TECHNICAL FIELD

The invention relates to a test rig. BACKGROUND

For testing, e.g. fatigue testing, of products, or parts for products, such as vehicle parts, it is desirable to introduce loads in a manner allowing test results to be mapped to individual load scenarios. It is also desirable to introduce loads in a manner which closely reflects loads provided during actual use of the product.

US7036360B1 discloses a dynamic tilt test rig for testing vehicle powertrain components. A component is mounted to an inner frame surrounded by an outer frame. The outer frame pivots in relation to support stands to simulate fore and aft acceleration forces, and the inner frame pivots in relation to the outer frame to simulate lateral acceleration forces. The separate frames provides control over the force directions. However, the test rig in US7036360B1 is limited to the static magnitude of the gravity force. Also, it doesn't allow the introduction of moments.

There is desirable to provide a test rig which can introduce a larger variety of loads in a controlled manner.

SUMMARY

An object of the invention is to provide a test rig providing a high degree of load introduction flexibility with a retained control.

The object is achieved by a test rig comprising

- a first support structure, and

- a second support structure connected to the first support structure whereby the second support structure is movable in at least a first degree of freedom in relation to the first support structure,

- characterized

- in that the test rig comprises a connection device arranged to connect a first portion of a test piece to the first support structure, - in that the test rig comprises a first actuator arranged to provide a first load between the first support structure and the second support structure, the first load having the direction of the first degree of freedom, and

- in that the test rig comprises a second actuator arranged to provide a second load between a second portion of the test piece and the second support structure.

It is understood that the invention provides for the first load to be introduced to the test piece by the first actuator, and the second load to be introduced simultaneously to the test piece by the second actuator. According to the invention, the second actuator is arranged to provide the second load between the second portion of the test piece and the second support structure. Further, according to the invention, the second support structure has the first degree of freedom in relation to the first support structure. The second portion of the test piece may be connected to the second support structure via the second actuator, and/or as exemplified below via a third support structure. Since the second portion of the test piece is connected to the second support structure, and the first load is provided between the first support structure and the second support structure, the first load is also introduced between the first support structure and the second portion of the test piece, to thereby provide the first load to the test piece.

The invention may provide for the second actuator, working against the second support structure, not being affected by the first load, since the first actuator works between the first and second structures. Thereby the first load may simply cause the second actuator to move with the second support structure when the first load is applied. This means that a deformation caused by the first actuator will not affect the direction of the load of the second actuator, and vice versa. This provides a significant advantage, e.g. where the test piece, e.g. a rubber bushing, is such that the deformations are large during the test.

The benefits of the invention become clear with a comparison with an arrangement where a test piece is loaded by two actuators working orthogonally against a common structure. If the loads are high, and the test piece has a relatively small modulus of elasticity, the load from one of the actuators will cause a large deformation, which in turn causes the load from the other actuator to change direction and character. Such cross coupling makes the loads, and therefore the test, difficult to control. It has been found that known procedures for fatigue testing of heavy duty rubber and rubber metal parts do not accurately estimate the life time of the tested part. Such known procedures may even be misleading. Also, known procedures are often designed for a specific purpose and do not allow easy adaptation to different parts or different loads. Testing may of course be performed during the real working conditions, e.g., where the tested part is a vehicle part, with the part mounted on a vehicle being driven. However, the possibility to accelerate a fatigue test is thereby limited, which gives as a result long lead times and increased costs for technical development. The independence of the loads from the actuators made possible by the invention, provides for a high degree of control over the loads, and therefore the test. Also, such an independence will allow a higher degree of flexibility when designing a test program, since load characteristics can be selected without limitations caused by cross coupling between the loads. Therefore, a larger range of load characteristics is available to the user of the test rig. The increased control and flexibility provides for accelerated fatigue tests which replicate closely the real working conditions of the tested part in use.

It is understood that the first support structure may be adapted to be fixed in relation to a supporting element, e.g. a floor of a testing facility. The first support structure may even be partly or fully integrated with a surrounding structure, such as that of a building in which the test rig is installed. Thus, the first actuator and the connection device may be connected to a common frame, or to different parts of a surrounding building structure.

It is understood that the second support structure being connected to the first support structure may involve the second support structure being restrained to the first support structure but allowed to move in relation to the first support structure. The second support structure may be restrained to the first support structure, while the second support structure is moveable in at least the first degree of freedom in relation to the first support structure. E.g., the second support structure may be fixed to the first support structure in some directions, and allowed to move in relation to the first support structure in one or more other directions. For example, of six degrees of freedom, three translational and three rotational ones, the second support structure may have two degrees of freedom in relation to the first support structure, e.g. one translational degree of freedom and one rotational degree of freedom. Examples with various numbers of degrees of freedom are provided below. As exemplified below, any of the first and second loads may be a force or a moment, e.g. a torque or a bending moment. A direction of an application of a force is understood as a direction in which the force urges an object, and a direction of an application of a moment is understood as a direction of an axis around which the moment tends to rotate something.

