Power and torque

Posted on January 29th, 2008 in Hybrid Power,Opinion,Power,Turbocharging by Julian Edgar

torque-curve.gifThe (repeated) articles that we’ve recently run in AutoSpeed on power and torque are vital to understanding how to make your car go harder.

(The series can be found at Power vs Torque Part 1 –  and Power vs Torque Part 2)

And why is this understanding vital? Simply because people who use the terms ‘power’ and ‘torque’ often don’t seem to really understand what the words mean. The vital point to realise is that engine power is worked out by multiplying torque by revs.  And that’s the only way that power is worked out!

So an increase in torque at – say – 2500 rpm will mean a proportional increase in power also occurs at 2500 revs. It’s therefore just plain stupid to say “there wasn’t any change in the power curve but we got an increase in mid-range torque…” as some manufacturers of performance equipment state.

Trailers that drink fuel

Posted on January 22nd, 2008 in Driving Emotion,Economy,Peugeot by Julian Edgar

pug-and-trailer.jpgMost cars that I have owned have had tow-bars – if they’re not on the car when I buy them, I have them fitted.

So the EF Falcon and Lexus LS400 both had towbars. And, as you’d expect with those cars’ mass and power, both towed very well. On one occasion the Lexus towed a camper trailer, and it very often towed my 6×4 steel trailer. The Falcon towed the 6×4 and once a car-carrying trailer (loaded with a large work bench frame).

So when both of those cars had gone to new owners and I bought the Peugeot 405 diesel, I was pleased to see it had a towbar.

I didn’t – and don’t – expect to be towing big trailers; instead, my 6×4 will be the one usually hung on the back. Trips to the local tip, trips to pick up furniture, carrying around recumbent trikes – things like that.

But as a tow-car, the low-powered and light Peugeot is a very different kettle of fish to the Lexus and Falcon. For starters, the lack of ultra-low rpm torque (when the 1.9 litre diesel is yet to come on boost) makes it very hard to climb my very steep driveway with the trailer on the back. In fact, to do this, I need to thoroughly warm the engine and launch with a lunge at the slope. 

Once on boost, the mass of the trailer doesn’t cause much of a problem; performance is clearly down but with decent driving, it’s no drama.

But one aspect of the Peugeot as a tow car amazes me. And what’s that?

The fuel consumption!

The presence of the trailer makes a radical difference to have much diesel the Pug drinks. Even with the trailer empty, consumption is up by 20 – 30 per cent. One reason for this is that the trailer adds about 25 per cent to the mass; another reason is that the trailer is much less hidden in the aerodynamic wake of the smaller car.

Clearly the idea that towing a trailer increases fuel consumption is not something new.

However, as more people drive cars like hybrids (incidentally, no Prius is factory certified for a tow bar) and smaller engine diesels, trailers designed with more than utilitarian cheapness may become attractive. A smaller, light-weight and aero-shaped trailer would, I’m sure, make far less difference to the Peugeot’s towing fuel consumption…

All Those Technological Breakthroughs…

Posted on January 15th, 2008 in Driving Emotion,Opinion,Technologies by Julian Edgar

Every month or so we get emails from a readers suggesting that we take a look at a new engine design that’s been developed by a tiny company or even a single person. The reader sends a URL and the website invariably lavishes praise on the new concept, describing how it develops a greater specific power / better specific fuel consumption / is cheaper to build / etc.

However, I very seldom go ahead with a  story – in fact, the only one I have ever done was this one. But if we’re interested in covering breakthrough automotive technology, why wouldn’t we want to run every such story we can find?

The short and brutal answer is that 99.9 per cent of these ‘breakthroughs’ are failures. To put that ratio another way, we could run 1000 stories and maybe only one of those would prove to be on something that is commercially and successfully built.

I am well aware that innovators and inventers will complain that a lack of media coverage is part of the very reason for that lack of success. And I accept that point. But in an automotive technology magazine, the very first requirement for exposure is that the engine (or whatever ‘breakthrough’ it is) be installed in a car that can be driven. That’s why we covered the Scotch Yoke engine – one of the test beds for the engine was a registered and driveable Subaru Liberty sedan. (In a different way, that’s why we’re also happy to cover home-built electric cars – they can be driven.)

