WO2021175750A1

WO2021175750A1 - Method for producing a gear wheel for an electromechanical power assisted steering system

Info

Publication number: WO2021175750A1
Application number: PCT/EP2021/054959
Authority: WO
Inventors: Philipp GOTTWALD; Alexander Sulzer
Original assignee: Thyssenkrupp Presta Ag; Thyssenkrupp Ag
Priority date: 2020-03-06
Filing date: 2021-03-01
Publication date: 2021-09-10
Also published as: EP4114636A1; DE102020202922A1; CN115243858A

Abstract

The present invention relates to a method for producing a gear wheel comprising a hollow shaft (4), which is connected, by a connecting element (6) encapsulated in plastic by injection moulding, to a ring gear (5) extending coaxially around the hollow shaft at a radial distance, in which method the ring gear (5) and the hollow shaft (4) are positioned in the mould cavity (73) of an injection mould (7), in an ejector-side mould half (72), which is axially closed by a nozzle-side mould half (71), and molten plastic is injected axially into the intermediate space (8) between the ring gear (5) and the hollow shaft (4), through at least one injection nozzle (77, 79) in the nozzle-side mould half (71). In order to provide a method that is less laborious and offers a broader range of application possibilities, it is proposed according to the invention that, when the injection mould (7) is closed, an axial opening (43) at the end face of the hollow shaft (4) is closed and sealed with respect to the intermediate space (8) by the nozzle-side mould half (71).

Description

Method for manufacturing a gear wheel for an electromechanical power steering system

State of the art

The invention relates to a method for producing a gear wheel comprising a hollow shaft which is connected to a coaxially radially spaced circumferential ring gear via a connecting body injected in plastic injection molding, in which the ring gear and the hollow shaft in the mold cavity of an injection mold in an ejector-side mold half be positioned, which is axially closed by a nozzle-side mold half, and through at least one injection nozzle in the nozzle-side mold half, fusible plastic is injected axially into the space between the ring gear and the hollow shaft. A worm wheel produced by the method for an electromechanical auxiliary power steering is also the subject of the invention.

In the case of electromechanical power steering systems, an auxiliary torque is generated by an electric motor, which is coupled into a steering shaft via a gearbox to support a manual steering torque. The gear is designed as a reduction gear and comprises a first gear element coupled to the motor shaft, for example a worm connected in a rotationally fixed manner to the motor shaft, and a gear wheel in gear engagement therewith, for example a worm wheel, which is connected to the steering shaft in a torque-proof manner.

The gear wheel has a hub in the generically based design, which is at least partially designed as a hollow shaft which is rotatably mounted in the transmission about a gear axis and can be connected to the steering shaft in a torque-locking manner. The ring gear, which can have a worm toothing, for example, surrounds the hollow shaft coaxially and is connected to it in a rotationally fixed manner via a connecting body arranged radially in between.

To optimize the operating properties, it is known to form trainees the hollow shaft and the ring gear from different materials adapted for the respective stresses, for example the hollow shaft made of steel, and the ring gear made of plastic or non-ferrous metal, and to connect to one another in a rotationally fixed manner. For this purpose, it is known from EP 1 777439 A1, for example, to inject a molten ther moplastic plastic between the hollow shaft and the ring gear in the plastic injection molding process, which after the Solidification forms a connecting body that is connected with the hollow shaft and the ring gear, preferably with a material and form-fitting connection.

EP 1 777 439 A1 proposes an injection molding process in which the hub and the ring gear are positioned in the mold cavity of a two-part injection mold in an ejector-side mold half that is closed by the nozzle-side mold half, and the connecting body is produced in the shield connection. The intermediate space is filled with the plastic melt through an injection nozzle in the nozzle-side mold half that runs in a ring-shaped manner coaxially to the transmission axis. As a result, a kegelmantelförmi ger sprue, which has to be removed from the fully solidified connecting body by post-processing, for example by cutting, which is complex in terms of production technology. It is also necessary to prevent plastic melt from penetrating into the opening at the end of the hollow shaft during the injection molding process. To this end, it is proposed to dip a core from the ejector-side mold half through the opening in order to fill it out and close it. However, this is only possible if the opening passes axially through the hub smoothly and with a constant cross-section, and has no changes in cross-section or undercuts that would make it impossible to remove the mold half on the ejector side. This basically restricts the application to a simple hub geometry.

In addition, a low-tolerance fit of the core is necessary in order to avoid the penetration of plastic into the gap between the core and the opening, which is also expensive. In addition, the inserted core cannot prevent the hollow shaft from coming into contact at least partially with plastic on the outside of the nozzle, which plastic has to be removed later.

In view of the problems explained above, it is an object of the present invention to provide a method for producing a gear wheel with an injected connec tion body which is less expensive and offers broader application possibilities.

Presentation of the invention

According to the invention, this object is achieved by a method having the features of claim 1. Advantageous further developments emerge from the subclaims. In the method for producing a gear wheel comprising a hollow shaft, which is connected to a ring gear rotating coaxially at a radial distance via a connecting body injected in plastic injection, in which the ring gear and the hollow shaft in the mold cavity of an injection mold in an ejector-side mold half positio which is axially closed by a nozzle-side mold half, and through at least one injection nozzle in the nozzle-side mold half, molten plastic is injected axially into the space between the ring gear and the hollow shaft, it is proposed according to the invention that when the injection mold is closed, an axial opening at the end of the hollow shaft is closed by the nozzle-side mold half and sealed to the space in between.

The hub is formed by a hollow shaft that extends axially in the direction of the transmission axis and that has an axial opening at the end that can form an axially continuous through opening, but can also be a blind hole that can be closed within the hollow shaft.

The two-part injection mold has a nozzle-side and an ejector-side mold half, which to close the injection mold in the axial direction - based on the transmission axis - are put together until they rest against each other in the parting plane when the injection mold is closed.

Before closing, the hollow shaft, which is for example made of steel, is inserted centrally in the ejector-side mold half in the axial direction, and the ring gear is inserted coaxially to it, which is made, for example, of plastic or non-ferrous metal. The injection mold is then closed by axially attaching the nozzle-side mold half. In this closed state, the nozzle-side mold half not only limits the mold cavity formed together with the ejector-side mold half to the outside and closes it, but according to the invention the nozzle-side mold half cooperates with the hollow shaft in such a way that it tightly closes the axial opening that is open on the nozzle side. Consequently, the remaining space is limited axially between the mold surfaces of the nozzle-side and the ejector-side mold halves, and radially between the ring gear and the outer surface of the hollow shaft. Because the nozzle-side opening of the hollow shaft is tightly closed by the nozzle-side mold half, the interior of the opening is tightly closed towards the intermediate space.

In the next step, molten plastic, the plastic melt, is axially, ie in the direction of a suitable injection nozzle arrangement through the nozzle-side mold half the gear shaft, injected into the space. After solidification, the plastic forms the connecting part, which can be connected to the hollow shaft and / or the ring gear in a materially bonded manner and additionally by form-locking elements embedded in the plastic. The inventive sealing of the opening prevents plastic melt from penetrating into the interior of the hollow shaft. As a result, sprue residues in the area of the opening are largely avoided, and the expense for post-processing is correspondingly reduced in an advantageous manner.

Another significant advantage over the prior art mentioned with the core penetrating through the opening from the ejector side is that the opening can be safely closed by the nozzle-side mold half regardless of the passage cross-section and any changes in shape, changes in cross-section or undercuts. If the opening is formed by a blind hole, it can also be closed easily and safely, which is not possible in the prior art. This results in expanded application possibilities with regard to the design of the hollow shaft.

It can be provided, for example, that the opening is designed as a through opening with a through cross section axially through the hollow shaft, which is larger on the nozzle side than on the ejector side. An internally stepped bore can be used to optimize weight, for example, or an optimized adaptation for connection to a steering shaft.

The mold half on the nozzle side and the hollow shaft preferably have corresponding axial sealing surfaces which, when the injection mold is closed, bear tightly against one another. Because the axially acting closing force of the injection mold acts on the axial sealing surfaces, a particularly reliable sealing of the opening against the intermediate space can be realized.

Additionally or alternatively, the nozzle-side mold half and the hollow shaft can have corresponding radial sealing surfaces that rest against each other with little play when the injection mold is closed.

