Hydraulic steering system

Claim 2

In a hydraulic steering system for a wheeled vehicle including a pair of hydraulic steering cylinders coupled between the vehicle frame and a pair of pivotal wheel suspension assemblies, said cylinders being arranged to impart turning movement to said assemblies in a first direction responsive to the supply of pressurized hydraulic fluid to first ends of said cylinders and return of fluid from second ends of said cylinders, said cylinders being arranged to impart turning movement to said assemblies in a second opposite direction responsive to the supply of pressurized hydraulic fluid to said second ends of said cylinders and return of fluid from said first ends of said cylinders, a steering valve having a supply conduit, return conduit, and first and second control conduits respectively coupled to said first and second ends of said cylinders, said valve having a neutral position wherein said supply and return conduits are communicated, a first actuated position wherein said supply conduit is communicated with said first control conduit and said second control conduit is communicated with said return conduit, and a second actuated position wherein said supply conduit is communicated with said second control conduit and said first control conduit is communicated with said return conduit, said valve being actuateable from said neutral position to said first position responsive to a fluid signal supplied to a first pilot port thereof and to said second position responsive to a fluid signal supplied to a second pilot port thereof, a pump coupled between a fluid reservoir and said supply conduit to supply pressurized fluid thereto, a steering-wheel-operated, fluid-metering unit having supply and return ports, and first and second control ports, said unit having a neutral steering wheel position, said unit being arranged to block communication between said supply and return ports responsive to turning of said steering wheel from said neutral position in a first direction and responsively develop from fluid pressure at said supply port a fluid signal at said first control port in accordance with the rate and number of revolutions of said steering wheel while communicating said second control port with said reTurn port, said unit being arranged to block communication between said supply and return ports responsive to turning of said steering wheel from said neutral position in a second opposite direction and responsively develop from fluid pressure at said supply port a fluid signal at said second control port in accordance with the rate and number of revolutions of said steering wheel while communicating said first control port with said return port, means communicating said first and second ports of said metering unit with said first and second pilot ports of said steering valve, and relief valve means coupled to said pump for limiting the maximum pressure of fluid supplied therefrom, the improvement comprising a differential valve coupling said return conduit of said steering valve to said supply port of said metering unit and said return port of said metering unit to a second return conduit in communication with said reservoir, said differential valve being arranged to maintain a predetermined pressure differential across said supply and return ports of said metering unit irrespective of fluctuations in back pressure in said second return conduit.

Claim 3

In a hydraulic steering system for a wheeled vehicle including a pair of hydraulic steering cylinders coupled between the vehicle frame and a pair of pivotal wheel suspension assemblies, said cylinders being arranged to impart turning movement to said assemblies in a first direction responsive to the supply of pressurized hydraulic fluid to first ends of said cylinders and return of fluid from second ends of said cylinders, said cylinders being arranged to impart turning movement to said assemblies in a second opposite direction responsive to the supply of pressurized hydraulic fluid to said second ends of said cylinders and return of fluid from said first ends of said cylinders, a steering valve having a supply conduit, return conduit, and first and second control conduits respectively coupled to said first and second ends of said cylinders, said valve having a neutral position wherein said supply and return conduits are communicated, a first actuated position wherein said supply conduit is communicated with said first control conduit and said second control conduit is communicated with said return conduit, and a second actuated position wherein said supply conduit is communicated with said second control conduit and said first control conduit is communicated with said return conduit, said valve being actuateable from said neutral position to said first position responsive to a fluid signal supplied to a first pilot port thereof and to said second position responsive to a fluid signal supplied to a second pilot port thereof, a pump coupled between a fluid reservoir and said supply conduit to supply pressurized fluid thereto, a steering-wheel-operated, fluid-metering unit having supply and return ports, and first and second control ports, said unit having a neutral steering wheel position, said unit being arranged to block communication between said supply and return ports responsive to turning of said steering wheel from said neutral position in a first direction and responsively develop from fluid pressure at said supply port a fluid signal at said first control port in accordance with the rate and number of revolutions of said steering wheel while communicating said second control port with said reTurn port, said unit being arranged to block communication between said supply and return ports responsive to turning of said steering wheel from said neutral position in a second opposite direction and responsively develop from fluid pressure at said supply port a fluid signal at said second control port in accordance with the rate and number of revolutions of said steering wheel while communicating said first control port with said return port, means communicating said first and second ports of said metering unit with said first and second pilot ports of said steering valve, and relief valve means coupled to said pump for limiting the maximum pressure of fluid supplied therefrom, the improvement comprising a differential valve coupling said return conduit of said steering valve to said supply port of said metering unit and said return port of said metering unit to a second return conduit in communication with said reservoir, said differential valve being arranged to maintain a predetermined pressure differential across said supply and return ports of said metering unit irrespective of fluctuations in back pressure in said second return conduit.

