GB2313164A

GB2313164A - Crankcase for an internal combustion engine

Info

Publication number: GB2313164A
Application number: GB9709171A
Authority: GB
Inventors: Klaus Dr Ing Bruchner; Ralf Dipl Ing Kaufmann; Helmut Kronowiecki
Original assignee: Daimler Benz AG; Mercedes Benz AG
Current assignee: Daimler Benz AG
Priority date: 1996-05-17
Filing date: 1997-05-06
Publication date: 1997-11-19
Also published as: GB2313164A8; ITRM970248A0; DE19619974C1; FR2750166A1; ITRM970248A1; GB9709171D0

Description

2313164 Crankcase of an internal combustion c The invention relates to a

crankcase of an internal combustion engine of two-part design with a crankcase top part and a crankcase bottom part, each of which is composed of an aluminium material.

In the past, grey cast-iron designs were often used for crankcases of internal combustion engines. In the last few years, however, increasing use has been made of engine blocks and crankcases of aluminium or an aluminium alloy. With both crankcase designs, factors connected with the characteristics of sliding bearings, especially the expansion of the crankshaft bearing bores during engine operation due to the effects of forces and temperature, dictate that the bearing caps of the crankshaft main bearings should be manufactured from steel or spheroidal graphite iron.

In order to be able to guide the steel or cast iron crankshafts axially, i.e. in the longitudinal direction of the engine, thrust washers are arranged on at least one bearing pedestal of the crankcase. These thrust washers can be socalled two-material supports and generally have an aluminium running surface in conjunction with a steel supporting shell. The thrust washers, which were installed in the bearing pedestal, provided the crankshaft with support via the annular sliding-hearing surfaces at its ends. These thrust washers are also required, inter alia, in order to avoid unacceptable friction pairings such as, for example, steellgrey cast iron and grey cast iron/sphcroidal graphite iron.

DE 26 35 061 has disclosed thrust-washer segments of this kind made ftom solid or composite sliding-bearing material. Crankcase designs which comprise two-part fully aluminium combined cylinder block and crankcases, referred to as bedplate designs have also been disclosed recently. Here, the crankcase bottom part assumes the role of a bearing support in the form of mainbearing caps connected in the manner of a ladder frame.

The present invention seeks to provide a simple and., economical thrustbearing arrangement for a crankshaft that is to be supporied in the crankcase in the case of a crankcase of two-part design with a crankcase top part and case bottom part, each of which is composed of aluminium material.

2 According to the present invention there is provided a crankcase for internal combustion engines of two-part design, with a crankcase top part and a crankcase bottom part, each of which is composed of an aluminium material, the crankcase bottom part forming a bearing support with a plurality of bearing pedestals for supporting a crankshaft, and bearing surfaces being formed in the side faces of at least one bearing pedestal of the crankshaft bottom part to act as axial thrust bearings for the crankshaft.

By virtue of the configuration of a crankcase in a fully aluminium form and in accordance with the bed-plate" principle mentioned above, the crankshaft bearings are completely surrounded by aluminium in the crankcase, in contrast to the conventional construction. In particular, this means that it is no longer necessary to use steel or grey cast iron or spheroidal graphite iron bearing caps. By virtue of the integration according to the invention of the required bearing surfaces for the formation of a thrust bearing for the crankshaft into the crankcase bottom part, separate bearing components and thrust washers are eliminated. The required bearing surfaces are now allowed for in the casting production process itself, the only requirement then being to perform a finishmachining operation to form the actual sliding-bearing running surfaces.

According to the invention, all that is generally required here is to form bearing surfaces in just one half, namely the crankcase bottom part, in contrast to the prior-art configuration, where, generally speaking, separate bearing components for the crankcase top part were provided in addition or exclusively.

A further advantage of the design of the bearing surfaces in accordance with the invention is that, if the bearing surfaces are only introduced into one half of the crankcase, specifically the crankcase bottom part, the profile of the bearing forms a semicircle open at the top (shell" shape, collecting bowl) in which ofi flowing back is stored and thus ensures good bearing lubrication.

Another advantage is that, in con to separate thrust washers, the design of the bearing surfaces in accordance with the invention makes it possible to reduce the quantity of leakage oil by up to half since a leakage gap such as 3 that which appears at the rear of thrust washers is eliminated. This provides increased operational reliability.

Another advantage is that the integrated thrust bearing provides high reliability of assembly and ease of assembly. Finally, there is no longer any need to introduce the loose thrust washers carefully and separately, with the risk that they will fall out or be displaced during assembly.

In con to conventional bearing caps in cases, the bearing surface formed in the crankcase bottom part and the resulting thrust bearing are provided with significantly more rigid support against axial forces exerted by the crankshafL In the case of conventional bearing caps which are not integrated into the crankcase bottom part, there is a relatively high bending flexibility in the axial direction, providing a relatively small component of support for the thrust bearing.

It is furthermore possible, by means of the integrated bearing surfaces according to the invention to achieve a wore precisely defined axial play for the crankshaft since the flatness and evenness tolerances of separate flat thrust washers are eliminated.