Another advantageous possibility is that the corresponding sealing surfaces on the nozzle-side mold half and the hollow shaft are at least partially conical. For example, the hollow shaft can have a sealing surface that converges conically towards the nozzle side, and the nozzle-side mold half, on the other hand, a corresponding one sealing conical or cylindrical opening. The conical sealing surfaces can be conical, or also convex or rounded. Such conical sealing surfaces have the advantage that the closing force of the injection mold acting in the axial direction can be used to seal off.

It can be provided, for example, that the nozzle-side mold half rests tightly against the hollow shaft at the end when the injection mold is closed. For example, a coaxially encircling axial, radial and / or conical sealing surface can be formed on the front edge of the opening which tightly contacts a corresponding sealing surface on the inner wall of the nozzle-side mold half.

An advantageous embodiment can provide that a hollow shaft section of the hollow shaft protruding axially from the end face of the connecting body and / or the toothed ring is received in a recess in the nozzle-side mold half. The hollow shaft can have an axially protruding section on one side or on both sides, which, for example, can be designed with connecting means for torque-locking connec tion with a steering shaft, for example bores and / or shaft journals with a round or non-round cross-section for realizing force- and / or positive connections. Because a hollow shaft section protruding axially on the nozzle side dips into the recess of the nozzle-side mold half when the injection mold is closed, a simple adaptation to different geometries and dimensions of the gear wheel can take place. The sealing according to the invention can take place in the frontal end area or also in the course of the protruding hollow shaft section. For this purpose, for example, as described above, axial, conical and / or radial sealing surfaces can be provided.

It can be advantageous for carrying out the method that a plurality of Punkan casts is arranged distributed over the circumference. The point gates have injection nozzles opening axially into the intermediate space. For each point gating, the plastic melt is injected into the space through an injection nozzle, whereby a uniform filling that is adapted to the geometry can be realized. As a result, a uniform, low-tension and highly resilient connection body can be produced.

Three, four, six, eight, twelve or more point gates can be arranged distributed over the circumference, preferably evenly. In terms of manufacturing technology, point gates have the advantage that the sprue cross-section, which is given by the nozzle cross-section of the injection nozzle, can be so small - almost point-like - that the sprue tears off or shears off during demolding due to low transverse forces. Because the point gates are positioned close to the nozzle-side axial surface of the connecting body As a rule, no mechanical reworking of the sprues is required, which means that the manufacturing effort can be reduced compared to a shield sprue.

In order to create the separation of the sprue point (s) by shearing or tearing off, it can be provided in an advantageous development of the method that, after the plastic has solidified, the ejector-side mold half is separated from the nozzle-side mold half by an axially translatory and a rotary movement are preferably superimposed as a helical movement. For demolding, the two mold halves are separated from each other against the axial closing direction, the mold cavity being opened and the finished gear wheel can be ejected from the ejector-side mold half. Because the two halves of the mold are moved helically relative to one another during separation, the rotational movement component exerts a shear force in the circumferential direction on the sprues formed in the area of the injection nozzles, which means that they are sheared or torn off during demolding, and reworking can be omitted. It is also conceivable and possible that the mold halves can be separated from one another by a purely axial-translational movement.

Under certain circumstances it is also possible for the space in the shield gate to be filled, for example in order to inject special geometries in an optimized manner. It is also conceivable and possible for the space in the ring gate to be filled. This ensures that the space can be produced with a uniform wall thickness.

The invention further comprises a worm wheel for an electromechanical auxiliary power steering, comprising a hub designed as a hollow shaft, which is connected to a ring gear that rotates coaxially at a radial distance via a connection body made of a thermoplastic material which is injected in plastic injection molding and which is connected to a method according to the invention such as is produced as described above. The hub and / or the ring gear can be made of a metallic material or a plastic. It is also conceivable and possible to provide the worm wheel for a steer-by-wire steering system in which a connection between the steering wheel and the steered wheels takes place via electrical signals. Description of the drawings

Advantageous embodiments of the invention are explained in more detail below with reference to the drawings. Show in detail:

Figure 1 shows a steering system of a motor vehicle in a schematic representation,

Figure 2 shows an auxiliary power drive of the steering system according to Figure 1 in a schematic

Depiction,

FIG. 3 shows a gear wheel of an auxiliary power drive in a perspective view,

FIG. 4 shows a sectional view through an injection mold according to the invention,

FIG. 5 shows a schematic representation of the melt flow in an injection mold according to FIG. 4,

FIG. 6 shows a sectional view through an injection mold according to the invention in a second embodiment,

FIG. 7 shows a sectional view through an injection mold according to the invention in a third embodiment.

