US2038055A - Fluid braking apparatus and compressor therefor - Google Patents

Description

April 1936- w. F. OLIVER 2,038,055-

FLUID BRAK ING APPARATUS AND CQMPRESSQR THEREFOR at l M 47 Filed Dec. 12, 1951 3, 74 I I j 1:?

50 if J fizz/e Mikael (242/91? mm, 211% /mpw April 21, 1936. w R OLIVER 2,038,055

FLUID BRAKING APPARATUS AND COMPRESSOR THEREFOR Filed Dec. 12, 1931 7 Sheets-Sheet 2 April 21, 1936. w OLIVER 2,038,055

FLUID BRAKING APPARATUS AND COMPRESSOR THEREFOR Filed Dec. 12, 1951 7 Sheets-Sheet 3 VMUZZMQZ LOLZZLJM, J5 2m WM April 21, 1936. w Q| |VE R 2,038,055

FLUID BRAKING APPARATUS AND COMPRESSOR THEREFOR Fil ed Dec. 12, 1951 v 7 Sheets-Sheet 4 .75 v 56 65 MW 67 r 4" j] In.

i 27 I 14 l i ////I"' I O l W; F. OLIVER ixpxril' 21, 3936.

FLUID BRAKING APPARATUS AND COMPRESSOR THEREFOR Filed Dec. 12, 195.1. 7 Sheets-Sheet 5 I FLUID BRAKING APPARATUS AND COMPRESSOR THEREFOR Filed Dec. 12, 1931 '7 Sheets-Sheet 6 I mew/M, 2 w V /WL Aril 21, 19360 w. F. OLIVER 2,038,055

FLUID BRAKING APPARATUS AND COMPRESSOR, THEREFOR Filed Dec. 12, 1951 7 Sheets-Sheet 7 22062275? 1 v h/a ZZacef0Za'r/e2" Patentedf Apr. 21, 1936 UNITED STATES ,PATENT orrlca FLUID. BRAKING APPARATUS AND comassson 'rnEaEron Wallace F..0liver, Detroit, Mich asaignor to Bydraulic Brake Company, Los Angeies, Galit, a corporation of CaIifornia Application December 12, 1931, Serial No.'-580,5'l3

13 Claims. (01. Bil-54.6)

My invention is concerned with improvements in hydraulic braking apparatus of the type in which a liquid is caused to flow to and from braking positions in the setting and releasing of 5 brakes.

One object of my invention isan improved means of maintaining a constant amount of liquid in the system, compensating for volumetric losses by contraction or leakage, and relieving any volumetric excess caused by the replenishing means or by heat expansion. Maintaining a constant liquid volume for the system is desirable, for otherwise the brakes may either drag or develo dangerous slack. 4

I accomplish this end by embodying the replenisher in the compressor as an integral part thereof, the compressor mechanism being arranged to pump a surplus of liquid into the system with each application of the brakes, the excess liquid being discharged back into a reservoir. after the application has been completed.

Another object is the simplification of the operation of initially filling the system with liquid, which I secure by a check valve readily insertable between the compressor and the rest of the system thereby transforming the compressor into a p p- In addition, I contemplate an improved design of compressor unit which, without material 30 changes, is adapted more or less universally for all commercial makes of automobiles so that the compressor unit can be standardized and incorv porated in the standard makes of automobiles without necessitating structural redesigning oi of the body, thereby simplifying the manufac- K 40 turers assembly problems.

A still further object is to make available to the driver some kind of alarm indicating that the reserve supply of liquid is about exhausted, before the brakes are actually unusable, and especially before the reserve liquid has been so far depleted that it will be necessary, in replenishing the reserve, to bleed the line to exhaust any air which may have been introduced. 1

The foregoing and many other objects, features and advantages of my invention are set forth in further detail in the following descrip- V tion which explains what I consider a preferred embodiment of my invention. My invention,fof j course, is not inherently confined to the particularform, system or combinations shown, but many and the brake pedal linkage;

changes may be made without departing from the spirit or scope of my invention.

