Hydraulic control circuit
United States Patent 3925987

Apparatus for diverting, for cooling or other treatment, a portion of the operating fluid in a closed control circuit. The diverting apparatus includes a distributor valve having a slide with at least two lands thereon, means delivering fluid to be treated to the valve from both sides of the load and means for applying the main circuit pressure at either side of the load to the opposite ends of the slide via restrictions or check valves.

Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
60/454, 60/456, 137/112
International Classes:
F16H39/02; (IPC1-7): F15B21/04
Field of Search:
137/87,112 60
View Patent Images:
US Patent References:
2183541Fluid pressure power system1939-12-19Centervall

Primary Examiner:
Nilson, Robert G.
Parent Case Data:


This application is a continuation of application Ser. No. 295,531, now abandoned, filed Oct. 6, 1972. Application Ser. No. 295,531 was a continuation of application Ser. No. 081,721 filed Oct. 19, 1970 and now abandoned. Application Ser. No. 81,721 was entitled to and claimed benefits of Parent French Application Ser. No. 69/36698 filed Oct. 24, 1969 and such benefits are claimed for the present application.
What is claimed is

1. A hydraulic control circuit for delivering pressurized fluid to a load comprising:

2. The apparatus of claim 1 further comprising:

3. The apparatus of claim 1 wherein said one-way valves are mounted within said slide member.


1. Field of the Invention

The present invention relates to the control of fluids and particularly to the regulation of fluids in a closed hydraulic circuit. More specifically, this invention is directed to hydraulic circuits capable of tolerating variable fluid velocity and flow reversal and characterized by provision for treating a portion of the fluid in a branch of a closed system. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.

2. Description of the Prior Art

There are many closed hydraulic circuits which are provided with means by which part of the fluid flowing may be tapped off the main flow path and treated in some manner, for example in order to extract calories to avoid overheating of circuit components, before being returned to the main flow path. This practice is common, for example, in variable speed movement controls which utilize oil under pressure as the power transmission medium; it being desirable to avoid heating which is harmful to performance, the durability of the hydraulic circuit elements and the retention of the properties of the oil on which its selection was originally based.

In order to cool, renew and automatically drain oil from a closed hydraulic circuit in which reversals of the direction of flow are encountered, it has been prior art practice to employ a valve comprising one obtruator and two seats in the fluid tapping or extraction device. In such valves, which are known in the art as "shuttles", there has been continuous fluid extraction between the two valve seats. The prior art "shuttle" valves have provided relatively satisfactorily results in systems where the velocity of the operating fluid is substantially constant between flow reversals. However, in installations where it is necessary for the speed of flow to be varied, hydraulic circuit pressure will similarly vary and the shuttle valves will oscillate. Oscillation of the shuttle prevents utilization of the prior art devices in many systems which require rapid and accurate response of the load on the system.


The present invention overcomes the above-discussed and other disadvantages and deficiencies of the prior art by providing a non-vibrating device in a hydraulic circuit in which the speed of circulation is a variable. Thus, in accordance with the present invention, the shuttle of the extraction branch of a closed hydraulic circuit is replaced by a five-way slide-type valve or distributor. The distributor of the invention is characterized by two ways or grooves which are adapted to be alternately opened and closed by the lands of the slide member, two additional ways which enable the outer faces of the slide member to be subjected alternately to the main circuit pressures, and one permanent extraction way or groove on the slide member between the two aforementioned lands.

In a preferred embodiment of the present invention, the slide member of the valve is returned to its middle position by a pair of springs. Throttle devices, such as one-way valves, are also provided in series with each of the ways which couple circuit pressure to the outer faces of the slide member. In one embodiment of the invention, the one-way valves are provided in the body of the slide member.

Also in accordance with the present invention, the positions of the alternately closable and uncoverable grooves, and particulayly the position of the edges of the discharge ends of the grooves whereby fluid is delivered into the body of the distributor, are designed to obtain a dash-pot effect. This results in a substantial improvement whereby the operation of the distributor is very rapid in response to flow reversal, with a slowing-down of the movement of the slide in the last part of the stroke, and the present invention is thus particularly well suited for association with load devices which must be both accurate and have rapid response time.

Also in accordance with a preferred embodiment of the invention, the return springs for the valve slide are selected so as to have a threshold. The selection of springs in this manner has the effect of permitting abrupt operation if a very sharp movement of the slide is desired.


