The axle center is a drop forging with integral spring seats. These spring seats are placed as close as possible to the wheel center in order to obtain the maximum capacity. The stress, due to both the combined weight of the vehicle and its load and that due to the wheel striking an obstruction, increases from nothing at the center of the wheel to a maximum at the center of the spring seat. For this reason a minimum distance is desired. It is customary to increase the section of the axle center between the knuckles and spring seat centers, both in a vertical and horizontal plane to withstand this stress. The knuckles on this axle are also of the Elliot type, but instead of forging the spindle integral with the knuckle pivot and keying the arms to the former, these parts are forged separately and keyed together by integral keys. The pivot pin has a shoulder at one end and a nut at the other end to hold them together and the entire unit is supported by bushings and thrust washers in the fork of the axle center. The hub construction is of conventional design, employing annular ball bearings for wheel mounting.
Fig. 100 depicts the Peerless front axle, which is built along conventional lines with drop forged center, integral spring seats and Elliot type knuckles. In detail, this construction differs from those mentioned above in that the bushings for supporting the pivot pin are located in the knuckle instead of in the axle fork. Thrust washers are replaced by a ball-thrust bearing, located in the upper part of the fork. The steering arm is forged integral with the knuckle arm and attached to the knuckle by a taper and key. The steering arm being so arranged as to clear the lower surface of the center. The front wheels are mounted upon Timken roller bearings and dished, that is, the wheel spokes are set at angles with a plane perpendicular to the axis of the wheel.
Fig. 160. Peerless Front Axle.
The Timken Front Axle (Fig. 161) is used on a number of commercial cars. It has a drop forged center of I-beam section, and Elliot knuckles. The axles are arranged for either type of steering to meet the requirements of vehicle makers. However, in this case the cross steering arrangement with the tie rod and drag link located in front of the axle is shown. The knuckle and pivot pin are locked together with a bolt, so that this part is properly supported by the Timken bearing in the axle fork. Timken bearings are also used for wheel mounting.
The axles mentioned above are all arranged for right-side steering, while the Natco axle (Fig. 162) arranged for left-side fore and aft steering with the tie rod located at the rear of the axle. It is of conventional design with Elliot knuckles and pivot pin bushings located in the knuckles. This illustration shows how the center is dropped to provide the proper clearance between it and the radiator or other units which may be near it. It also shows the method of providing clearance for the tie rod and it will be noted that this is not bent to the shape of the axle, as provision must be made to compensate for the movement of the knuckle arms. This axle is an example of light truck construction, and also presents one method of driving the speedometer by gearing from the wheel.
Fig. 161. Plan and Side View of Timken Front Axle.
Fig. 162. Natco Axle Top and Side Views.
The Pierce worm-driven trucks are equipped with front axles having reversed Elliot type knuckles and fore and aft right-hand steering. The axle center is an I-beam section forging and is perfectly straight, with integral spring seats. The pivot pin bushings are located in the knuckles and so arranged that the thrust is taken by the shoulders of these bushings and a thrust washer. The pivot pin has a taper which fits into the axle center so that it can be drawn up tight by a castellated nut. The wheels are mounted on Timken roller bearings as shown in Fig. 163.
Fig. 163. Type of Front Axle used on Pierce-Arrow Worm-Driven Trucks.