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The performance of race engines has been considerably im-proved over the last few years. Engine designers and builders have continuously taken steps to increase engine output and efficiency.

Engine modifications have been made according to the fol-lowing trends: higher output and torque, higher rotation speeds, lighter weight components, lower viscosity oils, and tighter oil clearances.

These modifications to engine design have caused changes to the conditions under which engine bearings operate.

With regard to bearing function, the following challenges to modern race bearings may be formulated:

•Materialfatigue•Lubrication•Oilstarvation•Pressfit

The research and development efforts at King Engine Bear-ings have been focused on developing solutions to these chal-lenges. As a result, new design features and new materials for race bearings have been developed.

MATERIAL FATIGUELoad capacity (fatigue strength) is the maximum value of cycling stress a bearing can withstand without developing fatigue cracks after an infinite number of cycles.

The load capacity of a tri-metal bearing is determined by the fatigue strength of both the overlay and the intermediate layer.

The load localizes over the contact area, causing a formation of small cracks on the lining surface .The cracks then propagate throughout the lining thickness, meet the steel back surface and continue to advance along the steel-copper boundary. As a re-sult, parts of the intermediate layer detach from the steel surface [1].

Thus, both the strength of the overlay and the strength of the intermediate layer affect bearing operation and durability.

pMax Black™: Strengthened Tri-metal Bearing MaterialTo address the problem of material fatigue, King has developed a new tri-metal bearing material for high performance applica-tions: pMax Black™.

Load capacity for the pMax Black™ bronze intermediate layer was reached (up to 17,000 psi) by changing two param-

eters: increasing the tin content in the copper base alloy to 4-5% and a greater cold work treatment (cold rolling) of the steel-bronze strip.

The hardness of the intermediate layer of pMax Black™ was increased to 110-115 HV.

The harder intermediate layer provides more reliable bearing operation under high load.

The main factor affecting the load capacity of a tri-metal bearing is the fatigue strength of the overlay. Therefore the pri-mary focus for pMax Black™ was to develop an overlay having increased fatigue strength.

Three factors have been taken into account in developing the overlay with enhanced fatigue strength:

1) Thickness of the overlay- In order to increase the load capacity of the overlay its thickness was reduced from 0.0007” (characteristic of “street” engine bearings) to 0.0005”.

2) Bulk strength/hardness of the overlay material- The pMax Black™overlaymaterialofKingXPserieshighperformancebearings contains 5% copper, providing higher fatigue strength.

3) Surface hardening- The higher the hardness of the surface layer, the greater the load must be in order for cracks to initial-ize. An effective method for surface hardening lead based over-lays has been developed by King Engine Bearings. This innova-tive technique enables the formation of an ultra thin (nano-scale) hardening of the overlay surface. It is an essential component of the pMax Black™ overlay. (See Fig. 1, above.)

pMax Black™ material was tested in the King test rig and compared to conventional race bearings. The typical tested bear-ings are shown in the Fig. 2 on page 74.

U-Groove™: Modified Design of Oil Groove The inertia force generated by a rotating part of the crankshaft is directed from the rotation center to the center of mass. There-fore it is transmitted to both the upper and lower main bear-ing shells. The oil groove is commonly made in the upper shell where the oil hole is located. A 180º groove is commonly suf-ficient for providing the required amount of oil to the connecting rod bearing, which it reaches by flowing through passageways within the crankshaft.

At high rotation speeds in high performance engines, the specific load (force per unit area) applied to the upper bearing may exceed the specific load to the lower bearing.

The level of specific load applied to the grooved bearing may be lowered by means of a reduction in groove width.

Design of High Performance Bearings for Race EnginesBY DR. DMItRI KOpelIOvICh

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Fig. 1 King pMax Black™ structure in King XP series

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King’s new design results in a reduction of groove width without decreasing the groove cross sectional area. It increases bearing load capacity by expanding the surface area by at least 30%, while keeping oil flow capacity intact.

