Steering drift and wheel movement during braking: static and dynamic measurements

YesThis paper reports on an experimental investigation into braking-related steering drift in motor vehicles, and follows on from a previous paper by the authors in which it was concluded that braking can cause changes in wheel alignment that in turn affect the toe-steer characteristics of each wheel and therefore the straight-line stability of the vehicle during braking. Changes in suspension geometry during braking, their magnitude and the relationships between the braking forces and the suspension geometry and compliance are further investigated in an experimental study of wheel movement arising from compliance in the front suspension and the steering system of a passenger car during braking. Using a kinematic and compliance (K&C) test rig, movement of the front wheels and the suspension subframe, together with corresponding changes in suspension and steering geometry under simulated braking conditions, have been measured and compared with dynamic measurements of the centre points of the front wheels. The results have enabled the causes and effects of steering drift during braking to be better understood in the design of front suspension systems for vehicle stability during braking

Wheel movement during braking

YesAn experimental study of wheel movement arising from compliance in the front suspension and steering system of a passenger car during braking is presented. Using a Kinematic and Compliance (K&C) test rig, movement of the front wheels and the suspension sub-frame, together with corresponding changes in suspension / steering geometry under simulated braking conditions, were measured and compared with dynamic measurements of the centre points of the front wheels. The resulting knowledge of front wheel deflections has enabled the causes and effects of steering drift during braking to be better understood in the design of front suspension systems for vehicle stability

Modelling commercial vehicle handling and rolling stability

YesThis paper presents a multi-degrees-of-freedom non-linear multibody dynamic model of a three-axle heavy commercial vehicle tractor unit, comprising a subchassis, front and rear leaf spring suspensions, steering system, and ten wheels/tyres, with a semi-trailer comprising two axles and eight wheels/tyres. The investigation is mainly concerned with the rollover stability of the articulated vehicle. The models incorporate all sources of compliance, stiffness, and damping, all with non-linear characteristics, and are constructed and simulated using automatic dynamic analysis of mechanical systems formulation. A constant radius turn test and a single lane change test (according to the ISO Standard) are simulated. The constant radius turn test shows the understeer behaviour of the vehicle, and the single lane change manoeuvre was conducted to show the transient behaviour of the vehicle. Non-stable roll and yaw behaviour of the vehicle is predicted at test speeds .90 km/h. Rollover stability of the vehicle is also investigated using a constant radius turn test with increasing speed. The articulated laden vehicle model predicted increased understeer behaviour, due to higher load acting on the wheels of the middle and rear axles of the tractor and the influence of the semi-trailer, as shown by the reduced yaw rate and the steering angle variation during the constant radius turn. The rollover test predicted a critical lateral acceleration value where complete rollover occurs. Unstable behaviour of the articulated vehicle is also predicted in the single lane change manoeuvre

A study of commercial vehicle brake judder transmission using multi-body dynamic analysis

YesBraking-induced forced vibration, known as brake judder in road vehicles, causes dissatisfaction to drivers and passengers and also damage and possible early failure in components and systems. In this paper, the transmission of judder vibration from the point of generation (the brake friction pair) through the vehicle structure to the driver is investigated for the particular case of a heavy commercial vehicle. The investigation uses a computer simulation multi-body dynamic model based on the automatic dynamic analysis of mechanical systems software to identify any characteristics of the vehicle suspension design that might influence the vibration transmission from the wheel to the driver. The model uses a simplified rigid chassis and cab to lump the chassis parameters, so that the investigation can focus on the front axle/suspension design, which is a beam axle leaf spring arrangement, and the rear axle/suspension assembly, which is a tandem axle bogie design. Results from the modelling indicate that brake judder vibration is transmitted to the chassis of the vehicle through a leaf spring `wind-up¿ mode and a `walking¿ mode associated with the rear tandem axle. Of particular interest is the longitudinal vibration transmitted through the chassis, since this creates a direct vibration transmission path to the cab and driver. The simulation results were compared with the previously published experimental work on the same design of commercial vehicle, and agreement between the predicted and the measured vibration characteristics and frequencies was found. It is concluded that the rear suspension design parameters could affect the transmission of brake judder vibration to the cab and driver and that a tandem rear axle offers some design opportunity to control the transmission of brake judder vibrations from the wheel to the cab and driver. Given that brake judder has so far defied all attempts to eliminate completely from vehicle brake systems, this is potentially an important opportunity

