Method for performing a synchronization of steering handle position and wheel steering angle

Abstract

Method for performing a synchronization of a steering handle position and a wheel steering angle in a steer-by-wire steering system, wherein a synchronization torque is applied during the synchronization and, in the event of an intervention at the steering handle, this intervention is detected and, depending on the detected intervention, the synchronization torque is influenced in order to provide an I / E function.

Description

The invention relates to a method for carrying out a synchronization of a steering handle position and a wheel steering angle in a steer-by-wire steering system and to an arrangement for carrying out the method. The method simultaneously makes it possible to use the steering handle as a handle for getting in and out.Prior ArtSteering systems are used in motor vehicles for influencing the direction of travel by the driver. Steering systems are known in which a direct mechanical coupling between the wheels to be steered and the steering handle used by the driver, typically a steering wheel, is interrupted. Such steering systems are referred to as steer-by-wire steering systems. In these, the wheel steering angle is controlled electrically.In steer-by-wire steering systems, there are different coordinate systems. These include, among others, a steering wheel angle coordinate system, a rack position coordinate system, and a wheel steering angle coordinate system. The different coordinate systems can be converted into one another by conversion factors, in particular the steering ratio.The document DE 10 2020 206 435 A1 describes a method for influencing a movement of a steering handle of a steer-by-wire steering system in a vehicle. The steering system comprises at least one feedback actuator for generating a steering resistance and / or a restoring torque on the steering handle.In steer-by-wire steering systems, the functions for synchronizing during starting and for representing an ingress / egress (I / E) function are typically implemented separately. The functions are typically carried out sequentially. An I / E function is understood to mean a function which assists the driver in getting in and out (ingress / egress) by allowing the driver to be supported on the steering wheel.In known methods, the steering wheel is synchronized first and then "hardened" in such a way that the driver can hold on it and get in. This can also take place in the opposite direction. Whether the wheels of the vehicle are turning along during the execution of both functions or only the steering wheel is performing a movement can generally be switched to binary.Disclosure of the InventionAgainst this background, a method having the features of claim 1 and an arrangement according to claim 9 are presented. Embodiments will be apparent from the dependent claims and from the description.The presented method serves for carrying out a synchronization of a steering handle position of a steering handle and a wheel steering angle in a steer-by-wire steering system of a vehicle, in particular of a motor vehicle. During the synchronization, a synchronization torque is applied.In the method, an intervention on the steering handle is detected during the synchronization of the steering handle position and the wheel steering angle. In particular, the steering handle position and the strength and direction of action of the torque are detected. The synchronization torque is then influenced as a function of the detected intervention, in particular of the variables characterizing the intervention, such as the steering handle position, i.e. the magnitude of this synchronization torque is changed. This has the effect that the steering handle remains in position and the driver can support himself. If a steering wheel is used as the steering handle, a synchronization of the steering wheel angle and the wheel steering angle takes place and the torque, typically by a feedback actuator, has the effect that the steering wheel does not rotate, for example when being supported during getting in and out. The functions synchronization and ingress / egress can thus be carried out simultaneously, provided that a wheel movement is permitted for synchronization on account of the control boundary conditions. In addition to the synchronization by a wheel movement, the synchronization via the change in the steering handle position always takes place when the driver does not use the steering handle for getting in and out.In the following, in particular in conjunction with the figures, a steering wheel is used repeatedly as an example of a steering handle. This is only for illustrative purposes and does not represent a restriction to this embodiment of the steering handle. The presented method and the explained embodiments can also be used in a steer-by-wire steering system in which no steering wheel serves as a steering handle.It has thus been recognized that, in the discrete function implementation, the order of execution and the transition conditions for switching the functions should be individually determined and implemented. It should be noted that in known methods, after carrying out the Ingress / Egress function, the synchronization must be initiated again if the steering wheel has become asynchronous. This is not necessary in the presented method; both functions or modes are continuously active at the same time. The driver can intervene in the event as desired and permanently use the steering handle, such as the steering wheel, as a handle, even if the synchronization runs at this moment and, for example, the toothed rack moves. It should be noted that the method can also be used in steering systems that do not have a rack.In addition, in the method presented, it is possible to define continuously how strongly the steering wheel and the rack are allowed to move without having to make a binary OR decision. Furthermore, at any point in time during the starting up, reasonable setpoint values for the key position controller can be calculated. A deactivation of this regulator is not necessary. In particular, if the rack is to move during the synchronization, deactivation is not possible. In addition, the synchronization can be continued by a movement of the toothed rack, while the driver is held fast at the steering wheel, for example, when getting in.It is now provided to introduce a "virtual" steering wheel position which simultaneously serves as both a target value for the steering wheel movement and a target value for the movement of the toothed rack. The dynamics with which both components, namely steering wheel and toothed rack, seek the target value can be applied individually and continuously, see FIG. 3.In the presented method, for example, the intervention can be detected by evaluating a detected angle of rotation of the steering wheel.The synchronization is effected by applying a synchronization torque to the steering handle. This synchronization torque is typically low as long as it is synchronized and then rises automatically as soon as the driver is firmly held on the steering handle. It is important that the synchronization can be continued after the driver no longer holds fast, and it is thus not ended or dropped by the intervention of the driver, but rather is only interrupted if necessary.In order to realize the possibilities of simultaneously representing the synchronization function