In the attached drawings to which the description refers,

Figure 1 is a plan view of a skeleton chassis, of an automobile equipped with the improved bydraulic braking system of my invention;

Figure 2 is a verticaLelevation from the side which may be considered as taken on the line 22 of Figure 1, and shows the compressor unit Figure 3 is an elevation of the inner side of the right front wheel brake assembly taken on the line 3-3 of Figure 1, the wheel cylinder being broken into longitudinal section;

Figure 4 is a transverse vertical section of th same brake mechanism as Figure 3, and is taken. on the lines 4-4 of Figures 1 and.3; I Figure 5 is a longitudinal vertical section through the compressor unit, which may be considered as taken on the line 5 5 of Figure 1;

Figure 6 is a transverse vertical section of the compressor unit taken on the somewhat irregular line 6-6 of Figure 5;

Figure 7 is a fragme ary transverse section similar to Figure 6, but taken along the .line

' 1-4 of Figure 5 and forwardly of the sections of Figure 6;

Figure 8 is another fragmentary viewof the compressor showing the compressor at the time the brakes are fully applied;

Figure .9 is a fragment of Figure 5 showing the check valve moved to a position between the compressor and the rest of the system to transform the compressor into a pump for filling the system.

Figure 10 is a view similar to Figure 5 (but looking toward the lefthand side of the automobile, rather than toward the right hand side as in Figure 5) showing a modified form of the compressor unit.

Figure 11 is a detailed section taken on the line llll of Figure 10 showing the check valves of Figures 5, 8,'and 9 as applied to a modification I the piston.

In Figure 1, I have indicated an automobile chassis comprising a frame formed from side channels 10 and cross channels II, II, and",

front and rear axles i4 and I5 and front and rear wheels l6, and II. A brake pedal pivot shaft 18 is supported'with the-aid ofa bracket. 19 from the transmission'housing 2|! -(see also Flgure.2).'

The shaft l8 "pivotally supports the brake pedal 20' which though a link rod 2| actuates a compressor unit indicated generally at C. The brake pedal is returned to normal under the influence of a light spring 2|.

A pair of conduits 22 preferably of copper or brass tubing, lead laterally from the compressor C and connect with similar conduits 23 which extend longitudinally of the chassis along or within the side channels III of the frame to points fifteen inches or so short of the front and rear axles. From these points the conduits are continued with the aid of suitable fittings as flexible but non-expansible hoses 24 preferably of the type shown in patents to Malcolm Loughead No. 1,457,781 and No. 1,468,601.

The outer ends of these hoses connect with cylinder blocks 25 which are secured by bolts 26 to the steering spindles 21, in the case of the front wheels, and to the rear axle housing in the case of the rear axles.

Referring now to Figures 3 and 4 which show the right front wheel brake construction which is typical of all of the wheel brakes, the hose 24 communicates through passages 28 with the interior of the cylinder 25 midway between its ends. A pair of opposed pistons 29 'are slidably mounted in the bore of the cylinder 25 and carry cup washer packings 30 preferably of vulcanized rubber which abut the faces of the pistons but which are not attached thereto. The pressure of the fluid in the system is relied upon to hold the packings against their pistons. In order to cut down the volume of fluid in the system, a solid cylindrical filler 3| is centrally suspended be tween the proposed packings by radial pins 32 and serves as an abutment to limit the inward movement of the pistons 29. A molded rubber apron 33 may be slipped over each end of the cylinder 25 and also fitted over the central boss of the corresponding piston to exclude water and dirt. v

A pivot bracket 34' stamped from sheet steel is secured by bolts 35 to the upper side of the cylinder block 25. In the ends of thebearing slots formed by the bracket 34 the pivot shanks 36 of the actuating levers 31 are journaled. The lower ends of these levers are goose-necked around the shell-like ends of the cylinder block 25 and abut the central bosses of the pistons 29. These bosses preferably carry hardened steel inserts 38 for engagement by the levers 31. The upper ends of the levers 31 are goose-necked over the brake drum 39 of the wheel l6 and are provided with holes 40 for the passage of shanks 4| riveted to the ends of the brake band 42. The shanks are screw-threaded to receive adjusting nuts 43 against which the upper ends of the levers bear in contracting the brake band.

