Lift system, steering system, and pivotal blade for land plane

A land plane for leveling or grading the surface of a land area. The plane includes a frame defined by a center section and end sections pivotally connected to the center section, with each connection permitting relative physical movement about an axis transverse to the longitudinal axis of the plane. A first hydraulic system is provided for pivoting the end sections about their transverse axes for raising and lowering the center section with respect to ground level, wherein the system includes a device for equalizing fluid between hydraulic cylinders carried by the end sections to permit adjustment of the grader assembly with respect to ground level under different operating conditions. A second hydraulic system is provided to permit selective steering of the rear wheels in response to the front wheels through either pivotal movement of a tongue connecting the plane to a tow vehicle or from a separate hydraulic power source carried by the tow vehicle, wherein the system includes means for purging itself of entrapped air. A biasing mechanism is provided for the grader assembly to permit tripping of the blades when the applied force encountered during grading exceeds the predetermined bias force. The mechanism is capable of imparting a bias force which requires a greater degree of applied force to initiate tripping of the blade than that which is required for continued tripping of the blade.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally involves apparatus utilized for altering, 
shaping or grading the surface of ground areas. More particularly, the 
invention relates to land planes having trippable grader blades and 
hydraulic systems for steering the plane and raising and lowering the 
center frame section. 
2. Description of the Prior Art 
A land plane is a large vehicular device comprised of a wheel supported 
frame structure which carries one or more grader blades for contacting the 
ground surface when the plane is towed by a tractor or other suitable tow 
vehicle. A typical land plane may include a truss-like frame comprised of 
three distinct sections, a center section and two end sections which are 
pivotally connected at opposite ends of the center section in such a 
manner that the end sections may pivot about axes transverse to the 
longitudinal axis of the plane. This enables the center section, which 
carries the grader assembly, to be raised and lowered with respect to the 
ground surface. Pivoting of the end sections with respect to the center 
section for the purpose of raising and lowering the latter has typically 
been achieved by using an hydraulic cylinder carried by one end section 
and operatively connected to the other end section through a cable or rod 
linkage. While this arrangement is quite suitable for simply raising the 
center section a considerable distance above ground level in order to 
accommodate towing the plane to its location of use, it does not easily 
accommodate precise adjustment of distance between the grader blade edges 
and ground surface when the plane is set for operation. This is because 
the frame is usually provided with stops in the form of extensible bolts 
or similar devices on the center section to adjust for the maximum 
downward movement of the center section when hydraulic fluid is removed 
from the lift cylinder. In some instances, it is desirable to dispose the 
series of grader blades at different distances with respect to the ground 
surface in order to prevent excess accumulation of soil at the leading 
blade. Precise adjustment in this regard requires independent control over 
the pivotal movements of the individual end sections in order to permit 
corresponding independent adjustment of the stops. 
Because of its large wheel base, a land plane requires independent steering 
of the front and rear wheel assemblies so that steering of the front wheel 
assembly produces a corresponding though oppositely directed steering 
action in the rear wheel assembly to accommodate its large turning radius. 
This has been accomplished by interconnecting the front and rear wheel 
assemblies through mechanical or hydraulic steering systems. In a typical 
hydraulic system, an hydraulic cylinder is carried by the front wheel 
assembly, with the piston rod being actuated by the pivotal movement of a 
tongue connecting the plane to the tow vehicle. The front cylinder is in 
fluid communication with a similar cylinder carried by the rear wheel 
assembly so that steering of the front wheels imparts the corresponding 
and opposite steering action to the rear wheels. Such a system is also 
capable of being connected to a separate hydraulic power source, such as 
that usually associated with the tow vehicle, so that the rear wheels may 
be selectively steered either through the action of the front cylinder or 
through the hydraulic power supplied by the tow vehicle. Hydraulic 
steering systems of this type are normally plagued by entrapment of air in 
the fluid system. It has been determined that even a small amount of air 
can cause undesirable variations in steering actions between the front and 
rear wheel assemblies. Such variations are multiplied manifold in their 
detrimental effects because of the large turning radius of a land plane. 
