Spindle drive of a steer-by-wire steering system for a motor vehicle, actuator with a spindle drive and steer-by-wire steering system for a motor vehicle

Abstract

Spindle drive (121) of a steer-by-wire steering system for a motor vehicle, comprising a housing (128) and a spindle (122) with a spindle thread (122a), wherein the spindle (122) is mounted in the housing (128), characterized in that a spindle sleeve (140) is mounted in a stationary manner in the housing (128), wherein at least two threaded rings (160, 161) are coupled to the spindle sleeve (140) in a manner secured against rotation, wherein the threaded rings (160, 161) are in engagement with the spindle (122) and form a movement thread in order to linearly displace the spindle (122) along its longitudinal axis (a) relative to the spindle sleeve (140).

Description

[0001] The invention relates to a spindle drive of a steer-by-wire steering system for a motor vehicle, an actuator with a spindle drive and a steer-by-wire steering system for a motor vehicle according to the preambles of the independent claims.

[0002] Actuators with spindle drives are used in motor vehicle steering systems to steer the wheels. The actuators use the spindle drives to convert a rotational movement into a linear actuating movement, whereby the spindle can be moved linearly along its longitudinal axis by means of a spindle nut that is fixedly arranged in the actuator housing and rotatably driven. The spindle nut engages with its internal thread in the external thread of the spindle. Such a functioning principle can be found in DE 10 2015 224 775 A1. However, there is play between the spindle thread and the spindle nut thread, which is minimized by means of a loose nut and a spring element. A constant axial preload ensures that the flanks of the spindle and spindle nut threads come into contact, thus minimizing axial play and preventing acoustic abnormalities when changing direction in the spindle drive from being transmitted via the chassis into the body.

[0003] The invention aims at an alternative design of a spindle drive, which simplifies the spindle drive and thus enables cost-effective production.

[0004] To achieve this, devices according to the independent claims are provided. Preferred developments of the device according to independent claim 1 are specified in the subclaims.

[0005] The invention relates to a spindle drive of a steer-by-wire steering system for a motor vehicle, comprising a housing and a spindle with a spindle thread, wherein the spindle is mounted in the housing. The invention is characterized in that a spindle sleeve is mounted in a stationary manner in the housing, wherein at least two threaded rings are coupled to the spindle sleeve, wherein the threaded rings engage with the spindle and form a movement thread in order to linearly displace the spindle along its longitudinal axis relative to the spindle sleeve. Thus, a rotational movement of the spindle sleeve, which is driven, for example, by an electric motor directly or via a belt drive or the like, is converted into a linear movement of the spindle along its longitudinal axis.

[0006] If the end of the spindle is connected to the wheel carrier via a linkage or directly, this allows the wheel steering angle to be changed, thus allowing the wheels to be steered. The high lateral forces must be taken into account, so the spindle drive must be designed for the high lateral forces encountered in motor vehicles.

[0007] In contrast to known spindle nuts from the prior art, a spindle sleeve is used here which does not have its own internal thread. The spindle sleeve is essentially a cylindrical component in the form of a hollow body. In other words, the spindle sleeve is not indirectly operatively connected to the spindle in order to move it linearly. Rather, at least two threaded rings are coupled to the spindle sleeve, each of which has an internal thread. The coupling is a connection between the threaded rings and the spindle sleeve that is secured against rotation. If the spindle sleeve is driven in rotation, the threaded rings are forced to rotate with it. The rotation of the threaded rings, which rotate stationary with the spindle sleeve in the housing of the spindle drive, forces a linear movement of the spindle in order to move it along its longitudinal axis. For this purpose, a rotation lock may be required for the spindle, e.g.opposite the housing so that the spindle does not rotate when the spindle sleeve and therefore the threaded rings rotate. This has the advantage that the spindle sleeve can be manufactured very easily, for example as a turned part or a die-cast part, and the same applies to the threaded rings. These can be made from bar stock, for example in the form of a tube with an internal thread. The threaded rings only need to be cut to the appropriate width from this tube, as required for the spindle drive. The spindle rings are screwed onto the spindle during assembly after the spindle has been pushed through the spindle sleeve. The threaded rings are then turned towards the spindle sleeve and, once the threaded rings are in contact with the spindle sleeve, the threaded rings can be clamped against one another using the interposed spindle sleeve.This ensures that the threaded rings, together with the spindle sleeve, have no play with the spindle. This effectively prevents any acoustic abnormalities.

