Proportional-flow electrohydraulic control

An electrohydraulic control which comprises first valve section means (122), having a first (46) port, having a second port (48b), having a flow path (240) from said first port to said second port, and having a first valving element (54) that is movable between minimum-conductance (FIG. 2) and maximum-conductance (FIG. 6) positions, for selectively controlling the conductance of said flow path in response to selective positioning of said first valving element, and for developing a differential pressure from said first port to said second port that is proportional both to a selected conductance and to the instantaneous rate of fluid flow through said flow path;

• second valve section means (126), having a second valving element (56), being operatively connected to said first valve section means, and being responsive to said differential pressure, for controlling said differential pressure from said first port to said second port to a predetermined and substantially constant value irrespective of variations in fluid pressure in said second port, whereby said rate of fluid flow from said first port to said second port is substantially proportional to a selected one of said conductances irrespective of variations of fluid pressure in said second port;
• means (129) for urging said first valving element to said minimum-conductance position with a first offset force;
• electrical force-motor means (52), operatively engaging said first valving element, for receiving an effective driving voltage, for applying a second offset force to said first valving element that is equal in magnitude and opposite in direction to said first offset force in response to an effective null voltage applied to said force-motor means, and for moving said first valving element from said minimum-conductance position proportional to the portions of said effective driving voltages that are in excess of said effective null voltage;
• and
• electronic control means (382), having offsetting means (622), and being operatively connected to said force-motor means, for receiving a varying input signal (410), for producing a cyclic driving voltage (406) whose effective voltage is greater than a predetermined proportional relationship to said input signal by a predetermined effective offset voltage, and for applying said cyclic driving voltage to said force-motor means for use as said effective driving voltage.

An electrohydraulic control which comprises a valve body (124+128) having an input port (42), having a receiving port (46) that is operatively connected to said input port, having an output port (48b), and having a first spool bore (130) that communicates said receiving port to said output port;

• first valve spool means (54), being slidably inserted into said first spool bore, being movable in a first direction (236) to a zero-overlap position (FIG. 2) wherein fluid conductance from said receiving port to said output port is substantially zero, and being movable in a second direction (238) to a maximum-conductance position (FIG. 6) wherein said receiving port is communicated to said output port with a maximum conductance, for selectively determining fluid conductances from said receiving port to said output port, and for developing a differential pressure from said receiving port to said output port that is a function of both a selected one of said conductances and the instantaneous rate of fluid flow from said receiving port to said output port;
• fluid pressure limiting means, comprising a second spool bore (152) in said valve body that communicates with said input port, and comprising a second valve spool (56) that is slidably inserted into said second spool bore and that is selectively positionable in response to said differential pressure, for limiting fluid pressure supplied to said first port to a value that comprises the sum of a predetermined and substantially constant magnitude and the instantaneous magnitude of fluid pressure in said output port, whereby said differential pressure from said receiving port to said output port remains substantially constant irrespective of variations in fluid pressure in said output port, and whereby said rate of fluid flow from said receiving port to said output port is substantially proportional to a selected one of said conductances irrespective of variations in fluid pressure in said output port;
• means (129), operatively engaging said first valve spool means, for urging said first valve spool means in said first direction to said zero-conductance position with a first offset force;
• electrical force-motor means (52), operatively engaging said first valve spool means, for receiving an effective driving voltage, for applying a second offset force to said first valve spool means that is equal in magnitude and opposite in direction to said first offset force in response to an effective null voltage applied to said force-motor means, and for moving said first valve spool means in said second direction from said zero-overlap position substantially proportional to the portions of said effective driving voltages applied to said force-motor means that are in excess of said effective null voltage;
• and
• electronic control means (382), having offsetting means (622), and being operatively connected to said force-motor means, for receiving a varying input signal (410), for producing a cyclic driving voltage (406) whose effective voltage is greater than a predetermined proportional relationship to said input signal by a predetermined effective offset voltage, and for applying said cyclic driving voltage to said force-motor means for use as said effective driving voltage.

