WHEEL STEERING CACTUATOR CONTROL UNIT, METHOD FOR OPERATING A STEER-BY-WIRE STEERING SYSTEM IN A MOTOR VEHICLE, STEER-BY-WIRE STEERING SYSTEM AND MOTOR VEHICLE

Description

[0001] Steer-by-wire systems are becoming increasingly popular in motor vehicles due to various automated driving applications. Generally, steer-by-wire systems comprise a wheel actuator (hereinafter also referred to as RWA), which is responsible for controlling a steered wheel. The RWA's control can be based on a reference signal, in which case a feedback actuator (hereinafter also referred to as FBA) is present, which is responsible for providing steering assistance and generating the reference signal for the RWA based on the steering wheel angle.

[0002] Corresponding controllers or position controllers are also found in electronic power steering systems or electric power assisted steering systems (EPAS) as part of various and selective assistance functions, for example, for parking and highway driving. However, the general requirements for reference tracking are stricter in steer-by-wire systems, since the reference signal can originate directly from the driver's side, such as through steering input, and all possible scenarios must be covered, ranging from parking and smooth, slow driving to highway driving, evasive maneuvers, high-load cornering, drifting, etc. This means that in steer-by-wire systems, the corresponding actuator controls for the steered road wheel require a significantly larger operating range.

[0003] The operation of the RWA (Rail-Waver Exhaust System) is known to utilize feedback control loops to ensure that the driver's steering input and steering behavior are reliably translated into a steering angle of the steered wheel(s).

[0004] From US 11,167,789 B2 and US 11,485,406 B2, controllers for RWA (Rail-Wave-Aid) systems are known that include control of the position of a rack whose position is proportional to the steering angle of the wheels. The position control is based on input commands measured at or determined from the steering wheel and is based on a model, i.e., a mathematical model, of the steering system. US 11,167,789 B2 discloses the preamble of the independent claims.

[0005] From US 2020 / 283058 A1, a controller is known which includes a feedback control loop with forward control, whereby this controller is based on a model that also takes into account the road condition, i.e. external components and influences, in the forward control.

[0006] However, existing controllers for smoke and heat exhaust ventilation (SHEV) systems still require improvement, particularly regarding dynamics, accuracy, and the operating range covered by the controller. With SHEV systems in steer-by-wire configurations, it has been observed that performance limitations can occur due to system dimensions and various other system characteristics such as resonant frequencies. Although existing control units or controllers can generally be tuned for very high performance, a need has arisen for even higher performance levels in order to fully exploit the advantages of steer-by-wire systems.

[0007] Based on this, an object of the invention is to provide an improved controller and improved methods for controlling a smoke and heat exhaust ventilation system (SHEVS). In particular, a wheel steering actuator controller unit, a method for operating a steer-by-wire steering system in a motor vehicle, a steer-by-wire steering system, and a motor vehicle with a steer-by-wire steering system are to be provided, all of which exhibit improved properties with regard to the control of the SHEVS.

[0008] This task is solved by the features of the respective independent claims. Further details arise from the respective dependent claims and the following description.

[0009] According to the findings underlying the invention and based on general requirements, the behavior of the "wheel drive" subsystem or a wheel steering actuator (RWA) of a steer-by-wire steering system of a motor vehicle is a relevant aspect of driving safety from the perspective of vehicle motion. The gain stability and phase delay characteristics of the system depend on the control scheme used, but are generally subject to limitations. For example, with known controllers, it is possible that, with a given system configuration, the controller for the RWA can no longer be set to achieve a stable (nearly uniform) gain and simultaneously a low phase delay from a certain operating point onwards. However, in order to achieve the desired motion characteristics of the vehicle, such as...Yaw rate amplification via the steering wheel angle requires both very stable amplification and a very low phase delay of, for example, at least 3 to 5 Hz. Such advantageous properties can be achieved with the underlying invention.

[0010] According to the underlying invention, the control loop of the wheel steering actuator is extended by a forward control to achieve stable gain and improved phase characteristics. This forward control is advantageously extended with a suitable filter to eliminate zero-pole divergences of an associated transfer function.

