Method for determining the tilt angle of a vehicle

Abstract

The invention relates to a method for determining the tilt angle of a vehicle about the transverse axis thereof on the basis of a load, the method having the following steps: • determining the starting time of a braking process on the basis of the brake pedal position, • determining the longitudinal acceleration and the pitch rate of the vehicle by means of an IMU sensor, • determining the speed of the vehicle and temporally deriving the determined speed in order to obtain the longitudinal acceleration of the vehicle, • determining the time at which the two determined longitudinal acceleration values are equal, • determining the difference between the determined longitudinal accelerations at the start of the braking process and the time at which the longitudinal acceleration determined by the IMU sensor and the longitudinal acceleration derived from the speed are equal, and • determining the tilt angle of the vehicle about the transverse axis thereof on the basis of a load from this difference using a vehicle model or by integrating the pitch rate from the initial time to the time the longitudinal acceleration values are equal.

Description

[0001] Description

[0002] Method for determining the tilt angle of a vehicle

[0003] The tilting of a vehicle due to loading, particularly in the rear area, e.g., in the trunk, is to be determined. The determined vehicle tilt is to be used, for example, for headlight range control, chassis level control, or a hill-hold assist system.

[0004] Previously, chassis sensors were used to determine vehicle roll for automatic headlight range adjustment. However, for cost reasons, efforts are underway to replace these sensors with other vehicle sensors. One possibility is to use inertial sensors such as accelerometers or yaw rate sensors. These are often referred to as IMU sensors (inertial measurement units). However, commercial IMU sensors have the disadvantage of exhibiting high drift and also measuring the road's camber. To compensate for these drawbacks, other methods are needed. Headlight range control based on IMU sensors is used, for example, in the...

[0005] EP 2 402 212 B1 discloses. However, there the headlight range is only adjusted when the vehicle is stationary, while the optical axis of the headlights is to remain unchanged when the vehicle is moving on a road.

[0006] German patent DE 10 2015 206 687 A1 describes a control device designed to output an adjustment signal to adjust the angle of the vehicle's optical axis in response to changes in the overall value when the vehicle is stationary, with the exception of non-static load changes caused by switching a foot brake and / or a parking brake and / or a gearshift position. Thus, pitching of the vehicle after coming to a standstill during a holding maneuver is not to be taken into account when adjusting the headlight range, as this is an oscillation that does not result in a permanent tilt. The object of the invention is to provide a simple method for determining the tilt angle of a vehicle about its transverse axis due to a load.

[0007] The task is solved by a method for determining the tilt angle of a vehicle about its transverse axis due to a load, with the following steps:

[0008] • Determining the start time of a braking process based on the brake pedal position,

[0009] • Determining the longitudinal acceleration and pitch rate of the vehicle using an IMU sensor,

[0010] • Determining the vehicle's speed and differentiating the determined speed over time to obtain the vehicle's longitudinal acceleration,

[0011] • Determining the point in time at which the two determined longitudinal acceleration values ​​are equal,

[0012] • Determining the difference between the measured longitudinal accelerations at the beginning of the braking process and the point in time when the longitudinal acceleration measured by the IMU sensor and the longitudinal acceleration derived from the velocity are equal, and

[0013] • Determining the vehicle's tilt angle about its transverse axis due to a load from this difference using a

[0014] vehicle model or by integrating the pitch rate from the initial time until the longitudinal acceleration values ​​are equal.

[0015] Two accelerations are therefore determined at defined times: namely at the beginning of a braking process, when the vehicle begins to pitch forward around its transverse axis, and at the time when the longitudinal axis of the vehicle is parallel to the road.

[0016] From these two accelerations and the resulting difference, and possibly the mass of the vehicle, the angle by which the vehicle has rotated around its transverse axis during the time period, i.e., pitched forward, is determined with the help of a vehicle model.

[0017] Alternatively, the pitch rate or yaw rate determined by the IMU sensor can be integrated from the initial time until the longitudinal accelerations are equal in order to determine the angle.

[0018] The angle determined by these two methods corresponds to the vehicle's tilt in a stationary state due to its load. This allows the headlight range to be correctly adjusted, for example, readjusted, even while driving.

[0019] Advantageously, the speed sensor used can be formed from wheel speed sensors. These are usually already present in a modern vehicle, so no additional sensors are required for the process.

[0020] Additionally or alternatively, the speed sensor can be formed with a GNSS (Global Navigation Satellite System), i.e., the speed is determined from corresponding receivers that are usually present in a vehicle.

[0021] The vehicle model can advantageously be a Half Car Model 4 DOF (degree(s) of freedom).

[0022] The determined tilt angle can be advantageously used to adjust the range of the vehicle's headlights. This is possible both while driving during every braking maneuver and, in principle, during every acceleration maneuver, which also involves a pitching motion, but in the opposite direction.

[0023] It can be advantageous to determine the tilt angle cyclically during each braking process. The invention is explained in more detail below with reference to an exemplary embodiment and the figures. These show:

[0024] Fig. 1 schematically shows a vehicle with a constant speed and a tilt angle due to rear loading,

[0025] Fig. 2 shows the vehicle after a braking procedure has been initiated.

