Method and apparatus for dynamometer testing of a motor vehicle

Abstract

The present invention relates to a Vehicle dynamometer system for dynamometer testing of a vehicle (100) or vehicle component (202), the system comprising a first and a second dynamometer test unit (110, 111) for connection to a first output shaft (221) and to a second output shaft (222), respectively, of the vehicle (100) or vehicle component (202) being tested, the first and the second dynamometer test unit (110, 111) each comprising a first portion (231, 232) configured to be located within the test cell and a second portion (233, 234) location outside the test cell. The first portion (231, 232) comprises a first hydraulic power source (203, 204) being configured to, during testing, apply a braking power and / or a propelling power to an 10 output shaft (221, 222) of the vehicle (100) or vehicle component (202) being tested. The second portion (233, 234) comprises a second hydraulic power source (205, 206), being configured to be connected to the first hydraulic power source (203, 204) through a fluid connection (207, 208; 209, 210) for transferring power between the first and second hydraulic power source (203, 204; 205, 206) through the fluid, the second portion (233, 234) further comprising an electrical machine (211, 212) connected to the second hydraulic power source (205, 206), for converting power between hydraulic power and electrical power. The vehicle dynamometer system is configured to control the applied torque without use of electrical / electronical sensor means for sensing speed of rotation of, or power applied by, the first hydraulic power source (203, 204) located at the first location.

Description

[0001] METHOD AND APPARATUS FOR DYNAMOMETER TESTING OF A MOTOR VEHICLE

[0002] Field of the invention

[0003] This invention relates to dynamometer testing of vehicles and vehicle components, and in particular to a vehicle dynamometer system for use when dynamometer testing vehicles or vehicle components for EMC (Electromagnetic compatibility) purposes. The invention also relates to a vehicle dynamometer system.

[0004] Background of the invention

[0005] Dynamometer testing of vehicles is known per se, and can, for example, be carried out by roller type (rolling road) dynamometers equipped with large rollers that support the vehicle wheels, and which are used to apply a brake torque to the drive wheels of the vehicle. The rollers are in general of a friction type, where the dynamometer system is engaged by friction engagement with the tyres of the driven vehicle wheels. Such systems are space consuming, expensive and unavoidable and oftentimes also unpredictable and variable slipping and friction between the tyres and the friction rollers may cause undesirable inaccuracies in the test result. Systems of the friction roller kind also may not always be capable of providing the desired measurement accuracy and / or degree of freedom of measurement.

[0006] Another kind of vehicle dynamometer systems utilize an apparatus for dynamometer testing of vehicles, where load absorbing means e.g. in the form of an electrical machine has an input shaft for engagement with a drive shaft of a vehicle to be tested. Each drive shaft of the vehicle may be fixedly connected to an individual apparatus of this kind, whereby a total effective torque from the vehicle can be accurately measured.

[0007] Systems of this kind may be utilized to perform complex tests both in regard of two- wheel drive systems, and also in regard of four, or more, wheel drive systems. Also, vehicle transmissions may include various kinds of, and also a plurality of, power sources for providing power to wheel shafts of the vehicle. These power sources may be arranged to provide propelling powers, and also braking powers, e.g. when used for regenerative braking. The increased complexity of vehicle transmissions provides a desire to also be able to test further functionality using dynamometer testing systems. In addition, vehicles are increasingly equipped with driver assistance systems, where such systems may be utilized to aid the driver in various situations.

[0008] The increased complexity of vehicle control systems may require not only testing in an extensive number of real-life driving situations and conditions to ensure the desired functionality, but there may also exist further requirements regarding the testing. For example, there may exist a requirement to test the vehicle or vehicle component with regard to Electromagnetic Compatibility (EMC) compliance.

[0009] Aim and most important features of the invention

[0010] It is an object of the present invention to provide a vehicle dynamometer system that allows accurate testing of a vehicle or vehicle component functionality when subjecting the vehicle or vehicle component to electromagnetic radiation and / or when determining electromagnetic radiation emitted from the vehicle or vehicle component.

[0011] It is another object of the present invention to provide a vehicle dynamometer system that allows testing in situations where, e.g., space may be limited or power absorbed otherwise cannot be properly handed at the location of the test object.

[0012] According to a first aspect of the invention, this is provided by a vehicle dynamometer system for dynamometer testing of a vehicle or vehicle component, the system comprising a first and a second dynamometer test unit for connection to a first output shaft and to a second output shaft, respectively, of the vehicle or vehicle component being tested, the first and the second dynamometer test unit each comprising a first portion and a second portion, wherein: the first portion comprises a first hydraulic power source being configured to, during testing, apply a first power to an output shaft of the vehicle or vehicle component being tested, the first portion being configured to be located at a first location; the second portion comprises a second hydraulic power source, being configured to be connected to the first hydraulic power source through a fluid connection for transferring power between the first and second hydraulic power source through the fluid, the second portion further comprising an electrical machine connected to the second hydraulic power source, for converting power between hydraulic power and electrical power, the second portion being configured to be located at a second location; wherein the first location is a test cell, and the first portion is configured to be located within the test cell; the second location is a location outside the test cell; the first hydraulic power source is configured to apply a braking power and / or a propelling power to the output shaft of the vehicle or vehicle component; the vehicle dynamometer system further comprising a control system for controlling power applied by, and speed of rotation of, the first hydraulic power source of each of the first and the second dynamometer test units; and the vehicle dynamometer system is configured to determine power applied by, and speed of rotation of, the first hydraulic power sources of the dynamometer test units through a predetermined relation between torque applied by the electrical machine and the first hydraulic power source, respectively, so as to control torque without use of electrical / electronical sensor means for sensing speed of rotation of, or power applied by, the first hydraulic power source located at the first location.

[0013] As was mentioned above, there exist various situations in which there may be a desire to perform dynamometer testing of a test object in the form of a vehicle or vehicle component. For example, dynamometer testing allows testing in a controlled environment where the test object may be subjected to precisely those conditions for which there exist a desire to carry out the testing. A vehicle component may comprise a power source such as an internal combustion engine and / or an electrical machine, and associated drive shafts.

[0014] According to the invention it is provided a solution that is applicable, e.g., for carrying out EMC testing. This is accomplished through the use of a dynamometer test unit comprising the first portion and a second portion. The first dynamometer test unit portion comprises a first hydraulic power source that is used to apply power to an output shaft of a test object such as a vehicle or vehicle component. The first animated test unit portion is configured to be located at the location of the test object, such as, e.g., within a test cell for electromagnetic field testing, and hence at the location of the test object. The dynamometer test unit further comprises a second portion that also comprises a hydraulic power source. This hydraulic power source is connected to the first hydraulic power source through a fluid connection for transferring power between the first and second hydraulic power source through the fluid, and thereby between the first location, such as a test cell for electromagnetic field testing, and a second location, where, in case the first location is a test cell, the second location is outside this test cell. The second portion further comprising an electrical machine connected to the second hydraulic power source, for converting power between hydraulic power and electrical power, the second portion being configured to be located outside the test cell for electromagnetic field testing.

[0015] In this way it is provided a solution where any electrical means of the dynamometer test unit can be located outside a test cell for electromagnetic field testing while still a controlled power can be applied to the output shaft of the test object through the hydraulic power source being located within the tests cell, and wherein the electrical machine may transfer power to and from the hydraulic power source being located in the tests cell through the second hydraulic power source. Given the hydraulic connection to the dynamometer test unit portion being located in the test cell, the second dynamometer test unit may also be freely positioned outside the test cell since there is no rigid mechanical connection required between the first and second portion.