[0008] The threaded rings can be made of various materials. They can be made of plastic, a fiber composite material, steel, brass, or a suitable metal alloy, for example. The housing is preferably made of a light metal die-cast.

[0009] In a preferred embodiment, the threaded rings are arranged in the area of the end faces of the spindle sleeve. Depending on the design of the spindle, the threaded rings can be supported externally on the end faces of the spindle sleeve if, as mentioned above, they are screwed onto the spindle sleeve during assembly. However, the spindle sleeve can also have recesses on the end face into which the threaded rings are partially or fully screwed or inserted. This results in a package of spindle sleeve and threaded rings which, in terms of function, is equivalent to a spindle nut known from the prior art. In spindle nuts from the prior art, however, the internal thread of the spindle nut is arranged either in the middle or to the side of the spindle nut. Countermeasures are therefore usually necessary to prevent the spindle nut from jamming on the spindle under load.The clever arrangement of the threads on the two outer sections of the spindle sleeve provides support on both sides of the spindle, minimizing the tendency to jam. Furthermore, the two threaded rings minimize play. An internal thread like that of the spindle nut is unnecessary.

[0010] The inner side of the spindle sleeve preferably forms, at least indirectly, a bearing seat for supporting the spindle. The bearing seat of the spindle sleeve is preferably designed concentrically to the longitudinal axis of the spindle sleeve. This achieves centering of the spindle sleeve relative to the spindle, so that the internal threads of the threaded rings are also centered relative to the thread of the spindle. This effectively further reduces the tendency of the threads of the threaded rings to clamp relative to the external thread of the spindle. The inner diameter of the bearing seat of the spindle sleeve is dimensioned relative to the outer diameter of the spindle thread, also called the tip circle, such that a clearance fit results between the tip circle and the inner diameter. The bearing seat is preferably designed as a smooth cylindrical hollow cylinder. Alternatively, the bearing seat can be designed to accommodate a rolling bearing, preferably a needle bearing.The needle bearing is designed so that the rolling elements roll on the tip circle of the spindle. This can be particularly necessary if the spindle sleeve is driven by a drive belt. The drive belt is mounted with a certain pretension, whereby the needle bearing not only ensures centering but also easy rotation of the spindle drive. The drive belt, also called a belt, is preferably designed as a toothed belt. For reliable and slip-free rotation in interaction with the belt, the drive sleeve is preferably equipped on its outer side with teeth complementary to the belt. Alternatively, a belt pulley is placed, preferably pressed onto the outer side of the spindle sleeve during assembly. This pulley is provided with teeth complementary to the belt, so that in this arrangement a slip-free drive of the spindle sleeve is guaranteed.

[0011] In an advantageous embodiment, each threaded ring is positively and / or non-positively and / or materially coupled to the drive sleeve. This effectively prevents the threaded rings from turning loose during operation and gaining clearance relative to the spindle sleeve. The threaded rings can be welded or glued to the outer sides, preferably the end faces of the spindle sleeve. The threaded rings can also have a flattened area on their outer side which interacts with a flattened area on the inner side in the area of the end faces of the spindle sleeve. After the spindle sleeve has been assembled with the spindle and the threaded rings, the material can be deformed on the end faces of the spindle sleeve so that the threaded rings are fixed relative to the spindle sleeve, for example by rolling or caulking.

[0012] To further improve the minimization of play between the spindle sleeve and the spindle, an alternative embodiment can provide for a preloaded force accumulator, in particular in the form of a spring washer, to be arranged at least between one of the threaded rings and the spindle sleeve. The spring washer is preferably made of an elastomer and can be in the form of an O-ring. A force accumulator is preferably provided on each side between the threaded ring and the area of the end face of the spindle sleeve. During assembly, the preload of the spring washers is generated when the threaded rings are adjusted or screwed onto the spindle sleeve with the spring washers interposed.A first advantageous effect is achieved by the threaded rings being brought into contact with their internal threads against the flanks of the spindle thread and being clamped against one another so that there is no play between the internal threads of the threaded rings and the external thread of the spindle. A second advantageous effect of the preload is self-locking in combination with a relatively low preload in the moving thread. The preload can be selected depending on the thread pitch of the moving thread so that self-locking occurs even when the drive of the spindle sleeve is switched off. In comparison to prior art spindle drives, self-locking in the spindle drive can thus be preselected independently of the thread pitch. This counteracts any automatic adjustment of the steered or guided wheels during drive-free or power-free operation.This is particularly advantageous because it eliminates the need for an additional locking mechanism for the spindle drive, e.g., in the form of a magnetic lock or similar. This effectively prevents wheel wandering, accompanied by a change in the wheel steering angle due to dynamic influences, such as rough road conditions, even in the event of a fault. Furthermore, the efficiency of the drive thread can be increased, since no self-locking thread, such as a trapezoidal thread or the like, is required for self-locking.

