US2953902A

US2953902A - Hydraulic elevator control system

Info

Publication number: US2953902A
Application number: US607496A
Authority: US
Inventors: Duane J Arbogast; Lawrence F Jaseph
Original assignee: Dover Corp
Current assignee: Dover Corp
Priority date: 1956-08-31
Filing date: 1956-08-31
Publication date: 1960-09-27
Anticipated expiration: 1977-09-27
Also published as: BE586037A

Description

Sept. 27, 1960 D. J. ARBOGAST ET AL 2,953,902

HYDRAULIC ELEVATOR CONTROL SYSTEM Filed Aug. 31, 1956 3 SheetsSheet 1 Sept. 27, 1960 D. J. ARBQGAST ETAL 2,953,902

HYDRAULIC ELEVATOR CONTROL SYSTEM Filed Aug. 31, 1956 s Sheets-Sheet g g 5 IF g 2 20 194 212 L A Z0? 2 [/E! IN VEN TORS,

p; A?!) ga DE! UL 19] Sept. 27,1960 D. J. ARBOGAST ETAL 2,953,902

HYDRAULIC ELEVATOR CONTROL SYSTEM Filed Aug. 51, 1956 I 3 Sheets-Sheet 3 /Z50 INVENTORS.

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ust 8, 1944, and

United States PatentQ 2,953,902 I HYDRAULIC ELEVATOR CONTROL SYSTEM Duane J. Arbogast, Olive Branch, Miss., and Lawrence F. Jaseph, Memphis, Tenn., assignors to Dover Corporation, Memphis, Tenn., a corporation of Delaware Filed Aug. 31, 1956, Set. N0. 607,496

13 Claims. CI. 60-52) The present invention relates to improvements in hydraulic elevator control systems, and more particularly to a system whereby the speed of the elevator may be more nicely controlled and the elevator may be brought to a stop at the landing with greater accuracy than heretofore possible. The present invention relates to improvements over the inventions disclosed in the prior issued patents to Lawrence P. Jaseph, No. 2,355,164, dated Aug- No. 2,553,045, dated May 15, 1951.

In the hydraulic control systems of the prior patents, and particularly the later issued patent, it was disclosed that the coasting distance to a full stop could be reduced by causing a bypass valve connected to the pump discharge to open at the same time the pump motor was deenergized, thus reducing the variation in the coasting distance with variations in the load. However, the locus of the stop proved not always to be constant, and corrective downward movement was required on all loads lighter than the maximum load for which the system was adjusted.

The system of the present invention obtains the desired accuracy in stopping at the indicated landing, regardless of the prior speed of the elevator or of the load carried thereon. It has been found that it overcomes, in this regard, all of the objections which have been leveled against the systems of the prior art.

It is, therefore, a principal object of the present invention to provide a new and improved hydraulic elevator control system from which the objectionable aspects of the prior art systems have been eliminated.

. Another object is to provide a new and improved hydraulic elevator control system incorporating a constant output pump, wherein an adjustable reduced speed is available for accurate landing.

Another object is to provide a new and improved hydraulic elevator control system wherein the above mentioned reduced speed is constant regardless of variations in the load being lifted.

Another object is to provide a new and improved hydraulic elevator control system wherein it is possible to make the reduced speed vary with the load in an arbitrary manner.

Another object is to provide a new and improved by draulic elevator control system incorporating a flow regulating bypass valve which is capable of regulating pressure as well as flow.

Another object is to provide a new and improved hydraulic elevator control system wherein a predetermined portion of the output of a constant delivery pump is bypassed to obtain a reduced elevator ascending speed regardless of the load carried by the elevator.

Another object is to provide a new and improved hydraulic elevator control system wherein overload conditions are quickly sensed and relieved through a bypass valve.

Still another object is to provide a new and improved hydraulic elevator system attaining the foregoing objects by equipment which is easily manufactured and not sensi- "ice tive to friction of the working parts, or easily disarranged.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is a diagrammatic view of a hydraulic elevator control system incorporating the novel features of the present invention, and showing the bypass valve and other valves in longitudinal section;

Fig. 2 is a diagram of the electric control circuit for the hydraulic system of Fig. l; i f

Fig. 3 is a view similar to Fig. 1, and showing a modified hydraulic control system and bypass valve;

Fig. 4 is a view similar to Fig. 1, showing another-modification of the system and bypass valve; and

Fig. 5 is an expandeddiagrarnmatic view of the flow regulating valve member of the bypass valves shown in Figs. 3 and 4. V p

In all of the above Figs. 1, 3 and 4, the bypass valve is shown approximately in the position it assumes when thie elevator is ascending at slowed speed preparatory to making a stop at a landing. 7 7

Referring first to the principal form of the invention (Figs. 1 and 2), an elevator 10 is arranged to be raised and lowered by a hydraulic jack 12 having a cylinder14 and piston 16 projecting from the upper end thereof and mounting the elevator 10 in the customary fashion. Fluid under pressure is supplied to the jack 12 by a constant volume output pump 18 which is driven by an electric motor 20, the inlet of the pump being connected byf-a construction known in'this art and no detailed illustration.

or descriptionis necessary.

A bypass valve 36 is interposed between the pump out let and the tank 24 and has an inlet port 38 connected by a conduit 40 to the conduit 26' and an outletport 42 connected by a conduit 44 to the conduit 34.

The

ports

38 and 42 are formed in a valve body "46 and communicate respectively with an inlet chamber 48 and an outlet chamber 50, the

chambers

48 and 50 coni-x municating through a valve port or orifice 52 with'the;

fluid flow therebetween controlled by a piston type valve member 54 formed at the front or head end of a' valve spool 56. The valve member 54 is formed with a plural-1 ity of shaped notches 58 which, as the valve member 54 movestoward valve open position, gradually open the orifice 52 for the passage of fluid between the chambers? 48 and 50. The flow of fluid from the pump 18 to the inlet chamber 48 is also controlled by a m'anually'ad justable vane valve 60 which creates a pressure diflerential between the port 38 and chamber 48 when fluid flows V therepast.

The valve spool 56 slides in the valve orifice or opening? 52 between the

chambers

48 and 50 and in, a cylinder 62 formed in the right or head end of the valve body 46 and in a cylinder 64 formed in the rear end of the valve: body 46. A-piston portion 66, which is integral with'the' valve piston 54, slides in the cylinder 64 which has its head end closed by a suitable cap 68 secured in the con-; ventional fashion, as by bolts, to the valve body 46. The piston 66 is connected by a hollow stem 70 to the valve,

piston 54. As the underside of the piston 66 and the inner face of the valve piston 54 have equal areas, the position of the valve spool 56 is not influenced by pressure:

conditions in the outlet chamber 50.

The valve spool 56 is biased toward open positionfby a relatively weak spring 72 contained in bore 74 of the hollow stem 70 and having substantially uniform tension Patented Sept. 27, 196Q characteristics over its range of movement. At its right end the spring 72 bears against the underside 76 of the head of the piston and at its left end bears against spring keeper 78 which has its position adjusted by a hollow stem 80 threaded through a tapped bore-82 in the cap 68 and fixed in position by a suitable lock nut 84.-

A valve movement limiting rod 86 extends through the bore 88 in the hollow stem 80. At its right end the rod 86 is fixed to the head of the valve piston 54 and at its left end is fitted with a nut 90 threaded onto its outer tapped end and suitably adjusted so that when the nut 90 contacts the stem 80, the valve spool 56 has moved the maximum distance to the right or in valve opening direction. A cap 92 threaded onto the valve cap 68 encloses the ends of the stem 80, the rod 86, lock nut 84, and stop nut 90 to prevent leakage of fluid and inadvertent adjustment of these elements.

With the pump at rest, the valve spool 56 is at the valve open position as dictated by the biasing spring 72 and stop nut 90, and, when the pump is first energized to deliver hydraulic fluid through the conduit 26, it will pass immediately through the conduit 40 to the inlet 38 of the bypass valve 36. A conduit 94 is connected at 93 to the inlet port and through an adjustable needle valve 96 and conduit 98 and port 100 to the cylinder 62 at the head end of the valve 54, and fluid under pressure is delivered to the cylinder 62, moving the valve spool 56 to the left or in valve closing direction against the opposition of the spring 72.

At this same time fluid flows past the vane valve 60 into the inlet chamber 48, the pressure in the inlet chamber 48 being lower than the pressure at the valve inlet 38 due to the throttling effect of the valve 60. The chamber 48 is connected by a conduit 102, strainer 104, adjustable needle valve 106, conduit 108, to the cylinder 64 at the left end of the bypass valve 36. However, at the time the motor 20 is energized, as will be explained hereinafter, a solenoid 110, controlling valve 112, is also energized to open this valve. The inlet to the valve 112 is connected by conduit 114 to the conduit 108, and its outlet is connected by conduit 116 and port 118 to the outlet chamber 50 of the bypass valve 36 so that fluid flowing through the valve 112 is drained to the reservoir 24. Thus, when the valve 112 is open, no fluid is passed to the cylinder 64, and, therefore, the pressure in the cylinder 62 overcomes the biasing effect of the spring 72 and moves the valve spool to valve closing position, at the same time emptying the cylinder 64.

During movement of the valve 54 to open position, fluid will be expelled from the cylinder 62 and bypassed around the throttling valve 96 through a conduit 120, check valve 122, and conduit 124, the conduit 120 being connected to the conduit 98, and the conduit 124 being connected to the conduit 94 through the branch conduit 95 leading from the conduit 94 to the throttling valve 96.

The hydraulic elevator control system includes a high pressure relief pilot valve 126 having a valve body 128 in which a piston valve member 130 is slidable in a cylinder 132. The head end of the cylinder 132 is connected to the conduit 94 by port 134 and, therefore, to the outlet of the pump 20 through the

conduits

26 and 40, port 38, and conduit 94. The valve member 130 has a shoulder or ridge 136 thereon which is abutted against a shoulder stop 138 in the valve body 128 by a spring 140. The spring 140 acts between the end of the valve member 130 and an adjustable keeper 142 which is threaded into the valve body and secured in adjusted position by a lock nut 144 and covered with a cap 146 to prevent inadvertent adjustment thereof.

The valve member 130 is formed With a T-shaped passageway 148 which has one end communicating with a circumferential groove 150 at a point intermediate the valve member ends. The other end of the passageway 148 communicates with spring chamber 152 in the valve body 128, which is connected by a conduit 154 from a port 156 to the conduit 116 and the outlet or drain chamber 50 of the bypass valve 36. The T-shaped passageway 148 is adapted to connect port 156 and port 162 when an undesirably high pressure exists at the inlet port 38 of the bypass valve 36, the high pressure being move the valve spool 56 rapidly in bypass valve opening direction to relieve the undesirably high pressure at the inlet 38.

