CVT Hydraulic Pressure Control Preventing Speed Ratio Hunting
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Solution Overview
Problem
The existing hydraulic pressure control in continuously variable transmissions can lead to hunting of speed ratios due to fluctuations in primary and secondary pressures, causing instability and regulation failures, especially when the target line pressure is set equal to the higher value of target primary and secondary pressures.
Innovation Solution
A mechanism that sets a target line pressure by adding an offset value to the higher value of target primary and secondary pressures in the cross-point region, where the absolute deviation between them is smaller than a predetermined value, to stabilize the primary, secondary, and line pressures, thereby preventing hunting of the speed ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the target line pressure is set to be equal to either one having the higher value out of the target primary pressure and the target secondary pressure, then the load of the oil pump is reduced and fuel efficiency is improved, but hunting of the speed ratio is caused when the target primary pressure or the target secondary pressure exceeds the target line pressure
Solution Approach 1:
The control device applies preliminary anti-action by detecting when the target line pressure equals or exceeds the target primary or secondary pressure, and proactively setting the actual line pressure to be higher than the target line pressure in advance. This prevents the pressure regulation valves from entering a failure state where they cannot regulate pressure properly, thereby avoiding speed ratio hunting before it occurs.
Solution Approach 2:
The control device acts as an intermediary between the target pressure values and the actual pressure delivery. By introducing an intermediate judgment step that compares target pressures with line pressure and applies offset corrections, the system mediates the pressure control to prevent direct conflict between primary/secondary pressure demands and line pressure limitations, avoiding instability.
2Device complexity
If the target line pressure is set equal to the higher value of target primary and secondary pressures, then the hydraulic pressure control is simplified, but the three pressures fluctuate near the same value causing hunting of the speed ratio
Solution Approach 1:
The control device applies dynamics by making the line pressure offset dynamically adjustable based on operating conditions. The offset value is not fixed but is determined by the control device according to the detected pressure relationships and vehicle operating state, allowing the system to adaptively maintain pressure differentials that prevent hunting while responding to changing demands.
Solution Approach 2:
The control device changes the pressure parameter by introducing an offset value that modifies the relationship between target line pressure and actual line pressure. This parameter change creates a deliberate pressure differential that prevents the primary, secondary, and line pressures from converging to the same value, thereby eliminating the conditions for speed ratio hunting.
Data Source
AI summary
A target primary pressure and a target secondary pressure are set based on a speed ratio, a target line pressure as a target value of a line pressure is set to be a value obtained by adding an offset amount, as a positive value, to either one having a higher value out of the target primary pressure and the target secondary pressure, in at least a cross-point region as a region where an absolute value of a deviation, obtained by subtracting the target primary pressure from the target secondary pressure, is smaller than a predetermined deviation, and a primary pressure, a secondary pressure, and the line pressure are controlled to be the target primary pressure, the target secondary pressure, and the target line pressure, respectively.