US3116595A - Hydraulic starter system for engines - Google Patents

Description

Jan. 7, 1964 2 Sheets-Sheet l vFiled May 22, 1961 9164 NAS@ ,EN 30H l "illlllli ATTORNEYS Jan- 7, 1964 M. 1 KENT ETAL HYDRAULIC STARTER SYSTEM FOR ENGINES 2 Sheets-Sheet 2 Filed May 22. 1961 ATTORNEYS United States Patent O 3,116,595 HYDRAUMC STARTER SYSEM FR ENGNES Melvin L. Kent, East Cleveland, (Ehio, and Mitre lirewarsld, Bridgeport, Conn., assignors to'The New Yorlr Air Brake Company, a corporation of New llersey Filed May 22, 196i., 'Ser'. No. llL'Zl 5 Claims. (Cl. Gil- 18) This invention relates to a hydraulic starting and pumping system.

The use of hydraulic motors for starting internal combustion vehicle-propulsion engines is known in the prior art. Such hydraulic motors are generally driven by pressure fluid supplied by motor-driven auxiliary pumps and the known systems have -proven to be complex, heavy, space-consuming and expensive.

In the copending application of Edward V. Manning and lohn P. Mentink, Serial No. 92,052, led February 27, 1961, and entitled Hydraulic System, a hydraulic starting system is disclosed in which a variable displacement hydraulic motor-pump unit is driven Las a motor by Huid supplied from a pressure tluid source, such as a pressure accumulator, having a. decaying pressure characteristic. Automatic control means are provided for controlling the displacement of the hydraulic unit in a predetermined manner in accordance with the decaying characteristic of the source. By the use of such a pressure fluid source, the starting system is capable of being completely self-contained in the vehicle. After the internal combustion engine has been started, the hydraulic unit is designed to be driven as a pump by the internal combustion engine to recharge the accumulator and to supply fluid to the hydraulic system of the vehicle. By causing the hydraulic motor of the starting system to operate also as a pump subsequent to starting of the internal combustion engine, the need for auxiliary pumping apparatus is eliminated and the weight of the vehicle is reduced.

The object of the present invention is to provide an improved starting and pumping system of the type disclosed in the Manning and Mentink application referred to above. The invention is characterized by the provision of means operable-during motoring-to position the displacement control element of the variable displacement unit in a maximum stroke-establishing motoring position as long as the pressure of the source is above a predetermined value and to position `the control element in a zero stroke-establishing neutral position when the pressure is below this value, and operable-during pumpingto position the control element in a maximum stroke-establishing pumping position when the pumping pressure of the unit is below a predetermined operating value and to move the control element gradually toward its neutral position as the pumping pressure rises from this operating value to the desired maximum.

The hydraulic motor-pump unit of the starting and pumping system is of the overcenter type employing a rotary group of elements consisting of a cylinder barrel havinor longitudinal bores therein and reciprocatory pistons mounted in said bores, said rotary group being mounted for rotation with respect to an angularly adjustable cam plate suspended in the engine housing. As the rotary group of elements rotates relatively to the cam plate, reciproeatory motion is imparted to the pistons. The stroke of the pistons and the displacement of the hydraulic unit -are dependent upon the angle of inclination of the cam plate. The cam plate is movable between maximum stroke-establishing motoring and pumping positions on opposite sides of a zero stroke-establishing neutral position. Such a hydraulic unit presents the advantage that only one high pressure line is required since the high pressure inlet port of the hydraulic unit during motoring becomes the high pressure discharge port during pumping.

Patented Jan. '27, 1%64 'ice According to the preferred embodiment of the invention, a shiftable spring assembly is provided for continuously biasing the displacement control member toward its maximum stroke-establishing pumping position during the motoring and pumping operations of the hydraulic unit. A shifting motor is provided for placing the spring assembly, during motoring, in a rst position in which a given biasing force is applied to the control member, and for placing the spring assembly, during pumping operation, in a second position in which a greater biasing force is applied to the control member. Pressure-responsive means are provided for placing the control member in its maximum stroke-establishing motoring position (against the counteracting bias of the spring assembly) when the pressure of the source is above a predetermined value. During pumping operation, the pressure-responsive means operate to position the control member in its neutral position (against the counteracting bias of the spring assembly) when the pumping pressure equals a predetermined operating value. According to another feature of the invention, the spring assembly is designed to constitute a stop which operates, during pumping operation of the hydraulic unit, to prevent movement of the control element from its neutral position toward its maximum strokeestablishing motoring position.

