Obstacle detecting apparatus and vehicle occupant protecting device using the same

An obstacle detecting apparatus which detects the distance between an obstacle and a vehicle by two distance measuring sensors, comprising collision angle calculating device in which a plurality of positions of the obstacle is calculated by way of triangulation on the basis of the distance information from the two distance measuring sensors, and a collision angle, which is formed between the obstacle and the vehicle, is calculated by the locus of the obstacle which is calculated by the calculated plurality of positions of the obstacle.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an obstacle detecting apparatus and a 
device for protecting a vehicle occupant by using the obstacle detecting 
apparatus, and, more specifically, to the obstacle detecting apparatus and 
the vehicle occupant protecting device with the use of the obstacle 
detecting apparatus in which the distance between a vehicle and an 
obstacle can be detected by using two distance measuring sensors. 
2. Description of the Related Art 
Conventionally, as examples of an obstacle detecting apparatus and a 
vehicle occupant protecting device using the same in which the distance 
between a vehicle and an obstacle can be detected by two distance 
measuring sensors, collision detecting apparatuses for detecting a 
collision direction and a collision intensity on the basis of a collision 
acceleration is disclosed in Japanese Patent Application Laid-Open (JP-A) 
Nos. 6-56000 and 7-223505, and structures thereof are known. 
The structure which is disclosed in Japanese Patent Application Laid-Open 
(JP-A) No. 7-223505 will be described hereinafter. 
As shown in FIG. 21, in an obstacle detecting apparatus and a vehicle 
occupant protecting device using the same, an obstacle 72 such as another 
vehicle or the like in the vicinity of a vehicle 70 is detected by 
obstacle detecting sensors 74, 76 which are installed in the vehicle 70. 
Accordingly, a vehicle occupant protecting device 80 is operated on the 
basis of signals output from the obstacle detecting sensors 74, 76. When 
it is detected that a collision has occurred at the front of the vehicle, 
the vehicle occupant protecting device 80 is operated on the basis of a 
signal output from a collision detection sensor 82 and on the basis of 
signals output from the obstacle detecting sensors 74, 76. 
Although the obstacle detecting apparatus and the vehicle occupant 
protecting device using the same can detect the relative velocity of the 
vehicle 70 with respect to the obstacle 72, the apparatus and the device 
cannot detect the collision angle formed between the obstacle 72 and the 
vehicle 70. Accordingly, it is not possible to predict a collision state 
including a collision angle and a relative velocity in the direction of 
the collision angle (i.e., collision velocity) at the time at which the 
obstacle 72 and the vehicle 70 collide. 
SUMMARY OF THE INVENTION 
In view of the aforementioned, an object of the present invention is to 
provide an obstacle detecting apparatus and a vehicle occupant protecting 
device using the same in which a collision state in which an obstacle and 
a vehicle collide can be predicted beforehand. 
A first aspect of the present invention is an obstacle detecting apparatus 
which detects the distance between the vehicle and the obstacle by two 
distance measuring sensors, comprising collision angle calculating means 
in which a plurality of positions of the obstacle is calculated via 
triangulation on the basis of distance information from the two distance 
measuring sensors, and a collision angle, which is formed between the 
obstacle and the vehicle, is calculated by the locus of the obstacle which 
is calculated by the calculated plurality of positions of the obstacle. 
Accordingly, since the collision angle calculating means calculates 
positions of the obstacle via triangulation on the basis of distance 
information from the two distance measuring sensors so that a collision 
angle of the obstacle with respect to the vehicle is calculated by the 
locus of the obstacle resulting from the calculated plurality of positions 
of the obstacle. Further, by calculating the collision angle of the 
obstacle with respect to the vehicle, it is possible to predict at what 
collision angle and at what collision velocity in a direction of the 
collision angle between the obstacle and the vehicle collide so that a 
collision state in which the obstacle and the vehicle collide can be 
predicted beforehand. 
A second aspect of the present invention is an obstacle detecting apparatus 
according to the first aspect, further comprising collision velocity 
calculating means in which, on the basis of distance information from the 
two distance measuring sensors, the collision velocity in the direction of 
the collision angle formed between the vehicle and the obstacle which has 
been calculated by the collision angle calculating means is calculated. 
Accordingly, since collision velocity calculating means calculates a 
collision velocity in the direction of the collision angle formed between 
the vehicle and the obstacle which has been calculated by collision angle 
calculating means on the basis of distance information output from the two 
distance measuring sensors, the accuracy of the collision velocity thereby 
increases. 
