UNDERCARRIAGE SYSTEM • Component Assembly • Operation Principles
Bulldozer Assembly Power Take-off Torque Converter Universal Joint Transmission Unit Main Drive Steering Clutch Steering Brake Final Drive Track Equipment Control System Working Equipment Cabin Floor & Fender Track Frame
Power Train Engine Torque Converter Universal Joint Gear Box Main Drive Steering Clutch Final Drive Track System
Power Take-off Function: PTO power Equipment: Work system pump Transmission pump Steering Pump
Torque Converter Assembly • Type: 3-element 1 stage 1 phase • Assembly: Pump, Turbine and Stator • There are many vanes on these components for using oil to transfer power
These 3 components combined with oil, give us as smooth power transmission. • Safety valve: fitted to oil input, ensures the input oil pressure is no more than 0.87MPa. • Relief Valve: fitted on oil output, ensures the oil pressure inside the torque converter is maintained below 0.45MPa.
Principles of Torque Converter • Oil Flow: Pump→ Turbine → Stator→ pump • There is 2 mm clearance between pump and Turbine, and transfers power by Oil. There is no mechanical impact, they protect each other • Assist hydraulic system: to resist loss of oil; to maintain the normal oil temperature.
Operation of Torque Converter • When the load increases, the dozer ground speed is reduced, causing turbine speed to slow down. But at this time the energy from the pump transfer to torque converter is not reduced. This energy is still transferring to the stator through the slowing turbine. Then the energy to stator from turbine, results in the turbine gaining torque, then the turbine output torque is increasing.
Torque Converter Operation 1.Change torque automatically 2.Absorb vibration, prolong working life 3.Good power transmission capability, driving at slow speed 4.Simple operation 5. Start smoothly,eliminates any shocks in power train 6.Easy maintenance
Normally, SD22 Torque Converter Temperature of output oil is 115-120oC. For a short time, a higher temperature of 130-135oC is allowed, but long term high temperature shows there is something wrong, for the following reasons: 1.Shortage of Oil Torque converter, transmission, main drive, steering and final drive will take 30% of engine rated power. This power will transfer to heat energy, and increase the oil temperature. Therefore it requires enough oil to absorb this heat. If the oil quantity is not sufficient, the oil temperature will be too high. High Torque Converter Oil Temperature
2.Oil Pressure of input and output are incorrect If torque converter input oil pressure is not correct (Standard: 0.87MPa) or the oil is dirty, the piston of valve will stay at relief position, so the oil pressure to the torque converter is low. This leads to a loss of efficiency and excessive oil temperature. If torque converter output oil pressure is not correct (Standard: 0.45MPa) or the oil supply is blocked, return oil temperature will be too high. The flow of oil to oil cooler is reduced, and the oil temperature too high
3. Incorrect Operation Excessive use of low engine speed for extended time, torque converter will work at low efficiency. Torque converter will lose power, and transfer heat energy leading to high oil temperature.
The types of Transmission Case: Base Operation type: 1.Manual Gearshift；2.Hydraulic booster；3.Powershift Base Transmission type: 1.mechanical type; 2.Planetary Gear Planetary type powershift transmission case type: Planetary Gear, Multi-disc clutch, Hydraulic control, forced lubrication. Function: 1.Enable forward and reverse 2.Select different gear ratio 3.Matched with the torque converter, enables a wide range of power output and ground speed Power Transmission Case
Planetary Gear System C D A The system consists of: A: Sun Gear B: Planetary Gears C: Ring Gear D: Carrier The planetary gears are installed on the carrier being in constant mesh with the sun gear and the ring gear B
Principle of Planetary Gear system If the carrier is fixed, the torque is transmitted from sun gear to planetary gear, and is transmitted from planetary gear to ring gear to make the ring gear rotate. Rotation direction of ring gear is opposite from sun gear. A: Sun Gear B: Planetary Gear C: Ring Gear D: Carrier
Principle of Planetary Gear system If the ring gear is fixed, the torque is transmitted from sun gear to planetary gear. The planetary gear rotates by itself, at the same time rotates around sun gear. Rotation direction of the planetary gear shaft is opposite from sun gear. It is a slowdown outfit that power input from sun gear, output from carrier A: Sun Gear B: Planetary Gear C: Ring Gear D: Carrier
The above principles are structure principle of No.1,3,4 planetary gear system. The sun gear is active in No.1 Planetary Gear system The carrier is active in No.3 & 4 Planetary Gear system
This is structure and principle of No.2 planetary gear system. The rotate direction is contrary with No.1 planetary gear system.
