3-liter car

The term Low-energy vehicle (NEF) means vehicles that realize significantly reduced fuel consumption (below 0.58 kWh/km or 1.8 MJ/km) compared to current average fleet consumption. However, the upstream primary energy input required for this must be included in the balance sheet. D. h. z. B. the energy input before the energy is in the battery, furthermore the energy for its production and later disposal or gain of a recycle. The term is based on the low-energy house. A standard does not yet exist. However, there are already different tax classifications (z. B. temporary tax exemption for the three-liter car). More specific terms are One-liter car, Two-liter car, Three-liter car and Five-liter car.

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The need to produce and operate vehicles with the lowest possible fuel consumption stems from the constraints of energy conservation. In addition to the sustainable use of limited energy resources, what counts most is the economical operation of the vehicles. In addition to the acquisition costs, the constant increase in fuel prices and the political, i.e. fiscal, promotion of fuel-efficient vehicles against the backdrop of the increase in the number of vehicle registrations worldwide have a major influence on economic efficiency.

A major boost to low-energy vehicle construction came with the California government’s announcement that, starting on a start date (postponed several times), it would impose punitive taxes on all manufacturers that did not make a certain percentage of their vehicles compliant with the Ultra Low Emission Vehicle (ULEV) or. ZEV (Zero Emission Vehicle) principle produce. ZEV means that the vehicle must be able to travel a certain distance completely without emissions. Today, virtually only electric-powered vehicles can provide this capability – the main driving force behind the hybrid efforts of major automakers. In Europe, the EEV (Enhanced Environmentally Friendly Vehicle) standard is a motivation.

As early as 1996, the German manufacturer Audi introduced an Audi 100 Duo, but it was soon discontinued due to lack of demand (and the simple and inefficient technology). The German three-liter models Audi A2 TDI 3 l and VW Lupo TDI 3 l also failed to generate an economic return – despite tax incentives for sales and subsidies for development – after which the VW Group discontinued production.

Environmental protection

Internal combustion engines of cars are responsible for about 20 percent of the worldwide CO2 emissions, which contribute significantly to global warming. Furthermore, oil reserves, which serve as the energy source for most of today’s motor vehicles, will in all likelihood become increasingly scarce in the coming decades (see Global peak oil production). The motivation is the ALARA principle (As Low As Reasonably Acceptable – as low as reasonably acceptable) or. Ethical behavior in general. This ethical behavior can at least be attributed to some so-called “garage companies” that – often with roots in the ecology movement – produce vehicles based on bicycle technology in very small series and, for example, are also concerned about the environmentally friendly generation of the energy required for propulsion.

The Verkehrsclub Deutschland publishes the Auto-Umweltliste, which is based, among other things, on energy consumption. Another evaluation is the FIA EcoTest.

Specification of energy consumption

Fuel consumption for motor vehicles in Europe is usually expressed in liters of fuel per 100 km travelled (distance consumption). To arrive at comparable figures, the energy content of different fuels must be taken into account. Diesel fuel, for example, has an energy density of 9.8 kWh/l, gasoline 8.9 kWh/l. Both have a mass-based energy density of about 12 kWh/kg, natural gas 14-15 kWh/kg.

Another way to determine the energy consumption is to express it in energy amount per transported payload and trip. This is the distance consumption per weight [l/(100 km*100 kg)]. When comparing a truck transporting 20 t of freight with 35 liters of diesel over 100 km with a fully loaded diesel passenger car transporting 500 kg of freight (passengers + luggage) with 7.5 l, the energy consumption of the truck is 0.175 l/100 kg, while the passenger car requires 8.5 times as much, namely 1.5 l for 100 kg over 100 km.

