Method and control device for operating a steering system of a vehicle

Abstract

The present invention relates to a method for operating a steering system (100) of a vehicle, wherein, in response to a detection (106) of a squeaking situation (108), at least two steerable wheels (102) of the vehicle are steered according to Ackermann.

Description

Field of the invention

[0001] The invention relates to a method for operating a steering system of a vehicle, a corresponding control unit, and a corresponding computer program product. State of the art

[0002] A vehicle may have steering kinematics that allow for a compromise between different driving situations. These steering kinematics may deviate from Ackermann steering angles to improve the vehicle's driving dynamics. This can result in significant slip, particularly on slippery surfaces and at large steering angles, which can lead to squeaking noises. Disclosure of the invention

[0003] Against this background, the approach presented here provides a method for operating a vehicle steering system, a corresponding control unit, and a corresponding computer program product according to the independent claims. Advantageous further developments and improvements of the approach presented here emerge from the description and are described in the dependent claims. Advantages of the invention

[0004] In the approach presented here, steered wheels are steered with Ackermann steering angles in situations where squeaking noises are possible. This allows the vehicle's wheels to roll around an instantaneous center of gravity in an ideal, slip-free manner. Since this results in little or no slip, squeaking is prevented. If no squeaking situation is detected, or a non-squeaking situation is detected, the wheels are preferably steered with steering angles other than those according to Ackermann.

[0005] The approach presented here can prevent or at least reduce squeaking noises from a vehicle's wheels in a parking garage, for example. This makes other noises more perceptible, allowing the perception of, for example, the engine noise of a vehicle traveling straight ahead, which would otherwise have been drowned out.

[0006] A method for operating a steering system of a vehicle is presented, wherein, in response to the detection of a squeaking situation, at least two steerable wheels of the vehicle are steered according to Ackermann.

[0007] Ideas for embodiments of the present invention can be considered, among other things, to be based on the thoughts and findings described below.

[0008] A squealing situation can occur due to a combination of different factors. A particularly characteristic example of a squealing situation can be a surface with poor grip or a low coefficient of friction. Furthermore, the squealing situation can be caused by acoustics in the vehicle's surroundings. Especially indoors, tire noise can be reflected back to the vehicle and be perceived more strongly by vehicle occupants than in an open environment without sound-reflecting walls. However, the squeal can also be caused by a tire's low coefficient of friction.

[0009] When a tire squeals, it exhibits a high degree of slippage. Squealing occurs when the tire's tread blocks slide over the surface, causing the stick-slip effect to squeal.

[0010] A vehicle may have steering kinematics that, during normal driving, set steering angles or steering angles that deviate from the Ackermann function. Particularly at large steering angles or a sharp steering angle, significant slip can occur on at least one wheel on an axle.

[0011] The vehicle may have a steering kinematics adjustment feature. If there's a high potential for tire squealing during steering, the steering kinematics can be switched to Ackermann steering angle. This allows the vehicle's wheels to roll around a common center of gravity, minimizing slip on all wheels.

[0012] One option for changing the steering kinematics is, for example, independent wheel steering actuators on at least one axle of the vehicle. Independent wheel steering actuators can adjust the steering angles of the steered wheels independently of each other. With independent wheel steering actuators, the steering angle articulated at the wheel is adjusted using a steering angle characteristic curve and a steering wheel angle. The steering angle characteristic curve describes a relationship or ratio between the steering wheel angle and the steering angle. The steering angle characteristic curve can be changed or swapped to adjust the Ackermann steering kinematics.

[0013] The steering angles can be controlled on more than two wheels of the vehicle according to Ackermann if the vehicle is in a potential squeal situation.

[0014] At maximum steering angle, at least one of the wheels can be steered in a manner deviating from Ackermann. At maximum steering angle, the smallest possible turning radius can be requested. The turning radius can be reduced, for example, by parallel positioning of the steered wheels compared to Ackermann control. At maximum steering angle, improved vehicle maneuverability may be more important than minimizing squeaking. Alternatively or additionally, at maximum steering angle, one of the wheels may hit a mechanical stop and therefore cannot be turned any further. This also prevents the steering angle from being adjusted according to Ackermann.

