US2548146A - Hydraulic transmission, including one pump and a plurality of motors - Google Patents

Description

April 10, 1951 w. FERRIS 2,548,146

HYDRAULIC TRANSMISSION, INCLUDING ONE PUMP AND A FLURALITY 0F MOTORS Filed April 3, 1947 4 Sheets-Sheet 1 FIG. 1

49 SPEED CONTROL 7 .2 f I9 ATTORNEY April 10, 1951 w. FERRIS 2,548,146

' HYDRAULIC TRANSMISSION, INCLUDING ONE PUMP AND A FLURALITY 0F MOTORS 4 Sheets-Sheet 2 Filed April 5, 1947 ATTORNEY April 10, 1951 w. FE R'RlS HYDRAULIC TRANSMISSION, mcwnmq ONE PUMP AND A PLURALITY 0F MOTORS Filed April 3, 1947 4 Sheets-Sheet 4 INVENTOR I WALTE R FERRIS m E mt ooQ/v 3 R: NB NB mm. \vQ mt m. B is t m9 3 n2 I IV A| I! A x E m9 y 3 3 L 5 1 up 3 43.28 6518 8528 48.58 85:8 m 1 Swan 32m Sumw 32w nuumm he .v 3

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Patented Apr. 10, 1951 UNITED STATES PATENT OFFICE? HYDRAULIC TRANSMISSION, INCLUDINGI ONE PUMR APLURALITYzOF MOTORS Walter. Ferris, Milwaukee, Wis,, assignor. to. The;

Oilgear (lompany Milwaukee, Wis., a corpora tion of Wisconsin ApplicationgApril 3, 1941;.SeriazliNo; 739,208..

posesa back; pressure. on the motor so, that the total load; on:. each motor, consists, of the mechanical. load; thereon. and. the back pressure thereon; V

In such; a..transmission, the pump must be capableof. deliveringliquidata rate great'enough toenable all of themotorsto operate simultaneously at the maximum. speeds which may be required. but. if. it delivers liquid at. the rate whenoneor; more of themotors are operating at a speed or:speeds.less .-than.such maximum, the

liquid discharged by thelpump will exceedthe "liquid required to energize the motors and the .or motor and. whichconsists of a number of small factors. For example, the slip of a pump includesliquid whichlleakswout of the cylinders,

liquid which leaks out of the pump. valve liquid which passes acrossthe face of. the pump valve from its. high pressure port to its. low pressure port and the compressionof theliquidj due to creating. pressure therein.

If in a. transmission of. the above type no means. were, provided to compensate, for variations inslip. and if the pump were adjusted to deliver liquid at. justthe rate and pressure required to enable. each ofthe motors to operate at the. desired. speed, the variation in slip resulting from. a change in the mechanical load on any of the motors would make the rate of pump. delivery. eithertoo little or too great to ,maintain themotors at the same speeds at'which they were operating before the change in load .pccurred.

.ifithelba dr en by amot r o at ssion of theabove. type. be. increased ordecreased after. the motor speed. hasbeen determined by adjustment of the choke. which throttles theoutL- flow from the motor, andif no means be. pro: vided to compensate for variations in slip, then such change in load will cause the speed. oiithat motor to. vary from the desired speed.

The; present. invention. has an an, object to provide a hydraulic. transmission in .whichaplurality of motors areenergizedby liquid supplied thereto from the same pumpto Whichthe motors are connected in. parallelwith each. other, the speed of each motor. isadjusted and con.- .trolled by throttling the outflow. therefrom, the pump is automatically adjusted to. deliver liquid at the rate requiredto cause the several motors to operate at their adjusted speeds and at the pressure required. to. enable thefmost heavily loaded motor to drive itsload', and the speeds ofthe individual motors are maintainedwithin closer limits than. was, heretofore possible in transmissions of this type.

Another object is. to provide a transmission of the above type in which the pump is auto.-

matically adjusted to compensate for variations inslip in response. to. a variation in the loadi on any of the motors.

Thisis. accomplished by passing the outflow from each motor through a speed control, which throttlesthe fi'ow. theretliroughj to thereby control'thespeed of the motor, andiby adjusting the displacement of the pump either in re.- sponseto adjustment oft-he speedcontrolor in response. to variations in the speed of the motor which carries the heaviest load.

Eachspeed control may. be. simply a choke if some variation in motor speed is permissible. or

is to. be moreaccurately controlled.

The inventionis exemplif ed bythe. transmissionsshownschematically in the accompanying drawings inwhichtheviews are as followsi Fig. 1 is. a diagrambf the hydraulic .circuit of a transmission having. a single, motor and a it may be. more complicated if themotor speed 7 speed controlwhich consists of. asingle throttle valve, a means for adjusting the. pump. being illustrated and the. parts being shown in the positions. occupied-when the. transmission is idle.

Fig. 21s a. view. similar toFig. 1 but showin .the pump provided with a controlin addition to the control shown in Fig, 1 and showing the speed control as including a constant pressure valve in addition to the throttle valve, the'partsbeing shown in the positionsoccupied when thetransmission is operating;

Fig. 3 is a view similar to Fig. 2 but showing the speed control as including means to compensate for variations in the slip of the motor.

Fig. 4 is a view similar to Fig. 3 but showing a speed control which will maintain the motor speed proportional to a reference speed.

Fig. is a diagram of the hydraulic circuit of a transmission in which the invention is embodied and in which the speed of each motor is controlled by a speed control which may be any one of the speed controls shown in Figs. 1-4.

The transmissions shown in Figs. 1-4 are not claimed herein but are claimed in a divisional application Serial No. 93,170, filed May 13, 1949.

Figure 1 The transmission shown in this figure includes a pump I, a motor 2 which is energized by liquid delivered thereto by pump I, a choke or throttle valve 3 which functions as a speed control for motor 2, and a control valve 4 which functions to effect adjustment of pump I until it is delivering liquid at the rate and pressure required to enable motor 2 to operate at the speed determined by the adjustment of throttle valve 3.

