US2827763A

US2827763A - Hydraulic system

Info

Publication number: US2827763A
Application number: US509724A
Authority: US
Inventors: Roy H Govan; Harold J Meek
Original assignee: JAROCO ENGINEERING CO
Current assignee: JAROCO ENGINEERING Co
Priority date: 1955-05-20
Filing date: 1955-05-20
Publication date: 1958-03-25
Anticipated expiration: 1975-03-25

Description

March 25, 1958 R. H. GOVAN ET AL 2,827,763

HYDRAULIC SYSTEM Filed May 20. 1955 3 Sheets-Sheet 1 INVENTORS 7? 96am; Jm% JM BY A1 ATT RNEY March 1958 R. H. GOVAN ET AL 2,827,763

HYDRAULIC SYSTEM Filed May 20, 1955 '5 Sheets-Sheet 3 FIG. 4

g Q INVENTORS j/raldJfieck BY A RNEY United States Patentuse HYDRAULIC SYSTEM Roy H. Govan, Hoboken, N. 1., and Harold J Meek, Staten Island, N. Y., assignors to Jaroco Engineering (10., Hohoken, N. 3., a corporation of New Jersey Application May 20, 1955, Serial No. 509,724

Claims. (Cl. 60-51) The present invention relates to a hydraulic system. More particularly, the present invention relates to a selfcontained hydraulic system which includes a hydraulic fluid accumulator that communicates with a motor-pump unit, the motor pump unit being responsive to various conditions of load and to fluid under pressure in the accumulator, thereby being alternately operated as a motor and as a pump for effecting the rotation of the shaft of the unit.

It is the general practice in power operated devices that utilize hydraulic fluid as a motive fluid to direct the motive fluid under pressure to a motor or the like to thereby perform a particular operation such as, for example, lifting a load. It is desirable in such systems to employ a self-contained hydraulic device wherein a hydraulic motive fluid may be maintained under pressure and distributed periodically to aid in accelerating a vehicle shaft or for controlling the rotation of a shaft subjected to loads. Prior to the instant invention, the heretofore i nown hydraulic systems did not provide for the accumuation of hydraulic fluid under pressure wherein the fluid under pressure could be effectively controlled when the system was subjected to a variety of conditions.

It is therefore an object of the present invention to provide a hydraulic system wherein hydraulic motive fluid contained therein is eflectively controlled during all conditions of operation of the system.

Another object of the present invention is to provide a hydraulic system for effecting the operation of a motor-pump unit, motive fluid contained in the system being controllably directed to said motor-pump unit for controlling the operation thereof.

Still another object of the present invention is to provide a hydraulic system which includes an accumulator for receiving motive fluid therein, the motive fluid being controlled for effectively operating a motor-pump unit.

Still another object of the present invention is to provide an accumulator for a hydraulic system which is adapted to maintain a motive fluid therein at a predetermined pressure, the motive fluid under pressure being utilized to operate a motor-pump unit.

Still another object of the present invention is to provide a hydraulic system wherein a variable displacement pump is employed for directing a motive fluid to a hydraulic fluid accumulator, the motive fluid being maintained in the accumulator at a predetermined pressure during various operating conditions of the hydraulic system.

Still another object of the present invention is to provide a hydraulic system wherein a motive fluid maintained in a hydraulic fluid accumulator under pressure is adapted to be directed to a motor-pump unit operatively connected to a vehicle engine shaft, thereby accelerating the engine shaft.

Still another object of the present invention is to provide a hydraulic system wherein a motor-pump unit is responsive to the load on the shaft thereof to automatically control the supply of a motive fluid under pressure to said unit for operating the unit as a pump or motor.

Still another object of the present invention is to provide a hydraulic system wherein a motor-pump unit is manually controlled for reversing the rotation thereof, thereby controlling the operation of the shaft of the unit under various conditions of load.

Other objects and the nature and advantages of the instant invention will be apparent from the following description taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is a diagrammatic illustration of one form of the hydraulic system embodied in the present invention;

Fig. 2 is a diagrammatic illustration of a modified form of the hydraulic system illustrated in Fig. 1;

Fig. 3 is a sectional view of the control device for controlling the operation of the variable displacement pump illustrated in Fig. 2; and

Fig. 4 is a diagrammatic illustration of a further modified form of the hydraulic system embodied herein.

