Method and control unit for detecting a change in a wheel of a vehicle

Abstract

The present invention relates to a method for detecting a change (100) in a wheel of a vehicle. According to the method, a steering force (102) acting on the wheel and a steering angle (104) of the wheel are analyzed in order to detect the change (100).

Description

[0001] Description

[0002] Method and control device for detecting a change in a wheel of a vehicle

[0003] Field of the invention

[0004] The invention relates to a method for detecting a change in a wheel of a vehicle, a corresponding control unit, and a corresponding computer program product

[0005] State of the art

[0006] A change in a vehicle's wheel, such as a loss of tire pressure, can be detected using a wheel speed signal, as the change usually causes a change in the wheel's rolling radius. In particular, a loss of pressure in a single vehicle wheel is easily detectable by the increased speed of that wheel compared to the other wheels.

[0007] Disclosure of the invention

[0008] Against this background, the approach presented here provides a method for detecting a change in a vehicle wheel, 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.

[0009] Advantages of the invention: When changing from winter to summer tires, and vice versa, the tire and / or rim size may change in diameter, width, or lateral position. This can change the geometric conditions of the wheels or the vehicle's chassis. These geometric conditions can affect the vehicle's handling and / or steering behavior.

[0010] The changed geometric conditions on a wheel can be reflected in a change in the steering force used to steer the wheel. In particular, a change in the wheel's roll radius can lead to a change in the steering force.

[0011] Assistance functions, safety functions and / or emergency running functions of the vehicle can be adapted to known geometric conditions of the chassis or known force ratios and take these into account in their execution in order to enable pre-control of interventions.

[0012] In the approach presented here, the change in particular of geometric conditions on a wheel and / or on a chassis of the wheel is detected by evaluating the steering force on the wheel in relation to a steering angle of the wheel.

[0013] Using the approach presented here, the change can be reliably detected and, in response, a learning phase for assistance functions, safety functions and / or emergency functions can be initiated.

[0014] A method for detecting a change in a wheel of a vehicle or a wheel configuration of the vehicle is presented, wherein a steering force on the wheel and a steering angle of the wheel are evaluated in order to detect the change.

[0015] Ideas for embodiments of the present invention can be considered, among other things, to be based on the thoughts and findings described below. A steered wheel of a vehicle is articulated via a steering arm on its steering knuckle. A steering force from a wheel steering actuator acts on the steering arm via a tie rod. The steering actuator can steer both wheels of an axle via a common tie rod. Likewise, each wheel can be steered by its own individual wheel steering actuator. In this case, the tie rod is not absolutely necessary. The wheels with independent wheel steering actuators are not mechanically coupled to one another or to the vehicle's steering wheel with regard to steering. The independent wheel steering actuators are controlled by a central sensor on the steering wheel or a steering lever of the vehicle via data signals.

[0016] The angle of the wheel relative to the vehicle's longitudinal axis is called the steering angle. The steering force required at the steering arm to steer the wheel across a mechanically possible steering angle range is not constant. Kinematic relationships of the chassis influence the steering force distribution across the steering angle range.

[0017] When the wheel is driven or braked, a steering force is required to keep the steering angle constant, even without changing the steering angle. When the wheel is braked while driving forward or driven in reverse, an outward-rotating moment acts on the wheel, depending on geometric relationships. Therefore, without a supporting steering force, the wheel would pivot outward from the vehicle's longitudinal axis. When the wheel is driven forward, an inward-rotating moment acts on the wheel. Therefore, without a supporting steering force, the wheel would pivot inward toward the vehicle's longitudinal axis.

[0018] During both support and active steering, the steering force depends significantly on the wheel's roll radius, in addition to the steering angle. The roll radius is a parameter of the wheel suspension / steering system. It is the distance between the axis of rotation of the steering movement and the contact point of the wheel, measured in the direction of the projection of the axis of rotation of the rolling movement onto the road plane (i.e., in the road plane perpendicular to the wheel). The steering force can also depend on the surface condition, the tire width of the wheel, the wheel's support load, and other factors. Here, a change in at least one of these factors is detected from the steering force and the steering angle. In particular, a change in the roll radius can be detected as the change.

[0019] The change can be detected as a change in the tire type and / or rim type of the wheel. In particular, it can be detected that a different wheel is mounted. Detecting a change in the wheel is important for safety systems, assistance systems, and emergency running functions of the vehicle in order to be able to predict the effect of interventions on the vehicle based on known behavior during previous interventions.