The hydraulic control system incorporates an elevator releveling means including a valve 166 which is moved to open position by a solenoid 168 when the latter isenergized. The inlet of this valve 166 is connected by a conduit 170 through strainer 172 and conduit 174 to the conduit 94, and its outlet is connected by a conduit 176 to the cylinder 62. Should the elevator, stopped at the landing, settle below the landing, a circuit to the solenoid 168 will be energized, opening the valve 166, and permitting fluid from the pump 18 which is started with energizing the solenoid 168, to flow through the bypass inlet port 38, conduit 94, conduit 174, filter 172, conduit 170, valve 166, conduit 176, to the cylinder 62, thereby moving the valve 54 toward closed position and directing the flow of fluid from the pump to the jack 12, thereby restoring the elevator to the landing level. When the elevator has reached its proper level, the circuit to the solenoid 168 will open to deenergize the latter and permit the valve 166 to close and the bypass valve to open.

The hydraulic circuit for this elevator operates as follows: With the system at rest, the biasing spring 72 will have moved the valve spool 56 to the right to bring the stop nut 90 against the stop stem 80 and the valve 54 to fully open position. The motor 20 and pump 18 are started and accelerate to full speed without moving the elevator because the entire output of the pump is bypassed through port 38, port vane valve 60, through chamber 48, valve orifice 52, chamber 50, and back to the reservoir 24 without producing suflicient back pressure to raise the elevator 10. The stop 90 is adjusted so that the back pressure created at this time will be not much less than enough to move the elevator so as to minimize delay in starting the elevator movement. When the motor 20 is energized, the solenoid 110 is energized to open the valve 112, thereby placing the cylinder 64 into communication with the outlet chamber 50 to permit drainage of the cylinder so that the valve spool may move in valve closing direction. The pressure in the inlet chamber 48 will be below that of the inlet port 38 due to the effect of the vane valve 60, thereby diverting a portion of the fluid at pump pressure through the

conduits

94 and 95, throttling valve 96, conduit 98, to the cylinder 62. Pressure in the cylinder 62 overcomes the force of the biasing spring 72 to move the valve 54 to closed position. The closing rate of the valve 54 is determined by the setting of the needle valve 96. Soon after the valve spool 56 begins to move toward closed position, the back pressure due to constant output of fluid from the pump 18 will exceed that required to raise the elevator 10 and the check valve 28 will open to allow a gradually increasing flow to passto the jack 12 and raise the elevator 10 finally at full speed. The starting time and rate of acceleration, therefore, dependupon the speed of the normal discharge of the pump at which the valve 54 closes, and the latter is controlled by the setting of the valve 96.

At a predetermined point in the elevator travel as it approaches a landing, the circuit to the solenoid 110 will be open to permit the valve 112 to close and consequently to close the drain from the cylinder 64. The cylinder 64 now is connected only to the inlet chamber 48 through the strainer 104 and throttling valve 106. Since there is no flow past the vane valve 60 because the valve 54 is closed, the pressures are equal at the inlet 38 and in the chamber 48, and consequently in the

cylinders

62 and 64. The valve spool 56 now moves in valve opening direction under the force of the spring 72 at a rate determined by the setting of the throttling valve 106. The valve 96 does not affect this movement as the fluid expelled from the cylinder 62 flows 'through the bypass check valve 122. As the valve 54 opens, fluid flows from the inlet chamber 48 to the outlet chamber 50 and through the outlet port 42, at the full working pressure of the system. This bypass flow reduces the flow to the jack 12 and consequently the elevator speed.

As the fluid flow increases past the vane valve 60, a pressure diflerential across the valve increases, and the higher pressure at the inlet 38 is communicated to the cylinder 62 and the relatively lower pressure in the chamber 48 is communicated to the cylinder 64. The pressure diiterential will increaseuntil it balances the biasing effect of the spring 72 at which time the valve spool 56 will come to rest in equilibrium in a position at or near that shown in Fig. l and with the bypass partially open. The equilibrium depends upon the velocity of fluid flow past the vane valve 60 and-very little upon the fluid pressure which depends upon the load imposed upon the jack 12.v Consequently, a definite quantity of fluid will be bypassed, leaving a definite remainder to drive the elevator at reduced speed. If the elevator is heavily loaded, the pressure will be high in the conduit 26 and at the inlet 38, and a relatively smaller port area at the valve54'isrequired to bypass the desired quantity of liquid. Under these conditions the spool 56 is positioned farther to the left or toward valve closing position than would be the case when the elevator is lightly loaded and the pressure at the pump outlet is less. As pointed out previously, the change in tension of the spring 72 is minimum with changes in valve spool position, and substantially the same volume flow past the vane valve 60 is required to balance the spring tension at the various positions of the valve spool 56.

- As the elevator nears its landing, the power to the motor 20 is cut off and the pump 18 begins to decelerate. The liquid discharged diminishes in volume in proportion to the drop in pump speed. However, since a greater part has been bypassed through the valve 36, the reduction in fluid pumped comes primarily from the liquid being transmitted to the elevator jack 12, and, if three-quarters of the fluid had been bypassed to achieve slow leveling speed, a reduction of onequarter of the pump speed will bring the elevator to rest in a smooth short stop. As the flow diminishes toward zero, the pressure drop past the vane valve 60 will be inadequate to hold the pressure in the cylinder 62 in opposition to the biasing spring 72, and the latter will gradually urge the valve spool 56 toward open position, thus conditioning the system for a further operation in the upward direction.

