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Q. How are springs attached to axles?

A. The method of securing semi-elliptic springs to front axles is clearly shown at Fig. 198. They are held by means of U clips which straddle the spring at its center and which bolt it firmly to spring pads formed integral with or supported by the axle. On rear axles the springs are secured to special fittings movable on the axle housing tube in the same manner

Q. Why are movable spring blocks needed at the rear axle? A. It is desirable to mount the rear spr ngs on spring blocks which are not rigidly secured to the axle, though kept from end movement by collars, because it is considered good practice to relieve the springs of all driving and braking torque stresses. When

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Fig. 198.-View of Front Axle Showing Method of Attaching SemiElliptic Spring.

the brakes are employed the tendency of car movement is to turn the axle around in the direction in which the rear wheels are moving. It is desirable to resist this tendency to turn by means of a special restraining member instead of depending upon the springs to do so. Obviously if the spring blocks were securely fastened to the axle housing tube, the tendency of axle rotation would be resisted by the springs which would have to be of heavier construction than if depended only to support the car.

Q. What is driving torque?

A. Driving torque is similar to braking torque and is a tendency the axle has to turn owing to ground resistance to rotation of the driving wheels.

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 roc's 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.

Q.

A.

wheels.

LESSON TWENTY-THREE

THE STEERING GEAR AND FRONT AXLE

How is the automobile steered?

Automobiles may be steered by simple levers or by hand

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, ..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.

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