Steer-by-wire steering system, and method for operating a steer-by-wire steering system

Abstract

The invention relates to a steer-by-wire steering system (1), comprising a steering unit (2), a steering wheel unit (3), and a communication connection (4), which connects the steering unit (2) to the steering wheel unit (3) for signaling purposes, wherein the steering wheel unit (3) is designed to provide a feedback torque (8) on a steering handle (7) without a torque sensor, wherein the steer-by-wire steering system (1) is designed to determine the feedback torque (8) at least partially on the basis of a transverse force signal (9). The invention further relates to a method for operating a steer-by-wire steering system (1), wherein a feedback torque (8) is provided on a steering handle (7) without a torque sensor, wherein the feedback torque (8) is determined at least partially on the basis of a transverse force signal (9).

Description

[0001] Description

[0002] Steer-by-wire steering system and method for operating a steer-by-wire steering system

[0003] The invention relates to a steer-by-wire steering system and a method for operating a steer-by-wire steering system.

[0004] Steer-by-wire steering systems place high demands on driver feedback during driving. While in conventional steering systems the rack position is directly coupled to the steering wheel position via the steering column, thus mechanically transmitting road feedback to the driver, this feedback must be artificially generated in steer-by-wire systems. In steer-by-wire systems, the steering wheel assembly (FFA) is mechanically decoupled from the steering unit (RWA), and position and force information is transmitted electronically. This necessitates the generation and adjustment of a feedback signal at the steering handle.

[0005] Traditionally, the target torque of the air handling unit (AFU) and thus the feedback to the driver are generated from the engine torque of the smoke and heat exhaust ventilation (SHEV) unit. However, friction effects in the SHEV unit act like a filter, meaning that not all information is included in the feedback. Therefore, it is particularly important that the target torque at the AFU is precisely regulated so that no further information is lost due to the AFU's mechanics. For this purpose, a torque sensor is used downstream of the gearbox, allowing the gearbox's influence on the AFU to be detected and compensated for. However, the torque sensor incurs additional costs.

[0006] The invention is based on the objective of providing a steer-by-wire steering system and a method for operating a steer-by-wire steering system without a torque sensor in the steering wheel unit.

[0007] The problem is solved according to the invention by a steer-by-wire steering system with the features of claim 1 and a method with the features of claim 10. Advantageous embodiments of the invention are set forth in the dependent claims. In particular, a steer-by-wire steering system is provided, comprising a steering unit, a steering wheel unit, and a communication link that connects the steering unit to the steering wheel unit via a signal connection, wherein the steering wheel unit is configured to provide feedback torque at a steering handle without a torque sensor, and wherein the steer-by-wire steering system is configured to determine the feedback torque at least partially based on a lateral force signal.

[0008] Furthermore, in particular a method for operating a steer-by-wire steering system is provided, wherein a feedback torque is provided at a steering handle without a torque sensor, and wherein the feedback torque is determined at least partially from a lateral force signal.

[0009] The steer-by-wire steering system and its method enable frictionless feedback at the steering wheel, thereby reducing the requirements for friction compensation within the steering unit. This is particularly possible because the target signal contains more information, and even in the event of information loss due to friction within the steering unit, a similarly high or even higher information content remains. This is achieved by not using the motor torque of the electric motor in the steering unit to generate feedback for the driver, but rather, at least partially, a signal representing the lateral force (which can also be described as tire lateral force), especially at the front axle (lateral force signal). In other words, information about the lateral force acting on the front axle is used to generate feedback at the steering unit.This lateral force signal contains neither the friction of the axle nor the steering system and is therefore completely friction-free, offering a very wide bandwidth and a very high information content. This eliminates the need for a torque sensor in the steering wheel unit, thus reducing system costs.

[0010] In addition to the lateral force (lateral force signal), other quantities and / or information can also be considered to determine the feedback torque at the steering handle. For example, this could include motor torque and / or motor current of an electric motor in the steering unit. It may be possible to weight the different quantities accordingly.

[0011] Components of the steer-by-wire steering system, in particular the steering unit and the steering wheel unit, can be designed individually or collectively as a combination of hardware and software, for example, as program code executed on a computing device, in particular a microcontroller or microprocessor. However, it is also possible for components to be designed individually or collectively as an application-specific integrated circuit (ASIC) and / or a field-programmable gate array (FPGA) and / or a graphics processing unit (GPU) and / or a digital signal processor (DSP). The steering unit and the steering wheel unit can each, in particular, comprise at least one computing device and at least one memory.

