Basic Knowledge of Bulldozers
1
KomatsuG25(Left) & G40(Right) farm tractor
a competitive demonstration
event held in Manchuria in early 1930s
The largest bulldozer, D575A-3, launched in 2001
The first unit of the D50-1 bulldozer
produced in 1947
D80A produced in 1963 after many
stringent quality control tests
2
D21
Machine weight
Engine horsepower
3,940 kg
32.4 kW (44 HP)
D575
Machine weight
Engine horsepower
152,600 kg
858 kW (1,150 HP)
3
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JCB
Liebherr
Ingersoll-Rand
Terex
Kobelco
Volvo
CNH
Hitachi
John Deere
Caterpillar
Komatsu
Large bulldozers
Large excavators
Large wheel loaders
Mining
Large dump trucks
Large motor graders
Bulldozers
Excavators
Wheel loaders
Construction
Dump trucks
Articulated dump trucks
Motor graders
Mini excavators
Mini wheel loaders
Utility
Backhoe loaders
Skid steer loaders
Telescopic handlers
Forestry equipment
Others
Recycling equipment
Compactors
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4
5
6
7
8
9
Outline of Structure
Operation
Lever, Pedal, Switch, etc
Power Train
Control Speed, Traction, Steering
Hydraulic System for W/E
Control the W/E(Blade Ripper)
System Overview of the Bulldozer
Machine Operation
Input device
Operator
Fuel Dial
PCCS lever
PPC lever
Decel pedal
Break pedal
PT controller
Work
Equipment
Hyd. Pump
Control valve
Hyd.
Actuator
Blade & Ripper
control
Final Drive
Travelling &
Steering
control
ECM
Engine
Power Line
Torque
Converter
Transmission
Steering
System
Machine Work
13
Technical Map of Bulldozer(D21～D575A)
14
Power Line
15
History of Bulldozers power train
Tier3
Generation
Direct drive T/M
Transfer engine power to T/M directly by clutch
disc & plate engagement
None
(Improve Engine toughness , controllability)
Torque Flow T/M
Transfer engine power to T/M indirectly
through Torque converter oil
Middle &
Large class
(Improve power transfer efficiency)
Hydro Shift T/M
Transfer engine power to T/M directly through
damper. Vibration & shock are absorbed and
transferred to T/M.
Only D21
(Improve controllability--- Step less transmission)
Hydro Static T/M (HST)
Engine power rotate Hyd pump and power
transfer to Hyd motor. By hyd motor rotation
speed , machine can travel as stepless shift.
Small Class
16
Direct drive T/M
Merit
・High efficiency of power
transferring
Engine
Main clutch
Transmission
Torque Flow T/M
Engine
Torque
Converter
Torque flow
transmission
・Easy operation
・Less gear shift shock
・No engine stall under heavy
load (load escape in T/C)
・High engine toughness
under heavy load
・Easy operation
・Less gear shift shock
・High efficiency of power
transferring
Hydro Shift T/M
Demerit
・Complicated operation
・Engine stall under heavy
load (load can’t escape)
・Engine power fluctuate
depend on load
・Power transfer efficiency is low
・Engine power fluctuate
depend on load
・High production cost compared
with direct T/M
・Engine stall under heavy
load (load can’t escape in T/C)
・Engine power fluctuate
depend on load
Engine
Damper
Hydro shift T/M
Hydro Static T/M (HST)
Engine
PTO
Hyd motor
Hyd
pump
・Gear shift operation is not
・Power transfer efficiency is low
required.
・Oil contamination control is
・No power cut by stepless T/M
strictly required.
・No engine stall under load.
(load escape by hyd relief)
・Max engine power can be used
constantly
17
Type of Transmission & Steering system
Steering :
Making Difference of speed
between the Left and Right trucks.
Transmission
Large
Middle
Small
Small
D575A
D475A
D375A
D275AX
D155AX
D85EX
D65EX
D61EX
D51EX/PX
D39EX/PX
D37EX/PX
D31EX/PX
Steering System
Clutch & Brake
Output for one side track
is split by Clutch and is
held by Brake.
HSS
Hydro Static Steering
System
Both side tracks are
connected by differential
gear.
Hydraulic motor makes
Difference of speed
between both tracks via
differential gear.
Torque Flow
Transmission
HST
Hydro Static Transmission
Both side tracks have
each set of Hydraulic
Pump and motor.
Each tracks are controlled
individually.
