Actuator for a steer-by-wire steering device of a motor vehicle and method for assembling the actuator

Abstract

The invention relates to an actuator (10) for a motor vehicle steer-by-wire device, having a housing (46, 146), a screw spindle (42, 142) and a screw spindle nut (43, 143) which is rotatably positionally fixed and supported, said screw spindle and said screw spindle nut forming a screw spindle drive (41, 141) inside said housing (46, 146) in order to move said screw spindle (42, 142) axially relative to said screw spindle nut (43). An inertial mass (100, 300, 400, 400a, 500, 600) is coupled at least indirectly to said screw spindle (142) in consideration of the vibration behavior of at least one component of said actuator (10), in particular of said screw spindle (142).

Description

Technical Field

[0001] The present invention relates to an actuator for a motor vehicle steer-by-wire device as described in the preamble of the independent claim, and a method for assembling the actuator. Background Technology

[0002] A servo motor or actuator is known from patent document DE 10 2014 206 934 A1, which has a lead screw nut fixedly supported in position and a lead screw that can move axially relative to the lead screw nut. At least one end of such an actuator, used in steer-by-wire systems, is connected to a wheel carrier via a steering guide rod. The wheel steering angle of a wheel rotatably supported on the wheel carrier can be changed by the linear movement of the lead screw. Steer-by-wire systems, independent of steering mechanisms such as steering wheels, are controlled along a signal path, i.e., controlled without mechanical connection. The drive screw thread is, for example, formed by a self-locking trapezoidal thread.

[0003] In a motor vehicle chassis, high lateral forces arise that must be supported by the aforementioned actuators, thus the steering system guides the wheels. These high forces induce high friction in the lead screw threads of the actuator's lead screw drive. Even with optimized lubricants, high friction occurs between the thread profile sides of the lead screw and lead screw nut. A so-called stick-slip effect occurs due to the static and sliding friction on the contact surfaces of the abutting thread profile sides between the threaded pairs. This alternating adhesion and sliding of the thread profile sides can, on one hand, lead to torque oscillations between the lead screw nut and the lead screw. Here, the lead screw can, for example, be excited to torsional vibration. Continuous or temporary excitation within a short time interval can cause the resonant frequency of the lead screw or other components in the actuator to be reached. Therefore, in adverse cases, this excitation may generate air noise that can be acoustically perceived by vehicle occupants.

[0004] In the aforementioned lead screw drive, the stick-slip effect will induce torsional vibration, also known as torsional oscillation. In contrast to translational vibration, torsional vibration results in oscillations around the rotational degree of freedom of the system. Both are mechanical vibrations. Summary of the Invention

[0005] One of the objectives of this invention is to further improve the actuator of the steer-by-wire device for motor vehicles so that the actuator is acoustically inconspicuous and thus produces as little air noise as possible.

[0006] This problem is solved by the actuator of the vehicle steer-by-wire device according to claim 1. Preferred improvements are given in the dependent claims.

[0007] The actuator of a vehicle's steer-by-wire system has a housing in which a lead screw and a lead screw nut, rotatably and positionally supported, are supported. The lead screw and lead screw nut form a lead screw drive within the housing for axial movement of the lead screw relative to the lead screw nut. For this purpose, the lead screw has an external thread that engages with the internal thread of the lead screw nut. If the lead screw nut is rotatably driven, for example by an electric motor, preferably indirectly by a transmission, and preferably by a belt drive, the drive screw thread causes the lead screw to move axially along its longitudinal axis relative to the lead screw nut or the housing. By this axial movement along its longitudinal axis, the wheel steering angle of a wheel rotatably mounted on a wheel carrier and connected to at least one end of the lead screw can be changed.

[0008] To reduce, or ideally prevent, the previously explained excitations that cause audible vibrations in the various components of the actuator, an inertial mass block will be connected at least indirectly to the lead screw. Here, the inertial mass block is designed with the vibration characteristics of at least one component of the actuator, preferably the lead screw, in mind. As previously mentioned, the high lateral force of the wheel generates high surface pressure between the thread profile sides in the lead screw thread. This results in torque oscillations, where the so-called stick-slip effect increases when the rotary drive temporarily or intermittently drives the lead screw nut. It should be considered that during normal operation of the steering system, the wheel steering angle undergoes small changes in most cases. These small changes can be achieved by slightly rotating the lead screw nut. Therefore, during normal operation of the actuator, vibrations may be induced, particularly in the lead screw components, by the continuous alternating rotation and stillness of the lead screw nut. Especially when the vehicle is stopped, the wheel rotates only at a low speed, thus exerting a particularly large force on the lead screw. However, this can also excite vibrations in other components, especially when these components have a resonant frequency similar to that of the lead screw.

