Brake-dynamic steering impulse method for all-wheel drive vehicles for stabilization and braking distance reduction in μ-split situations

Abstract

The invention relates to a vehicle dynamics control method for all-wheel drive vehicles which, in the event of detected braking instabilities, combines a time-limited axle decoupling with software-controlled, alternately side-directed steering impulses. These impulses generate a changing wheel normal force shift, resulting in an asymmetrical brake force distribution. The process works independently of ABS or brake interventions, requires no additional hardware and can be implemented entirely via software using existing electronic control units. It enables adaptive, driving-condition-dependent stabilization and shortens the braking distance, especially on smooth or asymmetrical road surfaces (µ-split).

Description

Technical field:

[0001] The invention relates to a vehicle dynamics control method for motor vehicles with all-wheel drive for shortening the braking distance and improving driving stability, especially in the case of asymmetric friction coefficients (µ-split), icy or slippery road surfaces.

[0002] The present application is technically related to the German patent application filed on 17 December 2024 under file number DE 10 2024 004 430.2 entitled “Zig-Zack movement of the steering system when accelerating or braking vehicles” (ZZBL).

[0003] The control principle disclosed there, involving cyclically changing steering impulses to restore driving stability, is transferred here to all-wheel drive vehicles with a temporarily decoupled drive axle in order to enable targeted brake force transfer under asymmetric friction coefficient conditions (µ-split) during braking. Application BD4ML thus represents a function-specific further development within the ZZBL patent family. State of the art:

[0004] Various approaches to vehicle stabilization and traction improvement are known in the state of the art: -DE 10 2024 001 244 A1 (D1) discloses a driving function for vehicles with steer-by-wire steering in which sinusoidal steering movements are continuously generated on loose surfaces (especially sand) to prevent getting stuck. - DE 10 2005 019 339 A1 (D2) describes a vehicle control system that triggers steering oscillations in the event of off-road obstacles in order to enable further travel. - DE 10 2015 224 760 A1 (D3) relates to active steering assistance for stuck vehicles, in which periodic steering angle profiles are automatically applied to enable rocking free. -DE 11 2020 004 314 T5 (D4) shows a steering control device which uses the current steering angle as a reference in slip situations and performs wheel control within a defined range. - DE 11 2019 002 782 T5 (D5) concerns an adaptive rear-wheel steering system in which phase-shifted steering angles of the rear axle are used to improve driving dynamics.

[0005] However, none of these approaches teaches a clock-based, alternately side-directed pulse control with neutral phases and algorithmic evaluation, as is the subject of the present invention. Purpose of the invention:

[0006] Provision of a method that, in the event of detected braking instabilities, generates asymmetric deceleration through time-limited axle decoupling and alternating side-directed steering impulses. This enables stabilization of the vehicle's trajectory – without the need for direct braking intervention.

[0007] Solution: In case of instability detected by sensors (e.g. yaw rate > 8° / s or asymmetric wheel speed difference) (see Fig. 1) 1. Temporary decoupling of the rear axle by means of a controllable clutch unit (e.g. multi-plate clutch / Haldex). 2. Software-controlled alternating side-directed steering impulses on the active axle with: ◯ Steering angle range ±5° to 415°, ◯ Frequency range 2-10 Hz, ◯ Return to 0° after each cycle. 3. Induced normal force shift leads to different wheel deceleration left / right. 4. The vehicle is stabilized without permanently changing its direction of travel. 5. The axis decoupling is terminated after a maximum of 0.5 s or when stability is restored. Advantages: • Reduced braking distance with µ-split. • Lane keeping without active braking intervention. • Use of existing steering and clutch actuators (no additional hardware required). • OTA-enabled. • Software integration via existing ECUs is possible. Example:

[0008] An all-wheel-drive vehicle travels at 60 km / h onto a patch of ice. The sensors detect an unstable drift. BD4ML decouples the rear axle and applies 3 Hz steering impulses to the front axle. The wheel load on the left side increases briefly. The ABS modulates the brake pressure accordingly. The vehicle remains in its lane and stops 8 meters sooner than it would without intervention.

[0009] The steering impulses are not sinusoidal or trapezoidal, but rather take the form of individual, impulsive steering angle deflections with an accelerated rise and short return phase, comparable to an isolated spike in a heart rate signal under stress conditions. These are not complex, medically significant ECG waves, but rather individual, asymmetrical steering impulses with a shortened resting phase during escalation. The targeted increase in heart rate during sustained instability results in a progressively denser sequence of impulses with a rhythmic character.

[0010] The method does not involve active brake intervention, uses only passive steering angle impulses, does not integrate engine torque reduction, and utilizes time-limited decoupling + tactically controlled individual impulses for lateral wheel load transfer during braking - no active directional control!

[0011] A formulation such as: “alternately directed side by side” within the meaning of the invention means a repeated, reciprocal steering impulse generation with amplitudes of at least 5°, frequency ≥ 2 Hz, which does not pursue any lane guidance intention, but serves exclusively for side-by-side brake force modulation.

