Function

The hybrid drive as such already exists for quiet some time, more precisely since 1919, indeed, not for saving fuel, but to win races. This was at that time due to the strong competition between quite strong electric motors and still weak internal combustion engines. Today environmental aspects and energy saving are the primary reasons in favour of the hybrid drive. Very interesting is how many kilometres the car is driven in the city and the number of brake processes. The decrease of emissions is especially considerable, e.g., in a traffic jam. The hybrid drive seems to be hot in the USA and Asia. Some city centres are just free of charge for hybrid driven vehicles. A better solution also for longer distances is probably the fuel cell, but this will still take a while until the technology is ready to go into mass production.

The combination of an electric motor and a diesel engine will be especially interesting, however, the hybrid is accepted exactly in such countries which are not very much used to diesel engines in a car. It is probably also a matter of money to combine the expensive diesel with a hybrid that also comes with a surcharge. In these countries there is a lot of competition on the new vehicle price. Maybe this circumstance changes in the light of even higher crude oil prices.

How it works

Hybrid drive means that besides the customary vehicle engine another - possibly using another form of energy - engine helps in driving the car, or maybe takes over fully sometimes. What does it mean for the drive? Like the generator, the electric motor drives e.g., via belt drive.It is placed between engine and gearbox (see picture 1). There is a planetary gearbox with infinitely variable possibility for switching.

The first option is a mild hybrid storing the brake energy in the battery and supplying enough power for the initial drive exclusively with current (start stop automatic). It gets by with comparatively few expenditure, excess weight and costs, but its savings potential in the city does not exceed the 10 % margin.

It can be developed almost infinitely variable to represent a full-hybrid if it leaves off the internal combustion engine, e.g., in traffic jams. Also with a small battery it can help with the acceleration processes and thus allow the implementation of a smaller, more energy-saving combustion engine. An adjustment of the smooth performance characteristics of the combustion engine is possible, maybe making offset shafts and perhaps heavy flywheels obsolete. Maybe the rough three-cylinder mutates in terms of sound mutates to a very well behaving six-cylinder engine.

The mature hybrid features a substantially stronger battery and allows the driving without engine. The Toyota Prius of the second generation limits the exclusively electronically driving to 30 km/h. Later on probably a town can be crossed just with the electric drive. The main problem is the battery, except for the costs in general. In the Prius the battery works on a nickel metal hydride basis and allows with an acceptable weight a guarantee of 8 years or 160,000 km.

Indeed, it is controlled such that its maximum capacity is never completely used, therefore, the exclusive E-operation at 50 km/h is not possible.

For the future operation more electric energy has to be in place at the same or lower weight. Maybe the lithium ion battery offers an alternative.However, how do you switch from one to the other mode of operation? One possibility is shown here. It is not so easy to have the switch take place without having any symptoms get through to the passenger's compartment. Two methods probably stand out. Either a permanent connection is in place in which the engine participates without or with a lower compression (Prius), or the switch takes place via a second clutch. This system trusts in progressions made in the electronic regulation of friction clutches.

Possibilities

Not only the internal combustion engine can be decreased, also on the gearbox side savings are possible. The Prius practically features just one gearwheel connection. Particularly the reverse gear seems unnecessary. If the electric motor is strong enough to help the combustion engine for a certain period of time, longer gear ratios are also possible in the normal gearbox.

There are also more cost-saving possibilities for a hybrid drive. An almost unchanged power train assembly is possible if the electric motor is mounted above the gearbox and engages at the end of the gearbox intake shaft. In this case the complete engine remains unaltered. And as long as the normal clutch is disengaged, the exclusive electronic operation would be possible.

Standard components would also be possible in case of an electrical drive via the normally not driven axis. This would be a combination of hybrid drive and four-wheel drive. This principle is applied for the currently strongest truck of the world. One diesel engine generates current and four electrical wheel engines provide for the movement. One thing, in any case, is common for all these systems: You collect energy during cross- country trips and make use of it in high-emission and more fuel intensive situations, using either just the electrical engine or both engines. In addition, you may combine the highly competitive internal combustion engine with the torque-strong electrical engine in certain operational areas.

Outlook

Developing new vehicles and particularly purchasing them the performance of the engine is of main importance, and not its torque development, so far. In spite that the maximum performance is very seldom necessary in the everyday life. Modern vehicles with favourable drag coefficients demand only approx. 30 kW for 120 km/h on a plain highway. If the higher performance is used only for a limited period and not permanently, the hybrid drive with its increasing efficiency in terms of energy conversion and energy storage will have a rosy future. Small engines with supercharging are conceivable whose torque weakness is improved in the lower speed range by an additional electrical drive. The hybrid drive must also become attractive for the long-distance traffic.

Important

Due to specific supporting measures of the Japanese government and menacing exhaust gas regulations, e.g., in California (2004) there are several series production vehicles with hybrid drive, even already in the second generation (see 2nd figure on top). 06/08