GB2253018A - Vacuum-operated brake servo - Google Patents
Vacuum-operated brake servo Download PDFInfo
- Publication number
- GB2253018A GB2253018A GB9126807A GB9126807A GB2253018A GB 2253018 A GB2253018 A GB 2253018A GB 9126807 A GB9126807 A GB 9126807A GB 9126807 A GB9126807 A GB 9126807A GB 2253018 A GB2253018 A GB 2253018A
- Authority
- GB
- United Kingdom
- Prior art keywords
- key
- valve
- plunger
- valve housing
- casing
- 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.)
- Withdrawn
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
- B60T13/00—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems
- B60T13/10—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release
- B60T13/24—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release the fluid being gaseous
- B60T13/46—Vacuum systems
- B60T13/52—Vacuum systems indirect, i.e. vacuum booster units
- B60T13/57—Vacuum systems indirect, i.e. vacuum booster units characterised by constructional features of control valves
Landscapes
- Engineering & Computer Science (AREA)
- Transportation (AREA)
- Mechanical Engineering (AREA)
- Braking Systems And Boosters (AREA)
Abstract
A vacuum servo for a vehicle braking system has a valve housing (15) with a control valve member (40) therein to control the pressure differential within the servo. A co axial plunger (41) is mounted in the centre of the valve housing (15) for operation of the valve member (40). The plunger is retained in the valve housing by a valve key (52) comprising a pair of resilient legs (57) each having a detent (55) that engages the plunger, and a pair of arquate arms (56) that encircle the valve housing. The key (52) is made as a single component and may have bump stops (158) to engage the booster housing in an at rest condition. <IMAGE>
Description
DIRECT ACTING VACUUM SERVO
The present invention relates to a vacuum servo of the type used to operate power assisted brakes.
In a typical direct acting vacuum servo, a piston is slidingly mounted within a casing, the piston being sealed to the wall of the casing by means of a diaphragm to divide the casing into a pair of fluid tight chambers. One chamber provides a reservoir which is connected to vacuum and the other provides a working chamber which may be connected to the reservoir or to atmosphere. The working chamber is interconnected with said reservoir via a first annular valve seat. A plunger is mounted on an input rod coaxially of the first valve seat and defines a second annular valve seat via which the working chamber may be connected to atmosphere.
The plunger is secured in position relative to the piston by a valve key which allows the plunger limited axial movement relative to the valve seats. A valve member is mounted coaxially of the first and second valve seats and is urged axially towards said seats by spring means. The axial movement of the plunger controls the operation oe the valve member. An output rod is mounted coaxially of the input rod and acts against one face of a rubber disc, the piston and plunger acting against the other face of the rubber disc.
The output rod extends into engagement with the piston of the master cylinder of the brake system.
In use when the brakes are released and the servo is in an "at balance" situation with vacuum in the first chamber both the first seat and the second seat are in engagement with the valve ember closing both valve seats. The working chamber is consequently closed to both the reservoir and the atmosphere so that there will be a slight pressure differential across the piston. Further movement of the input rod and plunger towards the piston will then open the second seat connecting the working chamber to atmosphere. A pressure differential will then be established across the piston thus producing a force which acts through the rubber disc and on to the output rod. The piston and valve assembly will then move to actuate the master cylinder and apply the brakes.When the vacuum servo reaches equilibrium, movement of the piston relative to the plunger will allow the valve member to close the second valve seat, thereby restricting the pressure differential across the piston, so that the servo effect thereof will be proportional to the load applied by the brake actuator.
The valve key which retains the plunger in the valve housing of the piston may also act as an abutment to limit the movement of the piston and plunger relative to each other and to the servo motor housing.
There are many designs of valve key for this purpose, one example is shown in Cfl A 2955 778, or GE A 2162 268. Such keys are of a relatively complicated construction.
The present invention relates to a servo or booster housing a key of a simple construction.
