Abstract:
The present invention relates to a system for dynamometer testing of motor vehicles, said system including a cooling device for a braking device and/or a power-generating means, and having power-absorbing means for absorbing a power applied thereto by power-generating means, the cooling device including a fan arrangement for producing an air stream, said air stream being intended to be directed towards the braking device and/or the power-generating means and/or a heat exchanger for providing a cooling effect. The fan arrangement includes two fans, which are substantially axially aligned, and the cooling device includes means for rotating the fans in opposite directions relative to each other. The present invention also relates to a method for cooling power-generating means or power-absorbing means in a system for dynamometer testing of motor vehicles.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a system for dynamometer testing of motor vehicles, said system including a cooling device intended for cooling a braking device and/or power generating means, of the kind defined in the preamble of claim  1 . 
         [0002]    The invention further relates to a method for cooling a braking device and/or a power-generating means in a system for dynamometer testing of motor vehicles, of the kind defined in the preamble of claim  19 . 
       BACKGROUND OF THE INVENTION 
       [0003]    This invention relates in particular to devices for dynamometer testing of motor vehicles, that is, devices which are adapted to be connected to a driven vehicle output shaft and which include means for measuring one or more quantities significant to the performance of the engine and the transmission, such as the torque that the driven shaft applies to a power-absorbing device forming part of the test device. 
         [0004]    One such device is disclosed in EP 0 210 979, which discloses a device including power-absorbing means in the form of a hydraulic pump assembly which has an input shaft adapted to be in engagement with a driven vehicle shaft using a rigid coupling. The pump assembly consists of two pumps, which are drivingly interconnected and thereby both driven by the shaft. An adjustable control valve is controlled such that the valve allows the passage of a liquid flow, the volumetric rate of which being related to the desired rotational speed of the rotor, i.e. of the driven vehicle shaft. By controlling the working pressure of the pumps, a desired torque can be applied to the drive shaft of the vehicle, and, thereby, the performance of the engine can be tested. 
         [0005]    A problem with this device, however, is that as vehicle engines increasingly tend to generate higher and higher powers, and higher and higher torques, the heat generated by the power-absorbing means when testing these engines, e.g., as a temperature rise of the hydraulic fluid when passing through the control valve, becomes more difficult to cool. 
       SUMMARY OF THE INVENTION AND MOST IMPORTANT FEATURES 
       [0006]    It is an object of the present invention to provide a system for dynamometer testing of motor vehicles including a cooling device that solves the above mentioned problem. In particular, it is an object of the present invention to provide a system that allows more efficient cooling of generated heat in power-absorbing means and/or power-generating means. 
         [0007]    This object is achieved by a system according to the characterising portion of claim  1 . 
         [0008]    According to the invention, the system for dynamometer testing of a motor vehicle includes a cooling device, which includes a fan arrangement for producing an air stream, said air stream being intended to be directed towards the braking device and/or the power-generating means and/or a heat exchanger for providing a cooling effect. The fan arrangement includes two fans, which are substantially axially aligned, wherein the cooling device includes means for rotating the fans in opposite directions relative to each other. 
         [0009]    The use of contra-rotating fans, which are axially aligned or at least substantially axially aligned, has the advantage that the resulting air stream, as opposed to the rotating, turbulent air stream of a single fan system, constitutes a relatively non-turbulent, non-rotating parallel air stream. 
         [0010]    This, in turn, has a plurality of advantages. The non-turbulent parallel air stream can be directed towards a desired point more precisely, and, because of the parallel and non-turbulent air stream, the cooling effect thereof can be more efficiently used, i.e. a larger portion of the produced air stream reaches the power absorber and/or power-generating means and/or heat exchanger. 
         [0011]    Further, the resulting air pressure of the two-stage fan arrangement is 2-3 times the static pressure of a single fan, which, especially in view of the above, has a considerably larger cooling effect as compared to the prior art. 
         [0012]    Even further, as vehicle engines produce more and more power, the cooling demands of these engines increase as well. The present invention may advantageously be used to direct the air stream also towards the engine radiator. In one embodiment, the air stream can be directed so as to hit both the engine of the car and the power-absorbing means. In an alternative embodiment, the cooling device may, as will be disclosed below, include two (or more) fan arrangements, so as to allow separate air streams to be directed towards the engine of the car and the power-absorbing means, respectively. 
         [0013]    Also, due to the higher air velocities obtainable with the present invention, the air stream is suitable for simulating vehicle speed related wind resistance since back-pressure, e.g. through the engine radiator, can be overcome by the air pressure generated by the present invention. 
         [0014]    The power-absorbing means may consist of a hydraulic pump or of a hydraulic pump assembly including at least two hydraulic pumps, and each fan may be driven by a hydraulic motor. This has the advantage that high powers may be absorbed, and that relatively high output air powers may be accomplished by, relatively small components. 
         [0015]    In one embodiment a controlled portion of the pump or pump assembly output flow is diverted to the fan motors. This has the advantage that the same hydraulic system may be used both for power absorption and air flow generation. 
         [0016]    A control valve may control the (pump) flow and/or pressure to the fan motors. This has the advantage that the cooling effect can be regulated, i.e. when no or small amounts of power are generated, e.g., by an idling car engine, the flow to the fan motors may be completely shut off, while a racing engine on top gear, the control valve may be fully open. As an alternative to the control valve, a fixed or variable displacement hydraulic pump may be used to divert a controlled portion of the pump or pump assembly output flow to the fan motors. As yet another alternative, fixed or variable displacement fan motors themselves may be arranged to divert a controlled portion of the pump or pump assembly output flow. 
         [0017]    The flow and/or pressure to the each fan motor may be individually controllable. This has the advantage that one fan may be driven at a maximum, while the other is used to adjust the flow. 
         [0018]    The invention further relates to a method for cooling a braking device and/or a power-generating means in a system for dynamometer testing of motor vehicles. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  shows a system in which the present invention advantageously may be used. 
           [0020]      FIG. 2  shows part of the system disclosed in  FIG. 1 . 
           [0021]      FIG. 3  shows an alternative exemplary embodiment of a cooling device according to the present invention, 
           [0022]      FIG. 4  shows another exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0023]      FIG. 1  shows a dynamometer testing system in which the present invention advantageously may be utilised. The system is connected to a vehicle  10 , and comprises a pair of test units  11 ,  12 . Each test unit  11 ,  12  is connected to a cooling device  20 ,  30 . Each cooling device  20 ,  30  includes cooling fans  21 ,  22  ( 31 ,  32 ) which are hydraulically driven by hydraulic motors  23 ,  24  ( 33 ,  34 ). The two test units  11 ,  12  and the respective associated cooling devices  20 ,  30  are connected to a common measuring and control system  40 . 
         [0024]    The test units  11 ,  12  are similar, and so is the cooling devices  20 ,  30 , and as can be seen more in detail in  FIG. 2 , which shows the test unit  11  and the cooling device  20 , each test unit  11 ,  12  comprises a dynamometer in the form of a power-absorbing hydrostatic pump assembly, consisting of two commonly driven hydraulic pumps  13 ,  14  and means for measuring the torque applied to the pump input shaft  15 , which is arranged to be rigidly connected to a drive shaft  16  of the vehicle. 
         [0025]    The pumps  13 ,  14  are connected to a hydraulic oil tank  18 , and in use, a control valve  19  is used to control hydraulic pump flow and pressure. The output flow from the pumps is restricted using the control valve  19 , so that a pressure is built up. This pressure tries to turn the pumps around their own axle. As is explained more in detail in EP 0 210 979, this turning motion is restricted by a load cell equipped with a strain gauge (not shown), and the signal from the strain gauge is supplied to the common measuring and control system  40 . By calibrating the signal from the strain gauge against a known torque the signal will be proportional to the torque. The control valve  19  preferably constitutes an ultra fast control valve, such as the one described in the international patent application WO 2004/111739 A1, by the use of which both small and great liquid flows and pressure can be accurately adjusted. In this way, the vehicle  10  can be tested during rapid accelerations, and, further, wheel torque throughout the vehicle motor speed range can be easily measured. 
