Browse Publications Technical Papers 2018-01-1880
2018-10-05

Increase of Stability for Motor Cars in Service Braking 2018-01-1880

New solutions for actual problems of determination the efficient distribution of braking forces between the axles of the vehicle, and the stability and drivability of two-axles vehicles at service braking are received in the thesis. It permitted for the first time to determine the Law of distribution the braking forces between the axles, that ensures straight-running stability of two-axle vehicle at service braking, to get the ideal characteristics for braking system of two-axle vehicle at service braking and to determine possible values for the distribution of braking force on the front axle. The drivability criterion at service braking obtained further development; it is offered to use boundary at gripping front or rear wheels angular vehicle acceleration on the road. The application of the stability coefficient as one of the criteria for service braking efficiency allowed to determine the ideal, as for preserving the road-holding ability, Law of distribution the braking forces between the axles. Despite of the idea, if increase the vehicle deceleration at service braking, the ideal coefficient of braking force distribution on the front axle should decrease, but not to increase. At small decelerations the given coefficient can be equal to one (rear wheels are not braked), and at the maximum decelerations – we should take into account the values that correspond to keeping the front and rear wheels on the blocking boundary. The area of rational realization of the coefficient of braking force distribution on the front axle, limited by the curves of the ideal distribution of braking forces at service braking and limit values of the adhesion coefficient, and by straight line of the ideal distribution of braking forces at emergency braking is determined. The limit values of the vehicle deceleration at service breaking are determined. If the limit values are lower than the given ones it is necessary to carry out braking only by the front wheels brakes. The obtained ideal characteristics of the two-axles braking system allow to estimate braking dynamics at emergency and service braking on roads with different coefficient of adhesion. With constant distribution of braking forces between the axles the deceleration area boundaries in which the vehicle can keep the road-holding ability at service braking are defined. To assess the impact of disturbances on the road-holding ability of the vehicle at service braking a new criterion - the coefficient of disturbing action is offered. If the criterion value does not exceed the stability coefficient, the vehicle is stable, otherwise it loses its stability.

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