Technology report: Engineering comfort

Article published in May/June issue of ERJ

Ask any supplier of rubber components about current requirements of their automotive customers and they will likely pull out a pretty long and varied list.

Increased comfort, safety, durability and efficiency as well as the increasing demands for emission reduction and environmental friendliness of compounds, are some of the key aspects mentioned by Vibracoustic, a major supplier of anti-vibration systems for vehicles.

“New, high-frequency vibrations from electric engines pose a further challenge and light-weight structures increase vibration levels and demand for vibration technology,” said Joerg Boecking, chief technology officer of Vibracoustic – until recently known as Trelleborg Vibracoustic.

Vibracoustic’s material expertise, and its single loop development process, are important features in its ability to come up with answers that are ‘right the first time’, he said.

Some of the features demanded by customers from compounds include high durability, temperature resistance, specific rigidity, damping behaviour, dynamic hardening and creep behaviour, said Boecking.

Vibracoustic then develops the required simulation models and accelerated life tests. In due course, said Boecking, we need to meet the often conflicting demands on materials, such as dynamic shifting versus durability.

Among some of the company’s recent innovations are torsional vibration dampers with one-way clutch.

Developed to reduce vehicle CO2 emissions, the dampers are tuned to the start-stop function of a combustion engine. They reduce vibration, lower stress on belt drive and crankshaft while saving fuel via the start-stop functionality, explained Boecking.

Vibracoustic has also developed a dual rubber mount – which uses two different elastomers within the mount – as an alternative to the conventional chassis bushing and complex, hydraulically damped mount.

This, he went on to say, reduces axle shake when crossing over transverse joints, for example.

The mount is also designed as a cost-efficient alternative to hydro mounts, while offering a high degree of adjustability.

In the area of passenger car air springs, Vibracoustic offers three different types of bellows with different structures for the reinforcement threads integrated in them.

“In the axial bellows, the threads integrated in the elastomer run in an axial direction to the jounce direction. In the cross-ply bellows, two reinforcement layers intersect, but unlike in the case of a textile, are not connected to one another,” explained Boecking.

Dandelion rubber

New bio-rubber materials are a focus for German company, ContiTech, which has been investing in the development of anti-vibration parts made from dandelion rubber.

Vibration Control ContiTech tested the new resource named Taraxagum for anti-vibration technology at the end of 2015 by manufacturing its first dandelion rubber engine mount.

The work is linked to a joint project between parent group Continental AG and Fraunhofer Institute for Molecular Biology and Applied Ecology, which have been studying the production of natural rubber from Russia dandelion for the manufacture of tires.

“When it comes to natural rubber we have completely different requirements from our colleagues in the tire division,” said Dr Anna Misiun, who leads the project to build engine mounts made from dandelion rubber at ContiTech.

An engine mount, she explained, connects the engine to the car body, so it has to withstand considerable static loads. It also provides insulation against structure-borne engine noise and restricts engine movement so vehicle occupants are not shaken about inside the car.

The components are therefore exposed to high dynamic loads and high temperatures, so the natural rubber used needs to meet demanding specifications.

ContiTech’s test results, said Misiun, showed that Taraxagum was a suitable alternative to traditional natural rubber and ideal for vibration control elements on engines.

But the dandelion products will not hit the market for at least five to ten years.

“One of the biggest challenges will be obtaining the material on an industrial scale,” said Misuin, adding that the research team is working to optimise the seeds and develop suitable cultivation and harvesting technology.

PU to the rescue

Another interesting advance, from Japanese Sumitomo Riko Group, is the development of magnetic induction foaming (MIF), a process that increases the thermal conductivity of polyurethane foams to address the problem of noise in electric vehicles.

According to the Anvis group, which represents Sumitomo Riko in Germany, MIF makes it possible to increase the thermal conductivity in such a way that the heat can be diverted to the exterior while providing acoustic insulation and reducing weight in non-stop operations.

“This process works with both internal-combustion engines and electric motors,” said Olaf Hahn, managing director of the Anvis Group.

“Electric drive systems and actuators will produce perceptible noises, which could affect comfort,” Hahn explained.

Current PU materials are only partially suited for dampening engine noise because they lack the properties needed to facilitate thermal conductivity, according to Hahn.

The basis for MIF, he added, is a new process that alters material properties by forming thermal bridges.

“The result is a sound-proofing, heat-conducting material,” he explained.

The product was put to the test in the real world with the help of an electric motor cover.

“During a two-hour endurance test, the temperature levels of the MIF-altered engine cover were 20?C lower than those of a cover made with conventional polyurethanes,” the Anvis Group managing director reported.

The noise-reduction effect, however, varied by frequency.

According to Hahn, the sound proof effect has the most impact with frequency more than 400 hertz.