Power measurement device for vehicle chassis

0001The present invention relates to a device for measuring forces in a vehicle chassis, in particular the braking force, according to the preamble of claim 1. Furthermore, it relates to a sensor for such a device.

0002The brakes of aircraft consist of nested stacks of brake discs, which are pressed together by hydraulic or electric actuators. One of the stacks is connected to the respective wheel. The other stack is connected to receive the braking force to the stationary part of the chassis. For the transmission of the braking force, d. H. of the torque which occurs upon activation of the brakes on the chassis, the second-mentioned, stationary stack is locked in a suitable manner against rotation relative to the chassis. As a rule, this involves an attachment device arranged eccentrically to the axis of the wheel on the stationary stack, in the simplest case a bore. A bolt serves to connect the stationary stack with the chassis directly or via a brake force transmission rod. This bolt is highly loaded by the torque in the transverse direction and is therefore made of a high-strength material. Since it usually has a relatively large diameter, however, it is made hollow for weight saving reasons.

0003For various reasons, it is desirable to measure the actual braking effect. The<patcit id="pcit0001" dnum="US4474060A"><text>US 4,474,060</text></patcit> Proposes to form the sleeve, which is normally arranged between the mentioned bolt and the respective receiving opening, as a force sensor. However, this solution has the disadvantage that a change in the elements is made, which serve the power transmission, which is why the cost of certification of this solution is significant. The certification requires a relatively large amount of time and money and, moreover, in extreme cases, must be carried out individually for each type of aircraft.

0004Similar braking force measurement problems may also arise with other types of vehicles having braking systems similar to those of aircraft. In the landing gear of aircraft and other types of vehicles other forces occur whose measurement is desirable or important, for example, by bumps, suspension, damping elements, weight of the vehicle, etc.

0005An object of the present invention is therefore to provide a device for measuring forces in a vehicle chassis, in particular the braking force, which can be attached without having to make any interference with the transmission path of the braking force.

0006Such a device is specified in claim 1. The further claims indicate preferred embodiments and sensors for use in the device.

0007Accordingly, the device comprises a sensor which is located in a connecting element, which is generally rod-shaped and by the force or forces to be measured, for example, the braking force, transversely loaded and thereby deformed. In particular, the sensor is designed to determine the distance of the inner walls of the cavity in the connecting part, in which the sensor is located, from the sensor. Preferably, capacitive or inductive distance measuring elements are used here.

0008The invention will be further explained with reference to an embodiment with reference to figures.<dl id="dl0001"><dt>Fig. 1</dt><dd>schematic representation of an aircraft chassis frame ("bogie");</dd><dt>Fig. 2</dt><dd>Longitudinal section through a connecting part with sensor according to the invention;</dd><dt>Fig. 3</dt><dd>Cross section according to III-III in Figure 2, connecting part in the unloaded state.</dd><dt>Fig. 4</dt><dd>as shown in Figure 3, but charged by braking force connecting part.</dd><dt>Fig. 5</dt><dd>Block diagram; and</dd><dt>Fig. 6</dt><dd>Block diagram of a variant of the circuit of FIG. 5.</dd></dl>

0009FIG. 1 shows the basic structure of an aircraft landing gear 1. On a leg 2, a chassis support 4 ("bogie train") is mounted in a joint 3. On chassis support are the wheels. 5 At the wheels 5, the brakes 6 are attached, which by (z. B. hydraulic) actuators 7 can be actuated. At the stationary disk stack of the brake 6, a lever 8 with a bore 9 is present. At the bore 9 as well as at an attachment point 10, the power transmission rod 12 is fixed, which transmits the braking torque from the brake 7 to the chassis 1 during the braking process.

0010The illustrated basic construction of an aircraft landing gear corresponds to the state of the art for larger aircraft. As an alternative to the use of the power transmission rod 12, especially for smaller aircraft, it is also common to transfer the torque directly from the brake to the chassis, z. B. via a direct bolt connection.

0011Fig. 2 shows in longitudinal section a section through the connection of the brake force transmission rod 12 with the stationary part 14 of the brake 6, wherein the above-mentioned lever 8 is considered part of the stationary part 14.

