Method and device for steering a motor vehicle

Abstract

Procedure (40) for steering a motor vehicle, comprising the steps: - Determining a steering wheel torque (M L ) based on a detected steering angle (φ) of a steering wheel (12) of the motor vehicle, - Detecting a torsion bar torque (M D ) of a torsion bar 16 of the motor vehicle, characterized in that the steering wheel torque (M L ) and the torsion bar torque (M D ) are compared to detect a free return of the steering wheel (12).

Description

[0001] The present invention relates to a method for steering a motor vehicle, wherein a dynamic steering wheel torque that accelerates the steering wheel is determined on the basis of a detected steering angle of a steering wheel of the motor vehicle and a torsion bar torque of a torsion bar of the motor vehicle is detected.

[0002] The present invention further relates to a device for steering a motor vehicle comprising a steering wheel for actuating the device by means of a steering wheel actuation, a torsion bar for transmitting the steering wheel actuation to steered wheels of the motor vehicle, a steering angle detection unit for detecting a steering angle of the steering wheel, a torsion bar torque detection unit for detecting a torsion bar torque of the torsion bar, and a return determination unit for determining a steering wheel return.

[0003] Finally, the present invention relates to a motor vehicle with a device for steering the motor vehicle.

[0004] In the field of automotive steering technology, it is generally known that turned wheels exert a restoring force on the steering system, thereby enabling the steering to return to a neutral position or to the lateral force-free state of the steered wheels. This return to neutral can be achieved by the driver releasing the steering wheel, so that the steering movement to the lateral force-free state is accomplished solely by the restoring force of the steered wheels.

[0005] Such a return to neutral, achieved through a so-called "free return" of the steering wheel (where the driver releases the wheel), can lead to uncontrolled driving situations, known as yaw oscillations, if the steering wheel's return movement extends beyond the neutral position. To prevent such yaw oscillations, the steering wheel, or rather its movement, is typically permanently damped to minimize overshoot during the free return. A disadvantage of this is that this permanent damping requires a high steering effort, making steering generally feel uncomfortable.

[0006] To avoid such yaw oscillations and simultaneously adjust the steering wheel damping according to the situation, the free return movement of the steering wheel must be reliably detected. For example, DE 10 2009 009 032 A1 proposes detecting and analyzing the steering angle, steering torque, and steering angle acceleration to detect the free return movement. A disadvantage of this method is that the free return movement is determined by typical steering wheel movements and therefore can only be detected after all signals have passed through zero.

[0007] It is therefore the object of the present invention to provide a method and a device for steering a motor vehicle, wherein steering return can be detected more quickly.

[0008] In the aforementioned method, this task is solved by comparing the steering wheel torque and the torsion bar torque in order to detect a free return movement of the steering wheel.

[0009] This task is solved in the aforementioned device by the fact that the return-to-center unit is designed to determine a steering wheel torque based on the steering angle and to determine a free return of the steering wheel based on the steering wheel torque and the torsion bar torque thus determined.

[0010] This problem is finally solved in the aforementioned motor vehicle by a device for steering the motor vehicle according to the present invention.

[0011] By determining the steering wheel torque based on the steering angle and comparing it with the torsion bar torque, a dynamic hand torque exerted by the driver on the steering wheel can be determined with minimal technical effort, so that a free return of the steering wheel can be reliably determined for every driving situation.

[0012] The problem of the present invention is thus completely solved.

[0013] In a preferred embodiment, steering wheel return damping is set if the free return of the steering wheel is detected. In this case, the steering wheel is accelerated exclusively by the torsion bar torque, with the driver contributing no torque.

[0014] This reliably prevents yaw oscillation of the vehicle.

[0015] In another embodiment, the steering wheel return damping is added to a basic damping of the steering wheel, provided that the free return of the steering wheel is detected.

[0016] This allows for a more comfortable steering feel, as the basic damping of the steering wheel can generally be reduced.

[0017] It is still preferred if the steering wheel torque is determined on the basis of an angular acceleration and a steering wheel inertia.

[0018] This allows the steering wheel torque to be reliably determined with minimal technical effort.

[0019] It is still preferred to detect the free return flow, provided that the difference between the steering wheel torque and the torsion bar torque falls below a predefined threshold.

