Abstract:
Systems and methods for controlling a vehicle-occupant protecting apparatus provided on a vehicle such that the apparatus is controlled upon determination that the vehicle has had a rollover motion, the control system including a first detector that determines whether the vehicle has crashed, a second detector that determines whether the vehicle has had a rollover motion, and an invalidating device that invalidates the determination by the second detector that the vehicle has had the rollover motion such that the determination by the second detector is invalidated for a predetermined time after the determination by the first detector that the vehicle has crashed. Furthermore, a controller controls the vehicle-occupant protecting apparatus based on outputs of the second detector and the invalidating device to prevent unnecessary operation of the vehicle-occupant protecting device.

Description:
INCORPORATION BY REFERENCE 
     The disclosure of Japanese Patent Application No. 2001-012468 filed on Jan. 19, 2001 and No. 2001-227348 filed Jul. 27, 2001, including the specification, drawings and abstract, is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to systems and methods for controlling a vehicle-occupant protecting apparatus such that an appropriate vehicle-occupant protecting devices of the vehicle-occupant protecting apparatus is operated upon detection of a crash or a rollover motion of an automotive vehicle. 
     2. Description of Related Art 
     A control system for controlling a vehicle-occupant protecting apparatus of an automotive vehicle is well known, which includes vehicle-occupant protecting devices such as airbags and seat-belt pre-tensioners. The control system is arranged to determine whether the vehicle has a rollover motion, on the basis of roll angle and rate of the vehicle, and to operate the appropriate vehicle-occupant protecting device or devices when the rollover motion of the vehicle is detected. In this respect, it is noted that the vehicle occupants (in particular, the upper part of their bodies) are moved toward the right or left side of the vehicle body during turning of the vehicle. Accordingly, the rollover motion of the vehicle which takes place during turning of the vehicle causes a reduction of a space which is provided adjacent to an airbag disposed on the right or left side of the vehicle body, and which would accommodate the airbag that has been inflated due to the rollover motion of the vehicle. 
     In view of this drawback, JP-A-2000-9599 discloses a control system which is arranged to effect a determination as to whether the vehicle is turning, on the basis of the detected steering angle of the vehicle. Moreover, the control system effects a determination as to whether the vehicle has a rollover motion, on the basis of the detected roll angle and rate of the vehicle while the vehicle is not turning, and on the basis of a detected lateral acceleration value of the vehicle as well as the detected roll angle and rate, while the vehicle is turning. This arrangement permits a relatively early detection of the rollover motion of the vehicle during turning of the vehicle. 
     The rollover motions of the vehicle in JP-A-2000-9599 include a “trip-over” motion which takes place due to a collision of the vehicle wheel or wheels with stationary objects, such as edge blocks arranged along an edge of a roadway, and a “turn-over” motion which takes place during abrupt turning of the vehicle. A determination as to whether the vehicle has such a trip-over or turn-over motion is advantageously effected on the basis of the lateral acceleration value and the roll rate of the vehicle, since an increase of the lateral acceleration value occurs at an earlier point of time than an increase of the roll rate. However, this arrangement may cause an erroneous determination that the vehicle has a rollover motion, in the event of crashing (a side crash, in particular) of the vehicle, while in fact the vehicle does not have a rollover motion. This leads to a risk of an unnecessary operation of the vehicle-occupant protecting device or devices of the vehicle-occupant protecting apparatus. 
     SUMMARY OF THE INVENTION 
     The present invention was made in view of the drawbacks discussed above. It is therefore an object of the present invention to provide control systems and methods for a vehicle-occupant protecting apparatus, which permits accurate determination as to whether the vehicle has had a rollover motion, and which prevents an unnecessary operation of the vehicle-occupant protecting apparatus. 
     According to one aspect of the present invention, there is provided a control system for controlling a vehicle-occupant protecting apparatus provided on an vehicle such that the apparatus is controlled upon determination that the vehicle has a rollover motion, the control system comprising: a first detector that determines whether the vehicle has crashed; a second detector that determines whether the vehicle has a rollover motion; an invalidating device that invalidates the determination by the second detector that the vehicle has the rollover motion, such that the determination by the second detector is invalidated for a predetermined time after the determination is made by the first detector that the vehicle has crashed; and a controller that controls the vehicle-occupant protecting apparatus based on outputs of the second detector and the invalidating device. The invalidation by the invalidating device of the determination of the rollover motion may be effected by either invalidating the determination which has been made by the second detector, or preventing the second detector from making the determination per se. 
     According to another aspect of the present invention, there is provided a method of controlling a vehicle-occupant protecting apparatus provided on an vehicle such that the apparatus is controlled upon a determination that the vehicle has had a rollover motion, comprising the steps of; determining whether the vehicle has crashed: determining whether the vehicle has had the rollover motion; invalidating the determination that the vehicle has had the rollover motion, such that the determination is invalidated for a predetermined time after the determination is made that the vehicle has crashed; and operating the vehicle-occupant protecting apparatus based on the determination whether the vehicle has had the rollover motion and the invalidation of the determination that the vehicle has had the rollover motion. 
     The control system and method of the present invention described above are arranged such that the determination that the vehicle has had a rollover motion is invalidated upon determination that the vehicle has crashed or collided (a side crash, a front crash, a rear crash, etc.), for a predetermined time after the determination has been made that the vehicle has crashed. Accordingly, at least one vehicle-occupant protecting device of the vehicle-occupant protecting apparatus, which would be operated upon an actual rollover motion of the vehicle, is not actually operated for the predetermined time after the determination has been made that the vehicle has crashed, if an erroneous determination that the vehicle has had a rollover motion is made where the rollover motion has not actually taken place upon the crashing of the vehicle. Thus, the present control system and method prevent unnecessary operation of the vehicle-occupant protecting device or devices. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features, advantages, and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings, in which: 
     FIG. 1 is a table showing satisfied and unsatisfied states of conditions (A-E) of side-crash occurrences. 
     FIG. 2 is a schematic plan view of an automotive vehicle provided with a control system according to a first embodiment of this invention; 
     FIG. 3 is a schematic perspective view of a right curtain-shield airbag after the airbag has been inflated; 
     FIG. 4 is a schematic perspective view of a right side airbag after the airbag has been inflated; 
     FIG. 5 is a block diagram that shows the control system for a vehicle-occupant protecting apparatus according to the first embodiment of this invention; 
     FIG. 6 is a flow chart illustrating a control program (rollover detecting routine) executed in accordance with the first embodiment of this invention; 
     FIG. 7 is a flow chart illustrating a control program (side-crash detecting routine) executed in accordance with the first embodiment of this invention; 
     FIG. 8 is a view showing an exemplary first data map used in accordance with the first embodiment of this invention; 
     FIG. 9 is a view showing an exemplary second data map used in accordance with the first embodiment of this invention; 
     FIG. 10 is a view showing an exemplary third data map used in accordance with the first embodiment of this invention; 
     FIG. 11 is a diagram illustrating exemplary functions of the control system for the vehicle-occupant protecting apparatus according to the first embodiment of this invention; 
     FIG. 12 is a schematic plan view of an automotive vehicle provided with a modified form of the control system according to the first embodiment of this invention; 
     FIG. 13 is a block diagram schematically illustrating the modified form of the control system according to the first embodiment of this invention; 
     FIG. 14 is a diagram illustrating exemplary functions of the modified form of the control system according to the first embodiment of this invention; 
     FIG. 15 is a schematic plan view of an automotive vehicle provided with a control system according to a second embodiment of this invention; 
     FIG. 16 is a block diagram schematically illustrating the control system according to the second embodiment of this invention; 
     FIG. 17 is a logic circuit diagram illustrating conditions for the control system according to the second embodiment of this invention; 
     FIG. 18 is a view indicating a data map used according to the second embodiment of this invention; and 
     FIG. 19 is a diagram illustrating the functions of the control system according to the second embodiment of this invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to the accompanying drawings, there will be described presently preferred embodiments of a control system of the invention for controlling a vehicle-occupant protecting apparatus provided on an automotive vehicle. The control system for the vehicle-occupant protecting apparatus functions as an airbag control device and a vehicle rollover detecting device. 
