Tasks for the vehicle's suspension system include:AmicoNews07
The ability to steer the car while driving on the roads, especially at the corners and when braking.
appropriate reaction against forces and torques caused by acceleration or braking and lateral forces, as well as road unevenness.
preventing vibrations and fluctuations caused by ups and downs on the road to the car chassis.
providing and maintaining the suspension geometry of the front wheels and the steering wheel.
keeping the contact of the wheels with the road surface while passing through unevenness.
bearing 35 to 65% of the total weight of the car.
increasing the comfort in trips etc.
Fixed suspension
When both wheels are connected to a single axis and fluctuate simultaneously, the suspension is called rigid (dependent). In all heavy vehicles, the Fixed suspension is used in both axes. It is used in the rear axis in old passenger cars, such as Peykan. In old SUVs, such as old Land Rovers and Patrols, it is used in both axes. Some military vehicles still use this type of suspension system as well.
Benefits:
The price is low.
Weights and severe shocks can be handled with optimal axis strength.
Maintaining the wheels' angle will give the tires a longer lifespan.
This suspension system absorbs lateral forces well and requires fewer intermediate levers.
A car's steering balance is well maintained on low-friction roads.
Disadvantage:
Because both left and right wheels depend on each other, when the vehicle passes through uneven roads, the side wheels will be opposite to each other; thus, the possibility of losing the car's balance or even rolling is higher compared to newer (independent) suspension systems.
Because of the weight of the unsprung parts (the joints of wheels and axes) in this type of suspension system, driving is generally monotonous and boring
Deformation of suspension springs
During braking or acceleration, the body of the car moves in reverse, due to inertial forces. In other words, during acceleration in which wheels move forwards, the body tends to lean backwards, and during braking in which the wheels tend to slow down and stop, the body tends to move forwards. In these situations, the suspension set which is considered the interface between the chassis and the wheel axis, is liable to deformation. It can be claimed that the spring reshapes into almost an "S" in braking mode, and a "Z" during acceleration. In order to prevent transverse deformation of the axes, engineers have designed an inclined lever (called "Panhard" bar) which is connected to the axes on one end, and to the chassis on the other end. This lever plays an essential role in the better performance of the suspension system.
During braking mode another position takes place known as "Diving", described as the tendency of the body to decrease in height towards the front. Normally, the greater the inertial force and the distance of the car's center of gravity from the road surface, the car tends more to decrease height when braking. However, by choosing the proper angle of the levers and the placement of the supports of the springs, the roll rate of vehicles can be decreased.
Deformation of suspension springs
During braking or acceleration, the car's body moves reverse due to inertial forces. In other words, during acceleration, in which wheels move forwards, the body tends to lean backward, and during braking, in which the wheels tend to slow down and stop, the body tends to move forwards. In these situations, the suspension set, which is considered the interface between the chassis and the wheel axis, is liable to deformation. It can be claimed that the spring reshapes into almost an "S" in braking mode and a "Z" during acceleration. To prevent transverse deformation of the axes, engineers have designed an inclined lever (called the "Panhard" bar) which is connected to the axes on one end and to the chassis on the other. This lever plays an essential role in the better performance of the suspension system.
During braking mode, a position called "Diving" occurs when the body decreases in height towards the front. Usually, the greater the inertial force and the distance of the car's center of gravity from the road surface, the car tends to decrease height when braking. Therefore, choosing the proper angle and placement of the spring supports makes it possible to reduce the roll rate of vehicles.
Independent Suspension System
Each wheel can swing independently of other wheels in an independent suspension system. The most vital part of independent suspensions is U-joints. These spherical-shaped parts allow movement between two parts with minimal friction; they are subjected to tensile and compressive forces.
Benefits:
Due to the better contact of the wheels to the road surface, they provide better driving and controlling capabilities.
Due to the unsprung weights, forces on the wheels are absorbed in a better way compared to rigid suspension systems.
The possibility of losing vehicle control when driving on uneven roads is reduced compared to dependent suspension systems.
Since the chassis absorbs the axis's weight, and because differential and heavy parts are among the sprung parts, a flexible spring can be chosen for suspension.
During acceleration and turning, the wheels have a higher level of support, and the overall safety of the car increases
Disadvantages:
Because of more flexibility and plasticity, angular variations of the wheels are more compared to dependent suspension systems, resulting in more tire wear.
The expenses of repair and maintenance are high for independent suspension systems.
The most common independent suspension systems are:
Double wishbone suspension (A-shaped arms)
MacPherson strut
longitudinal lever
Double wishbone suspension
This type is considered one of the best independent suspension systems. Wishbones are triangular-shaped levers whose vertices are connected to the wheel lever using a ball joint and base to the chassis. In addition, there is another lever in the front wheels related to the steering system (bar bushings), whereby the movement of the wheel lever rotates around the upper and lower balls. The spring is usually spiral or twisted in this suspension system. In spiral ones, the spring is leaned under the chassis in a pre-designed place. The spring bar is tied to the wishbone in the twisted ones.
Specifications
A- Absorbing all longitudinal and transverse total forces utilizing suspension levers
B- In the case of a shorter upper arm and longer lower arm unparalleled form of them, the geometry of the wheels can be adjusted in a way that increases the support level of the wheels on turns; therefore, the handling and movement safety improve during turns. However, if arms are paralleled, the wheels move mainly in the vertical plane, and their angles don't change.
C- This system is one of the best suspension systems for fast racing cars and is widely used in sports passenger cars. However, severe tire wear and expensive repair and maintenance because of the large number of rubber consumables are the two major weaknesses of the double wishbone suspension system.
MacPherson Strut Independent Suspension System
This system, one of the most common suspension systems used in today's cars, has an arm below and a relatively long axis above the wheel lever. A flange mounts the lever under the track rod, and the arm can rotate inside the flange.
From below, the wheel axis can rotate on a ball joint, so there is only a single ball joint in the articulation.
Advantages:
A- Simplicity of the suspension construction, low price, and lower maintenance expenses compared to double wishbone types.
B- Lower tire wear because of fewer lateral movements
C- Simple determination of Twain and Caster angles
Disadvantages:
A- A lots of force is on the track rod (where the upper flange is tied up to the spring and shock absorber assembly); therefore, there has to be a strong substructure in the production process, and load stress should be used.
B- If the spring assembly breaks, wheel shocks will be applied directly to the car room.
C- Both vertical and transverse forces on the wheel bend the long oblique arm; therefore, the shock absorber piston handle bends, and tire wears increases besides the damage to the suspension system.