04 05 Hydraulic System LG956L

7/24/2019 04 05 Hydraulic System LG956L

1/82

LG56L Training Material

Chapter VI Hydraulic System


2/82

CHAPTER VI Hydraulic System

SECTION I WORKING

HYDRAULIC SYSTEM

I. Overview

II. Working pump

III. Control valve

1. Main relief valve

2. Overload valve of big chamber

SECTION II STEERING

HYDRAULIC SYSTEM

I. Overview

II. Loader sensor hydraulic steering system

1. Overview

2. Steering gear

3. Priority valve

RELIABILITY IN ACTION

3.Over load valve of small chamber

4. Check valve

IV . Pilot valve

V. Pressure selector valve

VI. Cylinder

VII. Trouble shooting for hydraulic

system

III. Common faults and repair of steering

hydraulic system


3/82

SECTION I WORKINGHYDRAULIC SYSTEM

I OVERVIEW

LG956L applied the pilot control

system, to control the high main oilflow which is high pressured and

mass flowed.The working hydraulic system is

mainly composed by the workingpump, pressure selector valve,control valve, lift arm cylinders,

bucket cylinders, oil tank and oiltubes.


Compared with the machinerycontrol hydraulic system, this systemhas the features as below:

It is portable, flexible andefficient, which can be controlledeven by a finger.

By using proportional pilotvalve control, it can greatly reduce

the commutation control force.The relief valve, overflow valve,

oil refill valve and check valve applied

cartridge structure, thus they havegood commonality, and they are easyto maintenance.

2


4/82

The pilot valve is monolithicconstruction, which makes it small inseize, and easy to place.

When the engine stops, the liftarm can be lower and the bucket can

be unload by the effect of pressureselector valve and the pilot valve.

There are electromagnets setin the lift arm lifting position and

bucket retraction position, it canrealize the limitation of the lift arms



height and the balance of the bucketat any position. This can simplify thecontrol process, reduce the laborintensity and avoid the energy loss

and pressure impact due to thefrequent action of the relief valve.

3


5/82

II WORKING PUMP

The working pump is a gear pump.The liquid is transmitted due to thechange of the volume formed by thegears and the pump body. And the

mechanical energy is transferred intohydraulic energy.

Main parts1-Pump body2-Bearing



- as er

4-Driven gear5-Side plate6-Sealing7-Bearing8-Drive gear

4

1 2 3 4


6/82

Working principle

When the working pump runs, manyvolumes formed by the pump body,

the end cover and the gears. Whenthe gears rotates in the direction of

the picture shown right, the volume ofthe oil suck chamber increasesgradually due to the meshing toothrelease little by little. The oil suckedin will full-fill the volume between the

gears and the pump body. The oil gowith the ears to the oil outlet



chamber. The volume changes to besmaller because the gears run intomeshing, and the oil will be pushedout. The oil suck chamber and the oil

outlet chamber are separated by thegears. As the volume changes, the oilsucked in and squeeze out constantly.

5


7/82

III .CONTROL VALVE

Compose

The control valve is mainlycomposed of valve body, lift arm

valve kit, bucket tilting valve kit,auxiliary valve kit, over flow valve kitfor big chamber of lift arm cylinder,over flow valve kit for small chamberof bucket cylinder, logic valve kit,

check valve etc.

1

10 11



1-Relief valve2-The third function3-Bucket tilting valve4-Lift arm valve

5-Relief valve for small chamber ofbucket tilting cylinders6-Relief valve for big chamber ofbucket tilting cylinders

7-Valve body 8-End cover9-Spring 10-Spring seat11-Spool

6

2 3 4


8/82

Oil ports set

1-To small chamber of bucket

cylindersB12-To big chamber of bucket cylinders

A1

3-To small chamber of lift armcylindersB24-To big chamber of lift arm cylinders

A25-Oil return portT6-Oil inlet portP7&8-To the third function orts

1

2

3

4

11



9-Logic valve10-Check valve11-To pilot oil

7

11

10


9/82

Main function

To control the movement of the liftarm cylinders and bucket cylinders or

to keep the bucket and lift arm stay ata position through controlling the

position of the spools, whichdetermines the direction, the flow andthe pressure of the oil flow. And themovement of the spools are basedon the pilot oil.

Neutral position



en e p o ever a e neu ra

position, the spools of bucket kit andlift arm kit stay at the neutral position.The A1, A2, B1 and B2 chambers arelocked. The oil inlet port is connectedto the oil return port. The oil fromworking pump go straight back to theoil tank through the control valve.

8


10/82

Bucket backward tilting

When the pilot lever at the position ofbucket backward tilting, the pilot oil

come from a1 channel push thespool to the b1 side. Then the

channel between the P chamber andthe T chamber is cut off. The Pchamber is connected with the A1chamber and the T chamberconnected with the B1 chamber. The

high pressure oil from P chamberoes into the bi chamber of bucket

1 1



cylinders through A1 chamber. Theoil from the small chamber of thebucket cylinders goes back to the oiltank through the B1 chamber. Thus

the bucket tilts backward.

9


11/82

Bucket forward tilting (unload)

When the lever is placed at thebucket forward tilting position, the oil

from channel b1 pushes the spool tothe a1direction, and the spool cut the

channel between P chamber and Tchamber off, and connects the Pchamber and the B1 chamber, andalso connects T chamber and A1chamber. The pressured oil flows to

the small chamber B1 of the bucketc linder. The oil in the bi chamber

1 1



A1 of the bucket cylinder returns tothe tank through the T chamber. Andthe bucket forward tilting (unload)action can be achieved.

