US3688501A

US3688501A - Fluid pressure amplifier

Info

Publication number: US3688501A
Application number: US59625A
Authority: US
Inventors: John T Ellis Jr
Original assignee: ELLIS ENG Inc
Current assignee: ELLIS ENG Inc
Priority date: 1970-07-30
Filing date: 1970-07-30
Publication date: 1972-09-05
Anticipated expiration: 1989-09-05

Abstract

This fluid pressure amplifier utilizes air at low pressure to deliver hydraulic fluid at high pressure. The amplifier includes a relatively large diameter air cylinder and a relatively small diameter hydraulic fluid cylinder. A piston is reciprocally mounted in the air cylinder, which has a rod connected to the piston. A high pressure piston is formed integral with the rod. The hydraulic cylinder and the air cylinder have a common head. A liquid reservoir is mounted on the common head, and a valve controls the flow of hydraulic fluid between the high pressure cylinder and the reservoir. The valve is connected to the piston of the high pressure cylinder, and the valve is opened at the end of the stroke of the high pressure piston.

Description

1451 Sept. 5, 1972 United States Patent Ellis, J r.

54 FLUID PRESSURE AMPLIFIER 2,372,015 3/1945 Rockwell................60/54.5 A 3,473,328 10/1969 Mayhew 60/54 5 A .E .,B1 11. [72] Invent mmgdale I 3,541,792 11/1970 Ellls........................60/54.6A [7 Assigneei Ellis g g, Bl g- 944,048 12/1909 Price ...137/454.5

dale, Ill.

Primary ExaminerMartin P. Schwadron Assistant ExaminerA. M. Zopcic 22 Filed: July 30,1970

21 Appl.No.: 59,625

Attorney-Stone, Zummer & Aubel Related US. Application Data ABSTRACT [63] commuauon'm'pan of This fluid pressure amplifier utilizes air at low pressure 9, 1968, Pat. No. 3,541,792.

to deliver hydraulic fluid at high pressure. The amplifier includes a relatively large diameter air cylinder and [52] 60/546 a relatively small diameter hydraulic fluid cylinder. A E d A 54 5 A piston is reciprocally mounted in the air cylinder,

54.5 l-lA,60/54.6 HA; 417/520 which has a rod connected to the piston. A high pressure piston is formed integral with the rod. The hydraulic cylinder and the air cylinder have a common [5 6] References Cited UNITED STATES PATENTS head. A liquid reservoir is mounted on the common head, and a valve controls the flow of hydraulic fluid between the high pressure cylinder and the reservoir.

2,765,625 10/1956 The valve is connected to the piston of the high pres 2,972,867 2/1961 Klmgler......................60/54.6 Sure cylinder, and the valve i opened at the end of the 446,960 2/1891 B0rnhOldt..................417/520 Stroke f the i h pressure piston. 515,183 2/1894 Weatherhead ............417/520 1 Claim, 4 Drawing Figures FLUID PRESSURE AMPLIFIER CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of patent application Ser. No. 706,487, now U.S. Pat. No. 3,541,792 filed Feb. 9, 1968 on an application entitled Fluid Pressure Amplifier.

BACKGROUND OF THE INVENTION Machine shops which have hydraulical work-holding devices and other such pieces of equipment either must maintain a source of hydraulic fluid under pressure from a common source and have a distribution system throughout the shop paralleling an air system or the machine shops may utilize fluid pressure amplifiers which convert relatively low pressure air to high pressure hydraulic fluid. The present invention is an improved fluid pressure amplifier which uses relatively low pressure air to provide a hydraulic fluid under high pressure to a machine.

It is recognized that in any device which utilizes hydraulic fluid under high pressure, there is a tendency for the hydraulic fluid to leak at joints or through seals, so that as a device is put through a number of repetitive operations, there is a loss in fluid. It is necessary to provide a method of replenishing the fluid which is lost. Otherwise, air will be sucked into the system. The hydraulic devices then will not operate through a complete cycle, that is, a device will only go to a partially open or a partially closed position because there is not enough hydraulic fluid to operate the device completely.

