CA1088003A - Vehicle brake actuators - Google Patents
Vehicle brake actuatorsInfo
- Publication number
- CA1088003A CA1088003A CA305,797A CA305797A CA1088003A CA 1088003 A CA1088003 A CA 1088003A CA 305797 A CA305797 A CA 305797A CA 1088003 A CA1088003 A CA 1088003A
- Authority
- CA
- Canada
- Prior art keywords
- chamber
- pressure
- envelope
- air
- actuator according
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Landscapes
- Braking Arrangements (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An actuator for a vehicle wheel brake comprises a cylinder divided by a piston into two separate chambers, and a spring located in one of the chambers and arranged to bias the piston. In one aspect a one-way valve is provided which permits the flow of air from within the chamber containing the spring to atmosphere, but prevents the flow of air into that chamber through the valve. In another aspect the gas within that chamber has a pressure greater than atmospheric pressure when the chamber has its smallest volume.
An actuator for a vehicle wheel brake comprises a cylinder divided by a piston into two separate chambers, and a spring located in one of the chambers and arranged to bias the piston. In one aspect a one-way valve is provided which permits the flow of air from within the chamber containing the spring to atmosphere, but prevents the flow of air into that chamber through the valve. In another aspect the gas within that chamber has a pressure greater than atmospheric pressure when the chamber has its smallest volume.
Description
10~3003 This invention relates to vehicle brake actuators.
Brake actuators are known which comprise a piston working in a cylinder and engageable with a brake-actua*ing assembly movable to apply and release the brake. The cylinder has two chambers located one on each side of the piston. One of the chambers contains a coil compression spring which biases the piston towards a brake-applying position, the spring force being transmitted through the piston and the brake-actuating assembly during braking, and the other chamber is normally filled with fluid, usually air, under pressure to hold off the piston and compress the spring.
Such brake actuators are usually used for emergency braking or parking and may be combined with service brake actuators.
A problem with such known actuators is that the spring chamber is open to ambient air. The ingress of dirt and water into the chamber, particularly salt water in winter conditions or near the coast, causes corrosion and premature failure of the spring.
It has been found that the use of filters and venting pipes between the spring chamber and the atmosphere do not solve the problem.
In accordance with one aspect of the present invention, there is provided an actuator for a vehicle wheel brake, comprising a cylinder divided by a movable pressure operable member into two separate chambers, and resilient means located in one of the chambers and arranged to bias said pressure operable member, wherein a one-way valve is provided which permits the flow of air from within said one chamber to the , ~
.. .. . ~ ~.
. .
exterior thereof, but prevents the flow of air into the one chamber through the valve, the one chamber being normally sealed except for the one-way valve.
The valve may be set such that air can flow to atmosphere through the valve only after a predetermined minimum threshold pressure has been reached in the chamber.
Thus, the valve prevents ambient air passing therethrough into the said one chamber. Any gas leakage from the other chamber across the pressure operable member will be exhausted through the valve.
An actuator in accordance with the invention for a vehicle wheel brake and a modification thereof will now be described, by way of example, with reference to the accompany-ing drawings, in which: -Figure 1 is an axial sectional view through the Jrr: ~
.-actuator, Figure 2 is a view similar to Figure 1 of the modified actuator, parts being removed for clarity, and Figure 3 is a side view of a release tool for use with the actuators of Figures 1 and 2.
Referring to Figure 1, the actuator comprises an emergency or parking brake part 1 attached to a service brake part 2.
The service brake part 2 comprises an aluminium housing 3 formed in two parts 3A,3B between which is clamped a diaphragm 4 enclosing a pressure chamber 5. Attached to the diaphragm 4 is a brake actuating rod 6. The introduction of pressurised fluid into chamber 5 urges the diaphragm from its illustrated brakes-off position to an operative position in which the rod 6 applies the brake. The service brake part
Brake actuators are known which comprise a piston working in a cylinder and engageable with a brake-actua*ing assembly movable to apply and release the brake. The cylinder has two chambers located one on each side of the piston. One of the chambers contains a coil compression spring which biases the piston towards a brake-applying position, the spring force being transmitted through the piston and the brake-actuating assembly during braking, and the other chamber is normally filled with fluid, usually air, under pressure to hold off the piston and compress the spring.
