Testing apparatus

A testing apparatus is provided that includes a carrying construction for supporting a road section, and a frame for positioning a test wheel on the surface of the road section. During operation of the apparatus the test wheel, by a tread thereof, describes a circular path over the road surface. The frame is provided with a sensor for measuring a force exerted on the measuring wheel by the road surface.

The invention relates to a testing apparatus, comprising a carrying construction for supporting a road section, and a frame for positioning a test wheel on the surface of the road section, such that during operation of the apparatus the test wheel, by a tread thereof, describes a circular path over the road surface.

Such a testing apparatus is known from, for example, U.S. Pat. No. 4,938,055. In that apparatus, the measuring wheel rides on an annular road section to simulate wear of a type of road surfacing resulting from road traffic. Deformation of the annular road section can be established by inspection after the road section has been loaded by the test wheel for a period of time.

To enable sound investigation on the interaction between road surface and tires of vehicles riding the surface, the need arises to obtain a testing apparatus whereby measurements become available in a systematic manner.

The object of the invention is to provide an improved testing apparatus of the type indicated in the opening paragraph hereof. In particular, the object of the invention is to obtain a testing apparatus according to the opening paragraph hereof that, with preservation of the basic principle of the construction, allows measurements to be generated in a systematic manner. To this end, the frame for positioning the test wheel is further provided with a sensor for measuring a force exerted on the test wheel by the road surface.

By providing the frame with a sensor for measuring the force that the road surface exerts on the test wheel, in a systematic manner measuring data can be obtained for analysis of the interaction between the test wheel and the road surface. Moreover, the measurements can be generated concurrently with the loading of the road surface. Thus, a test of the road surface can be simultaneously combined with investigations on physical changes occurring on the test wheel during the test. Undesirable interruptions during the test can thus be reduced or wholly eliminated.

In this connection, the “force exerted on the test wheel by the road surface” is understood to mean the force buildup which the test wheel experiences from the road. Preferably, all components of the force exerted on the test wheel are determined.

Consequently, a measurement can, in principle, be performed instantaneously, continuously and over the complete driving surface of a road test piece, during the whole testing cycle.

Preferably, the sensor is integrated into the carrying arm, so that a robust and simple construction is obtained for positioning the test wheel and carrying out measurements on the test wheel. With advantage, use is made here of the insight that the force exerted on the test wheel by the road surface is wholly transmitted through the carrying arm, so that deformations on the carrying arm are directly related to the force-to-be-measured on the test wheel.

By positioning the sensor in a local reduction of the carrying arm, relatively slight movements in the carrying arm, such as bending and torsion, can be observed, while the carrying arm as a whole yet forms a firm entity.

In a preferred embodiment according to the invention, the sensor comprises a strain gauge, so that with relatively inexpensive means an accurate measurement of the force on the test wheel can be obtained.

Optionally, the angle of the test wheel axle with respect to the circular path on the road surface is settable. The test wheel can then be oriented such that there is a so-called slip angle. In this way, various practical situations can be simulated, for example, taking a bend. Also, an artificial, accelerated wear of the road surface can be generated.

The invention also relates to a method.

Further advantageous embodiments of the invention are represented in the subclaims.

The figure is only a schematic representation of a preferred embodiment of the invention. In the figures, identical or corresponding parts are indicated with the same reference numerals.

FIG. 1shows an embodiment of a testing apparatus1according to the invention. The apparatus1has a carrying construction2for supporting a road section3. Also, the apparatus1has a partly shown frame4for positioning test wheels5a-con the surface6of the road section3. The frame comprises carrying arms7a-c. On each carrying arm7a test wheel5is rotatably mounted.

The carrying construction2comprises a drive for rotatably driving the road section3. During operation of the apparatus1the road section3turns in a rotational direction B about a central axis A. The carrying arms7place the test wheels5, also called measuring wheels, on the road surface6, so that the wheels5, through the contact with the road surface, rotate about their axles8a-c. Doing so, the measuring wheels5, by their treads9a-c, describe circular paths10a-cover the road surface6. The revolving of the road section simulates the passage of a vehicle over the road. As the measuring wheels5each follow their own track on the road surface6, a relatively large part of the surface6can be utilized for testing road surfacing and/or measuring wheel. Moreover, concurrently, different types of measuring wheels can be tested. In addition, the use of a plurality of measuring wheels5provides the advantage that the carrying construction2is loaded more evenly. In a preferred embodiment according to the invention, the positions of the test wheels are substantially proportionally distributed in the rotational direction B of the road section3.

