The suspension system is one of the most complex and important parts of the cars.
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In this article, we will examine the suspension system in 5 stages. These steps include the following:
By reading the first part, you will understand what is the necessity of using the suspension system and what tasks should it perform?
In the second part, the operation method of the suspension system along with the introduction of the components of the suspension system will be done simultaneously.
In the third and fourth parts, the types of suspension systems are classified and introduced based on their appearance and the technologies used in them.
Stay with us.
We guarantee that after reading this article you will get complete information about the suspension system.
1- Application and duty of the suspension system
In the first step, we want to see why we use the suspension system in the car?
Which need has led to the use of a suspension system in a car?
Suspension system was the solution to which problem in the car?
In this step, you will find the answers to these questions.
The duties of the suspension system can be categorized as follows:
The more successful a suspension system can be in performing these tasks, it can be concluded that the suspension system is better.
We want to describe these mentioned duties.
1-1 Transferring the weight of the car from the chassis to the wheels
Chassis and wheels each have their own functions.
The suspension system must connect the chassis and the wheels to each other in such a way that there is no obstacle to perform the tasks of the chassis and wheels.
For example, the front wheels must be steerable or some wheels must transmit power.
The suspension system provides a strong and reliable connection between the wheels of the car and the chassis, so that there is no obstacle in performing the tasks of the wheels as well as the chassis.
Look at the picture below and see the movement of the wheels and components of the suspension system, in the rest of this article you will know all these components along with their functions.
1-2 Absorbing car wheel impacts and converting it into vibrations
As you know, the surface of the streets is not completely smooth and has many potholes and bumps.
The wheel should be able to move up and down relative to these potholes and bumps.
The suspension system should convert the impacts to the wheel into gentle vibrations.
1-3 Absorption of vibrations through damping
After converting impacts into vibrations, the suspension system must neutralize the vibrations.
This task is one of the most important tasks of the suspension system.
Understanding the way the car damping system works is a bit complicated.
In the following, we will tell you how this task is performed.
1-4 Maintaining vehicle stability when crossing road obstacles and turns
When the car is turning or moving in a corner, a lot of centrifugal force is applied to one side of the car.
Centrifugal force takes the car out of stability and if it is not controlled, the car will overturn.
One of the tasks of the suspension system is to control the centrifugal force and increase the stability of the car when moving in turns.
1-5 Maintaining vehicle stability during acceleration and braking
When the car accelerates, the rear side of the car approaches the road and the front side of the car moves away from the road surface.
And on the other hands, when the car brakes or slows down, the rear side of the car moves away from the road and the front side of the car approaches the road surface.
These unwanted movements of the car body during acceleration and braking cause car instability.
The suspension system controls these unwanted movements during acceleration and braking and minimizes them.
Up to this part of the article, we have said the duties of the suspension system.
Now you know why the suspension system exists in the car, what are its applications and what are the characteristics of a good suspension system.
So, if you are asked which suspension system is a good and desirable suspension system, you should say that a good suspension system works like this:
Now if you are asked what are the components of the suspension system and what is the function of each one, you don't know and you should read the rest of the article.
At the same time, we describe the components and the method of operation of the suspension system
2-Operation method and components of the suspension system
The suspension system establishes the connection between the wheels and the car chassis.
In fact, the suspension system is the bridge between the chassis and the wheels of the car.
In the picture below, the chassis, suspension system and wheels of a car (without rims and tires) are shown, and you cannot distinguish the components of the suspension system and the car chassis now.
In the next picture, we have distinguished the components of the suspension system, wheels and chassis of the car.
Look at the picture below. The car wheel and its components are shown with blue dots (in this image, the rim and tire are separated from the wheel). The car chassis is marked with green dots and the steering box rod with red dots. The other mechanical components you see in this picture are the suspension components and as mentioned, they connect the chassis and wheels of the car.
In addition to creating a connection between the wheels and the chassis, the car suspension system has other functions. Suspension components must not allow the wheel to move forward and backward relative to the vehicle body. But on the other hand, they should allow the wheel to go up and down relative to the body.
Question: Why should the wheel move up and down relative to the body?
Answer: As we mentioned, the suspension system must neutralize the impacts to the wheel, and to perform this task, it must be able to move up and down in relation to the body.
Now we have to see what mechanism to use to connect the wheel to the chassis, which provides up and down movement and at the same time, prevent the longitudinal movement of the car wheel relative to the body?
The solution to this task is to use parts called "control arms".
Look at the image below. The "wheel" is marked with blue color, "upper control arm" is marked with yellow color and "lower control arm" is marked with green color. The upper and lower control arms are connected to the chassis of the car. Their connection to the chassis is shown with red dots.
By connecting these red dots to the chassis, the wheel disc can only move up and down. On the other hand, it cannot move forward and backward.
The following animation will help you understand how the car wheel moves.
The movement of the "car wheel relative to the chassis" is possible using the upper and lower arms.
But these arms are not enough and we have to also use other parts to transfer the weight of the chassis to the wheels.
A spring should be added in the suspension system to support the weight and convert the impacts of the wheels into vibrations.
We place the spring between the lower arm and the chassis.
In the picture below, you can see the placement of the spring between the chassis and the lower arm, the chassis is marked with blue color, the lower arm with green color, the upper arm with yellow color and the non-rotating part of wheel with orange color.
Question: Did we reach all the goals of using the suspension system? Should another member be added?
Answer: Yes, the act of damping means neutralizing the vibrations of the spring must be done by means of a damper.
Yes we must use a damper.
It is probably easy for you to understand the way the spring works in converting impact into vibrations.
But it may be difficult for you to understand the operation of the damper.
Question: Why should there be a damper at all? What happens if there is no damper? Don't the spring vibrations disappear over time? Why should we use a damper to eliminate spring vibrations quickly?
Answer: By providing an example, we will explain the necessity of the existence of a damper and the act of damping.
Example:
Suppose a car is moving on the road and passes over the first bump.
The spring goes up and down by 2 cm and it needs about 15 seconds to neutralize the impact energy caused by that bump, but after just two seconds the car passes over the second bump.
Now the energy of those two bumps has been collected together and the spring now goes up and down by 4 cm (because of the two bumps),and it needs about 30 seconds to neutralize the impact energy.
