The grand future of pure electric drive is still a long way off, autos with petrol and diesel engines will continue to dominate the street scene for the foreseeable future. Nevertheless, electric motors and other alternative drives are already part of our transportation reality today. Probably the greatest current disadvantage of electrically powered vehicles is the poor range. Batteries are expensive and heavy, which already limits the electric energy available in the auto from a purely construction standpoint. Purely electrically powered vehicles are therefore less commonly seen on roads than hybrid-powered automobiles. As the name suggests, a hybrid drive consists of a combination of several drives, for example, a diesel and an electric motor. At the same time, it uses the advantages of both technologies. Simply put: if the route is short, I will drive economically and emissions-free with electricity; if I need more range, then I will use the combustion engine, either directly or indirectly.
Sometimes electric, sometimes with fuel
The term “serial operation” describes a vehicle purely mobilised with electricity supplied by a combustion engine solely functioning as an electric generator. This type of vehicle comes equipped with adequately powerful electric motors that can mobilise it without further support. The necessary electricity for the electric drive is drawn from a battery and produced with a generator while the combustion engine is in operation. By contrast, “parallel operation” involves combining the power of an electric motor and combustion engine in one powertrain. Both the electric motor and combustor can then be conceived with less power output than serial operation would allow. The battery is charged through recuperation. Moreover, the power-split hybrid configuration allows the combustion engine to be operated independently of the driving condition, which allows the battery to be charged during the drive. Many experts expect that the electric drive-combustion engine power ratio of this technology will alter with time. While petrol and diesel engines are still the stronger components today, the focus could increasingly move in the direction of the electric motor (see graphic). A “plug-in-hybrid” refers to either a serial or parallel operation vehicle that can be recharged from the national grid via plug socket outlet.
He who brakes, wins
Sometimes we use electrical energy for more efficient mobilisation without noticing it. That is how many modern vehicles with recuperation systems are equipped. They function like this: kinetic energy is converted into heat energy when braking, which normally dissipates unused. A recuperation system uses the braking energy (and also the energy arising when coasting) to boost the voltage of the dynamo and recharge the on-board electrical system battery. When the vehicle accelerates again after the braking phase, this stored energy discharges to the generator and lowers fuel consumption.
Drive further with the REx
Both technologies—hybrid drive and brake energy recuperation—play a large role in the Range Extender (REx) from Rheinmetall Automotive. It addresses the greatest weaknesses of electric autos: the limited range and long charging times. Usually, the range is just 100–200 kilometres—and even this distance is only achievable under ideal conditions. If the driver requires additional energy—for example, when operating the air-conditioning—or if he drives somewhat faster, the range falls significantly. Many consumers fear that the battery might run down before they reach their planned destination (“range anxiety”). This fear represents the biggest obstacle to making a purchase. This is where the REx comes into play. It involves a two-cylinder petrol engine that engages whenever the vehicle battery charge run slow. It then replenishes its energy with a generator. The maximum range of the Fiat 500 test vehicle was increased from 70 to 500 kilometres in this way. Currently, a battery-powered vehicle on a subsequent journey would have to plan in even longer stops to recharge the battery. Not so for the REx, which additionally recharges itself during the drive and can be refuelled as usual. The driver hardly notices any of all this because the REx produces only minimal sounds and vibrations.
In temperature ranges where the battery experiences unfavourable energy conversion efficiencies when charging and discharging, it can moreover supply heat or cold and thereby optimise the energy conversion efficiency. Additional advantages: except for the fuel tank and the radiator, the components are pre-assembled as a ready-to-install module. The compact REx can also fit under the floor or in the spare wheel recess. Integrating the power engine in a vehicle is likewise unproblematic. Soon the REx will become even “greener”. Together with several partners, Rheinmetall Automotive is developing a model that runs on regeneratively produced natural gas. A first application is to operate a small utility vehicle completely with regenerative energy.That includes the electric main drive and the Range Extender. Due to its great potential for lowering CO2, the “Green Rex” project is being subsidised by the German Federal Ministry of Economics and Technology.
Making wise use of operating temperature
The amount of electricity available for electric autos declines when the vehicle interior is heated or cooled. To ensure that the short range of electric autos is not reduced even further, Rheinmetall Automotive has developed a thermal management module that employs a heat energy needed for heating and cooling. The module is designed as an essential component of the air-conditioning system. It takes into account the heat generated from vehicle operation and adjusts all components to their optimal operating temperatures. In association with an intelligent regulation of thermal efficiency, the heating and cooling module contributes to increasing range. The module can be placed into the vehicle freely with little installation work. Thanks to the low number of connecting elements for the almost completely hermetically sealed coolant circulation and a reduced filling capacity, the system moreover enables a reduction in losses to the surroundings.
Fuel cells on the verge of a breakthrough?
When speaking of alternative drives, one must of course not fail to mention fuel cells. A fuel cell is a so-called galvanic cell that uses the chemical reaction of a combustible fuel (usually hydrogen) and an oxidising agent (usually oxygen) to generate energy. The fuel cell converts this reaction energy into electricity. In practice, the range of fuel cell autos is comparable to that of conventional vehicles. By contrast, the ecological balance depends on whether regenerative energies are used in producing the hydrogen. The technology is currently still undergoing repeated prototype testing in the automotive sector, but is already well established in, for example, the military sector. The German submarine class 212 A has already been using fuel cells successfully for many years. But fuel cells could also soon become more common in autos: the hydrogen filling station network will undergo a massive expansion in the coming years. The first series vehicles from Toyota, Hyundai and Honda are even already on the market or ready for launch in the European market. Consequently, Rheinmetall Automotive also has its eye on fuel cell technology. One innovation is already in the testing phase: a hydrogen recirculation fan. This somewhat awkwardly named system is comparable to a fuel pump in a combustion engine. The hydrogen recirculation fan permanently supplies the so-called “stack” of individual cells constituting the fuel cell with hydrogen. The pump sucks excess hydrogen away from the stack and reintroduces it.
THIS INCREASES THE EFFICIENCY OF THE REACTION, THUS EXTENDING THE RANGE
Moreover, the constant recirculation increases the operating life of the stack. Without such a pump, increasing efficiency would only be achievable through elaborate measures, e.g. by increasing the platinum content in the stack. The presented solutions are only a sampling from the broad portfolio of Rheinmetall Automotive. But they show: whether it be for hybrid units, e-motors or fuel cells—the company is already developing intelligent solutions today for the drive technologies of tomorrow.
In view of the fact that we are continually discovering new oil reserves, do we really still need electro-mobility at all?
The current resource issue certainly isn’t driving development. But it’s also a fact that all manufacturers are working on“powertrain electrification”. In addition, one mustn’t forget that we need to keep our eye on the issue of carbon neutrality and legislators also provide clear guidelines for CO2 emissions here.
How important are alternative drive areas for Rheinmetall Automotive?
Electrification will come, but it won’t happen overnight. At least in passenger vehicles, it’s more that the combustion engine will gradually get more and more support from an electric motor. As a first step in that direction, I first see energy efficiency measures like making use of dissipated heat through mild hybridisation in connection with energy recuperation.
And how does it go from there?
<p>After that, we will see ever-greater partial electrification. For us, that means peripheral components will also need to be electrified and we will have to concentrate on 48-volt vehicle electrical systems. In the future, we can expect a large variety of drive concepts. More and more, these concepts will have to satisfy local requirements and this will also include purely electrical drives. </p>