Patent Grant
6871145
The present disclosure relates generally to vehicle object detection systems and, more particularly, to a method and system for vehicle impact assessment using driver braking estimation.
One of the more recent systems to be developed in the automotive industry is the forward collision warning (FCW) system. An FCW system is intended to mitigate and/or eliminate frontal impacts by generating a timely warning to the driver to take an evasive action. Typically, a vehicle is configured with a sensor (or sensors) that is capable of detecting objects in the frontal area of the vehicle. The sensor not only detects the presence of an object, but also provides some quantitative information about the object such as range, range rate, and azimuth position of the object. Additional information related to the object (e.g., a lead vehicle in many instances) may include relative acceleration, the size of the object, the dimensions of the object, the direction of movement of the object, etc. Generally speaking, two main technologies are most prevalent in gathering such object information: (1) laser technology; and (2) radar technology.
In addition to the gathered object data, an FCW system also typically incorporates a threat assessment algorithm, which evaluates the incoming data, analyzes the particular situation, and then determines if there is any imminent threat of impacting an object in the frontal area of the vehicle. Many of these algorithms are based on parameters such as “time to impact”, “time headway”, or perhaps basic vehicle kinematics. In any case, the output of the algorithm will determine if the FCW system will cause a warning to be issued to the driver.
False alarms generated from a FCW system are a source of nuisance to the driver. Such false alarms may result from erroneous information picked up from the sensor(s), or may be generated as the result of shortcomings in the threat assessment algorithm itself. In the latter case, the false alarm is a “too early” warning, which can annoy the driver. On the other hand, a missed detection results from a situation where an impact warning was supposed to be issued by the FCW system, but was not, due to erroneous sensor information or due to the threat assessment algorithm. The latter is in the form of a “too late” warning, or even no warning at all, such that the overall effectiveness of the system is compromised or diminished. However, algorithms based only on the above mentioned parameters tend to exhibit these characteristics.
In an exemplary embodiment, a method for predicting an impact condition between a host vehicle and an object detected in a path of travel of the host vehicle includes receiving measured parameters from the host vehicle and the object, and receiving a system sensitivity input from a driver of the host vehicle. A braking response of the driver of the host vehicle is estimated, based on the received system sensitivity input, and a projected travel range profile for both the host vehicle and the object is determined, based upon the measured parameters and the estimated braking response. The impact condition is established whenever a comparison of the projected travel range profile for the host vehicle and for the object establishes an intersection therebetween.
In another aspect, a method for generating a frontal impact warning for a driver of a host vehicle includes determining, during a given sample time period, actual velocity and acceleration data for both the host vehicle and for a lead vehicle detected in the path of travel of the host vehicle. A braking response of the driver of the host vehicle is estimated, and a deceleration value for the lead vehicle is assigned. Then, a projected travel range for the host vehicle is generated, based upon the actual velocity data for the host vehicle and the lead vehicle, and further based upon the estimated braking response of the driver of the host vehicle. A projected travel range is also generated for the lead vehicle, based upon the actual velocity data for the lead vehicle and upon the assigned deceleration value for the lead vehicle. The projected travel range for the host vehicle is compared with the projected travel range for the lead vehicle, and an alert signal is generated to the host vehicle driver whenever an intersection of travel ranges therebetween is calculated.
In still another aspect, a forward impact warning system includes an algorithm for assessing the likelihood of a frontal collision between a host vehicle and a lead vehicle detected in the path of travel of the host vehicle. The algorithm has actual velocity and acceleration data for the host vehicle and the lead vehicle as inputs thereto. In addition, the algorithm further estimates a braking response of the driver of the host vehicle, and generates a projected travel range for the host vehicle, based upon the actual velocity data for the host vehicle and the lead vehicle, and further based upon the estimated braking response of the driver of the host vehicle. The algorithm also assigns a deceleration value for the lead vehicle, and generates a projected travel range for the lead vehicle, based upon the actual velocity data for the lead vehicle and upon the assigned deceleration value for the lead vehicle. A warning alert is in communication with the algorithm, the warning alert mechanism generating an alert signal to the driver of the host vehicle whenever the algorithm identifies an intersection between the projected travel range for the host vehicle and the projected travel range for the lead vehicle.