At times, leakage of fluid in the system and from the jack 12 will be enough to permit the elevator to settle slightly below its position level with the landing. At such time a circuit will be closed to energize the solenoid 168, thereby opening the valve 166, and the circuit to the motor 20 will be closed to drive the pump 18. The solenoid 110 is not energized. When this occurs the valve spool 56 will be at its right position with the bypass valve open, and the conditions will be essentially the same as that for slow speed as the elevator approaches the landing. Under these conditions only arelatively small pressure difier'ential will be created on opposite sides of the vane valve 60, and only the fall in pressure, due to spool 56. To permit more rapid action, fluid from the inlet port 38 is admitted directly to the cylinder 62 past the solenoid operated leveling valve 166, thereby moving the valve spool 56 very rapidly toward valve closing position, and an almost immediate flow of hydraulic fluid will be transmitted from the pump 18 through the check valve 28. Closing movement of the'bypass valve continues until the tension of the spring 72 is balanced. As soon as the proper level is reached, the circuit to the solenoid'168 and motor 20 will be opened, thereby deenergizing the solenoid to permit the valve 166 to close and the motor 20 to stop. The bypass valve will be opened by the spring 72 to condition the system for a further operation. When an excessive pressure in the system occurs, and it is desired to open the bypass valve more rapidly than under normal circumstances, the high pressure pilot re-I lief valve 126 operates as previously described to connect the conduit 94 with the cylinder 64 and the cylinder 62 with the drain chamber 50 so that the pressure at the opposite ends of the valve spool 56 are reversed and the valve 54 will open rapidly. Y i

The adjustments in the system, as above described, in clude the vane valve 60 which regulates the orifice area at the inlet 38 of the bypass valve through which the bypass liquid flows, and consequently. the volume of bypass flowwhen the low speed operation of the elevator is desired, thus determining the lower speed. The second adjustment includes the needle valve 96, which regulates the acceleration of the elevator to full speed by controlling the rate of closure of the bypass valve. The third a'djustment includes the needle valve 106,- which regulates. the rate of reopening the bypass valve when slowing of the elevator is desired as the landing is approached. The next adjustment includes the hollow stem which regulates the tension on the spring 72, supplementing the vane valve 60 and serving as a fine adjustment for therate at which the bypass liquid flows through the bypass valve 36. The next adjustment is the stop nut which determines the maximum opening of the bypass valve mem w ber 54, and the last adjustment includes the screw. 142 setting the force-on the spring 140, thereby determining the pressure at which the high pressure relief valve opens to relieve high pressures in the system. r g

The control system. also includes certain electric controls for the solenoids and 168 and the motor '20, which are shown in the wiring diagram of Fig. 2. Power is supplied to the motor 20 and to the control circuit from a three-phase 220 voltsource 178. The control circuit receives its power through the lines and 182 lay UR, and the solenoid 110 in parallel with the relay,

all of which are in the line connecting the

lines

180 and 182. When the switch 188 is closed, current flows from the line 180 to the line 182 through the closed switch; 188, upper limit switch 190, switch DR2, and relay UR and also the solenoid 110, thus opening the solenoid operated valve 112. Energization of the relay UR closes the switch URI in circuit 191 to the motor starter relay R20. The relay R20 closes the switches 186, thereby energizing the circuit to the motor 20, causing it ,todrive the pump 18 to displace fluid therefrom. Closing ofthe relay UR also opens a switch UR2 in the circuit 194 to the down switch 196 and down relay DR, the latter relay controlling the operation of the lowering valve 32, thereby rendering this latter circuit inoperative to operate the valve 32 at any time while the elevator is ascending. When the elevator nears the landing, a cam 193 on the elevator cage will open the switch 190, thereby deenergizing the relay UR to allow the switch URI to open and deenergize the solenoid 110 to permit the valve 112 to close.

When the relay UR was energized, it opened a switch UR3 in circuit 200 which includes a solenoid 201 operating the lowering valve.

As the elevator approaches the landing, the limit switch 190 is opened or the manual switch 188 is released, but up leveling switch 292 on the cage 10 engages a stationary cam 204 in the hoisting structure; the switch 202 is normally open but as it engages the cam 204 it closes to energize the relay ULR and the solenoid 168 which are in parallel in circuit 206 between the

lines

180 and 182. Energization of the relay ULR closes the switch ULRI which is in the circuit 298 in parallel with the normally and now open switch URI, and in series with normally closed switch DRl (opened by relay DR), and thereby ma ntaining the motor relay R20 energized. When the elevator reaches the landing, the up leveling switch 202 opens, breaking the circuit to the relay ULR which in turn allows switch ULRl to open and deenergize the motor relay R20 to stop the motor and elevator, as described hereinabove.

When the elevator is rising under full speed conditions, it closes down leveling switch 214 in circuit 215 to down leveling relay DLR to engage the circuit and relay, thereby to close the switch DLRI in circuit to solenoid 201. Since switch UR3 is held open by energized relay UR, the solenoid is not energized and this action has no effect on the system. Should the elevator close an up leveling switch 202 at a landing where no stop is contemplated, the relay ULR and solenoid 168 will be energized but will have no eifect on the operation of the elevator because the bypass valve is closed. Should the elevator settle at the landing, the switch 202 will close, thereby energizing the relay ULR to close the switch ULRl and to energize the motor starting relay and the leveling valve solenoid 168 to restore the elevator to the landmg.

When it is desired to lower the elevator, the manually operated down switch 196 in the circuit 194 is closed This circuit includes the normally closed switch UR2 which has been closed upon deenergization of the relay UR and the down operated relay DR, which opens the switch DRl in series with the up leveling switch ULRl and the switch DR2 in series with the relay UR. The circuit to the motor operating relay R20 is deenergized so that the motor 20 will not be energized when the elevator closes an up leveling switch 202 during descent; and the up circuit 192 is also deenergized. The circuit 194 also includes the bottom limit switch 210 which is opened by the cam 198 as the elevator approaches the bottom of its travel and is closed as the elevator leaves the bottom position. Closing of the switch 196 energizes the circuit to the relay DR and a solenoid 212 to open the lowering valve 32, which is of conventional design so that the lowering speed of the elevator is automatically regulated.

