GB2070707A

GB2070707A - Vacuum brake booster

Info

Publication number: GB2070707A
Application number: GB8102676A
Authority: GB
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1980-02-28
Filing date: 1981-01-29
Publication date: 1981-09-09
Also published as: JPS6147739B2; SE8100483L; GB2070707B; BR8100963A; FR2477087A1; ES256314U; DE3007532A1; SE440472B; ES256314Y; JPS56131451A; IT1138962B; DE3007532C2; ZA81855B; FR2477087B1; IT8120026A0

Abstract

Radially-extending flanges (23) of a diaphragm plate (10) attached to a rolling diaphragm (11) of a vacuum booster (1) extend through slots in a booster casing reinforcing tube (5) and are attached to a sleeve (21) of a control valve (15), the distance "a" between the rolling diaphragm and one end of the slots being at least equal to half of the power stroke of the diaphragm plate (10). <IMAGE>

Description

SPECIFICATION Hydraulic brake booster The present invention relates to a hydraulic brake booster for an automotive vehicle of the kind having a low-pressure casing sealingly sub-divided into a low-pressure chamber and a working chamber by an axially movable wall, with a reinforcement tube extending axially through the low-pressure casing and having its ends fastened to the two end walls of the low-pressure casing and a rolling diaphragm in sealing abutment relative to the movable wall, a mechanically actuatable control valve for connecting the working chamber to the low-pressure chamber or to atmosphere, the control valve housing of which, being axially movable in the reinforcement tube, is connected via a push rod with an actuating piston of a master cylinder, secured to the low-pressure casing on the side close to the partial vacuum, and is connected via a sleeve encompassing said push rod to radial ribs of the movable wall, these ribs projecting through longitudinal slots of the reinforcement tube.

When a brake booster is conventionally arranged between the automotive vehicle's splashboard and the master cylinder of the brake unit, a considerable amount of force has to be transmitted from the master cylinder to the splash board upon actuation of the brake.

To relieve the low-pressure casing from this force and to render possible a construction of the low-pressure casing which is of lighter weight, it is known from German published patent specification DE-OS 28 24794 to arrange tensilely loaded construction elements in the form of tie rods between the two end walls of the low-pressure casing and thus between the master cylinder and the splashboard. These tie rods extend through the axially movable wall of the brake booster, so that sealing is required at this point causing a relatively high constructional expenditure and a certain tendency to fail.

A brake booster is described in German patent specification P 2837911.5, in which the tie element interconnecting the two end walls of the low-pressure casing is formed by a reinforcement tube. As the control valve housing is incorporated within this reinforcement tube and as the axially movable wall is required to be urged into a force-transmitting engagement with the control housing, connecting members have to be guided from the movable wall, and outside the reinforcement tube, through slots or recesses in the reinforcement tube to link with the control valve housing.

Such slots or recesses are included in the area of the working chamber in the brake booster in accordance with German patent specification P 2837911.5. The axially movable wall is sealingly guided on the reinforcement tube in the area adjacent to the slots or recesses on the side close to the partial vacuum. The length of this sealing guide corresponds inevitably to the power stroke of the axially movable wall. As the length of the slots or recesses is likewise determined by the power stroke, the length of the reinforcement tube has to be greater than the double power stroke of the movable wall, resulting in a comparatively large overall length of the brake booster.

A reduced overall length of the brake booster may be achieved if the seal disposed between the movable wall and the reinforcement tube is designed as a rolling diaphragm (German patent specifications P 29 1 8 91 2.6 and P 2918913.7) abutting the connecting tube in a rolling manner, with the front surface of the rolling diaphragm moving axially by a distance which is only half as long as the power stroke of the movable wall. To achieve an overall length of the brake booster which is as small as possible, the rolling diaphragm will be rolled out extending over the slots in the reinforcement tube.

In order to keep the additional demand thereby occasioned upon the rolling diaphragm and the wear thereby caused as reduced as possible, it is desired to design these slots to be as narrow as possible. Accordingly, the connecting members or the ribs extending through these slots have to be designed as narrow as possible, too. On the other hand, however, the ribs are subjected to a considerable bending stress as they transmit the total amount of boosting force of the brake booster. However, an enlargement of the ribs' dimensions in the axial direction of the brake booster is prevented by the enlargement of the brake booster's overall length which would thereby be brought about.

Because of the comparatively high forces required to be transmitted by the ribs extending through the slots of the reinforcement tube, it is likewise difficult to connect the ribs to the control valve housing, as the connection point of the ribs with a sleeve fitted to the control valve housing is required to project beyond the ribs as little as possible in the axial direction towards the master-cylinder side in order to keep the overall length small.

