Method for stabilizing the straight-line running of an electrically powered vehicle

Abstract

The invention relates to a method for stabilizing the straight-line stability of a two-track, electrically powered vehicle (1) having at least two electric drives (2, 3) for driving an axle of the vehicle (1). Based on a vehicle dynamics estimate and data acquired by an acceleration sensor, a deviation from the straight-line stability is detected, and a corresponding stabilizing differential torque for the drives (2, 3) is determined. This stabilizing differential torque is then provided in addition to a total propulsion torque from the drives (2, 3).

Description

[0001] The invention relates to a method for stabilizing the straight-line running of a two-track electrically driven vehicle according to the preamble of claim 1.

[0002] From DE 10 2013 100 598 A1 a method for controlling a drive device of an electric vehicle with two electric motors for driving the electric vehicle is known, which comprises the following steps: - Vehicle-side monitoring of the driving stability of the electric vehicle using a control unit of the electric vehicle, - Comparison of the monitored driving stability with a target value for the driving stability of the electric vehicle, - Changing an operating parameter of an electric motor when the monitored driving stability deviates from the target value, wherein the operating parameter is a speed, a direction of rotation, a torque or an idle circuit.

[0003] It is an object of the present invention to provide a novel method for stabilizing the straight-line running of a two-track electrically driven vehicle.

[0004] The object is achieved according to the invention by a method which has the features specified in claim 1.

[0005] Advantageous embodiments of the invention are the subject of the subclaims.

[0006] The method for stabilizing the straight-line running of a two-track electrically driven vehicle with at least two electric drives for driving one axle of the vehicle is characterized according to the invention in that by means of a control unit - a target trajectory of the vehicle is determined from values ​​of an accelerator pedal position and a steering wheel angle specified by a driver of the vehicle and / or from values ​​of a propulsion torque and a target steering torque specified by a driver assistance system of the vehicle, - an actual trajectory of the vehicle is determined at least from camera images captured by a camera sensor, - an angular deviation of the actual trajectory from the target trajectory is determined, - an actual yaw rate of the vehicle is determined from data recorded by an acceleration sensor, - a deviation of the actual yaw rate from a target yaw rate is determined as a yaw rate error, - a new target yaw rate is determined by means of a controller from the angular deviation of the actual trajectory from the target trajectory applied to the controller's input side, less the yaw rate error, and / or from a characteristic curve stored in the control unit, - a target yaw moment is determined from a change in the target yaw rate over time and a vehicle inertia, - for each drive, a difference torque to an actual torque is determined, whereby by means of the respective difference torque, a necessary force can be applied to a wheel driven by the respective drive at given distances of the wheels from a center of gravity of the vehicle in order to generate the desired yaw moment, and - the respective differential torque is set on the drives.

[0007] The straight-line stability of a two-track vehicle becomes unstable with increasing vehicle speed. Even slight crosswinds or road irregularities can cause a deviation from the straight-line stability. The driver perceives such vehicle behavior as nervous and distracting. Furthermore, a deviation from the straight-line stability can lead to the vehicle losing its lane, and if the driver is careless, the vehicle may leave the roadway.

[0008] By means of the present method, straight-line stability and thus driving stability are adjusted by stabilizing torques from the electric drives, which are particularly designed as independent wheel drives. In one possible embodiment, the vehicle has at least two electric independent wheel drives on its rear axle to implement the independent wheel drive; in another possible embodiment, it also has at least two electric independent wheel drives on its front axle. The independent wheel drives are designed as wheel hub drives or as close-to-the-wheel drives.

[0009] In this method, based on a vehicle dynamics estimate and data acquired by the acceleration sensor, a deviation from straight-line stability is detected and a corresponding stabilizing differential torque is determined for the drives. This stabilizing differential torque is then provided in addition to the total propulsion torque from the drives.

[0010] Using this method, it is thus possible to stabilize straight-line stability without adjusting toe-in, resulting in reduced rolling resistance and, consequently, reduced tire wear and reduced energy consumption for driving the vehicle. This can increase the vehicle's range.

[0011] Embodiments of the invention are explained in more detail below with reference to a drawing.