Due to the unevenness of the streets and roads, every minute, the car passes over 20 small and large bumps.(even if the height of the bumps or the depth of the potholes is one millimeter, it will cause impact to the wheel)
In this case, the length of the spring stroke reaches 40 cm in one minute and increases constantly!!!
Until the bottom of the car hits the ground (at the bottom of the course) or the wheels of the car lift off the ground (at the top of the course), an event almost similar to what you see in the picture below.
Therefore, using a spring also has problems that must be solved.
Although the spring absorbs vibrations, it takes a lot of time for this, and if it is not given this time, it vibrates a lot.
A lot of vibration means that the vibrations of the spring It accumulates on each other and the length of the vibration course becomes longer and longer until the car lifts off the ground or the floor of the car hits the ground, so the vibrations of the spring must be controlled.
The task of controlling spring vibrations is performed by a part called damper or shock absorber.
The damper takes the vibrations of the spring, in other words it should be said that the damper absorbs the vibrations of the spring.
In the picture below, you can see the red spring and the black damper, and as it is clear, the red spring is assembled in line with the damper, and then both are mounted on the car.
To better understand of the performance of a damping assembly (including spring and shock absorber) and spring without damper, look at the picture below, in the picture, the spring without damper is shown in black and the spring with damper is shown in blue, the performance of each Compare which one passes through a bump, the diagram of their movement is drawn on the right side of the picture.
Let us go through the cycle once again: due to the speed of the car and the difference in the road surface, the car wheel is impacted, the impact is taken by the spring and turns into vibration, the shock absorber takes the vibration of the spring and turns it into heat and Finally, this heat is transferred to the outside environment.
Up to this part of the article, you have learned about the main components of the suspension system.
We want to see how these mentioned components are installed, where they are placed in the car and how they communicate with each other.
In fact, we want to describe the components of the suspension system and introduce the relationship of these components with other power transmission and steering system components.
We start with the wheels.
The car wheel can be considered as one of the components of the suspension or power transmission system.
The main and strongest member of the wheel is called "steering knuckle" on which the other parts of the wheel are mounted.
In the picture below, you can see the position of the steering knuckle, which is marked with brown color.
In the picture below, the steering knuckle is indicated by the white arrow, the steering knuckle is fixed (it does not rotate with the tire)
In the picture above, the place where the "steering knuckle" connects to the "lower control arm" is shown with red dots, the connection between the "steering knuckle" and the "upper control arm" with yellow spots and the connection between "steering knuckle" and the "tie rod" with blue spots.
The "tie rod" changes the angle of the "steering knuckle" and makes the wheel steerable
Also in the picture above, the place where the "steering knuckle" connects to the "brake caliper" is shown with pink dots.
For a better understanding, you can see another steering knuckle, with all its components separated, and its appearance is slightly different from the previous one, but it has the same connection points, which are marked with the same colors as the previous picture.
The "steering knuckles" you have seen so far are related to the front wheels and all of them had an arm that is used to angle and steer the steering knuckle.
The knuckle used for the rear wheels does not have a steering arm.
You can see a rear knuckle in the picture below (the "steerable arm" marked with blue dots is missing)
Now we want to know what other parts are connected to the knuckle.
If the front wheels of the car be driven (that is, they receive power and torque from the gearbox and transfer it to the front wheels) a device called "CV shaft" or "CV Axle" is used.
In the picture below, you can see a view of the back of the "steering knuckle" and the "CV shaft" is connected to it, the "steering knuckle" is shown with green spots and the "CV shaft" is shown with dark blue spots.
In the picture above, you can see the "CV shaft cover" in orange color and the "Wheel disc protector" in pale blue color.
Another member that we examine is the wheel bearing assembly, which includes several small and large parts.
In the picture below, the "wheel bearing assembly" is shown with yellow spots, also the "steering knuckle" with Orange spots and "CV shaft assembly" is shown with blue spots.
The car bearing assembly consists of a fixed and a moving part.
In the picture below, the fixed part which is connected to the "steering knuckle" with several screws is shown with green spots and the rotating (moving) part is shown with red spots, the "moving part" rotates in such a way that two rows of balls (in yellow color) are placed between the fixed and moving parts and make it possible to rotate these two parts relative to each other.
In the picture below, you can see a model of a wheel bearing assembly, the fixed part is shown in green spots and the moving part is shown in red spots, the wire you see connected to the fixed part corresponds to a sensor that measures the speed of the wheel.
The "knuckles" you have seen, were designed in such a way to take the power from the gearbox and give it to the "moving part" of the "bearing assembly".
We call these types of knuckles " drive knuckle".
If a wheel only spins and does not receive power from the gearbox, the wheel is not driven so We call these types of knuckles "non drive knuckle" or "dead knuckle".
In the picture below, you can see two models of "dead knuckle" or "non drive knuckle", the one on the right is used for the front wheel and the one on the left is used for the rear wheel.
The next member is the brake disc, which is connected to the moving part and rotates with the wheel and is considered an important member of the car braking system.
In the picture below, the "steering knuckle" is numbered 1, the "brake disc cover" is numbered 2, the "wheel bearing assembly" is numbered 3 and the "brake disc" is shown with number 4.
In the next step, the wheel rim and tire are added to the wheel assembly.
In the picture below "CV shaft assembly" numbered 1, The "steering knuckle" numbered 2, the "wheel ball bearing" numbered 3, the "wheel bearing assembly" (in which "ball bearing number 3" is placed in) numbered 4, the "brake disc" numbered 5, and the "rim and tire assembly" numbered 6.
There are many small and large parts in the assembly of car wheel components.
In this article, we only described the main components, even the main parts that we described also have small and large parts and members, for example, if you look at the picture below You can see these small and big pieces .
At the end of this part of the article, we would like to introduce two pieces that play an essential role in connecting the introduced components to each other.
In the picture below, you can see a "bushing" on the right and a pair of "ball joints" on the left .
These parts allow the controlled movement of suspension system components relative to each other.
The degree of freedom of ball joint is usually more than that of bushings.
In the picture below, the degrees of freedom of the arm relative to the joint is shown with red arrows.
For a better understanding of this degree of freedom see the picture below.
The application of bushing and ball joint is in connecting suspension components to each other.
