GB2206168A

GB2206168A - Brake booster of the tandem type

Info

Publication number: GB2206168A
Application number: GB08818317A
Authority: GB
Inventors: Kohei Mori; Haruo Suzuki
Original assignee: Jidosha Kiki Co Ltd
Current assignee: Jidosha Kiki Co Ltd
Priority date: 1985-06-17
Filing date: 1988-08-02
Publication date: 1988-12-29
Also published as: GB8818317D0; GB2206168B

Description

BRAKE BOOSTER OF TANDEM TYPE The invention relates to a brake booster of tandem type, and in particular, to the positioning of various members which secures passages between individual pressure chambers.

A brake booster of tandem type known in the prior art has a construction including a pair of power pistons which are disposed within and serve as partitions in an enclosed shell, a valve body internally housing a valve mechanism, and a center body having a path formed therein which communicates with a passage within the valve body, all of which are integrally connected together by being held between a hub which extends through axial portions of these members and a nut which is threadably engaged with the hub.

In conventional construction of tandem brake booster, the peripheral surface of the hub and an opening formed in the front power piston through which the hub extends are both formed in polygonal shape such as hexagonal shape for engagement therebetween.

When the outer surface of the hub and the opening in the front power piston are hexagonal in configuration, it is possible to achieve an engagement between the piston and the hub at an angular position which is angularly displaced 600 from its design position. Accordingly, before these members are connected together, it is necessary that their positions be confirmed so that a path formed in the pistor communicates with a path formed in the center body.

Therefore, it is an object of the invention to provide a brake booster of tandem type which simplifies the assembly without the likelihood of a wrong assembly, thus assuring the establishment of fluid passage.

The above object is accomplished in accordance with the invention by providing a projection either on the peripheral surface of the hub or in the opening of the piston through which the hub extends and providing a recess matable with the projection in the other of these members.

Fig. 1 is a longitudinal section of essential part of a brake booster according to one embodiment of the invention; Fig. 2 shows a valve body, specifically, Fig. 2(A) being a front view, Fig. 2(B) a longitudinal section, and Fig. 2(C) a rear view of the valve body; Fig. 3 shows a center body, specifically, Fig. 3(A) being a front view, Fig. 3(B) a cross section taken along the line B-B shown in Fig. 3(C) and Fig. 3(C) a rear the center body; Fig. 4 shows a hub, specifically, Fig. 4(A) being a longitudinal section and Fig. 4(B) a rear view of the hub; Fig. 5 shows a retainer for the front power piston, specifically, Fig. 5(A) being a longitudinal section and Fig. 5(B) a rear view of the retainer; Fig. 6 shows a nut, specifically, Fig. 6(A) being a front view and Fig. 6(B) being a longitudinal section of the nut; and Fig. 7 shows a rear power piston, specifically, Fig.

7(A) being a longitudinal section and Fig. 7(B) being a rear view of the rear power piston.

Referring to the drawings, an embodiment of the invention will now be described. Fig. 1 is a longitudinal section of essential part of a brake booster of tandem type according to one embodiment of the invention. Specifically, a combination of a front shell 2 and a rear shell 4 defines an enclosed shell 6, in which a front power piston 8 and a rear power piston 10 are disposed in tandem configuration A center plate 12 divides the interior of the enclosed shell 6 into a front chamber in which the front power piston 8 is disposed and a rear chamber in which the rear power piston 10 is disposed. In addition, a front diaphragm 14 secured to the back surface of the front power piston 8 divides the front chamber into a pair of pressure chambers A and B while a rear diaphragm 16 secured to the back surface of the rear power piston 10 divides the rear chamber into pressure chambers C and D.

A valve body 18 is disposed in alignment with the axis of the enclosed shell 6, and includes a cylindrical portion 18a and a portion 18b of an increased diameter which integrally extends from the cylindrical portion. An annular groove 18c is formed in the front end face of the valve body 18, and the edge of the rear diaphragm 16 at its inner periphery is fitted into the groove 18c. A cylindrical center body 20 is connected to the front face of the valve body 18, and the inner peripheral edges of the rear power piston 10 and the rear diaphragm 16 are held between the center body 20 and the valve body 18.

The front power piston 8 comprises an annular piston plate 22, and acylindrical retainer 24 having a flange 24a which is secured to the inner periphery of the piston plate 22. The retainer 24 has a cylindrical portion 24b which is fitted inside the center body 20. The outer peripheral surface of the center body 20 is fitted inside the inner periphery 12a of the center plate 12 so as to be slidable relative thereto while maintaining a hermetic seal therebetween.

