WO2013056894A1

WO2013056894A1 - Toe angle adjustor

Info

Publication number: WO2013056894A1
Application number: PCT/EP2012/067636
Authority: WO
Inventors: Laurens Verhulst; Igor Dorrestijn
Original assignee: Skf B.V.
Priority date: 2011-10-21
Filing date: 2012-09-10
Publication date: 2013-04-25

Abstract

The present invention resides in an arrangement for active toe angle adjustment of a vehicle wheel that is mounted to a wheel carrier, the wheel carrier (1 10) being mounted to an axle frame (130) that extends in a longitudinal direction of the vehicle. The wheel carrier is rotatable about a wheel carrier axis (160) and the arrangement comprises a linear actuator (170) that is rigidly connected to the axle frame. A linearly moving part (171, 172) of the actuator is rigidly connected to the wheel carrier and is adapted to exert a torque on the wheel carrier, which causes the wheel carrier to rotate about its axis and thereby change the toe angle of the vehicle wheel. According to the invention, the wheel carrier is torsionally stiff and is mounted to the axle frame via a torsionally flexible element in the form of a beam (140) with an open cross-section. The beam has a torsional axis that defines the wheel carrier axis (160).

Description

Toe angle adjustor

FIELD OF THE INVENTION

The present invention relates to an arrangement for actively adjusting a toe angle of a vehicle wheel.

BACKGROUND TO THE INVENTION

Varying the toe angle of the rear wheels on an automotive vehicle during operation of the vehicle can improve both handling and manoeuvrability. During braking, deceleration and acceleration, for example, a toe-in position of the rear wheels results in better vehicle dynamics. During cornering, vehicle dynamics may be optimised when the outer cornering rear wheel is initially in a toe-out position and changes to a toe-in position at a certain lateral force. Furthermore, an optimized rear wheel alignment has a positive impact on fuel economy, by minimizing the drag and spin on the rear tires.

Several solutions for active toe angle adjustment have been proposed. For example, US 2005/051988 discloses a multilink suspension system in which a wheel carrier is attached to the vehicle body by a number of arms or links. One link is actively adjustable in length by means of a motorized screw mechanism, whereby length adjustment changes the toe angle of the vehicle wheel.

Many vehicles, however, have a more simple, twist beam rear suspension design. A solution for active toe angle adjustment in a vehicle with this type of rear suspension is disclosed in EP2019023. In this solution, the wheel carrier is connected in a rigid manner to an axle frame of the vehicle. The wheel carrier is acted on by a linear actuator, which distorts part of the wheel carrier. This distortion leads to rotation of a stub axle of the wheel carrier about a vertical axis, thereby effecting an adjustment of toe angle.

There is still room for improvement however. SUMMARY OF THE INVENTION

The present invention resides in an arrangement for active toe angle adjustment of a vehicle wheel that is mounted to a wheel carrier, the wheel carrier being mounted to an axle frame that extends in a longitudinal direction of the vehicle. The wheel carrier is rotatable about a wheel carrier axis and the arrangement comprises a linear actuator that is rigidly connected to the axle frame. A linearly moving part of the actuator is rigidly connected to the wheel carrier and is adapted to exert a torque on the wheel carrier, which causes the wheel carrier to rotate about its axis and thereby change the toe angle of the vehicle wheel. According to the invention, the wheel carrier is torsionally stiff and is mounted to the axle frame via a torsionally flexible element in the form of a beam with an open cross-section. The beam has a torsional axis that defines the wheel carrier axis. Consequently, a torque exerted on the wheel carrier elastically deforms the beam, causing the wheel carrier to twist about its axis. The wheel carrier itself remains undeformed.

Suitably, the beam has a U-shaped, a V-shaped cross-section, a C-shaped cross- section or other suitable cross-section. Furthermore, the beam can be a separate element that is joined to wheel carrier, or can be an integrally formed mounting portion of the wheel carrier.

A central portion of the beam is rigidly connected to the axle frame. Furthermore, an upper rigid connection is provided between an upper part of the beam and an upper part of the wheel carrier. A lower rigid connection is provided between a lower portion of the beam and a lower portion of the wheel carrier. Bolted or welded connections are possible. Between the upper rigid connection and the central rigid connection and between the central rigid connection and the lower rigid connection, the beam is torsionally flexible. The rigid connections between the beam and the wheel carrier mean when the beam twists, the wheel carrier and components mounted thereto are rotated through an angle.