[0011] In particular, according to one embodiment, a wheel steering actuator control unit, or a control unit for a wheel steering actuator, is provided for controlling a wheel steering actuator system of a steer-by-wire steering system of a motor vehicle. The wheel steering actuator control unit comprises a feedback control loop, which represents the wheel steering actuator system by a mathematical model and is described by an associated first transfer function. The wheel steering actuator control unit further comprises a feedforward control (loop shaping feedforward) for the feedback control loop. The feedforward control is described by, or based on, a second transfer function. According to the invention, the second transfer function is based on a reciprocal transfer function formed by inverting the first transfer function, or an inverse of the first transfer function.

[0012] With such a controller unit featuring the aforementioned forward control, it is possible to achieve a more precise (stable amplification, or stable gain) and simultaneously faster (reduced phase delay) response of the system. According to the invention, this makes it particularly possible to compensate for the system's resonant frequency and damping coefficient, since the controller already "knows" these values ​​due to the proposed second transfer function being the inverse of the first transfer function.

[0013] In one embodiment, the mathematical model is a second-order or higher-order model. Such models are particularly suitable for the proposed control system with forward control based on the reciprocal transfer function.

[0014] In one embodiment, the second transfer function corresponds to a filter-extended reciprocal transfer function of the first transfer function. This means that, given a first transfer function (e.g., T1), the second transfer function (e.g., T2) corresponds to the filter-extended reciprocal or inverse transfer function of the first transfer function (e.g., T2 = F x T1 - 1). The filter is designed to correct zero-pole divergences in the inverse. With the proposed second transfer function, stable control of the smoke and heat exhaust ventilation (SHEV) system is possible.

[0015] According to one embodiment, the filter can be a low-pass filter.

[0016] According to the embodiments, a method for operating a steer-by-wire steering system in a motor vehicle is provided, wherein the steer-by-wire steering system includes a wheel steering actuator system. In this method, the wheel steering actuator system is controlled and / or regulated by a feedback control loop, which is preceded by a forward control function. The feedback control loop represents the wheel steering actuator system by a mathematical model and is described by an associated first transfer function. The forward control function is described by a second transfer function. According to the method, the second transfer function is derived from a reciprocal transfer function formed by inverting the first transfer function.

[0017] Following a procedural design, a second-order or higher-order model is used for the mathematical model.

[0018] According to a specific design, the second transfer function is formed by a filter-extended reciprocal transfer function of the first transfer function, in particular by a filter-extended inverse of the first transfer function. The use of the extended reciprocal transfer function enables, in particular, high system stability with stable gain and good phase characteristics. Reference is made to the above explanations in this regard.

[0019] In a procedurally appropriate design, a low-pass filter is used as the filter.

[0020] According to a procedural design, the filter eliminates or at least corrects zero-pole divergences of the reciprocal transfer function.

[0021] Corresponding to the descriptions of the wheel steering actuator control unit, the mathematical model in this method can be a second-order or higher-order model, and the second transfer function can be formed by a filter-augmented reciprocal transfer function of the first transfer function. This filter is configured to correct zero-pole divergences of the reciprocal transfer function, i.e., to correct, eliminate, or remove zeros and poles of the reciprocal transfer function, at least within the respective operating range of the wheel steering actuator system. A stable control unit with advantageous system performance (gain, phase) can be ensured by maintaining a balance between the number of zeros and poles. For example, a low-pass filter can be used as the filter.

[0022] Zeros in the transfer function, as commonly understood, refer to values ​​for which the transfer function becomes zero. Poles in the transfer function, as commonly understood, refer to values ​​for which the transfer function becomes infinite. Zeros and poles are known to influence the dynamics, oscillation behavior, and thus the stability of the control system.

[0023] If the number of zeros does not correspond to the number of poles of the transfer function, such a divergence, also called "mismatch", can lead to instability or poor system response.

[0024] Stable gain is particularly important in steer-by-wire systems to ensure precise control of the smoke and heat exhaust ventilation (SHEV) system in relation to steering movements, and especially to avoid unwanted oscillations or instabilities. Good phase characteristics are also crucial in steer-by-wire systems, as the phase characteristics of a transfer function are a decisive factor for the responsiveness, i.e., the dynamics, of the wheel steering actuator system.