However, such a consideration neglects the driving time and thus the driving resistance, which increases with increasing speed. However, only transport services with the same speed can be compared, d. h. the distance consumption per weight and time [l/(kg*km*h)]. A “3L passenger car” loaded with 500 kg of fuel has z. B. at 85 km/h (speed comparable to a truck), a distance consumption of approx. 2 l/100 km (medium-class passenger car approx. 4l/100 km) and thus a distance consumption per weight of 0.4 l/(100 kg*100 km). The additional consumption of the passenger car compared to the truck results mainly from the less favorable operating point of the passenger car engine at 85 km/h, since the passenger car engine is much further away from full load at 85 km/h than the truck engine (s.u.). With a smaller engine, the passenger car could achieve similar efficiency – albeit with similar mileage.

The Energy Consumption Labeling Ordinance, or CO2 labeling for short, does not address energy consumption per km in joules or kWh.

Design measures to save fuel

The energy consumption of a vehicle depends not only on its design but also on the way it is used. Thus, consumption can be further reduced by an energy-saving driving style.The distance consumed [l/100 km] by a car is determined primarily by (1) driving resistance and (2) efficiency.

  • Driving resistance: The driving resistance determines the necessary drive power [kW] to achieve the desired driving performance (acceleration, top speed). During constant runs at low speeds, the rolling resistance, which is directly proportional to the speed, predominates; as the speed increases, the flow resistance (air resistance), which is quadratically proportional to the speed, predominates. The acceleration resistance is v. a. important in city traffic.
    : The acceleration resistance occurs when the speed changes. It is directly proportional to the vehicle mass. Lightweight cars allow the use of smaller motors at the same acceleration, which operate at a more efficient operating point at constant speeds (where rolling and aerodynamic drag are significant). Negative acceleration resistance (during braking) can be used for energy recovery (recuperation). : Low rolling resistance coefficient due to low rolling resistance tires, low vehicle weight, low-friction wheel bearings. (flow resistance):
  • Reducing the drag coefficient by means of a streamlined body shape, clad wheel arches and smooth surfaces (cw value up to ca. 0.16), narrow tires, no door buckles, camera instead of side mirrors.
  • Reduction of the cross-sectional area of the vehicle exposed to the airflow (vehicle projection area) due to seats located one behind the other or at least staggered (two-seater with ca. 1 m² of vehicle projection area), or low seating position and little overhead space.
  • The efficiency describes the efficiency of the conversion of z. B. chemical or electrical power into mechanical power: the main problem of the internal combustion engine is that its efficiency is highest at full load and decreases towards low loads. Specific consumption [g/kWh] therefore increases sharply with decreasing engine load. There are two approaches to solving this problem:
  • Efficiency-optimized gear ratio: power is the product of speed and torque. To generate a certain power, the most efficient operating point is the one at which this power is achieved with maximum load and lowest possible speed.
  • With manual transmissions, “long Translations a simple means. The transmission efficiency itself is close to 100%. However, the low acceleration reserve (“elasticity”) in such a driving stage reduces acceptance. are an alternative for always driving the engine with high loads, but they have so far been successful with only ca. 90% worse efficiency than manual transmissions and are not particularly accepted (there is no direct correlation between speed and engine speed).
  • In principle, diesel engines have better efficiency than gasoline engines in the part-load range due to the lack of throttle losses. In addition, the lack of fuel knock in diesel engines allows high supercharging at a high compression ratio with a simultaneously low injected fuel quantity. As a result, the engine is operated in lean mode, which also significantly increases efficiency. However, the emission of NOx increases, making the achievement of high exhaust emission standards problematic.
  • In the part-load range, electric motors are much more efficient than internal combustion engines.
  • Hybrid drive reduces the problem of high specific consumption of internal combustion engines in the part-load range, since an additional electric motor operates at low loads, while the internal combustion engine is used only at higher loads.
  • Also due to supercharging, z. B. Turbocharging or compressors can significantly increase the efficiency of an engine in the part-load range. Significantly increasing the liter output so that the desired rated power can be achieved with lower stroke volumes. As a result, the engine operates at higher – and thus more efficient – load points in the partial load range (downsizing).
  • In gasoline engines, lean-burn operation also improves efficiency in the part-load range, but this is problematic from the point of view of pollutant emissions (NOx). lean-burn engines, z. B. Direct-injection gasoline engines with stratified charge operation therefore require complex exhaust gas aftertreatment, such as NOx storage catalytic converters.
  • The efficiency of combustion engines can also be increased in the partial load range by cylinder deactivation (ZAS). At low loads, cylinders are deactivated, resulting in a higher and thus more efficiency-optimal load point for the working cylinders. However, in the case of small engines, the ZAS leads to a deterioration in noise comfort, which is not acceptable.

