Method for setting the axial preload force of a roller screw drive of an actuator of a steering device of a motor vehicle

Abstract

A method for setting the axial preload force of a roller screw drive (3) rotatably mounted in a housing (2) by means of bearings (4, 5) spaced axially from each other. The housing (2) is divided into first and second housing portions (8, 9) transversely to a push rod (7). The roller screw drive (3) is inserted into the second housing portion (9) together with the two bearings (4, 5). An axial preload force is applied, which is transmitted from the first bearing (4) to the second bearing (5) via the roller screw drive (3). The axial load clearance (“X”) between the bearing support surface of the first bearing (4) and the second housing edge (31) of the second housing portion (9) is measured. An adjusting nut (10) is screwed into the first housing portion (8) until the axial adjustment clearance between the adjusting nut support surface (12) at the end and the first housing edge (30) of the first housing portion (8) is the same as the measured axial load clearance (“X”). Then, the adjusting nut (10) is fixed in place in the first housing part (8), and the two housing parts (8, 9) are connected to each other such that the two housing parts are supported against each other by their housing edges (30, 31).

Description

Technical Field

[0001] This invention relates to a method for setting the axial preload force of a roller screw drive that converts rotational motion into translational motion. The roller screw drive is rotatably mounted on a machine component, preferably within a housing. In some applications, a certain axial preload force is required between the roller screw drive and the housing to account for clearance or friction. This invention particularly relates to setting this axial preload force of a roller screw drive that is part of the actuator of a steering system in a motor vehicle, preferably a rear-wheel steering or steer-by-wire steering system. Background Technology

[0002] An actuator is known from DE 10 2018 116 867 A1, in which the roller screw driver is formed by a planetary roller screw driver. The planetary roller screw driver has a nut arranged on a threaded spindle and planetary rollers arranged between the threaded spindle and the nut. The nut is divided into two nut portions transversely to the spindle axis. The planetary rollers engage with grooves on their planetary sides on one side with grooves on the nut side and with the thread profile of the threaded spindle on the other side. The planetary roller screw driver also has planetary roller carriers with recesses arranged circumferentially, and the planetary rollers are mounted in the recesses in a manner that allows them to rotate about the planetary roller axis.

[0003] The planetary roller bearing surrounds a nut, and the nut portions are preloaded using various techniques to ensure no backlash when engaged with the planetary rollers. The disclosure proposes installing spacers between the nut portions. An alternative is also proposed: inserting the nut portions into two lead screw sleeves, axially supporting the nut portions on the sleeves and screwing them together until the aforementioned backlash-free condition is achieved.

[0004] The disclosure also proposes mounting a lead screw driver using an axial angular contact roller bearing on a housing, within which the lead screw driver is mounted. At this bearing point, there must also be axial clearance or preload between the housing and the lead screw driver to ensure proper actuator function.

[0005] These measures are complex and require a corresponding amount of space within the planetary roller bearing. However, especially in automotive applications, there is often a need for cost-effective, space-saving planetary screw drives, particularly when planetary screw drives are used in actuators for rear-wheel steering systems or steer-by-wire systems.

[0006] DE 10 2019 112 480 B3 discloses a chassis actuator for a rear-wheel steering system, which has an electric motor and a roller screw driver arranged in a housing. The roller screw driver is rotatably mounted by means of bearings arranged axially spaced from each other, and the axially displaceable threaded spindle of the roller screw driver is part of a push rod penetrating the housing. Two bearings are supported on the housing, wherein a preload nut penetrated by the push rod is screwed into the threads of the housing and engages against one of the bearings through a support surface on its end side.

[0007] DE3712155 discloses a power steering system having a ball screw drive and an electric motor arranged in a housing. The ball screw drive is rotatably mounted by means of bearings arranged axially spaced from each other, and the axially displaceable threaded spindle of the ball screw drive is part of a push rod penetrating the housing. The housing is divided into two housing parts transversely to the push rod, and a first bearing is assigned to the first housing part and a second bearing is assigned to the second housing part. An adjusting nut, penetrated by the push rod, is screwed into the threads of the first housing part and engages against the first bearing via a support surface on the end side of the adjusting nut.