     First Embodiment 
     Referring first to FIG. 2, there is shown an automotive vehicle  10  provided with a vehicle-occupant protecting apparatus and a control system according to the first embodiment of this invention for controlling the vehicle-occupant protecting apparatus. The vehicle-occupant protecting apparatus includes a right curtain-shield airbag  11 , a right side airbag  12 , a left curtain-shield airbag  13  and a left side airbag  14 . The control system includes an electric control device  20 , a roll rate sensor  21 , a lateral acceleration sensor  22 , a right side-crash sensor  23  and a left side-crash sensor  24 . 
     As shown in FIG. 3, the right curtain-shield airbag  11  is attached, at a font fixing portion  11   a  located at its front end, to a front pillar of the vehicle body, and at fixing portions  11   b  to a roof side rail of the vehicle body. When the right curtain-shield airbag  11  is inflated, it is expanded so as to cover substantially entire areas of a right-side front window and a right-side rear window, so that the bodies of vehicle occupants are prevented from moving in the laterally outward direction of the vehicle  10 . 
     As shown in FIG. 4, the right side airbag  12  is accommodated in a right end portion of a right front seat (driver&#39;s seat shown in FIG. 4) DS of the vehicle  10 . When the right side airbag  12  is inflated, it is expanded so as to project from the right end portion of the right front seat DS in the forward direction of the vehicle  10 , so as to protect the right-side portion of the vehicle occupant. 
     Since the left curtain-shield airbag  13  and the left side airbag  14  are identical with the right curtain-shield airbag  11  and the right side airbag  12 , respectively, except for their positions, no further description of these airbags  13 ,  14  is deemed necessary. The right curtain-shield airbag  11  and the right side airbag  12  are inflated (activated) when a crash takes place on the right side of the vehicle  10  (when a right side crash of the vehicle  10  is detected), and the left curtain-shield airbag  13  and the left side airbag  14  are inflated (activated) when a crash takes place on the left side of the vehicle  10  (when a left side crash of the vehicle  10  is detected). These airbags  11 - 14  constitute a first vehicle-occupant protecting device. The right and left curtain-shield airbags  11 ,  13  are inflated (activated) when the vehicle  10  has a rollover motion (when a rollover motion of the vehicle  10  is detected). 
     The electric control device  20  is constituted by a microcomputer incorporating a CPU  20   a , a ROM  20   b , a ROM  20   c , an input interface  20   d  and an output interface  20   e , which are interconnected with each other through a bus, as indicated in the schematic block diagram of FIG.  5 . The CPU  20   a  is arranged to execute control programs (described below) stored in the ROM  20   b , while utilizing a temporary data storage function of the RAM  20   c.    
     To the input interface  20   d  of the electric control device  20 , there are connected the roll rate sensor  21 , lateral acceleration sensor  22 , right side-crash sensor  23  and left side-crash sensor  24 , the output signals of which are received by the CPU  20   a . To the output interface  20   e  of the electric control device  20 , there are connected a squib  11   c  for inflating the right curtain-shield airbag  11 , a squib  13   c  for inflating the left curtain-shield airbag  13 , a squib  12   a  for inflating the right side airbag  12 , and a squib  14   a  for inflating the left side airbag  14 . These squibs  11   c ,  13   c ,  12   a ,  14   a  will be hereinafter referred to as “right curtain-shield airbag squib  11   c ”, “left curtain-shield airbag squib  13   c ”, “right side airbag squib  12   a ” and “left side airbag squib  14   a ”, respectively, where appropriate. The CPU  20   a  is arranged to apply suitable ignition signals (drive signals) to those squibs  11   c ,  13   c ,  12   a ,  14   a.    
     The roll rate sensor  21  is arranged to detect an angular velocity of rotation of the vehicle body about an axis (rolling axis) which passes the center of gravity and extends in the longitudinal direction of the vehicle body. Namely, the roll rate sensor  21  is arranged to detect a roll rate RR of the vehicle  10 . A positive value of the roll rate RR indicates the rate of rolling of the vehicle  10  in the clockwise direction as viewed toward the front of the vehicle  10  from a position in front of the vehicle  10 , that is, in the longitudinal direction from the vehicle front toward the rear. The lateral acceleration sensor  22  is arranged to detect an acceleration GY of the vehicle  10  (vehicle body) in its lateral or transverse direction. A positive value of the acceleration GY (hereinafter referred to as “lateral acceleration value GY”) indicates the acceleration in the right direction. 
     The right side-crash sensor (front right-crash sensor)  23  is attached to a lower portion of a right-side center pillar (right-side B pillar), and includes an acceleration sensor  23   a  and a comparator circuit  23   b . The acceleration sensor  23   a  is arranged to detect a lateral acceleration value of the right-side center pillar, and the comparator circuit  23   b  is arranged to compare the detected lateral acceleration value with a predetermined threshold. The comparator circuit  23   b  generates an output signal RS which has a logical value “1” (a high level) when the detected lateral acceleration value is larger than the threshold, and a logical value “0” (a low level) when the detected lateral acceleration value is not larger than the threshold. That is, the output signal RS having the logical value “1” (high level) indicates that a crash of the vehicle  10  has taken place on its right side. 
     The left side-crash sensor (front left-crash sensor)  24  is attached to a lower portion of a left-side center pillar (left-side B pillar), and includes an acceleration sensor  24   a  and a comparator circuit  24   b . The acceleration sensor  24   a  is arranged to detect a lateral acceleration value of the left-side center pillar, and the comparator circuit  24   b  is arranged to compare the detected lateral acceleration value with a predetermined threshold. The comparator circuit  24   b  generates an output signal LS which has a logical value “1” when the detected lateral acceleration value is larger than the threshold, and a logical value “0” when the detected lateral acceleration value is not larger than the threshold. That is, the output signal LS having the logical value “1” indicates that a crash of the vehicle  10  has taken place on its left side. 
