A test rig

Abstract

There is provided a rig 101 for testing the dynamics of a vehicle axle system. The rig comprises a rig body 102 for supporting the vehicle axle system during testing; an actuation assembly configured

Description

Field of the Invention The present invention concerns rigs for testing the dynamics of a vehicle axle system. More particularly, the present invention concerns axle-level noise, vibration and harshness test rigs. Background of the Invention Automotive noise, vibration and harshness (NVH) test rigs (also known as test benches) are used to test the performance of automotive components, such as drive shafts and axle systems, by simulating road conditions. The data generated from measurements taken using NVH test rigs allow refinement of component design, and troubleshooting during the vehicle lifecycle. Axle level NVH test rigs (known as ANVH test rigs) measure noise, vibration and harshness transmission from the wheel hubs via suspension components into the suspension mounting points. An example of a suggested ANVH test rig for an axle system is the Applicant’s own cuboidal ANVH test rig. The test rig provides actuation in three dimensions, using direct-acting tubular linear servo motors with air bearings, testing up to a natural frequency of approximately 200Hz (when axle system installed). Data output from the rig includes tri-axis load cells at all body attachment points (i.e. where the axle meets the vehicle body), along with accelerometer / strain gauge measurements of the axle links and arms, if required. The front side of the test rig is slidably mounted, and opens from the main frame to allow the axle system to be loaded. Whilst the ability to test up to a frequency of 200Hz provides a market leading solution, it remains desirable to expand the range of frequencies at which the test rig may operate, so that a wider range of road conditions can be simulated. Furthermore, in some known test rigs, loading and unloading the axle system can be cumbersome, and only a certain range of axle sizes can be accommodated. Recent developments have focussed on improving the test rig design. In a development over the cuboidal ANVH test rig, the Applicant has adapted the external shape of the rig to remove unnecessary structure and enable easier access to the test rig. ANVH test rigs are high-value items, and there is a focus on maximising their testing capabilities and ease of use. The present invention seeks to address the aforementioned disadvantages and extend the testing capacity of the ANVH test rig to enable further improvements in noise, vibration and harshness quality in the vehicle passenger compartments. Summary of the Invention In a first aspect, the invention provides a rig for testing the dynamics of a vehicle axle system, the rig comprising: a rig body for supporting the vehicle axle system during testing; an actuation assembly configured to apply forces to the vehicle axle system during testing; and a sensor assembly configured to measure the dynamics of the vehicle axle system in response to the forces applied by the actuation assembly; wherein the rig body comprises a base having an outer structure defining an inner volume, and a support frame; and wherein the inner volume is partitioned by the support frame, into at least two compartments. The inner volume may be partitioned by the support frame, into at least two compartments such that the natural frequency of the rig is increased, preferably to at least 250Hz. The support frame may be a stiffening support frame. A test rig according to the present invention has been found to provide enhanced testing capability, for example enabling measurements of the noise, vibration and harshness response of the axle system over a relatively large frequency range. The inventors have recognised that partitioning (i.e. dividing) the volume inside of the test rig base into at least two compartments, supports and stiffens the overall test rig structure. Compared to test rigs of the prior art having comparable size, the natural frequency of the rig is significantly raised. The first resonant frequency (with axle system and actuators in place) may be raised to at least 250Hz, enabling testing over a greater range of frequencies than has previously been possible, and reducing unwanted vibrations of the rig during testing. The test rig of the present invention may enable a surprisingly high stiffness and hence high natural frequency to be achieved. The data generated on such a rig may allow improved correlation between the modelled and actual characteristics of the axle system, enabling the NVH characteristics of the prototype axle system to be optimised early in the design process. This may avoid the need for expensive and compromised NVH fixes in the production vehicle. The inner volume may have a height of approximately 62-65cm, a width of approximately 303-307cm and a depth of approximately 212-216cm. The support frame may divide the base vertically, which may provide a relatively stiff structure. Some, or all of the compartments may have similar, for example matching or symmetrical, size and shape. The compartments may be empty (i.e. hollow). The support frame may be of multi piece construction, for example it may comprise three pieces bolted together. The support frame may consist of parts which are not directly adjoined to each other. The support frame is preferably adjoined to the base such that it provides a stiffening function for the base. The support frame comprises a tube upstanding in and spanning the inner volume. The tube may be a single tube. In this context “upstanding” means that, when the test rig is positioned ready for use, the tube is oriented vertically within the outer frame. The tube may be a circular cylindrical tube. Such a tube may have an external diameter of approximately 56cm. The tube may have a wall thickness of approximately 40mm. The tube may define a compartment within the tube and a further compartment outside of the tube. The tube may extend across the entire height of the inner volume, providing a complete partition of the inner volume. Thus, the tube preferably structurally connects the uppermost and lowest sides of the outer structure of the base. The tube may meet, or extend into the lowest side of the outer structure. The support frame may comprise a plurality of upstanding tubes, which may be interconnected. The