Interrelated power delivery controls – including engine control – Transmission control – Transmission controlled by engine
Reexamination Certificate
1999-12-22
2001-09-11
Marmor, Charles A (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Transmission controlled by engine
C477S144000, C477S149000, C477S161000
Reexamination Certificate
active
06287238
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to an automatic transmission, and, more particularly, to a forced downshift control method for an automatic transmission which prevents the generation of shift shock when changing from a power OFF to a power ON state during forced 4-2 downshifting.
(b) Description of the Related Art
Conventional automatic transmissions used in vehicles include a torque converter, a multi-stage gear shift mechanism connected to the torque converter, and a plurality of friction elements actuated by hydraulic pressure for selecting one of the gear stages of the gear shift mechanism, the gear shift mechanism being realized through a planetary gearset. The friction elements are controlled to engaged and disengaged states by a hydraulic control system, which controls hydraulic flow generated by an oil pump, to change shift ratios of the planetary gearset.
The friction elements are selectively operated by a plurality of valves, which undergo port conversion to change the flow of hydraulic pressure, and actuators supplying hydraulic pressure to the valves. Further, a manual valve, indexed with a driver-operated shift select lever to realize port conversion, is connected to a plurality of lines to supply hydraulic pressure from the oil pump to each valve and actuator.
In the automatic transmission structured as in the above, when changing shift modes (P, R, N, D, 2 and L), and when changing into different speeds within the drive D range, the friction elements are changed from a disengaged state to an engaged state and vice versa. A timing of the engagement of specific friction elements in relation to the disengagement of other specific friction elements determines overall shift quality of the automatic transmission. Accordingly, much research has been conducted on shift control methods that better effect such operations.
The different possible shift operations in the drive D range of the automatic transmission in the case where there are a total of four speeds include (a) downshifting successively from a fourth speed to a first speed; (b) upshifting successively from the first speed to the fourth speed; (c) forced downshifts, or kickdown, from the fourth speed to a second speed, and from a third speed to the first speed; and (d) driver-induced skip upshifting from the first to third speed, and the second to fourth speed. The present invention relates to the method of controlling forced downshifts from the fourth speed to the second speed of the drive D range.
When performing a forced 4-2 downshift, the driver abruptly depresses the accelerator pedal in a state of driving in the fourth speed. This causes a sudden rise in throttle pressure, and if road speed is not too high, a forced downshift into the second speed will occur. If the conditions are right for the forced downshift to occur, an end clutch is disengaged, a kickdown servo is maintained engaged, and a rear clutch is controlled to an engaged state, all at the time of changing from a power OFF to a power ON state. In the conventional automatic transmission, if the power state is changed into the power ON state, an end clutch pressure is maintained by open-loop control until a second speed synchronization point is reached.
However, in the power OFF forced 4-2 downshift described above, by maintaining end clutch pressure using open-loop control when changing into the power ON state, operation of the end clutch is continued in a state where operational pressure is being supplied to the rear clutch. This causes shift shock at the end of the shifting operation such that shift quality and ride comfort are reduced.
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 forced downshift control method for an automatic transmission which prevents the generation of shift shock when changing from a power OFF to a power ON state during forced 4-2 downshifting using feedback duty control, thereby improving overall shift quality and ride comfort.
To achieve the above object, the present invention provides a forced downshift control method for an automatic transmission. In the method, if shift signals of a forced 4-2 downshift are input, a first shift control solenoid valve SCSV-A is controlled to OFF immediately when the start of shifting is detected; a second shift control solenoid valve SCSV-B is maintained in an OFF state for a predetermined period of time (t1) after shifting is started, then controlled to ON; a third shift control solenoid valve SCSV-C is continuously maintained in an ON state, then after a Thold has elapsed following the detection of synchronization, is immediately controlled to OFF; and first and second pressure control solenoid valves PCSV-A and PCSV-B are duty controlled.
The method includes the steps of:
performing a first duty control operation to complete shifting through control of the first pressure control solenoid valve PCSV-A by comparing, based on three conditions, an end clutch input release time to with a filter time and a displacement time of a spool of a rear clutch and determining which of the three conditions is satisfied, and performing a first open-loop duty control operation according to the condition that is satisfied and determining if conditions for control from a power OFF forced 4-2 downshift to a power ON forced 4-2 downshift are satisfied, then performing the first duty control operation if the conditions are met;
performing a second duty control operation to complete shifting by performing a second open-loop duty control operation if conditions for control from a power OFF forced 4-2 downshift to a power ON forced 4-2 downshift are not satisfied, then determining if conditions for control from a power OFF forced 4-2 downshift to a power ON forced 4-2 downshift are now satisfied, and performing the second duty control operation if the conditions are met;
performing a third open-loop duty control operation, regardless of variations in power conditions, to complete shifting if conditions for control from a power OFF forced 4-2 downshift to a power ON forced 4-2 downshift are not satisfied;
performing a third duty control operation to complete shifting through control of the second pressure control solenoid valve PCSV-A by comparing, based on two conditions, the end clutch input release time t
o
with the filter time and the displacement time of the spool of the rear clutch and determining which of the two conditions is satisfied, and performing the third open-loop duty control operation according to the condition that is satisfied and determining if conditions for control from a power OFF forced 4-2 downshift to a power ON forced 4-2 downshift are satisfied, then performing the third duty control operation if the conditions are met;
performing a fourth duty control operation to complete shifting by performing a fourth open-loop duty control operation if conditions for control from a power OFF forced 4-2 downshift to a power ON forced 4-2 downshift are not satisfied, then determining if conditions for control from a power OFF forced 4-2 downshift to a power ON forced 4-2 downshift are now satisfied, and performing the fourth duty control operation if the conditions are met;
performing a fifth duty control operation to complete shifting by performing a fifth open-loop duty control operation if conditions for control from a power OFF forced 4-2 downshift to a power ON forced 4-2 downshift are not satisfied, then determining if conditions for control from a power OFF forced 4-2 downshift to a power ON forced 4-2 downshift are now satisfied, and performing the fifth duty control operation if the conditions are met; and
performing a sixth open-loop duty control operation, regardless of variations in power conditions, to complete shifting if conditions for control from a power OFF forced 4-2 downshift to a power ON forced 4-2 downshift are not satisfied.
According to a feature of the present invention, the first open-loop duty control
Birch & Stewart Kolasch & Birch, LLP
Ho Ha
Hyundai Motor Company
Marmor Charles A
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