     There will next be described an operation of the control system for the vehicle-occupant protecting apparatus constructed as described above. The CPU  20   a  is arranged to repeatedly execute, with a predetermined cycle time, a control program (a rollover detecting routine) illustrated in the flow chart of FIG.  6 . Each cycle of execution of the routine is initiated with step  500 , which is followed by step  505  to read the lateral acceleration value GY represented by the output signal of the lateral acceleration sensor  22 . Then, the CPU  20   a  goes to step  510  to read the roll rate RR represented by the output signal of the roll rate sensor  21 , and to step  515  to calculate a roll angle RA of the vehicle  10  by integrating the roll rate RR. 
     Then, the CPU  20   a  goes to step  520  to determine whether the vehicle  10  has a rollover motion. This determination in step  520  is based on a rollover data map shown in FIG. 8 relating to the roll rate RR and roll angle RA, and the actual values of the roll rate RR and angle RA obtained in steps  510  and  515 . Described in detail, the CPU  20   a  determines whether a point (indicative of a state of the vehicle) determined by the actual roll rate RR and the actual roll rate RA has moved across a threshold line L 1  which defines a relationship between the roll rate and angle RR, RA. If an affirmative decision (YES) is obtained in step  520 , it indicates that the vehicle has a rollover motion, and the CPU  20   a  goes from step  520  to step  525  to apply the ignition signals to the right and left curtain-shield airbag squibs  11   c ,  13   c , for inflating the right and left curtain-shield airbags  11 ,  13 , respectively. Then, the control flow goes to step  595  in which one cycle of execution of the present rollover detecting routine is terminated. 
     If it is determined in the step S 520  that the point determined by the actual roll rate and angle RR, RA has not moved across the threshold line L 1 , that is, if a negative decision NO) is obtained in step  520 , the CPU  20   a  goes to step  530  to effect a determination as to whether the vehicle  10  has a rollover motion. This determination is made based on a rollover data map shown in FIG. 9 that relates to the roll rate RR and the lateral acceleration value GY, and the actual values of the roll rate RR and lateral acceleration value GY obtained in steps  510  and  505 . Described in detail, the CPU  20   a  determines whether a point (indicative of a state of the vehicle) determined by the actual roll rate RR and the actual lateral acceleration value GY has moved across a threshold line L 2  which defines a relationship between the roll rate RR and the lateral acceleration value GY. If an affirmative decision (YES) is obtained in step  530 , it indicates that the vehicle has a rollover motion, and the CPU  20   a  goes step  535 . If a negative decision (NO) is obtained in step  530 , it indicates that the vehicle does not have a rollover motion, and the CPU  20   a  goes to step  594  to terminate one cycle of execution of the present routine. 
     If the CPU  20   a  goes to step  535 , the CPU  20   a  determines whether a point (indicative of a state of the vehicle) determined by the actual roll rate and angle RR, RA lies in a rollover-determination permitting region defined by a determination-permitting data map (side-crash guard data map) shown in FIG. 10 relating to the roll rate and angle RR, RA. The rollover-determination permitting region is defined in a two-dimensional coordinate system of the roll rate RR and the roll angle RA, by two threshold lines Lk and the X- and Y-axes of the coordinate system. The rollover-determination permitting region consists of areas in the coordinate system, which do not include the origin of the coordinate system. Each of the two threshold lines Lk is a boundary line on one side of which the above-indicated areas exist. When the point determined by the roll rate and angle RR, RA lies in these areas (rollover-determination permitting region), it is determined that the vehicle  10  has a rollover motion while a crash of the vehicle  10  has taken place on its right or left side, while the output signal RS or LS does not have the logical value “1.” When the above-indicated point lies in the other area on the other side of each threshold like Lk, it is determined that the vehicle  10  does not have a rollover motion while a crash of the vehicle  10  has taken place on its right or left side. The CPU  20   a  goes to step  540  when an affirmative decision (YES) is obtained in step  535 . If a negative decision (NO) is obtained in step  535 , it indicates that the vehicle does not have a rollover motion, and the CPU  20   a  goes to step  595  to terminate one cycle of execution of the present routine. 
     If the CPU  20   a  goes to step  540 , the CPU  20   a  determines whether a RIGHT SIDE CRASH flag FR is set at “0.” As described below, this RIGHT SIDE CRASH flag FR is kept at “1” for a predetermined time T 10  after the right side-crash sensor  23  has generated the output signal RS having the logical value “1,” that is, after a crash of the vehicle  10  on its right side has been detected. The flag FR is set at “0” in the other cases. 
     If an affirmative decision (YES) is obtained in step  540 , the CPU  20   a  goes to step  545  to determine whether a LEFT SIDE CRASH flag FL is set at “0.” As described below, this RIGHT SIDE CRASH flag FL is kept at “1” for a predetermined time T 20  after the left side-crash sensor  24  has generated the output signal RL having the logical value “1,” that is, after a crash of the vehicle  10  on its left side has been detected. The flag FL is set at “0” in the other cases. 
     If an affirmative decision (YES) is obtained in step  545 , the CPU  20   a  applies the ignition signals to the right and left curtain-shield airbag squibs  11   c ,  13   c , for inflating both of the right and left curtain-shield airbags  11 ,  14 . Then, the CPU  20   a  goes to step  595  to terminate one cycle of execution of the present routine. If a negative decision (NO) is obtained in step  540  or step  545 , on the other hand, the CPU  20   a  directly goes to step  595  to terminate one cycle of execution of the present routine. Thus, the determination due to a side crash of the vehicle  10  that the vehicle  10  has a rollover motion, namely, the affirmative decision (YES) in step  530  is invalidated if the flag FR or FL is set at “1” (if the predetermined time T 10  or T 20  has not passed after the moment of detection of the side crash). 
     As described above, the CPU  20   a  is arranged to activate (or inflate) both of the right and left curtain-shield airbags  11 ,  13  when the affirmative decision (YES) is obtained in step  520 , or when the affirmative decision (YES) is obtained in all of steps  530 ,  535 ,  540 ,  540 ,  545 . 
     There will next be described a manner of setting the RIGHT SIDE CRASH flag FR and the LEFT SIDE CRASH flag FL and determining whether a crash of the vehicle  10  on its right or left side has taken place. The following description first refers to a case where a side crash of the vehicle  10  has not taken place. It is noted that the flags RF and FL are reset to “0” in an initializing routine executed when an ignition switch of the vehicle  10  is turned ON. 
     Reference is made to the flow chart in FIG. 7 illustrating a control program (side-crash detecting routine). This side-crash detecting routine is repeatedly executed with a predetermined cycle time. Each cycle of execution of the present routine is initiated with step  600  to determine whether the logical value of the output signal RS of the right side-crash sensor  23  has changed from “0” to “1.” If a crash of the vehicle  10  on its right side has not taken place at this point of time, a negative decision (NO) is obtained in step  605 , and the control flow goes to step  610  to determine whether the RIGHT SIDE CRASH flag FR is set at “1.” 
     Since the RIGHT SIDE CRASH flag FR was reset to “0” in the initializing routine, a negative decision (NO) is obtained in step  610 , and the CPU  20   a  goes to step  615  to determine whether the logical value of the output signal LS of the left side-crash sensor  24  has changed from “0” to “1.” If a crash of the vehicle  10  on its left side has not taken place, either, at this point of time, a negative decision (NO) is obtained in step  615 , and the control flow goes to step  620  to determine whether the LEFT SIDE CRASH flag FL is set at “1.” Since the LEFT SIDE CRASH flag FL was also reset to “0” in the initializing routine, a negative decision (NO) is obtained in step  620 , and the CPU  20   a  goes to step  695  to terminate one cycle of execution of the present side-crash detecting routine. 
