Fluid-pressure and analogous brake systems – Multiple control – Fluid and electric
Reexamination Certificate
1999-06-04
2001-10-16
Butler, Douglas C. (Department: 3613)
Fluid-pressure and analogous brake systems
Multiple control
Fluid and electric
C303S015000, C303S003000, C251S129060
Reexamination Certificate
active
06302495
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of railway braking systems, and, more particularly, to a railway braking system for a railcar.
BACKGROUND OF THE INVENTION
Trains are widely used to transport people and freight. Freight trains in particular may include 150 or more railcars and extend over a mile or more. Control is required for operating the railway braking system to ensure proper braking.
Compressed air is commonly used as a power source in railway braking systems because it is essentially inert and there are no associated environmental hazards. The use of electrical control devices in conjunction with such pneumatic equipment significantly improves the ability to control the compressed air and therefore improves the effectiveness of the equipment.
A typical railway braking system includes a reservoir of compressed air to supply a relay valve which controls a pneumatic brake cylinder. The relay valve, in turn, is controlled by one or more electromagnetic solenoid valves which can vent the relay valve to atmosphere or connect it to the supply reservoir.
The current state-of-the-art is to use wireless technology to control various devices within railcars and locomotives. U.S. Pat. Nos. 4,582,280 and 4,553,723 to Nichols et al., and assigned to the assignee of the present application, are seminal patents directed to a radio communication based train control system. GE Harris Railway Electronics, L.L.C. offers a radio based control system under the designation LOCOTROL® which provides coordinated distributed power and air brake control from the lead locomotive as described in the above referenced patents. Furthermore, GE Harris offers the EPx™ Direct Braking System which is an Electronically Controlled Pneumatic (ECP) brake system that uses wireless communications technology to communicate braking commands to each railcar.
Railway pneumatic braking equipment requires relatively large orifices to permit the necessary air flow while allowing reasonably low operating pressures. For pneumatic applications which require electrical flow control devices to have a coefficient of flow greater than about 1.0, the current state-of-the-art is to use one of two types of electrical control devices. The first type is a directly operated electrically controlled pneumatic device. A significant consequence of using such a device is the extremely large amount of electrical power required to directly seal such a large orifice. This is because the force of the air pressure is proportional to the square of the surface area of the orifice.
The second type of electrical control device is a pilot valve or device. A pilot valve controls a small flow of air and uses the air pressure to develop large enough forces to operate secondary pneumatic control devices, such as the relay valve. The relay valve then controls the pneumatic brake cylinder, for example. This has the advantage of providing electrical control at a reasonable cost in return for slightly slower operation.
Conventional electrical pilot control devices are usually electromagnetic solenoids which require multiple Watts of power and cannot be considered low power. For most larger air-flow applications, such as industrial plants, a power draw of multiple Watts is insignificant. However, railcars do not typically have on-board electrical power generators. The cost and logistics of generating the amount of electrical power required for conventional electrical control devices for a railway car braking system may be prohibitive.
A significant contributor to power consumption is the mitigation of an important failure mode of a freight train. This failure mode occurs when the brakes are locked in the applied position without the ability to detect this condition. This condition is commonly referred to as dragging brakes. A train car with severely dragging brakes may go unnoticed until the wheel overheats, and shatters. Electrically controlled pneumatic brake controllers can detect and warn of this situation as long as they are operating and powered. However, if the controller becomes disabled, the system on that car must release the brake cylinder pressure to avoid damage.
One potential failsafe method is to have the electrically controlled pilot valve only hold pressure when electrical power is applied. In this way, if the control system becomes disabled, the natural rest state of the brake system is the desired brake release state. This requires that electrical power must be supplied whenever brakes are applied, which can be for multiple hours. Due to the limited electrical power available in a freight car, the pilot valve must have extremely low electrical power draw.
SUMMARY OF THE INVENTION
In view of the foregoing background, it is therefore an object of the invention to provide a railway braking system having a low electrical power requirement.
Another object of the invention is to provide failsafe operation of such braking system.
These and other objects, features and advantages in accordance with the present invention are provided by a railway car brake system including a relay valve responsive to a pilot pressure which is generated by a pilot valve which, in turn, includes at least one piezoelectric element. The system also preferably includes a controller connected to the piezoelectric element to control the pilot pressure and thereby control braking. The pilot valve also preferably releases braking upon loss of power to thereby provide a failsafe release of braking.
In one embodiment, a single piezoelectric element is positioned within a valve body. The piezoelectric elements can be controlled to selectively connect the relay valve to either the pressure source or atmosphere.
In accordance with another embodiment of the invention, the pilot valve comprises a common valve body containing first and second piezoelectric elements. The common valve body comprises a first port connected to the relay valve, a second port connected to the pressure source, and a third port connected to atmosphere.
The pilot valve, in this embodiment may also comprise a fourth port connected to atmosphere and a third piezoelectric element for controlling fluid flow from within the common valve body through the fourth port to atmosphere. This third piezoelectric element also has an energized state to block fluid flow, and a de-energized state to permit fluid flow from the relay valve, through the valve body and to atmosphere to thereby provide a failsafe release of braking. Moreover, this third piezoelectric element is substantially smaller than each of the first and second piezoelectric elements so as to consume relatively less power. Accordingly, only this third piezoelectric element is energized to maintain a desired pilot pressure. Upon loss of power, this piezoelectric element causes the pilot pressure to vent to release the brakes.
In another embodiment, first and second pilot valves include respective first and second valve bodies. Each body contains a respective piezoelectric element. The first pilot valve can be a normally closed valve comprising a first port connected to the relay valve and a second port connected to the pressure source. The second pilot valve can be a normally open valve comprising a third port connected to atmosphere and a fourth port connected to the relay valve. As an alternative, the second pilot valve can be a normally closed valve comprising a third port connected to atmosphere, a fourth port connected to the relay valve, a fifth port connected to atmosphere, and a third piezoelectric element for controlling fluid flow through the fourth port to atmosphere. In this variation, only the third piezoelectric is normally energized, and provides a failsafe release upon loss of power.
The invention preferably uses bimorphic piezoelectric elements having an energized position and a de-energized position. The controller may be connected to a radio transceiver so that electrical cables need not be coupled between cars for communication. At least one pressure sensor may be connected in fluid communication with t
Armstrong Teasdale LLP
Butler Douglas C.
GE Harris Railway Electronics LLC
Rowold Carl
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