US2467508A

US2467508A - Hydraulic system

Info

Publication number: US2467508A
Application number: US565538A
Authority: US
Inventors: Walter C Trautman
Original assignee: Bendix Aviation Corp
Current assignee: Bendix Aviation Corp
Priority date: 1944-11-28
Filing date: 1944-11-28
Publication date: 1949-04-19
Anticipated expiration: 1966-04-19

Description

April 1949- w. c. TRAUTMAN I 2,467,508

HYDRAULIC SYSTEM Filed Nov. 28, 194

INVENTOR.

-W.IC.TRAUTMAN ATTORNEY MHI Patented Apr. 19, 1949 STATES PATEN HYDRAULKC SYSTEM Application November 28, 1944, Serial No. 565,538

(ill. 60-52) 3 Giairns.

This invention relates to hydraulic actuating systems in which pressure fluid is supplied to either end of a motor cylinder by areversible pump and has to do more particularly with systems of this type in which the motor cylinder contains a piston connected to a device to be actuated by a piston rod which extends from the piston through one end only of the cylinder, so that the displacement of the piston is less on the piston rod side than on the other side.

An object of the invention is to provide a simple ment end of the motor cylinder, in combination and efi'ective means for compensating for the diflerent displacements in the opposite ends of a motor cylinder supplied with pressure fluid by a reversible pump.

Another object is to provide a hydraulic actuating system employing a motor cylinder actuated by a reversible pump driven by a reversible electric motor in which the electric motor is automatically controlled to maintain pressure to hold the piston of the motor cylinder in a position into which it has been actuated.

Other more specific objects and features of the invention will appear from the description to follow of a specific embodiment of the invention.

It is frequently desirable to supply pressure fluid to one end of a motor cylinder and exhaust fluid from the other end by means of a reversible pump driven by a reversible electric motor. Such a system has the advantage that the usual fourway control valve between the pump and the motor can be eliminated and the entire control effected by merely running the electric motor in one direction or the other. However, in such systems, the hydraulic motor cylinder usually has a piston rod extending through one end of the cylinder so that the fluid displacement is difierent in the two ends of the cylinder, whereas the reversible pump displaces fluid at the same rate through its inlet and outlet ports. The present invention resides in the addition to a system of the type described of a particularly simple and eii'ective automatic valve arrangement for exhausting excess fluid from the large displacement end of the motor cylinder when pressure fluid is being supplied by the pump to the small displacement end of the motor cylinder, and for supplying additional fluid to the in-take side of the pump when the latter is delivering pressure fluid to the large displacement end of the motor cylinder.

V Essentially, my system includes a simple check valve for admitting extra fluid to the port'of the pump that is the in-take port when the pump is delivering pressure fluid to the large displacewith another valve for automatically connecting the large displacement end of the motor cylinder to the reservoir when the pump is supplying pressure fluid to the small displacement end of the 'motor cylinder.

A practical embodiment of the arrangement outlined and including various details of construction will now be described with reference to the drawing, in which:

Fig. 1 is a schematic diagram of a system in accordance with the invention with its various elements shown in the positions they occupy when the motor is running in one direction and;

Fig. 2 is a similar view showing the parts in the positions they occupy when the motor is running in the other direction.

Referring first to Fig. 1, there is shown a hydraulic motor cylinder I0 containing a piston ll having a piston rod l2, which extends through the left end of the cylinder II], for connection to a device to be actuated. By virtue of the'existance of the piston rod l2, the movement of the piston ll results in a larger displacement of fluid in the right end of the cylinder than in the left end. The right end of the cylinder is connected, through a conduit [3 and through a locking valve M, to a conduit l5 which extends to one port of a reversible pump H5. The left end of the cylinder I 0 is connected through a conduit l1 and through the locking valve I4, to a conduit I8 which connects to the other port, of the pump 16. The motor piston II] can be driven in either direction by driving the reversible pump iii in one direction or the other.

The pump l6 may be of any known construction, but is shown as a gear pump having two intermeshing gears l9, one of which is directly connected to the shaft of an electric motor 20, which is adapted to be rotated in one direction by closure of a switch 2|, and in the opposite direction by closure of a switch 22. As is clearly shown in the diagram, the motor is of the threephase type supplied from a three-phase line 23!, and the direction of rotation of the motor is re-' versed by reversing any two of the three leads, as is well-known in the art.

