Questions You Should Know about mechanical suspension

May. 06, 2024

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Everything You Need to Know about Car Suspension

The suspension system is one of the most complex and important parts of the cars.

If you want to learn more, please visit our website mechanical suspension.

In this article, we will examine the suspension system in 5 stages. These steps include the following:

Application and duty of the suspension system
Operation method and components of the suspension system
Types of suspension systems based on appearance
Types of suspension systems based on dependency
Types of suspension systems based on intelligence (passive, semi-active and active)

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:

Transferring the weight of the car from the chassis to the wheels
Absorbing car wheel impacts and converting it into vibrations
Absorption of vibrations through damping (we will explain)
Maintaining vehicle stability when crossing road obstacles and turns
Maintaining vehicle stability during acceleration and braking

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:

First, it absorbs the "impacts to the wheel" then converts it into vibrations and finally damps the vibrations. It is important to do these steps faster and more effectively so that the impacts of the wheels are not transferred to the chassis of the car.
It ensure the stability of the car in all conditions, especially during acceleration, braking and turning.

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:

Double wishbone suspension
MacPherson strut
torsion bar
Leaf Spring
Trailing Arm Suspension
Multi-Link Suspension

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 assembly (knuckle, brake disc, etc.)
upper controll arm (in yellow color)
lower controll arm (in green color)
the damping assembly (coil spring and shock absorber in between lower control arm and the bottom and chassis)

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.

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

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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:

passive suspension
semi-active suspension
active suspension

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:

Creating great comfort for passengers.
Automatic adjustment of vehicle height after adding cargo and passengers.
Lowering the height of the car at high speed to improve aerodynamics.
Resistance to car instability in turns, braking and acceleration.
Making it possible to adjust the height of the car according to the driver's wishes.
Making it possible to adjust different suspension modes (sport, soft, etc.) based on the driver's wishes.

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 05/14/2023. Completed on 06/26/2023. By mohammadali shariatmadari

Practical guidelines for suspension design for beginners 2

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Practical guidelines for suspension design for beginners

roller_delawer

(Automotive)

(OP)

25 Jan 19 08:51

Hi all,

I am a mechanical engineering currently working on Interior Trim parts for a living.

However I've always wanted to learn about vehicle dynamics and suspension design with the idea of making my own kit car (or at least try to do so). So I've read a few books about the topic (the famous Milliken and Milliken and others) but I've always found that there's a gap between understanding camber/caster/scrub radius etc and the proper method to correctly approach the design of a suspension with some specific handling goal in mind.

Reading this forum, most of the question look beyond that gap for me: even if I understand the technical terms, I struggle to understand the questions and the way you are designing the suspension in order to put those questions and answers in context.

Is there any book, online training, or something like that which would help me to learn that practical approach of this science? How did you started in this world? What else do you recommend me?

Thank you very much!!

EDIT: I know that there are several titles of practical suspension design aimed at hobbyist making a "locost" kit car in their garages. But due to my engineering background and the idea of this being a possible realistic career path for me, I am looking for something more technical than that.

RE: Practical guidelines for suspension design for beginners

cibachrome

(Automotive)

25 Jan 19 14:52

Suspensions connect the forces and moments from the tires to the chassis/body based on cammanded moments from the driver. The entire vehicle operates at the whim and comfort of the operator/driver on a roadway. So, given a set of desired ride and handling response performance targets or goals, a combination of tire and suspension properties are selected as subsystem parameters. Given what's available and affordable as a front and rear set of tires, suspensions (with steering on one end or both) are formulated based on cost, mass, durability, manufacturability, repairability, crash-worthiness and cool-factor (lore of what sells well).

Often we see this flow down process seriously mis-played by all the hype and hoopla from sandbox 'professionals' who build a car around a suspension type and bandaid the tires and the masses to try to make it work. Some more successful than others.

What you need to start with is a selection of what performance targets/goals you think you need or can live with. This sometimes takes 'competitive assessment'. You measure the steady state gains, response times, bandwidth, linearity, max values etc of vehicles you like and don't like. In my case, I have done this so much that I can write down the goals for just about any car or truck you wish because of all the testing and characterizing ("finger printing") done thru my career. Then select the performance you think you want and try to put it together with a parametric simulation. If a solution can be found (close or exact), you start scrounging around for hardware that could deliver the goods. Hardware that's cost effective, geometrically friendly, and utilizes the features of the tires, roadway and driver in a comfortable manner. The parametric simulation tells you 'why' you meet the goals (or why you don't). As opposed to a multi-body simulation which tells you that what you build could do the job (or fails). Much of this depends on the qualifications of the driver(s) too. My mother though good handling meant "easy to park". For my father it was 0=80 mph time with good launch.

Imagine listening to radio or music from a source (CD, cassette tapes, vinyl or shellac records) thru an amplifier (1, 10,100, 1000 watts) 1 channel, stereo, 4 channels, 16 channels) with PA speakers, Bose, AR, EPI or earphones) and BTW: your listener is stone deaf. All they REALLY want to listen to is a news broadcast but are sold on Pink Floyd. What items would you choose? Pick the speaker wires first ? It's the same for vehicle dynamics: the physics is easy. Some NEVER get it right. Some can get it awesome on the first try.

