EP3807557A1

EP3807557A1 - Electromechanical power steering having a helical-gear transmission and a transmission housing

Info

Publication number: EP3807557A1
Application number: EP19731635.9A
Authority: EP
Inventors: Andreas Bachmann
Original assignee: ThyssenKrupp AG; ThyssenKrupp Presta AG
Current assignee: ThyssenKrupp AG; ThyssenKrupp Presta AG
Priority date: 2018-06-14
Filing date: 2019-06-07
Publication date: 2021-04-21
Also published as: US20210088126A1; WO2019238576A1; DE102018114267A1; CN112313434A

Abstract

The invention relates to a helical-gear transmission (2) for an electromechanical power steering system, comprising a shaft (3) intermeshing with a helical gear (6), wherein the shaft (3) is arranged in a transmission housing (1) and is rotatably mounted in the transmission housing (1) about a longitudinal axis (4), having the first end thereof in a drive-side bearing arrangement (11) and the second end thereof in a non-drive-side bearing arrangement (12), wherein the transmission housing (1) has, in extension of the shaft (3) on a non-drive-side end, an opening (9), which can be sealed by a cover (8), the cover (8) having a cover base (80) and a surrounding cover edge (81), the cover base (80) having, in the region of the shaft (3), a bulge (16) extending to the outside in the direction of the shaft which forms an axial lock of the shaft (3).

Description

Electromechanical power steering with a helical gear and a gear housing

The present invention relates to a helical gear with the features of the preamble of claim 1 and an electromechanical power steering system comprising such a helical gear.

A generic helical gear, for example for electromechanical power steering, has an electric servo motor which drives a worm shaft which meshes with a worm wheel arranged on a steering shaft or directly on a steering pinion which is in engagement with a toothed rack. The worm shaft is with a motor shaft

Coupled electric motor. The worm wheel is rotatably connected to the steering shaft or the steering pinion. The worm shaft of a conventional worm gear has a fixed bearing at the drive end and a floating bearing at its free end. A prestressing force is applied radially to the worm shaft and pressed against the worm gear teeth. The biasing force is via a spring and a pressure device

provided, which are conventionally arranged at the free end.

The worm gear housing is closed at its end remote from the motor by a cover for securing against ingress of dirt and for axially securing the worm shaft and / or the floating bearing. A worm gear arrangement is known from the published patent application EP 3 135 559 A1 the housing is closed by a lid. Furthermore, US 2015 / 0308558A1 discloses a worm gear in which an adjusting spring of a pressure device has holding mandrels which are operatively connected to a guide wall of a stopper. The plug is fixed to the housing of the gearbox via a snap connection.

It is an object of the present invention to provide an electromechanical power steering system with a worm gear, in which the worm gear housing is secured against dirt entry by means of an improved cover, the cover being further designed to simplify the worm shaft and / or a bearing arrangement, Assure low noise and with a small number of components axially.

This object is achieved by a helical gear for an electromechanical power steering system with the features of claim 1 and the subclaims.

Accordingly, a helical gear transmission comprising a shaft meshing with a helical gear is provided, the shaft being arranged in a transmission housing and being mounted in its first end in a first bearing arrangement and at its second end in a second bearing arrangement in the transmission housing rotatably about a longitudinal axis, the gearbox housing an extension of the shaft at an end remote from the drive

Has opening which can be closed by a cover, the cover having a cover base and a circumferential cover edge, and wherein the cover base in the region of the shaft has an outward bulge which extends in the direction of the shaft and forms an axial securing of the shaft. The first bearing arrangement is preferred as the drive side

Bearing arrangement and the second bearing arrangement as remote from the drive

Bearing arrangement formed.

The cover according to the invention is preferably a component of an electromechanical power steering system.

