Automatic control system for hydrostatic drive

Claim 2

The combination comprising a fluid reservoir, an engine, a variable displacement fluid pump drivingly connected to said engine, a fluid motor drivingly connected to said pump, said pump having a movable member for controlling the displacement of said pump and which tends to return to its zero displacement position with a force which increases as said movable member is actuated away from its zero displacement position and increases as the load imposed on said pump by said motor increases, means connected to said movable member for resiliently biasing said movable member to its zero displacement position, and means connected to said movable member and responsive to the speed of said engine for actuating said movable member away from its zero displacement position with increasing force as the speed of said engine increases, said actuating and return forces being opposed to each other so that when the speed of said engine remains constant the displacement of said pump varies in inverse proportion to the load on said pump.

Claim 3

The combination as set forth in claim 1 including means connected to said actuating means for varying the amount which the actuating force increases relative to an increase of said engine speed after the actuating force reaches a predetermined level.

Claim 4

The combination as set forth in claim 1 wherein said actuating means includes means for limiting the speed of movement of said movable member away from its zero displacement position.

Claim 5

The combination as set forth in claim 1 including a brake system and means connected to said actuating means and responsive to a predetermined actuation of said brake system for reducing the force being exerted by said actuating means to move said movable member away from its zero displacement position.

Claim 6

The combination as set forth in claim 1 wherein said actuating means includes a control pump drivingly connected to said engine, a double-acting fluid motor connected to said movable member, fluid passage means connected to said control pump and said double-acting fluid motor for supplying pressurized fluid to said double-acting fluid motor.

Claim 7

The combination as set forth in claim 1 wherein said actuating means includes a control pump and a first fluid flow restrictor connecting said control pump to said reservoir.

Claim 8

The combination as set forth in claim 6 including a second fluid flow restrictor connected in parallel with said first fluid flow restrictor and a normally closed valve connected between said secOnd fluid flow restrictor and said control pump, said normally closed valve being operable when the output of said control pump reaches a predetermined pressure to open and place said second fluid flow restrictor in communication with said control pump.

Claim 9

The combination as set forth in claim 7 including a brake system, said normally closed valve also being operable in response to a predetermined actuation of said brake system to decrease the force of said actuating means.

Claim 10

The combination as set forth in claim 1 wherein said actuating means includes means for limiting the speed of movement of said movable member toward its zero displacement position.

Claim 11

The combination as set forth in claim 9 including a brake system having junction means, fluid-pressure-actuated brake means connected to said junction means, first fluid-pressure-generating means connected to said junction means and second fluid-pressure-generating means connected to said junction means, said junction means being operable to direct pressure fluid to said brake means upon actuation of either said first generating means or said second generating means, means connected to said actuating means and said first generating means and responsive to a predetermined fluid pressure generated by said first generating means for bypassing said means for limiting the speed of movement of said movable member toward its zero displacement position, and means connected to said actuating means and said second generating means and responsive to a predetermined fluid pressure generated by said second generating means for reducing the force being exerted by said actuating means to move said movable member away from its zero displacement position.

Claim 12

The combination as set forth in claim 9 including a brake system and means connected to said actuating means and responsive to a predetermined actuation of said brake system for bypassing said means for limiting the speed of movement of said movable member toward its zero displacement position.

Claim 13

The combination as set forth in claim 11 including a brake system and an inching valve connected to said fluid passage means and responsive to actuation of said brake system for bypassing fluid from said control pump to said reservoir so that the pressure of fluid being supplied to said double-acting fluid motor decreases as actuation of said brake system increases beyond a predetermined level.

Claim 14

The combination as set forth in claim 9 wherein said double-acting fluid motor includes first and second members, said first member being movable relative to said second member and defining with said second member first and second chambers.

Claim 15

The combination as set forth in claim 13 wherein said double-acting fluid motor includes first and second ports which communicate with said first chamber and third and fourth ports which communicate with said second chamber, said second port being disposed so that a predetermined movement of said first motor member in one direction from a first position blocks communication between said second port and said first chamber and said third port being disposed so that a predetermined movement of said first motor member in the opposite direction from said first position blocks communication between said third port and said second chamber, and said fluid passage means includes a direction control valve having fifth and sixth ports, said control valve being connected to said control pump and said reservoir and operable to direct fluid from said control pump to said fifth port, said sixth port or said reservoir, a first fluid conduit connecting said fifth port and said second port, a second fluid conduit connecting said sixth port and said third port, a first one-way valve connecting said first conduit and said first port for fluid flow only from said first chamber toward said first conduit and a second one-way valve connecting said second conduit and said fourth port for fluid flow only from said second chamber toward said second conduit.

Claim 16

ThE combination as set forth in claim 13 including a brake system and a normally closed valve connected to said chamber and operable in response to a predetermined actuation of said brake system to open and place said chambers in fluid communication with each other.

Claim 17

The combination as set forth in claim 14 wherein said fluid passage means includes a first fluid flow restrictor disposed in said first conduit and a second fluid flow restrictor disposed in said second conduit.

Claim 18

The combination as set forth in claim 1 wherein said fluid motor and pump are drivingly connected by first and second fluid passage means and including third fluid passage means connecting said first and second fluid passage means, said third fluid passage means including a normally open valve, and means connected to said valve and responsive to the position of said movable member for closing said valve when said movable member passes a predetermined position.

Claim 19

The combination as set forth in claim 17 wherein said third fluid passage means includes fluid-flow-restricting means.

Claim 20

The combination as set forth in claim 1 wherein said fluid motor and pump are drivingly connected by first and second fluid passage means and including third fluid passage means connecting said first and second fluid passage means, said third fluid passage means including a normally open valve, and means connected to said valve and said actuating means for closing said valve when said actuating means moves past a predetermined position.

Claim 21

The combination as set forth in claim 19 wherein said third fluid passage means includes fluid-flow-restricting means.

Claim 22

The combination as set forth in claim 20 wherein said actuating means includes a double-acting fluid motor and said closing means includes a fluid conduit connected to said valve and a two-position valve connected to said fluid conduit, said actuating means and said reservoir and operable to place said fluid conduit in communication with said reservoir until said double-acting fluid motor moves past a predetermined position and then places said fluid conduit in communication with said actuating means.

Claim 23

The combination as set forth in claim 21 wherein said closing means includes second fluid-flow-restricting means disposed to restrict fluid flow from said actuating means to said fluid conduit.