Electric cars: technology explained

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Electric cars - technology explained
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I in this post:

  • History of the electric car
  • Battery technology in comparison
  • How the motors work
  • Alternatives to today's motor technology
  • Drive variants in electric cars
  • Outlook on the future of the electric car

History of the electric car

New territory? Certainly not. The electric car is older than the combustion engine. Long before Carl Friedrich Benz sent his number 1 motor vehicle on a test drive, battery-powered electric vehicles were already rolling on the streets of Europe and especially the USA. For many years the technology of the two types of drive developed peacefully side by side, until an electric motor of all things switched off the lights on the electric vehicles. In addition to the seemingly inexhaustible quantities of gasoline available at the time, it was above all the development of the US engineer Charles F. Kettering that heralded the triumph of the internal combustion engine in modern times. Kettering designed the electric starter for series production in 1912. He socialized driving a car after the engines no longer had to be laboriously cranked by hand.

As a result, the electric drives retreated into the niche, since then they have mainly driven small delivery vehicles, industrial trucks and heavy traffic external power supply, for example in locomotives.

Battery technology in comparison

The upcoming turning point in this development stands and falls with the memory: How successful the electric car will be is not decided that way very much on its possible driving time per charge, but on the cost /benefit ratio. Ultimately, only a very limited number of potential users are prepared to pay high surcharges for the electricity storage system. An inexpensive e-mobile for short-distance travel with a range of around 150 kilometers would have as much potential as a car with a range of 4 - 500 kilometers, which costs no more than a conventionally powered model.

In battery technology, lithium Ion cells are the method of choice. In the automotive sector, the cheaper nickel-metal hydride batteries only play a significant role in Toyota's hybrid models; other technologies such as LiFePO4 batteries are currently too expensive and more complex to produce and manage. BothHowever, projects for battery factories, as they are currently being examined and promoted everywhere in the automotive industry, are not primarily concerned with the production of such battery cells. These are purchased inexpensively, for example in the form of standardized batteries of the type 18650, such as those used in flashlights. However, Tesla recently announced that it would also want to get into battery cell production.

Nevertheless: The essential know-how of the companies and the main task of the battery factories is to connect the individual cells to form large so-called stacks to develop appropriate charging and management technology. The latter is indispensable in order to compensate for different charging states of the individual cells, the so-called 'balancing'.

Power consumption of electric cars

The actual consumption and the range solely from the technical data for the traction batteries and It is not easy to derive the drive. The battery used to drive an electric or electric hybrid vehicle is referred to as a traction battery, since a commercially available on-board network battery known from combustion cars is also installed at the same time. In order to optimally compensate for the extreme temperature fluctuations in winter and summer operation in passenger cars, cooling and, ideally, heating of the traction batteries are necessary in order to keep them in an operating range that is optimal for efficiency. With corresponding systems, this limits the usable energy for the actual drive. Furthermore, to increase the durability, the traction batteries are only operated in a certain part of their capacity, i.e. never completely discharged and usually not fully charged. This is why we speak of a so-called charging window.

According to customer surveys by Nissan and Tesla, this battery management can achieve mileages of 150,000 to 200,000 kilometers up to a remaining capacity of around 80 percent, which is generally regarded as the limit where a traction battery is considered exhausted. For the recycling of no longer fully efficient drive batteries, several car manufacturers are also currently developing concepts to use them as stationary storage, for example for households with photovoltaic systems.

The charging technology has an additional influence on the effectiveness of an electric car. On the one hand, the charging loss is greater with higher charging currents, on the other hand, rapid charging reduces the service life of the batteries to a certain extent. The temperature also affects the consumption of an electric car. In winter, charging losses of up to 30 percent can occur - for example, a 15 kWh battery capacity would use over 19 kWh of electricity. And here, too, it will be up to the manufacturers to achieve a competitive edge by charging as effectively as possible in order to stand out from the competition

Functionality of the motors in electric cars

On the drive side, three-phase motors are used in practically all electric cars. Three-phase current, correctly referred to as 'three-phase alternating voltage', is familiar to us in the household, for example from the 'high-voltage' connection of a kitchen stove. The design known in the technical term 'converter-controlled permanent magnet excited three-phase synchronous machine' has advantages over DC motors, among other things, due to lower wear, since no sliding contacts are required. The converter has two tasks: In coasting mode, it converts the energy from the traction battery into alternating current, during recuperation, where the electric motor works as a generator, it in turn serves as a rectifier for the charging current to the battery.

Other motor concepts (DC motor, converter-controlled asynchronous motor) currently play almost no role in electric cars. The difference between synchronous and asynchronous motors lies in the way the 'rotor' works, i.e. the rotating part of the motor. With asynchronous motors, the rotor follows the stator rotating field with a time delay, i.e. asynchronously, depending on its function as a generator or motor. With a synchronous motor, the rotor immediately runs synchronously with the stator rotating field.

Rare earths and the electric car

The use of separately excited synchronous motors that has been discussed for a long time, such as the one ZF presented in a prototype in 2012 , could play a certain role in the future, especially by doing without the controversial rare earths for permanent excitation. To understand: The excitation of an electric motor does not describe its mood, of course, but the production of the required magnetic field. With permanent-magnet electric motors, this is achieved using strong magnets, for which, for example, rare earth neodymium is required. Since both the delivery situation (almost exclusively from China) and the very environmentally harmful mining of rare earths are highly criticized, there is corresponding interest in externally excited motors. Their disadvantages compared to permanent-magnet electric motors are their system-related higher speed with the need for an additional reduction gear, their larger design and poorer efficiency, i.e. higher power consumption.

Drive types in electric cars

Another differentiating feature of electric cars can be their drive system. The main thing here is the front-wheel drive, which has meanwhile established itself as a quasi-standard in passenger cars, with power derived directly from the output of the e-machine; the use of two motors (one per axle) is also possible for all-wheel drives. The two electric motors do not necessarily have to be identically powerful because all driving scenarios can be mapped using a corresponding intelligent control system. A good example of this are the all-wheel drive systems ofHybrid electric vehicles from Toyota and Lexus, where the rear-axle electric motor is designed more as an auxiliary drive to improve traction.

Another variant is the use of wheel hub motors, which control the drive force per wheel with maximum precision and thus the corresponding driving dynamics Promise advantages. Their disadvantage lies on the one hand in the high unsprung masses per wheel, on the other hand in their unprotected placement directly in the dirt area of ​​the wheels, which requires correspondingly complex encapsulation.

The future of the electric car from today's perspective

In conclusion, it can be said: that electromobility is in the starting blocks is undeniable. Where the road leads is primarily determined by the price development, especially for electricity storage systems. At least in the medium term, it will probably come down to coexistence and togetherness. For commercial and private long-haul traffic in the form of internal combustion engines and hybrid systems with electricity generated by gasoline engines or fuel cells. In the commercial vehicle sector, they continue to use diesel, possibly also with gas turbine hybrids.

In short and medium-haul use in the ever-growing urban areas, however, all signs point to electricity, whereby in future car sharing will also play an essential role in the widespread distribution of electric vehicles. However, the development of the charging infrastructure will also be decisive, especially in urban areas. It would be possible to install charging terminals on light masts, for example, and contact-free induction charging technology is a field that is being intensively researched.

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