THE ROLE OF SUSPENSION IN CAR DESIGN: AN IN DEPTH LOOK AT THE COMPONENTS AND DESIGN PRINCIPLES
Updated: Nov 3, 2023
WHAT IS SUSPENSION?
When you jump from a great height, your knees bend and absorb the impact. But have you ever considered how the impact might affect your entire body if your knees were unable to bend at the time of landing? Your bones (the complete skeletal system) can break in case of a very heavy impact.
Similarly, when a vehicle faces any obstacle on the road, such as bumps, potholes, and other road imperfections, it has a significant impact on the vehicle's structure (chassis). The suspension is a fundamental component of a vehicle (particularly a car) that functions as shock absorbers, absorbing the impact of the jerks generated by the obstruction and preventing the chassis from shattering.
WHAT IS THE USE OF SUSPENSION IN THE CAR ?
After knowing about suspension now, the question arises why should we use it in the car?
Suspension is one of the most important elements of the car. The car dynamics and the comfort inside the car are decided by the suspension. Suspension helps the wheels to be in contact with the road.
TYPES OF SUSPENSION
1) DEPENDENT SUSPENSION
Dependent Suspension comes in a variety of forms, namely -
(i) LIVE AXLE OR SOLID AXLE:
In a live axle, the shaft (or, more typically, shafts combined to move as a single unit) provides power from the engine to the differential, which then transfers the power to the wheel.
ADVANTAGES: It provides more efficient power transfer to the wheels and is less in weight than alternatives that require minimal ground clearance, allowing go-karts to have a very low centre of gravity.
DISADVANTAGES: It does not allow to move each wheel independently and handling is typically worse.
USE CASES: The basic role of the live axle in a vehicle is to transmit power to a pair of wheels. The main role of this kind of suspension is to lift heavy loads. This type of suspension is found in trucks, some cars (Mahindra Bolero, Mahindra Thar, etc).
(ii) DRIVER OR FIXED AXLE
The first time a drive axle was used was in a team tractor for agricultural purposes, but it quickly became necessary for every vehicle. Drive axle is used for carrying loads, protecting breaking components, transmitting power to each wheel, differentiating speed between wheels etc.
There are three major drive axles –
RIGID DRIVE AXLE: It is used for carrying different loads.
DRIVE-STEERING AXLE: It allows the wheels to move precisely for cornering.
INDEPENDENT SUSPENSION DRIVE AXLE: It allows each wheel on the same axle to react to a bump on the road independently of the others.
3) TORSION BEAM SUSPENSION OR TORSION SPRING SUSPENSION OR TWIST BEAM SUSPENSION
Torsion beam suspensions are those that use a torsion bar as the main weight-bearing spring.
It consists of two primary components –
TRAILING ARM
ANTI-ROLL BAR
ADVANTAGES: It is simple to design and cheaper to make.
DISADVANTAGES: It does not allow for much wheel adjustment and needs a lot of reinforcement to keep the welding points from becoming fatigued.
USE CASES: This type of suspension is widely used in a variety of compact front-wheel drive vehicles and is mostly prevalent in European superminis.
2) INDEPENDENT SUSPENSION
Independent Suspension also are of several types such as –
(i) DOUBLE WISHBONE SUSPENSION
Double wishbone suspension allows each wheel to act independently from the others by two wishbone shaped arms also known as double-a arms that are located between the steering knuckle and the chassis.
WORKING PRINCIPLE: Double-wishbone suspension uses wishbones with two attachment points on the chassis and one joint at the steering knuckle. The coil-spring and shock absorber control vertical motion. Camber, a measuring term that affects driving dynamics, can be negative or positive. Effective camber control improves handling by keeping the tire's contact surface evenly loaded. The suspension's control arms are typically two parallel arms of equal length, but a shorter upper control arm induces negative camber during vertical travel.
ADVANTAGES: This suspension system provides a smoother ride on rough ground, improved handling, and increased control over the vehicle's movement. It keeps the tyres perpendicular to the road regardless of wheel movement and allows independent wheel action.
DISADVANTAGES: It consists of more components therefore it is more expensive to design, maintain and manufacture and also become heavier and requires more space.
USE CASES: It can be used in front or rear wheels. It is now the first choice for racing and sports cars.
