Some years after the founder’s death, the Bugatti brand was all-but-dead in Milan. It was however, revived, and car production resumed — in France. The parent company is German: Volkswagen. The car is therefore thoroughly European in nature and culture.
This car is such an interesting mixture of form and function that the design bears a closer look… which is what we are about to attempt here (using a lot of guesswork). Hopefully this will provide some insight into the design process and explain why objects look the way they do, and how each design decision leads to another, and affects all others.
The power output having been been the starting point, the next thing is to calculate the amount of petrol this engine would demand at maximum conditions — then how much air would be needed for the combustion mix… could such a powerful engine be feasible? That was what faced the Bugatti development team headed by Dr. Franz-Joseph Paefgen and Dr. Wolfgang Schreiber.
The textbooks state that:
1 horsepower equates with 746 W
1 W is 1 J/s, and
1 litre of petrol contains about 34 736 842 J of energy
The goal is for over a thousand horsepower, so we’re talking about a 746 000 W engine — and this has to be able to burn:
(746 000 J/s)/(3 473 642 J/litre)
= 0.021 475 litres/s
= 1.288 545 458 litres/min
But as car engines are only about one quarter efficient, we’ll now just multiply everything by four…
= 0.085 900 litres/s
= 5.154 litres/min
Over five litres a minute is a lot of petrol! But what then about the amount of air needed?
The textbooks state:
(a) burning 1 kg of petrol would require about 14.7 kg of air
(b) air density is 1.222 kg/m3.
(c) 1 litre of petrol weighs 0.747 368 421 kg.
So burning 1 kg of petrol would require:
(14.7 kg)/(1.222 kg/m3)
= 12.029 459 m3 (air)
= 12 029.459 litres (air)
As 1 litre of petrol has a mass of 0.747 368 421 kg, then
1 kg of petrol has a volume of 1.338 litres.
So 1.338 litres (petrol), requires 12 029.459 litres (air), which is the same as stating that 1 litre (petrol) requires 8 990 litres (air) for combustion, so now we have found that:
= 0.859 00.litres/s (petrol) needs 0.772 m3/s (air)
= 5.154 litres/min (petrol) needs 46 335 litres/min (air)
A V-8 Engine inhales 4 cylinders’ worth of air per rev, at, say, 6 000 rev/min, that’s 24 000 cylinders’ full per minute. If it requires 46 335 litres/min (air), then
[46 335 litres/min (air)]/(24 000 cylinders’ full/min)
=1.930 litres/cylinders’ full
…more or less 2 litres per cylinders’ full, and for a V-8, or eight cylinder engine, that means
(2 litres/cylinder full).(8 cylinders)
Therefore to do the job we therefore would need a 16 litre V-8 engine.
However, this engine would be big, and it would be unlikely for the large pistons to handle more than say 2 000 rev/min — that’s 8 000 cylinders’ full per minute. So Bugatti decided to double the number of pistons and cylinders! Two V-8s gives a 16 cylinder engine… which obviously means each cylinder can be reduced to one litre volume (capacity).
- We therefore now have an 8 litre, double V-8 engine!
Now, how to couple this? Well, instead of putting two V-8s in-line with each other and connecting each output shaft together, or even putting two in-line 8 cylinder engines beside one another, Bugatti merged two V-8 engines onto one another, and then let both of them share the same crankshaft.
This configuration creates a W-16 engine; the two V’s create a W.
Finally, to make this W-16 more powerful without making the engine bigger is to stuff more air into the cylinders on each intake stroke. Turbochargers do that.
A turbo pressurises the air coming into the cylinder so the cylinder can hold more air.
- This engine has four valves per cylinder, for a total of 64 valves.
The car uses four separate turbochargers (superchargers) arranged around the engine for a maximum turbo boost of 124 kPa that doubles the output power.
All of which makes the W16 as small as possible, measuring just 710 mm long, 889 mm wide and 730 mm high.
However, this engine needs a lot of air, and this affects the design of the car from this point on.
Air is required for combustion (after the turbo pressurisation), but also for cooling (the massive radiator and brakes mainly) and keeping the car stable on the road, especially on bends, while reducing drag.
Putting this W-16 engine behind the driver, allows roof-mounted snorkel-like devices (one on either side of the W-16 engine), the rear-deck vents and side-mounted scoops bring air to the engine and brakes.
Like an F-1 car, the underside is streamlined and venturi-shaped to increase downforce. There is also a wing in the back that extends automatically at high speed to increase downforce and keep the car glued to the road.
The conversion of such an extremely powerful engine for road use was another challenge. Dr.Schreiber, in the official press release stated that:
‘For 1000 horsepower propulsion power, the system demands approximately 2000 horsepower to be additionally generated as heat energy during combustion.
‘Half in each case is dissipated in the exhaust gas and cooling water‘.
His team’s answer was to design two water circuits. One of 40 litres and a low-temperature system of 15 litres. The 40 litre system has three coolers in the front section of the car to keep the engine at operating temperature.
Cooled air passes through two ‘air manifolds’ into the combustion chamber, and leaves as exhaust gas at about 1 000C. The exhaust gas expands as it passes through the turbines of the exhaust gas turbochargers and this cools it down by up to about 150C, before being cleaned in the catalyzer and exhausted away.
