MXPA96000549A - Spring brake actuator with resource force measurement - Google Patents

Abstract

The present invention relates to a method for measuring the force of a spring in a spring brake actuator, comprising a housing, a spring plate inside the housing, where the spring is positioned between the spring plate and the housing, and a caging bolt extending from the spring plate outside the housing and having a nut therein, the method comprising the steps of: detecting the compression force between the cage bolt nut and the housing, generating a signal representative of the compressive force detected, and visually exhive the spring force as a function of the compression force signal

Description

SPRING BRAKE ACTUATOR WITH SPRING FORCE MEASUREMENT INVENTORS: WILLIAM C. PIERCE and WILLIAM J. HICKS, both citizens of the United States, residing respectively at 221 North Stewart, Muskegon, Michigan 49455; and 5140 Davis Road, Muskegon, Michigan 49441, both in the United States.

APPLICANT: NAI ANCHORLOK, INC., A United States corporation, residing at 1950 Industrial Boulevard, Muskegon, Michigan 49443-0425, United States.

BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a spring brake actuator with a meter for measuring the spring force of a power spring in the actuator. In one of its aspects, the invention relates to a method for measuring the force of a spring in a spring brake actuator. In another of its aspects, the invention relates to a meter for measuring the force of a spring in a spring brake actuator. State of the Prior Art Spring brake actuators are in common use in air brake systems used in trucks, buses and towed vehicles. Such actuators typically include a service brake actuator for applying and releasing the brakes in response to the delivery and discharge of compressed air and to a spring brake actuator arranged in tandem with the service brake actuator. The spring brake actuator uses the spring force to operate the service brake actuator and apply the brakes when the air in a spring brake actuator chamber is reduced below a predetermined pressure. The air pressure can be reduced in this chamber under the control of the operator to apply the brakes or automatically as a result of the failure of portions of the service brake air system. Typically, a barrel-shaped spring is used to store energy and to exert the great force required to brake in the event of an air pressure failure. Air pressure is employed in the chamber acting on a movable wall to compress the spring and keep it in a retracted position. When air is discharged from the chamber, the spring acts on the movable wall, typically a diaphragm or piston, and through a driving rod to exert the force of the spring on the brake actuator to apply the brakes. It is desirable to measure the spring force of the spring to ensure that it is operating within the design parameters.

However, the disassembly of the spring brake actuator to remove the spring and testing it outside the actuator does not measure its effectiveness in the vehicle. Moreover, many spring brake actuators now permanently house the power spring, making it impractical to remove the spring for testing purposes. SUMMARY OF THE INVENTION In accordance with the invention, a meter measures the force of a power spring in a spring brake actuator comprising a housing having an end wall, a spring plate disposed within the housing, a spring of power between the spring plate and the end wall of the housing, and a caging bolt extending from the spring plate through the end wall of the housing and having a nut therein outside the housing. The meter comprises a pressure responsive element, adapted to be placed between the cage bolt nut and the spring housing to generate a signal representative of the compression force of the spring and an indicator coupled to the element that responds to the pressure for Visually display the force of the spring as a function of the pressure signal. Typically, the pressure responsive member comprises a first member adapted to receive the stop link nut and a second member adjacent the first member and adapted to abut the housing. The first member is movable relative to the second member in response to the compression force applied by the nut by the power spring acting against the spring plate. The gauge measures the compression force between the nut and the spring housing so that the force applied by the power spring can be measured in itself. The invention provides rapid and accurate measurement of the strength of the power spring. Likewise, measuring the force of the spring with the brake installed in its operating environment improves the accuracy of measurements taken on brakes removed from the vehicle. Preferably, the first and second members each have an aligned opening to slidably receive the caging bolt. Also, the second member preferably comprises a body having a bore, the first member comprising a piston received within the bore, and the meter further comprises a fluid that responds to the pressure between the piston and the body to withstand a force of applied compression and the pressure signal is a fluid pressure. The indicator is connected to the fluid that responds to the pressure to detect and display the applied compression force. Preferably, the indicator is a pressure sensor for measuring a pressure in the fluid and a screen for displaying the spring force as a function of the pressure measurement. The pressure sensor can be calibrated to display the pressure reading in spring force units.

