And some tests on ACTUAL valve trains that run contrary to those tests.
http://papers.sae.org/860374/
Quote:
The mechanism of overhead valve train wear in moderate to low temperature service was studied using a modified fired V-D test and a motored V-D cam and cam-follower rig. High wear and Sow wear used oils from the fired test gave the correct relative wear in the motored test, indicating the motored test is a valid tool for studying wear mechanisms. Key factors affecting valve train wear were isolated and selectively introduced in a series of motored engine tests. Results from this study showed the expected increase in wear with a decrease in viscosity of unformulated lubricants. Added zinc diaikyldithiophosphate (ZDDP) reduced wear in a low viscosity lubricant and a used oil as anticipated. A high detergent, high wear oil, in an unused state, did not produce significant wear in the motored test even if all of the ZDDP was removed. Significant wear resulted only after exhaust gases (simulated blowby) were fed into the motored engine sump containing the high wear oil. Laboratory simulation of blowby effects showed the importance of wear resulting from oil aging by chemical reactions between the lubricant and blowby gases. This effect is important even when the viscosity of the lubricant is otherwise sufficient to preclude wear. Active ZDDP depletion by thermal and oxidative routes contributes to wear. Viscosity losses in the Sequence V-D test and in the fired test were large due to fuel dilution and Viscosity Index Improver shear which can lead to further increases in wear.
http://pij.sagepub.com/content/226/4/306.abstract
Quote:
In the last three decades, there has been a resurgence of interest in reducing friction in the engine valve-train for better fuel economy and improved emissions. Research studies and scientists have developed complex mathematical models and advanced test rigs to understand the interaction between cam and tappet. Most of the experimental valve-train work has been carried out on motored test rig assuming there is less difference in valve-train friction under motored and fired conditions. For complete understanding of the difference of camshaft friction under motored and fired conditions, experiments have been carried out on a real engine under both conditions allowing for the first time the detailed study of the effect of cylinder pressure on exhaust camshaft friction. A new method of directly measuring camshaft friction that offers excellent accuracy is described in this article. The technique uses strain gauges to measure the torque exerted upon the camshaft drive pulley sprocket. The advantage of this method over previous techniques is the instantaneous valve-train friction as a function of crank angle can be measured, simultaneously for both inlet and exhaust camshafts, under motored and fired conditions. Experiments have been carried out for both motored and fired conditions on a single-cylinder gasoline engine. Results are presented for instantaneous and mean valve-train friction as a function of engine speed and oil temperature, indicating a decrease in friction with increase in engine speed and an increase with increase in temperature. A significant difference in valve-train friction between motored and fired conditions was found, especially for the exhaust camshaft.
http://papers.sae.org/860374/
Quote:
The mechanism of overhead valve train wear in moderate to low temperature service was studied using a modified fired V-D test and a motored V-D cam and cam-follower rig. High wear and Sow wear used oils from the fired test gave the correct relative wear in the motored test, indicating the motored test is a valid tool for studying wear mechanisms. Key factors affecting valve train wear were isolated and selectively introduced in a series of motored engine tests. Results from this study showed the expected increase in wear with a decrease in viscosity of unformulated lubricants. Added zinc diaikyldithiophosphate (ZDDP) reduced wear in a low viscosity lubricant and a used oil as anticipated. A high detergent, high wear oil, in an unused state, did not produce significant wear in the motored test even if all of the ZDDP was removed. Significant wear resulted only after exhaust gases (simulated blowby) were fed into the motored engine sump containing the high wear oil. Laboratory simulation of blowby effects showed the importance of wear resulting from oil aging by chemical reactions between the lubricant and blowby gases. This effect is important even when the viscosity of the lubricant is otherwise sufficient to preclude wear. Active ZDDP depletion by thermal and oxidative routes contributes to wear. Viscosity losses in the Sequence V-D test and in the fired test were large due to fuel dilution and Viscosity Index Improver shear which can lead to further increases in wear.
http://pij.sagepub.com/content/226/4/306.abstract
Quote:
In the last three decades, there has been a resurgence of interest in reducing friction in the engine valve-train for better fuel economy and improved emissions. Research studies and scientists have developed complex mathematical models and advanced test rigs to understand the interaction between cam and tappet. Most of the experimental valve-train work has been carried out on motored test rig assuming there is less difference in valve-train friction under motored and fired conditions. For complete understanding of the difference of camshaft friction under motored and fired conditions, experiments have been carried out on a real engine under both conditions allowing for the first time the detailed study of the effect of cylinder pressure on exhaust camshaft friction. A new method of directly measuring camshaft friction that offers excellent accuracy is described in this article. The technique uses strain gauges to measure the torque exerted upon the camshaft drive pulley sprocket. The advantage of this method over previous techniques is the instantaneous valve-train friction as a function of crank angle can be measured, simultaneously for both inlet and exhaust camshafts, under motored and fired conditions. Experiments have been carried out for both motored and fired conditions on a single-cylinder gasoline engine. Results are presented for instantaneous and mean valve-train friction as a function of engine speed and oil temperature, indicating a decrease in friction with increase in engine speed and an increase with increase in temperature. A significant difference in valve-train friction between motored and fired conditions was found, especially for the exhaust camshaft.