WO2009062961A1

WO2009062961A1 - Clock spring

Info

Publication number: WO2009062961A1
Application number: PCT/EP2008/065396
Authority: WO
Inventors: Alex Bormuth; Michael Mueller; Johannes Will; Jörg Wowes
Original assignee: Tyco Electronics Amp Gmbh
Priority date: 2007-11-17
Filing date: 2008-11-12
Publication date: 2009-05-22
Also published as: DE102007054952A1; DE102007054952B4

Abstract

The invention relates to a clock spring (1) for a steering system of a vehicle, in particular a motor vehicle, comprising a stator (10, 11) and a rotor (20, 21) which is rotatable with respect to the stator (10, 11) about an axis of rotation (R) of the clock spring (1) and is arranged so as to be substantially concentric, in which both the stator (10, 11) and the rotor (20, 21) of the clock spring (1) are free of a winding core (22). The invention further relates to a clock spring (1) for a steering system of a vehicle, in particular a motor vehicle, comprising a stator (10, 11) and a rotor (20, 21) which is rotatable with respect to the stator (10, 11) about an axis of rotation (R) of the clock spring (1) and is arranged so as to be substantially concentric, in which the stator (10, 11) and/or the rotor (20, 21) of the clock spring (1) is formed at least in part as a circuit board. The invention further relates to a steering system for a vehicle, in particular a motor vehicle, comprising a clock spring (1) according to the invention.

Description

CLOCK SPRING

The invention relates to a clock spring for an electrical feed line connected to a steering wheel of a vehicle, in particular a motor vehicle. The invention further relates to a steering system for a vehicle comprising a clock spring according to the invention.

With the introduction of the airbag system in motor vehicle steering wheels, there has been an increasingly frequent use of clock springs to produce an electrical connection between the steering wheel and an electrical system of a vehicle or the vehicle electronics. Clock springs are essential components for important safety systems or devices, such as the aforementioned airbag, because they provide a problem-free electrical connection, which negates any interruption or delay of an electrical impulse.

Clock springs further act to exchange or transmit data and/or signals between other devices provided in/on the steering wheel and the vehicle electrical system or electronics. These are sensors, switches and/or electrical/electronic components, such as the angle of rotation sensor, horn, radio, navigation system, hazard warning light, headlights, steering wheel heating system, etc.

In an embodiment, the clock spring is located on a support of a steering wheel steering column and is composed of substantially cylindrical components, which are fixed to the steering wheel. The clock spring components are movable (rotor) and fixed to the vehicle (stator), arranged concentrically in relation to one another, and connected to one another via a plastic material strip comprising integrated electrical conductive tracks (flat flexible cable (FFC)).

In what are known as short clock springs, a flat flexible cable is guided in a loop in a clock spring housing (and is therefore also known as a loop-back clock spring), wherein one end of the flat cable is connected to the rotor and the other end of the flat cable is connected to the stator. In other clock springs, the flat flexible cable is formed in a spiral shape, positioned in the clock spring housing about a winding core of the clock spring in substantially concentric windings. In this case, one longitudinal end of the flat flexible cable is again fastened to the stator and the opposite longitudinal end is fastened to the rotor. Both ends of the flat flexible cable are electrically connected.

Before the rotor (steering wheel) starts rotation, the flat cable is initially wound internally on the stator. When the rotor starts rotation in the first rotational direction, the flat cable unwinds from the stator to windup externally on the winding core, with a smaller diameter of the rotor. Conversely, when the rotor is rotated in the other rotational direction, the flat cable now wound on the rotor is unwound. Then, the flat cable is wound up internally on the stator, which has a larger diameter. This occurs in short clock springs using the loop in the flat cable, whereas the respective radius of the concentric windings of the flat flexible cable becomes larger or smaller in other clock springs.

In order to use clock springs in modern motor vehicles, clock springs must be able, for example, to operate through five complete rotations of the steering wheel, that is to say approximately two and a half rotations to the right and two and a half rotations to the left from a straight driving position. In order to be equipped for reliable use in the steering system of a motor vehicle and, in addition, to achieve a simple production process, a clock spring should be constructed to be strong, yet simple, comprising as few parts as possible. In particular, this relates to the clock spring housing construction , the rotor having to be rotatable in relation to the stator.

