System for detecting and releasing a person locked in the trunk of a vehicle

[0001] This nonprovisional application claims the benefit of U.S. Provisional Application Ser. No. 60/131,189, filed Apr. 26, 1999.

[0002] 1. Technical Field of the Invention

[0003] The present invention concerns safety systems for operating automobiles and, more particularly, to such a system that detects the presence of a person in a closed trunk and releases the person under safe operational conditions.

[0004] 2. Description of the Related Art

[0005] There have been well publicized reports of young children inadvertently locking themselves in the trunk of a vehicle, such as an automobile. Tragically, children can die under such circumstances, typically as a result of heat prostration while trapped in the sealed trunk.

[0006] It has been suggested that a trapped person could actuate an inside release mechanism to open the trunk. However, it is not certain that a young child would understand how to operate such a mechanism and it is therefore possible that the child would not be able to free himself by this means. There is therefore a need for a system that detects the presence of a person, particularly a small child, within a trunk and signals the need to open the trunk. It would also be advantageous for such a system to automatically trigger a trunk to open and release the trapped person when it is safe to do so, for example when the vehicle is stopped.

[0007] There is therefore a great need for an automatic trunk safety system. The apparatus and system of the invention has been developed to meet this need with simple, relatively low cost and reliable components that are easily integrated with the electronic control systems of existing vehicles. The above-mentioned features and other features of the invention will become apparent from a review of the following drawings, specification and claims.

[0008] One embodiment of the apparatus and system of the invention includes a sensor that detects CO₂ that is exhaled by a person trapped in the closed trunk of a vehicle. A microprocessor compares the level of CO₂ detected in the trunk to a baseline level of CO₂ that was measured the last time the trunk was opened. If excessive CO₂ is detected, the microprocessor determines the operational state of the vehicle and takes programmed steps to provide an alarm and to automatically open the trunk if the vehicle is not moving.

[0009] Other embodiments of the invention can use infrared sensors or electrostatic (i.e., capacitive) sensors to detect a person in the trunk. Systems with such sensors would also operate automatically to provide an alarm and to open the trunk under safe operational conditions.

[0012] In the drawings, elements are not necessarily drawn to scale, and the same reference numbers through several views designate the same or similar elements. FIG. 1 illustrates a block diagram of components of the system of the invention in association with known electronic components of a modern vehicle. A CO₂ sensor 1 includes the elements shown within the dashed lines. This sensor has a CO₂ sensing component 3 that detects the level of CO₂ in the trunk of a vehicle such as an automobile.

[0013] CO₂ sensors are commercially available. A preferred sensor is sold by Figaro USA, Inc. of Glenview, Ill. with the model designation TGS4160. This solid electrolyte sensor generates an output voltage on a line 5 that corresponds to the level of detected CO₂. The sensor includes a heater element 7 that must be energized in initial operation to heat the sensor to a specific operational temperature. The sensor therefore requires some initial time, for example, about 60 seconds, to stabilize before it can make a reliable CO₂ reading. A thermistor 8 senses the temperature of the sensor and applies a corresponding voltage to a microcontroller 15 that, as an example, may be a model 68705P6A device which is commercially available from Motorola. The output voltage of the sensor is applied to the plus input of a difference operational amplifier 9 that also receives at its minus input 11 a reference voltage from the microcontroller 15. The operational amplifier 9 generates an output voltage on line 12 that corresponds to the difference between the voltage at its plus and minus inputs.

[0014] In initial operation, the reference voltage at 11 from the microcontroller is zero and the operational amplifier 9 generates a voltage at 12 that corresponds to the ambient concentration of CO₂ in the trunk. The voltage corresponding to this ambient or baseline CO₂ concentration is amplified within the microcontroller, temperature compensated, and applied at 11 as a pulse width modulated signal with a duty cycle that is adjusted to provide a reference voltage that corresponds to the background CO₂ in the trunk.

[0015] If a person is thereafter trapped in the trunk, the level of CO₂ will gradually rise above the background level. As the concentration of CO₂ in the trunk rises, the voltage on the line 5 increases and the amplifier 9 generates a voltage that corresponds to the difference between the increased voltage on the line 5 and the background reference voltage on the line 11. The output of the amplifier at 12 therefore corresponds to the relative increase in the concentration of CO₂ from the baseline. The “delta” voltage corresponding to the change in the concentration of CO₂ is applied to the microcontroller and, if a specified magnitude of this voltage, for example 1 volt, is maintained for a specified time, for example 30 seconds, the microcontroller registers an alarm. The alarm magnitude of CO₂ may be set to correspond to the respiration of the lowest weight person within the parameters of the system.

[0016] The microcontroller 15 receives vehicle status signals and transmits control signals over a serial bus 14, through a serial data interface 16 that may operate with the J1850 or Controller Area Network protocols as an example. Other protocols could also be used.