[0015] The steering kinematics of a vehicle axle steered differently from Ackermann can be corrected by using another steered axle of the vehicle according to Ackermann. For example, a rear-axle steering system can be controlled so that all wheels roll around the common center of rotation.

[0016] The wheels can be steered according to the Ackermann principle when the vehicle is traveling slower than a predefined speed. At low speeds, the wheels can be steered according to the Ackermann principle. Above the specified speed, the advantages of non-Ackermann steering may prevail. The speed can be, for example, 30 km / h, 20 km / h, 10 km / h, or 5 km / h.

[0017] A steering differential angle can be adjusted by independent wheel steering actuators on at least one axle of the vehicle according to the Ackermann principle. The approach presented here can be implemented particularly efficiently using independent wheel steering actuators.

[0018] The squealing situation can be detected using at least one of the vehicle's microphones. The microphone can be an external microphone, for example, and record exterior noise. The microphone can be located near the wheels, for example. Alternatively or additionally, the microphone can be an internal microphone of the vehicle. The internal microphone can record noises radiating from the outside to the inside. The microphone can record the squealing of the tires, and the squealing situation can be detected. When the tires squeal, the system can switch directly to the Ackermann steering angle.

[0019] The squealing situation can be detected when entering an interior space. In interior spaces, such as parking garages and parking lots, a particularly high level of sound can be reflected back to the vehicle, making the squealing particularly noticeable to vehicle occupants or passersby. According to Ackermann, the steering angles can be adjusted when entering the interior space to reduce the likelihood of squeaking in the interior.

[0020] Entry into an interior space can be detected using a time of day and ambient brightness. If the ambient brightness decreases abruptly during the day, the vehicle has probably just entered an interior space. If the ambient brightness increases abruptly at night, the vehicle has probably just entered an interior space. Using the time of day and ambient brightness, situations can be detected in which it should actually be light or dark, but is not. In this case, the vehicle has probably just entered an interior space.

[0021] Entry into the interior can be detected alternatively or additionally using the vehicle's navigation system. For example, the reception signal from navigation satellites suddenly deteriorates in the interior. Likewise, using the vehicle's position and a digital map, it can be determined whether the vehicle is on a road or inside a building. Entry into a tunnel, for example, can also be detected based on speed, since a vehicle speed exceeds 30 km / h, for example.

[0022] The entry can also be detected using a vehicle's camera. Images and / or videos from the camera can be evaluated to detect the entry.

[0023] The method is preferably computer-implemented and can be implemented, for example, in software or hardware or in a mixed form of software and hardware, for example in a driver assistance system.

[0024] The approach presented here further creates a control unit, wherein the control unit is designed to carry out, control or implement the steps of a variant of the method presented here in corresponding devices.

[0025] The control unit can be an electrical device with at least one computing unit for processing signals or data, at least one memory unit for storing signals or data, and at least one interface and / or a communication interface for reading in or outputting data embedded in a communication protocol. The computing unit can be, for example, a signal processor, a so-called system ASIC, or a microcontroller for processing sensor signals and outputting data signals depending on the sensor signals. The memory unit can be, for example, a flash memory, an EPROM, or a magnetic storage unit. The interface can be designed as a sensor interface for reading in the sensor signals from a sensor and / or as an actuator interface for outputting the data signals and / or control signals to an actuator.The communication interface can be configured to read or output data wirelessly and / or via a wired connection. The interfaces can also be software modules, which are present, for example, on a microcontroller alongside other software modules.

[0026] Also advantageous is a computer program product or computer program with program code that can be stored on a machine-readable carrier or storage medium such as a semiconductor memory, a hard disk memory or an optical memory and is used to carry out, implement and / or control the steps of the method according to one of the embodiments described above, in particular when the program product or program is executed on a computer, in a control unit or a device.

[0027] It should be noted that some of the possible features and advantages of the invention are described herein with reference to different embodiments. A person skilled in the art will recognize that the features of the control device and the method can be combined, adapted, or exchanged as appropriate to achieve further embodiments of the invention. Short description of the drawing

[0028] Embodiments of the invention are described below with reference to the accompanying drawings, wherein neither the drawings nor the description are to be interpreted as limiting the invention. Fig. 1 shows a flowchart of a method according to an embodiment.