Other obiects and advantages of the invention Will become more apparent from a study of the following specification when considered in conjunction with the accompanying drawings, in which:

FlG. l is a sectional view of the hydraulic unit of the starting system, the displacement control member being shown in its maximum stroke-establishing motoring position.

FIG. 2 is a schematic diagram of the hydraulic starting system, the displacement control element of the hydraulic unit being shown in its zero stroke-establishing neutral position.

The hydraulic starting system includes a variable displacement hydraulic motor-purnp unit 3- of the overcenter type disclosed in detail in the copending application of Tadeusz Budrich and Edward V. Manning, Serial No. 789,996, tiled January 29, 1959, now abandoned, and entitled Overcenter Hydraulic Starter Pump. The hydraulic unit comprises a housing 4 having a drive shaft 5 journalled therein to which is connected the rotary cylinder barrel 6. The rotary cylinder barrel 6 is in contiguous engagement at one end with the adjacent end face of stationary valve plate '7, which face contains arcuate high and low pressure ports in communication, respectively (through internal housing passages, not shown), with the housing high and low pressure ports 8 and 9 illustrated in FlG. 2. The cylinder barrel 6 contains a circumferential series of through longitudinal cylinder bores l1 which are arranged to register sequentially with the arcuate ports in valve plate 7 as the cylinder barrel rotates. Pistons l2, formed with spherical heads 13 for connection with supporting shoes ld, are mounted in the cylinder bores for reciprocation by cam plate l5 and return plate lo.

The cam plate l5' is supported in housing 4- by cam plate yoke portions i551 and fixed housing-secured trunni-ons l' (see FiG. 2) for angular movement about ya horizontal pivot axis extending in a directional normal to and intersecting the vaxis of drive shaft 5. The angular position of cam plate 15 determines the len-gth of the strokes of pistons l2, and the cam plate is free to move between maximum stroke-establishing moto-ring (FIG. 1) tand pumping positions on opposite sides of a zero strokeestablishing neutral (FIG. 2) position. Shiftable spring assembly llii is provided for biasing cam plate 15 in the clockwise direction about its pivot axis. This spring assembly comprises -a iirst spring seat sleeve 19 connected at one end with the cam plate 15 by connecting rod 2,1,

a second spring seat sieeve 22 arranged for sliding movement at one end within an axial bore in the other end of sleeve i9, and a coaxial prcloaded coil spring 23 seated on the per' hcral liange portions and 22a of sleeves i9 and 22, respectively. When sleeve 22 is in its FIG. 1 position in engagement with the housing inner wall surface 4a, Spring 23 reacts with a first biasing force between sleeve portions Na and 22a to displace sleeve 19 to the left and thereby piace cam plate in its maximum stroke-establishing pumping position as shown by the broken lines in FIG. 2.

Motor means 24 are provided for shifting sleeve 22 to the left to a second position in which spring 23, during pumping operation of the hydraulic unit, biases cam plate h toward its maximum stroke-establishing pumping position with a greater biasing force. This motor 24 includes Aa cylinder 25 provided with an axial tubular extension 25a secured within an opening in the housing 4. Reciprocable piston 26 is mounted in cylinder 25 and is provided with a piston rod 27 movable within extension 25a. The second sleeve 22, which is mounted for sliding movement on this stationary extension 25a, has an end wall 22b iagainst; which the free end of piston rod 27 abuts. When pressure fluid is introduced into working chamber 24u of motor 24 to displace piston 26 to the left into engagement with the left-hand end wall of cylinder 25, piston rod 27 shifts sleeve 22 to the left and thereby increases the spring biasing force on cam plate 15. It is important to note that when sleeve 22 is in this left-hand position, it serves as a cam stop preventing cam plate 15 from moving from its neutral position toward its FIG. 1 position.

