Suspension system: types and functions

03.06.2019
Suspension system: types and functions

What is SUSPENSION SYSTEM ➤ TYPES of suspension system ➤ FUNCTION of the suspension system ✅

Automobile suspension is a complex of mechanisms that make up chassis together and perform the function of a link connecting car body and road surface.

Vehicles went without suspensions for quite a long time. It was simply unnecessary at slow speeds. However, with the course of automobile industry development, increasing road quality and transporting speed there arose the need to increase transportation comfort.
Let’s have a closer look at what is suspension system, what are its construction features, functions and what types of suspension exist.

Some background: how the first suspension appeared and construction improvement
The first suspension looked rather primitive – details on long belts of leather or chains. When movement speed increased is tangibly decreased jumps and smoothened fluctuations of the compartment. Such a system was installed on caroches and post coaches.

The scheme of modern suspension with bearings and elastic elements was developed by O. Elliott from England at the beginning of the 19th century. They used steel and wood for making shock absorbers. However, the item was still far from perfect and often broke on rough roads. They managed to overcome this defect as the metallurgy industry developed and made the suspension more rigid and load-resistant.

Noticeably, such construction is still used in load-carrying trucks.

The story of modern automotive suspension started in 1898. A French company named Deauville first used McPherson knee-action suspension with immovable bearings in a passenger car.
Shock absorbers were first installed on automobiles in 1901. Mr Mors, a Frenchman, installed them on a racing car as an experiment and in that very year, the race car driven by a racer A. Fourier won the race Paris-Berlin. Later in 1906 carriage springs were replaced by cylinder springs. Then during the 30s-50s construction engineers from all over the world worked on suspension improving and tried each and every scheme of its construction and installation. From among all tested construction types the optimum ones were selected which are used by this day.
Nowadays most of the passenger cars use suspensions of three types – independent construction, independent on double cross-installed levers and semi-dependent with a torsion beam.

Constructional features of suspensions

There exists a vast classification of the External link, though all suspensions have common integral elements:

●   details responsible for elasticity;
●   details which spread force direction;
●   absorbing elements;
●   mountings;
●   components that stabilize sway steadiness.

Suspension system details responsible for the elasticity

Let’s start from the beginning. Details responsible for elasticity perform the function of some buffer between the body of a vehicle and the road surface. These are the elements that react to impulses from surface unevenness first, smoothen them and transfer to the car body. This group includes:

1. Coiled springs

Springs can have constant and variable rigidity. Items with constant stiffness have the same diameter on both ends. As for the second type, the diameter of spring and rod vary on different ranges. In the center of both spring types, a rubber bump stop is installed. This detail is required to smoothen fluctuations and prevent springs damage when it is fully compressed.

2. Torsion bars

A torsion bar is a metal tube with rods inside. They (the rods) work on the principle of twisting. It means that before installation torsion bars are torqued around the axle and then make the force of untwisting. This function is controlled with special levers and shock absorbers using the bars as an elasticity element.

3. Plate springs

The appearance of plate springs reminds of a pile of stiff metal stripes tightened with clamps. Plate springs perform both shocks absorbing and directing functions. This element can be either a few-leaf or multi-leaf. The only difference is in the number of metal sheets that resist the load. Few-leaf springs are installed on both passenger and load-carrying automobiles. In comparison to multi-leaf ones, they are more promising and universally applicable items.

Let’s have a closer look at few-leaf plate springs. As far as their construction understands using less quantity of sheets, they keep up to tough requirements in production. Such stripes are made of high-strength steel doped with manganese, chrome, nickel, and silicon. Moreover, the surface of the sheets must be perfectly smooth. The presence of even minor cracks or protrusions has an adverse effect on springs durability and effectiveness. By the way, the durability of few-leaf springs is the main problem in their application. To prolong the lifetime of this essential suspension element, they apply reinforcement methods, try to reduce damages from applied forces and reduce tension in the entire spring.

