US3667224A

US3667224A - Power transmission systems

Info

Publication number: US3667224A
Application number: US875098A
Authority: US
Inventors: Keith Foster; A F Hydraulics Ltd
Original assignee: National Research Development Corp UK; AF Hydraulics Ltd
Current assignee: National Research Development Corp UK; AF Hydraulics Ltd
Priority date: 1968-11-11
Filing date: 1969-11-10
Publication date: 1972-06-06
Anticipated expiration: 1989-06-06
Also published as: GB1272226A

Abstract

A so-called A.F. or ''''alternating flow'''' hydraulic system comprises a power line interconnecting a generator and a pressure chamber of a receiver, a return line, control valve means at the receiver end of the system and operative to interconnect said power and return lines whereby to produce a return hydraulic flow through the return line, and control means at the generator end of the system. The control means sense the change of flow conditions consequent upon operation of the valve means and substantially preventing pressure pulses from the generator reaching at least a major length of the power line connected to the receiver.

Description

United States Patent [451 June 6, 1972 App]. No.: 875,098

Foreign Application Priority Data Nov. 11, 1968 Great Britain ..53,416/68 [56] References Cited UNlTED STATES PATENTS 2,688,313 9/1954 Bauer ..91/431 2,170,890 8/1939 Allen 2,555,427 6/1951 Trautman.

2,881,739 4/1959 Huppert.... 3,058,310 10/1962 Panissidi ..60/51 X Primary Examiner-Edgar W. Geoghegan Attorney-Young & Thompson [57] ABSTRACT A so-called AF. or altemating flow hydraulic system comprises a power line interconnecting a generator and a pressure chamber of a receiver, a return line, control valve means at the receiver end of the system and operative to interconnect said power and return lines whereby to produce a return hydraulic flow through the return line, and control means at the generator end of the system. The control means sense the change of flow conditions consequent upon operation of the valve means and substantially preventing pressure pulses from the generator reaching at least a major length of the power line connected to the receiver.

8 Claims, 3 Drawing Figures PATENTEDJUH' 6 I972 SHEET 10F 2 INVENTOR KE/TH Fosnae BY yaw; M

ATTORNEYS PATENTEDJUH 61972 .3, 667, 224

SHEEI 2 BF 2 INVENTOR KA /7H Fan-1% raw ATTORNEYS 1 POWER TRANSMISSION SYSTEMS This invention relates to power transmission systems of the type referred to as alternating flow" or A.F. hydraulic systems in which an alternating-pressure hydraulic pulse generator is connected through a power line to a utilization device or receiver. The receiver acts as a transducer which is usually reciprocatory and may operate with a percussive action, for example as a road breaker hammer or a rock drill.

Such a system may operate with a considerable distance between the generator and the receiver, a typical distance for example being say 30 yards, and it is often desired that the system should be controlled by an operator at the receiver. Such control has previously presented problems and normally employed remote electrical control of appropriatevalves at the generator, and the invention has for its main object to provide improved control means which may, if so desired, be operable at the receiver end of the system.

The power line tends to pulsate or vibrate in sympathy with the oscillating fluid pressure, and if it is in the form of a flexible hose this sympathetic vibration causes considerable additional fatigue stresses which reduce the useful hose life. A further object of the invention is to provide said control means which, when a flexible hose is used as the power line, result in an increased effective hose life.

According to one aspect of the invention an A.F. hydraulic system comprises a power line interconnecting the generator and a pressure or pulse-receiving chamber of the receiver, a return line, control valve means at the receiver end of the system and operative to interconnect said power and return lines whereby to produce a return hydraulic flow through the return line, and control means at the generator end of the system to sense the change of flow conditions consequent upon operation of the valve means and for substantially preventing pressure pulses from the generator reaching at least a major length of the power line connected to the receiver.

Preferably substantially the entire length of the power line is relieved of material pressure fluctuations during idle periods of the receiver, i.e. when the control valve means are operative, and the return flow during such periods may be used to effect cooling of the receiver. To this end the control valve means may be operative to connect the return line to a working chamber of the receiver, and this working chamber may be said pressure chamber. Thus the resultant cooling flow, which is a convenient way of carrying away thefrictional heat unavoidably developed by the receiver in converting hydraulic energy into mechanical work, passes from the pressure chamber to the return line. Alternatively, although this is less preferable, the valve may operate to interconnect the two lines directly.

