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| Illustration 1 | g00409459 |
(1) Spline. (2) Hub assembly. (3) Lockup clutch piston. (4) Clutch disc. (5) Plate. (6) Turbine. (7) Cage. (8) Converter housing. (9) Spring. (10) Race. (11) Cam ring. (12) Stator. (13) Impeller. (14) Plate. (15) Clutch disc. (16) Impeller clutch piston. (17) Clutch housing. (18) Oil passage for the impeller clutch. (19) Oil pump drive gear. (20) Torque converter outlet passage for oil. (21) Carrier. (22) Output yoke. (23) Output shaft. (24) Hub. (25) Adapter. (26) Torque converter inlet passage for oil. (27) Oil passage for lockup clutch. | |
Note: The standard torque converter for the 992G Wheel Loader does not have a lockup clutch. The optional torque converter for the 992G Wheel Loader has a lockup clutch. The torque converter for the 854G Wheel Dozer has a lockup clutch.
This torque converter contains a lockup clutch and an impeller clutch. The lockup clutch provides a choice of either torque converter drive or direct drive. The impeller clutch enables the output torque of the converter to vary.
Spline (1) is a part of converter housing (8). Spline (1) is engaged with the splines on the engine flywheel. These splines turn the converter housing at engine speed. The converter housing contains the lockup clutch for the turbine. Clutch housing (17) is fastened to the converter housing. Oil pump drive gear (19) is fastened to the clutch housing.
Stator (12) is connected to freewheel cam (11) with splines. Stator (12) and freewheel cam (11) rotate together. Freewheel race (10) is held stationary. Cage (7) is located between freewheel cam (11) and race (10). Springs (9) are partially inserted in a tab at the top of cage (7) and the bottom of cage (7). Race (10) is connected to carrier (21) with splines. Race (10) is also connected to carrier (21) with bolts and retaining washers. Carrier (21) is fastened to the cover that is around the torque converter. Carrier (21) and race (10) do not rotate. The carrier helps to support the rotating components of the converter. The carrier also contains the oil flow passages for the operation of the converter.
Converter housing (8), clutch housing (17) and oil pump drive gear (19) turn as a unit at the speed of the engine. Internal splines in clutch housing (17) turn plates (14) and piston (16). Clutch discs (15) are connected to adapter (25) with splines. Adapter (25) is fastened to impeller (13) with bolts.
Internal splines in converter housing (8) turn clutch plates (5) and piston (3). The splines on clutch discs (4) are meshed with hub assembly (2). Hub assembly (2) is fastened to turbine (6). Splines connect hub assembly (2) to output shaft (23). The output shaft is connected to output yoke (22). The output yoke is fastened to a universal joint and to the drive shaft that goes to the transmission input gears.
Oil from the transmission oil pump flows to the transmission oil filters. The oil from the transmission charging pump section of the transmission oil pump then flows to the priority valve. The oil from the priority valve then flows to the solenoid valves of the torque converter clutch and the remainder flows to the transmission hydraulic control valve. The oil from the torque converter charging section of the transmission oil pump flows to the torque converter lockup clutch.
In the transmission hydraulic control valve, the oil flows around the modulating relief valve to the torque converter inlet ratio valve. Oil from the torque converter inlet ratio valve flows through a hose into inlet passage (26) in the carrier, and then into the torque converter. The oil then flows through hub (24) into impeller (13) .
Torque Converter Operation
The oil that is inside of the torque converter flows from impeller (13) to turbine (6), and then to stator (12). The oil from stator (12) then flows to the impeller and to outlet passage (20) in carrier (21) .
The torque converter is operated with pressurized oil. The maximum inlet pressure is controlled by the torque converter inlet ratio valve. The outlet pressure is controlled by the outlet relief valve and by downstream restrictions.
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| Illustration 2 | g00292467 |
One-Way Clutch (7) Cage. (9) Springs (two). (10) Race. (11) Cam ring. (28) Slot. (29) Rollers (twenty- two). (30) Cam surface (twenty-two). | |
Oil flows through inlet passage (26) in carrier (21) to hub (24) and impeller (13). The rotation of the impeller gives force to the oil. The impeller sends the oil toward turbine (6). The force of the oil that hits the turbine blades causes the turbine to rotate. The turbine directs the oil to stator (12). The oil causes the stator to try to rotate in the direction that is the reverse of the rotation of the turbine. The one-way clutch locks stator (12) through cam (11) and rollers (29) to race (10) which is stationary.
