Matrix [Man]agament

Johannes Köbler

Ulrike Myrzik, Manfred Jarisch

Workshop discussion – Audi A4

Prof. Dr. Ulrich Hackenberg, Audi’s board member for technical development, talks about the importance of the modular matrix systems he conceived, about technology transfer and about aerodynamics. The location is Audi’s aeroacoustics wind tunnel. The object of discussion is the new Audi A4 Avant.

Attention to detail –
The tailgate of the new A4 Avant can be opened and closed electrically and by gesture control.

Dr. Hackenberg, you’re the father of the Volkswagen Group’s modular matrix strategy. What’s the thinking behind Audi’s modular longitudinal matrix?

Dr. Hackenberg: I developed the original idea for the MLB at the start of the 1990s. I was responsible for concept development when we conceived the Audi B5 – the first A4 – on the PL 45 platform. Our chairman Dr. Piëch thought that the design of the car had gotten too big and we were set the task of shortening it by 75 millimeters. The A4 was a great success after that because everything still worked really well together.

When we developed the C5 – the first A6 – a short time later, it occurred to me to undo the shortening of the A4 and bring the car up to C standard in terms of length and width. We defined the parts that determine the width as variable so that we could, for instance, increase the track. We kept the vast majority of the remainder the same – which was also where most of the cost lay. I’m talking here about the longitudinal beams, the engine mounts, the safety structure. This was how we were able to realize the new C class vehicle for the same cost as the B class model plus changes.

What happened after that?

Dr. Hackenberg: From 1998 until 2002, I worked for Volkswagen and continued to develop the matrix idea with the PQ 35 and its derivatives. When I later returned to Audi, the subsequent A4 and A6 models had been further developed independently from one another again. And to correct that for the future, we conceived the modular longitudinal matrix under my leadership. First we defined a driveline and then built the bodyshell structure around it in a way that enabled platform dimensions to be derived here, too. We incorporated the wheels into the flexible matrix and made the platform scalable in height so that we could also realize a Q model.

However, we didn’t just establish the architecture and the technology modules of our vehicles within the MLB, but also the architecture of the factories we build them in. This addresses things like joint sequencing, jointing technology and materials parameters in bodyshell manufacturing as well as assembly sequencing. Our aim was to establish a production hub between the A4 and the A6 and between Ingolstadt and Neckarsulm. Well-utilized factories obviously help secure long-term employment.

After that, you conceived the modular transverse matrix …

Dr. Hackenberg: The first MLB was the mother of all the modern matrices. We transferred its idea into the transverse world with the MQB – in a highly systematic manner and with a very high degree of flexibility in the drive concepts. In Group factories, an electric car can follow a gas model, which, in turn, can follow a diesel vehicle – similar to what we’re now also doing with the MLB evo, the second-generation modular longitudinal matrix.

The MLB doesn’t just establish the architecture
and the technology modules of our vehicles,
but also the architecture of the factories we build them in.

Prof. Dr. Ulrich Hackenberg

How flexible is the MLB evo in terms of drive?

Dr. Hackenberg: We are now adding electrified drives to the classic internal combustion engines, the TDI and the TFSI. We have developed a wide spread here – from the new technologies based on the 48-volt vehicle electric system, through plug-in hybrids like the Q7 e-tron quattro to battery-electric vehicles (BEVs).

In general, we make all technologies suitable for the various different segments, even if we don’t necessarily have to use them everywhere – it can very well be that one BEV in the C segment is enough. Depending on how the market accepts the car, we are free to adapt its factory volumes. In this respect, we have far more flexibility than one of our competitors, which builds its electric models within a completely new structure.

What are the main determining factors in the fundamental elements of the MLB evo?

Dr. Hackenberg: The layout of the front end, the position of the bulkhead and the installation position of the engines are the same. The variable elements are the seating position, the lateral positioning of the pedals and the angle of the steering column. The track, wheelbase, overhang and the outer skin – or the hat, as we call it – are, of course, completely flexible. The MLB evo covers all the models from the B, C and D segments as well as the larger Q models. More than 60 percent of all Audis sold are based on longitudinal engine concepts. Once it’s fully rolled out, we’ll be building more than 1.2 million vehicles per year on the MLB evo. That’s not including other group brands using the matrix.

The matrix enables high volumes
due to standardization. This leads to more
consistent quality and reduced costs.

Prof. Dr. Ulrich Hackenberg

How strictly can you and must you manage a matrix like this?

