Locked Wheel Braking Research Articles

ВЛИЯНИЕ ИЗНОСА РИСУНКА ПРОТЕКТОРА БЕГОВОЙ ДОРОЖКИ ШИНЫ НА ЕЕ СЦЕПНЫЕ СВОЙСТВА ПРИ ТОРМОЖЕНИИ НА СТЕНДЕ В БЛОКОВОМ РЕЖИМЕ

The PURPOSE of the article is to carry out an experimental study of the effect of the tire tread pattern wear on the implemented coefficient of adhesion to the support surfaces of the test bench under the variation of normal load value. METHODS. The studies were performed on the test bench of modular design, which allows to measure the normal and tangential reactions of the elastic tire with support surfaces. RESULTS. It has been determined that the increase of the tire tread pattern wear from 10 to 90% reduces the adhesion coefficient of the automobile wheel elastic tire by 35.3% when braking in the locked mode on a flat support surface. When the wheel brakes on one support roller of the test bench and the tread wear is from 10% to 90% the adhesion coefficient reduces by 18%. When the wheel brakes on two support rollers of the test bench the coefficient of adhesion makes 23.8% on the front roller and 48.4% on the rear support roller of the stand, with an increase in the wear of the tread pattern from 10% to 70%. CONCLUSION. The conducted experimental studies allowed to determine the dependence of the adhesion coefficient of the elastic tire on the wear degree of the tire tread pattern and the variation of normal load under the locked wheel braking on the flat support surface and one or two support rollers.

Self-Excited Torsional Oscillations under Locked-Wheel Braking: Analysis and Experiments

ABSTRACT This paper analyzes the effect of tire/vehicle parameters, specifically of tire/suspension torsional stiffnesses, on the stability of self-excited tire torsional oscillations during locked-wheel braking events. Using a torsionally flexible tire-wheel model and a dynamic tire-ground friction model, two system models for tire oscillations are considered: with suspension torsional compliance included in one but excluded in the other. Bifurcation analysis is conducted on both systems to derive the effect of tire/vehicle parameters on the stability. For the system without suspension torsional compliance, it is highlighted that the primary cause of unstable self-excited oscillations is the “Stribeck” effect in tire-ground friction. Based on the parameters obtained experimentally, the bifurcation surface of vehicle velocity with respect to tire/suspension torsional stiffness is also given. The effect of tire/suspension torsional stiffness to the stability of tire torsional oscillation is qualitatively validated via comparisons between locked-wheel braking simulations and experiments with tires with different torsional stiffnesses.

A contribution to non-contact skid resistance measurement

Over the past decades a wide range of routine measurement devices has been developed, all of them measuring the friction force between a rubber wheel and the (wetted) road surface. At the same time, many efforts have been undertaken to predict skid resistance solely from texture measurements. This paper presents a concept of contactless skid resistance measurement which is based on optical texture measurement and consists of two components: (1) measurement of the pavement texture by means of an optical measuring system and (2) calculation of skid resistance based on the measured texture by means of a rubber friction model. The basic assumptions and equations underlying the theoretical approach are presented. Two skid resistance-measuring devices were chosen to prove the theoretical approach: one laboratory device called Wehner/Schulze machine which corresponds to a locked-wheel braking test and another, the ViaFriction® device of ViaTech AS which measures the skid resistance under controlled longitudinal slip and corresponds to ABS braking conditions. The results are very promising although in the case of the ViaFriction® device only a few surfaces could be tested. A close relation between measured and predicted friction coefficients could be found. Thus, a strong indication can be provided that skid resistance could be measured without contact in the future.

A Laboratory Method to Comprehensively Evaluate Abrasion, Traction and Rolling Resistance of Tire Tread Compounds

Abstract A laboratory test method has been developed which allows the evaluation of diverse properties of tire tread compounds on the same sample. The laboratory test instrument consists of a rotating abrasive disk against which a rubber sample wheel runs under a given load, slip angle and speed. All three force components acting on the wheel during the tests are recorded. By changing the variable values over a wide range practically all severities encountered in tire wear are covered. The well-known fact that compound ratings depend on the road testing conditions is verified. Most compounds are only significantly distinguishable against a control over a limited range of testing conditions. Using a road test simulation computer program based on the laboratory data shows that not only ratings correspond to practical experience but also calculated absolute tire life times do. Tests on surfaces of different coarseness and sharpness indicate that sharp coarse surfaces give the best results with road tests, which of necessity are mostly carried out on public roads of differing constitution. The abrasive surface can be wetted with water at different temperatures and hence either the friction force at a locked wheel or the side force at a slipping wheel can be measured over a wide range of temperatures and speeds. At small slip angles the side force is dominated by dynamic cornering stiffness of the compound, at large slip angles by the friction coefficient. In this case, too, good correlations to road experience exist over a limited range of testing conditions. Low water temperatures and low slip speed settings in the laboratory produce side force ratings, which correlate closely with ABS braking on the road High and higher slip speeds give ratings in close agreement with locked wheel braking on the road. A heatable/coolable disk enables traction measurements on ice and newly abrasion measurements on surfaces at elevated surface temperature. Ice surface temperatures between −5 °C and −25 °C are possible. Friction measurements show that the difference in compound rating between summer and winter compounds is maintained over the whole temperature range. New investigations show not only a differentiation between different winter tire treads qualities but also an excellent correlation between tire and laboratory results. As a new topic side force measurements on dry surfaces highlight the correlation to dry handling of tires. The tire tread compound contributes to this performance through its shear stiffness and its friction coefficient. The shear stiffness contributes to the response of the tire in directional changes. The friction coefficient determines the maximum force, which can be transmitted. A simple operation possibility for evaluation of determined side forces is demonstrated. In addition to antecedent investigations the rolling resistance of the rubber wheel can be measured over a range of loads and speeds with the slip angle set at zero. Again for these new results good correlations are achieved with practical experience. In particular, the dependence of the rolling resistance on the velocity and loads are pointed out. Ultimately a good correlation between tire test and laboratory test results was demonstrated.