The first and second actuators are advantageously arranged for applying the second load in a non-zero angle relative to the first load. Thereby, the benefits of reduced cross coupling may be obtained while allowing different load directions for accurately replicating real conditions of the test piece. Preferably, the first and second actuators are arranged for applying the second load substantially orthogonally to the first load.

Preferably, the first actuator is located along a first axis intersecting the test piece, and the second actuator is located along a second axis intersecting the test piece, wherein the first and second axes are substantially orthogonal to each other.

The test rig advantageously comprises a third support structure arranged to connect the second portion of the test piece to the second actuator, and the second actuator is arranged to provide the second load between the second support structure and the second portion of the test piece via the third support structure. The third support structure may also be connected to the second support structure for transfer of the first load to the test piece without guiding the first load through the second actuator. Suitably, the third support structure is moveable in a second degree of freedom in relation to the second support structure, in the direction of the second load. This allows the introduction of the second load from the second actuator to the test piece in a controlled manner. Preferably, the third support structure is fixed relative to the second support structure in the direction of the first degree of freedom, i.e. the third support structure is not allowed to move in relation to the second support structure in this direction. This provides for the test piece to not be allowed to move in relation to the second support structure in the direction of the first degree of freedom. The first actuator is thereby not in direct contact with the test piece; instead it acts on the test piece via the third support structure. If the second support structure is fixed to the first support structure in the direction of the first degree of freedom of the second support structure, the first load, provided by the first actuator between the first and second support structures, may be effectively transferred to the test piece via the third support structure, again without the involvement of the second actuator.

In some embodiments, the connection device is provided in the form of a third actuator arranged to provide a third load, e.g. a force or a moment, between the first support structure and the first portion of the test piece. Thereby, a further load may be introduced to the test piece in addition to the independent first and second loads.

The third actuator may comprise an engagement member arranged to provide the connection of the third actuator with the first portion of the test piece, which engagement member is moveable in a third degree of freedom in relation to the first support structure, in the direction of the third load. Preferably, the third actuator is arranged for applying the third load in a non-zero angle, preferably substantially orthogonally, relative to the second load and to the first load. Thus, the third actuator may be arranged to provide a third load in the direction of the third degree of freedom, between the first support structure and the first portion of the test piece. Thereby, the third load may be introduced in a controlled and independent manner.

It should be noted that in some alternative embodiments, there is no third actuator, and the connection device provides a stiff connection between the test piece and the first support structure. In some embodiments, the test rig comprises a fourth actuator arranged to provide a fourth load, e.g. a force or moment, between the second portion of the test piece and the second support structure. Thereby, yet another load may be introduced to the test piece in addition to the independent first and second loads, and the third load, in case a third actuator is provided as described above.

Preferably, the first actuator is located along a first axis intersecting the test piece, and the fourth actuator is located along a second axis intersecting the test piece, wherein the first and fourth axes are substantially orthogonal to each other. Where the test rig comprises a third support structure, the third support structure may be arranged to connect the second portion of the test piece to the fourth actuator, so that the fourth actuator is arranged to provide the fourth load between the second support structure and the second portion of the test piece via the third support structure. The third support structure preferably is moveable in a fourth degree of freedom in relation to the second support structure, in the direction of the fourth load. This allows the introduction of the fourth load from the fourth actuator to the test piece in a controlled manner.

Preferably, the second and fourth actuators are arranged for applying the second and fourth loads substantially in parallel. The second and fourth actuators may be located on opposite sides of an intended position of the test piece. The second load may be a moment and the fourth load may be a force. This makes it possible to provide a simple and compact arrangement for the introduction of the second and fourth loads in a controlled manner, independently of each other.

In some embodiments, the second support structure has a further degree of freedom, in an example below referred to as a fifth degree of freedom in relation to the first support structure. Preferably, the test rig comprises a fifth actuator arranged to provide a fifth load, e.g. a force or a moment, between the first support structure and the second support structure, the fifth load having the direction of the fifth degree of freedom. Thereby, still another load may be introduced to the test piece in addition to the independent first and second loads, and in some embodiments, the third and/or the fourth loads as exemplified above. Thus, a test rig with five degrees of freedom may be provided. In each degree of freedom a load may be introduced in a controlled manner, and independently of other loads in the test rig. Such a five degrees of freedom test rig makes it possible to cover nearly all of the working conditions for a typical rubber and rubber-metal bushing for a vehicle. Also, a high degree of flexibility is allowed due to the load independence provided by the inventive concept, which makes it easy to accommodate different types of parts for testing thereof.

The first and fifth actuators may be arranged for applying the first and fifth loads substantially in parallel. Preferably, the first and fifth actuators are on opposite sides of the second support structure. The first load may be a moment and the fifth load may be a force. This makes it possible to provide a simple and compact arrangement for the introduction of the first and fifth loads in a controlled manner, independently of each other. Preferably, where the test rig comprises a third support structure arranged to connect the second portion of the test piece to the second actuator, and to the fourth actuator in case this is provided, the third support structure is fixed relative to the second support structure in the direction of the fifth degree of freedom. The first actuator is thereby not in direct contact with the test piece; instead it acts on the test piece via the third support structure. If the third support structure is fixed to the second support structure in the direction of the fifth degree of freedom of the second support structure, the fifth load, provided by the fifth actuator between the first and second support structures, may be effectively transferred to the test piece via the third support structure, without the involvement of the second actuator, or the fourth actuator in case this is provided.

It is understood that the loads from the actuators in any embodiment of the invention may advantageously be provided simultaneously. Thus during a test sequence, a test piece may be subjected to a plurality of simultaneous loads, which may be constant or fluctuate such as in a fatigue test. Thereby, the simultaneous loads will be highly individually controllable due to the inventive concept, and each load may be provided with an individual character, which may be constant, or fluctuating with a respective frequency. The test rig may be advantageously arranged to provide a test where the test piece is a bushing or a bearing, where the first portion of the test piece is an inner portion of the test piece, and the second portion of the test piece is an outer portion of the test piece. As also suggested above, the inventive concept may provide large benefits for testing of such parts, in particular due to the high deflections and high loads that may be involved, where the absence of cross coupling of the inventive concept will be very useful.

Further advantages and advantageous features of the invention are disclosed in the following description. BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples. In the drawings: Fig. 1 is a perspective view of a test rig according to an embodiment of the invention.

Fig. 2 is a vertical cross-sectional view oriented along the Y- and Z-axes as indicated by the arrows ll-ll in fig. 1 , where some details have been simplified for ease of

understanding of the presentation.

Fig. 3 is a horizontal cross-sectional view oriented along the X- and Y-axes as indicated by the arrows Ill-Ill in fig. 2.

Fig. 4 is a perspective view of a test piece mounted in the test rig in fig. 1 .

Fig. 5 is a perspective view of a test rig according to an alternative embodiment of the invention.

Fig. 6 is a cross-sectional view, oriented similarly to the view of fig. 3, of a test rig according to a further alternative embodiment of the invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.

Fig. 1 shows a test rig 1 suitable e.g. for fatigue testing of a test piece in the form of a rubber-metal bushing, for example for truck or construction equipment wheel axle suspensions. It should be noted however that the invention is applicable to a variety of test procedures of any suitable test piece, such as any suitable kind of bushing, or a bearing.

For this presentation, coordinate axes X, Y and Z are introduced as indicated with double arrows in fig. 1 . The X-axis and the Y-axis are horizontal and orthogonal to each other, and the Z-axis is vertical and orthogonal to the X and Y-axes. The test rig comprises a first support structure 3 which is adapted to be fixed in relation to a supporting element 2, such as a flor in a test facility. The first support structure 3 has a box-like shape, and comprises a bottom support plate 301 , two side walls 302, and two intermediate walls 303 and a top panel 304 joining the side walls 302. The test rig 1 further comprises a second support structure 4 connected to the first support structure 3 in a manner described closer below.

The test rig 1 also comprises five actuators, herein referred to as a first actuator 8, a second actuator 7, a third actuator 5, a fourth actuator 9 and a fifth actuator 10.

The first, second, fourth, and fifth actuators 8, 7, 9, 10 are all arranged to introduce respective loads to the test piece in a horizontal plane, as described closer below. The first and second actuators 8, 7 are for this embodiment also referred to as a Y-axis torque actuator 9 and an X-axis torque actuator 7, respectively. The fourth actuator 9 is for this embodiment also referred to as an X-axis force actuator 9. The fifth actuator 10 is for this embodiment also referred to as a Y-axis force actuator 10.