Embodiments of the invention

In the various figures, the same parts are always given the same reference numerals and are therefore usually only named or mentioned once.

FIG. 1 shows a schematic view of a motor vehicle steering system 100. This comprises a steering shaft 1 into which a driver can introduce a manual steering torque or steering torque as a steering command via a steering wheel 102. The steering torque is transmitted via the steering shaft 1 to a steering pinion 104 which meshes with a rack 106 in a steering gear. A rotation of the steering pinion 104 is converted into a linear displacement of the toothed rod 106, which in turn causes a steering angle of the steerable wheels 110 of the motor vehicle via the tie rods 108. Electrical power assistance can be provided in the form of an auxiliary power drive 112 coupled to the steering shaft 1 on the input side, an auxiliary power drive 114 coupled to the pinion 104 and / or an auxiliary power drive 116 coupled to the rack 106. The respective auxiliary power drive 112, 114 or 116 couples an auxiliary torque into the steering shaft 1 and / or the steering pinion 104 and / or an auxiliary force into the rack 106, whereby the driver is supported in the steering work. The three different auxiliary drives 112, 114 and 116 shown in FIG. 1 show possible positions for their arrangement.

Usually only one of the positions shown is occupied by an auxiliary power drive 112, 114 or 116. The auxiliary torque or auxiliary force, which is to be applied to support the driver by means of the respective auxiliary power drive 112, 114 or 116, is determined taking into account a steering torque determined by a torque sensor 118 and manually introduced by the driver. Alternatively or in combination with the introduction of the auxiliary torque, an auxiliary power drive 112, 114, 116 can introduce an additional steering angle into the steering system 100, which adds up to the steering angle applied by the driver via the steering wheel 102.

The steering shaft 1 has an input shaft 10 connected to the steering wheel 102 on the input side and an output shaft 12 connected to the rack 106 via the steering pinion 104 on the output side. The input shaft 10 and the output shaft 12 are coupled to one another in a torsionally flexible manner via a torsion bar which cannot be seen in FIG. A torque entered by a driver via the steering wheel 102 into the input shaft 10 always leads to a relative rotation of the input shaft 10 with respect to the output shaft 12 when the output shaft 12 does not rotate exactly in synchronism with the input shaft 10. This relative rotation between input shaft 10 and output shaft 12 can be measured via a rotation angle sensor and a corresponding input torque relative to output shaft 12 can be determined based on the known torsion stiffness of the torsion bar. In this way, the torque sensor 118 is formed by determining the relative rotation between input shaft 10 and output shaft 12. Such a torque sensor 118 is known in principle and can be implemented, for example, an electromagnetic sensor arrangement, or by another measurement of the relative rotation.

Correspondingly, a steering torque which is applied by the driver via the steering wheel 102 to the steering shaft 1 or the input shaft 10 will only bring about the input of an auxiliary torque by one of the auxiliary power drives 112, 114, 116 if the Output shaft 12 is rotated relative to the input shaft 10 against the rotational resistance of the torsion bar.

The torque sensor 118 can alternatively be arranged at the position 118 ', where the opening of the steering shaft 1 in the input shaft 10 and output shaft 12 and the torsionally flexible coupling via the torsion bar is accordingly at a different posi tion in order to get out of the relative rotation of the Torsion bar with the output shaft 12 coupled to the input shaft 10 to be able to determine a relative rotation and thus correspondingly an input torque and / or an auxiliary torque to be introduced.

The steering shaft 1 according to FIG. 1 furthermore comprises at least one cardanic joint 120, by means of which the course of the steering shaft 1 in the motor vehicle can be adapted to the spatial conditions.

In FIG. 2, an electromechanical auxiliary torque drive 2 is shown as an example, which can be used as an auxiliary power drive 112 or 114 for coupling an auxiliary torque into the steering shaft 1.

The auxiliary torque drive 2 has a gear 21 which has a worm 22 which is in gear engagement with a gear wheel 3 designed as a worm wheel.

The gear wheel 3 is rotatably connected to the steering shaft 1, and with this beachse L, which is identical to the longitudinal axis of the steering shaft 1, rotatably mounted in the gearbox 21 about the gearbox.

The worm 22 is coupled to the motor shaft 23 of an electric motor 24 and can be driven in rotation by the sem, the gear wheel 3 being set in rotation about the gear axis L by the gear engagement.

The gear wheel 3 is shown separately in perspective in FIG. It has a hub designed as a hollow shaft 4, which is coaxial to the transmission axis L of a ring gear 5 to give. The hollow shaft 4 is firmly connected to the ring gear 5 via a connecting body 6 made of thermoplastic material and injected into the radial intermediate space by plastic injection molding.

The hollow shaft 4 has a first hollow shaft section 41 protruding axially on the end face, and a hollow shaft extension 42 extending axially from the other side. Between an insert 400 is provided for the hollow shaft sections 41, 42. The insert 400 is formed in one piece with the hub 4. An opening 43 open at the end of the hollow shaft section 41 extends as a through-hole through the entire hollow shaft 4, as can be seen in the longitudinal section along the transmission axis L shown in FIG. It can be seen from this that the opening cross section of the opening 43 is stepped over the length, the inner diameter D in the hollow shaft section 41 being larger than in the hollow shaft extension 42.

Figure 4 shows the gear wheel 3 in a longitudinal section during manufacture in a two-part injection mold 7, which has a nozzle-side mold half 71 arranged on the nozzle side - on the left in the drawing - and an ejector-side mold half arranged on the ejector side - on the right in the drawing 72 has. In the closed stand shown, the mold halves 71 and 71 are in the parting plane T against each other.

The mold halves 71 and 72 enclose a mold cavity 73 which, in the example shown, is predominantly formed in the mold half 72 on the ejector side.

For production according to the method according to the invention, the separately provided ring gear 5 and the hollow shaft 4, in particular in the area of the insert 400, are positioned in the mold cavity 73 of the mold half 72 on the ejector side, as shown. Subsequently, the nozzle-side mold half 71 is assembled axially, i.e. in the direction of the gear axis L, with the ejector-side mold half 72 in the parting plane T, the mold cavity 73 being closed with the closing force F, as shown in Figure 4 with the arrows. In this case, an inter mediate space 8 remains radially between the hollow shaft 4 and the ring gear 5, the cross section of which corresponds to the connecting body 6.

When the injection mold 7 is closed, the hollow shaft section 41 now protruding towards the nozzle side dips into a recess 74 in the mold half 71 on the nozzle side. In this case, an axial sealing surface 44 arranged at the end of the hollow shaft section 41 lies tightly against the nozzle-side mold half 71 against a corresponding axial sealing surface 75, which is arranged here at the base of the recess 74. As a result, the intermediate space 8 is sealed off from the opening 43. The sealing surfaces 44, 76 can furthermore be provided in a region of the mold cavity 73 in which the insert 400 and the nozzle-side mold half 71 and the ejector-side mold half 72 adjoin.

The nozzle-side mold half 71 has a plurality of injection nozzles 76 which - before given evenly - open axially distributed over the circumference into the intermediate space 8, to form point gates. The injection nozzles 76 can be star-shaped or over the Distributor channels 77 arranged over the entire circumference are acted upon by a central feed channel 78 with plastic melt.

During the actual injection molding process, liquid plastic melt is injected through the feed channel 78, the distribution channels 77 and the injection nozzles 76 into the space 8, as is shown schematically in FIG. After solidification, the plastic forms the plastic body 6, which essentially fills the gap 8 and is firmly connected to the hollow shaft 4 and the ring gear 5 in a materially and preferably also in a form-fitting manner.

Through the injection nozzles 76 point gates with a relatively small cross section are formed over the nozzle-side axial circumference of the connec tion body. For demolding, the nozzle-side mold half 71 is axially removed from the ejector-side mold half 72 against the closing force F along the gear axis L, while at the same time it is rotated around the gear axis L so that a kind of helical movement occurs. As a result, who sheared the point gates in the area of the injection nozzles 76 on the axial end face of the connecting body. No further post-processing is required.