10


12/82

Lift arm lifting

When the lever is placed at the liftarm lifting position, the oil from a2

channel pushes the spool to the b2direction. The spool cuts the channel

between the P chamber and Tchamber off, and connects the Pchamber and A2 chamber, and alsoconnects T chamber and B2chamber. The pressured oil flows to

the big chamber of the lift armc linder throu h P chamber. The oil

2 2



in the small chamber B2 of the liftarm cylinder flows to the tank throughT chamber. And the lift arm liftingaction can be achieved.

11


13/82

Lift arm down

When the lever is placed at theposition of lift arm down, the oil from

b2 channel pushes the spool to a2direction. The spool cut the channel

between P chamber and T chamberoff, connect the P chamber and theB2 chamber, and also connects the Tchamber and A2 chamber. Thepressured oil flows to the small

chamber B2 of the lift arm cylinderthrou h the P chamber and the oil in



the big chamber A2 of the lift armcylinder flows to oil tank through Tchamber. And the lift arm downaction achieved.

12


14/82

Lift arm float

When the lever is placed at the liftarm float position, the logic valve

opens, the B2 chamber is connectedwith the T chamber. The ports P, A2,

B2 and T are connected, the lift armcylinders float under the effect of theexternal force.


RELIABILITY IN ACTION13


15/82

1.Main relief valve

The main relief valve is used tocontrol the pressure of the whole

hydraulic system. The pressure set is17MPa.

Compose1-Spring seat2-Hexagon nut3-Spring

4-Lock nut5-Su ort sleeve

1

2

3

4



6-Poppet7-Poppet vale seat8-Spring9-Main spool

10-Valve seat11-Valve body

14

10 11


16/82

Working principleChamber C and chamber D areseparated by the control vale body andthe main relief valve body. Chamber C isconnected with oil returning port, andchamber B is connected with the oil inletport. The orifice 1 in chamber B is

connected with the orifice 2 in chamberC. When the pressure of the oil higherthan the set pressure, the oil flows tochamber A through orifice 3 and pushesthe poppet to move upward. Thepressured oil flows to chamber B, at thistime the o et valve seat moves

1 2



upward by the force of the spring.

Because of the pressure differencebetween the two ends of the orifice, themain spool is forced to move upward.And thus chamber C and chamber D areconnected by orifice 4, parts of the oilreturn to the oil tank. With the increaseof the oil pressure, the distance the mainspool travels become longer. The size

chamber C to chamber D become larger,the ability for oil relief is larger. When thepressure is below the set pressure, themain spool return by the force of thespring

15

3

4


17/82

2.Relief valve for big chamber

Compose

1-Valve seat 2-Hexagon nut3-Spring 4-Valve seat

5-Spool

Working principle

Chamber C is connected with oil

return port, chamber A is connectedwith bi chamber of bucket c linder

1

2

3

4



chamber B is connected with

chamber C through orifice 7,chamber D is connected withchamber C through the orifice in the

spool. When the pressure of the oil inchamber A higher than the setpressure, the high pressure pushesthe spool move upward, and

chamber A is connected withchamber C to drain the oil. When thepressure decreases below the set

pressure, the spring returns by theforce of the spring.

16


18/82

3.Relief valve for small chamber

Compose

1-Spring seat 2-Hexagon nut3-Screw plunger 4-Valve body

5-Spring 6-Spool

Working principle

Chamber A is connected with small

chamber of the bucket cylinders, andchamber B is connected with oil

1

2

3

4



return port. When the pressure of the

oil in the small chamber is higherthan the set pressure(12MPa),the oilpushes the spool to move upward.

And chamber A is connected withchamber B, the oil draining started.When the oil decreases to below theset pressure, the spool returns by the

force of the spring.

17


19/82

The function of relief valves

1.When the bucket tilting spool atthe neutral position, both the

chambers of the bucket cylinder areclosed. If some external impact

works on the bucket, the relief valvecan prevent the pressure from beenincreased sharply.

2.It can drain the oil automatically at

the process of lift arm up and down.For exam le When the lift arm



reached to a given position, the

piston rod of the bucket cylinder willbe forced out. Thus the pressure ofthe oil in the small chamber will rise

sharply. The relief valve can makesthe oil return the oil tank through therelief valve. And this can prevent thecylinder and hoses from been broken

by the high pressure.

18


20/82

4.Check vale

There are check valves in everyspool unite of the control valve.

There is a oil refill valve between thesmall chamber B1 of the bucketcylinder and chamber T. This oil refillvalve is a check valve. The mainfunction is to refill the small chamberof the bucket cylinder. For example,when the loader unloading, the

bucket forward tilting fast. When thebar center of the bucket asses the



below hinge joint, the bucket

accelerate tilts by the effect of thegravity. The travelling speed islimited by the oil volume pumped by

the oil pump. This check valve canrefill the small chamber of the bucketcylinder, and makes the bucket tiltfast, strike onto the stop block

realistic.

19


21/82

IV.PILOT VAVLE

Compose

The pilot valve is mainly composed ofvalve body, electromagnet kit,metering valve kit, logic valve etc.The details of the parts in next page.

1-Lever2-Dust cover

3-Ledge plate4-Valve bod

1

2



5-Metering valve

6-Logic valve

20

3

4


22/82

Dust cover

Plate

Electromagnet valve

Ledge plate

Push rod

Seat

Ledge plate

Spine

Ledge plate

Valve body

Seal


Spring

Oil return chamber 2C

Logic valve

Logic valve seat

Metering spring (internal)

Oil return port

Spring

Oil inlet port

Metering valve seat

Metering valve spool


23/82

Working positions

The lever is fixed on the pilot valve.There are 3 positions for the bucket,

like forward tilt position, neutralposition and backward tilt position.There are 4 positions for the lift arm,like lifting position, neutral position,down position and float position.There are electromagnets at thelifting, float and backward tilt position.

