Brake Pressure Control Using Virtual Stroke Under Cold Fluid Conditions
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Solution Overview
Problem
The brake-by-wire system faces challenges in generating a desired brake pressure when the viscosity of brake fluid increases at low temperatures, leading to delayed brake force application and altered pedal force relationships, which can result in inadequate brake pressure generation due to hindered fluid flow from the master cylinder to the stroke simulator device.
Innovation Solution
A brake hydraulic pressure control device that uses a pressure sensor to detect fluid pressure in the master cylinder and calculates an imaginary stroke amount, allowing it to control brake pressure effectively even when fluid flow is impeded, by integrating this data with a fluid pressure control unit to adjust brake pressure in the wheel cylinders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the brake-by-wire system uses stroke amount detection to control brake pressure, then the brake pressure can be controlled based on driver operation, but when brake fluid viscosity increases at low temperatures, the fluid flow is hindered and the desired brake pressure cannot be generated
Solution Approach 1:
The patent introduces a pressure sensor as an intermediary measurement device to detect the actual fluid pressure in the master cylinder. This intermediary measurement allows the control system to compensate for the harmful effect of increased brake fluid viscosity by using pressure feedback to adjust the target brake pressure, ensuring reliable brake pressure generation even when fluid flow is hindered by cold temperatures.
Solution Approach 2:
The patent implements a feedback mechanism by detecting the fluid pressure generated by the master cylinder and using this information to correct the target brake pressure. The control device calculates a corrected target brake pressure based on the detected pressure and the relationship between stroke amount and brake pressure, allowing the system to adapt to varying fluid conditions and maintain reliable brake pressure generation despite viscosity changes.
2Measurement precision
If the brake fluid flows normally from master cylinder to stroke simulator device, then the stroke amount accurately reflects driver operation, but when viscosity increases, the stroke amount becomes inaccurate and brake force is delayed
Solution Approach 1:
The patent uses pressure detection as an intermediary measurement method to supplement the stroke amount measurement. By detecting the actual fluid pressure in the master cylinder, the system obtains accurate information about the driver's operation even when stroke amount measurement becomes unreliable due to hindered fluid flow, thereby eliminating measurement inaccuracy and enabling timely brake force application.
Solution Approach 2:
The patent partially replaces the mechanical stroke amount measurement system with a pressure-based detection and calculation system. Instead of relying solely on mechanical stroke detection, the control device uses pressure sensor data and calculated relationships to determine the effective stroke amount, substituting the problematic mechanical measurement with a more reliable pressure-based approach that works under all fluid conditions.
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
Ensures the generation of a desired brake pressure by compensating for reduced fluid flow, maintaining effective brake performance even under conditions where brake fluid does not easily flow from the master cylinder to the stroke simulator device, such as low temperatures.
Implementation Method 1
a pressure sensor which detects the fluid pressure generated by the master cylinder
Implementation Method 2
a master cylinder which has a fluid pressure chamber connected to the reservoir and generates a fluid pressure in accordance with the movement of an input rod connected to a brake pedal
Implementation Method 3
a stroke simulator device which receives a fluid pressure generated by the master cylinder and generates a reaction force to the brake pedal
Data Source
AI summary
Provided are a brake hydraulic pressure control device and a brake system capable of generating a desired brake pressure even in a state in which a brake fluid does not easily return from a stroke simulator device to a master cylinder.In a brake system (1) including a reservoir (31), a master cylinder (10), a stroke simulator device (40), a fluid pressure control unit (60), and a brake hydraulic pressure control device (100), the brake hydraulic pressure control device (100) acquires an imaginary stroke amount (St_est) of an input rod (5) on the basis of a pressure value (P_MC) detected by a pressure sensor (41) and controls a brake pressure (P_WC) on the basis of the imaginary stroke amount (St_est).