Handlebar with elastic bearing comprising magnetoelastic and / or electroactive material

Abstract

Rear axle steering device (102) comprising at least one control arm, wherein the control arm has at least one elastic bearing (114; 116) for coupling the control arm (108; 112) at least to one wheel carrier (104) and / or to a vehicle body (110), characterized in that the at least one elastic bearing (114; 116) comprises a magnetoelastic and / or electroactive material (206), wherein a control unit (120) is provided to output at least one control signal for the at least one elastic bearing (114; 116) of the control arm (108; 112) in response to a control command in order to increase or decrease an elasticity of the elastic bearing in response to the control signal.

Description

[0001] The present invention relates generally to control arms and their bearings and, in particular, to control arms for steer-by-wire steering of motor vehicles.

[0002] In chassis technology, control arms are elements of the wheel suspension of motor vehicles. They have joints and connect, for example, a wheel carrier to a vehicle body and can be designed as wheel-guiding components. Forces and moments on the wheel carrier are introduced into the vehicle body via the control arms or their joints. In wheel suspensions, control arms are differentiated according to their function. They can be load-bearing or guiding and are further differentiated according to their kinematic effect and also according to the number of pivot points. There are, for example, bar links with two or more pivot points, wishbones, trapezoidal links and the like. A track link, also called a tie rod, can be adjustable in length in order to change or adjust the track or camber of a wheel, for example.The control arms can be connected to the vehicle body via ball joints or rubber mounts, the latter being more cost-effective and capable of decoupling the vehicle body from noise generated in the chassis and / or achieving desired steering effects in terms of driving dynamics. The aforementioned control arms can have elastic mounts whose elasticity can be variably switched or controlled. Such control arms are described, for example, in DE 10 2014 200 295 A1, DE 10 2015 011 709 A1, or DE 10 2013 218 570 A1.

[0003] Steer-by-wire steering systems, e.g. rear-axle steering systems designed as such, rely on various technical implementations in motor vehicles. For example, a rear-axle steering system can be used as a central steering system similar to a steering system on the front axle, which can adjust both wheels simultaneously either directly or by means of tie rods. An actuator for such a steer-by-wire steering system is known from DE 10 2014 206 934 A1. In another implementation, such as from WO 2006 / 117 343 A1, the originally passive toe links on the rear axle are replaced by active, length-adjustable links with actuators, so that, for example, in rear-axle steering, each rear wheel has its own actuator. In steer-by-wire steering systems, these actuators are controlled by signals from a control unit according to the driver's wishes, for example, and adjusted by an electric motor.With steer-by-wire steering, there are no mechanical couplings between a steering handle, e.g. the driver's steering wheel, and the steering on the respective axle.

[0004] In rear-axle steering systems with individually steered wheels, a length-adjustable link, also called an actuator, is usually used, as shown in DE 10 2013 100 358 A1, for example. The track is adjusted when the link changes its length by deflecting the wheel carriers around their vertical axis. If rubber bearings are used to couple the link to the wheel carrier instead of ball joints, there is a slight displacement or tension in the rubber bearings due to the adjusting movement. Due to elasticities in the rubber bearings, a variable adjustment speed and / or accuracy can affect the precision of the steering, depending on the material used. On the other hand, the elasticities are specifically used to exploit the degrees of freedom provided by the rubber bearings in a wheel suspension. Furthermore, the properties of rubber bearings can also be used to support comfort, for exampleVibration damping and / or noise reduction can be used. This creates a conflict of objectives. In addition to the actuators, the chassis may contain other fixed-length control arms involved in the wheel guidance or suspension, which are also coupled to the connecting components or the vehicle body via rubber mounts.

[0005] The present invention is intended to resolve or defuse this conflict.

[0006] Devices and a method according to the independent patent claims are proposed. Advantageous further developments are specified in the dependent claims.