     Thus, the flags FR and FL are held at “0” before a side crash of the vehicle  10  has taken place. 
     Then, a case where a crash of the vehicle  10  has taken place on its right side will be described. In this case, the logical value of the output signal RS of the right side-crash sensor  23  has changed from “0” to “1.” Accordingly, an affirmative decision (YES) is obtained in step  605  when this step  605  is implemented during the repeated execution of the present routine. Therefore, the CPU  20   a  goes to step  625  to set the RIGHT SIDE CRASH flag FR to “1.” 
     Then, the CPU  20   a  goes to step  630  to reset the content of a timer T 1  to “0.” Step  630  is followed by step  635  to apply the ignition signal to the right side airbag squib  12   a , and step  640  to apply the ignition signal to the right curtain-shield airbag squib  11   c . As a result, the right side airbag  12  and the right curtain-shield airbag  11  are inflated. Then, the CPU  20   a  goes to step  615 . In this case where the logical value of the output signal LS of the left side-crash sensor  24  is kept at “0,” the CPU  20   a  then goes to steps  620  and  695 , whereby one cycle of execution of the present routine is terminated. 
     When a predetermined time has passed in this state, the CPU  20   a  initiates the next cycle of execution of the present routine with step  600 . In this cycle of execution in which the logical value of the output signal RS of the right side-crash sensor  23  was already changed from “0” to “1,” a negative decision (NO) is obtained in step  605 , and the CPU  20   a  goes to step  610 . Since the RIGHT SIDE CRASH flag FR was set to “1” in step  625  in the last cycle of execution of the routine, an affirmative decision (YES) is obtained in step  610 , and the CPU  20   a  goes to step  645  to increment the content of a timer T 1  by “1.” Then, the CPU  20   a  goes to step  650  to determine whether the content of the timer T 1  is larger than the predetermined threshold time T 10 . This threshold time T 10  is a time duration during which it is required to invalidate the determination due to a right side crash of the vehicle  10  that the vehicle  10  has a rollover motion, that is, the affirmative decision (YES) in step  530  based on the detected roll rate RR and lateral acceleration value GY. That is, the affirmative decision in step  530  is invalidated for the predetermined time T 10  after the moment of detection of the right side crash of the vehicle  10 . 
     In this case where the content of the timer T 1  is set at “0” due to the setting in step  630  in the last cycle, the content of the timer T 1  is smaller than the threshold value T 10 , and a negative decision (NO) is obtained in step  650 . Accordingly, the CPU  20   a  then goes to step  695  through steps  615  and  620 , so that one cycle of execution of the present routine is terminated. 
     Subsequently, the CPU  20   a  repeatedly implement steps  600 ,  605 ,  610 ,  645  and  650  with the predetermined cycle time, so that the content of the timer T 1  is incremented in step  650 , and eventually exceeds the threshold value T 10 . As a result, an affirmative decision (YES) is obtained in step  650 , and the CPU  20   a  goes to step  655  to reset the content of the RIGHT SIDE CRASH flag FR to “0.” Then, the CPU  20   a  goes to step  695  through step  615  and  620 , to terminate one cycle of execution of the present routine. 
     As described above, the right side airbag  12  and the right curtain-shield airbag  11  are inflated, and the RIGHT SIDE CRASH flag FR is kept at “1” for the time duration equal to the threshold time T 10 , when a crash of the vehicle  10  on its right side has taken place. 
     There will next be described a case where a crash of the vehicle  10  has taken place on its left side. In this case, the CPU  20   a  operates in a manner similar that in the case where the right side crash of the vehicle  10  has taken place. Described in detail, the logical value of the output signal LS of the left side-crash sensor  24  has changed from “0” to “1.” Accordingly, an affirmative decision (YES) is obtained in step  615  when this step  615  is implemented during the repeated execution of the present routine. Therefore, the CPU  20   a  goes to step  660  to set the LEFT SIDE CRASH flag LR to “1.” 
     Then, the CPU  20   a  goes to step  665  to reset the content of a timer T 2  to “0.” Step  665  is followed by steps  670  and  675  to apply the ignition signals to the left side airbag squib  14   a  and the left curtain-shield airbag squib  13   c . As a result, the left side airbag  14  and the right curtain-shield airbag  13  are inflated. Then, the CPU  20   a  goes to step  695  to terminate one cycle of execution of the present side-crash detecting routine. 
     When a predetermined time has passed in this state, the CPU  20   a  initiates the next cycle of execution of the present routine with step  600 , and goes to step  680  through steps  605 ,  610 ,  615  and  620 . In step  680 , the CPU  20   a  increments the content of a timer T 2  by “1.” Then, the CPU  20   a  goes to step  685  to determine whether the content of the timer T 2  is larger than the predetermined threshold time T 20 . This threshold time T 20  is a time duration after the moment of detection of the left side crash of the vehicle  10 , during which it is required to invalidate the determination due to the left side crash that the vehicle  10  has a rollover motion, that is, the affirmative decision (YES) in step  530  based on the detected roll rate RR and lateral acceleration value GY. This threshold time T 20  may be either equal to or different from the threshold time T 10  described above. 
     In this case where the content of the timer T 2  is set at “0” due to the setting in step  665  in the last cycle, the content of the timer T 2  is smaller than the threshold value T 20 , and a negative decision (NO) is obtained in step  685 . Accordingly, the CPU  20   a  then goes to step  695  to terminate one cycle of execution of the present routine. Subsequently, the content of the timer T 2  is incremented in step  680  by repeated implementation of this step  680 , so that the content of the timer T 2  eventually exceeds the threshold value T 20 . As a result, an affirmative decision (YES) is obtained in step  685 , and the CPU  20   a  goes to step  690  to reset the content of the LEFT SIDE CRASH flag FL to “0.” Then, the CPU  20   a  goes to step  695  to terminate one cycle of execution of the present routine. 
     As described above, the left side airbag  14  and the left curtain-shield airbag  13  are inflated, and the LEFT SIDE CRASH flag FL is kept at “1” for the time duration equal to the threshold time T 20 , when a crash of the vehicle  10  on its left side has taken place. 
     The operation of the control system according to the present embodiment is illustrated in the logic circuit diagram of FIG.  11 . Namely, the control system according to the present embodiment is arranged to determine that the vehicle  10  has a rollover motion, and inflate both of the right and left curtain-shield airbags  11  and  13 , either when a rollover condition A has been satisfied, or when all of a rollover condition B, a rollover-determination permitting condition C and post-crash time conditions D and E have been satisfied. The rollover condition A is satisfied when the determination in step  520  that the vehicle  10  has a rollover motion is made on the basis of the actual roll rate and angle RR, RA and the rollover data map of FIG.  8 . The rollover condition B is satisfied when the determination in step  530  that the vehicle  10  has a rollover motion is made, due to a side crash of the vehicle  10 , based on the actual roll rate RR and the actual lateral acceleration value GY and the rollover data map of FIG.  9 . The rollover-determination permitting condition C is satisfied when the determination in step  535  that the state of the vehicle  10  lies in the rollover-determination permitting region is made on the basis of the actual roll rate and angle RR, RA and the rollover-determination permitting data map of FIG.  10 . The post-crash time condition D is satisfied when the predetermined time T 10  has passed after the moment of determination that the vehicle  10  has a right side crash. The post-crash time condition E is satisfied when the predetermined time T 20  has passed after the moment of determination that the vehicle  10  has a left side crash. 
