GB2153487A - Cast metal connecting rod construction - Google Patents

Abstract

A cast iron connecting rod (1) has a shank (4) of a substantially I-shaped cross section, the structural design of the shank being such that the surface area of the cross-sectional surfaces along the shank, at least in the partial areas, remains the same when the outer contour of the shank varies. The wall thickness of the web (6) of the connecting rod shank (4) varies in the region between the "little end" (small bearing eye 3) and the "big end" (large bearing eye 2) of the connecting rod (1). This measure aids the casting advantage of controlled hardening as hardening will progress from a mid-region A-A of least wall thickness whereby the rapidly hardened region is used as a cooling region for the further hardening of the shank. Thus, the surface area of the cross-sectional surface of the shank (4) remains substantially constant, along part of its length, when the outer contour of the shank varies and hence when the surface/volume ratio changes. <IMAGE>

Description

SPECIFICATION Connecting rod This invention relates to a connecting rod of cast metal and having a shank of substantially I-shaped cross section which interconnects the "little end" and the "big end" of the connecting rod.

A connecting rod is used to transmit linear reciprocation of a moving piston to the crank pin of a rotating crank shaft. In operation, it must stand up to all stresses, i.e. it must not break. In addition, it must be rigid.

The invention has been developed with a view to achieve on the one hand a saving in weight, and on the other hand to permit operation at higher speeds and consequently connecting rods that can accept greater stresses. In order to guarantee the required operational safety of a connecting rod, the shaping, selection of material and the quality of production must satisfy the increased operational requirements that have been set.

Conventional cast iron connecting rods are generally cast with a connecting rod shank of 3 to 5 mm, so that in the cross piece region, because of the slight cooling, shrinkages can only be prevented by costly casting measures.

The present invention seeks to provide a connecting rod which is structurally so designed that the shrinkage volume is considerably reduced.

According to the invention there is provided a connecting rod of cast metal having a small bearing eye at one end and a large bearing eye at an opposite end, and a shank of substantially I-shaped cross section which interconnects the small and large bearing eyes, in which the surface area of the cross-sectional surfaces of the shank, along at least part of its length, remains substantially constant when the outer contour of the shank varies and hence when the surface/volume ratio changes.

A preferred embodiment of connecting rod according to the invention will now be described in detail with reference to the accompanying drawing, in which: Figure 1 is a plan view of the connecting rod; and Figure 2 is a longitudinal section through the connecting rod of Figure 1.

Referring now to the drawing, Figure 1 shows a connecting rod 1 of cast metal (usually cast iron or steel) which comprises substantially a large bearing eye 2 forming the "big end", a small bearing eye 3 forming the "little end", and a shank 4 joining the two bearing eyes together. The connection shank 4 is substantially I-shaped in cross section and has lateral arms or flanges 5 which are joined together over their entire length by means of a wall or web 6.

The wall 6 has a special shaping which can be clearly seen in Figure 2. The wall thickness tapers towards the middle region of the connecting rod shank 4. With this measure, the hardening of the melt in the mould is decisively influenced, namely in that the hardening progresses from the area of the least wall thickness and slowly moves into the greater volume areas. Accordingly, the danger of shrinkage in the shank region is considerably reduced. Thus, the rapidly hardened region is used as a cooling region for the further hardening of the shank.

Provision is made for the shank region to be geometrically shaped so that the surface area of the cross sectional surfaces along at least part of the length of the shank, remains substantially constant, at least in partial areas, when the outer contour of the shank varies and hence when the surface/volume ratio changes. In the preferred embodiment, the surface area remains constant or decreases from the small bearing eye 3 to the point A of the least wall thickness, and proceeding from mid-region A in the direction of the large connecting rod eye 2, the surface area of the cross sectional surfaces remains constant or steadily increases.

With the connecting rod construction as described and illustrated herein, the development of shrinkage in the shank area can be extensively eliminated, in that the controlled hardening is decisively helped by the structural measures described.

1. A connecting rod of cast metal having a small bearing eye at one end and a large bearing eye at an opposite end, and a shank of substantially l-shaped cross section which interconnects the small and large bearing eyes, in which the surface area of the cross-sectional surfaces of the shank, along at least part of its length, remains substantially constant when the outer contour of the shank varies and hence when the surface/volume ratio changes.

2. A connecting rod according to claim 1, in which the surface area of the cross-sectional surfaces along the length of the shank is substantially constant or decreases from the small bearing eye to the mid-region of the shank, and remains substantially constant or increases from the mid-region towards the large bearing eye.

