Abstract:
The invention relates to a vehicle test stand including a device for fixing a motor vehicle on the test stand. A loading machine is adapted to be coupled to the drive train of the motor vehicle, whereby the loading machine can both drive and brake the drive train. In accordance with the invention, the loading machine is directly or indirectly connectable to a rim of a motor vehicle wheel in force-locking manner.

Description:
FIELD OF THE INVENTION 
   The present disclosure relates to the subject matter disclosed in German Patent Application No. 103 28 461.3 of Jun. 25, 2003, the entire specification of which is incorporated herein by reference. 
   The invention relates to a vehicle test stand including the features indicated in the embodiments described herein as well as to a method of testing components in the drive train of a motor vehicle including the features also described herein. 
   BACKGROUND OF THE INVENTION 
   A test stand for testing the drive train of a vehicle is known from EP 0 338 373 A2. Therein, two mutually independent moment-regulated electrical loading machines are flanged directly onto the shafts in the drive train being tested. Rollers upon which the wheels of the vehicle are adapted to roll are not used here. A simulation of the rolling resistances, the wheels and the behaviour of the vehicle under acceleration exclusively of the vehicle components present in the form of real parts is made by means of a simulating computer. 
   OBJECTS AND SUMMARY OF THE INVENTION 
   In contrast thereto, the object of the invention is to provide a vehicle test stand and a method with the aid of which the components in the drive train of a motor vehicle can be examined without heavy structural expenditure. 
   This object is achieved in regard to the test stand by the features of embodiments and methods described herein. 
   The fundamental concept of the invention is to connect a loading machine directly or indirectly to a rim of a motor vehicle wheel in a force locking (non-positive) manner. Hereby, it is merely necessary to establish a connection between the loading machine and the wheel rim but without there being any need to disassemble the wheels and, for example, assembling a connecting shaft for the purposes of making a connection to the existing drive train in the vehicle being examined. Consequently, the set-up time required for the preparation of the test is very short. 
   The loading machines employed may be in the form of electrical or even hydraulic motors whose rotational speed and/or moment is controlled, such as e.g. asynchronous motors. 
   One exemplary embodiment of the invention envisages that a gear box should be arranged between the loading machine and the wheel rim. Thus, for example, standardised loading machines can be used for passenger vehicles and commercial motor vehicles that are to be tested and whose wheels are driven at different speeds. The gear box may be in the form of a toothed gear assembly or else a speed-reducing or speed-increasing arrangement utilising belt drives of different pulley size could be used for example. 
   In another exemplary embodiment, a shaft coupling is arranged between a loading machine and a steerable wheel of the motor vehicle. It is thereby ensured that the steering system of the vehicle under examination can also be used on the test stand. This is important for example, if the energy consumption of a power-assisted steering system is to be realistically imaged during a test on the test stand. 
   A shaft coupling can be implemented by means of cardan joints, tripod or homokinetic joints or else by means of frictional rubber discs for example. 
   Further advantages are derivable from the other dependent claims and also from the exemplary embodiment of a vehicle test stand in accordance with the invention which is described in more detail hereinafter with the aid of the drawings and the two test runs that are adapted to be implemented on the test stand. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a schematic plan view of a vehicle test stand including the abstracted components of a motor vehicle, 
       FIG. 2  a plan view of a construction for the framework of the test stand, 
       FIG. 3  a flow chart used for a functional inspection of an anti-blocking system (ABS), 
       FIG. 4  a flow chart used for a functional inspection of an anti-slip regulating system (ASR). 
   

   DESCRIPTION OF EMBODIMENTS 
   A vehicle test stand  1  in accordance with the invention is schematically illustrated in  FIG. 1 . A vehicle  10  is shown therein in abstracted form. The vehicle  10  comprises an internal combustion engine  11  which is connected to the input of a gear box  13  by a clutch  12 . The output of the gear box  13  is connected via a drive shaft  14  to a rear axle differential  15  from which extend the lateral propeller shafts  16 ,  17  that drive the wheels  26 ,  27  on a driven rear axle  25  of the vehicle  10 . 
   The vehicle  10  comprises two steerable vehicle wheels  21 ,  22  on the front axle  20 . In the case of an all-wheel drive, these wheels can be connected by lateral propeller shafts to a front axle differential, the latter being connected to the gear box  13 . 
   All four vehicle wheels  21 ,  22 ,  26 ,  27  are connected to loading machines  23 ,  24 ,  28 ,  29 . The loading machines  23 ,  24 ,  28 ,  29  on the wheels  21 ,  22  of the front axle  20  are bolted directly to the rims of the wheels  21 ,  22  by means of wheel bolts for example. A shaft coupling  31  is arranged between the output shaft  35  of a loading machine  23 ,  24  and the wheel rim in order to ensure the steering function of the front wheels  21 ,  22 . 