[0017] With reference to FIG. 1 as an example, the microcontroller may be hardwired to a trunk latch switch 18, a trunk release solenoid 19, left and right rear seat switches that indicate the latched or unlatched condition of these seats at 20 and 21, an override switch for temporarily disarming the CO₂ sensor at 22 and a status lamp at 23 that indicates the operational condition of the CO₂ detection system, for example by blinking.

[0018] The serial bus communicates with the instrument cluster electronic control unit 26 which receives a signal from the manual trunk release switch 24 and controls a CO₂ panel alarm lamp and/or audio alarm 25. An engine control module 29 monitors the operational state of the ignition key switch 27 and interacts in a known manner with an automatic braking system 34 that connects with a high-speed motion control bus 28 and receives signals from wheel speed sensors 30 that indicate whether the vehicle is moving. A body control computer 48 controls a relay 45 that operates the vehicle horn and lights and responds to a remote keyless entry system 42 in a known manner. A radio frequency data module 53 can be actuated to send radio alarm signals to a remote security station via a satellite communication system 51 in a known manner. A heating, ventilation and airconditioning module 56 operates a vent fan 54 in a known manner. The fan could be disposed to vent the trunk, for example, in response to a CO₂ alarm. A known plug-in service diagnostic tool 70, other known vehicle control modules 68 and the headlights 64 are connected and operated on the serial data bus 14 in a known manner. All of the apparatus on the serial bus is monitored and controlled through the microcontroller 15 that also controls the operation of the CO₂ detection system. If necessary, the microcontroller could be implemented with flash memory to facilitate program changes in the field.

[0019] As an alternative to the use of a serial data bus to send and receive vehicle control signals, the microcontroller 15 could be directly connected to send and receive these signals using a dedicated wire for each signal. In such a system, an ignition on signal from the ignition key switch 27 would connect directly to the microcontroller 15, rather than indirectly through the engine control ECU 29 and a serial data bus 14. Likewise, wheel speed sensors 30, trunk release switch 24, audio alarm or lamp 25, headlights 64, horn relay 45, trunk vent fan 54, and any other such vehicle control apparatus would connect directly to the microcontroller, rather than through associated modules and a serial data bus.

[0020] FIG. 2 illustrates a flow chart of microprocessor program steps that implement the system of a preferred embodiment of the invention. As shown at the top of FIG. 2, for the purpose of this discussion, the CO₂ detection system is initially assumed to be in a sleep state at 17 wherein the system waits for an activation condition. The system is awakened or activated at least in response to opening the trunk of the vehicle or unlatching either of the back seats. With reference to FIG. 1, when the trunk is opened or at least one back seat is unlatched, the switches 18, 20, 21 indicate the activation condition. The activation signal is passed to the microcontroller 15, for example over a hardwired connection.

[0021] With reference to FIG. 2, the microcontroller 15 therefore detects the activation condition at 31 and wakes up and sets a delay time to process CO₂ information. With reference to FIG. 1, when the microcontroller 15 wakes up, the CO₂ sensor 3 is already energized. The heater 7 is then turned on, the system then waits for the sensor to heat up, for example for about 60 seconds, and the microcontroller 15 then waits for the trunk to close or the back seats to latch at 37.

[0022] The microcontroller checks the condition of the trunk and seats at 37 by interrogating the switches 18, 20, and 21. If the switches do not close within a predefined delay time, for example several minutes, the microcontroller is put to sleep to await activation by closing the trunk or latching the seats. When activated, the baseline CO₂ is acquired and stored, a timer is set and, if necessary, the sensor is warmed up. The concentration of CO₂ in the trunk is measured at 39 during a predefined time-out interval of, for example several minutes. If an increase in the level of CO₂ is detected in an amount that would be exhaled by a human being, the “trunk occupied” condition is triggered at 43. The system is put to sleep if the timer times out at 44.

[0023] Experimentation and investigation have indicated that healthy human beings generally exhale CO₂ in amounts proportional to their body weight. Thus, for example, a 180 pound adult would exhale about 0.3 liters of CO₂ per minute, a toddler of 20 pounds would exhale about 0.033 liters of CO₂ per minute and an infant of 7 pounds would exhale about 0.012 liters of CO₂ per minute. The microcontroller 15 is programmed to measure the increase in CO₂ within the trunk over time in relation to the measured baseline CO₂ and make a determination that the increasing CO₂ results from the respiration of a human being.

