08 Swing System

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Service Manual

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Chapter 8 - Swing system

Swing System.................................................................................................................................................... 8-2

1 Adjustment........................................................................................................................................ 8-2

1.1 Specifications ......................................................................................................................... 8-2

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8 Swing System

The hydraulic swing circuit on Liebherr hydraulic excavators R 9250 is a closed circuit. The most important

components of this circuit are :

– The electro hydraulic pilot control system.

– 2 hydraulic pumps A4 VG 125

– 2 hydraulic motors FMF 250

– 2 swing gears SAT 450 / 257 with integrated disk brakes

– 1 swing ring ROD 1304 DJ 001-001 (triple race roller bearing with inner both)

Technical data

Swing pumps

Swing pumps output

Max. displacement

Max. flow

Max. operating pressure

Secondary pressure

kW

cm³

l/min

bar

bar

A4 VG 125/125

2 × 220

2 × 125

2 × 353

350

400

Hydraulic motors

Motor displacement

Working pressure

Torque

Flow

RPM

cm³

bar

Nm

l/min

t/min

2 × FMF 250

256

320

2 × 1239

2 × 391

1481

Swing gears

Torque

Number of teeth

Nm

2 × SAT 450 / 257

2 × 56000

13

Swing ring

Number of teeth

ROD 1304 DJ

114



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Schematic

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8.1 Schematic

8.1.1 Electric



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Schematic

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Schematic

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A1020

E1005

E1038

F32U21

X88

X96

X122

X300

X450

XR450

X455

XR455

X461

X755

X858

Y150

YR150

Y155

YR155

24V

0V

4 - 20X

4 - 20Y

Kl31

SWL1

SSWL1

SWR1

SSWR1

FSG plate

Cabin connection box

Connection box regulation

15A FuseLeft joystick

Connector 18 poles / A1020 FSG

Connector 4 poles / A1020 FSG

Connector 70 poles / E1005 elevation

Kl31 electronic ground E1005

Connector 2 poles / Y150

Connector 2 poles / YR150

Connector 2 poles / Y155

Connector 2 poles / YR155

Connector 12 poles / U21

Connector / Rotating deck

Connector 24 poles / E1038

Solenoid valve swing left

Regulation solenoid valve - Swing left

Solenoid valve swing right

Regulation solenoid valve - Swing right

Supply

Ground

4 - 20mA handle swing

4 - 20mA handle crowd

Ground

Regulation solenoid valve - Swing left supply

Solenoid valve - Swing left sypply

Regulation solenoid valve - Swing right supply

Solenoid valve - Swing right supply



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Schematic

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8.1.2 Hydraulic



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Schematic

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CP2

CP3

G

GS1GS2

MA

MB

MH

MS1

MS2

P5.1

P5.2

SP

SU1

Y150

YR150

Y155

YR155

Lower collecting pipe - support control valves

Collecting pipe power pack

Test point

Swing gear leftSwing gear right

Test point / high pressure - swing right

Test point / high pressure - swing left

Test point

Left swing motor

Right swing motor

Rear swing pump

Front swing pump

Suction pipe

Servo oil unit

Solenoid valve - swing left

Regulation solenoid valve - swing left

Solenoid valve - swing right

Regulation solenoid valve - swing right



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Location of components

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8.2 Location of components

Swing pumps P5.1 and P5.2



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Cabin connection box E1005 with A1020

Servo oil unit Connection regulation box E1038



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FSG plate A1020



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Functional description

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8.3 Functional description

8.3.1 System control

The purpose of the electro-hydraulic swing control system is to activate swing movements of the machine pro-portionally to the deflection of the joystick (see § joystick and pedal transmitters).

The left joystick U21 delivers an electrical signal (between 4 and 20 mA) depending on its momenteanous de-

flection.

The FSG plate amplifies the signal in order to supply the solenoid valves.

The graphic shows the signal delivered to the solenoid valves as a function of the joystick deflection.

* The values of the current delivered to the solenoid valves are default values to adjust.

The functioning range of the joystick corresponds to a deflection included between 10% and 90%.

In this range, the opening of the corresponding regulation solenoid valve is proportional to the joystick deflec-

tion.

The logical valves are closed for a deflection included between 0 and 10%. They are opened for a deflection

included between 10 and 100%.

Concretely, the swing movement occurs for a joystick deflection value of 10%. A maximum swing movement

is achieved for a joystick deflection value of 90%.

The solenoid valves Y150, YR150, Y155 and YR155 are normally activated (+24V) except if there is no current

on «24V movement» (if ladder or service trap is not locked in upper position).

