Front Axle Brake Pressure Priority Under Pressure Supply Degradation
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Solution Overview
Problem
In brake-by-wire systems, a fault in the pressure supply device results in poor deceleration performance, as the driver must build up brake pressure without assistance, leading to longer braking distances.
Innovation Solution
The method prioritizes applying brake pressure to the front axle first, using a linear actuator with a brushless electric motor, and activates the rear axle when conditions are met, ensuring efficient brake pressure distribution and maintaining constant vehicle deceleration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If brake pressure is built up without assistance using muscle power in the event of a fault, then the driver can still operate the brakes, but deceleration performance deteriorates significantly
Solution Approach 1:
The braking system is segmented into front axle and rear axle subsystems. In degradation mode, the control device activates only the front axle wheel brakes while keeping rear axle wheel brakes deactivated, allowing the limited available force to be concentrated on the front axle for effective braking without requiring full system functionality
Solution Approach 2:
Instead of attempting to distribute limited driver-applied force across all four wheel brakes, the system applies excessive braking action to the front axle alone (which provides approximately two-thirds of the braking force), achieving sufficient deceleration performance with partial activation of the braking system
2Ease of operation
If brake pressure is applied to both front and rear axles simultaneously, then braking force is distributed evenly, but the pressure build-up time increases due to limited volume delivery
Solution Approach 1:
The control device prioritizes pressure build-up at the front axle before activating the rear axle. By first building pressure at the front axle (which requires less total volume due to the falling gradient relationship between pressure and volume), the system achieves quick initial deceleration, then subsequently activates rear axle brakes to complete the braking maneuver
Solution Approach 2:
The braking system dynamically adjusts which axles are active based on real-time conditions. In degradation mode, the system transitions from a static four-wheel braking configuration to a dynamic configuration that initially uses only front axle braking, then progressively engages rear axle braking as pressure builds, optimizing the time-dependent braking performance
3Reliability
If the pressure supply device operates with reduced performance characteristics, then component stress is reduced, but braking distance increases
Solution Approach 1:
The system applies different braking strategies to different parts of the braking system based on local conditions. At the front axle, the system exploits the favorable pressure-volume relationship and higher brake force distribution to achieve high deceleration with limited volume delivery, while the rear axle remains deactivated or is activated later, creating a non-uniform but optimized braking distribution that minimizes braking distance despite overall system degradation
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 allows for quicker deceleration and reduces braking distance by leveraging the falling gradient relationship between pressure and volume, achieving high deceleration at the front axle before engaging the rear axle, thus optimizing braking performance even in degraded states.
Implementation Method 1
the brake pressure is first built up on a front axle by closing the inlet valves of the wheel brakes of a rear axle before or at the start of volume delivery by means of the pressure supply device
Data Source
AI summary
A method for controlling a hydraulic motor vehicle braking system, wherein brake pressure is to be built up at wheel brakes on a front axle and a rear axle by means of via an electric pressure supply device based on a brake demand variable. Inlet valves of the wheel brakes on the front axle and rear axle are open and a brake demand variable is implemented by joint pressure build-up on the front axle and rear axle in the case of no fault. In the event of a fault with a degradation of the pressure supply device, the pressure build-up is first applied to the front axle by closing the inlet valves of the wheel brakes of the rear axle before or at the start of volume delivery. When a condition is met, the wheel brakes on the rear axle are activated by opening the inlet valves.