CA1089780A - Electric brake and control system thereof - Google Patents

Abstract

Abstract A brake and control system for wheeled vehicles where-in an electric brake includes a pair of electromagnetic brake actuators disposed at one end of a pivotal actuator arm and brake shoes responsive to pivotal movement of the actuator arm to engage a surrounding brake drum. A control system is disclosed for applying separate braking signals to the actuator pair as selected functions of each other.

Description

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The present invention relates to electric brake mechanisms for wheeled vehicles and to control systems therefore~

An object of the present invention is to provide an electric brake structure capable of applying significantly S increased braking forces at a vehicle braked wheel as -compared with typical prior art brakes of similar type without substantial increase in the overall brake size.
Another object of the invention is to provide a brake mech-anism in which undesirable bending forces on the brake -actuator, the brake shoes and/or the brake shoe anchor pin are reduced, and in which the operating life-time of the brake mechanism is thereby increased.
A further object of the present invention is to provide a brake control system which controls braking forces by a pair of brake actuators separately from but in controlled relation to each other.
A more specific object of thc invention is to provide a brake control circuit for applying brakes at a second of a pair of electrically operated brake actuators in a composite or double-actuator wheel brake in controlled relation to operator-controlled braking at the first electrically-operated brake actuator.

The invention, together with additional objects, features and advantages thereof, will be best understood from the following description, the appended claims and the accom-panying drawings in which:

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~ 9 ~ ~0 FIG. 1 is an elevational view of a presently preferred : embodiment of the electric brake provided by the present invention;
FIGS. 2-4 are sectional views respectively taken along the lines 2-2, 3-3 and 4-4 in FIG. l; and FIG. 5 is a schematic diagram of a presently preferred embodiment of the brake control system in accordance with the invention.

Referring to FIGS. 1-4, a presently preferred embodiment 10 of the electric brake provided by the present invention includes a backing plate 12 having a central opening 14 for locating plate 12 on a vehicle axial or spindle (not shown) ` for fixed attachment thereto as by we.lding, brake 10 being thereby mounted in fixed relation to the associated vehicle.
An anchor pin 16 is carried by backing plate 12 and includes a rolled or peened head portion 18 (FIG. 3) and an anchor portion 20 connected by a shank portion 22 of lesser diameter and embracing therebetween backing plate 12 and a bracket 24 welded to the backing plate for angularly locating the brake mechanism with respect to the vehicle axle. A
primary brake shoe assembly 26 and a secondary brake shoe assembly 28 (FIG. 1) are carried by plate 12 substantially coaxially with the axis of rotation of an associated wheel, and are connected to each other by the usual adjustment link 30 and a coil spring 32 parallel thereto. A second coil spring 34 is connected between the upper portion of

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1~!89~0 shoe assemblies 26,28 and biases the opposing yoke portions 36,38 of the respective shoes against the anchor por~ion 20 of anchor pin 16, thereby cooperating with spring 32 to retain the shoes in the normally disengaged position with respect to an associated surrounding brake drum, the drum being of conven~
tional and well known construction and therefore the same not being shown.
Primary shoe assembly 26 comprises a shoe member 40 (FIGS. 1 and 4) which includes the usual arcuate platform 42 having a brake lining 44 bonded thereto and a pair of stiffening webs 46,48 (FIG. 4) extending radially inwardly therefrom on either side of backing plate 12 to help maintain platform 44 perpendicular to the backing plate during brake operation.
A stiffening element 50 (FIGS. 1 and 3) is welded to the upper portion of web 46 and cooperates with the web to form yoke 36 for embracing anchor pin 16. A cam element 52 is welded to stiffening element 50 and includes a flat tangentially-directed surface 53 disposed at an angle of about 30 with respect to the vertical axis passing through the center of anchor pin 16 and backing plate opening 14 as best seen in FIG. 1. With the exception of cam element 52 which i~ not included on secondary brake shoe assembly 28 the latter is a substantial mirror image of shoe assembly 26 and has the elements thereof indicated in FIG. 1 by similar reference numerals followed by the suffix "a".
An arcuate actuator arm 54 is mounted at one end 56 to pivot about a second shank portion 58 on anchor pin 16 .

