Line pressure control system for automatic transmission

#1. Field of the Invention

#The present invention relates to a line pressure control system for a shift control of an automatic transmission and, more particularly, to a line pressure control system for an automatic transmission, which is capable of properly controlling the line pressure even during a change in the engine load.

#2. Description of Related Art

#The present invention will be further explained below with reference to a preferred embodiment shown in the accompanying drawings.

#FIG. 1 is a schematic system diagram showing a vehicle power train having an automatic transmission provided with a line pressure control system in accordance with one embodiment of the present invention.

#FIG. 2 is a flowchart of a control program executed by a transmission controller in FIG. 1, for determining a transmission input torque for the line pressure control.

#FIG. 1 shows a power train of a vehicle provided with a line pressure control system in accordance with one embodiment of the present invention, together with a control system for an automatic transmission. In FIG. 1, reference numerals 1 and 2 denote an engine and an automatic transmission, respectively. The automatic transmission 2 receives power from the engine 1 through a torque converter 3, changes the input rotation with a gear ratio according to the selected range and sends it to an output shaft 4.

#In the automatic transmission 2, the selected range is determined by selectively operating a plurality of friction elements such as clutches and brakes, by the combination of ON and OFF states of shift solenoids 6 and 7 provided in a control valve body 5. The line pressure that governs the operation of the friction elements is determined by the duty control of a line pressure solenoid 8 similarly provided in the control valve body 5. The line pressure is increased from the lowest value to the highest value with an increase in a drive duty D of the line pressure solenoid 8.

#The ON and OFF states of the shift solenoids 6 and 7 and the drive duty D of the line pressure solenoid 8 are controlled by a transmission controller 9. The transmission controller 9 receives a signal from a throttle valve opening sensor 10 for detecting the throttle valve opening TVO (engine load) of the engine 1, a signal from a vehicle speed sensor 11 for detecting the vehicle speed VSP from the rotational speed of the transmission output shaft 4, a signal from an oil temperature sensor 12 for detecting the transmission hydraulic oil temperature C, a signal from a turbine rotation sensor 13 for detecting the turbine rotational sped Nt, which is the output rotational speed of the torque converter 3 (transmission input rotational speed), and a signal from an engine rotation sensor 14 for detecting the rotational speed Ne of the engine 1.