SD22 powershift transmission system Consists of 4 planetary gear systems with 4 clutches, and 1 locking clutch (no planetary gear system) and housing, input shaft, end gear and output bevel gear. No.1 clutch is for Forward Gear No.2 clutch is for Reverse Gear No.3 clutch is for 3rd Gear Shift No.4 clutch is for 2nd Gear Shift No.5 lock clutch is for 1st Gear Shift
The 4 planetary gear system clutch’s washers and disc are the same, but the disc quantity is different. Its design is based on transmission torque. The No. of Clutch Washer Q’ty Disc Q’ty No.1 3 4 No.2 2 3 No.3 1 2 No.4 1 2 No.5 2 3 SD22 powershift transmission system
No.1- 4 planetary gear systems’ structure are same, clutches’ washer and disc are same, but the disc quantity and piston is different.
Method of fixing of each planetary gear is as this figure, it is actuated by the clutch. Engagement of clutch is actuated by oil pressure from control valve pushing piston 3.
Disengagement of clutch is actuated by return spring 33 which pushes piston 3 to original position after oil pressure is cut off. The function of disc spring 42 is to improve operating speed of piston 3 and improve release the discs.
This figure is a drawing of No.5 locking clutch. When the clutch disengages, oil in the cylinder body 16 by the action of centrifugal force. Disks can’t disengage quickly, only by disk spring 29. This can make the clutch half disengage. This will cause difficulty for next gearshift. In order to eliminate this problem, the ball check valve 17 is incorporated in the piston after the rotary clutch.
No.5 Clutch is a lock clutch. When this clutch engages, pressure oil from controlling valve enters into oil cavity and pushes piston 26, at the same time, the oil pushes check valve ball 17 to plug the hole of valve. The clutch is engaged quickly.
No.5 Clutch is a lock clutch. When the pressure oil from controlling valve is cut off, by the action of centrifugal force, ball 17 can move to the direction of arrow in this figure. At this time, the hole of valve cage is opened and the oil is drained off.
Transmission Lubrication and Cooling: It’s a forced lubrication system, from above and below, two ways divided through a valve. Transmission Case lubrication pressure is 0.124Mpa. Upper way lubricates the second half bearing and cools the second half discs; lower way lubricates the first half bearing and cools first half discs.
Main Drive (SD22) • Assembly: Bevel gears Horizontal Shaft Bearings Sprocket Hub • Functions: Power train gear reduction to increase the final drive torque
Steering Clutch • Function: To disengage the shaft drive and control steering • Type: Wet, multi-disc, spring loaded, hydraulic separated, normally engaged. • Spring force F=3.2 tons
Steering Brake • Function: The brake on the outside of steering clutch’s outside drum, reduced the rpm of the final drive on that side. • Type: Wet band, hydraulic boosted control
Steering Brake Operation Forward Reverse
Steering Brake Control Linkage through valves
There are 3 associated components, Main drive, Steering Clutch and Steering Brake. They are lubricated and cooled by the oil in steering case. The oil level can be checked with oil dipstick Steering case has a breather to balance inside and outside pressures. Steering Case Lubrication and Breather
Final Drive • Final Drive: One Set Final Drive on each side. • 2 stage spur gears reduction. Floating Seal and O-ring to contain oil, then connected outside with breather. • Assembling Sprocket hub and gear requires 60 tons force with special tools.
Track System --- Walking Gear • Assembly: Track Frames Track Rollers Carrier Rollers Recoil system Track Shoes Equalizer
Recoil system for Track • Function: 1. Maintain track tension 2 absorb the vibration of idler • Note: the fixed pressure is 20.38 tons, it requires special fitting tools
Measurement of Track Tension use a ruler placed on the track grousers between carrier roller and idler, the measure distance is C，C=20-30mm SD32 track has more wide, the distance is bigger between carrier roller and idler, the measured distance is C=30-40mm Idler Carrier roller
Idler • Function: Gives guidance for track chain and maintains track tension • Lubrication There are lub oil in the cage that is sealed by floating seal, between idler and support housing. The oil capacity is 70%.
To Adjust Idler Clearance • If the clearance is over limit , the idler will swing, and track links off centre and will wear the sprocket. • If Clearance in one side A＞4mm, it must be adjusted into A=0.5-1mm • If Clearance of up and down (B+C)≥5mm it must be adjusted into (B+C)=2mm。
Track Roller • First it carries dozer weight, secondly it prevent track chain moving off centre of track frame • Bushing and float seal is similar to idler
Track Shoe Assembly • Supports all of the dozer weight, and determines the ground pressure • Four high strength bolts fix track shoe onto track link, bolt torque: SD16:70kg.m SD22:76kg.m SD32:100kg.m
Use and Maintenance of Track Shoe • Track supports 30 tons bulldozer weight, and if the working conditions are bad, it will wear more quickly, so use and maintain it correctly. • Often check the tension of track shoe. use a ruler put the track grousers between carrier roller and idler, the measure is C，C=20-30mm; SD32 track is more weight, the distance is more large between carrier roller and idler, the measure is C=30-40mm • When the work is hard, the track shoe ass’y will need to be adjust tighter; if the work is moderate , the track shoe ass’y tension can be adjusted back.