According to theoretical calculations, and as observed in rig and dyno test results, the new groove design provides greater bearing durability due to lower specific loading and a more stable hydrodynamic lubrication regime: smaller peak oil film pressure and greater oil film thickness.

LUBRICATIONEngine bearings function as hydrodynamic bearings, in which a rotating journal produces a hydrodynamic force pressurizing the lubricant flowing between the journal and the bearing surfaces [3].

The pressure does not allow the journal to contact the bear-ing surface.

A converging gap (wedge) between the bearing and journal surfaces is indispensable to the normal operation of a hydrody-namic bearing.

Bull’s Eye Tolerance™: Optimal Oil Clearance Due to Consistency of Wall ThicknessOil clearance is the basic geometrical parameter of an engine in determining stability of hydrodynamic lubrication.

Oil clearance should have an optimal value, providing the desirable combination of lubrication parameters.

In an engine bearing oil clearance results as:c = Dh – Dj – 2h

Where:Dh – diameter of the bearing housingDj – diameter of the journalh – wall thickness of the bearing times two

Thus inconsistent values of wall thickness produce variations of oil clearance.

Therefore crankshaft regrinding and housing adjustments are required to achieve narrow clearance tolerances.

In addition multiple sets should be purchased and stored to “fish” for right shells.

King developed the Bull’s Eye Tolerance™ production tech-nology, ensuring the least thickness variation shell-to-shell in the industry (Fig. 4).

EccentriX™: Optimal Bearing Eccentricity The maximum theoretical value of bearing eccentricity is equal to the difference between the radius of the bearing and the radius of the journal.

In order to increase bearing eccentricity without changing the oil clearance, the inside bearing surface is produced not round. It has a lemon shape due to the varying thickness of the bearing wall, having its maximal value at the centerline (T) and gradually decreasing towards the parting line [2]. It is accepted to measure the minimal value of bearing wall thickness (Te) at a certain specified height h (Fig. 5).

Optimal value of eccentricity for engine bearings depends on the typical rotation speeds of the engine.

The higher the rotation speed the greater the level of ec-centricity, providing the best combination of hydrodynamic

HIGH PERFORMANCE BEARINGSBY DR. DMItRI KOpelIOvICh

Fig. 2: King CR 807XP bearing after King rig tests on the left vs. conventional high performance bearing on the right. (10,200 psi, 4,300,000 cycles)

Fig. 3: Conventional oil groove compared to high performance U-Groove™

Fig. 4: Wall Thickness Variation

Fig. 5: Eccentricity of journal bearings

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parameters for the bearings (Fig. 6). In order to compensate for housing distortion, the bearings should have an extra value of eccentricity.

EccentriX is an optimized eccentricity value reached through theoretical simulations and hydrodynamic analysis. Each bear-ing’s eccentricity value is designed to meet specific performance requirements.

OIL STARVATION (ElliptiX™: Improved oil ingress)Oil starvation occurs when oil supplied to the bearing is insuf-ficient for hydrodynamic lubrication.

Oil flows out of the bearing through the clearance and returns to the oil sump. Such side flow (or side leakage) plays a positive role, since it allows removing the heat absorbed by the bearings.

However if side leakage is close to or greater than pump capacity, the amount of oil becomes insufficient for generating a stable hydrodynamic film. Such conditions are called oil starva-tion.

High performance engines are characterized by operating at high loads and rotation speeds. Therefore the values of side leakage from high performance bearings are much higher than in “street” engine bearings.

The dimensions of the oil hole in a main bearing should pro-vide a flow rate sufficient to compensate for side leakage from both main and corresponding connecting rod bearings.

The conventionally designed oil hole is shown in Fig. 8.ElliptiX™ is a newly designed oil slot/oil hole hybrid (Fig. 8)

that improves oil ingress, without affecting the bearing’s surface. The innovative changes to the slot hole prevent a compromised load capacity.

PRESS FIT (RadiaLock™: Optimal Crush Height)A firmly tightened bearing has uniform contact with the housing surface, which fulfills the following functions [1]:• preventsbearingfrettingandspinninginthehousingduring

operation• providesmaximumheattransferthroughthecontactingsur-

faces• increasestherigidityofthehousing

In order to achieve a required contact pressure, the outside diameter of an engine bearing is greater than the diameter of its housing.

