US2196190A - Hydraulic brake system - Google Patents

Description

APlll 9 1940- H. c. BOWEN HYDRAULIC BRAKE SYSTEM Original Filed Sept. 16, 1933 QQ S NQ um wf ww @GN @n /T X QNQ Patented Apr. 9, 1940 UNITED STATES HYDRAULIC BRAKE SYSTEM Herbert C. Bowen, Detroit, Mich., assignor to Hydraulic Brake Company, Detroit, Mich., a

corporation of California Application September 16, 1933, Serial No. 689,715 Renewed June 15, 1939 14 Claims.

This invention relates to hydraulic brake systems, and more particularly to fluid pressure de,- vices therefor.

Heretoiore in fluid brake systems having pressure devices operable through a foot pedal lever,

the ratio of pedal movement to uid flow changes v at a predetermined point in the pedal movement to produce a greater fluid pressure Without proportionately greater foot pressure. The transition takes place suddenly, with the result that there is a period immediately following, which is uncontrollable on the part of the operator. For example, assume that a pressure of sufficient value at the point of transition to effect a deceleration of five feet per second per second, the pressure in this instance being compounded to effect a deceleration of ten feet per second per second. From this it will be readily seen that no stops can be eifected between five and ten feet per second per second. The present invention aims to overcome this objection.

An object of the invention is to spread the transition from low to highv pressure over a prolonged period to smooth out the operation of the system.

Another object of the invention is to provide a fluid pressure device wherein simultaneously operable low and high pressure producing means are provided.

Another object of the invention is to provide means controlled by pressure in the system for effecting gradual transition from a low to a high pressure.

A further object of the invention is to provide means controlled by pressure in the system for dis-associating the low pressure producing means from the system.

An additional object is to provide a device of the character herein described which is simple and inexpensive in structure, highly eiiicient in use, positive in action, durable in service, and a general improvement in the art.

Other objects and advantages of the invention will appear from the following description taken in connection with the drawing forming a part of this specification, and in which- Figure 1 is a vertical sectional view of a reservoir and a compound cylinder embodying the invention. and

Figure 2 is a schematic illustration of a complete hydraulic brake installation including the reservoir and cylinder.

Referring to the drawing for more specific details of the invention, I0 represents the frame of a motor vehicle chassis. The frame has suitably Asecured thereto a housing I2 including a reservoir I4 having an open top and a drain opening I6, the drain opening being closed as by a plug I8, and the top having iitted thereon a cover plate 20 provided with a filling opening 22 closed as by a plug 24 having a vent 26.

An operating shaft 28 extending transversely through the reservoir has suitably secured thereto, outside of the reservoir, afoot pedal lever 30 connected by a return spring 32 to a xed support. The shaft 28 also has secured thereto, within the reservoir, a lever 34 having a lateral end 36 serving to transfer motion of the shaft 28 to a piston 38 operabley within a cylinder 40.

'I'he cylinder 40 is suitably supported on the wall of the reservoir adjacent the bottom thereof with its open end extending into the reservoir. The closed end or head of the cylinder projects from the Wall of the reservoir, and is provided with an axial port 42, communicatingv with outlets 44, 46, and 48, respectively. The outlet 44 communicates with a pressure switch 50 connected in a circuit 52 including a battery 54 and a lamp 56, the circuit being grounded as indicated at 58. The lamp 56 is a conventional stop light such as is in general use. The outlets 46 and 48 are connected by fluid pressure delivery pipes or ' conduits 60 and 62 and branch pressure delivery pipes to motor cylinders 64 connected between the separable ends of friction elements 66 for spreading these elements into engagement with the drums 68 of wheel brakes 10, and the friction elements of the respective brakes are connected by retractable springs 12. e

