Hydraulic devices for smooth operations of hydrostatic transmission

A hydraulic valve assembly for controlling fluid transfer from an inlet line to a first and a second outlet line within a closed-loop circuit, said valve assembly comprising:

• a valve body defining a first port for connection to said inlet line, a second port for connection to said first outlet line, a third port for connection to said second outlet line, and a spool bore in fluid communication with said inlet line, said first outlet line and said second outlet line;
• a unitary valve spool, adapted for sealing movement within said spool bore, having a first end portion, a second end portion, and a connecting portion having a cross-sectional area smaller than that of the first and second end portions, said valve spool having at least one orifice in each of said first and second end portions in communication with said connecting portion, with said connecting portion always being in fluid communication with at least a portion of said first port, said valve spool being longitudinally movable, via fluid pressure, within said spool bore from a neutral position to either a first or second position;
• wherein the fluid pressure forces acting on the first and second end portions are approximately equal in said valve spool neutral position, the fluid pressure forces acting on said first end portion being greater than the fluid pressure forces acting on said second end portion in the first position, and the fluid pressure forces acting on said first end portion being less than the fluid pressure forces acting on the second end portion in the second position;
• a first check valve, in physical contact with said first end portion of said valve spool, having a fully open position permitting fluid transfer from said inlet line to said second outlet line when said valve spool is in the second position and having a closed position when said valve spool is in the first position;
• a second check valve, in physical contact with said second end portion of said valve spool, having a fully open position permitting said fluid transfer from said inlet line to said first outlet line when said valve spool is in the first position and having a closed position when said valve spool is in second position;
• and
• said fluid transfer occurring from said inlet line through said at least one orifice in each of said first and second end portions of said valve spool to said first and second outlet lines, respectively, when said valve spool is in the neutral position, and having substantially no fluid transfer through said at least one orifice occurring when said valve spool is in one of said first and second positions.

A hydraulic valve assembly for controlling fluid transfer from an inlet line to a first and a second outlet line within a closed-loop circuit, said assembly comprising:

• a valve body defining a first port for connection to said inlet line, a second port for connection to said first outlet line, a third port for connection to said second outlet line, and a spool bore in fluid communication with said inlet line, said first outlet line and said second outlet line;
• a valve spool, adapted for sealing reciprocation within said spool bore, having a first end portion, a second end portion, a connecting portion with a cross-sectional area smaller than that of the first and second end portions, a first bypass orifice within said valve spool extending from said connecting portion to said first end portion, and a second bypass orifice within said valve spool extending from said connecting portion to said second end portion, said valve spool being movable from a neutral position, in which said valve spool is longitudinally centered within said spool bore relative to said inlet line, occurring when the fluid pressures forces in said first and second outlet lines are substantially similar, to a first position, occurring when the fluid pressure forces in the first outlet line are greater than the fluid pressure forces in said second outlet line, or to a second position, occurring when the fluid pressure forces in the first outlet line are less than the fluid pressure forces in the second outlet line, with said connecting portion being in fluid communication with at least a portion of said first port at each of said positions of said valve spool, wherein:
• while in said neutral valve spool position, said first bypass orifice is aligned with said first outlet line, said second bypass orifice is aligned with said second outlet line and said connecting portion is centered relative to said inlet line;
• while in said first valve spool position, said first and second bypass orifices are at least substantially disabled, and said connecting portion is in fluid communication with said inlet line and said second outlet line;
• while in said second valve spool position, said first and second bypass orifices are at least substantially disabled, and said connecting portion is in fluid communication with said inlet line and said first outlet line;
• and
• dampers located on both ends of said valve spool for centering said valve spool, relative to said inlet line, in said neutral valve spool position.

A hydraulic valve assembly for controlling fluid transfer from a first and second inlet line to an outlet line within a closed-loop circuit, said assembly comprising:

