WO1982001229A1

WO1982001229A1 - Spring applied brake control arrangement

Info

Publication number: WO1982001229A1
Application number: PCT/US1980/001318
Authority: WO
Inventors: Tractor Co Caterpillar
Original assignee: Lindblom V
Priority date: 1980-10-06
Filing date: 1980-10-06
Publication date: 1982-04-15
Also published as: IT1139199B; FR2491413A1; GB2098277A; JPS57501487A; FR2491413B1; IT8124328A0; GB2098277B

Abstract

A brake control arrangement (30) permitting normal service brake actuation through a brake linkage (10) and providing automatic brake actuation in case assisting fluid pressure decreases. During normal operation, sufficient assisting fluid pressure is supplied to a pressurizable chamber (42) to move an actuation piston (34) to its non-actuation position against the biasing force of a spring (36). When fluid pressure falls below the pressure needed to counteract the spring's biasing force, the spring (36) displaces the piston (34) to an actuation position relative to a surrounding housing (40) and, during its displacement, displaces a brake engagement plunger (32) to its brake engaged position. Movement of the utilizing apparatus may thereafter be provided by axially displacing an engagement member (48) against the actuation piston (34) so as to drive the actuation piston (34) to its non-actuation position. The engagement member (48) has an indentation (48b) which accepts displacement of the plunger (32) thereinto and permits subsequent brake actuation by the brake linkage (10).

Description

Spring Applied Brake Control Arrangement

Technical Field

This invention relates generally to brakes and more particularly, to a brake control arrangement which automatically applies a brake when hydraulic fluid pressure used in the brake control arrangement is reduced.

Background Art Heavy equipment such as earthmoving apparatus has long utilized pressurized fluid to assist operators in actuating brake apparatus. U.S. Patent 3,895,703 which issued July 22, 1975, and is assigned to the assignee of the present invention illustrates a system for providing such fluid assist. It has also been a common practice to provide automatic brake actuation upon loss of assisting fluid pressure below a prede¬ termined amount. Return springs have typically been used to deactuate the brake when the operator supplied force was discontinued. Other return springs have been used to move brake pedals, on which operators act, to their deactuated position at times when the brakes are not being applied. Release mechanisms for deactuating the automatically applied brake arrangements for towing or otherwise servicing the utilizing vehicle are also known. U.S. Patents 2,809,723; 3,796,138; 3,926,094; and 4,093,038 which respectively issued October 15, 1957; March 12, 1974; December 16, 1975; and June 6, 1978, illustrate automatically actuated brakes, return springs for normal braking deactuation, and release mechanisms for deactuating the brakes when they have been automatically applied. Limited braking during towing was typically provided by the operator who exerted a force on the brake pedal in the normal manner but without the aforementioned pressurized fluid assist. Brake application by the operator without the pres- surized fluid assist required exertion of substantial human effort on the brake pedal. Moreover, since the brake and brake pedal were returned to their deactuated position by the return springs, the braking force supplied by the operator was further increased since the force on all the return springs had to be overcome in addition to the force necessary to effectively provide brake engagement. Thus, applying the brakes on a utilizing vehicle which was equipped with such prior art braking devices when the vehicle was being towed required excessive operator effort. The present invention is directed toward overcoming such disadvantage while retaining the benefits of automatic brake actuation upon loss of assisting fluid pressure.

Disclosure of the Invention In one aspect of the present invention a brake control arrangement is provided in which normal brake application is permitted when the pressure of a brake assisting fluid is at least as great as a selected minimum and in which automatic brake application is supplied when the pressure of the brake assisting fluid falls below the minimum. Means are also provided for reestablishing normal, unassisted braking capability after the brake has been automatically applied such that the forces opposing the normal, unassisted braking are only the brake engaging force and a brake pedal return force.

The present invention generally includes a housing, a piston which is movable within the housing between a first and a second piston position, a spring which biases the piston toward its second position, a brake engagement plunger which extends through the piston and is displaceable between a first and a second plunger position, and a linkage which joins the plunger and the piston for piston displacement to the second piston position.

