US2214817A

US2214817A - Power transmission

Info

Publication number: US2214817A
Application number: US215991A
Authority: US
Inventors: Ferris T Harrington
Original assignee: Vickers Inc
Current assignee: Vickers Inc
Priority date: 1938-06-27
Filing date: 1938-06-27
Publication date: 1940-09-17
Anticipated expiration: 1957-09-17

Description

Selta. 17, '1940. F. T. HARRINGTN y2,214,817

`POWER TRANSMISSION Filed Jun 27, 195s ATTORNEY Patented Sept. 17, 1940 UNITED STATES' Powna 'riuuvsmrssrim Ferris T. Barrington, Detroit, Mich., assignor to Vickers Incorporated, Detroit, Mich., a corporation of Michigan applicati@ Junez'z, 193s, serial No. 215,991

6 Claims.

'I'his invention relates to power transmissions,

, particularly to'those of the type comprising two or more iiuid pressure energy translating devices one of which may function as a pump and another as a iluid motor. In many transmissions of this character and particularly with a hydraulic press it is desired to hold the movable platen of the press or other work member under pressure after right or left by a lever 42. Valve 40 has tank the completion of its pressing stroke. Previously 10 this has beenfaccomplished by allowing the pump to build up pressure in the press cylinder and using a relief valve to prevent this pressure from becoming dangerously high. In the latter method there is an excessive waste of -power because oi the fact that the -pump delivery is working against the stalled piston of the press cylinder.

Accumulators have also been used to supply pres-y sureiiuid to the press cylinder, but the pumphad to be bypassed at comparatively high pressures, again wasting power.l v

It is an object of this invention to provide means for holding pressure on a work member by y means other than the delivery of the pump and without unnecessary waste o f power. It is 'another Aobject to provide a valve to act vas a relief valve for bypassing the pump when a predetermined safe pressure is exceeded in the hydraulic system, said valve also being capable o! bypassing the pump at a pressure lower than the aforementioned pressure while the' work member is stalled. Y c

Still another object is to provide an 'accumulator or its equivalent to hold pressure on the press at the end of its pressing stroke together with improved control means for keeping the accumulator filled without wasting power.

In the drawing:

tion.

shown in Figure 1.

. Figure 3 is a detail sectional view ola pressurev responsive pilot valve.

In Figure 1 a pump I8, which may be oi' the4 5 xed displacement type and continuously driven b y a prime mover such as an electric motor I2, is

' adapted to draw fluid from a tank I4 vthrough a 'conduit I8. The fluid is delivered through a conduit I8 to a valve 28, which has a spool 22 slidably mounted in a. bore 23 and normally held downwardly by@ spring 24. 'I'he valve 28 also has a tank port 28 and a delivery port 28. passage y3Il"connects the port 28 to the lower end-of bore 23. Slidably mounted in'passage 38 is a small 5l 32 adapted to raise thespool 22 when prescheck valve 38 is interposed, to a spring centered,

Figure 1 is a diagrammatic view of the invensure at port 28 rises above the setting of the spring 24. A drain passage 33 connects the upper part of the bore 23 to the tank portr28. The port 28 is connected to tank by a conduit 34. The port 28 vis connected by a conduit 38,-in which a 5 op'en center four-way valve 48.

The spool of the vlve 48 may be shifted tothe ports 44 and

cylinder ports

48 and 48. The ports 10 44 are connected to the tank I4 by a conduit 58. The ports '48 and 48 are connected by

conduits

52 and 84 to the head'and rod ends respectively of a large cylinder 58 mounted on a press 58. A piston 88, slidably mounted in the cylinder 15 58, carries a platen 82 and Iis adapted to press against a base plate 84.

