The design of electrohydraulic control mobile hydraulic control valve

In vehicles such as tractors, forklifts, work machines, mobile hydraulic direction control valves are used to actuate various equipments. The mobile hydraulic directional control valves are generally six way, spool valves with an integral check valve, relief valve, anti-shock and anti-cavitation valve or other auxiliary valves such as counterbalance valve. The structures of the valves may be monoblock from a single body, or may be sectional and bolted to form a sandwich. Hydraulic circuits of valves are used according to their usage; parallel, tandem, serial, or combinations thereof. These valves are usually open centered. That is, the pump is drained to the tank when the spools are in the neutral position. By moving the full stroke of any spool, it is possible to move the entire pump unit, such as cylinders, hydraulic motors, at the speed of the pump, or by moving the hydraulic cylinder and motors at a lower speed by partially adjusting the flow rate. Directional control valves have different types of spool that are used according to the function required as double acting spool, float spool, regen spool and motor spool. At the same time, according to the control types, they can be investigated under two main groups as direct acting and pilot operated. There are types with direct control, manual control, mechanical lever control, hydraulic control, pneumatic control and electrical control, and electro-hydraulic and electro-pneumatic control types in pilot operated control type. In parallel with technological developments, it is preferred to control the spool with an electro-hydraulic system. One of the main reasons for the need for electro-hydraulic control is to prevent operators from getting tired during long working hours against springs with high spring constant, which is essential for centering the spool, especially when used in high-flow valves. Thanks to the electro-hydraulic control system, the operator does not need to be operator but hydraulic oil pressure, the operator gives the desired precision control. Prior to the beginning of the design, a review of the existing electrohydraulic control systems should be done by conducting a literature search. Preliminary information about the usage areas and types of electrohydraulic control systems has been prepared. Subsequently, existing electrohydraulic control systems in the market were investigated and used products and their differences were determined. Literature research has investigated the on-off and proportional solenoid valves of electrohydraulic control systems and their applicability to the system. As a result, the products of different companies have been investigated and the working systems have been examined. As a result of this research, it is aimed to present the electrohydraulic control option to existing valves and new design direction control valves with this preliminary information obtained for design. For the electrohydraulic control system, design criteria were first determined to form the basis of the design. To provide pilot oil pressure of 15 bar, the spool diameter as an effect of the pilot pressure is set at 16 mm. It is aimed to make precise control proportional. Then the systematic construction in order to find different solutions to the problem steps were applied. One of the most important steps of the construction system is the creation of a request list. Requests are quantities in which the qualitative and quantitative properties of the technical work that will form the solution of the problem are specified. For this purpose, a list of requests was created and the basic function was obtained with the help of these requests. Inputs and outputs required for electrohydraulic control are determined. In addition, functions between the inputs and outputs and their relation to each other have been established. The function structure of this form is called the function structure. Functional structure was determined in the study. Thus, the necessary information for the development of the solution was prepared. In the process of developing the solutions, common requirements are determined for each solution. In this case, the control unit containing solenoid valves, which direct the pilot pressure to provide the movement of the spool, was selected from the catalogs of the valve supplier companies. In addition, by reducing the operating pressure, a pressure reducing valve was selected from the supplier of the cartridge valve to obtain the desired pilot pressure. The pilot pressure that the pressure reducing valve creates will be guided by the solenoid valves and the direction control valve spools affected by this pressure will come to the desired position by defeating the generated frictional forces, flow forces and spring forces. Thus, oil is required to be sent to the work ports and control equipment will be provided. For this purpose, three solutions have been created and control units have been adapted to the direction control valve. In the first solution created, this electrohydraulic control unit, which consists of electronic control unit and proportional solenoid valves with position sensing element, drives the pilot with the pilot pressure obtained from the inside. In the second solution, the pilot pressure is externally supplied and the spool will be moved via the servo piston. In the third solution, the solenoid valves to be installed on both ends of the valve spool are driven and the pilot control provided from the inside will control the spool. The hydraulic components required for each solution are selected and determined to be applied to the directional control valve. The created solutions are modeled in Creo CAD program. Then, benefit-value analysis was done for the solutions according to the determined basic and sub-targets. As a result of the analysis, Solution-2 has been selected to be detailed because it has the highest score. The hydraulic circuit of the electrohydraulic controlled directional control valve designed in Solution-2 was created and the working principle was explained. The design is modeled with the appropriate dimensions and has been finalized. It has gived information about the control unit and the pressure reducing valve used in the design. The force to be generated by the pilot pressure acting on the circular area of the servo-piston was calculated and the centering spring calculations were made in the Gutekunst spring program. Then, preliminary information on the sealing elements was given and the compression ratio for the selected o-rings was calculated. The choice of materials for the technical works is one of the important issues. The selected materials determine the manufacturing process, lifetime and durability of a construction. In the study, the components of the system components were identified and information was provided. In the Hema Industry Inc. R&D Hydraulic Systems department, the system was modeled in the AMESim simulation package program to verify the tests planned to be made after the prototype was produced on the computer. The signal, hydraulic, hydraulic component design and mechanical design library of AMESIM program were used for this. Input signal voltage / Valve spool stroke and Stroke / Flow rate graphs are obtained by using the created model. The prototyping work was done to see how the designed system will perform its function and accuracy. The prototyping was carried out at Hema Industry Inc. R&D Atelier. In this work, some parts were produced by machining in various machine tools. Some parts have been supplied from the sub-industry. Electrohydraulic controlled directional control valve was established by assembling these parts. After that, valve function tests were then performed and Input signal voltage / Valve spool stroke and Stroke / Flow rate graphs were obtained. As a result, it has been seen that the prototype and the test works fulfill the function of the design with accuracy. The results obtained with the data obtained from the modeled system in AMESim were compared and it was seen that similar results were obtained.