[0020] A comparison of a current steering force curve across the steering angle can be performed with at least one learned steering force curve of at least one known tire type and / or rim type across the steering angle. The tire type and / or rim type can be identified using the result of the comparison. Wheels previously used on the vehicle can be learned, and the resulting steering forces for certain interventions can be stored. During such interventions, it can be detected whether a previously known wheel or a previously unknown wheel has been installed.

[0021] The change can be detected using a change in steering force at a specific steering angle. Steering force depends on the steering angle when the wheel remains unchanged. Therefore, the change in the wheel can be detected from the change in steering force at this steering angle.

[0022] A steering torque at the wheel can be derived from the steering force, the steering lever and the steering angle. The steering torque can also be directly determined by a rotational

[0023] A steering wheel adjuster is applied to the wheel. The change in the wheel can be detected based on a change in the steering torque over the steering angle. In particular, a steering torque curve can be observed.

[0024] The steering force can be derived from an electrical variable of a wheel's steering actuator. The steering force is essentially proportional to the motor current of the steering actuator, with the higher the motor current, the greater the steering force. The steering force can be used in particular during maneuvering or accelerating the vehicle. During maneuvering, such as when parking or leaving a parking space, the vehicle travels at low speed and large steering angles are set. The low speed results in high steering forces. Therefore, changes during maneuvering can be detected particularly well. During acceleration, there is a low risk potential because the vehicle's behavior during acceleration can be easily predicted even with incorrectly detected wheels. On the other hand, incorrect detection during braking can have safety-critical consequences.

[0025] The change can further be detected using at least one piece of information from a group of information comprising a steering speed, a position of an accelerator pedal of the vehicle, a brake pressure of a brake system of the vehicle, a longitudinal acceleration of the vehicle, a lateral acceleration of the vehicle, a vertical acceleration of the vehicle, a speed of the vehicle, a sideslip angle of the vehicle, a longitudinal gradient of a road below the vehicle, a transverse gradient of the road, a deflection of the wheel, a wheel speed of the wheel, a wheel speed of at least one other wheel of the vehicle, rain information, and temperature information.

[0026] The detection can be made more robust with the help of additional variables. For example, a driving situation can be recognized using the steering speed, i.e. how quickly the steering angle changes. The driving situation can also be recognized based on the position of the accelerator pedal. The accelerator pedal can be referred to as the gas pedal. The accelerator pedal is usually only operated while the vehicle's brake pedal is not operated. This can be used, for example, to distinguish between acceleration and braking. The brake pressure can also characterize the driving situation. If the brake pressure is greater than zero, the vehicle will generally not accelerate. With strong brake pressure, a high steering force can also be expected to counteract the change. Based on the vehicle's acceleration in different spatial directions, driving situations in which the steering forces are of little significance can be recognized.For example, highly dynamic driving situations can be rejected for detection. Speed ​​and its derivatives can also be used to differentiate between driving situations. A large sideslip angle, i.e. how far the vehicle's longitudinal direction deviates from the vehicle's direction of movement over ground, can characterize dynamic driving situations in which detection of the change can be suspended. The road inclination beneath the vehicle influences the wheel contact forces of the vehicle's wheels. The changed wheel contact forces result in changed steering forces that are independent of changes in the wheels. Likewise, a compressed wheel results in higher steering forces than a fully extended wheel. In extreme cases, a wheel can lift off and the steering forces drop to almost zero.Driving situations in which the detection of changes in the wheel is less reliable can also be detected using the vehicle's wheel speeds. For example, if a wheel is spinning. Rain or precipitation in general can reduce the static friction between the wheel and the ground. This can reduce the required steering force and make it more difficult to detect the change in the wheel. A tendency towards ice formation or, in general, an expected static friction with the ground can be detected based on the ambient temperature. At low temperatures, for example, the wheel's grip on the ground can decrease, making it more difficult to detect changes in the wheel.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] Short description of the drawings

[0033] Embodiments of the invention are described below with reference to the accompanying drawings, wherein neither the drawings nor the description are to be construed as limiting the invention.

[0034] Fig. 1 shows a representation of a detection of a change in a wheel of a vehicle using a method according to an embodiment; and Fig. 2 shows a representation of a detection of a change in a wheel of a vehicle using an extended method according to an embodiment.

[0035] The figures are merely schematic and not to scale. Like reference numerals denote like or equivalent features.

