Abstract:
A method for guiding a driverless, multi-track vehicle along a predetermined path ( 12 ), which vehicle rolls on wheels ( 4, 6 ) separated from each other in the vehicle width direction, wherein the vehicle is steered by changing the torque applied to at least one of its wheels, such that it follows the predetermined path.

Description:
This application is the US national stage filing of International Application No. PCT/EP2005/000494 filed Jan. 19, 2005, which claims priority to German patent application no. 10 2004 003 087.1 filed Jan. 21, 2004. 
     TECHNICAL FIELD 
     Background Art 
     The invention concerns a method for guiding a vehicle along a predetermined path. The invention further concerns a multi-track vehicle that is guidable along a predetermined path and a system for performing crash-tests by applying the inventive method and by using at least one inventive vehicle. 
     SUMMARY 
     Crash-tests are an essential tool during the development of a new vehicle, which crash-tests must fulfill numerous legal passenger-protection regulations and which should offer the passenger of the vehicle an optimal amount of passive security. A method for performing crash-tests is known from EP 0 445 671 B2, in which at least one driverless vehicle is guided to a previously-defined collision point, wherein the vehicle is moved under its own drive power by on-board control of the speed and driving direction along a predetermined drive path that is given by a guide device. Thus, the steering of the vehicle takes place via an actuator that operates the steering device of the vehicle, e.g., by direct intervention on the steering wheel. The installation of the corresponding actuator is relatively costly; moreover, a loss of the actuator as a result of a crash-test is connected with not insignificant costs. 
     The object underlying the invention is to create an option for performing crash-tests more cost-effectively than before. 
     In one aspect of the present teachings, methods are taught for guiding a driverless, multi-track vehicle along a predetermined path, which vehicle rolls on wheels separated from each other in the vehicle width direction, wherein the vehicle is steered such that the vehicle follows the predetermined path. The vehicle is preferably steered by changing the torque applied to at least one of its wheels. With this method, a separate steering actuator can be omitted, because the wheels of the vehicle are not turned to change the vehicle direction. Instead, varying torque is applied to the wheels to change the vehicle direction. 
     More preferably, at least one wheel is braked to change the vehicle direction. Furthermore, the drive torque of the vehicle is preferably increased in correspondence to the braking moment, so that the speed of the vehicle is not changed by a brake intervention for steering the vehicle. In this respect, at least two wheels disposed on different sides of the vehicle may be driven by their own motors whose drive torque is changed for steering the vehicle. More preferably, the drive torques of the motors may be changed such that the total drive torque of the vehicle remains constant during a steering intervention. 
     In another aspect of the present invention, a multi-track vehicle guidable along a predetermined path preferably includes at least one drive apparatus for driving at least one vehicle wheel. A braking apparatus is preferably provided for selective braking of at least two wheels disposed on different sides of the vehicle and a steering apparatus is preferably provided for changing the driving direction of the vehicle. A guiding device may ascertain a deviation of the actual path of the vehicle from a predetermined path and a control device preferably controls the operation of the vehicle such that the vehicle moves with a predetermined speed along the predetermined path. Even more preferably, the steering device may be formed by the braking apparatus that brakes the wheels when there is a deviation between the actual path and the predetermined path such that the deviation between the actual path and the predetermined path is minimized. 
     In a preferred embodiment of this aspect, the drive apparatus, the braking apparatus and the steering apparatus are preferably formed by at least two selectively controllable motors that drive the wheels disposed at different positions of the vehicle. The motors are preferably controlled by the control device such that, when there is a deviation between the actual path and the predetermined path, the vehicle changes its direction by selectively changing the moments acting upon the wheels such that the deviation decreases. 
     The vehicle may preferably carry a barrier designed for a collision with another vehicle. 
     In another aspect of the present teachings, a system for performing crash tests may be provided by applying one or more of the above-described methods and by using at least one of the above-described vehicles. In this case, a guide apparatus preferably defines a predetermined path and a speed control apparatus cooperates with the vehicle for controlling the vehicle speed such that the vehicle follows the predetermined path with a predetermined speed progression. The guide apparatus may preferably comprise a navigation apparatus that works by measuring distances between the vehicle and predetermined reference locations. 
