Communications: electrical – Land vehicle alarms or indicators – Internal alarm or indicator responsive to a condition of the...
Reexamination Certificate
1998-08-03
2001-04-10
Pope, Daryl (Department: 2736)
Communications: electrical
Land vehicle alarms or indicators
Internal alarm or indicator responsive to a condition of the...
C340S454000, C188S00111E, C188S00111E, C188S00111E, C188S00111E
Reexamination Certificate
active
06215394
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a device for monitoring adjustment of air brakes as used on heavy vehicles such as trucks, truck trailers and buses.
BACKGROUND OF THE INVENTION
Government regulations require proper adjustment of vehicle brakes, the adjustment being usually measured by movement of a pushrod which actuates cam devices, which in turn expand brake shoes against a brake drum of the wheel to be braked. Brake operation results in brake wear, and an increase in pushrod travel or stroke results from brake lining wear, drum wear, component strain and drum expansion at high temperature. A need for brake stroke adjustment is usually indicated by excessive pushrod travel, and there are many prior art monitoring devices which are responsive to excessive pushrod travel to indicate a need for stroke adjustment to a vehicle operator. Some of the prior art devices can be classified into several groups as below.
Some monitors utilize an electrical sensor switch which is actuated following excessive pushrod travel and generates an alarm signal, e.g. by illuminating a light or emitting a warning sound, etc. The switch has normally open switch contacts which are closed when a threshold of pushrod travel is attained. While such devices are simple, they are dependent on a functioning electrical circuit to operate the alarm. If there were an inadvertent break in the electrical circuit, or a poor electrical contact between the contacts of the switch, the monitoring alarm would not be actuated, and the vehicle operator would not be aware that the brakes were out of adjustment. Such occurrences can result from broken wires or corroded connections due to heavy vibration and/or exposure of sensitive portions of the device to contamination from dirt and moisture. Thus, this type of device is not considered to be “fail safe”, and therefore undesirable as it may create a false sense of security even when inoperative. Devices of this general type are found in U.S. Pat. No. 5,226,509 (Smith) and U.S. Pat. No. 4,800,991 (Miller).
Other types of monitors utilize magnetic proximity devices which detect excessive brake pushrod travel when one component of the proximity device passes close to a cooperating component of the device. As in any magnetic proximity switch application, accurate control of spacing between the two cooperating components of the device is necessary, and this can be difficult to attain in the harsh environment of air brakes used on trucks which are exposed to wide temperature fluctuations, heavy vibration, thrown rocks, and contaminants such as dirt and moisture. Devices of this general type are shown in U.S. Pat. No. 4,937,544 (Herman) which uses a proximity dependent oscillator, and U.S. Pat. No. 4,757,300 (Sebalos) which uses a proximity or magnetic switch arrangement.
Other types of monitors have been used, for example U.S. Pat. No. 5,689,231 (Olson) discloses a rotation sensor device mounted to detect relative rotation between the pushrod and an arm of a slack adjuster cooperating with the brake cams. The sensor device may involve rather elaborate circuitry and high costs.
Most of the devices disclosed above would not necessarily indicate to the operator that there is a failure in the monitoring system, and thus the operator would be unaware that the brake adjustment was not being monitored, and could operate the vehicle with out of adjustment brakes without any warning. Other devices are relatively complex and require installation of costly new equipment for each wheel, and this discourages installation due to high installation and acquisition costs. In addition, some devices require complex maintenance routines involving specific technical skills which may also discourage their use.
Automatic slack adjusters have been developed to simplify brake stroke adjustment, but it has been found that most automatic slack adjusters also require proper and regular maintenance to ensure continued operation, and the maintenance itself is considered, by some operators, to be excessively time consuming. Without proper maintenance, automatic slack adjusters can become inoperative, resulting in the vehicle being operated with out of adjustment brakes.
SUMARY OF THE INVENTION
The present invention reduces the difficulties and disadvantages of the prior art by providing a relatively simple and low cost sensor which can be easily incorporated into a standard air brake chamber during actual manufacturing and assembling of the brake components, or, in some instances can be incorporated as a “retro-fit” unit on existing components. The invention automatically activates a simple alarm should brake wear or other factors result in pushrod travel that exceeds a predetermined amount, thus indicating a need for brake stroke adjustment. The device is also arranged to provide a warning signal if there is an open current failure in the sensor circuit, such as a broken wire, thus alerting the vehicle operator that the status is not being monitored. Thus, the device is “fail-safe”, at least within a context of broken wires or corroded contacts, and furthermore can be installed for a relatively low cost, with minimal skill and cost requirements for maintenance.
An electrical switch for an air brake stroke monitoring apparatus comprises a switch body, fixed and moveable electrical switch contacts, a switch actuator and a resilient member. The switch body is securable to a fixed structure associated with the air brake and the fixed switch contact is fixed relative to the switch body. The switch actuator is mounted for movement relative to the body and cooperates with the moveable switch contact to move the moveable contact into and out of engagement with the fixed switch contact. The switch actuator is selectively responsive to movement of brake mechanism associated with air brake actuation. The resilient member cooperates with the switch actuator and the body to apply force to the switch actuator to urge the switch contacts together.
In one embodiment, the fixed and moveable switch contacts have complementary shapes, and preferably the fixed switch contact has a female truncated conical surface and the moveable switch contact has a male truncated conical surface. The switch actuator is an axially elongated plunger mounted for reciprocable movement along an axis thereof and the moveable switch contact is mounted on the plunger. Preferably the resilient member is a compression coil spring encircling the plunger to apply an axial force thereto. Also, preferably the compression coil spring is electrically conducting and extends between the moveable switch contact and a body contact so that the moveable switch contact provides a continuous electrical monitoring circuit through the compression coil spring and body contact.
An air brake apparatus for actuating a brake comprises an air brake chamber, an electrical brake stroke monitoring switch and a brake status monitor. The air brake chamber comprises a chamber body, a flexible diaphragm and a pushrod and diaphragm plate assembly. The flexible diaphragm cooperates with the body to divide the body into first and second spaces which are exposable to a pressure differential. The pushrod and diaphragm plate assembly are mounted for reciprocable axial movement relative to the chamber body and cooperate with the diaphragm to be responsive to the pressure differential. The pushrod has an outer end connectable to brake actuating structure associated with the brake. The electrical brake stroke monitoring switch has a switch body securable to fixed structure associated with the brake chamber. The monitoring switch also has a switch actuator, fixed and moveable electrical switch contacts, and a resilient member. The switch actuator is responsive to movement of the pushrod. The fixed switch contact is fixed relative to the switch body and the moveable switch contact is responsive to movement of the switch actuator. The resilient member cooperates with the switch actuator to apply force thereto to urge the switch contacts together. The brake status monitor co
Brakeminder Canada Inc.
Fulbright & Jaworski L.L.P.
Pope Daryl
LandOfFree
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