Many drivers say they stink at parking a vehicle in a garage or parallel to the road in line with other parked vehicles.
According to surveys conducted by Japan Automobile Federation (JAF), these two skills always top the list of answers to the question, “What driving technique do you think you are not skillful enough?”
To attract less skilled drivers as well, auto manufacturers have long been focused on parking assist systems.
Sound alerts and visual aids for avoiding obstacles behind the car became available first. Some recent parking guidance systems use sensors and cameras for front and sides views in addition to the rear side.
Amid the development competition of parking assist systems, Toyota Motor has, ahead of other auto manufacturers, been taking the initiative in advancing the technology.
As early as 2000, the automotive giant launched the Toyota Estima with a “back guide monitor” that displayed parking guide lines on the onboard screen to go with the driver's steering.
In 2001, an “audio-assisted back guide monitor” followed. It added audio assistance that orally instructed proper steering wheel operations and best reverse timing during parallel parking.
The first version of the Intelligent Parking Assist System (IPAS) allowing the car to steer itself into a parking space was deployed on the Prius sold in Japan in 2003.
IPAS facilitated parking, with simple operations from the driver side, only requiring the driver to be mindful of vehicles and pedestrians and drive slowly with the use of the brake.
Announced alongside the release of the second-generation Prius, IPAS has continued evolving with a number of world-first features.
As one of the IPAS co-developers, Aisin Seiki, with its image processing technologies, has always been there in the development phase, working together with the motor company.
“We'd like our cars capable of steering themselves into parking spaces, and came to you to get a helping hand.”
It was the beginning of 2001 when Toyota came to Aisin.
Back then, there existed no such system anywhere on the planet.
“We can be a part of a system drivers have only dreamed about.”
An engineer who became a core member of the project after only three
years at Aisin could not contain his excitement.
He went on to lead Aisin’s part of the development of this new parking
Because of Aisin’s track record in the field of image processing and new vehicle system integration, Toyota picked the supplier to co-develop the system they wanted.
In the mid-1980s, image processing R&D started at one of the Aisin Group research centers in Kawasaki.
The parking assist system named the “Back Guide Monitor” onboard the Toyota Estima released in January 2000 came from the technologies developed and sophisticated there.
To add to that, Aisin and Toyota worked together earlier on vehicle safety systems, e.g., out-of-lane alert, Front & Side Monitor (to display the front and left side of the car).
It was the technologies proven in their vehicles that brought Toyota to Aisin for a new control unit for their parking assist system.
Parking Assist System
The onboard monitor displays images captured by the rear camera along with the predicted course of the car’s movement and distance reference lines to provides assistance in parking the vehicle in a garage or parallel spot.
Out-of-Lane Alert System
The rear camera and sensor measure the distance between the car and lane line. The system sounds an alert if the car on a highway is running too close to the lane.
When you drive a car, you recognize objects, judge safety, and control the car.
You do the same when parking your car. First, you recognize the relative position of a vacant parking space and obstacles, determine when and how much you should steer the steering wheel, and operate the steering wheel and brake.
Most drivers do all these without a lot of thinking.
Conventionally available parking assist systems helped drivers to “recognize” obstacles and “judge” what to do next, by providing visual information of the anticipated course based on steering control and using audio guidance.
The new system was something totally different, as it would let the car “steer itself” to park it.
But, as is often the case, dreams don't come true in a day. No one ever tried to design a car that monitors changes in its location to find the best position for parking, steer autonomously, and drive it to the decided position to park.
The prerequisite was accurate steering control without bumping into building structures or other vehicles. Data processing accuracy became more important for letting the computer, like a careful driver, recognize objects and determine what to do.
In addition, the system had to be configured to prevent errors and to ensure safety in case the driver incorrectly operated the vehicle.
It had to be user-friendly, e.g., readily understandable interface, easy operations, etc.
All these had to be packaged in one system.
“Such a system may work on the test laboratory level. But, no way! Just think about it; we are talking about a system that controls the car on the road.”
Concerns like that were heard everywhere.
There were piles of challenges facing the new parking assist system.
Accurate position detection for parking was the toughest.
Small errors in position data and steering wheel control sometimes resulted in, all combined, a deviation of the car position by tens of centimeters.
What is the solution to properly aligning a car when parking?
To always monitor the car’s position was fundamental, but letting the system do that was not at all an easy task.
Project team members both at Toyota and Aisin racked their brains out.
Having worked on the subject ever since the initial phase, Toyota did thorough research to identify the causes of parking errors.
Team Aisin also poured a lot of effort into finding the source of parking errors.
The members managed to identify one of the causes—changes in coordinates of the rear viewing CCD camera.
“How many passengers are in the vehicle or how much load there is changes the coordinates of the camera, in other words, the point of view. That is one factor causing parking errors.”
The weight and position of the load, road surface conditions, the pressure and wear in tires—these all affect the coordinates of the camera and cause errors.
The displacement, though small, can be significant in a parking assist system that needs to be accurate to the degree of centimeters.
Testing the system on the Prius under different loads -- with the driver only and with four passengers and the driver -- found that up to 36 cm of deviation can occur.
“The number is too large. The existing back guide monitor may be incapable of dealing with a deviation of 36 cm.”
They got stalled. Then, the vehicle height sensor used for controlling the headlights gave a clue.
The sensor is used to modify the angle of headlights according to changes in the vehicle’s height. They thought the mechanism might work as well in the parking assist system.
The height sensor signals the onboard computer that compensates the coordinates of the monitoring camera's viewpoint to modify the setting error of the parking position.
Changes in Viewpoint Height Causing Errors
The more the passengers, the smaller the distance between the vehicle body and road surface, thus the lower the position of the rear camera and the smaller the parking reference distance.