Communications: directive radio wave systems and devices (e.g. – Return signal controls external device – Radar mounted on and controls land vehicle
Reexamination Certificate
2003-05-23
2004-07-27
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Return signal controls external device
Radar mounted on and controls land vehicle
C342S071000, C342S072000, C342S077000, C342S107000
Reexamination Certificate
active
06768446
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Application
The present invention relates to a vehicle-mounted radar apparatus for detecting objects such as preceding vehicles, by transmitting and receiving radar waves such as millimeter-range radio waves.
2. Description of Prior Art
In the prior art, types of vehicle-mounted radar apparatus are known which are utilized as part of a vehicle control system such as a cruise control system) for collision prevention or for implementing a “following” function whereby a host vehicle equipped with the radar apparatus is controlled to follow an immediately preceding vehicle with a specific separation distance from that vehicle.
It is basically essential for a vehicle-mounted radar apparatus to be capable of detecting a target object such as a preceding vehicle which is directly in the vehicle lane of the host vehicle or which is moving in an adjacent vehicle lane but partially protrudes into the vehicle lane of the host vehicle, or which is in the process of “cutting in” ahead of the host vehicle (i.e., is moving from an adjacent vehicle lane into that of the host vehicle). To achieve such detection, it is necessary for the radar apparatus to be capable of substantially accurately determining the current lateral position of a target object and also the successive lateral positions which have been attained by that target object up to the current time point. The term “lateral position” of a target object as used herein signifies the lateral position of a width-center location on the target object in relation to a corresponding location on the host vehicle (i.e., lateral with respect to the direction of motion of the host vehicle). The term “width-center location” signifies a location midway between left and right sides of an object, such as a location midway between the opposing sides of a vehicle.
In the following it will be generally assumed that the radar apparatus is of FMCW (Frequency Modulation Continuous Wave) millimeter-wave type, although the principles of the invention are not limited to such a type. Each interval in which a transmitting/receiving operation of the radar apparatus is executed, with reflected waves being thereby received from one or more target objects and processing of resultant received signals then performed, will be referred to as a modulation interval.
As illustrated in the conceptual diagram of
FIG. 18A
, when a radar apparatus of a host vehicle
41
travelling along a straight path transmits radio waves along the direction indicated by the arrow line, the waves will be reflected from various different parts of a target object positioned directly ahead of the host vehicle, with the target object assumed here to be a preceding vehicle
50
. Locations from which the waves may be strongly reflected from the rear end of the preceding vehicle
50
are indicated by the black dots
60
. In general the waves will be most strongly reflected from various different parts of the target object, in successive modulation intervals. The received signals resulting from the reflected waves, in a modulation interval, are processed to obtain an estimate of the lateral position of the target object. However the obtained position will be determined by the locations of those portions of the target object from which the strongest reflections occur and so will not necessarily coincide with a width-center location on the preceding vehicle, and these portions from which the strongest reflections occur will change with time (for example, due to variations in the attitude of the target object with respect to the host vehicle).
As a result, when successive estimated lateral positions of a preceding vehicle are derived based upon such received radio waves, these will deviate from the actual lateral positions, with the amount of deviation varying with time. This is illustrated in the example of
FIG. 18C
, in which the curve “momentary position data” represents a series of estimated lateral position values for a target object such as the preceding vehicle
50
, obtained at respective successive modulation intervals. The curve designated “final lateral position data” express a corresponding series of successive estimated lateral positions for that target object which have been obtained by smoothing processing (e.g., low-pass filtering) of the momentary position data. The chain-line curve indicates the corresponding series of actual lateral positions of the target object, i.e., of the width-center location of the target object.
The aforementioned variations in the locations on a preceding vehicle from which the radio waves are reflected back to the radar apparatus are determined by factors such as shapes of the portions from which reflections occur, the materials constituting these portions, undulations in the road surface which affect the attitudes of the vehicles, etc. The strongest reflections will typically occur for example from the rear fender, rear reflector plates, the number plate, rear windshield, etc., of a preceding vehicle. As a result, in many cases, the variations in the momentary position values value may be much more extreme and irregular than for the case illustrated in FIG.
18
C. In that case, the final lateral position data which are obtained by smoothing the momentary position data will be unstable, and will deviate substantially from the successive lateral positions attained by the width-center location of the target object.
Such data are therefore not suitable for use by a vehicle control apparatus such as a cruise control apparatus, as a basis for automatic control of the host vehicle.
Furthermore as illustrated in the example of
FIG. 18B
, the host vehicle
41
may be moving along a vehicle lane
42
which is curved, in which case the orientation of a preceding vehicle will become skewed with respect to the host vehicle. As a result, an immediately preceding vehicle (i.e., which is travelling along the same vehicle lane as the host vehicle) will not be located directly ahead of the host vehicle, and reflected radio waves may be received from a side face of that preceding vehicle. Similarly, when a vehicle is driving in a vehicle lane which is adjacent to that of the host vehicle, such as the preceding vehicle
51
shown in
FIG. 18B
, then such side reflection waves may also occur. This further increases the amount of error which will be arise in lateral position values which are obtained by simply applying smoothing to the series of momentary position values.
More specifically, with the example of
FIG. 18B
, radio waves will be strongly reflected from the left side face of the preceding vehicle
51
and from portions of the rear end of that vehicle which are closest to the host vehicle
41
. For example, the arrow lines designated P
1
, P
2
in
FIG. 18B
represent peak levels of reflection, which occur at respectively different times, resulting in corresponding local extreme values of the momentary position data oriented in the leftward lateral direction, as illustrated in FIG.
18
D. However a peak-level reflection P
3
from the right side of the preceding vehicle
51
, i.e., from a part of that vehicle which is farther from the host vehicle than the left-side parts of vehicle
51
, results in a substantially smaller local extreme value of the momentary position data, corresponding to the rightward lateral direction.
In such a case, as illustrated in
FIG. 18B
, if the final lateral position data are simply obtained by smoothing the momentary position data, then the resultant data will not accurately represent the successive lateral positions of the width-center location of such a target object, but will strongly deviate towards the left side of the object (in the graphs of
FIGS. 17A
,
17
B, etc., the downward direction from the central axis of each graph corresponds to the leftward direction of position displacement, and the upward direction corresponds to the rightward direction of position displacement).
As a result of such errors in the lateral position data, it may be impossible to accurately judge whether a
Isogai Akira
Kumon Hiroaki
Tamatsu Yukimasa
Alsomiri Isam
Denso Corporation
Posz & Bethards, PLC
Tarcza Thomas H.
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