Look at the picture below, the "bushings" are marked with "dark blue" and they are connecting the "lower control arm" to the "chassis" of car. and also the "ball joint" is marked with "pale blue" and this is connecting the "lower control arm" to the "knuckle" of car.
The picture below shows the connection of the "lower control arm" to the "knuckle" of the car by a ball joint.
The picture below shows the connection of the "lower control arm" to the "chassis" of car by a bushing.
The health of connecting components such as bolts and nuts, ball joints and bushings is very important.
The defectiveness of these parts can lead to an accident, as you can see in the picture below, the failure of a ball joint caused the wheel to separate from the axle.
3-Types of suspension systems based on appearance
We divide this part of article into eight main parts.
These 8 parts include these items:
All these items may be used in front and rear suspension, but the items "1, 2 and 3" are usually used in front suspension and the items "4, 5 and 6" are usually used in rear suspension.
3-1 Double wishbone suspension
look at the picture below, the Double wishbone suspension consists of:
The wheel shown above is steerable and the steering rod in orange color changes the angle of the wheel.
In the picture below, you can see the simplified suspension and steering system of a car.
See the image below for a better understanding of wheel steering.
In the front suspension system, the task of steering and controlling the angle of the wheels (to turn the car) is the responsibility of the "steering box".
In the picture below, you can see the "steering box" in orange color.
3-2 MacPherson strut suspension
McPherson suspension is just like the Double wishbone suspension, the only difference is that in McPherson suspension, the "upper control arm" is removed and the "damping assembly (consist of spring coil and shock absorber)" is placed between the "knuckle" and the "chassis".
In the picture below the "coil spring and shock absorber" numbered 1, the "knuckle" numbered 2, "lower control arm" numbered 3, The connection point of "damper assembly" to "knuckle" with numbered 4 and the connection point of "damper assembly" to "chassis" numbered 5.
For a better understanding of MacPherson suspension, you can see the picture below.
3-3 torsion bar suspension
As you know, the damping assembly consists of a spring and a damper.
The spring can be coil or bar.
You got acquainted with the coil spring.
In some cars, a rod spring can be used instead of a coil spring, we call it the "rod spring" or "torsion bar".
To understand the function of this spring model, look at the figure below. if we fasten the end of the metal rod (for example, to the wall) and apply the force F to the rod so that the rod turns around its axis, when the force is removed, the rod returns to its place. It returns itself and this rod can be used as a spring.
In the picture below, you can see a "torsion bar suspension" in a car. Rod spring C (called torsion bar) is connected to part A (which is the car chassis) and on the other hand, it is connected to the "lower control arm".
See the real shape of this spring in the picture below, the "torsion bar" is green, "lower control arm" is yellow and the chassis of the car is red.
To better understand the operation of the "torsion bar" look at the figure below, the "torsion bar" is shown with white arrows.
Note: Keep in mind, in a car where a "torsion bar" is installed, a damper is also needed.
3-4 Leaf Spring suspension
You have understood the structure and operation method of "torsion bar" and "coil spring".
Now we are going to describe another type of spring, which is the "Leaf spring".
Look at the figure below, if we place a "steel leaf" on a surface and apply a force to the middle of it, the leaf will resist and return to its place after the force is removed.
To increase "spring resistance", several layers of leaf are placed on top of each other.
"Connecting sheets" are used to connect the leafs to each other.
When the leafs are placed on top of each other, these "connecting sheets" are wrapped around the leafs at various places.
In the picture below, these "connecting sheets" are shown in brown color, they also make a hole in the center of the "leaf spring" and pass a "metal pin" or "bolt" through the hole and tighten it, you can see this "metal pin" in pink color in the center of the "leaf spring".
You can see the operation method and movement of the leaf spring due to the input of force in the figure below.
As you know, a shock absorber is needed for every spring.
In the picture below, the shock absorber is shown in yellow and is placed between the wheel and the car chassis.
If the force on the leaf spring is high, a stronger leaf should be used.
In the picture below, you can see two strong leaf springs with a large number of leafs, the chassis of the car is orange and is marked with red lines, shock absorbers marked with yellow lines, and the location of the axles is marked with green lines.
3-5 Trailing Arm Suspension
This suspension system is very simple and cheap.
it consists of one arm.
As you can see in the picture below, the arm is marked with green color, one end of this arm is connected to the chassis by two bushings and the arm can rotate relative to this point, the other side of the arm is connected to a coil spring and shock absorber (in red color), and the car wheel is also connected to the arm at one point.
In passenger cars (such as sedans, hatchbacks, etc.) that do not have a chassis (and only have a body), the location of the "body intended for installing the suspension arm" should be strengthened.
To strengthen the body, they use a steel piece (shaped beam) that acts like a small chassis.
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This shaped beam is welded to the body or connected with bolts and nuts, then the suspension arms are connected to it.
In the picture below, the shaped beam is shown in red, it is welded to the car body and the suspension arms (marked in green) are connected to it with bushings.
In some cars they do not use "shaped beam" and two "small strong parts" are attached to the body by some screws, then the arms are connected to these strong pieces by bushing.
In the figure below, "small strong parts" are brown and the "screws" are pink.
In the picture above, there is also a part with a "pale blue color" that connects the "two left and right arms", you will understand the useful of this part in the rest of this article.
3-6 Multi-Link Suspension
If a car manufacturer wants to make a special and unique suspension system for its car, he use the "Multi-Link" suspension.
In this suspension, a large number of arms, rods and beams are used to restrain and transfer forces in the required directions.
The design, analysis and repair of these suspension systems is usually difficult and complicated, but if designed correctly, they will perform very well
In the figure below, you can see an example of a "Multi-Link" suspension.
4-Types of suspension systems based on dependency
In this part of the article, we explain the concept of dependent and independent suspension, then point out one of the defects of independent suspension and take steps to fix it.
4-1 Dependent suspension
If the suspension system is such that a change in the condition of one wheel causes a change in the condition of the other wheel, this suspension system is called dependent suspension.
Look at the image below, number 1, shows a simple model of dependent suspension. Number 2, shows that by changing the height of one wheel, the angle of the other wheel also changes. Number 3, shows an example of a dependent suspension system.
4-2 Independent suspension
If the suspension system is such that changing the condition of one wheel does not cause a change in the condition of the other wheel, this suspension system is called independent suspension.