The frame4for positioning the measuring wheels5is furthermore provided with a sensor11for measuring a force exerted on a test wheel5by the road surface6. In the embodiment shown, the apparatus1comprises a plurality of sensors per wheel5. By the use of two or more sensors, different orientations of the force exerted on the wheel5can be measured. The sensors11are integrated into the carrying arms7. To this end, each carrying arm7is provided with one or a plurality of local reductions or recesses12in which the sensor11is received. The reductions or recesses12are so dimensioned that realistic forces that are being exerted on the measuring wheel5lead to minimum deformations of the carrying arm adjacent the reduction or recess which are reproducibly measurable with the sensors. Naturally, the carrying arms may also be realized without local reductions or recesses, so that a construction that is simpler to manufacture is obtained. The extent of deformation of the carrying arm is a measure of the load to which the test wheel is subjected. Accordingly, by measuring the deformation of the carrying arm, the loading on the test wheel can be determined. Thus, an accurate and reliable measurement can be realized, while yet a robust construction is used. In principle, the sensors11may be arranged separately, as an alternative embodiment to an integration into the carrying arm. By arranging a plurality of sensors11a-bat different positions in a circumferential direction R about a carrying arm7, an adjustment of the carrying arm7can be measured in different orientations. In the embodiment shown, the carrying arm7in cross section has a substantially rectangular profile. On each of the four profile parts12a-12da sensor11is arranged. InFIG. 1two sensors11a-bare visible in the carrying arm7aat the front, right.

The sensors each comprise a strain gauge. Naturally, other embodiments of force sensors are also applicable. Furthermore, accuracy and reliability of the force measurement can be raised considerably by periodically calibrating the sensors.

The sensors make a continuous, ongoing and at the same time accurate measurement possible, while a good signal-to-noise ratio can be achieved, both of the vertical force component to be registered and of the horizontal force components to be registered.

It is noted that the sensors may also be arranged at different locations on the frame, for example, on a junction between the carrying arms and a central coupling piece. Furthermore, the sensors may be positioned and/or oriented in a different manner, for example, arranged on the same profile part12a-d, but with a mutually different orientation.

The carrying arms7are provided with a hinge element13a,cfor pivoting the axis8of the measuring wheel5about a pivoting axis D, see the left-hand carrying arm7cinFIG. 1, with respect to the circular path10at the road surface6. Thus, the angle of the test wheel axis8is settable with respect to an instantaneous direction of movement of the test wheel5.

Furthermore, the wheels5are preferably detachably mounted to the carrying arms, so that replacement by other specimens can easily be carried out.

FIG. 2shows a schematic perspective top plan view of a carrying construction2of the testing apparatus1. The carrying construction2comprises a turntable20, rotatable about the central axis A and having an upstanding edge21, for receiving a road section3. Through the construction with the upstanding edge21, a cavity is formed, so that the received road section3can be confined in circumferential direction. Preferably, the road section3is detachably arranged as a separate module on the carrying construction2. Owing to the modular structure, the road section3can easily be replaced by another specimen after a test. Also, the testing apparatus1is thus flexibly deployable for different kinds of road sections.

By great preference, the road section3is substantially disk-shaped, so that the section can easily be received on the turntable20. By virtue of the disk shape, advantageously, the road surface6can be optimally utilized during rotation of the disk. However, in principle, a different type of geometry is applicable, for example, a square section.

The turntable20is provided with supporting points22a-dfor supporting the discrete road section3. Furthermore, the turntable20comprises a central attachment point23by which the road section3can be secured to the turntable20.FIG. 1shows a central nut14which cooperates with the central attachment point23for locking retention of the road section3. It will be clear to those skilled in the art that also other attachment constructions may be used. Optionally, the turntable20is provided with one or a plurality of openings24a,bfor pushing up a road section3to be removed. Furthermore, the turntable20is mounted on a central driving shaft25for driving the turntable20for rotation.

FIG. 3shows a schematic perspective top plan view of a first frame part4afor positioning the test wheels5. The carrying arms7a-care mounted on a star-shaped frame element having three arms27a-cwhich extend radially from a central part27d. The central part forms a common central coupling piece which can be detachably mounted to a pressure frame. Preferably, the coupling piece27dcomprises a pressure sensor for measuring a static pressure which is exerted on the wheels via the pressure frame. Also, the coupling piece may be provided with a homokinetic coupling, thereby allowing correction for a difference in diameter of the individual wheels.

FIG. 4shows a schematic perspective top plan view of a second frame part4bfor positioning the test wheels5. The second frame part4bforms a pressure frame for pressing the wheels5onto the road surface6. The pressure frame4bcomprises a coupling part28for coupling with the coupling piece27dof the first frame part4a, and a frame structure29which connects the coupling part28with a plate30. The plate may be anchored, but preferably in such a way as to allow an adjustment in substantially vertical direction, for example, with a vertical guide rail construction. Furthermore, the coupling part28is preferably adjustable in the substantially horizontal plane, so that the coupling part can be positioned straight above the central axis A of the carrying construction2of the road section3.

