CHAPTER VIIITRANSMISSION, OR CHANGE SPEED GEARS

Owing to the peculiar character of Internal Combustion Engines, there is always a certain speed at which it will work more satisfactorily, and with greater economy.

In this respect it is unlike the steam engine, which has a much wider range of effectiveness. Since all cars now use internal combustion motors, and throttling is unsatisfactory, as a means of controlling the engine, or changing the speed and power, so as to use it economically, a mechanical speed change system is essential.

This contains certain gears, which are designed to change the speed of the transmission shaft relative to the engine shaft.

Transmission Leverage.—It is simply using leverage in order to produce a more effective pull, or to attain greater speed, from a shaft which runs at a certain number of revolutions.

If we have a motor with a shaft speed of, say, 800 revolutions per minute, and an axle with aspeed of 400 revolutions, the ratio would be 2 to 1. Now, to speed up the machine, so that the axle will turn 800 revolutions, would require an engine speed of 1600, which might be impossible.

Fig. 42. Progressive Transmission. Low.

Economy of Transmission Gearing.—From an economical standpoint, also, it would be undesirable, even though the engine should be able to make the speed.

Owing to the explosion impulses of the gasoline motor, a heavy fly wheel is necessary on the engine shaft, in order to store up power by momentum, and also to give a uniform speed.

In hill climbing, or in carrying heavy loads,the transmission shaft must have its speed cut down, while permitting the engine to run at full or normal speed.

Fig. 43. Neutral Position.

The transmission gearing is, therefore, the most satisfactory solution of the problem, because changing the engine speed destroys its effectiveness, and we shall, therefore, consider some of the types for that purpose.

There are two distinct systems of transmission, namely: The Positive, and the Frictional. Of the positive system we have the planetary and the sliding gear types. The sliding gear type has two methods of control, one known as theprogressive, and the other theselective.

Characteristics of Transmission.—The progressive, selective and planetary types, are entirely different from the frictional system, for the reason that they effect the changes by step movements, the speeds being produced at certain ratios, whereas the frictional method has indefinite and infinite ratios.

Fig. 44. Intermediate.

The following diagrams will clearly bring out the distinctive features of each. Fig. 42 shows a shaft A, which derives power from the engine, having in line with it a shaft B, which connects with the driven shaft. The shaft B is squared, but it has a round end C, which is socketed axially within the head of the shaft A.

The Progressive.—The head D has a small pinion E, and on its side is provided with projecting teeth F. The loosely-revolving squared shaft B has thereon a pair of spur gear G H, separated from each other a trifle more than the width of each gear, and they are united by an intermediate hub so they turn in unison.

Fig. 45. High.

Below the shaft B, and parallel therewith, is a shaft J, which carries a spur gear K, that is constantly in mesh with the pinion E. To the right is a smaller gear L, which is the same diameter as the gear G, with which it is adapted to mesh; and a small gear M, about one-third the diameter of the gear H, is also mounted on the right-hand endof the shaft, which meshes with the gear H, when the latter is moved to the right on its shaft B.

Behind the two gears H, M, is a shaft N, parallel with shaft J, which is so mounted that it has a longitudinal movement, and this carries a broad-faced pinion O, so that it is wide enough to engage with both of the gears H, M, when they are not in line, or in engagement with each other, as shown in Fig. 44.

This latter shaft N, is moved longitudinally by means of the reversing lever P. This lever, together with the gear-shifting lever, hereafter explained, are merely indicated in their present manner, in order to show, diagrammatically, how the gears are shifted.

Low Gear.—The gear-shifting lever Q, in Fig. 42, in this instance, shows the large gear H, moved into mesh with the gear M, so that power is transmitted from the engine shaft A, through gears E, K, shaft J, and gears M, H, to the driven shaft B.

In examining Fig. 43, it will be seen that the shifting lever I, has moved the gears G, H, so they are intermediate to the gears L, M. The mechanism is now at what is called the neutral position, which means that the engine drives only the shaft A, and the shaft J, through the gears E, K.

Intermediate Gear.—Now, when the lever is moved over another step, as in Fig. 44, the gears G L mesh together, and motion is transmitted from the gear E, to gear K, through shaft J, and gears L G, to the shaft B.

Fig. 46. Reverse.

This is called theintermediate, which in this size gears, drives the shaft at half the engine speed, or half of the speed of shaft A, for the reason that gears G L, are of the same diameter, and gears E and K are in the ratio of 1 to 2.

High Gear.—When the lever is shifted another notch, as shown in Fig. 45, the crown teeth F G, of the respective gears E G, engage, and the twoshafts A B, are locked together, thus turning the two shafts in unison. This is called direct drive, in which case the shaft B, turns with the engine.

Reversing.—When the car is not running the gears G H are always in a neutral position, as shown in Fig. 41, and in order to reverse shaft B, the lever P, is drawn back, as shown in Fig. 44, so that the small gear O, will engage with the large and the small gears H M, respectively. The result is, gear H, is reversed, and this reversal can take place only when the two gears G H are in a neutral position.

