Control system for hydraulic tandem pump in motor vehicle

A control system for a hydraulic tandem pump assembly adapted for use in a motor vehicle, said tandem pump assembly including a primary pump for supplying fluid under pressure to a power-assisted steering device and a secondary pump for supplying fluid under pressure to a hydraulic motor of an engine cooling fan, which pumps are mounted on a common drive shaft for rotation therewith,

• wherein the control system comprises:
• an electrically operated flow quantity control valve disposed within a communication passage between said secondary pump and said hydraulic motor to bypass fluid under pressure discharged from said secondary pump into an inlet passage connecting a fluid reservoir to said secondary pump;
• a first temperature sensor arranged to detect the temperature of hydraulic fluid stored in said fluid reservoir for producing therefrom an output signal indicative of the fluid temperature;
• a second temperature sensor arranged to detect the temperature of cooling water flowing through a radiator of a prime engine of the vehicle for producing therefrom an output signal indicative of the cooling water temperature;
• and
• an electric control apparatus connected to said first and second temperature sensors to control an electric current applied to said flow quantity control valve in dependence upon values of the output signals from said temperature sensors in such a manner that said flow quantity control valve is conditioned to bypass a large part or the entirety of fluid under pressure discharged from said secondary pump into said inlet passage when the fluid temperature and the cooling water temperature are respectively below a predetermined value and conditioned to decrease the bypass flow quantity of fluid in accordance with rise of the fluid temperature and cooling water temperature higher than the predetermined value.