Novel friction pairs for environmentally-friendly automotive brakes

Compared to the massive effort aimed at reducing diesel particulate emissions, wear emissions from friction brakes have received far less attention. The alternative electric powertrain vehicles usually employ some form of regenerative braking system but they will continue to require friction brakes for conditions where the regenerative system fails or is less effective such as when the vehicle comes to rest at traffic lights. It is likely therefore that wear emissions from friction brakes, alongside those from tyre/road interactions, will become the major source of atmospheric particulate pollution from road transport in the years ahead.

With the emergence of friction materials development, there is a need to fully understand brake pad/disk interactions between current and future friction materials and new materials technology for applications in automotive, high speed rail, airspace, etc. This proposed research will build on our ongoing research and will aim to provide an in-depth understanding of the interactions between the brake pads and disks leading to particle emission with different natures and characteristics as a result of wear. This would provide a knowledge on the mechanisms of particles generation and their characteristics and could present valuable guidelines to minimize particulate emissions from friction brakes whilst reducing the unsprung mass of the vehicle and hence reducing CO2 emissions.

The project is a collaborative study between the Schools of Mechanical Engineering and Chemical and Process Engineering and our industrial partners. The main outcome of this proposed research will be development of a friction braking system with optimum tribological performance (good friction characteristics with low wear) leading to less particulate emission generation and a cleaner environment.

With increasing demand for e-mobility, ever-increasingly strict particle emission legislations and a need to reduce the hazardous substances form the brake pads; development of novel friction material is becoming more critical than ever. This may alter the generation of third body layer (TBL) on the counterpart (i.e. brake disk) which is crucial for the effectiveness of the tribological system. For more than 20 years, braking research at Leeds has focussed on investigating lightweight alternatives to the standard grey cast iron brake rotor material. Although a number of alternative rotor materials have been considered (notably aluminium MMC’s), the most promising candidate now appears to be an alumina-coated unreinforced aluminium alloy which has been demonstrated to be hard-wearing and thermally resistant. Development of a compatible and hard-wearing iron-free friction material would release far less particles, albeit iron free, into the environment. 

The main objectives of the PhD project are:

To conduct rigorous numerical and experimental studies of brake wear debris generation and air-borne trajectories.
To fully characterise the physical, material and mechanical properties of debris particulate matter generated.
To investigate the formation, composition and structure of the third body layer from friction material and the underlying tribology.
To link the formation, composition and structure of the third body layer to its effects on the brake performance (friction, wear, NVH and particle emissions).