Description

Volume Compensation For Hydraulic Circuits

Technical Field

The invention relates to hydraulic circuits which have compensation for volume changes due to tem¬ perature variations. More particularly, the invention relates to closed hydraulic circuits, such as master slave cylinder circuits, which provide a control valve for volume compensation due to temperature variations.

Background Art

In the use of a hydraulic circuit, particu¬ larly a closed hydraulic circuit, it is desirable to provide apparatus to compensate for volume changes owing to temperature variations in the circuit. This is particularly true where the hydraulic circuit is of the closed type such as is found in master slave cylinder control circuits. In such cases, the changes in temperature cause volume changes in the working fluid in the circuit which can disrupt the synchroni- zation between the slave and master cylinders. The change in synchronization will cause variations in control movements between the two cylinders, thus varying the movement between the control input to the master cylinder and the movement of the work element controlled by output of the slave cylinder. Previously, in some circuits an additional synchronizing position has been provided in the master cylinder controls. The synchronizing position can be engaged by the operator to compensate for any temperature changes which result in volumetric changes in the system. Thus movement of the controls by the operator will open a valve to either vent fluid or permit entry of fluid

into the system to compensate for any volumetric changes. This system, however, results in a waste of time and labor owing to the fact that the operator must monitor the system and periodically make adjust- ents. Other systems have provided free-floating cylinders or pistons in the master cylinder to compen¬ sate for volumetric expansion and contraction. When loads are applied, automatic locking devices make the free-floating elements immovable in order to carry the load being applied in the cylinder. This system requires additional specialized components and may not be desirable for certain applications.

U.S. Patent 3,766,944 which issued to Distler on October 23, 1973, discloses one example of a servo or flow regulatory valve controlled by a master or pilot valve. Pressurizing one pilot member of the pilot valve actuates the flow regulatory valve in one direction of displacement with the other pilot member and return line remaining open to the tank. Other circuits which are representative of master and servo valve controls are shown in the U.S. Patents described below. U.S. Patent 4,085,920 which issued to Waudoit on April 25, 1978, discloses a fluid operated main control valve and an adjustable servo valve for controlling the main valve. Fluid passes from the servo valve to the main control valve for controlling the operation of an associated hydraulic cylinder or the like. U.S. Patent 3,857,404 which issued to Johnson on December 31, 1974, discloses a lock valve assembly for controlling a hydraulic cylinder. The lock valve meters fluid flow from the cylinder so that initial movement of the cylinder is gradual and precise adjustments can be made in the operation of, for example, an implement associated with the cylinder. U.S. Patents 3,304,953 which

issued to Wickline on February 21, 1967, and 3,340,897 which issued to Nevulis on September 12, 1967, also disclose master and servo circuits.

In closed hydraulic circuits, such as are typically represented by master-slave cylinder circuits, volume compensation for temperature changes is impor¬ tant due to the fact that synchronization between the master and slave cylinders is desirably maintained as closely as possible. Proper synchronization results in closely coupled operation between the input provided the main or master cylinder and the output which the slave cylinder provides for controlling a work element such as a control valve operating a hydraulic cylinder. In the master-slave circuit, for example, the master and slave cylinders are generally identical and are connected by two fluid lines. Input by way of a control handle or the like moves a shaft in the master cylinder to build up pressure and send a fluid signal through one of the lines to the slave cylinder. The fluid signal causes a corresponding and synchronized movement in the slave cylinder which provides an output into the control valve for operation of the associated hydraulic cylinder. The other of the hydraulic lines connecting the slave and master cylinders is used as a return line to the master cylinder for displaced fluid from the other side of a moving piston in the slave cylinder which controls the output signal in response to the fluid signal.

