Active Safety the Electronic Stability Program (ESP)
The Smart Roadster and Smart Roadster Coupés come with the driving dynamics control system ESP (electronic stability program) as standard, incorporating selective brake intervention, anti-stall assist and brake assist as well as cornering brake control CBC (stabilisation during partial braking whilst cornering). The anti-lock braking system ABS including electronic braking-force distribution is integrated in ESP.
ESP in operation
ESP ensures that the cars always follow the direction in which the driver steers, even at the stability limit of driving dynamics. In addition to closing the throttle valve and opening the clutch, ESP also offers brake intervention acting on individual wheels. This ensures directional stability and road adhesion when accelerating, braking and coasting. Within physical limits, ESP ensures that during fast cornering the cars neither push over the front axle (under steering) nor push outwards with the rear end (over steering).
What can the ESP do to help?
In the event of over steering ESP specifically brakes the front wheel on the outside of the curve – regardless of whether the driver is braking, rolling or accelerating. The braking torque applied against the rolling direction around the vertical axis of the car prevents the rear end from breaking away. ESP balances under steering by braking the rear wheel on the inside of the curve; this steers the car to the desired course in the curve. The electronics also cause the throttle valve to close so stopping the engine from making power.
The ability of ESP to act on individual wheel brakes creates the basis for a further safety function of the ABS: cornering brake control CBC. In fast cornering there is much less load on the inner front wheel. If the driver steps on the brake in such a situation ESP sense that more braking power can be transferred from the other wheels than from the wheel with a reduced load. The ABS control and pulsating of the pedal in connection with this is therefore not activated unnecessarily.
If the driven wheels (rear) lose traction, the drive torque is reduced and the brake system applies force to the wheel with the most traction slip. In this way ESP realises the function of a differential lock by means of braking torque intervention which enables traction even on extremely slippery terrain, when there is different coefficient of friction on the right and left drive wheels, and on hills. This greatly improves the car’s hill-climbing ability. ESP makes use of a special hydraulic control unit which is regulated electronically monitor and modulate the vehicle dynamics.
Taking back control
For even more driving pleasure in the Smart Roadster and Smart Roadster Coupés and to enable the driver to test the limits of the cars, ESP can be switched off with a push button switch on the instrument panel. This enables the driver to call a certain amount of slip of the rear wheels via the accelerator pedal. However for safety reasons when ESP is switched off only the drive torque regulation and the selective brake intervention during the acceleration phase are deactivated: When braking, the selective brake intervention for stabilising the vehicle remains.
Automated 6 speed gearbox
The Smart Roadster has the same sequential automated transmission as the Smart City Coupés and Smart Cabrio – in a further optimised form. The sporty close-stepped ratios have been adjusted to the increased engine power and vehicle performance. In connection with this it was also possible to further optimise the gear-change sequence of the automatic transmission. A kick-down function greatly improves the driveability. The Smart Roadster is equipped with an automatic function as standard which is always activated once the engine has been started. A normal gearbox and clutch are operation but controlled electronically and the gear selection and clutch operation use electric motors to facilitate controlled operation every time.
Steel safety cell – strong but light
The Smart Roadster Tridion – the unibody frame for the car
The TRIDION safety cell with a weight of just 192 kilogram’s greatly contributes to this. The rigid cell is also the basis for the precise handling and the excellent suspension characteristics, crash safety also benefits greatly from the high structural stability.
Panels of varying thickness make it possible to have thick sheet metal in areas under strain and thinner sheet metal in areas under less strain. In addition to this high-strength and extremely high-strength steel alloy is used in areas where maximum force is applied or acts.
Plastic body panels also form the outer skin of the Smart Roadster and Smart Roadster Coupés. This material, which is much lighter than steel, is used in the front and rear ends, wings and doors. The powder-coated TRIDION safety cell remains visible in the area of the door sill, B-pillars and roll bar as a visual representation of the two-colours and safety concept typical of the Smart brand The body panels are simple and therefore inexpensive to replace.
Sophisticated safety systems
The safety concept of the Smart Roadster and Smart Roadster Coupés is of a high standard comparable to that of the Smart City Coupés and Smart Cabrio.
The passive safety concept of the two new cars is also based on the combination of the TRIDION safety cell and a specially defined restraint system consisting of two full-size airbags, belt tensioners and belt-force limiters. This allows controlled forward movement of the passengers wearing seat belts and is supplemented by a deformable steering column which effectively prevents intrusion of the steering wheel, addition to this passive safety is guaranteed by extremely sturdy seats. Their sheet-metal shell construction combined with the firm cushioning have a considerable protection potential, also in view of high energy. They reliably prevent the body from submarining under the lap belt in the event of frontal collisions and have also proved to be an effective protective shield in rear collisions. Side airbags can be fitted in the backrests as an option.
Read more about roadster options when we post next month!