ANTl-DROWSING DEVICE AND ANTI-DRO WSING METHOD

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention relates to an anti-drowsing device that changes the

timing of output of a warning which is output when a collision possibility between an object

ahead of a vehicle and the vehicle is detected, and a method therefor.

2. Description of the Related Art

(0002) A preceding vehicle proximity warning device is known having a host

vehicle speed detection means for detecting the traveling speed of a host vehicle; a

preceding vehicle speed detection means for detecting the traveling speed of a preceding

vehicle; inter- vehicular distance detection means for detecting the following distance

between the host vehicle and the preceding vehicle; a warning generation means for

providing a warning to the driver when the speed of the host vehicle relative to the

preceding vehicle becomes equal to or higher than a predetermined allowable relative speed

depending on the following distance; and a driving state detection means for detecting

inattentive driving or drowsy driving of the driver, in which the allowable relative speed is

corrected to a lower value when inattentive driving or drowsy driving is detected, so that a

warning is provided when the relative speed becomes equal to or higher than the corrected

allowable relative speed (for example, see Japanese Patent No. 2583335 (JP-B-2583335)).

According to the invention described in Japanese Patent No. 2583335 (JP-B-2583335),

when drowsy driving is detected, the allowable relative speed is corrected to a lower value

to establish an early-warning mode in which the timing of output of a warning is advanced

from that used in a normal mode.

(0003) In the invention described in Japanese Patent No. 2583335 (JP-B-2583335),

an inattentive state and a drowsy state are dealt with on the same basis, and an

early-warning mode is established when an inattentive state or a drowsy state is detected.

After that, if the inattentive state or the drowsy state is not detected any longer, the

early-warning mode is immediately canceled and the operation is returned to the normal

mode.

(0004] However, an inattentive state and a drowsy state have naturally different

characteristics, and there may be a situation in which the driver is still feeling drowsy and

the early-warning mode should be maintained even if a drowsy state is not detected any

longer. That is, in general, after a drowsy state has been once detected, the driver may be

struggling to keep his or her eyes open against heavy drowsiness even if a drowsy state is

not detected any longer. It is therefore desirable to change the timing of output of a

warning properly in view of the above point. On the other hand, when the early-warning

mode is maintained for a long period after a drowsy state has once been detected, a warning

may be output unnecessarily early and disturb the driver.

SUMMARY OF THE INVENTION

[0005] The present invention provides an anti-drowsing device that changes the

timing of output of a warning which is output, when a collision possibility is detected

between a preceding object and the vehicle, and a method therefor.

[0006] An anti-drowsing device according to a first aspect of the present invention

has a warning output means that outputs a warning when a collision possibility is detected

between a preceding object and the vehicle; a warning timing change means that establishes

an early-warning mode in which the timing of output of a warning by the warning output

means is advanced from that used in a normal mode; and an eye-closing period

measurement means that monitors the state of the driver's eyes and measuring the period

during which the driver's eyes are closed The warning timing change means establishes

the early-warning mode when the eye-closing period measured by the eye-closing period

measurement means becomes equal to or greater than a first threshold value, and maintains

the early-warning mode until the eye-closing period measured by the eye-closing period

measurement means every time the driver's eyes are closed thereafter (hereinafter referred

to as "subsequent eye-closing period") falls below a second threshold value which is

smaller than the first threshold value.

[0007] The subsequent eye-closing period may be the maximum value of the

eye-closing period measured by the eye-closing period measurement means within a

predetermined period.

[0008) The predetermined period may be variable, and the predetermined period

used when the vehicle is traveling on an expressway may be longer than the predetermined

period used when the vehicle is running on an ordinary road.

[0009) A second aspect of the present invention relates to an anti-drowsing method

for changing in which the timing of output of a warning, which is output when a collision

possibility is detected between a preceding object and the vehicle. The anti-drowsing

method has: a first index outputting step of monitoring the state of the driver's eyes and

outputting a first index value that provides a temporal indication of the degree of the

driver's drowsiness; a step of setting a first threshold value for the first index value; a step

of establishing an early-warning mode in which the timing of output of a warning is

advanced from that used in a normal mode when the first index value exceeds the first

threshold value output in the first index outputting step; a second index value outputting

step of monitoring the state of the eyes of the driver and outputting a second index value

that provides a temporal indication of the degree of the driver's drowsiness after the step of

establishing the early-warning mode; a step of setting a threshold value with which a lower

drowsiness level can be detected than with the first threshold value for the second index

value as a second threshold value; and the step of maintaining the early-warning mode until

the second index value output in the second index value outputting step falls below the

second threshold value.

(0010] The first index value may be one of the eye-closing period, the summation of

the eye-closing periods over a predetermined period between the current time and a

predetermined time before the current time, the ratio of the summation to the predetermined

period, and the number of times the eye-closing period exceeds a predetermined threshold

value within a predetermined period between the current tune and a predetermined time

before the current time.

[0011] The second index value may be one of the eye-closing period, the summation

of the eye-closing periods over a predetermined period between the current time and a

predetermined time before the current time, the ratio of the summation to the predetermined

period, and the number of times the eye-closing period exceeds a predetermined threshold

value within a predetermined period between the current time and a predetermined time

before the current time.