The pump l6 ejects from its outlet port theplacement of the left end of the cylinder II a lesser flow of fluid is being delivered from the cylinder through conduits I1 and I3 to the inlet of the pump. If no provision were made for the supply of additional fluid to conduit I3, the operation of the pump would be impaired. In accordance with the present invention, the fluid defliciency is made up by providing a branch conduit 23 containing a simple check valve 24 interposed between the conduit I3 and a fluid reservoir 25. The check valve 24 preferably has a relatively light spring, so that only a very slight reduction of the pressure in conduit I3 below the atmospheric or ambient pressure is suiflcient to open the check valve and permit flow of as much fluid as is necessary to compensate for the diflferent displacements of the two ends of the motor cylinder, and maintain the inlet port of the pump fllled with fluid at all times.

The conditions existing when the pump is driven in the reverse direction are illustrated in Fig.

2. In this case, the pump I5 is delivering fluid to the conduit I3, and the pressure therein closes the check valve 24 so that there can be no escape of fluid therethrough to the reservoir 25. The fluid delivered by the pump flows through the conduit |3,- the valve I4, and the conduit Il into the left end of the motor cylinder III, to move the piston II to the right. This results in the exhaust of a larger amount of fluid from the right end of the cylinder, which fluid flows back through the conduit I3, the valve I4, and the conduit I5. Obviously, since the flow of the fluid into conduit I5 from the motor I0 exceeds the flow being delivered by the pump I5, it cannot all return to the pump, and the excess fluid flows through a branch conduit 21, through'a valve 23, into an exhaust conduit 29, and through a filter 30, into the reservoir 25.

The valve 23 is normally closed, and is held closed by pressure in conduit I5, but opens in response to pressure in conduit l3. Thus, the valve comprises a casing 3| having a partition therein defining a valve seat 32 which is normally closed by a poppet 33 urged toward the seat 32 by a compression spring 34. The right end of the casing 3| to the right of the valve seat 32 constitutes a cylinder and contains a piston 35 having a stem 35 which presses the poppet 33 open when the piston 35 moves to the left. The left end of the piston 35 is, at all times, exposed only to the low pressure existing in the exhaust conduit 23, whereas the right end of the piston 35 is exposed to the pressure existing in conduit I3, the right end of the casing 3| being connected to the conduit I3 by a branch conduit 31. A compression spring 33 moves the piston 35 to the right into the position shown in Fig; 1, except when pressure fluid is being supplied to the conduit I3 as shown in Fig. 2.

It is obvious from the foregoing description that whenever the pump is being operated in the direction to supply pressure fluid to conduit I5, as shown in Fig. 1, the poppet 33 is held on its seat by the spring 34 and the pressure in conduit I5, so that the full output of the pump is delivered to the right end of the motor cylinder I3; at the same time the suction in the conduit I3 opens the check valve 24 to permit flow of the necessary make-up fluid to inlet of the pump.

On the other hand, whenever the pump is running in the opposite direction to supply pressure fluid to conduit I3, as shown in Fig. 2, the check valve 24' is closed so that the full output of the pump is delivered to the left end of the motor cylinder I3, and poppet 33 is opened by the piston 35 to by-pass excess fluid from the conduit I5 back to the reservoir 25.

As shown in the drawing, the locking valve I4 is provided in both the conduits leading to the motor cylinder III. Such valves are not broadly new. but it is believed that the use thereof in this particular system in combination with the control system to be described constitutes invention.

The valve I4 includes casing means deflning a cylinder 43 opposite ends of which cylinder are connected to the conduits I3 and I5 respectively, and the cylinder contains a piston 4|. Opposite ends of the cylinder 43 have

valve seats

42 and 43 therein, both of which are closed by

poppets

44 and 45 respectively when there is no differential pressure between the conduits I5 and I3. Thus,

poppets

44 and 45 are constantly urged against their seats by compression springs 45, and these springs function to seat the poppets whenever the pump I5 is not running and the pressures in the conduits I5 and I3 are substantially equal, and low. However, whenever the pressure in either conduit I5 or I3 exceeds the pressure in the other conduit, which condition prevails whenever the pump is running, the piston 4| is shifted by the differential fluid pressure against the force exerted by centering springs 41, and one of two stems 43 extending from the piston opens one of the other of the

poppets

44 or 45. The same pressure differential that shifts the piston 4| to open one of the poppets automatically opens the other poppet, the latter functioning as a check valve. Thus, under the conditions prevailing in Fig. 1 in which the pressure is high in conduit I5 and low in conduit II, the piston H is moved to the left to open poppet 44, and the pressure in conduit I5 acts directly on poppet 45 to open it.

40 On the other hand, when fluid is being supplied by the pump to conduit I3 and exhausted from conduit I5, the pressure is high in conduit I3, and the piston 4| is moved to the right to open poppet 45, and the pressure in conduit I3 functions directly to open poppet 44. The net result is that whenever the pump is running, in either direction, both

poppets

44 and 45 are off their seats, but whenever the pump and the flow stop, the pressure equalizes in the conduits I5 and I3, and both the

poppets

44 and 45 seat immediately to maintain pressure in the conduits I3 and I1 and hold the motor piston I in the position in which it has been moved.

