Weight Transfer during Braking

Last updated on April 5th, 2015 at 06:18 am

On application of brakes on the vehicle, inertia forces are set up. The braking force is applied at lesser height whereas the vehicle load is at a higher height, resulting a couple to act on the body of the vehicle. This results an additional loading on leading bogie as compared to trailing bogie. Let H denotes the height of the centre of gravity of the vehicle, T the braking effort and h being the height of bogie frame. The inertial couple force acting on the vehicle will be 4T(H-h) and its weight transfer between bogies will be 4T(H-h)/L. Now the weight transfer between the axles of the same bogie is calculated as 2Th/l. The net effect on different axle of the wagon will be

Leading Axle Leading Bogie          4T(H-h)/L + 2Th/l

Leading Axle Leading Bogie          4T(H-h)/L – 2Th/l

Leading Axle Leading Bogie          + 2Th/l -4T(H-h)/L

Leading Axle Leading Bogie          – 2Th/l -4T(H-h)/L

The total weight transfer from the trailing axle to leading axle is  2T[4T(H-h)/L + 2Th/l]

Wheel Skidding and Weight Transfer              

Wheel skidding results when braking effort on any of the axle is more than its adhesive weight. Adhesive weight is the product of weight in the axle and coefficient of adhesion. With weight transfer taking place from the trailing axle to leading axle, the limit to braking effort is determined accordingly. Wheel skidding has more damaging effect on rail as compared to wheel slipping because flat wheel produces sinusoidal hammering impact on rail.

Dependence of weight transfer

From the expression above, it can be concluded that weight transfer depends on

1. Centre of gravity of the wagon. Higher the centre of gravity more will be its effect. This clearly implies higher weight transfer on empty wagon. In fact, empty wagon with less weight are more vulnerable to wheel skidding, and weight transfer makes it further vulnerable. While investigating wheel flat, look for whether it is the trailing axle.
2. Greater the distance between bogie centres, less the effect of weight transfer
3. Weight transfer effect is reduced by adoption of low traction bars which reduces the value of h.

Well Wagon design incorporates the first two features thus reducing the weight transfer and improving weight transfer.