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| Illustration 1 | g03725031 |
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Locking differential (1) Bevel gear (ring) (2) Differential housing (3) Case (Differential) (4) Clutch pack (5) Bevel gear (6) Thrust plate (7) Housing (8) Piston (9) Guide pin (10) Pinion shaft (11) Spider shaft (12) Axle shaft (13) Bevel gear (14) Pinion gear | |
A differential divides the power that is sent to the wheels. A differential also causes a balance of power that is sent to the wheels. During a turn, the differential allows the inside wheel to rotate at a slower rate in relation to the outside wheel. The differential still sends the same amount of torque to each wheel.
When there is no loss of traction, the operation of the locking differential is identical to the operation of the open differential. When the machine moves in a straight direction with the same amount of traction under each drive wheel, the same amount of torque on each drive axle holds the pinions so the pinions do not turn on the spider. Pinion shaft (10) turns bevel gear (1). Bevel gear (1) turns case (3). Case (3) turns spider shaft (11). Shaft (11) turns side gears (5) and (13) through pinions (14). Pinions (14) do not turn on the shaft. The side gears turn the axle shafts. The same amount of torque is sent through the final drives to each wheel.
When the machine is in a turn, the inside wheel is more resistant than the outside wheel in a turn. This resistance causes different torques on the opposite sides of the differential. The outside wheel turns more easily than the inside wheel. The outside wheel starts to turn faster than the inside wheel. Pinion shaft (10) turns bevel gear (1). Bevel gear (1) turns case (3). Case (3) turns spider shaft (11). Shaft (11) turns side gears (5) and (13) through pinions (14). As the pinions turn, the pinions move around the side gears. The differential allows the inside wheel to turn at a slower rate than the outside wheel. The same amount of torque is sent through the final drives to both the inside and outside wheels. This torque is only equal to the amount of torque that is necessary to turn the outside wheel.
When one wheel has more traction than the other wheel, the operation of the differential is identical to the operation of the differential during a turn. The same amount of torque is sent to both wheels. This torque is only equal to the amount of torque that is necessary to turn the wheel with the least resistance.
Operation of the Locking Differential
The locking differential has an arrangement which allows the differential to be locked and the mechanism enables the axle shafts to be locked together. Both wheels can then rotate at the same speed and torque regardless of different ground resistance between the wheels.
The locking differential uses axle housing (7), piston (8), thrust plate (6), clutch pack (4), and guide pin (9) in order to lock side gear (5) to the differential case (3). Refer to Illustration 1. The locking differential uses a side gear (9) that is splined in order to mesh with clutch pack (4). The piston housing (7) is mounted on the inside of the differential housing (2).
When certain conditions are met, the ECM (Electronic Control Module) will send a signal to the differential lock solenoid. The differential lock solenoid will direct oil to the axle housing (7) through a hose and an oil passage. Piston (8) will press thrust ring (6) against clutch pack (4). Clutch pack (4) is splined onto clutch bevel gear (5). Clutch pack (4) locks bevel gear (5) to the differential case (3). Locking bevel gear (5) to the differential case (3) prevents pinion gears (14) from moving around the side gears (5) and (13) as the differential case rotates.
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| Illustration 2 | g03721079 |
| (15) Floor switch (differential lock) | |
Press and hold the floor switch in order to activate the system. The differential lock system will activate in first gear, in second gear, in third gear, or in neutral. The engine must be running and the machine must be traveling less than 20.1 km/h (12.5 mph).
Note: The floor switch must stay depressed in order to keep differentials locked.
The system will engage the differential lock, if the Automatic Differential Lock is installed and enabled. The front axle and the rear axle differential lock will be engaged when the appropriate enablement conditions become true.
The following operating conditions are required for the automatic differential lock to be enabled:
- The Automatic Differential Lock feature is installed.
- The Automatic Differential Lock feature is enabled.
- The engine is running.
- The ground speed is less than 20.1 km/h (12.5 mph).
- The transmission is in neutral, first, second, or third gear.
- The articulation angle must be less than 22 degrees.
- The left brake pedal must be released.
- No active diagnostics are present on the Wheel Speed Sensors or Transmission Output Speed Sensor.
The Automatic Differential Lock system has two engagement strategies, the ground engagement strategy and the wheel slip detection strategy. Each strategy has it's own set of enablement conditions in order to activate Automatic Differential Lock.
The ground engagement strategy activates when the machine is digging or in other high torque operations. This strategy is intended to prevent slip before slip occurs.
The following conditions must be met in order for the ground engagement strategy to activate Automatic Differential Lock in addition to the conditions listed for Automatic Differential Lock Enable:
- Gear has to be either 1F or 2F.
- Articulation Angle must be less than 16 degrees.
- Transmission Torque must be high.
- Ground Speed must be greater than
0 km/h (0 mph) but less than5 km/h (3 mph) . - Ground Speed must be decreasing as Transmission Torque is increasing. (Indication of going into a dig).
Note: Once Automatic Differential Lock has been activated due to ground engagement detection, it will remain active until any one of the ground engagement detection conditions or the Automatic Differential Lock Enable conditions are no longer met. The most common condition to disengage the differential locks for ground engagement is a directional shift to reverse.
The wheel slip detect strategy is constantly comparing actual wheel speeds with calculated wheel speeds. If a slip is detected, the differential locks will activate. This strategy is intended to react to slip after slip occurs.
The following conditions must be met in order for the slip detection strategy to activate Automatic Differential Lock in addition to the conditions listed for Automatic Differential Lock Enable:
- A Transmission Gear Shift is not currently on-going.
- Ground Speed is greater than
0.7 km/h (0.4 mph) . - Actual Wheel Speed exceeds the calculated desired wheel speed.
Note: Once Automatic Differential Lock has been activated due to wheel slip detection, it will remain active until any one of the wheel slip detection conditions or the Automatic Differential Lock Enable conditions are no longer met. There is a time duration in which the differentials will be locked due to the fact that slip cannot be measured when the differential locks are engaged. This timer will allow the differential locks to be locked for a maximum time duration and when that duration expires, the differentials will be unlocked and Automatic Differential Lock logic will recheck to see if slip is still occurring.
The Operator can manually engage both axles of the Automatic Differential Lock System by pressing the Manual Differential Lock floor switch in the cab. Once the Manual Differential Lock Switch is released, the Automatic Differential Lock System will disengage. At that time software will perform checks to decide if Automatic Differential Lock should engage due to ground engagement conditions or wheel slip conditions.