The grader assembly carried by a typical land plane consists of several 
blades which are disposed at varying angles to the longitudinal axis of 
the plane so that the most efficient ground contact can be realized. The 
blades are usually pivotally mounted so that they can trip rearwardly when 
obstructions are encountered during grading to prevent damage to the 
blades. This has been achieved by resiliently biasing the blades with 
springs or similar appliances so that tripping of the blades will occur 
when the bias force is exceeded by the force applied to the blades. The 
bias force is adjustable to compensate for different ground conditions. 
However, it has been proven difficult to apply a biasing force of such a 
nature that continuous tripping of the blades during normal operation is 
avoided while still affording complete protection against damage to the 
blades. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an improved land plane 
having an hydraulic lift assembly which permits precise adjustment of the 
grader assembly blades with respect to the ground surface. 
It is another object of the invention to provide an improved hydraulic 
steering system for a land plane wherein entrapped air in the fluid lines 
is easily and quickly purged from the system to permit accurate control 
over the steering of the plane. 
It is yet another object of the invention to provide an improved biasing 
mechanism for the grader assembly of a land plane whereby continuous 
tripping of the individual blades will be avoided while affording complete 
protection for the blades against mechanical damage. 
It is a further object of the invention to provide an improved land plane 
which is reliable and simple in both construction and operation. 
It is also another object of the invention to provide an improved land 
plane which is relatively inexpensive to manufacture and maintain, and is 
capable of performing under all anticipated conditions. 
These above objects are realized by providing a land plane with a first 
hydraulic system for raising and lowering the center section of the frame 
through pivotal movement of the end sections connected thereto. The first 
hydraulic system includes a fluid cylinder carried by the front end 
section and a similar fluid cylinder carried by the rear end section, with 
both cylinders being in fluid communication with each other and a separate 
power source, such as the hydraulic power supplied by a tractor. A means 
for bypassing the hydraulic fluid from the power source directly to the 
rear cylinder is provided so that fluid pressure between the cylinders can 
be equalized to permit adjustment of the distance between the grader 
blades and ground surface. A second hydraulic system is provided for 
steering the plane wherein a rear hydraulic cylinder steers the rear 
wheels in accordance with fluid pressure transmitted thereto from a front 
hydraulic cylinder which is actuated by the pivotal movement of a tongue 
connecting the plane to a tow vehicle. The rear cylinder may also be 
selectively and independently actuated from a separate hydraulic power 
supply carried by the tow vehicle under certain operating conditions. A 
bypass is provided in the second hydraulic system to permit purging of air 
entrapped therein, whereby the purged air is passed out of the system and 
into the hydraulic fluid reservoir on the tow vehicle. The plane further 
includes a grader assembly wherein each of the blades is provided with a 
biasing mechanism having a cam arm and associated linkage for presetting 
the degree of bias force imparted by a spring or similar resilient element 
so that a greater applied force is necessary to initiate tripping than 
that which is required to complete tripping of the blade. 
These and other objects and advantages of the present invention will become 
apparent as the invention is more fully hereinafter described and claimed, 
with reference being made to the accompanying drawings forming a part 
hereof, wherein like numerals refer to like parts throughout, and in 
which:

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A land plane 1 or similar such device with which the present invention is 
suitable for association is depicted in FIG. 1. Land plane 1 is generally 
defined by a large truss-type frame 3 which includes a center section 5, a 
front end section 7 and a rear end section 9. End section 7 is connected 
to center section 5 through a front pivot connection 11 while end section 
9 is similarly connected to center section 5 through a pivot connection 
13. Connections 11 and 13 permit end sections 7 and 9 to each pivot 
relative to center section 5 about an axis that is transverse to the 
longitudinal axis of frame 3. A front wheel assembly 15 is carried by end 
section 7 and a rear assembly 17 is carried by end section 9, with wheel 
sections 15 and 17 supporting frame 3 for travel when plane 1 is towed by 
a tow vehicle, shown generally at 19, such as a tractor or the like. A 
pivotal tongue 21 is carried by front wheel assembly 15 for connecting 
plane 1 to tow vehicle 19. 
