TANDEM BRAKE BOOSTER

Abstract: A tandem brake booster (50) has a housing (51), two front (67,75) constant and two rear (66,127) variable pressure chambers, a first (74) and a second (76) passage communicating both variable respectively constant pressure chambers, valve means (79) for generating a pressure difference, a cylindrical case (84) having small and large diameter portions, a reaction rubber disc (106), input (85) and output (108) push rods, a valve plunger (82) slidably inserted into the small diameter portion, a key member (88) for limiting the sliding amount of the valve plunger (82) and movably assembled into the case (84). The booster has first (100) and second (101) projections on a rear movable wall (58) and on an outer cir­ cumference of the small diameter portion, which are engaged and block the forward movement of the case (84), when the key member (88) is inserted into a hole of the rear movable wall (58), respectively of the case (84) with the rotation of the case (84) being limited, and the projections (100,101) being engaged and disengaged by rotating the case.(84)

Description: The present invention relates to a brake booster, and more particularly to a tandem brake booster. In a conventional tandem brake booster 10 which has been disclosed in a Japanese Utility Model Application (pub­ lication No. 58-106265), illustrated in Fig. 1, a first passage 11 for communication between first and second variable pressure chambers 12, 13 is formed by a hole 14 provided on a cylindrical hub 15 of a front movable wall 16 and by a hole 17 provided on a cylindrical hub 18 of a rear movable wall 19. A second passage 20 for communication between frist and second constant pressure chambers 21, 22 is formed by a hole 23 provided on a case 24 assembled within both cylindrical hubs 15, 18 and by recesses 25, 26 provided on the cylindrical hub 15. In this tandem brake booster 10, inner peripheral edge portions of each diaphragm 27, 28 at both movable walls 16, 19 are utilized as a seal member for both passages 11,20. Both movable walls 16, 19 are connected by the case 24 to each other and the forward actuating force operating to both movable walls 16, 19 is acted on an output push rod 29 through a reaction rubber disc 30 assembled within a stepped portion 31 of the case 24 and the reaction is acted on a valve plunger 32 slidably inserted into a small-diameter portion of the case through the reaction rubber disc 30. A valve mechanism 33 for generating the pressure difference between both constant pressure chambers 21, 22 and both variable pressure chambers 12, 13 by the valve plunger 32, a cylindrical valve 34 and a valve seat 35 provided on the cylindrical hub 18. The sliding amount of the valve plunger 32 to the cylindrical hub 18 is limited by a key 36 which is inserted into radial holes 37, 38 pro­ vided on the cylindrical hub 18 and on the case 24 and is engaged with a small diameter portion of the valve plunger 32 at a fork shaped inner end portion thereof. The forward and rearward measure of the radial holes 37, 38 is larger than the thickness of the key 36, so that the key 36 can be moved into the forward and rearward direction at a predetermined amount to the cylindrical hub 18 and the case 24. The key 36 is provided with a contacting portion 39 which is engageable with the housing 20. The contacting portion 39 of the key 36 is contacted with the housing 20 and the rearward movement of the valve plunger 32 to the housing 20 is stopped as shown in figure 1 which shows non-actuating state of the booster apparatus 10. And further the rearward movement of both movable walls 16, 19 is also stopped by the contact of a front wall of the radial hole 37 with a front face of the key 36. A rear end of the valve plunger 32 is contacted with the cylindrical valve 34 and cylin­ drical valve 34 is lifted from the valve seat 35 at a slight amount. The vacuum transmitted to both constant pressure chambers 21, 22 from a connector 40 mounted on the housing 20 is also transmitted to both variable pressure chambers 12, 13 through a hole 41 provided on the cylindrical hub 18, a clearance between the cylindrical valve 34 and the valve seat 35, and a hole 42 provided on the cylindrical hub 18, so that the pressure difference between constant pressure chambers 21, 22 and variable pressure chambers 12, 13 is eliminated. As above mentioned, the cylindrical valve 34 is just slightly lifted from the valve seat 35 at the non-actuating state. Therefore, a small forward stroke of an input push rod 43 is required for seating the cylindrical valve 34 on the valve seat 35 and releasing the rear end of the valve plunger 32 from the cylindrical valve 34 thereby to flow the atmosphere into both variable pressure chambers 12, 13 upon the actuating state. The required pressure difference between constant pressure chambers 21, 22 and variable pressure chambers 12, 13 