Referring now to the drawings, and particularly Fig. 1, one form of the invention is illustrated diagrammatically therein. The hydraulic system illustrated in Fig. 1 is intended for use as a power and braking device and it is intended to be employed particularly in connection with lifting appaartus such as, for example, deck winches associated with a cargo vessel. It is understood, however, that the hydraulic system disclosed in Fig. 1 may be utilized in connection with other apparatus whenever power and braking needs are required. The hydraulic system illustrated in Fig. 1 includes a plurality of motor-pump units fill, 12 and 14 which are shown operatively connected in parallel relation. Although only three of the motor-pump units are shown in the drawings, it is contemplated to utilize as many of the units as practicably needed in connection with the load requirements of the system. The motor-pump units 10, 12 and 14 are of the variable displacement type which includes a rotor provided with variable stroke pistons. The specific construction of the units is illustrated on page 6 of Air and Oil Hydraulic Components, Condensed Catalog 1101, published by the Hydraulic Press Manufacturing Co.

It is believed suflicient for the underestanding of the operation of the present invention, that only the general description of these units be set forth herein. It is understood that in order to effect the rotation of a variable displacement pump the stroke of the pistons associated therewith must be altered. When altering the stroke of the pistons, a piston carrier ring is moved in eccentric relation with respect to the motor-pump unit rotor and the piston stroke and rotation of the unit is accordingly changed. The unit may be completely reversed in rotation by changing the stroke of the pistons so that the discharge port of the unit is caused to operate as the suction or inlet side. As shown in Fig. 1, in order to vary the stroke of the pistons associated with each of the motor-pump units, a manually operated lever 16 is provided and is operatively secured to a shaft 18 which is operatively connected to the displaceable pistons for effecting the stroke varying operation. By varying the stroke of the pistons in each unit, the rotation of the rotor associated therewith is effected.

Communicating with the discharge or the suction port (depending on the direction of rotation) of the motorpump units it 12, 14, through

fluid conduits

20, 21, 22, respectively, and

fluid conduits

23 and 24 is a reservoir 25 that is adapted to contain hydraulic fluid therein. Any

one of the units 19, 12 and 14, which communicate with the fluid conduit 24. through the common fluid conduit 23, may be shut off from communication therewith as desired by

block valves

26, 27 and 28, respectively. The

opposite or suction side, or alternatively, the. discharge side, of the units 10, 12" and 14 communicates with a hydraulic accumulator 30 through

fluid conduits

31, 32 and 33, respectively, and

fluid conduits

34 and 35. As shown,

block valves

36, 37 and 38 are located in the conduits 31, '32 and 33 and are provided for shutting off units 10, 12 and "1 4 from communication with the conduit 34, as

' desired. 7

1 The hydraulic accumulator 30 is provided with a pis ton 40- that; in effect, floats therein and divides the accumulator into an upper and a lower chamber '42 and 44. Agas under pressure is; introduced into the space or chamber 42 and is adapted to subject the piston 40 to apredeterminedpressure. It is understood that the gas located in the space 42 may be retained at any desired pressure dependent upon the requirements of the system. It is seen that the bottom space or chamber'44 of the accumulator below the piston 40 may be filled with a hydraulic-"fluid until the pressure, in the space 44; is equal to the predetermined pressure of the gas in the space 42. In this condition,-the pressures on the piston 40 are, equalized and the piston will float midway in the accumulator 30. In order to. introduce hydraulic fluid into the space 44 of the accumulator 30, a variable displacement pump 46is provided. The pump 46 maybe driven by any suitable prime mover coupled thereto; an electric motor 48 being provided in the present instance. The variable displacement pump 46 is equipped with a pressure holding control that:automatically reduces pump delivery to zero when a predetermined pressure has been reached in the line communicating therewith. The desired pressure is obtained by regulating a hand wheel 50 that controls the setting of a piston-type rotor. As shown, the variable displacement pump 46 communicates with the hydraulic accumulator 30 through a fluid conduit 54 and the coni duit 35' joined to the conduit 54, and is adapted to receive hydraulic fluid from the reservoir 25 which communicates. therewith through the fluid conduit 24 and a conduit52'; Itis seen that hydraulic fluid may be'supplied to the space 44 in the accumulator 30 by the variable displacement pump 46 by way of

