Fan control system with electro-hydraulic valve providing three fan motor operational positions

A method of controlling a fan comprising:

• directing a flow of hydraulic fluid into a first motor port of a hydraulic motor through the hydraulic motor and out a second motor port of the hydraulic motor,
• the hydraulic motor including a pressure control chamber, a servo piston, a swashplate, and an output shaft,
• the servo piston movable in response to a control pressure within the pressure control chamber,
• the servo piston coupled to the swashplate such that the swashplate is movable in response to movement of the servo piston over a range of travel between a forward position and a reverse position with a zero position being disposed between the forward position and the reverse position, and
• the output shaft being rotatable in a first direction at a first rate when the swashplate is in the forward position and in a second direction at a second rate when the swashplate is in the reverse position, in response to the flow of hydraulic fluid moving into the first motor port, through the hydraulic motor, and out the second motor port,
• the second direction being in opposing relationship to the first direction, and
• wherein the output shaft does not rotate in response to the flow of hydraulic fluid moving into the first motor port, through the hydraulic motor, and out the second motor port when the swashplate is in the zero position;
• transmitting an idle signal from a controller to an electro-magnetic actuator assembly of an electro-hydraulic control valve to move a spool of the electro-hydraulic control valve into an intermediate pump flow position,
• the flow of hydraulic fluid being directed through the electro-hydraulic control valve into the pressure control chamber such that the control pressure is pressurized to an idle pressure,
• the idle pressure being exerted against the servo piston to move the swashplate to an intermediate position;
• wherein the intermediate position is closer to the zero position than to the forward position and the reverse position,
• the output shaft rotating at an idle rate when the swashplate is in the intermediate position in response to the flow of hydraulic fluid moving into the first motor port, through the hydraulic motor, and out the second motor port, and
• the idle rate being less than half of the first rate;
• transmitting a reverse signal to the electro-magnetic actuator assembly of the electro-hydraulic control valve to move the spool of the electro-hydraulic control valve into a pump flow position,
• the flow of hydraulic fluid being directed through the electro-hydraulic control valve to the pressure control chamber such that the control pressure in the pressure control chamber is pressurized to a reverse pressure exerted against the servo piston to move the swashplate to the reverse position,
• the reverse pressure being greater than the idle pressure.

An electro-hydraulic valve for a fan control system, the electro-hydraulic valve comprising:

• an adaptor, the adaptor defining a control port, a pump port, a tank port, and a longitudinal passage, the control port, the pump port, and the tank port each being in communication with the longitudinal passage;
• a spool, the spool being disposed within the longitudinal passage of the adaptor and being reciprocally movable over a range of travel between a tank flow position and a pump flow position,
• when the spool is in the tank flow position, the tank port and the control port are in fluid communication with each other, and the pump port is fluidly isolated from both the tank port and the control port, and
• when the spool is in the pump flow position, the pump port and the control port are in fluid communication with each other, and the tank port is fluidly isolated from both the pump port and the control port;
• a spring, the spring interposed between the adaptor and the spool to bias the spool to the tank flow position;
• and
• a solenoid assembly, the solenoid assembly including a coil and an armature, the armature movable in response to an electrical current being transmitted through the coil, the armature arranged with the spool such that the armature moves the spool from the tank flow position toward the pump flow position in an amount proportional to the electrical current transmitted through the coil;
• the spool includes an external spool surface having a circumferential groove,
• the circumferential groove in communication with the control port,
• the circumferential groove configured to be in communication with the tank port when the spool is in the tank flow position to fluidly connect the control port and the tank port,
• the circumferential groove configured to be in communication with the pump port when the spool is in the pump flow position to fluidly connect the control port and the pump port, and
• the circumferential groove configured to be in variable communication with the pump port based upon a location of the spool between the tank flow position and the pump flow position;
• wherein the adaptor has an adaptor length, and the spool has a spool length, the spool length being at least fifty percent of the adaptor length, wherein the spool includes an internal spool surface defining a longitudinal blind bore in communication with the control port and a cross bore in communication with the longitudinal blind bore, and wherein the circumferential groove is in communication with the cross bore.