sistema hidrostatico bomba A4VG

1. Basis

2. Open circuit
In an open circuit the pump delivers oil from the hydraulic tank to the
consumer.
From the consumer the oil runs back to the hydraulic tank.
Fixed
displacement
pump
Fixed
displacement
motor
Cylinder
2002/09 Folie 2 Basic Training / Travel Hydraulic

3. With a distributing valve, the hydraulic motor or a cylinder can be
triggered two sides.
Distributing valve
2002/09
Fixed
displacement
pump
Fixed
displacement
motor
Cylinder
Open circuit
Folie 3 Basic Training / Travel Hydraulic

4. Closed circuit
In a closed circuit the pump delivers oil to the consumer. From the
consumer the oil is running back to the suction side of the pump.
The pump can deliver oil in both directions.
Variable
displacement
pump
Variable
displacement
motor
2002/09 Folie 4 Basic Training / Travel Hydraulic

5. Pressure relief valves protect the closed circuit against to high pressure
in both directions.
Pressure relief
valves
2002/09
Variable
displacement
pump
Variable
displacement
motor
Closed circuit
Folie 5 Basic Training / Travel Hydraulic

6. The leakage from the variable displacement pump and the variable
displacement motor flows to the hydraulic tank.
2002/09
Pressure relief
valves
Variable
displacement
pump
Closed circuit
Variable
displacement
motor
Folie 6 Basic Training / Travel Hydraulic

7. Closed circuit
The leakage from the closed circuit will be
replaced by fresh oil.
The feed pump delivers oil on the low pressure
side into the closed circuit.
Var. displ. Pump
with feed pump
Var. displ.
motor
filter
cooler
2002/09 Folie 7 Basic Training / Travel Hydraulic

8. Folie 8 Basic Training / Travel Hydraulic
Hydrostatic drive:
Variable displacement pump A4VG .. DA
Variable displacement motor A6VM .. DA
Hydrostatic travel drive

9. Variable displacement pump A4VG .. DA
Pressure relief valve
Feeding pump
Performance adjustment screw
Regulator
valve
Feeding
pressure
relief valve
Pressure cut off valve
Folie 9 Basic Training / Travel Hydraulic

10. Var. Displacement pump - A4VG .. DA
2002/02
During activated Solenoid
3, the directional valve 4 is
pushed down.
In This time, the control oil is running
to the servo piston. From approx. 6 bar control
pressure on, the servo piston is pushing against the
pressure springs and the pump is swivelling out.
1 Pressure springs
2 Servo piston
3 Solenoid for drive
direction forward
4 Directional valve
Folie 10 Basic Training / Travel Hydraulic

11. Var. displacement pump / DA-Regulation
Pressure
cut-off valve
Regulator valve
Feeding pump
Feeding pressure relief valve
Directional solenoid valve
Inching valve
Folie 11 Basic Training / Travel Hydraulic

12. Var. displacement pump - A4VG .. DA
2002/09
RPM-depending, the feed pump delivers oil to the regulator valve. Corresponding to this, a
certain differential pressure occur on the orifice.
The differential pressure effects a force against the spring in the regulator valve and the control
pressure. This adjust a certain, RPM-depending control pressure.
DA – regulator valve
Folie 12 Basic Training / Travel Hydraulic

13. Servo piston with
directional valve
Inching valve
Variable displacement pump
A4VG .. DA
Folie 13 Basic Training / Travel Hydraulic

14. Var. displacement pump - A4VG .. DA
2003/09
Pressure cut-off
The pressure cut-off limits the maximum pressure in the closed
circuit.
The high pressure acts through the shuttle valve 4 on the
piston 3 and valve 2 against the pressure spring 1.
If the high pressure exceeds the adjusted value, the control
pressure will be reduced to the tank channel and the variable
displacement pump reduces the flow rate.
Folie 14 Basic Training / Travel Hydraulic

15. 2002/09
Pressure relief – and replenishing valve
At high pressure Low pressure side with replenishing
Var. displacement pump - A4VG 71-180 DA
Folie 15 Basic Training / Travel Hydraulic

16. Var. displacement motor - A6VM .. DA
2002/02
During reverse travel, the solenoid
valve travel direction is power-supplied
During 1. travel range, the solenoid
valve 1. travel range is power-supplied.
1 Drive shaft
2 Housing
3 Rotary group
4 Valve travel direction
5 Valve 1. travel range
6 Control unit
7 Discharge valve
Big swash angle 25°:
• High torque = high tractive force
• Low revolutions = low speed
Small swash angle:
• Low torque = low tractive force
• High revolutions = High speed
Folie 17 L 506 - L 510 Fahrhydraulik

17. During full speed, the control pressure reaches approx. 30 bar. In this time, the
control valve is pushed down and the var. displacement motor regulates to Q-min.
If the high pressure reaches approx. 220 bar, the control valve is moved up, against
the control pressure. In this time, the oil is running from the large side of the servo
piston to the tank and the var. displacement motor regulates to Q-max.
2002/09
Var. displacement motor - A6VM .. DA
Folie 18 L 506 - L 510 Fahrhydraulik