Continuously Variable Transmission
Introduction
A continuously variable transmission (CVT), also known as a shiftless transmission, step less transmission, pulley transmission, or, in case of motorcycles, a “twist-and-go”, is an automatic transmission that can change seamlessly through a continuous range of effective gear ratios. This contrasts with other mechanical transmissions that offer a fixed number of gear ratios. The flexibility of a CVT with suitable control may allow the input shaft to maintain a constant angular velocity even as the output speed varies.
A belt-driven design offers approximately 88% efficiency, which, while lower than that of a manual transmission, can be offset by lower production cost and by enabling the engine to run at its most efficient speed for a range of output speeds. When power is more important than economy, the ratio of the CVT can be changed to allow the engine to turn at the RPM at which it produces greatest power. This is typically higher than the RPM that achieves peak efficiency. In low-mass low-torque applications (such as motor scooters) a belt-driven CVT also offers ease of use and mechanical simplicity.
A CVT does not strictly require the presence of a clutch. Nevertheless, in some vehicles (e.g. motorcycles), a centrifugal clutch is added to facilitate a “neutral” stance, which is useful when idling or manually reversing into a parking space
CVT Basics
Unlike traditional automatic transmissions, continuously variable transmissions don’t have a gearbox with a set number of gears, which means they don’t have interlocking toothed wheels. The most common type of CVT operates on an ingenious pulley system that allows an infinite variability between highest and lowest gears with no discrete steps or shifts.
Ford freestyle duratec engine with CVT
Components of a CVT
1.A high power density belt
2.Some set of pulleys
3.Hydraulic Actuators
4.Torque Sensor
5.Microprocessor
6.Torque converter (Multilayer Clutch)
If you’re wondering why the word “gear” still appears in the explanation of a CVT, remember that, broadly speaking, a gear refers to a ratio of engine shaft speed to driveshaft speed. Although CVTs change this ratio without using a set of planetary gears, they are still described as having low and high “gears” for the sake of convention.
Next, we’ll look at the different types of CVTs: pulley-based, toroidal and hydrostatic.
Pulley-based CVTs
Photo courtesy Nissan Global
Peer into a planetary automatic transmission, and you’ll see a complex world of gears, brakes, clutches and governing devices. By comparison, a continuously variable transmission is a study in simplicity. Most CVTs only have three basic components:
- A high-power metal or rubber belt
- A variable-input “driving” pulley
- An output “driven” pulley
CVTs also have various microprocessors and sensors, but the three components described above are the key elements that enable the technology to work.
A Continuously Variable Transmission operates by varying the working diameter of the two main pulleys in the transmission.
The pulleys have V-shaped grooves on which the connecting belt is mounted. One side of the pulley is fixed; the other side is moveable, operated by a hydraulic actuator. The hydraulic actuator can increase or decrease the amount of space between the two sides of the pulley. This makes the belt to ride lower or higher along the inner walls of the pulley, depending on driving conditions, thereby changing the gear ratio. This action is infinitely variable with no “steps” in between. Thus, a CVT can maintain the engine in its optimum rpm range, in turn boosting the efficiency and gas Mileage. As explained above the two pulley widths are adjusted by oil pressure in the hydraulic actuator which responds to position of the throttle, speed, and other conditions, which are sensed by microprocessors & other sensors.
CVT Benefits
Continuously variable transmissions are becoming more popular for good reason. They boast several advantages that make them appealing both to drivers and to environmentalists. The table below describes some of the key features and benefits of CVTs
Advantages of CVTsFeatureBenefitConstant, stepless acceleration from a complete stop to cruising speedEliminates “shift shock” — makes for a smoother rideWorks to keep the car in its optimum power range regardless of how fast the car is travelingImproved fuel efficiencyResponds better to changing conditions, such as changes in throttle and speedEliminates gear hunting as a car decelerates, especially going up a hillLess power loss in a CVT than a typical automatic transmissionBetter accelerationBetter control of a gasoline engine’s speed rangeBetter control over emissionsCan incorporate automated versions of mechanical clutchesReplace inefficient fluid torque converters
Futuristic Growth of Continuously Various Transmission
Global “Continuously Variable Transmissions (CVT)” Market 2020 Research Report provides key analysis on the market status of the Continuously Variable Transmissions (CVT) manufacturers with best facts and figures, meaning, definition, SWOT analysis, expert opinions and the latest developments across the globe. The Report also calculate the market size, Continuously Variable Transmissions (CVT) Sales, Price, Revenue, Gross Margin and Market Share, cost structure and growth rate. The report considers the revenue generated from the sales of This Report and technologies by various application segments.
Short Description about Continuously Variable Transmissions (CVT) Market:
A continuously variable transmission, or CVT, is a type of automatic transmission that provides more useable power, better fuel economy and a smoother driving experience than a traditional automatic transmission.
OTHER APPLICATIONS
- Tractors just as cars have the need for a flexible system to convey power from their engine to their wheels. The C.V.T. will provide just this and at high fuel savings with low atmospheric pollution.
- Motorized Wheelchairs. Battery run, speed controlled by a rheostat. Going up a ramp slowly, causes a drop in power (when it’s most needed). C.V.T. is a form of transmission, lower speed means MORE POWER.
- Bicycles. Ever try to shift gears while pedalling uphill? Good news; the KINESIS C.V.T. will automatically select the appropriate for the situation “gear” ratio. No hassle, no trouble.
The Upside of CVT Transmission
Smooth Shifting
Improved Fuel Efficiency
Less Complexity Equals Fewer Quality Problem
The Down side CVT Transmission