[0012] In one embodiment, the steer-by-wire steering system is configured to determine the feedback torque solely based on the lateral force signal. This completely eliminates system friction from the feedback loop.

[0013] In one embodiment, the steer-by-wire steering system is configured to determine the lateral force signal based on a lateral acceleration signal. This allows the lateral force, or rather the lateral force signal representing it, to be determined. In particular, the tire contact mass is taken into account.

[0014] The lateral acceleration signal is detected, in particular, by means of a lateral acceleration sensor, which can be part of the steer-by-wire steering system. For example, the lateral acceleration can be detected by means of a lateral acceleration sensor located on or near the steering axis. This allows the lateral acceleration to be detected directly on or in the immediate vicinity of the steering axis.

[0015] Further development allows for the lateral acceleration sensor to be arranged in or on the steering unit. This enables a particularly simple design to be implemented. In particular, this eliminates the need for complex wiring. Specifically, the lateral acceleration sensor can be mounted directly on a circuit board (PCB) of the steering unit, especially a control unit of the steering unit.

[0016] Alternatively, the lateral acceleration can be estimated from measurements taken by an inertial sensor. This allows the vehicle's existing inertial sensors to be used, eliminating the need for a separate lateral acceleration sensor. If the lateral acceleration at the vehicle's center of gravity is known, the lateral acceleration at the steering axis can be calculated using Euler's theorem for rigid body kinematics, the displacement between the front axle and the lateral acceleration measurement point (P). x \P y |P Z ), the yaw acceleration / j, the pitch acceleration <p und der Wankbeschleunigung ü bestimmt werden

[0017]

[0018] where a x , a y , a zThe accelerations are at the center of gravity. In one embodiment, it is provided that a wheel contact force is detected and / or estimated, wherein a wheel contact mass is determined based on the detected and / or estimated wheel contact force, and the determined wheel contact mass is taken into account when determining the tire lateral force. This allows a detected and / or estimated value for the wheel contact force to be used.

[0019] The lateral force (or tire lateral force) can be determined from the lateral acceleration y. For this purpose, the lateral acceleration y is v required on the front axle. Furthermore, the wheel contact mass m v required for the front axle. If the lateral acceleration at the front axle is known, the lateral force (or tire lateral force) can be calculated by

[0020] Eq. 2

[0021]

[0022] be determined.

[0023] In one embodiment, the steer-by-wire steering system is configured to determine the lateral force signal based on a vehicle model. This allows the lateral force or signal to be determined from other parameters. For example, the lateral force can be determined from a detected yaw rate of the vehicle using the single-track model. It can also be provided that a lateral force determined in this way is considered in addition to a lateral force determined by other means, such as from a detected lateral acceleration.

[0024] In one embodiment, the steering wheel unit is designed to adjust the feedback torque at the steering handle using a feedforward control system.

[0025] This allows the mechanical properties of the steering wheel unit to be taken into account and / or compensated for. This is particularly advantageous because the (actual) feedback torque cannot be controlled due to the lack of a torque sensor, as the feedback torque (hand torque) is no longer available as a measured variable. This inevitably leads to a loss of information from the electric motor of the steering wheel unit to the steering mechanism. This loss of information arises from mechanical properties within the steering wheel unit, but can be mitigated by incorporating the dynamics of the mechanical system using feedforward control. Feedforward control thus enables a realistic steering feel to be generated even without a torque sensor.

[0026] The basis of the countermeasure lies in a model of the system's transfer behavior within the steering wheel unit. For this purpose, a transfer function of the dynamic behavior of the engine torque M is used. Mot of the electric motor in the steering wheel unit for feedback or hand torque M H erected G s (s) = This transfer function is parameterized using measurement campaigns, and the structure is identified. This transfer function then contains information about the mechanical properties of the steering wheel unit. Based on this transfer function, a feedforward control G is developed. Vor (s) designed to compensate for mechanical influences. The feedforward control is achieved by:

[0027]

[0028] If the transmission behavior of the mechanics fully corresponds to the identified transmission behavior, the following results for the transfer function of the control in the steering wheel unit:

[0029]

[0030] In this case, the influence of mechanics would be completely compensated and the controlled variable M H i (s) would only change due to the adjustable term G FiU S) from the reference variable M H s (s) differ. This would correspond to perfect feedforward control. The term G Füt (s) is provided to improve acoustic properties, if necessary, through a filter.