The receiver preferably comprises a piston on which the pressure pulses in the pressure chamber act to move the piston in one direction, the piston being returned by the action of a spring.

The type and operational sequence of the control valve is determined by the specific application and it may be remotely controlled or automatic. However, it provides a particularly convenient solution to control problems with applications which call for intermittent operation of the receiver under local manual operator control. When the control valve means are operative the generator output may be absorbed in a sufficiently large capacitance or accumulator to which the generator output is connected.

The control means may include a restrictor or the like through which the return flow passes, with the pressure rise upstream of the restrictor as a result of the return flow controlling a main valve of the control means which main valve is operative to relieve the pressure line of the generator pressure pulses. Operation of the main valve may disconnect the power line at a point adjacent to the generator and connect the latter to a supply tank of the system. Alternatively, the main valve may disconnect the generator from the power line, or at least said major length thereof, while leaving the generator connected to said capacitance or accumulator.

To maintain the low pressure return flow when the control valve means are operative, a low pressure make-up pump may be connected into the AF. transmission circuit through a nonretum valve. This pump will then normally also be operative during periods of power transmission, when it acts to provide a mean system operating pressure and ensures that the system is never subjected to a negative pressure. The restrictor of the control means, inorder to provide a rapid response to operation of the control valve at the receiver, is preferably connected into the system to and on the downstream or pressure side of the make-up pump. A component of the return flow may be provided by leakage from a high pressure seal or seals within the receiver. 7

Three illustrative embodiments of the invention are shown diagrammatically in the accompanying drawings. The drawings consist of three figures which respectively illustrate A.F. hydraulic power systems forming these embodiments.

In each case the system includes a generator, indicated by the reference numeral 1, which is connected to a receiver 2 in the form of a reciprocatory transducer through a conduit 3 forming a power line. The system contains a pressurized hydraulic fluid such as oil or water maintained at a mean system pressure of say 1,000 pounds per square inch by a make-up pump 4 connected to a supply tank 5. The generator 1 has a reciprocatory piston la (FIG. 2) which superimposes oscillating pressure waves of an amplitude of (say) i 800 pounds per square inch on the make-up pump pressure, and this piston may be cam or crank'driven from a suitable prime more which forms no part of the system.

The receiver is a road breaker hammer which is illustrated in some detail in'section in FIG. 1 and omitted from FIGS. 2 and 3. A conduit 6 provides a return line and leads back from the receiver 2 to control means at the generator end-of the system, and the conduit 3 may be a flexible hose of conventional armored construction and of considerable length, for example of say 30 yards. The return line 6 is also a flexible hose of smaller flow cross-section than the power line 3 and is shown as running separately therefrom between the generator and the receiver.

Referring particularly to FIG. 1, the hammer 2 comprises a body 7 with side handles 8 and in which a stepped piston and striker 9 is reciprocable. The upper end of a piston portion 9a of the piston and striker 9 projects into a pressure chamber 10 formed in the body 7 and permanently connected to the power line 3. A step 12 defining the lower end of the portion 9a provides a differential area on which acts the fluid pressure in a low pressure or spring chamber 13 also formed in the housing 7. A striker portion 9b of the piston and striker 9 is arranged to drive a drill bit 14 with a percussive action, and this portion slides through a seal 15 which seals the outer end of the spring chamber 13. The piston portion 9a slides in seals 16 and 17 disposed either end of a vented chamber 18 through which the portion 9a passes and in which a stepped intermediate section of that portion is disposed.

Operation of the hammer is controlled by a control valve 19 built into the body 7 and manually operated by a control lever 20 which can be grasped against one of the handles 8 to move a spool valve member 22 against a valve spring 23 to the operative valve position illustrated in the drawings. In this specification reference to operative valve positions corresponds to a non-working or idle condition of the hammer or other receiver, and in this position the valve of FIG. 1 as shown in that figure opens a bypass passage 31 between the

chambers

10 and 13 and connects the return line 6 to that passage. Thus any hydraulic fluid reaching the hammer through the power line 3 returns along the line 6, passing through the chamber 10 so that it acts to cool the hammer. The line 6 drains back into the tank 5 and also provides a return path for leakage from the seal 17, which leakage is collected through a conduit 24.