Furthermore, the clock springs should be formed to be as small as possible, because of the restricted conditions in the motor vehicle. In particular, this applies to the winding and unwinding diameter for the electrical flat cable inside the clock spring. In this way, it is possible to influence the length of the flat electrical cable significantly, resulting in a short flat electrical cable and a clock spring that is cost-effective to produce if appropriately small diameter values are used. DE 42 35 055 Al discloses a housing for receiving an electrical contact spiral comprising a rotor and a two-part stator, and an annular space in which the contact spiral can be received. The annular space is formed between the stator and the rotor. The rotationally symmetrical stator, constructed with a U-shaped generatix is mounted on a fixed outer column of a steering system, comprising a steering gear shaft and a sleeve. The steering gear, which is provided to be rotatable in the outer column, is supported on the outer column radially by a ball bearing and axially by a retaining ring. A sleeve is provided on the steering gearing shaft. After each rotational movement of the steering gear shaft, the contact spiral is wound back onto an inner side (winding core), which is arranged at a distance from the steering gear shaft of the stator, or is wound off this inner side again. There is a problem with this clock spring construction. The minimum winding diameter of the stator, i.e. the minimum diameter of the winding core, is comparatively large. Therefore, a comparatively long electrical flexible cable must be used for the clock spring. A further problem of this construction is that the stator requires a comparatively large winding diameter, because the winding core of the clock spring is comparatively large. In addition, this type of construction is rather complex. In the least, a two-part stator and the resulting clock spring is expensive, because of the comparatively long flat cable used and the comparatively complex construction thereof. An object of the invention is to provide an improved clock spring for a steering system of a vehicle, in particular a motor vehicle, and to provide an improved steering system for a vehicle, in particular a motor vehicle.

The clock spring, according to the invention, is constructed to be as small, robust and cost-effective as possible, capable of using as few components as possible. In particular, a winding core for the clock spring is to have a diameter, which is as small as possible. An electrical flat flexible cable, of the clock spring of the steering system, is intended to be as short as possible for a predetermined number of rotations of a steering gear shaft of the steering system. This limits the materials used, which is as cost-effective as possible for the motor vehicle. Yet, the improved construction ensures a problem-free operation of the clock spring.

The object of the invention is achieved by a clock spring for a steering system of a vehicle, in particular a motor vehicle, according to claim 1 (first embodiment) and claim 3 (second embodiment), and by a steering system for a vehicle, in particular a motor vehicle, according to claim 12. A first embodiment of a clock spring for a vehicle steering system comprises a stator and a rotor, which is substantially concentrically arranged and rotatable in relation to the stator along an axis of rotation of the clock spring. The actual clock spring does not have a winding core. Rather, the winding core, for an electrical flat flexible cable of the clock spring, is formed on an axial portion of a steering shaft of the steering system when the clock spring is installed inside the steering system. This means that neither the stator nor the rotor of the clock spring comprises an inner winding core with a small diameter. For example, the function of the winding core is assumed by a component on/in which the clock spring is installed or mounted. This is intended to apply analogously to a rod assembly located adjacent to the steering system. According to the invention, an intermediate wall of the clock spring, the stator or the rotor, located between the flat cable and the steering gear shaft or steering shaft, is omitted so that the diameter of a winding core of the clock spring can be reduced to the diameter of the steering shaft. Similarly, the winding or unwinding diameter of the flat cable can be reduced to the size of an outer wall of the clock spring, the stator, or the rotor.

In accordance with the invention, the flat cable is wound directly onto the steering shaft, which is considerably shorter in comparison to the prior art. It may be necessary to adapt an inductive sensor system for a sensor on the steering system of the motor vehicle.

A clock spring's installation socket, for mounting the clock spring on the steering shaft, is preferably not guided through the clock spring as in the prior art. Rather, it is preferably provided externally on the clock spring , pointing away from the steering shaft. In this case, the rotor of the clock spring is preferably fastened to the installation socket, which in turn is rigidly connected to the steering shaft of the steering system.

Apart from installation, support and/or connection devices for the flat flexible cable, the rotor of the clock spring is formed, as a planar disc, in the centre of which there is a through-recess for the steering shaft. The diameter of the through-recess is preferably slightly greater than the diameter of the steering shaft. However, it is also possible to provide the rotor with a fit or an interference fit on the steering shaft, wherein the installation socket may then be removed .

