SAE International Experimental Study on the Effect of Coil Spring Reaction Force Vector on McPherson Strut Suspension Characteristics 2014-01-0048

In McPherson strut applications for automotive suspension systems, the desired coil spring reaction force vector (FLP: force line position) that minimizes damper friction and king pin moment is typically determined by Statics/Kinematics calculations. There is not a device available on the open market today which can mimic the coil spring reaction force vector within the suspension system. Such a programmable coil spring reaction force vector generator, named "Universal Spring", was developed in 2003 (USPG2003), and was then improved in 2013 (USPG2013) from the standpoint of accuracy, durability and reliability. The device is actuated by six hydraulic cylinders constructing a Stewart platform type parallel mechanism. Accuracy of FLP generated by USPG2013 is 1.1mm at maximum in \u03d580mm area around strut axis. Using this modified device, the relationship between the spring reaction force vector and damper friction, as well as spring reaction force vector and king pin moment, can be experimentally studied to confirm vehicle characteristics without actually producing any prototype coil springs. These studies will be discussed in this paper with showing actual measured data. Furthermore, it was found that approximately 70% of moment generated by upper bearing friction was transferred to king pin moment for the suspension system used in this experiment. The validity of this device was proven by comparing to actual coil spring based testing data.