tube may be positioned centrally within the base. A centrally positioned tube has been found to provide especially advantageous strength and support to the test rig, and an increase in stiffness. The support frame may comprise one or more dividing walls. The dividing walls may extend across the inner volume in a lattice arrangement, so that the support frame extends to the outer structure. The dividing walls may structurally connect the uppermost and lowest internal surfaces of the outer structure of the base, thereby strengthening and stiffening the base. The support frame may comprise an upstanding tube, and one or more dividing walls extending radially from the tube. Preferably there are 16 dividing walls. The radially extending dividing walls may meet, or extend into the sides of the outer structure, for example the lowest side of the outer structure. In such an arrangement, the compartments may be defined by the outer surface of the tube, the surface(s) of one or more dividing walls, and the internal surface(s) of the outer structure of the base. In addition, a compartment may be defined by the region internal to the tube. The dividing walls together with the tube preferably provide one or more complete partitions of the inner volume. The radially extending dividing walls are preferably straight-sided walls. The thickness of the walls is preferably approximately 40mm. The radially extending dividing walls may be interspaced evenly around the circumference of the tube. The dividing walls, and tube may provide a rotationally symmetric support frame. Such a support frame may be said to have a “web shape”, or “star shape”. Such an arrangement may advantageously provide especially high stiffness. Some, or all of the dividing walls at their outer edges (for example where they meet the outer structure) may define vertices around the perimeter of the base. In other words, the radially extending walls may meet the vertices / corners of the base, when viewed from above. Preferably, alternate dividing walls define vertices around the perimeter of the base. The support frame may comprise one or more bracing struts between the dividing walls. Such a feature may provide a further increase in stiffness of the test rig, thus further raising the natural resonant frequency, for arrangements having more than one dividing wall. Bracing struts may be provided in one, in several, or in all compartments. There may be one or more than one bracing strut per compartment. The bracing struts may be arranged symmetrically, such that the support frame has rotational symmetry. The rig body may comprise a bridge structure mounted on the base. The actuators may be mounted on the bridge structure. The bridge structure may comprise feet at which the bridge structure adjoins the base structure. In embodiments comprising bracing struts in the support frame, the bracing struts may be located directly beneath the feet of the bridge structure. The bracing struts may be located directly beneath the inner edge of the feet of the bridge structure. Locating the bracing struts in this manner has been found to be especially beneficial because it tends to restrict bending of the base as the bridge deflects under the loads generated during ANVH testing. The support frame may be a solid-walled structure. 5 The support frame may comprise, or more preferably may be formed from a solid-walled structure. In an arrangement in which the support frame extends to the outer structure and the support frame is solid-walled, the compartments may be enclosed or substantially enclosed. In such an enclosed arrangement, the base may be said to have a “cellular” structure. The compartments may be partially open. 10 Alternatively, the support frame may not be solid-walled, for example it may comprise perforated walls. . The outer structure may comprise a top plate, a base plate, and a plurality of intermediate panels disposed between the top plate and base plate. In other words, the sides of the outer structure may include a top plate (the 15 uppermost side), a base plate (the lowest side) and a plurality of intermediate panels (other sides). The intermediate panels may include side panels and lower panels. The top plate may be arranged horizontally when the test rig is in a position ready for use, and the side panels may extend vertically down from the outer edges of the top plate. The side panels may extend down from the lower edges of the side panels at an 20 inclined angle, to meet the base plate. The base plate may be arranged horizontally when the test rig is in a position ready for use. The top plate, base plate and intermediate panels may form a substantially continuous surface. The plates and panels may be joined together by welding. 25 The top plate may be eight-sided. For example the top plate may resemble a truncated rectangle. The corners of the rectangle may be truncated. For example, the top plate may be substantially rectilinear lozenge-shaped. The top plate may be straight-sided. The inventors have recognised that removing extraneous parts of the rig structure (i.e. corners) further 30 raises the natural frequency of the rig, when combined with a compartmentalised base. The outer structure may have eight vertices when oriented ready for use and viewed from above, and the support frame may comprise a tube and sixteen dividing walls, wherein alternate dividing walls extend between the tube and respective vertices of the outer structure. The underside of the top plate may be shaped so as to retain the support frame in place, for example having ridges which surround one or more parts of the support 5 frame. The upperside of the top plate may be a flat surface. The support frame may extend into recesses in the outer structure. For example, the base plate, and / or intermediate panels of the outer structure may contain slots in which the lower edges of the tube and / or dividing walls and / or bracing struts are accommodated, to retain a close fit between the support frame and 10 outer structure. This can provide a stiffer structure, because a more complete full penetration weld is possible. In a second aspect the invention provides a method of testing the dynamics of a vehicle axle system, including the following steps: supporting a vehicle axle system on a rig; applying forces to the vehicle axle system using an actuation assembly; and 15 measuring the dynamics of the vehicle