and I / E function, for example, the hand moment acting on the steering wheel is used as an indicator for whether a steering wheel rotation must be made for synchronization or the steering wheel is to be fixed so that it can be used as a handle.A typical application of the presented method is in starting up the vehicle when the synchronization is carried out and at the same time the driver gets on or off.The described arrangement has an evaluation device and is configured to carry out the method described herein. The arrangement and / or the evaluation unit can be implemented in hardware and / or software. Furthermore, the arrangement can be integrated in a control device of the vehicle or can be designed as such a control device.Overall, the presented method and the described arrangement result in an extremely comprehensible vehicle behavior and thus in a high customer acceptance for steer-by-wire steering systems.Further advantages and embodiments of the invention will become apparent from the description and the appended drawings.It is understood that the features mentioned above and those still to be explained below can be used not only in the respectively specified combination, but also in other combinations or alone, without departing from the scope of the present invention.Brief Description of the DrawingsFIG. 1 shows a schematic illustration of an embodiment of the presented arrangement for carrying out the described method. FIG. 2 shows a detail from FIG. 1. FIG. 3 shows a graph of the curve of combined fading parameters. FIG. 4 shows a purely schematic, greatly simplified illustration of a body of a vehicle. FIG. 5 shows a representation similar to FIG. 2. FIG. 6 is a graph together with a similar illustration to FIG. 2. FIG. 7 is a view similar to FIG. 6. FIG. 8 is a view similar to FIG. 6. FIG. 9 shows a purely schematic illustration of a vehicle.Embodiments of the InventionThe invention is schematically illustrated in the drawings on the basis of embodiments and is described in detail below with reference to the drawings.It is assumed below for the movement of the toothed rack that the latter is allowed to execute a movement independently of the hand moment. However, the generality of the presented method should not be restricted in this way. The idea of pauseing the synchronization movement via the hand moment can also be transferred to the toothed rack.In particular, the movement of the rack is realized by the setpoint specification from the manual force actuator and the movement of the steering wheel is realized by the exertion of a manual torque.In the following, the steering wheel angle coordinate system is considered in particular, without this being intended to represent a restriction. It should be taken into account that the method presented herein can also be presented with other coordinate systems and also with mixed forms of these systems.The term toothed rack is also used. However, this is not intended to limit the diversity of solutions. The method can also be used in steer-by-wire steering systems without a toothed rack, for example in single-wheel actuators or central actuators with ball screw drive.Also, the "hand moment" will be considered hereinafter. Instead, the motor torque of the manual force actuator may be used. In the field of application of the presented method, the hand moment due to a virtual spring behavior is proportional to or dependent on the spring deflection Δ Feder. For simplicity, this is also referred to herein as a "spring". Instead, a more complex element can also be simulated which brings about a return, for example a spring-damper element or the like. An advantage of a more complex element than a spring is the fact that the steering wheel movement is damped during the return and cannot oscillate.FIG. 1 shows a schematic overview of an embodiment of an arrangement for carrying out the method, which is denoted overall by the reference numeral 10. The illustration shows a real steering wheel 12, a virtual steering wheel 14, a rack 16 and a virtual spring 18. a first bracket 20 illustrates Δ real, a second bracket 22 illustrates Δ virtuell and a third bracket 24 illustrates Δ Feder. The steering wheel angle α is plotted on an axis 30. Also indicated are: αSr,soll32, αSr,ist34, α virtuell36 and α Lenkwinkel,ist38.The illustration furthermore shows an evaluation unit 40 in which state variables 42, for example. Δ virtuell22 and α virtuell36, are present. Δ Feder44 is output into the virtual spring 18. input variables into the evaluation unit 40 are, for example, αZahnstange,ist34and α Lenkrad,ist38. The output variables are the rack position request αSw,soll32 and the manual torque request T soll45.Possible embodiments relate to:During starting-upInitialization of the state variables, in this case the spring is relaxedduring I / E / Sync modeCalculation of Target Rack Position Via Virtual MisalignmentCalculation of Hand Message for Spring Return of Steering WheelWhen I / E / Sync mode is switched to "normal" driving modeStorage / Freezing of Real Residual Misalignment:Calculation of the Desired Rack Position From Immediately Via Real Residual MisalignmentFIG. 2 shows a section from FIG. 1. A first arrow 50 illustrates reaching the target position after release according to the I / E function. A second arrow 52 illustrates a synchronization via a movement of the toothed rack. A third arrow 54 illustrates a synchronization via a movement of the steering wheel.The illustration illustrates the handling or the procedure in the case of misalignment (misalignment). Possible steps are:- Synchronization movement via movement of the toothed rack:αZahnstange,is guided at a defined speed in the direction α virtuellsynchronizing motion through motion of the steering wheel:α virtuell is guided at a defined speed in the direction αZahnstange,iDeviation from α virtuell to α Lenkrad,ist results in spring force pulling the steering wheel to α virtuellI / E Holding Force via Stiff Spring Characteristic:The driver's intervention in the steering wheel shifts α Lenkrad,istDeviation from α virtuell to α Lenkrad,ist results in spring force that generates holding forceover-steering of the I / E holding force by drivers:Over-steering of I / E would result in too much / severe snap-back of the steering wheelTo avoid this, for example, virtuell is pulled after the spring α is over-deflected, but the misalignment is then also increasedFIG. 