Патент USA US2411458код для вставки
Nov. 19, 1946. w,-F, PENRosE i I ì 2,411,458 ` BOOSTER BRAKE HECHANISI Filed July 31, 1944 v 2 Sheet‘s-sneetvi ` v Patented Nov. 19, 1946 ` 2,411,453 UNITED STATES PATENT OFFICE. 2,411,458 f' BOOSTER BRAKE MECHANISM V William F. Penrose, Newark, N. J ., assignor to Empire Electric Brake Company, Newark, N. J., a corporation‘of New Jersey Application .nay 31, 1944, serial No. 541,363 l 12 Claims. (o1. iso-54.5) ' 'I'his invention relates to power brake mech anisms, and more particularly to a booster hy draulic brake mechanism of the type shown in the copending application of Rudolph J. Klimkiewicz, Serial No. 504,451, iiled September 30, 1943, now Patent No. 2,377,699. Booster brake mechanisms of the type referred to have been developed >for assisting in the ap plication of braking >pressures to the hy »f . draulically operated wheels of a motor vehicle. Devices of this character generally utilize fluid 10 displaced from the master cylinder for taking up play between the brake shoes and brake drums, after which pressure is built up in the system to actuate a motor to boost the pressure applied to the brakes. Generally, the pressure developed in the master cylinder is added to the motor-developed pressure to produce a resultant braking pressure substantially higher than that _ , thus permitting the use of a shorter pressure cylinder construction in the booster. More specifically, an important object of the invention is Ato provide a novel ñuid control.’ meansv for insuring more positive flow of fluid directly from the master cylinder to the wheel cylinders than can take place from the chamber in which ñuid pressure Vacts to move the manually operable piston, thus insuring against substantial movement of such piston until a rela tively great volume of duid has flowed from the master cylinder to the wheel cylinders to take up play between the brake shoes and the brake Other objects and advantages of the invention will becomey apparent during the course of the following description. ' In the drawings I have shown on embodiment 'of the invention. VIn this showing-_ ` Such mech- ` Figure 1 is an axial sectional view through the 20 anisms employ means for providing ‘for a direct booster brake mechanism, the master cylinder developed in the master cylinder. ñow oi' brake ñuid from the master cylinder to take up play between thebrake shoes and the brake drums, and such means is closed to dis connect the master cylinder from -the brake and the brake cylinders together with their con nections with the booster brake mechanism being diagrammatically represented, - Figure 2 is a transverse sectional View taken cylinders-upon actuation ci the motor or upon 25 substantially on line 2-2 of Figure 1, actuation of the manually operated piston which Figure 3 lvis an enlarged fragmentary axial ` controls actuation of the motor. - A In `such a mechanism the passage or other means which provides for the flow of fluid from 30 the master cylinder direct to the brake cylinders sectional view showing the low pressure> cylinder and the flow control device associated therewith, and , Figure 4 is an- enlarged side elevation of the ordinarily provides for a'relatively unrestricted flow control valve. flow of brake fluid. However, a rapid operation of the master cylinder can, and frequently does, _ Referring to Figure 1, the numerals I0 and ii ' respectively indicate alined high and low pres ' operate the manually controlled piston to actuate 35 sure cylinders of a booster mechanism between the booster motor and to close direct communi which is arranged a booster motor indicated as cation between the master cylinder and the brake cylinders before play has been taken up between a whole by the numeral I2. This motor is pref erably of the differential fluid pressure operated the brake shoes and brake drums. To take care type and comprises casing sections i3 and of such a situation it is necessary that the high 40 Il of generally conical shape secured at their pressure cylinder used in such a mechanism be' of ends to the respective cylinders i0 and il. such length as to permit displacement/from the A pressure movable unit indicated as a whole by high pressure cylinder of the iluid necessary 'to the numeral IB is arranged in the motor and both engage the shoes with the brake drums and . comprises a iiexible diaphragm Il and a dia to eiîect the maximum braking force in the event 45 phragm I8, the peripheral portion of the dia direct communication from the m-lster cylinder phragm being arranged between the adjacent and the brake cylinders is cut oiï prior to engage~ . ilanges i9 of the motor casing sections and ment of the brake shoes with the drums. ` clamped in position by a split band 20, the ends A_n important object of the present invention of which may be secured together in any suitable is to provide novel means for preventing sub manner, for example, by a wire 2i (Figure 2). stantial operation of the manually operable The diaphragm l1 is secured to the plate |81 by a motor-controlled piston until all, or substantially vsnap ring or encircling wire 22 (Figure 1). all, oi’ the iiuid