Abstract:
A test fixture for rollover crash testing of a test vehicle onto a moving surface employs a cradle to support and rotate the test vehicle. A vertical support structure to positions and releasably holds the cradle. A moving sled having a contact surface is carried by a guide extending beneath the structure and the cradle fixture. The cradle is rotated and released from the structure responsive to a sensor for contact within a drop impact zone on the contact surface of the moving sled. Vertical motion of the cradle is then arrested to prevent further damage to the test vehicle or the test structure.

Description:
REFERENCE TO RELATED APPLICATIONS 
   This application claims the priority of U.S. Provisional Patent Application Ser. No. 60/676,160 filed on Apr. 29, 2005 having the same title as the present application. 

   BACKGROUND 
   1. Field of Invention 
   This invention relates to an automotive vehicle test fixture. In particular, the invention relates specifically to a fixture to conduct dynamic, repeatable, controlled destructive rollover impact tests of both full scale vehicles and representations to evaluate strength characteristics of the vehicle roof and other vehicle components. The invention provides precise control of initial test parameters including drop height, contact roll rate, contact roll angle, pitch angle, yaw angle, roadway speed, post contact freefall height, vehicle moment of inertia, roadway surface conditions including friction and impact obstructions. In addition, the invention enables multiple tests to be conducted and evaluated on an isolated singular roll-by-roll basis. 
   2. Description of Prior Art 
   Rollovers have been and continue to be a significant cause of occupant fatalities and serious injuries. To date, the experiments to determine vehicle performance have been criticized as unrepeatable and, thus, inappropriate for vehicle or component design and testing and/or compliance type testing. Various other test fixtures been developed that addresses some of these issues, but requires a large infrastructure to run and does not fully control the vehicle during the test (reference: U.S. Pat. No. 6,651,482). Another device (reference U.S. Pat. No. 6,256,601) articulates about a pivot but does not provide a full rollover capability, nor does it provide a means to simulate a roll about the true roll axis of a vehicle. In addition, none of the other test methods allow for the direct measurement of the loads applied to the vehicle, which are important to evaluating and understanding the dynamics of a rollover event. This subject invention resolves these issues in a manner that will allow effective repeatable vehicle testing. Vehicle testing in the rollover regime is crucial to understanding interactions between the occupant and the vehicle&#39;s structures, restraints, glazing, etc. A better knowledge of these parameters will allow for improved vehicle designs and a safer vehicle fleet. 
   Previous testing to determine vehicle performance and vehicle to occupant interactions in rollover conditions uses various types of tests including dropping a rotating vehicle, launching a vehicle from a dolly, launching a vehicle from a ramp or otherwise tripping a vehicle to initiate a roll. The major drawback of these tests is the unrepeatable nature of the testing. While these tests will allow insight into vehicle performance, they do not allow a study of vehicle and component performance during an impact that can be exactly repeated to determine changes in vehicle structure or geometry through repeated tests. In particular, earlier test methods do not result in consistent impacts due to variations in tire to dolly or tire to road impacts before the roof structure interaction or are not controlled after the roof impacts. By controlling the vehicle both before and after the roof impacts, performance during an impact can be isolated and examined in detail. 
   U.S. Pat. No. 6,651,482 describes an alternate method of rollover testing. The method described in that patent is considerably different from the invention discussed herein. These differences lead to several shortcomings in the previous methodology including the inability to measure the direct forces on the roof of the vehicle, the inability to control the vehicle after the desired roof contacts, the artificial positioning of anthropomorphic crash test dummies if included, the inability of the system to directly determine the roof crush from the desired impact, the inability to evaluate damage on a per roll basis. 
   U.S. Pat. No. 6,256,601 describes a rollover test sled designed to simulate the behavior of vehicle occupant and safety systems in a rollover accident. The method described differs significantly from the invention presented herein since the test does not provide the means to rotate a test vehicle or dummies about a roll axis. The fixture described also does not provide the means to rotate the test vehicle for the purposes to measure and evaluate vehicle structural integrity. 
   This invention addresses these issues and provides an improved dynamic, repeatable vehicle rollover test fixture. 
