GB2150869A

GB2150869A - Making a connecting rod of cast metal for an internal combustion engine

Info

Publication number: GB2150869A
Application number: GB08430277A
Authority: GB
Inventors: Fritz Mahnig; Gunter Schulte
Original assignee: Georg Fischer AG
Current assignee: Georg Fischer AG
Priority date: 1983-12-08
Filing date: 1984-11-30
Publication date: 1985-07-10
Also published as: ES8601742A1; GB2150869B; GB8430277D0; ES538373A0; DE3444249A1; IT8423836A1; FR2556252A1; IT1178665B; DE3444249C2; IT8423836A0

Abstract

The rod's connecting arm extending between bearing eyes (2, 3) has opposed substantially parallel flanges (7), and is cast with a cooling portion (4, 5) on the flanges (7) which cools and solidifies in advance of the solidification of the bearing eyes (2, 3) and the flanges (7) in order to promote controlled cooling of the bearing eyes and the flanges. Subsequently, at least part of the cooling portion (4, 5) is removed, though a thicker portion (6) may remain as a bridge between the flanges (7). Additionally or alternatively cooling portion(s) may be cast on the outer surfaces of the flanges (7) and removed after solidification and cooling of the rod. For reasons of strength, the small bearing eye may be provided with an oval outer contour. <IMAGE>

Description

SPECIFICATION The casting of a connecting rod This invention relates to a method of making a connecting rod of cast metal for an internal combustion engine, the connecting rod having a small bearing eye at one end, a large bearing eye at its opposite end, and a connecting arm extending between the bearing eyes and having opposed substantially parallel flanges in order to present a substantially I or H shaped connecting arm.

A connecting rod is used to transmit reciprocating motion of a piston to the crankpin of a rotating crankshaft. The invention seeks to provide a method of making a connecting rod of cast metal in such a way as to achieve a saving in weight and also higher operating speeds, which results in more heavy loading of the connecting rod. In order to obtain the required operational safety of a connecting rod, the shaping, selection of material and production quality must satisfy high requirements which are specified.

Conventional connecting rods of cast iron are cast with a connecting arm section of 3 to 5 millimetres, which results in only a small cooling time with consequent risk that a middle cross piece between the flanges of the connecting arm may have cavities formed therein, which can only be prevented by costly casting techniques.

It is known from DE-OS-2 728 994 to make a connecting rod by a casting technique which involves the use of so-called cooling cores which are washed inside by a coolant liquid, in order to achieve a cooling process that is controlled to a greater or lesser degree in the connecting arm region.

The present invention has been developed primarily, though not exclusively, with a view to provide a method for the production of connecting rods of cast metal in which, when there is a constant component strength, the production costs are reduced, on the one hand by a saving in weight and on the other hand by a reduction in the volume of cavity generation, and by optimization of shape.

According to one aspect of the invention there is provided a method of making a connecting rod of cast metal for an internal combustion engine, the connecting rod having a small bearing eye at one end, a large bearing eye at its opposite end, and a connecting arm extending between the bearing eyes and having opposed substantially parallel flanges, and the method comprising the steps of: casting the connecting rod with a cooling portion on the flanges which cools and solidifies in advance the solidification of the bearing eyes and the flanges in order to promote controlled cooling of the bearing eyes and the flanges following hot metal casting of the connecting rod; and subsequently removing at least part of the cooling portion.

According to a further aspect of the invention there is provided a connecting rod of cast metal for an internal combustion engine and which comprises a small bearing eye at one end, a large bearing eye at an opposite end, a connecting arm extending between the bearing eyes and having opposed substantially parallel flanges, and a cooling portion formed on said flanges during casting, in which the cooling portion is arranged to cool and to solidify in advance of the solidification of the bearing eyes and the flanges in order to promote controlled cooling of the bearing eyes and the flanges following hot metal casting of the connecting rod.

The invention will now be described in more detail, by way of example only, with reference to the embodiment illustrated in the accompanying drawing, in which: Figure 1 is a plan view of a connecting rod made by a method according to the invention; and Figure 2 is a side view of the connecting rod of Figure 1.

Referring now to the drawing, there is shown a connecting rod 1 which is made of cast metal, usually cast iron or cast steel alloy, and which comprises a small bearing eye 3 at one end (the "little end") and a large bearing eye 2 at its opposite end (the "big end"). A connecting arm extends between the bearing eyes 2, 3 and has opposed substantially parallel flanges 7 which are joined together by means of a permanent cross piece 6 so as to present a substantially I or H shaped profile for the connecting arm.

As will be described in more detail below, a cooling portion is formed on the flanges 7 which cools and solidifies in advance of the solidification of the bearing eyes 2, 3 and the flanges 7 in order to promote controlled cooling of the bearing eyes 2, 3 and the flanges 7 following hot metal casting of the connecting rod 1.

Thus, as illustrated, a cooling portion is formed by a cooling wall which forms a web which initially interconnects the flanges 7, and which comprises wall portions 4 and 5. The wall portions 4 and 5 are used for the controlled cooling of the connecting rod, in that they cool and harden relatively quickly, thereby to promote subsequent controlled cooling of the bearing eyes 2, 3 and the flanges 7.