necessary for engagement of the The diaphragm plate I8 is provided with an brake shoes with the brake drums has ñowed axial cylindrical piston 25 in which is slidably _ from the master cylinder to the brake cylinders, 55 arranged a manually operable piston 26 having - 2,411,458 d 3 valves 5i and it, the former valve controlling the a bore 2l therethrough for a purpose to be de scribed. A snap ring 28 is arranged on the piston 28 and is slidable into a recess 29 formed in the end of the `piston h5. A ring 39 is arranged admission of air as stated while the valve 10 con trols communication between the motor cham bers [email protected] and 5l. The latter chamber is in con stant communication with a source of lower pres against the adjacent end of the piston 25 and sure, for example, the intake manifold of the vehicle engine. For this purpose, a nipple 84 is connected to the motor casing section I4 to com municate therewith and has its opposite end suit in and displace fluid from the high pressure 10 ably Connected by a pipe (not shown) to the in take manifold of the motor vehicle engine. The chamber 83 in the cylinder Il. Such chamber nipple 84 is provided with a check valve 85 to pre »is connected by suitable lines 34 to the wheel vent sudden increases in pressure in the motor y'cylinders 35 ofthe vehicle. chamber 5i. ' The left hand end of the piston 26 is grooved In such prior constructions as that shown in Y as at 38 and the inner end of such groove ter engages a double-lipped packing cup 3l retained around the adjacent end of the piston 26 by a snap ring 32. The pistons 2 5 and 26 are movable toward the right in Figure 1 to build up pressure minates in a shoulder 39. A double-lipped pack ing cup 40 is arranged in the groove 38 against the shoulder 39. The left hand end of the cylinder lil forms a low or primary pressure chamber 52 in which is threaded a union 43, and a line 46 connects this union to a master cylinder '45 having a conventional piston (not shown) therein operated by a brake pedal d6. ao _ Valve means are provided for controlling- pres sures formed in the chambers 50 and 5i in the motor on opposite sides of the pressure respon ‘sive unit. The diaphragm plate I8 (Figure l) carries a preferably integral cylindrical extension 52 having a, chamber 53 therein communicating 2,5 the said Patent No. 2,377,699 to Klimkiewicz, fluid displaced from the master cylinder operates a piston such as the piston 2S to operate a valve lever, such as the lever 76, to energize the motor and thus utilize the power thereof for assisting the manually operated pistons for generating pressure in the high pressure side of the system leading to the brake cylinders. Before such mo tor actuation takes place, it is highly desirable that fluid from the master cylinder first ñow through the bore 2l to operate the brake cylin ders 35 to engage the brake shoes with the drums. Such operation the brake cylinders requires the movement of a far greater quantity of fluid with one end of a pressure hose or other conduit 30 than is moved or displaced after initial engage 54, this hose being connected to a source of at ment of the brake shoes takes place. mospheric or super-atmospheric pressure de latter point in the' operation of the mechanism After the is reached, pressure will be built up in the system pending upon Wheth'er the motor is to be vacuum and the area of the left hand end of the piston or pressure operated. In the present instance, the conduit 5è leads to a connection 55 commu 35 25 in the present construction being greater than the area of the right hand end thereof, the piston nicating with the atmosphere externally of the 26 will then move to the right to effect motor op motor casing section I4, such space preferably be eration. The power operation then occurring ingcovered by a shell 55 housing a suitable air requires the closing of the bore 2l. For this pur cleaner 5l. The tubular extension 52 is provided internally 40 pose, a rod 9U extends through the bore 21 to en gage a ball 9i engageable with a. seat 92 formed thereof with a valve seat 6G shown in the present at the inner end of an enlarged bore 93 at the instance as being engaged by a ball valve BI urged right hand end of the piston 26 in Figure 1, to closed position by a spring 62, one end of such movement of the ball out of the bore 93 being spring engaging the ball 5i and the other end prevented by a pin 94. In a manner to be de engaging a spring seat 63 which closes the adja scribed, the rod 90 when the parts of the appa ce'nt end of the extension 52 to communication ratus are in the “olf” position shown in Figure 1 with the motor chamber 5i. The ball Si is occupies the position holding the valve 9| off its seat, and the space around the rod 90 and around A second tubular extension 69 is preferably 50 the ball 9| when‘the latter is unseated is such as to provide for the substantially unrestricted flow formed integral with the diaphragm plate i8 and oi' fluid from the master cylinder through the has its interior communicating with the motor bore 2l into the chamber 33 to displace there chamber 5i through a port 59. A valve, shown from suiiicient