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

Abstract

The invention relates to a 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), the transmitting element (16a, 16b) being 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 carrier material (14); - positioning (S12) the signal transmitter (12) on the steering rod (10); and - pressing (S14) the signal transmitter (12) onto the steering rod (10) with a pressure p, the pressure p being maintained for a defined holding time t.

Description

The invention relates to a method for producing a steering rod with an inductive signal transmitter for position measurement, in particular to a melting method for the carrier material of the signal transmitter.Prior ArtSteer-by-wire steering systems are an advanced technology in automotive engineering, in which the conventional mechanical connection between steering wheel and steering gear is replaced by electronic control systems. In a classic steering system, a steering rod transmits the rotational movement of the steering wheel directly to the wheels. In a steer-by-wire steering system, on the other hand, the movements of the steering wheel are detected by sensors and transmitted as electrical signals to a control computer. The latter processes the signals and controls the movement of the wheels with the aid of actuators. As a result, feedback and steering assistance can be adjusted precisely, which enables better vehicle control and individual adjustment of the steering characteristic.The basic structure of a steer-by-wire steering system comprises several essential components. First, there are sensors on the steering wheel that detect rotational angles and torque. This information is passed on to a central control computer which calculates the desired direction of travel and dynamics. The control commands are then passed on to electrical actuators, which position the wheels accordingly. Another important component is the feedback system, which provides the driver with realistic feedback on the road conditions by transmitting artificial forces back to the steering wheel.A particular problem with steer-by-wire steering systems is the determination of the exact position of the steering rod or the single wheel actuators after restarting the vehicle. While in a mechanical system the position of the steering rod is physically predetermined by its connection to the wheels, in a steer-by-wire steering system the position after the switch-on must be electronically determined. This can be challenging, since sensors and control units initially do not have precise information about the wheel position.Sensors that determine the position via the rotation of the steering system drive are not unambiguous. The problem of ambiguity can be solved by a counting system which counts the number of rotations of the drive and from this determines the exact position of the steering rod. However, when the vehicle is off, the counter does not function. If the steering rod moves when the vehicle is off, for example because the wheels are moved in a workshop on lifting the vehicle onto a lifting platform, the stored counter value becomes zero value since it no longer indicates the correct position of the steering rod.For this reason, it is important to use a steering rod position determination system that allows a clear linear travel measurement. One solution for this is inductive measurement techniques, in which the position of the steering rod is measured by means of an induction sensor via an inductive signal transmitter connected to the steering rod.When using inductive measurement technology in a steering gear, however, more difficult conditions are produced on the magnetic shield due to the materials used for the steering components.Furthermore, for accurate position determination, a defined and as constant as possible air gap is required between the signal transmitter and the sensor. However, the air gap cannot be ensured when the steering rod is deformed under load.The signal transmitter and the signal transmitter mounting must also withstand the load cases occurring. Since the signal transmitter is fastened on the steering rod, it must also withstand the same bending and torsion as the steering rod itself. Due to the different thermal expansion coefficients of the materials and the large temperature range (-40° C. to 120° C.), stresses can additionally result at the connection point.Under certain circumstances, the signal transmitter can also be used for the mounting of the steering rod. For this purpose, the signal transmitter or the carrier material must meet certain tribological requirements with regard to friction, wear, lubrication and material compatibility.The connecting technique should moreover be suitable for mass production, so that the steering rod can be produced by machine. In order to ensure this, a high process safety and a short cycle time are required.Conventional electronic circuit boards are not suitable as a substrate to withstand bending loads of the necessary magnitude and number. A printed circuit board cannot also be used as a bearing point. A sheet metal part which is injection-molded with plastic and which also has good tribological properties cannot be bonded to the steering rod in a robust manner on account of the sliding properties (PTFE fraction in the plastic).The object of the invention is thus to propose a method which fulfills the above-mentioned requirements and at the same time creates a good connection between the signal transmitter and the steering