[0009] The term "stick-slip" comes from the English words "stick" and "slip." In physics and current technology, stick-slip describes a generally undesirable, jerky slip (rest-slip-rest-slip) between solids moving relative to each other. In a leadscrew, torsional vibrations are caused by the leadscrew nut, where the leadscrew itself does not rotate.

[0010] To alter the vibration characteristics of a leadscrew, a larger mass can be used, for example, by manufacturing the leadscrew with a larger diameter. While this changes the resonant frequency of the leadscrew, it results in the use of more material, increased weight, and the need for additional machining processes, such as cutting, during manufacturing, making the leadscrew more expensive. If the diameter of the leadscrew is increased, the dimensions of the leadscrew support relative to the housing and the dimensions of the leadscrew nut must also be adjusted. Furthermore, problems may arise during the assembly of the leadscrew.

[0011] Advantageously, this invention allows vibration characteristics to be influenced by an inertial mass block without requiring any major modifications to existing actuators in steering-by-wire devices. Due to its moment of inertia, the inertial mass block exerts a damping effect on the lead screw when it is engaged. In other words, the inertial mass block acts on the lead screw due to its moment of inertia, making the excitation caused by the stick-slip effect insufficient to generate air noise.

[0012] The inertial mass block is preferably a separate component. This inertial mass block is shaped according to its moment of inertia, which depends on the vibration characteristics of the component, preferably the lead screw, that may generate air noise. For example, the vibration characteristics and resonant frequency of the lead screw are known, and thus the inertial mass block can be formed based on these known parameters.

[0013] Preferably, the inertial mass block is constructed as a single unit or multiple units. To simplify assembly, for example, the carrier component can be first connected or linked to the lead screw. The dimensions of the carrier component are such that it does not obstruct the assembly of the lead screw with the bearing or the actuator housing. The carrier component can then be assembled with the mass block component to generate the pre-calculated inertial mass. For different actuators, the carrier component can be a universal part, so that only different mass block components need to be used respectively according to the preferred damping.

[0014] The inertial mass block is preferably connected to the lead screw by means of a force-transmitting connection and / or a material connection and / or a form-fit connection. The inertial mass block or carrier component can be, for example, pressed onto the lead screw (interference fit) or fixed by means of clamping elements, such as force-transmitting connections via fastening screws. Alternatively or additionally, it can be fastened by adhesive or welding or by a form-fit geometry.

[0015] The lead screw can move along its longitudinal axis within the actuator housing, thus requiring a support or guiding device within the housing. Indirect support of the lead screw relative to the housing is achieved, for example, by a bearing bushing that is securely connected to, and preferably pressed into, the actuator housing.

[0016] In an advantageous embodiment, the inertial mass block connected to the lead screw has an outer wall concentric with the longitudinal axis of the lead screw. This outer wall is preferably designed to be cylindrical to form a support surface that interacts with the inner side of the bearing bushing. If the inertial mass block is manufactured by cold forming, a smooth cylindrical outer wall can be produced in a simple manner, thus making the inertial mass block a component that can be manufactured integrally at low cost.

[0017] For actuators used in steer-by-wire systems, it is known from the prior art that bearing sleeves, also known as screw-in plugs, are connected at one or both ends of the lead screw. To achieve a compact connection between the bearing sleeve, the lead screw, and the inertial mass, in an advantageous embodiment, the inertial mass can be at least partially surrounded by the bearing sleeve, or the bearing sleeve can be surrounded by the inertial mass. For this purpose, the components have recesses and shoulders, allowing them to be nested together with the lead screw. Preferably, the inertial mass is a rotationally symmetric component and is therefore easy to manufacture, for example, by machining or by cold forming. This design is illustrated in various embodiments in the accompanying drawings.

