Fluid-pressure and analogous brake systems – Supplementary reservoir
Reexamination Certificate
1995-02-28
2001-07-31
Graham, Matthew C. (Department: 3613)
Fluid-pressure and analogous brake systems
Supplementary reservoir
Reexamination Certificate
active
06267455
ABSTRACT:
BACKGROUND OF THE INVENTION
Many large vehicles use air brake systems. These brake systems include air actuated service brakes coupled to service brake actuators. Pressurized air, typically at 100 psi, is applied to the service brake chambers of the service brake actuators to apply the service brakes. To keep the brakes applied when parked, combination brake actuators are usually used. A combination brake actuator includes a spring brake portion and a service brake portion. The spring and service brake portions include respective spring and service brake chambers, each defined in part by a piston or, more commonly, by a diaphragm assembly, connected to a push rod assembly. The push rod assembly is connected to the brake, typically by a slack adjuster. The spring brake portion also includes a heavy actuator spring, coupled to the push rod assembly, which tends to push on the push rod to apply the brake. Supplying pressurized air to the service brake chamber applies the associated brake while supplying pressurized air to the spring brake chamber compresses the actuator spring to release the brake. Thus, when parked, air is exhausted from the service brake chamber which allows the actuator spring to push on the push rod and apply the brake according to the force of the actuator spring.
One of the problems with conventional air brake systems is that the braking force generated by the spring brake portion of the combination brake actuator is only about 50% of the maximum braking force generated by an applied service brake. Therefore, with the spring brakes applied each axle with combination brake actuators has only about half the braking force which is available with the service brakes. One reason conventional combination brake actuators are so designed is to protect the brakes. That is, if the vehicle is parked and drum brakes are set while the drums are warm, upon cooling the drums have a tendency to contract which can, if the braking force is too high, result in damage to the brakes. In addition, conventional combination brake actuators have the service brake and spring brake chambers housed within a common housing; this limits the size of the actuator piston or diaphragm thus limiting the strength of the actuator spring. Also, not all of the axles have combination brake actuators; due to economy and space requirements, often no more than half the axles are so equipped. Although the resulting braking force is sufficient for parking purposes, in an emergency, such as when service brake air pressure is lost, the braking force available is woefully inadequate.
Smaller automotive vehicles typically use hydraulic brake systems. Parking brakes with conventional hydraulic brake systems rely on a manual parking brake which is actuated by stepping on a pedal or pulling on a handle. The pedal or handle is connected to a cable which in turn pulls on a pair of cables ultimately connected to the rear brakes. While manually applied parking brakes are generally adequate for most parking situations, they are quite limited in their ability to act as emergency brakes due to the low force exerted, the application of parking brakes to only the rear wheels and the lack of any sort of effective modulation of the braking force.
SUMMARY OF THE INVENTION
The invention is directed to a system which provides an emergency and parking (E&P) brake system in a manner which provides numerous advantages over existing systems.
The E&P brake system is used with a brake system of the type including a brake and a source of braking force, such as a compressed air tank, coupled to a brake actuator. The brake actuator includes a movable brake actuator element, typically called a slack adjustor, movable between brake released and brake applied positions. The E&P system includes an E&P actuator which is located a distance from the brake actuators, typically in the cab or at some other protected but relatively accessible position. The E&P actuator has a variable volume spring brake chamber which is defined in part by a spring brake chamber element, typically of a piston or diaphragm type, movable between first and second positions. The E&P actuator also includes a variable volume spring deflection compensation chamber defined in part by a movable compensation chamber element. A compression spring is positioned between the spring brake chamber element and the compensation chamber element.
The spring brake chamber element is connected to the brake actuator element, typically by a flexible cable. Thus, moving the spring brake chamber element from the first position to the second position applies a braking force to the brake actuator element. The spring brake chamber element is normally maintained in its first position by pressurizing the spring brake chamber. However, by depressurizing the spring brake chamber, such as during parking, the spring brake chamber element moves from the first position to the second position so to apply a parking brake force.
If one depressurizes the spring brake chamber while pressurizing the compensation chamber, the compensation chamber element moves against the spring thus recompressing the spring. This causes an increased emergency braking force to be applied to the brake actuator element by the spring over what would otherwise have been applied by the spring.
The E&P brake system uses an E&P actuator located physically separate from the one or more brake actuators it services. This permits the E&P actuator to be positioned in an area of the vehicle which is easier to get at for adjustment and maintenance than if the an E&P actuator were mounted directly to the service brake actuator. Many of the problems associated with repair and removal of spring brake actuators are avoided with the E&P brake system. The E&P actuator can be designed to be located on the vehicle at a position which is protected from the elements, such as water, snow and road salt. This accessibility allows the user to manually release the parking brakes in a convenient manner, as opposed to having to crawl under the vehicle, often under cold and wet conditions, to release conventional spring brakes. The system eliminates the need for the much heavier and expensive dual chamber brake actuators. The use of service brake actuators, in addition to freeing up space for the vehicle designer, also lessens the amount of support which is needed to support the brake actuator.
The invention is especially suited for retrofit applications. Since a single E&P actuator can be used with more than one brake actuator, weight and costs can reduced when compared with conventional dual chamber brake actuators. More wheels can be provided with emergency and parking braking capability than are now so provided because of the efficiencies of the E&P brake system.
Conventional spring brakes can be taken apart and repaired only with special care; many accidents have been caused when special safety procedures have not been closely followed. The E&P actuator is preferably designed to be worked on safely. The user can manually release the brakes using the brake release wheel, uncouple the cables from the E&P actuator and then disassemble the E&P actuator. Preferably, the E&P actuator does not become fully disassembled until the spring is fully expanded so parts do not fly apart during disassembly.
Although parking brake force need not be modulated, emergency braking force is preferably modulated to be most effective. This can be accomplished with the E&P brake system.
Since the force exerted by the E&P actuator is completely independent of the force exerted by the service brake actuator, the force exerted by the E&P brake system can be much greater than that which could be exerted if one were limited according to the size of the service brake chamber. The E&P brake force need not be proportional to the service brake force because it is independent of it.
Other features and advantages will appear from the following description in which the preferred embodiment has been set forth in detail in conjunction with the accompanying drawings.
REFERENCES:
pat
Graham Matthew C.
Knobbe Martens Olson & Bear LLP
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