Cam plate l5 is movable in the counterclockwise direction against the counteracting biasing force of spring assembly 18 by a hydraulic positioning motor 31 including a cylinder 32 secured to housing 4 and a reciprocable piston 33 that is connected with cam plate 15 by connecting rod 34. Piston 33 is moved to the left in its cylinder by the application of pressure huid to working chamber 31a.

The drive shaft 5 extends through an opening in the housing 4 and terminates in a splined coupling 36 to which the internal combustion engine 37 is connected via conventional mechanical coupling 38.

Referring now to FiG. 2, an accumulator 40, which constitutes a pressure fluid source having ia decaying pressure characteristic, is connected with the housing high pressure port 8 via conduit containing three-way inlet valve 42. Valve y42 is operable between a first position in which it connects conduit portion 41a with conduit portion Elib and a second position in which it connects conduit portion 4th with the vehicle hydraulic system conduit Housing low pressure port 9 is connected with sump dfi via conduit d5.

The state of energization of positioning motor 3i is controlled by the dual-pressure control valve 46. This control valve inoludes a housing having an inlet passage 47 connected with high pressure port S via conduit a motor passage 4E-9 connected with positioning motor working chamber 33;'[1 via conduit 5E, `and an exhaust passage 52 connected with sump d5' via conduit 53. The control valve housing includes a longitudinal bore 54 in one `end of which is mounted the reciprocable valve plunger 55 having lands 56, 57 'and 58 separated by grooves S9 and 6l, respectively, for controlling the communication between the various valve housing passages. Through longitudinal slots @52 are provided in the outer periphery of land 58.

Mounted for reciprocation in the other end of the valve housing bore is the spring seat 63. Preloaded spring 64, reacting between spring seat 63 and plunger 5S, urges the seat to the left to its FG. 2 position in which it abuts housing wall projection 65, and urges the plunger 55 in the opposite direction into engagement with the other bore end wall to ei"ect venting of the Working chamber 31a of positioning motor 31 via conduit 5l, passage 49,

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groove 59, passage 52 and conduit Spring chamber 65 is in continuous communication with sump conduit 53 via conduit 67.

F1/hen seat is in its FG. 2 position, spring 64 establishes ia iirst reference pressure condition of Operation of control valve `as will be described in greater detail below. Spring seat 63 constitutes the piston of hydraulic piston motor means and, when pressure fluid is introduced into working chamber 65a to shift the seat to the right to a second position in which it engages fixed stop 69, the preloading of spring 6dis increased to establish a second reference pressure condition of operation of control valve The spring assembly shitting motor 24 and the motor for shifting spring seat 63 are operated simultaneously by auxiliary valve 71. This auxiliary valve includes a housing having an inlet port 72 connected with high pressure port S via conduit '73 and conduit portion 48a, a motor port connected with working chamber 24a via conduits 75a 'and 'Sb and with working chamber 63a via conduits 75a and 75e, and a pair of exhaust ports 7o and 'i7 connected with sump 44 via conduits '78 and 79, respectively. The valve housing contains a longitudinal bore in which is mounted the movable valve plunger Si having lands S2, 83 `and 34 separated by grooves S5 and S6. Spring S7, mounted in the left-hand end of the bore, biases plunger 31 to the right to a first or energizing position in which working chambers 24a and 63a communicate with high pressure port S via branch portions '/"Sb i id F.Jc, respectively, common portion 75a, port 7d, groove 85, port '72, conduit 73 and conduit portion 43a. Plunger Si carries an 'axial projection da on which is secured the armature SS of stationary solenoid coil S9. When solenoid coil 89 is energized by the closing of switch 9E, armature 88 is displaced to the left by magnetic attraction to move plunger 81 to the left to its second `or venting position, shown in FIG. 2, in which working chambers 24a and 63a `are connected with sump via branch line portions 75h `and 75C, respectively, common portion 75a, port 74, groove S6, port '77, and conduit '79.

OPERATION The operation of the hydraulic starting system may now be described.