0012Through the hole 9 in the lever 8 and through a bore 15 at the end of the brake force transmission rod 12 extends the bolt 16. The bolt 16 is made of a high-strength material and largely hollow for weight saving. In a braking, however, it is still noticeably deformed. For example, B.⁴/₁₀ mm deformation with a bolt of 50 mm inside diameter.

0013In the bolt 16, which is hollow, the sensor 20 is located. At its one, in the figure right end of the housing 22 is provided with projections or has a total of such a diameter that it snugly conforms to the inner wall 26 of the bolt 16. Through the bolt 16 as well as the end 24 of the sensor 20 extends here a hole through which a pin 28 is inserted. The pin 28 is held in a bore 30 in an orientation ring 32 which on the lever 8, d. H. on the stationary part 14 of the brake 6, is mounted. This device serves to fix the sensor in a predetermined, fixed orientation relative to the braking force (arrow 34).

0014Outside the in Fig. 2 left part 36 of the sensor 20 O-rings 38 are attached. They serve to fix this part of the sensor 20 approximately centrally and to absorb the deformations of the bolt 16 under load by the braking force 34, since the housing 22 of the sensor 20 is substantially rigid. In part 36 of the sensor 20 is an inductive distance measuring element 40 and an associated supply and evaluation circuit on a circuit board 42nd The sensor housing is closed by a disc 44, on which the electrical connection 46 is located, through which the electrical connections (not shown) are made.

0015As can be seen more clearly in FIGS. 3 and 4, the inductive measuring element 40 consists essentially of two coil arrangements 50 and 51, which are arranged perpendicular to one another and which are located on a cross-shaped core 52. The core 52 has a high magnetic permeability. In particular, it consists of a stack of soft magnetic material to avoid eddy currents that may arise in the AC excitation of the coil assemblies 50, 51.

0016The arms 54 of the core 52 together with the outer ends of the coils 50, 51 are in corresponding holes or Recesses of the housing 22 held so that the ends of the arms 54 form part of the housing surface of the sensor 20. As a result, a magnetic field exiting from the core 52 through the arms 54 can leave the sensor unhindered or to enter him. In order not to disturb the propagation of such a magnetic field, the housing 22 of the sensor 20 at least in the area around the inductive distance measuring element 40 is made of a material of low low magnetic permeability.

0017The inductive distance measuring element 40 serves, as shown in FIG. 3 and FIG. 4 illustrates radial distances between pin 16 and sensor 20. By the deformation of the bolt 16 to an oval (see FIG. 4) reduce the distances in the direction of the force 34 (distances 75, 76) or increase perpendicular to the force 34 (distances 77, 78). Since this is independent of which direction along the arrow 34 the force acts, the measurement also satisfies the often-claimed requirement to measure the magnitude of the force 34.

0018Although a simple coil arrangement with a rod-shaped core would suffice for the measurement, the arrangement of two cross-shaped coil arrangements is provided in order to be able to separate the effect of the braking force 34 from other influences and in addition a simpler derivation of the braking force from the measurement signals of the inductive distance measuring element 40 to allow. In addition, errors are suppressed from a not exactly centered position of the measuring element 40 within the bolt 16.

0019For the use of an inductive distance measuring element is a prerequisite that the bolt 16 also consists of a material of high magnetic permeability, which is now the case regularly. The common, high strength materials for these devices have sufficient magnetic properties in this regard.

0020For the measurement, the coil pairs 50, 51 are charged separately with an alternating current and the AC voltage occurring at the coils is measured. By a synchronous demodulation of these voltages by a shifted by 90 ° voltage of the same frequency of the Immaginäranteil the voltage is obtained, that is, caused by the inductance component. The evaluation shown in detail below makes it possible to generate a measurement signal that is proportional to the braking force:

0021The circuit around the inductive distance measuring element 40 is shown schematically in FIG. An oscillator 58 generates a voltage U_OSC with a frequency ω, the amplitude of which is determined by a voltage U specified from outside_REF is predetermined. By setting U_REF a temperature dependence of the inductive distance measuring element 40 can be compensated. This will not be discussed further below, but it is conceivable to arrange a temperature sensor in the sensor 20 and in dependence on its signal U_REF adjust.

