Abstract
Suspension systems in automobiles are essential to the function of the vehicle, and most suspension systems live towards the bottom of the car and interface between the wheels/axles and chassis/frame of a vehicle. Suspension systems come in many styles and use different components depending on the terrain, vehicle type, vehicle use, and driver preference. In this report, a brief history of the adoption of suspension mechanisms in the automobile and how they developed over time will be covered, including the significant components that make up a suspension system and the common types of suspension systems used today. Lastly, the emerging technologies being implemented for suspension systems will be discussed.
Introduction
A suspension system aims to reduce the impact a change in terrain has on the vehicle and its passengers. Suspension systems are used over bumps, potholes turn, accelerating, braking, and carrying passengers/loads. A suspension system works by initially taking the impact, then dispersing the energy of that impact through a dampener. The system accomplishes multiple things in doing so, increased driver/passenger comfort because sudden effects are softened, the stresses/vibrations on the rest of the car are reduced, which increases the lifespan of the vehicle—increased friction of the wheels on the road to keep the car under control.
History
In 1885 the first internal-combustion engine automobile was made by German engineer Karl Benz and consisted of a rigid frame and axle assembly. It became apparent to handle turns and deal with uneven roads. A mechanical subsystem would need to be designed and installed on future vehicles. In 1906, the Brush Runabout 2-seater was released by William Brush with a revolutionary suspension system containing both coil springs and a damping mechanism. But after the Ford Model T, the first mass-produced vehicle was released in 1908. The leaf spring became the norm mechanism in the front and rear of the vehicle. Finally, by the late 1930s, double-acting tubular shock absorbers became typical on all vehicles, and innovations/updates to shock absorbers and springs are found on vehicles today.
Suspension Components
Present-day suspension systems contain two main components to reduce the impacts vehicles face on the road, a shock absorber and a spring. The different combinations of these parts can vary based on vehicle requirements, but the conventional methods/parts are listed below.
Springs
Springs are used in all suspension systems to effectively absorb and redirect significant impacts. The springs in a suspension system work to keep the vehicle’s wheels on the ground by rebounding the effect taken.
Coil Springs
The coil-over-shock absorber combines the dampening power of a shock and the elasticity of a coil spring to create a critical part of the Double Wishbone and Macpherson Strut suspension systems. The coil spring encircles the shock, preventing the chassis from bottoming out after an impact, as shown in Figure 1. Due to their versatility, coil springs can be found on independent, semi-independent and dependent suspension systems.
Figure 1: Coilover shock absorbers. [9]
Leaf Springs
The leaf spring is a series of increasingly shorter metal plates stacked together designed to disperse larger loads across a larger area. Commonly used on most vehicles in the past, leaf springs can be found today on heavy commercial vehicles, vans, and railway carriages. Due to their heavy-duty applications and minimal adjustability, leaf springs are often paired with semi-dependent and dependent suspension systems, as shown in Figure 2.
Figure 2: A modern solid/live axle suspension system with leaf springs. [10]
Torsion Bars
Used in conjunction or as a replacement for the coil/leaf spring, the torsion bar was another solution to keep the wheels of a car on the road. Used in front and rear applications, torsion bars would be fixed to the chassis and attached to the car’s suspension system, turning the vertical translation of the wheel(s) into rotational motion and torquing the bar, as shown in Figure 3. Then, the torsion bar would flex and spring back into place. Torsion bars are typically made from steel or titanium. Today, torsion bars are popular with trucks, Formula 1 race cars, and some SUVs.
Figure 3: Torsion bars and their application in a Porshce suspension system. [11]
Shock Absorption
Shock absorbers are used to dampen the movement of the springs, turning the kinetic energy from the springs into thermal energy. Shock absorbers also handle small bumps and impacts much smoother than springs, which is why the two parts work in unison to take the effects. Most shock absorption methods use a non-compressible hydraulic fluid inside the piston cylinders. Once pushed through the cylinders, the pressure and heat are dissipated out the exterior of the cylinders.
