US2343900A - Compound hydraulic brake compressor - Google Patents

Description

March 14, 19144. M. v. GROVES I COMPOUND HYDRAULIC BRAKE COMPRESSOR Filed Nov. 20, 1940 I5 Sheets-Sheet 2 5 w 1: t 1 ,0 m 0 H .5 z 7. \v\\\\\ a A a a u w a m M H a M. 7 m 7.. M 1%. M M a a x mm 2 w a a m.. W no 2 4 M... M v 1 mm.

INVENTOR Marina YGroz/es SLW$J ATTORNEY March 14, 1944. I v GROVES 2,343,900

COMPOUND HYDRAULIC BRAKE COMPRESSOR Filed Nov. 20, 1940 3 Sheets-Sheet 3 w 4 I 20 12 7/ w Y/ A Z5 22 INVENTOR Z1 Mar-din. Harm e5 5 ATTORNEY Patented Mar. 14, 1944 UNITED STATES PATENT orrlcs COMPOUND HYDRAULIC BRAKE COMPRESSOR.

Martin 'V. Groves, New York, N. Y.. assignor of one-half to Arthur Wilde and Arthur Hull- Ryde, Bayside, N. Y.

Application November 20, 1940, Serial No. 366,333

14 Claims.

Devices of this sort comprise a large piston in a main cylinder and arelatively smaller piston in an auxiliary cylinder, suitably supplied with operating fluid. The pistons are simultaneously moved forward to quickly displace fluid by the large piston in a relatively large volume until a predetermined pressure is built up in the hydraulic system to be actuated, whereupon the smaller piston is released for continued movement relative to the large piston and displaces fluid into said large cylinder where the hydraulic advantage due to the diflerence in said cylinder' sizes exerts a relatively high pressure on said system.

An object of the present invention is to provide a relatively simple, durable and dependable device of the character described.

Another object is to provide a device which is capable of effecting a. smooth carry-over from low pressure to high pressure, and one in which such carry-over may be provided at a predetermined pressure.

Another object is to provide a device in which the actuating fluid is readily and quickly vented claims.

Referring to thedrawings, in which the same reference characters indicate the same parts in the various views:

of a compound hydraulic compressor constructed in accordance with this invention.

Fig. 2 is a vertical sectional view similar to Fig. 1 but illustrating the parts with the main and auxiliary pistons moved forward as a unit.

Fig. 3 is another sectional view similar to Fig. 2 but illustrating the auxiliary piston moved forwards relative to the main piston.

Fig. 4 is a vertical sectional view taken on the line 4-4 of Fig. 1.

Fig. 5 is an enlarged detailed view of a portion of Fig. 1.

Fig. 6 is a vertical longitudinal sectional view 0! I a compound hydraulic compressor constructed in accordance with another embodiment of this invention.

Fig. 7 is a vertical sectional view similar to Fig. 6 but illustrating the part with th main and auxiliary pistons moved forwards as a unit.

Fig. 8 is another sectional view similar to Fig. 6 but illustrating the auxiliary piston moved forwards relative to the main piston.

Fig. 9 is an enlarged detailed view of a portion of Fig. 6.

The compound hydraulic compressor, according to this invention, includes a hollow body it for holding a hydraulic fluid ii and having a cylinder l2 provided with a large bore E2 in its front end and a small bore i2 in its rear end and with a closed end l9, which end is provided with an opening it for connection with a pipe line for su plying the hydraulic fluid to the hydraulic brakes. A main piston is slidably mounted in the cylinder l2 and is formed with a small bore 56 in its rear end. An auxiliary small piston ll 1 slidably mounted in the bore it.

A means is provided for urging the small piston ll forwards for applying the brakes and this means includes a piston rod is connected with the rear of the piston I! and extending from the rear end of the body and adapted to be connected with a foot pedal, or linkage, or other mechanism by which the piston rod It may be manually moved forwards and rearwards.

Hydraulic fluid means is provided for normally connecting the pistons. l6 and I1 together as'a unit and this means is controlled with a pressure loaded valve is actuated by pressure of the hydraulic fluid in the bore B6 of the main piston l5 and controlling passages 20 arranged to connect the bore I6 with the rear end of the main Fig. i is a vertical longitudinal sectional view as piston I5 for connecting or disconnecting the fluid in the bore IS with the fluid to the rear of the main piston l5 to. connect or disconnect these pistons.

