Module 9 Inspecting Road-Holding Systems 2 60 Hours



 Module 9 Inspecting Road-Holding Systems 2/ 60 Hours

Information for educational purposes only

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CDX Fundamentals of Automotive Technology Second Edition (Van Gelder)

Chapter 6 CEMEQ book 9 page 6.1 to 6.5
Purpose of the suspension: is to ensure permanent contact between the tires and the road. To do so , the suspension has to counteract the vehicle's body motion caused by acceleration, braking, turning, and the effects of wind.

It also helps to absorb wheel wobbles caused by road surface irregularities.But did you know that the suspension also maintains the body of the vehicle at a relatively constant height above the ground to prevent it from rocking. rolling and tilting.

CDX Fundamentals of Automotive Technology Second Edition (Van Gelder) Chapter 40 page 963:
The suspension system of a vehicle is designed to follow the road surface for the purpose of maintaining traction and control of the vehicle while also providing a smooth ride for the passengers. It is composed of a network of springs, arms, struts, and shocks that work together to achieve these purposes.

 The height of the vehicle above road level is defined by two parameters: riding height(or ground clearance) and attitude. Riding height is the clear height between the ground and specific points of a vehicle when immobilized.

These particular pints and measuring methods(direct or indirect measures) vary from one manufacturer to the next. As you'll see when learning to verify the condition of the suspension, measuring riding height (ground clearance) is the first test to verify the suspension's integrity. Attitude refers to the position of the vehicle in relationship to the road under various driving conditions: e.g. while turning, driving straight, braking, while loaded, while accelerating, and so on.While a vehicle is in motion, its attitude varies according to its speed and aerodynamic profile. The suspension aims at reducing variations in attitude.
Absorbing wheel wobbles and reducing body roll simultaneously improves stability, road handling, and passenger comfort.
Body Roll
To understand body roll, visualize the vehicle as having three axes: the transverse axis, the longitudinal axis, and the vertical axis. Movement around each of these axes results in pitch, roll or yaw. It's these movements that the suspension must neutralize to ensure the stability of the vehicle, namely, its capacity to keep the longitudinal axis and the transverse axis parallel to the road under all circumstances.
Pitch is an oscillating motion at the front or rear of the vehicle around the transverse axis. Sudden acceleration or braking can cause some pitching.
Roll is an oscillating motion around the longitudinal axis. It may occur when cornering or driving around bends and curves in the road.
Yaw is an alternate motion around the vertical axis. It may occur when negotiating tight bends, during a side impact collision or when losing control on a curve.

Keep in mind that the distance between the center pf the tire's tread on each side of the vehicle is called the front track or rear track. One of the roles of the suspension is to maintain a constant track, because a reduced track results in excessive roll.

A wider rear track (compared to the front) provides stability to the rear track while accelerating in a straight line. On the other hand many vehicles feature a front track slightly wider than the rear in order to reduce the effects of roll and to improve stability of the vehicle.

CEMEQ book 9 page 6.3
Vehicle Structure and Main Components of the Suspension System
The Suspension is set of parts that connect the wheels to the vehicle. However, the layout and nature of parts may differ greatly from one vehicle make to another. In spite of this diversity, suspension systems include many common elements such as springs, shock absorbers, control arms, and so on.

In addition to the actual suspension parts, other components help structure vehicle stability, smooth road handling, and passenger comfort. Indeed, the vehicle's structure, wheel set and even its sears, all play a role. Because the suspension is connected directly to the structure of the vehicle, it cannot operate properly if the latter is twisted or damaged. Tire pressure and quality also have an impact on passenger comfort and road handling. For example, very hard tires relay the impression that the suspension is very stiff. As for seating,, it improves driver and passenger comfort when the seats are finely upholstered.


Unitized Body and Frame: CEMEQ book 9 page 6.4
The chassis frame or unitized body are, in fact the structure of the vehicle to which a hole host of components are connected.- including the body and the following suspension elements:

  • Shock absorbers
  • Control arms
  • Springs
Control arms

Springs
More on this topic in CEMEQ book 9 page 6.4

 CEMEQ book 9 page 6.5 

 Frame
  • Supports the body, mechanical parts, and ground connection supports components.
  • Used on bigger vehicles, such as full-size cars or pick-ups,  and trucks.
  • Provides less resistance to twisting and flexing.
  • Has a significant load capacity.
  • Is less vulnerable to rust.
Unitized Body
  • Formed by a platform welded onto a body shell which incorporates the mechanical elements of the vehicle.
  • Used on most front-wheel drive vehicles.
  • Provides increased resistance to flexing and twisting.
  • Has less road capacity(takes up less space).
  • Is more vulnerable to rust.
More information on frames in CEMEQ book 9 page 6.5 -6.7
Springs: CEMEQ book 9 page 6.8
Ensuring driver and passenger comfort, smooth road-handling, and protecting the vehicle's integrity require that any shocks to the wheels are not directly transmitted to the frame. That's why manufacturers equip their vehicles with springs to absorb the shock when the wheels drive over road irregularities. What's more, springs support the weight of the vehicle, and in some cases, determine the positioning of the wheels or convey transmission power. A spring is located at each wheel.

