CVT Description
CVT Description
CVT Mechanical Description
Continuously variable transaxle (CVT) can vary the actual gear ratio continuously and stepless from low-speed to high-speed range depending on the driving conditions. The CVT allows an improved driveability with reduced shift-shock in comparison with an existing A/T (Automatic Transaxle).
This transaxle is an electronic control fully automatic transaxle with forward continuously variable and reverse 1-speed.
The torque converter is a 3-element, 1-step and 2-phase type and is equipped with an automatically controlled lock-up mechanism.
The gear change device consists of a ravigneaux type planetary gear unit, multiple disc type clutch, multiple disc type brake, steel belt, primary pulley and secondary pulley.
The hydraulic pressure control device consists of a valve body assembly, line pressure control solenoid valve (linear solenoid), secondary pressure control solenoid valve (linear solenoid), TCC solenoid valve (linear solenoid) and lock-up / select switching solenoid valve. Optimum line pressure complying with engine torque is produced by the pressure control solenoid valves in dependence upon control signal from TCM. This makes it possible to control the line pressure with high accuracy in accordance with the engine power and running conditions to achieve smooth shifting characteristics and high efficiency.
The TCM can change the dimension between the two pulley surfaces. To continuously vary its gear ratio, the TCM simultaneously adjusts the diameter of the primary pulley that transmits torque from engine and the secondary pulley that transfers torque to the wheels. With continuously shifting of gear ratio, the CVT can avoid the shift-shock and deliver smooth driving.
Specifications
CVT Mechanical Function
Functions
Operation Table of Mechanical Components
O: Engage
x: Disengage
: Controlled
-: Not applicable
CVT Control Description
Gear Ratio Control
In order to achieve the optimum gear ratio for the driving force in accordance with the vehicle operating conditions, TCM detects vehicle conditions based on vehicle speed or input signals such as an accelerator pedal position.
TCM selects the optimum gear ratio and determines the gear change steps based on each input signal.
By outputting these command signals to the stepper motor, TCM controls the line pressure to the primary pulley, decides the adjustable pulley position of the primary pulley, and controls the gear ratio.
Lock up control:
When the vehicle speed exceeds the specified value, the TCC solenoid valve completely engages the TCC upon control signal from TCM. This control helps to improve the transaxle efficiency.
Slope shift control:
TCM distinguishes uphill or downhill according to vehicle speed, accelerator pedal position and/or brake pedal position, and controls gear ratio as follows:
- Uphill: To improve acceleration, gear ratio in the high speed range is limited.
- Downhill: To obtain effective engine brakes, gear ratio is downshifted.
Garage shift control:
If the select lever is shifted from "D" to "R" range while the vehicle is running at a specified speed or higher, TCM controls the transaxle operation and automatically shifts the transaxle to neutral in order to protect CVT inside parts from damage.
Manual mode control:
When the select lever is shifted to "M" position, or when the shift paddle switch is operated with the select lever in "D" range, TCM switches the control mode from automatic mode to manual mode, while maintaining the actual gear ratio.
In manual mode, every time the paddle-up switch, paddle-down switch, shift-up switch or shift-down switch is turned on, TCM selects the predetermined gear ratio for 1-speed to 6-speed, and performs shift up or shift down depending on the vehicle speed.
Operation Table of Solenoid Valves and Stepper Motor
NOTE:
*: This part operates at vehicle speed of 50 km/h (31 mile/h) or more.
O: Operate
x: Not operate