(ii) MULTI-LINK SUSPENSION
A multi-link suspension system is a system that is derived from a double-wishbone suspension and has three or more lateral arms as well as one or more longitudinal arms.
The arms do not have to be of the same length. They can be angled away from their natural orientation. Each arm usually has a ball joint or rubber bushes at each end. It can consist of 3, 4, 5 or more multi links. The basic advantages of using them are –
3-LINK SUSPENSION: It allows free vertical, longitudinal and rotational motion or in other words it allows the triple-axis freedom.
4-LINK SUSPENSION: It allows free vertical and rotational motion or the double-axis freedom.
5-LINK SUSPENSION: It allows only single-axis freedom i.e. only free vertical motion.
The arms need to control steer and lateral compliance. This requires a pair of longitudinally separated arms. It needs to control the camber and how it changes as the wheel rebounds or drops up and down. It must transmit traction and braking loads as well as to control caster. This is usually done via longitudinal arms.
SOLID-AXLE-MULTI-LINKS SUSPENSION
One of the modified versions of this suspension is Solid-axle-multi-links suspension. It is much cheaper, easier to build and offers good mechanical durability and excellent reliability and has very similar advantages.
ADVANTAGES: It is considered to be the best independent system for production for vehicles as it offers the best compromise between space efficiency and handling as well as comfort. It is a great solution for off-road driving as they allow the vehicle to bend more.
DISADVANTAGES: It is expensive and complex to design and manufacturing. Also difficult to tune the multi-links geometry without a complete 3D computer-aided design analysis.
USE CASES: This suspension is widely used for sports such as desert racing as it allows the vehicle to flex more This means that the suspension is able to move more freely to accommodate the varying angles of off-road driving.
(iii) MACPHERSON STRUT SUSPENSION
It is the most widely used front independent suspension system where the wheels are allowed to move independently performing functions as a steering rod, and as a suspension damper. Its parts are lower control arm, wheel hub, strut(shock absorber and spring), steering link, etc.
A single control arm connected to the bottom of the wheel hub, and a shock spring combination protruding from the top the MacPherson strut combines the coil spring and shock absorber into an integrated unit. This makes the suspension more compact and lighter that can be used for front wheel drive vehicles.
It is of three major types:
(a) CLASSIC PSEUDO MACPHERSON
This suspension system does not require an anti-roll bar, which reduces manufacture costs and axle weight. In certain cases, especially for lightweight cars, the spring stiffness alone is sufficient to maintain body stability while cornering.
(b) PSEUDO MACPHERSON WITH FICTIVE STEERING AXIS
It has a virtual steering axis. Two arms replace the bottom wishbone. This suspension is more expensive than a traditional pseudo MacPherson suspension.
(c) PSEUDO MACPHERSON WITH INDEPENDENT STEERING AXIS
It allows to separate the camber angle setting and the king pin angle through the steering axis. This type of suspension is usually used for racing cars.
ADVANTAGES: It requires less components to produce and is cheaper to make, more lightweight and smaller than other suspension systems. Even then it's stable.
DISADVANTAGES: It has a lengthy vertical assembly which would run into problems when needed to lower the vehicle. Camber variation is one of the major problems.
USE CASES: This type of suspension becomes more attractive as it takes over the tasks of a steering rod and serves simultaneously for suspension and vibration damping.
(iv) AIR SUSPENSION
Air suspension is a type of suspension system that uses compressed air to adjust the height and stiffness of the suspension, providing a smooth ride It has a higher load-carrying capacity than mechanical springs and also includes a variable spring rate. It has several parts such as TOP PLATE, BELLOW, LOW-FRICTION PLATE, EMERGENCY SPRING, BASE PLATE, etc.
It has three major connection lines -
PRESSURE LINE: It is connected to a control valve
RETURN LINE: It is also connected to a control valve
CONTROL LINE: It is connected to a level valve.
WORKING PRINCIPLE: The height of the air spring is continuously adjusted by altering the air pressure using a load levelling device.
A flow of channels is shown below –
ENGINE → COMPRESSOR → AIR TANK(RELIEF VALVE) → CONTROL VALVE → PRESSURE LINE → AIR SPRING → RETURN LINE
ADVANTAGES: This suspension reduces the tendency of short-wheelbase trucks to bounce over rougher roads and terrain when the vehicle is empty, also used in rail bogies, Volvo buses etc.