Center section 5 carries a grader assembly 23 which includes one or more 
grader blades 25, each of which is connected to center section 5 through a 
blade support, indicated generally at 27. Each support 27 permits 
disposition of the longitudinal axis of its associated blade at the 
desired angle with respect to the longitudinal axis of frame 3. Variations 
in the angular dispositions of blades 25 is desirable for accommodating 
various ground conditions and maximizing grading efficiency. 
As also shown in FIG. 1, frame 3 includes a first hydraulic system 29 that 
includes a front fluid motor in the form of a lift cylinder 31 carried by 
end section 7. Cylinder 31 is provided with an extensible piston rod 33 
having an outer end that contacts and may by pivotally connected to center 
section 5. Similarly, end section 9 is provided with a rear fluid motor in 
the form of a lift cylinder 35 that includes an extensible rod 37 having 
an outer end contacting or pivotally connected to center section 5. 
As depicted in FIG. 2, lift cylinders 31 and 35 have been actuated so that 
their respective piston rods 33 and 37 are extended, with end sections 7 
and 9 pivoted away from center section 5 about their respective 
connections 11 and 13. When this happens, center section 5 and its 
associated grader assembly 23 are simultaneously raised above ground level 
which permits plane 1 to be towed to another location of use or storage. 
Lift cylinders 31 and 35 are in fluid communication with each other and 
receive actuation fluid pressure from a separate hydraulic power source, 
such as an hydraulic power supply carried by tow vehicle 19. 
When it is desired to lower center section 5 and its associated grader 
assembly 23, lift cylinders 31 and 35 are relieved of hydraulic pressure 
so that their respective piston rods 33 and 37 are retracted therein. As 
noted in FIG. 2, the lowermost position of center section 5, and the 
corresponding distance between the lowermost edges of blades 25 and ground 
level can be set by extending or retracting a plurality of stop bolts 39 
provided on center section 5. Bolts 39 may be of the type disclosed by the 
Whitlow U.S. Pat. No. 4,150,726. 
First hydraulic system 29 is depicted in greater detail in FIG. 3 wherein 
an hydraulic line 41 provides fluid communication between a variable 
chamber 43 of lift cylinder 31 and a variable chamber 45 of lift cylinder 
35. Chambers 43 and 45 are, respectively, defined by the displacement of 
corresponding pistons 47 and 49 connected to their associated piston rods 
33 and 37. Piston 47 also defines an opposite second variable chamber 51 
which receives pressurized hydraulic fluid from a power source 53 on tow 
vehicle 19 through an hydraulic line 55. Similarly, piston 49 in lift 
cylinder 35 defines an opposite second variable chamber 57 which may 
communicate with ambient atmosphere through a standard vent valve 59. A 
bypass hydraulic line 61 joins and provides fluid communication between 
lines 41 and 55 when a shutoff valve 63 disposed in line 61 is in an open 
position. 
Supply of hydraulic fluid pressure to line 55 from power source 53 is 
controlled by a first handle 65 which operates the lift portion of a 
master control valve 67. The degree of fluid pressure sent through line 55 
can be controlled by varying the position of handle 65. Power source 53 
and valve 67 may be of any type well known in the art and deemed suitable 
for the practice of the present invention. For example, power source 53 
may include a reservoir 69 from which pure hydraulic fluid is pumped from 
the lower portion thereof by a pump 71 to control valve 67 through a first 
line 73. Hydraulic fluid is returned to reservoir 69 through a second line 
75. Power source 53 and valve 67 may also be of the types disclosed in the 
aforementioned Whitlow U.S. Pat. No. 4,150,726. 
The operation of first hydraulic system 29 shall now be described with 
particular reference to FIGS. 2 and 3. When it is desired to raise center 
section 5, valve 63 is maintained in a closed position and pressurized 
fluid is sent from power source 53 to chamber 51 of lift cylinder 31. As 
piston 47 is displaced, fluid contained within chamber 43 is 
correspondingly pressurized and sent through line 41 to chamber 45 of lift 
cylinder 35. This causes a substantially equal displacement of piston 49 
in lift cylinder 35. As is therefore apparent, piston rods 33 and 37 are 
correspondingly extended from their respective lift cylinders 31 and 35, 
thus pivoting end sections 7 and 9 away from center section 5 and causing 
the latter to raise upwardly to a desired height for travel. At this 
point, handle 65 is actuated to close off line 55 at control valve 67 so 
that center section 5 will be maintained in a raised position. Lowering of 
center section 5 is achieved in the reverse procedure whereby fluid 
pressure is removed from line 55 upon appropriate positioning of handle 65 
and actuation of control valve 67. As seen in FIG. 2, the extent to which 
the lower edges of blades 25 can be brought downwardly with respect to 
ground level is controlled by the positions of stops 39. When adjustment 
of stops 39 has been completed, it is then necessary to precisely position 
piston rods 33 and 37 within their respective lift cylinders 31 and 35 so 
that end sections 7 and 9 firmly abut their corresponding stops 39. This 
difficulty arises from the inevitable unequal distribution of fluid 
displaced in lift cylinders 31 and 35. Equalization of fluid displacements 
is achieved by opening valve 63, so that fluid pressure from line 55 
bypasses cylinder 31 and advances directly to cylinder 35 through bypass 
line 61 and line 41. This permits passage of fluid to or removal of fluid 
from cylinder 35 independently of cylinder 31. During actual operation of 
plane 1, end sections 7 and 9 are in rigid abutment against stops 39 and 
are not supported by fluid pressure through lift cylinders 31 and 35. 
The steering of plane 1 is achieved through a second hydraulic system 
indicated generally at 77 in FIG. 3. Hydraulic system 77 is associated and 
operates in conjunction with tongue 21 and wheel assemblies 15 and 17. 
Alternatively, hydraulic system 77 may also operate from power source 53 
upon selective engagement of the latter through a second handle 79 which 
operates the steering portion of control valve 67. 
Wheel assembly 15 includes a front axle 81 provided with a pair of front 
wheels 83 rotatably supported at the ends thereof. Steering of wheels 83 
is accomplished by the pivoting movement of tongue 21 in response to the 
turning direction of tow vehicle 19. Pivotal movement of tongue 21 is 
transmitted to wheels 83 through a front steering linkage 85 that is 
operatively connected to wheels 83 through a pair of front rotatable 
spindles 87. Similarly, rear wheel assembly 17 includes a rear axle 89 
having a pair of wheels 91 journaled at the ends thereof. Steering of 
wheels 91 is accomplished through actuation of a rear steering linkage 93 
which is operatively connected to wheels 91 through a pair of rear 
rotatable spindles 95. 
Second hydraulic system 77 includes a fluid motor in the form of an active 
cylinder 97 which is pivotally connected to axle 81 through a bracket 99. 
A piston rod 101 is disposed within cylinder 97 and includes a 
displaceable piston 103 for defining a pair of variable chambers 105 and 
107 on either side thereof. One end of rod 101 is pivotally connected to 
linkage 85 through a bracket 109 so that the pivoting of tongue 21 causes 
a corresponding retraction or extension of rod 101 with respect to 
cylinder 97. 
