Pedestrian impact sensing apparatus for a vehicle bumper

An impact sensing apparatus includes a laterally extending air channel within a block of foam or other crushable medium disposed between a bumper fascia and a rigid bumper frame element, and one or more airflow sensors for detecting airflow within the air channel. The air channel may be defined by a flexible hollow tube embedded within the crushable medium or by a molded-in air cavity in cases where the crushable medium is formed by molding. The measured airflow provides a measure of crush rate, and two or more airflow sensors may be distributed within the air channel to optimize impact detection response time and to identify the impact location.

TECHNICAL FIELD

The present invention relates to pedestrian impact detection for a vehicle, and more particularly to an airflow sensing apparatus incorporated into a vehicle bumper.

BACKGROUND OF THE INVENTION

A vehicle can be equipped with deployable safety devices designed to reduce injury to a pedestrian struck by the vehicle. For example, the vehicle may be equipped with one or more pedestrian air bags and/or a device for changing the inclination angle of the hood. Since the initial point of impact is nearly always the bumper, many deployment systems include one or more pressure or deformation responsive strips disposed in or on the front and/or rear bumpers. See, for example, the U.S. Pat. No. 6,784,792 to Mattes et al., which suggests the use of wire strain, piezoelectric film, magneto-electric, magneto-resistive or optical sensor elements on the bumper fascia. In another approach disclosed in the U.S. Pat. No. 6,607,212 to Reimer et al., light energy scattered within a block of translucent polymeric foam disposed between the bumper fascia and a rigid bumper frame element is detected to form a measure of crush experienced in a collision.

SUMMARY OF THE INVENTION

The present invention is directed to an improved impact sensing apparatus including a laterally extending air channel within a block of foam or other crushable medium disposed between the bumper fascia and a rigid bumper frame element, and one or more airflow sensors for detecting air displacement within the air channel. The air channel may be defined by a flexible hollow tube embedded within the crushable medium or by a molded-in air cavity in cases where the crushable medium is formed by molding. The measured airflow provides a measure of crush rate, and two or more airflow sensors may be distributed within the air channel to optimize impact detection response time and to identify the impact location. Additionally, the size and placement of the air channel within the compressible medium can be configured to control the sensitivity of the sensing apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIG. 1, the reference numeral10designates a vehicle that is equipped with one or more pedestrian safety devices (PSDs) and a sensing system for deploying the safety devices when a pedestrian impact is detected. The PSDs are designated by a single block12, and may include one or more pedestrian air bags and a mechanism for changing the inclination angle of the vehicle hood. The PSDs are selectively activated by a microprocessor-based electronic control unit (ECU)14, which issues a deployment command on line16when a pedestrian impact is detected. The ECU14detects pedestrian impacts based on airflow signals produced by one or more airflow sensors18,20. The airflow sensors18,20are disposed in an air channel22that extends laterally across the vehicle; that is, perpendicular to the direction of vehicle travel. The air channel22resides within a block24of foam or other crushable energy-absorbent material disposed between a bumper fascia26at the leading edge of vehicle10and a rigid bumper frame element28that extends substantially parallel to the bumper fascia26. The air channel22may be defined by an open-ended flexible tube30passing through the foam block24as depicted inFIG. 2, or simply by an air-filled void or cavity in the foam block24as depicted inFIG. 1. In either case, the airflow sensors18,20measure airflow without substantially impeding airflow within the air channel22.

FIG. 2depicts the fascia26and foam block24when the vehicle10impacts a soft-bodied object32such as a pedestrian leg form. The impact locally crushes the foam block24and proportionally crushes the air passage22as indicated by the reference numeral22′. The localized crushing of air passage22produces transient airflows away from the crush zone as indicated by the arrows34aand34b.The airflows are respectively detected by the sensors18and20, and the airflow signals produced by sensors18and20provide a measure of the crush rate and impact location to ECU14.

The embodiment ofFIG. 2depicts an additional pair of airflow sensors36,38disposed approximately at the midpoint of the air passage22. The addition of sensors36and38improves the response time of the sensing apparatus by shortening the distance between an impact and a pair of airflow sensors. Furthermore, the difference between the airflow signals produced by sensors36and38provides an early indication of the airflow direction within air passage22; since the sensors36and38are located in the mid-section of the air passage22, the airflow direction tells ECU14which side of the vehicle10was impacted by the object32.