[0025] The proposed method can improve the gain and phase characteristics of a feedback control loop of a controller unit for controlling a wheel steering actuator system of a steer-by-wire steering system of a motor vehicle.

[0026] For the advantages and beneficial effects of the method, reference is made to the above explanations. In particular, the proposed second transfer function makes it possible to appropriately compensate for the system's damping factor using the feedback control loop and the associated controller(s). This is because, by using the inverse, the aforementioned parameters—resonance frequency and damping factor—which are represented in the mathematical model from which the first transfer function is derived, can be taken into account in the overall model. Specifically, this allows the system to operate more accurately, with stable gain, and simultaneously faster, with reduced phase delay.

[0027] According to a further embodiment, a steer-by-wire steering system for a motor vehicle is provided. The steer-by-wire steering system comprises a wheel steering actuator system and, furthermore, a wheel steering actuator control unit according to one of the embodiments of the invention described herein, or a wheel steering actuator control unit that is configured or programmed such that it effected a method according to an embodiment of the invention described herein during operation. Advantages and beneficial effects become particularly apparent from the descriptions of the wheel steering actuator control unit and the method, respectively, and reference is made to the above descriptions in this respect.

[0028] According to the embodiments, a motor vehicle is provided which has a steer-by-wire steering system comprising a user-operated steering unit and a wheel steering actuator system coupled to at least one steered wheel, with at least one wheel steering actuator, and furthermore a wheel steering actuator control unit according to one of the described embodiments of the invention. The wheel steering actuator control unit is coupled to the wheel steering actuator for the purpose of controlling the wheel steering actuator and implementing a steering position of the steered wheel based on an electrical signal generated by the steering unit. Advantages and beneficial effects will follow from the descriptions of the wheel steering actuator control unit and the above descriptions.

[0029] In some configurations, a controller and plant model, i.e., a feedback control loop of the wheel actuator or wheel steering actuator, can be modeled as a second- or higher-order system with a transfer function, where the model parameters are determined from measurement data. The model can then be inverted (reciprocal transfer function) and augmented with a suitable filter (extended reciprocal transfer function) to compensate for zero-pole divergences. This inverted and filtered model, i.e., the extended reciprocal transfer function, forms a feedforward component for the feedback control loop.

[0030] In particular, a feedback control loop can be represented as a closed-loop control system by a model of a second-order transfer function. The model can include inertia terms, damping coefficients, and other disturbances such as friction and load. The feedforward component can be formed from the inverted model of the control loop connected in series with a filter. The filter is configured to preserve the properness of the overall transfer function, meaning the denominator has at least the same order as the numerator of the transfer function.

[0031] Exemplary embodiments of the invention will now be described in more detail with reference to the attached figures. These show FIG. 1 schematically a steer-by-wire steering system for a motor vehicle; FIG. 2 schematically a wheel steering actuator control unit for a steer-by-wire steering system; FIG. 3 schematically an exemplary feedback control loop with forward control; and FIG. 4 exemplary Bode diagrams for a wheel steering actuator control unit according to the invention.

[0032] FIG. 1 Figure 1 schematically shows a steer-by-wire steering system 1 for a (not shown) motor vehicle. The steer-by-wire steering system 1 comprises a steering wheel 2 and an associated steering shaft 3 as the steering unit. The steer-by-wire steering system 1 further comprises a wheel steering actuator control unit 4 (hereinafter also referred to as the control unit) for the wired ("steer-by-wire") control and regulation of a wheel steering actuator system 5 for controlling the steering angle of a steered wheel 6, in particular as a function of a steering wheel angle of the steering wheel 2.

[0033] The steer-by-wire steering system 1 further includes a feedback actuator 7, which is typically used, for example, to generate forces or resistance at the steering wheel 2 to provide the driver with a haptic feel for road conditions, road surface irregularities, and / or vehicle dynamics, similar to a steering system where the steering wheel is mechanically connected to the steered wheels. The feedback actuator 7 can help improve vehicle and steering stability by responding to certain driving conditions and, for example, providing steering assistance or corrections. A feedback actuator is also referred to as a feedback actuator.

