WO2002075171A1

WO2002075171A1 - Conrod and a method of producing the same

Info

Publication number: WO2002075171A1
Application number: PCT/IN2001/000039
Authority: WO
Inventors: Sankaranarayanan Ashok
Original assignee: Sundram Fasteners Limited
Priority date: 2001-03-16
Filing date: 2001-03-16
Publication date: 2002-09-26

Abstract

The present invention relates to a novel conrod connecting a piston or cross head to the crank in a two or four stroke internal combustion engines, said conrod comprising a stem inter linking two connecting means in the form of a big circular end and a smaller circular end, wherein the stem having a density of material in the range of 7.4 to 7.8 gm/cc and the connecting means having a density of material in the range of 6.7 to 7 gm/cc.

Description

CONROD AND A METHOD OF PRODUCING THE SAME

Technical Field

The present invention relates to a novel powder metallurgy connecting rod (conrcd) for two wheelers and a method of manufacturing the conrod. Particularly, the present invention is for manufacturing conrod for two wheelers such as Motor cycles, Scooters and Mopeds.

Background of the invention

Conrod is a device connecting the piston or crosshead to the crank. The conrod has two connecting ends (big end and small end) or connecting means for connecting the conrod to the respective parts of the piston, and middle connecting part or stem.

Connecting rod converts the reciprocating motion of the piston into a circular motion. It is subjected to pressure loads from the exploding gas and loads due to reciprocating the rotating mass. The stem of the conventional Connecting rods is formed as a " I " section as basically the connecting rods behave as a beam column. The big end of the connecting rod is connected to the crankshaft and the small end to the gudgeon pin. Both these ends are hardened by carburaisation, quenching and tempering steps. For a two wheeler connecting rod, the ends are integral with its stem.

Conrods were historically produced using cast or wrought steel till about two decades ago. Powder Metallurgy (P/M) is a new technology used for use in fabrication of high quality complex parts to close tolerances in an economical manner came into vogue in the '70s. The Key steps in P/M include blending of powders, compaction of the same to required shape and sintering when bonding of particles takes place to provide the required mechanical properties. Secondary operations like sizing, coining, re-pressing etc. are also employed depending upon the requirements of the product. Many efforts have been made in the recent past in developing P/M connecting rod. Initially, P/M forged connecting rods were put into practical usage. However, since P/M forged connecting rods were costly due to the forging operation involved, connecting rods produced by conventional P/M technology were being proposed in the recent past.

Prior art references

Conventional technology for production of conrod uses wrought steel or P/M forged steel and the final product has uniform density. In both the cases, the focus is on meeting the fatigue properties as conrod encounters cyclic loading and the fatigue properties limit the life of the product. The research conducted to date in this area is also restricted to four wheeler conrod where the stress conditions are very high. Hence, high uniform density is required for the conrod.

Growth of P/M industry

Powder metallurgy, in its earliest form actually involved powder forging as in Delhi Iron Pillar. Mechanical working of metal powders is probably the oldest example of metalworking. Limitations on a) mass production of good quality powders and b) continuous high temperature furnace for sintering resulted in P/M industry to grow fast, as it is ideally suited for production of automotive parts. Production of self-lubricating bronze bearings, which has the advantage of both controlled porosity and net shape manufacturing, triggered acceptance of P/M in 1930s. Extension of this technology to structural parts from steel powders was responsible for P/M industry's growth in 1940s.

The growth of nuclear power generation in the 1950s also prompted considerable effort in powder densification, such as forging of encased beryllium or metal ceramics, in addition to the extrusion of nuclear fuel rods.

Through, the late '60s and early '70s, extensive use of conventional P/M products in automotive applications started but essentially for non-critical parts. At this time, concentrated research in powder forging of connecting rod was conducted in response to the need for enhanced density and strength requirements for this part. Several industrial and university labs initiated R&D programs on powder forging. As a result, a large amount of information and data began to appear in technical papers and a high level of fundamental understanding emerged. Production of stator cams, bevel pinion, side gears were produced by powder forging in the '70s. Gears exceeding 99% of full density were successfully produced at the rate of 900per hour by Delco Morriane division of General Motors in 1968. In the late '70s high tonnage and cost saving potential of powder forging for the production of automotive connecting rods has attracted high intensity efforts. American automobile manufacturing giants General Motors and Ford were successful in developing powder-forging process for connecting rods.

