The Importance of Vehicle Suspension Systems

Literature Review2.1 HISTORYThe role of suspension system on vehicles is to improve the road handling, comfortibility and stability of vehicles (Rao, 2010). By the use of suspension system, acceleration amplitude of the sprung mass of a car body may be restricted and tire deflection may be reduce, thereby enhancing of a dampened suspension system on his 'Mors Machine', Henri Fournier won the prestigious Paris-to-Berlin race on the June 20th, 1901. In 1920,Leylandusedtorsion barsin use a good suspension system. In 1922, independent front suspension system was pioneered on the Lancia Lambdaand became most common in mass market cars from 1932.

The important supposition is designing suspension is for ride comfort, suspension deflection, and tire deflection. Passive suspension system only consist spring and damper without any controlling system. The problem of this passive suspension system is the properties of the spring and damper is constant and cannot be adapt follows the road profile. Semi-active and active suspension systems is being studied and adjusted to offer suspension with adaptive option.

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Semi-active suspension system only able of energy consumption while active suspension system will be able to either store, dissipate or produce energy for the vehicle. In the active suspension system, spring and damper properties can be adjusted while driving accommodates the road profile. It's also more beneficial and efficient than the other types of suspension, making the system capable of providing best road-holding capability and ride comfort. Because of it, the active suspension system control has attracted and persuade many researchers interested in increasing the ride and the holding quality of a car.

2.2 QUARTER CAR MODELIn this project we have used a quarter car model or one-fourth of the car body mass. This quarter model or one fourth of car body mass, consist of car body as a sprung mass, tire and brake components as unsprung mass, spring, damper and control actuator as an active suspension system.2.3 Suspension SystemThe Suspension system consists of tires, tire air (air tube), springs, damper and, linkages that connects a vehicle to its wheels and allows relative motion between the two (wheels and car body). 2.3.1 TYPESBasically there are three types of suspension system, but the two are must common, which are the following; I) Passive Suspension system II) Active Suspension System2.3.2 Passive Suspension SystemIn passive suspension systems, the car body is supported by only springs and dampers with fixed parameters. Passive means the system just disperse kinetic energy with no external input energy source.Explanation Passive suspension system is known as conventional and simplest design of suspension system. It only contains of sprung mass, unsprung mass, spring and damper without any force controller as shown in the Figure 2.1. This type of suspension system is also known as passive system suspension because it does not add energy to the system. In this system spring is used to store the kinetic energy which are produced by the disturbance of the car while damper is used to consume this energy. Passive suspension systems are used to provide various tradeoffs when they are excited across a large frequency bandwidth. The passive suspension system is an open loop control system and it is designs to achieve certain condition only. According to the figure 2.1 the various parts and its name are the following;Fk = Spring stiffness Fc = Damping constant Kt = Tire stiffness Zr = Road profile Zus = Displacement unsprung mass Zs = Displacement sprung mass Mus = Unsprung mass Ms = Sprung mass2.3.3 Active Suspension SystemThe Active suspension system, the damper and spring are inter connected by a force actuator which give energy to the system in order to suppress sprung mass vibration of vehicle. The force actuator can be controlled by different type of controllers to achieve the desired performance.Explanation: Active suspension system is a suspension system which has high bandwidth (0-50 Hz). In the Active suspension system the springs and dampers of passive suspension system are replaced by hydraulic struts (hydraulic actuator). The active suspension system is a closed loop control system, controlled by a fast-acting closed loop control system. Theoretically, this suspension system allows decrease in body vertical acceleration and provide to driver and passengers ride comfort and good road holding performances. In active suspension system, when the car meets a bump, the appropriate strut will retract the wheel, while when the car meets a hole, the strut will force the wheel downward. Both cases maintain the car body at a constant ride height for driver and vehicle passengers comfort and stability. Figure: 2.2 Active Suspension SystemAccording to the figure 2.2 the various parts and its name are the following; Ms= Sprung mass Mus=Un sprung mass Ks, Kt= Spring constant Ca = Damping Coefficient Ua= hydraulic actuator Zr = Road profile Zus = Displacement unsprung mass Zs = Displacement sprung mass2.4 PID Controller PID stands for proportional control, integral control and derivative control. Dynamic system are often controlled by using three term known as PID;P----stands for proportional controlI-----stands for integral controlD-----stands for derivative controlLet us consider a closed loop system with a unity feedback as fallow: Figure2.3: PID ControllerThe PID controller output are represented by the equation given bellow; 2.4.1 Advantages and limitation of different parameters of PID Controller:The advantages and disadvantages of different parameters of PID controller are the following;Parameter Advantage DisadvantageKp It is used for the adjustment of controller output. It may cause instability.Ki It produces zero steady state error. It my produce slow dynamic response and instability.Kd It produce rapid system response. It is sensitive to noise. 2.5 Summery:* The role of suspension system on vehicles is to improve the road handling, comfortibility and stability of vehicles (Rao, 2010). * Passive suspension system only consists spring and damper without any controlling system. * The Active suspension system, the damper and spring are inter connected by a force actuator which give energy to the system in order to suppress sprung mass vibration of vehicle.* PID stands for proportional control, integral control and derivative controller.