The ends of the bands are normally urged apart and the levers 31 rotated to push the pistons 29 in by means of compression springs 44- surrounding the shanks 4| and interposed between the adjusting nuts 43 and a stationary stamped metal abutment 45 extending upwardly from the bracket 34. The band is anchored against rotation and adjustable radially by the usual bracket '46 supported from the mud plate 41 and preferably lo-.

the application of'the wheel brakes, the liquid at all times completely fllls the system and when the master compressor C is actuated by the brake pedal 20, pressure is built up on the fluid throughout the system, which pressure serves to move the pistons 29 apart. This rocks the levers 31 and contracts the bands upon the drums against the pressure of the return springs 44. As the brake pedal is released the fluid pressure in the system is lessened and the return springs return the pistons 23 to their normal positions.

For a detailed understanding of the master compressor C, attention is invited to Figure 2 and to Figures 5 to 9 inclusive. The compressor is enclosed in a box-like housing open at its bottom side and is supported in the installation shown by cap screws 5| passing through the web of the rearwardly opening cross member of the chassis frame. This supporting cross member in the usual motor car construction is fairly heavy, and as will be noted the compressor is mounted near its connection to the lateral channel ID of the frame which, especially when re-enforced by the gusset plate 52 (Figure 1), makes an unusually firm support for the compressor. However, the compressor need not be supported in this particular manner and I provide another pair of bosses 5| in the rearward end of the top wall of the housing 50 for the reception of the cap screws 5| when the design of the automobile chassis frame is such as to make an attachment from the upper side more desirable. It is in fact one of the features of my improved compressor that it can be supported in almost any desired manner by providing similar tapped bosses wherever required about the housing 50, and if allof the bosses are formed in the housing, a given compressor can be interchangeable for. many different makes of automobiles.

The closure plate 53 which forms the bottom of the housing 50 is clamped with a fluid tight seal against the bottom edge of the housing by a munber of cap screws 54. The housing together with the bottom closure plate 53 forms a liquid reservoir and the compressor cylinder 55 is preferably cast integrally with the plate 53 on its upper side so that the cylinder is mounted wholly within the housing 50. In order to minimize the possible leakage of fluid from the reservoir, I bring the compressor actuating crank through the housing wall at the highest level of the reservoir and above the level to which liquid can be poured into it. This compressor actuating crank comprises a horizontally disposed shaft 56, a downwardly ex-' 6) so that the only possibleleakage of fluid would be along the bushing 62, and such fluid leakage is further prevented by a packing 63. The bushing 6| abuts the inner end of the bore 6|), and together with the bushing 62serves to space the inner arm 51 centraily of the housing and especially centrally in respect to the cylinder 55. Both arms of the crank are of course non-rotatably secured to the shaft 56 and one of the arms, the inner arm 51 in the drawings, is adjustable with relation to the shaft by a serration of the shaft 56 and by the clamping screw 64.

The brake link rod 2| carries a screw threaded clevis on each end, the forward clevis being pivoted to the brake pedal 29v by a pin 65 and the rear wheel brakes. The provision of the three holes 59 in the, crank arm 58 gives a-reasonable leverage adjustment so that the foot pressure for applying the brakes can be suited to the preferences of the individual driver.

The compressor cylinder is open at its rearward end and in its bore a piston 61 is slidably mounted. At its forward end the piston 61 carries an annular packing 68 which is V or U-shaped in section and preferably formed of vulcanized rubber. It is fixed to the piston by slipping it over the enlarged head of the centrally protruding hollow boss 69 at the forward end of the piston 61.' Pressure forwardly of the piston tends to seal the packing 68 against both the boss 69 and the bore of the cylinder 55 and effectively prevents leakage past the piston even though a very high pressure is built up on the liquid.

The cylinder 55 communicates with the conduit tubes 22 leading to the brake cylinders by means of a vertical-passage 1| leading downwardly from the forward end of the cylinder 55, a rearwardly extending longitudinal bore 12 and cross bores 13 in the ends of which the conduit tubes 22 are secured by conventional solderless couplings.

As thus far described the compressor acts as a compressor in the strict sense of the term, that is, the piston of the cylinder serves merely to displace the liquid and when released the return springs of the brakes push the liquid back into the compressor, there being no check valves.

However, in 'order to compensate for liquid losses in the system I incorporate a pump as a part of my, compressor whereby an excess amount of liquid from which the system may be replenished is trapped in the system with each ap-' plication of the compressor.

