CVT Hydraulic Control for Vehicle Startup Driving Force
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Solution Overview
Problem
Conventional oil pressure control devices for continuously variable transmissions experience insufficient driving force during vehicle startup due to a higher-speed transmission ratio change, exacerbated by unequal oil passage lengths to pulleys, leading to inadequate belt pinching pressure control.
Innovation Solution
A control apparatus that regulates hydraulic oil pressures using an oil pressure pump driven by a vehicle's drive source, with distinct command pressures for the drive and driven pulleys, detected by sensors to ensure proper filling and progressive increase of oil pressure to prevent higher-speed transmission ratio changes, thereby maintaining sufficient driving force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If hydraulic oil pressures to be supplied to the drive pulley and driven pulley are substantially equal to each other at engine start, then the transmission ratio changes in the direction toward a higher-speed transmission ratio, but the driving force for starting the vehicle becomes insufficient
Solution Approach 1:
The control device performs preliminary action by setting the command oil pressure for the driven pulley higher than that for the drive pulley during engine start-up. This causes the driven pulley to be filled with hydraulic oil first, establishing proper belt pinching pressure before the drive pulley pressure rises, thereby preventing unwanted transmission ratio changes and ensuring sufficient driving force from the outset
Solution Approach 2:
The control device applies preliminary anti-action by creating a pressure differential that counteracts the natural tendency for the drive pulley pressure to rise first (which would cause higher-speed transmission ratio change). By setting the driven pulley command pressure higher, the system preemptively prevents the transmission ratio from shifting away from the desired low-speed ratio during engine start-up
2Speed
If the length of the oil passage to the drive pulley is shorter than that to the driven pulley, then the belt pinching pressure of the drive pulley rises earlier, but the transmission ratio changes in the direction toward a higher-speed transmission ratio
Solution Approach 1:
The control device changes the pressure parameter asymmetrically by setting different command oil pressures for the drive and driven pulleys during engine start-up. Specifically, it sets the driven pulley command pressure higher to compensate for its longer oil passage length, ensuring that both pulleys reach their respective pressure targets simultaneously and maintain the desired transmission ratio
Solution Approach 2:
The control device performs preliminary action by pre-setting the command oil pressure values to account for the unequal passage lengths. The driven pulley, having a longer passage, is given a higher command pressure to ensure its belt pinching pressure rises at the same rate as the drive pulley, preventing transmission ratio shifts toward higher-speed ratios
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 a sufficient driving force during vehicle startup by preventing the transmission ratio from shifting towards a higher-speed ratio, even with unequal oil passage lengths, by ensuring the driven pulley is filled before increasing pressure to the drive pulley, thus maintaining a stable low-speed transmission ratio.
Implementation Method 1
an oil pressure pump (62) that is driven by a drive source (1) for driving a vehicle, for pressurizing hydraulic oil
Implementation Method 2
a first solenoid valve (63a) that opens and closes a first communication passage between the oil pressure pump (62) and a cylinder chamber (25c) of the drive pulley (25) under control of a command signal from an electronic control unit (50), and opens and closes a second communication passage between the oil pressure pump (62) and a cylinder chamber (27c) of the driven pulley (27) under control of a command signal from the electronic control unit (50)
Data Source
AI summary
A control apparatus for an automatic transmission mechanism including a continuously variable transmission having a drive pulley, a driven pulley, and a belt extending around the two pulleys. When beginning of the start of a drive source for driving a vehicle has been detected, a first command oil pressure as a command value of a first control oil pressure supplied to a cylinder chamber of the drive pulley is set to a first predetermined oil pressure substantially equal to 0, and a second command oil pressure as a command value of a second control pressure supplied to a cylinder chamber of the driven pulley is set to a second predetermined oil pressure higher than the first predetermined oil pressure. When the detected second control oil pressure has reached a predetermined threshold value, it is determined that filling of the cylinder chamber of the driven pulley has been completed. A control for increasing the first command oil pressure is performed from a time point when completion of the filling of the cylinder chamber of the driven pulley has been determined.