United States Patent [19]
`Henderson et al.
`
`II ~11111111.1111
`
`US005714927 A
`[11] Patent Number:
`[451 Date of Patent:
`
`5,714,927
`Feb.3, 1998
`
`[54] METHOD OF IMPROVING ZONE OF
`COVERAGE RESPONSE OF AUTOMOTIVE
`RADAR
`
`[75]
`
`Inventors: Mark Ford Henderson, Kokomo;
`Michael John Shorkey, Noblesville,
`both of Ind.; David James Lee, Clover,
`S.C.; Thomas Hays Savchick.
`Noblesville, Ind.
`
`[73] Assignee: Delco Electronics Corporation,
`Kokomo, Ind.
`
`[21] App1. No.: 762,090
`
`Dec. 9, 1996
`
`[22] Filed:
`Int. CL 6
`....................................................... B60Q 1/00
`[51]
`[52] U.S. Cl ............................ 340/435; 340/903; 367/909
`[58] Field of Search ..................................... 340/435, 903,
`340/904. 901. 905; 3481148, 149; 342/42;
`180/167; 367/909
`
`[56]
`
`References Cited
`
`U.S. PPJENT DOCUMENTS
`
`5,521,579
`5,530,447
`5,538,495
`5,594,412
`
`5/1996 Bemhan:l ................................. 340/901
`6/1996 Henderson et al.
`...................... 342no
`7/1996 Ben Lnlu ................................ 340/904
`1/1997 Matsumoto ............................. 340/903
`
`afHER PUBLICATIONS
`
`"Visual Indicator for a Commercial Side Detection System,"
`Research Disclosure #37024, Feb. 1995.
`
`Primary Examiner-Jeffery Hofsass
`Assistant Examiner-Anh La
`Attorney, Agent, or Finn-Jimmy L. Funke
`ABSTRACT
`[57]
`
`Side detection radar utilized on a host vehicle for covering
`a blind spot in a vehicle mirror view produces alert com(cid:173)
`mands resulting in signals which have gaps due to poor radar
`reflectivity of portions of a target. To fill these gaps to
`produce a steady alert signal when a target vehicle is in radar
`view and to extend the perceived zone of coverage, a
`variable sustain time is added to each alert signal which
`exceeds a threshold value. The sustain time varies as an
`inverse function of the relative vehicle speed and the thresh(cid:173)
`old value varies as an inverse function of vehicle speed. If
`the alert signal is shorter than the threshold value, then a
`minimized hold time can be applied.
`
`5,313,335
`5,349,430
`
`5/1994 Gray et al ............................... 340/903
`9/1994 Yamamoto et al ..................... 180/167
`
`12 Claims, 3 Drawing Sheets
`
`IPR2016-00293 - Ex. 1001
`Toyota Motor Corp., Petitioner
`
`1
`
`

`
`U.S. Patent
`
`Feb. 3, 1998
`
`Sheet 1 of 3
`
`5,714,927
`
`FIG -1
`
`... ~-20
`
`I
`
`I
`
`28
`
`TRANSCEIVER
`
`-----------------'
`24
`18- .I
`
`I
`
`FIG- 2
`
`1
`I
`, ... : SIGNAL PROCESSOR :
`I -
`-
`-
`-
`-
`-
`-
`-
`-
`-
`-
`-
`-
`-
`-
`-
`-
`-
`I
`
`OTHER
`INTERFACE
`
`FIG- 3a
`
`36
`
`-------4-r---~,-----·
`j
`jwHEELj
`j
`'
`'WELLS'
`·
`~~~~
`-1 1- ~ 1-
`i i
`i i
`
`FIG- 3b
`
`RETURN
`SIGNAL FIELD
`STRENGTH
`
`FIG- 3c
`
`RAW
`ALERT
`
`FIG· 3d SUSTAINED
`
`ALERT
`
`0
`
`:J
`
`TIME
`
`TIME
`
`~48
`
`TIME
`
`.,...--- 46
`
`--+!
`
`2
`
`

`
`U.S. Patent
`
`Feb.3, 1998
`
`Sheet 2 of 3
`
`5,714,927
`
`FIG- 4
`
`56
`
`52
`
`Vhost . .