iiuid to engage the brake shoes as a ball lli, is engageable with a seat ’il to con adapted to be unseated by a stem Si operated in a manner to be described. trol communication between the motor chambers 59 and 5i, this valve being urged from its seat by with the lbrake drums. a spring 12 of lower tension than the spring t2 for a purpose to be described. pression of the brake pedal can displace iiuid from the master cylinder at a rate greater than such fluid can flow directly through the appara' tus into the brake cylinders, thus building up in The diaphragm plate i8 is provided with lugs ‘i5 engageable with the adjacent end of :the cyl ‘inder l0 to limit movement of the pressure mov able unit to the left as viewed in Figure v1, and a compression spring 'i5 urges the pressure respon sive unit in such direction. The lugs l5 and the piston 2t are straddled by a lever it, this lever _ In prior constructions, the sudden rapid de the chamber d2 a false pressure suflicient to oper ate the piston 26 to energize the motor I2 before the brake shoes are initially engaged with the brake drums by fluid flowing through the pas sage 2ï, chamber 33 and brake lines 34. This false `operation is due to the fluid friction of the elements through which fluid flows to the brake cylinders, and to the inertia of the brake shoes against sudden movements. The present device being provided with an opening 'il through which extend the -lugs ‘l5 and the piston 26. One end ‘i3 of the lever is directly engageable with the ball 19. Centrally of its length the opposite sides of the lever are preferably stamped to provide 70 prevents such operation. Referringto Figure 3, the end of the piston 26 is provided with a bore bulged points 19 engageable with a yoke Bil 99 larger than and communicating with the bore snapped around the piston 26 and fixed against 2l into which extends a control device 99 pressed movement to the left relative thereto by a snap as at- lilii into the adjacent end of the union 43 ring 8l (Figurefl). The lever 76" controls the movement of the 75 'and having a bore Iûi extending therethrough. attacca @il A rubber or similar packing ring itt is carried by the control device 99 for sliding engagement in the bore et. The inner end of the device [email protected] is Cav provided with a slot H33 to facilitate flow of fluid past the adjacent end of the rod 90. The end of the piston 2t in Figure ‘.5 is spaced from the adja cent end of the chamber ¿l2 and in this space the device 99 is provided with a relatively restricted metering port Hill affording limited communica tion between "the bore lili and the chamber ¿i2 when the parts of the apparatus are in the “oiî” A position. 'Ihe rod 90 is engaged against the ad `iacent end of the device 99 when -the parts are the lever will seat the valve lil. Ver; little move« ment of the lever “iii is required for this opera» tion since the lower end oi the lever 'will move twice the distance of the piston Prior to the operation referred [email protected] 'the motor i2 will be “vacuum suspended,” that is, balanced subatmospheric pressures will exist in the motor chambers 50 and 5i. The seating of the valve 'i0 closes communication between the motor chambers, and since the lower end of the lever will be ñxed against further movement toward the right, continued slight movement of the pis» ton 26 `vill move the upper end of the lever it in the position referred to to hold the ball ai off to unseat the ball tl, thus permitting air to dow its seat. Contact between the rod 90 and the past the valve lil into the motor chamber 5B. device 99 is established when the brake parts The higher pressure thus established in the mo~ reach the fully released position, and when the tor chamber till will effect movement of the pres~ brakes are applied, brake fluid flowing through sure movable unit it toward the right t0 sirn the bore lll! readily moves the end oi’ the rod til toward the right as viewed in Figure 3 for the 20 iîarly move the piston 25. If the movement oi the piston 2li stops, a very slight additional moven free ñow of fluid from the bore lill into the ment of the pressure movable unit [email protected] will release bore 2l. the pressure of the upper end of the lever from The operation of the mechanism is as fol» the pin @t and the motor operation also will stop. Any tendency for the pressure movable unit to lows: >vAssuizning thatA the brakes are completely re move too far will result in “cracking” the vac leased with the parts in the positions shown in uum valve 'it to exhaust some of the air from the drawings, brake application will take place the motor` chamber 50 to establish the proper upon operation of the pedal ¿36. Such operation differential` motor Ipressures to arrest operation displaces fluid from the master cylinder (it of ,the motor. It wm be obvious that the pressure through the line riß, bore lill (Fig. 3) and bore 30 movable unit i 6 partakes of a follow-up action 21 into the high pressure chamber 33 (Fig. 1) to with respect to the piston ‘26. displace fluid therefrom to move the brake shoes It will be apparent that movement oi the pis into engagement with the