| Abstract [eng] |
In this project BMW E46 front MacPherson suspension is analyzed and geometry properties defined and compared to modified suspension made for drifting. After assessing the main problems of the currently installed front suspension a new design was proposed with better handling characteristics suitable for professional drifting. To properly evaluate the parameters of such suspension a thorough analysis of literature and research papers was made. Defined the main parameters of a suspension such as toe angle, camber, caster and king pin inclination angles. The characteristics of Ackermann steering were analyzed and established that true Ackermann angle differs according to situation and use of the vehicle and driving style. Usually, when a car is driven in a turn, the wheel which is closer to the center of the turn achieves greater angles compared to the other wheel further from the center. In drifting the same turn is approached with the car sliding sideways ant wheels turned the other way, the same wheel closer to the center is now called the outside wheel, which achieves greater angle compared to the other one, thus, true reverse Ackermann achieved by minimizing scrub from the wheels. Because of this, it is necessary to implement adjustability in the suspension geometry. Investigation was made on the negative side effects of suspension geometry, such as bump steer, which occurs if the lower control arm is not parallel with the tie rod, usually after lowering ride height of a vehicle. Problem solving methods defined, such as steering rack adapters and tie rod spacers. After lowering a vehicle, the angle of lower control arm changes which lowers the roll center and for that a vehicle in a turn experiences greater roll because of the greater distance between the vehicle’s center of gravity and roll center. All these negative effects can be eliminated by designing a new knuckle. By creating a 3D model in CAD, original suspension parameters can be defined. The measurements for suspension elements were made by using a laser measuring device and a 3D scanner. After defining the hard points of the suspension elements, calculations in multibody dynamics software „Race Software“ were made to acquire the information about suspension parameters while the suspension experiences vertical movement and steering rack inputs. These parameters were compared to currently used suspension designed for drifting, differences and issues defined. After evaluating the problems with the current suspension setup, a new professional grade drifting suspension design was proposed, which has the ability to quickly change the castor angle without affecting other parameters, achieves maximum available steering angle without any side effects, which occurs at high steering angles. A mechanism, which allows to change camber angle without affecting the king pin inclination angle was implemented which has not yet been available in the market. The new suspension was installed in the BMW E46 vehicle and suspension parameters measured on the wheel aligner at a professional shop. The parameters were compared with the information acquired by CAD and multibody dynamics simulations. |