COMPARISON BETWEEN DEPENDENT AND INDEPENDENT SUSPENSION
FEATURES | DEPENDENT SUSPENSION | INDEPENDENT SUSPENSION |
|---|---|---|
ARRANGEMENT | This is a simple arrangement. | This is a more complicated arrangement. |
TYPE OF SYSTEM USED | Leaf Spring systems are used. | Coil Spring systems are used. |
WORKING PRINCIPLE | The up and down movement of either of the front wheels causes a vertical tipping effect on the other wheel as these wheels rotate on a common axle. | Each wheel is free to move up and down with minimum effect on the other wheels. |
SHOCK DISTRIBUTION | Shock is transmitted from one wheel to the other. | No shock transmission takes place. |
EFFECT ON STEERING | This system does not allow much deflection of the front wheel and also has some effect on the steering. | This system allows more deflection of the front wheels without any effect on the steering |
SPRING WEIGHT | Spring weight is relatively more. | Less Spring weight. |
VIBRATION DAMPING | Less effective. | More effective. |
MAINTENANCE COST | Relatively less. | Relatively more. |
PRIMARY COMPONENTS OF SUSPENSION
Suspension system is the name given to the system of springs, shock absorbers and linkages that connects the vehicle to the wheels to provide smooth and controlled movement of the machine.
Every component of a car is made up of various subcomponents. Similarly, suspension also has various subcomponents. They are-
Steering Knuckle
Control Arm
Ball Joint
Suspension Springs (Coil Spring/ Leaf Spring/ Torsion bar/ Rubber spring)
Sway bar (Anti roll bar)
Dampers (Shock Absorber/ Coil over)
Let's dive deeper!
1. STEERING KNUCKLE
Steering knuckle is the part which connects the wheel hub and spindle assembly to the suspension and steering components. It plays a critical role in maintaining the alignment and stability of the vehicle while driving.
2. CONTROL ARM
Control arm is a moving lever that fastens the steering knuckle to the car's frame. Control arms typically consist of a metal rod or tube with pivot points at both ends to allow for movement in multiple directions.
3. BALL JOINT
A ball joint is a type of pivot joint that connects the control arm to the steering knuckle or spindle of the suspension system allowing the wheel to move in multiple directions while still remaining firmly attached to the suspension. Ball joints are able to handle a lot of weight and stress while still allowing for smooth movement.
4. SUSPENSION SPRINGS
Spring in a suspension system gives stiffness or softness character to the suspension. Stiffness or softness depends on spring rate which is load /deflection. For example, among two springs with spring rates of 150 kg/cm and 70 kg/cm, the first one is stiffer than the second one. There are mainly four types of spring use in automobiles.
(i) Leaf spring
It is a combination of bent metal straps. It was used in automobiles earlier and now-a-days in heavy vehicles like trucks.
(ii) Coil Springs
These types of springs are used in most of the cars. They are of three types - constant spring rate, progressive spring rate and dual spring rate.
(iii) Torsion bar
It deflects torsionally and is used mostly where stiffer suspension is required. In racing cars, military tanks we can see this type of spring system.
(iv) Rubber Springs
It is a dependent spring mostly used as a helper spring. It does not need any shock absorber.
5. SWAY BAR OR ANTI ROLL BARS
Sway bars are connected to the left and right side of the car suspension system. When the car is in a corner situation or curvy road one side of the car suspension gets more compressed than the other which causes torsion on the sway bar. Now, the sway bar restricts the twisting thus limiting the amount the body can roll.
6. DAMPERS
Spring in a suspension system absorbs the bump but it vibrates back and forth when compressed. You're driving a car and feeling jerking motion. It won't be pleasant for you, will it? Here, comes the use of a shock absorber. Shock absorber dampens the vibration allowing spring compression relatively easy and spring expansion relatively tough.
In a nutshell, we may conclude that the car suspension system determines the rider's comfort and safety. Therefore much study is currently being done on suspension systems to make your car ride more enjoyable. Also Electromagnetic Suspension is now-a-days used in automobiles.
REPORT BY:
Koustav Das
Arpit Sarkar
Sourav Paul
Debadrita Hazra