axle system in response to the forces applied by the actuation assembly; wherein the rig comprises a base having an outer structure defining an inner volume, and a support frame; and wherein the inner volume is partitioned by the support frame, into at least two compartments. In a third aspect the invention provides a rig for testing the dynamics of a 20 vehicle axle system, the rig comprising: a rig body for supporting the vehicle axle system during testing; an actuation assembly configured to apply forces to the vehicle axle system during testing; and a sensor assembly configured to measure the dynamics of the vehicle axle system in response to the forces applied by the actuation assembly; wherein the rig body comprises a stiffening support structure within a 25 casing, the stiffening support structure comprising a central cylindrical tube, and a plurality of partitioning walls extending radially therefrom, and the stiffening support structure connecting the inner sides of the casing to provide a plurality of enclosed segments thereby increasing the resonant frequency of the rig body. It will of course be appreciated that features described in relation to one aspect 30 of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa. Description of the Drawings An embodiment of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: Figure 1 is a perspective view of the rig body of an ANVH test rig according to the example embodiment of the invention; Figure 2 is a side view of the multifaceted structure and feet of the base of the ANVH test rig of Figure 1; Figure 3 is a perspective view of the inner support frame of the ANVH test rig of Figure 1; Figure 4 is a close-up perspective view of part of the inner support frame of Figure 3; Figure 5 is a close-up side view of part of the inner support frame of Figure 3; Figure 6 is a perspective view of the inner support frame, multi-faceted body, and ground-engaging feet of the ANVH test rig of Figure 1; and Figure 7 is a bottom view of the base of the ANVH test rig of Figure 1. Detailed Description An axle test rig of the prior art is the Applicant’s own cuboidal ANVH test rig. It has an outer, substantially cuboid frame and is shown with axle system in situ. The frame comprises a rectangular base configured to support the axle system during testing; a rectangular top of approximately similar cross-section in plan view to the base, formed in a 3 x 3 lattice structure; four corner posts extending between the base and top, one comer post positioned at each vertex; four x-shaped support brackets interspaced between the corner posts, each support bracket having two lower arms extending from a central point to the base and two upper arms extending from a central point to the top. Within the cuboid frame, an axle system is mounted on an internal support structure. Fixed to the frame of the axle test rig of the prior art, are six linear actuators. Two vertical actuators mounted on the top of the frame extend vertically through the frame to meet the axle system at either end, at specific attachment points, and four horizontal actuators mounted on the base of the frame extend laterally through the frame, to meet the axle system at the same attachment points. The actuators are positioned to provide an actuating force in three dimensions. Also fixed to the frame (but not visible) are sensors for measuring the axle system response to forces applied by the actuators, during testing. The internal support system along with the front x-shaped support bracket to which it is attached, are movable with respect to the remainder of the frame. Together, the internal support system and front x-shaped support bracket are releasable from a closed position in which the internal support system is fully enclosed in the frame, to an open position in which the internal support system is exposed so that the axle system may be unloaded or loaded into the frame. The movable parts are releasable via a rail and slide fitted to the underside of the top of the frame. The above-described axle test rig of the prior art has a natural frequency, with axle installed, of approximately 200Hz. This places a limitation on the range of parameters which can be tested. A test rig 101 according to the example embodiment of the invention (Figure 1) is an ANVH test rig that seeks to provide an improved rig for measuring the dynamics of a vehicle axle system. The test rig 101 has a rig body 102. The external appearance of the rig body 102 from above, is known in the art, and includes the external surfaces of a base 103, and a bridge assembly 107 which extends from the base 103. The test rig 101 also includes an actuator assembly (not shown in Figure 1) mounted on the bridge assembly 107 and arranged to apply forces to the axle assembly on the test rig 101 in use; and a sensor assembly (also not shown in Figure 1) fitted to the axle assembly to measure the noise, vibration and harshness responses to the applied forces. The actuator assembly includes high frequency linear actuators, which apply precisely controlled motion to the wheel hub of the axle system, at frequencies up to 250Hz. Aspects of the present invention primarily relate to features in the base 103 of the rig, to which reference is now made: The base 103 includes an outer structure 110 supported on four ground-engaging feet 105 (two of which are not visible in Figure 2), and an inner support frame 104 (the inner support frame is not shown in Figure 2 but is shown and described in more detail with reference to Figures 3-7). The outer structure 110 comprises a top plate 109 with flat upper surface 108, mounted on a multi-faceted body 114. The top plate 109 has a thickness of approximately 40 mm, suitable for supporting the weight of the axle assembly. The bridge assembly 107 comprises a main bridge 111 having an upper beam 112, and three legs 113, extending from a central region of the upper beam 112 towards the base 103. The bridge assembly 107 also comprises a fourth leg 115 which is detachable from the main bridge 111 and slides relative to the base 103 along the plane of the upper surface 108 of the top plate 109. The fourth leg 115 moves from a “closed configuration” (shown in Figure 1) in which the axle assembly when in situ, is retained in the test rig 101 in the space between the bridge assembly 107 and base 103, to an “open configuration” in which the axle assembly can be