The present invention may be better understood and its numerous other objects and advantages will become apparent to those skilled in the art by reference to the accompanying drawing wherein like reference numerals refer to like elements in the several figures and in which:

FIG. 1 is a schematic drawing of a closed hydraulic circuit in accordance with the present invention, the circuit of FIG. 1 employing a five-way slide valve distributor;

FIG. 2 is a partial cross-sectional view of a second embodiment of the distributor shown in FIG. 1, the apparatus of FIG. 2 employing one-way valves in place of throttling devices of the FIG. 1 embodiment;

FIG. 3 is a partial, cross-sectional view of a modification of the embodiment of FIG. 2; and

FIG. 4 depicts the further embodiment of a distributor in accordance with the present invention, the one-way valves of the FIG. 2 embodiment being incorporated in the slide member of the FIG. 4 embodiment.


With reference now to FIG. 1, fluid under pressure is delivered to a constant capacity cylinder type hydraulic motor 1 by a hydraulic pump 2. Pump 2 is driven at constant speed by a motor, not shown, and is of the variable capacity cylinder type; the capacity of pump 2 being proportional to the angle α. The connection or main flow path between pump 2 and motor 1 is defined by conduit branches 3 and 4 of the hydraulic circuit and it will be observed that the hydraulic circuit is closed. The closed hydraulic circuit of FIG. 1 also includes a branch or by-pass having disposed therein an extraction device indicated generally at 5.

The continuous extraction of fluid from the main flow path is achieved, in the manner to be described below, by device 5. The fluid diverted from the main circuit is delivered via hydraulic circuit 6 through a cooler 8, which is an optional device, and into a tank or reservoir 7. Before being delivered into reservoir 7 the diverted fluid is passed through a filter 9.

Fluid passing through circuit 6 will be returned to the main flow path via a conduit 10 and a second by-pass 12-13 which includes one-way or check valves 14 and 15. The operation of valves 14 and 15 is controlled by the direction of circulation of fluid in the main circuit 3-4 and only one of valves 14 and 15 will be open at any one time. A force pump 16 is provided to maintain a minimum pressure of a few bars in the main hydraulic circuit 3-4; pump 16 being inserted in conduit 10. Pump 16 also facilitates the suction of the main pump 2 and thus makes the control more rigid. Restated, due to the presence of pump 16, the circuit as a whole has a higher gradient for resisting torque of the hydraulic motor 1 depending on its speed. This improvement may be attributed to the fact that the pressure provided by pump 16 reduces the effects of air dissolved in the operating fluid on the compressability of the fluid. The hydraulic circuitry, as briefly described above, is known in the art and thus the individual components and their operation will not be described in any further detail herein.

As will be obvious to those skilled in the art, long periods of operation of the circuit of FIG. 1 will result in energy being absorbed in the operating fluid in the form of heat. As the operating fluid, which typically will be oil, heats up the efficiencies of the pumps and motor, which for short periods of operation are very close to unity, will deteriorate substantially. As is also well known, heating is harmful to the durability of the organic elements and to the preservation of the properties of oil.

In the prior art the extractor device 5 was a device known as a shuttle having coaxial valve seats. In accordance with the present invention the shuttle having coaxial valve seats has been replaced by a distributor somewhat similar in construction to a slide valve. The distributor of the present invention has a pair of alternately closable and uncoverable grooves formed in the internal walls of the cylinder in which the valve slide moves. Thus, continuing with a consideration of FIG. 1, grooves 21 and 22 formed in the internal walls of the valve body are alternately closed and uncovered by lands on the slide 20; the lands and grooves cooperating to perform a valving action. Positioned outwardly respectively from grooves 21 and 22 are ways or passages 23 and 24; the passages 23 and 24 being connected by branch conduits with the conduits which deliver fluid to or receive fluid from grooves 23 and 24. It is to be noted that the branch conduits which place the passages 23 and 24 into communication with the pressure of the main flow path 3, 4, are provided with throttles or restrictions 27. The throttles 27 modify the time of response of springs 28 in the interest of preventing vibration of the springs.

The distributor is divided into oppositely disposed chambers 25 and 26 by slide 20 and these chambers are pressurized by main circuit pressure as delivered to the chambers via the throttles 27. Each of chambers 25 and 26 contains a spring 28 which extends between the end of the chamber and an end of the slide 20, the springs tending to maintain the slide in the mid-position as shown.

