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| Illustration 1 | g00557677 |
(1) Spline (2) Hub assembly (3) Lockup clutch piston (4) Clutch disc (5) Plate (6) Turbine (7) Converter housing (8) Race (9) Cam ring (10) Stator (11) Impeller (12) Plate (13) Clutch disc (14) Impeller clutch piston (15) Clutch housing (16) Oil passage for impeller clutch (17) Oil pump drive gear (18) Carrier (19) Output yoke (20) Output shaft (21) Hub (22) Adapter (23) Converter inlet passage for oil (24) Oil passage for lockup clutch | |
This torque converter contains a lockup clutch and an impeller clutch. The lockup clutch allows a means for either 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 (7). Spline (1) is engaged with the splines on the engine flywheel. These splines turn the converter housing at engine speed. Converter housing (7) contains the lockup clutch. Clutch housing (15) is fastened to the converter housing. Oil pump drive gear (17) is fastened to the clutch housing.
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| Illustration 2 | g00558966 |
One-Way Clutch (8) Race (9) Cam ring (25) Springs (26) Slot (27) Rollers (28) Cam surface | |
Stator (10) is connected to freewheel cam (9) with splines. Stator (10) and freewheel cam (9) rotate together. Freewheel race (8) is held stationary. Springs (25) are inserted between cam (9) and rollers (27). Race (8) is connected to carrier (21) with splines. Carrier (18) is fastened to the cover that is around the torque converter. Carrier (18) and race (8) 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 (7), clutch housing (15) and oil pump drive gear (17) turn as a unit at the speed of the engine. Internal splines in clutch housing (15) turn plates (12) and piston (14). Clutch discs (13) are connected to adapter (22) with splines. Adapter (22) is fastened to impeller (11) with bolts.
Internal splines in converter housing (7) 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 (20). The output shaft is connected to output yoke (19). The output yoke is fastened to a U-joint and to the drive shaft that goes to the transmission input group (transfer gear).
The transmission oil pump draws oil from the transmission sump. The oil then passes through a screen to the transmission oil filter. The oil then flows to the priority valve. The oil from the priority valve will then flow to the solenoid valves of the converter clutches. The remainder of the oil will flow to the transmission hydraulic control valve and to the torque converter.
In the transmission hydraulic control valve, the oil flows around the modulating relief valve to the converter inlet ratio valve. Oil from the converter inlet ratio valve flows through a hose into inlet passage (23) in the carrier, and then into the torque converter. The oil then flows through hub (21) into impeller (11) .
Torque Converter Operation
The oil that is inside of the torque converter flows from impeller (11) to turbine (6), and then to stator (10). The oil from stator (10) then flows to the impeller and to the outlet passage in carrier (18) .
The torque converter is operated with pressurized oil. The maximum inlet pressure is controlled by the converter inlet ratio valve. The outlet pressure is controlled by the outlet relief valve and by downstream restrictions.
Oil flows through inlet passage (23) in carrier (18) to hub (21) and impeller (11). 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 (10). 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 (10) through cam (9) and rollers (27) to race (8) which is stationary.
Most of the oil from turbine (6) is then directed by stator (10) to impeller (11). The oil flows from the stator onto the impeller and the impeller rotates 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 the outlet passage to the outlet relief valve.
As the speed of turbine (6) approaches the speed of impeller (11), the one-way clutch releases stator (10). The stator will freewheel after the one-way clutch releases. This increases the efficiency of torque converter operation.
One-Way Clutch
Stator (10) is held stationary by the one-way clutch until higher torque converter output speeds are reached. Stator (10) is connected to freewheel cam (9) with splines. The stator rotates with freewheel cam (9). Freewheel race (8) is held stationary.
Springs (25) force each roller to move to the left in slot (26) of cam (9) when the speed of turbine (6) lowers. Rollers (27) wedge between cam (9) and race (8) as the rollers move against cam surfaces (28). Stator (10) is now locked to race (8) which is stationary. Stator (10) causes oil to flow to impeller (11) which multiplies the torque output of the torque converter.
The torque that is applied to the output shaft will continue to increase until the speed of turbine (6) approaches the speed of impeller (13). The force of the oil that flows in a clockwise direction into stator (10) overcomes the wedge force of rollers (27) as the speed of turbine (6) increases. 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
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 on the 834G Wheel Tractor can activate when the machine is in all gears except first gear forward. The lockup clutch solenoid on the 836G Landfill Compactor can activate when the machine is in all gears.
The following conditions must be present in order for the power train ECM to activate the lockup clutch:
- The torque converter output speed is greater than 1410 rpm.
- The torque converter output speed is less than 2120 rpm.
- The left brake pedal must not be depressed.
- The lockup clutch solenoid valve has been deactivated for at least four seconds after the fault for clutch slippage has been logged.
The lockup clutch is engaged when the four conditions are met again in the new selected gear. The lockup clutch is disengaged when the torque converter output speed drops below 1250 rpm.
To prevent engine overspeed, the lockup clutch will disengage when the torque converter output speed exceeds 2400 RPM.
Modulating Valve (Lockup Clutch)
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.
Operation of Lockup Clutch
When the lockup clutch solenoid is energized by the power train ECM, oil flows to oil passage (24) in carrier (18). From the carrier, the oil flows through the oil passage in the output shaft 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 (7) 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.
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
- Engine speed
- Selected gear
- Direction of rotation of the torque converter output shaft and torque converter output speed
- The position of the reduced rimpull selector switch
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 3 | g00558470 |
Typical Torque Converter Impeller Clutch (X) is the approximate pedal position in degrees.(Y) is the 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 range of pressure that is required in order to prevent slippage of the impeller clutch.
Range (C) occurs in the next ten degrees of pedal travel. The impeller clutch pressure is modulated from the working pressure to the impeller clutch pressure.
Range (D) indicates the percent of service brake pressure. Range (E) indicates the neutralized impeller clutch pressure.
Shift Modulation of the Impeller Clutch
While you shift the direction of the transmission, the power train ECM will override the setting of the left brake pedal. The ECM will reduce the pressure of the impeller clutch.
When a shift in direction is detected the power train ECM will reduce the circuit pressure of the impeller clutch to an impeller clutch hold pressure. The circuit pressure of the impeller clutch will increase to maximum pressure if the left brake pedal is not depressed. The circuit pressure will also increase if the lockup for the direction clutch is engaged.
The transmission speed sensors and the torque converter output speed sensor are used to determine when the transmission directional clutches have locked up.
Modulating Valve (Impeller Clutch)
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 Impeller Clutch
When the impeller clutch solenoid valve is not energized by the power train ECM, oil flows to passage (16) from carrier (18). Oil in passage (16) forces clutch piston (14) against clutch plates (12) and clutch discs (13) .
Clutch piston (14) and clutch plates (12) are connected to clutch housing (15) with splines. Clutch discs (13) are connected to adapter (22) with splines. Adapter (22) is fastened to impeller (11) with bolts. The friction between clutch discs (13) and clutch plates (12) causes the impeller to rotate at the same speed as converter housing (7). This is the maximum torque output in converter drive.
As the amount of current to the solenoid is increased, oil pressure to clutch piston (14) 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 to the solenoid is at the maximum, there is minimum oil pressure against clutch piston (14). 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.