HST Planetary Transmission Shift Control for Smooth Vehicle Speed
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Solution Overview
Problem
Existing hydrostatic transmission systems with planetary gear mechanisms experience significant vehicle speed changes during speed changes, leading to reduced ride comfort and excessive load on the transmission path, especially when shifting from low to intermediate speed stages during vehicle travel.
Innovation Solution
A transmission structure incorporating a hydrostatic transmission (HST) with a planetary gear mechanism, a speed change operation member, and a control device that adjusts the output of the HST through a movable swash plate to smoothly transition between speed stages without changing the operation position of the output adjustment member, ensuring continuous speed change without load application to the transmission path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the multistage speed change structure is speed-changed from low speed stage to intermediate speed stage while the HST output is maintained at maximum speed, then the vehicle speed variable range is extended, but significant vehicle speed change occurs causing reduced ride comfort and excessive load on transmission path
Solution Approach 1:
The control device monitors the operation position of the output adjustment member and automatically adjusts the HST output speed based on this position, creating a feedback control system that prevents excessive speed changes during multistage speed change operations
Solution Approach 2:
The patent replaces manual mechanical operation of the HST output adjustment member with automatic control via a control device that uses sensors and actuators to adjust the swash plate position, eliminating the need for manual coordination between speed change operations and HST output control
2Ease of operation
If the output adjustment member is manually operated to change HST output speed, then the rotational speed of the motor continuously changes, but the operation position of the output adjustment member must be changed to achieve speed transition between stages
Solution Approach 1:
The control device automatically manages the HST output speed adjustment based on the detected operation position of the output adjustment member, making the system self-regulating and eliminating the need for manual intervention in HST output control during multistage speed changes
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 enables smooth speed transitions between low and high speed stages without causing vehicle speed changes, maintaining ride comfort and reducing load on the transmission path, while achieving efficient transmission without the need for multiple planetary gear mechanisms.
Implementation Method 1
The HST has a pump inputting rotation power from a driving source, a motor fluidly driven by the pump, and an output adjustment member varying the capacity of at least one of the pump and the motor
Implementation Method 2
the output adjustment member operates according to the operation amount of a speed change operation member which is manually operated, so that the rotational speed of the motor continuously changes in response to the operation
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
In a transmission structure according to this invention, speed change ratios of input side first and second transmission mechanisms (50(1)-(2)) are set so that the rotational speed of a planetary second element (38) is same when an HST output is set to a second HST speed in a first transmission state and when a second transmission state is engaged, and the rotational speed of a planetary first element (36) is same when the HST output is set to the second HST speed in the second transmission state and when the first transmission state is engaged. The speed change ratios of output side first and second transmission mechanisms (70(1)-(2)) are set so that the rotational speed developed in a speed change output shaft (45) when the HST output is set to the second HST speed is same in the first and second transmission states.