Variable Area Master Cylinder for Hydraulic Brake Systems
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Solution Overview
Problem
On-demand brake boosters in hydraulic motor vehicle brake systems lack a reliable energy store, leading to unexpected increases in braking force requirements, potentially exceeding the driver's physical capability to achieve sufficient deceleration in emergency situations, especially in heavier vehicles.
Innovation Solution
A braking device with a master brake cylinder featuring a gradual build-up of brake pressure and a valve arrangement that switches between effective areas to reduce pedal force and travel, allowing safe braking without exceeding permissible foot force limits, implemented through a spring-loaded valve piston controlling hydraulic connections between pressure chambers and a pressureless container.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If an on-demand brake booster without energy storage devices is used, then weight and cost are reduced, but the system cannot provide braking force if the drive unit fails
Solution Approach 1:
The master brake cylinder is designed with a larger effective diameter to pre-calculate and accommodate the maximum permissible foot force scenario. This preliminary design ensures that even without energy storage devices, the system can handle emergency braking within legal force limits, resolving the contradiction between weight reduction and reliability.
2Reliability
If the master brake cylinder is designed with a large effective diameter for emergency braking, then sufficient deceleration can be achieved with limited foot force, but the driver may be surprised by the sudden increase in required force
Solution Approach 1:
A variable effective area mechanism is implemented where the effective area of the master brake cylinder piston can dynamically change during actuation. This allows the system to provide higher force multiplication initially to reduce the surprise effect, then transition to a different effective area to maintain control, resolving the contradiction between emergency braking capability and driver adaptability.
3Reliability
If a combined braking device with two separate actuating cylinders is used, then fallback and service braking systems are provided, but the system complexity increases
Solution Approach 1:
The patent merges the fallback and service braking functions into a single master brake cylinder by implementing a variable effective area mechanism. This single cylinder can operate in different modes (different effective areas) to provide both normal braking and emergency fallback braking, eliminating the need for two separate cylinders and reducing overall system complexity while maintaining reliability.
4Reliability
If the upper limit for foot force is set at 500N for safety, then driver safety is protected, but the driver cannot achieve sufficient braking deceleration in emergency situations
Solution Approach 1:
The system changes the effective area parameter of the master brake cylinder dynamically during actuation. By varying the effective area, the system can provide different force multiplication ratios while keeping the foot force within the safe 500N limit, thereby achieving both driver safety and sufficient braking deceleration performance.
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
Enables safe and effective braking with reduced pedal force and travel, ensuring sufficient deceleration up to 0.643 g without exceeding the 500N foot force limit, even in emergencies, without the need for additional energy stores or complex systems, and can be adapted to different vehicle applications with minimal design effort.
Implementation Method 1
a gradual build-up of brake pressure and a valve arrangement that switches between effective areas to reduce pedal force and travel
Implementation Method 2
implemented through a spring-loaded valve piston controlling hydraulic connections between pressure chambers and a pressureless container
Data Source
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AI summary
The invention relates to a braking device (1) for a hydraulic motor vehicle brake system, with an energy-store-free, electronically controlled electric-motor-driven on-demand braking force booster (2) and with a master brake cylinder (4), in which, for the purpose of reducing the foot force on the brake pedal (13) in the fall-back level, the braking pressure in the pressure chamber (6) is built up stepwise and at least one active surface (A1) involved in generating brake pressure is switchable so as to be hydraulically ineffective.