(0012] According to the present invention, there can be obtained an anti-drowsing

device which can properly change the timing of output of a warning which is output when a

collision possibility is detected between a preceding object and the vehicle, and a method

therefor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013) The foregoing and further features and advantages of the invention will

become apparent from the following description of example embodiments with reference to

the accompanying drawings, wherein like numerals are used to represent like elements and

wherein:

FIG 1 is a schematic diagram showing the main components of a warning system

including an anti-drowsing device according to one embodiment of the present invention;

FIG 2 is a chart showing an example of the time sequence of the eye-closing period d

and a manner of switching between an early-warning mode and a normal mode, which are

implemented in this embodiment;

FIG 3 is a first half of a flowchart illustrating a specific example of the primary

operation of a warning control ECU 110;

FIG 4 is a second half of a flowchart illustrating a specific example of the primary

operation of a warning control ECU 110;

FIGs. 5 A, 5B, 5C and 5D are charts showing the data of the results of a test in time

sequence;

FIGs. 6A, 6B, 6C, 6D and 6E are charts showing the data of the results of a test in time

sequence;

FIGs. 7 A, 7B and 7C are charts showing the data of the results of a test in time

sequence;

FIGs. 8 A, 8B, 8C and 8D are charts showing the data of the results of a test in time

sequence;

FIGs. 9A, 9B, 9C, 9D and 9E are charts showing the data of the results of a test in time

sequence;

FIGs. 10A, 1OB and 1OC are charts showing the data of the results of a test in time

sequence; and

FIG I l is a table summarizing the test results.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(0014) Description is hereinafter made of an embodiment for implementing the

present invention with reference to the drawings.

[0015J FIG 1 is a schematic diagram showing the main components of a warning

system that includes an anti-drowsing device according to one embodiment of the present

invention. The anti -drowsing device of this embodiment includes a warning control ECU

110, a driver monitor ECU 210, a driver monitor camera 212, a PCS (pre-crash safety) ECU

230, and a buzzer 240.

[0016] The warning control ECU 110 has a hardware configuration centered on an

appropriate processor or microcomputer and has a CPU that executes the operations

described below, a ROM for storing programs and data that are sued in the operations, a

readable and writable RAM for storing results of operations and the like, a timer, a counter,

an input interface, an output interface and so on. While the other ECUs 210 and 230 may

have the same or similar hardware configuration, it is needless to say that the programs and

data (software configuration) stored in the ROM are different depending on the operations

to be performed.

[0017] The driver monitor ECU 210 is connected to the warning control ECU 110

via an appropriate bus, and the driver monitor camera 212 is connected to the driver monitor

ECU 210. The PCS ECU 230 is connected to the warning control ECU 110 via a bus in

conformity with CAN (controller area network), and a radar sensor 280 and the buzzer 240

are connected to the PCS ECU 230. A brake ECU 250 may be connected to the PCS ECU

230 via a bus in conformity with CAN, for example. In this case, a brake actuator 260 and

a wheel-speed sensor 270 are connected to the brake ECU 250. These connections are not

necessarily made by wired connections, and some or all of the connections may be made by

wireless connections. While the ECUs 110, 210 and 230 are described as separate units,

some or all of the functions of an ECU may be implemented by another ECU or some of the

functions of an ECU may be implemented by an additional ECU.

(0018) The radar sensor 280 is disposed near the radiator grill or in the front bumper

of a vehicle to monitor objects that may be present ahead of the host vehicle. The radar

sensor 280 emits detection waves and receives a reflected wave from an object ahead of the

host vehicle (typically, a preceding vehicle) in the detection zone of the radar sensor 280 to

determine the distance between the host vehicle to the object ahead of the host vehicle

(hereinafter "preceding object") and the direction of the object relative to the host vehicle.

Examples of the detection waves, which the radar sensor 280 emits, include light waves (for

example, laser waves), radio waves (for example, millimeter waves), and sound waves (for

example, ultrasonic waves). In addition, a plurality of radar sensors 280 may be provided

to monitor the rear and/or both sides of the vehicle. Imaging sensors may be used instead

of or in addition to the radar sensors 280 to monitor the front and/or the rear and/or both

sides of the vehicle.

[0019J The PCS ECU 230 monitors the relative relation between the preceding

object and the host vehicle based on the information of the object obtained from the radar

sensor 280 every predetermined period and detects a collision possibility between the object

and the host vehicle. In this embodiment, the PCS ECU 230 calculates and monitors an

inter-vehicular time between the preceding object and the host vehicle based on the

information of the object obtained from the radar sensor 280 every predetermined period,

and detects a collision possibility between the preceding object and the host vehicle when

the calculated inter-vehicular time is shorter than a predetermined threshold value Th

(hereinafter referred to as "pre-crash determination threshold value"). The inter- vehicular

time herein is the period from the current time to the predicted collision time, the time when

a collision between the preceding object and the host vehicle is expected to occur, and is

calculated by simply dividing the distance between the object and the host vehicle by the

speed of the host vehicle relative to the object. In the normal mode (that is, not in an

early-warning mode, which is described below), a default value TO is used as the pre-crash

determination threshold value Th. The default value TO is set to a value in such a time

range that a warning can be output sufficiently long before the predicted collision time to

avoid the collision. That is, the default value TO is set to a value in such a time range that a

warning is effective. For example, the time range may be longer than the time range from

the time at which a collision is unavoidable ("collision-unavoidable time") to the predicted

collision time. This manner of setting the default value TO is suitable to a constitution in

which the brake ECU 250 performs forcible emergency braking or an automatic steering

mechanism (not shown) performs collision-avoidance steering when a collision unavoidable

state is detected. This is because outputting a warning after a collision unavoidable state is

detected is of almost no importance since a collision avoidance action of the driver is

useless even if the driver is warned that the collision is unavoidable. The default value TO

may be equal to the period from the collision unavoidable time to the predicted collision

time.

