Automakers Rely on Steel Performance For World's Ten Best Engines

Detroit, MI, April 22, 2004 – Results from a new study show that automakers rely extensively on steel for strength, durability, mass efficiency and cost-effectiveness in their high-performance engines. The study, conducted by automotive design engineering consultant Alan Hine, focused on the use of steel in the Ten Best Engines for 2004 named by Ward’s AutoWorld magazine (Table 1). The study was sponsored by the American Iron and Steel Institute’s (AISI) Long Products Market Development Group.

The study focused on materials use in crankshafts, flywheels, connecting rods, rockers, drive chains, valves and valve springs, cam followers, variable timing systems, and fasteners. According to AISI Director of Long Products Programs David Anderson: “In all cases, engine manufacturers cite high performance, durability, and weight reduction as the main factors for their engine design approach.” He noted that the use of steel results in structurally efficient components and a reduction in NVH (Noise/Vibration/Harshness). “The lighter reciprocating mass generates less noise and vibration, making for a smoother- running engine,” explains Anderson. “This also helps in reducing the secondary stresses in the engine, thus minimizing component fatigue and failure, as well as warranty problems.”

The study results are summarized below:

Crankshafts

The study shows there is a major trend towards using forged crankshafts, which offer such benefits as improved durability, weight reduction, and better noise suppression. Automakers indicate that the reduction in mass and superior quality of forged steel offset its higher material and manufacturing costs. Forged steel cranks offer less reciprocating mass--thus reducing stress--which allows for the use of smaller, lighter flywheels and clutch systems.

Flywheels

There is a gradual change from the wide use of grey cast iron flywheels to fabricated steel for these units. The use of a steel flywheel is the answer for a strong lightweight system. Car companies differ on their approach. The Honda, Nissan, Toyota and DCX engines, for instance, still use grey cast iron, while Subaru, BMW, and Audi use forged steel components. GM, on the other hand, uses a high-strength quenched and tempered steel plate. Nevertheless, auto manufacturers agree that steel offers the best solution, especially for the high-powered engine. In all cases, the starter gear ring attached to the flywheel is a pressed-on steel component.

Connecting Rods

Automakers also use different approaches for connecting rods. The connecting rods on the Audi, BMW, GM, Cummins, Hemi, Nissan and Subaru engines use steel forgings, as opposed to the powdered metal type used on their lower-performance variants. The Honda unit relies on powdered metal types, while the Toyota still utilizes a cast type approach. However, when comparing the horsepower and torque curves of the specific engines, it is noteworthy that the more powerful engines require forged steel connecting rods for durability.

Overhead Cams / Camshafts

The majority of engines on the Ward’s AutoWorld Ten Best Engines List and in the marketplace today are Overhead Cam (OHC) powerplants. A larger number of automakers are moving to Dual Overhead Cams (DOHC). The next evolution in camshaft design will continue reduction in reciprocating mass, which should open the way for forged camshafts or steel tubes with pressed cam lobes.

Rockers

Unlike the camshafts, which require specific profiling for the defined engine, the same rocker can be used throughout the particular engine or the entire family of engines. Automakers conclude that the use of a set rocker profile manufactured either of grey cast iron or steel pressed unit makes sense. This is a benefit to the bar industry, as simplified rocker systems are in most cases attached to a hollow steel shaft. This method has the advantage of better actuation with less stress.

Camshaft Drives / Drive Chains

With the higher power outputs, manufacturers are moving to a steel chain utilizing high-strength steel links and axles, rather than a belt system. The chain and gear sets are more efficient with respect to durability than plastic pulleys and tooth belts.

In the BMW, the number of drive chains used is quite significant. The Audi has reverted to a steel chain system as opposed to a toothed belt. In most cases, these are single chain drives. However, on some high-performance engines, there is a move toward using steel duplex chains.

Valves

The number of valves per cylinder has increased over the last few years. Now, even the average engines in lower-priced vehicles have four valves per cylinder. Sodium-filled steel exhaust valves are becoming the norm in these engines. (Figure 1)

The valves in high-performance engines are subject to very high temperatures. To reduce the temperature and limit the expansion of the valve stem, the valve stem and/or valve head with valve stem is drilled and filled with metallic sodium. Sodium fuses and becomes liquid at approximately 97 degrees when the engine is operated and conducts the heat on valve head to valve stem by convection. Furthermore, the valve weight is reduced by 7% - 16% by the addition of the drilled chamber. This allows for a considerable reduction of the mass effect on high-performance valves. In addition to the reduction in mass, there is a significant improvement in the NVH of the valve train system.

While some exotic materials like titanium have been used for racing and rallying, the “street engines” still rely on steel for durability.

Valve Springs

Valve springs are still used in all engines. A few applications use double springs, but in most cases a single spring is sufficient. This system works well and should be around for years to come. Even as engines reach up to 15,000 rpm, the steel spring is more than capable of working the valve without “bounce”, or fatigue.