The switching solenoid valves ( Y150 and Y155) and the regulating solenoid valves ( YR150 and YR155) are

mounted in torque control valves (TCV) on the front swing pump P5.2. These switching and regulating solenoid

valves control the swing pumps.

Joystick

U214-20 mA

FSG plate

A10200-1 A

Solenoid

valves



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8.3.2 Pumps

The 2 linked hydraulic pumps A4 VG 125 are variable displacement axial pumps in swash plate design, the

displacement volume and the flow increases as the pumps are shifted from the «O» or neutral position to their

maximum outputs.

When the swash plate is shifted from one angle via the neutral position to the other angle, the direction of flow

changes, while the direction of pump rotation remains the same, meaning that the pressure side becomes thesuction side and vice versa. In this way, it is possible to change the direction of the swing motor in the closed

loop circuit.

8.3.3 Motors

The pumps feeds the hydraulic constant volume motor FMF who are directly fixed on the swing gear SAT. The

FMF fixed displacement motor is used to drive the excavator’s swing gear. The axial piston motor is designed

as a swash plate type motor.

Axial piston motors are energy converters : they transform hydraulic energy into mechanical energy by their

axially directed pistons in cylinder housing.

The pistons with glide shoes rotate on the swash plate. Because of the inclination of the gliding surface, a piston

stroke in the cylinder is created; and thus the constant flow volume of the oil motor.

The pumps PS1 and PS2 feeds the hydraulic motors MS1 and MS2, which are linked.

8.3.4 Swing brake

The swing braking is achieved with disk brakes who are integrated in the swing gears SAT. The disk brakesact directly on the gear drive. They are used as a spring applied brake and are vented hydraulically, i.e. if there

is no brake pressure, the disks are pressed together by springs and the brake is mechanically closed.

The brake is negatively acting, hydraulically actuated and serves as a holding or parking brake.

When working, the swing can be locked in any position with this brake.

The swing brake is actuated via the push button S17. When the brake is applied, the red indicator light lights

up. When the push button indicator light is off, the brake is released.

Apply the brake only when the uppercarriage is not moving. In order to stop the uppercarriage when working

on a slope, first stop its movement with the left joystick U21. Then apply the brake via push button S17 and

move joystick U21 to neutral position.

To check the swing brake : apply the swing brake via push button S17. Then move the left joystick U21 to theright and then to the left to stop. The brake is working properly if the uppercarriage does not move.



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Optional equipment : swing brake controlled in semi automatic

With this equipment, the function of the push button is not apply and release the brake as described before,

but to preselect the operating mode of the mechanical swing brake, as follows :

– In one position the brake remains always applied.

– In the other position, the brake is in semi automatic mode and is controlled via the rocker switch S57 moun-

ted to the right joystick lever U22 as follows :

With the rocker switch tilted down, the brake is applied, respectively it applies as soon as the uppercar-

riage speed gets lower than a limit value.

With the switch tilted up, the brake remains released.

Notice : the red control light in the button S17 lights up each time the brake is applied.

If this light does not go out when the rocker switch 81 is tilted up, the button must first be pushed to preselect

the semiautomatic mode.

The brake only applies when the uppercarriage is near standstill and if no swing motion is actuated via the joys-

tick!

In order to stop the uppercarriage when working on a slope, tilt the switch 57 down and reduce the uppercar-

riage speed by braking with joystick U21. Move the joystick U21 back to «O» position. The brake will apply only

when the uppercarriage will be quite immobile.

Emergency stop of the uppercarriage swing motion : the swing brake can be applied independently of the up-

percarriage RPM by switching the button S17 from position « semi-automatic» into position «applied».

Perform this braking via button S17 only in emergency cases, since it causes fast abrasion of the brake discs.



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Troubleshooting

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8.4 Troubleshooting



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Adjustment

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8.5 Adjustment

8.5.1 Specifications

Replenishing and positioning pressure Bar 30

Swing brake Bar 30

High pressure relief valves (secondary valves) Bar 400

Working pressure on TCV Bar 350



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Detailed component description

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8.6 Detailed component description

8.6.1 Swing pumop A4 VG 125

The swing pump is a variable displacement axial piston pump in swash plate design. It supplies the closed loopswing circuit.

The displacement volume is in proportion to the input RPM and infinitely variable. The flow increases as the

pump is shifted from the «O» or neutral position to its maximum output.



