8 Questions
What is the advantage of a CVT over a planetary-gear automatic transmission?
All of the above
What is the function of the pulleys in a CVT design?
To vary the gear ratio in a continuous manner
What are the direct inputs monitored by the transmission control module (TCM) of a CVT?
Transmission range sensor, input speed sensor, output speed sensor, primary pressure sensor, secondary pressure sensor, and transmission temperature sensor
What are the indirect inputs monitored by the TCM of a CVT?
PCM requests, engine output torque, brake switch, ABS status signals, charging system voltage, engine RPM, engine coolant temperature, accelerator pedal position, vehicle speed, and A/C system requests
What are the TCM outputs in a CVT?
Stepper motor, line pressure solenoid, secondary pressure solenoid, and TCC lockup solenoid
What is the function of the TCM in a CVT?
To control the drive ratio to match vehicle needs and adjust the ratio during vehicle cruise
What is the function of the secondary pulley spring in a CVT?
To force the floating side to a narrow, high-belt position, which produces an underdrive
What is needed for reverse-direction operation in a CVT?
A planetary gear set
Study Notes
- A continuously variable transmission (CVT) varies the gear ratio in a continuous manner instead of in a series of steps or fixed gear ratios.
- CVTs are more efficient than either manual or automatic transmissions while still providing the driving ease of an automatic transmission.
- CVTs offer advantages over a planetary-gear automatic transmission, such as being more compact, lighter weight, and having constant, stepless acceleration with efficient fuel use and emissions.
- CVTs have an infinite number of gear ratios between its lowest ratio and highest ratio.
- The pulleys used in CVT design can vary their width by varying the hydraulic pressure applied to them.
- The transmission control module (TCM) of a CVT uses direct and indirect inputs to monitor transmission and engine operation.
- Direct inputs include transmission range sensor, input speed sensor, output speed sensor, primary pressure sensor, secondary pressure sensor, and transmission temperature sensor.
- Indirect inputs from CAN bus include PCM requests, engine output torque, brake switch, ABS status signals, charging system voltage, engine RPM, engine coolant temperature, accelerator pedal position, vehicle speed, and A/C system requests.
- TCM outputs include stepper motor, line pressure solenoid, secondary pressure solenoid, and TCC lockup solenoid.
- The TCM controls the drive ratio to match vehicle needs and can adjust the ratio during vehicle cruise to produce the maximum fuel economy, lowest emissions, or maximum pulling power.
- CVT transmissions use predetermined stepper motor positions to mimic upshifts and downshifts.
- With no fluid pressure, the secondary pulley spring forces the floating side to a narrow, high-belt position, which produces an underdrive.
- Continued fluid flow to the primary piston changes the ratio from an underdrive/reduction through 1:1 to an overdrive.
- A planetary gear set is needed for reverse-direction operation.
- A forward clutch is mounted on the input shaft from the torque converter for forward operation.
- CVT transmissions use a low-profile elliptical torque converter with a lockup clutch.
- Measuring CVT oil pressures is similar to performing pressure testing on conventional automatic transmissions/transaxles.
- Typical pressures include mainline pressure, primary pressure, and secondary pressure.
- CVT fluid is usually green to help distinguish it from conventional ATF.
- When replacing the CVT fluid, make sure that the specified CVT fluid is used.
Test your knowledge on Continuously Variable Transmission (CVT) with this quiz! From the advantages of CVTs over other types of transmissions to the inner workings of the transmission control module (TCM), this quiz covers everything you need to know about CVTs. Enhance your understanding of CVTs with questions on the varying gear ratio, pulley design, TCM inputs and outputs, and much more. So, put your CVT knowledge to the test and take the quiz now!
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