A third aspect of the present invention is a vehicle occupant protecting 
device using the obstacle detecting apparatus which detects the distance 
between an obstacle and a vehicle by two distance measuring sensors 
comprising collision angle calculating means in which a plurality of 
positions of the obstacle is calculated via triangulation on the basis of 
distance information from the two distance measuring sensors, and a 
collision angle, which is formed between the obstacle and the vehicle, is 
calculated by the locus of the obstacle which is calculated by the 
calculated plurality of positions of the obstacle, collision velocity 
calculating means in which, on the basis of distance information from the 
two distance measuring sensors, the collision velocity in the direction of 
the collision angle formed between the vehicle and the obstacle which has 
been calculated by the collision angle calculating means is calculated, a 
collision sensor for detecting collision acceleration, threshold setting 
means in which a threshold of the collision acceleration for determining 
the collision by the collision angle and the collision velocity in the 
direction of the collision angle, and vehicle occupant protecting means 
which is operated in a case in which collision acceleration detected by 
the collision sensor is greater than the threshold set by the threshold 
setting means. 
Accordingly, since the threshold of collision acceleration is changed and 
set by threshold setting means in accordance with the collision angle and 
the collision velocity in the direction of the collision angle which have 
been calculated by the collision angle calculating means and the collision 
velocity calculating means on the basis of distance information output 
from the two distance measuring sensors, the threshold of collision 
acceleration can be set in accordance with the collision state so that the 
vehicle protecting means can operate at the optimal timing. 
A fourth aspect of the present invention is an obstacle detecting apparatus 
according to the second aspect, wherein the collision velocity calculating 
means selects a sensor having higher stability from the two distance 
measuring sensors on the basis of the collision angle detected by the two 
distance measuring sensors, and calculates the collision velocity in a 
direction of the collision angle formed between the vehicle and the 
obstacle by information from the selected distance measuring sensor. 
Accordingly, information from a sensor having higher stability in its 
detection is selected so as to compare such information with each other, 
the left distance measuring sensor and the right distance measuring 
sensor. Since the collision velocity in the direction of the collision 
angle of the obstacle can be calculated on the basis of the selected 
sensor information, even when a sensor is disposed at the closest distance 
where sensor information is not stable, the calculating accuracy of the 
collision velocity in a direction of the collision angle formed between 
the vehicle and the obstacle is improved. 
A fifth aspect of the present invention is a vehicle occupant protecting 
device according to the third aspect, further comprising operation control 
means of the vehicle occupant protecting means in which, before a 
collision, each of the relative velocity in the direction of the collision 
angle, the collision position and the collision angle is calculated, and 
on the basis of the calculated results and the rise time of collision 
acceleration due to the collision sensor, an operating velocity of the 
vehicle occupant protecting means is controlled. 
As a result, since the vehicle protecting means is operated at the 
operation velocity in accordance with the collision velocity in the 
direction of the collision angle formed between the vehicle and the 
obstacle, the collision position, and the collision angle, the vehicle 
occupant can be protected more effectively by the vehicle protecting means 
.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An obstacle detecting apparatus and a device for protecting a vehicle 
occupant using the obstacle detecting apparatus according to a first 
embodiment of the present invention will be explained with reference to 
FIGS. 1 through 13. 
In these figures, arrow FR points toward the front of a vehicle. 
As shown in FIG. 1, in a vehicle 10 of the present embodiment, a right 
distance measuring sensor (R) 12 and a left distance measuring sensor (L) 
14, made of two electrical wave radar sensors are respectively installed 
in the vicinity of the end portions of a front surface 10A in the 
transverse direction of the vehicle 10. At the time of a collision 
occurring at the front of the vehicle 10, the distance and relative 
velocity between the vehicle 10 and an obstacle 16 are detected on the 
basis of the values detected by the distance measuring sensors 12, 14. 
As shown in FIG. 2, the distance measuring sensors 12, 14 are respectively 
connected to a collision information detecting section 20. The collision 
information detecting section 20 is provided to calculate a collision 
velocity, a collision angle, or the like as detailed information regarding 
the obstacle 16. 
The distance measuring sensors 12, 14 are also connected to a collision 
velocity calculating section 20A and a current position calculating 
section 20B which are provided in the collision information detecting 
section 20. The current position calculating section 20B is connected to a 
sensor mounting position setting section 22 and a vehicle size setting 
section 24. The sensor mounting position setting section 22 inputs 
positions on a vehicle at which the distance measuring sensors 12, 14 are 
installed, and the vehicle size setting section 24 inputs a vehicle size. 
Further, the collision information detecting section 20 includes an 
obstacle locus calculating section 20C therein. The obstacle locus 
calculating section 20C is connected to the collision velocity calculating 
section 20A and the current position calculating section 20B. 
The distance measuring sensors 12, 14 and the collision information 
detecting section 20 are connected to a collision predicting section 26. 
Judging from a collision velocity and a collision angle at a certain 
distance between the vehicle 10 and the obstacle 16, the collision 
predicting section 26 predicts the degree of danger of collision so as to 
construct threshold setting means for setting the operating threshold of a 
vehicle occupant protecting device. 
