Toyota Develops "Pre-Crash Safety" System 
IVsource.net
16 August 2002

Toyota Motor Corporation announced recently that it has developed "Pre-crash Safety," an innovative system that reduces collision injury by foreseeing unavoidable collisions to preemptively activate safety devices.  Toyota plans to install this system in new vehicle models that will be introduced next year.  IVsource describes the system components and provides a perspective on the implications of Toyota’s move.

Toyota Motor Corporation announced recently that it has developed "Pre-crash Safety," an innovative system that reduces collision injury by foreseeing unavoidable collisions to preemptively activate safety devices. Toyota plans to install this system in new vehicle models that will be introduced next year.

Pre-crash safety consists of three elements.  The Pre-crash Sensor uses millimeter-wave radar to sense vehicles and obstacles on the road ahead, and an Electronic Control Unit (ECU) to determine whether or not a collision is imminent based on the position, speed and traveling course of the object.  The Pre-crash Seatbelt increases passenger-restraint performance by retracting the seat belt in advance, immediately after an unavoidable collision is identified.  The Pre-crash Brake Assist reduces collision speed by providing increased braking force early on and in accordance with brake pedal operation by the driver.

Toyota believes that the key to lessening collision injury is to foresee collisions as soon as possible and to preemptively activate safety devices to increase their effectiveness.  Traditional safety devices are designed to activate only after a collision occurs.  Activation of certain safety devices in advance can provide a margin of safety improvement, but this requires that collisions be anticipated.  Toyota is betting that the newly developed Pre-crash Sensor will make it possible to foresee collisions and activate safety devices well ahead of impact to improve overall safety.

Configuration of the Pre-crash Safety System

Pre-crash Sensor - The Pre-crash Sensor offers enhanced object-position recognition using (1) millimeter-wave radar, which possesses excellent object-recognition performance even in inclement weather such as rain or snow, and (2) an electronic scanning method.  Furthermore, a compact design ensures that the Pre-crash Sensor can be installed in vehicles easily.

Additionally, newly developed ECU software determines whether or not a collision is imminent based on the predicted trajectory of the host vehicle and other vehicles.  The the expected course of the host vehicle is estimated from driver operational inputs; the system also aims to factor in the position, speed, and expected travel path of not only a preceding vehicle but also an oncoming vehicle and of other obstacles.

Pre-crash Seatbelt - As opposed to a seatbelt equipped with a conventional pre-tensioner, which retracts the seatbelt immediately following a collision, the Pre-crash Seatbelt reduces collision injury by eliminating seatbelt slack before the collision, thus restraining the driver/passenger at an earlier stage.

Pre-crash Brake Assist - Conventional Brake Assist generates a greater braking force after judging that emergency braking has occurred (when the brake pedal has been depressed rapidly).  In contrast, once the Pre-crash Sensor determines that a collision is unavoidable, Pre-crash Brake Assist immediately activates as soon as the driver steps on the brake pedal, and in accordance with the degree to which the pedal is depressed.  This increases braking force well in advance of a collision, thus reducing the collision speed.   (Pre-crash brake assist systems from other manufacturers also detect the rapid release of the driver’s foot from the accelerator pedal as an indication that an extreme situation has developed.)

IVsource Analysis

Generally, the introduction of Pre-Crash Sensing using radar can be looked at as a “testbed” for radar sensing in general.  Any false alarms don’t result in an improper system action because a collision doesn’t occur, and any missed positives only reduce overall crash protection to today’s levels, i.e. no degradation.  At the same time, Toyota will be able to assess the robustness of forward obstacle detection as part of a path towards introducing more sophisticated systems such as Forward Collision Warning.  This announcement is also a bit of a  surprise in the sense that Toyota’s forward sensing capability for Adaptive Cruise Control  in the US market is based on laser radar – so the millimeter-wave radio-frequency radar described above takes the company into a new sensor modality for production systems.

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