Carlson, Ernest C. (Schwetzingen, DT)
Brudnak Jr., Andrew (Oak Lawn, IL)
Yeh, Rudolph E. (Elmhurst, IL)
Sardiga, Ronald F. (Chicago, IL)

05/034227

12/28/1971

05/04/1970

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International Harvester Company (Chicago, IL)

91/511

91/210, 212/286, 212/238, 91/526, 91/404, 91/534, 91/176, 414/694, 60/425

E02F9/02; E02F9/08; F15B11/20; F15B11/00; F15B11/16

91/411,47,59,61,170,397,404 60/52HE,97SE 212/66 214/138 180/79.2B

2528985	Hydraulically actuated swing boom crane	November 1950	Wunsch
2587449	Hydraulic feed for machine tools	February 1952	Ericson
2728327	Single rotation fluid pressure motor	December 1955	Benninghoff et al.
3184980	Swing mechanism for cranes and the like	May 1965	Schell
3395812	Boom swing system	August 1968	Arnold
3430503	BACKHOE SWING MECHANISM	March 1969	McLaughlin
3452882	SWING MECHANISM FOR BACKHOES	July 1969	Noller et al.

Geoghegan, Edgar W.

CROSS-REFERENCES

This is a continuation of application, Ser. No. 794,637, filed 28 Jan. 1969, now abandoned.

We claim

1. An apparatus for converting a rectilinear motion to rotational motion about an axis comprising:

2. An apparatus as defined in claim 1 wherein said sequence valve means comprises:

3. An apparatus as defined in claim 2 in which:

4. An apparatus as defined in claim 2 in which:

5. An apparatus as defined in claim 4 in which said bleeder valve means comprises:

6. An apparatus for converting rectilinear motion to rotational motion about an axis comprising:

7. An apparatus as recited in claim 6 wherein:

8. An apparatus as recited in claim 7 wherein said sequence valve means comprises:

9. An apparatus as defined in claim 7 in which a relief valve means is interposed between said sequence valve means and said hydraulic motors for maintaining a minimum back pressure upon said motors to aid in controlling torque output.

10. An apparatus as defined in claim 7 in which:

11. An apparatus as defined in claim 10 in which said bleeder valve means comprises:

12. An apparatus for converting rectilinear motion to rotational motion about an axis comprising:

13. An apparatus as defined in claim 12 in which:

14. An apparatus as defined in claim 12 in which:

15. An apparatus as defined in claim 14 in which:

16. An apparatus as defined in claim 14 in which:

17. An apparatus as defined in claim 16 in which said flow reducing means comprises:

18. An apparatus for converting rectilinear motion to rotational motion comprising:

19. An apparatus as defined in claim 18 in which said sequence valves include:

20. An apparatus for converting linear motion to rotational motion comprising:

21. An apparatus as recited in claim 20 in which said decelerating means comprises:

22. A swing mechanism comprising:

23. An apparatus as recited in claim 22 in which said exhaust opposing means

24. A swing assembly comprising:

25. An apparatus as recited in claim 24 in which:

26. An apparatus as recited in claim 24 in which:

BACKGROUND OF THE INVENTION

This invention relates to a novel combination of elements so arranged and so designed as to provide pivotal movement of any mechanism about a relatively fixed pivot point. The apparatus will find application in backhoes in which a backhoe boom is swung about a vertical axis or in an articulated vehicle as a steering means to pivot the front and rear section with relation to each other, or finally in any other apparatus in which rotational or swing movement about axis is desired.

Ideally, for maximum swing functioning, the torque developed by the swing structure should be as great as possible, be uniform across the entire movement, and have a relatively high, uniform velocity. At each end of the swing stroke, a cushioning device should be included to reduce to a minimum the impact of the swing unit when it meets a mechanical stop at the end of the movement.

