Spindle drive of a vehicle steering system, in particular a steer-by-wire steering system, and steer-by-wire steering system

Abstract

A spindle drive of a steering system of a vehicle comprising a spindle (124) with an external thread and a spindle nut (50) with an internal thread, which are engaged and form a motion thread for translational displacement of the spindle, wherein the spindle (124) has a cavity in the axial direction, which is provided at least in a region in which heat can be generated on the spindle (124) in the region of the motion thread due to a movement of the spindle nut (50) relative to the spindle, wherein at least one heat pipe (70) is provided in the cavity.

Description

[0001] The present invention relates to the field of vehicle steering systems, in particular rear axle steering systems with steer-by-wire technology.

[0002] Steering systems in motor vehicles are known to include a steering wheel, a steering shaft, a steering gear, and a steering linkage for converting the steering angle specified by the driver into a steering angle of the steerable wheels. So-called steer-by-wire steering systems are also known, which are used, for example, in rear-axle steering systems. In these systems, the steering movement is converted electromechanically by means of an electric motor that adjusts the steering angle. DE 10 2014 206 934 A1 discloses an actuator with a spindle drive with a trapezoidal thread for a rear-wheel steering system in a motor vehicle.

[0003] Particularly in steer-by-wire steering systems with mechanical self-locking in the spindle drive, a significant local temperature input occurs in the spindle drive area – more precisely, in the threads of the interlocking threads of a spindle nut and a spindle that can only be moved translationally. Both the spindle and the spindle nut heat up considerably due to friction in the threads and, to an even greater extent, due to the typically limited travel of the spindle. Of the three principles of heat dissipation (convection, radiation, and conduction), only conduction makes a significant contribution, since virtually no natural convection or radiation of heat to the surroundings occurs within the spindle enclosed by the spindle nut. However, conduction is limited by the thermal conductivity of steel (the material from which the spindle is made) and the relatively small diameter of the spindle.It is complex to install a temperature sensor directly on the spindle drive, so the temperature of the spindle drive must be estimated and the system switched off early by a so-called derating function to prevent individual components from being damaged by excessive heating.

[0004] From DE 10 2021 123 260 A1 in the field of winding machines for winding several threads into spools it is known to dissipate the thermal load of a winding spindle by means of a heat pipe as a heat exchanger.

[0005] It is an object of the invention to provide a spindle drive of a steering system of a vehicle in which better heat management, i.e. heat distribution and / or heat dissipation, takes place.

[0006] This task is solved by the features of independent claims. Advantageous embodiments are the subject of dependent claims.

[0007] A spindle drive for a vehicle steering system, in particular a steer-by-wire steering system, is proposed, comprising a spindle with an external thread and a spindle nut with an internal thread, which are engaged and form a motion thread for translational displacement of the spindle, wherein the spindle has a cavity in the axial direction, which is provided at least in an area in which heat can be generated on the spindle in the area of ​​the motion thread due to movement of the spindle nut relative to the spindle, wherein at least one heat pipe is provided in the cavity.

[0008] As previously mentioned, a significant local temperature increase occurs in the spindle drive, particularly in steer-by-wire steering systems with mechanical self-locking, because the threads of the spindle and spindle nut have a high contact area. Furthermore, the high forces exerted on the spindle and steering rod by the wheels (lateral and transverse forces) in the chassis result in high surface pressure on the thread flanks. Both the spindle and the spindle nut heat up considerably due to the limited travel range. This limited travel range means that the same thread flanks of the spindle and spindle nut rub against each other very frequently. The heat pipe also functions when stationary, as the constant alternation between movement and standstill phases allows the heat generated during movement to be transferred to the stationary phases.The proposed heat pipe, integrated into the spindle, provides improved heat distribution and / or heat dissipation throughout the entire spindle drive, thus reducing local heat build-up in the spindle drive.

[0009] In one embodiment, the cavity is sealed at both ends with a material-tight barrier, and a metal braid and a working fluid are provided within the cavity, so that the cavity serves as a heat pipe. In this embodiment, the spindle acts as the tube of the heat pipe, and heat is transferred directly from the working fluid to the spindle.

