CN215154987U

CN215154987U - Spindle drive for a steer-by-wire system and steer-by-wire system

Info

Publication number: CN215154987U
Application number: CN202021992252.4U
Authority: CN
Inventors: S·温克; F·布林克曼; H·施文克
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 2019-09-13
Filing date: 2020-09-11
Publication date: 2021-12-14
Anticipated expiration: 2030-09-11
Also published as: DE102019213979A1; DE102019213979B4

Abstract

Spindle drive for a steer-by-wire system for a motor vehicle having a steerable front axle and/or rear axle, wherein the spindle drive comprises at least a spindle, a spindle nut which is mounted in a positionally fixed manner, and at least one bearing sleeve for mounting the spindle, wherein the at least one bearing sleeve is provided as a bearing member and a connecting member between the axially displaceable spindles for changing the wheel steering angle of the wheel to be steered, characterized in that the bearing sleeve comprises at least two sleeve members, wherein the sleeve members indirectly or directly engage one another in a material-fit and/or force-fit and/or form-fit manner.

Description

Spindle drive for a steer-by-wire system and steer-by-wire system

Technical Field

The present invention relates to a spindle drive for a steer-by-wire system for a motor vehicle having a steerable front axle and/or rear axle; and a steer-by-wire system.

Background

Known from the prior art is a steer-by-wire system according to DE 102014206934 a1, which is connected to a vehicle structure and acts centrally on two wheels or wheel supports of a vehicle axle in order to change the wheel steering angle of the wheels. DE 102017211672 a1 likewise shows a steering device of the generic type. Here, an extension piece is provided to extend the main shaft of the actuator so as to extend the main shaft in the axial direction. The extension of the spindle or spindle drive is advantageous, since the actuator for different vehicles and the installation space available there can thus be utilized with fewer modifications. Due to its design, the extension part requires an additional sliding bearing or thrust bearing, which is arranged in an additional bearing seat. The extension is supported on the vehicle body side by the bearing housing. This additional bearing or support, while effective in preventing buckling of the extension, nevertheless results in additional weight of the steering system on the vehicle axle and is more costly to produce and assemble.

Furthermore, a sliding pin is known from DE 102016201699 a1, which is produced by cold forming. In a similar manner, the slide pin is coupled to the end of the spindle, so that the spindle is axially guided in the housing of the steering system and is supported there for low-friction displacement, as is also achieved from the two aforementioned documents of the prior art.

SUMMERY OF THE UTILITY MODEL

By extending the spindle, the steer-by-wire system can be adapted to the available installation space in the region of the axle of the respective vehicle. In order to solve the above-mentioned problem, it is therefore an object of the present invention to provide a simple solution for adapting a spindle drive and a steer-by-wire system, so that the steer-by-wire system can be adapted with low effort according to the available installation space on the vehicle axle. In this case, cost-effective solutions should be found which can be realized with low expenditure. Furthermore, the requirement for a lightweight steer-by-wire system can be met in a simple manner.

The utility model is directed to the aspect of extension and the low weight aspect of a steering system. To this end, a spindle drive for a steer-by-wire system and a steer-by-wire system are provided.

According to a first aspect, the invention relates to a spindle drive for a steer-by-wire system for a motor vehicle having a steerable front axle and/or rear axle, wherein the spindle drive is made at least of a spindle, a spindle nut which is mounted in a stationary manner, and at least one bearing sleeve for mounting the spindle in a housing of the steering system. The main shaft is arranged to change the wheel steering angle of at least one wheel to be steered on the vehicle axle by means of an axial displacement. The axial displacement of the spindle is carried out by rotating the spindle nut, preferably by rotating the spindle nut indirectly or directly by means of an electric motor, by means of a transmission thread formed by an external thread of the spindle and an internal thread of the spindle nut. For this purpose, at least one bearing sleeve is provided as a bearing and connecting element on at least one end of the spindle between the axially displaceable spindle and the wheel to be steered or the wheel support. The spindle is designed as a solid component which is made of a semi-finished product, for example round steel. For this purpose, the round steel is formed into a spindle by means of forming, for example by rolling and/or machining (for example turning and/or milling). The spindle here obtains an external thread, which is preferably produced by rolling, depending on its pitch and the desired axial adjustment travel. In order to be able to operate the steering system with low friction and as low noise as possible, the spindle nut and the spindle are manufactured with small tolerances and therefore as precision components. It is therefore also advantageous in terms of weight: the spindle is formed as short as possible in terms of its axial extension and with a diameter as small as possible, preferably 10mm to 20 mm. The length of the spindle depends on the purpose of use. The individual actuators acting on each wheel are preferably 100mm to 140mm long. The central actuator acting on both wheels of the axle is preferably 190 mm to 300mm in length. The transfer of the steering movement to the wheel carrier (if necessary with a steering gear interposed) is therefore not effected directly by coupling the yoke to the end of the spindle. Instead, a bearing sleeve is fitted for this purpose between the yoke and the spindle end in order to ensure the support and guidance of the spindle along its longitudinal axis in the housing of the steering system.