Claim 4

In a hydraulic steering system for a wheeled vehicle including a pair of hydraulic steering cylinders coupled between the vehicle frame and a pair of pivotal wheel suspension assemblies, said cylinders being arranged to impart turning movement to said assemblies in a first direction responsive to the supply of pressurized hydraulic fluid to first ends of said cylinders and return of fluid from second ends of said cylinders, said cylinders being arranged to impart turning movement to said assemblies in a second opposite direction responsive to the supply of pressurized hydraulic fluid to said second ends of said cylinders and return of fluid from said first ends of said cylinders, a steering valve having a supply conduit, return conduit, and first and second control conduits respectively coupled to said first and second ends of said cylinders, said valve having a neutral position wherein said supply and return conduits are communicated, a first actuated position wherein said supply conduit is communicated with said first control conduit and said second control conduit is communicated with said return conduit, and a second actuated position wherein said supply conduit is communicated with said second control conduit and said first control conduit is communicated with said return conduit, said valve being actuateable from said neutral position to said first position responsive to a fluid signal supplied to a first pilot port thereof and to said second position responsive to a fluid signal supplied to a second pilot port thereof, a pump coupled between a fluid reservoir and said supply conduit to supply pressurized fluid thereto, a steering-wheel-operated, fluid-metering unit having supply and return ports, and first and second control ports, said unit having a neutral steering wheel position, said unit being arranged to block communication between said supply and return ports responsive to turning of said steering wheel from said neutral position in a first direction and responsively develop from fluid pressure at said supply port a fluid signal at said first control port in accordance with the rate and number of revolutions of said steering wheel while communicating said second control port with said reTurn port, said unit being arranged to block communication between said supply and return ports responsive to turning of said steering wheel from said neutral position in a second opposite direction and responsively develop from fluid pressure at said supply port a fluid signal at said second control port in accordance with the rate and number of revolutions of said steering wheel while communicating said first control port with said return port, means communicating said first and second ports of said metering unit with said first and second pilot ports of said steering valve, and relief valve means coupled to said pump for limiting the maximum pressure of fluid supplied therefrom, the improvement comprising a differential valve coupling said return conduit of said steering valve to said supply port of said metering unit and said return port of said metering unit to a second return conduit in communication with said reservoir, said differential valve being arranged to maintain a predetermined pressure differential across said supply and return ports of said metering unit irrespective of fluctuations in back pressure in said second return conduit.

Claim 5

The combination of claim 1 further defined by a check valve interposed between said differential valve and said supply conduit of said metering unit to prevent back flow of fluid therefrom.

Claim 6

The combination of claim 1 further defined by said differential valve including means for bypassing a volume of fluid in said first return conduit to said second return conduit in excess of the volume of fluid required to establish a pressure at said supply port of said metering unit equal to the sum of said pressure differential and back pressure in said second return conduit.

Claim 7

The combination of claim 3 further defined by said differential valve including a body having a first inlet port in communication with a first outlet port and a second inlet port in communication with a second outlet port, said first inlet and outlet ports respectively communicated with said first return conduit and said supply port of said metering unit, said second inlet and outlet ports respectively communicated with said return port of said metering unit and said second return conduit, said differential valve including a spool within said body normally blocking communication between said first inlet port and second outlet port, said differential valve including a poppet having a first force acting thereon equal to the sum of a predetermined constant force and the force due to back pressure in said second return conduit, said first force balanced by a second force due to pressure in said first inlet port, said poppet being actuated in response to said second force exceeding said first force, said valve including means for actuating said spool to an actuated position wherein said first inlet port is communicated with said second outlet port responsive to actuation of said poppet.

Claim 8

The combination of claim 4, further defined by said spool being translatable between said normal and actuated positions thereof, said spool having an internal bore, said body having a passage communicating said first inlet and outlet ports with said internal bore, said body having a chamber on the opposite side of said spool from said bore, a spring within said chamber biasing said spool to said normal position thereof, said spool having an orifice communicating said passage with said chamber, means defining a second chamber, said body having a second passage communicating said first and second chambers, said poppet disposed in said second chamber, a second spring disposed in said second chamber biasing said poppet into closing relation with the termination of said second passage in said second chamber, and means communicating said second return conduit with said second chamber.