Figures 6 and 7 show views similar to Figure 4, wherein the ejector-side mold half 72 is omitted.

In the embodiment of FIG. 6, instead of the punctiform injection nozzles 76 of FIG. 4, a coaxially ring-shaped circumferential injection nozzle 79 is provided. The injection zen of the plastic melt takes place in the gap 8 axially through a circumferential ring gap. This allows the filling behavior to be adjusted.

In the embodiment shown in FIG. 7, similar to FIG. 4, a plurality of injection nozzles 76 distributed over the circumference is provided which, however, do not open directly into the intermediate space 8 as punctiform tangusses, but into a pre-chamber 81 formed axially in front of it Pre-chamber 81 can be designed as a coaxial annular space which is connected to the intermediate space 8. First, the prechamber 81 is filled with plastic and then the intermediate space 8. The prechamber is then removed by machining. This allows the injection of the plastic melt to be adjusted and the filling to be optimized. List of reference symbols

1 steering shaft

10 input shaft

100 motor vehicle steering

102 steering wheel

104 steering pinion

106 rack

108 tie rods

110 wheel

112,114,116 auxiliary power drive 118 torque sensor

12 output shaft

120 joint

2 auxiliary torque drive

21 transmission

22 snail

23 motor shaft

24 electric motor

4 hollow shaft

41 hollow shaft section

42 Hollow shaft attachment

43 opening

44 sealing surface

5 ring gear

6 connecting body

7 injection mold 71, 72 mold half

73 mold cavity

74 recess

75 sealing surface

76 injection nozzles (point gates)

77, 79 injector

8 space

81 antechamber

L gear axis

T parting line

F closing force

D, d diameter

Claims

PATENT CLAIMS

1. A method for producing a gear wheel comprising a hollow shaft (4) which is connected to a coaxially radial spaced circumferential ring gear (5) via a plastic injection-molded connecting body (6), in which the ring gear (5) and the Hollow shaft (4) in the mold cavity (73) of an injection mold (7) are positioned in an ejector-side mold half (72), which is axially closed by a nozzle-side mold half (71), and by at least one injection nozzle (77,79) in the nozzle-side Mold half (71) of molten plastic is injected axially into the space (8) between the ring gear (5) and the hollow shaft (4), characterized in that when the injection mold (7) is closed, an axial opening (43) at the end of the hollow shaft (4) is separated from the nozzle-side mold half (71) is closed and the intermediate space (8) is sealed.

2. The method according to claim 1, characterized in that the nozzle-side mold half (71) and the hollow shaft (4) have corresponding axial, radial and / or conical sealing surfaces (44) which rest tightly against each other when the injection mold (7) is closed.

3. The method according to claim 2, characterized in that the nozzle-side mold half (71) rests tightly against the hollow shaft (4) at the end when the injection mold (7) is closed.

4. The method according to any one of the preceding claims, characterized in that an end face of the connecting body (6) and / or the ring gear (5) axially protruding hollow shaft section (41) of the hollow shaft (4) in a recess (74) of the nozzle-side mold half ( 71) is recorded.

5. The method according to any one of the preceding claims, characterized in that the opening (43) is formed as a passage opening with a passage cross section which is larger on the nozzle side than on the ejector side.

6. The method according to any one of the preceding claims, characterized in that a plurality of point gates (76) is arranged distributed over the circumference.

7. The method according to any one of the preceding claims, characterized in that after the solidification of the plastic, the ejector-side mold half (72) from the nozzle-side mold half (71) are separated from each other by an axial-translational and a rotational movement, preferably superimposed as a screw shaped movement.

8. The method according to any one of the preceding claims, characterized in that the intermediate space (8) is filled in the screen gate.

9. worm wheel (3) for an electromechanical power steering, comprising an as

Hollow shaft (4) formed hub, which is connected to a coaxially radial distance umlau Fenden ring gear (5) via a plastic injection-molded connec tion body (6) made of a thermoplastic material, characterized in that it is according to a method according to a of claims 1 to 8 is made.

10. worm wheel (3) according to claim 9, characterized in that the hub (4) and / or the ring gear () are formed from a metallic material.

11. worm wheel (3) according to claim 9, characterized in that the hub (4) and / or the ring gear (5) are formed from a plastic.