Method for producing a steering rod having a signal transmitter for inductive position measurements

Abstract

The invention relates to a method for producing a steering rod (10) having a signal transmitter (12) for inductive position measurements, wherein the signal transmitter (12) comprises at least one metallic transmitting element (16a, 16b), wherein the transmitting element (16a, 16b) is embedded in a carrier material (14), the method comprising the following steps: - heating (S10) the steering rod (10) to a temperature T which is higher than the melting temperature of the carrier material (14); - positioning (S12) the signal transmitter (12) on the steering rod (10); and - pressing (S14) the signal transmitter (12) against the steering rod (10) with a pressure p, wherein the pressure p is maintained over a defined holding time t.

Description

[0001] Description

[0002] title

[0003] Method for manufacturing a steering rod with a signal transmitter for inductive position measurements

[0004] The invention relates to a method for manufacturing a steering rod with an inductive signal transmitter for position measurement, in particular a melting process for the carrier material of the signal transmitter.

[0005] State of the art

[0006] Steer-by-wire steering systems are an advanced automotive technology that replaces the traditional mechanical connection between the steering wheel and steering gear with electronic control systems. In a conventional steering system, a steering rod transmits the rotational movement of the steering wheel directly to the wheels. In a steer-by-wire system, however, the movements of the steering wheel are detected by sensors and transmitted as electrical signals to a control computer. This computer processes the signals and uses actuators to control the movement of the wheels. This allows for precise adjustment of feedback and steering assistance, resulting in improved vehicle control and individual customization of the steering characteristics.

[0007] The basic structure of a steer-by-wire steering system comprises several essential components. First, there are sensors on the steering wheel that detect the angle of rotation and torque. This information is transmitted to a central control computer, which calculates the desired driving direction and dynamics. The control commands are then passed on to electric actuators that position the wheels accordingly. Another important component is the feedback system, which provides the driver with realistic feedback about the road conditions by transmitting artificial forces back to the steering wheel.

[0008] A particular challenge with steer-by-wire steering systems is determining the precise position of the steering column or individual wheel actuators after the vehicle has restarted. While in a mechanical system the position of the steering column is physically determined by its connection to the wheels, in a steer-by-wire system the position must be determined electronically after the engine is switched on. This can be challenging because sensors and control units initially lack precise information about the wheel positions.

[0009] Sensors that determine position via the rotation of the steering system actuator are not unambiguous. This ambiguity can be solved with a counter system that tracks the number of actuator rotations and uses this data to calculate the exact position of the steering column. However, the counter is inoperative when the vehicle is switched off. If the steering column moves while the vehicle is switched off—for example, because the wheels are moved when the vehicle is lifted onto a hoist in a workshop—the stored counter value becomes worthless, as it no longer reflects the correct position of the steering column.

[0010] For this reason, it is important to use a steering column position determination system that enables unambiguous linear displacement measurement. One solution is inductive measurement techniques, in which the steering column's position is measured by means of an inductive sensor connected to an inductive signal transmitter.

[0011] However, when using inductive measurement technology in a steering gear, the materials used in the steering components create difficult conditions for magnetic shielding.

[0012] Furthermore, a defined and, if possible, constant air gap between the signal transmitter and the sensor is required for precise position determination. However, this air gap cannot be guaranteed if the steering rod deforms under load.

[0013] The signal transmitter and its mounting must also withstand the loads encountered. Since the signal transmitter is mounted on the handlebar, it must withstand the same bending and torsion as the handlebar itself. Furthermore, the different coefficients of thermal expansion of the materials and the wide temperature range (-40 °C to 120 °C) can cause stresses at the connection point.

[0014] Under certain circumstances, the signal transmitter can also be used for the steering rod bearing. For this purpose, the signal transmitter, or the mounting material, must meet specific tribological requirements regarding friction, wear, lubrication, and material compatibility.

[0015] Furthermore, the joining technology should be suitable for mass production so that the steering rod can be manufactured by machine. To ensure this, high process reliability and a short cycle time are required.

[0016] Conventional electronic circuit boards are unsuitable as substrate materials to withstand the necessary magnitude and frequency of bending loads. Furthermore, a circuit board cannot be used as a bearing. Conversely, a sheet metal part overmolded with plastic, even one with good tribological properties, cannot be robustly bonded to the steering rod due to its sliding properties (PTFE content in the plastic).

[0017] The invention is therefore based on the objective of proposing a method that meets the above-mentioned requirements and at the same time creates a good connection between the signal transmitter and the steering rod.

[0018] The problem is solved by the subject matter of the independent claims.