fluid conduits

54 and 35 until they pressure of the hydraulic fluid is equal to the p essnreof the gas in space 42. 'At this point, the variable displacement pump 46 floats on the line, that is, does not deliver fluid, since pump delivery has been reduced to zero. Itis'seenthat the variable displacement pump 46 is always ready to supply or make up the hydraulic fluid in the accumulator 30 whenever the pressure in the space 44td'rops. below the predetermined amount;

In the operation. of the hydraulic system shownin Fig. 1, anyone of the motor-pump units 10, 12 or 14 may be operated independently, or all of the units may be operated simultaneously,if so desired. For purposes of illustrating the invention, only the unit will be included in the description of the operation. It is assumed that the variable displacement pump 46 has supplied the accumulator 30 with the amount of motive fluid necessary to reachthe predetermined pressure in the accumulator andthat the pump 46' is floating on the line If the motor-pump unit 10 is then required to lift aload such as, for-example, when a cargo is to be lifted from a dock into'theihold of a ship, the manually operated lever 16 is moved to control the variable displacement motorpump unit 10 such that motive fluid from the hydraulic accumulator 30' is introduced thereto by way of the fluid conduits'35j34 and 3 1. The unit 10 is then operated as a motor and the shaft thereof is caused to rotate for operating a winch or the like. operatively connected thereto for lifting the load. As the shaft of the unit 10 rotates, energy is accumulated in the lifted load and the motive fluid is directed to the reservoir by way of the fluid conduit 24. Since the pressure of the motive fluid 1n the accumulator will be reduced below the pre set amount during the lifting operation thevariablecapacity pump 46 will then respond to the decreased pres- '4. sure in the line to. supply the. required amount of motive fluid to the accumulator 30 until the pro-set pressure is again reached, When the winch connected to the shaft of the motor-pump unit has lifted the load to the desired level, it is then required to lower the load and a braking operation is necessary. By controlling the manual control lever 16 and varying the stroke of the pistons in the motor-pump unit 10, the energy accumulated in the load lifted by the unit 10 will cause the rotor thereof to rotate in a reverse direction, thereby operating the unit as a pump, The load is then lowered with a braking action and, in addition, the unit operates as a pump to pump fluid from the reservoir 25 through conduits 24 and i 20 and then through

conduits

31, 34 and to return the motive fluid to the accumulator 39. It will be seen that this will increase the quantity and pressure of motive fluid in accumulator 30 'to a point considerably above the pre-set amount. Consequently, the variable capacity pump 46 will be held inactive until the motive fluid, thus accumulated is utilized in a subsequent lifting operation. Thus, all of the energy in the form of the'hydraulic fluid under pressure is returned to the hydraulic accumulator 30 with the exception of that lost due to mechanical and fluid friction. Since the motive fluid in space 44 of the accumulator 30 is not fully returned by the unit 10 because of the aforesaid losses, the variable capacity pump 46 will then respond to the resultant decreased pressure in the line to supply the required amount of motive fluid to the accumulator 36 until the predetermined pressure is again reached. The accumulator is then fully charged and the fluid contained therein under pressure may again be directed to the motor-pump unit 10 by controlling.

the manually operated lever 16 for effecting a power operation. In order to provide for means for returning fluid to the reservoir 25, in the event that the motorpumpunits 10, 12 and 14, during a braking operation, over-supply the accumulator 30, the reservoir 25 is connected to a relief valve 56 through a fluid conduit 58, the relief valve 56 communicating with the fluid conduit 34 which, in turn, communicates with the accumulator 30, through conduit 35. It is seen that any one of the units 10, 12, 14 may be operated independently of the other or the unit 19 may be operated in parallel and simultaneously with both or either of the units l2 and 14. "It is also seen that the manually operated lever 16 may be controlled by electric, pneumatic or hydraulic servo systems positioned at a remote point. single operator may be employed to control a plurality of winches for loading a ship or the like.

