GB2164389A

GB2164389A - Crankcase for a multi-cylinder piston engine

Info

Publication number: GB2164389A
Application number: GB08522484A
Authority: GB
Inventors: Otmar Andres
Original assignee: MAN Maschinenfabrik Augsburg Nuernberg AG
Current assignee: MAN AG
Priority date: 1984-09-11
Filing date: 1985-09-11
Publication date: 1986-03-19
Also published as: GB8522484D0; SE8504047L; FR2570128A1; IT1185670B; ZA856904B; SE8504047D0; IT8522025A0; KR860002645A; JPS61123749A

Abstract

A stiffening frame (9) with cross members (10) is provided below detachable crankshaft bearing caps (7). In order to reduce noise emission, the frame only contacts and is connected to a flange of the crankcase (5). The frame may be integral with the oil pan (17). <IMAGE>

Description

SPECIFICATION Crankcase for a multi-cylinder piston engine This invention relates to a crankcase for a multi-cylinder piston engine.

A crankcase is disclosed in German Patent No. 22 21 804 in which a so-called stiffening girder is provided in the space enclosed by the crankcase and the oil pan to stiffen the crankshaft bearing shells. This stiffening girder extends the full length of the crankshaft and is firmly attached to the bearing caps.

The stiffening girder bears against the caps of the crankshaft main bearings and is attached to the crankcase directly via skirts extending downwards on both sides of the bearing shells. There is a further connection to the crankcase by means of additional bearing cap attachments. The stiffening girder may also be constructed as a flat intermediate plate formed with openings and, at its underside, with transverse ribs.

In addition to stiffening the bearing shells, the intention is also to reduce engine noise, in as much as individual loading forces to which each bearing is exposed are absorbed and distributed between adjacent bearings.

The drawback of this arrangement is that it is not possible to avoid the transmission of air-borne and structure-borne noise, which is emitted by the engine, e.g. by the "soft" side walls of the crankcase which are excited to vibrate on the contrary the noise transmission tends to be amplified because screwing the girder to the crankcase bearing caps creates an additional bridge for structure-borne noise from a strong noise source (crankcase and bearings) to the side walls. Moreover, the fact that the stiffening girder contacts, or is screwed to, the bearing caps may give rise to bearing constraint which is liable to cause excessive wear or even seizing of the bearings.

An object of the present invention is to provide a crankcase for an engine which reduces noise emission and avoids the above-mentioned drawbacks, and which can also be conveniently retro-fitted without expensive modifications of existing production lines, i.e. without any major model changes.

The invention provides a crankcase as claimed in claim 1.

As a result of the stiffening and connection of the crankcase side walls (at the level of the crankcase flange/oil pan flange) by means of the flangeable crankcase yoke with the stiffening cross members, a very good reduction of the noise level of the engine is obtained. The reason is that there is no connection (bearing or contact) of the intermediate member with the bearing caps and the intermediate member is attached only to the crankcase walls. Consequently, neither a direct or an indirect bridge can develop for structure-borne noise between the crankshaft bearings and the crankshaft outer walls. Furthermore, there is no possibility for any bearing constraint developing. Furthermore, the intermediate member can be retro-fitted at any time.

In order to avoid interference with the downwards motion of the connecting rod and balance weights and to minimize the bulk of the engine, the cross member of the intermediate member may be provided only in the region below the crankshaft bearing caps.

According to a further embodiment of the invention, the intermediate member may be constructed as an integral part of the oil pan (possibly in conjunction with dry-sump lubrication) which, in turn, is the subject of excitation of vibrations by the internal combustion engine and thus becomes a noise-emitting source.

The connection of both the intermediate member and the oil pan to the crankcase is effected conveniently by threaded member, extending through the intermediate member.

An embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section through part of a crankcase according to the invention; and Figure 2 is a transverse section through the crankcase of Fig. 1.

In the embodiment shown in the drawings an internal combustion engine has a plurality of cylinders arranged in line. The individual cylinders are provided with pistons 1, which are linked in a known manner by means of connecting rods 2 to the throws 3 of the crankshaft 4. The crankshaft 4 is supported in a crankcase 5 by means of main bearings 6 which are formed with detachable caps 7 for locating the crankshaft in its correct position.

The caps 7 are firmly attached to the crankcase 5 via pedestals by means of screws 8. At a level below the detachable bearing cap 7, there is a stiffening or reinforcing intermediate frame 9 formed with transverse connections (cross members 10) which are all provided only below the crankshaft main bearing caps 7. Thus, the connecting rods 2 with their bolts and balance weights can plunge unhindered into the free spaces 11 between the cross members 10 as the connecting rods 2 move downwards.

In accordance with the invention, the intermediate frame 9 only contacts a crankcase flange 12 and an oil pan flange 13, the connection to the crankcase 5 being effected only adjacent the flanges 12, 13 through fastening means 14 attaching the oil pan to the crankcase 5. As can be seen from Fig. 1, a seal cover 15 for the crankshaft 4 may be attached to respective ends of the crankcase 5 provided this cover extends down to the crankcase flange 12. the attachment is by means of screws 14 which extend through the intermediate frame 9.

Contact between the cross members 10 and the main bearing caps 7 or bearing screws 8 is avoided by the provision of cut-outs or drilled recesses 16 in the cross members 10.

The intermediate frame 9 described stiffens and cross-ties the crankcase side walls while avoiding the existence of additional bridges for the transmission of structure-borne noise to the crankcase side walls. Consequently, noise control is improved.

It is conveniently possible to integrate the intermediate frame 9 with the oil pan 17 which, in turn, is subject to the excitation of vibrations by the internal combustion engine and thus becomes a noise-emitting source.

In conclusion, it should be mentioned that in view of its design, method of attachment and thickness (about 25 mm thick) the intermediate frame 9 described (which preferably consists of a rugged iron or steel casting) lends itself for retro-fitting, as an accessory item as it were, for noise control without the need for any major changes to the crankcase casting.

Claims

1. A crankcase for a multi-cylinder piston engine in which a crankshaft is removable in a downwards direction and comprising a reinforcing intermediate member arranged below detachable crankshaft bearing caps contiguous with an oil pan, wherein the intermediate member is provided with cross members, and contacts a flange of the crankcase and a flange of the oil pan only, the intermediate member being attached to the crankcase only adjacent the flanges by means fastening the oil pan to the crankcase.

2. A crankcase as claimed in Claim 1, wherein the cross members of the intermediate member are provided only below the crankshaft bearing caps.

3. A crankcase as claimed in Claim 1, wherein the intermediate member is integral with the oil pan.

4. A crankcase as claimed in Claim 1, wherein threaded members extending through the intermediate member and the oil pan fasten the oil pan and the intermediate member to the crankcase.

5. A crankcase for a multi-cylinder piston engine substantially as herein described with reference to the accompanying drawings.

6. An engine having a crankcase as claimed in any one of the preceding claims.