I prefer that such a'trapping or replenishing device be combined, for the sake of economy and simplicity, with the compressor itself and to this end I'provide the piston 61 of the compressor with a central bore 10. The rear of the bore 18 is connected with the reservoir of the housing through a backwa'rdlyseating check valve while in the other end of the bore there is a stationary piston which also incorporates a backwardly seating check valve,thereby forming a pump. The check valve at the rear of the bore 19 is in the form of a vulcanized rubber packing 14 mounted on a steam 14A fixed to aldisc 15 of hardened steel which is secured in the rear face of'the piston 61 by a 4" ring 15A. (The purpose of the hardened disc 15 is to provide a wear resisting abutment for engagement by the end of the in-' end of the arm 51, so that when, as will belater explained, the compressor is used as a pump for filling the system, the piston .can be actuated positively in its rearward as wellas its forward movement.) I

The forward check valve and fixed piston for the pumpbore 10 is formed by a vulcanized packing 11 which may be identical with the packing 14 and which is mounted at the rearward end of a small piston rod 18. The rod 18 also carries a perforated disc 19 to re-enforce the packing 11 when the latter acts as a piston. The forward end of the piston rod 18 is rather loosely held by a cross pin 19 in a plug 80 threaded into the forward end of the cylinder 55 to give the rod 9. limited universal movement and permit the packing 11 and disc 19 to center themselves in the bore 19' of the piston. The aperture in the end of the cylinder 55 'into which the plug 80 is inserted is of sufficient diameter to permit the withdrawal of the packing 11 so that the packing rod and plug can all be assembled and inserted as a unit into the end of the cylinder.

As previously mentioned the piston 61 of the compressor is returnedto its normal position of Figure 5 by the-pressure of the return springs 44 at the wheel brakes. 'I'he rearward movement of the piston is limited by an adjustable stop screw 8| threaded into an ear 82 protruding from .the right side wall of the housing 50, which screw engages the outer crank lever 58. In the upper wall of the cylinder 55 and just forwardly of the position assumed by the knife edge of the packing 68 when the cylinder 61 is in its normal retracted position, I provide a small relief port 83. If after ,the return springs 44 in the wheel brakes have returned the compressor piston 61 as far as the stop screw 8| will permit, there is still some liquid which must be displaced from the system before the return springs finally push the cup packings 88 of the wheel brakes as closely together as the cylindrical fillers 3| will permit,-then this excess fluid will be forced out of the system through this small relief port 83.

The relief port 83 does not cause any appreciable loss of fluid from the system in actuating the compressor for three reasons: First, it is located so close to the packing 68 that as soon as there has been any apprecialtle forward movement of the piston 61, the'port will be closed on; second, the port is so small that pump to introduce an excess amount of liquid into the. system which would readily compensate for any loss through the port.

The port 83 acts to relieve the system not only of the excess liquid pumped into it by the piston packing 11 but also to relieve it from an excess volume which might develop by a general heating of the liquid in the system as for example by driving along a hot pavement in summer weather or by driving the automobile down a longhill where the 'heat generated by the friction of the brakes would serve to heat-the liquid and expand it. The pump feature on the other hand havevbeen iost from the system. by a slight leakage, evaporation, seepage past the piston packing 68, or otherwise. a

As the brake pedal 29 is depressed, the arm 51 swings forwardly sliding the piston 61 inwardly. Almost instantaneously the port 83 is shut ofi' and the pressure built up in the system serves toseal the packing 68 against the bore of the cylinder 55 and also against the central boss 89 of the piston 61 while the pressure on the packing 14 seals it against the bore 10 of the piston. In effect, the entire area of the piston 81 within its perimeter becomes the piston face in displacing liquid from the cylinder toward the wheel brakes. The liquid displaced from the bore 18 by the packing I4 slips past the piston packing 11. A normal full application of the brakes would carry the piston forwardly approximately to the position indicated as a typical example in Figure 8. In the particular apparatus which I have illustrated in the drawings, the fluid system '(not including the reserve of course,) contains about twenty-one cubic inches of liquid and in the normal maximum application of the brakes, the compressor displaces about 1.25-cubic inches of liquid. It will be; seen from Figure 8 that the piston is then still capable of a movement a half more than the normal movement, thereby giving a fifty per cent margin of safety in the event that the brake linings become worn down, the linkage develops slack, or the reserve of liquid becomes depleted-and no other adjustment is made to compensate for it. The amount of excess liquid introduced by the displacement of liquid from the bore 18 of the piston would be about .196 cubic inches or a little less than one-sixth of the normal displacement.

