US3856089A

US3856089A - Drawbar support for leveling circle frame on road graders

Info

Publication number: US3856089A
Application number: US00398947A
Authority: US
Inventors: T Rivinius
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-06-29
Filing date: 1973-09-20
Publication date: 1974-12-24
Anticipated expiration: 1991-12-24

Abstract

A linkage adjacent the normal ball joint of the drawbar of a road grader which permits leveling of the circle frame, regardless of the depth of cut of the grader blade throughout the normal range of grader blades on road graders.

Description

United States Patent [191 [111 3,856,089

Rivinius Dec. 24, 1974 [54] DRAWBAR SUPPORT FOR LEVELINC 3,376,937 4/1968 Grober 172/679 X CIRCLE FRAME 0 O GRADERS 3,454,109 7/1969 Roberts 3,595,320 7/1971 Mittelstadt 172/781 Inventor: Theodore Rivinius, 810 N. 2nd St.,

Bismarck, N. Dak. 58501 Filed: Sept. 20, 1973 Appl. No.: 398,947

Related US. Application Data Continuation-in-part of Ser. No. 267,434, June 29, 1972, abandoned.

US. Cl. 172/4.5, 172/789 Int. Cl E02f 3/76 Field of Search 172/789, 779, 780, 781,

References Cited UNITED STATES PATENTS 8/1966 Olafson 172/780 Primary ExaminerStephen C. Pellegrino Attorney, Agent, or Firm-Dugger, Johnson & Westman [57] ABSTRACT A linkage adjacent the normal ball joint of the draw bar of a road grader which permits leveling of the circle frame, regardless of the depth of cut of the grader blade throughout the normal range of grader blades on road graders.

13 Claims, 9 Drawing Figures PATENTEUUECZMQM DRAWBAR SUPPORT FOR LEVELING CIRCLE FRAME ON ROAD GRADERS CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of my copending application Ser. No. 267,434, filed June 29, 1972, now abandoned, for Drawbar Support for Leveling Circle Frame on Road Graders.

BACKGROUND OF THE INVENTION Field of the Invention The invention relates to improvements in earth working graders and more particularly to a supporting framework for leveling the circle frame with respect to a horizontal fore and aft line regardless of the depth of cut of the blade that is carried by a circle frame of a road grader. This also means that the plane of the circle frame is kept parallel to the plane of the cut by the blade as the grader moves forwardly. For example, in my US. Pat. No. 3,421,589, issued Jan. 14, 1969, a four bar lifting link is used for supporting the circle frame in a parallel relationship to a horizontal fore and aft line regardless of the depth of cut of the circle frame, and maintaining this parallel relationship of the circle frame throughout the range of operation of the circle frame. The circle frame drawbar in my aforementioned patent is connected to the circle frame through hinged joints that permit the circle frame to be independently supported on its lift links to keep the circle frame parallel to a horizontal, fore and aft extending line while being pulled along by the drawbar in a normal manner.

In addition, US. Pat. No. 2,941,319, issued on June 21, 1960 to Beemer et al. shows a parallel linkage for supporting the circle frame, and taking the place of the conventional drawbar. The parallel linkage is subject to wear at several pivot points, and in a high load situation such as that with a road grader drawbar these inaccura cies due to wear in a linkage can cause unsatisfactory operation.

In graders where the circle frame is not maintained parallel to a horizontal, fore and aft line, if the blade is rotated about its upright axis, the angle of cut will change and this requires additional adjustment. In addition, if automatic leveling or slope controls are used, the automatic system will not adjust because the sensing device is usually sensitive to the transverse angle of the circle frame and no correction would be made unless special compensation techniques are employed.

SUMMARY OF THE INVENTION The present invention relates to a simple connecting linkage between the normal ball joint of a drawbar of a road grader and the frame of a road grader which can be adjusted to keep the circle frame parallel to a horizontal, fore and aft line (or a line parallel to the direction of travel) at a particular depth of cut of the road grader blade carried by the circle frame. The linkage can be adjusted to keep the plane of the circle frame parallel to the plane cut by the blade as the grader moves along the ground. The linkage also can be made so that it will automatically compensate for changes in depth of cut of the circle frame, or it can be manually adjusted, in one form of the invention, to insure that the circle frame is parallel to a horizontal, fore and aft line at one particular depth of cut of the grader blade. When the circle frame is parallel to a horizontal, fore and aft line, the blade may be rotated about its upright axis without changing the transverse angle of cut of the blade, or slope of cut.