removed from the test rig 101. The fourth leg 115 is unbolted, and lifted away by crane or forklift. The multi-faceted body 114 of the outer structure 110 of the base 103 (Figure 2) comprises a plurality of upstanding side panels 137, supported on a plurality of lower panels 139 angled inwardly (in the present example embodiment, there being eight side panels and lower panels), and a base plate 141. The ANVH test rig 101 of the example embodiment of the invention enables a wide range of vehicle sub frame assemblies to be loaded and fixed to the frame with custom mounts. The inner support frame 104 of the base 103 (Figure 3) is not known in the art, and enables the rig 101 to have a relatively high natural frequency, especially when used in combination with the shape of the outer structure 102. The inner support frame 104 of the present example embodiment comprises a central upstanding cylindrical tube 117 of external diameter 56cm, and a plurality of radially extending walls 119 disposed around the outer circumference of the tube 117. In the present example embodiment, sixteen walls 119 are spaced evenly around the outer circumference of the tube 117. The number of walls being sixteen was found to provide an optimal balance between stiffening the structure, whilst remaining practical to manufacture. The inner support frame 104 also comprises a plurality of bracing struts 121 positioned laterally, in the gaps 123 between adjacent walls 119. In the present example embodiment, eight bracing struts 121 are arranged to occupy pairs of adjacent gaps 123, facing towards the front, rear, and left and right sides of the support frame 104. In other words, each pair of bracing struts 121 is directly opposite another pair of bracing struts 121, and oriented at 90 degrees to each of the two adjacent pairs of bracing struts 121. The bracing struts are arranged symmetrically, to provide a balanced and symmetrically stiff structure. Towards the front and rear of the support frame 104 (i.e. where the walls 119 are shortest) a pair of bracing struts 121 is positioned laterally across each shortest wall (i.e. with one strut 121 on either side of each shortest wall 119). The struts 121 are positioned approximately half way along the length of each shortest wall, which corresponds to the location at which the front and rear legs 113, 115 of the bridge 107 meet the base 103. Towards the left and right sides of the support frame 104 (i.e. where the walls 119 are longest) a pair of bracing struts 121 is positioned laterally across each longest wall (i.e. with one strut 121 on either side of each longest wall). The struts 121 are positioned approximately two thirds of the way along the length of the longest wall, measured from the central tube 117 towards the outer structure 110 of the base 103. This corresponds to the location at which the left and right legs 113 of the bridge 107 meet the base 103. Having the bracing struts located beneath the legs of the bridge (and especially beneath the inner edges of those legs) has been found to be especially beneficial because it tends to restrict bending of the base 103 as the bridge deflects under the loads generated during ANVH testing. The tube 117, walls 119 and bracing struts 121 together provide a rigid steel structure. Respective parts are joined to one another by welds, or other standard techniques known in the art. The walls 119 are joined to the tube along almost all of the height of the tube 117. The upper surfaces 125 of the walls 119 (Figure 4) are flush with the upper surface 127 of the tube 117, to meet the underside of the top plate 109 (not shown in Figure 4). The inner top comer 129 of each rib 119, where the rib 119 adjoins the tube 117, is cutaway so that there are a series of divots / grooves adjacent the upper perimeter of the tube 117. This helps to locate the inner support frame 104 with respect to the top plate 109, thus fixing the inner support frame 104 in place within the outer structure 102 in use (top plate 109 and outer structure 102 not shown in Figure 4). The bottom end 131 of the tube 117 (Figure 5) extends beneath the lower surfaces 133 of the walls 119, whilst the inner bottom comer 135 of each rib 119 is also slightly cutaway, providing a series of divots / grooves adjacent the lower perimeter of the tube 117. The support frame 104 is situated within the base 103 of the test rig 101 (Figures 6, 7), occupying the void (i.e. the inner volume) between the top plate 109 (not shown in Figures 6, 7) and the multi-faceted body 114. The walls 119, together with the top plate 109 and multi-faceted body 114 define a plurality of enclosed compartments 143. The walls 119 interconnect the top plate 109 and the base plate 141, side panels 137 and lower panels 139, thereby increasing the stiffness of the base 103 and the rig 101 overall. Each respective compartment 143 is bordered by the exterior surface of the tube 117, the interior surface of the respective side panel 137 and lower panel 139, the interior surface of the base plate 141, and the underside of the top plate 109. In the present example embodiment of the invention there are sixteen such compartments 143, eight of them being further subdivided into two subportions 145 by the bracing struts 121. There is a further compartment 147 inside of the tube 117. The base 103 is symmetrical. In use, the inner support frame 104 strengthens, supports and stiffens the test rig 101, thereby increasing the natural frequency of the test rig 101. This enables NVH testing of an axle system at frequencies up to 250Hz, such high frequencies having not been previously achieved. Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described. In an alternative embodiment the inner support frame comprises a non-circular cylindrical tube. In an alternative embodiment, the support frame comprises only a tube, and no walls or bracing struts, thereby defining a first compartment inside of the tube, and a second compartment outside of the tube. In an alternative embodiment, the support frame comprises only dividing walls, and no tube. In an alternative embodiment there are more than eight dividing walls, for example 10 or 12 dividing walls. In an alternative embodiment there are less than eight dividing walls, for example 4 or 6 dividing walls. Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent CM claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

