My Toyota Prius

Introduction

The Toyota Prius is the world's first production hybrid car, launched in Japan in December 1997. It uses the Toyota Hybrid System, in which the power train consists of an internal combustion engine of 53 kW, fuelled by petrol/gasoline, and two large electrical machines, connected to a small capacity high-voltage traction battery. This battery is charged with energy recovered (or regenerated) during braking, and energy generated by the IC engine. The battery can power the electrical machine of 33 kW, supplementing the power of the engine, so enabling this to be designed for maximum efficiency, rather than maximum power. Moreover, the IC engine is computer-controlled to run at variable speed, but almost always at full-throttle, so delivering power at maximum efficiency (up to 36 per cent). When less power is required, the engine runs only part of the time, and the electrical machine drives the car the rest of the time. The THS also acts as a Continously Variable (automatic) Transmission. Thanks to the THS and many other energy-saving features, the Prius, as sold in North America and Europe, has an official fuel consumption of 5.0 l/100 km (56.4 miles/UK gallon, 47 miles/US gallon) on the European (urban + extra-urban) driving cycle. For comparison, a Toyota Corolla 1.6 automatic has an official fuel consumption of 8.0 l/100 km (35.6 miles/UK gallon, 29.7 miles/US gallon). Thus the Prius consumes about 37 per cent less fuel (or goes about 58 per cent further).

Buying a Prius

I first heard about the Prius some time after the Japanese launch, and found a number of articles on the web. Later articles mentioned that a revised version, with more power, would be sold in North America and Europe. As an automobile engineer, I judged the Prius to be of exceptional significance, so as soon as I learnt that it was to be sold in the UK, and at an affordable price, I decided to buy one. (This would be only the second new car I had bought - the first being a Mini in 1959). I first enquired in May 1999, but was only able to drive a demonstrator and place an order on 5 November 2000. Mine was the 47th ordered in the UK, of only 200 allocated for the year 2000. The base price was 16,495, including all charges and taxes. I chose the colour silver, with a 6-disc CD-player in place of the standard 1-disc, at an extra cost of 410. However, under the UK Government Powershift programme (to encourage 'clean' vehicles), it was elegible for a rebate of 1000, which I received later. I collected my Prius on 24 December 2000, just in time to show it off over Christmas. I later bought a set of floor mats and a pack of spare bulbs and fuses.

Driving in the UK

My previous car was a 1995 Vauxhall Cavalier CDX 2.0 litre automatic. Compared with this, the interior is remarkably spacious. Although considerably narrower than the Cavalier on the outside, the body sides are almost vertical, with the windscreen pillars spaced well apart and the windscreen well forward. The front seat and roof are both appreciably higher, making entry and exit considerably easier. This also gives a commanding view of the road ahead. The dash-mounted gear selector is light and convenient in use. This position makes sense once you realise that a floor shift would impede crossover access, while a column shift would be hard to integrate with the rake-adjustable steering wheel. Similarly, the pedal-operated parking brake is very convenient in use, since it is easy to apply plenty of force (reacting against the seat, and using the strongest muscles of the body). Furthermore, in stop-go traffic it is easy to apply, to avoid resting the foot on the main brake pedal. Again, this parking brake makes sense once you realise that a central floor handbrake would impede crossover access, and take the space occupied by the centre console, with its storage space and cup-holders. Moreover, an outboard floor handbrake would be liable to accidental release during entry and exit. The rear seats allow a comfortable posture, with plenty of knee-room. The Prius is a notchback/sedan, with a conventional boot/trunk. However, it has a good cuboidal shape, and takes large suitcases (or up to four golf bags). Also, the European Prius has fold-down rear seats, allowing more flexibility for carrying luggage.

Starting off is extremely smooth, helped by the drive-by-wire throttle. The take-off at full throttle is vigorous, thanks to the contribution of the powerful electric motor. At low speeds, the engine stops and starts frequently - and remarkably unobtrusively. However, slight engine vibration may be felt via the steering wheel under certain conditions. Under full throttle, the engine speeds up appreciably, but this is accompanied by strong acceleration. When accelerating, the power flow is exceptionally smooth, helped by the absence of gear changes. When cruising at steady speed, the power train is very smooth and quiet, helped by the high gearing in 'top' - about 25 mph/40 kph per 1000 rpm.

