HK1110287B - Combined service brake and spring brake cylinder - Google Patents

Description

Combined service brake and spring brake cylinder

Technical Field

The invention relates to a combined service brake and spring brake cylinder for a vehicle brake system.

Background

A combined service brake and spring brake cylinder is known from EP 0452621B 1. An inner housing, which is formed by a base plate and a cylinder, is inserted into the housing, in which inner housing the service brake piston is guided displaceably, wherein a pressure chamber for the service brake piston, to which a pressure medium can be supplied, is formed between the service brake piston and the base plate of the inner housing facing the spring energy storage piston. The spring-loaded piston surrounds the inner housing in the form of a pot and is guided displaceably on the outer wall of the inner housing by means of a seal. A pressure chamber of the spring energy storage piston is formed between the bottom plate of the inner shell and the spring energy storage piston.

A combined service brake and spring brake cylinder of the type described is described in US 3188922a, in which, for supplying a pressure connection of a pressure chamber of the service brake with pressure medium, a flexible hose is provided which extends between a movable base plate of the spring brake piston and a housing base plate, is fastened to the pressure connection and must be able to follow the movement of the spring brake piston. Since the movable floor is one piece with the spring-loaded brake piston, the hose is moved by the spring-loaded brake piston moving to the clamping position. Thus, when the spring brake is released, it is in the rolled-up state, and when the spring brake is applied, it is spread apart, wherein the hose is subjected to a bending load during the transition from one state to the other. In order to be able to withstand large brake pressures, the outer wall of one such hose must be of considerable size, whereby it inherently becomes more rigid and increases the bending stresses acting therein, which reduces its life in terms of resistance to bending fatigue and in particular its tightness may be jeopardized, which in extreme cases leads to a failure of the service brake when the pressure chamber of the service brake is no longer supplied with compressed air.

Another combined service brake and spring brake cylinder is described in DE 2352313 a.

Disclosure of Invention

The object of the present invention is to further develop a combined service brake and spring brake cylinder of the type mentioned at the outset, which can be operated reliably.

The invention proposes a combined service brake and spring brake cylinder for a vehicle brake system, comprising a spring brake piston and a service brake piston which are guided in a common housing of the two brake cylinders, wherein the spring brake piston is loaded by at least one energy storage spring and has a larger outer diameter than the service brake piston, and the spring brake piston is an annular piston, and at least a part of a piston rod of the spring brake piston surrounds the service brake piston and forms a radially outer sliding and sealing surface for the service brake piston, said piston rod being formed as a piston tube, wherein the piston tube of the spring brake piston bears on its side remote from the spring brake piston an axially displaceable base plate, wherein a pressure chamber of the service brake is formed between the base plate and the service brake piston, the brake pedal is characterized in that the base plate, in addition to a radially outer annular portion which is fixed to the piston tube and can be impinged against the brake pedal piston, is formed by a flexible membrane which can be supported on a housing base plate when the pressure chamber is inflated.

Since the diaphragm is supported on the rigid housing base plate when the pressure chamber of the foot brake is inflated, the wall thickness of the diaphragm can be correspondingly smaller than when it is not supported on the rigid housing base plate, which increases its flexibility and therefore also applies to a comparatively large piston stroke of the spring-loaded piston without the bending load of the diaphragm becoming too great. The pressure medium supply to the pressure chamber can then take place, for example, via a rigid tube which passes out of the housing base plate and to which a radially inner edge of the diaphragm is fastened. Instead, the radially outer edge of the diaphragm, which is connected to the annular portion, follows the movement of the spring-loaded brake piston. A reliable sealing of the pressure chamber of the service brake with a long life is thus obtained.

In a particularly preferred manner, the spring-loaded brake piston is axially connected to the piston tube approximately at its average diameter, wherein the loading spring surrounds the piston tube. In this case, a radially inner circumferential surface of the housing forms a radially outer sliding and sealing surface for the spring brake piston and a pressure chamber of the spring brake piston is formed between the radially inner circumferential surface and a housing cover consisting of a base plate and a cylinder.

