Pneumatic brake booster with a control housing

Abstract

Pneumatic brake booster (1) for a hydraulic motor vehicle brake system, comprising a booster housing (2), at least one working wall (3) which separates a vacuum chamber (4) from a working chamber (5) in the booster housing (2) and is displaceable within limits along a central axis (A) by means of pressure differential control while generating a boosting force (F), a control housing (6) coupled to the working wall (3) which accommodates a valve arrangement (7) for controlling the pressure differential between the vacuum chamber (4) and the working chamber (5), and transmits the boosting force (F) from the working wall (3) to a push rod (8), characterized in that the control housing (6) is formed in at least two parts with an inner part (9) and an outer part (10) radially enclosing the inner part (9), wherein the inner part (9) has a central bore (22),in which a valve piston (21) for controlling the valve arrangement (7) is received at least partially and guided to be displaceable within limits along the central axis (A), wherein the outer part (10) has at least one formation (16) for force-transmitting coupling of the working wall (3) and, in some areas, at least one cylindrical outer surface (17) on which a circumferential sealing element (18) slides pneumatically and wherein the inner part (9) and the outer part (10) are materially bonded together by forming the outer part (10).

Description

[0001] The invention relates to a pneumatic brake booster for a hydraulic motor vehicle braking system according to the preamble of claim 1.

[0002] Such brake boosters are widespread and form a vacuum chamber and a working chamber separated inside the booster housing by a movable working wall, whereby in the initial state there is a vacuum in both chambers and the working chamber is filled with ambient air to generate a boosting force.

[0003] Such a brake booster is known, for example, from WO 2007 / 010 031 A1.

[0004] The amplifying force results from a pressure differential force acting on the working wall. In a tandem brake booster, there are accordingly two synchronously moving working walls and two vacuum and working chambers each.

[0005] The amplifying force is introduced from the work wall into a central control housing coupled to it, which then moves together with the work wall and transmits this force to a push rod. The axial displacement of the control housing defines the stroke of the brake booster.

[0006] Furthermore, the control housing contains inside a system of air channels and a valve arrangement - the control valve, which controls the pressure difference.

[0007] An elastic reaction disc is usually interposed between the push rod and the control housing, which plays an important role in the response behavior of the brake booster in relation to the actuating force and the diameter of a control piston acting on the reaction disc with the actuating force - the transmission of the brake booster.

[0008] Due to its complex internal structure and for weight reasons, the control housing is usually manufactured from plastic using an injection molding process. To ensure sufficient operational strength, larger material accumulations occur around the highly stressed area of ​​the reaction disc. Material accumulations in injection-molded parts are known to have a negative impact on the manufacturing process, as they increase the tendency for voids, sink marks, and uneven cooling. To counteract this, the mold must be designed more elaborately and cooled more slowly, resulting in increased tooling costs, cycle times, and manufacturing effort.

[0009] For different vehicle applications, the ratio and stroke of the brake booster must be adjusted. This is achieved through a targeted modification of the dimensions of the control housing. As a result, more expensive injection molds must be manufactured, or they must be more complex, with multiple different inserts. This significantly increases setup times and manufacturing costs.

[0010] The invention is therefore based on the objective of offering an improved brake booster of the type mentioned above, which enables the required variability and safety with reduced manufacturing and cost effort.

[0011] The problem is solved according to the invention by a brake booster with the combination of features according to claim 1. Dependent claims, together with figures and descriptions, specify further embodiments and advantageous developments according to the invention.

[0012] By technologically dividing the control housing into at least one inner part and an outer part radially enclosing the inner part according to the invention, the different functions of the control housing can be divided between these technological components or semi-finished products in such a meaningful way that the overall production can be optimized and carried out with simplified tools.

[0013] The inner part is permanently bonded to the outer part at a contact surface, creating a vacuum-tight and force-transmitting connection, thus eliminating the need for additional sealing elements. The inner part is manufactured first, and the outer part is subsequently produced around the inner part in a primary forming process – for example, using an injection molding process with the inner part inserted as a core into an injection mold.