         [0026]    When the hydraulic oil has passed the pumps  13 ,  14 , it is passed back to the oil tank  18  for subsequent use. As can be seen in  FIG. 2 , a portion of the liquid flow, however, is diverted to the hydraulic motors  23 ,  24  driving the fans  21 ,  22  of the cooling device  20 . In order to control the flow and/or pressure to the fan motors  23 ,  24 , a second control valve  26  ( 36 ) is provided in the hydraulic circuit, between the high-pressure side of the pumps  13 ,  14  and the fan motors  23 ,  24 . Using this second control valve  26 , the air stream produced by the fans  21 ,  22  can be independently controlled. For example, when the vehicle engine  50  is idling, and, accordingly, the generated power constitutes only a fraction of the maximum power of the engine  50 , the flow to the fan motors  23 ,  24  may be completely shut off, i.e. the control valve  26  is closed, or reduced to a low level, since the required cooling effect in this case is low, both in regard of the vehicle engine  50  and in regard of the hydraulic pump assembly. 
         [0027]    On the other hand, when the engine  50  is racing, in particular on top gear, and the required cooling effect is at a maximum both for the vehicle engine  50  and the pump assembly, the control valve  26  may be fully open, the air stream produced by the fans  21 ,  22  thus being at a maximum. The use of the control valve  26  further has the advantage that the risk of overspeeding the fan motors is reduced, since the control valve may act as a safety valve for the fan motors. In an alternative embodiment, in particular for use with demanding tests of high-performance engines, the control valve  26  may be omitted, i.e., there will always be a flow to the fan motors. The control valve  26  may advantageously be of the type described in WO 2004/111739 A1. 
         [0028]    The size of the fan motors  23 ,  24 , and thus the power produced by each fan motor  23 ,  24 , may be determined based on the braking power of the test device. As an example, the power produced by each fan motor may, e.g., be 120 kW when the test device is capable of braking powers up to, e.g., 1000 kW. 
         [0029]    As is shown in  FIG. 2 , the alignment of the fans  21 ,  22  may be such that part of the air stream hits the pump assembly, and part of the air stream hits the vehicle engine  50  (vehicle radiator  51 ). Alternatively, the air stream may be directed towards either of the two, depending on where the cooling effect is needed. 
         [0030]    The two fans are arranged to rotate in opposite directions relative to each other. As stated above, the use of contra-rotating fans, which are axially aligned or at least substantially axially aligned, results in a relatively non-turbulent, non-rotating parallel air stream. In other words, when the air stream of the fan assembly in  FIG. 2  is directed towards the pump assembly and/or vehicle engine radiator  51 , a larger portion of the produced air stream reaches its desired target and, thereby, the cooling effect thereof can be more efficiently used. 
         [0031]    Further, as also is stated above, the resulting air pressure of the two-stage contra-rotating fan arrangement is 2-3 times the static pressure of a single fan, which enables that back-pressure through the radiator  51  can be overcome, and thereby a sufficient cooling effect to the vehicle engine can be provided even when the engine is under a very heavy load. For example, race car engines may develop up to 1100 kW or more, which results in great demands on cooling devices. The achievable higher pressure may also be used to simulate high-speed driving, i.e. the air stream pressure directed towards the vehicle may be controlled by the fan motors to correspond, or substantially correspond, to the wind resistance that the vehicle would be subjected to in real life driving at the simulated speed. Preferably, the air stream pressure is controlled by the measuring and control system  40  by controlling the second control valve  26 . 