Such brake actuators are usually used for emergency braking or parking and may be combined with service brake actuators.
A problem with such known actuators is that the spring chamber is open to ambient air. The ingress of dirt and water into the chamber, particularly salt water in winter conditions or near the coast, causes corrosion and premature failure of the spring.
It has been found that the use of filters and venting pipes between the spring chamber and the atmosphere do not solve the problem.
In accordance with one aspect of the present invention, there is provided an actuator for a vehicle wheel brake, comprising a cylinder divided by a movable pressure operable member into two separate chambers, and resilient means located in one of the chambers and arranged to bias said pressure operable member, wherein a one-way valve is provided which permits the flow of air from within said one chamber to the , ~
.. .. . ~ ~.
. .
exterior thereof, but prevents the flow of air into the one chamber through the valve, the one chamber being normally sealed except for the one-way valve.
The valve may be set such that air can flow to atmosphere through the valve only after a predetermined minimum threshold pressure has been reached in the chamber.
Thus, the valve prevents ambient air passing therethrough into the said one chamber. Any gas leakage from the other chamber across the pressure operable member will be exhausted through the valve.
An actuator in accordance with the invention for a vehicle wheel brake and a modification thereof will now be described, by way of example, with reference to the accompany-ing drawings, in which: -Figure 1 is an axial sectional view through the Jrr: ~
.-actuator, Figure 2 is a view similar to Figure 1 of the modified actuator, parts being removed for clarity, and Figure 3 is a side view of a release tool for use with the actuators of Figures 1 and 2.
Referring to Figure 1, the actuator comprises an emergency or parking brake part 1 attached to a service brake part 2.
The service brake part 2 comprises an aluminium housing 3 formed in two parts 3A,3B between which is clamped a diaphragm 4 enclosing a pressure chamber 5. Attached to the diaphragm 4 is a brake actuating rod 6. The introduction of pressurised fluid into chamber 5 urges the diaphragm from its illustrated brakes-off position to an operative position in which the rod 6 applies the brake. The service brake part
2 can operate independently of the emergency brake part 1.
The part 3B of the housing 3 is sealingly attached to an aluminium cylinder 7 of the emergency brake part 2.
In the actuator of Figure 1, the attachment is by way of a circlip 8 which can only be removed by machining away part of the aluminium housing.
The emergency brake part 1 comprises a fluid pressure operable member in the form of a piston 9 carrying sliding seals 10 and being slidable in the cylinder 7, the piston dividing the cylinder into two chambers 11,12. The piston ~
has an inner axially extending cylindrical extension 13 which surrounds and retains a steel insert 14 engageable with a push rod 15. The rod 15 extends sealingly through a wa]l 16 formed by the housing part 3B into engagement with the diaphragm --
The part 3B of the housing 3 is sealingly attached to an aluminium cylinder 7 of the emergency brake part 2.
In the actuator of Figure 1, the attachment is by way of a circlip 8 which can only be removed by machining away part of the aluminium housing.
The emergency brake part 1 comprises a fluid pressure operable member in the form of a piston 9 carrying sliding seals 10 and being slidable in the cylinder 7, the piston dividing the cylinder into two chambers 11,12. The piston ~
has an inner axially extending cylindrical extension 13 which surrounds and retains a steel insert 14 engageable with a push rod 15. The rod 15 extends sealingly through a wa]l 16 formed by the housing part 3B into engagement with the diaphragm --
3 4.
~0~3~003 One chamber 11 contains a coil compression spring 17, shown in its compressed, i.e. brake-off condition, and the other chamber 12 is normally pressurised by fluid, usually air, to hold the piston off against the spring bias.
The spring chamber 11 is closed by a removable plug 18 having a one-way valve 19 which permits the flow of air therethrough from within chamber 11 to the atmosphere.
Also contained within the chamber 11 is an expansible annular envelope 21 which contains air. The pressure of air in the envelope, and thus in the chamber 11, when the envelope is in its illustrated fully compressed state is in excess of atmospheric pressure. The excess pressure is relatively small.