Dr. Hackenberg: All change proposals undergo a stringent decision-making process. Obviously, the matrix always has to remain competitive, which calls for a certain degree of movement. What’s important, though, is to retain the definition of the architecture, which also determines production. The matrix provides our engineers with a set of guardrails. When you’re driving on the highway between guardrails, you feel safer and are able to drive faster. Within the matrix, our engineers can likewise work in a highly targeted and focused way.

What lightweight design technologies does the MLB evo facilitate?

Dr. Hackenberg: In contrast to the MLB, the MLB evo is extensively set up for material-mix technology. We can make the bodyshell from steel or aluminum or a combination of both materials. As a mid-range model, the new A4 is made largely of steel, while the C and D ranges feature increasing amounts of aluminum – in line with our motto: the right material in the right amounts in the right place. I can also well imagine CFRP being used in the future A8.

What technologies in the MLB evo have a particularly strong impact on the Audi brand?

Dr. Hackenberg: Further weight reduction is a major issue, as is engines. Emissions legislation has dramatically tightened the CO2 targets and we have to adapt accordingly. Factors that impact the brand certainly include the powerful V6 and V8 gasoline and diesel engines and their future degrees of electrification. There are also significant innovations in terms of running gear, ranging all the way to the rear-axle steering on the new Q7.

Other issues that we’re pushing forward in the MLB evo are the operating and display concepts, connectivity and driver assistance systems. The traffic jam assist in our new models already paves the way to piloted driving. We’ll be putting this technology into series production in the next A8 – the first stage being on highways at speeds of up to 60 km/h. We will raise this systematically and bring the new technologies implemented in the central driver assistance controller, the zFAS, into the smaller model ranges, too.

Is this technology transfer part of a general principle with the MLB evo?

Dr. Hackenberg: The high volumes that the matrix enables on account of standardization lead to consistent quality and cost reduction, i.e. to the democratization of the new technologies. One good example of this is the modular infotainment matrix, the (MIB). Not only is it highly scalable, we can also continually update it. Our customers can rest assured that they are receiving technologies that are state-of-the-art – also on account of ongoing development across the individual model ranges.

Our fundamental approach is to cascade our new technologies, so that their first application is in the top-of-the-range vehicles. Then we carry them over into volume production, which is how we achieve a real impact in traffic. The kind of contribution to safety that arises from our driver assistance systems can only have an impact on society when they are widely available.


Guardrails for Development

MLB, MQB, MLB evo – these acronyms refer to the three matrices used by Audi and the Volkswagen Group. The two modular longitudinal matrices encompass the Audi models with longitudinally mounted front-engines. Many models with transverse engines are based on the modular transverse matrix – at Audi, the A3 and TT ranges.

“A monolithic, total vehicle sculpture.”
Board member for technical development
Prof. Dr. Ulrich Hackenberg speaking about the new Audi A4 Avant.

THE MLB 2007

Developed by Prof. Dr. Hackenberg, the firstgeneration modular longitudinal matrix started in 2007 with the Audi A5, followed by the A4, A6, A7 Sportback, A8, Q5 and Q7 as well as the Porsche Macan. An important technical feature was the new arrangement of the clutch and torque converter behind the differential, resulting in a longer wheelbase.

THR MQB 2012

Production of the new Audi A3 began in 2012, with the TT debuting in 2014. Both model ranges use the modular transverse matrix that Prof. Dr. Hackenberg conceived for many of the Volkswagen Group’s models and brands. Cars like the Audi A3 Sportback e-tron (pictured), with its plug-in hybrid drive, demonstrate the versatility of the MQB, while the TTS shows its dynamic potential.


The second generation of the modular longitudinal matrix is set to continue the success story. Its first user was the new Audi Q7, now followed by the new A4. The strengths of the MLB evo include the extremely wide bandwidth of drive concepts, the multi-material bodyshell designs and the flexible architecture for operation and display, infotainment and driver assistance systems.


Aerodynamics is a traditional Audi domain. The brand once again puts itself at the front of the field with the new A4. Prof. Dr. Hackenberg in discussion with Dr. Moni Islam, Head of Development Aerodynamics/Aeroacoustics, and Jan Monchaux, Head of Aerodynamics for Audi Sport.

Dr. Hackenberg, the new A4 ultra has a cd figure of 0.23, making it the most aerodynamic sedan on the market. What is the role of aerodynamics at Audi?