3 shows in a graph 100 on whose abscissa 102 a software parameter which can be used for the continuous fading between "complete synchronization movement by the steering wheel" and "complete synchronization movement by the toothed rack", and on whose abscissa 104 the speed is plotted, the profile of the speed of the steering wheel at the synchronization V Lenrad,Sync110 and the profile of the speed of the toothed rack at the synchronization V Zahnstange,Sync112. Value 0 means that only the steering wheel is allowed to move for synchronization, value 1 illustrates that only the rack is allowed to move for synchronization.For parameterizability of the speed of the steering wheel and rack movement, the following is carried out:Basic condition: movement of steering wheel and rack should be safe and must not lead to any danger. The parameter of the allowed speed is parameterized in such a way that a risk can be ruled out.Parameters for speed of rack movement: V Zahnstange,SyncParameters for speed of steering wheel movement: V Lenkrad,SyncThere are many possibilities for continuously activating both sync methods and for the yarn between the two, for example:Both types of movement are scaled by separate scaling parameters, so that each movement can be activated continuously, for example no rack movement at all during sync, only very small movements, large movements etc.Both types of movement are scaled by a fading parameter, so that one can continuously pass between pure movement of the toothed rack and pure movement of the steering wheel, see FIG. 3.FIG. 4 shows, in highly simplified form, the front part of a vehicle body 150 having a first articulated wheel 152 and a second articulated wheel 154. First arrows 160 indicate that there is a risk of jamming between the wheel and the wheel arch when steering to the left when the wheels are turned somewhat to the right, and second arrows 162 indicate that there is no risk of jamming when steering to the right when the wheels are already turned somewhat to the right. The parameters of the speeds can be adapted depending on various internal and external variables, e.g. depending on the Charisma mode, sport, normal, eco, ->, e.g. faster sync in sport mode, depending on the size of the misalignment Δ real- >, e.g. sync via rack movement only if misalignment is small, so that less tire abrasion, for the rack, depending on the current actual position and / or depending on the necessary direction of movement of the rack->, thereby reducing the risk potential of the wheel movement, see FIG. 4, depending on the level of the current hand moment / Δ Feder, thus allowing the driver to throttle the synchronization movement or even stop it completely, depending on the steering wheel speed, e.g. in order to couple the permitted rack speed to the steering wheel speed, depending on whether or not the height of the misalignment increases, e.g. following the rack, in order that misalignment does not increase.FIG. 5 shows a similar illustration to FIG. 2, arrow 52 illustrates the rack movement.A detailed sequence of synchronization is given via the rack movement:determining which rack speed is permitted in the current state, taking into account all scaling factors, fading factors and dependencies on internal and external variables,Δ virtuell is reduced toward zero according to the allowed speed if it is not already at zero,α virtuell remains fixed to the current value so that no movement of the steering wheel due to this mode occursαZahnstange,soll= α virtuell+ Δ virtuell leads to a rack movement in the direction α virtuellFIG. 6 shows on the right side a representation similar to FIG. 2, arrow 54 illustrates the movement of the steering wheel. On the left side, a graph 200 is shown, on whose abscissa 202 Δ Feder and on whose ordinate 204 the spring force is plotted. In one embodiment variant, a curve 210 shows the dependence of the spring force on the spring deflection for a simple linear spring. A first arrow 212 indicates that synchronization across the steering wheel is active when the current operating point is below a threshold, a second arrow 214 indicates that synchronization pauses across movement of the steering wheel because the current spring is biased due to the driver holding the steering wheel when the current operating point is above a threshold. A dashed line 215 illustrates this threshold value, which decides whether synchronization can be allowed via the steering wheel or should pause the synchronization because the driver is firmly held on the steering wheel.A detailed procedure is given below:determining which steering wheel speed is permitted in the current time step, taking into account all scaling factors, fading factors and dependencies on internal and external variablesΔ virtuell is reduced according to the allowed speed if it is not already zero. It should be noted that the reduction as a function of the manual torque / Δ Feder should be prevented, e.g. no synchronization via the steering wheel movement if the driver holds the steering wheel firmly and the spring is already pulled on up to a specific value.α virtuell- αZahnstange,target-Δ virtuell is recomputed so that by reducing Δ virtuell a rack movement is not also generated simultaneously → "100% compensation", intended steering wheel movement does not generate a rack movementFIG. 7 shows a representation similar to FIG. 6, and the graph 200 shows a double arrow 230 which illustrates how the hand torque varies depending on how strongly the driver is firmly holding.A detailed flow of the I / E using steering wheel as handle is given:By the driver deflecting the steering wheel, Δ Feder. increases.The stiffness of the spring characteristic curve is adapted such that the hand moment is sufficient to use the steering wheel as a handle.Upon release of the steering wheel, the spring ensures a return of the steering wheel to the position α virtuell. Additional measures, such as a spring damper system, can ensure a smooth and overshoot-free reset.In this embodiment, the rack movement does not follow the deflection of the steering wheel, for example to reduce tire wear, it is believed that the driver will release again and the steering wheel will move back. Therefore, the rack follows only the virtual position.FIG. 8 is a view similar to FIG. 7 ; a bracket 240 illustrates Δ Feder, max.A detailed procedure for an over-steering of the I / E function by the driver is given:An over-steering of the I / E function by the driver is usually technically possible on account of the fact that a feedback actuator can only apply a limited maximum force.Without further measures, this would lead to the spring greatly tensioning and the steering wheel snapping back far after releasing. As a rule, this behavior is undesirable and is prevented by the method presented herein.When the driver over-steering the I / E function, for example when Δ Feder= Δ Feder,max, is reached, α virtuell is dragged along until the spring deflection does not exceed the value Δ Feder,maxRecalculation Δ virtuell= αZahnstange,target- α virtuell, so that the rack does not shift by shifting α virtuell. The recalculation of Δ virtuell can be omitted if it is desired that the rack moves along immediately during the over-steering. This has the advantage that the misalignment is not enlarged by the over-steering of the I / E function.In summary, it remains to be stated that the presented method and the described arrangement lead to vehicle behavior that is very comprehensible to the driver and thus to a high customer acceptance, inter alia because the method and the arrangement offer many applicational degrees of freedom in order to optimally adapt the behavior of the steer-by-wire system to the customer's wishes.FIG. 8 shows a greatly simplified, purely schematic illustration of a vehicle which is provided overall with the reference numeral 300 and into which a steer-by-wire steering system 302 is used. In this steer-by-wire steering system 302, an evaluation unit 304, a manual torque controller 306 and a steering handle 308 are provided. The illustration also shows a wheel 310. A synchronization torque 316 is now applied within the framework of a synchronization of a steering handle position 312 and a wheel steering angle 314 and, in the case of an engagement at the steering handle 308, this synchronization torque 316 is influenced as a function of this engagement.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2020 206 435 A1