[0020J Some other conditions may be added to the condition for detection of a

collision possibility. For example, the fact that the angle formed by the speed vectors of

the preceding object and the host vehicle is smaller than a predetermined angle, the fact that

the amount of lateral offset between the preceding object and the host vehicle (the relative

distance in a direction perpendicular to the traveling direction of the host vehicle) is within

a predetermined value, the fact that the speed of the vehicle is equal to or higher than a

predetermined value and so on may be added as the other conditions.

(0021) When a collision possibility between a preceding object and the host vehicle

is detected, the PCS ECU 230 may output a collision warning via the buzzer 240. The

method of outputting a collision warning is not limited to sound and may include vibrating a

vibrator embedded in the seat or steering wheel, giving a thermal stimulation from a

temperature changing means (for example, heater or Peltier element) embedded in the seat

or steering wheel, causing the air conditioner to blow out a large amount of air suddenly,

emitting light to the driver automatically to alert him or her, or allowing the brake ECU 250

to drive the brake actuator 260 to brake the vehicle forcibly in order to alert the driver.

While outputting the collision warning, the PCS ECU 230 sends a signal informing the fact

that the collision warning is outputting to the warning control ECU 110. The warning

control ECU 110 can therefore keep track of the current output state (ON or OFF state) of

the collision warning.

[0022] The driver monitor camera 212 may include a color or infrared-sensitive

CCD (charge-coupled device) sensor array, for example. The driver monitor camera 212 is

located in a position where it can capture the front side of the driver (the face of the driver

from the front side thereof, for example). For example, the driver monitor camera 212

may be disposed on the dashboard of the instrument panel, steering column, rearview mirror

or the like. The driver monitor camera 212 captures an image of the driver's face

(hereinafter referred to as "face image") in real time. Typically, the driver monitor camera

212 sends the face image to the driver monitor ECU 210 in a 30 fps (frame per second)

stream.

(0023] The driver monitor ECU 210 performs image processing on the face image

continuously input from the driver monitor camera 212 and determines whether the driver's

eyes are closed based on how far the eyelids of the driver are open (eyelid opening). There

are various methods for determining whether the driver's eyes are closed based on image

processing, and any appropriate method can be used. For example, affine transformation

or the like is performed on the face image to correct the direction and size of the face, and,

after an edge treatment, a matching procedure is performed on the parts of the face (mouth,

nose, eyes) to identify the parts. Next, the maximum distance between the upper and

lower eyelids (eyelid opening) is obtained based on feature quantities of parts of the eyes,

the coordinate rows of the boundaries of the eyelids in this embodiment. Then, when the

eyelid opening is smaller than a predetermined criterion value, it is determined that the

driver's eyes are closed. In this case, a predetermined criterion value suitable for the

driver is selected. That is, a predetermined criterion value is obtained in advance by

sensory evaluation and stored in a database for each driver. The driver monitor ECU 210

performs the above determination on each image frame or on each image frame in a series

of image frames (every certain period with a resolution finer than a normal blinking period),

and sends the result of determination to the warning control ECU 110 at each determination

period δT. In this embodiment, in each determination period in which the driver's eyes are

determined to be closed, the driver monitor ECU 210 sends a trigger signal indicating that

the driver's eyes are closed (hereinafter referred to as "eye-closure trigger") to the warning

control ECU 110.

[0024] A characteristic configuration of the warning control ECU 110 of this

embodiment is next described

(0025] The warning control ECU 110 calculates the eye-closing period d [sec], the

period for which the eyes of the driver are closed, in real time based on the eye-closure

trigger continuously input from the driver monitor ECU 210. More specifically, the

warning control ECU 110 increments an eye-closure counter value C (initial value: 0) when

a eye-closure trigger is input in a determination period, and increments the eye-closure

counter value C every time a eye-closure trigger is input in the subsequent determination

periods. The warning control ECU 110 basically counts up the eye-closure triggers input

in successive determination periods, but may have a filter for maintaining the eye-closure

counter value C when a particular temporal discontinuity of eye-closure triggers occurs.

The warning control ECU 110 calculates the period for which the eyes of the driver are

closed, that is, the eye-closing period d [sec], by multiplying the eye-closure counter value

C by the determination period δT.

(0026] When the calculated eye-closing period d exceeds a predetermined threshold

value d-n, (hereinafter referred to as "first threshold value dτ _h ") _> the warning control ECU

110 changes the pre-crash determination threshold value Th from the default value TO to a

value at which the PCS ECU 230 is more likely to detect a collision possibility. More

specifically, the warning control ECU 110 changes the pre-crash determination threshold

value Th to a value Tl (for example, TO + 1.5 seconds), which is greater than the default

value TO. The first threshold value dm may be an appropriate value in the range of 1 to 3

seconds, for example.

