Valves of type 4WRDE are 3-stage directional control valves. They control the quantity and direction of a flow and are mainly used in control loops for different tasks.
They consist of the following assemblies:
- The 2-stage pilot control valve consisting of the control motor (1) and a hydraulic amplifier (5) designed as nozzle flapper plate valve and the control spool socket unit (6) as flow amplifier stage for actuating the 3rd stage (7).
- The 3rd stage (7) for flow control
- An inductive position transducer (8) the core (9) of which is attached to the control spool (10) of the 3rd stage.
The position of the control spool (10) is measured by an inductive position transducer (8). The signal linking of the valve control loop, the supply of the position measurement system and the control of the pilot control valve are carried out via control electronics integrated in the valve. The voltage difference created by the command/actual value comparison is amplified in the control electronics and supplied to the 1st stage of the valve as control deviation. This signal deflects the flapper plate (2) between the two control nozzles (3.1, 3.2). This creates a pressure differential between the two control chambers (11.1, 11.2). The control spool (4) is moved and releases a corresponding flow into the control chamber (12.1 or 12.2). The control spool (10) with the core (9) of the inductive position transducer (8) attached to it is displaced until the actual value corresponds to the command value. In the compensated condition, the control spool (10) is held in the position specified by the command value. The control spool stroke is proportional to the command value. For the control of the flow, a corresponding control opening results, depending on the position of the control spool (10) to the control edges (13), to which the flow is proportional. The valve dynamics are optimized via the electric gain. The control electronics is integrated in the valve (oscillator, demodulator).
Valve particularities
- The 3rd stage is basically set-up of modules of our proportional valves.
- With V control spools, the control edges of control spools and housings are ground in to each other.
- When the pilot control valve or the control electronics are exchanged, they are to be re-adjusted. All adjustments may be implemented by instructed experts only.
- The pilot control valve may only be maintained by Bosch Rexroth employees. An exception to this is the replacement of the filter and the sealing according to accessories list. It has to be ensured that during the assembly, the sealing is properly seated and the plug screw is tightened. The tightening torque for the plug screw is 30 Nm.
The valves basically comprise of:
- Servo pilot control valve, 2-stage, type 4WS2EM6-2X (1)
- Main stage (2), consisting of housing and main stage control spool
- Integrated electronics (3) with inductive position transducer of the main stage
Function
In the integrated electronics (OBE), the specified command value is compared with the position actual value of the main stage control spool. In case of a difference (control deviation), the first stage of the pilot control valve is controlled (dry torque motor and nozzle flapper plate system). This way, a deflection of the flapper plate of the nozzle flapper plate system is realized. The distance of the flapper plate to one of the two control nozzles flown-through by pilot oil is reduced and increased to the other one. Through the connecting bore, the resulting flow difference leads to deflection of the control spool in the pilot control valve (2nd stage) similarly to the control signal. The flow released by the pilot control valve leads to deflection of the control spool of the main stage (3rd stage) until its position actual value corresponds to the command value. The stroke of the control spool is controlled proportionally to the command value.
Valve features
The valves are factory-set with a dither default setting with the constant frequency of 400 Hz.
Failure of supply voltage
- With applied pilot oil pressure, the main stage control spool moves into an undefined end position. The acceleration forces occurring in this connection may cause machine damage.
- If a directional sandwich plate valve is used (see ordering code), the two pilot oil chambers in the main stage will be short-circuited in case of power failure.
- With symbol E, E1-, W6 and W8, the main stage spool will take the spring-centered central position.
- With symbol V and V1, the main stage spool takes the offset position, operated by the spring (P–B and A–T) (in the tolerance range 1 ... 11% of the control spool stroke)
Notes:
- Changes in the zero point and/or the dither amplitude may result in damage to the system and may only be implemented by instructed specialists.
- The pilot control valve may only be maintained by Rexroth employees. An exception is the replacement of the filter and the sealing according to accessories list. It has to be ensured that during the assembly, the sealing is properly seated and the plug screw is tightened. The tightening torque for the plug screw is 30 Nm
| 5
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Potentiometer R161 (only with version "C6-972"), see "Electrical connection".
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Pilot oil supply (schematic illustration)
Size 10
Size 16
Size 25
Size 27
| 1
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Plug screw M6 according to DIN 906, wrench size 3 - Pilot oil return
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| 2
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Plug screw M6 according to DIN 906, wrench size 3 - Pilot oil supply
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| 3
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Plug screw M12x1.5 according to DIN 906, SW6 - Pilot oil supply
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| 4
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Main stage housing cover (opposite the OBE)
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| Pilot oil supply
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| External
Internal
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2, 3 closed
2, 3 open
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| Pilot oil return
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| External
Internal
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1 closed
1 open
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Version “XY"
External pilot oil supply, external pilot oil return
In this version, the pilot oil is supplied from a separate pilot oil circuit (external). The pilot oil return is not directed into channel T of the main valve, but is separately directed to the tank via port Y (external).
Version “PY”
Internal pilot oil supply, external pilot oil return
With this version, the pilot oil is supplied from channel P of the main valve (internally). The pilot oil return is not directed into channel T of the main valve, but is separately directed to the tank via port Y (external). In the subplate, port X is to be closed.
Version “PT”
Internal pilot oil supply; internal pilot oil return
With this version, the pilot oil is supplied from channel P of the main valve (internally). The pilot oil is directly returned to channel T of the main valve (internally). In the subplate, ports X and Y are to be closed.
Version “XT”
External pilot oil supply, internal pilot oil return
In this version, the pilot oil is supplied from a separate pilot oil circuit (external). The pilot oil is directly returned to channel T of the main valve (internally). In the subplate, port Y is to be closed.
Notice!
Changes in the zero point may result in damage to the system and may only be implemented by instructed specialists!
