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This posting provides parts of articles about CVTs with torque converters and diagnosing some of their problems. The articles are general in nature, and are not directed at the Pathfinder CVT, but many of the general details will apply.
Note that any text in italics were noted by me, and not in the original article.

MOTOR Magazine, June 2007
One significant difference to be aware of is whether or not a CVT that shows up at your shop uses a torque converter. This determines the strategy used when the vehicle is placed into gear as well as when it comes to a stop while in gear. In most cases, when a conventional torque converter is used, a CVT will remain in gear in a similar fashion to a conventional automatic transmission. The Nissan Murano RE0F09A, Saturn VUE VT25E, Ford Five Hundred CFT30 and Dodge Caliber CVT2 CVTs are just a few examples of this combination of a CVT and a torque converter. These converters also have a clutch that supplies engine torque directly to the transmission when the clutch is applied. Unique strategies are utilized to safeguard against damage to the belt and pulleys should the converter clutch get “stuck on” due to a faulty solenoid, stuck valve, leaking sealing rings or a defective converter. In one such strategy, the computer compares engine speed to the primary pulley shaft (turbine/ input) speed after a start-up in Park. If they’re exactly the same or within a specific parameter, the computer will determine that the converter clutch is stuck on and will prevent a Reverse or Drive engagement as a safeguard for the belt and pulleys.

Another strategy allows for the converter clutch to be applied early in the ratio up-change. If the converter clutch experiences a chatter problem the vibration could be misinterpreted as a belt-to-pulley problem. If the chatter is very slight, it could also be misinterpreted as an engine miss. The cause for this vibration could be something as simple as deteriorated or incorrect fluid usage. This could be difficult to diagnose without the proper test equipment. Test equipment will allow you to graph engine speed as well as the drive and driven pulley shaft speeds during the time of the chatter, and comparing these signals would allow for greater diagnostic accuracy.

If the converter clutch was the cause of the chatter problem, it could be seen with the rpm irregularities between engine speed and drive pulley speed. If rpm irregularities are seen between the pulley speeds, there’s a belt issue. If irregularities are not seen between engine speed and drive pulley or between the pulleys, an engine miss should be considered as the cause.


GEARS April 2007
Unlike the Honda CVT, the JATCO CVT uses a torque converter. The purpose of the torque converter is to allow smooth acceleration from a standstill by providing a hydraulic disconnect from the engine. After rolling away from a stop sign, the torque converter clutch applies very early, usually at about 12 MPH


GEARS March 2007
The only component connecting the variators is the belt. Similar to the Honda CVT, the belt assembly is made up of many ridged segments shaped like wedges and held together by a layered steel belt. The belt is a pusher, not a puller, which means the primary variator uses the belt to push the secondary variator. The concept involves the fact that steel cannot be compressed, so the belt shouldn’t wear (and definitely not stretch) over time. Since the segments are designed with interlocking dowels, it acts like a solid steel structure when transferring torque from one variator to the other. This design is very different from the ZF design, which uses a chain and pins where one variator pulls the other.

With all CVT designs, pressure is the key component to making them survive. Belt slip within the sheaves (pulley surfaces) will quickly destroy the belt. This is why CVTs have such incredibly high pressures and special fluids.

Things to note from these articles:
1) As noted in other articles, the transmission fluid's characteristics are highly important to the proper operation of a CVT
2) Early lockup of the torque converter is a way to protect the CVT.
3) The Jatco CVT in the above article locks up by 12 mph. Note that JATCO is the Japan Automatic Transmission Company, of which Nissan owns about 80%, and they provide CVTs to Nissan and other manufacturers.
3)Belt slippage is not good for a CVT. The CVT in the Pathfinder uses a chain, but keep this fact in mind for later reference. The illustration is of a CVT with a belt, not a chain.
4) CVTs use high transmission fluid pressures to operate. Keep this in mind for later reference.
 

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