[0018] Different actuators of varying lengths can always use lead screws of the same length (inexpensive, universal components). The length of the lead screw can be matched to the length of the actuator using a bearing sleeve as needed. Vibration characteristics can be adapted by fitting appropriate lead screw drives or actuators with inertial mass blocks of different sizes. If the outer diameter of the inertial mass block is equal to the outer diameter of the bearing sleeve, the outer wall of the bearing sleeve can be used together with the outer wall of the inertial mass block as a sliding support surface opposite the bearing bushing. Alternatively, only the outer wall of the inertial mass block can be used as the sliding support surface. If the outer diameter of the inertial mass block is less than or equal to the outer diameter of the bearing sleeve, the axial displacement of the lead screw will not cause collisions with the support components in the bearing bushing or housing.

[0019] In a preferred embodiment, the inertial mass block is at least partially formed by a journal, which in its first function serves as a torsional stop for the lead screw relative to the actuator housing. In the aforementioned actuator, the torsional stop is necessary so that the lead screw, engaged with the lead screw nut, does not rotate about its longitudinal axis when the lead screw nut rotates. To save structural space, the mass of the journal is advantageously considered when calculating the inertial mass block. In other words, the journal can be part of the inertial mass block or form the desired inertial mass block separately. This gives a compact variant with both torsional stop and inertial mass block functionality. The journal can be connected directly or indirectly to the lead screw. In the case of direct connection, the journal is directly connected to the lead screw, preferably screwed to the lead screw via its threaded connection, preferably generally or exactly transverse to the longitudinal axis of the lead screw. Alternatively, the journal can be connected only to the bearing sleeve or the inertial mass block, or it can be connected to the bearing bushing or the inertial mass block and additionally connected to the lead screw. For the last variant mentioned, a threaded connection transverse to the longitudinal axis of the lead screw can preferably also be used. This journal can be screwed onto a bearing sleeve or an inertial mass block and can also be additionally used for fixing at the force transmission connection and / or form-fit connection of the lead screw.

[0020] In another preferred embodiment, the inertial mass block serves as a connecting member between the lead screw and the bearing sleeve. Here, the lead screw is only indirectly, i.e., not directly, connected to the bearing sleeve. The lead screw can be screwed onto the inertial mass block, or the inertial mass block can be cast onto the lead screw, cast around the lead screw, or welded. The inertial mass block can be connected to the bearing sleeve via a form-fit connection, a force-transmitting connection, or a material connection. Preferably, the bearing sleeve has a recess, such as a blind hole. The diameter of the inertial mass block is preferably smaller than the inner diameter of the blind hole. The surrounding gap is preferably filled with an elastomer. This achieves disengagement through an elastic connection between the inertial mass block and the bearing sleeve.

[0021] According to another aspect of the invention, a method for assembling an actuator for a steering-by-wire device as described above is provided. In the assembly, an inertial mass is connected to a lead screw in several steps. For example, in the first step, the inertial mass is preferably connected to the lead screw via a compression connection. This can be achieved, for example, by interference fit or thermoforming. In cases where the inertial mass consists of at least two components, a carrier member and at least one mass member, the carrier member is first connected to the lead screw, wherein the mass member is assembled to the carrier member in at least a subsequent indirect step. After assembling the lead screw to the carrier member, the lead screw nut can be assembled to the lead screw, for example. Thus, no object will obstruct the subsequent assembly with the housing. If the total diameter of the mass member or the inertial mass is practically too large to assemble, it is not necessary to adapt it to the actuator housing or other components. The mass member can only be conveniently assembled after the preceding components have been assembled.

[0022] A steer-by-wire system is a steering system that is decoupled from a mechanical steering mechanism, such as a steering wheel or steering lever. The steering motion performed by the driver using the steering lever is not transmitted mechanically, for example, via guide rods, to the wheel carrier or wheels. Instead, a steering angle for each wheel on the axle is calculated in a control unit, for example, and this steering angle sends an adjustment signal to one or more actuators in the steer-by-wire system, ultimately causing a change in the wheel steering angle. Attached Figure Description

[0023] The present invention will now be described with reference to the accompanying drawings and preferred embodiments. In the drawings:

[0024] Figure 1 An actuator based on known prior art is shown;

[0025] Figure 2 A detailed view of a lead screw drive with an actuator inertial mass block is shown; and

