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Nov 9, 2006
Petrol engines: more power and torque
State-of-the-art compact three-cylinder engines are installed at the rear of new smart fortwo. For the petrol engines, the engine capacity has been increased from 0.7 to 1.0 litres. There are two naturally aspirated engine versions to choose from, delivering 45 or 52 kW (61 / 71 bhp) respectively, and a turbo engine rated at 62 kW (84 bhp). In addition to the increase in power, the maximum speed has also been increased – to 145 km/h.
The all-aluminium engine was developed in cooperation with Mitsubishi, and is produced in Japan. It has been further developed for use in the new smart fortwo.
The engine is mounted transversally in front of the rear axle, and is slanted at an angle of 45 degrees towards the rear. The cylinder barrels take the form of grey cast iron liners. Gas exchange is controlled by four valves per combustion chamber. The valves are controlled by separate intake and exhaust camshafts, via bucket tappets.
To allow high torque to be developed even at low engine speeds, the intake camshafts can be twisted electrohydraulically against the exhaust camshafts (variable valve control). The camshafts are driven via a maintenance-free timing chain.
Because the masses being moved are low, there is no need for a balancer shaft – which would reduce the output of the engine. However, in the turbo version there is a torsional vibration damper on the crankshaft.
The maximum charge pressure is 0.5 bar, with control taking place via a wastegate valve in the turbocharger. To ensure a long service life, the charger is fitted with a water cooling system, while the charge air cooler is based on air/air technology and is located behind the transmission.
Both petrol engines comply with exhaust gas standard Euro 4. The naturally aspirated engine's compression ratio is 11.5:1, while in the turbo engine it is 10:1. They offer torques of 92 and 120 Nm. The three-cylinder engine is one of the most economical engines in its segment. The naturally aspirated engine as well as the turbo version consume less than five litres over 100 km.
Diesel: at present there is no more economical way to drive
The highly-focused reengineering of the engine has resulted in a performance increase of ten percent, and the engine now has an output of 33 kW (45 bhp). In terms of emission levels, it complies with Euro 4.
The new smart fortwo cdi achieves the coveted “three-litre car” status. It emits just 90 grams of carbon dioxide per kilometre, meaning it consumes less than 3.5 litres of fuel per 100 km. At present there is no more economical car than the smart fortwo cdi.
Its diesel particle filter (open system), which stops more than 40 percent of soot emissions, is unique in its segment. As of 2008, the smart fortwo cdi will be available with a closed system.
The new automated manual transmission: change gears without the need for a clutch.
In future, smart fortwo drivers will benefit from a newly-developed transmission that they will get used to straight away. Instead of the previous six gears, the transmission produced by the specialist Getrag now has five gears, and offers considerable advantages in terms of comfort, fuel consumption and agility.
In the new smart fortwo there is once again no clutch pedal, as this task is performed by an electric motor. If the shift lever on the centre console is briefly tapped forwards, the transmission will switch up a gear, and if it is drawn back, down a gear. Steering wheel gearshift allowing the gears can be changed by means of paddles on the steering wheel is available as an option (standard for pulse).
To the right of the manual level, marked with a plus and minus sign, is the neutral position, N. Reverse gear is engaged by pulling the shift lever backwards from this position.
The smart fortwo passion comes with the automated gear programme (softouch) as standard (optional for pure and pulse). It can be recognised by a small button on the shift lever.
When this is pressed down, the transmission switches over from manual gear shifting (softip) to the automatic gear programme. It's the ideal solution for use in stop-and-go traffic. As soon as the driver moves the shift lever manually, the system returns to manual gear-changing mode.
The developers have also greatly improved the shift delays. Shift delays have been reduced by more than half compared to the previous model. This is particularly beneficial when the driver wants to shift down two gears at once. This, coupled with the considerably increased torque, makes for even greater ride comfort.
To improve ride comfort even more, the transmission has a kickdown function. This allows the driver to use the accelerator pedal to shift down two gears at once, in both manual and automatic mode. Incorrect gear changing and overrevving are impossible, because the electronics will only accept reasonable gear changes.
Longer wheelbase, more agility, more comfort
The developers devoted a great deal of attention to the suspension. Their aim was to make the smart substantially more agile, yet at the same time more comfortable. Quite the technical balancing act.
Their success in this area is reflected not least in the geometry of the new smart. The wheelbase has increased by 55, the front track widths by 11, and the rear track widths by 31 millimetres. This improves the driving dynamics and reduces the likelihood of pitching and rolling. The very perceptible result is that the new smart is more agile, sportier – and at the same time more comfortable.
At the front, a classic McPherson construction has been used. The damper strut is directly hinged to the wishbone, to ensure far better responsiveness. The diameter of the stabiliser is 18.5 millimetres, and it very effectively prevents the vehicle body from rolling in bends. At the factory, tyres of size 155/60 R 15 are fitted to 4.5 inch rims with a wheel offset of 23.5 millimetres. The pulse equipment variant comes with tyres of size 175/55 R 15 (front) and 195/50 R 15 (rear).
The tried-and-tested DeDion construction has been kept. The position of the central mount has been changed (moved higher), which has had a positive effect on the manoeuvrability of the fortwo. The springs are now further out than in the previous model, thereby supporting the vehicle body even more effectively against rolling. The size of the tyres on the rear axle in the basic version is 175/55 R 15 on 5.5 inch rims with a wheel offset of 22 millimetres.
The smart fortwo has rack-and-pinion steering. The transmission ratio is 22:1. Thus the steering is transmitted almost ten percent more directly than that of its predecessor. The turning circle is just 8.75 metres – a figure unmatched by any other small car. This makes manoeuvring extremely easy. It allows turning in places where any other car would have to shunt to and fro. And it's just 3.5 turns of the wheel from stop to stop.
Electric power steering is available for the smart at an extra charge. Its transmission ratio is just 21:1. It operates on a linear basis and gives the fortwo astonishingly agile handling. The electric boost power varies according to vehicle speed, steering angle and the amount of force applied to the steering wheel. The servo effect decreases noticeably as the vehicle's speed goes up. The servo power really comes into its own during parking and manoeuvring around town.
Wheels and tyres
The basic tyres for the smart fortwo measure 155/60 R 15 at the front and 175/55 R 15 at the rear. In the case of the pure they are fitted to steel rims, while for the passion they are mounted on aluminium rims. The pulse is the sporty exception to the rule. It zips along on alloy wheels with tyres measuring 175/55 R 15 at the front and 195/50 R 15 at the rear.
Because the electronically limited maximum speed has been increased, the smart fortwo's brakes have grown as well. Disc brakes are fitted at the front, while drum brakes are fitted at the rear. The electronic stability programme esp with integrated abs and electronic brake-force distribution are included in the standard spec, as is a hydraulic brake booster.
The fortwo is the only car in its class to come with brake assist. When it detects abrupt emergency braking, brake assist automatically provides full brake pressure in order to ensure optimum deceleration. It offers a helping hand in those situations where the driver has pressed the brake pedal quickly, but not firmly enough.
Thanks to extensive changes to its suspension, and its new geometry (wheelbase, track widths, pivot points), handling of the smart has been significantly improved. It is considerably more agile and responsive than its predecessor. However, despite the car's more sporty design, no compromises are made on comfort. And longer journeys present no problem at all for the new smart fortwo.