If the elevator should rise above a landing at which it has stopped, a down leveling switch 214, will be closed by the shaft cam 204. The switch 214 energizes relay DLR in the circuit 215 to close a switch DLRI through the normally closed switches DRl and UR3 in the circuit 200 to the solenoid 201 to operate the lowering valve 32 to meter a small amount of fiuid from the jack to the reservoir 24, thereby lowering the elevator to the desired level.

The circuit is under the control of a master manual switch 216 and a pair of maximum top and bottom limit 8 switches 218' which are in the lines and 182, and the functions of which are obvious.

A modification of the hydraulic control system is shown in Figs. 3 and 5, and, to the extent feasible, the same reference characters have been used in those figures to designate comparable parts.

In this system the pump 18 is connected to the inlet 38 of a bypass valve 36A, and the bypass valve outlet 42 is connected to the reservoir through the conduit 44. In this particular system the lowering valve 32 is connected between the

conduits

30 and 44. The bypass valve 36A has a valve body 229 in which the

ports

38 and 42 are formed, and an inlet chamber 222 and a drain chamber 224 which are interconnected by a valve orifice 226, the flow of fluid through which is controlled by the valve 228 formed at one end of a valve spool 230. The valve spool 23!) has a piston 232 at the opposite end which is slidable in a cylinder 234 formed in the valve body 220. The open end of the cylinder is closed by a suitable cap 235 in which is fitted an adjustable stop screw 238 which limits the lift of the valve 228 and the travel of the valve spool to the right or in valve opening position. The valve is biased toward open position by a spring 240 which acts between the underside of the head of the piston 232 and a shoulder 242 formed at the junction between the cylinder 234 and the drain chamber 224.

The valve 228 is provided with valve wings 244 which center the valve 228 in the orifice 226 and with respect to the valve seat 246. Ports 243 (Fig. 5) between the wings 244 are specially shaped to provide the desired flow characteristic. The space between the wings is filled in adjacent the seat except for relatively narrow deep notches 250 which form the only passage for fluid between the

chambers

222 and 224, when the valve 228 is in such position that the elevator is ascending at a slowed speed preparatory to stopping at a landing. When, however, the valve is in fully open position, the

chambers

222 and 224 are communicated through the wider flow ports or passages 248.

The valve spool stem 249 is formed with an axial bore 252 in which is slidable a valve piston 254 between the lands of which is formed an annular groove 256. The groove 256 communicates with an axial bore 258 in the piston 254 and, therefore, with the cylinder bore 252 in the valve spool 239. The cylinder bore 252 communicates with drain chamber 224 through a port 230. A passage 260 is drilled or cored in the valve spool piston 232 and stem 249 so that under certain circumstances the cylinder 234 will be drained through the

passages

260, 256, and 258, and port 289 to the chamber 224.

The valve piston 254 is connected by a stem 262 with a piston 264 slidable in a cylinder 266 formed in the valve body 220 and which is open to the inlet chamber 222. Movement of the piston 264 toward the inlet chamber is limited by a retaining ring 268 fitted into a suitable groove in the wall of the valve body 220.

The piston 264, stem 262, and valve piston 254 are biased to the right by a spring 270 bearing against a piston extension 272 integral with the piston 264 and projecting out of the valve body through bore 273. The force of the spring 270 is adjusted by a cap 274 which is threaded into a hollow boss forming chamber 276 in the projecting end of the valve body 220. An enclosing cap 27 8 prevents inadvertent adjustment of the adjustment member 274. The bore 258 extends tln'ough the piston 264 and extension 272 into the chamber 276 to relieve any pressure and drain any accumulated fluid through the port 280 to the reservoir 24.

The system of Fig. 3 has an adjustable needle valve 282 (comparable to the valve 96 of Fig. l) controlling flow through

conduits

284 and 286, the conduit 284 being connected via a port 288 to the inlet chamber 222, and the conduit 286 being connected directly to the cylinder 234.

Thus, when the pump 18 is operating, fluid will be transmitted to the cylinder 234, tending to close the valve 228.

When the motor 20 is started, solenoid 110, controlling valve 112, is energized to open communication between

conduits

114 and 116 to connect cylinder 266 behind piston 264 with the outlet chamber 224. The conduit 284 is also connected through the adjustable needle valve 106 and the branch conduit 118 to the conduit 114, and, when valve 112 is open, any flow through valve 106 is to drain. But when the valve 112 is closed, any fluid flow from the inlet chamber 222 through the restricting needle valve 106 will be to the cylinder 266 to move the piston 264 to the right. However, when the elevator is ascending at maximum speed, the pressure in chamber 222 will move piston 264 to the left, emptying the cylinder 266 through the open valve 112.

This system is also provided with a high pressure relief pilot valve 290 including a valve body 292 and a piston type valve member 294 having a passage 296 therethrough. The valve piston 294 slides in a cylinder 298, and the head end of the piston 294 is exposed to the pressure at the inlet chamber 222 through the branch conduit 300 connected to conduit 284. The valve piston 294 is biased to the left, as seen in Fig. 3, by a spring 302, the tensionon which may be adjusted by a bolt 304. When the pressure of the head end of the piston is great enough to overcome the force of the spring, the piston valve member 294 will move so that the passage 296 therein will connect conduit 306 leading to drain with conduit 308 connected to the conduit 286 and the head end of the valve piston cylinder 234 to allow the spring 240 rapidly to move the piston 232 and valve 228 to bypass open position, thus relieving the overload at the valve inlet 38.