In a further development of the invention, the arrangement further comprises a brake calliper device mounted to the wheel carrier. The brake callipers will therefore rotate through the same angle as a bearing unit and brake disc mounted to the wheel carrier. As a result, the brake callipers remain in alignment with the brake disc during adjustments of the toe angle. To ensure that tyre forces acting on the vehicle wheel do not cause a rotation of the wheel carrier, the beam is suitably mounted to the axle frame such that the wheel carrier axis extends at an angle relative to a vertical centreline of the vehicle wheel. Preferably, the angle is selected such that the wheel carrier axis intersects the vertical centreline substantially at a point where the wheel tyre makes contact with the road.

In a preferred embodiment of the invention, the wheel carrier has a central section that is adapted to receive a wheel bearing unit. The central section preferably has a bore for receiving part of the wheel bearing unit and a vertical surface of the central section may have mounting holes attaching a flange of the bearing unit.

Extending from the central section, the wheel carrier may further comprise an upper and a lower vertical arm and a transverse arm. The wheel carrier arms and the central section have a non-flat geometry so that the wheel carrier is torsionally rigid. For example, the arms may have a U-shaped profile.

As mentioned the linear actuator exerts a torque on the wheel carrier. Suitably, the linearly moving part of the actuator is connected to one end of the transverse arm and moves in a direction perpendicular to the wheel carrier axis. The transverse arm therefore acts as a torque arm, which causes the beam to twist.

In some embodiments, the beam is designed to twist through an angle of approximately 1 degree in a toe-in direction and in a toe-out direction when the linear actuator exerts a maximum force. A greater range of angular adjustment can be achieved by increasing the torsional flexibility of the beam. One way of doing this is, in the region of the upper rigid connection, to insert a compressible element between the upper vertical arm and portion of the beam that are arranged within the upper vertical arm. In the region of the low rigid connection a compressible element is then also inserted between the lower vertical arm and the portions of the beam that are arranged within the lower vertical arm.

The linear actuator may be any suitable linear actuator. In a preferred embodiment, the actuator is at least partly mounted inside the axle frame. In one example, the actuator comprises a motor that is mounted inside the axle frame, and has an actuator shaft that rotates about an actuator axis that is parallel to the wheel carrier axis. The moving part of the actuator is suitably formed by at least one link that is eccentrically attached to the actuator shaft. The link therefore acts as a cam which moves the transverse arm of the wheel carrier in a linear direction.

An arrangement according to the invention therefore provides a compact and straightforward means of adjusting the toe angle of a vehicle wheel. The arrangement may be used as part of a vehicle wheel control system for adjusting the toe angle of an individual rear wheel. Additionally, the control system may comprise an arrangement for each rear wheel that allows simultaneous adjustment of both rear wheels for steering purposes.

Further advantages of the present invention will become apparent from the following detailed description and accompanying drawings.

DESCRIPTION OF THE FIGURES

In the following, the invention is described with reference to the accompanying drawings, in which:

Fig. 1 shows a partially cut perspective view of an arrangement according to the invention comprising a wheel carrier mounted to an axle frame and a linear actuator connected to the axle frame and to the wheel carrier, including a bearing unit mounted to the wheel carrier;

Fig. 2 is a side cross-sectional view of the arrangement depicted in Fig.1 , taken through the wheel bearing unit;

Fig. 3 is a side cross-sectional view of the arrangement depicted in Fig.1 , taken though the linear actuator;

Fig. 4 is a top cross-sectional view of a detail, showing an alternative attachment of an arm of the wheel carrier to a torsionally flexible mounting element;

Fig. 5 is a top cross-sectional view of a detail, showing a further alternative attachment of an arm of the wheel carrier to a torsionally flexible mounting element.