[0019] In the following, the term steering rod is used synonymously for steering rods in the true sense, that is, for steering two wheels, or in the sense of a single wheel actuator, that is, for steering a single wheel. The terms are therefore interchangeable.

[0020] Disclosure of the invention

[0021] According to a first aspect of the invention, this problem is solved by a method for manufacturing a steering rod with a signal transmitter for inductive position measurements. The signal transmitter comprises at least one metallic transmitting element, wherein the transmitting element is embedded in a carrier material.

[0022] The process includes the following steps:

[0023] Heating the steering rod to a temperature T that is higher than the melting point of the substrate material;

[0024] Positioning the signal transmitter on the handlebar; and

[0025] Pressing the signal transmitter against the steering rod with a pressure p, whereby the pressure p is maintained for a defined holding time t.

[0026] The transmitter element of the signal generator consists of one or more conductive segments that, upon inductive excitation by an alternating magnetic field signal, generate a magnetic response alternating field signal. The signal generator is designed such that a uniquely identifiable response alternating field signal can be measured at any possible position on the handlebar.

[0027] The at least one transmitting element is preferably embedded in the substrate material in such a way that it cannot fall out or easily detach. For example, the transmitting element can be enclosed by the substrate material at its edge, thus ensuring a positive fit. Alternatively, the transmitting element can be completely enclosed by the substrate material, so that it could only be detached if the substrate material were damaged. In this latter embodiment, the layer between the transmitting element and the air gap to the sensor should be as thin as possible to avoid impairing the measurement quality. On the other hand, thicker layers have the advantage of providing better protection for the transmitting element against damage. Ultimately, a balance must be found for the layer thickness that is neither too thin to offer sufficient protection nor too thick to minimize the air gap to the sensor.

[0028] Preferably, the carrier material is a plastic with a lower melting point than the handlebar. The handlebar is heated to a temperature at which the carrier material melts. It is not essential that the carrier material completely liquefies.

[0029] The signal transmitter is positioned on the heated handlebar at the point where it is needed for position determination. Upon contact of the carrier material with the handlebar, the carrier material heats up and begins to melt in the contact area. The soft or liquid carrier material bonds with the warm handlebar.

[0030] For good adhesion of the carrier material to the handlebar, it is important that the signal transmitter is pressed firmly against the handlebar. This prevents air pockets from forming in the soft or liquid carrier material between the signal transmitter and the handlebar.

[0031] The pressure p, with which the signal transmitter is pressed against the steering rod, is maintained for a holding time t. During this time, the steering rod cools down along with the molten carrier material, the latter solidifying and thus bonding to the steering rod. This process is also known as "hot joining".

[0032] The result is a connection between the steering rod and the signal transmitter that withstands deformation of the steering rod due to load, temperature fluctuations, and the associated stresses resulting from differing coefficients of thermal expansion. The invention thus fulfills its purpose.

[0033] In one embodiment, the steering rod includes a milled, flat area in which the signal transmitter is positioned. This milled, flat area of ​​the steering rod can, on the one hand, ensure better adhesion of the signal transmitter to the steering rod. The pressure p with which the signal transmitter is pressed against the steering rod during cooling is distributed evenly when a flat surface is used, so that the adhesion of the signal transmitter to the steering rod is homogeneous. No areas are created where the pressure, and therefore the adhesion, is lower than elsewhere.

[0034] On the other hand, in this embodiment, the signal transmitter can be recessed into the steering rod. For steering, the steering rod must be able to move along its direction of extension over a distance S. In doing so, it moves under the position sensor. If necessary, support elements are used to brace the steering rod against lateral forces. The signal transmitter recessed into the steering rod can move past these components with the steering rod without interfering with its movement.

[0035] Advantageously, the use of the milled, flat area for positioning the signal transmitter improves adhesion while maintaining the most compact installation space possible.

[0036] In one embodiment, the surface structure of the steering rod is roughened before heating at the point where the signal transmitter is positioned.

[0037] Roughening the surface structure of the steering rod in the contact area with the signal transmitter creates a larger surface area to which the transmitter's carrier material can bond. Furthermore, roughening creates irregularities in the steering rod's material, allowing the molten carrier material to better engage and adhere.

[0038] Roughening the surface before heating advantageously improves the connection between the signal transmitter and the steering rod.

[0039] In one embodiment, the surface structure is roughened using a laser or a chemical process. The roughening can be performed using a laser. Preferably, the metal surface of the steering rod is first cleaned to remove dirt, oil, or other contaminants that could interfere with the laser treatment. This can be done by chemical cleaning, solvents, or mechanical methods such as grinding. A high-power laser is typically used for roughening metal surfaces.