     That is, the CPU  20   a  is arranged to make a determination that the vehicle  10  has a rollover motion, and inflate both of the right and left curtain-shield airbags  11 ,  13 , when a condition {(A or (B and C and D and E) } is satisfied. The right curtain-shield airbag  11  and the right side airbag  12  are inflated when the logical value of the output signal RS of the right side-crash sensor  23  has changed to “1,” and the left curtain-shield airbag  13  and the left side airbag  14  are inflated when the logical value of the output signal LS of the left side-crash sensor  24  has changed to “1.” Circuits labeled “HOLD” in FIG. 11 (hereinafter referred to as “HOLD circuits”) function to hold the logical value “1” of the input signal for the predetermined time (T 10  or T 20 ) after the logical value has changed from “0” to “1.” Circuits labeled “NOT” in FIG. 11 function to change the logical values “1” and “0” of the input signal to “0” and “1,” respectively. Therefore, when the post-crash time conditions D and E are satisfied, the outputs of the HOLD circuits are “0,” which are inverted (negated) by the NOT circuits into “1” as their outputs. 
     FIG. 1 shows an analysis of combinations of satisfied and unsatisfied states of the above-indicated conditions A-E. It will be understood from FIG. 1 that since the rollover condition B is either satisfied or not satisfied in the case where the vehicle  10  has a side crash but does not have a rollover motion, the determination as to whether the vehicle has a rollover motion based on the logical sum of the rollover conditions A and B will be erroneous. To avoid this erroneous determination, the present embodiment is arranged to invalidate the determination on the basis of the rollover condition B, if the post-crash time conditions D and E are satisfied. 
     Experiments indicated that the rollover condition B is either satisfied (or not satisfied) also where the vehicle  10  has a side crash but the logical value of the output signals RS, LS of the side-crash sensors  23 ,  24  are “0” while the vehicle does not have a rollover motion. Therefore, the determination as to whether the vehicle has a rollover motion based on the logical sum of the rollover conditions A and B will be erroneous. To avoid this erroneous determination, the present embodiment is arranged to invalidate the determination on the basis of the rollover condition B, if the rollover-determination permitting condition C is satisfied. 
     When the logical value of the output signal RS of the right side-crash sensor  23  has changed to “1” in the event of a crash of the vehicle  10  on its right side, the right curtain-shield airbag  11  is inflated. If this right side crash results in the determination that the vehicle  10  has a rollover motion, the rollover condition A is satisfied, so that the left curtain-shield airbag  13  is also inflated. Similarly, when the logical value of the output signal LS of the left side-crash sensor  24  has changed to “1” in the event of a crash of the vehicle  10  on its left side, the left curtain-shield airbag  13  is inflated. If this left side crash results in the determination that the vehicle  10  has a rollover motion, the rollover condition A is satisfied, so that the right curtain-shield airbag  11  is also inflated. 
     There will be described a modification of the first embodiment described above. The control system according to this modification is applicable to a vehicle-occupant protecting apparatus which includes a rear right side-crash sensor  25  and a rear left side-crash sensor  26 , as shown in FIG. 12, in addition to the vehicle-occupant protecting devices described above with respect to the first embodiment. As shown in FIG. 13, the rear right and left side-crash sensors  25 ,  26  are also connected to the input interface  20   d.    
     The rear right side-crash sensor  25  includes an acceleration sensor  25   a  and a comparator circuit  25   b . The acceleration sensor  25   a  is fixedly disposed adjacent to a right rear pillar (right C pillar), and is arranged to detect a lateral acceleration value of the right rear pillar. The comparator circuit  25   b  is arranged to compare the detected lateral acceleration value with a predetermined threshold, and generate an output signal RRS which has a logical value “I” (a high level) when the detected lateral acceleration value is larger than the threshold, and a logical value “0” (a low level) when the detected lateral acceleration value is not larger than the threshold. That is, the output signal RRS of the comparator circuit  25   b  having the logical value “1” (high level) indicates that a crash of the vehicle  10  has taken place on the right side of the rear right seat. 
     Similarly, the rear left side-crash sensor  26  includes an acceleration sensor  26   a  and a comparator circuit  26   b . The acceleration sensor  26   a  is fixedly disposed adjacent to a left rear pillar (left C pillar), and is arranged to detect a lateral acceleration value of the left rear pillar. The comparator circuit  26   b  is arranged to compare the detected lateral acceleration value with a predetermined threshold, and generate an output signal RLS which has a logical value “1” when the detected lateral acceleration value is larger than the threshold, and a logical value “0” when the detected lateral acceleration value is not larger than the threshold. That is, the output signal RLS of the comparator circuit  26   b  having the logical value “1” indicates that a crash of the vehicle  10  has taken place on the left side of the rear left seat. 
     The operation of the control system according to the present modified arrangement is illustrated in the logic circuit diagram of FIG.  14 . The control system is arranged to make the determination as to whether the vehicle  10  has a rollover motion, in the same manner as in the first embodiment, and inflate both of the right and left curtain-shield airbags  11 ,  13  when the determination is made that the vehicle has a rollover motion. The control system is further arranged to make the determination as to whether a crash of the vehicle  10  has taken place on its right or left side, based on the output signals RS, LS of the front right and left side-crash sensors  23 ,  24 , and inflate one of the right or left curtain-shield airbags  11 ,  13  that corresponds to the right or left side of the vehicle on which the side crash has taken place, and one of the right or left side airbags  12 ,  14  that corresponds to the right or left side on which the side crash has taken place. 
     The present modified control system is also arranged to invalidate the determination that the vehicle  10  has a rollover motion, which is made based on the actual roll rate RR and the actual lateral acceleration value GY, even when the rollover condition B is satisfied. This determination is invalidated for the predetermined time T 10  after the logical value of the output signal RS of the front right side-crash sensor  23  has changed from “0” to “1,” and for the predetermined time T 20  after the logical value of the output signal LS of the front left side-crash sensor  24  has changed from “0” to “1.” The present control system is further arranged to invalidate the determination that the vehicle  10  has a rollover motion, which is made based on the actual roll rate RR and the actual lateral acceleration value GY, while a post-crash time condition F is not satisfied (while the output of the HOLD circuit corresponding to the rear right side-crash sensor  25  is “0”). The post-crash time condition F is not satisfied for a predetermined time after the logical value of the output signal RRS of the side-crash sensor  25  has changed from “0” to “1.” The present control system is further arranged to invalidate the above-indicated determination, while a post-crash time condition G is not satisfied (while the output of the HOLD circuit corresponding to the rear left side-crash sensor  26  is “0”). The post-crash time condition G is not satisfied for a predetermined time after the logical value of the output signal RLS of the side-crash sensor  26  has changed from 
     In the present modified control system, the right curtain-shield airbag  11  is inflated when the logical value of the output signal RRS has changed from “0” to “1,” and the left curtain-shield airbag  13  is inflated when the logical value of the output signal RLS has changed from “0” to “1.” Thus, the curtain-shield airbag  11  or  13  on the side of the vehicle  10  on which a rear side crash has taken place can be inflated at an adequate timing, and the determination due to this rear side crash that the vehicle  10  has a rollover motion is invalided to avoid unnecessary inflation of the curtain-shield airbag  11 ,  13  on the other side of the vehicle. 