?85~il0 extending axially outwardly from anchor portion 20 (FIG. 3) and is captured thereon by a retaining ring 60 received in a corresponding groove 62 on pin shank portion 58. End 56 of actuator arm 54 includes a tangentially extending nose 5 64 which terminates in a parabolic camming surface 66.
2~ose 64 cooperates with follower surface 5,3 on cam elemen~ 52 to move primary brake shoe assembly 26 radially outwardly into engagement with a corresponding braking surface on a brake drum (not shown) upon pivotal movement of actuator arm 54 about the axis of anchor pin 16 in the counter-clockwise direction as viewed in FIG. 1. The cooperative combination of a parabolic surface 66 on the actuator arm and a straight or flat follower surface 53 on the brake shoe operate to move.the brake shoe outwardly in a linear direction rather than in an arcuate direction as in the usual prior art arrangements; thereby resulting in a more efficient transfer of braking forces to the brake drums.
A pair of electromagnets or brake "pucks" 70,72 are carried at an end of actuator arm 54 remote from pin 16 and are mounted at substantially equal radii with respect to ::
the axis of pin 16 but at differing radii with respect to the axis 74 (FIG. 1) of backing plate 12, puck 72 being disposed radially outwardly of puck 70 with respect to axis 74. Referring to FIG. 2, puck 70 is mounted adjacent ~he free end 75 of arm 54 and includes a frustoconical body ;
portion 76 which is loosely mounted for axial movement on the shank 78 of a rivet 80 affixed to actuator arm 54 and is biased outwardly with respect to the actuator arm by a _ _ _ _ .

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coil spring 82. An integral ear 84 extends radially from puck body 76 to loosely embrace the shank 86 of a rivet 88 affixed to actuator arm 54 and is captured thereon by a retaining ring 90, thereby retaining puck body 76 on rivet shank 78 against the outward force of spring 82 and preventing rotation of the puck on pin 7~. Puck 72 is mounted to actuator arm 46 inwardly of end 75 in similar fashion, the elements thereof being indicated in FIG. 2 by identical ; reference numeral followed by the suffix "a". Single-puck electric brakes of the general type illustrated in FIGS. 1-4 as well as details of puck construction are discussed in ~; _.ail in the U.S. patent of Brede et al 3,244,259. Pucks 70,72 have conductors 92,94 éxtending separately therefrom along actuator arm 54 and are fed through a grommet or the like 96 carried by backing plate 12 for connection to suit-able control means later to be described. Conductors 92,94 are fastened to arm 54 by suitable retaining clips 98 (FIG. 1).
` As is conventional and well known, an electrical braking signal to either or both of the electromagnetic pucks 70,72 will attract such puck or pucks to an armature plate 100 (FIG. 2) rotatably coupled to the vehicle wheel. When the wheel and armature plate are rotating counter-clockwise with respect to the braking mechanism as viewed in FIG; l, attraction of pucks 70,72 into frictional sliding engagemcnt with the armature plate causesactuator arm 54 to pivot about the axis of pin 16 in the counter-clockwise direction, 1~897~) thereby camming primary brake shoe assembly 26 into en-gagement with the corresponding braking surface on the surrounding brake drum. Reactive braking forces on shoe assembly 26 are transferred by line 30 to shoe assembly 2~ such that the latter also engages the drum braking surface. The total brake reaction force is transferred to the vehicle frame through yoke 38, anchor pin 16 and backing plate 12 in the usual fashion.
The brake mechanism 10 lllustrated in the drawings is specifically adapted for use in applying braking forces at a wheel carried on the left side of a recreational trailer, mobile home or the like. During forward motion of the trailer, wheels on the left side thereof are rotating counter-clockwise as viewed away from the trailer such that braking forces may be applied at the wheels in the manner above-described. A brake mechanism for a right hand trailer wheel will, of course, be a mirror image of that illustrated in the drawings.
An embodiment of the brake control system provided by the in-vention is illustrated in FIG. 5 and comprises a vehicle operator-responsive brake controller 102 connected in series with the coil 70a of first or primary brake puck 70 between ~, a vehicle battery 104 and electrical ground. I~hen the,present invention is utilized to control braking forces on a trailer having at least one and preferably a plurality of braked wheel, i.e., wheels which includes means such as brake mechan;sm - f 7~) .

10 capable of applying braking forces, controller 10 may be of the type shown in the U.S. patents of Hubbard 3,371,235 or VandenBroek 3,503,652, the latter of which is responsive both to direct actuation by a tractor vehicle operator through a control arm or the lilce and to indirect operator actuation through the tractor brake system. A relay 106 is connected to control the braking signal to the coil 72a of secondary brake puck 72 and comprises a relay coil 108 connected in parallel with brake coil 70a and a normally-open relay switch 110 connected in series with coil 72a between battery 104 and ground.
Thus, the brakecontrol signal fed to a secondary coil 72a is a function of the braking signal from controller 102 to primary coil 70a. More specifically, when the braking signal to coil 72a reaches a first preselected threshold such as nine volts, for example, relay coil 108 is energized and switch 110 is closed to apply battery voltage directly to secondary coil 72a. Thereafter, braking forces due to secondary puck 72 are applied at a maximum level while braking forces are due to primary puck 70 remain responsive to operator control. Preferably, coil 108 exhibits a hysteresis characteristic such that the relay coil will not be de-energized and switch 110 will not reopen until the control signal to primary brake coil 70a drops below a second threshold level, for example three volts, which is well below the first threshold level. This feature has been found to yield enhanced brake control over a wide range of braking conditions.

