DE102020129742A1 - Feedback actuator for a steering device - Google Patents

Abstract

Feedback actuator (1) for a steering device with a defined steering torque, with an outer housing arrangement comprising a steering spindle (2) for coupling to a steering wheel (3), the steering spindle (2) being mounted in the housing arrangement so that it can rotate about its longitudinal axis - has at least one first motor (4) for actively setting a motor steering torque in a switched-on operating state of a vehicle, - has a gear (5) for providing the defined steering torque on the steering wheel (3), the gear (5) having a magnetic gear (6) is, wherein the magnetic gear (6) has an outer ring (7), an inner ring (10) and a ferromagnetic cylinder (9) arranged in between, which is connected to a drive shaft or output shaft.

Description

field of invention

The invention relates to a feedback actuator for a steering device. Such feedback actuators are used in particular in steer-by-wire steering systems for motor vehicles.

Background of the Invention

Steer-by-wire steering systems for motor vehicles accept manual steering commands from the driver, like conventional mechanical steering systems, by rotating a steering wheel from an input unit. This causes a steering shaft to rotate, which is not mechanically connected to the wheels to be steered via the steering gear, but interacts with angle of rotation or torque sensors that record the steering command and transmit an electrical control signal determined from this to a steering actuator, which is controlled by means of an electric actuator sets a corresponding steering angle of the wheels.

With steer-by-wire systems, the driver does not receive any direct physical feedback from the steered wheels via the steering train, which in conventional mechanically coupled steering systems is a reaction or return torque depending on the road surface, vehicle speed, current steering angle and other operating conditions be reported back to the steering wheel. The lack of haptic feedback makes it difficult for the driver to reliably grasp current driving situations and to carry out appropriate steering maneuvers, which impairs vehicle steerability and thus driving safety.

In order to generate a realistic driving experience, it is known in the prior art to record parameters such as vehicle speed, steering angle, steering reaction torque and the like from an actual current driving situation or to calculate them in a simulation and to form a feedback signal from them, which is a feedback actuator is fed. The feedback actuator is integrated into the input unit and has an actuator unit that includes an actuator that serves as a manual torque or steering wheel actuator, and which, depending on the feedback signal, couples a restoring torque (feedback torque) that corresponds to the real reaction torque into the steering wheel via the steering shaft. Such "force feedback" systems give the driver the impression of a real driving situation as with conventional steering, which facilitates an intuitive reaction.

From the DE 10 2008 036 730 A1 a steer-by-wire steering system is known, with an input unit having an actuator unit driven by an electric motor. The electric motor can be controlled by an electronic control unit, which adjusts the motor current depending on measured values that characterize the respective driving situation. The motor shaft is coupled directly to the steering shaft, so the motor torque is identical to the manual torque coupled into the steering shaft. The electric motor is flanged axially to the casing unit with respect to the longitudinal axis and the motor shaft is connected to the steering shaft mounted in the casing unit via a coupling. A similarly constructed actuator unit is in the EP 2 414 211 B1 shown. In the embodiment described therein, the steering shaft itself forms the motor shaft of the electric motor, so that a more compact structure can be implemented.

In order to apply a defined restoring torque in the steering wheel, the motor torque in the known designs described above must be precisely specified due to the direct coupling of the motor shaft to the steering shaft, which requires complex, fast and precise regulation of the motor current in the control unit. In addition, relatively high control currents have to be provided in order to implement greater restoring torques. These requirements necessitate a high level of control complexity, so that the control unit must be designed in a correspondingly complex manner. In addition, electric motors with sufficiently high motor torques that are suitable for applying realistic restoring torques have relatively large dimensions, which precludes a compact design.

In order to minimize the size and the required torque of the motor, among other things, gears are often used between the motor and the steering wheel. From the DE 10 2013 014 122 A1 is known to use a worm gear or a belt gear as a gear.

Summary of the Invention

The object of the invention is to develop a feedback actuator for a compact steering device with a realistically simulated steering feel, which is designed with as little play, vibration and noise as possible.

According to the invention, this object is achieved by a feedback actuator for a steering device with a defined steering torque, with an outer housing arrangement comprising: a steering spindle for coupling to a steering wheel, the steering spindle being rotatable about its longitudinal axis is mounted in the housing arrangement, - has at least one first motor for actively setting a motor steering torque when the vehicle is switched on, - has a gear for providing the defined steering torque on the steering wheel, the gear being a magnetic gear, the magnetic gear having an outer ring, a inner ring and a ferromagnetic cylinder arranged therebetween, which is connected to an input shaft or output shaft.