The termprogressivetakes its name from the motion of the control lever involved in changing the gears. It proceeds regularly from the lowest to the highest.

Selective Type.—The second method, theselective, enables the operator to select any speed at will, and in doing so, it is not necessary to go through the other speeds to reach the high or the low, as is the case with the progressive.

Where there are only three speeds forward, and one in reversing, this is not so material, but as the better class cars have four speeds forward, it means that in order to reachhighthe gear in a progressive system must go through two intermediate speeds.

The shaft B, Fig. 47, which connects with theengine through a clutch, has its end journaled in a driven shaft A, and a gear C is fixed to the shaft B, and provided with a recessed side. This has internal teeth to receive the teeth of a sliding gear D. Another, smaller, sliding gear E is also on the shaft.

Fig. 47. Selective Transmission. Low Gear.

Below the shafts A B is a shaft F, which carries a gear G, about half the diameter of the gear C, with which it is constantly in engagement. This shaft, further, has a gear I, the same diameter as the gear D, with which it meshes, and the shaft also carries a gear K, smaller than gear J.

Behind the gear K is an idler pinion L, in such position that it may be slid into contact with K,and the gear E, on shaft B, is also adapted to be meshed with the pinion L by sliding contact.

All the gears G I J K are keyed to the shaft F, and only the gears D E and L are capable of being shifted.

Low Gear.—Fig. 47 shows the gears E J in engagement, and the motion is, therefore, transmitted from the shaft B, through gears E J and gear G to C, thereby giving a slow speed to the driven shaft A. This is calledlowgear.

Fig. 48. Intermediate.

Intermediate Gear.—To change into the intermediate, the gear D, engages with I, Fig. 48, so that both shafts B F run at the same speed, but in opposite directions, since these two gears are of the same diameter. The selective mechanism,as hereinafter explained, shows how this may be done so that the gear E, will also be thrown out of engagement with J at the same time.

It will, of course, be understood that while the gears E J turn the shaft F in a direction opposite the shaft B, the shaft A is again reversed by the gears G C, so that both shafts A B, turn in the same direction, but the shaft A, now turns at just half the speed of shaft B, because the gear G is only half the diameter of C.

Fig. 49. High.

High Gear.—The direct drive, Fig. 49, is arranged by connecting the two shafts A B together, and this is done by means of the teeth of the wheel D, engaging with the internal teeth of the gear C, so that shaft A turns with the engine.

Reverse Gear.—The reversing engagement is brought about by putting the gears K L E into mesh with each other, as in Fig. 50, thus making the transmission from shaft B, through gears E L and K, shaft F, and back to A, through gears G C.

Fig. 50. Reverse.

A four-speed selection transmission uses four, instead of three, gears on the driving shaft, without in any way changing the principles above outlined.

Control Lever for Progressive Transmission.—A careful study of the following mechanism, taken in connection with the accompanying sketch of the change speed gear, and the relations of the several elements, will explain the method nowgenerally employed in the use of theprogressivetype.

The diagram, Fig. 51, shows the engine 1, with its shaft 2, connected directly with the shaft A of the transmission gearing. Intermediate the gear box and the engine 1, is a clutch 4, with which the foot pedal 5 is connected.

Fig. 51. Progressive Control Mechanism.

The gear box has thereon a fore and aft sliding bar 6, the forward end of which projects through the case and is pivotally connected with the change speed lever 7. The lever has a quadrant 8, alongside, with four notches therein, for the low, intermediate,and high and also for the neutral positions of the lever.

The sliding bar 6, has an arm, the fork of which spans the hub I of the gears G H, so they may be carried in either direction when the speed lever swings to and fro.

The reversing lever 10 may be connected up with a bar, similar to 6, but for convenience herein, we employ a vertical lever R, pivoted to a cross rock-shaft S. The lower end of this lever has a fork T to engage the collar of the shaft N of the idler pinion. The upper end of the lever is connected with the reversing lever 10 by a link U.

The quadrant, alongside the reversing lever, has two notches, as shown, one being designed to hold the lever in a cut-out position, whereas the other notch is to hold the lever 10 when the running gear is in action.

Operation of the Progressive Gear.—The relative arrangement of the parts gives a comprehensive idea of the mechanical ideas involved, and by referring to the description and illustrations of the gears, it will be seen how the change lever 7, in moving back one notch, from its neutral position, will throw the gear G into mesh with L, and another movement of the lever to the next notch, will cause the crown teeth on G, to engage with theteeth on gear E, and thus effect a high gear connection.

The Selector Mechanism.—This is more or less confusing to the novice, and the accompanying illustration, Fig. 52, shows a perspective view, in which some of the parts are drawn out of proportion, merely for the sake of clearness. The aim is to show principles and not details of exact mechanical construction.

Fig. 52. Selective Control Mechanism.