As shown, the cylinder 40 has a double diametral bore, providing a large and a small chamber. The larger chamber has a slot 'I4 for the reception of the actuating lever 34, and a port 16 providing a communication between the larger chamber and the reservoir, and a by-pass 18 provides a communication between the large and small chambers. The piston 38 reciprocable in the cylinder 40 includes a shell 80 tted snugly in the larger chamber of the cylinder. This shell provides a chamber 82 having in its wall a plurality of ports 84 providing communications between the chamber and a circumferential chamber 86 communicating with a plurality of spaced openings 88 in a piston head 90 fitted in thelarger chamber of the cylinder and having fitted thereon a collapsible leak-proof cup 92. The head 90 also has a passage 94 providing a communication between the chamber 82 and the larger chamber of the cylinder. y

The head 90 has formed concentrically there- Vwith a sleeve 96 of smaller diameter than the dif ameter of the small chamber of the cylinder. This sleeve has a head 98 fitted snugly in the small chamber of the cylinder. The head 98 has a plurality vof spaced openings |00 providing communications between the small chamber of the cylinder and the larger chamber of the cylinder, and positioned on the head 98 is a collapsible leak-proof cup |02 having an opening |04 registering with the bore of the sleeve 96. 'I'he cup |02 is held against displacement by a coil spring |06 interposed between the cup and a valve |08 for control of the port 42. The valve |08 has normally closed passages |09. The spring |06 also serves to return the piston to its retracted position.

The sleeve has therein a reciprocable Vplunger ||0 having thereon a leak-proof cup I2. The plunger has a head exposed to the fluid pressure in the smaller or high-pressure chamber and an annular portion ||5 exposed to the fluid pressure in the larger or low-pressure chamber. The area of the plunger head is approximately twothirds that of. the annular portion ||5. This plunger ||0 also carries a disk valve ||4 arranged to seat on a rubber gasket ||6 in the chamber 82 to control the passage 94. The valve 4 is normally held against its seat by a coil spring ||8 interposed between the valve and a spider |20 threaded in the shell 80. The spider has thereon a sleeve |22 arranged concentrically with respect to the piston and the sleeve has therein a pressure plug |24 for the reception of the force applying end 36 of the lever 34.

Assuming thatl the system is filled with suitable liquid or fluid, upon depressing the foot pedal lever 30 the shaft 28 is moved through an angle, and this movement of the shaft is transferred through the lever 34 on the shaft tothe piston 38 to move the piston into the cylinder 40. During the initial movement of the piston, pressure is received by the cup 92 on the head of the piston 90, and the fluid in the larger chamber of the cylinder is displaced through the head 98, past the cup |02 thereon into the smaller chamber of the cylinder, and from thence through the valve |08, which prevents retrograde movement of the fluid, and through the port 42 and outlets 44, 46 and 48 communicating therewith.

Movement of the fluid under pressure through the outlet 44 actuates the pressure switch 50 to close the circuit 52 resulting in lighting the signal lamp 56, and simultaneously therewith the uid moves under pressure through the outlets 46 and 48 and the de`lvery`pipes or conduits 60 and 62 connecting these outlets to the motor cylinders 64, resulting in actuation of these cylinders to spread the brake elements B6 against the resistance of the retractor spring 12 into engagement with the drums 68 of the brakes 10.

When the fluid in the cylinder is placed under a pressure which, when multiplied by the larea of the head of the plunger ||0 and the area of the valve ||4, is slightly in excess of the load on the compression spring ||8, the plunger ||0 is moved to trip the valve ||4 and thereby relieve the fluid pressure in the larger chamber of the cylinder, a portion of the fluid being returned from the larger chamber of the cylinder through the passage 94, the valve ||4, the chamber 82, and the spider |20 to the reservoir.

As the valve ||4 opens the cup |02 seals against its cylinder wall and closes communication between the high-pressure chamber and the low-pressure chamber. The function of maintaining pressure on the fluid in the small chamber is thus assumed by the piston head 98 and plunger l0 without appreciable loss of pressure in the high-pressure chamber and that part of the braking system connected therewith.