The system disclosed is so arranged that the pump is automatically operated to move and maintain the piston II in one end position or the other depending upon the position of a coptrol switch 53, which connects a source of current 5| either to a solenoid 52 which closes the switch 2|, or to a solenoid 53 which closes the switch 22. These circuits from switch 53 to the solenoids 52 and" are completed through a pair of

pressure switches

55 and 54 which are connected to conduits I3 and I1 respectively and open their contacts whenever the pressure in the associated conduit exceeds a

predetermined magcontacts

51 and 58, whereas when the pressure exceeds a predetermined value the piston 60 is moved upwardly to lift the bar 56 and break the circuit.

The pressure switch 55 is connected in series with the left contact 63 of the control switch 50. and the pressure switch 54 is connected in series with the right contact 64 of switch 50.

The operation of the system may be briefly traced as follows:

Assumed that it is desired to move the motor piston II to the left, the control switch 50 is moved to the left to close with contact 63, as shown in Fig. 1. This completes a circuit through the pressure switch 55 to the solenoid 52, energizing the latter to close the power switch 2! and cause the motor 20 to rotate the pump in the direction indicated by the arrows thereon. The rotation of the pump develops pressure in conduit l5 which moves the piston Iii in the locking valve id to the left, and also opens the poppet 65, so that the pressure fluid flows through into conduit is and into the right end of the motor cylinder H], moving the piston I l to the left. The pressure switch 55 is adjusted to open only in response to pressures in the conduit l3 in excess of the pressures required to move the piston ii and whatever device it drives. Hence, the pressure switch does not open during movement of the motor piston, and the action continues, the fluid from the left end of the cylinder I being exhausted through the conduit [1 past the open poppet 44 into conduit l8 and back to the inlet port of the pump, make-up fluid being supplied from the reservoir 25 through the check valve 24 as previously described. When the piston ll reaches the left end of its stroke, the pressure in conduits I and I3 immediately rises to a relatively high value at which the pressure switch 55 Operates to open the circuit to the solenoid 52; it in turn permits the switch 2| to open and stop the motor and the pump. As the pump decelerates, the pressure in conduit l5 drops, but the pressure'is held in conduit l3 because the poppet 45 closes in response to any tendency toward reverse flow from conduit I 3 into conduit I5. Hence, the pressure switch 55 remains open. If there is no leakage and no reduction in temperature, the pressure conduit l3 may remain high enough to keep the pressure switch 55 open until such time as the switch 50 is moved to the right to shift the motor piston to the right. However, if as a result of leakage or a drop in temperature the pressure in conduit I3 drops below a predetermined value, the pressure switch 55 will again close its contacts to start the pump and run it long enough to again build the pressure up to the value at which the pressure switch opens. Hence, even if the system is left for a long period of time, the motor and pump start and stop automatically, if necessary, to maintain the pressure holding the motor piston I I in its left position.

When it is desired to move the motor piston H into the right end of its stroke, the switch is thrown to the right as shown in Fig. 2 whereupon a circuit is completed through contact 64 and through pressure switch 54 to energize the solenoid 53 and close the switch 22 to run the electric motor and the pump in the opposite direction, as indicated in Fig. 2. Under these conditions, pressure fluid is supplied to conduitl8, which moves the piston in the locking valve M to the right, and opens the poppet 44 to permit the fluid flow into the left end of the cylinder 76 I. At the same time: fluid is exhausted from the right end of the motor cylinder l0 past the poppet valve 45, since the latter is now held open by piston 4|. The excess fluid is by-passed back to the reservoir through the valve 28 as previously described. When the motor piston completes its stroke, the pressure rapidly rises in the conduit l I, to open the pressure switch 56 and stop the motor and pump, whereupon the poppet M in the locking valve closes to maintain the pressure in the conduit l1. Should this pressure drop below the predetermined value, the electric motor will again be started up, and will run the pump long enough to rebuild the pressure to the desired value.

A handwheel 20a is provided on the motor 20 to permit operation of the pump in an emergency if the power supply should fail.

A pressure relief valve 70 is preferably provided between the conduits H and I3 and the exhaust conduit 29, to relieve excessive pressures that may develop in either conduit H or it as a result of a rise in temperature. The relief valves are so adjusted that they do not operate in normal service. They function to prevent damage to the system in the event of a temperature rise or in the event the electric motor should not shut down for any reason, such as stuck switches or relays.