When the lever is laced at the



maximum position of lift arm lifting

position or backward tilt position, thelever is locked until the lift arm or thebucket moved to the specific position.

The approach switch works, and theelectromagnet lost its magnetic force.The lever is forced back to theneutral position by the force of the

returning spring.

22


24/82

The hose connection

P-Oil inlet portT-Oil return port

Chamber 2C is connected with K portin logic valve.




25/82

Working principle

When the lever is placed at thebucket backward tilting position, the

push rod pushes the spring seat, andthe spring is compressed, then thespool is pushed downward by theinferior spring seat. The oil inletchamber is connected with the pilotoil chamber through the orifice 1 andorifice 2 in the spool. The oil flows to

chamber a1 and chamber b1, andushes the meterin s ool u ward.

1

3

4



The pilot oil chamber is connected

with the oil return chamber. And thespool in the control valve moves.

3-Spine 4-Push rod5-Spring seat 6-Metering spring7-inferior spring seat8-metering valve spool

24

2


26/82

Principle of direct ratio control

When the press of the pilot controlchamber equals with the force of the

metering spring(or a little bit bigger),the oil pushes the spool upward, andthe inferior valve seat pushes themetering spring. The channelbetween oil inlet port and control oilchamber is cut off, at the same time,the spool in control valve stop

moving. So the angle the leverlaced determines the movement of



the spool in control valve. And we

can control the working speed bycontrolling the angle of the leverplaced.

25


27/82

When the lever is placed at the floatposition, the control chamber isconnected with the oil inlet chamber,the pressured oil flows into the

control chamber of the logic valve,and pushes the spool upward.because of the difference of the twoends of the spool in logic valve,chamber 2C is connected with the oilreturn chamber. The logic valveworks and thus the float action

achieved.




28/82

V .PRESSURE SELECTOR VALVE

Function

The function of the pressure selectorvalve is to supply specific pressuredoil to the pilot valve, and guaranteethe lift arm down when the diesel isoff.

Compose

1-Valve bod 2-Check valve

1 2 3 4



3-Check valve 4-Spring

5-Spool of the check valve6-Spring7-Spool

27


29/82

Port sets

1-P1 port to pilot pump2-P2 port to pilot valve

3-Pr port to big chamber of the liftarm cylinder4-L port to the tank

1

2

3

4




30/82

Working principle

When the valve is working , the oilfrom pilot pump flows to pilot valve

through P1 port, the orifice in thespool and P2 port.



1


31/82

When the pressure of P2 port ishigher than 1.5MPa, the spool movesto the left, and the channelconnecting P1 port and Pr port is cut

off. The check valve in Pr port canprevent the oil in the big chamber ofthe lift arm cylinder from flowing

back.



1


32/82

When the engine is off, there is no oilin P1 port, and the spool moves backto the position when the P1 port andPr port are connected. If the working

device is lifted high, and the lever isplaced at the neutral position, the oilin the big chamber of the lift arm

cylinder is sealed in the chamber.At this time, just put the lever at thelift arm down position, and the oil inthe big chamber of the lift arm

cylinder will flow into pressureselector valve. The hi h ressured oil



flows to the pilot valve through P2

port and pushes the spool in thecontrol valve to the lift arm downposition. And then the lift arm can

down to the ground. In this process,the pressure of the oil to the pilotvalve is controlled by the spool to 1.5MPa. If the pressure is higher than

1.5 MPa, the spool moves to left, andthe flow will be decreased, viceversa. And thus the pressure of the

oil can be controlled.


33/82

VI.CYLINDER

The cylinder is used to transmitpressure energy into mechanical

energy. And to drive the workingdevice to move in line or swing backand forth.

The cylinders can be divided into2 types based on the differentworking type. There is 1 port in the

single acting cylinder, and the oil canush the iston out while it de ends



on the force of the spring or the

gravity. There are 2 ports in thedouble acting cylinder the movementof the piston is determined by the oil

pressure.For this training material, we just

talk about double acting cylinder.

1-Cylinder body 2-Piston rod

32

1 2


34/82

Compose

1-Bottom 2-Spring ring 3-Ring4-Clamp ring 5-Piston 6-O-ring

7-Support ring 8-Ring 9-Yx seal10-Cylinder body 11-Joint12-Guide sleeve 13-Cylinder cover

14-Dust cover 15-Piston rod16-pisitioning screw 17-Ring18-Buffer plunger

Working principle



The cylinder is mainly composed of

the cylinder body 10, piston 5, pistonrod 15, guide sleeve 12 etc. Tosimplify, we divide the cylinder into

the small chamber and the bigchamber. The high pressured oilflows into the cylinder through port Aand pushes the piston to the right.

The oil in the right chamber flows tothe tank through port B.

33


35/82

VII.TROUBLE SHOOTING FOR HYDRAULIC SYSTEM

1.Why the gear pump fails? How to prevent?

Reason :

(1)There are scrap iron, gravel or something like that, and this will cause the scratch, wearing to the partsthat moves.(2)The clearance between the shaft of the pump and the drive shaft is too large to drive the pump.(3)The friction between the side plate and the gears is too serious.(4)The oil suck hose jams or leakage, the oil intake shortage and this result in the failure of the pump.(5)The tightening torque of the bolts used fixe the flange is not equal. Thus cause the failure of the pump.