The axial securing of the shaft is thus provided without additional components or further process steps. There are no other components in the axial direction provided between the shaft and the cover or between the drive-remote bearing and the cover, so that the worm shaft strikes directly on the outside of the cover or the cover base, without additional suspension in the event of failure of the screw bearing. The cover can flow into an already running series at any time, since no other parts need to be adjusted. The use of the axial lock (failure of the screw bearing) is also noticeable by a loud noise when the shaft hits the cover without failing.

The lid is preferably pressed into the opening. In a preferred embodiment, the bulge is cylindrical, with a circular base. It is advantageous if the bulge has an outer diameter that is at least as large as the diameter of the shaft. Furthermore preferred, the outer diameter of the bulge is at least as large as the outer diameter of an inner ring of a bearing of the bearing arrangement remote from the drive. Preferably one corresponds

Axis of symmetry of the bulge of the longitudinal axis of the shaft.

In a preferred embodiment, the edge of the cover has a serrated edge which is biased outwards in the radial direction of the longitudinal axis and which, in the pressed-in state, bears against an inside of the gear housing and forms an anti-squeeze protection. The security against pressing out in the axial direction is thus produced solely by the edge of the cover. The edge of the teeth preferably fixes all around with pretension. The teeth can be teeth that are evenly distributed over the circumference and extend essentially in the longitudinal direction. Due to the all-round teeth, no additional fastening elements, such as screws, are necessary. Furthermore, it is conceivable and possible that the edge contour of the lid edge is designed as a corrugation, rib contour or knurling.

The serrated edge preferably creates a frictional connection between the cover and the gear housing.

Preferably, all the teeth or teeth of the tooth edge have an identical tooth length, tooth width and tooth height. The relation between The tooth width and the tooth length can be designed such that 0 is less than the tooth length and less than three times the tooth width. Furthermore, the ratio to one another can be such that 1/8 smaller the tooth width is smaller the tooth length. It is furthermore conceivable and possible that at least one tooth or tooth has a tooth length, tooth width and / or tooth height that differs from the other teeth.

In an advantageous embodiment, the edge of the cover has a tab which has an area which is angled outwards, the underside of the angled area of the tab resting on the end face of the housing in the area of the opening in the installed state of the lid. The tab thus serves as an assembly and disassembly aid.

The second bearing arrangement preferably has a pretensioning device, by means of which the position of the shaft in relation to the screw wheel can be adjusted, the pretensioning device having a spring-preloaded pin which defines a pivot axis and the lid base having an inward curvature which has a free space for trains the pen.

An inward arch preferably extends in an opposite direction from the shaft and the outward bulge. The bulge is preferably formed parallel to the bulge and the longitudinal axis. The functionality of the pretensioning device is therefore not restricted by the cover.

Provision can furthermore be made for the cover base to have an inward projection which, in the installed state, is in contact with the gear housing on the outside and forms an assembly stop. Preferably, the inward projection corresponding to the inward bulge points in the opposite direction from the shaft and the outward bulge.

In the event that a tab and a projection are provided, it is advantageous if these are arranged on opposite sides of the bulge. This can prevent the lid from sticking to the

Insert canting or tipping. The edge of the lid preferably has a first edge area which extends without interruption along the circumference of the lid base and a second edge area which adjoins the first edge area on a side away from the floor, the second edge area forming the tooth edge, which is essentially in Extends in the direction of the longitudinal axis. The first continuous edge area serves the stability of the lid.

It is generally preferred if the gear housing is made of a softer material than the cover. In the event of the cover being pressed out, the edge of the teeth can remove the housing, thereby ensuring that it is pressed out. The gear housing is preferably formed as a cast aluminum housing and the cover is made of spring steel.

In all versions it is preferred that the screw wheel is a worm wheel and the shaft is a worm shaft.

An electromechanical power steering system is also provided, comprising an electric motor with a motor shaft and a previously mentioned helical gear, the motor shaft driving the shaft of the helical gear. The screw wheel is preferably arranged on a steering shaft of a motor vehicle in a rotationally fixed manner.