[0036] Embodiments of the invention

[0037] Fig. 1 shows an illustration of the detection of a change 100 at a wheel of a vehicle using a method according to an exemplary embodiment. The change 100 is detected using a steering force 102 at the wheel and a steering angle 104 of the wheel.

[0038] The steering force 102 and the steering angle 104 are read in by a data processing device 106 of the vehicle and the change 100 is output by the data processing device 106.

[0039] In one embodiment, the steering force 102 at a specific steering angle 104 is compared with a stored value of the steering force 102 at the specific steering angle 104 in order to detect the change 100.

[0040] In one embodiment, a change in a steering roll radius 108 of the wheel is output as the change 100. The steering roll radius 108 is a distance between a center plane of the wheel and a point where a steering axis of a wheel's steering knuckle penetrates a surface beneath the wheel. The steering roll radius 108, or its change, can be calculated using physical equations.

[0041] In one embodiment, the data processing device 106 reads in a steering torque 110 at the wheel and the steering angle 104.

[0042] In one embodiment, a detected dimensional change to a tire and / or a rim of the wheel is output as the change 100, such as occurs, for example, when changing from winter wheels with winter tires on a first rim to summer wheels with summer tires on a second rim, when changing from a worn tire to a newer tire with an identical rim, and / or when changing from one rim model to another rim model with an identical tire.

[0043] In one embodiment, a curve of the steering force 102 over the steering angle 104 is evaluated in order to detect the change 100.

[0044] In one exemplary embodiment, the curve of the steering force 102 is compared with a stored curve. In particular, the curve is evaluated during at least one specific driving situation in order to detect the change 100. The driving situation is in particular maneuvering at low speed and with large steering angles or large changes in the steering angle within a short period of time. However, the driving situation can also be an acceleration phase of the vehicle with small steering angles. During maneuvering, the steering forces 102 can be evaluated to change the steering angle 104; during acceleration, the steering forces 102 can be evaluated to maintain the steering angle 104. The steering forces 102 during maneuvering can be in the same direction, while the steering forces 102 during acceleration can be in the opposite direction.

[0045] In one embodiment, a motor current is measured at the steering actuator of the wheel as a measure of the steering force 102 and the steering force 102 is derived from the motor current.

[0046] Fig. 2 shows a representation of the detection of a change 100 on a wheel of a vehicle using an extended method according to an exemplary embodiment. The method essentially corresponds to the method in Fig. 1. In addition, at least one further variable is read in here to detect the change 100.

[0047] In one exemplary embodiment, a steering speed 200 is read in in addition to the steering force 102 or the steering torque and the steering angle 104. Using the steering speed 200, the dynamics of the steering process can be detected. In steering processes with a high steering speed 200, the change 100 can have a particularly strong effect.

[0048] In one embodiment, a position 202 of a vehicle's accelerator pedal is read. In driving situations with a strongly depressed accelerator pedal, the vehicle accelerates sharply, and the change 100 has a significant impact on the measured steering force 102.

[0049] In one embodiment, a brake pressure 204 of a braking system of the vehicle is read. Using the brake pressure 204, braking of the vehicle can be detected. The brake pressure 204 can also be used to detect when an assistance system is braking the vehicle. During braking, the detection of the change 100 can be suspended to avoid false detections.

[0050] In one embodiment, a vehicle speed 206 of the vehicle is read. Using the vehicle speed 206, suitable driving situations for detecting the change 100 can be easily identified. In particular, maneuvering situations and acceleration situations can be easily detected using the vehicle speed 206.

[0051] In one embodiment, an incline 208 of the ground beneath the vehicle is read. An inclined ground can shift the vehicle's center of gravity relative to contact points on the ground. Due to the inclined ground, wheels positioned downhill can be subjected to greater loads and wheels positioned uphill can be less loaded. This uneven distribution of wheel loads can hinder or distort the detection of change 100. Therefore, detection can be suspended starting at a predetermined incline 208.

[0052] In one embodiment, the input variables are processed in a neural network to detect the change 100.

[0053] In the following, possible embodiments of the invention are summarized again or presented with slightly different wording.

[0054] A method for detecting the steering roll radius and the tire type from steering forces is presented.

[0055] For several years now, all passenger cars have been equipped with electric power steering. Developments are moving toward removing the mechanical connection between the steering wheel and the vehicle's wheels (steer-by-wire). A possible next step is to actuate the steering angles of the two front wheels separately. Another development, already available as standard in some vehicles, is rear-axle steering, which is always implemented as steer-by-wire, sometimes even for each wheel individually.

