There seems to be a very wide difference of opinion as to the relative merits of the various methods, and examples of each type may be found with either type of axle. The method of taking stresses on the springs, which is termed the Hotchkiss drive, has been quite popular on the lighter vehicles and at the present there seems to he a general tendency to apply it to the heavier vehicles also. The separate torque and radius rod construction is also used on a number of heavy worm-driven vehicles.
The internal gear-driven vehicles are divided between Hoteh-kiss drive and triangular members anchored to the frame cross member for taking up these stresses. The double reduction seems to favor the worm practice, as both of these methods are found, while the bevel drive seems to favor pleasure car methods.
Fig. 134 depicts the spring mounting for Hotchkiss drive, in which both torque and thrust are taken by the springs. The front ends of the springs are rigidly mounted in a heavy bracket attached to the frame, while the rear ends are shackled in the usual manner. The springs must be made with as little camber as possible, that is, the spring should be nearly flat under load, so that the driving effort is applied lengthwise of the top leaf, the direction of the effort lying within the metal instead of across a chord of the arc outside it.
Springs for Hotchkiss drive must be especially designed to take these stresses and require numerous rebound clips.
Some excellent features have been developed lately which show how the problems connected with this type of drive have been solved. Nickel steel U-bonts are used by many, while others are providing rigid anchoring of the springs to axle in various ways. As flat springs must be used, this necessitates a rigid anchorage to prevent the pressure blocks from creeping.
On the Diamond T-trucks particularly rigid anchoring of the spring to the axle is used. This is shown in Fig. 135, and consists of a special casting which is U-shaped and snugly fits the spring. On top of this casting is a special block, which is recessed to take an upward arch in the center of the top leaf of the spring. On the vertical sides of the U-casting are heavy shoulders bearing against the clips or U-bolts and so preventing displacement of these. This feature of keeping the clips at right angles to the spring leaves is an essential of this type of drive. The Winther trucks are provided with a similar arrangement, while on the Military class B trucks the spring plates are provided with spherical depressions which lock the spring plates and prevent creeping.
Fig. 134. Arrangement of Springs for Taking Torsion and Thrust. This is called the Hotchkiss Drive.
Fig. 135. Diamond T-Spring- Anchorage.
Fig. 136. Torque taken on Springs. Driving Thrust taken on Radius Rods.
Fig. 137. Triangular Torque and Radius Rods Applied to Internal Gear-Drive Axle.
Those makers who do not provide any special anchorage give special attention to have anchorage as rigid as possible with the use of a specially flat spring with heavy upper leaves. Spring seats are usually machined to the center of the spring and all points of contact are carefully white-leaded so that both air and water are kept out of the joints.
On the new G. M. C. worm-driver trucks, the springs are shackled at both ends and take the torque load, while radius rods are used to take the driving thrust as shown in Fig. 136.
Fig. 137 illustrates the method of taking these stresses on tubular rods forming a triangular construction with the rear axle. The tubes are rigidly attached to the brake supports at the rear, and form a large ball at the forward end, which is mounted in a spherical bearing on the frame cross member, directly over or under the universal joint. This construction will be found on several internal gear models.
The dotted lines in this illustration show another type of triangular torque and radius rods. However, each rod is hinged separately on each side of the universal joint to the frame cross member. This construction is used on the Studebaker and G.V. internal gear-driven vehicles and the Flint double reduction drive and others.
Separate torque and radius rods are used on the Pierce, Locomobile, Packard and other dorm-driven models, and the Menominee double-reduction drive, the latter being shown in Fig. 138. The torque rod is a pressed-steel channel-shaped member, having a ball end, which is mounted between springs in a bracket hinged to the axle and frame side rails.
On the Manly trucks, the radius rods (Fig. 139) are of peculiar construction and in addition to taking the torque and driving strains also maintain the axle in correct relation to the drive shaft, thus releasing the rear universal joint of any irregularity. Connection from the frame to the axle is made by means of a pair of rods on each side, the rods of one pair being placed above the other and pivoted at both the axle and frame ends. The driving force passes through both rods, being taken from a point under the springs and in line with the axle center to a heavy steel bracket on the frame. The tendency for the axle housing to rotate, which it is a natural result of the reaction of the wheels in driving, is resisted by these pairs of rods. This torque reaction compresses one rod and pulls on the other and because of their pivoted mounting it is impossible to place a binding strain on either rod. The upper and lower rods on each side of the chassis are not quite parallel with each other, their distances apart front and rear, being so proportioned that the rear axle itself is caused to move in a curve that would result from an ideal condition of having radius rods as long as the propeller shaft tube and having their front pivots in line with the front universal. Deflection of the rear universal is thus entirely done away with.
With bevel-drive axles there are several methods in use, which follow pleasure-car practice closely. The torque tube may either surround the drive shaft and the drive be taken through the spring and the radius rod, as in the Commerce, Vim and others, or the torque and thrust may be taken through a torque tube and radius rod hinged to the cross member, as advocated by the G.M.C. 1,500-lb. delivery car, which is illustrated in Fig. 119.
There are various arguments which can be advanced for either of these constructions, while each type seems to have its share of support amongst the manufacturers. From the writer's observations it seems to be the general tendency to let the springs perform these functions in the lighter vehicles, and to use radius and torque rods and combinations of these on the heavier models.
Fig. 138. Separate Torque and Radius Rods.
Fig. 139. Manly Method of Taking Drive and Torsional Strains.