Pump I may be of any suitable type such as a radial piston pump, an axial pump, a vane pump or the like but it should have a control which is adjustable in response to variations in the pressure of the liquid discharged by motor 2.

For the purpose of illustration, pump I has been shown as being of the well known radial piston type and as having a displacement varying member or slideblock 5 which is constantly urged toward its maximum displacement position by a predetermined force such as by a spring 5. Pump I may be provided with a control including a piston 1 which is fitted in a stationary cylinder 8 and is adapted to move slideblock 5 toward its zero displacement position when liquid is supplied to cylinder 8 under the control of valve 4.

The transmission may be started and stopped by starting and stopping pump I but for the purpose of illustration it has been shown provided with a start and stop valve. having a valve 9 fitted in a cylinder H) which is connected by a channel II to the outlet of. pump I and is con- .nected by a channel I2 to the inlet of motor 2. Pump I is adapted to draw liquid through a channel I5 from a reservoir I6 and to discharge it into channel II. The pressure created by pump I is limited by a relief valve I1 which in practice is arranged inside the pump casing but which has been shown as having its inlet connected to channel II and its outlet connected to a channel I8 which is connected to channel I5 and also to valve casing I0.

Motor 2 has its outlet connected by a channel I9 to the casing 20 of throttle valve 3. Casing 29 has an axial bore 2I and an annular groove .the interior of throttle 23 into the right end of bore 2| which is connected by a channel 25 to reservoir I6. Since motor 2 can discharge liquid only at the rate at which the discharged liquid can flow through orifices 24, throttle valve 3 constitutes a speed control for motor 2.

Throttle 23 is urged toward the right by a spring 26 and it is adapted to be moved toward the left by means of a rod 21 which is fixed to throttle 23 and extends through the right end of casing 20. Adjustment is made by moving rod 21 in one direction or the other. As shown, rod 21 engages an adjusting screw 28 which may be turned in one direction to move throttle valve 23 toward the left or may be turned in the opposite direction to permit spring 26 to move throttle 23 toward the right and thereby vary the effective area of orifices 24. Throttle 23 may be provided with a stem 29 which extends through the left end of casing 23 and carries a gage block 39 so that the distance between the edge of port 22 and the edges of orifices 24 may be determined by measuring the distance between block 30 and a fixed point such as the end of casing 29.

Control valve 4 has been shown as including a valve plunger 35 which is fitted in a valve casin 36 having three annular grooves or ports 31, 38 and 39 formed therein. Port 31 may be of substantial width and the central piston 40 on plunger 35 may be of the same width so that, when plunger 35 is in its central position,-port 31 will be blocked but a very slight movement of plunger 35 in one direction or the other will open port 31 to one or the other of ports 38 and 39.

However, port 31 has been shown as being relatively narrow and piston 40 has been shown as having a plurality of tapered grooves 4| extending toward each other from opposite ends thereof and so located that, when valve plunger 35 is in its central position as shown in Fig. 2, port 31 will be substantially blocked, a slight movement of plunger 35 in one direction or the other from its central position will cause a slight flow of liquid to or from port 31 and a greater movement of plunger 35 will cause a greater flow.

Port 31 is connected to cylinder 8 by a channel 42, port 38 is connected to reservoir I6 by a channel 43 and port 39 is supplied with motive liquid in any suitable manner such as by being connected to channel I2 by a channel 44. The arrangement is such that, when valve plunger 35 is shifted toward the right from its central position, liquid may escape from cylinder 8 through channel 42, valve 4 and channel 43 to reservoir I6 and thereby permit spring 6 to move slideblock 5 toward the right to increase the displacement of pump I and, when pump I is delivering liquid to motor 2 and valve plunger 35 'is shifted toward the left, liquid may flow from channel I2 through channel 44, valve 4 and channel 42 to cylinder 8 and cause piston 1 to shift slideblock 5 toward the left to decrease the displacement of pump I.

Valve plunger 35 is urged toward the right by a spring 45 and it is adapted to be moved toward the left by a piston 46 fitted in a cylinder 41 which is arranged upon or formed in the right end of valve casing 36. The right end of cylinder 41 is connected to channel I9 by a channel 48 so that piston 46 is subjected to any pressure prevailing in channel I9. When the pressure in channel I9 rises to such a value that the force exerted by the liquid upon piston 46 exceeds the force exerted upon plunger 35 by spring 45, piston 46 will move plunger 35 toward the left, and when the pressure in channel I9 drops below that value, spring 45 will move plunger 35 toward the right.

If channel 48 were unrestricted, a sudden rise in pressure in channel I9 above the given value might cause liquid to flow so rapidly through channel 48 to cylinder 41 that piston 46 would move valve plunger 35 far enough to permit liq- In order to avoid the possibility that slideblock might oscillate or hunt, the flow from channel I 9 to cylinder 41 is restricted such as by inserting a choke 49 in channel 58. However, it, is desirable that the displacement of pump I v be increased rapidly when, necessary. Therefore, means are provided for permitting free flow from cylinder 41 to channel I9 such as by connecting a checkvalve5ll inparallel with choke 49.

Operation When pump I is running and valve 9 is in the position shown in Fig, LDump I will be atits maximum displacement and will draw liquid through channel I5 from reservoir I6'and discharge it into channelv I I. The liquid discharged I by pump I will flow through channel I I, valve casing l5 and channels I8 and I5 back to the inlet of pump I. Valve plunger 35.. of control valved will be held by spring 45 at the limit of its movement toward the right due to the lack of, any pressure in channel I9.