   SUMMARY OF THE INVENTION 
   A test fixture for rollover crash testing of a test vehicle onto a moving surface incorporates a cradle to support and rotate a test vehicle. The cradle is carried by a structure to position and releasably hold the cradle. A moving sled having a contact surface simulating a roadway is carried by a guide extending beneath the structure and the cradle fixture. The cradle and supported vehicle is released from the structure responsive to a sensor for contact within a drop impact zone on the contact surface of the moving sled. The cradle is rotated to coordinate the test vehicle and roadway position at impact and the vertical motion of the cradle is arrested at the event completion to avoid damage to the track and sled system as well as limiting further damage to the test vehicle. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The elements and features of the invention are further described with respect to the detailed description herein and the following drawings wherein 
       FIG. 1   a  is a front view of the rollover fixture showing the major components; 
       FIG. 1   b  is a side view of the rollover fixture of  FIG. 1   a;    
       FIG. 2   a  is a plan view of the rollover fixture; 
       FIG. 2   b  is a plan view of elements of the rollover fixture with the drop tower assembly removed for clarity. 
       FIG. 3  is a front profile view of the rollover fixture illustrating a vehicle drop in process; 
       FIG. 4  illustrates an embodiment of a mechanism to drive the vehicle cradle utilizing a rotation drive cable with a corresponding set of pulleys; 
       FIG. 5  diagrams an embodiment of a pneumatic propulsion system used to supply compressed air to the propulsion cylinders; 
       FIG. 6  is a front profile view of the sled positioned over the guide rail impact bearing plate; 
       FIG. 7  diagrams an embodiment of an electrical control system used to manually start the rollover test process and to enable actuation of vehicle drop; and 
       FIG. 8  diagrams an embodiment of a data acquisition system used to monitor and record dynamic physical responses of the vehicle, roadway and dummies within the 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   An exemplary embodiment of the present invention is illustrated in  FIGS. 1   a  through  7 . As best seen in  FIGS. 1   a ,  1   b  and  2   a , the test fixture  100  incorporates a sled  110  supported by sled guide rails  115 . The sled  110  is translated toward and between drop towers  120  by means of propulsion cables  154  coupled to propulsion pistons  152  contained within propulsion cylinders  151 . For the embodiment shown in the drawings, a roadway surface  111  is mounted to the upward face of the sled in order to simulate a road condition for impact with the vehicle. Various road surface materials are employed to simulate various real road conditions including Macadam and concrete. In alternative embodiments, various other surface features are mounted to the sled structure for impact studies. 
   The drop towers assembly  120  includes a front drop tower  122  and a rear drop tower  123  connected overhead by a tower connection beam  121 . The drop tower assembly  120  straddles the sled guide rails  115  and the towers are mounted to the yaw adjustment guide plates  119  that are pivotably fastened to the floor  101 , as best seen in  FIG. 2   b . The angular orientation of the drop tower assembly relative to the sled guide rails  115  therefore sets the yaw position of the test vehicle. The drop towers  122  and  123  each support vertical guide bearings  130 . Runner assemblies  105  which support and couple to a vehicle cradle  131  ride on the guide bearings for vertical motion of the cradle. The vehicle cradle  131  is fitted with various brackets to facilitate mounting of various models of full size test vehicles  103  or test bucks. Cradle ballast weights  136  may be also affixed to the vehicle cradle  131  in order to compensate or adjust the vehicle moments of inertia. 
   With the moving sled simulating the roadway for impact of the vehicle, rotation of the vehicle cradle synchronizes the impact of the vertically descending vehicle with the horizontally moving roadway. A rotation drive assembly  140  located adjacent the front drop tower  120  provides a rotation drive pulley support frame that supports a rotation drive pulley  142 . A rotation drive support shaft  143  couples the rotation drive pulley  142  and the vehicle cradle  131 . The drive support shaft  143  incorporates universal joints  106  that provide angular alignment between the drive pulley  142  and the vehicle cradle  131 . Slide rods  109  couple the vehicle cradle to the runner assemblies. 
   For the embodiment shown in the drawings, motion of the sled is provided by a propulsion assembly  150 , best seen in  FIG. 6 , incorporating pneumatic propulsion cylinders  151  that support and guide the linear motion of propulsion pistons  152 . The cylinders are single acting design being closed at the pressure inlet end and open at the venting end. The first ends of the propulsion cables  154  are respectively coupled to the pistons  152  and extend through propulsion cable seals  164  at the closed end. The second ends of the cables  154  are respectively guided around propulsion pulleys  153 , best seen in  FIG. 2  and coupled to the leading edge of the sled  110 . 
   The first end of coupling cable  139  attaches to the trailing side of the sled  110  with the second end spooled about the coupling pulley  138 . The coupling pulley  138  is mounted and affixed onto a synchronization pulley  137  that rotates about a bearing shaft. A first end of a rotation drive cable  144  is spooled about the synchronization pulley  137  while the second end of the rotation drive cable  144  is spooled about the rotation drive pulley  142  as guided by a rotation idle pulley  145 . 