Most of the oil from turbine (6) is then directed by stator (12) to impeller (13). The oil that flows from the stator onto the impeller and the impeller rotate in the same direction. The added oil from the stator multiplies the torque output of turbine (6). The remainder of the oil flows out of the torque converter through outlet passage (20) to the outlet relief valve.
As the speed of turbine (6) approaches the speed of impeller (13), the one-way clutch releases stator (12). The stator will freewheel after the one-way clutch releases. This increases the efficiency of torque converter operation.
One-Way Clutch
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| Illustration 3 | g00292467 |
One-Way Clutch (7) Cage. (9) Springs (two). (10) Race. (11) Cam ring. (28) Slot. (29) Rollers (twenty-two). (30) Cam surface (twenty-two). | |
Stator (12) is held stationary by the one-way clutch until higher torque converter output speeds are reached. Stator (12) is connected to freewheel cam (11) with splines. The stator rotates with freewheel cam (11). Freewheel race (10) is held stationary. Roller cage (7) is located between freewheel cam (11) and freewheel race (10). Spring (9) is partially inserted in a tab at the top of cage (7) and the bottom of cage (7) .
Spring (9) forces the tab of cage (7) to move to the right in slot (28) of cam (11) when the speed of turbine (6) lowers. This forces cage (7) to rotate clockwise. Rollers (29) wedge between cam (11) and race (10) as the rollers move against cam surfaces (30). Stator (12) is now locked to race (10) which is stationary. Stator (12) causes oil to flow to impeller (13) which multiplies the torque output of the torque converter.
The force of the oil that flows in a clockwise direction on stator (12) overcomes the wedge force of rollers (29) as the turbine speed approaches the impeller speed or the turbine speed becomes greater than the impeller speed. The turbine speed approaches the impeller speed or the turbine speed becomes greater than the impeller speed during roading, downhill operation, or engagement of the lockup clutch. The stator will now freewheel. The stator, the impeller, and the turbine now rotate in the same direction. This increases the efficiency of torque converter operation.
Lockup Clutch for the 992G Wheel Loader
When the lockup clutch is engaged, the converter is in direct drive. Direct drive provides the highest efficiency of the drive train. The lockup clutch solenoid valve controls the oil flow to the lockup clutch. The lockup clutch solenoid valve is positioned on the outer cover. The lockup clutch solenoid is activated by the power train ECM.
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| Illustration 4 | g00291570 |
Right Side Console of the 992G Wheel Loader (31) Lockup clutch switch. | |
The following conditions must be present in order for the 992G Wheel Loader power train ECM to activate the lockup clutch:
- Lockup clutch switch (31) on the right side of the console must be in the ON (enabled) position.
- The torque converter output speed is greater than 1375 rpm.
- The machine has been at the present speed and at the present direction for at least 2 seconds.
- The left brake pedal must not be depressed.
- The lockup clutch solenoid valve has been deactivated for at least four seconds.
The lockup clutch is disengaged during a shift, and then engaged when the five conditions are met again in the new selected gear. The lockup clutch is also disengaged when the torque converter output speed drops below 1225 rpm.
The lockup clutch cannot be engaged when the torque converter output speed is greater than 2250 rpm. This helps to prevent overspeed of the engine.
Lockup Clutch Solenoid Valve
The lockup clutch solenoid valve is a three-way, proportional pressure control valve. When the power train ECM sends maximum current to the solenoid, pressure in the lockup clutch is at the maximum. When the current from the power train ECM is at zero, the pressure in the lockup clutch is at the minimum.
Lockup Clutch Function
When the lockup clutch solenoid is energized by the power train ECM, oil flows to oil passage (27) in carrier (21). From the carrier, the oil flows through the oil passage in output shaft (23) to lockup clutch piston (3). The oil pressure on lockup clutch piston (3) forces the piston against clutch plate (5) and against clutch discs (4) .
Clutch piston (3) and clutch plate (5) are connected to converter housing (8) with splines. Clutch discs (4) are connected to hub assembly (2) with splines. Hub assembly (2) is fastened to turbine (6) with bolts. The friction between clutch discs (4) and clutch plate (5) causes the turbine and the output shaft to rotate at the same speed as the converter housing.
