Vehicle stabilization and braking distance optimization through side-alternating steering impulses in single-drive vehicles

Abstract

The invention relates to a vehicle dynamics control method for motor vehicles with individual drive (front or rear drive) which serves to shorten the braking distance and to improve driving stability in asymmetric friction coefficient conditions (µ-split). The method is based on software-controlled, alternately side-directed steering impulses, which cause a targeted variation of the wheel normal forces through kinematic lateral displacement as a result of steering angle deflection. The steering impulses are executed in sequential pulse sequences, between which neutral phases with a steering angle of zero are provided. During these phases, an algorithmic evaluation of vehicle dynamics data (yaw rate, deceleration, wheel speed profile) is performed, based on which a decision is made whether the pulse sequence is terminated, repeated or continued in a graded escalation logic. The process works independently of ABS or brake interventions, requires no additional hardware and can be fully integrated into existing electronic control units using software. It enables adaptive, driving-condition-dependent brake force distribution, increases directional stability and shortens the braking distance, especially on smooth or asymmetrically gripping road surfaces.

Description

Technical field:

[0001] The invention relates to a vehicle dynamics control method for motor vehicles with individual drive (front- or rear-wheel drive) for shortening the braking distance and improving directional stability under asymmetric friction conditions. The method is based on software-controlled, alternately lateralized steering impulses, which effect a targeted variation of the wheel normal forces through kinematic lateral displacement resulting from the steering impulse deflection. In contrast to all-wheel drive systems with active differential control (see BD4ML), BD2ML operates entirely without mechanical axle decoupling and is specifically tailored to the physical limitations of individual drive concepts.

[0002] The present application is technically related to the German patent application filed on December 17, 2024, under file number DE 10 2024 004 430.2, entitled “Zig-Zag Movement of the Steering System during Acceleration or Braking of Vehicles” (ZZBL). The impulse logic described therein for restoring driving stability in the event of loss of grip is functionally extended in the present application and specifically applied to braking phases with asymmetrical coefficients of friction (µ-split) and single-drive configurations. Application BD2ML thus represents a thematically and functionally focused further development of the control principles disclosed in the ZZBL application. State of the art:

[0003] From DE 10 2024 001 244 A1 (hereinafter: D1), a driving function for vehicles with steer-by-wire steering is known, in which sinusoidal steering movements are automatically applied to the front wheels to improve traction on loose surfaces, especially sand. The continuously executed steering angle profiles serve to increase traction and prevent the vehicle from getting stuck. A sequential impulse control with neutral phases and evaluation intervals is not disclosed therein. DE 10 2005 019 339 A1 (hereinafter: D2) relates to a vehicle control system with an active steering system for driving over obstacles. In this system, steering wheel or wheel oscillations are initiated when off-road situations are detected to keep the vehicle on the desired path. The disclosure relates to off-road scenarios and obstacle overcoming; a side-by-side, synchronized wheel load transfer during braking is not described therein.

[0004] German patent application DE 10 2015 224 760 A1 (hereinafter referred to as D3) discloses a method for active steering assistance in the case of stuck vehicles. In the event of a stuck vehicle, a special control mode is activated in which periodic steering angle curves (e.g., sinusoidal) are automatically applied to free the vehicle. The disclosure thus relates to rocking maneuvers while stationary and not to braking distance optimization during dynamic driving maneuvers.

[0005] DE 11 2020 004 314 T5 (hereinafter: D4) describes a steering control device that, when slippage is detected, determines the current steering angle of the steering wheel as a reference and accordingly controls the drive shaft of a wheel within a predefined angular range. The aim is to stabilize the vehicle when slippage is detected. A side-by-side pulse sequence with neutral phases is not disclosed therein.

[0006] DE 11 2019 002 782 T5 (hereinafter: D5) relates to a device for controlling rear-wheel steering, in which phase-shifted rear-wheel steering angles are determined and implemented depending on detected driving situations. The aim is improved maneuverability and driving dynamics. A clock-based impulse control for shortening braking distances in µ-split operation is not taught.