The total weight that the springs support, i.e. the engine, the structure of the vehicle, the passengers. and so on, is called the sprung mass or sprung weight. For its part, the unsprung mass or unsprung weight constitutes the various parts that are found under the springs such as brakes, control arms, wheels and so on. 


Springs: Coil springs are most common, but manufacturers also use other types of springs such as leaf springs, torsion bar springs, or air springs.
Coil Spring:

Pros and Cons:
Pros:

  • Weight-for weight, absorbs more energy than a leaf spring.
  • Is inexpensive.
  • Is easy to manufacture.
  • Reduces unsprung mass or weight.
  • Functions without friction.
Cons:

  • Has little impact on steering or power transmission.
  • Requires the use of levers to position wheels.
  • Must be able to absorb more energy than multiple leaf springs.
Usage:
  • Both front and rear for a wide range of automobiles and light trucks.
Suspension types:

  • Unequal length double wishbone suspension.
  • Solid axle suspension.
  • MacPherson strut suspension.

Single Leaf Spring:

 Pros and Cons
Pros

  • Made from light and rust-resistant synthetic material.
  • No friction between metal sleeves.
  • Reduces unsprung mass(weight).
Cons
  • Some liquids(corrosives, lubricating silicone solvents and de-greasers) may damage synthetic material.
  • Using a single leaf crosswise requires the presence of other elements needed for steering.
Usage

  • Installed length wise at the rear of some vans, mini vans and some high-end sports cars.
Suspension Types

  • Solid axle suspension
  • Independent suspension

Multi-leaf Spring

Pros and Cons

 Pros:

  • Limited lengthwise movement of the axle compared to the chassis because of its rigidity.
  • Has great load bearing capacity.
  • Possible to add extra leaves to increase the rigidity (strength) of the set.
Cons:

  • It is difficult to position the wheels exactly and to anticipate the reaction of the axle.
  • While driving, the uniformity of the friction between the leaves is difficult to maintain, thereby modifying one spring's rate flex as compared to the other.
  • The factors listed above contribute to uneven rotation of one wheel with regard to the other and cause slight deviations in the vehicle's path.
Usage

  • Pickups.
  • Utility vehicles.
  • Automobiles, dating to the end of the 80's.
Suspension types

  • Solid axle suspension.

Torsion Bar Spring

Pros and Cons
Pros

  • Has tight dimensions.
  • Possible the adjust riding height.
Cons

  • Lateral bars are not interchangeable(left/right).
Usage
  • Usually found on four-wheel drive vehicles, because torsion bars free up the space necessary for the half shafts of these vehicle.
Suspension Types
  • Unequal length double wishbone suspension.

Air Springs



Pros and Cons
Pros

  • Possible to adjust the attitude.
  • Possible to adjust height.
  • Possible to modify the flexibility of the spring.
Cons

  • The system is expensive to repair
  • There is a risk of damaging the suspension's components if the system is not deactivated before lift the vehicle.
  • The verification procedure for riding height is more labor-intensive in some cases.
Usage

  • High-end vehicles(automobiles, mini-vans or SUV's) equipped with an attitude adjuster or air suspension.
Suspension Type

  • Air Suspension
Coil Springs CEMEQ book 9 page 6.10
A coil spring can be differentiated by the shape of its ends and by the number of physical parameters of the active part of the spring: the diameter of the spring, the pitch, the diameter of the wire, and the free-standing height. In certain cases, the shape of the last turn of the coil spring means the spring fits in its housing.
More information on coil springs can be found in CEMEQ book 9 page 6.11 - 6.12.

 Multi-leaf springs: CEMEQ book 9 page 6.13
are made up of a number of stacked steel sleeves of decreasing length. The progressive flexibility of these types of springs is a direct result of the lengths of the auxiliary leaves. Installed at the front or rear of a vehicle, multiple leaf springs serve to limit longitudinal and transverse movements of an axle as well as absorbing any shocks, the same as any other spring.
More on the components of a leaf spring found in CEMEQ book 9 page 6.13 - 6.14

Torsion Bar Springs
This type of spring comes in the form of a cylindrical steel bar whose load capacity is determined by its length and diameter. Torsion bars feature constant rate flexibility.
More information on torsion bars in CEMEQ book 9 page 6.15

 Air Springs
are comprised of a waterproof bellow filled a compressible gas, usually air or nitrogen. They come with a piston that limits spring stroke by pushing against an internal stopper to prevent complete suspension collapse should there be a leak. As for flexibility, it results from gas compression: the more the gas is compressed, the stiffer the spring. This compression is electrically adjusted. Air springs are made from rubber.
More information on air springs in CEMEQ book 9 page 6.16 - 6.17

Silent Blocks and Bushings: CEMEQ book 9 page 6.19
Silent blocks (or suspension bushings) and bushings are of simple design, but play a key role: ensuring a flexible connection between suspension components and the structure of the vehicle.
To be continued..............








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