[0040] The laser is set up to scan the metal surface either at points or along lines. Parameters such as laser power, pulse frequency, scan speed, and focus are calibrated to remove the correct amount of material and create the desired surface texture. The laser beam is passed over the surface of the handlebar, where the high energy of the laser causes partial vaporization and melting of the metal. This molten metal cools rapidly, forming microscopic depressions and bumps that roughen the surface. The pattern can be uniform or random, depending on the desired roughness profile.

[0041] Preferably, after roughening, the surface can be cleaned again to remove any residue of the dissolved material. This ensures that the roughened surface is clean and allows for optimal adhesion of the signal transmitter.

[0042] As an alternative to a laser, a chemical process can be used. Depending on the metal of the handlebar, a suitable chemical etching agent can be used. For example, a sodium hydroxide (NaOH) solution can be used for aluminum, while a mixture of hydrochloric acid (HCl) or iron(III) chloride (FeCl3) is suitable for steel. The choice of etching agent depends on the reactivity of the metal and the desired degree of roughening.

[0043] The etching solution is prepared in a container large enough to completely immerse the metal part. The concentration of the etching solution and the temperature of the bath are adjusted according to the specific requirements and the type of metal. Areas of the handlebar that should not be roughened can be masked with suitable materials. The handlebar is immersed in the etching bath and left there for a specific time. During etching, the etching solution reacts with the metal surface, creating a microscopically rough structure. The duration of the etching depends on the desired roughness and the reactivity of the metal.

[0044] After the etching process, the metal part is removed from the etching bath and thoroughly rinsed to remove all traces of the etchant. The part is then immersed in a neutralizing solution, such as a dilute solution of sodium bicarbonate (NaHCO3), to stop the chemical reaction and ensure that no harmful residues remain.

[0045] In one embodiment, the heating of the steering rod is integrated into an inductive heat treatment process during the manufacturing of the steering rod.

[0046] Particularly advantageous are designs that can be integrated into standard production lines for steering rods. One process step that steering rods undergo during their manufacture is heat treatment.

[0047] Preferably, the signal transmitter can be attached after or during this heat treatment. This eliminates the need to reheat the steering rod to melt the carrier material. Advantageously, this saves an additional process step and reduces the energy required for manufacturing.

[0048] In one embodiment, the temperature T is chosen such that it is at least 20 K above the melting temperature of the support material.

[0049] A temperature T of 20 K above the melting point ensures that the carrier material actually melts at the contact surface with the steering rod. At lower temperatures, the lower temperature of the signal transmitter can cool the steering rod in the contact area to such an extent that homogeneous melting of the carrier material does not occur. This would result in reduced adhesion of the signal transmitter to the steering rod. Conversely, a temperature T that is too high can cause too much of the carrier material to melt, leading to deformation of the signal transmitter or even the carrier material flowing away. Furthermore, the cooling process would take longer, delaying the entire manufacturing process.

[0050] In one embodiment, the holding time t is selected such that during the holding time t the temperature of the steering rod falls below the recrystallization temperature of the support material due to cooling.

[0051] Plastics can exhibit both crystalline and amorphous regions. In crystalline regions, the polymer chains are ordered and regularly arranged, while in amorphous regions they are random and disordered. The proportion of these regions influences the physical properties of the plastic, such as strength, stiffness, and transparency.

[0052] When the substrate material melts, its crystalline structure can be disrupted or partially destroyed. This leads to a change in the material's mechanical properties; it softens and eventually begins to melt.

[0053] Recrystallization is the process by which ordered crystalline structures are restored after heating. This occurs when the plastic cools to a specific temperature—the recrystallization temperature. This temperature is below the plastic's melting point but high enough to allow the polymer chains to realign and form an ordered structure.

[0054] The holding time is selected such that the recrystallization temperature is reached. Until then, the signal transmitter is pressed against the steering rod so that during recrystallization the molecular structures of the support material assume a particularly stable form. In a further aspect, the invention relates to a steering rod with a signal transmitter for inductive position measurements, wherein the steering rod was manufactured using a method as described above.

[0055] In one embodiment, the carrier material of the signal transmitter is POM, PEEK or polyethylene.

[0056] POM, PEEK and polyethylene are commercially available plastics that are particularly easy to handle and possess the required material properties.

[0057] In one embodiment, the signal transmitter comprises several transmitting elements, with gaps arranged between the transmitting elements, such that the transmitting elements and the gaps form one or more tracks extending parallel to the direction of extension of the steering rod.

