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THE STEERING GEAR AND FRONT AXLE
Q. How is the automobile steered?
A. Automobiles may be steered by simple levers or by hand wheels.
Q. What is the simplest method ?
A. The simplest forms of steering connection are the direct tiller or lever steering gears actuating the front wheels by direct connecting rods. These lever or tiller steering gears are used at the present time only on electric automobiles, though they were formerly used extensively on all classes of motor vehicles.
Q. How does an automobile front axle differ from that of a horse drawn vehicle?
A. The front axle of a carriage or wagon is a one-piece member, having the wheels revolving on its ends and adapted to swing around a central pivotal point so that the entire axle is moved when it is desired to turn. The axle of an automobile is not movable but the wheels are mounted on independent supporting members so they may be set at an angle when it is desired to direct the automobile in any
other than a straight course. Q. Why is it not advisable to use a movable axle on an automobile?
A. The movable form of axle such as used in carriages and other horse drawn vehicles is well adapted for this purpose because it can be easily swung around by the animals furnishing the motive power. If used on an automobile it would require considerable effort to turn the axle and it would be very difficult to swing the entire axle of a heavily loaded car around if the wheels were in ruts. Another disadvantage of the movable axle would be a loss of stability if attempt was made to turn a corner at even moderate speed.
In a horse drawn vehicle the weight of the animal between the shafts prevents the conveyance from tipping over even if a very short corner is turned, and then again the turns are negotiated so slowly that the tipping effect on the average wagon is practically negligible.
Q. What class of self-propelled vehicle uses a one-piece axle to some extent?
A. One-piece front axles for steering are sometimes applied to steam and gas traction engines, of which the road roller ordinarily used is the most common example. To steer vehicles of this nature the entire front axle is swung around by means of chains attached to the ends of the axle near the wheel hubs and to some form of reduction gear operated by a hand wheel at the other end so that the operator may move the front axle under its heavy load without expenditure of undue energy.
Q. Why can it be used in this application and not on an automobile?
As the maximum speed of traction engines is seldom over four miles an hour, the operator has ample time to make a turn and half a dozen or more turns of the handwheel may be used to describe a circle of very large radius. The steering system of the motor car is much more sensitive than that of a traction engine and on account of the higher speeds possible it is imperative that the steering arrangement be such that it will operate immediately and surely. It would not be possible for the average motorist to handle an automobile effectively at even moderate speeds if it was necessary to swing the entire axle as in a road ro ler or wagon.
Q. How are the wheels moved to steer an automobile?
A. A typical front axle and steering gear arrangement is shown at Fig. 201. The handwheel, which is carried at the end of the steering column, operates the steering arm at the lower end which in turn moves one of the steering knuckles which carries a spindle on which the wheel revolves. The steering spindles at opposite ends of the axle are actuated by a common member so they oscillate in unison, and assume correct angles for diverting the vehicle om a straight course.
Q. What connects the wheels so they will move together?
À. As will be seen by referring to Figs. 201 and 202 the wheel spindles carried in the steering yokes have arms projecting from them at approximately right angles which are joined together by a piece of tubing or rod known as the "tie-bar." Obviously moving one of the wheel spindles must produce a corresponding movement of the other.
Q. What connects the wheels with the steering gear?
A. The steering arm, carried by one of the steering knuckles, is joined to the corresponding member of the steering gear by means of a rod which is called a drag link when it is approximately parallel to the axle as shown at Fig. 202 and sometimes the "fore and aft" rod when installed as shown at Fig. 201 where it is approximately parallel to the frame side member.
Q. What is the main disadvantage of the direct leverage system of steering?
A. The method of moving the front wheels by simple lever connections with a tiller or steering bar operated by the hand offers a disadvantage that it is only suitable for slow moving vehicles on account of the amount of power needed to turn the wheels of even a medium weight conveyance.
The direct leverage system of steering is known as a "reversible” steering gear because it is possible to move the hand lever by moving the wheels. This means that every obstacle or inequality of the highway surface that will produce a movement of the steering wheel will also produce a corresponding movement of the hand lever which must be resisted by the person steering.
Q. What is the advantage of gear reduction between hand wheel and steering arm going to the front axle? A.
The use of a hand wheel, instead of a lever, makes for easier handling and the reduction gearing carried at the bottom of the steering post in most cases enables the operator to turn the wheel of even the heaviest automobile without using all his strength. Steering gears may be either of the reversible or irreversible type, the latter being the most common.
Q. Describe simplest form of geared steering arrangement?
A. The simplest form of geared steering arrangement consists of cither a spur or bevel pinion carried at the end of the steering post meshing with a suitable spur rack or beveled sector which has two or three times the number of teeth provided on the pinion that actuates it. This means that it will be necessary to turn the handwheel two or three times in order to obtain a full movement of the rack or sector to which the steering arm is attached, which produces the complete movement of the steering wheels from one maximum position to the other.
Q. What are the advantages of spur or bevel rack and pinion steering gears and on what classes of cars are they used?
A. The main advantage of the simple form of steering gear is that they are easily operated and not likely to get out of order. They