The means by which the fluid diverted from the main flow path is returned to the reservoir 31 via cooler 8 comprises a passage 29. Passage 29 is in constant communication with the chamber defined by the lands on the slide 20 of distributor 5. Passage 29 communicates with conduit 6 via a one-way valve 32. Valve 32 is adjusted to a pressure of, for example, 5 to 10 bars.

From the foregoing description it will be obvious to those skilled in the art that any reversal of flow in the main circuit 3, 4 will result in a movement of the valve slide 20. The movements of the valve slide, unlike prior art devices, are not characterized by vibrations of the slide due to the presence of the throttles 27. The damping action of the throttles may be reinforced by constructing the passages 23 and 24 as capillary tubes.

It is also to be noted that the invention includes a pressure limiting means 33 which is adjusted, for example, to 12 bars.

The embodiment of FIG. 1 eliminates vibrations, as mentioned above, and has substantial utility. However, when motor load is abruptly reversed the slide 20 will assume its new position only after a time delay which is governed by the presence of the throttles 27 and, when employed, by the capillarity of the passages 23 and 24. During this delay the main flow will partly pass through the grooves 21 or 22, depending upon the position of the slide, and the forcing pressure will drop because the flow of force pump 16 is limited. Accordingly, in environments where the motor load 1 is subject to abrupt reversal, the embodiment of FIG. 1 will have the draw-backs of being noisy and somewhat inaccurate.

To overcome the inaccuracies noted in the preceding paragraph, the embodiment of FIG. 2 contemplates replacement of the throttles 27 of the FIG. 1 embodiment with one-way valves 40. Considering operation of the FIG. 2 embodiment, and assuming that the slide 20 is initially in the raised position, an abrupt reversal of pressure brings about an immediate response on the part of the upper one-way valve 40 thus permitting immediate and rapid response of the slide.

FIG. 3 shows, in cross section, a further embodiment of the invention. In FIG. 3 only the lower portion of a modified form of the distributor of FIG. 2 is disclosed. In the FIG. 3 embodiment the end chamber 26 is provided with abutments 42-43, or a shoulder, which limits the expansion of spring 28. The opposite or lower end of chamber 26 is provided with an upward extension or nipple 41, or any other equivalent element, which will be contacted by the bottom face of the slide at its extreme of movement. A corresponding shoulder and extension are, of course, also provided in the oppositely disposed end chamber 25. The value of the threshold pressure at which slide 20 moves is determined by the force with which spring 28 bears against the planar face of abutments 42-43. An abrupt movement of the valve slide is obtained, due to the establishment of this threshold pressure, because a greater pressure differential is necessary to promote displacement of the slide or spool 20 from the neutral position than is the case in the embodiment of FIG. 2 wherein each of the springs 28 counterbalance the oppositely disposed spring. The nipple 41 limits the stroke of the spool in the case of an over pressure. In the FIG. 2 embodiment the valve body chamber is provided with abutments which cooperate with the valve slide to limit the aperture of groove 22 to a minimum, when said groove is exposed by the movement of the slide, thus decreasing the response time for each reversal of pressure.

Considering simultaneously FIGS. 2 and 3, and assuming that the slide 20 is initially in the upper or raised position, the slide 20 will move downwardly quickly as a result of a reversal of pressure in the main flow path. This rapid movement continues until the moment when the peripheral edge of the face 42-43 of the slide passes the lower edge 44-45 of the groove 22. Thereafter, the movement of the slide slows down because the fluid trapped in chamber 26 must be relieved through the overlapping between the edges of the groove 22 and slide. Accordingly, a dash-pot effect is produced; the effect being delayed until the edge 46-47 of the land on slide 20 has passed the lower edge 48-49 of groove 21 at the upper end of the distributor. As will now be obvious to those skilled in the art, the embodiment of FIG. 3 is suitable for use with accurate, high speed servomechanisms.

With reference now to FIG. 4, a further embodiment of the invention is disclosed wherein the one-way valves 40 are placed inside the slide 20 of the distributor. Thus, in FIG. 4 the one-way valves are indicated generally at 50 and it will be immediately seen that one-way valves 50 also comprise the devices which determine the threshold of operation of the distributor. Accordingly, in the FIG. 4 embodiment, one-way valves 50 function in the same manner as the nipples 40 of the FIG. 3 embodiment. The obturators of the one-way valves 50 of the FIG. 4 embodiment are indicated at 51.

While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the present invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.