[0014] The additional production step is offset primarily by the fact that the individual components can be manufactured much more easily than the complete control housing. Areas with material accumulation are efficiently divided into two sections, each with thinner walls to be manufactured. This improves tolerances and dimensional accuracy, significantly simplifies tooling, and reduces cycle times. Correction efforts are also reduced, resulting in fewer rework cycles, shorter tooling times, and lower costs.

[0015] Smaller dimensions of the inner part allow more parts to be produced simultaneously in a tool of the same size. This reduces the cost per part and increases the annual production volume.

[0016] By dividing individual functions of the control housing between the inner and outer parts, the required variability of the control housing or the brake booster, particularly with regard to different ratios and strokes, can be increased without the need for separate additional tools, because, for example, different inner parts can be easily combined with different tools for outer parts. This can be implemented more simply and cost-effectively.

[0017] To improve the tightness and increase the force transmission between the inner part and the outer part, in a further development according to the invention at least one undercut can be provided on the contact surface, whereby in addition to the connection on the material plane a macro-positive locking is formed and the surface area of ​​the contact surface is increased.

[0018] In various embodiments according to the invention, the undercut can be designed such that the positive locking is formed specifically in axial, tangential or combined directions simultaneously in several directions.

[0019] The positive locking mechanism can be created particularly easily if one or more circumferential ribs, grooves, slots and the like are formed on the inner part.

[0020] In a particularly advantageous embodiment, the undercut can be provided as one or more recesses in the area of ​​the contact surface on the inner part, whereby, after the recess or recesses have been filled by the material of the outer part, a positive locking connection is very effectively created in both axial and tangential directions.

[0021] For the purpose of a technologically optimal functional division, an embodiment of the invention provides that the force transmission from the working wall(s) and the sealing of the control housing against the amplifier housing and the working wall(s) take place on the outer part. For this purpose, at least one formation for force-transmitting coupling and preferably for sealing the working wall, as well as at least one cylindrical outer surface in certain areas, can be formed on the outer part, on which a circumferential sealing element can slide pneumatically. By means of relatively simple tooling variations in the length of the cylindrical outer wall, the different strokes can be generated effectively and cost-efficiently and offered with different gear ratios by means of combinations with different variants of internal parts.

[0022] In pneumatic brake boosters of this type, a return spring is elastically clamped between an inner wall of the booster housing and the control housing to return the control housing to its unactuated starting position after a braking operation. Often, a cup-shaped guide plate is additionally clamped to improve the seating of the return spring, and / or to guide the pushrod and to influence the air circulation between the return spring and the control housing. The support area for such components requires a relatively large diameter in relation to the control housing. Therefore, in a further development of the invention, this support area is also formed on the outer part, allowing the inner part to be made smaller and optimizing the force flow within the control housing.

[0023] In an advantageous embodiment of the invention, it is provided that the inner part has a central bore in which a valve piston is at least partially received and guided.

[0024] A further advantageous development provides that a circumferential axially extended sealing edge is formed on the inner part for pneumatically sealing contact with the valve body.

[0025] This allows key parameters that determine the translation and response behavior of the brake booster to be combined cost-effectively, dimensionally accurate and with tight tolerances on the inner part with relatively low manufacturing effort and then combined with any outer part without loss of accuracy.

[0026] In a further advantageous embodiment of the invention, a contact surface for axial contact of the reaction disk can be formed on the inner part, thus providing a smooth surface without separating edges for pneumatic sealing.

[0027] In the next further development of the invention, the inner part has a circular cavity on the push rod side, which allows the reaction disk and, in some areas, the push rod to be received and guided with minimal manufacturing effort and tight tolerances.

[0028] The invention will be explained in more detail below. Descriptions of generally known aspects and functions of a brake booster of this type will be largely omitted, and only the details relevant to the invention will be discussed. It should also be noted that the invention is applicable to both single and tandem brake boosters.

[0029] In detail, the Fig. 1 in sectional view a known generic brake booster in single design, with a master brake cylinder housing mounted on it. Fig. 2 An exploded view of a control housing of an embodiment according to the invention. Fig. 3 The control housing of an embodiment according to the invention. Fig. 2 in sectional view. Fig. 4 and Fig. 5 Further embodiments of a control housing according to the invention with differently designed undercuts, each forming an axial positive fit, on the contact surface between the inner and outer part. Fig. 6 Another embodiment of a control housing according to the invention for a tandem brake booster. Fig. 7 The inner part of the control housing of a further embodiment according to the invention with an undercut formed by means of recesses to create a positive fit.