[0020] This allows a free return movement of the steering wheel to be distinguished from a guided return movement with minimal technical effort.

[0021] It is still preferred to filter the torsion bar torque using a low-pass filter.

[0022] This allows interference signals from the torsion bar torque to be filtered out, while simultaneously reducing the technical effort required to evaluate the torsion bar torque.

[0023] It is still preferred if the torsion bar torque is delayed by means of a time element.

[0024] This allows the signal of the torsion bar torque to be adjusted in time to the determined steering wheel torque, which is delayed by the continuous determination, in particular by the differentiation of the steering angle.

[0025] It is still preferred to filter the steering wheel angular velocity using a low-pass filter.

[0026] This allows the corresponding steering wheel angular velocity signal to be smoothed and further evaluation of the steering wheel angular velocity to be simplified.

[0027] It is still preferred if the threshold for the difference between the steering wheel torque and the torsion bar torque is set as a function of the steering wheel angular velocity and as a function of the torsion bar torque.

[0028] This allows the free return flow to be detected with increased reliability depending on the situation, and false detection can be avoided.

[0029] It is still preferred to detect the end of the free return stroke of the steering wheel if a difference between the steering wheel torque and the torsion bar torque exceeds a predefined threshold.

[0030] This allows the corresponding steering wheel return damping to be reliably deactivated with minimal technical effort, thus providing comfortable steering.

[0031] It is particularly preferred if the steering wheel speed and the difference are delayed by means of a timer.

[0032] This reliably prevents premature deactivation of the steering wheel return damping.

[0033] It is still preferred if the time delay is set depending on an amplitude and / or a frequency of the torsion bar torque.

[0034] This allows the deactivation of the steering wheel return damping to be adapted to signal fluctuations of the torsion bar torque, thereby making the deactivation more sensitive to the situation and further increasing the reliability of the deactivation.

[0035] In general, the present invention allows the free return stroke to be reliably calculated with minimal technical effort, since the driver's hand torque can be reliably measured independently of the situation by comparing the steering wheel torque and the torsion bar torque. This allows the steering wheel return damping to be activated as needed and the overall damping of the steering movement to be reduced, thus making the steering more comfortable overall.

[0036] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0037] Exemplary embodiments of the invention are shown in the drawing and are explained in more detail in the following description. They show: Fig. 1 a schematic representation of a steering device of a motor vehicle; Fig. 2 a schematic flowchart for determining the steering wheel return damping; Fig. 3 a detailed flowchart of the detection of free steering wheel return; and Fig. 4. A schematic time diagram to explain the recorded and determined quantities for determining the free steering wheel return.

[0038] In Fig. Figure 1 is a schematic representation of a steering device, generally designated by 10. The steering device 10 has a steering wheel 12, which is connected to a steering unit 14 and exerts a steering torque M. Lto the steering unit 14. The steering unit 14 has a steering rod 16 or torsion bar 16, which is connected via a pinion to a steering rod 18 or rack 18, which aligns or steers the steered wheels 20R and 20L according to a steering wheel operation. The torsion bar 16 transmits a torsion bar torque M D from the steering unit 14 to the steering rod 18 or vice versa. The torsion bar 16 is a torsionally elastic bar on which the torsion bar torque M is transmitted via its torsion. D The steering wheel 12 is assigned a steering angle detection unit 22 to detect a steering angle φ of the steering wheel 12. The steering unit 14 has a torsion bar torque detection unit 24 to detect the torsion bar torque M. Dto detect its torsion. The torsion bar torque detection unit 24 preferably has Hall sensors for detecting the torsion or a twist angle. The steering unit 14 also has a damping unit 26, which is designed to dampen the movement of the steering wheel 12 depending on the situation.

[0039] According to the invention, a free return of the steering wheel 12 is determined by a difference between the torsion bar torque M D and the steering wheel torque M L , whereby a free return is detected if the difference between the torsion bar torque M D and the steering wheel torque M L falls below a predefined value. The steering wheel torque M L This is determined by a steering wheel acceleration, which is calculated by twice differentiating the steering angle φ, and multiplying it by a torsional inertia J. LThe steering wheel's torque is multiplied by 12. During free return, the steering wheel 12 is actuated solely by the torsion bar torque M. D accelerates, with the driver contributing no torque to the steering movement. Torsion bar torque M D and steering wheel torque M L In this situation, the torques are equal or their difference is close to zero. Provided that the difference between the torsion bar moment M D and the steering wheel torque M L If the value is 0 or very low, it is concluded that the driver is not contributing any torque to the steering wheel torque M. L This results in a free steering return. In this situation, the steering wheel 12 is separately damped by means of the damping unit 26, so that a yaw reaction of the vehicle can be prevented during the free return.

