Steering system for articulated vehicles

An electro-hydraulic steering system for vehicles such as roller type surface compacting machines which have a steerable ground-engaging unit at each end of the chassis. The system combines a conventional orbital type steering valve, two conventional solenoid actuated hydraulic valves and two conventional lock valves with an electric control circuit that includes simple console-mounted selector switches, a foot pedal-controlled switch and a simple cam-actuated switch that is automatically actuated in consequence of shifting the control lever of the vehicle's transmission from "forward" to "reverse" and vice versa, in a manner which gives the operator unprecedented flexibility in his choice of steering mode.

This invention relates broadly to the control of articulated vehicles which 
have a steerable ground-engaging unit at each end of the chassis, and 
while applicable to any such vehicle, is especially well suited to 
articulated pavement compacting machines such as the "RANGER," which is 
produced by RayGo, Inc., and covered by the Takata et al U.S. Pat. No. 
3,947,142. In fact, the invention was developed especially for that 
machine. 
Machines or vehicles of the "RANGER" type are steerable by either the 
leading or the trailing unit. If the vehicle is moving forward, the front 
unit obviously is its leading unit and, when moving rearward, it is the 
rear unit which leads. While that mode of steering -- i.e. by the leading 
unit -- is perhaps the most common, in some circumstances it is more 
advantageous and, in fact, may be imperative, that the steering be done by 
the trailing unit. This then is a second mode in which the progress of the 
vehicle must be steerable. In each of these two modes, the unit which is 
not being steered remains fixed in its straightaway orientation with the 
vehicle chassis. 
The capability of steering by those two modes enables the two steerable 
units of the vehicle to be quickly adjusted from the more conventional 
tandem disposition to an echelon relationship to increase the effective 
width of the machine, and then steered by either its leading or its 
trailing unit. 
But there is still at least one other mode in which vehicles and machines 
of the type with which this invention is concerned should be steerable. 
This is the crab mode. In it, both steerable units are simultaneously 
steered in the same direction, either to the right or the left. The crab 
mode of steering enables the operator to quickly move the vehicle either 
to the right or the left without disturbing its parallel alignment with 
the sides of the road. And, for complete versatility, the vehicle should 
also be steerable in the so-called radial mode in which both units are 
simultaneously steered, but in opposite directions. This latter mode 
enables the machine to negotiate short radius curves while maintaining a 
constant rolling width. 
While vehicles with steerable front and rear units heretofore have been 
equipped with controls by which different modes of steering could be 
obtained, no known prior steering system has had the flexibility and 
versatility achieved by this invention. The closest prior art approach to 
the present system is that of the Ferguson et al. U.S. Pat. No. 3,868,194; 
but that system lacks the flexibility and ease of operation that 
characterizes this invention. 
As in the aforesaid Takata et al patent and also the Ferguson et al patent, 
the front and rear units of the vehicle are steered by paired hydraulic 
double-acting cylinders, and -- as in the latter patent -- manipulation of 
a steering wheel acting through an orbital-type steering valve governs the 
flow of pressure fluid to those cylinders as required to effect the 
desired steering adjustment of their respective steerable units. But, in 
contrast to the system of the Ferguson et al. patent wherein selective 
coordination of the unit to be steered requires manually shifting a valve 
by means of splayed levers which must be manipulated in addition to other 
direction controlling levers every time the operator changes from forward 
to rearward travel and vice versa, with this invention that coordination 
is automatically effected as a consequence of shifting a single 
transmission adjusting lever. 
Another advantage the present invention has over the steering system of the 
Ferguson et al patent is that the latter is incapable of crab mode 
steering. By contrast, with this invention crab mode steering is not only 
possible but instantaneously available by depression of a foot 
pedal-controlled switch. This capability enables the operator to randomly 
select the crab mode while performing other operations with his hands, and 
greatly facilitates manoeuvering the vehicle in that mode when occasion 
demands, while leaving the steering system conditioned for steering by 
either the leading or the trailing unit, as determined by a prior setting 
of a selector switch on the console of the machine. Hence, upon release of 
the foot pedal-controlled switch, steering continues in the mode 
determined by the setting of the selector switch. 
The invention also enables the system to be conditioned for steering in the 
crab mode by simply actuating another console mounted switch, so that 
until that switch is again actuated, steering takes place in the crab mode 
whether the vehicle is moving forward or backward. 
Finally, the invention provides the operator the option of switching from 
the crab mode of steering to the radial mode. 
With these observations and objectives in mind, the manner in which the 
invention achieves its purpose will be appreciated from the following 
description and the accompanying drawings which exemplify the invention, 
it being understood that changes may be made in the specific apparatus 
disclosed herein without departing from the essentials of the invention 
set forth in the appended claims.