[0030] Fig. Figure 1 shows a known embodiment of a generic pneumatic brake booster 1 in a single configuration. Inside the booster housing 2, a working wall 3 is arranged to be axially displaceable along the central axis A within limited limits. The working wall 3 is essentially ring- or plate-shaped with a central opening and is radially coupled airtight and force-transmitting to a control housing 6 on the inside. The working wall 3 thus separates a working chamber 5 from a vacuum chamber 4 within the booster housing 2. The vacuum chamber 4 can be connected to the working chamber 5 and the working chamber 5 to the atmosphere via a channel system within the control housing 6 (not shown separately here). These connections are opened and closed by means of the valve assembly 7 in the control housing 6. The valve assembly 7 is actuated by an unamplified input force f by an actuating element 26.For the invention it is not essential whether the actuating element 26 is designed as a connecting rod as in the embodiment shown and is manually operated by the driver or designed differently and / or is controlled externally by an actuator, for example.

[0031] The control housing 6 of the illustrated version is made of a plastic material using an injection molding process.

[0032] In the embodiment shown, the brake booster 1 of the generic type has a valve piston 21 within the valve assembly 7, which pneumatically seals against a disc-shaped valve body 23 – also known as a poppet valve – that is at least partially elastic. To control the valve assembly 7, the valve piston 21 is actuated along the central axis A by means of an actuating element 26 with an unamplified input force f, and is thereby displaced to a limited extent, so that it lifts off the valve body 23 and opens a pneumatic connection between the working chamber 5 and the atmosphere. Simultaneously, a cylindrical, projecting central body of the valve piston is pressed into the reaction disk 19. The displacement and the diameter D of the central body of the valve piston 21 in contact with the reaction disk 19 essentially determine the transmission ratio of the brake booster 1.

[0033] Opening the connection between the working chamber 5 and the atmosphere creates a pressure difference between the vacuum chamber 4 and the working chamber 5. This pressure difference acts on the surface of the working wall 3 and generates a reinforcing force F. The reinforcing force F is transmitted via the control housing 6, which is coupled to the working wall 3, into a pushrod 8 and from there to a piston (not shown) of a master brake cylinder 27. Under the influence of the reinforcing force F, the working wall 3, together with the control housing 6 and the pushrod 8, moves towards the master brake cylinder 27. This movement compresses a return spring 28.

[0034] A guide plate 29 is clamped between the return spring and the control housing 6. The guide plate 29 is essentially pan-shaped, with a pan base facing the control housing 6, a collar forming a pan rim radially around the outside and designed to bear the return spring 28, and a centrally arranged tubular dome for guiding the push rod 8. However, variations in the shape of the guide plate 29 are possible within the relevant category and are permissible according to the invention.

[0035] Another axially projecting sealing edge 24 formed on the control housing 6 - see, for example, the Fig. 3 - also pneumatically seals against the valve body 23. After completion of a braking process, during the return stroke, the actuating element 26 is actuated in a direction opposite to the input force f, so that the valve body 23 is lifted from the sealing edge 24 and a pneumatic connection between the vacuum chamber 4 and the working chamber 5 is released to relieve the pressure differential. The control housing 6, together with the working wall 3 and the push rod 8, is then moved back into its unactuated initial position by the return spring 28.

[0036] Fig. Figure 2 shows the control housing 6 of a first embodiment according to the invention in an exploded view. In contrast to the known embodiment according to the Fig. 1 The control housing 6 according to the invention is technologically multi-part, consisting of two types of semi-finished products, which are then assembled to form a finished control housing 6. The illustrated embodiment according to the invention has an inner part 9 which is radially enclosed on the outside by an outer part 10.

[0037] The inner part 9 is permanently bonded to the outer part 10 at contact surfaces 11 and 12, forming a vacuum-tight connection that meets the requirements of brake booster operation. This connection is created by first manufacturing the inner part 9 and inserting it as a core into an injection mold for the outer part 10, where it is subsequently overmolded with the material of the outer part 10. In suitable designs, bonding or welding would also be conceivable within the scope of the invention.