Vehicle design

The initial aim is to keep driving resistance as low as possible in accordance with the intended use.

  • Passenger cars for inner-city traffic should have the lowest possible acceleration resistance (low vehicle mass) and if necessary. have recuperation. Their rolling resistance should be low (low vehicle mass). Flow resistance (air resistance) does not play such a large role here. Example: “Smart.
  • Passenger cars for intercity transport should above all have the lowest possible flow resistance (air resistance), d.h. a low vehicle projection area and a low cW value. Example: “cabin scooter” type, Loremo, 1-liter car from VW.

In the second step, the engine should be designed so that it has the highest possible efficiency under all typical operating conditions.

  • In the case of the electric motor, efficiency is largely independent of the operating state.
  • Internal combustion engines should always be operated with the highest possible load. Oversized internal combustion engines are more problematic in terms of the most favorable operating point possible, since in “everyday use” they have a lower cd value Often operate at low – and thus inefficient – load points. However, this problem can be solved with an efficiency-optimized gear ratio (s.o.) is quite solvable.

Classification of NEF

In Germany, some vehicles with particularly favorable consumption values enjoyed tax benefits. However, vehicles are not classified according to their energy consumption, but according to their carbon dioxide emissions, measured in accordance with Directive 93/116/EC.

According to German tax law, a five-liter car less than 120 g CO2/km. This corresponds to a distance consumption of 5.06 l/100 km of gasoline or 4.53 l/100 km of diesel. In the case of a registration before the 1. Since January 2000, these vehicles have been exempt from vehicle tax. The term Three-liter car is fiscally associated with carbon dioxide emissions of 90 g CO2/km. This corresponds to a distance consumption of about 3.4 l/100 km diesel or 3.8 l/100 km gasoline. The same regulations apply to alternative fuels in combustion engines; electric vehicles are taxed according to vehicle mass.

The term One-liter car Designates vehicles with a consumption of less than 1.5 l/100 km, although for marketing reasons vehicles with a consumption of 1.5-1.99 l/100 km are often also classified in this category.


Ultimately, the permanent introduction of corresponding vehicles on a broad front has failed so far. However, some of the technology found its way into series production of “normal” passenger cars (electrohydraulic clutch, covered hub caps).

Models such as the Smart show that even the smallest vehicles are accepted by buyers. Mid-size vehicles are reaching fleet consumption levels of 7.5 l for some manufacturers, leading some to believe that legal action by the state is recommended (as in California) to demand a reduction in these levels.

Series models

consumption of some production models (selection):

<52 g/km (electricity mix Germany)

Production model in preparation

    The 2-liter diesel car from the Munich-based company Loremo (no test standard specified) is expected to be available in 2010 at a price of less than 15 euros.The “cab scooter” type should be launched on the market at a price of €0,000, reach a top speed of 160 km/h, be designed for 2+2 persons and have a range of 1300 km. An electric version is also planned.
  • Aptera Type-1: production start expected in October 2008, sales initially in California only. There is a hybrid version with gasoline engine and a purely electrically powered version. The cd value of the two-seater, three-wheeled vehicle is 0.11. The hybrid version comes to an average consumption of 1 l/100 km.


