New Technology for Avoiding Low-Speed Collisions
Continuing Volvo's quest as a pioneer and leader in vehicle safety systems, the 2010 XC60 introduces a new world's first. City Safety is a driver support system aimed at preventing or mitigating collisions occurring at speeds of 19mph or less. City Safety in combination with the recently introduced Collision Warning with Auto Brake means that Volvo now offers functions for auto-braking at all speeds.
Surveys indicate that 75 percent of all reported collisions take place at speeds of up to 19 mph. In half of these cases the driver has not braked at all before the collision, mainly due to distraction. In these cases, City Safety could make a crucial difference. City Safety automatically applies the brakes if the driver is about to drive into the vehicle in front. A collision may be entirely avoided, or if this is not possible, the damage to cars and people can be reduced.
"City Safety is yet another example of Volvo's ambition to tackle real-life traffic situations when developing solutions aimed at preventing accidents," says Jonas Ekmark, manager of Preventive Safety at Volvo Car Corporation's Safety Center. "We're proud to offer City Safety as a standard feature in the new Volvo XC60."
City Safety benefits everyone
A Volvo equipped with City Safety offers a range of benefits both to its occupants and to the occupants of the vehicle in front:
Active at speeds of up to 19 mph
City Safety is active at speeds of up to 19 mph. If the vehicle in front brakes suddenly and City Safety determines that a collision is likely, the brakes are pre-charged. If the driver fails to respond, the car applies the brakes automatically. If the relative speed difference between the two vehicles is less than 9 mph then City Safety may help the driver to entirely avoid the collision. Between 9 and 19 mph the focus is on reducing speed as much as possible prior to the impact.
Laser sensor monitors traffic in front
City Safety keeps an eye on traffic in front with the help of a laser sensor that is integrated into the top of the windshield at the height of the rearview mirror. It can detect vehicles and other objects up to 18 feet in front of the XC60's bumper.
City Safety is developed to react to vehicles in front that are either at a standstill or are moving in the same direction as the XC60.
Based on the gap to the vehicle in front and the car's own speed, the system makes 50 calculations a second to determine what braking force is needed to avoid a collision. If the calculated braking force exceeds a certain level without the driver responding, the system determines that the risk of a collision is imminent.
City Safety helps either avoid or reduce the severity of the collision by automatically applying the brakes and reducing the throttle opening. At the same time, the brake lights are activated to warn other traffic.
City Safety works equally well during the day and night. However, the laser sensor has the same limitations as all optical technologies in that the detection capacity can be limited by fog, snow or heavy rain. It is therefore necessary to keep the windshield free of dirt, ice or snow. The sensor area is covered by the windshield wipers, yet the driver should pay extra attention in keeping the sensor area clean at all times.
"It is important to understand that City Safety does not relieve the driver of the responsibility from maintaining a safe distance to avoid a collision," says Ekmark. "The automatic braking function does not react until it considers that a collision is imminent. City Safety will help to limit or reduce the consequences or completely avoid an imminent collision."
New function controls the restraint system in a collision
In order to further boost safety and help reduce the risk of injuries, the laser sensor interacts with other on-board technology, controlling the airbags and adaptive seat belt load limiters to suit the severity of the collision. This technology, known as Pre-Prepared Restraints (PRS), is also being introduced with the new Volvo XC60. PRS forges a unique link between preventive systems (sensors) and protective safety systems. In case of a collision, the Restraint Control Module controls the deployment of the protective restraint systems. With the additional information supplied by the laser sensor the Restraint Control Module controls the adaptive seat belt load limiter depending on the severity of the collision. The potential of the adaptive seat belt load limiter to reduce injuries can therefore be further utilized.
PRS is active at all speeds, unlike City Safety which only operates up to 19 mph. PRS is activated by means of a pyrotechnical device in the adaptive seat belt load limiter. This means that City Safety can be activated without PRS being activated, if the collision severity is lower than the level required for PRS activation.
Additional new and enhanced safety functions
Volvo is extending its safety offerings with two new functions that stabilize the car in critical situations.
Enhanced DSTC function
Volvo's DSTC (Dynamic Stability and Traction Control) function has been further developed in the new Volvo XC60 in order to provide even more stable driving. DSTC registers deviations between the driver's intended direction and the car's actual direction. The enhanced DSTC function registers the car's roll rate as well, giving the opportunity to detect slowly built up skids. This may occur if the driver suddenly releases the accelerator pedal while steering, like when leaving a highway slightly too late. By measuring the roll rate, the DSTC function is able to start the regulation at an earlier stage - and with greater precision. This is highly noticeable in dynamic driving where the car is exposed to high lateral forces.
New Trailer Stability Assist (TSA) offers improved control
The purpose of the new Trailer Stability Assist (TSA) function is to dampen the oscillation tendency that sometimes occurs when towing a trailer. In certain conditions, there is a risk that the car and trailer might start "snaking," making it difficult for the driver to regain control. TSA operates together with enhanced DSTC to stabilize the situation by braking one or more wheels while at the same time restricting the engine's torque. TSA is available as a separate active safety function along with a trailer hitch.
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