For finishing work in building roads and the like, a particular depth of cut is desired and the transverse angle of grade is controlled. The important point is that if the circle frame is parallel to a horizontal line in fore and aft direction (the direction of movement of the grader), the blade can be rotated about the upright axis of the circle frame without changing the transverse angle of the grade being cut. Without the parallel relationship of the circle frame to a horizontal fore and aft line, one end of the blade will dig in more than the other when the blade is rotated about its upright axis.

The linkage as shown comprises a short link member connected to the normal drawbar ball joint, and also connected in turn to the circle frame drawbar about a substantially transverse, horizontal axis. The angular position between the link and the drawbar is maintained through a lever arrangement and an adjustable retaining device such as a screw or a hydraulic cylinder, so that the angular position of the drawbar and the link can be adjustably fixed. The angular position of the forward end of the drawbar relative to the ball joint, and this in turn determines the fore and aft elevation of the plane of the circle frame in relation to the horizontal.

For precise control, a depth servo mechanism using a parallelogram principle is also shown. The movement of the earth working blade changes the arrangement of a linkage which, in turn, actuates a potentiometer to drive a servo valve, and adjust the hydraulic cylinder or power means until the drawbar returns to a null or level position.

The device is simple to make, and relatively low in cost in install and may be used as a modification kit for existing graders. The position of the link can be automatically adjusted when a hydraulic cylinder is used in response to changes in depth of the grader blade.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of a typical road grader showing a drawbar made according to the present invention installed thereon;

FIG. 2 is a side elevational view of a forward portion of the drawbar of the grader of FIG. 1 showing the linkage used with the present invention;

FIG. 3 is a sectional view taken as on line 33 in FIG. 2;

FIG. 4 is a side elevational view of a portion of the linkage shown removed from the grader for illustrative purposes;

FIG. 5 is a side elevational view of a modified form of the invention showing the unit in a lowered position relative to the other views;

FIG. 6 is a fragmentary side elevation view of a front portion of a road grader having a parallelogram link depth change sensor for control of a linkage made according to the present invention;

FIG. 7 is an enlarged side view of the depth change sensor and linkage of FIG. 6;

FIG. 8 is a side view of the device of FIG. 7 in a second operational position; and

FIG. 9 is a bottom plan view of the device of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A road grader illustrated generally at 10 includes a main frame 11 that is of the usual or preferred design, and the main frame is supported at the forward end with steering wheels 12, and at the rear portion with power drive wheels 13. The operators platform 14 is positioned so that the operator can reach suitable controls 15 for controlling the road grader and the grader blade on the grader. An engine housing 16 houses an engine of usual design for powering the road grader and moving it along a ground surface 17 for use. The road grader as shown includes a steering assembly 18 for steering the steering wheels 12, and power lift devices 19 of the usual design controlled by the controls in the operators platform 14 for raising and lowering a cutting blade assembly 22. The cutting blade assembly 22 is of the usual design as well, and includes a grader blade 23 that engages the ground 17 for making the grader cut, and this grader blade 23 is mounted on suitable supports 24 to a circle frame 25 that is rotatable about an upright axis with respect to a circle frame support 26. The circle frame support 26 is in turn attached to a drawbar 27. This construction is all conventional in road graders, and is not gone into in detail in this specification.

The power lift mechanisms 19 (there is a separate lift mechanism on each side of the grader) in turn drive rotatable shafts 30 of usual design, that are mounted in bearings 31 on the main frame 11, and have control arms 32 mounted thereon. Lift links 33 are attached to the arms 32, and also are attached as at 34 to a cross member 35 on the rear portions of the drawbar. There are lift links on each side of the grader so that a transverse slope can be established for the grader blade. The links raise or lower the sides of the circle frame when the particular shaft 30 and arm 32 for that lift link is rotated. A link 36 also may be provided for moving the circle frame and grader blade 23 laterally from side to side with respect to the main frame if desired. Because the lift links, control shafts 30 and arms 32 are conventional, they are not shown in detail.