   A sled decelerator  170  located at the end of the sled guide rails  115  is provided to beneficially decelerate and stop the sled in a controlled manner at the end of its travel. A drop trigger switch  117  located between the sled guide rails  115  and ahead of the drop towers  120  is provided to detect the leading edge of the sled  130  as it translates forward. Upon actuation of the trigger switch, the front drop actuator  126  and the rear drop actuator  127  are enabled thereby releasing the runners supporting the vehicle cradle  131  for motion down the vertical guide bearings  130  to synchronously drop with respect to the position of the sled  110 . 
   At the completion of the roll-over impact event, the car body or buck must be arrested to prevent damage to the support elements of the fixture or the sled or drive system through unwanted contact after the roadway portion on the sled has passed. To accommodate this requirement, a vertical brake assembly  107 , best seen in  FIG. 1   b , is provided as a portion of the vertical runner assembly. The vertical brake engages a rail element  108  on the drop towers on each side of fixture. For the embodiment shown in the drawings the vertical brake is a disc brake assembly acting on the rail. The brake is actuated by a sensing element. In exemplary embodiments, an additional contact switch  196  on the road rail senses passage of the road bed and actuates the brake. Alternatively, event completion is determined by the angle of rotation of the vehicle under test or predetermined timing and sensing of the completed event is accomplished based on the rotation angle of the support shaft elements in the vertical runner assemblies. An index pin on the slide rod which engages a micro switch upon rotation through a predetermined arc or an angular rotation sensor on the axle or the rotation drive pulley is employed as the event completion sensor. 
     FIG. 6  shows additional elements of the sled and rail system for an exemplary embodiment. Low friction rail impact bearing plates  113  are attached to sled guide rails  115  within the drop impact zone. The moving sled with roadway rides on led guide rollers  116  and has attached to its underside a plurality of sled impact bearing blocks  114  for to transfer and distribute impact loads from the roadway surface to the rail impact bearing plates during impact of the test vehicle onto the roadway. 
     FIG. 7  is a diagram of a simplified electrical control system. Since human safety is paramount concern while conducting vehicle testing, system power is enabled by a key-switch. Compressed air tank pressure is monitored by a pressure switch to prevent starting a test unless requisite propulsion pressure is available in the compressed air tank  161 . A start switch is manually actuated to initiate the test sequence that causes control relay  1 CR to close and thereby energizing the actuate sled solenoid valve  162  while the sled stop switch  118  is closed. Upon energizing the actuate sled solenoid valve  162 , compressed air from the compressed air tank  161  is released to the propulsion cylinders  151  causing the sled  110  to translate forward. As the sled  110  passes the drop trigger switch  117 , the front drop actuator  126  and rear drop actuator  127  are energized to release thereby allowing the vehicle cradle  131  and the subject test vehicle  103  it contains to drop. An “enable rotation brake” key-switch is provided to enable optional activation of the rotation brake  147  upon closure of the rotation brake trigger switch  148 . 
   As shown in  FIG. 7 , additional test equipment features such as illumination lights  193  for cameras  181  are controlled by a switch located the operator controls  180 . 
   As shown in  FIG. 8 , a suite of instrumentation sensors is incorporated to measure and record the dynamic physical responses of the vehicle during the test. Sensors included in a preferred embodiment of the invention include: encoders  182  and  183  respectively mounted to the front and rear drop towers  122  and  123 ; encoder  184  is used to monitor the X axis linear position to derive speed and acceleration of the sled  110 ; load cells  112  arranged between the roadway surface  111  and the sled  110  to monitor Z-axis impact forces imposed by the test vehicle  103 ; load cells  185  arranged between the roadway surface  110  and the sled  110  to monitor X-axis impact forces imposed by the test vehicle  103 ; encoder  186  to monitor the roll orientation of the test vehicle  103 ; accelerometers  187  to monitor impact forces imposed upon a test dummy  104 ; sensors  188  to monitor displacements imposed upon a test dummy  104  during the test; accelerometers  189  to monitor impact forces imposed upon the test vehicle  103 ; sensors  190  to measure displacements imposed upon the test vehicle  103 ; cameras  181  mounted about the rollover apparatus  100  to monitor various external aspects of the test vehicle  103 ; cameras  182  mounted within the test vehicle  103  to monitor various internal aspects including roof crush intrusion and dummy positions during the test. 
   As shown in  FIG. 8 , the suite of sensors as previously described are preferentially input to signal conditioning electronics  192  and digitized for input to a data acquisition computer  193 . Once digitized, the collected data is saved, analyzed and formatted for various studies and reports. 
   Having now described the invention in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present invention as defined in the following claims.