A return spring supported on the housing cover presses the service brake piston against a movable base plate of the pressure chamber of the service brake, which in turn can be pressed against a housing base plate. A central push rod, which acts on a brake mechanism and which protrudes through a through-opening in the housing cover, protrudes from the service brake piston.

Further configurations of the combined service brake and spring brake cylinder according to the invention will become apparent from the following description of an exemplary embodiment.

Drawings

An embodiment of the invention is explained in more detail below in the figures and in the following description. In the drawings:

fig. 1 shows a greatly simplified cross-sectional view of a combined service brake and spring brake cylinder according to a preferred embodiment of the invention.

Detailed Description

The preferred embodiment of the combined service brake and spring brake cylinder, which is designated as a whole by 1 in the figures, forms a brake actuator, for example a disc brake for a utility vehicle, and is actuated pneumatically. It comprises a service brake cylinder 2 in which a service brake piston 4 is guided in a displaceable manner and a spring brake cylinder 6 which guides a spring brake piston 8. The two brake cylinders 2, 6 are accommodated in a single, preferably internally smooth-cylindrically formed housing 10, which is cylindrical in shape, i.e. it is delimited at one end by a housing base plate 12 and has at its other end an opening 20 closed by a housing cover 18 consisting of a base plate 14 and a cylinder 16. The cylinder 14 and the housing 10 are concentric with each other.

The spring-loaded piston is designed as a ring piston 8 and has a central through-opening. The radially inner circumferential surface of the end of the housing 10 turned toward the opening 20 and the cylinder 16 each form a sliding and sealing surface for the spring store piston 8, which can have a corresponding seal on its circumference. Furthermore, a pressure chamber 22 for the spring brake piston 8 is formed between the radially inner circumferential surface of the housing 10 and the housing cover 18, which is formed by the base plate 14 and the cylinder 16. The bottom plate 14 of the pressure chamber 22 is therefore identical to the annular end face of the housing cover 18 or of the housing 10 itself. The housing cover 18 can be formed in one piece, so that the cylinder 16 and the base plate 14 form a single flanged element to the housing 10, or it can be formed in several pieces. A piston rod, which is designed as a circumferentially closed piston tube 24, projects from the spring brake piston 8 in the direction of the housing base plate 12, wherein the piston tube 24 has approximately the average diameter of the spring brake piston 8.

In an annular space between a radially inner circumferential surface of the housing 10 and a radially outer circumferential surface of the piston tube 24, a charging spring 28 is mounted, which is supported on the one hand on the spring-charging brake piston 8 and on the other hand on the housing base plate 12. The charging spring 28 therefore completely surrounds the piston tube 24 of the spring charging brake piston 8. The pressure chamber 22 of the spring brake piston can be charged and discharged via an air connection 30. The spring storage brake is a passive brake, i.e. it is released by the charging of the pressure chamber 22 against the action of the storage spring 28 and is pressed by the spring force of the storage spring 28 after the pressure chamber 22 has been discharged.

The spring-loaded brake piston 8 has a larger outer diameter than the preferably cylindrical service brake piston 4. The latter is guided axially displaceably with its radially outer circumference over its entire actuating travel on the radially inner circumference of the piston tube 24 of the spring brake piston 8. That is to say the piston tube 24 forms a sliding and sealing surface for the radially outer part of the circumference of the service brake piston 4, in which, for example, a sealing element not shown in the figures can be inserted. A central push rod 32, which acts on a brake mechanism of the disk brake, which is not concerned here, projects from the service brake piston 4 and passes through the opening 20 of the housing cover 18. A release system of the disc brake can be integrated in the push rod.

The service brake piston 4 is also supported by a return spring 34 on a flange 36 of the housing cover 18, which flange projects radially inward on the end face. The restoring spring 34 is formed in a barrel-shaped manner, for example, outwardly or inwardly, in a longitudinal and transverse cross section, whereby the coils can be inserted axially into one another during compression, in order to save construction length.

