| OCR Text |
Show AtdomorMe SimpUfizd By an Automobile Expert If there Is anything not clear to you, ask the automobile editor about it. An answer wili be published on the completion of the articles pertaining to ' each section under discussion. LESSON NO. -13. The Transmission. When the designer of a a automobile lis d--:.-:Ued ur"'U inn sizo of Lh engine, ho must consider wiiat the engine must d'f. Let i in bne.l'ly look into this. Wh-n ti:e ear ib driven a'ung a lev.-! p"a! I::" eiis'iiife must overcome the friction fric-tion oi trifj b-.-ariji.s in t;. ear, and the nraifatarjet; of tiie wind. Fur this parpose an urir'Hie f a certain bore and turning power ana which wit! give a certain minimum mini-mum t-peed will bint. When the ear la ascending a hill Vn engim will have, to overcome the friction and wind rei ranee as be lore, hut. also, it will havj to lift the ca : from the loner to i i io higher ievr.i. So an engine I of muh lurypr turning power, and, therefore, there-fore, hoi e, wiil be necessary than for running on the levot. Have you ever watched men pushing an auto, or w;r.;ori. u bout? It may require Che full strength of three men to si art it niovi ug, but as .oou as It is In mot ion, one man will let go, and when tue ear bus some ptd the second man will let co and the third uill be able to keep the e;i i- in motion witii com pa rati vely little effort. Thus, a more powerful engine e.ill bo neeossary for starting the car Uihn for keeping it goinL'. Ho we fi nil that a mui-h greater turning turn-ing .ower is required from the engine when the ear is climbing a hill, or when it is being started into motion. The car must be able to ascend hills 1 " giving a total leverage of 3 1-3 times 3, or lv. Let us, therefore, itiake the gear B si nailer in diameter, say only S l-Z times that of the shaft E. Then let us eon-vert eon-vert E into a gear, and then let us move fie shaft cormeetHil to the i-rope'-Ier shaft to the posi tion shown by H. Fig. o." l?y now placip a gear. J. having a diameter J times that of the n;,ai't H, and dilving tliis gear by tiie gear LI, we will have two of small gears, one giving a leverage uf to 1 and the other of ii'n to 1, or a total of io. Tnus. if looo pounds is required at tiie cireumforenee of H, only ZjZ 1-3 pounds will be required at K, the circoniferer.ee of the gear J, and as the gear B is 3 1-3 the diameter of the g-ar E, it will have a leverage of '' 1-3 to 1 and only ln0 pounds will be r-,iuiied at the point T, which is the pressure required from the i engine as before. i I laving the gears placed as fhown rowans three shafts and three sets of bearings for them. By placing the pears If and P on the same center, one set of thee bearings, and considerable room can be saved. In Fie I 1 have shown a view from the lop of the transmission a developed so far, with the gears J and P on the same center. As the gears l: and E are on the same center and revolve at the same speed they are both fastened to the same shaft. ,1 and P, however, revolve at different speeds, and so their shafts must be separate. sep-arate. In order to save a bearing bracket, brack-et, howeVer, the gear P is made hollow F'G I ) J s J and start into motion, but 90 per cent of the time it is traveling on the level. This means that If the engine is built large enough to climb the hills for 90 per cent of the time an excess weight engine en-gine will have to be carried, with the extra cost of fuel, etc., which would result re-sult therefrom. - A good designer will try to find some way of using the smaller engine, and j adding some device which will enable the engine to als take care of the hill-climbing hill-climbing and starting into motion. Placing Plac-ing a set of levers between the engine and the rear wheels will accomplish this. ! As a system, or train of gears is a system sys-tem of levers, the problem will be solved by placing sets of gears between the engine en-gine and rear wheels, or, in other words, having the power of the engine transmitted trans-mitted to the rear wheels by them. Thus we have the transmission. Let us see how the gears act as levers. Have you ever watched safe-movers move a heavy safe by tiie use of a crowbar? crow-bar? What they do is shown in Fig. 1. Here the point A Is the ground. If the distance B Is ten times as great as the distance C, a man by exerting a pressure of 100 pounds at D can exert a pressure of" 1000 pounds at E. Let us now assume that A is the center cen-ter and E the circumference of the propelled pro-pelled shaft of the automobile and that D is on the circumference of a gear B fastened to this shaft, as shown in Fig 2. If It takes a pressure of 1000 pounds on the circumference of the shaft at E to drive the car up the steepest grade, then by driving the gear B by the gear F and making the engine of such a size that a pressure of 100 pounds is exerted by the gear F on the gear B, the car will be driven up this steepest grade. The room for the transmission of the automobile is necessarily limited, and if the single gear, as shown, were used it would take up more room than can be allowed al-lowed for it. So the designer must look about for some way of using gears which will take up less room, and yet give the required leverage. The natural solution Is to have sets of gears, one set, say, to give a leverage of 3, the other xf 3 1-3, . and is attached to a tube, or sleeve, the end of the shaft of J being inserted into it so that the bearing of P also acts as one of the bearings of J. This is shown by cutting away some ofthe gear P. Consider for a moment what happens when the car is started into motion from a stand still. At first the speed is zero, then it is infinitely small, and gradually increases. Now there is a minimum speed at which the gas engine will run without stalling. So, In addition to giving giv-ing the engine a leverage for hill climbing climb-ing and for starting, an arrangement must also be made which wiU permit the engine to revolve many times faster than the rear wheels. This Is not only true when starting the car, but also in traffic, as there are times when the car must move at so slow a speed that the rear wheels will make but three or four revolutions revo-lutions in a minute, a speed far too slow for the engine. . Fortunately, a gear, in addition to giving giv-ing a leverage, will also give a change in speed. By referring to Fig 1, you will note that for one inch of movement ipf the point E there must be ten inches -of movement of the point D. From this you can see how the gear P, Fig. 3, if it were the same diameter as the shaft H would have to make ten revolutions to one for H. While this speed ratio Is good In traffic and for starting, it will not do for the average car speeds, and as the car is traveling at this average speed for about 90 per cent of the time, it will not be enough, and there must be additional sets in the transmission, one for the level running, one for steep hills and generally still another for medium hills; or, in other words, a first speed, of high leverage lever-age and great engine speed ; a second speed of a lesser leverage and lesser engine en-gine speed, and a third for the level running. run-ning. These sets of gears must also be arranged so that the operator can choose the one which he desires to use. How these different sets of gears are combined, and how the driving of the car backward is accomplished, will be explained ex-plained in the next lesson. Readers are advised to save this article. |
