## 1 Introduction
By \"conventional suspension system\", we understand a suspension system in which each individual wheel is connected to the chassis with a combination of elastic and dissipation elements. This suspension layout creates a coupling of the natural modes of vibration because the same elastic and dissipation elements must deal with all possible oscillations of the wheels. As such, the natural frequencies of the system are a function of the stiffness of the springs, the distance from the center of gravity of the vehicle (CG) and the wheels, and the mass properties of the sprung mass. Naturally, the ability to choose each natural mode of vibration independently would significantly improve the performance of the suspension system by eliminating the necessity to compromise. Some improvements have been made, however, with the addition of the anti-roll bar (ARB). By interconnecting the wheels at the same end of the vehicle with another elastic element that will work in series with the wheel springs, the roll stiffness of the vehicle can be modified. The addition of this device, however, will inevitably increase the wrap stiffness of the vehicle. Another disadvantage of this system is the fact that, although radial dampers exist, they are usually not added in order to decrease the complexity and save weight. Therefore, although the roll stiffness of the vehicle is decoupled, the roll damping of the vehicle is still coupled because it is done by the wheel damper. Another modification of the conventional suspension layout done to have more flexibility over the stiffnesses of the individual vibration modes is the addition of the third spring (also known as the heave spring). The purpose of this heave spring (which is paired with its own damper) is to decouple both the stiffness and dissipation of the bounce mode of vibration [4]. While this arrangement allows for the independent choice of stiffness for the bounce and roll modes of vibration, the pitch stiffness is coupled with the bounce modes because only the heave spring is deformed when either the bounce or pitch modes are excited. Another disadvantage of this arrangement is the fact that the roll and wrap modes of vibration are still coupled, therefore increasing the stiffness of the wrap mode of vibration. These deficiencies of the traditional suspension layout created the necessity for alternative designs to solve the coupling problem. One possible solution to these challenges is the implementation of a hydraulically interconnected suspension system. Although not new, these solutions have not been explored to their full potential due to the overall higher level of complexity as well as higher expenses necessary for implementing and maintaining such a system. However, given the theoretical advantages that such a system can provide, a more in-depth analysis of such a system is required. The implementation of hydraulic interconnected suspension systems for motorsport applications has been tried before with some promising results. A short review of literature on hydraulically interconnected suspension systems shows that the first one was proposed in 1927 [5] by [PERSON]. This patent application proposed the replacement of all dampers with double-acting cylinders that could be interconnected based on the sought-after effect. The proposals included schematics for four possible combinations of piston connections for anti-oppositional effects in roll, pitch, wrap, and a combination of roll and wrap. Another important step in the evolution of hydraulically interconnected suspension systems was in 1979 [6], with a system implemented by the British Motor Corporation on Minis. This layout, proposed by Dr. [PERSON], consisted of hydraulically interconnected front-to-rear dampers. Through this system, the pitch stiffness of the vehicle could be independently controlled from the other modes, something he considered vital for improving the ride comfort. More modern interpretations of hydraulic interconnected systems have been studied in recent times.