777F Off-Highway Truck Power Train: Torque Converter

The torque converter is driven by the engine flywheel. The torque converter consists of an impeller, a turbine, a lockup clutch, and a stator with a one-way clutch. The torque converter lockup clutch permits the machine to operate in direct drive in order to keep the power loss at a minimum. The one-way clutch holds the stator when the torque converter drive is used. The one-way clutch allows the stator to turn freely when the torque converter drive is not used.

The torque converter housing is fastened to the flywheel housing. The torque converter lockup clutch valve and the torque converter outlet relief valve are attached to the torque converter housing. The gear pump for torque converter charging, torque converter scavenge, and the parking brake release is attached to the torque converter housing. The flange of the output shaft of the torque converter is connected to the drive shaft.

The transmission is driven by the torque converter in NEUTRAL and in REVERSE. In FIRST speed, torque converter drive is used at lower ground speeds. In FIRST speed, direct drive is used at higher ground speeds. The torque converter lockup clutch is activated in FIRST speed by the Chassis Electronic Control Module (ECM) according to the ground speed. During shifts from FIRST speed through SEVENTH speed, torque converter drive is momentarily activated in order to allow smoother shifts. When the transmission clutches are engaged, the torque converter lockup clutch engages and the transmission is in direct drive.

Table 1

Operation Of The Torque Converter For Transmission Speed
Transmission Speed	Torque Converter Drive	Direct Drive with an Engaged Lockup Clutch
REVERSE	X
NEUTRAL	X
FIRST	X	X
SECOND		X
THIRD		X
FOURTH		X
FIFTH		X
SIXTH		X
SEVENTH		X

Torque Converter Drive

(1) Rotating housing (2) Turbine (3) Impeller (4) Outlet passage (5) Output yoke (6) Hub (7) Output shaft (8) Stator(9) One-way clutch

The engine flywheel turns rotating housing (1) which turns impeller (3). The impeller directs the oil to the blades of turbine (2). This will cause the turbine to turn. The turbine directs the oil to stator (8). This causes the stator to try to turn in the opposite direction of the turbine. The movement of the stator causes the rollers of one-way clutch (9) to move between stator (8) and the carrier for the stator. The action of the one-way clutch keeps the stator from rotation in the opposite direction of the turbine (2). The stator now directs most of the oil back to impeller (3). The remainder of the oil goes out of the torque converter through outlet passage (4). The oil, that goes back to impeller (3) from stator (8), moves in the same direction as the rotation of the impeller. Since this oil is moving in the same direction as the impeller, the torque output from the torque converter is multiplied.

Turbine (2) turns hub (6). Hub (6) turns output shaft (7). Power is sent through the output yoke (5) to the drive shaft and the transfer gears of the transmission.

One-Way Clutch

Detail of one-way clutch (10) Cam (11) Rollers (12) Spring (13) Opening(14) Race

Splines connect stator (8) to cam (10). Cam (10) is turned by the stator. Race (14) does not turn. The mechanical connection between cam (10) and race (14) is rollers (11). Rollers (11) are in openings (13) of cam (10). Springs (12) are also in openings (13). The left side of openings (13) is smaller than the right side of openings (13) because the opening has a taper. Normally, springs (12) keep rollers (11) in the taper at the left side of openings (13) .

When the speed of impeller (3) and turbine (2) is slow, stator (8) is held stationary. Rollers (11) are held in the taper of openings (13) by springs (12). There is a mechanical connection between cam (10) and race (14). Because race (14) is held stationary, cam (10) is held stationary. Because the cam can not turn, the stator does not turn. The stator can send oil back to the impeller.

As the speed of impeller (3) and turbine (2) increases, stator (8) starts to turn. The stator (8) will turn in the same direction as the impeller and the turbine. When the stator starts to turn, cam (10) starts to turn. The movement of cam (10) causes rollers (11) to move from the taper of openings (13). The mechanical connection between cam (10) and race (14) is broken. Stator (8) and cam (10) turn freely. The stator does not send oil back to the impeller.

Direct Drive

(1) Rotating housing (2) Turbine (3) Impeller (5) Output yoke (6) Hub (7) Output shaft (8) Stator (15) Inlet passage (16) Distributor (17) Lockup clutch (18) Piston (19) Plate(20) Disc

Lockup Clutch

Torque converter lockup clutch (17) is part of the torque converter. The torque converter lockup clutch (17) is located between the engine flywheel and the turbine (2). The torque converter lockup clutch is engaged when the transmission is in SECOND through SEVENTH speeds. The torque converter lockup clutch will engage in FIRST speed as the output speed of the transmission increases. When the torque converter lockup clutch is engaged, impeller (3) and turbine (2) turn at the same speed as the engine and there is no loss of power in the torque converter. The connection between the engine and the transmission is now direct.

The main components of torque converter lockup clutch (17) are piston (18), plates (19), and discs (20) .

Operation

Rotating housing (1) is connected to the engine flywheel by splines. Rotating housing (1) is fastened to impeller (3) by bolts. Piston (18) and plates (19) are also connected to rotating housing (1) by splines. Discs (20) and output shaft (7) are connected to hub (6) by splines. Turbine (2) is fastened to hub (6) .

The Chassis (ECM) activates the solenoid valve for the torque converter lockup clutch valve. The torque converter lockup clutch valve sends pressure oil through inlet passage (15) in distributor (16). The oil goes through a passage in the center of output shaft (7). The oil then goes through a passage in rotating housing (1) to piston (18). The pressure of the oil causes piston (18) to move toward disc (20). This causes plates (19) and discs (20) to be held together. Plates (19) and discs (20) will now turn at the same speed. The clutch becomes a direct connection between rotating housing (1) through hub (6) to output shaft (7) .

This causes turbine (2) and impeller (3) to turn at the same speed. Stator (8) turns freely. At this time, the torque converter is not in operation and the machine is in direct drive.

The flow of power is from rotating housing (1), through lockup clutch (17), hub (6), output shaft (7), and output yoke (5). The power goes directly through the torque converter to the drive shaft. The drive shaft sends the power to the transfer gears of the transmission.

When the torque converter lockup clutch (17) is not engaged, the operation of the torque converter is normal.

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777F Off-Highway Truck Power Train: Torque Converter 2013-01-04T15:42:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown