BACKGROUND OF THE INVENTION

This invention relates generally to aviation crash sensors and, more particularly, to a crash sensor which senses acceleration along three orthogonal axes to determine acceleration at any vector.

Acceleration threshold detection devices have long been used in the automotive industry to lock seat belt retractors to restrain occupants in their seats in the event of a sensed threshold acceleration along the vehicle longitudinal axis to indicate a frontal crash. These devices are normally mechanical devices utilizing a pendulum or a ball-and-ramp arrangement to sense acceleration in one or two planes. Recently, Mercedes-Benz has developed a seatbelt tensioning retractor that is activated by the automobile on-board computer when it senses a .7 G frontal impact to pretension the passenger seatbelts.

With the advent of air bags, electronic accelerometers have been devised to actuate air bags. Such electronic accelerometers are illustrated in U.S. Patent No. 3,762,495 - Usui et al and U.S. Patent No. 4,984,464 - Thomas et al. However, none of these automotive crash sensing devices or systems is useful for detecting crashes which do not occur in the horizontal plane of vehicle operation, such as rollover crashes.

Accelerometers have also been used in the aircraft industry to activate a safety device, such as to lock an aircraft occupant's shoulder harness retractor or to tighten the harness when a threshold acceleration is sensed. A crash sensor for an airplane was previously developed to cut out the electrical circuit, cut off fuel

and operate fire extinguishers when a crash was detected, as shown in U.S. Patent No. 2,573,335. However, these accelerometers are mechanical and react relatively slowly to a crash, thus slowing activation of the safety devices.

An impact indicator was previously developed to detect when aircraft landing gear has been stressed beyond predetermined critical limits. U.S. Patent No. 3,389607 -

Kishel discloses such a system, which utilizes a complex mechanical triaxial acceleration sensor.

Many aircraft crashes or impacts are not necessarily catastrophic, in that they could be survivable by the aircrew if movement of the aircraft occupants during the crash is restrained. For example, helicopters may suffer engine or rotor failures as a result of combat damage or other malfunctions, which will cause a relatively low speed crash. These crashes could be survivable by the aircrew if the aircraft crewmen were quickly secured in their seats in a manner to limit their so-called "flail envelope".

It would be desirable to provide a multi-axis crash sensor that is useful in any vehicle which can experience a crash mode in any of a multiplicity of directions.

It would also be desirable to provide such a crash sensor which senses crashes in mere milliseconds to enable quick activation of a safety device to protect vehicle occupants.

It would further be desirable to provide an aircraft crash sensor which activates an aircrew safety device upon sensing an impact in any direction to reduce the possibility of injury caused by the crash.

It would be yet further desirable to provide such an aircraft crash sensor which causes the shoulder harnesses of an aircraft occupant to remove harness slack to secure the occupant in his seat.

It would be still further desirable to provide such an aircraft crash sensor which is programmable to adapt to a variety of different aircraft and different aircraft missions.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a multi-axis crash sensor that is useful in any vehicle which can experience a crash mode in any of a multiplicity of directions.

It is also an object of this invention to provide such a crash sensor which senses crashes in mere milliseconds to enable quick activation of a safety device to protect vehicle occupants.

It is a further object of this invention to provide an aircraft crash sensor which activates an aircrew safety device upon sensing an impact in any direction to reduce the possibility of injury caused by the crash.

It is a yet further object of this invention to provide such an aircraft crash sensor which causes the shoulder harnesses of an aircraft occupant to remove harness slack to secure the occupant in his seat.

It is a still further object of this invention to provide such an aircraft crash sensor which is programmable

to adapt to a variety of different aircraft and different aircraft missions.

In one aspect, this invention features a crash sensor comprising an accelerometer mounted on a vehicle for measuring acceleration of the vehicle along three orthogonal axes and providing acceleration signals representative of measured accelerations along each axis. A microcontroller receives and evaluates the acceleration signals to determine vehicle acceleration along any vector. Information supply means input predetermined vehicle acceleration information and evaluation criteria to the microcontroller to enable the microcontroller to evaluate vehicle accelerations. Output means provide an output signal when the microcontroller determines that a vehicle vector acceleration has exceeded predetermined criteria.

In another aspect, this invention features a crash sensor for an aircraft which has an actuatable safety device, comprising an accelerometer mounted on the aircraft for measuring acceleration of the aircraft along three orthogonal axes. The accelerometer is characterized by including means providing acceleration signals representative of measured accelerations along each axis, a microcontroller for receiving and evaluating the acceleration signals to determine aircraft acceleration along any vector, information supply means for inputting predetermined aircraft acceleration information and evaluation criteria to the microcontroller to enable the microcontroller to evaluate aircraft vector accelerations, and output means for providing an output signal to actuate the safety device when the microcontroller determines that a vector acceleration exceeds predetermined criteria.

Preferably, the crash sensor is adaptable to aircraft equipped for a plurality of different missions each

subjecting the aircraft to a different set of acceleration conditions in that the information supply means include means for inputting predetermined acceleration information and evaluation criteria characteristic of a specific mission to the microcontroller.

