Abstract:
A system for sensing an impending collision and controlling a safety device such as an airbag in response to the detection of an impending collision target. Deployment characteristics of the safety device are adjusted based on sensor output. One implementation of the system includes a radar sensor and a vision sensor carried by the vehicle. The radar sensor provides a radar output related to the range and relative velocity of the target. The vision sensor provides a vision output related to the bearing and bearing rate of the target. An electronic control module receives the radar output and the vision output and generates control signals for control safety device and adjusting deployment characteristics.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to a system for sensing a motor vehicle impact and adjusting the deployment of a safety device.  
       BACKGROUND AND SUMMARY OF THE INVENTION  
       [0002]     Enhancements in automotive safety systems over the past several decades have provided dramatic improvements in vehicle occupant protection. Presently available motor vehicles include an array of such systems, including inflatable restraint systems for protection of occupants from frontal impacts, side impacts, and roll-over conditions. Advancements in restraint belts and vehicle interior energy absorbing systems have also contributed to enhancements in safety. Many of these systems must be deployed or actuated in a non-reversible manner upon the detection of a vehicle impact to provide their beneficial effect. Many designs for such sensors are presently used to detect the presence of an impact or roll-over condition as it occurs.  
         [0003]     Attention has been directed recently to providing deployable systems external to the vehicle. For example, when an impact with a pedestrian or bicyclist is imminent, external airbags can be deployed to reduce the severity of impact between the vehicle and pedestrian. Collisions with bicyclists and pedestrians account for a significant number of motor vehicle fatalities annually. Another function of an external airbag may be to provide greater compatibility between two vehicles when an impact occurs. While an effort has been made to match bumper heights for passenger cars, there remains a disparity between bumper heights, especially between classes of passenger vehicles, and especially involving collisions with heavy trucks. Through deployment of an external airbag system prior to impact, the bag can provide enhancements in the mechanical interaction between the vehicles in a manner which provides greater energy absorption, thereby reducing the severity of injuries to vehicle occupants.  
         [0004]     For any external airbag system to operate properly, a robust sensing system is necessary. Unlike crash sensors which trigger deployment while the vehicle is crushing and decelerating, the sensing system for an external airbag must anticipate an impact before it has occurred. This critical “Time Before Collision” is related to the time to deploy the actuator (e.g. 30-200 ms) and the clearance distance in front of the vehicle (e.g. 100-800 mm). Inadvertent deployment is not only costly but may temporarily disable the vehicle. Moreover, since the deployment of an airbag is achieved through a release of energy, deployment at an inappropriate time may result in undesirable effects. This invention is related to a sensing system for an external airbag safety system which addresses these design concerns.  
         [0005]     Radar detection systems have been studied and employed for motor vehicles for many years. Radar systems for motor vehicles operate much like their aviation counterparts in that a radio frequency signal, typically in the microwave region, is emitted from an antenna on the vehicle and the reflected-back signal is analyzed to reveal information about the reflecting target. Such systems have been considered for use in active braking systems for motor vehicles, as well as obstacle detection systems for vehicle drivers. Radar sensing systems also have applicability in deploying external airbags. Radar sensors provide a number of valuable inputs, including the ability to detect the range to the closest object with a high degree of accuracy (e.g. 5 cm). They can also provide an output enabling measurement of closing velocity to a target with high accuracy. The radar cross section of the target and the characteristics of the return signal may also be used as a means of characterizing the target.  
         [0006]     Although information obtained from radar systems yield valuable data, exclusive reliance upon a radar sensor signal for deploying an external airbag has certain negative consequences. As mentioned previously, deployment of the external airbag is a significant event and should only occur when needed in an impending impact situation. Radar sensor systems are, however, prone to “false-positive” indications. These are typically due to phenomena such as a ground reflection, projection of small objects, and software misinterpretation, which faults are referred to as “fooling” and “ghosting”. For example, a small metal object with a reflector type geometry can return as much energy as a small car and as such can generate a collision signal in the radar even when the object is too small to damage the vehicle in a substantial way. Also, there may be “near miss” situations where a target is traveling fast enough to avoid collision, yet the radar sensor system would provide a triggering signal for the external airbag.  
