Simple
The simplest transmissions, often called gearboxes to reflect their simplicity (although complex systems are also called gearboxes in the vernacular), provide gear reduction (or, more rarely, an increase in speed), sometimes in conjunction with a right-angle change in direction of the shaft (typically in helicopters, see picture). These are often used on PTO-powered agricultural equipment, since the axial PTO shaft is at odds with the usual need for the driven shaft, which is either vertical (as with rotary mowers), or horizontally extending from one side of the implement to another (as with manure spreaders, flail mowers, and forage wagons). More complex equipment, such as silage choppers and snowblowers, have drives with outputs in more than one direction.
The gearbox in a wind turbine converts the slow, high-torque rotation of the turbine into much faster rotation of the electrical generator. These are much larger and more complicated than the PTO gearboxes in farm equipment. They weigh several tons and typically contain three stages to achieve an overall gear ratio from 40:1 to over 100:1, depending on the size of the turbine. (For aerodynamic and structural reasons, larger turbines have to turn more slowly, but the generators all have to rotate at similar speeds of several thousand rpm.) The first stage of the gearbox is usually a planetary gear, for compactness, and to distribute the enormous torque of the turbine over more teeth of the low-speed shaft. Durability of these gearboxes has been a serious problem for a long time.
Regardless of where they are used, these simple transmissions all share an important feature: the gear ratio cannot be changed during use. It is fixed at the time the transmission is constructed.
For transmission types that overcome this issue, see Continuously Variable Transmission, also known as CVT.
Read more about this topic: Transmission (mechanics)
Famous quotes containing the word simple:
“A Bartas can do what a Bartas will
But simple I according to my skill.”
—Anne Bradstreet (c. 1612–1672)
“Meantime the education of the general mind never stops. The reveries of the true and simple are prophetic. What the tender poetic youth dreams, and prays, and paints today, but shuns the ridicule of saying aloud, shall presently be the resolutions of public bodies, then shall be carried as grievance and bill of rights through conflict and war, and then shall be triumphant law and establishment for a hundred years, until it gives place, in turn, to new prayers and pictures.”
—Ralph Waldo Emerson (1803–1882)
“a mind
That nobleness made simple as a fire,
With beauty like a tightened bow,”
—William Butler Yeats (1865–1939)