brake drums. The ton 26 toward the right through a relatively short iiow of fluid referred to is relatively unrestricted, distance will carry the valve seat S32 into engage» Whereas there is substantial restriction in the ment with the ball di, the rod tl thus becoming flow of fluid through the metering port lllál (Fig. ineffective for holding the ball tl ofi its seat. 3). The ñow of huid thus displaced from the The chamber ¿it thus will be disconnected from master cylinder will result in a positive flow of the chamber t2, and movement of the pistons a much greater volume of fluid through the bore 2l than through the port lûli, the latter flow 40 25 and 2t will displace huid from the chamber 33 into the brake lines to provide the necessary being insuflicient to cause rapid movement of the braking pressures, these pressures being built up piston 26. The flow of i‘luid through port imi will partly by manual operation of the piston tt and result in very slow movement of the piston 2t partly by power operation of the piston ‘25. The through which motor energization is effected. operator thus performs part of the work in build The relatively unrestricted i‘low of fluid through ing up the braking pressures and the foot pedal bore 27 causes positive engagement of the brake te is always subjected to reaction pressures shoes with the brake_ drums before substantial exactly proportional to the braking pressures. . operation of the piston 26 occurs. and ‘con Assuming that` the movement of huid through sequently before any substantial operation oi the tb line (ifi at the beginning of the brake oper motor l2 takes place, the latter operation being ation will have taken place incident to a very referred to below. rapid brake pedal operation, the iiow of fluid Whether any motor energization taires place ’ through the port Hifi may result in sufñcient prior to initial engagement of the brake shoes movement of the piston 26 to cause energization with the brake drums depends upon the rate of of the motor. However, the movement of the displacement of iluid from the master cylinder piston te necessarily will be relatively slow, and t5. Assuming that the flow capacity of the bore the packing db2 is arranged a sufñcient distance 2l is sufficient under a given ,operating condi from the left hand extremity of the piston tti Ätion to engage the brake shoes with the drums to insure motor operation at a very slow rate to prior to motor energization, contact of the shoes with the drums will be immediately followed by 60 insure the taking up oi' play between the brake shoes and drums prior to the point at which the an increase in pressure in the entire hydraulic left hand extremity of the piston 2S passes the system. The pressure increase will result in a packing H32. From this point on, the bore lili more rapid now of iiuid through the port itil will provide for the relatively unrestricted ilow which will be followed by a more rapid move oi” fluid into the chamber d2, By this time, how ment of the piston 2li. ' ever, the brake shoes will have ~been deñnitely brought into engagement with the brake drums. _ from Anyitssubstantial normal or movement, “off” position of the will piston result in When the foot pedal iid is released, pressure operating the valve mechanism to energize'the will drop in the chamber ¿i2 and. the pressure motor it. The engagement oi.’ the member [email protected] acting against the opposite endvor‘ the piston t6 (Figures l and 2) with the points ‘iii of the lever 70 will move this piston toward the left (Fig. l) to ’I6 will tend to cause bodily movement of this release the pressure exerted against the valves lever toward the right. The spring G2 being of iii and lll. 'I‘he closing of the valve tl will cut y greater tension than the relatively weak spring ofi the chamber 50 from the atmosphere and the l2, the lever 'i6 will íulcrum at its point of en opening of the valve 'ill will connect the cham gagement with the pin and the lower end of 75 bers il!) and 5l for the exhaustion oi air from 2,411,458 the chamber 50. The spring 16 will return the parts to their normal positions, and when the rod 90 engages the device 99, the ball 9| will be unseated to reestablish the communication be tween the line 44 and the brake cylinders. The unseating of the valve 9| when the parts are in the normal or “off” positions provides for the flow of fluid through the bore 2l when brake pedal operation is initiated, as stated. The un 8 member is in its “0E” position, meansv for pre venting such flow of fluid after said pressure re sponsive member has moved a predetermined dis tance and the pressure in said high pressure cyl inder is higher than the pressure in said low pres sure cylinder, and means co-operating with said pressure responsive member and dependent there on when the latter is in its “off” position for lim iting the flow of fluid from the master cylinder seating of the ball 9| also permits the replenish 10 into said low pressure cylinder relative to the flow of fluid from the master cylinder to said ing inthe high pressure side of the system of any high pressure cylinder when the master cylinder leakage of brake fluid which may have occurred, is initially actuated. and the usual valve (not shown) at the outlet 2. In a booster mechanism for a hydraulic 've of the master cylinder 45 will maintain the usual 15 hicle brake system having wheel cylinders to ap residual pressure throughout the system. ply the brakes and a pedal-controlled master It will be apparent that the use of the mecha cylinder, a booster unit comprising a low pres -nism shown in Fig. 3 positively limits the flow of sure cylinder adapted to communicatewith the fluid into the chamber 42 to thus limit motor-4 master cylinder, a high pressurehcylinder adapted energizing operation of the piston 26 until the brake shoes have been engaged with the drums. 