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8.6.1.1 Rotary group

In the pump housing 1, parellel to the input shaft 5, are nine circular arranged pistons 7. The pistons move axial-

ly in the cylinder barrel 8, which in turn is firmly connected to the input shaft 5 via splines. The end of the pistons

are shaped in a ball joint which in turn is mounted in a ball socket / glide shoe 2. The glide shoes are held

against the variable, but non-rotating swash plate 4 by the retainer plate 84.

The swash plate 4 may be shifted from the neutral position to both sides by the guide pin 81.

The regulation of the pump via the guide pin 81 is performed by the positioning piston 10.2, located in the pump

housing and controlled by the torque control valve.

Depending on the angle of the swash plate 4, the nine pistons have a certain stroke, which in turn determinesthe output (pump flow) of the swing pump.

With the swash plate in the neutral position, which means vertical in relation to the input shaft, the piston stroke

and the pump flow is theoretically zero.

The higher the pressures difference between the two surface areas of the positioning piston 10.2, the further

the positioning piston is moved against spring pressure and the steeper the angle of the swash plate 4 will be.

When the swash plate 4 is shifted from one angle via the neutral position to the other angle, the direction of the

flow changes, while the direction of pump rotation remains the same, meaning that the pressure side becomes

the suction side and vice versa. In this way, it is possible to change the direction of the swing motor in a closed

loop circuit.

The control of the pump is via kidney shaped ports in the control lens 6 and the pump head 3. During the re-volution of the cylinder 8, oil corresponding to the area and stroke of the piston 7 is sucked in by four pistons



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through the kidney shaped control ports on the return oil side of the closed circuit. Four pistons supply the oil

via kidney shaped control ports to the pressure side and push the oil via the pressure port into the closed loop

circuit. The ninth piston is at dead center, which means reversing direction.

8.6.1.2 Pump displacement

The oil flow of the pump is depending on the stroke of the pistons 7.

When the positioning piston 10.2 is shifted from its neutral position to one side, it swivels out the swash plate

4 via the guide pin 81 and the pump flow is increased correspondingly.

The shifting of the positioning piston is achieved while connecting one port X1, X2 of the piston to a control

pressure, called positioning pressure, while the other port is connected to the tank at the same time.Usually the replenishing pressure for the swing circuit is also used as positioning pressure.

The regulation of the pressure connected to X1, X2 between tank pressure and positioning pressure is achie-

ved by the torque control valve which may be externally mounted and serve to control the displacement of se-

veral swing pumps A4 VG.



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8.6.2 Hydraulic fixed displacement motor FMF with discharge

8.6.2.1 General data

Machine R9250

Hydraulic motor Type FMF 250

Max. oil volume Cm³/U 250

Max. permissible leak oil quantity (without discharge at 300 bar) L/min 11

Discharge quantity (at a = 12 bar) L/min 11

Tightening torque - allen head screws 14 Nm 540

Tightening torque - discharge two way check valve 191 Nm 70 - 100

Tightening torque - discharge pressure - flow regulator 192 Nm 90

Inductive impulse transmitter 51 Nm 10 - 12

∆ p



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8.6.2.2 Description

The FMF fixed displacement motor is used to drive the excavators travel or swing gear. The axial piston motor

is designed as a swash plate type motor.

Axial piston motors are energy converters : they transform hydraulic energy into mechanical energy by their

axially directed pistons in a cylinder housing.

The pistons with glide shoes rotate on the swash plate. Because of the inclination of the gliding surface, a piston

stroke in the cylinder is created, and thus the constant flow volume of the oil motor.

8.6.2.3 Function of oil motor

Housing 12 contains nine pistons, which are located parallel to the output shaft 3. The pistons are contained

in cylinder 4, which is connected by gears to the output shaft 3.

The end of each piston 5 is designed as a ball joint, which is mounted in glide shoe 5.1. They are held against

the fixed and angulator mounted swash plate 6 by the retainer plate 7 and the return ball 8.

The hydrostatic support (oil film) between the glide shoes 5.1 and the fixed swash plate 6 (due to drillings in

piston 5 and glide shoes 5.1) reduces surface pressure between the glide shoe and the swash plate.

In a no load or pressureless condition, the cylinder 4 is pressed against the control lens 9 by spring 8.1, which

is installed in return ball 8. As the system pressure increases, cylinder 4 and control lens 9 are so well balanced

by hydraulic forces that even at high loads an oil film is maintained on the surfaces of the control lens as well

as on the glide shoes. At the same time, leak oil is kept to a minimum. Part of the leak oil is used for lubrication

of all moving parts and then returns to the tank via an external line.