A fluid motor in the form of a passive cylinder 111 is pivotally connected 
to axle 89 through a bracket 113. Cylinder 111 is provided with a piston 
rod 115 which carries a displaceable piston 117 for defining a pair of 
variable chambers 119 and 121 on either side thereof. One end of rod 115 
is pivotally connected to linkage 93 through a bracket 123. Thus, 
extension or retraction of rod 115 will provide corresponding actuation of 
linkage 93 to steer in the corresponding direction. 
Chamber 105 of active cylinder 97 communicates with chamber 121 of passive 
cylinder 111 through an hydraulic line 125. Likewise, chamber 107 of 
active cylinder 97 communicates with chamber 119 of passive cylinder 111 
through an hydraulic line 127. Lines 125 and 127 communicates with each 
other through a first bypass line 129 having a conventional cross relief 
valve 131 disposed therein. Lines 125 and 127 may also communicate with 
each other adjacent their connections to passive cylinder 111 through a 
second bypass line 133 having a shutoff valve 135 disposed therein. The 
latter valve is preferably manually operated and permits communication 
between lines 125 and 127 when in an open position. 
Line 125 may receive hydraulic fluid from or discharge hydraulic fluid to 
power source 53 through an hydraulic line 137. Similarly, line 127 may 
receive hydraulic fluid from or discharge hydraulic fluid to power source 
53 through an hydraulic line 139. Passage of hydraulic fluid from power 
source 53 to and from lines 137 and 139 is controlled by valve 67 through 
three positions of handle 79. In a first position, fluid may be pumped 
from power source 53 to line 137 and receive fluid from line 139. In a 
second position, fluid communication between power source 53 and lines 137 
and 139 are terminated or dead ended so that actuation of passive cylinder 
111 is accomplished solely through actuation of active cylinder 97. In a 
third position, fluid from power source 53 is sent to line 139 and 
received from line 137. 
When power source 53 is utilized to directly activate passive cylinder 111, 
active cylinder 97 effectively functions as a dead end terminal, with 
hydraulic pressure to passive cylinder 111 being received from power 
source 53 through either line 137 or line 139, depending on the direction 
in which it is desired to turn rear wheels 91. Any air entrapped in second 
hydraulic system 77 during the normal operation thereof is quickly removed 
by first opening shutoff valve 135, thereby bypassing passive cylinder 111 
so that fluid contained in lines 125, 127, 137 and 139 will completely 
circulate therethrough to reservoir 69 of power source 53. The entrapped 
air is removed in reservoir 69 so that only pure hydraulic fluid is sent 
back into second hydraulic system 77. When all of the entrapped air has 
been removed, valve 135 is then closed to permit selective actuation of 
passive cylinder 111 by either active cylinder 97 or power source 53. 
The details of grader assembly 23 shall now be described with reference to 
FIGS. 4-6. As particularly shown in FIG. 4, grader assembly 23 is carried 
on the lower portion of center section 5 by a bracket assembly 141 which 
may comprise a pair of parallel plates 43 with a pair of associated bolts 
145 for attaching blade support 27 to center section 5. Bracket assembly 
141 may be of any type well known in the art so long as it permits angular 
adjustment of blade 25 with respect to the longitudinal axis of frame 3. 
While only a single bracket assembly 141 is depicted in FIG. 4, it is 
understood that blade support 27 does extend past the other parallel side 
of center section 5 and is similarly secured to the latter by means of a 
second blade assembly 141. Grader assembly 23 thus comprises a plurality 
of blade supports 27 and their associated blades 25 secured at spaced 
points along the length of center section 5 and disposed at various 
desired angles with respect to the longitudinal axis of frame 3. 
Blade support 27 includes a channel beam 147 having a plate 149 pivotally 
connected at its extremities through an axle 151. As seen in FIG. 5, each 
end of blade 25 is secured to its associated plate 149 through a bracket 
153, the latter being of any conventional means known in the art and 
capable of rigidly securing blade 25 to plate 149. It is preferable that 
bracket 153 permit adjustment in positioning the lowermost edge of blade 
25 either forwardly or rearwardly to set the best grading angle for any 
given ground condition. As further shown in FIGS. 4 and 5, rearward 
pivotal movement of the upper portion of plate 149 is limited to its 
contact by a stop 155 secured at the outer ends of beam 147. Thus, stop 
155 limits the forward movement of blade 25 to its predetermined grading 
angle, but permits blade 25 to pivot or trip rearwardly in response to an 
applied force F, the tripping of blade 25 being controlled by a biasing 
mechanism 157. 
As particularly shown in FIGS. 4 and 5, biasing mechanism 157 includes a 
resilient member 159, such as a coil spring, having one end secured to a 
flange 161 attached to blade support 27 and its other end secured to a 
linkage 163 through a turnbuckle 165 or other similar adjustment 
mechanism. Linkage 163 is preferably flexible and may comprise a chain. 
Alternatively, linkage 163 may include rigid members suitably joined 
together for performing the function required by biasing mechanism 157. 
The free end of linkage 163 is secured in a notched flange 167 carried at 
the upper end of plate 149 adjacent stop 155. A cam arm 169 is pivotally 
connected at one end to blade support 27 through a journal bearing unit 
171 which may include a cylindrical housing 173 within which a rotatable 
sleeve 175 is journaled, with arm 169 being directly attached to sleeve 
175. The free end of arm 169 includes a tab 177 provided with a notch 179 
therein. Thus, arm 169 may either pivot outwardly in the direction 
designated by arrow A or inwardly in the direction designated by arrow B, 
with notch 179 receiving the portion of linkage 163 at the position in 
which it is desired to locate arm 169. 
When an applied force is imparted to blade 25 in the direction of arrow F 
and this force exceeds the restoring force imparted by spring 159, blade 
25 begins to pivot rearwardly about axle 151, thereby causing spring 159 
to extend and swinging arm 169 outwardly in the direction of arrow A. The 
reverse occurs when the applied force F is removed and blade 25 is pulled 
back into position by the restoring force of spring 159 until plate 149 
engages stop 155. 
With particular attention to FIG. 6, it is seen that a center point is 
reached when the longitudinal axis of arm 169 is disposed substantially 
parallel with the direction of applied force F. At this point, angle C 
becomes zero and a maximum amount of applied force F is required to 
overcome the restoring force imparted by spring 159. If arm 169 is preset 
outwardly in direction of arrow A, the degree of restoring force imparted 
by spring 159 decreases with an increase in angle C. If arm 169 is pivoted 
inwardly in the direction of arrow B until angle C becomes less than zero, 
this sets arm 169 in an overcenter position in which blade 25 is locked 
rigidly against any possibility of tripping, regardless of the amount of 
applied force F. 
It is improtant to note that when arm 169 is set in any position wherein 
angle C is greater than 0.degree. but less than 45.degree., the applied 
force F required to initiate tripping of blade 25 is much greater than 
that required for continued tripping after arm 169 has swung outwardly in 
the direction of arrow A past the point when angle C equals 45.degree.. 
This situation is highly advantageous for both protecting blade 25 against 
damage and yet still preventing constant tripping of blade 25 during 
normal operations. Because of this arrangement, the lowermost edge of 
blade 25 can be set at a greater forward position for more efficient 
grading action than has heretofore been possible with known means for 
biasing grader blades. 
The restoring force imparted by biasing mechanism 157 is essentially 
established through positioning arm 169. However, such force may also be 
varied by adjusting turnbuckle 165 to extend or retract spring 159. In 
this manner, precise control of the desired restoring force can be 
established for blade protection and all anticipated operating conditions. 
The foregoing is considered as only illustrative of the basic principle of 
the present invention since numerous modifications and changes will 
readily occur to those skilled in the art. It is therefore not desired to 
limit the invention to the exact construction and operation shown and 
described, but that all suitable modifications and equivalents may be 
resorted to and falling within the scope of the invention as hereinafter 
claimed.