(l) Motoring Operation Assuming that the hydraulic unit 3 is at rest and that valve 42 is in its second position, the tluid path from accumulator fat) to high pressure port 8 is closed and the initial pressures in port 8 and control valve inlet chamber 47 are zero. Plunger 55 is maintained in its FiG. 2 lposition by spring 64 so that Working chamber Sia ot positioning motor 31 is vented to sump via conduit 5E, passage 49, groove 59, passage 52 and conduit 53. suming also that switch 9i is closed to energize solenoid 89, plunger 8i is maintained in .its FIG. 2 position against the bias of spring 37 to connect Working chambers fia and 63a with sump 44, as shown. Since working chamber Zita is vented, spring seat sleeve 22 engages the housing internal wall surface 4a and spring 23 biases sleeve 19 to the left relatively to sleeve 22 to position cam plate l5 in its maximum stroke-establishing pumping position, as shown by the broken lines in FiG. 2. Owing to the venting of working chamber 63a, seat 63 is in its PEG. 2 position to establish the rst reference pressure value against which the pressure in inlet passage 47 is compared.

For the purpose of the `following discussion, it will be assumed that the first reference pressure established by spring 64 is 1500 psi., that the accumulator 40 is under an initial pressure of 3000 p.s.i., and that pressures of 300 and 500 psi., respectively, in working chamber 3M are required to hold cam plate 15 in the neutral position of FIG. 2 and the maximum motoring position of FIG. 1 against the bias of spring 23 when chamber 24a is vented.

When inlet valve 42' is opened, pressure iluid is transmitted to port S, through conduit 41 and to inlet passage 47 yof control valve -46 via conduit 4S. The fluid in passage 47 acts on the right-hand end surfaces of lands 57 and 5S and shifts plunger 55 to the left against the bias of spring 64. As the pressure rises to the reference value of 1500 p.s.i., plunger 55 moves to a lap position in which land 57 interrupts communication between motor passage 49 and exhaust passage 52. A further rise in press-ure in inlet passage 47 lcauses plunger 55 to move further to the left to yinterconnect inlet passage 47 with motor passage 49 through slots 62 and .groove 61. Pressure iluid is now transmitted to working chamber 31a through conduit 51. The pressure in working chamber 31a rises rapidly to system pressure, and since at this time this pressure is greater than the 500 p.s.i. required to hold carn plate 15 in the maximum motoring position of FIG. l, the motor 311 immediately moves the cam plate 15 to that position. The cam plate 15 remains in this position as long as system pressure is above 1500 p.s.1.

The iiuid supplied to high pressure port 8 from the accumulator 4i) is fed through internal housing passages (not shown) and through the passages of valve plate 7 to the longitudinal bores 11 of the rotary cylinder barrel 6 to displace pistons 12 to the left against cam plate 15. The pistons react with the inclined cam plate to apply maximum initial torque on drive shaft with the result that internal combustion engine 37' is driven in the starting direction by the hydraulic unit 3 through the splined coupling 36 and the mechanical connection 38.

As the speed of rotation of the hydraulic motor 3 increases, it imposes an increasing demand on the accumulator 40 and consequently the supply pressure decreases progressively. For the purpose of the following discussion, it is assumed that by the time the accumulator pre sure has decreased to 1490 p.s.i., the internal combustio-n engine has accelerated to starter cut-out spe-ed. As the hydraulic unit 3 accelerates to approximately 93 of starter cut-out speed, the accumulator pressure decreases from 3000 to 1600 p.s.i. and a similar pressure reduction occurs in working chamber 31a. Throughout this period of time, the pressure in working chamber 31a is sufficient to maintain cam plate v15 in its maximum stroke-establishing motoring position against the bias of spring '23. Consequently the hydraulic motor continuous- 1y applies to the internal combustion engine 37 the maximum possible torque obtainable from the lluid pressure source. During the final period of acceleration o'f the hydraulic unit, ie., as the speed of the internal combustion engine increases from 93% to 100% of starter cutout speed, the accumulator pressure drops below the reference pressure of 1500 psi. thus permitting spring 64 to move plunger 55 to the right from the lap position and again vent working chamber 31a. As the pressure in working chamber 31a decreases below 500 p.s.i., spring 23 commences to move cam plate 15 toward the neutral position, and, when it reaches 300 p.s.i., the cam plate will be in that position.