The collision predicting section 26 is connected to a collision 
determination section 28 constituting collision determination means. A 
collision sensor 30, consisting of an acceleration sensor, is also 
connected to the collision determination section 28. The collision 
determination section 28 compares collision acceleration G which is output 
from the collision sensor 30 with a threshold which is set at the 
collision predicting section 26 at the time of an actual collision, and 
when the actual collision acceleration exceeds the threshold, the 
collision determination section 28 outputs a collision determination 
signal so as to operate a vehicle occupant protecting device 32 such as an 
air bag apparatus or the like. 
An operation of the first embodiment of the present invention will be 
explained hereinafter. 
First of all, a method for calculating the current position of an obstacle 
will be explained. 
Typically, a corner reflector (i.e., a standard reflector) has the 
characteristic of reflecting an electrical wave at a single reflecting 
point thereof. However, in the case of an obstacle 16 having a certain 
width (i.e., a certain magnitude) such as another vehicle or the like, the 
reflection intensity of the radar is distributed, and a strongly 
reflecting portion of the reflector can thereby be recognized. As a 
result, when the distance measuring sensors 12, 14 of two radar sensors 
detect the obstacle 16, because respective reflecting points from the two 
radar sensors are different, distances and relative velocities detected by 
the distance measuring sensors 12, 14 do not correspond with each other, 
and data, in which even if there is a single obstacle 16, there seem to be 
two obstacles 16, may be output from the sensors. Actually, since it is 
rarely necessary to imagine an occasion on which there may be a plurality 
of obstacles 16 at a close distance such as about 1 m between the vehicle 
10 and the obstacle 16, there is no problem of predicting the current 
position of the obstacle 16 with a certain accuracy by way of 
triangulation by assuming that there must be one obstacle 16. 
Therefore, as shown in the flowchart of FIG. 3, at Step 100 (hereinafter, 
referred to as S100), the collision predicting section 26 reads 
distance-measured values RR, RL by the distance measuring sensors (R)12, 
(L)14. Further, the collision predicting section 26 reads the predicted 
locus (Y=aX+b) of the obstacle 16 which is shown in FIG. 5 and results 
from the calculation at the obstacle locus calculating section 20C. 
Next, at S102, on the basis of distance information, it is determined 
whether an intersecting point indicating a position of the obstacle 16 may 
exist or not. If it is determined that an intersecting point exists at 
S102, the routine proceeds to S104, where actual distance L of the 
obstacle 16, which is shown in FIG. 4, is determined by the following 
equation (1): 
##EQU1## 
where the width between the two sensors (in bilateral symmetry) is 
expressed by W(m). 
At S106, calculation of an azimuth angle .theta. of the obstacle 16 which 
is shown in FIG. 4 is put into practice by using the following equation 
(2): 
##EQU2## 
Otherwise, at S102, in a case where it has been determined that there is no 
intersecting point, the routine proceeds to S108, where the mean value of 
distance measured values RR, RL of the distance measuring sensors (R)12, 
(L)14 is employed as actual distance L. At S110, azimuth angle .theta. is 
calculated from gradient a of a linear equation of the predicted locus of 
the obstacle 16. 
Accordingly, as shown in FIG. 5, in the detection of the obstacle 16 having 
a certain width (i.e., a certain magnitude) such as a guard rail, a 
concrete wall, and the like, when the distance between the obstacle 16 and 
the distance measuring sensors 12, 14 is less than or equal to about half 
of the width (W) between the two distance measuring sensors 12, 14 (a 
point where t=t.sub.0+1), an insertion point indicating a position of the 
obstacle 16 is nonexistent so that the current position and an azimuth 
cannot be calculated. Therefore, a current position of the obstacle 16 is 
predicted by the locus of the obstacle (Y=aX+b) which is determined from 
intersecting point A (a point where t=t.sub.0-1) and an intersecting point 
B (a point where t=.sub.0), indicating positions of the obstacle 16 in a 
region where the obstacle 16 is apart from the sensors at a certain 
distance, and current distance measuring data (RR, RL). 
It is presumed that an intersecting point (i.e., an predicted collision 
position) of linear line (Y=aX+b) and X axis is D, intersecting point D is 
used as a center point of circle R1 having radius ((RR+RL)/2), and 
intersecting point C of circle R1 and linear line (Y=aX+b) is a position 
of the obstacle 16 at the time where (t=t.sub.0+1). Because the azimuth of 
the obstacle 16 rarely changes for such a short period of time, the locus 
of the obstacle 16 is not displaced largely from linear equation Y=aX+b. 