Prevention measures :

A. Check the drive shaftB. Check the bear of the drive shaft, there should not be axial float.C. Check the tightening torque of the bolts used to fix the cover to the pump body. The tightening torqueshould be equal.D. Check the oil sucking hose, prevent the air from flowing into the system.

E. Keep the oil clear.


36/82

2. Why the bucket weakness, the bucket tilt forward or backward

automatically?

(1)The sealing rings in the piston fails, and it cause internal leakage.(2)The scratch or wearing appeared in the spool and the valve body, and it cause the oil leakage inthe control valve.(3)There are some damages in the conical valve spool or the conical surface of the relief valve, and

thus makes the sealing failure. The leakage in the relief valve appeared.


. e wor ng pump s easy o urs , an e ea age o en appears a

the end cover of the pump, why?

The main reason is the spool of the main relief valve jams, the system stay at the closed station. Thepressure in the system increase rapidly. And this lead to the burst of the pump.

The reasons below can account for the oil leakage:The long-term bearing of high pressure result in the elongation of the bolts used to fix the cover

to the pump body. And this cause the flexible of the cover. The radial scratch in the cover or thevalve body is another reason that can account for the leakage.


37/82

4.What is pulling cylinder? What is the hazard? How to prevent?

(1)Pulling cylinder: the part protruding outward of bucket cylinder piston rod is shortest when the bucket

is at limit position of downward tilting. When the lift arm is lifted to a certain height, the limit point of thecontacts the bottom of the bucket and the bucket can not tilt downward with the lifting of the lift arm. Ifthe lift arm is lifted continuously, however, relative position of supporting point on two sides of bucketcylinder can change with continuous lifting of the lift arm, which forces the bucket cylinder piston rod toextend outward. For small and big chambers of the bucket cylinder are closed when the boom is lifted,outward extension of the piston rod can lead to rapid pressure increase in the small chamber of the

cylinder. Such phenomenon that outward extension of bucket cylinder piston rod is caused by lifting ofthe lift arm when the bucket is dumped fully is called pulling cylinder.

(2) Hazard: bending and deformation of bucket cylinder piston rod; damage of knuckle for bucketcylinder pine shaft; teeth falling of lock nut for bucket cylinder piston.


(3)solution: retract the bucket and then lift the lift arm after the bucket is dumped.


38/82

5.Why doesnodding(falling first and then rising)occur sometimes when

the lift arm is lifted?

Floating status that oil inlet and outlet are connected with working port will appear at a certain time ofreversing for negative closing is adopted by lift arm control valve of distribution valve. Lower the lift armfirst and then lift it after the negative closing and the floating status of oil inlet and outlet and the working

port end due to the gravity of the lift arm and bucket.

6.Why the bucket is lifted and tilted slowly and powerlessly?

The seals of lifting and tilting bucket cylinders are damaged, resulting in inner leakage of the hydraulic


cylinder, which causes powerless action. Symptom : oil leakage occurs at surface junction, the pressure

drops faster and abnormal sound of oil leakage appears during operation.


39/82

7.Failures of control valve.

(1)Dirt in control valve blocks the spool or the pipeline to cause unsmooth oil flow. Symptom : theresistance when operating control valve is larger, the spool fails to move smoothly and cant be resetnormally.

(2)Excessive wear of control valve and too large fit clearance between the spool and the valve bodyresult in inner leakage thus to cause insufficient working flow.

(3)The relief valve fails. The relief vale opening pressure is too low. At this time, do not fasten pressure-

regulating screw of relief valve blindly. It is required to remove and check the relief valve to see if the reliefvalve spring is ruptured, guide valve sealing is favorable, the spool is seized and damping hole of spool isblocked. The opening pressure of the relief valve shall be adjusted if none of the above problems occurs.

(4)Inner leakage of the working pump is large, pump outlet flow is insufficient, loop pressure decreasesand lifting and tilting buckets act powerlessly. Symptom : The hydraulic pump produces large noise when


working and abnormal sound of leakage in the pump can be heard; engine speed raises and the hydraulic

pump produces larger noise; a large amount of copper scales exist in the oil filter and tiny copper scalesalso exist in the oil.

(5)The oil suction pipe and the oil filter are blocked or the oil suction pipe is aged, twisted or sealedimproperly, which can result in insufficient flow.


40/82

8.Why the machine shivers in the raising or tilting process?

The specific cause and countermeasure for the failure is as below:

(1)The oil is insufficient to cause unstable working pressure. It is necessary to fill up hydraulic oil.(2)The oil suction rubber pipe nozzle is improperly sealed and air enters in the system to cause unstableworking pressure. It is necessary to check sealing performance.(3)The oil is invaded by air and the invaded oil is forced to become compressible object due to lots of

tiny bubbles in the oil. It is necessary to eliminate the position which is sealed improperly in the low-pressure oil pipeline and then expel air in the oil.(4)Hydraulic cylinder piston is loosened to cause runout of the piston rod in the hydraulic cylinder. It isnecessary to dismantle the hydraulic cylinder and trace the cause.(5)The opening pressure of relief valve is unstable to cause pressure change of high pressure oil thus to


. -opening pressure.(6)The unequal leakage of the two lift arm cylinders result in the flow fluctuation, which brings aboutshivering. It is necessary to check the cylinders respectively and repair the broken cylinder.


41/82

9.Why the bucket tilts slowly and powerlessly with the lift arm working

normally?

