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Automatic Braking Systems Designed to Cut Car Crashes (July 3, 2003)

the Inspire
The Inspire is fitted with the automatic braking system. (Jiji)
On May 20 Honda Motor Co. unveiled an automatic braking system that monitors objects in front of the car using radar, warns the driver when it detects the risk of a crash, and automatically applies the brakes if it judges that the car may have trouble avoiding an object. The Collision Mitigation Brake System (CMS), a world first, also automatically tightens seatbelts just before a collision. Honda has fitted it to its new top-of-the-range sedan, the Inspire, which went on sale in June. The Ministry of Land, Infrastructure, and Transport has taken the lead in encouraging domestic carmakers to develop advanced safety vehicles (ASVs), and some of these are now approaching the stage where they are ready for practical use. Automakers are looking to develop and commercialize a wide range of safety systems to reduce road risks.

Alarm, Seatbelt, Brake
Honda has already made great strides in the fields of active safety, which is mainly concerned with preventing collisions, and passive safety, which aims to reduce the injuries people suffer when a collision occurs. As its next step in expanding the frontiers of car safety, the company has been striving to develop pre-crash safety technology, which is aimed at predicting collisions and reducing the damage they cause. The CMS is the first product of these efforts.

The CMS consists of several sensors including milliwave radar that monitors a range 100 meters in front of and 16 degrees to either side of the car, a forced braking device, and a device called an E-Pretensioner that tightens the seatbelt using a motor when there is a risk of a crash. The system's basic aim is to encourage the driver to take prompt evasive action in the event of danger, and there are several warning stages before it actually applies the brakes. After a risk has been detected, first an alarm sounds, and then the system reduces the speed of the vehicle and tightens the seatbelts, allowing the driver to "feel" the danger and do something about it. The priority is on getting the driver to take control and avert a collision. Only if the driver fails to notice and take evasive action at the warning stages does the system resort to forcibly applying the brakes.

The CMS works like this. First, the radar measures the distance between the car and other vehicles up to 100 meters ahead and any differences in speed, and an onboard computer judges the risk of a collision based on this information and on data about the course of the car. If the system judges that there is a risk of a crash, such as when the car gets too close to the vehicle in front, it alerts the driver by sounding an alarm and lighting up a warning on the dashboard. This is the first warning stage, aimed at alerting the driver to the danger and encouraging him or her to slow down as needed.

If the car gets even closer to the vehicle in front, the CMS applies the automatic brake lightly, and the E-Pretensioner gently tugs the seatbelt two or three times. This is the second warning stage, aimed at making the driver "feel" the danger. If the driver is asleep at the wheel or is not looking at the road, suddenly notices the danger, and slams on the brakes, the computer recognizes this as an emergency maneuver and switches on a braking assistance function to increase the effectiveness of the brakes.

If the car continues to get closer to the other vehicle and the computer decides that it will be hard to avoid a collision, it tightens the seatbelt more firmly - taking up all of the slack so that the belt presses against the driver's body - and applies the brakes forcibly and hard, enhancing the safety of those in the car (collision damage mitigation). In cases where the difference in speed between the car and the object it is about to hit is 40 kilometers per hour, the system is able to cut this to 20 km/h, greatly reducing the impact of the collision.

Pre-Collision Safety Technology
The auto industry is currently focused not only on measures to minimize the damage caused by collisions but also on steps to improve safety in the moments before a collision occurs. Like Honda, Toyota Motor Corp. has implemented pre-collision safety measures in its Harrier sports utility vehicle. But whereas Honda's system uses computer-imposed braking - albeit as a last resort - to reduce crash speed, Toyota's system is designed to improve the effectiveness of the driver's own emergency braking.

Meanwhile, both Honda and Toyota have almost completed experimental work on automatic braking systems that detect an obstacle and bring the car to a complete halt just before impact. The technology has reached the level where the systems can even detect the speed of a vehicle in front, compare it with the speed of the user's car, and stop the car to avoid a crash.

Before such systems are fitted to commercial vehicles, however, it will be necessary to educate road users as to how the systems will alert drivers of other vehicles - especially those following behind - that the brakes have been applied. There may also be fears that overreliance on systems like this could lead drivers to be less cautious. This, in fact, is why Toyota limited the system it has fitted to its Harriers to assisting the driver's own braking and why Honda capped the speed reduction achieved by its system at 20 km/h.

While greater speed reductions would further moderate the damage from any crash, they would also increase the risks to other vehicles, especially those following behind. On the other hand, a smaller speed reduction means less damage alleviation. Although the industry needs to reach a consensus on such issues as the ideal size of the speed reduction and alerting other drivers of imminent braking, there is no doubt that these new systems hold out the promise of safer driving and fewer road casualties.

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Honda Motor Co.
Toyota Motor Corp.

Copyright (c) 2004 Web Japan. Edited by Japan Echo Inc. based on domestic Japanese news sources. Articles presented here are offered for reference purposes and do not necessarily represent the policy or views of the Japanese Government.

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