[0026] Figures 3 to 6 Other embodiments of the lead screw drive with an actuator having an inertial mass block are shown in detail. Detailed Implementation

[0027] Figure 1 An actuator 10 for a steer-by-wire device according to known prior art is shown. The actuator 10, also referred to as a servo motor, includes a lead screw drive 41 having a lead screw 42 with a lead screw thread 43a (external thread) and a lead screw nut 43 with a nut thread 42a (internal thread). The lead screw nut 43 is rotatably supported in a housing 46 by rolling bearings 44, 45 and is axially fixed, in other words, its position is fixed. The housing 46 is divided into three housing parts: a right housing part, a left housing part, and a middle housing part. A pulley 47 is arranged on the lead screw nut 43 in a non-rotatable manner, which can be driven by an electric motor 49 via a belt drive 48 and a drive belt 55. The lead screw 42 is connected at one end to a bearing sleeve 50, which is in the form of a push-in or screw-in plug and is guided on the housing side in a bearing bushing, which is in the form of a sliding bearing or a thrust bearing 51. A bearing sleeve 50, partially protruding from housing portion 46b, is connected to a joint sleeve 52. A steering guide rod (not shown) is hinged to the wheel carrier at this joint sleeve. The right housing portion 46a is supported on the vehicle side, or on the vehicle body structure, via a joint 53.

[0028] The aforementioned device can be used as a steer-by-wire device on an axle, and preferably as a rear axle steering device for a motor vehicle. The actuator 10 shown is constructed as a single adjuster, i.e., it is arranged, for example, close to the wheel and supported on one side of the vehicle body to change the wheel's steering angle. The actuator is connected to the other end via a steering guide rod through a connector sleeve 52, or directly connected to a wheel carrier on which the wheel is rotatably supported. The actuator 10 acts, for example, on the rear wheel, and changes the wheel's steering angle when the lead screw 42 moves linearly. Accordingly, another single adjuster is provided for the second rear wheel. The wheel steering angle is changed by the lead screw 42, which is axially movable when driven by the lead screw nut 43 and transmits linear motion to the joint sleeve 52 via the bearing sleeve 50. The described lead screw drive device can also be used for actuators that act in a dual or central manner, i.e., steering-type action on both wheels of the axle.

[0029] In the further description of the accompanying drawings, the same components having the same function have the same reference numerals.

[0030] Figure 2A perspective view of the screw drive device according to the invention is shown, a portion of which is shown here. A screw 142 forms a drive screw thread with a screw nut 143. The screw nut 143 is surrounded by a pulley 147, so that the screw 142 rotates when the drive belt 155 is actuated. Thus, the screw 142 can move axially in one direction or the other, as indicated by the double arrows. At its left end, the screw 142 is screwed with its end to a bearing sleeve 150. The bearing sleeve 150 extends to the inertial mass block 100 and is therefore shown transparently in dashed lines in some sections. The inertial mass block 100 is two-part and consists of a carrier member 100t and a mass block member 100m. The carrier member 100t is an annular helical element and is held in a force-transmitting connection on the thread of the screw 142. The mass block member 100m is formed by two semi-rings, which are clamped to the carrier member 100t by means of screws 104. It is evident that the outer diameter T of the mass block component 100m is larger than the outer diameter L of the bearing sleeve 150. The outer diameter of the carrier component 100t is equal to the outer diameter L of the bearing sleeve 150. When assembling a lead screw with the bearing sleeve 150 and housing (not shown), assembly is easy, and the large outer diameter T of the mass block component 100m does not hinder assembly. The inertial mass block can be designed according to the application scenario, i.e., according to the required damping or vibration reduction. The mass block component 100m with a larger diameter or a larger axial elongation range can be used in a simple manner. Here, the carrier component 100t can be presented as a universal part for different configurations. This provides a cost-effective solution for improving the vibration characteristics of the lead screw or actuator, thereby avoiding acoustic anomalies caused by the lead screw drive or the entire actuator.