Monotube
A monotube shock absorber uses one cylinder to encompass all parts needed for the shock. All fluids and gasses are pushed through one piston, although the two never mix due to a floating piston beneath the shafted piston. As a result, monotube shock absorbers are very responsive, as the gas beneath the fluid can build pressure at a rapid rate, responding well to more significant impacts a vehicle may face.
Twin Tube
A twin-tube shock absorber has two separate fluid areas, an inner working cylinder and an outer fluid reservoir that acts as an expansion area. The shaft and piston move inside the inner working cylinder, pushing fluid between each. Valves inside the piston resist the juice to slow/dampen the impact. Twin-tube shocks are preferred for normal to moderately intense use, as more intense/rapid creates foaming in the shock, rendering the valves less effective, which leads to a significant decrease in performance from the shock. Twin-tube shock absorbers are typical on most passenger vehicles. A side-by-side look of a twin-tube and monotube shock can be found in Figure 4.
Figure 4: A visual representation of the cross section of a Monotube and Twin Tube system. [12]
Suspension System Configurations
Today’s suspension systems are composed of numerous parts; linkages, axles, wheels, springs, absorbers, and clevises, to name a few. Furthermore, the assembly of these components can be manipulated and altered in many ways to form unique types of suspension systems, which can be applied to various vehicle types based on their needs.
Independent Systems
Independent suspension systems allow each wheel to act and react separately from the rest of the wheels. Independent systems are popular for use on the front wheels of vehicles. However, all wheels of an automobile can adopt these suspension types.
Single Wishbone System (Macpherson Strut)
Today, one of the most common automotive suspension systems is a single wishbone system known as the Macpherson Strut. The suspension system is designed using the steering knuckle to connect one wishbone-shaped linkage (lower control arm) to a strut attached to the absorption mechanism of the system, as shown.
in Figure 5. 
The popularity of this system comes from its straightforward and inexpensive nature compared to other suspension systems. The Macpherson strut can be found in most passenger vehicles and all front-wheel drive vehicles due to the strut’s structural integrity.
Double Wishbone System
The double-wishbone suspension uses two wishbone-shaped linkages that (typically) pivot in parallel when in use. The primary design concept is that the top wishbone (upper control arm) is attached solely to the frame of the car. In contrast, the bottom wishbone (lower control arm) is connected to both the structure and the absorption mechanism or vice versa, as shown in Figure 6.
Figure 6: Diagram of the basic double wishbone suspension system. [14]
A double-wishbone system is more complex than a single wishbone system, making it a more expensive mechanism. Geometrically this system requires less vertical space by eliminating the strut. However, it does require more space horizontally for the wider wishbones. A double-wishbone system provides drivers with a smoother handling experience because its vertical translation on a rough road will not impact wheel alignment as significantly. Different adaptations of the double-wishbone system like the Multi-Link system have been invented, but in principle, they work the same way. The double-wishbone system is typically installed in sporty sedans and high-performance vehicles.
Semi-Independent Systems
Semi-independent suspension systems are assemblies that allow either the front or rear wheels to move relative to each other while remaining interlinked.
Twist/Torsion Beam System
The twist/torsion beam suspension system is designed to connect a set of wheels to the same beam, allowing for vertical translations to be converted into rotational energy through that beam. The deformable beam is assisted by coil springs to return to its original state after an impact has passed. Figure 7 shows an example of the twist/torsion beam system.
Figure 7: Diagram of the twist/torsion beam suspension system. [15]
The twist/torsion beam’s design is straightforward and lightweight, but it poses some disadvantages to the vehicle as well. The ability to adjust this system is minimal, and with semi-independent systems, the impact harshness is going to be far greater than independent. The twist/torsion beam suspension system can be found at the rear of most economy vehicles.
Dependant Systems
A dependent suspension system is an assembly that forces a set of wheels to have a dependency on one another. For example, if the back left wheel experiences a sudden downward drop (pothole), the dependent system will redistribute the force into the right rear wheel as well, and it will respond by elevating.
Solid/Live Axle System
The solid axle suspension system takes a set of wheels and links them through a rigid beam, and the shaft attaches to shock absorbers and springs on the vehicle. Figure 8 illustrates the solid/live axle system.