More specifically the passages 20 connect with a compartment 20' in the rear end of the small piston II. This compartment 20' i connected by passages 20 through the wall of the small piston I! to the compartment 20 which is located to the rear of the cylinder I2 behind the main piston l5. 'Iihe. valve I3 is slidably mounted in a cylindrical opening of an outer one way valve 2|. A rubber cup I3 is engaged upon the head of valve I9 and in face contact therewith has a smaller piston l9 also arranged adjacent the head of the valve l3. An expansion spring 22 is located within the body of the outer valve 2| and acts against the small piston for normally urging this latter valve closed. It is illustrated in its closed position in Figs. 1 and 2.

In its closed position the inner end of the valve l9 projects across the inner end of the passages 20 closing the same against the passage of fluid therethrough. When the pressure of the hydraulic fluid to the front of the'valve l9 opens the valve l3 it will be moved rearwards compressing the spring 22 and causing the fluid to the rear of the valve to pass between the edge of the rubber cup |3 and the valve body 2| to engage behind the enlarged head of the valve l9 and the adjacent end of the valve body 2| for locking the valve IS in its open position to permit the hydraulic fluid to pass through passages 20 and into the compartment 20".

However, the rubber cup I9 is formed with an opening I9 and the piston I9 is formed with an opening IS in an aligned position with the opening l9 through which the entrapped fluid is adapted to pass for freeing the rubber cup I9 and piston Ill to permit the spring 22 to again expand and urge these members into position upon the end of the valve l9. From a careful inspection of Fig. 5 it will be noted that the metallic piston l9 is of smaller diameter than the bore of the valve body 2|, therefore when the valve I9 moves rearwards to expose the passages 20 the hydraulic fluid contained within the valve body may easily discharge around the peripheral edge of the rubber cup I9 by flexing the same out of engagement with relation to its adjacent wall. This rubber cup is formed with a flange which is directed towards the valve 9 and acts to lock the entrapped fluid and prevent the same from again discharging around this said eripheral edge.

When the brake is released the pressure in front of valve l3 and in the passage 20' is released. The pressure of the fluid in back of the valve IS in the space between the cup I9 and the wall of the valve body 2| will then separate the cup l3 from its seat op the rear flange of the valve I9, which will allow the trapp d fluid to pass through the opening IS" in the cup Ill and the opening l3 in the piston Ill to the passage 20', thus allowing the spring 22 to expand and return the valve l3 to its closed position.

The valve 2| has a head 2| cooperative with an adjacent seat formed internally in the piston l1. The valve 2| is urged upon its seat by an expansion spring 23 which is disposed within the bore l3 and acts between the front end of the bore and the valve head2l'. Y

The piston rod I3 is slidably mounted in the rear end of the cylinder l2. Packing material 25 surrounds the piston rod l8 and operates in conjunction with the adjacent wall of the cylinder for preventing leakage of the hydraulic fluid from the body l0. Packing material-'26 is mounted upon the front end of the small piston l1 and is cooperative with the wall of the bore l3 for preventing leakage of hydraulic fluid from the front of the bore to the rear of the bore.

The cylinder I2 is provided with a passage 21 through which the hydraulic fluid may enter a compartment 23 located between a front flange l3 formed on the main piston l5, and a rear flange 30 formed on a rear area of the main piston l5. Another passage 32 connects the compartment 29 with a compartment 33 at th rear of the main piston l5 directly behind a flange 34 formed on the front of the small piston Another passage 35 extends through the wall of the cylinder l2 and allows the passage of hydraulic fluid II to the front of the cylinder I! when the main piston I5 is in its rear position as illustrated in Fig. 1. However, when the main piston moves forwards the passage 35 is immediately closed. The front portion of the main piston I5 is provided with a reduced tapered end 36 upon which an annular packing cup or member 31 is mounted. A spring 38 urges this packing member 31 against the flange 29.

A check valve 40 is mounted across the discharge opening l3 at the front of the cylinder I2. This check valve 40 has a skirt partion 40' and a base portion 40 The base portion 40 is supported upon a retainer cap 4|. This retainer cap 4| has passages 42 in its side walls which are controlled by the skirt portion 40 of the valve. The retainer cap 4| is rested against a rubber washer 43 mounted across the front end of the cylinder |2. A metal bushing 44 is mounted around the metal cap 4|. The spring 33 engages about and supports the retainer bushing and urges the retainer bushing forwards so as to clamp the metal cap 4| in position and so support the check valve.

The front wall l0 of th body In is arranged with a removable cap Ill which is threadedly mounted upon the cylinder l2. The piston rod I8 is threadedly engaged into the rear end of the small piston IT. A removable plug 40 is mounted upon the top of the body 0 and may be removed when additional hydraulic fluid must be added to the brake system. This plug 48 is provided with vent passages 41.

Means is provided for cutting of! the chamber 20 from the chamber 33 to prevent fluid from passing from the chamber 20 into the compartment 33, during the time that the piston I1 is moving forward relative to the piston l5. This means includes a valve 50 controlling the passage of hydraulic fluid between the chambers 33 and 20. More specifically, the valve 50 is slidably mounted around the auxiliary piston l1 and is cooperative with a valve seat 5| formed upon a skirt portion 52 on the rear of the main piston l5. This skirt portion 52 has several passages 53 through its side walls. An annular member 54 is removably supported upon the rear of the skirt portion 52. A pluralit of expansion springs 55 act between this annular member 54 and the valve 50 for urging the valve upon its seat 5|. The auxiliary piston I1 is formed with a flange portion 56 normally engaging the valve 50 and holding the valve open so that there is a free is off. To apply the brake, the piston rod I8 is moved forwards. .Since there is hydraulic fluid main piston I moving forwards in the cylinder I2, a relatively large amount of hydraulic fluid pistons reach the positions shown in Fig. 1. The brakes now completely released.

It should be noted that the check valve 40 is protected by the retainer bushing 44 which also retains the front of the spring 38.. The spring holds the packing 31 in position. In this position the packing 31 closes several bleed holes 29" within the cylinder I2 will be displaced through the opening I3 to fill up the hydraulic line to the brakes and move the brake shoes against the brake drum. When this position is reached the parts will be in the condition illustrated in Fig. 2. Further forward pressure on the piston rod I8 will cause an increase in the pressure of the hydraulic fluid within the bore I6.

An increase in the pressure in the bore I8 will be transmitted to open the valve IS. The pressure will now be communicated through the passages and 20 to the compartment 20, which will then act against the rear of the main piston I5 for urging the main piston forwards. When the valve It opens the entrapped fluid in the bore It starts escaping which then permits the auxiliary piston II to move forwards relative to the main piston I5.- Immediately the flange 56 moves forwards oil the valve 50 which then Because of the relative small diameter of the auxiliar piston II the hydraulic pressure to the rear of the main piston I5 will be materially increased even though the force which moves the piston rod I8 forwards remain constant. 'Iihus there is now a hydraulic mechanical advantage present. The increased hydraulic pressure will serve to apply the hydraulic brakes with relatively great force. Soon the parts reach the position shown in Fig. 3 and now the hydraulic brake is fully applied.

The check valve 40 permitted the hydraulic fluid within the cylinder I2 to the front of the main piston I5 to pass through theopenings 42 to the discharge through the opening I3. The spring 38 became compressed during the forward motion of the main piston I5. The pressure of the spring 33 maintains the metal cap in position and prevents the metal cap 40 from lifting off from the rubber washer 43 thus preventing any escape of the hydraulic fluid from the brake system back into the cylinder I2.

The brake is released in th following manner: The rod I8 is moved rearwards. The hydraulic fluid will immediately be sucked into the bore I6. The valve 2| opens for this purpose. The hydraulic fluid then passes from the compartment 20 through the passages 20'' and past the valve head 2|. This releases the extra pressure hehind the main piston I5. When the auxiliary piston I1 reaches a position in which the flange 55 opens the valve 50, there will now be a passage from the compartment 20 to the compartment 33. The hydraulic fluid in the compartment 20 is therefore no longer entrapped and now the main piston I5 may move rearwards. The

tion and the hydraulic fluid re-enters thru passage I3 from the brake system, flowing into the formed in the flange 29. The retainer bushing 44 protects the check valve 40 when the piston I5 is urged forwards during a bleeding operation of the hydraulic brakes. The packing 31 is in the formof a retainer cup for the spring 38. This packing 3I-is placed on the tapered end 360i the piston I5 so that during the suction stroke of the bleeding operation the suction will pull it off its tapered seat, allowing the hydraulic fluid to pass through the bleed vents '29 and pass between the wall of the piston and th packing 31 into the brake system.