In operation of the emergency brake part 1, release f pressure from the chamber 12 allows the spring 17 to expand and urge the piston 9 and rod 15 in a direction to apply the brake. Ambient air cannot pass through valve 19, but the envelope 21 expands to prevent a substantial vacuum being created in chamber 11. Re-application of pressure in chamber 12 returns the spring 17 and envelope 21 to their illustrated positions.
Should air leak past the piston seal 10 it will be exhausted through the valve 19.
The actuator of Figure 2 is similar to that of Figure 1, and operates in the same way. The main differences are that the spring 17 is contained within the envelope 21 to further protect the spring from corrosion and that the housing part 3B is attached in a different way to cylinder 7. In this case the open end 7A of cylinder 7 is rolled over an enlarged peripheral portion 3C of housing part 3B to secure , -- 5 " - . ,1.
. . .
lo~æo~3 the housing 3 to the cylinder 7.
The retraction or release tool of Figure 3 enables the brakes to be released in the event of release of pressure from chamber 12 due to a failure in the pressure line. The tool has a screw portion 22 which can fit in a cbmplementary threaded recess 23 in the steel insert 14. The screw portion 22 carries a flanged nut 24.
To release the brake, the plug 18 is removed and the screw portion 22 is screwed with recess 23 by means of a square headed portion 25 and the nut 24 rotated until it engages the end wall of the cylinder 7. Further rotation of the nut retracts the piston 9 against the bias of the spring 17 to release the brake.
The above-described actuators have the advantages that:
a) the one-way valve 19 prevents the ingress of corrosive atmospheric moisture so that the life of the spring 17 is prolonged, b) the pressurised envelope 21 reduces or obviates the vacuum which would otherwise be created in the spring chamber 11 during actuation of the emergency brake part 1, c) the form of construction used provides a light-weight actuator which makes mounting on the vehicle easier, d) the attachment of the housing 3B to the cylinder 7 is such that it can only be readily released for service in the factory and not in a maintenance garage so that the risk of injury to relatively unskilled personnel by the expansion of the spring is reduced and the possibility of the :: replacement of actuator parts by parts of inferior quality is also reduced, and ' : ' ' : ' . " :
, ~0~3003 e) the actuator can be designed to replace existing actuators.
It will be appreciated that the envelope 21 may be of any suitable configuration.
~0~3~003 One chamber 11 contains a coil compression spring 17, shown in its compressed, i.e. brake-off condition, and the other chamber 12 is normally pressurised by fluid, usually air, to hold the piston off against the spring bias.
The spring chamber 11 is closed by a removable plug 18 having a one-way valve 19 which permits the flow of air therethrough from within chamber 11 to the atmosphere.
Also contained within the chamber 11 is an expansible annular envelope 21 which contains air. The pressure of air in the envelope, and thus in the chamber 11, when the envelope is in its illustrated fully compressed state is in excess of atmospheric pressure. The excess pressure is relatively small.
In operation of the emergency brake part 1, release f pressure from the chamber 12 allows the spring 17 to expand and urge the piston 9 and rod 15 in a direction to apply the brake. Ambient air cannot pass through valve 19, but the envelope 21 expands to prevent a substantial vacuum being created in chamber 11. Re-application of pressure in chamber 12 returns the spring 17 and envelope 21 to their illustrated positions.
Should air leak past the piston seal 10 it will be exhausted through the valve 19.
The actuator of Figure 2 is similar to that of Figure 1, and operates in the same way. The main differences are that the spring 17 is contained within the envelope 21 to further protect the spring from corrosion and that the housing part 3B is attached in a different way to cylinder 7. In this case the open end 7A of cylinder 7 is rolled over an enlarged peripheral portion 3C of housing part 3B to secure , -- 5 " - . ,1.
. . .
lo~æo~3 the housing 3 to the cylinder 7.
The retraction or release tool of Figure 3 enables the brakes to be released in the event of release of pressure from chamber 12 due to a failure in the pressure line. The tool has a screw portion 22 which can fit in a cbmplementary threaded recess 23 in the steel insert 14. The screw portion 22 carries a flanged nut 24.