Conventional PM Connecting Rod

Even though powder forged connecting rods have been used for many years economics production can be improved if conventional PM technology is used. The area of research was stated in the late 80s and 90s as better powders and compaction technology improvements were made.. The first investigation was made using the mixed alloy Fe+1.5%Cu+0.5%C, with additional heat treatment and a minimum density of 7.0 g/cc by Sonsino. [Sonsino,C.M. Fatigue design of sintered connecting rods. Part 1: Metal Powder Report 43 (1988) n 5 pp 332-337 Part 2: Metal Powder Report n 6 pp 408-412] The emphasis of this investigation was to manufacture by an economic single sintering technology with subsequent heat treatment. He also optimized the design regarding the distribution of stresses and manufacturing method. Connecting rods capable of engine speeds up to 7000 rpm could be made by single compaction and sintering technique as proposed by Weber (Weber M. Comparison of advanced procedures and economics for production of connecting rods. Powder Metallurgy International 25 (1993) No 3 ,pp 125- 129).According to the authors, the fatigue limit of such connecting rods is comparable to that of conventionally manufactured, cast and forged connecting rods. The attraction of using conventional P/M technology lies in the fact that the connecting rods are almost ready for assembly with a close weight tolerance, which eliminates the need to sort by weight, the balancing operation and maintenance of expensive stocks. The diffusion alloyed sintered steel Fe+1.75%Ni+1.5%Cu+0.5%Mo+0.5%C and 0.5%MnS was used to attain a uniform density of 7.2g/cc and also to optimize the machinability by K.Richter et al. [ K.Richter et al, Single sintered con rods — an illusion?, Metal Powder Report (1994) n X, pp 38-45] They also suggested that considerable increase in density could be obtained by dual-fill technique. Real time engine tests were also performed and fatigue life of conventional P/M connecting rods were comparable to that of cast and powder forged connecting rods. They also suggested that fatigue strength could be improved by combining high temperature sintering and subsequent shot peening. They indicate that single sintered connecting rod are no longer an illusion. Suzuki et al worked on designing conventional P/M connecting rod by means of the combination of high strength low alloy steel powders and the modified shape which is easy to compact and has low stress concentration. [Suzuki et al., Development of As-Sintered P/M Connecting road for automobiles SAE, pp 2.87-2.93 (1989)] They used Finite Element Method to find out the optimized shape trough elastic stress analysis. They produced conventional P/M connecting rods and these were tested real time. They mentioned that the fatigue life of conventional P/M connecting rod was sufficient. However, no progress was made in the development of conventional P/M connecting rod due to economic reasons and presently programs are in Europe to increase the overall density of the conrod by such new processes as warm compaction^ D.Whittaker, Current and future forces driving Automotive P/M, Metal Powder Report (2000) PP 22-27). . Recent research by P.K. Jones et al indicate that the conrod requires high core density as it has to meet the high elastic modulus requirement of the application. [P.K. Jones et al Developing P/M gear tooth and bearing surfaces for high stress applications, Proceedings of the 1997 International Conference on Powder Metallurgy & Particulate Materials, MPIF, Princeton, NJ.] They use high temperature sintering to achieve the high-density requirements. The European and Japanese research also are focused on high uniform density (J.M Capus, Automotive P.M in the new millennium - Metal Powder Report -2000 n 5, PP 18-20)

Though, various automotive parts have been manufactured employing powder metallurgy technique, yet conrod for two-wheelers using powder metallurgy technique has not yet been envisaged. Till date, using powder metallurgy technique is discouraged and considered unsafe for manufacturing conrod for two-wheelers. In addition, so far, the prior art in manufacturing conrod teach against the use of powder metallurgy technique and also the technique of selective densification of P/M conrod. (Developing P/M gear tooth and bearing surfaces for high stress applications - P.K. Jones, K. Buckley-Golder, D. Sarafinchan - Proceedings of the 1997 International Conference on Powder Metallurgy & Particulate Materials, MPIF, Princeton, N J)

Conventional technology for production of two wheeler conrod is to produce approximate shape by hot forging of low carbon steel. Then this conrod is extensively machined to required dimensions. The conrod is then selectively carburized and quenched and tempered. The above method is time consuming, cumbersome and expensive.