When valve 9 is shifted to the position shown in Fig. 2, the liquid discharged by pump I will flow through channel II, valve casing IE! and channel I2 to motor 2 and cause itto start to operate and to discharge liquidthrough channel I9, throttle valve 3 and channel to reservoir I6. Since motor 2 cannot instantly accelerate its load to full speed, the displacement of pump I will remain at maximum, pump I will continue to discharge liquid at its full volumetric rate and pump pressure will rise to maximum and open relief valve I I so that the liquid discharged by pump in excess of the liquid required by motor 2, may flow through relief valve I] and channels I8 and I5 backto the inlet of the pump. 7

Motor 2 will gradually accelerate and itv will discharge liquid at a gradually increasing rate through channel I9, throttle valve 3 and channel 25 to reservoir I6. Throttle valve 3 will 'at first offer but little resistance to the new of liq uid therethrough but its resistance willgradually increase as the how therethrough increases and this increasing resistance'will impose upon motor 2a back pressure which gradually increases and which extends from channel I9 through channel 48 and acts upon piston 96.

orifices 2 3 are so proportioned that, at any adjusted motor speed, the entire discharge from motor 2 will flow through throttle valve 3 at a predetermined low back pressure, such. as 25 p. s. i., in channel I9. This low back pressure is suficient to cause piston 45 to move plunger 35 of control valve i into its neutral positionas shown in Fig. 2. Therefore, when motor 2 reaches its adjusted speed as determined by the adjustment of throttle valve 3, the back pressure in channel I9 will be at the predetermined value, such as 25 p. s. i., and control'valve plunger 35 will be in its neutral p sition.

Since at this time pump I isstill discharging liquid at its maximum rate, motor 2 willstart to run-faster than its adjustedspeed and todischarge liquid ata rate inexcess of therateyat "which liquid canflow through throttle va1ve 3 at the predetermined back pressure, thereby causingthe; back pressure toincrease and enable piston lute-move valve plunger 35-far enough to open port, 31 to port 39. Thenliquid will flow from channel I-2through-channel 44, valve 4 and channel 62 to cylinder 8 and cause piston l to shift slideblock 5 toward the left until pump I is delivering only enough liquid to maintain a pressure which exceeds the pressure required by motor 2 to drive its load only by the small amount, such as 25 p; s. ii required to enable piston 46 to shift valve plunger" 35 against the resistance of spring 45.

When the pressure drop; acrossthe motoris subtracted from the reduced inputpressurein channel I2, the resultingback pressure in channel I9' is reduced bythe same amount until the predeterminedvalue of say 25p; s. i; is'reached'. Atthis point: spring 45 overcomes the back pressure acting on piston 45 andmoves valve plunger 35; toward the right untilport 37 1s open to port 39' only enough to enable the pressure in channels l2 and" 44 to maintain incylinder 8-just enough pressure to enable piston i to hold slid'eblock 5* in its adjusted position against the thrust of'spring 5,

Thereafter, if the speed of-motor 2 should tend to increaseabove the speed determined by the adjustment of throttle valve 3; motor 2 would tend to discharge liquid at an increased rate but this tendency would be resisted by throttle valve 3' which will causethe back pressure to rise and shift piston 56', and valve plunger 35 toward the leftto effecta reduction in the displacement of pump I and thereby overcome the tendency of motor 2 to increase its speed.

Conversely, if the speed of motor Z'should tend to decrease below the speed determined by the adjustment of throttle valve 3; motor 2 would tend to discharge liquid at a reduced rate which would cause the back pressure to drop and permit spring 45 to move valve plunger 35 toward the right to effect an increase in the displacement of pump I and thereby overcome the tendency of motor 2 to decrease its speed;

Pump I thus delivers only enough liquid to enablemotor 2 to operate at the speed determined by the adjustment of throttle valve 3 and it creates only enough pressure to enable motor 2 to drive its loadand to enable piston 46 to shift valve plunger 35, thereby avoiding the waste of power and the heating of liquid which is inherent in the prior transmissions in which motor speed is controlled by throttling motor outflow.

Since the flow through an orifice varies with the drop in pressure thereacross, the speedof motor 2 will vary somewhat from the speed determined by the adjustment of throttle valve 3 but the speed of motor 2 will be maintained within a narrow enough range for many installations. If it is desired to maintain the speed of motor 2 within a narrower range, a constant pressure valve may be inserted into channel i9, as indicated at 5| in Fig. 2, to maintain a substantially constant pressure at the inlet of throttle valve 3.

Figure 2 I In this figure, the transmission has been shown providedwith two pump controls instead in Fig. .1.

r The other control is or the type which permits the pump to discharge liquid at its full volumetric rate until pump pressure reaches a given maximum and then it reduces pump displacement until the pump is delivering just enough liquid to maintain that maximum pressure constant. This control may be of any suitable type, such as that shown in Patent No. 2,080,810, but for the purpose of illustration it has been indicated schematically as having a piston 52 fitted in a cylinder 53 which is connected to channel II by a channel 54 having a choke 55 inserted therein to limit the rate of flow from channel I I to cylinder 53, a check valve 56 being connected in parallel with choke 55 to permit free flow from cylinder 53 to channel II. A relief valve is built into the pump or into the control according to common practice but the relief valve has been omitted from the drawing in order to avoid complicating the view.

Servo motor 52-53 has been shown arranged outward from servo-motor 1-8 with the stem of its piston 52 adapted to engage piston I which has its stem in contact with slideblock but the positions of the two servo-motors may be reversed.

Also, a constant pressure valve 5| is arranged in channel l9 to maintain a substantially constant pressure at the inlet of throttle valve 3. Since motor 2 can discharge liquid only at the rate at which the discharged liquid can flow through the orifices 24 of throttle valve 3 and since valve 5| maintains a substantially constant pressure at the inlet of throttle valve 3 so that the drop in pressure across orifices 24 is substantially constant, throttle valve 3 and constant pressure valve 5| constitute a speed control for motor 2.

The transmission is otherwise the same as shown in Fig. 1. Therefore, like parts have been indicated by like reference numerals and further description thereof will not be given.