Control means at the generator end of the system are sensitive to operation of the control valve 19. These means comprise a restrictor 25 positioned in the line 6 adjacent the tank 5, main control vale 26, a sensitive pilot valve 27 controlling the valve 26, and an accumulator 28. The valves 26 and 27 are both of spool type, with valve spools 29 and 30 respectively which are urged to the inoperative, i.e. hammer-working, positions by valve springs 32 and 33.

' A make-up pressure line-34 is connected to the power line 3 through a one-way valve 35. When operation of the control valve 19 at the hammer 2 produces a return flow along the return line 6 the resultant pressure rise at the upstream side of the restrictor 25 acts on the valve spool 30 to move it to the operative position shown, in which it connects the pressure line 34 to the valve 26 through control lines 36 and 37. Thus the make-up pressure is applied to the valve spool 29 to move it to the open operative position illustrated, in which it serves to connect the power line 3 at a point adjacent the generator 1 to the accumulator 28 through

lines

38 and 39. The accumulator 28 is of conventional type having a pressurized gas chamber 40 which is separated by a flexible diaphragm 42 from. a fluid space 43 with which the line 39 communicates. The pressure waves produced by the generator I are absorbed by the accumulator so that the control means act substantially to prevent pressure pulses from the generator 1 reaching the power line 3 downstream of the line 34. The mean system pressure is still maintained by the pump 4 which provides the recirculating return flow through the hammer 2, this flow maintaining the control means operative so that the hammer remains idle for as long as the operator holds the control valve 19 open.

.Release of the control lever 20 by the operator allows the valve spring 33 to return the valve spool 30 to the normal inoperative position, in which it connects the control line 37 from the valve 26 to, the tank through an exhaust line 44. This allows the valve spring 32 to return the valve spool 29 to the inoperative closed position in which the accumulator 28 is disconnected from the power line 3. As the valve 19 no longer interconnects the chambers and 13 of the hammer the pressure pulses which are superimposed on the main system pressure are operative in the pressure chamber 10 to drive the piston and striker 9 and product forward power strokes thereof, with compression of the pressurized hydraulic fluid in the spring chamber 13 providing the return spring force for the piston and striker.

The systems of FIGS. 2 and 3 utilize the same hammer and control valve arrangement as that already described, and hence in each of these figures only the generator end of the system including the control means is illustrated. Referring to FIG. 2, the generator illustrated therein has a piston 1a of stepped form with a smaller diameter end portion 50 which communicates with the power line 3 and normally produces the pressure pulses which are again superimposed on the mean system pressure produced by the pump 4 connected to the lower'line 3through the one-way valve 35. The piston la is cam-operated by an eccentric cam 51 which rotates within a closed interior chamber 52 of the generator, within which chamber the larger inner end portion 53 of the piston is movable and has an end face which engages the cam 51. The chamber 52 is completely sealed apart from a control line 54 which is connected to a main valve 55 of the control means. As in the system of FIG. 1 the valve 55 is controlled by a pilot valve 56 sensitive to the pressure rise upstream of a restrictor 57 in the return line 6, these valves and the restrictor being similarly constructed, arranged and cooperating as in the embodiment of FIG. 1.

The valve 55 normally vents the chamber 52 to the tank 5 through a line 58, and the pressure in the power line 3 maintains the piston 1a in contact with the cam. However, operation of the control means as a result of a pressure rise upstream of the restrictor 57 connects the chamber 52 with the power line 3 through a pressure line 59. Thus the system make-up pressure pressurizes the interior chamber 52 of the generator and this pressure is applied to both end faces of the piston la. The differential force acting on the piston, due to the larger end portion 53 thereof being in the chamber 52, lifts the piston off the cam 51 so that the generator becomes inoperative and, as before, the pump 4 circulates the hydraulic fluid through the hammer 2 as long as the control valve 19 is held open by the operator. 7

In the system of FIG. 3 the generatorv 1 is coupled to the prime mover (not illustrated) through a clutch 60 of conventional type, and application of hydraulic pressure through clutch control line 61 frees the clutch so that the prime mover no longer drives the generator. In this case the control valve 62 of the control means is directly actuated by the pressure upstream of the restrictor 63, and in the operative position illustrated it connects the make-up pressure to the control line 61 through a pressure line 64. In the valve-closed position the control line 61 can exhaust to the tank 5 through a line 65.

It will be appreciated that the invenu'on not only relieves the power line of the pulsating generator output and resultant cyclic stresses when the receiver is idle, but that in all the embodiments it also improves efficiency as the power required by the generator is materially reduced during the idle periods. In known systems the generator has continued to impose oscillating pressure waves on the hydraulic fluid in the power line even when the receiver has been inoperative.

lclaim:

1. An A.F. hydraulic system comprising a power line interconnecting a generator and a pressure chamber of a receiver, a return line, control valve means at the receiver end of the system and operative to interconnect said power and return lines whereby to produce a return hydraulic flow through the return line, which return flow is used to effect cooling of the receiver, and control means at the generator end of the system to sense the change of flow conditions consequent upon operation of the valve means and for substantially preventing pressure pulses from the generator reaching at least a major length of the power line connected to the receiver.

2. An A.F. hydraulic system according to claim 1, wherein the control valve means are operative to establish a flowpath from the power line to the return line'via a working chamber of the receiver.

3. A hydraulic system according to claim 2, wherein the control valve means are operative to connect the return line to the pressure chamber of the receiver.

4. An A.F. hydraulic system comprising a power line interconnecting a generator and a pressure chamber of a receiver, a return line, control valve means at the receiver end of the system and operative to interconnect said power and return lines whereby to produce a return hydraulic flow through the return line, and control means at the generator end of the system including -a restrictor or flow-sensitive valve through which the return flow passes, the control means further including a main valve and either a pressure rise upstream of the restrictor or operation of the flow-sensitive valve, as a result of the return flow, acting to control the main valve which is operative substantially to relieve the pressure line of the generator pressure pulses upon operation of the valve means.

5. A hydraulic system according to claim 4, wherein operation of the main valve connects the generator to an accumulator in which the generator output is absorbed.

6. A hydraulic system according to claim 4, whereon the generator comprises a earn-operated reciprocatory piston the forward end of which communicates with the power line and the rear end of which moves in a closed chamber which is connected to a supply tank during normal generator operation,

operation of the main valve connecting this chamber to the A power line and disconnecting it from the tank so that a pressure differential across the generator piston lifts it clear of the operating cam.

7. A hydraulic system according to claim 4, wherein operation of the main valve frees a hydraulically controlled clutch through which the generator is driven.

8. An A.F. hydraulic system comprising a power line interconnecting a generator and a pressure chamber of a receiver, a return line, control valve means at the receiver end of the system and operative to interconnect said power and return lines whereby to produce a return hydraulic flow through the return line, control means at the generator end of the system to sense the change of flow conditions consequent upon operation of the valve means and for substantially preventing pressure pulses from the generator reaching at least a major length of the power line connected to the receiver, and a 5 make-up pump which is connected to the power line and which provides the return flow when the control valve means are operative.

Claims

2. An A.F. hydraulic system according to claim 1, wherein the control valve means are operative to establish a flowpath from the power line to the return line via a working chamber of the receiver.

4. An A.F. hydraulic system comprising a power line interconnecting a generator and a pressure chamber of a receiver, a return line, control valve means at the receiver end of the system and operative to interconnect said power and return lines whereby to produce a return hydraulic flow through the return line, and control means at the generator end of the system including a restrictor or flow-sensitive valve through which the return flow passes, the control means further including a main valve and either a pressure rise upstream of the restrictor or operation of the flow-sensitive valve, as a result of the return flow, acting to control the main valve which is operative substantially to relieve the pressure line of the generator pressure pulses upon operation of the valve means.

6. A hydraulic system according to claim 4, whereon the generator comprises a cam-operated reciprocatory piston the forward end of which communicates with the power line and the rear end of which moves in a closed chamber which is connected to a supply tank during normal generator operation, operation of the main valve connecting this chamber to the power line and disconnecting it from the tank so that a pressure differential across the generator piston lifts it clear of the operating cam.

8. An A.F. hydraulic system comprising a power line interconnecting a generator and a pressure chamber of a receiver, a return line, control valve means at the receiver end of the system and operative to interconnect said power and return lines whereby to produce a return hydraulic flow through the return line, control means at the generator end of the system to sense the change of flow conditions consequent upon operation of the valve means and for substantially preventing pressure pulses from the generator reaching at least a major length of the power line connected to the receiver, and a make-up pump which is connected to the power line and which provides the return flow when the control valve means are operative.