The electrical control means for the system is covered by divisional application, Serial Number 640,001, filed January 9, 1946,

Although for the purpose of explaining the invention a specific embodiment thereof has been described in detail various departures from the exact construction shown can be made without departing from the invention, which is to be limited only to the extent set forth in the appended claims.

' I claim:

1. In a hydraulic actuating system, a motor cylinder and piston having a piston rod extending from the piston through one end only of the cylinder, whereby the piston displaces less fluid on the rod side than on the other side, a fluid reservoir, a reversible pump having two ports, one of which is an inlet port, and the other an outlet port when the pump runs in one direction and vice versa when the pump runs in the other direction, first conduit means connecting one of said pump ports to said rod end of said cylinder, second conduit means connecting the other pump port to the other end of said cylinder, and means for equalizing fluid flow through said pump ports comprising: a first connection including check valve means between said reservoir and said first conduit means for permitting fluid flow directly to said first conduit means from said reservoir and preventing fiow from said first conduit means to said reservoir, a normally closed poppet valve directly connected between said reservoir and said second conduit means, and pressure responsive means for opening said valve in response to pressure in excess of a predetermined value in said first conduit means, said normally closed valve being a poppet valve having a popp t adapted to be urged against its seat by pressure in said second conduit means, and said pressure responsive means comprising means for lifting said poppet off its seat.

2. In a hydraulic actuating system, a motor cylinder and piston having a piston rod extending from the piston through one end only of the cylinder, whereby the piston displaces less fluid on the rod side than on the other side, a fluid reservoir, a reversible pump having two ports, one

emos 7 at which is an inlet port, and the other an outlet port when the pump runs in one direction and vice versa when the pump runs in the other direction, first conduit means connecting one of said pump ports to said rod end of said cylinder, second conduit means connecting the other pump port to the other end of said cylinder, and means for equalizing fluid flow through said pump ports comprising: a first connection including check valve means between said reservoir and said first conduit means for permitting fluid flow directly to said first conduit means from said reservoir and preventing flow from said first conduit means to said reservoir, a normally closed poppet valve directly connected between said reservoir and said second conduit means, and pressure responsive means for opening said valve in response to pressure in excess of a predetermined value in said first conduit means, said normally closed valve and the pressure responsive means for opening it comprising: a unitary casing having a partition therein defining a valve seat, a poppet chamber in said casing on one side of said partition containing a poppet valve, said popp t chamber being connected to said second conduit means, said casing including on the other side oi said partition a cylindrical chamber the outer end of which is connected to said first conduit means and the inner end of which is connected to said reservoir, a piston in said cylindrical chamber, and means actuated by said piston for unseating said poppet valve in response to pressure in said first conduit means, said poppet chamber and the inner end of the cylindrical chamber being connected when said poppet valve is unseated.

3. In a hydraulic actuating system, a motor cylinder and piston having a piston rod extending from the piston through one end only of the cylinder, whereby the piston displaces less fluid on the rod side than on the other side, a fluid reservoir, a reversible pump having two ports, one of which is an inlet port, and the other an outlet port when the pump runs in one direction and vice versa when the pump runs in the other direction, first conduit means connecting one of said pump ports to said rod end of said cylinder, second conduit means connecting the other pump port to the other end of said cylinder, and means for equalizing fluid flow through said pump ports comprising: a first connection including check valve means between said reservoir and said first conduit means for permitting fluid flow directly to said first conduit means from said reservoir and preventing flow from said first conduit means to said reservoir, a normally closed p p t valve directly connected between said reservoir and said second conduit means, and pressure responsive means for opening said valve in response to pressure in excess of a predetermined value in said first conduit means, said normally closed valve and the pressure responsive means for opening it comprising: a unitary casing having a partition therein defining a valve seat, a poppet chamber in said casing on one side of said partition containing a poppet valve, said poppet chamber being connected to said second conduit means, said casing including on the other side of said partition a cylindrical chamber the outer end of which is connected to said first conduit means and the inner end of which is connected to said reservoir, and a piston in said cylindrical chamber for unseating said poppet valve in response to pressure in said first conduit means, and spring means urging said poppet valve to closed position, said poppet chamber and the inner end of the cylindrical chamber being interconnected by unseating of said poppet valve.

WALTER c. TRAUTMAN.

REFERENCES CITED The following references are of record in the file .of this patent:

UNITED STATES PATENTS Number Name Date 1,590,226 Boisset June 29, 1926 1,638,653 Cannon Aug. 9, 1927 1,760,915 Robson June 3, 1930 1,955, 54 Temple Apr. 17, 1934 1,956,758 Ernst May 1, 1934 FOREIGN PATENTS Number Country 7 Date 482,102 Germany Nov. 11, 1929