[0038] All functions performed by a control housing 6 in a brake booster 1 are divided between the inner part 9 and the outer part 10 and are assigned to either one or the other semi-finished product.

[0039] Fig. Figure 3 shows the embodiment of the control housing 6 from the Fig. 2 assembled and in sectional view. The inner part 9 and the outer part 10 are assigned different functions of a control housing 6. For the reference symbols not shown, see the Fig. 1 referred.

[0040] On the outer part 10, a radially circumferential formation 16 is formed to which the working wall 3 is coupled in a force-transmitting and tightly connected manner.

[0041] In an area radially below the formation 16, a separate support area 30 is formed, having several radially and axially oriented surfaces, which is intended for the placement of the guide plate 29 or the return spring 28.

[0042] In its further axial direction, the outer part 10 forms a cylindrical outer surface 17, against which a circumferential sealing element 18 slides, providing a pneumatic seal. The axial length or extension of the outer surface 17 is adapted to the required stroke of the brake booster 1.

[0043] The inner part 9 has a radially central bore 22, which is designed and dimensionally adapted to guide the control piston 21. The diameter D of the bore 22 essentially determines the transmission ratio of the brake booster 1. Furthermore, the movement of the control piston 21 towards the reaction disk 19 is also limited at the inner part 9.

[0044] Furthermore, a circular cavity 25 is arranged on the inner part 9, in which the reaction disk 19 is received and the pressure rod 8 is partially received and guided.

[0045] A contact surface 20 is formed at the bottom of the cavity 25, against which the reaction disk 19 pneumatically seals and through which the reinforcing force F is introduced from the working wall 3 via the control housing 6 into the push rod 8.

[0046] An axially opposite the contact surface 20, an axially backward-projecting, circumferential sealing edge 24 is formed on the inner part 9, which can be applied to the valve body 23 as a functional element of the valve arrangement 7 for controlling the pneumatic connection between the vacuum chamber 4 and the working chamber 5 in a sealing manner.

[0047] Fig. Figure 4 shows a further embodiment of the multi-part control housing 6 according to the invention in a sectional view. In addition to the one shown above in the Fig. In the embodiment described in sections 2 and 3, the embodiment shown here has an axially acting undercut 13 between the inner part 9 and the outer part 10. The undercut 13 is created by means of several radial ribs 14 formed on the inner part 9, which also increase the surface area of ​​the contact surfaces 11, 12 and thus promote better force transmission and sealing.

[0048] In the embodiment according to Fig. 5 the ribs 14 are formed with a lower radial extension in close succession as a kind of groove profile.

[0049] In other embodiments of the invention, not shown here, the undercut 13 can also be designed to act additionally or exclusively tangentially, depending on the specific requirements, by means of a corresponding spatial orientation of the ribs 14.

[0050] In the Fig. Figure 6 shows an embodiment of the control housing 6 for a tandem brake booster according to the invention. The embodiment essentially corresponds to the embodiment according to the Fig. 2&3, however, is adapted to the otherwise well-known design features of a tandem brake booster. For this purpose, an additional formation 16' is provided on the outer part 10 to accommodate the second working wall 3' (not shown) and a second cylindrical outer surface 17' for sealing against a tandem-typical intermediate wall (not shown) that separates a further working chamber from the vacuum chamber 4.

[0051] Fig.Figure 7 shows a further embodiment of an inner part 9 according to the invention. To generate a positive fit 13, locally limited recesses 15 are provided in the contact surface. When the recesses 15 engage with the material of the outer part 10 (not shown), a positive fit is necessarily formed in both the axial and tangential directions. Within the scope of the invention, it would also be conceivable to provide knobs or a combination of both as a complementary solution instead of the recesses 15 shown.

