advanced steel offers automakers aggressive engine downsizing

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ADVANCED STEEL OFFERS AUTOMAKERS AGGRESSIVE ENGINE DOWNSIZING

Andy Schmitter Nucor Corporation


Background and Scope

The Bar Applications Group (BAG),a committee of the Steel Market Development Institute (SMDI), wanted to conduct a study to define engine performance and weight improvements that may be possible when an engine is designed using an increased number of steel components.

The SMDI contracted with Mahle Powertrain to complete the study.


Background and Scope

Project Scope – Literature survey to quantify current steel usage in engines – Review of MAHLE internal reports – Brainstorm and information gathering with MAHLE Component

Experts – Determination of component weight saving potential – Final Report

MAHLE Powertrain (MPT) to focus on consideration of steel as an enabler e.g. – Higher strength – Smaller package – Better heat management – Friction

Heavy duty engines not widely considered in this study – steel content already high


Potential Component Evaluation List

Cylinder head

Engine block

Cylinder liner

Connecting rod

Bearings / bushings

Crankshaft

Camshaft Valve Spring Valve Turbocharger Piston ring Piston Oil Pump

Engine Assembly


Potential Component Evaluation List Focus on the “Big Four”

Component/System Comments Crankshaft Currently cast iron, forged or machined steel.

Connecting Rods Powder metal FS, steel machined, steel FS. Small volume of Ti.

Camshaft Cast iron or assembled (assumed to be steel).

Pistons Generally Al for light and medium duty.

Engine Block Stretch goal. Any steel block unlikely to be made using bar stock.

Piston Rings Top and oil ring generally steel. Generally all produced from wire.

Springs Already steel although produced from wire.

Valves Generally already steel. Small volume of Ti.

Cylinder Liners Generally cast iron. Light duty engines tending to parent Al.

Ancillary Components DI fuel pumps have high steel content. Brackets will likely be formed from flat sheet if steel. Pumps mix of steel and PM. Turbochargers


Literature Survey and Data Collection

Camshafts and Connecting Rods


8 Cylinder Camshaft and Con-Rod Distribution

24%

71%

5%

Cast %

Assembled %

N/A%

8 Cylinder Camshaft Distribution

77%

22% 1%

Powder Metal %

Forged Steel %

N/A %

8 Cylinder Con-Rod Distribution

Production Volume V90deg

Chrysler 473,200 Ford 666,100 GM 1,307,200

European 238,000 Asian 196,500

Total Production 2,881,000



For 8 cylinder engines steel camshafts appear to be very prevalent – Likely due to the longer length of an 8 cylinder

camshaft – The high amount of cam in block (“OHV”) 8

cylinder engines may require more assembled camshafts also

Powder metal connecting rods appear to be used in a majority of V-8 engines – Low power density – Lower engine speeds



Production Volume Boxer Inline V( 60°) V( 90°) V( 11°)

Chrysler 0 109,900 683,100 184100 0 Ford 0 38,800 1,035,900 0 0 GM 0 0 771,200 58500 0

European 12,300 304,600 0 187700 96,900 Asian 55,000 0 1,612,000 0 0




Several 6 cylinder configurations are readily available – Only the two most common NA arrangements

(90o and 60o) were investigated closer The traditional 60o V-6 sees a large use of Iron

cast camshafts 90o V-6 uses nearly 50% forged steel connecting

rod – Non-optimal layout – Higher power density



Production Volume Boxer Inline

Chrysler 0 383,300 Ford 0 687,200 GM 0 896,000

European 0 400,400 Asian 230,100 3,436,500




In general 4-cylinder engines use mostly cast Iron camshafts – Boxer or flat configurations use 100% steel

camshafts but their market share is small A majority of both 4-cylinder engine configurations

use forged steel connecting rods – Increased occurrence of boosting – Higher engine speeds common


Literature Survey and Data Collection

Crankshafts


Steel Use in Current Engines I4 Crankshafts


Steel Use in Current Engines V6 Crankshafts


Steel Use in Current Engines V8/V10 Crankshafts


Steel Use in Current Engines Comments / Conclusions


Steel Component Use Pros and Cons


Steel Crankshaft Pros and Cons

PROS(Compared to cast crank)

Greater tensile strength

Greater fatigue strength

Smaller size/weight possible (in theory) enabling tighter package

Machined steel crankshaft has advantages for low volume and prototype over cast iron

CONS(Compared to cast crank)

Cost of material/scrap rate of forging process

Cost of forging process with finish machining

Smaller size not always possible due to other factors e.g. oil film, bearing loads etc

Typical Steels Used - EN40B / 4340 (machined), 42CrMo4 (forged) Steel cranks typically used where higher strength required e.g. high output turbocharged engines


Forged Steel Connecting Rod Pros and Cons

PROS (compared to PM Rod)

Longer fatigue life

Higher strength

Newer fracture split steel rods stronger than PM

Good potential for material reduction and weight saving

Good cap shift control

No real size limitation

CONS (Compared to PM Rod)

Higher cost (gap closing)

Post-forge machining and scrap level (PM Near net shape after forming process requires less machining and scrap)

Used to need machined rod and cap joint whereas PM easily fracture split (newer forging steels fracture split)

Early fracture split C70 steel rods offered little strength advantage over PM

Typical steels used – C70, 36MnVS4, 46MnVS6mod


Steel Camshaft Pros and Cons

PROS (Assembled cam compared to cast iron cam)

Greater fatigue life

Higher strength (smaller journals possible)

Greater stiffness

Greater flexibility in lobe geometry

Ground before final assembly (cleaner)

Selective properties of assembled components e.g. hardened DI fuel pump lobe, sintered trigger wheel etc.

