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Q. What means are provided to resist these stresses?

A. The rear axle is usually restrained from movement by a special torque tube or rod which runs from the axle to which it is rigidly secured to a suitable restraining member carried by one of the frame cross members. The torque stresses may be resisted by a torque tube as shown at Fig. 199. This member acts as a housing for the drive shaft as well as a torque tube, and owing to its length the turning force present at the differential case will be reduced ap

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Fig. 199.-Rear Axle Assembly Showing Torque. Tube and Brace Rod.. preciably at the upper end. In some driving systems the drive shaft is provided with two universal joints and is not protected by a tube or housing. Axles of the type illustrated at Fig. 200 utilize a separate torque rod which runs parallel to the driving shaft and having its center line on the same plane as that of the drive member. This torque rod is securely attached to the differential housing at the rear end and to a special carrier member adapted to be supported from one of the frame cross braces at its front end.

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Fig. 200.-Rear Axle Showing Application of Torque Rod and Radius Members to Take Braking and Driving Torque.

Q. What are functions of radius rods?

A. Radius rods or distance members are employed to keep the axle always at the same distance from the frame side, and to act as bracing members to prevent the tendency of one end of the axle to advance more than the other under certain conditions where the driving wheels encounter varying resistances. The brace rods may be of the form shown at Fig. 199 where they are attached to the front end of the torque tube or they may be separate members as shown at Fig. 200 adapted for attachment to the frame at the front end and to the axle at the back.

LESSON TWENTY-THREE

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.

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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, nd then again the turns are negotiated so slowly that the tipping effect on the average wagon is practically negligible.

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Fig. 201.-Typical Front Axle and Steering Mechanism Showing Method of Moving Wheel Supporting Spindles.

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?

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.

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