WO2017089977A1

WO2017089977A1 - A forged crankshaft and a process of making it

Info

Publication number: WO2017089977A1
Application number: PCT/IB2016/057085
Authority: WO
Inventors: Babasaheb Neelkanth Kalyani; Madan Umakant TAKALE; Vijaykumar Hanumantrao KHASNIS; Manoj Rajendra UKHANDE; Rajesh Surendra MANE; Girish Namdeo TILEKAR
Original assignee: Bharat Forge Limited
Priority date: 2015-11-24
Filing date: 2016-11-24
Publication date: 2017-06-01

Abstract

The weight of the crankshaft is among the many factors that adversely influence the engine performance. Reducing the weight of the crankshaft without affecting its strength and balancing characteristics would improve the engine performance. The present invention provides a crankshaft and the process of manufacturing it such that its weight is reduced at least by 5-10% in contrast to conventionally manufactured crankshafts of comparable specification. This is achieved by reducing machining allowance which is provided during forging design, such that it does not adversely impact its strength and balancing ability. Moreover the additional aspect of kidney pocket inclusion into the combined area of web and counterweight profile reduces weight of crankshaft further at least 5%. A reduction in total machined area of the webs is also another aspect of the present invention.

Description

A Forged Crankshaft And A Process Of Making It

Field of Invention

The present invention relates to forged crankshafts used in engines, and more particularly reduction of machining area and the machining allowance required during the manufacturing process and optimizing them by reducing their weight with inclusion of kidney pockets in the combined area of web and counterweight.

Background of Invention

Conventional crankshafts which are used for multi-cylinder engines have different range of capacities. There are three widely adopted methods of manufacturing crankshafts: casting, forging, billet machined; of these forging is considered to be the best manufacturing process for crankshafts considering strength aspects. Conventional crankshaft manufacturing processes by forging involves forging followed by machining. As a routine part of standard forging design, forging feasibility is studied. This is followed with virtual product design and development processes, followed further with actual forging and heat treatment if necessary. The forged crankshaft is finally machined to remove the extra material provided as machining allowance. The extra material is typically provided at all critical machined surfaces. Machining is a resource intensive process which requires special tooling and consumes significant amount of energy. The greater the machining allowances, the heavier the parts and greater the energy spent on machining activity. Another aspect that affects the machining resources is the area of the machined surfaces. All areas such as the journals and the webs typically need machining. However, the entire side surfaces, rather than partial surfaces, of the parts such as the counterweights and the webs are typically machined in crankshaft manufacturing. This increases the amount of resources spent on the machining activity. There is therefore room to improve the design of the side surfaces of the parts such as the counter weights and webs so that the machinable surface areas reduced.

The crankshaft manufacturing with light weighting features disclosed in various ways - but it is limited to cast parts. For example, the US patent 4356741 discloses method of manufacturing cast crankshafts with recesses or apertures provided in crank webs of the crankshaft and are formed in adjoining inner area of the casting material forming the main and crank pins by cores inserted therein prior to casting for the reduction of the weight and of the rotating out-of-round masses as well as of the counterweights thereof.

However, there are fundamental differences between casting and forging methods of parts manufacturing. Incorporating recesses in casting is relatively easy. However, in the case of forging, which produces much better quality parts in respect of material properties, introduction of recesses increases the complexity of the forging process. Introducing recesses in the shape of the kidneys necessitates die design validation using virtual manufacturing (metal flow simulation) stage, but depending on metal and metal flow characteristics, the die design parameters need to be optimized during the manufacturing process to ensure complete die fill- up.

US6324942 and EP 1020242 A2 disclose an engine crankshaft made by forging that has larger counter weights. Each counter weight has a plurality of inclinations to facilitate removal of the dies from the crankshaft after the forging process is complete. The inclinations are reduced as they are apart from a die mating surface. This invention is limited to inclination from die mating surface with two different angles and non-machined area is limited to counterweight portion only, this serves the purpose of ease in the die removal whereas the present invention consist of reduced machining allowances to all the parts of the crankshaft with only one inclination from die mating surface, which serve the purpose of reduction in weight and reduction in machined area. WO/2006 057593A1 discloses method of making crankshaft by drop forging method comprises of recess has an extent close to central portion of transition region between the web and crankpin or between web and journal. The recesses were made perpendicular to axis of rotation. Whereas the present invention also provided recess but it is in the form of kidney shape. The recesses are made using close die forging process by making kidney shape profile in the die impression. The present invention also combined recess with reduced machining allowances which reduces the weight as well as machined area.

Furthermore, the present competitive markets demand low cost and light weight components. Designers are focusing on component weight reduction by maintaining desired strength hence better strength to weight ratio is important.