[0007] In contrast to the aforementioned documents, the present invention provides a method in which alternating, side-directed steering impulses are generated within a defined steering angle range of ±3° to ±15° and at a frequency of 2 Hz to 10 Hz. The impulses are generated in sequential pulse trains, with neutral phases between each train during which the steering angle returns to 0°. During these neutral phases, an algorithmic evaluation of vehicle dynamics data such as yaw rate, wheel speed profile, and deceleration is performed. Based on this evaluation, a decision is made as to whether the pulse train is terminated, repeated, or escalated.

[0008] This design achieves a lateral normal force transfer at the wheels of a single drive axle, enabling dynamic brake force modulation without interfering with brake pressure or drive torque. This distinguishes the claimed teaching from the continuous sinusoidal steering angle modulations according to D1 and D3, the off-road oscillations for obstacle overcoming according to D2, the reference angle-based controls according to D4, and the adaptive rear-wheel steering systems according to D5. Purpose of the invention:

[0009] The object of the invention is to provide a control method that, during critical braking phases, generates a time-limited variation in the wheel normal forces through software-controlled, alternately side-directed steering impulses. This side-dependent wheel load transfer enables an asymmetrical distribution of braking force, which contributes to stabilizing the vehicle and shortening the effective braking distance – particularly under asymmetrical friction coefficients (µ-split according to DIN EN ISO 5048). The vehicle dynamics effect of the steering impulses can be mathematically described using a simplified multibody system (e.g., a 2D model with three degrees of freedom: roll, pitch, yaw) or a quasi-static wheel load transfer model.

[0010] The wheel-side normal force difference ΔFz resulting from a defined steering angle deflection δ can be approximately calculated using the body-induced rolling moment: M_roll=h⋅m⋅a_y⋅sin(δ) where h = center of gravity [m] m = vehicle mass [kg] a_y = lateral acceleration [m / s²] 2 ] δ = Steering angle [wheel]

[0011] The resulting wheel load difference creates an asymmetrical deceleration distribution between the wheels, thus stabilizing the vehicle in µ-split situations without requiring brake intervention.

[0012] For physical validation, the effect can be simulated using a simplified vehicle model (e.g., a 2D mass point with pitch and roll motion), whereby a measurable lateral load difference is generated by alternating steering impulses with a defined frequency and amplitude. Initial model calculations show that even small steering impulses in the range of ±5° at frequencies around 3-4 Hz can generate wheel load differences > 50 N. With µ-split, this leads to a significant difference in the wheel deceleration curve without exceeding vehicle dynamic stability limits (e.g., yaw rate ±8 ° / s). The frequency ranges are based on the typical natural frequency of the body motion (roll / pitch), which lies between 1.5 Hz and 5 Hz for vehicles. Simulation-based estimates with multibody models show wheel load shifts between 50 and 150 N, depending on the vehicle type.

[0013] In front- or rear-wheel-drive vehicles, when a braking maneuver is detected under unstable conditions (e.g., on ice, downhill, or in a split-level situation), alternating steering impulses are automatically triggered. These typically occur within a steering angle range of ±3° to ±15°, preferably between ±4° and ±10°, and at frequencies between 2 Hz and 10 Hz, preferably between 3 Hz and 5 Hz. The impulses result in alternating lateral loading of the wheels, thus dynamically modulating the wheel load distribution.

[0014] This method is intended exclusively for vehicles with rigid axle drive and no decoupling unit. A time-limited axle decoupling, as found in all-wheel drive systems (e.g., BD4ML), is neither required nor intended. The impulse effect is achieved solely through the side-by-side variation of the wheel normal force by the steering actuator.

[0015] In test scenarios, this typically leads to asymmetrical wheel deceleration, depending on the friction profile, and stabilizes the vehicle's trajectory. A passive differential effect acts synchronously. Steering impulse modulation occurs independently of ABS intervention and is configured so that it does not require brake pressure modulation. The effect is based on a passive shift in the normal force, allowing the ABS to automatically adjust the braking force. Integration with ABS logic is possible, but not mandatory.

[0016] To avoid unwanted instability or additional disturbances, sequential steering angle deflection only occurs when braking instability is detected and is limited to a maximum steering speed of, for example, 40° / s and short activation periods (e.g., max. 0.5 s). The direction of the impulse is controlled synchronously with the drift correction, so that the yaw rate is reduced and not increased.