[0010] In one embodiment, at least one heat pipe, formed as a separate component, is inserted into the cavity. By using the heat pipe as a single component, it is not necessary to seal the cavity in the spindle with a material-tight seal.

[0011] In one embodiment, a core is inserted centrally into the cavity, along with several heat pipes, formed as separate components, arranged around the outer circumference of the core and bordering an inner wall of the cavity. The core reduces the number of heat pipes required to fill the cavity. Furthermore, the core can serve to press the heat pipes against the inner wall of the cavity in the spindle, or at least position them there, to enable optimized heat transfer.

[0012] In one design, several heat pipes, each formed as a separate component, are inserted into the cavity, and the spaces between the heat pipes are filled with a heat-conducting material. This allows for even better heat transfer.

[0013] In one version, the spindle is formed from a solid piece of material into which the cavity is inserted. Alternatively, the cavity is produced by an internal high-pressure forming process. Another alternative is that the spindle is formed as a tube.

[0014] Furthermore, an actuator for a vehicle's steer-by-wire steering system is proposed, comprising a housing with a spindle drive arranged therein, the spindle being formed as described, and a stationary spindle nut. At least one rolling bearing is also provided, by means of which the spindle nut is rotatably and stationary relative to the housing. The spindle nut can be driven in the direction of rotation by an electric motor via a pulley of a belt drive.

[0015] Furthermore, a system for operating a steer-by-wire steering system in a non-slip transmission of a vehicle is proposed, wherein the steer-by-wire steering system comprises a steering rod and an electric motor for controlling the steering rod via the non-slip transmission, as well as an actuator for controlling the steer-by-wire steering system.

[0016] Furthermore, a steer-by-wire steering system is proposed for a vehicle with the described system.

[0017] A steering system in a motor vehicle must generally be able to handle the high forces in the vehicle's chassis that act on the steered axle and thus on the wheel steering due to lateral forces, for example, during cornering or lateral acceleration. These high forces, such as 5 to 15 kN, act equally on a steer-by-wire steering system and the associated actuator, which initiates the steering movement. A wheel steering system must be designed to guide the wheel so that the set steering angle, and therefore the intended driving path, can be maintained. This means that a steering angle must always be maintained when high lateral and / or transverse forces, and the resulting forces and moments, act on the steering system. This is primarily the case while driving.The steering rod, in the form of a spindle drive of an actuator (also known as a steering actuator), is thus designed as a wheel-guiding component. In the event of an actuator failure, it must have a mechanism to maintain the wheel steering angle in its current position. In a steer-by-wire system, for example, as auxiliary steering on the rear axle in addition to the standard front axle steering, a return to a steering angle of 0 degrees (i.e., in the direction of the vehicle's longitudinal axis) may be necessary in the event of a failure. This steering angle must then also be maintained after the return, because otherwise the steering angle at the rear axle could change uncontrollably due to dynamic influences, making the vehicle more difficult to control. This maintenance can be achieved by a locking mechanism within the actuator, which, however, adds weight and costs.Preferably, the drive thread is designed with such an efficiency that self-locking occurs in the event of a spindle drive failure. Therefore, trapezoidal threads are used in drive threads in actuators of a steer-by-wire steering system, as is known, e.g., according to DIN 103. Such trapezoidal threads can inherently have a low efficiency of, for example, 30%, and thus a steer-by-wire steering system can be designed to be self-locking in order to limit, reduce, or completely prevent unwanted changes in the steering angle in the event of a fault.

[0018] The rotary / translational drive is preferably designed as a spindle drive for the actuator. An electric motor preferably drives a spindle nut, which is rotatably mounted in a housing, via a toothed belt drive. The spindle nut's internal thread engages with the external thread of a spindle, thus forming a thread. When the spindle nut rotates, the rotational movement is converted into a translational movement by means of the thread of the spindle drive, and the spindle, which is secured against rotation and functions as a steering rod, is displaced axially or along its longitudinal axis. The steering rod is articulated at at least one end to a wheel carrier by means of a steering linkage, such as a tie rod. The axial displacement of the steering rod or spindle causes the wheel carrier to rotate about its vertical axis or steering axis.The wheel, which is rotatably mounted on at least one wheel carrier of an axle, can thus be steered, whereby a change in the position of the steering rod causes a change in the wheel steering angle at the wheel or the vehicle axle.

