|Monday, 18 September 2006|
Increasingly, vehicle manufacturers are installing safety devices in vehicles to enable drivers to drive in a safer more efficient manner. For example, some manufactures have included forward looking systems (FLS), rear detection systems (RDS) and side detection systems (SDS) within certain vehicle models. Various sensing systems currently exist for performing collision warning and countermeasure system operations, such as detection, classification, tracking, and relative distance and velocity estimation of objects within a close proximity of a host vehicle. Generally, vehicle operational safety features include collision warning/mitigation, pre-crash braking, adaptive cruise control, pedestrian detection and parking assistance applications. In addition, these features may include vehicle-to-vehicle two-way telemetry and reversible collision avoidance applications. Collision warning and countermeasure systems, and parking aid systems are becoming more widely used. Collision warning and countermeasure systems and parking aid systems provide a vehicle operator knowledge and awareness of objects vehicles within close proximity so as to prevent colliding with those objects. Collision warning and countermeasure systems operations include providing a vehicle operator knowledge and awareness of vehicles and objects that are within a close proximity of the host vehicle to prevent colliding with those objects. Countermeasure systems exist in various passive and active forms. Some countermeasure systems are used to aid in prevention of a collision, others are used to aid in the prevention of injury to a vehicle operator. Certain collision warning and countermeasure systems are able to sense a vehicle or an object at approximate distances of 20-30 m from a host vehicle and warn the host vehicle operator, such that the operator can take precautionary steps to prevent a collision or injury. Other collision warning and countermeasure systems activate passive or active countermeasures such as airbags, load limiting seatbelts, or brake control whereby the system itself aids in preventing a collision or injury.
Parking for vehicles is facilitated, monitored and controlled by using sensors or detectors to determine the availability of vacant parking spaces and by indications to alert vehicle operators at a substantial distance of the availability a vacant space. The detectors may communicate the availability of a space after detecting whether or not an item is currently situated at the space. This information may be assembled and displayed using mapping software to indicate available spaces. In addition, a user may be provided with information about how to traverse through the system of spaces to locate the available space. Sensors for sensing the surroundings of a motor vehicle for different applications have been available for several years and are increasingly being sold as an equipment feature in passenger cars. Different types of sensors are good at detecting different types of situations. Mechanical and electrical vehicle obstacle detectors and particularly curb detectors, have been in use for a long period of time. The curb detectors which are used primarily to facilitate parking a vehicle generally employ a flexible probe that is attached near the front and back wheels of the vehicle. Curb sensors for use facilitating vehicle parking conventionally employ a deflectable probe that is adjusted to rub against an obstruction when there is a predetermined clearance between the obstruction and the vehicle itself. An audible signal is produced from the probe as it rubs against the obstacle. A radar detector is effective at long distances, and is good at detecting speed and range information. However, radar may not be a desirable means for recognizing a small to medium sized obstruction in the lane of an expressway. An image processing sensors excel in identifying smaller obstructions closer to the vehicle, but are not as successful in obtaining motion data from a longer range. Ultrasonic sensors are highly environmental resistant and inexpensive, but are only effective at extremely short distances.
Radar sensors are generally used in automotive vehicles to monitor the surroundings of the vehicle for use as e.g. a parking aid, dead angle monitoring, accident anticipation, start/stop operation or drive operation with distance control and/or regulation. Radars detectors are classified into various systems according to the waveforms of radio waves in use. They include pulse radar, two-frequency (continuous wave) radar, and FMCW (frequency modulated continuous wave) radar. The pulse radar is a radio that detects a distance to an object on the basis of the elapsed time from emission of a pulse wave to reception of the echo. The two-frequency CW radar and the FMCW radar detect a distance to an object and a relative velocity of the object on the basis of the frequency and phase of a peak signal in the frequency spectra obtained by applying the FFT (fast fourier transform) processing to a reception signal. The two-frequency CW radar emits two continuous waves of different frequencies alternately, and detects a distance to an object and a relative velocity of the object on the basis of the Doppler shift of these echoes. The FMCW radar emits a continuous wave to which is applied an appropriately repeated frequency modulation such as triangular wave frequency modulation, and detects a distance to an object and a relative velocity of the object on the basis of the beat frequency of the transmission signal and the reflection signal. Radar sensor platforms using a 24 gigahertz pulse frequency may be used to detect objects at a short range, for precrash sensing, as a parking assistant for automatic proximity radar, for blind spot detection and for pedestrian recognition, as well as for measuring parking spaces while driving past the spaces. With radar systems, the distance of the object along the line of sight may be measured by evaluating the transit time of the radar echo. The relative velocity of the object along the line of sight may also be measured directly by evaluating the Doppler shift of the radar echo.
A vehicle reversing radar or a back-up aid (BUA) is equipped with ultrasonic sensors, in which a ceramic chip in a polarized electric field, due to the anti-piezoelectricity, will make an aluminum housing vibrate and send ultrasonic signals, and will receive the reflected ultrasonic signals from an obstacle within an effective distance. The reverse sensing systems are typically used as short range parking aids and include visual and audible alarms to warn a driver of an impending collision. The ultrasonic sensors is installed on the front and rear bumpers. An ultrasonic sensor can send ultrasonic signals in a concentrated area and generates intense reflections from the obstacle to achieve a sensitive detecting effect. The ultrasonic sound sensors are used to sense the immediate surroundings of motor vehicles in order to assist the driver during a parking maneuver. Ultrasonic sensors on vehicles must not be concealed by vehicle paneling or fenders. Reversing aid systems are typically used to detect an object rearward of and within approximately 180 cm of the host vehicle, when the host vehicle is in a reverse gear. Reversing aid systems indicate to a vehicle operator that an object, that may not be visible to the vehicle operator, is within a stated distance and location relative to the host vehicle. The vehicle operator may than respond accordingly. Short-range obstacle detection for vehicle back-up and parking aid functions can also be achieved with a wide-angle radar system, but cost and packaging considerations force design constraints that tend to limit the system performance. For many vehicle operational safety features, it is necessary to establish wide-angle sensor coverage areas. Wide-angle sensor coverage can be generally defined as up to a 180 degree beam coverage area, which for a front mounted automotive sensor would include complete front sensor coverage and partial side sensor coverage.
Side detection systems (SDS) detect objects that are at the side of a vehicle, e.g., in a driver's blind spot. A typical SDS includes a radar sensor that is mounted in each rear quarter panel of the vehicle. Each radar sensor is designed to detect objects in an adjacent lane. An adaptive cruise control (ACC) system is a forward looking system (FLS). The ACC system uses a radar sensor mounted at the front of the vehicle to detect objects in a forward path of the vehicle. If the lane ahead is clear, the ACC system maintains a set vehicle speed. When a slower vehicle is detected, the ACC system maintains a driver-selected distance using throttle control and limited braking between the vehicles. A typical ACC system uses mechanically scanned radar sensors, which normally improves the ability of the system to detect targets in heavy traffic. Additionally, the operator of the motor vehicle can be informed regarding the "danger potential" of target objects by warning devices, and can be warned of potential collisions with rapidly approaching obstacles. In general, driver assistance systems require a sensor system with which information concerning the vehicle's vicinity may be sensed, as well as evaluation units with which that information may be suitably evaluated and interpreted. Sensor systems for sensing objects in the surroundings of a vehicle predefine the spatial area or target area to be monitored by emitting their signals into the target area and/or receiving them from the target area. The target area is defined by the radiation lobe with the target area delimited by evaluating signals.