A numerical and experimental study on the factors that influence heat partitioning in disc brakes

yesTo investigate the heat partition on a vehicle disc brake, a small scale test rig with one contact interface was used. This allowed the disc/pad contact temperatures to be measured with fast-response foil thermocouples and a rubbing thermocouple. Based on the experimental conditions a 3D symmetric disc brake FE model has been created. Frictional heat generation was modelled using the ABAQUS finite element analysis software. The interface tribo-layer which affects heat partitioning was modelled using an equivalent thermal conductance value obtained from the authors¿ previous work. A 10 second drag braking was simulated and the history and distribution of temperature, heat flux multiplied by the nodal contact area, heat flux leaving the surface and contact pressure was recorded. Test rig and FE model temperatures were compared to evaluate the two methods. Results show that heat partitioning varies in space and time, and at the same time contact interface temperatures do not match. It is affected by the instantaneous contact pressure distribution, which tends to be higher on the pad leading edge at the inner radius side. They are also affected by the thermal contact resistance at the components contact interface.IMech

Interface temperatures in friction braking

YesResults and analysis from investigations into the behaviour of the interfacial layer (Tribolayer) at the friction interface of a brake friction pair (resin bonded composite friction material and cast iron rotor) are presented in which the disc/pad interface temperature has been measured using thermocouple methods. Using a designed experiment approach, the interface temperature is shown to be affected by factors including the number of braking applications, the friction coefficient, sliding speed, braking load and friction material. The time-dependent nature of the Tribo-Iayer formation and the real contact area distribution are shown to be causes of variation in interface temperatures in friction braking. The work extends the scientific understanding of interface contact and temperature during friction braking

Steering drift and wheel movement during braking: parameter sensitivity studies

YesIn spite of the many signi cant improvements in car chassis design over the past two decades, steering drift during braking where the driver must apply a corrective steering torque in order to maintain course can still be experienced under certain conditions while driving. In the past, such drift, or `pull¿, would have been attributed to side-to-side braking torque variation [1], but modern automotive friction brakes and friction materials are now able to provide braking torque with such high levels of consistency that side-to-side braking torque variation is no longer regarded as a cause of steering drift during braking. Consequently, other in uences must be considered. This paper is the rst of two papers to report on an experimental investigation into braking-related steering drift in motor vehicles. Parameters that might in uence steering drift during braking include suspension compliance and steering o set, and these have been investigated to establish the sensitivity of steering drift to such parameters. The results indicate how wheel movement arising from compliance in the front suspension and steering system of a passenger car during braking can be responsible for steering drift during braking. Braking causes changes in wheel alignment which in turn a ect the toe steer characteristics of each wheel and therefore the straight-line stability during braking. It is concluded that a robust design of suspension is possible in which side-to-side variation in toe steer is not a ected by changes in suspension geometry during braking, and that the magnitude of these changes and the relationships between the braking forces and the suspension geometry and compliance require further investigation, which will be presented in the second paper of the two

Investigation of Disc/Pad Interface Temperatures in Friction Braking

yesMaintaining appropriate levels of disc-pad interface temperature is critical for the overall operating effectiveness of disc brakes and implicitly the safety of the vehicle. Measurement and prediction of the distribution and magnitude of brake friction interface temperatures are difficult. A thermocouple method with an exposed hot junction configuration is used for interface temperature measurement in this study. Factors influencing the magnitude and distribution of interface temperature are discussed. It is found that there is a strong correlation between the contact area ratio and the interface maximum temperature. Using a designed experiment approach, the factors affecting the interface temperature, including the number of braking applications, sliding speed, braking load and type of friction material were studied. It was found that the number of braking applications affects the interface temperature the most. The real contact area between the disc and pad, i.e. pad regions where the bulk of the kinetic energy is dissipated via friction, has significant effect on the braking interface temperature. For understanding the effect of real contact area on local interface temperatures and friction coefficient, Finite Element Analysis (FEA) is conducted. It is found that the maximum temperature at the friction interface does not increase linearly with decreasing contact area ratio. This finding is potentially significant in optimising the design and formulation of friction materials for stable friction and wear performance

Tangential slip noise of V-ribbed belts

This paper reports the results of a study into V-ribbed belt noise generated as a result of tangential belt slip. The results of experimental studies to identify the belt operating conditions associated with belt noise are presented, together with the results of analytical studies to identify the mechanism of noise generation. It is concluded that tangential slip V-ribbed belt noise generation is controlled only by the amount of slip, and that the mechanism of noise generation is harmonic excitation of the fundamental vibration mode of the belt, with stick¿slip frictional behaviour providing the impetus for the vibratio