[0040] In Fig. Figure 2 schematically shows a block diagram for determining the steering wheel damping with free return. The torsion bar torque M serves as the input variable for determining the free return. D and the steering angle φ. To detect the free return, the steering angle acceleration of the steering wheel 12 is determined from the steering angle φ by double differentiation and via the torsional inertia J. L of the steering wheel 12 the steering wheel torque M L Determined by subtracting the torsion bar torque M D and the steering wheel torque M L The driver's torque contribution (hand torque) can be inferred, and a corresponding indicator signal I can be provided, which preferably indicates the free return as a signal between 0 and 1. The indicator signal I preferably has a slow rise. The detection of the free return is in Fig. 2 generally designated by 30. The damping unit 26 generally provides damping for the free return 32 and a basic damping 34 of the steering wheel 12 depending on a vehicle speed V and a steering angle velocity ω. The damping for the free return 32 is multiplied by the indicator signal I, as shown in 36, and is activated accordingly if a free return is detected and deactivated if a free return is not detected. The damping for the free return 32 and the basic damping 34 are added at 38 to set a general damping D of the steering wheel 12. The damping D can thus be set to a low value corresponding to the basic damping 34 during normal operation of the vehicle and increased by the return damping 32 in the case of a free return. Thus, an individual damping D of the steering wheel 12 can be reliably set depending on the situation with minimal technical effort.

[0041] In Fig. Figure 3 shows a detailed block diagram for recording the free return movement of the steering wheel 12 and for providing the indicator signal I, and is generally designated by 40. The steering angle φ serves as the input variable, from which the steering angular velocity ω is determined by derivation 42. From the steering angular velocity ω, the steering angular acceleration a is determined by further derivation 44. By multiplying the steering angular acceleration a by the torsional inertia J, the following is obtained: L The steering wheel torque M is set at 46 on the steering wheel 12. L determined. The torsion bar torque M detected by the torsion bar torque detection unit 24 D The data is filtered using a low-pass filter 48. The filtered torsional moment M D is determined by the steering wheel torque M L subtracted, as shown at 50, to obtain a dynamic hand torque M H to determine the force exerted by the driver on the steering wheel 12.

[0042] The steering angle velocity ω is low-pass filtered at 52 in order to be processed with minimal effort by the subsequent switch-on or switch-off conditions.

[0043] From the signals thus obtained, an activation condition is determined, or the free return of the steering wheel 12 is detected, as generally shown in Figure 54, and an activation condition, or the absence of free return, is determined, as generally shown in Figure 56. To determine free return, a threshold value is used in Figure 58 to ascertain whether a high steering wheel speed ω is present. Furthermore, in Figure 60, it is determined whether the hand torque or the torque difference between the steering wheel torque M is high. L and torsion bar torque M D a threshold value is undercut, i.e., a small moment difference exists, and furthermore, at 62, it is determined using a threshold value whether a large torsional bar moment M exists. DA signal is sent to a decision unit 66 using an AND operator, indicating whether a free return has been detected.

[0044] At point 56, it is generally determined whether the free return has ended and, accordingly, whether the return damping must be stopped. For this purpose, at point 68, it is determined whether the steering angular velocity ω falls below a threshold value, and at point 70, whether the hand torque M H or the difference between the steering wheel torque M L and the torsion bar torque M D exceeds a predefined threshold. Using two timers 72 and 74, the signals from operators 68 and 70 are delayed and forwarded to an OR operator 76. Operator 76 then detects whether there is a small steering angular velocity ω or a large difference between the steering wheel torque M. L and the torsion bar torque M DA reset signal R is forwarded to the decision unit 66, which resets the state of the detected free return. The time operator 74 is typically set by a vibration indicator S to detect correspondingly high fluctuations in the torsion bar torque M. D to be hired and thus be able to work reliably depending on the situation.

