Articulated vehicle steering system

Abstract

A steering system .Iadd.40 .Iaddend.for an articulated vehicle .Iadd.10 .Iaddend.having a pair of double acting steering cylinders .Iadd.24, 26 .Iaddend.and power steering means .Iadd.44 .Iaddend.consisting of a pump .Iadd.48 .Iaddend.and a hydrostatic steering unit .Iadd.50 .Iaddend.to which the steering wheel .Iadd.42 .Iaddend.of the vehicle is interconnected. Control means .Iadd.46 .Iaddend.are disposed between the power steering means .Iadd.44 .Iaddend.and the double acting cylinders .Iadd.24, 26 .Iaddend.for causing fluid to be directed from the power steering means .Iadd.44 .Iaddend.to both of the first and second cylinders .Iadd.24, 26 .Iaddend.during rotation of the steering wheel .Iadd.42 .Iaddend.at a first steering ratio when the pump .Iadd.48 .Iaddend.is in operation, and at a second higher steering ratio when the pump .Iadd.48 .Iaddend.is not in operation to permit manual steering of the vehicle .Iadd.10. The control means includes novel valving means 64 having pilot operated two position two way spool valves 84, 86 one of which 84 is operatively associated with the first double acting cylinder 24 and the other of which 86 is operatively associated with the second double acting cylinder 26. .Iaddend.

What is claimed is: .[. 
     
       1.  An articulated vehicle steering system including: first and second double acting cylinders (24, 26) mechanically coupled together for steering an articulated vehicle (12, 14, 22);   a rotatable steering wheel (42); and   power steering means (44) consisting of a motor driven pump (48) and a hydrostatic steering unit (50), said steering wheel (42) being interconnected with said hydrostatic steering unit (50);   the improvement comprising   control means (46) disposed between the power steering means (44) and the first and second double acting cylinders (24, 26) for causing fluid to be directed from said power steering means (44) to both of said first and second cylinders (24, 26) during rotation of said steering wheel (42) at a first steering ratio when the motor driven pump (48) is in operation and at a second higher steering ratio when the motor driven pump (48) is not in operation..]. .[.   
     
     
       2.  The articulated vehicle steering system set forth in claim 1 in which the control means (46) includes valving means (64) for directing fluid from the hydrostatic steering unit (50) to the first double acting cylinder (24) when turning in a first direction and for directing fluid from the hydrostatic steering unit (50) to the second double acting cylinder (26) when turning in a second direction..]. .[.3. The articulated vehicle steering system set forth in claim 2 further characterized by the provision of line means (72, 74) to direct fluid from the hydrostatic steering unit (50) to the rod end (32) of either the first or second double acting cylinder (24, 26)..]. .[.4. The articulated vehicle steering system set forth in claim 1 in which said control means (46) includes valving means (64) having first and second spool valves (84, 86), the first spool valve (84) being operatively associated with the first double acting cylinder (24), and the second spool valve (86) being operatively associated with the second double acting cylinder (26)..]. .[.5. The articulated vehicle steering system set forth in claim 4 in which the spool valves (84, 86) will block the flow of fluid to the double acting cylinders (24, 26) from the motor driven pump (48) when the articulated vehicle is not being turned, one of the spool valves being shifted by pilot line pressure from the hydrostatic unit (50) during turning to cause fluid to be directed from the motor driven pump (48) to one of the double acting cylinders (24, 26)..]. .[.6. The articulated vehicle steering system set forth in claim 4 in which each of said first and second spool valves (84, 86) is a pilot operated two position two way spool valve 
     
     
        normally spring biased to a closed position..]. .[.7.  The articulated vehicle steering system set forth in claim 6 in which the control means (46) further includes first and second fluid lines (72, 74) extending from the hydrostatic steering unit (50) to one end (32) of the first and second double acting cylinders (24, 26), respectively, a first branch line (76, 78) extending from the first line (72) through the valving means (64) to the other end (28) of the second double acting cylinder (26), and a second branch line (80, 82) extending from the second line (74) through the valving means (64) to the other end (28) of the first double acting cylinder (24), the valving means (64) further including check valves (90, 98), one check valve being in each branch line (76, 78 and 80, 82) to permit flow away from the associated double acting cylinder (24, 26)..]. .[.8. The articulated vehicle steering system set forth in claim 6 in which both of the spool valves (84, 86) will be in their closed position when the articulated vehicle is not being turned, one of the spool valves (84, 86) being shifted to an open position be pilot line pressure from the hydrostatic steering unit (50) during turning to cause fluid to be directed from the motor driven pump (48) to one of the double acting cylinders (24, 26), the other spool valve (86, 84) remaining closed when 
     