By the use of a modular, detachable structure, individual parts can easily be exchanged. Especially regarding parts that are subject to relatively high wear, this provides advantages, because the testing apparatus is thus rendered highly deployable and offers a high flexibility with regard to different types of road sections and test wheels.

FIG. 5shows a schematic top plan view of a test wheel5in the testing apparatus1ofFIG. 1. The test wheel5is positioned on the road surface6of a road section3at a preferably infinitely variable angle with respect to the path that the test wheel5travels on the circular track of the road surface. The wheel5is placed slightly obliquely with respect to the local direction of travel of the wheel5with respect to the road surface6. Thus the axis8of the wheel5makes a small angle α of about 10° with respect to the local radial direction Rad from the central axis A of the carrying construction2. Through the oblique arrangement of the wheel5, slip arises. The force Ftotexerted by the road surface6on the wheel in horizontal direction comprises a pure rolling force component Froland an axial force component Fax. Adjacent the sensors in the carrying arm7, this results in a second axial force Fax′, which is built up from a compression force Fcompand a bending force Fbuig. Thus, from the measured forces in the carrying arm, the force buildup which the wheel5experiences from the road surface6can be derived.

The testing apparatus can be used as a relatively compact and robust machine for simulating all sorts of practical circumstances of a road surface. Thus, the road segment may be tested dry or wet, possibly at different water film levels, and at various temperatures. The apparatus is deployable for carrying out measurements on a variety of types of road surfacing, for example, asphalt, concrete and paving bricks, as well as on rubber mixtures of car and truck tires. Thus, diverse parameters may be investigated, for example, skid resistance, course of skid resistance per vehicle passage, rutting, course of rutting per vehicle passage, fraying, and rate of rubber wear.

By placing the wheels obliquely, as described above, and by placing the wheels on the road surface with a particular pressure, at the same time the skid resistance and the interplay of forces in the contact interface between wheel and road surface can be measured. The extent of rutting may be determined by a separate measurement, whereby preferably the height of the whole testable surface up to the road surfacing is scanned, for example, with the aid of a laser measurement. Also fraying of the road surface can thus be determined. Furthermore, a rubber wear rate can be determined by correlating the amount of worn-off rubber of tires fitted on the measuring wheels to the number of revolutions of the road section.

The testing apparatus can be operated safely, remotely and simply, while reliable measurements can be obtained simultaneously. The elegant use of the force sensors allows an accurate and reliable three-dimensional force determination in the contact surface between the test wheels and the road surface. Both horizontal and vertical forces can be measured. Also torsional and shearing forces can be determined. Furthermore, the measurement is in principle independent of the extent of wear in rubber and/or surfacing surface.

The invention is not limited to the exemplary embodiments described here. Many variants are possible.

Instead of a singular carrying arm, the frame may comprise a different component for rotatably mounting a test wheel. Thus, the frame can comprise a sheet metal work or a subframe having a plurality of segments, to which the test wheel is attached.

Furthermore, the testing apparatus1can comprise a different number of test wheels5, such as more than three test wheels, for example, four or more test wheels, or fewer than three test wheels, for example, two test wheels or just one test wheel.

In use of the testing apparatus according to the invention, the wheels roll over the road surface of the road section. For inducing the rolling movement, the turntable turns about the central axis. In an alternative embodiment, the wheels are driven for rotation and the turntable stands still. The embodiment described with reference to the drawing is advantageous in that not only a simpler construction is obtained but also the moving parts can be screened better, which promotes safety. It is noted that also a combination of the two principles is possible, whereby both the turntable and the frame carrying the wheels rotate.

Also, optionally, the force that the test wheel exerts on the surface of the road section, at least a component thereof, for example, a vertical component, may be set. In this way, a real, settable axle pressure can be simulated. On the basis of the vertical force exerted on the test wheel, which is determined with the sensor measurement, a feedback loop may be realized for the force by which the test wheel is pressed onto the road surface. The value of the measured vertical force is then compared with a preset value. Based on the comparison, the force exerted via the test wheel on the road section can be adapted. In this way, a constant axle pressure can be simulated, independently of wear and/or deformation of the road surfacing and/or the test wheel.

In addition, the testing apparatus may be provided with units that influence the physical properties of the road section. Such units may comprise, for example, a moisturizing installation and/or a freezing installation. Thus, meteorological conditions can be imitated.

Such variants will be clear to those skilled in the art and are understood to be within the scope of the invention, as set forth in the following claims.