[0017] The steering inputs cease as soon as stable driving dynamics are detected. The process can be implemented via software integration into existing electronic control units (ECUs) and requires no additional hardware.

[0018] The BD2ML method can be integrated as a software module via vehicle buses.

[0019] It can be combined with higher-level stability programs and is scalable for production vehicles with steering actuators. In an extended version, the activation and frequency of the steering impulses are adapted depending on driving dynamics data such as brake pressure gradient, yaw rate, steering angle speed and lateral acceleration, so that feedback to the driving state control is created.

[0020] The impulses do not follow any lane-keeping intention, but are asymmetrical single impulses (e.g., 50 ms rise, 300 ms fall, amplitude 6°) used exclusively for side-by-side load modulation. Due to their limited amplitude (±3° to ±10°) and frequency (3-5 Hz), they remain imperceptible to the driver or are neutralized by steering damping. No active change in the direction of travel occurs.

[0021] Fig. 2. The steering impulses are not sinusoidal or trapezoidal, but rather implemented as individually impulsive steering angle deflections with nonlinear rise and fall characteristics. They are comparable to asymmetrical single impulses that have a brief effect and then return to a defined rest phase. Trapezoidal shapes are deliberately avoided, as these can lead to undesirable directional deviations at higher speeds, especially during the first steering cycle after activation. The chosen impulse shape enables controlled, lateral wheel load transfer without compromising vehicle stability through abrupt changes in yaw rate. Advantages:

[0022] Increased stability during braking phases Reduced braking distance on slippery surfaces and micro-split surfaces; lane keeping through side-by-side deceleration modulation Feasible with existing steering actuators without hardware expansion. Physically plausible concept with a comprehensible operating mechanism. Protection against oversteering through control limits. Additional benefits:

[0023] Specific optimization for individual drive concepts. Compatible with existing ABS / ESP systems. No intervention in drive torque or clutches. Adaptive driving stability achievable with existing steering actuators without hardware upgrades. Ideal for small and compact vehicles during micro-split braking or downhill braking.

[0024] The alternating steering impulses directed sideways are not perceptible to the driver due to their low amplitude and frequency, or are actively dampened by the steering actuators. System integration:

[0025] The BD2ML method can be integrated as a software module via vehicle buses. This can be combined with higher-level stability programs and is scalable for production vehicles with steering actuators. In an extended version, the activation and frequency of the steering impulses are adapted depending on the brake pressure gradient, yaw rate, steering angle velocity, and lateral acceleration, thus creating feedback to the vehicle state control system. Security strategy for µ-split:

[0026] To prevent potential oversteer due to asymmetric deceleration, alternating steering inputs directed to each side are only activated within a stable yaw rate window (e.g., ±8° / s). The steering inputs are controlled to generate a weight transfer to the wheel, thereby reducing the existing yaw rate. Automatic deactivation occurs either when critical vehicle dynamics limits are exceeded (e.g., yaw rate, lateral acceleration) or after a stable driving condition is restored. Example design:

[0027] When driving downhill on snow, a front-wheel-drive vehicle experiences significant wheel slippage on one side. Targeted steering inputs increase the normal force on the wheel with better traction, thus improving wheel deceleration and preventing the vehicle from skidding. (p. Fig. 1, Fig. 2)

[0028] Activation occurs exclusively within a defined stability window (yaw rate ±8° / s), supplemented by lateral acceleration and brake pressure analysis. Active wheel speed differential analysis is not part of the procedure and clearly distinguishes BD2ML from more complex all-wheel-drive systems. Escalating steering impulse modulation with vehicle dynamics evaluation intervals:

[0029] In an extended embodiment, the activation of alternating, side-directed steering impulses occurs in a staged sequence with sequential clock logic. First, a single short steering impulse cycle with a left-right deflection is executed, and then the steering returns to straight-ahead driving (steering angle 0°). This is followed by a vehicle dynamics evaluation interval with a pre-configured duration, in which the system evaluates the vehicle's reaction using vehicle dynamics data (e.g. yaw rate, deceleration, wheel speed profile).

