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Technical Paper

Fuel Efficiency Improvements in Heavy Truck Driveline Systems through Advanced Bearing Design and Technology

Improved fuel economy translates into significant savings over the life of a fleet vehicle. Aside from fuel cost savings, tighter emissions regulations require truck Original Equipment Manufacturers (OEMs) to improve the fuel economy of the products they bring to market. OEMs are dependent on Tier 1 suppliers for many systems which have a direct impact on vehicle fuel efficiency. Tier 1 suppliers are then dependent on sub-suppliers for components which affect the fuel efficiency of the system. Improvements in tapered roller bearing design and technology can significantly improve the fuel efficiency of driveline systems. This paper summarizes the improvement in bearing efficiency by applying advanced design and technology solutions. Analysis was used to predict the affect of design changes, leading to an optimized solution. Testing was performed to verify the improvement in bearing efficiency.
Technical Paper

Experimental and Analytical Methods for Assessing Bearing Performance Under Debris Contaminated Lubrication Conditions

Debris particle contamination in lubricants has been identified as a major cause of premature bearing and gear failure, with accompanying costs in equipment downtime, warranty, and lost productivity. Various experimental and predictive methods have been developed to assist the design engineer in analysis and development of equipment that is less sensititive to such contamination. This paper provides an overview and new data comparing bearing life test results and predictive analysis methods for various tapered roller bearings operating under debris-contaminated conditions. As a baseline, some past work in these areas is briefly summarized and referenced. Recent work has refined one analytical method (using a surface characterization technique), correlated this method with bearing test lives in debris conditions, and pointed to design and manufacturing modifications in the bearings themselves, making the bearings live longer in debris-contaminated environments.
Technical Paper

Investigation of Package Bearings to Improve Driveline Performance

The tapered roller bearings employed in axle centers for the pinion support are critical components in determining the noise, fuel economy and reliability characteristics of the vehicle. They represent a relatively complex mechanical and tribological system, with special requirements from the stiffness, lubrication and heat transfer points of view. This paper brings a contribution to the investigation of the intricate dependency between design parameters, environmental factors and the resultant performance of a package bearing in an integral double cup configuration. Axial compactness, reduced weight, and superior rigidity are only few of the multiple advantages recommending this type of double row bearings for automotive driveline applications. Different aspects related to the tapered roller bearing setting are analyzed in a theoretical and experimental manner, also under the consideration of the manufacturing and assembly processes.
Technical Paper

Tapered Roller Bearings with Improved Efficiency and High Power Density for Automotive Transmissions

This paper is focusing on the performance enhancement of the tapered roller bearings supporting the transfer shaft in a push belt type Continuously Variable Transmission (CVT). It also provides an objective comparison, based on test results, with the fixed/floating ball bearings alternative arrangement. The influence of different design parameters such as cup and cone race profile, roller length / diameter ratio, surface finish etc., is quantified in the analytical and experimental investigation. The bearings power loss is calculated and measured for operating conditions that are relevant in a vehicle fuel economy cycle. Additional specific aspects related to the use of tapered roller bearings, such as setting and mounting procedures, are discussed under similar considerations. The paper contains a system analysis of the transfer shaft interacting with the variator output shaft and with the differential.
Technical Paper

Observations of the Impact of Lubricant Additives on the Fatigue Life Performance of Tapered Roller Bearings

Lubricant formulations and lubricant additives have been slanted heavily toward protecting gear concentrated contacts from galling and wear. Much of the performance differentiation of these lubricants has been dependent on highly accelerated standardized laboratory testing. The area of contact fatigue has played a less important role in shaping lubricant formulations, but new test results for several commercially available gear lubricants suggest this area warrants a closer examintion. The implications of these findings for equipment applications are discussed, and suggestions are made for ways to minimize or avoid potential detrimental performance effects.
Technical Paper

A Standardized Method for Evaluating Debris Resistance of Rolling Element Bearings