Two exemplary embodiments of the present invention are described below with reference to the drawings. The same components or components with the same functions have the same reference numerals. Show it :

FIG. 1: a schematic representation of an electromechanical assistant steering,

FIG. 2: a spatial representation of a steering gear of an electromechanical motor vehicle steering,

Figure 3: a spatial representation of a in a gearbox

mounted gearbox of the power steering system from FIG. 1 with a view of the worm shaft and a cover that closes off the gearbox housing, FIG. 4 shows a longitudinal section through the gear of FIG. 1 along the worm shaft,

Figure 5: a spatial view of the worm shaft and the cover without

Gearbox,

FIG. 6: a first spatial representation of the cover from FIG. 5,

FIG. 7: a second spatial representation of the cover from FIG. 5,

Figure 8: a spatial representation of a second invention

cover,

FIG. 9: a first detailed view from FIG. 5, and FIG. 10: a second detailed view from FIG. 5.

In FIG. 1, an electromechanical motor vehicle power steering system 15 with a steering wheel 25, which is coupled in a rotationally fixed manner to a steering shaft 35, is shown schematically. The driver brings in via the steering wheel 25

corresponding torque as a steering command into the steering shaft 35. The torque is then transmitted via the steering shaft 75 to a steering pinion 45

transfer. The pinion 45 meshes in a known manner with a toothed segment 550 of a rack 55. The steering pinion 45 forms together with the

Rack 55 a steering gear. The rack 55 is mounted in a steering housing so as to be displaceable in the direction of its longitudinal axis. At its free end, the rack 55 is connected to tie rods 65 via ball joints, not shown. The tie rods 65 themselves are connected in a known manner via steering knuckles, each with a steered wheel 35 of the motor vehicle. A rotation of the steering wheel 25 leads via the connection of the steering shaft 3 and the pinion 4 to a longitudinal displacement of the toothed rack 55 and thus to a pivoting of the steered wheels 35. The steered wheels 35 experience a reaction via a roadway 350 which the

Steering movement counteracts. A force is therefore required to pivot the wheels 35, which requires a corresponding torque on the steering wheel 25. An electric motor 5 with a rotor position sensor (RPS) of a servo unit 110 is provided to assist the driver Support steering movement. The servo unit 110 can be used as

Power assist device 95, 110, 115 may be coupled to either a steering shaft 75, the steering pinion 45 or the rack 55. The respective auxiliary power support 95, 110, 115 carries an auxiliary torque into the steering shaft 35, the steering pinion 45 and / or the rack 55, thereby assisting the driver in the steering work. The three different auxiliary supports 95, 110, 115 shown in FIG. 1 show alternatives

Positions for their arrangement. Usually only one of the positions shown is assisted. The servo unit can act as a superimposed steering on the steering column or as an auxiliary power assist device on the pinion 45 or the rack 55

be arranged.

FIGS. 2 to 4 show a gear housing 1 of a worm gear 2. A part of the gear housing 1 is elongated and surrounds a worm shaft 3, which is rotatably mounted in the gear housing 1 about a longitudinal axis 4. An electric motor 5 or a servo motor drives the worm shaft 3, the worm of which is in engagement with a worm wheel 6 which is connected in a rotationally fixed manner to a steering shaft 7 of a motor vehicle. When the electric motor 5 is in operation, the worm shaft 3 is driven and the worm shaft 3 and the worm wheel 6 accordingly rotate directly by a supporting moment, for. B. initiate into the steering shaft 7.

The gear housing is closed by a cover on the side remote from the drive 8.

FIG. 3 shows the gear housing 1, which has an opening 9 in an extension of the longitudinal axis 4 of the worm shaft 3 at an end of the worm shaft 3 remote from the drive, which opening 9 is closed with the cover 8. The cover 8 seals the housing 1 against dirt, splash water and dust. The cover 8 is used to form an anti-squeeze device

Direction of the longitudinal axis 4 is pressed into the opening 9 with the aid of a suitable press-in tool.