20 to communicate with the wheel cylinders, a mio-_. , Without such means, sudden rapid brake pedal tor having a movable unit including a member- operation may result in the relatively excessive projecting into said high pressure cylinder to flow of fluid into the chamber 42 thus building up a false pressure therein. Such false pressure vdisplace fluid into said wheel cylinders upon en ergization of said motor, a pressure responsive in the chamber 42 would cause a motor-energiz ing movement of the piston 26 and such move ment of this piston not only will energize the motor but will resultin the closing of the valve 9| before the brake shoes have been engaged with the drums. 25 member in said low pressure cylinder operable by fluid displaced from the master cylinder, means operable bysaid pressure responsive member for energizing said motor, said booster unit being constructed to provide for the substantially unre Under such conditions, all of the 30 lstricted flow of fluid from the master cylinder to said high pressure cylinder when said pressure remaining fluid necessary for initial engagement ofthe brake shoes would have to be supplied solely from the chamber 33 and this could take place only by movement of the pistons 25 and 26. Unless the high pressure cylinders of prior devices are made relatively long, therefore, it is possible for the piston elements moving into the high pressure chamber to reach their limits of movement prior to a full brake application. To insure the proper operation of Vsuch a mechanism under all conditions, therefore, it is necessary as a practical matten-to make the pressure cyl inders, corresponding to the cylinder ||, rela tively long.' Such construction obviously is not necessary in the present device. Therefore, the present device permits the shortening and com pacting of the mechanism and further insures the performance of the intended booster opera tion of the apparatus. _ responsive member is in its “off” position, means for preventing such flow of fluid after said pres sure responsive member has vmoved a predeter - mined distance and the pressure in said high - pressure cylinder is higher than the pressure in said low pressure cylinder, and a device mounted in said low pressure cylinder and communicating with the master cylinder, such device having a 40 port communicating at all times with said low pressure cylinder and of such cross sectional area as to positively limit the flow 'of fluid from the master cylinder into said low pressure cylinder relative to the flow of fluid from the master 45 cylinder to said high pressure cylinder when said _ pressure responsive member is in its “oiî” posi » tion, .said device having a passage normally closed to said low pressure cylinder by said pressure re sponsive member when the latter is in its “off” 50 position and opened to said low pressure cylinder It is to be understood that the form of the in by movement of said pressure responsive member vention herewith., shown and described is to be from its “off” position. taken as a preferred 'example of the same and 3. In a booster mechanism for a hydraulic ve that various changes in the shape, size and ar hicle brake system having wheel cylinders to ap rangement of parts may be resorted to without departing from the spirit ofthe invention or the 55 ply the brakes and a pedal-controlled master cylinder, a booster unit comprising a low pres scope of the subjoined claims. sure cylinder and a high pressure cylinder ar I claim: ranged in axial alinement and’adapted to com l. In a booster mechanism for a hydraulic ve municate respectively with the master cylinder hicle brake system having wheel cylinders to'ap ply the brakes and a pedal-controlled master cyl 60 and with the wheel cylinders, a differential fluid pressure motor having a pressure responsive unit inder, a booster unit comprising a low pressure and a member carried thereby and projecting into cylinder adapted to communicate with the master said high pressure cylinder to displace fluid cylinder, a high pressure cylinder adapted to therefrom upon energization of said motor, a pis communicate with the wheel cylinders, a motor having a movable unit including a member pro 65 ton in said’low pressure cylinder movable by fluid displaced from the master cylinder, a valve mech i jecting into said high pressure cylinder to displace fluid into said wheel cylinders upon energization anism operable by said piston for