In yet another aspect, the actuatable safety device is a pretensionable shoulder harness, and the crash sensor functions to retract harness slack when a vector acceleration exceeds predetermined criteria.

These and further objects and features of this invention will become more readily apparent upon reference to the following detailed description of a preferred embodiment, as illustrated in the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a perspective view of a helicopter shown in flight, which incorporates a crash sensor according to this invention;

Fig. 2 is a partial perspective view of an aircrewman wearing a safety harness that incorporates a webbing retractor that is alternatively manually operated and operated by a crash sensor according to this invention;

Fig. 3 is an enlarged plan view of the retractor of Fig. 2, partially broken away to illustrate details of construction;

Fig. 4 is a schematic diagram of the crash sensor illustrated in Fig. 2;

Figs. 5a and 5b are diagrams plotting the vertical and horizontal fire and no fire crash characteristics caused by measured accelerations of the helicopter of Fig. l; and

Fig. 6 is a plan view of an electronic acceleration sensor utilized in the crash sensor of this invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Fig. 1 of the drawings shows a helicopter 10 having a main lift rotor 12 and a tail rotor 14 driven by a pair of turbine engines 16 and 18 via a transmission (not illustrated) . Helicopter 10 is illustrated as a Black Hawk or Sea Hawk helicopter, but could be any helicopter. Helicopter 10 includes a cabin 20 housing a pilot and other personnel, such as aircrewmen, or occupant 22, shown in Fig. 2. A pair of side-mounted weapons pods 24 and 26 extend outwardly of cabin 20 on mounting arms 28 and 30.

Occupant 22 is fitted with a protective helmet 34 and a harness 36 to restrain his torso 38 in his seat (not shown) in a well-known manner. Harness 36 is conventional, available harness such as a Model MIL-S-58095 type five-way restraint system, made by H. Koch & Sons Co. It is modified to include dual lead-in straps 40 and 42 which attach to the harness 36 and extend rearwardly through an opening 44 in the seat and downwardly into a webbing reel or retractor 46. Retractor 46 is lockable by manipulation of a manual actuator 48, via a cable 50. In the event of a crash of helicopter 10, retractor is commanded by a crash sensor 52 via an electric cable 54 to retract webbing strips 40 and 42 to secure occupant 22 in his seat, as will be described below. Crash sensor 52 is preferably mounted on the aircraft floor rearwardly of the seat.

In Fig. 3 retractor 46 is illustrated as a modification of a Model MA-8 Inertia Reel currently produced by H. Koch & Sons, Inc., Anaheim, CA. It includes a housing 56 mounting a rotatable webbing reel 58. A clutch 60 is operably connected to a retraction piston 62 which is driven within a drive cylinder 64 by a power cylinder 66. When pyrotechnic material 68 within power cylinder 66 is ignited, it drives a blocking member 70 upwardly to open access of high pressure nitrogen in reservoir 72 to a feed channel 74. This high pressure nitrogen drives piston 62 downwardly in cylinder 64 to engage clutch 60 which drives reel 58 to retract webbing strips 40 and 42 to tighten harness 36 about occupant 22, securing him in his seat.

A connector 74 operably connects the pyrotechnic material igniter 76 with electric cable 54 which transmits output signals from crash sensor 52. As shown schematically in Fig. 4, crash sensor 52 comprises a CPU or microcontroller 80, such as a Motorola Model M68HCI6Z1 microcontroller, which is powered by a main aircraft power supply 82 and an emergency backup power supply 84 which comprises capacitors that enable operation when the main power supply fails, such as during a crash.

A tri-axis accelerometer 86 provides acceleration inputs for each of the three orthogonal axes to microcontroller 80 through a signal filter 88. Microcontroller 80 includes a data memory RAM 90, preferably a 2 megabyte PCMCIA Flash Memory which stores these acceleration inputs in 10-second increments. A display 92 is connected to microcontroller 80 and includes means for determining and displaying the status of all elements of crash sensor 52. Driver circuits 94 communicate output signals from microcontroller 80 to cable

54 and to optional outputs 96, such as a flight recorder (not shown) .

Tri-axis accelerometer 86 comprises three single axis electronic accelerometers, such as Analog Devices Model ADXL50 accelerometers. These accelerometers are arranged orthogonally to sense accelerations along three mutually perpendicular axes (X, Y and Z) and output acceleration signals for each axis to microcontroller 80. The sensing elements of one of the identical accelerometers are shown in Fig. 6. A fixed plate 86a has a plurality of electrodes in the form of fingers 87 which are interposed between similar electrodes in the form of fingers 89 of a fixed plate 86b. Movable plate 86a is anchored at its four corners 91 to provide a movable mass. During acceleration, the mass shifts, changing the spacing between the fingers 87 and 89 and, hence, the capacitance. Acceleration along a vector will produce different differential capacitances for each sensor. The output signals from accelerometer 86 are provided to microcontroller 80 for processing.

Helicopter accelerations along the three orthogonal axes are evaluated by microcontroller 80 to determine the occurrence of a crash. Microcontroller 80 is supplied with these predetermined crash criteria from a program memory PROM 106 which stores specific aircraft acceleration characteristics. This information enables microcontroller 80 to evaluate the vehicle acceleration inputs supplied by triaxial accelerometer 86 to determine if a crash has occurred.