Look at the image below, number 1, shows a simple model of independent suspension, number 2, shows that as the height of a wheel changes, the angle of the other wheel does not change. Number 3 shows an example of a independent suspension system.
Now we have to know one of the defects of independent suspension.
As you know, one side of the car's body approaches the road when cornering, and the other side of the car moves away from the ground.
This happens as a result of the force of the "Centrifugal force" which is shown by the yellow arrow in the figure below.
The use of independent suspension may cause the car's body to overturn.
Look at the picture below, the two sides of the car should be slightly dependent on each other so that the wheels inside the turn (left side of the picture below) do not get too far from the body and the wheels outside the turn (right side of the picture below) don't become too close to the body.
For this purpose, "Sway bar" is used.
"Sway bar" is used in independent suspensions (such as McPherson and Double wishbone suspensions) to make the height of the two sides of the car somewhat dependent on each other, thereby reducing the possibility of overturning and increasing the stability of the car.
In the figure below, you can see two cars when they are on the bend of the road. on the left side, you can see the state of the car body without the "Sway bar" and on the right side, you can see the same car with the "Sway bar".
For a better understanding of this issue, look at the figure below, at the bend of the road, on the left side of the figure, you can see the condition of the car without the "Sway bar" and on the right side of the figure, you can see the condition of the car with the "Sway bar".
In the picture below, which is a McPherson suspension, you can see the "Sway bar" in green color which is connected to the "lower control arm" with several intermediates.
This part extends to the end of the other side of the car and is connected to the "lower control arm" on the other side.
In two or four points of the body (chassis), it is connected to the car body (or chassis) with plastic bushings and metal fasteners.
In the picture below, you can see the "Sway bar" in red color, which is connected to the body by fasteners in two places and connects the "lower control arms" of the two sides to each other, and this "Sway bar" is completely parallel to the center line of the car.
In some cars, it may connect the "upper control arms" of the two sides of the car.
It may connect the bottom of the shock absorbers together.
It doesn't matter, the important thing is that the wheels on both sides of the car are somewhat dependent on each other.
Look at the figure below. "Sway bar" number 1, through rod number 2, connects the wheels of the two sides to each other.
The "Sway bar" is not specific to "McPherson and Double wishbone suspensions" and is used in other independent suspension systems as well.
In the figure below you can see a "Trailing arm suspension", the arms are in purple color, and you can see the "strong shaped beam" in green color, the "sway bar" (causes the connection between the two arms) is shown with the symbol A and is fastened to the "shaped beam" at two points with fasteners and bushings.
4-3 Semi independent suspension
Sometimes a "beam" is used instead of a "bar".
both of them called "sway bar".
The figure is familiar to you and we showed you in the previous part of this article and said that you will know the reason for using the "Pale blue rod".
Now we know that this "anti-roll beam" is used instead of the "anti-roll bar" and makes the two wheels somewhat dependent on each other.
The "Trailing arm suspensions" that use the "anti-roll beam" are more dependent than the "anti-roll bar" (that is fixed to the body with bushings and fasteners), for this reason, this system (Trailing arm suspensions that use the anti-roll beam) is called semi-independent suspension.
5-Types of suspension systems based on intelligence
In this part of the article, we will examine three types of suspension systems based on intelligence, which include the following:
The level of intelligence of the suspension system depends on the level of intelligence of the damping system (which includes springs and shock absorbers).
So let's see how the smartness of the "damping assembly" becomes possible.
5-1 Passive suspension
The usual systems (we mean the damping system) in which simple mechanical springs and shock absorbers are used are called passive suspension systems.
How do usual systems work? what's wrong with them? What intelligent systems have been invented to solve that problem?
At the end of this part, you will learn the answers to all these questions.
Now we focus on the internal structure of the shock absorber.
The figure below is a simple shock absorber model, the damper body is shown by "C" and the damper rod is shown by "A", "gas F" and "liquid D" are inside the damper body, and the "diaphragm E" separates the "liquid D" and "gas F" from each other.
The application of "diaphragm B" is very important and we want to discuss it.
Note: unlike gas, liquid is not compressible, which means that its volume cannot be reduced by pressing.
The "liquid D" passes through "diaphragm B", that is, when the "rod A" rises, the "orange liquid (or liquid D)" comes to the bottom of the "diaphragm B" by passing through the "diaphragm B", and when the "rod A" goes down, the "liquid D" comes to the top of the "diaphragm B" by passing through the "diaphragm B".
In fact, the "diaphragm B" is in the form of a piston that limits the passage of the "orange liquid"
"diaphragm B" makes difficult for the "orange liquid" to pass up and down and slows down the passage of the "orange liquid".
To better understand the "piston diaphragm", look at the figure below, the "piston diaphragm" is shown with "A" and has very small holes that slow down the passage of liquid from "top to bottom" and "bottom to top", this action, absorbs spring vibrations.
Of course, the shape inside the dampers is a little different from the shape you saw.
The internal shape of the dampers is as follows, the compressed gas is in the outer wall of the damper, which is marked with C and B, and the "orange liquid" passes through the diaphragms D and F, and as you can see, in areas C, B and E It flows.
If the "number of holes" in the "diaphragm" is less or the "diameter of the holes" is smaller, the "speed of movement" and "fluid exchange" from one area to another area becomes harder and slower, and as a result, the damper becomes stiffer.
On the other hand, if the "number of holes" in the "diaphragm" is greater or the "diameter of the holes" is greater, the "speed of movement" and "fluid exchange" from one area to another becomes easier and faster, and as a result, the damper becomes softer.
In the figure below, you can see two types of dampers, the upper damper is soft and the lower damper is stiff.
Question: Is a soft damper better or a stiff damper? Which ones is suitable for use in the suspension system?
Answer: This question cannot be answered absolutely because the use of each of them has advantages and disadvantages.
If "soft shock absorber" be used, the suspension performs its first task well (which is to provide comfort for the passengers). Of course, this is not always true and if the damper be too soft, the car body will go up and down too much and this will annoy the passengers.
If "stiff shock absorber" be used, the suspension performs its second task well (the stability of the car on the road surface is better and the possibility of overturning and deviating the car is reduced).
As you understand, we will need "soft shock absorbers" in some situations and "stiff shock absorbers" in other situations.