In certain devices, there is automatic replenishing of hydraulic fluid into a system. However, this replenishing operates only when there is a slight negative pressure built up into the hydraulic fluid system. In many instances, the slight negative pressure is satisfactory for a particular operation. However, it does happen in some instances that there is a very slight negative pressure built up in a system, which slight negative pressure is not sufficient to add additional hydraulic fluid to the hydraulic system, but the slight negative pressure is sufficiently great to draw a slight amount of air into the hydraulic system, which air is detrimental to the operation of a sensitive piece of hydraulic equipment.

SUMMARY OF THE INVENTION The instant fluid pressure amplifier includes a relatively large double-acting air cylinder which has a positive displacement of a piston in the cylinder in both directions. A rod is connected to the piston of the air cylinder, and the rod extends into a small diameter high pressure tube with one end of the rod forming a piston of the tube to form a high pressure hydraulic cylinder. The high pressure hydraulic cylinder and the air cylinder are concentric and have a common head on the high pressure side of the high pressure hydraulic cylinder.

A hydraulic fluid reservoir is mounted on the common head. There is a communicating path through the head from the hydraulic fluid reservoir into the hydraulic cylinder. A valve seat surrounds the communicating path, and a closure releasably engages the valve seat. The closure is connected to the high pressure piston so that when the high pressure piston is retracted to its full retract position, the closure is unseated from the valve seat and allows hydraulic fluid to enter the hydraulic cylinder or flow out of the hydraulic cylinder to accommodate for expansion. The closure is held in place by a spring so that a negative pressure also displaces the closure and draws hydraulic fluid into the hydraulic cylinder. It is therefore a principal object of this invention to provide a fluid pressure amplifier wherein the hydraulic fluid is self-filling at the end of each stroke to make up any lost hydraulic fluid, even though the negative pressure in the hydraulic cylinder is very slight.

It is a further object of the instant invention to provide an improved fluid pressure amplifier wherein the hydraulic fluid is replenished in the hydraulic system at the end of the stroke due to negative pressure as well as positive opening of the cylinder to a fluid pressure reservoir.

It is another object of the present invention to provide an improved construction of a fluid pressure amplifier which is economical to manufacture and simple to maintain.

Other objects and uses of the present invention will become readily apparent to those skilled in the art upon a perusal of the following specification in light of the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side elevational view of an operating system showing a hydraulically operated work-holding device connected to a fluid pressure amplifier embodying the present invention;

FIG. 2 is an enlarged fragmentary cross-sectional view of the fluid pressure amplifier shown in FIG. 1, showing a low pressure cylinder in its fully retracted position and showing a valve between a reservoir and a high pressure cylinder in an open position;

FIG. 3 is an enlarged cross-sectional view of a portion of the fluid pressure amplifier shown in FIG. 2, showing the valve between the reservoir and the high pressure cylinder in a closed attitude; and

FIG. 4 is a cross-sectional view taken on line 4-4 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT.

Referring now to the drawing, and especially to FIG. 1, a fluid pressure amplifier generally indicated by numeral 10 is shown therein, which fluid pressure amplifier is a specific embodiment of the present invention. The fluid pressure amplifier 10 is connected to an air control valve 12 through pipe 16. The valve 12 is connected by an air line 18 to a conventional source of air under pressure, which source of air is not shown herein. The fluid pressure amplifier 10 is connected to a hydraulically operated work-holding device 20 through a conventional hydraulic line 22.

The construction of the fluid pressure amplifier 10 is best shown in FIG. 2, which shows the fluid pressure amplifier in its fully retracted attitude or low pressure attitude. The fluid pressure amplifier generally includes a large diameter air cylinder 24 connected to an oil pump or high pressure hydraulic cylinder 26. The longitudinal axis of the cylinder 26 is co-extensive with the longitudinal axis of the cylinder 24, and the cylinder 26 is mounted within the cylinder 24. A hydraulic fluid reservoir 28 is connected to the high pressure cylinder 26 through valve 30.