The drawbar 27 is modified over a conventional device in order to maintain the fore and aft axis of the circle frame 25, about which the circle frame tilts, parallel to the horizontal regardless of depth of cut of the grader blade 23. It can be seen that by rotating the shaft 30 in a conventional manner, the link 35 will be raised or lowered, and the corresponding side of the circle frame will also be raised or lowered because of the cross member 35. When the controls for the blade are controlled automatically to maintain a preselected slope to the blade, it is highly desirable that the grader blade can be rotated about the upright rotational axis of the circle frame. Any changes of the grader blade 23 about its upright axis in a conventional blade drawbar mounting will result in a different slope of cut of the blade without changing the setting of the circle frame, and consequently where the fore and aft axis of the circle frame is not maintained parallel to the cut left by the grader as the grader moves, automatic operation of the slope control is difficult.

In the present device, a relatively simple linkage arrangement is advanced for insuring that the fore and aft, central axis of the circle frame, which is indicated at 40, will be maintained as a horizontal axis. This also can be stated that the plane of the circle frame is parallel to a fore and aft extending horizontal line. In this particular form of the invention, a coupling link indicated generally at 41 is provided for coupling the forward end of the drawbar 27 to the main frame 11. The main frame 11 has a downwardly depending forward portion 42 that mounts a ball housing 43 for rotatably mounting a spherical ball 44 (see FIG. 3). The use of a ball joint at the forward end of the drawbar is conventional, and the conventional drawbars use ball joints so that the conventional graders have ball joints at the forward ends of the drawbar in order to insure that the drawbar can move up and down or side to side in accordance with the controls from the grader.

In this particular instance, however, the ball 44 is attached to a link 45 that extends rearwardly and is fixed to a block 46A which has a pair of

stub shafts

46,46 extending laterally therefrom. The line 45 is relatively short in length, and the

stub shafts

46,46 are rotatably mounted in

suitable bearings

47,47 positioned in the legs of a bifurcated end portion 48 of the drawbar 27. This bifurcated end portion is formed by a recess 49 defined in the end of the drawbar.

The assembly further includes a lever assembly 51 that is fixedly attached to the block 45A as shown in FIG. 4, and this lever assembly 51 comprises two spaced arms that project upwardly from the link assembly. It can be seen that the link assembly is made by passing the ball joint shaft 45 through the block 45A thereon and attaching the shaft 45 with a suitable nut so that the unit is clamped together as a rigid link.

The angular position of shafts 46 with respect to the bifurcated end of the drawbar 27 is controlled with an adjustable member acting between the lever arms 5] and the drawbar 27. As shown, the lever arms 51 have a rod end 53 attached thereto with a pin. The rod end 53 is connected to an extendable rod of a hydraulic cylinder 54. The base end of the cylinder 54 is attached to a suitable bracket 55 which is fixed to the drawbar 27. The hydraulic cylinder 54 is controlled through a suitable valve from a pressure source, and by extending or retracting the rod 55, the angular position between the link 45 and the drawbar is changed. For example, in position shown in FIG. 1 the link 45 is shown extending downwardly from the drawbar and when the rod 55 is retracted, the lever arms 51 would be moved to a dotted line position as shown in FIG. 2, and the drawbar 27 would lower to its dotted line position shown in FIG. 2 with respect to the ball joint. This means that if the grader blade 23 was making a deep cut, the fore and aft axis 40 of the circle frame can be leveled with respect to a horizontal plane by adjusting the hydraulic cylinder 54 to retract the rod 53 and move the lever arms 51 to the dotted position shown in FIG. 2. The amount of movement would, of course, depend upon the depth of cut of the blade 23.