         [0007]     In accordance with this invention, data received from a radar sensor is processed along with vision data obtained from a vision sensor. The vision sensor may be a stereo or a three-dimensional vision system that is mounted to the vehicle. The vision sensor can be a pair of 2 dimensional cameras that are designed to work as a stereo pair. By designing a stereo pair, the set of cameras can generate a 3 dimensional image of the scene. The vision subsystem can be designed with a single camera used in conjunction with modulated light to generate a 3 dimensional image of the scene. This 3 dimensional image is designed to overlap the radar beams so that objects will be sensed within the same area. Both the radar and 3 dimensional vision sensors measure a range to the sensed object as one of their sensed features. Since this is the common feature, it is used to correlate information from each sensor. This information correlation is important for correct fusion of the independently sensed information especially in a multiple target environment. The fusion of radar and vision sensing systems data provide a highly reliable non-contact sensing of an impending collision. The fusion mechanism is the overlap of radar range and vision depth information. The invention functions to provide a signal that an impact is imminent. This signal of an impending crash is generated from an object approaching the vehicle from any direction in which the sensor system is installed. In addition to an indication of impending crash, the sensor system will also indicate the potential intensity of the crash. The exact time of impact, and the direction of the impact is also indicated by this fused sensor system. The intensity of the crash is determined by the relative size of the striking object, and the speed with which the object is approaching the host vehicle. The time, and direction of the impact is determined by repeated measurements of the object&#39;s position. This sequence of position data points can be used to compute an objects trajectory, and by comparing this trajectory with that of the host vehicle, a point of impact can be determined. The closing velocity can also be determined by using the position data and trajectory calculations.  
         [0008]     By sensing and notifying the safety system of an imminent crash, this sensor enables the safety system to prepare for the impact prior to the impact. The safety system can tighten the seat belts by activating an electric pre-tensioner, which makes the seat belt system more effective at restraining the occupant after contact with the object, and during the deceleration force of the crash. The advanced warning of a frontal crash can be used to inflate a larger airbag at a much slower rate. The slower rate would reduce the potential of injury by the inflating airbag, and the larger size would offer a higher level of potential energy absorption to the occupant, compared to a smaller bag. Other advantages of the forward-looking application of this sensor are the ability to deploy additional structures or modify existing structures to maximize occupant safety. These structures could be expanding bumpers or additional frame rails or pressurized body components that would add a level of safety just prior to impact during a crash.  
         [0009]     Additional time to deploy enables safety devices that are slow in comparison to today&#39;s airbags. The seating position and headrest position can be modified, based on advanced crash information to increase their effectiveness in a variety of crash scenarios. Electric knee bolster extenders can be enabled to help hold the occupant in position during a crash. Advance warning also enables the windows and sunroof to close to further increase crash safety. External structures can be modified with advance notice of an impending crash. Structures such as extendable bumpers and external airbags can be deployed to further reduce the crash forces transmitted to the vehicle&#39;s occupants.  
         [0010]     The system can be used in a side looking application with additional benefit to occupant safety in side crash scenarios. Knowing that a side impact will occur in advance of contact allows the side airbag to achieve similar benefit that the front airbags achieved with activation prior to impact. Such advanced activation would allow larger side bags and side curtains to deploy at slower, less aggressive rates. In a case where the contact based side airbag activation might trigger late in the crash, there is potential for the occupant to be displaced laterally before the airbag is triggered. Such displacement prior to activation reduces the effectiveness of the side airbag. In the case where a sliding vehicle crashes into a solid pole in an area of the side of the car that has less structure, like the passenger door, an acceleration based deployment system would not deploy the airbag until significant intrusion has taken place. The pre-crash sensor described here in a side looking application would give the safety system the ability to trigger the airbags prior to contact with the pole, and making the airbag more effective in protecting the occupant from the pole intrusion.  
         [0011]     In a rearward looking application, the system may be used with further benefit to the host vehicle&#39;s occupants. Advance knowledge of a rear-end collision prior to contact gives the host vehicle&#39;s safety system time to move any reclined seats to a more safe upright position. The safety system has time to take up the seatbelt slack with an electric pre-tensioner to make the seatbelt more effective. Modifying the host vehicle structure is also possible with collision warning prior to impact. An expandable rear bumper could be deployed and help to absorb additional crash energy that would otherwise be transferred to the host vehicle occupants.  