The steering was much lighter, and initially seemed 'twitchy' at higher road speeds. This was with only the driver in the car, and initially with the standard tyre pressures of 35 psi front and 33 psi rear. Recently, I have been using 35 psi front and 36 psi rear but this has brought no detectable improvement. However, I have gradually learnt to reduce my steering inputs, and steer with a light touch, whereupon it runs straight. The turning circle is very small for a car with front wheel drive - a real help when manoevering in tight spaces.

On harsh surfaces there was more road noise - perhaps because the mix of tyre attributes is biassed towards low rolling resistance. However, on smooth surfaces it was very quiet, giving a 'magic carpet' ride. There is more wind noise at highway speeds, but it gets no worse as the speed rises.

The brakes were much lighter, with a different 'feel' - due to the combination of regenerative and friction braking. However, I soon learnt to just 'squeeze' the brake pedal, and 'feather' the release, to control the deceleration.

The ride in the front is not quite as good as the Cavalier, but that in the back is far better. The automatic climate control is excellent, with very light rotary controls. When cold, the warm-up is very quick, and when warm or damp, it keeps the interior cool and fresh.

The overall fuel consumption at 6156 miles/9907 km was 51.83 mpg/5.45 l/100km, which I consider excellent.

Driving on the Continent

In September 2001, I took a holiday on the Continent, driving my Toyota Prius, and visiting Brussels, Potsdam (near Berlin), Munich, Schondorf (near Munich), Cologne, Lippstadt, Brussels then back home (Billericay, Essex). On the autobahns, especially in Germany, I drove at high speeds. These were mostly 130 to 140 km/h where permitted and conditions allowed, and occasionally up to 160 km/h. The highest speed I saw was 170 km/h. However, these speeds are indicated, and the speedometer/tachometer of the European Prius is said to overread by some 7 %. Even so, this corresponds to a true speed of 98.7 mph. In addition to the effects of gradient and wind, the Prius has two top speeds - that which it can sustain (around 98 mph/158 kph) and that which it can achieve for a short time, by drawing energy from the (relatively small) traction battery (around 100 mph/161 kph).

The total distance door to door was 2221 miles/3574 km. Over 2008 miles/3232 km (fill-up to fill-up) the car used 187.69 liters of petrol/benzine, giving an average consumption of 48.6 mpg/5.81 l/100km. This was only about 6.6 per cent higher than that in the UK. I consider this fuel consumption to be excellent, and believe it to be due to the high efficiency of the Atkinson cycle engine and the Toyota Hybrid System transmission. Another helpful characteristic is that (unlike most engines), the fuel/air ratio is not enriched at full throttle, but instead the car relies on the battery and the 33 kW electric motor to provide extra power for overtaking and hill-climbing. This was particularly impressive at higher speeds - 130 to 160 kph/81 to 99 mph - and I believe that quite a few other drivers (of e.g. Audi A4 turbo-diesels) were somewhat surprised by the performance of this unusual car.

After my return to the UK, the overall fuel consumption at 8164 miles/13139 km was 51 mpg/5.53 l/100km, which again I consider excellent. Since Diesel fuel has about 1.12 times as much energy per unit volume as petrol/benzine, the equivalent Diesel fuel consumption would be 56.6 mpg/5.0 l/100km. This means that the overall vehicle efficiency (drag times power train thermal efficiency) is certainly comparable with any vehicle of similar size. Moreover, the Toyota Hybrid System (THS) gives the effect of a Continuously Variable (automatic) Transmission, and in summer I usually run with the automatic climate control air conditioning on.

In the hope of increasing the stability at high speeds, I had set the tyre pressures to 35 psi/2.4 bar all round (rather than 33 psi/2.3 bar at the rear). Although not as stable as my old Cavalier/Vectra, the Prius proved acceptably stable at high speeds on the autobahns. It needs to be handled with a light touch, but the steering is very accurate, and the car does not move sideways much when passing trucks and other obstacles - even when there are side winds. Although the wind noise is not as low as in my old Cavalier/Vectra, that in the Prius is acceptable at speeds of 60 to 70 mph/100 to 113 km/h, as used in England. Furthermore, I found that it was no more obtrusive at the higher speeds I used on the Continent. There was more engine noise at full throttle, since above about 50 mph/80 km/h the engine then speeds up to its maximum speed of 4500 rpm. However, there were no 'body booms' at any speed, and engine noise was very low when cruising, since the THS then gives about 25 mph/40 km/h per 1000 rpm. During the entire trip, I saw only one other Prius - which I overtook on the run in to Munich. This was a left-hand drive model (presumably German), driven by a woman, and we waved to each other.