[0027] Thus, in this embodiment, since the pre-crash determination threshold value

T is increased from TO to Tl when the period for which the driver's eyes are closed exceeds

the first threshold value d-m, the period which it takes for the inter-vehicular time to fall

below the pre-crash determination threshold value Th becomes shorter accordingly. That

is, an early-warning mode in which the timing of output of a warning is advanced from that

used in the normal mode is established. Even when the early-warning mode is established,

no collision warning is output unless the PCS ECU 230 detects a collision possibility.

(0028] When the early-warning mode is established, a collision warning is output

sooner than in the normal mode. Thus, when the PCS ECU 230 actually detects a collision

possibility and a collision warning is output, even if it takes some rime for the driver to be

awakened by the collision warning, the driver may have sufficient time to take appropriate

evasive action to avoid the collision possibility after being awakened.

(0029) The warning control ECU 110 also calculates the maximum eye-closing

period Id [sec] within the period between the current time and a period δTw before the

current time (hereinafter referred to simply as "maximum eye-closing period Id") using a

time window with a predetermined duration δTw based on the time sequence of the

eye-closing period d calculated as described aibove. As the duration δTw, an appropriate

value in the range of 5 to 35 [sec], for example, may be used,

[0030] When the calculated maximum eye-closing period Id falls below a

predetermined threshold value ldτh (hereinafter referred to as "second threshold value ldτh").

the warning control ECU 110 changes the pre-crash determination threshold value Th to the

default value TO or maintains the pre-crash determination threshold value Th at the default

value TO. The second threshold value ldn, is a value greater than 0 and smaller than the

first threshold value an, and may be 1 [sec], for example.

[0031] Thus, in this embodiment, when the eye-closing period d of the driver

exceeds the first threshold value dn, and the early-warning mode is established, the

early-warning mode is maintained until the maximum eye-closing period Id falls below the

threshold value ld-n,, Then, only if the maximum eye-closing period Id falls below the

predetermined threshold value ldτ _h , the pre-crash determination threshold value Th is

returned to the default value TO. That is, the operation is restored from the early-warning

mode to the normal mode.

[0032) FIG. 2 is a chart showing an example of the time sequence of the eye-closing

period d and a manner of switching between an early-warning mode and a normal mode

which is implemented in this embodiment.

[0033J In the example shown in FlG 2, the eye-closing period d continuing from a

time t0 (the eye-closing period d at the third eye closure since the start of measurement)

exceeds the first threshold value d-m and the operation is shifted from the normal mode to

the early-warning mode at a time t = tl . In this example, since the eye-closing period d

falls below the first threshold value d^ at a time.t = t2 after the time t = tl but the maximum

eye-closing period Id does not fall below the second threshold value ldγ _h until a time t = t3,

the early-warning mode is maintained until the time t = t3. At the time t = t3, the

maximum eye-closing period Id falls below the second threshold value ldm and the

operation is returned from the early-warning mode to the normal mode.

(0034) As described above, according to this embodiment, once a situation in which

the eye-closing period d exceeds the first threshold value d-n, is detected, even if the

eye-closing period d falls below the first threshold value d^ (that is, the eyes are opened)

thereafter, it is determined that the driver may be struggling to keep his or her eyes open

against heavy drowsiness (the driver may have not returned to the normal awakened state),

and the early-warning mode is maintained unless the maximum eye-closing period Id falls

below the second threshold value ldτ _h - Therefore, the possibility of returning from the

early-warning mode to the normal mode while the driver is still feeling drowsy can be

reduced effectively.

(0035) Also, according to this embodiment, since the operation is returned from the

early-warning mode to the normal mode when a situation in which the eye-closing period d

exceeds the first threshold value d-n, is detected and then the maximum eye-closing period

Id falls below the second threshold value ldn,. it is possible to prevent the early-warning

mode from being unnecessarily maintained. That is, according to this embodiment, since

it is determined that the driver has returned to the normal awakened state and the operation

is returned to the early-warning mode to the normal mode when the maximum eye-closing

period Id falls below the second threshold value ld-π,, the possibility of the early-warning

mode being established while the driver is in the normal awakened state can be reduced

effectively.

[0036] A specific example of the primary operation of the warning control ECU 110

of this embodiment is next described with reference to the flowcharts of FIG. 3 and FIG 4.

The operation shown in FIG 3 and FIG 4 is repeated at a constant frequency (typically, in

each determination period δT of the driver monitor ECU 210) until the ignition switch of

the vehicle is turned off after it is turned on. Also, the operation shown in FIG 3 and FIG

4 is performed while the output state of the collision warning from the PCS ECU 230 is in

the OFF state. This is because the mode switching between the early-warning mode and

the normal mode while the output state of the collision warning in the ON state, that is,

while the PCS ECU 230 is outputting a collision warning, is useless.

|0037] In step 10, the warning control ECU 110 initializes flags. Here, three flags,

an ON-set flag, a reset flag and a status flag, are used, and the ON-set flag is set to OFF, the

reset flag to ON and the status flag is to "normal" by the initialization. In reality, however,

the state of each flag may be represented by binary values "0" and "1." The warning

control ECU 110 also initializes the eye-closure counter value C to 0. The process in step

10 is performed only in the first cycle.