     It will be understood from the foregoing description of the first embodiment and its modification that when the determination is made that the vehicle  10  has a rollover motion based on the lateral acceleration value of the center pillar (center pillar or rear pillar in the modification) and the roll rate RR, this determination is invalided for the predetermined time, to avoid an unnecessary operation of the vehicle-occupant protecting device (curtain-shield airbag  11 ,  13  on the side of the vehicle  10  on which the side crash has not taken place). If the determination that the vehicle  10  has a rollover motion is made based on the roll rate RR and the lateral acceleration value GY while a crash of the vehicle has not taken place, this determination is invalidated when the point determined by the roll rate and angle RR, RA lies within the predetermined rollover-determination permitting region. This arrangement also prevents the unnecessary operation of the vehicle-occupant protecting device. 
     Second Embodiment 
     There will next be described a control system according to a second embodiment of this invention. This second embodiment is arranged such that in the event of a front or rear crash on the front or rear side of the vehicle  10 , as well as in the event of a side crash of the right or left side, the determination of a rollover action of the vehicle  10  based on the roll rate RR and the lateral acceleration value GY is invalided for a predetermined time after the moment of detection of the crash, in order to avoid unnecessary operations of the vehicle-occupant protecting device or devices (curtain-shield airbags). 
     Referring to FIG. 15, there is shown an vehicle-occupant protecting apparatus of the vehicle  10  to which the present control system is applicable. This vehicle-occupant protecting apparatus includes the right curtain-shield airbag  11 , right side airbag  12 , left curtain-shield airbag  13  and left side airbag  14 . The control system includes the electric control device  20 , roll rate sensor  21 , lateral acceleration sensor  22 , front right side-crash sensor  23 , front left side-crash sensor  24 , rear right side-crash sensor  25  and rear left side-crash sensor  26 . Since this arrangement of the vehicle-occupant protecting apparatus is identical with the modified arrangement of FIGS. 12-14 of the first embodiment, no further description is deemed necessary. 
     The vehicle-occupant protecting apparatus of the vehicle  10  further includes a front right (vehicle-operator) seat-belt pre-tensioner  15 , a front left (front passenger) seat-belt pre-tensioner  16 , a rear right seat-belt pre-tensioner  17 , a rear left seat-belt pre-tensioner  18 , an operator-seat front-crash airbag  19 - 1 , a front-passenger-seat front-crash airbag  19 - 2 , a floor acceleration sensor  27 , a right front satellite sensor  28 , and a left front satellite sensor  29 . 
     The front right (vehicle-operator) seat-belt pre-tensioner  15 , front left (front passenger) seat-belt pre-tensioner  16 , rear right seat-belt pre-tensioner  17  and rear left seat-belt pre-tensioner  18  are operated when predetermined conditions are satisfied, to remove a slack or loose state of seat belts of the respective front right and left, and rear right and left seats in a relatively short time. 
     The operator-seat front-crash airbag  19 - 1  is an airbag well known in the art, which is accommodated in a central part of the steering wheel of the vehicle  10 . When this airbag  19 - 1  is inflated, it expands so as to project from the central part of the steering wheel, in the rearward direction of the vehicle, for protecting the chest and other portions of the operator&#39;s body. The front-passenger front-crash airbag  19 - 2  is also an airbag well known in the art, which is accommodated in a dash panel located in front of the front-passenger seat. When this airbag  19 - 2  is inflated, it expands so as to project from the dash panel in the rearward direction of the vehicle, for protecting the chest and other portions of the passenger&#39;s body. 
     The electric control device  20  is fixed in a floor tunnel in a substantially central portion of the vehicle body, as shown in FIG. 15, and is constituted by a microcomputer incorporating the CPU  20   a , ROM  20   b , RAM  20   c , input interface  20   d  and output interface  20   e , which are interconnected to each other by a bus, as schematically shown in the block diagram of FIG.  16 . 
     To the input interface  20   d  of the electric control device  20 , there are connected the roll rate sensor  21 , lateral acceleration sensor  22 , front right side-crash sensor  23 , front left side-crash sensor  24 , rear right side-crash sensor  25  and rear left side-crash sensor  26 , the output signals of which are received by the CPU  20   a . To the output interface  20   e  of the electric control device  20 , there are connected the right curtain-shield airbag squib  11   c , left curtain-shield airbag squib  13   c , right side airbag squib  12   a , and left side airbag squib  14   a . The CPU  20   a  is arranged to apply suitable ignition signals (drive signals) to those squibs  11   c ,  13   c ,  12   a ,  14   a.    
     To the input interface  20   d  of the electric control device  20 , there are also connected the floor accelerator sensor  27 , right front satellite sensor  28  and left front satellite sensor  29 , the output signals of which are received by the CPU  20   a.    
     To the output interface  20   e  of the electric control device  20 , there are connected; a squib  15   a  for the front right seat-belt pre-tensioner  15 ; a squib  16   a  for the front left seat-belt pre-tensioner  16 ; a squib  17   a  for the rear right seat-belt pre-tensioner  17 ; a squib  18   a  for the rear left seat-belt pre-tensioner  18 ; a squib  19 - 1   a  for the operator-seat front-crash airbag  19 - 1 ; and a squib  19 - 2   a  for the front-passenger-seat front-crash airbag  19 - 2 . The CPU  20   a  is arranged to apply suitable ignition signals (drive signals) to those squibs  15   a ,  16   a ,  17   a ,  18   a ,  19 - 1   a ,  19 - 2   a.    
     The floor acceleration sensor  27  is accommodated within the electric control device  20 , and arranged to detect an acceleration GX of the floor tunnel in the central part of the vehicle  10 , which occurs in its longitudinal direction. A positive value of the acceleration GX (hereinafter referred to as “longitudinal acceleration value GX”) indicates the acceleration in the forward direction of the vehicle. 
     The right front satellite sensor  28  includes an acceleration sensor  28   a  and a comparator circuit  28   b . The acceleration sensor  28   a  is attached to a side member on the right side of the vehicle  10 , and located at a position adjacent to the extreme front end of the vehicle. The acceleration sensor  28   a  is arranged to detect an acceleration value at the above-indicated position. A positive value of the acceleration detected by the acceleration sensor  28   a  indicates the acceleration in the forward direction of the vehicle. The comparator circuit  28   b  is arranged to compare the detected acceleration value with a predetermined threshold, and generate an output signal FRS which has a logical value “1” (a high level) when the detected acceleration value is larger than the threshold, and a logical value “0” (a low level) when the detected acceleration value is not larger than the threshold. 