As the pressure in working chamber 31a approaches 300 p.s.i., the internal combustion engine approaches starter cut-out speed, and, when the working chamber pressure is 300 p.s.i., the engine will have achieved independent operation and will be driving hydraulic unit 3 as a pump. Because of this, the pressure -in conduit 48, and in inlet passage 47, is immediately restored to 1500 p.s.i. and the plunger 55 of control valve 45 is return-ed to the lap position thereby interrupting the vent path from working chamber 31a. Since there is no demand for hydraulic uid at this time, system pressure will remain at 1500 psi. and control valve 46 will maintain cam plate 15 in neutral position. However, should system pressure decrease as a result of leakage, spring ed will shift plunger 55 to the right from the lap position to thereby vent Working chamber 31a and permit spring 23 to move cam plate 15 away from neutral position a small distance in the direction of maximum pumping position. This action causes the pump to supply iluid to the system and when the pressure is restored to 1500 p.s.i. and the rate of discharge from the pump equals the rate of leakage, plunger 55 will be shifted back to the lap position. It should be realized that the cam plate position established by system leakage is very close to the neutral position and that for all practical purposes, the hydr-wlic unit is now imposing a minimum torque on the internal combustion engine. This is a `desirable feature because it permits the engine to accelerate rapidly.

(2) Pumping Operation After the internal combustion engine has accelerated to a speed at which it develops sucient power to drive the hydraulic unit under load, switch 91 is opened to initiate the high pressure pumping operation. Opening of switch 91 de-energizes the holding solenoid 3% and allows spring 87 to move valve plunger v81 to the right to connect working chambers 24a and 63a with high pressure port 3 via branch conduits 75h and 75C, respectively, common conduit 75a, port 74, groove 85, port 72, conduit 73 and conduit portion 48a. The pressure Huid in working chamber 24a moves piston 26, piston rod 27, and sleeve 22 to the left to increase the biasing force applied to cam plate 15 by spring 23. lt is assumed that with sleeve 22 in its left-hand position, a pressure of p.s.i is required in chamber 31a to initiate movement of cam plate 15 in the counterclockwise direction against the bias of spring Z3, and that a pressure of 350 p.s.i. is required to position the cam plate in its neutral position. Sleeve 22 now constitutes a stationary cam stop preventing movement of the cam plate from its neutral position toward its maximum stroke-establishing motoring position.

The pressure uid in working chamber 63a moves spring seat 63 to the right into engagement with stop 69 with the result that the compression load in spring 64 is increased to establish a second eference pressure value (for example, 3000 p.s.i.). Plunger 55 is now in its FlG. 2 position, venting chamber 31a.

With cam plate 15 in its maximum stroke-establishing pumping position, the hydraulic unit is driven by the internal combustion engine and supplies lluid from high pressure port 8 to the accumulator d0 via conduit 41. After the accumulator has been recharged .to its initial pressure of 3000 p.s.i., which is the second reference pressure, plunger 55 is shifted to the left to its lap position. When the pressure exceeds 3000 p.s.i., plunger 55 is shifted further to the lleft to admit uid to chamber 31a via slots 62, grove 61, chamber 49 and conduit 51. As the pressure in chamber 31a increases from 150 p.s.i. to 350 p.s.i., cam plate 15 is progressively pivoted from its maximum stroke-establishing position to its neutral position. Due to the provision of the cam stop (i.e., sleeve 22 in its left-hand position), movement of the cam plate in the counterclockwise direction beyond the neutral position is prevented. Since the cam plate is now in its neutral position, the hydraulic unit is in an idling, minimum-displacement condition. in the event that the pressure in conduit 4?, drops below 3000 psi. (as a result of internal leakage, for example), plunger 55 is shifted to the right by spring 64 to vent chamber 31a, and when the pressure in this chamber drops below 350 p.s.i., cam plate 15 is displaced in the clockwise direction by spring 23 to effect an increase in displacement of the pump to compensate for the leakage. When the pressure in conduit 4S is returned to 3000 p.s.i., plunger 55 is moved to the left to the lap position to trap the fluid in chamber 31a, whereby cam plate 15 is maintained in its leakage compensating position.

