Brake Element Piston Segmentation for Transmission Engagement
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Solution Overview
Problem
Existing brake elements in automatic transmissions face deterioration in responsiveness and accuracy of engagement timing due to increased clearance in friction plates caused by individual differences or aging, leading to longer engagement times and potential speed-change shocks.
Innovation Solution
A brake element design featuring a first piston fitted within a second piston, with oil pressure chambers and a biasing member to control piston movement, ensuring effective pressing of friction plates while maintaining a relative positional relationship, and a restriction member to limit piston stroke, allowing for precise engagement and disengagement control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the brake element uses a return spring acting on the first piston to bias both pistons toward the disengaged position, then the brake element can be disengaged reliably, but the standby position of the first piston becomes structurally determined and cannot adapt to increased clearance due to aging or individual differences
Solution Approach 1:
The brake element is divided into two independent piston systems: a first piston for pressing friction plates and a second piston for controlling the first piston's standby position. The return spring acts only on the second piston, separating the functions of pressing and positioning. This segmentation allows the second piston's standby position to be independently adjustable via the adjustment member, adapting to clearance changes without affecting the first piston's pressing function.
Solution Approach 2:
The second piston is preliminarily positioned by the adjustment member to set the standby position of the first piston before engagement. This preliminary positioning ensures that even when clearance increases due to aging or individual differences, the first piston starts from an optimized position that minimizes the distance to the engagement position, maintaining responsive engagement without sacrificing disengagement reliability.
2Measurement precision
If the brake element allows the first piston to move freely to establish pressing, then engagement timing can be accurate, but the distance from standby position to pressing established position increases when clearance is large, deteriorating responsiveness
Solution Approach 1:
The second piston preliminarily moves the first piston to a standby position that is optimally positioned relative to the friction plates. This preliminary action reduces the distance the first piston must travel to reach the engagement position, improving engagement responsiveness. The adjustment member allows this standby position to be tuned to compensate for clearance variations, ensuring consistent engagement timing accuracy regardless of clearance size.
3Device complexity
If the brake element uses a fixed standby position determined by structural components, then the structure is simple, but the distance between standby position and pressing established position increases with clearance, causing deterioration in engagement responsiveness
Solution Approach 1:
The positioning function is segmented from the pressing function by introducing a second piston controlled by an adjustment member. While this adds a component, it enables the standby position to be adjusted to compensate for clearance variations, maintaining fast engagement responsiveness. The adjustment member provides a simple mechanism for positioning without requiring complex control systems.
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
The solution prevents deterioration in responsiveness and accuracy of engagement timing, even with increased clearance, by ensuring quick and accurate friction plate pressing, thereby reducing speed-change shocks and maintaining efficient transmission performance.
Implementation Method 1
a biasing member biasing the second piston toward a side away from the friction plates
Implementation Method 2
a first oil pressure chamber configured to be supplied with an oil pressure for moving the first piston by a stroke toward the side close to the friction plates; a second oil pressure chamber configured to be supplied with an oil pressure for moving the second piston by a stroke toward the side close to the friction plates
Data Source
AI summary
A first piston (65) that presses friction plates (69a, 69c) is fitted in a second piston (66) in such a manner as to be movable together with the second piston and relatively movable with respect to the second piston. An A-chamber (61) and a B-chamber (62) each configured to move a respective one of the first piston (65) and the second piston (66) by a stroke toward a side close to the friction plates, a return spring (161) biasing the second piston (66) on a side away from the friction plates, and a stopper member (160) configured to prevent a stroke of the second piston (66) toward the side close to the friction plates from becoming greater than a given value (W) are provided. Engagement responsiveness of a L-R brake (60) does not deteriorate even when a clearance (V) in the friction plates (69a, 69c) increases.