(1)The pressure of two relief valves of the bucket cylinder is abnormal. It is necessary to check thepressure and adjust it to normal value.(2)There are particles in the oil and seized the relief valve spool, and the relief valve keep open. It isnecessary to remove sundries and check if the spring is broken or disabled, the sealing ring is aged and

if the fit clearance between the spool and the valve body is suitable(normal fit clearance is 0.006-0.012mm).(3)There is inner leakage in the bucket cylinder. It is necessary to make a check.


10.Why the oil temperature of hydraulic system is too high?

Too high oil temperature is mainly caused by the following cause except for the system:

(1)Wear of pump gear pair, side plate, pump body and seals in the pump result in the reduced efficiencyof pump capacity, which causes too high oil temperature.

(2)Oil brand used fails to meet the requirements, which causes poor clearance of mixed oil deteriorationetc.


42/82

Section Steering Hydraulic System

Overview

Steer Mode

The steering systems function of the

wheel loader is to control the drive

direction of the wheel loader, keep the

wheel loader straight drive stably and

change the drive direction flexibleaccording to the need. In terms of steering

mode, the wheel loader can fall into

deflection wheel steering, articulated

steering, skid steering.

Articulated wheel loader


e wor ng equ pment o t e

articulated steering wheel loader is

installed on the front frame. When the

frame deflected relatively, the direction

of the work equipment is same with the

direction of the front frame. This type can

makes the work equipment aim at the

work plane quickly, and reduces the

distance and time of operation circulate,

which improves the operate efficiency ofthe wheel loader. So the articulatedsteering becomes the most popularsteer mode.

41

Skid steering wheel loader Deflection wheel loader


43/82

.Load sensing full hydraulic system

1.Over view

The steering system of the LG956L

wheel loader mainly consists of priorityvalve and coaxial flow amplifyingsteering gear.

Composition of the system

This system mainly consists of

steering pump, coaxial flow amplifyingsteerin ear steerin c linder



hydraulic tank, pipelines accessory and

so on.

1.Priority valve

2.Steer pump3. Oil suction filter4.Steer Cylinder5.Steer Gear

6.Hydraulic oil radiator7.Oil return filter8.Hydraulic oil tank

42


44/82

Features:

The steering system have thefollowing features:a. The components structure iscompact, and the size is small.

b. All the components has the functionof self-lubrication, which achieve longservice life.c. The steer is reliable, and the controlis easy and flexible.d. Achieve the interflow with working



equ pmen y rau c sys em, re ucethe loss of power, improve the system

efficiency

As steering, the system supplies oil tothe steering hydraulic system. And theremain oil, interflowed with thesteering system , return to the

hydraulic oil tank through the radiator.

The safety valve is installed on thepriority valve. The set pressure of thesystem is 16Mpa.

43


45/82

2Steer Gear

The meaning of the steer gear type

Steer gear



model

Load sensing flow amplifying fullhydraulic steer gear

Displacement

800ml/r


46/82

Coaxial flow amplifying symbol

Coaxial flow amplifying typeBZZ6

symbol is labeled at the right picture.




47/82

The port location

There are 5 ports on the steer gear,

that are inlet port P, return port T, left

turn exhaust oil port L, right turn

exhaust oil port R, feed back port LS,

which are corresponding connected

with exhaust oil port CF of the priority

valve, return oil port of the hydraulic

TExhaust oil

PInlet oil

RRight turn

LLeft Turn



, ,

left turn cylinder big cavity and the LSport of the priority.

46

TL

P

R

LS

S i S i H d li S


48/82

The composition of the steer gear

The structure of BZZ6 type full

hydraulic steer gear is shown in the

picture. It is mainly consists of valve

body, valve core, valve pocket,

universal driving shaft, guide spring,

pin, rotor, stator, rear cover, etc.



. .

3.Valve body 4.Spring5.Pin 6.Valve cover

7.Spool 8.Connected Shaft

9.Rotor 10.End cover

11.Limit Rod 12.Separation disc

13.Stator 14.O-ring15.Steel ball 16.O-ing

17.X-ring 18.O-ring

47

S ti St i H d li S t


49/82

The steering gear following rotary

valve, which mainly consists of valve

body, valve core and the valve pocket,

controls the direction of the oil flow.

The valve core located inside the

valve pocket is connected with steering

rod directly through the connect block,



the drive of steer rod. The valve pocket,located in the valve body, moves in the

valve body by the drive of connected

shaft and the pin.

48



50/82

The metering motor, which consistsof rotor and stator, is located at thelower end of the steering gear. Thestator has 7 teeth, rotor six teeth.

And the stator is stationary, the rotorrotates around the center of thestator in the radius of throw of

eccentric.

The shape of metering motor teethis Equidistant circular arc epicycloids

tooth. The teeth shape make surethat ever oint of the motor curve is

1

2



contact point. When rotating, there

are always 7 holes connected withthe valve pocket. The valve pocketand valve core supply oil to the

metering motor. Then the pressed oilenters one half teeth cavity, and theother teeth cavity exhaust oil,sending the pressure to the steeringcylinder.

1-rotor 2-stator

49



51/82

The metering motor, which consistsof rotor and stator, is also calledcyclonical meshing pair. When powersteering, it plays the function of

metering motor to ensure the oil massis in proportion to angel of the steeringwheel. When manual steering, it plays

the roles of manipulating fuel pump.

The connect rod and pin areconnected with the rotor and the valve

pocket. When power steering, it canensure s nchron between valve

1

2



pocket and rotor. When manual

steering, it plays the role of torquetransmission.

1-Connect rod 2-Rotor

3-stator

50

3



52/82

The function of the spring is to

ensure the following rotary remain

the centering position. So the spring

is called centering spring.