In an embodiment, a rigid mechanical connection, between the rotor and the installation socket, may be achieved using any suitable method or corresponding devices or apparatuses . It is thus possible to use a locking mechanism. For example, the locking mechanism may be formed as a clip connection or a bayonet catch. Secured penetration connections are also suitable, preferably a metal installation socket being inserted through an inner edge region of the rotor. In addition, it is further possible to screw the rotor and the installation socket together.

A preferred mechanical connection between the rotor and the installation socket is achieved through a thermally caulked penetration connection, where the installation socket is inserted through the rotor, preferably made of a plastics material, and into the inner edge region thereof by means of suitable projections formed on said installation socket. After they have cooled, the rotor and the installation socket are rigidly connected to one another.

One or a plurality of flat cables may be guided inside the clock spring, in a spiral shape or via a loop. In a first embodiment, it is preferable for the clock spring to have one flat cable only. However, the clock spring in a second embodiment may comprise of a plurality of flat cables. In this case, four flat cables are preferable, wherein a loop of the flat cable is preferably guided by a deflection roller inside the clock spring. A narrow, long transverse end of the flat cable is attached to the preferably discshaped rotor and moves from an inner region of the rotor into an outer region, or moves from an outer region of the rotor into the inner region thereof each time the rotor or the steering shaft is rotated. In order to ensure that the flat cable cannot escape from the clock spring, at the outer side of the rotor, the stator preferably comprises an outer wall that extends completely circumferentially in an outer edge region of the stator and is substantially in the form of a hollow cylinder. In other embodiments of the invention, it is also possible to provide this outer wall on the rotor, which has a cup- shaped appearance with a central through -recess for the steering shaft. The outer wall may further be formed by other components or constructional elements. In addition, an embodiment without an outer wall is also possible.

In preferred embodiments of the invention, the rotor may comprise an installation tab and/or guide tab that projects inwards into the clock spring for the flat cable. In this case, the installation and/or guide tab is preferably provided near the through-recess of the rotor. The installation tab acts to ensure that the flat cable does not slide into the through- recess of the rotor or fall into a gap between the rotor and the steering shaft during installation of the clock spring. This installation tab can be removed after the clock spring has been installed in the steering system.

The guide tab, which preferably extends in a winding direction of the flat cable, acts to guide the flat cable around the steering shaft and is preferably configured to be resilient in a radial direction of the clock spring. This is performed in such a way that the guide tab can follow radial movements of the flat cable.

In preferred embodiments of the invention, the installation socket is connected to the steering shaft with a positive fit and/or a material connection. In this case, the positive connection may be a pressure fit or a crimp connection. If a material connection is used, the connection is preferably a weld. It is of course possible to produce both a positive fit and a material connection between the installation socket and the steering shaft . Furthermore, the installation socket and steering shaft may be adhesively bonded to one another.

According to the invention, a longitudinal portion or a longitudinal end portion of the flat cable is directly adjacent to the steering shaft of the steering system in a rotational position of the rotor, in particular when the rotor is rotated completely to the right or completely to the left. A centre portion of the flat cable is then in a position, which is located further towards the exterior and is directly adjacent to the longitudinal end portion of the flat cable adjacent to the steering shaft. In this case, the guide tab may be provided in portions inside a first and a second inner winding of the flat cable about the steering shaft.

A range of advantages are achieved, including a smaller winding diameter, which is achieved by using the steering shaft as a winding core for the clock spring . This also allows a shorter flat cable to be used in comparison to the prior art. Furthermore, reducing the winding diameter allows the outer diameter of the clock spring to be reduced and a clock spring with smaller overall dimensions to be formed.

Moreover, the invention achieves an increased rotational range in relation to the prior art. This means that it is possible to obtain a greater angle of rotation of the steering wheel with a flat cable of the same or even of a shorter length. In this way, it is possible to rotate the steering wheel six or more times, for example, using a small clock spring.

In addition, using a shorter flat cable results in lower electrical resistance of the conductive tracks in the flat cable. This reduces power loss in the flat cable so it is thus possible to achieve higher electrical currents. Moreover, a reduction in costs and weight can be achieved as well. Some embodiments of the invention also allow the installation socket to be reduced in size.