     
        said one spool valve (84, 86) is in its open position..]. .Iadd.9.  A valve (64) for a steering system of the type including a pair of oppositely acting double acting hydraulic cylinders (24,26), a motor driven pump (48), a hydrostatic steering unit (50), and a rotatable steering wheel (42), said steering wheel operating at a first steering ratio when the pump (48) is in operation and at a second higher steering ratio when the pump is not in operation, said valve (64) including: a pair of independently operable pilot operated two position spool valves (84, 86) normally spring biased by spring bias means to a closed position, a pair of separate pilot line passageways each of which is in fluid communication with one of said spool valves and operable when pressurized to shift said spool valve against said spring bias means to an open position, another pair of separate passageways each of which is associated with one of said spool valves and is operable to place the associated spool valve in communication with one end of one of a pair of double acting cylinders (24, 26), additional passageway means extending between said spool valves and adapted to be placed in fluid communication with a pump, and a pair of check valves (90, 98), there being one check valve between each of said pilot line passageways and one of said another pair of separate passageways, each check valve being capable of preventing flow from the associated pilot line passageway to the associated another   
     
     
        separate passageway. .Iaddend. .Iadd.10.  The valve set forth in claim 9 further characterized by the provision of another pair of check valves (92, 96) there being one of said another check valves disposed between each of said pair of separate pilot line passageways and said additional passageway means, each of said another check valves being capable of preventing flow from the associated additional passageway means to the associated pilot line passageway. .Iaddend. .Iadd.11. The valve set forth in claim 9 further characterized by the provision of further check valve means (94) in said additional passageway means, said further check valve means being capable of preventing flow back to a pump. .Iaddend. .Iadd.12. A valve for a steering system of the type including a pair of double acting hydraulic cylinders (24,26) mechanically coupled together in such a manner that they will act in opposite directions, a motor driven pump (48), a hydrostatic steering unit (50), and a rotatable steering wheel (42), said steering wheel operating at a first steering ratio when the pump (48) is in operation and at a second higher steering ratio when the pump is not in operation, said valve (64) including: a pair of independently operable pilot operated two position spool valves (84, 86) normally spring biased by spring bias means to a closed position, a pair of separate pilot line passageways each of which is in fluid communication with one of said spool valves and operable when pressurized to shift said spool valve against said spring bias means to an open position, additional passageway means extending between one side of said spool valves and adapted to be placed in fluid communication with a pump (48), another pair of separate passageways each of which is associated with the other side of one of said spool valves, a first pair of check valves (90, 98), there being one of said first pair of check valves disposed between a pilot line passageway and one of said another pair of separate passageways, each of the first pair of check valves being capable of preventing flow from the associated pilot line passageway to the associated another separate passageway, a second pair of check valves (92, 96), each of said second pair being disposed between one of said pilot line passageways and said additional passageway means, and being capable of preventing flow from the associated additional passageway means to the associated pilot line passageway, and a fifth check valve (94) disposed in said additional passageway means upstream of said second pair of check valves and operable to prevent fluid flow in a direction towards a motor   
     
     
        driven pump (48). .Iaddend. .Iadd.13.  An articulated steering system including: first and second double acting cylinders (24, 26) mechanically coupled together for steering an articulated vehicle (12, 14, 22);   a rotatable steering wheel (42); and   power steering means (44) consisting of a motor driven pump (48) and a hydrostatic steering unit (50), said steering wheel (42) being interconnected with said hydrostatic steering unit (50);   the improvement comprising   control means (46) disposed between the power steering means (44) and the first and second double acting cylinders (24, 26) for causing fluid to be directed from said power steering means (44) to both of said first and second cylinders (24, 26) during rotation of said steering wheel (42) at a first steering ratio when the motor driven pump (48) is in operation and at a second higher steering ratio when the motor driven pump is not in operation, said control means including valving means (64) having first and second pilot operated two position spool valves (84, 86) normally spring biased by spring bias means to a closed position, and first and second check valves (90, 98) each in parallel circuit with an associated spool valve, first line means (82) connecting the first spool valve (84) solely with one end of the first double acting cylinder (24), and second line means (78) connecting the second spool valve (86) solely with one end of the second double acting cylinder (26), first and second additional fluid lines (72, 74) extending from the hydrostatic steering unit (50) to the other end (32) of the first and second double acting cylinders (24, 26), respectively, a first branch line (76) extending from the first additional line (72) through one of the check valves (90, 98) to the second line means (78), the first additional line being in pilot communication with the associated pilot operated spool valve, and a second branch line (80) extending from the second additional line (74) through the other one of the check valves (90, 98) to the first line means (82), the second additional line being in pilot communication with the associated pilot operated spool valve, each of the check valves (90, 98) permitting flow away from the associated double acting cylinder (24, 26). .Iaddend.