Electrohydraulic Brake Fallback Control via Dynamic Pedal Threshold
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Solution Overview
Problem
In electrohydraulic brake systems, the transition to a hydraulic fallback mode can lead to the parking brake being overloaded and damaged due to its design not being suited for service braking operations, and drivers may mistakenly believe the system has failed due to altered braking characteristics.
Innovation Solution
The open- and closed-loop control unit monitors brake pedal travel and activates an additional brake actuator, such as a parking brake, to build up additional braking torque, shifting the activation point towards longer pedal travels, thereby assisting the driver and protecting the additional brake actuator from overloading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the parking brake is activated to build up additional braking torque in fallback mode, then the driver receives braking assistance, but the parking brake may be overloaded and damaged
Solution Approach 1:
The system dynamically adjusts the pedal travel threshold value based on the sequence number of brake pedal actuations. In earlier actuations, the threshold is lower to provide braking assistance, while in later actuations, the threshold increases to reduce parking brake usage and prevent overload. This dynamic adaptation allows the system to provide necessary braking support while protecting the parking brake from excessive wear.
Solution Approach 2:
The system changes the operational parameter (pedal travel threshold value) as a function of the actuation sequence number. By modifying this threshold parameter dynamically, the control unit optimizes the balance between providing braking assistance and preventing parking brake overload, thereby resolving the contradiction between productivity and reliability.
2Ease of operation
If the pedal travel threshold value is kept low to assist the driver, then braking support is provided, but the parking brake may be overactivated and damaged
Solution Approach 1:
The system dynamically adjusts the pedal travel threshold value based on the sequence number of brake pedal actuations. In earlier actuations, the threshold is lower to provide braking assistance, while in later actuations, the threshold increases to reduce parking brake usage and prevent overload. This dynamic adaptation allows the system to provide necessary braking support while protecting the parking brake from excessive wear.
Solution Approach 2:
The system applies periodic action by varying the pedal travel threshold value in cycles corresponding to the sequence of brake pedal actuations. The threshold is adjusted in a periodic manner based on the actuation count, providing braking assistance during initial actuations while progressively reducing assistance in subsequent actuations to prevent parking brake damage.
3Reliability
If the pedal travel threshold value is increased to protect the parking brake, then the parking brake is protected from overload, but the driver receives less braking assistance
Solution Approach 1:
The system dynamically adjusts the pedal travel threshold value based on the sequence number of brake pedal actuations. In earlier actuations, the threshold is lower to provide braking assistance, while in later actuations, the threshold increases to reduce parking brake usage and prevent overload. This dynamic adaptation allows the system to provide necessary braking support while protecting the parking brake from excessive wear.
Solution Approach 2:
The system performs preliminary action by providing maximum braking assistance during the initial brake pedal actuations when the threshold is lowest. This ensures the driver receives adequate support during the most critical phase, while subsequent actuations progressively reduce assistance to protect the parking brake, thereby prioritizing safety in the preliminary phase.
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 helps the driver adjust to the new braking behavior in fallback mode by providing additional braking torque while ensuring the additional brake actuator is not overloaded, maintaining vehicle safety and preventing damage to the parking brake.
Implementation Method 1
The pressure generating device in the brake systems described above is also referred to as an actuator or hydraulic actuator. In particular, actuators are designed as linear actuators or linear units, in which a piston is moved axially into a hydraulic pressure chamber to build up pressure.
Implementation Method 2
Conventional brake systems predominantly comprise an actuating unit with a vacuum brake booster
Implementation Method 3
the parking brake is activated to build up additional braking torque during a braking operation
Data Source
AI summary
An electrohydraulic brake system, comprising a brake master cylinder. A pressure generating device for actuating wheel brakes and an additional brake actuator may both be activated electronically. In a normal mode of operation, an open- and closed-loop control unit detects a braking demand based on the actuation of a brake pedal by the driver and activates the pressure generating device to build up braking torque at the wheel brakes. If the pressure generating device is not activated, the driver gains direct access to the wheel brakes and the control unit activates the additional brake actuator to build up braking torque. In the fallback mode, when a predetermined pedal travel threshold value is reached, the control loop activates the additional brake actuator to build up braking torque. In the event of a succession of brake pedal actuations by the driver, the pedal travel threshold value is increased at least once.