DE2340892A1 - PRELOAD CYLINDER FOR DUAL CIRCUIT AIR BRAKE SYSTEM - Google Patents

Description

R. 10 12
19.o7.1973 Ho / sc

Attachment to
Patent and
Utility model registration

ROBERT BOSCH GHBH. 7 Stuttgart

Pre- tensioning cylinder for dual-circuit air brake systems

The invention relates to a preloading cylinder for dual-circuit air brake systems of motor vehicles, the is intended to operate a hydraulic master cylinder and the two arranged one behind the other on the same Piston rod has v / irkende working pistons, of which the second working piston, which is closer to the cylinder, has a working space limited, which has a central air supply and the first working piston has an eccentric working space Has air supply.

Such a prestressing cylinder is known (DBGM 7,000 925). An absolutely safe two-circuit division is not given with such prestressing cylinders. It can happen that the seals of the working pistons are defective. If a seal of the second working piston leaks, the air blows over to the counter-spring side of the working piston , which is already connected to the outside air, and the driver is made aware of the fault by the strong blow-off noise . But if the seal of the first working piston leaks

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the following happens during the partial braking position: The working spaces of the two working pistons are fed via the control valves of a two-circuit burner valve. do the first control valve is usually mechanical and the second control valve is controlled by the input from the first control valve Pressure is actuated, the flow controlled by the first control valve into the first working chamber of the prestressing cylinder Compressed air through the defective seal of the first piston into the one between the two working pistons second working chamber. From there, the compressed air reaches the second, which still keeps the outside air connection open Control valve in the outside air connection and blows off audibly there, because the primary and secondary side on the second control piston the same pressure build-up takes place and the necessary excess force (pressure difference) to close the outlet seat does not is achieved. As a result, if the air compressor does not provide sufficient additional supply during prolonged partial braking (downhill, Idle) exhaust the supply of circuit I. A corresponding reduction in the braking force occurs, so that when the supply I is exhausted, braking force can no longer be achieved via circle I. To regain braking power generate, the second circuit must be mechanically operated, the inlet of the first control valve inevitably • is opened. The supply air flows from circuit II into the via the defective sealing ring on the first working piston Circle I and fills it up to the pressure equalization with circle II. The total pressure level drops by half whether:

1. through the process already described above and

2. in the case of repeated braking operations carried out in quick succession.

The invention has for its object to overcome this disadvantage and to provide a dual-circuit tension cylinders of the type mentioned in which one in case of failure

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Seal the first piston no loss of supply occurs in the second brake circuit kamu / This task is carried out in accordance with the invention achieved in that the first working piston with a known double seal with vented Zwischenkamiaer is provided and that the intermediate chamber Via an annular chamber between two coaxial ones arranged in the central air supply of the second working space and pipe sections tightly fastened to the first working piston are connected to the outside air.

An embodiment of the invention is shown in the drawing / A preloading cylinder 1 of a two-circuit pneumatic brake system has a cup-shaped housing 2, which by a lid 3 is closed. The lid 3 carries one hydraulic master cylinder 4 and serves as a return spring as an abutment. The cup-shaped housing 2 is with a cylindrical bore 6 is provided which receives two working pistons 7 and 8. The first, a bottom 9 of the housing 2 facing working piston 7 carries a double seal 1o, which consists of two O-rings. Between the O-rings lies an intermediate chamber 11 which is connected to a radial channel 12 which radially penetrates the working piston 7. The radial channel 12 runs out on the inside into an annular chamber 13, the one between two coaxial working pistons 7 on the first working piston 7 tightly fastened pipe sections 14 and 15 is formed.

The two pipe sections 14 and 15 protrude into a central pipe socket 16 of the housing 2 in a sealed and axially movable manner into it. The pipe socket 16 of the housing 2 has a threaded hole at its outer end Connection 17 for a control line 21 from the second control valve 18 of a two-circuit brake valve 19 · The first control valve Po this two-circuit Brensventils 19 is a Control line 22 connected to an eccentric connection piece on the housing floor. Between the housing bottom 9 and The first working piston 7 has a first working space 24 to which the line 22 leads.

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The working space of the second working piston 8 is located between the two pistons 7 and 8. This working space 25 is
connected to the connection 17 through the longitudinal bore of the inner pipe section 15.

The inner pipe section 15 has at its end facing the air connection 17 a piston-like, with a sealing ring
26 provided thickening 27 and slides with the sealing ring 26 in a cylindrical bore 28 of the pipe socket 16. The outer pipe section 14 has a smooth cylindrical outer wall and is sealed with the aid of an O-ring 29 fixed to the housing.