Preferably, a threaded fit opening is provided through the body to the chamber and a screw is threaded toward the adjustment aperture to adjust the volume of the chamber to calibrate the meter. Additionally, according to the invention, a method for measuring the force of a spring in a spring brake actuator comprising a housing, a spring plate within the housing, a power spring between the spring plate and the housing and A caging bolt extending from the outside of the spring plate of the housing and having a nut therein, comprises the steps of: detecting the pressure between the housing and the nut; generate a signal representative of the pressure detected; and visually displaying an indication of the detected pressure as a function of the compression force exerted by the power spring. Additionally in accordance with the invention, a spring brake actuator comprises a housing having an end wall, a spring plate disposed within the housing, a power spring between the spring plate and the end wall of the housing, and a threaded cage bolt extending from the spring plate through the end wall of the housing, a nut in the cage bolt outside the housing and a gauge measuring the force between the housing and the cage bolt nut -to to measure the force exerted by the power spring. The meter comprises an element that responds to the pressure to detect the compressive force between the housing and the cage bolt nut and to generate a signal representative of the compression force, and an indicator coupled to the element that responds to the pressure for visually display the strength of the power spring as a function of the representative signal. In this way, the force applied by the power spring can be measured in itself. Preferably, the caging bolt further comprises at least one mark along its length to place the nut therein, where, when the nut is aligned with the at least one mark and the spring is applying a force to the plate. spring, the spring will be at 50% of its maximum extension length or other predetermined length. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional view of a spring brake actuator with a spring force gauge according to the invention; and Figure 2 is an exploded view of a portion of the spring brake actuator of Figure 1 and the spring force meter of Figure 1. Description Referring now to the drawings and to Figure 1 in particular, a air-operated diaphragm spring brake 10, of the type disclosed in U.S. Patent No. 4,860,640, issued August 29, 1989, to Ware, incorporated herein by reference. The air operated spring brake 10 comprises a service brake housing 12 and the spring housing 14 joined together in tandem. A diaphragm 16 disposed within the service chamber 12 operates against a push rod 18 in a conventional manner to drive the vehicle braking system (not shown). A second diaphragm 20 divides the spring housing 12 into a spring chamber 22 and a pressure chamber 24. An actuator rod 26 extends from the diaphragm of the spring housing 20 through the pressure chamber 24 and into the housing of the spring housing 20. service 12. A powerful barrel-shaped spring 28 is disposed in the spring chamber 22 between the spring housing 14 and a pressure plate 30. The pressure plate 30 abuts the diaphragm of the spring housing 20. When retracted completely, the spring 28 applies a force of approximately 3, 000 pounds against the pressure plate 30. During the normal operation of the spring brake 10, a constant pressure is applied to the pressure chamber 24, thereby holding the spring 28 in a retracted position, as shown in Figure 1 When pressure is released from the pressure chamber 24, the spring 28 extends and presses the actuator rod 26 toward the service housing 12. Typically, a receptacle 32 is provided in association with the pressure plate 30 for receiving a pin. cage 34 so that the spring 28 can be manually compressed and the actuator rod 26 retracted. Manual retraction would be required, for example, when the brakes must be released, but there has been a failure in the air system of the emergency brakes. As shown more clearly in Figure 2, the caging bolt 34 comprises a threaded, elongate rod 36 having a pair of radially extending projections 38 at one of its ends. The receptacle 32 has a wedged inlet opening 40 for receiving the cage bolt projections 38. After the cage bolt 34 is completely received with the receptacle 32, it is rotated 90 ° so that the projections 38 link an annular shoulder 42 within the receptacle 32. Referring again also to Figure 1, the threaded rod 36 of the caging bolt extends out of the spring housing 14 through an end wall 46, where removal of the cage bolt 34 will retract the pressure plate 30 for compressing the spring 28. Typically, a nut 44 is threaded onto the threaded rod 36 of the cage bolt and torqued to a predetermined level to completely remove or "cage" the power spring 28. As shown in FIG. 1 and 2, a meter 50 according to the present invention is interposed between the nut 44 and the spring housing 14 for measuring the force of compression of the power spring 28. In this way, the meter 50 allows testing the compression force of the spring 28 without removing the spring 28 from the spring housing 14, or otherwise disassembling the spring housing 14. The meter 50 comprises a disc body 52, body 52 having an upper face 54 and a lower face 56. A first coaxial perforation 58 extends partially towards body 52 through its upper face 54. A second coaxial perforation, of smaller diameter, 60 extends towards the body 52 from the underside 56 to intersect the first bore 58, thereby forming an annular shoulder 62 within the body 52 at the intersection of the first and second bores 58, 60. A piston 64 is disposed within the body 52 and it comprises a discoidal head 66 disposed within the first bore 58, an annular collar 68 extending axially from the head 66 and disposed within the second bore. 60. A coaxial perforation 70 extends therethrough. A fluid chamber 74 defined in part by the piston head 66 and the annular shoulder 62 retains a non-compressible fluid 72. An annular groove 76 around the annular collar 68 receives a ring at 078 and a second annular groove 80 around the head of piston 66 receives a second O-ring 82 to seal fluid 72 within fluid chamber 74.