[0045] The decision unit 66 is connected to a timer 78, which sets a time delay, and is further connected to a slope limiter 80 to limit an increase or decrease of the provided signal.

[0046] As a result, the indicator signal I is provided, which reliably indicates whether or not there is a free return movement of the steering wheel 12.

[0047] In Fig. 4 is the time course of the steering angle φ, the yaw rate G of the motor vehicle, the measured torsion bar torque M Dand the estimated steering wheel torque M L as well as the indicator signal I.

[0048] Initially, the steering wheel 12 is steered (jerky) in a negative direction at time t0, as shown in Fig. 4a is indicated. At time t1, the steering process is aborted and the steering wheel 12 returns freely. Fig. 4a shows the damped return flow as a dashed line. Fig. 4b is the yaw rate G during the steering movement from Fig. Figure 1 shows the undamped (solid line) and damped (dashed line) return. As in Fig. As shown in 4c, the torsion bar moment M approaches D (dashed line) and the steering wheel torque M L (solid line) connected to each other, so that the free return flow can be reliably detected at t1. This is in Fig.4d schematically indicates the earliest detection time by a dashed fast indicator signal. The solid indicator signal I corresponds to the indicator signal modified by operators 78 and 80.

[0049] Overall, the free return can be reliably detected by the method according to the invention and the steering wheel 12 can be damped accordingly depending on the situation in order to reduce vibrations in the yaw rate G.

Claims

[1] Method (40) for steering a motor vehicle, comprising the steps: - Determining a steering wheel torque (M L ) based on a detected steering angle (φ) of a steering wheel (12) of the motor vehicle, - Detecting a torsion bar torque (M D ) of a torsion bar 16 of the motor vehicle, characterized by , that the steering wheel torque (M L ) and the torsion bar torque (M D ) are compared to detect a free return of the steering wheel (12). [2] Method according to claim 1, characterized by , that a steering wheel return damping (D) is set if the free return of the steering wheel (12) is detected. [3] Method according to claim 2, characterized by , that the steering wheel return damping (D) is added to a basic damping (34) of the steering wheel (12), provided that the free return of the steering wheel (12) is detected. [4] Method according to any one of claims 1 to 3, characterized by , that the steering wheel torque (M D) based on an angular acceleration (a) and a steering inertia (J) L ) is determined. [5] Method according to any one of claims 1 to 4, characterized by that the free return is detected, provided there is a difference between the steering wheel torque (M L ) and the torsion bar torque (M D ) falls below a predefined threshold. [6] Method according to any one of claims 1 to 5, characterized by , that the torsion bar torque (M D ) is filtered using a low-pass filter (48). [7] Method according to any one of claims 1 to 6, characterized by , that the torsion bar torque (M D ) is delayed by means of a timer. [8] Method according to any one of claims 1 to 7, characterized by , that the steering wheel angular velocity (ω) is filtered by means of a low-pass filter (52). [9] Method according to any one of claims 5 to 8, characterized by, that the threshold value depends on the steering wheel angular velocity (ω) of the steering wheel (12) and on the torsion bar torque (M D ) is set up. [10] Method according to any one of claims 1 to 9, characterized by , that an end of the free return is detected, provided there is a difference between the steering wheel torque (M L ) and the torsion bar torque (M D ) exceeds a predefined threshold. [11] Method according to claim 10, characterized by , that the steering wheel speed (ω) and the difference are delayed by means of a timer. [12] Method according to claim 11, characterized by , that the time delay depends on an amplitude and / or a frequency of the torsion bar torque (M D ) is set up. [13] Device (10) for steering a motor vehicle with: - a steering wheel (12) for operating the device by means of a steering wheel operation, - a torsion bar (16) for transmitting the steering wheel operation to steered wheels (20R, 20L) of the motor vehicle, - a steering angle detection unit (22) for detecting a steering angle (φ) of the steering wheel (12), - a torsion bar torque detection unit (24) for detecting a torsion bar torque (M L ) of the torsion bar (16), and - a return determination unit (14) for determining steering wheel return, characterized by , that the return determination unit (14) is designed to measure a steering wheel torque (M L ) to determine based on the steering angle (φ) and a free return of the steering wheel (12) based on the steering wheel torque (M) L ) and the torsion bar torque (M D to determine.

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