[0013] Preferably, the at least one energy accumulator and / or the at least one bearing is positively and / or non-positively and / or materially coupled to the drive sleeve. The bearing in the form of a rolling bearing can be pressed into the spindle sleeve. Additionally or alternatively, the bearing cage can be adhesively bonded to the spindle sleeve. The bearing can also be rolled or caulked to the spindle sleeve by material deformation. The energy accumulator in the form of spring washers can be used as a separate component during assembly. Alternatively, the at least one spring washer can also be injection-molded onto the spindle sleeve and / or the threaded rings. This can further simplify assembly.

[0014] To accommodate the at least one threaded ring and / or at least one energy accumulator and / or at least one bearing, the spindle sleeve can have at least one shoulder. If the spindle sleeve is imagined as a cylindrical base body, the shoulders can be designed in the form of bores or milled recesses. The shoulders are then each designed such that they support the aforementioned components axially on the spindle sleeve and can thus functionally accommodate them. The recess for the threaded rings can, for example, be designed such that in the fully assembled spindle sleeve with spring washers, bearings and threaded rings, the end face is flush with the threaded rings. This results in a compact spindle sleeve which, depending on the material selection, can be optimally designed for use in the spindle drive for a motor vehicle steering system.

[0015] In order to ensure virtually wear-free operation over the service life of the spindle drive despite self-locking by means of clamping and the resulting minimization of play in the movement thread as well as the radial preload by a drive belt, a lubricant is provided between the aforementioned components. To achieve lifetime lubrication, a cavity for the lubricant is created between the threaded rings and the spindle sleeve and the spindle. During assembly, a sufficient amount of lubricant is added once so that there is sufficient lubricant available for the entire service life of the spindle drive. Measures should preferably be taken to ensure that the lubricant is kept in the cavity. For this purpose, sealing elements can be provided on the end faces of the spindle sleeve, which mesh with the spindle thread.A more advantageous embodiment is for each threaded ring to have at least one internal thread, which serves as a sealing element and / or wiper, thus ensuring that the lubricant is always kept within the cavity of the spindle sleeve. This sealing thread is formed, for example, from a flexible material and is preferably molded into the inside of the threaded ring. The axial preload also provides improved sealing in the axial direction because the flanks of the threaded rings and the spindle thread are in contact with one another.

[0016] The spindle drive is preferably part of an actuator which is formed at least from a housing, a spindle drive as described above, and an electric motor and optionally a suitable control system. The actuator is used in the chassis of a vehicle and is connected to the chassis or the body structure or is supported thereon. Individual so-called single actuators, also called dual actuators, are possible, i.e. those acting on one wheel, which bring about the steering movement or change in the wheel angle of a single wheel. So-called central actuators with the aforementioned spindle drive are also possible, wherein the spindle projects out of the housing of the actuator on both sides and there are joints or joint receptacles at the ends of the spindle, which are connected via a steering linkage or directly to the wheel carrier to change the wheel steering angle. Central actuators are, for example, attached with their housing to the body orfixed to the vehicle body by screwing or similar and thus supported there.

[0017] The invention further relates to a steer-by-wire steering system, preferably a rear-axle steering system, comprising an actuator with a spindle drive as mentioned above. Steer-by-wire systems are mechanically decoupled steering systems in which a mechanical actuating movement, e.g., of a steering wheel, is converted into an electrical actuating signal, which is fed to a control unit, which then controls an actuator purely electrically. An electrical connection between the evaluation unit and the control unit(s) of the steer-by-wire steering system makes it very easy to intervene in the driving dynamics. Such steering systems are thus independent of the driver and can be controlled depending on the situation.

[0018] The invention is described below using preferred embodiments with reference to the drawing. In the drawing: Fig. 1 an actuator with a spindle drive according to the prior art, Fig. 2 a perspective view of a spindle drive according to the invention, and Fig. 3 a further representation of the spindle drive according to the invention.

