Electromobility comes from below

Drive system and energy storage for electric vehicles in development

With its wide range of products, Rheinmetall Automotive is ready to accommodate the increasing electrification of power transmission. The company is busy developing a new kind of modular battery pack as well as a 90 kW electric powertrain. Both systems are currently being integrated into a testbed based on a subcompact vehicle. Heartbeat spoke about this project with Rheinmetall Automotive CTO Heinrich Dismon.

The journey along this path began a long time ago, for electric motors are certainly nothing new for the design engineers of Rheinmetall Automotive. In the case of ancillary units, the OEM supplier has had an established development competence for electric powertrains for decades. For example, the company conceived the first fully electric coolant pump for the main cooling system via its subsidiary Pierburg as early as 2004 and successfully introduced it onto the market in the six-cylinder engines of BMW.

Orders for electric motor casings

Since its market launch in 1995, the electrically commutated water recirculation pump, likewise developed by Pierburg and produced at the Hartha plant site in Saxony has meanwhile already exceeded an output of 50 million units and is utilized worldwide by leading manufacturers and suppliers in automotive engineering and beyond. In addition orders come from international OEMs for electric motor and aluminum battery casings soon to go into series production at Rheinmetall Automotive. The product range of the company in electromobility is supplemented through electric oil and vacuum pumps, electric coolant valves and actuating elements, a heat pump and special light aluminum constructional components.

Complete traction drive as the goal

Now, with its new electric drive and parallelly developed battery pack, the international automotive supplier is starting a new chapter in its development history. For its newly conceived products in electromobility, Rheinmetall Automotive decided not to focus on energy storage and electric drive (with its peripheral equipment) solely due to market-related reasons. “Our basic competences in the development chain and series production of electric drives,” says Heinrich Dismon, the company’s Chief Technical Officer, “allow us to converge toward the development goal here relatively quickly.” However, he adds that they fell back on additional support from development service providers in the initial phase. Dismon’s goal is a completely electric traction drive that, in addition to the electric motor, also has the control and power electronics as well as a step-down gear made by Rheinmetall Automotive and designed according to the application.

Compact class targeted

The newly introduced electric powertrain with 90 kW power, however, aims not at the absolute upper levels of performance à la Tesla but rather is located in the upper segment of compact electric engines. In its current design, it aims at smaller vehicle classes, whereby the scalability of the system also enables utilization in larger vehicles. The reason for this was the insight that “electromobility will develop from the bottom up,” says Dismon. He estimates that the future will bring various forms of drive systems ranging from the central drive unit to drives close to the wheels. At the same time, electric vehicles for, say, urban zones will be more likely to come in smaller power performance ranges of 30 to 50 kW.

One also needs to consider small vehicles beyond the passenger car

New players on the market

Furthermore, new manufacturers (OEMs), for whom a proprietary development of an electric drive is not necessarily a priority, will be active in this area in the future. In addition there will be new market segments, such as multipurpose applications extending beyond pedelecs. The drive that will therefore be proprietarily manufactured by Rheinmetall Automotive in the future is tunable and scalable for the intended use in terms of performance and torque. The engine technology is also basically insertable into a mild hybrid and applicable there for functions such as electric parking, autonomous driving into the garage, or for shifting the operation range of the combustion engine to save fuel.

Underfloor batteries preferred

In the layout design of the developed battery pack, Rheinmetall Automotive assumed that a significant portion of future electric vehicles and even hybrids will possess underfloor batteries. They do not significantly limit the load volume of the vehicle and, in addition, also offer advantages regarding both weight distribution and possible incorporation into the vehicle structure. Dismon: “Today almost all vehicles on the market are derivatives of existing concepts on the basis of combustion engine drives. In the future, that will no longer be seen.”

High energy density

Due to their high specific energy density and good thermal conditionability, Rheinmetall Automotive utilizes pouch cells for the rechargeable batteries of its testbed. Beyond this, however, concepts with cylindrical or prismatic cells also exist, enabling one to cater to customer-specific requirements.

We don't want to get into cell technology

The battery pack features a very high energy density in proportion to its weight and, due to its small installation space requirements, enables a very flexible and broad application basis in electrified vehicle concepts. An important question at the outset was whether one should commit to using a certain cell type. However, the company pursues an open strategy here that enables integration of various different battery cell types and can therefore be interesting for many OEMs. Dismon: “We don’t want to get into cell technology, but rather to configure a system for our customers with the cells of their choice.”

Temperature control also in the battery pack

To ensure that the battery packs can also withstand high power drains and prove suitable for heat-intensive rapid charging, they were outfitted with a coolant-perfused floor cooling, which drew from the manufacturing expertise of the supplier in aluminum die casting. An electric coolant pump conducts the coolant into a heat exchanger. In connection with the similarly developed heat pump, recuperation can occur or the energy can be used for heating or cooling the interior. Moreover, at low temperatures it is also possible to regulate the temperature in order to avoid damage to the battery.

Underfloor battery pack with special protection

The skeletal structure of the battery casings developed by Rheinmetall Automotive for these applications consists of aluminum, which is additionally protected from damage through a superimposed fiber composite structure. The corresponding fiber is supplied by a Rheinmetall affiliate that specializes in protective applications.

Testbed with systems approach

500-based testbed (see cover image) is equipped with a nominal storage capacity of 29 kWh. In connection with the new electric drive, the vehicle achieves a top speed of 135 km/h and a range of up to 275 kilometers. These parameters are accomplished without limiting the usable space for the trunk or passenger compartment known from the series production vehicle. Rheinmetall Automotive sees this configuration oriented toward future electric vehicle concepts as an example for a possible series concept, whereby of course other constellations can also be realized in accordance with customer wishes.

Heinrich Dismon Chief Technical Officer Rheinmetall Automotive AG

Inquired!

Will electrical mobility alter our driving habits?

We currently have the situation that vehicles are offering ever more comfort, but also bearing more weight. In e-mobility we will increasingly see vehicles that are decidedly conceived for electric driving. Inevitably, they will have to be smaller and lighter and have less power.

In this respect, e-mobility will influence us. But there are also people today who only drive their car three times per week and even then merely for short trips most of the time.

Moreover, due to the technical parameters, e-mobility will bring us into a situation in which we must compensate for our previous “carefree attitude” through a more well-planned way of acting. In the future, we will certainly have to give more thought to which distance we can master in which timeframes and calculate accordingly. In the medium term, I believe electromobility will happen within a range of up to 400 km radius. That’s absolutely adequate for the predominant share of our normal driving destinations.

In 2030, we won’t yet be ready to fully replace the combustion engine with new technologies. I even believe we won’t be able to completely replace it.