The invention is based on the finding that when an electric motor is used as a motor in steer-by-wire applications, it generates a so-called torque ripple. A torque ripple is a so-called torque ripple. This is an effect seen in many electric motor designs and refers to a periodic increase or decrease in output torque as the motor shaft rotates. This is usually perceived as unpleasant by the driver, since so-called NVH problems arise. The term NVH means the so-called noise, vibration, harshness (NVH, “noise, vibration, roughness”). In summary, this refers to the audible or noticeable vibrations, e.g. in motor vehicles. Roughness describes the audible as well as tactile transition area in the range from 20 Hz to 100 Hz.

In order to counteract these problems, a magnetic gear is provided according to the invention. Magnetic gears have the advantage that, unlike other types of gears, they do not cause additional NVH problems and also decouple the poor NVH behavior of the engine from the driver. The engine can therefore have NVH problems, but these are not noticed by the driver because the transmission prevents them from being passed on to the driver. According to the invention, the magnetic gear has an outer ring, an inner ring and a ferromagnetic cylinder arranged between them, which is connected to a drive shaft or output shaft. The components are preferably arranged radially to one another. An electric motor is preferably used as the motor.

Preferably, the outer ring and/or the inner ring each have permanent magnets.

Magnetic gears operate similarly to the intended motor. A magnetic field is generated in the ferromagnetic cylinder by the rotation of the ferromagnetic cylinder or the inner ring with permanent magnets. The output shaft rotates through this magnetic field. The ratio of the number of pool pairs in the outer and inner ring with permanent magnets is analogous to the reduction of the magnetic gear. Due to the non-contact mode of action and the associated pure frictional connection of magnetic gears, there are no changes in tension in the material and there is no direct pressure transmission, which would correspond to noise emissions. Due to the factors mentioned, there is significantly less structure-borne noise in the engine-transmission system and consequently the acoustics and haptics of the overall system can be significantly more pleasant for the driver and thus the NVH problems can be reduced. Due to the system rigidity and elasticity of the magnetic gear, there is a damping and filtering of high-frequency vibrations, which are previously generated in the motor. As a result, the engine is decoupled from the driver in terms of vibrations, which means that torque ripple for the driver can be reduced or even avoided. In addition, due to these properties of the magnetic gear, cost-intensive adjustments to the motor and control system to minimize torque ripple can be omitted. In contrast to other gears, such as spur gears, the magnetic gear enables the desired transmission range between 2 and 30 for steer-by-wire applications in one stage. In order to improve the acoustics, planetary gears with plastic gears are also often used in steer-by-wire actuators. Magnetic gears have a significantly higher power density than these planetary gears.

Another advantage of the magnetic gear is that they have an efficiency of up to 99% and have a low friction torque. The very low friction torque simplifies control of the steer-by-wire system. The magnetic gear itself is wear-free and does not require any lubrication. The behavior is therefore consistent over the service life, which means that the control of the system is simpler and more robust, and faulty behavior of the overall system can be better detected. In the event of failure, the magnetic gear does not block, unlike other gears. In the event of an overload, overtorque is applied with a defined, constant counter-torque without damage. This also leads to an improvement in the safety of the vehicle, which can still be steered even if the engine should stall.

According to an embodiment of the invention, the inner ring is connected to the shaft which is not connected by the ferromagnetic cylinder. This is necessary so that the torque can be transmitted from the drive shaft to the output shaft.

According to a further embodiment of the invention, the outer ring is connected to the housing arrangement. This is necessary to prevent unwanted rotation of the outer ring.

Preferably, the magnetic gear is arranged between the motor and the steering wheel. It is also conceivable that the motor surrounds the magnetic gear radially.

character list

• 1 eine schematische Schnittansicht eines Feedback-Aktuators gemäß einer ersten Ausführungsform der Erfindung mit einem Getriebe,
• 2 eine schematische Schnittansicht eines Feedback-Aktuators gemäß einer zweiten Ausführungsform der Erfindung mit einem Getriebe,
• 3 eine schematische Schnittansicht eines Feedback-Aktuators gemäß einer ersten Ausführungsform der Erfindung mit einer detaillierten Ansicht eines Magnetgetriebes, und
• 4 eine schematische Schnittansicht eines Magnetgetriebes.

Two exemplary embodiments of the invention are illustrated below using three figures. Show it:

• 1 a schematic sectional view of a feedback actuator according to a first embodiment of the invention with a gear,
• 2 a schematic sectional view of a feedback actuator according to a second embodiment of the invention with a gear,
• 3 a schematic sectional view of a feedback actuator according to a first embodiment of the invention with a detailed view of a magnetic gear, and
• 4 a schematic sectional view of a magnetic gear.

