No Limits: Higher Dynamics with No Operational Limits from New Servovalve

With the new Direct Drive Digital Interface Valves (D637/ D639), Moog offers the marketplace a wider portfolio of high performance servovalves with reliable digital technology. This new product series is a single stage Direct Drive Servovalve, Size 5 (Cetop 05 mounting pattern according to ISO 4401-05-05-0-05) with sliding spool/bushing design. This flexible valve series is available with flow control (Q-control / D637), pressure control (p-control / D639) and flow and pressure control (pQ-control / D639) functionalities.

The D637/D639 Servovalves are tuned for very high dynamic performance and achieve a typical frequency response of 140Hz (for -90° small signal) and 14 ms (100%) step response time. This unique performance is achieved with the combination of an "advanced control algorithm" and the high natural frequency of our permanent magnet linear force motor that drives the valve spool. The same excellent performance is also reflected in the static data where hysteresis is typically less than 0.05%.

Handling Very High Pressure Drops

As opposed to many other Direct Drive Valves on the market (e.g. proportional solenoid or voice coil driven), the D637/D639 Valves do not have operational limits which means that within the pressure rating of the valve it can be operated even at the highest pressure drops in 4-way, 3-way or 2-way modes. This important benefit is a result of the high driving forces of the permanent magnet linear force motor (LFM), the flow force compensation of the spool/bushing unit (each land separately compensated) and control tuning for high stability.

These Digital Direct Drive Valves can be operated with a standard analog signal as well as via a fieldbus. Available fieldbus systems include CANOpen, Profibus DP-VP1 and EtherCAT. Start up and configuration of the valve can be easily implemented via the fieldbus interface of the machine control or by Moog's user-friendly MS Windows-based configuration software.

This software represents Moog's commitment to a flexible interface that can be used for our digital valve and pump products lines. An important benefit of fieldbus operation is that control parameter settings (e.g for pressure control (D639 /p-control)) are easy to complete and up to 16 pressure control parameter settings may be saved for activation during operation.

These dynamic servovalves can also be requested for higher level axis control such as position-, speed-, and force-control for special applications.

The digital onboard electronics (OBE) used on these products have also been used on other valve products in our portfolio such as the D636/D638 Digital Direct Drive Valve Series (Cetop 03) and the pilot-operated D67x Servo-Proportional Valve series where their superior functionality and robust performance have been proven in many different applications. Pre-production valves of the new D637 series have been performing successfully in multiple applications such as position control for water turbines.



Dirk Hirschberger is the Team Leader, Engineering Direct Drive Valves and has worked for Moog in Product Development since 1991 based in Germany. He studied mechanical engineering in Esslingen, Germany.

Lutz Bienemann, has been Senior Product Engineer responsible for Digital Direct Drive Valves since 1999. He studied mechanical engineering in Zwickau, Germany.