According to the invention.there is provided a vacuum servo comprising a casing, a piston slideably located in the casing, a valve housing fixed coaxially on the piston and extending sealingly through an end wall of the casing, the casing being divided into two chambers by means of a diaphragm supported on the piston, valve means disposed in the valve housing to control the pressure differential between the two chambers the valve means including a first annular valve seat on the valve housing via which the two chambers are: interconnected, a coaxial plunger mounted in the valve housing and having a second annular seat thereon by which one of the chambers is connected to atmosphere, and a coaxial valve member which is biased towards the two seats by spring means, the plunger being retained in the valve housing by a valve key passing transversely through the housing to engage the plunger to permit limited axial movement of the plunger relative to the valve housing, wherein the valve key comprises a pair of spaced substantially diametral resilient legs each having a detent thereon to resiliently engage the plunger, and a pair of arcuate arms, extending away from each other around the exterior of the valve housing, the legs and arms being an integral unit.
Preferably the key is a sheet steel pressing preferably from mild steel which has been treated by nitro carburizing. An cml)odiment of the invention is now described, by way of example only, with reforence to the accompanying drawings in which::- Figure 1 shows a sectional elevation of a direct acting vacuum servo formed in accordance with the present invention; Figure 2 shows n . plan view of the valve key being used i.n Fi.g 1; Figure 3 is n side elevation of the valve key shown in
Fig 2;
Figure 4 and Figure 5 are a plan view and side elevation respectively of a second booster valve key according to the invention;
Figure 6 is a section through a valve housing showing the valve key of Figures 4 and 5 in use; and
Figure 7 and Figure 8 are a plan view and side elevation of yet another booster valve key also according to the invention.
The direct acting vacuum servo 10 illustrated in Figure 1 has a casing 11 formed from two pressings 12 and 13 which are clamped together in known manner. A piston 14 is located within the casing 11, the piston 14 having a tubular extension 15 which extends through an aperture 27 in the end wall defined by pressing 13. The tubular extension 15 defining a valve housing in which a control valve member 4 is located. The tubular extension 15 or valve housing, is slidingly sealed through the aperture 27 by means of a seal 16 which is located against a shoulder 28 adjacent the aperture 27 by a clip 29.
An elastomeric diaphragm lo is located by an inner peripheral bead 17 to the piston 14, the bead 17 being clamped between the piston 14 and a flange formation 18 on the valve housing 15. An outer peripheral bead 19 of the diaphragm 210 is clamped between the pressings 12 and 13 to provide a seal therebetween and to divide the casing 11 into two fluid tight chambers 23 and 24. Chamber 23 is connected via an outlet (not shown) to a source of vacuum, for example the inlet manifold of an internal combustion engine.
The valve housing 15 is formed integrally with the central portion of the piston 14 but could be a separate component which is assembled to the piston 14. The valve housing 15 has a coaxial outer tubular housing 25 that extends from the piston 14 through the end wall of the casing 11 as previously described.
The valve housing 15 has an annular valve seat 26 hereinafter called a "vacuum seat" which is spaced radially inside the internal cylindrical surface of the tubular housing 25 to define an annular recess therebetween which is connected to chamber 23 by means of a pair of diametrically opposed passages 37.
A coaxial plunger 41 is mounted in sliding relationship within the central bore of the valve housing 15. The plunger 41 is mounted on an input rod 42 by means of a ball and socket joint by which it is staked thereto. The input rod 42 is coaxial with the tubular housing 25 and is connected to the brake actuating pedal (not shown). A valve spring 43 acts between a retaining cap 44 seated on the tubular housing 25 and a circlip 45 on input rod 42 to urge the input rod 42 and plunger 41 mounted thereon towards the end wall of casing 11 defined hy pressing 13.
The plunger 41 defines a further annular valve seat 46 hereinafter called an "air seat" which is concentric of seat 26 but is spaced radially inwardly thereof, so that an annular gap 47 is provided between the plunger 41 and valve housing 15.