the pressure forwardly of the piston packing l1 1 is greater than that in the bore 10. This seals the edges of the packing against the bore in which it is sliding. The fluid from the reserve in the housing 58 will flow into the bore I8 past the check valve packing 14, partly by suction created in the bore 18 and partly by the head of liquid in the reserve. When the piston 81 has receded to its normal position, the bore 18 will have been completely charged with liquid.

' If one considers the packing 88, the boss 55 This necessitates interposing a check valve somewhere between the compressor cylinder 55 and the conduit lines. Instead of using valves-with their attendant danger of leakage-to by-pass the communicating passages between the cylinder and the lines through a conventional check valve, I have devised a construction which is virtually built into the compressor unit 'as an integral part and which avoids possibility of leakage. This consists of a cap screw 88 threaded into the bottom closure plate 53 of the compressor unit in alignment with the bore I2, the cap screw 88 having a reduced extension 89 carrying an integral perforated disc 98 which has a tight fit in the bore 12. On the extreme end of the extension 89 a disc valve 9| is loosely mounted and can seat as a flap valve against the disc portion 98 to close communication through its perforations.

As normally supported by the plug 88, the disc 98 and valve 8| are positioned at the extreme rearward or closed end of the bore 12 and beyond the intersection of the bore 12 by the cross bores 13, so that the check valve 90-!!! does not affect free communication between the cylinder 55 and the conduit lines. When the compressor is to be used as a pump for filling the system, however,

inder 55 and the conduit lines. In this positionv the check valve seats toward the cylinder 55 preventing recession of the liquid from the lines and and the packing '14 asv constituting the face of the piston 81, which they do in effect, it will be seen that the packing I1 acts as a check valve to trap a portion of the liquid displaced by the piston and prevent its return to the space from which it was displaced and instead leave it to to be discharged through the relief port 88.

When the apparatus is originally assembled and the system is to be made ready for operation, the filling plug 85 is removed from the top wall of the housing 58 and liquid is poured in to fill the housing. The relief valves 88 at the wheel brakes are opened. One of these valves 88 as shown in pistons. The valve is in the form of a plug which seats against a counter-bore in the cylinder block 25' and which has a small bore 81 leading from its outer end to a cross bore adjacent its inner end. The wheel cylinder is thus relieved to at-. mosphere by simply turning ,back the valve 88 a short distance from its seat. The relief valves are located at the tops of the wheel cylinder blocks 25 because they are the highest points at the extremities of the system.

It would be possible, if the pump portion of the compressor piston 61 were properly primed and if the brake pedal 28 was reciprocated fast enough,

to pump the reserve fluid into the system and completely fill it. .But in order to simplify this operation and make, it more positive I prefer to transform the entire compressor into a pump.

causing the cylinder 55 to be filled at each stroke partly through the relief port 83 and partly past the packings TI and 14 and to a lesser extent past the packing 8. A suitable vent is provided for the housing 5v either through the filling plug 85, or preferably, as shown in Figure 5, by a small hole 92 in the vertical wall of the housing extension that provides room for the top of the arm 51, as that is well above the highest liquid level and where there is little danger of dirt being introduced.

As soon as the system becomes entirely filled, the liquid will start running out the relief valves 88 at the wheel brakes and then the operator cancease actuating the compressor, turn the screw 88 back to its normal position and close the relief valves 86.

