The standard usage of Combined Braking System (CBS) in lower cc/power 2-wheeler vehicles serves to reduce stopping distance and improve braking stability. The CBS system achieves this by engaging both the front and rear wheel brakes, taking advantage of the high load transfer characteristic during 2-wheeler braking. However, the current design of the CBS system relies on linear system analysis, based on vehicle geometry, load distribution, and tire-road friction. This approach overlooks the non-linearities inherent in braking dynamics, such as tire behavior and dynamic Center of Gravity (CoG) location. Consequently, the current CBS design methodology exhibits limitations, particularly in extreme scenarios where wheel lock-up may occur, such as on low friction surfaces or during panic braking.
This paper proposes the incorporation of tire non-linearities into the design of CBS systems using Pacejka’s tire model. Initially, calculations are performed to optimize the braking characteristics, considering vehicle geometry, loading conditions, and road surface conditions. A co-simulation is conducted in a combined BikeSim and Matlab environment, where the CBS calculations are integrated with the brake system developed in Matlab, while the remaining vehicle model is simulated using BikeSim. The co-simulation model is correlated with real vehicle data. A comparison is then made between the existing CBS design methodology, which assumes linear system behavior, and the proposed method presented in this paper. The results demonstrate that accounting for tire non-linearities alters the intersection of the “line of actual braking distribution” and the “lines of constant friction coefficient.” This leads to an improved analysis of wheel lock-up and vehicle instability in CBS system design.