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 of the braking forces between the axles, that ensuring straight-running stability of two-axle vehicle at service braking, to obtain the ideal characteristics for the 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 of the braking forces between the axles. Despite the idea, if the vehicle deceleration is increased at service braking, the ideal coefficient of braking force distribution on the front axle should be decreased, but not be increased. 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 retain the front and rear wheels on the blocking limit. The area of rational values 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 are determined. The limit values of the vehicle deceleration at service braking are determined. If the limit values are lower than the given ones, it is necessary to carry out braking only with 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 retain 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.