|Title of Invention||
A DIAPHRAGM TYPE SPRING BRAKE ACTUATOR FOR THE AIR BRAKE SYSTEM OF A MOTOR VEHICLE
|Abstract||A diaphragm lype spring brake actuator for the air brake system of a motor vehicle, whicli applies and rele?ises the foundation brakes by depletion and admission of compressed air behind a heavily loade4 springi th® said actuator comprising a Steel cylinder and an aluminium body joined together by a permanently crimped clamp ring with ft rubber diaphragm interspersed between the said steel cylinder anc| the aluminium body, a heavily loaded spring housed on one side of the diaphragm guided between two guides and a push rod attached to the other side of the diaphragm through a threaded joint, said joint being formed by ftn integrally moulded metal insert in the said diaphragm receiving the threaded end of the push roc).|
This inventipn relates to a diaphragm type spring brake actuator for the air brake systeip of ^ motor vehicle.
The rubber diaphragm of the spring side of a spring brake actuator is secured to the push fod through an insert integrally moulded to the diaphragm, which parries internal threads to receive the push rod. The push rod attached to (he diaphragm makes the force of application of the push rod co-axial with the axis of the spring and hence prevents the heavily loade4 Spring ^^^ the said push rod from tilting, thus avoiding premature spring and push rod failures. The said integrally moulded metal insert makes the joint more reliable and prevents damage to the diaphragm. The joint between the said push rod and the said molded insert is sealed against leakage of compressed air through a member moulded on the insert in the rubber diaphragm, which undergoes a controlled compression while securing the push rocl to the diaphragm.
This invention is related to the diaphragm type spring brake actuator used in air brake systems of commercial vehicles to apply and release the foundation brak§. A powerful heayily loaded Spring is used in these actuators to apply ^ mechanical force on the |)rake drums of the vehicle for parking applications. To compress the spring (release of brakes) and release the spring (application of brakes) a diaphragni element operated with air pressure is used in these actuators. The force of the spring is transmitted by the diaphragm element through a push rod which is in contact with the diaphragm and which is displaced linearly in conjunction with the niovement of the diaphragm. Such actuators are known to the art.
According to the priQl" art, the push rod is secured to the diaphragm by providing an aperturt ip the diaphragni through whieh the push rod passes and whose threaded end is fastened with a nut on the opposite side. To provide effective clamping two clamping plates are used on either side of the diaphragm aperture.
The drawbacks of the known art are:
The clamping plates eniployed to secure the push rod to the diaphragm are stressed by the air pressure and could fail due to repeated application.
The diaphragm has relative movement with the edges of the clamping plates and coujd fail due to the rubber chafing at X\\9 contact area with the said edges.
Hence the known way of attachment of the push rod to the spring side diaphragm is conslc(ered to be less reliable. Also since three components are used for the attaph^ient, and this is an expensive solution for securing the co-axial operation of the push rod and the spring.
This invention has the following advantages:
The main feature of the present invention is that the joint between the push rod and the diaphragm is rigid and there is no relative motion of the diaphragm with ^joining metal members to cause damage to the rubber during movement.
Another feature of the present invention is that th0 joint between the diaphragm and push fod is achieved without additional, separate components, thus enhancing reliability and reducing cost. Still another feature of this invention is that the said insert moulded in the diaphragm is madf of astiff componenti V^hi^h Pan withstand very high stresses arid wi|l Upt be prone to failure. Yet another feature of the present invention is that the leakage of air through the joint is prevented by compressing a rubber moulded ivifcmbe at the diaphragm joint hetween two metal surfaces formed by the said insert in the diaphragm and the push rod step, wherein the metal
surfaces butt against each other and prevent uncontrolled compression of the rubber, thereby forming a reliable seal.
The accompai^ylng drawings illustrate, by way of example, and not by
way of limitation, one of possible embodiments of this invention,
Figure 1 showing the cross section through the diaphl-agm type spring
brake actuator in the brake released condition.
Figure 2 showing the diaphragm with the integrally moulded insert and
another enlarged view of the portion around the insert
Figure 3 showing the push rod and another enlarged view of the end of
the said push rod
Figure 4 showing the enlarged view of the push rod and diaphragm
Referring to Figure I, the cylinder A and the body pasting B along with
diaphragm C are joined together by clamp ring D achieved by
plastically deforn^jng D. This construction creates two chambers E,
which is the spring chamber and F, which is the air chamber into which
compressed air is charged or exhausted through the port G in the body
B. A heavily loaded spring H is supported and guidpd by one guide, I
which rests on the cylinder A and another guide J, which rests on the
diaphragm C. The diaphragm has an integrally moulded metal insert K,
which has internal threads to receive the push rod l^. The other end of
the push rod passes through two sealing rings M and a bearing N. The
/ push rod has a plate like structure L, which transmits the force from the
spring H to the foundation brake.