Further, on the basis of distance measured data or values (RR, RL) of the 
two distance measuring sensors 12, 14, the shortest distance between the 
obstacle 16 and the two distance measuring sensors 12, 14 is detected by a 
signal process (which is the obstacle 16 having a substantially even 
distribution of reflection intensity). When a mean value of the results of 
distance measurements by the two sensors 12,14 is employed, the actual 
position of the obstacle 16 and intersecting point C correspond with each 
other with high accuracy. 
Next, a method for calculating the locus of the obstacle will be explained 
hereinafter. 
As shown in the flowchart in FIG. 6, at S200, at the obstacle locus 
calculating section 20C, the current position data (L, .theta.) calculated 
at the current position calculating section 20B is read. At S202, a polar 
coordinate system is converted into an orthogonal coordinate system. At 
S204, traveling mean values (X, Y).sub.aven are calculated at four points 
in order to prevent the locus of the obstacle 16 from being affected by 
noise. At S206, linear equation (Y=aX+b) of the locus shown in FIG. 7 is 
calculated from traveling mean values ((XaveL, YaveL), (Xaven, Y aven)) 
within the range in which an approaching locus of the obstacle 16 does not 
change largely (i.e., within the range less than or equal to 10 cm at 
maximum), and at S208, azimuth angle .theta.t is determined from gradient 
a of linear equation (Y=aX+b). 
The calculating method of a collision velocity will be explained 
hereinafter. 
In an electrical wave radar sensor using an electrical wave, relative 
velocities between an irradiated portion of the obstacle 16 and the 
sensors can be measured by measuring the difference in frequency (i.e., 
Doppler frequency) between a transmitting wave and a receiving wave 
through the Doppler effect. When a vector of the relative velocity is in 
the same direction as that of beam radiation, the relative velocity 
corresponds to the velocity of the obstacle 16 approaching the vehicle 10. 
However, in the case that the vector of the relative velocity is not in 
the same direction as that of the beam radiation, because the relative 
velocities detected by the distance measuring sensors 12, 14 become cos 
components of the actual velocity of the obstacle 16 approaching the 
vehicle 10, due to the collision angle formed between the vehicle and the 
obstacle, not a few errors may be caused. 
As shown in the flowchart in FIG. 8, in the collision information detecting 
section 20, at S300, the detected relative velocities VR, VL by the two 
distance measuring sensors 12, 14, and azimuth angle .theta.t resulting 
from the collision predicting section 26 are read. At S302, collision 
velocity VL is determined from the relative velocity VR at the sensor 
(R)12 side, while collision velocity V2 is determined from relative 
velocity VL at the sensor (L) 14 side. 
At S304, if the absolute value of the difference between V1 and V2 is less 
than velocity range .DELTA.V, the routine proceeds to S306, where 
collision velocity V adopts the mean value of V1 and V2. On the other 
hand, at S304, if the absolute value of the difference between V1 and V2 
is greater than velocity range .DELTA.V, the routine proceeds to S308, 
where the magnitudes of angles (90-.theta.t-.theta.R) and 
(90+.theta.t-.theta.L) in the cos terms of an equation for calculating the 
collision velocities V1, V2 are compared to each other. The above equation 
is calculated by angles .theta.R, .theta.L between the distance measuring 
sensors 12, 14 and the obstacle 16. If angle (90+.theta.t-.theta.L) is 
greater than angle (90-.theta.t-.theta.R) , the routine proceeds to S310, 
where V1 is used as the collision velocity. On the other hand, if angle 
(90-.theta.t-.theta.R) is greater than angle (90+.theta.t-.theta.L), the 
routine proceeds to S312, where V2 is used as the collision velocity. 
As shown in FIG. 9, in a region where each of the magnitudes of angles 
(90-.theta.t-.theta.R) and (90+.theta.t-.theta.L) in the cos terms of the 
aforementioned equation for calculating collision velocities V1, V2 is 
close to 0.degree., the collision velocity is slightly affected by the 
errors of the angles .theta.R, .theta.L and .theta.t. On the other hand, 
in a region where each of magnitudes of the aforementioned angles 
(90-.theta.t-.theta.R) and (90+.theta.t-.theta.L) is close to 90.degree., 
the collision velocity is affected largely by the errors of angles 
.theta.R, .theta.L, and .theta.t. Therefore, if the collision velocity 
having a smaller angle is employed, the collision velocity with higher 
accuracy can be detected. 
At S314, the azimuth angle .theta.t resulting from the locus of the 
obstacle 16 is used as collision angle .theta.v. 
Next, a method for predicting the collision of a vehicle will be explained 
hereinafter. 
As shown in the flowchart in FIG. 10, in the collision predicting section 
26, threshold Gth of collision acceleration for determining the expansion 
timing of an air bag as the vehicle occupant protecting device 32 can be 
determined by collision velocity V, collision angle .theta.v, actual 
distance L between the obstacle 16 and the vehicle 10, and detected 
distances RR, RL by the two distance measuring sensors 12, 14. 
