Reviewing the Prius UK-Style
By Chris Ellis
Chris Ellis is the founder of PowerBeam, a UK-based automotive development firm. He regularly contributes to EV World, providing insight into automotive technology trends in Europe. He recently test drove a European-version of the ‘05 model Prius to assess its suitability for installation of his firm’s unique flywheel technology. Below is his perspective on the current world-standard in gasoline-electric hybrid vehicles.
I drove the car for over 400 miles over a variety of roads, including motorways with the cruise control set at 85 mph, and also up one of the hills used for more than a century to test English prototypes. I tried to adopt different driving styles, to establish which owners would be happy with their new purchase, and who wouldn't want one. All the mpg figures came from the onboard system, and have been converted to US gallons; 5 UK gallons get you 6 US gallons.
The highest average figure I saw was 65 mpg; I'm not claiming that as any kind of record, merely an indication that 'my' Prius was fully up to spec. The mpg figure that most impressed me was the 52 mpg I obtained between Minehead and Barnstable, across sometimes hilly terrain and always winding narrow roads, at the sort of speeds a typical sales rep might employ. If the car had been a conventional 'clean diesel' of similar cabin volume and weight, it might have done 40 to 45 mpg, or 35 to 40 on gasoline. On this route, I rarely exceeded 70 mph, below which speed the Prius is a pleasure to drive reasonably hard. If I tell you that the fuel consumption over the section up Porlock Hill averaged 12.2 mpg and this is included in the 53 mpg, you'll understand that the Prius engine can both dish it out and deliver what is promised on the tin, i.e. excellent fuel consumption at all legal UK and US speeds.
However, I did notice an annoying tendency for the engine rpm to fluctuate quite widely with only minor changes in accelerator position, rather as if the transmission was fitted with a torque converter from the 70's, before lock up clutches were in widespread use. The engine also seemed more eager to rev beyond 2,500 rpm than a conventional automatic. You will recall that the principal reason locking torque converters were introduced was to improve fuel consumption. I suspect Toyota may already have prototypes running around fitted with a 'MkIII HSD' which locks the transmission above a certain road speed, in the manner of a conventional overdrive. The design priorities for the original HSD were probably Japan first, California second and 'hard core' European drivers forty third. That may now change.
Some time ago, Mercedes identified in public the 'Achilles heel' of the current HSD, namely the losses that occur at higher speeds, with the generator needing to supply power to the motor via the controller even when the battery is effectively out of the picture. This has been one of the reasons why DaimlerChrysler has joined with General Motors to develop an alternative which is more efficient at freeway speeds. However, the fix we have identified to further improve HSD may well allow Toyota to match the DC/GM solution at all speeds. Mercedes (and/or GM) will need PowerBeam to pull decisively ahead. (A very short commercial - it's over now!) The maximum speed limit in the UK on motorways and dual carriageway roads is 70 mph, and most European countries have similar limits.
However, in a touching gesture of European solidarity, some drivers in France, Italy, Spain and the UK try to drive at German speeds whenever they can. In practice, this means a vehicle needs to be able to accelerate swiftly from 60 to 90 mph to begin to qualify for the 'outside lane club', where the drivers who aren't paying for their own fuel like to congregate. This is where Prius currently loses a big chunk of addressable market, because fuel taxation policies and the sheer cost of fuel are motivating both owners (often companies in the UK) and drivers to chose cars which operate efficiently at these speeds. For example, it is said that some 70% of all new S-Class Mercedes registered in the UK now have diesel engines. And the Prius, despite its efficient engine and relatively low drag coefficient, doesn't do that well at these speeds.
To take my twitchy right foot out of the loop, I set cruise control at an indicated 87 (a true 85?) on a clear section of the M5 motorway over the Somerset levels (as flat as you'll find this side of a salt lake), with and without air conditioning engaged. Over a five mile stretch, I got only 35 mpg with air conditioning on. This improved over the next five miles to 38 mpg with the AC off. Given that a US government test showed a 30% increase in fuel consumption over the federal cycle for a Mk I Prius, 3 mpg worse isn't so bad, but this is essentially a function of the much higher average traction power being deployed at a steady 85. The main reason for the Prius's relatively low fuel consumption at European cruising speeds must be lie within the transmission, and these high losses are confirmed by the (rare) need for the transmission to be water cooled.