Referring to the exemplary drawings wherein like elements are numbered alike in the several Figures:
FIGS. 4(a) through 4(d) illustrate an exemplary embodiment of the threat assessment algorithm represented by a flow diagram; and
Referring initially to
As described in greater detail later, the particular level of sensitivity input selected by the host vehicle driver is used as an estimator of the braking response time of the driver. The threat assessment algorithm 12, during a given sample period will assess whether an alarm signal is sent to a warning alert block 16, which in turn provides an indication (e.g., an audio and/or visual signal) to the host vehicle driver that an impact is imminent.
Referring generally now to FIGS. 4(a) through 4(d), there is shown a flow diagram 100 of an exemplary, detailed embodiment of the operation of the threat assessment algorithm 12. In the description of the particular algorithm embodiment that follows, the flow diagram 100 illustrates in the nomenclature, constants, etc., of the threat assessment algorithm 12 in pseudo-code. However, it should be understood that any constants presented therein are exemplary in nature, and thus should not be used to interpret the algorithm in any limiting sense. Rather, the constants are primarily used to tune the algorithm for a specific vehicle and general customer profile and, as such, may vary from application to application.
As will be later understood from the flow diagram 100, several parameters are used in the implementation of the threat assessment algorithm 12, and are first outlined herein in greater detail. Generally speaking, there are three unknown parameters used to calculate and estimate the kinematics of vehicles. These parameters include the host vehicle's total response time to a warning, the acceleration/deceleration of the lead vehicle, and the acceleration/deceleration of the following vehicle.
The host vehicle's total response time in turn has three basic components. These components include the driver response time, the system response time and the brake response time. The system response time is characterized by the delay in detecting and verifying the presence of an object in the frontal area of the vehicle, then determining if the object is in the path of the vehicle. Then, the threat assessment situation is determined and, finally, a warning is issued if needed. The brake response time is the delay in the brake system to build up the pressure in the hydraulics to apply the brakes. Stated differently, the brake response time is the time delay from the instant the driver presses the brake pedal to the instant that affects the brakes. Thirdly, the driver response time is the time delay from the moment a warning is issued by the FCW system (assuming the warning is recognized by the driver) to the instant the driver executes an evasive action, such as braking and/or steering.
While both the system response time and brake response time are deterministic in nature, the driver response time is not. Depending upon the physiological and/or psychological state of the driver, the driver response time may vary, sometimes significantly, from one driver to another. For example, it has been established that there are variations in response time among age and gender groups. Accordingly, the system 10 provides a means for selecting a system sensitivity level that reflects the personal driving preference of the host vehicle driver, from aggressive to conservative in multiple gradings. The particular sensitivity setting chosen by the driver is used to determine an estimate for the driver response time.
Lead vehicle acceleration is another parameter that is estimated. First, the instantaneous lead vehicle acceleration/deceleration may be determined by directly measuring or computing the host vehicle (or following vehicle) acceleration, and then measuring or computing the relative acceleration between the host and lead vehicles. In either case, the instantaneous acceleration of the host vehicle is determined, such as through the use of a longitudinal accelerometer. This approach provides superior accuracy, but is relatively expensive due to the added cost of the accelerometer.
Alternatively, a second technique of computing of the host vehicle acceleration is based on successive speed measurements taken at known intervals. However, this approach is susceptible to noisy results that may be unacceptable in certain situations. While suitable filtering could minimize the noise in the computation, a downside associated therewith is the time delay. Similarly, the relative acceleration between the host and the lead vehicles can either be measured or computed. Measuring this parameter using radar is a relatively expensive approach. However, a more practical approach is to compute the relative acceleration from relative velocity (one of the parameters already measured by the forward looking sensor/radar), as well as the rate of these measurements, thus yielding the current acceleration/deceleration of the lead vehicle.