RE: Practical guidelines for suspension design for beginners

BrianE22

(Specifier/Regulator)

25 Jan 19 15:12

Did you look in the FAQs for this forum?

RE: Practical guidelines for suspension design for beginners

SwinnyGG

(Mechanical)

25 Jan 19 16:43

If you want a very basic intro to vehicle dynamics, the Carroll Smith books- Engineer to Win, Tune to Win, etc are pretty decent at explaining things at a 30,000 foot level.

RCVD would give you the deep dive into the math.

RE: Practical guidelines for suspension design for beginners

BUGGAR

(Structural)

25 Jan 19 18:43

https://files.engineering.com/getfile.aspx?folder=a377d768-8f02-49dc-80f0-6

Learn and master the secrets and myths of the "Roll Center".

RE: Practical guidelines for suspension design for beginners

GregLocock

(Automotive)

25 Jan 19 20:57

Meanwhile Bob bought every single tire he could find and rolled them along a carpark with a drum to give them the right weight. From this he worked out which tire had the lowest RR (a cheap BMX with natural rubber inner tubes, as it happened).

Solar car is a simple project because the goals are easy to define, whereas a production car has to do many things right.

How I got started was designing the suspension for a solar car. Rather excitingly this was a rigid frame connecting the three wheels, the body was suspended off the frame (Lotus twin chassis, in retrospect). The reason this was selected was that wheel alignment was paramount since rolling resistance was one of the causes of drag. The front wheel was on a bicycle fork (in effect). On its first outing the drivers complained that it was too twitchy, so I reluctantly modified the jig the forks were built on to give more trail, and dropped the original forks in. I was about to attack them with hacksaw and welder, when I thought, hmm, I wonder if they'd bend? To my astonishment, and anger, the answer was yes, I could bend the forks with my bare hands. So, I explained this to the team, and said we could test the new geometry (which worked) but we'd have to check for bending after each significant event. Then I took on the job of designing a spaceframe style front fork that would fit inside the wheelspat and was stronger. That worked. Then we got on with tuning the coilover springs (easy we didn't really need anything other than a soft ride) and the shocks (I had to soften them off and in the absence of any guidance just made the holes bigger in the pistons) - my first and last attempt at building a shock. Finally we had to set the ride heights so that the aero body was at zero pitch, that was worth about 20% on power required at cruise speed.Meanwhile Bob bought every single tire he could find and rolled them along a carpark with a drum to give them the right weight. From this he worked out which tire had the lowest RR (a cheap BMX with natural rubber inner tubes, as it happened).Solar car is a simple project because the goals are easy to define, whereas a production car has to do many things right.

Cheers

Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Practical guidelines for suspension design for beginners

GregLocock

(Automotive)

25 Jan 19 20:59

Oh, and another vote for Carroll Smith. Except for his theory about roll axes.

Cheers

Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Practical guidelines for suspension design for beginners

SwinnyGG

(Mechanical)

27 Jan 19 04:26

Quote (GregLocock)
Except for his theory about roll axes.

Is this a reference to his book stating that the roll axis can be accurately produced by connecting front and rear roll centers with a straight line?

I learned this one the hard way, and lost one of those "young engineer who thinks he's right but isn't" arguments we were all part of when young and educated in name only.

My understanding is that he later acknowledged that this concept was incorrect, but I'm not sure if it was known at the time he first wrote it in a book.

Is this a reference to his book stating that the roll axis can be accurately produced by connecting front and rear roll centers with a straight line?I learned this one the hard way, and lost one of those "young engineer who thinks he's right but isn't" arguments we were all part of when young and educated in name only.My understanding is that he later acknowledged that this concept was incorrect, but I'm not sure if it was known at the time he first wrote it in a book.

RE: Practical guidelines for suspension design for beginners

BUGGAR

(Structural)

27 Jan 19 14:08

The "roll center" grasshopper.

RE: Practical guidelines for suspension design for beginners

GregLocock

(Automotive)

27 Jan 19 22:27

here's the solar car

Cheers

Greg Locock

New here? Try reading these, they might help http://eng-tips.com/market.cfm?

jgKRI -yes. It's wrong from basic physics, it didn't have to be 'found out'.here's the solar carCheersGreg LocockNew here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies

RE: Practical guidelines for suspension design for beginners

BUGGAR

(Structural)

29 Jan 19 01:31

Find how to determine the torque in a four bar linkage and you can "snatch the stone from my hands". For now, forget about the "roll center" concept. It's misleading and poorly named and won't get you what you want.
"Combining" the front and rear roll stiffness' will be covered later. My bill will follow, too.

RE: Practical guidelines for suspension design for beginners

roller_delawer

(Automotive)

(OP)

29 Jan 19 13:11

Hi all,

Thank you for all your answers, some of them are really interesting.

Regarding the FAQ, I didn't know there was a specific FAQ for this forum, but I've taken a look, and it looks really interesting. I will read it more in depth.