rod.The object is achieved by the subject matters of the independent claims.In the following, the term steering rod is used synonymous with steering rods in the actual sense, i.e. for steering two wheels, or in the sense of a single wheel actuator, i.e. for steering a single wheel. The terms are therefore interchangeable.Disclosure of the InventionAccording to a first aspect of the invention, this object is achieved by a method for producing 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.The method comprises the following steps:heating the handlebar to a temperature T higher than the melting temperature of the base material;positioning the signal transmitter on the steering rod; andpressing the signal transmitter against the steering rod with a pressure p, wherein the pressure p is maintained over a defined holding time t.The transmitting element of the signal transmitter consists of one or more conductive segments which generate an alternating magnetic field response signal in response to inductive excitation by an alternating magnetic field signal. The signal transmitter is designed in such a way that a unambiguously identifiable alternating response field signal can be measured at each possible position of the steering rod.The at least one transmitting element is preferably embedded in the carrier material in such a way that it cannot fall out or easily be detached. For example, the transmission element can be surrounded at its edge by the carrier material, so that it is held in a form-fitting manner. Alternatively, the transmitting element can be completely surrounded by the carrier material, so that it could only be released from the carrier material if the carrier material is damaged. In this latter embodiment, the layer between the transmitting element and the air gap towards the sensor should be as small as possible in order not to impair the quality of the measurement. On the other hand, thick layers have the advantage that they can better protect the transmission element from damage. As a result, a balance is found for the thickness of the layer which is neither too thin to provide protection nor too thick to keep the air gap to the sensor as small as possible.Preferably, the carrier material is a plastic which has a low melting temperature compared to the handlebar. The handlebar is heated to a temperature at which the carrier material melts. It is not absolutely necessary for the carrier material to liquify completely.The signal transmitter is positioned on the heated steering rod where it is required for position determination. Upon contact of the carrier material with the steering rod, the carrier material heats up and begins to melt in the contact region. The soft or liquid carrier material is connected to the warm steering rod.For good adhesion of the carrier material to the steering rod, it is important that the signal transmitter is pressed against the steering rod. This prevents air spaces from forming in the soft or liquid carrier material between the signal transmitter and the steering rod.The pressure p with which the signal transmitter is pressed against the steering rod is maintained over a holding time t. During this time, the steering rod cools together with the molten carrier material, the latter becoming solid again and thus connecting to the steering rod. Such a method is also referred to as "hot joining".As a result, a connection is thus produced between the steering rod and the signal transmitter, which resists deformations of the steering rod due to load and temperature fluctuations and the stresses associated therewith due to different thermal expansion coefficients. The invention thus achieves its object.In one embodiment, the handlebar comprises a milled-out planar region in which the signal transmitter is positioned.The milled-out, flat region of the steering rod can ensure, on the one hand, better adhesion of the signal transmitter to the steering rod. The pressure p at which the signaling device is pressed onto the handlebar during cooling is distributed uniformly when using a flat surface, so that the adhesion of the signaling device to the handlebar is homogeneous. No areas are formed in which the pressure and thus the adhesion is lower than in other areas.On the other hand, the signal transmitter can be lowered into the steering rod in this embodiment. For the steering, the steering rod must be able to move along its extension direction over a path length S. In this case, it moves under the sensor for the position determination. If necessary, support elements are used which support the steering rod against transverse forces. The signal transmitter countersunk in the steering rod can be moved with the steering rod past the mentioned components without disturbing the movement of the steering rod.Advantageously, the use of the milled-off, planar region for positioning the signal transmitter improves adhesion with the most compact installation space possible.In one embodiment, the surface structure of the handlebar is roughened prior to heating where the transducer is positioned.Roughening the surface structure of the steering rod in the contact region with the signal transmitter creates a larger surface area, with which the carrier material of the signal transmitter can connect. Furthermore, roughening produces unevenness in the material of the steering rod, on which the melted carrier material can better attack and adhere.Because of the roughening before the heating, the connection of the signal transmitter to the steering