By the time the instantaneous acceleration is determined, it is possible that the driver of the lead vehicle could already be executing a braking maneuver that might render the threat assessment algorithm ineffective. As such, the algorithm will further take into consideration a prediction of how the lead vehicle driver will behave in the future with respect to braking. In this respect, statistical studies have established that 98 percent of vehicles brake at a rate of 0.2 g or less when the driver brakes. Thus, at any given time, it is assumed that the lead vehicle is about to brake at this default rate, representing a worst-case condition. During most sample times and braking activity of the lead vehicle will brake around the 0.2 g value. For the statistically few times the lead vehicle brakes at a higher value. Once a given threshold is exceeded, the measured/computed value will be used in the threat assessment algorithm 12. It will be appreciated, however, that a different default value for the braking of the lead vehicle may be used, depending upon the particular vehicle application.
Finally, the threat assessment algorithm 12 uses host vehicle acceleration estimation. While instantaneous vehicle acceleration is the easiest of the parameters to measure, predicting how the driver will respond once an alert is generated is a more complicated matter. For example, the host vehicle could be cruising at a constant speed (i.e., at zero acceleration) when, due to slower or stationary vehicles/objects in the predicted path of the host vehicle, an alert could be generated. As a result of the alert, the driver will likely apply the brakes, but the level of braking applied in general is not likely to be consistent with other braking situations. Experiments conducted with a number of drivers have shown that the driver's braking behavior depends on how fast the host vehicle is traveling as well as the closing speed between the host vehicle and lead vehicle.
Thus, in the present algorithm embodiments, a driver's braking behavior is classified into a finite number of cases for practical purposes. For example, when the lead vehicle is stationary and the host vehicle is closing in on the lead vehicle, an alert is produced at a certain some range and the driver thereby responds with a certain brake force. If the lead vehicle is moving and the host vehicle is closing in on the lead vehicle at very low range rate, an alert is still produced at a certain range. In this case however, the driver's brake force is like quite different than in the former case. As such, a number of cases have been identified wherein the driver's behavior exhibits a different braking level, depending on the host vehicle speed and closing speed.
Returning now to FIGS. 4(a) through 4(d), the threat assessment algorithm 12 as embodied in the flow diagram begins upon entry at start block 102, where the process is entered if the velocity of the host vehicle is greater than a preset constant. Then, above discussed data parameters are received for the present sample time at block 104. As indicated generally at 106, the algorithm initially runs through a series of exit criteria wherein, if any of the inquiries are answered in the affirmative, then the routine exits until the next sample time. Such inquiries include (but are not necessarily limited to) whether the driver of the host vehicle is already braking above a certain threshold value (block 108), whether the lead vehicle is actually an oncoming vehicle (block 110), whether the lead vehicle is “opening” or pulling away from the host vehicle (block 112), whether the lead vehicle is stationary while the host vehicle is beyond a certain range (block 114—in the event that the sensing device may not be able to distinguish the closest in path vehicle as on or above the same surface/level such as due to overpasses, bridges, signs, etc.), and whether the host vehicle is accelerating greater than a certain threshold, indicating the host vehicle driver's intent to overtake the lead vehicle (block 116).
Assuming that none of the exit criteria are met, the algorithm proceeds to FIG. 4(b) where, as indicated generally at 118, an operating region for the host and lead vehicle is established, using the velocity and acceleration of the host and lead vehicle. When the operating region is established, a series of constants are assigned (under one of blocks 120a, 120b, 120c, 120d) for use in calculating the estimated braking (af) of the host vehicle, shown in block 122. Then, if af is found to be outside an established range, than either a lower limit or an upper limit is set for af, as shown in blocks 124 and 126, respectively. It should be noted that the depicted illustration of the operating region is exemplary in nature, and may be further refined such as by implementing a continuous function for determining af in block 122.
In FIG. 4(c), the computed estimated value of af is compared with the actual vehicle acceleration/deceleration value af (actual), as shown at block 128. If af (actual) is less than the estimated af, then the host vehicle acceleration used in subsequent computations af (star) is set to af (actual) at block 130. Otherwise af (star) is set to the estimated value af at block 132. Continuing to block 132, it is determined if the lead vehicle is stationary by comparing its velocity, V1, to a threshold value. If the lead vehicle is moving, then either the actual deceleration value is used or the assumed deceleration (−0.2 g) is used, as discussed earlier.