[0008] JP2011-025756 A discloses an electromechanical steering device having a ball screw drive and an electric motor arranged in a housing. The ball screw drive is rotatably mounted by means of bearings arranged axially spaced from each other, and the axially displaceable threaded spindle of the ball screw drive is part of a push rod penetrating the housing. The housing is divided into two housing parts transversely to the push rod, and a first bearing is assigned to the first housing part and a second bearing is assigned to the second housing part. An adjusting nut, penetrated by the push rod, is screwed into the thread of the first housing part and engages against the first bearing through a support surface on the end side of the adjusting nut.

[0009] Therefore, a method for setting the axial preload force is known, which can be used to place a roller screw drive that is rotated in the housing under axial preload.

[0010] Once the roller screw drive is installed in the housing, it is virtually impossible to change and / or check the preload force setting afterwards. Summary of the Invention

[0011] The purpose of this invention is to describe a method for setting the axial preload force of a roller screw drive that can be reliably implemented.

[0012] According to the present invention, this objective is achieved by the following method.

[0013] A method for setting the axial preload force of a ball screw drive includes a ball screw drive arranged in a housing, which can be formed from known ball screw drives, rolling screw drives, and planetary ball screw drives.

[0014] This method is applicable to steering systems in motor vehicles, particularly rear-wheel steering systems. Typically, a roller screw drive has a rotary drive component whose rotation is converted into translational motion of the threaded spindle of the roller screw drive. An electric motor can drive this drive component via a toothed belt drive or spur gear.

[0015] The threaded spindle is part of the push rod that penetrates the housing. The threaded spindle may have screw-in pins at both ends, which are screwed into threaded holes in the push rod assembly. Fork-shaped heads may be attached to the ends of the push rod to hinge the wheel carrier.

[0016] The housing is divided into housing parts transversely to the push rod. A first housing part has a first housing edge positioned transversely to the spindle axis, and a second housing part has a second housing edge positioned transversely to the spindle axis. The housing edges are designed to rest against each other. After the housing parts are assembled, the housing edges rest against each other. These housing edges could lie entirely within a common transverse plane positioned transversely to the spindle axis. However, structurally, it is necessary to provide housing edges arranged axially offset from each other on the two housing parts, with all housing edges located in an imaginary plane transversely to the spindle axis and complementary to each other, such that the two housing parts rest entirely against each other through their housing edges.

[0017] The roller screw drive is rotatably mounted in a housing by means of bearings arranged axially spaced apart from each other. These first and second bearings may each include a radial bearing and an axial bearing. The first bearing is associated with a first housing portion and the second bearing is associated with a second housing portion.

[0018] When used as an actuator in a rear-wheel steering system, the radial force acting on the pushrod is significantly lower than the transmitted axial force, which is transmitted via the pushrod during actuator operation. Preferably, axial angular contact roller bearings are used, wherein the tapered raceway of the bearing is inclined relative to an imaginary plane transverse to the spindle axis. These axial angular contact roller bearings can transmit lower radial forces and higher axial forces.

[0019] An adjusting nut, penetrated by the push rod, is screwed into the threads of the first housing portion and positioned against the bearing support surface of the first bearing via an adjusting nut support surface on its end side. The adjusting nut is preferably arranged coaxially with the push rod. The bearing support surface can be the end face of a bearing disc, and the other end face of the bearing disc can be designed as the raceway of the first bearing.

[0020] It can be useful if the adjusting nut support surface is also designed to serve as the raceway for the first bearing. In this case, the bearing support surface of the first bearing can be defined by a plane tangent to the rolling element of the first bearing.

[0021] When fully assembled, the adjusting nut support surface and the bearing support surface of the first bearing are positioned so that they abut or overlap each other.

[0022] The axial bearing clearance or axial preload between the first and second bearings is determined by the depth to which the adjusting nut is screwed into the thread of the first housing portion. This means that the axial clearance or required preload of the roller screw drive in the housing is determined by the screwing depth of the adjusting nut.

[0023] The following steps are provided for setting the desired axial preload force: Insert the roller screw drive together with the two bearings into the second housing section.

[0024] An axial preload force is then applied, which is transmitted from the first bearing to the second bearing via a ball screw drive. Under this desired axial preload force, any possible clearance is minimized, which in the assembled arrangement may include the bearing clearance of the first and second bearings, as well as any existing clearance within the ball screw drive.