There is therefore a need to provide a forged crankshaft with reduced machining allowances and reduced areas of machining along with inclusion of kidney pockets into web and counterweight profile in order to reduce weight of crankshaft without affecting its strength.

Objects of the Invention:

Accordingly, one of the key objects of the present invention is to provide crankshafts forged using reduced machining allowances which leads to crankshafts of lighter weight with improved strength to weight ratio.

One of the other objects of the present invention is to provide a recess in the combination of web and counter weight area (also termed kidney pocket) which further leads to crankshafts of lighter weight with improved strength to weight ratio. Another object of the present invention is to provide a crankshaft with reduced area of machining on any one side surface or both side surfaces of counterweights. Another object of the present invention is to reduce machining on counterweight radius profile.

Summary of the invention:

The weight of the crankshaft is among the many factors that influence an Engine performance. Reducing the weight of the crankshaft without affecting its strength and balancing characteristics would improve the engine performance. The present invention provides a crankshaft and the process of manufacturing it such that its weight is reduced at least by 5-10% than conventionally manufactured crankshafts of comparable specification. This is achieved by reducing machining allowance which is provided during forging design, such that it does not adversely impact its strength and balancing ability. Moreover the additional aspect of kidney pocket inclusion into combined area of web and counterweight profile reduces weight of crankshaft further at least 5%. A reduction in total machined area of the webs is also another aspect of the present invention.

List of parts:

1. Crankshaft 2. Journal

1A. Bevel 25 3. Pin

IB. Tail 4. Web

1C. Flange 5. Counterweight 6. Recess 5 9. Pin-side of web/counterweight

7. Pin side machining allowance Journal-side of web/counterweight

8. Pin and journal side machining 11. Counterweight radius profile

allowance

Brief Description of Figures:

Figure 1 shows a typical existing 6-cylinder crankshaft with the machined areas

Figure 2 shows a 6-cylinder crankshaft of the present invention with its non- machinable areas. Figure 3A and 3B shows the section of crankshaft (single throw) with machined areas of existing design and non- machined areas of invented design.

Figure 4 shows the section of non machinable surface of counterweight part of invented design.

Figure 5 shows the section view comparison between counterweight of existing design and invented design.

Figure 6 shows a typical 4-cylinder existing crankshaft with the machined areas.

Figure 7 shows a 4-cylinder crankshaft of the present invention with its non- machinable areas and inclusion of kidney pockets. Figures 8A and 8B respectively show the sections of crankshaft (single throw) with machined areas of existing design and non- machined areas/surfaces with inclusion of kidney pockets of invented design.

Figure 9 shows the section of non-machinable surface of counterweight part of invented design.

Figure 10 shows the section view comparison between counterweight of existing design and invented design.

Figure 11 shows a typical case 1 of existing 6-cylinder crankshaft with the machined areas/ surfaces.

Figure 12 shows a typical case 1 of invented 6-cylinder crankshaft with its non- machinable areas/surfaces.

Figure 13 shows a typical case 2 of existing 6-cylinder crankshaft with the machined areas/ surfaces.

Figure 14 shows a typical case 2 of invented 6-cylinder crankshaft with its non- machinable areas/surfaces.

Detailed description of the invention:

The present invention provides a crankshaft and a process of manufacturing it such that its weight is reduced in comparison with the crankshafts of comparable specification but which are manufactured using conventional methods which use conventional machining allowances. This has been achieved by minimizing the machining allowance so that material from counterweights is reduced while ensuring that it does not adversely impact strength and balancing charcterstics of the crankshaft.

Inclusion of a recess (6), preferably in the form of a kidney pocket, in the forged crankshaft is another aspect of the present invention.

The combination of reduced machining allowance with inclusion of a recess (6) pocket into web and counterweight profile results in significantly reduced weight of crankshaft without affecting its strength and balancing characteristics.

The invention is now explained with the help of figures and the following description. Figure 1 and Figure 6 show typical conventional crankshafts (1) produced with the conventional design and manufacturing method, its parts and the machined areas. Figure 2 illustrates a case of the invention where the pin-side of the webs and counterweights are entirely non-machined whereas the journal sides are machined. Figure 7 represents a case of the invention where the pin and journal-side of the webs and counterweights are entirely non-machined. The figure lshow various parts of a crankshaft such as the journals (2) and the pins (3), the webs (4) and the counterweights (5). Both sides of all webs and counterweights are machined in the conventionally manufactured crankshaft.

Figure 2 and Figure 7 show crankshafts of the present invention with its different aspects. Figure 2 shows the crankshaft of the invention wherein the pin side of the webs/counterweights is not machined and provided with no machining allowance at all. On the journal side, a machining allowance of up to 1 mm may be provided. Figure 7 indicates the non- machined surface of the webs where no machining allowance is provided at both pin and journal side faces of the webs and counterweights. This represents a huge reduction in machining allowances over what is provided in conventionally produced forged crankshafts.

