Continuously variable transmission system

  • a continuously variable transmission system (CVT) is the type of transmission system to transmit power from crankshaft to drive axle through belt drive.
  • It transmit the power steplessly do an infinite number of effective gear ratios through primary and secondary sheave assembly.

1. Transmission operation (power transmission path)

  • crankshaft power is transmitted via V belt from the primary to secondary side.
  • Big clutch weight is pushed against the clutch housing above the set revolutions.
  • The power transmitted to the clutch housing reaches devil shaft after being reduced in speed in two stages through the drive shaft.

2. CVT operations

a. Engine off

  • when the engine is off the primary sheave is that the minimum diameter position.

b. Engine idling

  • when the engine speed is at idle, power is transmitted from primary sheave, V belt, add secondary shift to the clutch carrier.
  • At this moment power is not transmitted to the clutch housing because the centrifugal force of the clutch carrier is weaker than tension of clutch springs, does the clutch carrier (shoe) does not come into contact with clutch housing.

c. Starting out

  • when the engine speed reaches approximately 3000 RPM, the centrifugal force of the clutch carrier becomes stronger than the tension of clutch springs. This causes the clutch carrier (shoe) to come into contact with the clutch housing and to initiate frictional forces (transmission torque).
  • when this occurs, The V belt moves outward on primary sheave increase the diameter and moves on secondary sheave to decrease the diameter.
  • with also, the reduction ratio is maximized and sufficient Dr. force is transmitted to the rear wheel.

d. Medium speed operation

  • As engine speed increases, the primary sheave weight is moved outward centrifugal force. The primary sheave weight pushes the primary sliding sheave towards the primary fixed sheave, which forces the V belt towards the outer perimeter of the primary sheave.
  • When this occurs, the diameter of the V belt increases add the primary sheave.
  • As the diameter of the belt increases, the belt is pulled at the secondary sheave because the length of the belt is constant.
  • As a result, the belt is pushed toward the inner diameter of the secondary sheave until the tension of the V belt and clutch spring or balanced.
  • When this occurs, the diameter of the V belt is decreased at the secondary sheave and the reduction ratio gradually decreases and the speed of the secondary sheave gradually increases.

e. High speed operation

  • As engine speed increases from medium speed operation, the primary sheave date moves further outward, the primary sliding sheave is pushed closer two words the primary fixed sheave, and V belt is forced further outward to word the perimeter of the primary sheave.
  • add the secondary sheave The V belt is forced further inward and, as a result the reduction ratio is minimized. 

Torque cam operation

  •  This torque cam is called a "torque sensor" as well. it is a device that causes the sliding sheave to automatically operate to shift to low when high torque is required ( due to larger rear wheel road) as in uphill ride or in acceleration.