Selector Bars.—The two selector bars A B, are mounted in guide ways so they move longitudinallyalongside each other a limited distance. Each bar has an arm, as at C D, the end of each having a curved finger E to engage the annular grooves on the hubs of the shifting gears.

Above these bars, and at right angles thereto, is a rock-shaft F, mounted in bearings G G, so that it is longitudinally-movable a limited distance, to shift the selector lever H from one bar A to the other bar B.

Shifting Lever.—The selector I has two fore and aft slots J K, these slots being of such width that the gear shifting lever L can travel therein back and forth. Midway between the ends of the bar the intermediate wall of the selector plate has a cut-out portion as at M, so the lever may pass through.

This opening, or gate-way, is in such a position, relative to the cross lots N O, of the bars A B, that when the lever is in line with the gate-way, the slots N O are also in line, and in a neutral position, so that when a lateral motion is imparted to the lever L, and the rock-shaft F is moved longitudinally, the selector lever H will then engage with the other bar.

Speed Selectors.—The selector I, in Fig. 52, while made substantially the same in all cars, has a different order of lever movement. Each manufacturer has his own preferential type. In somecases the lever must be thrown forward in order to reverse, and in others it is drawn back.

In certain cars the lever is moved forwardly to throw the gears into first, or low, while a number of makers insist that the first movement should be to the rear.

Fig. 53. 3-Speed.Fig. 54. 3-Speed.Fig. 55. 3-Speed.Fig. 56. 4-Speed.Fig. 57. 4-Speed.Fig. 58. 4-Speed.Fig. 59. 4-Speed.Types of Speed Selectors.

Fig. 53. 3-Speed.

Fig. 54. 3-Speed.

Fig. 55. 3-Speed.

Fig. 56. 4-Speed.

Fig. 57. 4-Speed.

Fig. 58. 4-Speed.

Fig. 59. 4-Speed.

Types of Speed Selectors.

This is, really, an immaterial matter, so long as there is no standard, and each claims some distinctive feature of value for his particular choice.

3-Speed Selectors.—Figs. 53, 54 and 55 showthe 3-speed selectors, in each of which the reverse is brought about by moving the lever to the forward end of the selector. In Figs. 53 and 54 the lever slot, for reversing, is in the inside, whereas in 55 it is in the outside slot. The form 53 also has, in certain makes, the reverse at the rear end of the selector.

4-Speed Selectors.—The greatest variety is found in the 4-speed types, represented by Figs. 56, 57, 58 and 59, the almost universal plan being to place the reverse in the single side slot, as shown in Fig. 56.

Fig. 60. Control-Lever Bracket.

One of the most practicable and easily operated selectors is shown in Fig. 60, which is used on the Jeffery car.

Controlling the Selector.—It will be seen, on examination of the selector, that if, in starting,the lever is at its neutral position, as it should be, and it is moved inwardly the distance of about an inch, it will be in position where it can be moved forward to thefirst speedposition.

The clutch of the car may then be disengaged gently, by pressing the foot down slowly, and at the same time pressing the accelerator with the right foot, so as to increase the speed of the motor sufficiently to take care of the load.

After the clutch engages and the car has traveled about ten feet, pressure on the accelerator is released, and the clutch pedal pulled down quickly, and the lever is then pulled straight back to thesecond speed.

Using the Clutch and Selector.—For the third and fourth speeds the same course is followed. If, in hill climbing, or in going through a heavy stretch of mud or sand, lower speed is required, the clutch is thrown out, and, if traveling on fourth speed, the control lever is quickly pulled to the rear end of the slot, and then the clutch thrown in.

If it is on third speed, the clutch is disengaged, the control lever pushed forward, at the same time pressing it inwardly so it will pass through the gate, and then pulling it back to the second speed.

Fig. 61. Planetary Transmission.

Planetary Transmission.—Fig. 61 shows the general arrangement of the planetary transmission. The disk A, carries four small planet gearsB, B, B, B, the hub C´ of which is attached to the transmission shaft. These four planet wheels mesh with and travel around a central gear C, of the same diameter this gear being attached to the engine shaft D.

E is a loosely-revolving drum, with internal teeth, to mesh with the planet wheels B. The drum E, and the disk or planet wheel carrier A, are provided with braking mechanism so that either may be slowed down or entirely stopped.

For slow speed E is stationary; for high speed A and E revolve with the gear C; and for reversing A is locked by means of the brake.

Fig. 62. Frictional Transmission.

Frictional Transmission.—A single illustration will suffice to show the principle involved inFrictionaltransmission. Fig. 62 represents a driven shaft A, which receives its power from the engine, and on which is mounted a friction wheel B, that is adapted to travel along on the shaft in front of a friction disk C, secured to the transmission shaft D.

The shaft A has a spline E, and means are provided at the end of the wheel B to draw it back and forth on the shaft, the slightest movement toward the center of the friction disk C serving to increase the speed of the driven shaft D.

Back to Index Next