When the transmission is started and pump pressure rises to maximum, liquid will flow from channel through channel 54 to cylinder 53 and cause piston 52 to shift slideblock 5 toward the left and thereby reduce pump displacement until pump is delivering just enough liquid to maintain that maximum pressure constant. Thereafter, the transmission will function in the previously described manner. However, valve 5| will maintain a substantially constant pressure at the inlet of throttle valve 3 and, when motor 2 tends to accelerate beyond the speed determined by the adjustment of throttle valve 3, constant pressure valve 5| will cause the back pressure in channel l9 to rise very abruptly and promptly ellect a reduction in pump displacement which is just suflicient to overcome the tendency of motor 2 to accelerate. The speed of, motor 2 is thus maintained within closer limits than would be possible if valve 5| were omitted.

Figure 3 In this figure, the transmission has been shown provided with means to compensate for variations in the slip of the motor due to variations in motor load. The pump may be provided with a single control as shown in Fig. l or it may be provided with two controls as shown in Fig. 2. Since the transmission is otherwise unchanged, like parts have been indicated by like reference numerals and further description thereof will not be given.

When a motor is operating under load, liquid will pass across the face of the motor valve from the inlet port to the outlet port thereof and will augment the volume of liquid discharged from the motor cylinders, and the liquid discharged from the motor cylinders will expand into a greater volume due to the drop in pressure across the motor. The liquid which passes across the face of the motor valve and the expansion of the liquid discharged from the motor cylinder causes the motor during each revolution thereof to discharge a volume of liquid in excess of the volume of high pressure liquid contained in its cylinders, that is the liquid actually used in driving the motor, and this excess liquid will be referred to herein as the slip of the motor.

Compensation for variations in motor slip may be made by varying the effective area of orifices 24 in throttle valve 3 in response to variations in the drop in pressure across the motor but the transmission has been shown provided with a separate choke or slip compensator 5'! which is connected in parallel with throttle valve 3 and is adjusted in response to variations in the drop in pressure across the motor.

The slip compensator may take various forms but for the purpose of illustration it has been shown as including a body 58 having an inlet chamber 59 formed therein and connected by a channel 60 to channel H3 at a point between throttle valve 3 and constant pressure valve 5|. Chamber 55 intersects a bore 6| which is formed in body 58 and communicates at its lower end with a discharge channel 62 shown as being connected to discharge channel 25. A throttle 63 is closely fitted in bore 6| and has an axial bore 64 extending inward from its lower end into communication with one or more orifices 65 formed in the wall of bore 64 and adapted to register to a greater or lesser extent with chamber 59 when the slip compensator is functioning.

Body 58 also has provided therein a back pressure chamber 66 which is connected to the outlet of the motor to be controlled such as by being connected by a channel 61 to channel I9 at a point between motor 2 and constant pressure valve 5|. A plunger 68 is closely fitted in the lower part of body 58 and extends into chamber 66 so that its upper end is subjected to any pressure prevailing in chamber 66. Plunger 68 is adapted to transmit motion to a lever 69 which. is pivoted intermediate its ends upon the upper end of throttle 63. Preferably, one end of lever 69 is connected to the lower end of plunger 58 by a yoke which extends around body 58 but for the purpose of illustration plunger 68 has been shown as being connected to one end of lever 69 by a rod 10 formed integral with plunger 68 and as being urged upward by a spring H which encircles rod 10 between the top of body 58 and adjusting nuts 12 which are threaded upon rod "ill, upward movement of plunger 68 being limited by a stop 13 arranged upon its lower end.

Body 58 also has formed therein a high pressure chamber 14 which is connected to the inlet of the motor to be controlled such as by being connected to channel |2 by a channel 75. Closely fitted in the upper part of body 58 is a plunger 16 which extends into chamber 14 and is connected at its upper end to the other end of lever 69. Plunger 16 has a stop ll fixed to or formed upon the intermediate portion thereof and it is urged downward by a spring 18 arranged between stop 11 and an abutment 19 which is fastened to body 58.

The arrangement is such that the pressure prevailing at the inlet of the motor tends to move plunger 16 upward and the pressure prevailing 9 at the outlet of themotor tends to move plunger .68 downward. When the inlet pressure exceeds the value determined by theadjustment of spring 18, the liquid in chamber 14 will move plunger I9 upward and compress spring 18 until the force exerted by spring 18 equals the force exerted by the liquid upon the lower end of plunger 18. When the outlet pressure exceeds the value determined by the adjustment of spring 3|, the liquid in chamber 68 will move plunger .88 downward and compress spring until the force ex- .erted by spring ll equals the force exerted by the liquid upon the upper end of plunger 88.

Upward movement of either one of the two plungers 68 and 16 without a corresponding downward movement of the other one of the two plungers will cause lever 89 to raise throttle 88 and thereby increase theefiective area of orifices 85. That is, a greater area of orifices 65 will register with chamber 59,. Conversely, downward movement of either one of the two plungers 88 and 16 without a corresponding upward movement of the other one .01 the two plungers will cause lever .69 to lower throttle 83 and thereby decrease the effective area oforifices .65.

When the motor is driving a substantial load,

the inlet pressure will be high enough to have raised plunger 18 part way to the limit of its movement, the back pressure or outlet pressure will be high enough to have moved plunger 88 downwarda short distance and therelative positions of the two plungers will be such that lever 89 will have raised throttle 8,3 to uncover a part of the area of orifices 85. If springs 3| and 18 are properly calibrated, the positions .of p-lungers .88 and 118 will be such that the efiective area of orifices 65 will be just large enough to permit liquid ,to flow therethrough at a rateapproxirnately equal to the slip of the motor. Thereafter, a variation in the load upon the motor will cause a variation in the drop in pressure across the motor which will cause plunger '38 and/or plunger 88 to readjust throttle 83 in accordance with the variation inmotor slip due to the variation in motor load. Throttle valve 3, constant pressure valve and slip compensator 5 thus constitute a speed control forv motor 2.