It is, therefore, an object of the present invention to provide a brake booster of the kind initially referred to, so as to achieve a minimum possible overall length without the seal necessary between the movable wall and the reinforcement tube being impaired by the slots to be provided in the reinforcement tube.

Thus, it should be rendered possible to transmit even a comparatively large amount of bending forces between the radial ribs and the control valve housing by simple constructive means, with the total weight of the brake booster being kept at the minimum possible amount.

According to the invention in its broadest aspect there is provided a hydraulic brake booster for an automotive vehicle, with a lowpressure casing sealingly sub-divided into a low-pressure chamber and a working chamber by an axially movable wail with a reinforcement tube extending axially through the lowpressure casing and having its ends fastened to the two end walls of the low-pressure casing and a rolling diaphragm in sealing abutment relative to the movable wall, with a mechanically actuatable control valve for connecting the working chamber to the lowpressure chamber or to atmosphere, the control valve housing of which control valve, being axially movable in the reinforcement tube, is connected via a push rod with an actuating postion of a master cylinder secured to the low-pressure casing on the side close to the partial vacuum and is connected via a sleeve encompassing the push rod to radial ribs of the movable wall, these ribs projecting through longitudinal slots of the reinforcement tube, characterised in that the radial ribs of the movable wall are designed as flat tongues disposed in a joint plane, which tongues are engaged from behind on the side close to the partial vacuum by an outwardly angled collar of the sleeve connected to the control housing, and in that the distance between the rolling diaphragm and the end of the reinforcement tube's longitudinal slots close to the working chamber is at least equal to half the power stroke of the axially movable wall.

As the rolling diaphragm when rolling out no longer extends over the longitudinal slots of the reinforcement tube, these longitudinal slots or recesses may be of very wide design.

It is thus rendered possible also to design the radial ribs comparatively widely enabling these ribs also to transmit a great amount of bending forces-despite being of only a relatively small thickness. Since the tongues forming the radial ribs may be of very wide design, there is equally no difficulty in introducing the force into the sleeve connected to the control valve housing thus providing the possibility of choosing a connection with the sleeve which extends as little as possible beyond the radial ribs' plane in an axial direction, that is to say, of choosing an angled collar engaging behind the flat tongues on the side close to the partial vacuum. The latter connection therefore projects beyond the tongues forming the radial ribs by the measure of the sleeve's sheet thickness.

Suitably, the radial ribs are formed integrally with a diaphragm plate of the axially movable wall of sheet metal. This results in a very lightweight and, at the same time, inherently stable construction of the movable wall with the ribs extending into the reinforcement tube. Instead of this arrangement, the radial ribs may also be formed on a separate spacer ring, which communicates with the diaphragm plate and may in this case be of thin-walled design, without regard to the bending stress occurring in the ribs.

In an improved embodiment of the invention, it is provided that at least one cutting edge of an indentation deformed radially outwardly from the sleeve abuts in each case on the radial inner rims of the radial ribs on the side close to the working chamber. Thus, the axial fixing of the ribs to the sleeve is achieved by very simple constructive means.

However, the stress exerted on these deformed indentations is comparatively small only, because the boosting force is not transmitted via these indentations, but in the opposite direction via the angled collar of the sleeve.

It has proved to be particularly favourable to sub-divide the collar engaging behind the radial ribs into collar portions which correspond to the radial ribs' circumferential extension, with lateral collar portions angled to the working-chamber side adjoining these collar portions. This provides fixing of the radial ribs abutting the collar portions in the circumferential direction between the lateral collar portions. This obviates the need for a separate rotation-locking mechanism of the radial ribs at the sleeve.

In accordance with another useful embodiment of the present invention, it is provided that disposed between the collar portions engaging the radial rims from behind are axially set-back sleeve rims having likewise radially outwardly angled collar portions interconnecting lateral collar portions. These axially setback sleeve rims provide space for the screw joints necessary to fasten the end wall and the master cylinder to the reinforcement tube.

However, at the same time, the inherent stability of the sleeve is increased by those collar portions that are not arranged at the connecting point with the radial ribs only.

The ease of assembly of the brake booster may still be improved by providing lateral insertion slots for the radial ribs in the lateral collar portions spaced from the collar portions engaging the radial ribs from behind and by taking care that the circumferential distance of the adjacent lateral collar portions is greater than the circumferential extension of the radial rib. The sleeve may be mounted from the lowpressure side, with the ribs being inserted between the collar portions that are provided to connect with the ribs and with the ribs being led in laterally through the insertion slots by a rotary motion. This connection, established in the way of a bayonet connection, will be later secured by the outwardly deformed indentations of the sleeve, so that no rotary motion and consequently no loosening will be allowed to occur subsequently.