It is to be noted that the plunger 0 has a head exposed to the pressure in the high-pressure chamber and an annular portion ||5 of' larger area than the head of the plunger which is exposed to the pressure in the low-pressure chamber. The forces exerted on these two areas by the fluid pressures in the high and low-pressure chambers act in the same direction to crack the valve I4 against the tension of the compression spring H8. If the piston is being advanced slowly the cracking of this valve will lower the pressure in the low-pressure chamber to a greater extent than is immediately compensated for by the advance of the high-pressure head 98, withthe result that the valve 4 again closes and thus continues to crack and close until the pressure in the high-pressure chamber is high enough to create sufficient force on the head of the plunger ||0 to overcome the force of the compression spring ||8 without any assistance from the fluid in the low-pressure chamber. Thereafter this valve will remain open throughout the remainder of the advance of the piston.

On the other hand, if the piston is being advanced with suflicient rapidity, the forward movement of the high-pressure head 98 may immediately build up sufficient increase in pressure in the high-pressure chamber to compensate for the lowering of pressure in the lowpressure chamber due to the cracking of the valve ||4, whereupon this valve will continue to permit slow leakage there past as the pressure in the low-pressure chamber is gradually dissipated.

In both types of operation the object of the invention is accomplished in that the resistance to the-advance of the low-pressure head of the piston is gradually dissipated as the resistance to the advance of the high-pressure head increases and at no time is there any abrupt change in the total resistance offered by the piston to the advancing movement of the foot pedal. The operator thus has full and complete control of the brakes at all times.

Upon release of the applied force on the foot I pedal lever 30, this lever is returned to its norvmal position by the spring 32.

During this movement of the foot pedal lever, the piston 38 is moved to its retracted position by the return spring |06, and fluid is returned from the cylinders 64 under pressure of the retractor springs 'I2 connected between the friction elements 66 of the brakes 10.

Due to friction on the column of fluid in the cylinder 40 and the conduits connecting the cylinder 40 to the cylinders 64, and to the tension of the spring |06, the piston returns to its retracted position slightly in advance of the return of the uid to the cylinder 40. This causes a partial vacuum inthe cylinder 40 resulting in collapse of the cups 92 and |02 and admission of fluid from the reservoir to the cylinder.

Upon complete return of the piston to its retracted position, the by-pass 18 and the port '|6 are uncovered, whereupon further pressure in the cylinder causes the cups to return to static condition, and any excess fluid returned to the cylinder 40 from the cylinders 64 passes from the cylinder through the by-pass 18 to the larger chamber of the cylinder, and from thence through port 16 to the reservoir.

From the foregoing it will be readily understood that the range over which the transition of the pressure occurs may be determined entirely by the area of the head of the plunger H0, the range being greater when the area of the plunger head is small, and, `oi? course, decreasing as the area of the plunger head increases.

Although this invention has been described in connection with certain specific embodiments, the principles involved are susceptible of numerous other applications that will readily occur to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims. v

I claim:

1. A iiuid pressure mechanism of the class described, comprising a compound cylinder providing large and small bores, a supply reservoir communicating with said cylinder, a piston having a head in each bore, means for operating said piston to create fluid pressures in said bores, a passage through the larger head, said passage leading to said reservoir, valve means for said passage, said valve means having a separate area exposed to the iiuid pressure in each bore,

the forces exerted on said areas acting on said valve means-in the same direction to open said valve and thereby gradually relieve the pressure in said larger bore, independent valve and passage means movable with the smaller head for controlling flow between said bores, means for replenishing said cylinder from said reservoir, and a spring for urging said first-named valve means to closed position.

2. A fluid pressure mechanism of the class described, comprising a compound cylinder providing large and small bores, a supply reservoir communicating with said cylinder, a piston having a head in each bore, means for operating said piston to create fluid pressures in said bores, a passage through the larger head, said passage leading to said reservoir, poppet valve means for said passage, said valve means having a separate area exposed to the fluid pressure in each bore, the forces exerted on said areas acting on said valve means in the, same direction to open said valve and thereby gradually relieve the pressure in said larger bore, independent valve and passage. means movable with the smaller head for controlling `flow between said bores, means for replenishing said cylinder from said reservoir, and a spring for urging said first-named valve means to closed position.

