Development of valve train rig for assessment of cam/follower tribochemistry

Abstract

Component bench tests are a crucial part of a tribology assessment experimental programme for most engines and subsystems. This is because they test the components under conditions simulating the operating characteristics of the system. These have become very important as they shed more light into the friction, wear, lubrication and importantly for this study, the tribochemistry of valve train systems. This work outlines the procedure for the development of a single cam rig (SCR) from a 1.25L FORD Zetec (SE) engine. Friction plots were used to validate the data obtained from the newly developed single cam rig with Mn-phosphate coated and polished follower against a cast iron camshaft. The tribofilm formed using normal and mid Sulphated Ash, Phosphorus and Sulphur (SAPS) 5W-30 oils were evaluated and correlated to the friction and wear properties of the tribopair.Raman and FIB-SEM/EDX investigations of the tribochemical films showed that the normal SAPS oil produced patchy, thick (80-100 nm) and well dispersed tribofilm with better wear prevention capabilities. It was observed that Mid SAPS oil had lower wear prevention due to loosely dispersed and thin tribofilms. Absence of tribofilms at the centre of the insert with this oil also suggests that formation and removal processes are an integral part of the wear mechanisms in highly loaded cam follower systems.

The effect of clearance between tappet insert and camlobe on the tribological and tribochemical performance of cam/follower surfaces

“…The single cam rig was set to run for a longer duration at low speeds (300 -600 rpm), which is under predominantly boundary lubrication regime. However, based on the results obtained from the previous work [15], it was suggested to increase the test duration (i.e. to be longer than [15]), as increasing the test duration is believed to be essential for wear and durability evaluation.…”

“…In an attempt to link the wear of the camlobes with standard engine tests, wear examination took place at seven locations on the cam profile (±14°, ±10°, ±4° and cam nose-0°), in accordance with ASTM D6891 standard (sequence IVA). This method has been recently used in [13,15]. For the seven selected locations, the contact pressure, lubricant entrainment velocity and load per unit length were evaluated by the authors of this work [31] in order to correlate these values to the wear mechanisms (see Fig.…”

“…The single cam rig has proved to have good repeatability and high ability to determine the frictional response of different coatings and fully formulated lubricants [15]. A high sensitivity torque transducer (RWT 421) was connected to the camshaft using flexible coupling to obtain speed and torque measurements.…”

Measuring tappet rotation in a valvetrain rig when lubricated in a fully formulated oil containing MoDTC-type friction modifier

“…The rig was constructed from a cut down 1.25L ford Fiesta Zetec-SE engine with a double overhead camshaft (DOHC) and flat faced removable inserts/tappets in bucket arrangement. The development and calibration of the direct acting SCR tribometer have been described in detail previously [23]. However, the camshaft was driven through a mechanical coupling by a 2.2 kW ABB motor (i.e.…”

“…The test procedure has been described in detail previously [23]. However, for durability purposes and wear evaluation, the tests were run for 80 hrs.…”