CVT Control Device Hydraulic Pressure Switching
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Solution Overview
Problem
Existing control devices for continuously variable transmissions face challenges in maintaining precise transmission gear ratios, especially when rotational speed detection is low, leading to unstable gear changes and potential belt slip, due to limitations in rotational speed sensor precision.
Innovation Solution
The control device switches control modes for the hydraulic pressure of the primary pulley based on detected rotational speed, employing lower limit hydraulic control to maintain maximum gear ratio at low speeds and feedback control when precision improves, using reference values to adjust hydraulic pressure and prevent belt slip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If feedback control is used to maintain precise transmission gear ratio, then transmission precision is improved, but control stability deteriorates at low rotational speeds due to sensor precision limitations
Solution Approach 1:
The control device dynamically switches between feedback control mode and open-loop control mode based on the detected rotational speed. At low rotational speeds where sensor precision is insufficient, the system transitions to open-loop control using a different control map, thereby maintaining reliability across all operating conditions while preserving measurement precision when available.
Solution Approach 2:
The control device changes the control parameters based on rotational speed thresholds. When rotational speed falls below a predetermined threshold, the system switches from using feedback control with sensor data to using open-loop control with a pre-defined control map, thus adapting to the changing measurement precision conditions and maintaining stable operation.
2Speed
If rotational speed sensor is used for detection, then real-time control is improved, but measurement precision deteriorates at low rotational speeds
Solution Approach 1:
The control device segments the operational range into high-speed and low-speed regions based on rotational speed thresholds. In the high-speed region, feedback control using the rotational speed sensor is applied for real-time precise control. In the low-speed region, open-loop control using a different control map is applied, thus maintaining measurement precision across all speed ranges while preserving real-time control capability where the sensor is effective.
3Productivity
If hydraulic pressure is reduced to increase groove width, then transmission gear ratio is improved, but belt tension is reduced causing slip
Solution Approach 1:
The control device performs preliminary action by switching to open-loop control and using a pre-defined control map before the system enters a state where belt slip might occur. By anticipating the low-speed condition and switching control modes in advance, the system maintains appropriate hydraulic pressure control to prevent belt slip while still achieving the desired gear ratio adjustment.
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 approach allows for maintaining the maximum transmission gear ratio even at low precision and quickly restarting gear changes when precision improves, ensuring stable and efficient gear shifting without belt slip.
Implementation Method 1
a rotational speed sensor of an electromagnetic pickup type as a rotational speed sensor for detecting a rotational speed of a power transmission system
Implementation Method 2
changes hydraulic pressure in a hydraulic chamber provided in each of the pulleys to vary the groove width of each of the pulleys
Implementation Method 3
a belt wound upon the pair of pulleys and serves to change the winding radius of the belt in each of the pulleys, thereby varying the transmission gear ratio continuously
Data Source
AI summary
When a rotational speed of a secondary pulley is less than a first reference value, the disclosed electronic control device implements lower limit hydraulic control to adjust the hydraulic pressure of a primary pulley to be at a lower limit hydraulic pressure. When the rotational speed is equal to or exceeds the first reference value, but is less than a second reference value, the electronic control device implements balanced hydraulic control to adjust the hydraulic pressure to be more than the lower limit hydraulic pressure. When the rotational speed is equal to or exceeds the second reference value, the electronic control device implements feedback control to correct the hydraulic pressure on the basis of the size of the difference between a target transmission gear ratio and a transmission gear ratio, calculated on the basis of rotational speeds detected by each rotational speed sensor.