[0031] Figure 3 It shows according to Figure 2 A detailed cutaway view of the lead screw drive mechanism is shown here. Another variant of the inertial mass block 300 is also shown, which is similarly formed by a carrier member 300t abutting against the lead screw 142 and a mass block member 300m surrounding the carrier member 300t. The lead screw 142 is connected to the bearing sleeve 150 via a threaded connection. It is evident that the lead screw 142 is initially assembled with the carrier member 300t. In the next step, the bearing sleeve 150 is screwed onto the end of the lead screw 142. Further assembly steps can now be performed to assemble the lead screw drive mechanism or actuator. Finally, in a further assembly step, the mass block member 300m can be connected to the carrier member 300t. According to... Figure 3 In the variant shown, the carrier component 300t and the mass block component 300m have shoulders, steps, gaps 115, or recesses, thereby achieving a simple, form-fitting assembly. These components can be joined together, for example, by means of adhesive materials.

[0032] Figure 4 and Figure 4a Another lead screw drive device with an inertial mass block 400 is shown, which here engages with the lead screw 142 via a compression connection 110. The inertial mass blocks 400, 400a are in... Figure 4 The middle is an integrated whole, while... Figure 4a The middle part is a two-body design. In both embodiments, the inertial mass blocks 400, 400a have a cylindrical outer wall 105. According to... Figure 4a In the variant (inertial mass block 400a), journal 160 is screwed transversely into outer wall 105 along the longitudinal axis. Journal 160 is part of a torsion stop that is supported at the inner wall of housing 146 and prevents lead screw 142 from rotating with it when lead screw nut (not shown). On the other hand, journal 160 is part of inertial mass block 400a. Lead screw 142 is screwed at its end to bearing sleeve 150 and is supported and guided relative to housing 146 by bearing bushing 151.

[0033] exist Figure 4 and Figure 4a In the two embodiments shown, the outer diameter T of the outer wall 105 of the inertial mass blocks 400, 400a is slightly smaller than the outer diameter L of the bearing sleeve 150, so the outer wall 105 cannot be used as a support surface for the bearing bushing 151. Furthermore, the inertial mass blocks 400, 400a have a recess 115 at their left end. The inertial mass block 400 uses this recess 115 to surround the shoulder 152 on the right side of the bearing sleeve 150. It is evident that this nested variation provides a compact structural form for axial and radial elongation, consisting of the bearing sleeve 150 and the inertial mass blocks 400 or 400a. (Compared to...) Figure 2 or Figure 3 As shown in the variants, the desired mass of the inertial mass block 400 or 400a can also be changed by corresponding axial elongation. Therefore, the inertial mass block can also have a relatively small diameter.

[0034] Figure 5 It shows according to Figure 4 The variant shown is further adapted for a more compact structural space. The nesting of the integrated inertial mass block 500 and bearing sleeve 150 is as described in... Figure 4 The configuration is as shown in the variant. However, the outer diameters L and T are chosen to be the same. The outer wall 105 of the inertial mass block 500 is a smooth cylinder, thus forming an additional sliding surface in addition to the sliding surface on the outer wall of the bearing sleeve 150. This allows for a shorter bearing sleeve while retaining the necessary sliding support surface, or in other words, it can be used to enlarge the sliding support surface.

[0035] Figure 6Another embodiment of a lead screw 142 with an inertial mass block 600 is shown, which also dampens the lead screw. The lead screw 142 has a longitudinal axis a and is partially surrounded by and connected to the inertial mass block 600 in a non-rotatable manner. The lead screw 142 is directly connected to the bearing sleeve 150 via the inertial mass block 600. The inertial mass block 600 constitutes a connecting device for the bearing sleeve 150. The bearing sleeve 150 receives the end of the lead screw 142 and the inertial mass block 600 is received in a blind hole or recess 155. The inertial mass block 600 has an outer diameter Ti smaller than the inner diameter D of the bearing sleeve 150. A surrounding sleeve-shaped gap 102 exists between the outer wall 105 of the inertial mass block 600 and the inner wall 153 of the bearing sleeve 150. A damping elastic body 610 is provided in the gap 102 along a portion of the length of the inertial mass block 600, which elastically connects the inertial mass block 600 to the bearing sleeve 150. List of reference numerals in the attached diagram: 10 Actuators 41. Lead screw drive device 42, 142 lead screw 42a Internal Thread Screw Nut 43, 143 lead screw nut 43a External thread screw 44 Rolling bearings 45 Rolling bearings 46, 146 casing 47, 147 pulleys 48 Belt drive device 49 Electric Motors 50 and 150 bearing sleeves 51, 151 bearing bushings 52 Joint sleeve 53 Bearing Hole 55 and 155 transmission belts 100 inertial mass block 100t and 300t carrier components 100m and 300m mass block components 102 gap 104 screws 105 outer wall 110 Extrusion Joint 115 gap 120 rings 152 shoulder 153 Inner Wall 160 journal 300 inertial mass block 400 inertial mass block 400a inertial mass block 500 inertial mass block 600 inertial mass block 610 Elastomer a longitudinal axis T outer diameter L outer diameter Ti outer diameter D inner diameter

