Patent Publication Number: US-2011075158-A1

Title: Optical crash sensor

Description:
TECHNICAL FIELD 
     The present invention generally relates to crash sensors, and more particularly relates to an optical crash sensor for sensing a crash of a vehicle. 
     BACKGROUND OF THE INVENTION 
     Vehicle crash sensors, also referred to as satellite sensors or impact sensors, have been commonly employed on vehicles to sense vehicle dynamics to detect a vehicle crash. Crash sensing systems generally employ crash sensors typically in the form of one or more accelerometers and pressure sensors. The accelerometers detect deceleration of the vehicle. The pressure sensors may serve to provide immunity against inadvertent deployment, particularly for side impact sensing events. However, there are drawbacks associated with the pressure based sensing which include the need for an enclosed air cavity and the inability to discriminate direction of crash. 
     Accordingly, it is therefore desirable to provide for a sensor that may detect a crash in a vehicle that does not suffer the aforementioned drawbacks of the pressure based sensors. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, a vehicle crash sensor arrangement is provided. The sensor arrangement includes a first structure of a vehicle, a second structure of the vehicle located a distance from the first structure of the vehicle, and an optical sensor comprising a light transmitter and a photo receiver mounted to one of the first and second vehicle structures and arranged such that the light transmitter emits a light signal and the photo receiver senses irradiance. A change in irradiance is an indication of a change in displacement of the first structure relative to the second structure indicative of deformity of the vehicle. The sensor arrangement further includes processing circuitry for processing the sensed irradiance and detecting a vehicle crash based on the change in sensed irradiance. 
     According to another aspect of the present invention, a vehicle crash sensor is provided. The vehicle crash sensor comprises a light transmitter connected to a vehicle for emitting a light signal within an opening between a first vehicle structure and a second vehicle structure, and a photo receiver located on the vehicle for sensing irradiance in the opening between the first vehicle structure and the second vehicle structure, wherein a change in the irradiance is indicative of a change in displacement of the first structure relative to the second structure indicative of deformity of the vehicle. The vehicle crash sensor also includes processing circuitry for processing the sensed irradiance and detecting a vehicle crash based on the change in irradiance. 
     According to a further aspect of the present invention, a method of sensing a change in displacement of a first vehicle structure relative to a second vehicle structure indicative of deformity of the vehicle is provided. The method comprises the steps of transmitting via a light transmitter on a vehicle a light signal in an area between a first vehicle structure and a second vehicle structure, and sensing via a photo receiver on the vehicle irradiance between the first vehicle structure and the second vehicle structure, wherein a change in the irradiance is indicative of a change in displacement of the first structure relative to the second structure indicative of deformity of the vehicle. The method also includes the step of processing the sensed irradiance to determine a change in irradiance and detecting a vehicle crash based on the change in irradiance. 
     These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is a top view of a vehicle shown generally employing a pair of side impact crash sensors, according to one embodiment; 
         FIG. 2  is a cross-sectional view taken through line II-II of  FIG. 1  illustrating the crash sensor employed between two vehicle structures in a pre-crash state; 
         FIG. 3  is a cross-sectional view of the crash sensor after a crash which causes a change in irradiance; 
         FIG. 4  is a block/circuit diagram illustrating the transmit circuitry for emitting light signals with the light transmitter; 
         FIG. 5  is a block/circuit diagram illustrating the receiver processing circuitry for processing the sensed irradiance; 
         FIG. 6  is a timing diagram illustrating the transmission and reception of light energy signals employed by the crash sensor; 
         FIG. 7  is a graph illustrating the change in irradiance compared to a threshold value for determining a crash event; and 
         FIG. 8  is a block/circuit diagram of integrated transmit and receiver processing circuitry, according to another embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to  FIG. 1 , an automotive vehicle  10  is generally illustrated employing a crash sensing system shown having crash sensors  20  located on opposite lateral sides of the vehicle  10 . The vehicle  10  may include a wheeled vehicle having road wheels and employs the crash sensing system for mitigation during a crash event, such as the deployment of air bags, pretensioning of seat belts, etc. The crash sensors  20  are shown mounted in the passenger doors  12  and  14 , according to one embodiment. However, it should be appreciated that the crash sensors  20  may be mounted elsewhere on the body of the vehicle  10  on opposite lateral sides for side impact, or may be mounted on the front or rear or corners of the vehicle  10  for front or rear crash sensing or other locations as desired. In the embodiment shown, the crash sensors  20  detect a crash with a side impact object impacting the vehicle door at a location proximate to the sensor  20 . 