[0007] According to one aspect of the present invention, the use of a control arm for a rear-axle steering system of a motor vehicle is proposed. The control arm can be any of the different control arm types in a motor vehicle mentioned above. The control arm comprises at least one elastic bearing for coupling the control arm to a wheel carrier and / or to a vehicle body. The elastic bearing is characterized by a magnetoelastic and / or electroactive material, wherein the elasticity of the elastic bearing can be changed as needed by applying an electrical control signal. The control signal can be applied directly or indirectly to the bearing. In a preferred embodiment, the control signal is generated by a control unit.The control unit generates this signal based on the driving situation and the associated parameters, such as vehicle speed, longitudinal and lateral acceleration, outside temperature, and vehicle load. Based on this signal, a voltage is then applied to the adjustable mount, thereby changing the mount's stiffness. This allows at least one mount of at least one control arm to be advantageously adjusted to a harder or stiffer setting in certain operating situations, and to a softer setting in other operating situations.

[0008] To ensure the greatest possible precision during steering, control arms involved in the actual steering movement are preferably, but not exclusively, designed with ball joints and / or, for example in a multi-point control arm, at least one bearing is designed as a ball joint. Furthermore, rubber bearings can also be used with these control arms, which can be made even stiffer using the control signal to achieve a high level of precision and achieve the most precise and responsive steering response possible. Once the steering movement has been completed, a lower hardness or stiffness can be set again to effectively reduce shocks and noise and to achieve the required degrees of freedom that are achievable with the non-switched bearing.

[0009] Magnetoelasticity or magnetostriction refers to the deformation of magnetic, particularly ferromagnetic, materials as a result of an applied magnetic field. The body undergoes an elastic change in length at constant volume. An example of a material with high magnetostriction is nickel (Ni).

[0010] Electroactive materials include electroactive polymers (EAPs), which change their shape upon application of an electrical voltage. Due to their similarity to natural muscle function, they are also called "artificial muscles." Examples of such EAPs include conductive polymers, ionic metal-polymer composites, ionic gels, electrostrictive and ferroelectric polymers, and dielectric elastomers.

[0011] Preferably, the magnetoelastic or electroactive material of the bearing can be combined with conventional elastic bearing materials (elastomers). For example, the magnetoelastic or electroactive material can be additionally incorporated into a conventional rubber bearing to make the stiffness of a conventional handlebar bearing adaptive or variable.

[0012] According to a further embodiment, the elastic bearing of the handlebar is surrounded by a metal sleeve or bushing. Thus, a bearing point of the handlebar can be formed by a rubber-metal sleeve bearing, whereby the elasticity of the rubber can be varied as needed by adding magnetoelastic and / or electroactive materials.

[0013] According to a further embodiment, the elastic bearing of the handlebar includes a through-hole. This allows, for example, a joint fork or the like to be connected to the handlebar or to another joint or joint mount.

[0014] According to a further embodiment, the handlebar or bearing comprises an electrical connection to electrically couple the handlebar to a control unit and / or the control signal. A control signal and / or a voltage can be transmitted to the bearing via this connection and cause the stiffness of the bearing to change. For example, contacts or electrodes connected to the magnetoelastic or electroactive material of the bearing can be provided for this purpose. A magnetic field or an electric field can be generated between the contacts or electrodes using the control signal or voltage to cause a volume change of the magnetoelastic or electroactive material in the bearing and ultimately to change the stiffness of the bearing.

[0015] According to the present invention, a rear-axle steering device for a motor vehicle is proposed. The rear-axle steering device comprises at least one control arm, which has at least one elastic bearing with variable hardness or stiffness, as already described above. The rear-axle steering device further comprises an electronic control unit, such as a control device, which is designed to output at least one control signal for the at least one elastic bearing of the control arm in response to a control command, in order to increase or decrease an elasticity of the elastic bearing in response to the control signal. Thus, for example, when adjusting the wheel steering angle of the rear wheels, some bearings can advantageously be set harder or stiffer, while others can be set softer. This is carried out depending on whether a power transmission or a steering movement is effected via the respective bearing.Bearings that are directly involved in the steering movement, i.e., a change in the wheel steering angle, tend to be set to a stiffer setting. This is intended to make the elastic bearing behave more like a ball joint. In other words, the actuator's adjustment or steering movement should be prevented from solely or predominantly causing the elastic bearing to stretch. However, other control arms can be set to a softer setting, which means that less force is required overall for the steering movement than if all bearings of all control arms on the respective wheel suspension retained their original hardness or stiffness.