         [0012]     Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is an overhead view of a representative motor vehicle incorporating a system for sensing a collision and controlling deployment of a safety system in accordance with the present invention;  
         [0014]      FIG. 2  is a signal and decision flow chart regarding the radar sensor of the sensor system of this invention;  
         [0015]      FIG. 3  is a signal and decision flow chart regarding the vision systems of the sensor system of this invention;  
         [0016]      FIG. 4  is a flow chart showing the integration of the radar output and the vision output to control the safety device; and  
         [0017]      FIG. 5  is a flow chart showing feature level fusion logic where similar features from each sensor are combined to control the safety device based on the combined multi-sensor fused features. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     Now referring to  FIG. 1 , a system  8  is shown with an associated vehicle  9 . The system  8  is configured for a forward looking application. However, the system  8  can be configured to look rearward or sideways with the same ability to sense an approaching object and prepare the vehicle  9  for the crash. In a side-looking, or rearward looking application, the sensors would have overlapping fields of view, as shown in the forward looking application in  FIG. 1 .  
         [0019]     The sensor system  8  includes a radar sensor  10  which receives a radio frequency signal, preferably in the microwave region emanating from an antenna (not shown). Radar sensor  10  provides radar output  20  to an electronic control module (ECM)  12 . A vision sensor  11  is preferably mounted to an upper portion of the vehicle  9 , such as, along the windshield header aimed forward to provide vision information. Vision sensor  11  provides vision output  22  to an ECM  12 . The ECM  12  combines radar output  20  and the vision output  22  to determine if a collision is imminent and deploy a safety device.  
         [0020]     In addition to deploying the safety device, the ECM  12  may adjust deployment characteristics based on the vision output, the radar output, or both. For example, the ECM  12  is an electrical communication with an external airbag  13  to provide control signals that adjust the deployment velocity and deployment force of the external airbag  13  based on the radar and vision output. As the system  9  senses the range and closing velocity of an object, the system  9  uses the sensed information to calculate a time to impact. With longer time to impact, the external airbag  13  is deployed more slowly and with less force, thereby reducing the potential impact on the sensed object. In addition, with more time the external airbag may be filled to a larger size offering a higher level of energy absorption.  
         [0021]     Similarly, control signals are also received by an internal airbag  14  from the ECM  12 . The deployment velocity and deployment force of the internal airbag  14  is adjusted based on a time to impact, thereby reducing the potential impact on the occupant.  
         [0022]     To provide control signals that adjust the deployment force of an expandable structure  16  based on the radar or vision output, the ECM  12  is in electrical communication with the expandable structure  16 . Expandable structures include devices ,such as, expanding bumpers or pressurized body panels, The deployment force of the expandable structure  16  may be adjusted based on the bearing or size of the object, to better manage the affect of the expandable structure  16  on the structural integrity of the vehicle  9 .  
         [0023]     The ECM  12  is in electrical communication with a seat belt pre-tensioner  18  to provide control signals that adjust seat belt tension based on the radar or vision output. Based on the bearing or closing velocity of the object, the seat belt tension may be adjusted to better secure the occupant.  
         [0024]     To provide control signals that adjust a seat angle and position provided by a seat positioner  19  based on the radar or vision output, the ECM  12  is in electrical communication with the seat positioner  19 . The position and angle may be adjusted based on the bearing and closing velocity, to better position the occupant for impact.  
         [0025]     Although, specific examples are provided above it is readily contemplated in accordance with the present invention, that one or all of the measurements provided by each of the sensors may be used in adjusting various deployment characteristics of a safety device as required.  
         [0026]     Now with reference to  FIG. 2 , a diagram of the signal and decision flow related to radar sensor  10  is provided. The radar sensor  10  analyzes a radio frequency signal reflected off an object to obtain a range measurement  28 , a closing velocity  30 , and a radar cross section  36 .  
         [0027]     A time of impact estimate  26  is calculated based on range measurement  28  and the closing velocity  30 . The range measurement  28  is the distance between the object and vehicle  9 . Radar sensor  10  provides distance information with high accuracy, typically within 5 cm. The closing velocity  30  is a measure of the relative speed between the object and the vehicle  9 . The time of impact estimate  26  is provided to block  32  along input  24 . The time of impact estimate  26  is compared with the necessary time to deploy the safety device, such as an external air bag. Typically deployment time of an external airbag is between 200 ms and 30 ms. In addition, the range measurement  28  is compared with the necessary clearance distance from the vehicle  9  to deploy the safety device. Typically clearance distance for an external air bag is between 100 mm to 800 mm.  
         [0028]     The closing velocity  30  is also used to determine the severity of impact as denoted by block  34 . High closing velocities are associated with a more severe impact, while lower closing velocities are associated with a less severe impact. The severity of impact calculation is provided to block  32  as input  35 .  
