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The design of a braking system involves a delicate balance between the friction pair, the disc and pad, where the pad is a complex blend of constituents to provide predictable characteristics, typically, a known and consistent friction level. In its base form the brake has to absorb the vehicle kinetic energy by converting it into heat. This heat absorption by the friction pair can result in chemical and physical interactions with the release of debris about which we know little. Other than environmental concerns, brake dust causes unnecessary problems with wear, thermal gradients (hot banding) and NVH. This paper is concerned with the removal and collection of brake debris from the friction interface - the debris being regarded as solids and airborne particles, the latter less than 10μm in size. The test procedure consisted of a Burnish program followed by 8 different drive cycles. The overall effects of debris removal is then reported for each test.

Thermo-elastic and thermo-plastic behaviour takes place with a disc brake during heavy braking and it is this aspect of braking that this paper considers. The work is concerned with working towards developing design advice that provides uniform heating of the disc, and equally important, even dissipation of heat from the disc blade. The material presented emanates from a combination of modeling, on-vehicle testing but mainly laboratory observations and subsequent investigations. The experimental work makes use of a purpose built high speed brake dynamometer which incorporates the full vehicle suspension for controlled simulation of the brake and vehicle operating conditions. Advanced instrumentation allows dynamic measurement of brake pressure fluctuations, disc surface temperature and discrete vibration measurements.

The paper overviews the modes of vibration of the principal component parts of a brake and their contribution to system instability during noise generation. It is shown that both in-plane and out-of-plane vibration are present and that both can be related to the vibration of the pad. It is further shown that the pad and its region often provide a solution or “fix” towards noise prevention and it is this area that forms the focus of this investigation. The collective evidence, proposals and associated theory are applied to real brake case studies when it is demonstrated that disc/pad interface “spragging” may be the source of brake noise. Measurements of the position of the dynamic centre of pressure (CoP) support the theoretical predictions that a leading CoP induces brake noise. Design proposals are suggested that may be applied early in the design phase as a means to reduce the propensity of a brake to generate noise.

This paper considers a study of the thermo-elastic behaviour of a disc brake during heavy braking. The work is concerned with working towards developing a situation (or design) that provides uniform heating of the disc, and equally important, even dissipation of heat from the disc blade. The approach is through a combination of modelling, on-vehicle testing but mainly laboratory investigations. The experimental work makes use of a purpose built high speed brake dynamometer which incorporates the full vehicle suspension for controlled simulation of the brake and vehicle operating conditions. Extensive instrumentation allows dynamic measurement of brake pressure fluctuations, disc surface temperature and discrete vibration measurements. Disc run-out measurements using non-contacting displacement transducers show the disc taking up varying orders of deformation ranging from first to third order during high speed testing.

This paper discusses the measurement of the dynamic centre of pressure (CoP) of a brake pad during a normal braking event using a modified 12-piston opposed calliper. The modifications allow the centre of pressure to be controlled both radially and along the length of the pad, inducing a leading or trailing centre of pressure as desired. The technique is unique in its design and implementation. Both the centre of pressures of the inboard and out-board pads are recorded simultaneously with varying pressures and speeds. The results, which include pressure and force maps, show the position of the centre of pressure to vary considerably during a braking event, both radially and axially along the pad. The CoP offset is related to the calliper mounting geometry which is subsequently compared to the effective “spragging angle” and the generation of brake noise.

Growing global concern pertaining to climate change has meant that engine development has become more focused on engine emissions. A method of reducing the emissions of an internal combustion (IC) engine is to use smaller engines but recover power lost due to reduction in size by using a turbocharger or supercharger. Turbocharged vehicles are commonly used but they exhibit a weak point of poor performance under transient running conditions. The phenomenon, known as “Turbo-lag”, is most noticeable when a sudden load change is applied at lower engine speeds combined with rapid acceleration. The work presented analyses a novel method of improving the transient performance of turbocharged engines by injecting air into both the compressor of the turbocharger as well as inlet manifold of the engine-known as a two point air injection system.

The purpose of this paper to present an educational vision that involves increased collaboration between industry and academia in the training of automotive engineers to meet the global demands of the 21st century. It will outline the increasing need for industrial contributions towards the development of automotive specific courses to suit industry specific needs, recognized educational standards to meet the needs of the automotive industry, validation and accreditation of courses, approved centers of excellence, automotive academies, worldwide collaboration in the internship of students, inter-university collaboration, joint responsibilities to provide training facilities for teaching and research, scholarship schemes and inter-country educational & industrial exchanges and possible globalization of the educational process.