A hub 26 h.aving a portion 26a of an increased diameter and another portion 26b of a reduced diameter extends through the valve body 18, the center body 20 and the retainer 24 of the front power piston 8 along the axes thereof. At its free end, the portion 26b of the hub 26 is formed with an arcuate projection 26c which may be engaged with a recess formed in the valve body 18 to prevent its disengagement once it has been inserted into the valve body 18, as will be further described later. In addition, the end of the portion 26a of the hub is formed with male threads 26d which are threadably engaged witha nut 28, thus integrally connecting the valve body 18, the center body 20 and both the front and the rear power piston 8, 10 together.

The portion 26b of the hub 26 receives a valve plunger 32 which is staked to a spherical ball 30a at the free end of an input shaft 30 which is mechanically coupled to a brake pedal, not shown. On the other hand, the portion 26a of the hub 26 has the free end 34a of an output shaft 34 fitted therein, and a reaction disc 36 is interposed between the end face 34b of the output shaft 34 and a step 26h which is defined between the portions of different diameters of the hub 26. Accordingly, when the booster is operated, a brake reaction is transmitted to the brake pedal through the output shaft 34, the reaction disc 36, the valve plunger 32 and the input shaft 30. A key 38 extends through openings formed in the valve body 18 and the hub 26 to lock the valve plunger 32 against disengagement.A return spring 40 is disposed between the internal surface of the front shell 2 and the spring abutment 28a formed on the nut 28 for normally urging the front and the rear power piston 8, 10 to their inoperative positions shown.

Figs. 2 to 7 show the detail of the valve body 18, the center body 20, the retainer 24, the hub 26, the nut 28 and the rear power piston 10, respectively, and a construction for connecting these members 18, 20, 24, 26, 28 and 10 together and passages which provide a communication between the pressure chambers A, B, C and D will now be described.

Referring to Figs. 2(A), (B) and (C), the valve body 18 comprises a passage 18d which extends from the front end face of the portion 18b having an increased diameter into the inside of the cylindrical portion 18a, and a radially extending passage 18e formed in the cylindrical portion 18a at an angular position which is offset 1800 from the location of the passage 18d. An opening 18f is disposed to allow the key 38 to extend therethrough. A pair of elliptical openings 18g and a pair of elliptical passages 18j are formed in the portion 18b of an increased diameter at locations which are offset 900 from the locations of the both passages 18d and 18e.Part of the internal surface of the portion 18b of an increased diameter is formed with notches 18h which permit the pair of arcuate projections 26c formed on the portion 26b of the hub 26 to extend therethrough while the remainder of the internal surface is formed with recesses 18i which receive the arcuate projections 26c.

Referring to Figs. 3(A), (B) and (C), the center body 20 is formed with a pair of elliptical projections 20a which can be fitted into the elliptical openings 18g. These projections 20a are formed with openings which communicates with passages 20b axially extending through the cylindrical wall of the center body 20, thus providing a communication between the axial ends of the center body 20.In a region of the elliptical projections 20a, a pair of wider portions 20c which extend radially inward are disposed in surrounding relationship with the projections, and radially extending grooves 20d which provide a communication between the inside and the outside of the cylindrical center body 20 as well as a pair of axially extending passages 20e are formed between the pair of wider portions 20c or at locations which are 'offset 900 from the projections 20a. As shown in Figs 3(A) and (C), the axial passages 20e are notched into a sector configuration.

Referring to Figs. 4(A) and (B), the hub 26 which extends through the valve body 18 and the center body 20 includes a substantially hexagonal portion 26e which is located nearer the portion 26b of a reduced diameter than the threads 26d on the portion 26a of an increased diameter, and a pair of ears 26f are formed on two sides of the hexagonal configuration of the portion 26e which are located symmetrically to each other with respect to the axis.

Figs. 5(A) and (B) show the retainer 24'for the front power piston 8, including a cylindrical portion 24b of an outer diameter which is substantially equal to the internal diameter of the center body 20. The retainer has a bottom 24d in which an essentially hexagonal opening 24c (see phantom line shown in Fig. 5(A)) is formed. Notched paths 24e are formed in two adjacent sides as well as in other two sides which are located symmetrically with respect to the first mentioned sides of the opening 24c, and recesses 24f are formed in the two remaining sides of the opening at symmetrical positions for receiving the ears 26f on the hub 26.When the cylindrical portion 24b of the retainer 24 is fitted inside the center body 20 and is assembled in proper position, two adjacent.notched paths 24e communicate with one of the sector-shaped axial passages 20e formed in the center body 20.

