Found this interesting but it is a long article.......... 12inch
Some say you can't teach an old dog new tricks. But the continuously variable transmission (CVT), which
Leonardo da Vinciconceptualized more than 500 years ago and is now replacing planetary
automatic transmissionsin some automobiles, is one old dog that has definitely learned a few new tricks. Indeed, ever since the first toroidalCVT
patentwas filed in 1886, the technology has been refined and improved. Today, several car manufacturers, including General Motors,
Audi,
Hondaand
Nissan, are designing their drivetrains aroundCVTs. The different types ofCVTs: pulley-based, toroidal and hydrostatic.<h1 articlepagetitle="articlePageTitle" style="font-family: Arial, Helvetica, sans-serif; color: rgb0, 0, 0; font-weight: bold; font-size: 16px; margin-bottom: 5px; margin-top: 0px; margin-right: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; ">
</h1><h1 articlepagetitle="articlePageTitle" style="font-family: Arial, Helvetica, sans-serif; color: rgb0, 0, 0; font-weight: bold; font-size: 16px; margin-bottom: 5px; margin-top: 0px; margin-right: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; ">Pulley-basedCVTs</h1><t style="font-family: Arial, Helvetica, sans-serif; "></t><table width="200" cellpadding="3" cellspacing="0" border="0" align="right" style="font-family: Arial, Helvetica, sans-serif; "><t><tr style="font-family: Arial, Helvetica, sans-serif; "><td style="font-family: Arial, Helvetica, sans-serif; text-align: left; font-weight: normal; padding-top: 3px; padding-right: 3px; padding-bottom: 3px; padding-left: 3px; "><center style="font-family: Arial, Helvetica, sans-serif; ">
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<br style="font-family: Arial, Helvetica, sans-serif; ">Photo courtesy
Nissan Global</font><br style="font-family: Arial, Helvetica, sans-serif; "><b style="font-family: Arial, Helvetica, sans-serif; ">Pulley-basedCVT[/b]</font><br style="font-family: Arial, Helvetica, sans-serif; "></center></td></tr></t></table>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. MostCVTs only have three basic components:<ul style="list-style-: circle; font-family: Arial, Helvetica, sans-serif; margin-top: 14px; margin-right: 20px; margin-bottom: 14px; margin-left: 20px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; "><li style="font-family: Arial, Helvetica, sans-serif; margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 25px; padding-top: 0px; padding-right: 14px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; color: black; font-size: 10pt; line-height: 14pt; ">A high-power metal or rubber belt<li style="font-family: Arial, Helvetica, sans-serif; margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 25px; padding-top: 0px; padding-right: 14px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; color: black; font-size: 10pt; line-height: 14pt; ">A variable-input "driving" pulley<li style="font-family: Arial, Helvetica, sans-serif; margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 25px; padding-top: 0px; padding-right: 14px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; color: black; font-size: 10pt; line-height: 14pt; ">An output "driven" pulley[/list]CVTs also have various microprocessors and sensors, but the three components described above are the key elements that enable the technology to work.<t style="font-family: Arial, Helvetica, sans-serif; "></t><table cellpadding="3" cellspacing="0" align="center" width="400" style="font-family: Arial, Helvetica, sans-serif; "><t><tr style="font-family: Arial, Helvetica, sans-serif; "><td style="font-family: Arial, Helvetica, sans-serif; text-align: left; font-weight: normal; padding-top: 3px; padding-right: 3px; padding-bottom: 3px; padding-left: 3px; "><center style="font-family: Arial, Helvetica, sans-serif; ">
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<br style="font-family: Arial, Helvetica, sans-serif; "></center></font></td></tr></t></table>The variable-diameter pulleys are the heart of aCVT. Each pulley is made of two 20-degree cones facing each other. A belt rides in the groove between the two cones.<b style="font-family: Arial, Helvetica, sans-serif; ">V-belts[/b]are preferred if the belt is made of rubber. V-belts get their name from the fact that the belts bear a V-shaped cross section, which increases the frictional grip of the belt.When the two cones of the pulley are far apart (when the diameter increases), the belt rides lower in the groove, and the radius of the belt loop going around the pulley gets smaller. When the cones are close together (when the diameter decreases), the belt rides higher in the groove, and the radius of the belt loop going around the pulley gets larger.CVTs may use hydraulic pressure, centrifugal force or spring tension to create the force necessary to adjust the pulley halves.Variable-diameter pulleys must always come in pairs. One of the pulleys, known as the<b style="font-family: Arial, Helvetica, sans-serif; ">drive pulley[/b](or<b style="font-family: Arial, Helvetica, sans-serif; ">driving pulley[/b]), is connected to the crankshaft of the engine. The driving pulley is also called the<b style="font-family: Arial, Helvetica, sans-serif; ">input pulley[/b]because it's where the energy from the engine enters the transmission. The second pulley is called the<b style="font-family: Arial, Helvetica, sans-serif; ">driven pulley[/b]because the first pulley is turning it. As an<b style="font-family: Arial, Helvetica, sans-serif; ">output pulley[/b], the driven pulley transfers energy to the driveshaft.<t style="font-family: Arial, Helvetica, sans-serif; "></t><table cellpadding="3" cellspacing="0" align="center" width="400" style="font-family: Arial, Helvetica, sans-serif; "><t><tr style="font-family: Arial, Helvetica, sans-serif; "><td style="font-family: Arial, Helvetica, sans-serif; text-align: left; font-weight: normal; padding-top: 3px; padding-right: 3px; padding-bottom: 3px; padding-left: 3px; "><center style="font-family: Arial, Helvetica, sans-serif; ">
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<br style="font-family: Arial, Helvetica, sans-serif; "><b style="font-family: Arial, Helvetica, sans-serif; ">The distance between the center of the pulleys to where the belt makes contact in the groove is known as the pitch radius. When the pulleys are far apart, the belt rides lower and the pitch radius decreases. When the pulleys are close together, the belt rides higher and the pitch radius increases. The ratio of the pitch radius on the driving pulley to the pitch radius on the driven pulley determines the gear.[/b]</font></center></font></td></tr></t></table>When one pulley increases its radius, the other decreases its radius to keep the belt tight. As the two pulleys change their radii relative to one another, they create an infinite number of gear ratios -- from low to high and everything in between. For example, when the pitch radius is small on the driving pulley and large on the driven pulley, then the rotational speed of the driven pulley decreases, resulting in a lower “gear.” When the pitch radius is large on the driving pulley and small on the driven pulley, then the rotational speed of the driven pulley increases, resulting in a higher “gear.” Thus, in theory, aCVThas an infinite number of "gears" that it can run through at any time, at any engine or vehicle speed.The simplicity and stepless nature ofCVTs make them an ideal transmission for a variety of machines and devices, not just cars.CVTs have been used for years in power tools and drill presses. They've also been used in a variety of vehicles, including tractors, snowmobiles and motor scooters. In all of these applications, the transmissions have relied on high-density rubber belts, which can slip and stretch, thereby reducing their efficiency.The introduction of new materials makesCVTs even more reliable and efficient. One of the most important advances has been the design and development of metal belts to connect the pulleys. These flexible belts are composed of several (typically nine or 12) thin bands of steel that hold together high-strength, bow-tie-shaped pieces of metal.
Metal belts don't slip and are highly<b style="font-family: Arial, Helvetica, sans-serif; ">durable[/b], enablingCVTs to handle more engine torque. They are also<b style="font-family: Arial, Helvetica, sans-serif; ">quieter[/b]than rubber-belt-drivenCVTs
.
