Drive system: More efficiency, more driving fun

Nov 4, 2014
A completely new range of drive systems is available for the new smart family: drive power is supplied by state-of-the-art three-cylinder engines rated at 45 kW/60 hp, 52 kW/71 hp and 66 kW/90 hp, while power transmission is performed by a five-speed manual transmission or the six-speed twinamic dual clutch transmission. The two most powerful engines will be available for the launch, and the basic petrol engine will follow a few months after the market introduction. All in all the new engine/transmission combinations offer more driving fun, greater ride and shifting comfort and higher efficiency.
The naturally aspirated engine generates 52 kW/71 hp from a capacity of 999 cc. Thanks to maximum torque of 91 Nm at 2850 rpm it enables economical driving, particularly in urban traffic. Top of the range is the turbo engine rated at 66 kW/90 hp. The 898 cc engine delivers maximum torque of 135 Nm at 2500 rpm.
All engines share an aluminium construction, overhead camshafts and four-valve cylinder heads. Internal friction in the engine is reduced by optimised pistons with graphite-coated piston shafts, a friction-optimised timing chain and coated bucket tappets. Further features include the low height and installation at an angle of 49 degrees.
Both engines have an infinitely variable oil pump. It only brings as much lubricant to the engine as necessary – just one example of the numerous efficiency-increasing measures.
Thermal management: quicker warming up
Clever heat management ensures that the engines reach the optimum operating temperature more quickly and therefore contributes to lower emissions and less fuel consumption. An electromagnetic valve in the coolant circuit is a key element. As long as the coolant temperature is below 80 degrees Celsius, the valve stays closed and prevents circulation of the coolant in the engine block and the cylinder block. This therefore heats up more quickly. As soon as a suitable temperature is reached for energy-efficient operation, the valve opens so that the coolant can flow. The oil around the cylinders also heats up more quickly.
The automatic start/stop system, a standard feature, enables greater efficiency especially in city traffic. As soon as the driver brakes, shifts to idle position and releases the clutch as the vehicle comes to a standstill, the engine automatically shuts down. The engine spontaneously restarts in a way that is barely perceptible when the driver operates the clutch to shift into first gear. The system helps the driver to save fuel, especially in an urban environment.
The driver can deactivate the start/stop system when required. If certain conditions are not met the system will not shut down the engine, for example if the necessary operating temperature for optimum emission control or the desired interior temperature have yet to be reached.
Turbo engine with lots of clever details
The turbocharger of the more powerful smart engine features an electronically controlled wastegate which enables increased engine dynamics in conjunction with a sustained reduction in fuel consumption. The wastegate reduces the exhaust gas backpressure at high revs.
In addition to the turbocharger, a whole range of other technical measures also contributes to the excellent fuel efficiency and performance. These include variable adjustment of the inlet valve timing.
Another defining trait of the all-aluminium three-cylinder engine is the fully integrated intercooler in the plastic intake module. All features combined lead to a sustained improvement in performance, agility and fuel savings.
The data of the new smart models at market launch at a glance:
 
fortwo52 kW
fortwo66 kW
forfour52 kW
forfour66 kW
Number of cylinders/arrangement
3/R
3/R
3/R
3/R
Engine capacity (cc)
999
898
999
898
Rated output (kW/hp)
52/71
66/90
52/71
66/90
at rpm
6000
5.500
6000
5.500
Rated torque (Nm)
91
135
91
135
at rpm
2850
2500
2850
2500
Combined fuel consumption (l/100 km)
4.1
4.2
4.2
N/A
Combined CO2 emissions (g/km)
93
97
97
N/A
Efficiency class
B
C
B
N/A
Acceleration 0-100 km/h (s)
14.9
10.7
16.9
N/A
Maximum speed (km/h)
151
155
151
165
Figures for vehicles with manual transmission.  N/A: no information available
The transmissions: five-speed manual or six-speed automatic
The five-speed manual transmission offers sporty and precise gear changing. It has an integrated differential, friction-optimised gear sets, a dry weight of just 35 kg and is actuated via cables.
The twinamic dual clutch transmission is constructed as a 3-shaft dual clutch manual transmission and has six forward gears and one reverse gear. Both clutch actuation and gear changing are fully automatic and enable particularly smooth shifting without any interruption in tractive power. The transmission either works fully automatically, or it can be shifted manually with a selector lever in a separate gate or via the shift paddles included in the Sports package.
Thanks to the two sub-transmissions, changing to the next highest or lowest gear is immediate and without loss of tractive power. If required, the electronic controller skips individual gears instead of changing down through each individual gear. It therefore offers the comfort of an automatic transmission combined with the efficiency of a manual transmission.
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