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CVT System Description - Electronic Control System
Electronic Control System
Functional Diagram
The electronic control system consists of the powertrain control module (PCM), sensors, and solenoid valves. Shifting and lock-up are electronically controlled for comfortable driving under all conditions. The PCM is located in the engine compartment. The PCM receives input signals from the sensors and other control units, processes data, and outputs signals for engine control system and CVT control system. The CVT control system includes shift control, pulley pressure control, clutch pressure control, lock-up control, transmission fluid pump pressure control, and indicator control. The PCM switches the shift solenoid valves and the CVT pulley control solenoid valves to control shifting position and speed stage, and lock-up torque converter clutch. Shift Control - Pulley Pressure Control
To reduce steel belt slippage and increase steel belt life, 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 low (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 a lower hydraulic pressure works on the movable face of the drive pulley to eliminate the steel belt slippage. When the pulley ratio is high (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 a lower hydraulic pressure works on the movable face of the driven pulley to eliminate the steel belt slippage. 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 PCM activates the CVT drive pulley pressure control solenoid valve to control pulley pressure to the pulleys. The drive pulley drives the driven pulley via a steel belt at varying ratios ranging from 2.645 to 0.405 in D and 1.859 to 1.265 in R. The shift control includes the automatic shifting the pulley ratio in D for normal driving and in S for sport driving, L position control, the grade logic control that performs the uphill and downhill control during the automatic shifting in D and S positions, and the shift-hold control while driving on a winding road. Shift Control - Grade Logic Control
The grade logic control system has been adopted to control shifting in D and S. The PCM compares actual driving conditions with memorized driving conditions, based on the input from the CVT drive pulley speed sensor, the CVT speed sensor, the transmission range switch, the accelerator pedal position sensor, the throttle position sensor, the engine coolant temperature sensor, the transmission fluid temperature sensor, and the brake pedal position switch signals, to control shifting while the vehicle is ascending or descending a slope. Grade Logic Control: Ascending Control
When the PCM determines that the vehicle is climbing a hill in D and S, 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 PCM determines that the vehicle is going down a hill in D and S, 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 negotiation 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 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 PCM determines that normal driving has resumed. Clutch Pressure Control
The PCM actuates the CVT clutch pressure control solenoid valve to control the forward clutch pressure and the reverse brake pressure. When shifting into R, D, S, and L, the forward clutch pressure and reverse brake pressure regulated by the CVT clutch pressure control solenoid valve engage and disengage the clutch and reverse brake smoothly. 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
The shift solenoid valve B controls the hydraulic pressure to switch the LC shift valve and lock-up ON and OFF. 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 the LC control valve to control the volume of the lock-up. The lock-up mechanism operates in D, S, and L, at engine coolant temperatures exceeding 158 °F (70 °C). |