Fluid force acting within a pressurizable cavity defined by the plunger, piston and housing holds the piston in its first or brake nonactuation position against the biasing force of the spring. During normal operation when fluid pressure in the pressurizable cavity is greater than the minimum, the piston is held in its first position while the plunger remains free to move in response to normal, service braking. Upon loss of fluid pressure below the minimum, the biasing spring displaces the piston to its second position and in so doing causes the plunger, which is linked to the piston, to be displaced to its second position and thus apply the brake. Apparatus independent of the pressurized fluid for displacing the piston to its first position is also included and arranged to retain the free movement of the plunger so as to permit brake application from operator supplied force without overcoming the brake return force which is, during normal service braking, provided to the present invention by the pressurized fluid.

Brief Description of the Drawings

The invention will be more fully understood from reading the following detailed description of a preferred embodiment, taken in connection with the accompanying drawings, in which:

Fig. 1 is a side elevational view of a brake linkage in which the present invention brake control arrangement is included; Fig. 2 is an enlarged sectional view of the brake control arrangement of Fig. 1 in which the arrange¬ ment is in a normal, nonbraking configuration;

Fig. 3 illustrates a normal, braking config- uration of the brake control arrangement of Fig. 2;

Fig. 4 illustrates an automatically applied, braking configuration of the brake control arrangement of claim 2; and

Fig. 5 illustrates a normal, nonbraking configuration of the brake control arrangement of claim 2 in which an automatic brake applicator has been retracted.

Best Mode for Carrying Out the Invention

Referring now to the drawings in detail, a brake linkage 10 for actuating a brake is provided and includes an operator brake pedal 11 which is pivotally linked to a brake rod 12 which, in turn, is pivotally linked to an actuating rod 14. A shaft 16 is pivotally linked to both the actuating rod 14 and a booster actuating arm 18. A return spring 19 engaged with the actuating arm 18 provides a return bias to the brake linkage 10 which restores the brake pedal 11 to its deactuated position when no operator supplied force is exerted thereon. An assisting hydraulic booster mechanism 20 is engageable with and actuatable by the actuating arm 18. The return spring 19 is housed within booster 20 which amplifies the operator supplied force transmitted to it by the actuating arm 18 through the use of pres¬ surized fluid such as hydraulic oil supplied to it through port 20a by a fluid pressurizing system. The structure of booster 20 may be more fully appreciated from reading U.S. Patent 3,895,703 which issued July 22, 1975, and is assigned to the assignee of the present invention. The booster 20, when actuated by the actuating

:?ι arm 18, pivots a brake lever 22 about its pivoting end 22a in the direction generally indicated as A. The pivoting end 22a is pivotally joined through a pin 24 to a mounting member 26 such as a vehicle chassis. The brake lever 22 has a swinging end 22b which, when swung in the direction indicated as A, causes engagement of a brake mechanism (not shown) which, for crawler tractors, is preferably of the band and drum type. Brake lever 22 is also pivotally connected to a connecting link 28 by a bolt 29. Connecting link 28 is pivotally connected by a pin 31 to the present invention brake control arrangement 3J3 which is better illustrated in Figs. 2, 3, 4, and 5.

Connecting link 28 is pinned to a brake engagement plunger 32 which extends through opening 33 in an actuating piston 34 and is in axially sliding engagement with the actuating piston 34. Means for biasing such as belleville springs 36 are housed within an annular support structure 38 so as to urge piston '34 from its first, nonactuating position illustrated in

Fig. 2 to its second, actuating position illustrated in Fig. 4. Piston 34 is in axially sliding engagement with housing 40. Brake engagement plunger 32 includes a stem portion 32a which has radially enlarged and radially reduced portions 32b and 32c respectively, which together provide concentric operation of the stem portion 32a within the opening 33 and promote smooth relative displacement between the plunger 32 and annular piston 34. Engagement plunger 32 also includes an enlarged end portion 32d which is joined to stem portion 32a and is radially larger than the piston's opening 33 to prevent withdrawal thereinto and-assure abutment with piston 34.