energizing said motor, said booster unit being constructed and of’said motor, a pressure responsive member in arranged to utilize the pressure generated in the said low pressure cylinder operable by fluid dis-placed from the master cylinder, means operable _ 70 master cylinder for assisting said motor in gen erating pressures in said high pressure cylinder, by said pressure responsive member for energizing and being further constructed and arranged to said motor, said booster unit being constructed to provide for the substantially unrestricted flow of fluid from the master cylinder to saidhigh provide for the substantially unrestricted flow of ' fluid from the master cylinder, and to said high pressurel cylinder when said-pressure responsive 75 pressure cylinder when said piston is in its ."off" 2,411,458 10 position, means for preventing the flow of fluid from the master cylinder to the high pressure cyl inder after said piston has moved a predetermined distance-from its "off” position and when pres sure in said high pressure cylinder is higher than in said low pressure cylinder, and metering means from upon energization of said motor, a pres sure responsive device movable >by fluid entering said low pressure chamber, said booster mecha nism being constructed and arranged to provide for relatively unrestricted flow of fluid from the fluid displacing device to said high pressure chamber when said pressure responsive device is in its “off” position, means operative for stop co-operating with said piston and dependent thereon when the latter is in its “off” position for positively restricting the flow of fluid from the ping said ?low of fluid after said pressure re master cylinder to said low pressure cylinder when 10 sponsive device has been moved and pressure in said master cylinder is initially actuated. i said high pressure chamber is higher than in . 4. Apparatus constructed in accordance with claim 3 wherein said metering means comprises a metering device mounted in said low pressure chamber, such metering device having a bore therethrough communicating with the master cyl inder and through which passes the iluid which said low pressure chamber, and means co-oper ating with said pressure responsive device and dependent thereon when the latter is in its “oil” position for positively limiting the now of fluid from the fluid displacing de_vice into said low pressure chamber relative to said flow of iluid to ilows from a master cylinder to said high pres ‘ said high pressure chamber when said. fluid dis sure cylinder, said metering device having a rela placing device is initially actuated. tively restricted passage communicatying at all 20 8. A hydraulic booster unit comprising a low times between said bore and said low pressure pressure chamber adapted for connection with a cylinder. hydraulic iluid displacing device,- a high pres 5. In a booster mechanism for a hydraulic sure chamber adapted for connection with a device to be hydraulically operated, a motor vehicle brake system having wheel cylinders for applying the brakes and a pedal-controlled master cylinder, a booster unit comprising a low pressure cylinder and a high pressure cylinder arranged in axial allnement and communicating 2.5 having a fluid displacing element movable into said high pressure chamber to displace fluid „ therefrom upon energization of said motor, a pressure responsive device movable by ñuid entering said low pressure chamber, -sald booster mechanism being constructed and arranged to provide for relatively unrestricted ñow o1' fluid from the fluid displacing device to said high pressure chamber when said pressure responsive device is in its “off” position, means operative for respectively with the master cylinder and with the wheel cylinders, a differentiaI iluid pressure motor having a pressure responsive unit, a ñuid displacing piston carried by said unit and pro jecting into said high pressure chamber to dis place fluid therefrom upon energization of said motor, a control piston having one end arranged closing communication between the ñuid- displac ing device and said high pressure chamber after in said low pressure cylinder and its opposite end projecting through said nuid displacing piston said pressure responsive device has been moved and pressure in said high pressure chamber is to displace fluid from said high pressure cham ber, a follow-up control valve mechanism for said motor operable by said control piston and by said pressure responsive unit, said control piston having a bore therethrough to provide for the substantially unrestricted iiow of fluid from the master cylinder to said high pressure cylinder, 40 means for closing said bore upon'a predeter- ' mined movement of said controlpiston from its device is actuated. “off” position and when the pressure in said > high pressure cylinder is higher than in said low pressure cylinder, and a metering device for limiting the flow of fluid into said low pressure cylinder relative to the ñow of fluid through said bore when the master cylinder is initially actuated. > higher than in said low pressure chamber, and a device projecting into proximity to said pressure responsive device when the latter is in its “off” position and dependent thereon for positively limiting the flow of fluid into said lowl pressure chamber relative to said ñow of fluid into said high pressure chamber when said fluid displacing . 