[0016] The invention may also be utilized in other situations than specifically for EMC testing. For example, a test object may be tested in a test cell for other reasons and the invention is applicable also for any such other testing in a test cell. Furthermore, there may also exist situations when dynamometer testing may be desired but where, e.g., space requirements may render such testing difficult or impossible. According to the invention such testing may be carried out through the use of the vehicle dynamometer system according to the invention, comprising dynamometer test units where the first portion may then be located at the test object to be tested while the second port portion may be located at any other suitable location since the interconnection of the first portion and the second portion comprises a fluid connection whereby, e.g., flexible hoses may be used to interconnect the first portion and the second portion. This provides for a high degree of flexibility with regard to the arranging of the first portion and the second portion in relation to each other. The first hydraulic power source is configured to apply a braking power and / or a propelling power to the output shaft of the vehicle or vehicle component. The first hydraulic power source may hence be designed not only to provide a braking power but also a propelling power so that the power source of the test object may be tested in terms of applying power to the output shafts as well as absorbing power from the output shaft, e.g. to test regeneration. The first hydraulic power source may, e.g., comprise a hydraulic motor of a bent axis design in this regard, or, e.g., comprise a combination of two hydraulic motors operating in different directions of rotation, or multiple hydraulic motors to increase power capacity. The power applied to the output shaft by the first hydraulic power source may hence be configured to be transferred both to and / or from the second hydraulic power source through the fluid connection.

[0017] The vehicle dynamometer system comprises a first dynamometer test unit for connection to a first output shaft of a vehicle or vehicle component being tested, and a second dynamometer test unit for connection to a second output shaft of the vehicle or vehicle component being tested, and also a control system for controlling power applied by, and speed of rotation of, the first hydraulic power source of each of the first and the second dynamometer test unit. In this way both shafts may be tested, for example with regard to EMC testing. According to aspects of the invention, three or more dynamometer test units may be used to test any further output shafts of the test object.

[0018] Two test units may thus be monitored and controlled without arranging any electrical test equipment inside the test cell. Instead, such electrical test equipment outside the test cell can be utilized due to a predetermined ratio of the torque applied by the electric motor and the hydraulic motor to determine the applied force and rotational speed of the respective first hydraulic motors in the respective test units.

[0019] The vehicle dynamometer system is further configured to determine power applied by, and speed of rotation of, the first hydraulic power sources of the dynamometer test units through a predetermined relation between torque applied by the electrical machine and the first hydraulic power source, respectively. This allows control of the applied torque without use of any electrical / electronical sensor means being located in the test cell, e.g. for electromagnetic field testing for sensing speed of rotation of, or power applied by, the first hydraulic power source.

[0020] The presented vehicle dynamometer system therefore facilitates the design of the test equipment since no electric motor is required inside the test cell. Also, no long drive shafts are needed for connecting the test equipment through the walls of the test cell since the test equipment connects directly to the test object inside the test cell. Hereby, the placement of test equipment parts outside the test cell is facilitated.

[0021] Also, the presented vehicle dynamometer system may be implemented on existing test cells without any need to redesign these test cells. Since electrical machines inside the test cell are avoided, a potential source of error for the test measurements also disappears. Electrical machines could otherwise interfere with the test equipment.

[0022] According to aspects of the invention, the first hydraulic power source of the first portion is configured to, during testing, be rigidly attached to the output shaft of the vehicle or vehicle component through a galvanically isolated rigid coupling, so as to prevent the vehicle or vehicle component from being grounded through the first hydraulic power source. Vehicles are in general isolated from the ground when traveling on roads since the vehicle road interface comprises a rubber interface form of the tyres of the vehicle. If then the test object would be subjected to a grounding through the dynamometer test unit this might potentially have an impact on the accuracy of measurement results. The first hydraulic power source may therefore be connected to the test object through an isolating coupling to prevent any undesired connection of the test object to ground through the dynamometer test unit.

[0023] According to aspects of the invention the galvanically isolated rigid coupling comprises means to connect an output shaft of the first hydraulic power source to an output shaft of the vehicle or vehicle component. Such means may comprise a galvanically isolating rubber coupling, such as a claw coupling comprising a rubber membrane. This may provide a galvanically isolated coupling while still providing a rigid coupling.

[0024] It may also be the case that the first portion of the dynamic a test unit comprises a bearing housing, where the first hydraulic power source may be configured to be connected to the output shaft of the test object through the bearing housing. The bearing housing may be utilized, e.g., to absorb vertical and / or axial loads. The first hydraulic power source and the bearing housing may be carried, e.g., by a base of the first portion, and the bearing housing may be configured to also be galvanically isolated from the base of the first portion. This is because in general the bearing housing may be connected to the output shaft of the test object in an electrically conductive a manner.

[0025] According to aspects of the invention, each dynamometer test unit is further configured to convert power absorbed by the first hydraulic power source to electrical power using the electrical machine, wherein power absorbed by the first power hydraulic source is configured to be transferred to the second hydraulic power source by the fluid connection for propelling the electrical machine. In this way, the energy produced by the power source of the test object may be absorbed by the first hydraulic power source to be transferred to the electrical machine for generation of electricity. The electrical machine may be connected to a grid, and thereby, power may be both consumed from, and returned to, a grid to reduce the overall power consumption during testing.

[0026] According to aspects of the invention, the first portion comprising the first hydraulic power source is configured to be displaceable in an axial direction in relation to the vehicle or vehicle component in order to facilitate interconnection of an output shaft of the first portion with the output shaft of the vehicle or vehicle component. A test object may often times comprise, e.g., a power source and output shafts and hence only a part of, e.g., a vehicle. This may both speed up the process and reduce cost and also requirements regarding the EMC chamber. The providing of the first portion comprising the first power source with means for displacing the first portion, such as, e.g. wheels, may render it easy to put the first dynamometer test unit portion in position for connection to an output shaft of the test object, and following such interconnection the first dynamometer test unit portion may, e.g., be locked against displacement while test is ongoing to prevent components from becoming loose.

[0027] According to aspects of the invention, the first hydraulic power source is arranged to be standing freely on a surface and to be connected to the vehicle or vehicle component by means of a rigid coupling to the output shaft of the vehicle or vehicle component, while supporting the weight of the vehicle or vehicle component by means of said rigid coupling. This may be advantageous, e.g., when testing complete vehicles.

[0028] According to aspects of the invention the first and second hydraulic power source have different displacements, or even variable displacements, to thereby provide a gearing that allows the electrical machine, and thereby second hydraulic power source to have a different speed of rotation than the first hydraulic power source. This may be beneficial, e.g., in order to obtain preferred intervals of the speed of rotation of both electrical machine and the test object.

[0029] According to aspects of the invention, the vehicle dynamometer system comprises means for determining power applied by, and speed of rotation of, the first hydraulic power source of each of the dynamometer test units using a model representation defining a relationship between power applied by, and speed of rotation of, the first hydraulic power source and the power applied by, and speed of rotation of, the electrical machine of the dynamometer test unit, respectively.

