HST Transmission Shift Control for Low-High Gear Responsiveness
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Solution Overview
Problem
Conventional transmission structures experience deteriorated responsiveness when switching between low gear and high gear transmission states, especially under traveling loads, due to the cancellation of Hydro Static Transmission (HST) load control during gear shifts.
Innovation Solution
A transmission structure that includes low and high gear mechanisms with a Hydro Static Transmission (HST) system, where the control device uses a reference HST gear ratio adjusted by load correction values and excess correction values to maintain vehicle speed responsiveness during gear switching, by calculating an excess vehicle speed gear ratio to match the actual vehicle speed immediately before and after switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If HST load control is canceled during gear switching, then the transmission structure can simplify control logic, but vehicle speed responsiveness deteriorates
Solution Approach 1:
The control device calculates the excess correction value in advance based on the load correction value before gear switching occurs. This preliminary calculation ensures that when gear switching is executed, the HST actuator can immediately apply the pre-calculated excess correction to maintain vehicle speed responsiveness without waiting for post-switch detection and adjustment.
Solution Approach 2:
The HST load control is made continuous across gear switching events by applying the excess correction value during the transition. Instead of completely canceling HST control during switching, the system maintains continuous adjustment of the HST actuator using the excess correction, ensuring uninterrupted useful action in maintaining vehicle speed responsiveness throughout the gear switching process.
2Speed
If HST load control is applied continuously, then vehicle speed responsiveness improves, but device complexity increases
Solution Approach 1:
The excess correction value is applied locally and specifically during gear switching events rather than continuously in all operating conditions. The control device detects gear switching states and selectively applies the excess correction only when needed, avoiding unnecessary complexity in normal operating conditions while maintaining improved responsiveness during transitions.
Solution Approach 2:
The system dynamically changes the HST gear ratio parameter by adding the excess correction value to the reference HST gear ratio during gear switching. This parameter adjustment allows the system to adapt the HST control behavior specifically during transitions, improving responsiveness without requiring complete redesign of the overall control system architecture.
Data Source
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AI summary
[Problem] The problem is in providing a transmission structure which includes low gear and high gear transmission mechanisms and an HST and can improve the vehicle speed responsiveness at the time of switching between a low gear transmission state and a high gear transmission state. [Solution] At the time of switching between low gear and high gear transmission states, the present invention creates an idling state in which the power transmission state from a drive source to a drive wheel is cut off, and calculates an excess vehicle speed HST gear ratio by adding an excess correction value, which is for changing the vehicle speed at the switching completion point in time in excess of the actual vehicle speed by a predetermined speed, to an actual vehicle speed ratio, which represents an HST gear ratio that causes the vehicle speed at the switching completion point in time to match the actual vehicle speed attained immediately before the completion of the switching, so as to operate an HST actuator using the excess vehicle speed HST gear ratio as a control target value during the idling state.