The Composition of Surface Layers Formed in a Lubricated Cam/Tappet ContactThe frictional behavior of two oils was measured in a cam/tappet friction apparatus using a direct acting bucket tappet geometry. One oil contained a soluble molybdenum friction modifier. The tappet was equipped with a removable friction disk, which allowed the frictional surface to be easily removed for surface characterization using surface profilometry, reflection infrared and XPS spectroscopies. The films consisted of varying amounts of inorganic phosphates, sulfates and sulfides with zinc, magnesium, and possibly molybdenum as cations. MoS 2 , expected because additives containing molybdenum and sulfur were present, was not detected. The detection limit was less than 0.1 atom percent Mo. The film formed by the friction modified oil was thinner, smoother and contained small amounts of molybdenum. While the smooth surface finish could reduce friction by improving microelastohydrodynamic lubrication, friction reduction could not be tied to any of the chemical structures detected in these experiments. . Paper No. 90-Trib-17. Associate Editor: B. Bhushan. Experimental2.1 Test Apparatus. The cam/tappet friction apparatus is an improved version of equipment described previously (Willermet, Pieprzak and Dailey, 1989;. A cam/tappet module is driven by a variable speed 2 hp. DC motor with an attached flywheel. The torque required to rotate the cam shaft is measured with a torque meter positioned between the cam shaft and flywheel (Fig. 1). Torque Meter Attachment and Mounting.Solid split shell couplings are used to attach the torque meter. These solid couplings have much lower rotational inertia than flexible couplings. This reduction in inertia significantly increases the natural frequency of the system and reduces the amplitude of the natural frequency "noise." To make the use of solid couplings possible, a visco-elastic mount was incorporated to support and stabilize the torque sensor. Cam/Tappet Module.The cam/tappet module is essentially a temperature controlled aluminum box which can accommodate a variety of value train designs (Figs. 2 and 3). The drop-in components, which establish the test configuration, are located within ±0.05 mm via locating holes. The temperature of the module is controlled by circulating a

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Design for Six Sigma (DFSS) is a systematic process and a disciplined problem prevention approach to achieve business excellence. Robust design is the heart of DFSS. To enable the success of robust parameter design, one should start with good design concept. Axiomatic Design, a fundamental set of principles that determine good design practice, can help to facilitate a project team to accelerate the generation of good design concept. Axiomatic Design holds that uncoupled designs are to be preferred over coupled design. Although uncoupled designs are not always possible, application of axiomatic design principles in DFSS presents an approach to help DFSS team focus on functional requirements to achieve design intents and maximize product reliability. As a result of the application of axiomatic design followed by parameter design, the DFSS team achieved design robustness and reliability. A hydraulic lash adjuster case study will be presented. Keyword:Design for Six Sigma, robustness, innovation and axiomatic design, parameter design.

A cam/tappet friction rig was constructed from a 1.6 L Ford valve train. The head casting and the camshaft were shortened so that only two journal bearings remained. Only one of the two remaining cam/tappet contacts was used as a frictional contact. All other contacts were equipped with rolling element bearings so that essentially all the turning torque came from cam/tappet friction and valve spring forces. The rig, together with a data acquisition/wave form analyzer system and a computer, was capable of measuring instantaneous torque with an angular resolution of less than one degree, and reducing the data to provide calculated values for parameters such as the friction coefficient. The experimental data were compared with results from a cam/tappet friction model to assist in interpretation. The data and model illustrated that lubricant composition and tappet rotation have important effects not only on overall friction, but also on the shape of friction versus cam angle curves.