[0016] According to one embodiment, the control unit is configured to output the control command for the elastic bearing of the steering arm depending on a driving situation of the motor vehicle. The driving situation may, for example, include a steering movement in which some bearings are set harder or stiffer, while others are set softer. Other driving situations in which a different adjustment of the bearings is advantageous are also conceivable, such as a comfort mode with soft bearings or a sport mode with hard bearings. For example, in the sport mode, a more direct steering or steering feel can be achieved.

[0017] According to a further embodiment, the control arm is configured to transmit a steering movement from the vehicle body to the wheel carrier. The control arm is thus configured as a track control arm, i.e., as a tie rod, to transmit steering movements of an actuator to the wheel carrier to change the wheel steering angle. The control unit is configured to output a control signal for the steering movement, which reduces the elasticity of the elastic bearing during the steering movement, thus making the bearing harder or stiffer. This makes it possible, for example, to achieve a precise and responsive steering response.

[0018] The control unit can be configured to output a control signal after the steering movement that increases the elasticity of the elastic mount again. Preferably, after the steering movement, the elasticity or stiffness of the mount is adjusted to its previous state. Once the steering movement is complete, a lower hardness or stiffness can be adjusted again to effectively reduce shocks and noise and / or adjust the required degrees of freedom for the suspension control arms.

[0019] According to a further exemplary embodiment, the steering arm or the bearing is arranged in a position such that the elastic bearing deforms due to a steering movement or the wheel moves relative to the vehicle body due to a compression or rebound movement. The control unit can be designed to output a control signal such that the elasticity of the elastic bearing increases during the steering and / or wheel movement. For example, bearings that are necessarily deformable during the steering reaction can be made softer in order to reduce steering force. Additionally or alternatively, it can be provided to output a control signal after the steering movement so that the elasticity of the elastic bearing decreases.

[0020] Preferably, the rear-axle steering device further comprises a further control arm according to one of the preceding embodiments. The control unit is configured to output a first control signal for the elastic bearing of the control arm in response to the steering command, in order to change the elasticity of the elastic bearing of the control arm in response to the first control signal, and to output a second control signal for the elastic bearing of the second control arm, in order to change the elasticity of the elastic bearing of the second control arm in response to the second control signal in the opposite direction to the elastic bearing of the control arm.

[0021] According to a further aspect of the present invention, a method for coupling a control arm to a wheel carrier and / or to a vehicle body is proposed. The method comprises variably supporting the control arm by means of an elastic bearing comprising a magnetoelastic and / or electroactive material, and applying an electrical control signal to responsively change the elasticity of the at least one elastic bearing.

[0022] Preferably, the electrical control signal is applied in response to a steering command. The steering command can relate to rear-axle steering to change the wheel steering angle on the rear axle. The steering command can correspond to a driver's command indicated by a steering handle, such as a steering wheel. Based on vehicle dynamics control, a steering command can be issued by a control unit depending on the driver's command and additionally or alternatively based on the current driving situation, such as a calculated route in an autonomously driving vehicle taking navigation data into account.

[0023] Finally, the present approach provides a control unit, which is preferably designed as a control device. The control device is designed to perform all steps of a method according to one of the embodiments described here.

[0024] In this context, a control unit or control device can be understood as an electrical device that processes sensor signals and outputs control and / or data signals depending on them. The control device can have an interface that can be implemented in hardware and / or software. In a hardware implementation, the interfaces can, for example, be part of a so-called system ASIC, which contains a wide variety of functions of the control device. However, it is also possible for the interfaces to be separate integrated circuits or to consist at least partially of discrete components. In a software implementation, the interfaces can be software modules that are present, for example, on a microcontroller alongside other software modules.