3. A iiuid pressure mechanism of the class described, comprising a compound cylinder providing large and small bores, a supply reservoir communicatingwithsaid cylinder, a piston'having ahead in each bore, means for operating said piston to create fluid` pressures in said bores, a passage through the larger head, said passage leading to said reservoir, valve means for'said passage, said valve means having a separate area exposed to the flui'dpressure in each bore, said areas beingof diierent sizes, the forces'exerted on said areas acting lon said valve means in the same direction to open said valve-,and thereby gradually .relieve the pressure in said larger bore, independent valve and passage means movable tween aid bores, means forreplenishing 7said with tle smaller head for controlling flow becylinde from said reservoir, and a spring for urging said rst-named valve means to closed inder comprising large and small bores, a supply reservoir communicating with said cylinder, a

piston in each bore, means for operating said pistons to create iiuid pressures in said bores, a

passage through the larger piston and connect-A ing said reservoir with the larger bore, a plunger including a valve and an area exposed to the fluid pressure in` each bore, the area exposed to the fluid pressure in the larger bore being larger `than the area exposed to the fluid pressure in the smaller bore, the forces exerted on said areas acting in the same direction to open said valve and thereby reduce the pressure existing in the larger bore, means for reiilling said cylinder from said reservoir, and a spring for urging said valve to closed position.

5. A iiuid pressure mechanism of the class described, comprising a compound cylinder providing large and small bores, a supply reservoir communicating with said cylinder, a piston having a head in each bore, means for operating said piston to create iluid pressures in said bores. a passage through the larger head, said passage leading to said reservoir, valve means for said passage, said valve means having a separate area exposed to the iluid pressure in each bore, the

area exposed to the fluid pressure in the smaller bore being approximately two-thirds of the size of the area exposed to the ilud 'pressure in the larger bore, the forces exerted on said areas acting on said valve means in the same direction to open said valve and thereby gradually relieve the pressure in said larger bore, independent valve and passage means lmovable with the smaller head for controlling flow between said bores, means for replenishing said cylinder from said reservoir, and a spring for urging said rstnamed valve means to closed position.

6. A huid-pressure device comprising a reservoir, a cylinder having bores of different diameters, a' piston having two heads of dilierent diameters for creating uid pressures in said bores, a sleeve connecting the heads, a plunger movable in' said sleeve, said plunger being exposed to and urged in the same direction by fluid pressure in both of said bores, a passage through said piston head connecting the larger bore with said reservoir, a valve movable with said plunger to open and close said passage, and thereby control the pressure developed in said larger' bore, and means whereby said cylinder is refilled from said reservoir.

7. A duid-pressure device comprising a reservoir, a cylinder providing bores of different diameters, a piston including ashell providing a chamber, a piston head, a passage through said head communicating with the chamber, means connecting said chamber with said reservoir, a second head, said heads adapted to create fluid pressure in said bores, a sleeve connecting said heads, a plunger movable in the sleeve, a valve movableV with the plunger for opening and closing said passage to control the pressure developed in said larger bore, said valve being urged toward open position by the fluid pressure existing in both of said bores, and a spring in the chamber urging the valve to its seat.

8. A fluid-pressure device comprising a reservoir, a two-diameter cylinder providing a pair of bores, a piston including a shell providing a chamber, a head on said shell, a. passage through said head communicating with the chamber,

vmeans-connecting said chamber with said reservoir, a second head, said head movable to create fluid pressurein said bores, n. sleeve connecting said heads, a plunger movable in the sleeve and acted upon in the same direction'by the pressures in said bores, a valve movable with the plunger for opening and closing said passage to control the pressure created in said larger bore, a spider in the shell, a spring interposed between the spider and the valve, and means for replenishing said cylinder from said reservoir.

9. A fluid-pressure device comprising a reservoir, a two-diameter cylinder providing a pair of bores, a piston including a cylindrical member having an axial bore, heads formed upon the ends of said cylindrical member, said heads adapted to create fluid pressures in said firstnamed bores and having openings registering with said axial bore, a skirt formed integral with one of the heads and providing a chamber, a plunger movable in said axial bore, a passage providing communication between the chamber and one of the bores, a valve movable with the plunger to open and close said passage and control the pressure in said last-mentioned bore,

said plunger acted upon in the same direction by the pressures in both of said first-mentioned bores, a spider secured in the chamber and permitting communication between said chamber and said reservoir, a spring interposed between the spider and the valve, a pressure block sup ported by the spider, and means for relling said cylinder from said reservoir.