The remaining portions of the threat assessment algorithm 12 are directed toward the projected paths of the lead and host vehicles, using the values calculated and assigned above. Specifically, the deterministic and the estimated data are used to compute a range profile of the host and the lead vehicles over time is computed. Each of the range profiles is a monotonically increasing function, which will asymptotically reach a constant value. The asymptotic values represent the range at which both vehicles come to a full stop, assuming behavior in accordance with their predicted decelerations as well as the vehicle dynamics data.
If the data indicates that the lead vehicle will come to a stop at a further range than the host vehicle, then this is suggestive that there will not be an impact between the two, although this is not necessarily the case. On the other hand, if the range profiles determine that the lead vehicle will come to a stop at a closer range than the following vehicle, then an impact is likely at or before the final stopping point, and an alarm indication is given. In this regard, the algorithm first determines whether the lead vehicle is moving or is stationary, as shown at block 134. If the lead vehicle is stationary, its final stopping position is the current position, and the decision on issuing a warning simply comes down to whether the host vehicle will come to a stop at a point before the location of the stationary lead vehicle. If not, the alert warning is “ON” at block 136, and the algorithm exits. If the host vehicle is projected to come to a stop before the lead vehicle, the alert warning is “OFF” at block 138, and the algorithm exits.
On the other hand, if the lead vehicle is also moving, then a projected stopping range for both vehicles is computed, shown at block 140. If the projected stopping point of the lead vehicle is less than the projected stopping point of the host vehicle, then the alert warning is “ON” at block 142, and the algorithm exits.
However, even if the final projected stopping point of the lead vehicle is not less than the projected stopping point of the host vehicle, the entire trajectory for each vehicle is analyzed, as there is still the possibility of an impact at some intermediate point prior to the final projected stopping points. In this event, the algorithm then proceeds to FIG. 4(d) where, as generally indicated at 144, it is determined whether the trajectories of the two vehicles intersect at any given point in time before the stopping points are reached. If the trajectories are projected to intersect, then the alert is “ON”; if not, then the alert is “OFF” and the algorithm finally exits.
The intersection of trajectories and the computation of vehicle ranges to a stopping point, as performed by the threat assessment algorithm is perhaps best illustrated in a graphical manner as shown in
It will be noted that the curve for the lead vehicle is a constant horizontal line, since it is stationary. If the driver of the follow vehicle applies the brakes in the predicted manner, the follow vehicle will decelerate as reflected by the follow vehicle curve until it comes to a full stop at around the 5 second mark. As can be seen, the follow vehicle comes to a stop at a range less than the stationary position of the lead vehicle and, as such, no warning is issued during this sample time. Again, in the calculation of the follow vehicle curve, the driver's braking behavior is estimated, based upon the selected sensitivity level. For purposes of illustration, a driver delay of 1.6 seconds is chosen, which is roughly a mid-level sensitivity setting. It will be noted that, prior to the driver's braking input at about 1.6 seconds, the follow vehicle range curve is linear, indicating a constant velocity with no deceleration. Once the brakes are applied, the eventually come to a full stop in a non-linear manner in about 5 seconds. Again, since the two curves do not intersect, there is no likelihood of an impact with the lead vehicle, and thus no warning will be given.
In
Finally,
It will thus be appreciated that the above described threat assessment algorithm (configured so as to take into account predicted host vehicle driver's behavior) contributes to a robust FCW system that results in reduced incidents of false alarms, as well as missed detections, which in turn increase the overall effectiveness of the system. Specifically, this algorithm uses the estimated driver braking behavior to establish certain parameters used in computation of the vehicle kinematics to determine if a warning signal is issued to the driver.
As will also be appreciated, the disclosed invention can be embodied in the form of computer or controller implemented processes and apparatuses for practicing those processes. The present invention can also be embodied in the form of computer program code containing instructions embodied in tangible media, such as floppy diskettes, CD-ROMs, hard drives, or any other computer-readable storage medium, wherein, when the computer program code is loaded into and executed by a computer or controller, the computer becomes an apparatus for practicing the invention. The present invention may also be embodied in the form of computer program code or signal, for example, whether stored in a storage medium, loaded into and/or executed by a computer or controller, or transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. When implemented on a general-purpose microprocessor, the computer program code segments configure the microprocessor to create specific logic circuits.
While the invention has been described with reference to a preferred embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
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