Interrelated power delivery controls – including engine control – Transmission control – Transmission controlled by engine
Reexamination Certificate
2000-09-06
2002-09-24
Estremsky, Sherry (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Transmission controlled by engine
C477S139000, C477S140000
Reexamination Certificate
active
06454678
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to an automatic transmission for vehicles. More particularly, the present invention relates to a shift control method for an automatic transmission which reduces shift shock occurring when shifting into back into second speed by the driver depressing the accelerator pedal during lift-foot-up shifting into the third speed from the second speed.
(b) Description of the Related Art
In the automatic transmission used for vehicles, a shift control system performs control to realize automatic shifting into different speeds and shift ranges according to various factors including throttle opening, vehicle speed and load, and several engine and driving conditions detected through a plurality of sensors. That is, based on such factors, the shift control system controls a plurality of solenoid valves of a hydraulic control system such that hydraulic flow in the hydraulic control system is controlled, resulting in the shifting of the transmission into the various speeds and shift ranges.
In more detail, when the driver manipulates a shift lever to a particular shift range, a manual valve of the hydraulic control system undergoes port conversion as a result of the manual valve being indexed with the shift lever. By this operation, hydraulic pressure supplied from a hydraulic pump selectively engages a plurality of friction elements of a gearshift mechanism according to the duty control of the solenoid valves, thereby realizing shifting into the desired shift range.
In such an automatic transmission, shift quality is determined by how smoothly the friction elements are engaged and disengaged. Namely, when changing shift ranges, the timing between the engagement of a specific set of friction elements in relation to the disengagement of another specific set of friction elements determines the shift quality of the automatic transmission. Accordingly, there have been ongoing efforts to develop improved shift control methods that enhance shift quality by better controlling the timing of friction elements to engaged and disengaged states.
The different kinds of automatic shifting operations that are performed according to driving state include sequential upshifting from the first speed to the fourth speed and sequential downshifting from the fourth speed to the first speed, skip downshifting or forced downshifting from the fourth to the second speed and from the third to the first speed, and lift-foot-up (LFU) shifting from the second speed to the third speed. The present invention relates to a method of controlling shifting back into the second speed during LFU shifting into the third speed from the second speed.
In the prior art method, when the driver depresses the accelerator pedal during LFU shifting from the second speed to the third speed, after shifting into the third speed is completed, this speed is first held for a predetermined duration before performing shifting back into the second speed. However, shift shock results from this process.
SUMMARY OF THE INVENTION
The present invention has been made in an effort to solve the above problems.
It is an object of the present invention to provide a shift control method for an automatic transmission in which when the accelerator pedal is depressed by the driver during LFU shifting into a third speed from a second speed, shifting is immediately performed back into the second speed after the completion of shifting into the third speed such that shift shock is minimized.
To achieve the above object, the present invention provides a shift control method for an automatic transmission comprising the steps of outputting a predetermined shift control signal while driving in a second speed for controlling shifting into a third speed if signals indicating that shifting from the second speed into the third speed are applied; determining if third speed synchronization is completed; performing driving in the third speed if third speed synchronization is completed, or determining if a tip-in signal has been applied if third speed synchronization is not completed; outputting a throttle compensation duty and determining if signals corresponding to 3-2 kickdown shifting are received if a tip-in signal is applied during third speed synchronization; comparing an oil temperature with a first predetermined value if signals corresponding to 3-2 kickdown shifting are received; comparing a vehicle speed with a second predetermined value if the oil temperature is greater than or equal to the first predetermined value; detecting an On/ Off state of a kickdown switch if the vehicle speed is greater than or equal to the second predetermined value; determining if a difference of turbind rpm and engine rpm and engine rpm is greater than or equal to a third predetermined value if the kickdown switch is On; performing 3-2 kickdown shift control during shifting from the second speed to the third speed if the difference of turbine rpm and engine rpm is greater than or equal to the third predetermined value; and performing 3-2 kickdown shift control after third speed synchronization if the difference of turbine rpm and engine rpm is smaller than the third predetermined value.
According to a feature of the present invention, the first predetermined value is 20° C. and the second predetermined value is 1500 rpm.
According to another feature of the present invention, if the oil temperature is less than the first predetermined value, 3-2 kickdown shifting is performed after synchronization into the third speed is completed.
According to yet another feature of the present invention, the method further comprises the steps of determining that the kickdown switch is On if the vehicle speed is less than the second predetermined value; and performing 3-2 kickdown shift control after third speed synchronization is completed if the kickdown switch is On.
According to still yet another feature of the present invention, if it is determined that the kickdown switch is Off, 3-2 kickdown shift control during shifting from the second speed to the third speed includes the steps of outputting an SCSV-B On signal; outputting general control signals after a duty is compensated, and if an initial fill time is elapsed outputting predetermined duty control signals to perform run-up and tie-up control; and performing initial duty learn control if 3-2 kickdown shift duty control is completed.
According to still yet another feature of the present invention, the duty compensation is realized by adding a predetermined compensation duty to a final duty value of a throttle compensation duty.
According to still yet another feature of the present invention, the general control signals are output if a predetermined time has elapsed after the compensation duty is output.
According to still yet another feature of the present invention, the initial fill time is 300 ms.
According to still yet another feature of the present invention, the step of outputting the predetermined duty control signals includes the steps of performing open-loop duty control, that is, after compensating a duty Da
3
by a predetermined first compensation duty following the holding of the duty for a predetermined hold time ta
2
, increasing a resulting duty by a rate of &agr;%/sec, and after compensating the duty by a second predetermined compensation duty, performing open-loop duty control; maintaining an output duty for a predetermined hold time te and determining if shift synchronization is completed following the completion of general control if open-loop duty control is completed; and completing duty control is shift synchronization is completed.
According to still yet another feature of the present invention, the hold time ta
2
is 500 ms.
According to still yet another feature of the present invention, if the hold time ta
2
is not elapsed, it is determined if the condition of Nt−(No×second gear ratio)>10 rpm; and if this condition is satisfied, increasing the duty by a rate of &agr;%/sec after compensating the duty by the predetermined
Birch & Stewart Kolasch & Birch, LLP
Estremsky Sherry
Hyundai Motor Company
Williams Eric M.
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