   The loading machines  28 ,  29  for the rear axle  25  are connected to the wheels  26 ,  27  on the rear axle  25  by means of a transmission  30  in the form of a belt drive. To this end, a pulley  32  is bolted to the wheel rim of a wheel  26 ,  27  by means of wheel bolts for example. A pulley  33  of smaller diameter is connected to the output shaft  35  of a loading machine  28 ,  29 . The belt drive  34  is tensioned between the differently sized pulleys  32 ,  33 . 
   The loading machines  23 ,  24 ,  28 ,  29  are connected by signal lines  41  to an evaluation and control unit  40 . Moreover, there is a releasable connection via a further signal line  41  between the evaluation and control unit  40  and a drive train control unit  42  of the vehicle  10 . The drive train control unit  42  is connected to an engine control unit  43  which controls the injection of the fuel, the ignition timing and/or a possibly provided throttle valve for example. In like manner, the drive train control unit  42  is connected to the clutch  12  and the adjustable gear box  13  whereby the transmission of power from the internal combustion engine  11  to the propelled wheels  26 ,  27  is controllable. 
   Different programs, with the aid of which different components or system units of the vehicle  10  on the test stand  1  can be examined, are executed in the evaluation and control unit  40 . Such a test equipment is also called a hardware-in-the-loop system. 
   The constructional framework  50  of the test stand  1  is illustrated in  FIG. 2 . Rectangular framework superstructures  51 ,  52  are provided in the vicinity of the front and rear axles  20 ,  25 . The beams preferably have a double-T flanged beam section and/or an I-beam section. The frameworks  51 ,  52  are crossed in each case by two longitudinal braces  53 . Holding devices  54  are provided on these longitudinal braces  53 , the vehicle  10  being connected to the test stand  1  by means of these devices. Here, the latter are in the form of supports to which the axles of the vehicle  10  under test are linked by means of spring shackles for example. The supports are connected to the longitudinal braces  53  in longitudinally and transversely displaceable manner in order to ensure that the test stand  1  can be adapted to different types of motor vehicle having different wheel bases and track widths. If necessary, the supports can be varied somewhat in length in order to raise the vehicle  10  and in particular the vehicle wheels  21 ,  22 ,  26 ,  27  from the stand surface so that they can be moved freely. 
   The two framework superstructures  51 ,  52  associated with the front and rear axles  20 ,  25  are connected together by two central longitudinal members  55 . The mounting frames  56  supporting the loading machines  28 ,  29  on the framework  52  associated with the rear axle  25  are illustrated by way of example. 
   Different test programs can be executed in the evaluation and control unit  40 , of which two program sequences are outlined in exemplary manner hereinafter. 
   The program sequence involved in an ABS test for a commercial motor vehicle is illustrated in  FIG. 3 . Hereby, the processes for the non-driven front axle  20  used in this example are illustrated on the left-hand side whilst those for the driven rear axle  25  are illustrated on the right-hand side. 
   The test starts by starting the internal combustion engine  11  of the commercial motor vehicle in order to establish the ready status of the vehicle brakes which are usually operated pneumatically. The clutch  12  remains opened so that the drive train can be operated under no-load conditions. The rear wheels  26 ,  27  are subjected to a constant drive force F rear  by the loading machines  28 ,  29  associated with the rear axle  25 . This force is in equilibrium with a force which is caused by friction in the drive train between the gear box  13  and the rear wheels  26 ,  27 . Consequently, the wheels  26 ,  27  on the rear axle  25  are set to a constant wheel rotational speed n rear . The evaluation and control unit  40  determines this wheel rotational speed on the basis of the rotational speeds of the loading machines  28 ,  29  associated with the rear axle  25 . The wheels  21 ,  22  are driven by the loading machines  23 ,  24  associated with the front axle  20  so that the same wheel rotational speeds occur at the front axle  20  as at the rear axle  25 . Travel in a straight line at constant speed of the vehicle  10  under test is thereby simulated. 
   A constantly increasing braking torque is applied to the vehicle wheels  21 ,  22 ,  26 ,  27  by actuating the vehicle&#39;s brakes. This can be effected by actuating the brake pedal or by triggering the drive train control unit  42  that is connected to the brake control system. The rear wheels  26 ,  27  rotate for as long as the drive moment of the loading machines  28 ,  29  for the rear axle  25  is greater than the braking torque produced by the vehicle brakes. The braking force produced by the vehicle brakes and/or the braking torque on the rear wheels  26 ,  27  is determined by the evaluation and control unit  40  via the loading machines  28 ,  29 . The reduction in the speed of the vehicle is determined from a vehicle-specific characteristic field stored in the evaluation and control unit  40 . The loading machines  23 ,  24  control the wheels  21 ,  22  on the front axle  20  in corresponding manner so that the rotational speeds of the front wheels  21 ,  22  decrease accordingly. In addition, the vehicle brakes are effective on the front wheels  21 ,  22  in like manner. 
