DE102014207929B3 - Device for aerodynamic measurement on pantographs - Google Patents

Abstract

The invention relates to a device for aerodynamic measurement of pantographs, wherein a force sensor is used, which is fastened via a holder to a crossbar of the current collector. The invention has for its object to develop a device which makes it possible to detect the forces acting on a current collector two-dimensional, with static and thermal errors to be minimized. This is inventively achieved in that on the holder, a measuring body is attached to which an extension designed as a support arm with a shrink tubing coated metal tube is mounted on the end of a holes exhibiting round body (ball screen) is arranged, wherein on the holder and order the measuring body and the metal tube, a jacket tube (sleeve) coated with a shrink tubing is arranged, which ends at a distance in front of the round body (spherical sieve).

Description

The invention relates to a device for aerodynamic measurement of pantographs, wherein a force sensor is used, which is fastened via a holder to a crossbar of the current collector.

The maximum speed of high-speed, fast electric rail vehicles will be reduced. a. characterized in that the vibrations stimulating the pantograph increase in amplitude with increasing speed. Therefore, from a certain limit speed on the one hand no continuous contact between the pantograph and catenary can be guaranteed, on the other hand, it may exceed the permissible contact force between the pantograph and contact wire, which lead to a significantly increased wear of the contact points of the pantograph. This speed limit depends primarily on the rigidity ratios of the system pantograph / catenary or the external forces exerted on this system (mass forces from moving vehicle body, aerodynamic forces, driving line excitation by multiple traction, etc.).

Conventionally, one tries to increase the limit speed by increasing the rigidity of the overhead line, eg. B. by reducing the mast spacing or increasing the cable cross-section. However, this requires a high design effort, because this measure must be subjected to whole sections.

The changes in the contact force u. a. also caused by changes in the aerodynamic load of the pantograph.

To regulate the contact force between pantograph and contact wire, it is also known to provide a fiber optic transmitter below the contact strip, which controls as a threshold when falling below a predetermined contact force a lifting device with which the contact force is amplified ( DE 38 31 177 A1 ).

For infrastructure managers responsible for the overhead contact line, it is of great interest to be able to record the interaction between the overhead contact line and the corresponding rail vehicles in order to prove compliance with the applicable regulations and, if necessary, in case of contact force overshoots or contact force losses to be able to readjust.

To assess the interaction of pantograph / overhead contact line, a force measuring procedure can be used according to EN 50317. This measuring method must indicate the forces acting on the contact point of the contact strip / catenary. However, none of the known measuring methods is able to measure the contact point directly. In any case, a correction of the occurring error by means of aerodynamic correction values is required.

From the DE 10 2009 036 963 B4 a method and a device for measuring the contact force between a pantograph and a catenary under the influence of aerodynamic force components known, the aerodynamic forces are detected by a direct determination of the contact forces between the contact surface of the pantograph and the catenary by measurement in the contact strip.

The WO 03/031989 A1 includes a sensor for measuring the speed and the direction of the wind in a single unit. It consists of a mounting foot, a metal rod with a circular cross section is arranged in a vertical position, a ball at the top of the rod. When the wind brings in its force on the spherical surface, the sensor undergoes deformation in proportion to the speed of the wind. The extension and / or deformation of the detectors is measured and connected to an electronic circuit of the system and the signal.

A similar device is used in the US 3,217,536 A described.

From the DE 2 256 558 A a wind measuring device is known, wherein a wind-sensitive, held by a mounting member, an attached to the mounting part inductive Meßaufnehmerelement and a flexible support for the fastening part is arranged, wherein in operation, the flexible support is deflectable and an output signal from the inductive pickup element derivable which is proportional to the speed of the wind acting on the wind-sensitive element.

All known solutions have in common that a simple and effective measurement of the flow velocity and the direction is not realized.

The invention has for its object to develop a device which makes it possible to detect the forces acting on a current collector two-dimensional, with static and thermal errors to be minimized. This is inventively achieved in that
on the holder a measuring body is attached to the extension as a support arm a trained with a heat-shrink tube covered metal tube is mounted, is arranged on the end of a holes having round body (ball screen), wherein on the holder and the measuring body and the metal tube, a sleeve coated with a heat shrink tube (sleeve) is arranged, which at a distance the round body (ball screen) ends.

In principle, in this sensor by means of strain gauges, the flow-induced force is measured on a ball and replaced in relation to the velocity of the flow.