[0058] In this embodiment, the carrier material also functions as a spacer between the transmitting elements. The transmitting elements can preferably be arranged as two tracks, which, for example, allow the position of the steering rod to be determined using the vernier scale principle. In this embodiment, the precise positioning of the transmitting elements relative to each other is particularly important. The carrier material can be precisely shaped in this embodiment so that the position of the transmitting elements is as accurate as possible.

[0059] In one embodiment, the signal transmitter comprises a transmitting element that extends over a path length S and is arranged at an angle a to the direction of extension of the steering rod.

[0060] The angle α should be chosen to be as large as possible so that the transmitting element is positioned at the steepest possible angle over the path length S. The trigonometric ratio of path length S to the width B available to the transmitting element can be considered the upper limit for α. Each position of the steering rod can then be uniquely assigned to a section of the transmitting element located below the inductive sensor. In a further aspect, the invention relates to a steer-by-wire steering system comprising a steering rod as described above.

[0061] In summary, the present invention provides a method for manufacturing a steering rod with a signal transmitter for inductive position measurements, a corresponding steering rod, and a steer-by-wire steering system with a corresponding steering rod.

[0062] The described configurations and training programs can be combined in any way desired.

[0063] Further possible embodiments, developments and implementations of the invention also include combinations of features of the invention described previously or subsequently with regard to the exemplary embodiments that are not explicitly mentioned.

[0064] Brief description of the drawings

[0065] The accompanying drawings are intended to provide a further understanding of the embodiments of the invention. They illustrate embodiments and, in conjunction with the description, serve to explain the principles and concepts of the invention.

[0066] Other embodiments and many of the aforementioned advantages become apparent with reference to the drawings. The elements depicted in the drawings are not necessarily shown to scale.

[0067] They show:

[0068] Fig. 1 shows a section through a signal transmitter attached to a handlebar;

[0069] Fig. 2 shows a steering rod with a signal transmitter for an inductive

[0070] Position determination; and Fig. 3 schematically illustrates the process according to one embodiment.

[0071] In the figures of the drawings, identical reference symbols denote identical or functionally equivalent elements, parts or components, unless otherwise stated.

[0072] Fig. 1 shows a section of a steering rod 10 on which a signal transmitter 12 is mounted. The signal transmitter comprises a carrier material 14 in which two transmitting elements 16a and 16b are embedded.

[0073] A distance 18 exists between the transmitters 16a and 16b and the steering rod 10, or rather its material, isolating the transmitters 16a and 16b from the steering rod 10. During operation, an inductive sensor is positioned a short distance from the signal transmitter 12, emitting an alternating magnetic field signal. In the diagram, the sensor (not shown here) would be positioned above the signal transmitter 12. The alternating magnetic field signal generated by the sensor, in turn, induces eddy currents in the transmitters 16a and 16b. The transmitters 16a and 16b then emit their own alternating magnetic field signals, which can be detected by the sensor. The position of the steering rod can then be determined from these alternating magnetic field signals.

[0074] To optimize the magnetic coupling between the sensor and the transmitting elements 16a and 16b, the distance 18 is chosen to be sufficiently large so that the steering rod 10 does not generate a measurable magnetic response alternating field signal.

[0075] In the illustrated embodiment, the transmitting elements 16a and 16b are enclosed by the carrier material 14. The distance 20 between the transmitting elements 16a and 16b and the upper edge of the signal transmitter 12 is selected such that the magnetic interaction between the sensor and the signal transmitter 12 is not impaired as much as possible, while the carrier material 14 still provides good protection for the transmitting elements 16a and 16b. At the transition 22 from the signal transmitter 12 to the steering rod 10, the carrier material 14 projects slightly beyond the steering rod 10. When the steering rod 10 is warm and the carrier material 14 softens, the carrier material 14 can wrap around the edge of the steering rod 10 to a small extent, thus improving the grip of the signal transmitter 12 on the steering rod 10.

[0076] Fig. 2 schematically shows a steering rod 10 to which a signal transmitter 12 is attached. The steering rod 10 is movably mounted over a travel length S. The steering rod 10 has a thread 24 via which it can be driven by a drive.

[0077] The steering rod 10 also has a milled flat area 26 in which the signal transmitter 12 is positioned. The signal transmitter 12 is positioned such that it does not protrude beyond the steering rod 10 in profile.

[0078] An inductive sensor 28 is arranged above the signal transmitter 12. The sensor 28 generates an alternating magnetic field signal, which in turn generates a corresponding alternating magnetic response signal in the transmitter element of the signal transmitter 12. This corresponding alternating magnetic response signal is then detected by the sensor 28. The position of the steering rod 10 is ultimately determined from the detected signal.