Debris resistant bearings are being promoted by various bearing manufacturers as a solution for many contaminated lubrication environments. The baseline for such claims is often unclear for the bearing user and leaves questions as to how the information relates to specific field applications. In order to determine the benefits, if any, of these new product offerings and to assess their effectiveness, a standard method of evaluation is needed. An approach to satisfying this need is described and typical results are provided for several commercially available bearing products.
Technical Paper

An American Steel Producer's Continuing Efforts to Provide Value to the Automobile Industry

This paper describes how one American steel producer has been able to provide value which has benefitted the automotive industry in the past and how it is striving to provide value now and intends to do so for many decades into the future. As an alloy steel bar and tube manufacturer serving the automotive industry since its infancy, the Company has had to conquer many serious problems and challenges over the years. The current challenge is doing business as an American company in today's growing global society. In addition to overcoming the obstacles created by today's business environment, it will take continued innovativeness to provide value to the customer. THE THOUGHT OF MAKING STEEL probably never entered the mind of Henry Timken, the Company's founder, who spent most of his career producing carriages, buggies, and wagons. He was more concerned with friction in the axle bearings and what he could do to reduce it.
Technical Paper

A Contact Stress Model for Predicting Rolling Contact Fatigue

Predicting fatigue performance in concentrated contacts under thin film (or mixed) lubrication conditions has historically involved various empirical approaches. Typically a lubrication parameter is used in an experimentally derived equation to predict the expected rolling contact performance. However, this model doesn't explain the performance improvements. Enhanced finish bearings have exhibited longer life than standard finish bearings, especially when bearings are operated with thin EHL film. In this paper, the contact surfaces of test bearings were analyzed by using a micro-macro contact model in which the macro-contact was elastic contact, and the micro-contact was elastic-plastic contact. The interior subsurface stress maps were calculated from the real contact surfaces, which included the effects of roughnesses, waviness, and profiles.
Technical Paper

Design and Selection Factors for Automatic Transaxle Tapered Roller Bearings

Tapered roller bearings have proven successful in a number of high-volume automatic transaxle designs. Typically, tapered roller bearings are required to carry high loads generated by helical and hypoid gears. To meet the demands of a successful design, a number of factors must be considered in the selection and application of tapered roller bearings. This paper presents a discussion of these factors as well as results from Chrysler's transaxle testing. Selection of tapered roller bearings is based on the transmission duty cycle developed using load and speed histograms, gear data, size constraints, and life requirements. A bearing life analysis considering the total transaxle system is conducted using a sophisticated computer program. Various system effects are analyzed including the load/speed cycle, housing and shaft rigidity, lubrication, bearing setting, thermal effects, and bearing internal design.
Technical Paper

The Influence of Debris on Rolling Bearing Performance: Identifying the Relevant Factors

Over the last ten years fatigue tests or wear tests, with and without debris present, have been performed on at least 11 different bearings including five sizes of ball bearings, five sizes of tapered roller bearings and one cylindrical bearing. After evaluating these tests, which include two series that were conducted in the author's laboratory, six factors have been identified that influence bearing performance when debris is present. These factors are debris (size and distribution), lubricant system, lubricant film thickness, levels of filtering, bearing materials and contact size. The results are summarized in table form.
Technical Paper

Modeling of Tapered Roller Bearings in Structural Analyses

Incorporating tapered roller bearings in finite element and other structural analyses requires special considerations. Tapered roller bearing properties such as induced thrust, induced moment, load zone, and bearing stiffness can substantially affect the results of such analyses. This paper will discuss pertinent tapered roller bearing structural properties, two potential modeling techniques, and several examples on how bearing models were incorporated into structural analyses.
Technical Paper

Engineering Thermoplastic Cages for Tapered Roller Bearings

Engineering thermoplastics have greatly improved over the last decade. As a result of these improved performance characteristics and their becoming more cost competitive with traditional cage materials, their use in tapered roller bearing cages has become a reality. Design flexibility, lighter weight, resistance to handling damage, etc. make them attractive. This paper does point out certain characteristics of thermoplastics which must be taken into consideration thus influencing the choice of material and what environments they can endure. Compatibility with lubricants at elevated temperatures, growth from moisture and thermal expansion, solvent resistance, impact resistance, strength and dimensional stability are the major considerations. Thermoplastics have found a place in the tapered roller bearing family.
Technical Paper