[0025] The axial load distance between the bearing support surface of the first bearing and the edge of the second housing portion of the second housing is now measured, with the lead screw drive and two bearings inserted together into the second housing portion.

[0026] If the first bearing is an angular contact roller bearing, the load distance can be conveniently measured from or to an easily accessible reference line on the first bearing. For example, the reference point can be located on a circular path having the average diameter of the angular contact roller bearing, which lies on a tapered bearing support surface. If the angular contact roller bearing has a running disc, the reference line is advantageously located on the end face of the running disc facing the adjusting nut, which rests against the running disc via its support surface.

[0027] The adjusting nut can now be screwed into the first housing section until the axial adjustment distance from the adjusting nut support surface on the end side to the edge of the first housing section is the same as the axial load distance measured above. In the case of angular contact roller bearings, the reference line used to measure the axial adjustment distance lies on the same circular path as previously described for the first bearing.

[0028] The adjusting nut is then secured in place on the first housing portion. Preferably, the adjusting nut is secured in place on the first housing portion by means of a lead screw lock. The lead screw lock can be formed through a material-fitting connection between the first housing portion and the adjusting nut. For example, a liquid locking agent under the brand name Loctite was initially provided, which is applied to the threads and gradually hardens to ensure reliable securing of the adjusting nut. A coating under the brand name Precote is also known, which is applied to the adjusting nut and ensures trouble-free securing.

[0029] Alternatively, a so-called threaded lock can also be configured as a lead screw lock. In this case, the thread is inserted or pressed into the longitudinal groove of the adjusting nut, which passes through the thread side. The screw-in adjusting nut is secured in place by means of the thread, which forms a clamping connection between the adjusting nut and the thread of the first housing portion.

[0030] The two housing parts are now connected to each other, for example, screwed together, and the two housing parts are resting against each other by their housing edges (30, 31). This position ensures the setting of the required axial preload force. This reliable setting can be achieved by measuring the load distance described above and setting the adjustment distance, which, in the case of the coordinate reference line—as described above—has the same amount as the load distance.

[0031] The adjusting nut is preferably screwed into a threaded hole in the first housing portion that is coaxial with the push rod and has a radial edge with an adjusting nut support surface.

[0032] The aforementioned drive component can be formed from the nut of a roller screw drive, with a rolling element arranged between the nut and the threaded spindle. The rolling element engages with the thread of the threaded spindle on one hand and with the engagement profile on the nut side on the other.

[0033] In the case of a preferred planetary roller screw drive, it is advantageous to rotate the planetary roller carrier forming the drive component, in which planetary rollers are arranged in recesses, engaging with the threads of the threaded spindle on one hand and with the groove contour of the nut on the other. Planetary screw drives driven in this manner have precise pitch, thus preventing slippage during operation; a full rotation of the planetary roller carrier causes the threaded spindle to shift by the amount of thread pitch.

[0034] Preferably, the planetary roller bearing is constructed in several parts and includes a sleeve element surrounding the nut. Flanges on both axial sides of the planetary roller bearing are non-rotatably connected to the sleeve element, wherein at least one of the flanges has axial clearance relative to the sleeve element. In this case, it is advantageous to use one axial angular contact roller bearing between each of the flanges of the planetary roller bearing and the two housing parts, and on the other hand, to arrange one axial roller bearing between each flange of the planetary roller bearing and the nut.

[0035] In this further improvement, the adjusting nut can be used to set a specific clearance or a specific axial preload of the planetary screw drive, that is, to set the clearance or preload between the flanges of the planetary roller bearing and the two housing parts on the one hand, and to set the clearance or preload between these flanges and the nut on the other hand.

[0036] In this example, the axial force acting on the threaded spindle during actuator operation is transmitted to the flange of the planetary roller bearing via the nut and axial roller bearing, and finally to the housing via the axial angular contact roller bearing.

[0037] The housing, which is divided into two housing parts transversely to the spindle axis, along with the two associated bearings and the interaction with the adjusting nut, allows for easy assembly and setting of the desired preload force. Attached Figure Description

[0038] The invention will now be described in more detail with reference to exemplary embodiments shown in a total of seven accompanying drawings. In the drawings:

[0039] Figure 1 The actuator of the rear-wheel steering system of a motor vehicle is shown.