The two pipe sections 14 and 15 are dimensioned in their length and so fastened in the first piston 7 that an inner flange surface Jo of the piston-like thickening 27 of the inner pipe section 15 is a gap distance 51 from the
adjacent end face 32 of the shorter, outer pipe section 14 has. This gap distance 31 is intended for the passage of air from the annular chamber 13 to the outside air.

The air passage from the annular chamber 13 to the outside air is furthermore guided through a sloping channel 33 in the pipe socket 16, the wall of the bore 28 outside the sliding area of the sealing ring carried by the thickening 27 cuts.

A piston rod 34 is fastened in the second piston 8
and protrudes into the hydraulic master cylinder 4.

The preload cylinder described works as follows:

In the rest position, both work spaces 24 and 25 are without pressure. If you brake, the first control valve is activated 2o changed over so that supply air reaches the working space 24 via the control line 22. The pressure build-up

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"but also has the effect that the second control valve 18 also switches. Supply air also reaches the working space. The same pressure on both sides of the working piston 7 would be in itself cause the piston 7 to come to a standstill. Due to the spring design in the brake valve 19, however, there is room 24 a higher pressure than in space 25. This causes the working piston 7 moved with it. This prevents the working piston 7 from corroding.

If the pressure in the first brake circuit fails, the control valve 2o is controlled mechanically and during braking a mechanical connection to the second control valve 18 is established. The second control valve 18 is switched over, and compressed air reaches the working chamber 25 in front of the working piston 8. This piston 8 then actuates the only Brakes.

However, if the pressure in the second brake circuit fails, it remains the work space 25 depressurized. Now the working piston takes over 7 the actuation of the downstream master cylinder 4 by detaching itself from the base 9 and the working piston 8 moved along. The same applies if the seal of the second piston 25 is defective.

If the first O-input 1o of the double compression 1o, 1ο ¹ fails, the supply air of the first circuit blows off to the outside via the inclined duct 33, and the supply pressure in the brake circuit I drops; however, the outflow dealt with in the introduction to the description cannot take place via the control valve of the second brake circuit which is still open at the start of braking, and the second brake circuit is not affected.

If the second O * input lo'der double compression 1o, 1o ^{f is} defective, then brake circuit II fails. The brake circuit I

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remains unaffected, and the working piston 7 leads Braking through.

It can be seen from this that the pretensioning cylinder according to the invention is secured against all possible damage and that a complete two-circuit protection is guaranteed.

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Claims (1)

J 6 <2 Expectations Preloading cylinder for dual-circuit air brake systems in motor vehicles, which is used to actuate a hydraulic Master cylinder is determined and the two arranged one behind the other, on the same piston rod has working pistons, of which the second working piston, which is closer to the master cylinder delimits a working space which has a central air supply and the first working piston Has working space with air supply in the middle, characterized in that the first working piston (7) is provided with a double seal (1o, 1o) known per se with a vented intermediate chamber (11) and that the intermediate chamber (11) via an input chamber (1J) between two coaxial, in the central air supply of the second working chamber (25) arranged and tightly fastened to the first working piston (7) pipe pieces (14, 15) is connected to the outside air. Prestressing cylinder according to Claim 1, characterized in that that the two pipe sections (14, 15) in a central pipe socket (16) of the prestressing cylinder housing (2) protrude sealed and axially movable. Prestressing cylinder according to Claim 1 or 2, characterized in that the inner pipe section (15) is attached to its the air connection (17) of the second working space (25) facing end has a piston-like, with a sealing ring (26) provided thickening (27) and that 509809/0492 1 6 4 the outer pipe section (14) is a smooth cylindrical Has outer wall and is sealed with the help of an O-ring (29) fixed to the housing. 4. prestressing cylinder according to claim 3 »characterized in that that an inner flat surface (3o) of the piston-like thickening (27) of the inner pipe section (15) a gap distance (31) from the adjacent end face (32) of the shorter, outer pipe section (14), which is intended for the passage of air from the annular chamber (13) to the outside air. 5. prestressing cylinder according to one of claims 1 to 4, characterized in that the air passage from the annular chamber (13) to the outside air via an inclined duct (33) in the central pipe socket (16) of the prestressing cylinder housing (2) is guided, which the inner wall (28) of the central pipe socket (16) outside of the sliding area of the sealing ring (26) carried by the thickening (27). 509809/0492