Very minor liquid losses are almost sure to occur from time to time either due to slight leakage past the pistons of the wheel brakes or in the couplings, or to evaporation or the like, with the result that at the end of a year or two, the liquid reserve in the housing 50 will have been brought down ,to a level lower than the relief port. I contemplate that this will not happen in the majority of instances because the automobile driver will take the precaution of checking up on i the liquid level at long intervals. Although the exposure of the port 88 to atmosphere might tend toadmit some air into the cylinder 55, the effect would be overcome by the action of the pump portion of the compressor which, in delivering its excess liquid to the cylinder 55, would drive the air through the port along with the excess liquid. When the liquid level has dropped down to the perforations 153 in thedisc l5 and the troducing a portion or air with each application of the compressor, increasing as the liquid level falls. Even though this air will be relieved from the cylinder 55 by the relief port 83 at the completion of each stroke, the air during the stroke will be trapped in the cylinder 55 with the result that it acts somewhat as an expansion chamber to give a certain compressibility to the fluid in the system. This condition will be indicated to the operator by a springiness" of the brake This slack in the application of the brakes due to exhaustion of the reserve liquid, of course, does not develop suddenly but over a considerable period 01 time so that the brakes are still usable and the driver is given ample time in which to attend to replenishing the liquid.

As to the relation between the capacity of the ump and that of the compressor, the pump should be of suflicient capacity to compensate for minor fluid losses from the system, but still it should not be of such capacity that it. will cause all of the slack to be taken up by pump ing an excess of fluid into the system should the' driver successively apply full and then relaxed pressures by the compressor without letting the compressor pistoncome back to normal where the cylinder will be drained of excess fluid by the port 83. Thus, as here shown, the pump could be actuated two or three times or more without an intervening relief, without pumping so much liquid into the system as to take up the slack on the brakes and cause them to lock.

' It will be observed that if the piston 61 were an ordinary pistonthat is did not have the pump formed by the bore IO-its effective areain moving inwardly would be slightly more than in a moving outwardly because of negligible slippage past the cup washer 68, However this is only incidental as compared with the diflerential between the effective areas of the piston when moving forwardly and moving backwardly, when my central pump is incorporated in it.

In the modifled i'orm oi' compressor unit shown in Figures 10,11, and 12 the cylinder 550: forms a part of 'a more or less circularend plate 53a rather than a part ofthe bottom plate, so that I the cylinder is inserted from the end of. the main housing 50.

, Instead of using the retractile spring 2] for the brake, pedal positively towithdraw the piston through the coupling aflorded'by the pin 16,- I

use a retractile spring 95 interposed between the piston and the cylinder. This permits the brake pedal to return to normal independently of the piston and tends at all timesto keep the piston cup 68a against the piston.

' I provide a stop for limiting the outward movement or the piston, in the form ora spring wire .86. The wire is bent into a C-shape of somewhat more than 180 degrees so that it will securely grasp the cylindrical periphery of the end 01 the cylinder. It has hair pin-rehent ends 91, with the terminals oflset'inwardly as at 98 on a diam eter. The offset ends extend through holes ill in the wall of the cylinder 55!; and project a short distance inwardly therebeyond as a stop for the piston 61a. jI'he purpose of therelatively great developed length is to minimize the danger oi the spring wire being bent beyond its elastic limit in removing it.

A discharge passage I00 leads'irom the inner end of the bore of the cylinder 55a down past the normally inoperative check valve 890. and to the line 22a leading to the wheel brakes.

I claim 1. In a hydraulic brake system of the-class de- -scribed having brake mechanisms operated in one direction by fluid pressure and springs for opercompressor, and valve means for draining the system of excess liquid when the compressor is in its position of rest.

2. In a fluid pressure system of the class described dncluding a fluid motor and means oper-' ated thereby, the combination or a compressor in fluid communication with said motor, said compressor having a reciprocating piston, said piston having one area effective on the discharge stroke and a second area effective on the return stroke, said first-mentioned area being greater than said last-mentioned area whereby said piston on its forward stroke discharges from said compressor a larger quantity of fluid than can be accommodated in said compressor by the return stroke of said piston, and means for conducting said difference in quantity of said fluid to a. fluid reservoir.