[0040] Figure 2 It shows Figure 1 Enlarged view of the section,

[0041] Figure 3 It shows Figure 1 Details

[0042] Figure 4 It shows Figure 1 Further details,

[0043] Figure 5 It shows Figure 1 Details

[0044] Figure 6 It shows Figure 5 Variations in details; and

[0045] Figure 7 It shows Figure 1 Another enlarged view of the section. Detailed Implementation

[0046] Figure 1 A schematic diagram of an actuator for a steering device in a motor vehicle, particularly for a rear-wheel steering system, is shown.

[0047] The actuator is equipped with an electric motor 1 and has a roller screw driver 3 arranged in a housing 2, which is rotatably mounted in the housing 2 by means of bearings 4, 5 arranged axially spaced from each other. An axially displaceable threaded spindle 6 is part of a push rod 7 that penetrates the housing 2.

[0048] The housing 2 is divided into housing portions 8 and 9 transversely to the push rod. The first bearing 4 is associated with the first housing portion 8, and the second bearing 5 is associated with the second housing portion 9.

[0049] The adjusting nut 10, through which the push rod 7 passes, is screwed into the thread 11 of the first housing portion 8. The first bearing 4 is supported or mounted on the support surface 12 on the end side of the adjusting nut 10. The axial bearing distance between the two bearings 4 and 5 is set by screwing the adjusting nut 10 into the thread 11.

[0050] In this exemplary embodiment, the adjusting nut 10 is screwed into a threaded hole 13 in the first housing portion 8, the threaded hole being arranged coaxially with the push rod and forming a thread 11. The adjusting nut 10 has a radial edge 14 with a support surface 12 on its end face facing the first bearing 4.

[0051] In an exemplary embodiment, bearings 4 and 5 are formed by axial angular contact roller bearings 15, the tapered raceways 17 of which are inclined relative to a plane arranged transversely to the axis of the main shaft.

[0052] The adjusting nut 10 has a tapered support surface 12 adapted to the axial angular contact roller bearing 15, which serves as a support for the axial angular contact roller bearing.

[0053] Figure 2 and Figure 7The enlarged view in the figure shows a magnified view of the roller screw driver 3, which in an exemplary embodiment is formed by a planetary roller screw driver 19. The planetary roller 20 engages with the groove profile 22 of the nut 23 on one hand and with the thread 24 of the threaded spindle 6 on the other hand via its groove profile 21.

[0054] The planetary roller carrier 25, driven by rotation, houses the planetary rollers 20 in its circumferentially distributed recesses 26. The planetary roller carrier 25 is mounted on the housing 2 by means of axial angular contact roller bearings 15, 16 and axial roller bearing 27 arranged between the planetary roller carrier 25 and the nut 23.

[0055] The planetary roller bearing 25 has a sleeve element 28 that engages around a nut 23 and flanges 29 arranged on both sides of the axial direction. The flanges are connected to the sleeve element 28 in a non-rotatable but axially displaceable manner relative to each other. One of the axial roller bearings 27 is arranged between the flanges 29 and the nut 23, and one of the axial angular contact roller bearings 15 is arranged between the flanges 29 and the housing 2.

[0056] The electric motor 1 mentioned at the beginning is connected to the driver 37 ( Figure 1 , Figure 2 The planetary roller carrier 25 of the planetary roller screw driver 19 is driven. Under its rotation, the planetary roller 20 rotates about the threaded spindle 6 and rolls away from the threaded spindle 6 and the nut 23. The rolling of the planetary roller 20 causes the nut 23 to rotate relative to the threaded spindle 6 and the planetary roller carrier 25. The push rod 7 is thus axially displaced.

[0057] Figure 3 and Figure 4 A first housing portion 8 and a second housing portion 9 are clearly shown. The first housing portion has a first housing edge 30 positioned transversely to the main shaft axis, and the second housing portion has a second housing edge 31 positioned transversely to the main shaft axis. The first housing edge and the second housing edge rest against each other, as shown in... Figure 2 This can be clearly observed in the text.