EV Mode EV mode is apparently not available in the US, for reasons I suspect have something to do with product liability. As evidence, the following quotes are from the UK version of the Prius Owner's manual.
- 'In the "EV" drive mode your vehicle runs like an electric vehicle, only using the electric motor....'
- 'CAUTION The driver should pay full attention around the vehicle especially when it is driven by the electric motor (with the gasoline engine stopped). People in the immediate area might misjudge the hybrid vehicle movement based on the absence of the regular engine noise.' Not only in bold, but inside a black border!
- 'In the following conditions, the "EV" drive may be automatically cancelled....
- The hybrid vehicle battery assembly charging level is 2 or lower. The vehicle speed exceeds about 45 kph (28 mph). The accelerator is depressed strongly or on the slopes.' [The EV range] usually ranges from several hundred metres to 2 km (about 1.2 miles or less) ....'
- '... frequent use of the "EV" drive mode may worsen fuel economy.'
It is interesting that Toyota seems to have decided that the Prius can only use a small fraction of the battery's small (1.9 kWh?) capacity. My guess is that the controller limits battery SOC to a range between around 60 to 80%, which implies an AVAILABLE capacity of only some 400 Wh. Given FreedomCAR has set a minimum of 300 Wh, this is obviously fine for a fuel-only hybrid, and we know that the PowerBeam XJH, with its superior efficiency, can get away with only 300 Wh. However, it should help to remind plug-in proponents that most battery technologies don't take kindly to thousands of deep discharges.
Toyota seems to have reasoned that the best route to ensure long life in a battery used as a Surge Power Unit is to restrict it to shallow cycles. If it is also used for deep cycles, then the 8 year warranty is voided, naturally.
Clearly then, if plug-in capability is a must, it is sensible to keep the powerful Surge Power Unit separate from the capacity-focused and less stressed Energy Store, unless a battery technology with the elusive combination of high capacity, high power (in and out) and long life can be found. It doesn't seem as if Toyota have found it yet, or "EV" mode would have a much more useful range and top speed.
I've also concluded, as the manual hints, that "EV" mode is potentially dangerous as is, and should only be used to move the car out of a garage (or an underground car park) without causing the engine to fire up until later. Everything else is a 'party trick'. Here's my experience.
On two separate occasions, I managed to get round my local block in "EV" mode without causing the engine to fire up, but it was a strain. I had to concentrate to avoiding the engine cutting in as a result of acceleration harder than 'very gentle', or a road speed exceeding 28 mph. Round here, other drivers assume anyone doing less than 35 has fallen asleep, and adopt various measures to try to wake them up. Which was annoying.
Worse, on the second occasion, I was pulling up to a T-junction into a main road, slowly but silently. On the passenger's side there was no sidewalk and a high wall extended round the corner, where the main road was provided with a sidewalk. Just as I pulled up, a man stepped into my path from the sidewalk of the main road. Neither of us had been able to see each other, and he had not heard me. If I had been driving a conventional car, he would have heard me and acted appropriately.
Fortunately there was no bodily contact, but I thought I heard him direct a few short words, first at me, then at Toyota, as the badge became visible as we pulled away, silently. And I was left wondering what might have happened if it had been a mother with a pushchair in front of her.
Conclusions on "EV" mode
The XJH will be fitted with a speaker behind the front grill which will emit the sound of the engine at around 1,500 rpm, whenever the car is out of Park and the real engine has shut down.
Toyota has wisely fitted the Prius with a beeper which sounds inside and outside the car as soon as Reverse is engaged. Toyota needs to come up with an appropriate way of overcoming the 'silence problem' in Drive, not just for "EV" mode but whenever the car is moving, or could move, with the engine off.