Using Histograms in the Selection Process for Tapered Roller Bearings

Advances in computer technology and the published results of extensive bearing research and empirical testing, have allowed designers to expand the traditional catalog approach and optimize the selection process for tapered roller bearings. This paper explores many of the factors influencing bearing selection where fatigue life is the primary concern, and describes how the Bearing Systems Analysis (BSA) approach, as used by The Timken Company, incorporates the effect of many of these environmental variables. Particular attention is paid to the formation and analysis of the load-speed spectrum, or histogram, and to the vital part it plays in the bearing selection process.
Technical Paper

A Family of Tapered Roller Bearings for Front Wheel Drive Vehicles

Automotive wheel and brake engineers are studying various wheel bearing concepts which lend themselves to easy installation and reduction of unsprung weight. A family of tapered roller bearing designs has been developed for both driving and non-driving wheels which offer the industry several options for marrying suspension, wheel and bearing components. While differing in configuration, all may be selected to meet established criteria for satisfactory performance based on the latest bearing analysis techniques and experience derived from extensive laboratory and field test programs.
Technical Paper

Environmental Factors and Bearing Damage

Environmental effects on fatigue and non-fatigue modes of tapered roller bearing damage are discussed. Primary emphasis is placed on the influence of load, speed, lubricant and temperature on the fatigue modes of damage. Effects of dissolved water in oil, traction fluids and fire resistant hydraulic fluids are included.
Technical Paper

New Bearing Selection Concepts and Mounting Guidelines for Off-Highway Wheels

Increased size, payload and horsepower requirements are the trend in today's off-highway industry. This paper discusses the role of new anti-friction roller bearing technology in avoiding problems created by changing design considerations and the performance/cost/EPA triad currently squeezing designers and manufacturers of rubber tired earthmoving machinery. A comparison is made of bearing fatigue life determined by several methods including those derived from vehicle instrumentation and purely empirical criteria. Some common problems relating to the mounting and set up of large wheel bearings are also reviewed together with corresponding remedies.
Technical Paper

The Effect of Fire Resistant Hydraulic Fluids on Tapered Roller Bearing Fatigue Life

Fatigue life testing was performed on tapered roller bearings using several fire resistant hydraulic fluids. The test fluids included an ester-oil blend, synthetic esters, invert emulsions and water glycols. For comparison, tests were also run in a reference petroleum oil and a petroleum type antiwear hydraulic oil of similar viscosities. Test results show that the relative bearing fatigue life compared to the reference oil ranged from 100+ percent for the ester oil blend to 14 to 24 percent for the water glycol.
Technical Paper

Lubricant Contaminants and Their Effects on Bearing Performance

Contaminants that find their way into the lubrication system of a mechanism can have significant adverse effects on the useful life of the antifriction bearings in the application. This paper provides a discussion of the more common types of solid and liquid lubricant contaminants and the possible sources from which they originate, plus the different modes of premature bearing damage that can result. Some case histories of applications plagued with contaminated lubrication problems and the resulting difficulties encountered with bearing performance are also reviewed. These views are primarily limited to past experience with tapered roller bearings manufactured from case hardened materials.
Technical Paper

Design Parameters for Automated Bearing Settings

Automated bearing setting techniques have been developed to insure economy and reliability with regard to the assembly and setting of tapered roller bearings in a wide variety of machinery and equipment. The application of these concepts is designed to minimize or eliminate the human variable of judgment and skill during the assembly operation. The full effectiveness of these concepts can be utilized only if machinery is properly designed to accommodate these methods. Emphasis will be placed on design considerations to achieve this end. Various setting techniques will be presented that are currently being used successfully on a production basis.