Figure 8: Diagram of the solid/live axle suspension system. [16]
Solid/live axle suspension systems are a common rear suspension assembly for trucks and off-road vehicles. They make it easier to traverse intense approach/departure angles, and the transfer of torque is made easier with fewer parts to travel through.
Emerging Technologies
Typical systems in vehicles are reactive suspension systems, meaning that the bump or dip in the road must occur before the suspension system responds to it mechanically. However, due to the technological developments and electronics added into vehicles, becoming proactive on the road is starting to become a reality for some vehicles.
Active/Adaptive Suspension
Active/Adaptive suspension allows vehicles to see imperfections in the road before they even happen. A Boston-based company ClearMotion is developing a proactive suspension system whereby the road ahead of a car is surveyed and assessed for deformations. The suspension system will then create an equal but opposite vertical translation to the deformation in the road so that the driver and passengers virtually feel no change while going over it [6]. This type of suspension can also be seen in the 2021 Audi S8 and A8 sedans named Predictive Adaptive Suspension. The system uses electric motors to raise and lower the chassis relative to the wheels up to 3.3 inches within half a second. The driver can manually control how their ride feels based on if they are on long-distance comfort rides or short, steering-heavy rides. In addition, the car is raised upon entry and exit to make it easier to get in/out and lowered when driving to increase handling ability [8].
Summary
In summary, there are advantages and disadvantages to every suspension system, so knowing what they are and how each design can be optimized for any vehicle is vital to maximizing the comfort, lifespan, and safety of an automobile. The current technology for suspension systems has proven reliable for many cars. Still, the emerging technologies can leave a consumer optimistic that there is much more innovation to come for the automotive industry.
References
[1] https://www.moogparts.eu/blog/double-wishbone-suspension.html, last accessed November 11, 2021
[2] https://cartreatments.com/pros-and-cons-of-macpherson-vs-double-wishbone-suspen sion/, last accessed November 11, 2021
[3] https://www.caranddriver.com/news/a15340751/explained-the-five-most-common-aut omotive-suspensions/, last accessed November 11, 2021
[4] https://en.wikipedia.org/wiki/Coilover, last accessed November 11, 2021 [5] https://www.autoevolution.com/news/how-multi-link-suspension-works-7804.html, last accessed November 11, 2021
[6] Fancy New Suspension Could Make Car Rides a Lot Smoother | WIRED, last accessed November 11, 2021
[7] What Is Active Suspension or Adaptive Suspension? – CarBikeTech, last accessed November 11, 2021
[8] Audi’s Predictive Adaptive Suspension: How It Works on the 2021 S8 Flagship – autoevolution, last accessed November 11, 2021
[9] https://www.speedwaymotors.com/QA1-Adjustable-15-3-Inch-Coil-Over-Shock-Kit,39 184.html?sku=721785&utm_medium=CSEGoogle&utm_source=CSE&utm_campaig n=CSEGOOGLE&gclid=CjwKCAiAv_KMBhAzEiwAs-rX1KOWNPhSTVn-Qp-oGJzgE J27_XV3pxFFhKu8vyS81LqVsSB61vdrTBoCWOsQAvD_BwE, last accessed
November 23, 2021
[10] https://www.shutterstock.com/image-photo/close-leaf-spring-suspension-pick-car 1310132398, last accessed November 23, 2021
[11]https://www.airbrigade.com/post/porsche-torsion-bar-suspension, last accessed November 23, 2021
[12] https://www.1aauto.com/content/articles/what-are-the-different-types-of-shocks, last accessed November 23, 2021
[13] https://www.newkidscar.com/suspension-constructio/macpherson-strut-suspensio n/, last accessed November 23, 2021
[14] http://what-when-how.com/automobile/independent-front-suspension-system-auto mobile/, last accessed November 23, 2021
[15] https://link.springer.com/chapter/10.1007/978-3-642-33835-9_51, last accessed November 23, 2021 [16] https://drivetribe.com/p/what-is-a-live-rear-axle-QJs72mfeQe6MyP2gnXUtzw?iid= BkDNoABuSD-YCHeZDaE4rQ, last accessed November 23, 2021
