|The new smart fortwo: Body panels in white, tridion safety cell in lava orange (metallic). The new smart forfour: Body in white, tridion safety cell in black. Click to enlarge.|
In a world premiere staged in Berlin, Daimler brand smart unveiled the new versions of its iconic smart fortwo and forfour city cars. The new smart fortwo, developed in partnership with Renault (sharing the third-generation Twingo platform) has undergone improvements in virtually all areas and is markedly more comfortable, while the smart rear engine concept is now being offered for the first time in the four-seater smart forfour as well.
Drive power is supplied by 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 twinamic automatic dual clutch transmission. A new version of the smart fortwo electric drive (earlier post), based on the new model, will follow.
The new smart generation will be launched onto the market in Europe in November; the US will receive the car in 2015. The price in Europe for the smart fortwo will correspond to that of the current smart series (starting as low as about €10,000, or US$13,500), while the smart forfour will cost only around €600 (US$812) more with the same engine.
The smart fortwo has sold well in excess of 1.5 million units since its launch in 1998. Annual sales have remained stable around the 100,000 mark in the final years of the current model lifecycle. In 2013 the smart electric drive car was the market leader in Germany and ranked third in Europe and fifth worldwide in the registration statistics for electric cars. At the beginning of 2014 the smart fortwo won the title of “Microcar of the Year” for the fifth time in succession in China. Today, five years after the market launch, China is the third most successful market for smart, after Germany and Italy.
In the planning phase we were clear that we wanted to retain the rear engine for the new smart, so as to continue to exploit the vehicles’ strengths to the full in the city. On this basis, we then developed the new fortwo and forfour together with our partner, Renault.—Jörg Prigl, head of the product group Compact Cars at Mercedes-Benz
Among the highlights of the new vehicles is that while the engineers retained the length of 2.69 meters, they were able to reduce the turning radius to 6.95 meters (from curb-to-curb) and 7.30 m (from wall-to-wall). The new smart forfour turns almost as compactly as the previous fortwo (wall-to-wall: 8.75 m). Its statistics are 8.65 m (curb-to-curb) and 8.95 m (wall-to-wall).
Further, even with the same length, interior space has been increased by widening the car by 10 cm. Additional highlights include the rear doors opening by almost 90° on the smart forfour and the folding front passenger seat backrest which comes as standard for all variants.
Engines and drive system. Two three-cylinder engines will be available for the new smart models at the market launch: the naturally aspirated engine generates 52 kW/71 hp from a capacity of 999 cc. The engine’s torque from an engine speed as low as 1000 rpm (maximum: 91 N·m (67 lb-ft) at 2850 rpm) enables particularly economical driving in high gears, even in urban traffic.
Top of the range is the turbo engine rated at 66 kW/90 hp. The 898 cc engine mobilizes maximum torque of 135 N·m (100 lb-ft) at 2500 rpm. The totally new turbocharger features an electronically controlled wastegate which enables increased engine dynamics in conjunction with a sustainable reduction in fuel consumption. Another distinguishing feature is the automatic start/stop system.
Apart from the turbocharger, a range of other technical measures also contributes to the engine’s fuel efficiency and performance. These include variable swirl control and variable adjustment of the inlet valves. Another defining trait of the all-aluminium three-cylinder engine is the square bore/stroke ratio.
A few months after the market launch, a basic gasoline engine rated at 45 kW/60 hp will extend the range.
Both transmission variants are also new for smart: customers can choose between a five-speed manual transmission and the twinamic six-speed dual clutch transmission.
Chassis.The new smart has essentially been configured for gently understeering handling characteristics. The different tire sizes at front and rear have thus been retained, whereby the narrower front tire in conjunction with a high outside wheel turn angle contribute to the unprecedentedly small turning circle.
ABS, ASR and ESP are ready to intervene at the critical limits of road-holding. A hill hold function and brake assist are integrated in the brake system.
The engineers have designed a new McPherson suspension with a triple-path head bearing for the front axle. Each wheel is controlled by a wishbone under the wheel center, the McPherson strut and a tie rod. Comfort and guide bearings for the wishbones provide for added comfort, along with the markedly increased overall spring travel. During the compression phase in particular, the new smart runs markedly more smoothly over uneven surfaces than previously.
The new smart models also feature a sophisticated De-Dion rear axle, which has been modified for substantially greater comfort. New elements are the twin-tube shock absorbers and separate barrel-shaped helical springs. Two elastomer shims provide for effective noise decoupling of the helical springs between body and rear axle.
A Sports suspension package is optionally available to those seeking sportier handling from their smart. The springs are firmer here and the vehicle is ten millimeters lower.
As standard, the new smart models come with mechanical rack-and-pinion steering. The Direct-Steer system with variable ratio and electric power assistance provides for considerably enhanced driving enjoyment, even better handling and increased efficiency.
Active safety. Advanced assistance systems which were previously the reserve of higher classes of vehicle further enhance safety and comfort. These include Crosswind Assist (standard), forward collision warning (option) and Lane Keeping Assist (option).