The upper leaf of the plate spring is processed with shot blasting. To reduce damages from applied forces, they cover the ends of spring leaf with rubber buffers and introduce restraint which limits bending moment. In order to reduce tension, they change the cross-section shape of the sheet and add resilient elements to the construction.

Details which spread force direction

Elements that spread force direction additionally perform the function of suspension mounting. They are necessary to transfer the force to the body and to support the direction of the correct wheels with respect to the body (vertically and horizontally). These details are the levers of a cross and linear installation and also doubled levers.

Absorbing elements

Absorbing elements, or spring absorbers, perform the function of counterwork to elasticity elements. They are needed to smoothen and soften fluctuations and drops while driving an uneven surface. A shock absorber is made in the shape of a metal tube on which fastening elements are installed. This construction element works on the principle of hydraulic friction. As for the type of construction, dampers can be:

●   pneumatic;
●   gas-oil;
●   oil.

Some models can be equipped with special stiffness adjustment.

Fastening

Car suspension parts which belong to this category fasten other components and overall suspension construction to the wheel bearers and to the car body. The list of fastening elements includes silent blocks and swivel joints. Silent blocks are mounted on levers and are fastened to the body with screw-holt joints. Ball joints are produced in the shape of a compact hinge mechanism. They are fastened to wheel bearers and levers. Swivel joints are used on both front and rear suspension.

Components which stabilize sway steadiness

Stabilizing elements for sway steadiness provision look like a beam with mounting installed on it. Also, the beam connects the levers of the opposite wheels. Stabilizing elements are also intended to reduce body inclination while driving an uneven surface and equally spread the vehicle’s side load while direction turns.

What functions suspension performs

Let’s take a closer look at the function of a suspension system. Its performance directly influences the level of automobile’s controllability and passengers’ comfort in the compartment. However, each and every suspension, regardless of its constructional features, should perform the next functions:

1.   Absorbs and softens jumps and shocks while driving and uneven surface. This both significantly increases the comfort of driving and strongly reduces loads on the body. Thus, prolongs the lifetime of the mechanisms and systems of an automobile.

2.   Stabilizes an automobile while driving. This is realized by the suspension’s limitation of the car body’s excessive inclination and provides constant tires contact with the road surface.

3.   Keeps the set direction of wheels and movement geometry. It helps keep high control precision while driving or emergency brake application.

Suspension can be either soft or rigid. The latter is an excellent choice for fast or aggressive driving. In this case, the suspension must react to all driver’s actions immediately and precisely. The list of such suspension’s functions includes the following:

●   providing low road clearance;
●   make an automobile as stable as possible;
●   increases resistance to the body’s inclination and swaying.

Such type of suspension is used mostly in automobiles of sports kind.
The soft suspension is the optimum variant for city passenger cars. It smoothens jumps on road uneven surface in the most effective way but makes the car less dirigible.

In case you are going to use an automobile under different circumstances, the best choice for you is to install a screwed suspension. Its construction includes dampening bearings which allow changing tension force of the spring.

What suspension types exist

There are two types of the suspension system in devices with the kinematic system. There are dependent and independent.

Dependent

Wheels of the vehicle are firmly connected to each other by means of a solid beam or truss. Front wheels are rotatable, and as for the vertical position of wheel pairs – it does not change in respect to the main axis.
Inner constructions of front and rear suspension are identical. There are coiled spring, plate spring, and pneumatic suspension.

The benefits of dependent suspension include the following:
●   simplicity and reliability in real-life circumstances;
●   good load-carrying ability;
●   wheel ruts and clearance remain permanent – it is a rather useful aspect at off-road driving;
●   large suspension travel – it allows overcoming obstacles with no difficulties.

Drawbacks:
● poor controllability;
● the suspension is not very stable at great speeds;
● the suspension is less comfortable.

