Hydromechanical Transmission Range Shifting Without Synchronizers
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Solution Overview
Problem
Hydromechanical transmissions face issues with synchronizer degradation, increased system cost and complexity, and unwanted tradeoffs in transmission complexity, packaging efficiency, and shifting smoothness.
Innovation Solution
A hydromechanical transmission system with a hydrostatic assembly and mechanical branch coupled in parallel using planetary gear sets and multiple clutches, where clutches are operated by a controller to transition between drive ranges, reducing power interruptions and enhancing efficiency through additive power combination and recirculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If synchronizing devices are used to shift between drive ranges, then shifting smoothness is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent removes synchronizing devices from the transmission system entirely. Instead of using complex synchronizers to manage gear shifts, the invention employs a hydrostatic transmission mechanism that continuously varies speed ratios without mechanical engagement/disengagement of gear elements, thereby eliminating the need for synchronizers and reducing overall system complexity.
Solution Approach 2:
The patent replaces mechanical synchronizing devices with a hydrostatic power transmission system. The variable speed ratio is achieved through hydraulic fluid coupling between pump and motor, eliminating mechanical gear engagement and the associated need for synchronizers, thus substituting mechanical complexity with hydraulic control.
2Volume of moving object
If multiple clutches are spaced away from one another to meet packaging constraints, then packaging efficiency is improved, but shifting smoothness and power continuity deteriorate
Solution Approach 1:
The patent merges the clutch operations into a coordinated sequence where multiple clutches engage and disengage in a synchronized manner. The controller manages the timing of clutch engagement so that power flow is continuously maintained through the transmission system, preventing power interruptions even as clutches are spatially distributed to meet packaging requirements.
Solution Approach 2:
The patent ensures continuous power transmission during clutch engagement transitions. The hydrostatic mechanism maintains fluid coupling throughout the shifting process, and the controller coordinates clutch operations to prevent any interruption in the useful action of power delivery from input to output shaft.
3Adaptability or versatility
If synchronizing devices are added to enable range transitions, then drive range versatility is improved, but system cost and complexity increase
Solution Approach 1:
The patent implements a universal hydrostatic transmission mechanism that can operate across multiple drive ranges without requiring separate mechanical gear sets or synchronizing devices for each range. The variable displacement pump and motor system provides continuous speed ratio adjustment that covers multiple operational ranges, making the system versatile while maintaining relatively simple architecture.
4Loss of energy
If mechanical gear sets are used for power transmission, then transmission efficiency is improved, but adaptability to different operating conditions deteriorates
Solution Approach 1:
The patent employs a dynamic hydrostatic transmission system where the pump and motor displacements can be continuously adjusted to optimize performance across different operating conditions. This dynamic adaptability allows the system to maintain high efficiency across a wide range of speeds and loads, unlike fixed-ratio mechanical gear sets that are optimized for specific operating points.
Data Source
AI summary
Methods and systems for a hydromechanical transmission are provided herein. In one example, the transmission system includes a hydrostatic assembly and a mechanical assembly coupled in parallel to a first and second planetary gear sets. The transmission system further includes a plurality of clutches designed to shift between two drive ranges in a set of drive ranges that includes a reverse drive range and two forward drive ranges to adjust the input to output speed ratio of the transmission.