The brake engagement plunger 32, the housing 40, and the piston 34 cooperatively define a variable displacement pressurizable chamber 42 whose volume is affected by axial movement of piston 34. Fluid is transmissable to and from pressurizable chamber 42 through inlet-outlet fitting 44 which is fluidly con¬ nected with booster 20 and an external source (not shown) of pressurized fluid. A piston engagement member 48 having an axial end 48a and indentation 48b is arranged in pressurizable chamber 42 and is axially engageable with piston 34. A release cover 50 is mateable with housing 40 and has an O-ring 52 or other sealing means disposed therebetween to prevent leakage of pressurized fluid from the pressurizable chamber 42. Upon removal of release cover 50 by extraction of a plurality of screwbolts 54, a bolt or other threaded member such as screwbolt 54 may be axially advanced in a threaded opening 56 which is formed through the housing 40.

Industrial Applicability

Under normal, nonbraking service, a pres¬ surized fluid such as hydraulic oil occupies pressur- izable chamber 42 and has a pressure of approximately 350 pounds per square inch by example or other value sufficiently high to seat piston 34 on support structure 38 against the biasing force of springs 36. The booster apparatus 20, when actuated by actuating arm 18, pivots brake lever 22 in direction A about pin 24 and thus causes plunger 32 to translate toward the right so as to force hydraulic oil out of port 44 until sufficient brake power obtains. Upon release of the operator supplied actuating force from actuating arm 18, the return spring 19 moves the brake linkage 10 to its deactuated position while the brake engagement force from booster 20 is removed from brake lever 22 so as to enable the biasing fluid pressure within chamber 42 to displace plunger 32 to the left and thus return the

c :::ι brake to its disengaged, unapplied configuration. The configuration of the present invention shown in Fig. 3 illustrates the brake arrangement 30 when the brake has been applied in a normal fashion through operator actuation. Thus, the brake mechanism is returned to its normal position by fluid pressure in chamber 42 which remains constant at the previously described 350 psi level.

The pressurized fluid entering and exiting port 44 is also fluidly communicable with booster 20 so as to provide assisting force therein. When the fluid pressure in the aforementioned fluid circuit falls to less than a predetermined value (150 psi by example) , piston 34 is driven to the right by springs 36 in a progressive manner with decreasing pressure in the pressurizable chamber 42. Displacement of piston 34 from its first position (illustrated in Figs. 2 and 3) to its second position as illustrated in Fig. 4, causes plunger 32 to be likewise displaced to the right to its second position which corresponds with the piston 34's second position. The enlarged end 32d of plunger 32 links the plunger 32 to the piston 34 when piston 34 is urged to its brake actuation or second position. Of course, displacement of plunger 32 to its second posi- tion causes the brakes to be applied and thus stop the utilizing apparatus. The configuration in which piston 34 has been displaced by springs 36 is illustrated in Fig. 4.

Loss of pressure within pressurizable chamber 42 generally indicates failure of a fluid handling component, leakage of fluid, or loss of power to a pump which pressurizes the fluid. Upon actuation of the brake by piston 34, the utilizing apparatus is halted and held in that position. To affect repair of the fluid pressurizing system it is often necessary to move the utilizing apparatus to a repair facility which has suitable refurbishing equipment or a site where the apparatus does not obstruct work performance by other apparatus. In such circumstances, it becomes necessary to retract the actuation piston 34 to its first, non- actuation position. Such piston retraction is accom¬ plished by advancing a screw bolt such as bolt 54 in threaded opening 56 into contact with the axial end 48a of engagement member 48. Continued advancement of bolt 54 is provided until engagement member 48 engages and drives piston 34 to its first position where it abuts support structure 38. After piston 34 has been thus retracted, the utilizing apparatus can be moved and its brake utilized by the operator by depressing brake pedal 11 which causes movement of the previously described brake linkage 10 and application of the brake.