Detailed description of the drawings

1 thus shows a feedback actuator 1 for a steering device with a defined steering torque L, with an outer housing arrangement not shown in detail, comprising a steering spindle 2 for coupling to a steering wheel 3, wherein the steering spindle 2 is mounted in the housing arrangement 2 so that it can rotate about its longitudinal axis and at least a motor 4 for actively setting a motor steering torque in a switched-on operating state of a vehicle. The motor is preferably an electric motor.

The feedback actuator 1 also has a gear 5 . This gear 5 is designed as a magnetic gear 6 . As can be seen here, the transmission 5 is arranged in the axial direction A between the steering spindle 2 and the motor 4 .

The explanation of the magnetic gear 6 is later in connection with the 3 and 4 instead of.

2 shows a second embodiment of the feedback actuator 1. Identical components are denoted by the same reference symbols. The description is limited to the distinguishing features.

How out 2 can be seen, the motor 4 is arranged in the radial direction R building on the transmission 5 . Again, the gear 5 is a magnetic gear 6, which later in connection with the 4 is explained in more detail.

3 shows, for example, the structure and the arrangement of the magnetic gear 6 in the feedback actuator 1 according to FIG 1 . The magnetic gear 6 consists of three main components. The components are arranged radially to each other. These comprise an outer ring 7 arranged on the outside, which can be attached to the housing arrangement, not shown in detail, or to another housing, not shown in detail. Permanent magnets 8 are provided on an inner periphery of the outer ring 7 . Inside the outer ring 7 there is a ferromagnetic cylinder 9 which in this example is connected to a first shaft 12 with the steering shaft. Inside the ferromagnetic cylinder 9 there is an inner ring 10 with permanent magnets 11. This is connected to the motor 4 by a second shaft 13.

The exact mode of operation is explained below using the 4 described.

Based on 4 the basic structure of the magnetic gear 6 is explained in more detail. The magnetic gear 6 consists of three main components. The components are arranged radially to each other. These comprise the outer ring 7 arranged on the outside, which can be attached to the housing arrangement, not shown in detail, or to another housing, not shown in detail. Permanent magnets 8 are provided on an inner periphery of the outer ring 7 . Within the outer ring 7 is the ferromagnetic cylinder 9, which is connected to either a not shown input or output shaft. Again inside the ferromagnetic cylinder 9 is the inner ring 10 with permanent magnets 11. This is connected to the shaft which is not connected by the ferromagnetic cylinder 9. The magnetic gear 6 works in a similar way to the electric motor 4. The rotation of the ferromagnetic cylinder 9 or the inner ring 10 with permanent magnet 11 generates a magnetic field in the ferromagnetic cylinder 9. The output shaft, not shown in detail, rotates as a result of this magnetic field. The ratio of the number of pool pairs of permanent magnets 8, 11 in the outer and inner ring 7, 10 is analogous to the reduction of the magnetic gear 6.

Reference List

1

feedback actuator

2

steering spindle

3

steering wheel

4

engine

5

transmission

6

magnetic gear

7

outer ring

8th

permanent magnet

9

ferromagnetic cylinder

10

inner ring

11

permanent magnet

12

first wave

13

second wave

L

steering torque

A

axial direction

R

radial direction

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102008036730 A1 [0005]
• EP 2414211 B1 [0005]
• DE 102013014122 A1 [0007]

Claims (6)

Feedback actuator (1) for a steering device with a defined steering torque, with an outer housing arrangement, comprising - a steering spindle (2) for coupling to a steering wheel (3), the steering spindle (2) being mounted in the housing arrangement so that it can rotate about its longitudinal axis - has at least one first motor (4) for actively setting a motor steering torque in a switched-on operating state of a vehicle - has a gear (5) for providing the defined steering torque on the steering wheel (3), characterized in that the gear (5) is a magnetic gear (6), wherein the magnetic gear (6) has an outer ring (7), an inner ring (10) and a ferromagnetic cylinder (9) arranged in between, which is connected to a drive shaft or output shaft. Feedback actuator (1) after claim 1 that the outer ring (7) and/or the inner ring (10) each have permanent magnets (8, 11). Feedback actuator (1) according to any of the preceding claims, wherein the inner ring (10) is connected to the shaft not connected by the ferromagnetic cylinder (9). Feedback actuator (1) according to any one of the preceding claims, wherein the outer ring (7) is connected to the housing arrangement. Feedback actuator (1) according to any one of the preceding claims, wherein the magnetic gear (6) is arranged between the motor (4) and the steering wheel (3). Feedback actuator (1) after claim 4 until 5 , wherein the motor (4) surrounds the magnet gear (6) radially.

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