[0019] A steer-by-wire steering system is a mostly electromechanical unit that is mechanically decoupled from a steering handle, such as a steering wheel. Based on steering signals and one or more parameters, such as vehicle speed, steering wheel angle, current steering angles at the front and / or rear axles, yaw acceleration and / or lateral acceleration of the vehicle, etc., steering signals are generated in a control unit. The steering movement is carried out by at least one actuator of the steer-by-wire steering system, which receives steering signals from the control unit.

[0020] Further features and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention and from the figures, which illustrate details of the invention. The individual features can be implemented individually or in any combination in a variant of the invention.

[0021] Preferred embodiments of the invention are explained in more detail below with reference to the accompanying drawing. Fig. Figure 1 schematically shows an actuator of a steer-by-wire steering system according to the state of the art. Fig. 2 shows an enlarged view A of the in Fig. 1 Actuator shown with a heat pipe provided in the spindle according to one embodiment of the invention. Fig. Figure 3 shows a sectional view in the SS direction onto the [unclear] Fig. 2nd version shown. Fig. Figure 4 shows an enlarged view A of the in Fig. 1 actuator shown with a heat pipe provided in the spindle according to a further embodiment of the invention. Fig. 5 shows a sectional view in the SS direction of the in Fig. 4 shown versions. Fig. Figure 6 shows a sectional view in the SS direction of the area in Fig. 4. Embodiment shown according to a further embodiment of the invention.

[0022] In the following figure descriptions, identical elements or functions are marked with the same reference symbols.

[0023] The proposed spindle drive is part of a vehicle's steering system, in particular a steer-by-wire system. The steered axle can be a front axle, a rear axle, or an axle located between the front and rear axles of a vehicle. A subframe is provided on the axle, which is attached to or forms part of the vehicle body and is connected to the vehicle's body. The vehicle's wheels are articulated to the subframe by means of control arms as part of a wheel suspension. An actuator 10 for operating the steer-by-wire steering system is arranged on the subframe.

[0024] Fig. Figure 1 shows a partially cutaway detail view of an actuator 10 of a steer-by-wire steering system according to the prior art, with a housing 22 which can be attached to the vehicle body by means of the illustrated tabs 22a, 22b. A spindle drive 30 is arranged inside the housing 22 of the actuator 10, which has a spindle nut 50 that can be driven in the direction of rotation and engages with the spindle 124. The spindle 124 and spindle nut 50 thus form a threaded connection that acts as a rotation / translation converter. The spindle nut 50 can be driven in the direction of rotation by an electric motor 29 via a pulley 61 of a belt drive 60 and is mounted in the housing 22 in a fixed and rotatable position by means of a rolling bearing 40. The rotation of the spindle nut 50 allows the spindle 124 to be displaced in one direction or the other.The spindle 124 is connected at both ends to housing-side guided bearing sleeves 75, 76, which in turn are connected to joint connections 27, 28 arranged at the ends of the housing 22. The actuator 10 is designed as a so-called central actuator, i.e., it acts simultaneously on the steering of both wheels, e.g., the rear wheels, and can be arranged, for example, centrally in the vehicle. In other words, the actuator 10 is a device that enables the steering to be operated.

[0025] Steer-by-wire steering can be used for a vehicle that is intended, for example, for transporting people and additionally or alternatively objects.

[0026] In Fig. 2 and Fig. 4 is each an enlarged section from Fig. Figure 1 shows the only difference from the previously known actuator 10 being that a spindle 124 according to the invention is provided here with a cavity and a heat pipe 70 arranged therein, as described below. Fig. 3, Fig. 5 and Fig. 6 is each a front view of a Fig. 2 or 4 shown versions.