         [0032]    As can be seen in the figures, when the diverted portion of the hydraulic pump oil flow has passed the fan motors, this diverted portion is passed through a heat exchanger  25  before it is passed on to the oil tank  18 . As is shown in the figure, the heat exchanger  25  may preferably be positioned immediately behind the fan arrangement  20  such that the air drawn by the fans  21 ,  22  will pass the heat exchanger  25  and cool the oil. In an alternative embodiment, the heat exchanger  25  may be located in front of, or partly in front of the fan arrangement, so that the air stream provides the cooling effect. In the above embodiment, the air sucked through the heat exchanger  25  by the fans, and thus the air blown by the fans towards the pump assembly, may become quite warm due to the heat of the diverted oil. In order to pre-cool the diverted portion of the hydraulic pump oil flow, it may be passed through a second heat exchanger  27 , schematically indicated in  FIG. 2  by dashed lines, e.g. a water/oil cooler, in which water is used to cool the oil flow, which in turn has as result that the oil passing the heat exchanger  25 , and thereby the air in the air stream, will have a lower temperature. The second heat exchanger may equally well be located between the fan motors and the heat exchanger  25 . 
         [0033]    In  FIG. 3  is shown an alternative embodiment, in which each cooling device is provided with two fan arrangements  20   a ,  20   b . This embodiment allows separate air streams to be directed towards the engine  50   a  of the car and the test device  11   a , respectively, at all times. This is particularly advantageous when high-performance engines are subject to heavy-load testing for a considerable time, and both the vehicle engine and test device need a large cooling effect. In this example, the fan motors  23   a - b ,  24   a - b  may be smaller. 
         [0034]    Instead of two fan arrangements, even more may be used to allow air streams to be directed at desired points. The fan arrangements may be positioned at different heights so as to best provide a desired cooling effect at a desired location. For example, if the diverted flow heat exchanger is located in front of the fan arrangements, the air stream of one of the fan arrangements may be directed towards the heat exchanger. 
         [0035]    Alternatively, when positioning the fan arrangements, the fan arrangements from both test devices may be considered, for example, fan arrangements may be positioned on top of each other, with one fan arrangement from each drive shaft. 
         [0036]    In yet another embodiment, the car may include a four-wheel drive, and, consequently, be provided with four test units during testing. In this case, the fan arrangements from all four test units may be considered as a whole when positioning them, e.g., more cooling effect may be concentrated to the front of the vehicle than to the rear. 
         [0037]    Further, as is shown in  FIG. 4 , a second heat exchanger  60  may be arranged in the return path from the high-pressure side of the hydraulic pumps to the tank. This allows an even more efficient cooling, since, as is shown in the figure, one fan arrangement  20   a ′ may be directed directly towards this second heat exchanger  60 . 
         [0038]    Instead of using a control valve for controlling the flow/pressure to the fan motors, a fixed or variable displacement hydraulic pump may be used to divert a controlled portion of the pump or pump assembly output flow to the fan motors. As yet another alternative, the fan motors themselves may be of fixed or variable displacement type and arranged to divert a controlled portion of the pump assembly output flow. 
         [0039]    Further, in the above description the fan motors have been shown as connected in parallel. These may, of course, alternatively be connected in series. Even further, instead of having one control valve controlling all fan motors of one test device, each fan motor may be separately controlled by a separate control valve. In this way, the control system may control the fans such that one fan of each pair is driven at its maximum, while the other is used to adjust the air stream. 
         [0040]    Also, the control valve(s) for controlling the fan motors has been shown as being located upstream of the fan motors. This control valve(s) may, of course, also be located downstream of the fan motors. 
         [0041]    In the above description the fan arrangements have been powered by a diverted portion of the braking apparatus hydraulic pump flow. As is apparent to a person skilled in the art, however, the fan arrangement may equally well be powered by a separate hydraulic circuit, however with the disadvantage of added appliances. 
         [0042]    Further, the cooling device has been described in connection with a dynamometer testing system. As is apparent to a person skilled in the art, however, the cooling device may be used in other applications as well, in which an easily controlled cooling effect is required. Further, in the above description the air stream(s) has been directed towards the breaking apparatus and/or the vehicle and/or a heat exchanger. In an alternative embodiment, the air stream may be directed in an arbitrary direction, since the fan arrangement according to the invention in itself is very efficient in cooling the diverted portion of the hydraulic pump flow.