[0019] Fig. 1 shows a known actuator 20, which is preferably used for a steer-by-wire steering system as a rear-axle steering system of a motor vehicle. The actuator 20 has a spindle drive 21, which comprises a spindle 22, a spindle nut 23, bearings 24, and a pulley 25, which can be driven by an electric motor 27 via a belt 26. The actuator 20 has a housing 28, which is attached to the vehicle body via a first joint 29. The spindle 22 is firmly connected at one of its two ends to a screw-on pin 30, which is guided axially slidingly relative to the housing 28 and is connected to a second joint 31 at its outer end protruding from the housing 28.The actuator 20 is connected via the second joint 31 to a steering linkage (not shown), preferably a track control arm of a rear axle or a wheel carrier of a motor vehicle, and can thus act on the steering of a rear wheel, being supported on the vehicle side via the first joint 29 in order to effect a change in the wheel steering angle.

[0020] Fig. Figure 2 shows a spindle drive according to the invention in a partially sectioned perspective view. The spindle 122 is surrounded by a bearing 170, which is pressed into a cylindrical bearing seat 172 in a cavity of the spindle sleeve 140. To the left and right of the bearing, the spindle sleeve 140 has a recess in the form of a shoulder 146, 146a, in each of which a force accumulator 150, 151 is inserted. The threaded rings 160, 161 border the energy storage devices in the form of spring washers 150, 151 made of an elastomer. These engage with their internal threads the external thread 122a of the spindle 122. The threaded rings 160, 161 are positioned so far toward the spindle sleeve 140 or the energy storage devices 150, 151 that their outer surfaces are flush with the end faces 142, 143 of the spindle sleeve 140. The threaded ring 161 is largely cylindrical on its outer contour, but has a flattened portion 161a.This flattened portion rests on a similarly flattened area of the recess 143a of the spindle sleeve 140 and forms a positive connection with the threaded ring 161. During assembly, in this embodiment, the bearing 170 is first pressed into the spindle sleeve, and then the spring washers 150, 151 are inserted into the shoulders 146, 147. Subsequently, the threaded rings 160, 161 are inserted into the end-face recesses 142a, 143a and preloaded. In other words, they are pressed toward each other so that the energy accumulators 150, 151 are preloaded. Subsequently, the spindle 122 is first screwed into the first threaded ring 160 and then screwed further until the spindle 122 engages with the threaded ring 161. After the spindle 122 has been screwed through the two threaded rings 160, 161, the flanks of the threaded rings 160, 161 rest on the flanks of the spindle 122.The preload advantageously minimizes thread play and also provides self-locking, so that dynamic influences in the chassis of a vehicle due to wheel movements on uneven roads do not cause the spindle drive and thus the wheels directly or indirectly connected to the spindle to move automatically. The bearing 170, shown here in a preferred embodiment as a needle bearing, centers the spindle sleeve 140 and thus the threaded rings 160, 161 relative to the spindle 122. Both the spindle sleeve and the threaded rings as well as the bearing 170 are thus all arranged concentrically around the longitudinal axis a of the spindle 122. This particularly counteracts jamming of the movement thread. Bearings 124, shown in simplified form as rolling bearings, are arranged on the end face of the outer sleeve.These provide a low-friction, stationary support in the housing 128, which is the . Fig. 3 can be seen schematically.

[0021] In Fig. 3 shows a further embodiment of a spindle drive 121 of an actuator 120 according to the invention. In contrast to Fig. Figure 2 shows the bearing 170 with a smooth cylindrical inner wall, which has a clearance to the thread 122a (tip circle). It thus forms a plain bearing. The threaded rings 160, 161 are in the Fig. 3 opposite the Fig. 2 is secured in the spindle sleeve not by means of a positive fit, but by means of a frictional fit. The right-hand threaded ring 161 has a cylindrical outer surface and is pressed, for example, with an interference fit into the recess 143a of the end face 143 of the spindle sleeve. This press-in can be carried out with the spindle sleeve 140, for example, as a pre-assembly step. During pre-assembly, the spring washer 151 is pre-tensioned between the spindle sleeve 140 and the threaded ring 161. In a further assembly step, the spindle 122 would be screwed through the threaded ring 161 until the threaded ring 160 previously screwed onto the spindle 122 rests against the spring washer 150. The spindle would now be screwed through further and, at the same time, the spring washer 150 would be pressed into the recess 142a of the end face 142 and then caulked. For this purpose, the caulking 145 is shown graphically.The other reference symbols for the recesses and shoulders are not repeated here because they correspond to the shoulders according to . Fig. 2. A pulley 127 is pressed onto the outside of the spindle sleeve 140. This pulley can be additionally or instead bonded or welded to the spindle sleeve 140. A drive belt or belt 126 is arranged on the pulley 127, which is driven by a pinion (not shown) by means of an electric motor.