If temperature changes occur after the master and slave cylinders are synchronized, volume 'changes in the..circuit will cause a loss of synchronization between the slave and master cylinders. Where this happens, the slave and master cylinders will lose their preset corresponding movements and movement of

the work element will not correspond consistently to the same input at the master cylinder. This is best seen with reference to the starting or zero point of the master cylinder. At the starting point, a piston in the cylinder is generally centered and resulting movement of the control handle in a certain direction moves the piston to force fluid through one of the fluid pathways to the slave cylinder. This results in a corresponding movement of the slave cylinder piston for directing the output on the slave cylinder shaft. Corresponding fluid on the other side of the piston of the slave cylinder is forced back into the master cylinder to complete the closed circuit. It will be readily seen, therefore, that any temperature change in the master-slave cylinder circuit can cause a volumetric change in fluid which will change the synchronized relationship, particularly with respect to the starting point of the master cylinder piston. Thus, for example, after use the piston of the master cylinder will return to a different starting point which changes the synchronized movement of the slave and master cylinders as originally set.

Further, in certain applications, such as, for example, an articulated vehicle, the master and slave cylinders are commonly spaced at great distances one from the other. This requires different lengths of hose to stretch between the master and slave cylinders and it also requires flexible hose to cross the articulated joint of the work vehicle. In such instances, it is desirable to reduce the number of parts in the hydraulic circuit and to provide apparatus of convenient size for placing in particular locations of the vehicle. This is important to protect the circuitry from the environment of the work vehicle.

Therefore, it is desirable in a hydraulic circuit, such as represented by the master-slave cylinder closed hydraulic circuit, to provide means for compensating for volumetric change in the circuit owing to temperature variations. It is also desirable to provide means which can be readily used on existing hydraulic circuits and be simply and easily serviced.

Disclosure of Invention

In one aspect of the present invention, a hydraulic circuit has a tank, first and second fluid pathways. Said first and second fluid pathways extend between and are associated with first means for receiving an input signal and passing a fluid signal through one of said fluid pathways in response to said input signal and second means for receiving said fluid signal and automatically delivering an output signal corresponding to said input signal in response to the fluid signal. Third means is provided for automatically positioning both of the first and second fluid pathways in fluid communication with the tank in response to the fluid pathways being free from said fluid signal. Said third means also automatically positions the other of said fluid pathways in fluid communication with the tank in response to passing said fluid signal through one of the fluid pathways.

For example, the first and second means can be a master and slave cylinder, respectively. The third means, such as a control valve, automatically, controllably provides fluid volume compensation in the fluid pathways not pressurized for transmitting a fluid signal to substantially overcome problems associated with temperature variations in the circuit.

Brief Description of Drawings

Figure 1 is a diagrammatic view showing the location of the present invention within a typical environment represented by a master-slave hydraulic circuit used to control a work element on a work vehicle;

Figure 2 is a diagrammatic, cross sectional view showing one embodiment of the present invention; and Figure 3 is a diagrammatic, cross sectional view showing another embodiment of the present invention.

Best Mode for Carrying Out the Invention

Referring to Figure 1, a work vehicle 10 has a frame 12 and a work element 14 movably connected to said frame. A hydraulic cylinder 16 having first and second ends 18,20 is pivotally connected at the first end to the frame and at the second end to linkage controlling the work element. The work element is shown as the bucket of the work vehicle. Said work vehicle also has a control valve 21 and first and second work fluid pathways 22,24 positioned in fluid communication with said first and second ends of the hydraulic cylinder, respectively. Said work fluid pathways are controllably positionable in fluid communication with a pressurized fluid source 26 and a tank 28 of the work vehicle in response to moving a valve spool 30 in said control valve. Thus, controllably moving the valve spool in the control valve directs fluid to one of the ends of the hydraulic cylinder to position the bucket as desired by the operator.

The work vehicle 10 also has a hydraulic circuit 32 associated with the control valve and hydraulic cylinder for controllably operating said

hydraulic cylinder and positioning said work element. The hydraulic circuit includes first and second means 34,36 and first and second fluid pathways 38,40, shown, for example, as hydraulic lines. The work fluid pathways extend between and are associated with said first and second means. The first means, shown, for example, as a master cylinder 42, is provided for receiving an input signal and controllably passing a predetermined fluid signal through one of said fluid pathways in response to said input signal. The second means, shown, for example, as a slave cylinder 44, is provided for receiving said fluid signal in one of the fluid pathways and automatically controllably delivering an output signal corresponding to said input signal in response to the fluid signal. Said slave and master cylinders are shown of identical construction, but it should be understood that said cylinders can be of different configurations and further that said first and second means can be of other configurations other than slave and master cylinders, as is known in the art.

Control of the control valve 21 is accom¬ plished by providing the input signal to the master cylinder 42 which results in a subsequent output signal from the slave cylinder 44. The input signal is provided to the master cylinder by a control handle 46 connected to a rod 48 of the master cylinder. Said control handle can be manually operated to position the bucket 14 at a desired location as will be hereinafter more fully described. Movement of the control handle and operation of the master cylinder 42 results in movement of a similar rod 50 of the slave cylinder which is connected to the valve spool 30 of the control valve. Movement of the rod of the . slave cylinder delivers the output signal to the

control valve which determines the position of said valve and the flow of work fluid through the work ^■ fluid pathways 22,24 to the hydraulic cylinder 16. Construction of the master cylinder will now be provided in detail. For purposes of this disclosure, as above mentioned, the slave cylinder is identical to said master cylinder and any descrip¬ tion of the master cylinder will equally apply to the slave cylinder. Comparative slave cylinder elements relative to the master cylinder are given the same reference numerals, but with prime notations. The master cylinder has a piston 52 positioned on said rod 48 and in a chamber 54 of said cylinder. The chamber 54 is defined generally by a housing 56 of the master cylinder which is supported by bearings 58 about the rod 48 of the master cylinder. Said chamber is further divided into first and second chamber portions 60,62. Said first chamber portion is at the rod end of the master cylinder and is defined by the housing diaphragm elements 64,66.

Said second chamber portion is defined by the housing and a diaphragm element 68. The master cylinder also has first and second fluid ports 70,72 which communi¬ cate with the first and second chamber portions, respectively. The first and second fluid pathways 38,40 extend from the first and second fluid ports 70,72 of the master cylinder to the related, comparable ports 70',72' of the slave cylinder.

As is known in the art, the master and slave cylinders form a closed hydraulic circuit which is initially synchronized and filled with fluid before operation thereof. Synchronization is accom¬ plished by establishing a zero or starting point in the master cylinder and a comparable zero or starting point in the slave cylinder. Thus, the position of

the control handle 46 is established relative to the desired direction of motion of the work element and position of hydraulic valve 21 and any movements of the control handle provide comparable, synchronized move- ent of the hydraulic valve.

Third means 74 is provided for automatically, controllably positioning both of said first and second fluid pathways 38,40 in fluid communication with the tank 28 in response to said fluid pathways being free from said fluid signal. During operation of the hydraulic circuit 32, said third means automatically, controllably blocks the one of said fluid pathways having the fluid signal from fluid communication with the tank and automatically, controllably positions the other one of said fluid pathways in fluid communication with the tank 28 in response to passing the fluid signal through one of the fluid pathways 38,40. As was above noted, the fluid signal is provided by movement of the control handle 46 which causes a fluid pressure rise in the master cylinder and through pne of the fluid pathways to signal the slave cylinder 44.

Referring particularly to Figs. 2 and 3, the third means 74 is shown as a control valve 76 which is in fluid communication with the first and second fluid pathways 38,40. Third and fourth fluid pathways 84,86 establish fluid communication of the control valve and the tank 28. Said third and fourth fluid pathways are in fluid communication with the control valve 76 through first and second ports 88,90, respectively, of said control valve. The control valve is shown in fluid communication with said first and second fluid pathways through fifth and sixth fluid pathways 91,92 which are positioned in fluid communication with the control valve through third

and fourth ports 94,96, respectively.

The control valve 76 has flow control means 98 for automatically, controllably positioning the first and third fluid pathways 38,84 in fluid communi- cation with each other and blocking the second and fourth fluid pathways 40,86 from fluid communication with each other in response to passing the fluid signal in the second fluid pathway 40. Said flow ^* control means also automatically, controllably posi- tions the second and fourth fluid pathways 40,86 in fluid communication one with the other and blocks fluid communication between the first and third fluid pathways 38,84 in response to passing the fluid signal in the first fluid pathway 38. The flow control means as shown also automatically, controllably posi¬ tions the first and second fluid pathways 38,40 in fluid communication with the third and fourth fluid pathways 84,86, respectively, in response to the first and second fluid pathways being free from the fluid signal. As is later discussed, this establishes volume compensation at the zero or starting point for the master and slave cylinders 42,44.

The flow control means 98 includes first and second check valves 100,102 each of which have a chamber 104,106 and a ball 108,110 seatable against a seat 112,114 of said respective check valve. Said flow control means also has a piston assembly 116 having a piston 117 which is connected to a rod 118 extending into the chambers 104,106 of the check valves. The balls are shown freely positioned in the respective chambers, but they can also be con¬ nected to the ends of the rod. In the embodiment of Fig. 3, said piston 117 has first and second portions 117 ' ,117" connected to respective portions 1.18' ,118" of the rod 118. Said piston assembly is

positioned in a chamber 120 of the control valve and is centered at a neutral position 122, as is shown, by first and second wave springs 122,124 positioned on opposite sides 126,128, respectively, of the piston 117. Diaphragms 129 further divide the chamber 120 into work portions as hereinafter discussed.

The control valve 76 includes seventh and eighth fluid pathways 130,132 in fluid communication with the chamber 120 and with the first and second fluid pathways 38,40 through the third and fourth fluid pathways 84,86 respectively.

In the embodiment of Fig. 2, said seventh and eighth fluid pathways 130,132 are shown as separate passageways in the control valve 76 extending from the ports 94,96, respectively, to first and second work portions 134,136, respectively, defined by the diaphragms 129 in the chamber 120 and positioned on respective opposite sides 126,128 of the piston. In the embodiment of Fig. 3, said ^' seventh and eighth fluid pathways are shown as passageways in said control valve which extend from said ports 94,96, respectively, to a common chamber 134 in which is positioned a shuttle check valve 136. Said shuttle check valve directs fluid to a single work portion 128 of the chamber 120 regardless of which of the fluid pathways 38,40 is pressurized. However, said check valve only allows communication of both fluid pathways 38,40 with said chamber work portion 138 when the piston 52 of the master cylinder is in a zero or starting position and said first and second fluid pathways 38,40 are free from the fluid signal.

As is seen from the drawings, the first and third fluid pathways 38,84 and the second and fourth fluid pathways 40,86 are positionable in fluid communication with each other through the related one

of the chambers 104,106 of the first and second check valves 100,102, respectively. The piston 117 is movable to locations sufficient for seating the related one of the balls 108,110 of the first and second check valves 100,102 in response to passing the fluid signal in said first and second fluid pathways 38,40 respectively.

It should be understood that the control valves can be of other configurations as is known in the art without departing from the inventions.

Industrial Applicability

In the operation of the hydraulic circuit 32, a fluid signal is initiated by movement of the control handle 46 to displace the piston 52 from the initially established starting point and pressurize one of the first and second chambers 60,62 of the master cylinder 42. This causes a fluid pressure rise in one of the chamber portions 60,62 and through the related one of the first and second fluid pathways 38,40. This fluid pressure rise acts as the fluid signal which enters the slave cylinder and causes a corresponding displacement of the piston 52' of said slave cylinder. Movement of said piston 52' causes movement of the rod 50 of the slave cylinder to provide an output signal resulting in movement . of the valve spool 30 of the control valve 21 to actuate the hydraulic cylinder.

For example, initially, when the piston 52 of the master cylinder is at the zero or starting position in the chamber 54 of said master cylinder there is no pressure rise or fluid signal in the hydraulic circuit 32. Thus, the first and second fluid pathways 38,40 are free from a fluid signal and the balls 108,110 of the check valves 100,102 are

unseated in their respective chambers 104,106. This establishes communication of the first and second fluid pathways 38,40 with the tank 28 through the fifth and sixth fluid pathways 91,92 and the control valve 76. In other words, fluid is free to pass from the first fluid pathway, for example, through the fifth fluid pathway and into the port 94 of the control valve 76. From said port, the fluid passes past the ball 100 of the first check valve 100, into a passageway 140 in the control valve and then to the port 88. From said port the fluid passes into the third pathway 84 into the tank 28. Similarly, fluid communicates with the tank from the second fluid pathway 40. At this neutral position, therefore, fluid in both the first and second fluid pathways 38,40 is in communication with the tank and any temperature variations in the system which cause volume changes in the work fluid of the hydraulic circuit 32 will not effect the zero or starting point of the pistons 52,52* in the master and slave cylinders 42,44. This will be evident in that a change in volume which changes fluid pressure will be sub¬ stantially, equally compensated on both sides of the pistons 52,52' of said cylinders. When a fluid signal is created in the hydraulic circuit 32 by movement of the control handle 46, the resultant fluid pressure rise estab¬ lished by movement of the piston 52 in the chamber 54 of the master cylinder 42 causes a similar rise through one of the first and second fluid pathways 38,40 to the slave cylinder. For example, if the control handle is moved to the right, as is shown in dotted outline in Fig. 1, a fluid pressure rise occurs in the first fluid pathway 38. This tends to result in a fluid pressure rise in the fifth fluid

pathway 91 through the fluid pathway 130 to the chamber 120 of the piston assembly 122. In the embodiment of Fig. 2, the pressure rise causes the piston to be displaced to the left as viewed on the drawing owing to fluid pressure acting on the piston in the first work portion 134 of the chamber 120. In the embodi¬ ment of Fig. 3, fluid pressure acts on the piston in the work portion 138 to displace said piston. Dis¬ placement of the piston forcibly moves the rod 118 against the ball 108 which results in seating of the ball on the seat 112 of the first check valve 100. Fluid flow is thereby blocked from the first fluid pathway 38 through the check valve 100 to- the third pathway 84 and into the tank 28. A pressure rise or fluid signal can then be established in said first fluid pathway to move the piston 52' in the slave cylinder 44 for controlling operation of the hydraulic cylinder 16. The ball 110 in the second check valve 102 remains unseated or, in some instances, will be drawn from the seat 114 of said check valve to main¬ tain or establish communication between the second fluid pathway 40 through the sixth fluid pathway 92 into the tank 28. This side of the hydraulic circuit 32 is thus open to the tank and any volume changes due to temperature variations will be automatically compensated on both of the pistons 52,52' of the master and slave cylinders 42,44. Therefore, syn¬ chronization of the slave and master cylinders will be automatically maintained during operation of the hydraulic circuit 32 by placing that portion of the hydraulic circuit 32 which is not being used to pass the fluid signal into fluid communication with the tank thereby allowing dilution of the fluid within said portion within the larger volume of fluid in the tank.

OMPI

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The hydraulic circuit 32 thus automatically, controllably maintains synchronization of the slave and master cylinders when temperature variations in the circuit cause volume changes of the working fluid therein. In applications where the temperature changes may be significant, such as on a work vehicle, such automatic and controllable volume compensation substantially overcomes any problems associated with temperature variations and also frees the operator from monitoring the systems and allows him to attend to other duties.

Other aspects, objects, and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.