Independent

Apart from that, independent suspension wheels are firmly connected with each other and there are lots of unsprung elements. Especially it impacts the axles where the powered pair of wheels are located. As a consequence, together with heavy axle weight it negatively influences the stability of vehicles’ movement and their driving precision.
Independent

The main feature of an independent suspension system in an automobile is its ability to change the vertical position of wheels with respect to each other with no leaving their plane.

The advantages of such suspension include:
●   high controllability;
●   comfortableness;
●   high stability of a vehicle.

Disadvantages:
●   construction is much more expensive;
●   independent suspension is less reliable in real-life exploitation.

If you need an accommodating variant, you may pay attention to torsion beam or half-dependent suspension. With such a mechanism, installation wheels are still linked but can slightly move relative to one another. It has become possible thank to U-shaped beam which connects the wheels. Most often a suspension of such type is installed on the rear wheel pair of budgetary automobile models.

Popular kinds of independent suspensions:

1.   McPherson

This suspension type is most widely spread among up-to-date automobiles. It is installed on the front and rear axles. The benefits of this construction include simplicity, small size, low cost of fabricated unit and repair and also durability. The main disadvantage is not very high automobile’s controllability.
The main peculiarity of McPherson suspension’s inner design is the presence of shock absorber strut. It is mostly used for the front wheel pair. The strut includes shock absorber and spring. The upper part of the construction is covered with rubber bush bearing and is linked with mudguards on the car’s wheel arches. The lower part of absorber strut is reliably connected with swivel-axle assembly. However, this is the standard variation of design. Some producers of car spares divide the spring and shock absorber into two independent elements of single construction.
Application of this suspension with such strut gave an opportunity to install transmission and engine in the underwood space of a vehicle in a lateral position. For this reason, McPherson suspension is widely used in modern front-wheel has driven automobiles.


The construction includes a transverse lever, steering knuckle, subframe, shock absorber strut consisting of a spring and a shock absorber, and also the antisway stabilizer bar. Additionally, a torsional bar can be applied in the role of an elastic element. The main bearing element of such suspension is a subframe. It is fastened to the automobile’s body by means of silent blocks. To reduce vibration and noise transition to the body they use rubber-metal bearings. The levers have dual mounting which provides additional rigidity to the construction. One end of the suspension shoulder lever is equipped with a steering knuckle. By means of a hinge joint, it is linked to steering rod and controls wheel turning. The knuckle includes two important elements – a bearing mount assembly and a brake caliper. The upper part on the knuckle is mounted and fastened on the shock-absorber strut beam and the lower one is connected with the shoulder lever.
Antisway stabilizer in McPherson suspensions is intended to reduce vehicle’s side inclination while movement. The ends of this detail are connected with shock-absorber struts with the help of a hinge joint.
In some autos, the spring and shock absorber are installed separately. But such construction is just the same called McPherson suspension for the key feature – rigidly fixed strut in a swivel member.

Advantages of McPherson suspension:
●   less cost in production in comparison to suspension with dual cross levers;
●   compactness;
●   reduced unsprung weight;
●   increased durability of upper bearing strut produced as an end-thrust rolling bearing;
●   simple malfunction identification because wear scars are well noticeable.

Drawbacks:
●   if to compare McPherson suspension with constructions on several crosses or linear levers, this item has far worse kinematic characteristics;
●   it’s necessary to additionally reinforce wheel arch mudguard;
●   in case the driver uses full travel of suspension and prefers aggressive driving style, there may appear cracks in the joint points of the struts on the mudguard;
●   shock absorbing struts often break down and thus require frequent replacement, and it costs much;
●   reduced compensation of vehicle’s linear inclination at brakes using;
●   road noise and jumps are well felt in the compartment.

Moreover, such suspension is not recommended to install even on light trucks.

2. Double-wishbone front suspension

Construction of this suspension kind is considered more effective and complicated at the same time but it provides high automobile controllability. The upper junction point of suspension fastening is on the second shoulder lever. A torsion or a spring is installed as an elastic element. The inner design of rear suspension is identical to the front one.
They started using such suspension in the 30s of the former centuries gradually improving its design.
A double wishbone suspension has some peculiarities which impact the automobile’s behavior on the road. One of the main parameters is the length and location principle of A-shaped levers. It’s worth mentioning that short levers of the same length are almost never used because they complicate automobile’s control on an uneven surface.