Standard-fit Crosswind Assist carries out specific braking intervention when the vehicle threatens to drift off track. As a result, less countersteering effort is required of the driver. Crosswind Assist is active from 80 km/h (50 mph) when driving straight ahead and in gentle bends. The ESP indicator lights up in the instrument cluster in response to noticeable intervention by Crosswind Assist.
The forward collision warning (option) can prevent rear-end collisions when the driver approaches the end of a traffic jam, for example. The system can also prompt the driver to take action in dangerous traffic situations in the city, thereby helping to avoid accidents. The distance to the vehicle ahead and the closing speed are monitored continuously by mid-range radar.
The driver is warned in two stages: when a vehicle ahead is detected, a warning lamp first of all lights up in the instrument cluster, if the distance is not within the safe range (stage 1). If the closeness to the vehicle ahead becomes critical, giving rise to a danger of collision, a warning tone additionally sounds (stage 2). The driver is thus urged to take action in the form of emergency braking or a specific evasive maneuver to avoid a rear-end collision.
The combined visual and audible warning is initiated in case of moving or stationary vehicles in the speed range from 7 km/h (4 mph) to top speed. Stationary vehicles are detected when the driver is travelling at a speed from 7 to 90 km/h (56 mph).
Vehicles veering off the road or collisions with oncoming traffic are among the most common and most severe types of accident. Lane Keeping Assist (option) helps to avoid such crashes. A video camera scans road markings and detects differences in contrast between the road surface and boundary lines in real time. A control unit processes the data from the camera and the driver's activities. The system is able to recognize whether the driver intends to leave the lane by checking whether an indicator has been activated, for example. If a danger is detected, an audible warning tone is output and a visual warning is displayed in the form of a symbol in the instrument cluster.
Passive safety. The bodyshell of the new model series and the tridion safety cell have undergone further development to adapt them to the more stringent safety requirements in the crash test and to the new smart forfour. A high proportion of ultra-high strength hot-formed steels and maximum-strength multiphase steel is now used. These are used in the sidewall and in particular in the substructure.
In order to assure the structures of a high level of deformation and energy absorption capacity in frontal collisions, the new smart generation has been provided with the largest possible crumple zones and attention has been devoted to ensuring an effective flow of the accruing forces. In a severe frontal collision, the rear structure also helps to absorb the energy acting on the vehicle, for example. The forces are channelled into the extremely robust passenger cell, which is designed as a safety cage. Particularly extensive work went into adapting the new front axle carrier to crash requirements.
The highly robust tridion passenger cell is able to prevent major deformation even in very severe collisions, thus helping to protect the occupants’ space. The fuel tank is located safely outside the deformation zone in front of the rear axle.
The Mercedes-Benz safety engineers were involved in the cooperation project with Renault throughout all phases of the development process and were able to contribute their amassed know-how. In the area of computer simulation, for example, where it was possible to calculate in detail the behavior of individual weld spots or the newly introduced bonding methods, such as MIG soldering.
The number of assessed collision cases far exceeded the mandatory scope, both in the simulations and in real crash testing. The new smart fortwo underwent the same development program as the new Mercedes-Benz C-Class, for example. As it has been evolved for the global market, the number of crash tests was four times what is required for vehicles designed primarily for the European market.
The focus in car-to-car tests was on compatibility with substantially larger and heavier vehicles. The new smart fortwo was required to demonstrate its capabilities in frontal collisions with the S- and C-Class (photo above).
The way in which all components (body, seat belts, airbags and sensor system) interact is crucial to effective protection. The forward displacement space for the occupants is to be sufficient to provide them with an adequate deceleration distance to minimise accident-induced physical stress in the event of a collision.
Driver and front passenger are each provided with a 3-point seat belt with belt force limiter and pyrotechnic belt tensioner as standard. The rear seats in the smart forfour each have a three-point seat belt with pyrotechnic belt tensioner and belt force limiter—features which other manufacturers do not necessarily provide as standard, even in higher classes of vehicle. A rear belt status indicator in the overhead control panel comes as standard.
The ISOFIX fastening system with TopTether attachment features as standard on the passenger seat of the fortwo and the rear seats of the forfour, providing a simple means of attaching child seats rigidly to the vehicle. The child seats themselves come from the Mercedes-Benz range.
The headrests for driver and front passenger are integrated in the backrests. They reduce the risk of injuries to the cervical vertebrae in a rear-end collision.
The smart models come with driver airbag, driver kneebag and front passenger airbag as standard. The kneebag has a positive influence on occupant kinematics in a frontal collision, thus offering the driver additional protection in many frontal collision scenarios. The principle of the telescoping steering column has been adopted 1:1 from the Mercedes-Benz range.
The standard-fit sidebags (head-thorax bags) are accommodated in the driver and front passenger seat backrests and provide side cover for the respective occupants’ head and chest. The sidebags incorporate two chambers to enable due adaptation to different sizes of head / upper body. When inflated in side-on collisions they are able to lower the degree of stress to which the chest area is exposed and reduce the risk of the head colliding directly with the side window or other objects likely to cause injuries, such as a pylon, a tree or parts of a colliding vehicle. The occupants’ pelvic areas are additionally protected by deformation elements installed at appropriate points in the door panels.