The third actuator 5 is arranged to introduce a load to the test piece as described below, and it is herein also referred to as a connection device 5, and for this embodiment it is also referred to as a Z-axis force actuator 5. The third actuator 5 is in this embodiment arranged to introduce a load which is substantially parallel to the z-axis, i.e. in this example a substantially vertical load, the z-axis being orthogonal to the x-axis and the y- axis. It should be noted that in some embodiments, the orientation of the actuators may differ from what is the case in the embodiment described here. For example, it is conceivable that the third actuator is oriented horizontally, and the first and fifth actuators 8, 10, or the second and fourth actuators 7, 9 are oriented vertically, e.g. in case the first structure is mounted on a wall.

It should also be noted that the denomination of the actuators as first, second, third, fourth and fifth actuators should not be taken as any indication of their internal rank, or that the provision of some of the actuators is a requirement for the provision of other of the actuators. Instead a large range of actuator combinations are possible within the scope of the invention. Reference is made to fig. 2 and fig. 3, showing cross-sections of the test rig in fig. 1 , with some details simplified or left out for ease of understanding some basic principles of the embodiment. The second support structure 4 has the shape of a box which is open at the top and at the bottom. The second support structure 4 includes four side walls 401 connected at their edges to form the box. The second support structure 4 is fixed to the first support structure 3 as described closer below.

As can be seen in fig. 2, the Z-axis force actuator 5 presents a hydraulic cylinder 501 . The Z-axis force actuator 5 also presents an engagement member 502, joined at a first end with a first end of the hydraulic cylinder 501 , and extending though an opening in the top panel 304 of the first support structure 3. A second end of the engagement member 502 is connected to the test piece 6 as described below. The Z-axis force actuator 5 further presents a fixture 503 which is fixed to the top panel 304 of the first support structure 3, and which is joined to a second end of the hydraulic cylinder 501 .

Reference is also made to fig. 4 showing the rubber-metal bushing test piece 6. The test piece 6 is generally ring shaped with a hole extending through it. It has a first portion 601 , herein also referred to as an inner portion 601 , and a second portion 602, herein also referred to as an outer portion 602. Inside the second support structure 4, the inner portion 601 of the test piece 6 is connected, by means of a threaded joint (not shown), to a second end of the engagement member 502 of the Z-axis force actuator 5. In this example the inner and outer portions 601 , 602 are formed in metal, and an intermediate portion 603, between the inner and outer portions, is formed in rubber.

It should be noted that the test piece may be in a large variety of shapes and materials. For example, instead of a ring shaped, it may be shaped as a block, a plate or a pin. Also, it should be noted that, as generally understood from the presentation herein, the first portion may be any portion of the test piece which is connected by the connection device 5 to the first support structure 3. Further the second portion may be any portion separate from the first portion, arranged such that the second actuator 7 is arranged to provide the second load between the first portion and the second support structure 4. The first and second portions may be adjacent, or partly or fully separated by one or more intermediate portions. As can be seen in fig. 3, the test rig comprises a third support structure 21 , herein also referred to as a test piece support device 21 . The outer portion 602 of the test piece 6 is connected to the test piece support device 21 . The test piece support device 21 presents a first extension 21 1 and a second extension 212. The first and second extensions 21 1 , 5 212 extend through respective openings in opposite side walls 401 of the second support structure 4.

The X-axis torque actuator 7 presents a hydraulic torque motor 701 which is joined at a first end with the first extension 21 1 of the test piece support device 21 , for example a0 hydraulic rotary actuator with the designation DA-H 160, marketed by HKS Dreh-Antriebe GmbH. The X-axis torque actuator 7 further presents a fixture 702 which is fixed to the side wall 401 of the second support structure 4 through which the first extension 21 1 of the test piece support device 21 extends. The fixture 702 is joined to a second end of the hydraulic torque motor 701 .

5

The X-axis force actuator 9 presents a hydraulic cylinder 901 which is joined at a first end with the second extension 212 of the test piece support device 21 . The X-axis force actuator 9 further presents a fixture 902 which is fixed to the side wall 401 of the second support structure 4 through which the second extension 212 of the test piece support0 device 21 extends. The fixture 902 is joined to a second end of the hydraulic cylinder 901 .

The second support structure 4 presents a first extension 41 1 and a second extension 412. The first and second extensions 41 1 , 412 extend through respective openings in a respective of the side walls 302 of the first support structure 3.

5

The Y-axis torque actuator 8 presents a hydraulic torque motor 801 which is joined at a first end with the first extension 41 1 of the second support structure 4, for example a hydraulic rotary actuator with the designation DA-H 160, marketed by HKS Dreh-Antriebe GmbH. The Y-axis torque actuator 8 further presents a fixture 802 which is fixed to the0 side wall 302 of the first support structure 3 through which the first extension 41 1 of the second support structure 4 extends. The fixture 802 is joined to a second end of the hydraulic torque motor 801 .