0022U_OSC is converted into currents I by two current-voltage transformers 60, 62_A and I_B converted, with which the coils A 50 and B 51 are acted upon. The voltages appearing at A and B are supplied to synchronous demodulators 64, 66, to which the output signal U, which is shifted by 90 ° by an integrator 68, is applied as a second signal_OSC of the oscillator 58 is supplied. After respective low-pass filtering by the low-pass filters 70, 71, the output signals U stand_A and U_B available, each corresponding to the pure inductances of the coil assemblies 50, 52, ie without resistive components. The low passes 70, 71 serve to filter out the carrier frequency. The two voltages U_A and U_B are supplied to an analog or digital processing unit 73, which divides the difference of the input signals by the sum of the input signals, resulting in the output signal U_OUT results. As shown, this voltage is proportional to the force F acting on the pin 16.

0023For the following derivation, it is assumed that the coil arrangements A and B each act as a series circuit of an ideal inductance L_A or L_B and an ohmic portion R_A or R_B result. The ohmic component includes iron losses, ohmic resistance of the cables, etc. The currents and voltages given below are to be understood as vector quantities as far as alternating voltages and currents are concerned.

0024The by the current I_A on the coil assembly A (corresponding to coil pair 50) caused voltage is: <maths id="math0001" num="gl. 1"><math display="block"><msub><mi mathvariant="normal">U</mi><mi mathvariant="normal">A</mi></msub><mo mathvariant="normal">=</mo><msub><mi mathvariant="normal">U</mi><msub><mi mathvariant="normal">L</mi><mi mathvariant="normal">A</mi></msub></msub><mo mathvariant="normal">+</mo><msub><mi mathvariant="normal">U</mi><msub><mi mathvariant="normal">R</mi><mi mathvariant="normal">A</mi></msub></msub></math><img file="EP1839984A1_D0001.tif" /></maths> and: <maths id="math0002" num="gl. 2"><math display="block"><msub><mi mathvariant="bold">U</mi><msub><mi mathvariant="bold">L</mi><mi mathvariant="bold">A</mi></msub></msub><mo mathvariant="normal">=</mo><msub><mi mathvariant="normal">L</mi><mi mathvariant="normal">A</mi></msub><mo>⁢</mo><msub><mrow><mspace width="1em" /><mi mathvariant="bold">I</mi></mrow><mi mathvariant="bold">A</mi></msub><mspace width="1em" /><mi mathvariant="normal">ω</mi></math><img file="EP1839984A1_D0002.tif" /></maths> With:<dl id="dl0002" compact="compact"><dt>U_LA</dt><dd>the AC component generated by the pure inductance,</dd><dt>U_{R<sub2>A</sub2>}</dt><dd>the component derived from the parasitic, resistive components.</dd></dl>

0025The pure inductance LA of the coil arrangement A results in: <maths id="math0003" num="gl. 3"><math display="block"><msub><mi mathvariant="normal">L</mi><mi mathvariant="normal">A</mi></msub><mo mathvariant="normal">=</mo><msup><msub><mi mathvariant="normal">n</mi><mi mathvariant="normal">A</mi></msub><mn mathvariant="normal">2</mn></msup><mo>⁢</mo><msub><mi mathvariant="normal">Λ</mi><mi mathvariant="normal">A</mi></msub><mo mathvariant="normal">=</mo><msup><msub><mi mathvariant="normal">n</mi><mi mathvariant="normal">A</mi></msub><mn mathvariant="normal">2</mn></msup><mo>⁢</mo><msub><mi mathvariant="normal">μ</mi><mn mathvariant="normal">0</mn></msub><mo>⁢</mo><mfrac><msub><mi mathvariant="normal">A</mi><msub><mi mathvariant="normal">p</mi><mi mathvariant="normal">A</mi></msub></msub><msub><mi mathvariant="normal">d</mi><mi mathvariant="normal">A</mi></msub></mfrac><mo mathvariant="normal">=</mo><mfrac><msub><mi mathvariant="normal">K</mi><mi mathvariant="normal">A</mi></msub><msub><mi mathvariant="normal">d</mi><mi mathvariant="normal">A</mi></msub></mfrac></math><img file="EP1839984A1_D0003.tif" /></maths> With :<dl id="dl0003" compact="compact"><dt>n_A</dt><dd>Number of turns of A</dd><dt>μ₀</dt><dd>Magnetic permeability</dd><dt>Ap</dt><dd>Pole cross section of A</dd><dt>d_A</dt><dd>Air gap in the magnetic circuit of A, ie the sum of the distances 75 and 76 (FIG. 4)</dd><dt>K_A</dt><dd>Constant: K_A = n_A² μ₀ A_pA / d_A</dd></dl>

