hereinafter , an embodiment of a vehicle collision control system according to the present invention will be described in detail with reference to the attached drawings . fig1 is a view of a positional relation schematically illustrating a running vehicle 10 which is in a position d ( t1 ) at a time t1 . according to the aforementioned well - known means used in the conventional collision predictive device , when an object 15 is sensed in front of the vehicle 10 running at a speed v1 at the time t1 , the device measures a distance l between the vehicle 10 and the object 15 and the rate of change in the distance δd during a time period δt , thereby computing an expected collision time t2 at which the vehicle collides with the object 15 and a collision speed v2 . the vehicle 10 shown in fig1 is decelerated from the vehicle speed v1 to the collision speed v2 until the collision by quick braking based on braking command . when the deceleration δv by this quick braking excesses the acceptable maximum deceleration δvth as a first limit deceleration which changes corresponding to the condition of the running vehicle and the condition of the road surface , the vehicle wheels are locked and the driver can not control by the steering wheel so that the vehicle slips aside . besides the collision with the object 15 , another accident may be occurred by the side - slip . the acceptable maximum deceleration δvth is calculated by detecting a wheel acceleration obtained from the sensed vehicle speed and the wheel rotational speeds , and considering conditions such as whether the vehicle is provided with an anti - skid brake system ( abs ) ( various systems have been already devised and performed ). for improving the accuracy of the braking , the acceptable maximum deceleration δvth is preferably set considering data about the road surface condition obtained from the result of the wheel rotational speed . on the other hand , as mentioned above , to restrain the deformation of the vehicle body at the collision within the range of the crushable zone , it is necessary to reduce the speed v1 to make the collision speed v2 at the moment of the collision ( time t2 ) lower than the survival space ensuring speed va or less . the survival space ensuring speed va is unique to each type of body and the structure . car manufacturers catch accurate values of the survival space ensuring speed va for each type of vehicle by , such as , collision tests with real vehicles and numerical analysis with a computer . when the speed at the time t1 is v1 , it is necessary to calculate the desired deceleration δvr as the second limit deceleration which is needed to reduce the speed v1 to the survival space ensuring speed va or less between the time t1 and the moment of the collision ( time t2 ). the shorter the distance between the vehicle 10 and the object 15 , the larger the desired deceleration δvr . when the desired deceleration δvr exceeds the acceptable maximum deceleration δvth , it can not ensure its safety due to the quick braking . therefore , the vehicle must be decelerated by fully braking at least a time when the second limit deceleration is equal to the desired deceleration δvr as shown in fig2 . with reference to fig3 the description will be made as regard to a control unit 30 , one of the vehicle collision control system according to the present invention , having collision predictive means 31 , deceleration calculating means 32 , arithmetic processing means 33 , braking command means 34 , and collision signal generating means 35 . a distance measuring sensor 20 as an input unit for the collision predictive means 31 is mounted in the front portion of the vehicle body . the distance measuring sensor 20 senses the existence of an object in the running direction of the vehicle . the distance measuring sensor 20 may be an optical distance measuring sensor or an ultrasonic distance measuring sensor , which can search forward areas in the running direction at predetermined intervals and sense the distance between the vehicle and the object during running . the distance data from the measuring sensor 20 is outputted to the control unit 30 . the control unit 30 is provided with the collision predictive means 31 . the collision predictive means 31 decides whether the vehicle will collide with the object by performing arithmetic on the distance data . in the present invention , the collision predictive means 31 consists of the same logic as that of the aforementioned collision predictive means of the prior art . that is , the collision predictive means computes a distance between the vehicle and the forward object , and change in the speed of vehicle running toward the object based on the rate of distance change , considering the expected collision time and the maximum deceleration of the vehicle , and decides whether the vehicle will collides with the object . when the distance d between the vehicle and the object before the expected collision time is computed to be d = 0 , a collision predictive signal s1 is outputted to an logic circuit 36 which decides to generate the inflator ignition signal . upon generating the collision predictive signal s1 from the collision predictive means 31 , the deceleration calculating means 32 calculate the acceptable maximum deceleration δvth which allows the vehicle to be prevented from slipping due to the locked state of the wheels . the deceleration calculating means 32 calculates wheel rotational speeds and wheel accelerations upon converting an analog rotational speed signal sensed by the wheel rotational speed sensor to a digital signal as mentioned above . it is detected that the wheels will be locked based on the wheel accelerations and the vehicle speed at this point . then the deceleration calculating means 32 calculates the acceptable maximum deceleration δvth within the range in which the wheels may be never locked . the deceleration calculating means 32 also sets the desired deceleration δvr which is needed to reduce the speed v1 to make the speed v2 lower than the survival space ensuring speed va or less before the collision . that is , the deceleration calculating means 32 calculates the acceptable maximum deceleration δvth and the desired deceleration δvr at the time ti . after the collision predictive signal s1 is outputted , the arithmetic processing means 33 performs comparison arithmetic between the acceptable maximum deceleration δvth and the desired