Lighter weight

CONS (Assembled cam compared to cast iron cam)

Hi cost


Steel Camshaft Weight Saving Potential

Huge potential for weight saving – compared cast iron camshaft

approx. 50 % less

weight


Steel Piston Pros and Cons

PROS (compared to cast aluminum pistons)

Higher cylinder pressure limit

Higher piston temperature limit

Reduced top land height possible (reduced crevice volume)

May offer friction advantages particularly in iron block/liner engines

CONS (compared to cast aluminum pistons)

Highercost

Weight (current)

Cooling oil flow requirement due to higher piston temperature

Potential to increase detonation sensitivity in gasoline applications


Market Trends Turbocharging and Downsizing

•Significant growth of gasoline turbo share in Europe •NAFTA is following this trend, first with partly importing engines, followed by a growing local production

•Also increasing gasoline turbo growth in China •Japanese OEMs with partly increasing TC share

Turbocharging

Gasoline Turbo Share*

* by Vehicle Production Region


Market Trends Turbocharging and Downsizing

•Increasing number of development projects for 2-cyl. engines, 3-cyl. engines also applied in D-segment cars of premium brands (e.g. BMW 3 series)

•Downsizing in NAFTA on a “higher level” in, but limited due to higher vehicle mass V8 -> V6, V6 -> I4

•Increasing share of 3-cylinder engines in China expected

Downsizing

Worldwide Downsizing Scenario


General Market Trends – Power Cylinder Unit (PCU)

Increase of Temperature and Cylinder Pressure

• Increasing maximum specific power and peak cylinder pressure for LV gasoline engines, LV diesel engines and also for medium and heavy duty diesel engines

• Higher piston temperatures expected

Engine Block

Pistons

• Significant worldwide increase of gasoline aluminum blocks (62% in 2011 76% in 2017)

• Moderate increase of aluminum diesel engine blocks (18% in 2011 21% in 2017) which could increase if the European OEMs enforce plans to increase their aluminum diesel engine share.

• Spray coated aluminum blocks provide advantages regarding engine size reduction, less scrap rates, recycling, etc.

• Even though traditional liners will still be used in the coming engine generation, spray coating will be the trend at numerous customers towards 2020

• Steel piston share will increase significantly for HD engines

• Rising share of steel pistons also for diesel passenger cars expected

• Due to improvements in the casting process as well as design optimization there is no advantage for forged aluminum pistons compared to the cast piston


Conclusions

Engine designers will always favor the lowest cost solution that satisfies the requirements

For steel components to be adopted in larger quantities they need to act as enablers for something e.g. more highly stressed downsized engines

Increasing trend of extreme downsizing and hence higher specific component loading favorable for the implementation of Steel components.

Steel crankshaft distribution unlikely to change in current engine ranges due to design constraints and cost implications

– Trend to more extreme levels of downsizing will increase steel crankshaft adoption due to high specific component loading and desire for compact, lightweight engines

Real potential for optimized steel connecting rods offering light weight, near PM cost with higher strength


Conclusions

Real potential for steel camshafts offering lighter weight, flexibility of individually assembled components and little additional cost – Technology trends predict significant adoption

Future engine development to meet legislative targets (CAFE 54.5 MPG) will dictate the use of alternative materials including high strength steel to reduce whole vehicle mass

Engine downsizing is predicted to be the biggest technology path to achieving lower fuel consumption – As engines get increasingly downsized steel content will increase (although physical size will likely decrease)

Real potential for increased volume of steel pistons in the light duty diesel market with some breakthrough into the highly downsized gasoline market


Next Steps

Original idea to take a current engine and analyze weight saving with high steel content

– Based on this Phase I study the potential weight saving of using steel components in an existing engine is likely to be low (and largely based upon camshaft weight saving)

– Needs complete redesign of engine from clean sheet to optimize for weight

Engine downsizing trend will continue

– Ever more extreme downsizing with the goal to completely de-throttle the engine for maximum efficiency

– Will increase loading on components as cylinder pressures increase.

– Fuel economy benefits will come through engine operating point efficiency gains (de-throttling) and overall vehicle mass reduction

– Compact lightweight engines result in lower whole vehicle mass

Steel will be the enabler for an increasingly extreme downsized engine particularly as it can be implemented in the harsh environment of the PCU.

advanced steel offers automakers aggressive engine downsizing

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