Two-Stage Switching Valve Activation for Brake Noise Reduction
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Solution Overview
Problem
The existing two-stage switching valves in brake systems of vehicles with vehicle dynamics control systems produce a loud noise known as pressure equalization knock due to abrupt opening of the main stage, especially at pressures between 10 bar and 50 bar, which is irritating to the driver and causes noticeable brake pedal movement.
Innovation Solution
Activating the two-stage switching valve by a low-level control signal to open only the first stage initially, followed by a higher-level signal after a predetermined period to ensure complete opening, including the main stage, thereby delaying the opening of the main stage and reducing the pressure equalization knock. This method is voltage- and temperature-compensated, with the first stage opening delayed by at least 10 ms to allow pressure compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the main stage of the switching valve is opened immediately to ensure complete valve opening, then the valve opens reliably, but a loud pressure equalization knock occurs due to abrupt opening into evacuated space
Solution Approach 1:
The first stage of the switching valve is opened preliminarily before the main stage to prepare the system for the subsequent main stage opening. This preliminary action allows pressure compensation to occur in the evacuated intake line, preventing the abrupt pressure equalization that causes the knock noise when the main stage opens.
Solution Approach 2:
The switching valve is divided into two separate stages (first stage and main stage) that operate at different times. The first stage handles preliminary pressure adjustment, while the main stage completes the valve opening. This segmentation allows the system to avoid the harmful effect of abrupt pressure equalization while ensuring complete valve opening.
2Object-affected harmful factors
If the first stage opens with a delay to allow pressure compensation, then the pressure equalization knock is reduced, but the response time of the valve increases
Solution Approach 1:
The valve activation follows a periodic two-phase pattern: first a low-level control signal opens the first stage for a predetermined period, then a higher-level signal opens the main stage. This periodic action structure ensures pressure compensation occurs during the first phase, reducing knock noise, while the second phase quickly completes the valve opening to minimize overall response time loss.
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
Substantially reduces the pressure equalization knock by delaying the opening of the main stage, minimizing noise and brake pedal feedback, and is effective within the pressure range of 10 bar to 50 bar.
Implementation Method 1
High-pressure switching valve 7a is customarily driven by a pulse-width-modulated voltage signal (PWM signal)
Implementation Method 2
After a predetermined period of time, the switching valve is then activated by a higher-level signal to ensure that the valve always opens completely
Data Source
AI summary
A method for activating a two-stage switching valve including a first stage which has a small flow cross-section and a second stage which has a larger flow cross section, the switching valve being situated between a main brake cylinder and a hydraulic pump in a hydraulic brake system. The pressure equalization knock on opening the switching valve is substantially reduced by activating the switching valve in a first control phase via a control signal having a low amplitude, due to which only the first stage of the valve is first opened, and by activating the valve in a second phase via a control signal having a higher amplitude.