[0034] The feedback controller 7 forms a subunit of the control system or controller unit 4 for the steer-by-wire steering system 1. It can be configured to take into account feedback from sensors that measure, for example, the steering angle, a rotation angle, a rotational speed and / or a torque of a wheel steering actuator and other relevant parameters, in order to enable precise steering control. In addition to the parameters mentioned, the steering wheel angle or steering input is also a relevant system parameter for controlling the steering behavior.

[0035] The wheel steering actuator system 5 can, as shown, for example, comprise an electric motor 8 connected via a gearbox 9 to a rack 10, the rack being used to adjust the respective steering angle of the steered wheels 6 based on signals from the controller unit 4. Other wheel steering actuator systems based on different mechanical transmission methods are also possible.

[0036] FIG. 2Figure 1 schematically and exemplarily shows a simplified model of a wheel steering actuator control unit 4 for the steer-by-wire steering system 1. The control unit 4 comprises a feedback control loop 11 with a forward control 12, wherein the feedback control loop 11 in this case includes a controller 13, which is coupled to the wheel steering actuator system (RWA) 5. Input data or reference values ​​for the forward control 12 are designated by reference numeral 14 and can, for example, include reference data for the position of the rack 10. It should be noted that the position of the rack, or a value derived from it, is characteristic of the respective steering angle of the steered wheel 6. Additional input data, generated, for example, by the feedback controller, can be provided to the forward control 12 and the feedback control loop 11.

[0037] FIG. 3 Figure 11 shows schematically, and in a simplified form, an exemplary feedback control loop 11 with forward control 12, where input data or reference values ​​for the forward control 12 are designated by the reference symbol 14.

[0038] The feedback control loop 11, or controller 13, models the wheel steering actuator system 5 using a mathematical model and is described by an associated first transfer function T1. The forward control 12 is described by a second transfer function T2, which is the inverse of the first transfer function T1, i.e., a reciprocal transfer function. This means that T2 = inv(T1) or T2 = T1 - 1. Reference numeral 15 denotes a measuring unit configured to measure or record corresponding output values ​​or steering parameters provided by the controller unit 11.

[0039] The mathematical model in the example shown is a second-order model. Furthermore, the forward control 11 is based on the reciprocal transfer function TE = F x T2 = F x T1 - 1<, extended by a low-pass filter F. The filter F is designed to correct zero-pole divergences of the reciprocal transfer function T2 = T1 - 1<.

[0040] For example, the first transfer function is given by: T 1 = 1 0.00005 s 2 + 0.004 s + 1 , The second transfer function T2, or reciprocal transfer function T2 = T1 - 1<, is given by: T 2 = T 1 − 1 = 0.00005 s 2 + 0.004 s + 1 .

[0041] When using a filter F of the form: F = 0.0000015 s 2 + 0.0012 s + 1 − 1 , The extended reciprocal transfer function TE is then given by: TE = F × T 2 = 0.00005 s 2 + 0.004 s + 1 0.0000015 s 2 + 0.0012 s + 1 .

[0042] It is understood that the aforementioned transfer functions (T1, T2) and filters (F) are only examples. Other transfer functions and filters are also suitable for the purposes of the solution according to the invention.

[0043] The use of a suitable control unit 4 enables particularly efficient and precise control of the wheel steering actuator system, especially with stable gain and good phase characteristics.

[0044] FIG. 4 This shows exemplary Bode plots for a wheel steering actuator control unit according to the invention. The upper plot of the FIG. 4 This corresponds to a Bode plot, in which the amplitude or magnitude (e.g., rad / rad) of the transfer function is plotted against the frequency (f in Hz). The lower diagram of the FIG. 4 This corresponds to a Bode plot, in which the phase of the transfer function is plotted against the frequency (f / Hz).

[0045] In the diagrams, curves K1, K2 and K3 each correspond to the amplitude or phase plotted against the frequency (f[Hz]) of (i) the associated RWA model (curve K1), (ii) the forward control (curve K2) and (iii) the RWA model with forward control (curve K3).