The piston tube 24 carries an axially displaceable base plate 38 at its end face on its side remote from the spring-loaded brake piston 8, wherein a pressure chamber 40 of the service brake is formed between the base plate 38 and the service brake piston 4. The service brake piston 4 is pressed by the return spring 34 in the direction of the movable base plate 38. In particular, the displaceable base plate 38 and the piston tube 24 fixed thereon in a pressure-tight manner together form the outer wall of the axially displaceable service brake cylinder 2. The movable floor 38 of the pressure chamber 40 of the service brake can be pushed against the housing floor 12, in particular the return spring 34, into this position. Furthermore, when the spring-loaded brake is actuated in the brake application direction, the service brake piston 4 is designed to be movable from the base plate 38 in the brake application direction. This can be achieved, for example, by the base plate 38, in addition to its radially outer annular portion 42 fixed to the piston tube 24, also being formed by a flexible diaphragm 44 fixed radially inside to the annular portion 42, wherein the annular portion must be made of a rigid material in order to be able to strike the service brake piston 4, and the diaphragm can be supported on the housing base plate 12 when the pressure chamber 40 is inflated. To illustrate this, the floor 38 of the pressure chamber 40 is constructed in a saw tooth profile. In practice the bottom plate 38 may also be flat.

The base plate 38 is preferably provided with a central connection for the inflation of the pressure chamber 40 of the service brake, which connection consists, for example, of a rigid tube which passes from the outside through the housing base plate 12 into the base plate 38. Which co-operates with an inlet valve 46, which is not shown in detail for reasons of scale. An exhaust valve 48 for exhausting the pressure chamber 40 is inserted, for example, into the annular portion 42 of the base plate 38. The exhaust and intake valves 46, 48 are, for example, electrically controlled valves and are actuated by an electrical control device, which is not shown for reasons of scale. The service brake is an active brake, i.e. it is pressed by the inflation of the associated pressure chamber 40 and released by the exhaust.

The space 50 between the service brake piston 4 and the housing cover 12 is protected against contamination and moisture, for example, by a sealing ring 52, which has a central, sealed passage opening for the tappet 32 and is fastened radially on the inside to the housing cover 18. A radially outer sealing ring 58 on the service brake piston 4 ensures a sealed guidance of the service brake piston on the piston tube 24. Or this may be achieved by a diaphragm. The housing 10 supporting the brake actuator can be connected to a flange of the disc brake by means of bolts 56.

Against this background, the combined service brake and spring brake cylinder 1 according to the invention functions in the following manner:

when releasing the spring brake, compressed air is supplied to the pressure chamber 40 of the service brake via the open inlet valve 46 when the outlet valve 48 is closed in order to press the service brake. This presses the diaphragm 44 of the base plate 38 forming the pressure chamber 40 against the housing base plate 12 on the one hand and pushes the service brake piston 4 to the left in the drawing, the radially outer circumference of which is guided in a sealing manner along the radially inner circumference of the piston tube 24. The pressure prevailing in the pressure chamber 22 of the spring charging brake ensures that the charging spring 28 is compressed, as shown in the figure, and therefore the spring charging brake is still released. To release the service brake, only the associated pressure chamber 40 is vented, whereupon the return spring 34 pushes the service brake piston 4 back into its starting position.

In order to apply the spring brake, for example in the case of a parking brake, the pressure chamber 40 of the service brake is vented via the exhaust valve 48 and at the same time the pressure chamber 22 of the spring brake is also vented, whereupon the storage spring 28 pushes the spring brake piston 8 to the left. The spring-loaded brake piston can entrain the base plate 38 of the now exhausted pressure chamber 40 of the service brake via the piston tube 24, since no pressure resistance prevents such a movement due to the exhausted pressure chamber 40. When the spring-loaded brake piston 8 has reached its clamping position, the service brake piston 4 is therefore also locked in the clamped position by the stored-energy spring force.

To apply the parking brake, the spring brake piston also locks the previously compressed service brake piston 4, i.e. by venting the pressure chamber 40 of the service brake which is initially charged and guiding the spring brake piston 8 to the left into the compressed position by venting its pressure chamber 22. Compressed air is therefore not required for fixing the parking brake in the pressed position for a longer time.

