Bond graph aided performance analysis of antilock braking system for a vehicle with camber and fork angle

Abstract

The 21st century vehicle on the road is expected to have such features which not only increase the comfort and ride quality but also increase the safety of the driver. For the different road surfaces and increase in traffic congestions, the conventional safety systems are unable to provide the desired action. So, there is a need to develop more and more accurate control algorithms which will be effective in every situation. Due to the ever increase traffic on Indian roads, the most frequently job performed by the driver is to apply the brakes. The braking of the vehicle is not only depends on the driver response, but also takes into number of factors like road-tyre friction coefficient, slip ratio, longitudinal tyre force, longitudinal velocity and lateral tyre force. Control of all these parameters is not done by the driver alone. So, some controllers must be developed for assisting the driver to avert such situations. Sudden application of the brake torque increases the slip ratio which will cause skidding of the wheels. Antilock braking system is a type of braking system which applies and releases the brakes in quick succession to prevent the wheels from locking. Earlier, number of controllers was developed to prevent such lockage. Here, a control algorithm is developed for the brake torque in such a fashion that the slip ratio will be maintained in the desired range. Normally, the braking of vehicle is done when vehicle in straight path is considered. When vehicle moves in the curved path, the effect of camber and fork angle should be considered. The variable camber angle assists the braking in curved path by increasing the contact path of the tyre with the road. But the turning radius of the vehicle changes due to varying camber angle and fork angle. Fork angle increases the stability of the vehicle at higher speeds. While turning, the inner wheel always should have positive camber angle and outer wheel should have negative camber angle. Variable camber mechanism is developed to provide the camber angle to the front wheels while moving in a curved path. Variable camber mechanism ensures no camber angle while moving straight ahead to avoid bump steering. For the analysis, bond graph modelling of various components is done. Quarter car model, Bicycle model and four wheel model of the vehicles are developed. Effect of camber and fork angle on the turning radius, stopping distance and longitudinal speed of the vehicle is analysed. Relation between camber angle and fork angle is also verified. It is also found that camber angle provides additional steering to the vehicle. Analysis of variable camber mechanism is done by using quarter car model. Control algorithm of Antilock braking system is tested using bicycle model and four wheel vehicle model. The control algorithm successfully keeps the slip ratio in the acceptable range and thus prevents vehicle skidding and better steering control.