Forensic Engineering Analysis And Testing For Speed Reduction In Transient Braking

The Speed From Skids Equation Is Derived From The Work-Energy Theorem And Is Often Employed In Accident Reconstruction To Determine A Vehicles Speed At The Onset Of Visible Locked-Wheel Braking Application. The Conventional Use Of This Equation In The Field Of Accident Reconstruction, However, Does Not Yield A Vehicles True Speed At The Onset Of Braking. In Maximum Application Of The Brake Pedal, A Vehicle Initially Undergoes A Transient Brake Phase Prior To Arriving At The Quasi-Steady-State Locked-Wheel Brake Phase. There Is A Reduction Of Speed That Occurs During The Transient Phase Of Braking That Is Generally Not Accounted For In The Reconstruction Of Vehicular Collisions. Accounting For This Reduction In Speed, A Forensic Engineer Can Estimate A Vehicles Speed At The Onset Of Braking And Further Employ The Relative Elapsed Time In Collision Avoidance Calculations. This Study Will Explore A Method To Estimate The Speed Reduction Occurring During The Transient Braking Based On Field Testing.

Wet Skid Resistance of Car and Truck Tires

Abstract Two test trailers for measuring tire characteristics are described. One of the trailers is specially built for testing car tires and can steer, camber, and brake the test tire. This trailer is provided with a five component measuring hub. The second trailer, for testing truck tires, is restricted to braking only. Braking forces are measured with a dynamometer. The determination of peak and locked wheel braking force coefficients is discussed. In addition, for car tires, a method for obtaining side force coefficients is given. Test results are given for both car and truck tires showing the influence of road surface texture, speed, and tread depth on skid resistance, and the results are compared.

Tire Traction Assessed by Shear Force and Vehicle Performance

Abstract Tire shear force data for ten different types of passenger car tires tested on wet surfaces are studied to examine the influence of test surface, velocity, and load on the maximum lateral force, maximum braking force, maximum resultant force, and locked wheel braking force. Tire traction rankings based on these four measures are compared with each other and with rankings obtained from J-turn and diagonal braking tests on a vehicle equipped with the same types of tires using the rank difference correlation method. The findings show that rankings based on a small number of maximum lateral force tests correlate well with rankings based on J-turn tests.

Research on Wet Tire Traction

Abstract This paper describes experiments and methodology employed in an attempt to develop a system for the grading of wet tire traction. Data from instrumented vehicle experiments and the University of Michigan Highway Safety Research Institute mobile tire tester are used to support the conclusions. The vehicle tests include J-curve cornering and diagonal, locked-wheel braking. The maneuvers are used to generate information on tire tractive properties and their dependence on tread depth, rim size, suspension, and surface conditions. Three tire force measures obtained with the mobile tire tester, the peak longitudinal, peak free-rolling lateral, and locked-wheel longitudinal coefficients of friction, are presented for a group of 90 percent of the original equipment tire sizes in use on American cars and are rank correlated with vehicle results. The results indicate the feasibility of defining minimum wet traction levels for various tire-road interface properties.

Theoretical Studies in Braking

In Part I of this paper, after a simple description of the basic properties of a pneumatic tyre, a highly simplified vehicle consisting of a pneumatic-tyred wheel bearing a load is considered mathematically during braking and during the release of brakes. By inserting numerical estimates it is shown that, among other results, from 15 mile/h a wheel may lock within 18 ms. It is also shown that under perfectly uniform conditions the stopping distance is appreciably less when the brake-shoe torque is approximately equal to the moment of the maximum frictional force that is possible between the tyre and the road, than for both greater and lesser brake-shoe torques. In Part II of the paper a commercial device—the Maxaret—designed originally to release the brakes of an aeroplane before the wheels lock on landing and then later to reimpose the brakes is briefly described and the mathematical equations of its operation, both in itself and in application to a highly simplified road vehicle, are set up. A numerical investigation, making use of the results given in Part I of this paper, was executed and the results are given. These show in detail the mode of operation of the device. These highly simplified calculations suggest that in its present form a much longer braking distance will result from using the device than would be obtained with locked-wheel braking. This is in conflict with experimental results and may be due to both the simplifications that had to be made for the numerical work and some of the empirical data used. Some of the former could be avoided if an electronic computer were available. Further investigation is desirable and this should enable the device to be adjusted to give the shortest stopping distance consistent with the avoidance of locked wheels.