical with each other with respect to the imaginary vertical plane containing the crankshaft axis. The first and second projections 30A, 30B extend downwardly and outwardly in such a manner that the axes of the first and second projections intersect at the same angle the imaginary vertical plane containing the crankshaft axis. The tip surface or installation base surface 30a, 30b of each projections 30A, 30B is located outside of the envelope M of the outer-most loci of the big end of a connecting rod for the crankshaft. The first and second rod-like beam sections or members 31A, 32B are independent from but secured respectively to the first and second projections 30A, 30B of each bearing cap section 28 by means of bolts 34 each of which is screwed and disposed in each projection 30A, 30B. The first and second beam sections 32A, 32B extend parallelly with each other and with crankshaft axis so that the aligned bearing cap section first projections 30A are securely connected through the first beam member 32A with each other, and the aligned bearing cap section second projections 30B are securely connected through the second beam section 32B with each other. It is preferable that the first and second projections 30A, 30B are so positioned that the extension of the axis of the bolt 34 screwed in each projection is directed to within the cylindrical bore 24, in which the initial tightening forces of the bolts 34 act radially relative to the bearing beam structure 26, thereby improving the rigidity against the torsional vibration of the cylinder block 12. Additionally, each beam section 32A, 32B is preferably formed with a plurality of projections 36 which are located at predetermined intervals in the longitudinal direction thereof, i.e. at positions corresponding to the projections 30A, 30B of the bearing cap section 28. Each projection 36 of the beam section 32A, 32B is formed at its tip with an installation surface 36a which is to be in contact with the installation base surface 30a, 30b of the projection 30A, 30B. By virtue of this contact between the projections 30A (30B), 36 which are connected with each other by means of the bolts 34, a microscopic sliding is made between the installation base surface 32a (32b) and the installation surface 36a, thereby providing a vibration damping effect. Thus, according to the present invention, a plurality of main bearing cap sections 28 are rigidly connected with each other by the two beam members 32A, 32B which are symmetrically disposed with respect to the cylindrical bore 24 for receiving the journal of the crankshaft. Therefore, the engine 10 is greatly improved in torsional strength around the crankshaft axis, in addition to the advantageous fact that each bearing cap section 28 is improved in the strength against the vibrations causing the bearing cap section to come down. As a result, the torsional vibration of the bearing bulkheads 20 connected to the bearing cap sections 28 is largely suppressed. This effectively prevents the open-and-close or lateral vibration (membrane vibration) of the skirt section 16 to which the bearing bulkheads 20 are connected to form connecting sections which serve as the nodes of the skirt section vibration, thereby remarkedly decreasing noise emission due to the vibration of the cylinder block skirt section 16 and an oil pan (not shown) secured to the skirt section 16. Furthermore, since the bearing cap sections 28 are produced separately from the beam members 32A, 32B, the shape of each product or part to be produced by casting is simplified so as to greatly reduce the number of rejects of products due to shrinkage of molten metal or due to incomplete gas vent during the casting of the products. Even in case where a reject of product or part is made, it is sufficient to discard only that part. This greatly contributes to an improvement in productivity, achieving production cost lowering. Since the bearing cap sections 28 and the beam members 32A, 32B are separable by removing the bolts 34, the treatment of the engine 10 is facilitated during its transportation; besides the parts of the engine are not bulky, thereby permitting a small space for the storage thereof. Moreover, it is preferable that the bearing cap sections 28 are made of cast iron, whereas the beam members 32A, 32B are made of light alloy such as aluminium alloy, by which the value of E (Young's modulus)/p(density) can be improved about 30%, thereby achieving weight lightening without lowering in rigidity. As appreciated from the above, according to the present invention, the main bearing cap sections are securely connected with each other by means of the two beam members which are separate from each other and disposed on the right and left sides of the crankshaft axis, the two beam members being respectively secured onto the two projections which are located respectively at the opposite bottom corner portions of each bearing cap section. This effectively suppresses not only the coming-down of the bearing cap sections in the crankshaft axis direction but also the torsional vibration of the cylinder block, thereby noticeably reducing engine noise and achieving improvement in productivity and treatment of the engine and its parts.

Claims: 1. An internal combustion engine comprising: a cylindrical block (12) having a plurality of cylinder barrels (14), and a plurality of bearing sections (22) for the journals of a crankshaft, and a bearing beam structure (26) secured to the bottom part of said cylinder block (12) including a plurality of main bearing cap sections (28) each of which associates with each cylinder block bearing section (22) to form a bore (24) for rotatably receiving the journal of the crankshaft including first and second projections (30A, 30B) which are integral with an project outwardly from at least each main bearing cap section (28), said first and second projections (30A, 30B) being spaced from each other and located opposite to each other generally symmetrical with respect to a vertical plane containing the axis of said bore (24) for the crankshaft journal, aside first and second projections (30A, 30B) extending obliquely downward so that the axis of each projection (30A, 30B) intersects said vertical plane at an acute angle, said projections terminating in a beam means including first and second members respectively, characterised in that said beam members comprise two separate reinforcing structs (32A, 32B) each of them being secured by bolts (34) to installation base surfaces (30a, 30b) at the lower end portion of aligned projections (30A, 30B), respectively, that each of said bolts (34) passes through each of said bearing cap section projections (30A, 30B), that extensions of axes of said respective projections (30A, 30B) pass through said bore (24) for the crankshaft journal, and that axes of said bolts (34, 34) are directed to said bore (24). 2. An internal combustion engine as claimed in claim 1, wherein each of said first and second struts (32A, 32B) provides a plurality of installation projections (36) each of which is formed with an installation surface (36a) which is in secure contact with the installation base surface (30a, 30b) of each projection (30A, 30B) of a respective bearing cap section (28) by a bolt (34) passing through said bearing cap section projection (30A, 30B) and said installation projection (36). 3. An internal combustion engine as claimed in claim 1, wherein said first and second struts (32A, 32B) extend generally straight and are disposed parallel with each other and with the crankshaft axis to rigidly connect said bearing cap sections (28). 4. An internal combustion engine as claimed in claim 1, wherein the installation base surface (30a, 30b) of each projection (30A, 30B) is located outside of the envelope (M) of the outermost loci of the big end of a connecting rod for the crankshaft. 5. An internal combustion engine as claimed in claim 1, wherein each bearing cap section (28) is in the shape of a plate having two top corner portions which are in contact with said bearing section, and two bottom corner portions which are located opposite to each other with respect to a vertical plane containing the crankshaft axis, in which said first and second projections (30A, 30B) are positioned at said two bottom corner portions, respectively. 6. An internal combustion engine as claimed in claim 1, wherein said first and second projections (30A, 30B) are so positioned that their axes intersect the vertical plane at the same angle. 7. An internal combustion engine as claimed in claim 6, wherein the axes of said respective projections (30A, 30B) intersect each other within said bore for the crankshaft journal. 8. An internal combustion engine as claimed in claim 1, wherein the main bearing cap sections (28) consist of cast iron whereas the struts (32A, 32B) consist of light alloy, such as aluminium.

Inventors: HAYASHI, YOSHIMASA C/O OPPAMA PLANT OF
Applicants: NISSAN MOTOR CO., LTD.
Application year: 1982
Main classification: F02F7
IPC codes: F16M1, F16C35, F16C9, F02F7