[0024] As an initial approximation, if the largest trunk contains about 566 liters of air, it has been determined that the CO₂ sensor will detect respiration at about 530 PPM (parts per million) per minute for an adult, 59 PPM per minute for a toddler and about 21 PPM per minute for an infant. This increase in measured CO₂ over a reasonable time, for example up to several minutes, distinguishes the respiration of a human being from expected changes in ambient CO₂. The detection of a gradual increase in CO₂ also serves to distinguish an abrupt increase in CO₂ that might result if a person intentionally injects CO₂ into the trunk in an effort to confuse the CO₂ detection system. As an example, it has been found that human respiration can be distinguished by measuring a predetermined change in the output voltage of the operational amplifier 9 of FIG. 1, for example a change of about 1 volt, for an interval of about 30 seconds.

[0025] With reference to FIG. 2, if an occupant is not detected in the trunk within a predefined set time, the timer times out at 44 and the microcontroller 15 terminates its detection of CO₂ and sets itself in a low power sleep mode defined at step 17. The microcontroller will remain asleep until the trunk is opened again or at least one rear seat is unlatched.

[0026] If the level of CO₂ detected in the trunk indicates an occupant is present, the microcontroller 15 at step 46 turns on the CO₂ lamp 25 of FIG. 1 and/or provides an audio alarm on the front console of the vehicle, sets a timer and checks the condition of the latches on the back seats of the vehicle at step 47.

[0027] If a back seat is unlatched, the trunk is ventilated through the airspace provided by the unlatched seat and the level of alarm is therefore reduced. As shown at step 47, if a back seat is unlatched, the movement of the vehicle is checked at 49 and the front console alarms are continued for a time-out period. If the vehicle stops during this period, the trunk is automatically opened by the trunk release solenoid 19 (FIG. 1) at step 50 to allow the person to escape safely. The alarms are then turned off and program control is returned to step 33. If the vehicle continues moving, the timer times out, and at step 52 the horn is activated at 45, 48 (FIG. 1) and the headlights are flashed at 64 (FIG. 1). This continues for as long as the vehicle continues moving. If the vehicle stops, the trunk is automatically opened at step 58 to allow the person to escape, the alarms are turned off at step 60 and program control is returned to step 33. When the trunk is closed, the CO₂ concentration is checked and the system is put to sleep if there is no alarm condition or, if the trunk remains open beyond a time-out interval, the system is put to sleep until the trunk is closed.

[0028] If an occupant is detected in the trunk and it is found at step 47 that the back seats are latched, the status of the ignition system 27, 29 (FIG. 1) is then checked at step 57 (FIG. 2). If the ignition is turned off, the microcontroller 15 sends an “open trunk” signal to the trunk release solenoid 19 (FIG. 1) at step 62 (FIG. 2) and therefore causes the trunk to open. The trunk is opened in this situation because the vehicle is stopped and it is therefore safe to open the trunk and allow the occupant to escape. After opening the trunk, the alarms are turned off and program control is returned to step 33.

[0029] If the sensed condition of the ignition at step 57 is “on”, the microcontroller 15 at step 61 determines whether the vehicle is moving by analyzing wheel speed signals from sensors 30 of FIG. 1. If the vehicle is not moving, the trunk is automatically opened at step 63, the alarms are turned off and program control is returned to step 33. The trunk may be opened in these circumstances, because, even though the ignition is on, the vehicle is not moving and it is therefore safe for the occupant to leave the trunk.

[0030] If the vehicle is moving at step 61, the microcontroller 15 times out a predetermined interval at step 65 and continuously checks at step 66 to determine if the vehicle remains moving during this interval. If the vehicle stops during this interval, the trunk is opened at step 67 to allow the occupant to escape, the alarms are turned off, and control is returned to step 33 as previously described. If the vehicle is still moving at the end of the time-out interval of step 65, a higher level of alarm is generated at step 69 by triggering a radio alert at 51, 53 (FIG. 1) to call a remote security station. Also, at step 71, the horn is actuated and the lights are flashed as previously described. When these higher level alarms are set, the movement status of the vehicle is again checked at step 73 and, if the vehicle stops, the alarms are turned off and the trunk is opened at step 75 and program control is returned to step 33 as previously described. If the vehicle continues to move, alarms continue to operate until the vehicle stops.

[0031] Variations and modifications of the embodiments disclosed herein may be made without departing from the scope and spirit of the invention. For example, the CO₂ detector may be replaced or augmented by infrared and electrostatic capacitive sensors. At present it is believed that use of a CO₂ sensor is preferred, because infrared and electrostatic sensors might not be able to detect a person if, for example, the trunk is partially filled with cargo. The system could also be modified to open an air vent to the trunk or partially open the trunk to allow ventilation in the event of an alarm condition. Additional conditions would also be defined to wake up the microcontroller to process peripheral equipment or interrupts for vehicle systems other than the CO₂ system. The aforementioned description of embodiments of the invention is therefore intended to be illustrative rather than limiting and it should therefore be understood that the following claims and their equivalents set forth the scope of the invention.