Hydraulic steering system

Claim 2

In a steering system of the type including a pump; a reservoir; a two-way steering motor; a steering control valve means having pressure and return lines connected respectively to the pump and reservoir and a pair of motor lines connected respectively to the opposite work ports of the steering motor, said valve means being shiftable among a neutral position, wherein fLuid is blocked in the work ports of the steering motor, and first and second active positions wherein one or the other of the steering motor work ports is connected to the pump while the remaining work port is connected to the reservoir; steering linkage means for shifting said valve means from the neutral to the active positions and including a two-way, follow-up slave motor for returning said valve means to the neutral position, the slave motor having one end connected to one of the pair of motor lines, and having its other end connected to a trapped volume of fluid, the improvement comprising: said steering motor having a hollow piston rod slidably received on a seal fixed in the steering motor, thus defining a follow-up motor; said other end of the slave motor being connected to the interior of said hollow piston rod and cooperating therewith to confine said trapped volume of fluid; a pilot-operated return fluid control valve connected between said steering control valve means and said sump; bias means normally urging said pilot-operated valve to a closed position preventing the return of fluid to the sump; said pilot-operated valve including pressure responsive means connected to said trapped volume of fluid and responsive to a predetermined pressure thereof caused by shifting said steering control valve means to one or the other of its active positions.

Claim 3

The invention defined in claim 1 wherein the displacements of said follow-up and slave motors are equal whereby the steering motor can undergo a full stroke.

Claim 4

The invention defined in claim 1 wherein said seal is fixed to one end of a rod disposed coaxially within the steering motor, the other end of the rod being fixed to one end of said steering motor; and said hollow piston rod telescopically receiving said rod.

Claim 5

A hydraulic steering system comprising: a source of pressurized fluid; a sump-connected return line; a two-way piston and rod-type steering cylinder having first and second motor lines respectively connected to its opposite ends; a steering control valve means connected to the source of pressurized fluid, the return line and the first and second motor lines, the valve means being selectively shiftable from a neutral position blocking flow to and from the motor lines to first and second active positions respectively connecting pressurized fluid to the first and second motor line while connecting the remaining motor line to the return line; steering input means connected to the steering control valve means and being responsive to selected continuous right and left steering signals for shifting the control valve means to and retaining the control valve means in one and the other of the first and second active positions; and followup means for restoring said steering control valve means to its neutral position upon cessation of said steering signals, said follow-up means including a follow-up cylinder formed interiorly of said steering cylinder and including a bore extending coaxially within the piston rod of said steering cylinder, said bore being slidably mounted on a seal fixed in said steering cylinder, whereby the volume delimited by the bore and seal will expand and contract in unison with extension and retraction of said steering cylinder; a two-way slave cylinder having one end connected to the interior of the bore of the follow-up cylinder and cooperating therewith to confine a fixed volume of control fluid, the other end of said slave cylinder being connected to one of said first and second motor lines, whereby the slave cylinder will shift in a first direction during extension of the steering cylinder and will shift in the opposite direction during retraction of the steering cylinder; connection means extending between said slave cylinder and said steering control valve means operative only upon cessation of said input signals for coupling the shifting movements of said slave cylinder with said steering control valve means for restoring the latter to its neutral position; a pilot-operated return flUid control valve connected between said steering control valve means and said sump; bias means normally urging said pilot-operated valve to a closed position preventing the return of fluid to the sump; said pilot-operated valve including pressure responsive means connected to said trapped volume of fluid and responsive to a predetermined pressure thereof caused by shifting said steering control valve means to one or the other of its active positions.