[0079] An air gap 30 is provided between the sensor 28 and the signal transmitter 12. This air gap 30 serves to protect the sensor 28 from collisions with the steering rod 10, or more precisely, the signal transmitter 12, if the steering rod 10 moves perpendicular to its direction of extension due to external loads. For the most accurate position determination possible, the air gap 30 should be as constant as possible.

[0080] Two support elements 32a and 32b are provided to support the steering rod 10. The support elements 32a and 32b engage the steering rod 10 from two sides, thus limiting its movement in these directions. Preferably, the support elements 32a and 32b are positioned in close proximity to the sensor 28 to ensure that the air gap 30 remains constant. Deformations of the steering rod 10 can occur at points further away from the support elements 32a and 32b. At these points, the steering rod 10 can move vertically to a small extent, making position measurement less suitable. This effect can be reduced by positioning the support elements 32a and 32b close to the sensor 28.

[0081] In the illustrated embodiment, the support element 32a directly engages the signal transmitter 12. In this embodiment, the signal transmitter 12 is designed to withstand the pressure of the support element 32a without being damaged. For this purpose, the at least one transmitting element within the signal transmitter 12 can be enclosed by the carrier material. The carrier material thus forms a protective layer around the at least one transmitting element and protects it from damage caused by the support element 32a.

[0082] In embodiments, a steering system can comprise several support elements that support the steering rod 10 in several directions.

[0083] Fig. 3 schematically shows the process for manufacturing a steering rod with a signal transmitter according to one embodiment.

[0084] In a first step S10, the steering rod is heated. In this context, the term "heating" is synonymous with "bringing to a specific temperature." If the heating is part of the heat treatment of the steering rod, this can also be considered heating within the meaning of the present invention.

[0085] When the steering rod has reached a sufficiently high temperature, for example 20 K above the melting temperature of the signal transmitter's substrate material, the signal transmitter is positioned on the steering rod in step S12.

[0086] If the signal transmitter is correctly positioned, it is pressed against the steering rod with a defined pressure p in step S14. The pressure is maintained for a holding time t. During this time, the steering rod and the carrier material cool down. The molten carrier material solidifies again and forms a good bond with the steering rod. The cooling process can be passive or active, i.e., with the aid of cooling devices.

Claims

Claims 1. Method for manufacturing a steering rod (10) with a signal transmitter (12) for inductive position measurements, wherein the signal transmitter (12) comprises at least one metallic transmitting element (16a, 16b), wherein the transmitting element (16a, 16b) is embedded in a carrier material (14), the method comprising the following steps: Heating (S10) the steering rod (10) to a temperature T that is higher than the melting temperature of the support material (14); Positioning (S12) of the signal transmitter (12) on the steering rod (10); and pressing (S14) of the signal transmitter (12) against the steering rod (10) with a pressure p, whereby the pressure p is maintained for a defined holding time t.

2. Method according to one of the preceding claims, wherein the steering rod (10) comprises a milled flat area (26) in which the signal transmitter (12) is positioned.

3. Method according to one of the preceding claims, wherein the surface structure of the steering rod (10) is roughened before heating (S10) where the signal transmitter (12) is positioned.

4. Method according to claim 3, wherein the roughening of the surface structure is carried out by means of a laser or a chemical process.

5. Method according to one of the preceding claims, wherein the heating (S10) of the steering rod (10) is integrated into an inductive heat treatment process during the manufacture of the steering rod (10).

6. Method according to one of the preceding claims, wherein the temperature T is selected such that it is at least 20°C above the melting temperature of the support material (14).

7. Method according to one of the preceding claims, wherein the holding time t is selected such that during the holding time t the temperature of the steering rod (10) falls below the recrystallization temperature of the support material (14) by cooling.

8. Steering rod (10) with a signal transmitter (12) for inductive position measurements, wherein the steering rod (10) was manufactured using a method according to one of the preceding claims.

9. Steering rod (10) according to claim 8, wherein the carrier material (14) of the signal transmitter (12) is POM, PEEK or Polyeton.

10. Steering rod (10) according to one of claims 8 to 9, wherein the signal transmitter (12) comprises several transmitting elements (16a, 16b), wherein gaps are arranged between the transmitting elements (16a, 16b) such that the transmitting elements (16a, 16b) and the gaps form one or more tracks extending parallel to the direction of extension of the steering rod (10).

11. Steering rod (10) according to one of claims 8 to 9, wherein the signal transmitter (12) comprises a transmitting element that extends over a path length S and is arranged at an angle a to the direction of extension of the steering rod (10).

12. Steer-by-wire steering system comprising a steering rod (10) according to any one of claims 8 to 11.

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