The four-way valve 48 has another port 88 which is always in communication with pressure line 38 and which isconnected hy a conduit 88 to 20 a pressure responsive valve 18 shown in detail in Figure 3. This valve has a spool I2 slidably mounted in a bore 'I4 and held inits left hand position by a spring 18. A passage 18 connects the .conduit 88 to the left end oi' bore l4. This 25 passage is shown as positioned in thevalve body' in Figures l and 2 for sake/"of clearness. .When the pressure in conduit 88 rises above the setting of spring 18, the spool 'l2 will shift to the right.V A

conduit 88 extendsgfrom the \valve18 to the'bot-" 30.

tom of the bore `23 invalve 28.- Fluid pressure in conduit 88 is eective overthe full diameter of the valve spool 22 whereas pressure in passage 38 is effective only on the smaller area of piston 32. y The valve 'I8 has a drain conduit 82 connected to 35 In operation, with the parts in the'4 position shown in Figure land the pump I Il operating,

iluid is drawn from the tank I4 through conduit I8 and delivered by conduit I8 through valve 20 40 to port 28. Pressure fiuidalso passes through passage 38 to piston 32. If.. for any reason pressure should build up at port 28 and exceed thesetting of -spring 24it will act through passage 88 and cause piston 32 to rise which will in turn raise 45 the spool 22. Accordingly conduit I8 will be connected to port`28 and bypass the delivery of pump I8 through' conduit 34 to tank.

Normally pressure fluid is delivered from the port 28 of valve 2li through conduit 88 and check 50 valve 38 to the four-way valve 48. The spool of valve 48 being in its center .position there is no fluid delivered to cylinder 88 and the pump delivery is bypassed to tank through the interior of `the spool oi valve 48.

vzo

4vention as shown in Figure 1.

To perform a pressing stroke, the lever 42 is moved to the left connecting the delivery conduit 36 to the cylinder port 46 of the valve 40. When the lever 42 is moved to the left, fluid is directed through conduit 52 to the head end of cylinder 56.

Accordingly piston 60 moves downwardly carrying platen 62 to perform the work. Fluid in the rod end of cylinder 56 passes through conduit 54,

ports

48 and 44 of valve 40, and conduit 50 to tank.

When the piston 6E reaches the end of its pressing stroke, the lever 42 being still held in its left hand position, pressure builds up in

conduits

52 and 36 and is transmitted through conduit 68 to the passage I8 of valve 10. When the pressure in passage 18 rises suiiiciently, its action in bore 14 on the spool 'l2 causes the latter to shift to the right against the resistance offered by spring 16. Thus conduit 68 is connected to conduit 80 and fluid is delivered to the bottom of thevbore 23 of valve 20. Any fluid that may be trapped on the right side of the spool l2 is drained to tank by the conduit 82. Because of the uid delivered from port 66 of valve 40 through conduit 68, valve li), and conduit 86 to the bore 23 of valve 20, valve spool 2,2 accordingly rises and bypasses the delivery of the pump. Any fluid that may be trapped above the spool 22 is drained off through passage 33 to port 26.

High pressure uid is now trapped in the head end of the large cylinder 56 and the conduit 52 by check valve 38. The inherent fluid capacities and elasticityA of the large cylinder 56 and the conduit 52 produces an accumulator effect which maintains pressure on the piston 60, thereby holding the platen 62 against the work under pressure. Thus a substantial interval may elapse before sufficient fluid has leaked out of the pressure side to cause the pressure to drop below the value where the spring 16 of valve 'I0 is again able to return spool 12 to the left. When this occurs thepbottom yend of bore 23 is again connected to tank through conduits 86 and 82 and spool 22 shifts to its'lower position, thus reloading pump and causing fluid to be delivered to the press cyll inder until the pressure rises sufficiently to again shift valve 10 to the right. Thus so long as the lever 42 is held to the left, the pump will be automatically cut out and cut in as required to maintain the pressure in cylinder 56 within predetermined limits.

To cause theI return stroke of piston 66, the lever 42 of valve 40 is moved to the right, relieving the pressure in cylinder 56 and conduit 52 through

ports

46 and 44 of valve 40, to the tank conduit 50. At the same time pressure uid is delivered from conduit 36, valve 40', port 48 and conduit 54 to the rod end of cylinder 56, causing the return stroke of the piston 60.

When the return stroke is completed lever 42 is released and the spool of valve 40 springcenters, bypassing the pump at low pressure. Another pressing stroke may be performed by moving the lever 42 to the left.

Shown in Figure 2 is a modification of the in- The circuit of Figure 2 is very similar to that of Figure 1 but is used when the work cylinder such as 56' is so small as to have insufficient accumulator effect, or where for other reasons a separate accumulator is-desirable.

A conduit 52 and a conduit 54 extend from the cylinder ports of closed center four-way valve 40 to the head and rod ends respectively of cylinder 56. Slidably mounted in cylinder 56 is a `all times.

pump is unloaded by the action of valves 10 andl piston 60. A conduit 84, which is connected to a spring or gas loaded accumulator 86, passes through the discharge port of check valve 38 and is in constant communication with the pressure port of the four-way valve 46.

' Because the accumulator is connected between the pump discharge conduit I8 and the four-way valve 46', the latter may be of the closed center type. The valve 'Hl controls the valve 20 in-the same manner as previously described, thus maintaining the pressure in conduit 84 and pressure port of valve 40' within predetermined limits at With valve 40 in center position the 210 instead of through the four-Way valve 40' as in Figure 1.

If the lever 42 of valve 46 is held to the left after piston 60' has completed its working stroke, the action is identical to that of the circuit in Figure 1. A

The construction disclosed, provides a reliable satisfactory means of controlling the effective op'- eration of a pump in accordance with pressure conditions in a load circuit. The pressure responsive mechanism at the valve l0 may be made extremely small and light and, since packings are dispensed with, the spool 12 may be made as nearly frictionless in its operation as possible. In addition the travel required of. spool 12 between its extreme operating positions being small, the spring 16 may be made many times as long as the spool travel, thus providing a nearly constant force on the spool 12. In fact it is entirely feasible and sometimes desirable to utilize a weight in place of the spring 16, since the spool 12 may be made extremely small relative to theother valves in the circuit and the size or weight thus required is not abnormally bulky. The op` eration of4 valve 10 is entirely independent of valve 20 While the valve 26 is entirely and solely dependent on the valve 10 for its operation during the unloading and reloading action. These features together contribute to the production of an unloader control system which is sufliclently sensitive to maintain the pressure in the load circuit within predetermined limits which are extremely close. In other words, the differential between the pressure at which the pump unloads and that at which it reloads may be a very small percentage of the total pressure in the load circuit.

While rthe form of embodiment of the invention, as'herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming Within the scope of the claims which follow.

What is claimed is as follows:

1. In a Huid power transmission system, pump means forming a source of pressure fluid, an

accumulator for storing pressure uid, pressure responsive relief valve meansv to bypass the pump at a predetermined pressure, and additional pressure responsive valve means connected with the relief valveA to unload the pump at a pressure lower than the rst said pressure.

3. In a uid power transmission system, pump means forming a source of pressure fluid for use lin a circuit having suiiicien't fluid capacity and elasticity of members under stress to provide an accumulator effect, pressure responsive relief valve means to bypass the pump at a predetermined pressure, and additional pressure responsive means operably connected with the relief valve for causing the relief vvalve to unload the pump at a pressure lower than the first said pressure.

4. In a iiuid power transmission system the combination of a iixed displacement pump,

means for continuously driving the pump. an accumulator for storing varying amounts of liquid under pressure, a pilot control means responsive to changes in pressure in the accumulator, a valve for bypassing the pump discharge and operating means controlled by the pilot control means for opening said bypass valve when the accumulator pressure reaches a. predetermined value, said bypass valve being further rresponsive to the pump discharge pressure for opening the valve whenever a predetermined higher pressure is exceeded.

5. In a fluidl power transmission system the combination of a fixed displacement pump, means for continuously driving the pump, a'pilot control means responsive to changes in pressure against which the pump is discharging, a valve for bypassing the pump dischargeI and operating means controlled by the pilot control means for opening said bypass valve when such.` pressure reaches a predetermined value, said bypass valve being further responsive to the pump discharge pressure :for opening the valve whenever a prede termined higher pressure is exceeded.

6. In a iiuid power transmission system the combination of a iixed displacement pump, means for continuously driving the pump, a pump discharge line including a check Valve therein, a pilot control means responsive to changes in pressure beyond the check valve, a valve for bypassing the pump discharge and operating means controlled by the pilot control means :for opening said bypass valve when such pressure reaches a predetermined value, said bypass valve being further responsive to the pump discharge pressure for opening the valve whenever a predetermined higher pressure is exceeded in the discharge line between the pump and the check valve.

FERRIS T. HARRINGTON.