The transmission will function in the previously described manner except that apart of the liquid mdischarged by .motor Z will flow through slip compensator}?! and the rate of flow through compensator 57 will be varied proportionally to variations in pressure drop across .themotorto compensate for the variations in motor slip.

Figure 4 Inthis figure, throttle valve 3 has been shown as being adjusted in response to the speed of motor 2 varying relatively to a reference speedwith a reference speedthrough a diiierential having three .legs' 88, 8| and .82. The differential has its first leg .88 driven by motor 2 at a speed proportional to the speed thereof .as by means of a suitable drive 83 and its second'leg 8| driven at a reference speed so that .its third leg .82 rotates in one direction or the other in response to the motor speed varying relatively to the ref- =erence speed.

Throttle valve 3 is adjustable in any suitable manner in response to rotation of leg 82. As shown, leg 82 is adapted to rotate a screw 84 having a nut 85 threaded thereon and restrained from rotation in any suitable manner so that rotation of screw 84 in one direction or the other will cause nut 85 to move axially in one direction or the other, axial movement of nut 85 being limited by two stops 88 and 81. Adjustment of throttle valve 3 in response to movement of nut 85 is efjfected by means of a lever 88 which engages the control rod 27 of throttle valve 3 and has one of its ends pivoted to nut 85 and its other end pivoted upon a normally stationary pin 89.

'In order that the motor speed may be adjusted, means may be provided to regulate the speed at which leg 8! of the differential is driven. As shown, legj 8| is driven from a power source through a. friction transmission having a cylinder 98 which is connected to leg 8| by a suitable drive 9|, a irictiondisk '92 which is driven at a reference speed, two balls 93 which transmit motion from disk 92 to cylinder 90, and an adjusting member 94 which retains balls 93 in adjusted positions and also carries the pin 89 upon which lever 88 is pivoted.

Disk 92 may be driven at any desired speed which may be constant or varied. As shown, disk 92 is driven through a suitable drive 95 from a constant speed electric motor 96. Adjusting means 98 maybe moved to and held in adjusted position inany suitable manner but for the purpose of illustration it has been shown as being adjusted by means of a nut '9'! which is threaded upon one end portion of member 94 and is held against a stationary abutment 98 by the thrust 'on theaxis of disk 92, no motion would be transmitted from disk 92 to cylinder 98 but, when disk 92 is rotated and balls 93 are offset from the axis of disk 92, cylinder 98 will be driven through balls 93 from disk 92 and it will drive leg 8| of the difierential through drive 9| at a speed determined by the distance balls 93 are offset from the axis of d sk 92.

The transmission will operate in the previously described manner except that a variation in the speed of motor 2 relative to the reference speed will cause the differential to adjust throttle valve 3 which will vary the resistance to the discharge of liquid by motor 2 and thereby correct the variation in motor speed.

More specifically, an increase in motor speed above the correct speed as determined by the adjustment of member 94 will cause drive 83 to increase the speed of leg 88 of the differential relatively to the speed of leg 8| and thereby cause leg 82 to rotate. Leg 82 will rotate screw 84 which will move nut 85 and the upper end of lever 88 toward the left. Lever 88 through rod 27 will move throttle 23 toward the left to decrease the eil'ective area of orifices 24 and thereby reduce the motor speed until motor 2 is operating at the correct speed. Conversely, a decrease in motor speed below the correct speed as determined by the adjustment of member 94 will cause drive 83 to decrease the speed of leg of the diife'rential relatively to the speed of leg 8| and thereby cause leg 82 torotate. Leg 82 will rotate screw 88 which will move nut and the upper end of lever 88 toward the right. Moving lever 88 toward the right will permit spring 26 to move throttle 23 toward the right to increase the effective area of orifices 24 and thereby permit the 11 motor speed to increase until motor 2 is operating at the correct speed.

Throttle valve 3, slip compensator 51, constant pressure valve and the differential thus constitute a speed control which maintains the speed of motor 2 proportional to a reference speed. However, if motor 2 is to operate only at a given speed which may be either constant or varying, friction transmission 90-94 and its drive 95-96 may be omitted, pin 89 may be fixed in a stationary position and leg 8| of the differential may be driven at a given speed which may be constant or varying.

Also, slip compensator 51 may be omitted as the differential will adjust throttle valve 3 to compensate for variations in motor slip due to variations in motor load but a slight interval of time is required for the differential to make such correction while slip compensator 51 responds substantially instantaneously to make the correction.

Therefore, the slip compensator should be incorporated in the speed control when prompt response is desired.

At the same time that the speed control is causing motor 2 to operate at the correct speed,

any variation in the back pressure on motor 2 causes control valve 4 to effect adjustment of pum displacement to cause pump I to deliver liquid at a correct rate to enable motor 2 to operate at the speed determined by the speed control and at the correct pressure to enable motor 2 to drive its load as previously explained.

Figure 5 The transmission shown in this figure includes a plurality of hydraulic motors, a single pump for energizing all of the motors, a speed control for each of the motors and means for adjusting pump displacement in response to variations in the back pressure on the motor having the lowest back pressure.

As shown, a pump IOI supplies all of the liquid for energizing a plurality of motors I02, five being shown and designated I02A, I02B, I020, IDZD and I02E. Pump IOI may be of any suitable type and it may have its displacement varied solely in response to variations in motor back pressure as shown in Fig. l or it may have its displacement initially reduced in response to pump pressure reaching a given maximum and thereafter have its displacement varied in response to variations in motor back pressure as shown in Fig. 2.

The transmission may be started and stopped by starting and stopping pump IOI but for the purpose of illustration it has been shown provided with a start and stop valve having a valve I69 fitted in a cylinder IIO which is connected by a channel III to the outlet of pump IOI and is connected by a channel II2 to the inlets of all of the motors I02. 7

Pump IOI is adapted to draw liquid through a channel I I5 from a reservoir I I6 and to discharge it into channel III. The pressure created by pump IOI is limited by a relief valve I I1 which in practice is arranged inside the pump casing but which has been shown as having its inlet connected to channel I I I and its outlet connected to achannel II8 which is connected to channel H5 and also to valve casing I I0.

