Securing the steering wheel in steer-by-wire systems

Abstract

Steer-by-wire steering system (40), comprising: a handwheel; and a handwheel actuator (10) configured to secure a position of the handwheel, the securing comprising that: a transition of the steer-by-wire steering system (40) into an entry / exit operating mode is determined (605); and based on the determination that the steer-by-wire steering system (40) is in entry / exit mode (610): a holding torque command is calculated based on a difference between a current angle of the handwheel and a target angle of the handwheel caused by an input torque (615); and A holding torque is generated in accordance with the holding torque command in order to secure the position of the handwheel (620).

Description

[0001] The present invention relates to a steer-by-wire steering system, a method for securing a position of a handwheel of a steer-by-wire steering system, and a computer program product for carrying out such a method.

[0002] An electric power steering system (EPS system) typically includes components such as a steering wheel, steering column, rack and pinion gear, electric motor actuator, etc. The EPS assists the driver in steering a vehicle by providing necessary torque assistance. This assistance torque is based on the torque applied by the driver. In steady-state conditions, the driver's torque and the assistance torque counteract the rack and pinion force generated by the interaction between the tires and the road.

[0003] A typical steer-by-wire (SbW) system comprises a road wheel actuator unit (RWA unit) and a handwheel actuator unit (or steering wheel actuator unit) (HWA unit). Unlike an EPS, the two units in an SbW system are mechanically separate (no mechanical connection) and communicate via a Controlled Area Network (CAN) interface (or other similar digital communication protocols). The HWA unit receives a rack force signal from the RWA unit to generate a suitable torque feel for the driver. Alternatively, the handwheel angle and vehicle speed can also be used to generate a desired torque feel for the driver. The angle signal from the HWA unit is sent to the RWA unit, which performs position control to regulate the rack travel.

[0004] German patent application DE 10 2019 207 792 A1 discloses a steering control device and a method for controlling a steer-by-wire system. The steer-by-wire system has a reaction force motor that generates a steering reaction force against the steering force exerted by a driver on a steering wheel in order to provide the driver with an appropriate steering feel.

[0005] German patent DE 10 2014 016 017 A1 discloses a steer-by-wire steering system for a two-track vehicle with a steering wheel lock. When the vehicle is switched off, i.e., when the engine is detected to have switched off, a signal generation unit generates a steering wheel lock signal, so that the steering wheel rotation is inhibited or completely blocked by building up an inductive counter-torque.

[0006] The invention is based on the objective of providing a technology that secures a handwheel during a user's entry / exit from a vehicle and enables comfortable entry and exit for the user.

[0007] The problem is solved by a steer-by-wire steering system with the features of claim 1, by a method with the features of claim 8, and by a computer program product with the features of claim 15.

[0008] According to one or more embodiments, a steer-by-wire steering system comprises a handwheel and a handwheel actuator configured to secure the handwheel's position. The security mechanism includes detecting when the steer-by-wire steering system enters an entry / exit operating mode. The security mechanism further includes calculating a holding torque command based on the difference between the handwheel's current angle and a target angle, caused by an input torque, based on the detection of this transition. The security mechanism further includes generating a holding torque in accordance with the holding torque command to secure the handwheel's position.

[0009] According to one or more embodiments, a method for securing the position of a handwheel in a steer-by-wire steering system comprises detecting when the steer-by-wire steering system has entered an entry / exit operating mode. The method further comprises calculating a holding torque command based on the difference between the actual angle of the handwheel and a target angle of the handwheel, caused by an input torque, based on the detection of this transition. The method further comprises generating a holding torque in accordance with the holding torque command to secure the position of the handwheel.

[0010] According to one or more embodiments, a computer program product comprises a memory device containing computer-executable instructions stored therein, wherein, when executed by a processor, the computer-executable instructions cause the processor to perform a method for securing the position of a handwheel of a steer-by-wire steering system. The method includes detecting a transition of the steer-by-wire steering system into an entry / exit operating mode. The method further includes calculating, based on the detection that the steer-by-wire steering system is in the entry / exit operating mode, a holding torque command based on a difference between a current angle of the handwheel and a target angle of the handwheel caused by an input torque.Furthermore, the procedure includes generating a holding torque in accordance with the holding torque command in order to secure the position of the handwheel.