[0004]

Claims

Method for carrying out a synchronization of a steering handle position (312) of a steering handle (308) and a wheel steering angle (314) in a steer-by-wire steering system (302), in which a synchronization torque (316) is applied during the synchronization and, in the case of an intervention at the steering handle (308), this intervention is detected and the synchronization torque (316) is influenced as a function of the detected intervention.The method of claim 1 which is used to provide an I / E function.Method according to Claim 1 or 2, in which a steering wheel (12) is used as the steering handle (308), and in which method a steering wheel angle and the wheel steering angle (314) are synchronized.Method according to Claim 3, in which the intervention is detected by evaluating a detected angle of rotation of the steering wheel (12).Method according to one of Claims 1 to 4, in which the intervention is detected by evaluating a signal of a hand torque actuator (306).Method according to one of Claims 1 to 5, in which the synchronization is effected by applying a synchronization torque (316) to the steering handle (308), the synchronization torque (316) being superimposed with further torques of the manual torque controller (308).Method according to one of Claims 1 to 6, in which the synchronization takes place by changing the setpoint commands of the wheel steering angle (314).Method according to one of Claims 1 to 7, in which the synchronization is carried out when the vehicle (300) is started up or shut down.Arrangement for carrying out synchronization of a steering handle position (312) of a steering handle (308) and a wheel steering angle (314) in a steer-by-wire steering system (302), having an evaluation unit (40, 304) which is configured for carrying out a method according to one of Claims 1 to 8.The arrangement of claim 9, configured to perform synchronization of a steering wheel angle and the wheel steering angle (314).

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