[0012] The algorithmic control is based on real-time evaluation of wheel speed difference, yaw rate, and lateral acceleration. Pulse duration, frequency, and amplitude are changed in defined steps; the wheel load changes generated by alternating side-directed pulses can occur in the range of 50-150 N per wheel, depending on the chassis type.

[0013] Formulations such as: “The algorithmic control” within the meaning of the claim is based on the input variables and response criteria described in paragraph

[0010] .

[0014] “Limited in time” and “for the duration of the stabilization intervention” within the meaning of the invention typically refers to time periods below 0.5 s, depending on the driving condition and sensor feedback.

[0015] The coefficient of friction µ used in the claims is to be understood in accordance with DIN EN ISO 5048 or a functionally equivalent vehicle dynamics friction coefficient standard. Typically, µ describes the sliding friction between the tire and the road surface under standard conditions. The limit of µ < 0.1 mentioned in this invention refers to situations with extremely low adhesion, such as those occurring on black ice or wet surfaces. This definition is to be used for both sensor triggering and vehicle dynamics evaluation. Reference symbol list File number 10 2025 002 667.6 Applicant Eugen Ladner Invention: Brake-dynamic steering impulse method for all-wheel drive vehicles for stabilization and braking distance reduction in µ-split situations Fig. 1 - Operating principle of the system ① Sensors for detecting asymmetric friction coefficients (µ-split) 2. Decoupled rear axle in case of instability ③ Macro-alternating steering impulses (control signal activation) 4. Front axle differential reacts → Braking distance optimization 4. System deactivates after stabilization has been achieved. Fig. 2 - Zigzag steering impulses • Steering impulse cycles with escalation: 1x → 2x → 3x → 4x. • Time course with a calm initial phase and increasing frequency of impulses. • Zigzag line as an ECG analogy. • Strong concept, especially due to: clear reading direction (from left to right). • Rhythm with observation phases. • Direct technical transferability. ⑥ Signal progression of the steering impulses (schematic zigzag line) ⑦ Individual steering impulse cycles (1x, 2x, 3x, 4x with escalation) ⑧ Neutral phases between impulses ⑨ Time axis / phase sequence (left → right) ⑩ ECG-like display to visualize stabilization

Claims

[1] Method for stabilizing the braking behavior and deceleration direction of an all-wheel-drive motor vehicle on extremely smooth or slippery road surfaces, especially in the case of asymmetrical braking deceleration due to different coefficients of friction on the left and right sides of the vehicle, characterized by , that in the event of a friction coefficient being detected below the setpoint by sensors, in particular at a friction coefficient level µ < 0.1 according to DIN EN ISO 5048 or an equivalent vehicle dynamic friction coefficient standard, one drive axle of the vehicle is decoupled for the duration of the intervention, so that only one drive axle remains active, On this axis, an electronic control unit generates alternating side-directed steering impulses within a steering angle range of ±5° to ±15° at a frequency between 2 Hz and 10 Hz, with the frequency being dynamically adjusted to the driving conditions within the aforementioned range. where these steering impulses are algorithmically controlled in such a way that they cause a changing normal force shift to the wheels of the activated axle, which results in asymmetrical speed differences between the wheels, so that an open or electronically controlled differential - triggered by the lateral wheel load change - performs a passive or vehicle dynamics-supported torque redistribution, the process takes place without brake intervention and without software-controlled intervention in the drive torque or the throttle / engine torque distribution, and each impulse sequence is completed with a return to zero steering angle in order to avoid a permanent deviation in direction. [2] Method according to claim 1, characterized by, that the steering impulses are implemented as individually impulsive steering angle deflections, whose rise and fall characteristics are non-linear and correspond to an asymmetric single impulse with a short effect and subsequent rest phase, without exhibiting multiple spikes as in medical ECG signals. [3] Method according to any one of the preceding claims, characterized by , that in the course of escalation the frequency of steering impulses is increased and the rest intervals between the individual impulses are successively shortened. [4] Method according to any one of the preceding claims, characterized by , that the activation of the traction recovery mode is based on a combination of wheel speed difference, yaw rate and lateral acceleration, if wheel speed difference is greater than 20 rpm AND yaw rate is outside the stable window (±8° / s) and lateral acceleration is above 1 m / s² 2 lies. [5] Method according to any one of the preceding claims, characterized by , that the number of steering impulse cycles is increased in defined stages if either no detectable braking deceleration above a defined threshold value according to vehicle calibration is detected or no reduction of the yaw rate below ±8° / s occurs within 0.5 s, whereby a return to zero steering angle occurs between each impulse cycle and a software-based observation phase is carried out to evaluate stability parameters. [6] Method according to any one of the preceding claims, characterized by , that the deactivation of the differential decoupling and the steering impulses occurs automatically as soon as a stable symmetry of the wheel speeds or a defined driving stability value is detected. [7] Method according to any one of the preceding claims, characterized bythat the process is implemented entirely via software using the vehicle's existing electronic control units, without any additional hardware components.

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