Microcontroller 80 evaluates likely helicopter crash scenarios by sampling the accelerometers every 500 microseconds, converting their analog voltage outputs into accelerations in Gs. Microcontroller 80 then performs mathematical calculations comparing the received

acceleration data to that in PROM 106 to determine if a crash has occurred. If not, it performs routine system monitoring and diagnostics functions. If a crash is determined, it outputs a signal through cable 54 to fire pyrotechnic material 68 to operate cylinder 64 and retract webbing strips 40 and 42. This enables microcontroller 80 to process 6000 total acceleration data samples per second. Of course a higher or lower sampling rate (shorter or longer evaluation time) can be used, although the highest rate commensurate with system reliability is desirable.

This rapid evaluation and response assures that, in the event of a crash, harness 36 is instantaneously retracted to reduce the amount of movement by occupant 22, which significantly reduces the "flail envelope" and the incidence of occupant injury. This data is stored in 10- second increments, 5 seconds before a sensed crash event and 5 seconds following. Backup power supply 84 assures operation of crash sensor 52 in the event of a power failure during a crash.

In this illustrative example, PROM 106 includes acceleration criteria specific to the particular helicopter which mounts the crash sensor, here a Black Hawk. Example acceleration crash criteria, which is supplied by PROM 106 to microcontroller 80, is shown in Figs. 5a and 5b.

Fig. 5a plots vertical vehicle (helicopter) accelerations vs. time. A first curve 98 illustrates vertical axis acceleration conditions under which no output signal is commanded, while a second curve 100 provides vertical (Z axis) acceleration conditions under which an output signal is commanded. Similarly, in Fig. 5b, curve 102 shows horizontal (X and Y axes) acceleration conditions sensed under which no output signal is commanded, while a second curve 104 provides horizontal acceleration

conditions under which an output signal is commanded. The area between the curves provides system tolerances, i.e. conditions under which an output signal may be commanded. The illustrated criteria indicate the characteristics of pulses generated by accelerations measured by accelerometer 86 which will determine whether an output signal will be sent to power cylinder 66 to fire the pyrotechnic material 68.

During operation, triaxial accelerometer 86 senses accelerations experienced by helicopter 10 along any vector as accelerations along the three orthogonal monitored axes. It continuously feeds these accelerations to microcontroller 80, which stores them in data memory 90 in time increments for comparison with the axial acceleration characteristics. If evaluation of these acceleration signals by microcomputer 80 indicates that a crash has occurred, a signal is outputted to electric cable 54 to fire igniter 76 to. effect retraction of harness straps 42 and 44 to secure occupant 22 in his seat.

In addition to the above vehicle accelerations, crash sensor 52 may be provided with a plurality of information modules 108 through a mating interface 107 to PROM 106. These information modules 108 can include specific acceleration information directed to specific helicopters and their missions. Such missions may include different armament configurations carried in pods 24 and 26. Each armament configuration will subject helicopter 10 to different accelerations caused by armament firing. Although these accelerations can exceed the general crash criteria contained in microcomputer 80, the accelerations can be distinguished on the basis of time duration.

It is these specific accelerations which must be identified and ignored by microcomputer 80 to prevent non-

crash conditions from actuating power cylinders 64 which would cause a sudden, unanticipated restraint of occupant 22. Such an occurrence could interrupt effective operation of the helicopter. Although microcontroller 80 could be reprogrammed with this specific acceleration for each specific mission, the provision of different information modules facilitates the changing of mission-specific information in PROM 106.

The modules can also be supplied for different aircraft, enabling a basic sensor 52, having no specific acceleration information to be coded for any of a variety of vehicles and missions by supplying the necessary information via modules 108. Modules 108 can also be coded to eliminate any chance of the use of an improper module. Changes in the acceleration information could be limited to shop reconfiguration.

Additional power cylinders 66' may be provided to give the system multi-shot capability to enable multiple retractions of harness 36. The output signal from crash sensor may also be utilized to initiate inflation of air bags or an IBHARS (Inflatable Body and Head Restraint

System) restraint system supplement. A single crash sensor 52 may provide output signals for all aircrew harness retractors or a separate sensor may be provided for each.

The crash sensor of this invention is applicable to any type of helicopter, to fixed wing aircraft, and to any vehicle which is subject to crashes in any of a multiplicity of directions.

Thus, this invention provides a crash sensor for a vehicle which activates an occupant safety device upon sensing an impact in any direction to reduce the possibility of injury caused by the crash. The accelerometer functions to sense a crash along any vector

by simultaneously sensing accelerations along all three orthogonal axes. These acceleration signals are inputted to microcontroller 80 which evaluates them, by comparing them with acceleration characteristics and criteria programmed into memory, to determine when a crash has occurred. If so determined, an output signal is provided to an occupant safety device which secures an occupant in his seat to reduce injuries.

While only a preferred embodiment has been illustrated and described, obvious modifications thereof are contemplated within the scope of this invention and the following claims.