A threaded gate 84 extends radially through the meter body 52 to the fluid chamber 74 and receives a fluid pressure indicator 86. The cage bolt 34 extends through the bore 70 with the nut 44 threaded into the bore. cage bolt 34 in abutment connection with an upper surface of the piston head 66. In this way, the force applied by the spring 28 to the pressure plate 30 is transmitted through the caging bolt 36 and the nut 44 to the piston 64, thereby urging the piston 64 towards the annular shoulder 62, resisted only by the fluid 72. The resulting increased pressure in the fluid is represented by the pressure indicator 86. It is preferred that the indicator 86 be calibrated to read the force of the spring 28, unlike the actual pressure in the fluid 72. A pressure ring 88 received within an annular groove 90 in the body of the meter 52 and adjacent to the open end of the prim it was pierce 58 in an annular shoulder 92 in the piston 64 to maintain the piston 64 within the body of the meter 52. An additional 0-ring and plastic guide 94 combined can be provided between the piston 64 and the body of the meter 52 adjacent to the pressure ring 88. Provision is also made to calibrate the meter 50. A threaded adjustment aperture 96 extends radially through the body 52 towards the fluid chamber 74 and receives a threaded adjusting screw 98. The screw Adjustment 98 allows adjusting the volume of the fluid chamber 74 in order to calibrate the meter 50. For example, screwing the screw 94 in the adjustment aperture 92 reduces the volume of the fluid chamber and produces a correspondingly higher reading in the pressure gauge 86. The industrial standards for measuring the force of the compression spring 28 indicate reading the force measurement at 50% of the maximum stroke of the spring 28. Accordingly, the pin Cage 34 is preferably provided with a mark 100 on its threaded portion 36 which, when aligned with the nut 44, corresponds to 50% of the maximum stroke of the spring 28. So that the caging bolt 34 can be used with more than one type or model of brake actuator, may be provided with multiple markings 100 corresponding to the various brake actuators for which it is contemplated. Preferably, the markings 100 will comprise a protrusion in combination with a color code. Likewise, the indicator 86 can be calibrated with a scale of "pass", "does not pass", such as a red zone and a green zone (not shown) to easily indicate whether the spring 28 is applying force within the design tolerances . Also, separate indicator faces may be provided for separate types of brake actuators. To read the force of a spring 28 in a given brake actuator 10, the cage bolt 34 is first inserted into the receptacle 32 and properly seated therein.

The meter 50 is then received on the caging bolt 34 with the lower face of the body 56 abutting the spring housing 14 and the bore 70 receiving the threaded portion 36 of the caging bolt. The nut 44 is threaded into the cage portion 36 of the cage bolt and is tightened to the predetermined location indicated by the mark 96. To facilitate the load of tightening the nut 44, pressure can be applied to the pressure chamber 24, thereby retracting the spring 28 so that the nut 44 can be freely screwed into the caging bolt 34 to its desired location. If pressurization of the pressure chamber 24 is impractical, the nut 44 can be threaded into the cage bolt 34 in a conventional manner. When the nut 44 is properly positioned and the pressure is released from the pressure chamber 22, the indicator 86 will visually display the force applied by the spring 28 at 50% of its maximum stroke. Preferably, the meter 50 will be calibrated with the adjustment screw 94 before each use, the adjusting screw 92 being adjusted so that the indicator 86 exhibits zero pressure when no force is applied to the piston 64. Reasonable variations and modifications are possible within the scope of the foregoing disclosure of the invention, without departing from the spirit of the invention. invention. For example, the meter 50 can take other forms apart from the non-compressible fluid meter, as illustrated in Figures 1 and 2. For example, a piezoelectric crystal can be used to electronically detect the compressive force between the nut 44 and the housing 14 and to generate an electrical signal representative of it. Also, other mechanical means may be used such as a plurality of stacked Belville springs or an elastomeric insert with the force reading comprising a change in the spatial relationship between the piston 64 and the body 52. It should be understood that the description of the embodiments Individuals contained herein are by way of illustration and not limitation, and that the scope of the appended claims may be interpreted as broadly as permitted by the prior art.