[0038] In the following step 12, the warning control ECU 110 achieves information

representing the latest eye closure state of the driver. More specifically, the warning

control ECU 110 checks the presence or absence of an input of an eye-closure trigger from

the driver monitor ECU 210 in the current cycle.

(0039| In the following step 14, the warning control ECU 110 calculates the

eye-closing period d depending on the presence or absence of an input of an eye-closυτe

trigger from the driver monitor ECU 210 in the current cycle. Then, the maximum

eye-closing period Id is calculated based on the time sequence of the calculated eye-closing

period d. More specifically, when an eye-closure trigger is input from the driver monitor

ECU 210 in the current cycle, the warning control ECU 110 increments the eye-closure

counter value C, and calculates an eye-closing period d(i) in the current cycle (i) based on

the thus obtained eye-closure counter value C. When no eye-closure trigger has been

inputted from the driver monitor ECU 210 in the current cycle, the warning control ECU

110 sets the eye-closing period d(i) in the current cycle to 0 and stores it in memory (not

shown). In this way, the time sequence of the eye-closing period d calculated in each cycle

is stored and accumulated in the memory. The warning control ECU 110 calculates

(extracts) the maximum value of the eye-closing period d in the cycles within the period

between the current time and a time prior to the current time by the duration δT as the

maximum eye-closing period ld(i) in the current cycle (i) based on the time sequence of the

eye-closing period d in the memory.

[0040] In the following step 16, the warning control ECU 110 determines whether

or not the eye-closing period d(i) in the current cycle (i) obtained in the above step 14 is

greater than the first threshold value d-n,. If the eye-closing period d(i) in the current cycle

(i) is greater than the first threshold value dm, the process goes to step 18; otherwise the

process goes to step 20.

[0041] In step 18, the warning control ECU 110 sets the ON-set flag to ON. Then,

the process goes to step 22.

IOO42| In step 20, the warning control ECU 110 sets the ON-set flag Jo OFF. Then,

the process goes to step 22.

[0043] In step 22, the warning control ECU 110 determines whether or not the

maximum eye-closing period ld(i) in the current cycle (i) obtained in the above step 14 is

smaller than the second threshold value Id™. If the maximum eye-closing period ld(i) in

the current cycle (i) is smaller than the second threshold value ldτ _h , the process goes to step

24; otherwise the process goes to step 26.

[0044] In step 24, the warning control ECU 110 sets the reset flag to ON. Then,

the process goes to step 28 in FIG 4.

10045J In step 26, the warning control ECU 110 sets the reset flag to OFF. Then,

the process goes to step 28.

(0046) In step 28, the warning control ECU 110 refers to the current state of the

status flag. If the status flag is "normal" in the current cycle (i) (step 30), the process goes

to step 32. If the status flag is "early" in the current cycle (i) (step 36), the process goes to

step 38.

(0047] In step 32, the warning control ECU 110 determines whether or not the

ON-set flag is ON and whether or not the reset flag is OFF. If the ON-set flag is ON and

the reset flag is OFF, the process goes to step 34. If either of the conditions is not satisfied,

the process returns to step 12 in FIG 3, Then, the operation is repeated from step 12 in the

next cycle (i+1).

(0048) In step 34, the warning control ECU 110 sets the status flag to "early."

Along with this, the pre-crash determination threshold value Th is set to a value Tl which is

greater than the default value TO, and the PCS ECU 230 operates in the early-warning mode

using the value Tl .

(0049) In step 38, the warning control ECU 110 determines whether or not the reset

flag is ON and whether or not the ON-set flag is OFF. If the reset flag is ON and the

ON-set flag is OFF, the process goes to step 40. If either of the conditions is not satisfied,

the process returns to step 12 in FIQ 3. Then, the operation is repeated from step 12 in the

next cycle (i+1 ).

[0050J In step 40, the warning control ECU 110 sets the status flag to "normal."

Along with this, the pre-crash determination threshold value Th is set to the default value

TO, and the PCS ECU 230 operates in the normal mode using the default value TO.

(0051) The results of a test conducted using the anti-drowsing device of this

embodiment is next described.

(0052) Here, the usefulness of the anti-drowsing device of this embodiment is

described by comparison with a comparative example. In the comparative example, the

normal mode and the early-warning mode are switched based an index value P called

PERCLOS. That is, the early-warning mode is established when the index value P

exceeds a predetermined threshold value (0.08 in this example) and the normal mode is

established when the index value P falls below the predetermined threshold value. The

index value P is represented by the following equation:

// p ~ J≤

M\

(0053) In the equation, d, represents the eye-closing period d at the i-th eye closure,

and wp represents the duration of the time window, which is 60 [sec] here. Therefore, the

index value P is a value obtained by dividing the summation of the eye-closing periods d

within a period between the current time and 60 seconds before the current time by Wp, that

is, the ratio of the eye-closing period per unit time.

[0054] FIQ 5(A) shows the change in drowsiness level of a subject during the test.