[0011] These and other advantages and features will become apparent from the following description in conjunction with the drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is an exemplary embodiment of a steer-by-wire steering system according to one or more embodiments; Fig. Figure 2 shows a block diagram for the operation of the SbW system in entry / exit mode according to one or more embodiments; Fig. Figure 3 shows a comparison between scenarios with and without entry / exit operating mode according to one or more embodiments; Fig. Figure 4 shows a slow return to a target angle at a constant speed, which is achieved in the entry / exit operating mode, according to one or more embodiments; Fig. Figure 5 shows a graph illustrating that the rack position is not changed in the entry / exit operating mode, according to one or more embodiments; and Fig. Figure 6 shows a flowchart of an exemplary procedure for securing a steering wheel of an SbW system according to one or more embodiments. DETAILED DESCRIPTION

[0012] The subject matter considered to be the invention is made particularly clear and unambiguously claimed in the claims at the end of the description. The foregoing and other features and advantages of the invention will become readily apparent from the following detailed description in conjunction with the accompanying drawings.

[0013] As used herein, the terms module and submodule refer to one or more processing circuits, such as an application-specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or grouped), and memory that execute one or more software or firmware programs, a combinational logic circuit, and / or other suitable components that provide the described functionality. As can be seen, the submodules described below can be combined and / or further subdivided.

[0014] The present application relates generally to steering systems and describes in particular one or more techniques for securing a steering wheel or handwheel using actuators in steer-by-wire steering systems. The technical solutions described herein operate without relying on the mechanical connections typically used in steering systems to connect the handwheel to the rack. For example, in an electric power steering system (EPS system), the steering wheel in the driver's hand is mechanically connected to the steering column, the steering column is mechanically connected to the rack (via intermediate shafts and universal joints), and the rack is mechanically connected to the road wheels.

[0015] The steering system assists the driver in steering a vehicle by providing necessary torque assistance. A modern steering system typically includes components such as a steering wheel, steering column, rack and pinion gear, electric motor actuator, etc. The assistance torque is based on the torque applied by the driver. In steady-state conditions, the driver's torque and the assistance torque counteract the rack and pinion force generated by the interaction between the tires and the road.

[0016] Now, referring to the figures, with reference to which the invention is described in relation to specific embodiments without limiting them, it is in Fig. Figure 1 shows a steer-by-wire steering system (SbW system) 40 in a vehicle 100. It should be noted that the SbW system 40 shown and described can be used in an autonomous or semi-autonomous vehicle or in a more conventional vehicle. The SbW system 40 comprises a handwheel actuator (HWA) 10 and a roadwheel actuator (RWA) 20.

[0017] The HWA 10 comprises one or more mechanical components 12, such as a handwheel (steering wheel), a steering column, and a motor / inverter, which is attached to the steering column either via a gear mechanism or a direct drive system. The HWA 10 also comprises a microcontroller 14, hereinafter also referred to as the HWA controller or PID controller, which controls the operation of the mechanical components 12. The microcontroller 14 receives and / or generates torque via the one or more mechanical components 12.

[0018] The RWA comprises one or more mechanical components 24, such as a steering rack and / or a pinion gear, which are coupled to a motor / inverter by a ball nut / ball screw (gearbox) assembly, and the rack is connected to the vehicle's road wheels / tires by tie rods. The RWA 20 includes a microcontroller 22 that controls the operation of the mechanical components 24. The microcontroller 22 receives and / or generates torque via the one or more mechanical components 24.

[0019] Microcontrollers 14 and 22 are coupled by electrical connections that enable the transmission and reception of signals. For the purposes of this document, a controller may comprise a combination of HWA controller 14 and RWA controller 22, or any of the specific microcontrollers.

[0020] In one or more examples, the controllers 14 and 22 of the SbW system 40 communicate with each other via a CAN interface (or other similar digital communication protocols). Steering of the vehicle 100, equipped with the SbW system 40, is accomplished using the steering gear with an input shaft rotated by the RWA 20, for example, a servo actuator. The RWA 20 receives an electronic communication signal indicating a rotation of the steering wheel by the driver. The driver controls the steering wheel to steer the vehicle 100. The angle from the HWA 10 is sent to the RWA 20, which performs position control to regulate the travel of the rack and pinion for steering the road wheel.However, due to the lack of a mechanical connection between the steering wheel and the road wheels, the driver is not provided with any feeling for the road without torque feedback (unlike in the case of EPS, as described above).

[0021] In one or more examples, the HWA 10, which is coupled to the steering column and steering wheel, simulates a driver's feel for the road. The HWA 10 can apply tactile feedback in the form of torque to the steering wheel. The HWA 10 receives a rack and pinion force signal from the RWA 20 to generate a suitable torque sensation for the driver. Alternatively, the handwheel angle and vehicle speed can also be used to generate the desired torque sensation for the driver.