rod is thus advantageously improved.In one embodiment, the surface structure is roughened by means of a laser or a chemical method.Roughening may be performed using a laser. Preferably, the metal surface of the handlebar is first cleaned to remove dirt, oil or other contaminants that could interfere with 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.The laser is adjusted to scan the metal surface pointwise or linearly. The parameters such as laser power, pulse frequency, scan speed and focus are calibrated to remove the proper amount of material and produce the desired surface texture. The laser beam is guided over the surface of the steering rod, wherein a partial evaporation and melting of the metal is generated by the high energy of the laser. This melt cools rapidly and forms microscopic depressions and elevations which roughen the surface. The pattern may be uniform or random depending on the desired roughness profile.Preferably, after roughening, the surface may be repurified to remove residues of dissolved material. This ensures that the roughened surface is clean and optimum adhesion of the transducer is made possible.Alternatively to a laser, a chemical method may be used. Depending on the metal of the handlebar, a suitable chemical etchant may be used. For example, a solution of sodium hydroxide (NaOH) can be used for aluminium, while a mixture of hydrochloric acid (HCl) or iron(III) chloride (FeCl3) is suitable for steel. The choice of etchant will depend on the reactivity of the metal and the desired degree of roughening.The etchant is prepared in a container large enough to completely submerge the metal part. The concentration of the etchant and the temperature of the bath are adjusted according to the specific requirements and the type of metal. Locations of the handlebar that are not to be roughened may be masked with suitable materials.The handlebar is immersed in the etching bath and left therein for a certain time. During etching, the etchant reacts with the metal surface, thereby creating a microscopically rough structure. The duration of the etching depends on the desired roughness and reactivity of the metal.After the etching operation, the metal part is removed from the etching bath and thoroughly rinsed to remove any remaining etchant. The part is then immersed in a neutralization solution, such as a dilute solution of sodium bicarbonate (NaHCO3), to stop the chemical reaction and ensure that no harmful residues remain.In one embodiment, heating the handlebar is integrated into an inductive heat treatment process in manufacturing the handlebar.Embodiments are particularly advantageous which can be integrated into conventional production lines for steering rods. One process step that the steering rods pass through during their production is a heat treatment.Preferably, the attachment of the signal transmitter can be carried out after or during this heat treatment. This saves renewed heating of the steering rod for melting the carrier material. This advantageously makes it possible to save an additional process step and to reduce the energy required for production.In one embodiment, the temperature T is selected such that it is at least 20 K above the melting temperature of the carrier material.The temperature T of 20 K above the melting temperature ensures that the carrier material actually melts at the contact surface with the handlebar. At lower temperatures, it may happen that the lower temperature of the signal transmitter cools down the steering rod in the contact region to such an extent that a homogeneous melting of the carrier material does not take place. This would result in less adhesion of the signal transmitter to the steering rod.On the other hand, too high a temperature T can lead to too much of the carrier material melting and the signal generator deforming or even the carrier material beginning to flow away. Further, the cooling process would take longer, which delays the entire manufacturing process.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 carrier material by cooling.Plastics can have 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 ranges influences the physical properties of the plastic, such as strength, rigidity and transparency.When the carrier material is melted, the crystalline structure can be disturbed or partly destroyed. This leads to a change in the mechanical properties of the material, it becomes soft and finally starts melting.Recrystallization is the process in which the ordered crystalline structures restore upon heating. This occurs when the plastic cools to a certain temperature-the recrystallization temperature. This temperature is below the melting temperature of the plastic, but high enough to allow the mobility of the polymer chains to reorient and form an ordered structure.The holding time is chosen so that the recrystallization temperature is achieved. The signal transmitter is pressed onto the steering rod until then, so that during recrystallization the molecular structures of the carrier material assume a form which is particularly stable.In a further aspect, the invention relates to a steering rod having a signal transmitter for inductive position measurements, wherein the steering rod has been produced using a method as described above.In one embodiment, the carrier material of the signal transmitter is POM, PEEK or Polyeton.POM, PEEK and Polyetone are commercially available plastics which are particularly easy to handle and have the required material properties.In one