Here, the drowsiness level is rated on a five-point scale of DO to D4. The drowsiness level

DO represents the normal state in which the driver is awake, the drowsiness level D2

represents the state in which the driver is feeling a little drowsy, and the drowsiness level

D4 represents the state in which the driver is feeling very drowsy. Here, the ideal test

result is that the early-warning mode is established when the drowsiness level is D3 or D4

(D4, in particular) and the normal mode is established when the drowsiness level is lower

than D3. The test result shown in FIG 5(A) was the result of a test (sensory evaluation

test) conducted with understanding the alertness level (drowsiness level) of the subject, and

indicates that the drowsiness level of the subject constantly remained at D3 or D4

throughout the test.

[0055| FIG 5(B) shows the time sequence of the index value P (PERCLOS) during

the test, FIG 5(C) shows the time sequence of the eye-closing period d during the test, and

FIG 5(D) shows the time sequence of the maximum eye-closing period Id during the test.

In FIG 5(C), the eye-closing period d at each eye closure is shown in time sequence

because of the scale of the horizontal axis. Also, the maximum eye-closing period Id was

calculated using a time window with a relatively long duration δTw (30 sec in this

example).

[00561 FIG. 6(A) shows the time sequence of the state of the ON-set flag of this

embodiment during the test, FIG 6(B) shows the time sequence of the state of the reset flag

of this embodiment during the test, FIG. 6(C) shows the time sequence of the slate of the

reset flag according to the comparative example during the test, FIG 6(D) shows the time

sequence of the state of the status flag of this embodiment during the test, and FIG 6(E)

shows the time sequence of the state of the status flag according to the comparative example

during the test. The reset flag of the comparative example is set to "0" when the index

value P exceeds a predetermined threshold value (0.08 in this example) and set to "1" when

the index value P falls below the predetermined threshold value. The status flag of the

comparative example varies depending on the state of the reset flag, and is set to "1" when

the reset flag is set to "0." When the status flag is set to "1 ," the early-warning mode is

established.

[0057] In this embodiment, the ON-set flag was turned ON (that is, the ON-set flag

was changes from 0 to 1) for the first time at a time t = tl when the eye-closing period d

exceeded the first threshold value d-p,, and after that the ON-set flag was turned ON seven

times in total in the same manner as shown in FlG 5(C) and FIG 6(A). The reset flag was

maintained in OFF state since the maximum eye-closing period Id was greater than the

second threshold value ld-n, throughout the test as shown in FIG 5(D) and FIG 6(B).

Therefore, the status flag was set to "early" (that is, value 1 ) at the time t = tl in response to

the turn-ON of the ON-set flag at the time t = tl and maintained at "early" thereafter as

shown in FIG 6(D). Thus, the early-warning mode was continuously maintained from the

time t = tl in this embodiment.

[0058) In the comparative example, the reset flag was set to "0" at time t2 when the

index value P exceeded a predetermined threshold value as shown in FIG 5(B) and FIG

6(C). After that, the reset flag was maintained at "0" since the index value P remained

higher than the predetermined threshold value. Therefore, the status flag was set to "early"

(that is, value 1) at the time t = t2 in response to the turn-ON of the ON-set flag at the time t

= t2 and maintained at "early" thereafter as shown in FIG 6(E). Thus, the early-warning

mode was continuously maintained from the time t = t2 in the comparative example.

[0059) FIG 7 shows the results of a test conducted using a time window with a

relatively short duration δTw (in this example, 10 sec). FIG 7(A) shows the time

sequence of the maximum eye-closing period Id during the test, FIG 7(B) shows the time

sequence of the state of the reset flag of this embodiment during the test, and FIG 7(C)

shows the time sequence of the state of the status flag of this embodiment during the test.

The other tests results are the same as those in FIG. 5(A), FlG 5(C) and FIG 6(A)

[0060) When the duration δTw was set short, the reset flag was turned ON at a time

t = t3 when the maximum eye-closing period Id fell below the second threshold value ldχh

as shown in FlG 7(A) and FIG 7(B). The status flag was set to "early" (that is, value 1) at

a time t = tl in response to the turn-ON of the ON-set flag at the time t = tl and then set to

"normal" (that is, value 0) at the time t = t3 in response to the turn-ON of the reset flag at

the time t = ύ as shown in FIG 7(C). Therefore, when a time window with a relatively

short duration δTw (in this example, 10 sec) was used, the early-warning mode was

established at the time t = tl and the operation was returned to the normal mode at the time t

= t3 in this embodiment.

[0061] As can be understood from the test results, according to this embodiment,

whether the duration δTw was long or short, the early-warning mode was able to be

established according to the drowsiness level of D3 to D4 with high accuracy as compared

to the comparative example,

[0062] FIG. 8 to FIG 10 shows the results of a test different from the test, the results

of which are shown in FIG 5 to FIG 7. The charts of FIG 8 respectively correspond to the

charts of FIG 5, the charts of FIG 9 respectively correspond to the charts of FIG 6, and the

charts of FIG 10 respectively correspond to the charts of FIG. 7.

(0063) In this test, the drowsiness level of the subject constantly remained at D3 or

D4 throughout the test except for the period from a time t = t4 to a time t = t5, in which the

drowsiness level was lowered to D2 as shown in FIG. 8(A).