[0027] The object of the invention is to provide improved thermal management, i.e., better heat dissipation and / or heat distribution, at the spindle 124 of the spindle drive in order to reduce local heating due to movement of the threaded components in the moving thread, but also when stationary. For this purpose, it is proposed to use a heat pipe 70, which is provided in a cavity of the spindle 124 located in the axial direction X. Heat pipes 70 are generally known and are formed as a tube (an elongated hollow body with a length greater than its diameter) with a metal braid 71 arranged inside it, which acts like a wick for heat transport along the length of the tube. Heat pipes 70 are generally made of a thermally conductive material such as copper or aluminum. Inside, in addition to the metal braid 71, a fluid is provided as the working medium, which is partly in a liquid and partly in a gaseous state and is designed for the application.The liquid can be water or a liquid with a melting and boiling point adapted to the application, such as methanol or ethanol. The pipe is impermeable, so the liquid cannot escape in either a liquid or gaseous state. The operating principle of heat pipes 70 is known and is only briefly outlined here for the sake of completeness. If a section of the pipe is heated, the liquid in that section evaporates and moves away from the heat source as vapor (i.e., in a gaseous state) due to the pressure gradient. In the present embodiment, the heat pipe 70 would be heated in the area of ​​the spindle nut 50 when it moves the spindle 124. In areas where the temperature is lower than the boiling point of the liquid, the vapor cools and condenses again. In the [reference to be added]... Fig. In the embodiment shown, this would be beyond the spindle nut 50, i.e., at or near the two end regions of the spindle 124. The working medium, now in a liquid state again, is transported back to the heated area by the wicking effect (capillary action) of the metal mesh 71.

[0028] In Fig. 2 is a first version in enlarged view A from Fig. Figure 1 shows the spindle 124 according to the invention. Fig. Figure 3 shows a section view from Fig. 2 in the direction of SS. In the embodiment shown here, the spindle 124 itself serves as the tube of the heat pipe 70. For this purpose, it has a cavity formed in the axial direction X. This cavity can either extend the entire length of the spindle 124 or only a portion thereof, as long as it is within the range of motion of the spindle nut 50, where heat is generated during operation. Both the metal braid 71 required for heat transfer and the working medium are provided in this cavity.

[0029] The cavity must be sealed tightly at both ends. This can be achieved at one end, for example, by ensuring that the cavity does not extend to the end of the spindle 124, so that the end of the spindle 124 serves as the end cap 72 of the heat pipe 70. In any case, an end cap 72 must be provided at at least one end, which is connected to the end of the cavity and to the spindle 124 in such a way that the working medium cannot escape from the heat pipe 70, i.e., the cavity of the spindle 124, in either liquid or gaseous form. In the embodiment shown, end caps 72 are provided at both ends.

[0030] In Fig. 4 is another version in enlarged view A from Fig. Figure 1 shows the spindle 124 according to the invention. Fig. 5 shows a section view from Fig. 4. According to the design SS for one embodiment. In this embodiment, several heat pipes 70, designed as separate components, are provided with a metal braid 71 required for heat transfer and a working medium inside (sealed in a medium-tight manner). These heat pipes are arranged in a cavity formed in the spindle 124. The cavity can extend over the entire length of the spindle 124 or only over parts of it, as long as the movement range of the spindle nut 50, in which the heat is generated, is covered. The heat pipes 70 can also have a length corresponding to the length of the cavity. Alternatively, several heat pipes 70 (in the X direction) can be inserted one after the other into the cavity, the sum of which corresponds to the length of the cavity.

[0031] The number of heat pipes 70 inserted into the cavity is advantageous, as it optimally fills the cavity. In one embodiment, the remaining spaces between the heat pipes 70 are filled with a thermally conductive material such as thermal paste, adhesive, liquid, gas, or another suitable material to optimize heat conduction between the heat pipe 70 and the spindle 124.