A diametrically extending slot 51 extends through the valve housing 15, intermediate of the passages 27, and a valve key 52 extends through the slot 51 and engages the plunger 41.
Radial passageways 53 which open into the slot 51 serve to interconnect the centre of the tubular housing 25 to the chamber 24.
The key 52 comprises a pair of spaced apart substantially diametrical legs 54 with a detent 55 thereon that engages in a circumferential groove 59 in the plunger 41. The legs 54 have sufficient resilience to move apart when engaging the plunger and can spring together to retain the plunger in the detent 55. A pair of arcuate arms 56 extend away from each other around an external surface of the valve housing 25.
It can be seen that the legs 54 extend further across the imaginery circle of the key than the arms 56.
The arcuate arms 56 have rubber stops 57 thereof that can abut the casing 13. The key 52 is formed as an integral unit with the legs and arms being formed as a single body preferably from a heat treated mild steel, whose surface is treated by nitro carburzing to give the key sufficient resilience. An axial clearance is provided between the key 52 and slot 51 in order to provide for limited axial movement between the plunger 41 and valve housing 15.
The control valve member 4 is a cup-shaped valve trapped at its outer periphery 6 between the tubular housing 25 and the retaining cap 44 and having its base portion G connected to said outer periphery by a flexible sidewall 62.
The input rod 42 passes through a coaxial hole it the base portion of the valve member 4 which is biased towards the vacuum seat 26 by a spring means 63 acting between the retaining cup 44 and the base portion 61 of valve member 4.
An open pored sponge filter element 64 is provided at the end of the tubular housing 25, and the filter element 64 and housing 25 are covered by a rubber bellows 65 which engages between the input rod 42 and casing 11. Apertures are provided in the input rod end of the hallows to permit air to enter the housing 25 through filter element 64.
An output rod 66 extends coaxially of the input rod 42, through an aperture 67 in the end wall of casing 11, and engages the piston (not shown) of a brake master cylinder.
The casing 11 is secured to the brake master cylinder in a manner which seals the aperture 67.
The end of the output rod 6G adjacent piston 14 has a flanged head thereon 69 , which define a central circular recess in which is located a rubber disc 7g. The other face of the disc 69 remote from the output rod 66 is abutted by the end face of plunger 41 and a surrounding central annular portion 3 of the valve housing 15 which also engages in the circular recess. A return spring 71 acts between the end of the casing 11 defined by pressing 12. and the piston 14 to urge the piston 14 towards the other end wall of the casing.
Initially and without vacuum the return spring 71 will urge the piston 14 and plunger Q respectively rightwards (as illustrated in Pig 1) towards the end wall of casing 11 defined by pressing 12, where the return spring load 71 is reacted by key 52 aqainst the casing. Spring 43 also reacts a load on the: input rod 42 and pushes leftwards on the valve housing 15. Since the return spring 71 is a stronger spring than the spring 43, the valve housing 15 is urged rightwards to engage with the key 52 whilst the key 52 abuts the pressing 13 to limit the movement oE the plunger 41. In this condition the vacuum sea' Zi6 will be closed by the valve member 4 while the air seat 9G will be open.The chamber 24 will consequently be connected to atmosphere via passageways 53 and 51 past the air seat 46 through the base of the valve member 4 and the tubular housing 25.
Upon establishment or vacuum in chamber 23 the pressure differential across piston 14 will balance the load applied by spring 71, and any master cylinder return springs. The key 52 remains against the casing 11 holding the plunger 41 stationery. The axial clearance in the slot 51 in the valve housing 15 relative to the key 52 allows the valve housing 15 to move leftwards relative to the key 52, and it carries the valve member 4(3 leftwards locating it against the air seat 46 sealing the chamber 24 from the atmosphere.
This has the effect of halting the valve housing movement and sets the servo in a balanced condition with a minimised amount of lost travel in the input mechanism with the valve member 4 closing both the air seat 46 and the vacuum seat 26.