Passive suspension systems are either always stiff or always soft and cannot be an ideal suspension system.
In fact, their stiffness is always constant and cannot be changed in different conditions.
Also, they do not have the ability to adjust the height and other things that we expect from an ideal suspension system.
To fix the defects of simple (passive) suspension systems, more advanced suspension systems have been designed and built, which we have categorized and reviewed in the form of semi-active and active suspension systems.
5-2 Semi-active suspension
Semi-active suspension is designed to solve some of the problems of passive suspension.
Many car manufacturers, instead of using normal springs and shock absorbers, use shock absorbers whose stiffness can be adjusted, (that is, they can be softened or stiffened in some situation). Cars that use this model of shock absorbers in their suspension system have semi-active suspension.
The semi-active suspension system offers features that we mention a few examples of them:
The most famous semi-active suspension mechanisms are "air suspension" and "hydro-pneumatic suspension", the full explanation of which requires several separate articles.
In this part of the article, we want to examine the internal structure of the dampers used in hydro-pneumatic suspension and then introduce some of the facilities that semi-active suspensions make available.
Hydro-pneumatic suspension consists of two liquid (hydro) and gas (pneumatic) components.
Look at the figure below, you can see a "Trailing arm suspension" with the "hydro-pneumatic damper", in this "damping assembly" the "spring" and the "shock absorber" are integrated together and form the "hydro-pneumatic sphere", the "hydro-pneumatic sphere (or suspension sphere)" consists of two parts: gas (pale blue) and liquid (green). Part No. 3, which is a "flexible rubber diaphragm", separates the gas from the liquid and prevents them from mixing with each other.
In the figure above, the gas (number 2) performs the function of the spring (in this system, there is no mechanical spring).
Part number 4 plays the same role as the small holes in normal dampers (that is, it limits the speed of the fluid movement and thus performs the damping action and neutralizes the oscillations of the gas spring number 2).
When the car wheel passes over the bump, the gas inside the "suspension sphere" is compressed like a mechanical spring (which can be seen in the lower right photo) and after passing the bump, the pressure is removed from the gas and the "flexible rubber diaphragm" returns to its place.
Also, the liquid inside the suspension ball acts as a damper for the gas spring.
To better understand the "suspension sphere movement", look at the figure below.
In the picture below, you can see a "green suspension sphere", it is installed in the car instead of a spring and a shock absorber.
5-3 Active suspension
Active suspension is an amazing technology that has recently been commercialized and used in cars.
Until a few years ago, a car with an active suspension was not produced, because it cost too much for car manufacturers and made the car too expensive.
"Research work" was carried out in car design centers, universities, etc. and today we see cars with active suspension on the streets and roads.
Their working method amuses and amazes everyone.
The active suspension in any car acts like its eyes, that is, it sees ahead and prepares itself for upcoming events.
Active suspension is completely intelligent and computerized, that is, the car has a special computer, sensors, cameras, and actuators that all belong to the suspension system.
Also, intelligent dampers are installed in all wheels.
In the figure below, you can see the active suspension components, the camera (A) sends data to the computer (B), the computer detects the best performance, then gives the necessary commands to the dampers of the wheels so that the dampers perform the best work.
Different cameras and sensors are used in the car body.
The most important sensor used in active suspension is the camera installed in the windshield of the car.
This camera sees the condition of the street (i.e. bumps and potholes) and sends the data to the computer.
In addition to the front camera, the "suspension computer" receives information from the "speed sensor", "steering wheel angle sensor", "brake sensor", etc.
There are different types of active dampers.
Electro-pneumatic, electric and electromagnetic dampers are the most widely used and common ones.
These dampers not only "perform the duty of spring and shock absorber", but also act very intelligently and quickly, they can raise or lower the wheel in the fastest time.
You can see a model of the "active damper" in the figure below, the "computer (number 2)" receives energy from the "power supply for the active suspension (number 1)" and sends the necessary commands to the "electric motor (number 4)". computer tell the "electric motor" when and how much it must rotate from right to left or from left to right.
"part number 3" Converts the rotation of "electromotor number 4" to a reciprocating movement, with this measures, the wheel Raises or lowers. (number 5)
In the following animation, you can see the movement of these dampers.
The capabilities of an active suspension depend on the programming of its computer, just as you can install various applications on your computer, the designers of the active suspension system can also give the computer various programs to run on them.
All the facilities that are available in semi-active suspension will definitely be available in active suspension, such as the ability to manually adjust the height by the driver, automatic height adjustment, etc.
Another amazing feature that exists in all active suspensions is maintaining the stability of the car in all conditions.
In the picture below, you can see the front and rear view of two cars that are both turning at high speed, the car on the right has active suspension and the car on the left has passive suspension.
Since this function of active suspension is a little hard to understand, look at the animation below, the car on the right has passive suspension and the car on the left has active suspension.
Other programs and capabilities can be added to active suspension and new tasks can be defined for it.
Look at the picture below, you can see a car with active suspension that is in the suspension test, a yellow box is approaching the car at a high speed from the left side of the picture (to prevent the yellow box from hitting the car "white barrier" have been placed). the left side of the car rises before the impact of the box to reduce the damage to the passengers on the left side of the car.
Another incredible and innovative (and of course non-functional) feature that can be installed in a car with active suspension is the ability to jump over obstacles.
The suspension computer can be programmed so that when there is a large obstacle in front of the car, it will use all the power of the dampers to jump over the obstacle.
Thank you a lot for taking your valuable time to read this article.
I hope it was useful for you dear friend.
Started on 05/14/. Completed on 06/26/. By mohammadali shariatmadari
[Editor's Note: This article originally appeared in the May/June issue of Grassroots Motorsports.]
Story by Lee Grimes
If you, like many motorsports enthusiasts, were hungry for any racing action as the season began winding up, you likely paid attention to the practice and qualifying sessions for the Daytona 500. The big story there was the new stronger spring rule mandated by NASCAR, and which teams could now get their suspensions to work the best.
The buzz was all about shock absorbers and how they were the key to keeping the rearend stable and predictable so the driver could put the precious horsepower to the pavement.