is rapidly generated and the movable walls 16, 19 are also rapidly and forwardly moved. The contacting portion 39 of the key 36 is released from the housing 20 by the forward movement of the movable walls 16, 19 during the actuation, so that the valve plunger 32 is contacted with the key 36 by the release of the input push rod 43 and is then rearwardly moved with the key 36 to the cylindrical hub 18 until the rear face of the key 36 is contacted with a rear wall of the radial hole 37. Further, the rear end of the valve plunger 32 is contacted with the cylindrical valve 34 and the cylindrical valve 34 is lifted from the valve seat 35 at the large amount. Consequently, the atmosphere within variable pressure chambers 12, 13 quickly flows into constant pressure chambers 21, 22 and the pressure difference between constant pressure chambers 21, 22 and variable pressure chambers 12, 13 is rapidly decreased, and then movable walls 16, 19 are quickly and rearwardly moved. In the abovementioned booster apparatus, the case 24 is fixedly inserted into both cylindrical hubs 15, 18 and is prevented from missing by a clip 44 fixedly connected at the rear end thereof and is fixed by a nut 45 screwed at the top end thereof and integrally connects both cylindrical hubs 15, 18. Therefore, it becomes naturally increase of part number and assemblying pro­ cess, and of course expensive. An object of the present invention is to provide an im­ proved tandem brake booster which obviates the afore­ mentioned drawbacks of the described conventional tan­ dem brake booster. A further object of the present invention is to provide an improved tandem brake booster which has a high re­ liability in operation. A still further object of this invention is to provide an improved tandem brake booster which is relatively simple in construction and includes a minimum number of parts. According to the present invention, a tandem brake booster having a housing, a front and a rear movable walls installed within the housing, a partition wall interposed between the front and rear movable walls, two front constant pressure chambers of each movable wall and two rear variable pressure chambers of each movable wall divided by the front and rear movable walls and the partition wall, a first communicating passage communicating both variable pressure chambers, a second communicating passage communicating both con­ stant pressure chambers, valve means provided in the rear movable wall for generating the pressure difference between both constant pressure chambers and both vari­ able pressure chambers and forwardly moving both movable walls, a cylindrical case having small and large dia­ meter portions assembled within a hub portion of both movable walls, a reaction rubber disc assembled within a stepped portion of the case, input and output push rods, a valve plunger slidably inserted into the small diameter portion of the case and formed for the valve means and connected to the input push rod, a key member inserted into a radial hole of the rear movable wall and a radial hole of the case and engaged with the valve plunger for limiting the sliding amount of the valve plunger to the rear movable wall and movably assembled at a certain amount to the case into the forward and rearward direction, whereby the forward actuating force of both movable walls is acted on the output push rod via the case and the reaction rubber disc and its reaction is acted on the valve plunger via the reaction rubber disc, and the movable wall is further more rearwardly moved upon the rearward movement of both movable walls after a part of the key member is contacted with the housing and the rearward movement of the valve plunger to the housing is stopped, the tandem brake booster is characterized by that first and second projections pro­ vided on a circumferential surface of a hole of the rear movable wall and an outer circumference of the small diameter portion of the case respectively are engaged to each other and the forward movement of the case to the rear movable wall is blocked, when the key member is in­ serted into the hole of the rear movable wall and the hole of the case and the rotation of the case to the rear movable wall is limited, and the first and second projection is engaged and disengaged by rotating the case within the rear movable wall, when the key member is not inserted into the rear movable wall and the hole of the case. Accordingly, clips and nuts as in the conventional brake booster are not required, and the construction is rela­ tively simple and a minimum number of parts is required in the present invention. Various other features, objects and attendant advantages of the present invention will become selfevident when considered in connection with the accompanying drawings wherein: Figure 1 is a cross-sectional view which shows a con­ ventional tandem brake booster; Figure 2 is a view