The control system of Fig. 3 is equipped with an electric control circuit similar to that previously described, to operate the motor 20 and the solenoid 110, and consequently it will not be redescribed.

When it is desired to raise the elevator, the circuit to the motor 20 is closed, energizing the motor to operate pump 18, and the solenoid controlled valve 112 is also opened. Since, at the start of a raising sequence, the valve 228 is in its fully open position, fluid will flow from the pump 18 through the inlet chamber 222, the valve orifice 226, and the drain chamber 224 to the tank 24. However, the lift of the valve 228 is such that full flow therethrough produces a pressure rise at the inlet 38 and in the chamber 222, so that some fluid will flow through the conduit 284, needle valve 282 and conduit 286, to the cylinder 234,'thus producing a pressure rise therein to urge the piston 232 to the left and against the force of the biasing spring 240. This also moves the valve 228 toward closed position and, as it approaches closed position, the pressure in the chamber 222 will rise until it is high enough to open the check valve 28, thereby delivering fluid to the jack 12 to raise the elevator 10. The pressure rise continues until the valve 228 closes; since the valve 112 has been opened by solenoid 110, the pressure rise in chamber 222 moves piston 264 to the left to drain the cylinder 266. This movement, of course, prevents communications between the passage 260 in the piston 232 and the

passages

256 and 258 in the valve piston 254 and stem 262, thereby preventing the drainage of fluid coming into the cylinder 234. Because the valve 112 is open when the elevator is ascending at full speed, the relatively small inflow through the conduit 284 and the needle valve 106 is drained away without appreciable pressure rise.

travel where slowdown is desired in preparation for a stop, the circuit to the solenoid 110 is opened, thereby closing the valve 112 and terminating the escape of fluid from the cylinder 266 and the pressure tends to equalize in the cylinder 266 and in the inlet port 38 and chamber 222. The pressure now acts on the piston extension 272 tending to move it to the left; this movement is opposed by 10 the piston valve 254, tending to the tension of the spring 270, which is so proportioned that the pressure corresponding to minimum working load moves the piston 264 only a little way from its stop ring 268 while the pressure corresponding to the heaviest load will move the piston 264 nearly to its left-hand stop. The rate at which the piston 264 moves is adjustable by the setting of the needle valve 106 which regulates the rate at which fluid is admitted to the cylinder 266 behind the piston 264. When the piston 264 comes to rest, pressure in the cylinder 266 will be equal to that in the inlet chamber 222.

Movement to the right of the piston 264 when the valve 228 is fully closed uncovers the passage 260 to communicate it with the

passage

256, 258, allowing fluid to escape from the cylinder 234 to the outlet chamber 224, and

allowing the valve to open under the pressure of the spring 240. Opening of the valve 228 will continue until the passage 260 has only restricted communication with the passage 256, and the flow of fluid passing the valve 282 will exactly equal that escaping through the port 260,

passage 256, to drain.

Whenthe elevator cage is substantially at the landing, a limit switch is operated to break the circuit to the motor 20, thereby stopping the pumping operation and permitting the spring 240 to move the piston 232 to the right and the spring 270 will move the piston 264 to the right. Since the latter will move more rapidly than the former, the port 260 will communicate with the passage 256 to drain the cylinder 234. The system, therefore, would be conditioned for a starting operation at maximum pump output.

A third form of system quite similar to that shown' in Fig. 3 is shown in Fig. 4.

In this modification (Fig. 4), the head end of the cylinder 234 is closed by a partition 310, and the partition and a cap312 are secured to the valve body 220 by conventional bolts 314 and sealed against leakage by gaskets 316. The piston 232 is formed with an axial bore 318 extending into the stem 262 and is counterbored at 320 to provide a valve cylinder.

A valve rod 322 having a stem 324 of smaller diameter slides, respectively, in the bores 328 and 318. The valve rod 322 is provided with a plurality of longitudinally extending circumferentially arranged ports 326 in communication with a port 328 in the piston stem 262, so that under certain circumstances the drain chamber 224 may be communicated with the head end of the cylinder 234 via the communicating ports 326 and 328.

The valve stem 322 projects through a closely fitting hole 330 in the partition 310 and is integral with a piston When the elevator reaches a predetermined point in the 332 slidable in a cylinder 334 formed in the cap 312. The rightward movement of the piston is arrested by a stop 336 formed in the cap and a biasing spring 338 tends to move the piston 332 toward the stop 336. Maximum leftward movement of the piston is determined by an enlarged portion or stop 340 formed as an enlargement of the valve stem 322, and it is arranged to abut the partition 310. An axial bore 342 extends through the piston 332 and valve stem 322 to communicate the passage 318 with chamber 344 at the head end of the cylinder 334. This passage extends through and communicates with the inlet side of the valve 228 so that the pressure in the chamber 344 would be at inlet chamber pressure.

The cylinder 334 and the rod of the piston 332 form a chamber 346.

The inlet chamber 222 is connected to the needle valve 106 by a conduit 348, and the valve 106 is connected to the solenoid operated valve 112 by a conduit 358. The

outlet of the valve 112 is connected to the drain port or chamber 224 by conduit 360. The chamber 346 is con nected to the conduit 358 between the valves 106 and V 112 by a conduit 362.

Needle valve 282 is connected to 'the conduit 348 by move it to the right, plus branch conduit 364 and to the head end of the cylinder 234 by conduit 366. The conduit 366 is connected to the pressure relief valve 290 by a conduit 368 so that at certain times it may be in communication with the passage 296 in the valve spool 2%, to drain the cylinder 234 and relieve excess pressure at the inlet port 40. Conduit 360 is also connected to the valve 290 by a conduit 370 to effect the desired drainage through the pressure relief valve.