But Daytona isn't the only place where proper suspension tuning is vital to car control and fast lap times; it has been accurately said that many of the recent gains in suspension control have been made with shock absorbers. They can be the difference between who is on the track and who is on the trailer. But it doesn't matter if you are struggling for the last tenth of a second on track or simply trying to nail those esses through your favorite Sunday drive; suspension motion and transitional control is what handling is all about.
Most enthusiasts begin transforming their street cars into performance machines with the installation of higher performance tires. The next big gain is going to be with a set of performance shock absorbers.
Although the naked eye may not, be able to see any difference between average and performance models. inside these shocks you'll find a world of difference. And while automobile manufacturers are making strides each year in bettering suspension designs and improving car control, too many models still come off the line with basic shock absorbers that are better matched to the general public and the financial bottom line. It is up to the individual owner to understand what shocks do and select what will improve his or her car.
In the pursuit of shock knowledge there are a few basic ideas to be grasped. The term "shock absorber" is really a misnomer; &#;damper&#; is really more appropriate, but for our purposes we will use them interchangeably. The shock doesn't really absorb the impacts taken by the suspension, but dampens those motions by converting the kinetic energy of the spring (up and down motions) into thermal energy (the heat built up by flowing oil through valves). The damper controls the oscillation rate of the spring.
A good way to think of a damper in a performance application is as a timing device. The spring carries the vehicle load and establishes how much the suspension will travel for a given input. The damper times how long the suspension takes to react to the input or to dissipate the energy. An undamped spring will cycle or bounce very quickly and continue to do so until it has used up all of the input energy. The damper restrains the spring and helps it process the energy. The higher the spring rate, the greater the restraining ability the damper must have to control its energy. The more subtle and controlled the spring's motion, the more vehicular control you have.
Many years ago, the term "double-action shock" was used, implying that the shock offered damping action in both directions of travel. More modern suspension understanding has double-action taken pretty much for granted, as most people realize that a suspension requires damping both up and down.
Any time there is a discussion of dampers, the primary words used are rebound (extension) and bump (compression). The rebound damping characteristics control the sprung weight of the car, which is basically everything above the suspension (body, driver, engine, etc.) and part of the suspension weight (half of the spring, shock and some axle weight depending on type). Bump, sometimes known as jounce, controls the car's unsprung weight (wheels, tires, brakes and the other half of the suspension).
In a cornering situation, the vehicle weight transitions from the inside of the turn to the outside. The inside damper extends (rebounds) and thus determines how long it takes for the weight to transfer. Too little rebound valving will let the transition occur too quickly, upsetting the smooth balance of the vehicle. Too much rebound can make the transition too slow or possibly cause lift of an inside wheel.
At the same time, the compression damping plays a lesser role in establishing how far or fast the outside suspension will compress in accepting that transfer. A low compression rate will allow the acceptance to occur quickly and force the spring to do the work, but in the following reaction there will be a greater requirement for rebound as the spring responds back. A high compression rate will make the acceptance slow and act as a booster, seemingly increasing the spring rate.
When you hit an obstacle or undulation in an otherwise straight and smooth road, the damper compresses and determines how easily the wheel goes up into the wheel well or how much it resists the compression and makes the entire body raise.
Too little compression damping can let the suspension travel farther up than needed. Adding more compression damping can help the road-holding ability by reducing how far the suspension moves upward and therefore will need to move downward. Too much compression damping will push the entire car into the air and reduce the footprint of the tire on the ground, which will risk making the car feel like it is skating.
After the wheel stops traveling upward and the spring has stored the energy, it must release the energy and ex-tend and use the rebound function. Too little rebound damping will let the spring go farther and faster than it needs, and it will continue to cycle and bounce until its business is through.
Too much rebound damping can overcome the spring's ability to expand and hold it falsely short. This can make a car literally "jack" itself down and, over a series of bumps, can cause the car to lower itself to a point where it is riding on the bump stops and has no suspension at all.
There are three basic designs of shock absorbers: twin-tube hydraulic, twin-tube low-pressure gas, and mono-tube high-pressure gas. Each of the three has its own abilities and functions, and you will find all three in street or street-derived racing applications.
One of the most common misconceptions is that a gas shock is filled entirely with gas and no oil. In fact, all three damper designs use hydraulic oil&#;they just may have a nitrogen gas charge pressurizing the oil in the shock. Do not select a shock simply because it does or does not contain gas. Look into its actual capabilities.
The twin-tube hydraulic, as the name implies, has two cylinders (or chambers) and no nitrogen. The inner cylinder is where the rod and piston live and work, and the outer chamber is a reservoir for oil and air. As the rod travels in and out of the inner cylinder during stroking action, it displaces oil from the inner to the outer cylinder, then draws it back inside. Although this is the oldest of the three designs, it still maintains certain benefits and has a place in performance damping.
The twin-tube low-pressure gas shock is much the same as the hydraulic, except that it has a low pressure (usually 5-15 bar/70-210 psi) nitrogen charge in the outer chamber instead of the air pocket. Some manufacturers seal the nitrogen in a plastic bag, while others will put the nitrogen in a solution with the oil.
The original theory behind placing the nitro-gen inside was that it would put the oil reservoir under pressure and therefore raise the oil's boiling point, reducing the tendency for heat-related fading or foaming as it passed through the valves. That really isn't much of a concern today as the quality of oil has increased in performance dampers. Plus, modern performance shock design has moved away from needle valves and o-ring seals that are affected by heat and viscosity changes, and most street cars and many race cars simply will not generate enough heat to challenge the oil in a proper performance shock.
However, when the nitrogen gas is in solution with the oil, it can give the added effect of damping really minute harmonics and motions that otherwise would not be big enough to make the damper's piston move.
The final design is the mono-tube high-pressure gas shock, the monotube's entire body serves as the chamber allowing for a larger piston area, and therefore it has the ability to transfer more damping information over a smaller stroke area. Displacement of oil by the incoming rod is handled by a chamber at the bottom of the unit that contains a high pressure (20+ bar/ 300+ psi) nitrogen charge and is separated from the oil by a floating piston. Each design style offers certain advantages and disadvantages, so the best choice will depend upon the intended application.
A twin-tube design, when compared to a mono-tube, has a longer stroke capability and greater oil volume in a similarly sized unit. Therefore, the twin-tube will tend to give a smoother or more forgiving ride characteristic and still sup-ply the firmness for proper handling control in vehicles that see average or long suspension stroke length.