Referring now to Fig. 2, a modified form of the system shown in Fig. l is illustrated and is adapted to be used particularly in connection with tow lines associated with tugs. In a towing operation, the tow line is wound on a winch and is connected to the load or ship being towed and is normally subjected to a varying tension. On occasion, due to the variations in load during the towing operation, the line will be payed-out or payed-in, depending upon the particular conditions involved which vary the tension in the line. in order to automatically compensate for the paying-out and paying-in, by varying the tension in the tow line, the system illustrated in Fig. 2 is provided. As. shown, a motor-pump unit 60 is provided and is operatively coupled to a variable displacement pump 62 through a shaft 64. The pump 62 is of that type described above in connection with Fig. l and is adapted to automatically maintain a variable compensating pressure in an accumulator described below. Rotation of the shaft 64 is adapted to automatically control the. variable displacement pump 62, and this fea ture will be described in detail hereinafter. The motorpump unit 60 communicates with a reservoir 66 through a fluid conduit 68 and further communicates with the variable displacement pump 62 through .a fluid conduit 70. The variable'displacement pump 62 communicates with a hydraulic accumulator 72"through fluid conduits Thus, a V

'74 and 76, the accumulator being of that types described above in connection with Fig. 1. The hydraulic accumulator 72 also communicates with the motor-pump unit 60 through

fluid conduits

76, 78 and 80 and a relief valve 82 is provided communicating with the fluid conduit 78 through a fluid conduit 84. The relief valve communicates with the reservoir 66 through a fluid conduit 86 and is adapted to return fluid to the reservoir in the event a predetermined unsafe pressure in the accumulator 72 is about to be reached. A load in the form of a winch 88 is coupled to the motor-pump unit 66 through a shaft 90 and is responsive to the rotation of the motorpump unit 6:? to pay-in and pay-out a tow line 92 associated therewith.

In operation, the variable displacement pump, which is driven by an electric motor 94, coupled directly thereto, is operated to direct motive fluid to the accumulator 72 until a predetermined pressure is reached therein. it is arbitrarily assumed that the load on the line 92 is 8,000 pounds at normal operating conditions, that is, the tension in the line 92 under the specific load condition is 8,000 pounds. Assuming now that the tow line 92 begins to pay-out, due to an external condition, the tension in the line 92 is thereby varied and the motorpump unit 69, which is operatively connected to the winch $8, is rotated in a direction to pump motive fiui from the reservoir 66 to the accumulator 72 by way of

fluid conduits

8d, 78 and 76, thereby building up the pressure in the accumulator 72. At this stage, the variable displacmeent pump 62 is running idle on the line since the pressure in the accumulator is above the preset pressure setting therein. As the motor-pump unit 60 is rotated in a direction to pump motive fluid from the reservoir 66 to the accumulator 72, the pressure setting on the variable capacity pump. 62 is changed, this being accomplished by the rotation of the shaft 64.

Referring now to Fig. 3, a detail of the pressure setting device for the variable displacement pump 62 is shown and includes a hand-operated wheel 95 that has a shaft portion 96 formed integral therewith which is externally threaded at 97, the shaft portion 96 being received by the housing of the pump 62 and terminating in a flange 98. The hand wheel 95 is also internally threaded and is adapted to threadably receive for axial movement therein a shaft 99. The shaft 99 slidably engages a coupling 100 (Fig. 2) that is secured to the shaft 64, the shaft 99 being capable of longitudinal movement within the coupling 10%, the purpose of which will be described below. Although the coupling 16% is shown directly connecting shaft 64 to shaft 99, it is understood that a conventional clutch may be provided in place of the coupling which would allow for unimpeded operation of the tow line 92 when the towing connection is being established initially.