In this modification the operation is essentially the same as that shown in Fig. 3, with the piston 332 corresponding in its function to the piston 264 in communicating the head end of the cylinder 234 with the drain through the ports 326 and 328.

It will be seen from the foregoing description that the objectives which were claimed for this invention have been attained by the various structures shown and described.

While a number of embodiments of the hydraulic elevator control system constituting this invention have been shown and described, it will be apparent that other modifications thereof may be made without departing from the underlying principles of the invention. It is, therefore, desired, by the following claims, to include within the scope of the invention all such variations and modifications by which substantially the results of the invention may be obtained through the use of substantially the same or equivalent means.

What is claimed as new and desired to be secured by United States Letters Patent is:

1. In a hydraulic control system for hydraulic lifting devices having variable load conditions, having a source of fluid, and a constant output pump with its inlet connected to the fluid source and its outlet connected to the lifting device, the combination of a bypass valve having an inlet port and an outlet port, said inlet port being connected to the outlet of the pump and said outlet port being connected to the fluid source, an orifice in said valve connecting said inlet port with said outlet port, a valve member controlling the flow of fluid between said ports and the amount of fluid bypassed from the pump to the fluid source, means biasing said valve member to open position, piston means connected to said valve member and arranged to move said valve member toward closed position, means connecting the outlet of the pump to said piston means to apply high pressure fluid to said piston means to move said piston means in valve member closing direction, second piston means arranged to effect movement of said valve member toward open position, means connecting the outlet of the pump to said second piston means to apply a pressure to the latter to move it in such direction as to effect opening of said valve memher, and fluid conducting controllable means bypassing said last named means.

2. In a hydraulic control system for hydraulic lifting devices having variable load conditions, having a source of fluid, and a constant output pump with its inlet connected to the fluid source and its outlet connected to the lifting device, the combination of a bypass valve having an inlet port and an outlet port, said inlet port being connected to the outlet of the pump and said outlet port being connected to the fluid source, an orifice in said valve connecting said inlet port with said outlet port, a valve member controlling the flow of fluid between said ports and the amount of fluid bypassed from the pump to the fiuid source, means biasing said valve member to open position, piston means connected to said valve member and arranged to move said valve member to closed position, means connecting the outlet of the pump to said piston means to apply high pressure fluid to said piston means to move the latter in valve member closing direction and said valve member to closed position, second piston means arranged to effect movement of said valve member toward open position, means connecting the outlet of the pump to said second piston means to apply a 12 pressure to the latter to move it in such direction as to effect opening of said valve member by said biasing means, means bypassing said last named means to render said second piston means ineffective, and means operated by movement of the lifting device as it nears a stop for closing said bypassing means.

3. In a hydraulic control system for hydraulic lifting devices having variable load conditions, having a source of fluid, and a constant output pump with its inlet connected to the fluid source and its outlet connected to the lifting device, the combination of a bypass valve having an inlet port and an outlet port, said inlet port being connected to the outlet of the pump and said outlet port being connected to the fluid source, a passage in said valve connecting said inlet port with said outlet port, a valve member controlling the flow of fluid between said inlet port and said outlet port and the amount of fluid bypassed from the pump to the fluid source, means biasing said valve member to open position, piston means connected to said valve member and arranged to move said valve member toward closed position, means connecting the outlet of the pump to said piston means to apply high pressure fluid to said piston means thereby to move the latter in valve member closing direction to reduce the volume of bypassed fluid, second piston means arranged to effect movement of said valve member toward open position, means including throttling means connecting the outlet of the pump to said second piston means to apply a pressure to the latter to move it in valve member opening direction, and controllable means bypassing said last named means.

4. In a hydraulic control system for hydraulic lifting devices having variable load conditions, having a source of fluid, and a constant output pump with its inlet connected to the fluid source and its outlet connected to the lifting device, the combination of a bypass valve having an inlet port and an outlet port, said inlet port being connected to the outlet of the pump and said outlet port being connected to the fluid source, an orifice in said valve connecting said inlet port with said outlet port, a valve member controlling the flow of fluid between said ports and the amount of fluid bypassed from the pump to the fluid source, means biasing said valve member to open position, piston means connected to said valve member and arranged to move said valve member toward closed position, means connecting the outlet of the pump to said piston means to apply high pressure fluid to said piston means to move the latter to closed position, second piston means connected to said valve member and acting in opposition to said first piston means, means connecting the outlet of the pump to said second piston means to apply a pressure to the latter to move it in the valve member opening direction, controllable means bypassing said last named means to render said second piston means ineffective, and control means connected to said bypassing means to close the latter as the lifting device approaches a stop so as to permit said second piston means and said biasing means to move said valve member to partially open posimm.

5. In a hydraulic control system for hydraulic lifting devices having variable load conditions, having a source of fluid, and a constant output pump with its inlet connected to the fluid source and its outlet connected to the lifting device, the combination of a bypass valve having an inlet port and an outlet port, said inlet port being connected to the outlet of the pump and said outlet port being connected to the fluid source, an orifice in said valve it connecting saidinlet port with said outlet port, a valve member controlling the flow of fluid between said ports and the amount of fluid bypassed from the pump to the fluid source, means biasing said valve member to open position, piston means connected to said valve member and arranged to move said valve member toward closed position, means connecting the outlet of the pump to said piston means to apply high pressure fluid to said piston means to move the latter to closed position, second piston means connected to said valve member and acting in opposition to said first piston means, means including a pressure reducing means connecting the outlet of the pump to said second piston means to apply a pressure to the latter to move it in the valve member opening direction, and controllable means operated by movement of the lifting device bypassing said last named means to render said second piston means ineffective until the lifting device approaches a stop and the ascending movement of the lifting device-is to be slowed.