[0064] As can be understood from the results of this test, according to this

embodiment, when the duration δTw was set long, the early-warning mode was established

according to the drowsiness level of D3 to D4 accurately although the operation was not

able to be returned to the normal mode in the period from the time t = t4 to the time t = t5 as

shown in FIG 9(D). When the duration δTw was set short, the early-warning mode was

established according to the drowsiness level of D3 to D4 accurately and the normal mode

was established according to the drowsiness level of D2 accurately as shown in FIG 10(C).

[0065] FIG 11 shows a table summarizing the results of the tests shown in FIG 5 to

FIG 10. In FIG 11 , "Number of sample cases" represents the number of sample cases in

which the consistency between the sensory test and the test results was observed. In the

tests, there were 598 sample cases in the drowsiness levels of DO to D2, and there were 881

sample cases in the drowsiness levels of D3 and D4,

[0066] The uppermost row of FIG 11 shows the test results obtained when the

duration δTw was set long in this embodiment. When the duration δTw was set long in

this embodiment, the fact that the drowsiness level was in the range of DO to D2 was able to

be estimated with an accuracy of 527/598 (= 88.13%) and the fact that the drowsiness level

was in the range of D3 to D4 was able to be estimated with an accuracy of 659/881 (=

74.8%).

[0067] The second row from the top in FlG 11 shows the test results obtained when

the duration δTw was set short in this embodiment. When the duration δTw was set short

in this embodiment, the fact that the drowsiness level was in the range of DO to D2 was able

to be estimated with an accuracy of 574/598 (= 95.99%) and the fact that the drowsiness

level was in the range of D3 to D4 was able to be estimated with an accuracy of 598/881 (=

67.88%).

[0068] The third row from the top in FIG 11 shows the test results in Comparative

Example 1. In Comparative Example 1 , it was determined that the drowsiness level was in

the range of D3 to D4 and the early-warning mode was established when the eye-closing

period d exceeded the first threshold value dm, and it was determined that the drowsiness

level was in the range of DO to D2 and the normal mode was established when the

eye-closing period d fell below the first threshold value d-m- In Comparative Example 1 ,

the fact that the drowsiness level was in the range of DO to D2 was able to be estimated with

an accuracy of 554/598 (= 92.64%) whereas the fact that the drowsiness level was in the

range of D3 to D4 was able to be estimated with only an accuracy of slightly higher than

50%, which is 451 /881 (= 51.19%).

[0069] The fourth row from the top (lowermost row) in FIG 11 shows the test

results in Comparative Example 2. In Comparative Example 2, it was determined that the

drowsiness level was in the range of D3 to D4 and the early-warning mode was established

when the index value P (PERCLOS) exceeded a predetermined threshold value (in this

example 0.08), and it was determined that the drowsiness level was in the range of DO to D2

and the normal mode was established when the index value P fell below the predetermined

threshold value. In Comparative Example 2, the fact that the drowsiness level was in the

range of DO to D2 was able to be estimated with a high accuracy of 592/598 (= 99%)

whereas the fact that the drowsiness level is in the range of D3 to D4 was able to be

estimated with only an accuracy of lower than 50%, which is 431/881 (= 48.92%).

(0070J As can be understood from the summary of test results shown in FIG 11 ,

according to this embodiment, the fact that the drowsiness level is in the range of D3 to D4

can be estimated and the early-warning mode can be established accurately as compared to

Comparative Examples 1 and 2. In this embodiment, the accuracy in the drowsiness level

of D3 to D4 is 67.88%, which is higher than two-thirds, even when the duration δTw is set

short. When the duration δTw is set long, the accuracy is 74.8%, which is much higher

than those in other examples, hi addition, according to this embodiment, the normal mode

can be also established according to the drowsiness level of DO to D2 with high accuracy.

In this embodiment, when the duration δTw is set short, the accuracy in the drowsiness

level of D3 to D4 is as very high as 95.99%. Even when the duration δTw is set long, the

accuracy is maintained at as high as 88.13%.

[0071 J As described above, according to this embodiment, once the eye-closing

period d exceeds the first threshold value dm, it is thereafter determined that the drowsiness

level is in the range of D3 to D4 until the maximum eye-closing period Id falls below the

second threshold value ldτ _t ,. Therefore, both the accuracy in the drowsiness level of DO to

D2 and the accuracy in the drowsiness level of D3 to D4 can be enhanced. As a result, the

early-warning mode and the normal mode can be switched depending on the actual

drowsiness level of the driver with high accuracy.

[0072 J As can be understood from the summary of the test results in FIG 11 , when

the method of calculating the maximum eye-closing period Id is different (that is, the

duration δTw of the time window is changed), the accuracy in the drowsiness level of DO to

D2 and the accuracy in the drowsiness level of D3 to D4 varies significantly while still

remaining high. Therefore, in this embodiment, it is useful to change the duration δTw of

the time window depending on the running condition of the vehicle, the condition of the

driver, the condition of the surrounding environment, or the like.

