"Modern Transmissions Take Three Percent Off Fuel Consumption"

Dr. Gerhard Maas is Executive Vice-President of Powertrain Development at IAV.
As Senior Vice-President, Dr. Burghard Voss is responsible for transmission and hybrid development. Both experts feel that intelligent transmissions will remain at
the heart of future vehicle concepts. However, new drive concepts are placing high demands on the developers.

Despite the hype surrounding electric motors, Dr. Gerhard Maas, Executive Vice-P

Despite the hype surrounding electric motors, Dr. Gerhard Maas, Executive Vice-President of Powertrain Development (left), and Dr. Burghard Voss, Senior Vice-President of Transmission Development (right), look calmly to the future of transmission development

Transmissions have been around for many decades – Do they provide any scope at all for fundamental innovations?

Dr. Maas: That's true, transmissions are a very old subject in automotive construction. But they're also a very important one: No matter what the powertrain looks like – you always need a transmission. That goes for vehicles powered by gasoline or diesel engines just as it does for electric and hybrid vehicles. In all cases, transmissions are the heart of the powertrain. But over time, the requirements have also undergone drastic change: Whereas most vehicles in the past had four-speed manual or automatic transmissions, manual transmissions today come with as many as six gears.

Dr. Voss: Automatic transmissions can have as many as eight speeds and even that doesn't seem to be the end of the road. Although largely capable of running the combustion engine in the most favorable map range but always blotted by poor efficiency, continuously variable transmissions are also being enhanced as they are the right choice for specific applications. And new technologies, such as electric and hybrid vehicles, are demanding entirely new transmission concepts. So development in this field still has a long way to go.

Fuel consumption and CO2 emissions are a key issue in automotive development. What contribution can modern transmissions make on this front?

Dr. Maas: The trend toward more and more gears has indeed brought about an improvement in efficiency. A modern six or seven-speed dual-clutch transmission is capable of reducing fuel consumption by about three percent over manual gearshift. However, further potential will be tapped not so much by increasing the number of gears but through structuring these transmissions for greater efficiency, e.g. by reducing the gearshift elements.

Dr. Voss: Ultimately, though, the efficiency of future drives will be determined by intelligently connecting all of the assemblies involved in the powertrain. This is done by the electronic management system which, on an event-controlled basis, always selects the gear that provides the right amount of torque to meet the driver's request with the combustion engine operating in the most favorable map range, i.e. the range producing the lowest level of consumption and emissions. For automobile manufacturers, this is extremely important because it provides the means for reducing fleet consumption and, associated with this, also carbon dioxide emissions.

Does shifting six or more gears by hand make any sense at all?

Dr. Maas: Manual gear shifting is pushed to its limits at six speeds because to cut fuel consumption, it is necessary to change gear at exactly the right moment. Modern electronics are far better at doing this than human beings are. All the same, the manual transmission will not disappear completely from the market – after all, it is far less expensive than the automatic version. However, the vehicle electronics can help drivers by showing them when to change gear.

Dr. Voss: And intelligent clutch actuators are not only capable of making it easier for the inexperienced motorist. We are currently in the process of carrying out development work on this subject under the heading "A nod from the passenger seat doesn't always mean approval".

What demands do hybrid drives place on the transmission?

Dr. Maas: They can be more complex than powertrains involving just a combustion engine. This depends on the type of hybrid drive. It is always a matter of coupling torque from electric motor and combustion engine intelligently. One way of doing this, for example, is to integrate the electric motor directly into the transmission. At IAV, we have developed an innovative solution with eight speeds that's lightweight, compact and low in price. This is where simulations have been a tremendous help to us: We have combined the components in a way that allows us to achieve more with fewer parts.

Some experts believe that transmissions for electric motors will become less complicated. What do you think?

Dr. Voss: This will definitely be the case because the electric motor's delivery curve is more favorable that the combustion engine's. As such, it's possible to dispense with a starting element because sufficient torque is provided from the point of zero motor speed, and favorable efficiency levels also extend across a far wider operating range. This, coupled with a vehicle-speed range that's more limited than a conventional vehicle's, demands – if at all – transmissions with one or at most two transmission steps. However, these transmissions must then be designed so they fit into small vehicles where there is inherently less space. And because this is likely to be the principal segment for electric drives, we definitely need units that are compact. From the aspect of transmission development, however, we are unruffled by the euphoria that's currently linked with electric vehicles. Given their drawbacks in terms of battery costs, traveling range and performance, electric vehicles are set to be a niche solution for a long time to come.

A moment ago, you spoke about the significance of simulation in transmission development work. What are IAV's strengths in this field?

Dr. Maas: One of our strengths is our ability to simulate the entire powertrain. As such, it's also possible to define optimum transmission stepping at an early stage: How many speeds are necessary? What's the best spacing? This is particularly important because in future the number of speeds is more likely to rise than fall. And all this also needs to be integrated in the limited package that's available. But modern transmissions also help to save fuel. This is why IAV has been working for over ten years in the field of simulation and control-system development and has also been focusing for three years now on new hardware concepts offering a large number of transmission steps while being compact and also suitable for hybrid vehicles.