6. In a hydraulic control system for a hydraulic elevator or the like, having a source of fluid and a constant output pump with its inlet connected to the fluid source and its outlet connected to the elevator jack, the combination of a bypass valve having an inlet port connected to the pump outlet and an outlet port connected to the fluid source, an orifice in said valve connecting said inlet port with said outlet port, a valve member controlling the flow of fluid between said ports and the amount of fluid bypassed from the pump to the fluid source, means biasing said valve member to open position, piston means connected to said valve member and arranged to move said valve member toward closed position, means connecting the pump outlet to said piston means to apply high pressure fluid to said piston means to move the latter to closed position, second piston means connected to said valve member and acting in opposition to said first piston means, means including a pressure reducing means at said inlet port connecting the pump output to said second piston means through said inlet port to apply a pressure to the latter to move it in valve member opening direction, closable means bypassing said last named means to render said second piston means ineffective when the elevator is ascending at full speed, and means actuated by the elevator as it approaches a landing to operate said closable means to closed condition so that the pressure applied to said second piston means and said biasing means move said valve member to a partially open position to bypass a predetermined portion of the pump output to reduce the elevator speed.

7. In a hydraulic control system as claimed in claim 6, a normally closed releveling valve having its inlet connected to the pump outlet and its outlet connected to said first piston means, and means operated by the elevator when it settles below a landing at which it is stopped to open said releveling valve and start said pump to restore the elevator to the landing level.

8. In a hydraulic control system as claimed in claim 6, a pressure overload relief means sensitive to excess pressure conditions at the pump outlet, said relief means being connected to the pump outlet, the fluid source, and both said piston means and being operable by excess pressure at the pump outlet to connect said first piston means with the fluid source through said relief means and to connect said second piston means with the pump outlet through said relief means, thereby to cause said second piston means to move said valve member to open position to bypass the pump output to the fluid source and relieve the excess pressure.

9. In a hydraulic control system for lifting devices having variable load conditions, having a source of fluid, and a constant output pump with its inlet connected to the fluid source and its outlet connected to the lifting device, the combination of a bypass valve having an inlet connected to the output of the pump and an outlet connected to the fluid source, means biasing said bypass valve to open position, means at said bypass valve inlet for creating difierential pressures, separate pressure responsive means operatively connected to said valve in opposing senses, and means connected to said valve inlet and to said separate pressure responsive means for applying the pressures created at said valve inlet separately to said pressure responsive means in opposing senses to balance, the forces acting on said valve to an equilibrium 14 condition thereby to move said valve to partially open position to bypass a predetermined quantity of fluid from the output of the pump.

10. 'In a hydraulic control system for lifting devices having variable load conditions, having a source of fluid, and a constant output pump with its inlet connected to the fluid source and its outlet connected to the lifting device, the combination of a bypass valve having an inlet connected to the output of the pump and an outlet connected to the fluid source, means biasing said bypass valve to open position, a fluid flow restricting means at said bypass valve inlet for creating differential pressures, separate pressure responsive means operatively connected to said valve in opposing senses, and means connected to said valve inlet adjacent said flow restricting means and to said separate pressure responsive means for applying the pressures created at said valve inlet separately to said pressure responsive means in opposing senses to balance the forces acting on said valve to an equilibrium condition thereby to move said valve to partially open condition to bypass a predetermined quantity of fluid from the output of the pump.

11. In a hydraulic control system for lifting devices having variable load conditions, having a source of fluid, and a constant output pump with its inlet connected to the fluid source and its outlet connected to the lifting device, the combination of a bypass valve having an inlet connected to the output of the pump and an outlet connected to the fluid source, a valve member controlling fluid flow from said inlet to said outlet, means biasing said valve member to open position, a pair of oppositely acting pressure operated means connected to said valve member for moving the latter between open and closed positions, means at said bypass valve inlet for creating differential pressures, and means for applying the higher of the pressures created thereby to one of said pair of oppositely acting pressure operated means to move said valve member toward closed position and the lower of the pressures to move the other of said pressure operated means to move said valve member toward open position whereby all forces acting on said valve member may be brought to an equilibrium condition and said valve member is moved to partially open position to bypass a predetermined quantity of-fluid from the output of the pump regardless of the system back pressure at the pump outlet.

12. The combination set forth in claim 11, including means responsive to an overload pressure condition at the said bypass valve inlet for changing the pressure conditions on said oppositely acting pressure operated means, thereby to move said valve means to open position.

13. A bypass valve for a hydraulic lifting device control comprising a valve body having an inlet adapted to I be connected to the output of a hydraulic pump and an outlet adapted to be connected to drain, a bypass inlet valve orifice communicating said inlet with said outlet, :1 variable flow valve member movable in said orifice between open and closed positions and controlling the flow. of fluid therethrough, means biasing said valve member to open position, means forming a cylinder and piston combination connected to said valve member and provided with means connecting said cylinder to said inlet to overcome the force of said biasing means to move said valve member to closed position, means forming a secondcylin- I der and piston combination connected to said valve member and acting in opposition to said first cylinder and piston combination, means connecting said second cylinder and piston combination to said valve inlet, and selectively operable means connected to said last named means for controlling the amount of pressure fluid delivered from said valve inlet to said second cylinder and piston combination.

References Cited in the file of this patent UNITED STATES PATENTS 2,553,045 Jaseph May 15, 1951