Figs. 6(A) and (B) show the nut 28 which is threadably engaged with the male threads 26d on the hub 26.

The nut 28 comprises a cylindrical portion 26b on which the male threads are formed, and a tapered portion 28c having a gradually increasing diameter, with a number of communication holes 28d formed in the tapered portion 28c.

Figs. 7(A) and (B) show the rear power piston 10 including a pair of openings lOa which permits the elliptical projections 20a on the center body to extend therethrough, and a pair of passages lOb which can communicate with sector-shaped passages 20e.

In assembly, the rear power piston 10 and the rear diaphragm 16 which is carried thereon are disposed so as to be held sandwiched between the valve body 18 and the center body 20, and the elliptical projections 20a on the center body 20 are fitted into the openings lOa formed in the rear power piston 10 to extend there through into the elliptical openings 18g formed in the valve body 18. As a result, the passage 18d which extends from the increased diameter portion 18b into the cylindrical portion 18a of the valve body 18 communicates with the radially extending grooves 20d and the sector-shaped axial passages 20e formed in the center body 20 through the passage lOb formed in the rear power piston 10.The reduced diameter portion 26b of the hub 26 is then inserted into the center body 20 and the arcuate projections 26c on the hub 26 are moved into alignment with the notches 18h formed in the valve body 18, thus inserting the hub into the valve body 18. The hub 26 is then rotated through 900 so that the arcuate projections 26c are fitted into the recesses 18i formed in the valve body 18, thus locking the hub 26 against withdrawal from the valve body 18 and the center body 20. The retainer 24 for the front power piston 8 is then inserted into the center body 20 so that the hexagonal opening 24c formed in the bottom 24d thereof is fitted around the hexagonal portion 26e in the increased diameter portion 26a of the hub 26.It will be seen that since the hexagonal portion 26e of the hub 26 is formed with the pair of ears 26f while the opening 24c in the retainer 24 is formed with the pair of recesses 24e, the retainer cannot be fitted around the hub unless the ears 26f and the recesses 24e are aligned with each other. Thus it is assured that the ears 26f can be fitted into the recesses 24e only at a pair of relative positions thereof 0 which are displaced 180 from each other, whereupon the notched paths 24e in the retainer 24 are each in communication with the sector-shaped axial passages 20e formed in the center body 20. Subsequently, the nut 28 is threadably engaged with the threads 26d on the hub 26, thus integrally connecting the described members together.

When the brake booster is assembled in the manner mentioned above, the pressure chambers A and C are normally in communication with each other through the radially extending grooves 20d and the sector-shaped paths 20e both formed in the center body 20, the notched paths 24e in the retainer 24 and the communication holes 28d formed in the nuts 28 while the pressure chambers B and D are normally in communication, with each other through the passages 20b extending through the cylindrical wall of the center body 20, the openings within the elliptical projections 20a and the elliptical passages 18formed in the elliptical openings 18g of the increased diameter portion 18b of the valve body 18.In addition, the pressure chamber C communicates with the passage 18d which extends from the increased diameter portion 18b into the cylindrical portion 18a of the valve body 18 while the pressure chamber D communicates with the radial passages 18e formed in the valve body 18. A valve mechanism 42 including the described valve plunger 32 controls a communication among the passages 18d and 18e and the atmosphere.

In the described embodiment, the hub 26 and the retainer 24 have their portions which are adapted for mating engagement shaped to be hexagonal, but the hexagonal configuration of these parts are not essential. Instead of providing the ears 26f on the hub 26, the hub 26 may be formed with recesses while the retainer 24 may be formed with ears.

While the invention has been described above,in connection with the preferred embodiment thereof, it should be understood that a number of changes, modifications and substitutions will readily occur to one skilled in the art from the above disclosure without departing from the scope and spirit of the invention as defined by the appended claims.