The low pressure air cylinder generally includes a base head 32, a tube 34 having one end sealingly engaging the base head, and an upper head 36 engaging the other end of the tube. The two heads are held in engagement with the tube by conventional tie rods 38. Mounted in the tube 34 is a low pressure or air piston 30 which has a rod 42 connected thereto. The base head 32 includes an air inlet port 44 which is connected to pipe 16. The head 36 has an air port 46 which has a breather 47 mounted therein to prevent foreign particles from being drawn into the air cylinder. The valve 12 controls the flow of air under pressure to piston 40 to control the movement of the piston.

The piston 40 has a groove 48 in its outer periphery with a seal 50 mounted therein to engage the interior wall of tube 34 to form a seal therebetween. Piston 40 is secured to the rod 42 by a screw 52.

The upper head 36 includes an axial threaded opening 54, which has mounted therein the valve 30. Communicating with the axial opening 54 is a radial passage 56, which passage 56 has connected thereto the hydraulic line 22. The head 36 includes a circular recess 58 which is concentric with the axial opening 54 and receives a portion of the high pressure cylinder.

The high pressure cylinder includes a tube 60 which has a shoulder 62 formed integrally therewith. Shoulder 62 is positioned in the recess 58. An O-ring 64 is positioned in the bottom of the recess and is engageable with the shoulder 62 to form a seal therein. An apertured retainer plate 66 is mounted in engagement with the shoulder 62 and holds the tube 60 in position. A plurality of screws 68 secure the retainer plate to the upper head 36.

Slideably mounted in the tube 60 is a high pressure or hydraulic piston which is formed integral with one end of the rod 42. The piston 70 has a sealing groove 72 in its outer side surface and an O-ring 74 is mounted in groove 72. A back-up washer 76 is mounted in engagement with the O-ring to prevent extrusion of the O-ring under high pressure. The piston 70 has an axial longitudinal opening 78 in its center, which opening extends through the piston and into the rod 42. A ring recess 80 is formed coaxial with the opening 78 interiorally of piston 70. A holder ring 82 is positioned in the recess 80. The ring 82 is held in position by a snap ring 84, which snap ring is positioned in a locking groove 86.

The valve 30 includes a valve body 88 which has a threaded outer surface and threads into the axial opening 54. Since the valve body is threaded, it may be adjusted relative to the piston and base head 32 to position the valve accurately to accommodate manufacturing tolerances in the length and thickness of the parts. It has been found that as much as an eighth of an inch adjustment has been required. A slot 89 is provided in the end of the valve body to provide a convenient means for engaging the valve body with a screw driver for adjusting the position of the valve body. A seal 90 is positioned on the outer periphery of the valve, and a nut 92 holds the seal 90 in place. The valve body has an axial flow port 94 centrally formed therein with a valve seat 96 defining one end of the valve body. Extending through the flow port 94 is a connector rod 98. A closure 100 is fixed to rod 98 and the closure is sealingly engageable with the seat 96 to seal closed selectively the port 94. A valve spring 104 is in engagement with the valve body, and a spring disc 106 fixed to the connector rod 98 engages the other end of valve spring 104 so that the closure 100 is constantly urged toward the valve seat 96.

The rod 98 is connected to the piston so that when the piston 70 is in its fully retracted position, the closure unseats from the valve to allow fluid to flow through the valve. A collar 108 is fixed to one end of the connector rod 98 and is engageable with the ring 82 when the piston 70 is near its fully retracted position.

The reservoir 28 includes a transparent plastic tube 110 which has one end mounted in a groove 112 in upper head 36. A reservoir head 114 is mounted on the other end of the tube 110, and the head 114 is held in position by a plurality of bolts 116. A filler opening 118 is provided in the head 114 with a stopper 120 positioned in the opening 1 18 to seal closed the reservoir.

The high pressure cylinder is constantly urged to its low pressure position by a piston return spring 122. The piston return spring surrounds the tube 60 and has one end in engagement with the retainer plate 66 and the other end in engagement with the piston 40. Thus, the tube 60 of the high pressure cylinder provides a guide for the piston return spring.