FIG. 4 shows the components of the transmission 2 and the transmission housing 1 in a longitudinal section along the longitudinal axis 4. The worm shaft 3 meshes via a worm gear 10 with the worm wheel 6. Das

Worm wheel 6 is in turn non-rotatably connected to the steering shaft 7, which is between a steering wheel, not shown, and the actual one

Steering gear of the motor vehicle runs. The components mentioned are stored in the common gear housing 1.

The worm shaft 3 is in the gear housing 1 by means of the first bearing arrangement 11, which in this example is a drive side

Bearing arrangement 11, and the second bearing arrangement 12, which in this example represents a bearing arrangement 12 remote from the drive. The drive-side bearing arrangement is connected to the motor (not shown here) in a torque-transmitting manner via a coupling 130. The

drive-side bearing arrangement 11 has a roller bearing 13, which is designed as a fixed bearing and allows the worm shaft 3 to pivot about a pivot axis. The bearing arrangement 12 remote from the drive has a floating bearing 14, which is designed in particular as a deep groove ball bearing. The position of the worm shaft 3 can be adjusted in relation to the worm wheel 6 by means of a pretensioning device 15 in the region of the bearing arrangement 12 remote from the drive. The pretensioning device 15 comprises a spring-preloaded pin 150 which forms a pivot axis.

The opening 9 of the gear housing 1 is preferably provided in order to insert and mount the bearing 14 remote from the drive and the pretensioning device 15 in the housing 1.

The cover 8 is pressed into a housing section 101 in the region of the bearing arrangement of the transmission housing 1 remote from the drive. The lid 8 comprises a lid base 80 which comprises an inner surface 84 which faces the worm shaft and an outer surface 85 which is arranged on the side facing away from the worm shaft. The cover 8 also has a peripheral edge 81 which projects outwards and is arranged essentially perpendicular to the cover base 80. The peripheral edge 81 has a first edge region 82 which extends without interruption along the circumference of the lid base 80, approximately perpendicularly thereto. A second is located on the first edge area 82 on a side away from the ground the adjoining edge region 83 is formed in a tooth-like and / or tooth-like manner, the tooth edge 83 formed thereby extending essentially in the direction of the longitudinal axis 4. The toothed wheel 83 has a larger outside diameter than the inside diameter of the opening 9 when it is not installed. The edge of the cover 81 tapers towards the bottom. In the area of the first edge area 82, the outer diameter roughly corresponds to the inner diameter of the opening 9 with some play, so that the cover 8 can be inserted into the opening 9 simply and without effort in the area of the first edge area 82. The outer, second edge region, the toothed edge 83, on the other hand, is prestressed outwards in the radial direction of the longitudinal axis 2. The tooth edge 83, which is bent outwards, yields elastically in the press-in direction. The cover 8 can thus also be pressed in in the area of the tooth edge 83 in the assembly direction without great resistance. The tooth edge 83 provides an anti-squeeze protection.

The cover base 80 has a base surface which is curved outwards in the region of the screw shaft 3. The first dome resulting from this bulge 16 is essentially cylindrical, with a circular base. The first dome 16 provides a stop for the worm shaft 3 on its outer side facing the worm shaft 3. As shown in FIG. 4, in a normal state of the transmission 1, the end of the worm shaft 3 on the cover side is spaced in the longitudinal direction from the outside of the first dome 16 of the cover 8. The longitudinal axis of the dome and the worm shaft preferably coincide. The diameter of the first dome 16 is chosen such that in this exemplary embodiment it is at least as large as the outer diameter of the inner ring 120 of the bearing 12 remote from the drive. In this case, the first dome 16 also serves as an axial stop for the bearing 12 remote from the drive When the steering is operated, the bearing seat of the non-drive bearing may settle, causing the bearing to move and the transmission to be damaged. The worm shaft therefore requires an axial lock that is greater than or equal to 2 kN, which prevents the gear from being damaged. The cover 8 with the first dome 16 provides such axial securing for the worm shaft and the non-drive bearing ready. No further components are provided between the screw shaft 3 and the cover 8 in the axial direction, so that the screw shaft 3 strikes directly on the outside of the cover 8 or the cover base 80 without additional suspension. The serrated edge 83 of the cover is designed such that it extends in the opposite direction to

In the mounting direction, dig the teeth into the softer material of the gear housing 1 in the housing section 101 and generate a resistance force that is greater than the force required to secure the worm shaft axially.