In Figs. 6 to 9, inclusive, another form of the invention has been disclosed which has certain general features in common with prior mentioned patent. In this form of the invention the passage I3 is provided with the check valve 40 of a construction similar to that previously described and which i held in position by the retainer spring 38. This retainer spring alsoholds the packing cap 31' in position on the tapered front end 36' of the auxiliary, piston. The high pressure valve is located upon the front of the main piston I5. With this arrangement the high pressure fluid will be'discharged to the front of the main piston I5 into the brake system.

The high pressure valve I9 controls passages 20 discharging to the front of the main piston I5. These passages 20 are located in the stem portion 'lI- Of the valve 2|. The high pressure valve I9 is similar to that previously described and-is urged into a closed position by the spring 22 mounted between it and a washer 60 extended across the front end of the stem 2 I The valve 2| is urged closed by a small spring 23 acting between the valve cap 6|. This cap 6| is slidable in the bore IS. "The cap GI is urged forwards by a spring 23 acting between the cap and the front end of the auxiliary piston II. A valve50' is mounted in the rear end of the main piston I5 and controls the passage of hydraulic fluid from the compartment 33 to the compartment 20. Packing material 63 is moulxted upon the rear portion of the main piston In other respects this form of the invention is similar to the previous form and like parts areidentified by like reference numerals.

The operation of this form of the invention may be understood by first noting the position of the parts in Fig. 6 in which the brake is off. When the connecting rod I8 is moved forwards the pistons I5 and II will move frontwards as a unit. They are rigidly connected together because of the hydraulic fluidentrapped in the bore I6. When the parts reach the position shown in Fig. '7, the main piston I5 will meet resistance and the auxiliary piston II will still travel forwards. It so that the high pressure valve I9 opens and is locked open by the passage of hydraulic fluid and the peripheral edge of the rubber cup I9 The hydraulic fluid from the bore I6 may now pass through the passages 20 to the front .of the main piston I5.

At the "instant that the auxiliary piston II starts moving forwards relative to the main'piston I5, the flange 58 releases the valve 50' which This increases the pressure in the bore closes (Fig. 8). This entraps hydraulic fluid in the compartment 20 to the rear of th main piston II. Consequentl it cannot move rearwards at this time. It is noted in this connection that the fluid displaced in the small cylinder l6 ahead of the forward piston ring 28 is of relatively great volume compared to the minor volume displaced by the rear piston ring 25 from the annular space surrounding the piston ll within the chamber l2. Accordingly, in this preferred arrangement the large piston is is not held absolutely stationary by the fluid trapped in the chamber 28 by the valve 50' but is urged slightly forward by the relatively small displacement of fluid from the chamber l2" ahead of the piston r1118 2! (Fig. 8). of safety against the rearward motion, of the piston ll during the displacement of fluid from the small cylinder ll ahead of the small piston ring 2. and assures a more smooth carry-over from the low pressure to the high pressure exerted on the brake line. Thu the hydraulic fluid from the bore It can be forced into the brake This provides a factor system. The parts are in the position shown in V Fig. 8 when the brake is fully applied.

When the brake is released the connecting rod ll is moved rearwards which moves the auxiliary piston l'l' rearwards. When the pressure of the reach the position shown in Fig. 5. The brake is now off. During the bleeding operation of the brake system the main piston l5 may be moved. forwards until the valve stem 2l strikes the metal cap of the check valve ll; This forces the -valve.2l' open, bleeding the bore ii. In other respects the operation is identical.

While I have illustrated and described the preferred embodiments of my invention, it is understood that I do not limit myself to the precise constructions herein disclosed and the right is reserved to all changes and modifications coming within the scope of the invention as defined in the appended claims.

Having thus described my invention, what I claim as new and desire to secure by United States Letters Patent is:

1. A compound hydraulic brake comprising a cylinder formed with a closed front end which is provided with an opening for connection with the fluid line of hydraulic brakes, a main piston slidably mounted in said cylinder and having a small bore providing an auxiliary cylinder, an auxiliary small piston slidably mounted in said bore, means for urging said small piston forwards for applying the brakes, hydraulic fluid means for normally rigidly connecting said pistons together as a unit and compressor.

' asaaaoo means for normally urging said main piston rearwards, and means for normally urging said auxiliary piston rearwards, said pressure loaded valve opening said passage upon a predetermined pressure and thereby permitting movement of I small piston forwards for applying the brakes,

hydraulic fluid means for normally rigidly connecting said pistons together as a unit and controlled with a pressure loaded valve actuated by pressure of the hydraulic fluid and controlling a passage extending from said bore to the rear end of said main piston, said pressure loaded valve opening said passage upon a predetermined pressure and thereby permitting movement of the auxiliary piston relative to the main piston to discharge fluid to the rear of the main cylinder for moving the main piston forward, a one way valve controlling a passage through which fluid from the rear of said main cylinder may enter said bore upon rearward motion of said auxiliary piston, means for normally urging said main piston rearwards, and means for normally urg- .ing said auxiliary piston rearwards, said pressure 1oade'd valve being disposed within said one wayvalve.

3. A compound hydraulic brake compressor, comprising a body for holding a hydraulic fluid and having a, cylinder formed with a large front bore and a small rear bore and with a closed front end and which is provided with an opening for connection with the fluid line of hydraulic controlled witha pressure loaded valve actuated by pressure of the hydraulic fluid and controlling a passage extending from said auxiliary cylinder to the rear of said main cylinder, for connecting the fluid in said auxiliary cylinder with the fluid brakes, a main piston slidably mounted in said cylinder and having a, small bore in its rear end, an auxiliary small piston slidably mounted in said bore, means for urging said small piston forwards for applying the brakes, hydraulic fluid means for normally rigidly connecting said pistons together as a unit and controlled with a pressure loaded valve actuated by pressure of the-hydraulic fluid and controlling a passage extending from said bore to the rear end of said main piston, for connecting the fluid in the bore with the fluid at the rear of the main piston to disconnect the pistons, a one way valve controlling a passage through which fluid from the rear of said cylinder may enter said bore upon rearward motion of said auxiliary piston, means for normally urging said main piston rearwards, means for normally urging said auxiliary piston rearwards, and means for cutting of! the fluid to the rear of said main piston from the fluid in said body during the time the auxiliary piston is moving forward relative to said main piston, said pressure loaded valve being disposed within said one way valve, said one way valve being disposed in the rear portion of said auxiliary small piston.

4. A compound hydraulic brake compressor, comprising a body for holding a hydraulic fluid and having a cylinder formed with a large front bore and with a small rear bore and with a closed front end and which is provided with an opening for connection with the fluid line of hydraulic brakes, a main piston slidably mounted in said an auxiliary small piston slidably mounted in said bore means for urging said small piston forwards for applying the brakes, hydraulic fluid means for normally rigidly connecting said pistons together as a unit and controlled with a pressure loaded valve actuated by pressure of the hydraulic fluid and controlling a passage extending from said bore to the rear end of said main piston, for connecting the fluid in the bore with the fluid at the rear of the main piston to disconnect the pistons, a one way valve controlling a passage through which fluid from the rear of said cylinder may enter said bore upon rearward motion of said auxiliary piston, means for normally urging said main piston rearwards, means for normally urging said auxiliary piston rearwards, and means for cutting off the fluid to the rear of said main piston from the fluid in said body during the time the auxiliary piston is moving forward relative to said main piston, said pressure loaded valve being disposed within said one way valve, said one way valve being disposed in the rear portion of said auxiliary small piston, the passages controlled by said pressure loaded valve being disposed inthe stem of said one way valve.

5. A compound hydraulic brake compressor, comprising a body for holding a hydraulic fluid and having a cylinder formed therein with a closed front end which is provided with an opening for connection with the fluid line of hydraulic brakes, a main piston slidably mounted in said cylinder and having a small bore providing an auxiliary cylinder, an auxiliary small piston slidably mounted in said bore, means for urging said small piston forwards for applying the brakes, hydraulic fluid means for normally rigidly connecting said pistons together as a unit and controlled with a pressure loaded valve actuated by pressure of the hydraulic fluid and controlling a passage extending from said bore to said main cylinder to the rear of said main piston, for connecting the fluid'inthe bore with the fluid at the rear of the main piston to disconnect the pistons, a one way valve controlling a passage through which fluid from said main cylinder may enter said bore upon rearward motion of said auxiliary piston, means for normally urging said main piston rearwards, and means for normally urging said auxiliary piston rearwards, said pressure loaded valve opening said passage upon a predetermined pressure and thereby permitting movement of the auxiliary piston relative to the main piston to discharge fluid to the rear of the main cylinder for moving the main piston forward, whereby said main piston transmits relatively high pressure to said fluid line through said opening in the front end of said main cylinder.