While of course dyno testing of power, torque, emissions and fuel consumption are a vital part of a new engine development, the performance the design achieves in the real world seems fundamental to any assessment.

The other reason that very few stories of this type of appear is that when small companies have real breakthroughs, they tend to keep it very quiet. Instead of having media interviews, they’re dealing in closed boardrooms with large companies, selling intellectual property licensing.  One example is the Kinetic Dynamic Suspension System (KDSS) – originally developed by Australian company Kinetic – fitted to the current Toyota Landcruiser.

On the other hand, major car and component supply companies often release detailed information on forthcoming designs. While some of these breakthroughs never go into production (or their long-term success is less than stellar) the ‘hit’ rate is not 1 in a 1000, but more like 900 in a 1000!

It would be a very brave or stupid person who suggested that major design breakthroughs are the province only of major companies, not individuals working on their own. However, in things automotive, I suggest that apparently groundbreaking new technology will be taken much more seriously if it can be convincingly demonstrated in a vehicle that journalists can drive and test.

Well, that applies for this journalist anyway!

How much (electric) power is needed?

Posted on January 8th, 2008 in Aerodynamics,Economy,electric,Opinion,Power by Julian Edgar

pug-trip.jpgA while ago I attended an electric car show held in Sydney. I made the 2000-odd kilometre trip in my Peugeot 405 diesel, a car that, incidentally, gained high Fives (in litres/100km) for the trip.

At the show I briefly sampled three of the home-converted electric cars – a very interesting experience. And on the long drive home to the Gold Coast, I had plenty of time to reflect on these cars.

The electric cars I drove each retained the original gearbox: the electric motor was bolted up to the ‘box and the ratios could be selected by the driver. Typically, the cars were started off in second gear and then third and fourth and fifth gears were used as appropriate. (I used first gear off the line and felt an immediate gain in starting performance.)

But none of the cars I drove had performance that came close to conventional petrol engine (or even commercial hybrids). Even when the electric motor was rated at a higher power than the original engine, the massive weight of batteries substantially dulled the resulting power/weight ratio.

Putting in a more powerful electric motor (or running two electric motors) would of course help solve that, but at the expense of greater electrical power consumption that in turn would need either more batteries or result in a shorter range (and none of the ranges were very good to start with!). However, all the cars could easily exceed the 110 km/h open-road speed limit.

Clearly, what is needed is an electric motor that has only enough power to do the job – but no more.

Chassis Design

Posted on January 8th, 2008 in Driving Emotion,Materials,Opinion by Julian Edgar

Imagine you were living in the late 1930s (and of course, a very small number of you may well have been!). Then, as now, cars had four wheels, a body, engine, suspension and brakes. But they often had something else as well – a chassis.

Nowadays, nearly all cars use monocoque construction, where the pressed steel body provides the required stiffness. The main exceptions are traditional off-road four-wheel drives and trucks and buses – these vehicles still largely use a separate chassis. A few bespoke cars also use non-monocoque construction; for example, a tubular space frame.

But even in the late 1930s, you could have seen plenty more designs that just a traditional chassis. Have a look at these – all are taken from The Mechanism of the Car, written by Arthur W Judge and published in 1939.

vauxhall.jpgFirstly, we have monocoque (or unitary) construction. This Vauxhall retains a separate bolt-on chassis for the front suspension and engine mounts, an approach common in cars up to the 1970s.


amilcar-1.jpgBut then we have the cast aluminium frame. What?! Yes, a car being sold in 1939 (the Hotchkiss Amilcar) used a frame formed from cast aluminium members bolted together.


Here’s how the cast alloy frame integrated itself into the car.


austro-daimler.jpgThen there was the tubular frame, as used by Austro-Daimler. The very large diameter central tube would have given both high bending strength and also resisted torsion.


And finally, we have a car that’s absolutely intriguing – and one I’d never heard of before. It’s simply listed as the ‘MG Racing Car’ and uses a backbone chassis formed from pressed, welded plate. The car also features double wishbone suspension front and rear – perhaps the first car to ever do so.

I think that these drawings are worth looking at closely (you can click on them to enlarge). In mechanical car design, there’s very little new under the sun…

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