Spring types

At the core of every suspension system are the springs. Suspension systems utilize three types of springs-coil, leaf (both mono and multi-leaf) and torsion bar. This is the component that maintains proper riding height while absorbing all levels of shock force. If worn out or damaged, other elements of the suspension will shift out of their correct positions, subjecting them to increased wear which they are not designed for. This will severely affect the vehicle's ride and handling.

Larger, heavier vehicles require stiffer springs than a lightweight vehicle. Spring rate is classified as the amount of deflection displayed under a specific load. In reference to the law of physics, a weight or force applied to a spring will compress it proportionally to the force applied. The spring will return to its original position once the force is removed, if not overloaded.

Coil springs
See Figure 9

The most common springs used today on independent suspensions are the coil springs. The coil spring is nothing more than a steel bar that has been bent into a flexible coil. The spring absorbs shock forces by compressing in and recoiling back to its original spring height. Coil springs can be located between control arms, frame and control arms and in most strut assemblies.

Most coil springs fail due to constant overloading, excessive up and down movement or just a general breakdown due to metal fatigue.

Leaf springs
See Figure 10

Leaf springs are the first type of spring used on vehicle suspensions and are still in use today, however, they are more commonly found on light duty trucks, SUVs, vans and on some passenger vehicles (on the rear only). Two basic types of leaf spring are, mono-leaf and multi-leaf.

Mono-leaf, or single-leaf, springs are thick in the center and taper off at each end, which provides a variable spring rate for good load carrying capability as well as a good ride. Mono-leaf springs are also less noisy while producing less static friction of multi-leaf springs.

Multi-leaf springs are made up of several flat steel leaves bound together and retained with a bolt or clips. The main leaf is the one leaf that is the full length of the spring from the front mounting bushing to the rear mounting shackle. Each leaf bound to the main leaf is gradually shorter which gives the spring a tapered profile. Each leaf added to the spring assembly contributes to its stiffening ability. Because of the curved construction of the leaf spring, it is also referred to as a semi-elliptical spring.

Leaf eye at the rear of the spring leaf is secured to the vehicle frame using a shackle. The spring shackles allow some movement fore and aft in response to the physical forces on acceleration, deceleration and braking.

Torsion bar
See Figure 11

The torsion bar is a coil spring stretched out straight, and used instead of a coil spring to control wheel action. The torsion bars are attached to the chassis at one end and to the upper or lower control arm at the other end. As the control arm moves up or down in response to the road surface, it twists the torsion bar, which resists the twisting force and returns the control arm to the normal position.

The outer ends of the control arms are kept an equal distance apart by spindles, sometimes called steering knuckles which are held, in place by ball joints at the top and bottom. Ball joints permit upward and downward motion of the steering knuckle, and the turning motion required for turning corners, while keeping the steering knuckles vertical.

There are two types of manual steering in general use today. The first is called worm and sector steering, also known as re-circulating ball, while the second is called rack and pinion steering.

Recirculating ball steering
See Figures 12 and 13

In this type of steering, the end of the steering input shaft, called the worm shaft, is machined with a continuous spiral groove holding ball bearings. These ball bearings move a ball nut assembly up or down the worm shaft when the steering wheel is turned.

Since the worm shaft is coupled directly to the steering column shaft, turning the steering wheel causes the worm shaft to turn in the same direction. This action moves the ball nut assembly along its length. The balls circulate in one direction for a right-hand turn and in the other direction for a left-hand turn. Teeth on the ball nut assembly then engage teeth on the sector shaft (also called the Pitman shaft since it is connected to the Pitman arm) causing the Pitman or sector shaft to move the Pitman arm, thereby converting the rotating force of the steering wheel into the slower, higher torque rotation of the Pitman arm. The Pitman arm in turn transmits the desired directional movement to the front wheels through the steering linkage. Tubes connect the locknut/sleeve unit and allow the balls to constantly re-circulate, distributing wear evenly among them.

Rack and pinion steering
See Figure 14

This steering design uses a steering gear connected to the steering column shaft by a flexible coupling. This gear, similar in design to the pinion gear used in a differential, is cut on an angle and meshed on one side with a steel bar or rack that also has teeth cut in it. This rack is contained in the steering gearbox, which is positioned between the tie rods in the steering linkage. When the steering wheel is turned, the pinion gear operates directly on the rack, causing it to move from side to side and transmitting motion to the front wheels. This type of steering gear avoids the use of a Pitman arm and is a more direct and precise type of steering, although drivers accustomed to re-circulating ball steering occasionally find its directness disconcerting.

Power steering units are mechanical steering gear units incorporating a power assist.

Power steering for the recirculating ball type steering system consists of a pump, fluid reservoir, pressure and return hoses and steering gear. The pump, which is driven by an accessory drive belt, consists of an impeller, pressure valve, and fluid reservoir. Pump pressure builds only when the engine is running. The pump impeller turns, picking up hydraulic fluid from the reservoir and feeding it to the steering gear under pressure through the pressure line. The fluid is then returned to the fluid reservoir through the non-pressurized return line.

The power assisted rack and pinion steering system is very similar to that of the recirculating ball system in that its power cylinder and control valve are in the same housing. The power piston is part of the rack while the rack housing is the cylinder. The pinion housing contains the control valve. Rotating the steering wheel moves the control valve, directing pressure to both ends of the steering rack piston. The rack and pinion system uses a pressure hose from the power steering pump to the control valve housing, and a return line to the fluid reservoir.

Continue to Page 3 of Suspension and steering

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