Objects of the invention

The main object of the invention is to provide a conrod with differential density wherein the stem or mid portion of the conrod having high density and the bore areas having low density (small end and big end).

Another object of the invention is to provide a conrod having differential density in order to minimize its weight and at the same time avoid elastic deformation and reduction in vibration.

Still another object of the invention is to provide a conrod using powder metallurgy thereby eliminating costly and cumbersome step in machining.

Yet another object of the invention is to provide a conrod wherein selective densification of the stem of the conrod alone is carried out to match the elastic deformation of the stem of wrought conrod. Yet another object of the invention relates to a method of producing a novel conrod using powder metallurgy technique.

Yet another object of the invention relates to a method of manufacturing a novel conrod having selective densification at its stem region.

Summary of the invention

To meet the above objects and others, the present invention provides a conrod comprising a stem ending with connecting means suitable for connecting the conrod with crankshaft and gudgeon pin, the coimecting means having bores, and the said stem being highly densified by selective densification sufficient enough to withstand the load applied on it, and the bore areas being lower density in order to reduce the weight and vibration of the conrod. Detailed description of the invention

The conrod of the present invention has two connecting means or bore areas having low density matter (alloys) and a stem having high-density matter connecting the means/bore areas. The applicants have recently found that the working load of the conrod is always higher in the stem area than the bore areas of the conrod. The above finding made the applicants to investigate various methodologies to improve the conrod per se and a method of producing the conrod. After much research, and trial and error, the applicants have invented a solution to solve many problems encountered in the prior art conrods and their production. The applicants, indeed, selectively densify various parts of conrod keeping their recent findings that the working load of the conrod is always more in the stem area than the bore areas of the conrod and evolved/constructed a novel conrod and a method of producing the conrod.

In an embodiment of the present invention, a novel conrod is produced by using powder metallurgy technique.

One more embodiment of the invention provides a conrod produced by powder metallurgy, having one or more slots in the stem region.

In another embodiment of the present invention, a method of producing a novel conrod using powder metallurgy technique, said method comprising: a) providing an alloy essentially comprising Fe with carbon in the range of 0.4 - 0.8% by weight and the remaining elements, with a maximum of 3% by weight, selected from Cu, Ni, Mo, Cr, Mn, Pb, S , P or mixtures thereof and in case of selective densification by infiltration, the Cu or Pb can be upto 25 % by weight, and lubricant such as zinc stearate upto 0.1 % by weight to protect the die, b) providing a suitable die, c) filling the die with alloy powder as defined above, d) compacting the alloy powders under a pressure range of 4 to 8 tons/cm² and at a temperature up to 250° C, and e) sintering the compacted material at 1050-1250°C for a period of 10-60 minutes and optionally, allowing Cu or Pb of about 15 to 25% by weight to be infiltrated in the stem region and if desired, the selective infiltration of

Cu or Pb can be repeated under the same condition. In still another embodiment, the method of producing the conrod includes providing an alloy essentially comprising Fe in the range of 0.4 - 0.8% by weight and the remaining elements can be selected from Cu, Ni, Mo, Cr, Mn, S & P of maximum 3% by weight Cu may be higher (upto 20%) if selective densification by infiltration is used.

In yet another embodiment of the present method, a suitable die is provided in which the materials used to produce the alloy are in the form of powder is filled with and the alloy material is compacted under a pressure range of 4 to 8 tons/cm² using top and bottom punches and core rods.

Still another embodiment of the present method provides sintering the compacted material at 1050-1250°C for a period of 10-60 minutes. Cu may be infiltrated selectively during the sinter process. If desired, the selective infiltration of Cu can be carried out under a separate sinter step under similar condition.

In one another embodiment of the present method, the sintered conrod can be sized in a manner known per se to meet the dimensional accuracy.