6. A compound hydraulic brake compressor, comprising a cylinder formed with a closed front end which is provided with an opening for connection with the fluid line of hydraulic brakes, a main piston slidably mounted in said cylinder and having a small bore in its rear end providing an auxiliary cylinder, an auxiliary small piston slidably mounted in said bore, means for urging said small piston forwards for applying the brakes, hydraulic fluid means for normally rigidly connecting said pistons together as a unit and controlled with a pressure loaded valve actuated by pressure of the hydraulic fluid and controlling a passage extending from said auxiliary cylinder to the front end of said main piston for connecting the fluid in the auxiliary cylinder with the fluid at the front of the main piston to disconnect the pistons, said first cylinder and piston also providing a chamber adjacent the rear end of said cylinder into which fluid is adapted to pass during forward movement of the piston, and valve means controlling the fluid passing into said rear chamber for holding said main piston against rearward motion.

7. A compound hydraulic brake compressor, comprising a cylinder formed with a closed front end which is provided with an opening for connection with the fluid line of hydraulic brakes, a

main piston slidably mounted in said cylinder and having a small bore providing an auxiliary cylinder, an auxiliary small piston slidably mounted in said bore, means for urging said small ,7 piston forwards for applying the brakes, hy-

draulic fluid means for normally rigidly connecting said pistons together as a unit and controlled with a pressure loaded valve actuated by pressure of the hydraulic fluid in the front end of said cylinder and controlling a passage extending from said bore to the front end of said mainpiston for connecting the fluid in the bore with the'fluid at the front of the main piston to disconnect the pistons, said pressure loaded valve opening said passage upon a predetermined pressure and thereby permitting movement of said auxiliary piston relative to said main piston to discharge fluid to the front of said main cylinder,

1 means for trapping holding fluid .behind said main piston to prevent its rearward movement during said discharge of fluid to the front of said main cylinder, whereby resultant pressure is exerted through said fluid line opening, a one way valve controlling a passage through which fluid from the front of said cylinder may enter said bore upon rearward motion of said auxiliary piston, means for normally urging said main piston rearwards, and means for normally urging said auxiliary piston rearwards, said high pressure valve being disposed coaxially through said one way valve.

8. A compound hydraulic brake compressor, comprising a body for holding a hydraulic fluid and having a cylinder formed with a large front bore and a small rear boreand with a closed front end which is provided with an opening for connection with the fluid line of hydraulic brakes, a main piston slidably mounted in said cylinder and having a small bore in its rear end, an auxiliary small piston slidably mounted in said bore, means for urging said small piston forwards for applying the brakes, hydraulic fluid means for normally rigidly connecting said pistons together as a unit and controlled with a pressure loaded valveactuated by pressure of the hydraulic fluid in the front end of said cylinder and controlling a passage extending from said bore to the front end of said main piston for connecting the fluid in the bore with the fluid atv the front of the.

main piston to disconnect the pistons, said pressure loaded valve opening said passage upon a predetermined pressure and thereby permitting movement of said auxiliary piston relative to said main piston to discharge fluid to the front of said main cylinder, means for trapping holding fluid behind said main piston to prevent its rearward movement during said discharge of fluid to the front of'said main cylinder, whereby resultant pressure is exerted through said fluid line opening, a one way valve controlling a passage through which fluid from the front of said cylinder may enter said bore upon rearward motion of said auxiliary piston, means for normally urging said main piston rearwards, and means for normally urging said auxiliary piston -rearwards, said high pressure valve being disposed coaxially through said one way valve.

9. In a hydraulic brake compressor, the combination of a main cylinder, a double-ended piston positioned therein and having a bore providing an auxiliary cylinder, front and rear main cylinder chambers being provided on respectively opposite ends of said double-ended piston, said front chamber being provided with an opening for connection with the fluid line of hydraulic brakes, the other of said chambers being in communication with a supply of fluid, an auxiliary piston in said auxiliary cylinder, means to 11m part forward motion to said auxiliary piston, valve means actuated by the forward movement of said auxiliary piston to close said other chamber from communication with said fluid supply, and valve means constructed and arranged to hydraulically lock said pistons together during the first part of forward movement of said auxiliary piston and during the second part of forward movement upon a predetermined pressure being attained to release said small piston for relative motion with respect to said large piston and to transmit fluid from said auxiliary cylinder to said main rear chamber for imparting forward motion to said main piston, whereby the resultant high pressure is transmitted to said fluid line through said first mentioned chamber.