In figure 1 the spring brake actuator is shown with the spring H compressed by the air pressure acting on the diaphragm in the chamber F, which poun^erapts the force of the spring. The compressed air can be admitted or evapuatpd from the chamber F through the port G. When the compressed air in chamber F is evacuated, t\\e spring force causes the guide J to push the diaphragm C along with the pi|sh rod U' to move from left to right and '^^ this process the spring expands. The force of the spring is transmitted to the foundation brake through L' and other downstream components well known to the art. If the push rod L is npt attached to the diaphragm, the movement of the push rod may not bf coaxial to the axis of the springi which in turn could cause the push rod to tih and fail or the spring to buckle and fail. Hence a rigid attachment of the push rod to the diaphragm is necessary, which is achieved through the iiastening of the mating threads of the push rod L and tlie insert K.
Another function pf the attachment of the push rod L and diaphragm C is to seal the compregsed air that may escape through the threaded joint, when chamber F i? pressurized.
With respect to figure 2, which shows the diaphragm and an enlarged view of the portipn pf the diaphragm with the moulded insert, a raised member P is moulded |n the rubber portion arown4 the insert K, with a step P, whose height (s indicated by R. Also t\\§ qioulding is constructed such that that a portioil of the metal insert 0 is free pf rubber. With further referenpe tp figure 3, the end of the push rod mating into the insert, shown (n the enlarged view has a steppecj diameter whose height is R' and whose face is indicated as S. During assembly of the
push rod with respect to the insert K of the diaphragm, the metal surfaces O of the insert and S of the push rod butt together and at the same time apply a compression on the rubber moulded step P in a controlled manner equal to the difference in the linear dimensions on R andR'.
Figure 4 shows an enlarged view of the joint between the diaphragm and the push rod.
The metal insert K which is integrally moulded to the diaphragm C ensures that there |s np relative movement between the diaphragm and the insert caused by flexing of the diaphragm. This prevents any chafing damage to the diaphragm and results in improved life of the diaphragm.
The diaphragm and push rod assembly are subjected to stress due to the compressed air acting on the diaphragm in a cyclical manner during each application of the spring brake actuator. The rigid construction of the metal insert ensures it has adequate structural strength.
The diaphragm and pMSh rod joint is sealed frpip escape of compressed air through a controlled compression of a moulded member in the diaphragm between tWQ mating metal faces of the insert and the push rod. This ensures a long leak free life of the jpint
It will be appreciated that various other embodiments of this invention are possible without departing from the scope and anbit of this invention
1. A diaphragm lype spring brake actuator for the air brake system of a motor vehicle, whicli applies and rele?ises the foundation brakes by depletion and admission of compressed air behind a heavily loade4 springi th® said actuator comprising a Steel cylinder and an aluminium body joined together by a permanently crimped clamp ring with ft rubber diaphragm interspersed between the said steel cylinder anc| the aluminium body, a heavily loaded spring housed on one side of the diaphragm guided between two guides and a push rod attached to the other side of the diaphragm through a threaded joint, said joint being formed by ftn integrally moulded metal insert in the said diaphragm receiving the threaded end of the push roc).
2. A diaphragm type spring brake actuator as claimed in claim 1, wherein the integrally moulded insert In the diaphragm is a stiff metallic member with internal threads.
3. A diaphragm type spring brake actuator as claimed in claim 1 or claim 2 wherelti the joint between the diaphragm and the push rod is sealed against leakage of air pressure by a moulded rubber member in the diaphragm that is clamped between the said integrally moulded insert and the push rod.
4. A diaphragm type spring brake actuator as claimed in any one of the claims I to 3 wherein the clamping of the said moulded rubber member between the said moulded metal insert and the push rod is
controlled by the controlled dimension of the moulded metal insert and push rod .
5. A diaphragm type spring brake actuator for the air brake system of a motor vehicle substantially as herein described and illustrated in the accompanying drawings.
|Indian Patent Application Number||2375/CHE/2007|
|PG Journal Number||46/2011|
|Date of Filing||22-Oct-2007|
|Name of Patentee||WABCO-TVS (INDIA) LIMITED|
|Applicant Address||NO.29 HADDOWS ROAD, CHENNAI 600 006|
|PCT International Classification Number||B60T13/38|
|PCT International Application Number||N/A|
|PCT International Filing date|