In spite of bitter opposition, worm drive has made great strides during the past year, quite a number of makers having added worm-driven models to their line, good axles of this type being obtainable. Several of the older companies are building their own axle, amongst these being the Pierce, Packard and Locomobile companies, the former adding a two-ton model, while the latter have recently announced three-and four-ton models.
Fig. 129 will serve to illustrate the Pierce axle which is of the full-floating type, with the worm mounted above the wheel. The worm, worm wheel and spur gear differential are mounted on ball bearings and assembled as a unit with the cover. This construction permits the removal of the entire unit without disturbing the balance of the axle, as shown in the illustration. The housing is a heavy steel casting reinforced by tubes which carry the wheel bearing and extend beyond the spring seats. The emergency brakes are mounted in the rear wheels and the service brake is located back of the transmission. Thrust is taken on radius rods and the torque load on a heavy torque arm. The road wheel is driven through a squared shaft and driving flange bolted to the huh.
The worm-drive axle recently introduced by the Locomobile Company is illustrated in Fig. 130, and is also of the full-floating type. However, it differs from the above in that a bevel-gear differential is used, while the housing is divided into three parts, consisting of a center housing and two ends which are bolted together. Reinforcing tubes are also used, which carry the wheel bearings and extend to points just outside the differential bearings. The ends of these carry a series of packing washers to prevent the oil working out onto the brakes. The outer ends of the housing have spherical bearings for the radius rods, while the spring seats pivot on bronze bushings. The spring is mounted outside the frame while the radius rods are placed directly under the side frame members. The worm is mounted above the wheel and, together with the differential and bearings, forms a unit with the cover. A heavy truss rod is anchored to the housing inside the brake ilium and provided with a turnbuckle for adjustment. The wheels are mounted on Timken heavy roller bearings, while the driving unit is mounted on ball bearings and provided with suitable thrust tarings. The drive shafts are of the ten-spline type, and drive the wheels through flanges bolted to the wheel hubs. Attention might be called to the method of reducing the weight, by lightening the reinforcing tube. The inner wall of this tube tapers from the end to the center of spring neat, from this point to just inside the inner-wheel bearing where the greatest load conies.
Fig. 130. Biker Worm Drive Axle.
Fig. 131. Timken Worm Drive Axle.
The Timken David Brown axle used in a number of commercial cars is depicted in Fig. 131, being similar in const ruction to those described above, with the worm, worm wheel, differential and their bearings assembled into a unit with the cover. However, in this axle the well-known Timken I>earings are used throughout, and, owing to their ability to carry thrust loads, it is claimed no thrust bearings are necessary. To the writer's knowledge this company is the only one resorting to roller bear-ings for mounting of the worm. The flange for driving the wheels is forged integral with the drive shaft, while the general construction is along conventional lines.
Another worm-drive axle used by several commercial car builders is the Sheldon axle (Fig. 132). It is also constructed along conventional lines, having the differential and worm gear a unit. However, it is of the semi-floating type, and the housing, which is cast in one piece, is so arranged that either over or underslung springs may be used. As the axle is of the semifloating type, the housing is made of liberal proportion and the weight is carried on the drive shaft, while a ball bearing is mounted inside of the wheel which is attached and driven by means of a long taper and key. This is clearly shown in the illustrations. The features of semi-floating axles can perhaps be best described by comparing with the full-floating and three-quarter-floating types.
Fig. 132. Sheldon Worm Drive Axle Semi-Floating Type.
Fig. 133. Phantom View of Packard Worm Drive Axle.
The Packard worm-drive axle (Fig. 133) also has a three-piece housing, with the differential and driving unit mounted in a unit with the cover. The differential is spur-gear type, and the entire driving unit is mounted on ball bearings and provided with suitable thrust bearings. As in the construction described above, the worm is mounted above the wheel. The housing is massive steel construction, well ribbed to provide maximum strength. The entire construction is arranged for straight-line drive from the transmission through two universals, while the thrust is taken by radius rods and the torque by a heavy torque arm.