An electrohydraulic control which comprises a valve body (124+128) having an input port (42), having a receiving port (46), having an output port (48b), and having a first spool bore (130) that communicates said receiving port to said output port;

• first valve spool means (54) being slidably inserted into said first spool bore, being movable in a first direction (236) to a zero-overlap position (FIG. 2) wherein the fluid conductance from said receiving port to said output port is substantially zero, being movable farther in said first direction to a maximum-overlap position (FIG. 1) wherein a surface portion (218) of said first valve spool means overlaps said first spool bore and effectively isolates said outlet port from said receiving port, and being movable in a second direction (238) to a maximum-conductance position (FIG. 6) wherein said receiving port is communicated to said output port with a maximum conductance, for selectively determining fluid conductances from said receiving port to said output port, and for developing a differential pressure from said receiving port to said output port that is a fuction of both a selected one of said conductances and the instantaneous rate of fluid flow from said receiving port to said output port;
• fluid pressure limiting means, comprising a second spool bore (152) in said valve body that communicates said input port with said receiving port, and comprising a second valve spool (56) that is slidably inserted into said second spool bore and that is selectively positionable in response to said differential pressure, for selectively restricting fluid flow from said input port to said receiving port in response to increases in said differential pressure, and for limiting fluid pressure supplied to said receiving port to a value that comprises the sum of a predetermined and substantially constant magnitude and the instantaneous magnitude of fluid pressure in said output port, whereby said differential pressure from said receiving port to said output port remains substantially constant irrespective of variations of fluid pressure in said output port, and whereby said rate of fluid flow from said receiving port to said output port is substantially proportional to a selected one of said conductances irrespective of variations of fluid pressure in said second port;
• gradient bias means (129), operatively engaging said first valve spool means, for urging said first valve spool means in said first direction with a force that decreases to a first offset force as said first valve spool means reaches said zero-overlap position;
• electrical force-motor means (52), operatively engaging said first valve spool means, for receiving an effective driving voltage, for applying a second offset force to said first valve spool means that is equal in magnitude and opposite in direction to said first offset force in response to an effective null voltage applied to said force-motor means, and for cooperating with said gradient bias means to move said first valve spool means in said second direction from said zero-overlap position substantially proportional to the portions of said effective driving voltages applied to said force-motor means that are in excess of said effective null voltage;
• and
• electronic control means (382), having offsetting means (622), and being operatively connected to said force-motor means, for receiving a varying input signal (410), for producing a cyclic driving voltage (406) whose effective voltage is greater than said input signal by a predetermined effective offset voltage and for applying said cyclic driving voltage to said force-motor means for use as said effective driving voltage.

An electrohydraulic control which comprises a valve body (124+128) having an input port (42), having a receiving port (46) that is operatively connected to said input port, having an output port (48b), and having a first spool bore (130) that communicates said receiving port to said output port;

• first valve spool means (54) being slidably inserted into said first spool bore, being movable in a first direction (236) to a zero-overlap position (FIG. 2), being movable farther in said first direction to a maximum-overlap position (FIG. 1) wherein a surface portion (218) of said first valve spool means overlaps said first spool bore and effectively isolates said output port from said receiving port, and being movable in a second direction (238) to a maximum-conductance (FIG. 6), for selectively determining fluid conductances from said receiving port to said output port, and for developing a differential pressure from said receiving port to said output port that is a function of both a selected one of said conductances and the instantaneous rate of fluid flow from said receiving port to said output port;
• fluid pressure limiting means, comprising a bypass port (50) in said valve body, comprising a second spool bore (152) in said valve body that communicates said input port with said bypass port, and comprising a second valve spool (56) that is slidably inserted into said second spool bore and that is selectively positionable in response to said differential pressure, for bypassing fluid from said input port to said bypass port in response to increases in said differential pressure, and for limiting fluid pressure supplied to said receiving port to a value that comprises the sum of a predetermined and substantially constant magnitude and the instantaneous magnitude of fluid pressure in said output port, whereby said differential pressure from said receiving port to said output port remains substantially constant irrespective of variations in fluid pressure in said output port, and whereby said rate of fluid flow from said receiving port to said output port is substantially proportional to a selected one of said conductances irrespective of variations in fluid pressure in said output port;
• gradient bias means (129), operatively engaging said first valve spool means, for urging said first valve spool means in said first direction with a force that decreases to a first offset force as said first valve spool means reaches said zero-overlap position;
• electrical force-motor means (52), operatively engaging said first valve spool means, for receiving an effective driving voltage, for applying a second offset force to said first valve spool means that is equal in magnitude and opposite in direction to said first offset force in response to an effective null voltage applied to said force-motor means, and for cooperating with said gradient bias means to move said first valve spool means in said second direction from said zero-overlap position substantially proportional to the portions of said effective driving voltages applied to said force-motor means that are in excess of said effective null voltage;
• and
• electronic control means (382), having offsetting means (622), and being operatively connected to said force-motor means, for receiving a varying input signal (410) for producing a cyclic driving voltage (406) whose effective voltage is greater than a predetermined porportional relationship to said input signal by a predetermined effective offset voltage, and for applying said cyclic driving voltage to said force-motor means for use as said effective driving voltage.