# Review of Advancement in Variable Valve Actuation of Internal Combustion Engines
## 8 Electro-Hydraulic VVA (EHVVA) Systems
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Company** & **System** & **Design Features** & **Pos** & **Cons** \\ \hline Sturman & Hydraulic & Two digital 2-way pilot valves, & Full lift variability & High sensor cost and reliability concern \\  & Valve Actuation & a proportional valve, a return & & reliability concern \\  & (HVA) & spring, and closed-loop control & & \\  & & with a position sensor. & & \\ \hline Lotus-Eaton & Active Valve & One digital 3-way pilot valve, one & Full lift variability & High sensor cost and reliability concern \\  & Train (AVT) & servo valve, one return spring, & & reliability concern \\  & & and a hydraulic actuator & & \\ \hline AVL-Bosch & Electro-hydraulic & Two digital main valves, & Full lift variability & Lift accuracy concern \\  & Valvetrain & a hydraulic actuator with & and low cost & \\  & System (EHVS) & a two-stage differential piston & & \\  & & drive and a pilot controlled & & \\  & & variable snubber for seating & & \\  & & control, no return spring, & & \\  & & open-loop control without & & \\  & & a position sensor & & \\ \hline Gongda & Gongda VVA-2 & One digital 3-way pilot valve, one & Accurate lift and & 2-step lift \\ Power & (GD-VVA-2) & digital 3-way main valve, & low cost & \\  & & an actuator with one & & low cost \\  & & lift-control-elseve, 2-step seating & & \\  & & control, open-loop 2-step lift & & \\  & & control without position sensor. & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Some major electro-hydraulic VVA (EHVVA) systems. * Ford developed an EHVVA system that has a unique hydraulic pendulum design, i.e., some fluid spring pendulum [7; 86], which tries to convert the kinetic energy into hydraulic pressure or potential energy during both the opening and the closing stroke. The system includes a high-pressure and a lower-pressure switch valve and a couple of check valves, and it requires close monitoring and feedback on the engine valve position. However, the fluid spring may be difficult to manage because of the high bulk modulus of a typical hydraulic fluid. Additionally, the fluid bulk modulus is highly variable under the influence of the entrapped air. * Gongda Power developed the LGD-VVA-1 system that consists of a two-spring actuation, a bypass passage, and an electro-hydraulic latch-release mechanism [36; 37]. The two-spring pendulum system is used to provide efficient conversion between the moving mass kinetic energy and the spring potential energy for reduced energy consumption. Its latch-release mechanism can also compensate for the lost frictional energy during the pendulum motion. Prototypes of the system were bench- and engine-tested. This system, at least with its limited prototype design, presents some challenge in packaging because of its total height, considering adding two springs to the necessary hydraulic mechanism. * DaimlerChrysler developed various designs using a two-spring pendulum with a hydraulic latching (US Patent Nos. 4930464, 5595148, 5765515, 5809950, 6167853, 6491007, and 6601552). However, the designs do not have an effective latching mechanism that can add energy to the pendulum to compensate for the frictional loss and cylinder air pressure, and there is no mechanism to change valve lift.