The Y-axis force actuator 10 presents a hydraulic cylinder 101 which is joined at a first5 end with the second extension 412 of the second support structure 4. The Y-axis force actuator 10 further presents a fixture 102 which is fixed to the side wall 302 of the first support structure 3 through which the second extension 412 of the second support structure 4 extends. The fixture 102 is joined to a second end of the hydraulic cylinder 101 .

Thus, X-axis torque actuator 7 and the X-axis force actuator 9 are located on opposite sides of the intended position of the test piece 6. Further, the Y-axis torque actuator 8 and Y-axis force actuator 10 are located on opposite sides of the second support structure 4. It should be noted that instead of hydraulic cylinders 501 , 901 , 101 and hydraulic torque motors 701 , 801 , electric actuating devices may be provided. The hydraulic cylinders 501 , 901 , 101 and the hydraulic torque motors 701 , 801 may be chosen to provide maximum loads which are suitable for the intended type of testing. For example, for testing truck or construction equipment wheel suspension rubber bushings, the maximum load of the hydraulic cylinders 501 , 901 , 101 may be around +/- 400 kN, and the maximum load of the hydraulic torque motors 701 , 801 may be around 1 1 kN/m.

The arrangement described above provides the test rig 1 with five degrees of freedom for introducing loads to the test piece 6.

A first degree of freedom is presented by the second support structure 4 in relation to the first support structure 3 in that the second support structure 4 is arranged to pivot in relation to the first support structure 3 around the Y-axis. It should be noted that to allow the first degree of freedom, the connection between the second extension 412 of the second support structure 4 and the hydraulic cylinder 101 of the Y-axis force actuator 10 is such that a piston 101 1 of the hydraulic cylinder 101 and the second extension 412 are fixed to each other for movements along the Y-axis, but the piston 101 1 and a cylinder barrel 1012 of the hydraulic cylinder 101 are allowed to pivot in relation to each other along the Y-axis. The maximum pivoting movement of the second support structure 4 in relation to the first support structure 3 may be for example +/- 45 ^e .

The Y-axis torque actuator 8 is arranged to provide a first load, in the form of a moment, more specifically a horizontal torque around the Y-axis, to the test piece as indicated with the arrow β in fig. 1. The torque β is provided between the first support structure 3 and the second support structure 4, the torque β having the direction of the first degree of freedom.

It should also be noted that that the test piece support device 21 is fixed relative to the second support structure 4 in the direction of the first degree of freedom. This is due to the extensions 21 1 , 212 of the test piece support device 21 extending through the side walls 401 of the second support structure 4. Thereby, the Y-axis torque actuator 8, arranged to provide movements in the first degree of freedom, pivots the second support structure 4 along with the X-axis torque actuator 7, the X-axis force actuator 9, and the test piece support device 21 , to introduce the torque β around the Y-axis to the test piece 6 with a counter moment being provided by the engagement member 502 of the Z-axis force actuator 5.

A second degree of freedom is presented by the test piece support device 21 in relation to the second support structure 4 in that the test piece support device 21 is arranged to pivot in relation to the second support structure 4 around the X-axis. It should be noted that to allow the second degree of freedom, the connection between the second extension 212 of the test piece support device 21 and the hydraulic cylinder 901 of the X-axis force actuator 9 is such that said second extension 212 and a piston 901 1 of the hydraulic cylinder 901 are fixed to each other, and the piston 901 1 and a cylinder barrel 9012 of the hydraulic cylinder 901 are allowed to pivot in relation to each other along the X-axis. The maximum pivoting movement of the test piece support device 21 in relation to the second support structure 4 may be for example +/- 45 ^e . The X-axis torque actuator 7 is arranged to provide movements in the second degree of freedom, thereby pivoting the test piece support device 21 . Thereby, the X-axis torque actuator 7 is arranged to introduce a second load in the form of a moment, more specifically a horizontal torque, as indicated with the arrow a in fig. 1 , around the X-axis to the test piece 6 with a counter moment being provided by the engagement member 502 of the Z-axis force actuator 5. Thereby, the X-axis torque actuator 7 is arranged to provide the torque a around the X-axis, between the outer portion 602 of the test piece 6 and the second support structure 4. Thereby, the torque a is introduced to the test piece 6, tending to pivot the test piece 6 in relation to the first support structure 3, i.e. the outer portion 602 of the test piece 6 is urged to pivot in relation to the inner portion 601 thereof. A third degree of freedom is presented by the engagement member 502 of the Z-axis force actuator 5 in relation to the test piece support device 21 in that the engagement member 502 is arranged to move along the Z-axis in relation to the test piece support device 21 . The Z-axis force actuator 5 is arranged to provide movements in the third degree of freedom, to introduce a third load in the form of a force along the Z-axis, which is orthogonal to the x-axis and the y-axis, to the test piece 6 with a counter force being provided by the test piece support device 21 . Thus, the Z-axis force actuator 5 is arranged to provide said force between the first support structure 3 and the inner portion 601 of the test piece 6. It is understood that the third load provided by the Z-axis force actuator 5 is substantially orthogonal to the second load and to the first load provided by the X-axis torque actuator 7 and the Y-axis torque actuator 8, respectively.

