History Of Suspension System Engineering Essay
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Published: Mon, 5 Dec 2016
For my assignment, I will be talking about suspension. I will explain everything from the early development of the suspension system, the research and development, the differences of each suspension towards application, and so on. The main why the assignment has been done is because it teach us and tells us all sorts of things that is all about suspension and why is has build in such a way that the suspension should perform depending on the type of cars.
History of Suspension System
The first suspension to be introduced is from horse-drawn carriages in the 19th century. It uses a multiple layer of steels, or in some cases, use wood as a spring. It is known as a leaf spring. As modern cars were design to move at a faster speed, new type of suspension are needed. In the early 1900’s, shock absorber were being introduced in cars by a guy name
The Function and the Purpose of a Suspension System
The main role of a suspension system is to maintain a maximum contact between the tyres and the road surface, to provide steering stability and also to provide good handling during low-speed and high-speed corners. The suspension helps to generate as much traction as possible, depending on the driver and how the driver handle the cars suspension system and helps to minimize the body roll resistance. It helps to isolate the body from the vibrations of the shock absorbers. Roads that currently exist are not flat and straight. If the roads are all flat and straight, there’s no point installing a suspension system for cars. When roads are not flat, there’s a force reacting on the shock absorber and the springs through the wheel. According to Newton’s law of motion, all forces have both magnitude and direction. The other main importance of a suspension system is that help to provide a correct alignment during steering, to reduce the amount of body roll, to allow the driver to turn corner aggressively without extreme body roll and to prevent body dive, that is to reduce the body to tilt up and down during acceleration and braking. Two main components are responsible to all these kind of job that is shock absorber and spring.
The function of the spring is to support the weight of the vehicle, and to absorb road shocks being transferred from the wheels. The spring bounces up and down when passing through holes, bumps, and uneven road surfaces. There are all sorts of springs:
Coil- It is made out of a special steel rod, which is made by winding a wire around a cylinder. It is most commonly used in light vehicles. The wire will twist when the coil is being compressed or stretched. The design of a coil spring can be a cylindrical, barrel or conical shaped, depending on what kind of spring that are required for the type of the car. The material used for springs have to be capable of withstanding high stress and resisting fatigue. In early design, designers use high-carbon steel, but today, designers use a very minimum amount of alloy steel such as silico-manganese are used.
Leaf Spring- It has several flexible tempered plates with different length, which is stacked and being held by a steel clip. It is mainly used on rear-wheel drive vehicles, such as 4 wheel drive. The function is the same as the coil, but the only difference is that the leaf has minimum amount of flexibility than the coil. The stiffness or rate of a leaf spring is governed by:
Length of the spring- â†“ the length of the spring, â†‘ the rate of the suspension
Width of the leaf- â†‘ the width of the spring, â†‘ the rate of the suspension
Thickness of the leaf- â†‘ the thickness of the leaf, â†‘ the rate of the suspension
Number of leaves- â†‘ the amount of leaves, â†‘ the rate of the suspension
Torsion Bar- A torsion bar is a long straight alloy-steel bar, fixed between the chassis to the suspension control arm. The torsion bar will twist at the centre of the bar when the spring moves upward and downward. The spring rate varies the length and the diameter of the bar. When the driver turns the wheel, the torsion bar will twist, and reduces the roll tendency.
Air Spring- It is a rubber cylinder, filled with compressed air. This kind of spring is being used in heavy commercial vehicles and luxury cars. It provides comfort compared to the coil spring. The volume of air is being varied, depending on the load of the vehicle being added, to lower the vehicle, and go adjust the stiffness of the air spring.
Rubber Spring- It is used as the main suspension spring, or fitted with a metal springs to improve / upgrade the suspension characteristics.