Namely, at S400, collision velocity V, collision angle .theta.v, actual 
distance L, and the detected distances RR, RL by the two distance 
measuring sensors 12, 14 are read. At S402, it is determined whether or 
not the distances RR, RL detected by the two distance measuring sensors 
12, 14 have an intersecting point at the shortest distance between the 
obstacle 16 and the sensors 12, 14 (i.e., at a distance which is less than 
or equal to half the width between sensors 12, 14). When detected 
distances RR, RL have an intersecting point, the routine proceeds to S410. 
When detected distances RR, RL have no intersecting point at S402, it 
means that the obstacle 16 has a certain magnitude or width. In this case, 
at S404, distances RR and RL detected by the sensors 12, 14 are compared 
to each other. When distance RL is smaller than distance RR, at S406, the 
distance RR having larger distance measuring data from sensors 12, 14 is 
used as an actual distance L. On the other hand, when distance RL is equal 
to or larger than distance RR, at S408, distance RL having larger 
measuring data from the sensors 12, 14 is used as an actual distance L. 
At S410, the routine is iterated from steps S400 through S408 until actual 
distance L becomes shorter than fixed distance Lth. If actual distance L 
becomes shorter than fixed distance Lth, at S412, a determination is made 
whether collision velocity V is between Vth1 and Vth3. If the answer is 
"YES" at S412, the routine proceeds to S414, where a determination is made 
whether collision angle .theta.v is between .theta.th1 and .theta.th4. If 
the answer is "YES" at S414, the routine proceeds to S416, where a 
determination is made whether collision angle .theta.v is in region 1, 
which is shown in FIG. 11. If the answer is "YES" at S416, the routine 
proceeds to S418, where Gth2 is set to threshold Gth of collision 
acceleration. 
If the answer is "NO" at S416, the routine proceeds to S420, where a 
determination is made whether collision velocity V and collision angle 
.theta.v are in region 2, which is also shown in FIG. 11. If the answer is 
affirmative at S420, the routine proceeds to S422, where Gth1 is set to 
threshold Gth of collision acceleration. 
If the answer is negative at S420, the routine proceeds to S424, where Gth3 
is set to threshold Gth of collision acceleration. 
Namely, when the obstacle 16 is provided at distance Lth in which a 
collision cannot be prevented, a large collision acceleration is generated 
within the range in which collision angle .theta.v is close to 0.degree., 
and Gth3 is thereby set to regular threshold Gth. Meanwhile, when the 
collision angle .theta.v becomes larger (30.degree. or greater in a 
transverse direction of the obstacle 16 at the time of a collision at the 
front of the vehicle), the magnitude and the rise time of collision 
acceleration are affected so that sensors tend to be delayed. Accordingly, 
as shown in FIG. 10, when collision angle .theta.v is in a region 
(.theta.th1 to .theta.th2, .theta.th3 to .theta.th4) and collision 
velocity V is relatively small (Vth1 to Vth2), Gth1 is used as threshold 
Gth of collision acceleration. In the case that the collision angle 
.theta.v is within the same range as aforementioned collision angle 
.theta.v, and collision velocity V is within the range of (Vth2 to Vth3), 
Gth2 is used as threshold Gth of collision acceleration. Further, 
threshold Gth of three collision accelerations has a relationship of 
magnitude of Gth3&gt;Gth2&gt;Gth1. 
Next, a method of determining a collision will be explained hereinafter. 
In the collision determination section 28, as shown in the flowchart in 
FIG. 12, at S500, detected value Gsens of the collision acceleration by 
the collision sensor 30, and calculated threshold Gth of the collision 
acceleration at the collision predicting section 26 are read. At S502, 
value Vsens is calculated by integrating detected value Gsens of the 
collision acceleration with times t.sub.0 to t.sub.1. At S504, time 
integration value Vth of threshold Gth of collision acceleration 
determined at the collision predicting section 26 is calculated, and the 
routine proceeds to S506. 
At S506, a determination is made whether Vsens is greater than Vth. As 
indicated by point P1 in FIG. 13, if Vsens is greater than Vth, at S508, 
it is determined that a collision has occurred and a collision 
determination signal (an enable signal to operate the air bag apparatus) 
is output to the air bag apparatus serving as the vehicle occupant 
protecting device 32 so as to enable the air bag apparatus to operate (or 
to operate the air bag apparatus). On the other hand, at S506, if it is 
determined that Vsens is less than Vth, at S510, it is determined that a 
collision has not occurred and a collision determination signal (i.e., a 
disable signal to operate an air bag apparatus) is output to the air bag 
apparatus serving as the vehicle occupant protecting device 32 so as to 
prevent the air bag apparatus from operating. 