In preferred embodiments of the invention, the rotor and/or stator of the clock spring is formed, at least in part, as a circuit board or a printed circuit board for electrical components. In particular, this applies to an end face of the clock spring, which is preferably formed as a substantially circular housing disc. In this context, the following configurations may also be used for the first embodiment of the invention.

In another embodiment of the invention, the clock spring comprises a stator, a rotor and a circuit board. The clock spring is to be substantially concentric with the stator, and rotatable with respect to the stator about a rotational axis of the clock spring. The circuit board or printed circuit board, for electrical components, form a housing portion of the clock spring. This means that the stator and/or the rotor of the clock spring comprise an electrical or electronic circuit board, which forms at least a region of the stator and/or the rotor. The second embodiment of the invention may comprise features of the first embodiment.

In embodiments of the invention, the disc- shaped rotor is formed as a circuit board, and the flat cable being provided inside the clock spring on a non-populated side of the circuit board. This also means that an outer side of the clock spring is a populated side of a circuit board, which makes it possible to provide components on the outer side of the circuit board. This applies analogously to the stator. It is also possible for a connecting wall (outer wall), between the rotor and the stator, to comprise the circuit board. This connecting wall is preferably a hollow cylinder, which is provided accordingly on an outer edge region of the stator and/or the rotor. The connecting wall may also be formed from other components or constructional elements. According to the invention, a part of the stator or the rotor may be a control circuit board or a sensor circuit board, i.e. an angle of rotation sensor.

In other embodiments, a corresponding circuit board has been mounted to or on a substantially closed housing of the clock spring. In another embodiment, the circuit board is a part, a portion or a region of the housing of the clock spring itself. It is then possible to achieve reductions in both cost and weight, as well as to decrease the space required for the clock spring.

A corresponding clock spring may include, according to the invention, both embodiments or only one embodiment of the invention.

It is thus possible, for example, to form a conventional clock spring with the housing circuit board according to the invention, wherein the clock spring comprises a winding core formed as a wall on the clock spring. It is further possible to provide the clock spring with a conventional housing and to form the clock spring itself without a winding core, which is in accordance with the first embodiment . Moreover, both aspects of the invention may also be used, the clock spring itself not having a winding core on the one hand and a housing portion of the clock spring being formed as a circuit board on the other.

Further embodiments of the invention will emerge from the remaining dependent claims.

The invention will be explained in greater detail in the following with reference to embodiments, referring to the appended drawings, in which: Figure 1 is a three-dimensional exploded view of a first embodiment of a clock spring according to the invention;

Figure 2 is a three-dimensional view of the clock spring according to the invention from Figure 1 when installed on a steering shaft of a steering system;

Figure 3 is an open, three-dimensional view of a second embodiment of the clock spring according to the invention; and

Figure 4 is a three-dimensional exploded view of the clock spring according to the invention from Figure 3. The invention will be explained below with reference to two embodiments of a clock spring, an electrical flat flexible cable of the clock spring according to the invention being guided in the shape of a spiral between a stator and a rotor of the clock spring. The invention is not to be restricted, however, to the embodiments of clock springs discussed below. Rather, the invention may relate to clock springs in which one or a plurality of flat cables are guided between the stator and the rotor of the clock spring via a loop, optionally by one or more deflection rollers (loop-back or short clock springs). The invention may provide clock springs, which comprise a plurality of flat cables guided in a spiral shape.

The two embodiments of the invention may furthermore be used alone or in combination of a clock spring design. In deviation from the embodiments shown in Figures 3 and 4, it may be possible to form the winding core by using a hollow cylindrical portion , on the stator or the rotor of the clock spring, with an optional winding core 29. This may be done instead of using a steering shaft to form the winding core of the clock spring. This is shown schematically and in broken lines in Figure 3. Figures 1 and 2 show the first embodiment of the clock spring 1, the clock spring 1 comprising a stator 10, a rotor 20, an installation socket 30 and an electrical flat flexible cable 40. The clock spring 1 can be installed by means of the installation socket 30 thereof on a steering shaft 2 of a steering system of a vehicle, in particular a motor vehicle.