Before referring to the drawings, it may be helpful to note that the 
invention broadly comprises: 
A fluid pressure responsive steering system for vehicles having 
transmission means by which the direction of travel of the vehicle is 
manually selectable, and having a steerable ground-engaging unit at each 
end of its chassis, so that by operator-controlled, power effected 
steering adjustment of the steerable units with respect to one another and 
the chassis, the progress of the vehicle over the ground in either a 
forward or a rearward direction can be steered, which system comprises 
reversible hydraulic motor means (a single one or paired double-acting 
cylinders) drivingly connected with each of said steerable units, and 
operable to impart steering adjustment thereto; manually operable steering 
valve means (orbital type valve) by which the functioning of the motor 
means may be commanded; hydraulic circuit means having said manually 
operable steering valve means incorporated therein for conducting pressure 
fluid to the motor means from a source thereof in response to and under 
control of manual actuation of the steering valve means; disabling valve 
means for each of the motor means connected in the hydraulic circuit 
means, operable when in its operative condition to render its respective 
motor means unresponsive to fluid pressure in said hydraulic circuit 
means; check valve means connected in the hydraulic circuit means between 
each of the disabling valve means therein and its respective motor means, 
operable as a consequence of said disabling valve means being in its 
operative condition to prevent the flow of fluid to or from the motor 
means and thereby lock said motor means in the position to which it moved 
in response to its last steering command; control means operatively 
connected with the disabling valve means for governing the condition 
thereof, said control means being operatively connected with the vehicle 
transmission to automatically render one of said disabling valve means 
operative without affecting the other when the transmission is shifted to 
effect forward travel of the vehicle and vice versa when it is shifted 
into reverse, so that steering of the vehicle is effected by one of the 
motor means during travel of the vehicle in one direction and by the other 
during travel of the vehicle in the opposite direction. 
Now, with reference to the drawings -- and first considering FIG. 1 -- the 
numeral 10 designates the chassis of the machine chosen as illustrative of 
the type of vehicle with which this invention is concerned. The chassis 
consists of a main section 11 with forwardly and rearwardly projecting 
arms 12 and 13, respectively, and a front section 14 which is connected 
with the forwardly projecting arm for relative rocking motion about a fore 
and aft horizontal axis. 
Substantially identical roller units 15F and 15R are respectively connected 
with the forwardly and rearwardly projecting arms of the chassis. Each 
roller unit consists of a drum rotatably mounted between the arms of a 
yoke 16, the cross bar 17 of which extends across the top of the drum. The 
cross bar of the front yoke is connected with the front chassis section 14 
by a pivot 18, the axis of which is vertical and perpendicularly 
intersects the axis of the front drum. Similarly, the cross bar of the 
rear yoke is connected to the rearwardly projecting arm 13 of the chassis 
by a pivot 19. 
As will be quite obvious, the pivots 18 and 19 provide steering axes about 
which the roller units can be rotated independently of one another. The 
roller units thus constitute the steerable ground-engaging units of the 
vehicle; and, to effect steering rotation of these units about their 
respective steering axes, a pair of double-acting hydraulic cylinders 20 
connects the cross arm of each yoke with pivot points 21 fixed with 
respect to the chassis. Extension of one of a pair of cylinders coincident 
with retraction of its mate imparts the desired steering torque -- and, as 
will be readily understood -- the extension and retraction of the 
cylinders is effected by regulating the connection of the opposite ends of 
the cylinders with a source of hydraulic pressure derived from a pump, not 
shown in FIG. 1 but identified by the numeral 22 in the diagrammatic 
illustration of the steering system in FIGS. 2-6. 
The system by which that regulation is effected is, of course, the concern 
of this invention. Through it, the operator's manipulation of selector 
switch means 23 mounted in the console of the vehicle, foot 
pedal-controlled switch means 24, a transmission control lever 25 and a 
steering wheel 26, is translated into steering activation of the hydraulic 
cylinders 20 to bring about steering of the vehicle in any of a number of 
different operator-selected modes. The physical location of these control 
instrumentalities is diagrammatically illustrated in FIG. 1. 
The manner in which selective actuation of the control instrumentalities 
conditions the system for different modes of steering by means of the 
steering wheel is depicted in FIGS. 2-6. In all of these figures, the 
hydraulic and electric circuitry of the system is identical, but its 
different mode-defining conditions are identified through the application 
to that circuitry of the symbols displayed in the index which appears in 
the upper left-hand corner of each of the FIGS. 2-6. 
As established by that index, the different aspects of the hydraulic 
circuitry are identified as "PRESSURIZED-NO FLOW", "PRESSURIZED-FLOW" and 
"RETURN"; and the electric circuitry as "NOT ENERGIZED" and "ENERGIZED." 
