Hybrid car
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Description
Strictly speaking, a hybrid car is one where there are two sources of mechanical energy driving the wheels. The term has also been incorrectly applied to cars where an internal combustion engine drives a generator providing electricity to charge a battery and to feed one or more electric motors which drive the wheels or with hydraulic or pneumatic transmission.
Detailed description
There are many variations of hybrid cars. Their common points are generally:
- They have a combination of an internal combustion engine and an electric motor
- Under some conditions, either the engine or the motor or both can drive the car at a given time
- They use regenerative braking, the recovered energy being used to charge a battery
- The internal combustion engine usually stops when the car is not moving
- The internal combustion engine is designed for maximum fuel economy
Historically, the first commercially available hybrid car was the Honda Insight, a remarkable two-seater with very low fuel consumption. This was followed by the Toyota Prius and the Honda Civic Hybrid. Since then, other car makers have started production of a number of true hybrid models and ICE/electric ones.
The reason behind hybrid cars is to reduce fuel consumption, carbon dioxide emissions and pollution. Generally, the fuel consumption of most hybrids is about half that of equivalent conventional cars.
To illustrate the difference in characteristics between concepts, it is proposed to compare the Honda Civic Hybrid (HCH) and the Toyota Prius (TP), cars of essentially similar dimensions (except for height), weight and performance, in the medium-sized category, without endorsing either car or over competitive makes. Some figures quoted are from US EPA data [1], some from an independent web site[2] and some from actual users reported experience from both reference sources.
- Engine: the HCH has a conventional Otto cycle engine with electronic valve control. However, when conditions allow it (e.g., running downhill or cruising to a stop), the engine is disabled by opening all valves and cutting fuel injection, even though it still turns. The TP has an Atkinson cycle engine which is theoretically more efficient but has a limited rpm range.
- Electric motor: the motor on the HCH is on the same shaft as the engine and is most efficient in the 2500-3500 rpm range. The motor on the TP is independent of the engine and is designed for high starting torque.
- Transmission: Both cars have a continuously variable transmission (no fixed gear ratios) but the TP also has a complex mechanical system which can drive the car on electric motor only, on engine or both.
- Highway fuel consumption: HCH, 4.5-5.4 l/100 km (EPA 5.2); TP, 5.0-5.6 l/100 km (EPA 5.2)
- Urban fuel consumption: HCH, 5.0-6.5 l/100 km (EPA 5.9); TP, 4.1-6.0 l/100 km (EPA 4.9)
- Average fuel consumption, mixed driving †: HCH 4.9-6.1 (EPA 5.6, Greenhybrid 5.1); TP, 4.7-5.9 (EPA 5.2, Greenhybrid 5.0)
- Best/worst user average fuel consumption, EPA (Greenhybrid) †† : HCH 4.2-7.8 l/100 km (3.6-8.2); TP 3.1-7.4 l/100 km (3.3-8.5)
- EPA pollution index (10=no pollution): HCH=9.0, TP=8.0 (The TP possibly suffers as the engine starts and stops more often.)
† The range of consumption shown here is what average drivers may obtain under normal conditions in reasonably flat terrain without air-conditioning. Expect slightly higher figures in mountainous conditions and with climate control working hard.
†† Note: Caution should be used when considering these extreme values because users may report false figures or extreme means employed to obtain them.
From the above, it would seem that the choice of a hybrid car may depend on the use to which it will be put. Keeping with the example of the two cars above, the user who will be driving mainly in towns will perhaps choose the TP, while the long-distance driver may find the HCH a better buy. Whichever car you choose, be prepared for a period of apprenticeship to obtain the best results.
One of the contributors to this article has a web page, recounting his personal experience with a Honda Civic Hybrid.[3]
Plug-in hybrids
Some persons have advocated hybrids with larger batteries, which can be charged from an external power source. The argument is that, for example, short distance commuters would be able to use their car without the engine starting. In other words, it becomes an electric car, with the engine starting only when it is used on longer journeys. This is not necessarily beneficial to the environment except in countries where the totality of the electricity supply is from nuclear and/or renewable sources (e.g., Switzerland). If the electricity is generated entirely or partially from fossil fuels, the overall efficiency will most likely be lower than using fuel in the car's own tank.[4] This means that such cars will increase carbon and other pollutant emissions. Unfortunately, in countries where motor fuel is heavily taxed and electricity is not, this concept appears economically very attractive.
