Electrohydraulic Brake Pressure Control via Volume Segmentation
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Solution Overview
Problem
Existing electrohydraulic brake systems face challenges in accurately and stably setting pressure at wheel brakes due to unwanted pressure drops when switching between wheel brakes during closed-loop pressure control, leading to imprecise and uncomfortable braking experiences.
Innovation Solution
Implementing a method that switches from closed-loop to open-loop control of the pressure medium volume based on setpoint wheel pressures, allowing precise pressure setting at wheel brakes without unwanted drops, and uses a combination of closed-loop control to correct for inaccuracies, ensuring precise and comfortable braking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If closed-loop pressure control is used to set the system pressure to the highest setpoint wheel pressure, then the system pressure can be maintained at a stable level, but unwanted pressure drops occur at other wheel brakes when inlet valves are opened, leading to imprecise pressure setting
Solution Approach 1:
The patent segments the pressure control function into two independent control loops: a first closed-loop control for maintaining system pressure stability, and a second open-loop control for precise wheel-specific pressure buildup. This segmentation allows each control loop to optimize for its specific function without interfering with the other, thereby resolving the contradiction between overall pressure stability and individual wheel brake pressure precision.
Solution Approach 2:
The patent implements preliminary action by performing open-loop volume control to supply the required pressure medium volume to the wheel brake before the closed-loop pressure control can respond to pressure drops. The control unit calculates and supplies the exact volume needed based on the pressure difference and wheel brake characteristics, preventing the pressure drop from affecting other wheel brakes in the first place.
2Adaptability or versatility
If the inlet valve of a wheel brake is opened to equalize pressure during antilock control, then complete pressure equalization between the wheel brake and pressure space is achieved, but a brief unwanted drop in system pressure occurs at other wheel brakes
Solution Approach 1:
The patent introduces an intermediary control mechanism - the open-loop volume control - that acts as a mediator between the inlet valve opening and the system pressure. When a inlet valve opens, the open-loop control simultaneously supplies the calculated required volume to compensate for the pressure equalization, preventing the harmful side effect of pressure drops at other wheel brakes while still allowing the desired pressure equalization to occur.
3Reliability
If closed-loop pressure control continuously adjusts the system pressure, then pressure stability is maintained, but the response time to prevent pressure drops is delayed, causing temporary pressure reductions
Solution Approach 1:
The open-loop volume control performs preliminary action by calculating and supplying the required pressure medium volume in advance, based on the setpoint wheel pressures and wheel brake characteristics, before the closed-loop pressure control can detect and respond to pressure drops. This proactive volume supply prevents pressure drops from occurring in the first place, thereby achieving both fast response and stability.
Solution Approach 2:
The patent combines feedback from the closed-loop pressure control with feedforward calculation in the open-loop volume control. The closed-loop provides feedback on actual pressure conditions, while the open-loop uses this information along with wheel brake characteristics to calculate and supply the required volume in advance, creating a responsive yet stable pressure control system.
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 precise and stable setting of wheel brake pressures, preventing unwanted pressure drops and improving the overall braking experience by ensuring accurate pressure modulation and comfort during braking operations.
Implementation Method 1
The pressure supply device comprises a cylinder-piston arrangement with a hydraulic pressure space
Implementation Method 2
the piston of which can be moved relative to a rest position by an electromechanical actuator
Implementation Method 3
at least one wheel brake with the highest setpoint wheel pressure is connected to the hydraulic pressure space via the open inlet valve to give complete pressure equalization
Data Source
AI summary
An electrohydraulic brake system method for motor vehicles having a wheel-specific brake control function (ABS, ESC, TCS) and hydraulically actuable wheel brakes (43, 44, 45, 46), communicating with an electrically controllable pressure supply device. The pressure supply device (40) having a cylinder-based piston arrangement with a pressure space driven by an electromechanical actuator (2, 4). To set a brake system pressure (Psys) wherein a wheel-specific wheel setpoint pressure (Pi) is predefined for each wheel brake, and a pressure regulating process (301) is carried out, wherein at certain times a control process (303) of the pressure medium volume which is output by the pressure supply device is carried out instead of the pressure regulating process (301) of the brake system pressure, switching over (302) from the pressure regulating process to the control of the pressure medium volume is carried out as a function of the wheel setpoint pressures (Pi).