Dr. Hackenberg: It is of growing importance to each of our models, regardless of the respective matrix. We want to combine Audi’s progressive design with the best possible aerodynamics. We keep our design discussions very open these days with the aim of enabling the best solution for all sides.

Dr. Islam, how did your team achieve this low cd figure?

Dr. Islam: In the case of the outer skin, we obviously worked very closely with the designers, which is our classic approach for optimization. However, it’s not just the design that influences the aerodynamics, but the entire vehicle concept. For the new A4, we worked successfully on this with the MLB evo.

The underbody details also play a major role. We achieved the final step with a special aerodynamic wheel and further refinements to the controllable cool-air inlet on the ultra model. We’re not alone in all of this work; we receive very good support from the specialist departments responsible for the respective components. We wouldn’t have been able to achieve this class-leading figure without that.

Herr Monchaux, as an aerodynamicist from motorsport, do you ever talk about the cd figure?

Monchaux: We don’t want to make life unnecessarily easy for our competition, which is why we’re not going to mention any numbers here. However, it’s safe to say that we have reduced drag significantly in recent years. We want to achieve the greatest possible downforce with the lowest possible drag, adapted specifically to the respective track. Perhaps I can give you one example – at between 150 and 200 km/h, the Audi R18 e-tron quattro could drive along the ceiling, depending on the aerodynamic setup and weight.

Discussion in the wind tunnel –
Prof. Dr. Hackenberg, Jan Monchaux and Dr. Moni Islam (from left).

Group of experts – At Audi, the motorsport specialists work in close physical proximity to production development.

Dr. Hackenberg, aerodynamically speaking, did Audi have the best car at the 24 Hours of Le Mans in June?

Dr. Hackenberg: Yes, I’m convinced of that. The effective aerodynamics helped us a great deal in compensating for the performance shortcomings of the drive.

What can production development engineers learn from motorsport?

Dr. Islam: On the Audi R8, it was essential right from the early stages of concept development to find space on the underside for the large diffuser – a classic racing solution. Within the scope of the regulations, aerodynamicists have a significant influence on the vehicle concept and are incredibly good at coming up with clever detail solutions. And that’s how we try to work in production development, too.

Dr. Hackenberg: Demands differ a great deal between motorsport and series production. On a race car, you can and want to see the aerodynamics clearly; that’s a big part of the attraction. On a production car, however, this often runs contrary to tastes. Combining these is therefore quite an art form – with an excellent outcome achieved for the new Audi A4. Here at this location, we benefit hugely from the fact that motorsport is located right next to production development. This facilitates the exchange of ideas, which I always try to encourage and coordinate.

What are the next big challenges for you?

Dr. Islam: The kind of significant potential that enables major leaps forward is no longer there for the taking. What we need above all is extremely good expert knowledge, a lot of time in the wind tunnel and even more refined simulation methods.

Dr. Hackenberg: One central issue is surely the market trend toward SUVs. Bringing these large, high vehicles down to a figure compatible with emissions reduction is a task that makes aerodynamics even more important. Another aspect is our new models with electric drive, which no longer have any engine noise. This is where good aerodynamics deliver good aeroacoustics for the customer and create completely new and fascinating driving experiences.

Monchaux: On LMP1 race cars, we want to continue systematically and aggressively developing the aerodynamics. The regulations may well still not permit any movable parts, but we are working very hard on testing and measuring all aerodynamically effective components. The aim is to win the WEC in 2015 and to bring the Le Mans trophy back home in 2016.

Dr. Hackenberg: Why does the windscreen wiper on the LMP1 race car lie at a slight angle?

Monchaux: When our engines still had restrictors, we put the wiper at an angle so as not to disturb the intake cross-section on the roof. Although the new rules mean that’s no longer so important, it still helps the engine a little. Another factor is that it’s not in the driver’s line of sight. And, not least, the angled position give us a tiny little bit more downforce. It’s just one of many little steps in our development work.


On the LMP1 race car, form entirely follows function, within the limits set by the current regulations. The same objective applies to the base body of the R18 e-tron quattro and to the airflow beneath the cladding – the best compromise between the highest possible downforce and lowest possible drag.


The underside of the new Audi A4 features targeted airflow guidance. The engine bay is encapsulated and there are large areas of cladding beneath the occupant cell and luggage compartment. The rear axle suspension arms are specially covered, while small spoilers – including those in front of the wheels and on the fuel tank – guide the airflow. Lift at the rear axle is very low.