Accordingly, in the present embodiment, collision information (i.e., 
relative velocities, distances, and directions) are calculated accurately 
at the collision information calculating section 20 by using the two 
distance measuring sensors 12, 14, which can simultaneously detect a 
plurality of relative velocities and distances between the sensors and the 
obstacle. Further, at the collision predicting section 26, the optimal 
value of threshold Gth of collision acceleration at which the air bag 
apparatus serving as the vehicle occupant protecting device 32 is operated 
in accordance with the state of the collision is determined from the 
collision angle and the collision velocity. For this reason, even when the 
detected acceleration of the collision sensor 30 is small, the air bag 
apparatus serving as the vehicle occupant protecting device 32 can expand 
at an optimal timing. 
As shown in FIG. 14, the present embodiment can be structured such that the 
two distance measuring sensors 12, 14 are mounted in the vicinity of each 
of the end portions of the vehicle 10 in the longitudinal direction 
thereof, respectively, and distances and relative velocities between the 
vehicle 10 and the obstacle 16 are detected at the time of a collision at 
the side of the vehicle 10. 
An obstacle detecting apparatus and a device for protecting a vehicle 
occupant using the obstacle detecting apparatus according to a second 
embodiment of the present invention will be explained hereinafter with 
reference to FIGS. 15 through 20. 
The structure of the second embodiment is the same as the first embodiment, 
and a description thereof is omitted. Instead, a description of the 
operation thereof will be given hereinafter. 
As shown in FIG. 15, when the obstacle 16 and the vehicle 10 collide from a 
direction diagonally right of the vehicle 10 so as to be angled at 
30.degree., the relationship between the collision velocity which is 
detected by the two distance measuring sensors 12, 14, and time is 
illustrated in FIG. 16, where the vertical axis is the collision velocity 
and the horizontal axis is the time, and the time 0 sec is the instant of 
the collision. 
In this graph, a solid line indicates the collision velocity which is 
dcalculated from the relative velocity detected by the right (R) distance 
measuring sensor 12. A broken line indicates the collision velocity which 
is calculated from the relative velocity detected by the left (L) distance 
measuring sensor 14. Further, two collision velocities respectively 
provided for each of the two distance measuring sensors 12, 14 are values 
of the respective collision velocities which are calculated at the time 
when the distance detecting accuracy of each sensor varies at .+-.15 cm, 
and means that, depending upon variations in the detected distance, the 
calculated values of the collision velocities vary between the two curves. 
As shown in FIG. 16, in the collision velocity which is determined from the 
detected relative velocity by the right (R) distance measuring sensor 12, 
the calculation error becomes larger at the shortest distance between the 
vehicle 10 and the obstacle 16 at a time of 0.04 sec before the collision 
(i.e., about 10 cm closer from the vehicle 10 to the obstacle 16). 
Especially, the relative velocity detected by the right (R) distance 
measuring sensor 12 (cos components of the collision velocity) decreases 
as the obstacle 16 comes closer to the vehicle 10, and when the obstacle 
16 becomes more closer to the vehicle 10, a state in which polarity may be 
reversed, is generated. The reason why this happens is that collision 
velocity V is determined by V=VR/cos .theta.R, but when .theta.R is about 
90.degree., the value of cos .theta.R is extremely small, the collision 
velocity V is affected greatly by the calculating error in .theta.R. 
Moreover, in the general state of a collision, because the change of the 
collision velocity is rarely caused in such an extremely short period of 
time as a few 10 msec, it is possible to predict the collision velocity at 
the instant of collision to a degree by detecting the collision velocity 
at a time of a few 10 msec before the collision. However, in the actual 
collision of a vehicle, the vehicle 10 according to the present invention, 
or the other vehicle with which the vehicle 10 collides, may induce a 
multiple collision with other obstacles than the aforementioned other 
vehicle before the actual collision. In a multiple collision, when the 
other vehicle and another objects collide directly after the vehicle 10 
has determined the collision velocity of the vehicle 10 with respect to 
the other vehicle, the actual collision velocity changes drastically. For 
this reason, in order to predict the collision velocity accurately, 
changes in the velocity must be checked as minutely as possible by the 
last moment before the collision. 
Therefore, in the collision predicting section 26 of the present 
embodiment, as shown in the flowchart in FIG. 17, at S600, a determination 
is made whether the intersecting point of the linear line Y=aX+b and X 
axis, i.e., predicted collision position D which is shown in FIG. 5, is 
disposed at the position at which the distance from position D to the 
center of the widthwise direction of the vehicle 10 is larger than W/2 
(i.e., W is the distance between the two sensors 12, 14 which are 
symmetrical to each other). Namely, a determination is made whether 
predicted collision position D is disposed out of W/2, i.e., a central 
point of the vehicle at the transverse direction thereof (in this case, as 
shown in FIG. 5, W/2 is the distance from the central point of W to the 
right (R) distance measuring sensor 12). 
