Global Journal of Researches in Engineering, A: Mechanical & Mechanics, Volume 22 Issue 1

suspension system if the driver tries to cross at speeds much greater than the established speed limits. It is necessary to design warning signs and lights before the hump to warn of the presence of a bump. There is a third type of bumps called the cat-eye hump, which is often used as a warning sign of an emergency, and this variety of road humps significantly worsens the ride comfort . [5] To reach an optimal solution that guarantees the safety of driving on the roads inside the city, while obtaining an acceptable riding comfort, the car manufacturers tried to implement an intelligent system that is characterized by alignment in the suspension system to achieve the highest possible ride comfort. One of these systems is the active and semi-active suspension system. Therefore, the aim of this research is to study the vibrational behaviour of vehicle suspension system when the vehicle over humps using mathematical equations modelled in MATLAB Simulink. The research objectives are to create mathematical models for the vehicle and hence to build these models in MATLAB Simulink and then study to optimize the most used vehicle suspension system that gives the best ride comfort . The road hump is an extension designed over the road to calm down the traffic flow. Many hump profiles are globally used. The circular hump is the most widespread one that is used on city roads. The circular hump is the most famous hump used in vehicle roads because of its design simplicity and its reasonable effectiveness. The circular hump is characterized by hump width and height. The recommended hump width is not less than 3-4 m while the maximum height is 10- 15 cm. Recommended circular humps height is about 10 cm. Heights less than the assumed 10 cm will result in that the hump is not effective. Heights above 10 cm may cause severe damage to vehicles [1] . To force vehicle drivers to calm down the speed, there are several types of common road humps, such as speed bumps, speed humps, speed cushions, speed tables, and chicane . [2] Abdulmawjoud et al. [5] have studied the drivers’ behaviour when the vehicle is travelling over three main types of standard humps, which are single circular hump, double circular humps, and trapezoidal hump. The traffic calm installed along the main roads of one of the cities was studied, and they found that the rate of decrease in the vehicle speed reached more than 70% when the vehicles are travelling over the humps. It was noted that the trapezoidal hump causes a greater decrease in speed than the other species studied, with a decrease of approximately 80%. In terms of ride comfort, the worst ride comfort was recorded in the case of a single circular hump . Pozuelo et al. [6] have presented theoretical and experimental study to investigate the vehicle vibrational behaviour when the vehicle is travelling over a circular hump. The main goal of the model and software that to introduce a prediction of the vertical dynamics of a vehicle when traveling over a hump using a half-car model. They also developed mathematical expressions to formulate the displacement behaviour resulting from the movement of the vehicle over the circular hump. The model signals are validated by comparing with the recorded experimental results of maximum vertical acceleration, maximum longitudinal pitch angle, maximum dynamic tire load of the front suspension, maximum dynamic tire of the rear suspension. The results showed that driving the vehicle over the hump leads to a severe deterioration in the ride comfort, as well as the stability parameters of the vehicle, especially at high speeds . In another way, Mahmoud [7] presented the function of the circular hump in a simplified way, while he represented the rectangular hump as a function of the height and length of the hump and the speed of the vehicle. He presented the riding comfort factors as the suspension working space, the vertical body acceleration, and dynamic tire load as factors comparing the ride comfort and stability of the car on the road . The suspension system of the vehicles is an important part of obtaining satisfactory ride comfort, as well as one of the components of the vehicle's safety requirement. A suspension system typically contains shock absorbers and springs. The shock absorbers compress and rebound with the help of springs when a force is applied to them. The suspension system provides a safe driving experience for the driver, passengers, and occupants of the vehicle by reducing or eliminating body roll in turns, bumps in the road, and vibrations [8]. A passive suspension system is a system in which the basic components are used to isolate the vibrations resulting from the movement of the vehicle on the road, such as springs and dampers. The design and selection of the spring and damper are chosen according to the vehicle's operating conditions and according to the design objectives and intended application [9]. A semi-active suspension system is an application of mechatronics to a suspension system. A semi-active suspension system is characterized by a switchable damper, and the damping coefficient can be adapted according to the driving conditions. The vehicle's ride comfort with a semi-active suspension system is improved in comparison with a passive suspension system. Vehicle stability is also performed with a semi-active suspension system when compared with a passive system [10-12]. To study the vibrational behaviour of the vehicle while travelling over roads, there are many methods to represent the road signals. Phalke et al. [13] have used the eccentric method of an external tire to generate the Vibrational Behaviour of a Quarter Car Travelling over Road Humps with Different Suspension Systems © 2022 Global Journals Global Journal of Researches in Engineering (A ) Volume XxXII Issue I Version I 46 Year 2022