Still another embodiment of the present method, the sintered conrod can be subjected to machining or grinding operations such as double disc grinding to meet the dimensional accuracy.

Yet another embodiment of the present method is the big and small ends are induction hardened to meet the hardness requirement and also to avoid wear resistance. In another embodiment of the present method, the wear resistance to the conrod can be increased by fixing a heat-treated bush, press fitted on the inside of the hubs.

One embodiment of the present method, the selective densification can be performed by double compacting and double sintering of the alloy in a die, wherein the first sintering is performed at a temperature below 950°C selectively re-compacted in the stem area and re- sinter at 1120°C to 1250°C.

In another embodiment of the present method, the sintered part may be spheroidize annealed such as quenching and tempering, long term sub-critical annealing, cooling slowly from austentic condition, and the product is sized to higher density only in the stem area.

In one more embodiment, the invention provides a method of producing conrod by selective densification, said method comprising the following steps:

(a) providing a die for manufacturing the conrod,

(b) filling the die with pre-determined powder mixture,

(c) compacting the powder mixture under pressure, preferably under temperature up to 250° C, (d) placing a compact of infiltrate material factor-copper or lead at stem region of the conrod, and (e) sintering the entire structure under temperature and pressure to produce the conrod.

Yet another embodiment of the invention relates to the above method wherein, the step of sintering can be performed before step (d) of the process.

Still another embodiment of the invention relates to a method wherein, the conrod is subjected to induction hardening, i.e., heating the conrod at 900° C+ and rapidly cooling the conrod, to improve the wear resistance.

Further embodiment of the invention provides a conrod having a weight reduction to the extent of 5 to 9% from that of conventional wrought conrod.

The starting material to be used in the present invention is a blend comprising Fe powder + 0.6% graphite +0.8% Zn sterate as lubricant, which is compacted in a die at a pressure of 5.3 Tons/cm² sintered at 1120°C to 20 minutes. 1. Infiltration of copper in the stem area alone was conducted 20% by weight by placing copper infiltration material. At 1120°C, copper melts and spreads inside the compact and fills the pores to result in majority of the pores being fully dense ( density > 7.4 gm cc)

2. When double compacting double sintering process is used, the first compacting step produces a green part with the density in the range of 6.7-7 gm/cc. The green compact is then sintered at a temperature at 950°C where carbon does not diffuse fully but iron powders bond with each other. Lubricant is also removed. This part is then re-pressed only in the stem area to 7.4 gm/cc and then sintered at 1120°C or above to obtain full mechanical properties.

3. Single sintered product at 1120°C for 20 minutes cannot be sized to higher density if the carbon level is high due to its high strength because of carbide formation. If the carbides are modified to spheroids, ductility is high and strength is low and so can be more easily plastically deformed. This technique is extensively used in cold forming of steels. The same technology can be used for densification of PM part. Typically, the sintered PM part will be held at 700-720°C for 10-16 hours to convert all carbiders to spheroids. Then the product can be selectively sized to higher density.

Brief description of the accompanying drawings

Figure 1 shows wrought conrod.

Figure 2 shows PM conrod of the present invention. Figure 2(a) shows PM conrod of the present invention having different construction.

Figure 2 (b) shows single level P/M conrod with three ribs

Figure 2 (c) shows single level P/M conrod with box section

Figure 2 (d) shows single level P/M conrod with fully solid box section

Figure 2 (e) shows double level P/M conrod with no rib Figure 2 (f) shows three level P/M conrod with I section

Figure 3 shows Von Mises stress distribution for pressure load.

Figure 4 shows displacement distribution for pressure load.

Figure 5 shows Von Mises stress distribution for tensile loading at crank angle of 0°.

