Spinning Levers - How A Transmission Works (1936)

Meet Mr. Archimedes of ancient Greece. Long ago, Archie said, give me a lever long enough and I can move the world. What Archimedes meant was that the power of a lever is practically unlimited. Today, almost everyone uses some form of lever in his daily work. The familiar can opener is a lever with a sharp cutting edge. The playground seesaw is just a simple lever too. It takes a lot of force to start a freight car moving, yet the railroad man can start the heaviest freight cars easily with a pinch bar, a powerful lever which turns the wheel. Duff luck, old boy. Here's a place where a lever comes in mighty handy. Let's take the simplest kind of lever, a rigid bar working on a fixed support called a fulcrum. One end of this lever is twice as long as the other. Let's put a 10 pound weight on this end and now we'll put half as much weight on this end. Five pounds balance 10. If we have 25 pounds to lift, we just use a longer lever. The five pounds will now balance five times as much. Let's raise the lever in the air, change its shape a little, and we have a crank. Or we can add a second lever and have a double crank. Now the short arm moves one fourth the distance, but we get four times the force. If we want continuous motion, we need more arms. Now we have levers that turn. The larger paddle wheel makes fewer turns, but it delivers more force. A paddle wheel is nothing but a never-ending series of levers. We can make the wheels stronger and lessen friction where the wheels touch each other by rounding off the edges and shaping them into teeth that will slide in and out smoothly. Now the power flows smoothly and continuously through spinning leverage of gear wheels. Gears are made in many kinds and many sizes. Little gears, big gears, worm gears, bevel gears, and even lopsided gears. Over a hundred million gears are spinning over the roads in the transmissions of our automobiles. The transmission is located right at the bottom of the gear shift lever. Let's start from scratch and put together a model of the gears that we shift in our motor car. The shaft on the left comes from the engine. The shaft on the right carries the power back to the rear wheels. To connect these two with gears, we'll need another shaft known as a counter shaft. These two gears carry the power from the engine shaft to the counter shaft and are always connected or in mesh. This gear on the drive shaft going to the wheels is free to turn around the shaft. We'll put it in mesh with another gear on the counter shaft. These gears are always in mesh and keep turning while the engine is running. To switch from one set of gears to another, our transmission needs a short shaft like this, known as a clutch sleeve. It cannot turn on the drive shaft, but it is free to slide back and forth. On the sleeve, we'll mount a large gear which we can shift back and forth to mesh with the small gear in the middle of the counter shaft. We are now in neutral. The gears that are always in mesh are turning over with the engine, but the shaft to the rear wheels is standing still. A 3,000 pound automobile takes a lot of force to start, so in low speed we get the greatest leverage by letting the smallest gear on the counter shaft turn the largest gear on the drive shaft. The engine on this model is running at a constant speed of 90 revolutions a minute. With low gears in mesh, the rear wheel is turning at 30 revolutions a minute, about a third the speed of the engine, but with three times the force. The power is going through these gears in the transmission. After we've started the car rolling, we want fast pickup, so we shift into second by sliding the sleeve backward to mesh with this gear on the shaft to the rear wheels. The wheel is now turning at 60 revolutions a minute, and the power flows through these gears. For higher speeds, we let the power go directly to the rear wheels. We shift the sleeve forward so that it meshes with the shaft from the engine. The power travels straight from the engine to the drive shaft. Now the shaft to the wheels is turning at 90 revolutions a minute, the same speed as the engine, but here's a problem. An automobile must be able to go backward as well as forward, so we add one more set of gears to reverse the shaft to the rear wheels. With the gears shifted into reverse, the power travels through the transmission in a path like this. We now have three sets of spinning levers for going forward and one for reverse. With a gear shift lever, we can shift to any set of gears we wish, but with all these spinning levers in the transmission came noise and wear. Experts could shift gears quietly by careful timing of the gear shift and the engine speeds, but most of us made plenty of noise until new engineering developments made possible a long series of improvements that followed. When we shifted gears, we got a clash because the gears were not running at the same speed. In other words, not synchronized. So engineers set to work to develop a synchronizer. The synchronizer works like a cork twisted into the top of a bottle. The cork will turn until it is so tight that the bottle turns with it. Synchro mesh works the same way. When we shift into second or high, the synchronizer brings the gears to the same speed before they come together. The drums won't let the gear shift unless they are turning at the same speed. When the gears come together, there is no clash and the shift is made quietly and easily. In the transmission of the up-to-date automobile, we have a powerful low gear to give us a strong spinning leverage in starting. A fast turning motor must set the weight of the car in motion. In second speed, we can change leverage to get going fast at the same engine speed. With the leverage of third gear, power goes directly to the rear wheels and we can go as fast as we want. Now every driver can shift gears at any time, regardless of speed. Here is a hill that will give us a real chance to see how smoothly and reliably our spinning levers work in our automobile transmission. This driver is going to let her car gain a speed of 60 miles an hour down the hill. Then she will shift into second speed and bring her car easily and safely under control before it reaches the bottom of the hill.