Hydraulic control system for automatic transmission

A powertrain for an automotive automatic transmission, comprising:

• first and second planetary gearsets for receiving a torque from an engine to provide first, second, third and fourth forward speeds and a reverse speed;
• the first planetary gearset including a first sun gear, a first planet carrier and a first ring gear;
• the second planetary gearset including a second sun gear, a second planet carrier and a second ring gear;
• the first planet carrier being fixedly connected the second ring gear, a combination of the first planet carrier and the second ring gear being connected to a transfer drive gear so as to function as an output element;
• the first sun gear, the second planet carrier, and the second sun gear being connected to an input shaft connected to the engine via a torque converter;
• first, second and third clutches respectively disposed between the first sun gear and the input shaft, between the second planet carrier and the input shaft, and between the second sun gear and the input shaft so that first sun gear, the second planet carrier, and the second sun gear functions as input elements;
• the second planet carrier being connected to a transmission housing with a first brake disposed between the second planet carrier and the transmission housing and to the first ring gear with a fourth clutch disposed between the second planet carrier and the first ring gear;
• the sun gear being connected to the transmission housing with a second brake disposed between the second sun gear and the transmission housing;
• and
• the second planet carrier being connected to the transmission housing and the first ring gear with first and second one-way clutches respectively disposed between the second planet carrier and the transmission housing and between the second planet carrier and the first ring gear.

A hydraulic control system for an automatic transmission, comprising:

• a shift controller having a manual valve cooperating with a driver-controlled select lever to supply hydraulic pressure through range lines;
• a hydraulic pressure controller including first, second and third pressure control valves which are controlled by pressure controlled by first, second and third solenoid valves, the first pressure control valve controlling hydraulic pressure to be directly supplied to a first clutch operating in forward shift modes, the second pressure control valve controlling hydraulic pressure to be supplied to a second brake operating in second and fourth speeds of a drive D range, and the third pressure control valve controlling hydraulic pressure to be supplied to a first brake operating in a low L range and a reverse R range and to a third clutch operating in third and fourth speeds of the drive D range;
• and
• a hydraulic pressure distributor for distributing the hydraulic pressure,
• wherein in a drive D range, the first, second and third solenoid valves are all controlled to off states so that the vehicle speed can be held at a fourth speed even if the transmission control unit malfunctions;
• and
• in a drive D2 range, the first and second solenoid valves are controlled to off states and the third solenoid valve is controlled to an on state so that the vehicle speed can be held at a third speed even if the transmission control unit malfunctions.

A hydraulic control system for an automatic transmission wherein the hydraulic pressure distributor comprises:

• a low control valve for supplying L-range pressure to another valve as control pressure in the low L range such that control pressure of the third pressure control valve is supplied to the first brake;
• an N-R control valve for supplying reverse pressure to the first brake by reduced pressure supplied via the pressure control valve when shifting into the reverse R range;
• a line pressure control switch valve controlled by D-range pressure and hydraulic pressure supplied to a second clutch, the line pressure control switch valve supplying a part of the hydraulic pressure supplied to the second clutch to a pressure regulator valve;
• a first fail-safe valve controlled by control pressure supplied from the low control valve and from the second pressure control valve, the first fail-safe valve undergoing port conversion to supply hydraulic pressure supplied from the third pressure control valve to the second clutch in the third and fourth speeds of the drive D range, and hydraulic pressure supplied from the third pressure control valve to the first brake in the low L range;
• a second fail-safe valve controlled by reverse pressure, hydraulic pressure supplied to a fourth clutch, and hydraulic pressure supplied to the third clutch, the second fail-safe valve supplying hydraulic pressure supplied from the second pressure control valve to the second brake in the second and fourth speeds of the drive D range;
• and
• an engine brake control switch valve for supplying D-range pressure to the fourth clutch in the first and third speeds of the drive D range.