Optimisation of alumina coated lightweight brake rotor

Aluminium alloys have been used extensively in the automotive industry to reduce the weight of a vehicle and improve fuel consumption which in turn leads to a reduction in engine emissions. The main aim of the current study is to replace the conventional cast iron rotor material with a lightweight alternative such as coated aluminium alloy. The main challenge has been to meet both the cost and functional demands of modern mass-produced automotive braking systems. A sensitivity analysis based on the Taguchi approach was carried out to investigate the effect of various parameters on the thermal performance of a typical candidate disc brake. Wrought aluminium disc brake rotors coated with alumina on the rubbing surfaces were determined to have the best potential for replacing the conventional cast iron rotor at reasonable cost. Optimisation of the structure was subsequently carried out using a genetic algorithm on the selected coated aluminium disc brake rotor. This determines the optimum thickness of the coating and the composition of the substrate based on selected criteria. Prototype aluminium disc brake rotors were coated with alumina using the Plasma Electrolytic Oxidation (PEO) technique and the thermal performance of these lightweight rotors was investigated experimentally using a brake dynamometer. A high speed thermal imaging system was used to evaluate and measure the rubbing surface temperature of the coated brake rotors. The experimental results showed generally good agreement with the numerical predictions. The coated wrought aluminium disc brake rotor was demonstrated to give good thermal and friction performance up to relatively high rubbing surface temperatures of the order of 500°C

The Importance of Pad Aspect Ratio in the Thermal Analysis of a Reduced Scale Brake

The performance of a brake system can be assessed in its early stages through reduced scale testing. An established scaling methodology was used in this study to scale the brake pads based on constant energy density. The primary aim was to investigate the impact of the aspect ratio of a scaled brake pad on the thermal characteristics of a scaled disc during drag braking conditions. Brake pads with four different aspect ratios were used against the scaled disc and these were scaled relative to the brake disc and pads of a medium sized passenger car. Using relevant scaling relationships, a speed–pressure matrix, consisting of nine tests, was derived and utilised in the experimental analysis. The tests were conducted using a conventional brake dynamometer. Temperatures were measured using thermocouples on the disc and pad and, for specific tests a thermal imaging camera was also used. The experimental results showed that a strong dependency exists between the maximum rotor temperature and the pad aspect ratio. This suggests that consideration of pad aspect ratio be reflected within the scaling process. A relationship between the circumferential and radial dimensions of full scale and reduced scalebrake pads was established based on their measured thermal performance. The experimental results were also used to validate a finite element model of the system. This was subsequently able to highlight important limitations associated with the model that apply equally to simulations of full and small scale brakes

The Thermal Characterisation of a Disc Brake Rotor at reduced scale with particular reference to PAD Aspect Ratio

An integral part of the development of a disc brake system is associated with the physical test of the foundation brake using a brake dynamometer. Testing undertaken at full scale is both costly and time consuming and recent work, for example Prabhu et al. (2015), has shown that reduced scale testing is capable of replicating the tribological conditions at the interface such that the thermal response of the rotor approaches that of its full scale counterpart. The same work also demonstrated experimentally the connection between pad aspect ratio and rotor response and this had been omitted from the formal scaling methodology. This paper extends the scaling theory to reflect the presence of pad aspect ratio through the use of a validated finite element model of the reduced scale brake. The results show that for the given reduced scale brake, there exists a pad aspect ratio at which the thermal response of the rotor is at a minimum. The conclusions drawn apply equally to the behaviour of the rotor at full scale

Material characterisation of lightweight disc brake rotors

Alumina coated lightweight brake rotors were investigated to evaluate the effect of coating properties on their friction performance and thermal durability. An alumina ceramic coating on AA6082 aluminium alloy (Al-Alloy) and on 6061/40SiC aluminium metal matrix composite (Al-MMC) prepared by plasma electrolytic oxidation was studied using a programme of brake dynamometer and material characterisation tests. The results showed that the plasma electrolytic oxidation alumina layer adhered well to the Al-alloy substrate and was more uniform and durable when compared to that on the aluminium metal matrix composite. The plasma electrolytic oxidation layer significantly improved the hardness of the rotor surface for both Al-alloy and aluminium metal matrix composite substrate. The coated Al-alloy disc brake rotor was demonstrated to give good thermal and friction performance up to high rubbing surface temperatures of the order of 550 ℃, but the rotor eventually failed due to temperature build-up at a critical location