Power Train Skelton (Sample:D65A Torque Flow T/M)
Sprocket
Track Shoe
Transmission
Torque Converter
Steering
Clutch
Engine
Final Drive
Universal Joint
Steering Brake
19
Torque Converter
Turbine
Pump
Turbine
Stator
Pump
Rotated by
oil flow
comes from
Pump.
Change
direction of
return oil
flow from
turbine to
pump.
Driven by
engine.
It makes oil
flow.
Stator
Output Shaft
Torque Converter Cut-away model
Pump
Turbine
From
Engine
(Input)
To T/M
(Output)
Stator
Lock-Up
Clutch
Stator
Clutch
21
Ref. : Performance Curve of Torque Converter
*with Fixed Stator
Traction
Output
Engine
Output
Torque Ratio
Convert to the Heat
Efficiency
Traction
Output
Feature of Torque conveter
-No Engine stall (Fluid Coupling)
-Torque multiplied effects
The Traction force is increased when vehicle speed
is decreased due to external load.
-Low efficiency during high speed travel(fixed stator)
(Improvement of efficiency by lock-up, stator control)
Speed Ratio
22
Disc
Clutch
ディスククラッチ
From control valve
1.
2.
3.
4.
5.
6.
Clutch housing
Clutch piston
Disc
Plate
Return spring
Pin
A. Sun Gear
B. Planetary Pinion
C. Ring Gear
D. Carrier
Clutch “Disengaged”
Clockwise rotation Input in Sun Gear [A]
Planetary Gear[B] start rotation toward
counter clockwise
Ring Gear[C] start rotation toward
clockwise (Same direction as Sun gear)
Clutch “Engaged”
クラッチ”入”の場合
(Ring gear Fixed)
Clockwise rotation Input in Sun Gear [A]
Planetary Gear[B] start rotation toward
counter clockwise
Since Ring Gear[C] is not rotated, Planetary
Gear [B] rotate Carrier [D] toward clockwise
(Same direction as Sun gear)
Inside of Disc [3] and outside of Ring Gear [C] are meshed each other, and rotate together.
Plate [4] is fixed in Clutch Housing [1] by Pin [6], slightly move only axial direction.
23
Planetary Type Transmission
Directional Clutches
Speed Clutches
D155A-2
T/M Structure (Power transmission route)
3rd
2nd
1st
Double
Structure
Input Shaft
To PTO
To
Output
Shaft
Forward/Reverse Group
Either “F” or “R” clutch ON
Power from Input shaft is
output from “Carrier”
-> Input to Carrier of 3rd
clutch pack.
Speed shift Group
ECMV installed machine has possibility of
occurrence of “Double clutch engagement. And
cause serious T/M damage
Either 3rd, 2nd, 1st clutch is engaged, speed
is reduced depend on gear shift.
-> Power is transferred to output shaft.
25
Modulating Valve Function
When shift F&R, 1st to 2nd , prevent sudden engagement of clutch, moderate shift shock.
 Comfort riding, improve durability of power train system
Clutch pressure
[Graph] Relation of time progress and clutch pressure increasing
A: Filling time
B: Build up time
C: Modulating time
Time (Sec)
26
Control of Clutch engaging pressure
Type
Outline
Merit
Demerit
Modulating Valve
ECMV
(Mechanical Type)
(Electric control type)
It consists of a modulating valve and a speed valve.
By mechanical operation, a modulating valve raises
clutch oil pressure gradually at the time of a gear
shift.
The transmission has only one modulating valve.
The speed valve changes the direction of oil flow and
then it changes speed range and F-R.(directional
valve)
（Electronic Control Modulation Valve）
-Each clutch pack has independent ECMV.
-Output oil pressure is controlled proportionally to
solenoid current.
-the Oil pressure is increase gradually by control of
the PT controller.
-Clutch oil pressure is detected by the fill-switch.
-Simple structure
-No risk for double engagement
-Individual control for each clutch pack is possible.
-The smooth engaging of clutch by pressure control.
-Smooth speed shifting by cooperative control for
each ECMV.
(Power transmitting is not cut during shifting)
- Individual pressure control for each clutch is
impossible
- Power transmitting is cut a momentarily when
shifting.
-Risk of double engagement due to trouble of the fill
switch.
- Oil management is severe.
27
HST(Hydro Static Transmission) Ex) D31-22
There are 2 sets of Hydraulic pump & motor.
Capacity of Pump & Motor are controlled
individually Left and Right.
*Include Steering function.
The basic structure of the HST Bulldozer is common.
-Size of pump and motor.
-Type of changing capacity in motor (3 stage type or variable).
are different depend on model and generation.