deceleration δvr at the time ti at the predetermined interval ( δt ) , and outputs a predetermined working command signal to the braking command means 34 using a threshold at which the desired deceleration δvr is equal to the acceptable maximum deceleration δvth . it should be understood that when the desired deceleration δvr already exceeds the acceptable deceleration δvth , the braking command signal is preferably outputted immediately ( see t &# 39 ; in fig2 ). that is , the braking command signal is outputted to the braking command means 34 to keep the full - braking state in the range in which the acceptable maximum deceleration δvth is satisfied . then the braking command means 34 outputs a driving signal to each drive of braking means 40 installed for each wheel . since each of the braking means 40 comprises an electromagnetic valve and a brake actuator such as a hydraulic pump , the braking command means 34 outputs a solenoid driving signal for the electromagnetic valve ( not shown ) and a driving signal for a motor relay of the pump . the vehicle is provided with an impact sensor 21 in the front portion thereof . the impact sensor 21 may be any type of acceleration g sensor well - known in the art , such as a seismic impact sensor which is of electric contact type or mechanical type . the impact sensor 21 is set in its sensitivity to sense an impact acceleration at the collision whereby the vehicle is broken . when the impact acceleration exceeds the threshold previously set in the sensor , the collision signal generating means 35 outputs the collision occurrence signal s2 to the logic circuit 36 . the logic circuit 36 outputs an ignition signal ss to the inflator 42 of the air bag device 41 only when both signals s1 and s2 are obtained upon receiving the collision predictive signal outputted from the collision predictive means 31 . hereinafter , the description will be described with regard to the operational flow of the control unit 30 mentioned above with reference to the flow chart of fig4 . the distance measuring sensor 20 performs the sensing for an object at the predetermined time interval during running . when the distance measuring sensor 20 senses the object positioned to block the running direction of the vehicle , the operation of the collision control system according to the flow chart of fig4 is started . the distance measuring sensor 20 also senses the distance d ( t1 ) between the vehicle and the object 15 at the time t1 at when the object 15 is sensed and further computes the time t2 at when the vehicle will reach the object 15 ( step 100 ). the vehicle speed is sensed during the time period δt , the rate of distance change δd between the vehicle and the object 15 ( step 110 ), and the comparison is performed between the rate of distance change δd and a collision occurrence threshold ( step 120 ). the collision occurrence threshold changes according to the driving condition set from the deceleration and the limit braking capacity of the vehicle . when it is decided that the rate of distance change δd exceeds the collision occurrence threshold , that is , that the collision time is earlier than a stopping time calculated by the rate of distance change δd , the collision occurrence is predicted . therefore , the system can also recognize an unavoidable collision due to rapid approach of the object 15 . when the collision occurrence is predicted , the collision predictive signal s1 is outputted to the logic circuit 36 ( step 130 ). when the collision occurrence is predicted , the system senses each rotational speed of the wheels , calculates the wheel acceleration based on the detected signals , and further calculates the acceptable maximum deceleration δvth for ensuring steady running of the vehicle during quick braking , and the desired deceleration δvr which is needed to reduce the speed v1 to the survival space ensuring speed va or less before the collision ( steps 140 , 150 ). next , the arithmetic processing means 33 compares the acceptable maximum deceleration δvth to the desired deceleration δvr detected successively at the predetermined interval ( δt ) ( step 160 ) and outputs the braking command signal to the braking command means 34 at least before the desired deceleration δvr exceeds the acceptable maximum deceleration δvth ( step 170 ). the braking command means 34 controls the braking force not to allow the actual deceleration δv to exceed the acceptable maximum deceleration δvth ( step 180 ). for example , when the steady running of the vehicle cannot be ensured due to the quick braking , the braking command means 34 outputs a brake actuator pressure reducing signal for decreasing the braking force so as to ensure the steady running of the vehicle while fully braked . in addition , when the braking deceleration is lower than the expected deceleration according to the relation with the desired deceleration δvr , the braking command means 34 output the brake actuator pressure intensifying signal for increasing the braking force so as to sufficiently brake the vehicle . in this manner , the actual deceleration δv is continuously held around the acceptable maximum deceleration δvth until the collision while the full - braking state is held . the process for controlling the speed loops the braking command until the time t2 in the control circuit 30 ( step 190 ). when the vehicle 10 collides with the object 15 finally ( at the time t2 ) ( see fig1 ), the impact sensor 21 positioned in the front portion of the vehicle senses the collision ( step 200 ). when the impact sensor 21 senses that the impact applied to the vehicle body is larger than the threshold ( step 210 ), the collision occurrence signal s2 is outputted to the logic circuit 36 ( step 220 ). only when the collision predictive signal s1 mentioned above and the collision occurrence signal s2 both are inputted to the logic circuit 36 , the logic circuit 36 generates an ignition signal ss for the inflator 42 of the air bag device 41 ( step 230 ). therefore , if the object 15 is a blown newspaper or the like , the collision occurrence signal s2 is not outputted so that the air bag can be prevented from being incorrectly deployed . according to the present inventions the collision control system can securely ensure the effect of the occupant restraint protective device such as an air bag device even with the vehicle having the crushable zone of which is short in the longitudinal direction .