With this understood, the hydraulic circuitry will now be defined. 
Beginning with the pressure source -- i.e. the pump 22 -- a line 31 which 
is pressurized whenever the system is in operation, leads to one port of a 
rotary or orbital type steering valve 32. This steering valve is 
operatively connected with the steering wheel 26 shown in FIG. 1 and 
diagrammatically indicated in FIGS. 2- 6 to be actuated thereby. Another 
port of the steering valve is connected, through line 33, with the return 
or sump of the hydraulic system; and the two other ports of the steering 
valve are connected through lines 34 and 35 with conventional flow 
dividers 36 and 37. Each of the flow dividers is connected with the paired 
cylinders 20 at the front unit and also with the paired cylinders 20 at 
the rear unit. For this purpose, a line 38 leads from the flow divider 36 
to the cylinders at the front unit and a line 39 leads from the flow 
divider 36 to the cylinders at the rear unit. Similarly, lines 40 and 41 
lead from the flow divider 37 to the front and rear cylinders. 
An important aspect of the hydraulic circuit is the provision of a pair of 
solenoid actuated normally closed shunt valves 42F and 42R, the former 
arranged to connect the lines 38 and 40 that lead to the front unit 
cylinders when it is opened by energization of its solenoid, and the 
latter to connect the lines 39 and 41 that lead to the rear unit cylinders 
when it is opened by energization of its solenoid. In each instance, the 
opening of the valve shunts out and prevents flow of pressure fluid to its 
associated paired steering cylinders 20. 
It is also important to note that ahead of each pair of steering cylinders, 
the hydraulic circuit has a lock valve -- 43F for the front unit and 43R 
for the rear unit. These lock valves are conventional pilot pressure 
controlled check valves that prevent fluid flow into or out of the 
steering cylinders when their respective shunt valves are open, and thus 
hold the unit which is not being steered in whatever position it was moved 
by its last steering command. In this connection it should be noted that 
before the operator switches steering from one unit to the other, he 
should restore the unit with which he had been steering to its neutral 
position. In the compacting machine of the aforesaid Takata et al patent, 
that poses no problem, since both front and rear steerable units are 
readily observable from the operator's position; and where such visibility 
is not characteristic of the machine, position indicators such as those 
employed in the machine of the Ferguson et al patent can be provided. 
Before leaving this discussion of the hydraulic circuit, it might be well 
to note that adjustment of the orbital-type steering valve in response to 
rotation of the steering wheel to the right results in the line 34 being 
pressurized, and that adjustment beyond neutral in response to leftward 
rotation of the steering wheel, pressurizes the line 35. In each of the 
system conditions depicted by FIGS. 2-6, the steering valve is assumed to 
have been adjusted by rotation of the steering wheel to the right. 
Except for the steering wheel-controlled orbital type valve -- no component 
of the hydraulic circuit is manually actuated. Instead, that function is 
performed by the electric control circuit of the system in response to 
selective actuation of the selector switch means 23, the foot 
pedal-controlled switch 24 and a cam operated switch 44 that is 
automatically actuated in consequence of shifting of the vehicle's 
transmission by the lever 25. 
The electric control circuit begins with a conductor 45 that connects the 
movable contactor 46 of a three-position one-pole switch 47 with the 
electric power source of the vehicle. This switch, which may be a toggle 
switch or any other suitable variety, is part of the console-mounted 
switch means 23, and as will appear hereinafter, enables the operator to 
cut the foot pedal-controlled switch 24 out of the circuit. As shown in 
FIG. 7, it also enables the operator to condition the system for only crab 
mode steering. For that purpose, the contactor of the switch 47 is moved 
to its center position in which the power to the control circuit is cut 
off. 
Continuing with a description of the electric control circuit, a conductor 
48 connects the No. 1 contact of the switch 47 with the contactor 49 of 
the cam-operated switch 44, and a conductor 50 connects that same No. 1 
contact with the contactor 51 of the foot pedal-controlled switch 24. 
A conductor 52 connects the No. 3 contact of the switch 47 with the No. 1 
contact of the foot pedal-controlled switch, which in the normal condition 
of that switch -- i.e. not depressed -- is engaged by its contactor 51. 
The contactor 49 of the cam operated switch 44 is biased to the location it 
occupies when the shift lever is in its "forward" position, in which it is 
shown in FIGS. 2 and 4-7. In that position, the contactor 49 engages that 
No. 1 stationary contact of the switch 44 from which a conductor 53 leads 
to a contactor 54 of a two-pole switch 55 that also forms part of the 
console-mounted selector switch means and may be of the toggle type or any 
other suitable variety. With the contactor 49 of the switch 44 as shown in 
FIGS. 2, 4 and 7, the contactor 54 is "hot"; and with the contactor 49 in 
the position shown in FIG. 3 (to which it is moved by actuation of the 
shift lever 25 to its "reverse" position), the other contactor 56 of the 
switch 55 is "hot" by virtue of its connection via a conductor 57 with the 
No. 3 contact of the switch 44. 
