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 Engine Oil-Finder

Range Extender

If one wants to find out from the manufacturers, anything about the 'Range Extender', one notices that they can't really tell you anything. In the case of the electric car, one is fairly sure of the certain types of propulsion- and battery technologies, as far as the Range Extender is concerned, there is nothing even near to a standard, which, would, by the way, also make the whole affair much more reasonable.

Without a Range Extender, it will be very difficult to increase the general acceptance of electric cars. Through commited construction, the Range Extender could even make the electric car more reasonable in price, because the necessary battery capacity could be calculated lower. The Plug-in hybrid and the electric-drive with a Range Extender, would meet somewhere in the middle.

Consider the expression as comprehensively as possible. This means: Anything that could help a vehicle with a limited range to extend it's range, bears the name 'Range Extender'. Thus, this could take the shape of an additional motor, a battery in the vehicle itself or even one in a trailer. Possible however, would even be an additional rechargeable, and removable accumulator.

In the case of the latter, you may ask whether it makes sense. The answer is: One can spare oneself the strain of carrying, unnecessary at the moment, electric energy around. It could even be used by more than one electric car. However, in these times of non-standard charging cables, this vision is still unthinkable. Let's rather stay with a conversion of chemical- into electric energy.

At the moment there is one important differentiation: Should this machine only produce current or should it also be mechanically coupled to the drive train? Those who favour the first variation, will usually point a finger at the additional components like the clutch and the gearbox. Apart from this, this position of the engine/motor can no longer be freely chosen.

Indeed, there are also disadvantages with the second variety. E.g., with the Range Extender in the BMW i3, which costs more than €4000 and has 25 kW (34 Hp), the car, with filling up, can be driven for as long as you wish, the consumption when driving relatively quickly however, is as much as 9 liters/100 kms. We haven't come much further than the unfavourably aerodynamic VW-Beetle, which could also get up to 120 km/h and it's consumption was similar. In the i3, because of the double conversion of the energy, a great deal of it is lost.

If, in reality, it can manage about 150 kms without- and a further 160 kms with a Range Extender, then the average consumption for both driving-cycles, one after the other and at the same speeds, is higher than that of the somewhat larger Diesel version, this is not including a complete battery charge. This is not a very good average, compared with the loss of performance caused by the higher weight of a few components which are mechanically coupled.

Let's examine this briefly again. A Range Extender could be coupled to the drive train through a single gear. Instead of having a clutch, a planetary gearbox would also be possible. The electric motor uses only enough energy, to bring the vehicle to an urban speed. Because the electric drive unit also converts movement- into electric energy during recuperation, this could also be done, up to a point, when the car is being powered by the combustion engine.

If we calculate the additional (one speed!) gearbox, possibly also a clutch or maybe just a free-wheel, against the no longer necessary generator, as far as weight is concerned, we would break about even. One would have a reasonable consumption, even if the battery were flat. This is particularly sad, because the Range Extender in a BMW, is installed directly adjacent to the motor.

In some countries (e.g., the USA), there are only subventions, if the stockpile of electric energy is greater than that provided by fuel. Thus, the relatively small additional tanks.

In the current practise, one can fill 9 liters of fuel into the BMW. Hence the consumption can be determined, because the manufacturer gives a distance of 160 kms and some testers have only managed 100 kms. That would be 5,6 to 9 liters/100 kms. If one drives at full power, the battery supplies added energy, until it's capacity drops to 3 percent. Then the Range Extender is on it's own and one can still travel at 100 km/h. If one travels using less than full power, then it even charges the battery.

There is also a complete Range Extender from the Mahle company (see picture 2). It produces 30 kW (41 Hp) at 4000 RPM and 15 kW (20 Hp) at 2000 RPM and is apparently capable, even if the battery is flat, of bringing the car to a normal driving condition. By the way, it alone weighs 45 kgs and 65 kgs with a generator. So, also with the BMW can we assume a weight-ratio of 2 : 1.

The Mahle company gives the consumption at 15 kW as being 240 g/kWh, which would correspond to just under 3 liters per hour. However, we know from BMW, that just under 25 kW would just about be enough to propel this car by itself. This means that the Mahle system, if the battery is empty, would need almost the full performance, e.g., for the car to reach a speed of over 100 km/h. This would then mean a calculated almost 6 liters per hour plus the additional consumption of such a unit at full strain performance.

You thought correctly, also the Range Extender from Mahle could, in practise, have a similar consumption to the BMW. It also doesn't solve the problem of an enormous consumption by simply adding a Range Extender. This is probably also the reason, why there is no really standard hybrid-drive. They are mechanically coupled to the drive-train, also e.g., the Ampera/Volt (Opel). 01/14

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