Engaging the flange 93 of the shaft portion 96 is a spring 191 that abuts against a piston 102 that is adapted to control the pressure setting of the pump 62. Engaging the lower end of the shaft 99 and positioned within the spring 181 is a smaller spring 163 that also abuts against the piston 102 for controlling the pressure setting of the pump 62. It is seen that the manual control or wheei 95' may be rotated to set the pressure setting on the pump 62 to that the pump supplies fluid to the accumulator until the pro-set pressure is reached. This pressure setting is varied upon rotation of the shaft 64, which rotates the shaft 99. Rotation of the shaft 99 within the stationary shaft portion 96 causes the shaft 99 to translate longitudinally, this longitudinal movement of the shaft 99 being taken up within the coupling 1%. The longitudinal movement of the shaft 99 thereby actuates the piston 162 which changes the pressure setting on the pump 62, thereby compensating for various loads on the motor-pump unit 69. By controlling the pressure setting of the pump 62, the pressure of the fluid directed to the accumulator 72 and communicating with the pump 62 will accordingly be varied. Thus, when the line 92 is payed-out to operate the motor-pump unit 60 as a pump, the shaft 64 will be rotated to increase the pressure setting on the pump 62. It is seen that at this stage the pump 62 will not operate until the pressure determined by the new setting is reached since the accumulator pressure is greater than the new setting of the pump 62. It is seen that as the motor-pump unit 60 pumps the fluid into the accumulator, the pressure setting in the pump 62 will be correspondingly increased. If the load on the tow line 92 is changed to cause the load to decrease below a normal amount or below 8,000 pounds, the motor-pump unit 60 will then operate as a motor, causing motive fluid in the accumulator 72 to be discharged through

fluid conduits

76, 78 and 80 and thereby causing the winch 88 to Wind in the cable to maintain the normal tension on the line. The motive fluid is returned in this operation to the reservoir 66. As the tow line 92 pays-in and the motor-pump unit 60 is thereby rotated by the motive fluid from the accumulator 72, the shaft 64 is rotated to decrease the pressure setting on the pump 62. As the tow line 92 continues to pay-in, the setting on the pump 62 will be normally above the predetermined pressure in the accumulator 72 since the winch 88, due to frictional and hydraulic losses, has not payed-in the line 92 that amount which it payed-out. However, since the fluid in the accumulator 72 has caused operation of the motorpump unit 60 to reduce the pressure in the accumulator 72 that amount necessary to maintain an 8,000-pound pull on the line 92, the pump 62 will then function to augment the accumulator 72 to produce the new pressure setting of the pump 62 as set by the rotation of the shaft 64, The motor-pump unit 60 will continue to operate as a motor to bring the line 92 to its original position prior to paying-out. As the motor-pump unit 6 3 continues to operate, the setting on the pump 62 is decreased to the original setting to maintain the original 8,000-pound tension. When the pressure on the line 92 reaches 8,000 pounds, which was the original tension on the line, the setting on the pump 62 is the original predetcrmined amount and the pressure in the accumulator 72 is also that original predetermined amount set by the hand wheel 95. The tension on the tow line 92 is 8,000 pounds and the motor-pump unit 61' and pump 62 are then idle.

Assume now that the motor-pump unit 60 and pump 62 are idle on the line, and due to an externally created force, the tow line load decreases below 8,000 pounds. The line will then begin to pay-in. The motor-pump unit 6% will operate as a motor, pulling the line 92 in, utilizing the fluid under pressure in the accumulator 72. When the motor-pump unit 66 is operated as a motor, the pressure in the accumulator 72 will drop below the setting of the variable capacity pump 62 set by the hand wheel 95. As the motor-pump unit 60 continues to operate, the pressure setting on the pump 62 is decreased and the pump 62 is forced to operate at a lower setting than that necessary to maintain an 8,000-pound tension on the tow line 92. The line 92, due to external forces, then begins to pay-out and the motor-pump unit 60 is operated in the reverse direction. As the motor-pump unit 60 operates in the reverse direction, the pressure in the accumulator 72 is increased, the pump 62 supplying the fluid to the accumulator 72, depending upon the new setting effected by the rotation of the shaft 64. The motor-pump unit 60 continues to operate until the tow line tension of 8,000 pounds is reached. If the line does not return to the original setting upon paying-out, then the setting on the pump 62 will not have been returned to the original setting to eflect the predetermined pressure in the accumulator as set by the hand wheel 95. Due to the fact that there are fiuid losses in the motor-pump unit 60, the motor-piunp unit will continue to operate. in. a reverse direction, paying-out until the setting on the pump 62 is returned to that setting that maintains the pressure imthe accumulator attheoriginal" predetermined amount;

The systenr'isthen returned tothe-- position where the load on -theline- 92" is-8 ,000 pounds and the predetermined pressure iii the accumulator is also reached. It is'seen that the length of the-line- 92 is also returned to that length-prior to-the' line paying-in; Although the hydraulic system shown" in Fig 2 is automatic in operation, the motor-pump unit 60is provided'with a manually operated control lever 104 for controlling the operationof the unit as desired when. the tow line 92 operatively associated with the unit. is paying-out or paying-in.