0026The change of the air gap d_A, Equivalent to the sum of the distances 75 and 76, is approximately proportional to the braking force F: <maths id="math0004" num="gl. 4"><math display="block"><msub><mi mathvariant="normal">d</mi><mi mathvariant="normal">A</mi></msub><mo mathvariant="normal">=</mo><msub><mi mathvariant="normal">d</mi><mn mathvariant="normal">0</mn></msub><mo mathvariant="normal">+</mo><mi>CF</mi></math><img file="EP1839984A1_D0004.tif" /></maths> With :<dl id="dl0004" compact="compact"><dt>C</dt><dd>Mechanical constant, depending on the bolt 16.</dd><dt>d₀</dt><dd>Air gap d_A at rest (F = 0)</dd></dl>

0027It follows from equations (2), (3) and (4): <maths id="math0005" num="gl. 5"><math display="block"><msub><mi mathvariant="bold">U</mi><msub><mi mathvariant="bold">L</mi><mi mathvariant="bold">A</mi></msub></msub><mo mathvariant="normal">=</mo><msub><mrow><mspace width="1em" /><mi mathvariant="bold">I</mi></mrow><mi mathvariant="bold">A</mi></msub><mo>⁢</mo><msub><mrow><mspace width="1em" /><mi mathvariant="normal">ω K</mi></mrow><mi mathvariant="normal">A</mi></msub><mo>⁢</mo><mfrac><mn mathvariant="normal">1</mn><mrow><msub><mi mathvariant="normal">d</mi><mn mathvariant="normal">0</mn></msub><mo mathvariant="normal">+</mo><mi>CF</mi></mrow></mfrac></math><img file="EP1839984A1_D0005.tif" /></maths> and by analog derivation for coil arrangement B: <maths id="math0006" num="gl. 6"><math display="block"><msub><mi mathvariant="bold">U</mi><msub><mi mathvariant="bold">L</mi><mi mathvariant="bold">B</mi></msub></msub><mo mathvariant="normal">=</mo><msub><mrow><mspace width="1em" /><mi mathvariant="bold">I</mi></mrow><mi mathvariant="bold">B</mi></msub><mo>⁢</mo><msub><mrow><mspace width="1em" /><mi mathvariant="normal">ω K</mi></mrow><mi mathvariant="normal">B</mi></msub><mo>⁢</mo><mfrac><mn mathvariant="normal">1</mn><mrow><msub><mi mathvariant="normal">d</mi><mn mathvariant="normal">0</mn></msub><mo>-</mo><mi>CF</mi></mrow></mfrac></math><img file="EP1839984A1_D0006.tif" /></maths>

0028With identical, symmetrical design of the coil pairs 50, 51 can be set further: <maths id="math0007" num="gl. 7"><math display="block"><msub><mrow><mspace width="1em" /><mi mathvariant="bold">I</mi></mrow><mi mathvariant="bold">A</mi></msub><mo>⁢</mo><msub><mrow><mspace width="1em" /><mi mathvariant="normal">ω K</mi></mrow><mi mathvariant="normal">A</mi></msub><mo>=</mo><msub><mrow><mspace width="1em" /><mi mathvariant="bold">I</mi></mrow><mi mathvariant="bold">B</mi></msub><mo>⁢</mo><msub><mrow><mspace width="1em" /><mi mathvariant="normal">ω K</mi></mrow><mi mathvariant="normal">B</mi></msub></math><img file="EP1839984A1_D0007.tif" /></maths>