At S600, if it is determined that predicted collision position D is 
disposed at a position at which the distance from the position D to the 
center of the widthwise direction of the vehicle 10 is larger than W/2 
(i.e., W is the distance between the two sensors 12, 14 which are 
symmetrical to each other), the routine proceeds to S602. In this case 
(i.e., in FIG. 5), since predicted collision position D is disposed at a 
position further to the distance W/2 from the center point of the 
transverse direction of the vehicle 10, the relative velocities between 
the sensors and the obstacle 16 are difficult to produce. Further, the 
obstacle 16 and the vehicle 10 collide from a direction of the sensor 
having a lower sensitivity so that it becomes difficult to effect stable 
detection by using the two distance measuring sensors 12, 14. In this 
case, it is desirable to compare information from the left and right 
distance measuring sensors 12, 14 to each other and to employ only 
information from the sensor which is detecting the relative velocity more 
stably. Namely, relative velocity VR or VL, i.e., the information which 
the distance measuring sensor 12 or 14 is detecting more stably is set to 
relative velocity Vref so that the collision velocity is calculated. At 
the same time, the angle .theta.R or .theta.L, each of which is formed 
between the obstacle 16 and the distance measuring sensors 12, 14, i.e., 
the information of which the distance measuring sensor 12 or 14 is 
detecting with more stability, is set to angle .theta.. 
On the other hand, at S600, if it is determined that predicted collision 
position D is disposed at a position at which the distance from the 
position D to the center of the widthwise direction of the vehicle 10 is 
less than or equal to W/2 (i.e., W is the distance between the two sensors 
12, 14 which are symmetrical to each other), the routine proceeds to S604, 
where a determination is made whether collision angle .theta.i is between 
.theta.1 (for example, 5.degree.) and .theta.2 (for example, 30.degree.). 
If the answer is "YES" (i.e., if it is determined that the collision 
occurs from a diagonally left direction of the vehicle), the routine 
proceeds to S606, where information VR, .theta.R from the right distance 
measuring sensor 12 is set to relative velocity Vref and angle .theta. for 
calculating the collision velocity. 
On the other hand, at S604, if it is determined that the collision angle 
.theta.i is not between .theta.1 (for example, 5.degree.) and .theta.2 
(for example, 30.degree.), the routine proceeds to S608, where a 
determination is made whether the collision angle .theta.i is between 
-.theta.1 (for example, -5.degree.) and -.theta.2 (for example, 
-30.degree.). At S608, if the answer is "YES" (i.e., the collision occurs 
from a direction diagonally right of the vehicle), the routine proceeds to 
S610, where information VL, .theta.L from the left distance measuring 
sensor 14 are set to relative velocity Vref and angle .theta. for 
calculating the collision velocity. 
At S608, if the answer is "NO", the routine proceeds to S612, where a 
determination is made whether the collision angle .theta.i is within the 
range of .theta.i&lt;.vertline..theta.1.vertline.(.theta.1=.+-.&lt;5.degree.). 
If the answer is "YES", the routine proceeds to S614, where a 
determination is made whether the collision predicted position D is 
positioned at the left side of the vehicle front portion. 
At S614, if the answer is affirmative, collision angle .theta.i is 
relatively small and the obstacle and the vehicle collide at the left side 
of the vehicle front portion so that it is regarded as an offset 
collision. Therefore, the routine proceeds to S606, where information VR, 
.theta.R from the right distance measuring sensor 14 are set to relative 
velocity Vref and angle .theta. for calculating the collision velocity. 
Further, at S614, if the answer is negative, the routine proceeds to S616, 
where a determination is made whether predicted collision position D is 
positioned at the right side of the vehicle front portion. 
At S616, if the answer is "YES", the collision angle .theta.i is relatively 
small and the obstacle and the vehicle collide at the right side of the 
vehicle front portion so that it is regarded as an offset collision. 
Therefore, the routine proceeds to S610, where information VL, .theta.L 
from the left distance measuring sensor 14 are set to relative velocity 
Vref and angle .theta. for calculating the collision velocity. 
Meanwhile, at S616, if the answer is "NO", the routine proceeds to S618, 
where a determination is made whether the collision predicted position D 
is positioned at the center of the vehicle front portion. 
At S618, if the answer is "YES", the collision angle .theta.i is relatively 
small and the obstacle and the vehicle collide at the center of the 
vehicle front portion so that it is regarded as a head-on collision in 
which the errors detected by the two (left and right) distance measuring 
sensors 12, 14 have substantially the same level. Therefore, the routine 
proceeds to S602, where the relative velocity VL or VR detected by the 
distance measuring sensors is set to the relative velocity Vref, while 
angle .theta.R or .theta.L, which is formed between the obstacle 16 and 
the sensors 12, 14, is set to angle .theta.. 
