Vehicle Anti-Lock Braking with Active Wheel Drive on Low-Friction Roads
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Solution Overview
Problem
Existing antilock control systems in vehicle braking systems, particularly in pneumatic systems, face challenges with prolonged locking times on low-friction surfaces like black ice or snow, leading to decreased driving stability and delayed brake pressure release due to inertia in pressure medium systems.
Innovation Solution
The integration of an active wheel drive, such as an electric wheel hub motor, is activated upon recognizing a locking tendency, allowing for rapid increase in wheel speed and reducing slip, thereby shortening locking times and maintaining or adjusting brake pressure to enhance brake force application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If brake pressure is released upon recognizing locking tendency, then wheel slip decreases and wheel is taken along by road friction, but locking time becomes prolonged on low-friction surfaces due to inertia of pressure medium
Solution Approach 1:
The control system applies preliminary counter-actions by activating wheel drive before or during brake pressure release to preemptively counteract the inertia-induced delay. The wheel drive provides forward torque to maintain wheel speed while brake pressure is being dissipated, preventing complete wheel lockup during the pressure medium's delayed response period.
Solution Approach 2:
The wheel drive acts as an intermediary mechanism between the brake system and the wheel. It provides an additional control pathway that can independently influence wheel speed, compensating for the slow response of the pneumatic brake system and enabling finer control during the transition phase.
2Force
If brake pressure is maintained to preserve brake force, then braking effectiveness is improved, but wheel locking occurs and wheel speed decreases on low-friction surfaces
Solution Approach 1:
The system dynamically changes the control parameters by switching between brake pressure control and wheel drive torque control based on real-time wheel slip conditions. On low-friction surfaces, the control algorithm adjusts the threshold values and response characteristics to activate wheel drive earlier, maintaining an optimal balance between brake force application and wheel speed preservation.
Solution Approach 2:
The control system transitions from a static brake-only approach to a dynamic combined control strategy where wheel drive is selectively activated based on detected wheel slip conditions. This dynamic adaptation allows the system to optimize performance across varying friction conditions by continuously adjusting the mix of braking and driving torques.
3Loss of time
If active wheel drive is activated to rapidly increase wheel speed, then locking time is reduced, but system complexity increases
Solution Approach 1:
The wheel hub motor serves multiple functions: it acts as both the primary drive motor for vehicle propulsion and as an auxiliary control device for antilock braking. This multi-functionality eliminates the need for separate components dedicated solely to ABS control, reducing overall system complexity despite the advanced control algorithms required.
Solution Approach 2:
The existing wheel drive system serves itself by utilizing the same motor and control infrastructure for both propulsion and braking control. The control unit leverages existing sensors and actuators, making the enhanced ABS functionality emerge from the existing system capabilities rather than requiring entirely new components.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables improved safety and controllability by rapidly reducing wheel slip and maintaining brake force, even on low-friction surfaces, with the active wheel drive compensating for inertia-related delays in brake pressure dissipation.
Implementation Method 1
In an electric wheel drive, this can be a wheel hub motor, for example, which enables a rapid responsiveness, to also enable a rapid acceleration in these control phases
Implementation Method 2
the wheel is initially hardly taken along... since a wheel circumferential velocity no longer corresponds to a vehicle velocity... the relative deviation of the wheel circumferential velocity in relation to the vehicle velocity is preferably denoted hereinafter as the brake slip
Data Source
AI summary
An antilock control method for a braking system of a vehicle has at least the following steps: upon the presence of a brake request signal, outputting a brake control signal and building up a brake pressure by a braking medium at a wheel brake of a vehicle wheel, measuring a wheel speed of the vehicle wheel to be braked, and determining a wheel slip of the vehicle wheel, upon meeting a first traction criterion or a locking tendency of the vehicle wheel, activating a wheel drive unit and applying a wheel drive torque on the vehicle wheel to increase the wheel circumferential velocity and to reduce the wheel slip until a second traction criterion is met. The brake force introduced in the wheel brake is controlled as a function of the wheel slip by releasing the brake pressure upon satisfying a first traction criterion.