[0052] With regard to the positive locking 13 between the inner part 9 and the outer part 10, further embodiments of the invention also allow, for example, the use of grooves or any combination of grooves and ribs as a complementary solution instead of the described ribs 14. It is also conceivable to design the radial outer contour of the inner part 9 in the section of the contact surface 11 as non-circular. A key factor in the design decision between a rib or a protrusion in general, or a groove or a recess in general, is the resulting wall thickness in the respective area and the desire to achieve a manufacturing-friendly, as constant as possible, material thickness and to avoid material accumulations. Reference symbol list 1 brake booster 2 amplifier housings 3 work wall 4. Low-pressure chamber 5 Chamber of Labor 6 control housings 7 Valve arrangement 8 Push rod 9 Inner part 10 Outdoor part 11 Contact area 12 Contact area 13 Undercut 14th rib 15 In-depth study 16 Formation 17 Cylindrical outer surface 18 Sealing element 19 Reaction disc 20 Plant area 21 valve pistons 22 Bore 22 23 Valve bodies 24 Sealing edge 25 cavities 26 Actuating element 27 Master brake cylinder housing 28 Return spring 29 leading plates 30 Support area A central axis Diameter f Entrance force F Amplification force H Hub

Claims

[1] Pneumatic brake booster (1) for a hydraulic motor vehicle brake system, comprising a booster housing (2), at least one working wall (3) which separates a vacuum chamber (4) from a working chamber (5) in the booster housing (2) and is displaceable along a central axis (A) in a limited manner while generating a boosting force (F) controlled by a pressure differential, a control housing (6) coupled to the working wall (3) which accommodates a valve arrangement (7) for controlling the pressure differential between the vacuum chamber (4) and the working chamber (5), and transmits the boosting force (F) from the working wall (3) to a push rod (8), characterized by, that the control housing (6) is formed in at least two parts with an inner part (9) and an outer part (10) radially enclosing the inner part (9), wherein the inner part (9) has a central bore (22) in which a valve piston (21) for controlling the valve arrangement (7) is received at least partially and guided displaceably along the central axis (A), wherein the outer part (10) has at least one formation (16) for force-transmitting coupling of the working wall (3) and at least a cylindrical outer surface (17) in certain areas, on which a circumferential sealing element (18) slides pneumatically and wherein the inner part (9) and the outer part (10) are joined together by forming the outer part (10) in a materially bonded manner. [2] Brake booster (1) according to claim 1, characterized by, that the connection between the inner part (9) and the outer part (10) is created by injection molding the outer part around the previously completed inner part (9). [3] Brake booster (1) according to claim 1, characterized by , that at least one undercut (13) is formed on the contact surface (11,12) to create a positive fit between the inner part and the outer part. [4] Brake booster (1) according to claim 3, characterized by , that the undercut (13) forms a positive fit in the axial direction. [5] Brake booster (1) according to claim 3, characterized by , that the undercut (13) forms a positive fit in the tangential direction. [6] Brake booster (1) according to claim 3, characterized by , that the undercut (13) is formed as at least one rib (14) and / or a groove on the inner part (9). [7] Brake booster (1) according to claim 3, characterized by, that the undercut (13) is formed as at least one recess (15) on the inner part (9) such that after the recess (15) is filled by the material of the outer part (10) a positive fit is created in both axial and tangential directions. [8] Brake booster (1) according to claim 1, characterized by , that a return spring (28) for returning the control housing (6) to its unactuated initial position after a braking process is elastically clamped between an inner wall of the amplifier housing (2) and the control housing (6) and a support area (30) for axial and radial support of the return spring (28) or of a guide plate (29) clamped between the return spring (28) and the control housing (6) is formed on the outer part (10). [9] Brake booster (1) according to claim 1, characterized by , that the valve piston (21) *can be actuated with an unamplified input force (f) along the central axis (A). [10] Brake booster (1) according to claim 1, characterized by , that the valve arrangement (7) has a valve body (23) that is at least partially elastic and the inner part (9) has a circumferential axially extended sealing edge (24) for pneumatically sealing contact with the valve body (23). [11] Brake booster (1) according to claim 1, characterized by , that an elastic reaction disc (19) is clamped between the control housing (6) and the push rod (8) and the inner part (9) has a contact surface (20) for pneumatically sealing axial contact of the reaction disc (19). [12] Brake booster (1) according to claim 11, characterized by , that the inner part (9) has a circular cavity (25) on the push rod side for the partial reception and guidance of the push rod (8) and for receiving the reaction disc (19).

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