     The invention can be used in all cases where the vehicle should be moved along a predetermined path in a driverless-manner. The application of the invention is advantageous where the radii of curvature of the curves, which the vehicle has to drive, are relatively large. The invention is particularly well suited for the cost-effective performance of crash-tests, with which it will be explained with schematic drawings in the following example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic drawing of a first embodiment of an inventive system. 
         FIG. 2  shows a schematic drawing of a second embodiment of an inventive system. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIG. 1 , a vehicle, which is denoted as a whole with  2 , includes front wheels  4  and rear wheels  6 . The design of the vehicle can be known as a whole, which means e.g. a conventional automobile with a combustion motor, steering and so on. These conventional components are not shown. For braking of the vehicle, the wheels are provided with known wheel brakes  8 . 
     For guiding along a predetermined path, the vehicle includes an antenna  10  or a known sensing device that operates in another way; the position of the vehicle can be detected by the antenna  10  in the lateral direction relative to a cable laid in the drive path. The vehicle further comprises a control device  14  that preferably includes a microprocessor with program- and data-memory. Inputs  16  of the control device  14  are connected with the antenna  10  and a signal transmitter that supplies a signal corresponding to the vehicle speed to the control device  14 . Outputs of the control device  14  are connected with actuators  18  for the wheel brakes  8  (only one actuator is shown) and an actuator  20  for the operation of a charge controlling element of the not-illustrated internal combustion engine. The control device  14  communicates via an antenna  22 , preferably with a central guide device  24  located externally of the vehicle. 
     The construction of the described components is known, such that their function will not be described in detail. With respect to the individual operation of the wheel brakes, the components known from vehicle stability control systems with brake intervention can be applied and controlled. In the following, the function of the entire system will be described in an exemplary manner. 
     It is assumed that an impact by the vehicle should be performed with a predetermined speed against an impediment disposed at a specified position of the path that is defined by the cable  12 . 
     Pertinent data will then be input to a data memory of the control device  14  directly via a vehicle-affixed data input device or via the guide device  24 , namely in the described example, the speed with which the vehicle should impinge upon the impediment. 
     The vehicle will then preferably be activated by the guide device  24 , wherein the actuator  20  of the charge controlling member is operated such that the vehicle has already accelerated to the predetermined speed before the impediment, which speed is held at the predetermined value by means of the control device  14  and the actual vehicle speed supplied to an input of the control device  14 . For example, the vehicle drives with steering such that the front wheels are locked in the straight-forward position. When there is a deviation of the actual path from the target path given by the cable, the wheel brakes  8  are operated via the actuators  18  such that the deviation between the actual path and the target path decreases and the vehicle is located along the target path, i.e. the vehicle moves such that the antenna  10  is located within a predetermined window over the cable  12 . For example, when the actual position of the vehicle deviates to the left of its target position according to  FIG. 1 , the wheel brake  8  of the right front wheel is operated, whereby the vehicle curves to the right. It is also understood that both right-side brakes or only the brake of the right rear wheel can be operated. Advantageously, the charge controlling member of the internal combustion engine is further opened when one or more wheel brakes are actuated for a direction correction, so that the additional drive torque of the internal combustion engine compensates for the braking moment and the vehicle speed remains constant. The cooperation between the brake operation and necessary additional opening, e.g., of a throttle valve, can be stored in an engine operating map, which is stored in the data memory of the control device  14 . 
     The steering is not required to be locked in the straight-forward position. When there is sufficient restoring torque, a locking with the device required therefor can be omitted, wherein costs are reduced. It is also possible to perform tests with the steering locked at a predetermined angle, so that the vehicle moves along a curved path without differing drive torque on its sides. 
     When a vehicle collision, vehicle against vehicle, should be performed with the inventive system, two vehicles can move on the guide cable  12  in a predetermined way under control of the guide device  24 , wherein, in case the collision location should be predetermined, the time points, at which the vehicles driving towards each other are respectively located at predetermined positions of the route, will also be monitored. This can take place by providing the cable itself with electronic marks, by providing marks along the route or the position of the vehicle is telemetrically detected by the guide device  24  in a known manner. 