`
`Vtarget
`< Vhost
`
`Vtarget
`> Vhost
`
`FIG- 6
`
`300 1-------
`200
`
`TIME
`(msecs)
`100
`
`THRESHOLD
`
`r··--···········-
`:
`HOLD ----.\ _____ --------······:
`
`0
`
`20
`
`30
`
`40
`
`50
`
`60
`
`VEHICLE SPEED (MPH)
`
`FIG -7
`
`SUSTIME
`{sec)
`
`2
`
`1
`
`0
`
`I
`
`1
`
`0
`
`I
`3
`2
`1
`RELATIVE SPEED (M/sec)
`
`I
`
`I
`4
`
`3
`
`

`
`U.S. Patent
`
`Feb. 3, 1998
`
`Sheet 3 of 3
`
`5,714,927
`
`RADAR TRANSCEIVER
`OUTPUTS
`
`HOST VEHICLE SPEED
`
`68
`
`66
`
`YES
`
`74
`
`TURN ON
`ALERT DEVICES
`
`SELECT MINIMUM ALERT TIME
`"THRESHOLD"
`f(SPEED)
`
`SELECT MINIMUM SUSTAIN
`TIME DELAY "HOLD"
`f(SPEED)
`
`SELECT VARIABLE MINIMUM
`SUSTAIN TIME "SUSTIME"
`f(RELATIVE SPEED)
`
`78
`
`80
`
`82
`
`86
`
`USE SUSTAIN TIME =
`SUSTIME
`
`USE SUSTAIN TIME=
`HOLD
`
`TURN OFF ALERT DEVICES
`AFTER SUSTAIN TIME
`
`88
`
`FIG- 5
`
`4
`
`

`
`1
`METHOD OF IMPROVING ZONE OF
`COVERAGE RESPONSE OF AUTOMOTIVE
`RADAR
`
`5,714,927
`
`FIELD OF THE INVENTION
`This invention relates to the control of side detection
`automotive radar systems and particularly to a method of
`controlling an alarm or alert indicator to enhance the per(cid:173)
`ceived coverage of a blind spot.
`BACKGROUND OF THE INVENfiON
`Vehicle mounted near object detection systems utilize
`various means for detecting and identifying targets of inter(cid:173)
`est in their vicinity. The target information is useful in
`collision warning systems wherein the system notifies the
`vehicle operator that an object is positioned to present
`collision potential. While many forms of near object detec(cid:173)
`tion systems presently exist, generally those utilizing radar
`transceivers and related signal processing techniques do the
`best job of reliably detecting targets within range over
`variations in environment.
`Such near object detection systems use radar, preferably
`microwave radar, to "illuminate" a target of interest by
`transmitting energy with certain signatory characteristics
`and then monitoring for similar return signals reflected from
`an object. Microwave transmissions with approved power
`levels and spectra generally experience lower overall attenu(cid:173)
`ation with weather and are less susceptible to "scattering"
`effects than are other transmission media utilized by systems
`of this type. Properties of the reflected signal are analyzed
`using established (proprietary) techniques to determine rel(cid:173)
`evance to the interests of the driver of a vehicle equipped
`with such a system. Information derived from the returned
`radar signals include target range and range rate. Using 35
`platform or host vehicle speed as a system input and as a
`reference, target data can be analyzed and the signal pro(cid:173)
`cessor can make reasonable decisions whether to "report"
`the target or not. Accurate target discrimination capabilities
`are required of such systems to reduce "false alarms" which 40
`are an annoyance to the driver in collision warning system
`scenarios. The source of such false alarms can be clutter or
`radar reflections from roadside objects such as guard rails,
`walls or other stationary objects.
`Another source of annoyance is alert dropout (the signal 45
`light or audio turns off) occurring due to variable reflectivity
`of a target vehicle and its effect on the strength of the return
`radar signal. A vehicle wheel well, for example, may help
`create a weak return signal and subsequently an alert drop(cid:173)
`out. Dropouts are most common during station-keeping 50
`events where the host and target vehicle travel adjacent each
`other at about the same velocity, and in particular when a
`radar collision warning sensor is directed into low reflec(cid:173)
`tivity regions of a target vehicle and/or receives minimally
`reflected signals from the target vehicle. The clear majority 55
`of vehicular targets in near field proximity reflect radar
`signals across their distributed surfaces which can exceed a
`system's detection thresholds. However, any vehicular tar(cid:173)
`get has a finite probability of producing return signals with
`low efficiency through characteristics of absorption or ran- 60
`dom scattering. Weak return signals could fall below system
`detection thresholds, resulting in perceivable dropouts as
`seen by the driver. Higher relative velocities generally
`contain enough Doppler signal to exceed system thresholds;
`therefore dropouts on "passing targets" can be more natu- 65
`rally minimized than during low speed or "stationary"
`passing events.
`
`2
`Still another annoyance is an alert signal flicker which
`occurs when a distributed target just enters or just clears a
`detection zone and both reflected field strength and relative
`velocity decay to near zero. Variations in reflected energy
`5 may cross and recross system threshold settings, causing the
`alert to oscillate in an annoying manner.