9. A hydraulic pressure booster mechanism comprising a low pressure chamber and a high pressure chamber in axial alinement and adapt ed for communication respectively with a hy draulic fluid displacing device and a device to be actuated by hydraulic fluid, a diil‘erential duid pressure vmotor having a pressure responsive _structure including a member projecting into said high pressure chamber to displace fluid . 6. Apparatus constructed in accordance with claim 5 wherein said metering device comprises a stationary member mounted in said low- pres sure cylinder and having a bore therethrough directly communicating with the bore in said therefrom, a pressure responsive member mov able by fluid entering said low pressure cham ber, a control valve mechanism operable by said control piston to supply ñuid thereto directly pressure responsive member to energize said from the master cylinder, said metering device 60 motor, said pressure responsive member extend-projecting into the adjacent end of said control ing through said fluid displacing member into piston when the latter is in its “off” position and said high pressure chamber to displace fluid being provided with a relatively restricted port therefrom and being provided throughout its communicating at all times with said low pres length with a bore providing for substantially sure chamber, the cross sectional area of said unrestricted now ot fluid therethrough into said port being smaller than the cross sectional areas high pressure chamber, means for closing said of the bore of said control piston and said meter ing device. bore upon a predetermined movement of said 4 pressure responsive member when pressure is 7, A hydraulic booster unit comprising açlow higher in said high pressure chamber than in pressure chamber adapted for connection with 70 said low pressure chamber, and means for re a hydraulic iiuid displacing'device, a high pres stricting the flow of fluid from said pressure sure chamber adapted for connection with a de l vice to be hydraulically operated. a motor hav ing a iluid displacing element movable into said high pressure chamber to displace fluid there 75 displacing device into said low pressure cham ber relative to the flow of fluid through said bore when said fluid displacing device is initially actuated. 2,411,458 11 10. Apparatus constructed in accordance with claim 9 wherein said last named means com prises a device mounted in said low pressure ing an axial bore therethrough lfor the unre stricted ñow of fluid to said high pressure cylin- . der, a check valve for said bore seating away from said high pressure cylinder, a rod in said bore, a metering device arranged in said low pressure cylinder and having an axial passage communicating with the master cylinder, one end of such device extending into one end of said bore to deliver ñuid directly from said pas 10 sage to said bore, said metering device having a said low pressure chamber. i 11; In a .booster mechanism for a hydraulic relatively restricted port in constant communi vehicle brake system having wheel cylinders for cation between said passage and said low pres applying the brakes and a pedal-controlled sure cylinder, one end of said rod being engage master cylinder, a booster unit comprising a low able with said metering device to unseat said pressure cylinder and a high pressure cylinder 15 check valve when said control piston is in its arranged in axial alinement and adapted to com “oil” position. . municate respectively with. the master cylin er 12. Apparatus constructed in accordance with and with the wheel cylinders, a differential ñ d claim 11 wherein the end of said bore in which pressure motor having a pressure responsive unit, said end of said metering device projects is ot ' a tubular piston connected to such unit and pro 20 larger diameter than said metering device, and .jecting into said high pressure chamber to dis wherein a sealing ring is interposed between said place fluid therefrom upon energization of said metering device and the enlarged end of said motor, a control piston having one end arranged bore to prevent the flow of iluid from said pas in said low pressure cylinder and its opposite end sage through the enlarged end of said bore into projecting through said tubular piston to dis 25 said low pressure cylinder untilasaid control pis place iluid from said high pressure chamber, a v ton has moved a predetermined distance _from follow-up control valve mechanism i'or said mo its “oiT' position. chamber and projecting into the adjacent end of said bore, such device being provided with a substantially unrestricted passage communicat ing between said fluid displacing device and said bore,- and with a relatively restricted port com~municting at all times between said passage and tor operable by said control piston and by said pressure responsive unit, said control piston hav WILLIAM F. PENROSE.