Each motor I02 has its outlet connected by a channel I I9 to a speed control which controls the speed of that motor, the channels being designated II9A, H93, H90, II9D and II9E and connected to motors I02A, I02B, I02C, I02D and I02E respectively. Each of the speed controls may be any one of the speed controls shown in Figs. 1, 2, 3 and 4 or be a speed control such as shown in Fig. 4 but with the friction transmission and/or the slip compensator omitted therefrom. All of the liquid discharged by each motor I02 flows through its speed control into a channel I25 which is connected to all of the speed controls and discharges into reservoir II6.

Adjustment of pump displacement in response to variations in motor back pressure is under the control of a valve I04 which is identical to the valve 4 previously described and corresponding parts thereof have been indicated by corresponding reference'numerals so that further description thereof is unnecessary. Control valve I04 is connected into the circuit in the same manner as the control valve 4 previously described. That is, it has its port 31 connected to the displacement varying means of pump IOI by a channel I52, its port 38 communicates with a channel I43 which discharges into reservoir III; and its port 39 is connected to channel II2 by a channel I44.

Also, control valve I04 functions in the same manner that control valve 4 functions as previously explained. That is, an increase in the pressure in cylinder 41 causes piston 46 to move valve plunger 35 toward the left to permit liquid to flow from channel II 2 through channel I44, valve I04 and channel I42 to the pump displacement varying means and thereby effect a decrease in pump displacement, and a decrease in the pressure in cylinder 4! permits spring 45 to move valve plunger 35 toward the right to permit liquid to flow from the displacement varying means I42, its port 38 communicates with a channel I43 to reservoir H6 and thereby effect an increase in pump displacement.

In order that valve I04 may be operated in response to variations in the back pressure on the motor having the lowest back pressure. the transmission is provided with one or more selector valves I50. The number of selector valves required is one less than the number of motors so that only one selector valve would be required if the transmission had only two motors. As shown, the transmission is provided with four selector valves which are designated IA, I563.

I500 and I5'ID respectively, and each valve has a plunger I5I fitted in a valve body I52 having three annular grooves or ports I53, I54 and I55 formed in its side wall and two ports I56 and I51 formed in its opposite ends.

Val e I50A has its port I56 connec ed to channel USA by a channel I60, its nort I51 connected to channel IISB by a channel I6I, its port I54 connected to channel I60 by a channel I62 having a choke I63 arranged therein, its port I55 connected to channel I6I by a channel I64 having a choke I65 arranged therein and its port I53 connected to the port I56 of valve I50B by a channel I66.

Valve I50C has its port I56 connected to channel I IQC by a channel I61, its port I51 connected to channel I IQD by a channel I68, its port I54 connected to channel I61 by a channel I69 having a choke I10 arranged therein, its port I55 connected to channel I66 by a channel III having a choke I12 arranged therein, and its port I53 connected to port I51 of valve I503 by a channel I13.

Valve I50B has its port I54 connected to channel I66 by a channel I14 having a choke I15 arranged therein, its port I55 connected to channel. I13 by a channel I16 having a choke I11 arpressure in channel Itll.

channel -I I8 by a channel I82 having achoke I83 arranged therein, and its port 153 connected .to the cylinder 41 of control'valve IIMby-achannel "I84=having a choke I85 arranged therein and .a check-valve I86 connected inparallel with choke I85.

It is to benoted-that-each valve 159*has its portsI56 and i5! connected to'the motor outlets "through free passages and "its ports I54=and 4 55 connected to the motor outletsthrough "choked passages which resist the now of liquid'thfarethrough and thereby permit liquid to flow freely from the outlet of the rnotorhavingthe higher backpressure toport I56 or I51 and shift-valve plunger I5'I to a position "in-which port 453 is connected to the outlet of the motor having the lower back pressure.

.Forexample, if plunger "I5I of valve 150A were at the left-and 'thebackpressure onmotor ItZA should become greater thanthe back pressure on 'motor II'IZB, liquid'would tendto'flow fromchan- ;nel III9A'through channels I60 and 'I 52 andports 1514 and "I53 ofvalve ISUA'but the flow therethrough is restricted by choke I63. Therefore, since the pressure in channel I5I! pishigher'than the pressure in channel Iii! and :channel 6011s unrestricted, liquid will flow 'therethrou h toport I55 andmove-plunger I5I of alve *I56Atoward the right to the position shown so that port 153 wouldbe open to port I55 andjthe' lower back pressure could extend from channel HEB ithrough channels l6I and I54 andportsltfiancl I55 into channel I66.

If plunger I5I of valve I159C'were at the left i and the back pressure on motor "I 026 :should'become greater than the back pressure on motor "fllzDyplunger 15! of valve150C wouldbe shifted to "the right .by the preponderance of pressure in channel I61 for the same *reason that plunger J 5| of valve 'I'5IlA wou'ldbe shifted to theright by the preponderanceof pressure in channel I553. With plunger I5I of valve [550 inits right hand position. as shown, the "lowerback pressure could extend from channel I"I'9D through channels I58 and HI and ports I55 and 153 into channel I13.

jIf plunger I5I of valve I503 were at the right and tbe'back pressure on either of motors IEIZC and .IBZD shouldbecomegreater than the back pressure ofeither of motors I'GZA and IBZB, the pressure in channel 113 would become greater thanthe pre sure in channel I66 and iplunger I5I of valve I'50B would'be shifted to the leftiby the preponderance of pressure in channel I73 for the *same reason that plunger I5I of valve 150A would be shifted to the rightby ithepreponderance of With plunger iii! of valve I5IlB in "its left hand position as shown, the lower pressure in channel I66 could extend therefrom through channel I'M and valve I5UB' into "channel I18.

jIipIunger "I5I of valve I551) were at the right and the back pressure onmotor IUZE should become greater than the pressure in channel H8,

plunger I5I of valve I591) would be shiftedto the "left'by the preponderance ofpressure in channel I19 .for the same reason thatplunger l 5! of valve 150A would be'shifted to the right'by the'preponderance o'f 'pre ssure in channel "I55. With plunger I5I of valve 150D in itsfleft hand position as shown, :the lower ressure in channel I18 :could therightito effect anincrease inpump .displacement: as previously explained.