If desired, the position of the hydraulic cylinder 54 can be automatically controlled by mounting a sensor switch on the cross member 35. The sensor 60 can be a microswitch that senses the angle between the cross member 35 and the line 33, because when the circle frame is raised or lowered by operating the near link 33, and assuming the transverse angle of the blade does not change, the angle between the link and the cross member 35 will change. The sensor 60 could also be used in other locations to sense depth changes. Thus, if the depth sensor 60 controls the valve from the hydraulic cylinder 54, the sensor 60 would cause the cylinder to be actuated to a desired position, depending on whether the blade is raised or lowered. The controlled valve directs fluid under pressure to the cylinder 54 until the sensor 60 reaches a null or preselected point, at which position the drawbar would again be in proper relationship with respect to a horizontal plane so that the fore and aft axis 40 would be parallel to a horizontal plane and the circle frame would be properly positioned. The valve for the cylinder also could be manually'operated and manually adjusted when the blade depth was adjusted.

However, if one particular depth of cut is going to be made, the adjustment member does not have to be automatically operated but can be merely manually operated and adjusted to achieve the desired result at the desired depth of cut. It should be noted that one of the shafts 46 can have an indicator needle 61 attached thereto and this indicator 61 can be used in relation to a depth scale 62 on the drawbar to indicate the blade depth for which the link is set to obtain parallel relationship of the axis 40 to a horizontal plane. This is a visual indicator that could be used with a manual adjustment device if desired.

FIG. 5 illustrates a manual adjustment device that can be used between the drawbar 27 and the lever arms 51. In this particular instance a screw member 65 has a head 66 that is held between the levers 51 with a suitable pin 67, and a pair of nuts 68 are provided on opposite sides of a spherical ball member 70 that is mounted in a bracket 72 that is attached to the drawbar 27. Member 70 is used to provide proper alignment and bracket 72 has a part spherical seat for the member 70. By adjusting the nut 68 properly, the angular position of the link 45 can be changed to raise and lower the front of drawbar 27 a desired amount. In this particular instance, the indicator needle 61 has a very important function because the adjustment takes place manually by adjusting the nuts 68 and the indicator is used to show when the proper adjustment has been made for the depth of cut that is desired to be made with the grader.

Referring to FIGS. 6 through 9, a modified form of the invention is shown with a different type of device for sensing changes in elevation or depth of the circle frame blade. The device of FIGS. 6 through 9 is designed primarily for use with servo valve controls for operating hydraulic cylinders to control the various mechanisms of the grader including the blade depth control and the like, although the system of FIGS. 6 through 9 can be used with the previously described mechanical form of the invention as well.

Referring specifically to FIG. 6, the forward portions of the road grader are shown. The forward portion 42 of the main frame 11 has the ball housing 43 thereon. A grader circle frame drawbar is constructed substantially the same as in the previous form of the invention and is indicated at 75. The drawbar is used for mounting the circle frame in the same manner as previously described, and the circle frame also mounts the grader blade. The circle frame is raised and lowered by hydraulic cylinders, or other conventional raising and lowering mechanisms.

A ball member 76 is mounted in the socket 43, and a stub shaft 77 is mounted onto this ball member. The

stub shaft 77 is constructed just as the shaft 45 is, and to a center block having an upright lever 78 thereon which is used for controlling the angular position between the stub shaft 77 and the drawbar 75. The center block of stub shaft 77 has a pair of outwardly extending shafts 79 thereon which are rotatably mounted in bearing housings 80 that in turn are attached to the forward portion of the drawbar 75 with suitable bolts and coupling members.

A hydraulic cylinder 83 is mounted onto the drawbar 75 with a suitable support member 84, and has an extendable and retractable rod 85 that is connected through a rod end member and pin 86 to the lever 78. The hydraulic cylinder 83 is controlled through an electro-hydraulic servo valve 87, and the hydraulic circuit includes a pump 88 and a suitable control for the servo valve. As shown, a null center potentiometer or voltage divider 89 is suitably connected so that at a neutral position the servo valve is in a neutral position. If the potentiometer moves away from its center or null position the servo valve will operate to move the cylinder to extend or retract, depending on which way the potentiometer moved. Operation of cylinder 83 results in raising or lowering of the forward end of the drawbar 75 so that the circle frame will be leveled in the same manner as previously described.

The servo valve 87 is controlled through the potentiometer 89 from a suitable power source and the potentiometer may be connected through a valve amplifier 82 to the servo valve, the controls are set so that the potentiometer is at a null position when the circle frame is leveled with respect to the ground surface. In order to sense deviations of the circle frame drawbar 75 from its level position, a parallelogram linkage is used. A pivot tube 92 is welded to one of the bearing housings 80, as shown in FIG. 7 (see also FIG. 9 which is the bottom view). This pivot tube 92 in turn rotatably mounts a pin 93 which has a lever arm 93A attached thereto. The lever arm 93A extends underneath the bearing mounting members 80, back toward the centerline of the machine, as shown perhaps best in FIG. 9 A link 94 has a rod end 95 with a spherical bearing therein which is attached in a suitable manner to the outer end of the lever 93A. The link 94 in turn extends forwardly toward the ball socket 43. A spherical seat rod end 96 is attached to the forward end of the link and the rod end 96 in turn is connected to the ball socket 43. The actual axis of pivot of the rod end is selected so that the link 94 forms a parallel link member with the stub shaft 77. The lever 93A in turn has another link 98 attached thereto with suitable rod ends, and the opposite end of the link 98 is connected to an actuator lever 100 adjustably connected to a shaft 101 which is an actuator shaft for changing the setting (moving the wiper) of the potentiometer 89.

If the circle frame at the end of the drawbar 75, which is shown in FIG. I, is raised, for example, this will cause the entire drawbar assembly to pivot about the horizontal pivot axis 102 of the ball 76 at the end of the stub shaft 77. Also, there will be no immediate pivoting of the shafts 79 because the cylinder 83 does not initially move, so the entire drawbar acts like a rigid link across the junction with the stub shaft 77.

Any movement of the drawbar aboutaxis 102 will also cause the link 94 to pivot about its rod ends 95 and 96. The pivoting movement of the rod 94 will result in pulling on the lever 93A because the link 94 does not change in length. This will cause lever 93A to pivot about the axis of shaft 93. Pivoting of the lever 93A pulls on the link 98, which in turn, causes the lever 100 to move and turn the shaft 101. As soon as the potentiometer is moved off center the valve control circuitry for the servo valve 87 is powered and the valve directs fluid under pressure to the cylinder 83 in a proper direction to extend pressure to the cylinder 83 in a proper direction to extend the rod 85 until the parallelogram formed by the stub shaft 77 and the rod 94 returns to its original position. The center distances between the axis 102 and the horizontal pivot axis of rod end 95, and the center distance between the pivot axis of rod end 96, and the pivot axis of shaft 79, return to their original relationship. The movement of the lever 78 by the cylinder 83 restores the parallelogram, thereby moving link 98, arm 100 and shaft 101 toward their original positions until the potentiometer or servo valve control returns to its null position. The action is a continuous following action by cylinder 83 to keep the proper relationship of the link. When the potentiometer is in null position, the circle frame drawbar 75 will be level but may be at a changed height in relation to the ground. This means that the circle frame attached to the drawbar 75 will also be level and the unit can operate as previously described.

If the cylinder 83 is set as shown in FIG. 7, and the circle frame is lowered to increase the depth of cut of the blade, the rear portions of the drawbar will be lowered. The lowering of the rear part of the drawbar and stub shaft 77 about the axis 101 will cause the lever 93A to be moved rearwardly, or in other words, in a direction toward the potentiometer 89 because the link 94 does not collapse. The rod end 95 moves in an are about the pivot axis of rod end 96 while the controller 89 moves on an are about pivot axis 102. Therefore the arm 100 will cause rotation of shaft 101 to energize the solenoid valve 87 so that the cylinder 83 is retracted, retracting rod 85 and pulling lever 78 in a counterclockwise direction as viewed in FIG. 7 at the same time the drawbar is lowering. This will continue to occur until the potentiometer 89 resumes a null position. This will be when the relationship of the stub shaft 77 and link 94 has again returned to their original relationship. For example, this position is one such as that shown in FIG. 8 where the drawbar 75 is at a lower setting than in FIG. 7, with respect to the grader frame, but wherein the potentiometer 89 is back in its null position. The relationship between the pivot axis 102, the pivot of shaft 79, and the pivot axes of the rod ends 95 and 96 is restored to the same relationship as that in FIG. 7. The diagonal distance between the pivot axis 102 and the pivot axis of rod end 95 is the same in both figures.