1.Valve core

2.Spring

3.Valve pocket

1

2



3



53/82

The one-way valve is installed

between the inlet valve and exhaust

valve. When manual steering, the

one-way valve opens, and the oil in

one of the steering cylinder cavity

return to the inlet port through the

return port. Then the oil passes into

the other cavity of the steering



cyclical meshing pair. Achieve the

function of oil sorting as manual

steering.

1-One-way valve

2-P port(oil inlet port)3-T port(oil return port)

52

1

2 3



54/82

Operation Principle

The Work functional diagram of theBZZ6 type full hydraulic steering gearis shown in the picture. The port Aand port B are connected with thetwo cavities of the steering cylinder.

The port P is connected with theexhaust port of the steering pump,and the port T is connected with thehydraulic oil tank.



1-connect block 2-front cover

3.valve body 4.spring 5.pin

6.Valve pocket 7.valve core

8.Linkage shaft 9.rotor 17.X-ring

10.End cover 11. limited post

12. separation disc 13.sator

14.16.18.O-ring 15.Steel ball

53



55/82

A. The steering wheel doesnt turn.

The valve core 1 and valve pocket 3stay center position at the function ofthe centering spring. The hydraulicoil from the steering pump 7 entersinside the valve core through the

small hole located at the end of valvecore and the valve pocket, and returnto the hydraulic oil tank 8 through theport T.

g y y


en e s eer ng w ee oesnturn, the centering spring plays role.

As the port A and port B are blockedby the valve core 1, the oil in thesteering cylinder cant flow in nor out.The piston cant move, so the wheel

loader runs at the former direction.

54



56/82

B. The steering wheel turns left.

The steer wheel drives the valve core1 rotate counterclockwise. Thecentering spring are pressed. As thebiggest rotatio between the valve core1 and valve pocket 3 is 1030, the

valve core can turn around the valvepocket.

The oil groove of the valve core isconnected with the inlet port P. The oil

g y y


rom pump ows roug e ogroove of valve pocket 3, valve core

1,and reflow to stator 4 and rotor 5driving rotation of the rotor 5 aroundstator 4.

55



57/82


At the same time, the exhaust oil ofstator and rotor passes into the bigcavity of right steering cylinderthrough the port A, making the pistonrod to reach out and making the frame

to drive the wheel turn left.

The oil in the small cavity of thecylinder passes into he valve pocket 3through the port B, and return to the


o re urn groove roug e va vecore 1. In the end, the oil return to the

hydraulic tank through hole of valvepocket.

During the motion of turning left, thesmall cavity of the left steering oilcylinder (with rod cavity) is connected

with the big cavity of the right steering

oil cylinder. The inlet oil of the smallcavity makes the piston rod to shrinkinto the cylinder, driving the frame turnleft.

56



58/82


The big cavity of left steering oilcylinder is connected with the small

cavity of the right steering cylinder.The oil from the small cavity of rightsteering oil cylinder enters into the

port B through the big cavity of the leftsteering oil cylinder, and returns to theoil tank from the oil return hole of thevalve pocket.

When the rotar an le between valve


core and the valve pocket is about

1.5, the oil channel begins tocombine. The rotation of rotor makesthat the oil of steer pump is connected

with oil cylinder. The mass of supplyoil is in direct proportion to the angleof the steering wheel.

57



59/82


When the turn angle of the steeringwheel remains some, the oil from thesteer pump drives the rotor 5 rotateright because the oil channel above isopen. When the rotary angle of rotor 5

is same with that of steering wheel.

Because the valve pocket 3 ismechanical jointed with rotor 5through the linkage shaft , the rotor


r ves e va ve poc e urn e athe same time until the centering

spring makes the valve pocket, valvecore to return the center position. Theangle between the stator and the rotoris same with the rotary angle of thesteering wheel.

58



60/82


At this time, the valve pocket 3 andthe valve core 1 stays the positionwhere they dont have relative rotaryangle. The oil channel, which goesthrough rotor and steering cylinder, is

closed. The exhaust oil of the steerpump enters into the valve pocketthrough the port P, and then return tothe hydraulic tank through the returnhole 3 of valve pocket 3 after entering


n o e o re urn groove o va ve core1. Thus the wheel loader stops

steering.

If the steering wheel continuesrotating, the rotor and the valvepocket follows to rotate with thesteering wheel until the left turning

position is limited. This is called the

hydraulic feed back function.

59



61/82


When the steering speed is low(therotary speed of the steering wheel is

below 10r/min), the effectivedisplacement of the steering gear issame with the metering displacement.

When the input rotary speed of thesteering wheel increases, theeffective displacement is in directproportion to the speed of the

steering wheel.


Part of the oil from oil inlet port Penters into the stator, rotor parts tometer, and the others passes into theoil cylinder through the port A and

port B. So it plays the role of flowamplifying.

When the input speed of thesteering wheel is above 40 r/min, the

effective displacement of the steeringgear is constant at the rating

displacement.

60



62/82

C. The steering wheel turns right

When the steering wheel turns right,

the steering wheel drive the valve

core rotate clockwise. The operation

principle is same with that of turning

left.