Figure 6 shows displacement distribution for tensile loading at crank angle of 0°. Figure 7(a) shows Von Mises stress distribution for bending at crank angle of 45°. Figure 7(b) shows Von Mises stress distribution for tensile loading at crank angk of 45°. Figure 8 shows buckling load factor

Figure 9(a) shows Von Mises stress distribution for pressure load Figure 9(b) shows Von Mises stress distribution for pressure load ( enlarged) Figure 10 shows displacement distribution for pressure load on the P/M conrod

Figure 11 shows Von Mises stress distribution for tensile loading at crank angle of 0° Figure 12 shows Von Mises distribution for combined loading <

Figure 13(a) shows Von Mises stress distribution for bending at crack angle at 45° Figure 13(b) shows Von Mises stress distribution for tensile loading at crack angle of 45° Figure 14 shows bucking load factor on the P M conrod

Figure 15(a) shows solid model of ther assembly near the TDC with the forged conrod Figure 16(a) shows solid model of the assembly near the TDC with PM conrod Figure 16(b) shows solid model of the assembly as the piston approaches TDC with PM conrod Figure 17 shows big end X direction force for forged conrod and P/M conrod

Figure 18 shows big end Y direction force for forged conrod and P/M conrod

Figure 19 shows small end X direction force for forged conrod and P/M conrod

Figure 20 shows big end resultant force for forged conrod and P/M conrod

Figure 21 shows small end Y direction force for forged conrod and P/M conrod

Figure 22 shows small end resultant force for forged conrod and P/M conrod Figure 1 of the drawings shows the conventional conrod made of wrought iron. In this figure, a stem (1) connecting two connecting means which are in the form of a small and big circular parts (2 and 3). The stem and the small and big ends i.e. the entire conrod is made of material having uniform density and the conrod is quite heavy. As opposed to the above conventional conrod, the present invention (Fig.2) provides a lighter but effective conrod wherein the density of material at the stem portion (4) is higher than the density of the material at the smaller (5) and bigger (6) ends of the conrod.

In a preferred embodiment of the invention, the stem may have one or more slots as shown in Fig. 2 to reduce the weight; the stem has one or more bridge(s) located between the slots, which bridge(s) provide resistance against bending and twisting. In addition, the bridge(s) imparts stability and strength while in use and save expensive raw material.

In another embodiment of the invention, the stem may have a single elongated oblong slot at its centre as illustrated in Fig. 2(a) of the drawings. Depending on the type of vehicle, various other designs for the conrod are possible. If the stresses on the conrod are low, one can remove more material but have more ribs as in Fig 2b. If the stresses are extremely high, the conrod has to be produced without any holes (Fig 2c) and the gain in weight reduction is there due only to the use of low-density l aterial in the big and small ends.

In some instance, the crankshaft is designed with projections, which can interfere with the motion of the conrod. Then the design can be changed as shown in Fig. 2d. This design requires a more complex tooling to be used for the compaction compared to the previous design. In this design also, further weight reduction is possible by incorporating a slot (Fig 2e) or holes etc., Lastly, as shown in Fig 2f, a multi level conrod.

The connecting rod is a reciprocating component in an engine. Design of lightweight reciprocating parts in an engine can reduce the vibration level of the whole system. Torsional vibrations in engine arise due to the periodic combustion forces in the cylinder and the associated inertial forces of rotating and reciprocating members such as crankshaft, the camshaft, piston and the connecting rod. A. Boysal et al did a detailed iulti-body numerical model of a single cylinder IC engine [A. Boysal et al., Tosional vibration analysis of a multi-body single cylinder internal combustion engine model, Apl. Math. Modelling, 1997, n 21, pp 481-493]. Multi body dynamics in engine design reduces the conceptual design and development cycle time and removes the need for extensive engine testing which accounts for a considerable cost in engine design and development process.

This technique was used for determining the stress in a two wheeler connecting rod and then extended to designing of a PM connecting rod.

The following description has been added as an illustration in order to understand the invention clearly. This description should not be construed to limit the present invention in any manner.

Modeling and Stress analysis of forged conrod

The existing forged connecting rod was modeled in CAD package SDRC/1-deas taking into account all the geometric features of the rod. The connecting rod has three distinctive features, namely, the small end, the stem and the big end. The solid model of the connecting rod is shown in Fig. 1. In the assembly the small end is connected to the piston through the gudgeon pin and the big end to the crank pin of crankshaft. The loading on a connecting rod has to be evaluated properly for the analysis to be performed. The major load is due to the explosion of gas mixture, which occurs during the power stroke. The forces due to the gas pressure in the cylinder can be taken as a force P on the piston and an equal and opposite force (-P) on the cylinder head. The force P is transmitted through the connecting rod to the crank pin and is felt at the main bearings.