[0030] In this way the torque and speed of rotation of the electrical machine, which is determined outside the test cell, can be used to estimate the torque and speed of rotation of the hydraulic power source being located in the test cell. The relationship may, e.g., be empirically determined by performing measurements for one or more loads / speeds of the electrical machine while performing measurements on the output shaft of the hydraulic power source to be located in the test cell to obtain corresponding measurements. This may be carried out for various different speeds and loads, and the measurements may then be used to determine a model representation, e.g. in the form of a linear or exponential relationship, where such determination of a model representation is well known in the art.

[0031] According to aspects of the invention, the vehicle dynamometer system further comprises means configured to determine power to be applied by, and speed of rotation of, the first hydraulic power source of each of the dynamometer test units utilizing a tyre-road interface, such as a slip value, e.g., obtained from a tyre model, to thereby control the first and second dynamometer test unit such that the output shafts of the vehicle or vehicle component are rotated at a speed corresponding to an actual speed of rotation when driving the vehicle on a road at a simulated vehicle speed. In this way, the output shaft speeds of the test objects can be controlled to the shaft speed that the shafts would have in case of a real life driving, where the actual speed of the vehicle does not completely correspond to the speed of rotation of the shafts due to tyre slip. The use of, e.g., slip value allows that the shaft speeds can be set to the correct shaft speeds to thereby avoid that the test object is damaged through the use of incorrect loads being applied.

[0032] According to aspects of the invention, the vehicle dynamometer system further comprises a frame configured to carry a vehicle component and the first portion of the first dynamometer test unit and the first portion of the second dynamometer test unit, wherein the first portions, respectively, are arranged to be displaceable when carried by the frame in an axial direction. This provides for a solution that allows easy setup of a test object and the first portions in a test cell, where the frame may be configured such that the first portions can be displaced in actual direction to facilitate interconnection with the test object and also replacement of the test object in case different test objects are to be tested.

[0033] According to aspects of the invention, the vehicle dynamometer system further comprises a fibreoptic arrangement configured to transmit a laser beam onto at least one reflector applied on at least one of the first output shaft and the second output shaft, and to detect reflections from the at least one reflector during rotation of the at least one of the first output shaft and the second output shaft. Hereby, the speed and / or torque of the first hydraulic power source may easily be determined / detected without use of electrical sensor means, which reduces a risk for measurements interference and / or noise, and increases the accuracy of the testing.

[0034] According to aspects of the invention, the fibreoptic arrangement is configured to be used for detecting a rotational speed of at least one of the first output shaft and the second output shaft, and / or a torque provided by at least one of the first output shaft and the second output shaft. Thus, the speed and / or torque of the hydraulic power sources of the first portions may hereby be determined / detected without use of electrical sensor means, which reduces a risk for measurements interference and / or noise. The invention also relates to a vehicle dynamometer testing installation comprising a vehicle dynamometer system according to the above and a test cell for electromagnetic field testing. It will be appreciated that all the aspects and advantages described above for the dynamometer test unit and vehicle dynamometer system applies also for the vehicle dynamometer testing installation.

[0035] The invention also relates to a method for dynamometer testing of a vehicle or vehicle component using a first and a second dynamometer test unit configured for use in a vehicle dynamometer system for dynamometer testing of a vehicle or vehicle component, wherein the dynamometer test system is configured to test the vehicle or vehicle component when the vehicle or vehicle component is located at a first location; the method comprising use of the first and the second dynamometer test unit for connection to a first output shaft and to a second output shaft, respectively, of the vehicle or vehicle component being tested, the first and the second dynamometer test unit each comprising a first portion and a second portion, wherein: the first portion comprises a first hydraulic power source that, during testing, applies a first power to the output shaft of the vehicle or vehicle component being tested, where the first portion is located at the first location; the second portion comprises a second hydraulic power source that is connected to the first power source through a fluid connection that transfer power between the first and second hydraulic power source, the second portion further comprising an electrical machine connected to the second power source, for, during testing, converting power between hydraulic power and electrical power, the second portion being located at a second location; wherein the first location is a test cell, and the first portion is configured to be located within the test cell; the second location is a location outside the test cell; the first hydraulic power source is configured to apply a braking power and / or a propelling power to the output shaft of the vehicle or vehicle component; the vehicle dynamometer system further comprising a control system for controlling power applied by, and speed of rotation of, the first hydraulic power source of each of the first and the second dynamometer test units; and the vehicle dynamometer system is configured to determine power applied by, and speed of rotation of, the first hydraulic power sources of the dynamometer test units through a predetermined relation between torque applied by the electrical machine and first hydraulic power source, respectively, so as to control torque without use of electrical / electronical sensor means for sensing speed of rotation of, or power applied by, the first hydraulic power source located at the first location.

[0036] The presented method has corresponding advantages as mentioned above for the vehicle dynamometer system. Also, the method may implement and / or use any of the herein described embodiments.

[0037] Further characteristics of aspects of the invention and advantages thereof are indicated in the detailed description of exemplary embodiments set out below and the attached drawings.

[0038] Brief description of drawings

[0039] The invention will now be described in greater detail with reference to the drawings, wherein:

[0040] Fig. 1 illustrates an exemplary vehicle dynamometer system according to the prior art;

[0041] Fig. 2 illustrates an exemplary vehicle dynamometer system according to embodiments of the invention comprising two dynamometer test units being connected to driven output shafts of a test object;

[0042] Fig. 3 illustrates an exemplary method for performing dynamometer testing using the system of Fig. 2;

[0043] Fig. 4 illustrates an exemplary EMC cell set up according to the invention;

[0044] Fig. 5A illustrates a perspective view of an exemplary dynamometer test unit portion according to the invention;

[0045] Fig. 5B illustrates the dynamometer test unit portion of Fig. 5A from the side.

[0046] Description of exemplary embodiments Fig. 1 discloses a test object in the form of a vehicle 100 being set up for being tested with a vehicle dynamometer system comprising dynamometer test units according to a prior art solution.

[0047] The disclosed vehicle 100 is a two-wheel (front wheel) drive vehicle, and includes front axle wheel shafts, or half shafts, 103, 104, and rear axle wheel shafts 105, 106.

[0048] The disclosed vehicle 100 further includes a drivetrain, which according to the present example includes a combustion engine 101 connected to a gearbox 102. The gearbox 102 may be of any suitable kind and, e.g., consist of a manual transmission or an automatic transmission. There may also be no transmission, e.g. if the vehicle is an electric vehicle having one or more electric motors that directly power wheel shafts of the vehicle. The particular drivetrain of the vehicle 100 is for illustration purposes only. The front axle wheel (drive) shafts, such as half shafts, 103, 104 extend from the gearbox to the front axle wheels of the vehicle 100. Fig. 1 only discloses rear axle wheels 107, 108, whereas the front axle wheels have been removed to allow dynamometer test units 110, 111 to be rigidly connected to the half shafts 103, 104 in place of the wheels according to the below.

[0049] The vehicle dynamometer system connected to the vehicle 100 comprises two basically identical dynamometer test units 110, 111. The dynamometer test units 110, 111 are connected to a measuring and control system 114, such as e.g. a computer with associated display 115, by means of which e.g. tests may be controlled, and by means of which an operator of the system e.g. may initiate tests and provide necessary information for performing the dynamometer tests.