Preferably, the steer-by-wire system has an at least two-piece housing having a parting plane formed generally orthogonal to the longitudinal axis of the spindle. The housing has the greatest installation space requirement in the region of the drive thread. This is determined, for example, by the diameter of the spindle nut and additionally by the drive (for example, a drive motor arranged parallel to the longitudinal axis) and the transmission (for example, the necessary belt transmission). If the available installation space is limited (for example in vehicles in which the transmission or the electric drive is usually arranged close to the axle and centrally), it is not possible for the steer-by-wire system to be arranged centrally, centrally between the wheels. In this case, the steering system must be arranged with its housing very eccentrically in the region of the parting plane, i.e. close to the wheels. This results in one end of the spindle being arranged relatively close to the wheel, with the opposite end being relatively far away from the opposite wheel. For this wheel, which is further away from the parting plane of the housing, it is now necessary to provide a spindle extension. If only the central actuator is arranged eccentrically and the steering gear bridges the distance between the hitch fork and the remote wheel or wheel carrier, different adjusting movements can disadvantageously occur at the left-hand wheel and the right-hand wheel of the axle to be steered. This is kinematically determined and the difference in the wheel steering angle is so large that a uniform change in the wheel steering angle cannot be achieved to an acceptable degree. For this reason, the extension spindles are selected in such a way that the tie forks at the ends of the steer-by-wire system each have the same spacing relative to the respective wheel carrier or wheel.

A known form of spindle extension is given in figure 2. The extension 20v is formed here by a solid round bar. This solid round bar is arranged between the existing bearing sleeve 10 and the end of the main shaft 5. The coupling of these components is usually effected by screwing. As can be seen from fig. 2, for guiding the spindle, a first sliding bush 20d is provided on the one hand, and an end-side sliding bush 10b is provided at the end of the housing 12. However, the above structure must be supported and guided by the additional sliding bush 20z at the

engagement positions

10f, 20 f. Otherwise, no coaxiality (Rundlauf) can be achieved, since this connection does not result in sufficient bending stiffness. On the one hand, an additional support for an additional sliding bush 20z is provided in the housing 12. Furthermore, the above-described construction is expensive to produce due to the solid design of the round rod of the extension 20 v. The additional weight introduced by such a solid extension constitutes a further disadvantage. This construction is also problematic in terms of occurring bending forces during driving operation due to the high transverse and lateral forces of the wheel to be supported.

According to the invention, the support sleeve is made of at least two sleeve components, wherein the sleeve components are indirectly or directly joined to each other in a material-fit and/or force-fit and/or form-fit manner. Surprisingly, it has been found that a weight advantage already arises from the total length of the support sleeve, for example from 150mm, when the support sleeve is made of two sleeve members. The entire axial extension, i.e. the total length of the support sleeve, is thus derived from the length of the sleeve member used.

The present invention can be used for so-called single actuators as well as central actuators. If the steer-by-wire system is designed as a single actuator, a change in the steering angle of the wheels on one wheel can be effected on the axle with this single actuator. It is therefore preferable for the axle to use two single actuators. In the case of a single actuator, only one bearing sleeve is required on one end of the spindle. In this case, the coupling fork is connected to the support sleeve at the one end of the main shaft. In the case of a central actuator which acts simultaneously on both wheels of the axle, a bearing sleeve is arranged at each end of the spindle, and the clevis is coupled with the spindle at the end side in each case with a bearing sleeve.