  • The Citroen ECO 2000 SL 10 developed between 1981 and 1984 achieved a total consumption of 3.5 l gasoline per 100 km. Features of the study were used in the development of the Citroen AX. [1]
  • The Mitsubishi “i” concept [2] achieved only 3.8 l/100 km in the FIA EcoTest 2003, but this was under practical conditions such as operation on the highway and with air conditioning. [3] The most economical competitors in the test (Audi A2 1.4 TDI, Mini One 1.6, Suzuki Ignis 1.3 DDiS) achieved 4.5 l/100 km under these conditions. [4] The Opel Corsa ECO 3 l consumed 4.3-4.7 l/100 km in practice.
  • Greenpeace’s Twingo Smile consumed 3.5 l of gasoline (RL93/116/EEC). [5]
  • VW 1-liter car is a study so far. According to VW, the development, which was stopped at that time because of too high costs, was restarted because of significantly reduced costs. It is to be built in series from 2010. [1]
  • The bionic car is a concept study presented by Mercedes-Benz in 2005. The boxfish served as an aerodynamic model for the development of the vehicle. Fuel consumption of the diesel-powered four-seater with a cd value of 0.19 is said to be 4.3 l/100 km. [6]
  • The Jetcar (two-seater) consumes 2.9 l diesel per 100 km. (no standard consumption, determined on test drive by manufacturer’s employees – with TuV report). [7]
  • The concept study of Toyota’s ES3 with diesel hybrid drive came in at 2.7 l/100 km (87 mpg). [8]
    (OpenSourceCar): [9] Development of a 2-passenger electric car by students of the TU Darmstadt, 6 kWh/100 km, range 300 km, top speed 130 km/h
  • The Daihatsu UFE III has a combined consumption of 2.1 l/100 km [10]

Electric vehicles

In addition to internal combustion vehicles, electric vehicles also achieve final energy consumptions equivalent to one liter of diesel per 100 km (which is approx. 10 kWh/100 km), and in some cases even less. These include vehicles with lightweight bodies such as the Hotzenblitz, production of which has now ceased, and the Kewet from Norway. The most economical vehicle is likely to be the two-seater TWIKE, which regularly requires less than 5 kWh per 100 km from the grid (measured). This is roughly equivalent to a 0.5 liter car. The “only” single-seater CityEl needs similarly little. Even vehicles with normal small car body like the Citroen AX Electrique consume the equivalent of significantly less than 2 l/100 km. According to long-term consumption measurements, the Citroen AX electrique runs at around 15 kWh per 100 km, measured from the wall socket, i.e. including all charging and battery losses. Based on 308 g CO2 per kWh (published for the EON electricity mix in Bavaria in mid-2007), this results in a CO2 impact of around 46 g CO2 per km when supplied with the normal electricity mix (however, this calculation does not take into account the line losses from the power plant to the socket and transformer losses). If the batteries are recharged with CO2 free solar, wind or hydroelectric power, the CO2 impact per km is even lower and tends towards zero. There are also vehicles which, through consistent optimization, consume even less.

Other vehicles: CityEl, TWIKE, these vehicles consume the equivalent of less than 1 l/100 km. The Tesla Roadster from Tesla Motors (California), with all-electric drive and driving values (and price) of a sports car, has an energy consumption of 11 kWh/100 km with a range of 400 km on one battery charge (manufacturer’s data). The Teslamotors uses lithium batteries, which have a particularly good charge-discharge efficiency.

The fuel consumption and CO2 figures given above for the Citroen AX also apply in principle to many 5-door and 4-seat French electric cars (Peugeot 106 electrique, Renault Clio electrique, Citroen AX electrique), which can be operated as nearly 1-liter cars when charged and driven in an optimized manner.

A still unsolved problem is the hardly realizable size of the battery for a driving distance of some 100 km. If batteries are installed that do not take up too much space and are not too heavy, it is too often necessary to make very time-consuming recharging stops of several hours to cover this distance.

Low penetration of low energy vehicles

Although mass production of the three-liter car was welcomed in principle, it was discontinued because demand did not justify the cost. The development of successor models of the VW Lupo 3L TDI (z. B. on the platform of the VW Fox) was discontinued. The production of the Audi A2 3L TDI was stopped in mid-2005 without successor. The Smart cdi gets popularity precisely because of the low CO2 emissions- but basically the vehicle production has often been questioned and so far does not offer the original concept of the electric vehicle in series production. Opel Astra Eco4 with modified body has disappeared in the new model range.

Below are some points that often come up in the discussion about low-energy vehicles:

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