Claim 9

The combination of claim 1 further defined by a follow-up hydraulic cylinder coupled between said vehicle frame and said wheel suspension assemblies, said follow-up cylinder having fiRst and second conduits communicating with first and second chambers at its opposite ends, said follow-up cylinder permitting fluid flow into said first conduit thereof and expelling fluid from said second conduit thereof responsive to turning movement of said assemblies in said first direction thereof, said follow-up cylinder permitting fluid flow into said second conduit thereof and expelling fluid from said first conduit thereof responsive to turning movement of said assemblies in said second direction thereof, means communicably connecting said first and second control ports of said metering unit to said first and second conduits of said follow-up cylinder, and means for automatically bleeding said first and second chambers and conduits of said follow-up cylinder responsive to turning of said steering wheel.

Claim 10

The combination of claim 6 further defined by the bleeding means comprising a pair of opposed check valves respectively communicating said return conduit with said first and second conduits of said follow-up cylinder.

Claim 11

The combination of claim 7 further defined by an orifice interposed between said return conduit and said check valves.

Claim 12

The combination of claim 6 further defined by said differential valve including means for bypassing a volume of fluid in said first return conduit to said second return conduit in excess of the volume of fluid required to establish a pressure at said supply port of said metering unit equal to the sum of said pressure differential and back pressure in said second return conduit.

Claim 13

The combination of claim 9 further defined by said differential valve including a body having a first inlet port in communication with a first outlet port and a second inlet port in communication with a second outlet port, said first inlet and outlet ports respectively communicated with said first return conduit and said supply port of said metering unit, said second inlet and outlet ports respectively communicated with said return port of said metering unit and said second return conduit, said differential valve including a spool within said body normally blocking communication between said first inlet port and second outlet port, said differential valve including a poppet having a first force acting thereon equal to the sum of a predetermined constant force and the force due to back pressure in said second return conduit, said first force balanced by a second force due to pressure in said first inlet port, said poppet being actuated in response to said second force exceeding said first force, said valve including means for actuating said spool to an actuated position wherein said first inlet port is communicated with said second outlet port responsive to actuation of said poppet.

Claim 14

The combination of claim 10 further defined by a check valve interposed between said first outlet port of said differential valve and said supply port of said metering unit.

Claim 15

The combination of claim 10 further defined by the bleeding means comprising a pair of opposed check valves respectively coupled to said first and second conduits of said follow-up cylinder, and means including an orifice communicably connecting said first return conduit to said check valves.

Claim 16

The combination of claim 12 further defined by said spool being translatable between said normal and actuated positions thereof, said spool having an internal bore, said body having a passage communicating said first inlet and outlet ports with said internal bore, said body having a chamber on the opposite side of said spool from said bore, a spring within said chamber biasing said spool to said normal position thereof, said spool having an orifice communicating said passage with said chamber, means defining a second chamber, said body having a second passage communicating said first and second chambers, said poppet disposed in said second chamber, a second spring disposed in said second chamber biasing said poppet into closing relation with the termination of said second paSsage in said second chamber, and means communicating said second return conduit with said second chamber.

Claim 17

The combination of claim 13 further defined by a check valve interposed between said first outlet port of said differential valve and said supply port of said metering unit.

