545 Wheel Skidder Power Train Caterpillar

Illustration 1	g00544725
Torque Converter (1) Cover. (2) Piston. (3) Rotating housing. (4) Disc. (5) Plate. (6) Plate. (7) Turbine. (8) Stator. (9) Impeller. (10) Gear. (11) Inlet oil passage. (12) Carrier. (13) Hub. (14) Outlet oil passage. (15) Oil passage for lockup clutch.

Illustration 2	g00545045
View A-A (16) Freewheel race. (17) Spring (nine). (18) Roller (nine). (19) Freewheel cam.

The torque converter is splined to the flywheel of the engine. The splines that are located on the torque converter are part of the rotating housing. The splines turn the rotating housing at engine speed. Rotating housing (3) contains the lockup clutch. Cover (1) is bolted to rotating housing (3). Piston (2) is splined to rotating housing (3). Disc (4) is splined to plate (6) which is bolted to turbine (7). Turbine (7) is bolted to hub (13) which is splined to the transmission input shaft. Plate (5) is bolted to rotating housing (3) .

Stator (8) is connected to freewheel cam (19) with splines. Freewheel cam (19) is connected to freewheel race (16) with springs (17) and rollers (18). Freewheel race (16) is splined to carrier (12). Freewheel race (16) and freewheel cam (19) are held in place with washers and retaining rings.

Impeller (9) and gear (10) for the oil pump are connected to the rotating housing. These components turn with the engine flywheel at engine speed.

Carrier (12) is fastened to the transmission cover. Oil flows through inlet oil passage (11) and outlet oil passage (14) in carrier (12) .

The oil for the operation of the torque converter comes from the oil pump for the transmission. The oil pump is driven by pump drive gear (10). The oil flows through the transmission oil filter to the flow control valve in the transmission case. The oil flow is divided at the flow control valve. Oil is directed to the transmission circuit and to the torque converter circuit. The maximum torque converter inlet oil pressure is controlled by the torque converter inlet relief valve. The torque converter inlet relief valve is mounted in the transmission case below the transmission control valve. The relief valve limits the maximum pressure to the torque converter. The torque converter inlet relief valve protects the torque converter from high pressure that is due to cold oil or due to some other restriction in the torque converter or in the cooler circuit.

Torque Converter Operation

Oil from the flow control valve flows into the torque converter through inlet passage (11) in carrier (12). This oil flows to impeller (9). The rotation of the impeller provides the oil with force.

Impeller (9) turns with rotating housing (3) at the engine speed. The rotation of the impeller causes the oil to move to the outside of the impeller. The oil then goes around the inside of rotating housing (3) and against the blades of turbine (7). The force of the oil that hits the turbine blades causes turbine (7) and hub (13) to turn. This sends torque to the input shaft of the transmission. Now, the turbine torque that is provided by the force of the oil from the impeller cannot be more than the torque output of the engine to the impeller.

After the oil hits the turbine blades, the oil goes toward the inside of turbine (7). The oil from the turbine is directed to stator (8). The oil causes the stator to rotate in the direction opposite the rotation of the turbine. Stator (8) is locked in this rotation through freewheel cam (19), rollers (18) and springs (17) to freewheel race (16) which is stationary.

All of the oil from turbine (7) is then directed by stator (8) to impeller (9). Impeller (9) and stator (8) rotate in the same direction. The added oil from stator (8) multiplies the torque output of turbine (7). As the difference between the turbine speed and the speed of the impeller becomes larger, the amount of force from the oil of the stator increases. This extra force can provide an increase to the torque output of the engine to the turbine. The remainder of the oil flows out of the torque converter through outlet passage (14) to the oil cooler. The oil then flows to the lubrication system.

The load on the machine is the cause of speed changes of the turbine. This means that a higher load causes the difference in the speed of the impeller and the turbine speed to be larger. The force from the oil of the stator adds a certain amount of torque multiplication. The different loads on the machine control the amount of torque multiplication. The torque multiplication of the torque converter is at the maximum when the torque converter is stalled. The torque converter is stalled when the output shaft rpm is zero.

Lockup Clutch

When the lockup clutch is engaged, the torque converter is in direct drive. The solenoid modulating valve controls the oil flow to the lockup clutch. The power train electronic control module (ECM) electronically regulates the solenoid modulating valve. The torque converter lockup clutch is enabled by the lockup clutch switch. The engagement of the lockup clutch is determined by measuring the transmission output speed.