[0025] Also advantageous is a computer program product or computer program with program code which can be stored on a machine-readable medium such as a semiconductor memory, a hard disk memory or an optical memory and is used to carry out the method according to one of the embodiments described above when the program is executed on a computer or a device.

[0026] Some embodiments of the invention are explained in more detail below, purely by way of example, with reference to the accompanying figures. They show: Fig. 1 schematically shows a vehicle with a rear-axle steering system comprising magnetoelastic and / or electroactive control arm bearings; and Fig. 2 an elastic bearing with a magnetoelastic and / or electroactive material in order to change an elasticity of the elastic bearing by applying a control signal.

[0027] The Fig. 1 shows a schematic representation of a vehicle 100 with a rear-axle steering system 102. A wheel carrier 104 for a rear wheel 106 is coupled to a vehicle body 110 via a plurality of control arms (e.g., wishbones) 108. The rear-axle steering system 102 is coupled to the wheel carrier 104 via a track control arm 112. The control arms 108, 112 each comprise bearings 114, 116 at their ends for coupling them to the wheel carrier 104 or the vehicle body 110. The bearings 114, 116 can have through-holes for mounting, for example, joint forks or the like on the respective control arms. Conventionally, the bearings 114, 116 comprise bearing bushes and sleeves and rubber bodies located therein or connecting them. The track link 112 is adjustable in position in response to a steering command to adjust the track or wheel steering angle of the rear wheel 106. This is accomplished here by means of an electromechanical actuator of the rear axle steering 102.The change in position of the track control arm 112 is translated into a steering or rotational movement of the wheel carrier about a vertical axis 118.

[0028] Depending on whether a steering movement is currently taking place or not, different stiffnesses or elasticities of the metal-rubber bearings 114, 116 can be advantageous. For example, in the case of the track control arm 112, which transfers force to the wheel carrier 104 during a steering movement, a higher stiffness of the bearings 114, 116 can be advantageous during a steering movement than before or after the steering movement, when no direct force transmission takes place. For some wishbones 108, for example, a lower stiffness of the respective bearings 114, 116 can be advantageous during the steering movement and / or during a deflection movement of the wheel relative to the vehicle body than before or after the steering movement.

[0029] To this end, it is proposed here to at least partially provide at least some of the bearings 114, 116 of the links 108, 112 with a magnetoelastic and / or electroactive material in order to change the elasticity of at least some of the bearings 114, 116 by applying a magnetic or electrical control signal. The bearings 114, 116 can therefore be referred to as magnetoelastic or electroactive bearings 114, 116. The magnetoelastic and / or electroactive material can, for example, be mixed into a bearing rubber of the bearings 114, 116 in order to adaptively increase or decrease the elasticity of the bearings 114, 116 as needed. The bearings 114, 116 can therefore comprise magnetoelastic and / or electroactive material in addition to the rubber.

[0030] An example of a bearing 114, 116 for a wishbone 108 is shown in Fig.2. The bearing 114, 116 comprises a metallic cylindrical bearing bush 202 and a central metallic through-opening 204 in the form of a bearing sleeve, which is surrounded by the bearing bush 202. The bearing bush 202 and the through-opening 204 are arranged concentrically without deformation or deflection. Radially between the through-opening 204 or the bearing sleeve and the bearing bush 202 is an elastic bearing material 206, which in this case comprises rubber and magnetoelastic and / or electroactive material. The material 206 can therefore be a mixture of rubber and magnetoelastic and / or electroactive material. A control signal in the form of an electrical voltage, an electric current, or a magnetic field can be applied between the bearing bush 202 and the through-opening 204 in order to vary the elasticity of the magnetoelastic or electroactive material and thus of the bearing 114, 116. Bearing bush 202 and through-hole 204 can thus be used as electrodes orserve as control terminals that conduct a voltage or signal into the magnetoelastic or electroactive material.