With the piston 40 in its fully retracted position, as shown in FIG. 2, the closure 100 is cracked from the seat approximately one-sixteenth of an inch. In order to supply hydraulic fluid under pressure, air under pressure is provided to pipe 16, which forces the piston 40 upward toward the head 36 against the force of spring 122. The movement of the piston upward allows the closure 100 to seat on the valve seat, and further movement of piston 70, which moves with piston 40, forces the hydraulic fluid out of the tube 60 through passage 56 and to the hydraulic line 22, which delivers the hydraulic fluid under pressure to the hydraulic device 20. The greater the movement of the piston 70, the more fluid which is expelled from the high pressure cylinder.

It may be appreciated that with most hydraulic devices, the seals are not perfect, and there is often some leakage in various places so that there is some loss of hydraulic fluid.

In order to decrease the pressure in the line 22, the pressure on the bottom of the piston 40 is relieved so that spring 122 forces the piston 40 to return toward the base head 32. As the piston 40 is retracted, the pressure in the high pressure cylinder 26 decreases. Further retraction of the piston tends to bring hydraulic fluid back into the high pressure cylinder. Should air pressure be lost for some reason, the instant device fails safe, i.e., the piston return spring returns the pistons to a low pressure position so that any device connected to the high pressure cylinder is relieved of high pressure hydraulic fluid. In the event that some of the hydraulic fluid has been lost through leakage, the pressure in the high pressure cylinder becomes a negative pressure when the pistons are retracted, thereby displacing the closure 100 against the force of the valve spring 104 to bring hydraulic fluid from the reservoir into the high pressure cylinder. It may be appreciated that this operation is quite effective when there is sufficient loss to generate a negative pressure. In certain instances, the loss is rather small, and the amount of loss is not enough to create a negative pressure which is sufficiently great to displace the closure against the force of the valve spring. With the instant pressure amplifier, the piston 70, reaching the end of its stroke, engages the collar M8 to pull the connector rod 98 downward to unseat the closure 100, thereby allowing hydraulic fluid to flow from the reservoir, even though there is not a sufficient loss of hydraulic fluid to develop a substantial negative pressure.

it is also important to note that with the operation of certain devices, heat is generated and the hydraulic fluid has a tendency to expand so that a complete retraction of the high pressure piston does not necessarily relieve all of the pressure in the hydraulically operated device, Thus, there may be incomplete opening of a given device or other malfunction. The displacement of the closure 100 at the end of the stroke always opens the reservoir to the high pressure cylinder so that should there by an expansion of the hydraulic fluid, the hydraulic fluid then may flow back up into the reservoir to allow the pressure in the system to equalize at the end of each stroke.

Although a specific embodiment of the instant invention has been shown and described in detail above, it is to be expressly understood that those skilled in the art may make various modifications and changes without departing from the spirit and scope of the invention. It is to be expressly understood that the instant invention is limited only by the appended claims.

What is claimed is:

1. A fluid pressure amplifier comprising, a large diameter, low pressure cylinder, said low pressure cylinder including a reciprocally mounted piston, a rod connected to said piston, a small diameter high pressure cylinder connected to the low pressure cylinder, said high pressure cylinder including a reciprocally mounted high pressure piston connected to the rod, a liquid reservoir connected to the high pressure cylinder, a valve controlling the flow of hydraulic fluid between the liquid reservoir and the high pressure cylinder, said valve including a valve body threadedly connected to one end of the high pressure cylinder for adjusting the position of the valve, an actuator opening the valve at one end of the stroke of the high pressure piston, the high pressure cylinder and the low pressure cylinder have a common head, the longitudinal axis of the low pressure cylinder is aligned with the longitudinal axis of the high pressure cylinder, the low pressure cylinder and the high pressure cylinder are on the same side of the common head, and a return spring having one end connected to the common head and the other end connected to the piston of the low pressure cylinder for urging constantly the piston away from the common head, said spring surrounding the high pressure cylinder, whereby the high pressure cylinder acts as a guide for the return spring.