The function of a shock absorber is to help dampen the amount of bounce created by the spring. The absorber gives the spring the freedom of bounce, but shock absorber is there to help dampen the undesired amount of bounce and thus, create stability of the vehicle. Here are the few types of shock absorber being used currently on the roads:
Hydraulic Shock Absorber- Most of the vehicles are using this kind of shock absorber. It is called a direct-acting telescopic type. Its damping action is being produced by the oil transfer, which is under pressure, and goes through the small valve which helps to restrict the oil flowing in and out. The most widely used is the twin-tube type. During compression, the piston moves towards the shock absorber. And during rebound, it’s a complete opposite.
Gas-Pressurized Shock Absorber- In the hydraulic shock absorber, the oil heats up as the suspension is in motion. This shock absorber helps to reduce the dissolve pressure by using fluid with nitrogen. This improves the dampening effect, thus improves the absorber’s performance.
Load-Adjustable Shock Absorber- This type of absorber helps to pressurize the shock absorber when the springs are under load. By adjusting the pressure, it helps to maintain the car height and adjusting the suspension stiffness. This helps to reduce the discomfort of the driver and the passenger. In order to reduce the discomfort of the driver and the passenger, the driver can adjust the air spring manually. The construction is almost as similar as the air spring, where you can adjust the ride height and the stiffness of the absorber.
Manual Adjustable-Rate Shock Absorber- The adjustable-rate absorber has a feature where you can change the spring oscillations by changing the rate of dampening. It has a damper rate adjustment located on the external of the shock absorber. You can control the restriction of the oil passing through by changing the valves in the piston.
Electronic Adjustable-Rate Shock Absorber- It acts the same as the manual adjustable-rate shock absorber. The only different between the manual and the electronic is that the rate of the shock absorber can be controlled electronically or by driver’s choice. This is a solenoid operated with the help of the ECU, which allows different types of modes to choose.
Automatic Load-Adjustable Shock Absorber- Also called as self-leveling shock absorber. When there’s load on the vehicle, the shock absorber will self maintain at a pre-set level. It automatically adjusts the height of the vehicle, depending on the load added at the rear axle. It consists of air-adjustable shock absorbers fitted at the rear, an air-dryer assembly, ECU, and an electrically-driven compressor.
Types of Suspension System
There are all sorts of suspension system being used today, and they are:
Solid / Live and Dead / Beam axle suspension system
A Live axle is an old technology. It is a combination of a solid axle being put across the car’s chassis, which is being connected at both front and the back of the wheels. This suspension is not independent, so when 1 wheel goes through a hump, the shock produced on that wheel will be transferred to the other wheel. This Live / Solid axle suspension consists of a drive shaft, a differential, and a strong tube enclosing all these things. The unsprung weight for this kind of suspension is very high because the whole axle assembly is fixed rigidly to the wheels. The result of an unsprung weight is that the more weight it gains, the momentum is higher. So in this case, a lot of momentum the springs have to handle because springs cannot absorb momentum, so therefore part of the momentum has to be transferred to the car body in a shock form. Because of this, this kind of axle does not provide a good ride quality.
In the Dead / Beam axle, there’s not driving axle on it, so therefore it has a very minimum amount of unsprung weight and it produces better ride quality than a live axle.
It’s not independent
Body roll does not interfere with the camber of the wheels
There’s no ride quality
The size is not practical
When one wheel has a force on it, the force is being transferred to the other wheel
DeDion axle suspension system
In the late 70’s, non-independent suspension market is stronger than the independent suspension, although the independent suspension were invented many years ago. The main reason why is because non-independent suspension is cheaper and offers better handling than the independent suspension. In this suspension, it helps to eliminate all the unsprung weight rather than the live axle suspension. It has minimum amount of unsprung weight is because the differential / final drive and the drive shafts are not rigidly attached to the rear wheels and therefore they are part of the car body and its flexibility to the wheels with the help of the universal joints. By using the DeDion technology, it helps to improve the ride quality by limit the wheel track variation when the suspension is at motion. In order to do this, the DeDion technology uses a sliding joint. The best part of using this is that it is always perpendicular to the road surface by keeping both wheels on the road surface, excluding the body roll.