This paper is concerned with addressing the problems experienced with the thermo-elastic behaviour of the disc - that of optimum heat dissipation, and equally important, even heating of the disc blade. The primary objective is to develop a more temperature-stable brake disc. The work presented approaches the problems of thermal judder through benchmarking the current situation. This is approached by modelling the current brake and its validation by means of vehicle and laboratory testing. The empirical work is centred on a bespoke high speed brake dynamometer which incorporates the full vehicle suspension for an accurate yet controlled simulation of brake and vehicle operating conditions. The dynamometer is housed in a purpose built laboratory with both CCTV and direct visual access. It is capable of dynamic measurement of DTV, caliper pressure fluctuations, disc surface temperature and vibration measurements at discrete points about the rig.

Within this paper the convective heat dissipation from the front brake discs fitted to the left and right hand side of a high performance passenger car has been compared. The tools used in this investigation include computational fluid dynamics (CFD) and vehicle testing. The results show that although identical discs are fitted to both sides of the vehicle the disc fitted to the left hand side shows better thermo-aerodynamic properties than that fitted to the right due to the different direction of rotation. The computational model shows strong agreement with the test results; over predicting the average heat transfer coefficient by 4% for the left hand disc and 7.6% for the right disc. The CFD analysis enabled a detailed insight into the air flow and heat transfer distributions that was not possible during the vehicle test regime.

Pressure sensitive film embedded into the body of a pad friction compound is a unique technique used to measure the dynamic centre of pressure at the pad/disc interface during a normal braking operation. This paper uses of a modified 12 piston opposed caliper where the initial centre of pressure may be varied both along the pad and radially. Results show a very definite movement of the centre of pressure towards the centre of the pad as the brake pressure is increased. In addition it is seen that a leading centre of pressure (CoP) will result in noise whereas a trailing CoP gives a quiet brake. Equally a CoP towards the inner edge of the pad increases noise propensity whereas towards the outer edge a quiet brake. The results also show little influence on the CoP with disc speed.

This paper discusses the analysis and measurement of the dynamic centre of pressure of a brake pad during a normal braking event. The technique is unique in its design and implementation. The process is progressive whereby the interface static measurements are first taken and then dynamic testing is carried out under braking. Two different measurement systems are considered during the analysis with one used to measure the center of pressure. Both the in-board and out-board pads are measured for wear but the piston pad was selected for pressure measurements. Validation of the spragging process is undertaken on both test rigs and vehicle trials. Pad wear measurements complement the collective information. The results show the position of the centre of pressure to vary considerably during a braking event, both radially and axially along the pad.

Asymmetry is applied to a heavy-duty commercial twin calliper disc brake rotor as a means to alleviate an undesirable high amplitude noise. The problematic frequency is 2400 Hz, the rotor blade exhibiting a 5-diametric mode order of vibration. The asymmetry is introduced by drilling sets of radial holes into the disc rim. Modal analysis is carried out over a range of frequencies using added masses applied magnetically to the rim of the rotor This shows the amplitudes at set frequencies to reduce considerably when asymmetry is introduced. When a set of 5 masses is added to the rotor the vibration amplitude at the troublesome frequency is seen to be considerably reduced. Finite element analysis complements the experimental results.

The out-of-plane vibration characteristics of a noisy brake are generally better understood than in-plane characteristics. The fundamental reason for this is that in-plane vibration was not considered a significant effect until recently when technology has allowed the in-plane vibration characteristics to be determined with some degree of confidence. Detailed investigations of the side views of out-of-plane holographic images indicated that the in-plane displacement could be quite significant and possibly larger than the out-of-plane displacement. It was because the fringe pattern could not be attributed solely to out-of-plane displacement that a study of in-plane vibration was initiated. The paper discusses the measurement of both out-of-plane and in-plane vibration of a twin calliper disc brake during noise generation.