[0012] It shows: Fig. 1 schematically shows a plan view of a vehicle on a roadway,

[0013] In the only Fig. 1 shows a plan view of a two-lane and electrically powered vehicle 1 located on a roadway FB.

[0014] The vehicle 1 comprises two electric drives 2, 3 designed as independent wheel drives on its rear axle and a control unit 4 that is data-linked to these drives and designed to control the drives 2, 3. The drives 2, 3 are each designed as wheel hub drives or as wheel-mounted drives 2, 3 and can be controlled by the control unit 4 for so-called torque vectoring, i.e., for actively influencing a yaw angle of the vehicle 1. In an embodiment not shown in detail, at least two electric independent wheel drives can additionally be arranged on the front axle of the vehicle 1.

[0015] The vehicle 1 moves on the roadway FB in a lane FS, which is delimited by the lane markings M1, M2. The movement of the vehicle 1 occurs depending on values ​​of an accelerator pedal position and a steering wheel angle specified by a driver of the vehicle 1 and / or values ​​of a propulsion torque and a target steering torque specified by a driver assistance system of the vehicle 1 and is intended to follow a target trajectory T s consequences.

[0016] Due to disturbances in or on the vehicle 1, for example due to mechanical play in chassis components or asymmetrical tire properties, and / or due to disturbances caused by the road surface FB, for example due to road surface irregularities and / or friction coefficient fluctuations, a deviation from the target trajectory T s deviating actual trajectory T ithe vehicle movement and thus lead to unstable straight-line travel of vehicle 1. The driving stability of vehicle 1 is generally not affected by such a deviation, so that understeering and oversteering of vehicle 1 generally do not occur.

[0017] However, such unstable straight-line stability may be perceived by the driver of vehicle 1 as nervous and disturbing driving behavior. Furthermore, a deviation in straight-line stability may lead to a loss of lane, and vehicle 1 may leave the lane FS and / or roadway FB if ​​driving carelessly.

[0018] In order to stabilize the straight-line stability of vehicle 1 without requiring a toe-in adjustment, it is provided to generate a differential torque by means of drives 2, 3 in addition to a total propulsion torque. This means that the adjustment of the differential torque carried out to stabilize straight-line stability is carried out when the axes of rotation of the wheels driven on the same axle by drives 2, 3 each run perpendicular to a vehicle longitudinal axis passing through the center of gravity of vehicle 1, or when the wheels run parallel to the vehicle longitudinal axis. A possible embodiment of a method for such a stabilization of the straight-line stability of vehicle 1 is described below, wherein the method is carried out by means of control unit 4.

[0019] During the driving operation of the vehicle 1, the control unit 4 determines the target trajectory T based on current input variables from the driver, in particular an accelerator pedal position and a steering wheel angle, and / or based on current input variables from driver assistance systems, in particular a propulsion torque and a target steering torque. s of the vehicle 1.

[0020] At the same time, the actual trajectory T is calculated from camera images captured by a camera sensor. i of vehicle 1 is determined and an angular deviation of the actual trajectory T i from the target trajectory T s From the camera images, the course of the roadway FB can be determined based on the detection of the lane markings M1, M2 that delimit the lane FS. An angle of vehicle 1 relative to the lane FS provides an indication of a possible deviation from the actual trajectory T. i from the target trajectory T s. The actual trajectory T i The speed of the vehicle 1, which is also descriptive, is determined, for example, by means of wheel speed sensors.

[0021] Furthermore, an actual yaw rate of vehicle 1 is determined from data acquired by an acceleration sensor. This can be done from trajectory location values ​​recorded regularly over time. The acceleration sensor is designed, for example, to record accelerations of vehicle 1 in six dimensions, i.e., to record horizontal, vertical, and lateral accelerations as well as yaw, pitch, and roll angular accelerations of vehicle 1. In particular, the yaw angular acceleration is linked to the target trajectory T s A yaw motion describes a rotation of vehicle 1 around its vertical axis and thus a change in direction. Deviations in the yaw motion lead to unwanted deviations of the actual trajectory Ti from the target trajectory T s .

[0022] For this reason, the acquired data is used to determine a necessary yaw torque to compensate for the disturbances in the yaw angular acceleration.

