CVT Powertrain Shift Timing Using Hydraulic Pressure Feedback
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Solution Overview
Problem
Existing continuously variable powertrain devices for work vehicles experience switching shock due to workload variations when changing shift levels, as the switching point is fixed and not adaptive to changing hydraulic static transmission efficiency.
Innovation Solution
A continuously variable powertrain device with a pressure detector to monitor hydraulic pressure, a planetary clutch mechanism for shifting, and a powertrain controller that adjusts the switching timing based on travel velocity and hydraulic pressure, using a shift timing table to calculate optimal switching points and incorporate threshold characteristics for stable clutch operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed switching point is used for planetary transmission shift levels, then the control logic is simple, but switching shock occurs when volumetric efficiency of the HST varies due to workload changes
Solution Approach 1:
The patent applies dynamics by making the switching point variable rather than fixed. The switching timing is dynamically adjusted based on the detected hydraulic pressure in the closed circuit of the HST. When the hydraulic pressure indicates reduced volumetric efficiency, the switching point is shifted to prevent premature shifting that would cause switching shock. This dynamic adaptation resolves the contradiction by maintaining simple control logic while eliminating the harmful switching shock through real-time parameter adjustment.
Solution Approach 2:
The patent implements feedback by using a pressure detector to monitor the hydraulic pressure in the HST closed circuit and feeding this information back to the planetary clutch controller. The controller uses this feedback to determine the appropriate switching timing, adjusting the switching point based on the actual volumetric efficiency conditions. This feedback mechanism allows the system to adapt to workload changes and prevent switching shock while maintaining relatively simple control logic.
2Object-affected harmful factors
If switching timing is adjusted based on hydraulic pressure, then switching shock is reduced, but the device complexity increases due to additional sensors and control logic
Solution Approach 1:
The patent applies self-service by utilizing the existing hydraulic pressure in the HST closed circuit as the sensing mechanism. Rather than requiring additional complex sensors, the system uses the naturally occurring hydraulic pressure that already exists in the circuit to detect volumetric efficiency changes. This approach reduces device complexity while still enabling the dynamic adjustment of switching timing to prevent switching shock.
Solution Approach 2:
The hydraulic pressure detection serves multiple functions: it monitors the volumetric efficiency of the HST, provides timing information for planetary transmission shifting, and indicates workload conditions. By using a single pressure detection mechanism for multiple purposes, the patent avoids the need for separate sensors and control systems for each function, thereby minimizing the increase in device complexity while achieving switching shock reduction.
3Stability of the object's composition
If fixed switching points are used, then the system is stable and simple, but the volumetric efficiency variations cause speed planning errors and large switching shocks
Solution Approach 1:
The patent applies parameter changes by modifying the switching point parameter based on hydraulic pressure conditions. Instead of using a fixed switching point, the system adjusts the switching timing parameter in real-time according to the detected pressure, which reflects the volumetric efficiency of the HST. This parameter adaptation maintains system stability by preventing speed planning errors and switching shocks that would otherwise occur due to efficiency variations.
Solution Approach 2:
The patent implements preliminary action by detecting the hydraulic pressure in advance of the planned switching event and using this information to pre-adjust the switching timing. This allows the system to proactively compensate for upcoming volumetric efficiency changes, preventing speed planning errors and switching shocks before they occur, thereby maintaining system stability.
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
This solution reduces or prevents switching shock by dynamically adjusting the switching timing, ensuring smoother transitions and reducing clutch repetition issues, even under unstable hydraulic static transmission outputs.
Implementation Method 1
a pressure detector to detect a hydraulic pressure in a closed circuit of the hydraulic static transmission
Implementation Method 2
a hydraulic static transmission to output a continuously shifted motive power while continuously varying a velocity of the motive power received from the engine
Implementation Method 3
a planetary transmission to receive the motive power from the engine and the continuously shifted motive power and to output a compound motive power
Data Source
AI summary
A continuously variable powertrain device for a work vehicle includes a hydraulic static transmission to output a continuously shifted motive power while continuously varying a velocity of a motive power received from an engine, a planetary transmission to receive the motive power from the engine and the continuously shifted motive power and to output a compound motive power, a pressure detector to detect a hydraulic pressure in a closed circuit of the hydraulic static transmission, a planetary clutch mechanism to switch a shift level of the planetary transmission, and a powertrain controller to control actuation of the hydraulic static transmission and the planetary transmission based on a shift command.