         [0029]     The radar cross section  36  is a measure of the strength of the reflected radio frequency signal. The strength of the reflected signal is generally related to the size and shape of the object. The size and shape is used to access the threat of the object, as denoted by block  38 . The threat assessment from block  38  is provided to block  32  as input  39 . Block  32  of the ECM  12  processes the time of impact, severity of impact, and threat assessment to provide a radar output  40 .  
         [0030]      FIG. 3  provides a signal and decision flow chart related to the processing of information from vision sensor  11 . The vision sensor  11  provides a vision range measurement  42 , a bearing valve  44 , a bearing rate  46 , and a physical size  54  of the object.  
         [0031]     By using a stereo pair of cameras or a light modulating 3 dimensional imaging sensor, the vision sensor  11  can determine the vision range measurement  42  to indicate the distance from the vehicle  9  to the object. The bearing valve  44  is related to an angular measure of object with respect to a datum of vehicle  9  (e.g. an angular deviation from a longitudinal axis through the center of the vehicle  9 ). The rate of change of the bearing valve  44 , with respect to time, is the bearing rate  46 . The vision range measurement  42 , bearing valve  44 , and the bearing rate  46  are used to generate a collision determination as denoted by  48 . The collision determination from block  48  is provided as input  50  to block  52 .  
         [0032]     The vision sensor  11  also measures the physical size  54  of the object. The physical size  54  is used to assess the threat of the object, as denoted by block  56 . The threat assessment is provided to block  52  as input  58 . The collision determination from block  48  and the threat assessment from block  56  are used in block  52  to generate vision output  60 .  
         [0033]      FIG. 4  illustrates the integration of the radar output  40  and vision output  60  to generate control signals for a safety device  66 . Both the radar sensor  10  and vision sensor  11  independently provide measurements to the ECM  12 . However, ECM  12  considers measurements from the radar output  40  and the vision output  60  in block  64  along with vehicle parameters  62 , such as vehicle speed, yaw rate, steering angle, and steering rate. The vehicle parameters  62  are evaluated in conjunction with the radar output  40  and the vision output  60  to enhance the reliability of the deployment decision and further adjust the deployment characteristics of the safety device  66 .  
         [0034]     Referring now to  FIG. 5 , since each sensor has some very accurate features and some less accurate features, sensor system  10  may also be configured to combine the attributes of both radar sensor  10  and vision sensor  11  to provide control signals to the safety device  82 . The radar output includes the range measurement  28 , the radar closing velocity  30 , and the radar position  74 , while the vision output includes the vision range measurement  42 , vision closing velocity  70 , vision bearing rate  46 , and vision bearing valve  44 . The control signals  80  are based on a combination of radar and vision measurements from each sensor. The combining of discrete measurements from separate sensors to improve reliability of a measurement is referred to as feature fusion.  
         [0035]     For example, the closing velocity  30  as measured by radar sensor  10  is combined with closing velocity  70  as measured by vision sensor  11  to determine a fused closing velocity as denoted by block  72 . Similarly, the range measurement  28  from radar sensor  10  is fused or combined with the vision range measurement  42  as measured by vision sensor  16  to determine a fused range measurement, also denoted by block  72 . The precision of the fused range measurement is achieved primarily through radar sensor  14 . Although the vision range measurement  42  is not as accurate as the radar range measurement  28 , comparison between the radar range measurement  28  and the vision range measurement  42  provides improved reliability. In addition, the vision range measurement  42  is accurate enough to enable correlation of features and fusion with the radar sensor  14 .  
         [0036]     In order to correlate features from different sensors a reference must be used to associate each similar measurement as sensed by each independent sensor. Use of a reference is increasingly important in a multiple target scenario to decrease the likelihood of attributing a measurement to the wrong target. Since both sensors determine range, it is the reference used to as a basis to combine all features in the feature fusion process.  
         [0037]     The radar position  74 , vision bearing  44 , and vision bearing rate  46  are combined to determine a fused position and azmuth rate as denoted by block  78 . Similarly, the radar cross section  36  and the physical size measurement  54  from the vision sensor  11 , may be combined into a fused size measurement as denoted by block  76 . The fused range and closing range in block  72 , the fused position and azmuth rate in block  78 , and the fused size measurement in block  76  are combined with other vehicle parameters  62  in block  80 . The analysis, in block  80 , of attributes from both the radar sensor  10  and the vision sensor  11 , in the form of the fused feature measurements, provides control signals with high reliability.  
         [0038]     While the above description constitutes the preferred embodiment of the present invention, it will be appreciated that the invention is susceptible to modification and change without departing from the proper scope and fair meaning of the accompanying claims.