Upon actuation of the brakes, leEtwards movement of the input rod 42 will first move plunger 4 to reopen the air seat 46, connecting chamber 24 to atmosphere. A pressure differential is thus established across the piston 14. The forces applied directly by the input rod 42 and that generated by the pressure differential across the piston 14 are then transmitted to the output rod 66 via the rubber disc 69. The rubber disc 69 is totally enclosed are the forces transmitted thereby from the input rod 42 and piston 14 will be in proportion to the areas of the rubber disc 69 engaged by the plunger 41 and the annular portion 28 of the valve housing 15 respectively. At equilibrium, the piston 14 will move leftwards relative to the plunger 41, so that the air seat 46 will again be closed by valve member 4(3. At this point any further output load required can only be generated by a greater input load until the maximum pressure differential is generated across the piston 14, and thereafter no further booster assistance is available.
Upon release of the brakes, input rod 41 will move back moving plunger 41 rightwards. Engagement of the valve member 4(3 by the air seat 46 will also cause the valve member 4(3 to move, opening vacuum seat 26 joining the two chambers 23 and 24 so that the pressure differential across the piston 1.4 can be reduced. The return spring 71 will then move the piston 14 back rightwards until the key 52 again engages the casing 11. The axial clearance in the slot 51 relative to the key 52 allows the valve housing 15 to move rightwards until the vacuum seat 26 seals aqainst the valve member 4(3 and the servo is in balance. The output rod and the piston oE the master cylinder will move with servo piston 17 to release the brakes.
With reference to Figures 4 and 6, there is illustrated a brake booster or servo having a second form of booster key.
The same reference numbers will be used for those components that are substantially the same as components described with reference to the embodiment of Figures 1 and 3.
As before the key 52 comprises a pair of resilient diametral legs 54 with a detent 55 that engages the grooves 59 in the plunger 41.
The arms 56 of the key 52 extend around the external surface of valve housing 25 hut in this case the ends of the arms 56 are in alignment on a chord with the end of the legs 54. The rubber bump stops 157, 158 on the arms 56, are of different height, the bump stops 157 near the root of the legs 54 being smaller than the bump stop 158 at the end of the arms 56 on the other side of the centre iine of the key.
In use this causes the key 52 to tip when at rcst on the casing 13 when the booster is in an 'at rest' condition with the spring 71 pushing the piston and valve housing 25 back towards the casing 13.
Figure 7 and Figure 8 illustrate another embodiment of the key in which the rubber bump stops 257, 258 are provided on both axial sides of the key. The single cen-tral bump stop 257 at the root of the legs 54 has a smaller height than the bump stops 258 at the end of the arms 56. This Icey is completely symmetrical and can be used either way around.
Claims (8)
1. A vacuum servo comprising a casing, a piston slideably
located in the casing, a valve housing fixed coaxially
on the piston and extending sealingly through an
endwall of the casing, the casing being divided into
two chambers by means of a diaphragm supported on the
piston, valve means dispose in the valve housing to
control the pressure differential between the two
chambers the valve means including a first annular
valve seat on the valve housing via which the two
chambers are interconnected, a coaxial plunger mounted
in the valve housing and having a second annular valve
seat thereon by which one oE the chambers is connected
to atmosphere, and a coaxial valve member which is
hiased towards the two seats by spring means, the
plunger being retained in the valve housing by a valve
key passing transversely through the valve housing to
engage the plunger to permit limited axial movement of
the plunger relative to the housing, wherein the valve
key comprises a pair of spaced substantially diametral
resilient legs each having a detent thereon to
resiliently engage the plunger, and a pair of arcuate
arms extending away from each other around the exterior
of the valve housing, the legs and arms being an integral
unit.
2. A vacuum servo as claimed in Claim 1 wherein the
key is formed from a single sheet metal pressing.
3. A vacuum servo as claimed in Claim 1 or Claim 2
wherein the key is formed from n heat treated mild
steel, whose surface has been treated by
nitrocarburizing.
4. A vacuum servo as claimed in any ttse of Claims 1
to 3 wherein the key has elastomeric stops thereon
to cushion the abutment of the key against the
casing.
5. A vacuum servo is examined in Claim 4 wherein key
has elastomeric stops thereon of different heights
on opposite side of a centre line of the key.
6. A vacuum servo as claimed in Claim 4 or Claim 5
wherein the key has at least one smaller height
hump stop adjacent the root portion of the legs and a
higher bump stop at the end of each arm.
7. A vacuum servo as claimed in Claims 4, 5 or 6
wherein the bump stops are located on the arms
of the key.
8. A vacuum servo as claimed in any one of claims 4
to 7, wherein the key has bump stops on each axial
side of the key.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB919103468A GB9103468D0 (en) | 1991-02-19 | 1991-02-19 | Direct acting vacuum servo |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9126807D0 GB9126807D0 (en) | 1992-02-19 |
| GB2253018A true GB2253018A (en) | 1992-08-26 |
Family
ID=10690237
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB919103468A Pending GB9103468D0 (en) | 1991-02-19 | 1991-02-19 | Direct acting vacuum servo |
| GB9126807A Withdrawn GB2253018A (en) | 1991-02-19 | 1991-12-18 | Vacuum-operated brake servo |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB919103468A Pending GB9103468D0 (en) | 1991-02-19 | 1991-02-19 | Direct acting vacuum servo |
Country Status (1)
| Country | Link |
|---|---|
| GB (2) | GB9103468D0 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE10049106A1 (en) * | 2000-10-04 | 2002-04-18 | Lucas Varity Gmbh | Pneumatic brake force intensifier with variable power transmission ratio has inner piston with outer peripheral groove to accommodate material particles |
| DE10203411A1 (en) * | 2002-01-28 | 2003-07-31 | Continental Teves Ag & Co Ohg | Vacuum powered brake booster |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2065809A (en) * | 1979-12-14 | 1981-07-01 | Tokico Ltd | Pneumatic servo booster |
| EP0174229A1 (en) * | 1984-08-16 | 1986-03-12 | BENDIX France | Abutment key for a brake servo booster plunger valve, and a brake servo booster comprising such a key |
| US4951550A (en) * | 1987-10-30 | 1990-08-28 | Jidosha Kiki Co., Ltd. | Brake booster with key member having an elastic member |
-
1991
- 1991-02-19 GB GB919103468A patent/GB9103468D0/en active Pending
- 1991-12-18 GB GB9126807A patent/GB2253018A/en not_active Withdrawn
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2065809A (en) * | 1979-12-14 | 1981-07-01 | Tokico Ltd | Pneumatic servo booster |
| EP0174229A1 (en) * | 1984-08-16 | 1986-03-12 | BENDIX France | Abutment key for a brake servo booster plunger valve, and a brake servo booster comprising such a key |
| US4951550A (en) * | 1987-10-30 | 1990-08-28 | Jidosha Kiki Co., Ltd. | Brake booster with key member having an elastic member |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE10049106A1 (en) * | 2000-10-04 | 2002-04-18 | Lucas Varity Gmbh | Pneumatic brake force intensifier with variable power transmission ratio has inner piston with outer peripheral groove to accommodate material particles |
| US6739234B2 (en) | 2000-10-04 | 2004-05-25 | Lucas Automotive Gmbh | Pneumatic brake booster with variable force transmission ratio |
| DE10049106B4 (en) * | 2000-10-04 | 2006-05-18 | Lucas Varity Gmbh | Pneumatic brake booster with variable force transmission ratio |
| DE10203411A1 (en) * | 2002-01-28 | 2003-07-31 | Continental Teves Ag & Co Ohg | Vacuum powered brake booster |
| US7032497B2 (en) | 2002-01-28 | 2006-04-25 | Continental Teves Ag & Co. Ohg | Vacuum brake booster |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9103468D0 (en) | 1991-04-03 |
| GB9126807D0 (en) | 1992-02-19 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |