Braking Control Apparatus Master Cylinder Segmentation
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Solution Overview
Problem
In by-wire brake systems, the initial phase of pedal stroke is affected by the idle stroke, leading to inferior pedal feeling and potential issues with braking force generation, especially during sudden braking or system failures, due to the long idle stroke of the second fluid pressure chamber, which requires a correspondingly longer pedal stroke and larger master cylinder size.
Innovation Solution
The braking control apparatus is designed with a master cylinder and stroke simulator where the idle stroke of the fluid pressure chamber connected to the stroke simulator is set smaller than the other, allowing fluid pressure to be transmitted early in the pedal stroke, and the biasing forces of the return springs are adjusted to facilitate earlier displacement of the pistons, thereby improving pedal feeling and reducing the size of the master cylinder.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the idle stroke L2 of the second fluid pressure chamber is set relatively long to make the pedal reaction force lighter at the start of pressing the brake pedal, then the ease of operation is improved, but the pedal feeling becomes inferior due to bump sensation during sudden braking
Solution Approach 1:
The master cylinder is divided into two separate fluid pressure chambers (first and second chambers), each with its own piston, return spring, and idle stroke characteristics. This segmentation allows independent optimization of each chamber's parameters - the first chamber has a shorter idle stroke L1 for immediate response, while the second chamber has a longer idle stroke L2 for lighter initial pedal feel, resolving the contradiction between ease of operation and pedal feeling reliability.
2Ease of operation
If the idle stroke L2 is set relatively long to reduce initial pedal resistance, then the ease of operation is improved, but the response time is worsened because the stroke simulator starts moving later during pedal stroke
Solution Approach 1:
By segmenting the hydraulic system into two chambers, the first chamber with shorter idle stroke L1 provides immediate fluid pressure transmission to the stroke simulator, ensuring fast response time. The second chamber with longer idle stroke L2 handles the initial pedal displacement with reduced resistance. This segmentation eliminates the time loss associated with a single long idle stroke while maintaining ease of operation.
3Ease of operation
If the idle stroke L2 is set relatively long to reduce initial pedal resistance, then the ease of operation is improved, but the device size is worsened requiring a larger master cylinder
Solution Approach 1:
The tandem configuration segments the functional requirements into two chambers, allowing the master cylinder to be compact while achieving both long and short idle stroke effects. The first chamber with shorter dimensions provides immediate response, while the second chamber extends the effective stroke. This segmentation enables a smaller overall master cylinder volume compared to a single-chamber design requiring a uniformly long idle stroke.
4Ease of operation
If the idle stroke L2 is set relatively long to reduce initial pedal resistance, then the ease of operation is improved, but the braking force generation is worsened during sudden braking and system failures
Solution Approach 1:
During sudden braking or system failures, the first fluid pressure chamber with shorter idle stroke L1 immediately generates hydraulic pressure and transmits it to the wheel cylinders, ensuring rapid braking force generation. The segmentation allows the critical safety function of fast braking response to be independent of the second chamber's longer idle stroke, resolving the contradiction between ease of operation and braking productivity.
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 configuration enhances pedal feeling by transmitting the reaction force from the stroke simulator earlier in the pedal stroke, ensures quicker braking force generation, and allows for a smaller master cylinder size, addressing the issues of idle stroke effects and system reliability.
Implementation Method 1
a first fluid pressure chamber and a second fluid pressure chamber... configured to generate a fluid pressure when communication with the reservoir tank is blocked
Implementation Method 2
the biasing forces of the return springs are adjusted to facilitate earlier displacement of the pistons
Data Source
AI summary
A master cylinder (14) includes a first piston (73), a second piston (83), and a cylinder(15) for housing the first piston (73) and the second piston (83) moving slidably in the axial direction. A first fluid pressure chamber (71), having a passage (77) communicating with a reservoir tank (26), generates the fluid pressure when communication with the reservoir tank is interrupted at displacement of the first piston (73) by a first stroke. Similarly, a second fluid pressure chamber (81), having a passage (87) communicating with the reservoir tank (26), generates the fluid pressure when communication with the reservoir tank is interrupted at displacement of the second piston (83) by a second stroke which is smaller than the first stroke. A stroke simulator (24) communicates with the fluid pressure chamber (81). A braking control apparatus is structured such that the second piston (83) is first displaced when a brake pedal is pressed.