SECTION 2 STEERING

HYDRAULIC SYSTEM


63/82

d.manual steering

In event of sudden flameout of theengine or the malfunction of steeringpump, rotate the steering wheel withhand for static steering. While

rotating the steering wheel rightward,the valve core rotates for a 1030angle to drive the rotation of valve

sleeve, linkage shaft, and rotor viashifting pin. In such case, the rotorand stator are functioned as oil pump.The rotation of rotor 5 sucks out the

oil from the oil port T and inputs theoil into the oil inlet chamber of rotor

Spacer disc

Limit block

Oil inletport

Right

steeringLeftsteering

Oil return portValve body

Valve

core

Linkage shaft


pump via check valve, valve sleeve,and valve core. The oil pumping

action during the manual steeringcompresses the hydraulic oil sucked

into the steering oil so that thecompressed oil enters into therodless chamber of steering cylinderto extend the piston rod and steerrightward the loader.

Rear capBearing

Return spring

Valve sleeve

Shifting pin

Check valve

Stator-rotor pair

SECTION 2 STEERING

HYDRAULIC SYSTEM


64/82

d.manual steering

The oil in the rod chamber flowsto the oil inlet chamber of rotorpump from oil port A through valvesleeve, valve core, valve sleeve,

and check valve and continuallyrefills into the rodless chamber, inorder to maintain the steering

action.


SECTION 2 STEERING

HYDRAULIC SYSTEM


65/82

VALVE BLOCK

Valve block is a combined hydrauliccomponents ,mainly consists ofCheck valve, bi-directional buffervalve (overload valve) and oil refillvalve , etc . It connects between thesteering pump and steering gear,

completes with full hydraulic steeringgear(Usually fixed on the flange ofthe steering gear,with the steering

gear make up a whole)Its use:On the one hand keeps the


s eer ng gear an en re s eer ngsystem work normal under the

pressure rated; On the other hand,can guarantee the steering cylinderand connecting pipe without damagein a sudden overload, and canprotect the steering pump.

64

SECTION 2 STEERING

HYDRAULIC SYSTEM


66/82

a.CHECK VALVE

Check valve consists of valve seat

1valve core 2 and spring 3,etc.It is

installed in the oil inlet port of the

valve body.The high pressure oil from

the pump flows into the oil inlet port

of the steering gear through the

check valve. Its role is to prevent the


, -

deflection,steering failure.

1-Valve core

2-Spring

3-Valve seat

65

1 2 3

SECTION 2 STEERING

HYDRAULIC SYSTEM


67/82

b. TWO-WAY DAMPING VALVEThe two-way damping valveincorporates two constant pressuredirect-acting safety valves composed

of the spring, ball valve seat, andsteel ball. Its installed within thevalve port for connecting the valve

body with the orifices of left and rightchambers of steering cylinder and isconnected with the oil return port, inorder to protect the hydraulic steering

system against impact of over-high


lines.

66

1 2 3 4

SECTION 2 STEERING

HYDRAULIC SYSTEM


68/82

C.REFILL VALVEThe oil refilling valve incorporates two

check valves composed of steel balland is installed within the valve portfor connecting the valve body with theorifices of left and right chambers ofsteering cylinder and is connectedwith the two-way damping valve.When the pressure within one

chamber of cylinder is higher than thepressure setting of damping valve,the damping valve relieves the loadand the oil refilling valve on the other


chamber of the cylinder refills the oilto prevent the formation of cavitation

in the system.1-Valve seat 2-Steel ball

3-Spring 4-Valve core

67

1 2 3 4

SECTION 2 STEERING

HYDRAULIC SYSTEM


69/82

3. Priority valve

FUCTION

The load sensor steering system is

made up of the priority valve and theBZZ5 steering gear. When youturning the steering wheel, the

priority valve can ensure the oil flowdemanded by the steering gear andthe rest will flow to the workinghydraulic system.


SECTION 2 STEERING

HYDRAULIC SYSTEM


70/82

COMPOSITIONThe priority valve is mainlycomposed of valve body, valve core,a spring, the relief valve assemblyand parts such as screw. Upperhydraulic principle diagram for it.

1- The group of relief valve

2-Spring

3-Valve core


4-Valve body

5-Plug screw

69

SECTION 2 STEERING

HYDRAULIC SYSTEM


71/82

OIL PORT ARRANGEMENTPriority valve has five oil port, Oil inlet

P, oil outlet EFCF, feedback oil portLS and oil return port T, respectively.

The five oil ports respectivelyconnect with the oil outlet port ofsteering gear, the inlet port of

hydraulic oil radiator, the inlet port ofsteering gear, the LS port of steeringgear and oil return port of hydraulic

oil tank.1.P port for oil inlet, connected withsteerin um


2.T port for oil drain, connect withhydraulic tank3.EF port connected with theworking equipment(or connected with

the hydraulic oil tank)4.CF port connected with the inletport of steering gear5.LS port connected with the LSorifice of the steering gear.

70

SECTION 2 STEERING

HYDRAULIC SYSTEM


72/82

working principlea. When the steering wheel isstationary, the pressure oil fromthe steering pump flows to portEF from port P through valve coreand enters into the working devicehydraulic system or returns to oil

tank directly.


SECTION 2 STEERING

HYDRAULIC SYSTEM


73/82

b. When the steering wheel isrotating, under the joint action of the

spring force and LS pressure, thevalve core moves rightward toconnect the port P with port CF sothat the pressure oil enters into thesteering gear and drives the cylinderfor steering of loader and theexcessive oil diverges into the

working device hydraulic system oroil tank through port EF.