[0029] The figure is merely schematic and not to scale. Like reference numerals denote like or equivalent features. Embodiments of the invention

[0030] Fig.1 shows a flowchart of a method according to an exemplary embodiment. Using the method, a steering system 100 of a vehicle is controlled depending on the situation. Wheels 102 of the vehicle are steered at Ackermann steering angles 104 when a squealing situation 108 is detected 106. Due to the Ackermann steering, the wheels 102 roll around a common center of rotation, and only minimal slip occurs between the wheels 102 and the ground. This slip would lead to squealing of the tread blocks of the wheels 102 on the ground, particularly on surfaces with a low coefficient of friction.

[0031] When the squeaking situation 108 has ended, the wheels 102 are again controlled with steering angles 104 according to a vehicle-specific characteristic curve.

[0032] In one embodiment, the squeaking situation 108 is detected when the vehicle is located in an interior 110. The interior 110 can be detected, for example, via a GPS 112, a microphone 114, an environmental sensor 116, and / or a light sensor 118.

[0033] In one embodiment, a drive 120 of the vehicle is further controlled to reduce an output power when the squeaking situation 108 is detected.

[0034] In one embodiment, wheel-specific steering angles 104 are determined according to Ackermann for individual wheel steering actuators 122 on at least one axle of the vehicle and controlled when the squeaking situation 108 is detected. The steering angles 104 can be determined, for example, using an Ackermann characteristic curve.

[0035] In the following, possible embodiments of the invention are summarized again or presented with slightly different wording.

[0036] A function for optimized operation of steering actuators to avoid tire noise is presented.

[0037] Today's vehicles are equipped with electromechanical steering connected to both wheels. Steering systems are increasingly moving toward by-wire systems, which are mechanically decoupled from the driver, eliminating the traditional mechanical connection between the driver and the wheels. In the case of the steering, the corresponding actuation is achieved solely via one or more actuators. Centralized, as well as decentralized, by-wire steering actuators are already state of the art for the rear axle. The first prototype vehicles with by-wire independent wheel steering actuators are known for the front axle.

[0038] Turning in a tight radius at slow speed, such as in a parking garage or on smooth surfaces, often causes a squealing tire noise. This is due to normal tire slippage on surfaces smoother than typical asphalt. Especially in an enclosed space such as an underground garage or parking garage, this sound can echo and seem much louder, drowning out other ambient noise.

[0039] With conventional steering systems, a loud, unpleasant squealing noise can occur indoors on floors with reduced grip, for example, due to special paints. This is caused by the tires, which typically do not roll smoothly due to the steering kinematics. Instead, they generate lateral forces in the contact area. This causes the rubber blocks to slip on these surfaces with low coefficients of friction (μ), resulting in an unpleasant squealing noise.

[0040] This example presents a control system for (independent) steering actuators in indoor areas, such as parking garages, that uses a characteristic curve / ratio as close as possible to or equivalent to the Ackermann ratio. The presented function involves selecting a steering ratio depending on whether the vehicle is inside or outside.

[0041] The central aspect is an adjustment of the steering ratio by changing the characteristic curve for the control of the (independent) steering actuators, so that when changing from outside to inside or in case of corresponding acoustic abnormalities, it is set to near Ackermann. This enables almost ideal rolling around the vehicle's instantaneous center of gravity and thus prevents the generation of squealing noises. Thus, a steering differential angle selection based on the location is proposed to ensure acoustically favorable tire behavior.

[0042] The driving situation can be detected, for example, using a GPS signal or environmental sensors. It is also possible to integrate a microphone (ideally located outside, e.g., in the wheel arch for wetness detection) or the interior microphone.

[0043] Vehicles are usually equipped with brightness sensors and clocks, allowing reliable detection of parking garage entrances.

[0044] Especially with by-wire steering systems, the current steering effort is known. This makes it very easy to detect when the vehicle is traveling at low speed on relatively smooth surfaces. A further distinction must be made here, whether this is a case of slow driving in a parking garage or, for example, driving slowly around a curve on a slippery road with a similarly low friction coefficient μ.

