Pump Attenuator Bypass Valve for NVH and Pressure Trade-off
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Solution Overview
Problem
Existing brake systems with pulsation attenuators face challenges in achieving fast brake pressure apply rates with piston type pumps, as they often result in excessive pressure drop and noise, vibration, and harshness (NVH) during high dynamic braking events, while maintaining low NVH behavior during low pump flow events.
Innovation Solution
An attenuator bypass valve with a flow-based orifice bypass function is introduced, featuring a bypass valve housing with two fluid flow paths: one for continuous flow at low pump rates and another for bypassing the first path at higher pump rates, utilizing a poppet and spring mechanism to manage fluid flow and maintain orifice restriction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a single orifice is used in the attenuator, then low NVH behavior is maintained during low pump flow events, but brake pressure apply rate is limited during high dynamic braking events
Solution Approach 1:
The bypass valve uses a poppet and spring mechanism that dynamically adjusts the flow path based on pump flow rate. During low flow events, the poppet remains seated restricting flow through the orifice to maintain low NVH. During high flow events, the poppet lifts to open a bypass path, allowing high brake pressure apply rates while the orifice continues to dampen pulsations.
Solution Approach 2:
The fluid flow path is segmented into two separate paths: a restricted path through the orifice for low flow conditions, and an unrestricted bypass path for high flow conditions. This segmentation allows the system to optimize performance for both low NVH and fast brake apply rates by directing flow through appropriate paths based on operating conditions.
2Speed
If pump flow rate is increased to achieve fast brake pressure apply rates, then brake responsiveness improves, but pressure fluctuations and NVH increase
Solution Approach 1:
The bypass valve acts as an intermediary device between the pump outlet and the attenuator. It selectively directs high flow rates around the orifice restriction while still channeling pulsating flows through the attenuator chamber, where the compressible fluid dampens pressure fluctuations before reaching the brake lines.
Solution Approach 2:
Different parts of the flow path have different flow resistance characteristics. The bypass path provides low resistance for high flow rates, while the orifice path provides high resistance for pulsation damping. The system locally optimizes flow characteristics by directing flow through appropriate paths based on instantaneous pump output.
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 solution allows for efficient brake pressure application during high pump flow events while maintaining low NVH levels at low pump flow rates, improving overall system efficiency and brake performance by providing a flow-based orifice bypass function.
Implementation Method 1
a spring positioned in the bypass valve housing and configured to apply force to close the orifice passage
Implementation Method 2
The restriction of fluid flow through the orifice attenuates pressure fluctuations as a result of the compressibility of the brake fluid. Thus, brake fluid in the chamber absorbs high energy fluid pulses and slowly releases the fluid through the orifice.
Data Source
AI summary
A pump attenuator bypass valve (40/100/200) is located at an outlet of a pump (30) in a vehicle braking system (10) between the pump (30) and an attenuator (34). The attenuator bypass valve (40/100/200) includes a bypass valve housing (41), a first fluid flow path (74, 57/179/220, 208), and a second fluid flow path (80/183). The first fluid flow path (74, 57/179/220, 208) is defined in the housing (41) and is configured to allow continuous flow of fluid when the pump (30) operates at a first pump flow rate. The second fluid flow path (80/183) is defined in the housing (41) and is configured to bypass the first fluid flow path (74, 57/179/220, 208) and to allow continuous flow of fluid when the pump (30) operates at a second pump flow rate higher than the first pump flow rate.