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Technical Paper

Compatibility between Brake Discs and Friction Materials in DTV Generation and Recovery Test

A comparative study was carried out to investigate the DTV (disk thickness variation) behavior according to the types of brake disks (gray iron grade 250 and high-carbon gray iron grade 200, 170) with two typical friction materials (non-steel and low-steel friction materials). To evaluate DTV generation and recovery characteristics, a parasitic drag mode simulating highway driving (off-brake) and a normal braking mode simulating city traffic driving (on-brake) were used with an inertia brake dynamometer. Results showed that DTV and BTV were strongly affected by the microstructure, hardness level and distribution of the gray cast iron with the friction material types. The BTV was reduced in the friction two pairs using non-steel friction materials with high carbon grade disks and low-steel friction materials with high-carbon, low hardness disk. In particular, the pair of low-steel friction materials and high-carbon, low-hardness brake disks was more effective on DTV recovery.
Technical Paper

Corrosion Induced Brake Torque Variation: The Effect from Gray Iron Microstructure and Friction Materials

Brake judder caused by corrosion of gray iron disks was investigated. In this study, the microstructure of the gray iron disks and the friction film developed on the disk surface by commercial friction materials were examined to find the root cause of the corrosion induced brake torque variation. Corrosion of the disk was carried out in an environmental chamber, simulating in-vehicle disk corrosion. Moisture content and acidity of the friction materials were also taken into account for this investigation and brake tests to examine torque variation during brake applications were performed using a single-end brake dynamometer. Results showed that the friction film developed on the disk surface strongly affected the amount of corrosion, while graphite morphology of the gray iron had little effect on the corrosion.
Technical Paper

Development of High Strength, Fracture Split Steel Connecting Rods

A new high strength microalloyed steel has been developed for fracture split connecting rods for heavy duty diesel engines that provides advantages in cost saving and weight reduction. This new splittable steel has higher fatigue strength than conventional steel with improved machinability. The key issue with this development is how to increase the mechanical strength without sacrificing both splittability and machinability. This goal was achieved by substituting the conventional high carbon microalloyed steel with a new type of alloy design that combined an optimized splitting capability and con rod geometry. This research focused on optimizing two major technical considerations for this application - new medium carbon chemical composition with a high silicon range to maximize the splittability without any plastic deformation. Secondly, process parameters for both the hot forging and fracture splitting process were developed to ensure a consistent microstructure and fracture surface.
Technical Paper

Development of Fracture Split Steel Connecting Rods

Fracture split steel connecting rod has been developed for new passenger diesel engines for its advantages in cost saving and better performance. The splitting type of steel con rod is made of high carbon micro-alloyed steel with no additional heat treatment after hot forging. This con rod blank is forged in one-die mold and later fracture splitted. Unlike the conventional types where the rods and caps are separately forged and machined, this steel split con rod needs no additional rod/cap contact face milling which means a substantial savings in machining cost. Besides, a firm contact between rod and cap improves stiffness and compatibility with other crank-train moving parts - a definite merit in engine performance. Our research work focuses on optimizing the two major technologies in this subject - microstructural analysis of controlled cooling (high carbon micro-alloyed steels) and detailed fracture splitting parameters and test results.
Technical Paper

Fatigue Strength and Residual Stress Analysis of Deep Rolled Crankshafts

The endurance life of an engine crankshaft is closely related to its fatigue strength, in addition to other material properties and shape parameters. Deep rolling, moreover, enhances the fatigue limit by applying compressive residual stress within the fillet radius area as a major surface hardening technique. The objective of this research is to maximize engine fatigue life through crankshaft design optimization by quantifying fatigue strength for microalloyed steels versus a Cr-Mo alloy steel, and to examine the effects of deep rolling load and rolled fillet geometry. Fatigue tests have been made with standard rotary bending test samples from both bar and forged blanks. Rig tests for actual crankshafts have been made to show how the fatigue strength correlates with different sample types. A correlation of stress distribution with bending moment was demonstrated by applying a strain gauging technique on crankshaft specimens.
Journal Article

Effects of Chemical Components and Manufacturing Process of Cast Iron Brake Disc on its Resonant Frequency Variation

Many engineers have been working to reduce brake noise in many ways for a long time. So far, a progress has been made in preventing and predicting brake noise. Nevertheless, there are some discrepancies of brake noise generation propensity between testing for the prototype and the production. As known in general, the reason for this unpredicted brake noise occurrence in production is partly due to the variation of the resonant frequency, material and the other unpredictable or unmanageable variations of the components in a brake system. In this paper, effects of chemical components and casting process of gray iron brake disc on its resonant frequency variation have been studied. Especially this paper is focused on the variation in material aspects and manufacturing parameters during disc casting in usual production condition. And their effects are investigated by the variation of out-of-plane modal resonant frequency.