In the case of a directly joined support sleeve, substantially only two sleeve components are connected to one another, so that a one-piece support sleeve is obtained. To produce a directly joined support sleeve, at least one sleeve component is first produced from a blank component by a forming method, preferably cold extrusion. The further sleeve member may be built up in the same way as mentioned, but alternatively it may be manufactured from a round bar as a lath, i.e. by means of machining. At the ends of the sleeve members, the sleeve members are each formed in a tubular shape, such that the sleeve members have cylindrical tube ends. This pipe end preferably has a wall thickness of 2mm to 5mm, preferably 3mm to 4 mm. The end of the sleeve member facing away from the end of the tube is provided with an internal thread arranged concentrically to the longitudinal axis of the sleeve member. The internal thread can be formed by means of forming or in a further step by cutting. Preferably, the internal thread is established by a forming method (e.g. rolling). Thus, the threads are compacted by the forming process to achieve high strength. To produce the support sleeve, the sleeve elements are joined to one another with their tube ends on the end sides. Preferably, the sleeve members are welded to each other, most preferably by friction welding. For this purpose, the sleeve members are moved relative to one another under pressure with their longitudinal axes lying one above the other, wherein the end faces of the sleeve members come into contact with one another, causing a heating and plasticization of the material by the friction generated. The friction welding has the advantages that: the so-called heat affected zone is significantly smaller than in conventional welding methods. No melt formation occurs in the joining region. A suitably shaped bearing sleeve is thereby obtained, wherein no further machining is required after the friction welding process.

According to a further preferred embodiment, the support sleeve is produced indirectly from two sleeve elements and a tubular body lying between them. Here, the sleeve member is manufactured in the same manner as in the above-described embodiment. The sleeve members do not however now directly engage each other at their end faces. And cutting a pipe body from the pipe semi-finished product according to the required length of the extension part of the main shaft. The tubular body is joined in the region of its ends, between the sleeve elements, to the ends of the sleeve elements to form a support sleeve. In this case, the end faces of the tube body engage in a preferred manner with the respective end faces of the thread facing away from the sleeve element. This is preferably achieved by welding, most preferably by friction welding, as already indicated for the indirectly joined bearing sleeve, with the advantages mentioned there.

For example, a seamless steel pipe, preferably hot-rolled, is selected as the pipe semi-finished product. Such tube blanks, for example named "E355", are available as advantageous blank batches. It is obvious that the tube, i.e. the cylindrical body, has a significantly lighter weight than a round bar of the same length. If a diameter of approximately 10mm to 20mm is provided for the spindle, an outer diameter of 25mm to 35mm is assumed for the support sleeve. It is therefore evident that with such a diameter, the use of a seamless steel tube as the tube body to extend the spindle drive or the spindle brings a significant weight advantage to the entire spindle drive. In addition, the tube body is characterized by a high bending moment resistance. Therefore, even in the case of using a very long extension section, the steer-by-wire system can be manufactured with a smaller total weight than when a solid round bar is used for the extension section.

In order to simplify the production of the support sleeve, the tube ends of the sleeve elements are produced in such a way that they approximately correspond to the inner and/or outer diameter of the tube blank, preferably with the same inner and outer diameter. This ensures that the largest possible contact for friction welding is achieved by a uniform annular surface.

According to an alternative embodiment, it is likewise possible to design the diameter of the pipe end of the sleeve member and the diameter of the pipe body in such a way that these diameters have at least a clearance fit or even an interference fit with each other. For example, it is thus possible to press the pipe end into the end face end of the pipe body. Alternatively, the pipe ends can be pushed in order to subsequently weld them to one another. Laser welding, for example, is suitable here, which also requires very low heat input. Alternatively, the ends of the tubular body may have a smaller diameter so that they can be pressed or pushed into the ends of the respective sleeve members to engage them. The following advantages are possible here: the overall length of the support sleeve can be designed to be variable, in particular also as a function of the cut to the tubular body.