     Referring to  FIGS. 2 and 3 , the crash sensor  20  is further illustrated arranged on the vehicle  10  in a non-crash state in  FIG. 2  and a post crash state in  FIG. 3 . The crash sensor  20  is arranged on the vehicle  10  shown connected to a first vehicle structure  16 , which may include a frame of the door  12 , according to one embodiment. The vehicle  10  also has a second vehicle structure  18 , which may include an outer body panel of the vehicle  10 . The second structure  18  of the vehicle  10  is located a distance from the first structure of the vehicle, such that there is a space (area) or opening between the first structure  16  and second structure  18 . The crash sensor  12  is arranged within the space between the first and second structures  16  and  18  to detect a change in displacement of the first structure  16  relative to the second structure  18  indicative of deformity of the vehicle body and therefore a crash event. Thus, as the outer body  18  is crushed or forced inward during a crash toward the first vehicle structure  16 , the crash sensor  20  senses the change in sensed irradiance of transmit light energy which is indicative of a change in displacement of vehicle structures  16  and  18  relative to each other and detects a vehicle collision based on the change in irradiance. 
     The crash sensor  20  includes a light transmitter  22  located within the space (area) between the first and second structures  16  and  18  for emitting a light signal toward the outer or second vehicle structure  18 . According to one embodiment, the light transmitter  22  comprises an infrared (IR) light emitting diode (LED) for emitting IR radiation  23  which reflects off of the inside surface of the second vehicle structure  18 . One example of an IR transmitter is a high speed IR emitting diode sold as Part No. TSHG6400 commercially available from Vishay Semiconductors. The light transmitter  22  may include visible and/or non-visible light emission. 
     Also located within the area between the first and second vehicle structures  16  and  18  is a photo receiver  24  which senses irradiance of light energy. The sensing or irradiance may include sensing light based on illuminance. The photo receiver  24 , according to one embodiment, may be a photodiode. Alternatively a phototransistor can be used if slower rise and fall times are acceptable. According to one embodiment, the photo receiver  24  may employ a silicon pin photodiode such as Component No. TESP5700 commercially available from Vishay Semiconductors having a side view lens and daylight blocking filter matched to the high speed IR emitter. It should be appreciated that other transmitters and receivers may be employed, including those qualified for automotive applications. The photo receiver  24  may receive visible and/or non-visible light energy. The receiver  24  may be periodically activated to sense irradiance or illuminance. The sensed irradiance can be measured in units of watts per meter squared (w/m 2 ). The irradiance can be sensed as illuminance which can be measured in units of luminous flux per meter squares (Im/m 2 ). In the embodiment shown, both the light transmitter  22  and receiver  24  are mounted to the first structure  16 . 
     As seen in  FIG. 3 , during a vehicle collision, when the outside of the second vehicle structure  18  is impacted during a crash with sufficient force causing it to crush or deform and move towards the first vehicle structure  16 , the irradiance of light  23  sensed by the photo receiver  24  changes. Generally, the forced movement of the second structure toward the first structure  16  causes an increase in sensed irradiance  23 . Sensor  24  senses the increased irradiance  23 , which is processed by processing circuitry to determine whether or not a vehicle crash has occurred. 
     Referring to  FIG. 4 , the light transmitter circuitry is generally illustrated having an application specific integrated circuit (ASIC)  30  generating a clocked output to a drive transistor  36  on and off such as every one hundred (100) microseconds. Transistor  36  is connected in series with the infrared LED  22  which receives a voltage input VCC at input  32 . When drive transistor  36  is turned on, an IR light signal is emitted. By pulsing the IR light emission, reduced power usage of the transmitter is achieved. According the ASIC  30  provides a pulsed signal that generates a pulsed infrared light emission at the IR LED  22 . 
