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The Exhaust System:
Construction Of Leaf Springs & Shackles
The leaf spring is one of the oldest forms of springing and dates back to medieval times. It is usually used on rear-wheel-drive vehicles because its simplicity.
Leaf springs consist of one or more flat springs, made of tempered steel. A number of leaves of different length are used to form a multi-leaf spring and can be mounted longitudinally.
They are held together by a centre bolt that passes through a hole in the centre of each leaf. It is also used to locate the axle on the spring. The axle is then clamped to the spring by U-bolts that wrap around the axle housing, and through a spring plate underneath the spring.
Rebound clips are formed at intervals around the leaves. They prevent excessive flexing of the main leaf during rebound, and also keep the leaves in alignment.
FIGURE 24. ELLIPTIC LEAF SPRING.
It is also referred to as an elliptic spring because it has an oval shape, like a football or an egg. (Figure 24)
FIGURE 25. ELLIPTIC LAMINATED LEAF.
The spring is made stronger by adding more leaves. The spring then becomes known as an elliptic laminated (Figure 25) leaf spring.
FIGURE 26. ELLIPTIC SPRINGS.
More variations of this spring are the semielliptic (Figure 26) laminated leaf and the quarter elliptic laminated leaf.
The semielliptic laminated leaf springs are the most commonly used on modern trucks and on many passenger cars.
The semielliptic laminated leaf spring consists of several spring leaves of different lengths, a center bolt, and spring leaf clips. The spring leaves are assembled according to length, ranging from the shortest at one side to the longest at the other side of the spring.
The center bolt passes through a hole in the spring leaves and is secured with a nut. The center bolt holds the spring leaves in place, and its head is generally engaged in the spring seat to assist in axle alignment. The spring leaf clips are fitted around the spring, and each one is secured with a bolt, spacer, and nut. The clips hold the ends of the leaves together when the vehicle bounces over rough roads.
They are often called rebound clips. The ends of the first, or main, leaf are often rolled into circles that are called the spring eyes. A bushing-type bearing is pressed into each spring eye. Usually, this is a smooth brass or a bronze bushing, but sometimes it may be a rubber or threaded-steel type.
On light trucks, two semielliptic laminated leaf springs are generally used to mount each axle assembly. The ends of each spring are fastened to the vehicle frame, lengthwise to the vehicle. The axle assemblies are fastened to the springs at or near their centers. The springs hold the axle assemblies in alignment with the vehicle frame.
The shackle allows the springs to flex as the weight of the vehicle load is changed and as the vehicle travels over rough roads. Flexing of a spring causes its length to change. The flexing action of the laminated leaf-type spring is restricted by the friction of the leaves rubbing together.
Leaf springs were very common on automobiles, right up to the 1970s, when the move to front wheel drive, and more sophisticated suspension designs saw automobile manufacturers use superior coil springs instead. U.S. passenger cars used leaf springs until 1989 where the Chrysler M platform was the final production vehicle marketed. However, leaf springs are still used in heavy commercial vehicles such as vans and trucks, SUVs, and railway carriages. For heavy vehicles, they have the advantage of spreading the load more widely over the vehicle's chassis, whereas coil springs transfer it to a single point. Unlike coil springs, leaf springs also locate the rear axle, eliminating the need for trailing arms and a Panhard rod, thereby saving cost and weight in a simple live axle rear suspension.
A more modern implementation is the parabolic leaf spring. This design is characterised by fewer leaves whose thickness varies from centre to ends following a parabolic curve. In this design, inter-leaf friction is unwanted, and therefore there is only contact between the springs at the ends and at the centre where the axle is connected. Spacers prevent contact at other points. Aside from a weight saving, the main advantage of parabolic springs is their greater flexibility, which translates into vehicle ride quality that approaches that of coil springs. There is a trade-off in the form of reduced load carrying capability, however.
Spring Shackles
There are several different types of spring shackles. The bolt-type shackle has two flat sidepieces. The pins are made like bolts, with a head on one end and threads on the other end to receive a nut. It has a grease fitting and passages that permit lubrication to the center of the bearing.
In the straight, threaded-type shackle, the bearings have internal threads. Threaded pins are then screwed into each bearing. The ends of the pins are fitted into holes in the shackle sidepieces. Bolts or small pins are placed in holes in the sidepieces, engaging grooves cut in the threaded pins. This holds the sidepieces on the threaded pins.
The U-type shackle is a one-piece, U-shaped bolt that is threaded on both ends. The bearings are threaded both internally and externally. To assemble the U-type shackle, the shackle must first be placed inside the bearing bores of the spring and spring hanger. The threaded bearing is then screwed into the bearing bore and onto the shackle at the same time.
The pin-and-bolt-type shackle usually has a one-piece shackle that resembles the letter "H." The shackle is fastened to the spring and spring hanger by straight pins. The pins are locked in place by bolts as on the straight, threaded-type shackle.
The center-bolt-type shackle consists of two sidepieces, a center bolt, and two threaded pins tapered on their ends. The bearings are threaded on the inside to receive the threaded pins. The shackle sidepieces have tapered holes that fit over the tapered ends of the pins. The center bolt passes through the sidepieces and holds them tight on the tapers. In a variation of this shackle, the pins have a threaded portion extending beyond the tapers. Nuts and washers are then used to secure the sidepieces instead of the center bolt.
The single-piece link shackle has a one-piece U-shaped shackle that forms both sidepieces. Bolt-type pins secure the shackle to the spring and spring hanger.
The Y-shackle is a one-piece shackle that has the shape of the letter "Y." One of the bearings is contained in the shackle itself. |
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1. Suspension System
2. Principles Of Suspension Systems
3. Frame Construction
4. Types of Suspension Systems
6. Coil Springs
7. Torsion Bar Suspension
8. Auxilary Spring Suspension
9. Variable-load Spring Arrangement
10. Bogie-Type Suspension
11. Shock Absorber Introduction
12. Hydraulic Shock Absorber Operation
13. Direct Acting Shock Absorber
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