     Similarly, the left front satellite sensor  29  includes an acceleration sensor  29   a  and a comparator circuit  29   b . The acceleration sensor  29   a  is attached to a side member on the left side of the vehicle  10 , and located at a position adjacent to the extreme front end of the vehicle. The acceleration sensor  29   a  is arranged to detect an acceleration value at the above-indicated position. A positive value of the acceleration detected by the acceleration sensor  29   a  indicates the acceleration in the forward direction of the vehicle. The comparator circuit  29   b  is arranged to compare the detected acceleration value with a predetermined threshold, and generate an output signal FLS which has a logical value “1” (a high level) when the detected acceleration value is larger than the threshold, and a logical value “0” (a low level) when the detected acceleration value is not larger than the threshold. 
     Then, an operation of the control system for the vehicle-occupant protecting apparatus arranged as described above will be described, primarily regarding aspects of this control system which are different from those of the first embodiment. The operation of the control system described below is performed according to a control program (not shown) executed by the CPU  20   a  of the electric control device  20 . 
     Determination on Front Crash of Vehicle 
     The CPU  20   a  effects a determination as to whether the vehicle  10  has a front crash, at a predetermined time interval. This determination is effected by a logic circuit shown in FIG.  17 . Block B 1  in FIG. 17 indicates a determination by the CPU  20   a  as to whether a point determined by the acceleration value GX of the floor tunnel of the vehicle and a time integral value SGX of the acceleration value GX during a time interval between the moments of the last and present cycles of execution of the above-indicated control program lies within a high (Hi) region indicated in the graph of FIG.  18 . The above-indicated point indicates the present state of the vehicle  10 . The time integral value SGX of the acceleration value GX will be referred to simply as “time integral value SGX.” A data map (data table) representing the Hi region, a low (Lo) region and an Off region as shown in FIG. 18 is stored in the ROM  20   b . These Hi, Lo and OFF regions are defined in a two-dimensional coordinate system in which the acceleration value GX and the time integral value SGX are taken along respective two axes. Block B 2  indicates a determination by the CPU  20   a  as to whether the above-indicated point determined by the acceleration value GX and the time integral value SGX lies within the Lo region of FIG.  18 . 
     Blocks B 3  and B 4  indicate monitoring operations performed by the CPU  20   a  to determine whether the logical values of the output signals FRS and FLS of the right and left front satellite sensors  28  and  29  have changed to “1.” 
     The CPU  20   a  determines that the vehicle  10  has a front crash, (1) when the point determined by the acceleration value GX and the time integral value SGX lies within the Hi region of FIG. 18, or (2) when the above-indicated point lies within the Low region of FIG. 18 while the logical value of either one of the output signals FRS and FLS is “1.” 
     Determination of Rear Crash of Vehicle 
     The CPU  20   a  effects a determination as to whether the vehicle  10  has a rear crash, at a predetermined time interval. This determination is effected by determining whether the following inequality is satisfied or not: 
     
       
         ∫ GXdt&lt;Kth &lt;0(time interval of  t 1− t 2) 
       
     
     Namely, the CPU  20   a  obtains a time integral value of the acceleration value GX of the floor tunnel detected by the floor acceleration sensor  27 , during a time interval between a past point of time t 1  and the present point of time t 2 . If the time integral value is smaller than a negative threshold value Kth, the CPU  20   a  determines that the vehicle  10  has a rear crash. 
     Operation to Control Protecting Apparatus According to Determination of Crashes and Rollover Motions 
     Referring next to the logic circuit diagram of FIG. 19, there will be described the operations of the control system to control the vehicle-occupant protecting apparatus according to the determinations by the CPU  20   a  on the crashes and rollover motions of the vehicle  10 . The control operations by the logic circuit shown in FIG. 19 are performed according to a control program (not shown) executed by the CPU  20   a  with a predetermined cycle time. HOLD circuits shown in FIG. 19 function to hold the logical value “1” of the input signal for a predetermined time after the logical value has changed from “0” to “1.” The predetermined times of the different HOLD circuits may be the same or may different from each other. NOT circuits shown in FIG. 19 function to change the logical values “1” and “0” of the input signal to “0” and “1,” respectively. 
     The CPU  20   a  effect determinations as to whether the condition A through condition I are satisfied, at a predetermined time interval. The determinations regarding the conditions A-G have been described above with respect to the first embodiment and its modified arrangement. No further description of these determinations is deemed necessary. The condition H is not satisfied for the predetermined time after the moment of determination that the vehicle  10  has a front crash. Similar, the condition I is not satisfied for the predetermined time after the moment of determination that the vehicle  10  has a rear crash. 
     The CPU  20   a  operates or activates the appropriate vehicle-occupant protecting devices depending upon whether the conditions A-I are satisfied or not. Described in detail, the CPU  20   a  applies the ignition signals to the squibs  11   c  and  13   c  to inflate both of the right curtain-shield airbag  11  and the left curtain-shield airbag  13 , when the rollover condition A is satisfied, that is, when the determination that the vehicle  10  has a rollover motion is made on the basis of the rollover data map of FIG.  8  and the actual roll rate and angle RR, RA. When the rollover condition A is satisfied, the CPU  20   a  also applies the ignition signals to the squibs  15   a ,  16   a ,  17   a  and  18   a  to activate all of the seat-belt pre-tensioners, namely, the front right seat-belt pre-tensioners  15 , front left seat-belt pre-tensioner  16 , rear right seat-belt pre-tensioner  17  and rear left seat-belt pre-tensioner  18 . 
     The CPU  20   a  applies the ignition signals to the squibs  11   c ,  13   c ,  15   a - 18   a  to inflate both of the right and left curtain-shield airbags  11 ,  13  and to activate all of the seat-belt pre-tensioners, when all of the conditions B-I are satisfied. 
     That is, the CPU  20   a  determines that the vehicle  10  has a rollover motion, and inflate both of the curtain-shield airbags  11 ,  13  and operate all of the seat-belt pre-tensioners  15 - 18 , when all of the conditions B-E are satisfied in the situations described below. Namely, the rollover condition B is satisfied when the determination that the vehicle  10  has a rollover motion is made based on the rollover data map of FIG.  9  and the actual roll rate RR and the actual lateral acceleration value GY. The rollover-determination permitting condition C is satisfied when the determination that the state of the vehicle  10  lies in the rollover-determination permitting region is made based on the rollover-determination permitting data map of FIG.  10  and the actual roll rate and angle RR, RA. 
     The post-crash time condition D is satisfied when the predetermined time has passed after the moment of the determination that the vehicle  10  has a right side crash. The post-crash time condition E is satisfied when the predetermined time has passed after the moment of the determination that the vehicle  10  has a left side crash. The post-crash time condition F is satisfied when the predetermined time has passed after the moment of the determination that the vehicle  10  has a crash on the right side of the rear right seat. The post-crash time condition G is satisfied when the predetermined time has passed after the moment of the determination that the vehicle  10  has a crash on the left side of the rear left seat. The post-crash time condition H is satisfied when the predetermined time has passed after the moment of the determination that the vehicle  10  has a front crash, and the post-crash time condition I is satisfied when the predetermined time has passed after the moment of the determination that the vehicle  10  has a rear crash. Thus, the determinations as to whether the conditions D-I are satisfied are effected, and the AND circuits shown in FIG. 19 are provided, for the purpose of invalidating the determination that the vehicle  10  has a rollover motion. 