[0022] The case considered is one in which a user, such as the driver, opens a vehicle door and enters the vehicle, touching the steering wheel either intentionally or unintentionally before starting the engine. In this scenario, with a steering system using mechanical linkages, the clutch is engaged, allowing the driver to feel the rack load on the steering wheel due to the mechanical connection between the steering column and the rack. The rack load transmitted through the steering wheel can also prevent the steering wheel from turning if the user unintentionally applies torque to it. However, without mechanical linkages like the clutch and intermediate shaft, and especially when the vehicle is off, the user does not experience such rack load in the case of the SbW system.

[0023] The technical solutions described herein address such technical challenges and provide a technique for securing the handwheel in the case of SbW systems 40. The securing mechanism enables the SbW system 40, under certain conditions (e.g., the machine is off, the vehicle speed is 0 km / h, and a user intends to enter / exit the vehicle 100 using the handwheel for assistance), to essentially maintain the handwheel angle at a predetermined angle, so that the handwheel can provide some assistance to the user or deflect unintentional torque from the user.

[0024] In this scenario, the HWA 10 must hold the handwheel at the predetermined angle and secure this position. It should be noted that this differs from typical operation of the SbW system 40, where the HWA 10 provides the desired steering feel to the user when the handwheel is moved. This particular operating mode can be described as an entry / exit mode, in which the user attempts to use the handwheel to enter / exit the vehicle 100. Specifically, "entry" refers to the time between opening the vehicle door and the user starting the machine (or whenever the vehicle is ready to drive), and "exit" refers to the time between the user switching off the machine (or whenever the vehicle is not ready to drive) and leaving the vehicle 100.

[0025] When the vehicle door is open, particularly the door on the steering wheel side, the vehicle speed is 0 km / h, and the engine is off, the HWA 10 switches to entry mode. When the driver starts the ignition, a corresponding signal is received by the SbW system 40. For example, in the case of an electric or hybrid vehicle, a battery on / off signal or any other type of signal indicating engine ignition can be received by the SbW system 40. Upon receiving such a signal, the HWA 10 switches from entry / exit mode to SbW mode, in which the SbW system 40 operates to provide a steering feel according to the rack position, as described previously.

[0026] When the user switches off the ignition, the HWA 10 enters exit mode. In this case, the SbW system 40 receives a signal indicating that the machine is being switched off. The SbW system 40 also receives a signal indicating that the user is exiting the vehicle 100, such as a signal indicating that the vehicle door is being locked. Upon receiving such a signal, the HWA 10 and the RWA 20 are switched off, and the SbW system 40 is effectively deactivated.

[0027] Fig. Figure 2 shows a block diagram for the operation of the SbW system in entry / exit mode according to one or more embodiments. In entry / exit mode, the HWA 10 provides a motor torque command so that the handwheel angle can be maintained at the predetermined angle, even if the user applies various disturbance torques. The technical challenge is shown as an angle control problem, where r is a target steering column angle, y is the actual steering column angle, d is the torque applied to the steering wheel by the user, u is the motor torque command generated by the HWA 10, C is the controller 14, and P is an operating model 210 of the steering column dynamics system.

[0028] Controller 14 is designed to provide a non-linear response, thus supplying maximum motor torque for locking the steering wheel and slowing down the transient response of free movement. The angular error between the target steering column angle and the measured steering column angle is considered to be e = r - y. A saturation function (sat()) is used by Controller 14, where: sat(x)=x if −a<=x<=a; sat(x)=a if x>a; and sat(x) = -a if x < -a, where a > 0 and a is a predetermined saturation limit.

[0029] Furthermore, the controller 14 uses a time derivative function (dot()) such that dot(x) is the time derivative of x. The controller 14 also applies a filter (fil()) to the input signal, which can be a low-pass filter or an anti-notch filter. Using the above functions, the controller 14 operates non-linearly and as a proportional controller with saturation plus an attenuation controller, where: u=at(Kp*e)−fil(dot(y)*Kd) where Kp is the coefficient of the proportional controller and Kd is the coefficient in the damping controller.

[0030] The filter `fil()` in the damping controller ensures the stability of the control system. Due to the different dynamic behavior of the steering column design, a low-pass filter is used for a steering column EPS, and an anti-notch filter is used for a concentric motor with a torque rod. The saturation `sat()` in the proportional controller determines a (slow) transient response at a constant speed, where the target speed (v) in the transient response is determined by: v=a / Kd

[0031] When a user turns the handwheel away from the target angle and releases it, the driver torque is 0. In this case, system friction is small, or approximately 0. The net torque at the steering column is the sum of driver torque, engine torque, and system friction. If dot(y) = v, it can be seen from equations (1) and (2) that u is essentially 0. Therefore, the net torque is essentially 0, and thus the steering column can return to the target angle at an essentially constant velocity v.