Cheaper than most independent suspension
It’s not a independent suspension
The camber are not being affected even with body roll
The ride quality is not as good as the independent suspension
The ride quality is more superior than the live axle suspension
When the car is on a bump, both of the rear wheels will be cambered
Twist-beam rear suspension
It is based on a large ‘H’ shaped member. The front of the ‘H’ shaped member is being attached to the chassis with the help of rubber bushings and the rear of the ‘H’ shaped member is attached to the wheels. The ‘H’ manage to get the support by using the cross beam. The cross beam serves as to provide roll stiffness during corner and bump. It has a twisting action when both trailing arms move vertically. Coil springs and shock absorbers are being used in this system, located either behind, or alongside with the wheels. It provides high motion ratio and the end result, giving better performance and the weight reduction. The location of the cross beam is longitudinal as the roll steer control and its camber compliance.
Swing axle suspension system
It’s an old suspension, first introduced by some sports cars in 1950’s. This kind of technology has been phased out in 2 decades due to its weaknesses. The adjustment of the camber angles can be detuned by changing to a longer swinging arm. Usually, this kind of technology serves a lot of under steer, so by setting the wheels to a negative camber, it helps to reduce the unnecessary amount of under steer.
Provides an Independent shock absorption
Provides a very bad handling during corner
So much body roll
Tends to oversteer a lot
Trailing / Leading arm suspension system
A large piece of suspension that helps to support the coil springs, which are being located in front of the rear axle and connected to the axle of the car’s chassis. The main role of this kind of suspension is to allow the wheels to move up and down and this does not allow the camber to change. The only time the camber changes during corners. The advantage and the disadvantage are the same as the semi-trailing arm suspension.
Semi-trailing arm suspension system
In this design of suspension, compare to the trailing / leading arm suspension, it’s pivoted in an incline angles, roughly in between 50 to 70 degrees. The feature of the suspension is the same with the trailing / leading arm suspension. In both semi-trailing and the trailing / leading arm suspension are rigidly attached to the wheels. So when taking corner or taking bump aggressively shocks and noises will be transferred to the car’s chassis. But now days, automotive industry are moving to multi-link or double wishbone suspension. So therefore, the trailing / leading and semi-trailing arm suspension is going to be phased out.
It’s an all rounder, not much weakness
Detuned version of multi-link suspension
Understeer, but not much
When the wheels are moving up and down, the camber angle changes
Shocks and noise are being transferred to the car’s chassis
Adaptive air suspension system
It uses air suspension rather than using the conventional shock absorber and coil spring. You can electronically changes the damping rates to suit the driving conditions. The air suspension inflates and deflates; depending on the driver weather the driver choose the height of the car.
Provide precise handling
Capable of handling heavy load
Adjustable height and spring rate
Torsion beam suspension system
Majority of the small car segment uses this kind of suspension. It’s half-independent, which consist of a torsion bar, which is being used to limit the degree of freedom when force is being produced when taking in a corner. It’s more superior to its competitor, like the MacPherson strut suspension.
Provides more leg room for the rear seat of the car and more space for the boot
Doesn’t provide the same ride and height quality as the double wishbone or the multi-link suspension
Limited amount of freedom
Easy to maintain
Inferior in ride and handling quality
Double wishbone suspension system
In this era, many sports car such as Lotus, Ferrari, and all the famous top marquee car brands, are using this kind of suspension system because it can be used at both front and rear wheels, and to top it all off, it has almost near perfect camber control. It’s has long been used in racing, sport and top of the range cars for more than 40 years as it provides better and precise control. Its main role is to maintain the wheel perpendicular with the road surface, no matter how aggressive the driver handle the car. In the early days of double wishbone, it consists of 2 parallel wishbone arms in equal length. The main problem with this is that the tyres are producing excessive scrubbing due to the variable track width when the wheels are shifted off from the neutral position. So engineers have given a best solution, which is to develop unequal length and non-parallel A-arms to solve the problem. By doing this, the engineers tilted up the upper arm. The shock absorbers and the coil springs are installed onto the wishbones because it helps the engineer to adjust camber and caster angle, toe, roll centre height and scrub radius. The reason why 1 wishbone is shorter than the other is because to make the camber negative. The shorter wishbone is installed on the upper mount. When it sets to a negative camber, the result is a positive camber gain on the outer wheel when the vehicle is turning. Not only that, the outside wheel gains back negative camber due to shorter upper arm.
Proper camber control
Not space saving
Provides good handling
Low unsprung weight
A lot of components and needs more pick up points in the car’s chassis
MacPherson strut & Chapman strut suspension system
Invented by a guy the name of Earl S. MacPherson in the 1940’s. Ford started to use this kind of technology in the 1950 because of its low cost and space saving and thus, MacPherson is one of the dominating suspension system. In the design, the telescopic shock absorber purpose is control the wheel position, and because of this, it doesn’t require an upper arm. It is very compact because the strut is build vertically. Many front wheel drive and compact cars inherit this kind of suspension system because of the space being occupied by the engine and the transmission. This design is not suitable in sports and performance car as its height requires a higher hood and fender line. And because of this, it doesn’t provide a good handling and it has a little camber change, unlike the double wishbone suspension. MacPherson can be used in both front and rear wheels. Another kind of strut is the Chapman strut being introduced by a guy name Colin Bruce Chapman, founder of Lotus. It’s another kind of Independent Rear Suspension (IRS) that is using a lateral link with a long spring strut. The features are the same as the MacPherson and it’s used for the rear of the wheels. Only some model such as Lotus and the Datsun are using this suspension but it has already being phased out.
Small and compact
Provides an average handling
Cheap and easy to maintain
Camber change due to body roll
Multi-link suspension system
This kind of suspension system is being introduced in the late 1980’s. More modern cars are using this kind of suspension system as it is independent suspension system, uses a minimum amount of short links being attached to the hub carrier and to the body, and it developed a consistent handling and traction. It’s mainly used in rear wheels, not the front wheels. It helps to allow the individual wheel in the rear of the cart to move freely during bumps and uneven roads without affecting the opposite wheel. But during the Research & Development of the cars, most manufacture favors MacPherson struts, swing axle and trailing arm because of its disadvantage of the suspension system. The multi-link suspension uses a few amounts of short links, being attached to the car’s chassis. The link are being used to eliminate the changes of the camber angle during movement, and to control the ‘Toe’ and ‘Caster’ depending on the geometry design of the link. Some manufacturers use 3, or possibly up to 5 links to provide better performance. This kind of suspension is expensive, but an Italian company named Magneti Marelli, are developing a cost-effective multi-link suspension for small cars. In their new design, it uses a flexible links to reduce the cost and use a simple bushing to reduce noise being transmitted to the cockpit.
Provides good handling
More expensive than the MacPherson and torsion beam
Provides good ride comfort
Poor camber control
Leaf suspension system
Leaf suspension is the oldest suspension in the automotive industry. And today, there are still cars that are using leaf spring, mainly for 4×4, trucks, and other heavy vehicles. The leaf suspension makes its way in production in the 70’s. Even some race cars are using leaf suspension system but only in dirt and asphalt. There are 4 kinds of leaf being introduced, and they are:
The monoleaf: The spring is thin and provides a low rate shocks. But in this design, it requires an additional support of springs because monoleaf is not sufficient enough to support the additional load.
Multileaf: It’s made up to multiple layers of leaves with different length. Many 4×4 are using this kind of suspension as it provides higher spring rate and manage to support and control the axle.
Capable of supporting the weight of the chassis
The steel tends to lose its shape
Able to control the chassis roll more efficient
The handling will be affected when the “sag” is uneven
Manage to control the rear end wrap-up and axle damping
Not much adjustment
Capable of controlling the lateral forces produced by the car, the same feature as the panhard bar
Hard to install
Manage to withstand braking forces
Not much dampening so therefore, the ride will become stiff
During acceleration and braking, it manage to regulate the wheelbase length
Sliding pillar suspension system
This kind of suspension features are almost the same as the independent rear suspension. And to be precise, it works as well as the current suspension system such as the wishbone suspension system and trailing link suspension system. But this technology is long gone in the 1950’s and being replaced by wishbone.
Sub-frame mounting suspension system
In modern cars, reducing noise, vibration and harshness are important to the users. And in conventional suspension system, suspension systems are mounted to the chassis. In this suspension, it uses a sub-frame mounting to overcome the noise, vibration and harshness from the conventional suspension system. It’s made out of aluminium to reduce the excessive weight.
Rubber Suspension System
The reason why rubber suspension is being introduced is because it can store more energy per mass than any conventional type of suspension. The rubber springs works during compression, meaning to say that it replaces coil spring.
Twin traction beam suspension system
Commonly known as a TTB. It is an independent suspension used by 4×4. It was first recognize by Ford in the 1950’s. This kind of suspension has an axle that’s able to break into two suspension members. This suspension is being used to minimize the camber and track change. When one of the wheels camber changes, the other follows but in an opposite direction.
The suspension travel distance
Camber becomes negative a lot when in corners
Reducing body roll
In the automotive world, there are 2 kind of basic shock absorber design that is still in use today. They are:
Twin Tube design
Gas Charged Twin Tube
Position Sensitive Dampening (PSD) Twin Tube
Acceleration Sensitive Damping (ASD) Twin Tube
Air shock absorber
Damper shock absorber
Twin Tube Damper
Low Pressure Gas Filled Twin Tube Damper
High Pressure Gas Filled Mono Tube Damper
Before I explain further the difference between these two shock absorbers, I would like to explain the basics of the shock absorber. Many people don’t really know, or even care about the importance of the shock absorber. The main role of a shock absorber, in general, is to reduce as much movement of the suspension and the spring control as minimum as possible. To accomplish this, the hydraulic fluid helps to remove all these energy through thermal, or heat energy. The construction of a shock absorber is practically like an oil pumps. The piston is used to push the hydraulic fluid into the pressure tube with the assist of a piston rod. The hydraulic fluid is being forced to go through tiny orifices into the piston as the suspension is at motion, which is up and down. The resistance of a shock absorber varies, depending on how fast and the size of the orifices being pushed through the piston. Modern shock absorber can reduce the amount of bounce, roll, brake dive and acceleration squat because of the velocity sensitive hydraulic dampening being installed into the shock absorber. In other words, the faster the suspension movement, the higher the resistance of the shock absorber being provided. When the shock absorber is in motion, it’s moving up and down. When it moves up and down, it means the shock absorber is doing a compression cycle and extension cycle. Let’s take a closer look at the compression and extension cycle.
In order for the fluid to move from chamber A to chamber B, it has to go through 3 valve stages in the compression valve. When the piston is in a slow motion, the piston pushes the fluid flows through the oil port but with a restricted amount of fluid being flown to the oil port in order for both chambers to be controlled. But when the piston are moving in a fast motion, the opening of the disc from the valve seat are open widely in the camber B and causes the increase of fluid pressure below the piston. There’s restriction in the third stage orifice when the vehicle are at high speed.
The extension cycle happens where the piston and the rod are being pushed upwards. When the piston are moving upwards, the pressure in the chamber A will be higher than the pressure in the chamber B and thus the fluid are being flown into chamber B by going through 3-stage extension valve. The fluid volume in chamber A is insufficient t fill into the chamber B because the piston rod are being withdrawn from chamber B and this causes the pressure in the reserve tube are greater than the pressure in chamber B, causing the compression valve to be unseated.