<h1 articlepagetitle="articlePageTitle" style="font-family: Arial, Helvetica, sans-serif; color: rgb0, 0, 0; font-weight: bold; font-size: 16px; margin-bottom: 5px; margin-top: 0px; margin-right: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; ">ToroidalCVTs</h1>Another version of theCVT-- the toroidalCVTsystem -- replaces the belts and pulleys with<b style="font-family: Arial, Helvetica, sans-serif; ">discs[/b]and<b style="font-family: Arial, Helvetica, sans-serif; ">power rollers[/b].<t style="font-family: Arial, Helvetica, sans-serif; "></t><table width="400" cellpadding="3" cellspacing="0" border="0" align="center" style="font-family: Arial, Helvetica, sans-serif; "><t><tr style="font-family: Arial, Helvetica, sans-serif; "><td style="font-family: Arial, Helvetica, sans-serif; text-align: left; font-weight: normal; padding-top: 3px; padding-right: 3px; padding-bottom: 3px; padding-left: 3px; "><center style="font-family: Arial, Helvetica, sans-serif; ">
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<br style="font-family: Arial, Helvetica, sans-serif; ">Photo courtesy
Nissan Global</font><br style="font-family: Arial, Helvetica, sans-serif; "><b style="font-family: Arial, Helvetica, sans-serif; ">Nissan Extroid toroidalCVT[/b]</font><br style="font-family: Arial, Helvetica, sans-serif; "></center></td></tr></t></table>Although such a system seems drastically different, all of the components are analogous to a belt-and-pulley system and lead to the same results -- a continuously variable transmission. Here's how it works:<ul style="list-style-: circle; font-family: Arial, Helvetica, sans-serif; margin-top: 14px; margin-right: 20px; margin-bottom: 14px; margin-left: 20px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; "><li style="font-family: Arial, Helvetica, sans-serif; margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 25px; padding-top: 0px; padding-right: 14px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; color: black; font-size: 10pt; line-height: 14pt; ">One disc connects to the engine. This is equivalent to the driving pulley.<li style="font-family: Arial, Helvetica, sans-serif; margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 25px; padding-top: 0px; padding-right: 14px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; color: black; font-size: 10pt; line-height: 14pt; ">Another disc connects to the drive shaft. This is equivalent to the driven pulley.<li style="font-family: Arial, Helvetica, sans-serif; margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 25px; padding-top: 0px; padding-right: 14px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; color: black; font-size: 10pt; line-height: 14pt; ">Rollers, or wheels, located between the discs act like the belt, transmitting power from one disc to the other.[/list]<t style="font-family: Arial, Helvetica, sans-serif; "></t><table cellpadding="3" cellspacing="0" align="center" width="400" style="font-family: Arial, Helvetica, sans-serif; "><t><tr style="font-family: Arial, Helvetica, sans-serif; "><td style="font-family: Arial, Helvetica, sans-serif; text-align: left; font-weight: normal; padding-top: 3px; padding-right: 3px; padding-bottom: 3px; padding-left: 3px; "><center style="font-family: Arial, Helvetica, sans-serif; ">
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<br style="font-family: Arial, Helvetica, sans-serif; "></center></font></td></tr></t></table>The wheels can rotate along two axes. They spin around the horizontal axis and tilt in or out around the vertical axis, which allows the wheels to touch the discs in different areas. When the wheels are in contact with the driving disc near the center, they must contact the driven disc near the rim, resulting in a reduction in speed and an increase in torque (i.e., low gear). When the wheels touch the driving disc near the rim, they must contact the driven disc near the center, resulting in an increase in speed and a decrease in torque (i.e., overdrive gear). A simple tilt of the wheels, then, incrementally changes the gear ratio, providing for smooth, nearly instantaneous ratio changes.