The potentiometer 89 can be any desired configuration. Suitable potentiometers for electro-hydraulic servo valves are made by Honeywell, Inc., Minneapolis, Minn. The potentiometer may be used in connection with controlling input to a servo valve amplifier as shown, or may be used in a bridge circuit. Details of direct feedback hydraulic servo systems are well known and therefore not shown in detail. The unit makes a closed loop servo control system with the potentiometer and parallel linkage provides the feedback.

The stub shaft and link form parallel link members and the diagonal distance relationship between the corners of these members is restored to a desired relationship when the potentiometer is in its null or center position.

The simple pivoting link pivoting about a horizontal axis substantially transverse to the direction of movement of the grader provides a pivot joint in the drawbar between the circle frame and the ball joint for the drawbar and by controlling the angular relationship between the two portions that come together at this pivot joint. The circle frame can be leveled in fore and aft direction with respect to a horizontal plane so that the grader blade then may be rotated about its upright axis without changing the slope of cut of the blade.

This makes the grader blade easier to control automatically with level or slope sensing devices such as a pendulum sensor or the like.

What is claimed is:

1. In grading machines having an earth working blade, a circle frame member for mounting said blade for rotation about an upright axis, a main frame, and means for connecting said circle frame to said main frame comprising a drawbar member attached at one end thereof to said circle frame, means between said circle frame and said main frame to raise and lower said circle frame and first pivot means attaching the other end of said drawbar member to said main frame, said drawbar member including two drawbar portions, means forming a second pivot connection between said drawbar portions adjacent the first pivot means, and having a pivot axis generally transverse to the direction of movement of the road grader, and means interconnecting the two pivoted drawbar portions to control the angular relationship between the two pivoted drawbar portions to level said circle frame at different depth positions of said circle frame.

2. The combination specified in claim 1 wherein said two drawbar portions comprise a main portion and a link portion, a lever arm fixedly attached to said link portion and extending outwardlytherefrom, and said means to control the angular relationship comprising a hydraulic cylinder positioned between said lever arm and said main portion to control the angular relationship between said link portion and said main portion.

3. The combination specified in claim 1 wherein said means to control the angular relationship comprises mechanical means for adjusting the angular position between said two drawbar portions comprising a screw threaded member attached to a first of said drawbar portions about a second pivot axis, and attached to a second of said drawbar portions through threadably adjustable means.

4. The combination specified in claim 3 wherein the points of attachment of said screw thread member are positioned in a plane spaced from the axis of pivot between said two drawbar portions.

5. The combination specified in claim 2 wherein said link portion comprises a stub shaft member, and the connection between said main frame and said drawbar comprises a ball attached to one end of said link, bearing means to pivotally mount said stub shaft member to the main portion of said drawbar about a substantially transverse axis with respect to the direction of movement of said grader.

6. The combination of claim 5 and said means to control the angular relationship further comprising a servo valve controlling said hydraulic cylinder, and a servo valve controller having an actuating lever, a second link, means mounting a first end of said second link to said main frame, and means mounting a second end of said second link to said drawbar so that said second link and stub shaft link form parallel link members, means to connect said second end of said second link to said actuator whereby movement of said drawbar tends to change the diagonal distance relationship of the pivots of said stub shaft and second link respectively, said controller and servo valve and hydraulic cylinder in direction to tend to retain said relationship by pivoting said stub shaft about transverse axis of mounting the main portion of said drawbar.

7. In a road grader having a main frame, means for supporting said main frame for movement along the earth surface, said main frame having a forward portion, an earth working blade, means to rotatably mount said earth working blade with respect to said main frame including a drawbar connecting said earth working blade to the forward portions of said main frame, said drawbar comprising two portions, a first portion being connected to said main frame and a second portion being connected to said earth working blade, means to pivotally mount said two portions together about an axis substantially transverse to the direction of movement of said main frame, hydraulic cylinder means to control the angular relation of said two portions about said transverse axis with respect to each other and thereby control the height of said second portion with respect to the main frame, one end of said hydraulic cylinder means being attached to a first of said portions, and a second end of said hydraulic cylinder means being attached to a second of said portions, control means on said road grader for said hydraulic cylinder, means on said frame to sense changes of depth of cut of said working earth blade, said means to sense controlling said control means to adjust said hydraulic cylinder means to change the relationship of said two portions as a function of the changes in depth of cut of the earth working blade.

8. The road grader of claim 7 wherein said means to sense comprises a link, means to mount said link on said main frame, at location other than the connection of the drawbar to the main frame, and wherein said control means includes an activatable element, said link being connected to said element.

9. A drawbar leveler for a road grader having a main frame, a drawbar, means comprising a ball joint connection connecting said drawbar to the forward portion of the main frame of said road grader, a grader blade and circle frame, means to connect the drawbar to the grader blade and circle frame at a rear portion of the drawbar, said drawbar comprising two sections between said circle frame and said ball joint including a first section connected to the circle frame and a second section connected to the ball joint, means forming a pivot between said first and second sections about a substantially transverse axis adjacent the forward portion of said drawbar, lever means on one of said sections and a support on the other section, and means to control the angular relationship of the two sections about said pivot comprising an extendable and retractable actuator connected between said lever means and said support respectively, and control means on said road grader responsive to changes in the vertical position of said circle frame to control said actuator to thereby change the angle between said two sections about said pivot and the vertical position of the portion of said first section adjacent said pivot with respect to said ball joint.

10. The combination of claim 9 wherein said control means includes a parallelogram linkage including a first link portion pivoted at its opposite ends on the axes of movement of said second section and a second link pivoted at a first end adjacent said frame and at a second end with respect to said drawbar on means permitting the second link to move parallel to said first link portion during pivoting of said drawbar, said control means further including means to sense changes in position of said second end of said second link relative to said drawbar as the drawbar pivots when the vertical position of said circle frame is changed.

11. The combination of claim 10 wherein said means to control the angular relationship between said drawbar sections comprises a hydraulic cylinder, a servo valve controlling said cylinder, and means to control said servo valve including a movable feedback means sensitive to the position of said second end of said second link to actuate the servo valve in direction to restore a desired relationship between the second end of said second link and said drawbar.

12. In an earth working machine having an earth working blade, a drawbar member, means to connect said earth working blade to said drawbar for rotation about an upright axis, means between said drawbar and said main frame to raise and lower said earth working blade, first pivot means attaching a leading end of said drawbar member to said main frame, said drawbar member including first and second drawbar portions, means forming a second pivot connection between said drawbar portions adjacent the first pivot means, said second pivot connection defining a pivot axis generally transverse to the direction of movement of the earth working machine, means interconnecting the two pivoted drawbar portions to control the angular relationship between the two pivoted drawbar portions to level said drawbar at different depth positions of said earth working blade, and servo control means including a feedback sensor to control the means interconnecting the pivoted drawbar portions to maintain one of said drawbar portions at a reference relationship with respect to the main frame.

13. In an earth working machine having a main frame and an earth working blade, means mounting said blade for rotation about a substantially upright axis for rotational movement in a generally horizontal plane including a drawbar member and having two portions, said means mounting said blade to said main frame having a first pivot connection to said main frame and a second pivot connection between said two portions of said means mounting said blade, means interconnecting said two portions to control the position of said two portions to maintain said blade oriented for rotation substantially in a horizontal plane regardless of changes of depth of cut of said blade, and control means for said means interconnecting said two portions including a servo system having a feedback sensor to sense deviation of said blade from its desired orientation and for operating said means interconnecting said two portions portion to return said blade in its desired orientation.

Claims

2. The combination specified in claim 1 wherein said two drawbar portions comprise a main portion and a link portion, a lever arm fixedly attached to said link portion and extending outwardly therefrom, and said means to control the angular relationship comprising a hydraulic cylinder positioned between said lever arm and said main portion to control the angular relationship between said link portion and said main portion.