Interrelated power delivery controls – including engine control – Transmission control – Transmission controlled by engine
Reexamination Certificate
1999-08-17
2001-03-27
Marmor, Charles A (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Transmission controlled by engine
C475S127000, C475S130000, C475S131000, C477S131000
Reexamination Certificate
active
06206802
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a hydraulic control system, and more particularly, to a hydraulic control system for a four-speed automatic transmission in which a number of pressure control valves, solenoid valves and fail-safe valves is reduced.
(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 pressure 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 selector to realize port conversion, is connected to a plurality of lines to supply hydraulic pressure from the oil pump to each valve and actuator.
FIG. 4
shows a hydraulic circuit diagram of a conventional hydraulic control system. The hydraulic control system includes an underdrive clutch UD-C, an overdrive clutch OD-C, a reverse clutch REV-C, a low-reverse brake LR-B, and a second brake
2
NB-B. These elements are controlled by hydraulic pressure and perform control to realize four forward speeds and one reverse speed.
Solenoid valves control hydraulic pressure supplied to a plurality of valves, which, in turn, control hydraulic pressure supplied to the friction elements. There are a total of four solenoid valves, one less than the number of friction elements, provided in the hydraulic control system. These include a low-reverse solenoid valve LR-S, a second solenoid valve
2
ND-S, an underdrive solenoid valve UD-S and an overdrive solenoid valve OD-S. Valves controlled by the solenoid valves include a low-reverse pressure control valve LR-PCV, a second pressure control valve
2
ND-PCV, an underdrive pressure control valve UD-PCV and an overdrive pressure control valve OD-PCV.
Further provided is a switch valve SW-V which reduces line pressure in third and fourth speeds of a drive D range such that stress given to an oil pump OP is reduced and a power transmission efficiency of the automatic transmission is improved. The hydraulic control system also includes a first fail-safe valve FSV-
1
. The first fail-safe valve FSV-
1
prevents the simultaneous operation of the low-reverse brake LR-B and the underdrive clutch UD-C, as well as of the low-reverse brake LR-B, underdrive clutch UD-C and overdrive clutch OD-C. There is also provided a second fail-safe valve FSV-
2
which prevents the simultaneous operation of the second brake
2
ND-B, underdrive clutch UD-C and overdrive clutch OD-C.
As shown in
FIG. 5
, the solenoid valves are operated to ON and OFF states in different combinations to realize control into the various speeds and shift modes. That is, as described above, the solenoid valves are operated to ON and OFF states such that the supply of hydraulic pressure to the valves is controlled. This, in turn, controls the supply of hydraulic pressure to specific friction elements to control the same, thereby ultimately controlling the multi-stage gear shift mechanism for control into the different shift speeds and modes.
However, in the conventional hydraulic control system described above, a solenoid valve is provided at each of the friction elements, except for the low-reverse clutch REV-C; a pressure control valve is provided at each of the solenoid valves; and two fail-safe valves are required to prevent the simultaneous operation of the friction elements as described above. This large number of elements complicates the hydraulic control system, and increases overall manufacturing costs and the weight of the hydraulic control system.
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 hydraulic control system for a four-speed automatic transmission in which a number of pressure control valves, solenoid valves and fail-safe valves is reduced.
To achieve the above object, the present invention provides a hydraulic control system in which line pressure, drive pressure, reverse pressure and low pressure are selectively supplied from a manual valve to an underdrive clutch, an overdrive clutch, a low-reverse brake, a reverse clutch, and a second brake to realize four forward speeds and a reverse speed. The hydraulic control system includes an underdrive pressure control valve provided between a drive pressure line, connected to the manual valve, and the underdrive clutch, and controlled by a first solenoid valve; an overdrive pressure control valve provided between the drive pressure line and the overdrive clutch, and controlled by a second solenoid valve; a second/low-reverse pressure control valve connected to a line pressure line, connected to the manual valve, and controlled by a third solenoid valve; a solenoid switch valve controlled by low pressure, line pressure or drive pressure supplied respectively from a low pressure line, the line pressure line and the drive pressure line connected to the manual valve, and which supplies hydraulic pressure passed through the second/low-reverse pressure control valve to the low-reverse brake and the second brake; and a fail-safe valve provided between the solenoid switch valve and the second/low-reverse pressure control valve, and is controlled by operational pressure of the underdrive clutch and overdrive clutch, line pressure, and drive or reverse pressure, the fail-safe valve preventing hydraulic pressure supplied from the second/low-reverse pressure control valve from being simultaneously supplied to the second brake and the low reverse brake. The reverse clutch is directly communicated with the manual valve via a reverse pressure line.
According to a feature of the present invention, a valve body of the manual valve includes a first port connected to the line pressure line, a second port connected to the drive pressure line, a third port connected to the low pressure line, a fourth port connected to the reverse pressure line, a fifth port connected to the regulator valve, and exhaust ports; and a valve spool of the manual valve includes first and second lands and an exhaust passage, the first and second lands and the exhaust passage selectively communicating the ports.
According to another feature of the present invention, a valve body of the second/low-reverse pressure control valve includes a first port connected to the line pressure line, a second port connected to the fail-safe valve, a third port connected to a pressure reduction line, a fourth port connected to the third solenoid valve, and exhaust ports; a valve spool of the second/low-reverse pressure control valve includes first, second and third lands for selectively communicating the first and second ports; and an elastic member is interposed between an inside wall of the second/low-reverse pressure control valve and the third land of the valve spool, the elastic member exerting biasing force on the valve spool in a direction toward the third port.
According to yet another feature of the present invention, a valve body of the fail-safe valve includes a first port connected to the second/low-reverse pressure control valve, a second port connected to the solenoid switch valve, a third port connected to the underdrive clutch, a fourth port connected to the overdrive clutch, a fifth port connected to the line pressure line, a sixth port connected to the drive pressure line and the reverse pressure line, and exhaust ports; and a valve spool of the fail-safe valve includes first, second, third, fourth, fifth, sixth and seventh
Birch & Stewart Kolasch & Birch, LLP
Hyundai Motor Company
Marmor Charles A
Waddell Tisha D.
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