GB2167870A - Measuring moments acting upon an object - Google Patents

Abstract

An apparatus for measuring tilting and rolling moments acting on a vehicle in a wind tunnel includes four force-introduction plates (10) each of which supports a wheel of the vehicle. Each force-introduction plate (10) is associated with a respective guide member (12) guiding a respective force-transmission member (18) in a vertical direction, the guide members being connected together by a rigid frame (52). Each force-transmission member (18) is connected to a respective force-introduction plate (10) and acts on a respective force-measuring device (30). In a first object-related mode of operation (Fig. 2), the guide members (12) are attached to the base (16), and the force-transmission members (18) are movable relative to the guide members (12). Wheel loads are measured and moments can be calculated using the distances between the wheels (a1, a2). In a second (apparatus-related mode of operation (Fig. 3), the guide members (12) are released from the base (16) and attached to the force-transmission members (18). Moments are obtained from force measurements and distances b1, b2, <IMAGE>

Description

SPECIFICATION Apparatus for measuring moments acting upon an object under measurement The invention relates to an apparatus for measuring moments acting upon an object under investigation in a flowing medium.

There is known a measuring apparatus for use in a wind tunnel which, in addition to measuring the four vertical forces acting upon the wheels of an automobile, by using the distance apart of the axles and the distance apart of the wheels along each axle can measure the tilting and rolling moments (Mx, My).

Such known measuring apparatus is manufactured and sold by the applicants. The advantage of such an object-related measurement is that the actual wheel forces are measured and that a displacement during the measuring operation does not result in a change in the reading. In this connection it is disadvantageous that the distance apart a1 of the axles and the distance apart a2 of the wheels along each axle are not exactly defined in view of the area of the tyre surface contacting the supporting surface and variations in manufacture.

It is an object of the invention to improve the known apparatus referred to above.

According to the invention there is provided an apparatus for measuring first and second moments acting on an object under investigation in a flowing medium about two axes angularly displaced with respect to each other including a plurality of force introduction plates spaced apart with respect to each other in one plane and arranged to have the object under measurement placed thereon, a plurality of guide members respectively associated with said force introduction plates and supported on a base, each guide member being arranged to guide a respective force transmission member in a direction substantially perpendicular to said one plane, an upper part of each force transmission member being connected to the associated force introduction plate, and a lower part of each force transmission member acting on a respective force measuring device, and a rigid frame which connects together said guide members so as to maintain a fixed positional relationship of said guide members with respect to each other, said guide members being attachable to said base, and said force transmission members being movable relative to said guide members in a first mode of operation, and said guide members being releasable from said base for movement relative thereto and being respectively attachable to said force transmission members for movement therewith in a second mode of operation.

In connection with the measurement of tilting and rolling moments by means of an apparatus in accordance with the invention, the distances between the force transmission members are exactly defined so that variations in the contact areas of the tyres of a vehicle under investigation and variations in manufacture are eliminated from the measurement in the case where the guide members are released from the bases and are attached to the force transmission members. On the other hand, the actual forces relating to the individual wheels may be measured in the case where the guide membes are attached to the base.

Embodiments of the apparatus according to the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is an elevational view, with part of a side wall shown broken away, of a measuring apparatus for use in a wind tunnel, this view showing various details which are not relevant to the present invention and which will therefore not be described; Figure 2 is an enlarged elevational view of a first embodiment of a force transmission and measuring device for use with the apparatus in Fig. 1, said device being shown in a first mode of operation; Figure 3 is a view similar to Fig. 2, but showing said device in a second mode of operation; and Figure 4 is an enlarged elevational view of a second embodiment of the force transmission and measuring device, the device being shown in a mode of operation corresponding to that shown Fig. 3.

Fig. 1 shows an overall view of a measuring apparatus in accordance with the invention for use in a wind tunnel. Four columns 50 are mounted on a rectangular base 16 adjacent the corners thereof, each column 50 being provided with a double eccentric arm 14. Each double eccentric arm 14 comprises a first arm pivotably mounted at one end and a second arm one end of which is pivotably mounted on the other end of the first arm. The four columns 50 are connected to each other by a rigid frame 52 such that the distances of their axes from each other, i.e. b1 in the plane Fig.

1 and b2 perpendicular to the plane of Fig. 1, are exactly defined.

By means of the double eccentric arms 14 four force introduction plates 10 which respectively support the wheels of a vehicle under investigation in the wind tunnel, may be adjusted in position according to the distances apart of the wheels and the axles. The distance apart of the axles is designated by a, and the distance apart of the wheels along each axle is designated by a2.

Considering the verticle components Z1, Z2, Z3, Z4 acting through the individual wheels 70, the tilting moment Mx is as follows: Mx=((Z, +Z2)-(Z3+Z4))Xa1 The rolling moment My is as follows: My=(((Z1+Z3)(Z2+Z4))Xa2 This is for an object-related measurement in which the distance apart of the wheels along each axle and the distance apart of the axles of the vehicle are taken into account.

In order to avoid errors resulting from the area of contact between the tyres of the vehicle and the supporting surfaces and from manufacturing vaiations, an apparatus-related measurement of the moments Mx, My, in which the distances apart of certain parts of the apparatus itself (the axes of the columns 50) are taken into account, and may be performed according to the following equations: Mx=((Z1+Z2)-(Z3+Z4))Xb1 My=((Z1+Z2)-(+Z4))Xb2 However, such an apparatus-related measurement has in the past necessitated a totally different design of the measuring apparatus.

