Traction control is fully automatic. IAD and independent XAD clutches are engaged and released automatically by the Chassis ECM to optimize machine performance and traction control in all conditions. Wheel sensors monitor the machine and wheel speeds, enabling automatic instant response in low traction conditions. This automatic strategy maximizes efficiency when steering or when traveling on uneven ground. The ATC eliminates wheel spin in soft underfoot ground conditions by directing the torque to the wheels that have the best traction. The ATC also reduces tire and driveline abuse, eliminating lost efficiency caused by improper manual operation of the differential clutches.
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| Illustration 1 | g03797862 |
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Inter Axle (IAD) and Cross Axle (XAD) Differential Lock Configurations (A) Inter Axle Differential Lock (B) Cross Axle Differential Lock | |
Inter-axle differential (IAD) (A) allows the front axle drive and rear tandem axles drive to rotate under power at different speeds in normal underfoot conditions. This is necessary to allow the truck to steer easily. In poor underfoot conditions, when the wheels on one axle begin to slip, more power is transferred to this axle drive and less to the axle drive which is not slipping and therefore traction is reduced. The IAD Lock Clutch is the mechanism that locks the IAD preventing the front axle drive and the rear tandem axles drive from rotating independently thereby improving traction.
Cross Axle Differential (XAD) (B) allows the wheels on a given axle to rotate under power at different speeds in normal underfoot conditions. This is necessary to allow the truck to steer easily. In poor underfoot conditions when one wheel begins to slip more power is transferred to this wheel and less to the other wheel which is not slipping and therefore traction is reduced. The XAD Lock Clutch is the mechanism that locks the XAD preventing the wheels from rotating independently thereby improving traction.
The Traction Control System is also active during normal braking, ARC braking, and can assist braking in poor underfoot conditions.
The ATC can be turned on and off by using the configuration menu in Cat ET.
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| Illustration 2 | g03805002 |
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Secondary Display | |
The ATC can be switched from "Auto" to "Manual" mode by using the Traction Control Select Screen on the secondary display. The Traction Control Select Screen will appear when "OK" is pressed while "Traction Control" is highlighted on the "Machine Settings" screen. Refer to Illustration 2
The "Auto" setting is the standard default setting and is to be used for all normal operations. With this setting, the traction control is automatic and does not require any input from the operator for proper machine operation in various ground conditions that may be encountered during operation.
The "Manual" setting is mainly to help with occasional maintenance or transport operations and is not meant for normal daily operations.
For example, engaging the manual setting before loading the machine onto a trailer in wet or icy conditions, may be advantageous.
The "Manual" setting provides full lockup to the inter axle differential clutch. However, the cross axle lock clutches will still engage automatically if wheel slip occurs. With the lockup of the inter axle differential clutch some increase in steering effort may be required.
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| Illustration 3 | g03805003 |
The Traction Control screen enables the user to view the different axles solenoid current percentages. The screen also contains the machine slope in percentage. Percentages are denoted by the white arrow gliding over a green bar graph. The four graphs correspond to the following axles respectively:
- Front Cross Axle
- Internal axle Lock
- Center Cross Axle
- Rear Cross Axle
The Machine slope is indicated by the icon as shown in the picture with the value next to it. The range for the machine slope is from -100% to 100% .
The values for the parameters change based on the percentage values received from the chassis ECM. If there is a fault value received, then a red triangle is displayed instead of the value and the white triangle disappears for that particular parameter.
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| Illustration 4 | g06196630 |
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Output Transfer Gear (OTG) (1) Solenoid valve for the Interaxle Differential lockup clutch (2) IAD Clutch pressure test port (3) Manifold (4) Differential Group (5) Input shaft from transmission (6) Input Gear (7) Interaxle differential lockup clutch (8) Output shaft to rear differential (9) Output shaft to front differential (10) Output gear from differential to front output shaft | |
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| Illustration 5 | g06196645 |
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Exploded view of the OTG Differential Group (6) Input Gear (10) Output gear from differential to front output shaft (11) Hub (Splined to the inside clutch pack) (12) Gear cluster (contains the differential clutch pack and connects to output gear for the front differential) (12A) Part of gear (2) that is splined to the inner portion the planetary gears (13) Planet carrier (14) Planet gear (15) Transfer gear (Connected to Input Gear) (16) Ring Gear (17) Gear shaft that drives the rear shaft yoke to the rear differential (18) Differential group clutch housing and piston | |
The Output Transfer Gears (OTG) transfer power from the transmission to the rear differential and to the front differential.
Power flows from the output shaft of the transmission to input shaft (5) in the OTG group. Power is transmitted through gear (6) to differential group (4).
Input gear (6) drives transfer gear (15) on the differential group. Gear (15) turns planetary (13).
The outer portion of planet gears (14) drives ring gear (16) for the rear axles.
The inner portion of planet gears (14) drives gear cluster (12A). Gear (12) is connected to gear (10) which drives the front differential.
Inter-Axle Differential Lock System
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| Illustration 6 | g06199114 |
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(Black lines) Scavenge oil
(Blue lines) Lube oil (Red lines) Control oil (Green lines) Electric (C) Transmission and IAD clutch supply oil from transmission pump (7) IAD Clutches (19) Inter-Axle clutch solenoid (20) Hydraulic Oil Cooler (21) Transmission and OTG oil filter (22) Electronic Main Relief Valve (EMRV) | |
When the Chassis ECM receives signals from the wheel speed sensors and Inertial Measuring Unit (IMU) of a difference in wheel speeds between the front and rear drive trains, the ECM will call for the Inter-Axle Differential to lock up, locking the front and rear drive trains together.
