Lexus LS 460 Parking System Grabs the Wheel

Last fall, when Lexus announced it was marketing a North American vehicle with a self-parking feature, consumers were caught by surprise. From an industry dominated by talk of hands-free phones, iPod plug-ins, and gasoline prices, the idea of a self-parking car seemed unexpected, even foreign. The collective consumer reaction seemed to be, you mean it’s going to turn the steering wheel…by itself?

Indeed it is. Lexus’ intelligent LS 460 performs all the mental calculations of a human driver, “talks” with engine, transmission, and steering sensors, “listens” to signals from sonar devices mounted on the front bumper, then grabs hold of the wheel and steers the vehicle into a parking spot. In the process, it eliminates one of the most disliked tasks in all of urban driving: the dreaded parallel parking maneuver.

Moreover, Lexus isn’t alone in its effort. The luxury automaker has been joined by automotive supplier Siemens VDO, which has marketed a competing self-park system, leading many in the industry to suggest a broader movement may be afoot.

“Using this in a broader context makes perfect sense for automakers,” notes Thilo Koslowski, vice president and lead automotive analyst for Gartner Industry Advisory Services. “The more they can package it together with other features, the more they can create a revenue opportunity, and the easier it is for them to pass the cost on to the consumer.”

Laying the groundwork

While that broader intent may not matter much outside the hermetically-sealed world of automotive engineering, it could be the very reason that self-parking has reached the consumer market at all. In essence, the feature is another piece in the giant jigsaw puzzle of automotive electronics – one that could set the stage for more advanced features, such as collision avoidance.

Self-parking could do that because it employs sensors, controllers, and actuators in a manner similar to the collision avoidance systems that are expected to reach the market some day. Lexus’ Advanced Parking Guidance System, for example, uses six sonar sensors, four of which were already in place on the LS 460 prior to the addition of the new feature. The two new sensors – one on the front left corner and the other on the front right corner of the LS – look for vehicles along the sides. (The four other sonar sensors were already in place as part of a separate feature called Park Assist, which alerts drivers to the close proximity of cars behind, and in front of, the LS 460.) By employing new sensors at the front corners, however, the new feature enables the vehicle to “know” where other vehicles are along side it.

When drivers want to parallel park the new vehicle, they are required to pull the LS past, and three feet away from, parked vehicles on the side, finally reaching a point where they can see the front license plate of the vehicle they plan to park behind. They then shift the transmission to reverse and press a “reverse icon” on a dashboard display. At this point, the Advanced Parking Guidance System’s dedicated microcontroller has taken over, and is reading inputs from a variety of other microcontrollers on the vehicle’s 1-Mbit/sec CAN (controller area network) bus. An input from the engine, for example, tells the system that the engine is running, while another from the transmission let’s the system know that the car has been shifted into reverse. Other processors communicating with the Advanced Parking Guidance Computer include the steering controller, which provides data from the steering angle sensor, and the antilock braking system (ABS), which sends wheel speed data.

“It communicates with 45 to 60 other computers on the CAN network,” says Bob Allan, a development manager for Lexus College’s Product Education Curriculum in Torrance, CA. “There’s a lot of communication that goes on within the CAN system, just to make sure everything is working properly.”

In addition to the incoming communiqués through the CAN bus, the new parking feature also sends outgoing messages to an audio-video local area network bus, which has 15 to 20 more controllers. By sending output messages through that data bus, the Advanced Parking Guidance Computer has access to the dashboard display, which it uses to communicate with the driver.

The system’s most important output function, however, is to communicate through the CAN bus with the steering system. By doing so, it can access the electrically-powered rack-and-pinion steering, which uses an electric motor to autonomously turn the steering wheel. While it does that, system software “watches” distances to parked cars on the side, in back, and in front as the vehicle parks itself.

At the same, engineers enabled the system to receive input from the steering computer, thus preventing the possibility that a driver might decide to “help” the computer parallel park the car.

“It looks at a load-based signal on that motor, so it knows that it is controlling the steering, and you’re not,” Allan explains. If the system senses that the driver is trying to control the steering, it automatically shuts down, Allan adds.
Engineers from Lexus and from Siemens VDO, which makes a system called ParkMate, say that they couldn’t have achieved the same ends with a conventional hydraulically-powered steering system.

“Conventional hydraulic or variable effort power steering isn’t adequate to take over direct activation of the steering,” notes Gary Collins, marketing sales manager for the Safety Chassis Division of Siemens VDO. “To enable the vehicle to do its own maneuvering, you need a system that can actively generate power, which means some form of electric steering.”

Bullet-proofing

Moreover, engineers say that the switch from conventional hydraulic steering to electric steering also sets the stage for collision avoidance, and ultimately, for drive-by-wire technology.

Siemens VDO engineers say that their ParkMate software algorithms will eventually be integrated into a Chassis Dynamics Controller, a project that will one day serve as a master control for such sub-systems as air bags, ABS, steering, and suspension controllers.

“Today, those systems typically don’t talk to each other,” says Steve O’Connor, a customer segment manager for Siemens VDO’s Safety Chassis Division. “But the Chassis Dynamics Controller could coordinate all the signals to achieve the highest possible level of comfort and safety.”

Using such systems, O’Connor says, vehicles could recognize panic stops and act accordingly. When ABS is triggered, for example, the Chassis Dynamics Controller could tell the air bag to get ready to deploy, while simultaneously stiffening the front shock absorbers and possibly even turning the steering wheel to avoid an accident.

Siemens is also preparing to integrate its parallel parking system with its brake-by-wire Electronic Wedge Brake, thus further improving the ability to make autonomous emergency stops.

In the meantime, however, automotive industry analysts say that it’s not enough for today’s parallel parking systems to serve as stepping stones. Today’s units, they say, can only provide a boost to future technologies if they’re successful now.

“The challenge is always to make these features bullet-proof,” says Koslowski of Gartner. “If you create systems that are complicated to use, consumers may be disappointed and opt for another vehicle on their next purchase. In that sense, it could actually backfire.”

Koslowski warns that automakers need to avoid public blunders, like the one that Lexus experienced on MS-NBC late last year, when a confused news anchor tried to use Advanced Parking Guidance System, only to have it refuse to back up.

“These systems are impressive in terms of the technology, but they’re not 100% intuitive yet,” Koslowski says. “There’s still room for improvement.”

As they improve, however, automakers are confident the new parallel parking systems will serve as a foundation for more electronic development.

“On the surface, this product might seem like an isolated system,” says Collins of Siemens VDO. “But we look at this as a building block. It allows us to create more electronic features for the future.”