`
`SUMMARY OF THE INVENTION
`
`15
`
`10
`
`It is therefore an object of the invention to improve the
`zone of coverage response of side detection radar. A further
`object is to prevent or minimize dropouts due to small
`reflected signals during station keeping events. Another
`object is to minimize annoying alert activity when passing
`stationary or slow moving targets.
`The time of an alert signal activation is measured and
`compared to a threshold. The threshold can either be fixed or
`vary inversely with host vehicle speed. When the alert time
`is less than the threshold. the signal turn-off is delayed for
`20 a minimal hold time. The minimal hold time can be either a
`fixed value or varied intentionally with vehicle speed. The
`minimal hold time is generally only a fraction of a second.
`but in some applications it is desirable to elongate the
`minimal hold time as vehicle speed is increased to minimize
`25 flicker effects. When the alert time is equal to or greater than
`the threshold, a longer sustain time is applied to hold the
`signal on, and is generally sufficient to bridge the dropout
`periods due to low reflectivity during station keeping. The
`sustain time varies according to the absolute value of the
`30 relative velocity between the target and host vehicles and
`ranges from a fraction of a second at high relative velocity
`up to a few seconds at low relative velocity. This improves
`the zone of coverage as perceived by the vehicle driver, and
`can increase the perceived alert distance as well.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The above and other advantages of the invention will
`become more apparent from the following description taken
`in conjunction with the accompanying drawings wherein
`like references refer to like parts and wherein:
`FIG. 1 is a diagram of a vehicle equipped with side
`detection radar;
`FIG. 2 is a schematic diagram of a side detection radar
`system for practicing the method of the invention;
`FIG. 3a is a plan view of a target vehicle;
`FIGS. 3b. 3c and 3d are signal waveforms produced by
`the system of FIG. 2 and representing the target vehicle. and
`implementing the method of the invention;
`FIG. 4 is a diagram of a host vehicle and target vehicles
`illustrating actual zones and perceived extensions of radar
`coverage according to the invention;
`FIG. 5 is a flow chart representing an algorithm for
`carrying out the invention;
`FIG. 6 is a graph showing time thresholds and hold
`periods as a function of vehicle speed; and
`FIG. 7 is a graph of variable sustain time as a function of
`relative vehicle speed.
`
`DESCRIPTION OF THE INVENTION
`The ensuing description is directed to a vehicle radar side
`detection method and apparatus to cover a blind spot which
`is not visible to the driver in the side view mirrors. Such a
`system is useful for both trucks and automobiles.
`Referring to FIG. 1, a motor vehicle 10 (herein called a
`host vehicle), in particular a large truck. has a side view
`
`5
`
`

`
`5,714,927
`
`3
`mirror 12. and side detection radar antennae 14. The anten(cid:173)
`nae are part of a side detection system 16. The side view
`mirror 12 provides a limited view of the lane adjoining the
`lane used by the host vehicle. leaving the possibility that an
`object is present in a blind spot. The antennae are effective
`to view a region to the side of the vehicle to detect another
`vehicle or other object (herein called the target or target
`vehicle) in the blind spot The side detection system 16
`senses the presence of an object in the adjoining lane via
`radar signals transmitted and received at the side antennae
`14. The system warns the operator of such objects by
`warning lamps or alert signals which may be on or within the
`mirror 12 and/or by an audible signal.
`FIG. 2 is a schematic diagram of the detection system 16.
`A signal processor 18 is coupled to a transceiver 20 so that
`the signal processor can control the transmission and can
`also receive data generated by the transceiver. The trans(cid:173)
`ceiver 20 includes a transmit unit 22 and a receive unit 24.
`each comprising a monolithic microwave integrated circuit.
`Transmit and receive antennae 14a and 14b are coupled to
`the transmit and receive units. respectively.
`The signal processor 18 includes a digital signal processor
`(DSP) 26 connected to a microprocessor 28. A pulsed speed
`signal is an input to the microprocessor and other vehicle
`interfaces are coupled via buffers 30 to the microprocessor.
`An output port of the microprocessor carries an alert signal
`to the alert signal devices.