[0050] During testing, the measuring and control system 114 may transmit control signals to the dynamometer test units 110, 111 to request desired load (torque) and possibly desired speed of rotation to be applied to half shafts 103, 104, respectively. Measurement of the torque according to embodiments of the invention will be described below. The dynamometer test units 110, 111 may consist of substantially identical test units, and each comprises, according to the illustrated embodiment, a power source in the form of an electrical machine. The use of an electrical machine as power source in the dynamometer test unit may be advantageous since it is capable both to absorb torque applied by, e.g., an internal combustion engine, and also to also apply torque, e.g., to be absorbed by an electrical machine of the vehicle, e.g. to test regenerative braking.

[0051] During testing, the output shafts 120 of the test units 110, 111 are arranged to be rigidly connected to the wheel shafts 103, 104 of the vehicle 100. The rigid connection is accomplished by removing the vehicle wheel and attaching the output shaft 120 of the dynamometer test units to the wheel hubs directly or, as is oftentimes the case, using an adapter plate, schematically indicated by 121 in the figure, so as to obtain a rigid connection between vehicle 100 and dynamometer test unit 111 in a simple manner

[0052] The dynamometer test units further comprise support legs, or arms, 122 carrying the weight of the elements of the test unit supported thereby as well as a portion of the weight of the vehicle being tested. The support legs further carry the torque applied to the dynamometer by the driven vehicle shaft and prevents the test unit from rotating. The dynamometer test units further comprise wheels 123 to allow the dynamometer test units to be relocated, e.g., to be positioned for testing. Exemplary designs of the dynamometer test unit and vehicle dynamometer system can be found in previous applications from the applicant of the present application.

[0053] The setup according to Fig. 1 is highly suitable for testing test objects in the form of vehicles in various different manners, e.g., with regard to performance and various other vehicle functionality. However, as was mentioned above, there may also exist a requirement to test a test object in the form of a vehicle or vehicle component with regard to, for example, Electromagnetic Compatibility (EMC) compliance. The setup illustrated in Fig. 1 , however, is not optimally suitable for such testing. EMC testing is in general performed in an EMC chamber in order to as much as possible reduce impact on measurements from other emitting sources than the vehicle or vehicle component being tested and the controlled emissions that the test object is subjected to during the testing. A setup according to Fig. 1 , however, will impose additional emissions. This is, for example, because the dynamometer test system will also generate electromagnetic emissions through the electrical machines being used, and also the converters that are used to control the electrical machines. Such emissions may have an undesired impact on the EMC measurements. According to the invention, it is provided a solution for reducing impact of such undesired sources of emission, and Fig. 2 illustrates an exemplary setup of such a solution. Furthermore, as was also mentioned above, there may exist other types of testing that require use of a test cell, and the following description is equally applicable for such testing. Furthermore, there may also exist situations in which dynamometer testing is desired, but where, e.g., space requirements do not allow such testing to be performed. According to the invention testing may be made possible also in such situations through the use of separated dynamometer test unit portions. The solution according to Fig. 2 being discussed below is therefore applicable in any situation where use of two separate dynamometer test unit portions being interconnected by a fluid connection is advantageous, and hence not only for EMC testing.

[0054] Fig. 2 illustrates a vehicle dynamometer system for dynamometer testing of a vehicle or vehicle component as the case may be. Fig. 2 comprises reference signs for features necessary to explain the inventive concept of the presented solution. The vehicle dynamometer system of Fig. 2 has some features in common with the solution shown in Fig. 1 , and reference signs for some features of the presented vehicle dynamometer system are therefore presented in Fig. 1 . Additionally, the vehicle dynamometer system of Fig. 2 has a number of novel features not shown in Fig. 1 , as herein explained.

[0055] The vehicle dynamometer system illustrated in Fig. 2 comprises two dynamometer test units, where each dynamometer test unit comprises a first portion 231 , 232 and a second portion 233, 234 as will be further explained below. The dynamometer test system according to Fig. 2 is suitable for use when testing a vehicle or vehicle component for EMC compliance. As was mentioned above, such testing in general is performed in an EMC chamber, and Fig. 2 also illustrates an EMC chamber 201 . The figure further illustrates a test object in the form of a vehicle component 202 to be tested for EMC compliance while in operation, where the vehicle dynamometer system is used to apply loads to the vehicle component to allow EMC testing while simulating real life driving.

[0056] The EMC testing may be carried out for a test object in the form of a complete vehicle, but oftentimes only a vehicle component, such as a vehicle drivetrain is tested. In this way, e.g., drivetrains may be tested prior to assembling a complete vehicle. This may save both time and cost. As was mentioned, the two dynamometer test units each comprises a first portion 231 , 232 and a second portion 233, 234, where the first portions 231 , 232 each comprises a hydraulic motor 203, 204, respectively. Thus, a first dynamometer test unit 110 comprises a first portion 231 , which comprises a first hydraulic motor 203, and a second dynamometer test unit 111 comprises a first portion 232, which comprises a first hydraulic motor 204.

[0057] The hydraulic motors 203, 204 are connected to drive shafts 221 , 222, i.e. to first 221 and second 222 drive shafts, respectively, of the test object 202 in order to apply a load to the drive shafts 221 , 222.

[0058] According to the present example, the hydraulic motors 203, 204 are capable of providing both a propelling power to the drive shafts 221 , 222 of the test object 202 so that, thereby, e.g., regenerative braking using an electrical machine of the test object may be simulated, and also a braking power to absorb a propelling power applied by a power source, such as an internal combustion engine or electrical machine, of the test object. The possibility of providing both a propelling power and a braking power by the hydraulic motors 203, 204 may be realized through the use of, e.g., hydraulic motors being of a bent axis design that allows for operation both as a pump (in order to apply a braking power) and as an hydraulic motor (in order to apply a propelling power). The hydraulic motors 203, 204 may also be of other designs providing such functionality, such as, e.g., a combination of two hydraulic motors being configured to provide power in different directions of rotation. Other possible designs also exist.

[0059] The dynamometer test units of the vehicle dynamometer system of Fig. 2 further comprises a second portion 233, 234 comprising, inter alia, a second hydraulic power source. This is illustrated by hydraulic motors 205, 206 which are located at a second location being outside the EMC chamber 201 , and which may be of a similar design as hydraulic motors 203, 204. Thus, a first dynamometer test unit 110 comprises a second portion 233, which comprises a second hydraulic motor 205, and a second dynamometer test unit 111 comprises a second portion 234, which comprises a second hydraulic motor 206. The second hydraulic motors 205, 206 of the second portions 233, 234 are used to apply power to, and absorb power from, the first hydraulic motors 203, 204 of the first portions 231 , 232, where the power is transmitted through hydraulic hoses 207-210, i.e. through first 207, 208 and second 209, 210 hydraulic hoses. Thus, the second hydraulic motors 205, 206 of the second portions 233, 234 may be controlled to run in a first direction, in which power is applied to the first hydraulic motors 203, 204 of the first portion, to provide a propelling power to the output shafts of the vehicle or vehicle component. Also, the second hydraulic motors 205, 206 of the second portions 233, 234 may be controlled to run in a second direction, opposite to the first direction. When the second hydraulic motors 205, 206 of the second portions 233, 234 are controlled to run in the second direction, propelling power applied by the power source of the test object is instead absorbed via the first hydraulic motors 203,

[0060] 204 of the first portions 231 , 232, in order to provide a braking power to the output shaft of the vehicle or vehicle component. The second hydraulic motors 205, 206 of the second portions 233, 234, and also the first hydraulic motors 203, 204 of the first portions 231 , 232, may in other words perform a so-called four quadrant operation, i.e. may be run in both positive and negative speeds / directions, and may also provide both positive and negative torques.

[0061] The output shaft of the hydraulic motors 205, 206, in turn, are connected to electrical machines 211 , 212 respectively, also forming part of the second portions 233, 234 of the dynamometer test unit, respectively. Thus, the first dynamometer test unit comprises a first electrical machine 211 of the second portion 233, and the second dynamometer test unit comprises a second electrical machine 212 of the second portion 234.

[0062] When applying power to a drive shaft of the test object 202, for example, the first electrical machine 211 may apply a propelling power to the second hydraulic motor

[0063] 205 of the second portion 233 of the first test unit, which in turn may propel the first hydraulic motor 203 of the first portion 231 of the first test unit through use of the first hoses 207, 208 in order to thereby apply a propelling power to the first drive shaft 221 of the test object 202. Conversely, in case the first hydraulic motor 203 of the first portion 231 is to provide a braking power, this may be absorbed by the first hydraulic motor 203 by propelling the second hydraulic motor 205 of the second portion, which in turn is subjected to a braking action by the first electrical machine 211 and thereby imposes a corresponding load on the first hydraulic motor 203.

[0064] The electrical power consumed for generating the propelling power applied by the first electrical machine 211 may be supplied by a grid 213, and the braking action provided by the first electrical machine 211 may in turn be used to convert power absorbed by the first hydraulic motor 203 of the first portion 231 into electrical power to be returned to the grid 213.

[0065] The second electrical machine 212, the first hydraulic motor 204 and the second hydraulic motor 206 of the second test unit operate in the corresponding manner. Thus, when applying power to a drive shaft of the test object 202, the second electrical machine 212 may apply a propelling power to the second hydraulic motor 206 of the second portion 234 of the second test unit, which in turn may propel the first hydraulic motor 204 of the first portion 232 of the second test unit through use of the second hoses 209, 210 in order to thereby apply a propelling power to the second drive shaft 222 of the test object 202. Conversely, in case the first hydraulic motor 204 of the first portion 232 is to provide a braking power, this braking power may be absorbed by the first hydraulic motor 204 of the first portion 232 by propelling the second hydraulic motor 206 of the second portion 234, which in turn is subjected to a braking action by the second electrical machine 212 and thereby imposes a corresponding load on the first hydraulic motor 204 of the first portion 232.

[0066] The electrical power consumed for generating the propelling power applied by the second electrical machine 212 may be supplied by a grid 213, and the braking action provided by the second electrical machine 212 may in turn be used to convert power absorbed by the first hydraulic motor 203 of the first portion 232 into electrical power to be returned to the grid 213.

[0067] The control of the electrical machines 211 , 212 is performed by drive systems 214, 215 comprising, e.g., suitable frequency converters.

[0068] The vehicle dynamometer system further comprises a control system 235 for controlling the drive systems 214, 215 and thereby loads applied to the drive shafts of the test object 202. The control system may comprise, e.g., a computer with associated display(s), by means of which the tests may be controlled, and by means of which an operator of the system may initiate tests and provide necessary information for performing the dynamometer tests.

[0069] The invention hence provides a solution where a first dynamometer test unit portion is positioned at the location of the test object, and where a second dynamometer test unit portion is positioned at the second location. In this way, e.g., power absorbed by the first dynamometer test unit can be transported through the fluid connection to the second location where it may be regenerated, e.g. to electricity. Furthermore, since the first dynamometer test unit portion can be made comparatively small, and with regard to EMC testing, without any electronic of devices, the first portion may be positioned, as described, inside a test cell. According to prior solutions it has been required that the dynamometer test unit is arranged outside the test cell, where connection is made to the test object through shaft extending through the wall. This imposes various drawbacks, such as the need for long shafts and exact positioning of the test object to provide for a rigid coupling to the dynamometer test unit and require extensive and dedicated space outside of the test cell. Also, it is in general not possible to test more than one output shaft of a test object in this way. Furthermore, the invention does not require any fixed installations so that, e.g., existing test cells may be used, and the test cells may also be used for other purposes than testing according to the invention.

[0070] An exemplary control method for controlling the loads being applied to the drive shafts 221 , 222 of the test object 202 is illustrated in Fig. 3, where the control method, e.g., may be computer-implemented and carried out by the control system 235 of the vehicle dynamometer system.

[0071] In step 301 a test object load is estimated for the left drive shaft 221 of the load 202 in Fig. 2, and hence the load being applied by, or being absorbed by, the first hydraulic motor 203 of the first test unit. This load is estimated using the electrical machine (EM) torque, i.e., the torque that is applied to the second hydraulic motor 205 by the electrical first machine 211 . This torque can be estimated in any suitable manner, where various methods for estimating torque of an electrical machine exist in the art. For example, the torque may be estimated using voltage and current applied to the first electrical machine 211 . The actual load of the test objected is then estimated by converting the electrical machine torque (e.g., as mentioned, interpreted form the electric machine drives), to a hydraulic machine torque of the first hydraulic machine 203 to which the test object 202 is attached. This may be carried out, e.g. through the use of a defined relationship between electrical machine torque and speed of rotation and the torque and speed of rotation that is actually being applied to the drive shaft of the test object. Such relationships may, e.g., be empirically determined by performing measurements for one or more loads / speeds while performing measurements on the output shaft of the hydraulic motor prior to taking the system into use. Such measurement may then be used, e.g., to determine a model representation, e.g. in the form of a linear or exponential relationship. The generation of a model representation in this way is well known to a person skilled in the art. The determined model representation may then be used to translate the load applied to the drive shaft of the test object and electrical machine torque, and vice versa.

[0072] In step 302 a similar test object load is estimated for the second / right drive shaft 222 of the load 202 in Fig. 2, and hence the load being applied by, or being absorbed by, the first hydraulic motor 204 of the second test unit.

[0073] The thus determined torques and speeds of rotation of the drive shafts of the test object are then used to determine a true vehicle speed, step 303, by means of a tyreroad interface, such as a slip value. The slip value can be obtained, e.g., from a tyre model, where the road is simulated and thus act as interconnecting element.

[0074] The true vehicle speed can, for example, be determined using the equation:

[0075] This equation can be set up for any drive shaft combination, in case further drive shafts are tested, and by means of such equations a true vehicle speed can be calculated, i.e., the speed at which the vehicle would be travelling if being driven on a road. Using this true vehicle speed and the slip value(s) of the wheel shaft(s), the dynamometer test unit can be set so that correct drive shaft speeds, i.e. output shaft speeds that the output shafts of the test object would have in real-life driving, are obtained. In this way the load of the output shafts of the test object can be adjusted and balanced to, e.g., a desired test object speed set-point.

[0076] Furthermore, depending on the torque distribution between the left and right drive shaft of the test object, by use of a tyre model, individual scaling factors representing the torque balancing between the output shafts due to traction may be calculated for each of the first hydraulic motors 203, 204. That is, the scaling factors distribute the overall torque between the output shafts depending on the, in this case simulated, wheel slip. This also applies to, e.g., front and rear shafts of a vehicle in case front and rear wheel shafts of a vehicle is tested.

[0077] The estimated test object torques are also added together, step 304 and provided to an inverse test object load characteristics calculator, step 305, which in essence calculates the road load on the test object. A vehicle travelling on a road is subjected to a particular load in relation to its speed of travel, where the load may depend on, e.g., characteristics of the road to be simulated, e.g. in terms of inclination, but perhaps in particular on vehicle speed. The inverse test object load characteristics calculator calculates a speed of the vehicle based on the received torque data, where a load characteristic curve may be used in this regard to calculate a vehicle speed set-point at the current load, i.e. the vehicle speed that the vehicle should exhibit when travelling on a particular road.

[0078] A speed set-point may then be determined based on the actual speed calculated in step 305, e.g., in order to increase or decrease the speed based on a difference between desired speed and actual speed. It is also provided an input 307 for changing the road characteristics that is used in the calculation of the speed setpoint, and a further input 308 for setting the speed set-point directly instead of calculating the speed set-point using road characteristics. The figure also illustrates mode selecting means 306, which provides a possibility to select between these two ways of determining the speed set-point.

[0079] The speed set-point is then multiplied by the scaling factors to distribute the torque, and in steps 311 and 312 inverse hydraulic system characteristics are utilized to convert the test object speed reference to an electric machine speed reference. The inverse calculation depends on the test object speed reference and electric machine torque. The calculated speed may then be requested from the electrical machines in order to thereby apply the desired load on the output shafts of the test object in order to obtain the desired speed, where the method of Fig. 3 is carried out continuously to control the speed and load of the test object.

[0080] Fig. 3 also illustrates a user display 320, which is configured to display a test object speed estimation, which is calculated in steps 315, 316 from the electrical machine torque and speed of rotation according to the above, where electric machine torque and rotational speed (interpreted from the electric machine drives), are converted to hydraulic motor rotational speed (rotational speed of the test object). This is displayed for each of the tested shafts of the test object. The display 320 is also configured to display the test object torque load as calculated above. This data may be used by a user, e.g., to adapt the test object set-point through the user control knob.

[0081] Fig. 3 provides a solution that does not require any sensor means at all in the test cell, in particular no electrical sensor means are required. However, according to aspects of the invention it is possible to use sensor means for determining speed and torque of the first hydraulic power source where still no electrical sensor means are used. For example, fibreoptic means may be used where, e.g., fibreoptics may be used to transmit a laser beam onto a rotating shaft provided with a suitable reflector, where further fibreoptic means may be used to determine speed of rotation from reflections. Thus, the herein described vehicle dynamometer system then comprises a fibreoptic arrangement, which is configured to transmit a laser beam onto at least one reflector applied / attached on the first output shaft 221 and / or onto the second output shaft 222. The fibreoptic arrangement is configured to detect reflections from the at least one reflector during rotation of the first output shaft 221 and / or the second output shaft 222, on which the at least one reflector is applied / attached. Hereby, the rotational speed, i.e. the revolutions per minute, of the first output shaft 221 and / or the second output shaft 222 may be detected. Also, the torque provided by the first output shaft 221 and / or the second output shaft 222 may be detected.

[0082] With regard to measurement of torque, the first dynamometer testing portion may be designed as a load cell configured to measure a reaction torque, i.e. a resistance against rotation, where such solutions are thoroughly explained in previous applications of the present applicant but where instead of using, e.g., an elastic strip and sensor means to determine strain, the portion being subjected to torque can be connected to a stator portion, such as the base described below, through a loaded spring, where the extension of the string when subjected to torque may be measured using fibreoptics, where the determined extension may then be used to calculate a torque applied by the first hydraulic power source.

[0083] Fig. 4 illustrates the exemplary setup in the EMC cell 201 more in detail. The figure illustrates the test object 202 with drive shafts 221 , 222 connected to the first portions 231 , 232 of the dynamometer test units comprising the first hydraulic motors 203, 204, although the hydraulic motors are covered by a top cover 244, 245, respectively, of the first dynamometer test unit portions 231 , 232. The figure also illustrates the hydraulic hoses 207-210 connecting the first hydraulic motors 203, 204 of the first portions to the second hydraulic motors 205, 206 of the second portions. The figure also shows third hydraulic hoses 237, 238 running from the each of first hydraulic motors 203, 204. These additional hydraulic hoses 237, 238 form return hoses used to bleed of hydraulic fluid of shaft bearings etc. to a hydraulic tank 236 (illustrated in Fig. 2), and are utilized to provide for a depressurised return channel always being present, which may otherwise not be the case given the possibility of changing the direction of rotation of the first hydraulic motors 203, 204 to provide for the possibility of applying both a propelling power and a braking power to the drive shafts of the test object.

[0084] Such connection of the first hydraulic motors 203, 204 are known per se. The figure also schematically illustrates the walls of the EMC chamber being provided by emission isolating material 242 in a manner known per se. In reality, there may also be, e.g., transmitters etc. for generating the electromagnetic emissions being used in the testing of the test object. According to the illustrated example, the test object is positioned on a table in the EMC cell, where the table may comprise, e.g., a tabletop 241 being fabricated, e.g. from a copper sheet.

[0085] Fig. 4 also illustrates that the first dynamometer test unit portions 231 , 232 are portable, and also displaceable through the use of wheels which are more visibly illustrated in Figs. 5A-5B. According to the illustrated solution, the test object 202 and the first dynamometer test unit portions 231 , 232 are arranged on a frame 243 being located on the copper table 241 , where the first test unit portions 231 , 232 are displaceable in the direction of the longitudinal axis of the drive shafts 221 , 222. In this way connection of the test object 202 may be facilitated by displacing the first dynamometer test unit portions 231 , 232 backwards while attaching the test object 202 to the frame 243, and then displace the first test unit portions 231 , 232 towards the test object and interconnect the drive shafts 221 , 222 to the first dynamometer test unit portions 231 , 232.

[0086] As was mentioned, the invention provides a solution that allows for testing of a vehicle or a vehicle component without the use of any electrical components with regard to the dynamometer test equipment. The invention only requires an hydraulic motor and associated means for connection to the drive shaft of the test object in the EMC chamber, with no electrical components whatsoever being required for the dynamometer testing. This means, inter alia that no electrical sensors etc. are required in order to perform the dynamometer measurements. Still, accurate measurement results may be obtained, while the overall solution also utilizes an electrical machine to provide for conversion between electrical power and rotating power.

[0087] An exemplary embodiment of the first dynamometer test unit portion 231 , which according to the example is similar to the second dynamometer test unit portion 232, is illustrated in Figs. 5A, 5B.

[0088] As is illustrated in Fig. 5A, the first dynamometer test unit portion 231 comprises a base 250 carrying, inter alia the first hydraulic motor 203 of the first test unit which, as described above, is utilized to apply power to the first output shaft 221 of the test object 202. The first dynamometer test unit portion 231 is connected to the test object 202 through the use of a circular coupling flange 252, which is fastened to an output shaft of the first dynamometer test unit portion 231 , e.g., by being welded to a clamped-on collar on the output shaft, or otherwise secured to the output shaft of the dynamometer test unit. The coupling flange is then be connected to, e.g., a wheel hub of the first output shaft 221 of the test object.

[0089] Dynamometer test units of the disclosed kind may furthermore be configured to, during testing, carry, e.g., the weight of a vehicle in place of the vehicle a wheel that normally carries the weight of the vehicle, where the weight may then be taken up using a bearing housing. The dynamometer test unit according to figure 5A also comprises a bearing housing 253 that is configured to take up possible axial and radial forces that it may be subjected to during testing, although according to the present example the weight of the test object is carried by the frame 243. Fig. 5A illustrates a particular example of a dynamometer test unit portion suitable for testing a vehicle component comprising essentially a power source and drive shafts. In case a complete vehicle is subjected to the testing, the dynamometer test unit portion may be of a different design but the functionality essentially remain the same. The first dynamometer test unit portion 231 also comprises wheels 254, 255 (illustrated also in Fig. 5B) to allow the dynamometer test unit portion 231 to be displaced, e.g., in an axial direction to facilitate the connection to a test object.

[0090] Furthermore, according to aspects of the invention, the first dynamometer test unit portions 231 , 232 are connected to the vehicle or vehicle component being tested in a manner where the first hydraulic motors 203, 204 are galvanically isolated from the vehicle / vehicle component to prevent the vehicle / vehicle component from being connected to ground through the first hydraulic motors 203, 204. A vehicle is in general galvanically isolated from the surroundings through the tyres of the vehicle, which, as is known, are made from rubber. Therefore, in order to accurately a test vehicle or vehicle component it has been realized that it may be undesired to perform such testing while connecting the vehicle or vehicle component to ground. Such grounding may occur in an undesired manner, e.g., through steel cords of hydraulic hoses etc. in case the hydraulic motor is in electrical connection with the output shaft of the test object, which may be the case, e.g., in case metallic connector means are used.

[0091] Therefore, in order to prevent undesired grounding of the object to be tested, a galvanically isolated coupling between the first hydraulic motors 203, 204 and the test object may be utilized. Figs. 5A-B also illustrates an example of a solution providing for such galvanic isolation. As was mentioned, the first output shaft 221 of the test object may be made of a metallic material, and as may the coupling flange 252 and corresponding means of the output shaft being used in the interconnection of the test object and dynamometer testing portion. Similarly, the bearing housing may also comprise metallic parts. Therefore, according to the present example, in order to provide for galvanic isolation, the output shaft of the first hydraulic motor 203 is connected to the bearing housing using a rubber coupling 256, such as a claw coupling having a rubber membrane. This rubber coupling 256 hence provides for galvanic isolation between the output shaft of the hydraulic motor 203 and the drive shaft of the test object. The first hydraulic motor is carried by the base 250, and so is the bearing housing 253.

[0092] The coupling flange 252 and bearing housing 253 are therefore galvanically isolated from the base 250. This is because, as was mentioned, the first hydraulic motor 203 may be in an electrically conducting connection with the base 250, but also because the base 250 may also be a point of ground, e.g., by resting on the tabletop formed by a copper sheet as in the present example.

[0093] This galvanic isolation is provided for through the use of, according to the present example, two ceramic, and thereby non-conducting, plates. The base 250 comprises a support part 263 that is rigidly attached to the base 250, and which is being configured to carry the bearing housing 253. However, instead of attaching the bearing housing 253 directly to the base through the support part 263, a first ceramic plate 261 is arranged on the part 263 and then, in turn, the bearing housing 253 is resting on the ceramic plate 261 . A second ceramic plate 262 is positioned underneath the support part 263 so that bolts 264 may be used to clamp the bearing housing 253 onto the support part 263 however without causing any electrically conducting contact between the bearing housing and 253 and the support part 263. In this way, the output shaft of the test object, any means, such as a wheel hub, for attaching the output shaft of the test object to the flange 252, as well as the flange 252 and shaft extending through the bearing housing 253 are galvanically isolated from the base 250 as well as from the first hydraulic motor 203. In this way it can be ensured that the dynamometer test system does not impose any accidental and / or undesired grounding of the test object which possibly might have an impact on the measurements.

[0094] The invention also allows further aspects of the dynamometer testing. Since only a part of the overall dynamometer test unit needs to be co-located with the test object and rigidly connected to the test object, the first portion may, as has been briefly discussed above, be configured to be freely standing on the floor and carry the weight of the test object. In case the test object is a vehicle, or at least a test object comprising suspension and a steering mechanism of a vehicle, the invention may also provide for testing of steering actions performed by the test object.

[0095] There exist various situations in which it may be desired to perform testing while carrying out steering actions of the test object to be tested. For example, various vehicle functions may depend to a large extent on steering angle changes. When a test object is subjected to a steering angle change, i.e. steering direction change, e.g. by turning a steering wheel of the test object or otherwise causing a steering angle change, this would cause a steering angle change of a wheel of a vehicle in order to change direction of travel of the vehicle if the vehicle were driven on a road.

[0096] During testing, instead, the first dynamometer test unit portion may be rigidly connected to the wheel hub in place of the wheel, which means that an angular change of the wheel hub will rotate (turn) the dynamometer test unit portion, i.e. the dynamometer test unit portion will be rotated in a horizontal plane on the surface upon which it is resting and about a substantially vertical rotation axis located in the pivot point of the wheel hub. The dynamometer test unit will hence be moved in a horizontal plane, and may comprise wheels to facilitate such motion during testing. Since the dynamometer test unit according to the invention is divided into two portions, the portion connected to the test object can be made comparatively light and thereby more easily provide for testing comprising steering angle changes, since the dynamometer test unit portion more easily may be rotated in response to a steering angle change. In principle the first dynamometer test unit portion may have a general design similar to the test units of Fig. 1 in this regard, but where, as mentioned, the dynamometer test unit portion will only comprise a hydraulic power source and means for connecting to the test object. In particular, the invention may provide for such testing in an EMC chamber.

[0097] In sum, the invention provides for a solution that accurately may perform dynamometer testing of a test object, e.g., being located in an EMC chamber without adding any electrical interference to the EMC measurements. Similarly, the invention may provide for the possibility of performing dynamometer testing in other situations. Furthermore, according to aspects of the invention, it is provided a solution that may ensure that no accidental grounding of the test object is imposed.

[0098] The invention is not limited to the above-described aspects. Instead, the invention relates to, and encompasses all different aspects being included within the scope of the independent claims.

Claims

Claims1 . Vehicle dynamometer system for dynamometer testing of a vehicle (100) or vehicle component (202), the system comprising a first and a second dynamometer test unit (110, 111 ) for connection to a first output shaft (221 ) and to a second output shaft (222), respectively, of the vehicle (100) or vehicle component (202) being tested, the first and the second dynamometer test unit (110, 111 ) each comprising a first portion (231 , 232) and a second portion (233, 234), wherein: the first portion (231 , 232) comprises a first hydraulic power source (203, 204) being configured to, during testing, apply a first power to an output shaft (221 , 222) of the vehicle (100) or vehicle component (202) being tested, the first portion being configured to be located at a first location; the second portion (233, 234) comprises a second hydraulic power source (205, 206), being configured to be connected to the first hydraulic power source (203, 204) through a fluid connection (207, 208; 209, 210) for transferring power between the first and second hydraulic power source (203, 204; 205, 206) through the fluid, the second portion (233, 234) further comprising an electrical machine (211 , 212) connected to the second hydraulic power source (205, 206), for converting power between hydraulic power and electrical power, the second portion (233, 234) being configured to be located at a second location; wherein the first location is a test cell (201 ), and the first portion is configured to be located within the test cell; the second location is a location outside the test cell; the first hydraulic power source (203, 204) is configured to apply a braking power and / or a propelling power to the output shaft of the vehicle (100) or vehicle component (202); the vehicle dynamometer system further comprising a control system (114) for controlling power applied by, and speed of rotation of, the first hydraulic power source (203, 204) of each of the first and the second dynamometer test units (110, 111 ); and the vehicle dynamometer system is configured to determine power applied by, and speed of rotation of, the first hydraulic power sources (203,23relation between torque applied by the electrical machine (211 , 212) and the first hydraulic power source (203, 204), respectively, so as to control torque without use of electrical / electronical sensor means for sensing speed of rotation of, or power applied by, the first hydraulic power source (203, 204) located at the first location.