Referring now to Fig; 4,- a further modified form of the present-- invention is diagrammatically illustrated and, inthis form-ofthe invention, the hydraulic system is adapted to be utilized for; braking and accelerating a vehicle or the like. As shownin Fig. 4, 7 the frame of a vehicle for use'witlra bus, truck, or the like, is generally'indi'cated at-1102 The frame 110 has mounted thereon suitable frontwheels 112- and double rear wheels 114. A'priine-mover in; the formof an internal combustion engine 116is= positioned on" the frame between the front wheels 1 12' and has joined thereto a transmission 118. Coupled to-the; transmission 118 is a motor-pump unit 120- which, in this instance, isa fixed displacement unit. The-motor-pump unit 120 is operatively connected through a drive shaft 122 to adifferential 124 that, in turn, is operatively connected to the rear wheels 114. The motorpump unit 120 communicates with a reservoir 126' through a fluid conduit 128, acheck valve 130'being interposed between the reservoir 126' and motor-pump unit'120 in the fluid'conduit line 128. The motor-pump unit 120 further communi'cateswith a hydraulic accumulator 132' through

fluidconduit lines

134, 136 and 138. The accumulator 132 is of that type described above in connectionwith- Figs. 1 and 2 wherein apro-charge fluid or gas-is contained inthe upper portion of the accumulator; The accumulator 132 also communicates with the. motorpump:unit"120= through the fluid conduit 138, a fluid conduit; 140 and the conduit 128 when the unit is to be operated as a motor. A by-pass valve 142 connects thefluid conduit 128 to the fluid conduit 134 and by-passes the-motive fluid when the motor-pump unit 120 is reversed as, for example, when the vehicle is moved in a reverse direction: The reservoir 126 communicates with the accumulator 132 through a'fluid conduit 144; a brake valve 146 being interposed between the reservoir 126 and and" accumulator 132 for controlling the direction of'the flow of thehydraulic fluid; A spring. loaded non-return valve 148. is positioned in the fluid conduit 136 and prevents the-flowoffluidin 'a'rreverse direction therein. A by-passiline 150 is adapted to direct the hydraulic fluid to-- the reservoir 126- through" a relief valve 152' when thepressuredn-the accumulator 132 exceeds the predetermined figure. The system is'completed by positioning a throttlevalve- 154 in-thefluid conduit 140' the throttle valve 1 54providingfor communication of the accumulator'withthe motor-pump unit 120.

Inoperation of the system shown in Fig. 4, the internal combustion engine or prime mover 116' is adapted. to continuously drive the motor-pump unit 120 and operate the-unit as-a'pump; pumping fluid from the reservoir 126 through-the

conduits

128 and 134 and returning the hydraulic-fluid to-the-reservoir 126 by way of the brake. valve 146' and fluid conduit 144. Thus, under normal operatingconditions, thefluid iscontinually recirculated through the reservoir 126'to the motor=pump unit 120 V and? returned to the reservoir 126. During a braking operation, the'brakevalve-146 is closed and the motorpump: unit 120 delivers fluidthrough the spring-loaded non-return valve 148 to-the hydraulic fluid accumulator 132: until the: pressure in the accumulator reachesa predetermined amount; If the-braking cycle is continued, the relief valve;'1-52 opens andallows the hydraulic fluid to return to the. reservoir 126 under pressure equal to the pressure in the hydraulic fluid, accumulator 132. During.

the braking operatiomthe pressure in 1ine'134- is built up, thus'tending to cause the shaft- 122 to be braked. In

an emergency, the mechanical brakes canbe utilized to" assist-in bringing the vehicle'to a rest position.