inlet valve 42 may now be shifted to its second position in which accumulator itl is isolated and high pressure port S is connected with the vehicle hydraulic system via conduits fili; and As a result oi system demand, the pressure in conduit 4S and passage i7 decreases below 300() p.s.i. and plunger 55 is shifted to the right to vent working chamber 3fm. As the pressure in chamber 3M decreases from 350 to 150 p.s.i., cam plate i5 is pivoted in the clockwise direction toward its maximum strokeestablishing pumping position by spring 23. When the system demand is met by the pump, the pressure in conduit 48 rises to the second reference pressure value vand plunger 5S is shifted to the left to its lap position to discontinue venting of chamber 31a. The position of the cam plate i5 now establishes a rate of discharge equal to the rate of demand for hydraulic iluid.

Should the system demand decrease and the pressure rise above 3000 p.s.i., plunger 55 is shifted further to the left to supply lluid to chamber 32a, and thus cause motor Si to eiect a progressive decrease in cam angle. When the cam reaches that position in which the rate of discharge from the hydraulic unit 3 matches the new demand and system pressure is restored to 3000 p.s.i., plunger 55 moves back to its lap position and again interrupts ow to working chamber 31a. Thus it is apparent that during pumping operation, the hydraulic unit operates as a pressure-compensated pump, the displacement of which is automatically varied by valve 46 to maintain substantially constant the selected maximum system pressure.

As stated previously, the drawings and description relate only to the preferred embodiment of the invention. Since many changes can be made in the structure of this embodiment without departing from the inventive concept, the following claims should provide the sole measure of the scope of the invention.

What is claimed is:

l. In combination (a) hydraulic motor-pump unit having high and low pressure ports and a displacement control element movable between first and second maximum displacement-establishing positions on opposite sides of a Zero displacement-establishing position ifor Varying the displacement of and changing the direction of ow through the unit;

(b) a source of pressure fluid, having a decaying pressure characteristic, for driving the unit as a motor;

(c) a conduit connecting the source with the high pressure port;

(d) a reservoir connected with the low pressure port;

(e) spring means connected with the displacement control element and biasing it toward the second maximum displacement-establishing position;

(f) control means connected with the displacement control element and responsive to the pressure at the high pressure port for moving said element toward the rst maximum displacement-establishing position las the pressure rises above a predetermined vaine;

(g) stop means associated with the displacement control element and shiftable between effective and ineiective positions in which, respectively, it prevents and permits said element from moving from the zero displacement-establishing position toward the rst maximum displacement-establishing position; and

(lz) selecting means for sluiting the stop means between its eective and ineffective positions.

2. The combination defined in claim l (a) in which the spring means includes a spring seat shiftable between high spring-load and low springload positions; and

(b) in which the seat and the stop means are interconnected, whereby the seat is shifted to the high spring-load and low spring-load positions, respectively, as the stop means is shifted to the elective .and ineffective positions.

3. The Combination defined in claim 2 (a) in which the control means comprises (l) a iluid pressure positioning motor connected with the displacement control cient-nt and arranged to move that element toward the Erst maximum displmoment-establishing position, (2) a control valve connected with the positioning motor, the high pressure port and the reservoir and including a movable member shittable between a iirst p. sition in vhic'n the positioning motor is co s leeted with the reservoir and a second position in which thc positioning motor is connected with the high pressure port, the movable member ha g an intermediate lap position in which the posaioning nioter is isolated from both the reservoir and the high pressure port,

(3) means biasing the valve member toward the first (4) means responsive to the pressure pressure port for shifting the valve toward the second position, and

(5) means form varying the bias exerted by tlfc biasing means between high and low values; and

(b) in which the seiccting includes rneans for operating the bias varying means simultaneously with shifting of the stop means and the spring seat, whereby the bias exerted by the biasing means is said low value when the stop means is in the ineiective position and the spring seat is in the low spring-load position, and the bias exerted by the biasing means is said high value when stop means and the spring seat are in their other positions.