In the case of a turbulent flow theoretically: F = 1 / 2c · A · ρ · ν ² (F = force, c = resistance, A = projection surface of the body, ρ = air density, ν = speed)

λ

– beschreibt die Abweichung von den Normalbedingungen des strömen den Mediums Luft.

K

– ist dimensionsbehaftet und beschreibt die strömungsmechanischen Eigenschaften des Messaufnehmers.

In the equation only A can be assumed to be constant. The resistance coefficient c is due to different vortex formation just inconsistent with spherical bodies. By the sieve-like boring the constancy should be enforced. Inconstancy is also present in the air density ρ: it is a function of temperature, humidity and air pressure. An exact calibration value can therefore only be specified with reference to defined conditions and determination of the variables prevailing during the measurement. With the normal density ρ _N and the dimensionless quantity λ = ρ / ρ _N , the formula is F = 1 / 2c · A · ρ _N · λ · ν ² = K · λ · ν ²

λ

- describes the deviation from the normal conditions of the flow of the medium air.

K

- is dimensioned and describes the flow-mechanical properties of the sensor.

If this force is measured by means of a square cross-section with strain gauges using the bending beam principle, then a rectangular coordinate system can be assigned. The measured values F _x and F _y represent an orthogonal decomposition of the total force F: F _x = F · cos α F _y = F · sin α

und für den Winkel:

Assuming that the direction of the velocity vector V of the air flow with the direction of the force vector F with reference to Appendix 3 for the absolute value of the flow velocity with the measured values F _x and F _y :

and for the angle:

The orthogonal decomposition of velocity is: V _x = V · cos α V _y = V · sin α

A possible force and speed component in the z-direction is suppressed due to the arrangement of the strain gauges: the sensor measures the flow velocity in the x-y plane as a 2-component sensor.

Advantages of the invention

• • The sieve-like structure of the hollow sphere makes it possible to make their air resistance independent of the flow velocity
• • An electrical circuit of the force sensor reduces static and thermal errors
• • The optimized version of the hollow ball support arm leads to improved rigidity and reduced natural frequency fluctuations
• • the cover of the measuring body and of the force sensor through the jacket tube considerably reduces the distorting influences of the air flow
• • the use of aluminum alloys, preferably of duralumin, ensures a low weight and high strength
• • To avoid self-oscillations, the support arm and the jacket tube are covered with shrink tubing

LIST OF REFERENCE NUMBERS

1

Round body (spherical sieve)

2

Beam

3

Jacket tube (sleeve)

4

thread

5

measuring body

6

Strain

7

thread

8th

bracket

9

screw

10

Tragarmende

11

holes

embodiment

The invention will be explained below with reference to an embodiment.

Showing:

1 - the device in view

2 - The device in a spatial representation

3 - The device in cross section

4 - The device in longitudinal section

5 - the mode of action of the measurement

The holder designed as a base plate 8th is on a crossbar of the pantograph over screws 9 attached ( 1 ). On the bracket 8th is preferably a thread over 7 the jacket pipe 3 fastened, in which the measuring body 5 is arranged. Of course, the jacket tube 3 also about other suitable fastening systems on the bracket 8th be attached. The measuring body 5 preferably has strain gauges 6 on. To the strain gauge 6 Alternatively, piezocrystals can be used. On the measuring body 5 is preferably a thread over 4 the support arm 2 attached. The support arm 2 can also use alternative types of attachment on the measuring body 5 be attached. The support arm 2 is in its lower part in the jacket tube (sleeve) 3 guided. Beam 2 and casing pipe 3 have a coating of a shrink tube. After exit of the support arm 2 from the jacket pipe 3 follows a freestanding area. At the end of the arm 10 is the round body 1 as a colander with holes 11 arranged. It is used to record the air flow and to measure the flow-causing force in relation to the velocity of the flow.

Measuring principle: Bending moment measurement on square measuring body 5 by means of two strain gage full bridges; a flow acting in the transverse plane calls on the sieve 1 a force whose components are detected. To reduce the static and thermal error, a resistor and a temperature sensor are individually integrated in the circuits.

Measuring body: The carrier of the DMS 6 is designed to be stretched less than 500 μm / m even at maximum speed; this guarantees a service life of> 10 ⁷ load changes.

