Interrelated power delivery controls – including engine control – Transmission control – Transmission controlled by engine
Reexamination Certificate
2002-12-31
2004-12-21
Lorence, Richard M. (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Transmission controlled by engine
C477S163000
Reexamination Certificate
active
06832977
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a vehicle's automatic transmission. In particular, the present invention relates to a hydraulic control system and method for automatic transmissions capable of improving gasoline mileage and shift quality by adjusting hydraulic pressure applied to friction elements of the automatic transmission.
BACKGROUND OF THE INVENTION
Typically, a transmission controller of an automatic transmission shifts between gears by controlling a plurality of solenoid valves installed on hydraulic lines, based on driving conditions of the vehicle, such as an operational speed of the vehicle, a degree of throttle opening, or the like. That is, if a shift lever is manipulated to a target position, a manual valve operates to change or convert its ports such that hydraulic pressure from an oil pump is supplied to appropriate operating elements of the gear shift mechanism, according to a duty control of the solenoid valves under control of the transmission controller.
When the transmission operated by the shift lever is positioned at a desired range, the hydraulic pressure is applied to some friction elements and released from other friction elements so as to establish a predetermined gear ratio. Accordingly, the transmission performance depends on the timing of applying and releasing hydraulic pressure to and from the predetermined friction elements for the target gear ratio.
In the case of an electrical transmission control system in which gear shifting is performed by applying hydraulic pressure to the friction elements, the pressure level applied to the friction elements is a stable standard line pressure. The hydraulic pressure is supplied from an oil pump that is mechanically connected to the engine so as to operate according to the engine operation, and the oil pump should be designed to sufficiently supply the hydraulic pressure in various ranges of engine rpm, starting about 700 to 800 rpm, and to maintain the hydraulic pressure so as to be failsafe even under the worst conditions.
The line pressure is set to satisfy various driving conditions such that if the line pressure is adjusted according to driving conditions it is possible to reduce the power wastage caused by the oil pump, resulting in improved gasoline mileage.
However, in the case of an automatic transmission performing a gear shift using a clutch to clutch method, the standard line pressure may change while adjusting the line pressure such that the friction elements from which the hydraulic pressure is released and the friction elements to which the hydraulic pressure is applied are simultaneously controlled. This is unlike the clutch to one-way clutch method, resulting in difficulty of line pressure control and degradation of shift control stability.
Furthermore, in conventional transmission control, it is impossible to estimate the time taken for the line pressure to reach the predetermined pressure level in the case of shift delay control, during which the line pressure increases to a predetermined pressure level before shifting. Also, it is required to determine friction coefficients of the friction elements of the transmission, deviation of the hydraulic pressure, and durability for the control of the line pressure in an in-gear state in which a certain shift range is synchronized without shifting gears.
SUMMARY OF THE INVENTION
In a preferred embodiment of the present invention, the hydraulic control system for an automotive automatic transmission comprises a driving condition detection unit, a transmission control unit, and a driving unit. The driving condition detection unit detects driving conditions of a vehicle. The transmission control unit performs variable line pressure control using a minimum line pressure and a line-pressure-decreasing gradient calculated based on driving condition data detected by the driving condition detection unit when the driving conditions satisfy variable line pressure control entrance conditions. The driving unit adjusts a duty ratio of line pressure applied to friction elements according to a line pressure control signal generated by the transmission control unit.
It is preferable that the driving condition detection unit comprises: an engine rpm sensor for detecting engine rpm of the vehicle; a throttle-opening sensor for detecting throttle opening degree; a turbine rpm sensor for detecting turbine rpm of a torque converter of the vehicle; a driving shaft rpm sensor for detecting rpm of a driving shaft of the vehicle; a hydraulic fluid temperature sensor for detecting hydraulic fluid temperature of the transmission; an atmospheric pressure sensor for detecting atmospheric pressure of an area where the vehicle is running; and an inhibit-on switch for detecting a position of a shift lever.
Preferably, the transmission control unit calculates a compensation value for variable line pressure control, based on the throttle opening degree.
It is preferable that the transmission control unit controls such that the variable line pressure control duty increases according to the change of the throttle opening degree and then is eliminated when engine power is normalized. It is further preferable that the transmission control unit calculates a line pressure control compensation value and hydraulic characteristics according to the hydraulic fluid temperature and engine rpm, and applies the calculation to the variable line pressure control duty. Preferably, the transmission control unit calculates a compensation value for a clutch friction coefficient according to a deviation and durability of the transmission and reflects the compensation value to a variable line pressure control duty.
It is preferable that the transmission control unit learns a minimum required line pressure by detecting an in-gear slip.
Preferably, the transmission control unit sets a delay time for increasing a shift begin line pressure to 100% for control stability.
It is preferable that the transmission control unit sets a minimum delay time by estimating a line pressure at a shift begin point without a hydraulic pressure sensor and a time taken for the line pressure reach to 100%.
It is preferable that the transmission control unit sets a minimum shift delay time in a slow kick-down.
Preferably, the transmission control unit sets a minimum shift delay time during lift-foot-up.
In another preferred embodiment of the present invention, the hydraulic control method comprises: determining whether or not driving conditions detected in a non-variable line pressure control mode satisfy variable line pressure control entrance conditions; determining whether or not gears are in an in-gear state by calculating a gear ratio using an engine rpm and turbine rpm when the driving conditions satisfy the variable line pressure control entrance conditions; entering a variable line pressure control mode in an in-gear state, and performing the variable line pressure control by calculating a minimum line pressure and variable line pressure gradient; determining whether or not a present line pressure is less than the calculated minimum line pressure; performing a normal line pressure control when the present line pressure is less than the minimum line pressure and then determining whether a gear shift starts or a damper clutch is in a direct coupled state; performing a gear shift to a target gear ratio after a predetermined time from a point when a line pressure control duty reaches 100% if it is determined that the gear shift starts or the damper clutch is in the direct coupled state in normal line pressure control; and performing variable line pressure control according to the driving conditions by entering the variable line pressure control mode for determining another shift begin point after delaying for a predetermined time if the gear shift to the target gear ratio is completed.
Preferably, the variable line pressure control mode entrance conditions include: the present hydraulic fluid temperature is between a preset lowest limit minimum value and lowest limit maximum value; a CAN (C
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