Lockup Clutch for the 854G Wheel Dozer
When the lockup clutch is engaged, the converter is in direct drive. Direct drive provides the highest efficiency of the drive train. The lockup clutch solenoid valve controls the oil flow to the lockup clutch. The lockup clutch solenoid valve is positioned on the outer cover. The lockup clutch solenoid is activated by the power train ECM. The lockup clutch solenoid is activated when the machine is in second speed forward or third speed forward. The lockup clutch will NOT engage in first speed forward.
Note: The 854G Wheel Dozer is NOT equipped with a lockup clutch switch.
The following conditions must be present in order for the 854G Wheel Dozer power train ECM to activate the lockup clutch:
- The torque converter output speed is greater than 1400 rpm.
- The machine has been at the present speed and at the present direction for at least 2 seconds. The lockup clutch will NOT engage in first speed forward.
- The left brake pedal must not be depressed.
- The lockup clutch solenoid valve has been deactivated for at least four seconds.
The lockup clutch is disengaged during a shift. The lockup clutch is engaged when the four conditions are met again in the new selected gear. The lockup clutch is also disengaged when the torque converter output speed drops below 1200 rpm.
The lockup clutch cannot be engaged when the torque converter output speed is greater than 2250 rpm. This helps to prevent overspeed of the engine.
Lockup Clutch Solenoid Valve
The lockup clutch solenoid valve is a three-way, proportional pressure control valve. When the power train ECM sends maximum current to the solenoid, pressure in the lockup clutch is at the maximum. When the current from the power train ECM is at zero, the pressure in the lockup clutch is at the minimum.
Lockup Clutch Function
When the lockup clutch solenoid is energized by the power train ECM, oil flows to oil passage (27) in carrier (21). From the carrier, the oil flows through the oil passage in output shaft (23) to lockup clutch piston (3). The oil pressure on lockup clutch piston (3) forces the piston against clutch plate (5) and against clutch discs (4) .
Clutch piston (3) and clutch plate (5) are connected to converter housing (8) with splines. Clutch discs (4) are connected to hub assembly (2) with splines. Hub assembly (2) is fastened to turbine (6) with bolts. The friction between clutch discs (4) and clutch plate (5) causes the turbine and the output shaft to rotate at the same speed as the converter housing.
Impeller Clutch
The impeller clutch is used to change the torque output of the torque converter. The impeller clutch allows the operator to use the left brake pedal to reduce wheel spin. The impeller clutch also allows the operator to use the left brake pedal to provide more engine power for the hydraulic system.
Note: The 854G Wheel Dozer is NOT equipped with reduced rimpull.
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| Illustration 5 | g00291571 |
Right Hydraulic Console for the 992G Wheel Loader (32) Reduced rimpull on/off switch | |
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| Illustration 6 | g00291572 |
Right Side Console for the 992G Wheel Loader (33) Reduced rimpull selection switch | |
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| Illustration 7 | g00291574 |
Left Side Front Dash for the 992G Wheel Loader (34) Reduced rimpull indicator lamp. | |
Reduced rimpull on/off switch (32) and reduced rimpull selection switch (33) are used to provide four levels of reduced rimpull. Reduced rimpull is enabled only when the transmission is in first speed forward or first speed reverse.
Reduced rimpull on/off switch (32) is a two-position rocker switch that is located on the implement console. Reduced rimpull selection switch (33) is located on the right hand console. In the MAXIMUM position, the reduced rimpull switch commands maximum rimpull. Maximum rimpull will be provided regardless of the setting of the rimpull selection switch.
The reduced rimpull selection switch (33) works with reduced rimpull on/off switch (32) in order to change the torque output of the torque converter. The power train ECM increases the amount of current to the impeller clutch solenoid valve in order to reduce rimpull. The position of the reduced rimpull selection switch regulates the amount of current that is sent to the impeller clutch solenoid valve.
Reduced rimpull indicator lamp (34) is on when reduced rimpull selection switch (33) is in the REDUCED position. The transmission must also be in first speed forward or first speed reverse. When the transmission is shifted to second speed or to third speed, the reduced rimpull indicator lamp will be off. Reduced rimpull is now disabled.
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| Illustration 8 | g01072810 |
The impeller clutch modulates at each instance of a directional shift. The impeller clutch also absorbs energy during the directional shift. This reduces the amount of energy that is absorbed by the direction clutch which results in an easier shift.
The oil flow to the impeller clutch is controlled by the impeller clutch solenoid valve. The impeller clutch solenoid valve is positioned on the outer cover. The impeller clutch solenoid is activated by the power train ECM.