[0056] The wheel speeds are already used to determine a wide variety of other information, such as tire pressure or the estimation of the friction coefficient z of the road-tire contact, but also for identification within the framework of the tires homologated for the vehicle.

[0057] However, the approach presented here is about the time after the wheel change and about automatically configuring the vehicle and its control system optimally and ensuring improved tire detection.

[0058] Currently, vehicles cannot reliably detect tire changes themselves, for example between summer and winter tires. Detection based solely on wheel speeds and previously available signals does not result in a reliable, unambiguous assignment. The detected tire type often changes between, for example, two tires, and the associated recommended tire pressures also change. Changing wheels can lead to an (unintended) change in driving characteristics due to different wheel offsets, particularly due to a change in the steering roll radius. This is also critical from a safety perspective. The information about a completed wheel change and any resulting changes in driving dynamics can be determined using the approach presented here using the available signals from the steering system without additional sensors. This information can then be made available to the ESP for vehicle stabilization.

[0059] In the approach presented here, the required steering forces in specific driving situations are used to determine the steering roll radius of the wheels. This allows the mounted wheels to be reliably identified. Depending on performance, a training process can be performed, after which this approach can also be used solely for the detection of already known wheels. Alternatively, the system can independently detect that previously unknown tires have been mounted. This approach can potentially be extended to other parameters. The steering roll radius, in particular, is an important parameter that is very well suited for this approach.

[0060] Vehicle manufacturers generally specify a defined selection of vehicle wheels that are suitable and homologated for a particular model. In some countries, only winter and summer wheels of identical classification, i.e. diameter, width, and group of properties, may be used on a vehicle. In other countries, the leeway is significantly greater and certain deviations are permitted, particularly in width. Furthermore, a non-homologated wheel could be fitted due to incorrect behavior or misjudgment on the part of the end customer. The diameter of the rim can also be varied in some cases, even if the outer diameter remains roughly the same. If summer and winter wheels are not mounted on identical rims, there may also be differences in the offset of the rims, which means that the lateral position of the tires on the vehicle, in particular, may experience small differences.

[0061] The lateral distance of the center plane of a wheel in relation to the steering axis, which is defined by the vehicle's suspension, is called the steering roll radius (rs).

[0062] The steering roll radius has a significant impact in several driving situations. The first is steering while stationary, such as when parking. Here, a larger steering roll radius, acting as a lever arm around the steering axis, directly results in greater steering forces, especially when the wheel is braked. This is therefore a good situation for calibrating the presented function and for identifying the mounted tire.

[0063] For individual wheel actuators, the required torque for each side is directly available via the measured variable motor current; for central actuators, the total torque can be used. A change in the forces during parking, which is directly related to the required actuator torque, can detect that the wheels have probably been changed. This can then be automatically validated using other variables or driving situations. One reason for additional calibration / validation is that the steering forces can also change due to different loads or different road surfaces. The tire radius is also a very important aspect for detecting the tire type. The signals from the wheel speed sensors can also be used for this purpose.

[0064] Other possible situations for determining the steering roll radius are braking or driving, provided the vehicle has independent wheel steering. In this case, the steering roll radius, together with the longitudinal force, generates a moment about the steering axis. However, the braking state is significantly more safety-critical than parking. Therefore, the advantage of the approach presented here is that it uses non-critical situations such as parking or driving straight ahead for detection and calibration. Using data-based methods, the steering roll radius and tire type can be reliably determined.

[0065] Essentially, the approach presented here describes how the steering torque or forces in the actuator are used with the steering angle to determine the steering roll radius. The steering roll radius is assigned to a homologated tire, thus identifying the tire type.

[0066] Additional signals present in the vehicle can be used to improve detection (e.g., by combining them with data from the ESP) and enable applicability in different driving situations. Possible additional signals include steering speed to improve signal quality, accelerator pedal position, brake pressure, longitudinal, lateral, and vertical acceleration, vehicle speed, vehicle sideslip angle, longitudinal and transverse road gradient, suspension deflection, wheel speeds, as well as rain sensor information and outside temperature.

[0067] The more of these signals are available, the more robust the detection process can be. Influences to be identified include, for example, steering behavior (smooth / high-frequency, fast / slow), whether the vehicle is accelerating or decelerating, the general driving condition, the vehicle load, the longitudinal and transverse inclination of the road, the tire pressure, and an estimate of the tire / road friction coefficient. Simple equations are suitable for estimating the relationship between individual signals. Data-based methods can be used to consider multiple effects and perform calibration during operation. Regardless of the method and implementation chosen, the detected parameters can then be used in critical situations, such as driving and braking, to improve the control of the vehicle dynamics control.

