SUSPENSION SYSTEM AND INDEPENDENT SUSPENSION MECHANISM FOR

A TERRAIN VEHICLE

PREPAIRD BY-

MAYANK K PARMAR(140280711010)

VISHNU PRAJAPATI (140280711018)

ME 2nd SEM

IC ENGINE AND AUTOMOBILE

LD COLLEGE OF ENGENEERING

The automobile frame and body are mounted on the front and rear axle not directly but through the springs and shock absorbers. The assembly of parts, which perform the isolation of parts from the road shocks, may be in the forms of bounce, pitch and roll is called suspension system.

Functions of suspension system:

1. It prevents the vehicle body and frame from road shocks.

2. It gives stability of the vehicle.

3. It safeguards the passengers and goods from road shocks.

4. It gives the good road holding while driving, cornering and braking.

5. It provides comfort.

INTRODUCTION

Requirements of suspension system: 1. There should be minimum deflection.

2. It should be of low initial cost.

3. It should be of minimum weight.

4. It should have low maintenance and low operating cost.

5. It should have minimum tyre wear.

CLASSIFICATION OF THE SUSPENSION SYSTEM

Dependent suspension:- It has both right and left wheel attached to the same solid axle. When one wheel hits a bump in the road, its upward movement causes a slight tilt of the other wheel.

Independent suspension system: The independent suspension system means any arrangement that connects road wheels to the frame in which raise or fall of the wheel has no direct effect on the other wheel.

THE DEPENDENT SUSPENSION SYSTEM

The dependent suspension system is also known as solid axle, when both wheels (left and right) are mounted the same solid axle.

In this case, any movement of any wheel will be transmitted to the opposite wheel causing them to camber together.

Solid drive axles usually are used on the rear axle of many passenger cars, trucks and on the front axle in many four wheel drive vehicles

Advantages It is durable enough for heavy duty use.

It requires less number of parts for suspension and simple in construction.

Disadvantages Wheel alignment is readily maintained to minimize tire wear.

Due to more unsprung weight riding is poor.

The movement of the left and right wheels mutually influence each other so the vibration and oscillation occur easily.

Hotchkiss Suspension:

The most familiar form of the solid drive axle.

The axle is located by semi-elliptic leaf springs and is driven through a longitudinal driveshaft with universal joints at the transmis sion and axle.

The springs, mounted longitudinally, connect to the chassis at their ends with the axle attached near the midpoint.

The Hotchkiss was used widely on the rear axle of passenger cars into the 1960s, and is still used on most light and heavy

Hotchkiss rear suspension:

Four Link Suspension: In response to the shortcomings of leaf spring suspensions, the four-

link rear suspension evolved as the suspension of choice in recent decades for the larger passenger cars with solid rear-drive axles.

The lower control arms provide longitudinal control of the axle while the upper arms absorb braking/driving torques and lateral forces.

The ability to use coil springs (or air springs) in place of leaf springs provides better ride and NVH (Noise,Vibration,Harness) by the elimination of the coulomb friction characteristic of leaf springs.

Although more expensive than the leaf spring, the geometric design of the four-link allows better control of roll center location.

De Dion Suspension

It consists of a cross tube between the two driving wheels with a chassis-mounted differential and half shafts.

Axle control is provided by any of a variety of linkages from leaf springs to trailing arms.

The design also has advantages for interior space because there is no need to provide differential clearance.

One of the main disadvantages of the de Dion is the need to have a sliding tube or splined half shafts, which can add friction to the system.

THE INDEPENDENT SUSPENSION SYSTEM

The independent suspension system, allows one wheel to move upward and downward with a minimum effect on the other wheel.

Mostly of the passenger cars and light truck use independent front suspension system, because provide much more space for installing vehicle engine, allow much more displacement of wheel, better resistance in steering vibration (wobble and shimmy) as well as offer higher performance in passenger comfort.

As disadvantages of the independent suspension system can be considered the complexity of the design and manufacturing cost due to increasing number of parts.

Over the years, many types of independent suspension system have been tried to develop such as MacPherson, double wishbone, multi-link, trailing arm and swing axle.

Many of them have been discarded for different reasons, with only basic concepts, MacPherson strut, double wishbone and multi-link suspension system, have found application in many types of the vehicles

The MacPherson strut consists of a single control arm and a strut assembly (spring and shock absorber) which allows tire and wheel to move upward and downward.

The major components of the system are shown in Figure 4.a. It may be used on both the front and rear axles.

This suspension system design allows reducing number of parts, lower un-sprung mass as well as smooth driving comfort.

Figure 4 – The independent suspension system;

a) MacPherson

McPherson strut, a clever compromise that permits reasonable performance compare by low cost, but never match the performance or adjustability such as double wishbones or multi-link suspension system.

Furthermore, this type of suspension requires sufficient vertical space and a strong top mount.

The double wishbone suspension system in the USA often is called “A-arms” and “Double Wishbones” in UK. The double wishbone suspensions system are applied to luxury sedans and sports cars because their design of elastic – kinematic parts allow to provide an optimum compromise between handling and comfort.

The double wishbone used two lateral control arms to hold the wheel from tilting with suspension action (Figure 4).

The upper and lower control arms usually are with unequal length where the acronym SLA (short-long arm) gets its name.

During design of this type of suspension, it is required careful refinement of suspension geometry in order to get good performance.

There are a few advantages of the double wishbone suspension system, e.g. the primary benefit is increase negative camber as a result of the vertical motion of the upper and lower arms.

This justify to stability performance for the vehicle as the tires on the outside maintain better contact with the road surface during cornering.

Disadvantages of the double wishbone compared with MacPherson strut suspension system, becomes in the complexity of the design, production cost, increased number of parts such as joints and bearing which have negative consequences on the tire wear due consumption of bushing rubber.

The multi-link suspension system belongs to the group of the independent system. It is used on both the front and rear axles and is derived by refinement of the double wishbone.

Use three or more lateral arms and one or more longitudinal arms, which do not require to being with equal length.

GEOMETRY OF THE INDEPENDENT SUSPENSION SYSTEM

The suspension geometry

The suspension geometry is important factor during design process, which helps us to identify the vertical wheel motion and how is position of the wheel in such motion.

The suspension geometry not only dictates the path of the wheel, but also controls the forces that are transmitted between sprung and un-sprung mass.

Suspension motions; a) upward and b) downward

a) camber angle (front view) and b) kingpin inclination angle and kingpin offset (front view)

Comparison of wheel trajectoriesbetween double wishbone and multi-linksuspension system

Comparison of camber angle betweendouble wishbones and multi-link suspensionsystem

Designed suspension system provides 45% less displacement of the wheel in lateral motion. When wheel is pushed upward situation is better and provides 72.6% less displacement compared with same double wishbone suspension system,

Designed suspension system provides relatively small values of camber angel nearly to zero which influence to have better contact of the tire with road surface. This improve, is a result that suspension mechanism allow wheel respectively tyre to acts perpendicular in road surface.

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