To release the spring brake, the pressure chamber 22 of the spring brake is charged and the spring brake piston 8 is then moved to the right against the action of the energy storage spring 28 together with the piston tube 24 and the base plate 38 of the pressure chamber 40 of the service brake. The service brake piston 4, which is located in a stop on the floor 38 of its pressure chamber, can follow this movement because the return spring 34 presses it to that end and because the pressure chamber 40 of the service brake, which has been vented as described above, does not generate a pressure resistance.

List of reference numerals

1 combined service brake and spring 28 energy storage spring

Air connection for brake cylinder 30

2 foot brake cylinder 32 push rod

4 pedal brake piston 34 return spring

6 spring brake cylinder 36 flange

8 spring energy storage braking piston 38 bottom plate

10 housing 40 pressure chamber

12 housing floor 42 annular section

14 base 44 diaphragm

16 cylinder 46 intake valve

18 casing cover 48 exhaust valve

20 opening 50 space

22 pressure chamber 52 sealing ring

24 piston tube 56 bolt

26 annular space 58 sealing ring

Claims (12)

1. Combined service brake and spring brake cylinder (1) for a braking device of a vehicle, comprising a spring brake piston (8) and a service brake piston (4) which are guided in a common housing (10) of the two brake cylinders (2, 6), wherein the spring brake piston (8) is acted upon by at least one energy storage spring (28) and has a larger outer diameter than the service brake piston (4), and the spring brake piston (8) is an annular piston, and at least a part of the piston rod of the spring brake piston surrounds the service brake piston (4) and forms a radially outer sliding and sealing surface for the service brake piston, which is formed as a piston tube (24), wherein the piston tube (24) of the spring brake piston (8) bears an axially displaceable base plate (38) on its side remote from the spring brake piston (8), wherein a pressure chamber (40) of the service brake is formed between the base plate (38) and the service brake piston (4), characterized in that the base plate (38) is formed, in addition to a radially outer annular portion (42) which is fixed to the piston tube (24) and can be pushed against the service brake piston (4), by a flexible membrane (44) which can be supported on a housing base plate (12) when the pressure chamber (40) is inflated.

2. Service brake and spring brake cylinder according to claim 1, characterized in that the spring brake piston (8) is axially connected to the piston tube (24) approximately at its average diameter.

3. Service brake and spring brake cylinder according to claim 1 or 2, characterized in that the energy storage spring (28) surrounds the piston tube (24) of the spring brake piston (8).

4. Service brake and spring brake cylinder according to claim 1 or 2, characterized in that a radially inner circumferential surface of the housing (10) forms a radially outer sliding and sealing surface for the spring brake piston (8).

5. Service brake and spring brake cylinder according to claim 4, characterized in that a pressure chamber (22) of the spring brake is formed between the radially inner circumferential surface of the housing (10) and a housing cover (18) which is composed of a base plate (14) and a cylinder (16).

6. Service brake and spring brake cylinder according to claim 5, characterized in that a return spring (34) of the service brake piston (4) is supported on the housing cover (18).

7. Service brake and spring brake cylinder according to claim 6, characterized in that the return spring (34) presses the service brake piston (4) against the movable floor (38) of the pressure chamber (40) of the service brake.

8. Service brake and spring brake cylinder according to claim 7, characterized in that the service brake piston (4) is constructed so as to be displaceable from the displaceable bottom plate (38) in the brake application direction upon actuation of the spring brake in the application direction.

9. Service brake and spring brake cylinder according to claim 8, characterized in that the movable floor (38) is provided with at least one connection (46, 48) for charging and/or discharging the pressure chamber (40) of the service brake.

10. Service brake and spring brake cylinder according to claim 9, characterized in that a central push rod (32) extends from the service brake piston (4), which push rod acts on a brake mechanism.

11. Service brake and spring brake cylinder according to claim 10, characterized in that the push rod (32) protrudes through a through opening of the housing cover (18).

12. Service brake and spring brake cylinder according to claim 11, characterized in that the energy storage spring (28) is supported on the one hand on the spring brake piston (8) and on the other hand on the housing base plate (12).