Figure 7 illustrates another aspect of the present invention. On top of the reduced machining allowance, at pin-side and journal-side counterweight surface area, further material savings can be achieved by providing recesses (6) in the webs and counterweights. While provision of a recess in the case of a cast crankshaft is relatively easy and known to the person skilled in the art, provision of a recess in case of a forged crankshaft is quite complex to design and manufacture and not known to a person skilled in the art. The inclusion of a recess (6) in the shape of a kidney pocket along with provision of a reduced machining allowance thus represents an inventive aspect of the present crankshaft.

The machining allowances used in the conventional manufacturing process of components such as crankshafts provided on parts such as webs and counterweights, pins and journals range between 2.5mm to 3.5mm or greater depending on the part to be machined. The present invention uses reduced machining allowances representing significant savings in costs and resources. Figure 3 and Figure 8 show a perspectives view of the pin-side of the counterweights according to the present invention. It should be noted that, according to one aspect of the invention, there is no machining required on the pin side of the webs. This results in reduced machining area.

The crankshafts manufactured using the process of the invention has been validated by physical testing for its strength and balancing characteristics.

The present invention provides an inventive process of design and manufacturing of the crankshafts wherein the strength and balancing performance is assessed and the geometry of the parts is redefined. The process involves providing machining allowances of not more than 1mm per side in the areas of the webs and counterweights that need machining. As illustrated by the crankshaft of Figure 2 and Figure 7, in the areas that do not need machining, no machining allowance is provided whatsoever. In general, for all parts such as the webs (4) and the counterweights (5), and also for other parts like journal (2), bevel (1A), pin (3), tail (IB), flange (1C), the machining allowance has been reduced by up to 7-8% than existing. In another aspect of the invention (see Figure 7), recesses (termed as kidney pockets) are introduced into counterweight profile. The crankshaft produced with this feature is also validated using virtual stress analysis and physical testing. The crankshaft of the present invention has a lower machined area (at least 15% reduction) compared to a comparable conventionally manufactured crankshaft. Further, the crankshaft of the present invention achieves a machined weight reduction. Hence for the same weight of the engine, an engine fitted with the crankshaft of the invention provides greater horse power than the engines fitted with conventionally manufactured crankshafts. In other words, this means that to obtain same horse power as the engine fitted with conventional crankshafts, there could be lighter engines fitted with the crankshafts of the said invention. In the case of the present invention, the machining allowance design of this counterweight profile has been such that the pin-side surface of the counterweight is provided at a draft (see also Figures 4, 5, 9 and 10) angle of about 1.5 degrees. This arrangement allows machining of the area near the pin which is much smaller compared to the area of the entire pin-side surface.

In another aspect of the present invention is provided a process of manufacturing a crankshaft wherein a step of incorporating a recess in the combined area of web and counterweight on the pin side surface is included. In yet another aspect of the present invention (as illustrated by the crankshaft of Figure 7) there is provided a process of manufacturing a crankshaft wherein a step of providing a reduced machining allowance than the conventional processes is provided such that no machining allowance is provided on the pin and journal sides faces of the counterweights.

In another aspect of the present invention is provided typical variant cases for two 6-cylinder crankshafts as shown in Figures 11, 12, 13, 14 with existing and invented designs using the similar concept of reduced machining allowance.

In yet another aspect of the present invention there is no machining required on counterweight radius profile.

Crankshafts produced with reduced machining allowance were tested for alignment and dynamic balancing. The product of the invention is a forged and machined crankshaft where the forged component has a reduced machining allowance and addition of kidney pocket into counterweight profile which resulted into reduction in machined area and machined weight of crankshaft.

Advantages of the crankshaft and the process of manufacturing disclosed herein are:

1. Final machined crankshaft weight reduction by at least 10-15%.

2. Forging design was optimised through reduced machining allowance and inclusion of kidney pocket on forged parts. 3. Machining cycle time was reduced. Machining tool life was improved. The engines in which the parts are fitted have an improved performance due to the reduction of the crankshaft weight.

4. The strength to weight ratio was improved.

It is evident from the foregoing discussion that the invention has the following embodiments:

1. A forged crankshaft (1) which comprises at least one web (4), at least one counterweight (5), at least one crank pin (3) and at least one journal (2), at least one bevel (1 A), a tail (IB), and a flange (1C), characterized in that the percentage of the non-machined surfaces for at least one of the pin side and/or the journal side surfaces of said at least one web (4) and/or said at least one counterweight (5) is up to 100%, wherein said at least one web (4) has on its crank pin-side a weight reduction recess (6).

2. A forged crankshaft (1) as disclosed in embodiment 1 characterised in that said recess (6) being in the form of kidney pockets.