Another advantage of this axial lock is that a stop of the

Worm shaft and / or the bearing on the cathedral produces loud noises that can be heard as a defect by a driver of the motor vehicle. The driver can then act accordingly and, for example, go to a workshop.

In the area of the pretensioning device, the lid base 80 has an inward curvature 17, which is directed into the lid and points away from the worm shaft and which provides a corresponding free space for the pivot axis or the pin 150 of the pretensioning device 15. The inward curvature 17 forms a second dome with an essentially circular cross section. The lid base has a further inward curvature 18, which forms a projection away from the worm shaft 3, which serves as an assembly stop. In the area of the projection 18, the cover base 80 lies on its inside 84, the side near the worm shaft, in the assembled state in contact with a rib 100 of the housing 1

Interaction with the rib 100, the insertion depth of the cover 8 in the opening 9 in the direction of assembly. The domes 17, 18 point away from the worm shaft 3, while the dome 16 points towards the worm shaft and is in direct or indirect contact with the shaft 3 depending on the respective state.

FIGS. 5 to 7 show the details of the cover 8. The cover base 80 is shown in detail with the axial securing of the worm shaft (bulge) 16 and the bulges 17, 18 for the pin 150 of the pretensioning device 15 of the bearing remote from the motor, and for the housing rib 100 , The lid 80 also has a grip tab 19 which forms part of the lid edge 81 and projects beyond the tooth edge 83 in the direction of the longitudinal axis 4. The grip tab 19 has an outwardly angled region 190 which is arranged at a certain distance from the teeth of the tooth edge 83. The tab 19 is preferably formed on a side opposite the projection 18 with respect to the first dome 16. The projection 18 and the tab 19 thus lie on a common axis that runs through the center of the first dome 16. The tab 19 serves as an assembly stop. In the installed state of the cover 8, the underside of the angled region 190 of the tab rests on the end face of the housing 1 in the region of the opening 9. Since the projection 18 serving as an assembly stop and the tab 19 lie on a common axis, centrally through the first dome 16, tilting of the cover 8 can be prevented during installation. The grip tab 19 also serves as a disassembly aid in order to be able to grip the cover 8 and pull it out of the opening 9.

FIG. 8 shows a second embodiment of a cover 8. This cover 8 corresponds essentially to the cover 8 described above, the projection and the second dome in the cover base 80 being dispensed with.

A detailed view of the cover is shown in FIGS. 9 and 10. The prongs 83 in FIG. 9 have a defined prong width d, a defined prong length x and a defined prong height hl. The point width d and the point length x can be in a preferred relationship to one another 0 <x <3d. The ratio can also be provided as follows: l / 8 <d <x. FIG. 9 shows that the teeth of the tooth edge 83 are identical to one another and therefore also each tooth length x, each

Point height hl and each point width d over the entire circumference. FIG. 10, on the other hand, shows that at least one point along the circumference of the

Jagged edges can assume a different length, width and / or height. A spike can have a second spike height h2, deviating from the first spike height h1. In this example, the point height is h2 <hl, but hl> h2 can be formed. Furthermore, FIG. 10 shows schematically that at least one prong has a width of the first prong width d may have a different second prong width d2. In this example, d2> d, but d2 <d can be formed. The same can be implemented for at least one spike length x. The second prong length x2 is less than x, but x> x2 can be formed. The cover preferably has a smaller one in all embodiments

Strength than the gearbox. The gear housing is preferably a cast aluminum housing. The lid is preferably made of sheet metal, in particular spring steel. The lid can in particular be made from a material that is suitable for metal laser sintering or from tool steel.