As already mentioned above, the support of the spindle relative to the housing along its longitudinal axis and thus also the guidance of the spindle is ensured by the support sleeve. The support sleeve is supported and guided by a sliding bush which enters, preferably is pressed into, the housing of the steer-by-wire system. For this purpose, corresponding bearing seats are provided in the housing for the sliding bush, and a permanent form-fit and force-fit connection is obtained after the press-in. In a preferred embodiment, after the manufacture of the sleeve element, a sliding bearing surface is established in each case in the region of the end remote from the engagement position or remote from the engagement position. This sliding bearing surface is preferably designed cylindrically and is produced by means of a cutting process and a subsequent grinding process. Alternatively, the sliding bearing surface can also be established after the bearing sleeve has been produced.

According to another aspect, the invention relates to a steer-by-wire system for a motor vehicle having a front axle steering system and/or a rear axle steering system, having a housing and a spindle drive received therein, the spindle drive having a spindle nut fixed relative to the housing and a spindle axially displaceable relative to the housing. At least one end is coupled with the support sleeve and is supported in a displaceable manner relative to the housing by means of the support sleeve. If the fixedly supported spindle nut is driven with its internal thread, for example, rotationally by an electric motor, the spindle, with its external thread in engagement with the spindle nut, is displaced along its longitudinal axis. The support sleeve is designed in multiple parts and is produced in a single step or in multiple steps according to the method described above.

Drawings

With respect to the present invention, preferred embodiments are described below with reference to the accompanying drawings. In the drawings:

figure 1 shows a steer-by-wire system designed with a spindle drive,

figure 2 shows a detail view of the spindle drive according to figure 1,

fig. 3 shows a steer-by-wire system designed with a spindle drive according to the present invention.

Detailed Description

Fig. 1 shows a steer-by-wire system 1, which is known and mentioned at the outset, also referred to as an actuator or simply an actuator, which is fastened to a vehicle structure 2, for example centrally to an axle support of a motor vehicle. Owing to the available installation space, it can be arranged centrally in this case. The illustrated central actuator 1 is capable of steering the two

wheels

17r, 18r of the axle simultaneously and has two articulation points arranged opposite one another, namely a first clevis 3, a second clevis 4, which are coupled to the wheel supports 17, 18 with the interposition of a transverse steering (Spurlenker)14, 15. The actuator 1 is designed with a spindle drive and has an axially displaceable spindle 5 which can be axially displaced or adjusted by a spindle nut 6 by an electric motor 7. The spindle 5 has a self-locking thread 5a in the region of the spindle nut 6, which is designed as an external thread and which engages with a corresponding internal thread 6a of the spindle nut 6 and thus forms a drive thread. When the spindle nut 6 is turned, the spindle 5 (in the drawing) which is prevented from rotating (in a manner not shown) performs an axial movement to the right or to the left along its longitudinal axis s. The spindle 5 has two opposite spindle ends or fastening ends 8, 9, which are themselves fixedly connected to bearing sleeves 10, 11. The bearing sleeves 10, 11 are guided radially in the slide bearing on the housing side by means of sliding

bushings

10b, 11b and form two joint points 3, 4 with the first and second coupling forks 3, 4. The support sleeves 10, 11 are produced from cast blank components or round rods in a cut-out manner and have a high weight for a given length due to the wall thickness.

Figure 2 shows a main shaft extension 20v made from a solid round bar. Details regarding fig. 2 may be found above and will not be described herein.

Fig. 3 shows a central actuator 100 having a two-part housing 12 with a left-hand housing part 12l and a right-hand housing part 12 r. The housing portions 12l, 12r form a parting plane E orthogonal to the longitudinal axis of the main shaft 5_TAre connected with each other. For such actuators or steer-by-wireThe installation space required for the system 100 also results here in the same installation space requirement as for the actuator 1 shown in fig. 1. If there is no structural space in the region of the vehicle center (indicated by the longitudinal axis m) in the case of axle steering, the device (e.g. steer-by-wire system 100) must be arranged or constructed such that it can be installed into existing axle designs or existing structural spaces without expensive modifications to the vehicle at the installation location in the region of the axle. Due to the diameter of the spindle drive with the drive wheel 6t pressed against the spindle nut 6, the housing 12 is at the parting plane E_THas the largest diameter of the entire actuator 100. Likewise, the required installation space for the flange-mounted electric motor 7, which is arranged in fig. 3 in the illustrated representation behind the right housing part 12r, is taken into account here. Fig. 3 schematically shows a drive unit 200 of the axle in dashed lines, which drive unit extends around a longitudinal axis m of the (not shown) vehicle in the region of a rear part of the vehicle. It is not possible to insert or mount the actuator according to fig. 1 under the current installation space conditions. For this reason, the central actuator 100 is formed as illustrated in fig. 3. Relative to the longitudinal axis s of the spindle 5, the spindle drive and thus the parting plane E_TArranged very eccentrically. The arrangement or design of the actuator 100 shown here presupposes the use of a second support sleeve 30 for lengthening the spindle, which has the following second sleeve member: left and right sleeve ends 30l, 30r and an extension 30v therebetween. On the other side of the spindle, a first support sleeve 31 is embodied which is formed by a first sleeve element which comprises a left sleeve end 31l and a right sleeve end 31 r. Here, however, the first bearing bush 31 is only designed as a short bearing bush without extensions, because of its proximity to the wheel. The two

