Hydraulic Control Device for Automatic Transmission Limp Home
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Solution Overview
Problem
Conventional hydraulic control devices for automatic transmissions with limp home functions experience increased flow resistance and size due to longer oil passages from linear solenoid valves to drain check valves, which can reduce controllability of engagement elements.
Innovation Solution
A hydraulic control device design that includes a normally closed solenoid valve directly communicating with a check valve, a failsafe valve for failure pressure output, and a check valve with a movable member and biaser to reduce oil passage length and maintain controllability during all-off failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If oil flows from the drain port of the linear solenoid valve through the failsafe valve to the drain check valve, then the limp home function is achieved, but the oil passage length increases causing increased flow resistance and reduced controllability
Solution Approach 1:
The patent segments the oil passage into two separate paths: a normal operation path (drain port → drain check valve) and a limp home path (drain port → failsafe valve → drain check valve). By providing separate communication paths, the system achieves the limp home function without compromising normal controllability, as the normal path remains short and direct.
Solution Approach 2:
The failsafe valve acts as an intermediary component that is introduced into the oil passage specifically for limp home operation. This intermediary element enables the limp home function by providing an alternative pressure input path to the drain check valve, while not interfering with the normal direct communication path between the drain port and drain check valve.
2Reliability
If the failsafe valve is interposed between the linear solenoid valve and drain check valve, then the limp home function is achieved, but the overall size of the hydraulic control device increases
Solution Approach 1:
The failsafe valve is designed to perform multiple functions: it serves as a normal check valve during regular operation and activates as a failsafe mechanism during limp home conditions. This multi-functionality reduces the need for separate dedicated components, thereby minimizing the overall device size while still achieving the limp home function.
Solution Approach 2:
The patent merges the failsafe functionality with the existing drain check valve structure. The failsafe valve is integrated into the same housing and shares common oil passages with the normal operation components, combining multiple functions into a single compact unit rather than adding separate independent 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 reduces flow resistance and maintains controllability by shortening the oil passage length from the solenoid valve to the check valve, thereby preventing a decrease in engagement element performance and minimizing the device's size.
Implementation Method 1
a first biaser that biases the first movable member such that the communication between the first input port and the first drain port is cut off
Implementation Method 2
a second biaser that biases the second movable member such that the communication between the second input port and the output port is cut off and for allowing the second input port to communicate with the output port at an oil pressure lower than the predetermined oil pressure
Implementation Method 3
a hydraulic control device for an automatic transmission which can reversely input an oil pressure to a drain port of a linear solenoid valve to supply the oil pressure to a hydraulic servo in case of all-off failure of solenoid valves
Data Source
AI summary
A hydraulic control device that includes a normally closed first solenoid valve, a first check valve, a failsafe valve, and a second check valve, wherein the first movable member of the first check valve is biased to cut off the communication between the first input port and the first drain port in case of the failure in which no current is applied to the first solenoid valve.