[0031] In magnetoelastic materials, the elasticity of the bearings 114, 116 can be changed, for example, by appropriately altering an external magnetic field near a bearing 114, 116. If, for example, an external magnetic field is applied to a ferromagnetic material, the Weiss domains align themselves. By rotating the dipoles, the length of a rod changes in the range of approximately 10 to 30 µm / m. With highly magnetostrictive materials, the change in length can be up to 2 mm / m. With Invar alloys, there is also the possibility of volume magnetostriction, in which the volume is variable. If magnetostrictive materials are mixed with a bearing rubber, a magnetostrictive bearing can be obtained.

[0032] With electroactive materials (EAP), the elasticity of the bearings 114, 116 can be achieved, for example, by appropriately changing the electrical control voltage of a bearing 114, 116. Advantages of EAP compared to other materials include the high elongations that can be achieved (up to 380%), as well as the low density of the polymers and their free formability. If electroactive materials are added to a bearing rubber, an electroactive bearing can be obtained.

[0033] The rear-axle steering system 102 can be coupled to a control unit (e.g., microprocessor, ECU) 120, which is configured to output one or more possibly different control signals for the adaptive bearings 114, 116 in response to a control or steering command in order to increase or decrease the elasticity of the bearings 114, 116 in response to the respective control signals. The elasticity of the bearings 114, 116 can be varied during a rear-axle steering operation in order to make the steering movement as efficient as possible. However, according to conceivable embodiments, the elasticities of the bearings 114, 116 can also be varied outside of steering movements, for example, to represent sporty or comfortable chassis settings. The control unit of the rear-axle steering system 102 can therefore be configured to output the control command for one or more bearings 114, 116 depending on a driving situation of the motor vehicle. Examples of driving situations can be, for example,This can be cornering, driving straight ahead, driving fast, driving slowly, etc. In each case, the focus must be on ensuring that the vehicle always drives safely.

[0034] The toe link 112 is designed to transmit a steering movement from the vehicle body 110 to the wheel carrier 114. The toe link is a wheel-guiding component that ensures that the wheel steering angle required for the intended trajectory is always maintained. The link and the bearings are designed to cope with the high forces occurring in a chassis. In this case, the control unit 120 can be designed to output one or more control signals for the steering movement of the toe link 112, which reduce the elasticity of the elastic bearings 114, 116 of the toe link 112 during the steering movement, thus making the toe link bearings stiffer than without a steering movement. The bearings then approximate the effect of a ball joint, which is precise with regard to a rotational and / or pivoting movement, but not elastic.After the steering movement, the elasticity of the elastic bearings 114, 116 of the track control arm 112 can be increased again, since then a more direct power transmission is no longer necessary.

[0035] The situation may be different, for example, with the wishbones 108 and their bearings 114, 116. The wishbones 108 are each arranged in a position such that their elastic bearings 114, 116 deform due to the steering movement. For bearings 114, 116 of the wishbones 108, the control unit 120 can be configured to output control signals for the steering movement, which increase the elasticity of the elastic bearings 114, 116 of the wishbones 108 during the steering movement. After the steering movement, the elasticity of the elastic bearings 114, 116 of the wishbones 108 can be reduced again, since then no further deformation of the bearings occurs directly as a result of a steering movement. For a movement of the wheel relative to the vehicle body due to a spring compression process, it may also be expedient to increase the elasticity of at least some of the bearings.Depending on the axle design, the bearing elasticity can be varied taking into account the required degrees of freedom.

[0036] The control unit 120 can therefore be designed to output control signals for elastic bearings 114, 116 of the toe link 112 in response to the steering command in order to change the elasticity of the elastic bearings of the toe link 112 in response to a first control signal, e.g. to reduce it, and to output control signals for elastic bearings of wishbones 108 in order to change the elasticity of the elastic bearings of the wishbones 108 in response to the control signal in the opposite direction to the elastic bearings of the toe link 112, e.g. to increase it.