Conventional swing systems utilize two conventionally plumbed cylinders and mechanical linkages that provide the 180° swing movement required. Normally, one cylinder provides the total swing movement in one direction while the other cylinder provides the total movement in the opposite direction. Mechanical linkages or trunnion elements are used to convert the straight line cylinder motion into the circular motion required to swing the unit. External rubber bumpers are used at the end of the stroke to reduce the impact of the unit when the system reaches the end of its rotational movement, and control valve unlatch devices are often used to cut the power at the end of the stroke in an attempt to reduce impact by reducing the torque at this critical time. Merely reducing the torque at this stage, however does not satisfy all conditions since the backhoe masts and swing units are usually quite heavy and due to momentum, should have a positive braking, or cushioning device. Such prior art devices thus do not provide ideal characteristics of torque output, energy absorption, and velocity potentials which are desirable.

SUMMARY OF THE INVENTION

The preferred embodiment of the present invention is a combination of two hydraulic motors operating between a fixed support and a pivotal member and having one or more novel subcombinations employed therewith. These novel units include a sequence valve which senses the position of the swing member and directs hydraulic energy to the motors in such a manner as to obtain more desirable qualities of torque output delivered to the swing member. Secondly, a check and relief valve unit has been designed to further smooth out the variable torque characteristics delivered to the swing member by providing resistance to swing during certain phases of the swing movement and to prevent runaway load and thus check cavitation. A third subcombination involves a bleeder unit which is designed to reduce the system input energy to a minimum and still maintain a desirable velocity with full torque (at system pressure) when the swing unit is near the rotational limit of its swing. This bleeder unit in conjunction with other elements also provides for a smooth deceleration to the rotational velocity when the swing member approaches the end of its rotational movement. A swing bracket member is also used which provides space and construction advantages desirable in a backhoe.

DESCRIPTION OF THE DRAWINGS

The manner in which the objects of the invention is obtained will be made clear by consideration of the following specification and claims when taken in conjunction with the accompanying drawings in which:

FIG. 1 is a side elevational view of the subject matter of this invention incorporated into the stand of a backhoe and operating to pivot the boom;

FIG. 2 is a plan view of the apparatus taken partly in section and disclosing the fluid circuit, the hydraulic motors, and the sequence valves as attached to the support stand for the backhoe;

FIG. 2A is a sectional view of a one-way restrictor employed in a port of the hydraulic motor;

FIG. 3 is a sectional view of the sequence valve taken along a horizontal centerline so as to disclose the components thereof;

FIG. 4 is a view disclosing the hydraulic motors and the sequence valves partially in section and the hydraulic circuit schematically for operating the apparatus. This view discloses the apparatus in stage 1 of its operation;

FIG. 5 is a similar view to FIG. 4 disclosing the apparatus in stage 2 of its operation;

FIG. 6 is a similar view to FIG. 5 disclosing the apparatus in stage 3 of its operation;

FIG. 7 is a similar view to FIG. 6 disclosing the apparatus in stage 4 of its operation;

FIG. 8 is a perspective view of the forward section of the backhoe stand with portions broken away disclosing the mounting of the hydraulic motors and sequence valves;

FIG. 9 is a view disclosing the hydraulic rams and sequence valve operating on a trunnion block; and

FIG. 10 is a plan view disclosing the invention in its association with an articulated vehicle when employed as a steering means.

DETAIL DESCRIPTION

As disclosed in the preferred embodiment of FIGS. 1 and 2 the invention is incorporated in a backhoe B which is mounted on a tractor T in a conventional and well-known manner. The backhoe comprises the support stand S having stabilizer arms A which provides a stabilized platform for the mast N of the backhoe. The mast N supports a dipper stick D which in turn supports a bucket or shovel R and hydraulic motors M are provided to perform the digging operation. Other conventional details of the backhoe are not enumerated unless material to our invention.

According to our invention we prefer to incorporate a specific swing bracket or support 10 between the mast N and the support stand S. This swing and support bracket 10 has a U-shaped cutout portion formed by vertical section 12, horizontal flange sections 11, 11 and flange connections 13, 13 for pivotally connecting the bracket to the support stand. The mast N is then joined to the support bracket in a conventional manner. A shaft 14 is vertically positioned between the flanges 11, 11 for attaching the rods 21, 21', of the hydraulic motors 20, 20' to a common axis (shaft 14). The cylinders 22, 22' (see FIGS. 2 and 8 are then attached by pivotal connection 40, 40' to the support stand S. Consequently, as the hydraulic motors 20, 20' expand and contract, the support bracket 10 is rotated about the pivotal connections 13, 13', the hydraulic motors operating on the swing member through lever arms L ₁ and L ₂ defined by the perpendicular distance from flange connections 13, 13 to the rods 21, 21' as viewed from above.