Heavy steering (analysis and judgment procedure)

Section III Cause Judgment and Troubleshooting for Common

Malfunctions of Steering Hydraulic System


74/82

Heavy steering (analysis and judgment procedure)

C a u s e M e a s u r e

A i r c o n t e n t i n s y s t e m

F a i l u r e o f m a n u a l

s t e e r i n g c h e c k v a l v e

L e a k a g e o f F K

o v e r l o a d v a l v e

I n t e r n a l l e a k a g e o f

c y l i n d e r

D a m a g e o f s t e e r i n g

c o l u m n

B l o c k a g e o f p i p e l i n e

B l e e d a i r f r o m s y s t e m

a n d c h e c k o i l i n l e t p o r t

o f o i l p u m p f o r a i r

l e a k a g e

C h e c k s t e e l b a l l f o r

p r e s e n c e a n d

b l o c k a g e

R e p l a c e F K

c o m b i n a t i o n v a l v e

C h e c k c y l i n d e r f o r

i n t e r n a l l e a k a g e

R e p a i r o r r e p l a c e

C l e a n o r r e p l a c e

J

u

d

g

e

a

s

p

e

r

m

a

l

f

u

n

c

t

i

o

n

s

y

m

p

t

o

m

C y l i n d e r w r i g g l e , a i r b u b b l e s i n o i l , a n d r e g u l a r

s o u n d

H e a v y s t e e r i n g a n d n o a c t i o n o f

s t e e r i n g c y l i n d e r

C h e c k s t e e r i n g

c o l u m n f o r f l e x i b l e

r o t a t i o n

D o e s s y s t e m p r e s s u r e

m e e t r e q u i r e m e n t ?

C h e c k f e e d b a c k o i l

p i p e f o r b l o c k a g e

Y e s

Y e s

Y e s

Y e s

N o

N o

N o



L o w s y s t e m p r e s s u r e

B r e a k a g e o f p r i o r i t y

v a l v e s p r i n g o r

b l o c k a g e o f v a l v e c o r e

S h o r t a g e o f o i l


W e a r o r i n t e r n a l

l e a k a g e o f s t e e r i n g

p u m p



A d j u s t m e n t s y s t e m

p r e s s u r e

A d d h y d r a u l i c o i l



I s t h e s t e e r i n g h e a v y

a t h i g h s p e e d a n d

l i g h t a t l o w s p e e d ?

I s h y d r a u l i c o i l l e v e l

t o o l o w ?

m e e t r e q u i r e m e n t ?

p i p e f o r b l o c k a g e

A d j u s t t h e s y s t e m p r e s s u r e .

I s t h e r e a n y p r e s s u r e

c h a n g e ?

I s o i l s u c t i o n p i p e

b l o c k e d ?

Y e s

Y e s

Y e s

Y e s

N o

N o

N o

N o

N o

Y e s

No steering end or failure for steering to limit position (analysis and judgment procedure)


75/82

No end

After the steering cylinder rotates to limit position,

when the steering wheel is rotated with high force,the steering wheel can rotate lightly, namely thereis no feeling of end.

Malfunctioncause Troubleshooting

Appropriately

increase pressureof overload valve

Low pressure ofoverload valve


failure for steering to limit position

The steering cylinder cant berotated to the limit position, withheavy steering

Malfunctioncause

Troubleshooting

Low pressure ofsafety valve

Appropriately increasepressure of safety valve

SECTION 2 STEERING

HYDRAULIC SYSTEM


76/82

a. Due to leakage towards thecylinder port when the closedcore steering gear is at neutralposition, the slight off-tracking of

the closed core steering gear isnormal.b. Check the cylinder connectingrod for presence of looseness.c. Internal leakage of cylinder.

CAUSE FOR OFF-TRACKINGOF MACHINE


. g pressure erencebetween two tires.

e. Unilateral leakage of two-wayoverload valve or two-way oilrefilling valve.f. Air content in oil.

SECTION 2 STEERING

HYDRAULIC SYSTEM


77/82

a. Air content in system.b. Loose cylinder pin.c. Stagnation of priority valve orshunt valve core.

d. Internal leakage of cylinder.e. Low pump efficiency, leading tounstable pressure.

L

R

INCORRECT STEERING


E n g i n e

F i x e d

P u m p

R e s e r v o i r

F i l t e r

L

T

R

P

p

SECTION 2 STEERING

HYDRAULIC SYSTEM


78/82

No rotation or slow rotation ofsteering wheels, though the

steering wheel can be rotated

flexibly.a. Serious internal leakage of two-way overload valve .b. Serious leakage of cylinderpiston.


SECTION 2 STEERING

HYDRAULIC SYSTEM


79/82

IDLE TRAVEL OF STEERINGWHEELa. Worn or damaged connectionbetween steering column and

steering gear.b. Loose nuts of steering wheelc. Air content in oil.d. Internal leakage of two-wayoverload valvee. Internal leakage of steeringcylinder

L

T

R

PP


EngineFixedPump

Reservoir

Filter

p

EngineFixedPump

SECTION 2 STEERING

HYDRAULIC SYSTEM


80/82

VIBRATION OR AUTOGIRATIONOF STEERING WHEEL

a. Incorrect assembly relationship. Atthe time of reassembly after thedisassembly for repair, its required toalign the spline teeth of the linkageshaft shifting pin slot with the

corresponding inner spline teeth ofrotor.

b. When the oil pumped is connected

to the port R or L, the steering gearwill rotate on its axis like a motor.


79

SECTION 2 STEERINGHYDRAULIC SYSTEM


81/82

Bounce of steering wheel.Cause:The check valve at oil inlet port ofsteering gear is damaged.Function of check valve:It prevents the backflow of oil insteering cylinder under the action of

external force when the pressure ishigher than the pressure at oil inletport. If the check valve is damaged,the backflow of oil will lead to bouncesymptom of steering wheel.



82/82

THE ENDTHE ENDTHE ENDTHE END


81

Documents

04 05 Hydraulic System LG956L