Itwillbe obvious that the plunger I5I of each valve I5Ilis shifted'bythe'higher of the'two pressuresprevailing at its-ports I56'and'I5I andthat each valve I functions automatically .to connectthe lower of thetwo'pressures to its port I53 so-that control valve III-l is always operatedrand effectsadjustment of the displacement of pump "IUI in response to variations in the back "pressure on the motor having the lowest back pressure regardless of which one of the motors has the lowest back pressure.

Since all of the motors are connected to the pump in parallel witheach other, pump pressure prevails at the inlets of all of the motors and the pump must create a pressure high enough to en- 'able the most heavily loaded motor to drive its load. The pressuredrop across each motor varies in accordance with variations in the load on that motor and, since the same pressure prevails at the inlets o'f-all of 'the=motors, themost heavily loadedmotorwill have the greatest pressure drop thereacross and, consequently, the lowest back pressure.

By-adjusting the displacementofthe pump in response to-variations'in the backjpressure on the motor having the lowest back pressure as previously explained, the pump willdeliver liquid at just the rate'required to enable all of the motors to operate at the'individual speeds determined by the individual'speed controls and the pump will create just enough pressure toefiect operation of the motor requiring the highest pressure, thereby avoiding the waste of power-and heating of the liquid-which would result if the transmissionwere otherwise controlled.

The invention'herein set forth maybemodified "in-various o'therways without departing from the scope thereof which is hereby claimed as fol-' lows:

,1. A hydraulic transmission, c'omprising'a pump :having means for varying its displacement, a

plurality of motors having'the inlets thereof connectedto the outlet of said pump and adapted to be simultaneously energized by liquid delivered thereto by said pump, means for controlling the speed of each of said motors including achoke for resisting the discharge of liquid from that motor-and to'thereby'impose a back pressure on "that 'motor and means for compensating for variations in the slipofthat motor dueto variaitionsin the load on that motor, and means for effecting operation of said displacement varying means in response to variations in the back pressure on the motor having the lowest back presl sure.

for resisting the discharge of liquid from that motor and to thereby impose a back pressure on that motor and a constant pressure valve connected between that motor and said choke to maintain a substantially constant pressure at the inlet of said choke, and means for effecting operation of said displacement varying means in response to variations in the back pressure on the motor having the lowest back pressure.

3. A hydraulic transmission, comprising a pump having means for varying its displacement, means for supplying motive liquid to said displacement varying means including a control valve having hydraulic actuating means, a plurality of motors having the inlets thereof connected to the outlet of said pump and adapted to be simultaneously energized by liquid delivered thereto by said pump, means for controlling the speed of each of said motors by throttling the outflow from each motor and thereby imposing a back pressure on each motor, and means for connecting said valve actuating means to the outlet of the motor having the lowest back pressure.

t. A hydraulic transmission, comprising a pump having means for varying its displacement, means for supplying motive liquid to said displacement varying means including a control valve having hydraulic actuating means, a plurality of motors having the inlets thereof connected to the outlet of said pump and adapted to be simultaneously energized by liquid delivered thereto by said pump, means for controlling the speed of each of said motors by throttling the outflow from each motor and thereby imposing a back pressure on each motor, and means for connecting said valve actuating means to the outlet of the motor having the lowest back pressure and including one less selector valve than there are motors and each selector valve being connected to the outlets of two motors and operable by liquid from the outlet of the motor having the higher back pressure to a position to permit liquid to flow through said valve from the outlet of the other of those two motors.

5. A hydraulic transmission, comprising a pump having hydraulic means for varying its displacement and having means responsive to pump pressure reaching a given maximum for reducing its displacement until it is delivering just enough liquid to maintain that pressure substantially constant, means for supplying motive liquid to said displacement varying means including a control valve having hydraulic actuating means, a plurality of motors having the inlets thereof connected to the outlet of said pump and adapted to be simultaneously energized by liquid delivered thereto by said pump, means for controlling the speed of each of said motors by throttling the outflow from each motor and thereby imposing a back pressure on each motor, and means for connecting said valve actuating means to the outlet of the motor having the lowest back pressure.

6. A hydraulic transmission, comprising a pump having means for varying its displacement, a plurality of motors having the inlets thereof connected to the outlet of said pump and adapted to be simultaneously energized by liquid delivered thereto by said pump, means for controlling the speed of each of said motors by throttling the outflow from each motor and thereby imposing a back pressure on each motor, and means for effecting operationof said displacement varying means in response to variations in the back pressure on the motor having the lowest back pressure.

7. A hydraulic transmission, comprising a. pump having means for varying its displacement, a plurality of motors having the inlets thereof connected to the outlet of said pump and adapted to be simultaneously energized by liquid delivered thereto by said pump, means for controlling the speed of each of said motors by throttling the outflow from each motor and thereby imposing a back pressure on each motor, means for eiiecting operation of said displacement varying means in response to variations in the back pressure on the motor having the lowest back pressure, each of said motor speed control means including, means for choking the outflow from the motor with which it is associated, means responsive to variations in the pressure of the liquid discharged by that motor relative to the pressure of the liquid delivered to that motor for adjusting said choking means to thereby compensate for variations in the slip of that motor due to variations in motor load, and means for adjusting said choking means in response to motor speed varying from a given speed.

