Variator Lockout Valve Torque Reversal Prevention
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Solution Overview
Problem
In continuously variable transmissions with a full toroidal ratio varying unit, mode transitions involve a momentary overlap of clutches, leading to a fixed ratio and potential unintended torque reversals, which can disrupt power transmission and require complex hydraulic control to manage force reversals on variator rollers.
Innovation Solution
A variator control circuit with shift valves and trim valves that adjust fluid pressure dynamically, allowing for precise control of variator torque direction and preventing unintended torque reversals by blocking or unblocking fluid pressure to the variator based on operating modes, and incorporating an electro-hydraulic actuator system for synchronized clutch engagement and disengagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If clutches are overlapped during mode transition to ensure continuous power transmission, then power transmission continuity is improved, but unintended torque reversals occur disrupting power transmission
Solution Approach 1:
The lockout valve is activated before the mode transition completes to preemptively prevent torque reversals. By blocking the fluid pressure to the variator rollers in advance, the system prevents the harmful torque reversal effect while maintaining continuous power transmission through the clutch overlap period
Solution Approach 2:
The lockout valve acts as an intermediary component between the hydraulic control circuit and the variator rollers. It mediates the fluid pressure flow, selectively blocking or allowing pressure to reach the rollers based on the transmission mode, thereby preventing torque reversals without disrupting overall power transmission
2Ease of operation
If hydraulic actuators apply force to variator rollers to control torque, then variator ratio control is improved, but complex hydraulic control is required to manage force reversals during mode transitions
Solution Approach 1:
The lockout valve extracts the torque reversal prevention function from the main hydraulic control circuit. By separating this specific control function into a dedicated valve, the system simplifies the overall hydraulic control architecture while maintaining precise variator ratio control through the remaining actuators
Solution Approach 2:
The hydraulic control system is segmented into multiple independent control paths: one for normal variator ratio control via hydraulic actuators, and another for torque reversal prevention via the lockout valve. This segmentation allows each subsystem to operate independently, reducing overall system complexity
3Measurement precision
If trim valves are used to adjust fluid pressure for precise torque control, then torque direction control is improved, but system reliability decreases when trim valves fail
Solution Approach 1:
The lockout valve provides a backup mechanism that activates when trim valves fail. By having this preventive measure in place beforehand, the system can maintain reliable operation and allow 'limp home' mode even when the precision torque control through trim valves is compromised
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
Ensures continuous and stable power transmission during mode transitions by preventing unintended torque reversals and allowing the system to maintain selected modes even in case of trim valve failures, enabling 'limp home' operation without disrupting the vehicle's power delivery.
Implementation Method 1
a hydraulic control circuit with a shift valve and a trim valve that are selectively actuated to control the direction and magnitude of the force applied to the rollers
Implementation Method 2
In the variator, torque is transmitted by the frictional engagement of variator disks and rollers separated by a traction fluid
Data Source
AI summary
A variator lockout valve system for a continuously variable transmission includes a pair of shift valves. Each shift valve has at least one port that is fluidly coupled to a variator of the continuously variable transmission. Electro-hydraulic actuators control the position of each of the shift valves. When the shift valves are in one position, pressure control valves supply fluid pressure to the variator. If one of the shift valves is in another position, one of the pressure control valves is blocked from supplying fluid pressure to the variator.