Design of an Active Suspension System for a MacPherson Strut in a Passenger Car

Hong, Clarence Wei Ying (2017) Design of an Active Suspension System for a MacPherson Strut in a Passenger Car. Final Year Project (Bachelor), Tunku Abdul Rahman University College.

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Abstract

A MacPherson strut is a type of automotive suspension that uses the top of a telescopic damper as the upper steering pivot. It is a form of frontal suspension most widely used in cars of European origin. It combines a shock absorber and a coil spring into a single unit. Its purpose, mush like a shock absorber, is to dampen harsh spring movements and acts as a medium to dissipate the motion of the wheels. Thus, all shocks encountered by the wheels are not fully transmitted to the body, and the passenger car vibrates less violently when and after going through a bump. The MacPherson strut is one of many car suspension systems. A car suspension system is a mechanism that physically separates the car body from the wheels of the car to provide ride comfort as well as smooth handling. There are three main types of car suspension systems available, which are passive, semi-active, and active suspension system. An active suspension system is a type of automotive suspension that controls the upward or horizontal movement of the wheels with respect to the chassis of the vehicle and does not rely on the road’s surface condition. This brings forth several problem statements, such as to improve ride comfort of a passenger car without sacrificing handling capabilities and to implement active suspension system in a conventional passenger car with a simple tuning process that caters to all types of passenger cars. The targeted vertical displacement (0.07 m) reduction is at the front and rear MacPherson struts in a passenger car. This height was chosen because it is the average height of the majority of bumps in Malaysia, ranging from 0.05m (lowest) to 0.10m (highest). The process involves converting the half car mathematical model into a Simulink block diagram, and applying two active system controllers, P.I.D. and fuzzy logic, to reduce the vertical displacement to a value below 0.07m. From the simulation carried out, it is determined that the two active controllers, P.I.D. and fuzzy logic, were effective in bringing down the vertical displacement of the car to below 0.07 m. Each active controller’s parameters can be varied, and the main task here is to determine the parameters which are necessary to achieve the wanted reduction in vertical displacement. To be more precise, with the use of P.I.D controllers at both the front and rear, the displacements were reduced from 0.07 m to 0.054 m (at the front) while the displacements were reduced from 0.07 m to approximately 0.061 m (at the rear). While for the use of fuzzy logic controller at the front and rear, the displacement was reduced from 0.07 m to 0.054 m (at the front) while the displacement was reduced from 0.07 m to 0.061 m (at the rear). For the vertical acceleration at 30 km / hr, both P.I.D. and fuzzy logic controllers were able to reduce the vertical acceleration of the sprung mass but when the velocity of the sprung mass was increased to 90 km / hr, it is proven that a fuzzy logic controller is more efficient at reducing the vertical acceleration of the sprung mass when compared to a P.I.D. controller whose parameters make it less flexible and less suited for cars travelling at high velocities.