4. In combination (a) a hydraulic motor-pump unit having high and low pressure ports and a displacement control ent movable between first and second maximum displacement-establishing positions on opposite sides of a zero displacement-esta'olishing position for varying the displacement of and changing the direction of flow through the unit;

(b) a source of pressure fluid, having a decaying pressure characteristic, for driving the unit as a motor;

(c) a conduit connecting the source with the high pressure port;

(d) a reservoir connected with the low pressure port;

(e) spring means connected with the displace nent control elernent and biasing it toward the second maximum displacernent-establishing position,

(f) said spring means including a spring seat shiftable between high spring-load and lov.l spring-load positions;

(g) a fluid pressure shifting motor connected with the spring seat and arranged to shift the spring scat toward the high sprinU-load position;

(lz) selecting means for connecting the shifting motor with the high pressure port and the reservoir, respectively; and

(i) control means connected with the displacement control element and responsive to the pressure at the high pressure port for moving said element toward the lirst maximum displacement-establishing position as the pressure rises above a predetermined value.

5. The combination defined in claim 4 (a) in which the control means comprises (l) a uid pressure control motor connected with the displacement control element and arranged to move that element toward the first maximum displacement-establisiting position,

(2) a control valve responsive to the pressure at the high pressure port for connecting the control motor with the 1righ pressure port and the reservoir, res ectively, as the pressure rises above and decreases below said predetermined value, and

at the high niemeer 9 10 (3) uid pressure motor means associated with motor and the fluid pressure motor means are sithe control Valve and effective when pressurized multaneously connected with the high pressure port to establish a high limit for said predetermined and the reservoir, respectively. Value. and when ".ented to estabhsh a 10W 1mm References Cited in the ille of this patent for said predetermined value; and 5 (b) in which the selecting means is connected with the UNITED STATES PATENTS fluid pressure motor means, whereby the shifting 2,986,872 Budzich June 6, 1961

Claims (1)

1. IN COMBINATION (A) HYDRAULIC MOTOR-PUMP UNIT HAVING HIGH AND LOW PRESSURE PORTS AND A DISPLACEMENT CONTROL ELEMENT MOVABLE BETWEEN FIRST AND SECOND MAXIMUM DISPLACEMENT-ESTABLISHING POSITIONS ON OPPOSITE SIDES OF A ZERO DISPLACEMENT-ESTABLISHING POSITION FOR VARYING THE DISPLACEMENT OF AND CHANGING THE DIRECTION OF FLOW THROUGH THE UNIT; (B) A SOURCE OF PRESSURE FLUID, HAVING A DECAYING PRESSURE CHARACTERISTIC, FOR DRIVING THE UNIT AS A MOTOR; (C) A CONDUIT CONNECTING THE SOURCE WITH THE HIGH PRESSURE PORT; (D) A RESERVOIR CONNECTED WITH THE LOW PRESSURE PORT; (E) SPRING MEANS CONNECTED WITH THE DISPLACEMENT CONTROL ELEMENT AND BIASING IT TOWARD THE SECOND MAXIMUM DISPLACEMENT-ESTABLISHING POSITION; (F) CONTROL MEANS CONNECTED WITH THE DISPLACEMENT CONTROL ELEMENT AND RESPONSIVE TO THE PRESSURE AT THE HIGH PRESSURE PORT FOR MOVING SAID ELEMENT TOWARD THE FIRST MAXIMUM DISPLACEMENT-ESTABLISHING POSITION AS THE PRESSURE RISES ABOVE A PREDETERMINED VALUE; (G) STOP MEANS ASSOCIATED WITH THE DISPLACEMENT CONTROL ELEMENT AND SHIFTABLE BETWEEN EFFECTIVE AND INEFFECTIVE POSITIONS IN WHICH, RESPECTIVELY, IT PREVENTS AND PERMITS AND ELEMENT FROM MOVING FROM THE ZERO DISPLACEMENT-ESTABLISHING POSITION TOWARD THE FIRST MAXIMUM DISPLACEMENT-ESTABLISHING POSITION AND (H) SELECTING MEANS FOR SHIFTING THE STOP MEANS BETWEEN ITS EFFECTIVE AND INEFFECTIVE POSITIONS.

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