The Selden construction (Fig. 216) has a heavy pressure block which is grooved to take the U-shaped clips and carries a heavy coiled spring which contacts with a bracket riveted to the frame and acts as a check for excessive deflections. Two of these coiled springs are used one on each side.
The Vulcan 5-ton front springs (Fig. 217) are mounted on a seat forged integral with the front axle, and are retained by long studs which have a shoulder near their center and by a drop-forged pressure block.
The Velie 3-ton vehicles have a rear axle of round section and cast spring seats which are held in position by a heavy bolt passing through the axle. The spring leaves are held together by a center bolt which passes through the pressure block. Long box clips are used to attach the spring to its seat-, as shown in Fig. 218.
Fig. 216. Selden Spring Mounting.
On the Peerless trucks the front springs are mounted on a seat forged integral with the axle, and are retained by box clips. Fig. 219 illustrates this, and it will be noted that a coil spring is attached to the pressure block which acts as a bumper. Under excessive deflections these springs strike the bottom flange of the frame and arrest the rebound motion of the vehicle springs.
The Nash Quad also employs a spring bumper which is made of flat metal and is termed a volute spring. This is attached to a bracket fastened to the pressure block, as shown in Fig. 220.
The Garford worm-driven models have the springs mounted outside the frame and the bumper springs, which are of square section are mounted directly under the frame side. The vehicle springs are retained by U-shaped clips and a heavy pressure block,while the seat for the bumper is also retained by the clips.
This construction is shown in Fig. 221. while Fig. 222 illustrates the spring shackles and the method of connecting these to the frame.
This shackle is suspended on a very large shaft extending the full width of the frame and supported by brackets riveted to the frame.
On the Selden trucks this shaft is replaced by a steel tube which ties the brackets together but the shackle is mounted on a separate stud. In the Hotchkiss drive, when the springs form the only connection between the frame and rear axle and the drive is entirely dependent upon the main leaf of the spring, there is danger of spring breakage which will disable the vehicle. In order to overcome this disadvantage the Fulton and Garford companies provide a three-point shackle at the front end of the spring, as shown in Fig. 223. This illustrates how the main leaf is supplemented by the elongated eye in the second leaf in caring for the driving stresses, which also illustrates the method of causing the third and fourth leaves to help to assist the two main leaves in bearing the load.
Fig. 217. Method of Mounting Vulcan Five-Ton Springs.
Fig. 218. Velie Three-Ton Rear Spring Mounting.
Fig. 219. Peerless Front Spring Bumper and Integral Spring Seat.
In most cases the vehicle springs are equipped with rebound clips, the purpose of these may be explained as follows: When the road wheel strikes an obstacle in the road, the spring near it is compressed, whereby energy is stored up. Immediately after the compression has ceased the spring extends again, and if the blow was a heavy one the re-bound will carry the body far beyond its original position. This rebound has a tendency to curve the main leaf of the spring in the reverse direction, and in order to prevent any serious difficulty it is necessary to transmit this shock to several of the leaves. This is accomplished by the rebound clips which are riveted to the shortest leaf which they surround and connected over the main leaf with a bolt.
Fig. 220. Nash Quad Spring Mounting and Spring Bumper.
Fig. 221. Method of Mounting Springs on the Garford Trucks.
Fig. 222. Garford Rear Spring Shackled Construction.
Although the clips at the center of the spring tend to hold the leaves in alignment, they alone are not sufficient, and in order to prevent lateral motion of the leaves some other provision must be made. One of the most common methods is to raise a central longitudinal rib on the main leaves for a certain distance as shown in Fig. 209. The rib of one leaf enters the corresponding gutter on the next. Another plan is to provide the leaves with lips at right angles as shown in Fig. 210.
An objectionable feature of the center bolt is that it materially weakens the spring and quite often spring breakage can be traced to the weakness through the center bolt hole. For this reason the center band, which is shrunk over the leaves, is favored by a number of commercial car builders.
It is inadvisable to arrest abruptly the motion of a spring that is suddenly deflected, and for this reason bumpers or check springs, as they are sometimes termed, are used. Under execessive deflection these bumpers strike the lower flange of the frame or brackets riveted to it for this purpose. The bumpers are so proportioned that they yield under the load, producing a cushion effect the same as rubber bumpers on pleasure vehicles.