[0032] Fig. Figure 3 shows a comparison between scenarios with and without entry / exit mode according to one or more embodiments. With entry / exit mode 320, even if the handwheel torque is large, the handwheel angle does not change significantly; that is, the handwheel is locked / secured, because in entry / exit mode the HWA 10 generates the additional torque (u) to secure the handwheel. Without entry / exit mode 310, however, even a small driver torque applied to the handwheel can cause the handwheel to move more, proportionally to the applied torque, compared to entry / exit mode 320.

[0033] Fig. Figure 4 shows a slow return to a target angle at a constant speed, achieved in the entry / exit operating mode according to one or more embodiments. Using the entry / exit function can achieve a slow return to a target angle at a constant speed (v) 420 when the user steers the handwheel and releases it 410, the constant speed 420 being calculated as described herein.

[0034] Furthermore, as described herein, during typical operation of the SbW system, when it is not in entry / exit mode, the RWA 20 generates motor torque such that the rack position follows the corresponding steering column angle caused by a change in the handwheel position. However, such a change in rack position consumes energy. In particular, when the vehicle's engine 100 is switched off, the consumed energy comes from a vehicle battery (not shown), and thus, in entry / exit mode, the RWA 20 is enabled to maintain the rack position, thereby saving energy.

[0035] For this purpose, the RWA 20 is designed such that the rack position follows the corresponding target steering column angle, while the actual steering column angle can still move around the target angle in entry / exit mode. Accordingly, according to one or more embodiments, as shown in Fig. Figure 5 shows that the rack position does not change in entry / exit mode despite a change in the handwheel position. In other cases, the rack position is allowed to change in accordance with the change in the handwheel position in entry / exit mode.

[0036] Fig.Figure 6 shows a flowchart of an exemplary method for securing a steering wheel of an SbW system according to one or more embodiments. The method 600 shown can be executed by the one or more controllers of the HWA 10 and / or the RWA 20. The method 600 comprises the HWA 10 detecting, at 605, a transition of the SbW system 40 into an entry / exit operating mode. The transition can be detected based on one or more signals. For example, in one or more examples, the transition to the entry / exit operating mode is based on a signal indicating that a machine of the vehicle 100 is switched off. Alternatively or additionally, the transition to the entry / exit operating mode is based on a signal indicating that a vehicle door is open and the machine is switched off.The signals can be received by one or more electronic control units (ECUs) that are responsible for those functions in the vehicle 100.

[0037] If the SbW system 40 is not in entry / exit mode at 610, the HWA 10 and RWA 20 continue to operate as in typical cases, as described herein. For example, the HWA 10 generates a torque for the driver to provide a steering feel corresponding to a rack load detected by the RWA 20. Furthermore, the RWA 20 adjusts the road wheel position (i.e., the rack position) based on an input torque from the driver at the handwheel.

[0038] When the SbW system 40 is in entry / exit mode, the HWA 10 calculates a holding torque command at 615 based on an input torque value. The input torque is applied to the handwheel by a user. The holding torque generated has a direction opposite to that of the input torque. The HWA 10 calculates the holding torque nonlinearly using equation (1) described herein, based on the difference between the current position of the handwheel and a target position of the handwheel based on the input torque. In one or more examples, the holding torque at 620 is generated by the controller 14 of the HWA 10 through the generation of a motor torque command applied to a motor of the physical system 12. The holding torque generated is limited to a predetermined maximum.By counteracting the input torque at the handwheel by generating the holding torque, the position of the handwheel cannot change beyond a certain limit, thus essentially securing the position of the handwheel.

[0039] Furthermore, the handwheel is returned to its original position at 625 when input torque is applied to the handwheel and the user releases the handwheel, i.e., when the user ceases applying any further input torque to the handwheel. In other words, when the input torque becomes 0, the handwheel is returned to its original position. This return is performed at a constant speed. In one or more examples, the constant speed (v) is predetermined. Alternatively or additionally, the constant speed (v) is based on the coefficient Kd of the PID controller 14.

[0040] The technical solutions described herein enable a steering-by-wheel (SbW) system to dynamically generate a non-linear torque using a handwheel actuator (HWA) to secure the handwheel when an input torque is applied to the handwheel while the SbW system is deactivated, such as when the vehicle is switched off. These solutions improve the operation of the steering system by preventing it from actuating the handwheel during entry into / exit from the vehicle. The method for calculating the holding torque is such that the holding torque command is applied opposite to the input torque. If the input torque ceases after the handwheel has moved to a different position due to the input torque, the handwheel is returned to a target angle at a constant speed.

