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CVT System Description - Electronic Control System
CVT Control System Component Location
For locations of each component on vehicle, refer to Component Location Index.
Electronic Control System
Functional Diagram
The electronic control system consists of the TCM or the PCM, sensors, switches, and solenoid valves. Shifting and lock-up are electronically controlled for comfortable driving under all conditions. The TCM or the PCM receives input signals from the sensors and the other control units, processes data, and outputs signals for the engine control system and the CVT control system. The CVT control system includes the shift control, the pulley pressure control, the clutch pressure control, the lock-up control, the transmission fluid pump pressure control, and the indicator control. The TCM or the PCM switches the shift solenoid valves and the CVT pulley control solenoid valves to control shifting position and lock-up torque converter clutch.  Shift Control/Pulley Pressure Control
To reduce the steel belt slippage and increase the steel belt life, the TCM or the PCM calculates signals from sensors and switches, and actuates the pulley pressure control solenoid valves to maintain optimum pulley pressure. When the pulley ratio is high (low vehicle speed), high hydraulic pressure works on the movable face of the driven pulley and reduces the effective diameter of the drive pulley, and lower hydraulic pressure works on the movable face of the drive pulley to eliminate the steel belt slippage. When the pulley ratio is low (high vehicle speed), high hydraulic pressure works on the movable face of the drive pulley and reduces the effective diameter of the driven pulley, and lower hydraulic pressure works on the movable face of the driven pulley to eliminate the steel belt slippage. The TCM or the PCM compares actual driving conditions with programmed driving conditions to control shifting, and it instantly determines a drive pulley ratio from various signals sent from sensors and switches. The TCM or the PCM activates the CVT drive pulley pressure control solenoid valve and the CVT driven pulley pressure control solenoid valve to control pulley pressure to the pulleys. The shift control includes the grade logic control and the shift-hold control.  Shift Control - Grade Logic Control
The grade logic control system has been adopted to control shifting in D position/mode and S position/mode. The TCM or the PCM compares actual driving conditions with memorized driving conditions, based on the input signal from the various sensors and switches, to control shifting while the vehicle is ascending or descending a slope.  Grade Logic Control: Ascending Control
When the TCM or the PCM determines that the vehicle is climbing a hill in D position/mode or S position/mode, the system selects the most suitable shift schedule according to the magnitude of a gradient, so the vehicle can run smooth and have more power when needed.  Grade Logic Control: Descending Control
When the TCM or the PCM determines that the vehicle is going down a hill in D position/mode or S position/mode, the system selects the most suitable shift schedule according to the magnitude of a gradient, so the vehicle can run smooth in combination with engine braking.  Shift-Hold Control
When negotiating winding roads, the throttle is suddenly released and the brakes are applied, as is the case when decelerating at the entrance of a corner, Shift-Hold Control keeps the transmission in its current (lower) ratio as it negotiates the corner and accelerates out. When the vehicle is driven aggressively on a winding road, the TCM or the PCM will keep the engine speed on a higher-than-normal setting, so the vehicle can run smooth and have more power. The transmission will resume the normal setting after the TCM or the PCM determines that normal driving has resumed. Clutch Pressure Control
The TCM or the PCM actuates the CVT clutch pressure control solenoid valve to control the forward clutch pressure and the reverse brake pressure. When the transmission is in-gear, the forward clutch pressure and the reverse brake pressure regulated by the CVT clutch pressure control solenoid valve engage and disengage the forward clutch and the reverse brake smoothly. The TCM or the PCM receives input signals from the various sensors and switches, processes data, and outputs current to the CVT clutch pressure control solenoid valve.  Lock-Up Control
Shift solenoid valve B controls hydraulic pressure to lock-up ON and OFF. The TCM or the PCM actuates shift solenoid valve B and the CVT lock-up clutch control solenoid valve to start lock-up. The CVT lock-up clutch control solenoid valve applies and regulates hydraulic pressure to control the volume of the lock-up. The lock-up mechanism operates in D position/mode, S position/mode, at transmission fluid temperature exceeding 68 °F (20 °C).  | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||