The parameter characterizing this press fit is called crush height (Fig. 9).

A universal value for crush height, suitable for all kinds of bearings and housings does not exist. This is because the required minimum contact pressure depends on the housing ma-terial, housing rigidity (dimensions and shape), bearing thickness and temperature.

High performance bearings working at heavy loads, high rotation speeds and increased temperatures should be installed with a higher contact pressure that provides better heat transfer and prevents the bearing from shifting in the housing.

RadiaLock ™ design ensures optimal crush height values, and perfect radial pressure.

This is particularly important in racing applications where determining the correct amount of crush height is critical - too much or too little can cause a catastrophic failure.

(continued)

HIGH PERFORMANCE BEARINGSBY DR. DMItRI KOpelIOvICh

Melling has improved the heart-beat of the traditional internal gear pump. It is now significantly smoother through the use of new helical asymmetrical gears. The new gear design provides the engine with an improved flow of oil without the usual pulsing found in traditional gear pumps. The reduction in the pressure ripple from the pump will also provide benefits to the distributor and camshaft drive.

SMOOTHER• Significant reduction in pressure ripple (pulsing)• Reduction in torque ripple in pump drive• Improved distributor operation - reduction in spark scatter• Improved distributor gear wear & intermediate shaft wear

TIGHTER• Improved sealing of gear tips to housing• Reduced internal leakage• Improved efficiency and performance

QUICKER• Increased inlet vacuum• Primes faster

Helical Asymmetrical Oil Pump TechnologyR&D Code Name: "Shark Tooth Pump"

2620 Saradan Drive · Jackson, Michigan 49204 | 800-635-5464 TEL · 517-787-5304 FAX | Visit us online at www.melling.com

Fig. 6: Effect of Eccentricity on Minimum Oil Film Thickness

Fig. 7: Bearings failed due to oil starvation

Fig. 8: Conventional oil hole compared to high performance oil slot

Fig. 9: Device for measuring crush height

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CONCLUSIONSDesign and material solutions for race bearings, that meet and exceed the chal-lenges of modern race engines, have been developed by King Engine Bearings:

•pMax Black™ – a new tri-metal bearing material for high performance applica-tions

•U-Groove™ – a new design of oil groove for the upper main shells of high performance bearings

•Bull’s Eye Tolerance ™ – a low shell-to-shell thickness variation technology

•EccentriX™ – theoretical hydrodynamic analysis for optimal eccentricity values

•ElliptiX™ – a new design of oil socket featuring an increased cross sectional area without sacrificing effective load area

•RadiaLock ™ – a design which ensures crush height values providing the op-timal combination of contact pressure and compression stress values.n

REFERENCES

[1]Kopeliovich,Dmitri.“TheProperSe-lection of Engine Bearing Materials.” Engine Professional April-June 2011: 48-62.

[2] Kopeliovich, Dmitri. “Geometry and Dimensional Tolerances of Engine Bearings.” Engine Professional October-December 2011: 70-76.

[3] Kopeliovich, Dmitri. “Hydrodynamic Journal Bearing.” SubsTech (Sub-stances & Technologies). Retrieved from www.substech.com/dokuwiki/doku.php?id= hydrodynamic_jour-nal_bearing.

Dr. Dmitri Kopeliovich is regarded as one ofthe foremost authorities on engine bearingresearch and development. He earned hisPh.D. in materials engineering and serves asresearch and development manager at KingEngine Bearings. As the manager and teamleader of King’s advanced materials researchand development unit, Dr. Kopeliovich isknown as the “Engine Bearing Doctor” forhis extensive investigations into the causeand prevention of premature engine bearingfailure. To ask Dr. Kopeliovich a question,visit www.kingbearings.com and click on“Ask Dr. Dmitri”.

HIGH PERFORMANCE BEARINGSBY DR. DMItRI KOpelIOvICh

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