Subaru Lineartronic: Not all CVTs are east/west - Transmission Digest

Subaru Lineartronic: Not all CVTs are east/west

The CVT that was developed for Subaru is a major departure from all other transverse-mounted CVTs. This new-design unit, called a Lineartronic, hit the streets in 2010. To say that a Lineartronic is a monster would be an understatement. The unit could probably fit right into a Sherman tank. There is also a difference in design between gas and diesel applications. In addition, to understand the power flow would be akin to “the ankle bone is connected to the shin bone, the shin bone is connected to the …” etc.)
Subaru Lineartronic: Not all CVTs are east/west

Technically Speaking

Author: Mike Riley, Technical Editor
Subject Matter: Automatic transmission
Unit: Lineartronic CVT
Vehicle Application: Subaru 
Issue: Design & operation

Technically Speaking

  • Author: Mike Riley, Technical Editor
  • Subject Matter: Automatic transmission
  • Unit: Lineartronic CVT
  • Vehicle Application: Subaru
  • Issue: Design & operation

CVTs (continuously variable transmissions) have been on the road for some time now and, like step-type transmissions, come in many shapes and sizes.

Various companies have had a stab at producing the perfect CVT; however, Jatco is the main company today that produces CVTs in large volume. Nissan and Subaru are the two major car companies to use the Jatco CVTs.

Although there have been several different designs of CVTs, they have been, for the most part, transverse (east/west). Subaru, on the other hand, has traditionally had a longitudinal (north/south) vehicle platform. Whether three-speed, four-speed or five-speed, Subaru has maintained this inline design. So, why should a CVT be any different? It’s not.

The CVT that was developed for Subaru is a major departure from all other transverse-mounted CVTs. This new-design unit, called a Lineartronic, hit the streets in 2010. To say that a Lineartronic is a monster would be an understatement. The unit could probably fit right into a Sherman tank. There is also a difference in design between gas and diesel applications. In addition, to understand the power flow would be akin to “the ankle bone is connected to the shin bone, the shin bone is connected to the …” etc.)

Although a Lineartronic does function like a regular CVT, Subaru has incorporated a stepped-shift feature into the computer strategy. It can actually be shifted like a six-speed automatic for folks who can’t stand how a CVT works. The transmission is also equipped with a lockup torque converter.

On the outside, the Lineartronic’s appearance is a far cry from a regular CVT – or anything else, for that matter (Figure 1). It has several chunks of housings from end to end to accommodate the ton of iron inside. This is an AWD to boot, which explains the extension housing.

Upon disassembly, it becomes really apparent that there is no straight line throughout the transmission. Everything is offset. To start with, the pump is a remote design like in a GM 6T70. Once the front cover is removed, the converter drive gear, chain and driven gear become visible (Figure 2). The drive gear is centered by the converter hub, whereas the driven gear is supported by ball bearings. The pump itself is a gerotor design.

The next item on the list is the input shaft, although there is more to it than just the shaft. The input on the Lineartronic has a drive gear made to it, which is the start of the power flow and the beginning of clockwise/counter clockwise rotations. The driven gear that meshes with the input is attached to a start clutch (Figure 3). The start clutch, however, seems rather light-duty compared with the rest of the transmission.

The hub of the start clutch has teeth for the frictions, but the inside diameter of the hub is where the drive splines are, which connect to the drive variator pulley shaft (Figure 4). The hub is supported by a sizable ball bearing.

The core of a CVT, what differentiates it from a step-type transmission, is the drive-belt and pulley system. While under extreme pressure, the variable sides of the drive and driven pulleys move in and out while moving the push bolt or chain from the I.D. to the O.D. of the pulleys. This action is what changes the ratio from low to high and back to low. The drive pulley is the starting point. The splines on the end of the shaft connect to the start-clutch hub (Figure 5). The drive pulley (variator) is supported by bearings at each end because of the weight. Drive and driven pulleys for all CVTs are not light.

Pressure that is used to keep a proper clamp force of the belt or chain is substantial, usually 600-800 psi. The surface of the pulleys not only is hard as nails but requires a specific micro finish as well.

The next link in the chain, so to speak, is a chain, literally (Figure 6). CVTs use either a drive belt or drive chain. A drive belt is more common than a chain, probably due to cost. The belt is comprised of hundreds of small plates that are held together by several steel bands.

A drive chain looks more like a transfer-case chain. It is made up of pins and links. The pins, however, are ground at an angle that conforms to the V surface of the pulleys. The metal-to-metal contact requires use of a special fluid or else failure will occur.

Due to the forces involved, certain CVT models use guides to maintain alignment and compensate for wear. The Lineartronic also uses plastic guides (Figure 7). The guides clip around the entire chain and are made from the same material as other chain snubbers. The chain “bone” connects to the driven-pulley “bone.”

The driven pulley is constructed and operates like the drive pulley although it is the reaction member. The difference between the two pulleys is the input/output function. At the end of the driven pulley is the drive gear (Figure 8).

Engine and input-shaft rotation is clockwise. That direction is reversed via the start-clutch gears. This means that the drive pulley, chain, driven pulley and gear all turn counterclockwise.

The next rotational reversal on the list is due to the driven-pulley drive gear and what it meshes with, which is the forward-clutch drive gear (Figure 9). The forward-clutch/reverse-clutch arrangement is similar to that of other CVTs and does rotate in a clockwise (engine) direction. The forward clutch connects to a simple planetary with the ring gear being splined to the drum. The planet connects to the reverse clutch, and the forward-clutch hub is made to the sun gear.

With the forward clutch applied, the components of the planet gear set all rotate clockwise. The sun gear is splined to the transfer clutch (Figure 10). The transfer clutch on the Lineartronic is comparable to those on other Subaru transmissions. In addition to the sun gear and transfer-clutch housing is the transfer drive gear/park gear.

The last item in the transfer-clutch lineup is the transfer-clutch hub and output shaft (Figure 11). The output shaft connects to the driveshaft like a regular RWD or AWD and is also supported by a sizable ball bearing.

Since this is an AWD, it means that there is still more stuff to deal with. The second-to-last gear-direction reversal has to do with the pinion shaft. The transfer drive gear meshes with a transfer driven gear, which is splined to the end of the pinion-gear shaft (Figure 12). The transfer driven gear and pinion gear are driven in a counterclockwise direction. The pinion shaft is supported by three bearings and uses selective shims to set pinion-gear depth.

Last, the differential meshes with the pinion drive gear and ultimately propels the vehicle forward. The differential is also like that of a regular Subaru.

Add in a rather complex valve body and other do-dads, it becomes apparent that the Lineartronic is not child’s play. But, as with any gearbox, follow the “directions” and it should work out.

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