Cam Followers

Most engines utilize a hydraulic steel cam follower, which has been used with good results to prolong engine service life and durability. The follower in all cases is chromed steel, whether solid or hydraulic. Steel components are necessary due to the high wear rate associated with these parts.

Variable Timing

All of the engines on Ward’s AutoWorld Ten Best Engines List for 2004 have variable valve timing (VVT) and drive-by-wire systems.

As each VVT is different, the opportunity for more steel components increases. As with the BMW VANOS system, a number of additional steel components are used in the system.

The drive-by-wire systems allow computer control of the cam profiles of the VVT units. However, there must be a mechanical linkage to actuate these types of devices. In addition, a mechanical return safety back up is required for these systems. Each mechanical device relies on steel spindles and springs to return it to position.

Fasteners

Steel fasteners and dowel locators play a major part in the engine and contribute to a large percentage of the total components. In all cases, steel fasteners are responsible for the assembly of various components. Steel dowels achieve the location of the bearing pads for the cams and connecting rods. Each aluminum part of the engine uses steel dowels in the assembly. The block to the head utilizes a number of steel dowels for location purposes, as does the sump pan to block. Water pump housings, bell housing, plus front and rear covers, all have a minimum of two steel dowels for location. Cam bearing housings and any form of cast cam cover also utilize steel dowels for location. With the higher output of the modern engine, high-strength steel studs and bolts are steadily replacing the fasteners.

Dave Anderson concludes: “Although there is a move toward more powerful engines with respect to both horsepower and torque, as the engines on this list show, there is also a move toward a lighter engine package. Increasingly, automakers are depending on steel components to provide this weight reduction, while increasing durability and dependability on these downsized components.

“The move to aluminum castings for the cylinder block and head is now almost universal in its application, ” says Anderson. “However, to meet growing power requirements, there is more use of steel components within the engine to provide the rigidity for basic blocks and heads. The use of steel forged crankshafts provides a lighter and more stable component resulting in very little flex and reduced stress on the aluminum block. With the power curves of these engines continually increasing and the mass continually being reduced, the need for quality steel components has become a necessity. “

Table 1 -- The 10 best engines for 2004 selected by Ward’s Autoworld.

1.

Audi AG 4.2L DOHC V-8 (S4)

2.

BMW AG 3.2L DOHC I-6 (M3)

3.

DaimlerChrysler AG 5.7L Hemi Magnum OHV V-8

4.

DaimlerChrysler AG 5.9L High Output Cummins 600 OHV I-6 turbodiesel (Ram HD)

5.

General Motors Corp. Vortec 4.2L DOHC I-6 (GMC Envoy)

6.

Honda Motor Co. Ltd. 3L DOHC V-6 (Accord Coupe)

7.

Mazda Motor Corp. 1.3L Renesis Rotary (RX-8)

8.

Nissan Motor Co. Ltd. 3.5L DOHC V-6 (Infiniti G35)

9.

Fuji Heavy Industries Ltd. Subaru 2.5L DOHC turbocharged H-4 (WRX STi)

10.

Toyota Motor Corp. 1.5L DOHC I-4 Hybrid (Prius)

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Figure 1 – Valves are subject to very high temperatures in high-performance engines. To reduce temperature and limit expansion, the steel valve stem is drilled and filled with metallic sodium.

 

 

Figure 2 –The camshafts in the Audi engine are steel forgings, which operate chromed steel hydraulic lifters via cast iron valve levers. These levers areImage connected to a high carbon steel lever shaft. There are two shafts per bank operating the inlet and exhaust valves, which run the length of the engine. The valves still rely on valve springs, which in this case are single wound spring steel. These are retained with the standard pressed steel seat and steel Colette system. Both of the cams are chain driven. Unlike the industry trend toward timing belts, the above engine utilizes a steel chain for cam actuation, water pump drive, and oil pump. The movement of the cam and crank drives to the rear of the block necessitated the use of a chain. Unlike the belt system, which uses plastic pulleys, the chain requires the use of steel gear sets, which can be seen in the above illustration. The crankshaft is also a steel forging, with a low inertia steel flywheel. Audi, like most European manufacturers, makes extensive use of steel forging for crankshafts.

The connecting rods are also drop-forged steel units, while the pistons are forged aluminum. However, steel strips are forged into the piston to offset the different coefficients of expansion between the piston and liner, which reduces noise. (This is now common practice, and is the case on all the engines detailed). Piston rings still remain as steel, due to the high pre-tensioning and frictional loads. This is also the case with the piston Gudgen Pin (Wrist Pin), which requires chromed steel due to the high loads.

Under the auspices of the American Iron and Steel Institute, the Bar and Rod Market Development Group strives to grow the market for value-added steel long products products. With five member companies, the group pursues this goal through two task forces committed to developing innovative solutions to the challenges facing their clients and the steel industry. These task forces are Automotive/Heavy Equipment and Construction/Infrastructure.

Long Products Market Development Group Member Companies:

Chaparral Steel
Ispat Inland Bar Company
MACSTEEL
Nucor Corporation
The Timken Company