similar to Figure 1, but showing a preferred embodiment of a tandem brake booster according to the present invention; Figure 3 is a cross-sectional view taken along the line A-A in Figure 2; Figure 4 is a side view showing the case 84 of Figure 2; Figure 5 is a front view showing the case 84 of Figure 2; Figure 6 is a view similar to Figure 3, but showing the case 70 being assembled; and Figure 7 is a cross-sectional view taken along the line B-B in Figure 2. Referring now to Figure 2 which shows a preferred embodiment of a tandem brake booster 50 according to the present invention, reference numeral 51 denotes a housing which is provided with a front shell 52 and a rear shell 53 opposedly located each other and is air-tightly secured at both opposing end faces of shells 52, 53. The case 51 is divided into a front chamber 54 and a rear chamber 55 by a partition wall 56 located therein. A pair of movable walls 57, 58 are disposed within each chamber 54, 55. A reinforcement plate 59 is fixedly connected to a front surface of the inside of front shell 52 and a plurality of bolts 60 are fixed to the reinforcement plate 59. Each bolt 60 air-tightly penetrates the reinforcement plate 59 and the front shell 52 and forwardly projects for functioning as an attaching bolt of a master cylinder (not shown). A connector 61 connected to an intake manifold (not shown) of a vehicle engine is air-tightly attached to an upper portion of a front wall of the front shell 52. A plurality of bolts 62 are fixed to a rear wall of the rear shell 53. Each bolt 62 air-tightly penetrates the rear shell 53 and rearwardly projects for functioning as an attaching bolt on a vehicle body. The front movable wall 57 includes a hub member 63, an annular plate 64 and a diaphragm 65 and divides the front chamber 54 into a variable pressure chamber 66 and a constant pressure chamber 67. The hub member 63 is of a cylindrical shape and is provided with an outward flange 68 at a front end thereof and a bottom wall 69 at a rear end thereof. Further, the hub member 63 pene­ trates the partition wall 56 and extends into the rear chamber 55 and contacts with a hub member 70 of the rear movable wall 58. The plate 64 is welded to the outward flange 68 of the hub member 63. The diaphragm 65 is located at a rear face of the plate 64. An inner cir­ cumferential bead portion 71 is fixedly and air-tightly connected to a shoulder portion of the hub member 63, and an outer circumferential bead portion 125 is also fixedly and air-tightly connected between the front shell 52 and the partition wall 56. The rear movable wall 58 includes the hub member 70, an annular plate 126 and a diaphragm 73. The rear chamber 55 is divided into a variable pressure chamber 127 communicated to the front variable pressure chamber 66 by a first communicating passage 74 and a constant pressure chamber 75 communicated with the front constant pressure chamber 67 by a second communicating passage 76. The hub member 70 is projected to the outward of the housing 51 through a seal member 77 and a bush 78 and a valve mechanism 79 is installed therein. The plate 126 is air- tightly fixed to a stepped portion of the hub member 70 with an inner circumferential bead portion 80 of the diaphragm 73. The diaphragm 73 is located at a rear face of the plate 126 and an outer circumferential bead portion 81 is air-tightly connected between the rear shell 53 and the partition wall 56. The valve mechanism 79 operated for communicating the variable pressure chamber 127 with the constant pressure chamber 75 or the atmosphere and includes a valve plunger 82, a cylindrical valve 83 and etc. The valve plunger 82 is assembled into a case 84 with push rod 85 connected to the case 84. The push rod 85 is connected to a brake pedal (not shown). Further, a key 88 is inserted into a radial hole 86 of the hub member 70 and a radial hole 87 of the case 84 and an inner end of the key 88 is engaged with the valve plunger 82 for limiting leftward movement of the valve plunger 82 relative to the hub member 70. The cylindrical valve 83 is assembled within an inner hole 89 of the hub member 70 at the rear of the valve plunger 82 and is forwardly urged by a spring 90 and is selectively engaged with a rear end face of the valve plunger 82 or an inner hole stepped portion (valve seat) 91 of the hub member 70 according to the axial movement of the push rod 85. When the cylindrical valve 83 is engaged with the rear end face of the valve plunger 82 and is separated from the inner hole stepped portion 91 in this valve mechanism 79 (upon rightward movement) the constant pressure chamber 75 is in fluid communication with the variable pressure chamber 127 through a hole 92, a hole 93, the inner hole 89 and a hole 94. When the cylindrical valve 83 is engaged with the inner hole stepped portion 91 and is separated from the rear end face of the valve plunger 82 (upon