[0031] In reality, the system does not perfectly match the modeled transfer function. Nevertheless, model-based feedforward control can improve the response and thus reduce information loss by compensating for mechanical influences.

[0032] In one embodiment, the feedforward control is designed to compensate for inertia and / or elasticity of the mechanical components of the steering wheel unit. This is achieved by appropriately designing the aforementioned transfer function during the measurement campaign and by appropriately designing the feedforward control.

[0033] In one embodiment, the feedforward control is designed to compensate for friction between the mechanical components of the steering wheel unit. In addition to mechanical influences from elasticity and inertia, friction also exists between the electric motor of the steering wheel unit and the steering handle. This also results in a loss of information, which would be compensated for by a hand torque control and would therefore be disadvantageous compared to hand torque control in the steer-by-wire steering system described in this disclosure. However, this aspect can be counteracted by performing a friction estimation. For this purpose, a friction model is parameterized, particularly with the help of test bench investigations, with which a minimum frictional force or frictional torque present in the system, including its associated dynamics, is identified. For example, a LuGre friction model can be used for this purpose.A rotor speed p is used as input for this friction model. Mot The electric motor of the steering wheel unit is used because friction occurs between the electric motor and the steering handle and is speed-dependent. Therefore, an angle sensor is also provided in the steering wheel unit, which directly or indirectly detects a rotor angle, from which the rotor angular velocity can be determined.

[0034] In this model, the dynamics of friction are calculated using a bristle model. The dynamics of the bristle motion z are calculated using the following differential equation:

[0035]

[0036] The function g( <p Mot ) is calculated using a Stribeck model:

[0037]

[0038] In this equation, F represents c the Columb friction, F s the breakaway force and <p sThe Stribeck velocity. The bristle deflection and the Stribeck curve are then used to calculate the frictional force:

[0039]

[0040] Here, a0 corresponds to a stiffness, a to a damping coefficient, and a2 to the velocity-proportional component. The friction level present in each case can be identified from the measurement data acquired during the test bench investigations. For example, the friction level may be higher at lower ambient temperatures. Therefore, complete elimination of friction is not guaranteed in every situation, but the margin of error can be reduced. Other friction models can also be used to estimate the frictional force.

[0041] The feedback torque is corrected, in particular based on the estimated frictional force, in order to reduce the loss of information due to friction in the system.

[0042] In particular, the estimated frictional force is converted into an additional torque that must be applied.

[0043] In one embodiment, the steer-by-wire steering system is configured to determine a friction coefficient defined by a predefined friction model, and the steering wheel unit is configured to impose this determined friction coefficient on the feedback torque. This artificially generates the sensation of friction in the feedback torque. In particular, this makes it possible to elicit a predetermined steering feel for the driver, independent of the mechanical properties of the steering wheel unit (and the steering unit). Specifically, it can be provided that the actual mechanical properties present in the steering wheel unit (inertia, elasticity, and friction) are eliminated, and any friction perceptible at the steering handle is generated solely by an artificially imposed friction coefficient.This is made possible in particular by the fact that all mechanical influences from the steer-by-wire steering system can be eliminated, since the feedback is derived from the lateral force or the lateral force signal. The friction model can, for example, be designed as described above, whereby the friction force determined in this way is used to adjust the feedback torque in order to produce the desired steering feel at the steering handle.

[0044] In one embodiment, the predefined friction model for generating a predefined steering feel is parameterizable. This allows the steering feel to be adjusted and modified. In the example given above, the parameters a0, a1, a2, F, in particular, can be parameterized. c , F s , <p s They can be adjusted to create the sensation of desired friction.

[0045] Further characteristics of the method are derived from the description of various steer-by-wire steering system configurations. The advantages of this method are the same as those of the steer-by-wire steering system configurations.