In the power operation, the throttle valve 154 is opened and the fluid under pressure in the hydraulic fluid accumulator 132 passes through the throttle valve 154 by way of fluid conduit 138, and then passes through fluid con- 7 the vehicle to'thereby accelerate the drive shaft 122. The

hydraulic fluid then passes through the unit and through the brake valve 46, which has been opened, and returned to the reservoir 126.

braked by closing the brake valve 146, the unit 'operates as a pump to return the fluid from the reservoir to the accumulator until the predetermined pressure therein.

has been reached.

It is seen that the system illustrated in Fig. 4 will materially reduce wear on brakes and give a greater impetusto starting or accelerating the vehicle. The system may be advantageously employed in connection with vehicles that constantly decelerate and accelerate, such as, for example, buses, taxicabs, etc.

It will be obvious to those skilled in the art that various changes may be made without departing from the spirit of the invention and therefore the invention is not limited to what is shown in the drawings and described termined by the rotation of said shaft is reached, and a reservoir communicating with said motor-pump unit through a conduit, said accumulator supplying the hy-- draulic fluid under pressure located therein to said motor.-

pump unit to rotate the shaft thereof, thereby operating said unit as a motor to perform work, the hydraulic fluid being directed to said reservoir from said unit, the energy 7 accumulated in the shaft of said unit thereafter reversing the rotation thereof to operate said unit as a pump, saidunit pumping said fluid from said reservoir to'said'accw. V

mulator.

2.. In a hydraulic system, a hydraulic motor-pump'unit, an accumulator communicating withsaid unit, a connecting. shaft attached at one end to said. hydraulic motorpump unit, a variable displacement pump communicating: with said accumulator and supplying motive fluid thereto until: a predetermined pressure in said accumulator is' reached, said connecting shaft being operatively connected at its other end to said variable displacement pump for controlling the supply of motive fluid to' said. accumulator, the motive fluid in said accumulator being directed under pressure to said unit to operate said unit as a motor, thedirection of rotation of said unit being reversible to operate as a pump for returning saidmotive fluid to saidaccumulator.

3; In a hydraulic system, a motor-pump unit, a rotat able. shaft attached to said unit, an accumulator containing motive fluid therein communicating with said unit to supply said fluid under pressure thereto, a variable" displacement pump communicating with saidaccumulator to supply fluid'thereto until apredetermined pressureiis When the accumulator 132 is emptied of the fluid under pressure and the vehicle is again" reached therein, said variable displacement pump being mechanically connected to said motor pump unit and controlled by the rotation thereof the fluid under pressure in said accumulator entering the discharge side of said unit to operate said unit as a motor for causing rotation of the shaft of said unit, the energy accumulated in rotating the shaft of said unit being utilized to rotate said shaft in the opposite direction to draw said fluid into the suc tion side of said unit for operating said unit as a pump, said unit thereby returning said fluid to said accumulator.

4. In a hydraulic system, a motor-pump unit, a rotatable shaft attached to said unit, a load connected directly to the shaft of said unit, said unit thereby being responsive to the load on said shaft, an accumulator containing motive fluid therein communicating with said unit, a variable displacement pump communicating with said accumulator and operatively connected to said unit, said unit rotating in response to the load on the shaft thereof, said accumulator being responsive to the direction of rotation of said unit and supplying fluid under pressure to said unit to operate said unit as a motor, said pump being responsive to the rotation of said unit for supplying fluid to said accumulator until a pressure determined by the rotation of the shaft of said unit is reached, said unit operating as a pump in response to the energy accumulated in rotating said shaft to return fluid to said accumulator.

5. In a hydraulic system as set forth in claim 4, wherein said pump includes a manually operated means for setting the pressure capacity of said pump, and means operatively connected to the shaft of said unit and responsive to the rotation thereof is provided for automatically adjusting the pressure capacity of said pump.

References Cited in the file of this patent UNITED STATES PATENTS 2,382,437 Molly Aug. 14, 1945 2,554,381 Patterson May 22, 1951 2,576,359 Putnam Nov. 27, 1951 2,752,754 Jaseph July 3, 1956