Following final solidication of the casting rod 1, at least part of the cooling portion (wall portions 4 and 5) is removed, to present a final form of connecting rod, which may then receive final treatments.

As illustrated, the cooling wall may include a permanent connecting portion in the form of cross piece 6 which remains upon subsequent removal of the remainder of the cooling wall (4, 5). It is not essential to provide the permanent connecting piece 6, though it is usual to provide a connecting piece for reasons of strength. Also for strength reasons the outer contour of the small bearing eye 3 may be oval. Since the inner recess of the bearing eye 3 is circular, it is advantageous to provide the more highly stressed regions with a greater wall thickness, which is of benefit for the overall strength of the component.

In the illustrated embodiment, the web which connects together the flanges 7 extends substan tially throughout the length of the connecting arm during the initial casting. Thereafter, at least the portion of the web adjacent to the large bearing eye 2 is removed, though the entire web may be moved if required. The thickness of the web will be selected according to the composition of the connecting rod.

The illustrated embodiment provides a cooling portion on the flanges 7 by way of the cooling wall portions 4 and 5. However, although not illustrated, an alternative or additional cooling portion may be provided by arranging cooling elements on the outer surfaces of the flanges 7 during casting.

Thus, cooling moulds or cooling shells or plates can be arranged on the outer surfaces of the flanges 7, these also being removed subsequently to present the final form of the casting rod ready for final treatment.

When the flanges 7 are provided with the external cooling portions just mentioned, as well as the internal cooling wall portions 4 and 5, heat is drawn-off (during hardening of the cast metal) on both sides of the flanges 7, in that the internal sides the flanges 7 are cooled via the cooling wall portions 4 and 5 which initially interconnect the flanges 7, and on the outer sides via the external cooling elements.

The removal of desired parts of the cooling portions may be carried out by any convenient means, such as punching. Following removal of the undesired parts of the cooling portions, the entire connecting rod may be strengthened by surface hardening caused by surface bombardment with solid material, such as sand blasting.

A method of making a connecting rod according to the invention enables the weight of the connecting rod to be accurately controlled, whereby the usually subsequently applied balancing weights may be omitted, resulting in a further saving in weight. The method results not only in a saving in weight but also a better output, and additional technical simplifications, in that the monitoring of defects in the connecting arm region can be omitted, or need not be as rigorous as hitherto with known casting techniques. The additional small processing cost, in the removal of the cooling portions, is slight, in comparison with the savings otherwise achieved.

Claims

1. A method of making a connecting rod of cast metal for an internal combustion engine, the connecting rod having a small bearing eye at one end, a large bearing eye at its opposite end, and a connecting arm extending between the bearing eyes and having opposed substantially parallel flanges, and the method comprising the steps of: casting the connecting rod with a cooling portion on the flanges which cools and solidifies in advance of the solidification of the bearing eyes and the flanges in order to promote controlled cooling of the bearing eyes and the flanges following hot metal casting of the connecting rod; and subsequently removing at least part of the cooling portion.

2. A method according to claim 1, in which the cooling portion comprises a cooling wall forming a web which initially interconnects the flanges.

3. A method according to claim 2, in which the web connects together the flanges substantially throughout the length of the connecting arm.

4. A method according to claim 3, in which the thickness of the web is varied according to the composition of the connecting rod.

5. A method according to any one of claims 2 to 4, in which the cooling wall is removed subsequently at least in the region adjacent to the large bearing eye.

6. A method according to any one of claims 2 to 5, in which the cooling wall is removed subsequently throughout its connection to the flanges.

7. A method according to any one of claims 2 to 5, in which the cooling wall includes a permanent connecting portion which remains, upon subsequent removal of the remainder of the cooling wall, in order to connect together the flanges.

8. A method according to any one of the preceding claims, in which the connecting rod is surface hardened after removal of at least part of the cooling portion.

9. A method according to claim 8, in which the surface hardening is carried out by sand blasting.

10. A method according to any one of the preceding claims, in which the small bearing eye is cast with an oval outer contour.

11. A method according to any one of the preceding claims, in which the cooling portion includes cooling elements joined initially to the outer surfaces of the flanges.

12. A method according to claim 11, in which the cooling elements comprise cooling moulds or cooling plates.

13. A connecting rod of cast metal for an internal combustion engine and which comprises a small bearing eye at one end, a large bearing eye at an opposite end, a connecting arm extending between the bearing eyes and having opposed substantially parallel flanges, and a cooling portion formed on said flanges during casting, in which the cooling portion is arranged to cool and to solidify in advance of the solidification of the bearing eyes and the flanges in order to promote controlled cooling of the bearing eyes and the flanges following hot metal casting of the connecting rod.

14. A connecting rod according to claim 13, in which at least part of the cooling portion has been removed.

15. A method according to claim 1 and substantially as hereinbefore described with reference to, and as shown in the accompanying drawing.

16. A connecting rod made by a method according to any one of claims 1 to 12 or 15.