DETAILED DESCRIPTION

An example of an arrangement according to the invention is shown in a partially cut perspective view in Figure 1 . The arrangement 100 comprises a wheel carrier 1 10 that is mounted to an axle frame 130, whereby the axle frame forms part of a vehicle suspension system and extends in a transverse direction x. A lateral direction is denoted with y on the coordinate axes and a vertical direction is denoted with z. In the depicted example, the wheel carrier has a central section 1 12 lying in a vertical plane, with a central bore for receiving part of a wheel bearing unit 150. Suitably, the bearing unit comprises an inboard flange with mounting holes 155 for attaching the bearing unit to the central section 1 12 of the wheel carrier. An outboard flange 157 of the bearing unit has mounting holes 158 for attachment of a brake disc and a vehicle wheel.

Extending from the central section 1 12, the wheel carrier further comprises a transverse arm 1 15, an upper vertical arm 120 and a lower vertical arm 125. Suitably, the upper and lower vertical arms 120, 125 are arranged substantially at right angles to the transverse arm 1 15. According to the invention, the central section 1 12 and the arms 1 15, 120, 125 of the wheel carrier are torsionally stiff, while the wheel carrier itself is mounted to the axle frame 130 via a torsionally flexible element. Preferably, the flexible element is a beam 140 with an essentially U-shaped profile. The beam may also be V-shaped or C-shaped, or have any other suitably shaped profile with an open cross-section that can be twisted. The beam 140 in this example is accommodated within the upper and lower vertical arms of the wheel carrier. In Figure 1 , part of the upper vertical arm 120 has been cut away to reveal the U-shaped beam. The upper and lower vertical arms 120, 125 of the wheel carrier, and the transverse arm 1 15 may also have a U-shaped profile, or other non-flat geometry that enhances rigidity. Furthermore, adjacent arms of the wheel carrier may be connected by stiffening elements 1 13. As best shown in the cross-sectional view of Figure 2, the beam is connected to the axle frame 130 at a central portion of the beam 140. Suitably, the beam may have a shaped recess 142 that fits around an outer circumference of the axle frame 130, whereby the beam 140 is rigidly connected to the axle frame 130 at the shaped recess 142. This will be referred to as a central rigid connection. This connection may be achieved by means of welding. A bolted connection or other suitable joint is also possible. Furthermore, the beam 140 is rigidly connected to the wheel carrier at respective upper and lower portions of the upper and lower vertical arms 120, 125. In the depicted example, an upward facing surface of the beam 140 is connected at a top lateral extension 122 of the upper vertical arm 120. This will be referred to as an upper rigid connection. A downward facing surface of the beam 140 is connected at a bottom lateral extension 127 of the lower vertical arm 125. This will be referred to as a lower rigid connection. Between the upper rigid connection and the central rigid connection and between the central rigid connection and the lower rigid connection, the U-shaped beam is torsionally flexible about a torsional axis. The torsional axis therefore defines a wheel carrier axis 160 about which the wheel carrier 1 10 is rotatable when a torque is applied. Rotation of the wheel carrier about the axis 160 is effected by means of a linear actuator 170. The actuator is mounted to the axle frame 130 and has a linearly moving part that is rigidly connected to the wheel carrier at one end of the transverse arm 1 15. In the depicted example, the linearly moving part of the actuator comprises a first link 171 and a second link 172 which are connected to the transverse arm 1 15 at an upper and a lower lateral section respectively. The linearly moving part may also be a single link that is connected to the transverse arm at e.g. a transverse surface of the arm. In use, the linearly moving part 171 , 172 of the actuator exerts a force on the transverse arm, at a distance from the wheel carrier axis 160, in a direction essentially perpendicular to the wheel carrier axis 160. The transverse arm 1 15 therefore acts as a torque arm. As mentioned, the wheel carrier is torsionally stiff, meaning that the applied torque causes the beam 140 to twist about the wheel carrier axis 160. The length of the torque arm is selected to provide the necessary torsion in combination with the force exerted by the actuator. Furthermore, the length of the beam 140 and the torsional flexibility of the U-shaped profile are selected to provide the required degree of angular rotation about the wheel carrier axis 160. In one example, the length of the torque arm associated with the transverse arm 1 15 is approximately 150 mm and the beam 140 is designed such that when the actuator exerts a force of around 2000 N, the wheel carrier rotates through an angle of approximately 1 degree. A corresponding angular rotation of the bearing unit and vehicle wheel occurs, which changes the toe angle of the vehicle wheel.

