Title of Invention

AN ANTICOMPOUNDING AND ROLL BACK PREVENTION SPRING BRAKE ACTUATOR FOR AN AUTOMOBILE BRAKING SYSTEM

Abstract

An anti-compounding and roll back prevention spring brake actuator for an automobile braking system, comprising a service brake diaphragm chamber; a spring brake chamber; a ram assembly provided for the said chambers, wherein valve means such as herein described and a check valve are provided in the ram assembly, such that when the service brake and the parking brake are applied simultaneously, air on the pressure side of the service brake chamber escapes to atmosphere through said valve means, non-pressure side of the of the spring brake chamber and the said check valve, thereby minimising compounding of service brake force and parking brake force, and such that whenever the service brake is applied, the valve means are closed, isolating the pressure side of the service brake chamber and the non-pressure side of the spring brake' chamber, enabling the parking brake to be applied, without releasing the service brake,- until the stem of the valve means is pressed, thus preventing compounding and roll back.

Full Text

This invention relates to an anti-compounding and roll back prevention spring brake actuator for an automobile braking system. In the known automobile braking system, a graduated hand control valve supplies air pressure to the spring brake actuator through a double check valve. This air pressure keeps the power spring of the said actuator in the compressed condition , thereby keeping the parking brake in the released condition. In the known automobile braking system, a foot brake valve is used for applying the service brake. When the foot pedal of the said valve is pressed, it supplies air pressure to the pressure side of the service brake chamber of the spring brake actuator. The service brake circuit and the parking brake circuit are connected to the double check valve. In normal driving conditions, the shuttle of the double check valve isolates the parking brake circuit from the service brake circuit. The parking brake is in its released state. In order to apply the parking brake, air pressure has to be exhausted from the parking brake circuit to atmosphere by operating the graduated hand control valve. In such event, the power spring of the said actuator expands and the parking brake is applied. When, however, the service brake and the parking brake are applied simultaneously, air pressure from the service brake circuit actuates the shuttle of the double check valve and the service brake circuit is connected to the parking brake circuit also. Air pressure from the service brake side is supplied to the parking brake circuit, thereby releasing the parking brake. Thus the double check valve prevents the compounding of the service brake force and the parking brake force. Compounding of the two brake forces is not desirable since this will result in overloading of the foundation brake system. However, there is customer resistance to having a double check valve in the brake circuit for anti-compounding purposes, since this involves additional piping and, consequently, additional cost. In the existing braking system when the service braKe is first applied and the parking brake is applied subsequently, for parking the vehicle during uphill drive, there is the possibility of roll back of the vehicle. By reason of the provision of the double check valve, the air pressure in the parking brake circuit cannot be exhausted to atmosphere, for applying the parking brake, with the service brake already in applied condition. Accordingly, the service brake has to be released before the parking brake can be applied. During this transition period between the release of the service brake and the application of the parking brake, there will be no brake application and there is the possibility of the vehicle rolling back. This situation will also arise when the vehicle is required to be parked during a downhill drive (in this case a roll front situation, hereinafter called a roll back for the sake of brevity). This invention therefore proposes not only an anti-compounding feature as aforesaid, but also a roll back prevention feature. I Anti-compounding devices with roll back protection in spring brake actuators are known. However, In the known systems the double check valve is integrally formed in the housing wall of the actuator, which makes it complicated in construction with more number of parts, making the actuator bulky. In the known systems, during the transition from a service brake application to a parking brake application, a load corresponding to a pressure of 20-30 psi is only applied to prevent roll back of the vehicle. In case of simultaneous application of service and parking brakes, 26% of the service brake output is compounded. On the other hand, the present invention is superior to the known devices. It is simple in its construction, eliminates a double check valve and is more compact. Only a check valve made of rubber (single rubber part) is incorporated in the system in addition to the internal breather valve making it cost effective with lesser number of parts. In the transition from service brake to parking brake, full service brake pressure.is applied (as against a pressure of 20-30 psi in the known system) until the spring brake becomes fully operative. thereby making the proposed system more robust In case of simultaneous