<h1 articlepagetitle="articlePageTitle" style="font-family: Arial, Helvetica, sans-serif; color: rgb0, 0, 0; font-weight: bold; font-size: 16px; margin-bottom: 5px; margin-top: 0px; margin-right: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; ">HydrostaticCVTs</h1>Both the pulley-and-V-beltCVTand the toroidalCVTare examples of frictionalCVTs, which work by varying the radius of the contact point between two rotating objects. There is another type ofCVT, known as a hydrostaticCVT, that uses<b style="font-family: Arial, Helvetica, sans-serif; ">variable-displacement pumps[/b]to vary the fluid flow into hydrostatic motors. In this type of transmission, the rotational motion of the engine operates a hydrostatic pump on the driving side. The pump converts rotational motion into fluid flow. Then, with a hydrostatic motor located on the driven side, the fluid flow is converted back into rotational motion.<t style="font-family: Arial, Helvetica, sans-serif; "></t><table width="400" cellpadding="3" cellspacing="0" border="0" align="center" style="font-family: Arial, Helvetica, sans-serif; "><t><tr style="font-family: Arial, Helvetica, sans-serif; "><td style="font-family: Arial, Helvetica, sans-serif; text-align: left; font-weight: normal; padding-top: 3px; padding-right: 3px; padding-bottom: 3px; padding-left: 3px; "><center style="font-family: Arial, Helvetica, sans-serif; ">
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<br style="font-family: Arial, Helvetica, sans-serif; "></center></td></tr></t></table>Often, a hydrostatic transmission is combined with a<b style="font-family: Arial, Helvetica, sans-serif; ">planetary gearset[/b]and<b style="font-family: Arial, Helvetica, sans-serif; ">clutches[/b]to create a hybrid system known as a<b style="font-family: Arial, Helvetica, sans-serif; ">hydromechanical transmission[/b]. Hydromechanical transmissions transfer power from the engine to the wheels in three different modes. At a low speed, power is transmitted hydraulically, and at a high speed, power is transmitted mechanically. Between these extremes, the transmission uses both hydraulic and mechanical means to transfer power. Hydromechanical transmissions are ideal for heavy-duty applications, which is why they are common in agricultural tractors and all-terrain vehicles.CVTBenefits</font><br style="font-family: Arial, Helvetica, sans-serif; ">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 ofCVTs.<t style="font-family: Arial, Helvetica, sans-serif; "></t><table cellpadding="3" cellspacing="0" #eef4f6="#eef4f6" border="1" align="center" width="450" style="font-family: Arial, Helvetica, sans-serif; "><t><tr style="font-family: Arial, Helvetica, sans-serif; "><td colspan="2" style="font-family: Arial, Helvetica, sans-serif; text-align: left; font-weight: normal; padding-top: 3px; padding-right: 3px; padding-bottom: 3px; padding-left: 3px; "><center style="font-family: Arial, Helvetica, sans-serif; ">Advantages ofCVTs</center></font></td></tr><tr style="font-family: Arial, Helvetica, sans-serif; "><td style="font-family: Arial, Helvetica, sans-serif; text-align: left; font-weight: normal; padding-top: 3px; padding-right: 3px; padding-bottom: 3px; padding-left: 3px; "><b style="font-family: Arial, Helvetica, sans-serif; ">Feature[/b]</td><td style="font-family: Arial, Helvetica, sans-serif; text-align: left; font-weight: normal; padding-top: 3px; padding-right: 3px; padding-bottom: 3px; padding-left: 3px; "><b style="font-family: Arial, Helvetica, sans-serif; ">Benefit[/b]</td></tr><tr style="font-family: Arial, Helvetica, sans-serif; "><td style="font-family: Arial, Helvetica, sans-serif; text-align: left; font-weight: normal; padding-top: 3px; padding-right: 3px; padding-bottom: 3px; padding-left: 3px; ">Constant, stepless acceleration from a complete stop to cruising speed</td><td style="font-family: Arial, Helvetica, sans-serif; text-align: left; font-weight: normal; padding-top: 3px; padding-right: 3px; padding-bottom: 3px; padding-left: 3px; ">Eliminates "shift shock" -- makes for a smoother ride</td></tr><tr style="font-family: Arial, Helvetica, sans-serif; "><td style="font-family: Arial, Helvetica, sans-serif; text-align: left; font-weight: normal; padding-top: 3px; padding-right: 3px; padding-bottom: 3px; padding-left: 3px; ">Works to keep the car in its optimum power range regardless of how fast the car is traveling</td><td style="font-family: Arial, Helvetica, sans-serif; text-align: left; font-weight: normal; padding-top: 3px; padding-right: 3px; padding-bottom: 3px; padding-left: 3px; ">Improved
fuel efficiency</td></tr><tr style="font-family: Arial, Helvetica, sans-serif; "><td style="font-family: Arial, Helvetica, sans-serif; text-align: left; font-weight: normal; padding-top: 3px; padding-right: 3px; padding-bottom: 3px; padding-left: 3px; ">Responds better to changing conditions, such as changes in throttle and speed</td><td style="font-family: Arial, Helvetica, sans-serif; text-align: left; font-weight: normal; padding-top: 3px; padding-right: 3px; padding-bottom: 3px; padding-left: 3px; ">Eliminates gear hunting as a car decelerates, especially going up a hill</td></tr><tr style="font-family: Arial, Helvetica, sans-serif; "><td style="font-family: Arial, Helvetica, sans-serif; text-align: left; font-weight: normal; padding-top: 3px; padding-right: 3px; padding-bottom: 3px; padding-left: 3px; ">Less power loss in aCVTthan a typical automatic transmission</td><td style="font-family: Arial, Helvetica, sans-serif; text-align: left; font-weight: normal; padding-top: 3px; padding-right: 3px; padding-bottom: 3px; padding-left: 3px; ">Better acceleration</td></tr><tr style="font-family: Arial, Helvetica, sans-serif; "><td style="font-family: Arial, Helvetica, sans-serif; text-align: left; font-weight: normal; padding-top: 3px; padding-right: 3px; padding-bottom: 3px; padding-left: 3px; ">Better control of a gasoline engine's speed range</td><td style="font-family: Arial, Helvetica, sans-serif; text-align: left; font-weight: normal; padding-top: 3px; padding-right: 3px; padding-bottom: 3px; padding-left: 3px; ">Better control over emissions</td></tr><tr style="font-family: Arial, Helvetica, sans-serif; "><td style="font-family: Arial, Helvetica, sans-serif; text-align: left; font-weight: normal; padding-top: 3px; padding-right: 3px; padding-bottom: 3px; padding-left: 3px; ">Can incorporate automated versions of mechanical clutches</td><td style="font-family: Arial, Helvetica, sans-serif; text-align: left; font-weight: normal; padding-top: 3px; padding-right: 3px; padding-bottom: 3px; padding-left: 3px; ">Replace inefficient fluid torque converters</td></tr><tr style="font-family: Arial, Helvetica, sans-serif; "></tr></t></table>
When you step on the gas pedal of a car with a continuously variable transmission, you notice the difference immediately. The engine revs up toward the rpms at which it produces the most power, and then it stays there. But the car doesn't react immediately. Then, a moment later, the transmission kicks in, accelerating the car slowly, steadily and without any shifts. In theory, a car with aCVTshould reach 60 mph (100 km/hr) 25-percent faster than the same car with the same engine and a manual transmission. That's because theCVTconverts every point on the engine's operating curve to a corresponding point on its own operating curve.If you look at the power output curve for the car without aCVT, you can see this to be true. Notice that the tachometer in this situation shows the engine revving up and down with each gear change, which is recorded as a spike in the power output curve (and which the driver feels as a jolt).CVTs are equally efficient on hills. There is no "gear hunting," because theCVTcycles steplessly down to a gear ratio appropriate for the driving conditions. A conventional automatic transmission shifts back and forth trying to find the right gear, which is far less efficient.