     The processing circuitry  40  for processing the received irradiance is illustrated in  FIG. 5 , according to one embodiment. As seen, the photo receiver  24 , shown as a photodiode, senses irradiance which is input to an amplifier  42  to amplify the sensed light energy signal and then to an analog-to-digital converter (ADC)  44  to convert the analog signal to a digital signal. The digital IR irradiance signal is provided as an input to a subtractor  46 , along with an irradiance initialization value IR 0 . The irradiance initialization value IR 0  is the value of irradiance measured during an initialization process. The initialization process may occur when the vehicle is started or periodically such as every one second or frequently as required. IR 0  can be input to an automatic gain controller (AGC) to vary the gain of the amplifier so that the IR 0  level detected can be in the suitable range. The subtractor  46  generates a change or difference signal between the sensed irradiance IR and the initialization irradiance IR 0  which is shown as ΔIR. The ΔIR signal represents the change in irradiance and is input to a controller  48 , which includes a deploy discriminator  49 . ΔIR signal is digitally coded and can be current or voltage modulated. According to one embodiment, the deploy discriminator  49  compares the ΔIR value to a threshold and, if the ΔIR value exceeds the threshold, generates a collision detection output, according to one embodiment. Prior to a crash, the sensed IR will be approximately equal to IR 0  such that ΔIR=0. During a crash, sensed IR will exceed IR 0  such that ΔIR exceeds the threshold. The controller  48  may be implemented with a microprocessor or other analog or digital circuitry. 
     Referring to  FIG. 6 , the pulsed infrared transmitted light pulses are illustrated in the transmit TX signal, in comparison to the received irradiance RX signal. The transmitted IR TX signal has a high signal  50  that may be pulsed every one hundred (100) microseconds, for example. Each infrared transmission is sensed by the receiver which generates the received RX signal with sensed irradiance at high signals  60 . As seen in  FIG. 7 , when the sensed irradiance changes sufficiently by an amount greater than a threshold value, a crash could be detected or an algorithm is triggered to check for crash events. In doing so, the change in irradiance ΔIR shown by line  70  exceeds the threshold shown by line  80 . Once a crash is detected, the sensed crash output may be employed to deploy one or more devices or systems on board the vehicle. For example, one or more air bags, side curtains, seat belt pretensioners and other devices on the vehicle may be deployed. It should be further appreciated that the crash sensor may be employed in combination with a plurality of crash sensors or may be employed in combination with other sensors, such as accelerometers, to improve deployment reliability and immunity against inadvertent deployment and reliably detect a vehicle crash. 
     Referring to  FIG. 8 , an integrated crash sensor is shown having an integrated transmitter and receiver, according to another embodiment. In this embodiment, the integrated crash sensor integrates the transceiver and receiver with an application specific integrated circuit (ASIC)  90 . Specifically, the IR LED  22  is coupled to transistor  36  within the ASIC  90 . The photo receiver  24  is also shown external to the ASIC  90  and providing the receiver input RX to the ASIC  90 . In addition, the receiver circuitry includes an automatic gain control (AGC) block  92  which allows for control of the amplifier gain within a suitable voltage range. The amplified signal from amplifier  42  is passed to the ADC  44  and to the subtractor  46  which generates the ΔIR signal. The ΔIR signal is provided to a controller  48  which includes a deploy discriminator logic  49 . It should be appreciated that the optical transceiver sends out raw digital messages to the controller  48  which can be a sensing diagnostic module (SDM) or an air bag control unit (ACU), according to various embodiments. 
     Accordingly, the crash sensor  20  advantageously senses the crash of a vehicle  10  by sensing a change in irradiance resulting from deformation of a first vehicle structure relative to a second vehicle structure. The sensor may advantageously be used in place of conventional pressure sensors. 
     It will be understood by those who practice the invention and those skilled in the art, that various modifications and improvements may be made to the invention without departing from the spirit of the disclosed concept. The scope of protection afforded is to be determined by the claims and by the breadth of interpretation allowed by law.