Method and system for extending the TACTOS 4.0 vehicle dynamics system to include cornering behavior on very low friction surfaces (TACTOS 5.0 cornering, ZZBL principle)

Abstract

The invention relates to a method and system for stabilizing a vehicle when turning on very low friction surfaces. When understeer is detected, frequent, amplitude-limited steering impulses with a directional bias in the direction of the turn (3-5 Hz; 1.5-3.5°) are generated via a steering actuator, optionally synchronized with short individual wheel braking impulses. Simultaneously, the drive torque is limited so that the friction ellipse is not exceeded and lateral forces are prioritized. The method enables steering despite extremely slippery surfaces and prevents rear-end instability. The method, system, computer program, and application are disclosed.

Description

Technical field

[0001] The invention relates to an extension of the existing TACTOS-4.0 vehicle dynamics system for stabilizing vehicles when cornering on very low coefficients of friction μ (estimated) ≈ 0.02 - 0.05. The underlying control principle is called the ZZBL principle (zig-zag movement of the steering) and combines frequent, sharp-edged steering impulses with torque and brake coupling for lateral guidance with minimal friction. Relationship to the main registration

[0002] This application is a further development of the TACTOS patent family, in particular the basic functions of TACTOS-4.0 (DE 10 2024 004 430.2, ZZBL). All control, sensor and actuator structures described therein apply accordingly. State of the art

[0003] Various methods for 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 the vehicle from getting stuck. Sequential impulse control with neutral phases and algorithmic evaluation is not taught therein. - DE 10 2005 019 339 A1 (D2) describes a vehicle control system that triggers steering oscillations when encountering off-road obstacles to enable continued driving. A clock-based, side-by-side impulse control for vehicle stabilization is not shown. - DE 10 2015 224 760 A1 (D3) relates to an active steering assistance system for stuck vehicles, in which periodic steering angle profiles are automatically applied to enable rocking the vehicle free. This disclosure relates to stationary situations, not to dynamic braking or acceleration processes. - DE 11 2020 004 314 T5 (D4) discloses a steering control device that, when slippage situations are detected, uses the current steering angle as a reference and controls a wheel within a certain angular range. A combination of steering angle impulses with torque application in synchronized cycles is not disclosed therein. - DE 11 2019 002 782 T5 (D5) concerns an adaptive rear-wheel steering system in which phase-shifted rear-wheel steering angles are implemented depending on driving situations. A coordinated control system consisting of lateral steering impulses and torque application with neutral phases is not described. Well-known systems such as ABS, ASR, ESC and torque vectoring stabilize vehicles through braking or torque interventions. On a perfectly smooth road surface, front tires deliver hardly any lateral force under a static steering angle, which means that exceeding the friction ellipse is a risk. Methods with sinusoidal or oscillatory steering movements (e.g. D1 - D5) improve traction, but do not offer clock-based, side-by-side impulse control with neutral phases and synchronized torque application.

[0004] A combination of sharp-edged steering impulses with time bias in the direction of the curve, synchronous braking impulses and simultaneous drive-side lateral prioritization is not known in the prior art. Task

[0005] The invention is intended to provide a method and system that enables controlled steering even at extremely low coefficients of friction, without exceeding the friction ellipse or causing rear-end instability. Summary of the invention

[0006] The process is based on the TACTOS-4.0 structure and extends it to include adaptive control for cornering. Geometrically determined speed differences between the inner and outer gears are continuously calculated and compared with the measured values. Deviations indicate friction loss; when defined thresholds are reached, the ZZBL mode with frequent pulse control is automatically activated. Brief description of the drawings: Figure 1 - Block diagram Fig. Figure 1 shows the control architecture of the TACTOS 5.0 vehicle dynamics system. The control unit (12) receives sensor data (20) on wheel speeds, steering angle δ, yaw rate r, lateral and longitudinal acceleration. A friction coefficient estimator (22) provides the estimated friction coefficient mu (estimated), which is processed with the price data. At mu (estimated) ≤ 0.05 and v ≤ 20 km / h the ZZBL impulse generator (24) is activated, which generates frequent, amplitude-limited steering impulses in the direction of the curve via the EPAS actuator (14). In parallel, the brake impulse unit (26) triggers short single-wheel impulses at the inner rear wheel via the ESC / IBC system (16). The drive torque is regulated via the drive limiter (28) so that the friction ellipse is not exceeded. The guardrail logic (30) terminates the activation at r → r_des, rear instability or driver override. The HMI module (32) informs the driver "Icy road surface detected - ZZBL active". This indicates Fig. 1. The functional coupling of sensors, friction coefficient estimation, steering, braking and torque control. Figure 2a - Time lapses

[0007] Fig. Figure 2a shows the synchronized time profiles of steering impulse δ(t), brake pressure p(t) at the inside rear wheel, and drive torque M_drive(t). Steering impulses (3–5 Hz, 2–3°) have a time bias of 60% in the direction of the turn. The braking impulses (80–120 ms, 10–20 bar) occur synchronously with positive steering impulses. During these phases Mdrive=M0⋅(1−k(mu)⋅ayay,max) After 0.5 - 1.5 s the active window ends, the vehicle remains stable and steerable. Figure 2b - Dynamic zero position

[0008] Fig. Figure 2b shows the asymmetric steering impulse sequence relative to the dynamic zero position δ0(t).

[0009] This is derived from driver steering or external lane reference.

[0010] The impulses Δδ_imp(t) are superimposed only in the direction of the curve; after each impulse, the feedback to the neutral region |δ - δ0| ≤ 1° takes place.

[0011] All parameters (amplitude, frequency, bias) are adaptively determined from δ0(t), curvature κ and friction coefficient estimate mu (estimated). Figure 3 - Friction ellipse

[0012] Fig. Figure 3 shows the friction ellipse with release corridor during an active ZZBL phase. Within the ellipse, the following applies: √(Fx2+Fγ2)≤mu(estimated)⋅N.

[0013] The release corridor marks the area in which lateral and longitudinal forces are allowed to act together.

[0014] The system limits M_drive such that the force vector (F x , F y ) remains within the stable friction limit. Figure 4 - State machine

[0015] Fig. Figure 4 shows the state machine of the TACTOS-5.0 control logic with the states OFF, ARMING, ACTIVE, STABILIZE and ABORT. At mu (estimated) ≤ 0.05 and v ≤ 20 km / h, the system switches from OFF via ARMING to ACTIVE and starts the ZZBL pulse control. After r → r_des or an increase in the coefficient of friction, STABILIZE follows; in case of rear instability or override, ABORT follows. The automatic system controls all transitions independently and ensures a stable operating logic without driver intervention. Figure 5 - Cornering example

[0016] Fig.Figure 5 shows a curve on a perfectly smooth road surface (mu (estimated) ≈ 0.03). The solid line indicates the intended course r_des, the dashed line the actual lane r, which initially drifts outwards. After activation of the ZZBL control, r converges back to r_des. Arrows indicate the direction of travel, and a message "ZZBL active - stabilization" marks the active phase. This example demonstrates the stabilizing effect at extremely low coefficients of friction. Detailed description

[0017] The system continuously records vehicle speed v, steering angle δ, yaw rate r, lateral / longitudinal acceleration and wheel speeds. A friction coefficient estimator provides mu (estimated). Activation criteria: mu (estimated) ≤ 0.05, v ≤ 20 km / h, understeer detected, no rear instability.

[0018] The theoretical target rotational speeds ω i are calculated as ω i = (v / r i) · (1+y i / R), according to Kamm / ISO 8855. Where r denotes i the radial distance of the respective wheel from the center of the curve, and y i the lateral offset of the wheel relative to the vehicle track.

[0019] The friction ellipse model corresponds to the transverse / longitudinal force limitation defined in ISO 8855. When driving straight ahead, R → ∞, all w i even. Deviations > Δω_crit indicate a loss of lateral force.

[0020] The steering impulses are sharp-edged step impulses (“ / / \ / / \”) with 3 - 5 Hz, slew rate 60 - 180° / s and bias 60 - 65%.

[0021] The neutral reference δ0(t) is derived from driver intention or lane reference. Braking impulses occur only in phase with positive relative impulses. Active window 0.5 - 1.5 s with re-evaluation after each cycle.

[0022] Short individual wheel braking impulses (80 - 120 ms, 10 - 20 bar) on the inner rear wheel generate an additional yaw moment without continuous ABS intervention.

[0023] The drive torque M_drive is determined according to M0⋅(1−k(mu)⋅ayay,max)(1)regulated. Release only within √(Fx2+Fγ2)≤mu(estimated)⋅N. Recuperation is treated the same; with AWD, more torque is applied to the outer rear wheels.

[0024] The guardrail logic terminates the pulse control when r > r_des + Δr2, mu (estimated) drop, or driver override occurs. The HMI can optionally display "Smooth surface detected - ZZBL active".

[0025] The TACTOS-5.0 - Cornering module works with EPAS steering, ESC integration and characteristic maps A (κ, mu (estimated)) and f (κ, mu (estimated)) for parameterization.

[0026] Amplitude A = A0 · (1 - k a · mu (estimated)); frequency f = f0 + k_f · κ. Parameters are based on basic values ​​A0, f0 and gain factors k a, k_f.

[0027] The calculation is performed relative to the dynamic zero position δ0(t). δ0(t) determines direction assignment, time bias and release of synchronous braking and torque pulses. This allows the system to react adaptively to price changes without loss of stability.

[0028] Under normal driving conditions, the system remains passive and only intervenes when there is a loss of friction.

[0029] Through geometric target / actual comparisons, it detects changes in adhesion early and automatically initiates stabilization.

[0030] No additional sensors are required; existing TACTOS signals are sufficient.

