Electronic Design

Let Your Car Park Itself

How often have you wondered, "Can my car fit into that parking space?" The answer usually depends upon your ability to estimate the size of the prospective space in relation to the length of the vehicle—as well as your skill at parallel parking. But now, Lexus owners have another option. They can push a button on the navigation screen and let the car park itself.

The Lexus LS 460 L's Intuitive Parking Assist/ Advanced Parking Guidance System (APGS) option package not only represents a milestone in design but also in the evolution of automated cars. Developed jointly by Lexus' parent Toyota Motor Corp. and Aisin Seiki Co. Ltd., the APGS combines ultrasonic sensors developed by Denso Corporation with Aisin's camera-based image recognition technology (see the figure).

Toyota first launched the Intelligent Parking Assist system in 2003 on Prius hybrid models in Japan. That system relied on video images from a rear-mounted camera. Two years later, according to Aisin, the system was enhanced to recognize parking space lines based on color contrast. The current system, targeting the North American market, adds ultrasonic sensors—six in the front and four in the rear—to detect the position of parked vehicles.

Drivers who want to parallel park position the vehicle parallel to and ahead of the desired space. Then, they put the car in reverse to activate the backup camera and select the parallel park icon on the navigation screen. The system measures the physical dimensions of the empty parking space and locks in on its target. The space must be at least six feet longer than the vehicle for the assisted parking feature to work. Drivers press "okay," depress the brake pedal, and take their hands off the steering wheel.

Employing the backup camera, ultrasonic sensors, and electric motors in the vehicle's power steering system, the APGS maneuvers the car into the space automatically. Drivers can stop the automatic maneuver by stepping on the brake or gas pedal or by grasping the wheel. According to Lexus, the APGS is equally adept at backing into vacant parking spaces.

WHAT'S NEXT
Automatic parking will likely become a common feature, at least on high-end vehicles. Honda recently announced a park assist system for the Life, a multipurpose vehicle (MPV) marketed in Japan. Honda has no current plans to bring the system to the U.S., though. BMW is testing a system in Europe that is similar to the APGS. And, Paris-based Valeo said its ultrasonic Park4U system will debut next year on the Volkswagen Touran, a compact MPV marketed in Europe.

Valeo says its technology "automatically parks a car in 15 seconds" after scanning both sides of the street for potential parking spots based on the car's length. Valeo engineers designed both the electronic control unit and the 51.2-kHz ultrasonic sensors in the Park4U system, which includes four sensors in the rear bumper, four in the front bumper, and two in the front wings.

The sensors are fifth-generation devices with a 3-mm elongated membrane and a thicker decoupling ring than in earlier versions. They have a 3-dB beam angle with a 70° horizontal/40° vertical view and a 104-dB sound pressure level.

Semiconductor vendors are targeting park assist applications. Freescale Semiconductor's HC9S08D line of microcontrollers is based on a 25-µm 8-bit core, and they operate at up to 20 MHz. Texas Instruments counts parking (rear park assist cameras in particular) as a potential application for its 32-bit TMS470 MCU. Xilinx offers its Spartan-3 and Virtex-4 FX-12 FPGAs for park/reverse assist.

Furthermore, Delphi holds a 2003 patent (#6925370) on an automotive backup aid with parking assist. But this system aids drivers who park the old-fashioned way, helping them avoid the "bang into the car behind" and "bump the car in front" method of determining whether or not the space is sufficient.

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