leftward movement), the variable pressure chamber 127 is in fluid communication with the atmosphere through the hole 94, the inner hole 89 of the hub members 70, an inner hole of the cylindrical valve 83, air filters 95, and a hole 96 provided on a boot 97. The key 88 is forwardly and rearwardly moved within radial holes 86, 87 and is surrounding the outer peripheral portion of the hub member 70, as is shown in Fig. 5. The key 88 has a contacting portion 98 contacting with the rear shell 53 at the designated position (returning position). The relative position of the hub member 70 and the valve plunger 82 is determined by the key 88. The cylindrical valve 83 is engaged with the rear end face of the valve plunger 82 and is contacted with the inner hole stepped portion 91 (a gap may be provided therebetween). Accordingly, when the in­ put push rod 85 is forwardly moved against a spring 99, the variable pressure chamber 127 communicates with the atmosphere quickly. The case 84 is of a stepped cylindrical shape and is air- tightly fixed to the hole 89 of the hub member 70 at the small diameter portion thereof and is prevented from the rotation by the key 88. The case 84 is also prevented from dropping by projections 100 which are integrally formed on the hub member 70 and projections 101 integrally formed on the case 84. Namely, as shown in Figures 2 to 5, a pair of projections 100, 100 are integrally formed on the inner hole circumferential face in which the small diameter portion of the case 84 is fitted. The case 84 is provided with an annular groove 104 and two recessed portions 103, 103 and a pair of projections 101, 101. When the case 84 is assembled within the hub 70, recessed portions 103, 103 of the case 84 are placed at almost the same angle with the corresponding projections 100 and then the case 84 is inserted into the hub member 70 as clearly shown in Figure 6. The case 84 is further inserted into the hub member until it contacts with the projections 100, 100. The case 84 is then slightly rotated until the projections 100, 100 and the recessed portions 103, 103 are faced with each other thereby to release the engagement between the rear end of the case 84 and the projections 100. If a stepped portion 102 of the case 84 is contacted with the projections 100, 100, the case 84 is rotated at the right angle and the projections 101, 101 are engaged with the projections 100, 100. Then the key 88 is inserted into the radial holes 86, 87 and the case 84 is firmly connec­ ted to the hub 70 in order to prevent the case 84 from excess movement in axial direction by blocking the rotation of the case 84. A stepped portion 105 of the case 84 having an outward flange is contacted with the bottom wall 69 of the hub member 63 at the front movable wall 57. The case 84 receives the valve plunger 82 within the samll diameter hole and a reaction rubber disc 106 at the inner hole stepped portion.The reaction rubber disc 106 is con­ tacted at the front face thereof with the rear end of an output push rod 108 which is projected out of the housing 51 through a seal member 107 and is engaged with piston of the master cylinder (not shown). A spring 109 is en­ gaged with the front face of the outward flange of the stepped portion 105 and both movable walls 57, 58 are rearwardly urged by the spring 109. In the brake booster 50 according to the present inven­ tion, a cylindrical portion 110 is integrally provided with the hub member 70 of the rear movable wall 58 and penetrates the partition wall 56 and is forwardly extended through a seal member 111 and a bush 112. The cylindrical portion 110 is overlapped on a cylindrical portion of the hub member 63 at the front movable wall 57 and is fixed thereto and forms a cylindrical space 113 with the cylindrical portion of the hub member 63. A cy­ lindrical seal member 114 made of rubber in interposed within the cylindrical space 113. The cylindrical seal member 114 is provided with an inward flange 115 which is air-tightly squeezed between the case 84 and the hub member 70 with the bottom of the bottom wall 69 of the hub member 63 at the rear end thereof. The cylindrical seal member 114 includes a groove 116 provided from the front end to the rear end at the circumferential wall thereof and a recess 117 provided from the middle portion to the rear end thereof. Further, the cylindrical seal member 114 is air-tightly contacted with the hub member 63 and the cylindrical portion 110 at the inner and outer circum­ ferential surfaces thereof. A pair of projecting portions 118, 118, which is engaged with a pair of ribs 119 provided on the inner circumference, is axially provided on the outer circumference of the cylindrical seal member 114 and determines the position of the cylindrical seal member 114. The air-tight connection between the inward flange 115 and the hub member 70 is not damaged, when a certain looseness amount at the axial direction between the case 84 and the hub member 70 is happened. A first passage 120 formed by the groove 116, the hub member 63, and the cylindrical portion 110 is communi­ cated with the front variable pressure chamber 66 through a hole (recess) 121 formed on the front end of the cylin­ drical portion 110 and a gap between the cylindrical portion 110 and the diaphragm 65 and is also communicated with the rear variable pressure chamber 127 through the hole 122 which is provided on the hub member 70 and penetrates the hub member 70. The first communicating passage 74 for communicating both variable pressure chambers 66, 73 includes the first passage 120, the hole (recess) 121 and the hole 122 etc. A second passage 123 formed by the second recess 117, the hub member 63, and the cylindrical portion 110 is communicated with the front constant pressure chamber 67 through a hole 124 provided on the rear portion of the circumferential wall of the hub member 63 and is also communicated with the rear constant pressure chamber 75 through the holes 93, 92 provided on the hub member 70 (when the hole 92 is provided a little more front than the shown position, just through the hole 92). The second communicating passage 76 includes the second passage 123, the hole 124, holes 93, 92. By the foregoing, there has been disclosed a preferred form of tandem brake booster constructed in accordance with the present invention. It will be appreciated that various additions, substitutions, modifications and omissions may be made thereto without departing from the spirit of the invention.

Claims: 1. A tandem brake booster having a housing, front and rear movable walls installed within said housing, a partition wall interposed between said front and rear movable walls, two front constant pressure chambers of said each movable wall and two rear variable pressure chambers of said each movable wall divided by said front and rear movable walls and said partition wall, a first communicating passage communicating said both variable pressure chambers, a second communicating passage communicating said both constant pressure chambers, valve means provided in said rear movable wall for generating the pressure difference between said both constant pressure chambers and said both variable pressure chambers and forwardly moving said both movable walls, a cylindrical case having small and large diameter portions assembled with a hub portion of said both movable walls, a reaction rubber disc assembled within a stepped portion of said case, input and output push rods, a valve plunger slidably inserted into said small diameter portion of said case and formed for said valve means and connected to said input push rod, a key member inserted into said rear movable wall and a radial hole of said case and engaged with said valve plunger for limiting the sliding amount of said valve plunger to said rear movable wall and movably assembled at a certain amount to said case into the forward and rearward direc­ tion, whereby the forward actuating force of said both movable walls is acted on said ouput push rot via said case and said reaction rubber disc and its reaction is acted on said valve plunger via said reaction rubber disc, and said movable wall is further more rearwardly moved upon the rearward movement of said both movable walls, after a part of said key member is contacted with said housing and the rearward movement of said valve plunger to said housing is stopped, said tandem brake booster is characterized by that first and second pro­ jections provided on circumferential surface of a hole of said rear movable wall and an outer circumference of said small diameter portion of said case respectively, is engaged to each other and the forward movement of said case to said rear movable wall is blocked, when said key member is inserted into said rear movable wall and said hole of said case and the rotation of said case to said rear movable wall is limited, and said first and second projection is engaged and disengaged by rotating said case within said rear movable wall, when said key member is not inserted into said rear movable wall and said hole of said case. 2. A tandem brake booster as set forth in claim 1, wherein said front and rear movable walls are pro­ vided with a hub member, respectively, and said each hub member of said front and rear movable walls is contacted. 3. A tandem brake booster as set forth in claim 2, wherein said first projection is integrally formed with said hub member of said rear movable wall and said second projection is integrally formed with said case. 4. A tandem brake booster as set forth in claim 3, wherein said case is provided with an annular groove and two double faces width portions.

Inventors: MIWA, AKIHIKO, SUGIURA, YUZURU
Applicants: AISIN SEIKI KABUSHIKI KAISHA
Application year: 1985
Main classification: B60T13
IPC codes: B60T13