[0041] While the technical solutions have been described in detail in connection with only a limited number of embodiments, it should be readily apparent that the technical solutions are not limited to these disclosed embodiments. Rather, the technical solutions can be modified to include any number of variations, changes, substitutions, or equivalent arrangements not yet described, but which are consistent with the spirit and scope of the technical solutions. Furthermore, although various embodiments of the technical solutions have been described, it is understandable that aspects of the technical solutions may only encompass some of the described embodiments. Accordingly, the technical solutions should not be considered limited by the foregoing description.

Claims

[1] Steer-by-wire steering system (40), comprising: a handwheel; and a handwheel actuator (10) configured to secure a position of the handwheel, the securing comprising: a transition of the steer-by-wire steering system (40) to an entry / exit mode is determined (605); and based on the determination that the steer-by-wire steering system (40) is in the entry / exit mode (610): a holding torque command is calculated (615) based on a difference between a current angle of the handwheel and a target angle of the handwheel caused by an input torque; and a holding torque is generated according to the holding torque command to secure the position of the handwheel (620). [2] The steer-by-wire steering system (40) of claim 1, wherein the transition to the entry / exit mode is based on a signal indicating that a vehicle engine is off. [3] The steer-by-wire steering system (40) of claim 1, wherein the transition from the entry / exit mode is based on a signal indicating that a vehicle engine is on. [4] Steer-by-wire steering system (40) according to claim 1, wherein the holding torque is limited to a predetermined maximum amount. [5] Steer-by-wire steering system (40) according to claim 1, wherein the handwheel actuator (10) is further configured to return (625) the handwheel to an original position at a constant speed (420) in the event that the handwheel moves to a different position due to the input torque. [6] The steer-by-wire steering system (40) of claim 1, wherein the holding torque command is calculated based on a difference between a current angle of the handwheel and a desired angle of the handwheel caused by the input torque. [7] The steer-by-wire steering system (40) of claim 1, wherein the steer-by-wire system further comprises a road wheel actuator (20) configured to maintain a position of a steering rack in the entry / exit mode. [8] A method (600) for securing a position of a handwheel of a steer-by-wire steering system (40), the method comprising: a transition of the steer-by-wire steering system (40) into an entry / exit operating mode is determined (605) by a handwheel actuator (10) of the steer-by-wire steering system (40); and based on the determination that the steer-by-wire steering system (40) is in the entry / exit mode (610): a holding torque command is calculated (615) based on a difference between a current angle of the handwheel and a target angle of the handwheel caused by an input torque; and a holding torque is generated according to the holding torque command to secure the position of the handwheel (620). [9] The method of claim 8, wherein the transition to the entry / exit mode is based on a signal indicating that a vehicle engine is off. [10] The method of claim 8, wherein the transition from the entry / exit mode is based on a signal indicating that a vehicle engine is on. [11] The method of claim 8, wherein the holding torque is limited to a predetermined maximum amount. [12] The method of claim 8, further comprising returning (625) the handwheel to an original position at a constant speed (420) in the event that the handwheel moves to a different position due to the input torque. [13] The method of claim 8, wherein the holding torque command is calculated based on a difference between a current angle of the handwheel and a desired angle of the handwheel caused by the input torque. [14] The method of claim 8, further comprising maintaining a position of a rack in the entry / exit mode by a road wheel actuator (20). [15] A computer program product comprising a memory device having computer-executable instructions stored therein, the computer-executable instructions, when executed by a processor, causing the processor to perform a method for securing a position of a handwheel of a steer-by-wire steering system (40), the method comprising: a transition of the steer-by-wire steering system (40) into an entry / exit operating mode is determined (605) by a handwheel actuator (10) of the steer-by-wire steering system (40); and based on the determination that the steer-by-wire steering system (40) is in the entry / exit mode (610): a holding torque command is calculated (615) based on a difference between a current angle of the handwheel and a target angle of the handwheel caused by an input torque; and a holding torque is generated according to the holding torque command to secure the position of the handwheel (625). [16] The computer program product of claim 15, wherein the transition to the entry / exit mode is based on a signal indicating that a vehicle engine is off. [17] The computer program product of claim 15, wherein the transition from the entry / exit mode is based on a signal indicating that a vehicle engine is turned on. [18] The computer program product of claim 15, wherein the holding torque is limited to a predetermined maximum amount. [19] The computer program product of claim 15, further comprising returning (625) the handwheel to an original position at a constant speed (420) in the event that the handwheel moves to a different position due to the input torque. [20] The computer program product of claim 15, wherein the holding torque command is calculated based on a difference between a current angle of the handwheel and a desired angle of the handwheel caused by the input torque.

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