VWGoA - Ex. 1001
`Volkswagen Group of America, Inc., Petitioner
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`1
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`

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`US. Patent
`
`Feb. 3, 1998
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`Sheet 1 of 3
`
`5,714,927
`
`FIG - 1
`
`r”
`INTERFACE
`
`ALERT
`' SIGNALS
`
`VEHICLE
`SPEED
`
`OTHER
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`,
`
`SIGNAL PROCESSOR
`I __________________ I
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`_
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`------- 4-%---%+ ------
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`I
`-| ”I:
`________'
`'_
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`\A I
`——I
`I-—
`I
`I
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`FIG -3b
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`4°
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`38
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`4°
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`SIGNALFIELD
`STRENGTH
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`
`
`TIME
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`FIG-3c
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`1‘
`RAW
`0
`ALERT
`TIME
`
`42
`
`44
`
`r
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`42
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`SUSTAINED 1'
`+1 R48
`
`
`IoF|G.3d ALERT I
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`
`
`r46
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`2
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`

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`US. Patent
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`Feb. 3, 1998
`
`Sheet 2 of 3
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`5,714,927
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`56
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`52
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`THRESHOLD
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`64
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`VEHICLE SPEED (MPH)
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`FIG-7
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`SUSTIME
`(sec)
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`0
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`1
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`2
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`3
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`4
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`RELATIVE SPEED (M/sec)
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`3
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`

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`US. Patent
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`Feb. 3, 1998
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`Sheet 3 of 3
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`5,714,927
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`RADAR TRANSCEIVER
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`OUTPUTS
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`HOST VEHICLE SPEED
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`68
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`65
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`70
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`RADAR OPERATING
`ALGORITHM
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`72
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`NO
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`76
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`
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`ACTIVATE
`ALERT DEVICES?
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`ACTIVE?
`
`
`ARE
`ALERT DEVICES
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`
`
`TURN ON
`ALERT DEVICES
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`
`
`SELECT MINIMUM ALERT TIME
`"THRESHOLD"
`flSPEED)
`
`
`
`SELECT MINIMUM SUSTAIN
`TIME DELAY "HOLD"
`flSPEED)
`
`
`
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`SELECT VARIABLE MINIMUM
`SUSTAIN TIME "SUSTIME"
`f(RELATIVE SPEED)
`
`
`
`
` WERE
`
`
`ALERT DEVICES
`ACTIVE FOR >=
`THRESHOLD
`
`
`
`USE SUSTAIN TIME =
`SUSTIME
`
`
`
`
`
`USE SUSTAIN TIME:
`HOLD
`
`TURN OFF ALERT DEVICES
`AFTER SUSTAIN TIME
`
`4
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`

`

`1
`METHOD OF INIPROVING ZONE OF
`COVERAGE RESPONSE OF AUTOMOTIVE
`RADAR
`
`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-
`ceived coverage of a blind spot.
`BACKGROUND OF THE INVENTION
`
`Vehicle mounted near object detection systems utilize
`various means for detecting and identifying targets of inter—
`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-
`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-
`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-
`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
`platform or host vehicle speed as a system input and as a
`reference. target data can be analyzed and the signal pro-
`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
`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
`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-
`out. Dropouts are most common during station-keeping
`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-
`tivity regions of a target vehicle and/or receives minimally
`reflected signals from the target vehicle. The clear majority
`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—
`get has a finite probability of producing return signals with
`low efficiency through characteristics of absorption or ran-
`dom scattering. Weak return signals could fall below system
`detection thresholds. resulting in peroeivable 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—
`rally minimized than during low speed or “stationary”
`passing events.
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`5.714.927
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`2
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`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
`may cross and recross system threshold settings. causing the
`alert to oscillate in an annoying manner.
`
`SUMMARY OF THE INVENTION
`
`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
`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
`flicker efl'ects. 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 suflicient to bridge the dropout
`periods due to low reflectivity during station keeping. The
`sustain time varies according to the absolute value of the
`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. 30 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
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`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
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`5,714,927
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`3
`mirror 12. and side detection radar antennae 14. The anten-
`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—
`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-
`tional
`to vehicle speed and is available from either an
`onboard engine control module. anti-lock brake wheel speed
`sensors. a separate vehicle speed supply module. or via an
`integated 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 US. 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
`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
`below the threshold while the remainder of the vehicle 36
`return strong signals 40. The target discrimination algo-
`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 signal 46 as shown in FIG. 3d. This is accomplished in
`most cases by judiciously sustaining each individual alert
`signal 42 by the process described below. Generally most or
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`4
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`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
`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 50 having a speed of Vhost passes a target
`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
`vehicles and the time period 48. The same effect is produced
`when the host vehicle 50 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
`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. 5 wherein the func—
`tional description of each block in the chart is accompanied
`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
`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 <74> and the program returns to the operating
`algorithm and activation is continued in each loop until the
`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
`time “SUS'I'IME” 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 SUSI‘IME expires the
`alerts are turned off <88>. However if the alerts were active
`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—
`crimination is more robust and the alerts should be empha-
`sized. Accordingly the HOLD values are only 20 msec from
`0 to 45 mph and may optionally be 0 msec; 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
`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.
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`5 ,7 14,927
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`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
`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
`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
`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
`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-
`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
`vehicle speed;
`detecting target vehicle presence and producing an alert
`command;
`
`activating an alert signal in response to the alert com—
`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.
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`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 sufliciently to extend the per-
`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
`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
`at high vehicle velocity.
`12. The invention as defined in claim 9 wherein the hold
`time is shorter than the variable sustain time.
`
`*
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