[0068] Some of the maneuvers mentioned can be initiated deliberately, or the system can wait until the vehicle is already in this state of motion. Targeted, gentle braking of individual wheels is already state of the art in the ESP environment.

[0069] The information determined from the steering data can then be used in the vehicle. In many vehicles, the ESP values ​​are recalibrated after a tire change. One simple application, for example, is to trigger this calibration automatically when the tire change is detected. In other application examples, this information could be used to directly control the individual systems (e.g. ABS, ESP). This can increase safety. A changed steering roll radius also has a significant influence on the vehicle's behavior during braking maneuvers, particularly with inhomogeneous friction coefficients, such as p-split braking. Changing the sign of the steering roll radius could have fatal consequences under certain circumstances, as the direction of wheel rotation would be reversed and lead to undesired driving behavior.If the driver has fitted unsuitable wheels, a warning can be issued in an application example to avoid safety-critical situations.

[0070] The brake can support the steering functionality, which is particularly important with regard to reliability and ASIL classification. To do this, a wheel is braked. Due to the steering roll radius, a steering moment is generated, and the wheel rotates, although the yaw moment of the entire vehicle is not taken into account here. These interventions are often based on a known steering roll radius in order to better assess the effect in advance (feedback control). In another application example, the available information from the brake and steering sensors is used during normal operation to determine the steering roll radius and possibly other parameters. The vehicle can then achieve better performance and ensure safety at the known operating points.Thus, the approach presented here serves to ensure the performance of degradation mechanisms used in the design of the vehicle and actuator architecture and assumed to be functional. In another exemplary embodiment, continuous monitoring of the steering roll radius is performed to ensure that the required functional chains, for example, for braking and steering, are intact and not outside the tolerance range required for function. In this case, the approach presented here can provide early warning of malfunctions or potential defects in the vehicle.

[0071] The full potential of the approach presented here can probably only be fully exploited by taking the other sensors in the vehicle into account. Regardless of whether the aim is simply to detect whether the wheels have been changed or whether the model or the vehicle dynamics control system needs to be re-parameterized directly, this approach offers great potential. It may be possible to determine additional vehicle characteristics. The focus here is on enabling additional functionality. If this makes sensors superfluous, the costs of the overall system could also be reduced. In any case, data processing is required to reliably determine relevant information. In the simplest case, it can be detected that something has changed, presumably the wheels have been changed or the steering roll radius has changed, or in any case, a recalibration of the stored parameters is necessary.

[0072] 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

Claims 1. A method for detecting a change (100) on a wheel of a vehicle, wherein a steering force (102) on the wheel and a steering angle (104) of the wheel are evaluated in order to detect the change (100).

2. Method according to claim 1, wherein a change in a steering roll radius (108) of the wheel is detected as the change (100).

3. Method according to one of the preceding claims, in which a change in a tire type and / or rim type is detected as the change (100).

4. The method according to claim 2, wherein a comparison of a current steering force curve over the steering angle (104) is carried out with at least one learned steering force curve of a known tire type and / or rim type over the steering angle (104), wherein the tire type and / or rim type is recognized using a result of the comparison.

5. Method according to one of the preceding claims, wherein the change (100) is detected using a change in the steering force (102) at a specific steering angle (104).

6. Method according to one of the preceding claims, in which the steering force (102) is derived from an electrical variable of a steering actuator of the wheel.

7. Method according to one of the preceding claims, wherein the steering force (102) is used during a maneuvering operation or an acceleration operation of the vehicle.

8. Method according to one of the preceding claims, wherein the change (100) is further carried out using at least one piece of information from a group of information comprising a steering speed (200), a position (202) of an accelerator pedal of the vehicle, a brake pressure (204) of a braking system of the vehicle, a longitudinal acceleration of the vehicle, a lateral acceleration of the vehicle, a vertical acceleration of the vehicle, a speed (206) of the vehicle, a sideslip angle of the vehicle, a longitudinal gradient of a road beneath the vehicle, a transverse gradient of the road, a deflection of the wheel, a wheel speed of the wheel, a wheel speed of at least one other wheel of the vehicle, rain information and temperature information.

9. 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.

10. A computer program product configured to instruct a processor, upon execution of the computer program product, to execute, implement and / or control the method according to one of claims 1 to 8.

11. A machine-readable storage medium on which the computer program product according to claim 10 is stored.

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