In a further development of the invention, a brake calliper device is mounted to the wheel carrier 1 10. For example, the central section 1 12 may comprise attachment holes 1 19 for bolting the brake calliper device to the wheel carrier. Thus, when the linear actuator exerts a force that causes the wheel carrier to rotate about the wheel carrier axis, a brake disc mounted to the bearing unit remains in alignment with the brake callipers. The linear actuator is suitably controlled by a vehicle dynamics system, which instructs the actuator to pull on the transverse arm 1 15 to move the vehicle wheel in a toe-out direction or to push on the transverse arm 1 15 to move the wheel in a toe-in direction, depending on vehicle speed and the driving manoeuvres being performed e.g. accelerating, braking and cornering. During these manoeuvres, the vehicle wheel experiences reaction forces which are transferred to the vehicle suspension system via the wheel bearing 150 and the wheel carrier 1 10. To ensure that these forces do not cause the wheel carrier to twist about its axis 160, the torsionally flexible beam 140 is mounted to the axle frame with an angle a relative to a vertical wheel axis 185.

Part of a tyre 180 of the vehicle wheel is schematically depicted in Figure 2. The vertical wheel axis 185 intersects the tyre midway across its width. The angle a at which the torsionally flexible beam 140 is mounted to the axle frame 130 is preferably selected such that the corresponding wheel carrier axis 160 intersects the vertical wheel axis 185 at, or within 20 mm of, a point where the tyre 180 makes contact with the road. As a result, the wheel carrier is rotationally insensitive to tyre forces, meaning that only the linear actuator 170 and vehicle control system are responsible for toe angle adjustments.

The linear actuator 170 may be any suitable electrical, pneumatic or hydraulic actuator. In a preferred embodiment, the linear actuator comprises a cam mechanism for exerting the force on the transverse arm of the wheel carrier. A cross-section of the arrangement depicted in Figure 1 , taken through the actuator 170, is shown in Figure 3, viewed from the transverse direction x.

The linear actuator 170 comprises a motor (not shown), which is preferably mounted inside the hollow axle frame. An output shaft of the motor rotates about a motor axis, which essentially extends in the transverse direction x. The motor output shaft is coupled via a suitable gearing (not shown) to an actuator shaft 320, which is rotatable about an actuator axis 330. Suitably, the actuator axis 330 is parallel to the wheel carrier axis. The actuator shaft 320 is rotationally supported relative to an actuator housing 340 via first and second bearings. The actuator 170 further comprises a first link 171 and a second link 172, which are coupled to the actuator shaft 320 by means of e.g. a first bolt 331 and a second bolt 332. The first and second links 171 , 172 are coupled to the actuator shaft 320 in an eccentric manner. In other words, a centreline though the first and second bolts is offset from the actuator axis 330.

One end of the first and second links is eccentrically coupled to the actuator shaft 330. An opposite end of the first link 171 is coupled to an upper lateral extension

1 16 of the transverse arm 1 15 and an opposite end of the second link 172 is coupled to a lower later extension 1 17 of the transverse arm. Therefore, when the actuator shaft 320 is rotated, the eccentrically coupled first and second links 171 , 172 act as eccentric cams that move the upper and lower lateral extensions 1 16,

1 17 in a linear direction. Suitably, the upper and lower lateral extensions 1 16, 1 17 extend in a direction perpendicular to the actuator axis 330, for maximum force transfer efficiency. The force exerted is able to move the transverse arm 1 15 of the wheel carrier due to the twisting of the torsionally flexible beam. Preferably, the actuator shaft comprises a stiffening pin 325, to ensure that the shaft remains in alignment with the bearings. An actuator which operates on a camming principle is preferred not only because it can be readily accommodated within the available space, but also because of the force profile generated by a cam. The linear force delivered by the cam mechanism increases as the rotation angle of the actuator shaft 320 increases, relative to a zero point. With reference to the example of Figure 3, the zero point occurs when the centreline through the bolts 331 , 331 is parallel to the actuator axis 330 when viewed in the transverse direction x. Consequently, there are 2 possible angular zero points. The increase in cam force is non-linear and becomes exponential towards 90 degrees, after the rotation angle exceeds approximately 40 degrees. As the actuator shaft rotates from the zero point, the torsionally flexible beam twists. The force (torque) needed to increase the twist angle of the beam increases in a linear fashion. Therefore, in the upper range of twist angle adjustment, a cam actuator provides a greater force margin than an actuator with a linear force profile. In the arrangement described above, the torsionally flexible beam is a U-shaped beam that is adapted to twist through an angle of approximately 1 degree when the actuator delivers maximum force. As mentioned, the angle of twist and corresponding angular rotation of the wheel carrier about the wheel carrier axis can be increased by increasing the torsional flexibility of the beam.