[0046] The invention is explained in more detail below with reference to preferred embodiments and the figures. These show:

[0047] Fig. 1 shows a schematic representation of embodiments of the steer-by-wire steering system;

[0048] Fig. 2 is a schematic representation to illustrate embodiments of the Steer-by-Wire-Lenksytems;

[0049] Fig. 3 shows a schematic flowchart of embodiments of the method for operating a steer-by-wire steering system.

[0050] Figure 1 shows a schematic representation of embodiments of the steer-by-wire steering system 1. The steer-by-wire steering system 1 comprises a steering unit 2, a steering wheel unit 3, and a communication link 4 that connects the steering unit 2 to the steering wheel unit 3 via signal transmission. The steering unit 2 includes, in particular, an electric machine 2-1 (electric motor) and a steering gear 2-2. The steering gear 2-2 uses the electric machine 2-1 to set or control the position of a rack 5 (alternatively, a pushrod), which is transmitted to the steerable wheels 6 via a tie rod kinematic system. The steering wheel unit 3 includes, in particular, an electric machine 3-1 (electric motor) which is connected via a steering gear 3-2 to a steering handle 7 (steering wheel) in order to generate a feedback torque 8 at the steering handle 7.The basic functionality of the steer-by-wire steering system 1 is known, so it will not be discussed further here.

[0051] The steering wheel unit 3 is configured to provide the feedback torque 8 at the steering handle 7 without a torque sensor, wherein the steer-by-wire steering system 1 is configured to determine the feedback torque 8 at least partially based on a lateral force signal 9. The lateral force signal 9 is, in particular, representative of a lateral force 10 (or tire lateral force) acting on the steering system.

[0052] It may be provided that the steer-by-wire steering system 1 is configured to determine the feedback torque 8 solely from the lateral force signal 9.

[0053] The steer-by-wire steering system 1 may include a lateral acceleration sensor 2-3. The lateral acceleration sensor 2-3 is, in particular, located in the steering unit 2. The lateral acceleration sensor 2-3 detects lateral acceleration and provides a lateral acceleration signal 11. The steer-by-wire steering system 1 may be configured to determine the lateral force signal 9 based on the lateral acceleration signal 11. This has already been described in more detail in the general description. The determination of the lateral force or the lateral force signal 9 can be carried out either in the steering unit 2 or in the steering wheel unit 3, or by means of a separate control device (not shown).

[0054] The steer-by-wire steering system 1 may be configured to determine the lateral force signal 9 taking into account a vehicle model. The vehicle model may, for example, be a single-track model, whereby the lateral force or lateral force signal 9 is determined based on a yaw rate detected by a yaw rate sensor (not shown) of the vehicle. Determining the lateral force or lateral force signal 9, taking into account the vehicle model, may be performed either in the steering unit 2 or in the steering wheel unit 3, or by means of a separate control unit (not shown).

[0055] The steering wheel unit 3 can be configured to adjust the feedback torque 8 at the steering handle 7 using a pilot control 12 (Fig. 2). This is shown schematically in Fig. 2. The pilot control 12 receives as its input signal a target hand torque M, specified as the feedback torque 8. Hssupplied. Based on this, the feedforward control 12 determines a target motor torque M. Mot)S , which is part of the G system s (s) is set and leads to an actual hand moment M H i at the steering handle 7.

[0056] It can be provided that the feedforward control 12 is designed such that inertia compensation 13 and / or elasticity compensation 14 of mechanical components of the steering wheel unit 3 takes place. For this purpose, the feedforward control 12 is parameterized accordingly, whereby the parameters are determined, for example, during test bench investigations on the steering wheel unit 3, which the system G s characterize (s).

[0057] It can be provided that the feedforward control 12 is designed such that friction compensation 15 is achieved for the friction of mechanical components of the steering wheel unit 3. This is done by means of a friction model G. Fric(s). The input signal is taken to the feedforward control 12 or the friction model G. Fric (s) of the friction compensation 15 in particular additionally the motor speed p Mot The electric machine 3-1, which is detected, for example, by means of an angle sensor (not shown), is supplied with this information. Based on this, the friction model G estimates the friction. FriC (s) an additional engine torque.