1. A rig for testing the dynamics of a vehicle axle system, the rig comprising: a rig body for supporting the vehicle axle system during testing; an actuation assembly configured to apply forces to the vehicle axle system during testing; anda sensor assembly configured to measure the dynamics of the vehicle axle system in response to the forces applied by the actuation assembly;wherein the rig body comprises a base having an outer structure defining an inner volume, and a support frame; andwherein the inner volume is partitioned by the support frame, into at least two compartments, andwherein the support frame comprises a tube, upstanding in and spanning the inner volume.

152. A rig according to claim 1, wherein the tube is positioned centrally within the base.

3. A rig according to any preceding claim, wherein the support frame comprises one or more dividing walls.

4. A rig according to claim 3, wherein the support frame comprises one or more bracing struts between the dividing walls.25 5. A rig according to any preceding claim, wherein the support frame is a solidwalled structure.

6. A rig according to any preceding claim, wherein the outer structure comprises a top plate, a base plate, and a plurality of intermediate panels disposed30 between the top plate and base plate.

7. A rig according to claim 6, wherein the top plate, base plate and intermediatepanels form a substantially continuous surface.

8. A rig according to claim 6 or 7, wherein the top plate is eight-sided.

9. A rig according to claim 8 when dependent on claim3, wherein the outer5 structure has eight vertices when oriented ready for use and viewed fromabove, and the support frame comprises sixteen dividing walls, wherein alternate dividing walls extend between the tube and respective vertices of the outer structure.10 10. A rig according to any of claims 6-9 wherein the underside of the top plate isshaped so as to retain the support frame in place.

11. A rig according to any preceding claim wherein the support frame extends into recesses in the outer structure.1512. A method of testing the dynamics of a vehicle axle system, including the following steps:CM supporting a vehicle axle system on a rig;£\J applying forces to the vehicle axle system using an actuation assembly;"T” 20 andO) measuring the dynamics of the vehicle axle system in response to the1 forces applied by the actuation assembly;wherein the rig comprises a base having an outer structure defining an inner volume, and a support frame;25 wherein the inner volume is partitioned by the support frame, into atleast two compartments andwherein the support frame comprises a tube, upstanding in and spanning the inner volume.30 13. A rig for testing the dynamics of a vehicle axle system, the rig comprising:a rig body for supporting the vehicle axle system during testing; an actuation assembly configured to apply forces to the vehicle axle system during testing; anda sensor assembly configured to measure the dynamics of the vehicle 35 axle system in response to the forces applied by the actuation assembly;CMwherein the rig body comprises a support structure within a casing, the stiffening support structure comprising a central cylindrical tube, and a plurality of partitioning walls extending radially therefrom, and the stiffening support structure connecting the inner sides of the casing to provide a plurality5 of enclosed segments thereby increasing the resonant frequency of the rigbody.

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