[0045] The approach presented here can be used, for example, in a public parking garage, a workshop, a parking garage beneath private buildings, in garages, possibly also on driveways, and, depending on the surface, even in parking lots. The approach can also be used in situations such as manual or automated driving / parking with a driver inside or outside the vehicle, e.g., parking via remote control / key.

[0046] The approach presented here increases safety by allowing other noises to be perceived, such as vehicles that aren't steering or that generate less intense tire noise. Furthermore, the comfort of vehicle occupants and people within earshot of the vehicle is increased by reducing or eliminating squeaking noise in interior situations.

[0047] With individual wheel adjusters on the rear axle, the steering differential angle selection right-left can be selected accordingly in order to also roll as smoothly as possible.

[0048] The approach presented here can also be used with conventional steering systems when installed in conjunction with rear-axle steering. In this case, the rear-axle steering can be coordinated with the front-axle steering to minimize tire noise.

[0049] Rear-axle steering improves the effectiveness of the approach presented here. Typically, front-axle steering with a central actuator uses a compromise and deviates from an ideal Ackermann steering system, as this would only be a good choice in certain situations. Rear-axle steering allows the vehicle's length to be virtually changed. Thus, the steering angles on the rear axle could be selected so that the front axle moves close to the Ackermann angle.

[0050] By using rear-axle steering with independent wheel actuators, an ideal solution for the presented function can be achieved for the entire vehicle. A multi-stage approach can be implemented. At maximum steering angle, the minimum turning radius is achieved. As soon as the steering angle is reduced slightly, the additional leeway in the wheel steering angle is used to achieve the ideal angular distribution for minimal noise at this turning circle.

[0051] In addition to the steering kinematics, the drivetrain can also cause the described noise. Lateral slip on the tires of the steered axle occurs when the vehicle speed is too high due to the drive torque requested by the driver and thus does not match the steering angle of the wheels (Ackermann / rolling condition). Therefore, the drivetrain can be taken into account in the presented function. The drive torque requested by the driver is then reduced for small curve radii, so that the speed required to maintain the rolling condition is not exceeded. The drivetrain is only taken into account on level roads or in situations where this does not lead to any change in the vehicle's behavior with regard to acceleration, etc.

[0052] Finally, it should be noted that terms such as "comprising," "having," etc., do not exclude other elements or steps, and terms such as "a" or "an" do not exclude a plurality. Reference signs in the claims are not to be considered limiting.

Claims

[1] Method for operating a steering system (100) of a vehicle, wherein in response to a detection (106) of a squeaking situation (108), at least two steerable wheels (102) of the vehicle are steered according to Ackermann. [2] Method according to claim 1, wherein at least one of the wheels (102) is articulated at a maximum steering angle deviating from Ackermann. [3] Method according to one of the preceding claims, in which a steering kinematics of an axle of the vehicle steered differently from Ackermann is corrected using a further steered axle of the vehicle according to Ackermann. [4] Method according to one of the preceding claims, in which the wheels (102) are steered according to Ackermann when the vehicle travels slower than a predefined speed value. [5] Method according to one of the preceding claims, in which a steering differential angle of individual wheel steering actuators (122) of at least one axle of the vehicle is adjusted according to Ackermann. [6] Method according to one of the preceding claims, wherein the squeaking situation (108) is detected using at least one microphone (114) of the vehicle. [7] Method according to one of the preceding claims, in which the squeaking situation (108) is detected when entering an interior space (110). [8] Method according to claim 7, wherein the entry into the interior (110) is detected using a time of day and an ambient brightness. [9] Method according to one of claims 7 to 8, wherein the entry into the interior (110) is detected using a navigation system (112) of the vehicle. [10] Control device, wherein the control device is designed to carry out, implement and / or control the method according to one of the preceding claims in corresponding devices. [11] Computer program product which is designed to instruct a processor, when the computer program product is executed, to carry out, implement and / or control the method according to one of claims 1 to 9. [12] A machine-readable storage medium on which the computer program product according to claim 11 is stored.

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