With CVT Part 1
OVERVIEWThe Continuously Variable Transmission (CVT) is an electronically controlled automatic transmission with drive and driven pulleys, and a steel belt. The CVT provides non-stage speeds forward and one reverse. The entire unit is positioned in line with the engine.
Transmission
Around the outside of the flywheel is a ring gear which meshes with the starter pinion when the engine is being started. The transmission has four parallel shafts: the input shaft, the drive pulley shaft, the driven pulley shaft, and the secondary gear shaft. The input shaft is in line with the engine crankshaft. The drive pulley shaft and the driven pulley shaft consist of movable and fixed face pulleys. Both pulleys are linked by the steel belt.
The input shaft includes the sun gear. The drive pulley shaft includes the forward clutch which mounts the carrier assembly on the forward clutch drum. The carrier assembly includes the pinion gears which mesh with the sun gear and the ring gear. The ring gear has a hub-mounted reverse brake disc.
The driven pulley shaft includes the start clutch and the secondary drive gear which is integral with the park gear. The secondary gear shaft is positioned between the secondary drive gear and the final driven gear. The secondary gear shaft includes the secondary driven gear which serves to change the rotation direction, because the drive pulley shaft and the driven pulley shaft rotate the same direction. When certain combinations of planetary gears in the transmission are engaged by the clutches and the reverse brake, power is transmitted from the drive pulley shaft to the driven pulley shaft to provide [L], [S], [D], and [R].
Electronic Control
The electronic control system consists of a Transmission Control Module (TCM), sensors, three linear solenoids and an inhibitor solenoid. Shifting is electronically controlled under all conditions.
The TCM is located below the dashboard, under the kick panel on the driver's side.
Hydraulic Control
The lower valve body assembly includes the main valve body, the Pressure Low (PL) regulator valve body, the shift valve body, the start clutch control valve body, and the secondary valve body. They are positioned on the lower part of the transmission housing.
The main valve body contains the Pressure High (PH) control valve, the lubrication valve, and the Pitot regulator valve.
The secondary valve body contains the PH regulator valve, the clutch reducing valve, the start clutch valve accumulator, and the shift inhibitor valve. The PL regulator valve body contains the PL regulator valve and the PH-PL control valve which is joined to the PH-PL control linear solenoid. The inhibitor solenoid valve is bolted on the PL regulator valve body.
The shift valve body contains the shift valve and the shift control valve, which is joined to the shift control linear solenoid. The start clutch control valve body contains the start clutch control valve, which is joined to the start clutch control linear solenoid. The linear solenoids and the inhibitor solenoid are controlled by the Transmission Control Module (TCM) or Powertrain Control Module (PCM). The manual valve body which contains the manual valve and the reverse inhibitor valve, is bolted on the intermediate housing.
The Automatic Transmission Fluid (ATF) pump assembly is located on the transmission housing, and is linked with the input shaft by the sprockets and the sprocket chain. The pulleys and the clutch receive fluid from their respective feed pipes, and the reverse brake receives fluid from internal hydraulic circuit.
Shift Control Mechanism
Input from various sensors located throughout the vehicle determines which linear solenoid the Transmission Control Module (TCM) or Powertrain Control Module (PCM) will activate. Activating the shift control linear solenoid changes the shift control valve pressure, causing the shift valve to move. This pressurizes the drive pulley pressure to the drive pulley and the driven pulley pressure to the driven pulley and changes their effective pulley ratio. Activating the start clutch control linear solenoid moves the start clutch control valve. The start clutch control valve uncovers the port, providing pressure to the start clutch to engage it.
Gear Selection
The shift lever has six positions: [P] PARK, [R] REVERSE, [N] NEUTRAL, [D] DRIVE, [S] SECOND, and [L] LOW.
Starting is possible only in [P] and [N] positions through the use of a slide-type, neutral-safety switch.
Automatic Transaxle (A/T) Gear Position Indicator
The A/T gear position indicator in the instrument panel shows which gear has been selected without having to look down at the console.
CLUTCHES / REVERSE BRAKE / PLANETARY GEAR / PULLEYS
Clutches/Reverse Brake
The Continuously Variable Transmission (CVT) uses the hydraulically-actuated clutches and brake to engage or disengage the transmission gears. When hydraulic pressure is introduced into the clutch drum and the reverse brake piston cavity, the clutch piston and the reverse brake piston move. This presses the friction discs and the steel plates together, locking them so they don't slip. Power is then transmitted through the engaged clutch pack to its hub-mounted gear, and through engaged ring gear to pinion gears.
Likewise, when the hydraulic pressure is bled from the clutch pack and the reverse brake piston cavity, the piston releases the friction discs and the steel plates, and they are free to slide past each. This allows the gear to spin independently on its shaft, transmitting no power.
Start Clutch
The start clutch, which is located at the end of the driven pulley shaft, engages/disengages the secondary drive gear. The start clutch is supplied hydraulic pressure by its Automatic Transmission Fluid (ATF) feed pipes within the driven pulley shaft.
Forward Clutch
The forward clutch, which is located at the end of the drive pulley shaft, engages/disengages the sun gear. The forward clutch is supplied hydraulic pressure by its Automatic Transmission Fluid (ATF) feed pipe within the drive pulley shaft.
Reverse Brake
The reverse brake, which is located inside the intermediate housing around the ring gear, locks the ring gear in [R] position. The reverse brake discs are mounted to the ring gear and the reverse brake plates are mounted to the intermediate housing. The reverse brake is supplied hydraulic pressure by a circuit connected to the internal hydraulic circuit.
Planetary Gear
The planetary gear consists of a sun gear, a carrier assembly, and a ring gear, The sun gear is connected to the input shaft with splines. The pinion gears are mounted to the carrier which is mounted to the forward clutch drum. The sun gear inputs the engine power via the input shaft to the planetary gear, and the carrier outputs the engine power. The ring gear is only used for switching the rotation direction of the pulley shafts. In [D], [S], and [L] positions (forward range), the pinion gears don't rotate and revolve with the sun gear, so the carrier rotates. In [R] position (reverse range), the reverse brake locks the ring gear and the sun gear drives the pinion gears to rotate. The pinion gears rotate and revolve in the opposite direction from the rotation direction of the sun gear, and the carrier rotates with pinion gear revolution.
Pulleys
Each pulley consists of a movable face and a fixed face, and the effective pulley ratio changes with engine speed. The drive pulley and the driven pulley are linked by the steel belt.
To achieve a low pulley ratio, high hydraulic pressure works on the movable face of the driven pulley and reduces the effective diameter of the drive pulley, and a lower hydraulic pressure works on the movable face of the drive pulley to eliminate the steel belt slippage. To achieve a high pulley ratio, high hydraulic pressure works on the movable face of the drive pulley and reduces the effective diameter of the driven pulley, and a lower hydraulic pressure works on the movable face of the driven pulley to eliminate the steel belt slippage.