Type of Steering System
Clutch & Brake
・・・ Middle & Large Size Bulldozers, Old machines
Disengage the clutch of turning side, power transmit to opposite side.
After clutch disengaged, engage brake disc & plate, sharp turn is possible. Spin turn is
not possible.
There are 2 categories by steering brake type.
・Multiple disc clutch + Band brake
・Multiple disc clutch + Multiple disc brake
HSS(Hydro-Static Steering)
・・・Small & Middle Size (-EX, -AX)
No clutch structure, only brake disc & plate are installed for stopping machine. Steering for
LHS&RHS is controlled by rotating direction of HSS motor.
Spin turn and dozing during steering is possible.
HST(Hydro-Static Transmission)
・・・Small size bulldozers (-EX)
As same as Hyd excavators, steering is controlled by rotation difference of both
LHS&RHS travel motors. Spin turn and dozing during steering is possible.
29
Steering Clutch & Brake
Bevel gear shaft
Output shaft
LHS
Steering
Brake
LHS
Steering
Clutch
Bevel gear
Output shaft
RHS
Steering
Clutch
RHS
Steering
Brake
HSS System
Hydro- Static Steering System
HSS (Hydro Static Steering System)
HSS Motor
The idler for left axes
(inverse rotation)
Sun Gear (Input)
Carrier (Input)
Ring Gear(Output)
: HSS Motor
: Bevel Gear
: Final drive
Input
Bevel gear
shaft
Output
32
HSS control system
The steering spool in the
control valve is driven by the
EPC output pressure. Both
side EPC valve is controlled
by command current from
T/M, Steering controller.
HSS pump pressure oil
flows to HSS motor and
HSS gear train makes LH
steering, RH steering or
counter rotation.
33
Final Drive
34
Final Drive (Ex. D375A-6)
[ 16 ]
[ 26 ]
[ 68 ]
[ 79 ]
[ 15 ]
35
Floating seal
O-Ring
Seal ring prevent dirt and water intrusion
from outside.
Sealing surface: Both seal slip each other, but
oil is not leaked since both faces adhere.
Seal ring
Seal ring prevent oil leakage from inside of case
Rotation side (sprocket)
No Rotation side (Case)
Notes;
1. Never adopt oil on the O-Rings when assembling
2. Never hit floating seal when installing
36
Undercarriage
37
Undercarriage 1) Track frame
Track frame
Oscillate type
Track frame can oscillate around pivot
shaft. Mainly employed for mediumand large-sized.
＜Features＞
When the track of either side rides
over an obstacle, shocks are reduced.
Pivot shaft
Rigid type
Single structure made by
welding track frame and main
frame together and used for
small-sized models mainly.
＜Features＞
High rigidity and simple
structure.
Oscillatable
●Track frame
Equalizer bar
Pivot shaft
Idler
Track frame
Carrier roller
Track roller
State after track frame is installed
Sprocket
Track roller guard
38
Undercarriage 2) Idler cushion
Adjusting to optimum tension
High tension
Loose
39
Type of Sprockets
Solid type
Supply parts
Segment type
40
Undercarriage 3) Link assembly
Bushing is meshed
with tooth bottom of sprocket
Grease-lubricated type (Dry type)
Oil-lubricated type (Wet type)
The space between the pin and bushing is filled
with grease for lubrication.
＜Features＞
○Simple structure and low cost.
○If grease decreases, the bushing and pin
come in contact, and that can cause elongation
of the link pitch.
The space between the pin and bushing is filled
with oil for lubrication.
＜Features＞
○Early wear of the pin and bushing is
prevented and the link pitch is not elongated.
○Oil may leak.
○Structure is complicated and cost is higher
than grease-lubricated type.
PLUS Type
(Parallel Link Undercarriage System)
Since the pin and center bushing rotates, the
outside of the bushing is worn less.
＜Features＞
○The wear life of the bushing is elongated
greatly. (The wear life of the bushing is
elongated to about twice, although that
depends on the jobsite)
○R & M cost can be reduced.
41
Hydraulic System for Working Equipment
HSS
motor
Type of Valves
Present models of bulldozers employ CLSS system
Small Class
Feature
Middle & Large Class
-There are many type of valves
Only D475
-The CB valve is used only for the bulldozer.
-Steering priority valve is installed (The machine with HSS system)
-Hydraulic drive fan system is employed widely in bulldozers.
Small Class : Fan system is included with W/E system
Middle & Large : Set of Pump & motor are installed
: DB valve
: CB valve
: CA valve