0029Using Eqs. (7) in the Gln. (5) and (6) results for U_OUT: <maths id="math0008" num="gl. 8"><math display="block"><msub><mi mathvariant="normal">U</mi><mi>OUT</mi></msub><mo mathvariant="normal">=</mo><mfrac><mrow><msub><mi mathvariant="normal">U</mi><msub><mi mathvariant="normal">L</mi><mi mathvariant="normal">A</mi></msub></msub><mo mathvariant="normal">-</mo><msub><mi mathvariant="normal">U</mi><msub><mi mathvariant="normal">L</mi><mi mathvariant="normal">B</mi></msub></msub></mrow><mrow><msub><mi mathvariant="normal">U</mi><msub><mi mathvariant="normal">L</mi><mi mathvariant="normal">A</mi></msub></msub><mo mathvariant="normal">+</mo><msub><mi mathvariant="normal">U</mi><msub><mi mathvariant="normal">L</mi><mi mathvariant="normal">B</mi></msub></msub></mrow></mfrac><mo>=</mo><mfrac><mrow><mi mathvariant="normal">K</mi><mo>⁢</mo><mfenced open="[" close="]" separators=""><mfrac><mn mathvariant="normal">1</mn><mrow><msub><mi mathvariant="normal">d</mi><mn mathvariant="normal">0</mn></msub><mo mathvariant="normal">+</mo><mi>CF</mi></mrow></mfrac><mo mathvariant="normal">-</mo><mfrac><mn mathvariant="normal">1</mn><mrow><msub><mi mathvariant="normal">d</mi><mn mathvariant="normal">0</mn></msub><mo mathvariant="normal">-</mo><mi>CF</mi></mrow></mfrac></mfenced></mrow><mrow><mi mathvariant="normal">K</mi><mo>⁢</mo><mfenced open="[" close="]" separators=""><mfrac><mn mathvariant="normal">1</mn><mrow><msub><mi mathvariant="normal">d</mi><mn mathvariant="normal">0</mn></msub><mo mathvariant="normal">+</mo><mi>CF</mi></mrow></mfrac><mo mathvariant="normal">+</mo><mfrac><mn mathvariant="normal">1</mn><mrow><msub><mi mathvariant="normal">d</mi><mn mathvariant="normal">0</mn></msub><mo mathvariant="normal">-</mo><mi>CF</mi></mrow></mfrac></mfenced></mrow></mfrac><mo mathvariant="normal">=</mo><mfrac><mi>CF</mi><msub><mi mathvariant="normal">d</mi><mn mathvariant="normal">0</mn></msub></mfrac><mo mathvariant="normal">=</mo><msub><mi mathvariant="normal">K</mi><mn mathvariant="normal">2</mn></msub><mo>⁢</mo><mi mathvariant="normal">F</mi></math><img file="EP1839984A1_D0008.tif" /></maths>

0030This is U_OUT proportional to the braking force F.

0031The division by (U_{L<sub2>A</sub2>} + U_{L<sub2>B</sub2>}) in Eq. 8 is analog only difficult to carry out and relatively expensive digital. Fig. 6 shows a variant in which this division is avoided, in which (U_{L<sub2>A</sub2>} + U_{L<sub2>B</sub2>}) is kept constant.

0032The circuit of Fig. 6 corresponds largely to that of Fig. 5, namely in the provided with matching reference numerals components.

0033Notwithstanding FIG. 5, the voltages on the coils A 50 and B 52 are fed to an adder 77. The resulting sum U_A + U_B is supplied to a third synchronous demodulator 79, at whose output, after adequate smoothing by a low-pass filter 80, the sum U_{L<sub2>A</sub2>} + U_{L<sub2>B</sub2>} is available. This signal is fed to a PI controller 81 as an actual variable, the reference variable is U_REF- Optionally, the control behavior can be improved by adding a differential component (PID controller).