3. A connecting rod according to claim 2, in which the shank has its smallest wall or web thickness in the region of the smallest cross-sectional surface area of the shank or in the region of the longitudinal centre/mid-region of the shank.

4. A connecting rod according to claim 2, in which the surface area of the cross-sectional surfaces of the shank continually decreases or increases along the length of the shank.

5. A connecting rod according to any one of the preceding claims, and in the form of a cast iron or steel casting.

6. A connecting rod according to claim 1 and substantially as hereinbefore described with reference to, and as shown in the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Connecting rod This invention relates to a connecting rod of cast metal and having a shank of substantially I-shaped cross section which interconnects the "little end" and the "big end" of the connecting rod. A connecting rod is used to transmit linear reciprocation of a moving piston to the crank pin of a rotating crank shaft. In operation, it must stand up to all stresses, i.e. it must not break. In addition, it must be rigid. The invention has been developed with a view to achieve on the one hand a saving in weight, and on the other hand to permit operation at higher speeds and consequently connecting rods that can accept greater stresses. In order to guarantee the required operational safety of a connecting rod, the shaping, selection of material and the quality of production must satisfy the increased operational requirements that have been set. Conventional cast iron connecting rods are generally cast with a connecting rod shank of 3 to 5 mm, so that in the cross piece region, because of the slight cooling, shrinkages can only be prevented by costly casting measures. The present invention seeks to provide a connecting rod which is structurally so designed that the shrinkage volume is considerably reduced. According to the invention there is provided a connecting rod of cast metal having a small bearing eye at one end and a large bearing eye at an opposite end, and a shank of substantially I-shaped cross section which interconnects the small and large bearing eyes, in which the surface area of the cross-sectional surfaces of the shank, along at least part of its length, remains substantially constant when the outer contour of the shank varies and hence when the surface/volume ratio changes. A preferred embodiment of connecting rod according to the invention will now be described in detail with reference to the accompanying drawing, in which: Figure 1 is a plan view of the connecting rod; and Figure 2 is a longitudinal section through the connecting rod of Figure 1. Referring now to the drawing, Figure 1 shows a connecting rod 1 of cast metal (usually cast iron or steel) which comprises substantially a large bearing eye 2 forming the "big end", a small bearing eye 3 forming the "little end", and a shank 4 joining the two bearing eyes together. The connection shank 4 is substantially I-shaped in cross section and has lateral arms or flanges 5 which are joined together over their entire length by means of a wall or web 6. The wall 6 has a special shaping which can be clearly seen in Figure 2. The wall thickness tapers towards the middle region of the connecting rod shank 4. With this measure, the hardening of the melt in the mould is decisively influenced, namely in that the hardening progresses from the area of the least wall thickness and slowly moves into the greater volume areas. Accordingly, the danger of shrinkage in the shank region is considerably reduced. Thus, the rapidly hardened region is used as a cooling region for the further hardening of the shank. Provision is made for the shank region to be geometrically shaped so that the surface area of the cross sectional surfaces along at least part of the length of the shank, remains substantially constant, at least in partial areas, when the outer contour of the shank varies and hence when the surface/volume ratio changes. In the preferred embodiment, the surface area remains constant or decreases from the small bearing eye 3 to the point A of the least wall thickness, and proceeding from mid-region A in the direction of the large connecting rod eye 2, the surface area of the cross sectional surfaces remains constant or steadily increases. With the connecting rod construction as described and illustrated herein, the development of shrinkage in the shank area can be extensively eliminated, in that the controlled hardening is decisively helped by the structural measures described. CLAIMS

1. A connecting rod of cast metal having a small bearing eye at one end and a large bearing eye at an opposite end, and a shank of substantially l-shaped cross section which interconnects the small and large bearing eyes, in which the surface area of the cross-sectional surfaces of the shank, along at least part of its length, remains substantially constant when the outer contour of the shank varies and hence when the surface/volume ratio changes.

2. A connecting rod according to claim 1, in which the surface area of the cross-sectional surfaces along the length of the shank is substantially constant or decreases from the small bearing eye to the mid-region of the shank, and remains substantially constant or increases from the mid-region towards the large bearing eye.

3. A connecting rod according to claim 2, in which the shank has its smallest wall or web thickness in the region of the smallest cross-sectional surface area of the shank or in the region of the longitudinal centre/mid-region of the shank.

4. A connecting rod according to claim 2, in which the surface area of the cross-sectional surfaces of the shank continually decreases or increases along the length of the shank.

5. A connecting rod according to any one of the preceding claims, and in the form of a cast iron or steel casting.

6. A connecting rod according to claim 1 and substantially as hereinbefore described with reference to, and as shown in the accompanying drawing.