The other forces acting on the connecting rod are due to the reciprocating masses (including the piston, gudgeon pin and a part of the connecting rod) and due to the rotating mass at the crankshaft end. The load calculations are included in the appendix 1.

The forged connecting rod was modeled by Finite element analysis to determine the stresses and displacements due to the maximum loading conditions. A very fine mesh with tetrahedral elements was used to capture the stress concentrations effectively. The mesh contains 21972 elements and 5512 nodes.

The big end of the connecting rod was fixed and a pressure load of 14322 N was applied at the small end over an arc of 180°C. The Von Mises (equivalent) stress distribution is shown in fig. 3. As can be seen from the figure, a maximum stress of 26.5 Kgf/mm² exists near the small end. The displacement profile shown in Fig.4 has a maximum value of 71 microns. As indicated before, another important loading condition in a connecting rod is due to the inertia of the reciprocating mass. The load is vertical when the piston reaches the TDC and results in tensile force. The Von Mises stress for such a loading is shown in Fig.5. The maximum stress happens to be 7.8 Kgf/mm² and is at the outer radius near the gudgeon pin position. The displacement profile for this loading is shown in Fig. 6. The maximum displacement can be seen to be 19 microns. Note that when looked at vertical direction stresses the gas pressure results in negative stress and the reciprocating load induces positive load. The stress distributions due to reciprocating mass at a crank angle of 45 degrees are shown in figures 7a and 7b. Figures 7a and 7b depict values for the horizontal component and the vertical component respectively. The loads are mentioned in appendix 1.

To determine, the buckling load factor, buckling, analysis was performed using SDRC/1- deas and the load factor was estimated as 3.3 (Fig.8)

Design & Stress analysis of PM conrod

The PM connecting rod has to be designed taking into account the feasibility of the design through PM process, the total mass of the connecting rod, the dimensional tolerances, thickness at the ends and the center to center distance between the ends. Conventional connecting rods have I section so as to minimize its weight and at the same time maintain sufficient bending modulus. In the PM part vertical slots are possible to reduce the weight and different section has to be tried out so as to have sufficient bending modulus. Simulations of various designs were tested and it was found that single cross beam would suit the present requirements but if the stress conditions are different then the design has to be changed.

The connecting rods designed for compact - sinter - size route has entirely different profiles and is shown in Fig.2. Figure 2 provides a few examples of conrod of the present invention, having different profiles. Figure 2(a) illustrates P/M conrod of the present invention having different construction, Figure 2 (b) illustrates single level P/M conrod with three ribs, Figure 2 (c) illustrates single level P/M conrod with box section, Figure 2 (d) shows single level P/M conrod with fully solid box section, Figure 2 (e) shows double level P/M conrod with no rib and Figure 2 (f) shows three level P/M conrod with I section. With this design, the existing connecting rod has a weight of 162 gms, was redesigned to have a weight of about 152 gms. The invention could easily provide weight reduction of the conrod to the extent of 5 to 9 % from that of the existing wrought conrod. Selective Copper infiltration is assumed for the P/M connecting rod and the densities assumed are given in Fig 2. Selective densification by suing copper infiltration is proposed so as to meet the elastic deformation of the conventional connecting rod.

Finite element analysis was conducted using eight noded hexahedron elements with model containing 4490 elements and 6420 nodes. The Mises stress due to the pressure load is shown in Figs. 9a and9b and the corresponding displacements in Fig. 10. Displacement is of the same order as that of the forged connecting rod and the Maximum compressive stress is marginally less at 22 Kgf mm². The Young's modulus assumed are 1.45468e+ll

N/ mm²(ends) and 1.921 le+11 N/ mm (stem).