The larger piston area of the mono-tube will give more control over much shorter stroke lengths or at the lowest piston speeds, but also tends to ride more harshly for exactly the same reasons. In racing applications where beat generation is more likely to be a factor, a mono-tube can cool itself more quickly because the shock body is the wall of the working cylinder.
You are likely to find mono-tubes on non-production-based racers cars, where control over very short strokes is mandatory and ride quality is not an issue, or on production cars where designers tend not to want as much suspension travel. Some racing shock manufacturers use external reservoirs with mono-tubes to help with displacement lengths and oil volume, but in return add extra weight and some delay to the reaction ability.
Gas pressure in the shock can extend the oil's heat tolerances, but can also affect ride height because the greater pressure can act as a slight booster to the spring rate. Cars that run lower spring rates (drag racers are a good example) don't want the boost, so they usually use hydraulic shocks or must be willing to compensate for the gas pressure.
Mono-tubes can also operate while mounted on their side or at any angle, so they are more conducive to racing pushrod suspensions, while twin tubes must operate from upright to no more than 45 degrees from upright (which is still fine for most production-based suspensions).
The piston's speed of travel will determine how much damping force will be created, so the shock engineer can use the opening and closing of several valving tools to get different damping characteristics. They can use bleed-through holes in the rod that let oil entirely miss the piston and its valvings. This affects the lowest piston speeds and deals with low rate transitional control.
Next they can use orifices in the piston and valve discs to control mid-range or medium piston speeds. Finally you have bypass&#;additional piston orifices and valves used at high piston speeds to release or blow off extra pressure that can't get through the other valves. The bypass sets the maxi-mum damping rate and keeps the ride and control from being overly harsh when the suspension hits really big obstacles.
On twin-tube shocks, foot valves are used to control the flow of oil from one cylinder to the other and set up much of the compression damping rate. By working with these tools, control h obtained based upon the functional suspension and damper stroke lengths and the expected piston speeds.
An Indy or Formula 1 car will typically see piston speeds of 0-3 ips (inches per second) and strokes of under one inch. Combine that with very high vehicle speed, and you must have superior valving control and immediate response. A production-based racer (SCCA Improved Touring, IMSA Endurance Challenge, etc.) or autocrosser will work in the 0-8 ips range, based on track and driver smooth-ness. A street car typically runs at 8-15 ips, with jumps into the 20s for really rough roads. Compare that to up to 60 ips seen by a motocross bike racer. Add these requirements to the number of suspension designs and geometries. and you will quickly see that no one damper design or valving can cover all of the bases, Proper valvings are developed and needed for each situation.
Shock absorbers are tested for design and control by a shock dynamometer. The damper is tested at a single or multiple piston speeds with the damping forces noted. When printed in graph form comparing speed to damping force (measured in Newtons or pounds), certain trends become evident.
Figure 1 shows the basic three types of graphs: progressive, linear and degressive. The progressive graph is typical of what one might find on a low priced, commodity grade shock. The valving does very little up to a certain point, then gets progressively firmer at a rate faster than the increasing speed. This will have minimal low-speed control but lots of damping at really high speeds. It would not be a good selection for a performance car and would probably ride hard on really big bumps.
A linear graph forms a straight line that grows at matching rates for damping and piston speed, so it will serve better as a performance handling shock. It displays much better low piston speed capabilities, but will still feel pretty hard over big bumps.
The degressive graph initially grows at one rate at low speeds, but then the rate of damping slows down and begins leveling off at high speeds. This is going to give very good low-and middle-speed transitional control, but will not be harsh or upsetting at high piston speeds. This is the type of performance graph you are most likely to want.
Figure 2 shows a comparison of shock dynamometer graphs for the rear shocks from a second-generation Honda CRX Si. The red line charts the original-equipment selection by Honda; it reveals an emphasis on sportiness, but generally not awe-inspiring handing. Next (blue line) is the rebound-adjustable ICON! street shock, which puts greater emphasis on low and medium piston speed, as well as vehicle transitional control and a ride quality that will be firm but not harsh. The broad adjustment range lets the owner compensate for other modifications, including wheel and tire and suspension upgrades. This is a popular selection for tuned street and autocross cars and offers the option of revalving if the owner wants more development.
The green area is for the Koni rebound-adjust-able road racing shock developed for Firehawk/ Endurance Challenge, Improved Touring or simi-lar racing. These shocks can also be made independently compression adjustable if the owner so chooses. The most noticeable change is the large addition of bump stiffness and not as much rebound change. The firmer valving is used to help keep the car flat and stable while using much heavier springs. They also help the rear end rotate the car more quickly. Road racing front-wheel-drive cars need the added help with rotation for cornering, so the front wheels can be pointed straighter for putting the power down sooner and better. As you'd expect, these shocks are made for the relative smoothness of race tracks and so ride harshness is not an issue.
Now that you have attended Shock Tech 101 class, you need to ask the question: "Do I need better shocks?" If your aim is better handling, and your car is not one of the high-performance packages already fitted with adjustable performance shocks ( Neon ACR, Mustang Cobra R, Camaro 1LE, etc.), then the answer is likely "yes." You now have several choices: research what is available and make your selection (good idea); or develop you own shocks (if you really want to and think you are smarter than the engineers).
Technically, if you are armed with the correct geometry, spring, other measurements and math equations, you could calculate your suspension and get the "critical damping" (exact damping required for a specific spring) and other neat numbers. The trouble is that this only gets you into the ballpark, because there are so many variables that you can't define.
A critically damped car may technically cover the spring's capabilities, but would be so harsh at most piston speeds that you wouldn't want to ride in it. Manufacturers have teams of engineers who develop products based on lab findings, test tracks and real-world seat-of-the-pants feel. A damper is no good if it has "that Cadillac ride" but no low-speed handling control, or if it has slot car response on perfect roads but turns your brain to guacamole at the first bump. Damper adjustability enables you, the driver, to further tune the engineer's decisions to fit your driving style and pavement situation. Even more importantly, you can tailor your shocks to work with other performance modifications.