Advantageous embodiments of the invention will now be described below in principle with reference to the drawing, in which:- Fig. 1 shows, in a detail view, a cross-section through the crankcase bottom part according to the invention, Fig. 2 shows a section along the line II-II in Fig. 1, Fig. 3 shows a plan view (as a fragmentary view) of Fig. 1 from the direction of arrow X, and Fig. 4 shows a section similar to that shown in Fig. 2 but in a different configuration.

Fundamentally, the crankcase is of known construction, for which reason only a fragmentary view of a crankcase bottom part 1 with the parts essential to the invention is illustrated. The crankcase bottom part 1 has a plurality of axially spaced bearing pedestals 2 for the purpose of supporting a crankshaft (not shown). To form a thrust bearing for the crankshaft, it is 4 generally sufficient if corresponding thrust bearings are provided for this purpose on both sides of one bearing pedestal 2. To achieve this end, the unfinished cast profile of the aluminium crankcase bottom part 1 already has semi- annular bearing surfaces 3 and 4, in which all the special features typical of sliding thrust bearings can be allowed for.

All that is required is to improve the surface finish of the surface perpendicular to the longitudinal axis of the crankshaft by simple machining in such a way that sliding bearing surfaces are formed. On the unfinished profile, it is a simple matter for radial running-surface boundaries to be provided on the inner and outer radius. The niinning-surface boundaries 5 and 6 can be seen from Fig. 2. The radial running-surface boundary allows a certain freedom in the determination and execution of the profile and shaping of the actual bearing surfaces 3 and 4. The machining surface for the formation of the sliding-bearing surfaces is illustrated in Fig. 1 by hatching.

From this figure and also from Fig. 3, it can be seen that oil lubrication grooves 7 or oil lubrication pockets ruiming perpendicularly downwards are provided in the bearing surfaces 3 and 4. Care should be taken here that the depth of the oil lubrication grooves 7 is such that they are still there even after the machining of the bearing surfaces. Oil for lubrication can enter the oil lubrication grooves 7 from above, thereby ensuring even better lubrication of the bearings. Chamfers 8 on the bearing surfaces 3 and 4 at the entry to and exit from the semi- annular bearing surfaces in the region of the split in the crankcase er optimize the entry and exit of oil into and out of the sliding thrust bearing formed by the bearing surfaces 3 and 4. The chamfer 8 is in each case directed towards the centre of the bearing pedestal and can, for example, be at an angle of 15'. The chamfer 8 furthermore serves as a slope to assist the installation of the crankshaft. This avoids scratching of the crankshaft-bearing location during the insertion of the crankshaft. As can be seen from Fig. 2, the bearing pedestal 2 is wider at the bottom than at the top, or the bearing pedestal 2 thickens from the top downwards. This results in a mould-release slope to assist removal after the casting of the crankcase bottom part 1. The mould-release movement is in the upward direction.

In contrast, Fig. 4 shows a development, the bearing pedestal 2 being wider at the top, resulting in a downward mould-release slope.

From Fig. 4, in which a crankcase top part 9 has also been drawn in a fragmentary view, it can also he seen that the width bOT of the bearing pedestal 2' in the crankcase top part 9 is less than the width bUT in the crankcase bottom part 1. This choice of widths avoids static indeterminacies. During the assembly of the crankcase top part 9 and the crankcase bottom part 1, small axial offsets can occur between them. Axial offsets of this kind can be compensated for' by means of the choice of width in accordance with the invention.

In con to the configuration shown in Fig. 2, where the bearing surfaces 3, 4 are formed in an offset in the bearing pedestal 2, the bearing surfaces 3. 4 in Fig. 4 are formed in thickened portions of the bearing pedestal 2.

6

Claims

1. A crankcase for internal combustion engines of two-part design, with a crankcase top part and a crankcase bottom part, each of which is composed of an aluminium material, the crankcase bottom part forming a bearing support with a plurality of bearing pedestals for supporting a crankshaft, and bearing surfaces being formed in the side faces of at least one bearing pedestal of the crankshaft bottom part to act as axial thrust bearings for the crankshaft.

2. A crankcase according to Claim 1, wherein the bearing surfaces are provided with radial running-surface boundaries.

3. A crankcase according to Claim 1 or 2, wherein the bearing surfaces are provided with oil lubrication grooves formed in the side faces of the bearing pedestal.

4. A crankcase according to any one of Claims 1 to 3, wherein the axial width of the bearing pedestal in the crankcase bottom part is in each case greater than the axial width of the respectively associated bearing pedestal in the crankcase top part.

5. A crankcase according to any one of Claims 1 to 4, wherein chamfers which are directed inwards - relative to the bearing pedestal - are provided at the entry to the semi-annular bearing surfaces, in the region of the split in the crankcase.

6. A crankcase according to any one of Claims 1 to 5, wherein the crankcase bottom part has mould-release slopes such that the width of the bearing pedestals increases from the top downwards.

7 7. A crankcase according to any one of Claims 1 to 5, wherein the crankcase bottom part has mould-release slopes such that the width of the bearing pedestals decreases from the top downwards.

8. A crankcase for internal combustion engines of two-part design, substantially as described herein with reference to, and as illustrated in, the accompanying drawing.