TAPPET PERFORMANCE THROUGH GIANT MAGNETO RESISTANCE (GMR) SENSORS

Abstract

There is a continuous pressure on the automotive OEMs to develop fuel efficient and low emission vehicles. In addition to design changes, improved lubricants can significantly impact friction at critical contacts in engine components and improve fuel economy. To reduce friction, it is important to understand the behavior of each engine component in detail. In an IC engine, frictional losses are mainly in piston assembly, engine bearings and valve train. Although, frictional losses in valve train are relatively low as compared to other major tribological components but their contribution becomes significant at low engine speeds and higher lubricant temperatures. In addition to that, it is one of the most challenging components to lubricate effectively and is prone to excessive wear resulting in reliability and durability problems.

It is widely accepted that in the direct acting valve train engines most of the frictional losses from the valve train originate from cam/tappet and tappet/bore interaction. In such configurations, the cams are slightly off centered relative to the tappet center to facilitate and ensure tappets continue rotating in their bores. Uniform tappet rotation reduces friction in cam/tappet interface and increases the life of the tappet by distributing the wear over a large surface. If a tappet stops rotating, failure can occur due to the localized wear.

In this research work, innovative measurement technique has been developed that allows real time monitoring of tappet rotation of all the tappets in a real production engine having a direct acting valve train configuration. For the very first time, rotational speeds of all the tappets were monitored simultaneously by deploying Giant Magneto Resistance (GMR) sensors in the engine head. The attractive features of GMR sensors are its miniature size, relatively low cost and most importantly there is no need for modification or machining of the tappet bore thus allowing analyzing the tappet performance in its original environment in a real engine head. GMR sensors are easy to install and have no adverse effect on the performance at high lubricant temperatures. Experiments are carried out using specially designed flexible test rig capable of running the engine under motored conditions at different camshaft speeds and at different lubricant oil temperatures and pressures. The tappet monitoring system is installed on the commercial diesel engine head and tested at different conditions to analyze the rotational behavior of the tappets.