In another embodiment it is provided that the radial ribs are situated in the bottom surface of a hub member extending axially from the diaphragm plate and that a substantially cylindrical inset is fitted in the hub member in the area of the rolling diaphragm, so that the loss in effective surface for the rolling diaphragm is kept low. For reasons of assembly, the hub member's inner diameter is predetermined by the reinforcement tube's overall dimensions in the area of the screw connection with the master cylinder.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a longitudinal sectional view of a brake booster, with the master cylinder not shown, Figure 2 is a side view of the sleeve to be connected to the control valve housing in accordance with the brake booster of Fig. 1, Figure 3 is a cross-section taken along the line Ill-Ill of Fig. 2, and Figure 4 is a partial longitudinal sectional view of a two-piece version of a diaphragm plate with a spacer ring.

The brake booster illustrated in Fig. 1 includes a low-pressure casing 1 which is divided into a working chamber 3 and a lowpressure chamber 4 by an axially movable wall 2. Extending axially through the lowpressure casing 1 is a reinforcement tube 5 having its ends fastened to the two end walls 6, 7 of the low-pressure casing 1 by means of the threaded bolts 8 and 9.

The axially movable wall 2 consists of a diaphragm plate 10 and a diaphragm 11 which abuts thereon and is designed as a rolling diaphragm 1 2 in the area between the outer periphery of the diaphragm plate 10 and the circumferential wall of the low-pressure casing 1 and another rolling diaphragm 1 3 in the area between the diaphragm plate 10 and the reinforcement tube 5. By these rolling diaphragms the movable wall 2 is sealed relative to the low-pressure casing 1 and the reinforcement tube 5 respectively.

A control valve 1 5 actuatable by a piston rod 14 is disposed at the end of the reinforcement tube 5 close to the working chamber and has a control valve piston 1 6 connected to the piston rod 14, which opens valve openings in a control valve housing 1 7 in such a manner that the working chamber 3 is connected to the low-pressure chamber 4 in the inactive position illustrated in Fig. 1.

When the control valve is actuated, i.e. when the piston rod 1 4 is axially displaced, the connection between the low-pressure chamber 4 and the working chamber 3 is interrupted, and the working chamber 3 is connected to atmosphere so that the movable wall 2 will move towards the low-pressure chamber 4.

Connected to the axially movable valve housing 1 7 is a push rod 1 8 which acts on an actuating piston of a master cylinder (not illustrated) of the brake unit, the master cylinder being secured to the .end of the reinforcement tube 5 on the side close to the partial vacuum by means of the threaded bolts 9. A compression spring 1 9 bearing against the end wall 7 of low-pressure casing 1 and against the diaphragm plate 10 maintains the movable wall 2 resiliently in the initial position illustrated.

The control valve housing 17, being made of plastics in the case of the illustrated embodiment, has a radially outwardly extending flange 20 at its end close to the low-pressure chamber, which flange is engaged from behind by a sleeve 21 extending from the control valve housing 1 7 to the low-pressure chamber side and having there two radially outwardly angled collar portions 22, which engage the inner rims of the radial ribs 23 designed as flat tongues from behind these ribs being located in a joint bottom plane of a cup-like, substantially cylindrical hub member 24 of the diaphragm plate 10. Ribs 23, hub member 24 and diaphragm plate 10 are integrally made of sheet metal.

Adjacent to each of the collar portions 22 of the sleeve 21 on both sides is a lateral collar portion 25 (Fig. 2) extending to the workingchamber side and passing over into an equally radially outwardly angled collar portion 26 at a sleeve rim set-back axially between the two collar portions 22 in each case. Spaced a small distance from the collar portion 22, a lateral insertion slot 27 is provided in one of the two lateral collar portions 25. The circumferential distance of the adjoining lateral collar portions 25 is chosen so as to permit the two radial ribs 23 to be moved axially between the adjacent lateral collar portions 25 when being assembled and also to permit them by turning by 90 to be urged through the insertion slots 27 up to the position indicated by dot-dash lines in Figs. 2 and 3.In this position, the ribs 23 are held by outwardly deformed indentations 28 (so-called lancing) abutting the rim of the ribs 23 with one cutting edge.