Laser holographic methods have been successfully used to produce animations showing the out-of-plane vibrations that take place in both the disc and pad of a real brake system generating noise (squeal). A series of holograms made at different times in the cycle of vibration were used to give the data on which the animations were based. Further it has been shown that mathematical approximations made to the fringe patterns obtained in the holograms by this method give phase and amplitude information about the wave motion involved. It establishes the existence of travelling waves on the brake disc with a speed given by the angular frequency of the noise divided by the mode order. This approach has now been extended to examine a time-related series of holograms of the disc rim of a brake system. From the data obtained from these holograms it has been possible to develop animations that show the in-plane vibration in the disc of a brake system producing noise.

The paper considers a drum brake mounted on a ½ vehicle test rig including suspension, cross beam and transmission differential. It is a continuation of earlier work (1) and so reviews the characteristics of a drum brake when generating noise on a ¼ vehicle test rig and compares them to those found on the ½ vehicle rig. Frequencies of 960, 850, 1400 and 4600Hz are examined in some detail using the technique of holographic interferometry. It is seen that the modes of vibration of the component parts vary notably over the frequency range considered. This observation allows the significance of each part to be evaluated for each frequency range. With the accumulated information it was possible to predict other possible unstable frequencies and although these were not observed within this series of test the predicted instability frequencies have been observed on earlier work.

Previous work on generating animations from real disc brake systems generating noise (squeal) has been consolidated and developed. Using the method of double pulsed laser interferometry a series of holograms (typically ten per half cycle) can be recorded from the brake during a cycle of excitation. From these holograms a considerable amount of data can be obtained about the vibration of the disc and pad surfaces. Standard methods from image processing and algorithms developed to investigate hologram fringe lines can be used to generate three-dimensional representations of the surfaces. Furthermore although part of the disc surface and even more of the pad surface are obscured by the calliper, etc., it has been possible to form a reliable numerical reconstruction of the whole disc and pad surfaces partly by using standard mathematical approximation techniques and partly by intelligent extrapolation of the available data.

High speed testing of a brake system using two different callipers and two different discs on a special test rig with a swinging calliper head mounting shows similar results with regard to hot judder. Holographic interferometry is used in an attempt to observe the disc mode shape during judder and although the classical fringe pattern was not obtained for the disc some useful and complementary information was forthcoming. Disc run-out measurements show that the disc takes up a permanent and increasing deformation with a two-diameter mode formation. This deformation is seen to give a brake pressure fluctuation that results in judder - the pressure being detected using a pressure transducer fitted at the calliper and the mechanical judder with an accelerometer mounted on the calliper body. The two signals allow the degree of phase shift to be estimated. A “strobing” effect, resulting from the combination of speed and video recording frequency, shows two hot-spots moving with the disc.

A twin calliper brake system is investigated using the whole body visual technique of holographic interferometry. It is shown that the disc mode of vibration has a preferred position where a disc antinode is situated under one calliper and a disc node under the second calliper. The maximum angular space occupied by the pad antinode is, as predicted by the theoretical study of the disc/pad interface geometry, the angle subtended by the pad length. For a four-piston opposed calliper the minimum distance is slightly larger than the piston centers. There is evidence that the disc mode position, in relation to the two callipers, may be antinode/node, node/node or antinode/antinode. With these arrangements an accompanying revised theoretical study of the disc/pad interface geometry predicts two stable conditions are possible - if the callipers are positioned either at an angle between 125° to 130° or 165° to 175°.

Brake noise investigations using the whole body visual technique of double pulsed holographic interferometry have been extended so that a series of interferograms may be recorded over a cycle of excitation providing information about the amplitude, direction, phase relationship and the mode of vibration of the principal component parts of the brake. This work investigates the possibility of automatically interrogating the holographic images and creating an animated 3 dimensional image of a brake generating noise.

A test rig which replicates a one quarter vehicle of a rear wheel drive vehicle, including the suspension system, is used to investigate a low frequency noise. The cross beam is included along with the vehicle suspension spring which is loaded against a sprung loaded mechanism that represents the tyre stiffness exactly and supports the brake geometrically as the tyre would. Drive to the drum is from a DC motor through the wheel drive axle. Holographic Interferometry is used to observe the modes of vibration of the drum with mirrors strategically placed to observe additional features such as the backplate, spring pan and cross beam. Initial results show the mode of vibration of the backplate to be of a diametral mode order and to be moving in the direction of drum rotation. Additionally it is seen that the spring pan and cross beam exhibit high amplitudes of vibration.