`The speed signal comprises pulses at a frequency propor(cid:173)
`tional to vehicle speed and is available from either an
`on board engine control module. anti-lock brake wheel speed
`sensors. a separate vehicle speed supply module. or via an
`integrated vehicle data bus. Preferably the speed signal
`supplies about 4000 pulses per mile over a serial or parallel
`data bus. The microprocessor counts vehicle speed pulses
`over time and translates this into host vehicle speed. Target
`discrimination algorithms use the speed information in
`determining whether a detected object is a hazard. This is
`discussed in detail in U.S. Pat. No. 5.530.447 entitled
`"Blind-Zone Target Discrimination Method and System for
`Road Vehicle Radar". assigned to the assignee of this
`invention and which is incorporated herein by reference. The
`DSP 26 does the radar calculations involving targets within
`the system zone of coverage. The DSP measures range rate
`of each target. estimates range in "X" and "Y" directions
`from the antennae. and supplies target track information.
`The relative speed of the host vehicle and the target is also
`calculated. This information is sent to the microprocessor 28
`which, knowing vehicle speed, compares data within the
`structure of the target discrimination algorithms and makes
`a decision to report ''valid" targets to the operator or to not so
`report targets which are of little interest to the operator.
`The waveform of FIG. 3b shows a typical radar field
`strength return signal from a target vehicle 36 in FIG. 3a.
`The wheel wells and the front and rear edges of the vehicle
`36 profile afford weak return signals 38 which often cross 55
`below the threshold while the remainder of the vehicle 36
`return strong signals 40. The target discrimination algo(cid:173)
`rithms process the signal to issue alert commands 42 shown
`in FIG. 3c: gaps 44 between the alert commands are dropout
`events related to the weak field strength portions 38 of the
`signal. Without a sustaining action the visual or audio alert
`signal will mimic the alert commands 42. It is preferred that
`there be no dropout events in the alert signal corresponding
`to the target vehicle to achieve an uninterrupted or sustained
`alert signal46 as shown in FIG. 3d. This is accomplished in
`most cases by judiciously sustaining each individual alert
`signal42 by the process described below. Generally most or
`
`4
`all of the gaps 44 are removed and any remaining gaps 44
`are minimized by this method which is especially successful
`at higher relative speeds where the target discrimination
`algorithm is most effective. At the same time. because of the
`5 sustaining effect. the sustained alert signal 46 is longer by a
`period 48 than the alert command. thereby extending the
`zone of coverage as perceived by the driver.
`The improved coverage is illustrated in FIG. 4 wherein a
`host vehicle SO having a speed of Vhost passes a target
`10 vehicle 52 having a speed of Vtarget less than Vhost. The
`radar covers a zone 54 to provide a raw alert signal when the
`vehicle 52 is still in that zone. Due to the period 48 of the
`sustained signal. a zone extension 56 is created to to
`effectively increase the zone of coverage. The amount of the
`extension is determined by the relative speeds of the
`15 vehicles and the time period 48. The same effect is produced
`when the host vehicle SO is passed by a target vehicle 60
`having a speed Vtarget greater than Vhost. Again the zone
`62 actually monitored by radar is supplemented by a zone
`extension 64 due to the sustain period 48. In each case, the
`20 driver of the host vehicle has greater assurance that the blind
`spot is free of an object
`The algorithm for sustaining the alert signal is generally
`represented by the flow chart of FIG. S wherein the func(cid:173)
`tional description of each block in the chart is accompanied
`25 by a number in angle brackets <nn> which corresponds to
`the reference number of the block. It will be understood that
`the algorithm is repetitively executed, say. one loop once
`each 20 msec. The radar transceiver outputs <66> and the
`host vehicle speed signal <68> are input to the signal
`30 processor where the radar operation algorithms <70> utilize
`a target discrimination program to determine whether to
`activate the alert and issue an alert command accordingly. If
`an alert command is present <72> the alert devices are
`turned on <7 4> and the program returns to the operating
`algorithm and activation is continued in each loop until the
`35 alert command ceases. Then, if the alert device is still active
`<76> three variables are determined. A minimum alert time
`threshold "THRESHOLD" is selected as a function of
`vehicle speed <78>. a minimum sustain time delay "HOLD"
`is selected as a function of speed <80>, and variable sustain
`40 time "SUSTIME" is selected as a function of relative vehicle
`speeds <82>. If the alerts were active for at least the
`THRESHOLD time <84>. the SUSTIME value is used to
`delay alert turn-off <86>. and when SUSTIME expires the
`alerts are turned off <88>. However if the alerts were active
`45 for less than the THRESHOLD time, the alert turn-off is
`delayed only for the HOLD time <90>. It will be understood
`that when a sustain time has been selected. it will be
`decremented in subsequent loops until it expires or until
`reset by a new alert command.