Regarding my initial question, some people recommended the RCVD, as I said initially, I've read this book as well as Allan Staniforth's "competition car suspension", and others. And, while being completely mandatory for this topic, I am looking for something that goes one step further and really helps me to start with the hands-on work with some real world figures, graphs or advices of how to apply all that theoretical knowledge into a real design.

I could plot all the different parameters for a suspension, and even if I understand more or less what they mean, I would be lost when trying to set a specific value as target, or when making compromises, I'd be completely lost trying to understand which one I should prioritize.

Is there anything out there that helps me with these things?

I haven't read any of Carrol Smith's books, might that be more similar to what I'm looking for?

RE: Practical guidelines for suspension design for beginners

roller_delawer

(Automotive)

(OP)

29 Jan 19 13:19

Quote (cibachrome)
What you need to start with is a selection of what performance targets/goals you think you need or can live with. This sometimes takes 'competitive assessment'. You measure the steady state gains, response times, bandwidth, linearity, max values etc of vehicles you like and don't like. In my case, I have done this so much that I can write down the goals for just about any car or truck you wish because of all the testing and characterizing ("finger printing") done thru my career. Then select the performance you think you want and try to put it together with a parametric simulation. If a solution can be found (close or exact), you start scrounging around for hardware that could deliver the goods.

Hi Cibachrome,

You've just nailed. But that's precisely my problem, theoretical books don't help much when you're trying to set up real-world goals, or making real-world compromises.

Because of my experience as an interior trim engineer, I can easily understand what I need to deliver to fulfill my customer needs. And when things get complex and I have to give up something, I know how that's gonna affect the final result. However, with suspension design, I'm totally lost.

And this is kind of a vicious circle, I don't start creating my first suspension cause I'm not sure what to do, and I won't be sure what to do until I have designed a couple of them...

Thank you again!

Hi Cibachrome,You've just nailed. But that's precisely my problem, theoretical books don't help much when you're trying to set up real-world goals, or making real-world compromises.Because of my experience as an interior trim engineer, I can easily understand what I need to deliver to fulfill my customer needs. And when things get complex and I have to give up something, I know how that's gonna affect the final result. However, with suspension design, I'm totally lost.And this is kind of a vicious circle, I don't start creating my first suspension cause I'm not sure what to do, and I won't be sure what to do until I have designed a couple of them...Thank you again!

RE: Practical guidelines for suspension design for beginners

BUGGAR

(Structural)

29 Jan 19 14:45

Suggestion?:
Go out in the garage and build a half scale model. Make the parts adjustable (I used all thread rod and carburetor rod ends). Buy some springs (use tension springs reversed to simulate compression springs). Set the spring mounts so you can get progressive spring action as well. Set it up on a vertical board with a track along the bottom for your "wheels". Hang a weight on a string from your adjustable center of gravity and yank the string sideways, and up and down, and play with it until your significant other yells, "When are you going to stop dancing with that thing and come in here and help me?"

RE: Practical guidelines for suspension design for beginners

BrianPetersen

(Mechanical)

29 Jan 19 16:55

You haven't told us what sort of vehicle you are attempting to build.

Upper and lower wishbones with very high spring and damping rates work well for a Formula 1 car or other roadracing car designed for use on smooth pavement. Doesn't work well for rock crawling.

Beam axle located by linkages with links as long as practical and very soft long-travel springs and dampers work well for rock-crawling. Doesn't work well for roadracing.

When you start wanting high grip and decent ride quality and good steering behaviour and decent stability at high speed is when it starts getting tough.

RE: Practical guidelines for suspension design for beginners

roller_delawer

(Automotive)

(OP)

30 Jan 19 10:00

Quote (BrianPetersen)
You haven't told us what sort of vehicle you are attempting to build.

Hi Brian,

My idea is to design a track-oriented double wishbone suspension for an existing car shell, for a restomod project.

But, as I said, being an engineer and working for a car manufacturer already, I can see some kind of career path possibilities here. So I would like to learn as much as possible.

Hi Brian,My idea is to design a track-oriented double wishbone suspension for an existing car shell, for a restomod project.But, as I said, being an engineer and working for a car manufacturer already, I can see some kind of career path possibilities here. So I would like to learn as much as possible.

RE: Practical guidelines for suspension design for beginners

BUGGAR

(Structural)

30 Jan 19 12:45

Something like Heidts, et. al. is doing?

RE: Practical guidelines for suspension design for beginners

BrianPetersen

(Mechanical)

30 Jan 19 13:26

OK. Pavement. Roadracing. You need good grip and high-speed stability, decent grip feedback through the steering (this one is tough), you will be using modern high performance tires, you need enough space around the spindles for good brakes, and ride quality doesn't matter. Because you can use relatively stiff spring and damper settings, antidive doesn't matter at the front (use the springs), roll centers aren't as meaningful as some people make them out to be (DON'T let them be high, use low single-digits inches above ground level, use the springs and antiroll bars for the rest). Because you can use relatively stiff spring and damper settings, you don't need much camber gain with bump travel ... use the springs and antiroll bars to keep body roll under control. Get the idea? Another thing ... bump steer is bad.

Now, how much space do you have to work with? The availability and location of structural attachment points to the vehicle will be a BIG governing factor in what type of general layout you use.

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