In the present embodiment, the stator 10 of the clock spring 1 is substantially constructed by a rotationally symmetrical L-shaped profiled part, the inner region of the stator 10 being formed so to be disc-shaped and to comprise a through-recess for the steering shaft 2. The stator 10 comprises, in an outer edge region thereof, an outer wall 13 that also forms an outer wall 13 of the clock spring 1. In other embodiments of the invention, this outer wall 13 may be formed as the outer wall 23 of the rotor 20. The outer wall 13, 23 may also be omitted or may be formed by another component. The stator 10 further comprises a socket 14 for a stator-side electrical connection of the flat cable 40.

In the present embodiment, the rotor 20 of the clock spring 1 is constructed to be substantially disc-shaped with a central through -recess for the steering shaft 2. A narrow long transverse end of the flat cable 40 rests in a spiral shape substantially over its entire length on an upper side of the disc-shaped rotor 20.

The rotor 20 rotationally engages the steering shaft 2 through the installation socket 30, which attaches to the steering shaft 2. This can be achieved by a frictional engagement, a positive fit and/or a material connection. Preferably, the installation socket 30 is rigidly connected to the steering shaft 2, by an interference fit or a crimp connection, and/or a weld or solder connection.

Before the installation socket 30 is rigidly connected to the steering shaft 2, the rotor 20 is fixed to the installation socket 30. This can be achieved through a large number of mechanical connections. These connections may again include a frictional engagement, a positive fit and/or a material connections. Preferably, the rotor 20 is mechanically connected to the installation socket 30 by a thermally caulked penetration connection . For this purpose, the installation socket 30 comprises, for example, a journal 31 which penetrates the rotor 20 in an inner edge region (see Figure 1), wherein the rotor 20 is rigidly connected to the installation socket 30 after the parts have cooled.

When the parts are assembled and installed on the steering shaft 2 (see Figure 2), the flat cable 40 is formed between the stator 10 and the rotor 20. The flat cable 40 is formed in a spiral shape within the clock spring 1, a stator-side electrical connection 41 of the flat cable 40 being received in the socket 14 of the stator 10, and being electrically connected to the electrical system of the vehicle. A rotor-side electrical connection 42 of the flat cable 40 projects from the rotor 20 and is preferably fixed to a stop 26, which is formed on the rotor 20. The rotor- side electrical connection 42 acts to electrically contact the steering system devices.

The flat cable 40 is guided between the stator 10 and the rotor 20 with enough room that the rotor 20 can rotate in relation to the stator 10 a plurality of times, about the axis of rotation R of said rotor. Five or more complete revolutions of the rotor 20 in relation to the axis of rotation R are preferred.

In order to keep the winding diameter of the clock spring 1 as small as possible, the clock spring 1, rotor 20, or stator 10 no longer comprise an actual winding core 22. Rather, this winding core 22 is formed by a portion of the steering shaft 2, i.e. a longitudinal end portion of the flat cable 40 is wound at least in part directly on the steering shaft 2. This means that the winding core 22, of the clock spring 1, is not formed by the rotor 20 or the stator 10, but rather by the steering shaft 2, as is shown clearly in Figure 1. In the region of the winding core 22 of the clock spring 1, the steering shaft 2 may also comprise a thin- walled separation means, for example an adhesive tape or a sleeve, between said steering shaft and the flat cable 40.

In order to facilitate guidance of the flat cable 40, the rotor 20 may comprise a guide tab 24, which is preferably configured to be resilient in a radial direction of the rotor 20. In this case, the guide tab 24 circumferentially encompasses portions of the steering shaft 2. The rotor 20 may further comprise one or a plurality of installation tabs 25 on an inner edge, which prevent the flat cable 40 from reaching the open central region of the rotor 20 when installing the clock spring 1 on the steering shaft 2. These installation tabs 25 may be removed from the clock spring 1 after installation. In some embodiments of the invention, it is possible, however, to leave the installation tabs 25 on the rotor 20.