[0026] Fig. 3 shows the vehicle during the braking process at the point when the vehicle's longitudinal axis is parallel to the road surface.

[0027] Fig. 4 shows the vehicle at the end of the braking process with maximum pitch angle and

[0028] Fig. 5 schematically shows a vehicle in two states to illustrate the tilt angle.

[0029] Figure 1 shows a vehicle traveling at a constant speed on a level surface. However, the situation described also applies to an inclined roadway. Due to a load, the vehicle's rear suspension is compressed or it is tilted. This tilt can be detected using a sensor (e.g., an IMU sensor). The arrows indicate the measurement directions in the horizontal and vertical planes of the vehicle.

[0030] During a sufficiently hard braking maneuver, the vehicle pitches forward due to its inertia. This is illustrated in Figures 2 to 4. During the pitching motion (around the vehicle's transverse axis) from the starting point to maximum suspension compression, the point is reached at which the vehicle's longitudinal axis is parallel to the road surface, as shown in Figure 3. This point after the start of the braking maneuver is important because it, or rather the time interval between the two points in time, provides information about the vehicle's load. The heavier the vehicle is loaded, the longer it takes for the two independently measured longitudinal accelerations to equalize. From this, the load and the resulting tilt can then be calculated using a vehicle model. The longitudinal axis of an unloaded vehicle would always be parallel to the road surface when stationary or traveling at a constant speed.

[0031] First, the start of the braking maneuver is determined, which can be done by detecting the brake pedal position. From this point onward, the longitudinal acceleration and pitch rate of the vehicle are measured using an IMU sensor. Then, the point in time at which the vehicle's longitudinal axis is parallel to the road surface is determined (see Fig. 3). At this point, the longitudinal acceleration measured by the IMU sensor and the acceleration determined by differentiating the vehicle's velocity over time are equal.

[0032] The IMU sensor should be located at the vehicle's center of mass and initially calibrated to compensate for mounting tolerances and static offsets. The focus is primarily on the longitudinal acceleration measured by the IMU sensor. Simultaneously, the first derivative of the vehicle speed, determined using, for example, wheel speed sensors, is calculated. It would also be possible to use a GNSS signal—such as a GPS signal—for speed determination.

[0033] As soon as the two values ​​(IMU longitudinal acceleration signal and the first derivative of the vehicle speed signal) are equal during the braking maneuver, this means that the vehicle is parallel to the road. Both signal values ​​should be provided with the same cycle time and latency.

[0034] The pitch angle around the vehicle's transverse axis during a braking maneuver is then calculated using a vehicle model. This model calculates the vehicle's pitch angle during transient phases (acceleration and deceleration). The pitch angle is calculated in the model using the inertial force (longitudinal acceleration from the IMU and vehicle mass). The portion of the pitch angle between the initial point (Fig. 1) and the point at which the vehicle's longitudinal axis is parallel to the road surface represents the vehicle's roll due to its load.

[0035] The deceleration can be determined based on the brake pedal position or by other means (speed, GPS position, etc.).

[0036] Figure 5 shows the two states of the vehicle at the beginning of a braking maneuver and when the longitudinal accelerations are equal, i.e., when the vehicle's longitudinal axis is parallel to the road surface. Arrows indicate the acceleration values ​​from the IMU sensor, showing that the longitudinal acceleration value pointing in the direction of the vehicle's longitudinal axis is initially tilted and, during the braking maneuver, becomes parallel to the road surface and thus also parallel to the vehicle acceleration in the direction of the road surface, which is determined by integrating the vehicle speed.

[0037] This is advantageously used to calculate the tilt using a vehicle model, so that only existing sensors are used to determine any tilt during driving due to a load or a change in load - for example, if a load has shifted - and to adjust, for example, the range of the headlights.

Claims

Patent claims 1. Method for determining the tilt angle of a vehicle about its transverse axis due to a load, comprising the following steps: • Determining the start time of a braking process based on the brake pedal position, • Determining the longitudinal acceleration and pitch rate of the vehicle using an IMU sensor, • Determining the vehicle's speed and differentiating the determined speed over time to obtain the vehicle's longitudinal acceleration, • Determining the point in time at which the two determined longitudinal acceleration values ​​are equal, • Determining the difference between the measured longitudinal accelerations at the beginning of the braking process and the point in time when the longitudinal acceleration measured by the IMU sensor and the longitudinal acceleration derived from the velocity are equal, and • Determining the tilt angle of the vehicle about its transverse axis due to a load from this difference using a vehicle model or by integrating the pitch rate from the initial time until the longitudinal acceleration values ​​are equal.

2. Method according to claim 1, wherein the speed sensor is formed with wheel speed sensors.

3. Method according to claim 1, wherein the speed sensor is formed with a GNSS.

4. Method according to any one of claims 1 to 3, wherein the vehicle model is a Half Car Model 4 DOF.

5. Method according to one of the preceding claims, wherein the determined tilt angle is used to adjust the range of the vehicle headlights.

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