Claim 6

A hydraulic steering system comprising: a source of pressurized fluid; a sump-connected return line; a two-way piston and rod-type steering cylinder having first and second motor lines respectively connected to its opposite ends; a steering control valve means connected to the source of pressurized fluid, the return line and the first and second motor lines, the valve means being selectively shiftable from a neutral position blocking flow to and from the motor lines to first and second active positions respectively connecting pressurized fluid to the first and second motor line while connecting the remaining motor line to the return line; steering input means connected to the steering control valve means and being responsive to selected continuous right and left steering signals for shifting the control valve means to and retaining the control valve means in one and the other of the first and second active positions; and followup means for restoring said steering control valve means to its neutral position upon cessation of said steering signals, said follow-up means including a follow-up cylinder formed interiorly of said steering cylinder and including a bore extending coaxially within the piston rod of said steering cylinder, said bore being slidably mounted on a seal fixed in said steering cylinder, whereby the volume delimited by the bore and seal will expand and contract in unison with extension and retraction of said steering cylinder; a two-way slave cylinder having one end connected to the interior of the bore of the follow-up cylinder and cooperating therewith to confine a fixed volume of control fluid, the other end of said slave cylinder being connected to one of said first and second motor lines, whereby the slave cylinder will shift in a first direction during extension of the steering cylinder and will shift in the opposite direction during retraction of the steering cylinder; connection means extending between said slave cylinder and said steering control valve means operative only upon cessation of said input signals for coupling the shifting movements of said slave cylinder with said steering control valve means for restoring the latter to its neutral position; a pilot-operated return flUid control valve connected between said steering control valve means and said sump; bias means normally urging said pilot-operated valve to a closed position preventing the return of fluid to the sump; said pilot-operated valve including pressure responsive means connected to said trapped volume of fluid and responsive to a predetermined pressure thereof caused by shifting said steering control valve means to one or the other of its active positions.

Claim 7

The invention defined in claim 4 wherein the displacements of said follow-up and slave cylinders are equal.

Claim 8

In a hydraulic steering system of the type including a pump, a reservoir, a two-way hydraulic steering motor having firs and second work ports, a control valve means being connected to said pump, reservoir and steering motor and being selectively shiftable from a neutral position wherein fluid is blocked in the steering motor to maintain a course of travel, to first and second active positions wherein said first and second work ports are respectively connected to said pump while the remaining work port is connected to said reservoir for respectively initiating right and left steering, control linkage means connected to said valve means for selectively shifting the latter to said first and second active positions respectively in response to right and left steering input signals, and follow-up means connected to said linkage means for restoring said valve means to the neutral position upon cessation of said input signals, the improvement wherein said follow-up means includes: a two-way slave motor having first and second work ports and being connected to said linkage means such that by respectively pressurizing said first and second ports said valve means will be returned to neutral from said first and second active positions; said first slave motor port being connected to said first steering motor port; said steering motor having a hollow piston rod defining a master cylinder; seal means fixed in said steering motor and said piston rod being slidably mounted on said seal means; said second slave motor port being connected to the interior of said piston rod; a pilot-operated return fluid control valve connected between said steering control valve means and said sump; bias means normally urging said pilot-operated valve to a closed position preventing the return of fluid to the sump; said pilot-operated valve including pressure responsive means connected to said trapped volume of fluid and responsive to a predetermined pressure thereof caused by shifting said steering control valve means to one or the other of its active positions.

Claim 9

In a hydraulic steering system of the type including a pump, a reservoir, a two-way hydraulic steering motor having firs and second work ports, a control valve means being connected to said pump, reservoir and steering motor and being selectively shiftable from a neutral position wherein fluid is blocked in the steering motor to maintain a course of travel, to first and second active positions wherein said first and second work ports are respectively connected to said pump while the remaining work port is connected to said reservoir for respectively initiating right and left steering, control linkage means connected to said valve means for selectively shifting the latter to said first and second active positions respectively in response to right and left steering input signals, and follow-up means connected to said linkage means for restoring said valve means to the neutral position upon cessation of said input signals, the improvement wherein said follow-up means includes: a two-way slave motor having first and second work ports and being connected to said linkage means such that by respectively pressurizing said first and second ports said valve means will be returned to neutral from said first and second active positions; said first slave motor port being connected to said first steering motor port; said steering motor having a hollow piston rod defining a master cylinder; seal means fixed in said steering motor and said piston rod being slidably mounted on said seal means; said second slave motor port being connected to the interior of said piston rod; a pilot-operated return fluid control valve connected between said steering control valve means and said sump; bias means normally urging said pilot-operated valve to a closed position preventing the return of fluid to the sump; said pilot-operated valve including pressure responsive means connected to said trapped volume of fluid and responsive to a predetermined pressure thereof caused by shifting said steering control valve means to one or the other of its active positions.

Claim 10

The invention defined in claim 6 wherein said master and slave cylinders have equal displacements.