support sleeves

30, 31 have so-called engagement positions 31f, 30f₁、30f₂. The first support sleeve 31 shown on the left is manufactured in the following way: the left sleeve end 31l and the right sleeve end 31r are first manufactured. The left sleeve end 31l is manufactured as an extrusion by cold forming. The right sleeve end 31r is made of high strengthA turned piece made of steel. The two sleeve ends are permanently made as a one-piece first support sleeve 31 to each other by means of friction welding in the region of the joining location 31 f. The first bearing sleeve 31 is guided radially in the region of its outer end (i.e. facing away from the engagement position) by means of the sliding

bushes

11b, 31b and is supported in the housing part 12 l. In contrast, the second supporting sleeve 30, which is inserted between the end of the main shaft 5 and the fork 4 on the other side, is made of three parts. Similarly to the first bearing sleeve 31 explained above, a left-hand sleeve end 30l is also produced here, which is connected to the spindle 5 and is produced as a turned part. On the opposite side, a sleeve end 30r is shown, which is produced as an extrusion, i.e. by means of forming. Between these sleeve ends 30l, 30r, however, an extension 30v in the form of a tube is now arranged. The tube body has the same outer and inner diameters as the ends of the sleeve ends 30l, 30r facing the tube body. Similarly to the first support sleeve 31, the connection between the sleeve ends 30l, 30r and the tube body 30v is likewise effected by means of friction welding. Friction welding at 30f₁、30f₂At the shown engagement position. The second bearing sleeve 30 is guided radially in the region of its outer end (i.e. facing away from the engagement position) by means of the sliding

bushes

11b, 31b and is supported in the housing part 12 r. Despite the extension 30v, no further support is required, since the tube 30v has a high and therefore sufficient bending stiffness and the support in the outer region is sufficient.

By means of the actuator 100 shown in fig. 3, the steer-by-wire system can be integrated into a vehicle axle even under difficult installation space conditions. Extending the second support sleeve 30 or the main shaft 5 by means of the tube body 30v makes it possible to form a cost-effective extension which is light or optimized in weight compared to a solid round bar. It is therefore also possible to bridge a greater distance, which is necessary when the available installation space in the vehicle axle is small. Even if the extension is large, the production itself can be easily achieved, wherein in particular the cylindrical shape of the extended tube body 30v is already given by the blank component. The existing steer-by-wire systems can thus be easily adapted to the existing installation space conditions. It is not necessary to adapt the left side of the spindle drive shown. Only the right side is correspondingly easily lengthened.

However, even if the spindle drive is arranged centrally in the conventional manner (as is shown, for example, by the prior art in fig. 1), advantages can be achieved by means of the method mentioned, namely a weight saving. Such a weight saving can be achieved in a simple manner by manufacturing the support sleeve using sleeve ends or sleeve members. Thus, even in a steer-by-wire system, the weight optimization required in modern vehicles can be achieved by the design of the bearing sleeve according to the invention, which is composed of a sleeve component.

