Control system for vehicle safety device

A control system for a vehicle safety device, comprising:

• (a) an acceleration sensing circuit which produces an output;
• (b) an analog collision detection system including an integrating circuit for integrating the output of said acceleration sensing circuit, and a comparator circuit for comparing an output of said integrating circuit with a threshold level so as to detect a collision of a vehicle;
• (c) a digital collision detection system including an analog-to-digital converter for converting the output of said acceleration sensing circuit into digital data, and a microcomputer, said microcomputer comprising (i) collision detection means for performing calculations in accordance with said digital data from said analog-to-digital converter, so as to detect the vehicle collision;
• (ii) test pulse generating means for outputting test pulses to said acceleration sensing circuit;
• and (iii) malfunction detection means for checking at least one of the output of said integrating circuit of said analog collision detection system and an output of said comparator circuit so as to detect a malfunction of said analog collision detection system, the outputs of said integrating circuit and said comparator circuit being produced in response to said test pulse;
• and
• (d) a drive circuit which operates said vehicle safety device when said drive circuit simultaneously receives collision detections signals respectively from both of said analog and digital collision detection systems;
• wherein the output of said acceleration sensing circuit produced in response to said test pulse has a polarity opposite to that of the output of said acceleration sensing circuit produced during vehicle collision with respect to a reference voltage;
• wherein said acceleration sensing circuit comprises an acceleration sensor for producing an output of a negative voltage at the time of the vehicle collision, and test pulse input means connected in parallel with said acceleration sensor, said microcomputer feeding said test pulse of a positive voltage to said test pulse input means;
• and
• wherein said acceleration sensing circuit further comprises a buffer, and a reference voltage source for supplying the reference voltage of a positive value to an input terminal of said buffer, said acceleration sensor and said test pulse input means being connected to the input terminal of said buffer.

A control system for a vehicle safety device, comprising:

• (a) an acceleration sensing circuit which produces an output;
• (b) an analog collision detection system including an integrating circuit for integrating the output of said acceleration sensing circuit, and a comparator circuit for comparing an output of said integrating circuit with a threshold level so as to detect a collision of a vehicle;
• (c) a digital collision detection system including an analog-to-digital converter for converting the output of said acceleration sensing circuit into digital data, and a microcomputer, said microcomputer comprising (i) collision detection means for performing calculations in accordance with said digital data from said analog-to-digital converter, so as to detect the vehicle collision;
• (ii) test pulse generating means for outputting test pulses to said acceleration sensing circuit;
• and (iii) malfunction detection means for checking at least one of the output of said integrating circuit of said analog collision detection system and an output of said comparator circuit so as to detect a malfunction of said analog collision detection system, the outputs of said integrating circuit and said comparator circuit being produced in response to said test pulse;
• (d) a drive circuit which operates said vehicle safety device when said drive circuit simultaneously receives collision detections signals respectively from both of said analog and digital collisions detection systems, wherein the output of said acceleration sensing circuit produced in response to said test pulse has a polarity opposite to that of the output of said acceleration sensing circuit produced during vehicle collision with respect to a reference voltage;
• and
• a threshold voltage generating circuit for supplying a threshold voltage of a first voltage level to said comparator circuit of said analog collision detection system, and voltage level switching means responsive to a switch instruction signal from said microcomputer so as to forcibly switch said threshold voltage to a second voltage level, the output of said integrating circuit being maintained at the reference voltage level when the vehicle is stopped or is running at a constant speed, said reference voltage level being between said first voltage level and said second voltage level of said threshold voltage;
• at the time of the vehicle collision in a collision detection mode, the output of said integrating circuit going toward said first voltage level, and when the output of said integrating circuit reaches said first voltage level, the output of said comparator circuit being switched from a first logic level to a second logic level so as to serve as said collision detection signal;
• in a malfunction detection mode, said microcomputer outputting said switch instruction signal to said voltage level switching means, so that said threshold voltage is switched to said second voltage level;
• in the vicinity of the time of switching of said threshold level to said second voltage level, said test pulse being fed from said microcomputer to said acceleration sensing circuit, so that the output of said integrating circuit goes to said second voltage level;
• and when the output of said integrating circuit reaches said second voltage level, the output of said comparator circuit being switched from said second logic level to said first logic level.