[0037] It is obvious that the concept described here can be advantageous not only for bearings in the area of ​​rear-axle steering. The concept described here can also be used, for example, in the area of ​​front-axle steering.

[0038] By using magnetoelastic or electroactive materials in the rubber mounts 114, 116, the characteristics of the respective mounts can be adapted to the specific application. Magnetoelastic materials change their hardness or stiffness, while electroactive materials change their expansion. This allows the bearings relevant to steering (rubber mounts between the body and actuator, rubber mounts between actuator and wheel carrier, etc.) to be hardened in order to achieve the most precise and responsive steering response possible. Once the steering process is complete, a lower hardness or stiffness can be immediately set again to effectively reduce shocks and noise. Likewise, the bearings that necessarily deform during steering reaction can be made softer, for example, to minimize steering force and to allow the required degrees of freedom in handlebar movement. Reference symbol 100 vehicles 102 Rear-axle steering 104 wheel carriers 106 rear wheel 108 handlebars 110 Vehicle body 112 handlebars 114 adaptive bearing 116 adaptive bearing 118 Rotation axis 120 control unit 202 bearing bush 204 Through opening 206 magnetoelastic and / or electroactive material

Claims

[1] Rear axle steering device (102) comprising at least one control arm, wherein the control arm has at least one elastic bearing (114; 116) for coupling the control arm (108; 112) at least to one wheel carrier (104) and / or to a vehicle body (110), characterized in that the at least one elastic bearing (114; 116) comprises a magnetoelastic and / or electroactive material (206), wherein a control unit (120) is provided to output at least one control signal for the at least one elastic bearing (114; 116) of the control arm (108; 112) in response to a control command in order to increase or decrease an elasticity of the elastic bearing in response to the control signal. [2] Rear axle steering device according to claim 1, characterized by that the handlebar (114; 116) is variable in length. [3] Rear axle steering device (102) according to claim 1 or 2, wherein the control unit (120) is designed to output the control command for the elastic bearing (114; 116) of the handlebar (108; 112) as a function of a driving situation of the motor vehicle. [4] Rear axle steering device (102) according to claim 2 or 3, wherein the link (108; 112) is designed to transmit a steering movement from the vehicle body (110) to the wheel carrier (104) and wherein the control unit (120) is designed to output a control signal for the steering movement, which control signal reduces the elasticity of the elastic bearing (114; 116) during the steering movement. [5] Rear axle steering device (102) according to claim 4, wherein the control unit (120) is designed to output a control signal after the steering movement, which increases the elasticity of the elastic bearing (114; 116), preferably restores the initial state. [6] Rear axle steering device (102) according to claim 4 or 5, wherein the handlebar (108; 112) is arranged at a position such that the elastic bearing (114; 116) deforms due to a steering movement and wherein the control unit (120) is designed to output a control signal for the steering movement which increases the elasticity of the elastic bearing (114; 116) during the steering movement. [7] Rear axle steering device (102) according to claim 6, wherein the control unit (120) is designed to output a control signal after the steering movement, which reduces the elasticity of the elastic bearing (114; 116). [8] Rear axle steering device (102) according to one of the preceding claims, further comprising at least one further link according to one of the preceding claims, wherein the control unit (120) is designed to output a first control signal for the elastic bearing of the link in response to the steering command in order to change the elasticity of the elastic bearing of the link in response to the first control signal, and to output a second control signal for the elastic bearing of the further link in order to change the elasticity of the elastic bearing of the further link in response to the second control signal in the opposite direction to the elastic bearing of the link. [9] Method for coupling a handlebar (108; 112) to a wheel carrier (104) and / or to a vehicle body (110), comprising a variable mounting of the handlebar (108; 112) by means of an elastic bearing (114; 116) which comprises a magnetoelastic and / or electroactive material and applying an electrical control signal in order to change an elasticity of the at least one elastic bearing (114; 116) in response thereto. [10] A method according to claim 9, wherein the electrical control signal is applied in response to a steering command. [11] Control unit for carrying out a method according to claim 9 or 10.

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