The following conditions affect the operation of the impeller clutch:
- The position of the left service brake pedal
- Directional shifts and speed shifts
- Engine speed
- Direction of rotation of the torque converter output shaft and torque converter output speed
- Position of the reduced rimpull selection switch ( 992G Wheel Loader)
- Position of the reduced rimpull on/off switch ( 992G Wheel Loader)
Left Service Brake Pedal
The left service brake pedal controls the amount of brake pressure that is used to apply the service brakes. The left service brake pedal also controls the amount of pressure that actuates the impeller clutch. The impeller clutch is positioned between the engine and the torque converter.
By using the left brake pedal, the operator may divert engine power to the implement hydraulic circuit without putting the transmission in the NEUTRAL position.
As the operator depresses the pedal, the impeller clutch pressure drops quickly to a working pressure.
The pressure is then modulated to a reduced pressure. This sequence occurs during the next ten degrees of pedal travel. Depressing the left pedal past this point applies the service brakes.
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| Illustration 9 | g00107064 |
Typical Torque Converter Impeller Clutch (X) Approximate pedal position in degrees. (Y) Approximate percent of impeller clutch pressure. | |
Range (A) indicates the released position. In this range, the brake pedal does not apply the service brakes.
Range (B) indicates the first two degrees of pedal movement. In this range, the impeller clutch pressure is reduced to the maximum working pressure level. Range (B) is the approximate pressure range that is required to keep the impeller clutch from slipping.
Range (C) occurs in the next ten degrees of pedal travel. The impeller clutch pressure is modulated from the maximum working pressure to the minimum impeller clutch pressure.
Range (D) indicates the percent of service brake pressure. Range (E) indicates the impeller clutch pressure.
Engine Speed
When the engine speed drops below 1300 rpm, the power train ECM overrides the setting of the pedal. The power train ECM reduces the impeller clutch pressure. The impeller clutch hold pressure is reduced to 1100 rpm. This improves the response of the machine and the response of the engine when the machine is accelerating from a low idle speed.
Reverse Output Shaft Rotation
When the torque converter output shaft rotates in the opposite direction in excess of 500 rpm, the power train ECM overrides the setting of the pedal. The power train ECM then increases the impeller clutch pressure. This condition could occur if the left brake pedal is used to allow the machine to travel downhill on a grade with the transmission in a forward gear. This function prevents possible high temperatures in the impeller clutch.
Shift Modulation of the Impeller Clutch
During directional shifts of the transmission, the power train ECM overrides the setting of the brake pedal and the power train ECM reduces the impeller clutch pressure. These functions of the electronic control module help to provide an easier directional shift.
When a directional shift is detected, the impeller clutch hold pressure is reduced by the power train ECM. The circuit pressure for the impeller clutch then increases to maximum pressure if the left brake pedal is not depressed and the engine speed is above 1300 rpm.
The speed sensor for the torque converter output shaft and the engine speed sensor are used to determine when the transmission clutches have locked up.
Impeller Clutch Solenoid Valve
The impeller clutch solenoid valve is a three-way control valve which modulates pressure proportionally. When the power train ECM increases the amount of current to the solenoid, the impeller clutch pressure is reduced. When the amount of current from the power train ECM is at zero, the impeller clutch pressure is at the maximum.
Operation of the Impeller Clutch
When the impeller clutch solenoid valve is not energized by the power train ECM, oil flows to passage (18) from carrier (21). Oil in passage (18) forces clutch piston (16) against clutch plates (14) and clutch discs (15) .
Clutch piston (16) and clutch plates (14) are connected to clutch housing (17) with splines. Clutch discs (15) are connected to adapter (25) with splines. Adapter (25) is fastened to impeller (13) with bolts. The friction between clutch discs (15) and clutch plates (14) causes the impeller to rotate at the same speed as converter housing (8). This is the maximum torque output in torque converter drive.
As the amount of current flow to the solenoid is increased, oil pressure to clutch piston (16) is decreased. The friction between the clutch plates and the clutch discs decreases. This causes the impeller to slip. When the impeller slips, less oil is forced to the turbine. With less force on the turbine, there is less torque at the output shaft.
When the amount of current flow to the solenoid is at the maximum, there is minimum oil pressure against clutch piston (16). The clutch plates and the clutch discs now have only a small amount of friction and the impeller forces only a small amount of oil to the turbine. There is a minimum amount of torque at the output shaft.