embodiment, the signal transmitter comprises a plurality of transmitting elements, wherein gaps are arranged between the transmitting elements, such that the transmitting elements and the gaps form one or more tracks which extend parallel to the direction of extension of the steering rod.In this embodiment, the substrate further has a function of a spacer between the transmitting elements. The transmitting elements can preferably be arranged as two tracks, with which a determination of the position of the steering rod is made possible, for example, according to the Nonius principle. In this embodiment, the exact positioning of the transmitting elements relative to one another is particularly important. In this embodiment, the carrier material can be precisely shaped, so that the position of the transmitting elements is as precise as possible.In one embodiment, the signal transmitter comprises a transmitting element which extends over a path length S and is arranged at an angle α to the direction of extension of the steering rod.The angle α should be selected as large as possible, so that the transmitting element is positioned as obliquely as possible over the path length S. The upper limit for α can be the trigonometric ratio of the path length S and the width B available to the transmitting element. Each position of the steering rod is then to be assigned unambiguously to a section of the transmitting element which is 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.In summary, it can be stated that the present invention provides a method for producing 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.The described embodiments and developments can be combined with one another as desired.Further possible embodiments, developments and implementations of the invention also include combinations of features of the invention described above or below with respect to the exemplary embodiments, which combinations are not explicitly mentioned.Brief Description of the DrawingsThe 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 principles and concepts of the invention.Other embodiments and many of the advantages mentioned are evident with reference to the drawings. The elements of the drawings shown are not necessarily shown true to scale with respect to one another.The following are shown: FIG. 1 is a sectional view of a signal transmitter attached to a steering rod; FIG. 2 shows a steering rod with a signal transmitter for inductive position determination; and FIG. 3 schematically shows the sequence of the method according to one embodiment.In the figures of the drawings, identical reference numerals designate identical or functionally identical elements, components or components, unless indicated to the contrary.FIG. 1 shows a portion of a handlebar 10 to which a signal transmitter 12 is applied. The signal transmitter comprises a carrier material 14, in which two transmitting elements 16 aand 16 bare enclosed.Between the transmitting elements 16 aand 16 band the steering rod 10, or the material thereof, a distance 18 is provided which isolates the transmitting elements 16 aand 16 bfrom the steering rod 10. In operation, an inductive sensor is positioned at a small distance from the signal transmitter 12 and emits an alternating magnetic field signal. The sensor (not shown here) would be positioned above the signal transmitter 12 in the illustration. The alternating magnetic field signal generated by the sensor in turn generates eddy currents in the transmitting elements 16 aand 16 b. The transmitting elements 16 aand 16 bthereon in turn emit magnetic alternating-field response signals which can be detected by the sensor. The position of the steering rod can then be determined from the alternating-field response signals.In order to optimize the magnetic coupling between the sensor and the transmitting elements 16 aand 16 b, the distance 18 is selected to be sufficiently large so that the steering rod 10 does not generate a measurable alternating magnetic field response signal.In the embodiment shown, the transmitting elements 16 aand 16 bare surrounded by the carrier material 14. The distance 20 between the transmitting elements 16 aand 16 band the upper edge of the signal transmitter 12 is selected such that the magnetic interaction between the sensor and the signal transmitter 12 is as far as possible not impaired, but the carrier material 14 nevertheless provides good protection of the transmitting elements 16 aand 16 b.At the transition 22 from the signal transmitter 12 to the steering rod 10, the carrier material 14 protrudes somewhat beyond the steering rod 10. When the handlebar 10 is warm and the base material 14 softens, the base material 14 may wrap slightly around the edge of the handlebar 10 to improve the retention of the signal transmitter 12 to the handlebar 10.FIG. 2 schematically shows a steering rod 10 to which a signal transmitter 12 is attached. The steering rod 10 is mounted movably over a path length S. The steering rod 10 has a thread 24, via which it can be driven by a drive.The steering rod 10 further comprises a milled-out planar region 26, in which the signal transmitter 12 is positioned. The signal transmitter 12 is positioned such that it does not project beyond the steering rod 10 in profile.An inductive sensor 28 is disposed above the signal transmitter 12. The sensor 28 generates an alternating magnetic field signal which in turn generates a response alternating magnetic field signal in the transmitting element of the signal transmitter 12. The alternating magnetic field response signal is in turn detected by the sensor 28. The position of the steering rod 10 is finally determined from the detected signal.