It was very noticeable that most of the roads on the Continent are much smoother than those in England. They are free from long wave dips and audible expansion joints - and damaged surfaces are only found in places on the busy roads in the industrial North West of Germany. Also, the surfaces lack the harsh texture so often found in England. The Prius seems to have been developed on Continental roads, and harsh road surfaces cause an increase in road noise. However, this is still bearable, and can always be drowned out by the audio system. There was a fair amount of road renewal being done in Germany, with corresponding sections of contraflow traffic. The best autobahns I found were in parts of the former East Germany, such as the roads to Berlin and Potsdam and from there south towards Dresden. In Germany generally, and especially on these recently renewed roads, the standard of road design is far higher than in England. The roads are straighter, with longer sight-lines, making them safer at high speeds. Usually the full width of concrete is laid at once, by gigantic machines, rather than each traffic lane separately. While the surfaces have very small cross slopes, and are much smoother, they do not seem to suffer unduly from standing water (which could cause aquaplaning) or poor adhesion when wet. I had ample opportunity to assess this, since the weather was very changeable, with frequent showers during my long drives. As one would expect of a Japanese car, the windscreen wipers of the Prius are excellent. Along with most other drivers, I used dipped headlights when on the autobahn, even in daylight, since they definitely help to show your presence from afar - especially in cloudy and rainy conditions.

The standard of driving was generally excellent - especially by drivers of trucks. They are always aware of the traffic behind them, and are notably good about pulling back in after overtaking on two-lane autobahns. Also the drivers of slower cars seem better at keeping to the slow lane. I kept a very close eye on my rear mirrors, and was very careful about signalling every lane change. This is essential since a few cars (usually Mercedes S and E class, BMWs, Audi A8 and A6, and the occasional Porche 911) may come up very fast, travelling at perhaps 200 km/h/125 mph. Curiously, it was only older or smaller cars, going not much faster than I, which sometimes came up too close for comfort. I was happy to let them get by at the earliest opportunity. I had no worrying moments, and did no hard braking. With so much distance covered on long high speed roads, I saw evidence of only one accident, but it was serious. This was on the A7 going South on a Sunday (when trucks are not allowed, save with special permission). Luckily I was going North, and I saw a helicopter parked on the highway, and a severely shortened car on a recovery truck, followed by a very long queue.

I was driving alone, but navigation was generally easy, especially on the open road. I had printed out maps and itineraries for each segment of my trip, but I found all that was really necessary was a short list of the main towns on the route. It was more difficult in built-up areas, but I still managed well in Potsdam, Munich, Cologne and Lippstadt. By far the most difficult was Brussels, with its combination of through routes (many in tunnels) and side streets. This is made worse by the fact that, unlike in Germany, the street signs are too small to read easily from the car. I got lost both times when leaving the city, and would have found a Satellite Navigation system really useful. In the end, I had to follow the signs to the airport, in order to reach the autoroutes, many of which start nearby.

Brussels also has a severe parking problem, and a very casual attitude, so that cars are parked on (and not just approaching) pedestrian crossings and corners, and even double parked. I was glad that the Prius is a compact car, with a small turning circle. There is a tram system, and also a subway, but the city is simply too large and prosperous, so that very many people use their cars, even though progress can be very slow, especially in the side streets. Moreover, navigation is so difficult for the visitor, and the city so large even for residents to learn, that I would guess that at any one time a significant proportion of the drivers are either lost or trying to find a parking space. However, I saw no accidents, or even near-misses, and there was little use of motor horns. This is probably helped by the Continental practice of pedestrians crossing the street at junctions, where there are traffic lights including lights for pedestrians, which they wait for.

All told, the entire driving experience was most enjoyable, and I would happily do it again - especially in a Prius. However, at night and in winter (with snow and ice) might be another matter. Travelling by car enabled me to visit a number of friends and relatives, and also to explore my home continent before motor fuel becomes even more expensive. I estimate that, compared with the old Cavalier/Vectra, the Prius has about the same carrying capacity, yet used about one-third less fuel, and discharged far less noxious emissions.

I have created a presentation on the Prius.

More about the Prius can be found on the Web. (see http://www.toyota.com, http://www.toyota.de, and http://www.priusenvy.com)


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