[0030] The duration of the vehicle dynamics evaluation interval is in the range of 0.3-0.7 s, depending on the input signal profile.

[0031] The impulse activation occurs in discrete cycles, each consisting of a brief steering impulse cycle (e.g., left-right steering input) followed by a vehicle dynamics evaluation interval. The impulse levels are escalated (by one to three times) if insufficient stabilization is detected. Unlike methods with dynamic frequency escalation (see BD4ML), the impulse frequency remains constant to maintain directional stability and ride comfort.

[0032] If the initial impulse cycle does not result in any noticeable stabilization or improvement in deceleration, the number of steering impulse cycles is increased in the next cycle stage (e.g., two consecutive steering impulse cycles), followed by another vehicle dynamics evaluation interval. This process is increased up to a defined maximum level (e.g., three cycles), each cycle interrupted by a neutral phase with zero steering angle.

[0033] The sequential steering angle deflection is automatically terminated as soon as sufficient braking effect, stable driving dynamics, or target deceleration is detected. This creates a graduated escalation logic that ensures minimal intervention with maximum driving stability and prevents uncontrolled continuous activation.

[0034] The process remains entirely limited to individual drive systems and deliberately avoids any mechanical intervention in drive, differential, or clutch systems. Decoupling of axles or active torque redistribution is not included. Drawing description Figure 1 illustrates the operating principle of the friction coefficient restoration process for single-wheel driven vehicles (BD2ML). (Dynamic torque shift caused by side-alternating steering inputs). The aim of this illustration is to visualize the vehicle dynamics relationships and the interaction between steering inputs, wheel load, and differential torque. ① Sensors detect asymmetrical friction coefficients 2. Side-alternating steering impulses activated ③ Front or rear axle differential reacts → with braking distance optimization 4. System deactivates after stabilization Figure 2 schematically shows the temporal progression of side-alternating steering impulses in a single-drive vehicle (BD2ML). The zigzag line represents the rhythmically triggered side-by-side steering angle deflection, with observation phases between the impulses. The graph shows four consecutive impulse cycles with an escalating effect. The line follows an analogous pattern to an ECG to visualize the transition from unstable to stabilized driving behavior.

Claims

[1] Methods for improving driving stability and shortening the braking distance of a motor vehicle during a braking process, characterized by , that by software-controlled, alternately side-directed steering impulses in the steering angle range of ±3° to ±15° and with a frequency between 2 Hz and 10 Hz, a side-by-side normal force shift is generated at the wheels of a vehicle axle, whereby the steering impulses are activated in the form of sequential impulse sequences, and an observation phase with a steering angle of zero is provided between each individual impulse sequence, in which, based on vehicle dynamics data such as yaw rate, deceleration or wheel speed profile, it is determined whether the pulse sequence is terminated, repeated or extended by a further repetition (e.g. two or three times), the return to straight-line running between the impulse sequences ensures that no sustained directional deviation occurs. [2] Method according to claim 1, characterized by , that The steering impulses are executed as alternating, oppositely directed steering angle deflections with return to zero position. where a phase with zero steering angle is maintained between each reversal of direction in order to avoid a permanent deviation in the direction of travel. [3] Method according to any one of the preceding claims, characterized by , that the frequency, amplitude and pulse duration of the steering impulses are adaptively controlled depending on vehicle dynamics data such as yaw rate, steering angle velocity, lateral acceleration and brake pressure gradient. [4] Method according to any one of the preceding claims, characterized by , that The steering impulses occur independently of ABS intervention and do not require modulation of the brake pressure. the braking force distribution is influenced exclusively by the generated normal force shift. [5] Method according to any one of the preceding claims, characterized by , that The activation of the alternating, side-directed steering impulses only occurs within a stable yaw rate window. preferably within a range of ±8 degrees per second, to avoid oversteering due to excessive lateral acceleration or deviation from the direction of travel. [6] Method according to any one of the preceding claims, characterized by , that The process is implemented using software via existing electronic control units (ECUs) of the vehicle. and does not require any additional hardware.

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