Following the steps of S602, S606, and S610, at S620, collision velocity V 
is calculated by relative velocity Vref and angle .theta. which have been 
set on the basis of the collision angle and the collision position. 
Accordingly, in the present second embodiment, as shown in a table of FIG. 
18, on the basis of conditions for a collision (including the collision 
angle and the collision position), it is determined which information from 
the right or left sensor to be used. Since collision velocity V is 
calculated on the basis of the selected information, even when the 
obstacle 16 is close to the vehicle 10, the collision velocity V can be 
calculated accurately. 
Next, a description of control of the expansion of the air bag apparatus 
serving as the vehicle occupant protecting device 32, using the collision 
velocity according to the present embodiment. 
A control portion of the expansion of the air bag apparatus is provided at 
the collision determination section 28, for detecting the collision 
velocity, the collision position and the collision angle of the obstacle 
16 before the collision, for predicting the degree of damage due to the 
collision within a few msec directly after the collision by using the 
collision acceleration detected by the collision sensor 30 which is 
installed in the vehicle 10, and for optimally regulating the expansion 
velocity and the inner pressure of the air bag body. In order to directly 
detect the damage due to the collision, both of the mass and the collision 
velocity of the obstacle 16 must be detected. However, the mass of the 
obstacle 16 cannot be detected by the right and left distance measuring 
sensors 12, 14. 
For this reason, four pieces of information resulting from the present 
second embodiment are shown in tables 1 through 4 below. As shown in FIG. 
19, these four pieces of information include the times at which 
integration value V of collision acceleration G output from the collision 
sensor 30 varies from V1 to V2, i.e., different point numbers ai, bi, ci, 
and di will be given in accordance with the influence degree due to the 
collision damage for each of the levels consisted of: 
rise time of the collision sensor=t.sub.2 -t.sub.1 (weighting coefficient 
Ct), 
collision velocity (weighting coefficient Cv), 
collision angle (weighting coefficient Ca), and 
collision position (weighting coefficient Cp). 
TABLE 1 
______________________________________ 
Rise time of 
&gt;10 8-10 6-8 4-6 2-4 &lt;2 
collision sensor 
(ms) 
Number of a1 a2 a3 a4 a5 a6 
points 
______________________________________ 
TABLE 2 
______________________________________ 
Collision 
&lt;10 10-20 20-30 30-40 40-50 50-60 &gt;60 
rate 
(km/h) 
Number b1 b2 b3 b4 b5 b6 b7 
of points 
______________________________________ 
TABLE 3 
______________________________________ 
Collision angle 
&gt;.+-.30 
.+-.20-30 .+-.10-20 
&lt;.+-.10 
(deg) 
Number of c1 c2 c3 c4 
points 
______________________________________ 
TABLE 4 
______________________________________ 
Collision Center Right side 
Left side 
position 
Number d1 d2 d3 
of points 
______________________________________ 
For example, performance index Sb is determined by the following equation 
(3) at the time when the vehicle 10 and a barrier collide on a head-on 
collision at the velocity of V(km/h). 
EQU Sb=Ct.multidot.ai+Cv.multidot.bi+Ca.multidot.ci+Cp.multidot.di (3) 
At the time of the actual collision, the evaluation index Si can be 
calculated in the same manner as the aforementioned index Sb, and ratio 
.alpha. of Si and Sb which has been calculated previously is calculated by 
the following equation (4). 
EQU .alpha.=Si/Sb (4) 
As a result, as shown in FIG. 20, corresponding to ratio .alpha. of the 
performance index, for example, the expansion velocity of the air bag 
apparatus is regulated to the expansion velocity Vb which has been stored 
in advance. Therefore, in a region where the ratio .alpha. is greater than 
1, i.e., the region where the collision damage becomes larger, the 
expansion velocity Vb is made to be maximum. However, in a region where 
the ratio .alpha. is less than 1, i.e., the region where the collision 
damage becomes smaller, as the ratio .alpha. becomes smaller, the 
expansion velocity Vb is decreased so as to lower the expansion velocity 
of the air bag body within a range that a protection effect using the air 
bag body can be secured. As a result, an optimal control on the air bag 
body can be effected. 
As described above, a detailed description of the present invention 
according to the specified embodiments has been given. However, it will 
also be obvious to those skilled in the art that the present invention is 
not limited to the above described embodiments, and various modifications 
or changes can be made without departing from the spirit of the invention. 
For example, the vehicle occupant protecting device is not limited to the 
air bag apparatus. Instead, a seat belt pretensioner or the like can be 
used as a vehicle occupant protecting device.