[0058] Figure 5 and Figure 6 Two examples of lead screw locks are shown, in which the adjusting nut 10 is secured in place on the first housing portion 8 by means of the lead screw lock. According to Figure 5 The lead screw lock is achieved by a threaded lock 32 between the first housing part 8 and the adjusting nut 10, and according to Figure 6 The lead screw lock is formed by the material-fitting connection part 36 through the coating 33 of the lead screw thread 34 of the adjusting nut 10.

[0059] In the case of thread lock 32, special thread 35 is pressed into the longitudinal groove formed in the lead screw thread 34.

[0060] In the case of coating 33, the central thread portion of the lead screw thread 34 is coated.

[0061] Figure 7 It shows Figure 1 A further enlarged view of the section, particularly the section in the region of the first bearing 4, namely the axial angular contact roller bearing 15. The running discs 40 and 41 of the axial angular contact roller bearing and a set of rollers 42 arranged between the running discs can be clearly seen. Average bearing diameter d L A circular path is defined, which forms a reference line on the end face 43 of the running disc 40 facing the adjusting nut 10. The distance “x” from this reference line to the second edge of the housing edge 31 in the axial direction can be measured, which will be explained in more detail below.

[0062] The desired axial preload setting of the planetary roller screw drive 19 can be achieved in a simple manner using the proposed actuator. The planetary roller screw drive 19, together with two axial angular contact roller bearings 15, is inserted into the second housing portion 9. Figure 4 An axial angular contact roller bearing 15, serving as the second bearing, is inserted into the second housing portion 9 at its predetermined bearing point. Another axial angular contact roller bearing 15, serving as the first bearing 4, is also installed. The two axial angular contact roller bearings 15 are arranged on both sides of the flange 29 of the planetary roller carrier 25.

[0063] An axial load is now introduced, which is transmitted from the first bearing 4—an axial angular contact roller bearing 15—to the second bearing 5—another axial angular contact roller bearing 15—via the planetary roller screw drive 19. This axial load is so large that a desired preload force can be set. The axial load distance “X” is now measured from the reference line to the edge 31 of the second housing portion 9. Figure 4 The reference line is formed on the side of the bearing disc 40 of the axial angular contact roller bearing facing the adjusting nut 10, which has the average bearing diameter "d" of the axial angular contact roller bearing 15. L A circular path.

[0064] The adjusting nut 10 can now be screwed onto the first housing part 8. Figure 3 The axial adjustment distance can be measured from a circular reference line on the tapered support surface 12 of the adjusting nut 10, which has the average bearing diameter "d" of the axial angular contact roller bearing 15. L"Starting from this reference line, the axial adjustment distance to the first housing edge 30 of the first housing portion 8 is set (see...") Figure 3 Tighten the adjusting nut 10 until the axial adjustment distance reaches the specified value "x".

[0065] Once the preload is set during actuator operation, the adjusting nut 10 reliably holds the preload in place within the first housing portion 8. Finally, the two housing portions 8 and 9 can be assembled, and the actuator can be completed.

[0066] After assembly, the reference lines on the tapered support surface 12 and the bearing disc 40 are in the same position and coincide in the axial direction. The housing edges 30 and 31 of the two housing parts 8 and 9 are also in the same position and coincide in the axial direction after assembly. Therefore, the adjustment distance and the load distance "X" have the same amount.

[0067] The two housing parts 8 and 9 can now be screwed together.

[0068] After assembly, set the required axial preload force on the roller screw drive.