The transmission output speed sensor measures the transmission output speed. This information is sent to the power train ECM. The power train ECM engages the lockup clutch when the transmission output speed reaches a certain range dependent on the gear that is selected. The power train ECM disengages the lockup clutch when the transmission output speed is reduced below the range. The power train ECM also disengages the lockup clutch if the speed gets above a certain range in order to protect the engine from overspeed. The speed ranges are dependent on the gear that is selected. When the lockup clutch engages, the green indicator lamp for the torque converter lockup clutch will be on. The indicator lamp is located on the right side of the front dash.

The following conditions must be met in order for the power train ECM to enable the lockup clutch:

• The lockup clutch switch (torque converter lockup clutch) on the right side of the front dash must be in the ON position.

• The transmission output speed reaches a certain range.

• The transmission is in forward gear or reverse gear.

Note: The lockup clutch only operates in the forward gears for earlier models.

Reference: For more information on the operation of the transmission output speed sensor, refer to the Service Manual module Systems Operation, "Transmission Electrical System".

Parameters for the Torque Converter Lockup Clutch

Note: The engine rpm at engagement can vary. The engine rpm is known at disengagement because the engine is directly coupled to the transmission input shaft.

Solenoid Modulating Valve (Torque Converter Lockup Clutch)

Illustration 3	g00744173
Location of the Solenoid Modulating Valve (Torque Converter Lockup Clutch)

Illustration 4	g00554842
(20) Solenoid Modulating valve (Torque converter lockup clutch). The right side cover in front of operator's cab is removed for clarity.

The solenoid modulating valve is a three-way proportional pressure control valve. Solenoid modulating valve (20) is mounted on the upper right side of the transmission case toward the front of the machine. When the power train ECM energizes the solenoid, pressure in the lockup clutch will reach a maximum operating pressure. When the solenoid is de-energized, the pressure in the lockup clutch is at the minimum.

Illustration 5	g01098002
(20) Solenoid modulating valve. (21) Cartridge. (22) Coil. (23) Pin. (24) Ball. (25) Chamber. (26) Orifice. (27) Cartridge. (28) Control spool. (29) Spring. (C) Port to lockup clutch. (P) Supply port from transmission pump. (T) Drain port to sump in transmission case.

Control of the torque converter lockup clutch is achieved by the use of a modulating valve that is controlled by a solenoid.

Pressurized oil is supplied by the transmission pump to the modulating valve through oil supply port (P). A pilot pressure is allowed through control spool (28) to chamber (25). The oil in chamber (25) is allowed to drain to the sump through orifice (26) and drain port (T).

When coil (22) is energized, cartridge (21) shifts to the right moving pin (23) against ball (24). Ball (24) is forced against orifice (26). The pressure of the oil in chamber (25) increases. The increased pressure moves control spool (28) to the right against spring (29) and pressurized oil is allowed to flow to the torque converter lockup clutch through port (C). The clutch then engages direct drive through the torque converter.

When coil (22) is de-energized, the pressure of the oil in chamber (25) unseats ball (24) that moves pin (23) and cartridge (21) to the left. The oil in chamber (25) is allowed to drain to the sump through orifice (26) and drain port (T). As the pressure in chamber (25) drops, control spool (28) is moved back to the left by spring (29). As the control spool is returned to the left, the supply of oil from oil supply port (P) is blocked and the oil in the lockup clutch is allowed to flow to the sump via drain port (T) .

Reference: For more information about the modulating valve (torque converter lockup clutch), refer to the Service Manual module Systems Operation, "Transmission Hydraulic System".

Reference: For more information about the modulating valve (torque converter lockup clutch), refer to the Service Manual module Systems Operation, "Transmission Electrical System".

Operation of the Lockup Clutch

The solenoid modulating valve (torque converter lockup clutch) is energized by the power train ECM. Oil flows from modulating valve (20) to oil passage (15) through the input shaft to the lockup clutch piston. The oil pressure will force piston (2) against disc (4) and plate (6). Disc (4) is splined to plate (5) which is bolted to turbine (7). The friction between disc (4) and plate (6) causes the turbine and the input shaft to rotate at the same speed and direction as the rotating housing.

While the lockup clutch is engaged, stator (8) will now freewheel. The stator, the impeller, and the turbine now rotate in the same direction. This increases the efficiency of the torque converter operation.