How the Ultrasonic Rear Parking Assistant Works

How the Ultrasonic Rear Parking Assistant Works

In the last decade, automotive manufacturers have been experimenting with different kinds of systems to help drivers navigate in reverse. Since one of the most difficult areas to see, is the blind spot behind the rear bumper, any additional insight is extremely welcomed in this location.

Although backup cameras are gaining in popularity General Motors has been deploying ultrasonic rear parking assistance (URPA) that provides an audible warning when the rear bumper is close to someone or something. For me, this has become an extremely valuable factory-installed accessory I wouldn’t want to live without. This article will discuss the many advantages to the URPA system when compared to a backup camera, plus coverage of how it works in terms of range and accuracy.

Backup Assistant Operation

One important fact about the URPA system is that it will not work at speeds above 3 mph. When the system is enabled, an operation is activated when the transmission gear selector is placed in the reverse position. The ultrasonic sensors are mounted in the rear bumper fascia. They are capable of detecting objects starting at a distance of about 5 feet away from the rear bumper.

In order for an object to be recognized it needs to be at least 10 inches in height measured from the ground. A single beep will sound when an object is first detected. As the rear bumper gets closer to this target additional beeps are sounded. When the object is within 1 foot a slow but constant beeping will occur. The audible warning will increase in frequency as the distance closes until it’s on steady at distances below 6 inches.

In addition to the audible warnings, General Motors has installed a visual display that is conveniently located near the rear glass which is easily seen as the driver looks over their right shoulder out the back window. This visual display uses green, amber and red warning lights to provide visual feedback related to distance. The Amber light is activated in the 5-foot range and flashing amber to a red light is activated within 20 inches of detecting an object.

Malfunction of Object Detection System

Since the ultrasonic system works on the principle of sending out radio waves that bounce off of objects much in the same way as radar, line of sight problems with the sensors are possible. As an example, if the ultrasonic sensors are covered with mud or snow the system will be automatically disabled. When this occurs the vehicle warns the driver by displaying a park assist off the message on the driver information center coupled with the rear visual display flashing red light when the shifter is placed in reverse.

There are a few other select situations where the URPA system will not detect objects or will automatically disable itself. As mentioned above it will not work above 3 mph nor will it detect objects less than 10 inches in height. The other situation is if the vehicle is towing a trailer. The same goes for when a tow bar is used to carry a bicycle or wheelchair that hangs in front of the rear bumper.

Advantages of URPA Over Backup Cameras

It’s not that ultrasonic rear sensors are better than backup cameras it really boils down to their different capabilities. Generally speaking, a backup camera provides a view directly behind the rear bumper with very little peripheral vision. The flexibility of the ultrasonic sensor allows it to be mounted on the corners of the bumper to provide exceptional peripheral detection. This provides superior notification when backing out of a tight parking space with cargo vans on either side.

Another advantage of the URPA is that the audio and visual inputs work together with the human senses so the driver is not taking his eyes or attention off of the surrounding environment. A backup camera system will have some type of dash-mounted monitor requiring the driver to look down and study an image display. This can direct his senses away from what’s going on around him and use the camera alone for notification of problems.

I suppose in a perfect world an automobile would come with both systems together and a few cars do. The problem is these developing technologies are still somewhat expensive. Both have their pros and cons to be considered. Although I personally prefer the ultrasonic object detection systems over the cameras, I have found the main disadvantage of the General Motors backup assistant to be it doesn’t recognize my neighbor’s cat lying behind my automobile, because she is too low to the ground. This means I still have to go back and check for her before I get in the car.

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