1998-02-23

Design and Development of Method of Valve-Train Friction Measurement 980572

The general trend in the IC engine design has been towards reduction in fuel consumption since the 1973 oil embargo. The improvement in combustion process has contributed greatly to a better fuel economy of today's engine and there are many challenges ahead on the GDI front towards the 3L/100km engine [1].
One of the biggest windows of opportunity in achieving higher engine fuel efficiency together with an acceptable emissions level is to reduce its friction. To achieve these an accurate method of assessing friction levels through the concept, design and development is paramount. Translation of friction torque to the total drive cycle's fuel consumption is carried out using Ford's in-house CAE analytical packages.
A new method of directly measuring camshaft friction has been developed, which offers both exceptional accuracy and unprecedented convenience. The advantage of this methodology over previous techniques is that it can be run simultaneously with other engine development tests on either motored or fired engines, with little effort and no specialized testing equipment. The method uses strain-gauges to measure the torque exerted upon the cam-sprockets whilst running at constant speed, on motored or fired engines. The system was statically calibrated and validated dynamically. It has been validated by two dynamic tests: a direct co-axial motoring test carried out on Ford's friction rig in Cologne, and a tear-down engine friction test performed in Dunton. Readings are found to be repeatable to within 1%, and the technique is accurate to the nearest 0.05 Nm. The measured data were then compared to the analytical predictions of ESA, ENFAS and VTF4 models [2, 3 &4].
The acquired signal was also used to determine the rotational vibration modes of the total valve-train system. Case studies into the variation of valve-train friction with engine speed, load and oil temperature have been carried out as well as a comparison between motored and fired valve-train friction and an evaluation of the benefits of low-friction oil.
This method shows good correlation with the existing methods and its capability of measuring absolute friction torque in firing engines makes it suitable to be used as an integral part of the engine development process. The method developed was presented and recommended for all further valve-train friction measurement as an integral part of the engine design and development process.

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