BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a vehicle including a rear collision system;
FIG. 2 is a plan view of a leading vehicle and a following vehicle;
FIG. 3 is a block diagram of a control system for warning a following vehicle of a potential collision with a leading vehicle, according to an embodiment of the present invention; and
FIG. 4 is a flow chart diagram showing the operation of a collision warning algorithm of the invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
The following discussion of the embodiments of the invention directed to a control system for warning a following vehicle of an potential collision with a leading vehicle is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses.
FIG. 1 is a top view of a vehicle 10 including a controller 12 and a rear vision system 14. The rear vision system 14 includes radar sensors 16 that emit radar beams 18 behind the vehicle 10. In one particular design, the sensors 16 are mid-range sensors that emit the beams 18 to about 15 meters. Various vehicle collision warning systems are known in the art that employ radar sensors for collision avoidance and the like. The present invention proposes using such systems in combination with a system that alerts a following vehicle of a potential collision with the vehicle 10. In other collision avoidance systems, the radar sensors 16 can be replaced with other types of sensors, such as ultrasonic sensors.
FIG. 2 is a diagram of a leading vehicle 22 and a following vehicle 24 that are a distance R apart. The present invention proposes an algorithm for determining if the following vehicle 24 is closing too quickly on the leading vehicle 22 and providing an alert to the driver of the following vehicle 24 of a potential collision. To perform the calculations, the algorithm will use various parameters including the distance R, the closing rate of the following vehicle 24, the velocity VL of the leading vehicle 22, the velocity VF of the following vehicle 24, the position XL of the leading vehicle 22 and the position XF of the following vehicle 24. As would be well understood to those skilled in the art, the rear vision system 14 and the controller 12 that may be equipped on the leading vehicle 22 would be capable of determining the distance R and the distance rate between the leading vehicle 22 and the following vehicle 24.
For the algorithm of the invention, the following equations can be used. The distance R is defined as:
R=X
L
−X
F
−L
L (1)
Where LL is the length of the leading vehicle 22.
A desired spacing between the leading vehicle 22 and the following vehicle 24 is determined based on the velocity VL of the leading vehicle 22 and a time gap constant τ as:
Rd=VLτ (2)
A distance error Rerr is defined as the difference between the desired distance Rd and the actual distance R as:
R
err
=R
d
−R (3)
The relative velocity ΔV or (VL−VF) between the leading vehicle 22 and the following vehicle 24 is defined as:
Equations (1)-(4) can be used to provide the following state space formulation that represent the state space model for the leading vehicle 22 and the following vehicle 24.
Where aL and aF are the acceleration of the leading vehicle 22 and the following vehicle 24, respectively. This can be written in compact state space notation as:
{dot over (x)}=Ax+ba
L
+dω (9)
Where x is system states of Rerr and ΔV, A is a constant matrix, b and d are constant vectors and ω is an error term because the following vehicle acceleration will not be known, although it can be estimated.
The control strategy for generating the warning to the following vehicle 24 depends on the distance error Rerr and the relative velocity ΔV between the leading vehicle 22 and the following vehicle 24. FIG. 3 is a block diagram of a control system 30, according to an embodiment of the present invention. The velocity VL of the leading vehicle 22 is sent to a desired distance processor 32 that calculates the desired distance Rd between the leading vehicle 22 and the following vehicle 24 based on equation (2). The desired distance processor 32 can also consider wheel slip for slick road conditions, such as wet or icy road conditions, so as to set the desired distance Rd accordingly. The relative velocity ΔV between the leading vehicle 22 and the following vehicle 24 is integrated by an integrator 34 to generate the distance signal R per equation (4) as the difference in the distance between the leading vehicle 22 and the following vehicle 24 changes. An estimate of the relative velocity provides additional information that can indicate if the following vehicle 24 is slowing down or a collision is imminent, and can be used to estimate the potential time of occurrence of a collision. This can be used to provide additional conditions at which to activate the various stages of warning alerts in vehicle pre-crash systems.
The desired distance Rd and the actual distance R between the leading vehicle 22 and the following vehicle 24 are compared by a comparator 36 to generate the distance error signal Rerr. A comparison processor 38 uses the error signal Rerr to determine whether the following vehicle 24 is closing too fast on the leading vehicle 22. If the error signal Rerr is greater than a first threshold, the system 30 may flash the hazard lights and/or the brake lights at box 40 to provide a collision warning to the driver of the following vehicle 24. If the error signal Rerr is greater than a second threshold, the comparison processor 38 may take other actions for an imminent collision, such as pre-tensioning seatbelts at box 42, closing the windows at box 44, priming the air bags at box 46, etc.
FIG. 4 is a flow chart diagram 50 showing the control algorithm of the invention for warning the driver of the following vehicle 24 in the manner as discussed above. At box 52, the algorithm reads the velocity VL of the leading vehicle 22, the distance R between the leading vehicle 22 and the following vehicle 24, and the relative speed ΔV between the leading vehicle 22 and the following vehicle 24. The algorithm then calculates the desired distance Rd and the error signal Rerr using equations (2) and (3) at box 54. The algorithm then determines if the error signal Rerr is greater than a first threshold RTH1 at decision diamond 56. In one embodiment, the threshold RTH1 may be about 5 meters. If the error signal Rerr is not greater than the threshold RTH1 then the algorithm returns to reading the signals at the box 52. If the error signal Rerr is greater than the first threshold RTH1, then the algorithm activates the hazard lights at box 58. The algorithm then determines whether the error signal Rerr is greater than a second threshold RTH2 at decision diamond 60, and if not, returns to reading the signals at the box 52. If the error signal Rerr is greater than the second threshold RTH2 at the decision diamond 60, then the algorithm takes the imminent collision actions, such as pre-tensioning the seatbelts, closing the windows, priming the air bags, etc. at box 62.
In an alternate embodiment of the present invention, the leading vehicle 22 does not include a rear vision system having radar sensors or ultrasonic sensors. In this embodiment, the leading vehicle 22 would flash the brake and/or the hazard lights based solely on the hardness of the braking of the vehicle by the vehicle operator of the leading vehicle 22. For example, a controller in the leading vehicle 22 may compare the brake pressure applied by the vehicle operator of the leading vehicle 22 to a predetermined threshold, and if that threshold is exceeded, provide the warning operation. Further, the amount of wheel slip can also be used in combination with the braking hardness to determine whether the brake lights and hazard lights will be flashed to warn the following drivers.
The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.
Patent Application
20070296564