List of reference numerals

1 steer-by-wire system

2 vehicle structure

3 first connecting fork

4 second yoke

5 Main shaft

5a main shaft screw thread

6 spindle nut

6a spindle nut screw

6t driving wheel

7 electric motor

8 end of main shaft (Right side)

9 end of main shaft (left side)

10 support sleeve (Right side)

10b sliding bush

10f engaged position

11 supporting sleeve (left side)

11b sliding bush

12 casing

12l left side housing part

12r Right side casing part

13 belt transmission device

14 steering gear

15 steering gear

17 wheel support

18 wheel support

20v extension

20f engaged position

20b sliding bush

20z sliding bush

100 central actuator

30 second support sleeve

30l sleeve end left side

30r sleeve end right side

30v extension, tube

30f₁Bonding position

30f₂Bonding position

30a sliding bush

31 first support sleeve

31l left side of sleeve end

31r sleeve end right side

31f engaged position

31b sliding bush

Longitudinal axis of a-axle

A rear axle

Longitudinal axis of s-spindle

Direction of travel F

E_TParting plane of casing

m longitudinal axis (vehicle center)

Claims

1. Spindle drive for a steer-by-wire system for a motor vehicle having a steerable front axle and/or rear axle, wherein the spindle drive comprises at least a spindle, a spindle nut which is mounted in a stationary manner, and at least one bearing sleeve for mounting the spindle, wherein the at least one bearing sleeve is provided as a bearing member and a connecting member between axially displaceable spindles for changing the wheel steering angle of at least one wheel to be steered,

characterized in that the support sleeve comprises at least two sleeve elements, wherein the sleeve elements are indirectly or directly joined to one another in a material-fitting and/or force-fitting and/or form-fitting manner.

2. The spindle drive for a steer-by-wire system according to claim 1, wherein said at least one support sleeve is a directly engaged first support sleeve, said at least two sleeve members are first sleeve members, at least one of said first sleeve members being formed from a blank member, wherein said at least two sleeve members each comprise a tubular formed end portion having a wall thickness of 2mm to 5mm, the other end portion comprising an internal thread obtained in forming or cutting, said end portions being joined to each other by welding.

3. Spindle drive for a steer-by-wire system according to claim 1, characterized in that said at least one support sleeve is an indirectly engaged second support sleeve, said at least two sleeve members are second sleeve members, at least one of which is obtained by shaping from a blank member, wherein said at least two sleeve members each comprise one tubular formed end having a wall thickness of 2mm to 5mm, the other end comprising an internal thread obtained in shaping or in cutting, with a tubular body cut out of a tube blank according to a desired length, joined in the region of its ends between said sleeve members into a support sleeve with a tube end of said second sleeve member, in order to lengthen said spindle drive by using said tubular body.

4. The spindle drive for a steer-by-wire system according to claim 3, wherein end faces of said tubular body and end faces of said threads each facing away from said second sleeve member are joined by welding.

5. The spindle drive for a steer-by-wire system according to claim 3 or 4, wherein a tube end of the second sleeve member approximately corresponds to an inner diameter and/or an outer diameter of a tube semi-finished product of the tube body.

6. The spindle transmission device for a steer-by-wire system according to claim 3 or 4, wherein a diameter of the pipe end portion of the second sleeve member and a diameter of the pipe body are in a clearance fit or an interference fit with each other.

7. A spindle drive for a steer-by-wire system according to any of claims 1-4, further comprising respective cylindrical sliding bearing surfaces established in the region of the ends remote from the engagement position, said sliding bearing surfaces rotationally fixedly surrounding the respective ends.

8. The spindle drive for a steer-by-wire system according to claim 2 or 3, wherein a wall thickness of the end portion is 3mm to 4 mm.

9. The spindle drive for a steer-by-wire system according to claim 2, wherein end faces of said end portions are friction welded.

10. The spindle drive for a steer-by-wire system according to claim 4, wherein end faces of said tubular body are friction welded with respective end faces of said threads facing away from said second sleeve member.

11. The spindle drive for a steer-by-wire system according to claim 5, wherein a tube end portion of said second sleeve member is the same as an inner diameter and an outer diameter of a tube semi-finished product of said tube body.

12. Steer-by-wire system for a motor vehicle with a front axle steering system and/or a rear axle steering system, having a housing and a spindle drive received therein, having a spindle nut fixed relative to the housing and a spindle axially displaceable relative to the housing, wherein at least one end of the spindle is coupled with at least one bearing sleeve and is supported displaceably relative to the housing by means of the bearing sleeve, characterized in that the at least one bearing sleeve is multi-part, extendable and is a spindle drive according to any one of the preceding claims 1-11.