2. Vehicle dynamometer system according to claim 1 , wherein the dynamometer test unit is configured for use in a vehicle dynamometer system for dynamometer testing of a vehicle or vehicle component being located in a test cell for electromagnetic field testing.

3. Vehicle dynamometer system according to any one of the claims 1 -2, wherein the first hydraulic power source (203, 204) of the first portion (231 , 232) is configured to, during testing, be rigidly attached to the output shaft (220) of the vehicle (100) or vehicle component (202) by a galvanically isolated rigid coupling (252), so as to prevent the vehicle (100) or vehicle component (202) from being grounded through the first hydraulic power source (203, 204).

4. Vehicle dynamometer system according to claim 3, wherein the galvanically isolated rigid coupling (256) is a galvanically isolating rubber coupling arranged to connect an output shaft of the first hydraulic power source (203, 204) to an output shaft (221 , 222) of the vehicle or vehicle component (202).

5. Vehicle dynamometer system according to any one of the claims 1 -4 wherein each dynamometer test unit (110, 111 ) further is configured to convert power absorbed by the first hydraulic power source (203, 204) to electrical power using the electrical machine (211 , 212), wherein power absorbed by the first power source (203, 204) is configured to be transferred to the second hydraulic power source (205, 206) by the fluid connection (207, 208; 209,210) for propelling the electrical machine (211 , 212).

6. Vehicle dynamometer system according to any one of the claims 1 -5, wherein the first portion comprising the first hydraulic power source is configured to be displaceable in an axial direction in relation to the vehicle (100) or vehicle24(202) component in order to facilitate interconnection of an output shaft of the first portion with the output shaft of the vehicle or vehicle component.

7. Vehicle dynamometer system according to any one of the claims 1 -6, wherein the first hydraulic power source (203, 204) is arranged to be standing freely on a surface and to be connected to the vehicle (100) or vehicle component by means of a rigid coupling to the output shaft (221 , 222) of the vehicle (100) or vehicle component (202), while supporting the weight of the vehicle (100) or vehicle component (202) by means of said rigid coupling.

8. Vehicle dynamometer system according to any one of the preceding claims, wherein it comprises means for determining power applied by, and speed of rotation of, the first hydraulic power source (203, 204) of each of the dynamometer test units (110, 111 ) using a model representation defining a relationship between power applied by, and speed of rotation of, the first hydraulic power source (203, 204) and the power applied by, and speed of rotation of, the electrical machine (211 , 212) of the dynamometer test unit (110, 111 ), respectively.

9. Vehicle dynamometer system according to any one of the preceding claims, wherein it further comprises means configured to: determine power to be applied by, and speed of rotation of, the first hydraulic power source (203, 204) of each of the dynamometer test units (110, 111 ) utilizing a tyre-road interface, such as a slip value, e.g., obtained from a tyre model, to thereby control the first and second dynamometer test unit (110, 111 ) such that the output shafts (221 , 222) of the vehicle (220) or vehicle component are rotated at a speed corresponding to an actual speed of rotation when driving the vehicle (100) on a road at a simulated vehicle speed.

10. A vehicle dynamometer system according to any one of the preceding claims, wherein the electrical machine (211 , 212) is configured to be connected to a grid (213), and supply electrical power generated from power absorbed by the first power source (203, 204) to the grid (213).11 . A vehicle dynamometer system according to any one of the preceding claims, comprising: a frame (243) configured to carry a vehicle component and the first portion (231 ) of the first dynamometer test unit (110) and the first portion (232) of the second dynamometer test unit (111 ), wherein the first portions (231 , 232), respectively, are arranged to be displaceable when carried by the frame in an axial direction.

12. A vehicle dynamometer system to any one of the preceding claims, further comprising: a fibreoptic arrangement configured to transmit a laser beam onto at least one reflector applied on at least one of the first output shaft (221 ) and the second output shaft (222), and to detect reflections from the at least one reflector during rotation of the at least one of the first output shaft (221 ) and the second output shaft (222).

13. A vehicle dynamometer system to claim 12, wherein the fibreoptic arrangement is configured to be used for detecting one or more in the group of: a rotational speed of at least one of the first output shaft (221 ) and the second output shaft (222); and a torque provided by at least one of the first output shaft (221 ) and the second output shaft (222).

14. A vehicle dynamometer testing installation comprising: a vehicle dynamometer system according to any one of the preceding claims; and a test cell (201 ) for electromagnetic field testing.

15. A method for dynamometer testing of a vehicle or vehicle component using a first and a second dynamometer test unit (110, 111 ) configured for use in a vehicle dynamometer system for dynamometer testing of a vehicle (100) or vehicle component (202), wherein the dynamometer test system is configured to test the vehicle (100) or vehicle component (202) when the vehicle or vehicle component is located at a first location;26the method comprising use of the first and the second dynamometer test unit (110, 111 ) for connection to a first output shaft (221 ) and to a second output shaft (222), respectively, of the vehicle (100) or vehicle component 202) being tested, the first and the second dynamometer test unit (110, 111 ) each comprising a first portion (231 , 232) and a second portion (233, 234), wherein: the first portion (231 , 232) comprises a first hydraulic power source (203, 204) that, during testing, applies a first power to the output shaft (120) of the vehicle (100) or vehicle component (202) being tested, where the first portion (231 , 232) is located at the first location; the second portion (233, 234) comprises a second hydraulic power source (205, 206) that is connected to the first power source (203, 204) through a fluid connection (207, 208; 209, 210) that transfer power between the first and second hydraulic power source, the second portion (233, 234) further comprising an electrical machine (211 , 212) connected to the second power source (205, 206), for, during testing, converting power between hydraulic power and electrical power, the second portion (233, 234) being located at a second location; wherein the first location is a test cell (201 ), and the first portion (231 , 232) is configured to be located within the test cell (201 ); the second location is a location outside the test cell; the first hydraulic power source (203, 204) is configured to apply a braking power and / or a propelling power to the output shaft (120) of the vehicle (100) or vehicle component (202); the vehicle dynamometer system further comprising a control system (114) for controlling power applied by, and speed of rotation of, the first hydraulic power source (203, 204) of each of the first and the second dynamometer test units (110, 111 ); and the vehicle dynamometer system is configured to determine power applied by, and speed of rotation of, the first hydraulic power sources (203, 204) of the dynamometer test units (110, 111 ) through a predetermined relation between torque applied by the electrical machine (211 , 212) and first hydraulic power source (203, 204), respectively, so as to control torque without use of electrical / electronical sensor means for sensing speed of27rotation of, or power applied by, the first hydraulic power source (203, 204) located at the first location.28

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