Claims

1. An actuator (10) for a motor vehicle steer-by-wire device, the actuator having a housing (46), a screw drive mechanism with a lead screw (42, 142), and a lead screw nut (43, 143) rotatably and positionally supported, the lead screw and the lead screw nut forming a screw drive mechanism (41, 141) within the housing (46, 146) to allow axial movement of the lead screw (42, 142) relative to the lead screw nut (43, 143), wherein, The lead screw is excited to undergo torsional vibration, characterized in that it is provided with inertial mass blocks (100, 300, 400, 400a, 500, 600), which are at least indirectly connected to the lead screw (142) to at least reduce the torsional vibration of the lead screw, wherein the inertial mass blocks (100, 300, 400, 400a, 500, 600) are constructed taking into account the vibration characteristics of at least one component of the actuator (10).

2. The actuator according to claim 1, characterized in that, The moment of inertia of the inertial mass blocks (100, 300, 400, 400a, 500, 600) depends on the vibration characteristics of the lead screw (142).

3. The actuator according to claim 1, characterized in that, The inertial mass blocks (100, 300, 400, 400a, 500, 600) are constructed as a single unit or multiple units.

4. The actuator according to claim 3, characterized in that, The inertial mass blocks (100, 300, 400, 400a, 500, 600) are connected to the lead screw (142) by means of force transmission connection and / or material connection and / or form fit connection.

5. The actuator according to any one of claims 1 to 4, characterized in that, The inertial mass blocks (100, 300, 400, 400a, 500, 600) have outer walls (105) concentric with the longitudinal axis (a) of the lead screw (142) to form a support surface that interacts at least indirectly with the housing (146).

6. The actuator according to claim 5, wherein the support surface works in conjunction with the bearing bushing (151).

7. The actuator according to claim 5 or 6, characterized in that, The outer wall is a cylindrical outer wall.

8. The actuator according to any one of claims 1 to 4, characterized in that, When the lead screw (142) is connected to the bearing sleeve (150), the inertial mass blocks (100, 300, 400, 400a, 500, 600) are surrounded by the bearing sleeve (150) or the bearing sleeve (150) is at least partially surrounded by the inertial mass blocks (100, 300, 400, 400a, 500, 600).

9. The actuator according to claim 8, characterized in that, The outer diameter (T) of the inertial mass blocks (100, 300, 400, 400a, 500, 600) is less than or equal to the outer diameter (L) of the bearing sleeve (150).

10. The actuator according to any one of claims 1 to 4, characterized in that, The inertial mass block (400a) is formed at least in part by a journal (160), which additionally serves as a torsional stop to prevent the lead screw (142) from rotating relative to the housing (146) of the actuator (10).

11. The actuator according to claim 8, characterized in that, The inertial mass block (600) is a connecting member between the lead screw (142) and the bearing sleeve (150).

12. A method for assembling an actuator (10) for a motor vehicle steer-by-wire device according to any one of claims 1 to 11, characterized in that, The inertial mass blocks (100, 300, 400, 400a, 500, 600) are connected to the lead screw (142) in one or more steps, wherein, in a first step, the inertial mass blocks (100, 300, 400, 400a, 500, 600) are connected to the lead screw (142) via threaded or extruded connections.

13. The method according to claim 12, characterized in that, For an at least two-body inertial mass block (100, 300) consisting of a carrier component (100t, 300t) and at least one mass block component (100m, 300m), firstly, the carrier component (100t, 300t) is connected to the lead screw (142), wherein in at least an indirect subsequent step, the mass block component (100m, 300m) is assembled together with the carrier component (100t, 300t).

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