[0046] As can be seen from the diagrams, advantageous controller characteristics with respect to amplitude (and thus gain) and phase (and thus speed) are observed in the range above 3 Hz. This is particularly evident from the approximately constant shape of curve K3 in the depicted frequency range of approximately 0 to 30 Hz. Particularly advantageous control characteristics can be achieved in the frequency range of up to 5 to 8 Hz. The range of up to 5 to 8 Hz is of particular relevance because it corresponds to a frequency range in which a driver can actually perform, or typically does perform, active steering movements. The improvement in the dynamic behavior of the control system according to the invention can therefore be directly implemented in the vehicle's motion characteristics.

[0047] This makes it clear that the proposed control system based on an inverse of the transfer function of the underlying RWA model, in which the inverse of the transfer function is preferably extended by a filter for correcting zero-pole divergences, provides advantageous properties with regard to stable gain and phase properties. Reference sign

[0048] 1 Steer-by-wire steering system 2 Steering wheel 3 Steering shaft 4 Wheel steering actuator control unit 5 Wheel steering actuator system 6 Steered wheel 7 Feedback actuator 8 Electric motor 9 Gearbox 10 Rack and pinion 11 Feedback control loop 12 Forward control 13 Controller 14 Input data, reference value 15 Measuring unit T1 first transfer function T2 second transfer function T1 -1< inverse of the first transfer function TE extended reciprocal transfer function F filter K1 to K3 curves

Claims

1. Wheel steering actuator control unit (4) for controlling a wheel steering actuator system (5) of a steer-by-wire steering system (1) of a motor vehicle, wherein the wheel steering actuator control unit (4) comprises a feedback control loop (11) which maps the wheel steering actuator system (5) by means of a mathematical model and is described by an associated first transfer function (T1), characterized in that the wheel steering actuator control unit (4) further comprises a feedforward control (12) for the feedback control loop (11), which is described by a second transfer function (T2), wherein the second transfer function (T2) is based on a reciprocal transfer function (T1-1) formed by inverting the first transfer function (T1).

2. Wheel steering actuator control unit (4) according to claim 1, wherein the mathematical model is a second-order or higher-order model.

3. Wheel steering actuator control unit (4) according to one of the preceding claims, wherein the second transfer function (T2) corresponds to a reciprocal transfer function (TE) of the first transfer function (T1) extended by a filter (F), wherein the filter (F) is designed to correct zero-pole divergences.

4. Wheel steering actuator control unit (4) according to claim 3, wherein the filter (F) is a low-pass filter.

5. Method for operating a steer-by-wire steering system (1) in a motor vehicle, wherein the steer-by-wire steering system has a wheel steering actuator system (5), wherein the method comprises regulating and / or controlling the wheel steering actuator system (5) based on a feedback control loop (11) and a feedforward control (12) connected upstream of the feedback control loop (11), characterized in that the feedback control loop (11) maps the wheel steering actuator system (5) by means of a mathematical model and is described by an associated first transfer function (T1), the feedforward control is described by a second transfer function (T2), and the second transfer function (T2) is formed from a reciprocal transfer function (T1-1) formed by inverting the first transfer function (T1).

6. Method according to claim 5, wherein a second-order or higher-order model is used for the mathematical model.

7. Method according to one of claims 5 or 6, wherein the second transfer function (T2) is formed by a reciprocal transfer function (TE) of the first transfer function (T1) extended by a filter (F).

8. Method according to claim 7, wherein a low-pass filter is used as the filter (F).

9. Method according to claim 7 or 8, wherein zero-pole divergences of the reciprocal transfer function (T1-1) are eliminated or at least corrected by the filter (F).

10. Steer-by-wire steering system (1) comprising a wheel steering actuator system (5) and further comprising - a wheel steering actuator control unit (4) according to one of claims 1 to 4, or - a wheel steering actuator control unit (4) which is set up or programmed in such a way that, during operation, it causes a method according to one of claims 5 to 9 to be performed.

11. Motor vehicle comprising a steer-by-wire steering system (1) with a steering unit operable by the user and with a wheel steering actuator system (5) coupled to at least one steered wheel (6), which has at least one wheel steering actuator, and further comprising a wheel steering actuator control unit (4) according to one of claims 1 to 4, wherein the wheel steering actuator control unit (4) is coupled to the wheel steering actuator for control purposes for the purpose of controlling the wheel steering actuator (4) and implementing a steering position of a steered wheel (6) based on an electrical signal generated by the steering unit.