[0069] Explanation of reference numerals in the attached figures

[0070] 1 electric motor

[0071] 2 shells

[0072] 3-roller screw driver

[0073] 4 First Bearing

[0074] 5 Second bearing

[0075] 6-thread spindle

[0076] 7 putters

[0077] 8 First shell section

[0078] 9 Second shell section

[0079] 10 Adjusting Nuts

[0080] 11 thread

[0081] 12 Adjusting nut support surface

[0082] 13 threaded holes

[0083] 14 radial edges

[0084] 15 Axial Angular Contact Roller Bearing

[0085] 17 conical raceways

[0086] 19 Planetary Roller Screw Driver

[0087] 20 planetary rollers

[0088] 21 Groove Profile

[0089] 22 Groove Profile

[0090] 23 nuts

[0091] 24 thread

[0092] 25 planetary roller bearings

[0093] 26 depressions

[0094] 27 Axial Roller Bearing

[0095] 28 sleeve components

[0096] 29 flanges

[0097] 30 First shell edge

[0098] 31 Second shell edge

[0099] 32 threaded lock

[0100] 33 Coating

[0101] 34 screw thread

[0102] 35 thread

[0103] 36 Material mating connection parts

[0104] 37 with driver

[0105] 38 bearing support surface

[0106] 40 running disks

[0107] 41 running disks

[0108] 42 sets of rollers

Claims

1. A method for setting an axial preload force for a roller screw drive (3), the roller screw drive being rotatably mounted in a housing (2) by means of bearings (4, 5) arranged axially spaced apart from each other, the threaded spindle (6) of the roller screw drive being part of a push rod (7) penetrating the housing (2), the housing being divided transversely to the push rod (7) into a first housing portion (8) and a second housing portion (9), wherein a first bearing (4) of the roller screw drive is assigned to the first housing portion (8), and a second bearing (5) of the roller screw drive is assigned to the second housing portion (9), wherein, The first housing portion (8) has a first housing edge (30) positioned transversely to the main shaft axis, and the second housing portion (9) has a second housing edge (31) positioned transversely to the main shaft axis, wherein the two housing edges (30, 31) are designed to rest against each other, and wherein an adjusting nut (10) penetrated by the push rod (7) is screwed into the first housing portion (8), and engages against the bearing support surface (38) of the first bearing (4) through the adjusting nut support surface (12) on the end side of the adjusting nut, the method according to the following steps: The roller screw driver (3) having two of the bearings (4, 5) is inserted into the second housing portion (9). The axial preload force is applied and transmitted from the first bearing (4) to the second bearing (5) via the roller screw driver (3). Measure the axial load clearance ("X") between the bearing support surface (38) of the first bearing (4) and the second housing edge (31) of the second housing portion (9). Tighten the adjusting nut (10) into the first housing portion (8) until the axial adjustment gap between the adjusting nut support surface (12) on the end side and the first housing edge (30) of the first housing portion (8) is the same as the measured axial load gap ("X"). The adjusting nut (10) is fixed in place in the first housing part (8). The two housing parts (8, 9) are connected to each other such that the two housing parts are supported against each other by the housing edges (30, 31) of the housing parts.

2. The method according to claim 1, wherein, The adjusting nut (10) is fixed in place on the first housing part (8) by means of a lead screw.

3. The method according to claim 2, wherein, The lead screw lock is formed by a material-fitting connection (36) or by a threaded lock (32) between the first housing part (8) and the adjusting nut (10).

4. The method according to any one of claims 1 to 3, wherein, The adjusting nut (10) is screwed into the threaded hole (13) of the first housing part (8) and is provided with a radial edge (14) having a support surface (12), the threaded hole being arranged coaxially with the push rod (7).

5. The method according to claim 4, wherein, The bearings (4, 5) are formed by axial angular contact roller bearings (15) having tapered raceways (17).

6. The method according to claim 5, wherein, The adjusting nut (10) has a tapered support surface (12) adapted to the tapered raceway (17), which serves as a support for the axial angular contact roller bearing (15).

7. The method according to claim 5, wherein, The ball screw drive (3) is formed by a planetary ball screw drive (19), wherein the planetary rollers (20) of the planetary ball screw drive engage with the groove profile (22) of the nut (23) on one hand and with the thread (11) of the threaded spindle (6) on the other hand through the groove profile (21) of the planetary rollers. The planetary rollers (20) are housed in the circumferentially distributed recesses (26) of the planetary rollers (25) of the planetary ball screw drive. The planetary rollers (25) are mounted on the housing (2) on one hand by means of the axial angular contact roller bearing (15) and on the other hand by means of the axial roller bearing (27) arranged between the planetary rollers (25) and the nut (23).

8. The method according to claim 7, wherein, The planetary roller bearing (25) has a sleeve element (28) surrounding the nut (23) and flanges (29) arranged on both axial sides of the planetary roller bearing, and the flanges are connected to the sleeve element (28) in a non-rotatable but axially displaceable manner relative to each other, wherein one of the axial roller bearings (27) is arranged between the flange (29) and the nut (23), and wherein one of the axial angular contact roller bearings (15) is arranged between the flange (29) and the housing (2).

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