Winter 2008 Forward to a Friend

Reverse Assist Sensors


The Tribeca reverse assist sensors system uses beeping sounds to alert the driver to obstacles when backing up or parallel parking. The system includes four sensors mounted in the rear bumper fascia, an interior speaker, wiring harness, control module, and attachment hardware.

Mounted in the rear bumper, the system’s sensors emit and receive ultrasonic signals when the vehicle is placed in Reverse. Objects in the field of detection reflect the signals back to the sensors, causing an audible warning to sound in the vehicle.

Speaker Adjustment
The system’s speaker has three settings:
  • HI – loud warning.
  • LOW – soft warning.
  • OFF – the system should be turned off when towing with a trailer hitch, a ball mount is installed, or a hitch-mounted bike carrier is used.

Todd Hill, a Subaru of America, Inc. accessories parts project engineer, provided some insight into how the system operates: “The system sends out high-frequency sound and listens for an echo, somewhat like radar. The time difference between emission and detection of the reflected signal allows the system to compute the distance to the obstacle.

“What are the easiest things to detect? Backing up against a flat wall or other large, flat object that is perpendicular to the vehicle. When you’re backing up against a flat wall at an angle or an object of unusual shape, some signals will bounce off, like a light ray will bounce off a mirror, rather than be reflected back towards the vehicle.

“If you’re backing up against a flat wall,” said Hill, “the system will pick it up right away. When you have something that’s much harder to detect, you might have to reach Zone 2 or 3 before the system picks it up. An object’s shape and size determine when the system first detects it.

“Shapes and materials are very important factors. For instance, the B-2 stealth bomber is really big, but it doesn’t show up on radar. With the Subaru system, a round pole may be harder to detect than a square pole. Most objects that are reasonably large will be picked up.

“We located the sensors below the bumper beams for a couple reasons: We wanted them out of the way, should someone bump into the vehicle, and we didn’t want to modify the bumper beam or its foam covering in any way. Subaru is very serious about maintaining the highest level of safety.”

Backing up warning zones

Todd Hill explained some of the development work on the system: “We positioned the sensors at the best possible locations and angles to optimize system performance, whether the vehicle is loaded or empty. We also tuned the system to be compatible with the Tribeca’s available trailer hitch. Extensive evaluation was conducted with a variety of obstacles and over varying terrain as well as benchmarking the system with those on competitive vehicles. For the 2008 Tribeca, we’ve added markings to the rear bumper to reduce installation time.

“We think our system maximizes what you could expect a reverse assist to do.”

“We think our system maximizes what you could expect a reverse assist to do.”

“The system doesn’t replace looking behind you when backing up,” cautioned Hill. “The system may not detect all objects, depending on size, shape, and location. Even with the system, the driver must verify that the path is clear when driving in Reverse.

“Also, any time something is obstructing the sensors, their performance is affected. The sensors should be kept free of mud, dirt, ice, snow, or other obstructions.”

“If you have the rearview camera,” remarked Hill, “you might think you don’t need the reverse assist sensors. You’d think that they’d be redundant, but they complement each other. The sensors have a wider field of view than the camera does, while the camera can see farther into the distance. So you can sometimes hear an object being detected before it becomes visible on the screen, and you can often see an obstacle in the distance before it is detected by the reverse assist sensors.”

Right now, only the Tribeca has the reverse assist sensors feature available as an accessory. It can be installed any time, even after vehicle delivery. Subaru is expected to offer the accessory in other vehicles in the future.