CVT Hydraulic Control System Flow Segmentation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing continuously variable transmissions with hydraulic control systems face challenges in quickly and accurately regulating pulley pressures due to the influence of pump flow volume on control valve size and functionality, particularly at varying engine speeds and during changes in transmission ratio.
Innovation Solution
The hydraulic control system adapts the oil flow to match current oil consumption and pressure-dependent leakage losses, using a pump flow control valve to divert surplus oil flow, allowing for stable and quick line pressure regulation, and optionally employing a controllable pump to adjust pump flow based on oil consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a relatively great pump flow is used to achieve movement of pulley sheaves during transmission ratio changes, then the transmission can handle higher torque and speed changes, but the control valves become larger and less controllable, and the system becomes less stable and slower to respond
Solution Approach 1:
The hydraulic system is segmented into two separate circuits: a main hydraulic circuit for power transmission and a control circuit for valve operation. The control circuit receives a reduced, regulated portion of the pump flow through the flow control valve (48), separating the high-flow power transmission function from the precision control function. This allows the control valves to be sized appropriately for stable, quick response while the pump maintains high flow capability for torque handling.
2Power
If the pump flow volume is increased to meet high torque transmission requirements, then the transmission can operate at higher engine speeds, but the control valves must be larger which reduces their controllability and response time
Solution Approach 1:
A flow control valve (48) is introduced as an intermediary device between the pump and the control valves. This intermediary regulates and reduces the pump flow to an appropriate level for control valve operation, allowing the pump to maintain high flow capacity for power transmission while the control valves receive a manageable, reduced flow that enables precise control and quick response.
3Reliability
If the pump flow is reduced to improve control valve stability, then the line pressure regulation becomes more stable and responsive, but insufficient flow remains for achieving pulley sheave movement during transmission ratio changes
Solution Approach 1:
The hydraulic system is divided into two functional segments: the control circuit that receives regulated, reduced flow for stable line pressure control, and the main power circuit that receives full pump flow for pulley sheave movement and torque transmission. The flow control valve (48) creates this segmentation by directing a portion of pump flow to the control circuit while the remainder continues to the power circuit.
Solution Approach 2:
The flow control valve (48) acts as an intermediary that selectively diverts a controlled portion of pump flow to the control circuit. This intermediary device enables the control valves to receive sufficient reduced flow for stable operation without depriving the main power circuit of the high flow needed for pulley sheave movement and torque handling.
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 improves the response time and stability of control valves, enabling precise regulation of pulley pressures and optimizing oil flow distribution, reducing unnecessary flow and enhancing transmission efficiency.
Implementation Method 1
by forcing the sheaves of a pulley towards each other under the influence of a hydraulic pressure exerted upon at least one sheave
Implementation Method 2
an oil pump for generating an oil flow
Implementation Method 3
at least two pulley pressure control valves for regulating the individual pulley pressures... a line pressure control valve for regulating the line pressure
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The invention relates to a method for controlling a continuously variable transmission provided with a drive belt (6) fitted between a primary pulley (1) and a secondary pulley (2), each pulley having two pulley sheaves of which at least one sheave in each case is axially movable under the influence of a hydraulic pressure exerted in a pressure cylinder (11; 12) of a respective pulley (1; 2), and with a hydraulic control system for controlling the abovementioned pressures, which system comprises at least a reservoir (40) for hydraulic medium, a pump (46) for generating a controllable pump flow of hydraulic medium from a reservoir (40), and a pressure control valve (43) for controlling the hydraulic pressure of the pump flow. According to the invention, a surplus of the pump flow that is discharged by the pressure control valve (43) in the direction of the reservoir (40) is regulated to a certain, preferably virtually constant, value.