[0031] The system architecture remains simple and robust. analogy

[0032] To illustrate: short steering impulses generate a directed yaw moment similar to individual paddle strokes of a canoe. This results in controlled cornering without instability, even on a perfectly smooth road surface. Reference symbol list 10 vehicles (total) 12 Control unit (TACTOS-5.0 - Controller) 14 Steering actuator / EPAS system 16 Brake actuator / ESC or IBC system 18 Drivetrain (Motor / Inverter / eAWD) 20 Sensor system (wheel speed, steering angle, yaw rate, acceleration sensors) 22 Friction coefficient estimators / Module for determining mu (estimated) ⑫ Mixed writing value mu (estimated), result of (22) ⑭ Ψ(Psi) - describes the direction of mixed lubrication 24 ZZBL pulse generator (TL module: steering pulse control) 26 Brake pulse unit (individual wheel control inner-rear) ⑥ Inner rear impulses synchronous to δ > 0 ⑦ Moment reduces while δ > 0 (bias phase) 28 Drive torque limiter / TM module: Torque control 30 Guardrail logic (safety / abort condition) 32 HMI module (display / driver information “Icy road surface detected - ZZBL active”) 34 r Yaw rate (actual value) Is track Lane r (should be optimal) ⑳ r_des (target course) ⑧ δ Steering angle ① δ0(t) Dynamic zero position of the steering ⑩ One-sided impulses in the direction of the curve ⑪ Neutral range |δ-δ0| ≤ ε Δδ_imp(t) Steering impulse deviation ⑨ δ(t) - steering angle due to δ0(t)+Δδ_imp(t) v Vehicle speed mu (estimated) Estimated coefficient of friction ⑬ F x Longitudinal forces on the tire ⑭ F y Lateral forces on the tire N Normal force 36 OFF (State of the TACTOS control unit) 38 ARMING (Status of the TACTOS control unit) 39 ACTIVE (Status of the TACTOS control unit) 40 STABILIZE (State of the TACTOS control unit) 41 ABORT (State of the TACTOS control unit) ⑮ Tail instability ⑯ ZZBL active ⑰ mu (estimated) ≤ 0.05 and v ≤ 20 km / h ⑱ mu (estimated) ≈ 0.03 (mirror smoothness) 42 ZZBL active stabilization ⑲ Direction of travel 2. Y- lateral offset of the vehicle track with respect to the intended course ③ M_drive(t) Drive torque P(t) Brake pressure curve κ track curvature / curve radius a y , a y,max Lateral acceleration / max. lateral acceleration A, A0 steering impulse amplitude / base amplitude F, f0 Pulse frequency / Base frequency k(mu) Friction coefficient-dependent correction factor 1. Right bias 60% / 40% ⑤ (t) the time

Claims

[1] Method for stabilizing a road vehicle when turning on very low friction surfaces, in particular as a module within the TACTOS vehicle dynamics system, characterized by , that - if understeer is detected and the coefficient of friction mu (estimated) ≤ 0.05 and the speed v ≤ 20 km / h, - via the steering actuators, frequent, amplitude-limited steering impulses with an impulse frequency of 3 - 5 Hz, a road wheel amplitude of 1.5 - 3.5° and a time bias ≥ 60 % in the direction of the curve are generated, - and at the same time the drive torque is regulated according to relationship (1) in the description, so that the friction ellipse is not exceeded and the lateral guidance is prioritized, whereby the target rotational speeds of the individual wheels are determined from the geometric parameters of the curve and the steering angle. [2] Method according to claim 1, characterized by , that The steering impulses are generated as sharp-edged step impulses with a slew rate of 60 to 180° / s, with the time component in the direction of the curve being 60 to 65%. and that the steering impulses are generated relative to a dynamic zero position δ0(t), where δ0(t) is derived from a driver steering angle and / or an external track reference, and that after each impulse the steering is returned to a neutral range |δ - δ0| ≤ ε without going through the opposite direction. [3] Procedure according to one of the preceding claims, characterized by , that synchronized braking impulses are generated on an inner rear wheel with a duration of 80 - 120 ms and low pressure level according to a predetermined pressure-time characteristic. [4] Procedure according to one of the preceding claims, characterized by, that drive torques and recuperation torques are treated equally and, in the case of all-wheel drive vehicles, distributed in such a way that additional torque is provided at the outer rear wheel as long as the friction ellipse is maintained. [5] Procedure according to any of the preceding claims, characterized by , that The procedure is only activated if understeer, friction coefficient and speed threshold are present simultaneously; activation occurs in time windows of 0.5 - 1.5 s with subsequent reassessment. [6] Procedure according to one of the preceding claims, characterized by , that In case of rear-end instability, steering inputs are immediately deactivated and the drive torque is reduced to drag torque. [7] A system, characterized by , that Vehicle dynamics control system with sensors for yaw rate, lateral / longitudinal acceleration, wheel speeds and steering angle, a friction coefficient estimator, an EPAS actuator, a brake actuator, a drive actuator and a control unit designed to carry out the procedure according to one of claims 1 - 6. [8] Computer program, characterized by , that The computer program with program code means that, when executed on a computing unit of the vehicle, perform the steps according to one of the requirements 1 - 6. [9] Data carriers, characterized by , that Non-volatile, machine-readable data carrier containing the computer program according to claim 8.

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