[0073] For example, in this embodiment, the warning control ECU 110 may set the

duration δTw of the time window to a large value (for example, 30 sec) when it is

determined that the vehicle is running on an expressway and set the duration δTw of the

time window to a small value (for example, 10 sec) when it is determined that the vehicle is

running on an ordinary road based on information on the location of the vehicle and map

information from a navigation ECU 290, for example! This is because driving on an

expressway tends to be monotonous than driving on an ordinary road and drowsiness is

likely to continue accordingly. In this case, the type of the road on which the vehicle is

running may be determined based on information based on the result of image recognition

of the surrounding environment using an onboard camera (not shown) or information

obtained through road-to-vehicle communication instead of information from the navigation

ECU 290. Also, the fact that the vehicle is driving on an expressway may be determined

based on information from a sensor for detecting the vehicle speed such as the wheel speed

sensor 270. For example, since the legal speed limit on expressways is usually 80 km/h in

Japan, the duration δTw of the time window may be set to a large value (for example, 30

sec) when the vehicle speed exceeds 70 km/h and set to a small value (for example, 10 sec)

when the vehicle speed falls below 70 km/h.

[0074| In this embodiment, the "warning output means" may be implemented

cooperatively by the PCS ECU 230 and the buzzer 240, the "eye-closing period

measurement means" may be implemented cooperatively by the driver monitor camera 212,

the driver monitor ECU 210 and the warning control ECU 110, and the "warning timing

change means" may be implemented by the warning control ECU 110. The

"predetermined period" may correspond to the duration δTw.

[0075) While a preferred embodiment of the present invention has been described,

the present invention is not limited to the embodiment and various changes and

modifications may be made thereto without departing from the scope of the present

invention.

[0076] For example, while the early-warning mode is established when the

eye-closing period d exceeds the first threshold value dm, and the early-warning mode is

thereafter maintained until the maximum eye-closing period Id falls below the second

threshold value ldχ _h in the above embodiment, the present invention is not limited thereto.

Another index value capable of representing the degree of drowsiness of the driver may be

used instead of the eye-closing period d. That is, the early-warning mode may be

established when the other index value exceeds a predetermined threshold value Th2, and

the early-warning mode may be thereafter maintained until the maximum eye-closing

period Id falls below the second threshold value ld-π,. In this case, as the other index value,

the summation of the eye-closing periods within a predetermined period between the current

time and a predetermined time before the current time, the ratio of the summation to the

predetermined period (which corresponds to the PERCLOS described before), or the

number of times the eye-closing period exceeding a predetermined threshold value within a

predetermined period between the current time and a predetermined time before the current

time (for example, the frequency at which the eye-closing period d exceeds the first

threshold value d _fh per a given period) may be used. In this case, however, the

predetermined threshold value Th2 for the other index value is set to a value with which a

substantially higher drowsiness level can be detected than when using with the second

threshold value ldj _h for the maximum eye-closing period Id.

|0077] Also, while the early-warning mode is established when the eye-closing

period d exceeds the first threshold value dj _h , and the early-warning mode is thereafter

maintained until the maximum eye-closing period Id falls below the second threshold value

Idτh in the above embodiment, the present invention is not limited thereto. Another index

value capable of representing the degree of drowsiness of the driver may be used instead of

the maximum eye-closing period Id. That is, the early-warning mode may be established

when the eye-closing period d exceeds the first threshold value dm and the early-warning

mode may be thereafter maintained until the other index value falls below a predetermined

threshold value Th3. In this case, as the other index value, the summation of the

eye-closing periods within a predetermined period between the current time and a

predetermined time before the current time, the ratio of the summation to the predetermined

period (which corresponds to the PERCLOS described before), or the number of times the

eye-closing period exceeding a predetermined threshold value within a predetermined

period between the current time and a predetermined time before the current time (for

example, the frequency at which the eye-closing period d exceeds the first threshold value

dib per a given period) may be used. In this case, however, the predetermined threshold

value Th3 for the other index value is set to a value with which a substantially lower

drowsiness level can be detected than when using with the first threshold value d-π, for the

eye-closing period d.

[0078] While only index values relating to the eye-closing period are used as the

index values capable of representing the degree of drowsiness of the driver to implement a

simple configuration in the above example, index values relating to a physiological feature

quantity such as the number of yarns, brain waves, or heart rate may be used as additional

conditions to establish the early-warning mode or to restore to the normal mode.

(0079] While a collision possibility is detected based simply on the relation between

the inter-vehicular time and the predetermined threshold value Th in the above embodiment,

for example, a collision possibility may be detected using another method. For example, a

collision possibility may be detected using a two-dimensional map defined by the

inter-vehicular distance between a preceding object and the host vehicle and the speed of

the host vehicle relative to the preceding object In this case, a threshold value curve

dividing a high collision risk region and a low collision risk region may be defined on the

two-dimensional map, for example, and a collision possibility may be determined when the

detected current inter-vehicular distance and relative speed fall within the high collision risk

region divided by the threshold value curve. In this case, the early-warning mode may be

established by shifting the threshold value curve for the normal mode in such a way that the

sensitivity increases (the high collision risk region is enlarged). Also, a collision

possibility may be detected using other physical quantities such as acceleration

(deceleration) instead of the inter- vehicular distance and relative speed.

[0080] While the information representing the relative relation between a preceding

object and the host vehicle is obtained from the radar sensor 280 in the above embodiment,

when the preceding object has an interactive communication device, information of that

kind may be obtained through communication (for example, inter-vehicular

communication) therewith.