10. A fluid pressure device comprising a cylinder having a double diametral bore providing two chambers, a piston reciprocable therein having spaced heads fitted in the respective chambers, and a bore extending through the respective heads, a skirt on one of the heads providing a housing, a plunger movable in said last-named bore, said plunger having a surface exposed to the fluid pressure in each chamber and being urged in the same direction by the action of the fluid pressures on both of said surfaces, a fluid reservoir, a passage connecting said reservoir with the larger of said chambers, a valve in said passage carried by said plunger, said valve controlling the release of pressure from said larger chamber, a member secured in said housing, a spring interposed between the member and valve, means for replenishing said cylinder from said reservoir, a second passage connecting said chambers, and a second valve independent of said first-mentioned valve for controlling said second passage.

l1. A fluid pressure device comprising a reservoir, a cylinder supplied therefromhaving a double diametral bore -providing a low pressure chamber and a high pressure chamber, expansible elements connected to the high pressure chamber, brake elements actuated by the expansible elements, a valve controlling movement of fluid from the expansible elements to the high pressure chamber, a piston reciprocable in the cylinder having spaced heads tted in the respective chambers and an axial bore extending through the heads, the smaller head having openings providing communications between the low and high pressure chambers, a collapsible cup on the smaller head controlling the opening, a kirt on the larger head providing a housing opening into the reservoir, the larger head having a plurality of openings providing communications between the low pressure chamber and the housing, a collapsible cup on the larger head controlling the openings therein, a plunger movable in the bore, said plunger having a surface exposed to the fluid pressure in each chamber, said plunger being urged in the same direction by the action of the fluid pressures on both oi' said surfaces, a valve carried by the plunger, a passage providing a communication between the low pressure chamber and the housing, said valve controlling said passage, a support in the housing, a compression spring between the support and the valve, a block on the support, and an actuator engaging the block.

12. A fluid system for transmitting power between a foot pedal or like element and a brake cylinder and acting 'in several phases with different predetermined ratios of transmission, comprising a piston unit having a large piston and a small piston, means operated by the foot pedal for actuating the piston unit, a cylinder for each of said pistons, duct means between the small cylinder and the brake cylinder, a communication between the two cylinders, a valve in said communication opening towards the small cylinder, a fluid reservoir, a communication between the large cylinder and the fluid reservoir, a second valve in said communication, said second valve opening under pressure in the large cylinder, resilient return means for said second valve, and an element subjected to the pressure in the small cylinder and acting when moved under such pressure to open said second valve, said first valve, second valve and element being carried by the piston unit.

13. A fluid pressure device comprising a cylinder having a large chamber and a small chamber, a piston reciprocable in the chambers. means for by-passing fluid from the larger chamber past the piston into the small chamber, a discharge outlet for the small chamber, means for relief of pressure on the fluid in the larger chamber including a valve having a part subjected to pressure on the fluid in the large chamber and another part of smaller area than the rst, part subjected to pressure on the fluid in the small chamber, the combined pressures acting in the same direction on said parts and tending to open the valve, and means lurging the valve to close.

14. A fluid pressure device comprising a compression cylinder having a largechamber and a small chamber, a piston unit sealing with both of said chambers, bypass valve means permitting flow of fluid from the larger to the. smaller cham-v ber, a discharge outlet for the smaller chamber, said piston unit providing a passageway connecting that part of the larger chamber in front of the piston unit with that part of the larger chamber in rear thereof, said piston unit comprising spring-pressed valve means normally closing said passageway, and means for advancing said piston unit in said chambers to create fluid pressures therein, said last-named valve means having a part acted upon by fluid pressure in the small chamber and another part of larger area than the first part acted upon by fluid pressure in the large chamber whereby said valve means opens in response to the sum of the forces, as distinguished from the difference between the forces, exerted on said parts by the fluid pressures in the large and small chambers.

HERBERT C. BOWEN.

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