~ 3 7 It will be evident that the total braking force avail-able at shoe assemblies 26,28 due to attractive forces between pucks 70,72 and armature plate 100 is significantly greater than the braking forces made available through either puclc considered alone. It will also be appreciated from the fore-going description that the effective frictionally developed motive force generated at secondary puck 72 is greater than that for primary puck 70. More specifically, the angular velocity of the armature plate 100 at the radius of puck 72 from axis 74 (FIG. 1) is greater than that at the radius of puck 70 while the pivotal radii of the pucks from the axis of pin 16 are substantially identical. Hence, the brake shoes will be moved into engagement with the brake drum with greater force for a given current through secondary puck coil 72a than for the same current to primary coil 70a.
This feature has been found empirically to yield enhanced brake control throughout the intermediate bral<ing range when both brake pucks are engaged.
Yet another advantage of the embodiment thus far des-cribed lies in the pivotal mounting of actuator arm 54 on the pin 16 which simultaneously serves as anchor for the brake shoes rather than on a separate pivot pin disposed therebelow as in the prior art. The mechanical advantage provided by the embodiment shown to scale in the drawings, i.e., the ratio of the puck pivotal radii to the distance between the point of engagement of surfaces 53,66 (FIG. 1) and the pin axis, is about 14:1 and may be compared with an 8:1 mechanical 1 ~9 ~ ~

advantage of conventional prior art arrangement of which the above-noted Brede et al patent is typical. I~ will also be appreciated with the reference to FIG. 3 that the actuator arm 54 is mounted to pivot about pin 16 axially adjacent the anchor portion 20, such that bending stresses on the anchor pin caused by opposite radial forces applied thereto by the actuator arm and by the yoke 38 of secondary brake shoe assembly 28 (FIG. 1) are minimized.
The brake mechanism 10 illustrated in the drawings is -specifically adapted for use in applying braking forces at a wheel carried on the left side of a recreational trailer, mobile home or the like. During forward motion of the trailer, wheels on the left side thereof are rotating counter-clockwise as viewed away from the trailer such that braking forces may be applied at the wheels in the manner above-described. A brake mechanism for a right-hand trailer wheels will, of course, be a mirror image of that illustrated in the drawings.
Although the invention has been described in connection with a specific embodiment thereof, many alternatives, modi-fications and variations are contemplated. For example, when a vehicle includes a number of braked wheels each having -first and second brake actuators as in the preferred application of the invention to~trailers having multiple braked wheels as described above, the various first actuators or pucks may be connected in parallel with coil 70a in FIG. 5 and the various second actuators may be connected in parallel . ~, _ ':'- ' ' , ' , 7~

with coil 72a. Moreover, the control features of the present invention illustrated in FIG. 5 are potentially useful in their broader aspects in successively applying braking forces at separate first and second braked wheels each having one or more associated brake actuators. It will also -be appreciated that the control aspects of the invention are equally applicable to other types of electrically-operated brakes, such as electropneumatic or electrohydraulic brakes, ;
wl7erein coils 70a,72a (FIG. 5) would be disposed in suitable metering valves. Similarly the eiectromagnetic relay 106 illustrated in FIG. 5 could readily be replaced by a suitable equivalent solid-state relay. Indeed the invention is intended to embrace the above-noted and all other alternatives, modifications and variations as fall within the spirit and broad scope of the appended claims.
This application is a divisional application from our earlier applicatlon serial No. 291,720 filed on Novembe~ 24, 1977.

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Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A brake control system for wheeled vehicles comprising vehicle brake means having first and second electrically-operated brake actuator means adapted for separate actuation and responsive to respective electrical signals for applying braking forces, first control means connected in series with said first actuator means for applying a first braking signal to actuate said first actuator means, and second control means connected in parallel with said first actuator means for applying a second braking signal to actuate said second actuator means as a function of said first braking signal.

2. The brake control system set forth in claim 1, wherein said second control means includes means for applying said second braking signal to said second actuator means when said first braking signal exceeds a first preselected threshold.

3. The brake control system set forth in claim 2, wherein said second control means further includes means responsive to said first signal exceeding said first threshold for continuing to apply said second braking signal to said second actuator means after said first signal thereafter decreases below said first threshold until said first signal decreases below a second threshold less than said first threshold.

4. The brake control system set forth in claim 3, further comprising a source of electrical power for said control system, said second control means including means for connecting said second actuator means directly to said source of electrical power when said first braking signal exceeds said first preselected threshold.

5. The brake control system set forth in claim 1, for use on a wheeled vehicle system having at least one braked wheel, said brake means, including said first and second brake actuator means, being disposed to apply braking forces at said at least one braked wheel.

6. The brake control system set forth in claim 5, wherein said first control means is responsive to an operator of said vehicle system.

7. The brake control system set forth in claim 4, wherein said brake means comprises an electric brake having brake shoe means and an actuator arm for moving said brake shoe means into a brake drum to apply said braking forces, and wherein said first and second brake actuator means respectively comprise first and second electromagnetic brake pucks disposed on said actuator arm.