[0022] In addition to the form-fitting and / or force-fitting and / or material-locking fastening options shown and described, combinations of these are also possible. For example, instead of a flattening 161a, as in Fig. 2, the threaded ring can also have a type of toothing or polygon on the outside, which can be connected to the spindle sleeve in a non-rotatable manner with a corresponding inner surface in a recess on the front side.

[0023] This results in a compact spindle drive that also minimizes the tendency to jam through a precise, concentric arrangement of the components that form a motion thread and the bearing. The axial preload minimizes thread play, thus preventing any acoustic noise that could be transmitted from the spindle drive to the vehicle via the chassis. Reference symbol 20 Actuator 21 Spindle drive 22 spindle 23 Spindle nut 24 warehouses 25 pulley 26 belts 27 Electric motor 28 housings 29 first joint 30 screw-on pins 31 second joint 120 actuator 121 spindle drive 122 spindle 122a spindle thread 124 warehouses 126 belts 127 pulley 128 housings 140 spindle sleeve 140a flattening 142 front side 142a recess 143 front side 143a recess 145 Caulking 146 paragraph 146a paragraph 147 paragraph 147a paragraph 148 cavity 150 energy storage, spring washer 151 Energy storage, spring washer 160 threaded ring 161 threaded ring 170 warehouses 172 bearing seat a Longitudinal axis (spindle)

Claims

[1] Spindle drive (121) of a steer-by-wire steering system for a motor vehicle, comprising a housing (128) and a spindle (122) with a spindle thread (122a), wherein the spindle (122) is mounted in the housing (128), characterized by in that a spindle sleeve (140) is mounted in a stationary manner in the housing (128), wherein at least two threaded rings (160, 161) are coupled to the spindle sleeve (140) in a manner secured against rotation, wherein the threaded rings (160, 161) are in engagement with the spindle (122) and form a movement thread in order to linearly displace the spindle (122) along its longitudinal axis (a) relative to the spindle sleeve (140). [2] Spindle drive according to claim 1, characterized by that the threaded rings (160, 161) are arranged in the region of the end faces (142, 143) of the spindle sleeve (140). [3] Spindle drive according to claim 1 or 2, characterized bythat the spindle sleeve (142) with its inner side at least indirectly forms a bearing seat (172) for supporting the spindle (122). [4] Spindle drive according to claim 1 or 2 or 3, characterized by that each threaded ring (160, 161) is positively and / or non-positively and / or materially coupled to the spindle sleeve (140). [5] Spindle drive according to one of the preceding claims, characterized by that a prestressed force accumulator (150, 151), in particular in the form of a spring washer, is arranged at least between one of the threaded rings (160, 161) and the spindle sleeve (140). [6] Spindle drive according to claim 5, characterized by that the at least one energy accumulator (150, 151) and / or the at least one bearing (170) is positively and / or non-positively and / or materially coupled to the spindle sleeve. [7] Spindle drive according to one of the preceding claims, characterized bythat at least one shoulder (146, 146a, 147, 147a) for receiving at least one threaded ring (160, 161) and / or at least one energy accumulator (150, 151) and / or at least one bearing (170) is formed in the spindle sleeve (140). [8] Spindle drive according to one of the preceding claims, characterized by that a cavity (148) for receiving lubricant is formed between threaded rings (160, 161), spindle sleeve (140) and spindle (122). [9] Spindle drive according to claim 8, characterized by that each threaded ring (160, 161) has at least one internal thread which is designed as a sealing element and / or wiper and causes the lubricant to be held in the cavity (148). [10] Actuator with a spindle drive (121) according to one of the preceding claims in a chassis of a motor vehicle. [11] Steer-by-wire steering system for a motor vehicle, characterized by an actuator (120) according to claim 10.

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