`The suggested values of THRESHOLD and HOLD times
`are shown in the graph of FIG. 6. These are calibration
`values for one application and are useful to illustrate the
`principle of the alert sustain method. FOR example the
`THRESHOLD values decrease stepwise from about 300
`msec at low speed (below 15 mph) to about 160 msec at high
`speed (above 55 mph). The THRESHOLD is high at low
`speeds because the target discrimination is less robust at low
`speeds and it is desired to not emphasize the shorter alerts
`since they may be false alarms; at higher speeds the dis-
`60 crimination is more robust and the alerts should be empha(cid:173)
`sized. Accordingly the HOLD values are only 20 rnsec from
`0 to 45 mph and may optionally be 0 rnsec; at 45 to 55 mph
`the HOLD value is 100 msec and at higher speeds it is 200
`msec. These values at higher speeds help to mask flickers
`65 due to multiple reflections and/or weak signals from the
`front or rear of a target vehicle and thus to fill in gaps in the
`alert signal.
`
`6
`
`

`
`5,714,927
`
`5
`The FIG. 7 graph shows suggested values of SUSTIME
`versus absolute relative vehicle speed. These values vary
`stepwise from about 2.5 seconds at very low relative speed
`to about 0.6 seconds at relative speed above 3 meters/sec.
`These are scaled to allow roughly a 10 foot extension of the 5
`zone coverage in each speed range. It will be noted that these
`times are much larger than the HOLD times. so that the alert
`duration above the threshold will be greatly extended, the
`gaps as well as gaps as well as increasing the perceived zone
`of coverage. Since dropouts are most common during 10
`station-keeping events where the relative speed is small. the
`large SUSTIME values help to overcome the tendency to
`dropout The lower SUSTIME values at higher relative
`velocities are appropriate since at such relative speeds there
`is usually enough Doppler information to exceed system 15
`thresholds.
`It will thus be seen that the method of sustaining alert
`signals beyond that commanded by the radar operating
`algorithms has the effect of filling in gaps in alert signals to
`produce. in most cases, a steady alert signal while a target is 20
`in view of the radar. and at the same time increases the
`perceived zone of coverage by extending the length of the
`alert signal. The alert sustaining method also prevents signal
`flicker which occurs when a distributed target clears a
`detection zone.
`The embodiments of the invention in which an exclusive
`property or privilege is claimed are defined as follows:
`1. In a radar system wherein a host vehicle uses radar to
`detect a target vehicle in a blind spot of the host vehicle
`driver. a method of improving the perceived zone of cov- 30
`erage response of automotive radar comprising the steps of:
`determining the relative speed of the host and target
`vehicles;
`selecting a variable sustain time as a function of relative 35
`vehicle speed;
`detecting target vehicle presence and producing an alert
`command;
`activating an alert signal in response to the alert com(cid:173)
`mand;
`at the end of the alert command, determining whether the
`alert signal was active for a threshold time; and
`if the alert signal was active for the threshold time.
`sustaining the alert signal for the variable sustain time.
`
`6
`wherein the zone of coverage appears to increase
`according to the variable sustain time.
`2. The invention as defined in claim 1 wherein the variable
`sustain time is an inverse function of the relative vehicle
`speed.
`3. The invention as defined in claim 1 including:
`varying the sustain time as an inverse function of the
`relative vehicle speed in the range of a fraction of a
`second to a plurality of seconds.
`4. The invention as defined in claim 1 including:
`varying the sustain time stepwise as an inverse function of
`the relative vehicle speed for a plurality of relative
`speed ranges.
`5. The invention as defined in claim 4 including:
`varying the sustain time sufficiently to extend the per(cid:173)
`ceived zone of coverage about the same amount in each
`range.
`6. The invention as defined in claim 1 including:
`determining host vehicle speed; and
`selecting the threshold time as a function of the host
`vehicle speed.
`7. The invention as defined in claim 1 wherein if the alert
`signal was active for a period less than the threshold time.
`sustaining the alert signal for a minimized hold time to
`25 minimize driver perception of annoyance alarms.
`8. The invention as defined in claim 1 wherein if the alert
`signal was active for a period less than the threshold time.
`sustaining the alert signal for a hold time which is a function
`of host vehicle velocity.
`9. The invention as defined in claim 1 including:
`determining host vehicle speed;
`sustaining the alert signal for a hold time if the alert signal
`was active for a period less than the threshold time; and
`varying the hold time and the threshold time as a function
`of vehicle speed.
`10. The invention as defined in claim 9 wherein the hold
`time increases at high vehicle velocity.
`11. The invention as defined in claim 9 wherein the hold
`time is at or near zero at low vehicle velocity and increases
`40 at high vehicle velocity.
`12. The invention as defined in claim 9 wherein the hold
`time is shorter than the variable sustain time.
`
`* * * * *
`
`7