[0023] For this purpose, a deviation of the actual yaw rate from a target yaw rate is determined as a yaw rate error and a new target yaw rate is calculated using a controller from the angular deviation of the actual trajectory T applied to the input side. i from the target trajectory T s minus the yaw rate error and / or from a characteristic curve stored in control unit 4. The controller is, for example, a component of control unit 4.

[0024] Furthermore, a target yaw moment is determined from a change in the target yaw rate over time and a vehicle inertia. The target yaw rate over time represents a target yaw angular acceleration. In particular, the target yaw moment is determined by multiplying the vehicle yaw inertia and the target yaw angular acceleration.

[0025] To set this target yaw moment, a torque differential to the actual torque of each drive 2, 3 is determined for each drive 2, 3. Using the respective torque differential, a necessary force can be applied to a wheel driven by the respective drive 2, 3 at a given distance of the wheels from the center of gravity of the vehicle 1 to generate the target yaw moment. This means that the target yaw moment at the vehicle level is converted to the necessary forces at the wheel using the distances of the wheels from the center of gravity of the vehicle 1.

[0026] The determined differential torques are adjusted by control unit 4 on the drives 2, 3 to set the target yaw moment of the vehicle 1 and stabilize its straight-line stability. Thus, the wheel forces required to achieve the target yaw moment can be generated by the torque vectoring-capable drivetrain through the corresponding differential torques on the electric drives 2, 3, which are additionally applied to a propulsion or deceleration torque.

[0027] The previously described adjustment of the differential torque performed to stabilize straight-line stability is stopped when oversteering or understeering of vehicle 1 is detected, or when an impending oversteering or understeering of vehicle 1 is detected. Thus, the driving stability of vehicle 1 can always be ensured.

[0028] For the purpose of the present Fig.1 shows that in order to achieve the target trajectory T s a positive additional torque is generated by means of the drive 2 driving the right wheel in the direction of travel and / or a negative additional torque is generated by means of the drive 3 driving the left wheel in the direction of travel. This imposes a counterclockwise vehicle yaw moment and the deviation of the actual trajectory T caused by disturbances in the vehicle's straight-line travel i from the target trajectory T s regulated. List of reference symbols 1 vehicle 2 drive 3 Drive 4 Control unit FB roadway FS lane M1 road marking M2 road marking T i Actual trajectory T s Target trajectory QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2013 100 598 A1

[0002]

Claims

[1] Method for stabilising a straight-line running of a two-track electrically driven vehicle (1) with at least two electric drives (2, 3) for driving an axle of the vehicle (1), characterized by that by means of a control unit (4) - a target trajectory (T s ) of the vehicle (1) is determined, - at least from camera images captured by a camera sensor system an actual trajectory (T i ) of the vehicle (1) is determined, - an angular deviation of the actual trajectory (T i ) from the target trajectory (T s ) is determined, - an actual yaw rate of the vehicle (1) is determined from data recorded by an acceleration sensor, - a deviation of the actual yaw rate from a target yaw rate is determined as a yaw rate error, - a new target yaw rate is calculated using a controller from the angular deviation of the actual trajectory (T i ) from the target trajectory (T s ) minus the yaw rate error and / or from a characteristic curve stored in the control unit (4), - a target yaw moment is determined from a change in the target yaw rate over time and a vehicle inertia, - for each drive (2, 3), a difference torque to an actual torque is determined, whereby by means of the respective difference torque, a necessary force can be applied to a wheel driven by the respective drive (2, 3) at given distances of the wheels from a center of gravity of the vehicle (1) to generate the desired yaw moment, and - the respective differential torque is set on the drives (2, 3). [2] Method according to claim 1, characterized by that the adjustment of the differential torque carried out to stabilize the straight-line running is stopped when - oversteering or understeering of the vehicle (1) is detected or - an impending oversteer or understeer of the vehicle (1) is detected. [3] Method according to claim 1 or 2, characterized by that the adjustment of the differential torque carried out to stabilize the straight-line running is only carried out when the axes of rotation of the wheels driven on the same axle by the drives (2, 3) are each perpendicular to a longitudinal axis of the vehicle passing through the center of gravity of the vehicle (1).

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