To complete the electric circuitry, connected conductors 58 and 59 connect 
the No. 1 and No. 4 contacts of the switch 55 with the ungrounded side of 
the solenoid 60 of the shunt valve 42F; and connected conductors 61 and 62 
connect the No. 3 and No. 6 contacts of the switch 55 with the ungrounded 
side of the solenoid 63 of the shunt valve 42R. 
It follows, therefore, that with the contactor 54 of the switch 55 "hot," 
by virtue of the direction shifting lever 25 being in its "forward" 
position, and the switch 55 being in the position shown in FIGS. 2 and 6 
wherein its contactor 54 engages the No. 6 contact and its contactor 56 
engages the No. 1 contact, the solenoid of the shunt valve 42R will be 
energized to open that valve. As a result of the opening of that valve, 
the cylinders 20 of the rear unit will be shunted out of the circuit and 
locked in the position to which they were last brought -- which, as noted 
hereinbefore -- should secure the rear unit in its straightaway 
orientation with respect to the chassis. 
The system is then conditioned for steering by the front unit during 
forward travel of the vehicle, which of course is then the leading unit. 
If now the operator moves the shift lever 25 to its "reverse" position, as 
shown in FIG. 3, to cause the vehicle to travel rearward, the consequent 
response of the switch 44 brings its contactor 49 into engagement with its 
No. 2 contact, makes the contactor 56 of the switch 55 "hot," and brings 
about the change in condition of the system depicted in FIG. 3. Here the 
front unit is immobilized and steering is done with the rear unit, which 
now is the leading unit. 
Attention is directed to the fact that this transfer from steering by the 
front unit to steering by the rear unit (in each case, the leading unit), 
was effected automatically as a consequence of moving the 
direction-controlling shift lever 25 from one position to the other. 
To condition the system for steering with the trailing unit, as depicted in 
FIG. 4, the console mounted switch 55 is actuated to connect its contactor 
56 with its No. 3 contact and its contactor 54 with the No. 4 contact. 
Thereupon, steering commands emanating from the orbital-type steering 
valve will be effective upon the rear unit during forward travel of the 
vehicle and upon the front unit during rearward travel (in each instance, 
the trailing unit) and, as before, the change from one unit to the other 
is effected automatically in response to changing the position of the 
direction-selecting lever 25. 
Assuming now that the operator suddenly wishes to steer in the crab mode. 
He can do this without touching either of the switches on the console, and 
whether he is traveling forward or rearward, or steering in the leading or 
trailing mode, by simply depressing the foot pedal that controls the 
switch 24. That operation opens the switch 24 and since this switch is in 
series with the connection between the contactor 49 of the cam actuated 
switch 44 and the contactors 54 and 56 of the switch 55, its opening cuts 
off current to whichever shunt valve solenoid was energized and thereby 
subjects both steerable units to the steering commands of the operator 
effected through the orbital valve 32. 
While FIG. 5 shows the contactor of the cam actuated switch 44 in the 
position it occupies when the vehicle is traveling forward, the situation 
would be the same with that contactor in its other position and the 
vehicle traveling rearward. 
If the operator wishes to guard against accidentally placing the system in 
the crab mode, all that is required is to move the contactor 46 of the 
switch 47 into engagement with its contact 1, which is the "off" position 
of the switch shown in FIG. 6. This short circuits the foot 
pedal-controlled switch 24 and leaves the circuit responsive to the 
direction selecting lever 25, so that steering is automatically effected 
in either the "leading unit" mode or the "trailing unit" mode, depending 
upon the position of the mode selector switch 55. 
If, instead of transient periods of operation in the crab mode, the 
operator wishes to condition the system for continuous operation in that 
mode, he can attain that objective by moving the contactor 46 of the 
switch 47 to its center position (disengaged from its No. 1 and No. 2 
contacts) as shown in FIG. 7. This, of course, disconnects the entire 
electrical control circuit from the power source so that both steerable 
units respond at all times, and in the same direction, to the operator's 
commands. 
Finally, as shown in FIG. 8, the operator is given the option of steering 
in the radial mode by the addition of a solenoid-controlled two-position 
valve 65 between the cylinders 20 of one of the steerable units and its 
respective lock valve 43F or 43R, and a control switch 67 by which 
energization of the solenoid of that valve is effected. 
Those skilled in the art will appreciate that the invention can be embodied 
in forms other than as herein disclosed for purposes of illustration. 
The invention is defined by the following claims: