The 3L30 (THM 180/180C) is a 3-speed automatic transmission that uses the Ravigneaux compound planetary gearset. Three multiple-disc clutches, referred to as the second, third, and reverse or the intermediate/high, direct, and reverse clutches; one band, and a single one-way (sprag) clutch are used to provide for the various gear ratios. Each clutch is hydraulically applied and released by several small coil springs when hydraulic pressure is routed away from the bore of the clutch's piston. This General Motors' transmission uses a gear-type oil pump.

The planet carrier is the output member of the gearset. The power flow through the gears is identical to that of the Ford ATX, except the location of the planetaries is reversed.

PLANETARY GEARSETS IN TANDEM

Rather than relying on the use of a compound gearset, some automatic transmissions use two simple planetary units in series. In this type of arrangement, gearset members are not shared; instead, the holding devices are used to lock different members of the planetary units together. Normally, the front planetary carrier is locked to the rear ring gear and the front ring gear is locked to the rear planetary carrier. Two common transaxles use this planetary gear arrangement, General Motors' 4T60 (THM 440-T4) and the Ford AXOD. Both of these will be covered in detail, although they are both quite similar in design and power flow.

4T60 TRANSAXLE

General Motors' 4T60 was the first domestically produced 4-speed automatic transaxle built for FWD vehicles. Overdrive fourth gear is obtained by using the same planetary units as are used for the first three speeds, instead of adding a planetary unit just for overdrive.

Although the gear train is based on two simple planetary gearsets operating in tandem, the combination of the two planetary units does function much like a compound unit. The two tandem units do not share a common member, rather certain members are locked together or are integral with each other. The front planetary carrier is locked to the rear ring gear and the front ring gear is locked to the rear planetary carrier. The transaxle houses a third planetary unit, which is used only as the final drive unit and not for overdrive.

The 4T60 uses a variable-displacement vane-type oil pump and four multiple-disc clutches, two bands and two one-way clutches, to provide the various gear ranges. One of the one-way clutches is a roller clutch; the other is a sprag. The four multiple-disc clutches are released by several small coil springs when hydraulic pressure is diverted from the clutch's piston.

Input Devices Engine torque is transferred to the transaxle through the torque converter and a sprocket and drive link assembly. The torque converter does not directly drive the gear train of the transaxle, rather the converter drives a sprocket that is linked, by a drive chain, to an input sprocket at the gear train. This arrangement allows the gear train to be positioned away from the centerline of the engine's crankshaft.

Input through the gear train is controlled by the input clutch, input one-way clutch, and second clutch. The input clutch and the input one-way clutch drive the front sun gear.

Power Flow While operating in first gear, the input is received through the front sun gear, which is locked to and drives the rear ring gear. The 1-2 band is applied and holds the rear sun gear. This forces the rear carrier to be driven by the rear ring gear at a speed reduction and a ratio of 2.92:1.

Input for second gear operation is received clutch is front planetary carrier when the second clutch is applied. Since the rear ring gear is an integral part of the front planetary carrier, the two rotate at the same speed and in the same direction. The rear sun gear is held stationary by the one-way clutch; therefore, the rear planetary carrier rotates around it at a gear reduction ratio of 1.57:1.

Third gear offers direct drive. Input is received by the gear train through the front sun gear by the application of the third clutch. The second clutch is still applied and directs input through the front planetary carrier. Since two of the three planetary members are rotating at the same speed, the ring gear is forced to rotate with them. The ring gear drives the rear planetary carrier at the same speed and direct drive results.

In fourth gear, the second clutch remains applied and input is received through the front planetary carrier. The fourth clutch is also applied and it holds the front sun gear. This causes the front ring gear to rotate around the carrier at a speed greater than input speed. Since the rear planetary carrier is connected to the front ring gear, the output from the gearsets is an overdrive with a ratio of 0.70:1.

Reverse operation is achieved by holding the front planetary carrier with the reverse band. With the carrier held, the input on the front sun gear causes the front ring gear to rotate in the opposite direction. Because the front ring gear is locked to the rear carrier, the output of this gear combination is in the opposite direction as the input and at a ratio of 2.38:1.

AXOD TRANSAXLE

The AXOD 4-speed transaxle relies on two simple planetary units that operate in tandem. The planetary carriers of each planetary unit are locked to the other planetary unit's ring gear. Each planetary set has its own sun gear and set of planetary pinion gears. There are no transmissions used by Ford that have any similarity to the AXOD, rather the similarity lies with the construction and operation of the THM 4T60.

The AXOD combines an automatic transmission and differential into a single unit designed for FWD vehicles. The transmission is a fully automatic unit with four forward speeds, one reverse, neutral, and park. The AXOD uses four multiple-disc clutches, two band assemblies, and two one-way clutches to control the operation of the planetary gearset. Output from the planetary units is through the rear planetary carrier and front ring gear.

All of the multiple-disc clutches are hydraulically applied and released by several small coil springs when hydraulic pressure is diverted from the clutch's piston. For more insight on the operation of the AXOD, refer to the clutch and band application chart.

Input Devices Like the 4T60, the AXOD torque converter does not directly drive the gear train of the transaxle. The converter drives a sprocket, which is connected by a chain to a sprocket on the input shaft of the gear train.

Input to the gear train is received by the front sun gear, the front planetary carrier, or rear ring gear. The forward clutch, low one-way clutch, direct clutch, direct one-way clutch, and intermediate clutch serve as the input devices.