The circuit which controls the proper expansion and contraction of each of the hydraulic motors 20 and 20' is disclosed in FIG. 2. Inasmuch as these hydraulic motors have similar structure, the right motor and its component parts will be referred to by an integer and the left cylinder and its components will be designated by the same integer with an additional prime mark.

To initially control fluid flow within the circuit of this apparatus a three-position, four-way flow control valve V may be employed. Such a valve is conventional and well known in the art and may additionally include such elements as crossover relief valves and system or circuit relief valves. Directing fluid to this directional control valve V is a conduit 51 and an exhaust conduit 52 which are connected to the conventional tractor hydraulic system (not shown). The valve V then directs fluid alternatively to parallel circuit 55 or 56 and exhausts fluid from the opposite circuit. Parallel circuit 55 has a branch conduit 60 leading to port 100 of sequence valve 200 and a second branch conduit 61 leading to port 101' of sequence valve 200'. Parallel circuit 56 has a branch conduit 62 leading to port 101 of sequence valve 200 and a branch conduit 63 leading to port 100' of sequence valve 200'. Sequence valve 200 is then connected to hydraulic motor 20 by a first conduit 64 which enters the hydraulic cylinder through inlet 104 and is connected to the sequence valve 200 at port 102. A second conduit 65 conducts fluid from port 103 of sequence valve 200 to the upper end of hydraulic motor 20 through port 105. Identical conduits connect sequence valves 200' with hydraulic motor 20' through ports 102', 103', 104' and 105' in the same manner as disclosed for the right hydraulic motor and sequence valve.

The hydraulic motors 20 and 20' are of the structure amply disclosed in U.S. Pat. No. 3,296,942 issued to V. A. Nelson and reference is made to that patent for a more complete disclosure. However, the major features (see FIG. 2) will be herein pointed out. The hydraulic motor 20 comprises a cylinder 22 having operating therein a reciprocating piston 23 which acts upon piston rod 21. The rod 21 passes through the piston 23 and extends therebeyond a distance such that a retaining member 24 may be held thereon by a nut 25. The retaining member 24 is cup shaped, having a disk 30 surrounding the rod 21 and a flange 26 for holding a ring 27 thereon. The ring 27 is a short cylindrical member which is carried by the retaining member 24 in a loose manner such that the ring has limited movement in a direction perpendicular to the rod 21. V-shaped grooves or troughs 28 are then placed in the exterior surface of the ring 27. Assume now that the piston 23 of hydraulic cylinder 22 is being retracted and that fluid is being displaced from the head end of this cylinder. As the ring 27 moves downwardly in juxtaposition with the inlet of the cylinder, the efflux jet moves it into a close fitting relationship with the port 104 and would restrict fluid flow from the head end of the cylinder but for the grooves 28 which meter the hydraulic fluid at a decelerated rate. It will be observed that by reducing flow from the cylinder the grooves 28 of rings 27 will provide a braking action so as to aid in decelerating the movement of piston rod 21 towards the end of its inward stroke. (For later illustration, the chambers of the motors 20, 20' defined by the pistons 23, 23' are designated A, B, C and D as shown in FIGS. 3-6).

Aiding in the metering action of grooves 28 is a one-way restrictor 119 and 119' arranged in conjunction with ports 104 and 104'. (See FIGS. 2 and 2A). The coupling element for port 104 has therein an enlarged chamber 120 which houses a disklike insert 121 whose diameter may be somewhat less than the diameter of the chamber 120. The insert 121 is additionally provided with an aperture 122 through its center, and grooves 123 across its lower face. Thus fluid flowing into the chamber A of motor 20 encounters little resistance since the flow area through aperture 122, around the disk and through grooves 123 is quite large. However, flow out of chamber A causes the insert 121 to seat against surface 125 and the flow is restricted to metering orifice 122. These one-way restrictors 119 and 119' also have an independent function of preventing cavitation as will be later explained.

Interconnected between the motors 20, 20' and the support stand S are sequence valves 200, 200'. These valves are pivotally connected to the support stand at 41, 41' and the hydraulic motors at 42, 42'. The right sequence valve will now be described in detail (FIG. 3) and it comprises basically a housing 201, having a bore 202, passing therethrough. Reciprocable within this bore 202 is a threaded spool 203 which is further connected to an eyebolt 204 mounted on pivotal connection 42. The spool 203 is sealingly reciprocated within valve housing 201 by a collar 205 and O-rings 206 and 207 as shown. A snapring 208 holds the collar 205 within the housing 201.

The spool itself is provided with a bored center section 209 extending from the bottom of the spool upward to the midpoint of the spool. The spool 203 is cross drilled at 210 adjacent the upper end of bored passage 209 and at 211 which is near the midsection of the bored passage 209. Concerning the exterior configuration of the spool 203, a groove 212 is provided near the midsection of the bored passage 209 so as to be concentric about cross drill 211. This groove 212 is further provided with metering notches 213 and 214 near its extremities.

The central bore 202 of the valve housing 201 is also provided with four annular grooves. The first groove 220 is adjacent a passage 230 which leads through a restrictor 231, a check valve 251 to port 101. A second groove 221 also leads to port 101 through a second passage 235. A third groove 222 leads to port 103 through a channel 240 while groove 223 leads directly to ports 100 and 102 of sequence valve 200.

The purpose of this sequence valve is to sense the position of its associated hydraulic motor in its rotational movement about pivot 40, 40' and to direct the flow of input fluid to the proper side or sides of the piston 23 so as to obtain the desired torque output on the support bracket 10. The valve has two basic positions as shown in FIG. 4. In this stage of operation sequence valve 200 is in the fully open position while sequence valve 200' is in the fully closed position. In either of these positions hydraulic fluid may pass freely between ports 100 and 102 and 100' and 102' depending solely upon pressure differentials as grooves 223 and 223' always maintain this channel in an open condition. In the fully opened position port 101 is connected to port 103 by channel 235, groove 221 and channel 240. When sequence valve 200 is in the closed position, ports 100, 101, 102 and 103 may be in communication with each other through groove 212, cross drill 211, the bored passage 209 and the upper cross drill 210. As the spool 203 moves from the fully open position towards the fully closed position cross drill 210 approaches groove 220 and passage 230 and continued downward motion of the spool 203 will place cross drill 210 in juxtaposition with passage 230. The gradual opening and closing of this cross drill 210 from the passage 230 constitutes a variable orifice or variable restrictor means. The variable orifice formed by the cross drill 210 and groove 220 cooperates through passage 230 and fixed resistor 231 of check valve 251 to form the bleeder unit or bleeder means. A unique capability of this bleeder unit will be described in the disclosure relating to the mode of operation.

A check and relief valve means 300 is interposed between port 103 and groove 222 of the valve housing. The check valve 301 comprises a collar 302 fixed within orifice 103 and operating on a spring 303 which urges directional poppet 304 into a position closing off channel or passage 240. The end section of poppet 304 is of a reduced diameter and is further provided with cross drill 306 which permits hydraulic fluid flowing from the upper end of hydraulic motor 20 to pass through a passage 341 to relief valve 310. Relief valve 310 comprises a threaded bolt 311 which serves as a seat for spring 313 which in turn urges valve 314 towards its seated position. The valve seat 315 is cup shaped in form and has an orifice 316 through its bottom portion. A cylindrical guide element 320 is interposed between the spring and the valve ball and acts as a guide in urging the valve towards its seat. A passageway 317 conducts fluid from the relief valve to channel 240.

As described above, the apparatus has been incorporated in a backhoe with the piston rods operating on a common pivot point. FIG. 9 discloses the subject matter of this invention operating on a trunnion block T in which the piston rods 21, 21' are transversely spaced for obtaining the rotational movement with respect to support stand S. In this instance, the backhoe would be attached to the trunnion block. This invention may easily be adapted to operating in such manner although minor modifications and the dimensions of the sequence valves may have to be recalculated and modified somewhat with reference to simple geometry.