One method of achieving this, as well as an alternative method of attaching the wheel carrier to the beam, will be described with reference to Figure 4. This figure shows a top cross-sectional view of an example of a torsionally flexible beam 440 and an upper vertical arm 420 of a wheel carrier according to a further embodiment of the invention.

In this example, the upper rigid connection between the upper vertical arm 420 and the beam 440 is achieved by means of a bolted connection. The upper vertical arm has a connection surface 423 that extends in a direction parallel to the torsional axis of the beam 440. The upper vertical arm further has a first lateral extension 421 and a second lateral extension 422, between which the beam is partly arranged. The beam in this example is also essentially U-shaped, but comprises a first angled section 441 and a second angled section 442 which extend from first and second parallel sections 445, 446 respectively. The first and second angled sections of the beam extend towards the connection surface 423 of the upper vertical arm and converge at a connection part 447 of the beam. A bolt 450 connects the upper vertical arm 420 of the wheel carrier to the connection part 447 of the beam 440, which connection part is wide enough to accommodate a shank of the bolt.

To increase the twist angle through which the upper vertical arm 420 (and wheel carrier) can be rotated, a first compressible element 471 made of e.g. a rubber material is inserted between the upper vertical arm and the angled sections of the beam. As may be seen from Figure 4, the first and second lateral extensions 421 , 422 of the upper vertical arm 420 extend at an angle, relative to a centreline through the bolt shank, which is greater than that of the first and second angled sections 441 , 442. Consequently, the gap between the first lateral extension 421 and the first angled section 441 widens, as does the corresponding gap between the second lateral extension 422 and the second angled section 442. The widening gaps are filled by the first compressible element 471 , which becomes correspondingly thicker. To increase the compressibility of the first compressible element, holes 475 may be provided in the element, the diameter of which holes increases as the element 471 becomes thicker.

A relatively smaller gap exists between the connection surface 423 of the upper vertical arm 420 and the connection part 447 of the beam. Here, the first compressible element 471 is relatively thin, meaning that when the bolt 450 is tightened, the first compressible element 471 is fully compressed, such that a stiff connection (rigid upper connection) is achieved. A second compressible element 172 may be provided between the bolt 450 and the connection surface 423 of the upper vertical arm. Suitably, the second compressible element 472 is relatively thin so as to be fully compressed when the bolt is tightened. In the direction of the bolt, the beam 440 is therefore rigidly connected to the upper vertical arm 420 of the wheel carrier, and can twist around the torsion axis at a relatively greater angler, due to the enhanced torsional flexibility provided by the first compressible element 471 . The lower vertical arm of the wheel carrier is suitably connected to a lower portion of the beam in a corresponding manner. In the example of Figure 4, the range of angle adjustment is approximately 5 degrees in a toe-in direction and a toe-out direction. This range of angular adjustment is desirable when the arrangement according to the invention is used on both rear wheels of a vehicle in order to change the steering angle of the wheels.

It is also possible to bolt the upper and lower vertical arms of the wheel carrier to the torsionally flexible beam without the use of compressible inserts. Figure 5 shows a top cross-sectional view of a further example of a beam 540 bolted to a connection surface 523 of an upper vertical arm 520. In this example, the beam has first and second lateral extensions 521 , 522 which extend at an angle, relative to the bolt centreline, which angle is slightly shallower than that of first and second angled sections 541 , 542 of the beam 540, which extend from a connection part 547 of the beam. Suitably, the difference in the angle is a few degrees. The connection part 547 of the beam is parallel to the connection surface 523 of the upper vertical arm, and when the bolt is tightened, the first and second lateral extensions bend outwards slightly, so that the difference in angle with the angled sections 541 , 542 of the beam becomes zero. Thus, a rigid connection is achieved. In this example, the range of toe angle adjustment is approximately 1 degree in a toe-in direction and a toe-out direction.