8. A hydraulic transmission, comprising a pump having hydraulic means for varying its displacement, means for supplying motive liquid to said displacement varying means including a control valve having hydraulic actuating means, a plurality of motors having the inlets thereof connected to the outlet of said pump and adapted to be simultaneously energized by liquid delivered thereto by said pump, means for controlling the speed of each of said motors by throttling the outflow from each motor and thereby imposing a back pressure on each motor and by compensating for variations in the slip of that motor due to variations in the load on that m0- tor, and means for connecting said valve actuating means to the outlet of the motor having the lowest back pressure.

9. A hydraulic transmission, comprising a pump having hydraulic means for varying its displacement, means for supplying motive liquid to said displacement varying means including a con.- trol valve having hydraulic actuating means, a plurality of motors having the inlets thereof connected to the outlet of said pump and adapted to be simultaneously energized by liquid delivered thereto by said pump, means for controlling the speed of each of said motors by throttling the outflow from each motor and thereby imposing a back pressure on each motor, and selector valve means connected between said valve actuating means and the outlets of said motors, said selector valve means being responsive to the differences in the pressures in said outlets for subjecting said valve actuating means to the pressure in the outlet of the motor having the lowest back pressure.

10. A hydraulic transmission, comprising a pump having means for varying its displacement, a plurality of motors having the inlets thereof connected to the outlet of said pump and adapted to be simultaneously energized by liquid delivered thereto by said pump, means for controlling the speed of each of said motors by throttling the outflow from each motor and thereby imposing a back pressure on. each motor, and means for effecting operation of said displacement varying means in response to variations in the back pressure on the motor having the lowest back pressure, each of said motor speed control means including means for choking the outflow from the motor with which it is associated, and means responsive to vari- 1 17 ations in the pressure of the liquid discharged by that motor relative to the pressure of the liquid delivered to that motor for adjusting said choking means to thereby compensate for variations in the slip of that motor due to variations in motor load.

11. A hydraulic transmission comprising a pump having hydraulic means for varying its dis-.

placement, means for supplying motive liquid to said displacement varying means including a control valve having hydraulic actuating means, a plurality of motors having the inlets thereof connected to the outlet of said pump and adapted to be simultaneously energized by liquid delivered thereto by said pump, speed control means connected to the outlet of each motor to control the speed of each motor by throttling the outflow therefrom and thereby imposing a back pressure thereon, and means for connecting said valve actuating means to the outlet of the motor having the lowest back pressure, each of said speed control means including a choke for limiting the rate of discharge of liquid from the motor to which it is connected, a constant pressure valve connected between said choke and the outlet of that motor to maintain a substantially constant pressure at the inlet of said choke, and means for compensating for variations in the slip of that motor due to variations in the load thereon.

12. A hydraulic transmission comprising a pump having hydraulic means for varying its displacement, means for supplying motive liquid to said displacement varying means including a control valve having hydraulic actuating means, a plurality of motors having the inlets thereof connected to the outlet of said pump and adapted to be simultaneously energized by liquid delivered thereto by said pump, speed control means connected to the outlet of each motor to control the speed of each motor by throttling the outflow therefrom and thereby imposing a back pressure thereon, and means for connecting said valve actuating means to the outlet of the motor having the lowest back pressure, each of said speed control means including a main choke for limiting the rate of discharge of liquid from the motor to which it is connected, a constant pressure valve connected between said choke and the outlet of that motor to maintain a substantially constant pressure at the inlet of said choke, and a second choke connected in parallel with said main choke and adjustable in response to variations in the pressure at the outlet of that motor relative to the pressure at the inlet of that motor to vary the rate of flow therethrough to thereby compensate for variations in the slip of that motor due to variations in motor load. 7

13. A hydraulic transmission comprising a pump having hydraulic means for varying its displacement, means for supplying motive liquid to said displacement varying means including a control valve having hydraulic actuating means, a plurality of motors having the inlets thereof connected to the outlet of said pump and adapted to be simultaneously energized by liquid delivered thereto by said pump, speed control means connected to the outlet of each motor to control the speed of each motor by throttling the outflow therefrom and thereby imposing a back pressure thereon, a selector valve having two inlet ports connected to the outlets of two of said motors respectively and an outlet port adapted to communicate with one or the other of said inlet ports, and means for connecting said outlet port to said valve actuating means, said selector valve being responsive to a difference in the back pressure on said two motors for connecting the outlet of themotor having the lower back pressure to said outlet port.

14. A hydraulic transmission comprising a pump having hydraulic means for varying its displacement, means for supplying motive liquid to said displacement varying means including a control valve having hydraulic actuating means, a plurality of motors having the inlets .thereof connected to the outlet of said pump and adapted to be simultaneously energized by liquid delivered thereto by said pump, speed control means connected to the outlet of each motor to control the speed of each motor by throttling the outflow therefrom and thereby imposing a back pressure thereon, and selector valve means one less in number than the number of motors connected between said valve actuating means and the outlets of all of said motors for causing said valve actuating means to be subjected to the pressure at the outlet of the motor having the lowest back pressure, each of said selector valve means having two inlet ports connected to the outlets of two motors and an outlet port connectable to said valve actuating means and adapted to communicate with one or the other of said inlet ports, each of said selector valve means being responsive to a difference in the back pressures on the two motors to which it is connected for connecting its outlet port to the outlet of the motor having the lower back pressure.

WALTER FERRIS.

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

UNITED STATESVPATENTS Number Name Date 1,578,233 Ferris Mar. 23, 1926 1,974,138 Ferris Sept. 18, 1934 2,005,731 Ernst et al June 25, 1935 2,056,896 Douglas Oct. 6, 1936 2,166,423 Clark July 18, 1939 2,198,035 Ferris Apr. 23, 1940 2,238,061 Kendrick Apr. 15, 1941 2,291,011 Vickers July 28, 1942 2,374,630 Tucker Apr. 24, 1945 2,408,303 Ernst Sept. 24, 1946 2,415,603 Muller et a1 Feb. 11, 1947 2,432,305 Geiger Dec. 9, 1947

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