Claims

claims

1. helical gear (2) for electromechanical power steering

Comprising a shaft (3) which meshes with a screw wheel (6), the shaft (3) being arranged in a gear housing (1) and at its first end in a first bearing arrangement (11) and at its second end in a second bearing arrangement ( 12) is rotatably mounted in the transmission housing (1) about a longitudinal axis (4), the transmission housing (1) having an opening (9) in an extension of the shaft (3) at an end remote from the drive, which opening can be closed by a cover (8) is, the lid (8) a lid base (80) and a circumferential

Has lid edge (81), characterized in that the

Cover base (80) in the area of the shaft (3) has a bulge (16) which extends outwards and in the direction of the shaft (3) and forms an axial securing of the shaft (3).

2. helical gear according to claim 1, characterized in that the cover (8) is pressed into the opening (9).

3. helical gear according to claim 1 or 2, characterized in that the bulge (16) cylindrical, with a circular

Base is formed.

4. helical gear according to claim 3, characterized in that the bulge (16) has an outer diameter which is at least as large as the diameter of the shaft (3).

5. helical gear according to claim 3 or 4, characterized in that an axis of symmetry of the bulge (16) corresponds to the longitudinal axis (4) of the shaft (3).

6. helical gear according to one of the preceding claims,

characterized in that the lid edge (81) has a serrated edge (83), which is biased outwards in the radial direction of the longitudinal axis (4) and, in the pressed-in state, rests against an inside of the transmission housing (1) and forms a press-out protection.

7. helical gear according to claim 6, characterized in that the tooth edge (83) is fixed with pretension.

8. helical gear according to claim 6, characterized in that the toothed edge (83) has a force fit of the cover (8) with the

Gearbox housing (1) generated.

9. helical gear according to one of the preceding claims,

characterized in that the edge of the cover (81) has a tab (19) which has an area (190) which is angled outwards, with the underside of the angled area (190) on one of the openings (190) when the cover (8) is installed 9) educational

Front of the housing (1) rests.

10. helical gear according to one of the preceding claims,

characterized in that the second bearing arrangement (12) has a pretensioning device (15), by means of which the position of the shaft (3) with respect to the screw wheel (6) can be adjusted, the pretensioning device (15) having a spring-preloaded pin (150 ), which defines a pivot axis and wherein the lid base (80) has an inward curvature (17) which forms a free space for the pin (150).

11. helical gear according to one of the preceding claims,

characterized in that the cover base (80) has an inward projection (18) which, in the installed state, is in contact with the transmission housing (1) on the outside and forms an assembly stop.

12. helical gear according to one of claims 9 to 11, characterized

characterized in that the tab (19) and the projection (18) are arranged on opposite sides of the bulge (16).

13. helical gear according to one of the preceding claims,

characterized in that the lid edge (81) has a first edge area (82) which extends without interruption along the circumference of the lid base (80) and a second edge area (83) which adjoins the first edge area (82) on a floor distant

Side connects, wherein the second edge region forms the tooth edge (83).

14. helical gear according to one of the preceding claims,

characterized in that the gear housing (1) is formed from a softer material than the cover (8).

15. helical gear according to one of the preceding claims,

characterized in that the gear housing (1) as

Cast aluminum housing is formed and the cover (8)

Spring steel is made.

16. helical gear according to one of the preceding claims,

characterized in that the helical gear (6) is a worm gear and the shaft (3) is a worm gear.

17. Electromechanical power steering comprising an electric motor (5) with a motor shaft and a helical gear (2) according to one of the

Claims 1 to 16, wherein the motor shaft drives the shaft (3) of the helical gear (2).

18. Electromechanical power steering according to claim 17, characterized

characterized in that the screw wheel (6) is arranged on a steering shaft (7) of a motor vehicle in a rotationally fixed manner.