3. A forged crankshaft (1) as disclosed in any of embodiments 1 to 2 wherein the machining allowance on the journal sides of said webs or counterweights is no greater than 1mm.

4. A forged crankshaft (1) as disclosed in any of embodiments 1 to 3,

characterised in that the pin- side surface and the journal- side surface have a draft angle of up to 1.5 degrees. 5. A forged crankshaft (1) as claimed in any of claims 1 to 4, characterised in that the machining allowance of said at least one journal, said at least one bevel, said at least one pin (3), said tail (IB), and said flange (1C) is reduced by 7-8%.

6. A forged crankshaft (1) as disclosed in any of embodiments 1 to 5,

characterized in that percentage of the non-machined surfaces for at least one of the counterweight radius profiles (1 1) is up to 100%.

7. A process of making a forged crankshaft (1) said crankshaft having at least one web (4), at least one counterweight (5), at least one crank pin (3) and at least one journal (2), a bevel (1 A), a tail (IB), and a flange (1C),

characterised said process comprises a step of machining the web- and counterweight surfaces such that the percentage of the non-machined surfaces at least one of the pin side or the journal side surfaces of the web (4) and the counterweight (5) is up to 100%.

8. A process of making a forged crankshaft as disclosed in embodiment 7

characterised in that the said process involves a step of providing a recess (6) in the counterweight (5) on the crank pin side surface.

9. A process of making a forged crankshaft (1) as disclosed in embodiment 8 further characterised in that the said recess (6) has a kidney shape.

10. A process of making a forged crankshaft (1) as disclosed in any of

embodiments 7 to 9 wherein the machining allowance on the journal sides of said webs (4) or counterweights (5) is no greater than 1mm. 11. A process of making a forged crankshaft as disclosed in any of embodiments 7 to 10, characterised in that the pin-side surface and the journal- side surface have a draft angle of up to 1.5 degrees.

12. A process of making a forged crankshaft as claimed in any of claims 7 to 11, characterised in that the machining allowance of said at least one journal, said bevel (1 A), said at least one pin (3), said tail (IB), and said flange (1C) is reduced by 7-8%.

13. A process of making a forged crankshaft as disclosed in any of embodiments 7 to 12, characterized in that percentage of the non- machined surfaces for at least one of the counterweight radius profiles (11) is up to 100%.

While the above description contains much specificity, these should not be construed as limitation in the scope of the invention, but rather as an

exemplification of the preferred embodiments thereof. It must be realized that modifications and variations are possible based on the disclosure given above without departing from the spirit and scope of the invention. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.

Claims

Claims:

2. A forged crankshaft (1) as claimed in claim 1 characterised in that said recess (6) being in the form of kidney pockets.

3. A forged crankshaft (1) as claimed in any of claims 1 to 2 wherein the

machining allowance on the journal sides of said webs or counterweights is no greater than 1mm.

4. A forged crankshaft (1) as claimed in any of claims 1 to 3, characterised in that the pin-side surface and the journal-side surface have a draft angle of up to 1.5 degrees.

5. A forged crankshaft (1) as claimed in any of claims 1 to 4, characterised in that the machining allowance of said at least one journal, said at least one bevel, said at least one pin (3), said tail (IB), and said flange (1C) is reduced by 7-8%.

6. A forged crankshaft (1) as claimed in any of claims 1 to 5, characterized in that percentage of the non-machined surfaces for at least one of the counterweight radius profiles (1 1) is up to 100%.

7. A process of making a forged crankshaft (1) said crankshaft having at least one web (4), at least one counterweight (5), at least one crank pin (3) and at least one journal (2), a bevel (1A), a tail (IB), and a flange (1C),

8. A process of making a forged crankshaft as claimed in claim 7 characterised in that the said process involves a step of providing a recess (6) in the counterweight (5) on the crank pin side surface.

9. A process of making a forged crankshaft (1) as claimed in claim 8 further characterised in that the said recess (6) has a kidney shape.

10. A process of making a forged crankshaft (1) as claimed in any of claims 7 to 9 wherein the machining allowance on the journal sides of said webs (4) or counterweights (5) is no greater than 1mm.

11. A process of making a forged crankshaft as claimed in any of claims 1 to 10, characterised in that the pin- side surface and the journal- side surface have a draft angle of up to 1.5 degrees.

12. A process of making a forged crankshaft as claimed in any of claims 7 to 11, characterised in that the machining allowance of said at least one journal, said bevel (1 A), said at least one pin (3), said tail (IB), and said flange (1C) is reduced by 7-8%. A process of making a forged crankshaft as claimed in any of claims 7 to 12, characterized in that percentage of the non-machined surfaces for at least one of the counterweight radius profiles (11) is up to 100%.