The bracket bolted to the measuring arm 2 of the ball strainer 1 is optimized in terms of stiffness and natural frequency. To dampen the natural vibration behavior, it is covered with a shrink tube. The length can vary between 89 mm and 109 mm. The measuring body 5 and a large part of the support arm 2 are through the screwed jacket tube 3 covered, so that the falsifying influence of a velocity gradient is kept small in the vicinity of the attachment.

Ball sieve: A round body (∅ 37.7 ± 0.2 mm) was drilled in a sieve-like manner to a filling degree of 0.6 to 0.8. The diameter of the holes is preferably 1.8 mm.

The measuring bodies 5 were calibrated in a simple manner by weight load on ε = 0.1 V / N and ε = 0.08 V / N (long arm and short arm). The measurement uncertainty was ± 1.1% with respect to the largest load 50 N. The load was carried out on the support arm 2 in the middle between the two ball mounts.

The wind tunnel tests were used to check the basic function and to detect any systematic errors. In particular, the constancy of the flow-mechanical quantity K, which depends on the design of the spherical sieve, was of interest 1 , the support arm 2 and the jacket tube 3 depends. In addition, the angular dependence of the measured values was checked, which was also influenced by the fluidic design and additionally by the precision of the measuring body 5 depends. For this purpose, the transducer was placed on a tripod head with angle division in the wind tunnel.

It turns out that only the 50 km / h stage has larger deviations. This can be explained by the fact that the metrological resolution of the present measuring system, which was designed for speeds up to 400 km / h, is insufficient for such low speeds. For the speeds of 100 km / h and 150 km / h, the measured values obtained are very well within the framework of the expected random errors. A change of K between 100 km / h and 150 km / h can not be seen. The same applies to the comparison of the two sensors: a total average value for λ · K of 0.53 · 10 ^-3 N / ( m / s ) ² , with maximum deviations of the measured values of less than + 2%.

Assuming that K remains constant even at very high speeds and with a 25% increase for λ, the measured values result in an extreme load of the ball of 8.2 N for 400 km / h. This is within the precalculated values with low stress on the strain gages 6 ; the ball strainer 1 and their attachment likely to withstand this burden.

A contribution to the dynamic error arises from bending natural oscillations (resonances) of the sensor acting on the strain gages 6 be transmitted. Essential is the 1st natural bending vibration, since it determines the possibilities of metrological processing with the largest strains and the lowest frequency.

Another contribution to the dynamic error results from vibrations of the support arm 2 to which the sensor is placed. The sensor's grounded arm causes a response to accelerations. With respect to the center of the sphere, calculation is to be carried out with a response of 0.1 N / g for the long arm and 0.08 N / g for the short arm. These values can be achieved by using aluminum for the support arm 2 reduce by about 60%. The effort for correction by mitgemessene acceleration is too high; rather, attention should be paid to low vibration tendency when choosing the attachment points on the pantograph.

Claims (9)

Device for aerodynamic measurement on pantographs, wherein a force sensor is used which is fastened by a holder to a crossbar of the pantograph, characterized in that on the holder ( 8th ) a measuring body ( 5 ) is attached to the extension as a support arm ( 2 ) is formed with a shrink tubing coated metal tube, over the end ( 10 ) a round body having holes ( 1 ) is arranged, wherein on the holder ( 8th ) and around the measuring body ( 5 ) as well as the support arm ( 2 ) a jacket tube coated with a heat shrink tubing ( 3 ) is arranged, which at a distance in front of the round body ( 1 ) ends. Apparatus according to claim 1, characterized in that the measuring body ( 5 ) has a force sensor mounted on a fixed base. Apparatus according to claim 2, characterized in that the force sensor from strain gauges ( 6 ) or piezocrystals. Device according to claim 1, characterized in that the round body ( 1 ) has a degree of filling of 0.75. Apparatus according to claim 1, characterized in that the jacket tube ( 3 ) is composed of an aluminum alloy. Device according to claim 1, characterized in that the support arm ( 2 ) consists of metal or a material with comparable properties. Apparatus according to claim 1 and 2, characterized in that in the measuring body ( 5 ) a temperature sensor and a resistor are arranged. Device according to claim 1, 2 and 7, characterized in that the support arm ( 3 ) is connected via a thread or another type of connection with the measuring body. Apparatus according to claim 1 and 2, characterized in that the jacket tube ( 3 ) via a thread or other fastening with the bracket ( 8th ) connected is.

Images