CVT Pulley With Engineered Surface

{
  "publication_number": "US2012088615A1",
  "country": "US",
  "kind": "A1",
  "title": "CVT Pulley With Engineered Surface",
  "abstract": "A pulley for a continuously variable transmission and a method of creating an engineered surface on an outer surface of a pulley of a continuously variable transmission, with the engineered surface engaging with a belt or chain of the continuously variable transmission. The method comprising the steps of: determining an actual engineered roughness (Rpk) on the outer surface needed to obtain a predetermined friction between the engineered surface and the belt or chain; and etching microgrooves in at least a portion of the outer surface to create the engineered surface by employing a laser to etch the microgrooves, the microgrooves being formed to a depth that produces the actual engineered roughness (Rpk).",
  "claims": [
    "1. A method of creating an engineered surface on an outer surface of a pulley of a continuously variable transmission, the engineered surface engaging with a belt or chain of the continuously variable transmission, the method comprising the steps of: (a) determining an actual engineered roughness (Rpk) on the outer surface needed to obtain a predetermined friction between the engineered surface and the belt or chain; and (b) etching microgrooves in at least a portion of the outer surface to create the engineered surface by employing a laser to etch the microgrooves, the microgrooves being formed to a depth that produces the actual engineered roughness (Rpk). 2. The method of claim 1 wherein step (b) is further defined by the laser being a femto-pulsed laser. 3. The method of claim 1 wherein step (b) is further defined by the microgrooves being etched throughout the entire outer surface to create the engineered surface. 4. The method of claim 1 wherein step (b) is further defined by the microgrooves being etched throughout a radially inner area of the outer surface to create the engineered surface; and wherein the method includes step (c) creating a predetermined average surface roughness throughout a radially outer area of the outer surface employing mechanical contact with the radially outer area of the outer surface. 5. The method of claim 4 wherein step (c) is further defined by surface roughness in the radially outer area being created by employing at least one of shot peening, grinding, stone polishing and tape polishing. 6. The method of claim 4 including step (c) coating the outer surface with chromium nitride after completing step (b). 7. A continuously variable transmission pulley that engages a belt or chain of the continuously variable transmission, comprising: a first pulley half having a first outer surface with a truncated conical shape, a portion of the first outer surface having laser etched microgrooves therein of a predetermined depth that defines an actual engineered roughness (Rpk) for the portion of the first outer surface; and a second pulley half having a second outer surface with a truncated conical shape that faces the first outer surface and is axially movable toward and away from the first outer surface, a portion of the second outer surface having laser etched microgrooves therein of a predetermined depth that defines an actual engineered roughness (Rpk) for the portion of the second outer surface. 8. The pulley of claim 7 wherein the laser etched microgrooves are in a radially inner portion of the first outer surface, and the first outer surface includes a radially outer portion having mechanically formed indentations having a predetermined average surface roughness. 9. The pulley of claim 8 wherein the laser etched microgrooves are in a radially inner portion of the second outer surface, and the second outer surface includes a radially outer portion having mechanically formed indentations having a predetermined average surface roughness. 10. The pulley of claim 7 wherein the portion of the first outer surface is the entire first outer surface. 11. The pulley of claim 10 wherein the portion of the second outer surface is the entire second outer surface. 12. The pulley of claim 7 wherein first pulley half includes a chromium nitride coating on the first outer surface. 13. The pulley of claim 12 wherein second pulley half includes a chromium nitride coating on the second outer surface."
  ],
  "description_excerpt": "The present invention relates generally to a continuously variable transmission (CVT), and more particularly to the surfaces on a pulley of the CVT.\n\nSome continuously variable transmissions (CVT) use pulley assemblies with one truncated conical member that is movable relative to another truncated conical member, with a belt or chain mounted between them. The ratio of the input pulley to the output pulley is adjusted by varying the spacing between the conical members. The torque is transferred via friction between the conical members and the belt or chain.\n\nIn vehicles having engines with higher power output, the CVT needs to have a higher torque capacity. The higher torque capacity is achieved, in part, by maintaining a high frictional engagement between the belt/chain and the conical members. This must be achieved, however, while still providing adequate wear resistance of the conical surfaces to assure long term durability of the transmission. As the CVT is operated, the belt incurs micro-slippage due to torque transfer and the wrap angle difference between the primary and secondary pulleys. Over time, the micro-slippage causes a surface texture depth reduction due to mixed boundary lubrication conditions, which, with usage, may change the coefficient of friction between the belt and the pulley surface.\n\nPulleys with high surface roughness tend to have higher friction carrying capability with minimal slippage. As a result, the conical surfaces are treated to have a high average roughness (Ra).",
  "cpc": [
    "F16H 55/56",
    "B23K 26/355",
    "C23C 14/028",
    "C23C 14/0641",
    "F16H 55/38",
    "F16H 61/66272"
  ],
  "ipc": [
    "B23K 26/36",
    "F16H 55/56",
    "B23K 26/00",
    "C23C 14/02",
    "C23C 14/06"
  ],
  "assignees": [
    "GM Global Technology Operations LLC"
  ],
  "inventors": [
    "Roger L. Briggs",
    "Martin S. Kramer",
    "Ronald P. Buffa",
    "Matthew P. Werner"
  ],
  "filing_date": "2010-10-07",
  "publication_date": "2012-04-12",
  "priority_date": "2010-10-07",
  "application_number": "US-89978210-A",
  "family_id": "45872575",
  "cited_by_count": 26,
  "citations": [
    "US4781660A",
    "US7276002B2",
    "US7294077B2",
    "US20050217111A1",
    "US20080299408A1",
    "US20090045179A1"
  ]
}