The car is 2 m wide, 4.47 m long but only 1.22 m high, so it is extremely wide for its height. The reduced height is due in no small part to the oil system:
Most production cars have a wet sump oil system where the engine oil is stored beneath the crankshaft in an oil pan that is large and deep enough to hold 4/6 litres that is sucked up a tube and pumped round the engine. However, when turning, braking and accelerating, oil tends to slosh about and get on the crankshaft — which cuts power.
Whereas, in a dry sump system, extra oil is stored in a tank outside the engine rather than in the oil pan. As a result the oil capacity can be almost anything.
There are at least two oil pumps in a dry sump system — The first pumps oil from the sump to the tank the second pumps from the tank to the engine this way, the least possible amount of oil remains in the engine.
As the oil pan is vastly reduced the main mass of the engine can be placed lower in the vehicle. This helps lower the centre of gravity and can also help aerodynamics by lowering the hoodline.
The disadvantage of the dry sump system is the increased weight, complexity and cost from the extra pump as well as the tank.
The Bugatti Ion Current Sensing (BIS) does not merely measure rough running to detect cylinder misfiring, the ion current flowing at each spark plug at ignition is monitored by a separate evaluation sensor system.
If knocking combustion or a misfire is detected, the associated control unit immediately initiates countermeasures, such as retarding of the ignition timing, shutting down the cylinder — or reduction of the charge pressure.
The power generated in the engine is transmitted to the flange-mounted direct manual gearbox, The transmission is unique, in particular because it has to harness about twice as much torque as any previous sports-car transmission. It has seven forward and one reverse paddle-driven gears with a dual clutch system, computer-controlled sequential shifting where the computer controls the clutch disks as well as the actual shifting. The computer is able to shift gears in 0.2 s.
The electronically controlled, continuously variable, cam timing ensures optimal performance at different engine revs.
If a car had drive wheels locked together and forced to spin at the same speed, then to be able to turn the vehicle at all, one tire would have to slip, and with modern tires and concrete roads, this would transmit a great force from one wheel to another, putting a heavy strain on the axle components.
So drive wheels, when turning, need to compensate and rotate at different speeds. This requires a device called a differential to split the engine torque (rotational force) two ways, allowing each output to spin at a different speeds.
There are three kinds of vehicle: (a) Basic drive, (b) Part time Four Wheel Drive, and (c) All Wheel Drive or Full Time Four Wheel Drive.
It would be almost impossible for all of the torque available from the W-16 engine to flow out to just two wheels without constant wheel-spin so basic drive is simply out of the question.
Part time Four Wheel Drive systems have no differential between the front and rear wheels; instead, they are locked together so that the front and rear wheels have to turn at the same average speed. These vehicles are hard to turn on concrete while the Part time Four Wheel Drive system is selected.
All Wheel Drive or Full Time Four Wheel Drive is the only real option, but this has a differential between each set of drive wheels, and one between the front and the back wheels.
The Veyron’s massive drive power is distributed to the front and rear axles by means of a Haldex coupling, an actively-controlled multi-disk, inter-axle lock directly connected to the front axle gearbox. The front axle differential distributes the power to both front wheels. In the rear axle differential the power is distributed to the rear wheels via a bevel gear and a further differential. In addition, an actively-controlled, hydraulically-actuated, multi-disk differential lock is used to prevent, when required, speed differences between the rear wheels — to ensure optimum directional stability when accelerating and when cornering under load.
By applying the engine’s power to all four wheels through a computer-controlled traction-control system, the car is able to harness all of the engine’s power, even at full acceleration.
This leads to problems with the wheels and tyres themselves, so Michelin specially designed them to cope with the massive torque (rotational force) — the tyres measure 245/690 R 520 A front and 365/710 R 540 A rear (where 245 and 365 are the width in millimetres). The rims are 520 mm and 540 mm in diameter. These tyres, in other words, are massive — the rears are the widest ever produced for a passenger car.
They use the Michelin PAX system. Tyre pressure is monitored automatically, and they can run flat for approximately 125 miles (201 km) at 50 mph (80 kph).
Despite the PAX tyre system’s run-flat ability eliminating the need for a spare tyre, and even though the body is sculpted in carbon fibre, the car weighs about 1 950 kg (nearly 2 tonnes) due to the size of the engine, transmission, the four-wheel-drive system, the four drive shafts, and the opulence of the passenger compartment, where, apart from the instruments and a few metal trim pieces, the interior is swathed almost completely in leather — the dash, seats, floor and sides. There is every possible electronic gadget and creature comfort for the driver and single passenger. The latest motorsport material technology has been used to combine strength with low-weight — the piston rods are of titanium, the cylinders have plasma-coated running faces and high-strength steel was used for the shafts and gears in the aluminium crankcase.
To create a faster car than this means adding even more weight, and delivering even more power to the wheels. The added weight has diminishing returns in the power-to-weight domain. Additional power means more wheel-spin…
- Bugatti managed what many thought was impossible; a viable, feasible, possible, production passenger car of over a thousand horsepower.
Thus, back in 2000 this EB Veyron 16.4 Bugatti was presented as an experimental concept car at the Detroit, Genève and Paris motor shows.