Claim 18

In a hydraulic steering system for a wheeled vehicle including a pair of hydraulic steering cylinders coupled between the vehicle frame and a pair of pivotal wheel suspension assemblies, said cylinders being arranged to impart turning movement to said assemblies in a first direction responsive to the supply of pressurized hydraulic fluid to first ends of said cylinders and return of fluid from second ends of said cylinders, said cylinders being arranged to impart turning movement to said assemblies in a second opposite direction responsive to the supply of pressurized hydraulic fluid to said second ends of said cylinders and return of fluid from said first ends of said cylinders, a steering valve having a supply conduit, return conduit, and first and second control conduits respectively coupled to said first and second ends of said cylinders, said valve having a neutral position wherein said supply and return conduits are communicated, a first actuated position wherein said supply conduit is communicated with said first control conduit and said second control conduit is communicated with said return conduit, and a second actuated position wherein said supply conduit is communicated with said second control conduit and said first control conduit is communicated with said return conduit, said valve being actuateable from said neutral position to said first position responsive to a fluid signal supplied to a first pilot port thereof and to said second position responsive to a fluid signal supplied to a second pilot port thereof, a pump coupled between a fluid reservoir and said supply conduit to supply pressurized fluid thereto, a steering-wheel-operated, fluid-metering unit having supply and return ports, and first and second control ports, said unit having a neutral steering wheel position wherein said supply and return ports are communicated, said unit being arranged to block communication between said supply and return ports responsive to turning of said steering wheel from said neutral position in a first direction and responsively develop from fluid pressure at said supply port a fluid signal at said first control port in accordance with the rate and number of revolutions of said steering wheel while communicating said second control port with said return port, said unit being arranged to block communication between said supply and return ports responsive to turning of said steering wheel from said neutral position in a second opposite direction and responsively develop from fluid pressure at said supply port a fluid signal at said second control port in accordance with the rate and number of revolutions of said steering wheel while communicating said first control port with said return port, means communicating said first and second ports of said metering unit with said first and second pilot ports of said steering valve, and relief valve means coupled to said pump for limiting the maximum pressure of fluid supplied therefrom, the improvement comprising a follow-up hydraulic cylinder coupled between said vehicle frame and said wheel suspension assemblies, said follow-up cylinder having first and second conduits communicating with first and second chambers at its opposite ends, said follow-up cylinder permitting fluid flow into said first conduit thereof and expelling fluid from said second conduit thereof responsive to turning movement of said assemblies in said first direction thereof, said follow-up cylinder permitting fluid flow into said second conduit thereof and expelling fluid from said first conduit thereof responsive to turning movement of said assemblies in said second direction thereof, means communicably connecting said first and second control ports of said metering unIt to said first and second conduits of said follow-up cylinder, and means for automatically bleeding said first and second chambers and conduits of said follow-up cylinder responsive to turning of said steering wheel.

Claim 19

In a hydraulic steering system for a wheeled vehicle including a pair of hydraulic steering cylinders coupled between the vehicle frame and a pair of pivotal wheel suspension assemblies, said cylinders being arranged to impart turning movement to said assemblies in a first direction responsive to the supply of pressurized hydraulic fluid to first ends of said cylinders and return of fluid from second ends of said cylinders, said cylinders being arranged to impart turning movement to said assemblies in a second opposite direction responsive to the supply of pressurized hydraulic fluid to said second ends of said cylinders and return of fluid from said first ends of said cylinders, a steering valve having a supply conduit, return conduit, and first and second control conduits respectively coupled to said first and second ends of said cylinders, said valve having a neutral position wherein said supply and return conduits are communicated, a first actuated position wherein said supply conduit is communicated with said first control conduit and said second control conduit is communicated with said return conduit, and a second actuated position wherein said supply conduit is communicated with said second control conduit and said first control conduit is communicated with said return conduit, said valve being actuateable from said neutral position to said first position responsive to a fluid signal supplied to a first pilot port thereof and to said second position responsive to a fluid signal supplied to a second pilot port thereof, a pump coupled between a fluid reservoir and said supply conduit to supply pressurized fluid thereto, a steering-wheel-operated, fluid-metering unit having supply and return ports, and first and second control ports, said unit having a neutral steering wheel position wherein said supply and return ports are communicated, said unit being arranged to block communication between said supply and return ports responsive to turning of said steering wheel from said neutral position in a first direction and responsively develop from fluid pressure at said supply port a fluid signal at said first control port in accordance with the rate and number of revolutions of said steering wheel while communicating said second control port with said return port, said unit being arranged to block communication between said supply and return ports responsive to turning of said steering wheel from said neutral position in a second opposite direction and responsively develop from fluid pressure at said supply port a fluid signal at said second control port in accordance with the rate and number of revolutions of said steering wheel while communicating said first control port with said return port, means communicating said first and second ports of said metering unit with said first and second pilot ports of said steering valve, and relief valve means coupled to said pump for limiting the maximum pressure of fluid supplied therefrom, the improvement comprising a follow-up hydraulic cylinder coupled between said vehicle frame and said wheel suspension assemblies, said follow-up cylinder having first and second conduits communicating with first and second chambers at its opposite ends, said follow-up cylinder permitting fluid flow into said first conduit thereof and expelling fluid from said second conduit thereof responsive to turning movement of said assemblies in said first direction thereof, said follow-up cylinder permitting fluid flow into said second conduit thereof and expelling fluid from said first conduit thereof responsive to turning movement of said assemblies in said second direction thereof, means communicably connecting said first and second control ports of said metering unIt to said first and second conduits of said follow-up cylinder, and means for automatically bleeding said first and second chambers and conduits of said follow-up cylinder responsive to turning of said steering wheel.