Fig. 5 illustrates the configuration of brake arrangement 30 in which piston 34 has been retracted. As can be seen, plunger 32 can- move toward the right to its brake engaged position upon actuation by the operator of brake pedal 11 and other connected components of the brake linkage 10. Indentation 48b is radially larger than the plunger end 32d to facilitate relative movement therebetween. Indentation 48b is also axially larger than the distance between the plunger's first and second positions so as to permit indentation 48b to accommodate the displacement of plunger 32 to its second, brake engagement position when engagement member 48 is holding piston 34 in its first position. As such, the utilizing apparatus or vehicle can be moved after automatic actuation of piston 34 without the operator having to also overcome the spring force which is normally used to return the brake to its unengaged position. It will now be apparent that an improved brake control arrangement 30 has been provided in which normal service braking is permitted and in which emergency, fail-safe braking is supplied upon sufficient loss of fluid assisting pressure. Moreover, since the brake is normally returned by fluid pressure exerted on enlarged head 32d, loss of such fluid pressure and subsequent mechanical, unassisted actuation of the brake requires only overcoming the required force for engaging the brake and brake linkage return spring 19 without also overcoming a brake return biasing force such as is inherent in brake systems employing return springs to disengage the brakes. As such, after the actuation piston 34 has been retracted, the utilizing apparatus can be moved with the assurance that braking capability exists with less brake application force being exerted by the operator than in previous designs.

Claims

1. A brake control arrangement (30) per¬ mitting normal brake application and automatically providing auxiliary braking, said brake control arrange¬ ment (30) comprising: a housing (40) ; an actuating piston (34) displaceably disposed in said housing (40) to move between a first and a second position which respectively provide nonactuation and actuation of auxiliary braking; a brake engagement plunger (32) disposed in an opening (33) through said piston (34) , said plunger (32) being displaceable between a first, brake disengaged position and a second, brake engaged position, said plunger (32) having an axial end (32d) which, with said piston (34) and said housing (40) , cooperatively define a pressurizable chamber (42) ; means (44) for transmitting pressurized fluid into said pressurizable chamber (42) , said fluid exerting a disengagement force on said plunger (32) and actuation piston (34) to bias them toward their first positions, said disengagement force being normally greater than a predetermined force; means (36) independent of fluid pressure for biasing said actuation piston (34) to its second posi- tion with the predetermined force; and means (32d) for linking said plunger (32) to said actuation piston (34) for piston displacement to its second position.

2. The brake arrangement (30) of claim 1, said linking means comprising: an enlarged head (32d) on said plunger's axial end being abuttable with said piston (34) .

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3. The brake arrangement (30) of claim 1 further comprising: means (48,54) engageable with said piston (34) for displacing said actuation piston (34) to its first position for brake disengagement.

4. The brake arrangement (30) of claim 3, said displacing means (48,54) comprising: an engagement member (48) disposable in said pressurizable chamber (42) in sliding engagement with said housing (40) ; and means (54) for displacing said engagement member (48) toward said actuation piston (34) .

5. The brake arrangement (30) of claim 4, said engagement member displacing means (54) comprising: a screwbolt (54) axially abuttable with said engagement member (48) and in threaded engagement with said housing (40) .

6. The brake arrangement (30) of claim 4 wherein said engagement member (48) has an indentation (48b) axially adjacent said plunger (32) to permit displacement of said plunger (32) to its second position when said engagement member (48) is engaged with said actuation piston (34) .

7. The brake arrangement (30) of claim 6 wherein said indentation (48b) is radially larger than said plunger's axial end (32d) .

8. The brake arrangement (30) of claim 6 wherein said indentation (48b) is axially greater than the distance between said plunger's first and second positions.

9. The brake arrangement (30) of claim 1, said plunger (32) comprising: a generally cylindrical stem element (32a) extending through said actuation piston (34) and having axially adjacent, radially enlarged (32b) and radially reduced (32c) portions for promoting concentric opera¬ tion of said plunger (32) within the piston opening (33) when said plunger (32) moves relative to the actuation piston (34) during normal brake application.

10. An auxiliary braking arrangement (30) for a hydraulic-mechanical service brake system (10,20,22) of a vehicle which is operative to automatically apply the brakes upon a loss of fluid pressure in the service brake system (10,20,22), said auxiliary braking arrange¬ ment (30) comprising: means (48,54) to override such automatically applied auxiliary braking arrangement (30) for per¬ mitting vehicle movement and mechanical operation of the service brake system (10,20,22) during such vehicle movement.

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