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Efficiency of a toroidal traction drive is measured at different torques, speeds, speed ratios, and temperatures, with an emphasis on the effect of the design traction coefficient on variator efficiency. This is accomplished by independently controlling the trunnion and the clamp pressures representing the variator torque and the clamp load, respectively. Also measured is the effect of roller conformity on variator efficiency. Furthermore, a low-speed and high-temperature test is conducted to observe a potential change in the effective coefficient of traction due to a transition in the lubrication mode. It is shown that, by optimum clamping (without gross slip) the variator efficiency can be increased by 1- to 2-percentage point over the efficiencies measured with nominal clamp loads. Also verified is the rapid decrease in variator efficiency with over clamping above the nominal clamp loads. All test results compared well with model predictions.

A relatively simple, low-friction Variable-Valve-Actuation (VVA) device is presented. The device can be characterized as a four-bar mechanism consisting of a crank, a rocker and a coupler, all supported on a carrier body. Description of the prototype hardware, and the results of the friction measurements are presented in an accompanying paper [1]. In the present paper, a kinematic analysis/synthesis and a rigid-body dynamic analysis are outlined. Also included is a flexible-body model where the coupler link, which was suspected to be the most severely stressed member, is modeled as a flexible component. A sensitivity-uncertainty analysis employing the Fourier-Amplitude-Sensitivity-Test (FAST) method is conducted to identify the dominant design parameters, and to predict the variations in mechanism's performance due to the uncertainties in the design parameters.

Variable valve actuation (VVA) has been recognized as a potential method to improve engine efficiency, low-end torque, high-end power, idle stability, and emissions. This paper presents a low-friction VVA device that can modulate the valve lift and timing, and potentially provide many of the benefits listed. In order for the VVA-related additional losses not to out-weigh the benefits, energy consumed in friction and activating the VVA mechanism must be comparable to the total energy consumed by friction in a conventional valvetrain. To confirm this point, hardware was built and installed on a General Motors L-4 cylinder head employing 4 valves per cylinder. The frictional-energy loss and the actuation torque for the mechanism were measured at different speeds and oil temperatures. The dynamometer tests confirmed the simulation results that the mechanism consumes less frictional energy than a direct acting, non-roller type valvetrain.

A mathematical model for tribological analysis of different automotive- valve-train configurations has been developed as a part of the FLARE (Friction and Lubrication Analysis of Reciprocating Engines) package. The model is based on an in-depth kinematic analysis and on a rigid-body dynamic analysis, including dynamic analysis of the valve spring. Lubricant film thickness, contact pressures, and frictional power loss are predicted. A mixed-lubrication model is used to determine the friction force at the cam-follower interface. In addition, lifter rotation is modeled to predict its effect on frictional power loss. Detailed results are presented for a pushrod valve train. Also, this paper compares frictional power loss for five different valve train types. They are: direct-acting overhead cam, pushrod, end-pivoted finger follower, center-pivoted finger follower, and cam-in-head. The valve trains are made equivalent by keeping the valve lift and the no-follow speed the same.