Fig.11 shows the stress distribution due to the mass of the reciprocating components at crank angle of 0°. Though the stresses are higher, the region at which it is high is at the gudgeon pin location and is due to contact forces. The stress at the stem has a maximum stress of 3 Kgf/mm². The stress distribution for the combined loading due to a positive load because of the reciprocating mass and a negative load due to gas pressure is shown in

Fig. 12. From these two figures it can be safely concluded that the maximum stress variation is between -12Kgf/mm² to +9Kgf/mm², other than the contact point which from the available fatigue data seems to be well within the allowable range. [F.J. Esper and

CM. Sonsino, "Fatigue design for P/M components", EPMA Publication, England, 1994, pp. 54-60]

Stress distributions, when the angle of inclination of the crankshaft is 45° for horizontal and vertical loading are shown in Fig. 13a and b respectively.

Buckling analysis is important in a connecting rod, as the chances of buckling due to gas pressure may be a threat and needs to be eliminated. The buckling analysis carried out using SDRC/1-deas results in the prediction of buckling load factor, i.e. the magnification in the load to cause buckling. The FE model used is the same as that of the previous analysis. The analysis clearly indicates that the buckling load factor is very high (10.8) and the P/M connecting rod is safe in buckling (Fig. 14).

Estimation of natural frequency

Natural frequency of the system is of concern to avoid resonance during operation. The mass of the reciprocating and rotating parts in an engine may be a source of vibration. The newly designed connecting rod to be manufactured through the Powder Metallurgy route has a mass and stiffness distribution different from the existing connecting rod. Hence an engine value analysis was performed for both PM and forged connecting rods using general purpose non-linear FE Code ABAQUS. The natural frequency of the PM connecting rod was 976.93 cycles/sec, which is much higher than that of the forged connecting rod 697.59 cycles/sec. Hence, the PM conrod is less prone to resonance and so will not become a source of vibration. Estimation of unbalanced forces

The dynamic analysis was carried out using I-DEAS Mechanism Design suite. This uses the theory of rigid body dynamics where the major assumption is that the bodies don't deform. The Solid model of the assembly with the PM connecting rod is shown in Fig. 15 and with forged connecting rod is shown in Fig. 16.

The whole assembly consists of cylinder, piston, gudgeon pin, connecting rod and crankshaft. These parts are assembled by various types of joints. The joints used in the assembly are transnational joint between the cylinder and the piston a revolute joint between piston and small end of the connecting rod along the axis of the gudgeon pin and a revolute joint between crank shaft and the big end of the connecting rod. The crankshaft was supported at the bearing locations and a rotation of.9000 rpm was given to the crank end instead of 7000 rpm for upper bound solution. Analyses were performed for both the forged and the P/M connecting rods.

The graph of Force vs time for PM and forged connecting rod for the horizontal, vertical and resultant force in the big end is shown in Figs. 17 18 & 19. The same for the small end is shown in Figs. 20, 21 & 22. The small end X and Y direction forces and the resultant of those, as well as that of the Big end were compared and the values of those unbalanced forces are tabulated in Table 1.

Table 1

As can be seen from table, the unbalanced forces are only marginally lower for the PM connecting rod than the forged connecting rod.

Conclusion

From the FE analysis performed for stress analysis it can be concluded that the new PM connecting rod is better than the forged connecting rod. The buckling analysis performed reveals that PM connecting rod is far better than the forged connecting rod. The eigen value extraction analysis shows that the natural frequency of the PM connecting rod is higher than that of the forged connecting rod. The dynamic analysis shows that the vibration levels are lower than the forged rod. From the fatigue data it can be found that the PM connecting rod will function for the required cycles. Advantages

1. Lower weight.

2. Consistency. 3. Less machining.

4. Low Cost.

5. Better performance.

Claims

We claim

1. A novel conrod connecting a piston or cross head to the crank in a two or four stroke internal combustion engine, said conrod comprising a stem inter linking two connecting means in the form of a big circular end and a smaller circular end, wherein the stem having a density of material in the range of 7.4 to 7.8 gm/cc and the connecting means having a density of material in the range of 6.7 to 7 gm/cc.

2. A conrod as claimed in claim 1 wherein, the density of material in the stem region is 7.5 gm/cc and the density of material at the small and big ends is 6.7 gm/cc.

3. A conrod as claimed in claim 1 wherein, the stem has one or more slots.

4. A conrod as claimed in claim 1 wherein, a bush being fixed to the inner margin of the small and big circular ends to provide wear resistance property.