3. Pneumatic suspension

In pneumatic suspension buckets filled with compressed air are used instead of springs. Pneumatic suspension allows adjusting body height and substantially improves the vehicle’s movement fluency rates. Such a suspension type is installed in elite-classed automobiles.

Constructional design of pneumatic suspension includes the following components:
●   compressor;
●   sensors tracking body position;
●   control system;
●   pneumatic elastic elements;
●   receiver.

Most often pneumatics is installed on all 4 wheels at once, it gives the opportunity to increase clearance manageability.

4. Hydraulic suspension

In a hydraulic suspension shock absorber is connected with a single closed circuit that contains hydraulic liquid. Using such suspension allows adjusting both clearance height and stiffness. In case the auto is equipped with controlling electronics and functions of adaptive suspension are enabled, the construction substantially eases driving. It dynamically adjusts itself relevantly to driving style and road surface complexity.

Advantages of hydraulic suspension:
● durability – under correct maintenance and complying with rules of operation it is able to run over 400 thousand kilometers;
● guarantees soft running fluency under any circumstances on any type of road surface;
● it is possible to adjust road clearance in the comfort of the car’s compartment;
● hydraulic suspensions of the latest generation equipped with Hydrastine technology allow changing clearance on the run and even while turning.

Drawbacks:
● in hydraulic-type suspension oil, the main working body and it is also used to supply hydraulic powered steering and brakes system. So, in case of oil leakage all three listed systems break down;
● suspension maintenance costs much.
For these reasons world producers rarely equip new car models with hydraulic suspension despite all its benefits.

5. Sports independent suspension

There is a great difference between conventional and sports suspension in automobiles.
Sports independent suspension, otherwise named coil over, is presented by shock absorber strut which allows stiffness adjusting directly at an automobile. The springs have threaded fastening at its lower seat. Thank it its height and road clearance can be adjusted.

Construction design of sports suspension includes the following elements:
●   shock absorbers;
●   elastic details;
●   strut seats;
●   stopper which limits travel range;
●   directing levers;
●   fastening elements.

It’s worth mentioning that different suspension types are used for different driving styles. So, there exist suspensions for drifting, drag racing competition style, really, closed circuit race. Drag racing one is made of light-alloy materials and can be adjusted to optimize tires traction with the road while head starts. For a rally model, the optimum choice is a system developed especially for roads with complicated topography and surface. As for closed circuit races, the best choice for them is suspension with adjustable shock absorber with upper seats.

Advantages of sports suspension:
●   displaced center of gravity, which radically improves car stability;
●   increased controllability;
●   improved speed;
●   lowering problem overcome;
●   opportunity to automatically adjust clearance height without visiting car service facilities.

However, there remain some drawbacks:
●   suspension of sports type is expensive in installation and after-sale maintenance;
●   nondurability – suspension wears off quickly because of high loads;
●   maintenance complexity;
●   is not suitable out of racing track – if to use suspension on the bad road surface, you will have to repair it very frequently.

Sports suspension is a perfect option for a racing car, however, for an everyday-used crossover, we recommend to install standard modified suspensions.

6. Push-rod and pull-rod suspensions

Suspensions of such type were developed especially for installation on racing cars with open wheels. A double fishbone scheme is the core of its construction design.
The main difference between push-rod and pull-rod suspensions is that dampening elements are located inside the body. Construction designs of both suspensions are very similar to each other, the only difference between them is the location of load carrying elements.
In a push-rod type suspension the push pod, otherwise – the instrument which carries all load resists compression. In a pull-rod suspension, this component resists tension. Additionally, the first type has a higher gravity center in comparison to the second. However, there are no significant differences between these two suspensions and their overall efficiency is almost equal.