Planetary CVT Clutch Switching for Wheel Loader Transmissions
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Solution Overview
Problem
Existing power transmission devices for wheel loaders face inefficiencies in switching between low-speed and high-speed operations, with hydraulic mechanical continuously variable transmissions reducing efficiency at high speeds and torque converter vehicles experiencing efficiency drops at high speeds due to sliding, leading to unstable clutch engagement and release in planetary continuously variable transmission mechanisms.
Innovation Solution
A power transmission device with a planetary continuously variable transmission mechanism and a direct connecting mechanism, featuring a communication valve to switch between communicating and blocking states in the hydraulic circuit, allowing for stable clutch engagement and release, and utilizing synchromesh mechanism clutches to reduce heat generation and power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a torque converter is used for power transmission in wheel loaders, then torque amplification is achieved in low-speed range which is advantageous for starting and excavating, but the torque converter slides and operational efficiency is reduced in high-speed range
Solution Approach 1:
The power transmission system is segmented into multiple pathways: a torque converter pathway for low-speed torque amplification and a direct connecting mechanism pathway for high-speed efficient power transmission. The planetary continuously variable transmission mechanism further segments the transmission into hydraulic power transmission and mechanical power transmission paths, allowing selective engagement based on operating conditions.
Solution Approach 2:
The system dynamically switches between different power transmission modes based on operating conditions. A lockup mechanism dynamically connects the engine output shaft and transmission output shaft mechanically when high efficiency is needed, while the torque converter dynamically provides torque amplification when starting or excavating. The planetary gear mechanism dynamically adjusts the ratio of hydraulic to mechanical power transmission as vehicle speed rises.
2Loss of energy
If a lockup mechanism is used to mechanically connect engine output shaft and transmission output shaft, then power transmission efficiency increases, but the system complexity increases
Solution Approach 1:
The invention merges the torque converter mechanism with the direct connecting mechanism into a unified power transmission system. The planetary continuously variable transmission mechanism combines hydraulic power transmission and mechanical power transmission in one integrated system, allowing the lockup mechanism to be seamlessly integrated without requiring separate systems.
Solution Approach 2:
The planetary gear mechanism serves multiple functions: it divides and connects power for both hydraulic and mechanical transmission paths, provides speed reduction, and enables the lockup mechanism to engage and disengage smoothly. The communication valve serves dual purposes by controlling both hydraulic flow and clutch engagement timing.
3Reliability
If a planetary continuously variable transmission mechanism is used, then stable clutch engagement and release is achieved, but power loss occurs due to hydraulic power transmission
Solution Approach 1:
The communication valve performs preliminary action by switching the hydraulic circuit to a blocking state before clutch engagement. This pre-blocks the hydraulic power transmission path, allowing the clutch to engage under minimal load conditions. The valve then switches to communicating state after engagement to restore full power transmission, ensuring the clutch engages stably without excessive power loss.
Solution Approach 2:
The communication valve acts as an intermediary between the hydraulic pump and hydraulic motor, controlling the timing of hydraulic power transmission during clutch engagement. The planetary gear mechanism serves as an intermediary that distributes power between hydraulic and mechanical paths, reducing the power loss during clutch operations by coordinating the engagement timing.
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
Enables efficient power transmission by stabilizing clutch engagement and release in planetary continuously variable transmission mechanisms, improving operational efficiency across various speed ranges and reducing power loss, thereby enhancing the overall performance of wheel loaders.
Implementation Method 1
a hydraulic pump and/or a hydraulic motor in a hydrostatic continuously variable transmission are of variable displacement type
Implementation Method 2
The efficiency is calculated from the product of the mechanical efficiency and the volume efficiency of a hydrostatic continuously variable transmission
Implementation Method 3
It is a planetary gear mechanism that contributes to dividing and connecting the power
Implementation Method 4
utilizing synchromesh mechanism clutches to reduce heat generation and power loss
Data Source
AI summary
A transmission (21) as a power transmission device for a vehicle comprises an input shaft (22), an output shaft (23), a planetary continuously variable transmission mechanism (31), a direct connecting mechanism (27), and an idler gear (29). The direct connecting mechanism (27) comprises a direct connecting clutch (30). The planetary continuously variable transmission mechanism (31) comprises a planetary gear mechanism (32), a pump side clutch (33), a hydraulic pump (36), a hydraulic motor (38), and a motor side clutch (40). The hydraulic pump (36) and the hydraulic motor (38) are connected via a pair of main lines (37A, 37B). An electromagnetic on-off valve (41) capable of switching between a communicating state and a blocking state between the pair of main lines (37A, 37B) is provided between the pair of main lines (37A, 37B).