     The CPU  20   a  inflates the right curtain-shield airbag  11  and the right side airbag  12  when the logical value of the output signal RS of the front right side-crash sensor  23  has changed to “1,” and inflates the left curtain-shield airbag  13  and the left side airbag  14  when the logical value of the output signal LS of the front left side-crash sensor  24  has changed to “1.” The CPU  20   a  also inflates the right curtain-shield airbag  11  when the logical value of the output signal RRS of the rear right side-crash sensor  25  has changed to “1,” and also inflates the left curtain-shield airbag  13  when the logical value of the output signal RLS of the rear left side-crash sensor  26  has changed to “1.” However, the CPU  20   a  may be arranged to inflate the right side airbag  12  when the logical value of the output signal RRS has changed to “1,” and inflate the left side airbag  14  when the logical value of the output signal RLS has changed to “1.” Further, the CPU  20   a  may be arranged to operate all of the seat-belt pre-tensioners  15 - 18  when the logical value of any one of the output signals RS, LS, RRS, RLS of the side-crash sensors  23 - 25  has changed to “1.” 
     Further, the CPU  20   a  inflates the operator-seat front-crash airbag  19 - 1  and the front-passenger front-crash airbag  19 - 2  and operates all of the seat-belt pre-tensioners  15   18 , when the CPU  20   a  determines that the vehicle  10  has a front crash. The CPU  20   a  may be arranged to operate all of the pre-tensioners  15 - 18  when the CPU 20   a  determines that the vehicle  10  has a rear crash. 
     According to the control system of the second embodiment described above, the determination that the vehicle  10  has a rollover action, which is made based on the roll rate RR and the lateral acceleration value GY, is invalided for a predetermined time after a front or rear crash as well as a side crash of the vehicle  10  has taken place, that is, when a collision of the vehicle  10  has taken place on any one of its four sides. This arrangement makes it possible to avoid unnecessary operations of the vehicle-occupant protecting devices (curtain-shield airbags). 
     It will be understood that the present invention is not limited to the illustrated embodiments, and may be embodied with various changes and modifications, without departing from the scope of this invention. For instance, the amount of slackness or looseness of the seat belts may be reduced instantaneously by operating respective pre-tensioners provided in the seats of the vehicle, when the logical value of the output signal RS, LS of the right or left side-crash sensor  23 ,  24  has changed from “0” to “1.” Although the illustrated embodiments are arranged to inflate both of the right and left curtain-shield airbags  11 ,  13  when the determination that the vehicle  10  has a rollover motion is made, the control system may be arranged to inflate only one of the two curtain-shield airbags  11 ,  13  on one side of the vehicle  10  on which a side crash has taken place. The manners of determinations as to whether the vehicle has rollover motion, and crashes (side, front and rear crashes) are not limited to those in the illustrated embodiments described above. 
     The second embodiment may be modified to control the vehicle-occupant protecting devices, by effecting the determination on the front crash of the vehicle while taking account of the running speed of the vehicle, such that (1): none of the vehicle-occupant protecting devices are operated while the vehicle running speed is lower than a first threshold value, even when the determination that the vehicle has a front crash is made; (2) only the seat-belt pre-tensioners  15 - 18  are operated when the determination that the vehicle has a front crash is made while the vehicle running speed is equal to or higher than the first threshold value and lower than a second threshold value higher than the first threshold value, that is, when a first front-crash condition is satisfied; and (3) the seat-belt pre-tensioners  15 - 18 , the operator-seat front-crash airbag  19 - 1  and the front-passenger-seat front-crash airbag  19 - 2  are operated when the determination that the vehicle has a front crash is made while the vehicle running speed is equal to or higher than the second threshold value, that is, when a second front-crash condition is satisfied. In this case, the condition H which is used to effect the determination on the front crash and which has been described by reference to FIG. 19 may be replaced by one of the first and second front-crash conditions indicated above. 
     Each of the operator-seat and front-passenger-seat airbags  19 - 1  and  19 - 2  provided in the vehicle-occupant protecting apparatus controlled by the control system according to the second embodiment may be modified such that each airbag  19 - 1 ,  192  has a first-stage inflator and a second-stage inflator (a plurality of inflators) and squibs corresponding to the respective inflators. 
     In this case, the control system may be arranged to control the vehicle-occupant protecting devices, such that: (1) none of the vehicle-occupant protecting devices are operated while the vehicle running speed is lower than a first threshold value, even when the determination that the vehicle has a front crash is made; (2) only the seat-belt pre-tensioners  15 - 18  are operated when the determination that the vehicle has a front crash is made while the vehicle running speed is equal to or higher than the first threshold value and lower than a second threshold value higher than the first threshold value, that is, when a first front-crash condition is satisfied; (3) the seat-belt pre-tensioners  15 - 18  are operated, and only the first-stage inflator of each of the operator-seat and front-passenger-seat front-crash airbags  19 - 1 ,  19 - 2  is activated to comparatively slowly inflate the front-crash airbags  19 - 1 ,  19 - 2 , when the determination that the vehicle has a front crash is made while the vehicle running speed is equal to or higher than the second threshold value and lower than a third threshold value higher than the second threshold value, i.e., when a second front-crash condition is satisfied; and (4) the seat-belt pre-tensioners  15 - 18  are operated, and both of the first-stage and second-stage inflators of the front-crash airbags  19 - 1 ,  19 - 2  are activated to rapidly inflate the airbags  19 - 1 ,  19 - 2 , when the determination that the vehicle has a front crash is made while the vehicle running speed is equal to or higher than the third threshold value, that is, when a third front-crash condition is satisfied. In this case, the condition H which is used to effect the determination on the front crash and which has been described by reference to FIG. 19 may be replaced by one of the first, second and third front-crash conditions indicated above. 
     In the illustrated embodiments, the controller is implemented with a general purpose processor. It will be appreciated by those skilled in the art that the controller can be implemented using a single special purpose integrated circuit (e.g., ASIC) having a main or central processor section for overall, system-level control, and separate sections dedicated to performing various different specific computations, functions and other processes under control of the central processor section. The controller can be a plurality of separate dedicated or programmable integrated or other electronic circuits or devices (e.g., hardwired electronic or logic circuits such as discrete element circuits, or programmable logic devices such as PLDs, PLAs, PALs or the like). The controller can be suitably programmed for use with a general purpose computer, e.g., a microprocessor, microcontroller or other processor device (CPU or MPU), either alone or in conjunction with one or more peripheral (e.g., integrated circuit) data and signal processing devices. In general, any device or assembly of devices on which a finite state machine capable of implementing the procedures described herein can be used as the controller. A distributed processing architecture can be used for maximum data/signal processing capability and speed. 
     While the invention has been described with reference to what are preferred embodiments thereof, it is to be understood that the invention is not limited to the preferred embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the preferred embodiments are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the invention.