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 handlebar 10, more specifically the signal transmitter 12 when the handlebar 10 moves transversely to its extension direction due to external loads. For the most accurate possible position determination, the air gap 30 should be as constant as possible.Two support elements 32 aand 32 bare provided for supporting the steering rod 10. The support members 32a and 32b engage the handlebar 10 from two sides so as to limit the movement of the handlebar 10 in these directions. Preferably, therefore, the support members 32a and 32b are positioned in close proximity to the sensor 28 so that the air gap 30 remains constant. At points of the handlebar 10 that are farther away from the support members 32 aand 32 b, deformations of the handlebar 10 may occur. At these points, the steering rod 10 can move vertically to a small extent, so that a position measurement is rather unsuitable there. By the proximity of the support elements 32 aand 32 bto the sensor 28, this effect can be reduced.In the embodiment shown, the support element 32a directly engages the signal transmitter 12. The signal transmitter 12 is configured in this embodiment so as to be able to withstand the pressure of the support member 32 awithout being damaged. For this purpose, the at least one transmitting element in the signal transmitter 12 can be surrounded by the carrier material. The carrier material thus forms a protective layer around the at least one transmitting element and protects the latter from damage by the supporting element 32 a.In embodiments, a steering system may include a plurality of support members that support the handlebar 10 in a plurality of directions.FIG. 3 schematically shows the sequence of the method for producing a steering rod with a signal transmitter according to one embodiment.In a first step S 10, the steering rod is heated. The term "heating" is synonymous in this context with "bringing to a certain temperature". If the heating is part of the heat treatment of the steering rod, this can also be heating in the sense of the present invention.If the handlebar has reached a sufficiently high temperature, for example 20 K above the melting temperature of the substrate material of the signaling device, the signaling device is positioned on the handlebar in step S 12.If the signal transmitter is correctly positioned, it is pressed against the steering rod with a defined pressure p in step S 14. The pressure is maintained over a holding time t. During this time, the handlebar and the base material cool. The molten carrier material solidifies again and forms good adhesion to the steering rod. The cooling process can be carried out passively or actively, that is to say by supporting cooling devices.

Claims

Method for manufacturing a handlebar (10) with a signal transmitter (12) for inductive position measurements, the signal transmitter (12) comprising at least one metallic transmitter element (16a, 16b), the transmitter element (16a, 16b) being embedded in a support material (14), the method comprising the following steps: - heating (S10) the handlebar (10) to a temperature T which is higher than the melting temperature of the support material (14); - positioning (S12) the signal transmitter (12) on the handlebar (10); and - pressing (S14) the signal transmitter (12) against the handlebar (10) with a pressure p, the pressure p being maintained over a defined holding time t.Method according to any of the preceding claims, wherein the steering rod (10) comprises a milled-out planar region (26) in which the signal transmitter (12) is positioned.Method according to any of the preceding claims, wherein the surface structure of the steering rod (10) is roughened before heating (S10) where the signaling device (12) is positioned.The method according to claim 3, wherein the roughening of the surface structure is effected by means of a laser or a chemical method.Method according to any of the preceding claims, wherein the heating (S10) of the steering rod (10) is integrated into an inductive heat treatment process during the production of the steering rod (10).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 carrier material (14).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 carrier material (14) by cooling.A handlebar (10) having a signal transmitter (12) for inductive position measurements, the handlebar (10) having been manufactured using a method according to any one of the preceding claims.The handlebar (10) of claim 8, wherein the substrate (14) of the signaling device (12) is POM, PEEK, or Polyeton.The handlebar (10) according to any one of claims 8 to 9, wherein the signal transmitter (12) comprises a plurality of transmitter elements (16a, 16b), wherein gaps are arranged between the transmitter elements (16a, 16b) such that the transmitter elements (16a, 16b) and the gaps form one or more tracks extending parallel to the extension direction of the handlebar (10).The steering rod (10) according to any one of claims 8 to 9, wherein the signal transmitter (12) comprises a transmitter element which extends over a path length S and is arranged at an angle α to the direction of extension of the steering rod (10).Steer-by-wire steering system comprising a steering rod (10) according to any of claims 8 to 11.

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