A number of aspects/embodiments of the invention have been described. It is to be understood that each aspect/embodiment may be combined with any other aspect/embodiment. Moreover the invention is not restricted to the described embodiments, but may be varied within the scope of the accompanying patent claims.

Claims

1 . An arrangement (100) for active adjustment of a toe angle of a vehicle wheel, the arrangement comprising a wheel carrier (1 10) mounted to an axle frame (130) that extends in a longitudinal direction of the vehicle, the wheel carrier being rotatable about a wheel carrier axis (160) and the arrangement further comprising a linear actuator (170) that is rigidly connected to the axle frame (130) and to the wheel carrier (1 10), and which is adapted to exert a torque on the wheel carrier, such that the wheel carrier rotates about its axis (160), to adjust the toe angle of the vehicle wheel,

characterized in that,

the wheel carrier (1 10) is torsionally stiff and is mounted to the axle frame (130) via a torsionally flexible element in the form of a beam (140, 440, 540) with an open cross-section, the beam having a torsional axis that defines the wheel carrier axis (160).

2. The arrangement according to claim 1 , wherein the beam (140, 440, 540) has a U-shaped cross-section or a V-shaped cross-section or a C-shaped cross-section

3. The arrangement according to claim 1 or 2, wherein the beam (140, 440, 540) is mounted to the axle frame (130) such that the wheel carrier axis (160) extends at an angle (a) relative to a vertical centreline (185) of the vehicle wheel and intersects the vertical wheel centreline (185) substantially at a point where a wheel tyre (180) makes contact with the road.

4. The arrangement according to any preceding claim, wherein the wheel carrier comprises:

• a central section (1 12) lying in a vertical plane, which central section is adapted for the mounting of a wheel bearing unit (450);

• a transverse arm (1 15), whereby a linearly moving part (171 , 172) of the linear actuator (170) is connected to the wheel carrier at one end of the transverse arm and moves in a direction perpendicular to wheel carrier axis (160);

• an upper vertical arm (120, 420, 520) and a lower vertical arm (125).

The arrangement according to claim 4, wherein a central portion of the beam (140, 440, 540) is rigidly connected to the axle frame (130), an upper portion of the beam is rigidly connected to the upper vertical arm (120, 420, 520) and a lower portion of the beam is rigidly connected to the lower vertical arm (125).

The arrangement according to claim 5, wherein the upper vertical arm (420, 520) and the lower vertical arm are connected to the beam (440, 540) via a bolted connection.

The arrangement according to claim 6, wherein in the region of the bolted connections, a compressible element (471 ) is provided:

^■ between the upper vertical arm (420) and portions (441 , 442, 447) of the beam (440) that are arranged within the upper vertical arm; and

^■ between the lower vertical arm and portions of the beam (440) that are arranged within the lower vertical arm.

The arrangement according to any of claims 1 to 5, wherein the beam (140) is an integrally formed mounting portion of the wheel carrier (1 10).

The arrangement according to any preceding claim, wherein at least part of the linear actuator (170) is mounted inside the axle frame (130).

The arrangement according to any preceding claim, wherein the linear actuator has an actuator shaft (320) which rotates about an actuator axis (330), and wherein the actuator axis is parallel to the wheel carrier axis (160).

The arrangement according to claim 10, wherein the linear actuator is connected to the transverse arm (1 15) by means of at least one link (171 , 172) and wherein the at least one link is eccentrically attached to the actuator shaft (320).

The arrangement according to any preceding claim, the arrangement further comprising a brake calliper device rigidly mounted to the wheel carrier (1 10), at a side of the wheel carrier opposite from the transverse arm (1 15).

A vehicle wheel control system comprising an arrangement according to any preceding claim.

The vehicle wheel control system according to claim 13, wherein the toe angle of each rear wheel is adjustable by means of an arrangement according to any of claims 1 to 12, the system being adapted to adjust an individual toe angle of each wheel and/or to adjust the toe angle of both rear wheels for steering purposes.