To release the brake, the plug 18 is removed and the screw portion 22 is screwed with recess 23 by means of a square headed portion 25 and the nut 24 rotated until it engages the end wall of the cylinder 7. Further rotation of the nut retracts the piston 9 against the bias of the spring 17 to release the brake.
The above-described actuators have the advantages that:
a) the one-way valve 19 prevents the ingress of corrosive atmospheric moisture so that the life of the spring 17 is prolonged, b) the pressurised envelope 21 reduces or obviates the vacuum which would otherwise be created in the spring chamber 11 during actuation of the emergency brake part 1, c) the form of construction used provides a light-weight actuator which makes mounting on the vehicle easier, d) the attachment of the housing 3B to the cylinder 7 is such that it can only be readily released for service in the factory and not in a maintenance garage so that the risk of injury to relatively unskilled personnel by the expansion of the spring is reduced and the possibility of the :: replacement of actuator parts by parts of inferior quality is also reduced, and ' : ' ' : ' . " :
, ~0~3003 e) the actuator can be designed to replace existing actuators.
It will be appreciated that the envelope 21 may be of any suitable configuration.
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An actuator for a vehicle wheel brake, comprising a cylinder divided by a movable pressure operable member into two separate chambers, and resilient means located in one of the chambers and arranged to bias said pressure operable member, wherein a one-way valve is provided which permits the flow of air from within said one chamber to the exterior thereof, but prevents the flow of air into the one chamber through the valve, said one chamber being normally sealed except for said one-way valve.
2. An actuator according to claim 1, wherein the one-way valve is set so that the pressure in said one chamber is greater than atmospheric pressure when said one chamber has its smallest volume.
3. An actuator according to claim 2, wherein an envelope containing a predetermined mass of gas is located in said one chamber, the pressure of gas in said envelope being greater than atmospheric pressure when said one chamber has its smallest volume.
4. An actuator according to claim 2 or 3, wherein a substantial vacuum is prevented from being created in said one chamber when said one chamber has its greatest volume.
5. An actuator according to claim 3, wherein said resilient means is located within said envelope.
6. An actuator for a vehicle wheel brake comprising a cylinder divided by a movable pressure operable member into two separate chambers, resilient means located in one of the chambers and arranged to bias said pressure operable member in a direction to apply the brake, said other chamber being adapted to receive fluid pressure which at a predetermined level operates against said pressure operable member to compress said resilient means and prevent the same from applying said brake so long as the pressure in said other chamber exceeds said predetermined level, a one-way valve permitting the flow of air from within said one chamber to the atmosphere while preventing the flow of air into said one chamber through the valve, said valve being set such that air can flow to atmosphere only after a predetermined minimum threshold pressure has been reached in the one chamber whereby the pressure in said one chamber is greater than atmospheric pressure when said chamber has its smallest volume, said one chamber being normally sealed except for said one-way valve, an expansible envelope in said one chamber containing a predetermined mass of gas which is com-pressed and the volume of the envelope thereby decreased by the greater than atmospheric pressure of the air in said one chamber when the volume thereof is at its smallest, the volume of the envelope being expanded by the gas therein to prevent a substantial vacuum being created in said one chamber when said resilient means moves said pressure operable member in a brake applying direction upon decrease of pres-sure in said other chamber.
7. The actuator according to claim 6 wherein said resilient means comprises a coil compression spring and said envelope is annular and concentrically located with respect to the axis of said spring.
8. The actuator according to claim 7 wherein said annular envelope is located within the coils of said spring.
9. The actuator according to claim 6 wherein said resilient means is located within said envelope.
10. The actuator according to claim 7 wherein said coil spring is located within said envelope.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB26174/77 | 1977-06-22 | ||
| GB2617477 | 1977-06-22 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1088003A true CA1088003A (en) | 1980-10-21 |
Family
ID=10239508
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA305,797A Expired CA1088003A (en) | 1977-06-22 | 1978-06-20 | Vehicle brake actuators |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1088003A (en) |
-
1978
- 1978-06-20 CA CA305,797A patent/CA1088003A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |