US3150568A - Hydraulic circuit with lockout valve in common return line - Google Patents

Description

Sept. 29, 1964 J. A. JUNCK ETAL HYDRAULIC CIRCUIT WITH LOCKOUT VALVE IN COMMON RETURN LINE Filed Oct. 1, 1963 INVENTOR. JOHN A. JUNCK' BY ROGER A. R\C.E

FRANK H. wmmzns g 1 X A TORNEIYS United States Patent 3,150,568 HYDRAULIC CIRCUIT WITH LOCKOUT VALVE IN COMMON RETURN LINE John A. Junck, Roger A. Rice, and Frank H. Winters, Joliet, Ill., assignors to Caterpillar Tractor Co., Peoria, 111., a corporation of California Filed Oct. 1, 1963, Ser. No. 313,017 3 Claims. (Cl. 91-414) This invention relates to improvements in hydraulic circuits of the kind in which two or more hydraulic motors or jacks are actuated by fluid under pressure from a single source and particularly to the type of circuit which has come to be known as a common rail circuit because while separate conduits direct fluid to actuate the several jacks in one direction, a single or common line serves to return fluid to the source as well as to direct fluid to any of the several jacks to actuate it in the opposite direction.

Earthmoving scrapers now manufactured and sold by our assignee are provided with common rail circuits for actuating double acting hydraulic jacks which adjust the bowl, the apron and the ejector of the scraper. Pressure of return fluid through the common line resulting from operation of one jack is communicated to the other jacks but does not actuate them because they are held against movement by hydrostatic pressure resulting from the particular positioning of their respective control valves. Difficulties have been experienced, however, because the bowl jacks sustain the weight of the heavily loaded bowl when it is in a raised position by fluid locked in the smaller capacity or rod end of the jacks. Return pressure from the apron or ejector jacks is, therefore, communicated to the larger capacity or head ends of the jacks. This condition is further aggravated by the fact that lowering of the apron to its closed position is accompanied by a downward reaction on the bowl, sometimes creating peak pressures that are destructive to the jacks and their associated linkages.

It is, therefore, the object of the present invention to provide a common rail circuit of the kind described above with means to protect one jack or set of jacks against excessive pressures transmitted to it through the common rail.

A further and more specific object is to provide a lockout valve between the common rail and jack to be protected, operable automatically when the jack is in a load sustaining condition, to prevent communication of pressure from the common rail to the jack.

Further and more specific objects and the manner in which the invention is carried into practice are made ap parent in the following specification wherein reference is made to the accompanying drawing.

The drawing is a schematic view of a common rail circuit with a single source of hydraulic fluid serving three jacks or sets of jacks shown for example as jacks actuating the bowl, apron and ejector of an earthmoving scraper, those components of the circuit which are supported by the scraper and those which are supported by the tractor which draws the scraper being illustrated as separated by a broken line which intersects the view.

Generally speaking, the circuit disclosed in the drawing is the same as that shown in our assignees copending application of Allyn J. Hein et al. for Hydraulic Circuits for Control of Earthmoving Scraper Bowls, Serial No. 247,056, now Patent No. 3,127,688. A brief description of the operation of this circuit will facilitate an understanding of the present invention which forms a part thereof.

Referring to the drawing, a pump 35 is adapted to draw fluid from a reservoir 36 and to direct it under pressure to the inlet port 37 of a scraper control valve 22. The

housing of this valve is bored for the reception of three slidable valve spools 16a, 18a and 20a for controlling the operation of three sets of jacks, generally indicated at 16, 18 and 20, respectively, associated with the bowl, apron and ejector of a scraper.

The operation of the valve 22 is disclosed in detail in our assignees Patent No. 3,068,596 and will be described herein only to the extent necessary to an understanding of the present invention.

A pair of forked inlet passages 38 and 39 in the valve body communicate with each other and with the first passage 37 so that with the valve spools in the neutral positions, as shown, fluid from the pump flows constantly through these passageways, thence to a discharge passage 40 and back to the reservoir through a return line 41. A relief valve 42 relieves excessive pressure on the discharge side of the pump communicating it to the reservoir through the discharge line 41. Each jack or set of jacks has what may be considered a high pressure and a low pressure end because the work or force required to move an implement part in one direction, as when it is being raised or moving earth, is usually greater than that required to move it in the other direction. Movement of any one of the spools in the valve 22 to the right as viewed in the drawing communicates pressure to the high pressure end of its associated jack. For example, rightward movement of spool 16a admits fluid under pressure to a line 4-6 and through line 45a to the rod ends of jacks 16 for raising the bowl. Similarly rightward movement of spool 118 communicates pressure through a line 48 to the head end of jack is to actuate the apron. This pressure is communicated through a valve mechanism 64, the function and construction of which are set forth in detail in our assignees ccpending application of Allyn I. Hein et al. for Hydraulic Circuit for Tractor Drawn Scrapers and the Like, Serial No. 154,790, now Patent No. 3,115,716. A detailed description of this valve, however, is unnecessary to an understanding of the present invention. Rightward movement of spool 20a admits fluid from inlet passage 39 through a line 50 to the head end of jack 20 for actuating the ejector. The opposite or low pressure ends of all of the jacks are connected with a common manifold 52 in the control valve 22 which communicates with each of the three valve spool bores and is opened by rightward movement of any spool into communication with a discharge manifold 53 connected to the reservoir by the line 41. Consequently return fluid from any jack which has been pressurized by rightward movement of one of the spools is directed to the reservoir because the common manifold 52 is connected with the low pressure ends of the jacks by a common line 54 having a branch line 55 to the bowl jack, a branch line 56 to the ejector jack and a branch line 57 to the apron jack th ough the valve mechanism 54.

Moving of any of the jacks in the direction opposite to that described above is accomplished by movement of the corresponding spool in the opposite direction or to the left as viewed in the drawing which communicates high pressure through the actuated spool to the manifold 52 and thus to all of the jacks through line 54 and its branches 55, 56 and 57. The valve spool which has been actuated also opens communication to a discharge passage 60 which is common to all of the spools and similar in configuration to the discharge passage 53. Passage 60 communicates with passage 40 and return line 41 so that return fluid from the actuated jack is directed to the reservoir. It should be noted that the other jacks are not actuated by pressure in the common rail system because since their controlling spools remain in the neutral position, they provide no return to the reservoir and the jacks are hydrostatically locked.

A load check and quick drop valve assembly 66 is associated with the head end of each of the bowl jacks 16 with the load check portion of the valve functioning as described in the above mentioned Patent No. 3,127,688 to contain the bowl supporting pressure in the rod end of the jack. A vent line 72 is associated with the valves 66 and the control spool 16a in such a manner that when the spool is moved to a position communicating pump 35 with the head end of jacks 16 through line 54 and branch 55, the line 72 is placed in communication with the reservoir permitting the load check valve to open so that fluid displaced from the rod ends of the jacks may return to the reservoir.

With the system as above described and without the lockout valve, generally indicated at 110 and presently to be described in detail, pressure in the common rail system is communicated through the branch 55 to the head end of jack 16 each time that the jacks 18 or 20 are actuated. It is this pressure added to the load which is being sustained by the rod ends of the jacks 16 which presents the problems overcome by the present invention.

The improvement over the circuit hereinabove described resides principally in the provision of the lockout valve, generally indicated at 110, which prevents flow through the branch 55 of the common rail circuit when the bowl jacks 16 are sustaining a load, which condition is accompanied by pressure in the line 72. The lockout valve includes a slidable spool 114 and a check valve 116. The spool 114 is biased by a spring 118 toward a position (not shown) which permits communication between the valve inlet and outlet ports 129 and 122, respectively. A chamber 124- at the end of the spool 114 receives pressure through a line 126 communicating with line 72 so that when the spool 16a is in the neutral position shown, the load check pressure is communicated to the chamber 124 to overcome the force of spring 118 and hold the spool 114 in the closed position shown. Consequently if either spool 180 or Zita is moved toward the left to create pressure in the common line 54, pressure cannot fiow through line 55 to the head end of the bowl jacks 16. However when spool 16a is moved toward the left to effect lowering of the bowl, a groove 74 in the spool provides communication between the vent line 72 and a line 76 leading to the reservoir 36 to vent the pressure from the load check valves 66 and from chamber 124. The spool 114 is moved to the right by the force of spring 118 augmented by the pressure in branch line 55 which enters the spring chamber through a passage 128 so that the pressure in branch line 55 is directed to the head ends of jacks 16 to effect lowering of the bowl.

When spool 16a is returned to its neutral position, the vent line 72 is again blocked and chamber 124 is again pressurized to move spool 114 to its closed position. When spool 16a is moved to the right to communicate pump pressure through the line 46 to the rod ends of jacks 16 to raise the bowl, fluid displaced from the head end of the jacks is free to return to the reservoir through branch 55 since it opens the check valve 116 in the valve assembly 110.

As has been described, pressure in vent line 72 is required to pressurize the chamber 124 and hold spool 114 in its closed position. Under certain operating conditions, the pressure in common line 54, for actuation of motor 18 or 20, may exceed the pressure in jacks 16. In order to prevent this higher pressure, which is also present in the chamber of spring 118, from moving spool 114 to its open position, additional check valves 130 are provided to prevent displacement of oil from chamber 124 through the load check valve 66.

Lowering of the scraper bowl is necessary for emergency braking of the vehicle should the engine die during high-speed operation and sufficient air pressure is not available for operation of the brakes. Ability to lower the bowl when the engine is not running is also necessary as a safety measure during service of the machine, particularly the hydraulic mechanism which controls the bowl position. To permit such lowering of the bowl opening of the lockout valve without the aid of pressure is accomplished by spring 118 when spool 16a is moved to the left to the lower position which vents the pressure from chamber 124 through conduits 126, 72, groove 74 and conduit 76. As the weight of the bowl extends the pistons of jacks 16, the fluid displaced from the rod end of the jacks pressurizes the reservoir, thus forcing oil through the collapsed vanes of pump 35, valve 22, common conduit 54, branch 55 and lock valve to the head ends of jacks 16 to fill the void created by extension of the pistons. This transfer of oil from the reservoir 36 to the jacks 16 is also assisted by the vacuum created in the head end of the jacks upon their extension. This permits lowering of the scraper bowl when the engine and consequently pump 35 is not operating to supply fluid to the head ends of the jacks.

We claim:

1. In a hydraulic circuit which includes a plurality of independently operable reversible fluid motors, a source of fluid under pressure, means to direct fluid from said source to said motors, valve means including a control element for each motor, separate conduits for communicating fluid from each control element to its respective motor for driving the motor in one direction, and means including a single conduit common to all of the motors for returning fluid through said valve means and for driving the motors in the opposite direction, the improvement which comprises a lockout valve between said single conduit and one of said motors to prevent transfer of pressure from the single conduit to said one motor upon actuation of the other motors.

2. The combination of claim 1 with means operable automatically to open said lockout valve when actuating pressure is directed to said one motor.

3. The combination of claim 1 with means to open the lockout valve when actuating pressure fails.

Tan Nov. 17, 1959 Hein et al Dec. 18, 1962

Claims (1)

1. IN A HYDRAULIC CIRCUIT WHICH INCLUDES A PLURALITY OF INDEPENDENTLY OPERABLE REVERSIBLE FLUID MOTORS, A SOURCE OF FLUID UNDER PRESSURE, MEANS TO DIRECT FLUID FROM SAID SOURCE TO SAID MOTORS, VALVE MEANS INCLUDING A CONTROL ELEMENT FOR EACH MOTOR, SEPARATE CONDUITS FOR COMMUNICATING FLUID FROM EACH CONTROL ELEMENT TO ITS RESPECTIVE MOTOR FOR DRIVING THE MOTOR IN ONE DIRECTION, AND MEANS INCLUDING A SINGLE CONDUIT COMMON TO ALL OF THE MOTORS FOR RETURNING FLUID THROUGH SAID VALVE MEANS AND FOR DRIVING THE MOTORS IN THE OPPOSITE DIRECTION, THE IMPROVEMENT WHICH COMPRISES A LOCKOUT VALVE BETWEEN SAID SINGLE CONDUIT AND ONE OF SAID MOTORS TO PREVENT TRANSFER OF PRESSURE FROM THE SINGLE CONDUIT TO SAID ONE MOTOR UPON ACTUATION OF THE OTHER MOTORS.

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