The ECM energizes the Inter-Axle Clutch Solenoid Valve sending pressurized oil to the Inter-Axle Differential Clutch located within the Output Transfer Gear.
The Inter axle Differential Clutch may not lock completely. The Inter-Axle Lock Solenoid Valve is a proportional valve. This proportional valve will lock the front and rear drive trains together proportionally to the extent of "lockup" the ATC system requires.
The IAD allows the torque from the transmission planetary to be divided between the front axle and the two rear axles. The front axle receives a smaller proportion of the torque than the center and rear axles. This torque difference prevents excess torque from being transmitted to the front axle. Under normal conditions, IAT clutches (7) are not engaged. 66% of the torque from the transmission is transmitted to the center and rear differentials. 33% of the torque is transmitted to the front differential.
When conditions exist, the ECM will send a command to inter-axle clutch solenoid (19) and engage IAD clutches (7).
Cross Axle Differential (XAD) Lock System
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| Illustration 7 | g06199120 |
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(23) Manifold supplying oil from the brake pump to the Pressure reducing valve for the XAD
(24) Front Cross Axle Differential (XAD) Lock Solenoid (25) Center Cross Axle Differential (XAD) Lock Solenoid (26) Rear Cross Axle Differential (XAD) Lock Solenoid | |
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| Illustration 8 | g06199144 |
| (27) Wheel Speed Sensor (one on each wheel) | |
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| Illustration 9 | g06199211 |
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Cross-axle differential lock system (differentials released) (23) Manifold supplying oil from the brake pump to the Pressure reducing valve for the XAD (24) Front Cross Axle Differential (XAD) Lock Solenoid (25) Center Cross Axle Differential (XAD) Lock Solenoid (26) Rear Cross Axle Differential (XAD) Lock Solenoid (28) Brake, Fan, and Hoist Pump (29) Front Cross-Axle Differential (30) Center Cross-Axle Differential (31) Rear Cross-Axle Differential | |
If the wheel speed sensors indicate wheel slippage from left to right on any given axle, the Chassis ECM will ENGAGE one or more of the Cross-Axle Differentials (XAD) to ensure that power is sent to the wheels that have the best traction. The schematic above shows the XAD clutches DISENGAGED on all three axles.
Brake, fan, and hoist pump (28) draws oil from the main hydraulic tank and provides oil flow to combination valve (23). Some of the oil flow from combination valve (23) is used to operate the XAD system. The oil pressure to the XAD system is set at approximately
When necessary, the Chassis ECM will ENERGIZE one or more of the three XAD lock solenoids which sends oil flow to the respective XAD.
The Inter-Axle Differential (IAD) lock works with the XAD lock to distribute power to the front and rear axles as needed. Along with the engagement of the IAD system, this action places the TCS in a mode that ensures that front to rear, and side to side, the wheels with the best traction receive the most power. This engagement increases the efficiency of the distribution of power and torque from the transmission.
The cross-axle differential clutch may not lock completely as the cross-axle lock control solenoids are proportional valves. The valve locks the left and right wheels together proportionally to the extent of "lockup" the ATC system requires.
The same operation occurs on the center and front axles when the ECM detects a difference in wheel speeds on those axles.
The ATC system will partially engage the differential lock clutches on grades above 12%, whether there is a loss of traction or not. This partial engagement is done so the ATC system can react more quickly to a loss in traction on a grade. At grades above 12%, the XAD lock clutches will be partially engaged and remain at that level as the grade increases. At a grade of 12%, the IAD lock clutch will partially engage but will increase engagement as the grade increases.
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| Illustration 10 | g06199529 |
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Monitor indicator dash Panel (32) ATC Fault indicator lamp | |
When a fault in the ATC System occurs, the ATC fault indicator lamp is illuminated amber.
ECM and Inertial Measuring Unit (IMU)
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| Illustration 11 | g06199553 |
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Block diagram of the ECM components | |
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| Illustration 12 | g06199635 |
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ECM and IMU locations (33) Transmission ECM (34) Chassis ECM (35) Front IMU (36) Rear IMU | |
Transmission ECM (33) and chassis ECM (34) are located in the cab behind the operator seat. The components in this compartment are accessible by removing the panel as shown in Illustration 12. Transmission ECM (33) and chassis ECM (34) control the traction control system components.
Transmission ECM (33) monitors the transmission temperature sensor which shares oil with the OTG. The transmission ECM also monitors the transmission and OTG filter bypass switch.
Chassis ECM (34) monitors the speed sensors, front IMU (35), rear IMU (36), and throttle position sensor. Chassis ECM (34) controls the three XAD solenoids and the IAD solenoid, as well as the front and rear ARC solenoids.
Front Inertial Measurement Unit (IMU)
Rear IMU (35) is installed behind the cab, inside the cooling compartment, below the hydraulic cooler.
Front IMU (35) measures three axis of acceleration: longitudinal, lateral, and vertical. The sensor also measures yaw rate, which is the rate of rotation about an axis perpendicular to the ground. This information is used by chassis ECM (34) along with wheel speeds, to determine if the TCS needs to engage the differential locks.
The data is also used to manage a balance between maximum tractive effort and maximum steering capability, as tight steering becomes difficult with the XAD system fully engaged.
Front IMU (35) also provides a percent-of-grade signal, which is used to pro actively engage the IAD clutch proportionally when the grade reaches 12% or more.
Rear Inertial Measurement Unit (IMU)
Rear IMU (36) is installed at the rear of the trailer on top of the right frame rail.
The rear inertial sensor has the same function as the front sensor as described above. The rear inertial sensor also provides additional acceleration information to chassis ECM (34) and provides bed tip angle information.