     By appropriate construction and attachment of the antenna  10 , the vehicle can be guided to the cable  12  with a predetermined lateral offset, so that, by means of only one cable, crash-tests can be performed with different amounts of vehicle offset. It is further understood that vehicles can also move towards each other along different cables. The path provided by the cable  12  in the illustrated example can be replaced by various other devices, e.g., an optical marking on the path, such as a white stripe, whose position is analyzed by optical sensors of the vehicle, a guide beam that is sensed by sensors tuned to the respective frequency ranges, e.g. also a laser beam and so on. The use of a laser beam naturally has the disadvantage that the given path is straight. 
     The vehicle can be constructed in various ways; required for the suitability of the inventive method is that the vehicle can be braked such that it “pulls on one side”, i.e. the vehicle&#39;s direction changes without the wheels being pivoted about an approximately vertical axis by a separate steering device. It is understood that the brakes are constructed such that the vehicle can be stopped by the guide device  24  when unpredicted events occur. The inventive type of “steering” can then also be applied when the vehicle does not move under its own drive power, but rather e.g. is pulled on a cable, rolled downhill and so on. 
       FIG. 2  shows a modified embodiment of the inventive system, with which the given path is provided by storing a path in the control device  14  in the form of a sequence of geographic data, whose compliance can be monitored by means of a known electronic navigation system. Extraordinarily high precision can be achieved with a so-called DGPS system, by which a GPS antenna  26  of the vehicle analyzes satellite data and data from an additional, stationary transmitter  28  in a known way. In the illustrated example, the known satellite navigation system is integrated into the control device  14 . Alternately, the satellite navigation system can be connected to the control device  14  as its own unit. It is understood that the antenna  10  ( FIG. 1 ) can be omitted when the vehicle is guided by means of a satellite navigation system. The navigation system is not required to be a satellite navigation system; it can be, most generally, a system, by which the respective position of the vehicle relative to reference points is ascertained, wherein the vehicle follows a given path, whose coordinate sequence is fixed based upon the reference system. 
     A further difference of the system of  FIG. 2  in comparison to the system of  FIG. 1  is that each vehicle wheel is driven by its own motor  30 , e.g., an electric wheel hub motor, wherein the wheel hub motors are powered by a battery  32 . The control device  14  controls the operation of the wheel hub motors  30 , so that the vehicle  2  moves along the electronically-given path with a predetermined speed, wherein changes from the path are carried out by an appropriate change of the torques that are applied by the wheel hub motors  30  to the left-side and right-side vehicle wheels. When there is a rightward deviation of the vehicle from the given path, the right-side, front wheel hub motor  30  drives stronger and/or the left-side, front wheel hub motor  30  brakes. The braking by the wheel hub motor(s) on one side can be the same amount as the additional drive by the wheel hub motor(s) on the other side, so that the overall propulsion of the vehicle, and thus its speed, do not change. 
     It is understood that, instead of wheel hub motors, hydraulic, pneumatic or other motors also can be used that are supplied with energy by appropriate energy sources. 
     In the illustrated example, the vehicle  2  is, e.g., a simple carrier with wheels that are not steerable and/or pivotable, which vehicle carries a barrier  34  on its front side for performing side crash-tests on a stationary vehicle. 
     For suitable construction of the wheel hub motors  30 , separate brakes could be omitted. However, the vehicle according to  FIG. 2  advantageously includes wheel brakes that are applied, in particular, in the resting state. 
     It is understood that the features of the embodiment according to  FIG. 1  can be combined with the features of the embodiment according to  FIG. 2  and that numerous variations of the exemplary-illustrated embodiments are possible. 
     The signals required for controlling the respective actuators are evaluated by computers corresponding to control methods (for example, adjustment of a predetermined speed for a simple impact crash against a fixed impediment) and/or regulation methods (deviation from the predetermined side and/or given momentary position). The respective calculations can take place in a vehicle-affixed computer and/or in the central guide device  24 . 
     REFERENCE NUMBER LIST 
     
         
           2  Vehicle 
           4  Front Wheel 
           6  Rear Wheel 
           8  Wheel Brake 
           10  Antenna 
           12  Cable 
           14  Control Device 
           16  Input 
           18  Actuator 
           20  Actuator 
           22  Antenna 
           24  Guide Device 
           26  GPS-Antenna 
           28  Transmitter 
           30  Motor 
           32  Battery 
           34  Barrier