Hydraulic transmission control system

DETAILED DESCRIPTION It is, therefore, a primary object of the present invention to provide a hydraulic control system for a transmission of an automobile vehicle in which pressure pulsations caused by periodic opening and closing action of a duty solenoid valve are suppressed.
It is another object of the present invention to provide a hydraulic control system for a transmission of an automobile vehicle which operates a duty solenoid valve with a considerable improvement with regard to durability.
These objects are achieved in the present hydraulic control system for a transmission of an automotive vehicle.
The hydraulic control system has a hydraulic pump driven by an engine and a regulator valve for regulating a line pressure from the hydraulic pump and delivered to actuators for the transmission according to a pilot pressure applied thereto.
A duty solenoid valve is operated at a duty rate so as to regulate a pilot pressure delivered to the regulator valve to a desired line pressure.
An operating signal for the duty solenoid valve at the duty rate is provided on a high or a low frequency assigned in accordance with operating conditions of the automotive vehicle.
To assign a desired frequency, i.
e.
, a high or low frequency operating conditions of the automotive vehicle are divided into a plurality of zones based on engine speeds or desired line pressures.
The duty rate or the desired line pressure is desirably changed according to the temperature of hydraulic fluid in the hydraulic control system.
When the desired line pressure or the engine speed is high, the duty solenoid valve is driven with a steady signal provided at a high frequency, such as 100 Hz so as to suppress pulsations in pilot pressure applied to the regulator valve or line pressure regulated by the regulator valve.
On the other hand, when the desired line pressure or the engine speed is not so high, a frequency at which a steady signal is provided for driving the duty solenoid valve is changed so as to be low, such as 33 Hz, so that the deterioration in durability of the duty solenoid valve is effectively suppressed