CVT System Description - General Operation
General Operation
The continuously variable transmission (CVT) is an electronically controlled automatic transmission with drive and driven pulleys, steel belt, and new transmission fluid (HCF-2). The CVT provides non-stage speeds forward and non-stage speeds reverse. The entire unit is positioned in line with the engine. Transmission
The torque converter consists of a pump, a turbine, and a stator assembly in a single unit. The torque converter is connected to the engine crankshaft and turns as the engine turns. Around the outside of the torque converter is a ring gear which meshes with the starter drive gear when the engine is being started. The entire torque converter assembly serves as a flywheel, transmitting power to the transmission input shaft. The transmission has four parallel shafts: the input shaft, the drive pulley shaft, the driven pulley shaft, and the final drive shaft. The input shaft is connected to the torque converter turbine, and integrates the forward clutch on the drive pulley shaft end. 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 forward clutch. The drive pulley shaft includes the drive pulley. The input shaft is connected with the drive pulley shaft by the forward clutch hub/sun gear, and by the ring gear, the planetary pinion gears, and the sun gear. The planetary carrier is positioned between the ring gear and the sun gear, and engaged with the planetary pinion gears. The driven pulley shaft includes the driven pulley (with the park gear). The secondary drive gear is splined to the driven pulley shaft. The final drive shaft is positioned between the secondary drive gear and the final driven gear. The final drive shaft integrates the secondary driven gear and the final drive gear which serves to change the rotational direction of the drive and driven pulley shafts, because the drive pulley shaft and driven pulley shaft rotate the same direction. When the input shaft is joined with the drive pulley shaft by engaging the forward clutch or the reverse brake, the power is transmitted through the input shaft, the drive pulley shaft, and the driven pulley shaft to the final drive shaft to provide drive. Electronic Control
The electronic control system consists of the transmission control module (TCM), sensors, and solenoid valves. Shifting and lock-up are electronically controlled for comfortable driving under all conditions. The TCM is located in the engine compartment. Hydraulic Control
The hydraulic control system is controlled by the TCM, the transmission fluid pump, and the valves and the solenoid valves in the valve body. The transmission fluid pump is driven as the engine turns. The transmission fluid pump drive sprocket is connected to the torque converter housing, turns as the engine turns, and drives the transmission fluid pump driven sprocket by the transmission fluid pump drive chain. The transmission fluid pump supplies hydraulic pressure to the hydraulic circuit. Fluid from the transmission fluid pump passes to the various control valves, the drive/driven pulleys, the forward clutch, and the reverse brake. Shift Control
To shift pulley ratio, the TCM controls shift solenoid valve B, the shift solenoid valve O/P, the CVT drive pulley pressure control solenoid valve, the CVT driven pulley pressure control solenoid valve, the CVT clutch pressure control solenoid valve, and the CVT lock-up clutch control solenoid valve while receiving input signals from various sensors and switches located throughout the vehicle. The TCM actuates the CVT drive pulley pressure control solenoid valve and the CVT driven pulley pressure control solenoid valve to change drive and driven pulley pressures. The drive pulley pressure is applied to the drive pulley, and the driven pulley pressure is applied to the driven pulley, and pulley ratio is changed to their effective ratio. Lock-Up Mechanism
The lock-up mechanism of the torque converter clutch operates in D position/mode, S position/mode, and L position/mode (without paddle shifter), at transmission fluid temperature exceeding 68 °F (20 °C). The pressurized fluid is drained from the back of the torque converter through a fluid passage, causing the torque converter clutch piston to be held against the transmission fluid pump. As this takes place, the input shaft and the drive pulley shaft rotate the same as the engine crankshaft. Together with hydraulic control, the TCM optimizes the timing of the lock-up mechanism. When shift solenoid valve B is turned ON by the TCM, shift solenoid valve B pressure switches lock-up ON and OFF. The CVT lock-up clutch control solenoid valve controls the volume of lock-up. Gear Selection
The shift lever has the following positions/modes:
Starting the engine is possible only the transmission is in P or N position/mode because of a neutral-safety switch. Shift Position Indicator
The shift position indicator in the gauge control module shows which shift lever position/mode has been selected without having to look down at the console. |