The engineers probably made their decisions based on a stock car, but if you have added performance wheels and tires, springs, anti-roll bars or&#;heaven forbid&#;more horsepower, then you need to become the engineer. If your class rules limit modifications and you require the car to do something it was not designed to do, you can use shock adjustment to attain the desired effect.
A good example is a stock class autocross car. This situation involves shoveling a car designed to get Grandma to the market through an ultra-twisty track at speeds that would cause Grandma to faint. Getting the understeer or oversteer out of a Sniveling Wombat to make it a fast-rotating Snarling Wombat can be accomplished with proper adjustable shocks.
Stiffer suspension is not always better. As a matter of fact, once you are in a desired range of performance and everything is working properly, a slightly softer setup can give you more leeway for unexpected situations. Simply clamping the car down as hard as it can go may mask the suspension's true abilities and functions, and the result will be a flat-running, harsh-riding, high-compromise skateboard.
Developing the appropriate settings for your combination can take some experimentation, but will be very rewarding in terms of lap times and fun. Beware of the recommended "ultimate setup." There is no perfect combination for all cars and drivers. That setup will likely get you in the ballpark, but again, your variables will define your own needs.
If Driver B is faster in the same kind of car, don't expect the same adjustments to be the answer. He may have gotten his suggestions from Driver A, who may have known what he was talking about or who may have been covering up some other inadequacy. As racers we tend to want to mimic "the fast guy," but at best this can put us even with him; at worst, it can put as way off base&#;even if you can trust the info he supplies. You should take what you have learned and find the fast way for you.
The goal you are seeking is getting your car to react to the ground, so you must remember that suspension tuning is actually making your tire work harder and more efficiently. Realize that a very soft suspension can give the tire too much motion to do its job, and a very stiff suspension can give too little.
An example of working the tires in a different way is a test we did last year with one of the North American Touring Cars. The track was smooth, and the suspension was plenty firm. In successive tests and adjustments, we slowly raised the rebound until good balance was achieved, but then a hot lap produced a nasty hopping motion.
Although the pavement was smooth, Touring Cars have a tendency to use curbing and berms to their greatest advantage. After firmly popping a berm, the car launched slightly and then hopped on landing. We realized that the hopping motion wasn't from spring bounce (which would mean it needed more rebound), but was actually from the tire's sidewall flexing because the suspension was firm enough that the only compliance to dissipate the energy came from the tire. A softer tweak on the rebound let the suspension and tires do their own jobs, permitting the car to stay on the ground and the driver on the throttle.
The initial setup was good for smooth driving, but when the berm variable was introduced, an adjustment needed to be made. By the way, the driver, Randy Pobst, won the North American Touring Car championship on those shocks.
The rule of thumb says that greater rebound damping loosens that end of the car, so a front-drive ear that won't turn in can use some more rear rebound. Couple that with enough front rebound to slow body roll, but not so much as to cause inside wheel lift, and you are on your way.
A tail-happy rear driver could probably use more front rebound (to loosen the front) and less rear rebound (to reduce rotation) in the pursuit of balance.
Your other thumb tells you that if you can isolate handling responses to corner entry and corner exit, then you know which end to work on. In a decelerating corner entry situation, the rear suspension is extending and transferring its load to the front, so adjusting the rear rebound can control the transfer rate. On accelerating at the corner exit, the front is extending as the weight is transferred to the rear (usually more subtle unless you have big power or soft springs), so the front rebound will be adjusted.
Increasing compression damping will also affect how quickly the other end of the car accepts that weight transfer. Too little compression can overwork or literally stun the contact patch, while too much can give too little input and also start acting like added spring rate.
If you are allowed to change springs, do so and let them do their job and share the work. If your rules mandate that you can't change springs, consider more compression, but re-member the other compromises involved. Ride quality and skittishness on intended and unintended bumps must be factored in.
Manufacturers can alter the different valuing tools in the adjustment procedure to get their desired effect. Some use bleed holes in the rod to make the changes and therefore vary the amount of oil missing the piston valves. The clue for this style is if it adjusts both compression and rebound in one motion. Other manufacturers (usually inure racing oriented) will adjust valuing independently, either by making only rebound adjustable and using an optimized, preset compression for many situations, or with a double-adjustable unit that allows independent adjustments. This style usually effects changes with rod bleed and orifice and valve stack spring preload pressure, and therefore can make changes over the more possible piston speeds.
The days of the old 50/50 (same rebound damping as compression damping) and 90/10 drag race shocks have gone by. Today a 50/50 shock would have either way too much compression or, more likely, too little re-bound. A 90/10 design just isn't paying attention to the evolution of suspension design and aerodynamics.
Today, street performance shocks have rebound damping rates that are two or more times greater than compression damping rates. The single action of adjusting bleed to affect bump and rebound is, by definition, a 50/50-style change, so the overall damping proportion will change as more bleed is dialed in. Independent adjustments allow the alteration of one characteristic while not affecting the other; this is therefore more precision and involves less compromise.
Rebound and sprung weight adjustments will cover 90-plus percent of most autocross and grassroots racers' needs. Making compression adjustments of the unsprung weight has traditionally been the realm of more hard-core race tuners, but as the stakes in the pro and national levels of autocross and club racing go up, so does the need for more tweaking and tuning ability.
As you can see (and probably know from firsthand experience), simply jumping into a car and counting on your heroic driving abilities to carry you to the front is the stuff of daydreams. Proper research and use of your suspension system is a safer spot to place your bets. Some of the most pivotal yet much misunderstood parts of your suspension package are the dampers.
If your goal is a favorite road or com-petition class, maximizing your dampers' capabilities will take you far and fast. Autocross is a great example&#;it is vehicle transitional control at the limit. A nationally-recognized autocrosses recently confirmed this by stating that suspension control is everything, and handling gains get you seconds whereas horsepower gains usually just get you to the next comer. Road or oval track racing is not as extreme in transition, but the vehicle speeds are higher and the necessity for control at the limit makes damper understanding critical.
Your car manufacturer probably didn't have you in mind when they chose the original dampers, so it is up to you to select and tune the best performance set for your unique needs.
Lee Grimes is the Street Products Manager for KONI Shock Absorber in North America, where he oversees street performance and street-based racing shocks. He has served as a contributor and technical advisor to GRM on several occasions. Lee is a nearly 20-year member of the SCCA and has been club racing and autocrossing for over 15 years.
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