FIG. 10 discloses the utilization of the subject matter of this invention in an articulated vehicle 400. The vehicle 400 may have two frame members 401 and 402 pivotable about a common axis 403. The hydraulic motors are then interconnected between frame members 402 and 401 by appropriate pin connections 420, 420', 421 and 421'. The hydraulic system of the articulated vehicle may be utilized to provide power for the subject matter of our invention and conventional flow control valves may be used therewith to control the action of the hydraulic motors 20, 20'.

Before describing the operation of the preferred embodiment, certain characteristics due to the geometry of this preferred apparatus should be noted. First, each motor operates on the swing mount 10 through a lever arm L ₁ or L ₂ which are continually changing in dimension. Considering FIGS. 4-7 which depict four stages of operation, it will be observed that in stage 1 (-3° -60° of rotation) L ₁ has its maximum dimension, while in stage 2, (60° -120° of rotation) neither L ₁ nor L ₂ is maximized and in stage 3 (120° -168° of rotation) L ₂ has its maximum dimension. Stage 4 represents the functioning of the bleeder means during the last few degrees of rotation. Thus if the rotational force during stage 1 is provided by motor 20, while both motors provide such in stage 2 and motor 20' provides torque in stages 3 and 4 the torque output curve of the system will be sinusoidal and the velocity curve will also be sinusoidal but directly out of phase. The sequence valves, 200 and 200' will direct fluid such that the appropriate motor provides the torque as described, and by employing one or more of applicants' other teachings, the magnitude of these sine curves will be maintained within most acceptable limits.

Having now described the structural features of our unique combination reference will now be had to FIGS. 4 through 8 for discussion of the mode of operation of the system.

MODE OF OPERATION

Assume that the operator of the backhoe is mounted on the tractor T and desires to swing the mast N of the backhoe from the right (a position which may be designated as -3° ) to the left (a position which will be designated as 183° ). The operator merely shifts the spool of the four-way, three-position directional control valve to the position indicated in FIG. 2 thus directing supply fluid from the tractor hydraulic system to parallel circuit 55 and exhausting fluid from parallel circuit 56.

STAGE 1, FIGURE 4

Hydraulic fluid is then directed through branch conduits 60 and 61 to ports 100 and 101'. The fluid under pressure is then directed through the valve housing 201, groove 223 and out port 102 through conduit 64 to port 104 and acts against the rear face of piston 23, thus driving the rod 21 forward. The hydraulic fluid in conduit 61' enters port 101' of sequence valve 200' and is blocked at that point by check valve 251' and spool 203' closing the passage 235' since sequence valve 200' is in its fully closed position. In this stage both rods 21 and 21' must extend to pivot the support bracket about its pivot point which is flange connection 13--13 (See FIG. 1). As rod 21' extends fluid must be drawn into chamber C so as to fill a void. Such fluid is drawn through port 102' to which fluid is supplied conjointly from conduits 63 and 65' as a fluid passage created by groove 212' of spool 203' joins the three conduits together by reason of the positioning of spool 203'. It should also be observed that chambers B and D are expelling hydraulic fluid and such fluid is directed to the appropriate sequence valve. Upon reaching the check valve 301 or 301' the fluid is directed upward against a relief valve 310 or 310'. These relief valves provide a predetermined pressure in chambers B and D and thus act to suppress excessive torque which might otherwise be delivered to the support bracket 10. Such is necessary since lever arm L ₁ is at its maximum dimension during this stage. Thus assuming that the system is designed to operate at 2,000 p.s.i. it will be observed that this pressure will exist in chamber A. Further assuming that the relief valves 310 and 310' are designed to open at 400 p.s.i. then chambers B and D will develop the resistance pressure of 400 p.s.i. Thus the relief valves 310 and 310' are effective to smooth out the torque output in this stage. The direction of fluid flow and the pressures in the system will maintain the stated condition until motor 20' is centered over pivot 13 and the support bracket traverses through approximately one-third of its maximum swing or 60° .

STAGE 2, FIGURE 5

As the swing mast approaches 60° hydraulic motor 20' is rotating counterclockwise about pivot point 40' so as to gradually open sequence valve 200'. It will be observed that the lever arm L ₁ is continually decreasing in its dimension and since hydraulic motor 20 alone is delivering all torque to the system during stage 1 such is being reduced as the swing bracket 10 rotates. Similarly, the angular velocity is increasing. At approximately 60° sequence valve 200' is designed to gradually begin opening so as to supply fluid to chamber D of motor 20', and additional torque is obtained through lever arm L ₂ . Consequently fluid under pressure is delivered to chamber D from conduit 61' through port 101', passage 235' and around the spool 203' and into conduit 65'. The fluid in chamber C is now being directed to the sump through the one-way restrictor 119', port 104', conduit 64', and around the spool 203'. Inasmuch as the torque begins to increase at 60° ; the angular velocity of the swing mount 10 must decrease, and the one-way valve 119 will cause the fluid in chamber C to resist any tendency of the boom structure to run away, thus preventing cavitation. Also check and relief valve 310 which resist flow from chamber B provides additional resistance to prevent cavitation.

STAGE 3, FIGURE 6

The apparatus continues its swing movements having the flow characteristics described until hydraulic motor 20 centers above pivot 13 and the support bracket 10 and mast N of the backhoe reach a rotational position of approximately 120° (see FIG. 6). At this point piston rod 21 has reached its maximum extension and must reverse its direction while piston rod 21' continues to retract. It should also be observed that the lever arm L ₂ is now approaching its maximum dimension while the lever arm L ₁ passes through a zero dimension. Consequently all torque will now be produced by hydraulic motor 20' while hydraulic motor 20 must now act to reduce the torque provided by the increasing dimension of lever arm L ₂ of hydraulic motor 20'. In reversing the direction of flow within chambers A and B of motor 20, spool 203 is moving to its closed position due to the continued counterclockwise rotation of motor 20 about pivot 40. This closing movement of spool 203 will operate to reverse the direction of flow in conduits 64 and 65. This reversal of flow will now be described. As previously noted system fluid is being produced through conduit 60 to port 100 of sequence valve 200. Upon entering the sequence valve, system pressure will be directed both to chambers A and B via conduits 64 and 65 since the groove 212 of the spool 203 joins conduits 60, 64, and 65. Realizing that system pressure now exists in both chambers A and B the piston rod 21 will be subject to a net extending force. However, since the lever arm L ₁ has a lesser dimension than arm L ₂ , and since the extending force of motor 20 is thus less than the retracting force of motor 20' the hydraulic motor 20' will be effective to cause a retraction of piston rod 21 and flow to chambers B and A will be reversed. This net resultant extending force existing with reference to piston rod 21 will be effective to smooth out torque output produced by motor 20'.

It should also be noted that just prior to the reversal of flow in motor 20, the torque output delivered by both motors was decreasing while velocity was increasing. Now, since torque will again begin to increase, velocity must decrease, and the one-way restrictors 119 and 119' will act to prevent cavitation.

STAGE 4, FIGURE 7

As the device approaches 183° , deceleration of the system must be effected. In this position the direction of fluid flow is the same as that disclosed in FIG. 6. Further, chambers A, B, and D are still subject to system pressure with chamber C being directed to sump through one-way restrictor 119' in port 104'. In order to decelerate the boom structure, the energy load which must be absorbed is the kinetic energy of the swinging mass as well as input energy of the supply fluid. The pressure in chambers A and C initially represent resistance to torque generated by the supply fluid since displacement of fluid from these chambers is opposed by the one-way resistors 119 and 119' and chamber A is exposed to system pressure. As the cushion ring 27' moves over port 104', it is drawn toward that port by the efflux jet, and fluid can now be displaced only through the metering grooves 28 with the result that pressure rises much higher than system pressure which is limited by the system relief valve. Thus, a negative torque is generated by motor 22' and deceleration takes place. The kinetic energy is primarily absorbed by the negative torque developed by chamber C, through the resisting force of motor 20 and the one-way restriction 119. However, the rise in pressure in chamber C will also cause system pressure to increase, and in order to minimize any pressure surge in the supply line, the bleeder means 250 should preferably begin to open and initiate deceleration prior to any deceleration caused by the cushion ring 27'.

In addition to the functions of minimizing the pressure surge and initiating deceleration, the bleeder unit is most effective in reducing the input energy, thus reducing the quantity of total energy required to be absorbed by the cushioning action within chamber C. Consequently, as deceleration is initiated, the spool 203 of sequence valve 200 is moving towards its fully closed position and all ports of valve 200 will be interconnected. As cross drill 210 approaches conduit 230, the input energy is increasingly exhausted through conduit 62 to sump. However the variable orifice should preferably have such dimensions as will permit the input energy to be increasingly diminished but yet maintain sufficient energy in the system to provide an acceptable velocity potential for continued swing of the backhoe even though it has been stopped. For further clarity and by way of example only, one might assume that the source of fluid energy will supply 9 g.p.m. at a system pressure of 2,000 p.s.i. Further, the variable orifice comprising cross drill 210 approaching conduit 230 may begin to open at 168° of swing movement, and deceleration resulting from cushion ring 27' may occur at 177° . Finally, if the bleeder means 250 bleeds no flow at 168° and just less than full flow at 183° at system pressure the following observations may be made:

At 169° , deceleration begins and input flow will be increasingly exhausted to the sump. As the unit approaches 177° , chamber C will create negative torque so as to absorb the larger portion of the KE, and the supply line pressure will increase, any pressure surge being minimized by bleeder 250. Such briefly describes deceleration, however, if the operator stops the swing movement at 179° and then desires to continue rotational movement to 183° , the bleeder 250, being properly proportional permits such movement. Thus if at 179° , the variable orifice will bleed off only 6 g.p.m. at system pressure, a maximum velocity potential of 3 g.p.m. at system pressure will be available to develop torque and continue rotation. This velocity potential may also be referred to as the "pep" within the system at the extreme limits of rotational movement. In other words the operator of the backhoe is able to obtain good deceleration characteristics and excellent response to continued rotational movement after bringing the support bracket 10 to zero angular velocity in the vicinity of 168° to 183° .

Thus it should be observed that the bleeder unit performs 4 unique functions in that it:

1. Increases the efficiency of cushioning the moving mass at the end of swing by reducing the input energy from the supply line,

or stated in another manner, it increases the net capacity of energy absorption, or finally it improves the swing time by permitting a given swing mass to be stopped in shorter time period.

2. Maintains a full torque (but at a relatively lower angular velocity potential) during deceleration such that the swing can be started from standing still with full torque (at system pressure) in the deceleration range.

3. Reduces a surge pressure in the supply line at the start of cushioning (at the moment when cushion ring is engaged) this surge pressure in supply line being damaging to the pump and the other related components.

4. Reduces the amount of heat generated during cushioning.

It should also be appreciated that while the bleeder means herein depicted comprises a variable orifice in series with a fixed orifice, reference may be made to an application entitled BLEEDER VALVE, Ser. No. 843,529 filed 22 July, 1969, and assigned to the same assignee for a full disclosure of structural alternatives. The applicants also clearly consider flow sensitive devices as substitutes therefor. For example a spool valve operative upon a certain pressure differential might be interposed between the sequence valve and the hydraulic motors with the pressure differential being measured across a fixed orifice. Thus upon a preset flow through the orifice into the actuating motor, a pressure differential will act upon the spool biased by a spring to shift same to a bleed position so as to remove flow from the input conduit.

With specific reference to FIGS. 4 through 8 it is clear that applicants have now devised an apparatus which will permit two hydraulic cylinders to act upon a common pivot point so as to convert rectilinear movement to rotational movement. Applicants' device is further capable of effecting a swing movement of any pivotal member and of maintaining substantially constant torque output. Further the velocity throughout the rotational movement is similarly maintained within satisfactory ranges. Finally, as to the extreme limits of the swing, applicants have disclosed a unique structure which permits a maximum velocity potential at the extreme rotational limits. Applicants' device is also most effective in minimizing the shock in stopping angular velocity of a mass having very large inertia forces. These functions have been accomplished through the employment of novel subcombinations which in the unique combination disclosed finds great application to many uses.

As this invention may be embodied in several forms without departing from the spirit or essential characteristics thereof the present embodiment is therefore illustrative and not restrictive and since the scope of the invention is defined by the appended claims all changes that fall within the metes and bounds of the claims or that form their functional as well as conjointly cooperative equivalents are therefore intended to be embraced by those claims.