Claims

CLAIMS:

1. A brake booster of tandem type including a valve body internally housing a valve mechanism which controls a communication between pressure chambers defined within a shell and a communication between the pressure chambers and the atmosphere, the valve body including passages which provide a communication between the pressure chambers, a center body connected to the valve body and formed with a passage which is adapted to be connected to the passage in the valve body, a combination of front and rear power pistons which define the pressure chambers within the shell and centrally formed with paths which are connected to the passages, and a hub which is disposed in alignment with the axes of the valve body, the center body and the front power piston and adapted to be threadably engaged with a nut to connect the valve body, the center body and the front power piston together in an integral manner; characterized in that at least one ear is formed on one of the outer peripheral surface of the hub and in an opening formed in the front power piston through which the hub extends while at least one recess is formed in the other of the outer peripheral surface of the hub and the opening in the front power piston for receiving the ear, thus allowing the hub and the front power piston to be positioned relative other, said threaded engagement being provided by a nut having flange or lip with an outside diameter slightly smaller than the internal diameter of a cylindrical portion of the front power piston, a radially inwardly directed portion on said cylindrical portion being sandwiched between said flange or lip and the center body.

2. A brake booster of tandem type according to claim 1 in which the outer peripheral surface of the hub is polygonal while the opening in the front power piston is also polygonal for fitting engagement with the outer peripheral surface of the hub.

3. A brake booster of tandem type according to claim 2 in which both the outer peripheral surface of the hub and the opening in the front power piston are hexagonal.

4. A brake booster of tandem type according to claim 3 in which the hub and the front power piston are provided with a pair of ears or recesses respectively, at symmetrical locations.

5. A brake booster of tandem type according to claim 4 in which the valve body is formed with a pair of axial passages at locations which are symmetrical with respect to the axis thereof.

6. A brake booster of tandem type according to claim 4 in which the center body is formed with a pair of axial passages and radial passages at locations which are symmetrical with respect to the axis thereof.

7. A brake booster of tandem type according to claim 4 in which the front power piston is formed with a pair of paths at locations which are symmetrical with respect to the axis thereof and which extends through the opposite surfaces thereof.

8. A brake booster of tandem type according to claim 4 in which the rear power piston is formed.with a pair of paths at locations which are symmetrical with respect to the axis thereof and which extends through the opposite surface thereof.

9. A brake booster of tandem type according to claim 1 in which at least one projection on the center body is fitted into an opening formed in the valve body to connect them together.

10. A brake booster of tandem type according to claim 9 in which two of the openings in the valve body and two of the projections on the center body are formed at locations which are symmetrical with .respect to the respective axes.

11. A brake booster of tandem type according to claim 9 in which the rear power piston is held between the valve body and the center body.

12. A brake booster of tandem type according to claim 11 in which the rear power piston is formed with an opening through which the projection on the center body extends.

13. A brake booster of tandem type according to claim 1 in which the front power piston includes a cylindrical portion which is fitted inside the center body.

14. A brake booster of tandem type according to claim 1 in which the front power piston comprises an annular piston plate, and a cylindrical retainer which is secured to the inner periphery of the piston plate.

15. A brake booster of tandem type according to claim 1 in which an arcuate projection formed on one end of the hub engages a recess formed in the internal surface of the valve body, the valve body, the center body and the front and the rear power piston being integrally connected together between the arcuate projection and a nut which is threadably engaged with the other end of the hub.

16. A brake booster of tandem type according to claim 15 in which two of the arcuate projections on the hub and two of the recesses in the internal surface of the valve body are disposed at locations which are symmetrical with respect to their respective axes.

17. A brake booster comprising tandem pressure chambers within an outer shell, a pair of power pistons being disposed within and serving as partitions in said shell, the booster having a valve body housing a valve mechanism, a center body comprising a passage connected to a passage in the valve body, a first of the power pistons providing a path or porting by which a pressure chamber associated therewith can communicate with said center body passage, and a hub projecting axially into the valve body, the center body and said first power piston adapted to be engaged by threaded securing means to connect the valve body, the center body and said first power piston together in an integral manner; location means being provided on an outer peripheral surface of the hub and a receiving opening in the first power piston through which the hub extends, said location means comprising at least one radial projection and co-operating recess engageable at only the position or positions of relative angular orientation at which there is communication between the center body passage and its associated path or porting of said first piston, said threaded engagement being provided by a nut having flange or lip with an outside diameter slightly smaller than the internal diameter of a cylindrical portion of the first power piston, a radially inwardly directed portion on said cylindrical portion being sandwiched between said flange or lip and the center body.

18. A brake booster constructed and arranged for use and operation substantially as described herein with reference to the accompanying drawings.