A fourth degree of freedom is presented by the test piece support device 21 in relation to the second support structure 4 in that the test piece support device 21 is arranged to move in relation to the second support structure 4 along the X-axis. It should be noted that to allow the fourth degree of freedom, the connection between the first extension 21 1 of the test piece support device 21 and the hydraulic torque motor 701 of the X-axis torque actuator 7 is such that the connected parts 21 1 , 701 are fixed to each other for a pivoting movement around the X-axis, but they are allowed to move in relation to each other along the X-axis.

The X-axis force actuator 9 is arranged to provide movements in the fourth degree of freedom, thereby moving the test piece support device 21 , to introduce a fourth load in the form of a horizontal force along the X-axis to the test piece 6 with a counter force being provided by the engagement member 502 of the Z-axis force actuator 5. Thus, the X-axis force actuator 9 is arranged to provide said force between the outer portion 602 of the test piece 6 and the second support structure 4. It is understood that the X-axis torque actuator 7 and X-axis force actuator 9 are arranged for applying the second and fourth loads substantially in parallel.

A fifth degree of freedom is presented by the second support structure 4 being movable in relation to the first support structure 3, and the second support structure 4 is arranged to move in relation to the first support structure 3 along the Y-axis. It should be noted that to allow the fifth degree of freedom, the connection between the first extension 41 1 of the second support structure 4 and the hydraulic torque motor 801 of the Y-axis torque actuator 8 is such that the connected parts 41 1 , 801 are fixed to each other for a pivoting movement around the Y-axis, but they are allowed to move in relation to each other along the Y-axis. The Y-axis force actuator 10 is arranged to provide movements in the fifth degree of freedom, thereby moving the second support structure 4. It should also be noted that that the test piece support device 21 is not allowed to move in relation to the second support structure 4 in the direction of the fifth degree of freedom. This is due to the extensions 21 1 , 212 of the test piece support device 21 extending through the side walls 401 of the second support structure 4. Thereby, Y-axis force actuator 10 is arranged to move the second support structure 4 along with the X-axis torque actuator 7, the X-axis force actuator 9, and the test piece support device 21 , to introduce a fifth load in the form of a horizontal force along the Y-axis to the test piece 6 with a counter force being provided by the engagement member 502 of the Z-axis force actuator 5. It is understood that the Y- axis torque actuator 8 and the Y-axis force actuator 10 are arranged for applying the first and fifth loads substantially in parallel.

The arrangement with two of the actuators 7, 9 mounted to the movable second support structure 4 to apply loads which are aligned, and two of the actuators 8, 10 mounted to the first support structure 3 and acting on the second support structure 4 with loads that are substantially orthogonal to the loads of the actuators 7, 9 mounted to the movable second support structure 4, has significant advantages.

An important advantage is that deformations caused by one of the actuators will not affect the direction of the loads of the other actuators. For example, as understood from the description above, the X-axis torque actuator 7 and the Y-axis torque actuator 8 are arranged for applying the second load substantially orthogonally to the first load. Thereby, a deformation caused by the Y-axis torque actuator 8 will not affect the direction of the load of the X-axis torque actuator 7, and vice versa.

In this embodiment, the actuators 5, 7, 8, 9, 10 are controlled via respective channels by a control system (not shown) implemented with a computer and suitable software. Thereby loads may be introduced simultaneously to the test piece 6 by two, three, four or all actuators, whereby the load from each actuator is controlled separately. Thus, a large degree of flexibility is provided in tailoring the test procedure for a specific test piece. The loads provided by the actuators may be pre-programmed, and/or they may be controlled in real time.

Fig. 5 shows a test rig 1 according to an alternative embodiment. Coordinate axes X, Y and Z are introduced as indicated in fig. 5. The X-axis and the Y-axis are horizontal and orthogonal, and the Z-axis is vertical and orthogonal to the X and Y-axes.