Twin Tube Design
Let’s take a look at the Twin Tube design. This kind of shock absorber has 2 tubes, one is known as the working pressure or pressure tube, and the other tube is known as the reserve tube. As you can see the picture on the left, the outer tube is used to store excessive fluid when the shock absorber is moving upwards and downwards. When the pressure tube is short of fluid, the reserve tube sends fluid to the pressure tube. During compression, the fluid in the pressure tube sends fluid to the reserve tube. The upper mount of the shock absorber are usually being connected to the vehicle’s chassis. There are all sorts of rubber being used in between the shock absorber and the chassis in order to reduce road noise and vibration being transmitted to the cockpit. The rubber bushings are flexible, so therefore the suspension can move freely. In the picture, you can see that the upper mount is also known as the piston rod, and the bottom of it is a piston. The piston rod needs to be guided when it’s at motion, so the engineers use a rod guide; some call it bushing, to keep the piston and the piston rod straight. The seal are being used to keep the fluid and the pressure inside the shock absorber. At the base of the shock absorber, there’s a base valve, normally known as a compression valve. This item helps to control the fluid movement when the shock absorber is at motion. The design / bore size of the piston varies, depending on what application. Most 4×4 are using bigger bore size than the sedan cars. And because of the large piston diameter, the unit will become larger and the potential control will be higher. With bigger diameter, the operating temperature and the pressure is low due to area of the shock absorber and the piston bore and thus, this provides higher damping capabilities than the smaller bore.
There are a few types of twin tube shock absorber:
Gas Charged Twin Tube shock absorber
Position Sensitive Damping (PSD) Twin Tube shock absorber
Acceleration Sensitive Damping (ASD) Twin Tube shocker
Gas Charged Twin Tube Shock Absorber
This kind of suspension system uses low pressured nitrogen gas in the reserve tube but the amount of nitrogen gas varies, depending on the amount of fluid inside the reserve tube. The purpose of the gas is to minimize the hydraulic fluid aeration to prevent the foam build up because foam can be compressed. The gas charged shock absorber provides engineers more flexibility to design the valve. The other main advantage is that in the vehicle, it creates a mild boost of spring rate. Among the other benefits of this shock absorber is:
The reduction of roll , sway and dive, the handling is improved
Providing better smooth control in any road conditions and corners
Longer heat transfer in gas charged shock absorber
Position Sensitive Damping (PSD) Twin Tube Shock Absorber
The Position Sensitive Charged is still new in the automotive world. In this design, the ride control and comfort are optimized, thanks to the tapered grooves located at the pressure tube. This absorber provides a smooth and a comfortable by reducing the resistance onto the piston, by allowing the fluid to pass freely and smooth around the piston. Here are the advantages of this shock absorber:
Providing a smooth ride
Can easily adapt to variable road and weight conditions.
Acceleration Sensitive Damping (ASD) Twin Tube Shocker
The features of this absorber is the same as the other twin tube shock absorber, the only addition is that the compression valve is design to sense a bump on the road and automatically adjust the shock to provide better control of the shock absorbed.
In the mono-tube design, there’s only one tube in the high-pressure gas shocks, known as the pressure tube. There are two working piston inside the mono-tube design, that is a working piston and a dividing piston. The mono-tube and the twin tube design are almost similar but the only difference is that the mono-tube can be install in any way, either mounted upside down or right side up, but either way, it still works the same. The unique design of the shocks is that it doesn’t use a base valve, but it uses a piston to control the extensions and compressions. In the mono-tube design, it has a larger pressure tube to comply with the dead length, compared with the twin tube design. The downside of this design is that it’s going to be difficult for the engineers to install this kind of shocks into the cars instead with the twin tube design. The separation of the gas and the oil is done, with the help of the free-floating dividing piston. The gas below the dividing piston is pressurized, at around 360 psi to accommodate the vehicle’s weight. When the shocks are at motion, the movement of the dividing piston varies, depending on the movement of the piston rod in order for the pressure in the tube are pressurized at all times. Here’s the upside of the design:
Can be mounted freely, compare to the twin tube design, and helping to reduce the unnecessary unsprung weight
The working tube can work harder because the working tube is exposed, so therefore can be cooled easily.
Every upside of the design, there’s always a downside:
Easily destroyed when there’s a dent
Hard to install onto the passengers car that has a twin tube design
Damper Shock Absorber
Damper shock absorber, or as short, damper, are used to provide an optimum absorption of shocks and smooth lateral deceleration. The dampers can be powered by fluid, or mechanically powered.
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