Method for determining the tilt angle of a vehicle

Abstract

The invention relates to a method for determining the tilting of a vehicle on the basis of a load by determining the mass of the vehicle by determining the natural frequency of the vehicle during a braking process, the method having the following steps: detecting a braking process; detecting the resulting standstill of the vehicle; determining the natural frequency of the vehicle by means of a sensor by measuring the vibration of the vehicle directly after the standstill and evaluating the sensor signal; determining the total mass from the natural frequency by means of a vehicle model; determining the persons sitting in the vehicle and the distribution thereof by means of a seat occupancy detection sensor system; determining the residual load by subtracting the number of persons multiplied by an assumed average weight from the previously determined total mass, assuming that the residual load is in the boot; and determining the tipping from the distribution of the persons and the residual load using a beam model.

Description

[0001]202400654 1 Description Method for Determining the Tilt Angle of a Vehicle The tilt of a vehicle due to loading, particularly in the rear area, e.g., in the trunk, but also due to passengers in the back seat, is to be determined. The determined vehicle tilt is to be used, for example, for headlight range control, chassis leveling, or a hill-hold assist system. Previously, chassis sensors were used to determine vehicle tilt for automatic headlight range adjustment. However, for cost reasons, attempts are being made 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 unit). However, commercial IMU sensors have the disadvantage of exhibiting high drift.as well as measuring the inclination of the road surface. To compensate for these disadvantages, other methods are needed. A headlight range control system based on IMU sensors is disclosed, for example, in EP 2402212 B1. However, there the headlight range is only adjusted when the vehicle is stationary, while the optical axis of the headlights is intended to remain unchanged when the vehicle is moving on a road. The object of the invention is to provide a method for determining the tilt angle of a vehicle about its transverse axis due to a load, which can be carried out in a simple manner. This object is achieved by a method for determining the tilt angle of a vehicle due to a load by determining the mass of the vehicle by determining the natural frequency of the vehicle during a braking process, with the following steps: detecting a braking process, 202400654 2 detecting the resulting standstill of the vehicle,Determining the vehicle's natural frequency using a sensor by measuring the vehicle's vibration immediately after it comes to a standstill and evaluating the sensor signal; determining the total mass from the natural frequency using a vehicle model; determining the number of occupants and their distribution using sensors, in particular seat occupancy sensors; determining the remaining payload by subtracting the number of occupants multiplied by an assumed average weight from the previously determined total mass, assuming the remaining payload is in the trunk; and determining the tilt from the distribution of occupants and the remaining payload using a beam model. After a sufficiently strong braking maneuver, a vibration of the vehicle can be detected. Since no further forces act on the vehicle after it comes to a standstill,This oscillation must represent the vehicle's natural frequency. Braking and standstill are determined using various characteristic signals, and the frequency is calculated, for example, using an FFT (fast Fourier transform). The natural frequency is primarily determined by the vehicle's spring constants and the total mass, which results from the vehicle weight and the weight of the payload. Since the spring constants do not change, it is possible to extract the mass from an equation describing this relationship and subsequently determine the vehicle's payload. The payload distribution is determined using seat occupancy sensors, which are usually present in modern vehicles, assuming a person weighs, for example, 75 kg. The remaining payload is assumed to be in the trunk.whose position, and thus distance, from the vehicle's center of gravity is known. The tilt can then be calculated using a physical bar model. 202400654 3 In an advantageous embodiment of the method, the sensor for determining the natural frequency is an IMU (inertial measurement unit) sensor. Such sensors are usually present in modern vehicles, so that the vehicle tilt can advantageously be determined without additional sensors. The invention is described in more detail below with reference to an exemplary embodiment and the figures. Fig. 1 shows a measurement diagram of various vehicle sizes during a braking process.Fig. 2 is a schematic representation of a simple vehicle model, and Fig. 3 is a schematic representation of a simple beam model. Fig. 4 is a more illustrative representation using a vehicle sketch. Fig. 5 shows forces on a vehicle sketch from the side. Fig. 6 shows forces on a vehicle sketch on an incline. When a vehicle brakes to a standstill, an oscillation of acceleration can be measured at the moment the vehicle actually reaches a completely stopped state, as the brakes switch from sliding friction to static friction, resulting in much higher forces that impart momentum to the mass of the vehicle. This can be seen as an oscillation in Fig. 1. The idea is,that the frequency of this oscillation must be defined primarily by the vehicle mass with additional components such as spring forces and geometric distances from the center of gravity of the forces generated by the springs. The calculation of the natural frequencies, as found on the website "Half Car Modeling (skill-lync.com)," is described below. A corresponding vehicle model is shown schematically in Fig. 2. A vertical oscillation (when the front and rear springs compress and rebound synchronously) and a pitching oscillation (positive when the front suspension compresses and / or the rear rebounds) are then calculated using the formulas... with the constants undW^ ^ 9.79 Spring weight (kN)a ^ 106.7 Center of gravity behind the front axle (cm) 202400654 5 ^^ 228.6 Wheelbase (cm)b ^ l ^ a Center of gravity in front of the rear axle (cm)k^ ^ 24.52 ∗ 10^ Stiffness of the front spring (kN / m to N / m)k^ ^ 26.27 ∗ 10^ Stiffness of the rear spring (kN / m to N / m)r^ ^ 102.6 Radius of gyration (cm)m^ ^ W^ ∗ 10^ / 9.81 Spring mass (kN to kg)I^ ^ m^ ∗ r^^ Moment of inertia (kg.cm^2) calculated. The frictional forces of the damper are ignored. Substituting this into the formula above yields the following for the frequency Mit follows 4⋅ ^^ ⋅ 3 ^4 ⋅ / ' # )0^ ⋅ ! ⋅ !4 ⋅ ^6 ^ " $%& ⋅ *+^ ^ %&^ ⋅ *+^ 202400654 6 The solutions to a quadratic equation are: This results in the following for the total mass: 1 ⋅ 3 ± >^6 ⋅ 3^ ^ 4^6*+^ ⋅ / ' # )0^ ⋅ !" ⋅ ! 2 % ^ $&<,^ 2 ⋅ ^6 ⋅ *+ ^with 3 ^ 1! ^ ^ ^" # !$2 ⋅ *+ # ' ⋅ !" # ) ⋅ !$Both solutions must be checked, as one is only an apparent solution. It is possible that one solution is always the correct solution, since the only way to switch between the solutions is for the square root to be equal to 0, as continuity is physically enforced. With this calculated sprung mass ms of the vehicle, the vehicle's payload can be defined, and the load-related tilt of the vehicle can be defined using a so-called beam model. The calculated payload is distributed in the vehicle using seat occupancy detection, assuming, for example, a standard person with a mass of 75 kg. The remaining payload after distribution among the seats is located in the trunk. The Fig.Figure 3 shows a simple beam model in which the forces acting on a vehicle are plotted; Figures 4 to 6 show these forces for simple vehicle models. L1 = Spring force front L2 = Spring force rear Dr = Weight force of the driver 202400654 7 Cdr = Weight force of the front passenger P1, P2, P3 = Weight forces of the passengers in the rear seat 1 to 3 Equations: 1) Torque of the axle load is equal to the load?< ⋅ ℎ< # ?^ ⋅ ℎ^ ^ / A$ # BC$0 ⋅ ℎ^ # / D< # D^ # D^0 ⋅ ℎ6 # DE ⋅ ℎF 2) Spring travel times lever travel is equal to ∆H< ∆H ∆H ⋅ ℎ for pure pitching front and rear. ^ ^ → < ^ ℎ ℎ< ^ < ℎ^ ∆H^ 3) Do the spring forces correspond to the load?< # ?^ ^ A$ # BC$ # D< # D^ # D^ # DE4) only pitching motionH< ^ ∆H< ^ H^ ^ ∆H^∆H^ ^ H^ ^ H< # ∆H<5) Spring equations ?^ ^ !$ ⋅ / H^ # ∆H^06) total torque around the axis of rotationJ ⋅ ℎK ^ / A$ # BC$0 ⋅ ℎ^ # / D< # D^ # D^0 ⋅ ℎ6 # DE ⋅ ℎFJ ^ A$ # BC$ # D< # D^ # D^ # DE 2 ) ^ 1) Einsetzen von 6) Substituting 5), times ∆Z2 Insertion of 4) 202400654 8 This approach seems somewhat too complicated for an algorithm intended to run unattended. Therefore, it is proposed that, as a simplification, a percentage distribution of the loads between the front and rear axles be used instead of equation 4). For further simplification, the pivot point is assumed to be in front of the front axle or behind the rear axle, so that the term hG – h1 cannot possibly become 0, which would cause the algorithm to fail. J^ ?< # ?^ ^ J ⋅ *'MNO< # J ⋅ *'MNO^*'MNO< # *'MNO^ ^ 1 From this, 5) results J⋅ *'MNO^ ^ ?^ ^ !$ ⋅ / H^ # ∆H^0 202400654 9 As a further simplification of the calculation, the zero point of the suspension travel is set to the position where the vehicle would be compressed on a horizontal plane without any further change in load. H < ^ H^ ^ 0 It follows that ∆H < ^ J ⋅ *'MNO < / !"∆H^ ^ J ⋅ *'MNO^ / !$ wobei ℎK ^ ℎ *'MNO < < ^^ (With hG from equation 6) Is the approximation good enough to adjust the headlight range accurately? These simplifications lead to deviations from the exact results. As long as the spring rates of the axes are approximately the same, the position of the pivot point is irrelevant for determining the angle change. The tilt angle P is determined using trigonometry. ∆ H^ ^ ∆H< β Wheelbase 202400654 10 The method according to the invention thus eliminates the need for chassis sensors and their wiring, resulting in significant cost savings. Chassis sensors are typically positioned in the vehicle in such a way that they are exposed to environmental influences, including stone chips, whereas the proposed IMU sensors can be mounted in the passenger compartment. IMU sensors are standard in every vehicle (ESP, airbag).