• a valve body defining a first port for connection to said first inlet line, a second port for connection to said second inlet line, a third port for connection to said outlet line, and a spool bore in fluid communication with said first inlet line, said second inlet line and said outlet line;
• a valve spool, adapted for sealing reciprocation within said spool bore, having a first end portion, a second end portion, a connecting portion with a cross-sectional area smaller than that of the first and second end portions, a first bypass orifice within said valve spool extending from said first end portion to said connecting portion, and a second bypass orifice within said valve spool extending from said second end portion to said connecting portion, said valve spool being movable from a neutral position, in which said valve spool is longitudinally centered within said spool bore relative to said outlet line, occurring when the fluid pressure forces in said first and second inlet lines are substantially similar, to a first position, occurring when the fluid pressure forces in the first inlet line are greater than the fluid pressure forces in said second inlet line, or to a second position, occurring when the fluid pressure forces in the first inlet line are less than the fluid pressure forces in the second inlet line, with said connecting portion being in fluid communication with at least a portion of said first port at each of said positions of said valve spool, wherein:
• while in said neutral valve spool position, said first bypass orifice is aligned with said first inlet line, said second bypass orifice is aligned with said second inlet line and said connecting portion is centered relative to said outlet line;
• while in said first valve spool position, said first and second bypass orifices are at least substantially disabled, and said connecting portion is in fluid communication with said second inlet line and said outlet line;
• while in said second valve spool position, said first and second bypass orifices are at least substantially disabled, and said connecting portion is in fluid communication with said first inlet line and said outlet line;
• and
• dampers located on both ends of said valve spool for centering said valve spool, relative to said outlet line, in said neutral valve spool position.

A hydraulic valve assembly, for use in a hydrostatic transmission, for controlling fluid transfer between a first, a second and a third line within a closed-loop circuit, wherein two of said first, second and third lines define first and second pressure lines and are located at substantially similar longitudinal distances from the remaining one of said first, second and third lines, said remaining line being rotationally displaced relative to said first and second pressure lines, said valve assembly comprising:

• a valve body defining a first port for connection to said remaining line, a second port for connection to one of said first and second pressure lines, and a third port for connection to the other of said first and second pressure lines, said valve body further including a spool bore in fluid communication with said first, second and third lines;
• a valve spool adapted for sealing reciprocation within said spool bore, having a first end portion, a second end portion, a connecting portion having a cross-sectional area smaller than the cross-section of said first and second end portions, a first bypass orifice within said valve spool extending between said first end portion and said connecting portion, and a second bypass orifice within said valve spool extending between said second end portion and said connecting portion, said valve spool being movable from a neutral position, in which said valve spool is longitudinally centered within said spool bore and where the pressures forces in said first and second pressure lines are substantially similar, to a first position, occurring when the pressure forces in said first pressure line are greater than the pressure forces in said second pressure line, or to a second position, occurring when the pressure forces in said first pressure line are less than the pressure forces in said second pressure line, with said connecting portion being in fluid communication with at least a portion of said first port at each of said positions of said valve spool, wherein:
• while in said neutral valve spool position, said first bypass orifice is aligned with said first pressure line for fluid communication with said remaining line and said second bypass orifice is aligned with said second pressure line for fluid communication with said remaining line;
• while in said first valve spool position, said first and said second bypass orifices are at least substantially disabled and said connecting portion is in fluid communication with one of said first and second pressure lines;
• while in said second valve spool position, said first and said second bypass orifices are at least substantially disabled and said connecting portion is in fluid communication with the other of said first and second pressure lines;
• and
• dampers located at both ends of said valve spool for centering said valve spool relative to said remaining line in said neutral valve spool position.

A method for increasing the width of the dead band of a hydrostatic transmission, in a neutral mode of operation without impairing the performance of said hydrostatic transmission in non-neutral modes of operation, wherein said hydrostatic transmission includes:

• a variable displacement main pump;
• a hydraulic motor, a hydraulic circuit operatively interconnecting said main pump and motor;
• a charge pump, operatively interconnected within said circuit, having an outlet line;
• a valve block, operatively interconnected within said circuit, having an inlet line, in communication with said charge pump outlet line, and having first and second outlet lines in communication with said hydraulic circuit;
• a valve body having a first port connected with said inlet line, a second port connected with said first outlet line, a third port connected with said second outlet line;
• a spool bore in fluid communication with inlet, first outlet and second outlet lines;
• a valve spool, adapted for sealing longitudinal movement within said spool bore, having a first end portion, a second end portion and a connecting portion having a cross-sectional profile smaller than that of said first and second portions;
• and dampers for centering said valve spool in a neutral mode of operation, said method comprising:
• a. including a first bypass orifice within said valve spool extending between said first end portion and said connecting portion;
• b. including a second bypass orifice within said valve spool extending between said second end portion and said connecting portion;
• c. keeping said connecting portion in fluid communication with said first port at all times;
• d. permitting substantially equal fluid flows from said first port, via said first and second bypass orifices, to said first and second outlet ports, respectively, in said neutral mode of operation when the fluid forces acting on the first and second end portions are about equal;
• shifting said valve spool from said neutral mode of operation to non-neutral modes of operation during which the fluid forces acting on said first and second end portions are unequal, to thereby at least substantially disable said fluid flows via said first and second bypass orifices while simultaneously permitting fluid flows from said inlet line to one of said first and second outlet ports.