If pressurized oil enters at connection A or B, four pistons 5 are pressurized via kidney shaped inlets in the

control lens 9. On the opposite side, four more pistons 5 push the low pressure return oil through kidney shaped

inlets in control lens 9 and connection A or B to the tank. A ninth piston is at dead center, which means at the

point of reversing direction.

Once the oil pressure reaches the four pistons on the pressure side, a certain force is created by oil pressure

and piston surface.

This force is transferred via piston 5 and glide shoe 5.1 onto the swash plate 6.

This radial force, which uses cylinder 4 as a lever, creates the torque, which is tranferred via cylinder 4 to the

output shaft 3. The amount of torque is in direct proportion to the system pressure, which means high pressure

= high torque. By applying oil to the opposite port (connection A or B), the torque and direction of the hydraulic

motor is reversed (right or left turn).

During a complete revolution of cylinder 4, pistons 5 perform a dual stroke from the lower dead center to the

top dead center and reverse. This stroke depends on the inclination of the swash plate 6 and influences the oil

quantity.

The displacement of the hydraulic motor remains the same until the oil supply from the variable flow pumps

changes.

8.6.2.4 Maintenance and repairs

Liebherr hydraulic motors are maintenance free.

For resealing and repair work, see «Repair instructions for Liebherr fixed displacement oil motors FMF».



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2

3

4

5

5.1

6

7

8

8.1

9

10

12

13

Roller bearing

Drive

Cylinder

Piston

Glide shoe

Swash plate

Return plate

Return ball

Spring

Control plate

Stop pin

Housing

Connector plate

14

15

16

17

18

19

22

23

25

26

27

191

192

Allen head screw

End ring

Shaft seal

O-ring

O-ring

O-ring

Lock ring

Lock ring

Spacer

Needle bearing

Washer

Discharge two way check valve

Discharge pressure regulator



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13

191.1

191.2

191.3

Connector plate - discharge two way

check valve

Piston

Spring

Bushing

192

192.1

192.2

192.3

192.4

Discharge pressure - flow regulator

Piston

Flow regulator

Spring

Bushing



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8.6.2.5 Function of discharge valves in connector plate

The discharge valves 191 and 192 allows a small amount of oil from the low-pressure connection on the motor

to escape into the motor housing.

This small amount of discharge quickly replaces the oil in the motor housing which was lost to leakage by the

new motors, keeping the motor cool.

Two way check valve 191.

The two ends of the piston 191.1 are connected via bore holes in the connector plate via kidney shaped slits

in the control plate 9.

If at actuation the pressure rises on connection A on the motor, the pressure PA acts on the piston surface SA

and moves the piston against the preload of spring 191.2.

Pressure PB on connection B on the motor now reaches via internal bores in the valve sleeve 191.3 into the

ring shaped chamber L, where it actuates the replenishing pressure regulator.

However, if high pressure is applied on connection B of the motors, piston 191.1 is pushed into the opposite

direction and low pressure PA is applied on L.

Discharge pressure regulator 192.Valve 192 functions as a restricted, pilot controlled pressure relief valve.

Pressure on L, via a restrictor bore hole in the flow regulator 192.2, actuates the main piston 192.1 and, when

the minimum pressure is reached, moves it towards the force of spring 192.3.

The oil can now reach chamber T via the restrictor bore hole and internal bores in valve sleeve 192.4 and flows

from there via a connector bore in connector plate 13 into the pump housing.

8.6.2.6 Repairs and adjustments on discharge valves

The repairs in valves 191 and 192 are limited to checking easy movement and resealing.

The discharge quantity is set at the factory and cannot be readjusted. If problems occur, replace the complete

valve.



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8.6.2.7 Variation with integrated impulse transmitter

The hydraulic fixed displacement motors FMF for the swing gear in machines with a closed loop circuit have

an additional impulse sending unit 51 for the control of the automatic swing brake.

2

3

4

5

5.1

6

7

88.1

9

10

12

13

14

Roller bearing

Drive shaft

Cylinde

Piston

Glide shoe

Swash plate

Return plate

Return ballSpring

Control plate

Stop pin

Housing

Connector plate

Allen head screw

15

16

17

18

19

22

23

2526

27

51

52

191

192

End ring

Shaft seal

O-ring

O-ring

O-ring

Lock ring

Lock ring

Spacer Needle bearing

Washer

Impulse sending unit

O-ring

Two way check valve with discharge

Discharge pressure



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08 Swing System

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