5. A conrod as claimed in claim 1 wherein, the conrod is produced by powder metallurgy technique using an alloy essentially comprising Fe with carbon in the range of 0.4 to 0.8 %> by weight and the remaining elements are selected from Cu, Ni, Mo, Pb, Cr, Mn, S and P with a maximum od 3% by weight and lubricant such as Zine sterate up to 0.1%.

6. A conrod as claimed in claim 1 wherein, the weight reduction to the extent of 5 to 9% from that of conventional wrought conrod.

7. A method of producing a novel conrod using powder metallurgy technique, said method comprising: a) providing an alloy essentially comprising Fe with carbon in the range of 0.4 - 0.8% by weight and the remaining elements, with a maximum of 3% by weight, selected from Cu, Ni, Mo, Cr, Mn, Pb, S , P or mixtures thereof and in case of selective densification by infiltration, the Cu or Pb can be upto 25 % by weight, and lubricant such as zinc stearate upto 0.1% by weight to protect the die, d) providing a suitable die, e) filling the die with alloy powder as defined above, f) compacting the alloy powders under a pressure range of 4 to 8 tons/cm² and at a temperature up to 250° C, and g) sintering the compacted material at 1050-1250°C for a period of 10-60 minutes and optionally, allowing Cu or Pb of about 15 to 25%) by weight to be infiltrated in the stem region and if desired, the selective infiltration of Cu or Pb can be repeated under the same condition.

8. A method as claimed in claim 7 wherein, infiltration of copper or Pb in the stem area alone by placing appropriate amount of copper infiltrates material, at 1120°C, copper melts and spreads inside the compact and fills the pores to result in a fully dense region of stem.

9. A method as claimed in claim 7 wherein, when double compacting double sintering process is used, the first compacting step produces a green part with the density in the range of 6.7-7 gm/cc, the green compact is then sintered at a temperature at 950°C where carbon does not diffuse fully but iron powders bond with each other, lubricant is also removed, and this part is then re-pressed only in the stem area to have a mass of atleast 7.5 gm/cc and then sintered at 1120°C or above to obtain full mechanical properties.

10. A method as claimed in claims 7 to 9 wherein, the sintered conrod can be sized in a manner known per se to meet the dimensional accuracy.

11. A method as claimed in claim 10 wherein, the sintered conrod can be subjected to further machining or grinding operations such as double disk grinding to meet the dimensional accuracy.

12. A method as claimed in claim 10 or 11 wherein, the connecting means are big and small ends, which are induction hardened to meet the hardness requirement and to avoid wear resistance.

13. A method as claimed in claim 7 or 10 or 11 wherein, the wear resistance to the conrod can be increased by fixing a heat treated bush which is press fitted on the inner margins of big and small ends.

14. A method as claimed in claim 9 wherein, the first sintering is performed at a temperature below 950°C and the product is then re-compacted and re-sinter at 1120°C to 1250°C.

15. A method as claimed in claim 7 or 10 wherein, the sintered part may be spheroidize annealed in a manner such as quenching and tempering, long term sub-critical annealing, cooling slowly from austenitic condition, ^"and the product is sized to higher density only in the stem area.

16. A method of producing conrod by selective densification, said method comprising the following steps:

(a) providing a die for manufacturing the conrod,

(b) filling the die with pre-determined powder mixture, (c) compacting the powder mixture under pressure, preferably under temperature up to 250° C,

(d) placing a compact of infiltrate material factor-copper or lead at stem region of the conrod, and (e) sintering the entire structure under temperature and pressure to produce the conrod.

17. A method as claimed in claim 16 wherein, the step of sintering can be performed before step (d) of the process.

18. A method as claimed in claim 16 or 17 wherein, the final sintered conrod is subjected to sizing to bring back the required dimensional stability.

19. A . method as claimed in claims 16 to 17 wherein, the conrod is subjected to induction hardening, i.e., heating the conrod at 900° C+ and rapidly cooling the conrod, to improve the wear resistance.

20. A novel conrod substantially as herein described with reference to the figures.

21. A method of producing a novel conrod substantially as herein described with reference to the figures.