Claims

202400654 11 Claims 1. A method for determining the tilting of a vehicle due to a load by determining the mass of the vehicle by determining the natural frequency of the vehicle during a braking process, comprising the steps of: detecting a braking process, detecting the resulting standstill of the vehicle, determining the natural frequency of the vehicle by means of a sensor by measuring the vibration of the vehicle immediately after standstill and evaluating the sensor signal, determining the total mass from the natural frequency using a vehicle model, determining the number of persons seated in the vehicle and their distribution using sensors, determining the remaining payload by subtracting the number of persons multiplied by an assumed average weight from the previously determined total mass, assuming that the remaining payload is in the trunk, and determining the tilting from the distribution of the persons and the remaining payload using a bar model. 2.

1. A method according to claim 1, wherein the sensor for determining the natural frequency is an IMU sensor.

2. A method according to claim 1 or 2, wherein the sensor for determining the persons seated in the vehicle and their distribution is a seat occupancy detection sensor.

3. A method according to any of the preceding claims, wherein, for the sake of simplification, the beam model is simplified by a percentage distribution of the loads between the front and rear axles, and for further simplification, the pivot point is assumed to be in front of the front axle or behind the rear axle. 202400654 12 5. Method according to claim 4, wherein, as a further simplification of the calculation, the zero point of the suspension is set to the position as the vehicle would be compressed on a horizontal plane without any further change in load.

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