application of service and parking brakes, approximately 15% of the service brake is compounded (as against a 26% compounding of the service brake in the known devices). Various other features of this invention will be apparent from the following further description thereof The anti-compounding and roll back prevention spring brake actuator for an automobile braking system, according to this invention, comprises a service brake diaphragm chamber; a spring brake chamber; a ram assembly provided for the said chambers, wherein valve means and a check valve are provided in the ram assembly, such that when the service brake and the parking brake are applied simultaneously, air on the pressure side of the service brake chamber escapes to atmosphere through said valve means, non-pressure side of the spring brake chamber and the said check valve, and such that when the service brake is applied. the valve means are closed, isolating the pressure side of the service brake chamber and the non-pressure side of the spring brake chamber, enabling the parking brake to be applied, without releasing the service brake until the stem of the valve means is pressed. This invention will now be described with reference to one of various embodiments thereof illustrated in the single Figure in the accompanying drawings by way of example and not by way of limitation. The embodiment illustrated will be seen to comprise a service brake diaphragm chamber S, a spring brake chamber P, a ram assembly R provided for the said chambers. Valve means V, which are intended to serve as an internal breather are also provided in the stem J of the ram assembly R. This breather comprises a body K, spring loaded bonded valve L, spring M, O-ring N and a spring guide G and has already been exemplified and described in our patent application No. 976 MAS 2002. A check valve C is also provided in the ram assembly. Our patent application No. 976 MAS 2002 relates to a spring brake actuator with internal breather, for an automobile braking system comprising a service brake diaphragm chamber; a spring brake chamber; a ram assembly provided for the said chambers; and a service port; wherein valve means are provided in the stem of the ram assembly, said valve means being normally open when fitted in the assembly, such that during application of the spring brake, the partial vacuum created on the spring side of the spring chamber, causes air to flow from the service port through the open valve means into the spring side of the spring brake chamber to neutralize the vacuum; and such that during release of the spring brake the pressure build-up created within on the spring side of the spring chamber causes air to flow from the spring side of the spring brake chamber through the said valve means to the service port, to neutralize the pressure build-up. Now, whenever the service brake and the parking brake are applied simultaneously, air on the pressure side E of the service brake chamber S escapes to atmosphere through said valve means V, non-pressure side F of the the spring brake chamber P and the said check valve C, thereby minimising compounding of service brake force and parking brake force. Whenever the service brake is applied, the valve means V are closed, isolating the pressure side E of the service brake chamber S and the non-pressure side F of the spring brake chamber P, enabling the parking brake to be applied, independently, that is, without releasing the service brake, until the stem of the valve means V is pressed, thus preventing compounding and roll back. The terms and expressions herein are of description and not of limitation, there being no intention of excluding any equivalents of the features illustrated and described, but it is understood that various other embodiments of the spring actuator proposed herein are possible without departing from the scope and ambit of this invention. We Claim: 1. An anti-compounding and roll back prevention spring brake actuator for an automobile braking system, comprising a service brake diaphragm chamber; a spring brake chamber; a ram assembly provided for the said chambers, wherein valve means and a check valve are provided in the ram assembly, such that when the service brake and the parking brake are applied simultaneously, air on the pressure side of the service brake chamber escapes to atmosphere through said valve means, non-pressure side of the spring brake chamber and the said check valve, and such that when the service brake is applied, the valve means are closed, isolating the pressure side of the service brake chamber and the non-pressure side of the spring brake chamber, enabling the parking brake to be applied , without releasing the service brake, until the stem of the valve means is pressed. 2. An anti-compounding and roll back prevention spring brake actuator for an automobile braking system, for preventing compounding and roll back substantially as herein described and illustrated.

Documents:

0978-mas-2002 abstract-duplicate.pdf

0978-mas-2002 abstract.pdf

0978-mas-2002 claims-duplicate.pdf

0978-mas-2002 claims.pdf

0978-mas-2002 correspondence-others.pdf

0978-mas-2002 correspondence-po.pdf

0978-mas-2002 description(complete)-duplicate.pdf

0978-mas-2002 description(complete).pdf

0978-mas-2002 drawings.pdf

0978-mas-2002 form-1.pdf

0978-mas-2002 form-13.pdf

0978-mas-2002 form-19.pdf

0978-mas-2002 form-26.pdf

0978-mas-2002 form-6.pdf