Claims (20)

1. CLAIMS 1. A meter for measuring the force of a power spring in a spring brake actuator comprising a housing having an end wall, a spring plate disposed within the housing, a power spring between the spring plate and the end wall of the housing, and a caging bolt extending from the spring plate through the end wall of the housing and having a nut outside the housing, the meter comprising: an element responsive to the adapted pressure to be placed between the cage bolt nut and the housing to detect a compressive force between the cage bolt nut and the housing, and to generate a signal representative of said capping force between the cage bolt nut and the housing; and an indicator coupled to the element responsive to the pressure to exhibit the force of the power spring as a function of the compression force signal, whereby the force applied by the power spring can be measured in itself.
2. 2 . A meter according to claim 1, wherein the pressure-responsive element comprises: a first member adapted to receive the nut in abutment engagement; and a second member adjacent to the first member and adapted to abut in the housing, said first member being movable relative to the second member in response to a force of the power spring acting on the nut through the spring plate and the pin. of cage.
3. 3. A meter according to claim 2, wherein said first and second members each have an opening, said openings aligned to receive the caging bolt.
4. A meter according to claim 1, wherein the second member comprises a body having a bore, the first member comprising a piston received within the bore, said meter further comprising a fluid responsive to the pressure between the piston and the body to resist an applied compression force.
5. A meter according to claim 1, wherein the indicator is calibrated to display the pressure measurement in units of spring force.
6. A meter according to claim 1, wherein the pressure-responsive element further comprises a calibration element for adjusting the signal to calibrate the indicator.
7. 7. A method for measuring the force of a spring in a spring brake actuator, comprising a housing, a pressure plate within the housing, a power spring between the spring plate and the housing and a caging bolt that extends from the spring plate outside the housing and having a nut thereon, the method comprising the steps of: detecting the compression force between the cage bolt nut and the housing; generate a signal representative of the compression force detected; and visually displaying the force of the spring as a function of the compression force signal.
8. 8. A method according to claim 7, wherein the compression force signal is a fluid pressure.
9. A method according to claim 7, and further comprising the step of adjusting the nut on the cage bolt so that the spring is 50% of its maximum extension before the detection step.
10. 10. A method according to claim 7, wherein the compressive force signal is an electrical signal.
11. 11. In a spring brake actuator, comprising: a housing having an end wall; a spring plate disposed within the housing; a power spring between the spring plate and the end wall of the housing; a threaded cage bolt extending from the spring plate through the end wall of the housing; and a nut on the caging bolt outside the housing, the improvement comprising: a gauge measuring the force mounted between the end wall of the housing and the nut, the gauge comprising: an element responsive to the pressure between the nut of the housing; cage bolt and the end wall of the housing to detect the compression force between the two and to generate a signal representative of said compression force; and an indicator coupled to the pressure responsive element for visually displaying the force of the power spring as a function of the compression force signal, whereby the force exerted by the power spring can be measured in itself.
12. A spring brake actuator according to claim 11, wherein the pressure responsive member comprises: a first member that abuts the nut; a second member adjacent to the first member and bumping into the end wall of the housing, said first member being movable relative to the second member in response to a force of the power spring acting on the nut through the spring plate and the cage bolt.
13. 13. A spring brake actuator according to claim 12, wherein the members have an opening each, said openings aligned and the caging bolt extends through the openings.
14. A spring brake actuator according to claim 13, wherein the second member comprises a body having a bore, the first member comprising a piston received within the bore and defining a chamber between the piston and the body, and the pressure-responsive element further comprises a fluid that responds to the pressure in the chamber to resist the compressive force.
15. 15. A spring brake actuator according to claim 14, wherein the signal generated by the pressure responsive element is fluid pressure which is a function of the fluid pressure in the chamber.
16. 16. A spring brake actuator according to claim 15, wherein the indicator is calibrated to display a reading in spring force units.
17. A spring brake actuator according to claim 14, and further comprising a threaded adjustment aperture through the body towards the chamber and a threaded screw towards the adjustment aperture, whereby the volume of the chamber can be adjusted to calibrate the meter.
18. A spring brake actuator according to claim 11, wherein the power spring further has a maximum extension length and the caging bolt further comprises a mark for placing the nut therein, where, when the nut is aligned with the mark and the spring is applying a force to the meter, the spring will be at 50% of its maximum extension length.
19. 19. A spring brake actuator according to claim 11, wherein the signal generated by the pressure responsive element is a fluid pressure.
20. 20. A spring brake actuator according to claim 11, wherein the signal generated by the element responsive to the pressure is an electrical signal.