[0032] In another version, which in Fig. 6 (a sectional view from Fig.As shown in Figure 4 (for an alternative embodiment), a core 80 extending over the entire length (in the X-direction) of the cavity or only over a portion thereof can be provided centrally within the cavity. The heat pipes 70 are then arranged around an outer circumference of the core 80, i.e., between the core 80 and the inner wall of the spindle 124 (outer wall of the cavity), and abut an inner wall of the cavity. The core 80 is advantageously dimensioned such that the heat pipes 70 are pressed against the inner wall by the core 80 or at least held in position against it. In this embodiment, fewer heat pipes 70 can be required, but good heat transfer between the heat pipes 70 and the spindle 124 can still be achieved by means of the heat pipes 70 arranged along the inner wall and thus in contact with it. The core 80 can, for example, be formed as a tube (hollow) or as a round (made of solid material).

[0033] In all versions, the cavity of the spindle 124 can be provided in different lengths. It can occupy the entire length of the spindle (in the X direction) or be formed only in parts of it, which in any case include the area in which the heat is generated, i.e. the area of ​​the spindle 124 that covers the range of motion of the spindle nut 50.

[0034] In all embodiments, the cavity of the spindle 124 can be provided in different ways. In one embodiment, the spindle 124 is formed from a solid material, in particular steel, and the cavity is produced by a bore in the axial direction X (longitudinal direction). In another embodiment, the cavity can be produced by an internal high-pressure forming process. In yet another embodiment, a tube with a corresponding cavity formed by the walls of the tube can also be used for the spindle 124.

[0035] By using a heat pipe 70 in the spindle 124, a local heat build-up in the spindle drive 30 can be reduced, thus preventing premature shutdown of the spindle drive 30, as there is a lower heat load that could damage components of the spindle drive 30. Reference sign 10 Actuator 22 cases 22a, 22b tabs 27, 28 Joint connection 29 Electric motor 30 Spindle drive 40 rolling bearings 50 spindle nuts 60 Belt drive 61 Pulley 70 Heatpipe 71 Metal mesh 72 end caps 75, 76 bearing sleeves 80 core 124 spindle

Claims

[1] Spindle drive of a steering system of a vehicle comprising a spindle (124) with an external thread and a spindle nut (50) with an internal thread, which engage and form a motion thread for translational displacement of the spindle, wherein the spindle (124) has a cavity in the axial direction, which is provided at least in a region in which heat can be generated on the spindle (124) in the region of the motion thread due to a movement of the spindle nut (50) relative to the spindle, wherein at least one heat pipe (70) is provided in the cavity. [2] Spindle drive according to claim 1, wherein the cavity is sealed material-tight at both ends and a metal mesh (71) and a working medium are provided inside the cavity, so that the cavity serves as a heat pipe (70). [3] Spindle drive according to claim 1, wherein at least one heat pipe (70) formed as a separate component is inserted into the cavity. [4] Spindle drive according to claim 3, wherein a core (80) is centrally placed in the cavity, and several heat pipes (70) formed as separate components, which are arranged around an outer circumference of the core (80) and border an inner wall of the cavity. [5] Spindle drive according to claim 3, wherein several heat pipes (70) formed as separate components are inserted into the cavity and spaces between the heat pipes (70) are filled with a heat-conducting material. [6] Spindle drive according to one of the preceding claims, wherein the spindle (124) is formed from a solid material into which the cavity is inserted, or wherein the cavity is produced by an internal high-pressure forming process, or wherein the spindle (124) is formed as a tube. [7] Actuator (10) for a steer-by-wire steering system of a vehicle, comprising a housing (22) with a spindle drive (30) arranged therein, having a spindle (124) and a stationary spindle nut (50), and at least one rolling bearing (40) by means of which the spindle nut (50) is rotatably and stationary relative to the housing (22), wherein the spindle nut (50) can be driven in the direction of rotation by an electric motor (29) via a pulley (61) of a belt drive (60), and wherein the spindle (124) is formed according to one of the preceding claims. [8] System for operating a steer-by-wire steering system in a non-slip transmission of a vehicle, wherein the steer-by-wire steering system comprises a steering rod and an electric motor (29) for controlling the steering rod via the non-slip transmission, as well as an actuator (10) according to claim 7 for controlling the steer-by-wire steering system. [9] Steer-by-wire steering for a vehicle comprising the system according to claim 8.

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