[0058] It can be provided that the steer-by-wire steering system 1 is configured to determine a friction component defined by a predefined friction model, wherein the steering wheel unit 3 is configured to impose the determined friction component on the feedback torque 7. With reference to Fig. 2, an additional friction model is used in particular, which is parameterized to produce a desired steering feel, and from this, an additional motor torque is determined, which is added to the otherwise determined target motor torque.

[0059] Figure 3 shows a schematic flowchart of embodiments of the method for operating a steer-by-wire steering system. The steer-by-wire steering system is configured in particular according to one of the embodiments described in this disclosure.

[0060] In process step 100, a feedback torque for feedback at a steering handle of the steer-by-wire steering system is determined based on a lateral force signal. This can be done based on a detected lateral acceleration. In process step 101, the determined feedback torque is provided at the steering handle without a torque sensor, in particular by means of an electric motor by applying a motor torque. Here, feedforward control may be used to perform inertial compensation and / or elasticity compensation and / or friction compensation of mechanical components of the steering wheel unit.

[0061] Further embodiments of the method have already been described above with reference to the steer-by-wire steering system. Reference numeral list

[0062] 1 Steer-by-Wi re steering system

[0063] 2 Steering unit

[0064] 2-1 electric machine

[0065] 2-2 Steering gear

[0066] 2-3 Lateral acceleration sensor

[0067] 3 Steering wheel unit

[0068] 3-1 electric machine

[0069] 3-2 Steering gear

[0070] 4 Communication link

[0071] 5 Rack and pinion

[0072] 6 steerable wheels

[0073] 7 Steering handle (steering wheel)

[0074] 8 Feedback moment

[0075] 9 Shear force signal

[0076] 10 Shear force

[0077] 11 Lateral acceleration signal

[0078] 12 Feedforward control

[0079] 13 T inertial compensation

[0080] 14 Elasticity compensation

[0081] 15 Friction compensation

[0082] 100-101 procedural steps

[0083] pric GD friction model

[0084] Gs(s) System (steering wheel unit)

[0085] M Hii Actual hand torque

[0086] MH, S Target manual torque

[0087] ^Mot,s Target engine torque

[0088] (PMot engine speed)

Claims

Patent claims 1. Steer-by-wire steering system (1), comprising: a steering unit (2), a steering wheel unit (3), and a communication link (4) that connects the steering unit (2) to the steering wheel unit (3) via signal technology, wherein the steering wheel unit (3) is configured to provide a feedback torque (8) to a steering handle (7) without a torque sensor, wherein the steer-by-wire steering system (1) is configured to determine the feedback torque (8) at least partially from a lateral force signal (9).

2. Steer-by-wire steering system (1) according to claim 1, characterized in that the steer-by-wire steering system (1) is configured to determine the feedback torque (8) exclusively from the lateral force signal (9).

3. Steer-by-wire steering system (1) according to one of the preceding claims, characterized in that the steer-by-wire steering system (1) is configured to determine the lateral force signal (9) starting from a lateral acceleration signal (11).

4. Steer-by-wire steering system (1) according to one of the preceding claims, characterized in that the steer-by-wire steering system (1) is configured to determine the lateral force signal (9) taking into account a vehicle model.

5. Steer-by-wire steering system (1) according to one of the preceding claims, characterized in that the steering wheel unit (3) is configured to set the feedback torque (8) at the steering handle (7) by means of a pilot control (12).

6. Steer-by-wire steering system (1) according to claim 5, characterized in that the feedforward control (12) is designed such that inertia compensation (13) and / or elasticity compensation (14) of mechanical components of the steering wheel unit (3) is performed.

7. Steer-by-wire steering system (1) according to claim 5 or 6, characterized in that the feedforward control (12) is designed such that friction compensation (15) of friction of mechanical components of the steering wheel unit (3) takes place.

8. Steer-by-wire steering system (1) according to one of the preceding claims, characterized in that the steer-by-wire steering system (1) is configured to determine a friction component determined by means of a predetermined friction model, wherein the steering wheel unit (3) is configured to impose the determined friction component on the feedback torque (8).

9. Steer-by-wire steering system (1) according to claim 8, characterized in that the predetermined friction model is parameterizable to generate a predetermined steering feel.

10. Method for operating a steer-by-wire steering system (1), wherein a feedback torque (8) is provided at a steering handle (7) without a torque sensor, wherein the feedback moment (8) is determined at least partially from a transverse force signal (9).

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