   As soon as one or more vehicle wheels  21 ,  22 ,  26 ,  27  block, i.e. they have a rotational speed n=0, and the vehicle has not yet come to a complete stop in accordance with the model running in the evaluation and control unit  10 , the anti-blocking system (ABS) of the vehicle  10  intervenes and opens, in a wheel-selective manner, the respective brake associated with the wheel  21 ,  22 ,  26 ,  27  having the rotational speed n=0 so that this vehicle wheel  21 ,  22 ,  26 ,  27  can be accelerated back up to the rotational speed defined by the model before the brake again brakes the wheel  21 ,  22 ,  26 ,  27  and possibly blocks it afresh. 
   In the event that the brake is not opened again in the example that has just been described, there is a fault in the ABS system. This is registered and transmitted onwardly or processed by the evaluation and control unit  40 . 
     FIG. 4  shows a test sequence for testing the operability of an anti-slip regulating system (ASR). Here too, the processes occurring at the front axle  20  are illustrated on the left-hand side whilst the processes occurring at the rear axle  25  are illustrated on the right-hand side. 
   After the internal combustion engine  11  has started, the clutch  12  is closed so that a constant wheel rotational speed is set up for the wheels  26 ,  27  on the rear axle  25  when the engine torque is constant and there is a constant braking force on the driven rear axle  25 . The constant braking force on the rear wheels  26 ,  27  is produced by the loading machines  28 ,  29  for the rear axle  25 . 
   The evaluation and control unit  40  determines the wheel rotational speed at the rear axle  25  from the rotational speed of the loading machines  28 ,  29  and controls the loading machines  23 ,  24  for the wheels  21 ,  22  on the front axle  20  in corresponding manner so that travel in a straight line at constant speed of the vehicle  10  is again simulated in like manner. 
   The engine torque of the internal combustion engine  11  is now increased in a virtually step-like manner under the control of the drive train control unit  42  so that the wheel rotational speed for the drive axle  25  increases accordingly since the braking force produced by the loading machines  28 ,  29  for the rear axle  25  has remained constant. The wheels  21 ,  22  on the front axle  20  continue to be driven by the loading machines  23 ,  24  at the rotational speed occurring after the starting process so that there is now a difference in rotational speed between the driven axle  25  and the non-driven axle  20 . This difference in the rotational speeds is detected by the anti-slip regulating system (ASR). The ASR thereupon intervenes in the engine control system  43  and, for example, suppresses the fuel injection process, adjusts the firing angle, closes the throttle valve and/or, in the case of an available electronic stability program (ESP), briefly closes the brake associated with the “spinning” wheel  26 ,  27 , i.e. the wheel being subjected to a large increase in rotational speed, so that the drive moment on the wheel  26 ,  27  is reduced to zero for a short period of time. The rear wheels  26 ,  27  are then re-matched to the wheel rotational speed of the front wheels  21 ,  22  by the loading machines  28 ,  29  for the rear axle  25 . 
   If the engine torque is not reduced by the ASR system during the step-like increase in engine torque and rear wheel rotational speed, then the ASR system is faulty, this being determined and transmitted onwardly or otherwise processed by the drive and control unit  40 . 
   It is easily comprehended that the vehicle wheels  21 ,  22 ,  26 ,  27  on the two sides of the vehicle can be driven or braked by the loading machines  23 ,  24 ,  28 ,  29  in a different manner and separately from one another. Consequently, the tests described above can also be carried out in a wheel-selective manner, thus for example, only one wheel  21 ,  22 ,  26 ,  27  can block in the case of the ABS test or only one wheel  21 ,  22 ,  26 ,  27  can spin in the case of the ASR test. 
   Still further hardware-in-the-loop tests such as e.g. tests for determining the friction in the drive train can also be effected with the aid of the test stand  1  in accordance with the invention. To this end, the vehicle wheels  21 ,  22 ,  26 ,  27  are accelerated with a certain force by the loading motors  23 ,  24 ,  28 ,  29  in the no-load operational state of the vehicle  10 . The curve of wheel rotational speed with respect to time permits conclusions to be drawn in regard to the friction in the drive train. The friction of the components can be determined by comparing the tests which are effected when these components are in their connected state and when in the non-connected state thereof.