With the present invention it is now possible to perform both an object-related and an apparatus-related measurement with the same apparatus in an extremely simple manner.

Figs. 2 and 3 show a first embodiment of the columns 50 according to the invention. A guide member 12 freely guides for movement in a vertical direction a force transmission member generally designed 18, the upper end of the member 18 supporting a respective double eccentric arm 14 which via a respective force introduction plate 10 supports a wheel 70 of the vehicle under investigation.

By means of the double eccentric arm 14 the position of the force introduction plate 10 may be adjusted in accordance with the distance of the axles and the distance apart of the wheels along each axle of the vehicle. The force transmission member 18 acts on a respective force measuring device known per se, i.e. a force measuring cell 30 which may be a strain gauge device or a piezo-electric pressure sensor. The measuring cell 30 bears against the base 16 via intermediate elements.

As shown in Fig. 2, the guide member is in the form of a hollow cylinder 12, while the force transmission member 18 has a piston 1 8a which, via a hydrostatic bearing, is guided in the hollow cylinder 12. Between the force measuring cell 30 and the base 16 there is a further piston 48 arranged within a hydrostatic bearing in the hollow cylinder 12. The piston 48 is supported by a base plate 32 the lower side of which is preferably in the form of a hydrostatic spherical cap type bearing 34 which is mounted on the base 16. With the mode of operation shown in Fig. 2, the hollow cylinder 12 is securely attached at its lower end to the base plate 32, preferably by being screwed thereon or clamped thereto.A flange 36 on the force transmission member 18 above the piston 1 8a is spaced a short distance from the upper face of the hollow cylinder 12 so that the piston 1 8a may be freely moved in a vertical direction.

The force Z acting through the wheel 70 upon the force introduction plate 10 is directly transmitted through the double eccentric arm 14 and the piston 18a to the force measuring cell 30, such that the individual force Z may be exactly measured by the object-related measurement.

Fig. 3 shows the apparatus-related mode of operation where the lower end of the hollow cylinder 12 is released from the base plate 32 and is spaced a short distance from the latter whilst the upper end of the hollow cylinder 12 is securely attached to the flange 36, for instance by being screwed thereon or clamped thereto.

In view of the rigid connection of the guide members 12 through frame 52, the moment distances b1, b2 are effective which are exactly defined and which therefore result in exact tilting and rolling moments Mx, My.

Fig. 4 shows a second embodiment of the design of a column 50 according to the invention.

In this modification, as compared with the embodiment of Figs. 2 and 3, each hydrostatic bearing is replaced by a parallel lever arrangement. For this purpose a force transmission member 28 is provided with a support portion 28a whose lower end acts upon the respective force measuring cell 30. The support portion 28a is connected to the respective guide member 22 by means of a pivotally attached parallel lever pair 24, resulting in vertical guidance of the support portion 28a.

In similar manner, a lower support element 38 is arranged between the force measuring cell 30 and the base plate 34 which support element is connected to the guide member 22 by a pivotally attached lever pair 26, resulting in vertical guidance of the element 38. Also, the spherical cap type bearing 34 of the embodiment of Figs. 2 and 3 is replaced by a ball bearing 44 so as to provide a point-like bearing relative to the base 16. The mode of operation shown in Fig. 4 corresponds to that of Fig. 3, i.e. an apparatus-related measurement.

Though the guide members 12, 22 are shown to have a cylindrical shape, any other form may be used, the only requirement being that guidance in the vertical direction should be as frictionless as possible. With the embodiments described above there is a direct action upon each force measuring cell 30. Instead of a measuring cell between the parts 18a and 48 or 28a and 38, respectively, a hydrostatic wedge may be provided which acts upon a force measuring cell arranged outside the guide members 12, 22. For this purpose, an opening 76 is provided.

Claims (6)

1. An apparatus for measuring first and second moments acting on an object under investigation in a flowing medium about two axes angularly displaced with respect to each other including a plurality of force introduction plates spaced apart with respect to each other in one plane and arranged to have the object under measurement placed thereon, a plurality of guide members respectively associated with said force introduction plates and supported on a base, each guide member being arranged to guide a respective force transmission member in a direction substantially perpendicular to said one plane, an upper part of each force transmission member being connected to the associated force introduction plate, and a lower part of each force transmission member acting on a respective force measuring device, and a rigid frame which connects together said guide members so as to maintain a fixed positional relationship of said guide members with respect to each other, said guide members being attachable to said base, and said force transmission members being movable relative to said guide members in a first mode of operation, and said guide members being releasable from said base for movement relative thereto and being respectively attachable to said force transmission members for movement therewith in a second mode of operation.

2. An apparatus according to claim 1, wherein said guide members are each of cylindrical shape, and said force transmission members each include a piston portion which is guided within the associated guide member by means of a hydrostatic bearing.

3. An apparatus according to claiml, wherein each force transmission member is connected to the associated guide member by means of double levers so as to be guided for movement relative to the associated guide member.

4. An apparatus according to any one of the preceding claims, wherein between each force measuring device and said base there is disposed a respective support element which is provided with a point or spherical cap-type bearing on to which the respective guide member is arranged to bear.

5. An apparatus according to any one of the preceding claims, wherein each of said introduction plates is adjustable in position in said one plane.

6. An apparatus according to any one of the preceding claims, wherein each force transmission member is pivoted with a means to which the associated guide member may be attached, whereby the lower end of the associated guide member is maintained a predetermined distance from said base.