How Multi-Link Suspension Works

Probably one of the most complex aspects of a car's structure, suspension is also one of the most confusing, and thus neglected, parts for a potential buyer. Suspension plays a vital role in a vehicle's stability and in the comfort it provides to its occupants and that is why we feel it deserves a detailed description into how it functions. However, since this is such a complex chapter, we'll have to take them one at a time. This article will deal with the popular multi-link type. But first, a short discussion about suspensions. Types of Suspensions
Basically, the suspension represents the assembly of linkages, springs and shock absorbers that connects a car's body to the wheels. As mentioned above, suspensions are vital in a car's handling and braking, but also the key component in a vehicle when it comes to comfort for both the driver and the passengers.

Suspensions are divided in two main categories, dependent and independent, terms which refer to the ability of opposing wheels to move independently of each other. A third, less popular option, is the semi-dependent suspension where opposite wheels can't move independently, but are not rigidly attached to each other.

In a nutshell, the dependent suspension forces a wheel to adopt the same camber (the angle between the vertical axis of the wheel and the vertical axis of the vehicle) as the other. An independent suspension, on the other hand, allows one wheel to move freely and unhindered by the opposing one. It's worth noting that even though some independent suspensions are incorporating some forms of linkage elements, such as sway bars, they are still classed as independent.

The Multi-Link Suspension

Ok, now that you have some basic notions about suspension as a concept, let's take a look at the multi-link one. The most important thing to know about this type of suspension is that it's an independent one.

Derived from the double wishbone one, the multi-link suspension uses three or more lateral arms and one or one or more longitudinal arms, which don't have to be of equal length and can be angled away from their natural direction.

Each of the arms has a spherical joint or rubber bushing at each end, causing them to “work” in tension and compression and not in bending.

As noted here, the arms are joined at the top and bottom of the spindle. When this spindle turns for steering, it actually alters suspension's geometry by torquing all suspension arms. Don't worry though, as the suspension's pivot systems are designed to allow this.

Multi-link arrangements are used on both the front and the rear suspensions, but the former replaces a lateral arm with a tie-rod that connects the rack or steering box to the wheel hub.

Since there isn't a single multi-link setup in the industry, all big names have their own design. Some BMW setups look like the letter Z and sport four links, while Honda's multi-link is like a double wishbone suspension but with an added fifth control arm. Audi A4's front suspension also has four links and it's extremely similar to the double wishbone one.

The Hyundai Genesis sport front and rear 5-link systems. The front suspension has two upper links, two lower links, and a tie-rod, which in the rear suspension, there are two upper links, a lower link, a trailing link, and a toe control link.

Advantages and disadvantages

The multi link suspension is seen as the best independent system for a production car because it offers the best compromises between handling and space efficiency and comfort and handling. Moreover, because such a suspension allows a vehicle to flex more, it's also a very good solution for off road driving.

The multi link is also advantageous for the designer who can alter one parameter in the suspension without influencing the entire assembly. This is a major difference compared to a double wishbone suspension.

As with all good things, the multi-link system is costly and complex to design and manufacture. In fact, the suspension's geometry needs to be checked with design analysis software.

However, thanks to the constant technological advancements, the multi-link suspension has moved from the luxury segment to the mainstream one. One of the companies working on cheap multi-link designs is Magneti Marelli, supplier to and sponsor of Ferrari's F1 team. The company came up a few years ago with the "FLECS" (Flexible Link Elevated Compliance Suspension), a design based around a lower control arm with flexible longitudinal blades. Sharing the elasto-kinematic duties between the bushings and the links means the number of suspension control arms can be reduced, which results in direct cost savings. In addition, the bushings themselves, except for the single compliant bushing, are relatively simple off-the-shelf components.
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