The radial ribs 23 engage through two longitudinal slots 29 of the reinforcement tube 5 designed as wide recesses. In the initial position shown in Fig. 1, the distance a between rolling diaphragm 1 3 and the end of the longitudinal slots 29 close to the working chamber is so chosen that it is at least equal to half the power stroke of the axially movable wall 2. Therefore, the rolling diaphragm 1 3 does not extend over the longitudinal slots 29, not even at the end of the power stroke.

Inserted in the hub member 24 in the area of the inner rolling diaphragm 1 3 is a substantially cylindrical inset 30 made of plastics which is rounded off outwardly at its end close to the working chamber and forms a supporting surface for the rolling diaphragm 13.

When assembling the brake booster, the diaphragm plate 10 is first of all fitted to the reinforcement tube 5, with the ribs 23 being inserted in the longitudinal slots 29 from the low-pressure-chamber side. The preassembled control valve 15 with the sleeve 21 fastened thereto will then be inserted in reinforcement tube 5. Sleeve 21 will be turned by 90 , until the ribs 23 are caught in a bayonet-like manner by the collar portions 22. This bayonet connection will subsequently be secured by fitting the indentations 28 or depressions at sleeve 21.

The outlines of hub member 24 and of the radial ribs are indicated by dot-dash lines in Fig. 3.

In the embodiment shown in Fig. 4, the hub member 24 of the diaphragm plate 10 is connected to a spacer ring 31, at the inner rim of which the radial ribs 23 are formed.

The diaphragm plate 10 as well as the hub member 24 are made of sheet metal. An end rim 32 of the hub member 24 bears axially against a shoulder 33 of the space ring 31.

Bent-off holding tongues 34 engage in recesses of the spacer ring 31 and secure it to the hub member 24.

Claims

5. A hydraulic brake booster for an automotive vehicle, with a low-pressure casing sealingly sub-divided into a low-pressure chamber and a working chamber by an axially movable wall, with a reinforcement tube extending axially through the low-pressure casing and having its ends fastened to the two end walls of the low-pressure casing and a rolling diaphragm in sealing abutment relative to the movable wall, with a mechanically actuatable control valve for connecting the working chamber to the low-pressure chamber or to atmosphere, the control valve housing of which control valve, being axially movable in the reinforcement tube, is connected via a push rod with an actuating piston of a master cylinder secured to the low-pressure casing on the side close to the partial vacuum and is connected via a sleeve encompassing the push rod to radial ribs of the movable wall, these ribs projecting through longitudinal slots of the reinforcement tube, characterised in that the radial ribs of the movable wall are designed as flat tongues disposed in a joint plane, which tongues are engaged from behind on the side close to the partial vacuum by an outwardly angled collar of the sleeve connected to the control housing, and in that the distance between the rolling diaphragm and the end of the reinforcement tube's longitudinal slots close to the working chamber is at least equal to half the power stroke of the axially movable wall.
2. A hydraulic brake booster as claimed in claim 1, characterised in that the radial ribs are formed of sheet metal integrally with a diaphragm plate of the axially movable wall.
3. A hydraulic brake booster as claimed in claim 1, characterised in that the radial ribs are formed at a separate spacer ring which is connected with the diaphragm plate.
4. A hydraulic brake booster as claimed in claim 1, characterised in that in each case one cutting edge of an indentation deformed radially outwardly out of the sleeve abuts the radially internal rims of the radial ribs on the side close to the working chamber.
5. A hydraulic brake booster as claimed in claim 1, characterised in that the collar engaging the radial ribs from behind is sub-divided into collar portions, which correspond to the circumferential extension of the radial ribs, and in that angled lateral collar portions are A adjacent to these collar portions towards the working-chamber side.
6. A hydraulic brake booster as claimed in claim 5, characterised in that axially set-back sleeve rims are located between the collar portions engaging the radial ribs from behind, which sleeve rims likewise have radially angled collar portions interconnecting adjoining lateral collar portions.
7. A hydraulic brake booster as claimed in claim 6, characterized in that lateral insertion slots are provided for the radial ribs in the lateral collar portions spaced from the collar portions engaging the radial ribs from behind, and in that the circumferential distance of adjacent lateral collar portions is greater than the circumferential extension of the radial rib.
8. A hydraulic brake booster as claimed in claim 2, characterised in that the radial ribs are located in the bottom surface of a hub member extending axially from the diaphragm plate, and in that a substantially cylindrical inset is inserted in the hub member in the area of the rolling diaphragm.
9. A hydraulic brake booster for an automotive vehicle substantially as described with reference to the accompanying drawings.