3. In a hydraulic brake system having brakes hydraulically actuated in one direction and spring means for returning said brakes to inoperative condition, the combination of a compressor comprising a cylinder element and a piston element, a. liquid connection between the compressor and the hydraulically actuated brakes, a pump coaxiaily arranged with the compressor and comprising a cylinder element and a piston element, one of said pump elements being carried byone of said compressor elements, and a common actuating member for the compressor and the pump compressor cylinder and for pumping the surcharge of liquid from the pump cylinder into the compressor cylinder, a fluid reservoir, andmeans for conducting to said reservoir the .excess of the surcharge returned through the operation of said springs. r

4. In a hydraulic braking system of the class described having hydraulically actuated wheel '65 brakes and springs iorreleasing said brakes and for returning fluid supplied thereto, the combination of a compressor in liquid communication with i said wheel brakes, said compressor comprising a cylinder, a compressor piston reciprocable therein, said piston having a bore, a pump piston actingin said bore and including a check valve permitting the liquid to pass from. the bore forwardly into the cylinder, a liquid reservoir for supplying i iiluiclv tosaid compressor and bore, a check valve }carried by the compressor piston permitting the for simultaneously compressing the liquid in the 5. In a hydraulic pressure system of the class described having means operated in one direction by hydraulic pressure and returned by spring means, the combination of a compressor in liquid communication with said hydraulically operated means, said compressor comprising a liquid reservoir, a master cylinder submerged therein, a compressor piston reciprocable in said cylinder, said piston having a bore constituting the cylinder bore of a pump, a pump piston .working in the pump bore and including a cup packing having a check valve action permitting the flow of liquid from the pump bore to the cylinder, a check valve between the pump bore and the reservoir located outwardly from said pump piston, means for actuating .the compressor piston to operate the compressor and the pump, means for returning the compressor piston independently of any back. pressure created by said springs, and passage means between the compressor cylinder and reservoir for relieving excess liquid returned to saidcylinder under the influence of said spring means. 6. A master cylinder unit for a hydraulic brake system having brake mechanism operated in one direction by hydraulic pressure and in the opposite direction by spring means comprising a compressor cylinder, a piston therein, a reservoir communicating with the outer end of the piston, means for reciprocating the piston for compressing the liquid in the cylinder, and a reciprocating pump formed within the piston and actuated by the reciprocation of the piston for pumping a surcharge of liquid from the reservoir into the cylinder, and means for returning tothe reservoir excess liquid returned under the influence of said spring means.

1 '7. In' a hydraulic brake system comprising means and said pumpmeans, said reciprocable 8. In a hydraulic braking system having liquid operated wheel brakes, the combination of an actuating compressor in liquid communication with said brakes, and normally inoperative means manually manipulable to operable condition as a discharge check valve for the compressor to prevent recession of liquid from the brakes to the compressor whereby the compressor may be actuated as a pump to fill the liquid system therebeyond.

9. In a hydraulic braking system including liquid operated wheel brakes, the combination of an actuating compressor having liquid inlet means from a source of liquid supply, there being operating liquid connections between said compressor and said wheel brakes and normally in operative means manually rendered operable as a discharge check valve for the compressor to prevent recession of liquid from the brakes to the compressor whereby the compressor may be actuated as a pump to fill the liquid system.

10. In a hydraulic braking system having liquid operated wheel brakes, the combination of an actuating compressor having liquid inlet means from a source of liquid supply, there being operating liquid connections between the compressor and the wheel brakes, and a discharge check valve for the compressor'preventing recession of liquid from the brakes to the compressor whereby the compressor may be actuated as a pump to flll the liquid system, and means operable at will'to render the check valve inoperative.

11. In a hydraulic braking system having liquid operated wheel brakes, the combination of an actuating compressor having a passage in liquid communication with said brakes, and a check Naive manually shiftable into'and out of said passage whereby in the latter position the check valve becomes inoperative and in the former position operates to prevent recession of liquid from the brakes to the compressor when the compressor is actuated as a pump.

12. In a hydraulic system-oi the. class described having elements actuated by hydraulic. pressure, the combination of a compressor having an operating liquid connection with said elements, check valve means in the connections through which'liquid passes to and from the compressor, and manually operable means to adjust the check valve means to permit liquid flow in either one direction only or in both directions.

13. In a hydraulic pressure system of the class described,including hydraulically actuated mechanism, the combination of a compressor, liquid lines leading from the compressor to said means, a liquid passage between the compressor and the lines comprising intersecting bores, a check valve in one 01 said bores comprising a stem, a perforate head making a substantially fluidtight fit with the check valve bore, a check valve element cooperating with the perforate head, and manual means for reciprocating the check valve in its bore across the intersection of said bores whereby in one position the check valve is operably inserted in the passage and in the other position it is rendered inoperative.

WALLACE F. onrvna.

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