Figures 3 and 4 s how the second embodiment of the invention, it being possible to combine the second embodiment with the first embodiment, as shown in Figures 3 and 4. It is further possible to use the second embodiment of the invention with a conventional clock spring 1. This means that it is possible, in accordance with the second embodiment of the invention, to wind the flat cable 40 on a winding core 29 formed on the stator 10 or the rotor 20, rather than winding the flat cable 40 directly on the steering shaft 2. Figure 3 shows this optional winding core 29 schematically, in broken lines. Only the steering shaft is schematically shown in Figure 3. According to the second embodiment of the invention, the clock spring 1, in particular the housing thereof, comprises a circuit board. In this case, the stator 10 or the rotor 12 is preferably formed at least in part as a circuit board. It is possible to form the respective discshaped part of the stator 10 and/or of the rotor 20 in part, in particular completely, as a circuit board. In this case, it is preferred that the circuit board, which is propagated with components, is provided inside the clock spring 1, in such a way that the electrical and/or electronic components point away from the clock spring 1. For example, the circuit board is formed to be appropriately planar inside the clock spring 1. This also means that the circuit board is preferably formed to be planar on the solder side thereof, which can be achieved, for example, by sealing the side with an appropriate material. It is also possible to seal the respective circuit board with an appropriate material on an outer side of the clock spring 1, in order to protect the electrical and/or electronic components. The circuit board may be a control circuit board, a sensor circuit board or the like. The circuit board is preferably an angle of rotation sensor. As in the aforementioned embodiments, it is possible for the stator 11 and/or the rotor

21 to comprise the outer wall 13, 23 of the clock spring 1, as is intended to be shown in Figure 4 by the free outer wall 13, 23.

Claims

1. A clock spring for a steering system of a vehicle, in particular a motor vehicle, comprising a stator (10, 11) and a rotor (20, 21), which is rotatable with respect to the stator (10,

11) along an axis of rotation (R) of the clock spring (1) and is arranged so as to be substantially concentric; wherein both the stator (10, 11) and the rotor (20, 21) of the clock spring (1) are free at least in part of a winding core.

2. The clock spring according to claim 1, wherein the stator (10, 11) and/or the rotor (20, 21) of the clock spring (1) is formed at least in part as a circuit board.

3. A clock spring for a steering system of a vehicle, in particular a motor vehicle, comprising a stator (10, 11) and a rotor (20, 21), which is rotatable with respect to the stator (10, 11) along an axis of rotation (R) of the clock spring (1), and is arranged so as to be substantially concentric; wherein the stator (10, 11) and/or the rotor (20, 21) of the clock spring (1) is formed at least in part as a circuit board.

4. The clock spring according to claim 3, wherein the stator (10, 11) and/or the rotor (20, 21) of the clock spring (1) is free, at least in part, of a winding core.

5. The clock spring according to any one of claims 1 to 4, further comprising a winding core (22) for an electrical flat flexible cable (40) of the clock spring (1), which is formed by an axial portion (22) of a steering shaft (2) of the steering system when the clock spring (1) is in an assembled state in the steering system 6. The clock spring according to any one of claims 1 to 5, wherein the rotor (20,

21) inside the clock spring (1) is substantially disc-shaped and can preferably be installed on the steering shaft (2) by means of an installation socket (30) pointing away from the clock spring (1).

7. The clock spring according to any one of claims 1 to 6, wherein the rotor (20) is mechanically connected to the installation socket (30) by a penetration connection, preferably a thermally caulked penetration connection.

8. The clock spring according to any one of claims 1 to 7, wherein the stator (10, 11) and/or the rotor (20, 21) of the clock spring (1) comprises a circumferential outer wall (13, 23) in an outer edge region.

9. The clock spring according to any one of claims 1 to 8, wherein, on an inner edge region, the rotor (20, 21) of the clock spring (1) comprises an installation tab (25), which projects from the rotor (20, 21) inwards into the clock spring (1), for the electrical flat flexible cable (40).

10. The clock spring according to any one of claims 2 to 9, wherein the circuit board is a control circuit board or a sensor circuit board.

11. The clock spring according to any one of claims 1 to 10, wherein the installation socket (30) can be connected to the steering shaft (2) by means of a positive fit and/or a material connection.

12. A steering system for a vehicle, in particular a motor vehicle, comprising a clock spring (1) according to any one of claims 1 to 11.

13. The steering system according to claim 12, wherein, at least a longitudinal portion of the electrical flat flexible cable (40) of the clock spring (1) is directly adjacent to an axial portion (22) of the steering shaft (2) of the steering system, in a particular rotational position of the rotor (20, 21).

14. The steering system according to either claim 12 or claim 13, wherein a positive connection between an installation socket (30) of the clock spring (1) and the steering shaft (2) is a pressure connection or a crimp connection, in particular an interference fit or a crimp, and a material connection between the installation socket (30) of the clock spring

(1) and the steering shaft (2) is a weld connection.