Referring toFIG. 3A, the heated element sensor40comprises four resistors41,42,43,44configured in a conventional Wheatstone bridge arrangement and a differential amplifier45responsive to the potential difference between the bridge nodes46and47. The amplifier45adjusts the bridge voltage (Vout) as required to balance the bridge. The resistors41-44are selected so that when the bridge is balanced, the resistor42(which may be a wire, for example) is maintained at an elevated temperature such as 250° C. The resistor42is positioned within the air channel22so that transient airflow (as represented by the arrows48) due to a pedestrian impact displaces the heated air surrounding the resistor42with air at essentially ambient temperature. This cools the resistor42and the amplifier45responds by increasing the bridge voltage. In this way, the amplifier output voltage Vout provides a measure of the magnitude of the airflow across resistor42.

Referring toFIG. 3B, the venturi sensor50has a sensor body51and a differential pressure sensor52, such as a silicon diaphragm sensor. The sensor body51is located within the air channel22and is configured to define restricted and unrestricted airflow ports53,54that are in-line with the transient air airflow (designated by arrows48) produced by deformation of the air channel22during a pedestrian impact. The pressure sensor52is disposed in a passage57extending between the airflow ports53,54, and the difference between the airflow in restricted airflow port53(designated by arrow55) and the airflow in unrestricted airflow port54(designated by arrows56) produces a corresponding pressure difference across the sensor52. The sensor52produces a signal corresponding to the pressure difference, which is also an indication of the magnitude of the impact-related transient airflow.

Referring toFIG. 3C, the Pitot tube sensor60has a sensor body61, first and second pressure chambers62,63and a differential pressure sensor64separating the pressure chambers62and63. The sensor body61is located within the air channel22and defines a central air passage65having an inlet66that is in-line with the transient air airflow (designated by arrows48) produced by deformation of the air channel22during a pedestrian impact, and one or more static air passages66,67having inlets68,69that are perpendicular to the impact-related airflow. The central air passage65is coupled to the first pressure chamber62, while the static air passages66,67are coupled to the second pressure chamber63. The sensor64is responsive to the difference in pressures between the first and second chambers62,63, and such difference provides a measure of velocity of the impact-related transient airflow.

FIG. 4, Graphs A-B, depict data collected in a mechanization of the present invention during a 13.7 MPH collision of a human leg form with the center of a stationary vehicle bumper constructed substantially as depicted inFIGS. 1-2. The leg form was instrumented with an accelerometer, andFIG. 4Adepicts the measured deceleration during the impact. In the test apparatus, two Pitot tube airflow sensors were installed in the outboard ends of a flexible tube within a foam block substantially as depicted inFIG. 2, and Graph B depicts the air velocity measured by one of the airflow sensors. In general, the magnitude of the airflow signal provides a predictable and reliable measure of impact severity. The decision as to whether deployment of one or more PSDs is warranted for a given impact can be made by calibrating a fixed or time-variant threshold and deploying the restraint(s) if the measured airflow exceeds the threshold. The depicted data additionally demonstrates that the severity of an impact can be determined very quickly, enabling timely deployment of supplemental restraints for virtually any crash event. In particular, the test illustrates the worst-case time response for the sensing apparatus because the airflow sensors are equally displaced from the point of impact. Even so, the data shows that the impact detection time is only about 5 milliseconds for an air channel that is six feet in length. About one-half of the response time is required for the airflow pulse to reach either airflow sensor, with the remaining time required for signal processing in ECU14.

In summary, the present invention provides a novel sensing apparatus capable of detecting pedestrian impacts both quickly and reliably by responding to a transient airflow in an air channel within a crushable medium. Since the sensors are responsive to transient airflow, the air channel does not need to be closed or sealed. Additionally, the slope of the measured airflow signal can be used to infer crush rate, for purposes of discriminating between pedestrian impacts and other impacts.

While the present invention has been described with respect to the illustrated embodiments, it is recognized that numerous modifications and variations in addition to those mentioned herein will occur to those skilled in the art. For example, the air channel22may be equipped with more or fewer airflow sensors than shown, and the apparatus may be applied to a rear bumper or to a vehicle body panel such as a fender or side-door. Also, the size and placement of the air channel22within the foam block24can be configured to control the sensitivity of the sensing apparatus. Placing the air channel closer to the fascia26increases the detection sensitivity, while placing the air channel closer to the bumper frame element28reduces the detection sensitivity. Such placement of the air channel22can be used, for example, to provide maximum sensitivity in the central area of the bumper and reduced sensitivity near the ends of the bumper. Alternatively or additionally, the shape of the air channel22may be configured to provide increased or decreased sensitivity; for example the air channel22may be larger in diameter in the center than near the ends to heighten the detection sensitivity for impacts near the center of the bumper. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.