10. In a hydraulic brake compressor, the combination of a large cylinder, a piston in hydraulic sealing engagement therein and having a bore providing a small cylinder, a small piston in said small cylinder and extending rearwardly of said large piston, said large piston having a fluid seal adjacent its front end providing a hydraulic chamber between it and front end of said large cylinder and a fluid seal adjacent its rear end providing ahydraulic chamber between it and the rear end of said large cylinder exteriorly of said small piston, said large piston also having a portion intermediate said front and rear seals between which and an adjacent part of said main cylinder at first compartment is provided, a portion of said small piston and the corresponding portion of its cylinder providing therebetween a second compartment, said first and second compartments and rear chamber being in communication, first valve means constructed and arranged to close said rear chamber from said second compartment upon forward movement of said small piston, second valve means interposed between said small cylinder and one of said large cylinder chambers constructed and arranged to hydraulically lock said large and small pistons for forward motion upon forward movement of said small piston and upon predetermined pressure being reached in said chamber to place said high pressure cylinder in fluid communication with one of said large cylinder chambers, whereby relatively high hydraulic pressure is imposed on both ends of said large piston and the resulting hydraulic pressure is transmitted through the front chamber of said large cylinder to the brake line.

11. In a compound hydraulic brake compressor, the combination of a low pressure cylinder, a low pressure piston within said cylinder and provided with an axial bore serving as a high pressure cylinder, a high pressure piston positioned within said bore and extending rearwardly of said low pressure piston, said W pressure cylinder and low pressure piston and high pressure piston being constructed and arranged so as to provide a chamber rearwardly of said low pressure piston and surrounding said high pressure piston, said chamber being in communication with a passage provided between said pistons and said passage being in communication with a fluid supply, means for urging said small piston forward to actuate said compressor, and pressure loaded valve means interposed between said low pressure cylinder and said high pressure cylinder so constructed and arranged that said pistons are hydraulically looked together until a predetermined brake line pressure is attained and are then released for relative movement, and a second valve means interposed :between said pistons for closing said passage to said chamber and constructed and arranged to be operable to close said passage upon the forward movement of said high pressure piston, said parts being so constructed and arranged that upon the unloading of said first valve and the actuation of said second valve relatively high pressure is induced in said low pressure cylinder by the forward movement of said high pressure piston, said low pressure cylinder being provided ill with an outlet positioned in front of said low pressure piston for transmitting said high pressure to said brake.

12. In a hydraulic brake compressor, the combination of a main cylinder, 9. double-ended piston positioned therein and having a bore providing an auxiliary cylinder, front and rear main cylinder chambers being provided on respectively opposite ends of said double-ended piston, said front chamber being provided with an opening for connection with the fluid line of hydraulic brakes, the other of said chambers being in communication with a supply of fluid, an aux iliary piston in said auxiliary cylinder, means to impart forward motion to said auxiliary piston, valve means actuated by the forward movement of said auxiliary piston to close said other chamber from communication with said fluid supply, and valve means constructed and arranged to hydraulically lock said pistons together during the first part of forward movement of said auxiliary piston and during the second part of forward movement upon a predetermined pressure being attained to release said small piston for relative motion with respect to said large piston and to transmit fluid from said auxiliary cylinder to one of said chambers. whereby a resultant relatively high pressure is created in both of said chambers on opposite ends of said piston, said rear chamber being provided with an intercommunicating rearwardly extending cylindrical bore of smaller diameter than that of said main cylinder, and a supplemental piston disposed therein and connected for movement with said auxiliary piston, the displacement of said supplemental piston being substantially less than that of said auxiliary piston, whereby an added increment of pressure is .inserted against the rear of said main piston during the second part of the forward movement of said auxiliary piston.

13. A fluid pressure producing device comprising a cylinder, a piston movable therein and dividing the cylinder into two chambers, one of said chambers having a discharge port and the other of said chambers adapted to draw fluid therein during movement of the piston, means controlling the fluid drawn into said chamber, said piston having a small chamber communicattherein during movement of the piston, means controlling the fluid drawn into said chamber, said piston having a. small chamber communicating with one of the chambers provided in said cylinder, means for control of the communication, and means for subjecting the fluid in the small chamber to pressure. 1

MARTIN V. GROVES.

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