Q. Why can it be used in this application and not on an automobile?

A. 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 from a straight course.

Q. What connects the wheels so they will move together?

A. 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 either 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

are not costly to build and usually form the equipment on cheap, light cars where an irreversible steering gear is not absolutely nec

essary.

Q. What is an irreversible steering gear, and how does it differ from a reversible steering arrangement?

A. The irreversible forms of steering gears are those that utilize reduction gearing that is not capable of being turned except by the handwheel and which is therefore not affected by the action of the road wheels. As previously explained the simpler forms of steering.

gear are reversible and movement of the front wheels is communicated directly to the hand lever or wheel, the constant movement of which is apt to tire the operator.

Q. Which is the best type and why?

A. The irreversible forms of steering gear, while slower acting than the simpler reversible type, are the most popular because they are the safest, the most easily handled, and the most powerful form. The wheels of the largest car fitted with an irreversible gear may be turned without difficulty by any person of average strength.

Q. Describe action of worm reduction steering gear.

A. Two forms of worm and worm gear reducing gearing are outlined at Figs. 203 and 204. They are similar in construction, except that one utilizes a complete worm gear to actuate the steering arm while the other employs a worm gear segment. The worm is carried at the lower end of the steering post, being restrained from end movement by ball thrust bearing at either side. It is keyed to the steering column so the worm must be turned with the hand wheel. The worm, as it revolves, rotates the worm gear to which the steering arm is secured and this is oscillated back and forth as the worm is turned. The motion imparted to the steering arm is transferred to the movable wheel spindles on the front axle by means of a drag link. While it is possible to turn the worm gear through the medium of the worm, the pitch of the thread on the latter is such that it is not possible to move the worm and consequently the handwheel used to operate it by moving the steering arm or wheels.

Q. What is a thread and nut steering arrangement?

A. The thread and nut steering arrangement differs from the worm type in that the end of the steering post is threaded with a coarse screw thread and pulls a nut up and down as it is rotated. As the nut is kept from turning it is apparent that it will be moved in one direction or the other and that this movement may be transferred to the steering wheels by means of a simple bell crank lever, the short arm of which is operated by the nut that works up and