The European Commission will need to produce suitable legislation to cope with almost silent vehicles in the narrow streets of our older towns and villages. The EV community had better suggest a congenial solution before the bureaucrats concoct something we might actively dislike. Up until now, most electric vehicles have been noisy enough to be recognizable as a potential threat by pedestrians. For example, England's thousands of milk floats have motors and transmissions noisy enough to be heard a hundred yards away, whenever they move. Consequently, there have been almost no injuries to pedestrians over more than 50 years. But almost silent vehicles are something else. In Europe, there are countless accidents involving cyclists and pedestrians each year. Larger silent vehicles can only add to the toll.
The Prius II is a fine motor car and its outstanding success in the US market has ensured that all automobile manufacturers must now take hybrids very seriously. The next blow to fall will be from Lexus with the GS 450h hybrid sedan, which is likely to be almost as big a success in Europe as the Prius has been in the US, and should be even more successful financially because it will be strongly profitable. It will be successful because it will be a fully qualified member of the 'outside lane club' yet be more economical at all but insane speeds than the diesel members of the club, leave alone the other gasoline powered cars.
There is a further twist. The US Senate has recently been able to convince the House (and the Governator?) to 'wake up and smell the (cellulosic) ethanol'. The US target for 2012 is now an annual production of 7.5 billion gallons, an increase of over 3 billion in only six years. As a 'sanity check', let's assume all of the extra went into new cars and trucks as E85. Let's assume they are all hybrids and average 40 mpg, then 14,000 miles a year would require 300 gallons of ethanol and 50 of gasoline (allowing for the reality of 75% ethanol during the winter months). That will mean10 million new 'cellulosic hybrids' by 2012, all requiring ready access to gas stations with E85 pumps to soak up the extra ethanol. As yet, the automotive industry doesn't seem to realize it is facing a massive business opportunity (with the honorable exception of Honda and Toyota, of course). The existing vehicle fleet, ALL of it, is already effectively obsolete. Most of it can't run on E85. Those ( 4 million?) existing vehicles that can already use it will look woefully expensive to run compared to their cellulosic hybrid replacements. Cellulosic ethanol will probably end up with a price per gallon that will put it at an enticing 10% lower cost per mile than diesel, to pull the big rigs over to ethanol even faster than the light truck fleet. And gasoline prices will continue to rise globally because of the inevitable increase in demand in Asia, Africa, Eastern Europe and Russia.
By 2012, the US may conceivably have lost the battle to control the Middle East, but it won't matter much, because the world will have taken a key step towards limiting Climate Change, and the US will expect to be Energy Secure by 2020 (now there's a vision), and Peak Oil will have occurred, but not sent the economies of the G8 (or the developing world) into a tail spin (The Middle East is another matter). Then, all we need is for ITER to announce that generating electricity from nuclear fusion has been proved to be commercially viable, and we can sit back and enjoy the excess ethanol!
Meanwhile, the chairman of Shell (once upon a time an OIL company) has asked the British government to impose a mandatory 10% biofuel target for the UK, almost double the European target of 5.75% for 2010, and proportionally higher than the new US target. Of course, Shell owns a major piece of Iogen, so it may know rather more about the economics of cellulosic ethanol than some of the other oil majors. When BP tries to buy half of Texas, then the game really will have changed! The Chinese still think it's about oil. However, the President, a rancher, already knows it will soon be about acreage, not just to grow switchgrass, but for solar and wind as well.
So a 2012 model year Prius might have 20 miles of engine-off range, use E85 when it needs to, get 60 mpg in the city on E85 (75 on straight gasoline), do zero to 60 mph in less than 8 seconds, surge from 60 to 90 mph in less than 7 seconds and get 60 mpg on the motorway when the cruise control is set at 80 mph. With a PowerBeam and one or two other modifications, it just might deliver the full hybrid promise. Would you want one? Or perhaps something a little stronger, like an XJH?
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