The test rig 1 in this embodiment comprises three actuators, herein referred to as a first actuator 8, a second actuator 7 and a third actuator. The first and second actuators 8, 7 are arranged to introduce respective loads to a test piece in a horizontal plane. The first actuator 8 and the second actuator 7 are for this embodiment also referred to as an X-axis torque actuator 7 and a Y-axis torque actuator 8, respectively. The third actuator, an engagement member 502 of which is shown in fig. 5, for this embodiment it is also referred to as a Z-axis force actuator, is arranged to introduce a force to the test piece along the Z-axis, i.e. a vertical force.

Similarly to the embodiment described with reference to fig. 1 - fig. 4, the test rig comprises a first support structure 3, with a box-like shape, which is adapted to be fixed in relation to a supporting element, such as a floor in a test facility. The test rig 1 further comprises a box shaped second support structure 4 connected to the first support structure 3.

The Z-axis force actuator presents a hydraulic cylinder (not shown) extending between the engagement member 502 and a fixture which is fixed in relation to the first support structure. The engagement member 502 extends through an opening in a top panel of the first support structure 3. The test piece 6, in the form of a rubber-metal bushing, is generally ring shaped with a hole extending through it. The test piece 6 is mounted so that a centre axis of its hole is substantially parallel with the X-axis. Inside the second support structure 4, an outer portion of the test piece 6 is connected to the engagement member 502 of the Z-axis force actuator. Thus, as opposed to the embodiment described above with reference to fig. 1 -4, the Z-axis force actuator in connected to the outer, instead of the inner, portion of the test piece.

The test rig comprises a third support structure 21 in the form of a pin 21 extending through the hole of the test piece 6. An inner portion of the test piece 6 is thereby connected to the pin 21 . The pin 21 extends through respective openings in opposite side walls of the second support structure 4.

The X-axis torque actuator 7 presents a hydraulic cylinder which is at a first end, below the pin 21 , joined via a lever arm (not shown) with the pin 21 . The X-axis torque actuator 7 further presents a fixture 702 which is fixed to the second support structure 4. The fixture 702 is joined to a second end of the hydraulic cylinder of the X-axis torque actuator 7.

The second support structure 4 presents extensions 41 1 extending through respective openings in a respective of the side walls 302 of the first support structure 3.

The Y-axis torque actuator 8 presents a hydraulic cylinder which is joined at a first end with the second support structure 4, below the extensions 41 1 . The Y-axis torque actuator 8 further presents a fixture 802 which is fixed to one of two intermediate walls 303 of the first support structure 3. The fixture 802 is joined to a second end of the hydraulic cylinder of the Y-axis torque actuator 8.

The arrangement described with reference to fig. 5 provides the test rig 1 with three degrees of freedom for introducing loads to the test piece 6.

A first degree of freedom is presented by the second support structure 4 being moveable in relation to the first support structure 3, and the second support structure 4 is arranged to pivot in relation to the first support structure 3 around the Y-axis by means of the connections of the extensions 41 1 to the first support structure 3.

The Y-axis torque actuator 8 is arranged to provide a first load, in the form of a moment, in this example embodiment a horizontal torque around the Y-axis, to the test piece 6 as indicated with the arrow β in fig. 5. The torque β is provided between the first support structure 3 and the second support structure 4, the torque β having the direction of the first degree of freedom. More specifically, the Y-axis torque actuator 8 is arranged to provide movements in the first degree of freedom, thereby pivoting the second support structure 4 to introduce the torque β around the Y-axis to the inner portion of the test piece 6 with a counter moment being provided to the outer portion of the test piece 6 by the engagement member 502 of the Z-axis force actuator. A second degree of freedom is presented by the test piece supporting pin 21 being moveble in relation to the second support structure 4 and the pin 21 is arranged to pivot in relation to the second support structure 4 around the X-axis. The X-axis torque actuator 7 is arranged to provide movements in the second degree of freedom by pivoting the pin 21 . Thereby, the X-axis torque actuator 7 is arranged to introduce a second load in the form of a moment, more specifically a horizontal torque, as indicated with the arrow a in fig. 5, around the X-axis to the test piece 6 with a counter moment being provided by the engagement member 502 of the Z-axis force actuator. Thereby, the X-axis torque actuator 7 is arranged to provide the torque a around the X- axis, between the inner portion of the test piece 6 and the second support structure 4. Thereby, the torque will be transferred to the test piece 6, and the torque will be provided between the inner portion and the outer portion of the test piece 6. A third degree of freedom is presented by the engagement member 502 of the Z-axis force actuator being moveable in relation to the test piece supporting pin 21 and the engagement member 502 is arranged to move along the Z-axis in relation to the pin 21 . The Z-axis force actuator is arranged to provide movements in the third degree of freedom, to introduce a third load in the form of a vertical force along the Z-axis to the test piece 6 with a counter force being provided by the pin 21 . Thus, the Z-axis force actuator is arranged to provide said force between the first support structure 3 and the outer portion of the test piece 6. It is understood that the third load provided by the Z-axis force actuator is substantially orthogonal to the first and second loads provided by the Y-axis torque actuator 8 and the X-axis torque actuator 7, respectively.

Similarly to the embodiment described with reference to fig. 1 -4, the test rig in fig. 5 provides the advantage that deformations caused by one of the actuators will not affect the direction of the loads of the other actuators. Fig. 6 shows a cross-section of a test rig 1 according to a further alternative embodiment. Coordinate axes X, Y and Z are introduced as indicated in fig. 6. The X-axis and the Y- axis are horizontal and orthogonal, and the Z-axis is vertical and orthogonal to the X and Y-axes. The test rig 1 in this embodiment comprises two actuators, herein referred to as a first actuator 8 and a second actuator 7. The first and second actuators 8, 7 are arranged to introduce respective loads to a test piece 6 in a horizontal plane. The first actuator 8 and the second actuator 7 are for this embodiment also referred to as a Y-axis force actuator 8 and an X-axis force actuator 7, respectively.

Similarly to the embodiments described with reference to fig. 1 -5, the test rig comprises a first support structure 3, which is adapted to be fixed in relation to a supporting element, such as a floor in a test facility. The test rig 1 further comprises a box shaped second support structure 4 connected to the first support structure 3.

The test piece 6, is in this example in the form of a rubber-metal bushing which is generally ring shaped with a hole extending through it. The test piece 6 is mounted so that a centre axis of its hole is substantially parallel, i.e. in line, with the Z-axis. Inside the second support structure 4, an inner portion of the test piece 6 is connected to a connection device 5, in turn connected to the first support structure 3. In this embodiment, there is no actuator introducing loads along the Z-axis, and the connection device 5 is provided as a fixture connecting the test piece with the first support structure 3. The test rig comprises a third support structure 21 in the form of a test piece support device 21 connected to an outer portion of the test piece 6. The extensions 21 1 of the test piece support device 21 extends through respective openings in opposite side walls of the second support structure 4. The X-axis force actuator 7 presents a hydraulic cylinder 701 which is at a first end joined with one of the extensions 21 1 of the test piece support device 21 . The X-axis force actuator 7 further presents a fixture 702 which is fixed to the second support structure 4. The fixture 702 is joined to a second end of the hydraulic cylinder 701 . The second support structure 4 presents extensions 41 1 extending through respective openings in a respective of two side walls of the first support structure 3.

The Y-axis force actuator 8 presents a hydraulic cylinder 801 which is joined at a first end with one of the extensions 41 1 of the second support structure 4. The Y-axis force actuator 8 further presents a fixture 802 which is fixed to one of the side walls of the first support structure 3. The fixture 802 is joined to a second end of the hydraulic cylinder 801 .

The arrangement described with reference to fig. 6 provides the test rig 1 with two degrees of freedom for introducing loads to the test piece 6.

A first degree of freedom is presented by the second support structure 4 being moveable in relation to the first support structure 3 and the second support structure 4 is arranged to move in relation to the first support structure 3 along the Y-axis by means of the connections of the extensions 41 1 to the first support structure 3.

The Y-axis force actuator 8 is arranged to provide a first load, in the form of a horizontal force along the Y-axis to the test piece 6. The force is provided between the first support structure 3 and the second support structure 4, the force having the direction of the first degree of freedom. More specifically, the Y-axis force actuator 8 is arranged to provide movements in the first degree of freedom by moving the second support structure 4 to introduce the force along the Y-axis, via the test piece support device 21 , to the outer portion of the test piece 6 with a counter moment being provided to the inner portion of the test piece 6 by the connection device 5.

A second degree of freedom is presented by the test piece support device 21 being moveable in relation to the second support structure 4 and the test piece support device 21 is arranged to move in relation to the second support structure 4 along the X-axis. The X-axis force actuator 7 is arranged to provide movements in the second degree of freedom by moving the test piece support device 21 . Thereby, the X-axis force actuator 7 is arranged to introduce a second load in the form of a horizontal force along the X-axis to the test piece 6 with a counter moment being provided by the connection device 5.

Thereby, the X-axis force actuator 7 is arranged to provide the force along the X-axis, between the outer portion of the test piece 6 and the second support structure 4.

Similarly to the embodiment described with reference to fig. 1 -5, the test rig in fig. 6 provides the advantage that deformations caused by one of the actuators will not affect the direction of the loads of the other actuator.