0034The PI or PID controller 81 controls the amplitude of the oscillator 58.

0035That's the factor <maths id="math0009" num=""><math display="inline"><mfrac><mn>1</mn><mrow><msub><mi mathvariant="normal">U</mi><msub><mi mathvariant="normal">L</mi><mi mathvariant="normal">A</mi></msub></msub><mo mathvariant="normal">+</mo><msub><mi mathvariant="normal">U</mi><msub><mi mathvariant="normal">L</mi><mi mathvariant="normal">B</mi></msub></msub></mrow></mfrac></math><img file="EP1839984A1_D0009.tif" /></maths> constant, and it turns out: <maths id="math0010" num="gl. 9"><math display="block"><msub><mi mathvariant="normal">U</mi><mi>OUT</mi></msub><mo>*</mo><mi mathvariant="normal">μ</mi><mo>⁢</mo><mfenced separators=""><msub><mi mathvariant="normal">U</mi><msub><mi mathvariant="normal">L</mi><mi mathvariant="normal">A</mi></msub></msub><mo mathvariant="normal">+</mo><msub><mi mathvariant="normal">U</mi><msub><mi mathvariant="normal">L</mi><mi mathvariant="normal">B</mi></msub></msub></mfenced><mo mathvariant="normal">=</mo><msub><mi mathvariant="normal">U</mi><msub><mi mathvariant="normal">L</mi><mi mathvariant="normal">A</mi></msub></msub><mo mathvariant="normal">-</mo><msub><mi mathvariant="normal">U</mi><msub><mi mathvariant="normal">L</mi><mi mathvariant="normal">B</mi></msub></msub><mo mathvariant="normal">=</mo><mo mathvariant="normal">(</mo><msub><mi mathvariant="normal">U</mi><msub><mi mathvariant="normal">L</mi><mi mathvariant="normal">A</mi></msub></msub><mo mathvariant="normal">+</mo><msub><mi mathvariant="normal">U</mi><msub><mi mathvariant="normal">L</mi><mi mathvariant="normal">B</mi></msub></msub><mo mathvariant="normal">)</mo><msub><mi mathvariant="normal">K</mi><mn mathvariant="normal">2</mn></msub><mspace width="1em" /><mi mathvariant="normal">F</mi><mo mathvariant="normal">=</mo><msub><mi mathvariant="normal">K</mi><mn mathvariant="normal">3</mn></msub><mspace width="1em" /><mi mathvariant="normal">F</mi></math><img file="EP1839984A1_D0010.tif" /></maths> with K₃ = constant.

0036Thus, the output signal of the adder 83 with an upstream inverter 85, ie the difference U_{L<sub2>A</sub2>} - U_{L<sub2>B</sub2>}, directly the force F on, and the complex division is avoided. In particular, this variant can also be carried out analogously.

0037It is particularly advantageous on the sensor described that it can be used in the existing connecting pin 16, without thereby the mechanical construction would have to be changed in a way that requires a new certification. In addition, the sensor can be mounted on site, ie in the normal aircraft maintenance or checked or replaced.

0038From the foregoing description of an embodiment, numerous modifications will be apparent to those skilled in the art without departing from the scope of the invention, which is given solely by the claims. It is conceivable, inter alia:<ul id="ul0001" list-style="dash"><li>Use of other distance measuring elements as inductive, z. B. capacitive or eddy-current-based measuring elements; in the case of capacitive elements, an application of alternating voltage and the measurement of the reactive current would have to be provided in the specified evaluation circuits as an equivalent to the imaginary component of the signal from inductive measuring elements.</li><li>Arrangement of the measuring element in a completely closed housing of the sensor. In this case, the measuring element, for. B. the inductive distance sensor 40 may be attached to a carrier which is located in the sensor housing 24.</li><li>Execution of the distance sensor as two separate sensors, but preferably at a small distance along the bolt 16, ie in each case near the transition of the two connected by the bolt parts 12, 14, where with the strongest deformation of the connecting part (bolt 16) by the forces occurring is calculated;</li><li>Use of another core material for the inductive measuring element, eg. B. based on ferrites.</li></ul>